Improvement Of Thickness Uniformity Of Micro-electroformed Layers By Ultrasonic Agitation

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 such fields as aeronautics, astronautics, bio-medicine and electronic communication. However, the thickness uniformity has seriously limited the development of micro electroforming technology and dramatically influenced the dimensional accuracy of micro metal devices fabricated by electroforming. In this paper, ultrasonic agitation was performed for improving the thickness uniformity of electroformed layers during electroforming process and its influence mechanism was investigated. Additionally, a new thickness measuring method was adopted to obtain the thickness of large electroforming area.The formation cause of saddle-shaped cross-section profile was analyzed by considering the effect of the migration current and diffusion current and the formation of cap-like cross-section profile was explained according to the fluidic friction-electrophoresis theory. The final profile of the layer depends on the combined actions of migration current, diffusion current and fluidic friction-electrophoresis.In order to measure the thickness of electroformed layers precisely, a new nondestructive measuring method adopted inductance micrometer was presented. In this measurement, the layer with the thickness of several micrometers can be accurately measured and the absolute error is less than0.2μm.In this paper, the influences of ultrasound on the thickness uniformity of individual microstructure, grating structure and large area electroforming layer were investigated by electroforming experiments based on UV-LIGA technology. The results show that the cross-section profile of individual microstructure can be transformed from saddle-shape to cap-like shape by performing ultrasonic agitation and the uniformity can be improved. For the thickness distribution within the grating structure, the employment of ultrasonic agitation can improve the uniformity but can not transform the profile. For the large area electroforming, the thickness uniformity can not be improved by performing ultrasonic agitation.The Ultrasonic mechanism was investigated in this paper, which shows that ultrasonic can reduce the thickness of diffusive layer, and thereby improve the thickness uniformity of electroformed layers. However, cavitation erosion can destroy the narrower resist mold and restrict the dimensional accuracy of microstructures.An ultrasonic electroforming device was designed by fixing an ultrasonic generator on the electroforming device. Additionally, a fixing device, an ultrasonic horn and a tool head were designed for improving ultrasonic electroforming device in the future.