Overview of SMT Assembly Technology
Surface Mount Technology (SMT) is a more recent method of arranging electronic components on printed circuit boards (PCB). Before this method was developed, engineers would use leads to connect electronic components through holes in circuit boards. It took careful planning to ensure that we made all the leads correctly on different kinds of boards. Therefore, a technology called SMT comes in. The electronic manufacturing industry highly utilises this technology because of its reliability and production of consistent results.
In Electronic SMT assembly, the PCB assembly technology places leadless or short lead components (SMC/SMD) on a PCB or other substrate surfaces. It assembles them using reflow soldering or dip soldering.
SMT assembly is an alternative to through-hole PCBA manufacturing. SMT PCB manufacturing and assembly is a structured chain process where electronic PCB bare boards are put together with the help of automated equipment that places SMD components on the surface of the PCB. Surface mount PCB manufacturing and assembly encompass a wide range of products in addition to component placement and soldering.
With time, the SMT assembly technique evolved into the dominant method used for circuit board assembly today. Every sector of the electronic manufacturing industry uses boards created in this manner. If you need China PCBA smt service for your electronic projects, please contact us today to get a cheaper SMT assembly quote.
FS Technology's SMT PCB Assembly Capabilities
Usually, the electronic products that are designed with a PCB include various electronic components, including capacitors, resistors and others according to the circuit diagram/schematics of the design. Hence, different electronic/electric equipment and products require the use of various SMT processing technology, ultimately determining whether the electronic components and printed circuit boards can work together correctly. This means that process control measurements must be implemented both prior to and during SMT processing to optimise PCBA processing and assembly. In turn, these measurements will ensure that costly errors are prevented in the future, product failure rates are reduced and the reputation of PCB SMT assembly factories is protected.
FS Tech provides customers with a complete PCB SMT service process as our production workshop is equipped with 7 fully automatic high-speed SMT production lines and uses the most advanced SMT assembly equipment including automatic board loading machines, automatic solder paste printing machines, SPI solder paste thickness detectors, multi-temperature zone reflow soldering machines, AOI (automatic optical inspection) equipment, x-ray inspection machines, baking machines, stencil cleaning machines, etc. In order to meet specific SMT assembly requirements of customers to the greatest extent, FS Technology does accept precision electronic component mounting such as with 0201 component packages, 0.4 mm pitch BGAs (ball grid arrays), QFN (quad-flat no-leads) packages, etc. Below, the capabilities of FS Technology are demonstrated in terms of production capacity and quality assurance.
SMT Manufacturing Capacity
- Production line: 7 automatic rapid SMT PCB assembly production lines
- Capacity: 52 million placements per month
- Max Board Size: 680×500 mm Smallest:0.25″x0.25″
- Min Component size: 0201 – 54 sq. mm. (0.084 sq. inch), long connector, CSP, BGA, QFP
- Speed: 0.15 sec/chip, 0.7 sec/QFP
- Types of PCB: single-layer, multi-layer, single-sided, double-sided, rigid, flexible, rigid-flex, HDI, high-frequency PCBA, etc.
- Applicable fields: wearable medical equipment, aerospace, 5G base stations, new energy self-driving cars, etc.
SMT Quality Qssurance
- More than 15 of our personnel are involved in the quality control department, effectively controlling and managing essential processes like incoming material inspection, input quality control processes, outgoing quality control processes, etc.
- Equipped with 5 electronic engineers who are constantly putting forward constructive improvement suggestions on DFM manufacturability and the engineering process, effectively improving product quality and overall production efficiency.
- Electronic information display boards are implemented along the production line, ensuring functional supervision of the PMC production planning process and delivery times.
- Electrostatic bags or electrostatic protective foam (PE foam) is used for safety in packaging and to ensure the safety of the product(s) during transportation.
Complete PCB SMT Assembly Service Process
FS Technology has been engaged in the PCB assembly industry for 20 years, we know every step of the PCB assembly process, and can complete your order with high quality and quickly. In order to build your confidence in FS Technology’s SMT assembly service, we will show you the complete assembly process.
Preparing for the SMT Assembly Process
As a professional turnkey SMT PCBA manufacturer, in order to ensure the quality of the assembly, FS Technology will review the customer’s DFM file and check the electronic PCBA components before the assembly process starts.
