Research Papers

Solid State Bonding of Silver Foils to Metalized Alumina Substrates at 260°C

[+] Author and Article Information
Chu-Hsuan Sha, Pin J. Wang, Wen P. Lin, Chin C. Lee

 Electrical Engineering and Computer Science, Materials and Manufacturing Technology, University of California, Irvine, CA 92697-2660

J. Electron. Packag 133(4), 041007 (Dec 09, 2011) (3 pages) doi:10.1115/1.4005295 History: Received February 13, 2011; Revised June 28, 2011; Published December 09, 2011; Online December 09, 2011

Silver (Ag) foils are bonded to alumina substrates by a low temperature solid state bonding process. The alumina substrate is premetalized with 40 nm titanium tungsten (TiW) and 2.54 μm gold (Au). The bonding temperature is just 260 °C, compatible with the peak reflow temperature of lead-free (Pb-free) solders used in electronic industries. The Ag foil is quite soft and ductile. It can deform to mate with the Au surface on alumina. Thus, only 1000 psi of static pressure is needed to bring Ag atoms and Au atoms within atomic distance on the interface. Ag has superior physical properties. It has the highest electrical and thermal conductivities among the metals. Scanning electron microscope (SEM) images show that the Ag foil is well bonded to the Au layer on alumina. A standard shear test is performed to determine the shear strength of the bonding. The shear strength of five samples tested far exceeds the strength requirement of MIL-STD-883 G standard.

Copyright © 2011 by American Society of Mechanical Engineers
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Figure 1

Cross-sectional SEM images of Ag foil bonded to alumina substrate coated with 40 nm TiW and 2.5 μm Au at: (a) low magnification (×60) showing the Ag foil well bonded to the alumina substrate, (b) medium magnification (×2000) revealing the Ag/Au/alumina structure, and (c) high magnification (×5000) exhibiting deformation of Ag and Au to mate with each other at the Ag-Au interface and to bring the Ag atoms and Au atoms within atomic distance for achieving bonding.

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Figure 2

Force–displacement curves of five samples. The fracture force of each sample is also shown. The size of Ag foils is 6 mm × 6 mm.

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Figure 3

Optical image of sample #1 after the shear test. One-third of the Ag foil was sheared off and curled up.



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