Thank You

At 08:47 AM 10/30/2000 -0500, you wrote:
>Hi Mike,
>The charts in question show a temperature rise above ambient, not an
>absolute temperature.  You should take your maximum current (300mA) and
>determine the proper trace width for the location of the trace (inner Vs
>outer layer) using the appropriate temperature rise curve.  There are other
>things you should take into consideration, such as the proximity of the
>trace to a component which is dissipating significant power, because that
>component's heating effect will cause the "ambient" temperature near the
>trace to be higher.
>Here is a simple example:
>Max ambient temperature for the PWB = 70 C.
>Safe operating temperature of PWB = Tg - safety margin = 90 C (remember,
>this is only an example).
>Your allowable temp rise would be 90-70 = 20 C.
>Assuming your trace is on an internal layer, with 1 oz/ft^2 copper, using
>the 20 C temp rise curve from Figures 3-4c and the 1 oz curve from 3-4b
>gives you a minimum trace width of .005".  In this case, your .012" trace is
>quite sufficient.
>This is probably over-simplifying things a bit, but I hope it points you in
>the correct direction.
>Regards,
>Mike
>
>Michael E. Boldt
>Electronic Packaging Engineer
>Moog Inc., Motion Systems Division
>East Aurora, New York 14052
>
>My name is Mike Cubon and I work for ITW Chronomatic. We manufacture Polymer
>Thick Film circuits and I have a technical question about figure 3-4 in
>IPC-D-275. There are three graphs that show current rating for different
>conductor traces at different temperatures. Are there any charts or perhaps
>a formula for calculating current capacity below the temperatures shown. The
>application is automotive and will be tested to -40C. The max. current will
>be 300mA and trace width will be .012 inches.
>
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