Research On Bonding Mechanism And Processing Method Of Ultrasonic Welding For Polymer Micro Components

Instead of traditional materials like silicon and glass, polymer has been gradually applied to the manufacture of MEMS devices and systems. As a pivotal step in the MEMS manufacture, the bonding of polymer micro components has been the pain in the neck due to kinds of reasons, presently restricting the development of polymer MEMS technology. Owing to many merits of the plastic ultrasonic welding technology, the novel approach has gained unceasing development and application in the MEMS research field in recent years, and will become an effective technological approach to solve the present problem of the bonding for polymer micro components.The ultrasonic welding for polymer micro components is still in the stage of theoretical analysis and experimental study. The key problems lie on that first the bonding mechanism is complicated and still not quite recognized; second the micro components are apt to be over-distorted or even locally damaged resulting from excessive melting. So for the sake of achieving precise bonding of polymer micro components, and generalizing the ultrasonic welding technology for polymer micro components, this paper started with two aspects containing correlated mechanism and experimental means, correlated research was conducted including the bonding mechanism of polymer, the ultrasonic precise welding method for polymer micro components, and the precise bonding of a piezoelectric micro pump using this method.Using Materials Studio software and based on molecular dynamic simulation, the interfacial inosculation behavior during melting joint of two-layered structure of polymethyl-methacrylate(PMMA) interface system was observed. Under different temperatures and pressures, interfacial molecular chains'motion was simulated, also the strain of the system, diffusion coefficient of the total atoms, interfacial inosculation depth and binding energy were calculated, and influencing rule of factors like temperature and pressure to the interfacial inosculation behavior was analyzed. The simulation results revealed the molecular inosculation behavior between PMMA interfaces during bonding process from molecular size, providing theoretic guidance for the bonding mechanism on ultrasonic welding for polymer micro components.An ultrasonic welding system with ultrasonic horn of high frequency and low amplitude was adopted. Based on the adaptive pressure welding method, the ultrasonic energy was precisely controlled to maximumly reduce the thermal deformation thus to ensure the shape precision of micro components. Experimental results showed that the influence of polymer surfaces'characteristic difference on the bonding quality was reduced; bonding quality was improved and the ultrasonic precise welding for polymer micro components was achieved.A piezoelectric membrane micro-pump was developed. Compositive micro-check-valves were fabricated using SU-8 resist photolithography. The micro-valve subassembly was precisely packaged using ultrasonic precise welding method. The micro pump was fabricated using ultrasonic bonding and glue bonding. The flow velocity of the micro pump was tested. The liquid flowed calmly without leak, and the ultrasonic welding method for polymer micro components proposed in this paper was validated.