Note: Descriptions are shown in the official language in which they were submitted.
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ACID BATH FOR COPPER PLATING
FIELD OF THE INVENTION
The invention relates to an acid bath for galvanic
precipitation of bright and smooth copper coatings and
their use.
BACKGROUND OF THE INVENTION
It has long been known that certain organic substances
can be added in small quantities to acid, in particular the
most widely used sulfuric acid, copper electrolytes in
order to obtain bright copper coatings instead of a matte
crystalline precipitation. For this purpose, for example,
polyethylene glycol, thiourea, gelatins, molasses, instant
coffee, "base" dyes and thiophosphoric acid ester have been
used. However, such baths no longer have practical
importance since the quality of the copper coatings
obtained do not meet today's requirements. So these
coatings are either too brittle or they are not bright
enough or they precipitate in a relief formation in certain
current density areas.
The addition of polyalkylimines in connection with
organic thio compounds (DE-PS 1246347, February 15, 1968)
and polyvinyl compounds in a mixture with oxygen-containing
high-molecular compounds and organic, in particular
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aromatic thio compounds (DE-AS 1521062, November 18, 1971)
is known. However, copper electrolytes of this type do not
permit the use of high cathodic current densities and the
precipitated copper coatings can also only be nickel-coated
after a prior intermediate treatment. In the above named
DE-AS 1521062, an acid copper bath is also described, which
in addition to a polymer oxygen-containing compound with
hydrophilic group, contains at least one substituted
phenazonium compound dissolved in it. With these monomer
phenazonium compounds, there is room for improvement in the
current density that can be used and the aging behavior.
In addition, combinations of organic thio compounds and
non-ionogenic wetting agents with other dyes, for example
crystal violet (EP-PS 71512, June 5, 1985), amidene (DE-PS
2746938, April 9, 1987), phthalocyanine derivatives with
aposafranine (DE-PS 3420999, October 15, 1987) are known.
Instead of dyes, undefined conversion products of
polyamines with benzylchloride (DE-PS 2541897, January 21,
1982) and/or epichlorhydrine (EP-PS 68807, April 1, 1987)
or those with thio compounds and acrylamide (EP-PS 107109,
February 24, 1988) are used.
The previously known baths all produce non-uniform
deposits; this is particularly true of the combination with
thio compounds containing nitrogen.
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Baths that contain polymer phenazonium compounds (DE-
PS 2,039,831, January 5, 1972) resulted in progress; these
are mainly used in combination with non-ionogenic wetting
agents and organic sulfur compounds.
In fact, it is the state of the art to add non-
ionogenic wetting agents to the acid copper baths, however
this did not eliminate the fine roughness.
The use of ~-naphthol-polyglycolether as an addition
to a copper bath will be disclosed in DE-OS 37 21 985
(January 12, 1989) (Example 2) and GB-A-2075063 (November
11, 1981), but not in combination with polymer phenazonium
compounds.
DE-PS 3104108 (February 5, 1987) describes a
fluoroborate bath that contains ~-naphtholethoxylate in
combination with a phthalocyanine dye. The electrolyte
itself shows only a moderate smoothing in comparison to
polymer phenazonium compounds. With high smoothing, the
disadvantage of these baths is a fine roughness (pitting,
nodules) on the coating, which seriously impairs the
decorative appearance, particularly of large-surface parts.
This roughness does not result from floating particles in
the electrolyte, rather it is a result of a defective
precipitation in the cathodic double layer. This occurs
especially with nitrogen-containing sulfur compounds (so-
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called thiourea derivatives) and with phenazonium
compounds.
The task of this invention is to prevent the
disadvantages described and additionally not to impair the
advantageous smoothing.
SiJMMARY OF THE INVENTION
According to one aspect, the invention an aqueous acid
bath for galvanic deposition of bright and smooth copper
coatings, said bath comprising: a (3-naphtholalkoxylate of
the formula I
~0(CHZCH20)n(CH-CH20)m-H I
CH3
in which n = 0 to 50 and m = 0 to 50, wherein n + m > 3;
at least one nitrogen-containing thio compound selected
from the group consisting of thiourea, thiourea
derivatives, or heterocyclic compounds containing S and N;
and a polymer phenazonium compound.
