An experimental investigation of silicon wafer surface roughness and its effect on the pull-strength of plated metals

Plated silicon wafers with surface roughness ranging from 0.4 to 130 microinches, subjected to tensile pull-strength tests, were analyzed. Results show that the measured pull-strength of plated metals decrease with increasing silicon surface roughness, effecting a weakening of the cohesive strength of the wafer, possibly caused by microcracks or 'etch pits' in the silicon surface. The mean value of pull-strength for all wafers plated with the Ni-Cu-Cu sequence exceeded the required 450 g/0.02 sq cm, and at Ra = 0.4 microinches, the mean pull-strength for the Ni-Cu-Cu and Ni-Cu wafers were 2290 and 850 g/0.02 sq cm, respectively. The development of standardized methods for measuring contact pull-strength is suggested. These results may have some bearing on solar cell arrays problems.