Special Section on Theory and Practice of MEMS/NEMS/MOEMS, RF MEMS, and BioMEMS

Improved MEMS structure for stress-free flip-chip packaging

[+] Author Affiliations
Jinxing Liang

Waseda University, Graduate School of Information, Production, and Systems, Kitakyushu 808-0135, Japan and Sakamoto Electric Manufacturing Co., Ltd., Fukuoka 811-0202, Japan

Toshitsugu Ueda

Waseda University, Graduate School of Information, Production, and Systems, Kitakyushu 808-0135, Japan

J. Micro/Nanolith. MEMS MOEMS. 8(2), 021118 (May 14, 2009). doi:10.1117/1.3134087
History: Received August 15, 2008; Revised February 26, 2009; Accepted April 01, 2009; Published May 14, 2009
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We present a new method for stress-free microelectromechanical systems (MEMS) flip-chip packaging. Residual stress, which is mainly generated during the reflow process, is a notorious problem in flip-chip packaging. The residual stress reduces the bump fatigue life and device performance owing to the deformation. Underfill encapsulation is a common way to reduce the residual stress in a flip-chip integrated circuit (IC) packaging process. However, it cannot be applied to MEMS packaging because MEMS devices usually include moving microstructures. We intend to resolve this problem by improving the MEMS structure, designing spring beams to introduce electrical pads. The residual stress, which is caused by the mismatch of the coefficient of thermal expansion (CTE) between the MEMS device and the package substrate, can be absorbed through the deflection of spring beams. By using this idea, a quartz MEMS-based capacitive tilt sensor, which was bulk etched and composed of vertical comb electrodes in wafer thickness for achieving large initial capacitance, was successfully packaged. A high melting point alloy Au80Sn20 was used as the solder joint material. The thermal cycling test and sensitivity evaluation experimental results demonstrated the effectiveness of the proposed method.

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© 2009 Society of Photo-Optical Instrumentation Engineers

Citation

Jinxing Liang and Toshitsugu Ueda
"Improved MEMS structure for stress-free flip-chip packaging", J. Micro/Nanolith. MEMS MOEMS. 8(2), 021118 (May 14, 2009). ; http://dx.doi.org/10.1117/1.3134087


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