Can't understand the meaning of each layer of the PCB?
Can't understand the meaning of each layer of the PCB?
PCB drawing can use many softwares, such as Protel 99 SE (predecessor of Altium Designer), Altium Designer, Candence, etc. The drawing of PCB needs to be operated on different layers.
The mechanical layer defines the appearance of the entire PCB board (at present, most manufacturers prohibit the wiring layer according to the keepout layer). In fact, when we say the mechanical layer, we refer to the overall structure of the PCB board. The forbidden wiring layer is the boundary that defines when we are laying the copper with electrical characteristics, that is to say, after we define the forbidden wiring layer first, in the subsequent laying process, the wires with electrical characteristics that we have laid are impossible to exceed the forbidden wiring. layer boundaries.
top overlay and bottom overlay are silkscreen characters that define the top and bottom layers, which are the component numbers and some characters that we generally see on the PCB.
The multilayer layer is actually similar to the mechanical layer. As the name implies, this layer refers to all layers of the PCB board.
Top paste and bottom paste are the top and bottom pad layers, which refers to the copper and platinum that we can see exposed outside, (for example, we draw a wire on the top wiring layer, which we see on the PCB. It is just a line, it is covered by the whole green oil, but we draw a square or a dot on the top paste layer at the position of this line, and this square and this dot are printed on the board. There is no green oil, but copper and platinum.
The two layers of top solder and bottom solder are just the opposite of 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 film output, there is actually part of the actual effect of the solder mask. Not green oil, but tinned, silvery white!
1 Signal layer
The signal layer is mainly used to lay out 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/ground planes. This type of layer is only used for multi-layer boards, mainly for laying power lines and ground lines. We call double-layer boards, four-layer boards, six-layer boards, general 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 board dimensions, data marks, alignment marks, assembly instructions and other mechanical information. This information varies depending on the requirements of the design company or PCB manufacturer. Execute the menu command Design|MechanicalLayer to set more mechanical layers for the board. In addition, mechanical layers can be attached to other layers to output the display together.
4. Solder mask layer
Apply a coating of paint, such as solder mask, to areas other than the pads to prevent tin from tinning in those areas. Solder mask is used to match the pads during the design process and is generated automatically. Protel 99 SE provides Top Solder (top layer) and Bottom Solder (bottom layer) two solder mask layers.
5 Paste mask layer (solder paste protection layer, SMD patch layer)
It has a similar function to the solder mask, except that the pads of the corresponding surface-mounted components are soldered by the machine. Protel99 SE provides Top Paste (top layer) and Bottom Paste (bottom layer) two solder paste protection layers. Mainly for SMD components on PCB boards. If the board is all placed with Dip (Through Hole) components, there is no need to output a Gerber file for this layer. Before attaching the SMD components to the PCB board, each SMD pad must be coated with solder paste first, and the paste mask file must be required for the stencil used for tin coating before the 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 introduced above to find out the difference between the two, because from the film image The two filmstrips are very similar.
6 Keep out layer (prohibit wiring layer)
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Used to define areas on the board where components and routing can be efficiently placed. A closed area is drawn on this layer as a routing effective area, and automatic placement and routing cannot be performed outside this area.
7 Silkscreen layer
The silk screen layer is mainly used to place printing information, such as the outline and annotation of components, various annotation characters, etc. Protel 99 SE provides Top Overlay and Bottom Overlay two silk screen layers. 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 to establish electrical connections with different conductive pattern layers, so the system specially sets up an abstract layer—multi-layer. Generally, pads and vias are arranged on multiple layers. If this layer is closed, the pads and vias cannot be displayed.
9 Drill layer
The drilling layer provides drilling information (such as pads, vias need to be drilled) during the manufacturing process of the circuit board. Protel 99 SE provides Drillgride (drilling instructions map) and Drill drawing (drilling map) two drilling layers.
The distinction between solder mask and solder flux
Solder mask: solder mask, refers to the part on the board to be painted with green oil; because it is a negative output, the actual effect of the part with solder mask is not green oil, but tinned, silvery white!
Soldering flux layer: paste mask, which is used when the machine is patched. It corresponds to the pads of all patch components. The size is the same as the top layer/bottom layer layer. It is used to open the stencil to leak tin.
Point: Both layers are used for soldering on tin, not one with tin and the other with green oil; then whether there is a layer that refers to the layer with green oil, as long as there is this layer in a certain area, it means this Is the area covered with insulating green oil? For the time being I have not encountered such a layer! The pads on the PCB we drew have solder layers by default, so the pads on the produced PCB are covered with silver-white solder, and it is not surprising that there is no green oil; but the PCB we painted There is only a toplayer or bottomlayer layer in the wiring part on the board, and there is no solder layer, but the wiring part on the finished PCB board is covered with a layer of green oil.
That can be understood like this:
1. The meaning of the solder mask layer is to open a window on the green oil of the whole piece of solder mask, the purpose is to allow welding!
2. By default, the areas without solder mask should be covered with green oil!
3. The paste mask layer is used for SMD packaging!
The SMT package uses: toplayer layer, topsolder layer, toppaste layer, and the top layer is the same size as the top paste, and the top solder is a circle larger than them (generally 0.1mm larger). The DIP package only uses: topsolder and multilayer layer (after some decomposition, I found that the multilayer layer is actually top ayer, bottom layer, top solder, bottom solder layer size overlap), and top solder/bottom solder is higher than top layer/bottom layer Big circle.
Question: Is the sentence "tin or gold plated only when the copper layer corresponding to the solder layer has copper"? This sentence is said by a person who works in a PCB factory. What he means is: if the effect of the part painted on the solder layer is to be tinned, then the corresponding part of the solder layer must have copper skin (ie. : The area corresponding to the solder layer should have a part of the top layer or bottom layer)! Now: I have come to a conclusion: "The copper layer corresponding to the solder layer will be plated with tin or gold only if there is copper" This sentence is correct! The solder layer represents the area that does not cover the green oil!