U.S. patent application number 15/163437 was filed with the patent office on 2016-09-15 for method of electroless gold plating.
The applicant listed for this patent is TOYO KOHAN CO., LTD.. Invention is credited to Nobuaki MUKAI.
Application Number | 20160265115 15/163437 |
Document ID | / |
Family ID | 49916103 |
Filed Date | 2016-09-15 |
United States Patent
Application |
20160265115 |
Kind Code |
A1 |
MUKAI; Nobuaki |
September 15, 2016 |
METHOD OF ELECTROLESS GOLD PLATING
Abstract
A method of electroless gold plating includes a step of forming
an underlying alloy layer on a base material and a step of forming
a gold plate layer directly on the underlying alloy layer by
electroless reduction plating using a cyanide-free gold plating
bath. The underlying alloy layer is formed of an M1-M2-M3 alloy,
where M1 is at least one element selected from Ni, Fe, Co, Cu, Zn,
where Sn, M2 is at least one element selected from Pd, Re, Pt, Rh,
Ag and where Ru, and M3 is at least one element selected from P and
B.
Inventors: |
MUKAI; Nobuaki; (Yamaguchi,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
TOYO KOHAN CO., LTD. |
TOKYO |
|
JP |
|
|
Family ID: |
49916103 |
Appl. No.: |
15/163437 |
Filed: |
May 24, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
14414655 |
Jan 13, 2015 |
9388497 |
|
|
PCT/JP2013/068956 |
Jul 11, 2013 |
|
|
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15163437 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C23C 18/52 20130101;
C23C 28/00 20130101; C23C 30/00 20130101; Y10T 428/24967 20150115;
C23C 18/48 20130101; Y10T 428/12875 20150115; Y10T 428/12931
20150115; Y10T 428/12944 20150115; C22C 21/06 20130101; Y02E 60/50
20130101; Y10T 428/12722 20150115; C23C 18/1831 20130101; Y10T
428/24975 20150115; C22C 19/00 20130101; C23C 18/32 20130101; B32B
15/043 20130101; C23C 18/36 20130101; B32B 15/01 20130101; B32B
15/018 20130101; C23C 18/54 20130101; Y10T 428/1291 20150115; Y10T
428/12972 20150115; C23C 18/40 20130101; C23C 18/50 20130101; C23C
18/1653 20130101; C23C 18/34 20130101; Y10T 428/12917 20150115;
Y10T 428/12889 20150115; Y10T 428/12896 20150115; C22C 5/02
20130101; C23C 28/02 20130101; Y10T 428/2495 20150115; C23C 18/165
20130101; H01M 8/0228 20130101; Y10T 428/12868 20150115; Y10T
428/12861 20150115; C23C 18/1651 20130101; Y10T 428/12882 20150115;
C23C 18/1633 20130101; C23C 18/44 20130101; Y10T 428/12903
20150115; Y10T 428/12924 20150115; Y10T 428/12937 20150115; C23C
28/021 20130101; C23C 30/005 20130101; Y10T 428/12715 20150115;
C23C 18/16 20130101; C23C 18/42 20130101; B32B 15/017 20130101;
C23C 18/38 20130101; Y10T 428/12708 20150115 |
International
Class: |
C23C 18/42 20060101
C23C018/42; C23C 18/50 20060101 C23C018/50; C23C 18/16 20060101
C23C018/16 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 13, 2012 |
JP |
2012-157180 |
Claims
1. A method of electroless gold plating comprising: forming an
underlying alloy layer on a metallic base material; and forming a
gold plate layer directly on the underlying alloy layer by means of
electroless reduction plating using a cyanide-free gold plating
bath, wherein the underlying alloy layer is formed of an M1-M2-M3
alloy, and M1 is at least one element selected from Ni, Fe, Co, Cu,
Zn and Sn, M2 is at least one element selected from Pd, Re, Pt, Rh,
Ag and Ru, and M3 is at least one element selected from P and
B.
2. The method as set forth in claim 1, wherein a ratio of each
element in the M1-M2-M3 alloy is that M1 is 20 to 50 at. %, M2 is
30 to 50 at. %, and M3 is 20 to 30 at. %.
3. The method as set forth in claim 1, further comprising forming a
modifying layer on the metallic base material in order to enhance
the interfacial adhesion property between the metallic base
material and the underlying alloy layer before forming the
underlying alloy layer.
4. The method as set forth in claim 1, wherein the thickness of the
underlying alloy layer is 0.01 to 1.0 .mu.m.
