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Via structures are unavoidable to connect signal paths when a multilayer circuit board is used to increase the signal density. It however becomes clear recently that high-speed via transmission causes not only impedance discontinuities but also the undesirable leak of signal power as the emission with the parallel plate transmission mode between the solid ground planes. In order to solve above problems, the suppression method for them is proposed in this paper. The proposed method is expanding a part of the clearance around the signal via as a fan shape. As a result of the 3D electromagnetic simulation, we confirmed that it could improve the levels of the signal power emissions from signal via from 57% to 30%. This method might be available to low-cost production of the multilayer circuit board in the next generation, in the point that it is applicable to conventional low-cost substrate manufacturing methods.

When a multilayer board is used to increase the signal density, via structures are unavoidable to connect signal paths. However, it becomes clear recently that high-speed via transitions cause not only impedance discontinuities but also undesirable power radiations which have the parallel plate transmission mode between ground planes. In order to solve above problems, expansion of a part of the clearance as a fan shape around the signal via is effective. This method is available to low-cost production of the multilayer board in the next generation, in the point that it is applicable to conventional lowcost substrate manufacturing methods.

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