Hermetically sealed on-chip packaging of MEMS devices (original) (raw)
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Challenges in the packaging of MEMS
Proceedings International Symposium on Advanced Packaging Materials. Processes, Properties and Interfaces (IEEE Cat. No.99TH8405)
The packaging of Micro-Electro-Mechanical Systems (MEMS) is a field of great importance to anyone using or manufacturing sensors, consumer products, or military applications. Currently much work has been done in the design and fabrication of MEMS devices but insufficient research and few publications have been completed on the packaging of these devices. This is despite the fact that packaging is a very large percentage of the total cost of MEMS devices. The main difference between IC packaging and MEMS packaging is that MEMS packaging is almost always application specific and greatly affected by its envirotient and packaging techniques such as die handling, die attach processes, and lid sealing. Many of these aspects are directly related to the materials used in the packaging processes. MEMS devices that are functional in wafer form can be rendered inoperable after packaging. MEMS dies must be handled only from the chip sides so features on the top surface are not damaged. This eliminates most current die pick-and-place fixtures. Die attach materials are key to MEMS packaging. Using hard die attach solders can create high stresses in the MEMS devices, which can affect their operation greatly. Lowstress epoxies can be high-outgassing, which can also affect device performance. Also, a low modulus die attach can allow the die to move during ultrasonic wirebonding resulting to low wirebond strength. Another source of residual stress is the lid sealing process. Most MEMS based sensors and devices require a hermetically sealed package. This can be done by pm~el seam welding the package lid, but at the cost of further induced stress on the die. Another issue of MEMS packaging is the media compatibility of the packaged device. MEMS unlike ICS often interface with their environment, which could be high pressure or corrosive. The main conclusion we can DISCLAIMER Portions of this document may be illegible in electronic image products. Images are produced from the best available original document. , , draw about MEMS packaging is that the package affects the performance and reliability of the MEMS devices. There is a gross lack of understanding between the package materials, induced stress, and the device performance. The material properties of these packaging materials are not well defined or understood. Modeling of these materials and processes is far from maturity. Current post-package yields are too low for commercial feasibility, and consumer operating environment reliability and compatibility are often difficult to simulate. With fu~her understanding of the materials properties and behavior of the packaging materials, MEMS applications can be fully realized and integrated into countless commercial and military applications.
Journal of Microelectromechanical Systems, 2000
A variety of microelectromechanical system devices requires encapsulation of their crucial fragile parts in a hermetically sealed cavity for reasons of protection. Hermeticity of the cavity and controllability of the ambient (gas pressure and gas composition) can be critical to the device performance. In order to minimize damage during handling, the cavity is preferably realized at the same time the device is fabricated, i.e., at wafer level. This paper reports the development of a hermetic packaging technique satisfying all the above. The method is referred to as the indent-reflowsealing (IRS) technique, which relies on a multiple-chip fluxless solder-based joining technique and seal. Key process steps are the creation of an indent in the solder, the plasma pretreatment of the bonding surfaces, the pre-bonding (or sticking) of the chips and, the closing of the indent during a low-temperature (220 C-350 C) solder reflow in a clean controlled ambient using a designated oven. As opposed to other methods, the IRS method allows a greater flexibility with respect to the choice of the sealing gas and pressure, thereby offering a very hermetic seal and compatibility with low-cost high-throughput batch fabrication techniques. Flip-chip assemblies based on SnPb (67/37) solder and Au as the top surface metallization, have been reflowed in a forming gas ambient and have next been characterized on shear strength, hermeticity, and susceptibility to thermal stresses. The method has been successfully implemented in the process flow of an electromagnetic microrelay for the realization of the cavity housing the electrical contacts. [476] Index Terms-Flip-chip bonding, fluxless solder bond, hermetically sealed cavity, MEMS packaging, metallic seal, microrelay.
Self-aligned 0-level sealing of MEMS devices by a two layer thin film reflow process
Microsystem Technologies, 2004
Many micro electromechanical systems (MEMS) require a vacuum or controlled atmosphere encapsulation in order to ensure either a good performance or an acceptable lifetime of operation. Two approaches for wafer-scale zero-level packaging exist. The most popular approach is based on wafer bonding. Alternatively, encapsulation can be done by the fabrication and sealing of perforated surface micromachined membranes.
Metal-bonded, hermetic 0-level package for MEMS
2010 12th Electronics Packaging Technology Conference, 2010
This paper presents a zero-level packaging technology for hermetic encapsulation of MEMS. The technology relies on the "chip capping" of the MEMS using a metallic bond made by means of diffusion soldering of a Cu-Sn system at a temperature of around 250°C. For this, on a "capping wafer" a sealing ring (or bond frame), composed of a double layer of Cu/Sn, is grown, and on the MEMS wafer a matching ring of a single Cu layer is made. Next, the "capping chip" is assembled onto the "MEMS die", either in a die-to-wafer (D2W) or a wafer-to-wafer (W2W) fashion. The thicknesses of the layers (Cu/Sn and Cu) and the bonding process parameters (temperature and force profile) have been optimized so as to achieve a strong, hermetic package, that remains stable up to temperatures as high as ~415°C. Leak testing, based on the "membrane deflection method", revealed that the packages are air tight and He leak tight. No noticeable change of the deflection of the cap (thinned down to 20-50 μm) was observed as a result of pressurizing the packages for 11 days under He at 30 MPa.
MEMS Resonators: Getting the Packaging Right
Microelectromechanical Systems (MEMS) resonators have been investigated for over forty years but have never delivered the high performance and low cost required of commercial oscillators. Packaging technology has been one of the primary limitations. MEMS resonators must be enclosed in very clean environments because even small amounts of surface contamination can significantly change resonator frequency. In addition, since the packaging can dominate the product cost and the applications are often cost sensitive, the packaging should be inexpensive. These requirements have now been met by SiTime' s MEMS-First TM wafer-level encapsulation and packaging technology.
IEEE Sensors Journal, 2009
This paper presents the design and implementation of Pirani vacuum gauges for the characterization of vacuum packaging of microelectromechanical systems (MEMS). Various Pirani vacuum gauges are fabricated with two different standard in-house fabrication processes, namely the silicon-on-glass (SOG) process and dissolved-wafer process (DWP). The Pirani gauges utilize meander-shaped suspended silicon coils as the heaters and two isolated silicon islands in the close proximity of the heater that function as dual-heat sinks to enhance the sensitivity and dynamic range as compared to a microbridge with a single heat sink. The gauges are designed to occupy an area of 4 mm 1.5 mm. The DWP Pirani gauge fabricated with a structural thickness of 14 m and a gap of 2 m shows a measured sensitivity of 4 2 10 4 (K/W)/Torr in a dynamic range of 10-2000 mTorr. The SOG Pirani gauge fabricated with a structural thickness of 100 m and a gap of 3 m shows a lower measured sensitivity of 3 8 10 3 (K/W)/Torr in a dynamic range of 50-5000 mTorr;