Intermetallic Slid Bonding (Cu-Sn And Au-Sn) For Wafer Level Encapsulation
Authors: K. Wang, K.E. Aasmundtveit, and N. Hoivik, Ph.D. Company: IMST - Department of Micro and Nano Systems Technology, Vestfold University College Date Published: 10/3/2011
IWLPC (Wafer-Level Packaging)
Abstract: Intermetallic SLID (Solid Liquid Inter-Diffusion) bonding technique has shown several advantages for high density and 3-D wafer-level encapsulation and integration. Various binary intermetallics have been explored as bonding materials for the SLID technique. Among them, the binary metallic systems (Cu-Sn, Au-Sn) show rich existence of intermetallics with their melting points between high melting point metal (Cu, Au) and low melting point metal (Sn). These properties make them as ideal materials for the SLID bonding process. In this paper, we report the research progress on the SLID (Cu-Sn and Au-Sn) for wafer bonding techniques at HiVe. For the Cu-Sn wafer-level hermetic encapsulation, optimized width of the sealing frames (Cu-Sn) for encapsulation application is designed to be about 200 µm. The encapsulation SLID bonding process was performed at temperatures 150 to 300 oC. Even higher post-annealing temperature up to 350 oC has shown no negative side effects on the metallographic behaviors of the SLID bonded Cu-Sn sealing frames. For the Au-Sn system, the maximum temperature of bonding processes was extended to 350 oC. The Au-Sn SLID bonded joints are thermally stable at temperatures above 400 oC, where a single, homogeneous intermetallic phase with chemical composition of Au:Sn >5:1 (Au-rich phase) was observed in the bond line as verified by Scanning Electron Microscopy (SEM) - Energy-dispersive X-ray spectroscopy (EDX). Meanwhile, microstructure and shear strength of the SLID micro joints are also reported for the above two binary metallic systems.