Sorry I didn't indicate it but both the solder spheres and the soldering
alloy are eutectic Sn 63/ Pb 37. 
The pin outs are shown below

 


Tom Gervascio
Principal Process Engineer
Sypris Electronics
Desk/VoiceMail    813-972-6763
Beeper                 813-887-0098

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Werner Engelmaier /*
Sent: Tuesday, December 18, 2007 7:14 PM
To: [log in to unmask]
Subject: Re: [TN] BGA failures after OMPAC underfill

Hi Tom,
While you are not saying it, i am assuming your are using LF-SAC.
If so, than 214.5 C temperature under the center BGA joints is
insufficient for good soldering. By the way, time above liquidus (TAL)
of 84 sec is totally irrelvant for assuring good soldering; you need
about Liquidus+20C for 5 seconds at that solder ball.
Less squashed balls indicate that some balls (typically in the center)
did not melt and collapse. While I hate that SJ geometry [it gives you 2
stress concentration regions near the interfaces reducing reliability],
proper 'controlled collapse' is an indication of adequate wetting in the
whole array.
I have no idea where P16, J12, N7, M8 are located.
Pressing on fractured SJs externally is a temporary fix [you are making
electrical contact] which has been used for some Apple and Sony laptops
(see my column in Global SMT & Packaging magazine, October 2007). 
Indeed, if in fact you have interfacial failures, Black Pad is one
possibility -however, you need to confirm this failure mode.

Werner



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