U.S. patent application number 13/162198 was filed with the patent office on 2012-01-26 for coating and electronic component.
This patent application is currently assigned to TDK CORPORATION. Invention is credited to Hisayuki ABE, Yuhei HORIKAWA, Atsushi SATO, Kenichi YOSHIDA.
Application Number | 20120018191 13/162198 |
Document ID | / |
Family ID | 44359480 |
Filed Date | 2012-01-26 |
United States Patent
Application |
20120018191 |
Kind Code |
A1 |
YOSHIDA; Kenichi ; et
al. |
January 26, 2012 |
COATING AND ELECTRONIC COMPONENT
Abstract
The present invention provides a coating 10 provided on a
conductor 20, the coating 10 has a first layer 12 containing
palladium and a second layer 14 containing gold from the conductor
20 side, the first layer 12 has a first region 31 on the conductor
20 side and a second region 32 arranged nearer to the second layer
14 than the first region 31, and the second region 32 has a higher
phosphorus concentration than the first region 31.
Inventors: |
YOSHIDA; Kenichi; (Tokyo,
JP) ; HORIKAWA; Yuhei; (Tokyo, JP) ; SATO;
Atsushi; (Tokyo, JP) ; ABE; Hisayuki; (Tokyo,
JP) |
Assignee: |
TDK CORPORATION
TOKYO
JP
|
Family ID: |
44359480 |
Appl. No.: |
13/162198 |
Filed: |
June 16, 2011 |
Current U.S.
Class: |
174/126.2 |
Current CPC
Class: |
C23C 18/1655 20130101;
H01L 24/03 20130101; C23C 28/02 20130101; H01L 2224/05147 20130101;
C23C 18/1651 20130101; H01L 2224/03464 20130101; H01L 2224/05139
20130101; C23C 18/54 20130101; H01L 2924/14 20130101; C23C 18/32
20130101; H01L 2224/04042 20130101; H01L 2224/05164 20130101; H01L
2924/01015 20130101; H01L 2224/05144 20130101; C23C 18/42 20130101;
H01L 2224/05644 20130101; H01L 2924/00 20130101; H01L 2924/14
20130101; C23C 18/1637 20130101; H01L 2224/0401 20130101; H01L
24/05 20130101; H01L 2224/05083 20130101 |
Class at
Publication: |
174/126.2 |
International
Class: |
H01B 5/00 20060101
H01B005/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 20, 2010 |
JP |
2010-163128 |
Claims
1. A coating provided on a conductor, comprising: a first layer
containing palladium and a second layer containing gold from the
conductor side, wherein the first layer has a first region, and a
second region arranged nearer to the second layer than the first
region, and wherein the second region has a higher phosphorus
concentration than the first region.
2. The coating according to claim 1, wherein the first layer has an
inside layer including the first region and an outside layer
including the second region, from the conductor side.
3. The coating according to claim 1, wherein at least one of the
first region and the second region has the phosphorus concentration
decreasing with decreasing distance to the conductor.
4. The coating according to claim 2, wherein at least one of the
first region and the second region has the phosphorus concentration
decreasing with decreasing distance to the conductor.
5. The coating according to claim 1, wherein the phosphorus
concentration in the first region is not more than 0.01% by mass
and the phosphorus concentration in the second region is more than
0.01% by mass and not more than 7% by mass.
6. The coating according to claim 2, wherein the phosphorus
concentration in the first region is not more than 0.01% by mass
and the phosphorus concentration in the second region is more than
0.01% by mass and not more than 7% by mass.
7. The coating according to claim 3, wherein the phosphorus
concentration in the first region is not more than 0.01% by mass
and the phosphorus concentration in the second region is more than
0.01% by mass and not more than 7% by mass.
8. The coating according to claim 1, wherein the first layer has
the thickness in the range of 0.1 to 0.4 .mu.m.
9. The coating according to claim 2, wherein the first layer has
the thickness in the range of 0.1 to 0.4 .mu.m.
10. The coating according to claim 3, wherein the first layer has
the thickness in the range of 0.1 to 0.4 .mu.m.
11. The coating according to claim 1, comprising an underlying
layer containing nickel between the conductor and the first
layer.
12. The coating according to claim 2, comprising an underlying
layer containing nickel between the conductor and the first
layer.
13. The coating according to claim 3, comprising an underlying
layer containing nickel between the conductor and the first
layer.
14. An electronic component comprising a signal transmission part
having the coating as defined in claim 1, and the conductor coated
with the coating.
15. An electronic component comprising a signal transmission part
having the coating as defined in claim 2, and the conductor coated
with the coating.
16. An electronic component comprising a signal transmission part
having the coating as defined in claim 3, and the conductor coated
with the coating.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a coating provided on a
conductor, and an electronic component having a conductor coated
with the coating.
[0003] 2. Related Background Art
[0004] An electronic component has a signal transmission part for
exchange of signals with an external device. For this signal
transmission part to perform the exchange of electric signals with
the external device, the signal transmission part needs to have
high electrical conductivity and therefore copper or a copper-based
alloy is generally used as a base material of the signal
transmission part. However, copper or the copper-based alloy has
the property of being easily corroded by oxygen in air or by
corrosive gas, and therefore there has been investigation to form
such a coating layer that a nickel plated film and a gold plated
film were laid on a surface of the base material, for the purpose
of controlling and preventing corrosion.
[0005] For example, Japanese Patent Application Laid-open No.
2010-37603 (Patent Literature 1) proposes that an electroless
nickel film is formed as an underlying layer on a base material of
a connection terminal part and then a displacement electroless gold
plated film and a reduction electroless gold plated film are
successively formed thereon.