DFM Check
Before SMT PCBA production starts, the design file is checked carefully to ensure it works. This step, which we call “Design for Manufacturability” (DFM), is when we review the design requirements of a PCB. The engineers evaluate any features that could be missing, redundant, or otherwise problematic. The stage helps find mistakes in the design and lets the designers get rid of all the flaws quickly, making it possible to make the product successful.
Electronics Components Checking
After the DFM step, the process will move on to the next step: SMD components service. During this phase, engineering staff verifies that all components have been ordered and received according to the BOM and the PCB board. If there are any errors, they work with the client to fix them before we begin assembly.
Formal SMT Electronic Assembly Process
Step 1: Solder Paste Application
The initial step is to use SMT solder paste to attach the components to the board at the proper places. It then establishes electrical connections. A stencil and squeegees, which help place the solder paste in the right places, are needed to apply all the solder paste. The solder paste comprises small pieces of solder and a specific chemical called a PCBA flux.
Solder Paste Techniques
- Flux and Tin: The solder paste is often a blend of flux and tin. Although jet printing is quickly gaining popularity for large-scale SMT assembly operations, this is the most typical solder paste printing technique.
- Jet Printing Solder Paste: Without the requirement for stencil equipment, solder paste may be applied directly to the PCB pad using a non-contact printing method called jet printing. Over a million-solder paste “dots” per hour are precisely put to create the perfect solder paste typography for each pad location on the board.
Selection of Solder Paste
The type of solder paste used varies depending on the needs of the product and its qualities. During the reflow stage of the PCB SMT process flow, for example, some SMD electronic components can’t handle very high temperatures, so we must use a lower temperature. Before choosing the right product for a project, it is essential to know all its qualities and criteria.
Screen Printing for Solder Paste
First, let’s ensure everyone understands what we mean when discussing SMT printing. Screen printing, which does not need direct contact, and contact stencil printing are both a part of the process, which includes adding solder paste to the pads of the circuit board. Due to the nature of SMT assembly system, this sort of technology must use screen printing of the contact variety.
The soldering paste has to be mixed thoroughly before anything further can be done. Regarding the viscosity, the paste may considerably impact the printing quality. The goal is to meet the standards of the current printing standard. Because it might affect the printing quality, you want the viscosity to be similar to the advised range.
The largest size of SMT printed circuit boards that the machine can handle, controls for correct screen alignment and repeatability of print, and the board hold-down mechanism are all critical aspects of a screen printer for solder paste. The most common way to spread solder paste is with stencils. This method is used for both rework and mass production.
Step 2: Placing of Components
Contrary to earlier times, the PCB assembly process at this step is now entirely automated. Robotic pick-and-place machines now carry out the previously human task of picking and placing surface mount components. As a result, SMT PCB assembly companies use pick-and- place machines, which select and put components at high speed using a vacuum or gripper nozzle. These advanced surface mount equipment precisely position the components on the board in their intended locations.
CTE Consideration while Component Placement
We must consider many things to determine the tolerance and spacing for where to put SMT components. CTE, which stands for coefficient of thermal expansion, is one of the most important things to consider when spacing and arranging SMT components. Several printed circuit boards have glass epoxy as the base, and they use ceramic chip carriers that don’t have any lead. When the CTE difference between the ceramic carriers and the epoxy substrate gets too big, the solder connection may break after about 100 cycles.
Step 3: Automated Optical Inspection
The PCB is then sent to automated optical inspection (AOI) equipment before reflow soldering to ensure that there were no errors made during the pick and place procedure and that all parts were placed correctly.
In automated detection service, the machine scans the PCBA using the camera. A comparison is made between the tested solder junctions and the certified parameters in the database. When the picture is processed, it checks to see any defects on the PCBA; it either shows marks or uses automated signals to indicate that the board needs to be repaired.
They use high-speed and high-precision visual processing technology to find mounting problems and soldering mistakes on PCBA boards automatically. PCBA boards may offer online inspection solutions to increase production efficiency and welding quality. These solutions can vary from fine-pitch, high-density boards to low-density, large-size boards, and they can come in various sizes.
