Determination and Monitoring of Through Hole Diameters in Printed Wiring Boards During Electrolytic Plating Using Acoustic Diffraction

摘要

In this paper, we describe a method to monitor and determine the change in the diameter of a through hole in a printed wiring board during electrolytic plating. Since the change in the radius of such a hole directly relates to the thickness of the deposited layer of material inside the hole, actual plating thicknesses may be determined in situ, thus potentially permitting an online optimization of the plating process itself. Fundamentally, our method is based on the evaluation of the diffraction pattern emanating from a circular aperture in a thin acoustic baffle, when subjected to an acoustic field. First experiments in a nickel plating bath have shown that thickness changes of a few micrometers in a 3 mm (0.12 in.) through hole can be detected.