Silkscreen On PCB
1. The location of the display
In 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, silk screens 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 silkscreen on the via 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. Do not press silk screen on high-speed signal lines (such as clock lines, etc.)
This suggestion is for high-speed signal lines on the top or bottom layer, because these signal lines can be considered as microstrip lines.
The speed of the signal running on the microstrip line (phase velocity) is related to the medium. If the silk screen is pressed to the line, as shown in the figure below, the medium will become inhomogeneous, causing the phase velocity to change and eventually appearing as an impedance discontinuity. , affect the signal quality.
Of course, the signal line in the inner layer will not have such a problem.
4. 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.
5. 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.
6. 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.
7. 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.
8. 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.