PCB fabricators have their own sets of standard via sizes to choose from when they drill, but they can generally use any standard drill size. Usually, a PCB fabricator can make PCB via holes as small as 0.15 mm with 0.6 mm a common size.
PCB Via Size
A PCB via size can vary depending on its positioning, purpose, and other factors, which is why each PCB manufacturer offers several PCB drill sizes. Most fabricators can create holes as small as 0.15 mm or larger holes of 1 mm or more. When considering the size of the hole you need, you also need to consider the annular ring, or the copper pad that surrounds the drilled hole, it will form.
How do you calculate the annular ring? The ideal annular ring equals the diameter of the copper pad minus the diameter of the drilled hole divided by two, which gives the drill the best chance of hitting the center of the pad for optimal connectivity.
Standard Via Sizes
There aren’t necessarily any standard PCB via sizes in PCB manufacturing because PCB standard via sizes tend to vary between manufacturers and PCB fabricators. However, there are commonly used drill sizes that many PCB manufacturers prefer to use, and they may refer to them as standard PCB drill sizes. One of the most common sizes is 0.6 mm, but 0.2 mm and 0.3 mm are also commonly used.
PCB Via Types
You can use each standard via size to create various types of PCB vias, depending on the PCB’s layers, construction, design, and purpose. Three of the most common PCB via types are:
1.Plating Through Hole
Plating through hole (PTH) is a via that travels through all layers of the PCB to connect the top and bottom layers. You should be able to see through a PTH from one end of the PCB to the other. A PTH can be either plated or non-plated. A non-plated through-hole has no conductivity, whereas a plated through-hole has plating, which means it’s conductive through all layers of the PCB.
2. Blind Via
A blind via connects an outer layer – either the top or bottom – of a PCB to one or more inner layers, but it does not get drilled completely through the board. Blind vias can be challenging to drill with precision, so they usually cost considerably more to make than a PTH.
3. Buried Via
A buried via can also increase the cost of a PCB because of its difficulty to create. This type of via sits within the inner layers of a PCB to connect two or more internal layers. You cannot see a buried via the outer layers of the PCB.
Via Filling Procedures
It’s sometimes necessary to fill PCB vias, such as lowering the risk of trapping air or increasing conductivity. Some common ways to fill vias include:
Via tenting creates a solder mask over the PCB via rather than filling the hole with material. This can be a quick, simple, and cost-effective option to cover a via, but it’s possible for tented vias to reopen over time.
2. Via Plugging
The via plugging process fills the hole with a non-conductive material and seals it with a mask. Via plugging also covers the annular ring and does not result in a smooth, finished surface.
Via filling creates a permanently filled hole using resin. A popular type of via fill is via-in-pad, in which the manufacturer fills the hole with a conductive material, plates the surface with copper, and smooths the surface for finishing. The process makes it possible to route signals to other areas of the PCB.
There are a few things to consider during the process of creating your PCB. First, you should learn what is aspect ratio in PCB design. Aspect ratio is the thickness of the PCB in relation to the via’s drilled hole diameter, and it determines the reliability of copper plating on a PCB. The higher the ratio, the more difficult it will be to get a reliable plating, which can influence the type of via and plating method you choose.
A buried or blind via might serve your PCB better with a high aspect ratio of 15:1, while PTH can work well with a low aspect ratio, like 2:1. How do you choose the thickness of PCB copper? Generally, vias in outer layers – like through-holes – need thicker copper layers than internal buried vias. The voltages used with your PCB will also influence copper thickness. High-voltage applications usually need thicker PCB copper than low-voltage applications.