Buried vias are plated connections between the inner layers of a multi-layer PCB that do not emerge on either of the outer layers. Buried vias are created by drilling and copper plating the inner layer core (pairs) of a multi-layer PCB in the same way as a standard 2 layer or indeed for a multi-layer plated through hole PCB.
There is no problem with the depth of the buried via because at the time of plating, the hole is open at both ends and the plating chemistry can freely penetrate. If the buried via PCB is designed with buried vias passing between even numbered pairs of inner layers, construction is straightforward. It is not recommended to design buried vias passing between odd numbers of inner layers.
Sequential build up of multi-layer PCBs using multiple printing, bonding, and plating sequences allow complex inter-connection structures to be built.
If careful consideration is taken with the practicalities of fabrication, then blind vias, buried vias and through hole vias may be combined on the same PCB.
Buried vias are less costly to manufacture than blind vias, but as a guide, the use of buried vias is unlikely save costs unless the overall layer count is reduced by at least 4 layers.
We produce a wide variety of buried via pcbs. Ask us to quote.