Hello all, Our company has always used HASL finish on our products. Recently however, we have a had a problem on a couple of boards that I have been told cannot be avoided with HASL, and we should switch to ENIG(electroless nickel immersion gold). I have searched this forum and learned all kinds of interesting and worrysome things about ENIG and wanted some more info. We have a PCB with a ground plane side that is almost all tinned(very little soldermask) This is due to needing to mount a heatsink directly to the pcb, and needing a good thermal contact. During HASL, some solder gets trapped in vias or pools on the surface and during reflow this solder can sometimes run out and form peaks that will push through the thermal gasket used and short to the grounded heatsink. I agree that ENIG will not have this pooling or excess solder problem, but I am worried about the reliability of it, ie. black pad syndrome or nickel oxidation of the pads. Also the problem of weak solder joints if the right temp profile isn't used and a proper intermetallic bond isn't formed. I have been told ICT will catch black pads, but am not sure if I believe it, or if it will catch the weak bonds. Can you tell me if ICT testing will always pick up black pads, or if components may appear to connect at first but after time or temperature variations may turn into cold solder joints? Thank you for your responses.
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