An investigation of capped glass frit sealed mems devices in contemporary accelerometers

Hermetic sealing is a stringent design constraint for contemporary MEMS devices such as accelerometers, gyroscopes, resonators, IR bolometers and RF devices. MEMS capping using glass frit seals is the most commonly used technique in practice. In this paper an investigation of glass frit sealed MEMS capping techniques in commercially-available inertial accelerometer sensors is reported. Destructive testing was the primary methodology used to characterize the accelerometer parts. X-ray analysis was used to identify the internal structure of the accelerometers. Microscopy and SEM analysis were then used to accurately measure the seal dimensions and the proportionate relationship with overall dimensions. EDX analysis of the glass frit was conducted to establish its composition. As a further investigative step, test samples were chemically decapped and analyzed. It was observed that four of the five samples maximized cap footprint area over the base silicon of the part. All samples featured glass frit voiding, and examples of both insufficient and excessive glass frit coverage were identified. The results of the investigation were compared for common themes: cap structure, glass frit seal, glass frit voiding and cap singulation techniques. This identified points of similarity in the industrial assembly processes. A clearer understanding of industry practice in accelerometer packaging was obtained particularly in cap structure; glass frit defects and glass frit composition.