A customer asked me some questions about his product. (Didn't have a clue!) So........I was curious (like always) if someone out there might have some ideas as to possible answers to these. Product: 2 sided FR-4 PCB .028 1/1 (very small in size). SMOBC with HASL finish. The part has a couple of very small components. Then it gets set into a small plastic housing (1 side) and has pins (component leads) soldered into place. The whole assembly then gets potted in a black epoxy. Part of their customer requirements is to test this assembly in 85/85 (Temp/Humidity) and apply constant bias voltage. They need to meet at least 1000 hrs. The problem they have ran into is that the copper traces (big guys) are migrating under the soldermask (LPI) to other traces and are failing the test. When they rip apart the assembly they are seeing both traces and soldermask separating both ways. The question that pops up is FR-4 a wise choice for this type of product? Is soldermask beneficial or would bare traces encapsulate better rendering a more electromigration resistant bond? Is a solder finish the best for the potting medium to bond to? Just Curious. The above comments are of my own opinion, and not necessarily that of my employer. http:\www.hadco.com:8080 Dave Hoover (aka, Groovy) NPI Mgr HADCO TC2 Watsonville, CA