Printed circuit board assembly is the core link in the manufacturing of electronic products. It refers to soldering and fixing electronic components (such as resistors, capacitors, IC chips, etc.) onto a bare board (PCB) to endow the circuit board with complete functions. For beginners, understanding the PCB assembly process is the first step to mastering electronic manufacturing technology.
Next, this guide will comprehensively introduce what PCB assembly is, its assembly process, and why it is crucial for product performance and reliability. The PCB assembly process introduced in this article is applicable to everything from simple consumer electronic devices to highly reliable aerospace electronic systems, medical equipment, and even military communication systems. By having an in-depth understanding of these contents, you will fully master the basic knowledge of PCB assembly manufacturing. All right, let's first understand what PCB assembly is!
What is PCB Assembly？
The full name of PCBA is Printed Circuit Board Assembly, namely PCB assembly, which is the second stage in the entire electronic manufacturing process. This process occurs after the completion of the PCB fabrication of the bare board. It is the process of soldering components onto the circuit board according to the design drawings to endow it with electrical functions. The entire process of PCB assembly usually includes the following several links:
Solder paste Printing (SMT)
Component Picking and Place
Welding (reflow soldering or wave soldering)
Cleaning and post-treatment
Functional testing and quality inspection
The application of PCBA is extremely extensive. Almost all kinds of electronic products, such as smart wearable devices, industrial control systems, medical electronics, communication equipment, etc., have their presence. Often, people confuse PCB manufacturing with PCB assembly. Here is a table clearly listing the differences between the two processes:
|
Item
|
PCB Fabrication
|
PCB Assembly (PCBA)
|
|
Definition
|
The process of producing bare PCBs without any electronic components
|
The process of soldering and assembling electronic components onto PCBs to make them functional
|
|
Purpose
|
To manufacture a physical circuit board with conductive traces and structural layers
|
To build a functional electronic module ready for integration
|
|
Output Product
|
Bare PCB
|
Fully assembled circuit board (PCBA)
|
|
Main Process Steps
|
Material cutting → Inner layer imaging → Lamination → Drilling → Plating → Outer layer etching → Surface finishing
|
Solder paste printing → Component placement → Reflow/Wave soldering → Cleaning → Testing → Packaging
|
|
Includes Components
|
No components included
|
Includes components such as ICs, resistors, capacitors, connectors
|
|
Functionality
|
No functionality, serves only as a structural and conductive base
|
Fully functional and ready to be used as part of an electronic system
|
PCB assembly and PCB manufacturing complement each other. Only when the assembly is completed can the PCB truly "come alive."
The Importance of PCB Assembly
The quality of PCB assembly directly determines the performance, stability and service life of electronic products. For medical equipment, any functional failure may affect patient safety. This field has extremely high requirements for the stability and consistency of PCBA. In the military industry, the requirements for PCBA are also extremely strict. Because military PCBA often involves multi-layer structures, high-density interconnection and complex reliability verification. PCBAs must be able to withstand extreme environments such as high temperatures, high humidity and high vibration in the military industry.
In addition to some of the extremely demanding fields mentioned above, circuit board assembly also requires good craftsmanship in consumer electronics and IoT smart devices. Overall, PCB assembly is related to the integrity and conductivity of electrical connections, the stability of high-speed signal transmission, the thermal management performance of the entire machine, product lifespan and anti-aging ability, etc.
Types of PCB Assembly
According to the packaging form of components, PCB assembly can be classified into three types: SMT, THT and hybrid assembly.
|
Assembly Method
|
Component Type
|
Mounting Method
|
Soldering Process
|
Typical Applications
|
|
SMT Assembly
|
Surface-mount devices (SMD)
|
Components are mounted directly on PCB surface pads
|
Reflow soldering
|
High-density, compact, and highly automated electronic products
|
|
THT Assembly
|
Through-hole components (DIP, PTH)
|
Component leads go through PCB holes and are soldered underneath
|
Wave soldering or manual soldering
|
Products requiring high mechanical strength and load capacity (e.g., power boards)
|
|
Hybrid Assembly
|
Combination of SMT and THT
|
SMT first, then THT, combining both mounting methods
|
Reflow + wave soldering/manual
|
Most modern electronic products (e.g., industrial control, communication devices)
|
PCB Assembly Process - Step by Step Explained
PCB assembly is a crucial link in the electronic manufacturing process. From component preparation to soldering and forming, every step requires high precision and process control. Below, we will introduce in detail the standard PCB assembly process. It is hoped that this can help you fully understand how circuit boards move from drawings to physical objects.
1. Preparation before assembly
Before assembling the PCB, the following several documents need to be prepared first:
BOM (Bill of Materials) : It contains detailed information such as the model, package, quantity, and specification of all components. The Bom table is the foundation of the entire PCB assembly.
Gerber files and drilling files: They are used to guide the production of circuit boards, including circuit layers, pads, silk-screen printing and drilling positions. This is a document used to ensure the accuracy of PCB manufacturing.
