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May 2007

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Subject:	Re: Current vs. Temperature (IPC vs. PCBTEMP)
From:	mattyk <[log in to unmask]>
Reply To:	(Designers Council Forum)
Date:	Wed, 9 May 2007 11:42:00 -0400
Content-Type:	text/plain
Parts/Attachments:	text/plain (65 lines)

Well I'll tell you for the internal thickness you need more like 110mils
with a 20 degree rise for the 5 amps.

Also, IPC has two charts, one for internal and one for external.  

-----Original Message-----
From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of Jack
Olson
Sent: Wednesday, May 09, 2007 11:30 AM
To: [log in to unmask]
Subject: [DC] Current vs. Temperature (IPC vs. PCBTEMP)

I have a situation where I need to run several parallel traces, all carrying
5amps simultaneously.
They are run side by side in batches of 3-4 (20 in all)

I remember hearing that the IPC chart tested external traces and doubled the
requirement for internal, so if I use a 40mil trace for 5amps (2oz), an
80mil would suffice for internal.
I've since heard (from Jouppi?) that this internal number is over-rated. Is
that true?

If I use Doug Brook's PCBTEMP calculator (http://ultracad.com) and type in
my 2oz, 40mil, external trace I get a 16 degree rise, which is fine. but
when I switch to INTERNAL, with 80mil I get a 29 degree rise. not
acceptable.

SO MY QUESTION IS:
If the internal IPC chart was over-rated, why am I getting a higher temp in
the PCBTEMP calculator for internals?

I must have heard it wrong about the IPC charts?

Also, for any of you working with power out there, I'm concerned that these
calculators are thinking of a SINGLE trace around a bunch of normal traces.
How much different are my results going to be if I am running LOTS of 5amp
traces side by side?
I don't have access to ThermalMan or HavardThermal (or any other tools
except PCBTEMP)

hot and bothered,
Jack

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