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RE: Potential heating problem


Perhaps the rather handy little calculator available for free download form
this website will help you out.  The specific file of interest is

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

	-----Original Message-----
	From:	Jack Andresen [SMTP:jandresen@xxxxxxxxxx]
	Sent:	Monday, May 07, 2001 13:22
	To:	Sterling Vaden
	Cc:	Dave Dwelley; stds-802-3-pwrviamdi@xxxxxxxx
	Subject:	Re: Potential heating problem


	To understand your figures. Your traces are 1.4 mils thick because
	are internaland have no overcoat, correct?. The traces are 10 mils
	but how long and how much space between traces. 

	By my calculations, your traces have about .75 ohms per foot. I get
	ohms from your stated voltage drop and the current.So the total
	of your traces is about 6.9 inches. Am I in the ball park?

	With your total of 2.95 Watts, the equivalent surface are is about
	sq in. with your 60 degree C over ambient, However, you say the
	temperature is 90 to 107. How can the surface temperature be higher
	the temperature source, namely the PC traces. Please explain 

	Jack Andresen
	Sterling Vaden wrote:
	> I have been running a little informal test of current carrying
capacity. I
	> am currently (get it) running 2.6 Amperes through a pair of traces
(.010 X
	> .0014) wired in series, embedded in the inner layers, one directly
above the
	> other, of the test board shown. The temperature rise is
approximately 60
	> degrees C over ambient yielding 98 to 107 C as measured on the
surface of
	> the pcb. No discoloration of the board material has been noted.
The traces
	> are dissipating 1.138 X 2.60 = 2.96 W. No catastrophic failure has
	> noted.
	> Now. I predict that if traces are failing at .250 A, those must be
	> traces indeed!
	> Sterling Vaden
	> Dave Dwelley wrote:
	> > 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 panel
	> > >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
	> > >pins. 3) Running a pair between the 110 punch down pins. 4) In
	> > >there is very little space for both compensation and wiring
	> > >leaving margins between pairs of traces. 5) People are afraid
of too
	> > >fine traces
	> > >But it is important to recognize here is no general standard
for patch
	> > >panel traces (as pointed out in one of the responses).
	>                              Name: pcbCurrentCapacity.doc
	>    pcbCurrentCapacity.doc    Type: Winword File
	>                          Encoding: base64