Electronic Design - The PCB board design layout rules are like this

PCB board design needs to be set at different points in different stages. In the PCB layout stage, large grid points can be used for device layout;

For large equipment such as ICs and non-positioned connectors, a grid accuracy of 50 to 100 mils can be used for layout. For passive small devices such as resistors, capacitors and inductors, 25 mil grids can be used for layout. The accuracy of the large grid points is conducive to the alignment of the device and the aesthetics of the layout.

PCB board design layout rules:

1. Under normal circumstances, all components should be placed on the same side of the circuit board. Only when the top components are too dense, can you place some devices with limited height and low heat generation, such as chip resistors, chip capacitors and stickers. The chip IC is placed on the lower layer.

2. Under the premise of ensuring the electrical performance, the components should be placed on the grid and arranged in parallel or perpendicular to each other to maintain a clean and beautiful appearance. Under normal circumstances, the components are not allowed to overlap; the components are arranged in a compact manner, and the components should be arranged on the entire layout. Even distribution, uniformity and consistency.

3. The minimum distance between adjacent components on the circuit board should be less than 1MM.

4. The edge of the circuit board is generally not less than 2mm. The best shape of the board is rectangular, with an aspect ratio of 3:2 or 4:3. When the scale of the circuit board is larger than 200MM*150MM, the circuit board should be considered. Mechanical strength.

In the PCB board design, the unit of the circuit board should be analyzed and the layout design should be carried out according to the function. When laying out all the components of the circuit, the following principles must be met:

1. Arrange the position of each functional circuit unit according to the flow of the circuit, so that the layout is convenient for signal circulation and the signal is as consistent as possible.

2. Take the core component of each functional unit as the center and surround it. The components should be uniformly, integrally and compactly arranged on the PCB board design to minimize and shorten the leads and connections between the components.

1. When making the package library, pay attention to the one-to-one correspondence between the schematic pins; if the pins do not correspond, component isolation will occur when the PCB is obtained.

2. Any trace on the PCB board design will cause a delay when the signal passes through the high-frequency signal. The main function of the serpentine trace is to compensate for the smaller delay in the "same group" signal line. These components usually have no or less logic than other signals; the most typical is the clock line, which usually does not need to go through any other logic processing, so its delay will be less than other related signals.

Since the application has different functions, if the serpentine trace appears on the computer board, it is mainly used as a filter inductor to improve the anti-interference ability of the circuit. The serpentine track on the computer motherboard is mainly used for certain clock signals, such as PCIClk, AGPClk, and has two functions: 1. Impedance matching; the use of serpentine lines in filter inductors helps to improve the stability of the motherboard and graphics card, helps eliminate the inductance caused by the long straight line of current passing through, and reduces the crosstalk between the lines, which is especially obvious at high frequencies. .

3. When the mounting parts on the welding surface adopt wave soldering production process, the axial direction of the resistor and capacitor should be perpendicular to the wave soldering transmission direction, and block and SOP (PIN distance greater than or equal to 1.27 mm). The axial direction of the component is parallel to the conveying direction. Active components with active pitch less than 1.27 mm (50 mils), such as IC, SOJ, PLCC and QFP, can avoid wave soldering.

4. The distance between BGA and adjacent components> 5 mm. The distance between other SMD PCB components is> 0.7 mm; the distance between the outside of the mounting component pad and the outside of the adjacent insertion component is greater than 2 mm; the PCB with crimping components, the crimping connector is not within 5 mm There should be inserted components or equipment, and there should be no installation components or equipment within 5 mm of the welding surface.

5. The layout of the IC decoupling capacitors should be as close as possible to the power supply pins of the IC, and the loop formed between the power supply and the ground should be as short as possible.

6. When placing components, it should be considered that devices using the same power supply should be placed together as much as possible to facilitate future power supply separation.

7. The layout of the resistor container used for impedance matching purposes should be reasonably arranged according to its nature. The layout of the series matching resistor should be close to the driving end of the signal, and the distance should not exceed 500 mils. The layout of matching resistors and capacitors must distinguish the source and end of the signal. For multi-load terminal matching, it must be matched at the far end of the signal. .

8. After the PCB layout is completed, print out the assembly drawing for the schematic designer to check the correctness of the device package and confirm the signal correspondence between the board, backplane and connector. After wiring, you can start wiring and confirm.