Note: Descriptions are shown in the official language in which they were submitted.
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BATHS OF ORGANIC SULFONATE SOLUTION
FOR BISMUTH AND BISMUTH ALLOY PLATING
BACKGROUND OF T~, INVENTION
This invention relates to bismut;h and bismuth alloy plating
baths. More particularly, it is concerned with bismuth and
bismuth alloy electroplating baths which use an organic sulfonic
acid as a co-soluble complex salt of` bismu~h and the ~etal other
than bismuth and give smooth electroplated deposits without the
emission of highly pollutlng matter.
Bismuth is extensively used as a lubricant in nuclear reactor
construction as well as in such newly opened fields as the manu-
facture of recti~ier and ohmic contacts. These applications
require relatively thick plates, approximately from 30 to 100
~m in thickness. With conventional complex salt baths such as
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perchlorate, glycerate-tartrate, and Trilon baths, however, the
resulting deposits ~ree of trees dendrite are at best 10 ~m
thick. Ordinary baths using no complex s~lt provide only coarse=
crystal films.
Fast progress of the electronic industry in recent years has
created demands Lor various bismuth-base alloys of low-melting
points. Increasing importance is being attached to these low=
melting solders because o~ the introduction o~ semiconductors
with more and more dellcate thermal properties. Ordinary sol-
ders, typi~ied by the Sn-Pb alloy, have the disadvanta~e of
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so-called low-temperature brittleness. Component parts soldered
with them become brittle when placed in environmcnts below ordi
nary temperature, as are encountered by the soldered parts of
devices and apparatus for use in superconductive and space
development projects. For services in such severe environments,
therefore, low-temperature resistant solders are desirable.
Examples are Bi-Sn, Bi-In, Bi-Pb, Bi-Co, Bi-Ni, Bi-Sb, Bi-In-Sn,
and Bi-Sn-Pb alloys. Since the st;~ndard electrode potential of
bismuth is far nobler than those of tin, indium, and lead, there
occurs practically no codeposition of these alloying elements
from their simple solution. To make their deposition potentials
as close to one another as possible, a camplex salt bath must
be used instead!
Varied 8i-Sn alloy plating baths, for example, in the ~orm
of sulfate, chloride, perchlorate, boro~luoride, and alkali
baths, have hitherto been reported. Nevertheless, because o~
the electric potential difference, it is dlfficult to codeposit
a relatively large proportion of bismuth to tin, and an electro-
deposit of the low-~elting alloy can hardl~ be obtained. As for
the Bi-In alloy plating from a perchlorate bath, the limitation
to the current density range over which the codeposit is formed
makes it rarely possible to obtain thick, good alloy plates.
SU~ARY OF THE INVENTION
The present invention has resulted ~rom investigations made
in view o~ the foregoine. It i9 ai~ed at providing a pl-tin~
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bath which consists essentially of an organic sulfonic acid that
seldom poses a pollution problem and salts of bismuth and a metal
other than bismuth, and gives substantially better electrodepo-
sits than those from conventional inorganic acid baths, and
permits easy control of the bath in alloy plating, inasmuch as
the electrodeposit composition is close to the metal proportion
in the bath. Thus the investigations have led to the discovery
of useful acids for the above purpose.
In the case of Bi-Sn alloy pl~ating, a major disadvantage is
that, where the electric potential difference between tin and
bismuth is too wide for the passage of current, bismuth can be
lost by its contact deposition on the anode tin surface. It has
now been found that the plating bath of the invention character-
istically inhibits to a large measure the unwanted bismuth
deposition on the anode tin surface.
DETAILED D~SCRIPTION OF THE INVENTION
The organic sulfon~c acids to be used in accordance with the
invention are sulfonic acids as aliphatic or nonbenzene alicyclic
compounds of the general formula ~I)
(Xl) n ~ ~ -S Os~
wherein R is a Cl 5 alkyl radical, Xl is a halogen atom or
hydroxyl 9 aryl, alkylaryl, carboxyl, or sulfonyl radical which
may be in any optional position of the alkyl radical, and n is
an integer of O to 3, and aromatic sulfonic acids having various
substituen~s o~ The formula (I.)
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I~(X2)m ~
wherein X2 is a halogen atom or hydroxyl, alkyl, aryl, alkylaryl,
aldehyde, carboxyl, nitro, mercapto, sulfonyl, or amino radical,
or two Xz's which may combine with a benzene ring to form a
naphthalene ring, and m is an lnteger of 0 to 3.
Examples of these organic sulfonic aclds are methanesulfonic,
ethanesulfonic, propanesul~onic, 2-propanesulfonic, butanesulfon-
ic, 2-butanesulfonic, pentanesulfonlc, chloropropanesulfonic,
2-hydroxyethane-l-sulfonic, 2-hydroxypropane-l-sulfonic, 2-hy-
droxybutane-l-sul~onic, 2-hydroxypentanesulfonic, allylsulfonic,
~-sulfoacetic, 2- or 3-sulfopropionic, sul~osuccinic, sulfo-
maleic, sulfofumaric, benzenesulfonic, toluenesulfonic~ xylene-
sulfonic, nitrobenzenesulfonic, sulfobenzoic, sulfosalicylic,
2nd benzaldehydesuifonlc acids. These acids are used alone or
as a mixture of two or more. Their bismuth salts and salts of
metals other than bismuth are prepared in the usual manner.
