JP2013091833A - Reducing electroless silver plating solution and reducing electroless silver plating method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a reducing electroless silver plating solution that can form a plated film having favorable film characteristics and a favorable appearance by preventing decomposition of the silver to maintain the stability of the silver in the plating solution and by preventing an underlying metal or the like from becoming excessively roughened; and a reducing electroless silver plating method using the silver plating solution.SOLUTION: The reducing electroless silver plating solution contains an aqueous silver salt and a reducing agent, and contains cyanide ions at 0.006×10to 12.5×10mol/L.

Description

  The present invention relates to a reduced electroless silver plating solution and a reduced electroless silver plating method. More specifically, the solution is stable and a good plating film can be formed without excessively roughening a base metal or the like. The present invention relates to a reduced electroless silver plating solution and a reduced electroless silver plating method using the silver plated solution.

  Silver plating has been used for decorative purposes in the past, and in recent years it has been widely used in the fields of electrical industry, optical industry, other electromagnetic shielding, sterilization coating, etc., taking advantage of its electrical properties and high reflectance. ing. Among them, electroless silver plating is widely used in that the film thickness can be controlled and a plating film having a required film thickness can be easily formed.

  Electroless silver plating is roughly divided into a substitution type and a reduction type. Substitutional electroless silver plating is relatively excellent as a plating solution and is widely used in the market (see, for example, Patent Documents 1 and 2). However, substitutional electroless silver plating has a problem that the base substrate is limited because silver plating is deposited by a substitution reaction with the base metal.

  On the other hand, reduction type electroless silver plating is a method in which a reducing agent is contained in a plating solution, and a water-soluble silver compound is reduced to metallic silver to deposit silver plating on the underlying metal. A good silver plating film can be formed without roughening the surface and without limiting the type of the base material.

  The reduced electroless silver plating solution contains a silver cyanide compound such as potassium silver cyanide as a water-soluble silver salt, particularly from the viewpoint of the stability of the solution. When this silver cyanide compound is used as a water-soluble silver salt, generally, cyan of a molar ratio of 2 times or more with respect to silver is contained in the plating solution.

  In addition, in the reduced electroless silver plating solution, a method of improving the stability of the solution by adding a cyanide compound such as potassium cyanide has been proposed, and a large amount of free cyanide is present in the plating solution. (For example, Patent Document 3 and Non-Patent Document 1).

  However, although excess cyan present in these conventional plating solutions can suppress the decomposition of silver in the plating solution and enhance the stability as described above, for example, a metal made of nickel or copper, etc. The object to be plated is dissolved and the surface thereof is excessively roughened, and a plating film having good film characteristics cannot be formed.

  On the other hand, in recent years, cyan-free reduced electroless silver plating solutions have also been proposed (for example, Patent Documents 4 and 5). However, in such a cyan-free electroless silver plating solution, since cyan does not exist in the plating solution, the surface metal is not excessively roughened by dissolving the base metal or the like, but compared with a plating solution containing cyan. Stability is significantly inferior. For example, as described in Patent Documents 4 and 5, a technique for improving stability by adding an additive in a cyan-free silver plating solution has also been proposed, but it still has sufficient stability. Absent. Further, in such a cyan-free electroless silver plating, as the film thickness is increased, a yellowish silver film is formed, and there is a problem in the appearance of the plating film.

JP 2000-309875 A JP 2002-180259 A JP-A-5-279863 Japanese Patent No. 3937373 JP 2003-268558 A

“Electroless plating basics and applications” edited by Nikkan Kogyo Shimbun p176-177

  Therefore, the present invention has been made in view of the above-described conventional situation, and prevents the decomposition of silver in the plating solution to maintain stability, and the metal or the like of the plating base is excessively roughened. Provided is a reduced electroless silver plating solution capable of forming a plating film having good film characteristics and good appearance, and a reduced electroless silver plating method using the silver plating solution The purpose is to do.

