Restrictions on the diameter of buried via holes
When designing a multi-layer PCB, you may have the option of choosing between using a blind via or buried via hole. While it may seem that these options are similar, there are some key differences that can affect your choice. These two options are useful when you have limited space on your circuit board and need to make connections between layers.
A blind via extends from one side of the outer layer (either the top or bottom) and connects to at least one inner layer, but does not pass through the entire circuit board. They are used in PCB design primarily to free up space, and are also useful for BGA assembly as they can help reduce signal interference.
A buried via, on the other hand, passes between at least two inner layers but does not come to either surface of the circuit board. They are also used primarily to improve signal integrity by reducing the chance of interfering with other signals on the inner layers, so they are often found in HDI PCBs.
To manufacture a blind or buried via hole, you need to drill holes through the copper pads of the inner layers of your circuit board. Once these holes have been drilled, they are then filled with a non-conductive material such as epoxy. After this step, the holes are then exposed and plated with copper through a process called electro-coating.
The plated copper then forms the connections between the inner layers of your circuit board. When you use a buried or blind via, it is important to keep in mind that they aren’t visible from the surface of the board, so you will need to mark them on your design to ensure that you don’t accidentally bury or blind a component on your circuit board.
Are there any restrictions on the diameter of buried via holes?
If you’re using a buried or blind via, it’s a good idea to use them sparingly because they will add to the cost of your circuit board. However, they can be very useful when you have a high-density circuit board that needs to save space.
In addition to being useful for ensuring that your inner circuit layers are properly connected, buried and blind vias can also help you to meet density requirements or constraints for traces and pads on your PCB. Having these connections in the inner layers allows you to maximize the functionality of your circuit board while keeping it small and compact.
There are a few restrictions on the diameter of buried via holes, but these are generally not a concern for most designers. The first restriction is that the buried via must be no more than twice as wide as the diameter of the copper pad it’s connecting to. This is necessary to prevent shorting, which can cause the board to fail.
The other restrictions are that the buried via must be no more vertical than half of the distance between its top and bottom edges, and that the via must be surrounded by metal to prevent it from being brittle. These rules are typically enforced by the fabricator during the manufacturing process.
