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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