  As a result of intensive studies in order to solve the above-described object, the present inventors maintain the stability of the plating solution by controlling the cyan concentration in the plating solution, and excessively roughen the base metal and the like. The inventors have found that a plating film having good film characteristics and excellent appearance can be formed, and the present invention has been completed.

That is, the reduced electroless silver plating solution according to the present invention is a reduced electroless silver plating solution containing a water-soluble silver salt and a reducing agent, and is 0.006 × 10 ⁻³ mol / L to 12. Contains 5 × 10 ⁻³ mol / L of cyanide ion.

  In the reduced electroless silver plating solution according to the present invention, the water-soluble silver salt is preferably a silver salt other than a cyanide compound, and the cyanide ion is preferably contained as an alkali metal cyanide.

  In the reduced electroless silver plating solution according to the present invention, the reducing agent is preferably at least one selected from hydroxylammonium sulfate and hydroxylammonium acetate.

  Further, the reduced electroless silver plating solution according to the present invention preferably has a pH of 8 to 11.

Moreover, the reduced electroless silver plating method according to the present invention is a reduced electroless silver plating solution containing a water-soluble silver salt and a reducing agent, and is 0.006 × 10 ⁻³ mol / L to 12. Electroless silver plating is applied to an object to be plated using a reduced electroless silver plating solution containing cyanide ions at 5 × 10 ⁻³ mol / L.

  According to the reduced electroless silver plating solution and the reduced electroless silver plating method according to the present invention, the decomposition of silver in the plating solution is prevented to improve the stability of the solution, and the plating base and It is possible to prevent an excessively roughened object to be plated such as a metal, and to form a plating film having good film characteristics and excellent appearance.

It is a graph which shows the relationship of the film thickness of the plating film with respect to the plating time when a reducing agent is changed.

  Hereinafter, a specific embodiment (hereinafter referred to as “this embodiment”) of the reduced electroless silver plating solution according to the present invention will be described in detail.

  The reduced electroless silver plating solution according to the present embodiment is a reduced electroless silver plating solution containing a water-soluble silver salt and a reducing agent, and the water-soluble silver salt is reduced to metallic silver by the reducing agent. Then, a silver plating film is formed by depositing silver plating on an object to be plated such as a base metal.

In the reduced electroless silver plating solution according to the present embodiment, the plating solution containing a water-soluble silver salt and a reducing agent contains cyanide ions prepared in a predetermined concentration range. It is said. Specifically, containing cyanide ions ^{0.006 × 10 -3 mol / L~12.5 ×} 10 -3 mol / L.

  Conventionally, a reduced electroless silver plating solution to which a water-soluble silver salt such as potassium potassium cyanide or a cyanide compound such as potassium cyanide is added as an additive has excellent liquid stability, but is made of, for example, copper or nickel. It was not possible to form a plating film having good film characteristics by excessively dissolving and roughening the metal or the like of the plating base.

  On the other hand, cyan-free plating solutions have also been developed in order to avoid excessive dissolution of the base metal, etc., but silver plating solutions with particularly low solution stability can be made free of cyan by using cyan-free plating solutions. The silver was rapidly decomposed and the stability of the plating solution was significantly impaired. Further, with such a cyan-free plating solution, a yellowish plating film is formed, and a plating film having a good appearance cannot be formed. Such a silver plating film having a poor appearance has also caused a decrease in reflectance when used for an LED device, for example.

In contrast, the reduction type electroless silver plating solution according to the present embodiment, the cyanide ions ^{0.006 × 10 -3 mol / L~12.5 ×} 10 -3 mol / L in the plating solution It is made to contain.

  According to such a reduced electroless silver plating solution, only the advantages of both an electroless silver plating solution using a conventional cyan compound and a cyan-free electroless silver plating solution can be obtained, and the stability of the solution is high. A plating film having excellent film characteristics can be formed without excessively roughening the object to be plated such as a base metal. Moreover, according to this reduced electroless silver plating solution, a beautiful white silver plating film is obtained and has a good appearance. For example, when applied to an LED device, the reflection characteristics can be improved. It becomes.

