Telescoping blind via in three-layer core

A dual blind via interconnection unit for a multilayer PCB, comprising:

• a pair of opposed coaxial blind vias transversing a pair of dielectric layers;
• and
• at least one bridge pad disposed between said pair of blind vias, wherein each of said pair of dielectric layers is in physical contact with said bridge pad, and wherein said bridge pad is adapted to electrically interconnect said pair of opposed coaxial blind vias without electrically interconnecting any other blind vias,
• wherein a first bridge pad of said at least one bridge pad lacks electrical connectivity to others of said at least one bridge pads, and
• wherein each pair of opposed coaxial blind vias in said dual blind via interconnection unit are coaxial,
• said pair of opposed coaxial blind vias extend from a corresponding pair of capture pads, and
• each of said corresponding pairs of capture pads have a diameter less than a diameter of a corresponding one of said bridge pads.

A method for forming a multilayer printed circuit board (PCB), comprising:

• a) providing a metal clad first dielectric layer having a first metal clad side and a second metal clad side;
• b) forming a bridge layer from said second metal clad side, wherein said bridge layer comprises a plurality of bridge pads disposed on said first dielectric layer, and wherein said first metal clad side comprises a first metal layer;
• c) providing a second dielectric layer disposed on said bridge layer, wherein said second dielectric layer has a second metal layer disposed thereon;
• d) forming a first blind via through said first dielectric layer, wherein said first blind via extends from said first metal layer to a first side of at least one of said plurality of bridge pads;
• and
• e) forming a second blind via through said second dielectric layer, wherein said second blind via extends from said second metal layer to a second side of said at least one of said plurality of bridge pads,
• wherein said each of said bridge pad is coaxial in a z direction with a corresponding one of said first blind via and with a corresponding one of said second blind via, and
• wherein, in the absence of an interstitial bridge pad therebetween, at least a portion of said first dielectric layer is fused to at least a portion of said second dielectric layer, and
• said corresponding one of said first blind via extends from a corresponding first capture pad to a first side of each of said bridge pads,
• said corresponding one of said second blind via extends from a corresponding second capture pads to a second side of each of said bridge pads, and
• said corresponding first capture pad and said corresponding second capture pad each have a diameter less than a diameter of said bridge pad therebetween.

A method for forming a multilayer printed circuited board (PCB), comprising:

• a) forming a pseudo three-layer core, said pseudo three-layer core including:
• a first metal layer;
• a first dielectric layer disposed on said first metal layer,
• a plurality of spaced apart interstitial bridge pads disposed on said first dielectric layer;
• a second dielectric layer disposed on said plurality of spaced apart interstitial bridge pads;
• and
• a second metal layer disposed on said second dielectric layer;
• and
• b) forming a plurality of interlayer interconnection units for interconnecting said first metal layer and said second metal layer, wherein each of said interlayer interconnection units includes:
• a first blind via disposed on a first side of one of said plurality of interstitial bridge pads, wherein said first blind via extends from said first metal layer through said first dielectric layer;
• and
• a second blind via disposed on a second side of one of said plurality of interstitial bridge pads, wherein said second blind via extends from said second metal layer through said second dielectric layer, wherein said interstitial bridge pad is coaxial in a z direction with said first blind via and with said second blind via, and wherein each of said interlayer interconnection units include coaxially formed corresponding first blind vias and second blind vias, and
• said first blind via extends from a corresponding first capture pad to a first side of each of said plurality of interstitial bridge pads,
• said second blind via extends from a corresponding second capture pads to a second side of each of said plurality of interstitial bridge pads, and
• said corresponding first capture pad and said corresponding second capture pad each have a diameter less than a diameter of said interstitial bridge pad therebetween.

A method for forming a multilayer printed circuit board (PCB), comprising:

• a) a step for forming a pseudo three-layer core, wherein said pseudo three-layer core includes:
• a first metal layer;
• a first dielectric layer disposed on said first metal layer;
• a plurality of bridge pads disposed on said first dielectric layer;
• a second dielectric layer disposed on said bridge pads;
• and
• a second metal layer disposed on said second dielectric layer;
• and
• b) a step for forming a plurality of interlayer interconnection units for electrically interconnecting said first metal layer and said second metal layer, wherein each of said interlayer interconnection units includes:
• a pair of opposed coaxial blind vias, and
• one of said plurality of bridge pads disposed between, and in electrical contact with, said pair of blind vias,
• wherein each pair of opposed coaxial blind vias in each of said plurality of interlayer interconnection units are coaxial,
• said pair of opposed coaxial blind vias extend from a corresponding pair of capture pads, and
• each of said corresponding pairs of capture pads have a diameter less than a diameter of a corresponding one of said bridge pads.

A method for forming a pseudo three-layer core for a PCB, comprising:

• a) providing a first metal layer;
• b) providing a first dielectric layer on said first metal layer;
• c) forming a plurality of bridge pads on said first dielectric layer;
• d) providing a second dielectric layer on said plurality of bridge pads;
• e) providing a second metal layer on said second dielectric layer;
• f) forming a first blind via on a first side of each of said plurality of bridge pads, wherein said first blind via extends from said first metal layer through said first dielectric layer;
• and
• g) forming a second blind via on a second side of each of said plurality of bridge pads, wherein said second blind via extends from said second metal layer through said second dielectric layer,
• wherein each of said plurality of bridge pads is coaxial in a z direction with said first blind via and with said second blind via,
• said first blind via extends from a corresponding first capture pad to a first side of each of said plurality of bridge pads,
• said second blind via extends from a corresponding second capture pads to a second side of each of said plurality of bridge pads, and
• said corresponding first capture pad and said corresponding second capture pad each have a diameter less than a diameter of said bridge pad therebetween.

An apparatus for forming a pseudo three-layer core for a PCB, comprising:

• a) means for providing a first metal layer;
• b) means for providing a first dielectric layer on said first metal layer;
• c) means for forming a plurality of bridge pads on said first dielectric layer;
• d) means for providing a second dielectric layer on said plurality of bridge pads;
• e) means for providing a second metal layer on said second dielectric layer;
• f) means for forming a first blind via on a first side of each of said plurality of bridge pads, wherein said first blind via extends from said first metal layer through said first dielectric layer;
• and
• g) means for forming a second blind via on a second side of each of said plurality of bridge pads, wherein said second blind via extends from said second metal layer through said second dielectric layer,
• wherein each of said plurality of bridge pads is coaxial in a z direction with said first blind via and with said second blind via,
• said first blind via extends from a corresponding first capture pad to a first side of each of said plurality of bridge pads,
• said second blind via extends from a corresponding second capture pads to a second side of each of said plurality of bridge pads, and
• said corresponding first capture pad and said corresponding second capture pad each have a diameter less than a diameter of said bridge pad therebetween.