Introduction and use of PCB TH through holes

Introduction and use of PCB TH through holes

What is a through hole?

A Through Hole (TH) is a hole by various names - through, through, through, plated through, etc. - A through hole (TH) is a hole in a PCB that can be drilled, reamed, or milled all the way through. This means that if you guessed that the hole in the center of the image is TH, you are right. The holes on the left are blind holes and the holes on the right are interrupted holes.

The history of vias

From the 1950s to the 1980s SMT (Surface Mount Technology) developed rapidly, and through-hole technology was once dominant in electronic assembly technology. During this time, every component on the PCB is a through-hole component.

Since then, SMT has been widely adopted due to its advantages over TH components and changing technical requirements. However, TH is still a common method for passing electrical connections from one layer to another (think breakout boards and header pins).

The PCB initially had traces on one side, then on both sides, and later added multiple layers. A through hole or Plated Through Hole (PTH) is then designed to make contact with the conductive layer.

Through Hole Components

There are two types of components that fall into the TH category: axial components and radial components. There are wires on both ends of the axial assembly. Radial, on the other hand, has wires that protrude from the bottom of the device.

These types of components are especially useful during testing and prototyping phases where manual adjustments and replacements are common. Each type can be converted to the other by bending the leads to mimic the other

TH components can be installed manually or automatically by a plug-in installation machine. Both methods solder two leads to pads on opposite sides of the PCB. This process will then complete the circuit.

Whether through-holes are required

There are many reasons why SMT surpasses TH, but each method has its pros and cons. Let's take a look at the pros and cons of TH.

THs are a more convenient choice for hobbyists and engineers during the development phase because they are breadboard pinhole compatible and easy to replace. Components and circuits can be tested on a breadboard before upgrading to a PCB. Although they eat up space below the top layer, engineers often prefer larger vias when prototyping because it's easier to use on breadboards.

Through-hole mounting (THM) also provides a degree of reliability when subjected to ambient stress. Passing components through the board increases the strength of the physical connection. They can withstand more stress than SMDs and continue to operate efficiently. In fact, THM is widely used in aerospace and military products where boards and assemblies are required to withstand accelerations, impacts and extreme temperatures.

The ability of THMs to withstand mechanical stress also lends itself well to prototyping. For those who have to spend hundreds of dollars on a prototype board, the relative affordability of TH components is a small win for engineers and manufacturers. Sometimes you can't even choose between TH or SMD because not every component you need comes in SMD form.

However, there is a reason why SMT surpasses TH technology - there are multiple reasons indeed. Unfortunately, as mentioned before, TH takes up more board space and requires punching holes, which increases the cost of the PCB. Drilling also increases the time required to manufacture. Manually installing TH components is not as reliable as installing SMT components and is not an ideal prototyping situation.

Compact, high-speed and high-frequency designs have eliminated the TH in its heyday and replaced it with SMT, which is designed to meet the high demands of ever-changing technology. For many good reasons, SMT isn't going anywhere, but neither is TH technology. For some cases, choosing to use TH and TH components has more advantages than cost.