U.S. patent application number 15/025321 was filed with the patent office on 2016-08-11 for reductive electroless gold plating solution, and electroless gold plating method using the plating solution.
This patent application is currently assigned to KOJIMA CHEMICALS CO., LTD.. The applicant listed for this patent is KOJIMA CHEMICALS CO., LTD.. Invention is credited to Tomohito KATO, Hideto WATANABE.
Application Number | 20160230287 15/025321 |
Document ID | / |
Family ID | 55399615 |
Filed Date | 2016-08-11 |
United States Patent
Application |
20160230287 |
Kind Code |
A1 |
KATO; Tomohito ; et
al. |
August 11, 2016 |
REDUCTIVE ELECTROLESS GOLD PLATING SOLUTION, AND ELECTROLESS GOLD
PLATING METHOD USING THE PLATING SOLUTION
Abstract
The present invention has an object to provide an electroless
gold plating solution capable of suppressing the corrosion of a
substrate metal and realizing excellent wire bondability, and
containing no hazardous substance. In order to achieve the object,
as a reductive electroless gold plating solution used for formation
of an electroless plated gold film on a surface of a plating target
by electroless plating, an electroless plating solution containing
a water-soluble gold compound, citric acid or a citrate salt,
ethylenediaminetetraacetic acid or an ethylenediaminetetraacetate
salt, hexamethylenetetramine, and a chain polyamine having an alkyl
group having 3 or more carbon atoms and 3 or more amino groups is
adopted.
Inventors: |
KATO; Tomohito; (Saitama,
JP) ; WATANABE; Hideto; (Saitama, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KOJIMA CHEMICALS CO., LTD. |
Saitama |
|
JP |
|
|
Assignee: |
KOJIMA CHEMICALS CO., LTD.
Saitama
JP
|
Family ID: |
55399615 |
Appl. No.: |
15/025321 |
Filed: |
August 21, 2015 |
PCT Filed: |
August 21, 2015 |
PCT NO: |
PCT/JP2015/073551 |
371 Date: |
March 28, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C23C 18/1651 20130101;
C23C 18/44 20130101; C23C 18/32 20130101; C23C 18/1637
20130101 |
International
Class: |
C23C 18/44 20060101
C23C018/44 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 25, 2014 |
JP |
2014-170558 |
Claims
1. A reductive electroless gold plating solution used for formation
of an electroless plated gold film on a surface of a plating
target, comprising: a water-soluble gold compound; citric acid or a
citrate salt; ethylenediaminetetraacetic acid or an
ethylenediaminetetraacetate salt; hexamethylenetetramine; and a
chain polyamine having an alkyl group having 3 or more carbon atoms
and 3 or more amino groups.
2. The reductive electroless gold plating solution according to
claim 1, wherein the gold plating solution has a pH of 7.0 to a pH
of 9.0.
3. The reductive electroless gold plating solution according to
claim 1, wherein the chain polyamine is
3,3'-diamino-N-methyldipropylamine or
N,N'-bis(3-aminopropyl)ethylenediamine.
4. The reductive electroless gold plating solution according to
claim 1, comprising a thallium compound as a deposition
accelerator.
5. A method of electroless gold plating, comprising forming an
electroless plated gold film on a surface of a plating target using
the reductive electroless gold plating solution according to claim
1.
6. The method of electroless gold plating according to claim 5,
wherein one of copper, palladium, gold and nickel is present on the
surface of the plating target.
7. The method of electroless gold plating according to claim 6,
wherein the surface of the plating target includes an electroless
plated palladium film formed on a surface of an electroless plated
nickel film.
8. A plated product, obtained by electroless gold plating by the
method of electroless gold plating according to claim 5.
Description
TECHNICAL FIELD
[0001] The invention disclosed in the present filing relates to an
electroless gold plating solution, an electroless gold plating
method using the electroless gold plating solution, and a plated
product obtained by plating by the electroless gold plating method.
More specifically, the invention relates to reductive electroless
gold plating technology capable of plating directly a surface of a
plating target.
BACKGROUND ART
[0002] In recent years, while requirements for higher performance
and higher multi-function of electronic devices have been raised,
further downsizing has been demanded on printed wiring boards used
in these electronic devices. In order to cope with the downsizing,
micronization of circuit patterns is progressing and along with the
micronization of circuit patterns, advanced mounting technologies
have been demanded. Generally in the field of printed wiring
boards, as technologies of joining mounting components and terminal
components, technologies using soldering and wire bonding have been
established.
[0003] For the purpose of securing the connection reliability of
these junctions using soldering and wire bonding, plating is
undergone as the surface treatment for wiring pads that are
mounting portions and terminal portions of circuits on printed
wiring boards. The plating includes a technology of carrying out
nickel plating, palladium plating and gold plating in order on a
circuit pattern formed of a metal having a low electric resistance
such as copper. A plated nickel film is to prevent the erosion of a
copper circuit by soldering; and a plated palladium film is to
prevent the diffusion of nickel constituting the plated nickel film
to a plated gold film. Then, the plated gold film is formed in
order to provide excellent wetting performance of a solder,
realizing a low electric resistance.
[0004] As conventional technologies of the above-mentioned plating
technology, there are, for example, Patent Literature 1 to Patent
Literature 3 described below. An electroless gold plating method
described in Patent Literature 1 is a method of forming a plated
gold film on nickel by using an electroless gold plating solution
containing a reducing agent, and involves formation of an immersion
plated gold film as a catalyst for electroless gold plating on
nickel.
[0005] Further an electroless gold plating method described in
Patent Literature 2 is a method of forming an electroless plated
gold film of a plated film laminate in which an electroless plated
nickel film is formed on a surface to be plated of an electronic
component through a catalyst; an electroless plated palladium film
is formed on the electroless plated nickel film; and the
electroless plated gold film is further formed on the electroless
plated palladium film, and involves the formation of the
electroless plated gold film by first electroless gold plating
using an electroless gold plating bath containing a water-soluble
gold compound, a complexing agent, formaldehyde and/or a
formaldehyde bisulfite salt adduct, and a specific amine
compound.
[0006] Further a reductive deposition-type electroless gold plating
solution for a palladium film described in Patent Literature 3 is
an electroless gold plating solution enabling the direct formation
of a plated gold film on the palladium film, and is composed of an
aqueous solution containing a water-soluble gold compound, a
reducing agent and a complexing agent, wherein at least one
compound selected from the group consisting of formaldehyde
bisulfites, Rongalite and hydrazines is contained as the reducing
agent.
