Hermetic packaging of Kovar alloy and low-carbon steel structure in hybrid integrated circuit (HIC) system using parallel seam welding process

This work aims to characterize the microstructure and temperature field of the hermetic packaging structure by welding the cover made of Kovar alloy and the base made of a low-carbon low-alloy steel (i.e., #10 steel) using parallel seam welding (PSW) process. The microstructure of welded joints and distribution of elements were analyzed by scanning electron microscopy (SEM) equipped with energy dispersive spectrometer (EDS). Welding mechanism of PSW is discussed and temperature field of PSW is studied by a nonlinear transient finite element analysis. In FEM simulation, the surface contact pair is created to form weld beam and the heat generated by a pulse current is taken as a moving heat source. The results show that the maximum temperature in the weldment is 1105.3 °C, which is below the melting point of Kovar alloy and #10 steel (both in 1400~1500°C). The cross-sectional microstructure analysis results of the welded joint show that welded junction is localized between the plating layers of two base materials, both Kovar alloy and #10 steel did not melt during the welding process. Numerical simulation value of the temperature at the plating coat layer on Kovar side is larger than that on #10 steel because of boundary conditions and thermal conductivity. Same phenomenon can be seen at the location 3 mm away from the weldment. The temperature on the node of Kovar with a distance of 5 mm from the weldment is 796 °C.