[SI-LIST] Re: IPC-2152 trace current/temperature calculator
- From: Jack Olson <pcbjack@xxxxxxxxx>
- To: Doug Brooks <dbrooks9@xxxxxxxxxxxxxxx>
- Date: Wed, 13 Jan 2010 13:38:27 -0600
Doug,
I apologize for using the word WRONG in my last post.
You have my sincere gratitude for the papers you have written and the tools
you have developed and shared so unselfishly. I really appreciate those
contributions and I intend to make good on my promise to buy you a lunch
someday for letting me use your utilities for FREE for so long (smile)
While I agree that it would be very difficult to implement all the new data
in IPC-2152 into a simple tool, the one thing that jumped out at me was the
proximity to planes. Most of the other factors can't influence the result by
more than a few percent. And I'm not a programmer either, but it seems like
it would be easy to add the distance to nearest plane, even if you want to
derate it somewhat for safety margin. Although I'm not a "thermal guy", I
was on the IPC committee (did you see my name on page iii? twice? My mom
did! Ha) anyway (sorry about that shameless puffery) I would cheerfully help
you any way I can, if you ever try to implement more of it into your tool. I
even have a few formulas that were interpolated (?) from the curves in an
excel spreadsheet.
By the way, we were considering incorporating the fusing data on your
(UltraCAD.com) site into the standard, but we didn't want to delay the
publication. maybe next revision....
Finally, I totally agree with you that the historical chart has withstood
the test of time (because in most cases it is very conservative), but what
is need is a safer way to "push the envelope" if the designer needs to use
smaller features.
Do you have any interest in developing a free thermal simulator for
us? (grin)
thanks, Doug
Jack (aka "the new guy")
p.s. PLEASE accept my apology for implying that your calculator is wrong
.
On Wed, Jan 13, 2010 at 1:13 PM, Doug Brooks <dbrooks9@xxxxxxxxxxxxxxx>wrote:
> 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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> Check out our resources at http://www.ultracad.com
>
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