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Installation Technologies for Critical Applications: THT and OFA in PCB Assembly

Installation Technologies for Critical Applications: THT and OFA in PCB Assembly

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PCB Assembly has evolved significantly since the emergence of Surface Mount Technology (SMT) and Surface Mount Devices (SMD) in the 1970s, followed by rapid development in the 1980s. Initially, there was a widespread expectation that SMT would completely replace the traditional method of Through Hole Technology (THT), where components are mounted through holes in printed circuit boards (PCBs), primarily due to the elimination of these holes. However, THT, also known as “pin mounting,” which revolutionized early electronic circuit assembly, has maintained its relevance in specialized applications. Recently, there has been renewed interest in equipment tailored for the installation of THT components.

This article delves into the characteristics, advantages, and disadvantages of various printed circuit board installation methods. Before exploring these methods, it is crucial to clarify the terminology, as different terms are used to describe these techniques today, sometimes leading to confusion or debate.

Understanding PCB Assembly

There are two primary technologies in PCB assembly: Through-Hole Technology (THT), also known as “pin mounting,” and Surface Mount Technology (SMT). In THT, components are inserted through holes in the PCB and soldered in place, traditionally utilizing axial and radial orientations for components like resistors and capacitors. In contrast, SMT involves attaching components directly onto the PCB surface using solder paste, followed by heating in convection or infrared ovens to achieve a secure bond between components and the board.

Additionally, it’s important to distinguish terms like “volumetric mounting,” which encompasses non-planar methods outside of SMT, and “mounted mounting,” referring to chassis-based installations with wire connections rather than PCBs. The term “DIP” originally denoted chips with a dual-row leg arrangement but has since become ambiguous. Therefore, using “DIP” broadly for any pin mounting is considered inaccurate.

A notable advancement is Odd Form Assembly (OFA), which involves installing irregularly shaped or non-standard components into holes on the PCB. Unlike traditional THT, OFA allows for more versatile component placements, accommodating axial, radial, and various other configurations such as connectors, screens, chokes, and switches. This versatility reflects current trends where OFA technology is increasingly preferred for diverse applications, although classic THT methods still persist, notably in sectors like LED screen manufacturing.

THT And OFA In PCB Assembly

Through-Hole Technology (THT)

Definition and Process

Through-Hole Technology (THT) is a traditional method where component leads are inserted into drilled holes on the PCB and soldered in place. This technique ensures strong mechanical bonds, making it suitable for high-reliability applications.

Advantages of THT

  • Durability: High resistance to mechanical stress due to large soldering areas.
  • Component Replacement: Easy replacement of components during testing or prototyping.
  • Mechanical Strength: Suitable for components like connectors that require frequent connections and disconnections.

Limitations of THT

  • Size Constraints: Limited miniaturization potential due to the need for through-holes.
  • Routing Restrictions: Through-holes can restrict conductor routing on multilayer PCBs.
  • Multiple Cycles: Requires both reflow and selective soldering processes for mixed assemblies.

Odd Form Assembly (OFA)

Definition and Process

Odd Form Assembly (OFA) refers to the installation of non-standard shaped components into PCB holes, extending the principles of THT. OFA is increasingly used with specialized equipment capable of handling various pin components.

Advantages of OFA

  • Versatility: Capable of mounting various non-standard components.
  • Reliability: Ideal for harsh environments requiring high durability, such as aerospace and military applications.

