[SI-LIST] Re: IPC-2152 trace current/temperature calculator
- From: Jack Olson <pcbjack@xxxxxxxxx>
- To: Arjun Bingipur <arjun.bingipur@xxxxxxxxxxxxxx>
- Date: Thu, 14 Jan 2010 09:11:11 -0600
No, I created those charts myself, using the data in the new spec (which was
obtained from the Lockheed Martin and Naval Surface Warfare Center, Crane
Division experiments)
The reason I created the "modifier" system is because the way the document
is laid out, you have to read all kinds of extra stuff (including the
Appendix!!!) just to get a decent result. The charts give you a starting
number, but then the text describes all kinds of things that can influence
the number. I tried to condense what was there into an introductory approach
to deriving a better answer than the historical charts could have ever
provided. It is the SIMPLEST, in other words.
I couldn't put too many charts in the article (and PCDesign magazine was
already complaining about the length!) so for example I showed how to use
the universal chart (based on 3oz copper) and modify the result for any
other copper
thickness to get a decent approximation, but of course you will NOT have to
do this if you have all of the temperature curve charts in the spec itself,
because it contains ALL the copper thicknesses for both internal and
external.
And maybe I don't have to say this, but there are other considerations that
may influence your result. For example, this data is provided for traces in
STILL AIR, and since most of our designs are in sealed housings these
numbers are good enough for us, but if you have designs with good air flow,
you may get better results with even smaller traces. On the other side of
the coin, if you use a specific distance to your nearest plane but your
nearest plane is chopped and split,
your results may vary. And finally, I didn't even address parallel traces at
ALL, and just about every design has those.
so...
To summarize I can only say
1) this is a better starting point than IPC has ever provided before
2) It is only an approximation, so add some derating "wiggle room"
3) You may need thermal simulation to prove your own results
4) get the spec, it contains much more than I could put into that little
article
(that's why I don't envy Doug the task of trying to make a calculator.
everything needs a disclaimer!)
http://pcdandf.com/cms/magazine/209/6850/
hope that helps,
Jack
.
On Thu, Jan 14, 2010 at 5:06 AM, Arjun Bingipur <
arjun.bingipur@xxxxxxxxxxxxxx> wrote:
> Jack,
>
> As per your document, If we are trying to obtain the final trace width
> using the new universal chart rather than the conservative chart, we
> need to be able to modify the values according to the modifier charts.
> But, having gone through IPC 2152, I do not find the modifier chart
> information. However, I'm currently having access only to the IPC 2152 -
> final Draft document, dated December 2008. Does the released IPC 2152
> spec contain this information or am I missing anything here?
>
> Regards,
> Arjun
>
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
> On Behalf Of Jack Olson
> Sent: 13 January 2010 19:38
> To: Doug Brooks
> Cc: SI-LIST
> Subject: [SI-LIST] Re: IPC-2152 trace current/temperature calculator
>
> 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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