Emergency!!! We have a small run (5) of very dense boards that have an immersion tin finish. They were built in April/May and have a heavy tarnish appearance on them, smd pads and through holes. We are being asked to apply ssd to the surface mount pads but I am afraid it will not solder too well!!! Can this be cleaned or does the tarnish create issues that cannot be corrected when solderability is considered?? The customer has agreed to replace the boards with new ones if necessary but I hate to throw away boards that are otherwise OK. Can we clean the tarnish off?
Matt: You're correct. Do not mess with these boards. If the immersion tin [imm tin] is discolored, it will not solder with routine processes. Ask your customer to return the boards to his / her fabricator and have the imm tin replated. The fabricator should be happy to do this.
Long term, your customer should consider a fabricator that has better process controls and can turn their plating tanks more frequently.
Convince your customer by hand dispensing paste on the discolored pads and reflowing the board.