SMT007 Magazine

SMT007-Aug2019

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32 SMT007 MAGAZINE I AUGUST 2019 Feature by Tim Seifert SPECIALTY COATING SYSTEMS (SCS) Designers and manufacturers of electronics are under pressure to make packages smaller, lighter, and more environmentally friendly. They also need to ensure that their new tech- nologies perform reliably in their operating environments, which may include exposure to chemicals, moisture, electrical charges, and extreme temperatures while maintaining com- pliance to a growing number of stringent envi- ronmental, safety, industry-specific, govern- mental, and/or biological regulations. In this article, I will take a closer look at Parylene con- formal coatings and the role they can play in helping manufacturers address current and future challenges in the electronics industry. Developed by Union Carbide scientists in the late 1950s, Parylene is the generic name for a unique series of polymeric organic coating materials. They are polycrystalline and linear in nature, possess useful dielectric and barrier properties per unit thickness, and are chem- ically inert. Parylene coatings are ultra-thin, pinhole-free, and truly conform to components due to their molecular level polymerization— basically "growing" on the substrate surface one molecule at a time. Parylene coatings are applied in a vapor deposition process rather than by dispens- ing, spraying, brushing, or dipping. The pro- cess begins by placing parts to be coated in the deposition chamber. The powdered raw mate- rial—known as "dimer"—is then placed in the vaporizer at the opposite end of the system. The dimer is heated, causing it to sublimate to a vapor, and then heated again to break it into a monomeric vapor. This vapor is transferred into an ambient temperature chamber where it spontaneously polymerizes onto the parts, forming the thin Parylene film. The Parylene deposition process is carried out in a closed system under a controlled vacuum with the deposition chamber remaining at room tem- perature throughout the entire process. No sol- vents, catalysts, or plasticizers are used in the coating process. Because there is no liquid phase in this deposition process, there are no subsequent meniscus, pooling, or bridging effects as seen in the application of liquid coatings; thus, the entire part is equally protected. The molecu- lar "growth" of Parylene coatings also ensures not only an even, conformal coating at the thickness specified by the manufacturer, but because Parylene is formed from a gas, it also penetrates into every crevice—regardless The Role of Parylene Conformal Coatings in Next-gen Electronics ParyFree coated and uncoated board after salt-fog testing.

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