Packaging aging of power devices is a major cause of their failure. In recent years

online monitoring technology for packaging aging has received increasing attention. The thermal dissipation of power device packaging is divided into single-sided and double-sided cooling. Solder and bonding wires are the weak points of single-sided cooling packaging

while the chip-molybdenum interface is the weak point of double-sided cooling packaging. These weak points are all at the chip direct connection interface. Power cycling is the main method for evaluating the reliability of device packaging

primarily utilized by using on-state voltage drop and junction-to-case thermal resistance as aging characteristics which is applied to monitor package aging online. However

the on-state voltage drop mainly reflects bonding wire aging and cannot effectively indicate solder and chip-molybdenum interface aging. The thermal resistance of the chip direct connection interface accounts for less than 20% of the junction-to-case thermal resistance

making it less sensitive to aging. Traditional monitoring methods cannot accurately reflect packaging aging. This paper proposes a differential regional thermal resistance localization method based on one-dimensional heat transfer and transient thermal conduction theory

which can be used for online monitoring of the aging of any package structure along the heat transfer path by backward differencing the junction temperature sequences in the cooling process of the power cycle with the heating power converted into differential thermal resistance. This paper develops an online monitoring system

achieving the first online monitoring of chip direct connection interface aging in rigid press-pack devices during power cycling. Power cycling results show that the sensitivity of the differential regional thermal resistance localization method to chip direct connection interface aging is 4.80 times that of traditional monitoring methods

closely matching the simulation result of 5.19 times

and verifying the correctness of the simulation process and the effectiveness of the new monitoring method for device packaging aging.