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Shock
MECHANICAL SHOCK:

Mechanical shock is the exposure of the quartz resonator to an impact. Mechanical shock can occur in a wide range. Dropping a crystal onto the floor onto the floor is one example. An example of extreme mechanical shock would be a crystal utilized in the electronic circuit of an proximity fuse of an artillery shell fired from a 155 mm gun.

Mechanical shock has two components, intensity measured in Gs and duration measured in milliseconds. Dropping a crystal from table-top height onto a hard floor can result is shock in excess of 1,000 g’s over a period of about 3 milliseconds. The crystal in the artillery shell experiences about 16,000 g’s for 12 milliseconds. Higher shock levels usually have shorter duration, 0.25 milliseconds and lower shock levels can have a duration as long as 20 milliseconds.

The effects of mechanical shock range from frequency shifts, intermittent operation an/or total destruction due to the stress sensitivity of the resonator. Stress sensitivity is a function of the mechanical design of the resonator and shock survivability is a consideration when developing the design. Design, selection of material, internal mounting structure and processes can all be optimized to enhance a resonators ability to survive mechanical shock. A resonator’s ability to tolerate mechanical shock can be tested by exposing the device to a calibrated shock, then measure and compare the pre- and post-test performance.

Military specifications, MIL-PRF-3098/H and MIL-STD-202F Method 213 TC C&D, set the typical standard and test conditions for mechanical shock for crystals:

< 4.0 MHz: 100g, 6 mS, half-sine, 3 blows each plane
> 4.0 MHz: 500g, 1 mS, half-sine, 3 blows each plane

Shock

THERMAL SHOCK:

Thermal shock is the sudden exposure of a quartz resonator to wide temperature changes – very cold to very hot and vice versa. An example would be taking a crystal resonator from –65 C to 125 C. Slow-start, frequency shift, intermittent or complete failure to resonate can be the result of thermal shock if incompatibility exists between the package and the quartz wafer. Similar to mechanical shock design, selection of material, internal mounting structure and processes can all be optimized to enhance a resonators ability to survive thermal shock. A design’s ability to tolerate thermal shock can be tested by exposing the device to a rapid change in temperature and then comparing the resonator’s pre- and post test performance. A leak test typically follows the thermal shock test to determine if thermal shock has damaged the package seal integrity.

Military specifications, MIL-PRF-3098/H and MIL-STD-202F Method 207 TC B, set the typical standard and test conditions for thermal shock for crystals:

-65 to +125 C (in air), 30 minutes per extreme, 5 cycles

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