Technical Field
[0001.] The present invention relates to a lead-free solder alloy for joining a
glass part with a conductor to a metal terminal and a glass article using the lead-free
solder alloy.
Background Art
[0002.] Some glass articles for automotive and architectural uses have conductor
wires formed thereon as defoggers in order to ensure visibility. Further, rear and
side windows for automotive vehicles are sometimes equipped with glass antennas.
The glass antennas have respective patterns of conductor wires, called "antenna
patterns", formed on surfaces of glass plates.
[0003.] These conductor wires are connected to metal terminals for power
supply (referred to as "power supply terminals"). The power supply terminals are
conventionally joined to glass parts by lead-containing solders. However, lead is
generally a highly toxic environmental pollutant substance so that the influences of
lead on the health and environment, notably the deleterious effects of lead on the
ecosystem and the pollution of the ecosystem by lead, are becoming a matter of
concern. In particular, there is a concern that, in the case where glass articles with
lead-containing solders are thrown out as waste, lead may be eluted into the
environment upon adhesion of acid rain etc. to these solders.
[0004.] The use of lead-free solders in electronic boards has thus been spreading
rapidly in the home-appliance industry. However, solders for joining glass parts and
metal terminals are required to achieve a higher level of joint strength than those of
solders for electronic boards and are likely to cause, in response to sudden
temperature changes, problems such as deterioration in joint strength and cracking
of glass surface by concentration of stress on the solder joints between the glass
parts and the metal terminals due to difference in thermal expansion coefficient
between glass and metal.
[0005.] A Sn-3Ag-0.5Cu solder alloy (Sn-based solder alloy containing 3
mass% of Ag and 0.5 mass% of Cu) is currently used as the mainstream of the lead-

free solder for electronic boards and regarded as one of reliable solder alloys
because of its high joint strength on electronic boards (see Patent Document 1).
[0006.] There are also known various solder alloys such as Sn-Zn-Bi alloy (see
Patent Document 2) and Sn-In-Ag alloy (see Patent Document 3) for electronic
boards.
Prior Art Documents
Patent Documents
[0007.] Patent Document 1: Published Japanese Translation of PCT
International Application No. 2009-509767
Patent Document 2: Japanese Laid-Open Patent Publication No. H08-164495
Patent Document 3: Japanese Laid-Open Patent Publication No. H09-326554
Summary of the Invention
Problems to be Solved by the Invention
[0008.] The Sn-Ag-Cu solder alloy, which is the current mainstream of the
electronic board solder, has high joint strength on electronic boards as mentioned
above. However, this solder alloy is a high-rigidity metal material having a high
Young's modulus of 50 GPa and thus cannot be used as it is for joints between rigid
glass and metal parts.
[0009.] More specifically, the Sn-Ag-Cu solder alloy as disclosed in Patent
Document 1 may have a problem such as solder joint separation, glass cracking etc.
with the application of mechanical stress or stress due to difference in thermal
expansion coefficient.
[0010.] The Sn-Zn-Bi solder alloy as disclosed in Patent Document 2 is being
improved in terms of Young's modulus. The use of the Sn-Zn-Bi solder alloy has
however recently been restricted in view of the fact that this solder alloy contains Bi,
which is also highly toxic as in the case of lead.
[0011.] The Sn-In-Ag solder alloy as disclosed in Patent Document 3 is
expected to be suitable for automotive uses as the Young's modulus of this solder
alloy can be limited to a lower value. It has however become apparent that the Sn-

