Paul and John,

I love those "Azteque rituals" - sacrificial maidens and blood letting.

To clarify my unclear explanation yesterday: I meant drill a hole (as small as possible to
accomodate small gauge thermocouple wire "tips") as one in, and one nearest, BGA pads and
insert thermocouple "tip" from the PCB's bottom side. Seal the tips into position and secure
the wires on the board's bottom side. Have the tip just protruding into the area where the
solder paste would be to derive very accurate readings as the thermal profile is revealed
during reflow.

A reading may be made (optional) by the second thermocouple (nearest the pad with the TC tip
in it) to determine the offset for the thermal drain effected by the one "in the paste."
It's the only thermal drain possible, when process properly effected, and varies only a few
degrees depending on TC size.

This process may be done on several areas on the test PCB (a reject board, spare working
board, or representative test sample board). It may be done in several areas for the same
BGA, depending on device size, location on the board, and proximity to other thermal masses.

This process may also be done, of course, for other device types. It is especially useful
for unusual or very large and often difficult to solder parts as coils, some inductors,
connectors, etc.

Solder paste may be printed before thermocouple placement. It may be "hand syringe printed"
where the holes have been drilled, after thermocouple placing and securing, over the TC
tips.

The words are not coming easily (altitude change at new location?), but I hope this helps. I
know many of you are using similar schemes. I just don't know of a better way to get inside
a solder joint in the making.

Enjoy,

Earl Moon

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