| Bonding is one of the key procedures of manufacturing microfluidic chips. The micro structure on the substrate can form seal micro channel net only by bonding. The bonding process decides the quality of manufacturing chips. The bonding efficiency can improve a lot by introducing ultrasonic polymer welding technology to the bonding of microfluidic chips. The ultrasonic bonding process has some advantages, such as the chips have little distortion after bonding, external substance free, higher bonding strength, shorter bonding time, have no limitation in biological compatibility, etc. Ultrasonic welding technology often used to bond micro pump or valve, it is seldom used to bond microfluidic chips. Traditional ultrasonic welding technology is suit to macro polymer material, when it is used to the bonding of microfluidic chips which key dimension is in the level of micron, there are some problems about bonding quality and precision. By researching on the ultrasonic micro-melting or non-melting bonding method of polymer microfluidic chips, we can resolve this problem and get good bonding quality.First, this paper introduces the relate ultrasonic bonding theory and experiment research of polymer microfluidic chips, it proposed a ultrasonic micro-melting bonding method of polymer microfluidic chips and design a area contact micro energy director structure that is suit to this method, it can control the ultrasonic bonding process according to every bonding phase and finish the micro-melting process without melting material flow into the channel of microfluidic chips. But this bonding method must adopt very high amplitude, then some quality problems such as cavitations will be produced on some place of the chip for overheat. So a local solubility activated method and a thermally assisted non-melting method for ultrasonic bonding of polymer microfluidic chips are proposed. A local solubility activated method is based on ultrasonic local heating and temperature dependent solubility of PMMA in isopropanol (IPA). Energy director place a important role during ultrasonic bonding process, because it can make the ultrasonic vibration and the heating energy produced on special place that need it. The solvent should have no solubility for the substrate material at room temperature, but it have solubility for the substrate material when the temperature is below the material's glass transition temperature, only that can the two substrate be bonded for the solvent's solubility when the temperature of the bonding area is raised to a certain level. A thermally assisted method for ultrasonic bonding of polymer microfluidic chips take advantage of the material's molecule movement when the temperature of bonding area get to near the glass transition temperature. Under certain bonding pressure, the molecule of the bonding surface entwist with each other and form the strength between the two substrate as a result. Before the bonding process begin, the material should be heated up to a certain temperature which is below the glass transition temperature, the bonding surface is compact closely under external bonding force, the bonding surface's total temperature can rise up to the glass transition temperature after the ultrasonic vibration is placed on the bonding surface, then the big molecule is activated, they twist each other and form the bonding strength. The PMMA substrate and cover are bonded on Branson ultrasonic 2000xf assembly system successfully and the bonding process is optimized by using some experimental method. Last, the microfluidic chips are bonded very well. |
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