JP2022090514A - Method for forming gold plating film - Google Patents

Abstract

To provide a method for forming a gold plating film that can prevent a porous membrane from being clogged with gold fine particles.SOLUTION: The present invention discloses a method for forming a gold plating film on a base material by displacement electroless plating. The method includes the step of bringing a porous membrane containing an electroless gold plating solution into contact with the surface of the substrate. The electroless gold plating solution at least contains gold sulfite salt. The sulfate ion concentration relative to the sulfite ion concentration of the electroless gold plating solution remaining on the surface of the porous membrane after the step for contact, (sulfate ion concentration/sulfite ion concentration), is 16.0 or less.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to a method for forming a gold plating film.

Generally, the method of reducing and plating metal ions in a plating solution is roughly classified into an electroplating method using an external current and an electrolytic plating method not using external electricity. The latter electrolysis-free plating method further includes (1) a displacement-type electrolysis-free plating method in which metal ions in the solution are reduced by electrons released by the dissolution of the object to be plated and deposited on the object to be plated. 2) It is roughly classified into a self-catalytic reduction type electrolyticless plating method in which metal ions in the solution are precipitated as a metal film by electrons released when the reducing agent contained in the solution is oxidized. The electroless plating method is widely used in many fields because it enables uniform precipitation even on complicated shaped surfaces.

Substitutional electroless plating forms a metal plating film by utilizing the difference in ionization tendency between the metal in the plating solution and the base metal. For example, in the gold plating method, when a substrate on which a base metal is formed is immersed in a plating solution, the base metal having a large ionization tendency becomes ions and dissolves in the plating solution, and the gold ions in the plating solution become the base metal as a metal. Precipitates on top to form a gold-plated film.

For example, Patent Document 1 discloses an electroless gold plating bath. Patent Document 1 comprises adding 0.1 ng / L to 1 g / L of cyanide or a complex salt thereof as KCN to a non-electrolyzed gold-plated bath containing a non-cyanide gold salt, a complexing agent and a reducing agent, and the pH is adjusted. Disclosed is an electrolytic gold plating bath characterized by being 3.0 to 9.5.

Japanese Unexamined Patent Publication No. 2002-02874

As a result of various studies on the substitutional electroless plating method, the present inventors have found that when a gold plating film is formed using a porous film, the porous film may be clogged with gold fine particles. rice field.

Therefore, an object of the present disclosure is to provide a method for forming a gold-plated film, which can prevent the porous film from being clogged with gold fine particles.

The present inventors conducted diligent studies to solve the above problems, and found that by controlling the sulfate ion concentration with respect to the sulfite ion concentration of the electroless gold plating solution remaining on the surface of the porous film after plating. We have found that it is possible to prevent the porous film from being clogged with gold fine particles, and have reached the present disclosure.

Examples of embodiments of this embodiment are described below.

(1) A method of forming a gold plating film on a substrate by a displacement type electroless plating method.
A step of bringing a porous film containing an electroless gold plating solution into contact with the surface of the base material is included.
The electroless gold plating solution contains at least gold sulfite,
A method in which the sulfate ion concentration (sulfate ion concentration / sulfite ion concentration) with respect to the sulfite ion concentration of the electroless gold plating solution remaining on the surface of the porous film after the contacting step is 16.0 or less.
(2) A method of continuously forming a gold plating film on a plurality of substrates by a substitutional electroless plating method.
It includes a step of bringing a porous film containing a non-electrolytic gold plating solution into contact with the surface of a base material, and a step of recovering the base material on which the gold plating film is formed after the contacting step.
It is a method of repeatedly carrying out the contacting step and the collecting step.
The electroless gold plating solution contains at least gold sulfite,
There is a step of cleaning the electrolytic-free gold plating solution remaining on the surface of the porous film at least one of after the contacting step, before the recovering step, and after the recovering step and before the contacting step. death,
A method in which the sulfate ion concentration (sulfate ion concentration / sulfite ion concentration) with respect to the sulfite ion concentration of the electroless gold plating solution remaining on the surface of the porous film after the contacting step is 16.0 or less.
(3) The method according to (1) or (2), wherein the substrate is nickel or a nickel alloy.
(4) The method according to any one of (1) to (3), wherein the electroless gold plating solution is supplied from a plating solution chamber accommodating the electroless gold plating solution.
(5) The method according to (4), wherein the plating solution chamber is arranged in contact with the porous film.
(6) A film forming apparatus for forming a gold plating film on a base material by a displacement type electroless plating method.
Porous membrane and
A plating solution chamber for accommodating electroless gold plating solution, which is arranged in contact with the porous film, and
A pressing means for bringing the porous film into contact with the substrate by relatively pressing the plating solution chamber and the substrate.
A cleaning means for cleaning the porous membrane and
A film forming apparatus.

