chris, are all the fracture at corner of the sj? or across the outer row? corner sj - thermal stress, outer row - you possibly deal with mechanical flex of either board or module in relation to the other... my 2 cents. SRAM are low power device, j-heating possibly is not apply in this case (unless you got some hot components on the other side...). jk On Aug 7, 2014, at 2:45 PM, Chris Mahanna wrote: > My hypothesis goes something like this > > As Dave says "microstructure coarsening is more subdued". I'd add - > with very little banding compared to the damage accumulated at the > Sn grain interfaces. That is what I meant about this one being > odd. But then again... we don't see SnPb failures much these days. > My suspicion was that (relatively speaking) the sj was born that > way - as Joyce says: "way off eutectic, yielding high % of high > melting phase", rather than aged/evolved that way. > > I also suspected a relatively static mechanical load caused by > residual stress in the joints, as the board may not be too stable/ > flat during reflow. Average soldering cool-down rate was probably > over 6C/s at the time of solidus. These fractures were found in a > perimeter column. > > This BGA is a small 8M-bit SRAM. I would have thought it to be > pretty flexible. It is underfilled, which is a wildcard at the > moment. We are asking for the material part# now. > > So the suspicion was on the reballing, but you can see why the > confidence level is low. > > This is actual dirty laundry, so can't say the use environment, but > there is relatively benign thermal cycling and enough vibe that it > should be taken into consideration. > > Chris > > > > -----Original Message----- > From: TechNet [mailto:[log in to unmask]] On Behalf Of David Hillman > Sent: Thursday, August 7, 2014 1:10 PM > To: [log in to unmask] > Subject: Re: [TN] SJ fracture signature > > Yes, Chris, come as clean as you can or we'll send Clump/Kloumpios > to visit you. > > Dave > > > On Thu, Aug 7, 2014 at 11:44 AM, Stadem, Richard D. < > [log in to unmask]> wrote: > >> Okay, Chris. We've done our WAG speculating. Out with your >> suspicions, >> we must hear them. >> dean >> >> -----Original Message----- >> From: TechNet [mailto:[log in to unmask]] On Behalf Of Chris Mahanna >> Sent: Wednesday, August 06, 2014 1:49 PM >> To: [log in to unmask] >> Subject: [TN] SJ fracture signature >> >> We see hundreds of cracked solder joints every year, but I can't say >> that I've ever seen one quite like this. I have some suspicions, but >> I'll keep them to myself, as to not prejudice the crowd. >> EDS maps are forthcoming. >> >> This is a caught in-the-wild field failure of a 48-pin BGA >> Reballed to >> SnPb ENIG on board side Ni barrier on component side >> >> http://stevezeva.homestead.com/45268-1.JPG >> >> http://stevezeva.homestead.com/45268-2.JPG >> >> http://stevezeva.homestead.com/45268-8.JPG >> >> Thoughts? And Thanks to Steve! >> >> >> Chris Mahanna >> President, Technical Manager >> Robisan Laboratory Inc. >> >> >> _____________________________________________________________________ >> _ >> This email has been scanned by the Symantec Email Security.cloud >> service. >> For more information please contact helpdesk at x2960 or >> [log in to unmask] >> _____________________________________________________________________ >> _ >> >> _____________________________________________________________________ >> _ >> This email has been scanned by the Symantec Email Security.cloud >> service. >> For more information please contact helpdesk at x2960 or >> [log in to unmask] >> _____________________________________________________________________ >> _ >> > > > ______________________________________________________________________ > This email has been scanned by the Symantec Email Security.cloud > service. > For more information please contact helpdesk at x2960 or > [log in to unmask] > ______________________________________________________________________ > > ______________________________________________________________________ > This email has been scanned by the Symantec Email Security.cloud > service. > For more information please contact helpdesk at x2960 or > [log in to unmask] > ______________________________________________________________________ ______________________________________________________________________ This email has been scanned by the Symantec Email Security.cloud service. For more information please contact helpdesk at x2960 or [log in to unmask] ______________________________________________________________________