If this is like baseball, I'm batting ,500!!
I am not a chemist, I'm truly sorry if the explanation is not all that
accurate. But I do manufacture boards, and my chips do not crack.
Can someone then tell me why we bother having a preheat section in the
wave?
Cheers!
Eric
-----Message d'origine-----
De : [log in to unmask] [mailto:[log in to unmask]]
Envoyé : 17 novembre, 2003 22:05
À : [log in to unmask]; [log in to unmask]
Objet : Re: [TN] Not that our process is out of control or anything, but
--
In a message dated 11/17/2003 16:52:11, [log in to unmask]
writes:
>It is the preheat it the wave that is controlled (the infamous 2C/sec)
>to prevent thermal shock.
---This is correct.
>Once the chip has achieved a specified temp, all the materials have
expanded
equally and >after this point the rapid thermal change of hitting the
wave
does not affect the chip.
---Sorry, but there is no such condition; different materials will
always
have a differentiasl thermal expansion, unless they have identical CTEs.
>It is the different expanding properties of the two materials that
cause the
chip
>to crack.
---Quite correct.
>Once they have both expanded to their maximum state, the temperature
curve
is irrelevant.
---Sorry again, but there is no such state; as long as you raise the
temperature materials will expand, unless they have a negaqtive CTE.
Regards,
Werner Engelmaier
Engelmaier Associates, L.C.
Electronic Packaging, Interconnection and Reliability Consulting
7 Jasmine Run
Ormond Beach, FL 32174 USA
Phone: 386-437-8747, Fax: 386-437-8737, Cell: 386-316-5904
E-mail: [log in to unmask], Website: www.engelmaier.com
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