The Internet of things (IoT) allows us to connect everyday things to the internet. It is defined as a network of devices, vehicles, appliances, and other things that are connected. IoT is possible with the use of sensors, actuators, electronics, and software embedded into the later. Data collected from these physical devices are sent back and forth for better operation through network connectivity. A multitude of applications in defense, security, medical and industrial applications are available. Wearable devices, underwater systems, agricultural technologies, smart home applications, automotive, aviation systems and other areas of applications make use of IoT devices.

Parylene conformal coatings combine a number of properties that are attractive for use in a wide spectrum of applications. Their low dielectric properties, high mechanical strength, transparency, bio compatibility, chemical inertness against all of the common acids, bases and organic solvents, low water/gas permeability and thermal properties make them interesting for use in many industries. Also, pinhole-free Parylene conformal coatings with a thickness higher than 0.1 μm are possible and have been reported earlier [1]. Therefore, understanding their deposition process and characteristics is important.

Parylene coating process involves 3 steps: sublimation, pyrolysis, and polymerization. At the first step, which takes place between 120°C - 175°C, the dimer parylene powder precursor is sublimized and pyrolysed forming the monomers (see Figure). Next, Pyrolysis takes place which is defined as the thermal decomposition of materials at elevated temperatures (above 500 °C) in an inert atmosphere and this reaction is irreversible. Finally, monomers get deposited onto the substrate and all the other surfaces available in the deposition chamber. Monomers form long chained polymers at this step.

Parylene is a polymeric material that is commonly applied as a conformal coating layer in electronic applications. Parylene conformal coatings are used to provide environmental and/or dielectric isolation. They offer pinhole-free layers with low water permeability, high flexibility and high mechanical strength (see table). While parylene coatings are most frequently applied onto the electronic circuitry and sensors they also have impeccable properties that are beneficial for use in medical substrates.

Parylene is a conformal coating exhibiting extraordinary properties such as high mechanical strength and biocompatibility. It is a transparent (colorless) film in the UV-V is range of the solar spectrum (Parylene N and C absorb below ≈280 nm). The high transmittance of the polymers in the visible region (90%) make them eligible for use in optical applications. For further information on the optical properties of Parylene you can visit “Parylene’s Optical Properties and Performance”.

Multilayer conformal coatings are advantageous in resolving diffusion or stability issues. A vast amount of knowledge is available in the literature about the use of multilayered stacks of Parylene and stacks making use of different intermediate materials such as metals and so on. Mostly, use of Multiple layers of Parylene C was commonly reported for Medical Implants [1].

Under ambient conditions (room temperature, in air) Parylene is a lifetime conformal coating. The exposure to environmental stressors like temperature, oxygen, UV-light and chemicals can degrade the lifetime especially when two or more are existent at the same time.

Parylene is a chemically inert conformal coating [1]. It has a well-established chemical vapor deposition process and patterning methods. It is a great candidate for use in various application areas (health, aerospace, oil and gas, microelectronics, and so on.) due to its mechanical, physical, optical and chemical properties. Parylene is known to withstand highly corrosive environments and it can be utilized as a barrier material against various etchants in different processes (e.g. Hydrofluoric acid (HF), nitric acid, and acetic acid; potassium hydroxide; and tetramethylammonium hydroxide).

At Diamond MT we often get the question: “Can my xxx be parylene coated?”  The number of substrate surfaces that can be coated with parylene is plenty. In the table below a number of industrial applications that using Parylene conformal coatings are listed. The examples can be extended.

The stability and insulation property of Parylene conformal coating is critical for the reliable operation of electronic devices throughout their lifetime (PCBs, MEMS, sensors, implants and so on.). The failure mechanism of the conformal coating layers is known to be due to pore formation, blistering, delamination and thinning or pinhole formation due to dielectric breakage of the coating over time [1], [2]. Therefore, the surface where the interface between the conformal coating and the substrate will be formed is of high importance. The cleanliness of this surface has a great impact on the final results of the conformal coating process and the coatings durability. At Diamond MT we provide professional surface cleaning services ensuring the long lasting results for your components. Also, the parylene conformal coating thickness and parylene varieties required for different service are considerations to take into account. We offer our professional services to direct our customers. Some of the variables of different service conditions can be listed as:

Parylene XY is a transparent, thin (hundreds of nanometers to a few micrometers), well adhering, pin-hole and defect free conformal coating. They are coated uniformly on flat surfaces and component configurations with sharp edges, points, flat surfaces, crevices or exposed internal surfaces are coated uniformly without voids.

Oil & Gas industry makes use of sensors which face extremely high temperature and high pressure (HTHP) environments as in downhole drilling (>200°C and 30 kspi). In US natural gas supply lie in reservoirs below 15,000 ft. Wells at these depths pose environmental challenges of drilling due to the temperature, pressure and gasses. Increasing the lifetime of drilling equipment and possibility for recalibration of sensors that drift at such depths would save millions of dollars if they can be preserved under these HTHP environments. The packaging of sensors is a key element in providing this kind of protection.

Poly(para-xylylene) derivatives (parylenes) are used as conformal coatings in a wide range of applications in the automotive, medical, electronics, military and semiconductor industries. They are inert, transparent and have excellent barrier properties as dielectric thin films. Because their deposition takes placeunder vacuum sub-micron range crevices can be coated leading to excellent barrier properties (void free) and they have extraordinary purity that is of great importance in electronic applications. Not all parylene derivatives show same dielectric properties (Table 1). It is also important to note that dielectric properties of parylenes depend on their thickness thus their %crystallinity which is explained below.

The answer is “No!”

Parylene Process:

Hermeticity and Outgassing:

Parylene is a transparent polymer that offers uniform and pinhole-free conformal coatings for printed circuit boards, medical devices, and microelectronics. Varieties of parylene are made available through a modification of the molecular structure of para-xylylene (Parylene N, C, D, and F-AF4, and F-VT4). Each modification results in a set of material properties that are applicable in different service conditions.

Parylene conformal coatings are highly reliable and are highly sought after in applications such as military sensors to medical implants. Because, parylene coatings are colorless (transparent), thin (micro-scale) and uniformly deposited all over the target surface they are hardly visible to the naked eye. However, there are methods to detect or test the quality of the coatings that are designated by standards (MIL-STD, ASTM). These standards test coatings for the encapsulation properties of Parylene conformal coatings depending on where they will be used.  Leakage current and accelerated lifetime tests under different conditions (salty water, temperature, etc.)

Conformal coatings provide a long-term, stable and reliable encapsulation method for the electronic components from the environmental effects. Different industries and service conditions calls for different protective coatings. In some cases, changes in the requirements or mistakes would call for action to remove the coating. While some coating materials are easily removed, some are virtually impossible to remove without damaging the products (eg. epoxy) . The coating removal process has been standardized by the standard IPC-7711C/7721C titled Rework, Modification and Repair of Electronic Assemblies [1]. According to the IPC-7711C/7721C coating removal starts by the identification of conformal coating (Chart. 1) type and followed by the selection of the method to be used depending on the substrate and components. If prepared onsite the coating material is generally known, but if the coating was done elsewhere the following chart can be used to identify the type of conformal coating.

Polyurethanes (Urethane Resin- UR) are polymeric, flexible, insulating, hard and chemically resistant (Acid—Alkali—Salty water) conformal coatings that are used to protect electronic parts from chemical corrosion, oil, moisture, fungus, and static discharges. Polyurethane coatings are supplied as single or two-component formulas. These coatings are suitable for printed circuit board applications such as sensors in the oil and gas industry, automotive, agriculture and common electronics. Polyurethane can be optically excited under UV-light and fluoresces therefore its inspection is also straightforward. Optically transparent coatings with a bit of tint are visually suitable for encapsulation purposes. Maximum service temperature for these conformal coatings (depending on the type) is ˂130 °C.

Parylene films are highly employed in different applications because they are chemically inert, transparent in the visible range of the solar spectrum, offer high dielectric strength and insulation resistance, low moisture vapor transmission and gas permeability rates [1]. They can also be deposited as void-free layers on complex geometries in deep, narrow crevices.

Company meets strict requirements for aerospace and defense markets in the Southeast.

Implications of Parylene Coating Thickness:

Today, security systems rely on different types of advanced, intelligent and connected sensor technologies. Application areas are diverse: radar systems, vision, night vision (IR-cameras), acceleration- orientation-location detection (accelerometers, gyroscopes, GPS), chemicals (neural toxins, other toxic gasses, liquids, materials), wearable sensors (body temperature, relative humidity, location detection), barometric (under water), air flow (aerospace, missiles) and they are brought together for multifunctionality on PCB’s which carry many sensor at a time. Sensors used in military applications pose stringent requirements such as robustness under severe environmental conditions and require longevity of sensing functions. Some of the environmental conditions that are harsh on sensors can be listed as:

At Diamond MT, we offer parylene coatings of different polymeric varieties (N, C, and F) as listed in the following Table. The basic parylene molecule is the Parylene N (poly-para-xylylene) monomer. Modification of the Parylene N monomer by a functional group such as Chlorine and Fluorine leads to Parylene C (poly(2-chloro-para-xylylene)) and Parylene F, respectively. The derivatization of new varieties can be done by the addition of functional groups to Paryelene N main-chain phenyl ring and its alip

Parylene is a transparent polymer offering uniform and pinhole-free conformal coatings. Different varieties of parylene (Parylene N, C, D, AF4, and F) formed by a modification in their molecular structure. Each modification results in a set of material properties that are applicable in different service conditions. The basic type of parylene derivatives is the Parylene N (poly-para-xylylene) monomer.

