Font Size: a A A

Study On Internal Stress In Micro-electroforming Layer

Posted on:2015-04-04Degree:MasterType:Thesis
Country:ChinaCandidate:Z C TanFull Text:PDF
GTID:2181330467486113Subject:Mechanical and electrical engineering
Abstract/Summary:PDF Full Text Request
With the development of MEMS technology, the demand for micro metal devices is gradually increasing. Based on UV-LIGA technology, micro electroforming technology has been applied in fields such as aeronautics, astronautics, bio-medicine and electronic communication. However, the internal stress can easily result in electroforming layer cracking, blistering and delamination, which seriously affects the mechanical properties of metallic micro-devices and restricts the application and development of micro electroforming technology. The primary work of this study mainly focuses on the research of internal stress in the micro electroforming process conditions. In this paper, the influences of current density and thickness on internal stress were studied and the mechanisms of internal stress were discussed. Moreover, the method of introducing ultrasonic into the micro electroforming process to reduce the internal stress was proposed, which was proved to be effective through experiments. At last, the optimum process parameters were achieved from ultrasonic micro-electroforming experiments.In the micro electroforming solution system with additive, the micro electroforming experiments were finished by a self-developed ultrasonic micro electroforming equipment. The internal stress was measured by X-ray diffraction with the side-inclination method and stress measurement formula. The results indicate that the internal stress keeps increasing with current density within the range from0.2to2A/dm2and keeps decreasing when the thickness increases from3um to20um. Meanwhile, the current efficiency decreases with current density.In the condition of micro electroforming system with additive-solution, the generation of compressive stress in the electroforming layer mainly dues to the additive incorporated into the electrochemical activity points and also dues to hydrogen and other impurities trapped by electrochemical activity points, which expands the electroforming layer.The mechanism of electrochemical activity points trapping sodium dodecyl sulfate molecular cluster was studied from the perspectives of the organics adsorption kinetics in the electrode process, the adsorption type of the surfactant molecules in the electro forming layer and hydrogen adsorption kinetics in the electrode process. It gives a significant explanation for the generation of internal stress in the electroforming layer.The paper proved that introducing ultrasonic in the micro electroforming process has a marked effect on stress reduction, which can be explained from the aspects of ultrasonic reducing concentration polarization, improving ion transport capability, refining grain size and altering deposition preferred orientation. The experiment results indicate that the internal stress in the electroforming layer with ultrasonic is less than that with ultrasonic-free, and the internal stress decreases by27.5-146.6MPa, and73.4MPa averagely. The electroforming layer with ultrasonic shows a smoother surface and less pitting comparing to ultrasonic-free one. The electroforming layer has strong(111) fiber texture in ultrasonic-free solution and has strong (200) fiber texture in ultrasonic solution. With the increase of ultrasonic power, the internal stress keeps decreasing and gets the lowest value at200W, therefore,200W is the optimal ultrasonic power of ultrasonic micro electroforming. This work will make some contribution to the ultrasonic-stress reduction theory.
Keywords/Search Tags:Micro-electroforming, MEMS, Internal stress, Ultrasonic electrodeposition, XRD, Ultrasonic
PDF Full Text Request
Related items