Materials Science and Engineering A 396 (2005) 385–391
Solid-state reactions between Ni and Sn–Ag–Cu solders
with different Cu concentrations
W.C. Luo a , C.E. Ho a , J.Y. Tsai a , Y.L. Lin a , C.R. Kao a,b,∗
a
Department of Chemical and Materials Engineering, National Central University, Jhongli City, Taiwan
b Institute of Materials Science and Engineering, National Central University, Jhongli City, Taiwan
Received 17 August 2004; received in revised form 28 January 2005; accepted 3 February 2005
Abstract
It had been reported that, during the reflow of the Sn–Ag–Cu solders over the Ni-bearing surface finishes, a slight variation in Cu concentration produced different reaction products at the interface. In this study, we extended our earlier efforts to investigate whether this
strong Cu concentration dependency also existed for the solid-state aging reaction between the Sn–Ag–Cu solders and Ni. Specifically, five
Sn–3.9Ag–xCu solders (x = 0.2, 0.4, 0.5, 0.6, and 0.8) were reacted with Ni at 180 ◦ C. It was found that the strong Cu concentration dependency
disappeared after the solid-state aging at high temperatures for sufficient periods of time. For all the Cu concentrations studied, the same
intermetallic compounds, a layer of (Cu1 − y Niy )6 Sn5 and a layer of (Ni1 − x Cux )3 Sn4 , formed at the interface after aging. This study showed
that the initial difference in the intermetallic compounds right after reflow could be aged out at high temperatures. The growth mechanisms
for (Cu1 − y Niy )6 Sn5 and (Ni1 − x Cux )3 Sn4 were different, and were pointed out in this study.
© 2005 Elsevier B.V. All rights reserved.
Keywords: Sn–Ag–Cu; Interfacial reaction; Surface finish; Lead-free solder
1. Introduction
The Pb–Sn solder is an easily accessible material with
very good mechanical properties. Unfortunately, the Pb toxicity has led to the banning of Pb in solders. Two recent European Union directives, RoHS (Directive on the
restriction of the use of certain hazardous substances in
electrical and electronic equipment) and WEEE (Directive on Waste Electrical and Electronic Equipment), require new electrical and electronic equipments produced after July 1, 2006 to be lead-free. Several review papers had
been published on the status of Pb-free solders [1–4]. The
Sn–Ag–Cu solder family is regarded as one the most promising lead-free replacements for the Pb–Sn. The Sn–Ag–Cu
solder family has compositions (wt.%) near the Sn–Ag–Cu
ternary eutectic at Sn–(3.5 ± 0.3)Ag–(0.9 ± 0.2)Cu [5], and
the Sn–3.9Ag–0.6Cu solder has been recommended by a major industrial consortium [6].
∗
Corresponding author. Tel.: +886 342 27382; fax: +886 342 27382.
E-mail address: kaocr@hotmail.com (C.R. Kao).
0921-5093/$ – see front matter © 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.msea.2005.02.008
Nickel is a very common metal surface finish used in the
electronic packages. The function of Ni is to serve as a solderable diffusion barrier layer to prevent the rapid reaction
between the solder and the Cu layer below. The reactions between Ni and solders had been studied before [7–26]. It had
been reported that the reaction of Ni with liquid Sn–Ag–Cu or
Sn–Cu solders were very sensitive to the Cu concentration in
the solders [12–15]. At low Cu concentrations (≤0.2 wt.%),
only a continuous (Ni1 − x Cux )3 Sn4 layer formed at the interface. When the Cu concentration increased to 0.4 wt.%, a
continuous (Ni1 − x Cux )3 Sn4 layer and a small amount of discontinuous (Cu1 − y Niy )6 Sn5 particles formed at the interface.
