Thermo-physical and mechanical properties of Cu/Kovar laminated composites prepared by hot pressing and hot rolling
摘要
To balance the contradiction between the thermal conductivity and thermal expansion coefficient of Cu and Kovar lead frame materials, Cu/Kovar laminated composites were prepared using hot pressing and hot rolling. The effects of heterogeneous structure on mechanical and thermo-physical properties of the composites were studied. Macroscopic (multi-layers) and microscopic (grains and dislocations) heterogeneous structures are formed during hot rolling. As the passes of hot rolling increase, the strength of the laminated composites is influenced by multiple factors including the interface strength and quantity, intrinsic strength of the Kovar layer, and back stress of the heterogeneous structure. Specifically, the strength of the CKC3 composite reaches 716.8 MPa. The thermal conductivity of the Cu/Kovar composites improves with increased hot rolling passes due to the higher proportion of Cu. Meanwhile, the coefficient of thermal expansion decreases because of the increased number of layers and the special residual stress distribution of heterogeneous structures. For instance, the thermal conductivity of the CKC3 composite is 116.4 W m−1 K−1 (in-plane), while its coefficient of thermal expansion is 4.91 × 10–6 K−1. Compared to pure Kovar alloy, the thermal conductivity has increased by 584%, whereas the coefficient of thermal expansion coefficient remains comparable.