Here, when the content of cyanide ions is less than 0.006 × 10 ⁻³ mol / L, silver in the plating solution is decomposed and the stability of the solution is deteriorated. Further, as the plating film becomes thicker, the film becomes yellowish, and a plating film having a good appearance cannot be formed. On the other hand, when the content is more than 12.5 × 10 ⁻³ mol / L, the object to be plated made of metal or the like serving as the plating base is dissolved and excessively roughened by cyan existing in the plating solution. Therefore, even if a plating film is formed on the object to be plated, a plating film having good film characteristics cannot be obtained.

  Although it does not specifically limit as a cyanide ion source, For example, alkali metal cyanides, such as potassium cyanide and sodium cyanide, can be used. Further, a silver cyanide compound such as potassium silver cyanide may be used as a water-soluble silver salt, and this may be contained as part or all of the cyanide ion source so as to have the above-described content.

  Among these cyanide ion sources, it is particularly preferable to use an alkali metal cyanide. By using an alkali metal cyanide, the cyanide ion concentration can be appropriately and easily adjusted within the above-mentioned concentration range, and more efficiently and effectively maintaining the stability of the liquid and improving the film properties. A good plating film can be formed. Moreover, it is not necessary to add at any time even in continuous use, and the amount of silver in the plating solution does not increase and stability is not impaired as in the case of adding as a silver cyanide compound.

  In the reduced electroless silver plating solution according to the present embodiment, the water-soluble silver salt is not particularly limited as long as it is soluble in the plating solution. For example, silver nitrate, silver oxide, silver sulfate, silver chloride, sulfite Silver, silver carbonate, silver acetate, silver lactate, silver sulfosuccinate, silver sulfonate, silver sulfamate, silver oxalate and the like can be used. Further, as described above, a silver cyanide compound such as silver potassium cyanide may be used as the water-soluble silver salt. These water-soluble silver salts can be used alone or in combination of two or more.

The content of water-soluble silver salt, preferably to 0.1g / L~10g / L (0.9 × 10 -3 mol / L~90 × 10 -3 mol / L) as the silver concentration, 0 .1g / L~3.0g / L and more preferably in the ^{(0.9 × 10 -3 mol / L~30} × 10 -3 mol / L). By setting the content of the water-soluble silver salt in the range of 0.1 g / L to 10 g / L as the silver concentration, the deposition rate of silver plating can be improved and a more stable plating solution can be obtained. .

When a silver cyanide compound is used as the water-soluble silver salt, the content of the cyanide compound to be added or the cyanide compound to be added as the silver cyanide compound and the additive is the above-mentioned cyanide ion concentration. range, i.e. is contained so as to be ^{0.006 × 10 -3 mol / L~12.5 ×} 10 -3 mol / L.

  The reducing agent is not particularly limited as long as it is capable of reducing a water-soluble silver salt in a plating solution to metallic silver and is a water-soluble compound. For example, hydrazine and its derivatives, formaldehyde compounds, hydroxylammonium salts Saccharide, Rossell salt, borohydride compound, hypophosphite, DMAB (dimethylamine borane), ascorbic acid and the like can be used. These reducing agents can be used alone or in combination of two or more.

  Among these reducing agents, it is particularly preferable to use hydroxylammonium salts such as hydroxylammonium sulfate and hydroxylammonium acetate. The reason is that according to these reducing agents, the plating film thickness can be easily changed by controlling the plating time. This is because a plating film having characteristics can be easily formed.

