Supporting Information
Simultaneously synthesis nano and micro Ag particles and
their application as a die-attachment material
Jinting Jiua,*, Hao Zhanga,b, Shunsuke Kogaa,b, Shijo Nagaoa, Yasuha Izumi a, Katsuaki
Suganumaa
a
Institute of Scientific and Industrial Research, Osaka University, Ibaraki, Osaka 567-0047,
Japan
b
Graduate School of Engineering, Osaka University, Ibaraki, Osaka 567-0047, Japan
Email: jiu@eco.sanken.osaka-u.ac.jp
Abstract
A simple and large-scale two-steps polyol process was used to simultaneously synthesize nano and micro Ag
particle pastes, which were used to joint Ag-plated Cu sheets. The size and size distribution of the Ag particles
and less organics remainder determined the shear strength and conductivity of the Ag paste. A shear strength of
over 40 MPa and a resistivity of 5.1 cm were achieved at 200°C using a paste with nano-Ag below 800 nm
and micro-Ag of 1.5-4.2 m in diameter under a minor sintering pressure of 0.4 MPa. The Ag paste included too
huge and much micro-Ag particles, for example from 2-5.2 m only gave maximum strengths of 30 MPa due to
inhomogeneous sintering and the presence of large voids. These results are superior to those obtained with
nanoparticle Ag pastes and suggested that suitable submicrometer Ag particles replacing nanoparticles Ag will
be an excellent die-attachment material in microelectronic packaging.
Fig. S1. The preparation schematic diagram of Ag pastes. In the first step, 0.5 g of
poly(vinylpyrrolidone) (PVP, MW = 360000) and 1.0 g of silver nitrate (AgNO3) were dissolved to 50 g
of ethylene glycol (EG) at room temperature (RT), and then reacted at 150°C for 1 h. During the first
30 min of the reaction, a different solution comprising 1.0 g AgNO3 and 50 g EG was dropped in.
Acetone and ethanol were then used to wash the precipitate. Finally, the Ag nanoparticles were redispersed as seeds in ethanol (2.5 wt%) for future use. In the second step, 1.5 g of AgNO3 was
dissolved in 50 g EG to obtain a clear solution which was slowly dropped into a solution, prepared
and heated in advance, containing 5.0 g of seed solution and 50 g EG at 130, 150 and 200°C,
respectively. The solution was then left to react for an additional 30 min. Finally, the precipitation
was washed three times with acetone and ethanol to obtain pure Ag particle precipitates, which was
respectively mixed with a small amount of EG to obtain Ag pastes.
(a)
(b)
(c)
(d)
Fig. S2a. Ag nanoparticles prepared with one-step. The detail is 0.5 g of PVP was first added to 50 g
of ethylene glycol (EG) and completely dissolved using magnetic stirring at room temperature.
Afterwards, 1.0 g of silver nitrate (AgNO3) was added to the PVP solution and reacted at 150°C for 1
hour. During the reaction, another solution including 2.5 g AgNO3 and 50 g EG was dropped into the
solution to increase the size. The dropping time was 1 hours, after that the solution is left to react
another 1 hour. At last the precipitation was washed with acetone and ethanol for three times to get
the pure Ag nanoparticles precipitation. The diameter of Ag nanoparticles is about 300-500 nm with
irregular morphology (a). Comparing those Ag seeds (Fig. S1b), these Ag size was slightly increased
with clear sharp edge in these nanoparticles due to long reaction time. However, these Ag particles
are far smaller than those Ag particles prepared with two-steps process (Fig. S1c). Fig. S1d shows the
Ag particles prepared without PVP dispersant at same conditions with one-step.
Fig. S3. Traces of DTA and TG for Ag pastes prepared at different reaction temperature. These Ag
pastes have been dried at 100 0C for two weeks and then were analyzed with TG/DTA. Almost no
weight-loss was observed in these Ag pastes. It is noted that the DTA curves have been changed
comparing those curves before the two-week dry process (Fig. 3b). A clear exothermic peak
appeared in the figure 3b has been shifted to high temperature, which might implied that Ag
particles have been aggregated into big particles due to long-time dry process. These big aggregation
particles were sintered by surface diffusion and reallocation will need a high temperature leading to
an exothermic peak. These results also suggested that the organic compounds might correspond to
the low-temperature sintering of these Ag pastes.
(a)
(b)
(c)
Fig. S4. The SEM images of Ag particles prepared at 130 (a), 150 (b) and 200 0C after drying at 100 0C.
0
130 C down
0
150 C down
0
200 C down
0
130 C up
0
150 C up
0
200 C up
Fig. S5. The photos of joints after shear test. For Ag past prepared at 130 0C, it is clear that the Ag
paste has been left on the two sides, i.e. two copper sheets, which suggested that fracture occurred
in the Ag pastes not near the interface of copper and pastes. The result clearly implied these Ag
pastes have strong joint which has been confirmed with high shear strength. For other two pastes,
the fracture surface was near interface between Ag paste and substrates, which implied that the
strength was weak due to non-uniform sintering of Ag pastes.