In another aspect, the invention provides a process
for galvanic deposition of bright and smooth copper
coatings comprising the steps of: a) providing an
electrolyte bath comprising an aqueous acid bath as
described herein; and b) applying a cathodic current
density of from about 0.5 to about 12 A/dm2.
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DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Compounds of
Table 1
~-Naphthol-tetracosa (ethoxylate) n = m =
24; 0
~-Naphthol-eicosa (ethoxylate) n = m =
20; 0
~-Naphthol-octadeca (ethoxylate) n = m =
18; 0
~-Naphthol-hexadeca (ethoxylate) n = m =
16; 0
~-Naphthol-tetradeca (ethoxylate) n = m =
14; 0
Q-Naphthol-trideca (ethoxylate) n = m =
13; 0
Q-Naphthol-dodeca (ethoxylate) n = m =
12; 0
~-Naphthol-deca (ethoxylate) n = m =
10; 0
~-Naphthol-octa (ethoxylate) n = 8; m 0
=
~-Naphthol-hexa (ethoxylate) n = 6; m 0
=
b-Naphthol-tetracosa (propoxylate) n = 0; m 24
=
~-Naphthol-tetracosa (ethoxy) n = 24; m =
1-
-mono (propoxylate)*)
B-Naphthol-octadeca (ethoxy)- n = 20; m =
2
di(proproxylate)*)
~-Naphthol-mono (propoxy)- n = 24; m =
1
tetracosa (ethoxylate)*)
~-Naphthol-di (propoxy)- n = 20; m =
2
octadeca (ethoxylate)*)
+) mixed or block polymeride
are particularly suited as B-naphtolalkoxylate of the
general formula I.
Thiourea and thiourea derivatives and heterocyclic
compounds containing S and N are used as nitrogen
containing thiocompounds.
Table 2 contains examples of nitrogen-containing thio
compounds (so-called thiourea derivatives) or heterocyclic
compounds containing S and N and Table 3 of polymer
phenazonium compounds.
~~~3~~~
Table 2
Thiourea
N-Acetylthiourea
5 N-Trifluorocetylthiourea
N-Ethylthiourea
N-Cyanoacetylthiourea
N-Allylthiourea
0-Tolylthiourea
N,N'-Butylenethiourea
Thiazolidinethiol (2)
~-Thiazolinethiol (2)
Imidazolidinethiol (2) (N, N'-Ethylenethiourea)
4-Methyl-2-pyrimidinethiol
2-Thiouracil
Table 3
Poly(6-methyl-7-dimethylamino-5-phenyl-phenazonium sulfate)
Poly(2-methyl-7-diethylamino-5-phenyl-phenazonium chloride)
Poly(2-methyl-7-dimethylamino-5-phenyl-phenazonium sulfate)
Poly(5-methyl-7-dimethylamino-phenazonium acetate)
Poly(2-methyl-7-anilino-5-phenyl-phenazonium sulfate)
Poly(2-methyl-7-dimethylamino-phenazonium sulfate)
Poly(7-methylamino-5-phenyl-phenazonium acetate)
Poly(7-ethylamino-2, S-diphenyl-phenazonium chloride)
Poly(2,8-dimethyl-7-diethylamino-5-p-tolyl-phenazonium
chloride)
Poly(2,5,8-triphenyl-7-dimethylamino-phenazonium sulfate)
Poly(2,8-dimethyl-7-amino-5-phenyl-phenazonium sulfate)
Poly(7-Dimethylamino-5-phenyl-phenazonium chloride)
For the solutions according to the invention, mixtures of
the compounds listed in Tables 1, 2 and 3 are used.
The preferred quantity of the ~-naphtholethoxylate that
must be added in order to achieve a clear improvement in
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copper precipitation is about 0.005 to 3 g/liter,
preferably 0.01 to 0.25 g/liter.
