SMT Vs. Through Hole PCBA Technologies Compared

surface mount PCB assembly
An example of a surface mount PCB assembly
Resource: https://forum.arduino.cc

Which, between SMT and THT PCB assembly methods is best for your project? This comparison of SMT vs. through hole PCBA technologies is designed to help you identify the best solution for your application. It provides an overview of both technologies before comparing them side by side.

SMT PCB Assembly

SMT PCB assembly is the most used PCB assembly methods today. According to a recent report by Future Market Insights, a research firm, the global surface mount technology market is expected to grow at a compound annual growth rate of 11.8% from 2022 to 2032. Here is what it is, how it works, and the steps that the SMT process involves.

What is SMT

SMT is an acronym that stands for Surface Mount Technology. It refers to the process where electronic components are mounted on the surface of a PCB instead of inserting them into pre-drilled holes in the board.

The components are soldered directly onto the circuit board’s flat copper pads or tracks, which eliminates the need for bulky leaded components or discrete wiring.

SMT components are smaller than traditional THT components, so their leads can be placed closer together. This, in turn, allows the components to be mounted on both sides of a PCB, creating a much denser population of parts per square inch (PPI).

SMT Process

The SMT process involves several steps, each of which must be performed correctly in order to ensure a successful outcome. These steps include solder paste application, component placement, soldering, inspection and testing, rework/repair and PCBA cleaning.

1. Solder paste is applied to the copper pads on the PCB. This paste helps hold the components in place during soldering and also serves as a thermal bridge between the component’s leads and the board.

2. The next step in the SMT process is component placement, which involves placing all of the components onto their corresponding pads on the board. Once this is done, the board is subjected to an automated soldering process.

This SMT mounting process involves subjecting the components and PCB to a high temperature for an extended period of time. The heat melts the solder paste, which binds the leads of each component to its corresponding copper pads on the board.

3. After soldering is complete, the assembly is inspected and tested to ensure that all components are properly soldered and functioning correctly. If any problems are found, they can be corrected through rework/repair.

4. Finally, the board is cleaned to remove any flux residue or other contaminants that may have been left behind during the soldering process. That completes the SMT PCB assembly process, and the board is now ready for use.

Plated through hole technology PCB
Plated through hole technology PCB
Resource: https://www.youtube.com/watch?v=hpR4e1n0HKo

Through Hole PCB Assembly

In contrast to SMT assembly, through hole PCB assembly involves mounting components into pre-drilled holes in the board and soldering them in place with wire leads. This technique is not as popular or widely used as it once was, but it can still be a viable option for certain PCB assembly projects.

What is Through Hole Technology?

Through hole technology (THT) is a PCB board assembly process in which components are attached to the board by inserting their leads into pre-drilled holes. These are then soldered in place using a combination of manual and/or automated processes.

Unlike SMT, which is surface mounted, through hole components are inserted into the board and their leads soldered from underneath.

This allows for potentially greater mechanical strength between the component and PCB since components can be held more firmly in place by the solder which binds them to the board.

Through Hole Technology Process

The through hole technology process uses a few steps to ensure components are correctly and securely attached to a PCB. These steps include placing the components onto the board, soldering them in place and inspecting/testing the finished assembly for proper functionality.

1. First, components are placed into their respective holes on the PCB. This is done manually by an operator or with a machine such as a pick-and-place robot. Once all of the components have been placed, they must be soldered in place.

2. This involves passing the board through a soldering machine in a process called wave soldering. This machine passes a wave of molten solder over the board, which binds the components in place. Other methods used for the THT soldering process include selective and manual.

3. After all of the THT components have been soldered to the board, it must be inspected and tested for proper functionality using an X-ray machine and other equipment. If any problems are found, they can be corrected. Once the assembly is complete, it is ready for use.

_PCB board ready for assembly
An example of a PCB board ready for assembly
Resource: https://hackaday.com

SMT Vs. Through Hole

After the overview of the difference between SMT and THT PCB assembly processes, it is clear that both have their advantages and disadvantages. Here, now, is a thorough comparison of the two technology processes.

SMT Vs. Through Hole: Speed

SMT is a surface-mount process that involves soldering components onto the board from the top side. This can be done manually or with automated machines.

The through hole technology process, on the other hand, involves inserting components into pre-drilled holes and soldering them in place from beneath. Again, this can be done manually or using computer-controlled machines.

Comparing the two technologies, it is clear that SMT has a significant advantage when it comes to speed. This is because it’s usually automated, making it faster and cheaper than through hole technology.

SMT Vs. Through Hole: Component Size and Weight

Most often, PCB components are best if they are as small as possible. In this regard, the advantages of SMT over through hole because components become evident, since its components can be made much smaller when surface mounted.

SMT components can be as small as 11/2 to 13 times those of similar through hole components. Additionally, surface mounted components tend to be much lighter, weighing about a 1/10th of THT parts. This makes them easier to handle and allows for a higher level of miniaturization in the design process.

SMT Vs. Through Hole: Cost Comparison

In terms of cost, the overall price of both surface mount and through hole technologies will depend on the complexity and size of the assembly as well as the number of components that need to be added.

However, generally speaking, SMT is more cost-effective than through hole because it requires smaller areas to assemble parts. Without the need for holes on the PCB, the process also offers lower costs overall.

SMT Vs. Through Hole: Reliability

In terms of reliability, through hole technology is often considered to be more reliable since the components are soldered from beneath, making them physically stronger than those that are surface mounted.

However, this does not necessarily mean that SMT components are unreliable. With proper design and assembly techniques, both surface mount and through-hole assemblies can be designed to have reliable long-term performance.

Besides, SMDs are usually smaller, lighter and have fewer contact points than through-hole components, which can make them more reliable in certain applications. Also, the two technologies are often combined to create a more reliable product.

Conclusion

It is clear that both SMT and through hole technologies have their place in PCB assembly processes. The right choice for any specific design will depend on the complexity of the product, as well as cost and reliability considerations.

In some cases, a combination of both techniques may be necessary to produce the desired results. Ultimately, the best choice for any given application will depend on an in-depth analysis and comparison of both processes.

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