When the Cu concentration increased to 0.5 wt.%, the amount
of (Cu1 − y Niy )6 Sn5 increased and (Cu1 − y Niy )6 Sn5 became
a continuous layer. Beneath this (Cu1 − y Niy )6 Sn5 layer was a
very thin but continuous layer of (Ni1 − x Cux )3 Sn4 . At higher
Cu concentrations (0.6–3.0 wt.%), (Ni1 − x Cux )3 Sn4 disappeared, and only (Cu1 − y Niy )6 Sn5 was present. These studies
show that a precise control over the Cu concentration in the
solders is needed to produce consistent results during reflow,
which is a reaction between liquid solders and solid substrate.
386
W.C. Luo et al. / Materials Science and Engineering A 396 (2005) 385–391
This is because the types of intermetallic at the solder/Ni interface had been shown to have a clear effect on the fracture
strength and reliability of a device [27].
The objective of this study is to investigate whether this
strong Cu concentration dependency also exists for the reaction between Ni and solid Sn–Ag–Cu solders. In other words,
we would like to know whether this dependency still exist
during the aging of the solder joints.
2. Experimental
Five different Sn–Ag–Cu solders (Sn–3.9–Ag–0.2Cu,
Sn–3.9Ag–0.4Cu, Sn–3.9Ag–0.5Cu, Sn–3.9Ag–0.6Cu, and
Sn–3.9Ag–0.8Cu) were prepared from 99.99% purity elements. A balance with a 0.0001 g precision was used to weigh
the elements, producing a maximum composition error of
0.01 wt.%. Mixtures of the pure elements with the chosen
composition were sealed in quartz capsules evacuated to a
vacuum of 15 mm Hg, and then melted at 850 ◦ C for 250 h to
produce the solder ingots with different Cu concentrations.
For every reaction, a small piece of solder (200 ± 10 mg) was
cut from an ingot. The concentrations of Ag and Cu in such
solder pieces were checked by ICP (induction couple plasma)
spectrum analysis to ensure the composition is the same as
the ingot. Nickel disks (6.35 mm diameter × 0.50 mm thick,
99.995% pure) were utilized to react with the solder pieces.
Before reaction, each Ni disk was metallurgically polished
on both surfaces. The 1 ␮m diamond abrasive was used as
the last polishing step. The Ni disks were then cleaned with
acetone, etched in a 50 vol.% HCl solution (in methanol) for
30 s, and coated with a mildly active rosin flux. Each solder
piece was placed on a Ni disk and then reflowed through a reflow oven. The peak reflow temperature was fixed at 250 ◦ C,
and heating rate and cooling rate were both fixed at 1 ◦ C/s,
respectively. The time the solder was in the molten state was
120 s. After reflow, the samples were aged at 180 ◦ C for as
long as 5000 h.
After aging, the samples were mounted in epoxy, sectioned
by using a low-speed diamond saw, and metallurgically polished in preparation for characterization. The reaction zone
for each sample was examined using an optical microscope
and a scanning electron microscope (SEM). The compositions of the reaction products were determined using an electron microprobe, operated at 20 keV. In microprobe analysis,
the concentration of each element was measured independently, and the total weight percentage of all elements was
within 100 ± 1% in each case. For every data point, at least
four measurements were made and the average value was
reported.
3. Results
The interfaces between Ni and Sn–Ag–Cu solders right
after reflow were similar to what had been reported in Refs.
[12–15]. When the Cu concentration was 0.2 wt.%, only
(Ni1 − x Cux )3 Sn4 formed at the interface. When the Cu concentration increased to 0.4 wt.%, in addition to a continuous (Ni1 − x Cux )3 Sn4 layer, a small amount of discontinuous
Fig. 1. The cross-section view for the Sn–3.9Ag–0.2Cu/Ni interfaces that had been aged at 180 ◦ C for: (a) 0 h; (b) 150 h; (c) 500 h; (d) 1000 h.
W.C. Luo et al. / Materials Science and Engineering A 396 (2005) 385–391
Fig. 2. EPMA line-scan across the reaction zone for the sample shown
in Fig. 1d. The intermetallic compounds present are (Cu1 − y Niy )6 Sn5 and
(Ni1 − x Cux )3 Sn4 .