The ~-naphtholoethoxylates are known or can be
produced using methods known in and of themselves from ~-
naphthol with ethylene oxide and/or propylene oxide.
The individual components of the copper bath according
to the invention can generally contain the following,
advantageously within the following limit concentrations in
the ready-to-use bath:
l0
Standard oxygen-containing
high-molecular weight compounds
(referred to herein as oxygen-
containing high-molecular compounds) 0.005 - 20 g/liter
preferably 0.01 - 5 g/liter
Standard organic thio
compounds with hydrophilic
2o groups 0.0005 - 0.2 g/liter
preferably 0.001 - 0.03 g/1
Standard nitrogen-containing
thio compounds (so-called
thiourea derivatives) and/or
polymer phenazonium compounds 0.0001 - 0.50 g/liter
preferably 0.0005 - 0.04 g/liter
The basic composition of the bath according to the
invention can vary within wide limits. In general, an
aqueous solution of the following composition is used:
7
Copper sulfate (CuS04 5H20) 20 - 250 g/liter
preferably 60 - 80
g/liter or
180 - 220 g/liter
Sulfuric acid 50 - 350 g/liter
preferably 180 - 220 g/liter
ox
50 - 90 g/liter
Sodium chloride 0.02 - 0.25 g/liter
preferably 0.05 - 0.12 g/liter
Instead of copper sulfate, other copper salts can also be
used, at least in part. Sulfuric acid can also be
partially or completely replaced by fluoroboric acid,
methane sulfonic acid or other acids. The addition of
sodium chloride can be omitted partially or entirely if
halogen ions are already contained in the additives.
In addition, standard brighteners, smoothing agents or
wetting agents can also be contained in the bath.
To produce the bath according to the invention, the
individual components are added to the basic composition.
The operating conditions of the bath are as follows:
pH value:
< 1
Temperature: ' 15°C - 45°C, preferably
20°C - 30°C
Cathodic current density: 0.5 - 12 A/dm2,
preferably 2-4 A/dm2
The electrolyte motion is caused by blowing in air.
Copper with a 0.02 to 0.067% phosphorous content is used as
the anode.
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The invention also includes processes using the baths
according to the invention.
The following examples are used to explain the invention:
EXAMPLE 1
0.2 g/liter polyethylene glycol and
0.01 g/liter bis-(w-sulfopropyl)-disulfide, disodium
salt
as a brightening agent
and 0.02 g/liter polymer 7-dimethylamino-5-phenyl-
phenazonium chloride
are added to a copper bath of the composition
200.0 g/liter copper sulfate (CuS04 ~ 5Hz0)
65.0 g/liter sulfuric acid
0.2 g/liter sodium chloride.
At an electrolyte temperature of 27°C, with a current
density of 4 A/dmz and air blown in, a well smoothed, bright
copper coating is obtained that shows fine roughness
(pitting) on polished brass sheet metal when closely
examined.
If 0.025 g/liter of f3-naphtolalkoxylate of the general
formula I with n = 12 and m = 0 is also added to the bath,
the plating has a mirror finish and is well smoothed. No
voids can be found.
2~~3~~4
9
EXAMPLE 2
0.6 g/liter polyethylene glycol and
0.02 g/liter 3-mercaptopropane-1-sulfonic acid,
sodium salt
as a brightener
and 0.003 g/liter N-acetylthiourea
are added to a copper bath of the composition
80.0 g/liter copper sulfate (CuS04 ~ 5H20)
180.0 g/liter conc. sulfuric acid
0.08 g/liter sodium chloride.
At an electrolyte temperature of 30°C, with a current
density of 2 A/dm2, a bright copper coating is obtained on
scratched copper laminate, on which fine roughness
(pitting) is visible.
If 0.05 g/liter of the substance according to the invention
of the general formula I with n = 24 and m = 0 is also
added to the bath, the copper costing is bright and
contains no faults.
