PCB007 Magazine

PCB007-Jan2019

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52 PCB007 MAGAZINE I JANUARY 2019 several panels at a time either using a jig to hold them in position or hanging them from top clamps in a long row. In both methods, each panel has a slightly different plating effect, and therefore, a different copper thickness. This variation in copper thickness means that circuit performance is compromised. The target should always be for each circuit produced to be exactly the same. The vertical continuous plating (VCP) process offers a good solution to this problem of variation. Instead of dipping panels in a succession of tanks, the VCP process moves the panel in a linear motion through the critical process stages. In the case of the copper tank, this means that the panel is moved through a very long plating tank from one end to the other, and every panel in the batch has exactly the same process path; thus, the variation from panel to panel is absolutely minimal. For some people, VCP is a real gamechanger. It opens up possibilities for automating the process as it can easily be joined with horizontal pre- and post-processes. It also offers opportunities to use the simpler panel plating process route for circuits that previously could only have been manufactured by pattern plating. This reduces the number of process stages and the overall cost of the PCB. Additional benefits are that less copper is used as the variation in plated copper thickness is reduced. If you require a minimum of 25 microns of copper thickness in the hole and your variation across the panel is 10 microns, then you have at least 35 microns thickness in places. If you can reduce the variation across the panel to two microns, less copper is wasted. If you produce panels by the panel plating process followed by printing the image and etching, there is also an improvement in the possible etch speed and a reduction in the usage of etchant due to the same reduction in variation of copper thickness across the plated panel. There are a few variations of the VCP process that allow the advantages to be applied to many different types of panels. For example: • The machine can be formatted with a double track, which gives double the throughput from a similar process length • The machine can be formatted for thin materials, which can be processed without having to use plating frames; materials as thin as 50 microns can be transported without external support • Very long rigid and semi-rigid panels can be processed on a variant that has a completely linear transport system • Many of the developments applied to conventional plating lines can still be used—such as pulse rectification— to improve copper distribution and deep through-hole capability further • Insoluble anodes can be used that are zoned within the tank to improve flexibility for different panel lengths (e.g., switching off the bottom sections to match the panel length, which removes the requirement for bottom shielding) There are, of course, some negatives for the VCP process. First, the size of the equipment can be a downside. There is no way to overcome the amount of time it takes to plate copper onto Figure 3: Robot unloads to horizontal clean line.

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