Gold-tin eutectic bonding for hermetic packaging of MEMS devices with vertical feedthroughs


Torunbalci M. M. , Demir E. C. , Donmez I., Alper S. E. , Akın T.

13th IEEE SENSORS Conference, SENSORS 2014, Valencia, Spain, 2 - 05 November 2014, pp.2187-2190 identifier identifier

  • Publication Type: Conference Paper / Full Text
  • Doi Number: 10.1109/icsens.2014.6985473
  • City: Valencia
  • Country: Spain
  • Page Numbers: pp.2187-2190
  • Keywords: Wafer Level Hermetic Packaging, Au-Sn Eutectic Bonding, Vertical Feedthroughs

Abstract

This paper presents a new method for wafer-level hermetic encapsulation of MEMS devices using low-temperature (280 to 300 degrees C) Au-Sn eutectic bonding applied to the recently developed advanced MEMS (A-MEMS) process of the METU-MEMS Research Center, which uses an SOI cap wafer with vertical feedthroughs that does not need any complex via-refill or trench-refill process steps. The Au-Sn eutectic bonding process is achieved at 300 degrees C with a bond pressure of 2 MPa by using a sealing alloy thickness less than 1.5 mu m. The package pressure is characterized to be around 250 mTorr, without any getter activation. The remelting temperature of the Au-Sn bonding interface is measured by using differential scanning calorimetry (DSC) analysis and found to be around 280 degrees C, verifying that the bonding is achieved at the desired eutectic composition (80% Au and 20% Sn), also confirmed by the energy dispersive X-ray spectroscopy (EDS) analysis. The shear strengths of several packages are measured to be above 20 MPa, indicating a mechanically-strong bonding. The robustness of the packages is also tested by subjecting them to high temperature storage at 200 degrees C for 24 hours, and no degradation is observed in the hermeticity of the packages at the end of this period.