Packaging Options for MEMS Devices
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Packaging Options
for MEMS Devices Erik Jung
Abstract Microelectromechanical systems (MEMS) devices can be delicate structures sensitive to damage from handling or environmental influences. Their functionality may furthermore depend on sealing out the environment or being in direct contact with it. Stress, thermal load, and contaminants may change their characteristics. Here, packaging technology is challenged to extend from microelectronics toward MEMS and optoelectronic MEMS (MOEMS). Today’s approaches rely on modified single-chip packages derived from the microelectronics industry, wafer-level capping to enable the device to be packaged like an integrated circuit, or highly specialized packages designed to complement the function of the MEMS device itself. Selecting the proper packaging method may tip the scale toward a product success or a product failure. Choosing the right technology, therefore, is a crucial part of the product design. Keywords: microelectromechanical systems (MEMS), microelectronics packaging and integration.
The Role of Microelectromechanical Systems Packaging Microelectromechanical systems (MEMS) packaging plays an important role within the function of MEMS devices. Besides the electrical interconnection, the package can provide mechanical protection, media separation, or coupling (e.g., pressure). It may include signal conditioning devices, ambient conditioning (getters), and test functions. The design must enable the resulting package to be manufactured and assembled at low cost while providing the required system performance. Also, highreliability requirements, particularly under harsh conditions (e.g., within an automotive system, with extreme temperature differences and an aggressive ambient) must be fulfilled in order for the product to be accepted in the market. Bringing these requirements into one function is not easy. Therefore, today’s MEMS packages are tailored to the specific device, which may not be cost-effective for all types of products. Currently, packaging relies either on using well-established package types like TO-can (transistor outline metal can), butterfly, or ceramic packages, or—applicable only to high-volume products—dedicated package development. Wafer-level packages, developed for the microelectronics industry, are also finding a niche and potential widespread
MRS BULLETIN/JANUARY 2003
use in the packaging of MEMS devices. Their use can result in a substantial cost savings, as has been true in the microelectronics industry as well. MEMS packaging comprises all types of microstructured functional devices, ranging from accelerometers and IR sensors to microfluidic biochips. Packaging strategies depend on the specific requirements of the device. For this article, we focus on the packaging of movable structures (e.g., accelerometers, pressure sensors, and scanning mirrors).
protected wafer stack is then singulated (separated into single units). Scanning mirrors require not only protection from the outer world but also access to light to fulfill their function
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