PCB Assembly Process

Steps Involved in the PCB Assembly Process

Printed circuit boards are the core of electronic products. Most electronic devices feature PCBs. Therefore, it is important to understand what this board comprises. PCBs comprise components which are carefully assembled to achieve a desired outcome. The process of assembling these electronic components is what we refer to as PCB assembly.

The printed circuit board assembly process is crucial in PCB manufacturing. It is a straightforward and lengthy process. Therefore, the process requires careful attention to details. This is because the slightest mistake can have a drastic effect on the functionality of the PCBA. Therefore, it is vital to understand these steps and strictly follow them.

What does the PCB Assembly Process Entail?

The PCB assembly process involves steps in assembling electronic components on a board. Also, it is a critical process that determines the functionality of a board. The end result of the PCBA process is an assembled board. This assembled board is what you find in electronic devices.

The steps involved in a PCB assembly process might vary based on the type of assembly technologies used. However, some steps are very common in this process. For instance, soldering is a common step in PCB assembly. Also, the application of solder paste is a common step.

There is a rising demand for quality PCBs. Therefore, technicians pay more attention to this process. Also, this process often begins with a bare circuit board. This PCBA process requires a lot of material. These materials include solder paste, soldering iron, and soldermask among others.

A meticulous assembly process gives birth to a fully operational printed circuit board. Also, the printed circuit board assembly process can be manual or automated. The automated process is ideal for high-volume production of PCBs. Also, proper planning is ideal before the process starts.

Some preparatory steps are necessary before the PCBA process starts. This helps to evaluate the functionality of the PCB design. Also, the design file is crucial for the printed circuit board assembly. The PCB assembler checks the file for any problems that may affect the functionality of the PCB.

Therefore, design for manufacturability (DFM) is necessary. This helps to evaluate the PCB’s design specifications. Also, DFM helps to check for any missing or problematic features. DFM can eliminate unforeseen expenses and reduce the cost of manufacturing.

Steps Involved in the PCB Assembly Process

The PCB assembly process involves several steps. All these steps require careful attention. Also, each of these steps contributes to the performance of the PCB assembly process.

Solder paste screening

This is the first step in the PCB assembly process. Before attaching electronic components, you need to add solder paste to the board areas that require soldering. Solder screen helps to apply solder paste to these areas. Also, the solder paste comprises solder combined with flux.

This flux makes it easy to solder through-hole pin in components by applying solder paste in the hole. The assembler places the solder screen directly on the board. Then, a runner squeezes solder paste through the holes. Also, it is important to regulate the amount of solder applied to prevent soldering problems.

Placement of components

This stage involves placing electronic components on the bare PCB. Also, the board which already has solder paste goes through the pick and place machine. This machine picks and places components in the right position on the PCB.

The components stay in the right position due to the tension of the solder paste. The use of the pick and place machine is an automated process. Also, this machine places surface mount devices (SMDs) on the PCB. In the manual assembly process, the assembler uses a pair of tweezers. Also, the assemblers use the tweezers to manually pick and place the components.

However, machines have now replaced the use of tweezers. This is because humans are prone to making mistakes. Machines are more accurate than humans.

Reflow soldering

The next step after placing the components is the reflow soldering. Here, the assembler passes the board through a soldering machine. The printed circuit board goes through a reflow oven conveyor belt. The conveyor belt moves through the reflow oven. Also, the oven comprises several heaters that heat the PCB around 480 degrees Fahrenheit.

The printed circuit board keeps moving via the oven. After that, it goes through some coolers that solidifies and cools the melted solder. Also, this forms a solder joint that links the SMDs to the board.  Not all boards pass through the reflow soldering machine. However, some printed circuit boards pass through wave soldering machines.


This is an important aspect in the PCB assembly process. You have to test the board to evaluate its functionality. Also, poor connection quality or circuit short can result from movement during reflow. Checking for any defects and misalignment helps to prevent further problems in the PCB assembly.

Automatic optical inspection and X-ray inspection are ways to inspect the printed circuit board. Also, manual checks are another method of inspecting the circuit board. The automatic optical inspection is ideal for large quantities of boards. The X-ray inspection uses X-rays to check for any defect. Also, the X-ray machine enables a viewer to look through the layers.  

