What is SMD
“In the early stages of electronic circuit board production, via hole assembly was entirely done manually. After the first automated machines were launched, they could place some simple leads Pin components, but complex components still need to be placed manually for wave soldering
SMD
In addition to SMD, there are:
SMC: surface mount components. (Surface Mounted components)
Mainly include rectangular chip components, cylindrical chip components, composite chip components, and special-shaped chip components.
SMD Architectural Design Office
SMD Architectural Design Office is a world-renowned young architect design office. SMD has always been at the forefront of the world's architectural design and construction engineering industry. Since its establishment, it has completed design projects including office buildings, banks and Financial institutions, government buildings, public buildings, private residences, medical institutions, religious buildings, airports, entertainment and sports venues, school buildings, etc.
2 Development Editor
Surface mount components were introduced about two decades ago and ushered in a new era from passive components to active components and integrated circuits, which eventually became surface mount devices (SMD) and could be carried by pick and place equipment. Assembly. For a long time, people have believed that all pin components can eventually be packaged in SMD.
3 Component Editing
Classification
Mainly included. Chip transistors and integrated circuits
Integrated circuits include SOP, SOJ, PLCC, LCCC, QFP, BGA, CSP, FC, MCM, etc.
Examples are as follows:
1. Interconnect: Provides mechanical and electrical connection/disconnection, consisting of connecting plugs and sockets, connecting cables, brackets, chassis or other PCBs to PCBs; however, the actual connection to the board must be through Surface mount contact.
2. Active electronic components (Active): In analog or digital circuits, the voltage and current can be controlled by oneself to produce gain or switching, that is, have an effect on the applied signal. The reaction can change its basic characteristics.
b Passive electronic components (Inactive): do not change their own characteristics when an electrical signal is applied, that is, they provide simple and repeatable reactions.
3. Odd-form electronic components: their geometric shape factors are peculiar, but not necessarily unique. Therefore, they must be mounted by hand, and the shape of their shells (in contrast to their basic functions) is non-standard. For example : Many transformers, hybrid circuit structures, fans, mechanical switch blocks, etc.
Parameters
Parameter specifications of various SMT components
Chip resistors, Capacitors, etc.: Size specifications: 0201, 0402, 0603, 0805, 1206, 1210, 2010, etc.
Tantalum capacitors: size specifications: TANA, TANB, TANC, TANDSOT
Transistors: SOT23, SOT143, SOT89, etc.
SMD
melf cylindrical components: diodes, resistors, etc.
SOIC integrated circuits: size specifications: SOIC08, 14, 16, 18, 20, 24, 28, 32
QFP fine pitch integration Circuit PLCC integrated circuit: PLCC20, 28, 32, 44, 52, 68, 84
BGA ball grid array packaging integrated circuit: array spacing specifications: 1.27, 1.00, 0.80
CSP integrated circuit: The side length of the component does not exceed 1.2 times the side length of the chip inside, and the array spacing is lt; microBGA of 0.50
The statistical average diameter of the nozzle spray particles, there are many evaluation methods, usually arithmetic Statistical mean diameter, geometric statistical mean diameter, but the most commonly used is Sautel mean, referred to as SMD.
The principle is to approximate all fog particles with uniform diameter spheres with the same surface area and volume. The calculated sphere diameter is the Sotel average diameter.
Since this statistical average reflects the physical characteristics of the subject very well, it is the most widely used in practice.
SMD components (8 photos)
4 Features Editor
High assembly density, small size and light weight of electronic products, the size and weight of chip components are only It is about 1/10 of the traditional plug-in components. Generally, after using SMT, the size of electronic products is reduced by 40~60% and the weight is reduced by 60~80%.
High reliability and strong vibration resistance. The solder joint defect rate is low.
Good high frequency characteristics. Reduces electromagnetic and radio frequency interference.
Easy to realize automation and improve production efficiency. Reduce cost by 30~50. Save materials, energy, equipment, manpower, time, etc.
5 Inspection Editor
Soter Average Diameter
Surface assembly component inspection. The main testing items of components include: solderability, pin surfaceability and usability, which should be subject to sampling inspection by the inspection department. To test the solderability of components, you can use stainless steel tweezers to hold the component body and immerse it in a tin pot at 235±5℃ or 230±5℃, and take it out after 2±0.2s or 3±0.5s. Check the soldering terminals for tin staining under a 20x microscope. It is required that the component soldering terminals are stained with tin at least 90%.
