Influence of an Electrically Non-Conducting Heat Sink for Power Semiconductors on Radiated Interferences

Abstract

Power semiconductors are used in a growing number of applications. Furthermore, faster switching transients and therefore higher switching frequencies can be realised. This leads to higher radiated interferences at higher frequencies. In power electronic applications, often a cooling concept for the semiconductors is required to comply with the allowed temperature range. Typically, heat sinks are made of aluminium and their conductive behaviour can cause EMC problems. Via capacitive coupling, voltage transients are transferred from the power semiconductor to the heat sink, so that the heat sink behaves as an antenna and radiated interferences occur. Furthermore, a common mode current will appear if the heat sink is grounded. In this paper, a promising approach to reduce radiated interferences from the heat sink and solve the common mode issue by using an electrically isolating ceramic heat sink is presented. The influence of an aluminium nitride ceramic heat sink on cooling performance and EMC behaviour has been investigated. For this purpose, two geometrical identically heat sinks made from aluminium and aluminium nitride have been compared regarding thermal performance and radiated interferences characterised by S-parameters.