Fracture mechanics life prediction for microscale components, with application to wire bonding

Experimental and analytical results on the lifetime of 25 mu m diameter aluminum 1% silicon wire bonds subject to on/off current cycling are presented, along with related scanning electron microscopy of the heel area of the bond. The analytical results utilize a steady-state temperature solution for the wire in conjunction with finite element stress analysis to provide inputs to fracture mechanics calculations of fatigue crack growth. These calculations utilize macroscopic material properties, but with a fatigue crack growth threshold of zero. Good agreement between experiments and prediction was obtained, with scatter in the observations accounted for by consideration of a reasonable range of initial crack sizes. The results indicate that fracture mechanics techniques utilizing macroscopic material properties are applicable to life prediction of microscale components.<>