Many of you might be wondering, “What is the SMT process?” Printed Circuit Board (PCB) assembly involves mounting electronic components onto a board that has only circuits without any soldered components, following a board artwork design. The process includes mounting the components and soldering them to form electronic circuits.
With the trend towards miniaturization and lightweight products, such as smartphones, Surface Mount Technology (SMT) has become the mainstream. This is because it allows for the installation of smaller, space-saving components on printed circuit boards.
This article explains the following questions:
- I hope this can serve as a catalyst for solving problems in new product development and factory audits, drawing from 30 years of experience in assembly technology.
- As the development of the PCB assembly industry supports the future, I wish for an increase in people involved in the industry.
- I plan to write this article in a way that even beginners can understand the mechanisms of the PCB assembly process.
- Intended for newcomers to PCB assembly, people in related departments within companies, those interested in PCB assembly, and those interested in the manufacturing industry.
- For fabless manufacturers who outsource PCB assembly.
Electronic devices are all composed of semiconductor and other electronic components mounted on printed circuit boards. Without printed circuit board assembly, modern life would not be possible.
To produce printed circuit board products, they are manufactured in PCB assembly plants, where soldering is carried out in multiple stages.
Here, we will clearly explain the production process of printed circuit boards.
- The flow of the PCB assembly process
- The relationship with board artwork design
- The importance of assembly technology
- Guide to related articles
All electronic products are composed of semiconductors and other electronic components mounted on printed circuit boards. Without the assembly of printed circuit boards, modern life would be impossible.
The Overall Configuration of the Printed Circuit Board Assembly Line
The printed circuit board assembly process is mainly composed of two stages:
- SMT (Surface Mount Technology) process
- DIP (Dual In-line Package) assembly process
There are two methods for mounting components: manual assembly and using an automatic assembly machine. The automatic assembly machine is used to accurately place components on the board and perform soldering. Utilizing this automatic insertion machine can improve productivity and reduce costs.
What is the SMT (Surface Mount Technology) process?
Surface mount technology involves directly mounting components to the surface of the board using solder.
This method is particularly effective when components are being miniaturized and when there is a desire to reduce the size of the board. SMT allows for the creation of fast, compact, and highly reliable boards.
The SMT (Surface Mount Technology) process consists of multiple equipment stages.
Assigning a serial number to the board
Removing dust and other contaminants adhered to the board
Printing solder paste onto the board using a metal mask
Inspecting the condition of the cream solder print
Automatically mounting electronic components onto the board
Inspecting the state of component mounting before soldering
Soldering by heating at high temperatures
Inspecting the state of soldering
Manual inspection of soldering by personnel
It is the soldering process where electronic components such as “resistors,” “capacitors,” “transistors,” and “ICs” are mounted and installed onto the board using a “chip mounter” device.
Laser Marking Process
The printed circuit board assembly process begins with laser marking on each board.
The information printed includes serial numbers and version (Ver) assigned to each board, allowing the production and inspection status at each stage to be linked to the serial number for traceability purposes.
The barcodes are printed in formats such as QR codes or Data Matrix, with QR codes being more familiar to the general public. However, Data Matrix is more widely used globally.
Board Cleaning Process
There are various types of board cleaning devices, but a compact cleaner integrated into the board feeding device (loader), as shown in the image above, is adopted.
The surface of the printed circuit board is covered with various kinds of dirt, dust, etc., so the debris is removed using a cleaning device before entering the process.
There are various types of debris, including cuttings from the printed circuit board, silk screenings, laser marking scraps (residual removal), and dust.
When performing SMT assembly, it’s necessary to remove any debris because cream solder and components adhering to debris can lead to defects due to foreign material attachment on the board.
Solder Paste Printing
This process uses a stencil tool called a metal mask to print solder paste onto a printed circuit board (PCB).
The quality of the solder paste printing process is a critical factor in the overall quality of SMT (Surface Mount Technology) assembly, accounting for up to 70% of the total SMT quality.
When you hear about soldering, you may think of using a soldering iron. However, there is also a type of solder in a paste form called solder paste, which is an essential electronic material used in the printed circuit board (PCB) assembly process.
Solder Paste
Solder paste, also known as cream solder, is a type of solder that is made by mixing solder alloy with flux to create a creamy consistency.
It is an essential electronic material used in the SMT (Surface Mount Technology) assembly process. The quality of the solder paste printing process is a critical factor in the overall quality of the finished product, and therefore serves as an indicator of a factory’s technical capabilities in this area.
Metal Mask
A metal mask is a tool used in the SMT (Surface Mount Technology) assembly process to print solder paste only on the locations where SMT components will be mounted on the printed circuit board (PCB).
