PCB design experience - for reference

szjlczhang

PCB design experience - for reference [Copy link]

1. Pay attention to the definition of pins and the name of the package when making the schematic library.

When making the package library, pay attention to the one-to-one correspondence of the schematic pins; if the pins do not correspond, isolated components will appear when the PCB diagram is obtained.

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

Because of different applications, it has different functions. If the serpentine line appears in the computer board, it mainly plays the role of a filter inductor to improve the anti-interference ability of the circuit. The serpentine line in the computer motherboard is mainly used in some clock signals, such as PCIClk, AGPClk, and it has two functions: 1. Impedance matching; 2. Filter inductor. The use of serpentine lines helps to improve the stability of the motherboard and graphics card, helps to eliminate the inductance phenomenon generated by long straight wiring when current passes through, and reduces the crosstalk problem between lines, which is particularly obvious at high frequencies.

3. When the mounted components on the welding surface adopt the wave soldering production process, the axis of the resistor and capacitor should be perpendicular to the wave soldering transmission direction, and the axis of the resistor array and SOP (PIN spacing is greater than or equal to 1.27mm) components should be parallel to the transmission direction. IC, SOJ, PLCC, QFP and other active components with IN spacing less than 1.27mm (50mil) should avoid wave soldering.

4. The distance between BGA and adjacent components is >5mm. The distance between other SMD components is >0.7mm; the distance between the outer side of the SMD component pad and the outer side of the adjacent plug-in component is greater than 2mm; for PCBs with crimped parts, there should be no plug-in components or devices within 5mm around the crimped connector, and there should be no SMD components or devices within 5mm around the welding surface.

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

6. When laying out components, it is appropriate to consider putting components using the same power supply together as much as possible to facilitate future power supply separation.

7The layout of resistors and capacitors used for impedance matching should be arranged reasonably according to their properties. The layout of the series matching resistor should be close to the driving end of the signal, and the distance is generally not more than 500mil. The layout of the matching resistor and capacitor must distinguish the source and terminal of the signal. For the terminal matching of multiple loads, it must be matched at the farthest end of the signal.

8. After the 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 single board, backplane and connector. Only after confirmation can the wiring begin.

9, Set wiring constraints

1) Report design parameters

After the layout is basically determined, apply the statistical function of the PCB design tool to report basic parameters such as the number of networks, network density, average pin density, etc., in order to determine the number of signal wiring layers required. The following empirical data can be referred to for determining the number of signal layers: Pin density, number of signal layers, number of board layers Note: PIN density is defined as: board area (square inches) / (total number of pins on the board / 14) 10. Hole setting: Wire hole: The minimum aperture of the manufactured board depends on the thickness of the board, and the board thickness-to-aperture ratio should be less than 5--8. The preferred series of apertures are as follows:Aperture: 24mil 20mil 16mil 12mil 8milPad diameter: 40mil 35mil 28mil 25mil 20milInner layer thermal pad size: 50mil 45mil 40mil 35mil 30mil

szjlczhang

We are open during the Spring Festival, and you can order 12H expedited samples, SF Express