Effects of Acid Electrolytes and Electropolishing Conditions on Laser-Stencil Printing Performance

The electropolishing process has shown promising results for improving the surface finish of small apertures in laser-stencils. We report on the results of the investigations of the parameters that control the electropolishing process using highly concentrated phosphoric acid. The effect of the phosphoric acid solution on the finish of the polished small apertures and the effect of the electropolishing time were investigated. An optimized process was established through inspection of the polished stencil apertures of the laser-stencil. The results demonstrated that the acid solution for the electrolyte as well as the electropolishing time had a significant effect on the small stencil´s aperture quality and the solder paste´s stencil-printing performance. In particular, a 95 wt.% phosphoric acid-based electrolyte showed encouraging results in terms of surface smoothness, improved solder-paste printing, and surface-mount-technology yields. The most effective electropolishing times were 5, 10, and 20 s for stencils thicknesses of 0.05, 0.08, and 0.10 mm, respectively.