Thermal Resistance of Electrical Insulation for Bolted and Clamped Discrete Power Devices

In power electronic systems, TO-220 packaged electronic devices are bolted or clamped to a metal heat sink for cooling. When mounting high voltage TO-220 devices to touch-safe heat sinks, electrical insulation must be used between the device and the heat sink. This paper experimentally explores the thermal resistance between bolted and clamped TO-220 packages and the heat sink due to the electrical insulator. Aluminum oxide insulators are experimentally compared to commercially available polyimide thermal interface materials (TIMs). Various TIMs are explored to reduce the thermal contact resistance at the alumina/metal interface including screen printed phase change material. Results show that thermal contact resistance (TCR) at the alumina interface is significant under both clamped and bolted TO-220 diodes but can be reduced up to 70% with graphite sheets, thermal grease or phase change material.