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