CITATION LIST
Patent Literature
[Patent Literature 1]
[0007] Japanese Patent Laid-Open No. 05-222541
[Patent Literature 2]
[0008] Japanese Patent Laid-Open No. 2008-266668
[Patent Literature 3]
[0009] Japanese Patent Laid-Open No. 2008-174774
SUMMARY OF INVENTION
Technical Problem
[0010] The electroless gold plating method of the Patent Literature
1 has such a problem gold dissolves and corrodes substrate nickel,
and nickel thereby diffuses in a plated gold film, however, since
the immersion plated gold film is formed by depositing gold by
utilizing the difference in redox potential between nickel that is
a substrate and gold ions in the plating bath. When nickel diffuses
in the plated gold film, there arises a problem that the gold-gold
junction strength in wire bonding decreases. In order to prevent
such disadvantages, Patent Literature 1 forms an electroless plated
gold film on an immersion plated gold film to make the gold film
thickness large to thereby suppress a decrease in wire bondability.
The technology poses a problem of causing a rise in cost and poor
productivity, however, since formation of the immersion plated gold
film is essentially needed.
[0011] Further in the cases of the electroless gold plating method
described in Patent Literature 2 described above and of using a
reductive deposition-type electroless gold plating solution for a
palladium film described in Patent Literature 3 described above,
although the corrosion of nickel that is a substrate metal is
enabled to be suppressed, since the electroless gold plating bath
contains formaldehyde or a formaldehyde bisulfite salt adduct,
which is strongly toxic, it becomes difficult for the safety in
plating work to be secured.
[0012] Hence, in markets, there has been raised the requirement for
an electroless gold plating solution capable of suppressing the
corrosion of a substrate metal and realizing excellent wire
bondability and containing no hazardous substances.
Solution to Problem
[0013] As a result of diligent studies in order to solve the
above-mentioned problem, the present inventors have arrived at
providing an electroless gold plating solution, an electroless gold
plating method and a plated product, which are shown below.
[0014] The reductive electroless gold plating solution according to
the present invention is used for the formation of an electroless
plated gold film on a surface of a plating target, and contains a
water-soluble gold compound, citric acid or a citrate salt,
ethylenediaminetetraacetic acid or an ethylenediaminetetraacetate
salt, hexamethylenetetramine, and a chain polyamine having an alkyl
group having 3 or more carbon atoms and 3 or more amino groups.
[0015] The reductive electroless gold plating solution according to
the present invention has preferably a pH of 7.0 to a pH of
9.0.
[0016] In the reductive electroless gold plating solution according
to the present invention, the chain polyamine is preferably
3,3'-diamino-N-methyldipropylamine or
N,N'-bis(3-aminopropyl)ethylenediamine.
[0017] The reductive electroless gold plating solution according to
the present invention preferably further contains a thallium
compound as a deposition accelerator.
[0018] The method of electroless gold plating according to the
present invention includes forming an electroless plated gold film
on a surface of a plating target using the above-mentioned
reductive electroless gold plating solution.
[0019] In the electroless gold plating method according to the
present invention, one of copper, palladium, gold and nickel is
preferably present on the surface of the plating target.
[0020] Further in the electroless gold plating method according to
the present invention, the surface of the plating target preferably
includes an electroless plated palladium film formed on a surface
of an electroless plated nickel film.
[0021] The plated product according to the present invention is
obtained by electroless gold plating by the above-mentioned
electroless gold plating method.
Advantageous Effects of Invention
[0022] When the reductive electroless gold plating solution of the
present invention contains a water-soluble gold compound, citric
acid or a citrate salt, ethylenediaminetetraacetic acid or an
ethylenediaminetetraacetate salt, hexamethylenetetramine, and a
chain polyamine having an alkyl group having 3 or more carbon atoms
and 3 or more amino groups, it becomes easy for a plated gold film
to be thickly deposited on a surface of a plating target.
[0023] Further even in the case where a plated nickel film/plated
palladium film/plated gold film installed on an electric connection
site is formed by using the reductive electroless gold plating
solution of the present invention, the plated gold film can be
formed quickly on the surface of the plated palladium film without
being influenced by the film thickness of the plated palladium
film. Further when the reductive electroless gold plating solution
of the present invention is used, even in the case where an
electroless plated gold film is formed on a surface of an
electroless plated palladium film formed on a surface of an
electroless plated nickel film, the dissolution of nickel can
greatly be suppressed as compared with the case where an immersion
plated gold film is formed, and the diffusion of nickel in the
plated gold film is enabled to be prevented. Hence, when the
reductive electroless gold plating solution of the present
invention is used, a plated gold film capable of realizing high
junction reliability of wire bonding can be obtained.
[0024] Further since the reductive electroless gold plating
solution of the present invention has higher stability as a
solution as compared with conventional electroless gold plating
solutions and contains neither formaldehyde nor formaldehyde
bisulfite salt adduct, which is strongly toxic, it becomes easy for
the safety in plating work to be secured.
[0025] Additionally, in the reductive electroless gold plating
solution of the present invention, since the deposition reaction of
gold occurs only on the surface of gold, palladium, nickel, copper
or the like, which can become a catalytic nucleus, and does not
occur on portions having no catalytic nucleus, the selective
deposition property is excellent. Therefore, the plating solution
can avoid the formation of a plated gold film on portions having no
need of the deposition of gold, and is beneficial in that the raw
material can be saved.
BRIEF DESCRIPTION OF DRAWINGS
[0026] FIG. 1 is a graph showing a relation between the plating
time and the plated film thickness of a reductive electroless
plated gold film of an Example sample group 1A.
[0027] FIG. 2 is a graph showing a relation between the plating
time and the plated film thickness of a reductive electroless
plated gold film of Example 2.
[0028] FIG. 3 is diagrams showing relations between the film
thickness of a substrate plated palladium film and the deposition
rate of a plated gold film in the case of using electroless gold
plating solutions of Example 1 and Comparative Example 1.
[0029] FIG. 4 shows electron microscope photographs (.times.10,000
and .times.30,000) of a reductive electroless plated gold film of
an Example sample 1A-2.