SUMMARY OF THE INVENTION
[0006] The coating layer described in Patent Literature 1 was
produced in such a manner that in a displacement electroless gold
plating process, electrons to reduce gold ions in a plating
solution are generated by corrosion reaction of the nickel plated
film. For this reason, the nickel plated film is likely to be
corroded and thus easy to produce defects. In order to prevent
occurrence of such defects of the gold plated film, it is possible
to solve the problem by increasing the thickness of the gold plated
film to a sufficiently large level, but in this case, the cost of
the coating layer tends to increase because gold is expensive in
general.
[0007] On the other hand, in the case where the thickness of the
gold plated film is decreased or where no gold plated film is
formed, the nickel plated film is exposed as an outermost layer and
the corrosion resistance degrades.
[0008] The present invention has been accomplished in view of the
above circumstances and it is an object of the present invention to
provide a coating at low manufacturing cost and with adequately
excellent corrosion resistance. It is another object of the present
invention to provide an electronic component having a signal
transmission part with the coating, at low manufacturing cost and
with adequately excellent corrosion resistance.
[0009] For achieving the above object, the present invention
provides a coating provided on a conductor, the coating comprising:
a first layer containing palladium and a second layer containing
gold from the conductor side, wherein the first layer has a first
region on the conductor side, and a second region arranged nearer
to the second layer than the first region, and wherein the second
region has a higher phosphorus concentration than the first
region.
[0010] The coating of the present invention comprises the first
layer having the palladium-containing first region with the lower
phosphorus concentration on the conductor side and having the
second region with the higher phosphorus concentration than the
first region, on the second layer side. Since the second region in
this first layer has the higher phosphorus concentration than the
first region, it is excellent in corrosion resistance. On the other
hand, since the first region in the first layer has the lower
phosphorus concentration than the second region, it is superior in
adhesion to the conductor and it can be readily formed on the
conductor. Therefore, corrosion of the conductor can be adequately
suppressed without need for increasing the thickness of the second
layer containing gold.
[0011] The first layer in the coating of the present invention
preferably has an inside layer including the first region and an
outside layer including the second region, from the conductor side.
When the first layer has the layered structure as in this
configuration, it is feasible to more adequately suppress the
corrosion of the conductor.
[0012] At least one of the first region and the second region in
the coating of the present invention preferably has a region whose
phosphorus concentration decreases with decreasing distance to the
conductor. This allows the coating to be provided with adequately
excellent corrosion resistance, while ensuring a good deposition
characteristic of palladium on the conductor.
[0013] Preferably, the phosphorus concentration in the first region
in the coating of the present invention is not more than 0.01% by
mass and the phosphorus concentration in the second region is more
than 0.01% by mass and not more than 7% by mass. This allows the
coating to be provided with easiness to manufacture and corrosion
resistance together at higher levels.
[0014] The first layer in the coating of the present invention
preferably has the thickness in the range of 0.1 to 0.4 .mu.m. This
allows the coating to be provided with adequately excellent
corrosion resistance, while reducing the manufacturing cost of the
coating sufficiently.
[0015] The coating of the present invention preferably comprises an
underlying layer containing nickel between the conductor and the
first layer. This allows the thickness of the first layer to be
decreased while maintaining the excellent corrosion resistance,
thereby further reducing the manufacturing cost.
[0016] The present invention also provides an electronic component
comprising a signal transmission part having the aforementioned
coating, and the conductor coated with the coating. Since this
signal transmission part is configured so that the conductor is
coated with the coating having the above feature, it can be
manufactured at low manufacturing cost and with adequately
excellent corrosion resistance.
[0017] The present invention successfully provides the coating at
low manufacturing cost and with adequately excellent corrosion
resistance. It also provides the electronic component with the
signal transmission part comprising the coating at low
manufacturing cost and with adequately excellent corrosion
resistance.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 is a schematic cross-sectional view showing a
preferred embodiment of the signal transmission part with the
coating according to the present invention.
[0019] FIG. 2 is a schematic cross-sectional view showing another
embodiment of the signal transmission part with the coating
according to the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0020] The preferred embodiments of the present invention will be
described below with reference to the drawings as needed. In each
drawing, identical or equivalent elements will be denoted by the
same reference signs, without redundant description.
[0021] FIG. 1 is a cross-sectional view schematically showing the
signal transmission part with the coating according to an
embodiment the present invention. The signal transmission part 100
in FIG. 1 constitutes a signal transmission part of an electronic
component and has a conductor 20 and a coating 10 coating the
conductor 20. The coating 10 of the present embodiment is a coating
layer provided for preventing corrosion of the conductor 20. The
coating 10 has a multilayer structure in which a first layer 12
containing palladium as a main component and a second layer 14
containing gold as a main component are successively laid from the
conductor 20 side.
[0022] The first layer 12 is preferably a palladium plated film
formed by palladium plating. Such palladium plated film can be
formed by a displacement palladium plating process or a reduction
palladium plating process.
[0023] The first layer 12 in the coating 10 of the present
embodiment has a double-layered structure in which two layers of
different compositions are laid. Namely, the first layer 12 has an
inside layer 16 arranged on the conductor 20 side, and an outside
layer 18 being a layer with a different composition from that of
the inside layer 16 and arranged on the second layer 14 side.
[0024] A first region 31 in the inside layer 16 is a region
containing palladium as a main component, and a phosphorus
concentration thereof is lower than that of second region 32. The
first region 31 with the lower phosphorus concentration as
described above has an excellent deposition property on the
conductor 20 and thus can form a coating on a stable basis and with
excellent coatability on a surface of the conductor 20. On the
other hand, the second region 32 in the outside layer 18 is a
region containing palladium as a main component and a phosphorus
concentration thereof is higher than that of the first region 31.
When the phosphorus concentration is made higher in this manner,
the coating can be formed with excellent corrosion resistance. It
is noted that the entire inside layer 16 may be the first region 31
and the entire outside layer 18 may be the second region 32.
[0025] The phosphorus concentration of the first region 31 (inside
layer 16) is preferably not more than 0.01% by mass. If this
phosphorus concentration is more than 0.01% by mass, the excellent
coatability will degrade and it will likely become difficult to
form a film covering the conductor 20.
