Basic concept

Surface-mounting technology, called "SURFACE MOUNT TECHNOLOGY" in English, is called SMT. It is a surface mount component that is soldered to the printed circuit board pad and coated with solder paste, and then the surface mount components are accurately placed. On the pad coated with solder paste, the printed circuit board is heated until the solder paste melts, and the connection between the component and the printed circuit is realized after cooling.

2. Advantages of surface assembly technology:

1) High assembly density, using SMT, the electronic product can be reduced by 60% and the weight is reduced by 75%.

2) Reliability paste, the general bad solder joint rate is less than 10 parts per million, which is one order of magnitude lower than the wave soldering technology of through-hole components.

3) Good high frequency characteristics

4) Reduce costs

5) Easy to automate production.

3. Disadvantages of surface assembly technology:

1) The nominal value on the component is not clear, and the maintenance work is difficult.

2) It is difficult to repair and replace the device, and special tools are needed.

3) The coefficient of thermal expansion (CTE) between the components and the printed board is poor. With the advent of dedicated assembly and disassembly equipment and new low-expansion coefficient printed boards, they are no longer an obstacle to the further development of SMT.

4. Surface assembly process:

There are two basic processes in the SMT process, one is solder paste reflow soldering process, and the other is patch-wave soldering process. In actual production, it should be based on the type of components and production equipment used and the product requirements. Selecting different process flows, the basic process flow diagram is now as follows:

1) Solder paste - reflow soldering process, the process is characterized by simplicity and speed, which is conducive to the reduction of product volume.

2) SMD-wave soldering process, the process is characterized by the use of double-panel space, the volume of electronic products can be further reduced, and through-hole components are still used, the price is low, but the equipment requirements are increased, and the defects in the wave soldering process are more Many, it is difficult to achieve high-density assembly.

3) Hybrid installation, the process is characterized by making full use of the double-sided space of the PCB board, which is one of the methods to minimize the installation area, and still retains the low price of the through-hole components.

4) Both sides use solder paste-reflow soldering process. The characteristics of this process can make full use of PCB space, minimize installation area, complicated process control, strict requirements, and are often used in intensive or ultra-small electric products, mobile phones. It is one of the typical products.

We know that in terms of new materials, solder paste and glue are thixotropic fluids, and they cause defects that account for 60% of the total defects of SMT. Training to master these materials can guarantee SMT quality. SMT also involves a variety of assembly processes. Such as printing process, dispensing process, placement process,

The curing process, as long as the process parameters drift in any of the links, will lead to the production of defective products, SMT process personnel must have a wealth of process knowledge, monitor the process status at any time, predict development trends.