Analysis and experiments of ball deformation for ultra-fine-pitch wire bonding

This paper discusses ultra-fine-pitch bonding on a 50-mum bond-pad-pitch platform using phi23-mum gold wire. A technique for the bonding process and the bonding tool design was developed using the finite element method. It was possible to simulate and analyze the variation in the plastic deformation of ball bond when it was subjected to different loading conditions and capillary configurations. The analysis indicated that the critical bonding tool dimensions and bonding process parameters such as free air ball consistency and bonding force played critical roles in reliable bond deformation. A wire diameter of 23 mum with a capillary hole size of 28-30 mum would be robust for a mass production environment. A diameter of 32-33 mum is recommended as the average size of the free air balls for 50-mum bond-pad-pitch bonding using the phi23-mum gold wire. Based on the results obtained from the analysis, special bonding tool configurations were designed and fabricated. Actual bonding was performed to further validate the simulation results with experimental bonding responses. Comparison of the simulation results with the experimental data indicated that the actual ball size (38.5 mum) was approximately 3% larger than that (37.4 mum) obtained from the simulation.