I’m designing a PCB which is going to conduct a lot of DC current. I’m hoping to use a MOSFET which can take 10A Continuous but hopefully it’ll only ever see 5Amps. There seem to be a lot of MOSFET’s out there that will switch this kind of current my problem is that having looked at a track calculator:
The size of the tracks are stupid wide. Wider then the pins on the MOSFET. This is because the PCB Prototyping Service I was looking at only has 1Oz copper. Does anybody know a company who’ll prototype with a heavier copper board or know of some way around this problem.
Why not run the track at the recommended width and neck it down right before joining it to the pad size? Yes, the cross-sectional area goes down in that region but if done right, the length of the necked area is so small that the increase in resistance is negligible.
You might also consider pouring copper around the pin(s) of the MOSFET though you’ll have a thermal relief then. Again, the increased resistance caused by the small-ish thermal reliefs is offset by their very small length in proportion to the entire track.
If it’s a prototype you can solder copper wire to the tracks, to increase the current-carrying capacity. I’ve done that once or twice, to get a cheap prototype made with 35um copper.
I’ve seen high-current boards where the big traces had the mask removed and they just flowed a thick layer of solder on them. That would probably be your easiest and safest bet for a prototype. Wires would work too, as leon_heller suggested.
