Davis,

Did you adjust for the emissivity differenences in the materials?  The
Infrared temperature sensor should have an emissivity adjustment.  The default
is 1.0, and copper will have a lower value than the FR-4 due to the more
reflective nature of the copper.  Since the copper with current is the heat
generator, it seems unlikely that the FR-4 would be hotter.

Glenn

"Davis Chamblee" <[log in to unmask]> Wrote:
|
| I have been performing some ampacity tests on PCB traces using data from
| IPC-D-275 and from posts to this forum. My question concerns the test
| methodology. I'm running about 10 amps through a 150 mil, 2 oz trace. Using
| a non-contact infrared temperature probe I read significantly higher just
| off the side of the trace as opposed to directly on it. I'm sure this has
| to do with the ability of the copper trace to dissipate heat more
| efficiently than the FR-4 material, but am I safe to use the lower
| measurement for purposes of calculating temperature rise? I don't want to
| get problems down the road with the board delaminating or discoloring. For
| example: with an ambient of 24 C, I read 38 C on the trace, but 49 C
| adjacent to it. Is a 14 C rise correct, or would a more conservative 25 C
| rise be appropriate?
|
| As a side note, does anyone have suggestions as to recommendations for
| maximum allowable rise?
|
| Thanks for any help you can offer.
|
| Davis Chamblee
| VP of Engineering
|
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