JP7079436B1 - Plating method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a plating method capable of forming a high-quality plating film having an extremely thin and uniform film thickness and suppressing the occurrence of pinholes and discoloration.
SOLUTION. The present invention comprises a step of preparing a plated body 10 in which a first metal surface 11 made of a first metal and a second metal surface 12 made of a second metal are electrically conductive (continuously), and the plated body 10. The step of applying a voltage to the object to be plated 10 and the portion 16 to be plated of the object to be plated 10 are immersed in the plating solution 14 before being immersed in the plating solution 14, and the metal for coating, which is nobler than the first metal, is used. It has a step of coating at least a part of the plating target portion 16.
[Selection diagram] Fig. 1

Description

The present invention relates to a method for plating a metal surface.

Conventionally, as one of the means for forming a metal film on a metal surface, film formation by (wet) plating treatment is often used. In the wet plating process, an electroplating method is known as a method of forming a metal film by cathode reduction of metal ions in an aqueous solution using an external DC power source. On the other hand, there is an electroless plating method as a method of forming a metal film on a base material without using an external DC power supply, and a substitution type and an autocatalytic type are known. The substituted electrolytic plating method is a method of forming a metal film by reducing metal ions in an aqueous solution with electrons generated by elution of metal on the surface of the base material and precipitating them on the surface of the base material. In the self-catalyzed electroless plating method, the reducing agent added to the aqueous solution is oxidized on the surface of the substrate, and the electrons released at that time reduce the metal ions in the aqueous solution and deposit them on the surface of the substrate. It is a method of forming a metal film with.

There are various uses for the metal film formed by the plating process, and one of them is anti-corrosion and anti-corrosion applications. A method of forming a metal alloy at a metal contact portion is known (see, for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 2006-46619

However, the film formation by the electroplating method is difficult to form thin (for example, 3 μm or less) in the first place, and generally has a problem that pinholes increase. The pinhole can be filled by increasing the film thickness, but for example, when another film (metal film, resin film) or the like is to be laminated on the metal film (plating film). When it is desired to form a plating film only on a part of a part, it is not desirable to make the plating film thicker than necessary only for the purpose of burying pinholes.

Further, the electroless plating method can reduce the film thickness as compared with the electroplating method. However, when the object to be plated, which is in contact with dissimilar metals, is plated by a conventionally known electroless plating method, discoloration of the formed plating film and oxidation (burning) are likely to occur, and the quality (not an oxide) is high. ) It was difficult to deposit the metal for coating. For example, when another film is laminated on a plating film as a base, the adhesion may be deteriorated if the plating film is not formed in good quality such as discoloration. Was desired.

As described above, it has been very difficult or almost impossible to form a good plating film satisfying these demands by the conventional technique.

In view of such circumstances, the present invention is intended to provide a plating method capable of forming a high-quality plating film having an extremely thin and uniform film thickness and significantly suppressing the occurrence of pinholes and discoloration.

In the present invention, both the surface made of the first metal (hereinafter referred to as "the surface of the first metal") and the surface made of the second metal (hereinafter referred to as the "second metal surface") are exposed and electrically. By applying a voltage to the first metal via the second metal before immersing the metal to be plated in the step of preparing the body to be plated and immersing the metal to be plated. The step of setting the potential of the first metal surface to a predetermined potential range by canceling at least a part of the potential generation on the surface of the first metal due to the contact potential difference between the second metal and the second metal, and the voltage. The present invention comprises a step of immersing at least a portion to be plated on the surface of the first metal in an applied state in the plating solution and coating the portion to be plated with a coating metal nobler than the first metal. The potential range of the above is the potential range in which the first metal is ionized and the surface of the first metal is replaced with the coating metal .
Further, in the present invention, both the surface made of the first metal (hereinafter referred to as "first metal surface") and the surface made of the second metal (hereinafter referred to as "second metal surface") are exposed. The first step is to prepare an electrically conductive object to be plated, and by applying a voltage to the first metal via the second metal before immersing the object to be plated in the plating solution. The step of canceling at least a part of the potential generation on the surface of the first metal due to the contact potential difference between the metal and the second metal, and at least the portion to be plated on the surface of the first metal with the voltage applied. It has a step of immersing in the plating solution to form a replacement plating film at least at the site to be plated, and the replacement plating film has the first metal ionized and the surface of the first metal is the first metal. It relates to a plating method characterized by being a plating film replaced with a more noble coating metal.
Further, in the present invention, both the surface made of the first metal (hereinafter referred to as "first metal surface") and the surface made of the second metal (hereinafter referred to as "second metal surface") are exposed. The first step is to prepare an electrically conductive object to be plated, and by applying a voltage to the first metal via the second metal before immersing the object to be plated in the plating solution. The step of setting the potential of the first metal surface to a predetermined potential range by canceling at least a part of the potential generation on the surface of the first metal due to the contact potential difference between the one metal and the second metal, and the above. It has a step of immersing at least a portion to be plated on the surface of the first metal in a state of applying a voltage in the plating solution and coating the portion to be plated with a coating metal nobler than the first metal. The predetermined potential range is the potential range in which the potential of the surface of the first metal in the object to be plated overlaps the corrosion region of the first metal in the potential-pH diagram and the insensitive region of the coating metal. It relates to a plating method characterized by being present.
Further, in the present invention, both the surface made of the first metal (hereinafter referred to as "first metal surface") and the surface made of the second metal (hereinafter referred to as "second metal surface") are exposed. The first step is to prepare an electrically conductive object to be plated, and by applying a voltage to the first metal via the second metal before immersing the object to be plated in the plating solution. The step of canceling at least a part of the potential generation on the surface of the first metal due to the contact potential difference between the metal and the second metal, and at least the portion to be plated on the surface of the first metal with the voltage applied. It has a step of immersing in the plating solution and coating the plating target portion with a coating metal nobler than the first metal, the first metal being a relatively base metal, and the second metal. When the metal is a relatively noble metal, the contact potential difference is ΔV, the work function of the first metal is WF1, the work function of the second metal is WF2, and the electric element amount is e, the contact potential difference is The potential of satisfying the following formula (1) "ΔV =-(WF1-WF2) / e ... (1)" to ionize the first metal and replace the surface of the first metal with the coating metal. The range (hereinafter referred to as "substitutable potential range") is VR, the equilibrium electrode potential of the first metal (activity is 1E-6) is V1, and the equilibrium electrode potential of the coating metal (activity is 1). When V2 is used, the replaceable potential range satisfies the following equation (2) "V2 ≥ VR ≥ V1 ... (2)", and when the voltage is CP, the voltage is the following equation (3). The present invention relates to a plating method characterized by satisfying “V2-ΔV ≧ CP ≧ V1-ΔV ・ ・ ・ (3)”.