5. The method as set forth in claim 1, wherein the thickness of the
gold plate layer is 1 to 200 nm.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a Continuation of co-pending application
Ser. No. 14/414,655 filed on Jan. 13, 2015, which is a U.S.
National Stage of International Application No. PCT/JP2013/068956
filed on Jul. 11, 2013, for which priority is claimed under 35
U.S.C. .sctn.120; and this application claims priority of
Application No. 2012-157180 filed on Jul. 13, 2012 in Japan under
35 U.S.C. .sctn.119, the entire contents of all of which are hereby
incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Technical Field of the Invention
[0003] The present invention relates to a method of electroless
gold plating and a gold plate coated material.
[0004] 2. Description of the Related Art
[0005] Heretofore, as a method of forming a gold plate layer on a
surface of an electrical contact material such as used for
connectors, switches or printed wiring boards, there has been known
a method of performing electroless substitution gold plating on a
surface of a metallic base material.
[0006] However, such a method of forming a gold plate layer by
means of electroless substitution gold plating may involve problems
as below. That is, when the electroless substitution gold plating
is performed, the metallic base material as a material to be plated
with gold may locally dissolve to generate micro recesses at the
surface of the metallic base material. The micro recesses thus
generated will cause poor deposition of gold, so that pinholes may
occur at the surface of the gold plate layer to be formed. This may
lead to problems in that the obtained electrical contact material
deteriorates in its corrosion resistance and conductivity and
delamination occurs at an interface with solder when the electrical
contact material is connected with another component by
soldering.
[0007] On the other hand, in order to solve such problems due to
pinholes, there may be used a method of further performing
electroless reduction gold plating on the gold plate layer formed
by the electroless substitution gold plating thereby to cover the
pinholes. In this method, however, the gold plate layer may have to
be formed with a large thickness in total to allow the electroless
reduction gold plating to cover the pinholes, which may be
problematic in cost.
[0008] In view of the above, Patent Document 1 (Japanese Patent
Application Publication No. 2005-54267) discloses a method of
performing palladium plating to form a palladium plate layer on a
base material and thereafter forming a gold plate layer on the
palladium plate layer by means of electroless reduction gold
plating.
SUMMARY OF THE INVENTION
[0009] The above technique of Patent Document 1, however, employs a
cyanide-based gold plating bath to form the gold plate layer and
therefore requires treating the cyanide-containing waste liquid
having high toxicity, and is thus problematic in that the loads to
working environment and external environment are high. There may be
proposed to use a cyanide-free gold plating bath as substitute for
the cyanide-based gold plating bath to perform electroless
reduction plating on the palladium plate layer, but in this case a
problem may arise in that the gold plate layer obtained has a
considerably low coverage and also considerably low interfacial
adhesion property.
[0010] The present invention has been made in consideration of such
actual circumstances, and an object of the present invention is to
provide a method of electroless gold plating which can form a gold
plate film excellent in the interfacial adhesion property and
suppressed from the occurrence of pinholes and which is improved in
the loads to working environment and external environment.
[0011] As a result of intensive studies to achieve the above
object, the present inventor has found that the above object can be
achieved by forming an underlying alloy layer constituted of
certain elements on a base material and forming a gold plate layer
on the underlying alloy layer by means of electroless reduction
plating using a cyanide-free gold plating bath, and has
accomplished the present invention.
[0012] That is, according to an aspect of the present invention,
there is provided a method of electroless gold plating, comprising
a step of forming an underlying alloy layer on a base material and
a step of forming a gold plate layer directly on the underlying
alloy layer by means of electroless reduction plating using a
cyanide-free gold plating bath. The method is characterized in that
the underlying alloy layer is formed of an M1-M2-M3 alloy (where M1
is at least one element selected from Ni, Fe, Co, Cu, Zn and Sn, M2
is at least one element selected from Pd, Re, Pt, Rh, Ag and Ru,
and M3 is at least one element selected from P and B).
[0013] According to another aspect of the present invention, there
is provided a gold plate coated material comprising: a base
material; an underlying alloy layer formed on the base material;
and a gold plate layer formed on the underlying alloy layer. The
gold plate coated material is characterized in that the underlying
alloy layer is formed of an M1-M2-M3 alloy (where M1 is at least
one element selected from Ni, Fe, Co, Cu, Zn and Sn, M2 is at least
one element selected from Pd, Re, Pt, Rh, Ag and Ru, and M3 is at
least one element selected from P and B).
[0014] According to the present invention, there can be provided a
method of electroless gold plating which can form a gold plate film
excellent in the interfacial adhesion property and suppressed from
the occurrence of pinholes and which is improved in the loads to
working environment and external environment.