[0030] FIG. 5 shows electron microscope photographs (.times.30,000)
of reductive electroless plated gold films of an Example sample 2-2
and Comparative Example 2.
[0031] FIG. 6 shows an electron microscope photograph
(.times.5,000) of the surface of a plated nickel film after
peeling-off of a reductive electroless plated gold film and an
electroless plated palladium film from a plated film of an Example
sample 1A-2.
[0032] FIG. 7 shows electron microscope photographs (.times.3,000)
of surfaces of plated nickel films after peeling-off of reductive
electroless plated gold films from plated films of an Example
sample 2-2 and Comparative Example 2.
[0033] FIG. 8 is a cross-sectional observation photograph
(.times.30,000) of a reductive electroless plated gold film of an
Example sample 1A-6.
[0034] FIG. 9 shows electron microscope photographs (.times.500) of
an end portion and a central portion of a plated product in which a
plated film was formed under the same condition as in an Example
sample 1A-6.
[0035] FIG. 10 is a diagram showing relations of nickel dissolution
amounts in gold plating solutions in the case of using electroless
gold plating solutions of Example 1 and Comparative Example 1.
[0036] FIG. 11 is a diagram showing deviations of the film
thicknesses of electroless plated gold films of Example 2 and
Comparative Example 2.
[0037] FIG. 12 is a diagram showing the wire bonding performance of
electroless plated gold films of Example 2 and Comparative Example
2.
DESCRIPTION OF EMBODIMENTS
[0038] Hereinafter, embodiments of the reductive electroless gold
plating solution, the electroless gold plating method using the
plating solution, and the plated product plated by the method,
respectively, according to the present invention will be
described.
1. The Reductive Electroless Gold Plating Solution According to the
Present Invention
[0039] The reductive electroless gold plating solution according to
the present invention is used for the formation of an electroless
plated gold film on a surface of a plating target, and contains "a
water-soluble gold compound", "citric acid or a citrate salt",
"ethylenediaminetetraacetic acid or an ethylenediaminetetraacetate
salt", "hexamethylenetetramine", and "a chain polyamine having an
alkyl group having 3 or more carbon atoms and 3 or more amino
groups". Hereinafter, the respective components will be
described.
(1) A Water-Soluble Gold Compound
[0040] As a water-soluble gold compound used for the reductive
electroless gold plating solution according to the present
invention, any water-soluble gold compound of cyanide-based gold
salts and non-cyanide-based gold salts as long as the compound is
soluble in the plating solution and can provide a specific
concentration can be used. As specific water-soluble gold compounds
of cyanide-based gold salts, potassium gold cyanide, sodium gold
cyanide and ammonium gold cyanide can be exemplified. Further as
specific water-soluble gold compounds of non-cyanide-based gold
salts, chloroaurate salts, gold sulfite salts and gold thiosulfate
salts can be exemplified. Among these, potassium gold cyanide is
especially preferable. Further the water-soluble gold compounds may
be used singly or in a combination of two or more. Here, the
water-soluble gold compounds are not limited to the gold compounds
exemplified here.
[0041] The concentration of a water-soluble gold compound in the
reductive electroless gold plating solution according to the
present invention is preferably 0.0025 mol/L to 0.0075 mol/L. This
is because when the concentration of a water-soluble gold compound
is lower than 0.0025 mol/L, the deposition rate of a plated gold
film is slow and a desired-thickness plated gold film is hardly
obtained. This is because when the concentration of a water-soluble
gold compound is higher than 0.0075 mol/L, there arises a risk that
the stability of the plating solution decreases, and the high
concentration is an economical drawback.
(2) Citric Acid or a Citrate Salt
[0042] The reductive electroless gold plating solution according to
the present invention contains citric acid or a citrate salt. These
citric acid and citrate salt are used as a complexing agent capable
of forming a complex with gold ions. The concentration of citric
acid or a citrate salt in the reductive electroless gold plating
solution according to the present invention is preferably 0.05
mol/L to 0.15 mol/L. This is because when the concentration of
citric acid or a citrate salt used as a complexing agent is lower
than 0.05 mol/L, gold deposits in the plating solution and the
solution stability is inferior; and this is because when being more
than 0.15 mol/L, the complex formation excessively progresses and
the deposition rate of gold decreases, and a desired-thickness
plated gold film is hardly obtained.
(3) Ethylenediaminetetraacetic Acid (EDTA) or an
Ethylenediaminetetraacetate Salt
[0043] The reductive electroless gold plating solution according to
the present invention contains ethylenediaminetetraacetic acid
(EDTA) or an ethylenediaminetetraacetate salt. These
ethylenediaminetetraacetic acid and ethylenediaminetetraacetate
salt are complexing agents used by in combination with the
above-mentioned citric acid or citrate salt. The concentration of
ethylenediaminetetraacetic acid or an ethylenediaminetetraacetate
salt in the reductive electroless gold plating solution according
to the present invention is preferably 0.03 mol/L to 0.1 mol/L.
This is because when the concentration of
ethylenediaminetetraacetic acid or an ethylenediaminetetraacetate
salt used as a complexing agent is lower than 0.03 mol/L, gold
deposits in the plating solution and the solution stability is
inferior; and this is because when the concentration is more than
0.1 mol/L, the complex formation excessively progresses and the
deposition rate of gold decreases, and a desired-thickness plated
gold film is hardly obtained.
(4) Hexamethylenetetramine
[0044] The reductive electroless gold plating solution according to
the present invention contains hexamethylenetetramine. The
hexamethylenetetramine is used as a reducing agent which reduces
gold ions in the plating solution and causes gold to deposit on a
surface of a plating target.
[0045] The concentration of hexamethylenetetramine in the reductive
electroless gold plating solution according to the present
invention is preferably 0.003 mol/L to 0.009 mol/L. This is because
when the concentration of hexamethylenetetramine is lower than
0.003 mol/L, the deposition rate of a plated gold film is slow and
a desired-thickness plated gold film is hardly obtained; and this
is because when the concentration of hexamethylenetetramine is
higher than 0.009 mol/L, the reduction reaction rapidly progresses
and the gold salt in the plating solution may abnormally deposit,
and the solution stability is inferior and the high concentration
is an economical drawback.
