Etching process analysis based on etchant flow for high-density build-up substrate

A technique to predict the minimum line and space width of copper wiring on printed circuit boards is developed. Effects of the variations of copper thickness, resist width, and etching speed are taken into account as well as effects of copper thickness, anchor depth, and resist thickness. To develop the technique, dry film resists were evaluated with hardware experiments and theoretical calculations. From the experiments, the minimum pitch of lines are 80 μm (copper thickness 20 μm, anchor depth 2.8 μm, resist thickness 15 μm). With the process variation of the experiments, the calculation results for the minimum pitch of lines are 75 μm, which is almost the same as the experimental results. The minimum pitches of the lines formed by the subtractive method were obtained from theoretical calculations under the conditions that the copper thickness ranges from 8 μm to 20 μm and the anchor depth is 2.8 μm in order to estimate the dependence of the minimum pitch of the lines on copper thickness and variations of the processes.