A couple quick questions regarding temperature profiling of BGA's at a
re-work station.

I posted maybe a month back and from the (2) responses I gather that
drilling holes to feed the thermocouples from under the board is the
standard practice.

I tried this, however the best I could do was *attempt* to ensure that there
was contact between the tip of the thermocouple and a BGA solder ball.  (the
thermocouples came up from under the board, and I tried to place the BGA
such the tips of the thermocouples would be in contact with the side of a
BGA ball.  I have 3 thermocouples (middle, side, corner) under the BGA, and
the BGA is held down by chip bonder at 2 opposite corners)  When I tried
getting temperature values at the re-work station, I was getting
inconsistent numbers.

The other method I've tried was to use thermally conductive adhesive to hold
a thermocouple between the chip and the board (with no drilling -> ie. the
thermocouple wire lies flat against the board and held down by the adhesive
and the chip).  This method seems to result in more consistent temperature
readings.

Can anyone comment on whether the adhesive method is used and reliable, or
if theres something I'm doing wrong with the drilled board method?

Thanks,

Toby Chang
Process Engineerin Co-op
Leitch Technology International Inc.

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