Crystal oscillator plays a vital role in PCB (Printed Circuit Board) design, because it provides a stable clock signal, which is the basis for the normal operation of many electronic devices. In the design of PCBs containing crystals, the following key matters should be noted:

　　1. Crystal selection:

　　-Select the appropriate crystal frequency and quality factor (Q factor).

　　-Select the crystal type (e.g. HC-49U, SMD package, etc.) according to the application requirements.

　　2. Layout design:

　　-The crystal should be kept away from heat generating components to prevent overheating.

　　-Shorten the alignment between the crystal and the processor as much as possible to reduce parasitic capacitance and inductance.

　　-Use ground plane to reduce noise and improve signal stability and reliability.

　　3. Power and ground plane design:

　　-Ensure a clean and stable power supply for the crystal.

　　-Good design of power supply and ground plane to minimize power supply noise.

　　4. Selection and placement of decoupling capacitors:

　　-Place decoupling capacitors near the crystal and on the power supply pins to reduce power supply noise and improve power supply stability.

　　-Select decoupling capacitors with appropriate capacitance and withstand voltage.

　　5. Crystal packaging and mounting:

　　-Correctly mount the crystal according to the manufacturer's recommendations.

　　-Ensure that the solder joints are clean, full, and free of false soldering.

　　6. Alignment and wiring:

　　-Use as wide an alignment as possible to minimize inductance and capacitance.

　　-Avoid excessively long or looped alignments, which may lead to EMI or self-excited oscillations.

　　7. Anti-vibration and anti-interference:

　　-Consider the use of anti-vibration measures such as vibration damping pads or anti-vibration packages.

　　-Ensure that the PCB design meets electromagnetic compatibility (EMC) requirements.

　　8.Testing and Verification:

　　-Conduct rigorous testing after the design is completed to ensure that the crystal output is stable.

　　-Test power supply stability and decoupling effect.

　　9.Thermal Management:

　　-Consider the thermal management of the crystal and PCB board, because temperature changes will affect the performance of the crystal.

　　-If necessary, add a heat sink or use heat dissipation materials.

　　When designing, it is also necessary to follow the relevant national and industry standards to ensure the safety and reliability of the design. At the same time, the stability and accuracy of the crystal should be given enough attention considering its impact on the whole electronic system.