QPL Verification - a Key Element in Parylene Coating Specification

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1 QPL Verification - a Key Element in Parylene Coating Specification William Gleason, General Manager Para Tech Coating, Inc. (Para Tech) Copyright 2012, Para Tech Coating, Inc. CAPTION: Thin, transparent Parylene film has been lifted from a test coupon for digital micrometer measurement and other rigorous tests as part of the QPL certification process. Vacuum-deposited film has been used for decades to protect surfaces and components in aerospace electronics, medical technology, automotive and wide ranging industrial applications. While the Parylene formulation is molecularly specific (see article Sidebar), the Parylene dimer - the raw form of the coating - varies in purity and performance from one manufacturer to another. A deficient dimer formulation will degrade the ability of finished Parylene film to protect critical assemblies under harsh conditions. Manufacturers of critical systems are threatened by the possibility that a subcontractor might substitute counterfeit or fraudulent components or materials for Mil-Spec assemblies and other high risk devices. Such unauthorized and potentially undiscovered substitutions threaten the performance and ultimate reliability of such assemblies. A chemically based material such as Parylene dimer presents a particular risk, since it is very difficult to detect an inferior, non-qpl (Qualified Product List) material apart from destructive testing, and effective coating encapsulation is a key component in system reliability. The Defense Logistics Agency manages QPL operations through its Defense Supply Center, Columbus (see The QPL certification program is intended to assist design engineers and circuit manufacturers with the complex task of analyzing and qualifying products and materials such as Parylene dimer to ensure they conform to standards and meet the high

2 Para Tech Coating, Inc. Page 2 QPL Verification Article performance requirements of aerospace, defense, medical and other critical electronics applications. Today there are more than 30,000 products or components in eight categories that are covered by the ongoing QPL process. CAPTION - Parylene film is superior to liquid coatings in encapsulating and protecting delicate electronic circuits, yet it adds almost no mass, and is conforms absolutely to flat surfaces, around edges, and into crevices. Products submitted for QPL review are subject to extensive testing against detailed performance and quality requirements, and then validated by subsequent audits on a continuing basis. Products that achieve QPL status are listed by the Defense Logistics Agency Land and Marine in a qualified product database that is subject to ongoing additions, deletions and modifications. While non-qpl rated Parylene dimers may be sufficient for routine, non-critical coating tasks, there is no assurance that they meet the performance level required for the most demanding coating applications since they have not been subject to QPL testing. There may be no apparent difference in appearance between dimers of various suppliers, nor in their functionality for routine vacuum coating. Dimer performance can, in fact, only be determined by means of the thorough, sophisticated laboratory analysis involved in QPL testing. Higher performance, QPLqualified Parylene raw material may be more expensive than non-conforming dimers, but substitution of an inferior, non-qpl material compromises the performance of sophisticated, mission-critical components, with potentially severe and costly consequences. Therefore it is crucial for system specifiers and subcontracting decision makers to insist on the documented use of a QPL-listed Parylene dimer, along with optimal substrate cleaning, surface preparation and coating deposition procedure, in order to meet governing regulations.

3 Para Tech Coating, Inc. Page 3 QPL Verification Article The QPL program is a valuable resource for manufacturers as they identify and select a Parylene coating resource, as well as to those companies with in-house Parylene coating operations. Para Tech Coating, Inc. (Para Tech) supplies QPL-rated Parylene raw materials that are approved per QPL-46058, as specified for products under MIL-I Para Tech is one of only a few U.S. providers of QPL-rated Parylene dimer to both coating service customers and in-house Parylene coating operations, as well as to other Parylene coating suppliers. The QPL Process Para Tech has continuously met the stringent demands of periodic QPL testing. Para Tech Quality Control Manager Patricia Langraphi explains that the QPL listing process begins with coating of test coupons using the dimer under review, and submitting them to an authorized third party laboratory for detailed analysis of physical and chemical properties, in accordance with MIL-I-46058C Standard guidelines. The results of these tests are submitted to the Defense Logistics Agency (DLA) for review and approval, and with DLA authorization, the material is listed on the QML/QPL database (QPL database ( Associated Quality Issues The QPL rating program for dimer supports the broader electronic manufacturing quality requirements of customers following the AS9100 standard. This standard incorporates the full scope of the original ISO 9000 program, along with additional requirements specifically related to aerospace and defense industries. As QPL approval is an essential requirement for raw material used on defense projects, QMS certification based on aerospace standard AS9100 is an essential requirement for companies doing business with aerospace and defense organizations. In 2008, Para Tech s Aliso Viejo, California, headquarters became the first Parylene coating service facility in the country to achieve AS9000 QMS certification, and was subsequently upgraded to AS9100 Rev. C in In May, 2012, Para Tech s Middletown, Connecticut, facility also achieved QMS certification based on AS9100 Rev. C. According to Quality Assurance Manager Langraphi, maintaining AS9100 certification is a complex and continual process. Our quality management system is based on a robust system,

