ABSTRACT
Fracture by crack opening mode prevails because nonuniformity in the shear deformation of a solder joint creates a body rotation that results in crack opening stress rather than shear. While the crack growth in shear fatigue is found to vary sensitively with variations in the mechanical constraints on the assembly, such as solder shape and elastic modulus of the chip mold, it is also sensitive to variations in solder microstructure. This sensitivity to the assembly constraints and solder microstructure makes it ideal for investigating fatigue properties of solder joints as well as identifying the structural and microstructural features responsible for reliability failure.
