PCB Assembly

SMT Assembly vs. Through-Hole Assembly: Their Pros and Cons

difference between SMT and PTH assembly

As you know, once fabricated, PCBs (printed circuit boards) can be assembled using either one of the two technologies, i.e. SMT assembly and through-hole assembly, or using a combination of both. However, you may wonder how these two technologies differ from each other and which one you should opt for. In this case, check the comprehensive guide prepared by the experts at Viasion describing the two technologies and their pros and cons. This quick guide will help you understand the subject better to make the best decision for your next PCB-based project.

What is SMT Assembly?

PCB assembly is a step based on PCB bare board which is fabricated as designed. Similar to this concept, SMT assembly (Surface Mount Technology)  is the process of mounting some parts on the surface of the bare PCB using specific auxiliary apparatus. These components are solidified in their patch positions by melted solder paste with the help of reflow soldering ovens. Engineers carry out various inspections to ensure the final assembled PCB is devoid of any flaws or errors. Let’s learn more about the knowledge of PCB SMT assembly.

What is Through-Hole Assembly?

Unlike the SMT technique, the components are not mounted directly in this case. Instead, holes are first drilled in the PCB board, in which the leads of the components are inserted for connections. PTH or through-hole assembly process is comparatively more time-consuming and costly than SMT due to the extra steps involved. SMT technique is a newer technology, and it is faster, cheaper, and more efficient than PTH. SMT makes people think that the PTH is no longer required for assembly. However, the through-hole assembly technique continued to stay in demand due to its various benefits over SMT technology. Continue reading to understand the difference between the two technologies.

What is the difference between SMT and PTH assembly techniques?

The key difference between the two assembly processes is the drilling of holes. As mentioned earlier, SMT does not require the drilling of holes, whereas PTH cannot be carried out in the lack of drilling. This makes SMT a faster process but the extra steps of hole drilling, plating of holes, component lead insertion, etc. involved in PTH are more time-consuming.

The fewer steps in SMT assembly have also helped reduce the processing and handling costs. However, PTH is still quite in demand as many components cannot be mounted via SMT assembly, therefore, through-hole assembly is used for them. While SMT is more efficient, the PTH process can increase the durability of the PCBs. Devices that require high reliability are made with PCBs with stronger connections between layers. To achieve this, through-hole components are the best suited.

On the other hand, for small-sized electronic devices, SMT assembly is usually opted because SMT components are much smaller in size compared to PTH components. Additionally, a higher component density can be achieved via SMT, which further helps increase the functionality of the device without increasing its size.

In short, both SMT and PTH assembly have their benefits and drawbacks. Which assembly technique would be more suitable for a PCB depends upon the requirements of the electronic device. Below, their pros and cons are explained in detail for your better understanding.

The SMT assembly

Pros of SMT Assembly

SMT assembly process is quite sought-after for PCB fabrication due to its various benefits, such as low costs, assembly speed, high reliability and so on. Some of them are listed below:

  1. This technology allows automation as a pick-and-place machine can help carry out most of the process. This reduces the need for manual labor and thus, reduces the overall costs. Additionally, automation speeds up the assembly process.
  2. SMT also allows the assembly of small-sized components (surface mount devices or SMDs) that do not require a large-sized board for mounting purposes. This helps fabricate lightweight and portable PCBs.
  3. Since SMDs are quite small in size, a large number of them can be mounted on one PCB. Therefore, a high component density can be achieved by the SMT assembly process. This is especially useful for manufacturing small devices, like the handheld ones.
  4. Unlike through-hole technology, SMT does not require the drilling of holes and lead forming, which are quite time-consuming processes. These processes are not only more difficult to carry out but also add to the cost of the entire PCB. Thus, SMT assembly is much faster, simpler and cheaper than the PTH method.
  5. SMDs are less prone to vibration and shock as compared to their through-hole counterparts. This increases the reliability of a PCB fabricated with SMT technology.
  6. SMT assembly technique allows the combining of other assembly techniques. In other words, mixed technology PCBs that require a combination of both SMDs and through-hole components can be fabricated by using SMT along with PTH technology on the same PCB.

Cons of SMT Assembly

This assembly process is not 100% foolproof and has some disadvantages. However, an informed decision and a team of expert technicians can help avoid any losses due to these drawbacks. So, consult Viasion Technology Co. Ltd. professionals to understand how you can make the most of your money.