[0026] The phosphorus concentration of the second region 32
(outside layer 18) is preferably more than 0.01% by mass, more
preferably not less than 1% by mass, and still more preferably not
less than 3% by mass. If this phosphorus concentration is not more
than 0.01% by mass, the corrosion resistance of the first layer 12
will degrade and the adequately excellent corrosion resistance of
the coating 10 can become deteriorated. When the phosphorus
concentration is not less than 1% by mass, the first layer 12 can
have sufficiently high corrosion resistance. When the phosphorus
concentration is not less than 3% by mass, the excellent corrosion
resistance can be maintained sufficiently even if the thickness of
the first layer 12 is decreased. As a result, the thickness of the
coating 10 can be decreased.
[0027] The phosphorus concentration of the second region 32
(outside layer 18) is preferably not more than 7% by mass and more
preferably not more than 5% by mass. If the phosphorus
concentration is more than 7% by mass, the good coatability will
degrade and it will likely become difficult to coat the inside
layer 16. When the phosphorus concentration is not more than 5% by
mass, the outside layer 18 can be formed with good coatability.
[0028] The lower limit of the thickness of the first layer 12 is
preferably 0.1 .mu.m. If the thickness is less than 0.1 .mu.m,
coating over the conductor 20 by the first layer 12 will become
inadequate and the adequately excellent corrosion resistance will
likely degrade. The upper limit of the thickness of the first layer
12 is preferably 0.4 .mu.m in terms of manufacturing cost. The
corrosion resistance tends not to improve so much even if the
thickness of the first layer 12 is increased over 0.4 .mu.m.
[0029] The thickness of the second layer 14 is preferably not more
than 0.1 .mu.m and more preferably in the range of 0.01 to 0.08
.mu.m. If the thickness is more than 0.1 .mu.m, the manufacturing
cost of the coating 10 will tend to increase. If the thickness is
less than 0.01 .mu.m on the other hand, the adequately excellent
corrosion resistance can degrade.
[0030] The conductor 20 can be a material containing at least one
selected, for example, from copper, silver, and an alloy of these.
The conductor 20 preferably contains copper in terms of reduction
in manufacturing cost of the signal transmission part 100. An
example of the conductor 20 is a terminal functioning as a signal
transmission part and having an electrical conduction property. For
example, it may be a copper terminal, an antenna signal
transmission part, etc. provided on a circuit board to be mounted
on an electronic component. Examples of such electronic components
include active components such as transistors and integrated
circuits, passive components such as capacitors, inductors and
filters, and so on.
[0031] The signal transmission part 100 may be a connection
terminal disposed on an electronic component and adapted to supply
a power potential or a ground potential to the electronic
component, or a signal terminal for input or output of signal. This
signal transmission part 100 constitutes, in an electronic
component, a connection terminal to be connected to another member
by contact, bonding wire, or soldering, a transmission path of
electric signal for letting the electronic component act as an open
terminal, or a power transmission path. In this manner, the signal
transmission part 100 is applicable to various applications
requiring corrosion resistance.
[0032] A manufacturing method of the coating 10 in the present
embodiment will be described below. The manufacturing method of
coating 10 has a first palladium plating step of performing a
palladium plating process on a surface of the conductor 20 to form
the inside layer 16; a second palladium plating step of performing
a palladium plating process on a surface of the inside layer 16 to
form the outside layer 18 on the inside layer 16; and a gold
plating step of performing a gold plating process on a surface of
the outside layer 18 to form a gold plated film on the outside
layer 18. The details of each step will be described below.
[0033] The first palladium plating step is to form a first
palladium plated film on the surface of the conductor 20 after
subjected to an etching process. A method for forming the first
palladium plated film can be an electroless palladium plating
process such as the displacement palladium plating process or the
reduction palladium plating process. Either one of the two plating
processes can be optionally selected in order to form a desired
coating.
[0034] A plating solution (displacement reaction solution) to be
used in the displacement palladium plating process can be an
aqueous solution containing palladium sulfate, or the like. A
displacement palladium plated film is formed in such a manner that
palladium ions contained in the plating solution receive emitted
electrons produced by ionization of metal of the conductor 20. For
this reason, the plating solution does not have to contain a
reducing agent. However, the oxidation-reduction potential of
palladium in the plating solution needs to be higher than that of
the metal to be ionized from the conductor 20. The displacement
palladium plated film formed in such a displacement palladium
plating process is generated by displacement reaction in a portion
where the conductor 20 is exposed. For this reason, the
displacement palladium plated film can be uniformly deposited even
if the thickness is small. In the case where the inside layer 16 is
formed in a small thickness, therefore, it is preferable to form
the displacement palladium plated film by the displacement
palladium plating process.
[0035] A plating solution (reduction reaction solution) to be used
in the reduction palladium plating process can be an aqueous
solution containing diamminepalladium nitrite, or the like. The
phosphorus concentration of the inside layer 16 in the first layer
12 can be adjusted by varying a phosphorus concentration of the
plating solution used in formation of the first palladium plated
film. The reduction palladium plated film is formed in such a
manner that palladium ions in the plating solution receive
electrons emitted with oxidation reaction of a substance having the
reduction action in the plating solution, i.e., a reducing agent.
For this reason, the plating solution contains a reducing agent.
Since the plating solution used in the reduction palladium plating
process contains the reducing agent as described above, the
palladium plated film can be formed in a desired thickness,
independent of which kind of metal is contained in the conductor
20.
[0036] The reducing agent contained in the plating solution can be
selected, for example, from phosphorus compounds such as
hypophosphorous acid, phosphorous acid, and salts of these (e.g.,
sodium salt, potassium salt, and ammonium salt); carbon compounds
such as formalin, formic acid, and salts thereof; boron compounds
such as borofluorides and dimethylamine borane; and sulfur
compounds such as thiosulfuric acid, peroxysulfuric acid and salts
of these. The reducing agent may also be a multivalent metal ion,
e.g., bivalent tin ion, bivalent cobalt ion, or bivalent iron
ion.
