| 摘要 |
Disclosed are methodologies for defining matched-impedance footprints on a substrate such as a printed circuit board, for example, that is adapted to receive an electrical component having an arrangement of terminal leads. Such a footprint may include an arrangement of electrically-conductive pads and an arrangement of electrically-conductive vias. The via arrangement may differ from the pad arrangement. The vias may be arranged to increase routing density, while limiting cross-talk and providing for matched impedance between the component and the substrate. The via arrangement may be altered to achieve a desired routing density on a layer of the board. Increasing the routing density may decrease the number of board layers, which tends to decrease capacitance and thereby increase impedance. Ground vias and signal vias may be arranged with respect to one another in such a manner as to affect impedance. Thus, the via arrangement may be altered to achieve an impedance that matches the impedance of the component. The via arrangement may be also be altered to limit cross-talk among neighboring signal conductors. Thus, the via arrangement may be defined to balance the impedance, cross-talk, and routing density requirements of the system.
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