The polymer parylene (XY) is a reliable protective conformal film that safeguards the visual clarity and color of printed circuit boards (PCBs), similar electronic assemblies and other products.  XY optical clarity seldom diminishes to the extent either the coating or the underlying substrate becomes visually indistinct, although over-exposure to ultraviolet (UV) light may eventually interfere with optical perception.  However, in the majority of cases, colorless parylene generates advantageous optical properties for a wide range of uses -- including artwork/museum artifacts, cameras/sensors, computer touchscreens, healthcare/medical devices, light-emitting diode systems (LEDs), and optoelectronic components maintaining consistent aerospace, scientific, and telecommunication operations.

Parylene (XY -- poly(para-xylylene)) organic polymers are highly regarded through a wide range of industries – aerospace/defense, automotive, commercial, industrial, medical – for their utility as conformal coatings.  Chemically inert, colorless, linear/polycrystalline and optically clear, XY coatings provide exceptional barrier protection, dielectric reliability, and insulation for printed circuit boards (PCBs) and similar electronic assemblies whose components must maintain performance through all operating conditions.  Parylene conformal films safeguard function in the presence of biogases, biofluids, chemicals, moisture/mist, salt compounds, and temperature fluctuations. 

A natural process, corrosion enacts chemical/electrochemical reactions that degrade and gradually destroy materials or components within a functional environment.  The outcome can be dangerous and costly to repair.  

A primary function of all conformal coatings is maintaining sufficient insulation and avoiding dielectric breakdown while protecting printed circuit boards (PCBs) and related electronic assemblies. Providing a completely homogeneous coating surface, parylene (XY) conformal coatings are exceptionally corrosion-resistant, dense and pinhole-free. Among other performance advantages, ultra-thin XY protective films offer superior dielectric properties. Dielectric substances maintain electrical insulation, simultaneously transmitting electricity without conduction. They have the potential to store energy because they support electrostatic fields that release only low levels of thermal energy.

Company is looking to serve the aerospace, defense, and medical markets in Florida with the new location.

Conformal coatings primary purpose is protecting the performance of highly sophisticated electronics such as printed circuit boards (PCBs), sustaining their functionality through often unfriendly operating conditions.  Among the most important coating-requirement is safeguarding PCBs from the negative impact of moisture incursion.  Sources are many.  Liquidized obstacles to appropriate assembly function can result from unwanted contact with acid rain, aggressive solvents, atmosphere pollutants, chemicals, fog, high humidity, intermittent immersion, persistent rain, snow, salt water/mist and wet sprays of any kind. 

Chemically inert parylene (Poly-para-xylylene/XY) conformal film is often selected because its micron-thin protective films generate precise coating uniformity, regardless of substrate topography.  To this extent, XY far exceeds the capacities of liquid materials – resins of acrylic, epoxy, silicone or urethane – for a wide range of coating assignments.  It is true that pre-synthesized liquid coatings are easier to apply.  However, their conformal films are dimensionally thicker, making them difficult to position in constricted operating spaces.  Liquids are also generally less resistant to contaminant incursion and other problems that interfere with reliable performance of printed circuit boards (PCBs), and most other contemporary electronics, including biomedical implants.

Used for food production, indoor gardening/hydroponics, and horticulture, grow lights have both industrial and consumer applications.  Because total illumination intensity diminishes with distance from the point source (grow lightbulbs), production efficiency is enhanced by:

A specialized chemical vapor deposition (CVD) process attaches conformal coatings composed parylene (XY) to substrates.  CVD uniformly encapsulates all exposed substrate surfaces as a gaseous monomer; completely eliminating wet coatings’ liquid phase and need for post-deposition curing.  Synthesizing in-process, CVD polymerization requires careful monitoring of temperature levels throughout. 

Beneficial thermal properties of XY protective coatings include reliable performance through an exceptional range of temperatures.  Parylene is available in variety of material formats, prominently Types C, N, F, D and AH-4.  Each has a particular range of properties that determine its optimal uses.  Types C and N exhibit faster deposition rates than other parylenes, making them useful for a wider range of coating functions.  However, operating temperature is a significant determinant of use:  Much depends on chemical composition. 

• Used more frequently than other XY varietals, Parylene C is a poly-monochoro para-xylene.  It is a carbon-hydrogen combination material, with one chlorine group per repeat-unit on its main-chain phenyl ring.  In oxygen-dominated atmospheres, C conformal films regularly provide reliable assembly security at temperatures of 100° C (212° F/water’s boiling point) for 100,000 hours (approximately 10 years).  C is suggested for use in operating environments reflecting these temperature conditions.  Chemical, corrosive gas, moisture, and vapor permeability remain consistently low.  C generates exceptional vacuum stability, registering only 0.12% total weight-loss (TWL) at 49.4° C/10^-6 torr (1 torr = 1/760 SAP (standard atmospheric pressure, 1 mm Hg).   C can also be effective at temperatures below zero, to -165º C.
• With a completely linear chemical format, Parylene N is the most naturally-occurring of the parylene series.  Used less regularly than Type C, N is highly crystalline; each molecule consists of a carbon-hydrogen combination.  N’s melting point of 420° C is greater than most other XY types.  Vacuum stability is high, registering TWL-levels of 0.30% at 49.4° C, and 10^-6 torr.  These properties encourage higher temperature applications.  Compared to other XY varietals, N’s low dielectric constant/dissipation values also recommend uses with assemblies and parts subjected to higher levels of unit vibration during operation.  N’s electrical/physical properties are not noticeably impacted by cycling from -270º C to room temperature, adding to its versatility.  
•  Parylene F has fluorine atoms on its aromatic ring.  Possessing aliphatic -CH₂- chemistry, F’s superior thermal stability is attributed to this aliphatic C-F bond, compared to Type C’s C-C bond.   Better thermal stability, and reduced electrical charge/dielectric constant expand its use for ILD (inner layer dielectric) applications, such as those for ULSI (ultra large-scale integration), where a single chip can incorporate a million or more circuit elements.   F is a good choice for many microelectromechanical systems (MEMS)/nanotech (NT) solutions. 

• Originating from the same monomer as Type C, Parylene D’s chemical composition contains two atoms of chlorine in place of two hydrogen atoms.  Like Type C, D conformal films can perform at 134° C (273° F), dependably securing assembly performance in oxygen-dominated environs for 10 years, at a constant 100° C.  Parylene F resists higher operating temperatures and UV light better than C or N.  
• Parylene AF-4’s melting point is greater than 500° C.  It survives at higher temperatures/UV-exposure better than other parylenes for long durations because it possesses CF₂ units, situated between its polymer-chain rings.  

Sensors measure specific aspects of data-driven technology.  Included are such performance properties as acceleration, fluidity, humidity/temperature, position, pressure or vibration.  Sensors collect data  and respond with feedback for a multitude of electronic devices utilizing printed circuit boards (PCBs) and related sensitive electronics.  They have been successfully adapted for use across a wide range of applications, including aerospace/military, appliance, automotive, communications, consumer, industrial, medical and transportation uses.  

PCBs and the larger devices they power often need to function in harsh operating environments.  Conformal coatings -- liquid acrylic, epoxy, silicone and urethane resins, and chemical vapor-deposited (CVD) parylene – provide PCBs and similar electronics excellent barrier, dielectric and insulative protection through most performance conditions, sustaining their expected utility.  Substrate adhesion is necessary to conformal film reliability; coatings do not work if they delaminate or otherwise disengage from the components they are applied to protect. 

Parylene (XY) polymers provide robust, dielectric, micron-thin conformal coatings for a considerable range of electronic devices, most prominently printed circuit boards (PCBs).  XY’s unique chemical vapor deposition (CVD) application method synthesizes in-process, depositing gaseous parylene deep into a substrate’s surface.  CVD occurs on a molecule-by-molecule basis, conforming to all underlying contours, regardless of shape or position, to the nanometer, if necessary.  Pre-synthesized liquid coatings lack many of parylene’s performance properties, having far less ability to successfully and conformally penetrate crevices in the substrate

Cleaning the substrate is an essential element of preparation for conformal coating.  The reasons are easy to understand:

 Used as moisture and dielectric barriers, polymer parylene (p-xylylene/XY) coatings are conformal and pinhole free.  Applied by a unique chemical vapor deposition (CVD) method, parylene penetrates beneath substrate facades, simultaneously attaching above surfaces at the molecular level.  CVD generated films cover crevices, exposed internal regions, points and sharp edges uniformly, without gaps or breaches.  Compared to liquid coating materials – acrylic, epoxy, silicone and urethane -- XY film layers are micron-thin, enhancing their utility for microelectricalmechanical systems (MEMS) and nano technology (NT). 

          Many medical devices rely on sensors to detect and measures conditions affecting patient health.  Generally, physical properties within the body – heartbeat, blood pressure, breath rate, temperature, -- are recorded and transmitted to medical personnel/technology, allowing continuous physiological monitoring of health-specific disorders, to improve the quality of diagnosis and treatment. 

          Parylene’s (XY) reputation as the most versatile and reliable of major conformal coating materials is well-earned.  However, unlike liquid coatings –resins of acrylic, epoxy, silicone and urethane – parylene cannot be applied via relatively economical brush, dip or spray methods.  XY can be the most expensive of the major conformal coatings to use, a factor influenced both by:

Parylene (XY) polymer conformal films are recognized for their exceptional range of desirable functional properties for coating printed circuit boards (PCBs) and similar electronics.  Beneficial properties include biocompatibility, chemical/solvent resistance, dielectric/insulative reliability, and ultra-thin pinhole-free film thicknesses between 1-50 μm.  They also generate complete surface conformability, regardless of substrate configuration, exceeding the coating capabilities of liquid conformal materials, such as acrylic, epoxy, silicone and urethane.   

