U.S. patent application number 12/893454 was filed with the patent office on 2012-03-29 for iridium plating solution and method of plating using the same.
Invention is credited to MASAHIRO ITO.
Application Number | 20120073980 12/893454 |
Document ID | / |
Family ID | 45869526 |
Filed Date | 2012-03-29 |
United States Patent
Application |
20120073980 |
Kind Code |
A1 |
ITO; MASAHIRO |
March 29, 2012 |
IRIDIUM PLATING SOLUTION AND METHOD OF PLATING USING THE SAME
Abstract
Proposed are an iridium plating solution capable of easily
forming an iridium plating coat in which the occurrence of cracks
is suppressed as much as possible and an iridium plating method. In
the present invention, the iridium plating solution uses an iridium
compound obtained by adding, to an iridium (III) complex salt
containing a halogen as an anionic component, one or more compounds
selected from the following group and by stirring the resulting
mixture, the group consisting of a saturated monocarboxylic acid, a
saturated monocarboxylic acid salt, a saturated dicarboxylic acid,
a saturated dicarboxylic acid salt, a saturated hydroxycarboxylic
acid, a saturated hydroxycarboxylic acid salt, an amide and urea,
wherein the iridium plating solution includes at least one or more
of Fe, Co, Ni and Cu.
Inventors: |
ITO; MASAHIRO;
(Hiratsuka-shi, JP) |
Family ID: |
45869526 |
Appl. No.: |
12/893454 |
Filed: |
September 29, 2010 |
Current U.S.
Class: |
205/234 |
Current CPC
Class: |
C25D 3/567 20130101;
C25D 3/52 20130101 |
Class at
Publication: |
205/234 |
International
Class: |
C25D 3/54 20060101
C25D003/54 |
Claims
1. An iridium plating solution using an iridium compound obtained
by adding, to an iridium (III) complex salt containing a halogen as
an anionic component, one or more compounds selected from a
following group and by stirring a resulting mixture, the group
consisting of a saturated monocarboxylic acid, a saturated
monocarboxylic acid salt, a saturated dicarboxylic acid, a
saturated dicarboxylic acid salt, a saturated hydroxycarboxylic
acid, a saturated hydroxycarboxylic acid salt, an amide and urea,
wherein the iridium plating solution comprises at least one or more
of Fe, Co, Ni and Cu.
2. The iridium plating solution according to claim 1, wherein the
content of at least one or more of Fe, Co, Ni and Cu is 0.01 g/L to
10 g/L.
3. An iridium plating method wherein the plating solution according
to claim 1 is used, and plating is performed under the conditions
that the pH is 1 to 8, the temperature is 50 to 98.degree. C. and
the current density is 0.01 to 3.0 A/dm.sup.2.
4. An iridium plating method wherein the plating solution according
to claim 2 is used, and plating is performed under the conditions
that the pH is 1 to 8, the temperature is 50 to 98.degree. C. and
the current density is 0.01 to 3.0 A/dm.sup.2.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an iridium plating solution
and a method of plating using the same.
[0003] 2. Description of the Related Art
[0004] Iridium is a metal having high hardness and additionally
exhibiting excellent corrosion resistance to high-concentration
acids, aqua regia and halogens. Accordingly, the application fields
of iridium include hardening agents for specific metals and
catalysts as well as ornaments, and further iridium is industrially
widely used as anticorrosives and materials such as electric
contact materials.
[0005] As an iridium plating solution in such applications of
iridium, known is an iridium plating solution using an iridium
compound obtained by adding, to an iridium (III) complex salt
containing a halogen as an anionic component, one or more compounds
selected from the following group and by stirring the resulting
mixture, the group consisting of a saturated monocarboxylic acid, a
saturated monocarboxylic acid salt, a saturated dicarboxylic acid,
a saturated dicarboxylic acid salt, a saturated hydroxycarboxylic
acid, a saturated hydroxycarboxylic acid salt, an amide and urea
(see Japanese Patent Application Laid-Open No. 6-316786).
