Title:
Novel Bi-Layer Conformal Coating for Reliability Without Hermeticity MEMS Encapsulation
Novel Bi-Layer Conformal Coating for Reliability Without Hermeticity MEMS Encapsulation
Author(s)
Wong, C. P.
Wu, Jiali
Pike, Randy T.
Wu, Jiali
Pike, Randy T.
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Abstract
A flexible, smooth, and low profile conformal coating
was developed to accomplish the encapsulation of a microelectromechanical
system (MEMS) device that will be applied to
sense the static pressure on aircraft during real flight testing.
The encapsulant should be able to protect the MEMS device
and the multichip module (MCM) from adverse environmental
conditions, i.e., mechanical shock, temperature fluctuation, engine
fuel and oil contamination, and moisture/mobile ion permeation.
Presently, conventional packaging schemes for electronics cannot
satisfy this specific outdoor application, and a new encapsulation
combination has been designed in accord with the requirement
of reliability without hermeticity (RWOH). A bi-layer structure
was selected because of property limitations of a single material.
Pliable elastomeric silicones, are typically flexible, water repellant,
and abrasion resistant. The silicone encapsulant will be first
applied to planarize the MEMS surface and function as durable
dielectric insulation, stress-relief, and shock/vibration absorbers
over a wide humidity/temperature range. To compensate for the
deficiency of silicone on engine fuel/oil contamination, Parylene
C is to be deposited afterward. This bi-layer coating can achieve
excellent bulk properties, such as moisture and mobile ion barrier
resistance, chemical compatibility, and electrical insulation characteristics.
However, the poor adhesion of Parylene C to silicone
greatly restricts its application. To address this problem, silane
coupling agents were used as an adhesion promoter. Significant
adhesion im provement was achieved by placing an interlayer
silane coupling agent to provide interfacial bonding to the silicone
elastomeric surface and the Parylene C film. Furthermore, a possible
mechanism of adhesion enhancement will also be presented
in this study.
Index Terms— Bi-layer conformal coating, micro-electromechanical
system (MEMS), multichip module, Parylene C,
reliability without hermeticity (RWOH), silane coupling agent,
silicone elastomer.
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Date Issued
1999-07
Extent
178194 bytes
Resource Type
Text
Resource Subtype
Article