Conventional fusion bonding technology requires high temperatures, thus it may generate thermal stress, due to different coefficient of thermal expansion in the bonded materials, and result in wafer warpage or even cracks. Anodic bonding technology reduces the temperature effect to the bonded structure, but the high electrical field involved in the bonding process may seriously affect electrical circuits in the bonded devices. Moreover, bonding quality is highly dependent on the roughness and cleanness of the silicon wafer surface. In this paper, we present an easy wafer level packaging process employing SU8 contact printing, which doesn’t involve high temperature or electrical field and is relatively insensitive to the wafer surface condition. In this study, SU8 was firstly spin-coated on an AF-45 glass wafer, patterned with UV light exposure to define the packaging spacers and then baked at 95°C. After SU8 development, another layer of unbaked SU8, which is much thinner than the thickness of the patterned SU8, was printed on the surface of those packaging spacer with a roller. This glass wafer serves as the capping wafer and is finally aligned and pressed onto the bottom silicon substrate, which contains MEMS devices and their driving circuits, at certain pressure. The following UV cure and baking steps fully cross-linked the printed SU8 to form the bonding. In this study, different thickness of the patterned SU8 on the glass wafer (from ~40 to ~80 μm) and final baking temperature (from 95 to 135°C) were evaluated and tested. After wafer dicing, tensile bonding strength test was carried out and showed that the bonding strength of this SU8 printing technique is up to ~20 MPa. The bonding technique presented in this paper is especially suitable for temperature sensitive devices packaging. In this study, 3 different SU-8 thicknesses (~40, ~60 and ~80 μm) were tested with the spin speed varying from 1200 to 1800 rpm. After patterning of the SU-8 spacers, the same SU-8 type was used as the ‘ink’ for the contact printing. Using a roller, these spacers were covered with a thin layer of SU-8 (see Fig. 1(c)). The printed glass wafer was then aligned and pressed onto the silicon wafer with microstructures. Different final baking temperatures, or the bonding temperature, were evaluated.

Low Temperature Wafer Level Packaging of RF-MEMS Using SU-8 Contact Printing

Iannacci, Jacopo;
2006

Abstract

Conventional fusion bonding technology requires high temperatures, thus it may generate thermal stress, due to different coefficient of thermal expansion in the bonded materials, and result in wafer warpage or even cracks. Anodic bonding technology reduces the temperature effect to the bonded structure, but the high electrical field involved in the bonding process may seriously affect electrical circuits in the bonded devices. Moreover, bonding quality is highly dependent on the roughness and cleanness of the silicon wafer surface. In this paper, we present an easy wafer level packaging process employing SU8 contact printing, which doesn’t involve high temperature or electrical field and is relatively insensitive to the wafer surface condition. In this study, SU8 was firstly spin-coated on an AF-45 glass wafer, patterned with UV light exposure to define the packaging spacers and then baked at 95°C. After SU8 development, another layer of unbaked SU8, which is much thinner than the thickness of the patterned SU8, was printed on the surface of those packaging spacer with a roller. This glass wafer serves as the capping wafer and is finally aligned and pressed onto the bottom silicon substrate, which contains MEMS devices and their driving circuits, at certain pressure. The following UV cure and baking steps fully cross-linked the printed SU8 to form the bonding. In this study, different thickness of the patterned SU8 on the glass wafer (from ~40 to ~80 μm) and final baking temperature (from 95 to 135°C) were evaluated and tested. After wafer dicing, tensile bonding strength test was carried out and showed that the bonding strength of this SU8 printing technique is up to ~20 MPa. The bonding technique presented in this paper is especially suitable for temperature sensitive devices packaging. In this study, 3 different SU-8 thicknesses (~40, ~60 and ~80 μm) were tested with the spin speed varying from 1200 to 1800 rpm. After patterning of the SU-8 spacers, the same SU-8 type was used as the ‘ink’ for the contact printing. Using a roller, these spacers were covered with a thin layer of SU-8 (see Fig. 1(c)). The printed glass wafer was then aligned and pressed onto the silicon wafer with microstructures. Different final baking temperatures, or the bonding temperature, were evaluated.
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11582/300142
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