Russian Journal of Applied Chemistry, 2011, Vol. 84, No. 11, pp. 2002−2004.
Pleiades Publishing, Ltd., 2011.
Original Russian Text © S.P. Yatsenko, V.M. Skachkov, 2011, published in Zhurnal Prikladnoi Khimii, 2011, Vol. 84, No. 11, pp. 1917−1919.
Method of Fluxless Soldering of Dissimilar Materials
S. P. Yatsenko and V. M. Skachkov
Institute of Solid State Chemistry, Russian Academy of Sciences, Ural Branch, Yekaterinburg, Russia
Received June 10, 2011
Abstract—The method of ﬂ uxless soldering of dissimilar materials using the electrodeposition of solder components
(copper and gallium) was studied. The effect of a number of factors on the strength of soldered joints was studied.
The intensive development of technology, including
electronics, and the manufacture of new instruments and
devices often raises the question of joining dissimilar
materials with different properties.
Commonly, hard-to-join materials such as glass,
ceramics and metals from the group Si, Ge, Al, Ti, Zr,
Ta, etc., are joined at temperatures below 180°C using
as solder the alloys of composition (wt %): 2–98 Pb,
1–97.5 Sn, 0.5–60 Cd, and 0.05–10 Zn, which are ap-
plied to the soldered surfaces by the vibration, preferably
supersonic, methods .
Cathodic deposition of a copper layer onto one of the
joined surfaces with subsequent application (spraying)
of a paste of fusible alloy (gallium, indium, bismuth, or
tin alloy), whose composition is close to the eutectic, and
the heat treatment of the joined surfaces in the tempera-
ture range 70–150°C is the common method of ﬂ uxless
soldering of dissimilar materials .
These methods have several disadvantages, the most
important of which are the possibility of desoldering
of the article, when heated during working above the
liquidus temperature of the alloy, the lack of contact on
some surface areas due to nonuniform application of the
alloy to the joined surfaces, and the toxicity of solder
components (Pb, Cd).
The use of composite solders based on fusible alloys
[3–5] has the disadvantage caused by the necessity of
using spherical copper powders with grain size of about
40 μm. Very ﬁ ne (micrometer) powders are inconvenient
because of the small processing time, i.e., the reaction
of liquid gallium or its alloys to form intermetallic
compounds proceeds rapidly. Standard powders (ICP-
40, EMP-40) yield rather thick soldered layer, which is
highly undesirable for certain types of joints, such as in
In the study, we developed a method of low-tempera-
ture ﬂ uxless soldering, free from the above disadvantages,
using the electrodeposition onto the joined surfaces of
copper and gallium layers of a controlled thickness. The
method may be used for soldering thermo- and solar
panels and opto and radioelectronic equipment.
The known and widely used method of copper deposi-
tion is electrolysis of copper sulfate solutions containing
surface-active additives such as gelatin . Electrochemi-
cal deposition of gallium is performed in a sodium gallate
solution obtained by water leaching of a sinter of gallium
oxide and sodium hydroxide . However, it was unclear
without experimental studies whether it is possible to
obtain a strong junction of dissimilar materials by ﬂ uxless
soldering, in which layers of copper and gallium formed
by the electrodeposition on the surfaces being connected
are used as solder.
It was found that the strong joint, stable at high tem-
peratures, can be obtained by the successive electrodepo-
sition of copper and then gallium in the same range of the
cathodic current densities. In this case, a certain relation