Investigation of Temperature and Strain Rate Behavior of Lead-free Solder Sn96.5Ag3.5

In the late years, many countries will begin to prohibit using the lead-based solders in microelectronic packaging processes in view of inherent toxicity of lead-based solder alloys. The waste electrical and electronic equipment (WEEE) directive by EU has claimed that the use of Pb in consumer electronics will be banned after January 2006. Therefore, the development of lead-free solders replacing Pb-containing solders has been a crucial task for academe and microelectronic packaging industry. Due to the formation of fine Ag3Sn inter-metallic compound precipitates, Sn-Ag binary lead-free solders have some good mechanical properties (ductility, creep resistance and thermal resistance), and they were defined promising candidates substituting Pb-containing solders in microelectronic packaging and interconnecting. However, many mechanical properties of Sn-Ag alloys have not been clarified because Sn-Ag solder alloys used in microelectronic interconnecting process have not a long history. As the interconnecting materials in microelectronic packaging processes, mechanical properties of soldering alloys are important parts to impact the packaging quality, and determine the fracture and thermal fatigue behaviors of solder joint. Recently the trend of higher circuit board component densities results in the decrease of microelectronic packaging dimensions and the solder bump sizes. Therefore, the requirements for mechanical characteristics of lead-free solders will be more rigorous in packaging process. Thus, the research work about the mechanical properties of Sn-Ag binary solders is essential to microelectronic industry and academe. During microelectronic components and devices operating, the packaging and interconnecting materials would be subjected to the thermal-mechanical stress and strain which could affect the reliability and life of microelectronic components. Thus, in this study, it was focused on researching thermal-mechanical properties of the lead-free solder alloy Sn96.5Ag3.5 at different temperature ranging from 25 degC to 125 degC and various strain rate ranging from 10-5 S-1 to 10-1 S-1. Morphology of rupture surface and microstructure of this lead-free solder Sn96.5Ag3.5 were also analyzed by using the scanning electron microscope (SEM)