An investigation of microstructure and mechanical properties of UV-LIGA nickel thin films electroplated in different electrolytes

Abstract

Different electrolytes are used to fabricate nickel structures in MEMS devices by the LIGA or UV-LIGA process to meet different requirements. In order to investigate the microstructure and mechanical properties of nickel thin films electroplated in different electrolytes, four sets of nickel specimens were fabricated in different electrolytes: sulfamate bath with both saccharine and butynediol added (type A-I); sulfamate bath with saccharine added (type A-II); watts bath with saccharine added (type B); and chloride bath with saccharine added (type C). The function of these additives was to obtain the stress-free nickel films. The specimens were measured in our uniaxial tensile test system; their surface morphology and fractography, microstructure and texture were studied by SEM, TEM and XRD, respectively. The results show that the four sets of specimens have different mechanical properties and microstructures. The tensile strength of type A-II, type C and type A-I specimens increases with decreasing grain size, which is in accordance with the Hall–Petch law. In contrast, type B specimens have the highest value of ultimate tensile strength and elongation, but with the largest grain size among all the specimens. The XRD results show that there is no preferred orientation in type B while others have a preferred orientation in (2 0 0) along the growth direction. This might be the reason for the difference between type B and other types.