Closed vias are formed in a multilayer printed circuit board by laminating
a dielectric layer to one side of a central core having a metal layer on
each side. A second dielectric layer is laminated to the other side of
the central core. Closed vias in the central core have been formed by
drilling partially through but not completely penetrating the central
core, and then completing the via from the opposite side with a hole that
is much smaller in diameter to form a pathway that penetrates completely
through the central core from one side to another. The via is then plated
with metal to substantially close the smaller hole. Approximately one
half of the closed vias are situated such that the closed aperture faces
one dielectric layer and a remainder of the closed vias are situated such
that the closed aperture faces the other dielectric layer. Resin from one
dielectric layer fills the cavities of approximately one half of the
closed vias, and resin from the other dielectric layer fills the circular
cavities of the remainder of the closed vias. The total amount of resin
migrated from each of the dielectric layers into the closed via cavities
is approximately equal.