JP5732224B2 - Reduced electroless silver plating solution - Google Patents

Description

  The present invention relates to a reduced electroless silver plating solution, and more particularly to a reduced electroless silver plating solution having excellent solution stability in a plating solution not containing a cyanide compound.

  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 necessary silver film thickness can be easily generated.

  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, reduced 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 and without limiting the type of the base material.

  However, most of the reported electroless silver plating solutions have been plating solutions using cyan as a complex. In recent years, there has been an emphasis on global warming, work environment improvement, and the like, and there is a need for a reduced electroless silver plating solution that does not contain a cyanide compound.

  However, in consideration of environmental problems, when a reduction-type electroless silver plating solution that does not contain a cyanide compound, so-called cyan-free, is considered, a problem arises in the stability of the plating solution. When the cyan compound is not contained as a complex, the silver compound in the plating solution is self-decomposed, and the plating solution cannot be stably held for a long period of time.

  In the past, in order to keep the cyan-free plating solution stable, for example, as described in Patent Document 3 or 4, a technique of adding a sulfur-based compound or iodine-based compound has been proposed, and the plating solution is stable. Although it has been reported that the stability has been maintained, it has not yet reached a level where sufficient stability can be maintained, and it is difficult to mass-produce and put it to practical use beyond a cyanide-containing plating solution It is.

JP 2000-309875 A JP 2006-316315 A Japanese Patent No. 3937373 JP 2003-268558 A

  Accordingly, the present invention has been made in view of such a conventional problem, and a reduced electroless silver plating having sufficient liquid stability in a reduced electroless silver plating solution not containing a cyanide compound. The purpose is to provide a liquid.

  As a result of intensive studies to solve the above problems, the present inventors have obtained excellent liquid stability even with a cyan-free reduced electroless silver plating solution by adding a specific amine compound. I found out that

That is, the reduced electroless silver plating solution according to the present invention contains 0.1 to 100 mg / l of a water-soluble silver compound, a reducing agent, and a compound represented by the following general formula (1) as a liquid stabilizer. It becomes.

(In the formula, R represents an alkyl group or an aryl group, and m and n are each an integer of 1 to 3.)

  According to the present invention, it is possible to provide a reduced electroless silver plating solution having excellent liquid stability without containing a cyanide compound.

  Hereinafter, the reduced electroless silver plating solution according to the present embodiment will be described in detail. The reduced electroless silver plating solution according to the present embodiment contains at least a water-soluble silver compound, a reducing agent, and a liquid stabilizer.

  The water-soluble silver compound is not particularly limited as long as it is soluble in the plating solution. For example, silver nitrate, silver oxide, silver sulfate, silver chloride, silver sulfite, silver carbonate, silver acetate, silver lactate, silver sulfosuccinate, Silver sulfonate, silver sulfamate, silver oxalate and the like can be used. These water-soluble silver compounds can be used alone or in combination of two or more.

  The content of the water-soluble silver compound is preferably 0.1 to 30 g / l as the silver concentration. By setting the concentration in the range of 0.1 to 30 g / l, the deposition rate of silver plating can be improved and a plating solution having good stability can be obtained.

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

  As content of a reducing agent, it is preferable to set it as 0.1-30 g / l, for example. When the content of the reducing agent is less than 0.1 g / l, the water-soluble silver compound 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 30 g / l, it adversely affects the stability of the plating solution and is not preferable economically.

  Further, the reduced electroless silver plating solution according to the present embodiment contains a compound represented by the following general formula (1) as a liquid stabilizer.

  Here, in the said General formula (1), R represents an alkyl group or an aryl group, and m and n are an integer of 1-3, respectively.

  As the compound represented by the general formula (1), a compound having a Cas number of 68603-67-8 can be more preferably used, and examples thereof include benzyldiethylenetriamine chloride.

  The amount of the liquid stabilizer added is not particularly limited, but is preferably 0.1 to 100 mg / l, for example. When the addition amount is less than 0.1 mg / l, the self-decomposition of the plating solution cannot be sufficiently suppressed, and the stability of the plating solution cannot be improved. On the other hand, when the addition amount is more than 100 mg / l, the effect of liquid stability cannot be further increased, which is not economical. Moreover, when there is too much addition amount, a plating deposition rate will fall and it will become impossible to form the silver plating film of the desired film thickness.

  Thus, the reduced electroless liquid silver plating solution according to the present embodiment adds the compound represented by the general formula (1) as a liquid stabilizer. Thereby, in the reduced electroless liquid silver plating solution according to the present embodiment, the self-decomposition of the silver compound in the plating solution can be suppressed, and the stability of the plating solution can be maintained over a long period of time.

