Finite Element Analysis and Experiments of Ultra-Fine-Pitch Wire Bonding

摘要

The demand for increased computing power and more complex IC devices with increased functions per chip results in higher I/O count packaging. With the shrinkage in IC size and the decrease in pad pitch, the trend is moving from the current fine-pitch mass production to even lower pad pitch, such as the 50μm and 40μm. Given the tight constraint, the bonding process and bonding tool design become more complex, which produces smaller bond deformation in a repeatable manner. Those problems associated with open wire, bond liftoff, surface contamination, etc., have now become more sensitive and difficult to control. This paper discusses the UFP (ultra fine pitch) bonding process analysis on a 50μm BPP (bond pad pitch) platform using a 23μm gold wire. A diagnostic technique for the UFP wire bonding process and bonding tool design was developed using finite element analysis. The plastic deformation of ball bond was simulated by using a software package "Marck7.3". In addition, experimental data obtained from measuring the transducer horn displacement with a laser vibrometry technique have been adopted for the bonding simulation. 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 respect of reliable bond deformation. Based on the results obtained from the finite element analysis, special bonding tools were designed and fabricated. Actual bonding was performed to further validate the bonding responses with the simulation results.