ap-6-10.dvi


Acta Polytechnica Vol. 50 No. 6/2010

A Study of the Interface of Soldered Joints of SnInAgTi Active Solder
with Ito Ceramics

M. Provazńık, R. Koleňák

Abstract

This paper presents an analysis of the solderability ITO ceramics (In2O3/SnO2). The soft active solder SnInAgeTi was
used for the experiments. The solder was activated by power ultrasound in air without flux. An analysis of the interface
of the phases between the solder and the ceramic was carried out in order to discover the ultrasonic impacts on the active
metal and to identify the mechanism of the joint on the ceramic side.

Keywords: ultrasonic activation, active solder, ITO (indium-tin oxide) ceramics.

1 Introduction
Ceramic materials are increasingly used in technical
practice, especially in the field of electrotechnology.
There is enormous demand for conductive joining of
ceramics with metals. Soldering with the use of ac-
tive solders is a current trend in this area. These
solders contain an active element which reacts with
the surfaceof the ceramicmaterial. This enables it to
be wetted and a reaction layer created. The solders
have a very low wetting angle, enabling soldering at
low temperatures, without flux and additional pro-
tection.
The most widely used active metal is titanium.

The reactive product transforms the surface energy
of ceramics and enables wetting of the solder. The
active element moves from the whole solder volume
to the two solderedmaterials. At the interface of the
soldered joint, a reaction layer several μm in thick-
ness is created, which contains the reaction products
of the active elements and the substrate [1].
The solder is activated mechanically or with the

use of a veryhigh temperature to influence the active
element. The mechanical application is achieved by
scraping, by spreadingwith a metal brush (soldering
Cu,Al, orCrNi steel), by vibration, or by ultrasound
above 20 kHz (soldering ceramics and non-metallic
materials). The working cycle of the mechanical ap-
plication is approximately 10 times shorter than high
temperature activation, and does not require the ap-
plication of a vacuum or a protective atmosphere.

2 Experiments

A sample was made using the apparatus shown in
Fig. 1. The soldering process involves heating the
soldered materials with the use of a hot plate to the
soldering temperature in the range of 150–160◦C.
The maximum soldering temperature is limited to

160◦C, when surface oxidation of ITO ceramics in-
creases. Heatingby steps is chosen inorder toachieve
steadyheating of bothmaterials. A strap-shapedsol-
der made by fast cooling technology is placed on a
heated substrate, see Fig. 2. The solder is activated
by a titanium peak of the ultrasonic equipment af-
ter melt-down. The activation time was chosen in
the interval from 1 to 5 seconds in one contact point.
Tab. 1 presents the parameters of theUS equipment.
The solder is applied to the second substrate in the
same way. The two prepared parts are joined and
softly pushed. The presence of the active solder pro-
tects the high plasticity of the phase interface.

Fig. 1: Diagram of the apparatus for soldering by ultra-
sound

Fig. 2: Solder production by fast cooling technology [2]

70



Acta Polytechnica Vol. 50 No. 6/2010

Table 1: US equipment parameters

Output power –
intermittent service

[W] max. 400

Operative frequency [kHz] 40

Input power [W] max. 600

Time adjustment range [s] 0.1–9.9 for 0.01

The soldering samples were fixed after splitting,
and were prepared using a standard metallographic
methodology. The samples were then analyzed using
a light microscope and a scanning electron micro-
scope. For further documentation of the joint cre-
ation mechanism, rtg. diffraction analysis was used
for analyzing the concentration profiles of each ele-
ment.
Production principle of the active solder foil
1. The molten alloy is extruded by fine pressure of
an inert gas (argon, helium) through the rectan-
gular slot of a jet placed near the cooling disk.

2. The rotating cooling disk gradually touches the
molten solder. The disk creates a thin layer of
solid alloy which the roller takes away.
The solder in foil shape with parameters

0.15mm × 7 mm was made by the SAV Physical In-
stitute, Bratislava for experimental purposes. The
solder wasmade from foundry alloy by ready casting
in an ingot mould.

3 Experiment results

A differential thermic analysis was made on a sam-
ple of active solder. The process of this analysis
is recorded in Fig. 3. Using the DTA graphs we
can specify the thermal areas where there are pha-
sic metamorphoses. A temperature of 116◦C char-
acterizes the onset of molten eutectic Sn–In. A tem-
perature of 156◦C is the molten temperature of neat
indium.

Fig. 3: DTA of SnInAgTi solder

Fig. 4: Microstructure of SnInAgTi active solder [3]

Fig. 4 presents the heterogeneous microstructure
of theSnInAgTi soft active solder in themolten state.
A quantitative chemical analysis of the solder,

shown in Fig. 4, is described in Tab. 2. The dark
grains, specified as positions A1 and A2, are expres-
sively enriched with Ti and Ag. Other pallid grains
(areasA3, A4) and the matrix (position A5, A6) are
explicitly composed of In and Sn elements.

