| Summary: | 碩士 === 義守大學 === 材料科學與工程學系 === 92 === In this research, the basic properties、microstructures and the aging effects of Sn-0.7Cu、Sn-2.6Ag-0.6Cu、Sn-4.0Ag-0.5Cu lead-free solder balls and conventional Sn-Pb solder ball are investigated. In addition, commercial Ultra CSP 98L device with above mentimed solder balls and Sn-Pb、Sn-3.0Ag-0.5Cu、Sn-7Zn-Al（30-40ppm）paste are placed on OSP and NiAu PCB. After reflow, samples are gone through TCT and HTS reliability tests. DSC、SEM/EDX、EPMA/WDX are then utilized to study the mechanism of the IMC formation on the interface of the solder joints and the relations
among the microstructures solder joint strength and the reliability.
The results show that Sn-Pb solder ball consists of Sn-rich β phase and Pb-rich α phase solid solutions and both grains grown after long time aging. On the other hand, lead-free solder balls consist of Sn-rich β phase and eutectic IMC phases. Both sizes of β grains and IMC particles increase with aging time. The roundness of the solder balls after reflow decreases with increasing melting point of the solder materials. Due to the cyclying expansion and contraction of the TCT test, cracks are initiated on the interface of the solder ball and chip after 500 cycles and failed after 1000 cycles. Due to the thickness growth of the IMC on the OSP surface finished substrate, the joint strength decreases with increasing aging time of the HTS reliability test. For NiAu substrate, Ni layer acts as a barrier layer which in turn reduces the growth of the interfacial IMC. However, the gold embrittlement may occur which reduces the mechanical strength of
the solder joint.
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