Iain,

We use a thermocouple flex probe that attaches to the edge of the board by a
small clamping mechanism.  The tip of the thermocouple is held in place on
the board surface by flexing (slightly) the probe and clamping it in a fixed
position.  We have had very good results with this type of probe.  Contact
me off-line for more information [log in to unmask]

blm

Iain Braddock wrote:

> 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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