SMT capsulation is also a very important part of the patch.The so-called surface assembly technology refers to the assembly technology of electronic components with certain functions by placing the components with sheet structure or miniaturized components suitable for surface assembly on the surface of printed circuit board according to the requirements of the circuit and assembling them with reflow welding or wave soldering. The difference between installation and welding of SMT and THT components is shown in the figure. On the traditional THT printed circuit board, components and solder joints are located on both sides of the board, while on the SMT printed circuit board, solder joints and components are located on the same side of the board. Therefore, on the printed circuit board of SMT mounter, through holes are only used to connect the wires on both sides of the circuit board, the number of holes is much less, and the diameter of holes is much smaller. In this way, the assembly density of PCB can be greatly increased.
SMT surface mounting components have no difference in function from instrumentation components. The difference lies in the packaging of components. Surface mounted packages must withstand high temperatures during welding, and their components and substrates must have a matching thermal expansion coefficient. All these factors must be considered in product design.
The characteristics of SMT technology can be reflected by comparing with traditional through-hole cartridge technology (THT). From the point of view of assembly technology, the basic areas of SMT and THT are “paste” and “insert”. The differences between the two are also reflected in the various aspects of the substrate, components, component morphology, solder joint morphology and assembly process.
The main advantages of choosing suitable SMT capsulation are as follows:
1,SavingPCB area effectively.
3,Protectingthe interior of components from dampness and other environmental impacts.
4,Providinggood communication links;
5,Helpingheat dissipation and facilitatingtransmission and testing.
The selection and design of SMT surface mounting components is a key part of the overall product design. The designer determines the electrical performance and function of SMT components in the stage of system structure and detailed circuit design. In the stage of SMT design, the packaging form and structure of surface mounting components should be determined according to the specific conditions of equipment and process and overall design requirements.
Surface mounted solder joints are both mechanical and electrical joints. Reasonable selection has a decisive impact on improving PCB design density, productivity, testability and reliability.
Compared with the through-hole interpolation of components, surface assembly technology has the following advantages:
(1) Realizing Miniaturization. The geometrical size and space occupied volume of SMT electronic components are much smaller than those of through-hole plug-in components, which can generally be reduced by 60%-70%, or even 90%. The weight was reduced by 60%-90%.
(2) High speed of signal transmission. With compact structure and high assembly density, the assembly density can reach 5.5-20 solder joints/cm when mounted on both sides of the circuit board. Because of the short connection, small delay and high-speed signal transmission can be realized. At the same time, that more vibration resistance, impact resistance. This is of great significance for the ultra-high speed operation of electronic equipment.
(3) Good high frequency characteristics. Because the components have no lead or short lead, the distribution parameters of the circuit are naturally reduced and the radio frequency interference is reduced.
(4) It is conducive to the automation of production and the improvement of finished product rate and production efficiency. Because of the standardization of shape and dimension, serialization and consistency of welding conditions, SMT has a high degree of automation (automatic production line solution), which greatly reduces the failure of components caused by welding process and improves the reliability.
(5) Material cost is low. Nowadays, with the exception of a few varieties which are difficult to flake or have very high packaging precision, the packaging cost of most SMT components is lower than that of iFHT components of the same type and function, and the selling price of SMT components is lower than that of THT components.
(6) SMT (Surface Mounting Technology) technology simplifies the production process of electronic products and reduces the production cost. When assembled on PCB, the lead of components is not bent or cut short, which shortens the whole production process and improves the production efficiency. The processing cost of the same functional circuit is lower than that of through-hole insertion, which can generally reduce the total production cost by 30%-50%.
Deficiencies of Surface Assembly Technology
1,General power is small
3,Easy to damage
4,High requirements for welding technology: virtual welding, tin collection, volcanic crater, leak welding, bridging (connecting tin), stele and other phenomena are easy to occur.
5,Installation of components is prone to loss or damage.
6,It’s not easy to use visual inspection and it’s difficult to test.
7,Miniaturization and numerous types of solder joints complicate process and inspection
8,Large investment in equipment
9,Technology is complex,thatrequires higher training and learning costs.
10,Rapid development needs continuous follow-up
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