U.S. patent application number 13/820701 was filed with the patent office on 2013-07-04 for aluminum electroplating solution.
This patent application is currently assigned to HITACHI, LTD.. The applicant listed for this patent is Haruo Akahoshi, Hiroshi Nakano, Yoshinori Negishi. Invention is credited to Haruo Akahoshi, Hiroshi Nakano, Yoshinori Negishi.
Application Number | 20130168258 13/820701 |
Document ID | / |
Family ID | 45892602 |
Filed Date | 2013-07-04 |
United States Patent
Application |
20130168258 |
Kind Code |
A1 |
Nakano; Hiroshi ; et
al. |
July 4, 2013 |
ALUMINUM ELECTROPLATING SOLUTION
Abstract
The purpose of the present invention is to provide an aluminum
electroplating solution that allows aluminum electroplating to be
conducted efficiently and in a short period of time, can increase
the amount of electricity in the current of electroplating, and has
high solubility in a nonaqueous solvent. This aluminum
electroplating solution is characterized by comprising an aluminum
metal salt, an ionic liquid obtained by an organic compound forming
an ion pair with the aluminum metal salt, and an organic solvent
having a dielectric constant of 8 or less. It is preferable for the
volume percentage of the organic solvent in relation to the total
volume of the ionic liquid and the organic solvent to be at least
30%, and for at least one of the following to be included as the
organic solvent having a dielectric constant of 8 or less: hexane,
toluene, diethyl ether, ethylacetate, cyclohexane, xylene, benzene,
naphthalene, heptane, cyclopentyl methyl ether, and dioxane.
Inventors: |
Nakano; Hiroshi; (Tokai,
JP) ; Negishi; Yoshinori; (Hitachi, JP) ;
Akahoshi; Haruo; (Hitachi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Nakano; Hiroshi
Negishi; Yoshinori
Akahoshi; Haruo |
Tokai
Hitachi
Hitachi |
|
JP
JP
JP |
|
|
Assignee: |
HITACHI, LTD.
Tokyo
JP
|
Family ID: |
45892602 |
Appl. No.: |
13/820701 |
Filed: |
September 1, 2011 |
PCT Filed: |
September 1, 2011 |
PCT NO: |
PCT/JP2011/069895 |
371 Date: |
March 4, 2013 |
Current U.S.
Class: |
205/261 |
Current CPC
Class: |
C25D 3/665 20130101;
C25D 3/44 20130101 |
Class at
Publication: |
205/261 |
International
Class: |
C25D 3/44 20060101
C25D003/44 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 30, 2010 |
JP |
2010-220239 |
Claims
1. An aluminum electroplating solution comprising: an aluminum
metal salt, an ionic liquid obtained by an organic compound forming
an ion pair with the aluminum metal salt; and an organic solvent
having a dielectric constant of 8 or less, wherein a volume
fraction of the organic solvent in relation to a total volume of
the ionic liquid and the organic solvent is 75% or more.
2. (canceled)
3. The aluminum electroplating solution according to claim 1,
wherein the aluminum metal salt comprises at least aluminum
halide.
4. The aluminum electroplating solution according to claim 1,
wherein the organic solvent is at least one kind selected from the
group consisting of hexane, toluene, diethyl ether, ethylacetate,
cyclohexane, xylene, benzene, naphthalene, heptane, cyclopentyl
methyl ether, and dioxane.
5. The aluminum electroplating solution according to claim 1,
wherein the organic compound forming an ion pair with the aluminum
metal salt comprises at least one kind selected from the group
consisting of dialkyl imidazolium salt, aliphatic phosphonium salt,
and quaternary ammonium salt.
6. The aluminum electroplating solution according to claim 1,
wherein a molar ratio of the aluminum metal salt in relation to the
organic compound forming an ion pair with the aluminum metal salt
is 1 or more.
7. The aluminum electroplating solution according to claim 1,
wherein the aluminum electroplating solution is obtained by mixing
the aluminum metal salt with the organic compound forming an ion
pair with the aluminum metal salt to prepare the ionic liquid, and
then mixing the ionic liquid with the organic solvent.
8. The aluminum electroplating solution according to claim 1,
wherein the aluminum electroplating solution comprises a base metal
salt other than an aluminum metal salt.
9. The aluminum electroplating solution according to claim 1,
wherein a molar ratio of the aluminum metal salt in relation to the
organic compound forming an ion pair with the aluminum metal salt
is 3 or more.
