Hi David, I would appreciate it of you could share your pictures with me. thanks, Oscar On Fri, Dec 5, 2008 at 8:38 PM, David Tremmel <[log in to unmask]>wrote: > Hello Technetters, > > > > 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 which > adds tension to make good physical contact with the top of the die and the > bottom of the heat sink. > > > > The aftermarket heatsinks do not have adequate spacing from the top of the > board to the bottom of the arms which extend from the heatsink base and > after time, the spacing at the corner of the BGAs was severely compressed > to > the point where I could not put 2 pieces of paper underneath the corner > balls of the BGA. The solder spheres are 25 mil in diameter 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 with the solder spheres on the corner of the BGA are > subject to the greatest sheer forces. > > 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 J > > > > Thank you, > > > > David Tremmel > > <http://valurecovery.com/> http://ValuRecovery.com<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=4.3.16for 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 -----------------------------------------------------