In view of such circumstances, the present invention can provide a plating method capable of forming a high-quality plating film having an extremely thin and uniform film thickness and suppressing the occurrence of pinholes and discoloration.

It is a flow chart which shows an example of the process flow of the plating method of this embodiment. (A) external view, (B) external view, and (C) to (G) are schematic cross-sectional views showing an example of the object to be plated of this embodiment. It is a schematic diagram which shows an example of the plating method of this embodiment in time series. It is a conceptual diagram explaining the contact potential difference of a dissimilar metal junction. It is a phase diagram which shows the relationship of the reaction of zinc and copper. It is a conceptual diagram explaining the contact potential difference of a dissimilar metal junction. It is a figure which compares the state of plating by the conventional plating method, and the state of plating by the plating method of this embodiment. It is a figure which compares the state of plating by the conventional plating method, and the state of plating by the plating method of this embodiment. It is a schematic diagram which shows the current path of this embodiment.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following description, the parts with the same reference numerals represent the same configuration.

FIG. 1 is a flow chart showing an example of the processing flow of the plating method of the present embodiment. Further, FIG. 2 is a schematic view showing an example of the object to be plated 10 of the present embodiment, and FIGS. (A) and 2 (B) are external views showing an outline of the object to be plated 10. (C) to FIG. (G) are schematic views of a cross section of the object to be plated 10. Further, FIG. 3 is a schematic view showing an example of the plating method of the present embodiment in chronological order. In this drawing and each of the following drawings, some configurations will be omitted as appropriate to simplify the drawings. Then, in this figure and each subsequent figure, the size, shape, thickness, etc. of the member are appropriately exaggerated and expressed.

With reference to FIG. 1, the plating method of the present embodiment is referred to as a surface made of a first metal (hereinafter referred to as “first metal surface”) and a surface made of a second metal (hereinafter referred to as “second metal surface”). A step of preparing an object to be plated (step S01) in which (.) Is electrically conductive (continuous), and a step of applying a voltage to the object to be plated (step S05) before immersing the object to be plated in the plating solution. ), And a step (step S07) of immersing at least the plating target portion on the surface of the first metal in a plating solution and coating the plating target portion with a coating metal nobler than the first metal.

The plated body 10 of the present embodiment will be described with reference to FIG. 2A and 2B are schematic views showing the object to be plated 10. FIG. 2A is an external view of the object to be plated 10 before the plating treatment, and FIG. 2B is an external view of the body 10 to be plated after the plating treatment. be. FIG. 3C is a sectional view taken along line XX of FIG. B, and FIGS. D to G correspond to FIG. C of the object to be plated 10 before plating. It is a cross-sectional view.

In the plating method of the present embodiment, the plating target portion 16 of the object to be plated 10 is subjected to a plating treatment as shown in FIG. 16 is covered with a thin film (plating film) 13 made of a coating metal.

With reference to FIG. 2A, the object to be plated 10 of the present embodiment is a structure in which the first metal surface 11 and the second metal surface 12 are electrically conductive (continuously). As shown in FIGS. (C) and (G), the first metal surface 11 may be the surface of the first metal material 11M as a base material, and FIGS. As shown in F), it may be the surface of the first metal material 11M provided so as to cover any base material (structure) BD, BD1. Similarly, the second metal surface 12 may be the surface of the second metal material 12M as a base material, as shown in FIGS. (C), (F), and (G). As shown in FIGS. (D) and (E), the surface may be the surface of the second metal material 12M provided so as to cover any base material (structure) BD, BD2.

Any base material BD, BD1, BD2 may be a non-conductive material or a conductive material. Further, as shown in FIG. 3D, when the first metal material 11M and the second metal material 12M are provided so as to cover one arbitrary base material BD, the arbitrary base material BD is a single material. It may be composed of, or may be composed of joining, adhering, laminating, etc. of a plurality of materials (may be a composite material). Further, as shown in FIG. 3E, for example, the object to be plated 10 is covered with an arbitrary base material (first base material BD1) covered with the first metal material 11M and the second metal material 12M. Another arbitrary base material (second base material BD2) may be continuously provided (for example, by joining), or as shown in FIG. 3 (F), the first metal. An arbitrary base material (first base material BD1) covered with the material 11M and a second metal material 12M (second base material BD2) are continuously provided (for example, by joining). Alternatively, the first base material BD1 and the second base material BD2 may have the opposite configurations thereof.

Further, "the first metal surface 11 and the second metal surface 12 are electrically conductive (continuously)" means that the first metal surface 11 and the second metal surface 12 are joined, for example (atomic joining). , Directly and electrically conducting (continuous) by joining (joining due to melting, etc.), and electrically conducting (continuous) by directly contacting the first metal surface 11 and the second metal surface 12. Either the first metal surface 11 and the second metal surface 12 are electrically conductive (continuous) by being continuous via a conductive member such as another metal. It may be present, and the present invention is not limited to this example, and any configuration may be used as long as it can be energized between the first metal surface 11 and the second metal surface 12. That is, as shown in FIG. 6 (G), the first metal surface 11 (first metal material 11M) and the second metal surface 12 (second metal material 12M) are electrically connected via another metal material m. It may be a conductive (continuous) configuration.

Further, in this example, a case where the plated body 10 is a strip-shaped structure long in one direction (long in the left-right direction shown in FIG. 2) will be described, but the shape of the plated body 10 is not limited to this example. As will be described in detail later, at least a part (plating target portion 16) of the object to be plated 10 is immersed in a plating solution. That is, the object to be plated 10 is not limited to the illustrated example as long as it has a shape in which a part thereof is held by a jig or the like and at least the plating target portion 16 can be immersed in the plating solution.

Further, here, as an example, as shown in FIGS. 2B and 2C, the plating target portion 16 is a part of the object to be plated 10, specifically, the first metal surface 11 (substantially the entire surface). Suppose that That is, substantially the entire outer surface of the first metal material 11M is covered with the plating film 13. However, not limited to this example, the plating target portion 16 may be a part of the first metal surface 11 or a portion continuous with the entire first metal surface 11 and a part of the second metal surface 12. You may.

The first metal and the second metal are metals having different ionization tendencies, and specifically, the second metal is a metal that is relatively noble (smaller ionization tendency) than the first metal. Here, as an example, the first metal is a metal containing zinc (Zn) as a main component, and the second metal is a metal containing copper (Cu) as a main component.

