Unreflowed Solder Under QFNs

摘要

LOOKING THROUGH SOME recent x-ray images of what I would call "good bad" boards (at least, that is what they are for me, as they showcase "good" examples of how certain "bad" types of failure look under x-ray inspection), I came across a number of different issues that are different from "traditional" BGA/QFN problems mentioned in this space before. To wit, I noted some images showed where solder paste had not reflowed under the devices, and there was the presence of foreign object(s), such as discrete components, trapped under the package.