PCB News - An intuitive way to judge the number of PCB layers

1. Visual method

Because the layers in a PCB board are so tightly integrated, it's not always easy to see the actual number, but if you look closely at the split-plate faults, you can tell. If we are careful, we will find that there is a layer or several layers of white material sandwiched between PCB. In fact, this is the insulation layer between each layer, which is used to ensure that there will be no short circuit between different PCB layers. At present, multi-layer PCB boards use more single or double-sided wiring boards, and an insulating layer is placed between each layer and pressed together. The number of layers of PCB board represents several independent wiring layers, and the insulating layer between layers becomes an intuitive way for us to judge the number of layers of PCB.

What about PCB layers

2. guide hole and blind hole light method

Guide hole opto-optical method uses the "guide hole" on the PCB to identify the number of PCB layers. Its principle is mainly due to the multilayer PCB circuit connection adopts the guide hole technology. To see how many layers a PCB has, we can identify them by looking at the guide holes.

On a basic PCB, the parts are concentrated on one side and the wires are concentrated on the other. If you want to use a multilayer board, you need to punch holes in the board so that the pins can pass through the board to the other side, so the guide holes will punch through the PCB board. So we can see that the stitching of the part is welded to the other side.

For example, the board uses four layers, so the cable needs to be routed on the first and fourth layers (signal layer), and other layers have other uses (ground layer and power layer). The signal layer is placed on both sides of the power layer and ground layer to prevent interference between each other and facilitate the correction of the signal line. If some card guide holes appear on the front of the PCB, but can not be found on the back, then it must be 6/8 layer board. If the PCB board can be found on both sides of the same guide hole, naturally is the 4 layer board.

However, at present, many board card manufacturers use another method of wiring, which is only connected to some of the lines, and in the wiring using buried hole and blind hole technology. The blind hole is to connect several layers of internal PCB to the surface PCB without penetrating the entire circuit board.

Buried holes are only connected to the internal PCB, so they are not visible from the surface. Because the blind hole does not need to run through the whole PCB, if it is six layers or more, the light will not pass through when the board is facing the light source. So there is also a very popular saying before: through the hole whether light leakage to judge four layers and six layers or more PCB. This method has its truth, but also has the less applicable place, can be used as a reference method.

3. Accumulation method

This is not exactly a method, but an experience. But that's what we think is accurate. We can judge the number of PCB layers by the wiring and component position of some PCB board cards. Because in today's IT hardware industry, which is changing so fast, not many manufacturers have the ability to redesign PCBS.

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 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 that the number of PCB layers could be seen by placing PCB upright, and many people believed it. This claim was later proved to be a myth. How could the eye detect a distance smaller than a strand of hair, even if the technology of the time had been backward? Later this method continued and modified, gradually evolving into another measurement method. Many people now believe that you can measure the number of layers on a PCB with a sophisticated measuring instrument such as a "vernier caliper."

With or without that kind of sophisticated equipment, how can we not see that a 12-layer PCB is three times thicker than a 4-layer PCB? Different PCB will use different manufacturing process, 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 use at least 6 layers of PCBS to install dual cpus? This allows the PCB to have three or four signal layers, one grounding layer, and one or two power layers. Then the signal lines can be far enough apart to reduce interference with each other and have enough current supply. However, a 4-layer PCB design is sufficient for general boards, while a 6-layer PCB is too costly and does not provide much performance improvement.