1. What PCB back drill?
In fact, back drilling is a special kind of depth control drilling. In the production of multi-layer boards, such as 12 layer boards, we need to connect the first layer to the ninth layer. Usually we drill through holes (once), and then use copper. In this way, the first floor is directly connected to the 12th floor. In fact, we only need to connect the first floor to the 9th floor. The 10th floor to the 12th floor are like a pillar because there is no line to connect them. This pillar affects the signal path, which will cause signal integrity problems in the communication signal. So drill out the extra column (called stub in the industry) from the reverse side (secondary drilling). So it’s called back drilling, but generally it won’t be so clean, because the subsequent process will electrolysis a little copper, and the drill point itself is also sharp. So PCB manufacturers will leave a little bit. The length of stub left is called b value, which is generally in the range of 50-150um.
1. What PCB back drill?
In fact, back drilling is a special kind of depth control drilling. In the production of multi-layer boards, such as 12 layer boards, we need to connect the first layer to the ninth layer. Usually we drill through holes (once), and then use copper. In this way, the first floor is directly connected to the 12th floor. In fact, we only need to connect the first floor to the 9th floor. The 10th floor to the 12th floor are like a pillar because there is no line to connect them. This pillar affects the signal path, which will cause signal integrity problems in the communication signal. So drill out the extra column (called stub in the industry) from the reverse side (secondary drilling). So it’s called back drilling, but generally it won’t be so clean, because the subsequent process will electrolysis a little copper, and the drill point itself is also sharp. So PCB manufacturers will leave a little bit. The length of stub left is called b value, which is generally in the range of 50-150um.
5. Back drill production process?
a. A PCB is provided, and a positioning hole is arranged on the PCB, and the positioning hole is used for one drill positioning and one drill drilling of the PCB;
b. The PCB after drilling is electroplated, and the positioning holes are sealed with dry film before electroplating;
c. The outer layer pattern is made on the electroplated PCB;
d. Performing pattern electroplating on the PCB after forming the outer layer pattern, and performing dry film sealing treatment on the positioning hole before pattern electroplating;
e. The positioning hole used by the first drill is used for back drilling positioning, and the drill knife is used for back drilling the electroplating hole that needs to be back drilled;
f. After back drilling, the back hole shall be washed to remove the residual cuttings in the back hole.
6. If there are holes in the circuit board, how to solve the problem of drilling from layer 14 to layer 12?
1) If the board has a signal line on the 11th layer, and there are through holes at both ends of the signal line to connect to the component surface and solder surface, the components will be inserted on the component surface, as shown in the figure below, that is to say, on the line, the signal transmission is from component A to component B through the signal line on the 11th layer.
2) According to the signal transmission described in point 1, the function of through hole in the transmission line is equivalent to that of signal line. If we do not carry out back drilling, the signal transmission route is shown in Figure 5.
3) From the figure described in point 2, we can see that the through-hole section from the solder surface to layer 11 does not play any role in connection or transmission during the first good transmission. The existence of this section of through-hole is easy to cause the reflection, scattering and delay of signal transmission, so back drilling is actually drilling out the through-hole section without any link or transmission function, so as to avoid the reflection, scattering and delay of signal transmission and bring distortion to the signal.
Due to certain tolerance control requirements of drilling depth and thickness tolerance of plate, we can’t meet the absolute depth requirements of customers 100%, so is it better to control back drilling depth deeper or shallower? Our view on technology is that it is better to be shallow than deep, FIG. 6.
7. What are the technical features of the back drilling plate?
1) Most backboards are hard boards
2) The number of floors is generally 8 to 50
3) Plate thickness: more than 2.5mm
4) The thickness diameter ratio is large
5) The plate size is large
6) Generally, the minimum diameter of the first drill hole is > = 0.3mm
7) There are few outer circuits, and most of them are designed with square array of crimping holes
8) The back hole is usually 0.2mm larger than the hole to be drilled out
9) Back drilling depth tolerance: + / – 0.05mm
10) If back drilling requires drilling to m layer, the minimum thickness of medium from m layer to M-1 (the next layer of m layer) is 0.17mm
8. What are the main applications of the back drilling plate?
Backplane is mainly used in communication equipment, large servers, medical electronics, military, aerospace and other fields. Because military and aerospace are sensitive industries, domestic backplanes are usually provided by military and aerospace research institutes, R & D centers or PCB manufacturers with strong military and Aerospace background. In China, the demand for backplanes mainly comes from the communication industry, which is gradually growing in the field of communication equipment manufacturing.
Implementation of back drilling file output in Allegro
1. First select the back drill net and define the length. Click edit properties in the menu bar to open the dialog edit properties,