Hey all ya'll!!

(That better Doug? Hehehe...Doug told me last week that I wasn't using
"ya'll" properly...hehehe)

Just discovered 2 built-up assemblies at final QC that had some delamination
blisters, and we're trying to figure out what happened...

To give a little history about this board; we've been building them since
November of last year. It's a 14" X 13" PTH board, 4-layer, .062" thick FR4,
got close to 600 components on it. We build anywhere from 50-70 assemblies
per day of this board.

The bare boards have been coming from the same fab vendor and we've not had
this problem at all in the past...and again, it's just on these two
assemblies.

We've not been baking the boards because we've not had a problem with them
(we usually don't with FR4, we bake all our polyimide fabs though). I have
some pictures of the blisters at:

http://stevezeva.homestead.com/index.html

The questions I have are: Can this sort of thing happen for some other reason
that absorbed moisture? I don't think it was moisture related, the reason I
feel that is there were no blow-holes, or pin-holes in any of the solder
joints at all. It's been my experience that if a board has absorbed moisture,
you'll see that soldering problem as well.

I don't feel we over-temped the board either. I'm using the same wave profile
that was created back in November of last year, and we've waved thousands of
boards since then without a problem...

Can a cross section determine what caused the blisters?

Thanks!

-Steve Gregory-