The metal mask is placed on top of the PCB, and the solder paste on the metal mask is then printed onto the PCB.
The metal mask is made of a very thin stainless steel sheet, typically with a thickness of 80μm to 200μm, and has tiny holes cut into it with high precision to match the locations of the components on the PCB.
Backup plate jig
A backup plate is used as a printing substrate when printing solder paste for SMT component assembly on double-sided printed circuit boards (PCBs).
A flat printing substrate is sufficient for the first side assembly, but a backup plate is required for the second side assembly because the component-populated side faces down, which would otherwise result in poor solder paste printing quality.
Solder paste printing can suffer from poor adhesion and quality without proper support from below.
Since the component placement varies depending on the PCB, the support locations also change, which is why backup plates are dedicated to each PCB.
When SMT components are mounted on both sides of the PCB, a machine-specific backup plate may be used, and production is carried out using backup plates when SMT mounting is performed on both sides of the printed circuit board.
Adhesive (Bond)
Adhesive is an electronic material used to print (apply) instead of solder to temporarily fix components in place. It was formerly a major electronic component mounting method, but is now less commonly used. However, it is still frequently used in processes for products such as white goods.
Epoxy resin cures at a lower temperature than solder, around 150℃, to fix components in place. However, since it only fixes the components in place, soldering is required in a separate process.
There are two main methods for applying adhesive
- Printing with a metal mask
- Applying with a dispensing machine
SPI (Solder Paste Inspection)
Solder Paste Inspection Process
The solder paste inspection process is a critical step in printed circuit board (PCB) assembly that inspects the solder paste printing state of PCBs sent from the solder paste printing process. The printing state is inspected by 2D/3D images of the solder paste printing state (volume, height, area, displacement, shape).
Recent Developments
In recent years, in addition to solder paste printing, it has become possible to include bond printing state and foreign object inspection of the entire PCB.
Real-time Feedback
The inspection results are fed back to the solder paste printing process in real time, and solder paste printing defects are suppressed in advance by parameter correction and other measures.
It is said that the solder paste printing process accounts for 70% of the quality of SMT (surface mount technology), and the SPI (solder paste inspection) process is the quality gate of the SMT process.
SMT component mounting process
SMT Component Mounting Process
The SMT component mounting process is the step in surface mount technology (SMT) assembly where electronic components are placed on the solder paste printed areas using a chip mounter.
Most electronic components are supplied in standardized reels or trays in a regular arrangement. However, in rare cases, they may be hand-mounted. In such cases, they may be supplied in a state where they are not in reels or trays.
Most electronic components are supplied in standardized reels or trays in a regular arrangement. However, in rare cases, they may be hand-mounted. In such cases, they may be supplied in a state where they are not in reels or trays. The key to quality and efficiency lies in automating the process of mounting these components.
Chip mounter
Chip Mounter: The Key Player in SMT Assembly
A chip mounter is a machine that places electronic components on printed circuit boards (PCBs) after solder paste has been printed, prior to soldering. It is a key player in the surface mount technology (SMT) assembly process.
Chip mounters are also known as surface mount machines (SMMs). Four Japanese companies account for 80% of the global market share for chip mounters, which are used worldwide.
Chip mounters can handle a wide variety of components in terms of shape and size, and they place these components at high speed and with high precision.
Chip mounters operate at ultra-high speeds, with component placement speeds ranging from 0.1 to 1.0 seconds per component, depending on the type of chip mounter.
Pre-reflow inspection
Pre-reflow Inspection: Ensuring SMT Assembly Quality
Pre-reflow inspection is a critical step in surface mount technology (SMT) assembly that ensures the quality of the final product. It involves inspecting the printed circuit board (PCB) after solder paste printing and before reflow soldering to detect and correct any defects.
The Increasing Adoption of Pre-Soldering Inspection in SMT Manufacturing
Pre-soldering inspection is a critical step in surface mount technology (SMT) manufacturing that involves inspecting the printed circuit board (PCB) after solder paste printing and before reflow soldering. This inspection allows for the detection and correction of any defects before soldering, which offers several advantages over post-soldering inspection.
Reflow oven soldering
Reflow Oven Soldering: The Key to SMT Assembly
Reflow oven soldering is a critical step in surface mount technology (SMT) assembly. It involves heating a printed circuit board (PCB) with solder paste and mounted components to a temperature above the solder melting point, using a conveyor oven with multiple heaters. This process creates solder joints between the components and the PCB.
Temperature profile
Temperature Profile: A Critical Aspect of SMT Assembly
A temperature profile is a graphical representation of the temperature changes that a printed circuit board (PCB) experiences as it passes through a reflow oven. It is created by attaching thermocouples to specific points on the PCB and recording the temperature data over time.
