Perimeter Stitching via Pitch Selection for Circuit Board Shielding
Perimeter via pitch selection requires matching ground via spacing to less than one-twentieth of target frequency wavelength while verifying barrel plating thickness.
Aspect Ratio Plating
Electrochemical Deposition
Electroplating of copper into deep holes or vias represents a critical threshold in the fabrication of high-density interconnect circuit boards. This aspect ratio plating process determines the uniformity of the copper layer deposited along the walls of a drilled hole relative to the surface pad thickness. As circuit designs compress in size, the ratio of hole depth to drill diameter increases, making it harder to deliver fresh plating chemistry to the center of the hole.
Specialized chemical additives balance the deposition rate between the board surface and the hole interior when high-frequency circuits require deep, narrow holes for signal paths.
Process Dynamics
Liquid moves slowly through narrow vias, causing depletion of copper ions in the middle of the barrel. This depletion leads to thin copper walls at the center, which can fail under thermal stress or cause intermittent electrical open circuits during board operation. Pulse plating techniques and high-rate agitation are used to force the electrolyte through the microvias and stabilize the deposition rate.
Deposition Control
The ratio of plating thickness at the surface to that in the center of the via is measured by cross-section analysis after the plating step. Reliable board fabrication demands a plating index close to unity to ensure that vias can withstand subsequent soldering and assembly processes without fracturing. This geometric constraint restricts the maximum number of layers that can be interconnected by a single mechanical drilling step.