Thermal resistance is a major factor in determining the capabilities of discrete power devices. From a device’s thermal characteristics both the maximum power dissipation and maximum current can be derived for user applications.

Simple and cost-effective thermal management strategies improve heat conductance from the GaN FETs and optimize thermal performance. The impact of board-side cooling and backside cooling strategies are analyzed in How2AppNote012 - How to Get More Power Out of an eGaN Converter. A summary is shown below.

It is important to note that EPC GaN FETs can take advantage of dual-sided cooling to maximize their heat dissipation capabilities in high-power density designs. This is covered in detail in How2AppNote012 - How to Get More Power Out of an eGaN Converter.

Thermal interface materials (TIM) are a critical part of the cooling system when using top sided cooling. Since GaN devices are very small, effective cooling relies on the heat-spreading effect of the heatsink, however, the TIM layer does not benefit from this. Because of its small area, the TIM layer ends up being a significant contributor to the overall R_th,J-A, and therefore the use of high thermal conductivity materials is very beneficial. The TIM layer also has a very important second role: to electrically isolate the GaN devices from the heatsink since the top of EPC GaN FETs are connected to source potential.

EPC has gathered some information on TIM materials to help designer in their search:

TIM Pads

TIM compound and greases

The thermal design can be further optimized by using the GaN FET Thermal Calculator. The GaN FET Thermal Calculator allows the optimization of the thermal solution once the losses have been determined.

• How2AppNote012 - How to Get More Power Out of an eGaN Converter
• Thermal Management of Chip-Scale Devices
• Improving Thermal Performance of Chip-Scale Packaged Gallium Nitride Transistors
• Webinar: Thermal Management of GaN FETs