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PCB Tech

PCB Tech

PCB Tech

PCB Tech

Definition of each layer of PCB

Solder mask: solder mask refers to the part of the board to be coated with green paint; because it is a negative output, the actual effect of the solder mask is not green, but tinned, silver white!

Solder mask: paste mask is used for machine mounting, which corresponds to the pad of all SMT components. It is the same size as toplayer / bottom layer, and is used to open steel mesh and leak tin.

Key points: both layers are used for tin welding, not one for tin and one for green oil. Is there a layer for green oil? As long as there is such a layer on a certain area, it means that the area is covered with insulating green oil? I haven't met such a layer yet! By default, all the pads on the PCB board we draw have a holder layer, so it's not surprising that the pads on the PCB are coated with silver white solder, and there is no green paint. However, the routing part of the PCB we draw only has the top layer or bottom layer layer, and there is no solver layer, but the routing part on the PCB board is covered with a layer of green oil.

PCB layer

It can be understood as follows:

1. The meaning of solder mask is to open a window on the green oil of the whole solder mask to allow welding!

2. By default, areas without solder mask should be painted green!

3. Paste mask layer for chip packaging! SMT package uses: toplayer layer layer, topsolder layer and toppaste layer. The size of toplayer is the same as toppaste, and the topsolder is one circle larger than them. Dip encapsulation only uses: topsolder and multilayer layers (after some decomposition, I found that the multilayer layer is actually the size of toplayer, bottom layer, topsolder and bottomholder layers), and the topsolder / bottomlayer is one circle larger than toplayer / bottomlayer.

Question: is it correct to say that the copper layer corresponding to the holder layer can only be tinned or gold plated if there is copper?

This sentence is said by a person who works in a PCB Factory. His meaning is: if you want to make the effect of tin plating on the part of the holder layer, then the corresponding part of the holder layer should have copper skin (that is, the area corresponding to the holder layer should have the part of toplayer or bottom layer)! Now: I have come to a conclusion: the saying that "the copper layer corresponding to the holder layer can be tinned or gold plated only if there is copper on the corresponding copper layer"! The holder layer represents the area that does not cover the green oil!

Mechanical layer

Keepout layer

Top overlay

Bottom overlay

Top pad layer

Bottom paste

Top solder mask

Bottom solder mask

Drill guide

Drill drawing


The mechanical layer defines the appearance of the whole PCB board. In fact, when we say the mechanical layer, it refers to the overall structure of the PCB. The no wire layer is the boundary that defines when we distribute the copper with electrical characteristics. That is to say, after we define the no wiring layer, the wires with electrical characteristics can not exceed the boundary of the no wiring layer in the future. Top overlay and bottom overlay are silk screen characters that define the top and bottom, which are the component number and the component number we see on PCB Some characters. Toppaste and bottompaste are the top and bottom pad layers, which refer to the copper and platinum exposed to the outside. (for example, we draw a wire in the top wiring layer, and what we see on the PCB is just a line, which is covered by the whole green oil, but we draw a square or a dot on the toppaste layer at the position of this line The square and the point on the board are not green, but copper and platinum. The top and bottom layers are just opposite to the previous two layers. It can be said that these two layers are green layers. The multilayer layer is actually similar to the mechanical layer. Gu Ming en Yi, this layer refers to all the layers of PCB.

The top and bottom layers are just opposite to the previous two layers. It can be said that these two layers are the layers to be covered with green oil; because they are negative output, some of the actual effects of the holder mask are not green, but tinned and silvery white!

1 signal layer

The signal layer is mainly used to lay the wires on the circuit board. Protel 99 SE provides 32 signal layers, including top layer, bottom layer and 30 middle layers.

2 internal plane layer

Protel 99 SE provides 16 internal power / ground layers. This type of layer is only used for multi-layer boards, mainly for laying power lines and grounding wires. We call them double-layer boards, four-layer boards and six-layer boards, which generally refer to the number of signal layers and internal power / ground layers.

3 mechanical layer

Protel 99 SE provides 16 mechanical layers, which are generally used to set board dimensions, data marks, alignment marks, assembly instructions and other mechanical information. The information varies according to the requirements of the design company or PCB manufacturer. Execute the menu command design| mechanical layer to set more mechanical layers for the circuit board. In addition, the mechanical layer can be attached to other layers to output the display together.

4 solder mask layer

A coating, such as solder resist, is applied to all parts outside the pad to prevent tin from being applied to these areas. The solder mask is used to match pads in the design process and is automatically generated. Protel 99 SE provides two solder mask layers: top layer and bottom layer.

The function of SMD layer is similar to that of solder mask layer, but the difference is that the pad of surface bonded component is corresponding to machine welding. Protel99 se provides top paste and bottom paste protective layers.

It mainly aims at SMD components on PCB. If all the boards are equipped with dip (through hole) components, there is no need to output Gerber files in this layer. Before SMD components are pasted onto PCB, solder paste must be applied to each SMD pad. The paste mask file is required for tin coated steel mesh before film film can be processed.

An important point of the Gerber output of the paste mask layer should be clear, that is, this layer is mainly for SMD components. At the same time, compare this layer with the solider mask introduced above to clarify the different functions of the two layers, because the two film images are very similar from the film picture.

6 keep out layer

Used to define the area on a circuit board where components and wiring can be effectively placed. In this layer, a closed area is drawn as the effective area of routing. Outside this area, the automatic layout and routing cannot be carried out.

7 silkscreen layer

Silk screen layer is mainly used to place printed information, such as outline and label of components, various annotation characters, etc. Protel 99 SE provides top overlay and bottom overlay. Generally, all kinds of marking characters are in the top screen layer, and the bottom screen layer can be closed.

8 multi layer

The pad and through-hole on the circuit board need to penetrate the whole circuit board, and establish electrical connection relationship with different conductive graphic layers. Therefore, an abstract layer multi-layer is specially set up in the system. Generally, pads and vias should be set on multiple layers. If this layer is closed, pads and vias cannot be displayed.

9 drill layer

The drilling layer provides drilling information in the process of PCB manufacturing (such as pad, via hole needs drilling). Protel 99 SE provides drillgrid and drill drawing layers.