If I can add.... One military contractor I worked for years ago told me of their results on cycling PCB's over the full mil temp range. My eyes opened when he said they found the leads of ic's were pulling the copper pads off the PCB substrate material after approx. 50 cycles !! They were rather surprised also. So, just because a PCB cycles well several times & passes, doesn't mean it is going to work forever. We know that in the mil(itary) environment, it doesn't take long for a PCB assembly to be cycled 50 times ( Plane lands on deck, open cockpit, temp falls to outside temp, canopy closes, back into heat & sunlight, etc). Also, the change in temp is very rapid. No time for this gradual temp change ! I was told that having leaded ic's is a saving grace as the leads themselves are compliant & flex enough to absorb the CTE differences between PCB substrate material & IC packaging material. But having CLCC for mil temps ranges is asking for trouble. I guess it is best to spec (& use) leaded ic's Interested in hearing other people's comments..... Regards TDK -----Original Message----- From: Werner Engelmaier [mailto:[log in to unmask]] Sent: Sunday, October 17, 2004 9:00 AM To: [log in to unmask] Subject: Re: [TN] LCC process and manufacturing recommendations Hi Jorge and all, CLCCs have a large CTE mismatch with resin-based PCBs which translate to large expansion mismatches for larger-sized CLCCs and larger delta-T's. This does not create higher stresses in solder joints--those are limited by the yield strength of solder--but larger displacement strains in the SJs and thus larger plastic deformation. On a cyclic basis, these larger strains lead to much earlier creep-fatigue failure. Having thicker solder joints [balls, columns] or compliant leads [QFPs] reduces the strains in the solder for a given displacement. PLCCs are quite different, because they lack the large CTE-mismatch with PCBs. If you need more information, get a copy of IPC-D-279 and/or IPC-SM-785--or you could take one of my workshops. If CLCCs are indeed coming back, people simply have forgotten history, will be condemned to repeat it, and my consulting business will increase. 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 847-615-7100 ext.2815 ----------------------------------------------------- --------------------------------------------------- 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 847-615-7100 ext.2815 -----------------------------------------------------