Workable Methods to Determine the PCB Layer-count
You hope to verify the PCB layer count that the manufacturer sent you, is it the required 4-layer board or just double-sided board? Any method for quick verification rather than going to the work station?
Below listed several simple and easy-use methods to determine the number of PCB layers. #395cc0
1. Ocular Estimate
Although the PCB layers are closely laminated, you can still distinguish it if carefully observe the board edges.
Watch closely, we will see that one or more layers of white matter are sandwiched between the circuit board, which are in fact the insulation layers between every two circuit board layers to avoid short-circuit between different PCB layers.
For multilayer printed circuit boards, more insulation layers are sandwiched between the PCB copper layers. Count the number of insulation layers by eyes, you're able to know the number of PCB layers.
2. Via Hole/Blind Via Inspection
Determine the number of PCB layers by inspecting the via holes or blind vias. The principle is mainly based on the use of the via hole technology in the circuit connection of the multilayer circuit board. We're able to determine the number of PCB layers, by identifying the vias.
On the single-sided PCB boards, the parts are concentrated on one side and the pins are concentrated on the other side. If a multilayer PCB is to be used, it is necessary to punch holes in the board so that the component pins can pass through the board to the other side, we can see that the pins of the parts are welded to the other side.
For example, a 4-layer PCB board, signal traces are required to be routed on the 1st (TOP) and 4th (BOT) layers and the inner PCB layers play other roles (Ground layer and Power layer), the signal layers are placed on two sides of the GND & Vcc is to prevent mutual interference. If some of the vias appear on the top layer, but can't be found on the bottom side, it has a PCB layers of 6 or more, and if the same vias can be found on both sides of the PCB board, it is generally a 4-layer board.
However, currently more complex buried via technology is used in the circuit board manufacturing, this type of vias is only used to connect couples of inner layers, and invisible on the PCB surfaces. So determining circuit board layers count by inspecting vias is easy-use but also limited.
3. According to Experience
To be precise, this is not a type of method, but a type of practical experience, which however is what we feel is the most accurate. The number of PCB layers can determined based on the traces and components of a PCB board used for a certain industry.
They are traceable because even though upgrading of the hardware is so fast, there are few designers who have the ability to rebuild the design rules of those widely used electronics.