  More specifically, in the reduced electroless silver plating solution according to the present embodiment, as described above, cyanide ions are controlled within a predetermined concentration range in order to prevent excessive dissolution of the base metal and the like. doing. Therefore, when a reducing agent such as DMAB having a stronger reducing power is used, silver in the plating solution may be decomposed. In that respect, by using a hydroxylammonium salt such as hydroxylammonium sulfate or hydroxylammonium acetate, it is possible to prevent decomposition of silver in the plating solution and to cause a reduction reaction stably.

  In addition, when a reducing agent having a weaker reducing power such as hydrazine or formaldehyde is used, the deposition rate of silver is slow, so that a portion of the surface of the base metal or the like where silver is not deposited exists for a long time. Therefore, cyan in the plating solution may act on this portion and dissolve excessively. In this respect as well, by using hydroxylamines such as hydroxylammonium sulfate and hydroxylammonium acetate, it is possible to reliably deposit silver plating by a reduction reaction without dissolving the base metal, etc. Thus, the base metal or the like can be coated with a silver plating having a desired film thickness, and a plating film having good film characteristics can be formed.

  As described above, according to hydroxylammonium sulfate and hydroxylammonium acetate, a plating film having a desired film thickness can be easily formed, and the stability of the liquid is further improved. In this way, it is possible to form a plating film with good film characteristics more effectively.

  As content of a reducing agent, it is preferable to set it as 0.006 mol / L-0.12 mol / L, for example, and it is more preferable to set it as 0.006 mol / L-0.03 mol / L. When the content of the reducing agent is less than 0.006 mol / L, there is a possibility that the water-soluble silver salt in the plating solution cannot be reduced to metallic silver and sufficient silver plating cannot be deposited. On the other hand, if it is more than 0.12 mol / L, it may adversely affect the stability of the plating solution and is not preferable economically.

  The reduced electroless silver plating solution according to the present embodiment can be used in the range of 0 to 80 ° C. as the solution temperature, and particularly when used at about 30 to 60 ° C., the stability of the plating solution is further improved. Can be improved. If the temperature of the plating solution is too low, the silver deposition rate is slow and a long time is required to obtain a predetermined amount of silver deposition. On the other hand, if the temperature of the plating solution is too high, loss of the reducing agent due to the autolysis reaction and deterioration of the plating solution stability are likely to occur.

  Further, the pH of the reduced electroless silver plating solution can be used in the range of 2 to 14, but since the cyanide ion at a predetermined concentration is contained as described above, the pH is particularly set to 8 to 11. It is preferable to set it as the range. By setting the pH of the plating solution to 8 or more, generation of cyan gas can be effectively suppressed, and the plating solution can be used safely without adversely affecting the environment. In addition, the stability of the plating solution can be further improved. Further, by adjusting the pH to 11 or less, the stability of the plating solution and the film characteristics of the plating film can be further improved.

  The pH of the plating solution is usually adjusted by lowering the pH by using an acid having an anion portion of the same kind as the water-soluble silver salt, for example, sulfuric acid or water-soluble silver when silver sulfate is used as the water-soluble silver salt. When silver nitrate is used as the salt, nitric acid is used. On the other hand, when raising the pH, alkali metal hydroxide such as sodium hydroxide, ammonia or the like is used.

  Moreover, in the reduced electroless silver plating solution according to the present embodiment, a complexing agent can be added as necessary. Although it does not specifically limit as a complexing agent, A sulfite, a succinimide, a hydantoin derivative, ethylenediamine, ethylenediaminetetraacetic acid (EDTA), etc. can be used. These complexing agents can be used alone or in combination of two or more.

  The addition amount of the complexing agent varies depending on the type and is not particularly limited, but is preferably about 1 g / L to 100 g / L. By setting the concentration of the complexing agent in such a range, the deposition rate of silver plating can be improved, and a plating solution having further excellent stability can be obtained.

  In addition, additives such as a known surfactant, pH adjuster, buffer, smoothing agent, stress relieving agent may be mixed as necessary.

