While the through-hole assembly method may seem simple, the process requires precision and expertise to ensure high-quality, long-lasting connections. Despite the advent of surface mount technology (SMT), especially for applications requiring high mechanical strength and reliability under extreme conditions, through hole PCB assembly is still an essential part of in printed circuit board assembly process.

What is Through Hole PCB Assembly?

Through hole PCB assembly means through-hole parts are inserted into drills in the PCB and soldered from the bottom side of the PCB. Through-hole parts have a large length of leads to be soldered. The parts are soldered either manually or through the reflow oven. The parts need more space to be installed on the PCB, because they are large, like transformers, ICs, capacitors, and relay modules. So, most through-hole PCBs were designed as single layers only due to their size. Sometimes through-hole PCBs have both sides for component placement, but they need adjustment of all parts as per design.

For through-hole PCB assembly, drills are required to install THT parts on the PCB. so, leads are easily inserted in those holes for soldering. THT PCB assembly was an expensive method of PCB assembly, and it was also a time-consuming method compared to SMT assembly.

What is THT in Through Hole PCB Assembly?

In Printed Through-Hole assembly, THT is through-hole mount technology. Basically, it inserts the parts using its tails into holes on the PCB. And these leads are soldered onto the solder side of the board. After that, wave soldering is applied.

THT is the oldest technique for attaching PCB components. It’s used for axial lead parts like larger heatsinks, transformers, resistors, capacitors, etc. There are many components placed on PCBs using this PTH assembly technology, like connectors, edge-mount connectors, through-hole strips, etc. This Printed Through-Hole assembly technology is called hand mount technology because through-hole components are placed by hand. China through hole PCB assembly manufacturers are still using this technology in many PCB assembly.

Types of THT Parts Usded in Through Hole PCB Assembly

• Axial THT Parts

Axial THT parts in Through Hole PCB Assembly

In these parts, leads occur from the opposite side of the part. These are placed only in a horizontal direction.

• Radial THT Parts

Radial THT parts in Through Hole PCB Assembly

In these parts, all the leads are from one side to the component’s end. These parts are placed vertically or horizontally.

Process of Through Hole PCB Assembly

• Verify the Data Package

Firstly, the customer sent the full data package to through hole PCB assembly suppliers. They verify the whole requirements, parts count, and other PTH PCB assembly requirements. So it would be easy to know how to set up the production floor as per customer requirements. This supplied full data package includes a bill of materials, pick-and-place files (if needed), Gerber files, PTH PCB assembly documents, schematic files, etc.

• Component Placements

After the whole verification of the PTH PCB assembly data package, it’s time to place through-hole components. Basically, through-hole parts are mounted on the PCB manually. But now through-hole pcb assembly technology has improved. So, there are two types of methods used for part placement in the PCB through hole assembly. One is manual, and the other is automatic by the machine.

Now, many China through-hole PCB assembly manufacturers have automatic placement machines for mounting THT components on the board. It would be easy for us. But it needs X-Y coordinates for the component placement. It takes a short time to mount all THT parts on the PCB rather than manually placing them.

For automatic placement machines, we need to make a program and setup them first. So, it’d be easy for that machine. In manual placement, all parts are mounted on the PCB by hand. So, it’s taking a long time to mount them. Also, we need more experienced people to mount components on the PCB due to handling those parts with excellent placement.

• Components Soldering

After the Complete placement of THT parts, PCBAs go for soldering. Also, there are two methods for THT soldering.

Hand Soldering

Hand Soldering in Through Hole PCB Assembly

The first is manual soldering with iron, and the second is automatic wave soldering. Generally, wave soldering is preferred for THT assembly. In manual soldering, THT parts are soldered manually with a soldering iron. Soldering operators use soldering wire for soldering. So, it’s just melting that wire with the soldering iron, and the parts are soldered. 

Wave Soldering

In Wave soldering, the parts are automatically soldered in a wave soldering machine. So basically, that machine has flux. That flux was applied to the THT assemblies for soldered-together THT parts. Basically, wave soldering machines melt the solder at a specific temperature set by the production team. Basically, a wave soldering machine follows some key steps like flux spraying, heating, and soldering. Wave soldering has a big tank for soldering.

