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April 2001

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Date:
Tue, 10 Apr 2001 14:34:52 -0700
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yes , I have seen this . We had power to ground caps and since they all
connect to the same  ground, telling which one was shorted was tough.
Teradyne made a tester that would measure the most slightest change in
resistance and you could hone in within a inch or so of the short with it.
We ended up solder pasting and reflowing them on, then masking them over the
wave with a pallet ( call me if you are interested in this). The tester is
expenisve but if it happens more than 2-3 times a year it is worth it.

Jim Gleason
972-494-1911

-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Stephen R. Gregory
Sent: Tuesday, April 10, 2001 12:12 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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