Failure analysis and solution of crystal oscillator

Date：2022-06-02 15:47:54Views：1108

The quality of the crystal oscillator is directly related to the stability of the whole system. Therefore, how to select a crystal oscillator and how to view the main parameters of the crystal oscillator are compulsory courses for engineers. The selection of parameters is related to the stable operation of the system. The specific selection not only needs to control the crystal oscillator parameters in detail, but also needs to refer to the requirements of different systems. The function of crystal oscillator in the circuit is to provide basic frequency signals for the digital system. If the crystal oscillator does not vibrate, MCU will stop running, resulting in the failure of the whole circuit.

1. Incorrect crystal oscillator parameter selection causes the crystal oscillator to fail to vibrate

Solution: replace the crystal oscillator specifications and models that meet the requirements.

2. Failure of crystal oscillator due to internal quartz wafer fracture

The crystal plate inside the crystal oscillator is damaged due to damage during transportation, or falling, impact and other factors during use, resulting in the failure of the crystal oscillator.

Solution: replace the crystal oscillator. Attention: avoid damage during transportation; Avoid falling, heavy pressure, impact, etc. in the process of transfer and placement. In case of any of the above situations, please strictly follow the principle of "falling and not using".

3. Mismatch of oscillation circuit leads to failure of crystal oscillator

There are three main factors that affect the oscillation circuit: frequency difference, negative impedance and excitation power.

The frequency difference is too large, which causes the actual output frequency of the crystal oscillator to deviate too far from the nominal frequency, resulting in the IC unable to capture the frequency signal output by the crystal oscillator, resulting in the false impression that the crystal oscillator can not vibrate.

Solution: select crystal oscillator products with appropriate accuracy (PPM value).

If the negative impedance is too large or too small, the crystal oscillator will not vibrate.

Solution: if the negative impedance is too large, you can increase the values of crystal oscillator external capacitors CD and CG to reduce the negative impedance; If the negative impedance is too small, you can reduce the values of the crystal oscillator external capacitors CD and CG to increase the negative impedance. Generally speaking, the negative impedance value shall not be less than 3~5 times the nominal maximum impedance of the crystal oscillator.

Too large or too small excitation power will also cause the crystal oscillator to fail to vibrate

Solution: adjust the output excitation power of the oscillator circuit to the crystal oscillator by adjusting the size of RD in the circuit. Generally speaking, the smaller the excitation level, the better. In addition to low power consumption, it is also related to the stability of the oscillation circuit and the service life of the crystal oscillator. The selection principle of excitation power is to ensure the normal startup of crystal oscillator and the normal electrical parameters of crystal oscillator in operation.

4. Impurities or dust on the crystal plate inside the crystal oscillator will also cause the crystal oscillator to fail to vibrate

One of the manufacturing processes of crystal oscillator is quartz wafer electrode plating, that is, a layer of gold or silver is plated on the crystal wafer, which requires to be completed in the 10000 level dust-free workshop. If dust particles, tiny moisture or fine gold and silver residues remain on the electrode in the air, the crystal vibration will not start.

Solution: replace the crystal oscillator with a new one.

5. The crystal oscillator fails to vibrate due to air leakage

During the manufacturing process of crystal oscillator, it is required to vacuum the internal part and fill it with nitrogen. In case of poor sealing, the air tightness of crystal oscillator will be poor and air leakage will occur; Or the crystal oscillator has poor air tightness due to the mechanical stress of the product during the welding process, such as foot trimming; Will lead to the phenomenon that the crystal oscillator does not vibrate.

Solution: replace the crystal oscillator. It is recommended to select a crystal oscillator manufacturer with strong reliability and good reputation. In the process of crystal oscillator welding or chip mounting, it is also necessary to standardize the operation to avoid crystal oscillator damage caused by misoperation.

6. When welding, the temperature is too high or the time is too long, which leads to the abnormal internal electrical performance index of the crystal oscillator and the crystal oscillator does not vibrate

Solution: the welding process must be standardized, and the setting of welding time and temperature should meet the requirements of crystal oscillator.

7. Improper storage environment leads to deterioration of electrical performance of crystal oscillator and failure of crystal oscillator

Long time use or storage under high temperature, low temperature or high humidity conditions will cause deterioration of the electrical performance of the crystal oscillator, which may lead to no vibration.

Solution: use and store it under normal temperature and dry conditions as far as possible to avoid crystal oscillator or circuit board moisture. It is recommended that crystal oscillator products be pasted or welded to the circuit board as soon as possible. In addition, please upgrade the warehouse in strict accordance with the storage standards of electronic components to meet the storage conditions required for electronic components such as crystal oscillator.

8. MCU quality problems, software problems, etc. cause the crystal oscillator not to vibrate

Solution: determine whether it is genuine MCU. If there is a problem with the software burning program, the crystal oscillator may not start. Note: in this case, the failure of the crystal oscillator to vibrate is not a defective product.

9. The crystal oscillator fails to vibrate due to EMC problems

Solution: try to use metal encapsulated crystal oscillator. In addition, do not use the signal line under the crystal oscillator to avoid electromagnetic signal interference. Excessive electromagnetic interference will interfere with the normal frequency output of the crystal oscillator, so PCB wiring must be reasonable.

10. Failure of crystal oscillator due to ultrasonic wave

The circuit board with crystal oscillator is generally not recommended to use ultrasonic cleaning or packaging to avoid resonance and artificial damage to the crystal oscillator.

The above is the relevant content of crystal oscillator failure analysis compiled by the core detection team. I hope it will be helpful to you. Shenzhen Chuangxin Online Testing Technology Co., Ltd. is a well-known professional testing institution for electronic components in China, with 3 standardized laboratories covering an area of more than 1000 square meters. The scope of testing services covers: testing and verification of electronic components, IC authenticity identification, material selection for product design, failure analysis, function testing, factory incoming material inspection, X-ray testing of components and parts, tape braiding and other testing items.