High current PCBs

[OutToLunch]

D2Pak FETs have worked very well for passing large amounts of current straight to the pcb. There is also the added benefit of heatsinking directly into the copper on the board.

If you do go forward with it, I would suggest that this would work with 4 layers of 2oz copper (six layers would be better but more expensive). Top and bottom layers are used for power and signal. Don't make power traces, make large copper polygon areas. Second layer should be ground and ground only - no other traces or power planes at all. All component ground connections should come from the pin on a wide and VERY short trace to a via. Power connections should use multiple vias. Third layer should be power - input power and output power.

For a six layer board, the Top and Bottom layers are the same - power and signal. Second layer and fifth layer should be dedicated ground planes. Middle two layers would be power planes.

 

[dknguyen]

THe issue of using a 1oz 4-layer board (with logic) or a dedicated >1oz 2-layer board, is that the second option requires me to get about 20 boards worth (the cost per unit is actually much cheaper for what I get vs the first option). So if I go >1 oz, it costs me almost nothing to go straight to a 6oz board.

The most viable option it seems right now is to go with a 1oz 4-layer board and to solder wires between the power components almost on top of the leads covering the entire pad in a thick layer of solder between wire and lead. No power would actually be carried on the PCB, though the traces might try to act as a heatsink and it's possible they may get too hot (though there is the giant mass of wire and solder that is also heatsinking).
One external layer would be for logic components, the other would be for power components, and one internal layer would be ground. I don't know about the second internal layer, because as nice as it would be to have a logic power plane (all the motor currents are kept in wires), I found it a huge pain to route on a 2-sided board, and this logic circuit is going to be more complex than that circuit, so I kind of what to keep it logic routing...

I wasn't going going to make a star ground for the power grounds with wire, and the ground plane would be a ground for the logic, which would end up connecting to the power star ground (since that's where all the power enters). I was not planning on having any motor ground currents run on the ground plane.

 

[mneary]

What thickness wire are you using for this 100A?

 

[dknguyen]

Well if it was 50A I'd be using some silicone 12 gauge wire I have. If it was 100 amps, I'd guess I would just use twice as much wire. Nothing is stopping me from buying a couple feet of 8AWG wet noodle wire though- except that I have 100 feet of red and 100 feet of black 12AWG wire.