In-Ag solder alloy is not still sufficient in performance for outside uses such as
automotive vehicles. For example, the Sn-In-Ag solder alloy has difficulty in
ensuring a satisfactory level of acid resistance for uses under exposure to acid rain
etc., salt water resistance for uses under exposure to sea water, snow/ice inhibitor
etc. and temperature cycle resistance for uses under exposure to night-day
temperature differences in cold climates.
[0012.] In this way, lead-free solders for joints to conductors in vehicle glass
articles require higher performance than those for electronic boards
[0013.] It is accordingly an object of the present invention to provide a lead-free
solder alloy that is suitable for applications to vehicle glasses and to provide a glass
article using such a lead-free solder alloy.
Means for Solving the Problems
[0014.] There is provided according one aspect of to the present invention a
lead-free solder alloy for a vehicle glass, comprising: 26.0 to 56.0 mass% of In; 0.1
to 5.0 mass% of Ag; 0.002 to 0.05 mass% of Ti; 0.001 to 0.01 mass% of Si; and the
balance being Sn.
[0015.] There is provided according to another aspect of the present invention a
lead-free solder alloy for a vehicle glass, comprising: 26.0 to 56.0 mass% of In; 0.1
to 5.0 mass% of Ag; 0.005 to 0.1 mass% of Cu; 0.002 to 0.05 mass% of Ti; 0.001 to
0.01 mass% of Si; 0.001 to 0.01 mass% of B; and the balance being Sn.
[0016.] The lead-free solder alloys according to the present invention have good
joint strength to glass materials and high acid resistance, salt water resistance and
temperature cycle resistance for suitable applications to vehicle glasses.
Detailed Description of the Embodiments
[0017.] Hereinafter, the present invention will be described in detail below.
[0018.] The lead-free solder alloy according to the present invention contains, as
constituent components, In, Sn, Ag, Ti and Si and may optionally contain Cu and B.

[0019.] In the present invention, the In content of the solder alloy is preferably
in a range of 26.0 to 56.0 mass%. If the In content is less than 26.0 mass%, the
resulting solder alloy becomes high in Young's modulus and may cause glass
cracking. If the In content exceeds 56 mass%, the resulting solder alloy may cause
deterioration in joint strength in the occurrence of residual internal stress due to a
phase change of In3Sn/In3Sn+InSn4 or cracking even by temperature changes in a
room temperature range. The In content of the solder alloy is more preferably 31.0
to 51.0 mass% in the present invention.
[0020.] With the addition of appropriate amounts of Ag, Ti and Si to In and Sn,
the solder alloy can stabilize its crystal structure by fine crystal formation and retard
oxidization properties characteristic to In-containing alloy. The solder alloy can also
stabilize its target temperature range for good joint formation.
[0021.] During heat soldering (e.g. soldering by means of a soldering iron, gas
burner, heat blow, furnace, ultrasonic wave etc.), In-Sn binary alloy can form a
stable joint by low-melting eutectic at 117°C. In the case of soldering to a vehicle
glass, however, the solder alloy may reach a temperature close or equal to its
eutectic temperature. It is thus necessary to raise a liquidus temperature of the
solder alloy. The liquidus temperature of the solder alloy can be lowered with
increase of the Sn content and decrease of the In content. When the Sn content of
the solder alloy is increased, however, Sn crystals are overgrown and dispersed in
the joint by the action of heat during the soldering. This makes it likely that
separation of the solder joint will occur as the strength of the joint deteriorates with
the passage of time. In the present invention, Ag, Ti and Si are added in appropriate
amounts to In and Sn as a technique to form a stable joint without causing secular
change, separation, cracking etc. It is therefore possible to provide the low-melting
solder alloy such that the solder alloy can form a stable joint with fine crystal
structure and retard its oxidation properties for stable physical characteristics.
[0022.] Further, the solder alloy can form a natural oxide film with fine (spinel)
structure with the addition of appropriate amounts of Ag, Cu, Ti, Si and B to In and