[0006] The above-described iridium plating solution is effectively
used as a practical iridium plating solution being stable and
hardly decomposable and having a high current efficiency and a high
plating rate.
[0007] Even such an excellent iridium plating solution, however, is
pointed out as follows with respect to the plating properties and
conditions thereof. For example, when the iridium plating solution
is used for electronic parts for use in electric connection such as
lead pins (see Japanese Patent Application Laid-Open No. Hei
7-21867), cracks occur in the iridium plating coat to cause a
phenomenon in which electric properties are not sufficiently
satisfied as the case may be. In the electronic parts such as the
lead pins, usually iridium plating coats are applied to rhodium
substrates; however, as the price of rare metals such as rhodium is
escalated, a countermeasure is investigated in which the amount of
rhodium used in the substrate is reduced and plating processing is
performed so as for the iridium plating coat to be thick. When such
thick iridium plating coats are formed, conventional iridium
plating solutions lead to particularly remarkable occurrence of
cracks and electric properties are not sufficiently satisfied as
the case may be.
SUMMARY OF THE INVENTION
[0008] The present invention has been achieved under the
above-described circumstances, and an object of the present
invention is to propose an iridium plating solution capable of
easily forming an iridium plating coat in which the occurrence of
cracks is suppressed as much as possible and an iridium plating
method.
[0009] In the present invention, the iridium plating solution uses
an iridium compound obtained by adding, to an iridium (III) complex
salt containing a halogen as an anionic component, one or more
compounds selected from the following group and by stirring the
resulting mixture, the group consisting of a saturated
monocarboxylic acid, a saturated monocarboxylic acid salt, a
saturated dicarboxylic acid, a saturated dicarboxylic acid salt, a
saturated hydroxycarboxylic acid, a saturated hydroxycarboxylic
acid salt, an amide and urea, wherein the iridium plating solution
includes at least one or more of Fe, Co, Ni and Cu. The presence of
at least any metal of Fe, Co, Ni and Cu in the plating solution
effectively suppresses the occurrence of cracks in the iridium
plating coat.
[0010] In the iridium plating solution of the present invention,
the content of at least one or more of Fe, Co, Ni and Cu is
preferably 0.01 g/L to 10 g/L. When the concerned content is less
than 0.01 g/L, cracks tend to occur, and when the concerned content
exceeds 10 g/L, crystal growth is unstable.
[0011] Any metal of Fe, Co, Ni and Cu is preferably contained as a
soluble metal salt in the plating solution.
[0012] In the iridium plating solution in the present invention,
iridium is preferably contained in a content of 1 to 200 g/L, and
more preferably in a content of 10 to 20 g/L in terms of the metal
iridium concentration. When the iridium concentration is less than
1 g/L, the upper limit of the current density is small to make the
iridium plating solution hardly practically usable, and when the
iridium concentration is larger than 200 g/L, the iridium plating
solution is saturated to make iridium insoluble and at the same
time, the cost is expensive to be practically inappropriate.
Examples of the adoptable iridium (III) complex salt include
hexachloroiridic (III) acid salt, a hexabromoiridic (III) acid salt
and a hexafluoroiridic (III) acid salt, and preferably sodium
hexabromoiridate (III) and sodium hexachloroiridate (III).
[0013] Further, one or more compounds selected from the following
group are added preferably in a content of 0.001 to 1.0 mol/L and
more preferably in a content of 0.01 to 0.2 mol/L, the group
consisting of a saturated monocarboxylic acid, a saturated
monocarboxylic acid salt, a saturated dicarboxylic acid, a
saturated dicarboxylic acid salt, a saturated hydroxycarboxylic
acid, a saturated hydroxycarboxylic acid salt, an amide and urea.
Examples of the compounds adoptable as such compounds include
acetic acid, disodium malonate and oxalic acid, and preferably
disodium malonate. The reasons for setting the addition amount of
such a compound or such compounds at 0.001 to 1.0 mol/L are such
that when the addition amount is less than 0.001 mol/L, the effect
due to the addition is hardly exhibited, and when the addition
amount exceeds 1.0 mol/L, the deposition is disturbed.
