How to Assemble PCB

Overview: Have you found that the electronic devices in our daily life all have a common component – PCB Board. Since the birth of PCB in the 1840s, it has become the core of electronic manufacturing, and it exists in almost all electronic devices, such as TVs, mobile phones, stereos, refrigerators, etc. In this article, FS Technology will take you into our assembly workshop to understand how printed circuit boards change from PCB to PCBA, and what is the use of assembling a PCB?

Concepts to Know Before Learning How to Assemble a PCB

PCB Board: A circuit board that does not contain electronic components and looks like a green slate with dividing lines and spaces. The PCB board does not work and cannot provide functionality for electronic products until assembly is completed. The picture below is a 16-layer rigid PCB bare board produced by FS Technology.

16-layer rigid printed circuit board bare board

PCBA Board: A circuit board that assembles the PCB board and electronic components together by soldering and assembling. Usually the circuit boards we can see are assembled PCBA boards, which are electrically connected to components through the traces on the circuit board to provide corresponding functions for your electronic equipment. The picture below shows the PCBA board of the surgical light controller assembled by FS Technology for the customer.

Surgical light controller PCBA board

Electronic components: components used to assemble to PCB, including capacitors, transistors, hairsprings, springs, etc. In your electronic equipment, the PCB board acts as a carrier, and the PCBA component is the main body of the function output. The figure below shows the symbols of some electronic components in the PCBA board.

Symbol diagram of electronic components needed to assemble PCBA

THT: Through-hole assembly technology, one side inserts the component leads into the through holes of the PCB board, and the other side is welded by welding techniques such as wave soldering to form electrical connections. The package form used by small and medium-scale integrated circuits generally does not exceed 100 pins. The component body and the solder joints are distributed on both sides of the substrate respectively. In the PCBA assembly industry, we prefer to call it DIP assembly, which is the abbreviation of Dual Inline-pin Package. With the change of electronic products to miniaturization and the upgrading of enterprise automation production, the frequency of use of this technology is getting lower and lower. Employees of FS Technologies doing PCB DIP assembly.

DIP assembly line of FS Technology

SMT AssemblySurface Mount Technology Assembly. The components are placed on the surface of the printed board, and the components are soldered to the surface of the PCB board by soldering technology to make them have specific functions. SMT is currently the most used PCBA assembly technology. Compared with DIP assembly, it has the following advantages:

  • Speed up circuits while reducing wasted space
  • More stable in violent shaking environments
  • Is a cheaper way to assemble
  • Time needed to speed up the PCB manufacturing process

The picture below shows FS technology used in SMT assembly production line.

How to Assemble PCB Components on a Circuit Board

Different companies have different PCB assembly processes and service items, here we take the full turnkey assembly service of FS Technology as an example. When you choose FS Technology as the service provider for your electronic project, we will complete the following services for you: design → component procurement → production → assembly → transportation. This article revolves around how to do PCBA assembly, so we’ll walk you through our assembly process in more detail. Material sending → substrate baking → board machine → solder paste printing/red glue printing → PCB visual inspection or AOI optical inspection → SMT high-speed placement machine → universal machine placement → visual inspection before reflow soldering → reflow soldering → AOI optical inspection → rework or DIP assembly → manual insertion or machine automatic insertion → wave soldering → ICT/FCT testing → repair or storage. 

Specific explanation of assembling PCBA

Component Sourcing: Purchasing documentation is essential if you need a supplier to supply you with electronic components. After FS Technology receives your documents, we will review and purchase. In order to improve customer stickiness and gain customers’ trust, we will send all cheap alternatives to your mailbox and wait for your approval.

Solder paste printing: Apply an appropriate amount of solder paste to the circuit board, and place the stainless steel stencil on the circuit board accurately.

PCBA solder paste printing

Place components: The required electronic components are placed on the prepared PCB using mechanical equipment and soldered to the surface of the board.

solidified solder paste: In order to make the components more firmly attached to the board, the solder paste needs to be reflowed for a long time. (The length of time depends on different products)

Inspect the assembled PCB: After the above process is completed, the assembled PCB needs to be inspected. The specific inspection method can be viewed in the PCB assembly inspection. This chapter does not describe too much. The PCBA testing process includes the following types:

  • Manual inspection
  • AOI
  • X-ray inspection:

Welding: Solder components using plated through holes or PTH. (PTH: More Professional Soldering Method)

Functional test: After the soldering work is completed, the assembled PCB needs to be functionally tested to ensure that it can function properly. When the PCB signal fluctuates during the testing process, it means that the product quality is unqualified, and it is necessary to start all over again until a successful PCB is produced.