[0037] The reduction palladium plated film obtained by the
reduction reaction is deposited on the conductor 20 by electrons
emitted from the reducing agent. For this reason, an element in the
reducing agent is codeposited in the reduction palladium plated
film. Therefore, the phosphorus concentration in the reduction
palladium plated film can be adjusted by varying a content of the
phosphorus-containing reducing agent in the plating solution.
[0038] In this manner, the inside layer 16 consisting of the
displacement palladium plated film or the reduction palladium
plated film can be formed on the conductor 20. Next, the second
palladium plating step is carried out in such a manner that the
outside layer 18 is formed on the inside layer 16 to obtain the
first layer 12.
[0039] The second palladium plating step is to perform a palladium
plating process on a surface of the inside layer 16 consisting of
the palladium plated film, to form the outside layer 18 consisting
of a palladium plated film on the inside layer 16. In the second
palladium plating step, the surface of the inside layer 16 is
subjected to the reduction palladium plating process which was
described in the first palladium plating step. The outside layer 18
can be formed by this process. A plating solution to be used herein
needs to be one with a higher phosphorus concentration than the
plating solution for the reduction palladium plating employed in
the first palladium plating step. The phosphorus concentration in
the plating solution can be adjusted by varying a content of the
phosphorus-containing reducing agent in the plating solution.
[0040] When phosphorus in the compound of the reducing agent is
codeposited in the palladium plated film obtained by reduction
reaction, as in this case, the corrosion resistance of the
palladium plated film can improve. When the palladium plated film
contains phosphorus without exceeding a codepositable limit
concentration, the corrosion resistance tends to improve with
increase in phosphorus concentration.
[0041] On the other hand, the coatability of the palladium plated
film over an object to be plated, tends to become lower than in the
case without codeposition of phosphorus. This tendency becomes
stronger with increase in phosphorus concentration within the range
where the phosphorus concentration in the palladium plated film
does not exceed the codepositable limit concentration. Therefore,
the first layer 12 and coating 10 with desired coatability and
corrosion resistance can be formed by performing two or more
palladium plating steps to form a plurality of palladium plated
films with different phosphorus concentrations.
[0042] The gold plating step is to perform an electroless gold
plating process such as a displacement gold plating process or a
reduction gold plating process, to form the second layer 14
consisting of a gold plated film on a surface of the first layer
12. The gold plated film can be formed by a well-known method using
a commercially available electroless gold plating solution.
[0043] The coating 10 can be produced on the conductor 20 by the
above-described manufacturing method. Since the
phosphorus-containing palladium plated film is normally unlikely to
be deposited on the conductor 20, it is difficult to form the
palladium plated film uniformly covering the surface of the
conductor 20. In this manufacturing method, however, the palladium
plated film with the lower phosphorus concentration is first formed
on the surface of the conductor 20 and then the palladium plated
film with the higher phosphorus concentration, which is hard to
directly deposit on the surface of the conductor 20, is deposited
thereon. Then the gold plated film is formed on such palladium
plated film, thereby forming the coating 10 with high corrosion
resistance, without increase in manufacturing cost. The signal
transmission part 100 with the conductor 20 coated with the coating
10 as described above has adequately excellent corrosion
resistance.
[0044] Next, the coating as another embodiment of the present
invention will be described.
[0045] FIG. 2 is a cross-sectional view schematically showing the
signal transmission part with the coating of the present
embodiment. The signal transmission part 200 in FIG. 2 constitutes
a signal transmission part of an electronic component and has a
conductor 20 and a coating 11 coating the conductor 20. The coating
11 of the present embodiment is a coating layer provided for
preventing corrosion of the conductor 20. The coating 11 has a
multilayer structure in which an underlying layer 30 containing
nickel as a main component, a first layer 12 containing palladium
as a main component, and a second layer 14 containing gold as a
main component are successively laid from the conductor 20 side.
Namely, the coating 11 of the present embodiment is different from
the coating 10 of the above embodiment in that it has the
underlying layer 30 between the conductor 20 and the first layer
12. The constituent elements other than the underlying layer 30 of
the coating 11 can be the same as those of the coating 10.
[0046] The underlying layer 30 is preferably a nickel plated film
formed by an electroless nickel plating process. When such
underlying layer 30 is provided, the thickness of the first layer
12 can be decreased while maintaining the adequately excellent
corrosion resistance. This can reduce an amount of palladium and
thus reduce the manufacturing cost of the coating 11. In terms of
sufficient reduction in manufacturing cost, the thickness of the
underlying layer 30 is preferably not less than 2 .mu.m. On the
other hand, in the case where the signal transmission part 200 has
a function of signal transmission by high-frequency radio waves,
the signal tends to be transmitted through the outermost layer of
the conductor 20. In that case, if the underlying layer 30
containing nickel as a main component with low electrical
conductivity is adjacent to the conductor 20, a loss tends to
increase. From this viewpoint, the thickness of the underlying
layer 30 is preferably not more than 10 .mu.m. The thickness of the
underlying layer 30 is preferably suitably adjusted according to
the thickness of the conductor 20 and the frequency of the
signal.
[0047] A manufacturing method of the coating 11 according to the
present embodiment will be described. The manufacturing method of
coating 11 has a nickel plating step of performing an electroless
nickel plating process on a surface of the conductor 20 to form a
nickel plated film serving as the underlying layer 30; a first
palladium plating step of performing a palladium plating process on
a surface of the underlying layer 30 to form the inside layer 16; a
second palladium plating step of performing a palladium plating
process on a surface of the inside layer 16 to form the outside
layer 18 on the inside layer 16; and a gold plating step of
performing a gold plating process on a surface of the outside layer
18 to form a gold plated film on the outside layer 18. The steps
except for the nickel plating step in this manufacturing method can
be carried out in the same manner as in the aforementioned
manufacturing method of coating 10. Therefore, the nickel plating
step will be described below.
