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Reply To: | TechNet E-Mail Forum. |
Date: | Wed, 19 Apr 2000 17:18:38 +0100 |
Content-Type: | multipart/alternative |
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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.
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