Final inspection and functional test

A final inspection is necessary after the soldering step in the PCBA. Also, this inspection will check the functionality of the PCB. The functional test is the final inspection. Also, this test puts the board through power and simulated signals. Testers monitor the electrical characteristics of the PCB.

Other Soldering Methods

Although the reflow soldering process is commonly used, there are other soldering processes. These are wave soldering and manual soldering.

Wave soldering

This soldering involves the use of a wave soldering machine. Wave soldering involves passing printed circuit boards on a conveyor via a wave of molten solder. Also, the molten solder exposes component pads and leads. This soldering isn’t really common in the PCB assembly process. This soldering process is more commonly used for soldering THT components. Also, the machine helps to solder THT and SMT components on a PCB.

Manual soldering

Manual soldering is ideal for through-hole components. However, this type of soldering feels outdated. It is suitable for PCB design that comprises parts that are not suitable for wave or reflow soldering. Also, manual soldering is useful when the selective soldering machine can’t be used. The quality of manual soldering totally depends on the expertise and skills of the soldering technician.

Types of PCB Assembly Process

The PCBA process comprises different manual and automated steps. Also, there are several techniques used in assembling components on PCBs. There are three techniques of PCB assembly process. These are surface mount technology (SMT), through hole technology (THT), and mixed technology.

Through hole technology

The THT is a type of mounting technology used in the PCBA process. It involves inserting the pin-through-hole (PTH) components through holes already drilled in the PCB. The assembler then uses molten metal solder to affix the leads to pads on the opposite side of the board. THT was the first mounting technology used in PCB assembly. Also, THT involves the following steps:

  • Component placement

A professional engineer precisely places the components according to the circuit board design files. The placement of component must conform to the standards of THT. Therefore, this helps to guarantee high-quality products.

  • Inspection and rectification

After placing the component, the PCB is then inspected to ensure there are precisely placed. If there are any errors, the assembler will need to rectify them.

  • Wave soldering

You can now solder the THT components on the printed circuit board. This type of soldering moves the board slowly over a liquid solder at a very high temperature.

Surface mount technology (SMT)

Surface mount technology is a technique of PCB assembly process. It involves mounting SMD directly on the PCB surface using solder paste. SMD refers to surface mount devices. SMDs are always smaller than THT components. The major steps involved in SMT include:

  • Solder paste printing

The assembler applies solder paste on the board using a solder paste printer.

  • Component mounting

A pick and place machine will mount the component on the right position. Components will mount on pads due to the solder paste’s tension.

  • Reflow soldering

After placing the components on the right position, the PCB will pass through a reflow oven. The temperature of this oven must be 500OF. The assembler heats the solder paste until it forms reliable joints between the board surface and components.

Mixed technology

Electronic devices are becoming more complex. Therefore, these devices require more complex and integrated PCB boards. Most complex PCBAs comprise through-hole technology and surface mount technology. Mixed technology PCB assembly features the properties of SMT and THT. Mixed PCB assembly process can be double side, single side, one side SMT and one side THT.

Design Considerations for the PCB Assembly Process

When it comes to the circuit board assembly, you will need to make important decisions. The method of component placement and type of soldering are examples of this decision. The right decision will yield maximum efficiency.

Component selection

As regards the circuit’s schematic, the assembler selects components with some values. After that, it chooses the mounting technology. Also, PCB designers need to follow some guidelines during the selection of components. Choose more SMT components and select THT components only if SMT versions aren’t available. Also, make use of similar package types if the PCB design allows.

Type of soldering

Choosing the right soldering technique is important for your PCBA process. Also, the soldering technique should be ideal with the type of components you need to solder. Reflow soldering isn’t ideal in cases where there THT components are more. Wave soldering is ideal for only THT components in the assembly. Manual soldering is ideal only when you can’t solder THT component using selective or wave soldering methods.

Component placement

You can either place components manually or automatically. During component placement, ensure there is proper spacing and part orientation.


The PCB assembly process is a procedure that requires attentiveness and carefulness. Therefore, it is important to leave this task in the hands of an expert. We at RayMing offer professional PCB assembly services. Also, we ensure our customers get the best-quality PCBA.

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