Anodic bonding between LTCC wafer and Si wafer with Sn-Cu-based electrical connection

This paper describes electrical connection simultaneously established with anodic bonding between an LTCC (low‐temperature co‐fired ceramic) wafer and a Si wafer. The metal bonding pads were composed of Sn on Cu. Sn melts during anodic bonding, absorbing the height margin of the bonding pads to ensure entire contact between the LTCC and Si surfaces. This study first investigated formic acid vapor pretreatment before anodic bonding to remove Sn surface oxide on the bonding pads. The removal of the surface oxide proceeds at a process temperature of 150 °C or higher. By pretreatment at 250 °C, the Sn surface is smoothed due to the reflow effect, but the metal multilayer structure of the bonding pads does not significantly change after 5 minutes of pretreatment. The bonded metal pad was almost entirely uniform in both structure and composition throughout the thickness. The composition of the bonded pads was approximately Sn:Cu = 1:1 in atomic ratio, and might have a remelting temperature of ca. 415 °C, which is much higher than the solder reflow temperature in the device mounting process. © 2012 Wiley Periodicals, Inc. Electron Comm Jpn, 95(4): 49–56, 2012; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/ecj.10401