I am looking for information regarding surge current ratings of PCB traces.
I am familiar with the IPC curves (IPC-D-275 which is now IPC-2221) for
steady-state temp rise of a given trace geometry.  I am also familiar with
the NEC cable ampacity ratings.  I have browsed through archives and have
found some interesting posts on the subject by Ralph Hersey on 4.11.96 and
Bill Gaines on 4.8.96, but wonder if anyone knows of any additional
information.

I am trying to ensure that a given trace geometry will be protected by given
fuse.  The fuse will conduct an extreme amount of current for a short amount
of time (the i^2t curve).  I would like to find information that would allow
me to calculate the i^2t for a trace geometry.  The equation produced in
Bill Gaines' posting...

I=A * ((log(((Tm-Ta)/234+Ta)+1))/(33 * S)) **.5
I=current, Ampers, A=conductor area, cir mils, S=time current applied,
seconds, Tm=melting point of copper in dec C, Ta= ambient Temp in deg C.

does not seem to take into account any heatsinking or thermal impedance
presented by the PC board and or copper located around it.

Therefore, I am led to believe that a definitive "theoretical" answer would
most like require the use of computational fluid dynamics or other thermal
simulation technique.  I am wondering, however, if others have run into this
issue and how they may have reconciled the various empirical and/or
theoretical resources.

Thanks,
__________________________
Andrew A. Rockhill, P.E.
Sr. Analog Design Engineer
Plexus Technology Group
[log in to unmask]

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