The use of PCBs is common in a wide range of electronic devices. These include smartphones, laptops, tablets, and more. However, modern PCBs come with multiple layers for better signaling and routing. These multiple layers are connected through tiny holes called vias. This term stands for “Vertical Interconnect Access.” However, there are different via types in PCB designs. These tiny holes, or vias, differ from one another in many respects. In this article, I will discuss the basics of vias and their types in PCB design. So, let’s get started.
What Is a Via in a PCB?
Before discussing types, let’s first understand the basics of a via.
A via in PCBs is a small drilled hole present in its layers. These holes are useful to connect multiple layers stacked vertically. The holes are plated with copper to ensure they connect the layers electrically. This way, the signal (electrical) can pass through these holes to stabilize the connections. Without these holes, layers won’t connect.
In the old days, PCBs were simple with fewer connections, so they did not need multiple layers. Such larger PCBs were used only on larger devices. However, things have changed as modern PCBs require more connections. Instead of keeping all the connections on one surface, manufacturers use multiple layers, which makes life easier.
These connections are distributed across these layers, which reduces the size of PCBs as the layers are vertical to each other. If the connection were on the surface, it would make the PCB bigger and less organized. The holes are drilled in these layers so they connect. These tiny holes allow the passing of electrical signals for the working of these connections.
The wires (traces) remain more organized thanks to these tiny holes, ensuring an optimized PCB design. One of the standout advantages of vias is that signal propagation through these holes is very fast. This makes devices work more efficiently irrespective of device size. Remember, modern PCBs are more efficient and compact, making them easy to use in small electronic devices.
Different Via Types in PCB Design
As I said above, there are different types of vias. Each of these via types has its own specifications and use cases. In the section below, I will explore these types.
1- Through-Hole Via
A through-hole via is one of the most common types used in budget-friendly PCBs. In this type, a drilled hole is made across all the layers of PCBs. This means all the layers are electrically connected through this hole. This makes routing a lot easier and more consistent. The electrical signal from the top layer reaches the bottom layer through these conductive tiny holes. One of the standout advantages of through-hole vias is their affordability. You will see this in most budget-friendly PCBs.
2- Buried Via
As the name suggests, these vias are buried in the inner layer of the PCBs. The top and bottom don’t have these vias. Manufacturers typically prefer buried vias when they want to connect between internal layers. The holes are conductive, which means they can pass the signal efficiently. By using buried vias, you achieve higher routing density and save space. Manufacturers typically keep the traces and other components on the top layers. Unlike through-hole vias, buried vias are more complex and more costly to manufacture.
3- Blind Via
Blind vias are the type that connect the top layer to the layer present under it. It can also be used to connect the bottom layer to the layer above it. Simply put, this via starts from the visible part (top or bottom) and stops inside the layer. It can also connect the top layer to more than one layer present under it. However, this type of via does not extend to the last layer. So, it is not used in the internal layers of the via. This means the internal layers remain unused and their spaces can be used for different components.
4- Microvia
Microvia is one of the most common types of vias, meaning these holes are very small. They are generally laser-drilled with a size of around 0.05 mm – 0.15 mm (50–150 µm). This smaller size makes them ideal for use on higher-density PCBs. These tiny holes connect adjacent layers and take very little space. That’s why they are preferred for making compact PCBs for smaller devices. These microvias also provide higher routing density, a significant advantage.
Additionally, the speed of electrical signals passing through these holes is also very high. However, the high cost of microvias is a drawback. Remember, these microvias are also used in HDI (High-Density Interconnect) PCBs.
5- Stacked Microvia
Stacked microvias are a type of microvia placed over one another. This placement makes them look stacked. Interestingly, each microvia in this type connects from one layer to another. This way, the stacked microvias create a path by connecting one layer to another. This connection goes to the deeper layer, which creates a continuous path. Since the microvias are stacked, they take very little space. As a result, the components can be positioned close together within these layers, thereby improving the PCB’s compactness.
6- Staggered Microvia
Staggered microvias are a type of microvia, but they are not stacked on top of each other. In contrast, these vias are present in an offset pattern. Each microvia connects to an adjacent layer. However, these vias make a zig-zag pattern when connecting different layers. These vias are not in a single line or path. Due to the zig-zag pattern, the stress is distributed more evenly.
It is worth noting that staggered microvias are more space-consuming than stacked microvias. The reason is that these vias are in a zig-zag pattern, which goes vertically. Due to this spread-out arrangement, they take up more space, which is a drawback. However, the cost of these staggered microvias is not too high.
7- Filled Via
A filled via is a type of PCB via whose hole is filled with a special material. It means, unlike a normal via, which has an open hole, a filled via has no space inside. This filling material is either conductive or non-conductive, which mainly depends on the PCB model. After the hole is filled, the surface is usually made flat.
This flat surface makes it easier to attach other components. Moreover, because the surface is flat, manufacturers can place tiny components directly over the via. There is no need to worry that solder will flow into the hole during assembly. That’s why filled vias are mostly used in small and advanced PCBs, where every bit of space matters.
8- Via Stitching vs Via Tenting
Via stitching and via tenting are two different PCB techniques that serve different purposes. Via stitching means placing many vias close together. It improves electrical connections, reduces electrical noise, and helps heat spread across the PCB. Via tenting, on the other hand, refers to covering the opening of a via with a layer of solder mask.
This method is what protects the via from dust, moisture, and unwanted solder during assembly. As a result, the PCB becomes more reliable, clean, and safe. There is no doubt both methods are useful; however, they are chosen for different needs. PCB designers often use both techniques in the same PCB to improve its performance, reliability, and protection.
Conclusion
PCBs are among the most important components of modern devices. Today, these PCBs come with multiple layers to increase efficiency and reliability. However, these layers are not connected by chance. Instead, small holes are present that help attach different layers. Those holes are known as vias. But not all the vias are the same.
In this guide, I have discussed some common types of PCB vias, and you can see that each type varies in its purpose and design. Understanding how each type works makes it easier to create a board that performs well and lasts longer. Remember, there is no single via that is best for every PCB. The final right choice depends on your circuit, available space, performance needs, and budget.