[sdiy] Trace width and via diameter/hole size

[Bert Schiettecatte]

Hi Tim,

> That's a complicated question. I wonder what that
> program conciders when it makes its determination.
> 
> There is the fusing current, which the current at
> which a conductor becomes a fuse. Any current below
> that is fine, but you get voltage drops and thus heat. 
> Conductors are usually choosen  to limit the voltage drop 
> along its length. Ever wonder how they can get 140 amps 
> through a HexFet in a TO-220 package? It's because the length 
> is short enough to limit the voltage drop. 
> 
> If I calculated right, your trace has 0.06 ohms/inch.
> At 640mA the voltage drop would be 38.4mV, the power 
> dissipation would be 24.6 mW/inch.

Hmm.. How do I figure out if the traces will light up or what
Simple rule can I use to decide if I'm still ok with the PCB
Trace width? Is there a PCB guidelines table somewhere that 
Tells you the minimum track width for a certain current?

Thanks,
Bert