||Since the development of high-density integrated circuits (ICs), numerous studies have used 3D IC bonding technology to reduce processing temperatures and increase reliability. However, numerous stringent environmental conditions have been established for low-temperature processes. This has increased costs and created additional processing steps. Recently, researchers have proposed a couples-polishing activation-bonding (CAB) process. This process involves using ultrasonic vibration technology to induce interfacial friction, thereby increasing temperatures at the interface. Subsequently, atomic diffusion leaving copper contacts generate engagement. This process can be performed at room temperature.|
In this study, the finite-element method was used to establish a micro-copper block ultrasonic-vibration-bonding 3D simulation model. In addition, the effects of various ultrasonic-vibration frequencies on the stress, strain, and temperature fields of the interface were explored, and the effects of the coefficients of friction and amplitude on interface strain were analyzed.
The simulation results showed that at 50 kHz, the bonding process was successful after 1500 μs. The equivalent stress could be divided into stress upward, stress downward, and stress stabilization phases. Based on the results, it may be suggested that ultrasound-vibration frequencies affect energy transfer rates. The results obtained at 50 kHz showed that the outermost strain was less than 23% of the center strain.
By increasing the frequency, a critical frequency was determined regarding the period necessary to obtain a steady stress rate.
Finally, when the friction coefficient and amplitude were changed, at a fixed frequency, the coefficient of friction rose from 0.1 to 0.15, which was a larger increase in strain than 0.15 to 0.2. Regarding amplitude changes, when the frequency was low, the amplitude exhibited an increased effect on the maximum equivalent strain.