Development of nanocomposite lead-free electronic solders

Inert, hybrid inorganic/organic, nano-structured chemicals, can be incorporated into low melting metallic materials, such as lead-free electronic solders to achieve desired level of performance. The nano-structured materials technology of polyhedral oligomeric silsesquioxanes (POSS), with appropriate organic groups, can produce suitable means to promote bonding between nano-reinforcements and the metallic matrix. The microstructures of lead-free solder with surface-active POSS tri-silanols were evaluated using scanning electron microscopy (SEM). Wettability of POSS-containing lead-free solders to copper substrate was also examined. Steady-state deformation of solder joints made of eutectic Sn-Ag solder with varying weight fraction of POSS of different chemical moieties were evaluated at a range of temperatures (25°C, 100°C, and 150°C) using a Rheometric Solids Analyzer (RSA-III). Mechanical properties such as shear stress versus simple shear-strain relationships, peak shear stress as a function of rate of simple shear-strain and testing temperature were reported. The service reliability of joints made with these newly formulated nanocomposite solders was evaluated using a realistic thermomechanical fatigue (TMF) profile. Evolution of microstructures and residual mechanical property at different extend of TMF cycles were compared with joints made of standard, un-reinforced eutectic Sn-Ag solder.