Fabrication Of Metal Micro Devices And The Study On Improving Bond Strength Of Micro Electroforming Layers By Ultrasonic

With the development of MEMS technology, the demand for metal micro devices, which are the core-block of micro sensor/actuator components, is growing rapidly in medical, biological, aerospace and other fields. At the same time, the fabrication of micro devices based on UV-LIGA technology draws more public attention gradually. However, the bond strength between electroforming layers has important effect on the fabrication and their lives of the metal micro devices. This paper mainly focuses on two aspects:the fabrication process of metal micro devices based on UV-LIGA technology and the method for improving the bond strength of electroforming layers by ultrasonic. The results can provide reference for the fields related to UV-LIGA technology.A trans-scale micro-fuze safety device was fabricated by UV-LIGA technology. Firstly, the micro spring resist structure with aspect ratio6:1was fabricated with SU-8photoresist on metal substrate. Then, the nickel micro spring structure was obtained by micro electroforming technology. At last, the nickel micro spring with aspect ratio5:1and minimum linewidth of lOum was obtained after SU-8photoresist removal. The trans-scale micro-fuze safety device was completed after assembly between micro spring and accessory structure. This paper analyzed the cause of the problems such as unflatness of SU-8photoresist, the bubbles in the photoresist, the coming off of photoresist from substrate and surface crack. Some problems were solved such as the out-of-tolerance of linewidth and black phenomenon of channel based on the subsequent experimental researches.A six-layer metal micro structure was fabricated by UV-LIGA technology to meet the demands for aerospace and bio-engineering. Firstly, the pretreatment of substrate was carried out to make the surface roughness achieve to Ra0.04um. Then, UV-LIGA and positive alignment technology were adopted to fabricate the six-layer structure layer by layer. At last, the six-layer micro structure was obtained after the SU-8photoresist removal. Some problems have been discussed such as the high internal stress in layers, the bad bond strength between layers, the unflatness of layer surface, the difficulty of SU-8photoresist development, the out-of-tolerance of linewidth, the difficulty to make multi-layer resist and the SU-8removal. Based on these discussions, the process was optimized and the stratification of electroforming layers was solved, which increased the fabrication success rate of multi-layer structures. In order to solve the poor bond strength of electroforming layers in UV-LIGA process, the micro electroforming in ultrasonic field was studied. On the copper substrate, the nickel film was obtained by electroforming in ultrasonic field. The critical load was found in friction coefficient curve of scratch test based on the analysis of scratch morphology and curve. By this method, the bond energy between the film and substrate was calculated. The results show that the bond energy increases from3.58J/m2to14.66J/m2under the influence of ultrasonic field. This paper tries to explain the effect of ultrasonic field to the electroforming process and the mechanism of improving the bond energy from the perspective of mass transfer, which is influenced by the extreme physical and chemical conditions arise from ultrasonic cavitations. The method for improving the bond strength between electroforming layers by ultrasonic can provide reference for solving the stratification problem in manufacture of multi-layer structure.