Precautions for assembling PCB boards

Before assembling the PCBA process

DFM/DFA inspection

DFM/DFA inspection solves the previous question of how to assemble a PCBA, i.e., whether it can be assembled. No one wants to assemble a batch of unsuitable or defective PCBAs, most of the current turnkey manufacturers check the PCBA design and functional accuracy by DFM or DFA. A professional assembly company like FS Technology will judge the assembleability in combination with the manufacturing process, such as device analysis, pin analysis, pad analysis, etc.

Inspection of Assembly Materials

The core content of assembling PCBA is to place electronic components on the bare board and the assembled circuit board can play its due role in the device. If the quality of the electronic components used for assembly is not acceptable, even if the circuit board is assembled it is a failed product. In order to ensure that the components can work normally on the circuit board and do not have common PCB failures during operation, FS Technology has set up a special quality inspection department to be responsible for incoming material evaluation. The engineers in this department are responsible for the following work elements.

  • Whether the number and model of the BOM list
  • Sample testing by multimeter, test stand
  • Whether complex components are deformed, oxidized or broken

Uniform numbers

Before assembling the PCB, write the number on the front of the board. In order to prevent the loss of the mark, FS Technology generally writes the same mark on the side of the 96 looper. This number is permanently reserved, just like the ID card of the PCB board, and its purpose is to facilitate management.

During the assembly of PCBA

Take it lightly

I think this is nonsense, but there are still quite a few operators making this kind of low-level error, so I take the trouble to reiterate it. The price of the PCBA board is not cheap and relatively fragile. When you finish the assembly, in order to avoid damage, it must be handled with care, and the two PCB boards should be isolated or placed back-to-back.

Operate with gloves

This is a way of protecting components. The assembled PCBA board is littered with electronic components and is quite fragile, and the human body will generate static electricity then cause damage to the components, such as IC, so it is necessary to take necessary measures.


Testing is a job interspersed with the assembly process. After the circuit board enters the assembly workshop, manual visual inspection or AOI test is required for each step to ensure the correct assembly of electronic components. If errors are found in the testing process, repair them in time to desolder PCBA components.

After PCB assembly

Clean the circuit board

Professional manufacturers will add cleaning steps in each assembly or production process, but forget to clean the PCBA after the assembly is completed. FS Technology recommends that you check in the following ways to ensure that the assembled circuit board will not have any errors.

  • Use a professional PCB brush and cleaning solution to clean the surface of the board. If you use cotton balls, which are easy to lose hair, you need to pay attention to remove the remaining cotton wool.
  • Remove redundant pins
  • The front flying line should be concealed as much as possible, and the back flying line should take shortcuts in principle
  • The redundant device should be completely cut off.
  • Check all kinds of screws and keep them tight.

That’s all for “how to assemble a PCB board”. If you want to make your own PCBA business card, you need to have a wealth of assembly knowledge and a clear understanding of the PCB assembly process steps. Reading the dependencies below will help you in your assembly work.

List of PCB & PCBA Manufacturers in China

How to calculate PCB cost

High Frequency PCBA Design

Latest PCBA Blogs

Introduction of SMD components
PCB & PCBA Knowledge
Wilson Smith

What are SMD components?

What are SMD components Electronic devices with components attached to or mounted directly on the surface of the printed circuit board (PCB) are known as

Read More »
PCB Copper Thickness Guide
PCB & PCBA Knowledge
Wilson Smith

PCBA Copper Thickness Guidelines

PCBA Copper Thickness Guidelines PCBA stack-up will likely be among the last concerns on your mind, whether you’re a circuits designer or an engineer just

Read More »

What is a rigid flex PCBA

What is a Rigid Flex PCBA Rigid-flex board is a semi-rigid and semi-flexible circuit structure so project components can be connected on both parts. Rigid-flex

Read More »