How to tell how many layers a PCB has

深圳百能PCB

How to tell how many layers a PCB has [Copy link]

　　How to tell how many layers a PCB has? Judging the number of layers of a PCB is a skill that must be mastered. Shenzhen Kinji Electronics https://www.kinjipcb.cn/ has collected some information and hopes it can help you!

　　First, visual inspection. Since the layers in the PCB are tightly combined, it is generally not easy to see the actual number, but if you carefully observe the faults on the board, you can still tell them apart. If you are careful, you will find that there is one or more layers of white material in the middle of the PCB. In fact, this is the insulation layer between the layers, which is used to ensure that there will be no short circuit problems between different PCB layers. Because the current multi-layer PCB boards use more single- or double-sided wiring boards, and a layer of insulation layer is placed between each layer of the board and then pressed together, the number of layers of the PCB board represents the number of independent wiring layers, and the insulation layer between the layers has become the most intuitive way for us to judge the number of layers of the PCB.

　　Second, the guide hole and blind hole light method. The guide hole light method uses the "guide hole" on the PCB to identify the number of PCB layers. The principle is mainly because the circuit connection of multi-layer PCB uses guide hole technology. If we want to see how many layers a PCB has, we can identify it by observing the guide hole.

　　On the most basic PCB (single-sided motherboard), the components are concentrated on one side, and the wires are concentrated on the other side. If you want to use a multi-layer board, you need to punch holes in the board so that the component pins can pass through the board to the other side, so the guide holes will penetrate the PCB. Therefore, we can see that the pins of the components are soldered on the other side.

　　For example, if the board uses a 4-layer board, then the 1st and 4th layers (signal layers) need to be routed, and the other layers have other uses (ground layer and power layer). The purpose of placing the signal layer on both sides of the power layer and the ground layer is to prevent mutual interference and facilitate correction of the signal line. If some board guide holes appear on the front of the PCB board, but cannot be found on the back, then it must be a 6/8-layer board. If the same guide holes can be found on both the front and back of the PCB board, it is naturally a 4-layer board.

　　However, many board manufacturers currently use another routing method, which is to connect only some of the lines, and use buried vias and blind vias in the routing. Blind vias connect several layers of internal PCB to the surface PCB without penetrating the entire circuit board.

　　The buried via only connects the internal PCB, so it cannot be seen from the surface. Since the blind via does not need to penetrate the entire PCB, if there are six layers or more, the light will not pass through when the board is facing the light source. Therefore, there was a very popular saying before: judging the four-layer and six-layer or more PCB by whether the via leaks light. This method has its reasons, but there are also places where it is not applicable. It can be used as a reference method.

　　Third, the accumulation method. To be exact, this is not a method, but an experience. However, we think it is the most accurate. We can judge the number of layers of PCB by the routing and component positions of some public PCB boards. Because in the current IT hardware industry, which is updated so quickly, there are not many manufacturers who are capable of redesigning PCB.

　　For example, a few years ago, a large number of 9550 graphics cards used a 6-layer PCB design. Careful friends can compare it with the 9600PRO or 9600XT board type to see how different it is. Only some components are omitted, while a high degree of consistency is maintained on the PCB.

　　In the 1990s, there was a popular saying that the number of PCB layers can be seen by placing the PCB vertically, and many people believed it. This saying was later proved to be nonsense. Even if the manufacturing technology at that time was backward, how could the eyes distinguish the distance that was thinner than a hair?

　　Later, this method continued and modified, and gradually evolved into another measurement method. Now many people believe that the number of PCB layers can be measured with precise measuring instruments such as "vernier calipers", but we do not agree with this statement.

　　Regardless of whether there is such a precise instrument, why can't we see that the 12-layer PCB is three times thicker than the 4-layer one? Different PCBs use different manufacturing processes, and there is no unified standard for measurement. How can we judge the number of layers based on thickness?