PCB Tech - What is the purpose of PCB printed circuit board layers?

1. The top and bottom pad layers of the PCB circuit board layer:

Toppaste and bottompaste are the top and bottom pad layers, which refer to the copper platinum that we can see exposed. (For example, we drew a wire on the top wiring layer. What we see on the PCB is only It's just a line, it is covered by the entire green oil, but we draw a square or a point on the toppaset layer at the position of this line, and the square and this point on the printed board are not green. It's oil, but copper platinum.

The two layers of topsolder 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, solder: solder, paste: paste, paste, mask: mask, film, surface layer, etc. .

Simply take the top layer as an example: the full name of the solder layer in Protel 99SE is top solder mask, which means the solder mask layer. To understand it literally, it is to give the traces on the PCB a layer of green oil to achieve resistance. The purpose of soldering, in fact, is not the case. If you do not add a solder layer to the trace after routing, the green oil is added by default when the PCB manufacturer makes it. If the solder layer is added, the PCB will be added here after it is made. You will see bare copper foil everywhere. Can be understood as a mirror phase.

2. The past layer is used when the stencil is made before the PCB patch. It is used to apply solder paste. The electronic components of the patch are attached to the solder paste for reflow soldering. The difference between DrillGuide and DrillDrawing:

1. DrillGuide is used for guiding drilling, C8051 chip decryption, mainly used for manual drilling for positioning;

2. DrillDrawing is used to view the hole diameter. When drilling manually, these two files must be used together. But now most of them are CNC drilling, so these two layers are not very useful.

When placing positioning holes, you don't need to place content on these two layers. Just put the via pads of the corresponding aperture on the Michanical or TOPLAYER or bottomlayer layer. You can only place the disk diameter smaller.

As for the two layers of Michanical and MultiLayer:

1. Michanical is a mechanical layer, used to place mechanical graphics, such as the shape of the PCB;

2. MultiLayer can be called a multi-layer, the graphics placed on this layer have corresponding graphics on any layer, and the keepout layer that will not be screen printed on the solder resist is actually not used to draw the shape of the PCB, the keepout layer The real purpose of is to prohibit wiring, that is to say, after placing graphics on the keepout layer, there will be no corresponding graphics copper foil in the corresponding position on the wiring layer (such as toplayer and bottomlayer), and it is all wiring Floor. This will not happen after placing graphics on the Michanical layer.

3. 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 is the temporary boundary of copper that defines the electrical characteristics of our wiring. 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 bottom pad layer on the top layer, which refers to the copper platinum exposed to the outside (for example, we draw a wire on the top wiring layer, and 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 toppaset layer at the position of the line, and the square and this point on the printed board are not green It's oil, but copper platinum.

The two layers of topsolder 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. The multilaye layer is actually almost the same as the mechanical layer. As the name is good, this layer refers to All layers of the PCB board.

The concept of "Layer" is the same as the concept of "Layer" introduced in word processing or many other software to realize the nesting and synthesis of pictures, texts, colors, etc. The "Layer" of Protel is not virtual. It is the actual copper foil layers of the printed circuit board material itself. Nowadays, due to the dense installation of electronic circuit components. Special requirements such as anti-interference and wiring. The printed circuit boards used in some newer electronic products not only have upper and lower sides for wiring, but also have interlayer copper foil that can be specially processed in the middle of the board. For example, the current computer motherboard Most of the printed circuit board materials used are more than 4 layers. Because these layers are relatively difficult to process, they are mostly used to set up the power wiring layers with simpler wiring (such as Ground Dever and Power Dever in the software), and often use large-area filling methods for wiring (such as ExternaI P1a11e and Fill in the software). ). Where the upper and lower surface layers and the middle layers need to be connected, the so-called "vias" mentioned in the software are used to communicate. With the above explanation, it is not difficult to understand the related concepts of "multi-layer pad" and "wiring layer setting".

To give a simple example, many people have completed the wiring and found that many of the connected terminals have no pads when they are printed out. In fact, this is because they ignored the concept of "layers" when they added the device library and did not draw and package themselves. The pad characteristic is defined as "multi-layer (Mulii-Layer). It should be reminded that once the number of printed circuit board layers to be used is selected, be sure to close those unused layers, so as not to cause troubles and detours.