[SI-LIST] Re: IPC-2152 trace current/temperature calculator
- From: Doug Brooks <dbrooks9@xxxxxxxxxxxxxxx>
- To: Jack Olson <pcbjack@xxxxxxxxx>,SI-LIST <si-list@xxxxxxxxxxxxx>
- Date: Wed, 13 Jan 2010 11:13:38 -0800
Thanks for the link to your paper. Its a good contribution. Well done.
I'll consider trying to implement some of it in the next version of
the calculator.
But please understand that this is now the third version of our
calculator. We have never ever suggested that it is *RIGHT* or
*WRONG*. In fact, given that there are almost an infinite number of
combinations of
stackups
layer dimensions
trace dimensions and form factors
swiss cheese effects
component placement
component thermal effects
environmental effects
materials properties
etc
anyone would be a little foolish to suggests they even knew or could
know what *RIGHT* and *WRONG* really was.
Also, note that we did not help write the standard, nor were we a
member of any subcommittee
We don't even necessarily endorse the standard (and the IPC doesn't
necessarily endorse our calculator, at least as yet)
The calculator merely makes using the standard (right or wrong,
somehow defined) easier.
The calculator is actually based on 5, user selectable data sources.
These sources differ by as much as 40%. The new IPC-2152, Vacuum, is
the most conservative. The old IPC-D-275 is the most aggressive. The
old standard has been criticized through the years (with some
justification) BUT nevertheless many people think that it HAS
withstood the 50-year test of time! The data from another study,
reported in Design News in 1968, provides results that are in between
the other standards. The final decision of what results to use are
the system designer's responsibility, based on the risks he/she
understands and is willing to take. We don't endorse any one of the
data sources.
The trace current/temperature calculations are one of four
capabilities of the calculator. Others include an estimate of fusing
current (see an article on our web site), skin effect calculations
(including skin depth, crossover frequency, and frequency and
temperature adjusted trace resistance, see an article on our web
site), and basic Ohm's Law calculations for traces. The trace
current/temperature calculations and fusing current calculations can
be automatically adjusted for skin effects.
Again, we never suggest our calculators are *RIGHT* or *WRONG*. Just
that they make working with already established formulas and
relationships easier. We developed them for our own use, and make
some of them available to others --- as is and as represented.
Doug
At 08:45 AM 1/13/2010, Jack Olson wrote:
>Not to complain (kudos for developing the calculator!)
>but since proximity to planes has the most drastic effect
>over any of the other factors, and it is a fairly linear
>relationship, I'm curious why you didn't incorporate it.
>(only one extra box!) of course, not knowing about splits
>and "swiss cheesiness" of the plane, maybe you were
>simply afraid? (grin, kiddin' ya)
>There is a graph in this article if you are interested:
>http://frontdoor.biz/PCBportal/HowTo2152.pdf
>
>Unless I'm misunderstanding your calculator, I think your
>result will be about 50% WRONG in most cases (since
>most boards have planes these days)
>
>just trying to help,
>keep up the good work,
>Jack
>
>
>
> > From: dbrooks9@xxxxxxxxxxxxxxx
> > Subject: [SI-LIST] Re: IPC-2152 trace current/temperature calculator
> > Date: Tue, 12 Jan 2010 22:38:19 -0700
> >
> > I don't know if you have read the standard. There are a couple of= pages
> > that address thermal modeling, planes, alternative dielectrics, etc,= in a
> > very general manner. There are no quantitative adjustments included (= with
> > the possible exception of how to treat parallel conductors which is pr=
> > etty
> > straightforward, and pretty obvious.) There is a Figure A-13 that rela= tes
> > to some estimated factor adjustments that can be used based on the dist=
> > ancebetween the conductor and a plane for 1 Oz traces in .070 thick Polyim=
> > ide Board (and a single curve for 2 Oz traces). The calculator does n= ot
> > incorporate these adjustments in its calculations. But these adjustments=
> > caneasily be made to the calculated results if desired. Overall, the gene=
> > ralities included in the Standard apply equally well to the calculated
> > resu=
> > lts from the calculator.
> > The Calculator is based o= n Conductor Sizing Charts contained in the
> > Appendix (from Figure A-17, p 35= to Figure A-86, p83).
> >
> > Doug
> >
>
>
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