What is a via PCB and why is it important on printed circuit boards? A PCB requires vias or drilled holes to connect its layers. Knowing the standard via sizes used by PCB manufacturers can help you design your board to meet the needs of common drill sizes.
PCB manufacturers have their own set of standard through-hole sizes to choose from when drilling, but they can usually use any standard drill size. Typically, PCB manufacturers can make PCB vias as small as 0.15 mm in diameter, compared to the common size of 0.6 mm.
The size of a PCB through hole can vary depending on its location, usage, and other factors, which is why each PCB manufacturer offers several PCB drill bit sizes. Most manufacturers can make holes as small as 0.15 mm or larger as 1 mm or larger. When considering the size of the hole you need, you also need to consider the annular ring, or copper pad that surrounds the drilled hole, it will form.
How do you count the torus? The ideal annular ring is equal to the diameter of the copper pad minus the sum of the drill diameter divided by 2, which gives the drill the best chance of hitting the center of the pad for best connectivity.
There is not necessarily any standard PCB through-hole size in PCB manufacturing, as PCB standard through-hole sizes tend to vary from manufacturer to PCB manufacturer. However, many PCB manufacturers prefer to use commonly used drill sizes, which they may refer to as standard PCB drill sizes. One of the most common sizes is 0.6mm, but 0.2mm and 0.3mm are also commonly used.
PCB via type
You can use each standard via size to create various types of PCB vias, depending on the layers, construction, design and purpose of the PCB. The three most common types of PCB vias are:
Plated Through Hole
A plated through hole (PTH) is a via that penetrates through all layers of a PCB to connect the top and bottom layers. You should be able to see the PTH from one end of the PCB to the other. PTH can be plated or non-plated. A non-plated through hole is not conductive while a plated through hole is plated, which means it is conductive in all layers of the PCB.
Blind hole
Blind vias connect an outer layer (top or bottom layer) of a PCB to one or more inner layers, but do not drill completely through the board. Precise drilling of blind vias can be challenging, so blind vias are typically more expensive to manufacture than PTHs.
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Buried vias also add to the cost of the PCB due to their difficulty in manufacturing. This type of via is located in the inner layers of the PCB to connect two or more inner layers. You can't see buried stuff on the outer layers of the PCB.
things to consider
During the process of creating a PCB, there are a few things to consider. First, you should understand what is aspect ratio in PCB design. The aspect ratio is the thickness of the PCB relative to the diameter of the via hole, which determines the reliability of the copper plating on the PCB. The higher the ratio, the more difficult it is to get reliable plating, which affects your choice of via type and plating method.
Buried or blind vias will likely serve your PCB better with a 15:1 aspect ratio, while PTHs will work well with a lower 2:1 aspect ratio. How do you choose the thickness of PCB copper? Typically, vias in outer layers, such as vias, require a thicker copper layer than internal buried vias. The voltage used by the PCB also affects the thickness of the copper. High voltage applications typically require thicker PCB copper than low voltage applications.
through the filler
There are times when PCB via holes need to be filled, for example to reduce the risk of air entrapment or to increase conductivity. Some common methods of filling vias include:
through the tent
Via tenting creates a solder mask over the PCB vias instead of filling the holes with material. This can be a quick, easy, and cost-effective option for covering vias, but tented vias may reopen over time.
by clogging
The via plugging process fills the holes with a non-conductive material and seals them with a mask. Via plugging also covers the annular ring and does not result in a smooth, clean finish.
by filling
Via filling uses resin to create a permanently filled hole. Via filling is a common type of via filling in which the manufacturer fills the via with a conductive material, coats the surface with copper, and then modifies the surface. This process can route signals to other areas of the PCB.
PCB through-hole plating application
Manufacturers may use several different techniques to apply PCBs with through-hole plating to ensure their effectiveness. A common approach is to use a low viscosity ink that coats the inside of the via to form a conductive layer. The ink is then bonded through a heat curing process.
Another method is electroplating, where the PCB goes into an electroplating bath. During this process, copper is drawn through the vias and covers the walls of each PCB, resulting in a uniform thickness of conductive material. This method tends to be more lengthy and expensive than the inking process, but it also results in a more reliable coating and bond.
Sequential Drilling Blind Holes vs. Depth Drilling
There are two manufacturing methods for PCBs with blind vias. This can be done by laser drilling or by a method called successive layer building. Using a sequential build approach, pairs of layers are drilled and plated before bonding is applied. Since they have holes at both ends, electroplating is easy for electroless plating to penetrate the holes. It also allows blind vias to be designed in such a way that they can pass through multiple layers.
The ability to combine proper bonding, drilling and plating sequences makes it possible to create multiple blind via structures. It all depends on whether the blind vias can go through the even layers starting from the outer layers.
Simultaneous deep drilling or back drilling is the process of removing any unused copper barrel remnants from the vias. This typically occurs when high-speed signals are distorted as they travel through copper tubing between PCB layers. If the use of signal layers results in long stubs, then there will be a lot of distortion.
The PCB aspect ratio is defined as the ratio of the board thickness to the diameter of the drilled via. Blind vias require an aspect ratio of 1 to 1 or greater.
When deep drilling, the depth of the hole is defined by setting a drill pair detailing the start and end layers from that side of the plank. Calculate the drill diameter for deep drilling with the following formula:
Backdrill Size = Hole/Pad Hole Size + 2 x Design Rule Backdrill Oversized
PCB over-inductance calculator
PCB via inductance depends on several factors, including via size, annular ring size, aspect ratio, and drilling accuracy. You can find online calculators to help you figure out the proper PCB based on the dimensions you need to use.
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