The effect of injection molding PMMA microfluidic chips thickness uniformity on the thermal bonding ratio of chips

Injection molding PMMA microfluidic chips can significantly improve the efficiency of chips forming. However, due to the coexistence of macro and micro effects in the injection molding process, the thickness uniformity of molding substrates is poor, which will seriously affect the thermal bonding quality of chips. In this paper, 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. The results show that when the following three conditions were satisfied during injection molding process, chips bonding ratio reaches to 93.9 % and the distortions of micro-channels caused by thermal bonding were acceptable. Firstly, the cover plates flatness error is smaller than 50-60 mu m and substrates flatness error is smaller than 80-90 mu m. Secondly, the maximum thickness difference of stack chips (cover plate stack with substrate) is smaller than 70-80 mu m. Thirdly, chips thickness of the middle is larger than that of the two ends along their length direction and chips thickness distribute evenly along their width direction. These conclusions can be used for the parameters selection and moulds design during injection molding process of PMMA microfluidic chips.