AN 114: Board Design Guidelines for Intel Programmable Device Packages

ID 683481
Date 5/27/2022
Public
Document Table of Contents

1.2.3. Vias

Vias, or plated through holes, are used in multi-layer PCBs to transfer signals from one layer to another. Vias are actual holes drilled through a multi-layer PCB and provide electrical connections between various PCB layers. All vias provide layer-to-layer connections only. Device leads or other reinforcing materials are not inserted into vias.

The following table lists the terms used to define via dimensions.

Table 1.  Via Dimension Terms
Term Description
Aspect ratio The ratio of a via’s length or depth to its pre-plated diameter.
Drilled hole diameter The diameter of the actual via hole drilled in the board.
Finished via diameter The final diameter of a via hole after it has been plated.

The following table lists the three via types typically used on PCBs.

Table 2.  Via Types
Type Description
Through via An interconnection between the top and the bottom layer of a PCB. Vias also provide interconnections to inner PCB layers.
Blind via An interconnection from the top or bottom layer to an inner PCB layer.
Embedded via An interconnection between any number of inner PCB layers.

The following figure shows all three via types.

Figure 1. Types of Vias

Blind vias and through vias are used more frequently than embedded vias. Blind vias can be more expensive than through vias, but overall costs are reduced when signal traces are routed under a blind via, requiring fewer PCB layers. Through vias, on the other hand, do not permit signals to be routed through lower layers, which can increase the required number of PCB layers and overall costs.

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