Fabrication Of Microfluidic Chip Mold Based On Electrochemical Etching

With the development of MEMS technology,the application of microfluidic analytical systems is increasingly extensive in biology,medicine,environics fields and so on.As a key device in the process of microfluidic chip production,metal mold plays a significant role in the microfluidic chip industrialization.Furthermore,it is noteworthy that metal microfluidic chip mold fabricated by no back plate grow technique is now being used more and more widely in the injection molding,compression molding and other mass production fields for its high accuracy,relatively simple fabrication process,and longer service life.However,the performance of microfluidic chip mold is subject to the adhesion strength between electroforming layer and substrate in micro-electroforming process,which will influence the successful rate and the service life of the mold.The aim of this thesis is to remedy this defect.Taking nickel double cross microfluidic chip mold as the study subject,the study set out to assess the feasibility of a novel method combining through-mask electrochemical etching and micro-electroforming to fabricate the metal microfluidic chip mold.The main research contents and results are as follows:(1)The adhesion strength between electroforming layer and substrate was measured.According to the principle of shearing method,the experiment platform was set up and a set of metal fixtures was designed and manufactured at the same time.Shearing strength was measured under four different experimental conditions as follows: electroform directly,electroform after picking 20 s,electroform after etching 5 min,and electroform after etching 10 min.The results of the experiments showed that the mean shearing strength was 52.1MPa?103.4MPa?158.2MPa and 229.7MPa respectively in different conditions.What's more,the shearing strength after pickling 20 s,etching 5min and etching 10 min increased by 98.5%,203.6% and 340.0% respectively,compared with that of untreated samples.(2)The thesis gave an analysis to account for the mechanism of the increase of adhesion strength between electroforming layer and substrate after pickling and electrochemical etching.During the process of pickling,the impurities on the surface of metal substrate were removed due to the dissolution,rinse and chemical corrosion of the acid solution,which will make the surface quality of the metal substrate better,thereby contributing to improve the adhesion strength between the electroforming layer and the substrate.As for electrochemical etching,it was carried out to create the ‘piles' with certain depth.Together with the increased actual exposed area due to the lateral corrosion,the interfacial adhesion strength between the electroforming layer and the substrate can be improved.(3)The effects of current density parameters and etching time on the uniformity of etching depth and lateral etching were analyzed.The results showed that with the increase of current density and the etching time,the etching depth was more uniform and the lateral erosion was increased.The ratio of the etching depth to unilateral lateral erosion was about 1: 1.When the current density was at 10A/dm2,there were more serious lateral erosion phenomenons in the local areas during the etching process,and then films cracked and shed.Based on experiment data,a good etching morphology can be obtained when the current density was at 5A / dm2.(4)The double cross microfluidic chip molds were fabricated under three different experimental conditions as follows: electroform directly,electroform after etching 5min,and electroform after etching 10 min.In the course of post-processing,abscission of the electroforming layer was found in group of test pieces electroformed directly.For lack of enough adhesion strength between electroforming layer and metal substrate,the whole cross electroforming layer fell off after the films were removed.Concerning test pieces electroformed after etching 10 min,there were incomplete lines because films in the cross area fell off,which led to plenty of unnecessary electroforming layers.In the case of electroform after etching 5min,a group of double cross microfluidic chip molds with high adhesion and properties fit for application has been successfully fabricated,from which it was proved that the method combining through-mask electrochemical etching and micro-electroforming can be used to fabricate the double cross microfluidic chip mold.