Abstract
Various problems have constantly emerged during the copper etching process in the manufacturing industry of printed circuit board (PCB). The most common one is the undercut phenomenon beneath the etch resist resulted from undesirable isotropic etching. The etch factor is generally used as an indicator for evaluating the degree of undercut in an etching process and is a function of the copper line thickness and of the difference between the lower and the upper line width. Environmental parameters such as etch solution type, solution concentration, flow velocity, and temperature have a deterministic impact on the magnitude of an etch factor. The undercut problem does not cease to occur in the absence of an ideally anisotropic etching although it has indeed been alleviated after years of intensive research. On the other hand, new problems emerge along with new etching techniques. The PCB manufacturers that adopt the spray etching process in combination with conveyors are forced to deal with the annoying puddling problem. The puddling effect caused by insufficient mass transfer of the etch solution at the center portion of a board could lead to an unacceptable etch depth difference between the edge area and the center area and a loss of uniformity of etched copper film. Most of the available copper etching processes cannot efficiently resolve the puddling effect. The only one that has a satisfactory solution unfortunately calls for extra auxiliary equipment and a tremendous amount of maintenance work and cost. An alternative resolution to the problem has been developed and evaluated and the new technique is deemed feasible based upon a full-scale theoretical analysis. The principle is to adopt a jet stream to speed up the etching process by a higher flow rate and to enhance the anisotropic etching by a higher and more direct impact force from the stream. According to current research findings, the puddling effect seen in traditional etching processes was completely eliminated. The etching efficiency of this new technique is much higher that those by other traditional processes. The optimal etching rate is 375 μm/min under 4 mm jet distance at a flow rate of 70~75 LPM in FeCl3 solutions. The etching factor has attained a relatively large value of 7 which is much better than those obtained from currently available techniques. Base on these experimental observations, the new system is expected to increase throughput and to enhance etching factors in on-line application.