Role of annealed copper plasticity in process-induced warpage of SiC power modules

Substrates, such as active metal brazing (AMB) and direct bond copper (DBC), play a crucial role in the warpage performance of power modules, significantly impacting alignment precision, manufacturing yield, and long-term reliability. However, the effect of the plastic behavior of annealed copper (Cu) in substrates has received limited attention. This study investigates the process-induced warpage of a 750 V/400 A three-phase full-bridge silicon carbide (SiC) metal-oxide-semiconductor field-effect transistor (MOSFET) power module employing an AMB substrate, with particular emphasis on the influence of plastic deformation in the annealed copper layers (ACLs) on warpage behavior. A process-dependent three-dimensional (3D) nonlinear finite element analysis (FEA) model is developed by integrating the element birth-and-death technique with material and geometric nonlinearities. Besides accounting for the plasticity effect of the ACL, the pre-existing warpage of the AMB substrate is incorporated as the initial geometric condition, enabling the subsequent warpage evolution to be evaluated from a realistic starting configuration. Apart from that, the FEA model considers the elastoplastic behavior of the ACLs and SAC305 solder, the sequential thermal history of the manufacturing process, and the vacuum holding pressure applied during wire bonding. The analysis model is validated through comparison with warpage measurements derived from in-line 3D surface profilometry conducted at multiple manufacturing stages. The results demonstrate that neglecting ACL plasticity leads to substantial discrepancies in the predicted warpage and may even result in an incorrect warpage direction after die bonding. The vacuum holding pressure applied during wire bonding also induces irreversible deformation of the ACLs and redistributes the process-induced stress, thereby altering the subsequent warpage behavior. Finally, parametric analyses are performed to evaluate the effects of ceramic layer thickness, Cu layer thickness, and ceramic material properties on warpage evolution.