4 Para Tech Coating, Inc. Page 4 QPL Verification Article where AS9100 Rev. C requirements and quality principles are the foundation for all of our processes. Every aspect of our operation has been adjusted and refined to conform to the latest standard, Langraphi notes. We maintain certification based on a three-year cycle that involves verification of every individual process and of the entire system. A certification authority conducts periodic on-site audits to verify conformance of the QMS. The inability to demonstrate compliance to the standard requirements can result in major or minor non-conformance findings, and the possibility of suspension of certificate, she said. The results of periodic AS9100 audits are published in the Oasis database, which is open to review by coating service customers and prospects. Both our East Coast and West Coast Parylene coating facilities must operate on the basis on constant attentiveness to every aspect of quality in order to maintain the highest level of quality assurance. This is the standard of daily performance at Para Tech, Langraphi concludes. Conclusion The QPL rating of Para Tech dimer completes the circle of AS9100 requirements for fully competent vacuum deposition coating of electronic systems for the highest level of performance and customer peace of mind. This is a process that few providers are equipped to provide. Well-meaning, established and otherwise competent companies may inadvertently use counterfeit materials or processes, and it is imperative that every link the supply chain pays close attention to detail to ensure compliance with both materials and methods requirements. If the quoted cost for a system element seems too good to be true, investigate the supplier closely to make sure that the quotation covers and verifies QPL listings, along with every other aspect of production quality. xxxxx

5 Para Tech Coating, Inc. Page 5 QPL Verification Article (Article Sidebars) ILLUS - Diagrams of Parylenes N, C and D The Dimer CAPTION: There are three primary forms of Parylene, which differ at the molecular level. The raw dimer form of Parylene is a granular white powder, described chemically as poly-paraxylylene. There are different variants of the material: the most popular being Parylenes N, C and D, and the selection of the optimal dimer depends on the demands of each application. Parylene C has a chlorine atom on the benzene ring, resulting in a useful combination of electrical and physical properties; particularly low moisture and gas permeability. Parylene N has the highest dielectric strength of the three versions, with a dielectric constant value that is independent of frequency. Parylene N is commonly used in high frequency applications. Parylene D has two chlorine atoms added to the benzene ring, giving the deposited film an increased level of thermal stability. (Another common variant is Parylene F, which has a fluorinated atom on the benzene ring and provides advanced thermal and UV properties. This dimer is suited to high temperature coating applications.)

6 Para Tech Coating, Inc. Page 6 QPL Verification Article The Parylene Coating Process CAPTION: - Objects to be coated are cleaned, masked, and placed in a vacuum chamber, where the film is deposited at room temperature without physical stress forces. Parylene film is applied in a gas phase sequence beginning with conversion of the powdered dimer to a monomer gas under heat. The vapor moves to a roomtemperature vacuum deposition chamber where it forms on exposed substrate surfaces as a thin, transparent polymer film. This polymerization takes place without the introduction of any catalysts or solvents. This transparent film coating differs from conventional coatings in that there is no liquid phase, and physical manifestations common to liquid coatings such as meniscus and the tendency to pool and draw away from corners, are not seen. Since the coating is formed directly from a gas, it does not create cure stresses, and confirms closely to the underlying substrate without bridging between adjacent components. Parylene builds with equal thickness on flat surfaces and corners, edges and in crevices. xxxxx