Conference Paper

Transfer of metal MEMS packages using a wafer-level solder sacrificial layer

Center for Wireless Integrated Microsyst. (WIMS), Michigan Univ., Ann Arbor, MI, USA
DOI: 10.1109/MEMSYS.2005.1453997 Conference: Micro Electro Mechanical Systems, 2005. MEMS 2005. 18th IEEE International Conference on
Source: IEEE Xplore


This paper presents a modular, low profile, wafer-level encapsulation technology for 0-level MEMS packaging. Electroplated caps are formed on a carrier wafer then simultaneously transferred and bonded to a device wafer by a novel solder transfer method and transient liquid phase (TLP) bonding technology. The solder transfer method is enabled by the dewetting of the solder transfer layer from the carrier wafer, and TLP bonding of the cap to the device wafer during bonding. The nickel-tin TLP bond and transfer cycle has a maximum temperature of 300 °C and lasts about 2.5 hours. This approach has been demonstrated with nickel caps 5 microns thick, ranging in size from 200 μm 1 mm. They were transferred with a lead-tin transfer solder layer and bonded with nickel-tin TLP bonding with greater than 99% transfer yield across the wafer.

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    • "Thus, it is critical that the membrane forms a strong bond to the target wafer and is easily separated from the carrier wafer. Although transfer-bonding and detachment processes are well-established for the transfer of hard/stiff (high Young's modulus) materials [12], [14], [15], [17], [23]–[29], [31]–[34], most hard/stiff materials are not appropriate for some applications , including microfluidics and bioMEMS. Instead, soft/flexible materials (low Young's modulus), mostly polymers , are widely used in these applications because they are more flexible, less fragile, optically transparent, inexpensive, and generally easier to fabricate and they require a lower processing temperature. "
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    ABSTRACT: This paper reports a wafer-level transfer technique for forming thin, flexible, and freestanding parylene membranes. Parylene thin films (~1.3 mum) have been successfully transferred from one wafer to another to form a freestanding membrane encapsulating over wide and shallow cavities (< 5 mum deep and 2000 times 2000 mum<sup>2</sup> square) with fine alignment (< 3.0 mum) and 87% yield. Transferred membranes may be a composite of parylene/metal/parylene, contain through-hole patterns of diverse size (5 times 5 ~ 2000 times 2000 mum<sup>2</sup>), have mild tension (1.14 MPa), and remain freestanding and flat through various standard post-transfer microfabrication processes such as photolithography, evaporation, and wet etching. They also provide excellent sealing against pressure of up to 20 kPa and long-term stability over repeated deflection. This paper focuses on two areas: (1) the study of issues involving optimum transfer conditions, minimum achievable gap between transferred membranes and device wafers, patterned-film and composite-layer transfer, and aligned transfer; and (2) the characterization of the post-transfer membrane properties, including stress/tension, sealing capability, effects of post-transfer processing, and long-term stability after a repeated deflection.
    Preview · Article · Jan 2008 · Journal of Microelectromechanical Systems
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    ABSTRACT: This paper explores the use of transient liquid phase bonding for microsystem packaging applications. Two types of bonds are demonstrated: a thin-film evaporated indium-gold bond and an electroplated nickel-tin bond. Both bonds are formed at 300°C for about 1.5 hours in a conventional wafer bonder. The wafers were heated to over 400 °C for more than an hour after bonding without any signs of bond degradation. The indium-gold bond demonstrated good electrical contact, but poor permeability performance. However, the nickel-tin bond was void free and sealed cavities with bond ring widths as little as 50 μm. The cross section of the nickel-tin TLP bond was analyzed with EDAX software to verify the formation of intermetallic compounds.
    No preview · Conference Paper · Jul 2005
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    ABSTRACT: The stability of packages to protect a MEMS device against molding conditions is simulated and experimentally verified. A finite element method is used to predict the displacement of the cover of the package under influence of molding temperature and pressure. The model is verified using all organic packages of two different materials: ConforMask of Rohm-Haas and TMMF of Tokyo Ohka Kogyo Co. Ltd. The packages are made on wafer scale with a simple two layer dry film process. The process is inexpensive and compatible with CMOS processing. The experimental results were in good agreement with the modeling: the TMMF package (with relatively high Young modulus) withstands the molding pressure.
    No preview · Conference Paper · Jul 2007