What are the basic principles of PCB design for whole board layout? How to optimize and analyze?
Reasonable layout directly affects the life of the product, stability, EMC (electromagnetic compatibility), must from the overall layout, circuit board wiring condition and PCB manufacturing, mechanical structure, heat dissipation, EMI (electromagnetic interference), integrated and reliability, signal considered.
In general, place the fixed position of the components related to the mechanical size first, and then place special and larger components, and finally placed small components. At the same time, need consider layout requirements, high-frequency components should be placed as tight as possible, the signal line wiring can be as short as possible, thereby reducing the signal line interference.
Placement of positioning pins in relation to mechanical dimensions:
The power socket, switch, interface between PCB, indicator light are all positioning pins related to machine size. Typically, the interface between the power source and the PCB is placed at the edge of the PCB, and the PCB edge is spaced from 3mm to 5mm;The light emitting diode should be accurately placed according to the needs; and some fine-tuning switch components, such as adjustable inductance, adjustable resistance should be placed near the edge of the PCB position, to facilitate adjustment and connection; the need for frequent replacement of components must be placed in a position to less devices, easy to replace.
Placement of special components:
High power tube, transformer, rectifier and other heating devices, make more heating in high frequency condition, so the layout should be consider ventilation and heat dissipation, the components are placed on the PCB with air circulation.Large power rectifier tubes and regulating tubes shall be provided with radiators and keep away from the transformer.Electrolytic capacitor such as heat element should be away from the heating device, otherwise the electrolyte will be dried, resulting in the increase of resistance, poor performance, influence the stability of the circuit.
Easy to break components, such as adjustment tubes, electrolytic capacitors, relays, etc.,also need consider the convenience of repair.For testing points that need to be measured frequently, it is important to ensure that the test rod can be conveniently contacted when arranging components.Since the 50Hz leakage magnetic field is generated inside the power supply device, when it is connected to some parts of the low frequency amplifier, it will cause interference to the low frequency amplifier. Therefore, they must be separated or shielded.
According to the principle of the best amplifier line form, so the method is of the advantages of various grounding current in the closed flow, does not affect other circuit work. The input and output stages should be kept as far away as possible to minimize parasitic coupling interference between them.
Considering the signal transmission relationship between each unit function circuit, low frequency circuit and high frequency circuit should be separated, analog circuit and digital circuit separate.
The integrated circuit should be placed in the center of the PCB, so that the wiring of each pin is connected with other devices.
Inductors, transformers and other devices with magnetic coupling should be placed orthogonal to each other to reduce magnetic coupling. In addition, they have a strong magnetic field, which should be properly surrounded by large space or magnetic shielding to minimize the impact on other circuits.
The key parts of PCB to configure the appropriate high frequency decoupling capacitor in the input terminal of a power supply should be PCB 10 F ~ 100 F electrolytic capacitor, near the power supply pin integrated circuit are connected with a ceramic capacitor of about 0.01pF.
Some circuits also have an appropriate high frequency or low frequency choke to minimize the effects of high and low frequency circuits. This should be considered in schematic design and drawing, otherwise it will affect the performance of the circuit.
When the components are arranged, the spacing should be appropriate, and the space between them should be considered whether there is any breakdown or sparking between them.
The amplifier with push-pull circuit and bridge circuit should pay attention to the symmetry of the electrical parameters of the component and the symmetry of the structure, so that the distribution parameters of the symmetrical components can be consistent as much as possible.
After the manual layout of the main components is completed, the component locking method shall be adopted so that the components will not move in the automatic layout. That is, the Edit change command is executed, or Locked can be locked and no longer moved by the Properties selection of the component.
Placement of common components:
For common components, such as resistors, capacitors, several common and convenient welding etc. from components arranged in neat, space size, routing, and uses the automatic layout mode.
PCB layout design, the first manual layout method to optimize the location of some components, combined with automatic layout to complete the overall design of PCB.
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