Inner lead bonding for a resin molded chip size package

The present study investigated methods for bonding between semiconductor bonding pads and the metal bumps of a film carrier developed for use in chip-size packages (CSP). The structure of the film carrier is that of a copper circuit bearing a layer of insulating polyimide (PI) on both sides and connecting on one side with the exposed bumps, which in turn connect with the bonding pads. The bumps either have a copper core with a gold surface, or are all gold. In the first stage of the experiment, in which basic data were gathered, the ability of the bumps to bond via gang-bonding with the aluminum of the silicon chip was tested, using bumps with gold-plating of different thicknesses to give exposed heights of 10, 30 and 50 μm. Bump height is a decisive factor in the peeling strength of the bonding site; satisfactory results were not achieved with low bumps of 10 μm height. In the second stage, a method was sought which would help minimize production cost by ensuring successful bonding even with bumps of only 10 μm height. The three following methods were tested and found effective: (1) inserting a convex frame immediately beneath the film carrier on the side opposite the bumps; (2) using a film carrier containing a layer of thermoplastic material immediately beneath the bumps; and (3) undertaking scrubbing during the initial bonding phase