Low temperature thermocompression bonding of copper-copper bumps using gold alloy nanoparticles

• Main Author: Tan, Shi Liang.
• Other Authors: Wong Chee Cheong
• Format: Final Year Project
• Language: English
• Published: 2012
• Subjects: DRNTU::Engineering::Materials::Electronic packaging materials; DRNTU::Engineering::Materials::Microelectronics and semiconductor materials::Nanoelectronics and interconnects
• Online Access: http://hdl.handle.net/10356/48405
• Institution: Nanyang Technological University

One of the key methods to form interconnects between electrical packages and devices is by thermocompression bonding. The reliability of these metallic interconnects are often dictated by bonding parameters like temperature, time and pressure. Copper (Cu) which possesses outstanding mechanical, electrical and hermetic properties is often being used as the material for these metallic joints. Unfortunately, given the oxidative nature of Cu, high temperature (>300oC) is required in the process of bonding. However, in this study, we have successfully bonded copper to copper bumps with the aid of gold (Au) alloy nanoparticles at the bonding interface. A minimum bond strength of 20 MPa was achieved at bonding temperature of 150 °C under a bonding pressure of 400 MPa. We achieved this novel approach by “growing” Au alloy nanoparticles on copper bumps using the galvanic replacement method. The nanoparticles are believed to serve two main purposes. Firstly, to act as a partial passivation layer, protecting areas of the Cu bumps which the nanoparticles grew on, from oxidizing, as Au is relatively inert in nature. Secondly, to act as the mating interface to bond Cu to Cu bumps which in return brought down the bonding temperature. The presence of Au alloy nanoparticles aid to facilitate the low temperature bonding by promoting diffusion at the bonding interface.