There are many places where safety distances need to be considered in PCB design. Here, they are temporarily classified into two categories: one is electrical-related safety distances, and the other is non-electrical-related safety distances.

1. Electrical related safety distances

1. Spacing between wires

As far as the processing capabilities of mainstream PCB manufacturers are concerned, the distance between wires must not be less than 4mil. Line spacing is also the distance from line to line and line to pad. From a production perspective, the bigger the better if conditions permit, and 10mil is more common.

2. Pad aperture and pad width

In terms of the processing capabilities of mainstream PCB manufacturers, the pad aperture should not be less than 0.2mm if mechanical drilling is used, and should not be less than 4mil if laser drilling is used. The aperture tolerance varies slightly depending on the board material. It can generally be controlled within 0.05mm, and the pad width must not be less than 0.2mm.

3. The spacing between pads

In terms of the processing capabilities of mainstream PCB manufacturers, the distance between pads must not be less than 0.2mm.

4. The distance between the copper sheet and the edge of the board

The distance between the charged copper sheet and the edge of the PCB board shall not be less than 0.3mm. As shown in the figure above, set this spacing rule on the Design-Rules-Board outline page.

If a large area of copper is laid, there is usually a shrinkage distance from the edge of the board, which is generally set to 20mil. In the PCB design and manufacturing industry, generally, engineers often lay large areas of copper out of mechanical considerations for the finished circuit board, or to avoid curling or electrical short circuits due to copper being exposed on the edge of the board. The block is retracted 20mil relative to the edge of the board instead of spreading the copper all the way to the edge of the board. There are many ways to deal with this copper shrinkage, such as drawing a keepout layer on the edge of the board, and then setting the distance between the copper laying and the keepout. Here is a simple method, which is to set different safety distances for copper-laying objects. For example, the safety distance for the entire board is set to 10mil, and the copper-laying setting is 20mil. This can achieve the effect of shrinking the edge of the board by 20mil, and at the same time Eliminates dead copper that may appear within the device.

2. Non-electrical related safety distances

1. Character width, height and spacing

No changes can be made to the text film during processing, except that the character line widths with D-CODE less than 0.22mm (8.66mil) are thickened to 0.22mm, that is, the character line width L=0.22mm (8.66mil), and the entire character The width = W1.0mm, the height of the entire character H = 1.2mm, and the spacing between characters D = 0.2mm. When the text is smaller than the above standards, it will be blurry when printed.

2. Via-to-via spacing (hole edge to hole edge)

The distance from via (VIA) to via (hole edge to hole edge) is greater than 8mil.

3. Distance from silk screen to solder pad

Screen printing is not allowed to cover the soldering pads. Because if the silk screen covers the soldering pad, tin will not be applied to the silk screen area during tin application, which will affect the mounting of components. Generally, board manufacturers require a spacing of 8mil. If the PCB board area is really limited, a 4mil spacing is barely acceptable. If the silk screen accidentally covers the pad during design, the board manufacturer will automatically remove the silk screen left on the pad during manufacturing to ensure that the pad is tinned.

Of course, the specific situation should be analyzed in detail during design. Sometimes the silk screen is deliberately placed close to the pads, because when the two pads are very close, the silk screen in the middle can effectively prevent the solder connection from short-circuiting during soldering. This situation is another matter.

4. 3D height and horizontal spacing on the mechanical structure

When mounting components on the PCB, it is necessary to consider whether they will conflict with other mechanical structures in the horizontal direction and spatial height. Therefore, when designing, it is necessary to fully consider the compatibility between components, between the finished PCB and the product shell, and the spatial structure, and reserve a safe distance for each target object to ensure that there is no spatial conflict.

PCB board impedance control technology is an important link in PCB production. Impedance-controlled PCB boards can ensure the quality of signal transmission, but the cost will be relatively high. Non-impedance boards are relatively cheap, but in high-speed signal transmission environments, the signal transmission quality may decrease.

1. Definition and principles of impedance PCB and non-impedance PCB

Impedance control technology refers to controlling the impedance of electronic signals through the wiring design and manufacturing process of PCB boards to minimize distortion and reflection of signals during transmission. The impedance board uses special materials and manufacturing processes to control parameters such as line width, distance, load, etc. to ensure the stability and accuracy of signal transmission. Non-impedance boards use general PCB manufacturing processes and do not pay attention to signal impedance control.

