PCB Technical - The meaning of each layer of the PCB circuit board

Definition of PCB layer

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 silver-white!

Soldering layer

The paste mask is used for machine patching. It corresponds to the pads of all patch components. The size is the same as the toplayer/bottomlayer layer. It is used to open the stencil to leak tin.

Key points

Both layers are used for soldering. It does not mean that one is soldered and the other is green oil; then whether there is a layer refers to the green oil layer, as long as there is this layer on a certain area, it means that the area is What about the insulating green oil? For the time being, I have not encountered such a layer! The PCB board we drew, the pads on it have a solder layer by default, so the pads on the PCB board are made of silver white It’s not surprising that there is no green paint on the solder; but the traces on the PCB board we drew only have the toplayer or bottomlayer layer, and there is no solder layer, but the traces on the PCB board are made of a layer. green oil.

That can be understood like this:

1. The solder mask layer means to open a window on the whole piece of solder mask green oil, the purpose is to allow soldering!

2. By default, the area without solder mask must be painted with green oil!

3. The paste mask layer is used for patch packaging! SMT packaging uses: toplayer layer, topsolder layer, toppaste layer, and toplayer is the same size as toppaste, topsolder is a circle larger than them. DIP package only uses: topsolder and multilayer layer (after some decomposition, I found that the multilayer layer is actually toplayer, bottomlayer, topsolder, bottomsolder layer overlap), and topsolder/bottomlayer is a circle larger than toplayer/bottomlayer.

Question: "The copper skin layer corresponding to the solder layer has copper to be tinned or gold-plated" is this correct? This sentence was said by a person working in a PCB factory, and what he meant was: The effect produced on the part of the solder layer is tin plating, then the corresponding part of the solder layer must have copper skin (ie: the area corresponding to the solder layer must have the toplayer or bottomlayer part)! Now: I come to a conclusion: : "The copper skin layer corresponding to the solder layer is tinned or gold-plated only if there is copper" is correct! The solder layer means the area that does not cover the green oil!

The mechanical layer defines the appearance of the entire PCB board. In fact, when we talk about the mechanical layer, we mean the overall appearance of the PCB board. The forbidden wiring layer defines the boundary when we lay out the electrical characteristics of copper. That is to say, after we first define the forbidden wiring layer, in the future wiring process, the wiring with electrical characteristics cannot exceed the forbidden wiring. The boundary of the layer. Topoverlay and bottomoverlay are the silk screen characters that define the top and bottom, which are the component numbers and some characters that we generally see on the PCB. Toppaste and bottompaste are the top and bottom pad layers, which refer to the copper and platinum that we can see exposed. (For example, we drew a wire on the top wiring layer. What we see on the PCB is just It's just a line, it is covered by the whole green oil, but we draw a square or a point on the toppaste layer at the position of this line, the square and this point on the printed board will not have green It’s oil, but copper and platinum. The two layers of top solder and bottomsolder 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, and the multilayer layer is actually almost the same as the mechanical layer. Yes, as the name enyi, this layer refers to all the layers of the PCB board.

The two layers of top solder and bottomsolder 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 it is a negative output, the actual effect of the solder mask is not green, but tinned and silvery white!

1 Signal layer

The signal layer is mainly used to arrange the wires on the circuit board. Protel 99 SE provides 32 signal layers, including Top layer (top layer), Bottom layer (bottom layer) and 30 MidLayer (middle layer).

2 Internal plane layer (internal power/ground layer)

Protel 99 SE provides 16 internal power layers/ground layers. This type of layer is only used for multilayer boards, mainly used to arrange power lines and ground lines. We call double-layer boards, four-layer boards, and six-layer boards. Refers 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 the external dimensions of the circuit board, data marks, alignment marks, assembly instructions and other mechanical information. This information varies depending on the requirements of the design company or PCB manufacturer. Executing the menu command Design|MechanicalLayer can set more mechanical layers for the circuit board. In addition, the mechanical layer can be added to other layers to output and display together.

4 Solder mask layer

Apply a layer of paint, such as solder resist, to all parts other than the pads to prevent tin on these parts. The solder mask is used to match the pads during the design process and is automatically generated. Protel 99 SE provides two solder masks, Top Solder (top layer) and Bottom Solder (bottom layer).

5 Paste mask layer (solder paste protective layer, SMD patch layer)

Its function is similar to that of the solder mask, but the difference is the corresponding surface-mounted PCB component pads during machine soldering. Protel99 SE provides two protective layers of solder paste, Top Paste (top layer) and Bottom Paste (bottom layer).

Mainly for SMD components on PCB boards. If all Dip (through hole) components are placed on the board, there is no need to export Gerber files on this layer. Before attaching SMD components to the PCB board, solder paste must be applied to each SMD pad. The paste mask file must be used for the steel mesh used for tinning, and the film film can be processed.

The most important point of the Gerber output of the Paste Mask layer is to be clear, that is, this layer is mainly for SMD components. At the same time, compare this layer with the Solder Mask described above to find out the different functions of the two, because it is seen from the film picture. The two film images are very similar.

6 Keep out layer (prohibited wiring layer)

Used to define the area where components and wiring can be effectively placed on the circuit board. Draw a closed area on this layer as the effective area for routing. Automatic layout and routing is not possible outside this area.

7 Silkscreen layer

The silk screen layer is mainly used to place printed information, such as component outlines and annotations, various annotation characters, etc. Protel 99 SE provides two silk screen layers, Top Overlay and Bottom Overlay. Generally, all kinds of marked characters are on the top silk screen layer, and the bottom silk screen layer can be closed.

8 Multi layer

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-multilayer. Generally, the pads and vias must be arranged on multiple layers. If this layer is turned off, the pads and vias cannot be displayed.

PCB factories should focus on positioning high-precision multilayer circuit boards and HDI circuit boards, express prototypes and mass production. Products are widely used in high-tech fields such as communications, medical treatment, aerospace, industrial control, automotive electronics, computer peripheral products, and professional colleges.