CC7 Datasheet, PDF (2/3 Pages) MICORO CRYSTAL SWITZERLAND – Parts could be over-heated and permanently damaged.

2) Recommendations for Handling of Crystals in Ceramic Packages
Introduction
A crystal, compared to other passive elements, is a relatively fragile part due to its internal construction. The crystal blank consists
of pure Silicon Dioxide in crystalline form, cut as small plate with a thickness of approximately 0.1 mm. The material is very similar
to glass. The blank itself is attached at one end with 2 small dots of conductive epoxy on two small pedestals. 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.
Precautions
• Shock and vibration - Keep the crystal from being exposed to excessive mechanical shock and vibration otherwise the
crystal blank tends to break as any other glass would do. Micro Crystal guarantees that the crystal will bear a mechanical
shock of 5000g / 0.3ms. The following special situations may generate either shock or vibration:
→ Assembly machine selection - During pick & place fast placing machines will generate shocks or vibrations when
placing small elements. It is best to place the crystal on the second populated side of a two-sided PCB as the last part,
preferably with a slow placing machine used to place complex or “odd form“ parts.
• → 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 Washing and Welding - Avoid washing or welding processes using ultrasonic energy. These processes
can damages crystals due to mechanical resonance of the crystal blank.
Thermal shocks - Avoid steep temperature gradients. It might lead to breakage of the crystal blank like it would do to
any other glass. Infrared reflow processes in general are safe.
Rework high temperature exposure - Avoid overheating the package. The package is sealed with a sealring consisting
of 80% Gold and 20% Tin. The eutectic of this alloy is at 280°C. Heating the sealring 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. Air molecules will impede (or slow)
the movement of the tines causing the frequency to drop and the resistance to rise. In addition liquid metal might attach
to the crystal blank further altering the parameters or causing a short circuit. Most of the time parts are overheated when
removed from the PCB due to problems. If parts are removed (i.e. for analysis of failure mode) with excessive heat, all
traces for root cause analysis will be lost. Therefore use the following methods for removal:
→ Use a hot air gun set at 260°C
→ Use 2 temperature controlled soldering irons, set at 250°C, from both sides of the package at the same time, remove
part with tweezers when pad solder is liquid.
3) Package description
Package Description
Package material
Lid material
Seal
Seal material
Terminal
Ceramic Al2O3, black
Ceramic Al2O3, black
Solder seal ring (preform)
Au80/Sn20
Gold (> 0.5 μm) over Ni (3 μm)
over Tungsten
Moisture Sensitivity Level (MSL)
Moisture Sensitivity Level (MSL)
IPC/JEDEC J-STD-020-C
(released July 2004)
The part is qualified and compliant to
(MSL) Level 1