  As a plating method using the reduced electroless silver plating solution having the above-described characteristics, for example, the object to be plated is immersed in the reduced electroless silver plating solution adjusted to the above-described solution temperature and pH value. Apply silver plating. Alternatively, a plating treatment may be performed by bringing the plating solution into contact with the object to be plated by spraying or applying a reduced electroless silver plating solution to the object to be plated.

  As described above, this electroless silver plating method mainly reduces a water-soluble silver salt to metallic silver by a reducing agent contained in a plating solution, and then performs silver plating on a metal or other object to be plated. A plating film is formed by precipitating.

  The object to be plated for forming the electroless silver plating film is not particularly limited, and is applied to metal materials such as copper and nickel, various other conductive materials, and non-conductive materials. Can do. When a metal material is to be plated, after pretreatment such as degreasing is performed according to a conventional method, the plated object is directly immersed in a plating solution.

  Further, in order to perform plating treatment on non-metallic materials such as ceramics and plastics, after pretreatment such as degreasing treatment, the object to be plated is activated, and then immersed in a plating solution. The activation treatment may be performed according to a conventional method, for example, using a palladium catalyst (a catalyst-accelerator method, a sensitizing-activator method, etc.), a silver catalyst, a copper catalyst, or the like according to known conditions. Do.

As described above, the reduced electroless silver plating solution according to the present embodiment is a reduced electroless silver plating solution containing a water-soluble silver salt and a reducing agent, and is 0.006 × 10 ^−3. It contains cyanide ions at mol / L to 12.5 × 10 ⁻³ mol / L. According to such a reduced electroless silver plating solution, it is possible to effectively prevent the decomposition of silver in the silver plating solution and to improve the stability of the solution, and to coat a metal such as a base metal. It is possible to prevent an object from being excessively roughened and to form a plating film having good film characteristics and excellent appearance.

  Hereinafter, specific examples of the present invention will be described. Note that the present invention is not limited to any of the following examples.

<Plating solution stability and plating film evaluation>
Reducing electroless silver plating solutions shown below were prepared.

Example 1
Silver nitrate is 9.0 × 10 ⁻³ mol / L (1.0 g / L) as silver concentration, hydroxylammonium salt (hydroxylammonium sulfate) 1.24 × 10 ⁻³ mol / L as reducing agent, and EDTA0 as complexing agent An aqueous solution containing 15 mol / L (50 g / L) and further adding 1 mg / L of potassium cyanide so that the cyanide ion concentration in the plating solution is 0.006 × 10 ⁻³ mol / L using caustic soda. The reduced electroless silver plating solution was adjusted to pH 9.0.

(Example 2)
A reduced electroless silver plating solution was prepared in the same manner as in Example 1 except that 300 mg / L of potassium cyanide was added to adjust the cyanide ion concentration in the plating solution to 1.8 × 10 ⁻³ mol / L. .

(Example 3)
A reduced electroless silver plating solution was prepared in the same manner as in Example 1 except that 500 mg / L of potassium cyanide was added to adjust the cyanide ion concentration in the plating solution to 3.0 × 10 ⁻³ mol / L. .

Example 4
A reduced electroless silver plating solution was prepared in the same manner as in Example 1 except that 1000 mg / L of potassium cyanide was added to adjust the cyanide ion concentration in the plating solution to 6.5 × 10 ⁻³ mol / L. .

(Example 5)
A reduced electroless silver plating solution was prepared in the same manner as in Example 1 except that 2000 mg / L of potassium cyanide was added so that the cyanide ion concentration in the plating solution was 12.5 × 10 ⁻³ mol / L. .

(Comparative Example 1)
Instead of silver nitrate, 9.0 × 10 ⁻³ mol / L (1.0 g / L) of silver potassium cyanide as a silver concentration was added, and 300 mg / L of potassium cyanide was further added, so that the total cyanide ions in the plating solution were added. A reduced electroless silver plating solution was prepared in the same manner as in Example 1 except that the concentration was 19.8 × 10 ⁻³ mol / L.

