Protel 99 SE provides 16 mechanical layers, which are generally used to set the overall dimensions, data markers, alignment markers, assembly instructions, and other mechanical information of circuit boards. These information may vary depending on the requirements of the design company or PCB manufacturer. Executing the menu command Design | MechanicalLayer can set more mechanical layers for the circuit board. In addition, the mechanical layer can be attached to other layers to output the display together.

　　4 Solder mask layer

　　Apply a layer of paint, such as solder mask, to various areas outside the solder pad to prevent tin from being applied to these areas. The solder mask layer is used to match the solder pad during the design process and is automatically generated. Protel 99 SE provides two solder mask layers: Top Solder and Bottom Solder.

　　5 Paste mask layer

　　Its function is similar to that of the solder mask layer, except for the corresponding bonding pads of surface mounted components during machine welding. Protel99 SE provides two solder paste protection layers: Top Paste (top layer) and Bottom Paste (bottom layer).