Multi-connection vias for printed circuit boards

Abstract

As the performance of digital electronic components improves, maintaining the integrity of high-frequency signals through circuit boards becomes increasingly challenging. The dimensions and material parameters of in-plane circuit board features, such as striplines, microstrips and co-planar waveguides are tuned to control signal impedance. Conventional multi-layer vertical interconnects, which connect between board layers, are not impedance matched to the in-plane signal traces. Multi-connection vias, developed in this thesis, provide a method for matching the impedance of vertical and in-plane features by forming co-cylindrical waveguides. Solutions from a high-frequency full-wave solver provide insight into field interactions within multi-connection vias; and results from these simulations and signal integrity experiments indicate impedance "tuneability" by adjusting the multi-connection via dimensions. The results also suggest that features can be impedance-matched independent of via diameter. Multi-connection vias are formed by creating distinct conductor paths within cylindrical plated through-holes. The thesis explores several alternative manufacturing methods for fabricating these features. A specialized broaching machine and carbide-insert broaches were used to manufacture multi-connection vias for signal integrity experiments. Models of the broach tool and cutting force simulations resulted in several iterations of the broach design.

(cont.) Broaching multi-connection vias is challenging due to the small diameters and high aspect ratios of plated through-holes, as well as the unique copper-epoxy/resin material. Since the broaching process prefers larger plated through-holes to permit larger broach tools, a new method was developed to analyze the cumulative connection density of multi-connection via arrays. Multi-connection vias provide fertile ground for the development of corollary electronic products. Simulations for connector launches indicate that via impedance control can extend to board-mounted devices and connectors. Products that may benefit from multi-connection vias include by-pass capatrs, IC packages, test probes and pogo pins. The thesis presents a road map for commercializing multi-connection vias. Elements of the roadmap ... integration of new signal routability constraints in CAD/CAM software, manufacturing processes, machine tool design, board testing, and durability.