Sn. This makes the natural oxide film of the solder alloy more uniform and stable
than that of In-Sn binary alloy and contributes to prevention of surface corrosion.
[0023.] The crystal structure inside and at the surface of the solder alloy can be
obtained so as to secure durability to withstand environmental conditions, such as
heat resistance, corrosion resistance and weather resistance, and not to cause secular
change and separation of the solder joint from the substrate, by the formation of the
fine(spinel)-structured natural oxide film during heat soldering (e.g. soldering by
means of a soldering iron, gas burner, heat blow, furnace, ultrasonic wave etc.).
Namely, the natural oxide film can be made uniform to form a stable joint because
of the fine structure of the oxide film. As a technique to form such a stable joint by
fine uniform oxide film formation, Ag, Cu, Ti, Si and B are added in appropriate
amounts to In and Sn in the present invention. It is therefore possible to provide the
low-melting solder alloy such that the solder alloy can form a stable joint with fine
oxide film crystal structure and retard its oxidation properties for stable physical
characteristics.
[0024.] In the case where the solder alloy contains Ag, the Ag content of the
solder alloy is preferably in a range of 0.1 to 5.0 mass% in the present invention.
The addition of Ag provides a significant effect on the improvement of the
mechanical strength of the solder alloy. In the vehicle glass, silver wires can be
formed as defogger hot wires or antenna wires by screen printing, drying and firing
a silver paste. The addition of Ag to the solder alloy is effective in, when these
silver wires are joined by the solder to power supply terminals for contact to a
vehicle body, preventing the silver wires from being corroded by the solder. These
effects are small if the Ag content is less than 0.1 mass%. If the Ag content exceeds
5 mass%, the deposition of coarse Ag3Sn may occur to cause deterioration in joint
strength and fatigue strength. The Ag content of the solder alloy is more preferably
0.5 to 3.0 mass%.
[0025.] In the case where the solder alloy contains Cu, the Cu content of the
solder alloy is preferably in a range of 0.005 to 0.1 mass% in the present invention.
The resulting solder joint may not attain a sufficient level of joint strength if the Cu

content is out of this range. The Cu content of the solder alloy is more preferably
0.005 to 0.05 mass%.
[0026.] Although Ti is a very easily oxidizable element, the addition of Ti
makes it easier to form a bond in the case of soldering to an oxide. Further, the
liquidus temperature of the solder alloy can be raised by the addition of Ti. When
the Sn content of the solder alloy is increased, Sn crystals are overgrown and
dispersed in the joint by the action of heat during the soldering so that that
separation of the solder joint is likely to occur as the strength of the joint deteriorates
with the passage of time as mentioned above. The addition of Ti is also effective in
preventing such a problem. These effects are provided sufficiently even by the
addition of a trace amount of Ti. Thus, the Ti content of the solder alloy is
preferably in a range of 0.002 to 0.05 mass%, more preferably 0.005 to 0.03 mass%,
in the present invention.
[0027.] The addition of Si makes it possible that the structure of the solder alloy
can be made fine by the deposition of Si between boundaries of the respective metal
components during a process from a molten state to solidification of the solder alloy.
This effect is provided sufficiently even by the addition of a trace amount of Si.
Thus, the Si content of the solder alloy is preferably in a range of 0.001 to 0.01
mass%, more preferably 0.002 to 0.008 mass%, in the present invention.
[0028.] The addition of B together with Cu allows formation of the fine(spinel)-
structured oxide film during the heat soldering (e.g. soldering by means of a
soldering iron, gas burner, heat blow, furnace, ultrasonic wave etc.). The crystal
structure at the surface of the solder alloy can be thus obtained to secure durability
to withstand environmental conditions, such as heat resistance, corrosion resistance
and weather resistance, and not to cause secular change and separation of the solder
joint from the substrate. Namely, the oxidation properties of the solder alloy can be
retarded for stable physical characteristics. This effect is provided sufficiently even
by the addition of a trace amount of B. Thus, the B content of the solder alloy is
preferably in a range of 0.001 to 0.01 mass%, more preferably 0.002 to 0.008
mass%, in the present invention.

