The “Sandwich” Structure Packaging Technology Research Of A MEMS Accelerometer

With the astonishing development of MEMS(Micro-Electronic-Mechanical Systems), MEMS packaging technology is getting more and more attention. The development of packaging technology is restrained by various factors, such as materials, temperature, strength, air tightness, the structure of packaging device or chip, cost, and so on. This thesis was aimed at the packaging of MEMS accelerometer(silicon). The packaging requirements were presented. The thesis achieved the packaging of the MEMS accelerometer by groping the processing technology.Based on the characteristic of the suspension structure of the MEMS accelerometer, its’ detection principle was introduced and the packaging requirements were analized by Ansoft Maxwell software. The packaging requirements should satisfy that the translation should be less than 100μm, the rotating should be less than 1mrad, and the distance between the suspension die and top cap should be around 20±5μm. The simulation also demonstrated that the distance between the suspension die and top cap presents as the key point of MEMS accelerometer result In considerion of compatibility glass frit bonding was employed between suspension structure and bottom cap and solder bonding was used tween suspension structure and top cap.Bottom-up packaging method was used in our MEMS packaging. This thesis introduced the processing technology about the lower cover and upper cover which were bonded with the spring vibrator structure respective in 375℃@30min and 280℃@15min. In addition, the packaging alignment accuracy and the capacity spacing were carefully controlled. In order to realize the objectives, the specialized alignment fixture was designed. In order to achieve the target distance, the feeler gauge and moderate fouce were adopted. This thesis finally realized the package target requirements.The bonding strength was tested by tensile test. The experimental results showed that the solder bonding strength reached 6MPa and hermetic seal had been achieved. The calibration test indicated, when the capacity spacing descended from about 90μm down to 20μm, the capacity sensitivity improved from the 0.5V/g to the 120V/g. This result also illustrated a careful control during package can lead a high sensiticity.