For conformal coatings, elongation is a measure of material ductility -- a specific coating's ability to undergo significant plastic deformation before rupture.  A coating’s yield elongation is the maximum stress the material will sustain before fracture.  Thus, computed parylene (XY) elongation measurements represent the total quantity of strain the conformal film can withstand before failure.  While elongation is equal to a material’s operating failure strain, it has no exclusive units of measurements.  Typically,

Protecting printed circuit boards (PCBs) and similar electronics from the incursion of water is an essential responsibility of parylene (XY) conformal coating.  Suitable XY permeation barriers assure no form of liquid passes through to underlying components and that the water vapor transmission rate (WVTR) is minimal.  WVTR measures the level of water vapor migration through the applied barrier film, in terms of area and time.  Optimal WTVR ratings are represented by lower numerical values.  In comparison to liquid coatings, parylene typically provides lowest-level values, indicating better moisture barrier provision.  

Acrylic, epoxy, silicone and urethane coatings can be more quickly affected by water, its vapor, and other sources of moisture, such as: 

• acid rain,
• mists of other airborne pollutants,
• salt-air and
• chaotic weather.

          As the electrical components used to power printed circuit boards (PCBs) grow smaller, conventional conformal films become less effective for coating them.  Ongoing development of microelectricalmechanical systems (MEMS) and nano technology (NT), has little room for the thicker conformal films provided by liquid materials, such as acrylic, epoxy, silicone and urethane.   Nanocoats (NCs) are increasing in prominence, frequently surpassing micro-thin parylene (XY) for many MEMS/NT purposes.  

Hydrophobic Basics and Hydrophilicity

Parylene (XY) conformal coatings are applied to substrate materials through a specialized chemical vapor deposition (CVD) process that completely eliminates the liquid phase of wet coatings.  No initiators or catalysts are involved in CVD polymerization, which synthesizes truly conformal protective film in-process.  This is in stark contrast to wet coating materials such as acrylic, epoxy, silicone and urethane, which are synthesized prior to application via, brush, dip or spray methods.  Wet during application, liquid-coated substrates requiring further drying and curing.

With reliable moisture barrier properties, parylene (XY) conformal coatings generally have a hydrophobic surface when deposited onto substrates, causing liquids to form separate droplets on film surfaces.  While this outcome is useful for many XY applications, greater hydrophilic response, wherein XY molecules form ionic or hydrogen bonds with water molecules, can also be desired.  This can be achieved by applying glue or epoxy on top the deposited parylene; surfaces acquire enhanced hydrophilic properties, becoming more wettable. 

Parylene:  Properties and Processes

Taber tests are designed to measure a material’s capacity to withstand abrasion and its effects during operation.  Conformal coatings – both liquid and parylene (XY) – are

 Unlike liquid coatings – acrylic, epoxy, silicone and urethane – parylene (XY) does not use wet method application.  It can neither be brushed or sprayed onto substrate surfaces, nor will immersion – soaking the substrate in a bath of coating material – work.  In addition, XY’s:

The phrase “in-line parylene processing" is deceptive  because it does not accurately describe the method in which parylene (XY) is applied as a conformal coating.  It is true that some aspects of the traditional production line are relevant, but primarily in a fractional way. without the traditional station-to-station regimentation of standard in-line manufacturing processes.

          The polymer parylene (XY) provides exemplary, ultra-thin conformal coating for printed circuit boards (PCBs), solar cells, light emitting diodes (LEDs), medical implants, aeronautical/military equipment and numerous other products, with uniform, insulative protection in the nanometer (nm.) range. 

Operationally, a tube is a hollow cylinder composed of glass, metal, plastic or a similar substance, designed to contain or transport something, typically liquids or gases.  When many people think of tubing, they envision its use in construction or mechanics.  Tubing of this nature is defined not only by its purpose and the stuff its made of, but also by two dimensions -- outside diameter (OD) and wall thickness (WT). 

Although parylene (XY) is a well-recognized and often used conformal coating, misconceptions about what it is and can do are common.  These mistaken beliefs interfere with true understanding of parylene’s uses.  Five of the most consistent misconceptions – and appropriate corrective information – should clear things up.

Permeation barriers for electronic devices are essential to assure their ongoing performance through a wide range of operational environments.  Polymer flexible conformal coatings provide good barrier protection, protecting device substrates from unwanted incursion by solid contaminants, chemicals, gaseous permeation and liquid water or vaporous forms of moisture.  Permeability reduction improves with enhanced coating adhesion, minimizing the surface’s  

          Parylene (XY) conformal coatings are known and recommended because of their many beneficial performance characteristics.  They provide uniform, pinhole-free protective films with excellent barrier/dielectric/insulative properties, able to conform to virtually any substrate configuration.  One property in particular – micron-thin coating layers – distinguishes XY from liquid coating materials such as acrylic (AR), epoxy (ER), silicone (SR) and urethane (UR), which need to be applied at least twice as thick in most cases and frequently more, limiting their range of uses.  Parylene typically is applied at 0.1 to 50 microns (0.004 -2 mils), while the thicknesses of liquid coatings generally range from 25 to 250 microns (1-10 mils).  Compared to liquid processes, gravity and surface tension generate negligible impact with parylene, eliminating film bridging, pinholes, puddling, run-off, sagging or thin-out during application.  XY’s coefficient of friction coefficient can be as low as 0.25 to 0.30.

          Of the five most commonly used conformal coatings, four – acrylic (AR), epoxy (ER), silicone (SR) and urethane (UR) – are classified as wet materials, meaning they are applied to substrates by three basic types of liquid-based technology:

Generally applied at micron-thin coating layers, parylene (XY) offers numerous barrier, dielectric, insulative and similar protective benefits to printed circuit boards (PCBs) and related electronic assemblies.  One property of parylene applied in its normal range of 0.013 – 0.051 mm. (0.0005 to 0.002 in.) is exceptional optical clarity, which makes it suitable for coating lenses and other devices requiring visual transparency, like photosensitive components. 

          Each conformal coating material exhibits a range of unique performance properties that determine its product uses.  Relevant factors include the required coating-thickness necessary to assure reliable performance.  Like other coating types, parylene (XY) layer thickness is largely a function of several factors:  (1) substrate material, (2) the kind of assembly being covered, and (3) its operational purpose.  Chemically inert parylene is effective at far-thinner application thickness than liquid-applied materials for coating printed circuit boards (PCBs) and related electro assemblies: 

After pertinent research you’ve determined parylene (XY) is the best conformal film for your coating assignment.  Especially relevant were XY’s uniform protective and insulative properties, which are useful for numerous applications, ranging from printed-circuit boards (PCBs) to medical implants to military-grade purposes.  Among parylene’s other advantages are: 

Liquid conformal polymers – resins of acrylic (AR), epoxy (ER), silicone (SR) and urethane (UR) – use wet application processes to attach to substrates.  Most prominent of these are brushing the wet coating onto an assembly, dipping (immersing) the assembly in a bath of liquid coating, or spraying the conformal film onto the designated surface.  The coating materials are wet when they are applied.  If

Parylene conformal coating (XY) provides insulative protection for complex electronic circuit assemblies expected to function through rigorous operating conditions -- potential chemical, electrical, moisture and vapor incursion during performance.   Applied through chemical vapor deposition (CVD), parylene penetrates deep within substrate surfaces, generating a level of assembly security surpassing that offered by liquid coatings such as acrylic, epoxy, silicone and urethane.  Yet, although XY is applied in a vacuum, it’s capacity to provide these extraordinary qualities does not exist in one.  Parylene’s durable protective value depends on film adhesion, a quality subject to persistent, thorough inspection throughout the production process.

Unlike liquid conformal coatings joined to substrate surfaces by wet application methods, polymeric parylene (XY) uses a unique chemical vapor deposition (CVD) process to assure adherence.  There is no intermediate liquid phase.  Rather, cross-link polymerization of powdered raw XY-dimer converts the solid to a vapor at the molecular level, polymerizing XY directly as a transparent film on assembly surfaces.

Polymeric conformal coatings safeguard printed circuit boards (PCBs) from performance malfunction caused by contact with elements within their operational environment.  Included are:

Conformal coatings are used to protect printed circuit boards (PCBs) from dust, humidity/moisture, mildew/mold, temperature extremes, and other elements whose prolonged contact might interfere with assembly function. Coatings also enhance electrical clearance-tolerance, while safeguarding PCB components from contamination (particulate or otherwise), corrosive materials, and mechanical stress.

Diamond MT is an internationally recognized provider of conformal coating services, including equipment for implementing conformal coating processes.

With proper equipment and professional expertise, liquid conformal coatings and vapor-applied parylene readily provide printed circuit boards (PCBs) and similar electronics a durable overlay of protective, insulative film; parylene’s CVD processes ensure the coating actually penetrates the substrate surface, generating further device security.

Conformal coatings’ functional value stems from their ability to safeguard printed circuit boards (PCBs) and similar electronics from external threats to their performance. Composed of acrylic, epoxy, silicone and urethane polymer resin, coatings also provide layers of insulative protection. These liquid coatings are applied to PCBs by wet methods, primarily by brush, dipping (component immersion) or automated/manual spraying.

Originally published in the IPC Proceedings, the article “Effectiveness of Conformal Coat to Prevent Corrosion of Terminals“ was published online by circuit insight (http://www.circuitinsight.com/programs/54223.html). Author Michael Osterman is affiliated with the Center for Advanced Life Cycle Engineering, University of Maryland (College Park, MD).