(Cu1 − y Niy )6 Sn5 particles formed above (Ni1 − x Cux )3 Sn4 .
When the Cu concentration increased to 0.5 wt.%, the
(Cu1 − y Niy )6 Sn5 phase became a continuous layer over the
(Ni1 − x Cux )3 Sn4 layer. At higher Cu concentrations (0.6 and
0.8 wt.%), (Ni1 − x Cux )3 Sn4 was not detected, but a continuous (Cu1 − y Niy )6 Sn5 layer formed between Ni and the solder.
Fig. 1 shows the interfaces for the Sn3.9Ag0.2 Cu solder
with different aging time. As shown in Fig. 1a and b, only a
layer of (Ni1 − x Cux )3 Sn4 was at the interface after reflow and
after 150 h of aging. However, when the aging time increased
387
to 500 h and longer, a (Cu1 − y Niy )6 Sn5 layer formed over the
(Ni1 − x Cux )3 Sn4 layer as shown in Fig. 1c and d. These two
compounds (Cu1 − y Niy )6 Sn5 and (Ni1 − x Cux )3 Sn4 are based
on the Cu6 Sn5 and Ni3 Sn4 crystal structures, respectively, as
established using X-ray diffraction in an earlier study [12].
Right after reflow, the Cu atoms scattered randomly throughout the entire solder joint. However, after aging for sufficient
amounts of time, some of the Cu went back to the interface
and formed (Cu1 − y Niy )6 Sn5 . Fig. 2 is an EPMA line-scan for
the Sn–3.9Ag–0.2Cu solder joint that had been aged at 180
◦ C for 1000 h. As can be seen in Fig. 2, substantial amount
of Ni atoms were dissolved in (Cu1 − y Niy )6 Sn5 , reaching
about (Cu0.57 Ni0.43 )6 Sn5 . The compound (Ni1 − x Cux )3 Sn4
can also dissolve appreciable amount of Cu, reaching about
(Ni0.8–0.9 Cu0.2–0.1 )3 Sn4 , according to the data in Fig. 2. It
should be noted that the composition of (Cu1 − y Niy )6 Sn5 and
(Ni1 − x Cux )3 Sn4 here are quite similar to what had been reported for the solid-state reaction between Sn–Cu solders and
Ni by Chen et al. [26].
The formation of a (Cu1 − y Niy )6 Sn5 + (Ni1 − x Cux )3 Sn4
double-layer after the solid-state aging was not limited to
the Sn–3.9Ag–0.2Cu solder. For the Sn–3.9Ag–0.4Cu solder and the Sn–3.9Ag–0.5Cu solder, both (Cu1 − y Niy )6 Sn5
and (Ni1 − x Cux )3 Sn4 were present initially (after reflow), and
both (Cu1 − y Niy )6 Sn5 and (Ni1 − x Cux )3 Sn4 grew thicker and
became continuous layers, similar to those in Fig. 2d.
Fig. 3 shows the interfaces for the Sn–3.9Ag–0.6Cu
joints. As shown in Fig. 3a, only a layer of (Cu1 − y Niy )6 Sn5
was at the interface right after reflow. This is different from the case for Sn–3.9Ag–0.2Cu, where only
Fig. 3. The cross-section view for the Sn–3.9Ag–0.6Cu/Ni interfaces that had been aged at 180 ◦ C for: (a) 0 h; (b) 150 h; (c) 2000 h; (d) 5000 h.
388
W.C. Luo et al. / Materials Science and Engineering A 396 (2005) 385–391
Fig. 4. The cross-section view for the Sn–3.9Ag–0.8Cu/Ni interfaces that had been aged at 180 ◦ C for: (a) 0 h; (b) 2000 h; (c) 3500 h; (d) 5000 h.
