Research on Manual Layout Design of High Frequency PCB

Generally, the components in the fixed position related to the mechanical size are placed first, then the special and larger components are placed, and finally the small components are placed. At the same time, it is necessary to take into account the wiring requirements, the placement of high-frequency components should be as compact as possible, and the wiring of signal lines can be as short as possible, thereby reducing cross-interference of signal lines.

1.1 Placement of positioning inserts related to mechanical dimensions

Power sockets, switches, interfaces between PCBs, indicator lights, etc. are all positioning inserts related to mechanical dimensions. Usually, the interface between the power supply and the PCB is placed at the edge of the PCB and has a distance of 3 mm to 5 mm from the edge of the PCB; the indicator LED should be accurately placed as needed; the switch and some fine-tuning components, such as adjustable inductance, Adjustable resistors, etc. should be placed close to the edge of the PCB for easy adjustment and connection; components that need to be replaced frequently must be placed in a relatively small number of locations for easy replacement.

1.2 Placement of special components

High-power tubes, transformers, rectifiers and other heating devices generate more heat when operating at high frequencies. Therefore, ventilation and heat dissipation should be fully considered during layout. Place such components on the PCB where air is easily circulated. . High-power rectifiers and adjustment tubes should be equipped with heat sinks and away from the transformer. Electrolytic capacitors and other components that are afraid of heat should also be kept away from the heating device, otherwise the electrolyte will be baked, causing its resistance to increase, performance to deteriorate, and affecting the stability of the circuit.

Components that are prone to failure, such as adjustment tubes, electrolytic capacitors, relays, etc., should also be considered for ease of maintenance when placed. For test points that often need to be measured, care should be taken to ensure that the test rods are easily accessible when arranging components.

Since the 50 Hz leakage magnetic field is generated inside the power supply device, it interferes with the low frequency amplifier when it is connected to some parts of the low frequency amplifier. Therefore, they must be isolated or shielded. The amplifier stages are preferably arranged in a straight line according to the schematic diagram. The advantage of this arrangement is that the ground current of each stage is closed at the current stage and does not affect the operation of other circuits. The input and output stages should be as far apart as possible to reduce parasitic coupling interference between them.

Considering the signal transmission relationship between the functional circuits of each unit, the low frequency circuit and the high frequency circuit should be separated, and the analog circuit and the digital circuit are separated. The integrated circuit should be placed in the center of the PCB so that the pins are easily wired to other devices.

Devices such as inductors and transformers have magnetic coupling and should be placed orthogonally to each other to reduce magnetic coupling. In addition, they all have a strong magnetic field, and there should be a large space around them or magnetic shielding to reduce the influence on other circuits.

Appropriate high-frequency decoupling capacitors should be placed in the key parts of the PCB. For example, a 10μF~100μF electrolytic capacitor should be connected to the input end of the PCB power supply. A 0.01pF ceramic chip should be connected near the power supply pin of the integrated circuit. capacitance. Some circuits are also equipped with appropriate high frequency or low frequency chokes to reduce the effects between high and low frequency circuits. This should be considered in the schematic design and drawing, otherwise it will affect the performance of the circuit.

The spacing of the components should be appropriate, and the spacing should be considered whether there is a possibility of breakdown or ignition between them.

For amplifiers with push-pull circuits and bridge circuits, attention should be paid to the symmetry of the electrical parameters of the components and the symmetry of the structure, so that the distribution parameters of the symmetrical components are as uniform as possible.

After the manual layout of the main components, the component locking method should be used so that these components do not move during automatic layout. That is, if you execute the Editchange command or select Locked in the Properties of the component, you can lock it and no longer move.

1.3 Placement of common components

For ordinary components, such as resistors and capacitors, it should be considered from the aspects of neat arrangement of components, space occupation, ease of wiring and convenience of soldering.