Project 5: Reliability of Doped SnAgCu Solder Alloys with Various Surface Finishes Under Realistic Service Conditions

The electronic packaging industry has moved from eutectic Sn-Pb solder materials to near-eutectic SnAgCu (SAC) solder materials in the past decade because of the increasing awareness of health and safety concerns associated with the use of Lead (Pb). The reliability performances for SAC solder materials under thermal and isothermal aging conditions have been extensively studied and results show aging is universally detrimental to the solder joints reliability, which leads to a large degradation of mechanical properties including tensile strength, shear strength and fatigue behaviors. Numerous solutions have been proposed to mitigate the aging-induced mechanical properties degradation. One of the possible solutions is to develop “next generation” solder alloys with additional elements mixed with SAC solder alloys. This process is called solder doping. Common solder dopants include nickel (Ni), bismuth (Bi), antimony (Sb), and indium (In). Solder doping was observed to have substantial influence on mechanical properties of solder joints, such as an increase of solder ultimate tensile strength and shear strength. In this study, 7 commercial individual doped solder alloys along with SAC305 (Sn-3.0%Ag0.5%Cu) and SAC105 (Sn-1.0%Ag-0.5%Cu) solder alloys were used as test samples. Three types of surface finishes were applied on the copper pads of all test samples, which were Organic Solderability Preservative (OSP), Immersion Silver (ImAg), and Electroless Nickle Immersion Gold (ENIG). In the first part of the research, the effect of long-term room temperature aging on the cyclic stress strain and fatigue behaviors of SAC305, SAC105 and three doped solder alloys were studied. Prior III to testing, all the specimens were exposed to room temperature (25°C) for 4 years. Test specimens were then subjected to cyclic stress-strain loading under these two aging conditions (0 aging and 4 years aging). Failure data were carefully analyzed to study the effect of room temperature aging on the reliability of solder alloys. Results showed 4 years’ room temperature aging leads to a significant degradation on the fatigue properties, and doped solder alloys exhibited a better fatigue resistance than SAC solder alloys.