As a processing workshop, the following appearance inspections can be performed:
1. Visually or with a magnifying glass, check whether the soldering ends or pin surfaces of components are oxidized or have contaminants.
⒉The nominal values, specifications, models, accuracy, dimensions, etc. of components should be consistent with the product process requirements.
⒊The pins of SOT and SOIC cannot be deformed. For multi-lead QFP devices with a lead spacing of less than 0.65mm, the pin flatness should be less than 0.1mm (can be optically detected by the mounting machine).
⒋For products that require cleaning, the markings on the components will not fall off after cleaning, and the performance and reliability of the components will not be affected (visual inspection after cleaning).
6 Theory Editor
Inspection Methodology: This article explains that process monitoring can prevent circuit board defects and improve overall quality.
Inspections can often remind you whether there are still too many variables in your assembly process. Even after your manufacturing process can achieve consistent zero-defect production, some form of inspection or monitoring is necessary to ensure the desired level of quality. Surface mount assembly is a very complex series of events with a large number of individual actions. The trick is to build a balanced inspection and monitoring strategy without having to do 100s of inspections. This article discusses inspection methods, techniques, and manual inspection tools, as well as reviews automated inspection tools and using inspection results (number and type of defects) to improve process and product quality.
Inspection is a product-centered activity, while monitoring is a process-centered activity. Both are needed for a quality program, but the long-term goal should be less product inspection and more process monitoring. Product inspection is reactive (defects have occurred), while process monitoring is proactive (defects can be prevented) - clearly prevention is much more valuable than reactive reaction to already existing defects.
Inspection is actually a screening process because it attempts to identify unacceptable products for repair. The facts are clear: extensive inspections do not necessarily improve or guarantee product quality. The third of Deming's fourteen points says, "Don't expect mass inspections." Deming emphasized that a strong process should focus on establishing stable, repeatable, statistically monitored process goals rather than high-volume inspections. Inspection is a subjective activity and even with a reasonable degree of training, it is a difficult task. In many cases, you can call in a team of inspectors to evaluate a weld and get several different opinions.
Operator fatigue is the reason why 100 inspections often fail to find every manufacturing defect. Additionally, it is a costly, non-value-added operation. It rarely achieves the desired goals of higher product quality and customer satisfaction.
A few years ago we started using the term "process monitoring" instead of inspector because we wanted to change the mindset at the production site from reactive to proactive. An inspector usually sits at the end of the assembly line, inspecting the product. In an ideal situation, process monitoring activities are a balance between product inspection and process monitoring - for example, confirming that the correct process parameters are being used, measuring machine performance, and building and analyzing control charts. Process monitors assume a leadership role in these activities; they help machine operators complete these tasks. Training is a key factor. Process monitors and machine operators must understand process standards (e.g., IPC-A-610), process monitoring concepts, and related tools (e.g., control charts, Pareto charts, etc.). Process monitors also improve product quality and process monitoring. As a key member of the manufacturing team, inspectors encourage a defect-prevention approach rather than a find-and-fix approach.
Over-checking is also a common problem. In many cases, over-inspection is simply the result of a misunderstanding of the IPC-A-610 process standard. For example, for insert-mounted components, many inspectors also want perfectly soldered round feet on both sides of the board, with the through holes completely filled. However, this is not required by IPC-A-610. Inspection quality fluctuates with the intensity and concentration of the inspector's attention. For example, fear (management pressure) may increase concentration in a production site and quality may improve over a period of time. However, if mass inspection is the main inspection method, defective products may still be produced and may leave the factory.
Another term we should avoid is touch-up. Across the industry, many employees believe that touch-up welding is a normal and acceptable part of the assembly process. This is very unfortunate, as any form of rework and repair should be considered undesirable. Rework is often viewed as undesirable, but it is a necessary message to instil throughout the manufacturing organization. It is important to establish a manufacturing environment where defects and rework are considered avoidable and least desirable.
For most companies, manual inspection is the first line of defense. Inspectors use various magnification tools to get a closer look at components and solder joints. IPC-A-610 establishes some basic scaling guidelines based on inspecting component pad widths. The main reason for these guidelines is to avoid over-examination due to excessive magnification. For example, if the pad width is 0.25~0.50 mm, then the desired magnification is 10X, and 20X can be used as a reference if necessary.
