Hi Jan, 
Where you put the thermocouple depends as to what it is you want to measure.
In wave soldering you will get a definite temperature gradient from the
bottom side to the top side of the PCB. The gradient is less for thicker
copper plating in the hole because of the better heat transfer. The gradients
in the epoxy of the PCB will be larger because of the significantly lower
thermal conductivity.
So, if you are interested in solder reaching the top surface and to wet
properly, you place the thermocouple on the top land. If you are interested
in the overheating of the PCB you would want to place the thermocouple into
the epoxy at the bottom side of the PCB.
 
Werner Engelmaier
Engelmaier Associates, Inc.
Electronic Packaging, Interconnection and Reliability Consulting
23 Gunther Street
Mendham, NJ  07945  USA
Phone & Fax: 201-543-2747
E-mail: [log in to unmask]

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