High hermetic performance of glass frit for MEMS package

The wafer level hermetic packaging is a method of sealing micro-devices containing movable parts with a capping wafer in vacuum. The capping wafer is etched to form a cavity which will cover over the MEMS devices and the process is carried out at the wafer level before the device wafer is diced. Glass frit bonding is described as the most leak proof and robust sealing mechanism of all available methods. In this approach, the glass frit is stencil printed on the wafer and the wafer is thermo compression bonded to the subject device wafer under tightly controlled pressure in vacuum with 1000mBar of force at 440°C temperature for 10 minutes. This bath processing method gives cost advantages due to the process time reduction and hermetic seal over the wafer level packaging (WLP). The widths of seal ring were singulated to 4 different dimensions (200, 150, 100 and 50um) for leak rate test. The performance of this 0.2*0.2cm2 package shows lower leak rate even at 50um width seal ring. These devices also pass the level 3 reliability test and keep high hermetic performance (lower than 7*10-9 atm*cc/s).