How Blind and Buried Vias are Used

Posted 2/5/2020 by AdvancedPCB
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PCBs tend to be very crowded, and it can become difficult to connect the needed components to both sides of the boards. Often, the best way to get the room you need on the board – and to affix all the proper elements to the PCB board – is through the use of blind and buried vias. Of course, many are not entirely sure what blind and buried vias are or how they are used. It’s important to have an understanding of what they are and how they can help.

What is a Via?

A via is simply a hole, drilled or plated, that is in the PCB that will allow a signal to pass to the inner layer of the board or to the other side of the board. Vias often connect component leads to planes or signal traces. These allow a change to the signal layers. If the via goes completely through the PCB board, it is often called a through-via. You might also hear people refer to this as a through-hole.

Blind and buried vias are only available on boards that have at least four layers. They connect the inner layers with other inner layers that are adjacent to them or to adjacent surface layers.

A Closer Look at Blind Vias

When examining blind and buried vias, there are several different types of blind vias to be considered. There are photo-defined blind vias, controlled-depth blind vias, sequential-lamination blind vias, and laser-drilled blind vias.

  • Photo-defined blind vias. The creation of photo-defined blind vias requires laminating a photosensitive resin to a core. The photosensitive sheet will have a pattern on it that indicates the areas where the holes will be made. It is then exposed to light that causes the remaining material on the board to harden. The PCB is then put into an etching solution that removes the material from the holes that were created, which creates pathways. Copper is then plated in the hole and on the outer surface, which creates the outer layer of the PCB.
  • Controlled-depth blind vias. The creation of controlled-depth blind vias is very similar to creating through-hole vias. The only difference is that the drill used to make the holes is set so that it will only go partially through the PCB. Modern technology makes it possible to do this accurately so that the features below the hold will not come into contact with the drill. Once the hole is drilled, it will then be plated in copper. This is the least expensive option, but it does require that the holes are large enough that they can be made with a drill. While this will work for many PCB needs, it might not always be the right solution for everyone.
  • Sequential-lamination blind vias. Sequential-lamination blind vias are created using a piece of laminate that is extremely thin. The process is similar to creating a two-sided PCB, where the laminate will be drilled, plated, then etched. This method creates elements in the side that will form the second layer of the board. On the other side will be a copper sheet, which forms the first layer. This assembly is then laminated with the other layers of the board before going through the remaining steps to becoming a complete PCB. This method is not used as much today as it was in the past, because it is expensive.
  • Laser-drilled blind vias. Laser-drilled blind vias are made after the PCB has been laminated, but before the outer layer undergoes etching and lamination. There are different types of lasers used to make the holes today, but the results are the same.

A Closer Look at Buried Vias

When a via goes between two inner layers of a PCB but does not touch the surface of either side, it is called a buried via. Buried vias create connections between the inner layers. As the name suggests, vias are literally “buried” within the PCB. The functionality of a buried via is similar to that of a blind via, as the goal is to make sure that the PCB has the full functionality that is required. Buried vias help free up space in other areas of the board. To create buried vias, the inner layers with the vias are created first, and then other layers are added to the outside to build up the board.

The Benefits of Blind and Buried Vias

Because PCBs have limited amounts of space, blind and buried vias can be a huge benefit. They allow you to keep the PCB small, which is essential when working with electronics. The use of vias frees up space on the surface of the board; that space can then be used for other functions. Vias are a relatively simple solution, but you will need to be aware that the addition of blind and buried vias will add to the cost of the board.

Because there are many factors that go into getting the right PCBs with the correct blind and buried vias, it is important to work with a quality manufacturer.

Choose the Right PCB Manufacturer for Blind and Buried Vias

Adding blind and buried vias to your PCBs is a delicate process that’s best left to professional manufacturers. This means finding the right manufacturer for the job becomes very important. AdvancedPCB has led the PCB field for more than a quarter of a century and provides a range of services and technologies that can help to make your life easier. We can provide simple designs or complex boards according to your needs.

There are many benefits to working with us. We offer round-the-clock support, and we provide fast turnaround times. We also have instant online quotes available to give you an idea of how much your project will cost, as well as a way to track your order. Give us a call today with any questions you may have regarding blind and buried vias.

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