one of the biggest problems will be the trace / space that you need to observe. in general it is 0.075mm (3mils) per 1oz of copper. for the 4oz you need 0.3mm (12mils) spacing and tracks. The surface is flat enough for small components, so there should not be any assembly problems. not sure if you use ENIG or HASL for finish.
Okay, that's easy enough to follow. It's actually hard to find certain IC functions in packages greater than 0.5mm, which makes things difficult... Using a multilayer 2oz board might get my resistance back down to where I want, but what about the thermal performance of the traces? Some of them will likely need to take 30A DC continuous, and I'm worried that even if I use multiple layers, the inner layers will heat up too much. Also I was hoping to use the copper layers for some amount of heat spreading for power components, will dividing things into multiple layers severely degrade performance, even with lots of thermal vias?You should request the design rule documents of your PCB manufacturer. 0.5 mm pitch won't work with 4 oz however. It's O.K. for 2 oz, so if you want to combine fine pitch with high current, you have to go for something like all 2 oz multilayer. 2 oz also avoids the problme brought up with thick copper, it has still a plane surface.
There are special techniques combining coppper features of different thichness on outer layers like the "Iceberg" technology. See a brief description together with iceberg and standard thick copper design rules on this manufacturer site.
The previously suggested multilayer sandwich method will most likely achieve good results for standard power PCB designs at lower costs than these exotic methods.
Okay, that's easy enough to follow. It's actually hard to find certain IC functions in packages greater than 0.5mm, which makes things difficult... Using a multilayer 2oz board might get my resistance back down to where I want, but what about the thermal performance of the traces? Some of them will likely need to take 30A DC continuous, and I'm worried that even if I use multiple layers, the inner layers will heat up too much. Also I was hoping to use the copper layers for some amount of heat spreading for power components, will dividing things into multiple layers severely degrade performance, even with lots of thermal vias?
I think the error is that resistivity should be on the top of the right hand equation, not the bottom. Higher resistivity should mean higher resistance not lower.
Keith
The unit of conductivity is S/m not S/mil. Please apologize that I'm not used to calculate material parameters in imperial units and thus don't want to dive deeper into it.
Not to repeat previous detail considerations. Typically the trade-off ends up with 2 oz layers.Use multiple 1oz planes. Use like 3 to 4 planes for each high current signal.
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