GOALI: Effects of Processing and Microstructure on the Fracture Properties of Microelectronic Lead Free Solder Joints under Dynamic Loading Conditions

Naval Postgraduate School, Monterey CA

Investigators

Abstract

TECHNICAL: Solder a joint, which serve as mechanical and electrical interconnects in a package, are particularly prone to failure during a drop. Therefore the fracture behavior of solders at high strain rates is a critically important design parameter. Most handheld devices undergo thermo-mechanical cycling during service, and therefore, solder joints are likely to have existing low-cycle fatigue cracks, which propagate under a combination of tensile and shear loading. Therefore, a drop simply serves as a mixed mode, high loading rate fracture test on a pre-cracked solder joint. Hence it is critical to obtain fracture toughness data on solder joints, not only to predict survivability during service, but also to serve as a design parameter which may be adjusted through material and process parameters to improve life. In this work, PIs will conduct a comprehensive experimental plan to generate fundamental mechanistic insight into the role of several microstructural and test variables on the fracture of solder joints under rapid loading conditions. The outcome of this study will be the ability to design microelectronic solder joints with greater fracture toughness under drop conditions via better control of processing, microstructural and geometrical parameters. An additional outcome will be the transfer of experimental approaches developed through this work to the industry. The work will be of substantial fundamental importance in generating new mechanistic insights into the role of microstructure on dynamic fracture, being the first-ever study of fracture mechanics of solder joints under rapid loading conditions. Secondly, the work will be of practical importance by generating fracture toughness data on important solder joint systems, and by transferring the testing methodologies to the industry. Thirdly, the work will be of high technological significance by developing fracture mechanism maps, which can be utilized in the design and reliability assessment of new types of joining schemes as they are developed to meet emerging chip/package interconnection architectures. NON-TECHNICAL: With the proliferation of mobile electronics in everyday life (e.g., cellular phones, personal digital assistants, mp3 players and handheld computers), the ability of electronic packages to sustain impact loading under drop conditions has become a paramount reliability concern. The broader impact of the work lies in its technological relevance to the reliability of mobile electronic devices that touch upon nearly all facets of modern life, and is a topic of substantial current interest to the entire micro-systems industry. Throughout the project, PIs will work closely with their GOALI partner (INTEL) as well as Freescale Semiconductor to identify/address issues of emerging relevance. In addition to training graduate students and post-docs, PIs will hire summer high school student interns to work on the project through a local enrichment program, and hire high/middle school science teachers to work in their laboratory during summer and assist them in developing lesson modules relevant to the general area of this research.