|A change in the frequency
and/or the resistance of a quartz crystal unit with the passage of time.
Attributable to the relaxation of strain in the resonator and to mass transfer
mechanisms within the resonator package due to contamination. Other factors
include drive level, ambient temperature, wire fatigue, and frictional wear.
These factors are minimized by design considerations, including the mechanical
design of the mounting structure, and by the design and control of certain
manufacturing processes. Most of the aging effects of a crystal occur within
the first 60 days of operation leading to slower aging characteristics through
the first year. The integrity of the hermetic characteristics of the crystal
package are a major factor in determining how well a crystal will age.