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Subject: Re: 1206 Chip Capacitors end crack problem
X-Newsreader: Microsoft Outlook Express 6.00.2600.0000
Date: Tue, 29 Oct 2002 14:43:29 GMT
NNTP-Posting-Date: Tue, 29 Oct 2002 06:43:29 PST
Organization: EarthLink Inc. -- http://www.EarthLink.net
"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.
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