| A number of possible alternative solders are reviewed and it is concluded that the eutectic tin-silver solder may deliver the best mechanical properties at a reasonable cost. Because very little is known about this alloy, this research investigates the relationship between many different service and processing variables and the mechanical properties of this system. The aim is to develop a better understanding of the physical metallurgy controlling the behavior of eutectic tin-silver bonding systems, while providing the mechanical property data and sensitivity analysis crucial to process and design engineers. Knowledge of the limitations of the alloy and how and why it responds to changes in processing and service conditions will help expedite the acceptance of this new soldering system in the electronics industry.; This study looks at the effects of a large number of processing and service conditions on the microstructure, fracture toughness, bending strength, shear strength and shear creep resistance of Cu/96.5Sn-3.5Ag solder joints. In particular, the effect of surface roughness, joint thickness, solder chemistry, soldering temperature, soldering time, solidification rate, aging time, testing temperature and sample orientation are investigated. Although most of these variables affect the final mechanical properties, changes in the surface roughness of the copper and the aging time of the joint produce the most interesting and profound effects.; The microstructure of 96.5Sn-3.5Ag solder is rather unique. Although it is a eutectic alloy, dendritic networks of tin solidify first to make up roughly 50% of the microstructure. The remaining volume is composed of a coupled growth structure containing small Ag{dollar}sb3{dollar}Sn intermetallic needles in a matrix of Sn. This and other microstructural features found in Cu/96.5Sn-3.5Ag solder joints have important effects on the final mechanical properties.; The mechanical properties of eutectic tin-silver solder joints are comparable to those for the 63Sn-37Pb soldering system. In general, the creep properties of tin-silver solder are found to be superior to those of the lead-tin, while the fracture toughness and shear strength properties of the lead-tin solder are superior to those of the tin-silver system. |
