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Wafer Level Vacuum Packaging of MEMS Device by Solder Sealing

Author: SunYaNan
Tutor: AnBing
School: Huazhong University of Science and Technology
Course: Materials Engineering
Keywords: MEMS wafer level packaging vacuum packaging low-melting solder bonding vacuum gauge
CLC: TN305
Type: Master's thesis
Year: 2011
Downloads: 28
Quote: 0
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Abstract


MEMS wafer level packaging is considered to be an inevitable trend because of its advantages of small size and low-cost, which is easy to employ in the mass production of MEMS devices. Since many MEMS devices require vacuum environment, the development of vacuum packaging technology has the great significance. In this paper, we introduce a low-melting solder bonding for vacuum packaging technology and hope to satisfy the requirement of MEMS packaging.Firstly, we prepared the metal layer on a silicon wafer, which include the growth of metal transition layer and solder layer. The metal transition layer is a multi-layer that composite 100nm Ti /500nm Ni /50nm Au. The metal transition layer caused the warpage of 6-inch silicon substrate to be nearly 50μm. Evaporation and sputtering growth can not meet the requirements of the solder thickness, so we use the electroplating method to achieve solder layer. In the plating process, we have solved the plating adhesion, bubbles and edge effect problems.We achieve the wafer on the wafer vacuum packaging process by wafer bonding machine. The difficulty of packaging process technology lies in curve setting, holding the length of time will affect the final bonding. Through experiments, we found that 280℃, 25min can complete a good bonding, the air tightness and bonding strength of the samples can reach U.S. military standard MIL-STD-883 requirements.According to the needs of the vacuum testing, this paper designed a Pirani vacuum gauge with test range in the 0.1-10Torr. We Select Pt who has a large temperature coefficient of resistance, to be the thermistor vacuum gauge material. And the structural parameters is that line width of 7μm, best vacant size of 3μm, wich optimized by calculation. We use wafer-level packaging technology to realize a Pirani vacuum gauge vacuum packaging, with the test accuracy of 10mTorr.The leak rate test was performed on the wafer-level vacuum packaging samples. The He leak rate of all the samples are lower than 10‐8?atm?cc/s. It found that the larger width of the sample ring is not easy to leak in, and thus we determine that the best bonded ring width is 0.8mm. By pre-baking and integrating Ti getter film, the wafer level vacuum packaging can drop to 1torr of magnitude, and after 3 months of observation, the vacuum still maintains at that level.In this study, we accomplish a vacuum packaging technology by low-melting solder bonding, which has the potential to offer a hermetic packaging program of low-cost and small-size for MEMS devices.

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CLC: > Industrial Technology > Radio electronics, telecommunications technology > Semiconductor technology > General issues > The semiconductor device manufacturing process and equipment
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