ANALYSIS AND EXPERIMENTS OF BALL DEFORMATION FOR ULTRA-FINE-PITCH WIRE BONDING

This paper discusses ultra-fine-pitch bonding on a 50-μm bond-pad-pitch platform using ϕ23-μm 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 μm with a capillary hole size of 28–30 μm would be robust for a mass production environment. A diameter of 32–33 μm is recommended as the average size of the free air balls for 50-μm bond-pad-pitch bonding using the ϕ23-μm 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 μm) was approximately 3% larger than that (37.4 μm) obtained from the simulation.