US Patent 7932601 Enhanced copper posts for wafer level chip scale packaging

An enhanced wafer level chip scale packaging (WLCSP) copper electrode post is described having one or more pins that protrude from the top of the electrode post. When the solder ball is soldered onto the post, the pins are encapsulated within the solder material. The pins not only add shear strength to the soldered joint between the solder ball and the electrode post but also create a more reliable electrical connection due to the increased surface area between the electrode post/pin combination and the solder ball. Moreover, creating an irregularly shaped solder joint retards the propagation of cracks that may form in the intermetal compounds (IMC) layer formed at the solder joint.