  Although the mechanism by this liquid stabilizer is not certain, it is presumed that the plating liquid can be kept stable by the following two kinds of actions. That is, first, the compound, which is a liquid stabilizer in the plating solution, moves to the surface of the cathode (substrate), so that it is adsorbed on the cathode surface by the interaction between the cathode and the cation, thereby limiting the reaction field. Therefore, it is considered that the plating reaction is controlled and the plating solution can be stably maintained. In addition, since the compound has a pyramid type three-dimensional structure and can capture active and unstable silver ions in the plating solution and stabilize the silver ions, it suppresses the self-decomposition of the plating solution. Can be considered. Of course, because of the above functions, when the concentration of the compound increases, the reaction field decreases, and the active silver ions in the plating solution also extremely decrease, so the plating deposition rate decreases and is added excessively. Then the reaction stops.

  A sulfur-containing compound and / or an iodine-containing compound may be further added to the reduced electroless silver plating solution according to the present embodiment. Thus, by adding a sulfur-containing compound and / or an iodine-containing compound to the plating solution, the silver ions of the plating solution can be more effectively complexed to further improve the stability of the plating solution. it can.

  Although it does not specifically limit as a sulfur-containing compound, For example, thiourea, methylthiourea, tetramethylthiourea, 1-allyl-2 thiourea, ethylenethiourea, 1,1-diphenyl-2-thiourea, 1,3-dibutylthiourea 1,3-diethyl-2-thiourea, 1,3-dimethylthiourea, guanylthiourea, methylisothiourea sulfate, N-benzoylthiourea, N-methylthiourea, o-tolylthiourea, p-tolylthiourea, tetramethylthio Thiourea derivatives such as urea and trimethylthiourea, (2-mercaptoethyl) pyrazine, 2-mercapto-1-methylimidazole, 2-mercapto-5-benzimidazolecarboxylic acid, 2-mercapto-5-methoxybenzimidazole, 2-mercapto-5-methoxybenzothiazole, 5- Methyl-2-benzimidazolethiol, 2-mercapto-5-methylthio-1,3,4-thiadiazole, 2-mercapto-5-thiazolidone, 2-mercapto-6-nitrobenzothiazole, 2-mercaptobenzimidazole, 2- Mercaptobenzothiazole, 2-mercaptobenzothiazole, 2-mercaptoethanol, 2-mercaptonicotinic acid, 2-mercaptopyridine, 2-mercaptopyrimidine, 2-mercaptothiazoline, 3-amino-5-mercapto-1,2,4- Triazole, 3-mercapto-1,2,4-triazole, 3-mercapto-2-butanone, 3-mercapto-2-pentanone, 3-mercapto-4-methyl-4H-1,2,4-triazole, 3- Mercaptoisobutyric acid, 3-mercaptopropi Acid, isopropyl 3-mercaptopropionate, 3-methoxybutyl 3-mercaptopropionate, 4,6-diamino-2-mercaptopyrimidine, 4,6-dimethyl-2-mercaptopyrimidine, 4-amino-3-hydrazino- 5-mercapto-1,2,4-triazole, 4-mercaptobenzoic acid, 4-mercaptopyridine, 5-amino-2-mercaptobenzimidazole, 5-ethoxy-2-mercaptobenzimidazole, 5-mercapto- (1H) -Sodium tetrazolylacetate, 1H-1,2,3-triazole-5-thiol sodium, 6-amino-2-mercaptobenzothiazole, 8-mercaptoquinoline hydrochloride, mercaptoacetate ammonium, bis (2-mercaptoethyl) ether, Bis (2-mercaptoe L) Mercapto such as sulfide, ethyl 2-mercaptopropionate, ethyl 3-mercaptopropionate, methyl 3-mercaptopropionate, sodium 2-mercaptoethanesulfonate, sodium 3-mercapto-1-propanesulfonate, sodium mercaptoacetate 2,5,6-trimethylbenzothiazole, 2,5-dimethylbenzothiazole, 2- (2-hydroxyphenyl) benzothiazole, 2- (2-thienyl) benzothiazole, 2- (4-methoxyphenyl) Benzothiazole, 2- (methylthio) benzothiazole, 2- (methylthio) naphtho [1,2-d] thiazole, 2- (methylthio) thiazole, 2-acetamidothiazole, 2-acetylthiazole, 2-amino-4,5 -Dimethylthiazole, 2 -Amino-5-methylthiazole, 2-aminobenzothiazole, 2-aminothiazole, 2-ethoxythiazole, 2-ethylthiazole, 2-ethyl-4-methylthiazole, 2-hydrazinobenzothiazole, 2-hydroxybenzothiazole 2 (3H) -benzothiazolone, benzothiazole, thiazole, (−)-benzotetramizole, 1,2-benzisothiazol-3 (2H) -one, 2,2′-methylenebisbenzothiazole, 2,4 , 5-trimethylthiazole, and thiazoles such as 2,4-dimethylthiazole. These sulfur-containing compounds can be used alone or in combination of two or more.

