添加In對Sn-3Ag-2Sb銲點微結構與低週疲勞特性之研究

The goal of this research is to evaluate the effects of adding 1~5wt% Indium into Sn-3Ag-2Sb lead-free solder on melting point, microstructure, microhardness and the interfacial reaction with Cu substrate. Furthermore, the single lap specimens and high temperature storage were used to evaluate the low cycle fatigue and heat-resistance of Sn-3Ag-2Sb-xIn solder joints. Experimental results show that the melting point of Sn-3Ag-2Sb-xIn solders decreased with indium additions, but the gap between solidus and liquidus temperature (Mushy zone) was expanded at the same time. Indium addition into the Sn-3Ag-2Sb, lead to the partial substitution of Sn atoms in Ag3Sn by Indium. The formation of Ag-Sn-In compound is Ag3(Sn,In) in Sn-3Ag-2Sb-2In and Sn-3Ag-2Sb-3In samples. However, the compounds transform gradually into Ag2(Sn,In) when In addition reach 4wt% and over. After thermal storage for 625 hours, the transformation will be obvious even in Sn-3Ag-2Sb-3In. With the increase of indium additions or thermal storage time, the morphology of Ag-Sn-In compounds change from rod-like or disc-like into massive type. When Sn-3Ag-2Sb-xIn solders combine with Cu substrate, Ag-Sn-In and Cu-Sn-In IMC compounds were observed on the interfacial microstructure. After the 150℃ thermal storage, thickness of IMC layer will be raised as the Indium addition increasing. In the condition with constant displacement of 0.020mm, shear strength of the as-soldered joints is increased with greater In additions. The shear strengths are 34.33 N(Sn-3Ag-2Sb), 37.02 N(1 wt% In), 37.48 N(2 wt% In), 41.12 N(3 wt% In), 48.09 N(4 wt% In), 51.29 N(5 wt% In). Fatigue life of the as-soldered joint approximately increases with greater In additions, and 5 wt% In solder has better fatigue life. After 150˚C thermal storage, fatigue life will improve because of the softening of solder joints. So the fatigue life of 2wt% In and 3wt%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 4wt% In solder joint transit from solder fracture mode to mixture mode with increasing indium additions and storage time. In the meanwhile, fatigue life would be decreased. With compare of melting point, microstructure, fatigue life and interfacial behavior of Sn-Ag-Sb-xIn solder. The solder contains 3wt% Indium has better behaviors.