[0048] In the nickel plating step, a pretreatment is first carried
out for the surface of the conductor 20. Specifically, the surface
is etched with a commercially available etching solution and
thereafter an activation treatment is carried out with a
commercially available activation treatment solution. After that,
the conductor 20 subjected to the pretreatment is immersed in an
electroless nickel plating solution to form an electroless nickel
plated film on the surface of the conductor 20. Thereafter, the
palladium plating processes and the gold plating process are
carried out in the same manner as in the manufacturing method of
coating 10, to form the first layer 12 and the second layer 14,
thereby manufacturing the coating 11.
[0049] The above described the preferred embodiments of the present
invention, but it should be noted that the present invention is by
no means limited to the above embodiments. For example, the above
embodiments showed the examples wherein the first layer 12 had the
multilayer structure in which the two types of palladium plated
films with different phosphorus concentrations were laid, but the
first layer 12 may be a layer in which the phosphorus concentration
continuously decreases with decreasing distance to the conductor
20. This can form the first layer 12 with excellent corrosion
resistance, while ensuring the good deposition characteristic of
palladium plating on the surface of the conductor 20. The first
layer 12 with the phosphorus concentration increasing toward the
second layer 14 in this manner can be formed, for example, by
gradually adding a phosphorus-containing component in the plating
solution during the plating process, so as to gradually increase
the phosphorus concentration in the plating solution.
[0050] Furthermore, at least one of the first region 31 (inside
layer 16) and the second region 32 (outside layer 18) in the first
layer 12 may be a region (layer) in which the phosphorus
concentration continuously decreases with decreasing distance to
the conductor 20.
EXAMPLES
[0051] The contents of the present invention will be described in
further detail with Examples and Comparative Examples. It is,
however, noted that the present invention is by no means intended
to be limited to the examples below.
[0052] [Production of Signal Transmission Parts]
Example 1
<Etching Step>
[0053] Commercially available copper foil (10 .mu.m thick) was
glued to a commercially available glass epoxy substrate
(length.times.width.times.thickness=30 mm.times.30 mm.times.0.5 mm)
with an adhesive to obtain a substrate with copper foil
(conductor). An etching solution (temperature: 30.degree. C.) with
the composition shown in Table 1 was prepared separately from the
substrate. The conductor was immersed in this etching solution for
one minute to etch the surface of the conductor. After the etching,
the conductor was washed with water.
TABLE-US-00001 TABLE 1 Component Content sodium persulfate 100 g/l
sulfuric acid (98 mass %) 30 ml/l water rest
[0054] <Displacement Palladium Plating Step>
[0055] Next, a displacement reaction solution (30.degree. C.)
having the composition shown in Table 2 was prepared. The conductor
having been subjected to the etching as described above was
immersed in an aqueous solution (30.degree. C.) obtained by
diluting 30 ml of sulfuric acid (98 mass %) with 1 l of water, for
thirty seconds. Thereafter, the conductor was immersed in the
displacement reaction solution of Table 2 for one minute to form a
palladium plated film (inside layer 16) on the surface of the
conductor by displacement reaction. Thereafter, the conductor with
the inside layer 16 thereon was washed with water.
TABLE-US-00002 TABLE 2 Component Content palladium sulfate 1 g/l
(based on Pd) sulfuric acid (98 mass %) 30 ml/l water rest
[0056] <Reduction Palladium Plating Step>
[0057] A reduction reaction solution (temperature: 55.degree. C.,
pH: 6.0) having the composition shown in Table 3 was prepared. The
conductor with the inside layer 16 thereon was immersed in the
reduction reaction solution of Table 3 for five minutes to form
another palladium plated film (outside layer 18) on the inside
layer 16 by reduction reaction. Thereafter, the conductor with the
outside layer 18 thereon was washed with water.
TABLE-US-00003 TABLE 3 Component Content diamminepalladium nitrite
1.5 g/l (based on Pd) disodium ethylenediaminetetraacetate 10 g/l
sodium hypophosphite 3 g/l sodium formate 10 g/l water rest
[0058] <Displacement Gold Plating Step>
[0059] A displacement reaction solution (temperature: 80.degree.
C., pH: 5.0) having the composition shown in Table 4 was prepared.
The conductor with the first layer 12 consisting of the inside
layer 16 and the outside layer 18 was immersed in the displacement
reaction solution of Table 4 for twenty minutes to form a gold
plated film (second layer 14) on the first layer 12 by displacement
reaction. Obtained in this manner was the conductor with the
coating in which the first layer 12 consisting of the inside layer
16 and the outside layer 18 containing palladium, and the second
layer 14 containing gold were laid. This was defined as a signal
transmission part of Example 1.
TABLE-US-00004 TABLE 4 Component Content gold potassium cyanide 2
g/l (based on Au) sodium cyanide 30 g/l sodium carbonate 20 g/l
water rest
Example 2
[0060] The conductor with the coating thereon was obtained in the
same manner as in Example 1, except that the duration of immersion
of the conductor in the reduction reaction solution of Table 3 was
changed from five minutes to ten minutes in the reduction palladium
plating step. This was defined as a signal transmission part of
Example 2.
Example 3
[0061] The conductor with the coating thereon was obtained in the
same manner as in Example 1, except that the duration of immersion
of the conductor in the reduction reaction solution of Table 3 was
changed from five minutes to twenty minutes in the reduction
palladium plating step. This was defined as a signal transmission
part of Example 3.
