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 
> 
> 
> 
> 
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