PCB layout skills:
In the layout design of PCB, the unit of circuit board should be analyzed, and the layout design should be carried out according to the function. The layout of all components of the circuit should comply with the following principles:
1. The position of each functional circuit unit is arranged according to the circuit flow, so that the layout is convenient for signal flow, and the signal keeps the same direction as far as possible.
2. With the core components of each functional unit as the center, layout around it. The components shall be evenly, integrally and compactly arranged on the PCB to minimize and shorten the lead wires and connections between the components.
3. The distribution parameters between components should be considered when the circuit works at high frequency. In general, components should be arranged in parallel as far as possible, which is not only beautiful, but also easy to install and mass produce.
PCB layout rules:
1. The minimum distance between adjacent pad patterns of different components on the circuit board should be more than 1 mm.
2. Under normal circumstances, all components should be arranged on the same side of the circuit board. Only when the top layer components are too dense, can some devices with limited height and low calorific value, such as chip resistor, chip capacitor, chip IC, be placed on the lower layer.
3. On the premise of ensuring the electrical performance, the components should be placed on the grid and arranged in parallel or perpendicular to each other, in order to be neat and beautiful. In general, the components are not allowed to overlap; The arrangement of components should be compact, and the components should be evenly distributed in the whole layout.
4. Generally, the distance from the edge of the circuit board is not less than 2 mm. The best shape of the circuit board is rectangular, and the length width ratio is 3:2 or 4:3. When the surface size of the circuit board is larger than 200 mm by 150 mm, the mechanical strength of the circuit board should be considered.
General order of components placement:
1. Place the components closely matching with the structure, such as power socket, indicator light, switch, connector, etc.
2. Place special components, such as large components, heavy components, heating components, transformer, IC, etc.
3. Place small components.
1. Whether the circuit board size is consistent with the processing size required by the drawing.
2. Whether there are conflicts at all levels. For example, whether the components, frame and the level of private printing are reasonable.
3. Whether the layout of components is balanced and orderly, and whether all the components have been laid out.
4. Whether the commonly used components are convenient to use. Such as switch, plug-in board, plug-in equipment, components that need to be replaced frequently, etc.
5. Whether the distance between thermal components and heating components is reasonable.
6. Whether the heat dissipation is good.
7. Whether the interference of the line needs to be considered.
Special components and layout design:
In PCB, special components refer to the key components of high-frequency part, the core components of the circuit, the components vulnerable to interference, the components with high voltage, the components with high calorific value, and some heterosexual components. The location of these special components needs to be carefully analyzed, and the belt layout should meet the requirements of circuit function and production. Improper placement of them may cause circuit compatibility problems and signal integrity problems, which may lead to the failure of PCB design.
In the design of how to place special components, the PCB size should be considered first. When the PCB size is too large, the printed line is long, the impedance increases, the anti drying ability decreases, and the cost increases; If it is too small, the heat dissipation is not good, and the adjacent lines are easy to be disturbed. After the size of PCB is determined, the pendulum position of special components is determined. Finally, according to the functional units, all the components of the circuit are arranged. The layout of special components should follow the following principles:
1. Shorten the connection between high frequency components as much as possible, try to reduce their distribution parameters and mutual electromagnetic interference. The components that are easy to be disturbed should not be too close to each other, and the input and output should be as far away as possible.
Some components or wires may have high potential difference, so the distance between them should be increased to avoid accidental short circuit caused by discharge. High voltage components should be kept out of hand as far as possible.
3. Components weighing more than 15g can be fixed by bracket and then welded. Those heavy and hot components should not be placed on the circuit board, they should be placed on the bottom plate of the main box, and the problem of heat dissipation should be considered. Thermal components should be far away from heating components.
4. For the layout of adjustable components such as potentiometer, adjustable inductance coil, variable capacitor and microswitch, the structural requirements of the whole wrench should be considered. Some frequently used switches should be placed in the place easily touched by hand when the structure allows. The layout of the components should be balanced, and the density should be high.
The success of a product, one is to pay attention to the internal quality. But to take into account the overall beauty, both are more perfect wrench, in order to become a successful product.
How to set grid points in PCB layout design:
Different points need to be set in different stages of the design, and large grids can be used in the layout stage;
For large devices such as IC and non positioning connector, the grid precision of 50 ~ 100mil can be selected for layout, while for passive small devices such as resistance, capacitance and inductance, the grid precision of 25mil can be used for layout. The accuracy of large grid is beneficial to the alignment and layout of devices.