It is imperative that designers have a working knowledge of the plating processes used in printed circuit board manufacturing. A lack of this knowledge is a fast track to failure, particularly when designing complex via structures.
There are two primary methods of plating copper PCBs, panel plating and pattern plating. The panel plating method plates a uniform copper thickness across the entire panel surface before the circuit image is applied, which eliminates most copper plating distribution issues. The disadvantage is that because it adds copper thickness to the surface base layer, it makes maintaining fine line definition and consistency difficult. Pattern plating first covers the surface with a film used to define the circuit image, so that copper is only plated on the image, not the entire surface. Why this is important should become clear in the following paragraph.
Understanding which process your PCB supplier uses will influence how you design a board, or in the case of panel plating, limit the design. Copper that is not used to define trace width, spacing and circuit features (a majority of the surface copper), must be chemically etched off. When copper is etched, it is not just removed vertically, it is also removed horizontally (undercut), which means the circuit trace gets smaller and the spacing gets bigger. The thicker the copper, the more the trace is reduced. ASC fabricates most printed circuit boards with the pattern plating process. This process has major advantages in that only the base copper is required to be etched, resulting in more defined feature edges and the ability to process smaller trace widths.
Where the physics of etching really impact both the design, and the manufacturability of the PCB is with advanced via structures. This includes buried and blind vias, filled vias, microvias and stacked microvias. Anytime sequential lamination (lamination/plating/lamination/…) cycles are employed, additional surface copper is added and must be etched. Designers frequently do not consider this critical aspect of PCB manufacturing and end up with delays, scrap or a totally unmanufacturable design.
We invite you to visit ASC and let us give you a hands-on demonstration of the plating process and how it impacts your design.