Every inspector has a favorite inspection tool; there is a three-lens folding pocket magnifier used by mechanics that is better. It can be carried anywhere and has a maximum magnification of 12X, which is just right for fine-pitch soldering joints.
Perhaps the most common inspection tool is a microscope, with a magnification range of 10-40X. However, fatigue caused by continuous use of microscopes often leads to over-examination because magnification often exceeds the guidelines of IPC-A-610. It is of course useful when possible defects need to be scrutinized.
For general inspection, a video system with a variable zoom lens (4-30X) and a high-definition color monitor is preferred. These systems are easy to use and, importantly, less prone to fatigue than microscopes. High-quality video systems cost less than $2,000, and good microscopes are within this range. The added benefit of a video system is that more than one person can see the object, which is helpful during training or when the inspector needs a second opinion. Edmund Scientific has a wide range of magnification tools, from handheld magnifiers to microscopes to video systems.
In summary, establishing a balanced monitoring strategy between 0-100 checks is a challenge. From this point on, the critical inspection points we will discuss are inspection equipment.
Automation is wonderful; in many cases, more accurate, faster and more efficient than an inspector. But it can be quite expensive, depending on its complexity. Automated inspection equipment may dilute human awareness and give a false sense of security.
Solder paste inspection. Solder paste printing is a complex process that can easily deviate from the desired results. A clearly defined and properly executed process monitoring strategy is required to keep the process under control. At a minimum, manual inspection of coverage areas and thickness measurements is required, but it is better to use automated measurements of coverage, thickness, and volume. Use a range control chart (X-bar R chart) to record results.
Solder paste inspection equipment ranges from simple 3X magnifying glasses to expensive automatic in-line machines. Primary tools use optical or laser measurements for thickness, while secondary tools use lasers to measure coverage area, thickness and volume. Both tools are available offline. Level 3 tools also measure coverage area, thickness and volume, but are installed online. The speed, accuracy and repeatability of these systems vary, depending on price. More expensive tools offer better performance.
For most assembly lines, especially high-mix production, mid-level performance is preferred and is an offline, benchtop-mounted tool that measures coverage area, thickness, and volume. These tools are flexible, cost less than $50,000, and generally provide the desired amount of feedback. Obviously, automation tools cost much more ($75,000 - $200,000 USD). However, they are faster and more convenient to check boards because they are installed online. Best suited for high-volume, low-mix assembly lines.
Glue inspection. Glue dispensing is another complex process that can easily deviate from the desired results. As with solder paste printing, a clearly defined and properly executed process monitoring strategy is required to keep the process under control. It is recommended to check the glue dot diameter manually. Use a range control chart (X-bar R chart) to record results.
Before and after a dispense cycle, it is a good idea to place at least two isolated dots of glue on the board to represent each point diameter. This allows the operator to compare the quality of the glue dots during the Imperial Glue cycle. These points can also be used to measure glue dot diameter. Glue point inspection tools are relatively inexpensive and basically come in the form of portable or benchtop measuring microscopes. I am not aware of any automated equipment specifically designed for glue point inspection. Some automated optical inspection (AOI) machines can be adapted to perform this task, but may be overkill.
Confirmation of initial product (first-article). Companies often conduct detailed inspections of the first boards coming off the assembly line to verify the machine's settings. This method is slow, passive and inaccurate. It is common to see a complex board containing at least 1000 components, many without markings (values, part numbers, etc.). This makes inspection difficult. Verifying machine settings (components, machine parameters, etc.) is a proactive approach. AOI can be effectively used for the inspection of the first board.
Some hardware and software vendors also provide feeder configuration confirmation software.
Coordinating the verification of machine settings is an ideal role for a process monitor, who leads machine operators through the line qualification process with the help of a checklist. In addition to verifying the feeder settings, the process monitor should carefully inspect the first two boards using available tools. After reflow soldering, the process monitor should perform a quick but detailed inspection of critical components (fine-pitch components, BGAs, polarized capacitors, etc.). Meanwhile, the production line continues to assemble panels. To reduce downtime, the line should be filled with boards prior to reflow while process monitors inspect the boards after the initial two reflows. This can be a bit dangerous, but you can gain confidence in doing so by verifying the machine settings.
