High-density interconnects (HDI) PCB designs require the use of specialized vias to achieve the required levels of density and performance. The holes in printed circuit boards known as PCB vias are used for electrical connections between various PCB layers, mounting PTH components, and connections with external components (screws, connectors, etc.). There are a variety of types of vias available for PCB design, each with its own advantages and disadvantages. Selecting the best type of via and stackup type for high-density interconnect (HDI) PCB design requires careful consideration.
Let’s explore more about PCB vias, their types, and the best type to choose depending on HDI PCB design requirements.
What is a Via in PCB Design?
Vias are holes drilled through the layers of a printed circuit board to increase conductivity. Each hole serves as a conductor for the transfer of electrical signals between circuit layers. An electrical connection is made in the insulating material separating the PCB layers by filling the hole from the inside with copper (either through a galvanic process, riveting, or the insertion of a short tube of conductive material).
An electronic board might need some vias which connect all the layers of the stackup, just one of the two outer layers, or just two or more inside PCB layers depending on the particular requirements of the application.
Different types of vias in PCB
Even though all of these distinct via types have the same basic function, some PCB designs will benefit more from one via type than others. This article discusses the many via types used in printed circuit board design and how each one might help with electrical connections.
Through-hole vias are the most prevalent and straightforward PCB vias. Drilled through-hole vias connect the top layer of the PCB to the bottom layer.
PTH (plating through-hole with copper pads) and NPTH (non-plating through-hole without copper pads) vias are the two primary types of through-holes. When connecting electrically or mechanically with screws or connectors to fix the PCB, PTH vias are used for PTH assembly, whereas NPTH is utilized for mechanical connections.
However, the design of staggered vias is more difficult, they are less expensive to produce than stacked vias. This is due to the fact that stacked vias require far less precision and therefore do not overlap when creating multiple PCB layers.
In order to connect circuits across three or more circuit layers on separate PCB layers, stacked vias might be either blind or buried vias. Stacked vias are simpler to design than staggered vias, but they cost more to produce. This is due to the fact that holes on various layers must be drilled in the same location, and when the layers are combined, the holes create completely stacked vias with such a flat hole wall. Additionally, the PCB manufacturer must be extremely precise.
A copper-plated hole known as a buried via combines two or more internal layers of the circuit board and is inaccessible from the outside layers. This is not ever observable from the outside as it is often located inside the printed circuit board. Consequently, it is known as a buried via. In contrast to the blind via, a buried via cannot be easily drilled on the PCB whether it connects three or more inner layers. Only the necessary PCB layers can be used by the PCB manufacturer, who must then stack them together to electroplate the hole wall.
It is possible for holes-to-connect to overlap or not while drilling and stacking different PCB layers to create blind vias or buried vias. Both overlapping vias and staggered vias are a result of this variance in PCB via types.
An external layer of a multi-layer High-Density Interconnect PCB is connected to an inner layer by the use of this type of vias, which involves using a drill or laser to create a hole. Drilled and electroplated blind vias connect an internal layer of the PCB to the top or bottom layer.
When looking at the blind via the PCB towards the light, we cannot see the opposite side through the hole. It is challenging to construct and expensive to use this kind of via.
Drilling depth accuracy is necessary for blind vias. Direct drilling of blind vias on the PCB is possible although it is challenging. Electroplating is also made complicated by this. The essential circuit board layers are often drilled with holes by modern PCB manufacturers, who instead stack the layers to form blind vias and electroplate them.
A PCB via is known as a skip via is one that pierces many circuit layers without creating an electrical connection with any of the layers. It might be a buried via, a blind via, or an overlapping via.
It is the thinnest laser-drilled vias or holes, fewer than 150 microns in diameter. It just passes through two PCB circuit layers. Microvias are most typically utilized in HDI PCBs. They typically connect one layer of the PCB to its neighboring layer and have a considerably small diameter compared to physically drilled vias like through holes.
Drilling a microvia into a PCB external layer can create a blind via while drilling one into a PCB internal layer later can create a buried via. When connected by wires and are not overlapping, staggered vias are created when microvias on various PCB layers overlap with one another, they form overlapping vias.
Which Type Is the Right Choice for Your HDI PCB Stackup?
The structure of the board could have a laminated core with one or more layers that contain Microvias. These layers may be present on both sides or just one. Bling and PTH vias are allowed but buried vias are not allowed according to the Type I standard.
Use thin FR-4 dielectrics, which could shatter in high temperatures, of the overall number of layers. It can be necessary to solder without lead. For reliability, the length-to-hole-diameter ratio could be crucial. Always strive to keep it around 10 for the plated through-hole.
This form of via can be used on a laminated core and includes buried, blind, and Microvias. The sidewalls also require the placement of one or more Microvias layers. Although they don’t have to be on both sides, at least one of them must be present. Manufacturers may decide to stack or stagger them based on the buried vias, or they may decide to sway Microvias from other vias.
This approach, according to experts, is far more suitable for high-density boards. However, the same limitations that apply to the Type I method apply here as well. Microvias may only be positioned on exterior layers. This suggests some limitations for particular uses.
The main difference between Type II and Type III is that this method requires the addition of two or more Microvia layers to the sides. Along with buried, blind, and Micro vias, there are also Microvias on a laminated core. The layout of this Stackup can be used well for high-density PCBs with several layers.
The main advantage of Type III is the use of the outer layers for power and the ground plane. This can be accomplished by including Microvias in the inner layers and ensuring that there are adequate layers for signal routing. For even greater routing density, you can even employ stacked vias if you’re ready to spend more money.
High-Density Interconnect Printed Circuit Boards (HDI PCBs) are becoming increasingly popular and are able to achieve smaller form factors due to the integration of technologies such as microvias, blind vias, buried vias, and built-up. However, knowing the connection between surface routing and route to and through planes is necessary for effective routing. Therefore, having a high-end manufacturer will help you maintain optimal performance and reliability, and achieve effective routing.
Additionally, we at Vadzo are very comfortable with HDI PCB based designs enabling us to provide compact camera solutions with additional features. We also have the capability to customize our cameras to suit different mechanical requirements. We can refine your designs and determine the tolerances necessary for you to modify the HDI PCB designs. Furthermore, this is accomplished without affecting its suitability for your specific application. Our experts shall be glad to address any queries you have. We are delighted to assist you with the requirements your project must meet.
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