How to deal with PCB sensitive circuit?
1. How to deal with PCB sensitive circuit
(1) Power cord
According to the current of printed circuit board, widen the width of power line and reduce the resistance of loop as far as possible. In particular, attention should be paid to the direction of power supply in power supply lines and ground wires, which is contrary to the direction of data and signal transmission, that is, the way of power supply from the last stage to the front stage, which helps to enhance the anti-noise ability.
(2) Groundline
The principle of the design is to separate digitally and analogically. If there are both logic circuits and linear circuits on the circuit board, they should be separated as far as possible. The ground of low-frequency circuit should adopt single-point parallel grounding as far as possible. When the actual wiring is difficult, some of them can be connected in series and then grounded in parallel. High-frequency circuit should adopt multi-point series grounding, ground wire should be short and rental, high-frequency components should be surrounded by large area grid foil as far as possible. Grounding wire should be as thick as possible. If the grounding wire is made of very fine lines, the grounding potential changes with the change of current, which reduces the anti-noise performance. Therefore, the grounding wire should be coarsened so that it can pass three times the allowable current on the printed circuit board. If possible, the grounding wire should be more than 2-3 mm. The grounding wire constitutes a closed-loop circuit. Printed circuit boards consisting of only digital circuits, whose grounding circuits are clustered loops, can mostly improve the anti-noise ability.
2. What are the interference components in PCB
Source refers to the components, devices or signals that cause interference. It is described in mathematical language as follows: du/dt, where di/dt is large, is the source of interference. For example, lightning, relays, thyristors, motors, high-frequency clocks and so on may become interference sources. Propagation path refers to the path or medium through which interference propagates from an interfering source to a sensitive device. Typical interference propagation paths are through conduction of conductors and radiation in space. Sensitive components refer to objects that are easily disturbed. For example: A/D, D/A converter, single chip computer, digital IC, weak signal amplifier, etc.
3. It can be divided into radiation and conduction interference.
Radiation interference is that the interference source uses space as media to interfere its signal to another network. Conductive interference is to use conductive medium as a medium to interfere signals from one network to another. In high-speed system design(High speed PCB), integrated circuit pins, high-frequency signal lines and all kinds of connectors are common radiation interference sources in PCB board design. The electromagnetic waves they emit are electromagnetic interference (EMI), which will affect the normal operation of themselves and other systems.
4. How to deal with sensitive components in PCB
Components should be manufactured and maintained conveniently when placed. Capacitance polarity should be consistent. Heating components and sensitive components should be placed at a distance. Moisture sensitive components tend to be encapsulated in tape-and-reel systems. Each tape has a large number of components. When compared with pin components in IC trays, the key problem is that wet exposure lasts longer. Exposure time must be increased to dry storage time during setting and treatment.
