Issue:
Using exotic finishes on printed circuit boards like ENIG, immersion tin, silver, and OSP are appealing because they are lead-free. However, these materials are susceptible to oxidation and corrosion from exposure to moisture and humidity. This oxidation causes dewetting after soldering, which can lead to poor joints at assembly and ultimately lead to failure of the board.
Solution:
Careful handling will minimize oxidation and associated problems. Because even natural oils from human skin can tarnish these finishes, gloves are always recommended when handling PCBs with immersion surface finishes. The boards should be stored in airtight packaging to prevent oxidation due to humidity and moisture.
Examples:
PCBs with ENIG surface finish that have been heavily oxidized due to exposure to moisture:
Results of solder testing and the dewetting caused by the oxidation on the ENIG surface mount pads:
