To meet the increasing demand for high switch speed of avalanche bipolar junction transistors (ABJT) and to solve the heat dissipation problem of the commonly used SOT23 packaging, an optimized packaging design for ABJT using the clip bonding is proposed. In this paper, a series of analysis is conducted based on finite element simulation to study the thermomechanical performance of the novel clip bonding packaging. A comparison of the parasitic parameters, thermal and mechanical properties between clip bonding and wire bonding packaging demonstrates that the bigger bonding area leads to lower inductances and thermal resistance, as well as better heat dissipation performance and reliability. The thickness of the copper sheet is also optimized and the reliability analysis is conducted using the Hallberg-Peck model, demonstrating that the reliability of the clip bonding packaging is superior to the conventional SOT23 packaging using wire bonding.