There are several parts and components that play important roles in the functionality of a circuit board. The PCB via is an example of these parts. In electronic devices, a tiny green board transmits different signals. Vias serve as the building blocks of a PCB design.
For example, a PCB is available inside a smartphone with different components and chips that perform signals for several features and commands. Every time you touch the screen, one of the signals on the board is immediately activated. Vias perform most of these signals.
In this article, we will be talking about the roles of vias in PCBs. Also, we will talk about types like blind and buried vias.
What is a Via?
A via is a metallic hole that connects to the circuitry of a circuit board. This hole carries out electrical signals between the various layers of a PCB. Also, vias are holes that go through board layers for the sole purpose of conductivity. Every hole serves as a conductive pathway through which electrical signals transmit between circuit layers.
Vias pass through several levels on a PCB. The board design will determine if the hole will pass through all the layers from top to bottom. Some vias only penetrate the top or bottom layer. Some vias go through an inner layer. Vias are a crucial part of a circuit board. Therefore, PCB designers and manufacturers need to understand their roles perfectly.
Furthermore, a blind via serves as an electrical connection between layers in a multilayer board. The use of vias for connection in this board makes it easy to minimize PCB size. Also, manufacturers make the via hole conductive by placing copper cylinders in the drilled holes. Then they fill the inner layer of the via with a non-conductive material.
To define vias, one must understand the types available. Also, blind and buried vias are very crucial. Also, blind and buried vias are widely used. This is because blind and buried vias offer great benefits. Also, blind and buried vias are widely preferred among PCB manufacturers.
What are the Types of Vias?
There are different types of vias. However, the two main categories of vias depending on their position in the board layers are buried and buried vias. Blind or buried vias are commonly found in circuit boards
Blind via
A blind via is a hole that penetrates the bottom or top layer of a PCB. However, a blind via stops before any internal layers. Also, you can’t see through blind vias when you hold a PCB to the light. It is just like a hidden via. Manufacturers drill and electroplate blind vias from the bottom or top layer to an internal layer.
Drilling in blind vias can be mechanical or laser. Also, you have to be accurate with the drilling depth of the blind via. Also, you can drill blind via on the PCB directly. However, it could be very difficult to drill a blind via. That is the major reason most PCB manufacturers try not to use blind via.
Manufacturers create holes on the required PCB layers and pile up these layers to drill blind vias and electroplate. Also, a blind via helps to connect the PCB’s surface layer to the next layer.
Buried via
A buried via can connect the inner layer of a PCB. Also, it is ideal for circuit boards with dense routing. Manufacturers drill and electroplate these holes between the inner layers of the PCB. Also, buried vias help to link the circuit between the inner layers.
You can drill buried vias directly on the PCB, if it connects more than three inner layers. Therefore, the manufacturer can drill the holes only on the required PCB inner layers. Also, you can’t see the buried vias in the inner layers with the naked eye.
Other Types of Vias
There are other types of vias based on their location.
Through-hole
Through hole vias are the most obvious via type. These vias penetrate all the layers in a multilayer PCB. These holes are bigger than that of blind and buried vias. It is much easier to identify this type of via with the naked eye. When you hold a PCB with a via before the light, you will see the via. Also, the light will pierce through it.
Also, through holes vias are very easy to create. All you need to do is drill right through all the layers. Manufacturers use through hole vias for plated through holes technology.
Microvias
Vias which are under 150 microns are microvias. These vias are widely used on several high density interconnect (HDI) PCBs. Also, microvias are highly preferred because of their small hole size. The size of the hole takes less space on the circuit board. In this type of via, the layer connects to one another with copper plating.
Furthermore, it is easy to copper plate microvias. This is because they are in the shape of a cone. Aso, a microvia is capable of passing through two adjacent layers. However, it can’t go further. If a board design needs a via through several layers, you will need to stack multiple microvias accordingly.