2. Advantages and Disadvantages of  impedance PCB and non-impedance PCB

The main advantage of impedance plates is the high quality of signal transmission. The impedance-controlled PCB board can reduce signal distortion and reflection, and can also reduce signal interference and crosstalk, ensure that circuit noise is small, and improve signal transmission accuracy and stability. However, the cost of impedance control is relatively high, and the material and process requirements for PCB boards are also relatively high. In some special high-frequency and high-speed environments, impedance control may not fully meet the requirements. The main advantages of non-impedance boards are low production cost, simple production process and short manufacturing cycle. For some occasions where the transmission rate is not high and the circuit is simple, non-impedance boards can also meet the requirements. However, in some high-speed and high-frequency environments, non-impedance boards are prone to problems such as signal distortion, crosstalk, and noise, which will have a certain impact on the working stability and reliability of the circuit.

3. Applications of impedance PCB and non-impedance PCB

Impedance control technology is often used in high-speed signal transmission, high-frequency circuits, analog circuits and other fields. Usually in the design of high-speed AD, DA converters and high-speed digital signal processors, PCB boards using impedance control technology are required to ensure signal accuracy and stability. Non-impedance boards are usually used in some low-speed and low-frequency circuit designs, such as LED light bars, home appliance control boards, etc.

4. Manufacturing requirements and methods of impedance PCB and non-impedance PCB

The production of impedance-controlled PCB boards is highly demanding, requiring the use of high-precision manufacturing equipment and fine control of the materials and processes of the PCB boards. This can be achieved by using some high-impedance control design software and manufacturing processes. For example, during the design process, the upper and lower copper foils can be wired together to form a differential impedance. Use high dielectric constant dielectrics with controlled impedance greater than 1 such as FR4, ROGERS, etc. Non-impedance boards are relatively simple to make, and the process and material selection are also more flexible.

Impedance PCB and non-impedance PCB are suitable for different circuit design needs. Impedance PCB can ensure the quality of signal transmission in high-speed and high-frequency circuits, but the cost is relatively high. Non-impedance boards are suitable for the design of some low-frequency and low-speed circuits and have lower costs. Therefore, when selecting PCB board type, you need to make a reasonable choice based on the specific application environment and circuit design requirements.

Impedance PCB control technology can effectively improve PCB signal transmission efficiency, reduce signal interference, and ensure the reliability of data transmission.

1. The concept and function of impedance PCB

The impedance PCB refers to the geometric shape of the circuit board on the PCB, which is used to control the impedance matching of signals during PCB transmission. Impedance matching means that the impedance between the source and terminal is the same, so that neither the signal is reflected nor the signal is lost. In high-speed data transmission, the signal frequency is high, the signal waveform is seriously deformed, and signal reflection and signal loss are prone to occur, thus reducing the signal transmission efficiency. Therefore, the design of the impedance board is very important, which can help us control the impedance matching of the signal, reduce signal loss and reflection, and improve the reliability of signal transmission.

2. Design of impedance PCB

The design of the impedance PCB needs to consider board thickness, board dielectric constant, line width and distance, and the number of wiring layers. The larger the thickness of the board and the thinner the line width, the impedance of the signal will also increase; the larger the dielectric constant of the board, the impedance will also increase accordingly; the smaller the line spacing can also increase the impedance. Through the design of these parameters, the impedance of the signal can be effectively controlled and the stability of signal transmission can be improved.

3. Optimization of impedance PCB

The optimization of the impedance PCB mainly includes three aspects: trace layout, line width and line spacing optimization, and location optimization. In actual applications, the layout of the circuit board also has a great impact on impedance matching, so some optimization needs to be done. In terms of wiring layout, design principles such as focusing on route length, avoiding right-angle lines, and avoiding side-by-side lines can be adopted; for optimization of line width and line spacing, technologies such as microstrip lines and coaxial cables can be considered to make the signal impedance close to 50Ω. In addition, designers need to optimize the impedance plate through electromagnetic field simulation analysis.

4. Detection and diagnosis of impedance PCB

During the PCB manufacturing process, the impedance board also needs to be tested and diagnosed to ensure the accuracy of the impedance parameters. The main detection methods include self-test method, inter-board test method, and time domain reflection method. At the same time, once an impedance mismatch is discovered, it needs to be resolved promptly.

Impedance board control technology is an important method to improve PCB signal transmission efficiency and reduce signal interference. By designing and optimizing the impedance plate, signal loss and reflection can be reduced and the reliability of signal transmission can be improved. At the same time, the accuracy of the impedance parameters is ensured through the detection and diagnosis of the impedance PCB. Impedance plate control technology is an indispensable part of circuit design.

