DBC-Packaged Inverter Power Module for Integrated Motor-Inverter Design Used in 48 V Mild Hybrid Starter-Generator (MHSG) System

Abstract

This paper presents an improved package design of an inverter power module specialized for the 48 V starter- generator used in 48 V mild hybrid vehicles. The inverter module, called the mild hybrid starter and generator (MHSG), is integrated with its motor for size/volume reduction. However, the integrated motor-inverter presents supplementary challenges, such as limited cooling capabilities, in addition to the challenges resulting from the elevated voltage of 48 V of the mild hybrid systems. The proposed MHSG power module addresses these challenges. Parallel-connected metal-oxide-semiconductor field-effect transistor (MOSFET) dies were solder-bonded onto a direct bonded copper (DBC) substrate, and three DBC substrates (providing six legs) were assembled in a custom housing mounted on a forced air cooler. Shunt resistors and surface-mount device components were also soldered onto the DBC substrates. For improved stability and balance, ribbon bonding was used instead of wire bonding, the module components were repositioned, and DBC patterns were adjusted. The aforementioned approaches minimized the parasitic inductance, unbalanced/concentrated current density, and maximum temperature of the 48 V MHSG inverter module. The proposed module was validated through multiphysics finite-element method (FEM) simulations, manufactured prototypes, and experiments, all of which confirmed that the proposed module exhibits the electrical/thermal characteristics required for 48 V integrated MHSG systems.