Steve:

I tend to agree with Mike's comment.  You might give one of the blisters a
probe with a sharp Xacto blade to determine if it's soldermask or laminate.
Different set of causes for each.

Don Vischulis
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of [log in to unmask]
Sent: Wednesday, January 30, 2002 1:35 PM
To: [log in to unmask]
Subject: [TN] Laminate Blisters...


Hi all!

Got another strange one again (why me?). Ran 70 peices of a double-sided SMT
assembly. The board is a 6-layer FR4 board. PTH is hand-soldered.

Everything seemed to be going fine until the boards got to an inspector just
prior to test. I get paged to look at some blisters she said she was seeing.
I was pretty suprised because things were fine when they went through
surface mount.

I went to the inspector, and sure enough, this is what I saw. Go to:

http://www.stevezeva.homestead.com

They appear randomly at one of four plated mounting holes on the board, and
it's on random sides of the boards too...and it only happened on
19-assemblies. I can't find out when it happened. These mounting holes are
off away from anything that was hand soldered too...

Funny thing is they look like blisters, but the laminate isn't displaced
like you normally would see in a blister...to me, it's more like a sort of
delamination.

I didn't see anything like that during SMT processing, I mean you can't miss
something like that. But if it were due to excessive heat, I would expect to
see it on more assemblies. The same thing would apply if it were caused by
absorbed moisture wouldn't it? I would expect to see the problem on more
assemblies. The fabs are all the same date code by the way...

Anybody ever see something like this before?

-Steve Gregory-