What is a PCB back drill?

Back drilling is actually a special kind of deep-drilling control. In the production of multi-layer boards, such as the production of 12-layer boards, we need to connect the first layer to the ninth layer. Usually we drill through holes (one-time drilling) and then Chen Tong. In this way, the first layer is directly connected to the twelfth layer. In reality, we only need to connect the first layer to the ninth layer. The tenth to twelfth layers are not connected by wires, like a pillar. This column affects the signal path and causes signal integrity problems in communication signals. So the extra column (called STUB in the industry) was drilled from the reverse side (secondary drilling). So it is called back drill, but it is generally not so clean, because the subsequent process will electrolyze a little copper, and the drill tip itself is sharp. Therefore, PCB manufacturers will leave a small point. The length of the left STUB is called B value, which is generally in the range of 50-150UM.