PCB silkscreen printing is the use of screen printing technology to make printed circuit boards. The silk screen value is the silk screen layer. When drawing the pcb layer. The layer containing the text legend is used to mark components or add other information. This layer is called the silk screen layer.
The component shape, serial number, and other descriptive text are printed on the component surface or solder surface by screen printing to facilitate the plug-in (including the surface-mounted component patch) of the circuit board production process and the maintenance operation of the product in the future.
The PCB silk screen layer is generally placed on the top layer (Top), but for the electronic products with high failure rate and frequent maintenance, such as the motherboard of TVs, computer monitors, printers, etc., the silk screen layer can be set on the component side and the soldering surface. .
Many PCB engineers who draw PCB think that silkscreen does not affect the performance of the circuit, so it does not pay attention to silkscreen. However, for a professional hardware engineer, you must pay attention to these details.
The following describes the method of elegantly arranging PCB silkscreen.
In general, the silkscreen printing of resistors, capacitors, tubes, etc., do not use four directions when placing, this will lead to debugging, repair, welding, see silk screen is very tired (the board has to turn several directions) .
Therefore, it is recommended to place it in two directions at most, as shown in the figure below. This way, it will be very convenient to view the silk screen.
As shown in the figure below, if the components are too dense, and you can’t put on the silk screen, you can write a silk screen in the blank place nearby, mark the arrow, and then draw a frame,which is convenient for identification.
2、Do not try to Via’s on the silkscreen
As shown in the figure below, the via is on the silkscreen 8 . After the PCB is made, you will not know whether it is R48 or R49.
3、Do not Arrange the silkscreen on high speed signals(eg, clock lines, etc.).
This recommendation is for high speed signals on the top or bottom layer, because such signal circuit 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 uneven, causing the phase velocity to change, and finally the impedance is discontinuous. , affecting signal quality.
Of course, there will be no such problem
with the signal line of the inner layer.
4、The reading direction of silkscreen should be consistent with the direction of use.
As shown in the figure below, the reading direction of the silkscreen is the same as the direction of use of the chip, mainly when welding, reducing the probability of the welding being reversed.
Others, such as electrolytic capacitors, may not follow this recommendation because you can indicate positive and negative polarity.
5、The pin number should be marked on the silkscreen.
As shown in the figure below, the P3 connector is marked with 4 pin numbers for easy debugging/installation. In addition, it is best to mark the pin-intensive places, such as chips, FPC sockets, etc.
At the same time, it also meets the previous recommendation. The reading direction of P3 is the same as the direction of use of the connector.
6、Silkscreen printing of special electroni ccomponents.
For special components such as BGA and QFN, the size of the silkscreen 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、Silkscreen of the mount hole
Here, the silk screen of the screw is added near the mounting hole, and the length and the total number of screws are marked for easy installation.