(5) A Chain Polyamine
[0046] Further the reductive electroless gold plating solution
according to the present invention contains a chain polyamine
having an alkyl group having 3 or more carbon atoms and 3 or more
amino groups. The chain polyamine is an amine compound which acts
as a reduction auxiliary agent assisting the reduction of gold ions
in the plating solution. As the chain polyamine, specifically,
there can be used 3,3'-diamino-N-methyldipropylamine,
N,N'-bis(3-aminopropyl)ethylenediamine and the like. This is
because these are especially preferable from the viewpoint of the
performance of an obtained plated film, and the economic
efficiency.
[0047] The concentration of the chain polyamine in the reductive
electroless gold plating solution according to the present
invention is preferably 0.02 mol/L to 0.06 mol/L. By making the
concentration of a chain polyamine in the range of 0.02 mol/L to
0.06 mol/L, a high deposition rate can be maintained without
affecting the substrate metal film thickness. Further the throwing
power of a plated gold film can be improved and the plated gold
film can have a large thickness of 0.2 lam or larger. Further the
solution stability can be greatly enhanced.
(6) Other Components
[0048] The reductive electroless gold plating solution according to
the present invention, in addition to a water-soluble gold
compound, citric acid or a citrate salt, ethylenediaminetetraacetic
acid or an ethylenediaminetetraacetate salt,
hexamethylenetetramine, and a chain polyamine having an alkyl group
having 3 or more carbon atoms and 3 or more amino groups, as
described above, may contain a deposition accelerator. The
deposition accelerator used here includes thallium compounds and
lead compounds. It is preferable to use a thallium compound from
the viewpoint of making a thick plated gold film.
[0049] The concentration of a thallium compound as the deposition
accelerator in the reductive electroless gold plating solution
according to the present invention is preferably 1 mg/L to 10 mg/L.
When the concentration of a thallium compound as the deposition
accelerator is lower than 1 mg/L, it becomes difficult to make a
plated gold film thick. Further when the concentration of a
thallium compound as the deposition accelerator is higher than 10
mg/L, making the thickness larger than that cannot be accomplished
and the high concentration would be an economical drawback.
[0050] The reductive electroless gold plating solution according to
the present invention, in addition to the above-mentioned essential
components, may contain additives such as a pH regulator, an
antioxidant, a surfactant and a brightening agent.
[0051] The pH regulator is not especially limited, but includes
potassium hydroxide, sodium hydroxide, an ammonia water solution,
sulfuric acid and phosphoric acid. In the reductive electroless
gold plating solution according to the present invention, by using
a pH regulator, the pH is preferably maintained at 7.0 to 9.0. This
is because when the pH of the reductive electroless gold plating
solution is lower than 7.0, it becomes easy for the plating
solution to be decomposed; and when the pH is higher than 9.0, the
plating solution becomes too stable and the plating deposition rate
becomes slow, and it needs to take much time for a plated gold film
to be made thick. Further by regulating the pH condition at 7.0 to
9.0, even a plating target constituted from a material weak to
alkali can be plated. Further as the additives such as an
antioxidant, a surfactant and a brightening agent, known ones can
be used.
(7) The Plating Condition
[0052] The gold plating condition using the reductive electroless
gold plating solution according to the present invention is not
especially limited, but the solution temperature is preferably
40.degree. C. to 90.degree. C., and especially preferably
75.degree. C. to 85.degree. C. The plating time also is neither
especially limited, but 1 min to 2 hours is preferable, and 2 min
to 1 hour is especially preferable.
[0053] Since the reductive electroless gold plating solution
according to the present invention comprises, as essential
components, a water-soluble gold compound, citric acid or a citrate
salt, ethylenediaminetetraacetic acid or an
ethylenediaminetetraacetate salt, hexamethylenetetramine, and a
chain polyamine having an alkyl group having 3 or more carbon atoms
and 3 or more amino groups as described above, it becomes easy for
a plated gold film to be thickly deposited on a surface of a
plating target by the electroless plating method.
[0054] Further even in the case where a plated nickel film/plated
palladium film/plated gold film installed on an electric connection
site is formed, the plated gold film can be formed quickly on the
surface of the plated palladium film without being influenced by
the film thickness of the plated palladium film by using the
reductive electroless gold plating solution according to the
present invention. Further even in the case where an electroless
plated gold film is formed on a surface of an electroless plated
palladium film formed on a surface of an electroless plated nickel
film, by using the reductive electroless gold plating solution of
the present invention, the dissolution of nickel can greatly be
suppressed as compared with the case where an immersion plated gold
film is formed, and the diffusion of nickel in the plated gold film
can be prevented. Therefore, when the reductive electroless gold
plating solution of the present invention is used, a plated gold
film capable of realizing high junction reliability of wire bonding
can be provided.
[0055] Further the reductive electroless gold plating solution of
the present invention is high in the solution stability as compared
with conventional electroless gold plating solutions. For example,
in the case where continuous plating is carried out while a plating
solution is being replenished, the metal turnover (MTO, in which
the case where gold in a plating solution in making-up of an
electrolytic bath is all deposited is taken as 1 turn) is used as
an index of outwearing of the plating solution. Whereas MTO is 2.0
to 3.0 turns in the case of conventional reductive electroless gold
plating solutions, an MTO of 5.0 turns or more is enabled to be
realized in the reductive electroless gold plating solution of the
present invention.
[0056] Further since the reductive electroless gold plating
solution of the present invention contains neither formaldehyde nor
a formaldehyde bisulfite salt adduct, which is strongly toxic and
which is contained in conventional reductive electroless gold
plating solutions, it becomes easy for the safety in plating work
to be secured.
[0057] Additionally, with the reductive electroless gold plating
solution of the present invention, since the deposition reaction of
gold occurs only on the surface of gold, palladium, nickel, copper
or the like, which can become a catalytic nucleus, and does not
occur on portions having no catalytic nucleus, the selective
deposition property is excellent. Therefore, the plating solution
can avoid the formation of a plated gold film on portions having no
need of the deposition of gold, and is beneficial in that the raw
material can be saved.
2. The Electroless Gold Plating Method
[0058] Then, the electroless gold plating method according to the
present invention will be described. The electroless gold plating
method according to the present invention uses one of the reductive
electroless gold plating solutions described above and carries out
electroless gold plating on a surface of a plating target to
thereby form a plated gold film. The electroless gold plating
method carries out plating by a method of immersing a plating
target in an electroless gold plating solution as in usual
reductive electroless plating methods.