You will have more control over the process by using AOI inspection to cut down on defects and detect and get rid of issues early on in the assembly process. If difficulties are found early on, faulty printed circuit boards won’t be sent to later assembly stages. Additionally, automated optical inspection will cut down on the expenses of repairs and prevent the need to throw away irreparable circuit boards.
Step 4: Solder Reflow
All of the surface-mount components are now mounted, along with solder paste. Now, For the solder paste to attach PCB components to it correctly, it must solidify to the required specifications. Reflow soldering, a crucial step in PCBA board construction, is about to start. The solder paste and components assembly is transported over a conveyor belt to an industrial-grade reflow oven. The oven’s heaters melt the solder in the solder paste. Once it had finished melting, it moved along the conveyor belt and placed in front of several coolers. These coolers’ primary function is to reduce the solder’s temperature so that it can solidify.
Reflow ovens are tiny batch-box ovens used in laboratories. An integrated reflow oven is often the best option for large-scale PCBA design makers. Commonly employed in surface-mount technology printed circuit board production, an inline reflow oven has a series of heating zones followed by cooling zones. Reflow soldering ovens vary in length and throughput, which affects the number of cooling and heating zones. An onboard software provides a temperature setpoint to the zones during the reflow operation. The temperature at which the circuit board should operate in this region has been predetermined.
Stages of the Reflow Process
There are four stages to SMT solder reflow process:
Stage 1: Preheat
During the step known as “pre-heating,” the board’s temperature is gradually raised to the necessary level. This phase of the reflow soldering process needs careful supervision; Since accessing heat to the board and components may cause SMD patch components damage due to severe thermal stress, one must carefully watch this process. The temperature is recommended to rise at a pace of two to three degrees per second.
Stage 2: Thermal Soaking
After passing through the pre-heat phase, the PCBA boards undergo a thermal soak process. During this phase, the primary objective is to keep the surface mount device (SMD) thermals of the PCBA at the same level as it had been attained during the pre-heating phase. There are two reasons for this:
- First, ensure that all the places on the PCBA circuit board receive sufficient heat and that there are no cold patches due to the shadowing effect.
- The second purpose is to eliminate the solvents or volatiles that are included in the solder paste, as well as to activate the flux.
Stage 3: Reflow Stage
During the reflow step, the solder is heated to its melting point so that we may form the necessary solder connections. In the actual reflowing process, the flux is used to lower the surface tension at the junction of the metals to achieve metallurgical bonding. This opens the door for the individual spheres of solder powder to mix and melt together. It takes around 30–60 seconds to complete the reflow step.
Stage 4: Cooling Stage
Following the reflow step, the PCBA moves on to the cooling stage. At this point, the molten solder cools and solidifies, securing the PCB components. The temperature of the PCBA board as it cools down is typically between 30 and 100 degrees, and its rate of cooling is around 3 degrees per second on average.
Step 5: Inspection After Reflow
Following the reflow procedure, the PCBA SMT assembly process includes a crucial stage called quality inspection. The process’s length depends on the equipment and design requirements. Before mounting the components, verifying the solder paste is critical to ensure there are no printing problems.
Due to the board’s continuous movement throughout the reflow process, this stage aids in the detection of poor-quality connections, missing components, and faults. The PCB manufacturers use a variety of PCB assembly inspection procedures, including human inspections, automated optical inspection, and X-ray inspection, to evaluate the board’s performance, spot poor-quality solder, and find any potential hidden issues. The assembly crew makes the critical decision when the review is complete. PCB Boards that are found to have several functional problems are often discarded. However, the board is sent back for revision if there are minor errors.
Even though auto-optical inspection after a reflow oven has almost reached the standard configuration for surface-mount technology (SMT), not every SMT manufacturing line will be equipped with the technology.
Step 6: Cleaning Service
The SMT process includes reflow soldering, hand soldering, and other standard PCBA assembly methods for electronic devices. Cleaning PCBA makes the product last longer, ensures the surface is resistant enough and stops leaks from happening.
So, the completed SMT PCB board is wiped off with isopropyl alcohol wipes in the last phase of the process. This step removes any flux residue that may be present on the PCBA board.
