Low-pressure solid-state bonding technology using fine-grained silver foils for high-temperature electronics

Low-pressure solid-state bonding technology using fine-grained silver foils for high-temperature... A solid-state bonding technique using fine-grained silver (Ag) foils is presented. The Ag foils are manufactured using many runs of cold rolling and subsequent annealing processes to achieve the favorable microstructure. X-ray diffraction and pole figure measurement are performed to examine the crystal structure and grain orientations. Si chips are bonded to bare Cu substrates using the Ag foil as the bonding medium at 300 °C in 0.1 torr vacuum assisted by 6.9 MPa static pressure, which is much lower than that used in conventional thermal compression bonding. Cross sections prepared by focus ion beam show clear bonding interfaces with only a few voids smaller than 100 nm. The bonded structures do not crack after cooling down to room temperature, indicating that the ductile Ag layer is able to manage the strain induced by the large coefficient of thermal expansion mismatch between Si and Cu. The average shear strength of as-bonded samples is 29 MPa. High-temperature storage tests are conducted, and slight increase in strength can be observed after 300 °C aging. Fracture analyses show that the breakage occurs within the Ag foil rather than on the bonding interface. Transmission electron microscopy and energy-dispersive spectroscopy (TEM/EDX) are conducted for Ag/Cu interface after 200-h aging, and the result shows that slight diffusion proceeds during the aging. Since Ag has the highest electrical and thermal conductivities among metals, therefore the bonded structures reported in this paper probably represent the best possible design for high-temperature and high-power electronic packaging applications. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal of Materials Science Springer Journals

Low-pressure solid-state bonding technology using fine-grained silver foils for high-temperature electronics

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Publisher
Springer US
Copyright
Copyright © 2017 by Springer Science+Business Media, LLC
Subject
Materials Science; Materials Science, general; Characterization and Evaluation of Materials; Polymer Sciences; Continuum Mechanics and Mechanics of Materials; Crystallography and Scattering Methods; Classical Mechanics
ISSN
0022-2461
eISSN
1573-4803
D.O.I.
10.1007/s10853-017-1689-y
Publisher site
See Article on Publisher Site

Abstract

A solid-state bonding technique using fine-grained silver (Ag) foils is presented. The Ag foils are manufactured using many runs of cold rolling and subsequent annealing processes to achieve the favorable microstructure. X-ray diffraction and pole figure measurement are performed to examine the crystal structure and grain orientations. Si chips are bonded to bare Cu substrates using the Ag foil as the bonding medium at 300 °C in 0.1 torr vacuum assisted by 6.9 MPa static pressure, which is much lower than that used in conventional thermal compression bonding. Cross sections prepared by focus ion beam show clear bonding interfaces with only a few voids smaller than 100 nm. The bonded structures do not crack after cooling down to room temperature, indicating that the ductile Ag layer is able to manage the strain induced by the large coefficient of thermal expansion mismatch between Si and Cu. The average shear strength of as-bonded samples is 29 MPa. High-temperature storage tests are conducted, and slight increase in strength can be observed after 300 °C aging. Fracture analyses show that the breakage occurs within the Ag foil rather than on the bonding interface. Transmission electron microscopy and energy-dispersive spectroscopy (TEM/EDX) are conducted for Ag/Cu interface after 200-h aging, and the result shows that slight diffusion proceeds during the aging. Since Ag has the highest electrical and thermal conductivities among metals, therefore the bonded structures reported in this paper probably represent the best possible design for high-temperature and high-power electronic packaging applications.

Journal

Journal of Materials ScienceSpringer Journals

Published: Oct 12, 2017

References

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