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Through-hole electronics assembly: A guide to what it is, how it works, the benefits and applications

3 March, 2021

What is through-hole electronics assembly?

Through-hole assembly, also known as conventional assembly, is the process in which pin-through hole (PTH) components are inserted through holes that are drilled into printed circuit boards (PCBs) and then soldered to the pads on the opposite side, either by flow solder machine or by hand soldering. This process then completes the circuit.

Considered a linchpin of the electronics assembly industry for many years, through-hole manufacturing technology replaced early electronics assembly techniques such as point-to-point construction.

It grew in popularity during the 1950s through its use in the second generation of computers, with every component on a typical PCB being a through-hole component, before making way for surface-mount technology (SMT) in the late 1980s.

While SMT is still the most widely used PCB assembly process, through-hole electronics assembly is by no means losing its appeal and is still very much used in modern electronics to deliver electrical connections from one layer to another, including breakout boards and header pins.

What components make up through-hole electronics assembly?

There are two types of components that are responsible for the correct set-up of the through-hole assembly: axial and radial leads. Elongated box-shaped axial components have wire leads protruding from both ends, whereas radial have wire leads that come out and form the parallel of the circuit board. Multiple lead devices can also be made, with the use of semiconductor packages needed.

The axial and radial components are particularly beneficial during testing and prototyping phases where manual adjustments and replacements are often required. Each type can be converted into the other by bending the leads to replicate the other’s form.

What are the benefits of through-hole electronics assembly?

Knowing when to use through-hole manufacturing for your application is pivotal. Making the wrong choice will have a negative knock-on effect on your PCB assembly process – in terms of both efficiency and cost – and will also compromise the level of your application’s quality and performance.

Through-hole mounting provides many benefits, a key feature being it offers strong mechanical bonds, as the components are soldered on the circuit board either manually or by machine, enabling the solder to flow through the boards to bind together more effectively. This enhanced level of durability makes through-hole manufacturing ideal for bulkier components such as electrolytic capacitors or semiconductors in large packages where extra mounting strength is needed to cope with physical stress. It is also relatively inexpensive and has a high heat tolerance.

In industries where reliability and security are paramount, such as the aerospace and defence sectors, through-hole technology is the preferred assembly method for manufacturers so as to endure harsh environments where force, collisions and extreme temperatures are commonplace.

When should I use through-hole electronics assembly?

Knowing which applications through-hole electronics assembly is suited to is important, as this will enable you to determine whether it is the best solution. The below checklist offers a simple way to clarify whether it is the right electronics assembly method for your needs, with through-hole assembly being used in applications which are subjected to:

  • High voltage
  • Extreme temperature, hot and cold
  • High stress, either mechanical or environmental
  • Testing and prototyping
  • High speed operation

Ask the experts

While this guide offers an overview of through-hole assembly and its use, it is always best to seek the advice and expertise of your PCB assembly partner, as they will possess the correct know-how and insight to assist you with your requirements. Your PCB assembly partner will also be able to take into account any other potential factors that may result in an alternative solution to accurately meet your technology needs.

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