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September 2008

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TechNet E-Mail Forum <[log in to unmask]>, Inge <[log in to unmask]>
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Mon, 22 Sep 2008 13:22:51 -0700
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Migration
/Inge


----- Original Message ----- 
From: "James Verrette" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Friday, September 19, 2008 1:23 PM
Subject: [TN] Can desoldering and soldering fix a leaky MLCC


I had a case where I was measuring about 100k accross two nets on a PCB
Assembly with an Ohm meter.  I removed a .1uF X7R MLCC SMT 0402 size
from the board and the 100k short went away.  I measured the cap and the
ohm meter and the resistance was OL.  I put the capacitor back on the
board and remeasured the resistance and there was no short.  I looked
for obvious damage on the cap under a microscope, but didn't see
anything.

Is it possible that desoldering and resoldering by hand could cause a
leaky MLCC to stop leaking?  I am trying to find an explaination for
what made the 100k short circuit go away.  The only other expaination is
that there was something under the part that caused leakaget.  The
boards are assembled with no-clean flux, SnPb solder paste.

Based on what I have read flex cracks could cause the leakage we saw
before the modification, but could desoldering and soldering cause it to
go away?

Jim Verrette
Senior Electrical Engineer




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