Page 265 - An Introduction to Microelectromechanical Systems Engineering

244 Packaging and Reliability Considerations for MEMS

Quality Control and Reliability Standards

There are no standards that specifically govern the reliability of micromachined
components or MEMS in general. Instead, the MEMS industry derives its quality
and reliability guidelines from the quality standards of the systems into which
MEMS and microsystems are ultimately inserted. For example, the fabrication of
micromachined sensors used in automotive applications is frequently subject to the
quality management principles of QS 9000 standards initially set forth in 1994 by
Daimler-Chrysler, Ford, and General Motors for the entire auto industry in the
United States. The QS 9000 standard is itself an evolution of another quality man-
agement standard, ISO 9001, which was established by the International Organiza-
®
tion for Standardization of Geneva, Switzerland. Similarly, Telcordia Technologies
manages a set of quality and reliability standards specific to products and equipment
for the telecommunications industry. Table 8.7 lists a number of standards widely
used in industries and applications that have adopted MEMS and microsystems
technology.
These standards differ vastly in their impact on the manufacturers of
micromachined components. The ISO 9000 series and QS 9000 standards address
quality management principles such as methods for process control, documenta-
tion, and uniform procedures, but they do not specify particular tests or reliability
requirements. These standards leave the details of the qualification tests and
reliability specifications to the manufacturer, as long as they are well documented
and follow predescribed quality management principles. The typical result of the
ISO and QS standards is a manufacturing operation with clear controls over
its design and manufacturing processes. Mature companies often seek certifica-
tion by third parties specialized in auditing and reviewing quality management
systems.
Unlike the ISO 9000 and QS 9000 standards, the Telcordia, IEEE, and MIL
standards detail specific environmental and operational tests for qualification and
reliability. These tests have two purposes. The first one is to evaluate the product’s
performance under rigorous environmental conditions, in particular, shock and
vibration, temperature, humidity, and occasionally salt spray and altitude. Shock
and vibration tests simulate situations observed during handling and shipping, or in
high-vibration environments such as portable applications. Temperature testing
validates the overall thermal design of the product. Humidity tests checks for con-
densation effects on performance and reliability, particularly as they affect corro-
sion. Salt spray (as specified in MIL-STD-810) is largely unique to marine or
military applications and is not common for most commercial applications. Alti-
tude testing is useful for evaluating high-voltage insulation because low pressure
induces chemical changes in the insulating material.
The second purpose is to precipitate a failure of the product by stressing it under
the effect of carefully applied operational and environmental conditions over
extended durations. These tests include humidity and temperature cycling, thermal
shock, operation in damp heat, mechanical stressing, and burn-in—collectively, they
form the basis of accelerated life testing and they are casually referred to as “shake
and bake.” Burn-in, specified under MIL-STD-883, is common in the reliability test-
ing of electronic components and seeks to detect latent defects that will result
in infant mortality (failures that occur at a very early stage). During burn-in,