Conformal coatings composed of acrylic, silicone and parylene polymer materials are valuable for a wide range of aerospace applications, which can push technologies to their limits. Applied to printed circuit boards (PCBs) and related electrical assemblies, conformal coatings maintain device performance through difficult operational conditions. The presence of atmospheric variation, chemicals, humidity, mobile ion permeation, moisture, temperature fluctuation, or excessive vibration can generate:

Used for aerospace. automotive, commercial, defense, industrial and medical applications, conformal coatings are applied in film layers generally 30-130 microns (micrometers/μm) thick, or 0.0012-0.0051 inches (“). Conformal films’ exceptional thinness is their greatest asset. Coatings safeguard printed circuit boards (PCBs) and similar electronics from performance malfunction generated by unwanted contact with:

The value of polymeric conformal coatings for protecting printed circuit boards (PCBs) from functional retardants like dust, corrosion, moisture, and temperature fluctuations is well-known. What may be less known is, that as the electrical components used in PCBs become smaller, traditional conformal films are commensurately less effective for certain coating purposes. With the rise of microelectricalmechanical systems (MEMS) and nano technology, nanocoats are increasing in prominence, in many cases surpassing even micro-thin parylene not-liquid coatings in utility for MEMS/nano applications.

Conformal coating of an object occurs when an appropriate coating material is applied on-top and around an underlying substrate, to protect it from such environmental and performance concerns as chemical incursion and excess moisture. Liquid organic polymer conformal coatings – acrylic, epoxy, silicone and urethane – prevent:

Liquid conformal coatings provide inexpensive, easily-applied insulative protection for printed circuit boards (PCBs) and similar electronics. However, the films’ otherwise desirable insulative qualities can interfere with operation of the assemblies’ electrical components, items like capacitors, connectors, diodes, resistors, or transistors, if these are coated. Liquid coatings are designed to "wick" under components and in between connectors to provide a complete coat, through brushing, dip-immersion, or spraying. These methods work exceptionally well, rendering an overall, dielectric conformal film for the PCB.

Conformal coatings are non-conductive dielectric film-coverings applied over printed circuit boards (PCBs) to protect them from damage caused by chemical incursion, corrosion, current-leakage, dirt/dust, extreme temperatures, fungus, moisture, rain, salt-spray, wind and persistent, intensive vibrations both within and external to the device. These failure mechanisms can soon lead to PCB malfunction and eventual breakdown. Rugged coatings’ exceptional performance durability and versatility protect delicate, finely-tuned components.

Dielectric strength is a measurement of a conformal coating’s insulation effectiveness. The higher the numerical designation of strength, the more likely a coating is to resist dielectric breakdown -- a level of 7,000 is dielectrically stronger than 2,200. Conformal coatings with higher hydrophobic properties and lower extractible ionic impurities are less likely to attract water, rendering them less mobile, while enhancing existing dielectric strength

Long used to safeguard printed circuit boards (PCBs) and other essential automotive electronics from harsh operating environments, conformal coatings’ importance in auto-design/manufacture has never been greater. Fragile electronic components and the paths between them require protection for PCBs to perform reliably. Conforming to PCBs’ topographies, coatings insulate assembly components, safeguarding specialized electronics’ functional integrity through extreme operating conditions.

Selecting a suitable conformal material for coating printed circuit boards (PCBs), related electronics, or other devices requires recognition of each coating type’s unique combination of benefits and drawbacks. These must be considered in relation to a given application.

Accidentally discovered in 1947, by chemist Michael Szwarc, the polymer parylene originally bore his name, and was known for a brief period known as Szwarcite. Working to thermally decompose the solvent p-xylene at temperatures exceeding 1000 °C, Szwarc identified the monomer para-xylylene di-iodide as the only product resulting when para-xylylene was reacted with iodine.

Available in five basic material types, conformal coatings can be readily adapted as protective, insulating films for electronics. However, there can be some confusion about which type is best-suited for a specific use. Clearly defining the performance parameters for the component[s] to-be-coated helps coordinate the conformal film material with a unit’s functional requirements. Accurate assessment of environmental conditions like anticipated levels of corrosion, contact with foreign particulates, expected concentrations of moisture/salt spray, temperature fluctuations and vibrational range determine which coating type is best-suited to your electronics’ applications. Without appropriate protection, printed circuit boards (PCBs) and similar electronics will not survive harsh environments, and malfunction.

If, for some reason, you are told parylene is NOT a conformal coating, simply because it has no liquid phase of application, just walk away. And maybe have yourself a good laugh. For, as you may already know, parylene has repeatedly proven itself to be the most definitive of conformal coatings, for a variety of reasons, including:

Superior to liquid coatings like acrylic, epoxy, silicone and urethane, parylene conformal films offer unparalleled protection for aerospace printed circuit boards (PCBs) and related electronic assemblies. Their complete encapsulation conforms entirely to all device surfaces – flat, round, creviced or edged, while adding almost no weight to the covered device.

Selecting the best material/application method for your coating assignment prolongs assembly service-life and promotes optimal performance. The conformal coating industry is highly competitive, with competent providers available throughout the country. Compared to liquid resin coating materials – acrylic, epoxy, silicone and urethane – the polymer parylene generates superior conformal coating, but is more complex and expensive.

Conformal coatings provide reliable working security for PCBs. However, poor coating application or selection of the wrong coating material can cause assembly malfunction. In other cases, poorly manufactured PCBS may need component repair/replacement. When these problems arise, coating removal is necessary.

Diamond-MT is a leader in the highly competitive conformal coatings’ industry:

Printed circuit boards (PCBs) interconnect microchips and similar electronic components etched or laminated onto flat fiberglass/plastic panels. A variety of conformal coatings – liquid resins of acrylic. epoxy, silicone or urethane and chemically inert parylene -- assure proper insulation for PCBs. Such environmental conditions as contamination from debris, humidity within the unit, solvent incursion or the impact of human handling are minimized by conformal protection, reducing performance degradation while prolonging assembly life.

A variety of coating equipment is available for use in the conformal coating process. The most important for liquid coatings are described below.

Failures of PCBs and similar electronic assemblies can occur despite the protection of conformal coating. Contributing reasons include:

Conformal coatings differ in their material-specific performance properties as protective films for electronic assemblies. Knowing the operational characteristics of various coating-types and their functional association with assembly components supports successful film application. Issues that confound conformal coating selection and application result from potential post-application problems like:

Operationally, conformal coatings are applied to the surface of PCBs and related electrical components, to insulate and protect them during use. Coatings improve PCBs’ performance under any circumstances, but are especially valuable for their functional tolerance to harsher working environments.

Application methods must first reflect the targeted substrate’s susceptibility to the coating material. Liquid coatings – acrylic, epoxy, silicone and urethane – each possess specific performance properties. Optimal protection and operational efficiency depend on

In the highly competitive conformal coatings’ industry, these providers stand out:

Appropriately selected and applied, conformal coatings provide essential working protection for printed circuit boards (PCBs). However, removal of conformal coatings is necessary if the wrong coating material is selected relative to the PCB’s functional requirements, inadequately supporting its operating environment. Poor coating application can trigger failure mechanisms within the assembly, also calling for its removal and re-application.

Withstanding such complications to the operational environment as corrosion, fungus, oxidation, rain, salt water/mist, snow, temperature fluctuations or vibration is essential to long-term performance of electronic devices. Without suitable protection, printed circuit boards (PCBs) and similar electronics will not survive harsh environments, and malfunction. Prominent examples include:

Conformal coatings made of acrylic resin (AR) are very popular, because of their distinctive beneficial properties. They protect printed circuit boards (PCBs) and similar electronics from corrosion, dirt, dust, fungus, moisture, and thermal shocks. Exceptionally user-friendly, liquid AR can be simply applied by brush, dip, or manual/robotic spray, generally resulting in the fastest turnaround-time of all conformal coatings. Ease of application and rework generates low cost for both manufacturer and client. AR’s moisture protection is also very highly rated, adding to its utility for a wide range of coating uses.

Materially, parylene is the most distinctive of the major conformal coatings.  But just how does it differ from liquid coatings -- acrylic, epoxy, silicone and urethane??  

Printed circuit boards (PCBs) electrically connect and power all but the simplest electronic products.  To function as designed, PCBs and their components – capacitors, resistors, etc. – require protection against operating problems caused by corrosive liquids, dust, physical shock, temperature extremes and, in the case of medical implants, bodily fluids.  Conformal coatings are applied over PCBs to safeguard mechanisms and maintain functionality.  

Contributing to good performance for internal medical appliances, lubricity is a conformal coating’s ability to lower operational friction that might retard its function and endanger patient health.  Lubricious coatings offer essential protection for appliances like cardiac-assist devices (CADs), catheters, elastomers, guidewires, and stents.  Compared to an uncoated device, lubricious films can reduce frictional forces by more than 90%, dramatically decreasing potential harm caused by excessive insertion-force or internal puncture damage.  This relative ease of use is important for implants and similar devices that require navigation throughout the patient’s vascular system or other internal structure; otherwise, patients can suffer from abrasion generated between the device surface and blood vessel walls. 

Coefficient of Surface Friction

The degree of physical resistance a device demonstrates is numerically expressed by a coating’s coefficient of friction (µ), which quantifies:

• the magnitude of resistance a surface exerts on substances moving across it, or
• the minimum force necessary for an object to slide on a surface, divided by the forces pressing them together.

Static friction (µ_s) occurs when an object moves across a stationary surface; kinetic friction (µ_k) results for two objects simultaneously in motion, moving across each other.  Conformal coatings are used in both circumstances, especially for medical implants with moving MEMS/nano-tech components.

