When designing a PCB (printed circuit board), one of the most basic issues to consider is how many wiring layers, ground planes and power planes are needed to achieve the functions required by the circuit. The wiring layers, ground planes and power planes of the printed circuit board The determination of the number of plane layers is related to requirements such as circuit function, signal integrity, EMI, EMC, and manufacturing costs. For most designs, there are many conflicting requirements in factors such as PCB performance requirements, target cost, manufacturing technology, and system complexity. The stack-up design of the PCB is usually determined by a compromise after considering various factors. High-speed digital circuits and whisker circuits usually adopt multi-layer board designs. What factors affect PCB stackup design?

1. Layering

In a multi-layer PCB, it usually contains a signal layer (S), a power (P) plane and a ground (GND) plane. Power planes and ground planes are usually solid planes without separation, and they will provide a good low-impedance current return path for current from adjacent signal traces. The signal layer is mostly located between these power or ground reference plane layers, forming a symmetrical stripline or an asymmetrical stripline. The top and bottom layers of multi-layer PCBs are usually used to place components and a small number of traces. These signal traces must not be too long to reduce direct radiation generated by the traces.

2. Determine the single power supply reference plane (power plane)

The use of decoupling capacitors is an important measure to solve power supply integrity. Decoupling capacitors can only be placed on the top and bottom layers of the PCB. The traces, pads, and vias of the decoupling capacitor will seriously affect the effect of the decoupling capacitor. This requires that the traces connected to the decoupling capacitors should be as short and wide as possible during design, and the wires connected to the vias should also be considered. Keep it as short as possible. For example, in a high-speed digital circuit, you can place decoupling capacitors on the top layer of the PCB, assign layer 2 to the high-speed digital circuit (such as a processor) as the power layer, layer 3 as the signal layer, and layer 4 Set to high-speed digital circuit ground.

In addition, try to ensure that the signal traces driven by the same high-speed digital device use the same power layer as the reference plane, and this power layer is the power supply layer of the high-speed digital device.

3. Determine the multi-power reference plane

The multi-supply reference plane will be divided into several physical areas with different voltages. If there is a signal layer next to the multi-power layer, the signal current on the nearby signal layer will encounter an unideal return path, causing gaps in the return path. For high-speed digital signals, this unreasonable return path design may cause serious problems, so it is required that high-speed digital signal wiring should be kept away from multi-power reference planes.

4. Determine multiple ground reference planes (ground planes)

Multiple ground reference planes (ground layers) can provide a good low-impedance current return path, which can reduce common-mode EMl. Ground planes and power planes should be tightly coupled, and signal layers should be tightly coupled to adjacent reference planes. This can be achieved by reducing the thickness of the media between layers.

5. Reasonable design of wiring combinations

The two layers spanned by a signal path are called a “routing combination.” The best routing combination design avoids return current flow from one reference plane to another, but flows from one point (plane) of a reference plane to another point (plane). In order to complete complex wiring, interlayer conversion of wiring is inevitable. When converting between signal layers, it is necessary to ensure that the return current can flow smoothly from one reference plane to another. In a design, it makes sense to treat adjacent layers as a routing group. If a signal path needs to span multiple layers, it is usually not a reasonable design to use it as a routing group, because a path through multiple layers is not clear for return current. Although the ground bounce can be reduced by placing decoupling capacitors near the vias or reducing the dielectric thickness between the reference planes, it is not a good design.

6. Set the wiring direction

On the same signal layer, the direction of most wiring should be consistent and orthogonal to the wiring direction of adjacent signal layers. For example, you can set the wiring direction of one signal layer to the “Y-axis” direction, and set the wiring direction of another adjacent signal layer to the “X-axis” direction.

7. Adopt an even-numbered layer structure

From the designed PCB stackup, it can be found that the classic stackup design is almost all even-numbered layers, not odd-numbered layers. This emergency is caused by a variety of factors, as shown below.

It can be understood from the manufacturing process of printed circuit boards that all conductive layers in the circuit board are saved on the core layer. The material of the core layer is usually a double-sided cladding board. When the core layer is fully utilized, the conductive layer of the printed circuit board The number is even.

