For serious current capability, solder copper wire or precut copper foil or sheet to the unmasked traces on the PCB. You can achieve anywhere from a few oz to well over 100 oz copper traces on demand this way.
Sometimes having 400+ amps and fine pitch components on the same board is a nice thing to be able to do.
I've seen this done a number of times on higher quality power supplies. They just take a section of 18awg solid wire and snake it around where they need it. Down side here is that it has to increase the production time and labor costs substantially. So I would think this would be best left to where you need some really high current capacity in a limited amount of space, or the price bump won't have any significant effect on the profit margin. Anywhere 5 bucks can be a deal breaker on a final product, I can see where just tinning a trace would be the preferred solution.
wouldn't it be possible during manufacturing to mask off the board and electroplate extra ounces of copper on traces that needed high current carrying capabilities.
sometimes the board is done with a tin resist and electroplating to build up a 1/2-oz copper blank into a 1-oz copper board.
Something like this...
1. Drill all of the holes in a 1/2 oz. copper coated board.
2. Electroless copper coat to activate the vias.
3. Electroplate enough to stabilize the vias.
4. Mask the board to expose only the areas to be saved.
5. Electroplate 1/2 oz. of copper.
6. Electroplate tin.
7. Strip resist mask.
8. Etch in ammonium persulphate.
9. Strip the tin resist
10. Apply solder mask
11. Dip in solder for HASL
new steps 4 and 5 (and extra steps in between)
4. Mask the board to expose only high current traces
4.1 Electroplate 3 oz of copper
4.2 Strip the resist mask
4.3 Mask the board to expose all the traces to be saved, including high current traces
4.4 Electroplate 1/2 oz of copper
5 Electroplate tin
At this point, the board has 1 oz of copper everywhere, and 4 oz of copper on high current traces, and TIN resist everywhere.
I don't know if this would work. There might be severe undercutting on the 4oz copper areas, or maybe manufacturing processes wouldn't allow for the extra steps. The PCB designer would need to create an extra mask.
This is not "free" like the exposed soldermask, but is also not extra work during assembly like snaking wire or soldering copper foil or straps.