Reliability of MEMS packaging: vacuum maintenance and packaging induced stress
Reliability of MEMS packaging: vacuum maintenance and packaging induced stress
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DOI：
10.1007/s00542-005-0603-8
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发表时间：
2005-10-01
影响因子：
2.1
通讯作者：
Choa, SH
中科院分区：
文献类型：
--
作者：
Choa, SH
在这项研究中。讨论了MEMS封装的主要可靠性问题，包括真空保持和封装引起的应力，并提出了提高可靠性的设计考虑。MEMS振动陀螺仪传感器的制造与阳极键合晶圆级真空封装，然后芯片键合和引线键合工艺。采用环氧模塑料（EMC）封装陀螺仪传感器。在大量工作的基础上，提出了提高真空封装可靠性的几种方法。研究了阳极真空封装的两种主要失效机理，即泄漏和放气。通过优化键合工艺，有效地减少了泄漏。通过应用Ti涂层可以最大限度地减少腔内的放气。封装诱导应力主要是由用于制造封装的材料之间的热膨胀失配引起的。在阳极键合期间，对键合的晶片产生热机械应力，该应力随着温度而增加。EMC封装也会产生封装引起的应力。为了增加结构的抗变形的鲁棒性，用半折叠弹簧代替“蟹腿”型弹簧。结果表明，采用半折叠弹簧后，频移大大减小。
In this study.. the dominant reliability issues of MEMS packaging that include vacuum maintenance and packaging induced stress, are discussed, and design considerations to improve the reliability are presented. The MEMS vibratory gyroscope sensor is fabricated with anodically bonded wafer level vacuum packaging followed by die-bonding and wire-bonding processes. The epoxy-molding compound (EMC) is applied to encapsulate the gyroscope sensor. Several methods to improve reliability of the vacuum packaging are suggested based on extensive work. The two major failure mechanisms of anodic vacuum packaging, namely leakage and outgassing are investigated. Leakage is effectively reduced by optimization of the bonding process. Outgassing inside the cavity can be minimized by application of Ti coating. Packaging induced stress is mainly caused by thermal expansion mismatch among the materials used to fabricate the package. During anodic bonding, thermo-mechanical stress is generated to the bonded wafer, which increases with temperature. The EMC encapsulation also produces package-induced stress. In order to increase robustness of the structure against deformation, a "crab-leg" type spring is replaced with a semi-folded spring. The results show that the frequency shift is greatly reduced after applying the semifolded spring.