[0014] The iridium plating solution according to the present
invention may contain, where necessary, a buffering agent for
regulating the pH, such as boric acid and sulfamic acid.
[0015] The iridium plating method according to the present
invention is applied under the operation conditions that the pH is
set at 1 to 8, the temperature is set at 50 to 98.degree. C. and
the current density is set at 0.01 to 3.0 A/dm.sup.2, and
preferably under the conditions that the pH is set at 4 to 6, the
temperature is set at 80 to 90.degree. C. and the current density
is set at 0.1 to 0.8 A/dm.sup.2. The pH is set at 1 to 8 because
when the pH is lower than 1, the upper limit of the current density
is small to make the plating method impractical, and when the pH is
higher than 8, a hydroxide is produced to cause precipitation. When
the temperature is lower than 50.degree. C., deposition is made to
extremely hardly occur, and when the temperature is higher than
98.degree. C., practically unpreferably evaporation of water is
vigorous. When the current density is lower than 0.01 A/dm.sup.2,
the deposition rate is extremely small, and when the current
density is higher than 3.0 A/dm.sup.2, the generation of hydrogen
occurs to prevent the deposit from being deposited.
[0016] According to the present invention, it is possible to form
an iridium plating coat in which the occurrence of cracks is
suppressed as much as possible.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is an observation photograph of a plated surface in
Example 1;
[0018] FIG. 2 is an observation photograph of a plated surface
involving no metal addition;
[0019] FIG. 3 is an observation photograph of a plated surface in
Example 2;
[0020] FIG. 4 is an observation photograph of a plated surface for
a Co content of 20.0 g/L in Example 2;
[0021] FIG. 5 is an observation photograph of a plated surface in
Example 3;
[0022] FIG. 6 is an observation photograph of a plated surface for
a Ni content of 15.0 g/L in Example 3;
[0023] FIG. 7 is an observation photograph of a plated surface in
Example 4; and
[0024] FIG. 8 is an observation photograph of a plated surface in
Example 5.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0025] Hereinafter, the embodiments of the present invention are
described in detail with reference to Examples.
Example 1
[0026] In Example 1, a case where Fe was added to the iridium
plating solution is described. The solution composition of Example
1 was as follows.
[0027] Sodium hexabromoiridate (III): 15 g/L (in terms of iridium
metal)
[0028] Boric acid: 40 g/L
[0029] Disodium malonate: 0.02 mol/L
[0030] Iron sulfate heptahydrate: 0.01 g/L (in terms of iron
metal)
[0031] In Example 1, the iridium plating solution used an iridium
compound obtained by adding, to the above-described sodium
hexabromoiridate (III), disodium malonate as a dicarboxylic acid
salt and by stirring the resulting mixture with a magnetic stirrer
for 1 hour while the temperature of the mixture was being
maintained at 85.degree. C. by using a laboratory water bath. Iron
sulfate heptahydrate was added to the resulting iridium plating
solution to allow the plating solution to contain Fe in a content
of 0.01 g/L.
[0032] Then, a 2 cm.times.2 cm brass test piece was subjected to a
gold strike plating treatment to form a 1.0-.mu.m thick gold
plating coat, and then subjected to a formation of a 3.0-.mu.m
thick iridium plating coat. The plating conditions were such that
the pH was set at 3.5 to 4.0, the solution temperature was set at
80 to 85.degree. C. and the current density was set at 0.5
A/dm.sup.2.
[0033] The plating properties and conditions of the coated iridium
plating coat were observed by using a metallograph (magnification:
400.times.). The results thus obtained are shown in FIG. 1.
[0034] Additionally, for comparison, a sample was prepared in which
an iridium plating coat was formed by using a iridium plating
solution prepared without adding any one of Fe, Co, Ni and Cu. The
plating conditions were set as the same as the plating conditions
in the case where Fe was contained. The results thus obtained are
shown in FIG. 2.
[0035] As shown in FIG. 2, it was verified that the sample coated
with the iridium plating solution not containing Fe underwent the
occurrence of a large number of cracks on the surface thereof. On
the other hand, as shown in FIG. 1, in the case of the iridium
plating solution which was allowed to contain Fe, almost no cracks
were identified.