(Ni1 − x Cux )3 Sn4 was present initially. As the aging time
reached 150 h, a thin layer of (Ni1 − x Cux )3 Sn4 formed below
(Cu1 − y Niy )6 Sn5 , as shown in Fig. 3b. Both (Cu1 − y Niy )6 Sn5
and (Ni1 − x Cux )3 Sn4 grew thicker with the aging time,
as shown in Fig. 3c and d. The situation for the
Sn–3.9Ag–0.8Cu was similar. Fig. 4 shows the interfaces
for the Sn–3.9Ag–0.8Cu joints. One major difference between Sn–3.9Ag–0.8Cu and Sn–3.9Ag–0.6Cu was that for
Sn–3.9Ag–0.8Cu it took much longer for (Ni1 − x Cux )3 Sn4 to
formed. As shown in Fig. 4c, a clear (Ni1 − x Cux )3 Sn4 layer
was visible only after 3500 h of aging. Fig. 5 is an EPMA
Fig. 5. EPMA line-scan across the reaction zone for the sample shown
in Fig. 4d. The intermetallic compounds present are (Cu1 − y Niy )6 Sn5 and
(Ni1 − x Cux )3 Sn4 .
line-scan for the Sn–3.9Ag–0.8Cu solder joint that had been
aged at 180 ◦ C for 5000 h. As can be seen in Fig. 2, substantial amount of Ni can be incorporated into (Cu1 − y Niy )6 Sn5 ,
reaching about (Cu0.57–0.69 Ni0.43–0.31 )6 Sn5 .
Fig. 6 shows the interfaces for solders with different compositions that had been aged at 180 ◦ C for 5000 h. For all Cu
concentrations used, a layer of (Cu1 − y Niy )6 Sn5 and a layer of
(Ni1 − x Cux )3 Sn4 formed over the Ni layer. The observation
that, after aging, different solders eventually produced the
same compounds at the interface is quite surprising. These
results are in sharp contrast to the interfaces right after reflow, where the reaction products depended strongly on the
Cu concentration of the solder.
The growth kinetics for (Ni1 − x Cux )3 Sn4 is shown
in Fig. 7. As can be seen here, (Ni1 − x Cux )3 Sn4 grew
thicker as the aging time increased. In the reaction of
Sn–3.9Ag–0.4Cu/Ni, the thickness of (Ni1 − x Cux )3 Sn4 is the
highest compared to other solder compositions. This is probably because the (Cu1 − y Niy )6 Sn5 layer for this composition
is among the thinnest (Fig. 8). For the Sn–3.9Ag–0.8Cu/Ni
reaction, the (Ni1 − x Cux )3 Sn4 layer was not visible until the
aging time became longer than 2000 h. Fig. 8 shows that the
(Cu1 − y Niy )6 Sn5 thickness for this solder composition is the
highest. In summary, the (Ni1 − x Cux )3 Sn4 thickness correlates inversely with that of (Cu1 − y Niy )6 Sn5 . This indicated
that (Cu1 − y Niy )6 Sn5 is an effective diffusion barrier that can
hinder the growth of (Ni1 − x Cux )3 Sn4 .
Fig. 8 shows that the thickness of the (Cu1 − y Niy )6 Sn5
layer increased as the Cu concentration in the solder increased. This phenomenon is quite reasonable because the
W.C. Luo et al. / Materials Science and Engineering A 396 (2005) 385–391
389
Fig. 6. The cross-section view for the solders/Ni interfaces that had aged at 180 ◦ C for 5000 h for: (a) Sn–3.9Ag–0.2Cu/Ni interface; (b) Sn–3.9Ag–0.4Cu/Ni
interface; (c) Sn–3.9Ag–0.5Cu/Ni interface; (d) Sn–3.9Ag–0.6Cu/Ni interface; (e) Sn–3.9Ag–0.8Cu/Ni interface. For all the solder compositions, both
(Ni1 − x Cux )3 Sn4 and (Cu1 − y Niy )6 Sn5 formed.
