Parylene as Coating for Power Semiconductor Devices

Abstract

The introduction of wide band gap semiconductor devices leads to smaller package sizes, higher power densities and higher switching frequencies, which is advantageous compared to the power electronics based on the conventional silicon devices. However, due to the small insulation distances and the limited temperature range of available package materials, it is not possible to exploit these advantages completely. In this study, the properties of Parylene coatings as passivation layers in power semiconductor devices is investigated. The material would be particularly advantageous for double-side cooled power modules because it can fill the small gaps between different conductive layers, which is not possible with conventional packaging technologies. Parylene is promising to provide an excellent insulation performance even in these areas and exhibits a good temperature stability. Furthermore, this polymer acts as a barrier for humidity, dirt and corrosive gasses. Two types of Parylene were tested using the High-Voltage, High Humidity, High Temperature Reverse Bias (HV-H³TRB) test on substrate level and the better Parylene type also on automotive three-phase modules. The results are encouraging, although the performance strongly depends on the Parylene type and although a sensitivity to the respecive surface condition to be coated became apparent.