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76 MEMS and Microstructures in Aerospace Applications

TABLE 4.2
Cleanliness Requirements

Facility Type Cleanliness Requirements in Parts per Million
Mechanical manufacturing Not controlled
Electronic assembly 10,000
Electromechanical assembly 100
Inertial instrument 100
Optical assembly 100
Spacecraft assembly and test 100

NASA-STD-8739.7 ESD-control requirements are based on the requirements found
in MIL-STD-1686, Electrostatic Discharge Control Program for Protection of
Electrical and Electronic Parts, Assemblies and Equipment.
Manufacturing facilities consist of mechanical manufacturing, electronic manu-
facturing, spacecraft assembly and test, and special functions. Standard machine
shops and mechanical assembly are part of the mechanical manufacturing facilities.
In addition, plating and chemical treatment houses, adhesive bonding, and elevated
treatment vendors are included. Aerospace facilities normally have operations
performed under clean area conditions. In general, mechanical manufacturing
steps are not performed in clean controlled areas. Certain assemblies such as
electromechanical and optical components do need controlled clean rooms. Table
4.2 shows the different cleanliness requirements imposed in terms of particles per
unit volume as defined in FED-STD-209. Cleanliness requirements are measured in
particles (0.5 mm or larger) per cubic foot. Electronic part manufacturing facilities
also require clean room environments for parts prior to sealing. Assembly of parts
into the components and higher levels are normally performed under clean room (or
area) influence of space environmental factors and NASA EEE parts selection and
application conditions also. Assembly of spacecraft and test operations are often
performed in large hangar bays. Depending on the particular instrument, special
contamination controls may be required with optical equipment. Payload instru-
ments that require cryogenic temperatures, RF isolation, or the absence of magnetic
fields also require special handling.

4.4 SPACE MISSION-SPECIFIC ENVIRONMENTAL CONCERNS
The environmental concerns of the actual system mission are unique compared with
those related to the test, prelaunch, and the launch environments. For instance,
extreme vibrations and shock are not as prevalent during the mission as during test
and take-off. On the other hand, radiation is definitely a major concern for systems
operating in the mission environment, but there is little concern with radiation until
the system leaves the Earth’s atmosphere. The five mission-environmental factors

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