[SI-LIST] Re: Pulse current handling capability of PCB
- From: Richard Feldman <Richard.Feldman@xxxxxxxxxxx>
- To: "si-list@xxxxxxxxxxxxx" <si-list@xxxxxxxxxxxxx>
- Date: Tue, 15 Sep 2009 11:17:19 -0700
Twenty microseconds is short enough to design according to the
ADIABIATIC temperature rise of the conductor -- joules/area,
not watts/area, for a tolerable maximum temperature.
This is pretty undemanding on the scale of Deepak's problem.
In 1 oz Cu, a 10 mil trace can carry 100 amperes for 20 us,
with a temperature rise of about 13 degrees C.
(Voltage drop 5 volts, power 500 watts, energy 10 mJ into 2 mg of Cu.)
I'm not familiar with any IPC recommendations about impulse currents.
Impulse current ratings for wires and fuses are given in units of
ampere^2 * seconds (the I2T integral), and are proportional to SQUARE of
cross-sectional area.
For example, according to
http://www.bussmann.com/library/docs/ULSSI8_10_01.pdf,
an awg14 wire can withstand 47,000 A2s without damage to thermoplastic
insulation.
That's 217 A for one second, or 2170 A for 10 ms, or 48500 A for 20 us.
In the last case, mechanical Lorentz forces are as much a concern as heating.
Rich
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