Study On Interfacial Reaction And Brazing Rate Of Dissimilar Alloy Eutectic Brazing

Mo85Cu15 alloy has strong thermal conductivity and its thermal expansion coefficient is similar to that of GaAs for manufacturing high-power chips.Therefore,it is often used as a brazing substrate for high-power chips in high-density transceiver modules.The thermal conductivity and the Solder ability of Kovar alloy are similar to those of GaAs.It is often used as a substitute for GaAs in the research of chip brazing process,and is also a commonly used material for functional device assembly carriers.Because of its high silicon content,50%Si-Al has the advantages of light weight,good thermal conductivity and strong wear resistance.It is commonly used as a package for chip modules and Kovar substrates.At present,the chip package has the disadvantages of low solder penetration rate,difficulty in ensuring package reliability and consistency.The package quality of the chip has an important impact on the performance and life of the chip,but the whole process involves a variety of materials,and the interface reaction is very complicated.Exploring the reaction occurred during brazing of dissimilar materials and the influence mechanism of process parameters on the penetration rate is the necessary way to ensure the normal operation of the chip under high power conditions.In this paper,AuSn20 solder is used to weld Kovar alloy chip with molybdenum copper carrier,Kovar alloy substrate and aluminum silicon plate.Sn43Pb43Bi14 solder is used to weld molybdenum copper carrier and aluminum silicon shell.The surface of the plate has Ni/Au coating.The effect of process parameters on the macroscopic morphology of the weld was investigated by optical microscopy.The structure of the solder and the elemental diffusion and the reaction between the two solders and the substrate and the substrate were investigated by scanning electron microscopy and XRD.The mechanism of the influence of process parameters on the soldering rate of the chip was studied by the combination of X-ray detection and numerical simulation of the penetration rate,and the chip brazing process was optimized.The results show that:（1）In the weld of the Kovar substrate and the aluminum silicon plate,the solder undergoes eutectic reaction to form AuSn eutectic and Au₅Sn rod-shaped dendrites,and precipitates a large amount of Au.The joint connection form is that Sn interacts with the Ni plating layer to form Ni₃Sn₄,Au₅Sn surrounds the periphery of Ni₃Sn₄,and the solder intermediate layer forms AuSn eutectic and Au-rich regions.Elemental diffusion does not occur between the substrate elements and the solder.（2）In the weld of molybdenum-copper plate and aluminum-silicon plate,the eutectic reaction of the solder forms a Sn-rich region and a Pb-rich and Bi-rich region,and Sn and Au in the Sn-rich region react to form AuSn eutectic,rich in Pb and Bi regions.Pb reacts with Bi to form PbBi eutectic and Pb₇Bi₃.Mo and Cu in the substrate and Pb and Bi in the solder mutually diffuse to form a plurality of intermetallic compounds.The joint connection form is a connection between a plurality of intermetallic compounds and a PbBi eutectic and an AuSn eutectic.（3）Combining experiments and simulation results,it can be seen that when the welding temperature is 310°C,the welding time is about 60s-90s,the welding pressure is kept at 2-5g,and the size of the solder piece is slightly smaller than the chip,the solder penetration rate can be stably controlled.More than 95%.Applying a clamp of the same size as the solder to achieve a uniform and uniform pressure can improve the weld quality of the weldment.The simulation results of the penetration rate are in good agreement with the experimental results,but the positions of the pore distribution are different.