X-ray examination. Based on experience, X-ray is not necessarily mandatory for BGA assembly. However, it is certainly a good tool to have on hand if you can afford it. Its use should be recommended for CSP assemblies. X-rays are great for checking for solder shorts, but less effective for finding solder opens. Low-cost X-ray machines can only look down and are adequate for inspection of welding shorts. X-ray machines that can tilt the object under inspection are better for inspection.
Automated Optical Inspection (AOI). Ten years ago, optical inspection was used as a tool that could solve everyone's quality problems. The technology was later discontinued because it could not keep pace with assembly technology. In the past five years, it has re-emerged as a desirable technology. A good process monitoring strategy should include overlapping tools such as in-circuit testing (ICT), optical inspection, functional testing and visual inspection. These processes overlap and complement each other, and neither can provide adequate coverage on its own.
Two-dimensional (2-D) AOI machines can check for missing components, misalignment, incorrect part numbers and reversed polarity. In addition, three-dimensional (3-D) machines can evaluate the quality of weld joints. Some suppliers offer desktop, 2-D AOI machines for under $50,000. These machines are ideal for initial product inspection and small batch sample planning. In the higher performance categories, 2-D stand-alone or in-line machines range from $75,000 to $125,000, while 3-D machines range from $150,000 to $250,000. AOI technology has considerable promise, but processing speed and programming time are still limiting factors.
Data collection is one thing, but using that data to improve performance and reduce defects is the ultimate goal. Unfortunately, many companies collect a bunch of data without using it effectively. Reviewing and analyzing data can be laborious, and it is common to see this work performed only by engineering design staff and does not include production activities. Without accurate feedback, production proceeds blindly. Weekly quality meetings can be an effective method for engineering and production to communicate key information and drive necessary improvements. These meetings require a leader, must be well organized, and especially should be short (30 minutes or less). The data presented at these meetings must be user-friendly and meaningful (e.g., Pareto charts). When a problem is identified, an investigative researcher must be assigned immediately. To ensure a successful conclusion, meeting leaders must keep accurate records. Ending means root cause and corrective action.
7 Package Editor
Micro SMD wafer level CSP packaging:
Micro SMD is a standard thin product. There is a solder bump on one side of the SMD chip. Micro SMD production process steps include standard wafer fabrication, wafer repassivation, deposition of fusion solder bumps on I/O pads, backgrinding (only for thin products), protective encapsulation coating, The wafer selection platform is tested, laser marked, packaged into tape and reel form, and finally assembled on a PCB using standard surface mount technology (SMT).
Micro SMD is a wafer level chip size package (WLCSP), which has the following characteristics:
⒈ The package size is consistent with the die size;
⒉ Minimum I/O pins;
⒊ No underfill material required;
⒋ Wire spacing is 0.5mm;
⒌ Between chip and PCB No interposer is required.
Notes
Surface mounting precautions:
a. Micro SMD surface mounting operations include:
⒈ on PCB Printing flux;
⒉ Component placement using standard pick and place tools;
⒊ Reflow and cleaning of solder bumps (depending on flux type).
b. The surface mount advantages of micro SMD include:
⒈ Shipped in standard tape and reel packaging for easy operation (compliant with EIA-481-1 specifications);
⒈ p>
⒉ Standard SMT pick and place tools can be used;
⒊ Standard reflow soldering process.
Package size
Package size of SMD chip components:
Metric: 3216——2012——1608——1005——0603——0402
Imperial: 1206——0805——0603——0402——0201——01005
Note:
0603 has metric and imperial differences
The imperial system of metric system 0603 is metric system 0201
The metric system of imperial system 0603 is metric system 1608
Also note the difference between 1005 and 01005
1005 also has metric system , the difference between the imperial system
The metric system of the imperial system 1005 is the metric system 2512
The imperial system of the metric system 1005 is the imperial system 0402
As in ProtelDXP (Protel2004) and later versions There is a package library for SMD chip components, such as
CC1005-0402: used for chip capacitors, metric system is 1005, inch system is 0402 package
CC1310-0504: used for SMD capacitor, metric size is 1310, inch size is 0504 package
CC1608-0603: used for chip capacitor, metric size is 1608, inch size is 0603 package
CR1608-0603: Used for chip resistors, the package is 1608 in metric system and 0603 in imperial system. The dimensions are the same as CC16-8-0603, just for easy identification.
