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November 2006

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Date:
Wed, 15 Nov 2006 16:03:10 -0500
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Loan

Is there any chance that the BGA package is warping?  The thinking here
is that if the package is warping enough to keep the spheres above the
paste during liquidous, then as it the profile cools and the package
returns to its "normal" state, the solder will have also cooled, and
entered that pasty region where it cannot wet to the spheres, even if
they reestablish contact.  The spheres would then sit on top of those
"pillows".

If this is the case, my guess it that most of these would occur away
from the center - and more toward the corners of the perimeter.

This also fits in with your description that this same part is having
similar problems on other boards, where no other problems are apparent.

Bruce Tostevin
Benchmark Electronics
Hudson, NH

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Tempea, Ioan
Sent: Wednesday, November 15, 2006 10:58 AM
To: [log in to unmask]
Subject: Re: [TN] Separation in BGA joints

George, Victor,

foot-in-the-mud, head-on-pillow. It seems that you two are talking about
the same thing, but what is it and why is this happening?

The stencil is 6 mils thick with square apertures, the dimension equal
to the diameter of the pad. ENIG finish.

Time above liquidous is 65s.

Due to pressures from our customers we run many lead-free BGAs on leaded
paste at 220C. If this forms joints, why LF on LF would not form joints
at 246C, or let's say 230C if I am really off in my temp measurements?

Thanks,

Ioan
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