1. Visual inspection method

Considering the close integration of each layer in a PCB circuit board, it is generally not easy to determine the actual number. However, if the board faults are carefully investigated, they can still be identified. If we are more careful, we will see that there are one or more layers of white material sandwiched between PCB circuit boards. In practice, this is the insulation layer between each layer, which is used to ensure that there is no short circuit problem between different PCB circuit board layers. This is because at present, multi-layer PCB circuit boards use more single or double-sided wiring boards, and a layer of insulation is placed between each board and pressed together. The number of layers on the PCB circuit board represents the presence of multiple independent wiring layers, and the insulation layer between layers has become an intuitive way for us to determine the number of layers on the PCB circuit board.

2. Guide hole and blind hole alignment method

The guide hole alignment method uses the "guide holes" on the PCB circuit board to identify the number of layers on the PCB circuit board. The principle is mainly based on the consideration that the circuit connections of multi-layer PCB circuit boards are all made using via technology. We can determine how many layers a PCB circuit board has by investigating the vias.

On a basic PCB circuit board (single-sided motherboard), components are concentrated on one side, while wires are concentrated on the other side. If you want to use a multi-layer board, you need to drill holes on the board so that the component pins can pass through the board to the other side. Therefore, the conductive holes will be drilled through the PCB circuit board. So we can see that the pins of the parts are welded on the other side.

For example, if a 4-layer board is selected for the board, wiring needs to be done on layers 1 and 4 (signal layer). The other layers also have purposes (ground layer and power layer). The purpose of placing the signal layer on both sides of the power layer and ground layer is to prevent mutual interference and facilitate the correction of signal lines. If some board guide holes appear on the front of the PCB circuit board but cannot be found on the back, then it must be a 6/8 layer board. If the same conductive holes can be found on both sides of the PCB circuit board, it is naturally a 4-layer board.

But at present, many board manufacturers have chosen another type of wiring method, which is to only connect certain lines between them, and use buried hole and blind hole technology in the wiring. Blind holes are the connections between multi-layer internal PCB circuit boards and surface PCB circuit boards, without penetrating the entire circuit board.

The buried hole only connects to the internal PCB circuit board, so it is basically not visible from the surface. Considering that blind holes do not need to penetrate the entire PCB circuit board, if it is six layers or more, looking at the board facing the light source will not allow light to pass through. Therefore, there used to be a very popular saying that distinguishes four layer and six layer or more PCB circuit boards based on whether the vias can leak light. This method has its rationale, but it may not be applicable locally and can be used as a reference method.

3. Accumulation method

To be precise, this is not a type of method, but a type of practical experience. But this is what we consider accurate. We can determine the number of layers on a PCB circuit board based on the routing and component positions of certain public PCB circuit boards.

Article source: Jiangmen PCB Customizationhttp://www.yonghongpcb.com/