| In the first, the interfacial evolution and shear strength of SAC lead free solder were studied in detail on Cu and Ni substrate during multiple reflows and isothermal aging at 150oC. The eutectic SP solder were used as the control. Then the particle reinforced composite solders were successfully prepared by mechanically dispersing SiC nanoparticles and dendrite Ni micro-particles into the SAC solder paste. The Surface Adsorption Effect and reinforced mechanism rendered by nanoparticles were revealed. Lastly the research was emphasized on the intermetallic compound (IMC) microstructure, morphology and shear strength of SAC-xNi/Cu(Ni) joints in the process of reflow and aging. More details were given as following.During multiple reflows, the scallop like Cu6Sn5 IMC at interfaces of SAC(SP)/Cu grew by grain boundary diffusion controlling. Whereas for SAC(SP)/Ni joints, the IMC growth was controlled by the volume diffusion. The growth rate and grain size of Ni-Sn IMC was less than that of Cu-Sn. During aging, the IMC growth on Cu and Ni substrate was controlled by volume diffusion. After 50 h aging, duplex layer structure was displayed at the solder/Cu interface. They are Cu6Sn5 close to solder and Cu3Sn adjacent to Cu substrate. The strength of SAC joints was always higher than that of SP.Composite solder SAC-xSiC was fabricated, which never was reported in literatures. In comparison to SAC, the melting temperature of SAC-xSiC solders was lower by 1oC. The grain size ofβ-Sn sub-grain and Ag3Sn decreased significantly in the composite solder matrix. Addition of SiC nanoparticles in the SAC solder could improve the microhardness by 30-44%, which was in good agreement with the prediction of the classic theory of dispersion strengthening.The process characteristics of SAC-xNi composite solders were equal to that of the non-composite solder. Ni particles could wet well with SAC solder. During multiple reflows, the SAC-xNi/Cu interfaces showed two distinct Ni bearing (CuNi)6Sn5 regions in the IMC layer. The reaction between Cu and SAC-xNi composite solder was accelerated with the Ni addition increasing, but IMC grains were refined. IMC growth at SAC-xNi/Cu interfaces was controlled by the combination of volume diffusion and reaction diffusion. The quantity of free Cu atoms in the solder bulk influenced the IMC morphology and crystal structure of solder/Ni interfaces. The shear strength of SAC-xNi/Cu(Ni) was enhanced by Ni particle additions, and the joint fracture presented ductile mode.After aging 50h at 150oC, the interfacial IMC in SAC-xNi/Cu joints become duplex layer structure, i.e. (CuNi)6Sn5 and Cu3Sn. The volume diffusion is the main controlling process for each IMC layer growth. The addition of Ni particles could depress the growth of Cu3Sn layer. After aging, except for SAC-2Ni joint with single (NiCu)3Sn4 IMC layer, the interface of all joints presented duplex IMC layers, whose upper and lower IMC layers were comprised of (CuNi)6Sn5 and (NiCu)3Sn4, respectively. Shear test result showed partial brittle fractures at interfaces of SAC-1Ni/Ni(Cu) and SAC-2Ni/Ni(Cu) after 500h aging.
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