INDUSTRIAL APPLICABILITY According to the present disclosure, it is possible to provide a method for forming a gold plating film capable of suppressing clogging of gold fine particles in a porous film in an electroless plating method.

It is a schematic cross-sectional view for demonstrating the state at the time of film formation in one aspect of this Embodiment. It is a schematic cross-sectional view for demonstrating the state at the time of washing in one aspect of this Embodiment shown in FIG. It is a schematic cross-sectional view for demonstrating the state at the time of film formation and the state at the time of cleaning in one aspect of this Embodiment. It is a schematic cross-sectional view for demonstrating after film formation and washing in one aspect of this Embodiment shown in FIG. It is a figure which shows the initial value, the sulfate ion concentration / sulfite ion concentration of an Example, a comparative example, and the presence or absence of discoloration of a porous membrane of an Example, a comparative example.

One aspect (aspect 1) of the present embodiment is a method of forming a gold plating film on a base material by a substitution type electroless plating method, in which a porous film containing an electroless gold plating solution is formed on the surface of the base material. The sulfate ion concentration with respect to the sulfite ion concentration of the electroless gold plating solution containing at least gold sulfite and remaining on the surface of the porous film after the contact step. It is a method in which (sulfate ion concentration / sulfite ion concentration) is 16.0 or less.

According to this embodiment, it is possible to prevent the porous film from being clogged with gold fine particles. The present inventors speculated that the reason for this was as follows. In the method according to the present embodiment (method for producing a plating film), by contacting the porous film with the base material, gold ions are reduced on the base material and deposited on the base material to be plated. This reaction can be ^expressed by Au (SO ₃ ) ^23-3 + e- → Au + ₂ (SO ₃ ) ^2- . At this time, it is considered that an oxidative decomposition reaction of gold sulfite occurs as a side reaction. This side reaction can be represented by 3Au (SO ₃ ) _2-3 + 3O ₂ → ^2Au + Au ^{3 +} +6 (SO ₄ ) ^2- . It is considered that this side reaction reduces the complexing effect and causes Au to abnormally precipitate in the electroless gold plating solution. This abnormally precipitated Au does not necessarily precipitate on the substrate, and at least a part thereof exists in the electrolytic gold plating solution existing at the interface between the substrate and the porous film, and the pores of the porous film are present. It is considered that the porous film is clogged with gold fine particles due to the accumulation in. In the side reaction, sulfate ions are also generated along with the abnormal precipitation of Au. Therefore, by controlling the concentration of sulfate ions, it is possible to indirectly control the abnormal precipitation of Au, and it is possible to prevent the porous film from being clogged with gold fine particles. I guessed. According to the studies by the present inventors, it has been found that it is effective to control the concentration of sulfate ion as the concentration with respect to the sulfite ion concentration, that is, the sulfate ion concentration / sulfite ion concentration.

Another aspect (Aspect 2) of the present embodiment is a method of continuously forming a gold plating film on a plurality of substrates by a substitution type electroless plating method, and is porous including an electroless gold plating solution. It is a method including a step of bringing the film into contact with the surface of the base material and a step of recovering the base material on which the gold-plated film is formed after the step of contacting, and repeating the step of contacting and the step of recovering. The electroless gold plating solution contains at least gold sulfite and is a porous film at least one after the contacting step and before the recovery step and after the recovery step and before the contacting step. It has a step of cleaning the electroless gold plating solution remaining on the surface of the above, and the sulfate ion concentration (sulfate ion concentration / sulfate ion concentration) with respect to the sulfite ion concentration of the electroless gold plating solution remaining on the surface of the porous film after the contacting step. The method is such that the sulfite ion concentration) is 16.0 or less. In order to continuously form a gold-plated film on a plurality of substrates, the second aspect is the addition of a recovery step and a cleaning step to the first aspect. That is, it can be said that aspect 2 is a subordinate concept of aspect 1.

