Wouter van Ooijen wrote:

>> Why do you think the soldering is a special problem, though? Of course
>> assuming that the pins of a connector that's made for that current are
>> thick enough to carry it.
> 
> I am no expert at high currents (I am more into bits and bytes), so
> don't trust my intuition. My fear was: no matter how wide you make the
> PCB traces, all the current has to pass through each circle surrounding
> the connector pin (assuming the connection is a pin), as fars as these
> circles are not covered by solder (in which case the solder would
> probably take a large share of the current). When the soldered area is
> small the smallest such circle is also small.

I assume those "circles" you are talking about are the pads of the
connector pins? Let's say you need 10 A and choose 10 mm wide traces. With
35 um copper that's plenty and on the safe side. That trace has then a
cross section of 0.35 mm^2. (Sorry, I can't help it: see why it's easier to
use the proper unit for thickness instead of ounces of copper per square
foot? :)

Now just imagine that cross section. 0.35 mm^2 is not a whole lot, and
actually the pads (with solder) and pins are a lot thicker than the trace
itself. There may of course be a certain "current concentration" around the
pad, where the effective cross section through which the current flows is a
bit less. (Ah, now I think I understand what you meant with those circles:
actually the cross-sectional cylinders through which the current flows when
approaching a pin.) But a cylinder with 0.35 mm^2 area has a diameter of
3.2 mm (at a height of 35 um). That's usually where already the solder
starts to increase the thickness of the conductive material and therefore
the effective area.

Also the whole thing is a thermal question. There may be a locally higher
current density around a pin that creates more heat locally, but there's
also enough copper around to carry that heat away. So in practice, this is
not really a problem. That is, it may become a problem at /high/ currents
(that I've never worked with), but not at 10 A :)

Gerhard

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