MICROSTRUCTURE EVOLUTION AND CHARACTERIZATION OF NOVEL SOLDER ALLOYS FOR DEMANDING APPLICATIONS

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Prior to the implementation of Restrictions on Hazardous Substances (RoHS) regulations in 2006, Sn-Pb alloyshad been the predominant solder alloy in electronic industry due to their low cost, low melting temperature,excellent wettability and good reliability. Since 2006 there has been considerable debate and distress over whatalloy would replace dependable Sn-Pb. A Pb-free alloy made up of tin, silver (3.0%) and copper (0.5%)(SAC305) emerged as the industry standard during the RoHS transition because of its reasonable performance,low melting point compared to other alloys under consideration and compatibility with existing materials andprocesses. However, in the ensuing decade, electronic devices have been introduced in a myriad of newapplications. For example, in automotive applications, in addition to basic on/off switches, there are nowautonomous brake control systems, electronically controlled shock absorbers, hybrid power control systemsand LED lighting. With the increasing variety and density of electronic devices, their role to ensure the safetyof the vehicle and occupants becomes very critical. Therefore, the challenge is to guarantee the performanceand reliability of car electronics is greater than ever. For such applications the traditional SAC305 or similaralloys with poor creep resistance and unstable mechanical performance are not sufficiently reliable. Whenexposed to high service temperatures and thermal cycling, SAC305 undergoes significant microstructurechange, specifically, the coarsening of Ag3Sn and Cu6Sn5 particles, which leads to degradation of mechanicalproperties and poor creep resistance. Therefore, the electronics industry needs a new solder alloy with betterreliability than SAC alloys. To improve reliability of SAC alloys, alloying with Bi, Sb, In, Mn, Ni et al. hasbeen studied and suggested by some researchers. In order to develop a reliable solder alloy for high temperatureand demanding applications, further improvement of SAC-Bi alloy has been studied. In this project a newSAC-X solder alloy (X represents alloying additions Bi, Sb, Ni,...) with better reliability is introduced andstudied. The main objective of this project is to study effects of thermal cycling on the microstructure evolution