1. The mechanical layer defines the overall appearance of the PCB circuit board, representing its structural design.

2. The forbidden wiring layer establishes the boundaries for laying out copper with electrical characteristics. In other words, once the forbidden wiring layer is defined, subsequent routing must ensure that any electrical traces do not extend beyond these boundaries.

3. Top overlay and bottom overlay refer to the silkscreen layers that display component designators and various characters typically found on the PCB.

4. Top paste and bottom paste represent the pad layers on the top and bottom sides, which indicate exposed copper pads. For instance, if a trace is drawn on the top layer, it may be covered by green solder mask, but the pad at that trace’s location will be marked as a square or dot on the top paste layer, revealing the underlying copper.

5. The two layers of top solder and bottom solder are essentially the inverse of the previous two layers. These layers are intended to be covered with green solder mask, but since this is a negative output, the actual effect of the solder mask is not green but rather a tin plating that appears silvery white!

6. The multilayer layer is quite similar to the mechanical layer; it encompasses all layers of the PCB.

1 Signal Layer

The signal layer primarily serves to arrange the wiring on the circuit board. Protel 99 SE offers 32 signal layers, which include the Top Layer, Bottom Layer, and 30 MidLayers.

2 Internal Plane Layer (Internal Power/Ground Layer)

Protel 99 SE provides 16 internal power and ground planes. These layers are exclusively used for multilayer boards, primarily for organizing power and ground connections. The terminology such as double-layer, four-layer, and six-layer boards refers to the total count of signal layers and internal power/ground layers.

3 Mechanical Layer (Mechanical Layer)

Protel 99 SE features 16 mechanical layers, typically utilized to define the external dimensions of the circuit board, data markers, alignment marks, assembly instructions, and other mechanical details. This information may vary based on the requirements of the design firm or PCB manufacturer. By executing the Design|MechanicalLayer menu command, additional mechanical layers can be configured for the circuit board. Furthermore, the mechanical layer can be combined with other layers for output and display.

4 Solder Mask Layer (Solder Mask Layer)

A layer of paint, such as solder resist, is applied to all areas except for the pads to prevent solder on those sections. The solder mask is designed to align with the pads during the design phase and is generated automatically. Protel 99 SE includes two solder masks: Top Solder and Bottom Solder.

5 Paste Mask Layer (Solder Paste Protection Layer, SMD Patch Layer)

This layer serves a function similar to the solder mask but specifically corresponds to the pads of surface-mounted components during machine soldering. Protel 99 SE provides two solder paste protective layers: Top Paste and Bottom Paste. This layer is primarily for SMD components on PCB boards. If only through-hole (DIP) components are used, exporting Gerber files for this layer is unnecessary. Prior to placing SMD components on the PCB, solder paste must be applied to each SMD pad, and the stencil for applying solder must reference this Paste Mask file. It is crucial to clarify that the Gerber output for the Paste Mask layer is focused on SMD components, emphasizing the differences from the Solder Mask, as illustrated in the film images, which may appear quite similar.

6 Keep Out Layer (Prohibited Wiring Layer)

This layer defines areas where components and wiring can be effectively placed within the PCB design. A closed area is drawn on this layer to establish the valid routing zone, beyond which automatic layout and routing are not permitted.

7 Silkscreen Layer

The silkscreen layer is primarily used for placing printed information, such as component outlines, labels, and various annotations. Protel 99 SE provides two silkscreen layers: Top Overlay and Bottom Overlay. Typically, all types of marking characters are found on the top silkscreen layer, while the bottom silkscreen layer may remain unpopulated.

8 Multi-Layer (Multilayer)

Pads and vias on the PCB must traverse the entire board to create electrical connections with various conductive pattern layers. Therefore, the system incorporates a specialized layer known as multilayer. Generally, pads and vias must be configured across multiple layers; if this layer is disabled, pads and vias will not be visible.

9 Drill Layer (Drilling Layer)

The drilling layer supplies drilling information necessary for PCB manufacturing, such as which pads and vias require drilling. Protel 99 SE offers two drilling layers: Drillgrid (drilling indication map) and Drill Drawing (drilling diagram).
If you have any PCB manufacturing needs, please do not hesitate to contact me.Contact me