  1. Since the components are soldered directly, these soldered joints may be affected under extreme temperature or pressure conditions. Therefore, the technique is usually avoided to assemble PCBs for the devices that are expected to heat up too much.
  2. The SMT assembly process requires state-of-the-art equipment and trained staff. This requires a considerable investment of money.
  3. If the equipment is not programmed correctly or if the staff is not trained well, a lot of errors may occur in the PCB assembly. Solder-bridging, electrical opens, “tombstoning”, solder balling, and de-wetting are some of the common errors.
  4. Numerous joints and miniaturization may increase the difficulty in carrying out manufacturing and inspections.
  5. The strength of the solder joints is also subject to mechanical stress, therefore, a PCB SMT assembly is comparatively less reliable than a through-hole assembly.
  6. For small circuit prototyping or testing, SMT assembly processes are not suitable. This is because component switching or replacement is not possible in this assembly type. Engineers would need to assemble an entirely new PCB to test other combinations and design possibilities.
  7. Since SMDs are quite small in size, it becomes challenging to identify in case of repairing the PCB.
  8. Some components are not suited for SMT Assembly. As you know, pick-and-place machines are used to carry out the SMT assembly process. Many components are not suited for this automated technique, therefore, they require either PTH assembly or manual assembly.
  • Such components cannot withstand extreme temperatures because the SMT process includes conveying through the reflow soldering oven. These components may get damaged when exposed to extreme temperatures in the reflow oven.
  • Heavier components or the components with connector leads that require sturdier joints are better to not mount via surface mount technology.
  • While most SMDs are small, lightweight and delicate, too-light components may not be possible to assemble via SMT assembly. This is because an adequate mass-to-adherence ratio is required for this automated technology.

The PTH assembly

Pros of Through-Hole Assembly

Through-hole assembly technique (PTH) is an older technology than SMT. However, it is still prevalent and could not be completely replaced by the latter due to its distinct features. Below are some of them.

  1. As mentioned earlier, PCBs assembled via the PTH assembly process are more durable than those assembled by SMT assembly. This is because the connections made using component leads are sturdier and can withstand environmental stress better. Therefore, through-hole assemblies can resist extreme heat and pressure conditions. This makes them the go-to choice for devices used in defense and space applications.
  2. Heavier, large-in-size and bulkier components that cannot be mounted using the SMT process require through-hole technology for their assembly.
  3. Component connections made with leads are easier to replace and adjust. This simplifies the process of repair and replacement. Specialized equipment is not required to replace any component as they can be mounted simply with a soldering iron.
  4. Since the parts assembled by PTH are interchangeable, the through-hole assembly process is the go-to choice for prototyping and small circuit testing. It is also preferred for easy manual operations.
  5. PTH PCB assemblies have better power handling as the bonds between the board and the components are quite strong, which allows the PCB to handle high power and voltage easily without the risk of circuit failure.

Cons of Through-Hole Assembly

As every coin has two sides, this immensely beneficial assembly technology – PTH, also comes with some drawbacks. Find them below.

  1. The extra steps involved in the through-hole assembly process, like drilling and plating, make it more time-consuming. Therefore, the manufacturing and production efficiency is low in this case.
  2. Drilling holes and component connections require more space compared to the surface mounting technique. Therefore, small or miniature PCBs cannot be assembled via this process. PTH assembly boards are generally larger, which makes them unsuitable for small-sized devices.
  3. The component density is lower in through-hole assemblies due to the large-sized components and lead connection process.
  4. While the ease of manual operations makes it the preferred choice for many applications, the same feature increases the turn time and chances of human error. Skilled staff is required to carry out this assembly process.
  5. Like the SMT assembly process has a high chance of errors, through-hole assembly processes have a high risk of damage to the components. This is because the lead insertion process is tricky and may lead to bent or broken leads.

The SMT and PTH assembly

How to Select the Right Assembly Process for Your Project?

Both SMT and through-hole technology are extensively used in various applications ranging from consumer applications to defense and space industries. You may wonder if the two technologies have such drawbacks then how they are used in such crucial applications. This is because PCB engineers study the requirements of a device in detail and then choose a technology that best suits the device’s requirements. They use the right components and take necessary measures to avoid drawbacks like chances of error and damaged components. To determine which process is the right choice for a project, engineers consider points like:

  • The scale of the project
  • Device application
  • If the device is made for prototyping purposes
  • The components to be mounted
  • Size of the device
  • External and environmental conditions the device is expected to be exposed to
  • Reliability and durability needs
  • Budget and expected turn-time
  • Component density required
  • Device power handling capacity

In many cases, a combination of both technologies is employed to minimize the drawbacks and increase the advantages. So, talking to industry experts and hiring experienced professionals can make the most of your investment, considering the above-mentioned criteria. If you want to know more about the SMT assembly and through-hole assembly processes, get in touch with us today!

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