According to the studies by the present inventors, it has been found that the probability that the porous film is clogged with gold fine particles is remarkably increased when the contacting step is repeated a plurality of times. The present inventors speculate that this is because the above-mentioned abnormal precipitation is cumulatively generated by repeating the formation of the plating film. According to the studies by the present inventors, it has been found that it is effective to provide a step of cleaning the electroless gold plating solution remaining on the surface of the porous film in order to control the sulfate ion concentration / sulfate ion concentration. Was done. According to the present embodiment, by suppressing the clogging of the porous film with gold fine particles, it is possible to reduce the possibility that a normal film formation cannot be formed.

Hereinafter, this embodiment will be described in detail.

(Electroless gold plating solution)
The electroless gold plating solution used in this embodiment is an electroless gold plating solution containing at least a gold sulfite. The electroless gold plating solution contains, for example, a complexing agent in addition to the gold sulfite salt, and may contain an additive if necessary. Examples of the additive include a pH buffer and a stabilizer. A commercially available electroless gold plating solution may be used.

The electroless gold plating solution contains at least a gold sulfite salt, usually further contains a complexing agent, and may contain an additive if necessary.

Examples of the gold sulfite salt include gold ammonium sulfite, potassium gold sulfite, and sodium gold sulfite.

The content of gold sulfite in the electroless gold plating solution is preferably in the range of 0.5 g / L or more and 2.5 g / L or less as gold, and 1.0 g / L or more and 2.0 g / L or less. It is more preferably in the range. The upper limit value and the lower limit value of these numerical values can be arbitrarily combined to define a preferable range. When the gold content is 0.5 g / L or more, the gold precipitation reaction can be improved. Further, when the gold content is 2.5 g / L or less, the stability of the plating solution can be improved.

The complexing agent stably complexes gold ions (Au ⁺ ) and reduces the generation of Au ⁺ disproportionation reaction (the above-mentioned oxidative decomposition reaction) (3Au ⁺ → Au ³⁺ + 2Au), resulting in a liquid. It has the effect of improving the stability of. One type of complexing agent may be used alone, or two or more types may be used in combination.

Examples of the complexing agent include cyanide-based complexing agents and non-cyanide-based complexing agents. Examples of the cyanide complexing agent include sodium cyanide and potassium cyanide. Examples of the non-cyan complexing agent include sulfite, thiosulfate, thiolinate, thiocyanate, mercaptosuccinic acid, mercaptoacetic acid, 2-mercaptopropionic acid, 2-aminoethanethiol, 2-mercaptoethanol, and the like. Examples thereof include glucose cysteine, 1-thioglycerol, sodium mercaptopropanesulfonate, N-acetylmethionine, thiosalicylic acid, ethylenediamine tetraacetic acid (EDTA), pyrophosphate and the like. As the complexing agent, it is preferable to use a non-cyanide complexing agent from the viewpoint of handling, environment and toxicity, and it is preferable to use a sulfite among the non-cyanide complexing agents.

The content of the complexing agent in the electroless gold plating solution is preferably 1 g / L or more and 200 g / L or less, and more preferably 20 g / L or more and 50 g / L or less. The upper limit value and the lower limit value of these numerical values can be arbitrarily combined to define a preferable range. When the content of the complexing agent is 1 g / L or more, the gold complexing force is increased and the stability of the plating solution can be improved. When the content of the complexing agent is 200 g / L or less, the formation of recrystallization in the plating solution can be suppressed.

The electroless gold plating solution may contain additives as required. Examples of the additive include a pH buffer and a stabilizer.

The pH buffer can adjust the precipitation rate to a desired value and can keep the pH of the plating solution constant. One type of pH buffer may be used alone, or two or more types may be used in combination. Examples of the pH buffer include phosphates, acetates, carbonates, borolates, citrates and the like.

The pH of the electroless gold plating solution is preferably 5.0 or more and 8.0 or less, more preferably 6.0 or more and 7.8 or less, and preferably 6.8 or more and 7.5 or less. Especially preferable. The upper limit value and the lower limit value of these numerical values can be arbitrarily combined to define a preferable range. When the pH is 5.0 or more, the stability of the plating solution tends to be improved. When the pH is 8.0 or less, corrosion of the base material as the base metal can be suppressed. The pH can be adjusted, for example, by adding potassium hydroxide, sodium hydroxide, ammonium hydroxide and the like.

