| Folk's, | | I'm looking for information of how long you cna store a gold finish PCB before building it. I know there are problems with the gold disappearing into the underlying nickle over time / temperature etc but exactly how long do you have before this will cause serious problems ? | If the gold has dispersed is there any way to repair it ? |
It's not so much a question of the gold dissappearing as it is other factors at work. As you and Mike G. (below) said - there is very little gold applied over the nickel barrier.
The nickel is a barrier to prevent copper from "dispersing," as you say, into the gold. As such it is a two way barrier also preventing the gold from becoming part of it or getting through it.
The probems are really two:
1) Providing plating, or deposition, processes are effectively managed, the gold will stay in place for long periods (as with any surface finish, packaging storage, handling, shipping, etc. conditions (ISO 9000) are critical factors. If all requirements are met as required, gold shelf life is indefinite.
2) As we are talking a preferred maximum of 3-10 millionths" gold over 100-120 millionths" nickel over copper, it is vital the nickel barrier be as specified. However, the biggest problem is phosphorous/nickel intermetallic formations providing the embrittlement mechanism we all wish to avoid but no one has that fix yet.
It should be noted that when the nickel barrier is not as specified, copper causes the problems in the gold, and there is no fix.
Earl Moon
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