Here, the "metal containing zinc as a main component" means a metal containing 50% or more of pure zinc or a zinc alloy, and when it contains other components different from pure zinc or a zinc alloy, other components. The type and number of are arbitrary. Further, it may be a metal having a content of pure zinc or a zinc alloy of 100% (or substantially 100%). Hereinafter, in the present specification, the first metal may be simply referred to as "zinc (Zn)", which means "a metal containing zinc as a main component".

The "metal containing copper as a main component" means a metal containing 50% or more of pure copper or a copper alloy, and when it contains other components different from pure copper or a copper alloy, the type and number of other components. Is optional. Further, it may be a metal having a content of pure copper or a copper alloy of 100% (or substantially 100%). Hereinafter, in the present specification, the second metal may be simply referred to as "copper (Cu)", which means "a metal containing copper as a main component".

Further, as an example, the second metal and the coating metal are the same type of metal. That is, in the plating method of the present embodiment, as an example, in the object to be plated 10 in which the first metal surface 11 and the second metal surface 12 having different ionization tendencies are electrically continuous, they are relatively low-key (the ionization tendency is large). It can be said that the method is to replace the first metal surface 11 with a relatively noble coating metal and cover the first metal material 11 with the coating metal, and preferably, the first metal material 11M is covered with the second metal surface. It is a method of covering with the same kind of coating metal as No. 12.

As described above, in the present embodiment, for example, the substitution reaction (oxidation-reduction reaction) between the first metal on the first metal surface 11 and the coating metal proceeds. That is, the "surface" of the first metal surface 11 and the second metal surface 12 is a portion exposed to the outside, and in the case of the first metal surface 11, the substitution reaction with the metal ion of the coating metal can proceed. The term "part of the first metal surface 11 (second metal surface 12)" means a part of the surface direction (visible) rather than the thickness direction.

Hereinafter, each step of the plating method of the present embodiment will be described in detail with reference to FIGS. 1 and 3. First, the above-mentioned object to be plated 10 is prepared (step S01 in FIG. 1, FIG. 2 (A), FIG. 3 (A)). Also, prepare the counter electrode 15. Here, as an example, the counter electrode 15 is an electrode of a metal of the same type as the coating metal, specifically, a copper (Cu) electrode (mainly composed of copper), and is immersed in a predetermined plating solution 14. Further, a predetermined voltage is applied to the counter electrode 15 (connected to one electrode (for example, a positive electrode) of the power source E). The plating solution 14 is, for example, a solution containing metal ions (Cu ²⁺ ) of a coating metal. Specifically, for example, it is a solution of a strong acid (for example, pH = about 0.5) containing copper sulfate (Cu SO ₄ ) and sulfuric acid (H ₂ SO ₄ ) (FIG. 3 (B)).

Next, a predetermined voltage is applied to the object to be plated 10 before the object to be plated 10 is immersed in the plating solution 14 (without being immersed in the plating solution 14) (steps S05 in FIG. 1 and FIG. 3 (C). )).

By applying this voltage, a predetermined amount of electric charge is applied to the object to be plated 10. With reference to FIG. 3A, in the object to be plated 10, the first metal surface 11 and the second metal surface 12 are electrically conductive (continuously), and a contact potential difference ΔV is generated between the two. One is positively or negatively charged with respect to the other. Hereinafter, as an example, when the potential of the second metal surface 12 (copper) (potential of the earth reference, the same applies hereinafter) is specifically described, the first metal surface 11 which is the plating target portion 16 of the object to be plated 10 comes into contact with each other. Due to the potential difference ΔV, the second metal surface 12 is positively charged (potential is + V).

In this step, by applying a predetermined voltage, at least a part of the potential generated on the first metal surface 11 due to the contact potential difference ΔV of the first metal surface 11 with respect to the second metal surface 12 is canceled in advance. In other words, this voltage is a voltage at which the potential of the object to be plated 10, more specifically, the first metal surface 11 can be set within a certain range. The applied voltage and the potential of the first metal surface 11 set by the applied voltage will be described in detail later. Specifically, as shown in FIG. 3C, the object to be plated 10 is the other of the power source E. Connect to a pole (eg, negative electrode) (apply a negative voltage).

After that, as shown in FIG. 3D, the plating target portion 16 (here, the entire surface of the first metal surface 11) is immersed in the plating solution 14 in a state where a negative voltage is applied to the object to be plated 10 (FIG. Step S07 of 1, FIG. 3 (D). As a result, the first metal surface 11 (zinc) is replaced with copper ions (Cu ²⁺ ) in the plating solution 14, and copper is reduced and deposited on the surface of the plating target portion 16. Here, as an example, the application of a negative voltage to the object to be plated 10 is continued until substantially the entire plating target portion 16 is immersed in the plating solution 14. As a result, the entire surface of the first metal surface 11 is replaced with the coating metal (copper), and the plating target portion 16 is covered with the plating film 13.

As described above, in the present embodiment, the plated body is previously plated so as to cancel at least a part of the potential generated on the first metal surface 11 due to the contact potential difference ΔV of the first metal surface 11 with respect to the second metal surface 12. By immersing the object to be plated 10 in the plating solution 14 after applying a voltage to 10, the plating film 13 can be formed by an oxidation-reduction reaction (replacement plating). The thickness of the plating film 13 can be significantly reduced as compared with the plating film formed by the conventional electroplating method, and the generation of pinholes can be suppressed.

If the voltage applied to the object to be plated 10 is continuously applied even after the first metal surface 11 (zinc) of the plating target portion 16 is replaced with (all) the metal for coating (copper), it is continuously applied. (Automatically) shift to electroplating. Therefore, the voltage is continuously applied to the object to be plated 10 until substantially the entire surface of the first metal surface 11 is immersed in the plating solution 14, and after the substantially entire surface of the first metal surface 11 is replaced with the metal for coating. The plating film 13 is formed into a desired film thickness by an electroplating method, and the plating process is completed (FIG. 3 (E)).

Since a high-quality plating film 13 by replacement plating is formed on the lower layer, the plating film 13 by the continuous electroplating method can be formed to an arbitrary thickness. Therefore, the film thickness of the plating film 13 of the present embodiment can be formed to be, for example, 3 μm or less, specifically, about 100 nm to 3 μm, preferably about 300 nm to 2 μm, and more preferably about 500 nm to 1.5 μm. Further, since the lowermost layer of the plating film 13 is a film formed by replacement plating, the generation of pinholes can be suppressed even if the total film thickness is, for example, about 500 nm.

<Replaceable potential range and applied voltage>
In the plating method of the present embodiment, in the object to be plated 10 in which different metals are electrically conductive (continuously), a predetermined amount of voltage is applied (charged) to the object to be plated 10 in advance, and the metal due to the contact potential difference ΔV is applied. This is a method of performing replacement plating by immersing in a plating solution 14 after canceling out the amount of electric charge generated on the surface .

