If analog circuits (radio frequency) and digital circuits (microcontrollers) work alone, they may work well, but once they are put on the same circuit board and work together using the same power supply, the entire system is likely to be unstable. . This is mainly because the digital signal frequently swings between ground and positive power (3 V), and the period is extremely short, often on the ns level. Due to the large amplitude and small switching time, these digital signals contain a large number of high-frequency components that are independent of the switching frequency. In the analog part, the signal transmitted from the antenna tuning loop to the receiving part of the wireless device is generally less than 1μV.
Failure to adequately isolate sensitive lines and noisy signal lines is a common problem. As mentioned above, digital signals have high swings and contain large amounts of high-frequency harmonics. If digital signal traces on a PCB are placed adjacent to sensitive analog signals, high-frequency harmonics may couple through. The sensitive nodes of RF devices are usually the loop filter circuit of the phase-locked loop (PLL), the external voltage-controlled oscillator (VCO) inductor, the crystal reference signal and the antenna terminal. These parts of the circuit should be handled with special care.
Because the input/output signals have a swing of several V, digital circuits are generally acceptable for power supply noise (less than 50 mV). Analog circuits are quite sensitive to power supply noise, especially glitch voltages and other high-frequency harmonics. Therefore, routing power lines on PCBs containing RF (or other analog) circuits must be more careful than routing on ordinary digital circuit boards, and automatic routing should be avoided. It should also be noted that a microcontroller (or other digital circuit) will suddenly draw most of the current for a short period of time during each internal clock cycle. This is because modern microcontrollers are designed using a CMOS process.
RF circuit boards should always have a ground layer connected to the negative pole of the power supply. If not handled properly, some strange phenomena may occur. This may be difficult for a digital circuit designer to understand because most digital circuit functions perform well even without a ground plane. In the RF band, even a short wire can act like an inductor. A rough calculation shows that the inductance per mm length is about 1 nH, and the inductive reactance of a 10 mm PCB line at 434 MHz is about 27 Ω. If the ground layer is not used, most ground wires will be long and the circuit will not be able to guarantee the design characteristics.
This is often overlooked in circuits that contain RF and other parts. In addition to the RF section, there are usually other analog circuits on the board. For example, many microcontrollers have built-in analog-to-digital converters (ADCs) for measuring analog inputs as well as battery voltage or other parameters. If the RF transmitter’s antenna is located near (or on) this PCB, the emitted high-frequency signal may reach the analog input of the ADC. Don’t forget that any circuit trace may act like an antenna, emitting or receiving RF signals. If the ADC input is not processed properly, the RF signal may self-excite in the ESD diode of the ADC input, causing ADC deviation.
All connections to the ground plane must be kept as short as possible, and ground vias should be placed at (or very close to) the component pads. Never allow two ground signals to share a ground via, as this may cause crosstalk between the two pads due to the via connection impedance. Decoupling capacitors should be placed as close to the pins as possible, and capacitive decoupling should be used at each pin that needs decoupling. Using high quality ceramic capacitors with dielectric type “NPO”, the “X7R” will work well in most applications. Ideally the capacitor value should be chosen so that its series resonance is equal to the signal frequency.
For example, at 434 MHz, an SMD-mounted 100 pF capacitor will work well. At this frequency, the capacitive reactance of the capacitor is about 4 Ω, and the inductive reactance of the via is also in the same range. The series connected capacitors and vias form a notch filter for the signal frequency, enabling effective decoupling. At 868 MHz, a 33 pF capacitor is an ideal choice. In addition to the small value capacitor for RF decoupling, a large value capacitor should also be placed on the power line to decouple low frequencies. You can choose a 2. 2 μF ceramic or 10 μF tantalum capacitor.
Star wiring is a well-known technique in analog circuit design. Star wiring – Each module on the circuit board has its own power line from a common power supply point. In this case, star wiring means that the digital and RF parts of the circuit should have their own power lines, which should be separately decoupled close to the IC. This is a separation from numbers
An effective method for summing up power supply noise from the RF section. If a module with severe noise is placed on the same circuit board, an inductor (magnetic bead) or a small value resistor (10 Ω) can be connected in series between the power line and the module, and a tantalum capacitor of at least 10 μF must be used for these. Decoupling of the module’s power supply. Such modules are RS 232 drivers or switching power supply regulators.
In order to reduce interference from the noise module and surrounding analog parts, the layout of each circuit module on the board is important. Sensitive modules (RF section and antenna) should always be kept away from noisy modules (microcontroller and RS 232 driver) to avoid interference. As mentioned above, RF signals can cause interference to other sensitive analog circuit modules such as ADCs when transmitted. Most problems occur at lower operating frequency bands (such as 27 MHz) and at high power output levels. It is a good design practice to decouple sensitive points with RF decoupling capacitors (100pF) connected to ground.
If you use cables to connect the RF circuit board to external digital circuits, use twisted pair cables. Each signal line must be twisted together with the GND line (DIN/GND, DOUT/GND, CS/GND, PWR_UP/GND). Remember to connect the RF circuit board and the digital application circuit board with the GND line of the twisted pair cable, and the cable length should be as short as possible. The lines supplying power to the RF circuit board must also be twisted with GND (VDD/GND).

