What are the layers of the Printed circuit board, what are the meanings and functions of each layer, the following for your reference:

1.Signal layer
The signal layer is mainly used to arrange the wires on the printed circuit board. Protel99SE provides 32 signal layers, including Top layer, Bottom layer and 30 MidLayer.

2.Internal plane layer (internal power / ground plane)
The Protel99SE provides 16 internal power plane/ground planes. This type of layer is used only for multi-layer boards and is mainly used to arrange power and ground lines. We call double-layer, four-layer, and six-layer boards, which generally refer to the number of signal layers and internal power/ground layers.

  
3.Mechanical layer
The Protel99SE provides 16 mechanical layers that are typically used to set the board's form factor, data marks, alignment marks, assembly instructions, and other mechanical information. This information varies depending on the requirements of the design company or PCB manufacturer. Execute the menu command Design|Mechanical Layer to set up more mechanical layers for the printed circuit board. In addition, the mechanical layer can be attached to other layers to output the display together.

4.Solder mask layer (solder mask)
Apply a layer of paint, such as a solder mask, to each part of the pad to prevent tin on these areas. The solder mask is used to match the pads during the design process and is automatically generated. The Protel99SE offers two solder masks, Top Solder (top layer) and Bottom Solder (bottom layer).

5.Paste mask layer
It functions similarly to the solder mask, except for the pad of the corresponding surface-mount component when the machine is soldered. Protel99SE offers two solder paste layers, Top Paste (top layer) and Bottom Paste (bottom layer).