Displacement-controlled coining of large arrays of gold stud bumps

Abstract

Novel, simple, and low-cost, displacement-controlled coining (DCC) process is developed for coining of gold stud bumps. A bottom mold made of aluminium which contains an array of geometrically well-defined cavities (nests) with known and pre-defined depth values in each nest, is designed and manufactured to adjust areas of coined surfaces and heights of coined stud bumps during sequential displacement-controlled coining processes. A double-side polished, and thick Borosilicate glass substrate is used as a flat surface to be in direct contact with the tails of the stud bumps to be coined. Above the double side polished glass substrate, another thick and rigid mold is positioned to uniformly apply the displacement-controlled deformation force to the stud bumps via the polished surface of the glass substrate. With the proposed displacement-controlled coining process, height and bonding surface area of the stud bumps can be tailored for flip-chip bonding (FCB) processes, especially when the maximum applicable force configuration of a FCB tool is limited (maximum of 20 N) during thermo-sonic flip chip bonding (TSFCB) processing. The proposed technique can be used to simultaneously coin arrays of stud bumps with high precision, providing an alternative, cost-effective, precise, time-efficient processing of stud bumps prior to TSFCB applications.