An optimal structural design to improve the reliability of Al2O3–DBC substrates under thermal cycling

•Ladder shaped copper foil prolongs the thermal fatigue life of Al2O3–DBC substrate.•Thickness of each copper ladder should be equal to maximize the fatigue life.•Longer edge tail can prolong the fatigue life of various kinds of DBC substrates.

An optimal structural design of direct bonding copper (DBC) substrate with ladder shaped copper layers was proposed through numerical optimization approach in this paper. In order to study the fatigue mechanism and life, thermal–mechanical stress and strain distributions of DBC substrates under thermal cycling ranged from − 55 °C to 150 °C were simulated and analyzed by finite element (FE) method. Improved Coffin–Mason law was applied to calculate the fatigue life under thermal cycling, Chaboche constitutive model with non-linear kinematic hardening was used to describe the elastic–plastic behavior of ductile copper. Design of experiment method was applied to investigate the sensitivity of geometric parameters on the thermal–mechanical performance. The ladder shaped DBC substrate design with specific designed copper ladder thickness was demonstrated to be robust. The fatigue life of proposed design was about three times longer than the traditional one under thermal cycling test. Moreover, the length of edge tail of the second copper ladder played an important role on the fatigue life. The lifetime of the substrate can be improved by the increase of edge tail length. The simulated results of the DBC substrate fatigue life were verified by experimental results.