Coordinate File (Centroid/Pick and Place File) : It contains the X/Y coordinates of the components, rotation angles, packaging information, etc. It is used to guide the surface mount machine to place each component accurately and efficiently.
2. Files Review
Before all the documents are ready and before entering the production stage, the PCB assembly company will conduct detailed DFM and DFA evaluations. They will check whether the documents have problems such as short circuits, insufficient spacing between components, and silk-screen printing errors to ensure that the design is suitable for efficient and error-free manufacturing.
3. Solder Paste Printing
Solder paste printing is the process of precisely printing solder paste onto PCB pads using a specific stainless steel mesh, which is a prerequisite for SMT mounting. Subsequently, solder paste will play the role of conducting electricity and connecting components in reflow soldering.
4. Components Placement
After the solder paste is printed on the PCB pads, the high-precision pick and place machine will rapidly mount various SMD components onto the PCB according to the coordinate file (the position of components are corresponding to the solder paste, as the steel mesh is also customized according to the file). This process is fully automated, which ensures the accurate positioning of components and high efficiency, making it highly suitable for mass production.
5. Reflow Soldering
After the PCB is mounted and inspected by SPI for accuracy, it will enter the reflow soldering oven. As the temperature zone of the reflow oven gradually heats up, the solder paste will melt and then solidify during the cooling stage. At this point, the components will be firmly soldered onto the pads. Reflow soldering has very strict requirements for the temperature control curve, because once the temperature is not properly controlled, problems such as false soldering or component damage may occur.
6. Through Hole Assembly
For some high-power or high-strength-demanding devices, such as transformers, connectors, electrolytic capacitors, etc., the through-hole assembly needs to be used. Components can be inserted into the through holes of the PCB either manually or by a plug-in machine, and then ready for soldering.
7. Wave Soldering / Hand Soldering
Through hole soldering typically employs wave soldering equipment, allowing the bottom surface of PCBs to pass through molten tin waves for batch soldering. If it is a special structure or low-batch production, hand soldering can also be adopted, which can meet the diverse product demands.
8. Cleaning and Post-solder Processing
After the soldering is completed, it is necessary to remove the remaining flux, fluxes and impurities, and clean the circuit board. This can prevent corrosion and short circuits, and improve the insulation and reliability of the PCB surface. Some products will also undergo post-processing steps such as three-proof coating, functional testing, and packaging to ensure the stability of the finished product quality.
Quality Control in PCB Assembly
During the PCB assembly process, there are mainly the following types of quality control inspections:
1. Visual inspection: Manually check for any misalignment, missing parts or poor welding.
2. AOI Optical Inspection: The automatic inspection system scans the surface of the circuit board to detect potential defects.
3. Online Testing (ICT): Check whether the electrical connections at each test point are normal.
4. Functional Test (FCT) : Simulate the actual usage environment to ensure the normal operation of the board.
5. X-ray inspection (applicable to BGA/QFN) : It is used for components with invisible solder joints (such as BGA), and is often used in military PCB assembly or high-density assembly boards.
Click to learn about PCBasic’s quality control in the PCB assembly process.
After Assembly Services
After the PCB assembly is completed, there are various value-added services available for selection:
Conformal coating: Protect the circuit board from moisture, corrosion and dust through three-proof varnish.
Box Build Assembly: That is, providing complete PCB whole machine assembly services (PCB box build assembly services), including enclosure installation, cable routing, and assembly of supporting components.
Marking and packaging: label printing, laser marking, anti-static packaging, etc.
Here we introduce to you an outstanding Chinese PCB assembler - PCBasic.
PCBasic: A Reliable PCB Assembly Manufacturer
PCBasic is a professional PCB assembly manufacturer, providing high-quality circuit board assembly services to customers worldwide. Whether it is aerospace PCB assembly, medical PCB assembly, or consumer electronics products, we can provide reliable and efficient solutions. The following is a series of services related to PCBasic:
One-stop PCB manufacturing and assembly services
Full-process support from sample making to large-scale production
Complete quality certification system (ISO 9001, IATF 16949, ISO 13485)
Fast delivery + competitive prices
Complete PCBA solution
Conclusion
Understanding what is a PCB assembly and the difference from PCB manufacturing can help developers and purchasers make informed decisions. Every step of the PCB assembly process is crucial, and choosing a reliable PCB assembly service provider is equally important.
From medical equipment to aviation systems and then to smart hardware, high-quality printed circuit board assembly and professional PCB assembly companies are the cornerstones of the success of every product.
About PCBasic
Time is money in your projects – and PCBasic gets it. PCBasic is a PCB assembly company that delivers fast, flawless results every time. Our comprehensive PCB assembly services include expert engineering support at every step, ensuring top quality in every board. As a leading PCB assembly manufacturer, we provide a one-stop solution that streamlines your supply chain. Partner with our advanced PCB prototype factory for quick turnarounds and superior results you can trust.