Limitations of OFA

  • Complexity: Requires sophisticated machinery and precise handling.
  • Cost: Higher setup and operational costs compared to standard SMT processes.
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As a matter of fact, as we see, pin mounting technology (THT, OFA) has not disappeared anywhere and is still used as one of the main ones in electronic assembly. This provides additional incentives for assembly equipment manufacturers to develop automated installation solutions for these components that integrate into standard processes along with SMT technology. Let us recall that it was SMT that at one time made it possible to widely introduce automation of printed circuit board assembly, reduce costs, reduce assembly time (sometimes by an order of magnitude), and also reduce the dependence of product quality on the human factor.
Automated solutions for OFA processes must address not only the preparation and installation of the component, but also the system for delivering the component to the assembly area in the required technological packaging, and at the initial stage this limited the spread of automation of the installation of non-standard components. However, large components with high thermal output are not intended for SMT in principle. In addition, THT and OFA printed circuit assemblies often outperform SMT in harsh environments (transportation, power electronics, etc.) that place high demands on reliability, resistance to shock, vibration, high temperatures, etc. .
Typical platforms for OFA installation is from the manufacturer JUKI. Depending on the tasks, the machines are equipped with various types of mechanical grippers (grippers): pneumatic, servo-driven, vacuum, as well as a dosing head, screwdriver, optical inspection camera, height measurement sensor and others in various combinations.

Automated PCB Assembly

Advancements in Automation

At the same time, the disadvantages of pin mounting are also associated with through holes in the printed circuit board (more precisely, with “through metallized holes in the printed circuit board,” as written in GOST R 53386-2009 “Printed boards. Terms and definitions”):
– impossibility of further miniaturization of the printed circuit assembly. Strictly speaking, this is not a disadvantage – rather a limitation, due to which pin mounting can be successfully used in large-scale instrument making, where miniaturization is irrelevant, but cannot be used for mounting a smartphone. However, we emphasize that it was the inability, due to the hole, to reduce the dimensions of mounted components that once became the main reason for the emergence of SMD technology. The driver of this process was computer technology, which was in dire need of miniaturization. Old computers took up a lot of space, sometimes several rooms, so technologies were required to reduce the size of the computer;
– also a disadvantage in particular cases is the restrictions on the routing of conductors on the printed circuit board due to through holes in multilayer boards;
– since now THT and OFA boards are often mixed, that is, made using SMD elements, the manufacturer has to perform several productive cycles for one board: both reflow soldering and selective soldering.
Despite these limitations, the installation of THT and OFA is still relevant. Several decades of use speak in its favor, thanks to which the assembly mechanism is well developed in both manual and automatic modes and there is a variety of assembly equipment and technological equipment.

Typical THT and OFA installation operations are:

– preparing the board for soldering. If the work is performed manually by installers, then this stage can be divided into two technical processes: first, the component leads are prepared, molded and trimmed, then manual installation is carried out (“filling” in professional jargon), after which the board is ready for soldering. If the machine is working, then both the preparation of the board and the installation of the elements occur inside the mounting platform within the framework of a single technical process;
– soldering, which, again, can be carried out either manually or in group automatic soldering mode. The latter can be performed by the so-called solder wave, when molten solder in a special bath creates a continuous flow – a wave, washing the lower part of the printed circuit board with installed lead components. The solder wets the pads and leads of the components and works its way up through the holes to form solder joints. This technology processes absolutely all components on the board, unless special pallets are used to protect certain areas of the underside of the board. Another type of automatic soldering is selective . In this case, we can talk about mini-wave soldering: a small “nozzle” approaches each pin separately and solders it in accordance with the mode specified by the program. This mechanism is reminiscent of hand soldering.

Soldering Techniques in PCB Assembly

Manual Soldering Machine

If we return to manual soldering, it should be noted that the methods of this process have been honed over decades of practice, and in addition, recently a lot of digital soldering equipment has appeared that makes manual labor easier. Nevertheless, it would be appropriate to mention three factors. Firstly, with manual soldering, the human factor plays a big role, or more precisely, the possibility of human error during a technological operation. Secondly, the factor of increasing costs for manual labor, which always tends to rise in price, is important. The third significant factor is the search for personnel with the required level of qualifications (especially considering that sometimes this level has to be maintained when working in several shifts). Many manufacturers are faced with a shortage of workers with the necessary training to manually solder complex products, as well as the reluctance of young people to work in these specialties. This is understandable; a young specialist is much more interested in programming a soldering robot or even several such pieces of equipment. In recent years, this factor has become increasingly significant, so when choosing the degree of use of manual labor or automation, it must be taken into account.
VI-Soldering Robot SR250DD ~VI_副本
VI-Wave Soldering Acrab350 ~VI_副本
VI-I.C.T Selective Wave Soldering Machine SS550P2~vi.png

