Feasibility study for copper bump with tin plating bonding by using NCP adhesive and ultrasonic bonding technique

The aim of this project is to develop an alternative material for bumps of LCD driver ICs and to establish a feasible packaging process for the alternative material. With the continuously escalating price of gold, an alternative material to replace the widely used gold bumps in LCD driver IC packaging is eagerly demanded. Therefore, copper bumps are selected for evaluation in this study. To comply with the oxidation-prone and higher hardness characteristics of Cu bumps, nonconductive paste (NCP) resin and ultrasonic bonding are introduced as well in the packaging process. Compared with the commonly used thermo compression bonding technology for Au-bumped LCD driver IC packaging, the ultrasonic bonding method with NCP resin employs relatively lower temperature and bonding force. In the feasibility evaluation of the Cu bumps, the objective is to achieve a bonding reliability and adhesion quality similar to or even better than that of Au bumps under thermo compression bonding. In the experiment, fine tuning of some operative parameters was executed in order to get the positive results. These operative factors include the following: (a) NCP resin viscosity, (b) NCP resin dispense pattern, (c) dispense temperatures, (d) bonding sequence, (e) bonding temperature, (f) ultrasonic power, (g) bonding force, and (h) bonding time, which play key roles in the study.