Where higher-level surface lubricity is sought, lower µ-values are the objective; they signify lessened frictional resistance, minimizing non-release, dry-sticking challenges that interfere with devices’ performance.  For instance, a µ-value of 1 indicates an equal quantity of force is needed to either lift an object, or slide it across a level surface; these calculations compare an object’s weight to the total force required to make it move.  Most everyday objects and materials have a coefficient between 0 and 1; values closer to 1 are not feasible for medical purposes.  For medical devices, a µ-value:

• ranging from 0.01 to 0.1 is ideal,
• but remains difficult to achieve
• for application to the expansive degree of metallic and polymeric substrates used for medical appliances,
• which require highly-specified levels of abrasion resistance and non-thrombogenic properties,
• in addition to biocompatibility and lubricity.

Appropriate safety standards also need to be met.

Much depends on the materials comprising the touching surfaces.  Conformal coatings like Teflon (PTFE) and parylene, which provide high-level lubricity, maintain that level for a prolonged operational duration, making them very useful for specialized medical applications.

Properties of Reliable Coating Lubricity

Lubricated surfaces have lower levels of friction.  Wet hydrophilic coatings amass water as a source of lubricity, applied by liquid methods such as dipping or spraying the film substance onto substrates.  Applied to catheters or guidewires, they temporarily minimize development of thrombosis.  However, their lubricious function decreases with time, dissociating or dissolving from the matrix surface, leaving particulates in tissue or the bloodstream, endangering patient health.  Thus, they are less reliable long-term than hydrophobic coatings   

The Need for Cleanliness Testing                                          

As the name suggests, spray coating is a method of application where the conformal coating is sprayed directly onto the printed circuit board (PCB).  It is typically applied manually in a spray booth or by aerosol, although it can be automated/robotic, for selective coating assignments.

Conformal coatings insulate printed circuit boards (PCBs) and similar electronics; their protection increases devices’ tolerance to harsh environments.  The result is undisturbed function through a range of frequently harsh operating environments and performance conditions.  Conformal coatings provide these services for aerospace/defense, automotive, consumer, and medical devices.  They are adaptable for LED uses, as well as MEMS/nanotechnology, and other uses.

The conformal coating process requires watchful administration to ensure successful implementation.  Recognizing the unique properties of various coating-types is critical to selecting the kind most applicable to the project and its purposes, while meeting clients’ material and operational specifications.  Regardless of the coating material and the substrate, these five fundamental procedures are essential to good conformal films.

Managing the conformal coating process begins with a precise definition of coverage required.  Pre-process negotiations between the client, the coating provider, and end-user, clarify coating requirements.  They include agreement about whether:

Liquid application resins acrylic, epoxy, silicone and urethane are applied to electronic circuitry in a liquid format by brush, dip or spray techniques, either manually or through robotic processes; they require curing before they can be used. 

For various reasons, even people familiar with the variety of existing conformal coatings, their strengths, weaknesses and respective use often assume that the chemical vapor deposition (CVD) process used for parylene films incorporates a solvent, as an integral component of the procedure.  This is false, for the reasons detailed below.

          The value of polymeric conformal coatings for protecting printed circuit boards (PCBs) from functional retardants like dust, corrosion, moisture, and temperature fluctuations has been well-documented.  Conforming to the physical configurations of the exposed face of the PCB, conformal coating:

The parylene variants are resistant to solvents and protect substrates solvents.  This high level of security is maintained through temperatures of 150° C, seldom encountered in the actual use of PCBs or related electronics.  These properties are largely a development of the unique molecular structure of parylene polymers, rendering them:

The acronym UAV stands for an unmanned aerial vehicle, an aircraft piloted by remote control or onboard computers.  UAVs are an integral element of America’s unmanned aircraft system (UAS), consisting of three basic components:

Like any other renewable energy technology, electronics for solar (photovoltaic) panels are necessary for transforming, transmitting, and monitoring the system.  Unfortunately, system electronics can be fragile, and frequently are the panel’s weakest link.  Converting the sun’s light to electricity, solar panels have demonstrated their utility in numerous operational contexts.  The basic operational unit of panels, the solar cells themselves, can be used to power small scale products like calculators, re-chargeable batteries or watches; full panels can be adapted to a range of larger level operations, like powering homes, lighting systems or water treatment plants.

Applied as a conformal coating through a unique chemical vapor deposition (CVD) process, parylene provides micron-thin, resilient barrier protection for an exceptional range of electrical assemblies.  In comparison to liquid coatings -- acrylic, epoxy, silicon, urethane -- parylene is the coating-of-choice for protecting printed circuits boards (PCBs) and medical devices.  It’s films negate the impact of gravity and surface tension during the coating process; . 

The parylenes consist of a range of para-xylylene polymers whose desirable physical and electrical properties support expansive utilization as conformal coatings for electronic and medical devices  Parylene films are applied to substrates via a chemical vapor deposition (CVD) process, which deposits monomeric parylene vapor homogeneously and deeply into the surface of printed circuit boards (PCBs) and related assemblies/components. 

Perhaps the most reliable of the conformal coatings, parylene (para-xylylene di-iodide) is also one of the more expensive coating options.  Production costs typically encompass three primary expense categories -- raw materials, labor, and lot volume.  Of the three, labor expenses are generally the most costly, but raw materials can add significantly to production overhead; materials’ costs can be largely attributed to the raw parylene dimer required to make conformal coatings.   

Wearable devices have become familiar, ever more an integral component of everyday life, with expanded uses for many conventional activities.  Advanced med-tech -- ranging in format from external exercise monitors to implanted cardiac pumps, defibrillators and deep-brain sensors –- represent only a fraction of wearable medical devices currently applied for healthcare and treatment.  Smartphones and watches can be found everywhere; smart fabrics are used with increasing frequency for clothing and textiles.   Wearables reflect the expanding scope of the Internet of Things in most areas of human endeavor. 

          As use of wearables grows, manufacturers try to determine the optimal mix of form, function and technology that will encourage further consumer/ professional application of the devices.  In healthcare, wearables provide a range of status indicators (heart rate, physical activity levels, etc.) that monitor individual’s engagement of healthful (or unhealthy) activities.  In addition to focusing on improving their functional technology, battery life and consumer fashion, the need to safeguard wearables performance is a prominent concern.  All wearable devices are informed by technologies that need conformal protection for and from their functional environments.  Parylene films are the most appropriate choice for protection in just about every case. 

Conformal coating and potting are the most common methods of protecting printed circuit boards (PCBs) and cable connections destined for use in:

Outgassing occurs when previously adsorbed or occluded gases or water vapor are released from some material.  With respect to protective conformal coatings, outgassing encompasses the discharge of gases previously confined within a high-frequency printed circuit board (PCB) or similar assembly material, often resulting in functional difficulties. 

          Applied in a gaseous form to component surfaces through a chemical vapor deposition (CVD) process, parylene (Poly-para-xylylene) films protect printed circuit boards (PCBs) and similar electrical assemblies.  Gaseous CVD application supports efficient coating of complex component surfaces characterized by crevices, exposed internal areas, or sharp edges.  Depending on the specific use, parylene conformal coatings can be effective in the range of 0.1 - 76 microns' thickness, far finer than competing coating materials.  Equally as strong, adaptable and versatile parylene protects substrates with

While parylene provides a reliable, versatile conformal coating, it can require removal.  When circumstances necessitate removal of liquid coatings – acrylic, epoxy, silicone or urethane – a wide range of chemical solvents can be used to detach the film from the underlying substrate.  No single chemical material/process is equally successful for all uses, but solvent processes are employed most frequently because they do the least damage to printed circuit boards (PCBs) and their components.  Such is not the case with parylene. 

Although its basic component is remarkably small – with 25,400,000 nanometers included in just one inch(!!) -- nanotechnology encompasses a growing, interdisciplinary field with an unlimited future.  Nanowires and nanotubes are used in transistors for printed circuit boards (PCBs) and associated electronic assemblies.  Bio-nanobatteries, capacitators, LCDs, and microprocessors represent just a few nano-applications, which include uses for aerospace, agricultural, automotive, consumer, industrial, medical, military and oceanic products. 

If problems in a conformal coating defy reliable repair, coating removal may be the only solution.  Removing conformal coating from PCBs requires matching removal methodology with coating type and the component’s function.  A variety of factors – bubbles/voids, coating thickness, component failure, inadequate masking, poor adhesion, surface finish, among many others – can necessitate coating removal.     

Conformal coatings protect printed circuit boards (PCBs) and similar electronic assemblies used for a wide range of aerospace, automotive, consumer, defense and medical applications.  Coatings effectively cover PCBs, shielding them from contaminants, liquid incursions, temperature fluctuations and other conditions potentially hazardous to component performance.  However, problems can develop if their preparation, application, and drying processes are inappropriately managed. 

The engineering of functional systems at the molecular scale, nanotechnology encompasses management of individual atoms, combined into effective working units, often complex as machines.   Yielding advantages like enhanced chemical reactivity and strength than larger-scale structures, they offer greater control of the light spectrum and weigh significantly less.  Incredibly small, one nanometer is a billionth of a meter (10^-9 of a meter) -- one inch equals 25,400,000 nanometers; more illustratively, a sheet of newspaper is 100,000 nanometers thick.  

Masking tapes and boots both protect components for a selected range of masking functions.  Choosing between the two is crucial to achieving optimal masking protection.  Conductivity needs to be maintained in all cases.  In addition, such operational factors as the:

Conformal Coating Masking Boots

Printed circuit boards (PCBs) and related electrical assemblies benefit from the protection of conformal coatings.  However, because the films are insulative when dry, they can disrupt operation of the assemblies’ electrical components, items like capacitors, connector contacts, diodes, operational amplifiers, resistors, or transistors.  Conformal coating masking protects specified regions of PCBs and related assemblies from being conformally coated during film application. These components must remain uncoated to function as designed.  Consisting of masking appliances constructed with appropriate materials, masking systems prevent migration of conformal coatings into designated keep-out areas.  Masking processes enacted prior to coating application assure the conformal materials DO NOT invade designated keep-out areas. 

