Salt Mist, IP66, and Why Our Coating Spec Changed Twice
The first conformal coat passed lab spray tests and failed in service. The second passed in service and failed thermal cycling. The third one stuck.
A vehicle deck is not a chemistry lab. It is salt mist plus diesel residue plus brake dust plus thermal cycling, and a coating that passes one of those tests on a bench can fail the combined exposure in months. We learned this the slow way.
The three iterations
v1 — acrylic conformal
Passed salt-spray (ASTM B117) in the lab. In service, brake dust adhered to the surface and trapped moisture. Boards started showing leakage current within four months.
v2 — urethane conformal
Survived the brake-dust problem and the salt-mist problem. Failed thermal cycling at the connector joint over the first 30-day hot-route sailing — coating cracked, moisture wicked.
v3 — parylene + selective urethane
Conformal parylene under selective urethane at connector boundaries. Survived 14 months of pilot operation with zero coating-attributable failures.
Sources
- ASTM B117 — standard practice for operating salt-spray (fog) apparatus.
- IEC 60068-2-11 and IEC 60068-2-52 — environmental testing: salt mist and cyclic salt-mist tests.
- IPC-CC-830 — qualification and performance of electrical insulating conformal coatings.
- IEC 60945 — general requirements for shipborne marine equipment (environmental and durability).
- [VERIFY: 14-month coating service-life results are RoRoSafe pilot-operation data, not third-party qualified.]