John
Your paper sounds interesting, I would be interested in a copy.  It may
also help me with my current issue, cracking glass bodied diodes...
Thanks!

regards,

Graham Collins
Litton Systems Limited, Atlantic Division
(902) 873-2000 ext 215


> -----Original Message-----
> From: john maxwell [SMTP:[log in to unmask]]
> Sent: Thursday, October 02, 1997 9:20 PM
> To:   [log in to unmask]
> Subject:      Re: [TECHNET] [T] Cracking of 1206 components
>
> >I do not know which 'thermal shock issue' you investigated; heating
> too fast
> >or cooling too fast? Chip components, unless already defective, do
> not crack
> >on fast heating, but can do so on fast cooling. That can happen in
> >combination with pad designs that allow exessively large solder
> fillets. When
> >these large solder volumes cool, they shrink at ~25 ppm/C and the
> ceramic
> >chip components at only ~6 ppm/C. When you cool too fast the solder
> can not
> >creep fast enough to relax the stresses and component cracking can
> result.
> >
> >Werner Engelmaier
>
> To those that have experienced ceramic capacitor cracking.
>
> First, barium titanate capacitors have coefficients of expansion
> ranging
> from about 9 ppm/degree C for NPO glassy ceramics to about 11-12
> ppm/degree
> C for X7R and Z5U type materials. Alumina based chips like resistors
> have a
> CTE of approximately 6 ppm/degree C. With the rare exception of very
> large
> solder joints rapid cooling has not been a problem in capacitor
> cracking.
> Large fillet size coupled with excessive glass diffusion during
> termination
> firing is the usual culprit.
>
> The crack shape tells all and was documented in a paper I wrote in
> 1987
> while working for AVX which was titled "Cracks: The Hidden Defect". It
> was
> later made into an application note and may still be available at
> their web
> site located at avxcorp.com. If not contact me off the forum and I
> will
> send you a copy. Capacitor cracking can have many surprising sources
> so
> check the crack signature first to get a better idea on where to look
> for
> the root cause.
>
> Regards,
>
>
> John Maxwell
>
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