Using ultrasonic energy for reducing ACF bonding process time

In this paper, we develop the novel ultrasonic bonding method for mounting LCD driver IC which has a number of small bumps with high pin-density. Since the materials for bumps and pads are different metals, the an-isotropic conductive film (ACF) is used for adhesion. The conventional methods based on the thermal energy under pressure suffer from the high failure rate at high temperature process and, in particular, the low productivity due to the long bonding process time. To avoid these, the thermo-compression ultrasonic approach is newly proposed, and, validated by experiments. The experimental results show that lower values of bonding pressure and temperature than recommended by the ACF specification can be adopted for reliable bonding, which proves the feasibility of the ultrasonic bonding technique. In addition, we address a new concept of horn design for high precision bonding. Since the proposed method is utilizing the mechanical vibration, the misalignment between bumps and pads may be the major issue. To solve this, the active controllable horn design is further discussed.