Example 4
[0062] The conductor with the coating thereon was obtained in the
same manner as in Example 1, except that a reduction reaction
solution (temperature: 60.degree. C., pH: 7.5) having the
composition shown in Table 5 was used instead of the reduction
reaction solution of Table 3 in the reduction palladium plating
step. This was defined as a signal transmission part of Example
4.
TABLE-US-00005 TABLE 5 Component Content diamminepalladium nitrite
1.5 g/l (based on Pd) disodium ethylenediaminetetraacetate 10 g/l
sodium hypophosphite 10 g/l water rest
Example 5
[0063] The conductor with the coating thereon was obtained in the
same manner as in Example 4, except that the duration of immersion
of the conductor in the reduction reaction solution of Table 5 was
changed from five minutes to ten minutes in the reduction palladium
plating step. This was defined as a signal transmission part of
Example 5.
Example 6
[0064] The conductor with the coating thereon was obtained in the
same manner as in Example 1, except that a reduction reaction
solution (temperature: 60.degree. C., pH: 7.0) having the
composition shown in Table 6 was used instead of the reduction
reaction solution of Table 3 and the duration of immersion of the
conductor in the reduction reaction solution was changed from five
minutes to ten minutes, in the reduction palladium plating step.
This was defined as a signal transmission part of Example 6.
TABLE-US-00006 TABLE 6 Component Content diamminepalladium nitrite
1 g/l (based on Pd) disodium ethylenediaminetetraacetate 10 g/l
sodium hypophosphite 15 g/l water rest
Example 7
[0065] The conductor with the coating thereon was obtained in the
same manner as in Example 1, except that a reduction reaction
solution (temperature: 60.degree. C., pH: 7.0) having the
composition shown in Table 7 was used instead of the reduction
reaction solution of Table 3 and the duration of immersion of the
conductor in the reduction reaction solution was changed from five
minutes to fifteen minutes, in the reduction palladium plating
step. This was defined as a signal transmission part of Example
7.
TABLE-US-00007 TABLE 7 Component Content diamminepalladium nitrite
0.8 g/l (based on Pd) diethyl cyanophosphonate 20 g/l sodium
hydrogen phosphite 15 g/l water rest
Example 8
[0066] The conductor with the coating thereon was obtained in the
same mariner as in Example 1, except that a reduction reaction
solution (temperature: 80.degree. C., pH: 8.0) having the
composition shown in Table 8 was used instead of the reduction
reaction solution of Table 3 and the duration of immersion of the
conductor in the reduction reaction solution was changed from five
minutes to twenty minutes, in the reduction palladium plating step.
This was defined as a signal transmission part of Example 8.
TABLE-US-00008 TABLE 8 Component Content diamminepalladium nitrite
0.5 g/l (based on Pd) ammonium phosphate 20 g/l ammonium nitrate 5
g/l sodium hydrogen phosphite 15 g/l water rest
Example 9
[0067] <Etching Step and Reduction Palladium Plating
Step>
[0068] The conductor having been subjected to etching was obtained
in the same manner as in Example 1. A reduction reaction solution
(temperature: 55.degree. C., pH: 6.0) having the composition shown
in Table 9 was prepared. The conductor was immersed in the
reduction reaction solution of Table 9 for one minute to form a
palladium plated film (inside layer 16) on the conductor by
reduction reaction. After that, the conductor with the inside layer
16 thereon was washed with water.
TABLE-US-00009 TABLE 9 Component Content diamminepalladium nitrite
1.5 g/l (based on Pd) disodium ethylenediaminetetraacetate 10 g/l
sodium hypophosphite 1 g/l sodium formate 10 g/l water rest
[0069] The conductor with the inside layer 16 thereon was immersed
in the reduction reaction solution of Table 6 for ten minutes to
form another palladium plated film (outside layer 18) on the inside
layer 16 by reduction reaction. Thereafter, the conductor with the
outside layer 18 thereon was washed with water.
[0070] <Displacement Gold Plating Step>
[0071] The displacement gold plating step was carried out in the
same manner as in Example 1 to obtain the conductor with the
coating in which the first layer 12 consisting of the inside layer
16 and the outside layer 18 containing palladium, and the second
layer 14 containing gold were laid. This was defined as a signal
transmission part of Example 9.
Example 10
<Etching Step and Reduction Palladium Plating Step>
[0072] The conductor having been subjected to etching was obtained
in the same manner as in Example 1. The conductor was immersed in
the reduction reaction solution of Table 9 for one minute to form a
palladium plated film (inside layer 16) on the conductor by
reduction reaction. In a state in which the conductor was immersed
in the reduction reaction solution of Table 9, a sodium hydrogen
phosphite aqueous solution (concentration: 30 mass %) was dropped
into the reduction reaction solution for seven minutes. This
continuously increased the sodium hydrogen phosphite concentration
in the reduction reaction solution from 0 to 14 g/l. After
completion of dropping of the sodium hydrogen phosphite aqueous
solution, the conductor was kept immersed in the reduction reaction
solution for two more minutes. By this process, another palladium
plated film (outside layer 18) was formed on the inside layer 16.
Thereafter, the conductor with the outside layer 18 thereon was
washed with water.
[0073] <Displacement Gold Plating Step>
[0074] The displacement gold plating step was carried out in the
same manner as in Example 1 to obtain the conductor with the
coating in which the first layer 12 consisting of the inside layer
16 and the outside layer 18 containing palladium, and the second
layer 14 containing gold were laid. This was defined as a signal
transmission part of Example 10.
Example 11
<Etching Step and Activation Step>
[0075] The conductor having been subjected to etching was obtained
in the same manner as in Example 1. This conductor was immersed in
a commercially available activating agent (trade name: AT-450
available from C. Uyemura & Co., Ltd., temperature: 30.degree.
C.) for one minute to perform an activation treatment. Thereafter,
the conductor was washed with water.