[0036] Additionally, the Fe content was varied to be 0.005 g/L,
0.01 g/L, 0.5 g/L, 5.0 g/L and 10 g/L, and thus the crack
occurrence conditions were examined; consequently, the occurrence
of cracks was observed for 0.005 g/L, but no occurrence of cracks
was observed for the Fe contents of 0.01 g/L or more.
Example 2
[0037] In Example 2, a case where Co was added to the iridium
plating solution is described. The solution composition of Example
2 was as follows.
[0038] Sodium hexabromoiridate (III): 15 g/L (in terms of iridium
metal)
[0039] Boric acid: 40 g/L
[0040] Disodium citrate: 0.05 mol/L
[0041] Cobalt sulfate heptahydrate: 0.5 g/L (in terms of cobalt
metal)
[0042] In Example 2, the iridium plating solution used an iridium
compound obtained by adding, to the above-described sodium
hexabromoiridate (III), disodium citrate as a hydroxycarboxylic
acid salt and by stirring the resulting mixture with a magnetic
stirrer for 1 hour while the temperature of the mixture was being
maintained at 85.degree. C. by using a laboratory water bath.
Cobalt sulfate heptahydrate was added to the resulting iridium
plating solution to allow the plating solution to contain Co in a
content of 0.5 g/L.
[0043] Then, a 2 cm.times.2 cm brass test piece was subjected to a
gold strike plating treatment to form a 1.0-.mu.m thick gold
plating coat, and then subjected to a formation of a 3.0-.mu.m
thick iridium plating coat. The plating conditions were such that
the pH was set at 3.5 to 4.0, the solution temperature was set at
80 to 85.degree. C. and the current density was set at 0.5
A/dm.sup.2.
[0044] The plating properties and conditions of the coated iridium
plating coat were observed by using a metallograph (magnification:
400.times.). The results thus obtained are shown in FIG. 3.
[0045] As shown in FIG. 3, in the case of the iridium plating
solution which was made to contain Co, almost no cracks were
identified.
[0046] Additionally, the Co content was varied to be 0.005 g/L,
0.01 g/L, 0.5 g/L, 5.0 g/L and 10 g/L, and thus the crack
occurrence conditions were examined; consequently, the occurrence
of cracks was observed for 0.005 g/L, but no occurrence of cracks
was observed for the Co contents of 0.01 g/L or more.
[0047] Further, the Co content was set at 20.0 g/L, and the plating
properties and conditions were observed by using a metallograph
(magnification: 400.times.).
[0048] The results thus obtained are shown in FIG. 4. With the Co
content of 20.0 g/L, no normal deposition was attained.
Example 3
[0049] In Example 3, a case where Ni was added to the iridium
plating solution is described. The solution composition of Example
3 was as follows.
[0050] Sodium hexabromoiridate (III): 15 g/L (in terms of iridium
metal)
[0051] Boric acid: 40 g/L
[0052] Oxalic acid: 0.05 mol/L
[0053] Nickel sulfate hexahydrate: 0.5 g/L (in terms of nickel
metal)
[0054] In Example 3, the iridium plating solution used an iridium
compound obtained by adding, to the above-described sodium
hexabromoiridate (III), oxalic acid as a dicarboxylic acid and by
stirring the resulting mixture with a magnetic stirrer for 1 hour
while the temperature of the mixture was being maintained at
85.degree. C. by using a laboratory water bath. Nickel sulfate
hexahydrate was added to the resulting iridium plating solution to
allow the plating solution to contain Ni in a content of 0.5
g/L.
[0055] Then, a 2 cm.times.2 cm brass test piece was subjected to a
gold strike plating treatment to form a 1.0-.mu.m thick gold
plating coat, and then subjected to a formation of a 3.0-.mu.m
thick iridium plating coat. The plating conditions were such that
the pH was set at 3.5 to 4.0, the solution temperature was set at
80 to 85.degree. C. and the current density was set at 0.5
A/dm.sup.2.
