Fast low-temperature ultrasonically soldering porous Si3N4 ceramics in the air

In this work, porous Si3N4 ceramics were successfully and ultrasonically soldered using Sn9Zn2Al solder through sonocapillary and cavitation. Si3N4 ceramics were first ultrasonically wetted and then soldered. The results show that porous Si3N4 ceramics can be wetted in the air within extreme short time of 10 s under ultrasonic. The capillary filling distance of the solder into the ceramic micro-channels achieves a value of 60 μm within 10 s and increases with prolonged ultrasonic time and high ultrasonic power. The infiltrated solder tightly bonded with the ceramic rod. The shear strength of the joint increases at prolonged ultrasonic time and becomes stable after 60 s. A geometric model is built to analyze the infiltration mechanism of the solder, and the result shows that the acoustic pressure inside the solder can reach 4 MPa, which is much higher than the pressure (0.32–1.4 MPa) needed for the sonocapillary action. The wetting mechanism of the solder to the ceramic is analyzed based on the cavitation bubble dynamics calculation. The high liquid velocity, pressure and temperature caused by the collapse of the cavitation bubble serve as the main factors that wet the ceramic.