The voltage applied to the object to be plated 10 is a voltage in a certain range determined based on the materials and compositions of the first metal surface 11, the second metal surface 12, the coating metal, the plating solution 14, and the counter electrode 15.

The applicant of the present application mounts copper (Cu) as a coating metal on the surface 11 (zinc side) of the first metal in the object to be plated 10 in which the first metal is zinc (Zn) and the second metal is copper (Cu). Considered the case. In particular, as the plating film 13, copper as a high-quality metal that has a thin and uniform film thickness and suppresses the generation of pinholes in consideration of the case where a film such as another metal or resin is applied on the plating film 13. The purpose was to form a film (metal copper, Cu).

When the copper (metal copper) coating was first plated by a conventionally known substitution-type electroless plating method, the plating progressed, but the formed plating film discolored (copper oxide, etc. precipitates). Precipitation of copper as a metal was difficult.

As a result of evaluation under various conditions such as the composition and pH of the plating solution, the composition of the plating solution and the contact potential difference ΔV generated between zinc and copper affect the redox reaction between copper and zinc, and the plating film It was considered to be causing discoloration (precipitation of copper oxide, etc.).

With reference to FIG. 4, FIG. 4A is a schematic diagram showing the work functions of copper and zinc (energy difference between vacuum level VL and Fermi level FL). (B) is a structure in which copper and zinc are electrically conducted (continuously) (for example, a structure in which the surface of copper and the surface of zinc are in direct contact with each other (hereinafter referred to as copper-zinc contact)). It is a schematic diagram which shows the contact potential difference ΔV which occurs in the object to be plated 10 of embodiment).

As shown in FIG. 6A, the work function of copper (Cu) is 4.7 eV, and the work function of zinc (Zn) is 3.6 eV. Further, due to the difference in work functions between the two, as shown in Fig. (B), the copper-zinc contact body (plated body 10) is charged with a positive charge on the zinc side, for example, based on the copper side (+ 1.1 V =). -(3.6 eV-4.7 eV) / e, where e is an elementary charge).

FIG. 5 shows a reaction (for example, a redox reaction) between zinc (the surface of the first metal immersed in the plating solution 14 and replaced) and copper (the plating solution 14, the coating metal contained in the plating solution 14). It is a figure which shows the relationship of). The figure (graph) shown on the right side of the figure shows the reaction between copper and zinc (for example, redox reaction) in an aqueous solution system (Zn— _H2O system and Cu— _H2O system) calculated by the applicant of the present application. It is a state diagram showing the whole, the potential-pH diagram of the Zn— _H2O system when the activity of the dissolved zinc ion is ^10-6 , and the Cu with the activity of the dissolved copper ion being 1. It is a potential-pH diagram (here, referred to as "potential-pH diagram (synthesis)") drawn by superimposing the potential-pH diagram of the _-H2O system. In this case, the vertical axis indicates the equilibrium electrode potential of the aqueous solution with reference to the standard hydrogen electrode (vs. NHE (vs. SHE)). The horizontal axis is the pH of the plating solution 14.

The equilibrium electrode potential in the potential-pH diagram (synthesis) was calculated based on the activities of zinc ions and copper ions using the Nernst equation for the equilibrium electrode potential shown in the following (formula A). Here, zinc is a component that dissolves into an aqueous solution from a solid object to be plated 10, and does not originally exist in the aqueous solution. In the sense that it is a very small amount ^, the activity of dissolved zinc ions is 10-. It was set to ⁶ . On the other hand, copper is a component that precipitates from ions in the aqueous solution to the object to be plated 10, and is originally present in a large amount in the aqueous solution. Therefore, the activity of the dissolved copper ions is set to 1.

In the figure, the boundary line a indicates the equilibrium electrode potential (oxidation-reduction potential) when the activity of the dissolved zinc ion in the following zinc half-cell reaction (formula B) is ^10-6 , and the value is the value. -0.94 (V).

Zn ²⁺ + ^2e- = Zn (Equation B)

Further, the boundary line b indicates the equilibrium electrode potential (oxidation-reduction potential) of the following copper half-cell reaction (formula C), and the value when the activity of the dissolved copper ion is 1 is +0.34 (V). ).

Cu ²⁺ + ^2e- = Cu (Formula C)

In this potential-pH diagram (synthesis), the region (colored region) where the corroded region of zinc and the insensitive region (inert region, inactive region, stable region) of copper (metal for coating) overlap is zinc. Is ionized and copper is deposited, that is, the zinc surface of the copper-zinc contact (the region where the first metal surface 11 of the object to be plated 10 is replaced with copper (coating metal), and hereinafter, this region. Is referred to as "replaceable area SR".

That is, if the potential of the surface (first metal surface 11) of the copper-zinc contact body (replaced zinc side) and the pH of the plating solution 14 satisfy the conditions included in the replaceable region SR, zinc is eluted. Copper can be deposited. The potential range of the replaceable region SR (the potential at which the first metal surface 11 is replaced by the coating metal; hereinafter referred to as “substitutable potential range VR”) varies depending on the pH of the plating solution 14, and is shown in FIG. In the example of, the maximum (in the case of a strong acid of about pH <3) is +0.34 ≧ VR ≧ -0.94, and the minimum (in the case of a weak alkali of pH = about 8.1) is -0.047 ≧ VR ≧-. It is 0.94. In this embodiment, as an example, a case where a strong acid (pH <3) is used for the plating solution 14 and the replaceable potential range VR is +0.34 ≧ VR ≧ −0.94 will be described.

By the way, the zinc side (first metal surface 11) of the copper-zinc contact body (plated body 10) is relative to the copper side (second metal surface 12) as shown in the left figures of FIGS. 4 and 5. It is in a positively charged state (+1.1V =-(3.6eV-4.7eV) / e, where e is an electric element), and the potential of the replaceable region SR in the potential-pH diagram (synthesis). It is far (exceeded) from the upper limit of the range (substitutable potential range VR).

Therefore, the applicant of the present application forcibly applies the potential of the first metal surface 11 to the potential range for realizing the substitution, that is, the replaceable potential range VR, before the immersion in the plating solution 14 (before the substitution reaction starts). It was considered that the substitution reaction between zinc and copper proceeded well by setting to.

That is, a voltage is immersed in the plating solution 14 so that the potential of the object to be plated 10 charged positively (or negatively) due to the contact potential difference ΔV falls within the replaceable potential range VR (so as to cancel the charged state). It was decided to apply it to the object to be plated 10 before the plating.

