Note: Descriptions are shown in the official language in which they were submitted.
12~8882
The present invention relates to soldering alloys
for directly soldering oxide-containing silver contact materials,
particularly silver-tin oxide, onto contact supports.
Noble-metal-containing contact materials with inter-
collated metallic oxide, such as cadmium oxide, tin oxide or
indium oxide are usually soldered onto base support materials
such as iron, nickel or copper.
Since these compound materials must have a long son-
vice life in switching operations, a rigid soldered joint
between these materials is required.
In the art some of these solder joints are produced
in that the contact super layers are provided with layers of
fine silver or of silver-cadmium-(tin)-alloys, which are
readily solder able. Since these additional layers result in
higher costs in the production of solder able contact super layers
and since they contain a high amount of silver, processes
which avoid the production of a special solder able layer and
result in direct soldering are also known.
In German Auslegeschrift 2,365,450 it is disclosed
to back silver-metallic oxide materials with a silver-copper
alloy and to solder it subsequently to the support. The
application of reactive solders based on copper-silver-phosphorus
to contact materials is disclosed in German Offenlegungsschrift
2,438,922.
German Offenlegungsschrift 3,011,821 describes a
direct solder consisting of two members. In the soldering pro-
cuss a layer of Asp is to be reacted with a layer of Aged to
a homogeneous silver/copper/cadmium/phosphorus solder. German
Offenlegungsschrift 2,948,915 also describes a direct solder
of silver-copper-cadmium-tin-indium for soldering oxide-con-
twining silver contact materials to contact supports. This
solder wets the silver-metallic oxide materials quite well
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1;~18882
without resulting in brittle phases in the diffusion zone.
German Offenlegungsschrift 3,123,357 also describes a solder
which is suitable particularly for silver-tin oxide contact
materials and consists of the components silver-tin-indium-
geranium.
Therefore, quite a number of soldering alloys which
wet the silver-metallic oxides and do not form embrittling
reaction zones in the diffusion zone between contact materials
and solder and between support and solder are known. However,
the conventional soldering alloys have been used onto to a
limited extent. Particularly in silver-tin oxide materials
the main difficulty lies in that in most cases the junction zone
has a shorter service life than the extremely erosion-resistant
contact material.
The special problem of the contact materials soldered
onto the support lies in the build-up of stresses due to
differences in temperature. On the switching surface of the
contact super layers temperatures of more than 1000C are
attained due to the energy of the arc. On the opposite side
of the component parts the temperatures should not be sub-
staunchly above room temperature. This difference in temper-
azure decreases over a distance of, e.g., 3 millimeters.
Because of the constant changes of temperature when switching
this results in high shear and tensile stresses, which can no-
suit in peeling of the contact super layers. In contact super-
layers having an intermediate layer of fine silver these stresses
can be reduced to a certain degree by plastic deformations in
this very ductile layer. However, the service life of this
joint is limited by the low strength of silver or by the bond
of silver with the silver/metallic oxide. However, in contact
layers, which are directly soldered on, this kind of inter-
mediate layer cannot become effective. wherefore, the present
~218882
invention provides soldering alloys for directly soldering
oxide-containing silver contact materials, particularly silver-
tin oxide, onto contact supports, Leo soldering alloys
which readily wet the silver-metallic oxide materials and thus
are readily solder able. On the other hand, the soldering
alloys should be ductile so that they can reduce shear and
tensile stresses by plastic deformation and should have a
higher strength than silver so that the breaking strength is
not exceeded by shear and tensile stresses during switching
lo operations. In order to avoid additional stresses, these
soldering alloys should also be adapted to the other component
parts in the thermal coefficient of linear expansion.
According to the present invention there is
provided soldering alloys containing 20 to 35% by weight of
copper and 0.1 to 5% by weight of palladium in addition to
silver are used.
Surprisingly these alloys completely solve the
problem underlying the present invention. With regard to
service life of the soldered joint produced with these soldering
2Q alloys they surpass the conventional fine silver plating and
the direct solders known heretofore. Switching tests in
several relay systems, particularly in conjunction with the
highly erosion-resistant silver/tin oxide contact materials,
have shown a substantial superiority of the soldering alloys
according to the present invention with regard to the service
life of the component part. Furthermore, they readily wet the
conventional silver/metallic oxide materials without resulting
in brittle diffusion zones due to reactions on and with e.g.,
tin oxide.
Soldering alloys containing 24 to 32% by weight of
copper and 0.5 to 3% by weight of palladium have proved to be
particularly suitable.
1218882
By using soldering alloys containing 1% by weight of palladium
particularly economic alloys can be obtained. They also have
the advantage of a low operating temperature and of a slightly
increased service life.
The following examples will show the advantages
of the soldering alloys according to the present invention:
Example 1
Platelets of Axon (88/12) having the dimensions
9 x 9 x 1.25 mm3 were soldered with a soldering alloy of
silver and 26.6% of copper and 5% of palladium onto Cu-plated
steel supports under protective gas. The solder was added
via a solder foil. The number of connections in a AYE relay
were on the average 70,000 switching cycles in an ACT operation.
However, with contacts soldered conventionally to silver-
plated material only 30,000 switching cycles were obtained.
Example 2
Axon (88/12) platelets having the dimensions 14 x 15 x
2.3 mm3 were soldered with a solder having the composition
AgCu28Pdl onto Cut supports under protective gas. The number
of connections in a AYE relay were 120,000 (ag-plated material
COOK.
3Q
