Steve,
Bill is right. I have seen the similar problem couple of years ago and I
have asked the question on TechNet under subject called "Most weird problem:
Solder between epoxy & fab or epoxy & comp". Luckily, we were able to
identify the locations and found a solder suck into the epoxy cavity. Part
of the solution, I have asked our assembly house to change the epoxy to one
which has absorbs less moisture and also asked them to enforce the epoxy
life. You may want to search TechNet for help under author [log in to unmask]
and find the subject name mentioned above for reply from others.
I know this may not help in your immediate endeavor but defiantly need to
address once you are over with current situation.
re,
ken patel
-----Original Message-----
From: Campbell, William (wcampbel) [mailto:[log in to unmask]]
Sent: Tuesday, April 10, 2001 12:31 PM
To: [log in to unmask]
Subject: Re: [TN] Caps shorting on bottomside after wave...
Steve- first thing that comes to my mind after viewing the pic is
"encapsulation". How is the glue cured before wave solder? If the center
is not cured fully, it can outgas during a heat cycle like wave solder, and
then it sucks solder into the void, possibly causing a short. Hope it
helps!
Bill C
-----Original Message-----
From: Stephen R. Gregory [mailto:[log in to unmask]]
Sent: Tuesday, April 10, 2001 3:12 PM
To: [log in to unmask]
Subject: [TN] Caps shorting on bottomside after wave...
Hi all!
This is a weird one for me. We've got some boards that have 1210 .1uf
capacitors epoxied on the bottom and are waved. Test is now telling me that
there are capacitors shorted on the bottom...they can't tell me which one
(or
ones) because they are all in parallel in the circuit, and they can't tell
which one it is. So what test does is give the boards back to the operators
and have them take all the caps off (over 100) and hand solder them back on
the boards...then the board will pass test.
I stencil the glue down (I use loctite 368), the glue apertures in the
stencil more or less creates a dam of glue bewteen each pad. See the picture
at:
http://www.xdrive.com/share/986929035134m7P20WC5Rnno6fT1pb7n
I don't see how in the world a cap would short given the way the glue is
printed. I have not been able to physically see a short, nor has one been
shown to me. Test is just telling me there is a short, and when all the caps
get removed and then resoldered back down the board works...
Has anybody else ever had this weird problem? This just started here
recently...
Thanks!
-Steve Gregory-
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