Inner lead bonding technique for 500-lead dies having a 90- mu m lead pitch

A study was undertaken to investigate the possibility of 500-lead TAB gang bonding using a fully automated inner lead bonder. It resulted in establishing inner lead bonding techniques for 504-lead test dies 12.7 mm*12.7 mm with a 90- mu m lead pitch. The inner lead bonder has a maximum applied bonding force of 30 kgf, an alignment accuracy of 10 mu m, and an index time 3.9 s, including a 1-s bonding time. A discussion is presented of the machine's alignment accuracy, bonding accuracy, acceptable bonding conditions, the effects of tool planarity and parallelism on bond strength and bump deformation, and bond strength degradation caused by tool contamination, while using the test dies. The bonder had sufficient accuracy of machine alignment (+or-10 mu m) and process parameters to achieve good bonds. Optimal bonding ranges, which were not strict limitations, were established. Using a laser interferometer, it was possible to measure the diamond chip deformation at elevated temperatures. When a bonding tool having a planarity less than 1 mu m was set to make bond height difference between the ends of dies within 8 mu m, good bonds could be obtained. Increasing tool temperature was effective in extending the bonding count at which bond strength degradation took place. Tool cleaning restored the bond strength lost by this degradation. >