PCB News - SMT stands for Surface Mounted Technology

SMT stands for Surface Mounted Technology (abbreviation for Surface Mounted Technology)
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What is SMT:
SMT stands for Surface Mounted Technology (abbreviation of Surface Mounted Technology), which is currently the most popular technology and process in the electronics assembly industry.
What are the characteristics of SMT:
High assembly density, small size and light weight of electronic products. The volume and weight of chip components are only about 1/10 of that of traditional plug-in components. Generally, after SMT is adopted, the volume of electronic products is reduced by 40%~60%, and the weight is reduced by 60%~ 80%.
High reliability and strong anti-vibration ability. The defect rate of solder joints is low.
Good high frequency characteristics. Reduce electromagnetic and radio frequency interference.
It is easy to realize automation and improve production efficiency. Reduce costs by 30%~50%. Save materials, energy, equipment, manpower, time, etc. Computer placement machine, as shown

Why use SMT:
Electronic products are pursuing miniaturization, and the previously used perforated plug-in components can no longer be reduced
Electronic products have more complete functions, and the integrated circuits (ICs) used have no perforated components, especially large-scale, highly integrated ICs, so surface mount components have to be used

With mass production of products and automation of production, the factory must produce high-quality products with low cost and high output to meet customer needs and strengthen market competitiveness
The development of electronic components, the development of integrated circuits (IC), the diversified application of semiconductor materials
The electronic technology revolution is imperative, chasing the international trend
SMT basic process components:

Silk screen (or dispensing) --> Mounting --> (curing) --> Reflow soldering --> Cleaning --> Inspection --> Rework
Silk screen: Its function is to print solder paste or patch glue onto the PCB pads to prepare for the soldering of components. The equipment used is a screen printing machine (screen printing machine), located at the forefront of the SMT production line.
Dispensing: It is to drop the glue onto the fixed position of the PCB, and its main function is to fix the components on the PCB board. The equipment used is a dispenser, located at the forefront of the SMT production line or behind the testing equipment
noodle.
Mounting: Its role is to accurately mount surface mount components to a fixed position on the PCB. The equipment used is a placement machine, located behind the screen printing machine in the SMT production line.
Curing: Its function is to melt the patch glue, so that the surface mount components and the PCB board are firmly bonded together. The equipment used is a curing oven, located behind the placement machine in the SMT production line.
Reflow soldering: Its function is to melt the solder paste, so that the surface mount components and the PCB board are firmly bonded together. The equipment used is a reflow oven, located behind the placement machine in the SMT production line.
Cleaning: Its function is to remove the solder residues such as flux that are harmful to the human body on the assembled PCB board. The equipment used is a washing machine, and the location may not be fixed, it may be online or offline.
Inspection: Its function is to inspect the welding quality and assembly quality of the assembled PCB board. The equipment used includes magnifying glass, microscope, online tester (ICT), flying probe tester, automatic optical inspection
(AOI), X-RAY detection system, functional tester, etc. The location can be configured in a suitable place on the production line according to the needs of the inspection.
Rework: Its function is to rework the PCB boards that have failed to detect faults. The tools used are soldering irons, rework stations, etc. Configured at any position in the production line.

Introduction to SMT Common Knowledge
Generally speaking, the temperature specified in the SMT workshop is 25±3°C.
2. When printing solder paste, the materials and tools needed to prepare solder paste, steel plate, scraper, wipe paper, dust-free paper, cleaning agent, stirring knife.
3. The commonly used solder paste alloy composition is Sn/Pb alloy, and the alloy ratio is 63/37.
4. The main components in the solder paste are divided into two parts: tin powder and flux.
5. The main function of flux in soldering is to remove oxides, destroy the surface tension of molten tin, and prevent re-oxidation.
6. The volume ratio of tin powder particles to Flux (flux) in the solder paste is about 1:1, and the weight ratio is about 9:1.
7. The principle of obtaining solder paste is first-in, first-out.
8. When the solder paste is used in unpacking, it must go through two important processes to reheat and stir.
9. The common production methods of steel plate are: etching, laser, electroforming.
10. The full name of SMT is Surface mount (or mounting)
technology, Chinese means surface adhesion (or placement) technology.
11. The full name of ESD is Electro-static discharge, which means electrostatic discharge in Chinese.
12. When making SMT equipment program, the program includes five major parts, these five parts are PCB data; Mark data;
Feeder data; Nozzle data; Part data.
13. The melting point of lead-free solder Sn/Ag/Cu 96.5/3.0/0.5 is 217C.
14. The controlled relative temperature and humidity of the parts drying box is < 10%.
15. Commonly used passive components (Passive
Devices) include: resistance, capacitance, point sense (or diode), etc.; active components (Active
Devices) include: transistors, ICs, etc.
16. The commonly used SMT steel plate is made of stainless steel.
17. The thickness of commonly used SMT steel plates is 0.15mm (or 0.12mm).
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