Stabilizers can improve the stability of the plating solution. Examples of the stabilizer include a thiazole compound, a bipyridyl compound, a phenanthroline compound and the like.

As the electroless gold plating solution, a commercially available one may be used. Examples of commercially available products include Epitaph TDS-25, TDS-20 (Uyemura & Co., Ltd.), Flash Gold (manufactured by Okuno Pharmaceutical Industry Co., Ltd.), and the like.

(Porous membrane)
The porous film used in the present embodiment is not particularly limited as long as it can contain the above-mentioned electroless gold plating solution. The porous film may be in the form of a film such as a separator, or may be formed of fibers such as a non-woven fabric.

The porous member membrane is a membrane having a porous structure (tissue) having a large number of pores (particularly open pores) inside. Examples of the porous film include a foam having a sponge-like network skeleton, a particle aggregate in which particles are bonded to each other, and a fiber aggregate represented by a woven or knitted fabric or a non-woven fabric.

Examples of the material of the porous film include resin, metal, glass, ceramics and the like, but resin is preferable. Examples of the resin include a fluorine-based resin such as polytetrafluoroethylene and a polyolefin-based resin.

As the porous membrane, a commercially available one may be used. Examples of commercially available products include "Poreflon (registered trademark) membrane" and the like.

The average pore diameter of the porous membrane is, for example, 0.05 μm or more and 100 μm or less, and preferably 0.1 μm or more and 80 μm or less. The upper limit value and the lower limit value of these numerical values can be arbitrarily combined to define a preferable range. When the average pore diameter is within the above range, the porous film can be impregnated with a sufficient amount of electroless gold plating solution.

The film thickness of the porous membrane is preferably 10 μm or more and 200 μm or less, and more preferably 20 μm or more and 160 μm or less. The upper limit value and the lower limit value of these numerical values can be arbitrarily combined to define a preferable range. When the film thickness of the solid electrolyte membrane is 10 μm or more, the solid electrolyte membrane is not easily torn and the durability is excellent. When the thickness of the solid electrolyte film is 200 μm or less, the pressure required for the electroless gold plating solution to pass through the solid electrolyte film can be reduced.

As one embodiment, the porous membrane may have an ion exchange functional group. Examples of the ion exchange functional group include an anionic group capable of capturing a metal ion, a cationic group capable of capturing an anion, and the like, and it is preferable to have an anionic group.

The anionic group is not particularly limited, but is, for example, a sulfonic acid group, a thiosulfonic acid group (-S ₂ O ₃ H), a carboxy group, a phosphoric acid group, a phosphonic acid group, a hydroxy group, a cyano group and a thiocyano group. At least one selected from.

(Base material)
The base material used in this embodiment is an object to be plated, and is not particularly limited. The substrate is usually composed of metal. The metal constituting the base material is not particularly limited as long as it is a metal having a higher ionization tendency than gold, and may be, for example, copper, nickel, cobalt, palladium, or an alloy containing at least two of these. In one embodiment, the substrate is nickel or nickel alloy. When the base material is nickel or a nickel alloy, gold plating can be easily formed by the substitutional electroless plating method. The base material may contain components other than metal. For example, when the substrate is nickel, it may contain phosphorus (P). In one embodiment, the substrate may be another substrate plated with metal. For example, the base material may be another base material such as copper obtained by electroless Ni-P plating.

The substrate can have any shape. Examples of the shape of the base material include a plate-like object such as a flat plate or a curved plate, a rod-like object, a spherical object, and the like. Further, the object to be plated may be one that has been finely processed such as grooves and holes, and is, for example, wiring for electronic industrial parts such as a printed wiring board, an ITO substrate, and a ceramic IC package substrate. May be good. The base material may be a plating film formed on a product such as a resin product, a glass product, a ceramic component, or a metal component.

(Contact process)
The method for forming the gold plating film of the present embodiment includes a step of bringing the porous film containing the electroless gold plating solution into contact with the surface of the base material. The process is also referred to as a contact process.
In the contacting step, a gold-plated film is formed on the base material by depositing gold on the base material.
The contact step can be carried out by the following method using, for example, the following film forming apparatus.