• Cleaning

The assemblies have come to this stage with many unwanted solderings. So PCBA vendors are using some ionic purities, water, and other solvents to clean the PCBAs. There are many errors after soldering, like shorts and improper soldering. With the help of cleaning, we can easily remove those types of errors. DI water is the is the most efficient method that is used by the assembly vendors. DI water is the most powerful method of cleaning.

• QA Inspection

The QA inspection team inspects the whole THT assembly using some inspection methods, like functional testing. The QA team applied many tests, like AOI, ICT, and FPT, to improve the quality of PCBAs. These inspection methods verify various aspects of PCBA. The quality inspection team inspects the whole PCBA with visual and automatic inspection to find errors if any; otherwise, it passes those boards to the shipping team for packaging and shipping. Functional testing plays the most crucial role in through-hole PCB assembly. It checks whole THT parts connections for electrical connections.

• Packaging and Shipping

After receiving PCBAs from the quality inspection team, the packaging team marks PCBAs with appropriate barcode stickers and markings as required. And pacing the PCBs with billing documents using bubble wrap and different packaging methods. And then ship the PCBAs to the appropriate locations. If any split orders are required, then orders are placed in multiple kits.

Advantages of Through Hole PCB Assembly

• More Reliability

Through parts are installed on the PCB using the drills. So, it has more stress levels for environmental causes. THT parts provide strong connections on the PCB and also provide high reliability and enhancement. That’s why it’s used in the aerospace industry due to its reliability.

• Easily Removed and Replaced

Sometimes, parts fail at the production stage or come defective from electronic stores. That time parts need to be changed. So, THT parts are easily removed and replaced with new parts as compared to SMT assembly.

• Strong Part Connection

Since the pins of the components are soldered through the through holes, they have strong stability after soldering.

• Enhanced Testing

THT PCBA provides high testability, for all leads are tested with functional testing.

• Easy for Debugging

THT Parts are very easy to mount manually for prototype boards. So, it’s easy to replace the defective parts or change the parts.

• Easy-to-get Prototype Boards

Because the through-hole PCB assembly is the assembly of components with pins, the density of components on the board is not high, and the components are easy to distinguish, so this assembly method makes it easy to prototype the board.

Disadvantages of Through Hole PCB Assembly

Disadvantages of Through Hole PCB Assembly

• Time Consumption

THT components need more time to be placed. Some PTH components come in a loose package, it is very time-consuming to insert into the PTH holes one by one.

• Higher Possibility of Errors

THT is less dependable, for through-hole assembly often requires manual labour to insert and solder components. This process introduces the possibility of human error, such as misalignment or insufficient solder, which can affect the reliability of the final product.

• More Space Needed

THT parts need more space for part placement, and THT parts do not provide a higher density than SMT parts. We cannot handle this part when you do fine pitches due to its tiny leads. THT is not available when routing closely around the THT parts. Traces may be damaged in drilling PTH holes, so through holes PCB assembly need more space and area.

Viasion: Have the Ability to Realize Your Ideal Through-hole PCB！

Advantages of Choosing Us to be the Through Hole PCB Assembly Suppliers

• 16 Years of Experience

We have 16 years of experience in the through-hole PCB assembly. We, as through hole PCB assembly suppliers, have a mature team and manufacturing system to fabricate the intended products for the customers.

Ideal for

• Through-hole PCB assembly
• Component procurement
• In-house assembly
• Meet Flexible Assembly  Requirements

We can offer flexible through hole PCB assembly services for small batches or medium-scale production. The types of through holes are different according to the different PCB and so are quantity requirements and quality requirements. So the customers need flexible through hole PCB assembly suppliers to meet their engineering needs.

• High Quality

We as China through hole PCB assembly manufacturers suppliers prioritise quality in every aspect of our assembly. Our through-hole PCBs would pass a rigorous quality assurance process, ensuring the through-hole PCB assembly meets the highest standards and performs reliably in their subsequent applications.

• Delivery within the Agreed Deadline

After the customer places an order, we can manufacture the finished product within the delivery period and deliver it on time. We are punctual without compromising on the quality of our products. So we can guarantee time efficiency, and you can trust us for our through hole PCB assembly services.

• More Competitive Prices among Similar Merchants

We as China through hole PCB assembly manufacturers offer competitive pricing on services to help you optimise your project budget without sacrificing the quality and reliability of through hole PCB.