That's what my calculator says, too.
my questions are:
1) Is that number over-rated?
2) What if I have 6 of those in parallel?
thanks,
Jack
On 5/9/07, mattyk <[log in to unmask]> wrote:
>
> 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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