The film forming apparatus used in this embodiment is a film forming apparatus for forming a gold plating film on a base material by a substitution type electroless plating method, and is arranged in contact with the porous film and the porous film. The plating solution chamber for accommodating the electroless gold plating solution and the pressing means for bringing the porous film into contact with the substrate by relatively pressing the plating solution chamber and the substrate are provided. It is a membrane device. The pressing force at the time of pressing is not particularly limited, and is preferably 0.05 MPa or more and 5 MPa or less, and preferably 0.1 MPa or more and 1 MPa or less. The upper limit value and the lower limit value of these numerical values can be arbitrarily combined to define a preferable range. Further, it is preferable that the film forming apparatus used in the present embodiment is provided with a cleaning means for cleaning the porous film.

The film forming apparatus can supply the electroless gold plating solution to the substrate through the porous film by pressing the porous film against the substrate by the pressing means. Then, the metal of the base material becomes ions and dissolves in the electroless gold plating solution, and the gold ions derived from the electroless gold plating solution are reduced and deposited on the surface of the base material to form a gold plating film.

Further, the method for forming a gold plating film according to the present embodiment also has an effect that the gold plating film can be formed by using a small amount of gold plating solution. That is, in the conventional electroless gold plating method, a gold plating film is generally formed on the object to be plated by immersing the object to be plated in a gold plating solution. In order to immerse the object to be plated in the gold plating solution, it is necessary to use a relatively large amount of gold plating solution. On the other hand, since the amount of the gold plating solution used in the method for forming the gold plating film according to the present embodiment is substantially only the amount of impregnating the porous film, the amount used for immersing the conventional base material. Less than. Therefore, the method according to the present embodiment can form a gold plating film by using a small amount of gold plating solution.

In the method for forming a gold plating film according to the present embodiment, the sulfate ion concentration (sulfate ion concentration / sulfate ion concentration) with respect to the sulfate ion concentration of the electroless gold plating solution remaining on the surface of the porous film after the contacting step is determined. It is 16.0 or less, preferably 14.0 or less, more preferably 13.0 or less, particularly preferably 12.0 or less, and most preferably 11.0 or less. The lower limit is not particularly limited, and examples thereof include 0.5 or more and 1.0 or more. In the method for forming a gold-plated film according to the present embodiment, it is possible to prevent the porous film from being clogged with gold fine particles by setting the sulfate ion concentration / sulfite ion concentration to 16.0 or less.

The plating temperature (temperature of the plating solution chamber) in electroless gold plating is, for example, 50 ° C. or higher and 95 ° C. or lower, preferably 60 ° C. or higher and 90 ° C. or lower. The upper limit value and the lower limit value of these numerical values can be arbitrarily combined to define a preferable range. When the plating temperature is 50 ° C. or higher, the precipitation rate of the gold plating film can be improved. Further, when the plating temperature is 95 ° C. or lower, decomposition of components in the plating solution can be suppressed.

The plating time depends on the plating temperature, but is, for example, 1 to 60 minutes.

(Recovery process)
The method of continuously forming the gold-plated film, which is one aspect of the present embodiment, includes a step of recovering the base material on which the gold-plated film is formed after the step of contacting. The process is also referred to as a recovery process. The method of recovery is not particularly limited as long as the base material on which the gold-plated film is formed can be recovered by the contact step.

In the method of continuously forming the gold-plated film, which is one aspect of the present embodiment, the gold-plated film can be continuously formed on a plurality of substrates by repeating the contact step and the recovery step. When the contact step and the recovery step are performed and the next contact step is performed, the gold plating film can be continuously formed on the plurality of substrates by replacing the substrate.

(Washing process)
In the method of continuously forming a gold-plated film, which is one aspect of the present embodiment, at least one of after the contacting step and before the collecting step, and after the collecting step and before the contacting step. It includes a step of cleaning the electrolytic-free gold plating solution remaining on the surface of the porous film. The process is also referred to as a cleaning process.

According to the study by the present inventors, the sulfate ion concentration (sulfate ion concentration / sulfate ion concentration) with respect to the sulfate ion concentration of the electrolyzed gold plating solution remaining on the surface of the porous film after the contacting step by providing the cleaning step. ) Can be suppressed, and the contact step and the recovery step can be efficiently repeated. Therefore, by providing the cleaning step, the productivity can be improved and the cost can be reduced as compared with the case where the porous membrane is replaced every time the contact step is performed once or several times.

The cleaning step may be performed after the contact step and before the recovery step, or after the recovery step and before the contact step. If it is performed after the contact step and before the recovery step, the electroless gold plating solution remaining on the surface of the base material on which the gold plating film is formed may be washed at the same time.

