title: Effects of ultrasonic agitation on adhesion strength of micro electroforming Ni layer on Cu substrate.
abstract: Micro electroforming is an important technology, which is widely used for fabricating micro metal devices in MEMS. The micro metal devices have the problem of poor adhesion strength, which has dramatically influenced the dimensional accuracy of the devices and seriously limited the development of the micro electroforming technology. In order to improve the adhesion strength, ultrasonic agitation method is applied during the micro electroforming process in this paper. To explore the effect of the ultrasonic agitation, micro electroforming experiments were carried out under ultrasonic and ultrasonic-free conditions. The effects of the ultrasonic agitation on the micro electroforming process were investigated by polarization and alternating current (a.c.) impedance methods. The real surface area of the electroforming layer was measured by cyclic voltammetry method. The compressive stress and the crystallite size of the electroforming layer were measured by X-ray Diffraction (XRD) method. The adhesion strength of the electroforming layer was measured by scratch test. The experimental results show that the imposition of the ultrasonic agitation decreases the polarization overpotential and increases the charge transfer process at the electrode-electrolyte interface during the electroforming process. The ultrasonic agitation increases the crystallite size and the real surface area, and reduces the compressive stress. Then the adhesion strength is improved about 47% by the ultrasonic agitation in average. In addition, mechanisms of the ultrasonic agitation improving the adhesion strength are originally explored in this paper. The mechanisms are that the ultrasonic agitation increases the crystallite size, which reduces the compressive stress. The lower the compressive stress is, the larger the adhesion strength is. Furthermore, the ultrasonic agitation increases the real surface area, enhances the mechanical interlocking strength and consequently increases the adhesion strength. This work contributes to fabricating the electroforming layer with large adhesion strength.
authors.affiliation: Key Laboratory for Precision & Non-traditional Machining Technology of Ministry of Education, Dalian University of Technology, Dalian 116024, People's Republic of China.
authors.forename: Zhong
authors.initials: Z
authors.lastname: Zhao
authors.affiliation: Key Laboratory for Precision & Non-traditional Machining Technology of Ministry of Education, Dalian University of Technology, Dalian 116024, People's Republic of China; Key Laboratory for Micro/Nano Technology and System of Liaoning Province, Dalian University of Technology, Dalian 116024, People's Republic of China. Electronic address: duliqun@dlut.edu.cn.
authors.forename: Liqun
authors.initials: L
authors.lastname: Du
authors.affiliation: Key Laboratory for Micro/Nano Technology and System of Liaoning Province, Dalian University of Technology, Dalian 116024, People's Republic of China.
authors.forename: Zheng
authors.initials: Z
authors.lastname: Xu
authors.affiliation: School of Electrical Engineering and Information, Dalian Jiaotong University, Dalian, People's Republic of China.
authors.forename: Ligeng
authors.initials: L
authors.lastname: Shao
keywords: Adhesion strength; Compressive stress; MEMS; Micro electroforming; Polarization; Ultrasonic agitation