A method of forming a plurality of bump structures on a substrate includes forming an under bump metallurgy (UBM) layer on the substrate, wherein the UBM layer contacts metal pads on the substrate. The method further includes forming a photoresist layer over the UBM layer, wherein the photoresist layer defines openings for forming the plurality of bump structures. The method further includes plating a plurality of layers in the openings, wherein the metal layers are part of the plurality of bump structures. The method further includes planarizing the plurality of bump structures after the metal layers are plated to a targeted height from a surface of the substrate.