[0059] In the electroless gold plating method according to the
present invention, it is preferable that one of copper, palladium,
gold and nickel is present on a surface of a plating target, which
is an object of the treatment. The presence form thereof may be any
one as long as one of copper, palladium, gold and nickel is present
on a surface of a plating target. It is more preferable to use
particularly a plating target itself constituted from copper or a
plating target having any film composed of copper, palladium, gold,
nickel or an alloy containing these metals on the surface of the
plating target. The alloy containing these metals may include, for
example, gold cobalt. Gold, palladium, nickel, copper or an alloy
containing these metals becomes a substrate metal for electroless
gold plating in the present invention, and exhibits a catalytically
active effect to hexamethylenetetramine as a reducing agent
contained in the above-mentioned reductive electroless gold plating
solution. It is preferable that as the film to be formed on a
surface of a plating target, particularly an electroless plated
palladium film, an immersion plated gold film or a plated copper
film is used. For example, in the case where mounting portions and
terminal portions of circuits of printed wiring boards have
undergone electroless nickel plating on their surfaces, it is
preferable that an electroless plated palladium film is formed on
the surface of the electroless plated nickel film. This is because
when the plated nickel film has a plated palladium film formed on
its surface, it is especially effective in that the plated nickel
film is prevented from being diffused in the plated gold film.
3. The Plated Product
[0060] Then, the plated product according to the present invention
will be described. The plated product according to the present
invention is characterized in that a surface of a plating target
undergoes electroless gold plating by using one of the
above-mentioned electroless gold plating solutions and by the
above-mentioned electroless gold plating method. It is preferable
to make a surface of a plating target undergo electroless gold
plating particularly by using the reductive electroless gold
plating solution having a pH of 7.0 to 9.0. Further, the presence
form thereof may be any one as long as one of copper, palladium,
gold and nickel is present on a surface of a plating target. It is
more preferable to use particularly a plating target itself
constituted from copper or a plating target having any film
composed of copper, palladium, gold, nickel or an alloy containing
these metals on the surface of the plating target. It is preferable
that as the film to be formed on a surface of a plating target,
particularly an electroless plated palladium film, an immersion
plated gold film or a plated copper film is used. It is preferable
that a plating target including an electroless plated palladium
film on its surface is particularly one having an electroless
plated nickel film as an underlayer of the electroless plated
palladium film formed on its surface. This is because the plating
using the above-mentioned reductive electroless gold plating
solution can especially suitably be used for the formation of
plated films of electric connection sites.
[0061] The embodiments according to the present invention described
hitherto are one aspect of the present invention, and it is natural
that changes and modifications may suitably be made without
departing from the gist of the present invention.
[0062] The present invention will be described more specifically
hereinafter by referring to Example 1 and Example 2 of plated gold
films fabricated by using the reductive electroless gold plating
solution of the present invention, Comparative Example 1 of a
plated gold film fabricated by using an immersion electroless gold
plating solution, and Comparative Example 2 of a plated gold film
fabricated by using a conventional reductive electroless plating
solution. Note that, it should be mentioned by way of caution that
the present invention is not limited to Examples described in the
below.
Example 1
[0063] In Example 1, by using a reductive electroless gold plating
solution to which the present invention was applied and using a
copper plate as a substrate, plated films composed of an
electroless plated nickel film/electroless plated palladium
film/electroless plated gold film were formed on the substrate.
Preparation of the reductive electroless gold plating solution: The
composition of the reductive electroless gold plating solution used
in the present Example is shown in the below. The plating condition
(pH, solution temperature) is shown together with the
composition.
[0064] Potassium gold cyanide: 5 mmol/L
[0065] Dipotassium ethylenediaminetetraacetate: 0.03 mol/L
[0066] Citric acid: 0.15 mol/L
[0067] Hexamethylenetetramine: 3 mmol/L
[0068] 3,3'-diamino-N-methyldipropylamine: 0.02 mol/L
[0069] Thallium acetate: 5 mg/L
[0070] pH: 8.5
[0071] Solution temperature: 80.degree. C.
Fabrication of plated films: Samples with a plated film as Example
1 were composed of an Example sample group 1A to an Example sample
group 1D. These Example sample group 1A to Example sample group 1D
were divided according to differences in electroless plated
palladium film thickness.
[0072] The Example sample group 1A was composed of an Example
sample 1A-1 to an Example sample 1A-6; and the each Example sample
was made by forming an electroless plated nickel film of 5 .mu.m in
film thickness on the surface of the copper plate, and thereafter
forming an electroless plated palladium film of 0.1 .mu.m in film
thickness on the surface of the electroless plated nickel film.
Thereafter, a reductive electroless plated gold film was formed on
the surface of the electroless plated palladium film by using the
above-mentioned reductive electroless gold plating solution
according to the condition of a corresponding plating time.
Specifically, in the Example sample 1A-1 to the Example sample
1A-6, the plating time conditions in the reductive electroless
plated gold film formation were made to be 10 min, 20 min, 30 min,
40 min, 50 min and 60 min, respectively, to thereby obtain samples
with a plated gold film.
[0073] The Example sample group 1B was composed of an Example
sample 1B-1 to an Example sample 1B-6, and fabricated as in the
Example sample group 1A, except that the film thickness of the
electroless plated palladium film was 0.2 .mu.m. Here, in each of
the Example sample 1B-1 to the Example sample 1B-6, the plating
time conditions in the reductive electroless plated gold film
formation were made different, as in the Example sample 1A-1 to the
Example sample 1A-6.
[0074] The Example sample group 1C was composed of an Example
sample 1C-1 to an Example sample 1C-6, and fabricated as in the
Example sample group 1A, except that the film thickness of the
electroless plated palladium film was 0.4 .mu.m. Here, in each of
the Example sample 1C-1 to the Example sample 1C-6, the plating
time conditions in the reductive electroless plated gold film
formation were made different, as in the Example sample 1A-1 to the
Example sample 1A-6.
[0075] The Example sample group 1D was composed of an Example
sample 1D-1 to an Example sample 1D-6, and fabricated as in the
Example sample group 1A, except that the film thickness of the
electroless plated palladium film was 0.6 .mu.m. Here, in each of
the Example sample 1D-1 to the Example sample 1D-6, the plating
time conditions in the reductive electroless plated gold film
formation were made different, as in the Example sample 1A-1 to the
Example sample 1A-6.
