Vias play a crucial role in the functioning of a PCB. A via hole is an electrical connection between different layers of a PCB. This hole helps to connect traces, polygons, and pads on several layers of a circuit board. The aim of manufacturing PCB vas is to enhance the available space on a board. However, there are several types of vias.
The role of vias in PCB design and production process is vital. However, how much do engineers know about them? We all understand vias are available in different types. The blind vias is a type of PCB vias. Therefore, we will be discussing blind via PCBs. This article provides answers to many questions about blind vias PCB.
What is a Via?
To understand blind vias PCB, it is important to have a complete knowledge on what a via is. A via is a hole in a circuit board that thermally and electrically connects pads and traces on several layers of a board. Also, a via is a plated or drilled hole that enables a signal to transmit to the inner layer of the PCB.
In addition, vias help to link components that lead to signal traces or planes. Therefore, these enable a change to the signal layers. There are several types of vias. However, the most important role is that they offer connection in PCB layers. Also, vias are usually a small hole drilled or plated via the PCB. Vias always cross two or more adjacent layers.
Also, vias are internally covered with copper. Therefore, this creates an electrical connection in the insulator that separates the PCB layers. The types of vias used depend on the specific requirements of an application. Vias are totally different from PTH holes. PTH holes are usually used for connecting through-hole components on the board.
However, PTH holes with bigger dimensions than vias can offer mechanical connection on some boards. PCB vias are crucial in multilayer PCBs. This is because they aid the design and production of these boards. Also, vias create paths for the flow of current between different layers of a board. Therefore, we can say vias are channels available in different sizes and types.
Vias play a crucial role in PCB design. They enable a PCB designer to reduce the distance of routing a trace to complete its connection. Also, vias are holes linked to the metal circuitry of a board.
What is a Blind via PCB?
A bind via PCB is a circuit board whose vias begin from the external side and cross internal layers without connecting its opposite side. Blind vias PCB can be very complex. Therefore, it is important to determine the exact time to stop the drilling process. This will help to achieve the intended degree of depth.
Also, blind vias help to maximize the number of connections between an external and internal layer. Therefore, this results in a reduction in the number of traces. In the long run, it reduces the final cost of the board. In addition, a blind via can help you to connect the surface layer of a PCB to the next layer.
They are often called blind vias because you can’t see it on the PCB surface. Blind vias begin on the top or bottom of the PCB. However, it doesn’t go through it. Blind vias are useful when there isn’t enough space on the top or bottom of a board. Mechanically drilled blind vias can connect an external layer to an adjacent layer.
A blind via only opens at one end. Therefore, it is not possible for the plating solution to flow through the hole. Also, this makes the plating process complex. Blind vias can widen breakout channels on the bottom and inner layers using blind vias. Also, you can use blind vias to reduce the PCB aspect ratio.
Features of Blind Vias
Blind vias are different from other types of vias. Therefore, they offer distinct features which include:
- Reduced trace width and space
- More holes than a traditional board.
- Higher pad density and wiring
- An inexpensive solution
How to Fabricate Blind Vias PCB
Generally, there are steps for fabricating a PCB. However, these steps provide limited via configurations. Typically, PCB fabrication starts with a core. Blind vias PCB follow a standard procedure. Also, this procedure is similar to that of a multilayer PCB. There are some basic rules to follow when fabricating blind vias PCBs.
- Blind vias must start from the top or bottom layer of the PCB
- They must not occupy an odd number of layers
- Also, they must never go through the entire PCB
- They must never start or end at the core or center of a PCB substrate
Blind vias in multiple layer boards create connection between the internal layers and the surface layer. However, it is a complex task to drill a bind based on the modeled depth. You should carefully select via sizes to ensure good metallization quality.
Also, the depth and diameter of the hole shouldn’t be more than 1. Therefore, the deep vias should feature large diameters. Huge vias indicate that there is a huge dielectric gap between PCB layers. You will need to create the vias in the center to create the blind vias. Prepreg will help to stack the PCB layers together.
The PCB manufacturer adds the blind vias to the PCB through drilling. It is crucial to be aware of the drill’s depth. The hole might not offer a great connection if it isn’t deep enough. Also, if the hole is too deep, it could cause distortion.
Therefore, for a blind via, you need to use a separate drill file to define the hole. A smaller hole indicates that there is a smaller distance between the inner layers and outer layers.
Types of Blind Vias
There are different types of vias, so are different types of blind vias.
Controlled-depth blind vias
These vias’ creation is similar to that of through-hole vias. However, there is a slight difference. The designer set the drill used to create the holes so that it can go partially through the circuit board. Modern technology has made this possible in a way that the features won’t come in contact with the drill. The designer will plate the hole in copper after drilling it.
