Study On The Electroplating Tin Process For Packaging Of The MEMS Accelerometer

MEMS devices have been widely studied in the world due to their advantages of small size, light weight, easy integration and low power consumption. However, many MEMS devices have their own special packaging requirements, and the packaging for MEMS devices faces enormous challenges. The research on the packaging technology for MEMS device is relatively backward, which seriously affects the process of the commercialization of the prodcuts. In this thesis, we have carried on the packaging requirement analysis for the MEMS acceleration sensor based on area changeable capacitive displacement sensing. In order to detect the capacitance signal of the MEMS acceleromoter, and improve sensitivity of the capacitance signal, realize electrical signal transmission from inside cavity to outside world. According to the ultimate fabrication goal, we need fabricate glass upper die that include the structure of electrode arrays of the capacitor, and complete the encapsulation with the middle silicon wafer including the spring-mass structure and the capacitor array structure.Through investigation and analysis of the packaging ways for MEMS accelerometer, we implement the packaging by electroplating tin solder bumps in this thesis. By groping for the electroplating process, the thickness uniformity and density of the solder bump has been optimized, and the thickness uniformity of the solder can be controlled within 5%. We have designed and fabricated the special fixture for electroplating process, and successfully solved the leakage problem in the electroplating process and improved the efficiency and stability of the electroplating. We have built an experiment platform to control the solder bump packaging thickness uniformity by loading the upper glass through 3 supporting point. We focus on finding solutions to etching sacrificial seed layers post electroplating. Dry etching is widely used, but it can potentially damage the existed function structures due to ion bombardment, which will lead to technological compatibility problems. Wet etching is simple, but etchants to the seed layer usually react with tin solder bump in priority. We have proposed a novel process to remove the under bump metallurgy by introducing of a sacrificial aluminium film. Eventually, we have successfully solved the problem. The experimental results show that the process has good compatibility with the MEMS device, and can be widely used in tin solder bump process with a feature size more than 100 microns.The thickness of the packaging ring is controlled to be ?33 ?4? ?m. The solder bonding strengh is?2.0?0.4?MPa. Test results showed that the process satisfy the packaging requirements for the MEMS accelerometer.