World Journal Of Engineering
METAL-METAL BONDING PROCESS
USING COPPER NANOPARTICLES
Yoshio Kobayashi1, Satoshi Ishida1, Kazuaki Ihara1, Yusuke Yasuda2 and Toshiaki Morita2
1
Department of Biomolecular Functional Engineering, College of Engineering, Ibaraki University,
4-12-1 Naka-narusawa-cho, Hitachi, Ibaraki 316-8511, Japan
2
Materials Research Laboratory, Hitachi Ltd., 7-1-1 Omika-cho, Hitachi, Ibaraki 319-1292, Japan
room temperature. The reaction time was 3 h.
A dark-red and muddy colloid solution was
produced.
Polypyrrole
(PPy)-coating
for
the
Cu
nanoparticles was performed by polymerization
of pyrrole (Py) in the presence of the Cu
nanoparticles. Ten μL of the HCl solution was
added to 10 mL of the Cu colloid. Then, 10 ml
of 0.17 M Py solution and 0.32 mL of 12.4 M
H2 O2 was added to the colloid in turn. The
reaction time for the PPy-coating was 24 h. A
dark-red colloid solution was also produced.
Introduction
A bonding technique is quite required to connect
solid state materials in various fields such as
civil engineering, construction industry and
electronics [1]. In bonding of metallic materials,
a process of annealing and pressurizing is
usually used. This process provides diffusion
of their components on their interface, and
consequently the metallic materials are bonded.
The bonding may be helped by inserting metallic
powders between the metallic materials, because
the metallic powders melt and diffuse into the
metallic materials during pressed under
annealing.
Among metallic powders, Cu
particles are promising materials for the metallic
bonding, because of low cost. However, they
face at a problem of easy oxidation in air [2,3],
which spoils bonding properties. Covering of
the particles with surfactants is a candidate as a
technique to solve the problem [4,5]. Coating
of the particles with solid shells can also be
another approach for the stabilization, because
physical barrier of coating materials will prevent
the particles from contacting oxygen molecules.
We have recently developed [6] a technique for
polymer-coating of metallic Cu nanoparticles in
an aqueous solution. The polymer-coated Cu
nanoparticles were chemically stable even in air.
The present work compared the polymer-coated
Cu nanoparticles with uncoated Cu nanoparticles
on metal-metal bonding property.
Apparatus and Procedures
The particles were characterized by transmission
electron microscopy (TEM) and X-ray
diffractiometry (XRD). Samples for TEM were
prepared by dropping and evaporating the
particle colloid on a collodion-coated copper
grid. For preparing powder samples for the
XRD measurements, supernatant of the particle
colloid was removed with decantation, and then
residue of the colloid was dried at room
temperature for 24 h in vacuum.
Bonding property was investigated with a set-up
shown in Fig. 1. The powder samples obtained
in the same procedure as used for the XRD
measurements were sandwiched between a large
Cu disc (diameter: 10 mm, thickness: 5 mm) and
a small Cu disc (diameter: 5 mm, thickness: 2.5
mm), and pressed under annealing at
temperatures of 250-400o C in air or H2 gas at 1.2
MPa for 5 min. After the bonding, shear
Experimental
Preparation
Colloids of Cu nanoparticles were prepared by
mixing of CuCl 2 and hydrazine.
Freshly
prepared 10 mL of 2 M hydrazine aqueous
solution containing 0.0005 M citric acid and
0.005 M cetyltrimethylammonium bromide
(CTAB) was added to 10 mL of 0.02 M CuCl 2
aqueous solution containing 0.0005 M citric acid
and 0.005 M CTAB under vigorous stirring at
Fig. 1 Sketch of procedures for bonding
discs and measuring shear strength.
(1) Small Cu disk, (2) Cu powder, (3)
large Cu disk.
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World Journal Of Engineering
Results and Discussion
Cu nanoparticles
Fig. 2 shows TEM images of the obtained
particles. Aggregates composed of particles
with a size of ca. 6 nm were observed in the
uncoated Cu particles. According to the XRD
measurement, besides several peaks due to
metallic Cu, peaks assigned to CuO were
detected. For the PPy-coated Cu particles, the
Cu particles with size of 27.6±11.1 nm were
coated with PPy shells. The size of the core Cu
particles was larger than the Cu size of the
uncoated particles, which indicated that the Cu
nanoparticles
were
grown
during
the
PPy-coating. In its XRD pattern, all the peaks
were attributed to metallic Cu, and no CuO
peaks were detected. This result indicated that
the PPy exerts protection against oxidation of
the Cu core. Thus, quite stable metallic Cu
nanoparticles could be fabricated with
PPy-coating.
1 mm
Cu disc
sintered layer
strength required for separating the bonded discs
was measured.
The disc-powder-disc joint
made using the nanoparticles was observed with
a scanning electron microscope (SEM).
Fig. 3 Cross-sectional SEM image of
the disc-powder-disc joint.
in H2 gas. The PPy shells probably formed
large voids among the Cu particles, which
resulted in prevention of the Cu particles from
sintering. This prevention provided no strong
bonding.
Conclusion
A metal-metal bonding by the use of Cu
nanoparticles was performed in the present work.
PPy-coated Cu nanoparticles did not help the
metal-metal bonding. In contrast, Cu discs
were strongly bonded for uncoated Cu
nanoparticles. A shear strength of 18.1 MPa
was recorded annealing at 400 o C in H2 gas.
References
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different metals used ultrasonic vibration. J. Mater.
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J.S. Direct writing of copper conductive patterns
by ink-jet printing. Thin Solid Films, 515 (2007)
7706-7711.
3. Kanninen, P., Johans, C., Merta, J. and Kontturi, K.
Influence of ligand structure on the stability and
oxidation of copper nanoparticles., J. Colloid
Interface Sci. 316 (2008) 88-95.
4. Zhang, X., Yin, H., Cheng, X., Hu, H., Yu, Q. and
Wang A. Effects of various polyoxyethylene
sorbitan monooils (Tweens) and sodium dodecyl
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Mater. Res. Bull., 41 (2006) 2041-2048.
5. Khanna, P.K., Gaikwad, S., Adhyapak, P.V., Singh,
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Marimuthu,
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Synthesis
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characterization of copper nanoparticles. Mater.
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6. Kobayashi, Y., Ishida, S., Ihara, K., Yasuda, Y.,
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Colloid Polym. Sci., 287 (2009) 877-880.
Fig. 2 TEM images of Cu nanoparticles
(left)
and
PPy-coated
Cu
nanoparticles (right).
Bonding property
With the use of the uncoated Cu particles,
annealing in air resulted in no bonding, because
the particles were oxidized to form CuO. In
contrary, strong bonding was realized annealing
in H 2 gas. A shear strength achieved 18.1 MPa
at an annealing temperature of 400 o C. Fig. 3
shows SEM images of cross-sections of the
bonded region.
Sintering of particles took
place and micron-sized domains were produced,
though some voids were also observed and no
large crack was formed.
This observation
confirmed the successful bonding.
In the case of the PPy-coated Cu particles, the
Cu discs were neither strongly bonded in air nor
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