We have done FEA (NASTRAN, ANSYS) on BGA balls by means of what they call Maxwell's rheological elasticity model. May be possible to share with you, Shean, if you are interested I can ask the guy who did this huge job a couple of years ago. You need a good math background to understand this report. Ingemar Hernefjord Ericsson Microwave Systems -----Original Message----- From: TechNet [mailto:[log in to unmask]]On Behalf Of Shean Dalton Sent: den 28 juli 2004 21:04 To: [log in to unmask] Subject: Re: [TN] BGA pad missmatch Hi Phil, I have been hoping for a response from someone who has practical experience with this, as it is interesting to me. That said, I suspect areas of concern would be for TCE. The larger pad size takes away solder from the bulk joint, effectively reducing the standoff height. Again, I suspect the reduced standoff height might reduce the "flexure" ability of the solder joint to "absorb" the TCE mismatch. And, using a larger sphere diameter may compensate for the large pad size, effectively raising the standoff height. Sure would be nice to do a finite elemental analysis. Have fun!, Shean Dalton Austin American Technology --------------------------------------------------- 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 -----------------------------------------------------