HDI PCB stands for High Density Interconnect Printed Circuit Board. Compared with traditional PCBs, HDI PCBs have higher circuit density, finer lines and spacing, and smaller via diameters.  HDI PCBs use advanced manufacturing techniques such as laser drilling, stacked vias, and microvias to increase the packing density of components on the board, thereby reducing board size and improving signal integrity. HDI PCBs offer several advantages over traditional PCBs, including:

1. Reduced board size: HDI PCBs allow more components to be packed into a smaller area, reducing overall board size.
2. Faster signal transmission: HDI PCB has shorter signal paths due to the smaller distance between components, resulting in faster signal transmission between components.
3. Improved reliability: HDI PCB has more interconnections between components, making it more reliable and less prone to failure.
4. Higher thermal performance: HDI PCB conducts heat more efficiently, resulting in better thermal management of the board.

HDI PCBs are commonly used in high-performance electronic devices such as smartphones, tablets, and laptops, as well as in aerospace and military applications where size and weight reduction is critical.

Rigid-Flex PCB is a board that combines a flexible circuit with a rigid board. Its advantages and disadvantages are as follows: advantage:

1. Flexible circuits allow more flexible circuit design, and high-density wiring can achieve smaller size and lighter weight.
2. Compared with rigid boards, Rigid-Flex PCB has good vibration resistance, tensile strength and bending resistance, and is suitable for high-demand industrial fields.
3. The assembly cost is relatively low, which can reduce the volume and weight of traditional rigid boards, while improving the design flexibility and reliability of electronic products.

shortcoming: 1. The manufacturing process of Rigid-Flex PCB is complicated and requires advanced production equipment, resulting in high cost.

2. Rigid-Flex PCBs may have lower reliability and durability compared to rigid boards.
3. For circuits containing high-frequency signals, the performance of flexible circuits may not be as good as rigid boards.

In addition, Rigid-Flex PCB has some design considerations that must be considered: 1. Design for flexibility: Rigid-flex PCBs must be designed to accommodate various bending and folding requirements of the final product. The flexible portion of the board should be located where bending will not damage sensitive components.

3. Component Placement: Component placement on a Rigid-Flex PCB is critical for optimal signal integrity and reliability. Components should not be placed on the flexible part of the board where they could be damaged when bent or folded.
4. Material selection: Rigid-Flex PCB material selection must take into account the required flexibility, durability and electrical performance. These materials must also be able to withstand the harsh environmental conditions of the final product.
5. Thermal management: Rigid-Flex PCB’s high-density circuit design is difficult to effectively dissipate heat. Thermal management must be a key consideration in the design process to prevent overheating and damage to boards and components.

Overall, Rigid-Flex PCB is a versatile and reliable PCB technology that offers many advantages over traditional rigid boards. However, its complexity and design considerations require expertise and experience to achieve a reliable and high-performance design.

1. Design quality: Design quality is crucial to determine the functionality and reliability of the PCB. Factors such as layout, routing, and component placement should be carefully considered.
2. Manufacturing process: The quality of the manufacturing process can greatly affect the performance of the PCB. High-quality materials, sophisticated manufacturing processes, and strict quality control all ensure that PCBs are manufactured to a high standard.
3. Component quality: The quality of components used on a PCB affects its reliability and lifespan. Using high-quality components ensures that the PCB will perform well for a longer period of time.
4. Environmental factors: The use environment of PCB will also affect its quality. Factors such as temperature, humidity, and vibration can all affect the performance of a PCB.
5. Testing and Validation: Proper testing and validation of the PCB ensures that it functions as intended and identifies and resolves any issues before the PCB is put into service.

Overall, ensuring the quality of a PCB requires attention to detail at each stage of the design, manufacturing, testing, and use process.