PTH assemblies: when tradition is still the smartest choice

There is a natural tendency in the electronics industry to assume that technological progress automatically renders what came before it obsolete. SMT revolutionised electronics manufacturing, made miniaturisation possible, accelerated production cycles and opened doors that once seemed firmly shut. All of that is true. And yet, anyone who genuinely understands industrial electronics knows that the story is never quite so straightforward.

PTH assemblies, based on Pin Through Hole technology, remain a deliberate, considered choice and are frequently the most intelligent option available. Not out of sentiment, but for concrete technical reasons that no subsequent innovation has yet managed to surpass.

What PTH assemblies are and how they differ from SMT

PTH technology involves inserting electronic components through drilled holes in the printed circuit board, with the component leads soldered on the opposite side of the board. It is a well-established technique, predating SMT, which uses the physical structure of the PCB to create a genuine mechanical anchor between the component and the substrate.

SMT, by contrast, mounts components directly onto the surface of the printed circuit board, without any drilled holes. This allows for considerably smaller dimensions, an exceptionally high component density and a highly automated production process. For many applications, particularly in consumer electronics and high-integration precision electronics, SMT is simply the right answer.

There are contexts, however, in which the mechanical connection offered by PTH is not a secondary detail. It is the primary requirement.

When PTH is the more robust choice

Industrial electronics routinely operates under conditions that consumer electronics never has to contend with. Continuous vibration, mechanical shock, extreme thermal cycling, high currents: these factors fundamentally change the criteria by which technology is selected.

Environments with vibration and mechanical stress

In an industrial machine, an electric motor, a motion system or a production plant, vibration is a constant presence. Components mounted on the surface using SMT are anchored solely through their solder pads: a reliable connection under static conditions, but potentially vulnerable when mechanical stress is sustained over a prolonged period.

PTH components, on the other hand, pass physically through the board. That connection does not rely solely on the solder joint, but on the entire mechanical path the lead takes through the substrate. In environments subject to vibration, this makes a measurable difference.

High-current connectors

Power connectors, input terminals and components managing high currents benefit enormously from through-hole technology. The larger cross-section of the lead, the mechanical anchoring to the board and the greater thermal mass available make PTH assemblies significantly better suited to these components than SMT, which often cannot offer the mechanical robustness or the dissipation capacity required.

High-voltage applications

In high-voltage applications, the creepage and clearance distances between conductors become a critical parameter. Through-hole components, which tend to be physically larger and designed with more generous isolation specifications, lend themselves naturally to these requirements. PTH makes it possible to maintain the necessary distances without compromising the integrity of the design.

The process: manual insertion and selective soldering

One of the aspects that distinguishes the production of PTH assemblies from SMT is the process itself. Whilst SMT lends itself to near-total automation, PTH often calls for a more involved approach.

Manual component insertion remains widespread practice, particularly for large components, specialist connectors or production runs where flexibility matters more than speed. In this context, the skill of the operator and the quality of the inspection and control processes become determining factors.

Selective soldering, meanwhile, represents the modern evolution of the PTH process: a technology that allows only the necessary points to be soldered with precision, integrating PTH assemblies into mixed production lines where boards carry both through-hole and SMT components. This hybrid approach is now very common in industrial electronics, where design rarely confines itself to a single technology.

PTH assemblies within the broader context of electronic and electromechanical assemblies

In modern manufacturing, electronic boards rarely exist in isolation. They form part of more complex assemblies that integrate mechanical components, cabling, connectors and supporting structures. In this setting, the concept of electronic and electromechanical assemblies describes precisely the production reality of those who manufacture, for instance, controls for industrial machinery, automation systems or human-machine interfaces.

In these environments, the robustness of PTH assemblies fits naturally with the nature of the end product: a system that must operate reliably for years, in uncontrolled conditions, with limited maintenance and high expectations of longevity.

Those who commission or design contract electronics for industrial applications understand this requirement well. The objective is not to select the most modern technology, but the most appropriate one. And more often than not, the most appropriate technology is PTH.

A hybrid approach: the reality of modern production

It would be an oversimplification to present PTH and SMT as competing alternatives. The reality is that the two technologies complement one another, and the best designs draw on both in the right measure.

A board for an industrial electronic control might carry microcontrollers and passive components mounted in SMT, taking advantage of the density and production efficiency that surface mount affords, whilst power connectors, relays and components subject to significant mechanical or thermal stress are handled using through-hole technology. The result is a design that is not ideologically committed to one approach, but engineered around what each part of the circuit actually demands.

This is the kind of thinking that characterises serious contract electronics manufacturing: the ability to read the application, understand its operating environment and make technology choices that serve the product rather than follow convention.

PTH assemblies are not a legacy. They are a tool, and like any good tool, their value lies entirely in knowing when and how to use them.