Right now the controller i have in the car is running a pair of Fuji 800amp single igbts. One as the switch the other with its g-e shorted as the freewheel diode. They are joined with a piece of 20x10mm copper bar. Thats a bad idea in theory as the link can ring like a bell and i go shooting down the road trailing flames like a dragster with a blown engine
. In practice its worked fine. Remember that app notes are based on ideal conditions with unlimited resources and infinte development times. They are a guide at best.
I used a piece of standard copper clad pcb board , roughly routed on the drill press to cary the link caps. Kind of a poor man's laminated busbar. I used a 1uf RC snubber across the switch as i was seeing some alarming ringing on turn on if i remember rightly. My advice would be to use 2 resistors and a schottky diode to shape the turn on and turn off. You really need a hard turn on to punch through the miller knee.
What is the ton and toff of the devices your using? Are you using emitter resistors?