Description
TECHNICAL FIELD
[0001] The present invention relates to an aluminum electroplating
solution using an organic solvent (non-aqueous solvent).
BACKGROUND ART
[0002] It is difficult to conduct an aluminum electroplating in
aqueous solution type plating bath, because aluminum has a high
affinity to oxygen and has a negative equilibrium potential
compared to hydrogen. Thus, in the aluminum electroplating, many
organic solvent plating solutions have been studied. Typical ones
of this organic solvent type plating bath include AlCl.sub.3 and
LiAlH.sub.4 or LiH dissolved in ether, or AlCl.sub.3 and
LiAlH.sub.4 dissolved in THF (tetrahydrofuran). However, all of
these plating baths contain LiAlH.sub.4 or LiH which are very
active in the baths, and thus react with oxygen or moisture, when
being present, to be decomposed and lower a current efficiency and
shorten a bath life also. Under the circumstances, Patent
Literatures 1 and 2 etc. report a molten salt electrolytic plating
solution containing a dimethylsulfone solvent as a safe and
low-cost plating solution.
[0003] Recently, Patent Literatures 3 and 4 etc. suggest an
aluminum electroplating method using, as a plating bath, a molten
salt comprising 1-alkyl or 1,3-dialkylimidazolium halide,
quarternary ammonium salt or alkylpyridinium halide, and
aluminumhalide etc. However, plating states of these plating baths
are largely changed due to a mixing of moisture, and thus even if
an electroplating is conducted under constant plating conditions, a
uniform plating coating is not always obtained.
CITATION LIST
Patent Literature
[0004] [Patent Literature 1] JP 2004-76031 A [0005] [Patent
Literature 2] JP 2006-161154 A [0006] [Patent Literature 3] JP
62-70592 A [0007] [Patent Literature 4] JP 1-272788 A
SUMMARY OF INVENTION
Technical Problem
[0008] However, conventional nonaqueous electrolytes generally have
a low solubility to an aluminum salt, it is difficult to conduct a
plating treatment at a heavy current in a short period of time, and
a plating operation cannot be efficiently conducted. Additionally,
when oxygen or moisture are present in an electrolyte, there were
problems that an aluminum salt reacts with those to be decomposed
to lower a current efficiency, result in a deteriorated plating
finish, and deteriorate the electrolyte.
[0009] In addition to these problems, in case of a high temperature
molten salt type nonaqueous electrolyte, 100.degree. C. or more is
necessary in an operation and there was a problem that it was
impossible to conduct an operation at an ordinary temperature.
Additionally, in case of an ordinary temperature molten salt type
nonaqueous electrolyte, an operable range is very narrow, and when
a concentration of an aluminum metal salt is increased for
decreasing a defect such as a non-precipitation of a plating film,
a viscosity of a liquid becomes high, and thus there were problems
that a precipitation speed of plating was decreased together with a
deteriorated plating level.
[0010] Thus, the purpose of the present invention is to solve the
above problems and to provide an aluminum electroplating solution
that allows aluminum electroplating to be conducted efficiently and
in a short period of time, can increase the amount of electricity
in the current of electroplating, and has a high solubility in a
nonaqueous solvent.
Solution to Problem
[0011] The aluminum electroplating solution of the present
invention is characterized by comprising an aluminum metal salt, an
ionic liquid obtained by an organic compound forming an ion pair
with the aluminum metal salt, and an organic solvent having a
dielectric constant of 8 or less. It is preferable for the volume
fraction of the organic solvent in relation to the total volume of
the ionic liquid and the organic solvent to be at least 30%, and
for at least one of the following to be included as the organic
solvent having a dielectric constant of 8 or less: hexane, toluene,
diethyl ether, ethylacetate, cyclohexane, xylene, benzene,
naphthalene, heptane, cyclopentyl methyl ether, and dioxane.
[0012] Other objects, features and advantages of the invention will
become apparent from the following description of the embodiments
of the invention.
Advantageous Effects of Invention
[0013] According to the present invention, a precipitation
efficiency of plating is enhanced, a uniformity of a film thickness
can be improved. Additionally, by applying the above plating, it
comes to be possible to provide parts having a steric shape with a
uniform plating applied.
DESCRIPTION OF EMBODIMENTS
[0014] Working embodiments of the present invention are explained
below.
