[SI-LIST] Re: Pulse current handling capability of PCB
- From: wolfgang.maichen@xxxxxxxxxxxx
- To: Jack Olson <pcbjack@xxxxxxxxx>
- Date: Tue, 15 Sep 2009 10:53:20 -0700
A 3D simulator (like HFSS) would of course be able to give an answer. But
for a first estimate, this is what I would do:
- since the pulse duration is relatively short, I doubt there will be much
heat transfer into the PCB material, thermal radiation into free space
etc. So I'd assume all the heat generated in the trace is used to heat the
trace itself.
- calculate resistance R (per unit length) of a copper strip of given
width and thickness - R = rho / (width * thickness) (rho = specific
resistivity of copper)
- the electrical energy converted into heat is W = I^2 * R *
pulse_duration
- calculate thermal capacity of that strip C_therm = its mass multiplied
by the heat capacity of copper
The temperature rise is then delta_T = W / C_therm, and final temperature
is room temperature plus delta_T.
That number should stay well below what your PCB can safely sustain, e.g.
somewhere less than 100 degC.
Wolfgang
Jack Olson <pcbjack@xxxxxxxxx>
Sent by: si-list-bounce@xxxxxxxxxxxxx
09/15/2009 07:43 AM
To
steve weir <weirsi@xxxxxxxxxx>
cc
si-list@xxxxxxxxxxxxx
Subject
[SI-LIST] Re: Pulse current handling capability of PCB
I am only familiar with the IPC minimum recommendations
and various articles in trade publications that refer to that.
(so I've never seen that equation.)
Where can I learn more about this specific subject?
I mean, how did you derive that 100W/sqin for 20us?
What if he had said 40us? 200us?
What if he had said 10Hz? 100Hz?
That's a subject I'd like to know more about...
Jack
.
On Tue, Sep 15, 2009 at 7:50 AM, steve weir <weirsi@xxxxxxxxxx> wrote:
> Assuming whatever is connecting to this is not limiting, then the rule
> of thumb is:
>
> Resistive loss density = I^2*0.5mW/( copper_weight * trace_width^2 )
where:
>
> resistive loss density is W/sq in
> copper weight is in oz / sq ft.
> trace width is in inches
>
> For even something as short as 20us I would stay below 100W / sq in.
>
> Steve.
> Deepak V.L wrote:
> > Hi Havermann, Pls find the answers below
> >
> > -is this a periodic surge event (>1Hz) or will it just happen "once a
> day"?
> > It is not a periodic surge, It can happen only once when the system is
> > switched on.
> >
> > -is this surge current the only current on this trace?
> > Yes
> >
> > -are there other traces on the surrounding area that might coheat this
> > trace?
> > No
> >
> > -whats the copper weight?
> > 1 oz
> >
> > -on which layer of how many layers
> > The traces are in the external layers (dobulb sided board)
> >
> > Thanks,
> > Depak
> >
> >
> > ----- Original Message -----
> > From: "Havermann, Gert" <Gert.Havermann@xxxxxxxxxxx>
> > To: "Deepak V.L" <deepak.vl@xxxxxxxxxxxxxx>; <si-list@xxxxxxxxxxxxx>
> > Sent: Tuesday, September 15, 2009 5:46 PM
> > Subject: AW: [SI-LIST] Pulse current handling capability of PCB
> >
> >
> > Dear Deepak,
> >
> > This depends on many factors:
> > -is this a periodic surge event (>1Hz) or will it just happen "once a
> day"?
> > -is this surge current the only current on this trace?
> > -are there other traces on the surrounding area that might coheat this
> > trace?
> > -whats the copper weight?
> > -on which layer of how many layers
> >
> >
> >
>
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> > persönlich haftende Gesellschafterin: HARTING Electronics Management
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> > -----Ursprüngliche Nachricht-----
> >
> > Von: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]
> Im
> > Auftrag von Deepak V.L
> > Gesendet: Dienstag, 15. September 2009 13:51
> > An: si-list@xxxxxxxxxxxxx
> > Betreff: [SI-LIST] Pulse current handling capability of PCB
> >
> >
> > Dear Experts,
> > Could someone please guide me how to select a trace width for carrying
a
> > 100A surge current for 20us over a PCB trace ?
> >
> >
> > Thanks in advance,
> > Deepak
>
>
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