Even-layer printed circuit boards have cost advantages. Due to the lack of one layer of dielectric and copper coating, the cost of raw materials for odd-numbered printed circuit boards is slightly lower than the cost of even-numbered printed circuit boards. However, because odd-numbered layer printed circuit boards require a non-standard laminated core layer bonding process based on the core layer structure process, the processing cost of odd-numbered layer printed circuit boards is significantly higher than even-numbered layer printed circuit boards. Compared with the ordinary core structure, adding copper cladding outside the core structure will lead to a decrease in production efficiency and a prolongation of the production cycle. The outer core layer also requires additional processing before lamination and bonding, which increases the risk of scratches and incorrect etching of the outer layer. The added outer layer treatment will significantly increase manufacturing costs.

When the inner and outer layers of a printed circuit board are cooled after the multi-layer circuit bonding process, different lamination tensions will cause the printed circuit board to bend to varying degrees. And as the thickness of the board increases, the risk of bending of a composite printed circuit board with two different structures increases. Odd-numbered circuit boards are prone to bending, while even-numbered layers of printed circuit boards can prevent the circuit board from bending.

During design, if there are an odd number of layers, you can use the following method to increase the number of layers.

If you design a printed circuit board with an even number of power layers and an odd number of signal layers, you can use the method of adding signal layers. The added signal layer will not lead to an increase in cost, but can shorten the processing time and improve the quality of the printed circuit board.

If you design a printed circuit board with an odd number of power layers and an even number of signal layers, you can use the method of adding power layers. Another simple method is to add a ground layer in the middle of the stack without changing other settings, that is, first lay out the odd-numbered printed circuit board layers, and then copy a ground layer in the middle.

In microwave circuits and mixed media (media with different dielectric constants) circuits, a blank signal layer can be added near the center of the PCB stackup to minimize stackup imbalance.

8. Cost considerations

In terms of manufacturing cost, with the same PCB area, the cost of multi-layer circuit boards is definitely higher than single-layer and double-layer circuit boards, and the more layers, the higher the cost. However, when considering factors such as circuit function and circuit board miniaturization, and ensuring signal integrity, EMl, EMC and other performance indicators, multi-layer circuit boards should be used as much as possible. Comprehensive evaluation shows that the cost difference between multi-layer circuit boards and single- and double-layer circuit boards is not much higher than expected.

PCB board edge safety distance refers to the minimum safety distance between the edge of the circuit on the PCB board and the board boundary. The determination of this distance is very important to ensure the reliability of the circuit and prevent interference between circuits. This article will discuss in detail the appropriate range of PCB board edge safety distance and its impact on circuit design.

1. Concept and background of PCB edge safety distance

PCB, the printed circuit board, plays a very important role in modern electronic products. The PCB board edge safety distance refers to the minimum safe distance between the circuit on the PCB board and the edge of the board. This concept is proposed to ensure the reliability of the circuit, prevent interference between circuits and meet safety requirements.

When designing a PCB board, you need to take into account the spacing between circuits and the spacing between the circuits and the edges of the board. This is because without proper spacing between circuits, mutual interference between circuits may occur, resulting in circuit performance degradation or even damage.

2. Parameter influencing factors of PCB board edge safety distance

1. Insulation material: PCB boards usually use materials with good insulation properties, such as FR4, which plays a very good role in isolating interference between circuits.

2. Working voltage: The higher the working voltage of the circuit, the safety distance between the edges of the board should also be increased accordingly to ensure that the current will not cause short circuit or breakdown.

3. Version requirements: Different circuit boards have different version requirements, and they also have different requirements for the safety distance between the edges of the board. For example, the requirements for civilian products and military products will be different.

4. Electromagnetic compatibility (EMC): The safety distance between the edges of the board will also be affected by electromagnetic compatibility. When designing, it is necessary to consider the electromagnetic crosstalk problem between circuits and reasonably determine the safe distance between the edges of the board.

3. Measurement and calculation method of PCB board edge safety distance

In actual design, how to measure and calculate the PCB board edge safety distance is also a crucial step. Here are two common methods:

1. Standard method measurement: According to the standard requirements, directly measure the distance from the edge of the board to the nearest circuit.

2. Electric field analysis method calculation: By using professional electromagnetic simulation software, the electric field distribution between the circuit and the board edge is simulated and analyzed to determine the board edge safety distance.