(Comparative Example 2)
Instead of silver nitrate, 9.0 × 10 ⁻³ mol / L (1.0 g / L) is added as the silver concentration of silver cyanide, and potassium cyanide is not added, and the cyanide ion concentration in the plating solution is 18.0. A reduced electroless silver plating solution was prepared in the same manner as in Example 1 except that x10 ⁻³ mol / L was used.

(Comparative Example 3)
A reduced electroless silver plating solution was prepared in the same manner as in Example 1 except that potassium cyanide was not added. That is, a cyan-free reduced electroless silver plating solution was prepared.

(Comparative Example 4)
A reduced electroless silver plating solution was prepared in the same manner as in Example 1 except that 2100 mg / L of potassium cyanide was added to adjust the cyanide ion concentration in the plating solution to 13.0 × 10 ⁻³ mol / L. did.

  Next, using the reduced electroless silver plating solution prepared as described above, reduced electroless silver plating was performed using a BGA substrate (manufactured by Uemura Kogyo Co., Ltd.) as an object to be plated.

Prior to the reduced electroless silver plating treatment, the steps shown in Table 1 below were sequentially performed as a pretreatment. That is, the BGA substrate as the object to be plated was subjected to a soft etching process with a 100 g / L sodium persulfate solution (SPS) after a cleaner process (degreasing) with ACL-738 (manufactured by Uemura Kogyo Co., Ltd.). . Subsequently, the etching residue is removed with a 10% sulfuric acid (H ₂ SO ₄ ) solution (pickling), a pre-dip treatment is performed with a 3% sulfuric acid solution, and then a Pd catalyst is applied with MNK-4 (manufactured by Uemura Kogyo Co., Ltd.) (Catalist). And after that, the metal film used as a foundation | substrate was formed using the electroless nickel liquid NPR-4 (made by Uemura Kogyo Co., Ltd.) and the electroless palladium liquid TPD-30 (made by Uemura Kogyo Co., Ltd.).

  The electroless silver plating treatment was performed by immersing the object to be plated in the above-described reduced electroless silver plating solution at 60 ° C. for 20 minutes. Then, after the plating treatment, the temperature was allowed to stand for 100 hours at 60 ° C., and the stability of the plating solution, and the solder joint strength and appearance of the plating film were evaluated by the presence or absence of self-decomposition of the plating solution. The evaluation results are shown in Table 2 below.

  In addition, the solder joint strength of the plating film is evaluated by reflow treatment at 240 ° C. once. When the solder breaking mode is 16 or more out of 20, the joint strength is good (◯) and less than 16 Was evaluated as poor bonding strength (x). Further, the appearance of the plating film was visually confirmed when the film thickness of the silver plating film was 0.5 μm.

As shown in Table 2, the reduction in Examples 1 to 5 to control the cyanide ion concentration in the plating solution in the range of ^{0.006 × 10 -3 mol / L~12.5 ×} 10 -3 mol / L The type electroless silver plating solution showed good solution stability without decomposition of silver in the plating solution. Moreover, in these Examples 1-5, the solder joint strength was strong and it was able to form the plating film which has a favorable film characteristic. Furthermore, the formed plating film was also white silver and had a beautiful appearance.

On the other hand, the comparison in which the cyanide ion concentration in the plating solution is 19.8 × 10 ⁻³ mol / L, 18.0 × 10 ⁻³ mol / L, and 13.0 × 10 ⁻³ mol / L, respectively. In the reduced electroless silver plating solutions in Examples 1, 2, and 4, although the decomposition of silver was prevented by excessive free cyanide in the plating solution, a plating film having poor solder joint strength and poor film characteristics was formed. This is presumably because the base metal was excessively dissolved and roughened by excessive free cyanide present in the plating solution.