Step 7: Testing Service
It’s now time to test PCBA. The tool that uses in-circuit test methods allows the identification of manufacturing flaws inside a printed circuit board assembly. In most cases, testers can determine whether resistors, capacitors, or transistors are present.
Testing is an essential step in SMT PCBA processing, and it plays a significant role in ensuring the quality of PCBA. A human visual examination, an inspection using a solder paste thickness gauge, an automated optical inspection, an X-ray inspection, an online test, a flying probe test, and other ways are among the primary testing procedures.
Additionally, rapid SMT assembly processing is a procedure that is considered to be somewhat sophisticated. The standards for technicians are incredibly stringent, and even highly experienced technicians may invariably run into issues. In this situation, we need to continue testing, using the appropriate instruments and equipment to carry out the testing more than once. Check to see if there are no issues with the product’s quality.
During the SMT manufacturing services, we must use several different testing procedures for detection to ensure that we may maintain the quality of the PCBA. This allows for the timely identification and correction of any faults or flaws that may occur.
The Trend of PCBA SMT Automated Assembly
Why Surface Mount PCB Assembly?
To make it easier for you to comprehend why SMT Surface Mount Technology is preferable, we have outlined some essential advantages of this technology below.
- SMT is very reliant on advanced SMT assembly machines, and not so much on us humans. One of the most significant benefits of using such an assembly system is the opportunity to fully automate this procedure, which becomes possible through this assembly.
- Compared with the manual assembly method of DIP assembly, SMT hardly makes any mistakes in the process.
- Compared to through-hole assembly, lead wires pass through the holes to connect components. But SMT components are soldered right onto the PCB, the overall makeup is far less complex.
- The geometric dimensions and the volume of SMT SMD electronic components are much less than those of thru-hole components. Consequently, the components used in SMT electronic assembly may weigh as little as one-tenth of what their traditional through-hole equivalents do.
- Due to the significantly reduced size of the components used in surface mount assembly, it is now feasible to pack them closer. At the same time, surface mount technology which uses solder paste, significantly increases the number of connections that can be made for each component.
- Another advantage of SMT assembly is that it uses efficient circuit board space. Special thanks to SMT assembly, engineers can now finagle complex electronics into smaller SMD assemblies.
- One of the reasons SMT assembly was conceived as it reduces PCBA manufacturing costs.
- SMT mounting results in a noteworthy decrease in electrical PCB thermal noise.
- The absence of threading increases the amount of surface area used.
Future of Surface Mount Technology
We have previously defined that SMT breadboard assembly is now widely used for PCBA production. The fact that most SMT producers have already implemented this technology is not surprising. The trend will continue over the next years as SMT becomes the standard technique for making PCBAs.
When competition is high, consumers win. SMT has become one of the most popular technologies and processes in the electronics assembly industry because of its flexibility, enabling manufacturers to produce smaller devices. If your project requires it, please contact FS Technology for a quote for your SMT assembly services. Therefore, the price of SMT printed circuit boards (PCBs) is currently high. But producers keep trying to lower their costs and services than the market standard. That means consumers can count on high-quality boards at reasonable prices.
Already, we can see that the SMT sector is making progress. The degree of automation that has been achieved is relatively high, and companies are working hard to provide outstanding services. The progression of technology makes everything, including SMT, more accessible as time goes on, and this is unavoidable.
Future developments in the sector are readily apparent. The researchers will keep looking for methods to increase the boards’ versatility while keeping them dependable. The industry will also consider user experience and environmental considerations.
The above content covers the majority of how FS Technology’s PCB SMT assembly service works, which includes our capabilities, quality assurance and an overview of the steps within the PCBA SMT process. Along with the products for our customers, FS Technology can additionally provide all service reports on PCB assembly and manufacturing, DIP assembly, mechanical assembly, 5G multi-layer high-frequency circuit board manufacturing, etc. With new developments in diminishing the size of technology and circuit boards, from using through-hole to surface-mount components, you should consider adding SMT aspects to your projects after weighing both the pros & cons. With a transparent and affordable service, FS Technology assists its customers from the very start of the assembly process, whether you are completely new to PCBA or an experienced maker in the commercial field. If your electronic project requires high-level manufacturing and assembly capabilities, please use the contact form above to easily request your SMT assembly price list and quotation.
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