Parylene deposition takes place at the molecular level.  Applied at room temperature through CVD processing, the typical thickness of parylene conformal film is in the microns-range. 

           Conformal coatings are surface treatments applied to a wide range of products and devices used for aerospace, automotive, biomedical, consumer, military and numerous other purposes.  Their primary objective is providing a protective film that supports a selected device’s ease of use, operating function, and service life, through an exceptional variety of working environments.  Liquid Teflon (PTFE) and parylene are two of the more widely used hydrophobic conformal coatings. 

Selection of the material used to coat a medical device is very influenced by the operational environment it will encounter when implanted in the body.  Pertinent operational/performance factors typically include:

Biocompatible parylene conformal coatings provide superior protection for medical stents.  They represent an enabling technology consistently applied to medical devices of all types for 35 years, to diminish problems stemming from surface microporosity and consequent biofluid corrosion after implant.  Providing a reliable barrier to chemicals and moisture, parylene’s static and dynamic coefficients of friction are comparable to those of Teflon.

A metal alloy of nickel (Ni) and titanium (Ti), nitinol (NiTi) exhibits the properties of shape memory and superelasticity, which make it very useful for adaptation to conformal coatings.  However, like parylene, nitinol is often difficult and expensive to produce; the extreme reactivity of the alloy’s titanium component requires exceptionally tight compositional control during combination and manufacture.  

It is possible to remove unwanted conformal coatings from PCBs in-shop.  The process can often be accomplished by either the assembly’s original equipment manufacturer (OEM) or an end-user, but the capacity to do so doesn’t always exist.  For these parties, conditions affecting the poor coating may:

Sometimes problems with conformal coating are too complicated or difficult to repair.  This can occur when bubbles develop in the coating during the application process; bubbles cause voids in the coating that defeat its protective, insulating purpose, suggesting the need for removal.  Other situations that lead to inadequate coverage, and may favor coating removal, rather than repair include: 

• Coating application that’s either too thick or thin for the project’s purposes.
• Component surface finishes that adapt poorly to the conformal material chosen for coverage.
• Disparities in surface tension/surface energy.
• Gravity issues that negatively impact application of liquid coating.
• Improper mixture of two-part materials.
• Inadequate fixturing or placement of assembly components in the coating area.
• Inadequate masking implementation.
• Incorrect interpretation of coating requirements.
• Residue on the coating surface during coating application.
• Poor, uneven coating application.

Overly thick film application or use of coating equipment/materials unsuited to the assignment are major causes of coating problems.  In these cases, complete or partial removal of the conformal film from the PCB may be the best solution. 

Thus, it is important before beginning any conformal coating assignment for designers and users to recognize the various types of conformal coatings and their interactions with the parts/materials they cover, to protect the products in their respective end-use environments, for the expected design-life of each component. 

Industry Standards

             When removal is the best option for your coating problem, it is advisable to consult prevailing industry standards for appropriate process guidelines.  For instance, IPC-7711/7721 delineates recommended procedures for conformal coating removal from, and replacement onto, PCBs.  IPC-A-610 is a widely-held standard for electronic assemblies, offering users limited but valuable criteria for conformal coating applications.   Designed and constructed with the intent of obtaining maximum confidence in the materials with minimum test redundancy, IPC-CC-830B qualifies the definition, use and conformance of all conformal coatings types for PCBs.  In most cases, coating removal is required when assemblies don’t meet the requirements of IPC-CC-830, concerning overall quality conformance of each

The Logistics of Coating Removal                                                               

The logistics of coating removal are largely dependent on the type of coating material, its position on the PCB, and the board’s components.  Proper identification of the coating material, and the methods used for its original application, are essential to correct determination of the removal method.  Once these have been identified, determination of the appropriate removal method can be achieved. 

In many cases, chemical strippers can dissolve conformal coatings from PCBs.  Acrylic films are typically removed easily by soaking in a solution of stripping fluid, followed by mild mechanical abrasion if necessary.  These two processes also work for coatings such as epoxy, silicone and urethane; however, since these substances have higher levels of chemical resistance than acrylic, complete coating removal is more difficult and time-consuming.  In all cases, the stripping solution’s compatibility with the PCB’s components needs to be verified to minimize potential damage during the removal process.

Chemical removal does the least damage to PCBs; it is effective for the liquid coatings -- acrylic, epoxy, silicon and urethane.   Chemical methods work less well for parylene films, since the substance is chemical inert.  Abrasion, laser, mechanical, plasmatic and thermal removal methods are more successful for parylene films; they also work for liquid coatings in many cases.

Recently applied coating is more easily detached from substrate surfaces than older coatings, regardless of the material, unless the coating itself has begun to decay with age.  Larger areas of the board respond best to complete submersion in a tank of stripping fluid.  Gentle abrasion using a soft bristle brush will also eradicate coatings.  

Summary                                                

Please remember that the removal of conformal coating generally requires use of exceptionally caustic and potentially dangerous chemicals; the safety of process operators, the product being treated and the immediate environment can be jeopardized by use of inappropriate  removal materials and methods.  Consultation with a certified conformal coating specialist is highly recommended prior to removing conformal coating.  To this end, the professionals at Diamond MT are eminently qualified, and would be glad to be of assistance.

To discover more about conformal coating rework and removal, download our whitepaper now:

Defects to either the PCB assembly or its conformal coating can be sufficient to cause coating removal.  Whether repair technologies address the circuit board’s components or the conformal film, subsequent post-repair coating (recoating) processes need to address:

• Conformal coating applied incorrectly can cause PCB malfunction.
• Selecting the wrong coating material from among acrylic, epoxy, parylene, silicone or urethane can be a source of board failure, if it does not support the PCB’s operating environment.

Removing the coating may be necessary if these conditions prevail.

Conformal coatings are designed to protect printed circuit boards (PCBs), assuring they work under all operational circumstances.  However, cases emerge where boards fail to function despite conformal coating protection.  Such non-performance can be a consequence of:

            Not completely understood, electrically conductive tin whiskers are crystalline structures between 1-2 millimeters (mm) that can grow from surfaces where tin is used as a final finish; surfaces finished with electroplated tin are particularly susceptible to whisker growth.  Although their occurrence was originally documented during the 1940s, no real solution has yet been devised to prevent their development, which may reach 10 mm in some cases.  This is unfortunate because tin whiskers have the capacity for generating arcing and short circuits between electrical elements of printed circuit boards (PCBs) and related electronic equipment.    

Tin Whiskers:  Their Origin and Impact

Physically, tin whiskers result from the spontaneous growth of tiny, filiform hairs or tendrils upon tin surfaces.  These structures can create electrical paths, often within the presence of compressive stress during component operation.  Because they usually develop in a functional environment that supports short circuits or arcing, tin whiskers don't need to be airborne to damage electronics.  Among other problems, the four main risks with tin whiskers are:

• Stable short circuits in low voltage, high impedance circuits. 
• Transient short circuits may develop where tin whiskers span tightly-spaced circuit elements maintained at different electrical potentials.
• Metal vapor arcs result when a whisker-short occurs in a high-current/voltage environment. They are perhaps the most destructive of electronic system failures attributed to tin whiskers.
• Contamination from debris resulting from tin whisker presence can interfere with component performance.

Other adverse consequences of tin whiskers include:

• Behaving like miniature antennas in fast digital circuits or at frequencies above 6 GHz, generating a negative impact on circuit impedance and stimulating reflections.
• Causing failures in relays, a source of deep concern for relay-functions as important as those for nuclear power facilities.
• In outer space (or any vacuum), tin whiskers can short circuit high-power components, ionizing and potentially conducting hundreds of amperes of current, exponentially increasing the short circuit’s damage.
• Tin whiskers have caused malfunction and recall of medical pacemakers.
• Whiskers located in computer disk drives can break, resulting in bearing failures or head crashes.

Conformal Coatings Mitigate the Effects of Tin Whiskers

Selecting a tin whiskers’ mitigation strategy is important; because the source of their growth is unknown, they cannot be entirely eliminated.  Although ceramic coatings have proven successful, conformal films made from polymeric compounds such as vapor-deposited parylene, or wet application acrylic and urethane, deflect whiskers away from the coating surface.  For instance, studies conducted by NASA seeking tin whisker control for space craft have shown urethane conformal coatings successfully mitigate tin whisker growth.   In addition, some acrylic wet coatings, such as HumiSeal 1B31, also mitigate tin whisker’s problems.  For various reasons, other conformal coatings -- epoxy, and silicone – are less effective minimizing the development of tin whiskers and their impact on PCB performance.

Perhaps the most effective conformal coating for alleviation of tin whisker related issues is parylene.   Deposited in gaseous form, through a chemical vapor deposition (CVD) process, parylene seeps deep into substrate surfaces, penetrating spaces as minute as 0.01mm.  In doing so, it forms a pinhole-free protective film that is ultra-thin but exceptionally durable.  Chemically inert and of high tensile strength, parylene retains its stability throughout a wide range of temperatures.  Because it can be applied at room temperature, parylene application is stress-free.  These properties combine to support superior mitigation of tin whiskers.

. However they are applied, conformal coatings create a physical barrier over electronic components that stops tin whisker damage.  Conformal coatings:

• Form a protective film that safeguards assembly circuitry and components, physically separating them from each other.
• Substantially diminish tin whiskers bridging between the separated components.
• Lower whiskers’ capacity to generate arcing and shorts.

