[SI-LIST] Re: Thermal Profile WITHIN a trace
- From: steve weir <weirsi@xxxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Wed, 01 Aug 2012 00:24:28 -0700
Doug, In most cases the thermal resistance of the path between the
copper and the sink in any direction is much greater than through the
copper owing to the facts that: 1) the copper is never more than a few
mils thick for even 3oz Cu, and 2) Cu has good thermal conductivity (
about 400W/(m*K) ). So you can reasonably approximate the copper
through its thickness as an isotherm.
Steve
On 7/31/2012 2:59 PM, dbrooks9@xxxxxxxxxxxxxxx wrote:
> Assume a typical trace carrying moderate current. It has still ai= r on one
> side and board material on the other side. It will reach an equili= brium
> temperature above the ambient based on the i^2*R heating and the conv=
> ectioncooling. I am wondering about the thermal profile WITHIN the trace. =
> We would normally assume that copper is such a good thermal conductor that =
> the thermal profile would be uniform. But we would assume that the conducti=
> vity is so good that the current density would be uniform, too, and we know=
> that there are exceptions to that (e.g. skin effect.) Since the boundary c=
> onditions would be different at the still air and at the board material, I =
> believe there must be a thermal profile within the trace.
> How much variation might there be in point temperatures within the = trace?
> Carrying this argument one step further, as= sume we measure the temperature
> of the trace using two methods:1= . Measuring the resistance (therefore
> measuring the average temperature of = all points within the trace)2. Using
> an IR microscope (therefore= measuring the temperature at one point on the
> surface of the trace.)= Assuming the measurements are correctly made, how
> much difference migh= t there be in the measurements based on internal
> thermal profiles?
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