PCB layout
There are two types of surface mount packages: non-solder shield definition (NSMD) and solder shield definition (SMD). Compared with the SMD method, the NSMD method can strictly control the copper etching process and reduce stress concentration points on the PCB, so this method should be preferred.
In order to achieve a higher height above the ground, it is recommended to use a copper clad layer with a thickness less than 30 microns. A copper clad layer with a thickness of 30 microns or more will reduce the effective height above the ground, thus affecting the reliability of welding. Additionally, the width of the trace between the NSMD pad and the ground pad should not exceed two-thirds of the pad diameter. It is recommended to use the pad sizes listed in Table 1:
PCB layouts using via-in-pad structures (micro vias) should comply with NSMD pad definitions to ensure adequate lubrication on the copper pads. Welding zone thereby enhancing the welding effect.
Considering the internal structural performance, the organic solderability protection (OSP) coating circuit board treatment method can be used, and copper OSP and nickel-gold plating can be used:
⒈ If adopted Nickel-gold plating method (electroplating nickel, depositing gold), the thickness should not exceed 0.5 microns to avoid embrittlement of the soldering joint;
⒉ Since the flux has surface tension, in order to prevent the components from rotating, the printed lines should be Symmetrical in the X and Y directions;
⒊ It is recommended not to use the hot air solder leveling (HASL) circuit board processing method.
Printing process
Screen printing process:
⒈ The template is electroplated and polished and then laser cut.
⒉ When there are less than 10 solder bumps and the size of the solder bumps is small, the apertures should be offset as far away from the pads as possible to minimize bridging problems. When the number of welding bumps exceeds 10 or the welding bumps are large, there is no need to offset.
⒊ Use type 3 (particle size is 25-45 microns) or precision flux printing.
Component placement
Micro SMD placement can use standard pick and place tools, and the following methods can be used for identification or positioning:
⒈ Visual positioning of packages system.
⒉ Vision systems that can locate individual weld bumps are slow and expensive.
Other characteristics of micro SMD placement include:
⒈ In order to improve placement accuracy, it is best to use an IC placement/precision pitch placement machine instead of a chip-shooter .
⒉ Since the micro SMD solder bumps have self-centering properties, they will correct themselves when placed offset.
⒊ Although the micro SMD can withstand a placement force of up to 1kg for 0.5 seconds, it should be placed with no force or as little force as possible. It is recommended to place the solder bumps into the flux on the PCB and penetrate more than 20% of the flux height.
Soldering cleaning
Reflow soldering and cleaning:
⒈ Micro SMD can use industry standard reflow soldering process.
⒉ It is recommended to use nitrogen for cleaning during reflow soldering.
⒊ According to J-STD-020 standard, micro SMD can withstand up to three reflow soldering operations (maximum temperature is 235°C), compliant.
⒋ Micro SMD can withstand reflow soldering temperatures up to 260°C for up to 30 seconds.
Soldering rework
The key factors that produce micro SMD rework are as follows:
⒈ The rework process is the same as that of most BGA and CSP packages.
⒉ The parameters of reflow soldering should be completely consistent with the original parameters of reflow soldering during assembly.
⒊ The rework system should include local convection heaters with forming capabilities, bottom preheaters, and component pick-and-place machines with image overlay capabilities.
Quality Inspection
The following is the reliability check of the solder joints when the micro SMD is installed on the FR-4 PCB, as well as the mechanical test results. Testing included the use of daisy chain components. Product reliability data is listed separately in each quality inspection report of the product.
Welding quality inspection
Welding reliability quality inspection:
⒈ Temperature cycle: IPC-SM-785 "Accelerated Reliability of Surface Mount Welding Parts" should be followed Testing Guidelines for Sexuality Testing.
⒉Package shearing: As part of the production process, the shearing data of the solder bumps should be collected during packaging to ensure that the solder ball (solder ball) is tightly combined with the package. For a solder bump with a diameter of 0.17mm, the average package shear force recorded per solder bump was approximately 100gm. For welding bumps with a diameter of 0.3mm, the package shear force of each welding bump is greater than 200gm. Depending on the materials and surface mount methods used, the measured package shear values ??will vary.
⒊ Tensile test: Fix a screw on the back of the component and pull the assembled 8-solder bump micro SMD component vertically until the component is pulled away from the circuit board. For welding bumps with a diameter of 0.17 mm, the average pulling force recorded was 80 gm per welding bump.
