微小SACはんだの引張強さに対する初晶Snの形状と分布形態の影響

抄録

The miniature specimens made from Sn-3.0Ag-0.5Cu (SAC) solder tend to show 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 applying 10 % strain to miniature SAC solder specimens made by casting were conducted. The shape and distribution morphology of primary Tin crystal in the specimen after the tensile test were also investigated, and they were compared between high-strength specimens and low-strength specimens. The shape of each Tin crystal was represented as an ellipse by employing an image processing method. The length and the angle to the loading direction of the major axis of an approximate ellipse were used for representing the size and the distribution morphology of a tin crystal, respectively. Tin crystals the size of which was in the range from 10 μm to 15μm were most frequently observed irrespective of the strength of the specimen. Meanwhile, the orientations of the tin crystals in the size range were different depending on the strength. Namely, tin crystals the orientation of which made 0-10° and 80-90° to the loading direction were observed frequently in the high-strength specimens, but 30-40° were frequent in the low-strength specimens.