The cleaning step may be performed every time the contact step is performed, or may be performed after the contact step is performed a plurality of times, but it is preferable to perform the cleaning step every time the contact step is performed.

The washing can usually be carried out using a liquid such as water or alcohol, and water is preferable. As the water, it is preferable to use purified water (pure water), for example, ion-exchanged water, distilled water, or the like.

The temperature of the liquid used for cleaning is usually 10 to 90 ° C, preferably 15 to 50 ° C. The upper limit value and the lower limit value of these numerical values can be arbitrarily combined to define a preferable range. The above range is preferable because it has an excellent balance between cost and detergency.

When the gold plating film is continuously formed, the sulfate ion concentration / sulfate ion concentration increases, but by providing the cleaning step, the increase can be suppressed as compared with the case where the cleaning step is not performed. According to the study by the present inventors, the increase in the sulfate ion concentration / sulfate ion concentration is moderated by performing the cleaning step, but the increase is completely completed when the repeated contact step, the recovery step, and the cleaning step are performed. It was found that it is difficult to suppress this, and the sulfate ion concentration / sulfate ion concentration may gradually increase. Further, if the sulfate ion concentration / sulfite ion concentration is equal to or less than a predetermined value (16.0), the porous film will not be clogged with gold fine particles even if the concentration is increased, but if it exceeds the predetermined value, the porous film is porous. It was found that the film was clogged with gold fine particles and discoloration of the porous film was observed. Therefore, when the sulfate ion concentration / sulfate ion concentration reaches a predetermined value or approaches a predetermined value, the gold-plated film should be suitably formed by taking measures such as replacing the porous film. Can be done.

The cleaning method is not particularly limited. For example, a shower head may be used to wash away the electroless gold plating solution remaining on the surface of the porous film, and a cleaning bath or a cleaning tank is provided to provide the porous film. (For example, the porous film installed and arranged in the plating solution chamber) may be immersed in a washing bath or a washing tank.

Hereinafter, one embodiment of the present embodiment will be described together with a configuration example of the film forming apparatus. FIG. 1 is a schematic cross-sectional view for explaining a state of the film forming apparatus 1 at the time of film formation. The film forming apparatus 1 used in the present embodiment is an apparatus for forming a gold plating film by a substitution type electroless plating method, and gold is transferred onto the base material 3 by reducing gold ions derived from the electroless gold plating solution 2. A gold-plated film is formed on the surface of the base material 3 which is the object to be plated.

In the film forming apparatus 1, the porous film 4, the plating solution chamber 5 for accommodating the electrolytic-free gold plating solution 2 arranged in contact with the porous film 4, and the plating solution chamber 5 and the base material 3 are relative to each other. (Not shown) is provided with a pressing means (not shown) that brings the porous film 4 into contact with the base material 3 by pressing against. The plating solution chamber 5 is formed by a housing 6. The porous film 4 is attached to the open end of the housing 6, and together with the housing 6, the electroless gold plating solution 2 is housed in the plating solution chamber 5. That is, the housing 6 has a plating solution chamber 5 for accommodating the electroless gold plating solution 2, and has an opening on the base material 3 side of the plating solution chamber 5. The porous membrane 4 is attached to the housing 6 so as to seal the opening of the housing 6. Further, the film forming apparatus 1 may include a mounting table 7 on which a base material is placed. Further, the film forming apparatus 1 is provided with a pressing means (not shown) on the upper part of the housing 6 via a cushioning member (not shown) such as a spring. The pressing means may be, for example, a hydraulic or pneumatic cylinder. As a result, the porous film 4 can be pressed against the surface of the base material 3 to form a gold-plated film. Further, the porous film 4 can be gently pressed against the surface of the base material 3 by the cushioning member (not shown). The film forming apparatus 1 is provided with a shower head 8 for cleaning the electroless gold plating solution remaining on the surface of the porous film. By applying a liquid such as water to the porous film via the shower head 8, the electroless gold plating solution remaining on the surface of the porous film can be washed. The film forming apparatus 1 does not require an electrode such as an anode.

