Analysis of Deformation Process in Ball Bonding in LSI Packaging. Analysis of the Non Steady-State Metal Flow by Physical Simulation.

Abstract

In the ball bonding process in LSI packaging, complex non steady-state metal flow occurs in the wire ball during the process, and solid-phase bonding occurs between the wire ball and terminal pad. Optimum process design of ball bonding requires detailed analyses of the metal flow characteristics of the wire ball used in the process. The authors proposed the physical simulation method to analyze the ball bonding process. The physical ball bonding simulation and quantitative analyses, using the enlarged plane-strain models of the capillary tool made of SKD-61 steel and the wire ball and terminal pad of 1050 aluminum, were carried out successfully. Then, sequential variation of the outer profile of a wire ball and of the flow velocities, strain rates and strain in a wire ball during the process could be obtained. The simulation method is available to aid the optimum design of the process conditions of ball bonding, such as capillary tool configuration, punch speed, process temperature and terminal pad thickness, to achieve ball bonding with sufficient bonding strength, high reliability and narrow terminal pad pitch spacing.