The controlled-depth blind vias are a great option. However, it requires that the holes are big enough. Regardless of the benefits, it might not be the best option in some cases.
Laser-drilled blind vias
These vias are usually created after laminating the PCB. However, this must happen before the PCB outer layer goes through etching and lamination. These days, there are several types of laser used to create the holes. However, the results are still the same.
Photo-defined blind vias
These vias’ creation requires the lamination of a photosensitive resin to a core. Also, the photosensitive sheets will feature a pattern that shows where to make the holes. After this, the designer exposed the board to light. This makes the remaining material on the PCB to harden. The board is then inserted in an etching solution. This gets rid of the material from the created holes. The PCB manufacturer then creates the PCB outer layer after plating copper in the hole.
Sequential-lamination blind vias
The creations of these vias require a piece of very thin laminate. Also, the creation process is similar to that of a two-sided PCB. Therefore, this method makes elements in the side that will create the board’s second layer. There will be a copper sheet on the other side. Then, this will form the first layer. The sequential-lamination method is rarely used since it is very expensive.
Important Considerations about PCB Vias
It is important to put these considerations in mind when choosing a via type.
A via is very short, but it could cause issues with tight signal integrity requirements. For example a thru-hole via that links the top two layers in a ten layer PCB will feature 8 layers of metal in it. Therefore, these layers of unnecessary metal could result in interference.
Also, it is crucial to identify problems like these and solve them. The solution is to eliminate the unused metal before it functions as an antenna. In this case, you will need some PCB design tools such as Cadence Allegro. This tool will help to detect the problem before manufacturing the board.
Some manufacturers create a standard via with a mechanical drill. However, it is crucial to understand that the smallest drill size depends on the thickness of the PCB. Also, mechanical drills are limited by how much material they can drill. Therefore, this depends on the relationship of the PCB thickness to drill size. For drill sizes, PCB manufacturers always demand for an aspect ratio not greater than 10:1.
When routing the dense area of a PCB, the designer must ensure that these areas don’t block routing channels. This can occur under dense areas such as high pin-count BGAs. Therefore, the use of blind vias becomes crucial in helping the BGA escape. This will help to route every pin. However, it is crucial routing planes and channels don’t block off under the part.
When choosing a via, you should consider its size. Manufacturers must ensure that there is a large annular ring after drilling the via. Also, a mechanical drill may wander during drilling. Therefore, a large annular ring will prevent drill breakout.
Roles of Vias in a PCB
Vias are very useful in PCB design and production. They offer a path for thermal and electrical energy to transmit within layers on your PCB. Vias are very important in multilayer PCBs.
Enhance signals and power transmission
Vias help to enhance signals and power transmission between PCB layers. However, you can route PCB components on a single plane if you are not considering vias.
Increase trace density
Vias increase the density of trace in multi-layered PCBs. This is because vias can run over and beneath each other in several directions. Vias enable different traces to connect with each other. Therefore, they function as vertical connection factors.
Distribute thermal and electrical energy
Vias create a path for the flow of thermal and electrical energy within layers on a board. The more energy discharged by an IC, the more vias needed.
Applications of Blind Vias PCB
Blind vias serve some purposes when used in circuit boards. It is crucial to know that you can reduce your PCB layers by enhancing the ball-grid channel. This is possible by making blind vias. Also, blind vias are applicable when it is difficult to penetrate through-hole vias for trace breakout of BGA. You can maximize the getaway channels on the internal layers and then reduce layers with blind vias.
Furthermore, blind vias can help to minimize the aspect ratio of your circuit board. PCB BGA components feature various pitches. For instance, a 400mm radius board has 127mm and 0.8mm pitch BGAs.
Blind vias are useful in high-density interconnect boards or HDIs. HDIs are well-known since they provide enhanced power delivery. With the use of blind vias, the board will be lighter and smaller. Therefore, this is helpful in designing electronics. Blind vias PCBs are widely used in medical devices, cell phones, and other small electronics.
Blind vias are very helpful. However, they can increase the cost of the PCB. This is because they require additional procedures. Also, these vias require additional testing and manufacturing procedures. Therefore, blind vias PCB are useful when it is ideally necessary.
Circuit boards can be very crowded at times. Therefore, it becomes complex to connect essential components to both sides. The blind vias is the best way to attach the necessary components to a PCB board.
Adding blind vias to your PCB is a great choice. However, not all PCBs require blind vias. Therefore, a good knowledge about blind vias and how to use them is important. This article has shed more light on blind vias and their impact on PCB functioning.