[0076] <Nickel Plating Step>
[0077] A reduction reaction solution (temperature: 45.degree. C.,
pH: 4.5) having the composition shown in Table 10 was prepared. The
conductor having been subjected to the activation treatment was
immersed in the reduction reaction solution of Table 10 for thirty
minutes to form a nickel plated film (underlying layer 30) on the
conductor by reduction reaction. After that, the conductor with the
underlying layer 30 thereon was washed with water.
TABLE-US-00010 TABLE 10 Component Content nickel sulfate 20 g/l
sodium hypophosphite 15 g/l sodium citrate 30 g/l ammonium chloride
30 g/l water rest
[0078] <Reduction Palladium Plating Step>
[0079] A reduction reaction solution (temperature: 60.degree. C.,
pH: 5.5) having the composition shown in Table 11 was prepared. The
conductor with the underlying layer 30 thereon was immersed in the
reduction reaction solution of Table 11 for one minute to form a
palladium plated film (inside layer 16) on the underlying layer 30
by reduction reaction. Thereafter, the conductor with the inside
layer 16 thereon was washed with water.
TABLE-US-00011 TABLE 11 Component Content diamminepalladium nitrite
1.5 g/l (based on Pd) disodium ethylenediaminetetraacetate 10 g/l
sodium formate 10 g/l water rest
[0080] The conductor with the inside layer 16 thereon was immersed
in the reduction reaction solution of Table 5 for five minutes to
form another palladium plated film (outside layer 18) on the inside
layer 16 by reduction reaction. Thereafter, the conductor with the
outside layer 18 thereon was washed with water.
[0081] <Displacement Gold Plating Step>
[0082] The displacement gold plating step was carried out in the
same manner as in Example 1, to obtain the conductor with the
coating in which the underlying layer 30 containing nickel, the
first layer 12 consisting of the inside layer 16 and the outside
layer 18 containing palladium, and the second layer 14 containing
gold were laid from the copper foil side. This was defined as a
signal transmission part of Example 11.
Example 12
[0083] The conductor with the coating in which the underlying layer
30 containing nickel, the first layer 12 consisting of the inside
layer 16 and the outside layer 18 containing palladium, and the
second layer 14 containing gold were laid from the copper foil side
was obtained in the same manner as in Example 11, except that the
conductor with the inside layer 16 thereon was immersed in the
reduction reaction solution of Table 8 instead of the reduction
reaction solution of Table 5 for twenty minutes in the reduction
palladium plating step. This was defined as a signal transmission
part of Example 12.
Comparative Example 1
[0084] The etching step and the activation step were carried out in
the same manner as in Example 11. Then the nickel plating step was
carried out to immerse the conductor in the reduction reaction
solution shown in Table 10, for forty minutes to form a nickel
plated film (underlying layer 30) on the conductor by reduction
reaction. In this manner, the conductor with the coating consisting
of the underlying layer 30 containing nickel was obtained. This was
defined as a signal transmission part of Comparative Example 1.
Comparative Example 2
[0085] A nickel plated film (underlying layer 30) was formed on the
conductor in the same manner as in Comparative Example 1.
Thereafter, the conductor with the underlying layer 30 thereon was
washed with water and the displacement gold plating step as in
Example 1 was carried out to form a gold plated film (second layer
14) on the underlying layer 30. Obtained in this manner was the
conductor with the coating in which the underlying layer 30
containing nickel and the second layer 14 containing gold were
laid. This was defined as a signal transmission part of Comparative
Example 2.
Comparative Example 3
[0086] The conductor with the coating in which the underlying layer
30 consisting of a nickel plated film and the layer consisting of a
gold plated film were laid was obtained in the same manner as in
Comparative Example 2. A reduction reaction solution (temperature:
90.degree. C., pH: 7.5) having the composition shown in Table 12
was prepared. The conductor with the underlying layer 30 and the
second layer thereon was immersed in the reduction reaction
solution of Table 12 for ten minutes to form another layer of a
gold plated film by reduction reaction. Obtained in this manner was
the conductor with the coating in which the underlying layer 30
containing nickel and the second layer consisting of two layers
containing gold were successively laid from the copper foil side.
This was defined as a signal transmission part of Comparative
Example 3.
TABLE-US-00012 TABLE 12 Component Content gold potassium cyanide 2
g/l (based on Au) sodium hypophosphite 10 g/l sodium citrate 50 g/l
ammonium chloride 75 g/l water rest
Comparative Example 4
[0087] The conductor with the coating in which the underlying layer
30 containing nickel and the second layer consisting of the two
layers containing gold were successively laid was obtained in the
same manner as in Comparative Example 3, except that the duration
of immersion in the reduction reaction solution of Table 12 was
changed from ten minutes to twenty minutes. This was defined as a
signal transmission part of Comparative Example 4.
Comparative Example 5
[0088] The conductor having been subjected to etching was obtained
in the same manner as in Example 1. The conductor was immersed in
the reduction reaction solution of Table 9 for ten minutes to form
a palladium plated film (inside layer 16) on the conductor by
reduction reaction. Thereafter, the conductor with the inside layer
16 thereon was washed with water.
[0089] The displacement gold plating step was carried out in the
same manner as in Example 1, to obtain the conductor with the
coating in which the first layer consisting of the inside layer 16
containing palladium and the second layer 14 containing gold were
laid. This was defined as a signal transmission part of Comparative
Example 5.
Comparative Example 6
[0090] The conductor having been subjected to etching was obtained
in the same manner as in Example 1. The conductor was immersed in
the reduction reaction solution of Table 3 for five minutes. After
the immersion, the conductor was taken out of the reduction
reaction solution and the surface of the conductor was observed. It
was observed that palladium was plated in a macular pattern on the
surface of the conductor. In this manner, the copper foil was
exposed in the surface of the conductor, resulting in a failure in
forming a palladium-containing layer.
