A nano-indentation study on the plasticity length scale effects in LIGA Ni MEMS structures

This paper presents the results of a nano-indentation study of the effects of strain gradient plasticity on the elastic-plastic deformation of LIGA Ni MEMS structures plated from sulfamate baths. Both Berkovich and North Star indenter tips were used in the study to investigate possible effects of residual indentation depth between the micro and nano scales on the hardness of LIGA Ni MEMS structures. A microstructural length scale parameter, Î = 0.89 μm, was determined for LIGA nickel films. This is shown to be consistent with a stretch gradient length scale parameter, Is, of ∼0.36 μm.