PCB design (Allegro) related issues [updated from time to time]

1. Are the middle two layers of a 4-layer PCB set to be positive or negative?
Explanation: If you need to take a signal, use a positive film (conductor); if the neutral line is power and ground, use a negative film (plane), of course, you can also use a positive film for power and ground, which is time-consuming and consumes software resources.
Positive film: line drawing Local copper is reserved, and copper is removed where there is no line.
Negative film: copper is removed where the line is drawn, and copper is reserved where there is no line.
2. How to add vias?
(1) Define the vias, of course the vias must be done first
(2) Select Setup->Constraints->physical
(3) Click the vias at the back of the form
(4) After the Edit Via List pops up, select the VIA via on the left, Click OK
(5) In the process of drawing the line, double-click the left mouse button to change the layer, and the defined via will be automatically added (make sure there is a defined VIA in the VIA under Options)
If you want to place the VIA on the entire board, you can proceed under place->Via Arrays.
If you want to place a single VIA on the copper layer, you can use Add connect (F3) to double-click the copper layer or place the VIA.
3. What should I do if I want to modify the package of the chip when drawing the PCB layout?
(1) Open the relevant .dra file for modification
(2) Save the modified package file, and then generate the .psm file, file->Create Symbol, the .dra and .psm files are saved in the previously specified psmlib file folder
(3) to open the corresponding file OrCAD schematic regenerate netlist. That is, after saving, on the main page, select the .dsn file, and then find the "Create Netlist" button in the toolbar, and generate the corresponding netlist file in the corresponding Allegro folder
(4) Open the previous PCB file, re-import the netlist, File->Import->Logic
(5) Then in the Generaledit mode, select the symbol to be replaced, then right-click to select Unplace Component, and then click in the place menu bar Manually add the modified components
4. How to add via and assign the network
https://blog.csdn.net/mmhh3000/article/details/39451463
5. After changing the constraint settings, all shapes must be redo smooth
https: //www.eda365.com/forum.php?mod=viewthread&tid=100141
6. When using allegro to pave the PCB, how to set the via avoidance
https://jingyan.baidu.com/article/ab0b5630685c8dc15afa7d2e.html
7. About analog ground and digital ground
http://www.51hei.com/bbs/dpj-101014-1.html
8. The silk screen of the device in allegro has been deleted, now I want to add it
https://wenwen.sogou.com/ z/q602542490.htm (I haven’t tried this).
Another method is to unplace the component, then replace it, and manually click it.
9. The corner frame of the large resistance capacitor should be changed from board geometry/soldmask_top to package geometry/silkmask_top, to prevent accidentally soldering to the ground when soldering later