Numerical Analysis of the Welding Behaviors in Micro-Copper Bumps

In this study, three-dimensional simulations of the ultrasonic vibration bonding process of micro-copper blocks were conducted using the finite element method. We analyzed the effects of ultrasonic vibration frequency on the stress field, strain field, and temperature field at the copper bump joint surface. The results showed that the bonding process is successfully simulated at room temperature. The stress curve of the bonding process could be divided into three stages: stress rising stage, stress falling stage, and stress stabilization stage. Moreover, it was found that the end of the curve exhibited characteristics of a solid solution phase at higher frequencies. It is hypothesized that the high-density dislocations formed at this stage may result in conveyance channels that facilitate the atomic diffusion at the contact surface. The simulation results indicated that copper micro-bump bonding occurs at an ultrasonic frequency of 50 kHz or higher.