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.

Influence of ultrasonic combined supercritical-CO2 electrodeposition process on copper film fabrication: Electrochemical evaluation

“…This is due to the effect of microbubbles explosion from the supercritical CO 2 affects nucleation growth during the electrodeposition. Notably, the observed diffraction pattern in US-SC-CO 2 -15 W cm −2 displays the most significant full width at half maximum (FWHM), which indicated that ultrasonic agitation would lead to the smallest grain size [16] , [23] , [24] . Similar to the previous reports, the grain sizes are calculated from the Scherrer equation [38] , [39] , [40] , [41] , [42] .…”

“…In recent decades, ultrasonic-assisted electrodeposition has been widely used to improve the quality of electrodeposited materials [22] , [23] , [24] . It is due to the fact of high energy from the ultrasonic irradiation that creates cavitation effects such as mass transport processes, acoustic streaming, surface activation, and micro jetting formation [25] .…”

To reduce the passivation layer of Cu substrate by the ultrasonic assisted electrochemical potential activation method

“…Nowadays, owing to the cavitation and the micro jet effects, the ultrasonic assisted method was widely used in the electroplating field. The beneficial effects include producing nano grained hydroxyapatite coating, compacting the nice contact and reducing the internal stress [11][12][13]. Generally, the properties of the electroplating layer can be refined by the ultrasonic assisted method [14,15].…”

Corrosion Behavior of the Nickel/nickel Interface During the Copper Sacrificial Layer Releasing Process in Micro-Electroforming

“…To electroform a multilayered microstructure successfully, the adhesion between adjacent layers is critical, which signi cantly affects the mechanical performance, reliability and serve time of the micro device [6][7]. Weak interface bonding can even lead to the warpage or delamination of electrodeposited layers and nally result in the fabrication failure.…”