PCBA Assembly Crystal Burned Out Cause Situation Analysis

Based on the internal structure of the crystal oscillator and the working principle of the differences, the crystal oscillator is burned out of the situation should be divided into two categories.

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Passive crystal is burned out in the following two cases:

1、Improper hand soldering operation

If the use of high temperature or a long time on the guide foot parts of the heating, will lead to crystal vibration internal wafer silver plating layer damage, resistance is super poor and other issues, triggering the crystal vibration does not vibrate.


2、Excitation power is too large

According to the different areas of application, select the appropriate excitation power of the crystal oscillator, do not just to change the output frequency of the crystal oscillator, arbitrarily change the circuit input to the crystal oscillator to stimulate the size of the power. Because the circuit to provide too much excitation power may lead to quartz wafer amplitude, so too much heat generated by the quartz wafer vibration area of the temperature increases. The quartz wafer itself experiences a gradient temperature rise, which directly destabilises the frequency. Since the wafer may be mechanically deformed beyond its elastic limit, the crystal lattice may be irretrievably displaced, resulting in permanent frequency deviation of the output frequency of the crystal. In more serious cases, the quartz wafer is shattered, resulting in the complete failure of the crystal to vibrate (stop vibration), which is what we call “burned out”. Caused by the equivalent resistance becomes large (Note: the general crystal resistance value of 10 ~ 100Ω), affecting the crystal vibration, and in serious cases cause the crystal vibration stop. Excessive excitation power may also lead to lead to the solid wafer and the base of the conductive adhesive damage, such as fracture, the consequence is to cause the crystal oscillator internal circuit breakage, crystal vibration stop.


In the circuit application of passive crystals, the voltage applied to the crystal terminals is very low, so the passive crystal is rarely burned out. This type of accident occurs more often in the improper application of active crystals, and therefore requires special attention.

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Active crystal is burned out is also divided into the following two points:

1、The wrong direction of the voltage input

Quartz crystal oscillator is usually used: one foot hanging, two feet ground, three feet to the output, four feet to the voltage.

Correct connection of voltage: the voltage input must be connected to the voltage input pin (VCC) of the crystal. If wrongly connected to the ground pin, the crystal will be current “burned out”.


2、Input voltage parameter selection error

General input voltage: 1.8V, 2.8V, 3.3V, 5V. If 5V is supplied to the active crystal oscillator with a rated voltage of 1.8V, it will bring a high risk of crystal burnout.


A special reminder for active crystals: active crystals will only be destroyed if they are fed into an overloaded high-voltage power supply. Do not connect the input voltage wrongly or inversely.

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