Almost all the PCB electronic equipment we can see, from electronic watches and calculators to computers, communication electronic equipment and military weapon systems, as long as there are integrated circuits and other electronic components, the electrical interconnection between them will use the printed circuit board.Simply put, PCB printed circuit board (also known as printed circuit board) is through the printed wires on the circuit board to realize the electrical connection of the solder pad and through hole, etc., at the same time, it also provides a variety of electronic components such as integrated circuit fixed assembly of mechanical support.It can realize wiring and electrical connection or electrical insulation between various electronic components such as integrated circuits. It also provides soldering resistance pattern for automatic soldering.Provide identifying characters and graphics for component assembly, inspection and maintenance.Because they use Printed Circuit boards produced by photographic plate printing technology, they are called Printed Circuit boards, namely Printed Circuit boards, or PCB for short.
In the early stage of assembling electronic components on PCB, Through Hole Technology (THT) is adopted to install the components on one side of the board, and the lead pin is inserted into the corresponding mounting Hole of the printed circuit board. Then, it is welded and fixed on the other side with the circuit welding plate on the printed circuit board.This kind of installation technology has the advantages of less investment, relatively simple process, low cost of base materials and printed circuit technology, wide range of application, etc.At the same time, the construction of plug-in installation technology and PCB connection is better. For example, the socket of the wiring needs to withstand the pressure, so they are usually THT packaging.However, in this way of installation, components need to take up a lot of space, and to drill a hole for each pin, their pins also need to take up two sides of the space, and the solder joint is also large, there are some drawbacks.
With the trend of miniaturization of electronic products, the previously used perforated plug-in components have been unable to shrink, while the functions of electronic products are becoming more and more perfect, the integrated circuit (IC) used has no perforated components, especially the large-scale and highly integrated IC, which has to use the surface patch components.With the emergence of SMT, the mounting mode of components on PCB has gradually evolved from single through-hole mounting (THT) to surface mounting (stick), or mixed installation of plug and stick.At present, there are more and more kinds of double-sided pasted components applied in PCB.
Because the PCB used for SMT and the PCB used for THT are different in design, material and so on, in order to distinguish, PCB used for SMT is usually called Surface Mount Printed Circuit Board (SMB).In a broad sense,SMT substrates are not limited to printed circuit boards, but also include ceramic substrates, silicon substrates, enameled steel substrates and other substrates.Narrow sense of SMT with substrate refers to SMB.