BRIEF DESCRIPTION OF DRAWINGS
[0015] FIG. 1 is a set of SEM photographs of surfaces of gold plate
coated materials obtained in Examples and Comparative Examples.
[0016] FIG. 2 is a graph which shows concentrations of dissolved
ions from the gold plate coated materials obtained in Examples and
Comparative Examples.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0017] The method of electroless gold plating according to the
present invention will hereinafter be described.
[0018] The gold plate coated material obtained through the method
of electroless gold plating according to the present invention
comprises an underlying alloy layer and a gold plate layer on a
base material, and is characterized in that the underlying alloy
layer is formed of an M1-M2-M3 alloy (where M1 is at least one
element selected from Ni, Fe, Co, Cu, Zn and Sn, M2 is at least one
element selected from Pd, Re, Pt, Rh, Ag and Ru, and M3 is at least
one element selected from P and B).
[0019] <Base Material>
[0020] The base material is not particularly limited. Examples of
the base material include steel, stainless steel, Al, Al alloy, Ti,
Ti alloy, Cu, Cu alloy, Ni, and Ni alloy. The shape and form of the
base material are not particularly limited, and may be
appropriately selected depending on the use. For example, the base
material may be used after being worked into a necessary shape or
form depending on its use, such as a conductive metal component
worked into a linear form or a plate or sheet-like form, a
conductive member obtained by working a plate or sheet into an
irregular form, and an electronic device component worked into a
spring-like or tubular form. The thickness (such as diameter and
sheet or plate thickness) of the base material is also not
particularly limited, and may be appropriately selected depending
on the use.
[0021] <Underlying Alloy Layer>
[0022] The underlying alloy layer is an underlying layer for
smoothly forming the gold plate layer and is formed of an M1-M2-M3
alloy. Here, the M1-M2-M3 alloy is constituted of M1, M2 and M3
which are different elements from one another, where M1 is at least
one element selected from Ni, Fe, Co, Cu, Zn and Sn, M2 is at least
one element selected from Pd, Re, Pt, Rh, Ag and Ru, and M3 is at
least one element selected from P and B.
[0023] The method of forming the underlying alloy layer is not
particularly limited. The underlying alloy layer can be formed by
an appropriate method such as electrolytic plating, electroless
plating and sputtering. As will be described later, it is
particularly preferred that the underlying alloy layer is formed by
electroless plating.
[0024] M1 in the M1-M2-M3 alloy is at least one element selected
from Ni, Fe, Co, Cu, Zn and Sn. One element may be solely used, or
two or more elements may be used in combination, such as in Ni--Fe,
Ni--Co and Ni--Cu. Each element that constitutes M1 is an element
having a property capable of independently forming a plate layer on
the base material, and has an action to allow the underlying alloy
layer to adhere tightly to the base material. In view of preventing
the plating liquid from self-decomposition and enhancing the
stability of the plating liquid, it is preferred to use at least
one element selected from Ni and Co as M1, and particularly
preferred is to use Ni.
[0025] M2 in the M1-M2-M3 alloy is at least one element selected
from Pd, Re, Pt, Rh, Ag and Ru. One element may be solely used, or
two or more elements may be used in combination. Each element that
constitutes M2 is an element having an autocatalytic action, and
acts as a catalyst for the reaction of a reductant in the plating
bath when deposited on the base material, i.e., has an action to
continuously progress the metal deposition reaction. In view of
keeping low cost, it is preferred to use at least one element
selected from Pd and Ag as M2, and particularly preferred is to use
Pd.
[0026] M3 in the M1-M2-M3 alloy is at least one element selected
from P and B. One element may be solely used, or two elements may
be used in combination, such as in P-B. Each element that
constitutes M3 is a metalloid that constitutes a reductant in the
plating bath for forming the underlying alloy layer, and will be
unavoidably incorporated into the underlying alloy layer in general
when the underlying alloy layer is formed. In view of preventing
the plating liquid from self-decomposition and enhancing the
stability of the plating liquid, it is preferred to use P as
M3.
[0027] The ratio of each element in the M1-M2-M3 alloy is
preferably such that M1 is 20 to 50 at %, M2 is 30 to 50 at %, and
M3 is 20 to 30 at %. The M1-M2-M3 alloy may slightly contain
impurities, which are unavoidably mixed therein, to such an extent
that allows the gold plate layer to be appropriately formed on the
M1-M2-M3 alloy and prevents the occurrence of unformed parts and
pinholes in the gold plate layer. Examples of such unavoidable
impurities include a heavy metal, such as Pb, Tl and Bi, which is
added as a stabilizer that prevents the plating liquid from
self-decomposition and stabilizes the plating liquid. In view of
reducing the environmental load, Bi may preferably be used as the
stabilizer. By adjusting the composition ratio of the M1-M2-M3
alloy within the above range, the underlying alloy layer may be
smoothly formed on the base material, and the gold plate layer to
be formed on the underlying alloy layer can also be smoothly formed
with reduced occurrence of pinholes.
