Investigation On The Thermal Bonding Of The Injection Molding PMMA Microfluidic Chips

Polymer microfluidic chips are finding numerous applications in areas such as biological applications, food and environmental health inspection and chemical synthesis systems nowadays. PMMA is a highly attractive substrate material for polymer microfluidic chips because of its low cost, easily fabrication and chemical properties.At present, hot embossing method is mainly used to form the substrates of the chips. Then, the cover plate and the substrate are sealed to be a microfluidic chip with enclosed micro-channels. Compared with the conventional hot embossing method, the injection molding method can significantly improve the productivity of the chips. However, injection molding microfluidic chips have the micro-size structures in the macro-size substrates, due to the coexistence of macro effects and micro effects the thickness uniformity of the molding substrates is poor. Besides, the residual stresses in the demolding process will redistribute and cause the chip shrinkage and warpage. Due to the functional requirements of the final microfluidic system, the quality of micro-channels, effective bonding area, and bonding strength must be taken into account during the thermal bonding process, and they are regarded as the bonding quality standards of the microfluidic chip. In this paper, the effect of injection molding PMMA microfluidic chips thickness uniformity on the thermal bonding quality of the chip was studied by simulations and experiments. A method of water pretreatment for thermal bonding PMMA microfluidic chips was studied. The mechanisms of water pretreatment method were discussed.Firstly, the chips were divided into three groups according to the three different injection molding parameters and they were measured by screw micrometer. The effect of injection molding PMMA microfluidic chips thickness uniformity on the thermal bonding ratio and the quality of micro-channels was studied by experiments and simulations.Secondly, the acceptable thickness distribution of injection molded PMMA chips to meet the approval of thermal bonding standard was discussed. These conclusions can be used for the parameters selection and moulds design during injection molding process of PMMA microfluidic chips.Thirdly, a method of water pretreatment for thermal bonding PMMA microfluidic chips was studied. The bonding ratio of microfluidic chip under different pretreatment time was studied and the mechanism of this method was discussed. This method can increase the effective bonding area and improve the bonding strength of the microfluidic chip compared to the conventional thermal bonding method. The experimental result shows that this method can increase the effective bonding area, improve the bonding quality of the microfluidic chip compared to the conventional thermal bonding method. The bonding rate of the chips has been improved significantly at the optimal water pretreatment time. The pollution to the micro-channels is avoided and the material performance of the microfluidic system will not be changed by this water pretreatment method. This method is available for the biochemical analysis of the chip, and holds the benefits of easy-operation, high-efficiency and low-cost properties.