Parylene Coatings and COTS Electronics
Dielectric and non-conductive, parylene conformal coatings provide dependable protection for printed circuit boards (PCBs) and related electronic assemblies. They safeguard components from contaminants, corrosion, dust, fungus, moisture, salt spray, temperature extremes, and, in the case of implantable medical appliances, often harsh bodily fluids.
In comparison to parylene’s specialized chemical vapor deposition (CVD) method of substrate attachment, other conformal coatings -- acrylic, epoxy, silicone and urethane – rely on liquid application techniques. Each coating material has its strengths, and selection of a particular type depends the PCB’s specific use and the type of environment for which it is intended.
Commercial off-the-shelf (COTS) assemblies and devices have been increasingly used for military purposes. Although COTS electronics are generally NOT designed for military applications, escalating budgetary constraints within the Department of Defense have combined with increasingly stringent Restriction of Hazardous Substances’ (RoHS) directives to encourage their use. The exclusive custom design that typified most military devices in the past has been modified for COTS-adaptation for many non-critical products.
Parylene’s superior coating capacities are recommended for COTS military, and other specialized, applications, which upgrade their conventional consumer uses for functioning in far more severe and punishing operating environments. Solutions that work without fail in a consumer device generally require significantly added protection in fighter aircraft. In comparison to liquid coatings, parylene conformal films are recommended for ruggedized products where reliable, dedicated electrical, biological or environmental protection is required. They represent the optimal conformal choice for product ruggedization.
Ruggedized products are designed to ensure superior performance during operating conditions exemplified by extreme temperatures, material intrusions of dust, rain, soot, water or wind, and persistent, intensive vibrations both within and external to the device. Because of the unusual, punishing performance ecosystems characterizing rugged objects’ operational expectations, internal components require ruggedization to safeguard their installed electronics. Protecting delicate, finely-tuned components requires conformal coatings of exceptional performance durability and versatility. No other conformal coatings displays parylene's versatility for ruggedized applications.
In addition to military embedded systems utilized through extended duration for in-field and on-site service, rugged devices have demonstrated reliable functionality for aerospace computing, emergency healthcare/public safety situations, and specialized scientific research or undersea/arctic exploration/surveying. These represent a range of operational environments characterized by exceptional compression/stress, radical changes in temperature, and variable atmospheric conditions where components and devices require specialized, in-depth protection. The resistance to harsh working environments provided by parylene supports functionality where unprotected devices would otherwise fail.
Parylene Conformal Coatings for COTS Rugged Devices
Parylene coatings are:
- meet IPC-CC-830 requirements, and
- are itemized on the Defense Supply Center Qualified Parts List (QPL) for MIL-I-46058.
The MIL-STD-810F spec is especially relevant for product ruggedization. It details procedures for testing a device’s capacity to function:
- under low pressure/high altitude situations,
- in unexpectedly high or low temperatures,
- in rain or humidity,
- under conditions of shock, gunfire vibration, acceleration, and
- in the presence of salt fog or fungus, among a variety of difficult operational circumstances.
COTS components adapted for military purposes must meet the specifications of MIL-STD-810F, which stipulate performance standards in response to the impact of artillery/gunfire, extreme acceleration and the presence of contaminants ranging from shrapnel to blood, fungus to salt fog. COTS devices provided ruggedized parylene protection maintain operational performance. Ruggedized parylene films offer long-term surface insulation resistance (SIR) necessary for sustaining the optimal function of the protected electrical system. Among their other advantageous properties for COTS ruggedization are their ability to:
- generate a uniform, bubble-free conformal film,
- withstand vibrations,
- provide excellent barriers against biological, chemical, and moisture agents,
- suppress the formation of metallic whiskers,
- support MEMS- and nano-technologies,
- strengthen delicate PCB leads and connections by a factor of 10, with
- high dielectric strength, and
- mechanical/physical properties that support resistance to environmental tremors, jarring vibrations, and natural or man-made disasters.
Parylene ruggedized COTS electronics further withstand alterations in altitude, and interference generated by magnetic properties or radio frequencies. Approved as a military-spec conformal coating, parylene enhances the integrity of ruggedized devices without adding high cost, while retaining the device's functional capacity throughout exposure to these conditions. Standard brush, dip or spray liquid coating methods are unable to consistently protect PCBs and assemblies reduced to the MEMs- or nano-scale. In contrast, parylene’s CVD process penetrates deep within substrate surfaces to reliably safeguard the PCBs that power or guide military, and other, ruggedized products and systems.
Designed to withstand harsh environments, ruggedized products are increasingly numerous. They are manufactured to meet challenging performance standards for industrial, defense, aerospace, and commercial applications. Parylene is a mil-spec approved conformal coating which has been in use for years in military and aerospace applications for custom devices, and can enhance the integrity of COTS devices without adding high cost.
Rugged products function as expected throughout operating environments where excessive variations in temperature, intensive vibrations, unusual disparities of dryness or moisture, and high wind velocity are the norm. Assuring appropriate ruggedization is especially important for COTS electronics which are not designed for use under radical, uncompromising conditions. For these purposes, parylene conformal films provide persistently reliable protection, shielding components and exteriors under these conditions, without diminishing their functionality.