What is the role of the Assembly layer, and the silk screen is different?
The silk screen is a person who is hand-made, and there is a person who is given to the board.
The Assembly layer is an assembly layer, used to indicate the size of the device, which is obtained when the patch machine is welded.
The assembly layer can be placed in the nominal value of the device, such as the value of the resistance capacitor, which is very convenient to see the assembly repair.
When we draw PCB, we will definitely encounter Solder Mask and Paste Mask. It used to die. Solder Mask is a solder resist layer. Paste Mask is a solder paste layer, which is not very intention when using Protel, but uses Cadence When you make your own pad, you must understand the meaning of these.
Solder Mask [Welding Layer]: This is the abstraction layer! Some expressions, no. It is where the pads of the pad (surface plated pad, plug-in pad, via) are applied to the place, in order to prevent the PCB tin furnace (wave soldering), should not be on Tin Local upper tin, so it is called the solder welding layer (green oil layer), I think I will see this green oil as long as I have seen the PCB board, and the soldering layer can be divided into Top Layers R and Bottom Layers. The Solder layer is to reveal the pad, which is the small circle or small square circle we see when only the Solder layer is displayed. It is generally larger than the solder (the Solder surface means the soldering layer, which is to apply it to apply it. Gold soldering materials such as green oil, preventing no soldering from places in staining, this layer will expose all pads that need to be welded, and openings will be larger than the actual pads); when generating gerber files, you can observe Solder The actual effect of Layers. Draw a real rectangle on Solder Mask Layer, then this rectangle is equal to the opening window (not painted, not oily is a bright crystalline!) Solder Mask is a green oil, Blue oil, red oil, in addition to the pad, via, etc. Can not be applied (painted without soldering?) Other solder resist, this solder resist has a green blue red. . . When painting Cadence pads, Solder Mask is 0.15mm (6mil) than regular PAD.
Paste Mask Layers [Solder Paste Protective Layer] This is a positive display, there is no need. It is directed to the surface post (SMD) element, which is used to make a steel film (sheet), while the holes on the steel film correspond to the solder joint of the SMD device on the board. When the surface mount (SMD) device is welded, the steel film is lid on the circuit board (corresponding to the actual pad), then apply the solder paste, scrape the excess solder paste with a blade, remove the steel film In this way, the pad of the SMD device is added to the solder paste, and then the SMD device is attached to the top of the solder paste (manual or postal machine), and finally the SMD device welding is completed by the reflow solder. Usually, the size of the aperture on the steel film is substantially soldered on the board, and the solder paste protective layer is enlarged or reduced by designating an extended rule. For different requirements of different pads, you can also set multiple rules in the solder paste guard, and the system also provides 2 solder paste protective layers, which are top-layer solder paste protective layer (TOP PASTE) and underlying solder paste protective layer (Bottom) Paste) Draw a real rectangle on Paste Mask Layers, then this rectangle is equal to opening a window, the machine sprayed in this window [in fact it is the steel network opened a window, Water welding is tin]
At the same time, Keepout and Mechanical Layer are also easy to mix.
Keepout, Picture Box, determine the electrical boundary;
Mechanical Layer, the real physical boundary, the positioning hole is done according to the size of the Mechanical Layer, but the PCB factory engineer generally does not understand this. So it is best to delete the Keepout Layer layer before sending the PCB factory (the laboratory has occurred before the KEEPOUT LAYER did not delete the case of the PCB factory cut error boundary).
An assembly layer and a print layer are often encountered in the PCB. So what is the meaning of these two layers?
Silk print layer: The shape of the part is a graphic symbol representing the extension of the device. This layer data is often used when the PCB is designed. More appropriate, SilkScreen Lay will be printed on the PCB board.
Assembly: Place Bound Top / Bottom, Physical Profile Graphics. Can be used for DFA rules: DFM / DFA, is Design FOR manufacturing (M) / Design FOR assembly (a). This property is used for layout and outfit. It is a part of the board to check if the part is provided to check if there is a problem or other use so it isn's print board. The silk screen is definitely necessary but the assembly layer can be parenly (personal understanding)
Both words and negative slices are often encountered in the PCB, and the front and negative slices refer to two different display effects of one layer. Whether your layer is a positive or negative, the PCB board is the same. Just during the Cadence process, the data volume, DRC detection, and the software processing process is different. It is just two ways to express one thing. Positive film is, what do you see, what is it, you see a wiring is a wiring, it is true. The negative film is, what do you see, there is nothing, what you see is precise, it is necessary to corrupt the copper skin.
The advantage of the positive film is that if the moving element or the via needs to be rebound, there is a more comprehensive DRC check. The advantage of the negative film is that the moving element or the via does not need to be repaired, automatically update copper, and there is no comprehensive DRC check.
The hole is more than 10 mil (0.2 mm) in the drawing hole pad, and the outer diameter is more than 20mil than the hole, otherwise the pad is too small welding is inconvenient.
Original link: https://www.eeboard.com/news/pcb-8/
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