Development of a New-Generation RoHS IGBT Module Structure for Power Management

This paper describes the design considerations for a high electric power density IGBT module structure mounted with smaller, new-generation chips. We have investigated heat flow depending on the copper foil thickness of an alumina based direct-copper-bonding (DCB) substrate, junction temperature rise in relation to the chip arrangement, electromagnetic noise dominated by the cupper circuit pattern, and lead-free solder layer stress as affected by the coefficient of thermal expansion (CTE) of DCB.Low thermal resistance was obtained by using a 0.6 mm thick copper DCB substrate; consequently the CTE of the DCB increased to 16 ppm/K, which is nearly equal to that of the Cu base as a heat sink. The thick copper DCB substrate can lower the junction temperature of a small chip with a high electric power density and can improve the thermal cycling capability of the DCB substrate mounted with a lead-free solder on the Cu base. Moreover the thick copper circuit effectively reduces the electromagnetic noise generated on the DCB substrate. Thus we have successfully realized a high electric power density IGBT module structure.