How to identify the number of layers of the pcb circuit board
First, the visual method.
Since the layers in the PCB are tightly coupled, it is generally not easy to see the actual number, but if you look closely at the board fault, you can still distinguish it. Attentively, we will find that one or several layers of whiter materials are sandwiched between the PCBs. In fact, this is the insulating layer between the layers to ensure that there is no short circuit between different PCB layers. Because the current multi-layer PCB board uses more single-sided or double-sided wiring boards, and puts an insulating layer between each board and presses it together, the number of layers of the PCB board represents several wiring layers of independence.And the insulation layer between the layers becomes the most intuitive way to judge the number of layers in the PCB.
Second, the guide hole and the blind hole are on the light method.
The via hole light method uses the “via hole” on the PCB to identify the number of PCB layers. The principle is mainly due to the usage of the via hole technology in the circuit connection of the multilayer PCB. We want to see how many layers of PCB are visible by observing the vias.
On the most 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, 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 board. So we can see that the pins of the part are welded to the other side.
For example, if the board uses a 4-layer board, then the first and fourth layers (signal layer) need to be routed, and the other layers have other usages (ground layer and power layer), and the signal layer is placed on the power layer and both sides of the ground plane can prevent mutual interference and facilitate correction of the signal line. If some of the board guide holes appear on the front side of the PCB board but are not found on the reverse side, then it must be a 6/8 layer board. If the same guide hole can be found on both the front and back of the PCB board, it is naturally a 4-layer board.
The buried hole is only connected to the internal PCB, so it is not visible only from the surface. Since the blind holes do not need to run through the entire PCB, if it is six or more layers, the board will be viewed from the light source, and the light will not pass through. So there was a very popular saying previous: whether the four or more layers of PCBs were judged by whether the vias hole leaked light. This method has its own reasons, and there are places that are not suitable for use as a reference method.
Third, the accumulation method.
To be exact, this is not a method, but an experience. But this is what we think is the most accurate. We can judge the number of layers of the PCB by the routing of some PCB boards and the position of the components. Because the IT hardware industry is currently being updated so quickly, there are not many vendors that have the ability to redesign PCBs.
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