What Is Surface Mount Technology
SMT is surface mount technology, which is the most popular technology and process in the electronic assembly industry, called surface mount or surface mount technology. It is a circuit assembly technology that mounts the surface mount components without leads or short leads on the surface of the printed circuit board or the surface of other substrates, and then solders and assembles them by reflow soldering or dip soldering.
Therefore, surface mount technology refers to the abbreviation of a series of technological processes that are processed on the basis of PCB.
Surface mount technology is a new generation of electronic assembly technology and the most popular technology and process in the electronic assembly industry. It compresses traditional electronic components into devices that are only a few tenths of their volume.
Detailed Process of Surface Mount Technology Chip Processing
Material Sourcing, Processing and Inspection
The material purchaser conducts the original purchase of materials according to the BOM list provided by the customer to ensure that the production is basically correct. After the purchase is completed, the material inspection and processing are carried out, such as pin header cutting, resistance pin forming and so on. Inspection is to better ensure production quality.
Silk Printing
Screen printing, that is, screen printing, is the first process of SMT processing. Silkscreen refers to the leakage of solder paste or patch glue onto the PCB pads to prepare for component soldering. With the help of a solder paste printer, the solder paste is infiltrated through a stainless steel or nickel stencil to attach to the pads.
If the stencil used for screen printing is not provided by the customer, the processor needs to make it according to the stencil file. At the same time, because the solder paste used must be frozen, the solder paste needs to be thawed to a suitable temperature in advance. The thickness of solder paste printing is also related to the squeegee, and the thickness of solder paste printing should be adjusted according to the PCB processing requirements.
Dispensing
Generally in SMT processing, the glue used for dispensing is red glue, and the red glue is dropped on the PCB position, which plays the role of fixing the components to be soldered, and prevents the electronic components from falling off due to their own weight or instability during the reflow soldering process. drop or solder joints.
Dispensing can be divided into manual dispensing or automatic dispensing, which is confirmed according to process needs.
Mounting
Using the placement machine, the SMC/SMD components can be quickly and accurately mounted on the designated pad position on the PCB without damaging the components and the printed circuit board. Mounting is generally prior to reflow soldering.
Cure
The curing is to melt the patch glue, and the surface mount components are fixed on the PCB pads, generally using thermal curing.
Reflow Soldering
Reflow soldering is the soldering of the mechanical and electrical connections between the terminations or pins of surface mount components and the printed board pads by remelting the paste-loaded solder pre-distributed to the printed board pads.
It mainly depends on the effect of hot air flow on the solder joints, and the jelly-like flux undergoes a physical reaction under a certain high temperature air flow to achieve SMD welding.
Cleaning
After the soldering process is complete, the board surface needs to be cleaned to remove the rosin flux and some solder balls, preventing them from shorting between components.
Cleaning is to place the soldered PCB board in a cleaning machine to remove the harmful flux residues on the surface of the PCB assembly board or the flux residues after reflow soldering and manual soldering and the contaminants caused by the assembly process.
Detection
The inspection is to inspect the welding quality and assembly quality of the assembled PCB assembly board. AOI optical inspection, flying probe tester and ICT and FCT functional testing are required.
Repair
The rework of SMT is usually to remove the components that have lost function, damaged pins or wrong arrangement, and replace the new components. Check for missing components, wrong direction, virtual soldering, short circuit, etc.
Surface Mount Technology Features
High assembly density, small size and light weight of electronic products. The volume and weight of SMD components are only about 1/10 of those of traditional plug-in components. Generally, after surface mount technology is used, the volume of electronic products is reduced by 40%~60% and the weight is reduced by 60%. %~80%.
Surface mount technology products have high reliability and strong anti-vibration ability; low defect rate of solder joints, good high-frequency characteristics; reduce electromagnetic and radio frequency interference. And it is easy to realize automation and improve production efficiency. Reduce costs by 30% to 50%. Save material, energy, equipment, manpower, time, etc.
Why Surface Mount Technology uses a patch
There are many capacitors, inductors, resistors, and other components inserted on the circuit board. Due to the advancement of technology and the requirements of technology, the requirements for components on the circuit board are getting higher and higher, and they need smaller and smaller spaces. It is getting more and more efficient, so SMD components are researched. These components have a small footprint, and the efficiency of the machine placement machine is very high, and the problems are getting smaller and smaller.
Surface Mount Technology component classification
In the processing and production of surface mount technology chips, we always come into contact with a variety of materials, and electronic materials are divided into two types, surface mount technology components and surface mount technology devices. Among them, SMT components are also known as SMC components, including surface mount resistors, capacitors and inductors.
Surface mount resistors, whose resistance values are generally printed on the surface of the component, are usually three or four digits. When three digits are printed on the surface, the first two digits are significant digits, and the third digits are filled with zeros after the significant digits.
There are four main parameters, namely capacitance, size, error and coefficient. The size of the capacitance value varies with different media, and is generally represented by three digits. For aluminum electrolytic capacitors, the darker pole is called the negative pole. For ceramic capacitors, the capacitance value is not printed on the surface of the component, and components of the same color and size have different capacitance values.
Surface mount inductors, also known as magnetic beads, have similar surfaces and surface mount capacitors, but with a darker color, which can be distinguished by a tester and their inductance measured. Surface mount inductors are divided into wire-wound and non-wire-wound types. The main parameters are size, error, inductance, etc.
surface mount diodes. Two common types are glass diodes and plastic-encapsulated diodes. Diodes are widely used in life, such as light-emitting diodes used in mobile phones. Diodes of different materials can emit different colors of light. Within the pressure range it can withstand, applying different voltages will emit light with different brightness.
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