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350 MEMS and Microstructures in Aerospace Applications

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1.2 m. This work by Analog Devices, Inc. is an excellent example of the need to
tailor test plans to achieve a reliable program. An understanding of the failure
mechanisms specific to MEMS materials helps in developing and carrying out
quality assurance tests for MEMS devices in space. Tests dealing with temperature,
stiction, vibration, and shock will not be the same for all MEMS pieces, as their
size, material properties, and fragility make their failures in these aspects unique to
their experience in space. Chapter 15 discusses MEMS-specific failure modes in
greater detail.

16.2 DESIGN PRACTICES FOR THE SPACE ENVIRONMENT

To ensure a reliability-oriented design, researchers should first determine the
needed environmental resistance of the MEMS devices and its related subsystems.
The initial requirement is to define the operating environment for the equipment.
The Life Cycle Environment Profile (LCEP) is a tool used to define these require-
ments. In application, the use of de-rating and, in some cases, redundancy is also
included to assure the reliability of the design.

16.2.1 LIFE CYCLE ENVIRONMENT PROFILE
The LCEP is the starting point in tailoring application-specific tests. This analysis is
used in developing environmental design criteria consistent with the expected
operating conditions, evaluate possible effects of change in environmental condi-
tions, and provide traceability for the rationale applied in criteria selection for future
use on the same program or other programs.
The LCEP is a forecast of events and associated environmental conditions that
an item experiences from manufacturing to retirement. The life cycle includes the
phases that an item will encounter such as: handling, shipping, or storage before
use; disposition between missions (storage, standby, or transfer to and from repair
sites); geographical locations of expected deployment; and platform environments.
The environment or combination of environments the equipment will encounter at
each phase is also determined. All deployment scenarios should be described as a
baseline to identify the environments most likely to be associated with each life
cycle phase.
To develop a life cycle profile, the expected events should be described for an
item of equipment from final factory acceptance through terminal expenditure or
removal from inventory. Then identify significant natural and induced environ-
ments or combination of environments for each expected shipping, storage, and
logistic event (such as transportation, dormant storage, standby, bench handling,
and ready modes, etc.). Finally, describe environmental and stress conditions (in
narrative and statistical form) to which equipment will be subjected during the life
cycle. Data may be derived by calculation, laboratory tests, or operational meas-
urements, and estimated data should be replaced with actual values as determined.
The profile should show the number of measurements used to obtain the average
value of these stresses and design achievements as well as their variability

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