Preparation And Properties Of Metallization Layer Used For Packaging Transistors

With the development of semiconductor devices and electronics manufacturing, high-performance and high-reliability transistors are in need, packaging is getting more and more attention. Though electronic packaging technology and materials trend to be miniaturization, high-performance, high-reliability and low-cost, metallic packaging is still the best choice of ensuring transistors’ hermeticity in military and aerospace field. Hermeticity of seal between ceramic insulator and lead is poor in domestic metal tubes. Designing excellent metallization formula and sintering process, preparing dense metallization layer with good performance and improving alumina ceramic metallization process have great significance for the development of domestic semiconductor packaging industry.In this paper:Metallization layer was prepared by metallization formula with different ratio of molybdenum powder. Phase composition, surface morphology, bonding interface, tensile strength were assessed to determine the basic system, and then sintering process was optimized. Different content of activator oxide BaO and ZrO2 were added in metallization formula to research their effects on performance of metallization layer. Difference of their activation mechanism was analyzed.Result showed that when the mass ratio of SiO2, MnO, and Al2O3 is 50:35:15, glass phase is formed without crystallizing MnAl2O4, Mn2SiO4 and MnSiO3 after high temperature sintering. Performance of metallization layer is determined by metallization formula and sintering temperature. When Mo was 75wt.% and the sintering temperature was 1400℃, metallization layer has most excellent performance, the tensile strength reached 106MPa. When content of molybdenum powder is too low, too much glass phase distributed in metallization layer. Wettability of solder on metallization layer was poor, tensile strength decreased. When content of molybdenum powder was too much, too little glass phase melted and diffused. Metallization layer was not dense because of containing pores, tensile strength also decreased. Formation and diffusion of glass phase were promoted when sintering temperature increased, and the metallization layer was denser. Bond between ceramics and metallization layer was tight, tensile strength increased. When sintering temperature is too high, too much glass phase diffused to the surface and influenced wetting and spreading of the solder, tensile strength decreased.Addition of BaO or ZrO2 could improve properties of the metallization layer. The activation effect was best when content of BaO was 1.5 wt.%, tensile strength of metallization layer could reach 138MPa. For ZrO2, the optimum amount was 0.5 wt.%, tensile strength of metallization layer reached 121MPa. Activation mechanism of them was different. BaO could decrease viscosity of the glass phase in metallization layer. Diffusion of the glass phase between ceramics and metallization layer was promoted. Properties of the metallization layer were improved. When BaO was added, metallization layer was denser, bond between ceramics and metallization layer was tight, tensile strength increased. Excessive amount of BaO caused too much glass phase diffusing to the surface. Wetting and spreading of the solder were influenced, tensile strength decreased. Properties of the metallization layer were improved when little ZrO2 was added. Tensile strength increased because strength of glass phase was improved. But excessive amount of ZrO2 would weaken wettability of the glass phase on ceramics. Diffusion of the glass phase between ceramics and metallization layer was controlled. Metallization layer was not dense, bond between ceramics and metallization layer was not tight, tensile strength decreased.