Study on the Method to Analyze the Electrical Contact Resistances of Press-Pack IGBT devices

Electrical contact resistances are the link between the mechanical model and the electrical model, which should be accurately determined to analyze the electro-thermal distribution of the press-pack IGBT devices. However, determining the electrical contact resistances is very difficult because they are affected by pressure and material properties and cannot be measured directly. In this paper, a method to identify electrical contact resistances is proposed based the electrical contact theory for press-pack IGBT devices. Firstly, the mathematical model of electrical contact resistance is derived by considering contact pressure, surface roughness, surface micro-hardness and material resistivity. Then, a circuit model of single-chip press-pack IGBT device is established by using the presented electrical contact resistances. Furthermore, the surface characteristics of the materials are analyzed to determine the parameters of electrical contact resistances, especially the effects of the chip surface metal coating. Finally, the influence of pressure on the electrical contact resistance of each contact surface of the device is also analyzed. The relationship of the on-resistance of the sing-chip press-pack IGBT device with pressure is obtained by using four-point probing approach. The validity of the proposed model is demonstrated.