Friends who have done PCB design know that the design of PCB vias is actually very particular. Today, I will explain in detail the back drilling technology in PCB circuit board production.
1. What PCB back drill?
Back drilling is a special kind of deep hole 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-time drilling), Then sink copper. In this way, the first layer is directly connected to the 12th layer. In fact, we only need to connect the first layer to the ninth layer. Since the 10th to the 12th layer are not connected by lines, they are like a pillar: this pillar will cause signal integrity problems. Drill off the revers side (secondary drill). That's why it's called back drilling.
2 Advantages of back drilling
1) Reduce noise interference; 2) Improve signal integrity; 3) Reduce local plate thickness;
4) Reduce the use of buried blind holes and reduce the difficulty of PCB production.
3. What is the function of back drilling?
The function of back drilling is to drill out the through-hole segments that do not play any connection or transmission role, so as to avoid reflection, scattering, delay, etc. of high-speed signal transmission.
4. Working principle of back drilling production
Relying on the micro-current generated when the drill tip touches the copper foil on the substrate surface to sense the height of the board surface when the drill is drilled down, then drill according to the set drill-down depth, and stop when the drill-down depth is reached.
5. Back drilling process
a. There are positioning holes on the PCB, and use the positioning holes to perform one-drill positioning and one-drill drilling on the PCB;
b. Electroplating is performed on the PCB after drilling, and the positioning hole is sealed with dry film before electroplating;
c. Make outer graphics on the PCB after electroplating;
d. Perform pattern plating on the PCB after forming the outer pattern;
e. Use the positioning hole used by the first drill to perform back drilling positioning. Back drilling with a drill;
f. Wash the back-drilled hole with water to remove the remaining drill cuttings in the back-drilled hole.
6. Application fields of back drilling board
The backplane is mainly used in communication equipment and large servers. Medical electronics, military, aerospace and other fields.
