Power module reliability evaluation

Power devices to which high voltages or large currents are applied in power conversion circuits suffer from switching losses in switching operations that perform on/off state transitions during power conversion operations and conduction losses due to voltage drops in the conduction state, causing their temperature to rise. When operation is stopped, the temperature drops to the ambient temperature. Thus, the temperature rise and drop is repeated at each operation and shutdown. Power devices are mounted on lead frames or copper-plated ceramic substrates using bonding materials such as solder, and current is drawn out by bonding wires. The power module is then encapsulated with a resin material or the like for protection. Since these materials have different coefficients of linear expansion with respect to temperature, stress is applied to the junction interface when temperature changes are applied. Repeated stress changes during temperature rise and fall cycles cause stress degradation of the junction, and as the junction deteriorates, cracking and delamination occur, leading to degradation of electrical performance. In order to realize highly reliable systems, bonding materials and methods that do not deteriorate or are resistant to deterioration are desired, and we are developing such materials and methods. We conduct evaluation by changing the method of heat application depending on the part to be evaluated, such as exogenous thermal cyclic tests and endogenous thermal power cycle tests.

Research work