Example 2
[0076] In Example 2, by using the reductive electroless gold
plating solution as in Example 1 and using a copper plate as a
substrate, plated films composed of an electroless plated nickel
film/immersion electroless plated gold film/reductive electroless
plated gold film were formed on the substrate. Samples with a
plated film as Example 2 were composed of an Example sample 2-1 to
an Example sample 2-6. The Example sample 2-1 to the Example sample
2-6 were each made by forming an electroless plated nickel film of
5 .mu.m in film thickness on the surface of the copper plate, and
thereafter forming an immersion electroless plated gold film of
0.07 .mu.m in film thickness on the surface of the electroless
plated nickel film. Thereafter, a reductive electroless plated gold
film was formed on the surface of the immersion electroless plated
gold film by using the above-mentioned reductive electroless gold
plating solution according to the condition of a corresponding
plating time. Here, in each of the Example sample 2-1 to the
Example sample 2-6, the plating time conditions in the reductive
electroless plated gold film formation were made different, as in
the Example sample 1A-1 to the Example sample 1A-6.
COMPARATIVE EXAMPLES
Comparative Example 1
[0077] In Comparative Example 1, by using an immersion electroless
gold plating solution and using a copper plate as a substrate as in
Example 1, plated films composed of an electroless plated nickel
film/electroless plated palladium film/electroless plated gold film
were fabricated on the substrate.
Preparation of the immersion electroless gold plating solution: The
composition of the immersion electroless gold plating solution used
in Comparative Example 1 is shown in the below. The plating
condition (pH, solution temperature) is shown together with the
composition.
[0078] Potassium gold cyanide: 10 mmol/L
[0079] Ethylenediaminetetraacetic acid: 0.03 mol/L
[0080] Citric acid: 0.15 mol/L
[0081] Thallium acetate: 50 mg/L
[0082] pH: 4.5
[0083] Solution temperature: 80.degree. C.
Fabrication of plated films: Samples with a plated film as
Comparative Example 1 are composed of a comparative sample group 1A
to a comparative sample group 1D. These comparative sample group 1A
to comparative sample group 1D are divided according to differences
in electroless plated palladium film thickness.
[0084] The comparative sample group 1A was composed of a
comparative sample 1A-1 to a comparative sample 1A-6; and the each
comparative sample was made by forming an electroless plated nickel
film of 5 .mu.m in film thickness on the surface of the copper
plate, and thereafter forming an electroless plated palladium film
of 0.1 .mu.m in film thickness on the surface of the electroless
plated nickel film. Thereafter, an immersion electroless plated
gold film was formed on the surface of the electroless plated
palladium film by using the above-mentioned immersion electroless
gold plating solution according to the condition of a corresponding
plating time. Specifically, in the comparative sample 1A-1 to the
comparative sample 1A-6, the plating time conditions in the
immersion electroless plated gold film formation were made to be 10
min, 20 min, 30 min, 40 min, 50 min and 60 min, respectively, to
thereby obtain samples with a plated gold film.
[0085] The comparative sample group 1B was composed of a
comparative sample 1B-1 to a comparative sample 1B-6, and
fabricated as in the comparative sample group 1A, except that the
film thickness of the electroless plated palladium film was 0.2
.mu.m. Here, in each of the comparative sample 1B-1 to the
comparative sample 1B-6, the plating time conditions in the
immersion electroless plated gold film formation were made
different, as in the comparative sample 1A-1 to the comparative
sample 1A-6.
[0086] The comparative sample group 1C was composed of a
comparative sample 1C-1 to a comparative sample 1C-6, and
fabricated as in the comparative sample group 1A, except that the
film thickness of the electroless plated palladium film was 0.4
.mu.m. Here, in each of the comparative sample 1C-1 to the
comparative sample 1C-6, the plating time conditions in the
immersion electroless plated gold film formation were made
different, as in the comparative sample 1A-1 to the comparative
sample 1A-6.
[0087] The comparative sample group 1D was composed of a
comparative sample 1D-1 to a comparative sample 1D-6, and
fabricated as in the comparative sample group 1A, except that the
film thickness of the electroless plated palladium film was 0.6
.mu.m. Here, in each of the comparative sample 1D-1 to the
comparative sample 1D-6, the plating time conditions in the
immersion electroless plated gold film formation were made
different, as in the comparative sample 1A-1 to the comparative
sample 1A-6.
Comparative Example 2
[0088] In Comparative Example 2, by using a conventional reductive
electroless gold plating solution and using a copper plate as a
substrate as in Example 2, plated films composed of an electroless
plated nickel film/immersion electroless plated gold
film/conventional reductive electroless plated gold film were
formed on the substrate.
Preparation of the conventional reductive electroless gold plating
solution: The composition of the reductive electroless gold plating
solution used in Comparative Example 2 is shown in the below. The
plating condition (pH, solution temperature) is shown together with
the composition.
[0089] Potassium gold cyanide: 0.015 mol/L
[0090] Potassium cyanide: 0.03 mol/L
[0091] Sodium hydroxide: 0.8 mol/L
[0092] Dimethylamine borane: 0.2 mol/L
[0093] Lead compound: 5 mg/L (in terms of lead)
[0094] pH: 13
[0095] Solution temperature: 70.degree. C.
Fabrication of a plated film: In Comparative Example 2, an
electroless plated nickel film of 5 .mu.m in film thickness was
formed on the surface of a copper plate, and thereafter, an
immersion electroless plated gold film of 0.05 .mu.m in film
thickness was formed on the surface of the electroless plated
nickel film. Thereafter, by using the above-mentioned reductive
electroless gold plating solution, a reductive electroless plated
gold film of 0.20 .mu.m in film thickness was formed on the surface
of the immersion electroless plated gold film.
[Evaluations]
[0096] Then, the plated gold films in Example 1 and Example 2
fabricated by using the reductive electroless gold plating solution
of the present invention were evaluated for the deposition rate,
the surface form and the like. Hereinafter, these evaluations will
be described specifically, if required, by comparing Example 1 and
Example 2 with Comparative Example 1 of the plated gold films
fabricated by using the immersion electroless gold plating solution
and Comparative Example 2 of the plated gold film fabricated by
using the conventional reductive electroless plating solution.