[0015] The aluminum metal salt used as an aluminum source can
include an aluminumhalide. The aluminumhalide used can include an
anhydrous salt such as aluminum chloride and aluminum bromide. When
an aluminum concentration in a plating solution in relation to the
organic compound forming an ion pair with the aluminum metal salt
is equimolar or less, a precipitation speed of plating is
remarkably lowered and thus a higher concentration results in a
better precipitation uniformity of plating. It is better that the
aluminum concentration in the plating solution in relation to the
organic compound forming an ion pair with the aluminum metal salt
is equimolar or more, preferably 1.5 times or more, more preferably
3 times or more.
[0016] The organic compound forming an ion pair with the aluminum
metal salt used can include a halide of an organic compound cation
such as dialkyl imidazolium salt, aliphatic phosphonium salt, and
quaternary ammonium salt. The dialkyl imidazolium salt suitably
used can include 1,3-dialkylimidazoliumhalide which includes
1-ethyl-3-methylimidazolium chloride ([EMIM].Cl),
1-ethyl-3-methylimidazolium bromide ([EMIM].Br),
1-ethyl-3-methylimidazolium iodide ([EMIM]I),
1-butyl-3-methylimidazolium chloride ([BMIM]Cl),
1-butyl-3-methylimidazolium bromide ([BMIM].Br),
1-butyl-3-methylimidazolium iodide ([BMIM].I) etc. Additionally,
the aliphatic phosphonium salt suitably used can include
ethyltributyl phosphonium chloride ([EBP].Cl), ethyltributyl
phosphonium bromide ([EBP].Br), ethyltributyl phosphonium iodide
([EBP].I) etc. The quaternary ammonium salt suitably used can
include tetraethyl ammonium bromide ([E4N].Br), trimethylethyl
ammonium chloride ([M3EN].Cl), tetrabutyl ammonium chloride
([Bu4N].Cl) etc.
[0017] An ionic liquid having an ion pair formed is formed by
mixing the above-mentioned aluminum metal salt with the organic
compound forming an ion pair with the aluminum metal salt according
to the following reaction.
Al.Xn+R.Ym=(Al.R)(Xn)(Ym) (expression 1)
[0018] (In the expression 1, X and Y represent a halide, R
represents an organic compound cation, and n and m represent a
valence number and are an integer of from 1 to 4.)
[0019] The following example is a reaction in case of using
aluminum chloride as the aluminum metal salt and using
1-ethyl-3-methylimidazolium chloride as the organic compound
forming an ion pair with the aluminum metal salt.
##STR00001##
[0020] As mentioned above, a mixing of an aluminum salt with an
organic compound such as a dialkylimidazolium salt forms an ion
pair to obtain a melt (ionic liquid). This ionic liquid can
function as an electroplating solution. However, although it is
desired that a concentration of aluminum is high as a plating
solution, when a molar ratio of the aluminum metal salt in relation
to the organic compound forming an ion pair with the aluminum metal
salt is e.g. 3 or more, a viscosity becomes higher to lower a
fluidity due to a higher concentration of aluminum, and a uniform
plating precipitation cannot come to be obtained from such an ionic
liquid. Thus, in the present invention, by dissolving an ionic
liquid having a high viscosity into an organic solvent, even the
molar ratio of 3 or more can lower a viscosity to be able to be
suitably used as a plating solution. Additionally, although a
higher volume fraction of the organic solvent results in a
relatively lower ion concentration of aluminum, an apparent
diffusion coefficient becomes large due to a lowering of a
viscosity, and thus a large electric current can come to be
uniformly applied to a surface to be plated. Thus, a uniform
plating can be obtained on a substrate face.
[0021] It is preferred that a nonpolar solvent having a dielectric
constant of 8 or less is used as the organic solvent. In case of
using a polar organic solvent having a high dielectric constant,
the aluminum and the organic compound having an ion pair formed are
dissociated and a precipitation efficiency of a plating becomes
lowered. Reasons therefor are because the Coulomb force between
positive and negative ions in the ionic liquid is in inverse
proportion to a dielectric constant of a medium, a higher
dielectric constant of a solvent becomes a lower Coulomb force, a
dissociation of a metal salt becomes easy, and a dissociation of an
ion pair of the aluminum metal salt and the organic compound
becomes easy. Thus, a dielectric constant of the organic solvent is
preferably 8 or less, more preferably 5 or less. Such an organic
solvent can include hexane (dielectric constant of 2.0), toluene
(dielectric constant of 2.4), diethyl ether (dielectric constant of
4.3), ethylacetate (dielectric constant of 6.0), cyclohexane
(dielectric constant of 2.0), xylene (dielectric constant of 2.5),
benzene (dielectric constant of 2.3), naphthalene (dielectric
constant of 2.5), heptane (dielectric constant of 1.9), cyclopentyl
methyl ether (dielectric constant of 4.8), and dioxane (dielectric
constant of 2.1), and any one or plural kinds thereof can be used.