[0028] Respective elements for the M1-M2-M3 alloy may be
arbitrarily combined to be used. In view of preventing the plating
liquid from self-decomposition and enhancing the stability of the
plating liquid, Ni--Pd--P alloy and Co--Ag--P alloy are preferred,
and Ni--Pd--P alloy is particularly preferred.
[0029] Formation of the underlying alloy layer of M1-M2-M3 alloy
can be performed by plating on the base material using a plating
bath which contains elements represented by M1, M2 and M3 and to
which a reductant and a complexing agent are added (underlying
alloy electroless plating bath). For example, when forming an
underlying alloy layer of Ni--Pd--P alloy, the underlying alloy
electroless plating bath to be used can be obtained by mixing a
nickel plating bath and a palladium plating bath which are commonly
used. Examples of the nickel plating bath include a plating bath
that contains: a nickel salt such as nickel chloride, nickel
sulfate, nickel nitrate and nickel acetate; a phosphorus-containing
reductant such as hypophosphite; and a complexing agent such as
citric acid. Examples of the palladium plating bath include a
plating bath that contains: a palladium salt such as palladium
chloride; a phosphorus-containing reductant such as hypophosphite
and phosphite; and a complexing agent such as thiodiglycolic acid.
When the nickel plating bath and the palladium plating bath are
mixed to prepare the underlying alloy electroless plating bath, it
is preferred that nickel chloride is used as the nickel salt and
palladium chloride is used as the palladium salt. Mixing ratio of
the nickel plating bath and the palladium plating bath may
appropriately be set in accordance with the ratio of respective
elements that constitute the Ni--Pd--P alloy. The above exemplifies
the case in which the underlying alloy layer is formed of Ni--Pd--P
alloy, but also in the case in which the underlying alloy layer is
formed of other alloy than Ni--Pd--P alloy, there may be used an
underlying alloy electroless plating bath obtained by appropriately
adjusting a plating bath which contains respective elements of M1,
M2 and M3 and to which a reductant and a complexing agent are
added.
[0030] It is preferred that the underlying alloy layer is formed
using the above-described underlying alloy electroless plating bath
under a condition of pH of 4.0 to 7.0, a bath temperature of
30.degree. C. to 50.degree. C., and an immersion time of 5 to 20
minutes.
[0031] The thickness of the underlying alloy layer may preferably
be 0.01 to 1.0 .mu.m, and more preferably 0.05 to 0.2 .mu.m. The
thickness of the underlying alloy layer being within the above
range allows the gold plate layer to be smoothly formed on the
underlying alloy layer by means of electroless reduction
plating.
[0032] In the present invention, when the underlying alloy layer is
formed on the base material, the underlying alloy layer may be
formed directly on the base material, but a modifying layer may be
provided to enhance the interfacial adhesion property between the
base material and the underlying alloy layer. The modifying layer
may appropriately be formed in accordance with properties of the
base material and the underlying alloy layer. In view of enhancing
the interfacial adhesion property with the underlying alloy layer,
the modifying layer may preferably be a layer that contains the
same element or elements as M1 of the M1-M2-M3 alloy which
constitutes the underlying alloy layer. For example, when Ni--Pd--P
alloy is employed as the underlying alloy layer, the modifying
layer may preferably be a Ni-based layer that contains Ni as the
element represented by M1. When such a Ni-based layer is formed by
means of electroless reduction plating, the Ni-based layer may be a
Ni--P plate layer. One modifying layer may be provided, or two or
more modifying layers may also be provided. When two or more
modifying layers are provided, components that constitute
respective layers may be or may not be the same. The method of
forming the modifying layer or layers is not particularly limited.
The modifying layer or layers can be formed by an appropriate
method such as electrolytic plating, electroless plating and
sputtering.
[0033] <Gold Plate Layer>
[0034] The gold plate layer is a layer that is formed directly on
the underlying alloy layer by using a cyanide-free gold plating
bath to perform electroless reduction plating.