Deposition rate: There is shown in FIG. 1 a relation between the
plating time and the plated film thickness of the plated gold films
of the Example sample group 1A (the Example sample 1A-1 to the
Example sample 1A-6) in Example 1 using the reductive electroless
gold plating solution according to the present invention. There is
similarly shown in FIG. 2 a relation between the plating time and
the plated film thickness of the plated gold films of Example 2
(the Example sample 2-1 to the Example sample 2-6) using the
reductive electroless gold plating solution according to the
present invention. Here, in FIG. 2, there is shown an electron
microscope photograph (.times.10,000) of the plated gold film of
the Example sample 2-2 obtained by making the plating time to be 20
min.
[0097] It is confirmed from FIG. 1 that the plated gold film formed
on the surface of the electroless plated palladium film by using
the above-mentioned reductive electroless gold plating solution was
formed stably at a rate of 0.15 .mu.m/30 min without being
influenced by the thickness of the plated gold film formed.
[0098] It is confirmed from FIG. 2 that the reductive plated gold
film formed on the surface of the immersion electroless plated gold
film by using the above-mentioned reductive electroless gold
plating solution was formed stably at a rate of 0.17 .mu.m/30 min
without being influenced by the thickness of the plated gold film
formed.
Influence of the thickness of the electroless plated palladium film
on the deposition rate of the plated gold film: Then, comparing
Example 1 with Comparative Example 1, there will be described the
influence of the thickness of the electroless plated palladium film
on the deposition rate of the plated gold film. FIG. 3 shows a
relation between the film thickness of the electroless plated
palladium film and the deposition rate of the plated gold film in
the Example sample group 1A (the Example sample 1A-1 to the Example
sample 1A-6) to the Example sample group 1D (the Example sample
1D-1 to the Example sample 1D-6) each in which the plated gold film
was formed on the surface of the electroless plated palladium film
by using the reductive electroless gold plating solution. FIG. 3
also shows, together with the relation, a relation between the film
thickness of the electroless plated palladium film and the
deposition rate of the plated gold film in the comparative sample
group 1A (the comparative sample 1A-1 to the comparative sample
1A-6) to the comparative sample group 1D (the comparative sample
1D-1 to the comparative sample 1D-6) each in which the plated gold
film was formed on the surface of the electroless plated palladium
film by using the immersion electroless gold plating solution.
[0099] It is found from FIG. 3 that in the plated gold films formed
by using the immersion electroless gold plating solution of the
comparative sample group 1A to the comparative sample group 1D, the
thicker the plated palladium film being the substrate metal, the
more the deposition rate of the plated gold film decreased. By
contrast, it can be confirmed that the plated gold films formed by
using the reductive electroless gold plating solution of the
Example sample group 1A to the Example sample group 1D were formed
at a stable rate irrespective of the thickness of the plated
palladium film being the substrate metal.
Surface form of the plated gold film: Then, the surface form of the
plated gold film formed on the surface of the electroless plated
palladium film by using the reductive electroless gold plating
solution of the present invention was observed. FIG. 4 shows
electron microscope photographs (.times.10,000 and .times.30,000)
of the plated gold film surface of the Example sample 1A-2 in which
the reductive electroless plated gold film was formed in a film
thickness of 0.1 .mu.m out of Example 1. The surface form of the
reductive electroless plated gold film formed on the surface of the
immersion electroless plated gold film by using the reductive
electroless gold plating solution of the present invention was
further observed. FIG. 5 shows an electron microscope photograph
(.times.30,000) of the plated gold film surface of the Example
sample 2-2 in which the reductive electroless plated gold film was
formed in a film thickness of 0.13 .mu.m out of Example 2. As a
comparison, there was observed the surface form of the reductive
electroless plated gold film formed on the surface of the immersion
electroless plated gold film by using the conventional reductive
electroless gold plating solution. FIG. 5 shows an electron
microscope photograph (.times.30,000) of the plated gold film
surface of Comparative Example 2 in which the reductive electroless
plated gold film was formed in a film thickness of 0.13 .mu.m.
[0100] It can be confirmed from FIG. 4 and FIG. 5 that the
electroless plated gold film was densely formed not only by using
the reductive electroless gold plating solution of the present
invention, but by using the conventional reductive electroless gold
plating solution.
Surface form after peeling-off of the electroless plated gold film:
Further there were observed the surface forms of the plated nickel
films after the electroless plated gold film or the electroless
plated gold film and the electroless plated palladium film were
peeled off from the each plated film shown in FIG. 4 and FIG. 5.
FIG. 6 shows an electron microscope photograph (.times.5,000) of
the plated nickel film surface after the electroless plated gold
film and the electroless plated palladium film were peeled off from
the state of FIG. 4. FIG. 7 shows electron microscope photographs
(.times.3,000) of the plated nickel film surfaces after the
electroless plated gold film was peeled off from the state of FIG.
5.
[0101] As apparent from FIG. 6 and FIG. 7, in any of Examples and
Comparative Examples formed by using the reductive electroless gold
plating solutions, no local corrosion of the plated nickel film was
observed.
Cross-sectional form of the plated film: Then, the cross-section of
the plated film having the layer structure of the electroless
plated nickel film/electroless plated palladium film/electroless
plated gold film of Example 1, in which the plated gold film was
formed on the surface of the electroless plated palladium film by
using the reductive electroless gold plating solution of the
present invention was observed. FIG. 8 shows a cross-sectional
photograph (.times.30,000) of the plated film of the Example sample
1A-6, in which the reductive electroless plated gold film was
formed in a film thickness of 0.3 .mu.m. It can be confirmed from
FIG. 8 that the electroless plated gold film formed by using the
above-mentioned reductive electroless gold plating solution was
formed uniformly on the surface of the plated palladium film.
Selective deposition property of the plated gold film: Then, there
are shown in FIG. 9 electron microscope photographs (.times.500) of
an end portion and a central portion of a plated product whose
plated film was formed under the same condition as in the Example
sample 1A-6 out of Example 1, in which the plated gold film was
formed on the surface of the electroless plated palladium film by
using the reductive electroless gold plating solution of the
present invention. It can be confirmed from FIG. 9 that the
electroless plated gold films were formed uniformly similarly in
the end portion and the central portion of the plated product.
