Research On Mechanism And Experiment Of Laser Electrochemical Micromachining Process

Laser electrochemical etching process, which is combined with laser machining process and electrochemical etching process, is a new compound etching technique. It has been found extensive applications in MEMS(Micro Electro Mechanical System) industry. To develop the technique of laser electrochemical etching process, in this dissertation, the mechanisms and experiments of continue laser and pulse laser electrochemical micromachining processes were furtherly studied.On the thermal effect of continue laser interacting with matter in liquid, to solve the complex phenomenon of transient explosive boiling by laser heating material in liquid, simplified methods, which is exchange-heat coefficient of liquid boiling simulating the explosive boiling effect on the temperature field of laser heating matter in liquid, were brought forward according to the characteristic of continue laser heating. On basic of it, the temperature solution model of material in liquid by laser heating was founded.To further understand the mechanism of laser ectrochemical etching metal, the temperature field induced by laser heating metal at the liquid-solid interface was investigated. On basis of the simplified methods solving the transient explosive boiling when continue laser heating material in liquid, the transient temperature fields of the experiments on laser immobility and laser scanning micromachining metal in liquid were simulated by FEM software ABAQUS. As known from simulation results, laser immobility heating cann't obtain metal melting point, but brings big temperature gradients in laser-irradiated micro-zone. Simulation of laser scanning indicates that it realizes the effect of pulse laser heating due to scanning and liquid cooling.808nm semiconductor laser was adopted for the laser-induced electrochemical etching process with the stainless-steel sample in sodium nitrate solution, and then maskless and single-step patterning stainless steel was obtained. To reduce the fixed-point transverse etching, laser scanning was also adopted to meliorate the transverse etching, improve the etching quality and obtain a figure of minimum line-width 62.5um. By analyzing the microcosmic images of laser immobility and laser scanning etching in liquid, semiconductor laser electrochemical process was experimentally studied. Simulatingly, the experimental phenomenon and mechanism of laser electrochemical etching metal were furtherly investigated by the temperature fields of laser heating metal in liquid. Thermal effect analysis confirms the process of laser electrochemical etching stainless steel is a coupling process of laser photothermal effect which helps to induce electrochemical dissolution.On basis of the complex phenomenon characteristic of transient explosive boiling by pulse laser heating material in liquid, the method, which is that heat conduction is dominating, was brought forward to solve the temperature field of short-pulse laser heating; the thermal effect of excimer laser interacting with matter in liquid affecting on the coupling technics was studied. Laser plume shock-wave theory and vacuole theory were adopted to analyze the mechanical effect characteristic of short-pulse laser electrochemical micromachining process. Simultaneously, the removal mechanism of brittle material by mechanical effect, which is induced by high-energy and short-pulse laser machining in liquid, was discussed. On basis of it, a theoretical model of material removal rate was proposed; the experiment of laser machining under water was adopted to validate the model and experiment results indicate that brittle material removal rate by shock force acting is relatively great. By the study of thermal-mechanical effect during short-pulse excimer laser interacting with matter in liquid, the thermal effect is little and the mechanical effect is marked.A novel silicon etching technique, excimer-laser electrochemical etching silicon, was studied. The experiments of micromachining silicon by laser-induced electrochemical etching were carried out, with 248nm excimer laser of great power as light source and KOH solution as electrolyte. Comparing with laser etching in air, the etching quality and etching rate of the coupling techinecs were analyzied; good surface and rapid etching rate were obtained. In summary, the coupling technique contains laser etching, electrochemical etching and coupling effects of laser and the solution; and laser etching is dominating. In the coupling effects, mechanical effect of laser micromachining in liquid has great effect on material etching. By the study of thermal-mechanical effect during short-pulse excimer laser interacting with matter in liquid, the mechanism of the coupling process was further understanded. As a result, this process has the ability of machining large aspect ratio microstructures.