More specifically, first, for the plating solution 14, a solution containing copper ions (Cu ²⁺ ) and sulfate ^ions (SO _4-2 ), which are easy to handle, is used from a theoretical and practical point of view, and pH = 0. Adjusted to about 5. As a result, the replaceable potential range VR becomes +0.34 ≧ VR ≧ −0.94.

Then, a voltage is applied to the object to be plated 10 to cancel at least a part of the electric charge (+ 1.1 V with respect to the second metal surface 12) charged on the first metal surface 11. Hereinafter, the voltage that cancels at least a part of the charge fluctuation on the first metal surface 11 due to the contact potential difference ΔV is referred to as “charge pump voltage CP”.

The charge pump voltage CP of the present embodiment is a voltage capable of offsetting at least a part of the charge fluctuation on the first metal surface 11 due to the contact potential difference ΔV , preferably the potential of the first metal surface 11 of the object to be plated 10. Is a voltage within the replaceable potential range VR (+0.34 ≧ VR ≧ −0.94). Specifically, the charge pump voltage CP is, for example, a negative voltage of −0.76V (0.34V −1.1V) ≧ CP ≧ −2.04V (−0.94V −1.1V).

Here, it is desirable that the counter electrode 15 is, for example, an electrode capable of continuously releasing metal ions of the coating metal into the plating solution 14, and here, an example using a copper electrode is shown.

Then, while maintaining the application of the charge pump voltage CP, the object to be plated 10 is immersed in the above-mentioned plating solution 14 adjusted to pH = 0.5. As a result, the first metal surface 11 and the plating solution 14 of the object to be plated 10 are placed under the condition of the replaceable region SR, and the first metal surface 11 (zinc) is replaced with the coating metal (copper).

This substitution reaction proceeds under the condition of the substitutable region SR while the zinc constituting the first metal surface 11 is present. That is, the charge pump voltage CP is continuously applied at least from the start of immersion of the plating target portion 16 to the time when substantially the entire portion is immersed in the plating solution 14.

The coating metal (plating film 13) deposited on the surface of the object to be plated 10 due to the substitution reaction can significantly suppress the generation of pinholes and can significantly reduce the film thickness as compared with the case of the electroplating method. .. Then, when the charge pump voltage CP continues to be applied even after the first metal surface 11 is completely replaced with the coating metal, electroplating is continuously and automatically performed on the object to be plated 10, and plating is performed. The film thickness of the film 13 increases (for example, the voltage when copper is adhered by electroplating is generally about 1 to 5 V in an acidic bath (pH = 0.5)).

Even in the case of continuous transition to electroplating, the lower layer of the plating film 13 is a good film (layer) formed by replacement plating. That is, even if pinholes are generated by the electroplating, there is no problem from the viewpoint of covering the base material BD, and the electroplating can be completed when the desired thickness of the plating film 13 is formed. Is.

That is, the charge pump voltage CP is applied before the body 10 to be plated is immersed in the plating solution 14, until at least the plating target portion 16 (for example, substantially the entire surface of the first metal surface 11) is immersed in the plating solution 14. The application is continued for a while. When the coating metal is deposited on the plating target portion 16 and the plating film 13 has a desired film thickness (by continuing electroplating for an appropriate time, etc.), the application of the charge pump voltage CP is terminated. Alternatively, the object to be plated 10 is taken out from the plating solution 14.

In this way, according to the plating method of the present embodiment, it is possible to form a high-quality plating film 13 by replacement plating at least in the lowermost layer. Specifically, the plating film 13 can be formed of a film-forming metal (for example, metallic copper), suppresses the generation of pinholes, and can be formed into a thin and uniform film thickness. Further, when the replacement plating is completed, the plating film 13 continuously shifts to electroplating, so that the film thickness of the plating film 13 can be controlled by the application time of the charge pump voltage CP while immersed in the plating solution 14.

As a result, the film thickness of the plating film 13 can be controlled to an arbitrary thickness, and for example, a thin film of 3 μm or less, which was difficult to generate pinholes in the prior art, can be formed. More specifically, for example, about 100 nm to 3 μm, preferably about 300 nm to 2 μm, more preferably about 500 nm to 1.5 μm can be formed, and for example, even if the film thickness is about 500 nm, pinholes are generated. Can be suppressed. For example, when the plating film 13 having a film thickness of 1 μm or less is formed, the charge pump voltage CP is continuously applied for 1 to 2 minutes after the plating target portion 16 is immersed in the plating solution 14, and electroplating is performed. Further, as the plating solution 14, an easy-to-handle solution composed of copper sulfate and sulfuric acid can be used.

As described above, in the plating method of the present embodiment, the base metal (first metal) side of the object to be plated 10 having the first metal surface 11 and the second metal surface 12 that are electrically conductive (continuously). This is a method of coating the surface of the metal with a relatively noble coating metal (coating with a metal (non-metal oxide) film), and the first metal is used before the object to be plated 10 is immersed in the plating solution 14. A charge pump voltage CP that cancels at least a part of the potential generation based on the contact potential difference ΔV of the first metal surface 11 with respect to the second metal surface 12 generated on the surface 11 is applied.

Specifically, the contact potential difference ΔV between the first metal surface 11 and the second metal surface 12, which are the parts to be plated 16 of the object to be plated 10, and the first metal surface 11 and the coating metal (coating existing in the plating solution 14). Based on the potential-pH diagram (synthesis) showing the redox reaction of the metal ion of the metal, the potential of the first metal surface 11 in the object to be plated is the potential of the replaceable region SR in the potential-pH diagram (synthesis). Determine the charge pump voltage CP so that it is set within the range of.

In other words, when the potential range in which the first metal is ionized and the first metal surface 11 is replaced with the coating metal is defined as the replaceable potential range VR, the first metal surface is applied by applying the charge pump voltage CP. The potential of 11 is set within the replaceable potential range VR.

Then, with the charge pump voltage CP applied (while applying), the object to be plated 10 is immersed in the plating solution 14.

<Application example>
Again, the object to be plated 10 of the present embodiment may be such that the first metal surface 11 and the second metal surface 12 are electrically conductive (continuously). For example, as shown in FIGS. 2 (E) to 2 (G), the base material BD or the object to be plated 10 may be a dissimilar metal bonded body.

For example, as an example of a dissimilar metal joint, there is a structure in which copper and aluminum are directly bonded by pressure welding or the like. The dissimilar metal joint of copper and aluminum (copper-aluminum joint) has a wide range of applications as various parts due to the ease of handling the material and the cost. However, even in this case, a contact potential difference between dissimilar metals is generated, which causes galvanic corrosion, which is another well-known problem.

