Design And Fabrication Of Micro Energy Director On Microfluidic Chip For Ultrasonic Bonding

Nowadays, polymer microfluidic chips enjoy a great success experiencing an increased acceptance in various application fields , such as analytical chemistry, biological, pharmaceutical development and chemical synthesis systems. Apart from the functional enhancements, the impressive growth of the microfluidic chips also owes to the dramatic reduction of their fabrication cost. During its fabrication process, bonding is the key procedure to almost all microfluidic chips. Up to now, several methods for the bonding of polymer substrates have been studied, including thermal bonding in convection oven or in hot embossing machine, gluing, laser lamination, and surface modification. Micro ultrasonic bonding is a promising technique in this category. Other than conventional direct thermal bonding, this method has higher efficiency, lower deformation and can realize selective package.In order to take ultrasonic bonding of Polymer micro fluidic chip into reality, an auxiliary microstructure named micro energy director was designed and fabricated on the PMMA substrate, and the microchannel fabricated on the same substrate meanwhile. By using of Branson2000xf ultrasonic assembly system, the PMMA micro fluidic chip with cross microchannel has been bonded successfully.The major work on design and fabrication of micro energy director has been done as follows:1. Design of micro energy directorThe structure and size have been decided by investigating of the principle of ultrasonic plastic welding and its part design guidelines, The isosceles triangle cross section shaped micro energy director is 70.52°in top angle and 150μm in length of base. This structure can be taken into reality by hot embossing with silicon mold.2. Fabrication process of silicon moldThe dimension of silicon mold is 52mm×27mm×1mm, and the mold with micro energy directors and microchannels for hot embossing has been fabricated by multi-photolithography and two times of anisotropic etching.3. Fabrication of PMMA substrate by hot embossing By dint of Taguchi optimization method, the optimized parameters for hot embossing were decided. Under the embossing temperature of 140℃, holding time of 300s,and embossing pressure of 1.65MPa, the microstructures can be replicated with high accuracy. The feature size of PMMA substrate is 50mmx25mmx2mm.4. Ultrasonic bonding for Microfluidic chipThe PMMA substrate and cover have been bonded on Branson ultrasonic assembly system (2000xf) successfully, then the structure of micro energy director which has design and fabricated in this paper is proved.