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From: Boris Mohar
Subject: Re: 1206 Chip Capacitors end crack problem
X-Newsreader: Forte Agent 1.92/32.572
Date: Tue, 29 Oct 2002 10:04:13 -0500
NNTP-Posting-Date: Tue, 29 Oct 2002 10:07:00 EST
Organization: Bell Sympatico
On Tue, 29 Oct 2002 14:43:29 GMT, "Bob"
>"Joseph Goldburg" wrote in message
>> HI All,
>> I have some 1206 SMD chip cap's which ocasionally
>> crack on the ends after I receive them from the SMT board
>> The 1206 chip caps are in the middle of the PCB 4' x 4'
>> Any pointers to common failures would be appreciated.
>As another poster (Dave) pointed out, it's the reflow temperature profile
>that's the problem. The capacitor manufacturer specifies a max dT/dt (change
>in temp vs time). The difference in coefficient of expansion of the cap vs
>the pcb material is to blame.
>Make sure your assembly house is NOT soldering these caps by hand with a
>solering iron. The sudden increase in temperature that a cap sees when the
>iron tip hits it will be too much for it. A hot air tool is recommended for
>hand soldering smt parts.
I hand solder SMT parts including 1206 all the time. Never cracked
one. I do this under a stereo microscope using a Metcal MX soldering
iron with 700 degree STTC137 or STTC144 tips. Capacitors are from
different manufacturers. If there were any cracks I would have seen them
and if they were to small to see than they would show up as a malfunction
since many of these caps were not for generic decoupling bur for timing
If the board is not scored deep enough it could be happening during
depanelization. The highest flex is in the middle.
Viatrack Printed Circuit Designs
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