If the blistering originates from the vias and they are
covered with soldermask, then I would suspect the
soldermask in the hole isn't fully cured. This could lead
to blistering.
Thank you,
Eddie Rocha
South Bay Circuits
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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