Soldering Temperature Setting: A Key Process in SMT Assembly
Soldering temperature setting is a critical process in surface mount technology (SMT) assembly. It is the process of determining the optimal temperature for soldering components to a printed circuit board (PCB). This process requires a deep understanding of the materials and processes involved in SMT assembly, as well as the ability to troubleshoot problems.
Appearance inspection process (automatic, visual)
Visual Inspection Process: Ensuring SMT Assembly Quality
The visual inspection process is a critical step in surface mount technology (SMT) assembly that ensures the quality of the final product. It involves inspecting the printed circuit board (PCB) after reflow soldering to detect and correct any defects in the solder joints.
AOI inspection (automatic visual inspection)
Automated Optical Inspection (AOI) in SMT Assembly
Automated optical inspection (AOI) is a critical process in surface mount technology (SMT) assembly that ensures the quality of the final product. It involves using a machine vision system to inspect the printed circuit board (PCB) after reflow soldering to detect and correct any defects in the solder joints and components.
Optical Character Recognition (OCR) in SMT Inspection
Optical character recognition (OCR) is a valuable tool in SMT inspection that goes beyond simply detecting defects. It allows for the identification of printed characters, such as barcodes and serial numbers, on printed circuit boards (PCBs). This information can be used to improve the traceability and quality of SMT assembly.
Visual appearance inspection
Post-AOI Visual Inspection: Ensuring SMT Assembly Quality
Post-AOI visual inspection is a critical step in surface mount technology (SMT) assembly that ensures the quality of the final product. It involves visually inspecting the printed circuit board (PCB) after automated optical inspection (AOI) to verify the accuracy of the AOI results and to identify any defects that may have been missed.
BGA Rework: A Critical Skill in SMT Assembly
BGA rework is a specialized process that is used to repair defective ball grid array (BGA) packages on printed circuit boards (PCBs). BGAs are a type of surface-mount technology (SMT) component that is commonly used in high-performance electronics. BGA rework is a complex and challenging process that requires specialized equipment and skilled technicians.
Board artwork design
PCB Artwork Design: A Critical Task for SMT Manufacturing
PCB artwork design is a critical task in surface mount technology (SMT) manufacturing that has a significant impact on both the quality and efficiency of the assembly process. The quality of the design can affect the following factors:
The Rising Importance of PCB Artwork Design in SMT Manufacturing
The field of printed circuit board (PCB) and component assembly, once considered a mature technology, is facing a new challenge: the loss of institutional knowledge and expertise due to the retirement and transfer of veteran engineers. This knowledge gap is leading to an increase in unexpected problems and difficulties in troubleshooting, highlighting the growing importance of PCB artwork design in SMT manufacturing.
Feedback Mechanism for SMT Assembly Issues: Driving Quality Improvement
A well-designed feedback mechanism for identifying and addressing issues in the printed circuit board (PCB) assembly process is a powerful tool for driving quality improvement in both existing and new products. By capturing and analyzing data on defects and failures, manufacturers can gain valuable insights into the root causes of problems and implement corrective actions to prevent their recurrence.
The Importance of PCB Artwork Design in SMT Manufacturing
In the ever-competitive electronics manufacturing industry, printed circuit board (PCB) assembly companies are constantly facing pressure to reduce costs. While there are many ways to achieve cost savings, one often overlooked area is PCB artwork design.
Fostering soldering technology
Soldering Skills: A Vital Craft in SMT Manufacturing
Soldering is a critical skill in surface mount technology (SMT) manufacturing. It requires a high level of dexterity and precision to create reliable solder joints that meet the stringent requirements of electronic devices.
The Importance of In-House Training for SMT Manufacturing
In surface mount technology (SMT) manufacturing, the ability to perform specialized technical tasks such as failure analysis and soldering is critical to maintaining quality and efficiency. Outsourcing these tasks to external vendors can be a costly and time-consuming alternative, and can have a negative impact on the overall profitability of the factory.
SMT process summary
This article has explained the content mentioned above.
The process of printed circuit board assembly varies widely, from automated steps to those requiring skilled craftsmanship.
Modern life is inconceivable without electronic devices, which are composed of a diverse range of printed circuit board products.
Electronic devices have become as essential to our lives as food, though recently, mass-produced items are often manufactured overseas.
Relying on foreign production for electronic devices can lead to vulnerabilities in our lifestyle, similar to current concerns about energy dependency. In times of need, our way of life could be jeopardized.
I believe that producing printed circuit board assembly domestically is important to safeguard our lifestyle.
Those interested in printed circuit board assembly are encouraged to join this industry.
The development of the printed circuit board assembly industry will support the future of Japan.
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