Packaging of MEMS devices is more complex than that of IC devices because in some cases it needs to provide protection from the environment while in other cases it needs to allow access to the environment to measure or affect the desired physical or chemical parameters.10 MEMs have to eventually connect to the outside world while withstanding the extreme thermal and environmental conditions in which they must operate. Care should be taken for environmental protection, electrical signal conduit, mechanical support, and thermal management paths.
Packaging of MEMs is very complex. A package must also provide communication links through optimum interconnect scheme, remove heat through suitable selection of heat sinks, and provide robustness in handling and testing. Packaging includes the use of hermetic packages and vacuum systems.10 (Getters are reactive materials used for removing traces of gas from vacuum systems.11)
Reliability is important in the aerospace industry where mission success can be deterred by a single small failure. NASA has established the reliability assurance group that supports the MEMs technology group as well as other groups to research reliability concerns. Reliability of MEMs depends on the materials used, sharp corners, adhesion issues, bonding, poor process capability, etc. Reliability data along with standardization and statistical analysis should be done to gain confidence in the reliability of MEMs.10
Some of the more common failure modes associated with MEMs are: Failure by Stiction and Wear, Delamination, Environmentally Induced Failures, Cyclic Mechanical Fatigue, Dampening Effect, and Packaging. Remember that traditional mechanical analysis may not directly apply to MEMs due to the large surface area to volume ratio.
Reliability tests such as those shown in “Evaluation of Thermo-Mechanical Stability of COTS Dual-Axis MEMS Accelerometers for Space Applications” in the Instructional Materials section provides an example of MEMs reliability testing.
MEMs compatibility issues with existing hardware, processes, bulk micromachining, clean room standards, etc., can all become an issue. Care should be taken when MEMs are to be designed, fabricated, and introduced into existing systems.
Due to the recent explosion in MEMs, standards that are associated with these products are evolving. The emergence of standardized material characterizations, the presence of reliable material properties, processing effects and variables during design and manufacturing will be key factors in MEMs standardization.13 See "MEMs Standardization" on this module for more information.
Integration into the outside world or existing systems poses problems such as reliability, functionality, durability, and compatibility. All aspects of integration should be considered before incorporating MEMs into existing systems.