Swelling of PMMA-structures in aqueous solutions and room temperature Ni-electroforming

Abstract

 LIGA-structures are known to have a lateral dimensional precision of 1 μm and below. These specifications strongly depend on the process parameters. Fabrication of 400 μm tall nickel LIGA-structures by electroplating of X-ray patterned (DXRL) resist structures revealed much higher distortions. These are caused on the one hand by thermal expansion of the structured resist since the electroforming is usually performed at 52 °C, but on the other hand to a higher degree by swelling of the resist in the aqueous electroplating bath. Reducing the electrolyte temperature not only eliminates the thermal expansion but also particularly reduces the swelling. At room temperature the latter is reduced by a factor of 3 in comparison to the usual 52 °C-bath leading to an overall reduction of the deformation of up to 80%. In this paper the experimental data are presented and the results are explained. Furthermore first microstructures electroplated at room temperature with optimized precision are shown.