I'm designing a board that should handle a reasonably high current (30A) I would like to keep this on 2 layers (70um). For routing reason I need to apply the ground on the bottom layer (while positive is applied on top layer along with the 'load') in the bottom layer I have also shunt resistors. Is it possibile and 'safe' to handle such large current trough via stitching? There's some rule of thumb to 'size' vias in such cases (number and diameter)?.
PS I'm working in DC (up to 50V).