| Summary: | 碩士 === 國立成功大學 === 機械工程學系碩博士班 === 94 === The goal of this research is to evaluate the effect of In additions (0~10 wt%) on the melting point and microstructure of Sn-Ag-2Sb lead-free solder. The reliability of low cycle fatigue of the solder joint is estimated by the thermal storage test for 150˚C.
Sn-3Ag-2Sb-xIn in form of solder balls with 1.15 mm in diameter are fabricated. Solder balls were re-flowed with Cu substrate in the form of single lap shear specimen, and then annel in 150℃for 225 and 625 hours, respectively. Experimental result show the melting points of Sn-Ag-Sb-xIn solder are decreased with higher In additions. The melting points are 223.1℃(Sn-3Ag-2Sb) and 192.9℃(10 wt% In). The range between solidus and liquidus pasty will expand with the addition of indium. Microstructures of the Sn-3.5Ag and Sn-3Ag-2Sb solders are similar and can be characterized as consisting of β-Sn dendrite and interdenritic eutectic network. In atoms are almost solved in the β-Sn when adding 1 wt% In into the Sn-Ag-Sb solder, and In atoms may replace Sn of Ag3Sn compounds to be Ag3(Sn,In). The Ag2(In,Sn) and InSb compounds are observed as the content of In addition increased to 5 wt%. For Sn-3Ag-2Sb-10In, the percentage of indium in Ag2(In,Sn) compounds is increased, and the amount of InSb is increased. Ag3Sn compounds aren’t found in 5 wt%In and 10 wt%In solders. From the 3-D observations of Sn-Ag-Sb-In solder, the morphology of InSb can be concluded to two types : plate-like and piece-like, but the shapes of Ag2(In,Sn) compounds’ cannot be determined.
In the condition with constant displacement of 0.020mm, shear strength of the as-soldered joints is increased with higher In additions. The shear strengths are 42.3 N(Sn-3Ag-2Sb), 46.7 N(1 wt% In), 70.0 N(5 wt% In) and 80.4 N(10 wt% In). Fatigue life of the as-soldered joint approximately increases with greater In additions, and 10 wt% In solder has better fatigue life. The reason is the plastic strain of the solder joint decreases with higher In additions. The lesser plastic strain the better fatigue life and the rate of load-drop is increased with higher In additions. After 150˚C thermal storage, fatigue life will improve because of the softening of solder joints. So the fatigue life of 1 wt% In solder joints are higher than as-soldered. The thickness of the Intermetallic Compound(IMC) are also increased after thermal storage. The fracture modes of 5、10 wt% In solder joint transit from solder fracture mode to mixture mode then into IMC fracture mode with increasing indium additions and storage time. In the meanwhile, fatigue life would be decreased.
Key word：lead-free solder、Ag2In、low cycle fatigue、Sn-Ag-Sb-In
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