Study Of Ultrasonic Precise Bonding For Polymer Microfluidic Devices

With the advantages of great variety, low price and easy for fabrication et al, polymer was widely employed in biochemical MEMS. So the package of polymer micro devices became key technique in MEMS. The bonding methods used in micro assembly includes adhesive bonding, thermal bonding, solvent bonding, laser bonding, etc, which have limits in some respects. Ultrasonic bonding technique has the advantages of high efficiency, local heating and no foreign materials introduced, which indicates great potential in micro assembly. The ultrasonic bonding technique used in MEMS now is almost the same to the plastic ultrasonic welding for bulk devices and it has no deep studies in precise control of energy and optimization of interfacial fusion quality. So in this paper ultrasonic bonding was studied in polymer fusion mechanism of polymer interface, ultrasonic precise bonding method and optimization of intercial fusion quality to realize the precise fusion bonding for microfluidic devices.Fusion mechanism of polymer interface was studied in micro scale firstly. Molecular dynamics simulation was employed to simulate the diffusion and entanglement of macromolecular chains between polymer interfaces. System deformation, diffusion coefficient, diffusion depth and binding energy were calculated to analyse the movement tendancy of macromolecular chains during polymer fusion bonding. The influences from factors of pressure and temperature to the features of fusion bonding including device deformation, size of fusion layer, bonding strength, etc were studied. It provided theoretical foundation for the research of ultrasonic precise bonding method.Ultrasonic precise bonding equipment was established for microfluidic devices. High frequency, low amplitude ultrasonic transducer was employed to decrease the deformation of micro devices and also weaken the destruct to the microstructures in low strength. Based on the equipment ultrasonic precise bonding method with the feedback of polymer mechanical behavior was proposed. The mechanism was that the glass transition behavior of polymer components was detected by the changing of mechanical behavior and this information was made as the signal to control ultrasonic energy. Based on this idea two methods including measuring the pressure transfer efficiency and the ultrasound propagation efficiency were designed for ultrasonic precise bonding. Based on the feedback of pressure transfer efficiency an extended adaptive pressure ultrasonic precise bonding method was also designed. In experiments it was verified that the interfacial fusion degree could be controlled by the new ultrasonic bonding methodsTo improve the interfacial fusion quality further, according to the energy directors used in plastic ultrasonic welding for bulk devices micro energy director array was proposed for ultrasonic precise bonding of microfluidic devices. Energy director structures in micrometer size were fabricated on the bonding surface to concentrate ultrasonic energy to small area and provide spaces for the spread of polymer components in viscous state, which could improve the forming quality. The micro energy director array was fabricated by hot embossing. The influence from the factors of structure size and distribution size to fusion degree was studied in experiments. Results indicated that fabricating micro energy director array in proper size on the bonding surface could improve the utilization of ultrasonic energy and make the bonding process more controllable.Piezoelectric micro pump was designed with SU-8 micro valve fabricated by ultraviolet lithography. Ultrasonic precise bonding was applied in the packaging of pump and sealing of micro valve. In the bonding process the micro valve structure in low strength was verified in good condition. The flow velocities of liquid pumping corresponding to the frequency of piezoelectric elements were measured in experiments.