COMSOL Simulated Cu Deposition in Electroforming Process to Prepare Miniature Probe
Simulation of the thickness change of the casting layer during the electroforming process is an important way to guide pro-duction to reduce costs and improve the quality of electroforming.Micro-electroforming technology is a metal micro-structure prepara-tion technology.Compared with ordinary mechanical processing,it can obtain high-purity micron products with precise dimensions and smooth surface.Due to its small size,high surface and physical and chemical performance requirements,the micro-probe has always been a difficult point in the material preparation process.It is feasible to prepare the probe tube by the micro-electroforming process,but the uneven current density distribution leads to the difference in the thickness of the electroforming layer which restricts the im-provement of the quality of the probe tube.A combination of simulation and experiment is used to explore the preparation process of the micro copper tube.After demolding,a probe tube with a certain strength that can support the probe is obtained,the surface is flat and compact,the roughness meets the requirements of use,and the signal transmission is not hindered.Choose copper as the electroform-ing deposition metal,and configure the electroforming liquid with copper pyrophosphate as the main salt.Determine the polarization curve through electrochemical tests and determine the model input parameters.Use the COMSOL electroplating module to use the"sec-ondary current distribution"interface to establish the electroforming flow field and electric field model,and simulate the flow field mass transfer in the electroforming copper process.The current density distribution on the surface of the electroforming cathode was simulated,and the deposition time when the cast layer reached the same thickness under different current densities was explored.Un-der the same exploration process,the micro-probe needle tube was prepared through experiments,and the surface morphology and roughness of the samples in the actual preparation process were studied by scanning electron microscope(SEM)and Micro XAM white light interferometry.The electroforming process conditions with high dimensional accuracy and low surface roughness were obtained and compared with the simulation results.The results showed that under the system of pyrophosphate electroforming copper casting so-lution,when the reaction temperature was 35 ℃ and pH of the system was 8.6±0.1,the result of copper deposition in the electroform-ing experiment was consistent with the physical model established by simulation.The boundary value of the simulated electroforming time was 300 min,and the target value of the predicted thickness was set to 90 μm.When the current density was in the range of 2.0～4.5 A·dm-2,with the increase of current density(I),the simulated deposition time distribution range was 270～125 min,while the electrodeposition rate increased from 0.333 to 0.720 μm min-1.The simulation showed that the electric force lines gather at the tip where the cathode intersected on the bottom surface of the cylinder,and the current density was relatively high.The experimental pro-cess under the same conditions showed that the I was 3.5 A·dm-2,and when the predicted thickness reached 90 μm,the thickness er-ror and reaction time error of the electroforming layer during the electroforming process were the smallest,which were 0.55％and 5.00％,respectively.The experimental electrodeposition rate was basically consistent with the deposition rate calculated by simulation.When other electroforming conditions remained unchanged and I was set to 3.5 A·dm-2,the surface of the electroforming layer of the sample is the densest,the surface grains are fine after SEM image was enlarged,and the surface quality was the highest.Under this process condition,the surface of 3D topography of the cast layer is also the smoothest and uniform,with a minimum roughness of 297 nm,which met the requirements of the probe.The simulation results were in good agreement with the experimental results,indicating that it was feasible to use the model to simulate the copper deposition in the electroforming process to prepare micro-probes.Aiming at the phenomenon of uneven thickness of micro-electroforming,COMSOL could be used for simulation.By changing the peripheral elec-troforming diagram of the target graphic as a current collecting ring,setting different current densities and observing the current distri-bution,as a result uniform conditions were feasible.In addition,the use of ultrasonic vibration could strengthen the convection of the solution near the cathode surface and reduced the thickness of the diffusion layer,thereby weakening the saddle shape due to diffusion and improving the uniformity of the casting layer.It had broad application value in the subsequent field of micro and small material preparation.Regarding this study,we could discuss the electroforming process under different electroforming time,temperature and ultrasonic conditions in the later stage.These factors affected the thermodynamic and dynamic parameters of the reaction process.By improving the reaction thermodynamics and kinetic conditions,the electroforming rate and forming uniformity were accelerated.For multilayer electroforming,exploring the bonding properties and mechanical properties between casting layers would also be very mean-ingful work.At the same time,other cast metal could be selected for electroforming process exploration.The above-mentioned research could be carried out under the optimal conditions of COMSOL simulation to provide support for exploring the universality and accuracy of COMSOL.
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