Micro Crystal

Real Time Clock / Calendar Module

RV-8564

39/40

19.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.