RE: Potential heating problem
Jack:
Perhaps the rather handy little calculator available for free download form
this website will help you out. The specific file of interest is
PCBTEMP.ZIP.
http://www.contrive.it/Download.html <http://www.contrive.it/Download.html>
Peter Schwartz
Applications Engineer
Micrel Semiconductor
Phone: 408.435.2460
FAX: 408.456.0490
peter.schwartz@xxxxxxxxxx
-----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
Stirling,
To understand your figures. Your traces are 1.4 mils thick because
they
are internaland have no overcoat, correct?. The traces are 10 mils
wide
but how long and how much space between traces.
By my calculations, your traces have about .75 ohms per foot. I get
.43
ohms from your stated voltage drop and the current.So the total
length
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
5.4
sq in. with your 60 degree C over ambient, However, you say the
surface
temperature is 90 to 107. How can the surface temperature be higher
than
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
been
> noted.
>
> Now. I predict that if traces are failing at .250 A, those must be
small
> 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
mils.
> > >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 here is no general standard
for patch
> > >panel traces (as pointed out in one of the responses).
>
>
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