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Megasonic has obvious advantages in overcoming the limitations of electroforming process based on its low cavitation effect, high sound intensity and acoustic streaming. In this paper, megasonic was employed to achieve uniform electroformed layer in electroforming process. Impedance values, resonant frequencies were measured in order to get a high-efficiency megasonic source. Considering the directions of acoustic radiation and combining with other functional modules, an integrated megasonic electroforming equipment was designed and set up. Then, nickel was electroformed on copper substrates without megasonic wave, with single directional megasonic wave and with bidirectional alternating megasonic wave, respectively. The planeness value (PV) of electroformed layer is 15.03 μm without megasonic agitation, and the PV of electroformed layer is 15.36 μm with single directional megasonic wave radiation. Bidirectional alternating megasonic wave assisted electroforming has an outstanding performance on the uniformity of electroformed layer, which achieves the lowest planeness value (PV = 10.91 μm) of all the electroforming experiments. Besides, the bidirectional megasonic wave assisted electroforming can achieve better surface quality than other conditions too.

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Micro electroforming, as a mature micromachining technology, is widely used to fabricate metal microdevices in micro electro mechanical systems (MEMS). However, large residual stress in the local positions of the micro electroforming layer often leads to non-uniform residual stress distributions, dimension accuracy defects and reliability issues during fabrication of the metal microdevice. To solve this problem, a novel design method of presetting stress release geometries in the topological structure of the metal microstructure is proposed in this paper. First, the effect of stress release geometries (circular shape, annular groove shape and rivet shape) on the residual stress in the metal microstructure was investigated by finite element modeling (FEM) analysis. Two evaluation parameters, stress concentration factor KT and stress non-uniformity factor δ were calculated. The simulation results show that presetting stress release geometries can effectively reduce and homogenize the residual stress in the metal microstructures were measured metal microstructure. By combined use with stress release geometries of annular groove shape and rivet shape, the stress concentration factor KT and the stress non-uniformity factor δ both decreased at a maximum of 49% and 53%, respectively. Meanwhile, the average residual stress σavg decreased at a maximum of 20% from  −292.4 MPa to  −232.6 MPa. Then, micro electroforming experiments were carried out corresponding to the simulation models. The residual stresses in the metal microstructures were measured by micro Raman spectroscopy (MRS) method. The results of the experiment proved that the stress non-uniformity factor δ and the average residual stress σavg also decreased at a maximum with the combination use of annular groove shape and rivet shape stress release geometries, which is in agreement with the results of FEM analysis. The stress non-uniformity factor δ has a maximum decrease of 49% and the average residual stress σavg has a maximum decrease of 37% from  −257.0 MPa to  −162.0 MPa.