RV-8523 Datasheet, PDF (56/57 Pages) MICORO CRYSTAL SWITZERLAND – Real Time Clock

Micro Crystal
Real Time Clock / Calendar Module
RV-8523
20.HANDLING PRECAUTIONS FOR CRYSTALS OR MODULES WITH EMBEDDED
CRYSTALS
The built-in tuning-fork crystal consists of pure Silicon Dioxide in crystalline form. The cavity inside the package is
evacuated and hermetically sealed in order for the crystal blank to function undisturbed from air molecules,
humidity and other influences.
Shock and vibration:
Keep the crystal / module from being exposed to excessive mechanical shock and vibration. Micro Crystal
guarantees that the crystal / module will bear a mechanical shock of 5000g / 0.3 ms.
The following special situations may generate either shock or vibration:
Multiple PCB panels - Usually at the end of the pick & place process the single PCBs are cut out with a router.
These machines sometimes generate vibrations on the PCB that have a fundamental or harmonic frequency
close to 32.768 kHz. This might cause breakage of crystal blanks due to resonance. Router speed should be
adjusted to avoid resonant vibration.
Ultrasonic cleaning - Avoid cleaning processes using ultrasonic energy. These processes can damages
crystals due to mechanical resonance of the crystal blank.
Overheating, rework high temperature exposure:
Avoid overheating the package. The package is sealed with a seal ring consisting of 80% Gold and 20% Tin. The
eutectic melting temperature of this alloy is at 280°C. Heating the seal ring up to >280°C will cause melting of the
metal seal which then, due to the vacuum, is sucked into the cavity forming an air duct. This happens when using
hot-air-gun set at temperatures >300°C.
Use the following methods for rework:
• Use a hot-air- gun set at 270°C.
• Use 2 temperature controlled soldering irons, set at 270°C, with special-tips to contact all solder-joints from
both sides of the package at the same time, remove part with tweezers when pad solder is liquid.
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