1 Conventional through-hole plating
The most common and inexpensive interconnection technology between layers is the traditional through-hole plating. Figure 1 shows an example of a six-layer plated through-hole board.
In this technique, all holes are drilled through the panel, regardless of whether they are applied like component holes or like vias. The main disadvantage of this technique is that through-holes take up precious space in all layers, regardless of whether the layer needs to be electrically connected or not.
2 Buried Holes
Buried holes are plated through-holes that connect two or more layers of a multi-substrate. Buried holes are in the inner structure of the board and do not appear on the outer surface of the board. Figure 2 shows a multi-substrate with buried holes.
Compared with the traditional plated through-hole structure, buried holes save a lot of space. Buried-hole technology can be used when the signal line density is high and more holes are needed to connect the signal layers, and more signal routing paths are needed. However, because buried-hole technology requires more procedural steps, the advantage of line density is to increase the cost of the board.
3 Blind holes
Blind holes are plated through holes that connect multiple substrate layers to one or more layers, and they do not go through the full thickness of the board. Figure 3 shows an example of a typical blind hole technique. Blind holes can be used on both sides of a multi-substrate, and they can connect through-holes and component holes that pass through the board.
Blind holes can be stacked on top of each other on the board layers and can be made smaller so that more space can be provided or more signal lines can be laid out.
For SMDs and connectors, blind hole technology is particularly useful because they do not require large component holes, but only small vias to connect the outer surface to the inner layer. On very dense and thick multiple substrates, weight can be reduced by using surface mount technology, which also provides designers with ample design space.