amount of Cu available increased with the Cu concentration in
the solder. It is interesting to estimate how much Cu in the solder had gone back to the interface to become (Cu1 − y Niy )6 Sn5
after 5000 h of aging. Alternatively, we can ask how thick
would (Cu1 − y Niy )6 Sn5 had been if all Cu had gone back to
the interface to form (Cu1 − y Niy )6 Sn5 . Fig. 9 is a comparison between the measured thickness of (Cu1 − y Niy )6 Sn5 after
5000 h of aging and the estimated thickness by assuming all
Cu had formed (Cu1 − y Niy )6 Sn5 at the interface. In calculating the estimated thickness, the density of (Cu1 − y Niy )6 Sn5
was taken to be the same as that of Cu6 Sn5, which was reported to be 8.28 g/cm3 [28]. The solder used in each sample
was 200 mg, and the wetting area (the area that the solder was
in direct contact with the Ni substrate) of each sample was
0.16 cm2 . The values for the composition of (Cu1 − y Niy )6 Sn5
were from the EPMA measurements. It can be seen from
Fig. 9 that the measured thickness was always slightly smaller
than that of the estimated thickness. In other words, after
5000 h of aging, most, but not all, of the Cu atoms had gone
back to the interface.
4. Discussion
According to earlier studies [12–15], the reaction product right after reflow was very sensitive to
the Cu composition in the solder. With increasing
Cu concentration, the reaction product switched from
(Ni1 − x Cux )3 Sn4 to (Cu1 − y Niy )6 Sn5 + (Ni1 − x Cux )3 Sn4 ,
then to (Cu1 − y Niy )6 Sn5 . However, this strong sensitivity
to the Cu composition disappeared when the solder joints
were subjected to aging at high temperatures for sufficient
390
W.C. Luo et al. / Materials Science and Engineering A 396 (2005) 385–391
Fig. 9. The measured thickness of (Cu1 − y Niy )6 Sn5 after aging at 180 ◦ C
for 5000 h. Also shown is the estimated thickness obtained by assuming all
Cu in the solder had come back to the interface to form (Cu1 − y Niy )6 Sn5 .
Fig. 7. The thickness of (Ni1 − x Cux )3 Sn4 vs. the aging time at 180 ◦ C.
amounts of time. Fig. 6 shows that aging at 180 ◦ C for
5000 h can make all the solder joint have the same type
of intermetallics compounds at the interface, i.e. a layer of
(Cu1 − y Niy )6 Sn5 over a layer of (Ni1 − x Cux )3 Sn4 . This result
indicates that the initial difference due to Cu concentration
may disappear as the solder joints are subjected to solid-state
aging at high temperatures for a sufficient period of time.
A recently established Cu–Ni–Sn 240 ◦ C ternary
isotherm, shown in Fig. 10 [29], provides rationalization
for such a strong dependence on the Cu concentration
for the solder joints right after reflow. The temperature
Fig. 8. The thickness of (Cu1 − y Niy )6 Sn5 vs. the aging time at 180 ◦ C.
of the isotherm (240 ◦ C) is quite close to the temperature used in this study for the reflow (250 ◦ C), and the
isotherm should provide a good approximation. According
to this isotherm, the phase fields that are in equilibrium
with the Sn phase [denoted as (Sn)] include one threephase field, (Sn) + (Cu1 − y Niy )6 Sn5 + (Ni1 − x Cux )3 Sn4 ,
and two two-phase fields, (Sn) + (Ni1 − x Cux )3 Sn4 and
(Sn) + (Cu1 − y Niy )6 Sn5 . Notice that the (Sn) single-phase
field is very small in size, and this is the reason why a
small change in Cu concentration can produce completely
different results. When the Cu concentration in solder
was high (x = 0.6 and 0.8), the interface represented a
tie-line in the (Sn) + (Cu1 − y Niy )6 Sn5 two-phase field,
and (Cu1 − y Niy )6 Sn5 formed next to the solder. When
the Cu concentration was low (x = 0.2), the interface
represented a tie-line in the (Sn) + (Ni1 − x Cux )3 Sn4 twophase field, and (Ni1 − x Cux )3 Sn4 forms next to the (Sn)
phase. When the Cu concentration was in-between, the
(Sn) + (Cu1 − y Niy )6 Sn5 + (Ni1 − x Cux )3 Sn4 three-phase field
dominated, and both (Cu1 − y Niy )6 Sn5 and (Ni1 − x Cux )3 Sn4
formed.
