引張強さにばらつきを示す微小SACはんだ試験片内部における初晶Snの形状と分布形態

抄録

To evaluate the strength reliability of fine-pitch solder joints based on a finite element analysis (FEA) precisely, the material parameters for the analysis should be estimated by mechanical testing using a miniature specimen. Then, we have conducted tensile tests using a miniature specimen of Sn3.0Ag-0.5Cu (SAC) solder and found out the tensile strength of the specimen showed larger variation in the tensile strength than the ordinary size specimen. This means that the comparison of the internal structure between high-strength specimens and low-strength specimens will give valuable information to propose a method for giving high strength to solder joints in electronic equipment. Therefore, in this study, the tensile tests and tension-strain maintenance tests, which can evaluate the tensile strength and the creep strength respectively, were conducted using miniature SAC solder specimens. The shape and distribution morphology of primary Tin crystal in the specimen after the tests were also investigated, and they were compared between the high-strength specimen and the low-strength specimen and between the high-creep resistance specimen and the low-creep resistance specimen. In the specimens having high tensile strength and high creep resistance, there was much existing primary Tin crystal in the same direction for the tensile direction. In the specimens having low tensile strength and low-creep resistance, there were much existing primary Tin crystal in the direction from 40 to 50 degrees for the tensile direction.