Conclusion

Tin whiskers can generate arcing and short circuits leading to systemic failures in PCBs and similar electrical assemblies, significantly damaging and otherwise altering their performance expectations.  Vital devices, equipment and facilities such as pacemakers, power plants, and even satellites have had their function diminished by the presence of tin whiskers.  Determining methods for preventing or slowing tin whisker growth is difficult because:

• outside of some evidence they are the product of mechanically- and thermally-induced stresses,
• the exact mechanism behind their development is not fully understood.

Where they develop, mitigation of tin whiskers is essential to limiting their impact on assembly performance.  Conformal compound coatings such as parylene, and to a lesser extent acrylic and urethane, can stop tin whiskers from;

• penetrating an applied protective barrier,
• bridging electrical components and
• creating arcing or a short.

While it is impossible at the moment to completely prevent the occurrence of tin whiskers, their mitigation with conformal coatings will dramatically limit whisker growth and equipment damage.  Vapor-deposited parylene and wet coatings such as acrylic and urethane, provide generally good tin whisker defense.  Other traditional wet conformal coating materials such as epoxy and silicone are mostly ineffective as protection against the development and effect of tin whiskers.   

High-tech electronic systems increasingly regulate automotive management functions for emissions’ controls, fuel systems, fluid monitoring, lighting, and powertrain mechanics, frequently comprised of miniaturized, multi-layer MEMS/Nano packages.  Systems’ survival in hostile vehicular environments typified by condensation, corrosive fluids and vapors, excessive temperatures, humidity and prolonged UV exposure is partially assured by protective conformal coating.  

            Protection of printed circuit boards (PCBs) is most often achieved with either potting or conformal coating.  The selection of which method to use depends upon the PCB’s purpose and how much protection it requires.  Potting offers the strongest shielding barrier, but is also affected by a range of operational disadvantages that can offset its functional benefits.  Conformal coatings generate reliable barrier protection, which frequently circumvent the problems inherent in potting.  This is particularly the case with parylene, a non-liquid conformal coating. 

Parylene Varietals:  Matching Material to Purpose

A common generic name for Poly-para-xylylene, parylene forms a protective plastic film when applied to substrate surfaces.  Application is achieved through a chemical vapor deposition (CVD) process in a vacuum, as a gas to targeted substrate surfaces.

Parylene’s CVD method of application generates exceptionally lightweight yet durable conformal coatings, with superior barrier properties.  Compared to liquid processes, the effects of gravity and surface tension are negligible, so there is no bridging, thin-out, pinholes, puddling, run-off or sagging.

Despite parylene’s numerous benefits as a conformal coating, it has several disadvantages that should be recognized before it is used.  Failure mechanisms that can emerge from parylene coatings have limited its wider scale application in comparison to liquid conformal films such as acrylic, epoxy, silicon, and urethane.  In many situations, wet coatings can provide better performance and lower cost (or both) for many applications. 

Despite conformal coatings’ ability to dependably protect substrate surfaces of printed circuit boards (PCBs) and related electrical components, problems can sometimes occur which compel their removal.  Chemical removal, which does the least damage to PCBs, is fine for wet coating substances like acrylic, epoxy, silicon and urethane.   Chemical removal methods are far less successful for parylene, despite the use of a chemical vapor deposition (CVD) process for its film application. 

Due to its excellent ability to stop the passage of gases, liquids, or radiation onto circuit board components, parylene is often considered to be the ultimate conformal coating for the protection of devices, components, and surfaces in many industries.

Understanding the characteristics of various conformal coating types, and their interactions with the extreme range of products and materials to which they are applied, ensures optimal function, performance reliability and product-life.   Designers and users of conformal coatings should be aware of the properties of various types of conformal coatings and their interactions with the parts/materials they cover, to protect the products in their respective end-use environments for the expected design-life of each component.  

Parylene Coatings and COTS Electronics

Methods for Measuring Conformal Coating Thickness

Application of parylene’s xylylene monomer employs a chemical vapor deposition (CVD) process implemented under a vacuum.  Unlike wet coating application methods – brushing, dipping, spraying, etc. – parylene CVD is not line-of-sight.  Because the vaporous monomer envelopes all sides of the assembly being coated, appropriate process control allows vacuum deposition of an entirely conformal coating, one that penetrates deep into any crevices, rivulets, or sharp edges and points that exist on the assembly’s surface.  The resultant parylene film is insulating, ultra-thin, and pinhole-free, exhibiting superior protective barrier qualities and very low moisture permeability.

Parylene Conformal Coatings

Often considered the ultimate conformal coating, Parylene is well suited to protect many types of products and devices.

  The National Aerospace and Defense Contractors Accreditation Program

In addition to cracking, a range of associated issues may interfere with successful coating of parylene films.  Because it is applied via CVD, parylene generates a structurally continuous film covering a PCB or similar assembly.  In CVD, the interaction of vapor-phase chemical reactants formulate a non-volatile solid film on a substrate, useful for a variety of applications like corrosion resistance, erosion defense, and high temperature protection. 

Parylene is often considered the ultimate conformal coating for the protection of devices, components, and surfaces in the electronics, instrumentation, aerospace, medical, and engineering industries.

NASA certification is essential to aerospace conformal coating applications, and thus is sought after by many firms in the industry.  In addition to 8739.1, other NASA standards, such as ASTM E595 – a test developed by NASA to determine levels of coatings’ volatile content, appropriately screening low outgassing materials for use in space – are inspection and performance parameters applicable to aerospace uses. 

The AS9100/9120 and ISO9001 qualification are international aerospace standards for quality assurance, development, production, installation, and servicing also relevant to quality workmanship for aerospace products and the firms that manufacture them; equally relevant are IPC-CC-830 and IPC--A-610 classifications, from the Association Connecting Electronics Industries, often considered equivalent to NASA 8739.1 for aerospace conformal coatings.  Nadcap’s AC7120 Rev A - Nadcap Audit Criteria for Circuit Card Assemblies is also applicable. 

One liquid coating type that rivals the use of parylene is silicone conformal coating (Type SR), which cures rapidly, is reliably dielectric and displays exceptional stability across a wide temperature range.  These properties make it parylene’s chief performance competitor, for many purposes.  Further comparison delineates their benefits and disadvantages relative to each other.

The Workmanship Standards developed by the National Aeronautics and Space Agency (NASA) are essential to assuring reliable performance of the aeronautic, defense and space equipment it uses and monitors.  

Designers must keep costs in mind when designing a project.

Parylene C is the most widely used parylene type for conformal coatings.  It is classified as a poly-monochoro para-xylene, produced from dimer material, with one chlorine group per repeat unit on its main-chain phenyl ring.  As a conformal coating, Type C can be deposited at room temperature via CVD.  The resulting film exhibits low chemical, moisture, and vapor permeability, making it particularly useful where protection is needed from corrosive gases.  C’s alliance of electrical and physical properties distinguish it uses from those Parylene F, a consequence of their different chemical composition; F has a fluorine atom on its benzene ring, in contrast to C’s chlorine atom. 

Acrylic (AR) and polyurethane (UR) conformal coatings are among the best known and most commonly used conformal coating materials.  As liquid coatings, both can be applied to substrates through a variety of methods:

Basic Thermal Properties of Parylene Conformal Coatings 

CVD-generated parylene combines high thermal stability with a low dielectric constant, minimal moisture absorption, and other advantageous properties which sustain its adhesion to substrate surfaces.  Among the most beneficial of the parylenes’ thermal properties is their ability to function at an exceptional range of temperatures.  Depending on the parylene type, they are operative at temperatures as low as -271º C, and as high as 450º C, representing an ability to perform within a span of 721º C.  

How do you ensure that a potential conformal coating provider has the professional credentials and expertise necessary to avoid costly mistakes?

The Need for Adhesion Testing

Applied mechanical processes stimulate the binding force between surface molecules required for parylene adhesion to substrates, which is essential to both good parylene performance and assembly/component functionality.  The emergence of conditions characterized by non-adherence and delamination squander parylene’s typically exceptional substrate protection against chemical attack, corrosion and moisture, as well as its superior dielectric insulation (er = 3.1).  

Coating thickness is critical to the proper functioning of your printed wiring assembly, circuit board, or electronic device.

Characteristics of Noble Metals

Selecting the appropriate pre-treatment procedures is a key factor to this success of parylene adhesion to any substance.  Procedures vary quite considerably, according to the materials designated for conformal coating and substrate.  Chemically inert surfaces like gold, silver and other noble metals, and nonpolar thermoplastics such as parylene, are extremely difficult to bond; they require additional surface treatments besides cleaning.  

Bubbles and foam are two of the leading causes of failure during conformal coating inspections. Because of this, it’s worth looking at these defects more closely.

            Parylene only adheres to substrates mechanically, and this can require assistance from additive substances; parylene’s chemically-based adherence is nonexistent.  Adhesion is a consequence of molecular attraction stimulating the surface unification of two dissimilar substances; their joining creates a significant physical bond between them.  Of the two primary types of adhesion, chemical adhesion results when a compound joins with another, because they share sufficient mutual chemical interaction to form a bond with each other.  Because parylene is chemically inert, chemical adhesion is impossible; it adheres using the other method -- mechanical adhesion.  Applied mechanical processes can stimulate this binding force between surface molecules.   

A photochemical process used to preserve conformal coatings, adhesives, and inks, UV curing generates a variety of value-added properties in comparison to conventional curing techniques.  Applying high-intensity UV light to dry (cure) coatings or other substances, UV curing can provide instant results, increasing production speed while reducing the need for and number of typical set-up and clean-up processes.  Lowered operating costs and increased production capacity are further advantages of UV curing for many coating materials and processes. 

Conformal Coatings are polymeric materials used to protect circuitry, parts, and related components. They are most commonly used to protect printed circuit boards (PCBs) and electronic devices.

