A New Flip-Chip Bonding Method Using Ultra-Precision Cutting of Metal/Adhesive Layers

Abstract

We have developed a new method of flip-chip bonding for LSI packaging that uses ultra-precision cutting of Au bumps to create an extremely smooth Au surface (R_a<10 nm) with very low peak-height variations. A major advantage of cut Au bumps is that they need less bonding force than non-cut bumps. Cut Au bumps were successfully bonded under low-temperature (180°C) and low-pressure (300 MPa/bump) conditions. This new method of planarization was also applied to adhesive layers with metal bumps, where the bonding force between adhesive layers could assist the connection between bumps. Simultaneous bonding of cut adhesive/bumps was evaluated by chip-on-chip (COC) type specimens. In this research, electroplated Au bumps and benzocyclobutene (BCB) were selected as the metal and adhesive layers. It was possible to bond chips with cut BCB/Au bumps together by applying a very low pressure (60 MPa/bump) .