Power electronic circuits are used in electric vehicle or hybrid electric vehicle to drive the main electric motor. All the transistors and diodes in a sealed power electronic package will experience repeated high current cycling during their service life. The aluminum bonding wires which connect these devices to the rest of the circuit will experience repeated thermal strain cycling. When design a power electronic package, the thermal fatigue durability of these bonding wires would be a concern. A power electronic module with pure aluminum bonding wires of 0.5mm in diameter from a vendor was power cycled with the following schedule. Each transistor in the circuit was on for 10 seconds with the current at 400 Amperes followed by the transistor being off for 30 seconds. The wires from the diodes to the copper trace lines are about twice as long as those from the transistors to the copper trace lines.