Next, let us discuss the reasons for the strong Cu
concentration sensitivity to disappear after the solid-state
aging. According to the Cu–Ni–Sn isotherm in Fig. 10,
Fig. 10. The Cu–Ni–Sn isotherm at 240 ◦ C. This isotherm was adapted from
Lin et al. [29].
W.C. Luo et al. / Materials Science and Engineering A 396 (2005) 385–391
(Cu1 − y Niy )6 Sn5 is not in thermodynamic equilibrium with
Ni. Therefore, for the cases of high Cu concentrations, where
there was only a layer of (Cu1 − y Niy )6 Sn5 over Ni, there
was driving force for the (Ni1 − x Cux )3 Sn4 phase to nucleate
and grow between the (Cu1 − y Niy )6 Sn5 layer and the Ni
layer. For the cases of low Cu concentrations, where these
was only a layer (Ni1 − x Cux )3 Sn4 over Ni, the Cu inside
the solder would diffuse back to the interface and formed
a layer of (Cu1 − y Niy )6 Sn5 over the (Ni1 − x Cux )3 Sn4 layer.
In this case, the Cu inside the solder existed in the form
of Cu6 Sn5 . The compound Cu6 Sn5 would decompose and
release the Cu atoms. The Cu atoms then diffused back to the
interface to react with Sn and Ni to form (Cu1 − y Niy )6 Sn5 .
The driving force for Cu6 Sn5 to resettle back to the interface
is to seek Ni so that the composition of (Cu1 − y Niy )6 Sn5
can approach (Cu0.57 Ni0.43 )6 Sn5 . A ternary compound
such as (Cu1 − y Niy )6 Sn5 usually has a lower free energy
compared to its binary counterpart Cu6 Sn5 . Kinetically,
the factor enables this to occur is that Cu is a fast diffuser
in Sn, and the diffusion rate of Cu in Sn is fast enough
for the process to happen. In fact, the growth mechanism
for (Cu1 − y Niy )6 Sn5 is quite similar to the well-known
resettlement of (Au1 − z Niz )Sn4 in those solder joints that
utilize the Au-bearing surface finishes [18,21,22].
Acknowledgment
This work was supported by the National Science Council
of R.O.C. through grants NSC-93-2216-E-008-001 and NSC93-2214-E-008-002.
References
[1]
[2]
[3]
[4]
[5]
[6]
[7]
[8]
[9]
[10]
[11]
[12]
[13]
[14]
[15]
5. Conclusions
In this study, the effect of a small perturbation in the Cu
concentration on the solid-state aging reaction between the
Sn–Ag–Cu solders and Ni was investigated. It was found that
the strong sensitive to the Cu composition after reflow disappeared if the samples were subjected to solid-state aging
at high temperatures for a sufficient period of time. For all
the Cu concentrations, the same type of the intermetallics
compounds formed at the interface after long-term aging. A
layer of (Cu1 − y Niy )6 Sn5 over a layer of (Ni1 − x Cux )3 Sn4
was found at the interface. This study shows that the initial
difference in the intermetallics compounds right after reflow
can be aged out at high temperatures. The growth mechanisms for (Cu1 − y Niy )6 Sn5 and (Ni1 − x Cux )3 Sn4 are different. The (Cu1 − y Niy )6 Sn5 layer grew by the resettlement of
the Cu atoms in the solder. In fact, the growth mechanism
for (Cu1 − y Niy )6 Sn5 is quite similar to the well-known resettlement of (Au1 − z Niz )Sn4 in the solder joints that utilize the
Au-bearing surface finishes. The (Ni1 − x Cux )3 Sn4 layer grew
by the reaction of the Ni layer and the (Cu1 − y Niy )6 Sn5 layer.
