A novel ultrasonic precise bonding with non-constant amplitude control for thermalplastic polymer MEMS

Ultrasonic bonding has been emerging paving the way in micro assembly, with the high demand in fusion quality control. Under this background a novel ultrasonic precise bonding method based on non-constant amplitude control is proposed. A two-step bonding process, including frictional heating and viscoelastic heating, divided by the vibration propagation is designed. In step I, initial melting of the contacting surfaces is achieved at the amplitude bigger than the critical value. In step II, the whole interfacial fusion is realized at smaller amplitude to weaken the ultrasonic cavitation effect. The primary parameters in this method, including the amplitudes for the two steps and the conversion point, are studied. Results indicate that whole fusion bonding can be achieved with the flaws restrained. The proportion of cavity reduces to less than 2% when the amplitude for step II is set at a smaller value.