  Further, in the reduced electroless silver plating solution in Comparative Example 3 in which the plating solution does not contain cyan but is cyan-free, although a plating film having high solder joint strength and good film characteristics is formed, cyan is not used. By not containing it, silver in the plating solution was decomposed, and the stability of the solution could not be secured. Further, when the reduced electroless silver plating solution of Comparative Example 3 was used, a yellowish yellow silver plating film was formed, resulting in a very poor appearance.

From the above results, by the cyanide ion concentration range of ^{0.006 × 10 -3 mol / L~12.5 ×} 10 -3 mol / L in the plating solution, the liquid to suppress the decomposition of silver It was found that a film having excellent appearance can be formed by precipitating white silver and forming a beautiful silver. Furthermore, it was found that by setting the cyanide ions in the above-mentioned concentration range, it is possible to prevent a metal material or the like serving as a plating base from being excessively roughened and to form a plating film having good film characteristics.

<About reducing agent>
Then, as described above in Examples 1-5, the reduction was controlled cyanide ion concentration in the range of ^{0.006 × 10 -3 mol / L~12.5 ×} 10 -3 mol / L type electroless silver plating In the liquid, preferred reducing agents were examined. In the experiment, the composition of Example 2 was used as a basic composition.

(Example 6)
Reduction in which the cyanide ion concentration is 0.006 × 10 ⁻³ mol / L in the same manner as in Example 2 except that hydrazine (hydrazine sulfate) 1.24 × 10 ⁻³ mol / L is added as a reducing agent. A type electroless silver plating solution was prepared.

(Example 7)
Reduced electroless silver having a cyanide ion concentration of 0.006 × 10 ⁻³ mol / L as in Example 2, except that 1.24 × 10 ⁻³ mol / L of formaldehyde was added as a reducing agent. A plating solution was prepared.

  Using the reduced electroless silver plating solution prepared in Example 2 and Examples 6 and 7, the relationship between the film thickness of the silver plating film and the plating time was examined. In FIG. 1, the graph about the measurement result of the film thickness with respect to the plating time when changing a reducing agent is shown.

  As shown in FIG. 1, in the electroless silver plating solution in Example 2 using a hydroxylammonium salt as a reducing agent, the film thickness of the silver plating film obtained by extending the plating time also increases substantially linearly. It can be seen that the film is formed by the silver deposition due to the reduction reaction. On the other hand, in Examples 6 and 7 using hydrazine or formaldehyde as a reducing agent, it can be seen that after a predetermined time has elapsed, the film thickness is not so thick. This is presumably because hydrazine and formaldehyde cause silver to be precipitated by the reduction reaction, but the factors due to the substitution reaction also work greatly, so that the base metal is slightly dissolved.

From this, in the reduced electroless silver plating solution in which the cyanide ion concentration was controlled in the range of 0.006 × 10 ⁻³ mol / L to 12.5 × 10 ⁻³ mol / L, hydroxylammonium sulfate as a reducing agent was used. And by using hydroxylammonium salts such as hydroxylammonium acetate, the reduction reaction can proceed more effectively, and a plating film with good film properties can be formed without causing dissolution of the underlying metal by the substitution reaction. I understood that I could do it.

Claims (5)

A reduced electroless silver plating solution containing a water-soluble silver salt and a reducing agent,
Reduced electroless silver plating solution containing cyanide ions of 0.006 × 10 ⁻³ mol / L to 12.5 × 10 ⁻³ mol / L.   The reduced electroless silver plating solution according to claim 1, wherein the water-soluble silver salt is a silver salt other than a cyanide compound, and the cyanide ion is contained as an alkali metal cyanide.   The reduced electroless silver plating solution according to claim 1 or 2, wherein the reducing agent is one or more selected from hydroxylammonium sulfate and hydroxylammonium acetate.   The reduced electroless silver plating solution according to any one of claims 1 to 3, which has a pH of 8 to 11.   A reduction type electroless silver plating method of applying electroless silver plating to an object to be plated using the reduction type electroless silver plating solution according to any one of claims 1 to 4.

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