Examples
[0029.] The present invention will be described in more detail below by way of
the following examples. It should be noted that the following examples are
illustrative and are not intended to limit the present invention thereto.
[0030.] Solder alloys of Examples 1-8 shown in TABLE 1 and Comparative
Examples 1-5 shown in TABLE 2 were each produced by mixing alloy components
at their respective contents, and then, melting the resulting mixture in a vacuum.
[0031.] On the other hand, soda lime glass substrates having a size of 350 mm ×
150 mm and a thickness of 3.5 mm were provided and each processed by screen
printing with a black ceramic paste and a silver paste in the same manner as in an
ordinary process of forming, on a vehicle glass, a black frame and a silver busbar
part for conductor-to-terminal connection. The black ceramic paste was printed
through a screen of mesh size #180 onto the soda lime glass substrate and dried.
The silver paste was next printed through a screen of mesh size #200 on the ceramic
print and dried to form silver prints (size: 12 mm × 70 mm, 15 locations). The
resulting screen-printed glass substrates were finished by heat treatment as
reinforced glass boards.
[0032.] The above-produced solder alloys were applied with a thickness of 2
mm to terminals of C2801P (brass plate) according to JIS H 3100. The terminals
with the solder alloys were set on the glass substrates and soldered to the silver parts
of the glass substrates by heating and melting the solder alloys with hot air of 300°C
or higher, respectively.
[0033.] The thus-obtained test samples were tested by the following joint
strength test, appearance test, temperature cycle test and salt water spray test.
[0034.] The initial joint strength was determined according to JIS C 62137 by
performing a tensile test operation on the sample with the use of a push-pull gauge.
The sample was rated as "passing" in the joint strength test when no separation of
the solder joint occurred under the application of a tension of 80 N.

[0035.] The initial appearance was determined by visually checking the
occurrence or non-occurrence of a crack in the surface of the solder joint. The
sample was rated as "passing" in the appearance test when there was seen no crack
in the surface of the solder joint.
[0036.] The temperature cycle test was performed with reference to the
procedure of thermal cycle resistance test according to JIS C 2807. More
specifically, the sample was subjected to 100 thermal cycles assuming an operation
of changing the sample temperature from 20°C (3 minutes) to -30°C (30 minutes), to
20°C (3 minutes), to 85°C (30 minutes) and then to 20°C (3 minutes) as one thermal
cycle. The sample was rated as "passing" in the temperature cycle test when there
was seen no appearance change (crack) in the surface of the glass substrate after 100
thermal cycles. It is herein noted that, in JIS C 2807, the lower temperature value is
set to -25°C.
[0037.] The salt water spray test was performed by spraying an 5% aqueous
NaCl solution onto the solder joint at a spray pressure of 0.1 MPa in an atmosphere
of 35°C continuously for 100 hours, 200 hours and 300 hours. The sample was
rated as "passing" in the salt water spray test when the joint strength of the solder
joint was 80 N or higher after the test.
[0038.] The solder compositions and test results are shown in TABLES 1 and 2.
In TABLES 1 and 2, the results of the salt water spray test are indicated by the
following symbols: " × " as failing after the test of 100 hours; "Δ" as passing after
the test of 100 hours; "○" as passing after the test of 200 hours; and "⦾" as passing
after the test of 300 hours; and the passing and failing grades of the other tests are
indicated by the symbols "○" and " × ", respectively.

[0039.] As shown in TABLE 1, the samples of Examples 1 -8, each of which had
the solder composition according to the present invention, were good in terms of
both of joint strength and appearance.
[0040.] By contrast, the samples of Comparative Examples 1-5, each of which
did not have the solder composition according to the present invention, were poor in
term of either or both of joint strength or appearance. These lead-free solder alloys
were not suitable for joints between metal terminals and glass articles.
Industrial Applicability
[0041.] The lead-free solder alloy according to the present invention is suitable
for joints between metal terminals and glass articles and is thus applicable to a wide
field of uses such as automotive and architectural conductor wires and glass
antennas.
[0042.] Although the present invention has been described with reference to the
above embodiments, various modifications and variations of the above embodiments
can be made based on the knowledge of those skilled in the art without departing
from the scope of the present invention.

WE CLAIM:
1. A lead-free solder alloy for a vehicle glass, comprising:
26.0 to 56.0 mass% of In;
0.1 to 5.0 mass % of Ag;
0.002 to 0.05 mass % of Ti;
0.001 to 0.01 mass % of Si; and
the balance being Sn.
2. A lead-free solder alloy for a vehicle glass, comprising:
26.0 to 56.0 mass% of In;
0.1 to 5.0 mass% of Ag;
0.005 to 0.1 mass % of Cu;
0.002 to 0.05 mass% of Ti;
0.001 to 0.01 mass% of Si;
0.001 to 0.01 mass% of B; and
the balance being Sn.