What is a through-hole PCB and why is it important on printed circuit board? A PCB requires through-holes or boreholes to connect its layers. Understanding the standard through-hole sizes used by PCB manufacturers can help you design boards to meet common bit sizes.

Standard through hole size

PCB manufacturers have their own set of standard hole sizes to choose from when drilling holes, but they can usually use any standard hole size. In general, PCB manufacturers can make the diameter of PCB through holes as small as 0.15 mm, compared to the normal size of 0.6 mm.

PCB through-hole size requirements

This is an in-depth study of the size requirements.

PCB through hole size

The size of a PCB through hole can vary depending on its location, use, and other factors, which is why every PCB manufacturer offers several PCB bit sizes. Most manufacturers can make holes as small as 0.15 mm or larger holes of 1 mm or larger. When considering the size of the hole required, you also need to consider the ring or copper pad around the hole, which will form.

How do you calculate rings? The ideal ring is equal to the sum of the diameter of the copper pad minus the diameter of the drill hole divided by 2, which gives the rig the best chance of hitting the center of the pad for optimal connectivity.

Standard through hole size

There is not necessarily any standard PCB through-hole size in PCB manufacturing, as the standard PCB through-hole size often varies from manufacturer to PCB manufacturer. However, many PCB manufacturers prefer to use common bit sizes, which they may refer to as standard PCB bit sizes. One of the most common sizes is 0.6 mm, but 0.2 mm and 0.3 mm are also commonly used.

Type of PCB through hole

You can use each standard through-hole size to create various types of PCB through-holes, depending on the layer, construction, design, and purpose of the PCB. The three most common PCB through-hole types are:

Plated through hole

Electroplated through-holes (PTH) are through-holes that run through all layers of a PCB to connect the top and bottom layers. You should be able to see PTH from one end of the PCB to the other. PTH may be plated or non-plated. Non-plated through holes do not conduct electricity, whereas plated through holes are electroplated, which means that they conduct electricity in all layers of the PCB.

Blind hole

Blind holes connect the outer (top or bottom) layers of the PCB to one or more inner layers, but do not completely drill through the board. Precise drilling of blind holes can be challenging, so they are typically more expensive to manufacture than PTH.

embedded

Embedded holes can also increase the cost of PCB because they are difficult to manufacture. The holes are located in the inner layer of the PCB to connect two or more inner layers. You can’t see the buried material on the PCB’s outer layer.

Things to consider

There are a few things to consider when creating a PCB. First, you should know what aspect ratio is in PCB design. The aspect ratio is the PCB thickness relative to the diameter of the through hole, which determines the reliability of the copper plating on the PCB. The higher the ratio, the more difficult it is to obtain reliable plating, which affects the type of hole and plating method you choose.

Embedded or blind holes may serve your PCB better with an aspect ratio of 15:1, while PTH can work well with a low aspect ratio of 2:1. How do you choose the thickness of PCB copper? Usually, through holes in the outer layer (e.g., through holes) require a thicker layer of copper than the buried through holes inside. 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.

By filling program

Sometimes PCB through-holes need to be filled, for example to reduce the risk of trapping air or increase electrical conductivity. Some common ways to fill through holes include:

Through the tent

The through-hole tent creates a solder barrier layer over the PCB through-hole rather than filling the hole with material. This can be a quick, easy and cost-effective option to cover the through-holes, but the tent-style through-holes may reopen over time.

By blocking

The through-hole plugging process fills the hole with non-conductive material and seals it with a mask. Through-hole clogging also covers the ring and does not produce a smooth, glossy surface.

By filling

Through-hole filling uses resin to create a permanently filled hole. A through-hole fill is a common through-hole fill in which the manufacturer fills the through-hole with conductive material, coats the surface with copper, and then trims the surface. This process can route signals to other areas of the PCB.

PCB through hole plating applications

Manufacturers may use several different techniques to apply the PCB via through-hole plating to ensure its effectiveness. One common method is to use a low viscosity ink that covers the inside of the through-hole to form a conductive layer. Then through the heat curing process to bond the ink.

Another method is electroplating, in which the PCB goes into an electroplating bath. In this process, copper covers the walls of each PCB through holes, resulting in an even thickness of the conductive material. This method tends to be more lengthy and expensive than the inking process, but it can also form a more reliable coating and bond.

Sequential drilling blind drilling and deep drilling

PCBS with blind holes can be manufactured in two ways. This can be done by laser drilling or by a method called continuous layer construction. Using the sequential construction method, pairs of layers can be drilled and electroplated before bonding is applied. Because they have holes at both ends, electroplating is easy to penetrate for chemical coatings. It also allows blind holes to be designed in such a way that they can pass through multiple layers.

The ability to combine appropriate bonding, drilling and plating sequences makes it possible to create multiple blind hole structures. It all depends on whether the blind hole can pass through even layers from the outer layer.

Simultaneous deep drilling or reverse drilling is the process of removing any unused copper drum residue from the through hole. This usually happens when high-speed signals are distorted as they pass through copper tubes between PCB layers. If using a signal layer results in long transversals, there will be a lot of distortion.

PCB aspect ratio is defined as the ratio of the plate thickness to the diameter of the borehole. Blind holes require aspect ratios of 1 to 1 or greater.

When deep drilling is carried out, the depth of the hole is defined by setting up a pair of holes that specify the starting and ending layers from the side of the board. The bit diameter for deep drilling is calculated by the following formula:

Back drill size = Hole/pad hole size + 2 x Design rules Back drill size is too large

PCB overinductance calculator

PCB through-hole inductance depends on several factors, including through-hole size, ring size, aspect ratio, and drilling accuracy. You can find online calculators to help you calculate the right PCB according to the size you need to use.