A bismuth plating bath contains such an organic sul~onic acid
and its bismuth salt. In the case o~ 2 bismuth alloy plating
~ath, such an organic sulfonic acid, its bismuth salt, and
ano~her or two ar more metal salts are contained.
The total concentration of bi6muth and another metal
salt of the organic sul~onic acid is, in terms of the metals,
from 0.5 to 200 gJ~t preferably from lO to lO0 g/~. The
concentration of the free organic
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sulfonic acid to be pre~ent in the plating bath is
stoichiometrically at least an equivalent to the concentration
of the bismuth and other metal salts in the bath. Preferably,
the concentration of the free organic sulfonic acid is
30-400 g/Q.
The plating bath of the invention may contain peptone, gela-
tin, nonionic surfactant, or other additive effective in avoiding
burnt deposits due to exeessive current lntensity and in inhibit-
ing dendritic growth. The concentration of the additive usually
ranges from 0.01 to 50 g~l, preferably from 0.05 to 20 g/l.
*
Among typical nonionic surfactants for this use are "Epon 740",
"Liponox N-105", and "Neugen EN".
~ X A M P L E S
While the present invention is illustrated by the following
several examples in which certain plating bath compositions and
operating conditions are used, it should be noted that the inven~
tion is not limited thereto but may be ~ariously embodied with
changes in the compositions and conditions to realize the objects
of obtaining uniform, smooth plated deposits.
Throughout the examples, the outward appearance of the plate
obtained was e~aluated by the Hull cell test.
Example 1
Bismuth (as bismuth methanesulfonate) 20 g/l
Free methanesul~onic acid 150 "
Gelatin 5 "
Temperature 25C
Current density range 0.5-S A/dm
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Example 2
Bismuth tas bismuth 2-hydroxypropanesulfonate) 15 g/~
Free 2-hydroxypropanesulfonic acid 100 "
"Epon 740"
Temperature 30C
Current density range 0.2-3 A/dm2
Example 3
Bismuth (as bismuth sulfosuccinate) 30 g/2
Free sulfosuccinic acid . 200
Peptone 5 "
Temperature 20C
Current density range 1-6 A/dm2
Example 4
Bismuth (as bismuth p-phenolsulfonate) 25 g/~
Free p-phenolsulfonic acid 120
Peptone 2
Temperature 25C
Current density range 1-5 A/dm2
Example 5
Bismuth (as bismuth p-toluenesulfonate) 6 g/~
Free p-toluenesulfonic acid 150
Gelatin 3 "
Temperature 30C
Current density range 0.2-S A/dm2
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Bismuth (as bismuth sulfosalicylate) 10 g/Q
Free sulfosalicylic acld 200 "
"Liponox N-105"
Temperature 30C
Current densit~ range 0.5-5 A/dm2
With the platin~ baths of Examples 1 to 6, Hull cell tests
were conducted under the conditions of 1 A and 5 min. Each
example gave a grayish white smooth electrodeposit.
Example 7
Bismuth ~as bismuth methanesulfonate) 2 g/Q
Divalent tin (as stannous methanesulfonate) 18 "
Free methanesulfonic acid 150 "
"Neugen EN" ` 5 "
Temperature 25C
Current density range 0.5-3 A/dm2
Example 8
Bismuth (as bismuth benzenesulfonate) 12 g/2
Divalent tin (as tin benzenesulfonate) 8 "
Free benzenesulfonic acid 120 "
Peptone 2 "
Temperature 30C
Current density range 0.2-5 A/dm2
Example 9
Bismuth (as bismuth 2-hydroxypropanesulfonate) 10 g/~
Divalent tin (as stannous 2-hydrox~propanesulfonate)
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Lead (as lead 2-hydroxypropanesulfonate) 4.4 "
Free 2-hydroxypropanesulfonic acid 180 "
Gelatin 7 "
Temperature 20C
Current density ran~e 0.1-3 A/dm2
The plating baths of Examples 7 to 9 were subjected to Hull
cell tests under the conditions of 1 A and 5 minO All gave gray-
ish white smooth electrodeposits.
In order to con~irm the composition of the electrodeposit
formed by the bismuth alloy plating, plating was carried out by
600-coulomb constant current electrolysis, using a stainless
steel plate (0,3 x 3 x 5 cm) as the cathode, with cathode rocking
at a rate of 2 m/min, while ~arying the current density over a
range of 0.5 - 3 A/dm2. After each run the electrodeposit formed
was scraped off by a knife and dissolved in 6N-HN03 with the
~pplication of heat. Tin was separated and the bismuth in the
solution was determined by the atomic absorption-spectroscopy,
The results are given in Table 1.
T a b 1 e
Dk (Ajdm2) 0.5 1.0 2.0 3.0
Bi in electrodeposit, % 26,0 20.4 13,8 15.3
Current efficiency, % 89.2gO.3 73.2 56.4
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