[0035] As described above, in the present invention, an excellent
gold plate layer can be formed without pinholes by forming the
underlying alloy layer of M1-M2-M3 alloy on the base material and
forming the gold plate layer on the underlying alloy layer by means
of electroless reduction plating. Therefore, according to the
present invention, when a gold plate coated material formed with
such a gold plate layer is used for various materials such as an
electric contact material, it is possible to effectively prevent
the deterioration in corrosion resistance and conductivity and the
occurrence of delamination of solder when the gold coated material
is connected with another component by soldering. In addition,
according to the present invention, the layer of M1-M2-M3 alloy is
formed as the underlying alloy layer thereby to allow the gold
plate layer to be formed using a cyanide-free gold plating bath,
and it is therefore possible to reduce loads to working environment
and external environment. That is, there may not arise problems due
to increased loads to working environment and external environment,
which would be problematic if a cyanide-based gold plating bath was
used.
[0036] As the cyanide-free gold plating bath to be used when
forming the gold plate layer, there can be used a cyanide-free gold
plating bath which is commonly used for electroless reduction
plating, i.e., a plating bath that contains one or more kinds of
gold salts, such as chloroauric acid salt, gold sulfite, gold
thiosulfate, and gold thiomalate. The gold plate layer may
preferably be formed using the cyanide-free gold plating bath which
contains gold salt or salts as described above under a condition of
pH of 7.0 to 8.5 and a bath temperature of 55.degree. C. to
65.degree. C. Immersion time in the gold plating bath when forming
the gold plate layer is not particularly limited, and can be set
depending on the necessary film thickness of the gold plate
layer.
[0037] Conventionally, as the method of forming a gold plate layer
on a base material, there has been used a method in which the
electroless substitution plating is performed directly on the base
material to form the gold plate layer. However, such a method of
performing the electroless substitution gold plating involves
problems in that the metallic base material as a material to be
plated with gold may locally dissolve to generate recesses at the
surface of the metallic base material, and the recesses thus
generated will cause poor deposition of gold, so that pinholes may
occur at the surface of the gold plate layer to be formed. In order
to cover the pinholes thus generated, there has also been used a
method of further performing electroless reduction gold plating
after the gold plate layer is formed by the electroless
substitution gold plating. In this method, however, the gold plate
layer may have to be formed with a large thickness in total to
allow the pinholes to be covered, which may be problematic in
cost.
[0038] In contrast, according to the method of electroless gold
plating of the present invention, the layer of M1-M2-M3 alloy is
formed as the underlying alloy layer thereby to allow the gold
plate layer to be formed using the electroless reduction plating
without performing electroless substitution gold plating, and the
problems due to such pinholes can thus be solved. In particular,
according to the present invention, the layer of M1-M2-M3 alloy is
formed as the underlying alloy layer thereby to allow the gold
plate layer to be smoothly formed using the electroless reduction
plating. Therefore, the gold plate layer may not have to be formed
with a large thickness to solve the above-described problems due to
pinholes.
[0039] The above-described method of electroless gold plating as
disclosed in Patent Document 1 (JP 2005-54267 A), i.e., a method of
performing electroless reduction palladium plating to form a
palladium plate layer on a base material and thereafter forming a
gold plate on the palladium plate layer by means of electroless
reduction gold plating, employs a cyanide-based gold plating bath
when forming the gold plate layer and therefore requires treating
the cyanide-containing waste liquid having high toxicity, and is
thus problematic in that the loads to working environment and
external environment are high.
[0040] In contrast, according to the method of electroless gold
plating of the present invention, a cyanide-free gold plating bath
can be used to form the gold plate layer, and the loads to working
environment and external environment can therefore be reduced.
[0041] The thickness of the gold plate layer may preferably be 1 to
200 nm, and more preferably 5 to 100 nm. If the thickness of the
gold plate layer is unduly small, a uniform gold plate layer will
not be formed on the underlying alloy layer, so that the corrosion
resistance, conductivity and soldering property may possibly
deteriorate when the gold plate layer is used as a part of a gold
plate coated material. On the other hand, unduly large thickness of
the gold plate layer may be disadvantageous in cost.
[0042] According to the method of electroless gold plating of the
present invention, the underlying alloy layer of M1-M2-M3 alloy is
formed on the base material, and the gold plate layer is formed on
the underlying alloy layer by means of electroless reduction
plating. Therefore, a gold plate coated material can be provided
which is formed with an excellent gold plate layer without pinholes
and which has good corrosion resistance, conductivity and soldering
property. Such a gold plate coated material according to the
present invention may be suitably employed as an electrical contact
material such as used for connectors, switches or printed wiring
boards.
