My first thought from your description was solder flux residue. Whether flux residue is harmless depends on which flux was used. Some flux is very corrosive and residue will damage the board over time. Other flux is formulated to be "no clean" and is supposed to not be harmful. Even with the "no clean" flux, I still prefer not to have a lot of residue but I don't know how much of a problem it really is. After soldering, I clean my boards with isopropanol and a brush.Although the stuff near the bottom of the circle looks like flux residue, the big white rectangle at the top definitely does not look like flux residue. It almost looks like the board has been subjected to extremely high temperatures there, but I can't be sure from the picture and normally a burned PCB will be black and charred, not white.
Please help us! Is the stain on the copper or on areas where there is NO copper?Paul
Is that 'white square' at the top just a reflection?Also.. (same as above).. it doesnt LOOK like there are any components or things to solder on that side of the board... so why would there be flux residue there?
Try removing with a soft toothbrush and IPA.
It's literally all over the PCB - not just where the copper is. Yes, apologies for the bad image. The white square is just reflection. The stains can be seen directly below it.The part of the PCB in the image indeed has no components.I don't have IPA at hand - it feels like the stains are almost part of the board though - I can't just rub them off.
Bet the board was made in China at a really low price.
I don't have IPA at hand - it feels like the stains are almost part of the board though - I can't just rub them off.
No, flux doesn't rub off without a solvent, its solid. Looks like the solvent wash was overburdened with flux andstarting to streak the boards, not unusual for cheap pcbs, anything to reduce cost.Chances of bad solder mask is very small, never seen that.
Ah, but that wasn't in China, was it?
Just curious, one of my PCBs is showing these weird marks, that look like hard water spots on a car. What exactly is it? Is it harmless? They actually appear on every square inch of this PCB and are non-removable.