In PCB board manufacturing, do you know the purpose of each layer? A printed circuit board is composed of multiple layers, and the classification of PCBs by layer also refers to the number of layers of the electrical layer. Understanding the purpose and meaning of each layer will help us better design and produce PCBs. Here, a 4-layer PCB is used as an example to illustrate the purpose of the layers of the printed circuit board.
1. Silkscreen Layers
The silk screen layer is divided into the top layer of silk screen and the bottom layer of silk screen. Generally, the white characters and wireframes on the PCB board manufacturing (if the solder mask layer of the board is white, the silk screen is black) are the silk screen layer, which are used to mark the bit number, component frame and some remark information.
2. SolderMask Layers
The solder resist layer is divided into top solder resist and bottom solder resist. Generally, the green oil on the surface of PCB board manufacturing (of course, there are other colors, the more commonly used ones are blue, green, red, yellow, but green is used by default) is the solder mask layer, which plays an insulating role. Note that this layer is a negative film, that is to say, there is no green oil in the place where there is a picture, and there is green oil in the place where there is no picture.
3. PasteMask Layers
The flux layer is divided into a flux top layer and a flux bottom layer. Also known as patch layer or steel mesh layer. Generally, a layer of tin or gold plating on the pad of the PCB board is the soldering flux layer, which assists in soldering and makes soldering easier. In the design, this layer is a positive film, that is, there is flux in the place where the drawing is drawn, and there is no flux in the place where there is no drawing.
4. Electrical Layers
The electrical layer includes the top layer, the middle layer (multilayer board) and the bottom layer, which have electrical connection properties, and most of the design work is to design this layer. Conduct reasonable wiring on the electrical layer, and reasonably connect the pins of the component package. Copper pours are also done on the electrical layers. For a 4-layer board, the inner layer will be set as the ground layer and power layer in the form of a negative film.
5. Mechanical Layers
Design some physical and mechanical properties on the mechanical layer, such as frames, slots, holes, etc. – Generally, there can be multiple mechanical layers, and the function of this layer can be customized, and dimensions can be marked, etc. There will be differences between this software, for example, the PCB in the picture uses Allegro and does not have multiple mechanical layers (Altium Designer has multiple mechanical layers). The outer frame and hollowing of the board are all done using Outline.
6. Assembly Layers
The assembly layer is divided into the assembly bottom layer and the assembly bottom layer. It is generally used during PCBA processing to mark the position and direction of component assembly. Of course, this layer can also be replaced by a silk screen layer. This layer is no longer displayed in the physical PCB, but can be printed out for the staff to view.
7. Keep-Out layer
Keep-Out layers include top layer, middle layer, bottom layer and all layers. The Keep-Out layer is mainly used for constraints. For example, some places do not allow copper laying or there are no traces and vias, etc., you can mark this area on the Keep-Out layer. The outer box is RouteKeepIn, and the circle is RouteKeepOut.
8. Drill Layer
The drilling layer contains drilling data such as vias, via pads, etc. The substrate is the insulating dielectric layer between the electrical layers. Commonly used are FR4 epoxy glass fiber, of course there are aluminum substrates, flexible boards and so on. Select the appropriate substrate according to the specific application. The solder resist layer and the solder flux layer are mutually exclusive. There is no solder resist layer where there is a solder resist layer, and there is no solder resist layer where there is a solder resist layer. Therefore, when displaying, use a solder resist layer with a more obvious effect. The above is an introduction to the use of each layer of PCB board manufacturing. If you have any questions or suggestions, you can contact HUIHE Circuits.