Cause analysis of the problem that the crystal oscillator does not vibrate

Date：2022-07-25 16:06:11 Views：1628

According to the differences of frequency point, frequency difference, load, active and passive, packaging, size and other parameters, the crystal oscillator is prone to frequency offset during operation, resulting in no vibration, resulting in the failure of electronic products to work normally. The following content helps you analyze the reason why the crystal oscillator does not vibrate, which is collated by the core detection network for your reference.

1、 Faulty soldering or tin connection of crystal oscillator

In this case, for the external patches of electronic products, the chips at any position may have bad patches. Under what circumstances will it cause faulty soldering or tin connection,

1. The crystal oscillator pad is too small, and the design is unreasonable, resulting in offset or not in place when placing the chip mounter. The pad is small, there will be less solder paste, and the welding will be unreliable, so the solution is to increase the pad.

2. The thickness of solder paste applied by the SMT machine is not enough, and the reflow soldering process is relatively complex. When the SMT elements are reflowed, the flux is too small or the temperature curve is unreasonable, resulting in the false soldering of the SMT welder.

3. The protection during transportation is not in place, and the solder paste falls off due to collision during transportation.

2、 Crystal destruction

1: There is a falling condition in the production process, which means that only the crystal oscillator circuit leads to excessive external impact force. Because the crystal oscillator circuit chip is relatively thin, it must be handled with care.

2: When the crystal oscillator circuit is welded to the circuit board, it is likely that the welding temperature is too high, resulting in poor crystal oscillator circuit.

3: During the electric welding operation, empty welding is caused, that is, false electric welding, so that the crystal oscillator circuit is not plugged in.

4: After the electric welding of crystal oscillator circuit, the solder wire is connected with the route, resulting in a short circuit.

5: In the leak detection process, it is under the condition of ethanol pressurization that the quartz crystal resonator is very easy to cause the case collision condition, that is, the integrated IC is very easy to collide with the case during vibration, and then the crystallization is very easy to produce time-to-time vibration and collapse or stop vibration;

6: During the pressure sealing, the vacuum packaging nitrogen filling is required inside the crystallization. If the pressure sealing is not good, that is, the tightness of the crystallization is not very good. Under the standard of ethanol pressure filling, its main performance is steam leakage, called Double leakage, which will also cause vibration stop;

7: Because the wall thickness of the integrated IC itself is very thin, when the encouraged output power is too large, the internal quartz integrated IC will be damaged, resulting in vibration stop;

8: The active load will reduce the Q value (i.e. quality factor), which will reduce the reliability of crystallization. It is very vulnerable to the nearby digital power amplifier components, and is in an unstable situation, which is in a state of vibration and depression when it occurs;

9: Because the crystallization is prone to mechanical equipment pressure and internal stress in the case of cutting feet and solder wires, and too high temperature of solder wires and too long efficacy time will harm the crystallization, which is very easy to cause the crystallization to be in critical damping, so that it will be in a state of stagnation when vibration occurs, or even stop vibration;

10: When soldering tin wire, when the tin bar penetrates through the small round hole on the PCB circuit board, causing the pin to be connected with the chassis, or crystallizing in the production process, the tin dot on the pin on the base and the chassis are connected to each other to produce a single leak, which will lead to short-circuit fault and then stop vibration;

11: When the crystallization frequency shifts and exceeds the error range of quartz crystal vibration too much, the core frequency of crystallization cannot be captured, resulting in the failure of integrated IC to vibrate.

3、 Selection of crystal oscillator

The selection of crystal oscillator is very important. Before model selection, it is best to contact the scheme supplier to obtain the electrical parameters of the required crystal oscillator. If the parameters do not match, problems are easy to occur.

1) The bypass capacitance of the crystal oscillator can help to vibrate and fine tune the output frequency of the crystal oscillator, which is generally about 10~20pf. However, when there is material mixing during the chip placement process, resulting in a large difference between the two bypass capacitors, the crystal oscillator will not vibrate. Or the designed bypass capacitance is unreasonable. When it is in the boundary parameter, it may not vibrate.

2) The crystal oscillator resistance is too large, which is easy to cause the crystal oscillator to fail to vibrate. Please select the crystal oscillator with small resistance value according to the circuit requirements.

3) The crystal oscillator gradually stops vibrating during operation, which is specifically manifested by touching the crystal oscillator pin by hand or heating it with an electric soldering iron and starting to work again. The reason may be that the negative impedance value in the oscillation circuit is too small. It is suggested to try to adjust the external capacitance value of the crystal oscillator to meet the loop gain of the oscillation circuit.

4) The excitation power is too large or too small. The crystal oscillator is hot. Excluding the influence of the working environment temperature on the crystal oscillator, the most likely situation is that the excitation power is too large. It is suggested to reduce the excitation power and increase the current limiting resistance to adjust the excitation power. If the excitation power is too small, it is recommended to increase the negative impedance of the circuit, or choose a crystal oscillator with small load capacitance.

4、 Crystal oscillator quality problem

1) In the production process, it is required to vacuum the crystal oscillator and fill it with nitrogen. If there is a poor pressure seal, it will lead to poor air tightness and air leakage of the crystal oscillator.

2) Crystal oscillator dld2 is out of tolerance. The manufacturing process of crystal oscillator is required to be completed in the 10000 level dust-free workshop. If small droplets of water vapor or fine dust particles in the air are attached to the quartz wafer electrode, dld2 will be out of tolerance, causing the crystal oscillator to fail to vibrate.

3) There is a problem with the quality of the crystal oscillator itself, which is more likely to occur in small brands or purchased disassembled components. When the defect rate is very high during the batch production of the crystal oscillator, the damaged crystal oscillator can be provided to the supplier for analysis, and the supplier is required to provide 8D report, find the problem point, and carry out rectification and control.

That's all for this article. I hope it can help you. Although the crystal oscillator is small, there are many cases that can cause the crystal oscillator to not work. It needs to be carefully analyzed to find the root cause and solve the problem. Otherwise, it will have a great impact on the quality stability of products and cause great losses to the company. Therefore, it needs to be treated with caution.