Interstitial Via Hole, or Inner Via Hole (IVH) is an embedded plated through-hole with connection of two or more inner conductor layers in a multilayer PCB but not extending fully through all the layers of the PCB. Blind vias are Interstitial Via Holes (IVHs). BVHs are Buried Via Holes.
The practical PCB manufacturing has seen a growing use of buried vias in PCB design. Blind via PCBs are used when the designed PCB is extremely packed and the designer needs more space on the top or the bottom, or lacks room on one of the PCB sides and does not need to design a connection by a through hole.
Production of PCBs with blind or buried vias varies greatly from the standard PCB production processes. Blind via PCBs are made just like regular multilayer PCBs, up to the drilling stage. They feature additional holes that connect only two layers in a four-layer board.
The multilayer circuit design process must consider the fact that buried via plating results in copper deposition (at +24 to +45μm) on the specific layer surface. Extra plating deposition on those layers must be then considered when planning the minimum permissible path thickness.
The buried PCB fabrication process for the vias is not unlike in typical PTH‘s followed by compound filling and pressing into a complete multilayer circuit pack. It is not possible to build microvias directly over buried vias, since there is no firm surface at those locations – instead, there is a metal ring with a hole in the middle.
The production of the structure is: first, holes are drilled through and each core is plated. Next, the mosaic image is deposited on the inner surface of the cores, and the multilayer pack is pressed. Production-wise, the structure of the process is not optimum because additional metal plating stages are needed. If the PCB facility has no machinery for microvia drilling, this is the only way to build those holes.
Variations in the number of layers of multilayer PCBs with buried vias can be different, but the complexity of the PCB or the number of buried and blind vias should never be too high. If a choice between making yet another blind hole and an additional pair of layers can be made, the latter option is better. Specifically, BGA IC‘s with the raster at 1.0 mm or even 0.8 mm do not require blind holes. BGA IC’s with the raster at 0.65 mm and 0.5 mm must feature blind holes. Unfortunately, no alternative solution exists. In any case, the build-up of multilayer circuits should be consulted with the PCB manufacturer beforehand.
ALIVH (Any Layer Interstitial Via Hole) is licensed by Panasonic and is common wherever you need microvias all the way through the board, especially smart phone.
ALIVH boards developed and commercialized by Panasonic are the world’s first multi-layer resin boards with an IVH structure in all layers. https://news.panasonic.com/global/topics/2011/4497.html