What are the differences between the layers of a PCB?

When designing a PCB, I found that many people do not understand the layers in the PCB well enough, especially novices, who have a vague understanding of the role of each layer. So today, let’s take a look at the differences between layers when using the Altium Designer software palette.

1. Signal layer
The signal layer is divided into Top Layer and Bottom Layer. This is a layer with electrical connections, which can place components and also arrange wiring.

2. Mechanical layer
Mechanical (mechanical layer) defines the appearance of the entire PCB board. The reason for emphasizing “mechanical” means that it does not have electrical properties, so it can be safely used for sketching shapes, sketching mechanical dimensions, placing text, and other tasks without worrying about any changes to the electrical properties of the board. A maximum of 16 layers can be selected for the mechanical layer.

3. Silk screen layer
Top Overlay and Bottom Overlay are used to define the screen printing characters for the top and bottom layers. They are some text symbols typically printed on the solder mask layer, such as component names, component symbols, component pins, and copyrights, to facilitate future circuit welding and error detection.

4. Solder paste layer
The solder paste layer includes a top layer of solder paste and a bottom layer of solder paste. It refers to the exposed surface of the solder pad that we can see, that is, the part that needs to be coated with solder paste before welding. Therefore, this layer is also useful for hot air leveling of pads and for making welded steel grids.

5. Solder resist layer
The solder mask layer is often referred to as “window opening”, including the top solder mask layer and the bottom solder mask layer. Its role is opposite to that of the solder paste layer, which refers to the layer to be covered with green oil. This layer does not adhere to solder, preventing short circuits of excess solder from adjacent solder joints during welding. The solder resist layer covers the copper film conductor to prevent the copper film from oxidizing in the air too quickly, but leaves a place at the solder joint and does not cover the solder joint.

Conventional copper plating or wiring is covered with green oil by default. If we treat the solder mask accordingly, it will prevent the green oil from covering and expose the copper.

6. Borehole layer
The drilling layer includes two drilling layers: Drill Gride and Drill Drawing. The drilling layer is used to provide drilling information during the manufacturing process of circuit boards (such as pads, through holes that require drilling).

7. Prohibit wiring layer
“Keep Out Layer is used to define the boundaries of a wiring layer. After defining a keepout layer, in future wiring processes, wiring with electrical characteristics cannot exceed the boundaries of the keepout layer.”.

8. Multilayer
Multi layer: The pads and through-holes on the circuit board penetrate the entire circuit board, establishing electrical connections with different conductive graphic layers. Therefore, the system has specially set up an abstract layer – Multilayer. Generally, pads and vias are set on multiple layers. If this layer is turned off, pads and vias cannot be displayed.

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