"Design Guidelines
[1] Use the minimum size drill bit for creating the via cylinder. This has less
to do with lowering the capacitance of the via and more to do with raising
its inductance. Since a via looks like a region of low impedance compared
to a traditional printed circuit board transmission line, raising the
inductance will increase its characteristic impedance to better match the
connecting lines.
[2] Use the minimum size pad that the PCB manufacturer allows. The pad is
the source of the most capacitance. The ideal case would be to connect
the transmission lines directly to the via cylinder.
[3] Do not use the minimum size ground clearance radius. This is counterintuitive
since in most cases, smaller is better. By having a small portion
of the connecting traces near the via NOT run over a ground plane, two
regions of higher impedance immediately before and after the via are
introduced. These regions of higher impedance will counter the lower
impedance characteristic of the via and better match the line. This effect
can also be accomplished by placing very small surface mount inductors
in series with the via immediately before and after.
[4] Use the thinnest printed circuit board possible. This will reduce the
overall height of all vias on the board. Reducing the height of the via will
decrease the length of the discontinuity that the signal has to pass
through.
[5] Place vias that connect the ground planes together near the signal vias
that pass through multiple ground planes. This provides a low
impedance path for the return current to flow when the signal changes
layers. This will reduce the discontinuities caused by the via."
Source: www.coe.montana.edu/ee/lameres/vitae/publications/a_thesis/thesis_002_msee.pdf
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