Here's what we do... we use 3 mil  (.003") diameter thermocouple wire, and
we route the wire to the ball that we select, with the wire exiting the BGA
between balls - using solder mask touch-up to tack the wires in
place.  Then we solder paste, place, and reflow the BGA device with our
rework system... once cooled, we tack the 4 corners of the BGA in place
using an adhesive (so that the BGA isn't accidently dislodged from its'
pads during reflow cycles).  After this operation, we have a fixture we can
use over and over again.


At 11:25 AM 11/07/2002 -0500, you wrote:
>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.
>

----------------------------------------------------------------
Bill Raymond, VP of Technology Development
Trenton Technology Inc.
1001 Broad Street
Utica New York   13501
Phone (315) 797-7534
Fax   (315) 797-7159
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