What is the function of each layer of PCB? (Detailed explanation)

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What is the function of each layer of PCB? (Detailed explanation) [Copy link]

Definition of PCB layers

Solder Mask

The solder mask refers to the part of the board that needs to be painted green. Because it is a negative output, the actual effect of the solder mask part is not painted green, but tinned, which is silver-white!

Solder layer

Paste mask is used when the machine is mounting the chips. It corresponds to the solder pads of all chip components. Its size is the same as the toplayer/bottomlayer layer and it is used to open the steel mesh to leak tin.

Key Points

Both layers are used for tinning and welding, which does not mean one for tinning and the other for green paint. So is there a layer for green paint? As long as this layer is present in a certain area, it means that the area is insulated with green paint? I have not encountered such a layer yet! The pads on the PCB board we drew have a solder layer by default, so the pads on the manufactured PCB board are coated with silver-white solder, and it is not surprising that there is no green paint. However, the routing part of the PCB board we drew only has the toplayer or bottomlayer layer, and there is no solder layer, but the routing part of the manufactured PCB board is coated with a layer of green paint.

That can be understood like this:

1. The solder mask layer means opening a window on the entire piece of green solder mask to allow soldering!

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

3. The paste mask layer is used for chip packaging! SMT packaging uses: toplayer layer, topsolder layer, toppaste layer, and toplayer and toppaste are the same size, and topsolder is one circle larger than them. DIP packaging only uses: topsolder and multilayer layer (after some analysis, I found that the multilayer layer is actually toplayer, bottomlayer, topsolder, and bottomsolder layers overlap in size), and topsolder/bottomlayer is one circle larger than toplayer/bottomlayer.

Question: Is it correct that "the copper layer corresponding to the solder layer will be tinned or gold-plated only if there is copper"? This sentence was said by a person working in a PCB factory. What he meant was that if you want to make the part drawn on the solder layer look like tin-plated, then the corresponding solder layer part must have copper (that is, the area corresponding to the solder layer must have a toplayer or bottomlayer part)! Now: I have come to a conclusion: "The copper layer corresponding to the solder layer will be tinned or gold-plated only if there is copper" is correct! The solder layer refers to the area not covered with green oil!

mechanical

keepout layer prohibits wiring layer

top overlay top screen printing layer

Bottom overlay bottom screen layer

top paste, top pad layer

Bottom paste bottom pad layer

Top solderTop solder layer

bottom solder bottom solder layer

drill guide, via guide layer

drill drawing via drilling layer

multilayer

The mechanical layer defines the appearance of the entire PCB board. In fact, when we talk about the mechanical layer, we are referring to the external structure of the entire PCB board. The forbidden wiring layer defines the boundary when we lay out 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 laid out cannot exceed the boundary of the forbidden wiring layer. Topoverlay and bottomoverlay are the silk-screen characters that define the top and bottom layers, which are the component numbers and some characters that we usually see on the PCB board. Toppaste and bottompaste are the top and bottom pad layers, which refer to the copper platinum that we can see exposed outside. (For example, we draw a wire on the top wiring layer, and what we see on the PCB is just a wire, which is covered by the entire green oil. But if we draw a square or a dot on the toppaste layer at the position of this wire, the square and the dot on the printed board will not have green oil, but copper platinum. The top solder and bottom solder layers are just the opposite of the previous two layers. It can be said that these two layers are the layers that are covered with green oil. The multilayer layer is actually similar to the mechanical layer. As the name suggests, this layer refers to all layers of the PCB board.

The top solder and bottom solder layers are just the opposite of the previous two layers. It can be said that these two layers are the layers to cover the green paint;

Because it is a negative film output, the actual effect of the part with solder mask is not green paint, but tin plating, which is silver-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, Bottom layer and 30 MidLayer.

2 Internal plane layer (internal power/ground layer)

Protel 99 SE provides 16 internal power/ground layers. This type of layer is only used for multi-layer boards and is mainly used to arrange power lines and ground lines. We call double-layer boards, four-layer boards, and six-layer boards, generally referring 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's 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. Executing the menu command Design|MechanicalLayer can set more mechanical layers for the circuit board. In addition, the mechanical layer can be attached to other layers for output display.

4 Solder mask layer

Apply a layer of coating, such as solder mask, to the parts other than the pads to prevent tinning 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 mask layers: Top Solder (top layer) and Bottom Solder (bottom layer).

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

It has a similar function to the solder mask layer, except that it corresponds to the pads of the surface-mounted components during machine soldering. Protel99 SE provides two solder paste protection layers: Top Paste (top layer) and Bottom Paste (bottom layer).

Mainly for SMD components on PCB. If the board is full of Dip (through-hole) components, there is no need to output Gerber files for this layer. Before attaching SMD components to the PCB, solder paste must be applied to each SMD pad. The steel mesh used for tinning must have this Paste Mask file so that the film can be processed.

The most important thing to understand about the Gerber output of the Paste Mask layer is that this layer is mainly for SMD components. At the same time, compare this layer with the Solder Mask introduced above to understand the different functions of the two, because the two film images are very similar.

6 Keep out layer

It is used to define the area on the circuit board where components and wiring can be effectively placed. Draw a closed area on this layer as the effective wiring area. Automatic placement and wiring cannot be performed outside this area.

7 Silkscreen layer

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

8 Multi layer

The pads and through-holes on the circuit board need to penetrate the entire circuit board and establish electrical connections with different conductive graphic layers. Therefore, the system specifically sets up an abstract layer - multi-layer. Generally, pads and vias are set on multiple layers. If this layer is closed, pads and vias cannot be displayed.

9 Drill layer

The drilling layer provides drilling information during the circuit board manufacturing process (such as pads and vias that need to be drilled). Protel 99 SE provides two drilling layers: Drillgride (drilling indication diagram) and Drill drawing (drilling diagram).

The difference between solder mask and solder paste

Solder mask: solder mask refers to the part of the board that needs to be painted green. Because it is a negative output, the actual effect of the part with solder mask is not painted green, but tinned, which is silver-white!

Paste mask: paste mask is used when the machine is mounting the chip. It corresponds to the soldering pads of all the chip components. It has the same size as the toplayer/bottomlayer layer and is used to open the steel mesh to leak tin.

Key points: Both layers are used for tinning and welding, which does not mean one for tinning and the other for green paint; then is there a layer for green paint? As long as there is this layer in a certain area, it means that this area is insulated with green paint? I haven't encountered such a layer yet! The pads on the PCB board we drew have a solder layer by default, so the pads on the manufactured PCB board are coated with silver-white solder, and it is not surprising that there is no green paint; but the routing part of the PCB board we drew only has the toplayer or bottomlayer layer, and there is no solder layer, but the routing part of the manufactured PCB board is coated with a layer of green paint.

That can be understood like this:

1. The solder mask layer means opening a window on the entire piece of green solder mask to allow soldering!

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

3. The paste mask layer is used for SMT packaging! SMT packaging uses: top layer, top solder layer, top paste layer, and the top layer and top paste are the same size, and the topsolder is one circle larger than them. DIP packaging only uses: topsolder and multilayer layers (after some analysis, I found that the multilayer layer is actually toplayer, bottomlayer, topsolder, and bottomsolder layers overlap in size), and the topsolder/bottomsolder is one circle larger than the toplayer/bottomlayer.

annysky2012

Thanks for sharing.

lihuanyang

Good stuff, it is instructive for designing PCB boards, but only these PCB manufacturing processes are not enough!