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Through-hole PCB Assembly Process

What is a through-hole PCB assembly?

Through-hole PCB assembly is a method for producing electronic circuits in which the components are installed through leads. It refers to the mounting process that inserts the leads to the drilled holes and solders the components on the board by wave soldering or manual soldering.

Over time, PCB design moved from single-sided boards to double-sided boards, then came the multi-layer boards. Through-hole PCB assembly is difficult to meet the requirements of modern electronics. Nowadays, SMT technology has largely replaced through-hole construction in PCB manufacturing. But through-hole PCB assembly is still irreplaceable in some applications, such as electrolytic capacitors, connectors, and large transformers.

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The features of the through-hole PCB assembly

· High reliability

The through-hole assembly provides higher environmental stress because the components are held on the board by using leads inserting into the holes rather than simply being soldered on the PCBs’ surface as the SMT components. Thus, through-hole assembly offers a more robust physical connection, making it the preferred process for the military and aerospace industry that have high-reliability requirements.

· Easy for manual operation

Through-hole components are easier to replace or adjust their position, making this assembly method widely used in the applications that need PCB testing and PCB prototyping.

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· Higher durability

With high heat resistance and high-stress tolerance, through-hole components often appear in industrial machinery and equipment. Because through-hole LEDs are very bright and durable, you can find them in the LED lights on giant billboards.

· Lower manufacturing efficiency

Due to the extra step of drilling and hold the components using leads, through-hole PCB assembly is time-consuming, which causes higher costs and lower production efficiency.

· Limited PCB design

Through-hole PCB assembly is not suitable for multi-layer PCBs because drilled holes must cover all layers of the board, which increases the difficulty of layout design and PCB manufacturing. And the entire size of the board would also be bigger than SMT PCBs, causing their application area is more restricted.

With the rapid development of technology, some manufacturing methods have been gradually phased out. Old techniques like through-hole technology may have their limitations, but they still have some advantages over new technologies. Through-hole technology proved to have a lasting effect due to its reliability and strength.

Before the invention of the SMT ( Surface mount technology) all components were assembled to the PCB with leads going through component holes in the board.

This technology dominated the industry till the end of the eighties.

Today most components placed use SMT and are known as Surface Mount Devices (SMD) which are more efficient, cost effective and adapted to denser boards.

Based on this you could think that THT devices would be now outdated and not used anymore, as SMT is more efficient, cost effective and adapted to denser boards. However THT offers specific benefits that keep it relevant.

The bonds created between THT components and the board are far stronger than SMT bonds, making THT the ideal choice for components that will undergo mechanical and environmental stress or high heat.

In case of prototyping THT components are also easy to change, making them perfect for testing and hobby users.

There are disadvantages too.

Through hole components are much bigger and the component itself is on one side of the PCB but the solder joint is on the other side, so using space on both sides.

THT also restricts the available routing area on inner layers since the holes must be drilled through all the PCB layers.

THT Mounting

Before the invention of the SMT ( Surface Mount Technology) all components were assembled to the PCB with leads going through component holes in the board.

This technology dominated the industry till the end of the eighties.

Today most components placed are SMT components. You could think that THT (Through Hole Technology) is now outdated and not used anymore, as SMT is more efficient, cost effective and adapted to denser boards.

However THT offers specific benefits that keep it relevant.

The bonds created between THT components and the board are far stronger than SMT bonds, making THT the ideal choice for components that will undergo mechanical and environmental stress or high heat.

In case of prototyping THT components are also easy to change, making them perfect for testing and hobby users.

There are disadvantages too.

Through hole components are much bigger and the component itself is on one side but the solder joint is on the other side, so using space on both sides. THT also restricts the available routing area on inner layers since the holes must be drilled through all the PCB layers.

The THT assembly process is not automated, depends on the skills of the operators, is thus less reliable and more expensive than SMT.

Before placing the TH components we first cut the leads to the required size.

Some components need to be placed at a certain distance of the board. We use ‘spacers’ from plastic or metal to place the components at the desired height.

The spacers are fixed by soldering, screwing or snap-fitting.

Some components are not just fixed on top of the boards, but are mounted from the side.

These are called edge mounted connectors. Edge mounted connectors are mainly used for high frequency applications. They need special attention for design and also during the mounting process.

To combine the advantages of SMD and THT, some applications require mixed technology components.

Most common are USB connectors, that need to be mounted on dense boards with little free space, so optimal for SMT technology, but need a good mechanical stability, only possible with TH leads.


Through-hole PCB Assembly Process

Manual Insert line or Automatic Inserter➡Wave Soldering Machine or Selective Soldering Machine➡Out feed Conveyor

Manual Insert line can sit 2-3 workers, manually insert the THT components to the bare PCB, If THT components on the PCB is few, less than 20 kind, Can use manual insert line, use 7 workers to do this job, each worker insert 2-3 kind THT components.


If there's THT components more than 20 kind, it need use the automatic insert machine, there's 2 different kind THT component, one kind is horizontal component, another kind is vertical component, each kind component need different automatic inserter to put on the PCB. This process can use Panasonic horizon inserter or vertical inserter.



Then use the Wave Soldering Machine solder the THT component on the PCB, this process can use wave soldering machine or selective soldering machine, solder the THT component on the PCB.


After Soldering The THT component on the PCB, the pins of the THT component maybe come out too long from the PCB, it need use the foot cutting machine to cut the pins neatly at around 1.5mm-3mm.

Keywords:

PCB Assembly line, LED Production line, SMT Automatic Assembly line, Semi Automatic SMT Assembly line, JUKI Assembly Line, Samsung Assembly Line, Hanwha Assembly Line, Panasonic Assembly Line, Siemens Assembly Line, FUJI Assembly Line, Yamaha Assembly Line.

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