It is often difficult to mount all the connections required on a PCB to a single layer. The solution to this problem is to use vias. They are barrel shaped conductive holes that allow multi-layer connections across PCBs. Although there are several through holes, the most commonly used are two. These are blind vias and buried vias. We believe they can bring some benefits to people who use vias in PCB.
Close observation blind vias
Several different types of blind viass should be considered when checking blind viass and buried viass. There are photo defined blind viass, controllable depth blind viass, sequential lamination blind viass and laser drilling blind viass.
- A blind vias defined by light. The creation of optical definition blind vias needs to laminate photosensitive resin onto the core. There will be a pattern on the film indicating the area where the hole is to be made. It is then exposed to light to harden the remaining material on the board. The PCB is then put into an etching solution which removes material from the formed holes to form a channel. Then copper is plated on the hole and outer surface to form the outer layer of PCB.
- blind vias with controlled depth. The creation of depth controlled blind viass is very similar to that of through holes. The only difference is that the drill used for drilling has been set to only partially pass through the PCB. Modern technology makes it possible to do this precisely so that the features below the cargo hold do not come into contact with the drill bit. After drilling, it is copper plated. This is the cheapest option, but it does require the hole to be large enough to be drilled. Although this can meet many PCB requirements, it may not always be the right solution for everyone.
- The blind viass are laminated in sequence. The sequential lamination blind vias is made of a very thin laminate. This process is similar to creating a double-sided PCB, drilling, plating, and then etching on the laminate. This method creates elements on the side that will form the second layer of the board. On the other side is the copper sheet that forms the first layer. Then, the assembly is laminated with other layers of the board before completing the remaining steps to form a complete PCB. Today, this method is no longer used because it is expensive.
- Laser drilling blind vias. After the PCB is laminated, but before the outer layer is etched and laminated, the laser drilling blind vias is made. Today, there are many types of lasers used to make holes, but the results are the same.
Check the embedded hole carefully
When the via passes through the two inner layers of PCB but does not contact the surface on either side, it is called buried vias. The burying hole establishes the connection between the inner layers. As the name suggests, vias are actually “buried” in a PCB. The function of buried through holes is similar to blind viass, because the purpose is to ensure that the PCB has all the required functions. buried viass help to free up space in other areas of the board. To create buried vias, first create an inner layer with vias, and then add other layers to the outside to build the circuit board.
What is the difference between blind vias and buried vias?
The blind vias connects the outer layer of the plate to one of the inner layers. However, it can’t run through the whole PCB all the time. Buried vias are located on the plate and will connect the inner layer without reaching the outer layer. There is also a through hole that runs vertically through the entire circuit board and connects all layers. It’s a relatively simple concept, understandable, and can provide some excellent benefits.
Many advantages of blind vias and buried vias
Many PCB boards are very small, and space is limited, so blind vias and buried vias can provide more space and choice for the board. For example, buried vias will help to release space on the surface of the board without affecting surface components or routing on the top or bottom layer. blind viass can help free up some extra space. They are usually used for fine pitch BGA components. Since the blind vias only passes through a part of the board, this also means that the signal residue is reduced.
Although blind viass and buried vias can be used in a variety of PCBs, they are often most commonly used in high-density interconnect PCBs or HDI. HDI is popular because they can provide better power transmission and higher layer density. By using hidden vias, this will also help make the circuit board smaller and lighter, which is very useful when creating electronics. They are commonly used in medical devices, tablets, laptops, mobile phones and similar small electronic products.
Although blind viass and buried vias are helpful for those who need them, they can also increase the cost of PCB. This is due to the extra work required to add them to the board, as well as the testing and manufacturing required. This means that you should only use them when you really need them; you want to have a compact and efficient board.
How to build blind vias and buried vias?
Through holes can be made before or after multilayer lamination. blind viass and buried through holes are added to PCB by drilling, which is very unstable. It is important for the builder to know and understand the depth of the bit. If the hole is not deep enough, it may not provide a good connection. On the other hand, if the hole is too deep, it may reduce the signal quality or cause distortion. If any of these things happen, it will not be feasible.
In blind viass, a separate drilling file is needed to define the hole. The ratio of the hole diameter to the bit diameter must be equal to or less than one. The smaller the hole, the smaller the distance between the outer layer and the inner layer.
For buried viass, each hole needs to be made with a separate drilling file. This is because they are connected to different parts of the inner layer of the board. The ratio of hole depth to bit diameter will not be greater than 12. If it is larger than this diameter, other connections on the board may be touched.
We recommend PCB manufacturing with advanced circuits. This will help to ensure that the design and construction of circuit boards including blind viass and buried viass are feasible. Failure to prepare and cooperate with high quality PCB manufacturers may lead to increased costs.
Our experts have the tools and techniques to ensure proper drilling depth. We can ensure that there is no air residue in the PCB during this process. The plating will be applied correctly to connect the inner layer.