Comparative study of microstructures and properties of three valuable SnAgCuRE lead-free solder alloys

• Published in: Journal of electronic materials 2006-05, Vol.35 (5), p.1095-1103
• Main Authors: Xiao, Weimin, Shi, Yaowu, Lei, Yongping, Xia, Zhidong, Guo, Fu
• Format: Article
• Language: English
• Subjects: Comparative studies; Condensed matter: structure, mechanical and thermal properties; Elasticity, elastic constants; Exact sciences and technology; Lead free solders; Materials science; Mechanical and acoustical properties of condensed matter; Mechanical properties; Mechanical properties of solids; Microstructure; Physics
• ISSN: 0361-5235; 1543-186X
• DOI: 10.1007/BF02692572

Lead-free solders with excellent material properties and low cost are essential for the electronics industry. It has been proved that mechanical properties of SnAgCu alloys can be remarkably improved with a minute addition of rare earth (RE) elements. For comparison and optimization, three valuable solder candidates, Sn3.8Ag0.7Cu0.05RE, Sn3Ag0.5Cu0.05RE, and Sn2.9Ag1.2-Cu0.05RE, were chosen due to the excellent properties of their own SnAgCu basic alloys. Wetting properties, melting temperature, bulk tensile properties, and joint tensile and shear properties were investigated. In addition, the microstructures of solder joints were observed and the effects of microstructure on mechanical properties were analyzed. Experimental results indicated that the tensile and shear strengths of solder joints were decreased from Sn3.8Ag0.7Cu0.05RE, Sn2.9Ag1.2Cu0.05RE, to Sn3Ag0.5Cu0.05RE, in order. Such difference in mechanical properties could be attributed to the influence of slightly coarse or strong Cu^sub 6^Sn^sub 5^ scallops in the reaction layer as well as superior eutectic network and large volume percentage of large primary intermetallic compounds (IMCs) inside the solder joints. It is also suggested that the size and volume percentage of large primary IMCs inside the solder be controlled. In addition, serration morphology was observed at the edge of large primary and eutectic IMCs in the three solder joints, which could be related to the content of Ag, Cu, and RE. The serration morphology was proved to be beneficial to mechanical properties theoretically. Furthermore, the three alloys investigated possessed similar wetting properties, melting temperatures, and bulk tensile properties. [PUBLICATION ABSTRACT]