Circuit design is a job that requires patience and care, as one error may affect the performance and reliability of the entire circuit. In circuit design, high-frequency and high-speed boards are a very important part because its characteristics will greatly affect the performance of the circuit. This article will elaborate on the characteristics of high-frequency and high-speed boards, including signal transmission, EMI suppression, wiring planning and material selection, while also providing some practical tips and suggestions to help speed up your circuit design.

1. Signal transmission

Signal transmission of high-frequency and high-speed boards is one of its most important features. Since high-frequency signals have very high frequencies and short wavelengths, special measures are required to ensure the quality and stability of signal transmission. A common method is to improve the signal-to-noise ratio and anti-interference ability of the signal by using differential signal pairs. In addition, during high-speed signal transmission, signal echo is also a factor that needs to be considered. Because signals travel quickly, echoes can cause signal distortion and performance degradation. In order to reduce echoes, appropriate termination resistors and snubber circuits can be used.

2. EMI suppression

EMI (electromagnetic interference) refers to the electromagnetic radiation generated by electronic equipment and the electromagnetic field interference felt, which can have a negative impact on the performance and stability of circuits. In the design process of high-frequency and high-speed boards, appropriate EMI suppression measures need to be taken. One of the commonly used methods is to reduce the area of the current loop and the path that forms the loop through reasonable layout of circuit traces. This can be accomplished by using ground plans, differential lines, and reducing power and ground current loops.

3. Wiring planning

The wiring planning of high-frequency and high-speed boards is a very important step in the design process. When planning wiring, factors such as circuit layout, wiring, power lines, and ground wires need to be considered. One common approach is to use different layers for routing. For example, you can use the inner layer for routing power and ground lines, and the outer layer for routing data lines. Through this method, the length and intersection of traces can be reduced, and signal distortion and noise interference can be reduced.

4. Material selection

The material selection of high-frequency and high-speed boards also affects the performance and reliability of the circuit. For example, different dielectric constants and dielectric losses affect the speed and transmission quality of signals. Therefore, when selecting materials, factors such as the dielectric constant, dielectric loss, thermal expansion coefficient, and thermal conductivity of the board need to be considered. At the same time, factors such as the cost and reliability of materials also need to be considered.

High-frequency and high-speed boards are a very important part of circuit design and require special attention to factors such as signal transmission, EMI suppression, wiring planning, and material selection. By using the appropriate techniques and measures, you can improve circuit performance and reliability and speed up your circuit design.

In PCB design, adopting appropriate wiring forms has a significant impact on the performance and reliability of the circuit. The following are several common wiring forms, each with its own advantages. Choosing the appropriate form based on specific design requirements will be more conducive to improving circuit performance and reliability.

1. Straight line routing: Straight line routing is the simplest and most common form of routing. It has the advantage of being direct and fast, which can reduce the delay of signal transmission. In circuit design, there are often signal lines that must be connected in a straight line, so using straight line routing can better meet this requirement.

2. 45 degree bend wiring: When it is necessary to introduce or lead the signal line into or out of the board, using a 45 degree bend wiring can reduce the reflection and interference of the signal line. Compared to right angle bending, 45 degree angle bending can better maintain the integrity of the signal.

3. Arc routing: Arc routing can reduce the radiation and crosstalk of signal lines, especially for high-frequency signals. If there are high-frequency signal lines in the design, using arc routing can reduce signal loss and distortion.

4. Node cross routing: In design, it is common to encounter situations where cross signals need to be connected. When cross routing nodes, attention should be paid to the distance between signal lines to prevent signal crosstalk. Interlayer routing, ground cutting, and other methods can be used to reduce signal interference.

5. Hard and flexible wiring: Hard and flexible wiring refers to signal transmission achieved through interlayer connections. It can improve the flexibility and reliability of design. Hard and flexible wiring is widely used in complex high-density circuit design, multi-layer board design, and so on.

6. Top/bottom wiring: In multi-layer board design, the top and bottom wiring can be used for shorter signal transmission paths, thereby reducing interlayer perforation and delay. At the same time, the top/bottom wiring can provide better shielding effect and reduce signal interference.

Although several common wiring forms are listed above, multiple factors need to be considered in actual design to choose the appropriate form. For example, the frequency characteristics of circuits, noise tolerance, power consumption requirements, and process constraints. When wiring, attention should also be paid to the separation between the signal, power supply, and ground wire, and the reasonable use of ground wire shielding technology.

In short, choosing the appropriate wiring form is crucial for the performance and reliability of the circuit. Based on specific design requirements and circuit characteristics, designers should comprehensively consider various factors and choose the optimal wiring form to optimize circuit design.