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.
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.
pert:
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.
Sorry, the white area is reflected light.
The ''stained'' areas cover pretty much the entire PCB surface (both sides) so it seems more than just a bit of flux residue to me.
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.
.
Paul_KD7HB:
Please help us! Is the stain on the copper or on areas where there is NO copper?Paul
It's literally all over the PCB - not just where the copper is.
xl97:
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?
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.
larryd:
Try removing with a soft toothbrush and IPA.
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.
Vitesze:
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.
The board has "solder mask" on both sides. It has been improperly applied or the press that was used to cure the epoxy was not hot enough to cure the epoxy.
Bet the board was made in China at a really low price.
Won't hurt anything, just looks bad.
Paul
Paul_KD7HB:
Bet the board was made in China at a really low price.
You betted correctly 
Vitesze:
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 and
starting to streak the boards, not unusual for cheap pcbs, anything to reduce cost.
Chances of bad solder mask is very small, never seen that.
MarkT:
No, flux doesn't rub off without a solvent, its solid. Looks like the solvent wash was overburdened with flux and
starting to streak the boards, not unusual for cheap pcbs, anything to reduce cost.Chances of bad solder mask is very small, never seen that.
Years ago we visited our local board mfg. You should see the errors there!
Paul
Ah, but that wasn't in China, was it?
Paul__B:
Ah, but that wasn't in China, was it?
No.
Near Portland, Oregon.
Vitesze:
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.
Started showing? Or had always been there?