PCB multilayer board refers to the multilayer circuit board used in electrical products. The multilayer board uses more single panel or double panel wiring boards. A printed circuit board with one double-sided as the inner layer, two single-sided as the outer layer, or two double-sided as the inner layer, and two single-sided as the outer layer is formed by alternating the positioning system and insulating bonding materials, and the conductive patterns are interconnected according to the design requirements. It is also called a four layer or six layer printed circuit boardMultilayer circuit board。

1. Signal Layers
Altium Designer can provide 32 signal layers, including top layer, bottom layer and mid layer. The layers can be connected with each other through Via, Blind Via and Buried Via.

(1) Top Layer

Also called component layer, it is mainly used to place components. For double-layer board and multilayer board, it can be used to arrange wires or copper coating.

(2) Bottom Layer

Also known as welding layer, it is mainly used for wiring and welding, and can be used to place components for double-layer boards and multilayer boards.

(3) Mid Layers

It can have 30 layers. It is used to arrange signal lines in multilayer boards, excluding power lines and ground wires.

2. Internal Planes
It is usually referred to as the internal electrical layer, which only appears in multilayer boards. The number of PCB layers generally refers to the sum of the signal layer and the internal electrical layer. Same as the signal layer, the interconnection between the inner electric layer and the inner electric layer, and between the inner electric layer and the signal layer can be realized through through holes, blind holes and buried holes.

3. Silkscreen Layers
A PCB can have two silk screen layers, the top layer and the bottom layer, which are generally white. They are mainly used to place printed information, such as the outline and label of components, various annotation characters, etc., to facilitate the welding of components and circuit inspection of PCB.

(1) Top Overlay

It is used to mark the projection outline of components, the label, nominal value or model of components and various annotation characters.

(2) Bottom Overlay

It is the same as the top screen layer. If all the marks on the top screen layer have been included, the bottom screen layer can be closed.

4. Mechanical Layers
The mechanical layer is generally used to place indicative information about the board making and assembly methods, such as the overall dimensions, size marks, data data, via information, assembly instructions and other information of PCB. The information varies according to the requirements of design companies or PCB manufacturers. The following examples illustrate our common methods.

Mechanical 1: It is generally used to draw the frame of PCB as its mechanical shape, so it is also called the shape layer;

Mechanical 2: we are used to place the PCB processing process requirements table, including size, plate, plate layer and other information;

Mechanical 13&Mechanical 15: Body size information of most components in ETM library, including 3D models of components; In order to simplify the page, this layer is not displayed by default;

Mechanical 16: The occupied area information of most components in the ETM library can be used to estimate the PCB size at the early stage of the project; For the simplicity of the page, this layer is not displayed by default, and the color is black.

5. Mask Layers

AlTIum Designer provides two types of mask layers: Solder Mask and Paste Mask, in which there are two layers: the top layer and the bottom layer, which will not be described in detail here.