Soldering Robot

Soldering robots are even closer to the manual labor of installers in their functionality and capabilities . Today they are widespread throughout the world and are gaining popularity in our country. They have 4 or more degrees of freedom, are equipped with a 3-, 4-coordinate Cartesian movement system in combination with a rotating head on a vertical axis on which the soldering iron is mounted. Compact dimensions that allow the robot to be installed on a standard installer’s workbench, a soldering point training system as a standard function, video monitoring using an installed camera, an automatic solder wire feed control system, selection of an effective trajectory of the soldering iron tip, stability of the soldering modes used, the ability to use soldering equipment in a nitrogen environment, reliable repeatability of operations – all this results in predictability and guarantee of the quality of the manufactured product. Interested in I.C.T-SR530 Soldering Robot

Soldering Robot 01
Soldering Robot 02
Soldering Robot 03

Wave Soldering Machine

You know how in wave soldering, PCBs are passed over a wave of molten solder to ensure all those through-hole components are soldered evenly? It’s like giving the board a smooth, consistent bath in solder, which is perfect for high-volume production lines. This method is efficient and reliable, ensuring a strong connection between components and the PCB. However, it’s primarily suited for assemblies where all components can withstand the same high-temperature soldering process. If you’re working with a mix of component types that have different heat tolerances, you might need to consider other soldering methods. Learn about I.C.T best-selling Acrab350

Wave Soldering Machine 01
Wave Soldering Machine 02
Wave Soldering Machine 03

Selective Soldering Machine

Now, let’s talk about selective soldering. This machine is all about precision. Instead of dipping the entire PCB, it lets you pinpoint exactly where each solder joint needs to go, whether it’s for SMT components on the surface or THT components through holes. This makes it ideal for assemblies that require a delicate touch or have components with varying thermal sensitivities. By selectively applying solder only where needed, it reduces the risk of overheating sensitive parts and ensures a high-quality, reliable solder joint. It’s a bit slower than wave soldering because it works on specific areas, but it offers unmatched control and flexibility for intricate PCB assemblies. Learn more about I.C.T-SS-550P2

On-line-Selective-Wave-Soldering-SS540~SP 01
On-line-Selective-Wave-Soldering-SS540~SP 02
On-line-Selective-Wave-Soldering-SS540~SP 03

Conclusion

THT and OFA continue to play vital roles in PCB Assembly, particularly for applications demanding high reliability and mechanical strength. While SMT dominates consumer electronics, the resilience and versatility of THT and OFA ensure their ongoing relevance in specialized fields. Automated PCB Assembly solutions further enhance the efficiency and precision of these technologies, cementing their importance in the evolving landscape of PCB Manufacturing.

Along with the standard ones, less common technologies can be noted, the so-called transitional ones on the way to surface mounting. For example, the “pin in paste” (PIP) technology, also known as “Through Hole Reflow” (THR), which involves preliminary application of solder paste into the through holes of the board and then pushing the pin through the hole (and paste). Thus, solder paste is pre-applied (as in SMT) and at the same time pin mounting is used, increasing the strength of the connection. The soldering process is performed in ovens – the same as SMT, but with more stringent restrictions so that molten solder does not leak out of the mounting holes.

All the technologies discussed in the article are well known to the team of specialists at I.C.T, which has been successfully operating for more than 24 years in the market of assembly and installation equipment for the electronics industry and related fields and has accumulated a colossal base of knowledge, skills and relationships with suppliers.

As the official distributor of world leading equipment manufacturers, I.C.T offers reliable machines and tools for automatic installation of the highest standards of quality and reliability at the best prices. At the same time, the company carefully monitors the latest developments in the field of electronic technologies, components, equipment, constantly being in development and expanding the range of services provided.

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