Electrodeposited 80Ni–20Fe (Permalloy) as a structural material for high aspect ratio microfabrication

This article summarizes results from a study directed toward evaluating electrodeposited 80Ni–20Fe as a structural material for the LIGA (German acronym for Lithographie, Galvanformung, Abformung, equivalent to lithography, electroplating and molding) process. Microstructure-property characteristics of pulsed plated and direct current (dc) plated samples were investigated. Little difference was observed in grain structure and crystallographic texture between each type of deposited sample, however, significant compositional modulation across each pulse in the pulse-plated samples was observed using energy dispersive X-ray spectral image analysis. Both types of electroformed samples were found to embrittle when subjected to heat treatments between 300 and 700 °C due to the presence of co-deposited sulfur. Electron microprobe and Auger analysis revealed that the observed embrittlement resulted from the migration of sulfur, entrained during the deposition process, to grain boundaries where it was present as both a uniformly dispersed grain boundary wetting agent as well as in coarse, blocky Ni/Fe sulfides. Conversely, samples heat treated at temperatures above 1000 °C were found to have recovered tensile ductility to values greater than the as-deposited samples.