  Although it does not specifically limit as an addition amount of a sulfur-containing compound, For example, it is preferable to set it as 0.01-500 mg / l. If the addition amount of the sulfur-containing compound is less than 0.01 mg / l, silver is not sufficiently complexed, so that a further stability improvement effect of the plating solution can be obtained. On the other hand, if the addition amount is more than 500 mg / l, the effect of improving the stability of the plating solution can be achieved, but the plating deposition rate is lowered, and it takes a long time to obtain a predetermined amount of precipitated silver, which is efficient. is not.

  Further, the iodine-containing compound is not particularly limited. For example, potassium iodide, potassium iodate, iodotyrosine, iodomethane, diiodomethane, 1,2-diiodoethane, acetyl iodide, 2-iodoethyl benzoate, and 2-iodo-2. -Methylpropane, 2-iodobutane, 1,2-bis (2-iodoethoxy) ethane, diiodomethane, 1,3-diiodopropane, 1,2-diiodoethane, 1,4-diiodobutane, 1,5-diiodopentane 2-iodoacetamide, 1-iodobutane, iodoethane, 1-iodo-3-methylbutane, 1-iodooctadecane, 1-iodopropane, 2-iodopropane, 3-iodo-1-propene, 3-iodopropionic acid, 1 -Iodo-2-methylpropane, 2-iodoethanol, 1- Hexadecane, 2-iodoacetamide, 5-iodouracil, 3-iodopyridine, 4-iodopyridine, iodobenzene, 5-iodo-2-methylbenzimidazole, 2-iodothioanizole, p-iodophenol, 1- ( Iodomethyl) -pyrrolidone, 3,5-diiodoanisol, 1-iodo-2-isopropylbenzene and the like. These iodine-containing compounds can be used alone or in combination of two or more.

  The amount of the iodine-containing compound added is not particularly limited, but is preferably 0.01 to 500 mg / l, for example. If the amount of the iodine-containing compound added is too small than 0.01 mg / l, a further stability improvement effect of the plating solution cannot be obtained. On the other hand, if the addition amount is more than 500 mg / l, the plating deposition rate is lowered, and it takes a long time to obtain a predetermined amount of precipitated silver, which is not efficient.

  Further, in the reduced electroless silver plating solution according to the present embodiment, a complexing agent may 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 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 even better stability can be obtained.

  In addition to the above components, the reduced electroless silver plating solution according to the present embodiment includes known surfactants, pH adjusters, buffering agents, smoothing agents, stress relaxation agents, and the like as necessary. These additives may be mixed.

  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. Can be good. 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.

  The pH of the reduced electroless silver plating solution can be used in the range of 1-14. In particular, the stability of the plating solution can be further improved by setting the pH of the plating solution to about 6 to 13. 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, and when raising the pH, alkali metal hydroxide, ammonia or the like is used.

  As a plating method using the reduced electroless silver plating solution according to the present embodiment, for example, an object to be plated is immersed in the plating solution adjusted to the above-described solution temperature and pH value. Moreover, you may make it contact a plating solution with respect to a to-be-plated object by spraying, application | coating, etc.

  The object to be plated on which the electroless silver plating film is formed is not particularly limited, and a metal material, other various conductive materials, and non-conductive materials can be used as the objects to be plated. 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.

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

(Example)
Contains 2.0 g / l of silver nitrate as silver concentration, 5.0 g / l of hydrazine as a reducing agent, 50 g / l of EDTA as a complexing agent, and 50 mg / l of a compound represented by the following general formula (1) as a liquid stabilizer A reduced electroless silver plating solution was prepared by adjusting the pH of the aqueous solution to 8.0 using potassium hydroxide. In Examples 1 to 36, compounds in which R, m, and n in the general formula (1) are as shown in Table 2 below were added.

Using a BGA substrate (manufactured by Uemura Kogyo Co., Ltd.) as an object to be plated, each step shown in Table 1 below was sequentially performed as a pretreatment prior to the plating treatment with the above-described reduced electroless silver plating solution. 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 the nickel plating film | membrane used as a foundation | substrate was formed after that using electroless nickel liquid NPR-4 (made by Uemura Kogyo Co., Ltd.).

  After performing this pretreatment, the object to be plated was immersed in the above-described reduced electroless silver plating solution and subjected to electroless plating at 60 ° C. for 20 minutes.

  After performing the plating treatment, the temperature was allowed to stand at 60 ° C. for 100 hours, and the stability of the plating solution was evaluated by the presence or absence of self-decomposition of the plating solution.

