Pulse Current PCB width calculator

[penrico]

Hey,

I have a board that have some signals, that will have non repetitive pulses of 8A 20 mSeg long.
The problem, is that my board don't have enoght space to use a 150 mils or more to meet the 8A current in average mode.

Do somebody has a I2t (current vs time) formula for the widht of trace in PCB?. Do somebody has something of information how to calculate the right trace width for a pulse current?

Thanks.

 

[FvM]

As a conservative estimation, you can put in the copper foil thermal capacity and a permissible overtemperature to calculate an I2t value.
I remember, that Raychem had published some I2t data of PCBs related to fuse dimensioning.

 

[svhb]

If you are in doubt, can you increase the thickness of the copper layers? This normally doesn't take more board space.

Can you just use a thinner track locally, and use a wide enough trace where possible? IMHO you can live safely with less than half of the 150mils for a single 20msec pulse.

Stefaan

 

[FvM]

From thermnal capacity, I calculate a Δt of 1.4 K for a 75 mils 1oz (35 um) trace. With 15 mils, Δt for a single pulse is below 40 K.
Resistive voltage drop and average power dissipation may be a more serious problem.