The shape evolution and application studies of electrodeposited bumps in electroforming

Abstract

Deposition around the microvias opening is crucial for desirable quality of metallic micro components and micro bumps in electroforming. This paper presents a numerical and experimental study of shape evolution of electrodeposition front on the extent of over-plating. Computational models based on kinetics of the electrode reaction are used to simulate the entire deposition process from start of deposition until the formation of bumps. The effects of the current density and microstructure geometries are discussed through analyzing the current density distribution along the transient cathode surface. When the current density is 4 A dm−2, the significant Ni craters are observed for microvias with diameters of 200 µm in the over-plating stage. The dent depths decrease as the current density and diameter decrease. For the 30 µm diameters, spherical structures in the over-plating stage form upon the photolithographic patterns for an applied current density of 1 A dm−2. Furthermore, the spherical surfaces enable the fabrication of hemispherical lenses with various curvature radii. Spherical structures are obtained by electrodeposition into microcavities. A numerical and experimental study is carried out to study the mechanics of shape evolution. The polymeric microlenses are replicated through a combination of PDMS molding and UV curing. This process demonstrates the potential of this method in the fabrication of microlenses.