Nonlinear Absorption Effect And Process Research Of Ultrashort-pulse Laser Transmission-connected Polymers In Microfluidic Chips

Polymer materials are widely used in the fields of microfluidic devices,microelectronic mechanical systems and other fields.Due to the advantages of good bio-compatibility,low chip production costs and other characteristics,they have broad commercial prospects especially in the field of microfluidic packaging.Although the traditional polymer bonding technology has many advantages,it still faces the potential thermal impact risk in micro precision machining.Compared with the traditional polymer connection technology,ultrashort pulse laser connection can effectively inhibit the diffusion of heat around the processing area,and there is no need to add an absorption layer at the connection interface.It has the outstanding advantages of high strength,good stability,small heat affected zone,high processing accuracy and high processing flexibility.In this paper,the method of combining theoretical derivation,experimental research and numerical simulation was adopted.Polymethyl methacrylate(PMMA)was selected as the research object to carry out the research on the nonlinear absorption effect and technology of the polymer connected to the microfluidic chip by picosecond laser transmission.The main research contents are as follows:(1)Systematic study of the energy transmission and absorption mechanisms of polymers under the action of ultrashort pulse lasers,including the dynamics and thermodynamic processes of ultrashort pulse lasers transmitting energy through the crystal lattice,the non-linear absorption effect of polymer on ultrashort pulse laser,the process in which conduction band electrons absorb multi-photon energy to produce avalanche ionization and plasma.On this basis,explore the interaction mechanism between ultrashort pulse laser and PMMA polymer.(2)Carried out the picosecond laser transmission connection test of typical PMMA polymer under multiple process parameters,and tested the subsequent properties of the connection joint such as the three-dimensional morphology,microstructure,shear strength and air tightness.The results show that the average shear strength of the weld is 17.1 MPa,the average width of the weld is 347.08 μm,and the edge of the weld is smooth,and the welding quality can be improved by reducing the pulse energy of the laser;during picosecond laser irradiation,the element migration of PMMA material was mainly C element and O element,which has a gain effect on the microhardness of the connection area;static leak testing of the weld area verified the good sealing performance of the weld.(3)Based on the Design-Expert V12.0 platform,the multi-process parameter design and response surface(RSM)analysis of the PMMA polymer picosecond laser connection were carried out,and the factors that had an important impact on the process variation were screened out.Used polynomial regression and reliability analysis methods to perform response surface(RSM)analysis of the optimization process.Obtained the control model and process guidelines of the polymer connection joint performance under the action of picosecond laser.The results show that the interaction of repetition frequency and focal length has the greatest effect on the weld width and shear strength,while the interaction of laser power and repetition frequency has the least effect on the weld width and shear strength.The optimization mathematical model was verified by randomly selecting the combination of process parameters,and the optimized process parameter combination that met the actual needs was obtained according to different optimization criteria.(4)Based on the ANSYS APDL platform,a finite element model of the transient temperature field of the polymer ultrashort pulse laser joining process was established,and the influence of multiple process parameters on the heat transfer behavior of the material and the evolution of the welding temperature field under the action of the ultrashort pulse laser were studied.It is found that the weld width increases with the increase of the laser power and repetition frequency,and decreases with the increase of the laser focal length.The reliability of the established temperature field model was verified by comparing the experimental and simulated values of the weld width under the same process parameters.