As more electronic devices become smarter, miniaturized, and interconnected, the importance of PCBs in them cannot be overstated. Printed circuit boards help to miniaturize the circuit while hosting most of the critical components, especially active ones, such as ICs. When assembling these components on the board, two key technologies are used: through-hole and surface mount. Let’s look at the differences between these two, as well as the best scenarios to use each one for your electronic product.
Differences Between Through-Hole and Surface-Mount Technologies
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Component Placement
Through-hole assembly literally requires holes to be drilled through the PCB, which gives the technology its name. As such, component placement in THT requires components with pin-like leads to push through the holes to the other side of the PCB where the solder pads are. The placement process here can be slightly complicated to achieve by machine so it might be automated or manual.
This is not the case with surface-mount technology. SMT refers to component mounting on the surface, meaning component placement is done directly on the soldering pads. SMD placement is easy to automate and uses pick-and-place machines, which makes the process faster than THT component placement.
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Soldering
THT component soldering is done on the opposite side of the component, where the leads protrude. The process is usually handled using wave soldering machines in mass assembly projects, where the wave touches the protruding leads as the PCB passes through on a conveyor.
On the other hand, SMT device soldering is done on the same side as the components. But first, a solder paste printer has to apply solder paste on the SMT pads using a stencil before component placement. Once the components are placed above this paste, the PCB heads into a reflow oven, which melts the solder to weld the parts to the board.
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Component Density
SMT devices are generally smaller than their THT counterparts because they don’t need large leads to insert through the board. Additionally, SMDs are designed to be compatible with automated production process machines, which can handle extremely tiny pieces. So they can be small, allowing you to fit more of them on the same real estate than THT parts to achieve a higher component density. The technology also supports double-sided PCB assembly, unlike THT which needs one blank side for the wave soldering process.
Through-hole technology also allows for double-sided assembly, but the bottom side must be soldered manually. But all in all, you’ll get a higher component density with surface-mount technology.
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Assembly Speed
SMT component assembly is faster primarily because the entire process is automated. THT parts assembly might require manual placement, which increases the assembly time and possibly human errors, which also take time to correct.
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Mechanical Strength
Using large leads that go through the boards might have its disadvantages, such as a larger size, but it shines on mechanical strength. Through-hole components are planted on the PCB, so they are strong enough to withstand extreme vibrations, mechanical stress, and harsh environmental conditions, such as temperature swings.
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PCB Weight
The larger THT components are also heavier than their SMT counterparts, which means the final PCB and electronic product will be heavier. Therefore, the former is more suitable for stationary devices while SMT is better for portable products. Think of desktop PCs vs. laptops.
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Assembly Cost
Since the entire process is easier to automate, SMT component assembly is cheaper, especially during high-volume production. The manual aspect required during THT assembly makes it costlier, but it might be the low-cost alternative during low-volume production. Hear me out. The machines that enable automation, such as pick-and-place, are expensive. The only way to justify their purchase is to handle high-volume production. So if doing PCB assembly or repairs as a hobby or in low quantities, THT is more cost-effective and even easier because the parts are large (simple to handle).
When To Choose THT or SMT
Through-hole technology is preferable when you want to assemble PCBs for industrial processes or machines where vibrations are extremely high. The strength of the mechanical joints between the components and PCBs makes the boards capable of withstanding such conditions while performing optimally and reliably. THT is also suitable for prototyping because the low-volume assembly costs are low.
SMT, on the other hand, is ideal for miniaturized electronics projects, such as implantables and wearables. Because SMDs are tiny, you can build high-density PCBs using this technology, which makes it possible to have miniaturized products with multiple functions. SMT is also ideal where cost-effectiveness is key during high-volume assembly.
Conclusion: Which Is the Best PCB Assembly Method For You?
Over 90% of PCBs assembled today use surface mount technology because it demonstrates more affordability, compactness, and efficiency during production. But this doesn’t mean it is the best technology for everyone. You have to look at your product’s requirements.
PCB fabricators and assemblers can assist with this technical task and advise you on the best way forward. Contact WellPCB or OurPCB to get free professional advice on the most suitable technology to use, as well as free quotes for your projects.
