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1. What kind of back drill?
Back drilling is actually a special type of depth controlled drilling. 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 drill) then Chen Tong. In this way, the first layer is directly connected to the twelfth layer. In fact, we only need to connect the first layer to the ninth layer. The tenth to twelfth layers are like a pillar because there are no lines connected. This pillar affects the signal path, can cause signal integrity problems in communication signals. So drill this extra column (called STUB in the industry) the reverse side (secondary drilling). It is called a back drill, but it is generally so clean because the subsequent process will electrolyze a little copper, the drill tip itself is also sharp. Therefore, PCB manufacturers will leave a small point. The length of this left STUB is called the B value, which is generally in the range of 50-150UM.
2. What are the advantages of back drilling?
1. Reduce noise interference;
2. Improve signal integrity;
3. The local plate thickness becomes smaller;
4. Reduce the use of buried blind holes reduce the difficulty of PCB production.
What is the effect of back drilling?
The role of back drilling is to drill through-hole sections that have played any connection transmission role, to avoid reflections, scattering, delays, etc. that cause high-speed signal transmission, to bring "distortion" to the signal. Except for factors such as design, board materials, transmission lines, connectors, chip packaging, vias have a greater impact on signal integrity.
Working principle of back drilling production
Relying on the drill bit, the micro current generated when the tip of the drill bit contacts the copper foil on the substrate plate surface is used to sense the height position of the plate surface, then the drill hole is drilled according to the set drill hole depth.
Five, back drilling production process?
a. Provide a PCB. The PCB is provided with positioning holes, the positioning holes are used to perform one-drill positioning one-drill drilling on the PCB;
b. Electroplating the PCB after drilling a hole, performing dry film sealing treatment on the positioning hole before electroplating;
c, making outer layer graphics on the PCB after plating;
d. performing pattern plating on the PCB after forming the outer layer pattern, performing dry film sealing treatment on the positioning hole before pattern plating;
e. Use the positioning holes used by a drill for back drilling positioning, use a drill to back drill the electroplated holes that need to be back drilled;
f. After back drilling, wash the back drilling with water to remove the remaining cuttings in the back drilling. Double-sided multilayer circuit board
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