Electronic Design - Grid Setting Technology of Printed Circuit Board

PCB design needs to set up different points in different stages, and large grid points can be used for device layout in the layout stage.

For large devices such as ICs and non-positioning connectors, a grid point accuracy of 50 to 100 mils can be used for layout, while for small passive components such as resistors, capacitors and inductors, a grid point of 25 mils can be used for layout. The accuracy of the large grid points is conducive to the alignment of the device and the aesthetics of the layout.

PCB layout rules:

1. Under normal circumstances, all components should be arranged on the same surface of the circuit board. Only when the top-level components are too dense, can some devices with limited height and low heat generation, such as chip resistors, chip capacitors, and chip capacitors, be installed. Chip IC, etc. are placed on the lower layer.

2. Under the premise of ensuring the electrical performance, the 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, the components are not allowed to overlap; the arrangement of the components should be compact, and the components should be arranged on the entire layout. The distribution is uniform and dense.

3. The minimum distance between adjacent land patterns of different components on the circuit board should be above 1MM.

4. The distance from the edge of the circuit board is generally not less than 2MM. The best shape of the circuit board is rectangular, and the aspect ratio is 3:2 or 4:3. When the size of the circuit board is larger than 200MM by 150MM, consider what the circuit board can withstand Mechanical strength.

PCB layout skills:

In the layout design of the PCB, the units of the circuit board should be analyzed, and the layout design should be carried out according to the function. When laying out all the components of the circuit, the following principles should be met:

1. Arrange the position of each functional circuit unit according to the circuit flow, so that the layout is convenient for signal circulation, and the signal is kept in the same direction as possible.

2. Centering on the core components of each functional unit, lay out around him. The components should be uniformly, integrally and compactly arranged on the PCB to minimize and shorten the leads and connections between the components.

3. For circuits operating at high frequencies, the distributed parameters between components must be considered. In general circuits, components should be arranged in parallel as much as possible, which is not only beautiful, but also easy to install and easy to mass produce.

Special components and layout design

In the PCB, special components refer to the key components of the high-frequency part, the core components in the circuit, the components that are susceptible to interference, the components with high voltage, the components with high heat generation, and some components of the opposite sex., The location of these special components needs to be carefully analyzed, and the belt layout meets the requirements of circuit functions and production requirements. Improper placement of them may cause circuit compatibility issues, signal integrity issues, and lead to failure of PCB design.

When placing special components in the design, first consider the PCB size. When the PCB size is too large, the printed lines will be long, the impedance will increase, the anti-drying ability will decrease, and the cost will increase; if the PCB size is too small, the heat dissipation will not be good, and adjacent lines will be easily disturbed. After determining the size of the PCB, determine the swing position of the special component. Finally, according to the functional units, layout all the components of the circuit. The location of special components should generally comply with the following principles during layout:

1. Shorten the connection between high-frequency components as much as possible, try to reduce their distribution parameters and mutual electromagnetic interference. Components that are susceptible to interference should not be too close to each other, and the input and output should be as far away as possible.

2 Some components or wires may have a higher potential difference, and their distance should be increased to avoid accidental short circuits caused by discharge. High-voltage components should be placed as far out of reach as possible.

3. Components weighing more than 15G can be fixed with brackets and then welded. Those heavy and hot components should not be placed on the circuit board, but should be placed on the bottom plate of the main box, and heat dissipation should be considered. Thermal components should be far away from heating components.

4. The layout of adjustable components such as potentiometers, adjustable inductance coils, variable capacitors, micro switches, etc. should consider the structural requirements of the whole wrench. Some frequently used switches should be Place it where your hands can easily reach. The layout of the components is balanced, dense and not top-heavy.

The success of a product must first focus on its internal quality. However, it is necessary to take into account the overall aesthetics, both of which are more perfect wrenches, to become a successful product.

The general order of component placement:

1. Place components that closely match the structure, such as power sockets, indicator lights, switches, connectors, etc.

2. Place special components, such as large components, heavy components, heating components, transformers, ICs, etc.

3. Place small components.

check of layout

1. Whether the PCB size and the processing size required by the drawing are consistent.

2. Whether the layout of the components is balanced, neatly arranged, and whether they have all been laid out.

3. Whether there are conflicts at all levels. Whether the components, the frame, and the level of private printing are reasonable.

4. Whether the commonly used components are convenient to use. Such as switches, plug-in board insertion equipment, components that must be replaced frequently, etc.

5. Whether the distance between thermal components and heating components is reasonable.

6. Whether the heat dissipation is good.