Modified thermosonic flip-chip bonding based on electroplated Cu microbumps and concave pads for high-precision low-temperature assembly applications

Thermosonic flip-chip bonding (TS-FCB) is known as a technique suitable for low-temperature bonding and has been used in many integration applications. In this paper, a modified TS-FCB based on microbumps and concave pads, is presented. Electroplated Cu microbumps, and etched invert-pyramid-shape bonding pads are used to enhance the bonding accuracy of the conventional TS-FCB technique. Experimental validation of the bonding approach is conducted. Reliable bonds, with significant increase in the post-bond accuracy, i.e. within 1 μm range in in-plane offsets, are obtained at 120°C using the proposed bonding approach. These achievements illustrate the ability to use this approach for high-precision low-temperature converging applications.