Comparative Example 7
[0091] The conductor having been subjected to etching was obtained
in the same manner as in Example 1. The conductor was immersed in
the reduction reaction solution of Table 5 for five minutes. After
the immersion, the conductor was taken out of the reduction
reaction solution and the surface of the conductor was observed. It
was observed that palladium was plated in a macular pattern on the
surface of the conductor. In this manner, the copper foil was
exposed in the surface of the conductor, resulting in a failure in
forming a palladium-containing layer.
Comparative Example 8
[0092] The conductor having been subjected to etching was obtained
in the same manner as in Example 1. The conductor was immersed in
the reduction reaction solution of Table 6 for ten minutes. After
the immersion, the conductor was taken out of the reduction
reaction solution and the surface of the conductor was observed. It
was observed that palladium was plated in a macular pattern on the
surface of the conductor. In this manner, the copper foil was
exposed in the surface of the conductor, resulting in a failure in
forming a palladium-containing layer.
Comparative Example 9
[0093] The conductor having been subjected to etching was obtained
in the same manner as in Example 1. The conductor was immersed in
the reduction reaction solution of Table 7 for fifteen minutes.
After the immersion, the conductor was taken out of the reduction
reaction solution and the surface of the conductor was observed. It
was observed that palladium was plated in a macular pattern on the
surface of the conductor. In this manner, the copper foil was
exposed in the surface of the conductor, resulting in a failure in
forming a palladium-containing layer.
[0094] [Evaluation of Signal Transmission Parts]
[0095] The signal transmission part in each of the examples and
comparative examples was cut along the lamination direction of the
first layer 12 and the second layer 14 and a cut surface was
observed with a transmission electron microscope (TEM) to obtain
the respective thicknesses of the first layer 12 and the second
layer 14. In the same cut surface, analysis was conducted by energy
dispersive X-ray spectrometry (EDS) to measure the phosphorus
concentrations of the inside layer 16 and the outside layer 18 in
the first layer. The results of these are provided together in
Table 13.
[0096] In accordance with HS C 5402-11-14, a single gas flow
corrosion test was conducted in the following procedure to evaluate
the corrosion resistance of the signal transmission part in each of
the examples and comparative examples. First, the resultant signal
transmission part was exposed to a contamination gas atmosphere
(temperature: 30.degree. C., relative humidity: 75%) containing 10
ppm of SO.sub.2 gas in volume term. A duration of the exposure was
four days. A surface of the coating after the exposure was observed
with an optical microscope (magnification: 50.times.) and the
number of pits detected in the field (length.times.width=6.0
mm.times.4.5 mm) was counted. The results are provided as the
evaluation results of anticorrosion in Table 13.
TABLE-US-00013 TABLE 13 1st layer 2nd layer Underlayer Evaluation P
content (mass %) T T T Pr/Ab of anticorrosion coating inside 16
outside 18 .mu.m .mu.m .mu.m 1st layer (pit count) cost Example 1
0% 0.05% 0.1 0.05 Ab Pr 7 A Example 2 0% 0.05% 0.2 0.05 Ab Pr 3 A
Example 3 0% 0.05% 0.4 0.05 Ab Pr 0 B Example 4 0% 1% 0.1 0.05 Ab
Pr 1 A Example 5 0% 1% 0.2 0.05 Ab Pr 0 A Example 6 0% 3% 0.1 0.05
Ab Pr 0 A Example 7 0% 5% 0.1 0.05 Ab Pr 0 A Example 8 0% 7% 0.1
0,05 Ab Pr 3 A Example 9 0.01% 3% 0.1 0.05 Ab Pr 0 A Example 10
0.01% 2% 0.1 0.05 Ab Pr 0 A Example 11 0% 1% 0.1 0.05 4 Pr 0 A
Example 12 0% 7% 0.1 0.05 4 Pr 0 A Comp Ex 1 -- -- Ab Ab 5 Ab
totally A corroded Comp Ex 2 -- -- Ab 0.05 5 Ab 188 A Comp Ex 3 --
-- Ab 0.30 5 Ab 41 B Comp Ex 4 -- -- Ab 0.50 5 Ab 2 C Comp Ex 5
0.01% 0.01% 0.1 0.05 Ab Pr 36 A Comp Ex 6 -- -- Ab -- Ab Ab -- --
Comp Ex 7 -- -- Ab -- Ab Ab -- -- Comp Ex 8 -- -- Ab -- Ab Ab -- --
Comp Ex 9 -- -- Ab -- Ab Ab -- -- Pr: present Ab: absent T:
thickness
[0097] The phosphorus concentration of the outside layer 18 in the
first layer in the signal transmission part of Example 10
continuously increased from the conductor 20 side toward the second
layer 14 side. The phosphorus concentration of the outside layer 18
in Example 10 shown in Table 13 is the phosphorus concentration of
the outside layer 18 on the second layer 14 side.
[0098] In Table 13, the coating cost was evaluated based on the
following criteria: "A" for the coating in which the thickness of
the first layer (palladium plated film) is not more than 0.2 .mu.m
and the thickness of the second layer (gold plated film) is not
more than 0.1 .mu.m; "B" for the coating in which the thickness of
the first layer is over 0.2 .mu.m and not more than 0.6 .mu.m and
the thickness of the second layer is over 0.1 .mu.m and not more
than 0.4 .mu.m; "C" for the coating in which the thickness of the
second layer is over 0.4 .mu.m.
[0099] The coatings in Examples 1 to 12 had the relatively small
thickness because the thickness of the first layer was 0.1-0.4
.mu.m and the thickness of the second layer 0.05 .mu.m. It was
confirmed that the coatings in Examples 1 to 12 had adequately
excellent corrosion resistance while they had the relatively small
thickness as described above.
[0100] The present invention provides the coating that can be
formed at low cost and with adequately excellent corrosion
resistance. It is also feasible to provide an electronic component
having the signal transmission part at low manufacturing cost and
with adequately excellent corrosion resistance, by provision of the
coating.
* * * * *