PCBA Solution–
In-house Parylene Coating

Parylene (poly-para-xylylene) is a vacuum-deposited polymer that forms an ultra-thin, pinhole-free protective layer through Chemical Vapor Deposition (CVD). Unlike liquid acrylics or silicones that are sprayed or dipped, Parylene grows molecule-by-molecule in a vacuum chamber, resulting in truly conformal coverage with no pooling, bridging, or thin spots—even under components and inside tight spaces.

Parylene coatings range from 0.1 to 50 microns, with 5-25 microns being standard for electronics. Unlike thicker liquid coatings, Parylene provides excellent dielectric protection and moisture barrier properties at just 5-10 microns—critical for miniaturized medical devices and microelectronics where added mass or dimensional change must be minimized.

Parylene offers exceptional dielectric strength (7,000V/mil), complete moisture barrier (WVTR <0.1 g·mm/m²·day), and solvent/chemical resistance without adding thermal stress. It's transparent, UV-stable, and operates from -200°C to +200°C. Most importantly, it provides USP Class VI / ISO 10993 biocompatibility for medical implants and FDA-regulated devices.

The process occurs in a specialized vacuum chamber at room temperature: (1) Raw dimer powder is heated to 150°C to vaporize; (2) Pyrolysis at 680°C cleaves the dimer into monomer gas; (3) Monomer enters the deposition chamber and polymerizes spontaneously on all exposed surfaces. No solvents, catalysts, or curing ovens are required, eliminating thermal stress on sensitive components.

While Parylene adheres well to clean metals, ceramics, and most plastics, we apply silane-based adhesion promoters (A-174) for noble metals (gold, silver) or low-surface-energy materials like silicone rubber. We also use plasma surface activation for critical medical devices to ensure coating retention during autoclave sterilization or long-term implantation.

Parylene cannot be dissolved by common solvents, making localized rework challenging. Removal requires mechanical abrasion (micro-blasting), laser ablation, or thermal methods. For components requiring occasional repair, we recommend designing selective coating barriers or using peelable masks during deposition to keep connector areas uncoated.

Higher costs stem from (1) specialized vacuum deposition equipment and batch processing limitations; (2) Raw dimer material costs significantly more than acrylic/urethane resins; (3) Masking labor is intensive since all surfaces get coated; and (4) Processing time is longer due to vacuum cycles. However, for high-reliability medical, aerospace, or implant applications, the cost-per-device is justified by unmatched protection levels.

Primary applications include: Medical (pacemakers, neurostimulators, hearing aids requiring biocompatibility); Aerospace/Defense (circuit boards in satellites and avionics exposed to extreme temperatures); Automotive (sensors in engine compartments); Consumer Electronics (hearing aids and wearables needing moisture protection); and MEMS devices where stiction prevention is critical.