Processes Involved in PCB Assembly and Manufacturing

PCB assembly and manufacturing are processes that involve several stages. Each of these stages is crucial in achieving a successful assembly and manufacturing. A circuit board that hasn’t gone through an assembly process is mainly a bare PCB. The PCB assembly process involves steps that produce the final PCB.

In this process, the printed circuit board is carefully populated with electronic components. Also, the PCB assembly process involves the integration of two different technologies which are through hole technology and surface mount technology. In this article, we will be explaining some details about PCB assembly process.

What is PCB Assembly?

PCB assembly involves placing components in the appropriate location on a PCB surface. It is a crucial process in PCB manufacturing. In PCB assembly, all essential components are carefully placed on the bare circuit board. A printed circuit board assembly is a fully assembled board. Also, an assembled circuit board offers great functionality in electronic devices.

A fully functional board offers a lot of benefits. The PCB assembly process produces a finished board with all the components installed and soldered on a PCB. Also, the PCB assembly process is the concluding part of PCB manufacturing. In this process, traces link components and connectors to each other.

The PCB assembly process comprises various automated and manual steps.

Types of PCB Assembly Technology

There are two main types of PCB assembly technologies. These are the surface mount technology and through hole technology.

Through hole technology (THT)

THT is a PCB assembly technique that involves the insertion of leads through already drilled holes in the PCB. These leads are then soldered to the pads by a method known as wave soldering or manual soldering. Also, THT PCB assembly is often performed manually or by insertion mount machines. In the late 1980s, THT was a popular method for mounting components.

Even though other technologies have replaced THT, it has remained relevant in today’s world. This is because of the benefits it offers.  Below are steps involved in THT PCB assembly.

Component placement

Component placement involves drilling of hole and then inserting the component leads through the hole in the circuit board. Also, the holes need to be drilled according to the specification in the design files. Also, the holes must have the right orientation and polarity.

Inspection and reactification

After placing the components on the board, the assembler places the board in a transport frame where it will be automatically inspected to evaluate the placement of the components. If there are any errors, the assembler must make necessary changes or adjustments

Wave soldering or manual soldering

The through hole components need to be properly soldered on the PCB. In THT PCB assembly process, there are two methods of soldering. These are wave soldering and manual soldering. Wave soldering process involves passing the circuit board over a wave of solder. Manual soldering process involves using soldering iron to apply solder to the PCB.  Wave soldering process is highly preferred among PCB assemblers. Also, wave soldering offers more benefits.

Surface mount technology (SMT)

SMT is a PCB assembly technique that involves mounting electronic components on the PCB surface with the use of solder paste. Here, the PCB assembler uses automated machine to pick and place components. Surface mount technology involves automated processes and as such it is faster.  These components don’t have leads.

Solder paste printing

The first step in SMT assembly is the application of solder paste on the bare PCB board. Solder paste is a mixture of solder and flux. Also, solder paste is usually deposited on areas where the components will stay. Solder paste application involves placing solder screen on the board and moving a runner across the screen.

 The runner squeezes the appropriate amount of solder paste needed through the holes.  The solder paste helps components to stay in place. Therefore, solder paste is a crucial material in SMT assembly. Solder paste

Pick and place

In this step, an automated machine known as pick and place machine carefully places the surface mount components on the PCB surface. The machine picks the surface mount components from the reels and places them on the right position on the circuit board. Also, the solder paste uses tension to hold the components firmly.

Reflow soldering

Reflow soldering is the next phase after placing components on the board. Here, the circuit board goes through reflow soldering machine. The machine comprises an oven with various temperature-controlled zones. Also, reflow soldering involves the use of pressure and high temperature to melt the solder. Once the solder paste has transformed to a liquid form, the PCB will go through a cooler.

Final inspection and testing

This step involves evaluating the functionality of the PCBs before they leave the factory. It is an important phase of SMT assembly.

Failures in PCB Assembly Process

PCB assemblers experience some challenges and failures during PCB assembly process. Understanding what causes these failures and how to prevent them is crucial in achieving a successful PCB assembly.

Joint solder fracture

During PCB assembly, fracture could occur on solder joint. This is a result of differences in the PCB’s thermal coefficients. Manual soldering could also cause joint solder fracture. Therefore, wave soldering or reflow soldering is a better option.


Dewetting happens when the electronic components has issues. Also, dewetting makes the solder joint loose and such, it fails to create connections. Contamination and corrosion are causes of dewetting. PCB assemblers can prevent dewetting through careful inspection of printed circuit boards.

Crack or Bend

During PCB assembly process, a board can experience crack or bend as a result of mechanical stress. A flex circuit can crack if bent beyond its bending strength while a rigid circuit can fail when exposed to repeated vibrations. You can prevent crack or bend during PCB assembly process by pre-baking and storing printed circuit boards in humidity-controlled places.


Printed circuit board assembly is a crucial process in PCB manufacturing. Also, PCB assembly services offer different types of PCB assembly. Some PCB assembly services offer both surface mount technology (SMT) and through hole PCB services.

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