FRACTURE BEHAVIOR OF A LEAD-FREE SOLDER/Cu JOINT SYSTEM

摘要

The quasi-static strength of a solder joint is often a critical performance parameter that is mainly governed by its fracture properties. In this study, the fracture toughness of a lead-free solder (96.5Sn_3Ag_0.5Cu)/Cu joint system has been measured using a double cantilever beam (DCB) specimen consisting of two Cu bars joined by a uniform layer of lead-free solder, 0.4 mm thick. The fracture toughness was measured at relatively low strain rates as a function of crack length and the initial crack tip geometry and phase angle. The crack front was often observed to be highly three-dimensional and variable, with sections advancing near both the upper and lower copper bars. The solder microstructures were analyzed along these fracture surfaces. Initially, the fracture toughness increased with crack length, attaining a steady-state value after 10-20 mm of crack extension. Both the steady-state value and the slope of the rising part of the R-curve were largely independent of the initial crack tip geometry.