Power and ground planes PCB can be modified such that they contain multiple copper sections connected to different potentials. These further enhance the convenience of planes – consider a plane that has multiple voltages on it distributing +5V to one section of your board and -5V to another section. That is exactly the division in the image of the split power plane above.
The section on the left side of the line down the center of the board is connected to +5V while the PCB section to the right is at -5V. There are a few performance issues to consider when splitting planes up, especially if it’s a ground plane. However, this topic is beyond the scope of this article, stay tuned for a future post on this subject.
Overlay or silkscreen layers provide, among other things, the text designators for your components on the top and bottom layers. If utilizing these layers, separate files should be provided to the fabricator for the top and bottom overlays. There is no need for PCB overlays on internal layers (you’d never be able to see them!). If you don’t care to have text on your board, these files are not necessary. However, text is immensely helpful, especially when debugging boards in the lab.
For example, if you want to know the potential at one terminal of resistor R2, you simply find the text “R2″ printed on your board and probe. This is much easier than the more tedious PCB option of referring back to your design on the computer or paper printouts. Overlay layers are also great for including your company name, design name, revision number and serial number of the board. Typically, blank boxes are printed for the revision and serial number so that they PCB can be written in later with a sharpie or stamped onto the board.
