Hot plate thermal layout

About this project

Project requirement is to design a hot plate which has 20x TO-247 devices mounted on one side. These devices need to be kept at a junction temperature of 150degC. The heat source is provided by power resistors mounted to the opposite side of the plate. Assuming all resistors have the same power output, what is the most practical layout to ensure that each device is kept within 1 degC of 150degC.