Hi Werner,
I had HOPs in the past and the analysis was a warpage at the component
corners that cause a delay in the soldering process (the flux was non
active till the package was cooled back and the balls come back to the
PCB pads).

I used a special flux in the solder paste that have longer active time.

I suggest to check if the BGAs have warpage during the reflow.

Reuven

e mail: [log in to unmask]


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Werner Engelmaier /*
Sent: Friday, January 18, 2008 2:58 PM
To: [log in to unmask]
Subject: Re: [TN] SV: [TN] SV: [TN] Solderability of Tin-Gold
Intermetallic

Hi Bev,
Just like George, I am struggling getting an understanding of you
problem.
To me, 'head-on-pillow' solder defects are almost always caused by 
insufficient peak temperature.
If these HOP's occurred essentially near the center of the BGA, you have
your 
answer,
If the HOP's are distributed over the whole array, than the root cause
is not 
insufficient peak temperature unless the whole reflow process is too
low.



Werner



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