391
[16]
[17]
[18]
[19]
[20]
[21]
[22]
[23]
[24]
[25]
[26]
[27]
[28]
[29]
J. Glazer, Inter. Mater. Rev. 40 (1995) 65.
M. Abtew, G. Selvaduray, Mater. Sci. Eng. R 27 (2000) 95.
K. Suganuma, Curr. Opin. Solid State Mater. Sci. 5 (2001) 55.
K. Zeng, K.N. Tu, Mater. Sci. Eng. R 38 (2002) 55.
K.W. Moon, W.J. Boettinger, U.R. Kattner, F.S. Biancaniello, C.A.
Handwerker, J. Electron. Mater. 29 (2000) 1122.
http://www.nemi.org/.
K.N. Tu, K. Zeng, Mater. Sci. Eng. R 34 (2001) 1.
K.N. Tu, T.Y. Lee, J.W. Jang, L. Li, D.R. Frear, K. Zeng, J.K.
Kivilahti, J. Appl. Phys. 89 (2001) 4843.
K.N. Tu, R.D. Thompson, Acta Metall. 30 (1982) 947.
Z. Mei, A.J. Sunwhoo, J.W. Morris Jr., Metall. Trans. A 23 (1992)
857.
C.E. Ho, Y.L. Lin, J.Y. Tsai, C.R. Kao, J. Chin. Inst. Chem. Eng.
34 (2003) 387.
C.E. Ho, Y.L. Lin, C.R. Kao, Chem. Mater. 14 (2002) 949.
W.T. Chen, C.E. Ho, C.R. Kao, J. Mater. Res. 17 (2002) 263.
L.C. Shiau, C.E. Ho, C.R. Kao, Solder. Surf. Mt. Tech. 14 (2002)
25.
C.E. Ho, R.Y. Tsai, Y.L. Lin, C.R. Kao, J. Electron. Mater. 31 (2002)
584.
C.E. Ho, L.C. Shiau, C.R. Kao, J. Electron. Mater. 31 (2002) 1264.
W.H. Tao, C. Chen, C.E. Ho, W.T. Chen, C.R. Kao, Chem. Mater.
13 (2001) 1051.
C.E. Ho, S.Y. Tsai, C.R. Kao, IEEE Trans. Adv. Pack. 24 (2001)
493.
C. Chen, C.E. Ho, A.H. Lin, G.L. Luo, C.R. Kao, J. Electron. Mater.
29 (2000) 1200.
C.M. Liu, C.E. Ho, W.T. Chen, C.R. Kao, J. Electron. Mater. 30
(2001) 1152.
C.E. Ho, W.T. Chen, C.R. Kao, J. Electron. Mater. 30 (2001) 379.
C.E. Ho, R. Zheng, G.L. Luo, A.H. Lin, C.R. Kao, J. Electron.
Mater. 29 (2000) 1175.
C.E. Ho, Y.M. Chen, C.R. Kao, J. Electron. Mater. 28 (1999) 1231.
M.S. Lee, C. Chen, C.R. Kao, Chem. Mater. 11 (1999) 292.
M.S. Lee, C.M. Liu, C.R. Kao, J. Electron. Mater. 28 (1999) 57.
W.T. Chen, R.Y. Tsai, Y.L. Lin, C.R. Kao, J. SMT 15 (2002) 40.
T. Greggirich, P. Holmes, J.C.B. Lee, C.C. S Lee, Proceedings of
the IPC/Soldertec Second International Conference on Lead-Free
Electronics, paper no. 28, Amsterdam, Netherlands, June 21–24,
2004.
H.P.R. Frederikse, R.J. Fields, A. Feldman, J. Appl. Phys. 72 (1992)
2879.
C.H. Lin, S.W. Chen, C.H. Wang, J. Electron. Mater. 31 (2002)
907.