Hence, it can be said also from the photograph of FIG. 9 that the
reductive electroless gold plating solution of the present
invention was excellent in the selective deposition property of the
electroless plated gold film. Influence of the nickel dissolution
in the gold plating solution: Then, with respect to Example 1, in
which the plated gold film was formed on the surface of the
electroless plated palladium film by using the reductive
electroless gold plating solution of the present invention, there
was investigated the influence of the dissolution of the
electroless nickel into the reductive electroless gold plating
solution. Specifically, there was examined the dissolution amount
of the substrate nickel into the electroless gold plating solution
in the case where 1 g of gold was deposited on the surface of the
electroless plated palladium film, by using ICP. As a comparison,
also Comparative Example 1 using the immersion electroless gold
plating solution was examined as in Example 1. FIG. 10 shows a
dissolution amount of the electroless nickel of Example 1 using the
reductive electroless gold plating solution and a dissolution
amount of the substrate nickel of Comparative Example 1 using the
immersion electroless gold plating solution. FIG. 10 indicates, for
the either case, a value when the dissolution amount of Ni into the
gold plating solution in the case where 1 g of gold was deposited
was examined by using ICP.
[0102] From FIG. 10, in Comparative Example 1 in which 1 g of the
plated gold film was deposited by using the immersion electroless
gold plating solution, Ni used as the substrate metal dissolved out
in 162 ppm into the immersion electroless gold plating solution. By
contrast, in Example 1 in which 1 g of the plated gold film was
deposited by using the reductive electroless gold plating solution
of present application, Ni used as the substrate metal dissolved
out in 0.2 ppm only into the reductive electroless gold plating
solution.
[0103] From the results of the evaluation tests, it can be said
that the reductive electroless gold plating solution according to
the present application could greatly suppress the dissolution of
the substrate nickel through the plated palladium film as compared
with the case of forming the immersion plated gold film, and nickel
was enabled to be prevented from diffusing into the plated gold
film.
Deviation in film thickness of the plated gold film: Then, there
was investigated the deviation in film thickness of the plated gold
film formed by using the reductive electroless gold plating
solution on the surface of the immersion electroless plated gold
film. Here, there was examined the film thickness of the reductive
electroless plated gold film of the Example sample 2-2 of Example 2
as an example using the reductive electroless gold plating solution
according to the present invention. As a comparison, there was
examined the film thickness of the reductive electroless plated
gold film of Comparative Example 2 using the conventional reductive
electroless gold plating solution. For the each case, the results
by the examination of the film thickness of 20 points are
collectively shown in Table 1. Further FIG. 11 shows the deviation
states.
TABLE-US-00001 TABLE 1 Example 2 (Example Comparative sample 2-2)
Example 2 Plating Time 20 min 1.5 min Film Average Value (.mu.m)
0.199 0.206 Thickness Maximum Value (.mu.m) 0.204 0.218 Minimum
Value (.mu.m) 0.194 0.182 Maximum - Minimum 0.01 0.036 (.mu.m)
Standard Deviation 0.004 0.013
[0104] The average value of the film thickness of the electroless
plated gold film of the Example sample 2-2 using the reductive
electroless gold plating solution according to the present
invention was 0.199 .mu.m; the difference between the maximum value
and the minimum value was 0.01 .mu.m; and the standard deviation
was pretty much as low as 0.004. By contrast, the average value of
the film thickness of the electroless plated gold film of
Comparative Example 2 using the conventional reductive electroless
gold plating solution was 0.206 .mu.m; the difference between the
maximum value and the minimum value was 0.036 .mu.m; and the
standard deviation was 0.013. Hence, it is found that by using the
reductive electroless gold plating solution according to the
present invention, as compared with the case where the conventional
reductive electroless gold plating solution was used, there was
provided the electroless plated gold film having a low deviation in
a considerably high level, that is, being uniform, across the
entire region. From the results, by using the reductive electroless
gold plating solution according to the present invention, the
entire of the surface of the plating target was enabled to undergo
plating more uniformly and the quality could be improved. Further
since the electroless plated gold film could be formed in a
required thickness, the formation of the electroless plated gold
film exceeding the required thickness was suppressed and an excess
burden of gold was enabled to be greatly reduced.
Wire bonding performance of the plated gold film: Then, there was
investigated the wire bonding performance of the plated gold film
formed by using the reductive electroless gold plating solution
according to the present invention. There was examined the strength
of wire bonding of the reductive electroless plated gold film of
the Example sample 2-2 of Example 2 as an example using the
reductive electroless gold plating solution according to the
present invention. As a comparison, there was examined the strength
of wire bonding of the reductive electroless plated gold film of
Comparative Example 2 using the conventional reductive electroless
gold plating solution. Specifically, a gold wire of 25 .mu.m in
wire diameter was joined to the reductive electroless plated film
of the Example sample 2-2 and Comparative Example 2 each by using a
wire bonding apparatus; the wire was pulled by a pull tester and
the strength of the wire bonding was examined. For the each case,
20 points were examined and the maximum value, the minimum value
and the average value of the wire bonding strength were determined.
The examination results are shown in FIG. 12.
[0105] The maximum value of the wire bonding strength of the
electroless plated gold film of Example 2 (the Example sample 2-2)
using the reductive electroless plating solution according to the
present invention was 6.0 gf; the minimum value thereof was 4.8 gf;
and the average value thereof was 5.3 gf. Then, the maximum value
of the wire bonding strength of the electroless plated gold film of
Comparative Example 2 using the conventional reductive electroless
plating solution was 6.0 gf; the minimum value thereof was 4.8 gf;
and the average value thereof was 5.3 gf. From these results, it is
found that the electroless plated gold film obtained by using the
reductive electroless plating solution according to the present
invention provided an excellent wire bonding strength, almost the
same as the case using the conventional reductive electroless
plating solution. Hence, it can be said that the reductive
electroless gold plating solution of the present invention enables
to provide a plated gold film capable of realizing the high
junction reliability of wire bonding.
INDUSTRIAL APPLICABILITY
[0106] The reductive electroless gold plating solution of the
present invention greatly suppresses the dissolution of the
substrate metal such as nickel and palladium, and enables the
plated gold film to be deposited at a high deposition rate in a
thick deposition on the surface of the substrate metal. Hence, the
present invention enables the plated gold film high in the wire
bonding junction reliability to be provided.
* * * * *