How not to trick your BGA friends
Continuing with yesterday's theme, I have a couple examples that should have been fine, but due to issues at the board house, improper storage or contamination, ended up very much not fine.
Behind door number one, we have an OSP finish that will make you very unhappy. That's "Organic Solderability Preservatives" in long hand. I've also heard it called "Organic Surface Preservative", but close enough. It is a nice flat surface which is good for BGAs. Years ago, it had a reputation for being poor quality, "cheap", but newer formulas seem to work pretty good in both leaded and lead free. In this case, the darker pads were likely contaminated in some way - either at the board fab house or subsequently in handling.
Next is the worst example of surface degradation I've ever seen. Yes, it's an extreme outlier case, but this is where a silver board can go if it wasn't built with the best quality control, was stored too long, was exposed to polluted air or other contamination and had bad luck. This board probably has all of those issues, but any one alone can be problematic. Silver board especially should be stored in a cool dark place; preferably sealed in the original packaging.
OSP can also mean Oregon State Patrol, but they don't care about BGAs. Just safe driving.