It can get complicated when trying to transfer so much current. The current carrying capacity of copper is based on its thermal charecteristics, ie how much current the copper can carry without significant temp rise, and thus resistance rise, then more temprise etc etc then a very smelly PCB with black scorched bits, but if the necked area of copper is small then he temperature rise at that point will not be so great as copper is a good thermal conductor. In situations like this simulation software is useful, I use outside expert help as the software is expensive and has a learning curve, if that is not available, I would have the board built and test it at the extremes of the temperature range using a thermal camera and/ortemp probes fastened to the board.
If this product is going to be sold in the USA you will have to get UL certification, for current of this value they will measure the PCB temp rise.
Sorry there is no easy answer when you start moving this level of current, other than simulation and/or testing.