Technological Study On Low-voltage Electromagnetic Compaction And Liquid Phase Sintering Of Cadmium-free Silver-based Intermediate Temperature Filler Metals

Cadmium-free silver-based intermediate temperature filler metals have good wetting and clearance filling properties, low fusing temperature, and contain no poisonous elements, its brazed joint have excellent strength, plasticity, electrical conductivity and corrosion resistance, so has a wide application prospect in micro-electronic package, household appliance, aeronautics&astronautics, military industries. At present, preparation methods of Cadmium-free silver-based intermediate temperature filler metals are traditional rolling technology and rapid solidification technology. Traditional rolling technology has the disadvantages of many process steps, long production cycle, low efficiency and low rate of finished product. Rapid solidification is a kind of disruptive technology in preparation of materials, but the research of it in China is rather little, and no production enterprise have controlled this technology.Based on our studying team’feature, this paper introduces the powder metallurgy technology to the preparation of cadmium-free silver-based intermediate temperature filler metals, adopt low-voltage electromagnetic compaction to prepare cadmium-free silver-based intermediate temperature filler metals, open up a new way for preparing high density cadmium-free silver-based intermediate temperature filler metals. This technology overcomes disadvantages of the traditional rolling technology, such as long production cycle, and avoids traditional high-temperature melt casting, decrease the brittle phases, improve the rate of finished product, so has great significance in the practical production.The compaction experiments are done with the self-made electromagnetic forming machine, on low-voltage electromagnetic compacting Ag-22Cu-17Zn-5Sn cadmium-free silver-based intermediate temperature filler metals powders by way of indirect process. The effects of the technical parameters, such as discharge voltage, capacitor, discharge times, diameter height ratio of the compacts and coil turns, on the green density of ceramics were analyzed systematically, and the difference between electromagnetic compaction and static compaction on cadmium-free silver-based intermediate temperature filler metals was studied. The compaction experiments results show that, either improve discharge voltage, capacitor to increase discharge energy or increase coil turns to improves utilization rate can both effectively improve the relative density of the green body of cadmium-free silver-based intermediate temperature filler metals. From increasing the discharge times and diameter height ratio of the compacts can also improve the relative density of the green body to some extent. Compared with the traditional static compaction, the density of green body prepared by low-voltage electromagnetic compaction under high discharge energy and utilization rate is much higher than prepared by traditional static compaction, so low-voltage electromagnetic compaction is a effective method to obtain high-density cadmium-free silver-based intermediate temperature filler metals.At the same time, this paper studies the changes of Ag-22Cu-17Zn-5Sn compacts during liquid-phase sintering, and draws the conclusion that Ag-22Cu-17Zn-5Sn compacts would expand and the density decrease. Expansion mechanism has been studied by means of heat expansion testing, scanning electron microscope (SEM), X-Ray diffraction (XRD), electron probe microscopic analyzer (EPMA) techniques and metal diagrams. Because of the high Zn additive solubility in Ag, the liquid zinc penetrates into the grain boundaries of Ag particles and leaves pores at the prior Zn particle sites, which brings about the solid particle grain growth and the increase in the volume of the specimen as a whole. The unbalanced diffusion between elements leads to imbalanced mass flow between the solid/liquid interface, resulting in the solid particle grain growth an d overall expansion of the specimen.