1. Traditional plated through hole
The most common and cheapest interlayer interconnection technology is the traditional through – hole plating technology. Figure 1 shows an example of a six – layer plated through – hole plate.
In this technique, all holes are drilled through the panel, regardless of whether they are used as component holes or through holes. The main drawback of this technique is that the through hole takes up precious space on all the layers, regardless of whether the layer needs to be electrically connected.
2 buried hole
Buried hole is a plated through hole connecting two or more layers of multiple substrates. Buried hole is in the inner layer structure of the circuit board and does not appear on the outer surface of the circuit board. Figure 2 shows a multi-substrate plate with buried holes.
Compared with the traditional plated through hole structure, the buried hole saves a lot of space. When the signal line density is very high, more hole positions are needed to connect the signal layer, and more signal line paths are needed, buried hole technology can be adopted. However, because buried hole technology requires more procedural steps, circuit density has the advantage of increasing the cost of the circuit board.
3 blind hole
Blind holes are plated through holes that connect the surface layer of a multisubstrate plate to one or more layers without passing through the full thickness of the plate. Figure 3 is an example of a typical blind hole technique. Blind holes can be used on both sides of the multi-substrate, which can connect through the hole and through the hole of the component of the circuit board.
Blind holes can be stacked on top of each other and can be made smaller to provide more space or lay more signal lines.
Blind hole technology is particularly useful for SMDS and connectors because they do not require large component holes, only small through holes to connect the outer surface to the inner layer. On very dense and thick multisubstrate, the use of surface-mount technology can reduce weight and provide designers with ample design space.