Table 2: Quantitative analysis of SnInAgTi solder [3]

Ti Ag In Sn
[at. %] [at. %] [at. %] [at. %]

A1 3.1 27.6 55.1 14.3

A2 1.9 29.3 53.0 15.8

A3 0 0.3 11.3 88.5

A4 0 0 12.1 87.9

A5 2.7 0 64.7 32.7

A6 0 0 71.4 28.7

In order to identify the phasic composition of
the solder after moulding, a radiographic diffraction
analysis was made by the SAV Physical Institute,
Bratislava, which identified the following phases:
In3Sn, InSn4, Ti6Sn5, Ag3Sn, AgIn2, Ti3Ag [3]. We
can identify the dark areas of the solder as theTi3Ag
phase, which demonstrates the high affinity of tita-
nium to silver.
Fig. 5 shows the phasic interface of solder and

ITO ceramics. The concentration profiles of the in-
dividual elements across the interface demonstrate
that Ti participates in the creation of the joint, but

71



Acta Polytechnica Vol. 50 No. 6/2010

Fig. 5: TheSnInAgTi– ITOinterface, and the concentra-
tion profiles of the individual elements over the interface

it is supposed that Indium has the greatest effect on
the creation of the joint. A provable effect of power
ultrasound is that the solder is able to fill the narrow
spaces among the ceramic grains, proving that there
is a high degree of ceramic wetting when soldering is
performed.
Indium markedly supports the creation of the

joint at this monitoring interface. The experiments
show clearly that the mission of an active element in
solder does not always have to appear. In this case,
the Ti is indifferent (it does not create any provable
phases). It remains fixed in the solder (mainly in the
Ti3Ag phase) and it does not participate markedly
in creating the joint.
Since indium has a high affinity to oxygen, we

can assume that it combines in the soldering process
with atmospheric oxygenwith complex oxide genesis
of indium,which provides an input into the reactions
with the surfaceof the ITOceramicsby the simplified
model shown in Fig. 6.

Fig. 6: Simplified model of the creation of the joint be-
tween ITO ceramics and SnInAgTi solder [4]

4 Our contribution to new
findings

Our contribution to work on this topic can be sum-
marized as follows:
• a soft active SnInAgTi solder has been designed
and manufactured by methods of fast cooling,

• our analyses of the phase structure of the sol-
der has identified the following phases: In3Sn,
InSn4, Ti6Sn5, Ag3Sn, AgIn2, Ti3Ag,

• the SnInAgTi solder drenched ITO ceramics
with the use of power ultrasound,

• studies of the interfaces have shown thatwhen a
joint with ITO ceramics is created, indium from
the solder participates preferentially.

72



Acta Polytechnica Vol. 50 No. 6/2010

5 Conclusion
The results of our experiments have verified the pos-
sibility of creating a soldering joint between a metal
and an ITO ceramic. The soldering joint is produced
with the use of mechanical activation power ultra-
sound on air, without flux. It has been proved that
an SnInAgTi solder reacts with the surface layers of
the connected metals by creating reactive products
of various thicknesses and qualities. This proves that
the solid substrates dissolve in the solder and create
diffusion joints.
There is no evident diffusion area on the interface

between the solder and the ITO ceramics. The sol-
der is able to leak into the spaces between the grains,
and in this wayamechanical joint is created. Indium
plays a major role in creating the joint. Indium cre-
ates oxide inputs that react with the ceramics and
create a chemical bond.

Acknowledgement

This paper has been preparedwith support from the
VEGA1/0381/08Project—Research into the Influ-
ence of Physical and Metallurgical Aspects of High
Temperature Soldering upon the Structure ofMetal-
lic and Ceramic Materials’ Joints, and the APVT
20-010804 Project — The Development of a Lead-
free Soft Active Solder and Research into the Sol-
derability of Metallic and Ceramic Materials using
Ultrasonic Activation.

References

[1] Chang, S. Y., Tsao, L. C., Chiang1, M. J.,
Chuang, T. H., Tung, C. N.: Active soldering
of indium tin oxide (ITO) with Cu in air using
an Sn3.5Ag4Ti(Ce, Ga) filler, Journal of Mate-
rials Engineering and Performance, 2003, No. 4,
pp. 383–389.

[2] Koleňák, R.: Solderability of metal and ce-
ramic materials by active solders. 1st ed. Dres-
den, Forschungszentrum Dresden, 2008. (Scien-
tific monographs). ISBN 978-3-941405-03-5.

[3] Adamč́ıková, A.: Study of ceramics wetting by
lead-free solders, Master’s thesis, 2007.

[4] Koleňák, R: The Development of a Lead-free Soft
Active Solder and Research into the Solderabil-
ity of Metallic and Ceramic Materials using Ul-
trasonic Activation, Final report of grant project
APVT 20-010804. Trnava, 2008.

Ing. Martin Provazńık
E-mail: martin.provaznik@stuba.sk
Institute of Production Technologies
MTF STU, Trnava, Slovak Republic

doc. Ing. Roman Koleňák, PhD.
E-mail: roman.kolenak@stuba.sk
Institute of Production Technologies
MTF STU, Trnava, Slovak Republic

73