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January 2008

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Subject:
From:
Werner Engelmaier /* <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, [log in to unmask]
Date:
Fri, 18 Jan 2008 15:43:14 EST
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text/plain
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Hi Bev & All,
I do not know why nobody responded to my e-mail. I said:
"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."

I am still betting on insufficient peak temperature. HOP implies a large 
pasty range; thus your solder(s) are not near eutectic. Whatever alloy they 
actually are, the insufficient peak temperature was too low to get them fully liquid 
to join up.

Werner



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