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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Vision Technologies, Inc.
6500 Taylor Road
Wendell, NC 27591-8700
Telephone (919) 365-5747
Toll free (800) 418-7907
Email [log in to unmask]

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