Mechanical property evaluation and failure analysis of cantilevered LIGA nickel microposts

An experimental apparatus has been built to measure the elastic modulus and bending strength (modulus of rupture) of LIGA nickel posts. The apparatus uses the static cantilever beam bending approach to measure mechanical properties in a direction parallel to the growth direction. Experimental results are presented for two sets of largely identical posts constructed using an overplating method. One set was electroplated using a Watts bath, and the other set was electroplated using a sulfamate bath. For the Watts bath, the measured modulus of elasticity was slightly lower than that of bulk nickel (182 GPa), while, for the sulfamate bath, it was approximately half (93 GPa). The strength properties of the two sets of posts also differ dramatically. Microhardness measurements, Focused Ion Beam images of grain structure, and scanning electron microscopy (SEM) micrographs of failure regions are used to further characterize and explain the differences in the results. This integrated testing approach yields a consistent set of data regarding material properties, grain size/structure and failure mechanisms. Potential sources of experimental error are also identified and improvements in experiment design are suggested to reduce these errors.