In addition, the surface of aluminum is not stable to the environment because an oxide film is easily formed, or when another film is laminated on the surface of a copper-aluminum junction as a base material, it is homogeneous due to the difference in the material of the base material. There is also a problem that it is difficult to stack various films.

Therefore, the entire copper-aluminum joint is covered with a single metal film, or the aluminum part (including the joint between the two) is continuously covered with a copper film from the copper part of the copper-aluminum joint. It is possible to solve the problem by covering it. And even in such a case, the plating method of this embodiment can be adopted.

By the way, although aluminum is a lower metal than copper, it is difficult to directly replace the surface of aluminum with copper. Specifically, the oxide film formed on the aluminum surface is difficult to dissolve in an acidic copper plating solution (plating solution for copper replacement) for replacing copper, and replacement does not proceed, while alkaline copper plating. The liquid requires a complex for generating copper ions and a reducing agent, and is toxic, so that it cannot be easily carried out.

Therefore, a zinc film (layer) is formed on the surface of the aluminum portion of the copper-aluminum joint by zincating treatment. As a result, in the copper-aluminum joint, the first metal surface 11 of zinc covering the aluminum serving as the base metal BD and the second metal surface 12 of copper (second metal material 12M) are electrically conductive (continuously). It becomes the object to be plated 10 (see FIG. 2F), and the first metal surface 11 can be replaced with copper, which is a coating metal, by the plating method of the present embodiment. Since a known method can be adopted for the zincating treatment in this case, details are omitted, but the aluminum portion of the copper-aluminum joint is immersed in the plating solution for the zincating treatment without applying a voltage, and electroless plating is performed. To apply. The number of zincating treatments is arbitrary. As a result, a copper-zinc contact body (plated body 10) in which the aluminum portion is covered with a zinc metal film (first metal surface 11) can be obtained. Therefore, this is washed and dried, and the plating method of the present embodiment is performed. Is plated.

FIG. 6 is a schematic view showing the contact potential difference ΔV of the object to be plated 10 in which the aluminum surface of the copper-aluminum joint is zincated. FIG. (A) is a schematic diagram showing the work functions of copper, aluminum, and zinc, and FIG. 6 (B) is a schematic diagram showing the contact potential difference ΔV generated in the object to be plated 10.

For example, even in the case of a configuration in which copper and zinc are electrically continuous afterwards due to a zincate treatment or the like (whether or not copper and zinc have, for example, an atomic bond or a direct bond, etc.). ), If both are electrically continuous, for example, via aluminum, a contact potential difference ΔV occurs.

The work function of aluminum (Al) is 4.1 eV. That is, in this case, the contact potential difference ΔV of the object to be plated 10 is + 1.1 V (=-((3.6 eV-4.1 eV) + (4.1 eV-4.7 eV)) on the zinc side, for example, based on the copper side. ) / E, where e is an elementary charge) is charged. When considering the contact potential difference ΔV between copper and zinc that are electrically conductive (continuous) in this way, the work function of the metal intervening between them is offset (regardless of the magnitude of the ionization tendency of the metal). To. That is, also in this case, the object to be plated 10 can be treated as a copper-zinc contact body (see FIGS. 4 (F) and 5), and the plating film 13 of high-quality metallic copper by the plating method of the present embodiment described above. Can be formed.

FIG. 7 is a diagram showing an example of the result of plating treatment by the conventional plating method and the plating method of the present embodiment, and is an external photograph of the objects to be plated a to d. The bodies a to d to be plated are all structures in which the aluminum portion of the copper-aluminum joint is zincated, and the first metal surface 11 of zinc and the second metal surface 12 of copper are electrically continuous copper-. It is a zinc contact body, and a part of the first metal surface 11 was set as a plating target portion 16 and plating treatment was performed under different conditions. The figure (A) is the result of the object to be plated a, the figure (B) is the result of the object to be plated b, the figure (C) is the result of the object to be plated c, and the figure (D) is the result of the object to be plated d.

Further, FIG. 8 shows the results of examination of the plating films formed on the four samples (objects a to d) shown in FIG. 7, and FIG. 8 (A) shows the electrochemistry performed on the four samples. It is the measurement result of the measurement (reduction method), and FIG. 3 (B) shows the thickness (Å) of copper oxide for four samples (plated bodies a to d) based on the measurement result of FIG. It is a calculated table. In addition, FIG. 8 also shows the measurement results of the copper base material (without plating) and the film thickness of copper oxide on the surface of the copper base material for comparison.

In the electrochemical measurement (reduction method) shown in FIG. 8, the surface of the sample was electrochemically reduced with a boric acid buffer aqueous solution, and the time change of the reduction potential was measured. The vertical axis of FIG. 6A is the reduction potential (V vs. AgCl), and the horizontal axis is the energization time (sec). The energization time corresponds to the time required for reduction, that is, the film thickness of the oxide film formed by the plating treatment. Further, in FIG. 3B, among the copper oxides, cuprous oxide (Cu ₂ O) is reduced in the range of −0.35 V to −0.6 V, and the film thickness is calculated. The film thickness was calculated assuming that copper (CuO) is reduced in the range of −0.6 V to −0.85 V.

With reference to FIG. 7, the plating solution used for the plating treatment of the object to be plated a shown in FIG. 7A is a mixed solution of copper sulfate and sulfuric acid similar to that of the present embodiment, but has a pH of 3. Adjusted to .5. Further, the plating solutions used for the plating treatment of the objects to be plated b to d shown in FIGS. (B) to (D) are all the plating solutions 14 (mixed solution of copper sulfate and sulfuric acid) of the present embodiment described above. , PH = 0.5).

FIG. (A) is an object to be plated a in which the plating target portion 16 of the first metal surface (zinc) 11 is electroless plated by a conventional method. In this case, a film that was severely discolored to dark brown was formed on the plating target portion 16. As a result of measurement by electrochemical measurement (reduction method) with reference to FIG. 8, a film containing cupric oxide ₍ CuO) as a main component and cuprous oxide (Cu2O) is formed. It turned out. Since cupric oxide (CuO) is dark brown and cuprous oxide (CuO) is reddish brown, it is explained that the plating target site 16 was formed of a mixture of these, and as a result, a dark brown film was obtained. Will be done.

FIG. 3B is an object to be plated b in which the plating target portion 16 of the first metal surface (zinc) 11 is electroless plated by a conventional method. In this case, the plating target portion 16 turned reddish brown, and as a result of measurement by electrochemical measurement (reduction method), it was found that a film containing cuprous oxide (Cu ₂ O) as a main component was formed (). See FIG. 8).

