When it comes to new hardware products, the smaller the better, especially for wearable technology products and IoT products.

One of the keys to smaller hardware products is of course the smaller printed circuit board (PCB).

If small size is critical to your product, then the technology to reduce PCB size is to use blind and buried vias. Their use can make the components on the PCB package more tightly.

Vias are channels that connect the traces between the various board layers. Standard vias that pass through each layer of the board actually reduce the available wiring space, even on layers that are not connected to these vias. The less space available for wiring means the larger the board size.

This is the emergence of so-called buried vias and blind vias to help eliminate this problem. Blind vias connect the outer layer to the inner layer, while buried vias connect the two inner layers.

However, designers need to consider the use of blind vias and buried vias.

The first problem with blind and buried vias is cost. Compared with conventional vias, the process of manufacturing blind and buried vias is more complicated, which will greatly increase the cost of the circuit board.

For mass production, the cost of blind buried vias will be reduced to a more manageable level, but for a small amount of HDI circuit board proofing production, the cost will increase greatly. In many cases, the use of blind and/or buried vias will triple the cost of PCB proofing!

The second problem with using them is that they have strict restrictions on the layers that can be used for connectivity. To understand their limitations, you must understand how to stack layers to make a circuit board.

In the above figure, via #1 is a classic via, via #2 is a blind hole, and via #3 is a buried via.

When using this layer stack, blind vias can only be used to connect L1 to L2, or to connect L3 to L4.

On the other hand, buried vias can only be used to connect L2 to L3.

You cannot use blind holes to connect L1 to L3, or L2 to L4. This is because the start and end of each through hole must be located at the far end of the core part to maintain structural integrity during the drilling process.

It becomes more complicated because you do not have to choose the stack of copper, core, copper, prepreg, copper, core, copper as shown above, but choose the stack as copper, prepreg, copper, core, copper, Prepreg, copper.

With this layer, blind holes can now be created to connect L1 to L3, or L2 to L4, but not L1 to L2 or L3 to L4.