Through These Methods To See The Number of PCB Board Layers

As a hardware development engineer, for the PCB is familiar, in the usual communication use, we often mention single panel, double panel, four-layer board, etc., according to different application scenarios with different layers of the board, but because the layers of the PCB are closely combined, it is generally not easy to see the actual number, but if you carefully observe the board fault, You can still tell.

Insulating layer

Carefully, we will find that there is a layer or several layers of white material in the middle of the PCB, in fact, this is the insulation layer between the layers, to ensure that there is no short-circuit problem between different PCB layers. According to the industry, the current multi-layer PCB board uses more single or double sided wiring board, and puts a layer of insulation between each layer of the board after pressing, the number of layers of the PCB board represents several layers of independent wiring layer, and the insulation layer between layers has become an intuitive way for us to judge the number of layers of the PCB.

Pilot hole and blind hole light method

The pilot hole to light method uses the "pilot hole" on the PCB to identify the number of PCB layers. The principle is mainly due to the use of pilot hole technology in the circuit connection of multi-layer PCB. If we want to see how many layers the PCB has, we can identify it by observing the pilot hole. On the basic PCB (single-sided motherboard), the parts are concentrated on one side, and the wires are concentrated on the other side. If you want to use a multi-layer board, then you need to punch holes in the board, so that the component pins can pass through the board to the other side, so the pilot hole will punch through the PCB board, so we can see that the pins of the parts are welded on the other side.

For example, the board uses a four-layer board, then it is necessary to line the first and fourth layers (signal layer), and the other layers have other purposes (ground layer and power layer), the signal layer is placed on both sides of the power layer and the ground layer for the purpose of preventing interference between each other, and to facilitate the correction of the signal line.

If some board guide holes appear on the front of the PCB board, but can not be found on the back, then it can be basically concluded that it is a 6/8 layer board. If the same pilot hole 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 wiring method, that is, only some of the lines are connected, and the buried hole and blind hole technology are used in the wiring. The blind hole is to connect several layers of the internal PCB to the surface PCB without penetrating the entire circuit board. The buried hole is only connected to the internal PCB, so it is not visible from the surface. Since the blind hole does not need to run through the entire PCB, if it is six layers or more, the board is facing the light source to see, the light will not come through. Therefore, there is also a very popular saying before: to judge four and six layers or more PCB by whether the light leaks through the hole. This method has its reason, there are also less applicable places, the industry believes that this method can only be used as a reference method.

Accumulation method

It is not a method, exactly, but an experience. But this is what we think is accurate. We can judge the number of PCB layers by the location of the wiring and components of some PCB boards. Because in the current IT hardware industry that updates so fast, there are not many manufacturers that have the ability to redesign PCB after all. For example, a few years ago, a large number of 6-layer PCB design 9550 graphics card, careful friends can compare it and 9600PRO or 9600XT board type how many different? Just omit some components, while maintaining a high degree of consistency on the PCB. In the 1990s, there was a popular saying at that time: the PCB can be placed vertically to see the number of PCB layers, and many people believed it. This statement later proved to be nonsense, even if the manufacturing process at that time was backward, how can the eye distinguish the distance that is smaller than the hair? Later, this method continued and modified, and gradually evolved another measurement method. Now there are many people believe that you can use "vernier calipers" and other precision measuring instruments to measure the number of PCB layers, this statement we also feel to be verified.

And regardless of whether there is that kind of precision instrument, how can we not see that the 12-layer PCB is 3 times the thickness of the 4-layer? We all know that different PCB will use different manufacturing processes, there is no unified standard to measure, how to judge the number of layers according to the thickness?

In fact, the number of PCB layers has a great impact on the board. For example, why do you need to use at least 6 PCB layers to install a dual CPU? Because this can make the PCB has 3 or 4 signal layers, 1 ground layer, 1 or 2 power layers. Then the signal lines can be far enough apart to reduce interference with each other, and there is enough current supply. However, the general board using 4-layer PCB design is completely enough, the use of 6-layer PCB is too wasteful, and there is no performance improvement.