Abstract
The objective of this study was to investigate the microstructure, adhesive strength, and the thickness of interfacial intermetallic compound layers of Sn-Ag-X/Cu (Sn-3.5Ag, Sn-3Ag-0.5Cu, Sn-3.8Ag-0.7Cu)solder joints under different cooling rate (4.7oC/s~1.4oC/s). The SnAgCu/Cu soldered joints were isothermally aged at 200oC,for different storage time of 0, 25, 225 and 625 hrs respectively to study the thermal aging effects on adhesive strength of solder joints. The results showed that the solder layer adjacent to the Cu substrate of temperature below the actual melting point of solder due to quick cooling rate. The IMC(Intermetallic Compound) growth rate increases with increasing Cu content of solder and decreasing cooling rate。The morphology of IMC become rougher by slow cooling, and conversely, flat by quick cooling. The shear strength results show that the average shear strength of SAC solder higher than the average shear strength of SA35 sodler. The shear strength of solder joints decreased with increasing temperature and increasing cooling rate. The fracture position of solder joints at as-soldered occurred at the inside of solder. When the testing temperature increased, that fracture behavior of solder joints would chang from the inside of solder to the IMC layer . The shear strength of solder joints breaked at the inside of solder is higher than solder joints breaked at the interfacial surface. The fracture behavior of the joints is closely linked with the growth of the IMC layer and the variations of the mechanical properties of the IMCs .
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