A double-sided board is a printed circuit board that is covered with copper on both sides including Top (top layer) and Bottom (bottom layer). Both sides can be wired and soldered, with an insulating layer in the middle, which is a commonly used printed circuit board. Both sides can be routed, which greatly reduces the difficulty of wiring, so it is widely used.
Strictly speaking, the double-sided board is a very important PCB board in the circuit board. It’s use is very large. It is also very simple to see whether a PCB board is a double-sided board. I believe that friends can totally understand the single-sided board, the double-sided board is the extension of the single-sided board, which means that the single-board circuit is not enough to go to the opposite side. The double-sided board also has an important feature of having a via hole.
There are wiring on both sides of the double-sided board, but to use the wires on both sides, it is necessary to have a proper circuit connection between the two sides. This “bridge” between circuits is called a via. The via is a small hole filled or coated with metal on the PCB board, which can be connected to the wires on both sides. Because the area of the double-sided board is twice as large as the single-sided board, the double-sided board solves the difficulty of interleaving wiring in the single-sided board (it can be connected to the other side through the hole), and it is more suitable for more complicated circuits than the single-sided board.
The production process of double-sided board
The production of double-sided board is more complicated than that of single-sided boards. The main reasons are as follows:
(1) The top and bottom layers of the copper-clad board must be wired.
(2) The wires on the top layer and the bottom layer should be connected with metalized vias.
Among them, the via metallization is particularly critical, which is also the core process of double-sided board production. The so-called via metallization is to coat a layer of metal on the inner wall of the via hole in order to connect the printed wires of the top layer and the bottom layer. At present, the domestic via metallization mainly adopts the electroless copper plating process. There are two types of electroless copper plating process:
① First electrolessly plate thin copper, then electroplating the whole board to thicken the copper layer, and then transfer the pattern.
② Thick copper is electrolessly plated first, and then the graphics are transferred directly.
Both are widely used. However, the chemical copper plating method is harmful to the environment, and it will be gradually replaced by more advanced black hole technology, tin / palladium direct plating technology, and polymer direct plating technology.
The production process of double-sided board
The manufacturing method of the PCB double-sided board is generally made by the inner layer pattern first, and then the single-sided or double-sided substrate is made by printing and etching, and it is included in the designated layer, and then heated, pressed and bonded, as for the subsequent drilling the hole is the same as the double-sided plated through-hole method. These basic production methods have not changed much from the construction methods dating back to the 1960s, but as the materials and process technology (such as: pressure bonding technology, solving slag generated during drilling, and improvement of film) become more mature, the attached the characteristics of the multilayer board are more diverse.
The development history of double-sided board
Printed circuit board manufacturing technology started in the mid-1940s. From the mid-1940s to the 1950s, the electronics industry was in the age of electronic tubes, and most of the printed circuit boards used were single-sided board, mainly used in civilian electronic products such as radios and televisions. In the early 1960s, due to the widespread use of transistors, the volume of electronic components was reduced, and the mounting density was greatly increased. The printed circuit board developed from a single-sided board to double-sided board, and the application range was also extended to industrial and military fields. The appearance of integrated circuits in the 1960s allowed the popularization of double-sided metallized printed circuit boards and the appearance of multilayer printed circuit boards and flexible printed circuit boards capable of twisting and stretching. Since the 1970s, due to the development of large-scale and ultra-large-scale integrated circuits, electronic equipment has become increasingly miniaturized and miniaturized, and surface mounting technology has developed rapidly. The pins of surface-mounted devices are packaged without leads or horizontally, and can be flat on the surface of the printed circuit board. The welding of the pins and the printed circuit board does not need to be punched, which greatly improves the installation density of components, increases the reliability of the system and facilitates the automation of production.
The processing level of printed circuit boards is also constantly improving. At present, the standards for measuring the processing level are the minimum allowable width of the wire, the minimum distance between the lines, the positioning accuracy of the hole, and the number of PCB layers.