[0056] The plating properties and conditions of the coated iridium
plating coat were observed by using a metallograph (magnification:
400.times.). The results thus obtained are shown in FIG. 5.
[0057] As shown in FIG. 5, in the case of the iridium plating
solution which was made to contain Ni, almost no cracks were
identified.
[0058] Additionally, the Ni content was varied to be 0.005 g/L,
0.01 g/L, 0.5 g/L, 5.0 g/L and 10 g/L, and thus the crack
occurrence conditions were examined; consequently, the occurrence
of cracks was observed for 0.005 g/L, but no occurrence of cracks
was observed for the Ni contents of 0.01 g/L or more.
[0059] Further, the Ni content was set at 15.0 g/L, and the plating
properties and conditions were observed by using a metallograph
(magnification: 400.times.). The results thus obtained are shown in
FIG. 6. With the Ni content of 15.0 g/L, no normal deposition was
attained.
Example 4
[0060] In Example 4, a case where Cu was added to the iridium
plating solution is described. The solution composition of Example
4 was as follows.
[0061] Sodium hexabromoiridate (III): 15 g/L (in terms of iridium
metal)
[0062] Boric acid: 40 g/L
[0063] Acetic acid: 0.02 mol/L
[0064] Copper sulfate pentahydrate: 0.01 g/L (in terms of copper
metal)
[0065] In Example 4, the iridium plating solution used an iridium
compound obtained by adding, to the above-described sodium
hexabromoiridate (III), acetic acid as a monocarboxylic acid and by
stirring the resulting mixture with a magnetic stirrer for 1 hour
while the temperature of the mixture was being maintained at
85.degree. C. by using a laboratory water bath. Copper sulfate
pentahydrate was added to the resulting iridium plating solution to
allow the plating solution to contain Cu in a content of 0.01
g/L.
[0066] Then, a 2 cm.times.2 cm brass test piece was subjected to a
gold strike plating treatment to form a 1.0-.mu.m thick gold
plating coat, and then subjected to a formation of a 3.0-.mu.m
thick iridium plating coat. The plating conditions were such that
the pH was set at 3.5 to 4.0, the solution temperature was set at
80 to 85.degree. C. and the current density was set at 0.5
A/dm.sup.2.
[0067] The plating properties and conditions of the coated iridium
plating coat were observed by using a metallograph (magnification:
400.times.). The results thus obtained are shown in FIG. 7.
[0068] As shown in FIG. 7, in the case of the iridium plating
solution which was made to contain Cu, almost no cracks were
identified.
[0069] Additionally, the Cu content was varied to be 0.005 g/L,
0.01 g/L, 0.5 g/L and 1.0 g/L, and thus the crack occurrence
conditions were examined;
[0070] consequently, the occurrence of cracks was observed for
0.005 g/L, but no occurrence of cracks was observed for the Cu
contents of 0.01 g/L or more.
Example 5
[0071] In Example 5, a case where Co was added to the iridium
plating solution is described. The solution composition of Example
5 was as follows.
[0072] Sodium hexachloroiridate (III): 5 g/L (in terms of iridium
metal)
[0073] Boric acid: 20 g/L
[0074] Disodium malonate: 0.10 mol/L
[0075] Cobalt sulfate heptahydrate: 0.5 g/L (in terms of cobalt
metal)
[0076] In Example 5, the iridium plating solution used an iridium
compound obtained by adding, to the above-described sodium
hexachloroiridate (III), disodium malonate as a dicarboxylic acid
salt and by stirring the resulting mixture with a magnetic stirrer
for 1 hour while the temperature of the mixture was being
maintained at 85.degree. C. by using a laboratory water bath.
Cobalt sulfate heptahydrate was added to the resulting iridium
plating solution to allow the plating solution to contain Co in a
content of 0.5 g/L.
[0077] Then, a 2 cm.times.2 cm brass test piece was subjected to a
gold strike plating treatment to form a 1.0-.mu.m thick gold
plating coat, and then subjected to a formation of a 3.0-.mu.m
thick iridium plating coat. The plating conditions were such that
the pH was set at 3.5 to 4.0, the solution temperature was set at
80 to 85.degree. C. and the current density was set at 0.2
A/dm.sup.2.
