2, according to the circuit function layout

If there is no special requirements, as far as possible in accordance with the schematic components of the arrangements for the layout of the components, the signal from the left into the output from the right, from the top input from the bottom of the output. In accordance with the circuit process, the arrangement of the various functional circuit unit position, so that the signal flow more smoothly and maintain the same direction. With each functional circuit as the core, around the core circuit layout, component arrangement should be uniform, neat, compact, the principle is to reduce and shorten the lead between the various components and connections. The digital circuit part should be separated from the analog circuit section.

3, the distance from the edge of the PCB board

All components should be placed within 3 mm from the edge of the PCB, or at least the distance from the edge of the PCB board is equal to the plate thickness, due to the use of pipelayers in high-volume production and for wave soldering. , But also to prevent the deformation caused by the shape of the PCB board edge, causing copper film broken lead to waste. If the PCB board too many components, forced to be more than 3mm, you can add the edge of the PCB board 3mm auxiliary side, in the auxiliary side to open V-shaped groove, in the production by hand breaking apart.
 
4, the order of the components placed

First place the fixed position with the structure in close contact with the components, such as power outlets, lights, switches and plug-ins and so on. And then placed special components, such as heating elements, transformers, integrated circuits. Finally, place small components, such as resistors, capacitors, diodes, and so on.
 
PCB board wiring

PCB board wiring rules are as follows:

1) line length

Copper film should be as short as possible, in the high-frequency circuit should be the case. The corner of the copper film should be rounded or angled, and the right angle or sharp angle in the high-frequency circuit and wiring density will affect the case of electrical performance. When the double-panel wiring, the two sides of the wire should be perpendicular to each other, oblique or curved alignment, to avoid parallel to each other to reduce the parasitic capacitance.
  
2) line width

The width of the copper film should be in order to meet the electrical characteristics of the requirements and easy to produce as a criterion, its minimum value depends on the current flowing through it, but generally should not be less than 0.2mm. As long as the board area is large enough, copper wire width and spacing the best choice 0.3mm. Under normal circumstances, 1 ~ 1.5mm line width, allowing the flow of 2A current. For example, the ground and power lines are best to use a line width greater than 1mm. When the two wires are between the integrated circuit board pads, the pad diameter is 50 mils, the line width and line spacing are 10 mils. When the pad is taken between a line, the pad diameter is 64 mils, line width and line The spacing is 12mil. Note the conversion between metric and imperial, 100mil = 2.54mm.
 
3) line spacing

The spacing between adjacent copper film lines should meet the electrical safety requirements, and in order to facilitate production, the spacing should be as wide as possible. The minimum spacing can withstand at least the peak of the applied voltage. In the case of low wiring density, the spacing should be as large as possible.

4) Shield and ground

The common ground of the copper wire should be placed as far as possible on the edge of the circuit board. In the PCB board should be as much as possible to retain the copper foil to do the ground, so that can enhance the shielding capacity. In addition, the shape of the ground wire is preferably made into a loop or a grid. Multi-layer PCB board as a result of the use of internal power and ground dedicated layer, which can play a better shielding effect.

PCB board ground

1, the ground of the total impedance interference

The ground on the circuit diagram represents the zero potential in the circuit and serves as a common reference point for the other points in the circuit. In the actual circuit, there is bound to cause common impedance interference due to the presence of ground (copper film) When wiring, you can not connect points with ground symbols, which can cause harmful coupling and affect the normal operation of the circuit.

2, how to connect the ground

Usually in an electronic system, the ground is divided into systematically, chassis (shield), digital (logical) and analog ground, etc., in the connection to the ground should pay attention to the following:

1) Properly select single point ground and multipoint ground

In the low-frequency circuit, the signal frequency is less than 1MHz, wiring and components between the inductance can be ignored, and ground circuit resistance generated by the voltage drop on the circuit a greater impact, it should be a single point grounding method. When the frequency of the signal is greater than 10MHz, the impact of ground inductance, it is appropriate to use the nearest ground multi-point grounding method. When the signal frequency between 1 ~ 10MHz, if the use of single-point grounding method, the ground length should not exceed the wavelength of 1/20, or should be multi-point grounding.

2) digital ground and analog ground separately

PCB board has both digital circuits, and analog circuits, should make them as far as possible, and the ground can not be mixed, should be connected with the power supply to the ground (the best power supply are also connected). To maximize the area of ​​the linear circuit. General digital circuit anti-interference ability, TTL circuit noise margin of 0.4 ~ 0.6V, CMOS digital circuit noise margin for the power supply voltage of 0.3 ~ 0.45 times, while the analog circuit as long as the micro-level noise, Enough to make it work is not normal. So the two types of circuits should be separated from the layout and wiring.

3) as thick as possible

If the ground is very fine, the ground potential will change with the current changes, resulting in the interference of the electronic system signal, especially the analog circuit part, so the ground should be as wide as possible, generally more than 3mm is appropriate.

4) The ground wire forms a closed loop

When the PCB board only digital circuit, it should make the ground to form a loop, which can significantly improve the anti-jamming capability, it is because when the PCB board has a lot of integrated circuits, if the ground is very fine, will cause a larger grounding The potential difference, and the ring ground can reduce the grounding resistance, thereby reducing the ground potential difference.

5) grounding of the same level circuit

The same level of circuit grounding should be as close as possible, and the level of the power supply filter capacitor should also be connected to the level of the ground.

6) the connection of the ground line

The total ground line must be strictly in accordance with the high frequency, intermediate frequency, low frequency order level from weak to strong electrical connection. High-frequency part of the best use of large area surrounded by ground to ensure a good shielding effect.