[0043] Moreover, such a gold plate coated material according to the
present invention may also be suitably employed as a separator for
fuel cells, which is a member of a fuel cell. In particular, a
separator for fuel cells has a surface formed with irregularities
that function as flow channels for fuel gas or air, and takes a
role to collect electrons generated at an electrode. Therefore, the
irregular part may have to be smoothly formed with a gold plate
layer, and the corrosion resistance and conductivity are also
required. To this end, the gold plate coated material according to
the present invention can be suitably used as such a separator for
fuel cells because the gold plate coated material according to the
present invention is formed with the gold plate layer by means of
electroless reduction plating so that the gold plate layer is
smoothly formed even for the irregular part to exhibit excellent
corrosion resistance and conductivity.
EXAMPLES
[0044] The present invention will be more specifically described
hereinafter with reference to examples, but the present invention
is not limited to these examples.
Example 1
[0045] Electroless plating was performed to form a Ni--P layer
(content ratio of P: 12 wt %) on 5086 aluminum alloy of 5000 series
provided by JIS H4000 (Si: 0.4 wt %, Fe: 0.5 wt %, Cu: 0.1 wt %,
Mn: 0.2 wt %, Mg: 3.5 wt %, Zn: 0.25 wt %, Cr: 0.25 wt %, and Al:
the balance) to have an arithmetic mean roughness Ra of the surface
of 0.1 nm and a thickness of 10 .mu.m, and a base material having a
total thickness of 1.27 mm was thus prepared. Thereafter, the
prepared base material was degreased and then washed with water,
and electroless plating was performed using a Ni--P plating bath
(ICP NICORON GM-NP, available from Okuno Chemical Industries Co.,
Ltd.) to form a Ni--P plate layer (content ratio of P: 7 wt %) with
a thickness of 2 .mu.m on the base material.
[0046] Subsequently, for the base material formed with the Ni--P
plate layer, plating was performed using a plating bath as below
under a condition of 40.degree. C. and 7 minutes to form a
Ni--Pd--P alloy layer with a thickness of 0.79 .mu.m on the Ni--P
plate layer. The plating bath was obtained by mixing a Pd plating
bath and a Ni--P plating bath as below with a ratio of (Pd plating
bath):(Ni--P plating bath)=3:1 (volume ratio). With regard to the
palladium salt, reductant and complexing agent in the plating bath,
conventionally-known compounds were used.
[0047] <Pd Plating Bath>
[0048] Palladium salt: An amount as Pd of 0.15 wt % in the Pd
plating bath
[0049] Reductant: 1.8 wt %
[0050] Complexing agent: 0.63 wt %
[0051] Water: 97.2 wt %
[0052] pH: 5.8
[0053] <Ni-P Plating Bath>
[0054] Nickel salt (nickel chloride): 1.8 wt %
[0055] Reductant (sodium hypophosphite): 2.4 wt %
[0056] Complexing agent: 2.4 wt %
[0057] Water: 93.2 wt %
[0058] pH: 5.2
[0059] Next, for the base material formed with the Ni--P plate
layer and the Ni--Pd--P alloy layer, electroless reduction plating
was performed using a cyanide-free electroless reduction gold
plating bath (SELF GOLD OTK, available from Okuno Chemical
Industries Co., Ltd.) under a condition of 60.degree. C. and 4
minutes to form a gold plate layer with a thickness of 55 nm on the
Ni--Pd--P alloy layer, and a gold plate coated material was thus
obtained.
[0060] Thereafter, for the obtained gold plate coated material,
measurement was conducted using an inductively coupled plasma
emission spectrometer (ICPE-9000, available from SHIMADZU
CORPORATION). The composition of the Ni--Pd--P alloy layer was
Ni:Pd:P=34:42:20 (at %), and the remainder was unavoidable
impurities.
[0061] Appearance Evaluation of Gold Plate Layer and Confirmation
of Gold Undeposited Part
[0062] For the gold plate coated material thus obtained, visual
observation and observation using a scanning electron microscope
(S-4800, available from Hitachi High-Technologies Corporation) were
conducted to confirm the appearance of the gold plate layer and
presence or absence of gold undeposited part with respect to the
surface of the obtained gold plate coated material. Evaluation
results are listed in Table 1.
[0063] Evaluation of Interfacial Adhesion Property of Gold Plate
Layer
[0064] Next, for the gold plate layer of the gold plate coated
material, evaluation of the interfacial adhesion property was
conducted. Specifically, the evaluation of the interfacial adhesion
property was performed through: conducting a peel test by applying
a pressure sensitive adhesive tape (NICETACK powerfully adhesive
tape, available from Nichiban Co., Ltd.) to the gold plate layer of
the gold plate coated material and then peeling off the tape; and
thereafter observing the delamination state of the gold plate
layer, and evaluation was conducted in accordance with the criteria
as below. Evaluation results are listed in Table 1.
