Study Of The Demolding Process In Hot Embossing Of Polymer Microfluidic Chip

PMMA micro-fludic chip is fabricated by hot embossing method. Hot embossing forming method is one of the very important methods to produce micro-fludic chip, and usually consisits of three stages: hot embossing fillings pressure holding,cooling demolding, and among them the cooling demolding process is very important, which can affect the quality of the product, because the bonding between the mold and the interface of the polymer can result in the wreckage of the micro-structure. Due to the different expansion coefficent between the PMMA and the metal mold(called thermal mismatch below), residual stress will exist in the substrate, which can cause the deformation and warpage. This thesis is focusing on the thermal residual stress and mainly study how the process parameters(temperature, time, pressure) affect the residual stress, also the stress variation trend is studied when the deformation reaches minimization. Finally theoretical research and simulation analysis are done in the FEA environment.Main jobs done in the experiment as follows:Process parameters' influence on the deformation of the chip is studied through the PMMA hot embossing experiment and the optimization parameters leading to the least deformation are determined by the regress analysis, which is prepared for the later stress analysis. Then the hot embossing experiment is redone using the determined parameters, in this way the deformation--time relationship of the substrate is figured out during the hot embossing process.Work finished in the simulation and theory including:Using the datas from the above experiment, data process method is utilized to get the strain—time relationship of the substrate and theσ(t),which describe the stress—time relationship of the substrate during the cooling stage, is found out according to the calculous model of the visco-elastic theory.Residual stress is also studied depending on theory of Plate and Shell at the small flexibility in the board warpage mechanics.In order to study the distribution of strain and residual stress on the surface of chip, under the guidance of finite element analysis, the micro-channels model are built and the strain and stress in demolding are studied by using ANSYS softwareOn the aspect of calculating the demolding force, this thesis borrows ideas from injection molded process: rectangle model with bottom. Use classical mechanics to gain the formula of demolding force and the method on how to reduce the demolding force is also discuss.