A study on lateral thermosonic bonding technology

Abstract

In this thesis, we study the ACF interconnection technology for mounting a LCD driver IC which has a number of bumps with high density. Since the materials for bumps and pads consist of different metals, the anisotropic conductive film (ACF) should be used for adhesion. The conventional method based on the thermal energy under pressure suffers from the low productivity due to the long bonding process time. Motivated by such difficulty, thermosonic bonding which utilizes lateral ultrasonic vibration together with conventional method is proposed, and, validate by experiments. However, lateral thermosonic bonding has a potential problem of mis-alignment between bumps and pads due permanent deformation of epoxy caused by lateral vibration. To solve the problem of mis-alignment, solutions, which are based on the elasticity of ACF according to degree of cure, are suggested, and, validated by experiment. From the experimental results, the suggested solution could reduce the bonding time and avoid mis-alignment at the same time. Moreover, in ACF interconnection, the curing degree of epoxy is an important parameter because overcuring of epoxy degrades the reliability. Motivated by this problem, mechanism for desired degree of cure controlled by pressure is newly proposed, and, validated by experiment. The proposed method using the pressure as a control parameter to obtain the desired degree of cure has advantages such as prevention of overcuring and convergence of curing degree within specific region.