Investigation on Spraying Uniformity in Etching Process of FPCB with 18 μm Line Pitch

In the wet etching process of the flexible printed circuit board (FPCB), to obtain a symmetrical and stable circuit structure and improve the yield, it is necessary to control the uniformity of the etchant velocity and pressure on the surface of the FPCB as far as possible. In this paper, a numerical method implemented with Euler multiphase flow model is proposed to study the spraying uniformity of the wet etching process of the FPCB. A 3D full model of the multi-nozzle array is established to study the velocity distribution of the etchant in the spraying domain. The FPCB sample is manufactured based on the process parameters obtained by the parametric study. In the experiment, pressure sensors are applied to monitor the etchant pressure on the surface of the FPCB and the cross-section of the FPCB circuit is observed, which validates the numerical simulation method. The results of simulations demonstrate that when the nozzle rotation angle θ is 1.3°, the distribution of the low-speed flow zone on the surface of the FPCB is about 60 mm along the X axis direction, and the standard deviation of the pressure is reduced by 67.6% compared to 0°. The cross-section of the FPCB circuit is close to an isosceles trapezoid with an 18 μm line pitch, which is the center-to-center distance between the adjacent circuit lines.