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January 1998

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Subject:
From:
Brad Kendall <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Tue, 27 Jan 1998 10:48:11 -0500
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I used two methods when I was setting up the BGA process.  First I used
"practice" boards that I could perform destructive testing on.  On those I
drilled very small holes in the PCB under the 4 corners and the center of
the BGA.  Keep in mind this board had already been though reflow once so
the BGA was soldered on. I then placed thermocouples through the holes,
taped the wire to the bottom of the board and ran them though the oven.

The way I profiled the wave solder for BGA was to push the thermocouples
under the edge of the part as far as I could, then tape them in place.
This is an area you really want to watch.  We were getting lots of trapped
heat under the BGA during wave solder, even with tented vias.  This was
causing temps near or at the reflow temp and causing the joints to crack.
You should attemt to mask off the surface of the board opposite the BGA.
We made Kapton tape squares and added them to the prewave process to block
the heat and that dropped the temp under the BGA by 30C.

Brad Kendall
Hella Electronics Corp.

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