Via-in-Pad
This is one of the most popular vias today. Via-in-Pad involves using vias on ball grid array (BGA) pads. Here, the manufacturer places the vias on the BGA pads of the circuit board. Also, this design has gained more popularity because it reduces the amount of space needed for vias.
Therefore, this via enables a PCB manufacturer to design smaller PCBs that demand for less space.
Benefits of Vias
Both buried vias and blind vias have their benefits. Also, other types of vias have their advantages. The technology of printed circuit boards will determine the type of via to use.
Signal routing
Vias help to enhance signal routing in printed circuit boards. Most printed circuit boards use blind or buried vias for denser boards. Also, microvias are ideal for much denser boards.
Power routing
Vias are widely used for ground and power nets. These vias will carry more current. Also, they are always restricted to bigger through-hole vias.
Trace density
Vias increase trace density in multiple layers boards. This is because you can run vias beneath and over each other in several directions. Vias enable different traces to connect with each other. Therefore, vias serve as vertical connection factors.
Signal transmissions
Vias help to enhance signal and power transmission between layers. For instance, blind vias can help to effectively transmit signals between layers in a board. You will need to route PCB components on a single plane if you don’t want to integrate vias.
Considerations for Creating Vias
There are tips that help you create good vias for PCB design. It would be of great help if you integrate maximum via structures in a PCB design. Below are considerations to keep in mind when creating PCB vias.
Signal integrity
Vias can cause signal integrity problems if it is not well created. For example, A through hole via connecting the top two layers in an eight layer PCB will have 6 layer pcb of unnecessary metal. This unnecessary metal can result in interference. Therefore, it is crucial to detect problems like these and find solutions to them. You can back drill the via to get rid of the unused metal from the line. Photo defined areas can also affect signal integrity.
The board thickness will determine the acceptable drill size when using mechanical drills. Also, a mechanical drill has a limit to how far they can penetrate through before they are unreliable. PCB manufacturers always demand an aspect ratio of 10:1 for their drill sizes.
The aspect ratio is an important consideration in designing vias. Also, you can use microvias with an aspect ratio of 1:1 if you need a smaller hole. Smaller holes require a smaller aspect ratio.
Routing density
In cases where you are routing the dense areas of a board, ensure you don’t use vias to block up the ground plane return paths. Also, this could occur under dense parts such as pin-count BGAs where hundred vias are in a small area. The outer layers and hole depth can enhance routing density.
Annular ring
The via pad size is crucial. Ensure large annular ring remains after drilling the via. Also, a sufficient annular ring will keep the via in check. Without enough annular ring, a drill breakout may compromise the via.
Design Tips for Vias
Here are PCB design tip for creating vias:
- Make use of smaller vias particularly in HDI boards. This helps to reduce stray inductance and capacitance.
- Use controlled depth for blind vias and buried vias.
- Ensure you fill via-in-pads unless they are within thermal pads.
- Ensure a minimum aspect ratio for high-speed vias to prevent signal reflections. Therefore, this offers better signal integrity and electrical performance.
- You can use blind vias and through hole vias for some pad arrangement on a BGA.
- Use staggered vias rather than stacked vias. This is because you will need to fill and planarize stacked vias.
- Also, use vias in the thermal pads under QFNs to allow the flow of solder to conductive planes. Thermal vias offer secure solder joints for thermal pads. Therefore, prevent the solder from floating the package during PCB assembly.
- Check the hole diameter and fine pitch BGA components for via-in-pad.
- Also, check the copper foils and component leads.
- Ensure you check the outer layer. The outer layer helps to create a good via
- Check the blind via for any irregularities
Conclusion
Vias create pathways for the flow of thermal and electrical current between different layers in a board. Also, these vias vary in type and size. The requirement of a circuit board determines the type and size of vias to use. Also, vias help to enhance signal integrity in circuit boards.
Annular rings and multilayer lamination are important in the entire board. Also, copper pad and surface components are crucial in designing vias. Multiple vias and signal traces are widely used in PCBs. The outer layers are also important
