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November 2002

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Subject:
From:
Dave Sorg <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Fri, 8 Nov 2002 10:27:06 -0600
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Theoretically, the best place to put the TC is in the ball itself by
drilling into its center from the back side of the board. However, that
requires some very precise drilling and it's difficult to verify that the
TC tip is in the correct place. It's easier with a 1.27mm pitch BGA than
with a tighter pitch/smaller ball, but either way it's time consuming and a
pain.

What we actually do is to drill the board (1/64" bit)through a pad from the
top side of the board prior to placing the BGA. Then we feed a .005" TC
(Omega 5SC-TT-K-36-36)through the hole from the bottom so the TC tip is
even with the top of the pad and hold it in place with Loctite 3751 light
setting adhesive placed at the bottom of the hole. Then we reflow the part
onto the board. We use this method whether we are profiling on our Air Vac
rework machine or our reflow oven for production purposes. We typically get
many reflow cycles out of it and it seems to give us readings that result
in good reflow profiles.

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