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'Circuit Board Trace thickness'
1997\08\26@125538 by

Can anyone tell me what is the minimum thickness for a 1/2 ounce
copper trace on FR4 would be to carry 1 amp continuous?  FWIW, the
trace would be about 1/2" long.  I would also be interested in the
souce of such information.

TIA,

Tim
According to the IPC-D-275 specs. for a 0.5 oz copper trace to carry an amp
of current you need a thickness of at least 0.030 inches.  The data was
obtained from figure 3-4 from said spec.

David
10C temp rise=  35 mils width
30C temp rise= 18 mils width
source: Bishop Graphics reference book (now out of print, I believe)
James
PS: won't a 1/2"trace have some possible heat sinking to whatever
it is connected to?

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{Quote hidden}

>On Tue, 26 Aug 1997  Tim Crist <tjcristCCGATE.HAC.COM> wrote:
>     Can anyone tell me what is the minimum thickness for a 1/2 ounce
>     copper trace on FR4 would be to carry 1 amp continuous?  FWIW,
>     the trace would be about 1/2" long.  I would also be interested in
>     the source of such information.
>

A 100 mills should be adequate.  A more complete answer would depend
on what temperature rise and voltage drop is acceptable in your
application.

Lunchtime,
Marv
Can anyone tell me what is the minimum thickness for a 1/2 ounce copper
trace on FR4 would be to carry 1 amp continuous?  FWIW, the trace would be
about 1/2" long.  I would also be interested in the source of such
information.

Resistance of the trace can be figured out from the cross sectional area of
the copper trace , cross sectional area of the plating on the trace,
resistance of the copper, resistance of the plating, length of the trace.

Minimum trace width is important for two reasons:

1) Maximum affordable voltage drop of the trace. The current through the
trace, its' resistance and ohms law can give you the voltage drop.

2) How thin can you make it without it burning out.  The current through
the trace, and its' resistance gives you the power dissipated in the trace,
and that has an associated temperature rise in the conductor.  The glue
that holds the copper to the fiberglass can only stand so much heat.
Pretty soon a hot trace melts the glue, the trace lifts off the board, the
trace heats even more because the fiberglass was acting like a heat sink,
and the copper melts and the trace burns out.

Engineers seem to get picky when it comes to voltage drops and tend to
widen traces.  PWB designers that are driven to get ten pounds of stuff
into a 5 pound bag tend to narrow them as much as possible.

Figure 3-4 in the IPC-D-275, is a set of charts to aid estimating
temperature rises in traces.  The chart says that for 1 Amp, on a 1/2 ounce
copper PWB, that a 20 mil wide trace will cause a 20 degree temp rise in
the trace.  Typical Fiberglass Pwb material is stable up to about 125
degrees C.  So the pwb can then be used up to 105 degrees ambient.

You say 20 mil????  Get real.  If the trace is on a connector, then the
heat from the current through the wire and the gold pin needs to be added.
Solder is not as good as copper... Add a little heat there.  If its' near a
hot transistor???? Add some there too.  The Pwb vendor etching traces a
little thin this week? Add some heat there....

I typically make traces that carry more than ~100 mA at least as wide as
pads they run to, and always much wider than the IPC charts allow.  Higher
currents may require careful planning.  I have run wide traces on all
available layers, and added copper stubs wherever they fit to make heat
sinks, and specified extra thick copper plating on the PWB.  You can also
open up the solder mask along the trace, so that the trace will pick up
extra solder plating during the wave solder process.

Sorry about the ranting.... but heat is the enemy and I get a little
mercenary at times.

Joe
>     Can anyone tell me what is the minimum thickness for a 1/2 ounce
>     copper trace on FR4 would be to carry 1 amp continuous?  FWIW, the
>     trace would be about 1/2" long.  I would also be interested in the
>     souce of such information.
>
>     TIA,
>
>     Tim

You need to specify the width and the max voltage drop and/or temp rise