What is the basic principle of pcb non layout? What is the idea of pcb layout?

What is the basic principle of pcb non layout? What is the idea of pcb layout?

The design process flow of PCB includes schematic design, electronic component database login, design preparation, block division, electronic component configuration, configuration confirmation, wiring and final inspection. In the process, no matter what process problems are found, they must be returned to the previous process for reconfirmation or correction. Next, let me introduce to you the basic principle of non layout of PCBs? What is the idea of pcb layout?

1、 What are the basic principles of pcb layout?

1. During the layout, ensure that the total wiring is as short as possible and the key signal lines are as short as possible; High voltage and high current signals are completely separated from weak signals of low current and low voltage; Separate analog circuit from digital circuit; High frequency circuit and low frequency circuit are separated; The spacing of high-frequency components shall be sufficient.

2. The circuit unit structure of layout design refers to the circuit structure placement in the principle, and the specific layout needs to be based on the signal flow direction and device function in the schematic diagram.

3. The core components of the circuit function block shall be placed first, and then the surrounding circuit components shall be placed with the core components as the center. The layout requires that the components be evenly distributed.

4. Plug in components of the same type shall be placed in the same direction in X or Y direction; Polarized discrete components of the same type should also be consistent in the X or Y direction as far as possible to facilitate production and inspection (mainly for manual welding).

5. The heating components shall be evenly distributed to facilitate the heat dissipation of the single board and the whole machine. The temperature sensitive components other than the temperature detection components shall be far away from the components with large heat.

6. The decoupling capacitor of the integrated circuit shall be close to the power supply pin of the chip as far as possible to form the shortest loop with the power supply and ground. The bypass capacitance should be evenly distributed around the integrated circuit (according to the empirical judgment standard, the smaller the capacitance, the smaller the decoupling range, and the closer to the power pin).

7. Circuit units with the same structure shall adopt "symmetrical" layout as far as possible.

8. The layout of impedance matching resistance capacitance devices shall be reasonably arranged according to their properties. Common termination matching includes: source end series matching, terminal parallel matching, Thevenin termination, RC network matching, diode matching. Among them, the layout of the series matching resistor should be close to the transmitting end of the signal, and the distance is generally not more than 500mil. The layout of matching resistance and capacitance must distinguish between the transmitter and receiver of the signal. For multi load terminal matching, it must match at the farthest end of the signal and be placed according to different terminal matching functions.

9. Filter, protection, isolation and other components of interface signal shall be placed close to the interface connector, following the principle of "protection first, filtering later", so ESD, TVS components shall be placed close to the connector.

10. The plug-in devices, ICs and heavier devices shall be placed on the same side to avoid interference with the structure. Sufficient space shall be reserved around the plug-in in the board, and the specific distance shall be determined according to the specific packaging and physical objects.

2、 What is the idea of pcb layout?

1. First of all, we will place the components with structural requirements, and pay attention to the placement of one pin of the connector according to the imported structure.

2. Pay attention to the height limit requirements in the structure during layout.

3. If the layout is to be beautiful, it is generally positioned according to the outer frame or centerline coordinates of the component (aligned in the center).

4. The overall layout shall consider heat dissipation.

5. In the layout, it is necessary to consider the evaluation of wiring channels and the space required for equal length.

6. The power flow direction shall be considered and the power channel shall be evaluated during the layout.

7. High speed, medium speed and low speed circuits shall be separated.

8. High current, high voltage and strong radiation components shall be kept away from low current, low voltage and sensitive components.

9. Analog, digital, power and protection circuits shall be separated.

10. The interface protection device shall be placed as close to the interface as possible.

11. Requirements for placement sequence of interface protective devices:

(1) The sequence of lightning protection devices for general power supply is: varistors, fuses, suppression diodes, EMI filters, inductors or common mode inductors. If the schematic diagram is missing, any of the above devices shall be arranged in sequence;

(2) Generally, the sequence of protective devices for interface signals is: ESD (TVS tube), isolation transformer, common mode inductance, capacitance, resistance, and any device above shall be arranged in sequence if the schematic diagram is missing; The "line type" layout shall be carried out in strict accordance with the sequence of schematic diagrams (with the ability to judge whether the schematic diagrams are correct).

12. The level conversion chip (such as RS232) is placed close to the connector (such as serial port).

13. Devices susceptible to ESD interference, such as NMOS and CMOS devices, should be as far away from areas susceptible to ESD interference as possible (such as the edge area of a single board).

14. Clock device layout:

(1) The crystal, crystal oscillator and clock distributor shall be as close as possible to the relevant IC devices;

(2) The filter of the clock circuit ("Π" type filter shall be used as far as possible) shall be close to the power input pin of the clock circuit;

(3) Whether the output of crystal oscillator and clock distributor is connected with a 22 ohm resistor in series;

(4) Whether the unused output pins of the clock distributor are grounded through resistance;

(5) The layout of crystal, crystal oscillator and clock distributor shall be far away from high-power components, radiator and other heating devices;

(6) Whether the distance between crystal oscillator and board edge and interface device is greater than 1 inch.

15. Whether the switching power supply is far away from AD  DA converter, analog device, sensitive device and clock device.

16. The layout of switching power supply shall be compact, and the input/output shall be separated. The layout shall be strictly in accordance with the requirements of the schematic diagram, and the capacitance of switching power supply shall not be placed randomly.

17. Capacitors and filter devices:

(1) The capacitor must be placed close to the power pin, and the smaller the capacitance is, the closer the capacitor is to the power pin;

(2) EMI filter shall be close to the input port of chip power supply;

(3) In principle, one 0.1uf small capacitor for each power supply pin, one or more 10uf large capacitors for an integrated circuit can be increased or decreased according to the specific situation. What are the basic principles for PCB assembly and PCB processing manufacturers to introduce the non layout of PCBs? What is the idea of pcb layout?