The more accurate way in my view, because it  changes  the
environment the least, is to use fine  thermocouple wire  that can be fed in
between the solder balls and the wire either glued or taped at  least 0.5
inches away from the PGA so not to interfere much with the environment.
        Regards,
        Ramon

> -----Original Message-----
> From: Tobias.Chang [SMTP:[log in to unmask]]
> Sent: Thursday, November 07, 2002 11:25 AM
> To:   [log in to unmask]
> Subject:      [TN] profiling BGAs
>
> 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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