In the electronic design, after the project schematic design is completed and compiled, the PCB design is required. PCB design first requires the first step of design: component layout after determining the shape of the plate, the design of the laminate, and the overall partitioning concept. Place each component in its proper position. And layout is a crucial part. The pros and cons of the layout results directly affect the effect of the wiring, which affects the entire design function. Therefore, a reasonable and effective layout is the first step in the success of PCB design.
Before the PCB layout, the circuit is partitioned by module according to the whole function. In the regional planning, the analog part and the digital part are isolated according to the function, and the high frequency circuit is isolated from the low frequency circuit. After the partition is completed, consider the key components in each area and place the other components in the area in a proper position with the focus on the key components. When placing components, consider internal circuit traces between subsystem circuits, especially timing and oscillator circuits. In order to remove the potential problem of electromagnetic interference, the component placement and layout should be systematically checked to facilitate the routing, reduce electromagnetic interference, and try to be aesthetically pleasing on the premise of satisfying the function.
The success of a product, on the one hand, requires good functional quality, on the other hand, it requires aesthetics, and it is necessary to lay out your circuit board like a handicraft. These questions and problems often arise in the layout of PCB components.
Does the PCB shape match the whole machine? Is the spacing between the components reasonable, and whether there is a conflict in level or height?
Whether the PCB needs imposition, whether to reserve the process side, whether to reserve the mounting hole, how to arrange the positioning hole?
How to consider impedance control, signal integrity, power signal stability, power module cooling?
Is it necessary to replace the components that need to be replaced frequently, and is the adjustable component easy to adjust?
Is the distance between the thermal element and the heating element considered?
The overall board EMC performance, how to layout can effectively enhance the anti-interference ability?
Excellent PCB component layout principles
First divide the area. According to the functional unit of the circuit, all the components of the circuit are considered as a whole, and each functional circuit unit is divided into a general area according to the module, so that the layout is suitable for signal circulation, and the direction is kept as consistent as possible.
As shown in the above figure, the general functional modules such as the power supply section, the core control section, the signal input processing section, the signal output processing section, the connector section, the human-computer interaction section, and the like. Divide the module area according to the actual function of the board. The general principle is that the power supply is concentrated on the board side, the core control part is in the middle of the board, the signal input part is on the left side of the core control part, and the signal output part is on the right side of the core control part. The connector part should be placed on the edge of the board as much as possible, and the human-computer interaction part should be rationally laid out considering the requirements of ergonomics. Under the premise of ensuring electrical performance, the components of each functional module should be placed on the grid and arranged parallel or perpendicular to each other in order to be neat and beautiful.
The layout is then centered around the core component of each functional module circuit. Components should be evenly, integrally and compactly arranged on the PCB to minimize and shorten leads and connections between components to facilitate wiring and reduce electromagnetic interference. In the PCB, special components such as power devices, tunable devices, heat and heat sensitive devices, key components in the high frequency part, core chips, susceptible components, bulk or heavy devices, high voltage devices, and some For heterosexual components, the location of these special components needs to be carefully analyzed, and the layout must meet the requirements of the circuit function and the production requirements. Inappropriate layouts can create circuit compatibility issues, signal integrity issues, and lead to PCB design failures. The location of special components is generally subject to the following principles when laying out:
The DC/DC converter, switching elements and rectifiers should be placed as close as possible to the transformer, with the rectifier diodes as close as possible to the voltage regulator and filter capacitor. To reduce the length of its line.
The electromagnetic interference (EMI) filter should be as close as possible to the EMI source. Minimize the connection between high frequency components and 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.
For the layout of adjustable components such as potentiometers, adjustable inductors, variable capacitors, microswitches, etc., the structural requirements of the whole wrench should be considered. Some switches that are often used should be placed in the hand if the structure allows. The place of contact. The layout of the components is balanced and dense.
The heating element should be placed on the edge of the PCB for heat dissipation. If the PCB is mounted vertically, the heating element should be placed above the PCB. The thermal element should be kept away from the heating element.
In the power supply layout, try to make the device layout convenient for the power line wiring. Consider reducing the area of ​​the input power loop during layout. When the circulation is satisfied, the input power line is prevented from running on the full board, and the area enclosed by the loop is too large. The position of the power cable and the ground wire is well matched to reduce the influence of electromagnetic interference. If the power and ground wires are not properly matched, many loops will occur and noise may be generated.
High and low frequency circuits have different methods of interference and interference suppression due to different frequencies. Therefore, in the component layout, the digital circuit, analog circuit and power supply circuit should be arranged separately according to the module. The high-frequency circuit is effectively isolated from the low-frequency circuit, or is divided into small sub-circuit module boards, and connected by connectors.
In addition, the layout should pay special attention to the distribution of devices with strong and weak signals and the path of signal transmission. In order to minimize interference, after the analog circuit part and the digital circuit part are separated, the high, medium and low speed logic circuits are also used in different areas on the PCB, and the PCB board is divided by frequency and current switching characteristics. The noise component is farther away from the non-noise component. The thermal element is farther away from the heating element. The low level signal path is away from the high level signal path and the unfiltered power line. Separate the low-level analog circuit from the digital circuit to avoid common impedance coupling between the analog circuit, the digital circuit, and the power supply common return line.
Switching the application of various grids in the placement of PCB components;
Application of the component alignment tool. Various ways to intelligently align and arrange to help you locate easily;
Smart placement of components, highlighting, and component placement (Smart placement);
Global batch editing changes the properties of components and various objects to make your changes easier;
3D intelligent real-time display, detecting the matching of components in the PCB board and the whole board
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