Engineers who are just getting started or just entering the electronic design position, may don't know how to construct a good PCB, or even what the layers are, how to define and distinguish when they get a board. Next, we will take you to uncover the veil of PCB and explain each layer in detail.
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Layer |
Description |
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Top Layer |
Mainly used to place components , and can be used for wiring for laminates and multilayer boards |
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Mid Layer |
There can be up to 30 layers, which are used to route signal lines in multilayer boards |
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Bootom Layer |
Mainly used for wiring and welding, sometimes components can also be placed |
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Top Over layer |
Used to mark the projection outline of the component, the label, nominal value or model of the component, and various annotation characters |
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Bottom Over layer |
It has the same function as the top silk screen layer, if all kinds of labels are contained in the top silk screen layer, then the bottom silk screen layer is not needed |
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Internal Planes |
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Mechanical Layers |
The mechanical layer defines the appearance of the entire PCB board. It is generally used to set the external dimensions of the circuit board, data marks, alignment marks, assembly instructions and other mechanical information. |
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Solder Mask |
There are two layers of top solder mask and bottom solder mask, which areautomatically generated by Prote PCB corresponding to the pad and via data in the circuit board file |
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Anti-solder layer |
There are two layers, Top Past Mask and Bottom Past mask, which are used to correspond to the solder joints of SMD components during the soldering furnace, and are also output in negative form |
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Keep Out Layer |
Define the boundary of the wiring layer. After the forbidden wiring layer is defined, in the subsequent wiring process, the wiring with electrical characteristics cannot exceed the boundary of the forbidden wiring layer. |
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Multi Layer |
Refers to all layers of the PCB board. The pads and penetrating vias on the circuit board should penetrate the entire circuit board and establish electrical connections with different conductive pattern layers |
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NC Drill |
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Drill Drawing |
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Signal Layers: Signal layers include Top Layer, Bottom Layer, and Mid Layer 1…30. These layers are all layers with electrical connections, that is, the actual copper layer. The middle layer refers to the middle board layer used for wiring, and the wires are distributed in this layer.
Top Layer: The top signal layer, also known as the component layer, is mainly used to place components. For double-layer boards and multi-layer boards, it can be used to arrange wires or copper. The bottom signal layer (Bottom Layer), also known as the soldering layer, is mainly used for wiring and soldering. For double-layer boards and multi-layer boards, it can be used to place components. The middle signal layer (Mid-Layers) can have up to 30 layers, which are used to arrange signal lines in a multi-layer board, which does not include power lines and ground lines.
Internal Plane: Internal Plane 1...16. This type of layer is only used for multi-layer boards. These layers are generally connected to the ground and power source, becoming the power layer and the ground layer. They also have electrical connections and are also actual copper Layer, but this layer is generally not wired and is composed of a whole piece of copper film.
Internal Plane is usually referred to as the inner electric layer, it only appears in multi-layer boards. The number of PCB layers generally refers to the sum of the signal layer and the inner electric layer. Same as the signal layer, the inner electric layer and the inner electric layer, and the inner electric layer and the signal layer can be connected to each other through through holes, blind holes and buried holes.
Silkscreen Overlay: Including the top silkscreen layer (Top overlay) and the bottom silkscreen layer (Bottom overlay). The silk screen characters that define the top and bottom layers are generally some text symbols printed on the solder mask, such as component names, component symbols, component pins and copyrights, to facilitate future circuit soldering and error checking.
A PCB board can have up to 2 silk screen layers, which are the top silk screen layer (Top Overlay) and the bottom silk screen layer (Bottom Overlay). They are generally white and are mainly used to place printed information, such as component outlines and labels. A kind of annotation characters, etc., to facilitate the soldering of PCB components and circuit inspection. The top silk screen layer (Top Overlay) is used to mark the projection outline of the component, the label of the component, the nominal value or model, and various annotation characters. The bottom silk screen layer (Bottom Overlay) is the same as the top silk screen layer. If all the labels on the top silk screen layer are included, the bottom silk screen layer can be closed.
Paste Mask: also called the soldering layer, including the top layer of solder paste (Top paste) and the bottom layer of solder paste (Bottom paste), refers to the exposed surface mount pads that we can see, also It is the part that needs to be coated with solder paste before soldering. Therefore, this layer is also useful for hot air leveling of pads and for making welded steel mesh.
Mechanical Layers: Up to 16 mechanically processed layers can be selected. To design a double panel, you only need to use the default option Mechanical Layer 1. The mechanical layer defines the appearance of the entire PCB board. It is generally used to place indicative information about the manufacturing and assembly methods, such as the outline dimensions of the PCB, size markings, data materials, via information, assembly instructions and other information. Designed as PCB mechanical shape, the default LAYER1 is the shape layer. Other LAYER2/3/4, etc. can be used for mechanical dimension marking or special purposes. For example, when certain boards need to be made of conductive carbon oil, LAYER2/3/4, etc. can be used, but the purpose of the layer must be clearly marked on the same layer.
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.
Keep Out Layer: Defines the boundary of the wiring layer. After the forbidden wiring layer is defined, in the subsequent wiring process, the wiring with electrical characteristics cannot exceed the boundary of the forbidden wiring layer. Many designers also use the mechanical shape of the PCB. If there are KEEPOUT and MECHANICAL LAYER1 on the PCB at the same time, it mainly depends on the completeness of the appearance of the two layers.
Generally, MECHANICAL LAYER1 shall prevail. It is recommended to use MECHANICAL LAYER1 as the shape layer when designing. If you use KEEPOUT LAYER as the shape, do not use MECHANICAL LAYER1 to avoid confusion! Drill layer (Drill Layer): Including the drill guide and the drill drawing, it is the data of the drilling. The drilling layer provides drilling information during the circuit board manufacturing process (such as pads and vias require drilling). Protel 99 SE provides two drilling layers, Drill gride and Drill drawing.
Multi-layer: Refers to all layers of the PCB board. The pads and penetrating vias on the circuit board need to penetrate the entire circuit board and establish electrical connections with different conductive pattern layers. Therefore, the system is specially set up with an abstract layer—multi-layer. Generally, the pads and vias must be arranged on multiple layers. If this layer is closed, the pads and vias cannot be displayed.
Solder mask: solder mask refers to the part of the board that needs to be painted with green oil; because it is a negative output, the actual effect of the part with solder mask is not painted with green oil, but tinned and silvery white!
Soldering layer: paste mask, which is used for machine patching. It corresponds to the pads of all patch components. The size is the same as the top layer/bottom layer. It is used to open the stencil to leak tin.