Technical Support

Questions and Answers about SMT assembly

Many people will have questions about SMT assembly, such as “What is SMT assembly”? “What are the attributes of SMT assembly?” In the face of various questions from customers, I have compiled a list of questions and answers for you to answer your questions.

Q1:What is SMT assembly?

A1:SMT, short for surface mount technology, is an assembly technology used to paste components (SMC, surface mount component or SMD, surface mount device) to bare PCB (printed circuit board) through the application of a series of SMT assembly equipment.

Q2: What equipment is used in SMT assembly?

A2: In general, the following equipment is suitable for SMT assembly: solder paste printer, mounter, reflow oven, AOI (automatic optical inspection) instrument, magnifying glass or microscope, etc.

Q3: What are the attributes of SMT assembly?

A3: Compared with traditional assembly technology, i.e. THT (through-hole technology), SMT assembly leads to higher assembly density, smaller size, lighter product weight, higher reliability, higher impact resistance, lower defect rate, higher frequency, reduced EMI (Electromag netic interference) and RF (radio frequency) interference, higher throughput, more automation access , lower cost, etc.

Q4: What is the difference between SMT assembly and THT assembly?

A4: SMT assemblies differ from THT assemblies in the following ways.

a. Components used in THT assemblies have longer leads than SMT assemblies;
b. THT assemblies require drilling holes in the bare circuit board, while SMT assemblies do not because the SMC or SMD is mounted directly on the PCB;
c. Wave soldering is mainly used for THT assembly, while reflow soldering is mainly used for SMT assembly;
d. SMT assembly can be automated, while THT assembly depends only on manual operation;
e. Components used for THT assembly are heavy, high and bulky, while SMC helps to reduce more space.

Q5: Why are SMT components widely used in electronics manufacturing?
A5: Firstly, current electronic products have been striving to achieve miniaturization and light weight, which is difficult to achieve with THT assembly;

Second, in order to make electronic products functionally integrated, IC (integrated circuit) components are largely utilized to meet large-scale and high-integrity requirements, which is exactly what SMT assembly can do.

Third, SMT assembly is adapted to mass production, automation and cost reduction, all of which meet the needs of the electronics market;
Fourth, the application of SMT assembly to better promote the development of electronics technology, integrated circuits and semiconductor materials for a variety of applications;
Fifth, SMT assembly meets international electronic manufacturing standards.

Q6: In which product area SMT assembly is used?
A6: Currently, SMT assemblies have been used in advanced electronic products, especially computer-based and telecommunication products. In addition, SMT assemblies have been applied to products in various fields, including medical, automotive, telecommunication, industrial control, military, aerospace, etc.

Q7: What is the common manufacturing process for SMT assembly?
A7: The SMT assembly procedure usually includes solder paste printing, chip mounting, reflow soldering, AOI, X-ray inspection and rework. Visual inspection is performed after each step of the procedure.

Q8: What is solder paste printing and its role in SMT assembly?
A8:Solder paste printing is the process of printing solder paste on the pads on the PCB so that the SMC or SMD can stick to the board through the left solder paste on the pads. Solder paste printing is achieved by the application of stencils with many openings where the solder paste will remain on the pads.

Q9: What is chip mounting and its role in SMT assembly?
A9: Chip mounting contributes to the core meaning of SMT assembly, it refers to the process of quick placement of SMC or SMD on the SMT assembly. The solder pads are left on the PCB pads. Therefore, based on the adhesion of the solder paste, the component will temporarily stick to the surface of the board.

Q10: Why are solder types used in the SMT assembly process?

A10: Reflow soldering is used in SMT assembly to permanently fix the components on the PCB and is performed in a reflow oven containing temperature zones. In the reflow process, the solder paste is first melted at high temperatures in the first and second stages. As the temperature decreases, the solder paste will harden and therefore the components will be fixed to the corresponding pads on the PCB.


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