Use for PCB All Layers

This Gold Phoenix PCB Knowledge Center article explains the function and use of each PCB layer type. The working layers can be broadly divided into 7 categories: signal layers, internal planes (internal power/ground layer), mechanical layer, solder mask layer, silkscreen layer, others and system work layer.

1. Signal Layers

Signal layers include the top layer, bottom layer, and intermediate layers 1 through 30. The signal layer is used primarily for placement of components (top and bottom) and routing. The signal layer is a positive layer — i.e., the wires or other objects placed on the surface are areas covered with copper.

2. Internal Planes (Internal Power/Ground Layer)

Internal power/ground layers (referred to as inner layers) are dedicated to the arrangement of power lines and ground wires. The lines or other objects placed at these levels are copper-free regions — i.e., these layers are negative.

Each internal power/ground layer can be assigned an electrical network name. The PCB editor automatically connects that layer to pads with the same network name (i.e., electrical connection) in the form of pre-pulled connections. The internal power/ground layer can also be cut into multiple sub-layers, meaning each internal power/ground layer may carry two or more power supplies, such as +5 V and +15 V.

3. Mechanical Layer

The mechanical layer is generally used to place indicative information about the board and assembly methods, such as physical dimension lines, dimensional markings, data, through-hole information, and assembly instructions.

4. Mask (Solder Mask, Solder Paste Protection Layer)

Solder mask (top solder mask and bottom solder mask): The solder mask is a negative layer — the pads or other objects placed on the layer are areas without the mask material. Usually, in order to meet manufacturing tolerance requirements, the manufacturer often requires specifying a mask expansion rule to enlarge the solder mask openings. For different requirements of different pads, multiple rules can be set in the solder mask layer.

Solder paste protection layer (top paste and bottom paste): The solder paste protection layer is similar to the solder mask layer, but when the reflow soldering technique is used to mount SMD components, the solder paste protection layer is mainly used to establish the stencil printing pattern. This layer is also negative.

Similar to the solder mask, the solder paste layer can also be enlarged or reduced by specifying an extension rule. For different requirements of different pads, multiple rules can also be set in the solder paste protection layer.

5. Silkscreen (Screen Printing Layer)

Top overlay (top silkscreen layer) and bottom overlay (bottom silkscreen layer). The silkscreen layer is mainly used to draw the outline of components, the reference designator numbers, or other text information. When a PCB library element is placed on a printed circuit board, the reference designator and outline of the element are automatically placed on the silkscreen layer.

6. Others (Other Work Layers)

In addition to the above work layers, there are the following layers:

Keepout Layer

The keepout layer is used to define the areas where components are placed and routing is restricted. In general, line segments (tracks) and arcs are placed on the keepout layer to form a closed area, allowing automatic routing to be confined within or excluded from this closed area.

Note: If any part of the circuit or all circuitry is to be automatically placed or automatically wired, then a prohibited routing area shall be defined on the keepout layer at least.

Multilayer

This layer represents all signal layers. Components placed on the multilayer automatically appear on all signal layers. Through the multilayer, pads or through-hole vias can be quickly placed into all signal layers.

Drill Guide

Drill Drawing

The drill guide layer and drill drawing layer are mainly used to draw drill hole drawings and the location of boreholes.

The drill guide layer is mainly compatible with manual drilling and older circuit board manufacturing processes. For modern manufacturing processes, the drill drawing layer is more commonly used to provide drilling reference files.

Drill hole information is typically specified in the drill drawing work layer. When generating a drill file on a printout, a code diagram containing the drill hole information and a drill hole position map is produced. This is usually used to guide circuit board processing.

Note: Whether or not the drill drawing layer is set to a visible state, the drilling information generated automatically at the output is visible in the PCB document. The drill drawing layer contains a special legend string, where the location of the string determines where the drill map information is generated on the printout.

7. System (System Work Layers)

DRC Errors Layer

The DRC Errors layer is used to display information that violates the design rules check. When the layer is turned off, the DRC error is not displayed on the workspace diagram, but the online design rule checking function will still work.

Connection Layer

This layer is used to display electrical connections between components, pads, and vias, such as broken net markers or ratsnest lines, but the actual tracks are not included. When the layer is turned off, these connections do not show up, but the program still analyzes its internal connections.

Pad Holes

When this layer is opened, the inner hole of the pad is displayed on the board surface.

Via Holes

When this layer is opened, the inner hole of the via is displayed on the board surface.

Visible Grid 1 / Visible Grid 2

These two layers are used to display grid lines.

Summary

• Top layer / Bottom layer: Component placement and routing; SMD pads on top and bottom

• Mid-layers (1–30): Used for routing traces or copper pour

• Internal planes: Power and ground distribution (negative layers)

• Mechanical layer: Board dimensions, assembly information

• Solder mask: Protective layer with pad openings (negative layer)

• Solder paste: Stencil layer for paste application (negative layer)

• Silkscreen: Component outlines, reference designators, text

• Keepout: Defines restricted areas

• Multilayer: Pads and vias visible on all signal layers

• Drill guide/drawing: Drill hole specifications

• System layers: DRC errors, connections, pad/via holes, visible grids