Additionally, a boiling point of the organic solvent is preferably
40.degree. C. or more, and a too low boiling point is not preferred
because countermeasures against an exhalation and flammability etc.
of the organic solvent such as a sealing and cooling etc. become
excessive. Additionally, a volume fraction of the organic solvent
in relation to a total volume of the ionic liquid and the organic
solvent is preferably 30 vol % or more, further preferably 50 vol %
or more, desirably 75 vol % or more. However, a too high volume
fraction of the organic solvent results in a too low ion
concentration of aluminum, and more than 90 vol % causes a lowering
of a current efficiency of plating. Thus, the volume fraction of
the organic solvent is preferably 90 vol %.
[0022] When a transition metal salt of Ni, Co, or Cu etc. or a
refractory metal salt of Ti, W or Mo is added as a base metal salt
in addition to an aluminum salt, these elements are contained in
the resulting plating film and a thermal stability can be enhanced.
In case of e.g. nickel, nickel chloride or nickel sulfate etc. can
be added so as to be a concentration of from 0.01 to 20 mol % while
an amount of the aluminum salt added can be controlled so that a
total metal salt concentration of the nickel salt and the aluminum
salt is constant. Similarly, also in case of other base metal
salts, a metal salt etc. with a chloride can be added.
[0023] From the viewpoint of an operability, a plating treatment
temperature is preferably from 10 to 60.degree. C., further
desirably 40.degree. C. or less. When the temperature is less than
10.degree. C., a viscosity becomes high and a whole plating film
has a tendency to become black.
[0024] When an aluminum electroplating is conducted at an electric
current density of from 0.01 to 10 A/dm.sup.2 by a DC or a pulse
electric current as plating conditions, a current efficiency
becomes good and a uniform plating can be made. It is not preferred
that an electric current density is too high, because an organic
compound is decomposed, a plating layer is non-uniformized and
further a current efficiency becomes lowered. It is desired that a
plating is conducted in a dry inert gat atmosphere because the
plating solution is unstable to oxygen or moisture.
[0025] In case of conducting a continuous plating, it is necessary
to keep an Al ion concentration in a bath at a constant range by
supplying an Al ion in a plating bath. In this instance, when an
anode electrode is an aluminum-made anodic dissolution, an Al ion
is automatically supplied according to an amount of electricity in
the current, an Al ion concentration can be kept at a constant
range without supplying an aluminum halide, and further a bath
composition is not changed.
[0026] The organic solvent used for washing, after the plating,
includes saturated aliphatic hydrocarbons such as hexane and
dodecane, and aromatic hydrocarbons such as benzene, toluene,
hexylbenzene and dodecylbenzene. They do not adversely affect even
if being mixed into a plating solution. Of them, aromatic
hydrocarbons having an alkyl substituent, particularly alkylbenzene
having an alkyl substituent of 8 or less carbon atom, is especially
preferred because they do not adversely affect a plating even if
being mixed into a plating solution. A boiling point of the organic
solvent is preferably 40.degree. C. or more, and a too low boiling
point is not preferred because countermeasures against an
exhalation and flammability etc. of the organic solvent such as a
sealing and cooling etc. become excessive.
[0027] The present invention is explained in more detail by
referring to the following examples, but the present invention is
not limited to these descriptions.
Example 1
[0028] 1-ethyl-3-methylimidazolium chloride (commercially available
from KANTO CHEMICAL CO., INC.; [EMIM]Cl) and anhydrous aluminum
chloride (Wako Pure Chemical Industries, Ltd., AlCl.sub.3) were
used. A weighing capacity was conducted in a glove box at a
humidity set to 5% and a temperature set to 25.degree. C., and
AlCl.sub.3 was added so as to be a molar ratio of
[EMIM]Cl:AlCl.sub.3=1:3 to obtain a 100 ml melt. The above
mentioned melt was dissolved in 300 ml toluene (Wako Pure Chemical
Industries, Ltd.), and a plating solution was prepared so as to be
400 ml in a total volume. The resulting electrolyte 400 ml was
charged into a polypropylene-made electrolytic bath having
longitudinal.times.transversal.times.height of 100 mm.times.50
mm.times.100 mm.
