| I am having problems processing immersion gold boards. The achieved solder joints appear acceptable a la IPC-A-610, but the resultant joint does not fully cover the land, i.e. you can still see an outline of gold pad. | What is the best way to achieve a "better" joint on gold ???? |
As has often been pointed out, immersion chemistry is hairy. Immersion gold is porous and has organics co-deposited which will eliminate much hope of a decent solder flow, even assuming the underlying nickel has not oxidised, which is all too common. IMHO, this finish is more cosmetically appealing than technically desirable (and VERY profitable for the PCB maker). Your experience is very common and wetting balance tests on this finish often give horrendous results.
IF the problem is more with the nickel underplate (or copper) being oxidised through the porous gold, then using a good, strong, water-soluble paste should achieve wetting. IF the problem is due to the gudge which goes on with the gold, then there is little that can be done to improve the situation.
Sorry, I know this isn't helpful, but it's the best I can say.
Brian
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