The screen printing layer of the PCB board is the text layer. Its function is to facilitate the installation and maintenance of the circuit, and print the required logo patterns and text codes on the upper and lower surfaces of the PCB board, such as component labels and nominal values. Profile shape and manufacturer logo, production date, etc. So what are the specifications and requirements for screen printing of PCB boards? How to add pcb silk screen? Next, follow us to learn more about the specifications and requirements of silk screen printing.
The silk screen layer is the text layer, which belongs to the top layer in the PCB and is generally used for annotation. The principle of the correct character layout of the silk screen layer is: "No ambiguity, see the seam and insert the needle, and be beautiful and generous". This is a special layer for printing required logo patterns and character codes on the upper and lower surfaces of the printed board in order to facilitate circuit installation and maintenance.
1. Specifications and requirements for screen printing of PCB printed circuit boards
1.1. All components, mounting holes and positioning holes have corresponding silk screen labels. In order to facilitate the installation of the finished board, all components, mounting holes and positioning holes have corresponding silk screen labels. The mounting holes on the PCB are screen printed with H1, H2. Hn for identification.
1.2. Silkscreen characters follow the principle of left-to-right, bottom-up. Screen-printing characters should follow the principle of left-to-right and bottom-up as much as possible. For electrolytic capacitors, diodes and other polar devices, try to keep them in each functional unit as much as possible. the same direction.
1.3. There is no silk screen on the device pad and the tin track that needs to be tinned, and the device number should not be blocked by the device after installation. (The density is higher, except for those that do not need silk screen printing on the PCB)
1.4. In order to ensure the soldering reliability of the device, it is required that there is no silk screen on the pad of the device; in order to ensure the continuity of the tin-lined tin track, it is required that there is no silk-screen on the tin-lined tin track; in order to facilitate the device insertion and maintenance, the device location number is different. It should be covered by the device after installation; the silk screen should not be pressed on the via holes and pads, so as not to cause part of the silk screen to be lost when the solder mask window is opened, which will affect the training. The screen spacing is greater than 5mil.
1.5. The polarity of polar components is clearly indicated on the silk screen, and the polarity direction mark is easy to identify.
1.6. The number of PCB light-painting files is correct, each layer should have the correct output, and there should be a complete number of layers output.
1.7. The identifier of the device on the PCB must be consistent with the identifier in the BOM list.
1.8. The direction of the directional connector is clearly indicated on the silk screen.
1.9. There should be a barcode position mark on the PCB. If the space of the PCB board allows, there should be a 42*6 barcode screen printing frame on the PCB, and the barcode position should be considered for easy scanning.
1.10. The screen printing position of the finished board information such as PCB board name, date, version number, etc. should be clear. The printed board information such as board name, date, version number, etc. should be printed on the PCB file, and the position should be clear and eye-catching.
1.11. There must be complete relevant information of the manufacturer and anti-static mark on the PCE.
2. How to add silk screen printing of PCB printed circuit board
2.1. Placement
Generally speaking, when placing the screen printing of resistors, capacitors, tubes and other devices, do not use four directions, which will cause the screen printing to be very tiring when debugging, repairing, and welding (the board needs to be turned in several directions) . Therefore, it is recommended to place it in two directions, so that the silk screen will be checked in a very comprehensive way. If the components are too dense and the silk screen cannot be placed, you can write the silk screen and mark the arrow in the blank area nearby. It is best to draw a frame to make it easier to identify.
2.2. Try not to hit the via hole on the silk screen.
After the hole is punched in the word 8, you will not be able to tell whether it is R48 or R49 after the board comes back.
2.3. Do not press the silk screen on high-speed signal lines (such as clock lines, etc.).
This recommendation is for high-speed signal lines on the top or bottom layer, because these types of signal lines can be considered as microstrip lines. The speed (phase speed) of the signal on the microstrip line is related to the medium. If the silk screen is pressed against the line, the medium will become uneven, resulting in a change in the phase speed, which will eventually manifest as impedance discontinuity and affect the signal quality. Of course, this problem will not exist in the signal lines of the inner electrical layer.
2.4. The reading direction of the silk screen should be consistent with the direction of use.
The reading direction of the silk screen is the same as the direction of use of the chip, mainly when welding, to reduce the probability of reverse welding. Others, such as: electrolytic capacitors, etc., can also not follow this recommendation, because you can indicate the positive and negative polarities.
2.5. The pin number should be clearly marked on the silk screen.
On the P3 connector, 4 pin numbers are marked for easy debugging/installation. In addition, it is best to mark the places where the pins are dense, such as: chips, FPC sockets, etc. At the same time, it also conforms to the previous suggestion. The reading direction of P3 is the same as that of the connector.
2.6. Silk screen for special packaging.
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, otherwise, it will be difficult to align, which will affect the welding.
2.7. Silk screen of mounting holes.
Here, the silk screen of the screws is added near the installation holes, and the length and the total number of screws are marked at the same time, which is convenient for installation.
2.8. Ambiguity of silk screen printing.
The most commonly used RS232, many people will mark RX and TX, but the PC side also has RX and TX, when to use crossover cable, when to use non-crossover cable? This leads to the ambiguity of silk screen printing, which makes people foolishly confused. Here, two arrows are added to indicate the flow of the signal, so that you can see how to wire it at a glance. Not only RS232 can do this, other, such as: SPI, etc., with transceiver signal lines, can do this.
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