[0078] The plating properties and conditions of the coated iridium
plating coat were observed by using a metallograph (magnification:
400.times.). The results thus obtained are shown in FIG. 8.
[0079] As shown in FIG. 8, in the case of the iridium plating
solution which was made to contain Co, almost no cracks were
identified.
Example 6
[0080] In Example 6, a case where Ni was added to the iridium
plating solution and the plating conditions were varied is
described. The solution composition of Example 6 was as
follows.
[0081] Sodium hexabromoiridate (III): 10 g/L (in terms of iridium
metal)
[0082] Boric acid: 30 g/L
[0083] Oxalic acid: 0.05 mol/L
[0084] Nickel sulfate hexahydrate: 0.5 g/L (in terms of nickel
metal)
[0085] In Example 6, the iridium plating solution used an iridium
compound obtained by adding, to the above-described sodium
hexabromoiridate (III), oxalic acid as a dicarboxylic acid and by
stirring the resulting mixture with a magnetic stirrer for 1 hour
while the temperature of the mixture was being maintained at
85.degree. C. by using a laboratory water bath. Nickel sulfate
hexahydrate was added to the resulting iridium plating solution to
allow the plating solution to contain Ni in a content of 0.5
g/L.
[0086] Then, a 2 cm.times.2 cm brass test piece was subjected to a
gold strike plating treatment to form a 1.0-.mu.m thick gold
plating coat and then subjected to a formation of a 3.0-.mu.m thick
iridium plating coat, and thus the deposition efficiency was
measured. The plating conditions were such that the pH was set at
2.0 to 8.5, the solution temperature was set at 40 to 95.degree. C.
and the current density was set at 0.01 to 2.0 A/dm.sup.2.
[0087] The deposition efficiency was measured when the solution
temperature was set at 85.degree. C., the current density was set
at 0.5 A/dm.sup.2 and the pH was varied.
[0088] When the pH was 0.5, the deposition efficiency was found to
be 0% and no deposition occurred. When the pH was 3.0, the
deposition efficiency was found to be 85% and no cracks were
identified. When the pH was 4.0 to 7.0, the deposition efficiency
was 95% to 100% and no cracks were identified. Further, when the pH
was 8.5, the hydroxide precipitate occurred.
[0089] Next, the deposition efficiency was measured when the
current density was set at 0.5 A/dm.sup.2, the pH was set at 3.5
and the bath temperature was varied.
[0090] When the bath temperature was 40.degree. C., the deposition
efficiency was found to be 0% and no deposition occurred. When the
bath temperature was 50.degree. C., the deposition efficiency was
found to be 35% and cracks were identified. When the bath
temperature was 60.degree. C. to 70.degree. C., the deposition
efficiency was found to be 40% to 60% and no cracks were
identified. When the bath temperature was 80.degree. C. to
95.degree. C., the deposition efficiency was found to be 90% to
100% and no cracks were identified. When the bath temperature was
increased to 99.degree. C., the evaporation of water from the
plating bath was vigorous and it was difficult to perform stable
plating treatment.
[0091] Next, the deposition efficiency was measured when the bath
temperature was set at 85.degree. C., the pH was set at 3.5 and the
current density was varied.
[0092] When the current density was 0.01 A/dm.sup.2, the deposition
efficiency was found to be 50% and no cracks were identified. When
the current density was 0.02 A/dm.sup.2 to 1.0 A/dm.sup.2, the
deposition efficiency was found to be 90% to 100% and no cracks
were identified. When the current density was 1.5 A/dm.sup.2, the
deposition efficiency was found to be 60% and no cracks were
identified. When the current density was 3.0 A/dm.sup.2, the
deposition efficiency was found to be 20% and cracks were
identified. When the current density was increased to 3.5
A/dm.sup.2, hydrogen was evolved and no normal deposition was
attained.
[0093] It is possible to easily form an iridium plating coat in
which the occurrence of cracks is suppressed as much as
possible.
* * * * *