Research On Ultrasonic Bonding And Its Heat Affected Zone For Polymer Microfluidic Devices

Polymer microfluidic chips have become a research hotspot due to their advantages such as low cost, portability, high analyzing speed, small sample etc. In the manufacture of polymer microfluidic chips, bonding or sealing chips is the pivotal process and it affects the quality of microfluidic chips directly. Among large number of bonding techniques, Ultrasonic bonding is a potential method for mass-production of polymer microfluidic chips owning to its advantages like short cycle time, high bonding strength, foreign substances free and so on. Ultrasonic welding is a well established process to join parts from thermoplastic polymers in the macroscopic world. However, when it's applied to microfluidic chips bonding, the micro structures in the chips are easily damaged or even destroyed and bonding precision is difficult to meet due to micro dimension. To improve bonding quality, a novel micro joint including energy director and flow blocks is presented and chips are well sealed by ultrasonic fusion bonding. In addition, a new bonding method named thermal assisted ultrasonic bonding for polymer multi-layer microfluidic devices is brought forth and four-layer chips were joined and studied.In this paper, polymer ultrasonic fusion bonding was first studied. Although ultrasonic fusion bonding has many known merits such as high efficiency, simple operating mode, and high bonding strength and so on, experimental results showed polymer reacted severely and the phase changed in the process of bonding. Shortcomings such as low uniformity and difficulty in the control of fusion flow were found when applying ultrasonic fusion bonding to bond polymer micro-fluidic chips. Considering the structure of present micro-fluidic chips' micro joint and the characteristic of ultrasonic fusion bonding, in this paper, a novel micro joint with a flow-block matching with energy directors, and an additional energy balancing structure was proposed. To ensure precise structure of polymer chips, silicon mould was first produced using silicon processing, then the cover and substrate of microfluidic chips was made using hot-embossing method. Three kinds of sizes of the micro-joint were made to analyze the influence of micro joint on bonding result. Using the made polymer micro-fluidic chips, experiments using ultrasonic fusion bonding method in the mode of energy control were conducted. Results showed that the fusion flow was controlled well and the uniformity was improved. For the sake of more function modules integrated in smaller size, polymer multi-layer microfluidic devices will become an important development trend of micro-fluidic chips. Based on the present ultrasonic heating mechanism, a hot-assisted ultrasonic bonding method was proposed to bond polymer multi-layer chips. In this method, multi-layer chips was first heated to a certain extent, then were bonded using ultrasonic fusion bonding method. In this paper, a four-layer chip was proposed and then bonded using thermal assisted ultrasonic bonding method; later the bonding results were also tested. Base on the temperature measuring equipment, interfacial temperature was measured in the process of ultrasonic fusion bonding and thermal assisted bonding, and heat affected zone on the process of bonding were analyzed.