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When laying out a printed circuit board, one of the first things to consider is the type of components. Whether you’re planning to use surface mount or through hole technology, it largely depends on the PCB’s application and electrical requirements.
It’s also possible to vary the configurations of common component types such as capacitators, resistors and diodes to influence the appearance and size of the PCB. So, what is the best option?
Through-hole PCB
Through-hole technology (THT) was the most common manufacturing technique for many years. Components with long leads were inserted, often by hand, into the plated through holes of each PCB. These leads were then soldered in place to interconnect the holes permanently.
Through-hole assembly was standard practice until the 1980s, when it was anticipated that it may start to die out due to the rise of new technology. However, it has proved resilient and is still used today, as manufacturers have recognised it still has a valuable role to play in PCB assembly.
What is surface mount technology?
PCB designers often use the more modern technique of surface mount assembly today. Widely known as surface mount technology or SMT, this method utilises components with leads that attach to the surface of the PCB only, so there’s no need for a hole.
Almost all modern electronic hardware is manufactured with SMT, which is crucial to the performance of today’s high-quality electronics. In addition, surface mount PCB assembly has reduced the processing and handling costs significantly.
Surface mount vs through hole assembly
The majority of today’s electronic hardware is manufactured using surface mount technology, which has become a vital part of PCB design.
The main difference between surface mount and through hole assembly is the fact SMT boards don’t need to have holes drilled through them – through-hole assembly process involves drilling holes through the PCBs, making the process longer and more costly.
SMT components are significantly smaller and can be mounted on both sides of the board. This means many more components can be fitted onto a surface mount printed circuit board, enabling more compact, yet higher performing PCBs to be created.
Through-hole component leads pass through the board to connect its layers. With SMT assembly, they are replaced by small components known as “vias” to enable a conductive connection between the different layers.
Advantages of surface mount technology
Surface mount technology allows for smaller printed circuit boards with higher component density. Some components of surface mount PCBs are higher performing, with more interconnection pins and shorter leads that permit higher speeds.
As a result of fewer drilling holes being required, the costs are lower and the production line faster. The SMT components can be added at a rate of thousands per hour, compared with less than a thousand per hour for through hole mount.
In addition, the solder joint formation is more reliable, and it’s easily repeatable by using programmed reflow ovens.
SMT has performed better and been more stable in shake and vibration conditions. This method has improved the performance and quality of PCBs overall. It has also reduced the costs of processing and handling.
It is commonly used for consumer electronics, telecommunications, medical devices and industrial control systems.
Advantages of through-hole mounting
Through-hole technology has remained resilient because it offers a number of advantages, including niche applications and reliability. Through hole components are often used for products which need particularly strong connections between layers.
Secured by leads that run through the PCB, this enables the components to withstand more stress than SMT boards. For this reason, through-hole technology is often used in aerospace and military products that may be prone to high temperatures, extreme acceleration or collisions.
It is also commonly used in prototyping and test applications that may require manual adjustments and replacements.
The THM assembly process is more expensive, and time consuming because of the need to drill holes and soldering on both sides of the PCB. This method also limits the available routing area on multi-layer boards, as the drilled holes need to pass through all the layers.
In conclusion, while through-hole’s popularity as a means of PCB assembly has undeniably declined in recent years, it’s a misconception that it will ever disappear from use altogether. Surface mounting will almost always prove more cost-effective than through-hole mounting and research suggests it is used in more than 90% of PCBs today. However, certain applications will continue to require THM assembly well into the future.