Thread Links Date Links
Thread Prev Thread Next Thread Index Date Prev Date Next Date Index

RE: Potential heating problem

I found this data relating minimum PCB conductor trace width for 1A current
carrying capability on the internet.  It was originally abstracted from
"Reference Data for Radio Engineers," Howard W. Sams & Co.,  Page 5-35,
Sixth Edition (ISBN 0-672-21218-8 ).  I cannot vouch for the data here, as I
don't have my copy of that book  here at work with me (it's in a box at home
- but I can find it, or borrow someone else's copy, if that's desired...).

For 20 deg C rise @ 1A:
1/2 oz 0.010 "
1 oz 0.005"
2 oz 0.002"
3oz 0.001"

For 60 deg C rise @ 1A:
1/2oz 0.007"
1oz 0.003"
2oz 0.001"

We are looking for a 175mA/trace current carrying capability.  So if we
allow a 20 deg C  rise, and use a factor of 0.333 (my own ballpark guess) as
a multiplier for the necessary trace width, this rough estimate says that
the absolute minimum trace width for the conductors should be (0.333 x
0.010") = 0.0033".  Call this 4mils to be conservative, and it looks like 5
mils is probably OK even with unplated 1/2 oz copper.

As you can tell, this is not my area of expertise, but I believe the data is
out there to make some pretty well informed decisions.

Comments, anyone?

Peter Schwartz
Applications Engineer
Micrel Semiconductor
Phone:	408.435.2460
FAX:	408.456.0490

	-----Original Message-----
	From:	Dave Dwelley [SMTP:ddwelley@xxxxxxxxxx]
	Sent:	Monday, May 07, 2001 10:28
	To:	stds-802-3-pwrviamdi@xxxxxxxx
	Subject:	Re: Potential heating problem 

	Do these miniature traces affect our 20 ohm wiring budget?

	What's the typical DC resistance of a patch panel?

	Dave Dwelley

	Jack Andresen wrote:

	But let me go back to original issue. I have looked at many patch
	PC boards and for various reasons, the traces run from 10 to 18
	Possible reasons:

	1) Making pairs of traces 100 ohm.
	2) Trying to get between the RJ45 pins.
	3) Running a pair between the 110 punch down pins.
	4) In general, there is very little space for both compensation and
wiring while leaving margins between pairs of traces.
	5) People are afraid of too fine traces

	But it is important to recognize there is no general standard for
patch panel traces (as pointed out in one of the responses).