PCB multi-layer board and the meaning of each layer

11/01/2023 Seektronics

PCB board-Solder-Mask-layer and Paste-Mask-layers difference and the other layers of the detailed meaning of the introduction

Protel 99 SE provides 32 signal layers, including the Top layer, Bottom layer and 30 Middle layer.


Top signal layer: also known as the component layer, mainly used to place components, for multilayer boards can be used for wiring.


Mid Signal Layer: up to 30 layers, used to lay signal lines in multilayer boards.


The bottom signal layer : also known as the solder layer, mainly used for wiring and soldering, and sometimes can also be placed on the components.


Silkscreen layer: The silkscreen layer is mainly used for placing printed information, such as component outline and labeling, various comment characters, etc. Protel 99 SE provides two silkscreen layers, Top Overlay and Bottom Overlay. Generally, various annotation characters are placed on the top screen printing layer, and the bottom screen printing layer can be closed.


Top silkscreen layer: used to mark the projected outline of the component, the component's mark, nominal value or model number and various comment characters.


Bottom Overlayer: The same function as Top Overlayer, if all kinds of marking are contained in Top Overlayer, then it is not needed in Bottom Overlayer.


Internal power: usually called the internal power layer, including the power supply layer, reference power layer and ground plane signal layer. Protel 99 SE provides 16 internal power/ground layers. This type of layer is used only for multilayer boards and is mainly used for laying out power and ground wires. We call double-layer boards, four-layer boards, and six-layer boards, generally referring to the number of signal layers and internal power/grounding layers.


Mechanical Layer: The layer that defines the mechanical data of the board in the design. Protel 99 SE provides 16 mechanical layers, which are generally used to set the board's form factor, data marks, alignment marks, assembly instructions, and other mechanical information. This information varies depending on the requirements of the design company or the PCB manufacturer. Execute the menu command Design|Mechanical Layer to set more mechanical layers for the board. In addition, the mechanical layer can be attached to other layers and displayed together with the output.


Solder Resist Layer: There are two layers, the Top solder mask, and the Bottom Solder mask, which are automatically generated by Protel PCB corresponding to the pad and over-hole data in the board file, mainly used for laying solder resist paint. This layer uses negative output, so the pads and holes shown on the board layer represent the area of the board without the solder resist, that is, the part that can be soldered. A layer of paint, such as solder resist, is applied to the areas other than the pads to prevent these areas from being soldered. Protel 99 SE provides two solder mask layers, Top Solder and Bottom Solder. Solder Mask is the negative, i.e., the place where the design drawing is *drawn*.


Paste Mask: There are two layers, the Top Past Mask and Bottom Past Mask, which are used to correspond to the SMD component solder joints when passing through the soldering furnace, and are also output in the form of a positive piece. Protel 99 SE provides two solder paste protection layers, Top Paste and Bottom Paste. The paste is out of the positive piece, there will be solder paste where something is drawn.


Keep Out Layer: Define the wiring area where the signal lines can be placed, and place the signal lines into the functional range defined by the bit. Used to define the area on the board where components and wiring can be effectively placed. In this layer to draw a closed area as a wiring effective area, outside the area is not automatically layout and wiring.


MultiLayer: pads and vias on the board to penetrate the entire board, and different conductive graphics layer to establish electrical connections, so the system is set up specifically to an abstract layer, multi-layer. In general, the pads and through-hole are set on the multi-layer, if the layer is closed, the pads and through-hole can not be displayed. Usually, appear in combination with the through-hole or through-hole pad design, used to describe the layer characteristics of the cavity.


Drill: The drill layer provides information on the drilling of the board manufacturing process (such as pads, and vias that need to be drilled).


The difference between Solder Mask and Paste Mask: The solder mask is the solder resist layer, which is used to expose the pads, which is usually referred to as the green oil layer, in fact, is to dig holes in the green oil layer, the pads and other places that do not need to be covered by green oil to expose.


paste mask industry commonly known as "stencil" or "steel plate". It is a separate stencil, above the SMD pads on the location of the hollow. Generally, the shape of the hollow is the same as the SMD pads, but the size is slightly smaller. This stencil is used to apply the paste to the SMD pads in the SMD automatic assembly soldering process.


Paste Mask layers: The solder paste protection layer (for stencil), is for surface mount (SMD) components, this layer is used to make the steel film (sheet), and the holes on the steel film correspond to the SMD device solder joints on the board. When soldering the surface mount (SMD) devices, the steel film is first covered on the board (corresponding to the actual pads), then the solder paste is applied, the excess solder paste is scraped off with a squeegee, the steel film is removed, so that the pads of the SMD devices are added to the solder paste, and then the SMD devices are attached to the solder paste (manually or by bonder), and finally the soldering of the SMD devices is completed by reflow machine. Usually, the size of the aperture on the film is smaller than the actual solder on the board.


The difference between Solder Mask and Paste Mask: Solder Mask is negative, that is to say, the design drawing *drawing graphics place * in the actual production, is * no green oil *. The paste is positive, there will be something drawn where there will be solder paste.