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 --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 1.8e To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 -----------------------------------------------------