Tom,

>1.  Since not all the components are on the board, how accurate are the
>temp readings?

Not very.

>2.  Should I take measurements with the first loaded board w/
>solderpaste?  If so, where should I place the thermalcouples?

Apart from a mix of experience and judgement there are two other
possibilities for determining thermocouple locations:

a) Build a computational model of the the board during the process.
This is time consuming and expensive, but we have shown that it can
be fairly accurate in predicting what will happen. You can also check/
design your reflow profile using the model or do "what if?" design
studies on e.g. component locations using the model.

b) Buy a reflow oven with an IR scanner in it, which will let you
verify the peak temperature of every component on the board. This
also lets you check every board hits the right temperatures.

David Whalley
Loughborough University

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