Some good PCB wiring skills and key points

Some good PCB wiring skills and key points
process wiring is a skill in PCB design is limited and limited Even engineers who have laid wires for more than ten years often feel that they cannot wire because they have seen various problems and know what the consequences would be if they laid wires, So I don't know how to do it But there are still masters They have very rational knowledge. At the same time, they carry some self creating feelings. The wires they laid are beautiful and artistic
Here are some good wiring skills and key points: First, let's make a basic introduction The number of layers of PCB board can be divided into single layer, double layer and multi-layer, and now the single layer is basically eliminated Double layer boards are widely used in audio and communication systems, and they are usually used as power amplifiers That's enough From the perspective of through-hole, it can be divided into through-hole, blind hole and buried hole The through hole is a hole directly from the top layer to the bottom layer; The blind hole passes through the middle layer from the top or bottom layer, and then does not continue to pass The advantage is that the through-hole position is not blocked from beginning to end Other layers can still be wired at the position of the through-hole; Buried through-hole means that the through-hole is buried from the middle layer to the middle layer, and the surface is completely invisible Before automatic routing, the lines with high requirements shall be routed with interactive pipes in advance. The edges of input and output terminals shall not be adjacent and parallel to avoid reflection interference If necessary, ground wires can be added for isolation, and the wiring of two adjacent layers should be perpendicular to each other, because parasitic coupling is easy to occur in parallel The routing rate of automatic routing depends on good layout. Routing rules can be preset, such as the number of wire bends, the number of vias, and the number of steps Generally, exploratory wiring is carried out first, short wires are connected quickly, and then through labyrinth wiring, the global wiring path is optimized for the wiring to be routed Overall wiring effect
PCB board
For layout, one principle is to separate digits and analogies as much as possible, and one principle is that low speed should not be close to high speed The basic principle is to separate digital grounding from analog grounding Because digital grounding is a switching device, the instantaneous current of the switch is very large, and it will decrease when it does not move Therefore, digital grounding cannot be mixed with analog grounding
1. Precautions for wiring between power supply and ground wire
(1) A decoupling capacitor should be added between the power supply and the ground wire.  The power supply must be connected to the chip pin after passing through the decoupling capacitor Generally speaking, decoupling capacitor has two functions: one is to provide transient large current of the chip, the other is to eliminate power supply noise. On the one hand, this is to make the power supply generate noise The impact on the chip should be as small as possible On the other hand, the noise generated by the chip shall not affect the power supply
(2) Widen the power and ground wires as much as possible.  The ground wire is wider than the power line The relationship is: ground wire > power wire > signal wire.
(3) A large area of copper layer can be used as a ground wire
2. Processing when digital circuits and analog circuits are mixed
Nowadays, many PCB boards are no longer single function circuits, but they are composed of digital circuits and analog circuits. Therefore, it is necessary to consider the mutual interference between them when wiring, especially the noise interference on the ground wire. Because of the high frequency of digital circuits and the strong sensitivity of analog circuits, the high frequency signal lines should be as far away from sensitive analog circuit equipment as possible for signal lines, but for the entire PCB board, The grounding wire PCB board is not sensitive to the outside and can only have one node. Recall that the common grounding problem of digital circuit and analog circuit must be in the PCB board and the inside of the . The grounding of digital circuit and analog circuit is actually separated, only in the PCB The interface between the board and the outside world (such as a plug, etc.) There is a short circuit between the digital circuit and the analog circuit Please note that there is only one connection point, and some people do not have a common position on PCB on this issue, which depends on the system design
3. Processing of line corners
Usually there will be changes in the thickness of the wires of the wire For the change of line thickness, the right angle difference and 45 degree angle are better, and the fillet is positive However, for PCB design, fillet is usually determined by signal sensitivity Normally, for ordinary signals, a 45 degree angle is sufficient Only those very sensitive lines need to use fillets
4. Check the design rules after wiring
No matter what you do, you must check it after you finish As we do in exams, if we have time, we must check our answers This is an important way for us to get high scores Similarly, we draw lots of PCB boards s With this kind of pipeline, we can be more sure that the circuit board we draw is a qualified product We generally check the following aspects:
(1) Whether the distance between wire and wire is reasonable and meets the production requirements
(2) Which the width of the power line and the ground line is appropriate, whether the power supply and the ground line are tightly coupled (low wave impedance), and whether there are PCB boards anywhere that can broaden the bottom line
(3) When measures have been taken for key signal lines, such as short length, protective line, input line and output line
(4) Whether the analog circuit and the digital circuit have their own independent ground wires.
(5) Why the graphics added to the PCB will cause short circuit of signal
(6) Modify some unsatisfactory line shapes.
(7) Whether there is a process line on the PCB, whether the solder mask meets the production process requirements, whether the size of the solder mask is appropriate, and whether the character logo is pressed on the device keyboard to avoid affecting the power quality
(8) When the edge of the outer frame of the power ground layer in the multi layer board is reduced, for example, the copper foil of the power ground layer exposed outside the board is easy to cause short circuit
In a word, the above skills and methods are based on experience, which is very worthy of our learning and reference when drawing PCB boards In the process of drawing PCB, we must have solid theoretical knowledge and rich experience in addition to skilled use of drawing tools and software Practical experience, which can help you to complete the PCB board quickly and efficiently drawing charts But it is also very important. That is, you must be careful. Whether wiring or general layout, you must be very careful and careful, because one of your small mistakes may lead to waste of the final product, and then find no problems. So we would rather spend more time in the drawing process to carefully check the details, rather than go back to check whether there are problems, which may take more time In short, drawing a PCB pays attention to details