Fast solid-phase bonding based on indium film-modified copper crystal structure

The special shape of Cu/In layer and ultrasonic vibration are used to realize fast bonding at room temperature, thus solving the problems of high thermal stress and signal delay caused by high temperature in the traditional reflow soldering process. The indium film-modified copper crystal microlayer substrates are used as bonding couples, and ultrasonic vibration and pressure are applied to the bonding contact area to realize the rapid solid-phase bonding of two copper substrates. The microstructure, intermetallic compounds and average shear strength at the bonding interface are analyzed by scanning electron microscopy, transmission electron microscopy, X-ray diffraction (XRD) and bond strength tester. Under ultrasonic vibration and small pressure, the micro-cone structures of Cu/In layers are inserted into each other to form a stable physical barrier structure. The atoms of the thin indium layer at the bonding interface transform into the high-quality phase Cu₂In by rapid diffusion driven by ultrasonic energy. When the thickness of the indium layer at the bonding interface is 250 nm, the bonding pressure is 7 MPa, and the bonding time is 1 s, the relatively optimal bonding quality is obtained, and the holes at the bonding interface disappear. The results of heat treatment experiments show that this solid-phase bonding technique can obtain good bond strength without additional heat treatment. The special morphology of the Cu/In layer and ultrasonic vibration allow the bonding to be completed quickly at room temperature. The bonding quality is good and small bond sizes can be obtained.