⒋ Drop test: The object of the drop test is a micro SMD package with 8 welding bumps installed on a 1.5mm thick PCB. The diameter of the welding bumps is 0.17mm. Drop 7 times on the first side, 7 times on the second side, 8 times on the corner, and 8 times horizontally, for a total of 30 times.
If the test result is that the impedance in the daisy chain loop increases by more than 10, it is deemed to have failed the test.
⒌ Three-point bending test: Use a test plate with a width of 100mm to perform a three-point bending test, and twist the midpoint with a force of 9.45 mm/min. The test results show that even if the torsion force is increased to 25mm, there is no damage to the welding bump.
Thermal Characteristics
In accordance with IA/JESD51-3 regulations, an inefficient thermal conductivity test board is used to evaluate the thermal characteristics of the micro SMD package. The performance of SMD products depends on the product die size and application (PCB layout and design).
8 Moisture-proof Editor
Moisture-proof management regulations for SMD parts:
Purpose
To ensure that all moisture-sensitive devices are protected during storage and use Effective control to avoid the following two points:
① The welding quality of parts affected by moisture.
② Moist parts will cause cracks in the plastic body and pins when heated to high temperatures. Slight cracks will cause leakage in the case, causing the chip to slowly fail due to moisture, affecting the product life. Serious cracks will directly damage the components. .
Scope of application
Applicable to the storage and use of all moisture-sensitive parts.
Content
⒊1 Inspection and Storage
⒊1.1 All plastic-encapsulated SMD parts have been sealed in moisture-proof packaging when leaving the factory. It cannot be opened at will. The warehouse keeper confirms the model and quantity of the SMD parts from the packaging when receiving the materials and conducting IQC inspection. When the package must be opened, the number of unopened packages should be minimized. After inspection, the SMD parts should be returned to the original package in a timely manner, and then used a vacuum machine to evacuate and seal the opening.
⒊1.2 All unsealed SMD parts will be put online as soon as possible.
⒊1.3 Storage environment requirements for moisture-sensitive parts: room temperature is below 30°C and relative humidity is below 75.
⒊2 Production use
⒊2.1 Control the number of unsealed packages according to the production schedule. PCB, QFP, and BGA should be controlled within 12 hours, and SOIC, SOJ, and PLCC should be controlled within 48 hours. Completed within hours.
⒊2.2 For unused SMD parts, put them back into the bag, add desiccant, use a vacuum machine to vacuum and seal the mouth.
⒊2.3 When using SMD parts, first check the humidity value of the humidity indicator card. If the humidity value reaches 30 or above, it must be baked. The company uses SMD parts to equip the humidity display card with a six-circle type. , the humidity is 10, 20, 30, 40, 50, 60 respectively. How to read: If the circle of 20 turns pink and the circle of 40 is still blue, then the 30 next to the lavender between blue and pink is the humidity value.
⒊3 Moisture removal and drying
⒊3.1 If the humidity of the indicator card is found to be above 30 when opening, high-temperature drying is required. Oven temperature: 125℃±5℃. Drying time is 5~48 hours. The specific temperature and time vary from different manufacturers. Please refer to the manufacturer's drying instructions.
⒊3.2 There are two types of QFP packaging plastic trays: non-high temperature resistant and high temperature resistant. The high temperature resistant ones include Tmax=135, 150 or 180℃ and can be put directly into baking. The non-high temperature resistant ones The tray cannot be placed directly in the oven for baking.
9 Requirements for editing
Process requirements for mounting SMD on flexible printed circuit board FPC:
With the development of miniaturization of electronic products, a considerable number of For surface mounting of consumer products, due to the assembly space, the SMD is mounted on the FPC to complete the assembly of the whole machine. Surface mounting of SMD on FPC has become one of the development trends of SMT technology. For surface mounting The process requirements and attention points are as follows.
Conventional SMD mounting
Features: The mounting accuracy is not high, the number of components is small, and the component types are mainly resistors and capacitors. Or there are individual special-shaped components.
Key processes: 1. Solder paste printing: FPC is positioned on a special printing pallet based on its appearance. It is generally printed with a small semi-automatic printing machine, or manually printed. However, The quality of manual printing is worse than that of semi-automatic printing.
⒉ Mounting: Generally, manual mounting can be used, and individual components with higher position accuracy can also be mounted using a manual placement machine.
⒊Welding: Generally, the reflow process is used, and spot welding can also be used in special circumstances.