You may wish to send the photos to the Technet's treasured and respected photo archivist, Steve Gregory at [log in to unmask] for posting on his web site as has become the custom here Joe In a message dated 12/7/2008 11:45:24 A.M. Pacific Standard Time, [log in to unmask] writes: Just for info. There is no attachment with pictures, I tried the link in the E-mail and that wasn't the pictures either. -------------- Original message -------------- From: David Tremmel <[log in to unmask]> > Hello Technetters, > > > > Since I have had some people wanting to see pictures, I have resubmitted my > email with some corrections. > > > > I had someone who got a used Xbox360 that failed and when we disassembled > it, we found they had put an aftermarket heat sink on two of the largest > BGAs. > > > > The original Microsoft heatsinks make contact with the dies (the BGAs are > flipchip designs) and have four arms that extend past the corners of the BGA > and then have posts which go through the board to a latching piece on the > bottom of the PCB directly underneath the BGA which adds tension to make > good physical contact with the top of the die and the bottom of the heat > sink but does not add sufficient pressure to deform the PCB. The > aftermarket heatsinks have posts with spacers above the PCB and washers > below the PCB but the spacers above the PCB are not the proper length and > after time, the PCB warps upwards and the spacing at the corner of the BGAs > was severely compressed to the point where I could not put 2 pieces of paper > between the corner of the BGA and the PCB. The solder spheres are 25 mil > and are probably being compressed to less than 10 mil. > > > > Anywho, this is what I think has the failure mechanism is and I would > appreciate some feedback from the gurus: > > > > While the chip operates, it generates heat which expands the device to some > degree in the X,Y axis > > Part of the job of the solder spheres is to sink the heat to the logic board > so the thermal expansion of the BGA does not act like a sheer force at the > solder ball interfaces. The logic board also expands due to the heat and > any CTE differences between the BGA and the logic board deform the solder > spheres to some degree. The BGA substrate size is 35mm x 35mm and the > solder spheres on the corner of the BGA are subject to the greatest sheer > forces which, in this case, is detrimental. > > > > Due to the compression of the solder spheres at the corners because of the > poor heatsink design, they are unable to deform and any CTE difference > between the BGA and the logic board are turned into sheer forces and cause > ball/interface failures. > > I also think that the constant pressure of the lead free solder spheres > would greatly increase the chances of tin whiskers. > > > > I have a picture of just how bad the solder sphere compression is if anyone > is interested. > > > > Am I way off base? > > > > Thank you in advance for any correction in my theory. A confirmation would > be better!! > > > > Thank you, > > > > David Tremmel > > http://ValuRecovery.com > > > > > --------------------------------------------------- > Technet Mail List provided as a service by IPC using LISTSERV 15.0 > 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 15.0 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 ----------------------------------------------------- **************Make your life easier with all your friends, email, and favorite sites in one place. Try it now. (http://www.aol.com/?optin=new-dp&icid=aolcom40vanity&ncid=emlcntaolcom00000010) --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 15.0 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 -----------------------------------------------------