What are the recommended ways to cool the UJ4 series of SiC JFETs? We are using them in an unusual traction motor inverter designs ranging from 30kW to 200kW. We currently have models utilizing the TO247-4L and D2Pak. Their total volume is just too large for our customer’s liking. Options we have tried so far have been soldering the TO247-4L back plate directly to the bus bar and cooling the busbar while using that connection for current capacity. We have attached the D2Pak to a single layer ceramic board and had a cooling plate on the opposite side of the board. This kept everything cool, but the power density is about half of what we need as the JFETs are attached to the bus bars and phase outputs with copper standoffs through traces on the ceramic PCB. Our current project has TO247-4L packages with the back plate soldered to ceramic insulators. The ceramic insulating plates are then soldered to a copper heatsink. While this solution works on paper, getting the solder joints flowed without overheating the JFETs. In this last configuration, each FET is isolated from each other.
So, any idea or recommendation on how to cool 36 TO247 packages in an area that is 10"x6"?