Depends on what the via is used for. If it’s a ground via then size doesn't really matter. If it is a signal via top level the via should be as wide as the trace it is attached to but more important is the board stack up the material used and the layer thicknesses as this will define the via impedance. The trace and via impedance should be the same so that the via does not add any reflections back onto the signal trace.
That depends on what the via is used for and at what the design frequency is. If the vias are signal vias used in a high speed design then the choice of via size, placement and routing are all important and should be carefully considered. Vias have impedance characteristics. For example if the vias are electrically long it can have some inductance. If the vias connect to internal metal planes they can have some capacitance. Using an electromagnetic simulation tool to route and analyse the vias is suggested in such cases.
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cblair
Forum Coordinator
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