Influence of Thermal Coupling on Lifetime Under Power Cycling Test

In this article, the influence of thermal coupling in power modules on lifetime under power cycling test (PCT) is investigated. In a full-bridge power module for electric vehicle application, the thermal coupling is strong due to high power density and causes lateral temperature difference. In PCT, at the same maximum junction temperature
T
_vjmax
and temperature swing Δ
T
_vj
, the influence of thermal coupling on lifetime and failure mode is investigated. The root cause of why thermal coupling influences lifetime and the failure mode is discussed by finite-element analysis. Transient thermal impedance is used to calibrate the simulation model. The Influence of thermal coupling on chip surface and solder layer temperature distribution is analyzed under the same test conditions. Furthermore, two parameters are extracted from the temperature distribution of chip surface as flags of failure mode determination. Finally, taking thermal coupling into account, combined with direct copper bonding structure, an improved layout is recommended in terms of lifetime.