4. Appropriate range of safety distance between PCB board edges

When determining the safe distance from the edge of the PCB board, it needs to be considered based on the specific application scenarios and product requirements. Generally speaking, a reasonable safe distance from the edge of the board should meet the following conditions:

1. Minimum safe distance between circuits: ensure that arc breakdown and mutual interference will not occur between circuits. According to different circuit design requirements, this distance needs to be within a certain range.

2. Electromagnetic compatibility (EMC) requirements: Ensure that the circuit does not produce electromagnetic interference that affects other circuits or equipment when working. According to the standard requirements of different countries and industries, the safety distance from the edge of the board will also be different.

3. Safety requirements: Ensure that the circuit will not cause safety risks and will not cause short circuit, overheating or other faults within its design life. Depending on different application scenarios and product requirements, a larger safety distance from the board edge is sometimes required.

To sum up, the safety distance from the edge of the PCB board is one of the important parameters to ensure the reliability and safety of the circuit. Its proper setup and design will help reduce interference between circuits, prevent short circuits and failures, and meet electromagnetic compatibility requirements. During the specific design, it is necessary to comprehensively consider the circuit type, operating voltage, version requirements, safety requirements, etc., with the help of appropriate measurement and calculation methods, and clearly stipulate them in the design specifications to ensure that the safety distance from the edge of the PCB board is set correctly. Reasonableness and reliability.

PCB (Printed Circuit Board) is a very important component of electronic products. It connects various electronic components and provides electrical connections and mechanical support. Crosstalk is a common problem during PCB design and manufacturing that can negatively impact circuit performance. This article will detail the causes of crosstalk on PCBs and provide some solutions.

1. Causes of crosstalk

1. Electromagnetic interference (EMI)

Electronic equipment generates electromagnetic radiation during operation. Changes in current and voltage on signal lines will generate magnetic fields, causing changes in charge and current on nearby lines, thus causing crosstalk. Electromagnetic interference mainly originates from high-frequency signals, ground return flow and power supply return flow.

2. Signal Integrity (SI)

Signal integrity refers to the ability of a signal to maintain stability and accuracy while traveling through a circuit. When signals are transmitted in PCBs, they are affected by factors such as impedance mismatch, signal coupling, and backflow, which can lead to signal distortion and crosstalk.

3. Power supply noise

Power supply noise refers to changes in voltage and current caused by power supply voltage fluctuations, power line impedance mismatches, and other electrical factors. Power supply noise can couple to other lines through the power lines, causing crosstalk.

4. Asynchronous clock system

When there are multiple clock sources on the PCB, since the frequency and phase of each clock source may be different, mutual interference between signals will occur, resulting in crosstalk.

2. Solution

1. Electromagnetic shielding

In order to reduce electromagnetic radiation and electromagnetic interference, electromagnetic shielding measures can be used on the PCB. For example, add ground wires, power wires, or electromagnetic shields next to high-frequency lines to reduce the level of interference.

2. Reasonable wiring and layout

Proper wiring and layout can reduce signal coupling and crosstalk. First, the length and area of signal lines should be minimized to avoid intersection and overlap of signal lines. Secondly, avoid placing high-frequency and low-frequency lines on the same level, as well as placing signal lines and power lines in adjacent locations.

3. Impedance matching

To ensure signal integrity, impedance matching should be implemented in the PCB design. Add an impedance matching resistor at the end of the signal line to ensure normal signal transmission. In addition, PCB software simulation tools can be used to optimize impedance matching.

4. Optimize power supply design

Optimizing the power supply design can reduce the impact of power supply noise on other lines. First, the length and impedance of the power cord should be minimized. Secondly, components such as power filter capacitors, power regulators, and power isolators should be added to the PCB to reduce power supply noise.

5. Synchronized clock system

In order to avoid the crosstalk problem of asynchronous clock systems, synchronous clock systems can be used. The synchronous clock system can ensure the consistency of the frequency and phase of each clock source and reduce crosstalk through synchronous control of clock signals.

The above is a detailed introduction to the causes and solutions of crosstalk on PCB. Through reasonable design and optimization measures, crosstalk problems can be effectively reduced and the performance and reliability of PCB can be improved. However, in practical applications, different electronic equipment and circuit systems may have different crosstalk problems, and the solutions will also be different. Therefore, in the PCB design and manufacturing process, it is necessary to comprehensively consider the specific situation and apply various measures flexibly to solve the crosstalk problem in the best way.