FIG. 3C is a body to be plated c (body to be plated 10) on which the plating film 13 is formed by the plating method of the present embodiment. No discoloration was observed in the plating film 13 formed on the plating target portion 16 of the first metal surface 11 (comparable to the second metal surface 12 (copper)), and the electrochemistry of FIG. 8 (A) was observed. The measurement result by the measurement (reduction method) also shows the same profile as the copper substrate, and the film thickness of cuprous oxide (Cu ₂ O) is judged to be the same from the table in FIG. 8 (B), which is good. It was found that the metallic copper plating film 13 was formed.

FIG. 3D shows the object to be plated d when 3.2 V is applied as the charge pump voltage CP outside the replaceable potential range VR in the plating method of the present embodiment. The composition of the plating solution 14 is a mixed solution of copper sulfate and sulfuric acid, and the pH is 0.5. The plating target portion 16 was darker than the object to be plated B in FIG. 7B, and a bronze-colored plating film was obtained. In the measurement by the electrochemical measurement (reduction method) of FIG. 8A, the reduction time of cuprous oxide (Cu ₂ O) was long and the measurement was interrupted. It is presumed that this plating film is composed mainly of cuprous oxide (Cu ₂ O).

As described above, in the plating methods of FIGS. (A), (B), and (D), it was presumed that the substitution reaction via the oxide occurred. On the other hand, in the plating method of the present embodiment, it can be said that a good metallic copper plating film 13 can be formed by appropriately selecting the pH of the plating solution 14 and the charge pump voltage CP based on the replaceable region SR.

As described above, according to the present embodiment, at least the aluminum portion of the copper-aluminum joint (dissimilar metal joint) can be covered with the metal copper plating film 13. The film thickness is, for example, 3 μm or less, specifically, about 100 nm to 3 μm, preferably about 300 nm to 2 μm, and more preferably about 500 nm to 1.5 μm. Further, since it is a replacement plating, it is possible to suppress the occurrence of pinholes even if the film thickness is, for example, about 500 nm.

It is difficult to make the plating film formed by the electroplating method a thin film thickness (for example, 5 μm or less), and the film thickness must be further increased in order to bury frequently occurring pinholes. There was a problem that affected the appearance shape (size) of the.

According to this embodiment, since the plating film 13 can be formed which is significantly thinner than the case of the electroplating method and is uniform and hardly causes pinholes, the appearance shape of the copper-aluminum joint (dissimilar metal joint). It is possible to take reliable measures against galvanic corrosion without significantly damaging the galvanic corrosion.

Further, by covering the aluminum portion with the copper plating film 13, substantially the entire outer surface of the copper-aluminum joint (dissimilar metal joint) can be made of the same metal (here, copper). Therefore, when another film (metal film or resin film) is laminated or coated using this as a base material (base), the stability and adhesion of the film can be improved.

As described above, in the plating method of the present embodiment, if the first metal surface 11 and the second metal surface 12 having different work functions are electrically continuous, they are not in contact (bonded). Alternatively, another conductive material (other metal) may be interposed between the two.

Further, as the plating method of the present embodiment, the case where the first metal surface 11 is zinc, the second metal surface 12 is copper, and the coating metal is copper has been exemplified, but these metals are not limited to the above examples. That is, the step of preparing the object to be plated 10 in which the first metal surface 11 and the second metal surface 12 are electrically continuous, and the second metal surface 12 generated on the first metal surface 11 as a reference. 1 A step of applying a voltage (charge pump voltage) to the object to be plated 10 so as to cancel at least a part of the potential generated by the contact potential difference ΔV of the metal surface 11, and a plating solution 14 for at least a part of the object 10 to be plated. Any plating method may be used, which comprises a step of immersing in and performing replacement plating on at least a part of the object to be plated 10.

For example, the first metal surface 11 may be a metal surface containing nickel (Ni) as a main component or a metal surface containing iron (Fe) as a main component.

FIG. 9 is a diagram schematically showing a current circuit that is a premise of the plating method of the present embodiment. Each element of the plating solution 14 (metal ion for coating), counter electrode 15, power supply, second metal surface 11, first metal surface 11, and replaceable potential range VR has an earth-referenced potential, and the current shown in the figure. It can be said that it constitutes a circuit. Therefore, even if any metal is used, the plating method of the present embodiment can be adopted as long as the current circuit can be configured (satisfying the potential relationship). Specifically, each concept of the plating method of the present embodiment and numerical values are determined as follows, and it can be said that the plating method of the present embodiment has the following steps.

(1) Contact potential difference ΔV: The contact potential difference ΔV of one of the first metal surface 11 and the second metal surface 12 (for example, the surface of the second metal) as a reference (for example, the plating target portion 16 side) is calculated.

(2) Pourbaix diagram (synthesis): A state diagram is created by synthesizing the potential-pH diagram of the first metal and the potential-pH diagram of the coating metal (plating solution 14 containing the coating metal ion). The coating metal does not have to be the same as the second metal.

(3) Substitutable region SR: In the potential-pH diagram (synthesis), a region where the corroded region of the first metal and the insensitive region of the coating metal overlap is determined.

(4) Substitutable potential range VR: A potential range in which the first metal is ionized and the first metal surface 11 is replaced with the coating metal (potential range of the replaceable region SR) is specified.

(5) Charge pump voltage CP: At least a part of the potential generated by the contact potential difference ΔV is offset so that the potential of the object to be plated 10 (first metal surface 11) charged by the contact potential difference ΔV falls within the replaceable potential range. Calculate the voltage (positive voltage or negative voltage) to be (adjusted or corrected). It is not necessary to cancel all the potential generations corresponding to the contact potential difference ΔV, and a part of the potential generation may be offset.

(6) Plating liquid 14: The components and pH are appropriately selected according to the material of the first metal surface 11 and the metal for coating and the replaceable range.

(7) Counter electrode 15: Adopt an arbitrary electrode material capable of emitting metal ions of the coating metal, immerse it in the plating solution 14 and apply a voltage (connected to one electrode of the power supply as the counter electrode of the object to be plated 10). do.

(8) Body to be plated 10: Before being immersed in the plating solution 14, a charge pump voltage CP is applied (connected to the other pole of the power supply), and the plating solution 14 is immersed in the state where the application is continued to perform replacement plating. conduct. If necessary, electroplating is continuously performed to form a plating film 13 having a predetermined film thickness, and then the plating process is terminated (voltage application is terminated, removal from the plating solution 14 and the like).

Further, it can be said that the contact potential difference ΔV in the plating method of the present embodiment is a value satisfying the following relationship (Equation 1).

