PCB Tech - PCB component layout principles and practical tips

In electronic design, after the project schematic design is compiled and passed, it is necessary to start the PCB design. After the PCB design first determines the board shape size, stack design, and overall partition concept, the first step of the design is required: component layout. Put each component in its proper position. The layout is a crucial link. The pros and cons of the layout result directly affects the wiring effect, thus affecting the entire design function. Therefore, a reasonable and effective layout is the first step to a successful PCB design. Is also a vital part

PCB component layout principles and practical tips

Before PCB layout, the circuit is partitioned by modules according to the entire function. In 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 to the appropriate position focusing on the key components. When placing components, consider the internal circuit routing between subsystem circuits, especially timing and oscillation circuits. In order to remove the potential problems of electromagnetic interference, the component placement and layout should be checked systematically to facilitate wiring, reduce electromagnetic interference, and try to be as beautiful as possible under the premise of satisfying functions.

Common PCB layout problems and confusion

The success of a product requires good function and quality on the one hand, and beauty on the other. It is necessary to lay out your circuit board like carving a handicraft. There are often these questions and troubles in the layout of PCB components.

Do PCBs need to be made up, do they need to reserve process edges, do they reserve mounting holes, and how to arrange the positioning holes?

Does the PCB shape match the whole machine? Is the spacing between the components reasonable? Is there any level or height conflict?

How to consider impedance control, signal integrity, power signal stability, and power module heat dissipation?

Is the distance between the thermal element and the heating element considered?

The EMC performance of the whole board, how to layout can effectively enhance the anti-interference ability?

Is it easy to replace components that need to be replaced frequently, and are adjustable components easy to adjust?

Excellent PCB component layout principles

First divide the area. According to the functional units of the circuit, all the components of the circuit are considered as a whole, and each functional circuit unit is divided into general areas according to the modules, so that the layout is suitable for signal flow, and the direction is kept as consistent as possible.

According to the actual function of the circuit board, the module area is divided. The general principle is that the power supply part is concentrated on the edge of the board, the core control part is in the middle of the board, the signal input part is located on the left side of the core control part, and the signal output part is located on the right side of the core control part. The connector part should be arranged on the edge of the board as much as possible, and the human-computer interaction part should be reasonably arranged in consideration of 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 in parallel or perpendicular to each other in order to be neat and beautiful.

Then take the core component of each functional module circuit as the center and lay out around this center. The components should be uniformly, integrally and compactly arranged on the PCB, and the leads and connections between the components should be minimized and shortened to facilitate wiring and reduce electromagnetic interference. In the PCB, special components such as power supply devices, adjustable devices, heating and heat-sensitive devices, key components of high-frequency parts, core chips, components that are susceptible to interference, devices with large volume or weight, high-voltage devices, and some For heterogeneous components, the location of these special components needs to be carefully analyzed, and the layout must meet the requirements of circuit functions and production requirements. Inappropriate layout may cause circuit compatibility issues and signal integrity issues, leading to failure of PCB design. The location of special components should generally comply with the following principles during layout:

For the layout of adjustable components such as potentiometers, adjustable inductance coils, variable capacitors, micro switches, etc., the structural requirements of the entire wrench should be considered. Some frequently used switches should be easily placed in hand if the structure permits. The place to be touched. The layout of the components is balanced and dense.

The heating element should be arranged on the edge of the PCB to facilitate heat dissipation. If the PCB is installed vertically, the heating element should be arranged on the PCB

The electromagnetic interference (EMI) filter should be as close as possible to the EMI source. Try to 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.

square. Thermal components should be far away from heating components.

In the power supply layout, try to make the device layout convenient for the routing of the power line. The layout needs to consider reducing the area of the input power loop. Under the condition of satisfying the circulation, avoid the input power line from running across the board, and the area of the loop circle is too large. The position of the power cord and the ground wire are well matched to reduce the influence of electromagnetic interference. If the power line and the ground line are not properly matched, there will be many loops and noise may be generated.

Due to the different frequencies of high and low frequency circuits, their interference and methods of suppressing interference are also different. Therefore, in the component layout, the digital circuit, analog circuit, and power circuit should be laid out separately in modules. Effectively isolate the high-frequency circuit from the low-frequency circuit, or divide it into small sub-circuit module boards, and connect them with connectors.

In addition, special attention should be paid to the distribution of strong and weak signals and the signal transmission path in the layout. In order to minimize interference, after the analog circuit part is separated from the digital circuit part, the high, medium, and low speed logic circuits must also use different areas on the PCB. The PCB board is partitioned according to frequency and current switching characteristics. The noise components should be farther away from the non-noise components. The thermal element is farther away from the heating element. Low-level signal channels are far away from high-level signal channels and unfiltered power lines. Separate low-level analog circuits and digital circuits to avoid common impedance coupling between analog circuits, digital circuits, and power supply common loops.