Medical circuit boards play an important role in the modern medical field. Understanding the classification of medical circuit boards helps us better understand their applications and development.

1. Sensor circuit board
One type of circuit board widely used in the medical field is sensor circuit board. These circuit boards are mainly used to collect patients’ physiological data, such as heart rate, blood pressure, body temperature, etc. The sensor circuit board uses various sensors and signal processing circuits to accurately sense the patient’s physiological state and transmit the data to the monitoring circuit board for analysis.

2. Monitoring circuit board
Monitoring circuit boards are mainly used to monitor changes in patients’ conditions, including electrocardiogram, respiratory monitoring, blood oxygen saturation, etc. This type of circuit board usually integrates multiple sensors and data processing modules to comprehensively monitor and record the patient’s physical condition. The main function of the monitoring circuit board is to provide real-time condition data to help medical staff judge the patient’s health status in a timely manner.

3. Therapeutic circuit boards
Therapeutic circuit boards are mainly used to provide medical treatments, such as pacemakers, defibrillators, etc. This type of circuit board usually includes a control part and an output part. The control part is used to perform corresponding control according to the patient’s condition, and the output part is used to output treatment signals or current. The application of therapeutic circuit boards can effectively help patients restore health or improve their quality of life.

4. Auxiliary circuit boards
Auxiliary circuit boards provide support for medical equipment, including power supply management circuit boards, communication control circuit boards, etc. These circuit boards do not come into direct contact with the patient and are primarily used to provide power management and data transmission functions. The reliability and stability of auxiliary circuit boards are crucial to the normal operation of medical equipment and the accurate transmission of information.

Different types of circuit boards play an important role in medical equipment and are of great significance to improving medical standards and improving patients’ quality of life. Having a certain understanding of the classification and application of these circuit boards will help us better understand the development and application prospects of medical circuit boards. It is believed that with the continuous advancement of technology, medical circuit boards will play a more important and extensive role in the medical industry.

FR4 substrate material is a substrate material widely used in electronic products. This article will delve into the key parameters of FR4 substrate materials, including dielectric constant, coefficient of thermal expansion, glass transition temperature and electrical breakdown strength. Through the detailed elaboration of these parameters, it helps readers understand the performance of FR4 substrate materials and its important role in electronic products.

1. Dielectric constant
Dielectric constant is one of the important parameters to measure the electrical insulation properties of materials. For FR4 substrate materials, their dielectric constant determines the propagation speed and wavelength of electromagnetic waves in the material. The smaller the dielectric constant, the faster and higher the frequency of electromagnetic waves propagating in the material. When the dielectric constant of the FR4 substrate material approaches 1, the impedance matching performance of the material is better, which can improve the speed and quality of signal transmission.

2. Thermal expansion coefficient
The coefficient of thermal expansion is one of the key parameters that measures the change in length of a material under temperature changes. For FR4 substrate materials, their thermal expansion coefficient determines whether deformation occurs under temperature changes, which affects the stability and reliability of electronic products. Reasonable control of the thermal expansion coefficient of the FR4 substrate material can avoid stress concentration and mismatch between components caused by temperature changes.

3. Glass transition temperature
Glass transition temperature refers to the critical temperature at which a material changes from a glassy state to a solid state. For FR4 substrate materials, their glass transition temperature determines the material’s mechanical properties and insulation properties under high temperature conditions. The higher glass transition temperature can ensure that the FR4 substrate material can still maintain good physical and electrical properties in high temperature environments, improving the reliability and stability of electronic products.

4. Electrical breakdown strength
Electrical breakdown strength refers to the maximum voltage that a material can withstand under the action of an electric field. For FR4 substrate materials, their electrical breakdown strength determines the material’s insulation capabilities and reliability. Higher electrical breakdown strength means that the material can withstand higher operating voltages and can effectively prevent equipment damage or failure caused by electrical breakdown.

FR4 substrate material is a commonly used substrate material in electronic products, and its key parameters have an important impact on product performance. Dielectric constant, thermal expansion coefficient, glass transition temperature and electrical breakdown strength are important indicators to measure the performance of FR4 substrate materials. By reasonably controlling these parameters, the signal transmission speed, stability and reliability of electronic products can be improved. In future applications, research and further optimization of key parameters of FR4 substrate materials will be an important direction to provide better support and guarantee for the development of electronic products.