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PCB screen printing layer is the text layer, its role is to facilitate the installation and maintenance of the circuit, printed on the upper and lower surfaces of the PCB board on the required logo pattern and text code, such as component labels and nominal values, components outside Profile shape and manufacturer's logo, production date, etc. So what are the specifications and requirements for silk screen printing on PCBs? Pcb silk screen how to add it?
Detailed silk screen layer
The silk screen layer is a text layer and belongs to the top layer in the PCB. It is generally used for annotation. The correct layout principle of the silk screen layer is: "No ambiguity, no seams, beautiful appearance." This is to facilitate the installation and maintenance of the circuit, and to print the upper and lower surfaces of the printed board with special layers such as logos and letter codes.
Pcb screen printing specification and requirements
1.All components, mounting holes, positioning holes have a corresponding silk screen marking In order to facilitate the installation of the finished plate, all components, mounting holes, positioning holes have a corresponding silk screen number, PCB mounting holes on the screen printing with H1, H2. Hn identifies.
2. The principle of silkscreen characters follows from left to right and from bottom to top. The silkscreen characters follow the principles from left to right and from bottom to top as much as possible. Electrolytic capacitors, diodes, and other polar devices are kept as possible within each functional unit. The direction is the same.
3. Device pad, the need to tin solder tin on the silk screen, the device position number should not be blocked after installation. (Higher density, except for silk screen on PCB)
4, in order to ensure the reliability of the device's welding, the device pad is required no silk screen; In order to ensure the continuity of the tin channel of tin, the tin channel of tin need to be no silk screen; In order to facilitate device insertion and maintenance, the device position number is not Should be blocked by the device after installation; screen printing can not be pressed on the conduction hole, pad, so as to avoid opening the resistance welding window caused by the loss of part of silk screen, affect training. Silk screen spacing is greater than 5mil.
5. The polarity of the polar components is clearly shown on the silk screen, and the polarity mark is easy to identify.
6. The number of PCB light-painted documents is correct, each layer should have the correct output, and a complete number of layers of output.
7. The identifier of the device on the PCB must be consistent with the identifier in the BOM list.
8. The orientation of the connector with a direction indicates clearly on the screen printing.
9. There should be a bar code position mark on the PCB When the space on the surface of the PCB board is allowed, there should be a 42*6 bar code silk screen frame on the PCB. The position of the bar code should be considered for convenient scanning.
10, PCB board name, date, version number, etc. made of information board silk screen location should be clear. The PCB file should have the board name, date, version number, etc. printed on the board to be silk screened. The location is clear and eye-catching.
11. The PCE must have the manufacturer's complete relevant information and anti-static logo on it.
Pcb silk screen how to add
1. the location of the displayIn general, when screens of resistors, capacitors, tubes, etc. are placed, do not use four directions. This will result in debugging, maintenance, and welding. Look at the screen printing and it is very tiring (the board must be turned in several directions). .Therefore, it is recommended to place it in two directions as shown in the figure below. In this way, the silk screen will be viewed in a very respectable way
As shown in the figure below, if the components are too dense and can not accommodate silk screen printing, you can write silk screens on the nearby blank areas and mark them with arrows. It is better to draw a frame, so that you can identify some of them.
2. Try not to hit the silk screen on the hole
As shown in the figure below, the hole is hit in the 8 word. After the board is returned, you can't tell whether it is R48 or R49.
3. the direction of reading silk screen should be consistent with the direction of use.As shown in the figure below, the direction of reading of the screen printing is consistent with the direction of use of the chip, mainly when welding, reducing the probability of welding reverse.Others, such as electrolytic capacitors, may also not follow this recommendation because you can indicate positive and negative polarity.
4. The pin number should be clearly marked on the silk screen.As shown in the figure below, P3 connectors are marked with 4 pin numbers to facilitate debugging/installation. In addition, it is also best to label the place where the pins are dense, such as: chips, FPC sockets, etc.At the same time, it also complies with the previous recommendation. The reading direction of P3 is consistent with the direction of use of connectors.
5. special packaging silk screen.For special packages such as BGA and QFN, the size of the silk screen should be exactly the same as the size of the chip (as shown in the figure below). Otherwise, it will be difficult to align and affect the soldering.
6. installation hole silk screen.Here, the silk screen of the screw is added near the mounting hole, and the length and the total number of screws are marked to facilitate the installation.
7. Ambiguous screen printing.The most commonly used RS232, many people will mark RX and TX, but the PC side also has RX and TX ah, when to use cross-line, when not to cross?This led to the ambiguity of silk screen printing, making people indistinguishable.Here, two arrows are added to the direction of the indicator signal (as shown in the figure below) so that you can see at a glance how to wire it.It is not just RS232 that can do this. Others, such as SPI, can send and receive signal lines.
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