A Partial Discharge Inception Voltage Modeling Approach

Abstract

A partial discharge inception voltage modeling approach promoting design-for-reliability considerations in advanced power modules is presented. As power modules are being operated at higher voltages and become more compact to meet power density demands, there is an increased risk of partial discharge, the silent precursor to electrical breakdown that degrades insulation material. The trade-off between voltage class and module compaction must be quantified. This work presents a methodology to model the tradeoff for any substrate and encapsulant material. A surface charge density-based partial discharge inception voltage (PDIV) model was developed to overcome the challenges in electric field-based models. The model consists of a closed-form equation that accepts finite element simulation results as input and produces PDIV as output. The model was experimentally validated for various trace gaps in a 12/25/12 mil alumina DBC using Dow Corning 3-6635 dielectric gel. An expected trend of diminishing returns was observed between PDIV benefit and trace-gap. This approach quantifies this diminishing returns point. To design for reliability, the maximum operating voltage must be limited to the PDIV. For a material set and manufacturing process, this methodology can be used to determine the voltage class and trace gap design rules.