Cyber colleagues,

I would like to get others' views on the following subject.

When attempting to measure the thermal profile of a populated board
through a forced convection reflow oven what is considered the best form
of thermocouple attachment & why?

I believe there are four general methods of attachment.

1)    T/c tip bonded to the lead/pad with something like a 2 pack epoxy
quick drying, covering the tip.

2)    T/c tip touching lead/pad bedded onto a thermal compound paste
with it covering it.

3)    T/c tip soldered to lead/pad.

4)    T/c embedded through board directly adjacent to lead/pad with
compound covering tip.


Option 1 -  Easy to apply and as the bonding agent isn't very thermally
conductive perhaps less likely to be influenced by the higher air
temperature in the chamber.

Option 2 -  Easy to apply but perhaps influenced more with the air
temperature although being sunk by the board.

Option 3 -  Difficult to achieve as the tip isn't very receptive to SnPb
solder.

Option 4 -  Time consuming, destructive but perhaps less influenced than
the others with air temperature.

I appreciate that the temperature will also depend on where it is
attached on the board power plane etc.  

Finally, but on a different but connected note, what would be the
consequence if some of the joints had only just managed to get a few
degrees above liquidus - reliability? Perhaps if you've read this one Mr
Engelmaier it may be up your street?

CIA Iain.