For ICs, non-positioning connectors, and other large devices, 50- to 100-mil lattice points can be used for layout. For passive small devices such as resistors, capacitors, and inductors, 25 mil grids can be used for layout. The accuracy of the large grids facilitates the alignment of the devices and the aesthetics of the layout.
PCB layout rules:
1. Under normal circumstances, all components should be placed on the same surface of the circuit board. Only when the top layer components are too dense, can some devices with limited height and small heat content, such as chip resistors, chip capacitors, Chip ICs are placed at lower levels.
2. Under the premise of guaranteeing electrical performance, components should be placed on the grid and arranged parallel or perpendicular to each other, in order to be neat and beautiful. Under normal circumstances, no overlap of components is allowed; the arrangement of components should be compact, and the components should be arranged on the whole surface of the grid. Uniform distribution, density and consistency.
3. The minimum spacing between adjacent pad patterns of different components on the circuit board should be above 1MM.
4. From the edge of the circuit board is generally not less than 2MM. The best shape of the circuit board is a rectangle, the aspect ratio is 3:2 or 4:3. When the circuit board is more than 200MM by 150MM, should consider the circuit board can withstand Mechanical strength.
PCB layout techniques:
In the layout design of the PCB, it is necessary to analyze the elements of the circuit board. According to the function layout design, when the layout of all components of the circuit, it is necessary to comply with the following principles:
1. Arrange the positions of each functional circuit unit according to the circuit's flow, so that the layout is convenient for signal circulation, and the signal is kept in the same direction as possible.
2. Focus on the core components of each functional unit and lay out around him. The components should be evenly, integrally, and compactly arranged on the PCB to minimize and shorten the leads and connections between the components.
3. In the work of high-frequency circuits, to consider the distribution parameters between components. The general circuit should arrange parallel components as much as possible, which is not only beautiful, but also easy to dry and easy to mass production.
Special components and layout design
In the PCB, special components refer to the key components in the high-frequency part, the core components in the circuit, the components that are subject to interference, the components with high voltage, the components that generate large amounts of heat, and some heterogeneity components. The location of these special components requires careful analysis, with the requirements for layout and circuit functionality and production requirements. Improper placement of them may cause circuit compatibility issues, signal integrity issues, and lead to PCB design failures.
In the design of how to place special components, first consider the size of the PCB. When the PCB size is too large, the printed lines are long, the impedance increases, the ability to resist drying decreases, and the cost increases. When the size is too small, the heat dissipation is not good, and the adjacent lines are susceptible to interference. After determining the size of the PCB, the pendulum position of the special component is determined. Finally, according to the functional unit, all the components of the circuit are laid out. When the layout of special components is laid out, the following principles must be observed:
1. Keep the connections between high-frequency components as short as possible and try to reduce their distribution parameters and electromagnetic interference between them. Components that are subject to interference should not be too close to each other and the input and output should be as far apart as possible.
2. Some components or wires may have higher potential difference, and their distance should be increased to avoid accidental short circuit caused by discharge. High-voltage components should be placed as close to the hand as possible.
3. The weight of more than 15G components can be used to fix the bracket, and then welding. Components that are heavy and hot should not be placed on the circuit board. They should be placed on the backplane of the main chassis and thermal issues should be considered. Thermal components should be far away from the heating components.
4. The layout of adjustable components such as potentiometers, adjustable inductors, variable capacitors, and micro-switches should consider the structural requirements of the whole block, and some frequently used switches should be used where the structure permits. Place it easily in your hand. The layout of components is balanced, and there is a degree of density that cannot be top-heavy.
One of the successes of a product is to focus on internal quality. Instead, it is necessary to take into account the overall aesthetics. Both are relatively perfect wrenches to become successful products.
Placement of components in general order:
1. Place components closely matching the structure, such as power outlets, indicator lights, switches, connectors, etc.
2. Place special components, such as large components, heavy components, heating components, transformers, ICs and so on.
3. Place small components.
1. The board size and drawings require processing dimensions are in line.
2. Whether the layout of the components is balanced, neatly arranged, or whether they have been completely finished.
3. There is no conflict at all levels. Such as the components, the frame, the level of need for private printing is reasonable.
3. The commonly used components are easy to use. Such as switches, plug-in boards, equipment that must be replaced frequently, etc.
4. Is the distance between the thermal components and heating components reasonable?
5. Heat dissipation is good.
6. Whether the line interference problem needs to be considered.