PCB Tech - Getting started with pcb needs to know

wiring

Features:

1. The placement direction of the components determines the direction of the PCB wiring

2. The wiring directions of adjacent layers are different, the surface layer of the two panels and the wiring body of the soldering layer are at 90°

3. The wiring direction of the rectangular circuit board is vertical, and horizontal wiring can easily cause congestion or even impossible wiring.

4. Try to ensure the wiring space. When it cannot be done, use specific components for wiring, and try to avoid setting up connection holes under the components.

Because when the circuit board fails, it is impossible to visually see the state of the connection hole under the component, whether it is short-circuited with other wiring or component pins.

Analog circuit part and digital circuit part

Including the wiring, the analog circuit part and the digital circuit part should be kept above 5mm to ensure that they are not interfered by signals.

When a symbol is used to represent the ground wire in the circuit diagram, the circuit board designer is required to analyze the circuit diagram and set a certain area. The power line and the ground line were originally designed first. For two-panel and four-layer boards, the wiring composition is completely different, because the power and ground lines are set in the inner layer, and the attention is mainly focused The layout of the signal line is fine. For beginners, it is recommended to learn from the design of the four-layer board. The wiring of the power cord and the ground wire has a great influence on the electrical and noise, so it should be carefully designed.

Take the two panels as an example:

○The power line and the ground line are designed in the same layer, the effect is the worst

○The ground wire is on the surface layer, and the power wire is on the soldering layer. General design

○The ground wire is on the surface layer, and the power wire is on the soldering layer. It is wired by copper foil and has a better anti-clutter effect. Because of the uncontrollability of CAD design, PCB design takes longer than simple wiring. Attention should be paid to ensure the minimum wiring width, to ensure that there will be no disconnection or blockage.

Simply put: the power line and the ground line are equivalent to the aorta and vein of the human body. It can also be thought of simply as a water pipe. The wider the line width, the greater the current flow that can be passed, and the faster the heat dissipation. The narrower the line width, the greater the resistance under the same voltage, the smaller the current flow that can pass, and the slower the heat dissipation.

Surface welding surface

For the power line and the ground line, a large-scale copper foil wiring method is used.

Precautions for wiring of two-layer circuit board power cord and ground wire

Normally, the power line is wired on the soldering surface, and the ground line is wired on the surface. Use copper foil for wide-area wiring, and then add more capacitance between the power line and the ground line, and there is basically no problem. But if electromagnetic interference is involved, the problem is different. When it exceeds 8MHz, problems like this may occur, and when it exceeds 25MHz, it becomes quite unstable. At this time, it is necessary to enclose the ground wire copper foil around the important components, and also design the ground wire copper foil on the welding surface.

What do you need to know about PCB

Wiring of the crystal oscillator

In order to resist interference, the components should be surrounded by ground copper foil as much as possible. What is not shown in the figure is that the ground copper foil can also be laid under the soldering layer crystal oscillator, and then the surface and the soldering surface are connected with connection holes. Strengthen anti-interference ability.

Use of thermal pad

When using a large piece of copper foil for the power line and ground line, use the heat-resistant pad as much as possible to design. This is because if the component pad is directly connected to a large piece of copper foil, the heat will be dissipated quickly during soldering, and the temperature of the melted solder is not enough, resulting in poor soldering or false soldering.

Thermal resistance pad

Introduction to PCB layout and design, power supply for analog circuits

The output part should be close to the power supply, and the high-sensitivity input part should be separated from the output part by a certain distance in order not to be affected by the output part.

Schematic diagram of analog circuit Schematic diagram of separation of digital circuit and analog circuit part of power input

DC power supply: When supplying power from the outside, it must first pass through the electrolytic capacitor, and then supply it to the internal circuit. The wiring method is usually as follows.

The two-layer panel, not through point A, but through point B, provides power to the internal circuit. The multi-layer panel also introduces power to the inner layer after passing through point B.