A frequent question we field here at DigiKey concerns product discoloration for solderable devices such as headers, solder pads for SMT resistors and capacitors, or the leads on board-mounted connectors. This discoloration is frequently taken as an indicator of oxidation on the products, rendering them unfit for use. Is this correct, and can product discoloration be used as a reliable indicator of damaging oxidation?
Unfortunately for quality assurance technicians everywhere, the answer is no. Discoloration can stem from many sources, among them ordinary manufacturing processes. Parts rarely look as neat and clean as their computer-generated sales imagery makes them seem. In addition, not all forms of product oxidation are visible. Rather than relying on visual checks, the recommended method for checking for oxidation is to perform conductivity tests on the products in addition to solderability tests if a few test parts can be spared. Unusually high resistance values, as well as poor solder performance, are much more certain indicators of oxidation than any visual discoloration. Do note that oxidation can also happen to the solder pads or plated through-hole pads on a PCB, as well - otherwise good products can end up falsely flagged as oxidized and useless if tested on a PCB that’s been poorly stored or maintained.
For information on how to keep your PCBs free of oxidation (also a good basis for avoiding unnecessary oxidation of other products), check out Oxidization of SMT Pads Can Be Avoided.
For some useful home remedies for clearing oxidation on commonly used metals, check out Removing Oxidation on Different Metals