PCB Layout as an important part of the hardware design, hardware circuit design in a reasonable case, it is an important indicator of performance. A lot of PCB Layout engineers are in accordance with the hardware engineers or PI SI engineers to give the constraints of the rules to complete the layout and routing, which is commonly known as "cable workers." They repeat and mechanically complete a piece of PCB Layout, after some time, some of them may have some experience: what to do long, which to go thick, which should be parallel to ensure the appropriate line distance, etc. The However, they rely on the so-called experience, a lot of knowing that I do not know why. I think, in order to have a breakthrough, it must be to broaden their knowledge. That is, PCB Layout engineers can not let others as their "pull workers" to look at.

First of all, you have to have a certain understanding of the circuit (of course, as hardware engineers, such as the design capability is not necessary, if the best, that);

Second, the need for SI / PI engineers to do PI / SI analysis of the ability (of course, the need to have the ability to RF simulation is not necessary, if it can, that the best). With this knowledge, you not only have the ability to design a good PCB, but also the hardware, SI / PI engineers theory of the capital, and even from the PCB design to give their circuit design recommendations.

Not much to say, from some of the PCB design to sum up some of the principles:

One on the layout

1. Layout, is the rational placement of circuit components. What kind of placement is reasonable, a simple principle is a clear division of the modular, that is a certain circuit-based people, get your PCB will be able to see which block is used to achieve what function.

2. Specific design steps: First, according to the schematic diagram, generate the initial PCB file, complete the PCB pre-layout, to determine a relative PCB Layout area, and then tell the structure, structure according to the area we give, and then according to the overall structure design , Give specific constraints.

3. According to the constraints of the structure to complete the board edge, positioning port and some of the drawing area drawing, and then complete the placement of the connector.

4. The principle of placing components: In general, the master MCU is placed in the center of the board, and then the interface circuit is placed close to the interface (such as network port, USB, VGA, etc.), and most interfaces have ESD protection There is a filtering process. The principle of follow is the first post-protection filter.

5. Then the power module, the general power supply module placed in the power supply entrance (such as system 5V), discrete power modules (such as module circuit power supply 2.5V) can be placed according to the actual situation in the same power network more intensive place.

6. Some of the internal circuit, no lead to the connector. We generally follow such a basic principle: high-speed, low-speed subregion, simulation, digital sub-region, interference source, sensitive receptor sub-region.

7. Then for a single circuit module, follow the circuit design when the current flow to design.

The overall layout of the circuit, probably is the case, welcome God to add and correction.

Second, on the wiring

1. wiring, the most basic requirement is to ensure that all networks are effectively connected. Connectivity, is very easy to do, effective and is a more vague concept. In fact, the signal in the circuit no less than two: digital signals and analog signals, the digital circuit is to ensure adequate noise margin, the analog signal, try to do zero loss.

2. Wiring, the general need to understand the entire PCB board stack design, that is, all the wiring layer planning as: the optimal wiring layer, sub-optimal wiring layer. The The The , The optimal wiring layer, that is, adjacent to the integrity of the ground plane, this layer we generally used to cloth important signals (including DDR in all the signals, differential signals, analog signals, etc.). Other signals (I2C, UART, SPI, GPIO) take other layers, and ensure that only important areas of this circuit-related signals (such as DDR, network port, etc.)

3. Then high-speed signal wiring need to consider reflection, crosstalk, EMC and other issues, so generally need to do impedance matching, such as single-line 50R, differential line 100R, etc., specifically to the actual design (the principle is to ensure equal impedance, continuous) , Crosstalk aspects of the main consideration 3W / 2W principles, including handling and so on.

4. Power and power circuit, first of all to ensure adequate carrying capacity, that is, the power of the entire return road as much as possible rough and short, from the EMC point of view, the return of the loop, the formation of loop antenna, external radiation May reduce the loop area.

The overall circuit wiring, probably is the case, welcome the gods to add and correct me.

Third, on the ground

1. Ground and ground design in the PCB design is a very important part, because the ground as an important reference plane, if the ground plane design problems, and other signals is no way to stabilize.

2. We are generally divided into the chassis and the system, the chassis is the name of the product is the sheet metal to connect to the ground, that is, as the entire circuit system reference plane.

3. The general principle of the system and the chassis is: the chassis and systematically divided, and then systematically through the magnetic beads and high voltage capacitors single point or multi-point connection.

4. Systematically: functionally divided into digital, analog, power ground. There 's always a debate about the division.

First of all, the layout is very reasonable circumstances, I think that can not split. What is the layout is very reasonable, that is, the digital area only digital signal, the analog area only analog signal, power area only power signal, and in their bottom there is a complete ground plane. Because the current and the flow is very similar, they are to the lower flow, they are below the existence of a complete ground plane, so from the shortest, the lowest principle, they return directly below, and will not go to other places to go.

However, sometimes, is not so ideal, there are some cross-regional, this time generally choose a single point of understanding, the use of 0R resistance (not recommended the use of beads, because the high frequency, the beads have a filtering effect). The location of the resistance near the intersection of the most dense place, is the flow of the smallest area.