FIG. 2 shows a schematic cross-sectional view for explaining the state of the film forming apparatus 1 at the time of cleaning. FIG. 2 is a schematic cross-sectional view showing a case where the plating solution chamber 5 moves upward after the contact step and the cleaning step is performed after the recovery step is performed. In the cleaning step, the remaining electroless gold plating solution 10 is washed, but the remaining electroless gold plating solution 10 may remain on the mounting table 7, for example, in addition to the surface of the porous film 4. It is preferable that these are also washed. Cleaning is performed by applying the liquid 9 to the porous membrane 4 or the like via the shower head 8. The arrow 11 in FIG. 2 means the flow direction of the liquid 9 and the residual electroless gold plating liquid 10 at the time of cleaning.

Hereinafter, another embodiment of the present embodiment will be described together with a configuration example of the film forming apparatus. The film forming apparatus shown in FIG. 3 has two head portions having an electroless gold plating solution 2, a porous film 4, a plating solution chamber 5, and a housing 6. The number of heads may be plural, and may be three or more. FIG. 3 is a schematic cross-sectional view for explaining a state in which one head (head on the left side of FIG. 3) of the film forming apparatus 1 is in a state at the time of film formation and the other head (head on the right side in FIG. 3) is in a state at the time of cleaning. It is a figure. The film forming apparatus 1 used in the present embodiment is an apparatus for forming a gold plating film by a substitution type electroless plating method, and gold is transferred onto the base material 3 by reducing gold ions derived from the electroless gold plating solution 2. A gold-plated film is formed on the surface of the base material 3 which is the object to be plated. Further, the film forming apparatus 1 used in the present embodiment has a plurality of heads, and when forming a film using one head, it is possible to clean the porous film constituting another head. .. That is, in the present embodiment, the contact step and the cleaning step can be performed simultaneously by using the two heads. Further, the two heads are connected by a connecting portion 12. In some embodiments, the connecting portion 12 may not be provided. When the connecting portion 12 is not provided, the film forming apparatus is usually configured so that each head can be moved independently.

In the film forming apparatus 1, the porous film 4, the plating solution chamber 5 for accommodating the electrolytic-free gold plating solution 2 arranged in contact with the porous film 4, and the plating solution chamber 5 and the base material 3 are relative to each other. That is, by pressing one head (head on the left side of FIG. 3) and the base material 3 relatively, a pressing means (not shown) for bringing the porous film 4 into contact with the base material 3 is provided. Be prepared. Further, in the film forming apparatus 1, when the porous film 4 constituting one head is in contact with the base material 3, the porous film 4 constituting the other head (head on the right side of FIG. 3) is liquid 13. It is soaked in and washed.

Further, the film forming apparatus 1 may include a mounting table (not shown) on which the base material is placed. Further, the film forming apparatus 1 is provided with a pressing means (not shown) on the upper part of the connecting portion 12 via a cushioning member (not shown) such as a spring. The pressing means may be, for example, a hydraulic or pneumatic cylinder. As a result, the porous film 4 can be pressed against the surface of the base material 3 to form a gold-plated film. Further, the porous film 4 can be gently pressed against the surface of the base material 3 by the cushioning member (not shown). The film forming apparatus 1 does not require an electrode such as an anode.

After the contact step and the cleaning step in FIG. 3 are completed, the two heads can be moved upward by moving the connecting portion 12 upward, and the recovery step can be performed. FIG. 4 shows the connecting portion 12 rotated by 180 ° about a substantially vertical axis before or after the recovery step. That is, the head on the right side in FIG. 4 is the head on the left side in FIG. 3, and the head on the left side in FIG. 4 is the head on the right side in FIG. In FIG. 4, the residual electroless gold plating solution 10 is present on the surface of the porous film 4 of the right head. On the other hand, there is no base material below the head on the left side, and the base material is installed in the base material installation planned portion 14 before the next contact step. By moving the connecting portion 12 downward after setting the base material, the state shown in FIG. 3 can be obtained, and the next contact step and cleaning step can be performed.

Hereinafter, the present embodiment will be described with reference to examples, but the present disclosure is not limited to these examples.

(Base material)
An electroless Ni-P plated Cu block was used as the base material. The Ni-P film constituting the Cu block is an object to be gold-plated, that is, an object to be plated.

