Mechanical design and analysis of direct plated copper film on AlN substrates for thermal reliability in high power module applications

For the high-power module applications, direct-plated-copper (DPC) aluminum nitride (AlN) substrate with a high thermal conductivity provide a good alternative to conventional aluminum oxide (Al₂O₃) substrate for better heat dissipation. However, the DPC AlN substrate suffers the delamination failures between Cu film and AlN substrate during thermal cycling, due to the higher thermal expansion coefficient mismatch with copper material. This study is to resolve the delamination problem of DPC AlN substrate during thermal cycling and further to provide important parameters for mechanical design for ensuring good thermal reliability. Prior to the analysis, the out-of-plane deformation measurement of a Cu-AlN bi-material plate subject to the solder reflow heating and cooling is conducted for evaluating the material property of the plated Cu film and residual stresses induced from the manufacturing and solder reflow process. The results show the hysteresis and Bauschinger-like behaviors for the Cu-AlN plate during the solder reflow heating and cooling. It is also found from finite element simulation that the Cu-film wedge angle and thickness significantly affect the maximum principal stress of AlN during thermal cyclic loading, and the predicted failure mode based on the maximum principal stress is consistent with experimental observation. The other factors, such as single-side and double-side Cu-film (sandwich-structure-alike) substrates and length difference of Cu film, will be presented and discussed as well.