Carrier-Level Packaging and Reliability of a MEMS-Based Safety and Arming Device
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Carrier-Level Packaging and Reliability of a MEMS-Based Safety and Arming Device Michael Deeds; [email protected] (Indian Head Naval Surface Warfare Center) Kevin Cochran (Indian Head Naval Surface Warfare Center) Rajesh Swaminathan (University of Maryland, CALCE) Peter Sandborn (University of Maryland, CALCE) ABSTRACT Packaging of MEMS devices introduces new challenges to the package architecture. MEMS systems include interfaces, processes, and materials foreign to the IC packaging industry. To build reliable MEMS systems, failure modes must be identified and understood. In addition, measurement techniques must be developed to interrogate critical aspects of the package. The present work addresses the architecture of the carrier-level packaging for a MEMS-based Safety and Arming device (S&A). The impact of moisture on packaged MEMS systems and test structures are investigated through an environmental conditioning program that includes thermal cycling and accelerated aging. MEMS switches are packaged in hermetic, non-hermetic, and ventilated configurations to facilitate in-situ monitoring of device health. A MEMS humidity sensor is included in these packages to allow interrogation of package environment characteristics. Mechanical MEMS test structures are put through the same environmental conditions as the MEMS switches. These structures provide additional data on the failure modes of the packaged switches. Push test structures provide cumulative data on friction, stiction, and material properties and dog bone structures isolate material property influences. KEY WORDS: MEMS, packaging, reliability, LIGA, DRIE, surface micromachining, bulk micromachining, environmental testing, hermetic, S&A INTRODUCTION In recent years an assortment of innovative MEMS devices have been demonstrated. Many of these devices exist solely in clean rooms or are one of a kind. The realization or commercialization of MEMS devices relies on packaging to transform MEMS devices to MEMS systems. To produce a reliable, cost effective system, packaging must be considered early in the design cycle. The device drives the functional requirements of the package. A device that is not designed for packaging can put enormous and unnecessary demands on the package (functional, performance and economic). MEMS packaging can build upon IC packaging, but significant differences in the package requirements necessitate new designs, processes, and evaluation techniques [1]. Perhaps the most striking characteristic of MEMS systems is that they react to and influence the external environment. In addition, the mechanical interaction between MEMS structures and the fact that moving structures exist inside the package require that additional issues, such as stiction, be addressed. Passivation techniques, which have greatly enhanced the reliability of IC packages, are not directly applicable to MEMS devices due to the relatively large-scale motion of its components. Finally, the introduction of new materials and processes on the chip introduces new failure modes a
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