(Gold plating solution)
As the electroless gold plating solution, a gold plating solution (a sulfite substituted gold plating solution, Epitus (registered trademark) TDS-25, manufactured by Uemura Kogyo Co., Ltd.) was used. The gold plating solution contains sodium gold sulfite as a gold salt, sodium sulfite and EDTA salt as a complexing agent, and a phosphate as a pH buffer. The pH of the gold plating solution was 7.3, and the gold concentration was 1.5 g / L. A part of the gold plating solution was collected, diluted 1000 times, filtered with a syringe, and sulfurous acid ion (SO _3-2- ) was used with an ion chromatograph (ICS ^- 5000 manufactured by Nippon Dionex Corporation). And the ion concentration [ ^μS ] of sulfate ion (SO _4-2 ) was determined, and the sulfate ion concentration / sulfate ion concentration was calculated. This value was used as the initial value.

[Example 1]
(Formation of plating film)
Electroless plating was performed using a film forming apparatus 1 having the configuration shown in FIG. 1 and equipped with WPW-045-80 (pore diameter 0.45 μm, thickness 80 μm) manufactured by Sumitomo Electric Industries, Ltd. as the porous film 4. ..

First, the plating solution chamber 5 was filled with the gold plating solution, and the porous film 4 was impregnated with the gold plating solution. The temperature of the gold plating solution was set to 80 ° C. Next, the porous film 4 was pressed against the Ni-P film by a pressing means and brought into contact with the Ni-P film to form a gold-plated film on the Ni-P film. The film forming area was 18 × 35 mm, the pressing force was 0.3 kN, and the film forming time was 10 minutes.

(Sulfate ion concentration / sulfate ion concentration)
A part of the gold plating solution remaining on the surface of the porous film after plating was recovered with a dropper. After diluting the recovered gold plating solution 1000 times, it is filtered by a syringe, and an ion chromatograph (ICS-5000 manufactured by Nippon Dionex Co., Ltd.) is used to determine the ion concentration of sulfite ion and sulfate ion [μS]. Was obtained, and the sulfate ion concentration / sulfite ion concentration was calculated.

(Recovery and cleaning)
The gold-plated base material was recovered, and pure water was sprinkled on the porous membrane 4 from the shower head 8 to wash it.

In Example 1, no discoloration was observed in the porous film 4, and the porous film was not clogged with gold fine particles.

[Examples 2 to 4, Comparative Example 1]
In Example 1, after the first formation of the plating film, the recovery of the base material, and the cleaning of the porous film, the formation and base of the plating film using the new base material by the same method as in Example 1. The material was recovered and the porous membrane was washed repeatedly. A new base material was used to form the plating film each time.

In total, when the plating film was formed twice (Example 2), 20 times (Example 3), 40 times (Example 4), and 80 times (Comparative Example 1), the porosity after plating was performed. A part of the gold plating solution remaining on the surface of the film was recovered with a dropper, and the sulfate ion concentration / sulfate ion concentration was determined and used as Examples 2, 3, 4, and Comparative Example 1.

At the time points of Examples 2, 3 and 4, no discoloration was observed in the porous film 4, and the porous film was not clogged with gold fine particles. On the other hand, at the time of Comparative Example 1, discoloration was observed in the porous film 4, and the porous film was clogged with gold fine particles.

[Comparative Example 2]
The plating film is formed, the base material is recovered, the plating film is formed using a new base material, and the base material is recovered by the same method as in Example 1 except that the porous film is not washed. Was repeated.

When the plating film was formed 10 times in total, a part of the gold plating solution remaining on the surface of the porous film after plating was recovered with a dropper, and the sulfate ion concentration / sulfite ion concentration was determined.

The results of Examples and Comparative Examples are summarized in Table 1 and FIG.

From Examples and Comparative Examples, when the sulfate ion concentration / sulfate ion concentration) is 16.0 or less, the porous film is not colored and it is possible to prevent the porous film from being clogged with gold fine particles. It was confirmed that.

Although the present embodiment has been described in detail above, the specific configuration is not limited to this embodiment, and even if there are design changes within the scope of the gist of the present disclosure, they are included in the present disclosure. It is a thing.

Claims (1)

It is a method of forming a gold plating film on a substrate by a displacement type electroless plating method.
A step of bringing a porous film containing an electroless gold plating solution into contact with the surface of the base material is included.
The electroless gold plating solution contains at least gold sulfite,
A method in which the sulfate ion concentration (sulfate ion concentration / sulfite ion concentration) with respect to the sulfite ion concentration of the electroless gold plating solution remaining on the surface of the porous film after the contacting step is 16.0 or less.

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