Hi Technos,

wanted to start a pilot run, but the first PCB that we soldered ended up full of blisters when it came out of the oven. It is a 6 layers, full ground and power planes, about 6"x7", not a high density one, pretty light stuff on it, the toughest part is a transformer which needs a little more heating. The profile peaks at 250C on the PCB itself and the PCB is made out of FR4, Tg 170.

I said to myself that it must be humidity, so I baked 1 board, 8H @ 125C, and passed it through the reflow again. Same blistering, almost to the same extent. Then I took a totally different PCB that was hanging around on my desk for about 3 months, reflowed it at 250C and got just a tiny blister, probably due to humidity this time.

The questions I have are:

is 250C too much for a properly manufactured PCB?

If it's not the humidity what else could it be?

Any other test that I could do to get a better idea of the root cause?

Thanks,
Ioan



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