[0065] .smallcircle.: Delamination of gold plate layer was not
confirmed.
[0066] x: Delamination of gold plate occurred.
Example 2
[0067] A gold plate coated material was obtained like in Example 1
except for substituting the above-described Ni--Pd--P alloy layer
with a Ni--Pt--P alloy layer and changing the condition, such as
immersion time, in the electroless reduction plating for forming
the gold plate layer thereby to form a gold plate layer with a
different thickness of 5 nm. The Ni--Pt--P alloy layer was formed
with a thickness of 50 nm on the Ni--P plate layer using a plating
bath as below under a condition of 35.degree. C., 10 minutes and pH
of 4.0. The plating bath was obtained by mixing a Pt plating bath
(IM-PT, available from JAPAN PURE CHEMICAL CO., LTD.) and the
above-described Ni--P plating bath used when forming the Ni--Pd--P
alloy layer with a ratio of (Pt plating bath):(Ni--P plating
bath)=3:7 (volume ratio). Evaluation was conducted like in Example
1. Evaluation results are listed in Table 1.
Example 3
[0068] A gold plate coated material was obtained like in Example 1
except for substituting the above-described Ni--Pd--P alloy layer
with a Co--Pd--P alloy layer and changing the condition, such as
immersion time, in the electroless reduction plating for forming
the gold plate layer thereby to form a gold plate layer with a
different thickness of 5 nm. The Co--Pd--P alloy layer was formed
with a thickness of 50 nm on the Ni--P plate layer using a plating
bath as below under a condition of 60.degree. C., 10 minutes and pH
of 8.5. The plating bath was obtained by mixing a Pd plating bath
(PALLA TOP, available from Okuno Chemical Industries Co., Ltd.) and
a Co plating bath as below with a ratio of (Pd plating bath):(Co
plating bath)=1:6 (volume ratio). Evaluation was conducted like in
Example 1. Evaluation results are listed in Table 1.
[0069] <Co Plating Bath>
[0070] Cobalt salt (cobalt sulfate): 10 g/L
[0071] Reductant (sodium hypophosphite): 25 g/L
[0072] Complexing agent (trisodium citrate): 30 g/L
[0073] Complexing agent (sodium tartrate): 30 g/L
[0074] Complexing agent (glycine): 7.58 g/L
[0075] Lead acetate: 0.3 ppm
Comparative Example 1
[0076] A gold plate coated material was obtained like in Example 1
except for not forming the above-described Ni--Pd--P alloy layer
but using a cyanide-free electroless reduction gold plating bath
(SELF GOLD OTK, available from Okuno Chemical Industries Co., Ltd.)
to perform electroless reduction plating directly on the Ni--P
plate layer. Evaluation was conducted like in Example 1. Evaluation
results are listed in Table 1.
Comparative Example 2
[0077] A gold plate coated material was obtained like in Example 1
except for using a Pd plating bath (PALLA TOP, available from Okuno
Chemical Industries Co., Ltd.) to form a palladium plate layer with
a thickness of 0.5 .mu.m on the Ni--P plate layer by means of
electroless plating as substitute for forming the Ni--Pd--P alloy
layer, and using a cyanide-free electroless reduction gold plating
bath (SELF GOLD OTK, available from Okuno Chemical Industries Co.,
Ltd.) to perform electroless reduction plating directly on the
palladium plate layer thus formed. Evaluation was conducted like in
Example 1. Evaluation results are listed in Table 1.
TABLE-US-00001 TABLE 1 Presence or Evaluation of Underlying layer
for absence of interfacial gold plate layer Evaluation of
appearance undeposited part adhesion property Example 1 Ni--Pd--P
Gold plate layer was Absent .smallcircle. alloy layer smoothly
formed without nonuniformity Example 2 Ni--Pt--P Gold plate layer
was Absent .smallcircle. alloy layer smoothly formed without
nonuniformity Example 3 Co--Pd--P Gold plate layer was Absent
.smallcircle. alloy layer smoothly formed without nonuniformity
Comparative Ni--P plate Gold plate layer was not Present
Unmeasurable Example 1 layer formed Comparative Pd plate
nonuniformity occurred in Present x Example 2 layer gold plate
layer
[0078] Results of Table 1 show that, in Examples 1 to 3 for which
the method of electroless gold plating according to the present
invention was used to form the Ni--Pd--P alloy layer, Ni--Pt--P
alloy layer or Co--Pd--P alloy layer as the underlying alloy layer
and form the gold plate layer directly on the formed underlying
alloy layer by means of electroless reduction plating using the
cyanide-free gold plating bath, the gold plate layer thus formed
exhibited good appearance without uneven plating and had good
interfacial adhesion property, and there was not confirmed any
undeposited part of gold. By contrast, in Comparative Example 1
without forming such an underlying alloy layer, there was not
formed any gold plate layer, so that the interfacial adhesion
property of gold plate layer was not able to be measured. Also in
Comparative Example 2 in which the palladium plate layer was formed
as substitute for the underlying alloy layer, results were such
that the gold plate layer had a considerably low coverage and the
interfacial adhesion property was also poor.