[0029] Next, an aluminum plate of purity 99.9% having
longitudinal.times.transversal of 75 mm.times.75 mm and a thickness
of 2 mm, as an anode electrode, and a copper foil having
longitudinal.times.transversal of 50 mm.times.50 mm and a thickness
of 0.1 mm, as a cathode electrode, were facing-positioned at an
interval of 30 mm each other in the electrolytic bath, and were
immersed in the electrolyte. A lead wire for connection with the
electrodes are passed through at a state that a lid of the
electrolytic bath is airtight, and were connected with a power
supply.
[0030] After the above operations were conducted in a glove box, it
was taken out outside.
[0031] An aluminum electroplating was conducted at an electric
current density -10 mA/cm.sup.2 for 20 minutes or an electric
current density -20 mA/cm.sup.2 for 10 minutes by using a constant
electric current source, to form an aluminum plating film on a
surface of a copper foil. It was conducted at a voltage of 3V or
less in the plating. Then, an evaluation of a current efficiency
and an observation of a surface state of the plating film were
conducted. The current efficiency was determined by determining a
precipitation amount of aluminum by actual measurement, comparing
this to a precipitation amount precalculated based on an electric
current value of a coulomb meter, and determining a ratio to the
latter precipitation amount calculated as a percentage.
[0032] In result of conducting as above, a plating state was good.
Additionally, in result of measuring film thicknesses of five
portions in a copper foil face, good results of a plating film
thickness of 4 .mu.m and a distribution within 5% were obtained.
Additionally, the current efficiency was as good as 97%.
[0033] As clear from these results, it was found that, when the
solvent and the solute as in the present Example were used, a large
electric current of a electroplating can be conducted, a plating of
aluminum can be achieved efficiently and in a short period of time,
and further a current efficiency was good, troubles due to a
deterioration of an electrolyte were avoided, good plating states
having a good uniformity were able to be obtained.
Examples 2 to 12
[0034] Aluminum chloride salts AlCl.sub.3 were dissolved by using
organic compounds and organic solvents shown at Table 1 so as to
become one of several salt concentrations A (mol/l), to prepare
plating solutions of Examples 2 to 12 as well as in Example 1.
[0035] An aluminum electroplating was conducted at an electric
current density -10 mA/cm.sup.2 for 20 minutes or an electric
current density -20 mA/cm.sup.2 for 10 minutes by using a constant
electric current source. Then, an evaluation of a current
efficiency and an observation of a surface state of the plating
film were conducted. It was conducted at a voltage of 3V or less in
the plating. The current efficiency was determined by determining a
precipitation amount of aluminum by actual measurement, comparing
this to a precipitation amount precalculated based on an electric
current value of a coulomb meter, and determining a ratio to the
latter precipitation amount calculated as a percentage. The results
are shown at Table 1.
[0036] As clear from these results, when the solvent and the solute
as in Examples 1 to 12 were used, a large electric current of a
electroplating can be conducted, a plating of aluminum can be
achieved efficiently and in a short period of time, and further a
current efficiency was good, troubles due to a deterioration of an
electrolyte were avoided, good plating states can be obtained. A
higher concentration of the aluminum salt was able to enhance a
current efficiency in the plating. Additionally, a higher
concentration of the organic solvent was able to lower a viscosity
and was able to decrease a film thickness variation. Furthermore,
when a base metal other than an aluminum salt is added as in
Examples 4 and 5, a current efficiency may be lowered but a film
thickness variation of the plating film was able to be
decreased.