ΔV =-(WF1-WF2) / e ... (Equation 1)
here,
ΔV: Contact potential difference between the first metal (surface) and the second metal (surface) with respect to the second metal (surface)
WF1: Work function of the first metal (relatively low metal)
WF2: Work function of the second metal (relatively noble metal)
e: It is an elementary charge, and "/ e" means that the unit eV (energy) of the work function is divided by the elementary charge e in order to convert it into the unit V of voltage.

Further, it can be said that the replaceable potential range VR in the plating method of the present embodiment is a value satisfying the following relationship (Equation 2).

V2 ≧ VR ≧ V1 ・ ・ ・ (2)
here,
VR: Substitutable potential range
V1: Equilibrium electrode potential of the first metal (activity is 1E-6)
V2: Equilibrium electrode potential of coating metal (activity is 1)
Is.

Further, it can be said that the charge pump voltage CP in the plating method of the present embodiment is a value satisfying the following relationship (Equation 3).

V2-ΔV ≧ CP ≧ V1-ΔV ・ ・ ・ (3)
here,
CP: Charge pump voltage
ΔV: Contact potential difference
V1: Equilibrium electrode potential of the first metal (activity is 1E-6)
V2: Equilibrium electrode potential of coating metal (activity is 1)
Is.

For example, when the coating metal and the second metal are of the same type, the plating film 13 may be continuously formed on the first metal surface 11 and the second metal surface 12.

In step S03 of FIG. 1, the immersion of the counter electrode 15 in the plating solution 14 and the application of the voltage are in no particular order.

It should be noted that the present invention is not limited to the above-described embodiment, and it goes without saying that various modifications can be made without departing from the gist of the present invention.

The plating method of the present invention can be used for plating a structure in which dissimilar metals are electrically conductive (continuous).

10 Object to be plated 11 1st metal surface 12 2nd metal surface 13 Plating film 14 Plating liquid 15 Counter electrode 16 Target site CP Charge pump Voltage SR Substitutable region VR Substitutable potential range

Claims (10)

Both the surface made of the first metal (hereinafter referred to as "the surface of the first metal") and the surface made of the second metal (hereinafter referred to as the "second metal surface") are both exposed and electrically conductive. Steps to prepare the object to be plated and
By applying a voltage to the first metal via the second metal before immersing the object to be plated in the plating solution, the first metal due to the contact potential difference between the first metal and the second metal. A step of setting the potential of the first metal surface to a predetermined potential range by canceling at least a part of the potential generated on the metal surface.
It has a step of immersing at least the plating target portion of the surface of the first metal in the plating solution in a state where the voltage is applied, and coating the plating target portion with a coating metal nobler than the first metal. ,
The predetermined potential range is a potential range in which the first metal is ionized and the surface of the first metal is replaced with the coating metal.
A plating method characterized by that. Both the surface made of the first metal (hereinafter referred to as "the surface of the first metal") and the surface made of the second metal (hereinafter referred to as the "second metal surface") are both exposed and electrically conductive. Steps to prepare the object to be plated and
By applying a voltage to the first metal via the second metal before immersing the object to be plated in the plating solution, the first metal due to the contact potential difference between the first metal and the second metal. With the step of canceling at least a part of the potential generation on the metal surface,
It has a step of immersing at least a plating target portion of the first metal surface in the plating solution in a state where the voltage is applied , and forming at least a replacement plating film on the plating target portion.
The replacement plating film is a plating film in which the first metal is ionized and the surface of the first metal is replaced with a coating metal nobler than the first metal.
A plating method characterized by that. Both the surface made of the first metal (hereinafter referred to as "the surface of the first metal") and the surface made of the second metal (hereinafter referred to as the "second metal surface") are both exposed and electrically conductive. Steps to prepare the object to be plated and
By applying a voltage to the first metal via the second metal before immersing the object to be plated in the plating solution, the first metal due to the contact potential difference between the first metal and the second metal. A step of setting the potential of the first metal surface to a predetermined potential range by canceling at least a part of the potential generated on the metal surface.
It has a step of immersing at least the plating target portion of the surface of the first metal in the plating solution in a state where the voltage is applied, and coating the plating target portion with a coating metal nobler than the first metal. ,
The predetermined potential range is a potential range in which the corroded region of the first metal and the insensitive region of the coating metal overlap in the potential-pH diagram.
A plating method characterized by that. Both the surface made of the first metal (hereinafter referred to as "the surface of the first metal") and the surface made of the second metal (hereinafter referred to as the "second metal surface") are both exposed and electrically conductive. Steps to prepare the object to be plated and
By applying a voltage to the first metal via the second metal before immersing the object to be plated in the plating solution, the first metal due to the contact potential difference between the first metal and the second metal. With the step of canceling at least a part of the potential generation on the metal surface,
It has a step of immersing at least the plating target portion of the surface of the first metal in the plating solution in a state where the voltage is applied, and coating the plating target portion with a coating metal nobler than the first metal. ,
The first metal is a relatively low metal and
The second metal is a relatively noble metal and
When the contact potential difference is ΔV, the work function of the first metal is WF1, the work function of the second metal is WF2, and the elementary charge is e, the contact potential difference is the following equation (1).
ΔV =-(WF1-WF2) / e ... (1)
The filling,
The potential range in which the first metal is ionized and the surface of the first metal is replaced by the coating metal (hereinafter referred to as “substitutable potential range”) is defined as VR, and the equilibrium electrode potential (activity) of the first metal. When 1E-6) is V1 and the equilibrium electrode potential (activity is 1) of the coating metal is V2, the substitutable potential range is the following equation (2).
V2 ≧ VR ≧ V1 ・ ・ ・ (2)
The filling,
When the voltage is CP, the voltage is calculated by the following equation (3).
V2-ΔV ≧ CP ≧ V1-ΔV ・ ・ ・ (3)
Meet, meet
A plating method characterized by that. The application of the voltage is continued until substantially the entire plating target portion is immersed in the plating solution.
The plating method according to any one of claims 1 to 4 , wherein the plating method is characterized by that. The second metal is a metal nobler than the first metal.
The plating method according to any one of claims 1 to 5, wherein the plating method is characterized by that. The second metal and the coating metal are the same type of metal.
The plating method according to any one of claims 1 to 6 , wherein the plating method is characterized by that. The film thickness of the plating film made of the coating metal is 3 μm or less .
The plating method according to any one of claims 1 to 7, wherein the plating method is characterized by that. The first metal is a metal containing zinc as a main component, and the second metal is a metal containing copper as a main component.
The plating method according to any one of claims 1 to 8, wherein the plating method is characterized by that. The object to be plated is a dissimilar metal joint.
The plating method according to any one of claims 1 to 9, wherein the plating method is characterized by that.

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