Pre-coating Essentials

Poor parylene adhesion negates many of the coating’s most-valued functional properties, including dielectric strength, and resistance to the effects of chemicals, corrosive agents, and moisture.  Surface treatments that amplify the interface adhesion between the deposited parylene and the coated substrate are therefore highly desirable.  These treatments entail depositing parylene on a clean hydrophobic surface before its chemical vapor deposition (CVD) process is enacted.

LED Lifespan as Effected by UV Light

Although LEDS are designed to provide as many as 100,000 hours of illumination under laboratory conditions, they are not nearly as resilient when subjected to persistent real-world, real-time usage.  Sensitive to electrical interference, moisture, UV light, and other persistent sources of physical damage, LEDs require protection to operate at levels anywhere near maximum efficiency.  Of all the conformal coatings available to deliver reliable safeguards on an ongoing basis, none surpasses parylene.

Delamination Problems of Parylene Conformal Coatings

Providing a uniform and pinhole-free substrate coating that is ultra-thin, lightweight and durable, parylene coatings completely conform to targeted components and assemblies.  Parylene CVD generates a structurally continuous film that, with appropriate pre-treatment, penetrates deep within substrate surfaces, rather than simply attaching themselves to substrates as liquid-application coatings do.  These provide effective, dielectrically efficient safeguards with coatings as thin as a fraction of a micrometer.   Parylene is chemically and biologically inert and stable, an excellent barrier material to abrasive chemicals, bodily fluids, solvents, liquid water and water vapor.

Once you've decided to use conformal coating for your device, a question that often comes up is:

Conformal Coatings and UV Trace

Conformal coatings provide exceptional protection for printed circuit boards (PCBs) and similar electrical assemblies, through a wide variety of operating circumstances, safeguarding their chemical, electrical, and/or mechanical properties. 

            Parylene has numerous outdoor applications.  However, a major drawback of most parylene types is limited resistance to direct contact with UV radiation.  Daylight is the most common source of UV light.  Prolonged exposure to its high energy radiation can cause objects extensive surface damage and lead to eventual malfunction of electrical light-generating assemblies within.  

You've done your research, chosen a conformal coating provider, and coated your device. Now you want to know if the coating properly adhered.

Conformal coatings are a protective, non-conductive dielectric layer that are added to a circuit board or electronic device.

Improving Parylene Adhesion

Parylene provides an entirely conformal, durable, pinhole-free substrate coating of extreme utility for an exceptional range of materials, products and purposes. Despite its many advantages, parylene's chemical structure can actually interfere with the reliable interface adhesion required for optimal performance. The chemical vapor deposition (CVD) process that generates so many of parylene's benefits also nullifies chemically-based substrate adhesion; only mechanical adhesion is possible.

Implementing optimal adhesion can require surface modification via application of adhesion promoting agents or methods. The materials and processes used for these purposes are largely dependent on the substrate surface and component's specific operational environments and functions. Although most adhesion promotion methods are used prior to CVD, several can be integrated into the coating-process itself, Among the methods of adhesion promotion used with parylene are:

• Thorough surface-cleaning, which stimulates enhanced adhesion by eliminating accumulated substrate contaminants whose presence can diminish overall coating quality.
• Heat-treating. for three hours at temperatures of 140°C, beneficially activates longer-term adhesion and insulation.
• Active, wired devices profit from bilayer component-encapsulation processes.

While these techniques have their uses for parylene adhesion promotion, the chemical monolayer Silane A-174 (3-Methacryloxypropyltrimethoxysilane - C10H20O5Si) is used most frequently to modify substrate surfaces and improve parylene adhesion.

The Uses of Silane A-174

Silane A-174's value as an adhesion promoting agent stems largely from its versatility. It can be successfully applied to substrate materials like elastomer, glass, metal, paper, plastic or quartz, among a wide range of surface substances. The A-174 silane molecule develops a robust chemical bond with the substrate, facilitating the improved surface adhesion capacity of parylene’s mechanical property. Optimal parylene adhesion is commonly achieved by a treatment with A-174 silane prior to initiating the CVD process. However, regarding appropriate procedural scheduling:

• it is recommended that A-174's application be completed after any necessary masking operations have been finished;
• depending on substrate materials, manual spray, soaking, or vapor phase silane processing techniques may be used to apply A-174.

Process Balance

While the silane promotes adhesion, the parylene assures protection. Thus, appropriately proportional intermixtures of silane A-174 and parylene need to be used, in all cases. Corrosion-resistance can be diminished where the relationship between parylene and silane is inexact, causing part and function deterioration from both beneath- and external to the conformal covering. This is especially the case with medical implants, where reliable component function is mandatory, despite being subjected to persistent exposure to often harsh bodily fluids.

Electronics manufacturers need devices that withstand heat, cold, rain, snow, vibration, fungus, oxidation, and corrosion through decades of operation.

Implantable Medical Devices and the Uses of Parylene

Defining MEMS

Ruggedized Products

Parylene Chemistry and Production Requirements

Removal of Conformal Coatings

The conformal coating process creates a protective barrier for product substrates. The type of coating material used is a consequence of several conditions:

Properties of Polytetrafluoroethylene (PTFE)

Protective Conformal Coatings

While parylene is an extremely effective conformal coating, its benefits only come into play when it is properly applied. When parylene is either applied incorrectly or is deposited on a surface that is not prepared for adhesion, the coating can become compromised. Luckily, common parylene defects can be identified, planned for and mitigated through proper procedures.

Parylene and Conformal Coatings 

Parylene Bio-compatibility

Parylene Deposition  

The Growing Internet of Things

The term Internet of Things ( IoT ) describes the expanding interactive capacities of smart networks of processing systems.  Increasingly communicating with each other, they drive enhanced smart automation in many fields, including: 

Overall the generic name parylene describes a distinct collection of polycrystalline and linear organic coating materials with innumerable applications.  The essential basis of today's parylene N, p-xylene, was inadvertently synthesized at England's University of Manchester in 1947.  The filmy residue resulted after high-temperature heating of compounds of toulene and the xylenes polymerized into para-xylene.  The substance immediately demonstrated an exceptional capacity for generating the fine but resilient surface-covering that characterizes today's range of parylene conformal coatings.  

Recognition of parylene's excellence as a conformal coating for many product uses has grown along with its application.  However, issues of barrier failure, current leakage, poor processing, and cost limit its further development and use.

Silicone and Parylene conformal coatings are a lot like humans and dogs. At first glance, we are very different from our canine friends. However, we have a lot in common -- noses, two eyes, hearts, dreams. In fact, we share 84 percent of our DNA with Rover (or Spot). So too with the two coatings. While both have some functional differences -- which we'll explore here -- they also have an important similarity. Parylene and Silicone are both some of the best choices for conformal coatings of your company's products.

Parylene's deposition process is unique among conformal coatings. Unlike others that start as a liquid, get deposited and dry, it starts as a solid. Parylene coating equipment turns it into a vapor, where it then deposits onto the substrate. This unique four-step method poses some challenges but also brings real advantages.

Conformal Coatings

Masking and Parylene Deposition

Choosing parylene gets you half way to protecting your company's products with the best possible conformal coating.  To close the circle, unless you have invested in the proper equipment and training, you also need to choose the right service to apply the coating. The Parylene coating industry, while it is a fairly niche business, is still a competitive market, but the very few top-quality providers are relatively easy to identify. Here are some of the attributes that you should actively seek:

If you have a printed circuit board or other item that needs protection, you typically have a choice between potting and conformal coating. While potting offers the largest and most powerful barrier against the outside world, it also carries some significant drawbacks. Conformal coating, especially with parylene, also offers a protective barrier, but does it without the challenges that potting poses.

While Parylene can coat just about anything, one of its most common uses is for protecting printed circuit boards. Product engineers specify Parylene because it offers a unique blend of five capabilities.

Wearables are no longer emerging technology -- they are here. Whether a wearable item is a medical device like an insulin pump, a smart watch or even a finely woven piece of smart fabric, they all have one basic fact in common. All of them contain technologies that need protection from the outside world and, in just about every case; parylene is the most appropriate choice for protection.

 Basic Dielectrics and Conformal Coatings

Light emitting diodes are gradually replacing all other types of lighting. As they move out of consumer electronics and into general purpose applications ,the demands on the technology are shifting. It's relatively easy to keep an LED safe when it is mounted in the front panel of a computer or hidden under a cover on an alarm clock. Protecting it when it is going to be exposed to the elements 24 hours a day, 365 days a year is more challenging.

Parylene can be used outdoors. However, it has one drawback that could limit its suitability in some outdoor applications: sunlight can yellow it. With this in mind, product designers specifying a coating for a product to be used where it will be subject to sunlight should carefully consider the coatings pros and cons before specifying it. Frequently, but not always, it remains the best choice.

Parylene and urethane conformal coatings share many characteristics. Both are physically strong, resistant to chemicals and mitigate tin whisker formation. This doesn't mean that the two compounds are interchangeable, though. While parylene offers a unique blend of capabilities, many projects choose urethane because of its cost, strength and other advantages.

Parylene Surface Protection

Implantable devices place a special set of requirements and challenges on their coatings. The moisture and broad mixture of chemicals that are found inside of the body are challenging in and of themselves. However, the body also has needs from the coatings that are placed within it. They need to be non-irritating and inert enough to be harmless. For most applications, the best choice is USP Class VI compliant parylene coatings.

The Need for Rugged Products

Parylene and acrylic conformal coatings represent two extremes of the types of compounds you can use to coat printed circuit boards, sensors, or other devices. While acrylic is popular and inexpensive, parylene offers some of the best performance of any coating compound.