TABLE-US-00001 TABLE 1 Organic Second Bath temperature Metal salt
compound Organic solvent metal salt .degree. C. Example 2
AlCl.sub.3 [EMIM].cndot.Cl toluene 30 80 mol % 20 mol % 30 vol %
Example 3 AlCl.sub.3 [EMIM].cndot.Cl toluene 30 80 mol % 20 mol %
50 vol % Example 4 AlCl.sub.3 [EMIM].cndot.Cl toluene NiCl.sub.2 30
70 mol % 22 mol % 50 vol % 8 mol % Example 5 AlCl.sub.3
[EMIM].cndot.Cl toluene TiCl.sub.4 30 70 mol % 25 mol % 30 vol % 5
mol % Example 6 AlCl.sub.3 [EMIM].cndot.Cl xylene 30 80 mol % 20
mol % 80 vol % Example 7 AlCl.sub.3 [EMIM].cndot.Cl cyclohexane 30
80 mol % 20 mol % 75 vol % Example 8 AlCl.sub.3 [EMIM].cndot.Cl
diethyl ether 30 80 mol % 20 mol % 75 vol % Example 9 AlCl.sub.3
[BMIM].cndot.Cl toluene 30 67 mol % 33 mol % 80 vol % Example 10
AlBr.sub.3 [EMIM].cndot.Br toluene 30 80 mol % 20 mol % 80 vol %
Example 11 AlCl.sub.3 [EBP].cndot.Cl toluene 30 80 mol % 20 mol %
80 vol % Example 12 AlCl.sub.3 [M3EN].cndot.Cl toluene 30 80 mol %
20 mol % 80 vol % Comparative AlCl.sub.3 [EMIM].cndot.Cl 30 Example
1 80 mol % 20 mol % Comparative AlCl.sub.3 [EMIM].cndot.Cl
propylene carbonate 30 Example 2 80 mol % 20 mol % 80 vol %
Comparative AlCl.sub.3 [EMIM].cndot.Cl acetonitrile 30 Example 3 80
mol % 20 mol % 80 vol % Electric Period Plating film current of
time Current thickness Film thickness mA/cm.sup.2 (minute)
efficiency % .mu.m Crystallinity variation % Example 2 20 10 88 3.5
dense 10 Example 3 20 10 95 3.9 dense 7 Example 4 10 20 90 3.7
dense 9 Example 5 10 20 88 3.6 dense 6 Example 6 20 10 96 4 dense 7
Example 7 20 10 94 3.8 dense 6 Example 8 20 10 93 3.7 dense 8
Example 9 20 10 95 3.9 dense 8 Example 10 20 10 96 4 dense 6
Example 11 20 10 90 3.7 dense 8 Example 12 20 10 90 3.7 dense 8
Comparative 20 10 15 0.5 nondense 40 Example 1 Comparative 20 10 2
0.1 nondense 50 Example 2 Comparative 20 10 2 0.1 nondense 60
Example 3
Example 13
[0037] According to the plating method as well as in Example 1, a
plating was conducted onto a material to be plated which is a
copper foil having a center folded at 90 degree in the L-shape. In
result of measuring film thicknesses of five portions of a copper
foil face, good results of a plating film thickness of 4 .mu.m and
a distribution within 8% were obtained. The current efficiency was
as good as 97%.
[0038] As clear from these results, it was found that, when the
solvent and the solute as in the present Example were used, a large
electric current of a electroplating can be conducted, a plating of
aluminum can be achieved efficiently and in a short period of time,
and parts having a uniform plating applied were able to be provided
even from a steric shape.
Comparative Example 1
[0039] A plating was conducted by using, as a plating solution, an
ionic liquid comprising 1-ethyl-3-methylimidazolium chloride (20
mol %) and aluminum trichloride (80 mol %) as well as in Example 1.
In this case, although it was conducted at an electric current
density of 20 mA/cm.sup.2, a good plating was not able to be
obtained to form a plating film having a black burned surface of an
aluminum plating. Additionally, a viscosity of the plating solution
was high, and thus a distribution of a film thickness became
large.
Comparative Example 2
[0040] A plating was conducted by using, as a plating solution, an
ionic liquid comprising 1-ethyl-3-methylimidazolium chloride (20
mol %) and aluminum trichloride (80 mol %), as well as in Example
1, dissolved in a polar solvent propylene carbonate (dielectric
constant of 65). In this case, although it was conducted at an
electric current density of 20 mA/cm.sup.2, a good plating was not
able to be obtained and almost aluminum was not precipitated. It is
understood that, when the ionic liquid is dissolved in such a polar
solvent, the aluminum salt and the organic compound having an ion
pair formed are dissociated to inhibit a plating reaction.
Comparative Example 3
[0041] A plating was conducted by using, as a plating solution, an
ionic liquid comprising 1-ethyl-3-methylimidazolium chloride (20
mol %) and aluminum trichloride (80 mol %), as well as in Example
1, dissolved in a polar solvent acetonitrile (dielectric constant
of 38). In this case, although it was conducted at an electric
current density of 20 mA/cm.sup.2, a good plating was not able to
be obtained and almost aluminum was not precipitated.
[0042] It should be further understood by those skilled in the art
that although the foregoing description has been made on
embodiments of the invention, the invention is not limited thereto
and various changes and modifications may be made without departing
from the spirit of the invention and the scope of the appended
claims.
* * * * *