[0079] FIG. 1 shows a set of photographs obtained by observing the
surfaces of Examples 1 to 3 and Comparative Examples 1 and 2 using
a scanning electron microscope. FIG. 1(A), FIG. 1(B), FIG. 1(C),
FIG. 1(D) and FIG. 1(E) correspond to Example 1, Example 2, Example
3, Comparative Example 1 and Comparative Example 2, respectively.
With regard to Examples 1 to 3, the gold plate layers were
confirmed to be uniformly formed, as shown in FIG. 1(A) to FIG.
1(C). With regard to Comparative Example 1, no gold plate layer was
formed on the Ni--P plate layer, as shown in FIG. 1(D). With regard
to Comparative Example 2, the gold plate layer was unevenly formed
(white parts in FIG. 1(E)), and undeposited parts of gold were
occasionally observed, as shown in FIG. 1(E).
Examples 4 to 6
[0080] Gold plate coated materials were obtained like in Example 1
except for changing the condition, such as immersion time, in the
electroless reduction plating for forming the gold plate layers so
that the thicknesses of the gold plate layers to be obtained would
be 36 nm (Example 4), 49 nm (Example 5) and 63 nm (Example 6).
Comparative Example 3
[0081] With regard to Comparative Example 3, a gold plate coated
material was obtained like in Example 1 except for not forming the
Ni--Pd--P alloy layer but forming a gold plate layer directly on
the Ni--P plate layer. The gold plate layer was formed with a
thickness of 35 nm using a cyanide-free electroless substitution
gold plating bath (FLASH GOLD NC, available from Okuno Chemical
Industries Co., Ltd.) to perform electroless substitution plating
under a condition of 55.degree. C. and 1 minute and then using a
cyanide-free electroless reduction gold plating bath (SELF GOLD
OTK, available from Okuno Chemical Industries Co., Ltd.) to perform
electroless reduction plating under a condition of 60.degree. C.
and 1 minute.
Comparative Examples 4 to 6
[0082] Gold plate coated materials were obtained like in
Comparative Example 3 except for changing the condition, such as
immersion time, in the electroless reduction plating for forming
the gold plate layers so that the thicknesses of the gold plate
layers to be obtained would be 78 nm (Comparative Example 4), 132
nm (Comparative Example 5) and 186 nm (Comparative Example 6).
[0083] Evaluation of Corrosion Resistance of Gold Plate Layer
[0084] For Examples 4 to 6 and Comparative Examples 3 to 6,
evaluation of corrosion resistance was conducted with respect to
the obtained gold plate coated materials. Specifically, the
evaluation of corrosion resistance was performed through: masking
each gold plate coated material with a polyimide tape to expose a
surface area of 35 mm longitudinal and 20 mm lateral; immersing the
gold plate coated material into sulfuric acid aqueous solution of
90.degree. C. (volume: 80 ml, pH: 1) for 50 hours; thereafter
taking out the gold plate coated material; and measuring
concentrations of ions (Ni, Pd and P) dissolved from the gold plate
coated material into the sulfuric acid aqueous solution using an
inductively coupled plasma emission spectrometer (ICPE-9000,
available from SHIMADZU CORPORATION). Results are shown in FIG. 2.
The results shown in FIG. 2 are represented by relative values of
the concentrations of dissolved ions (Ni, Pd and P) to a value of
100 when the thickness of the gold plate layer is 35 nm in
Comparative Example 3.
[0085] Results of FIG. 2 show that, in Examples 4 to 6 for which
the method of electroless gold plating according to the present
invention was used, the dissolution of ions was able to be
effectively suppressed to exhibit excellent corrosion resistance
even when the thickness of the gold plate layer was small. In
contrast, according to Comparative Examples 3 to 6 in which the
underlying alloy layer was not formed, results were such that the
dissolution of ions was not able to be suppressed, thus exhibiting
poor corrosion resistance of the gold plate layers, even when the
gold plate layer was formed with a large thickness.
* * * * *