We accept power cycle tests to evaluate thermal fatigue of power devices. ■ Short power cycle test (short cycle test) This is a test that repeats heat generation and cooling in a short time, such as a few seconds on and off for a few seconds. Due to the short cycle, heating and cooling are repeated only around the device (chip), and this test is mainly performed to evaluate wire bonding joints and metal connection materials under the device (chip). ■ Long power cycle test (Long cycle test) This test repeats heat generation and cooling over a long period of time, such as several minutes of energization ON and several minutes OFF. Allow sufficient heat generation time so that heat is transmitted to the Cu base plate, which is remote from the device (chip) that generates heat. Even when OFF, it takes a long time to wait until the heat that has spread throughout is cooled. The area of the joint near the Cu base plate is large, so the amount of linear expansion increases. For this reason, this test is mainly performed to evaluate the metal bonding material between the insulating substrate and the Cu base plate.