Mems Wafer-level Glass Solder Seal Process And Thermal Stress Analysis

Glass solder is printed on the wafer as sealing material. Many MEMS devices are sealed by low-temperature bonding. We can get the products with good air tightness, low cost, high bonding strength and good reliability by this way. In this paper the wafer level glass solder encapsulation technology for MEMS and thermal stress are studied by the finite element simulation and experimental methods in order to find the better packaging processes and provide reference for industrial mass production.The finite element analysis shows that the maximum thermal stress is in the outside corners of the glass solder. The thermal stress in the edges of glass solder is also high. The less thermal expansion coefficient and Young's modulus of sealing material can availably reduce thermal stress. There is only a small influence of the bond frame width of glass solder on the thermal stress. The thermal stress increases with the increase of glass solder's thickness and bonding temperature. By the finite element simulation and experimental research about screen printing, pre-sintering and bonding the paper gets the better package processing parameters. The frame width of screen is 0.3mm, the pressure of rubber scraper is 40N, the separating speed of wafer and screen is 2mm/s. The pre-sintering peak temperature is 440℃with 10min. The bonding temperature is 440℃, the bonding pressure is 30KPa and the cooling rate after bonding is 10℃/min. The thickness of glass solder is 0.005mm～0.01mm. Failures occur frequently in glass solder about shear strength test.The frame width of glass solder after bonding is increased excessively. To solve this problem we etch groove to limit the frame width of glass solder after bonding and get better shape of the glass solder. The better frame width of groove is 0.4mm or 0.5mm and the deepness is 0.01mm. The thermal stress is lower with groove than that without groove. After process optimization, we carry on a series of tests to the sealed units. The qualified rate is 90% in the leakage test,85% in the thermal reliability test, and 100% in the shear strength test. The results show that we get the high performance products after process optimization.