(Comparative example)
In Comparative Example 1, except that the compound represented by the general formula (1) was not added, the reduced electroless silver plating solution was prepared and the pretreatment step was performed in the same manner as in the example, and then the plating treatment was performed. The stability of the plating solution after being allowed to stand at 60 ° C. for 100 hours was evaluated.

  In Table 2, the compound shown to General formula (1) as a liquid stabilizer added in the Example, its addition amount, and the stability evaluation result of the plating solution of an Example and a comparative example are shown.

  As shown in Table 2, when the compound represented by the general formula (1) was added (Examples 1 to 36), the plating solution did not self-decompose and the plating solution maintained a stable state. It was. Moreover, with the reduced electroless silver plating solution used in these Examples, a good silver plating film could be formed without forming unevenness on the underlying nickel plating film.

  On the other hand, in Comparative Example 1 in which the compound represented by the general formula (1) was not added, the plating solution self-decomposed, and the plating solution could not be kept stable. In addition, silver plating was not deposited on the entire surface of the underlying nickel plating film, resulting in a locally uneven silver plating film.

  Next, a sulfur-containing compound and / or an iodine-containing compound is further added to the reduced electroless silver plating solution to which the compound represented by the general formula (1) is added as in the above-described Examples, and Examples 1-36 In the same manner as described above, the plating treatment was performed after the pretreatment step, and the stability of the plating solution after being allowed to stand at 60 ° C. for 100 hours was evaluated.

  In addition, a sulfur-containing compound and / or an iodine-containing compound is further added to the reduced electroless silver plating solution of Comparative Example 1 described above, and after performing the pretreatment step in the same manner as in Examples 1-36, the plating treatment is performed. The stability of the plating solution after being allowed to stand at 60 ° C. for 100 hours was evaluated. That is, in this experiment, the stability of the plating solution when only the sulfur-containing compound and / or iodine-containing compound was added without adding the compound represented by the general formula (1) was examined.

  Each evaluation result is shown in Table 3A and Table 3B. In the table, “◯” indicates that the plating solution was stable without self-decomposition, and “x” indicates that the plating solution was not stable due to self-decomposition.

  As shown in Table 3A and Table 3B, in the plating solution to which the compound represented by the general formula (1) is added, even when any sulfur-containing compound or iodine-containing compound is further added, the plating solution does not self-decompose. Remained stable. Moreover, with the reduced electroless silver plating solution used in these Examples, a good silver plating film could be formed without forming unevenness on the underlying nickel plating film.

  On the other hand, in the plating solution in which only the sulfur-containing compound or iodine-containing compound is added without adding the compound represented by the general formula (1), self-decomposition occurs in the plating solution, and plating is performed over a long period of time. The liquid could not be kept stable. In addition, silver plating was not deposited on the entire surface of the underlying nickel plating film, resulting in a locally uneven silver plating film.

  Next, benzylethylenetriamine chloride is used as the compound represented by the general formula (1) (the same plating solution as in Example 25), and the addition amount of the benzylethylenetriamine chloride is changed to evaluate the stability of the plating solution. In addition, the film thickness of the formed silver plating film was examined.

  The experimental method was the same as in Example 25 by adding the compound added in Example 25 described above in each case of 0.1 mg / l, 10 mg / l, 100 mg / l, and 1500 mg / l as the addition amount. The reduced electroless silver plating solution was prepared, and after performing the pretreatment step, the plating treatment was performed, and the stability of the plating solution after being allowed to stand at 60 ° C. for 1 hour and at 60 ° C. for 100 hours was evaluated. . Moreover, the film thickness (Ag film thickness) of the silver plating film formed after the plating treatment was measured. The silver plating film thickness was measured using a fluorescent X-ray film thickness meter (SFT 9550, manufactured by SII Nano Technology Co., Ltd.). Table 4 shows the evaluation results.

  As shown in Table 4, even when benzylethylenetriamine chloride, which is a compound represented by the above general formula (1), is added in any amount, no self-decomposition of silver in the plating solution occurs and it takes a long time. The plating solution could be kept stable.

  On the other hand, in terms of the film thickness of the formed silver plating film, it became thinner as the addition amount was increased, and when 1500 mg / l was added, no plating film was formed. This is because when the amount of the compound represented by the general formula (1) is too large, the concentration of the compound in the plating solution is increased, so that the reaction field of the water-soluble silver compound is reduced, and the plating solution It is considered that the active silver ions in the medium are extremely lowered, so that the plating deposition rate is lowered and the reaction is stopped.

  As is clear from the above results, by adding the compound represented by the general formula (1) to the reduced electroless silver plating solution, the self-decomposition of silver in the plating solution is suppressed, and over a long period of time. It turned out that it can be set as the plating solution which has the outstanding stability. The amount of the compound represented by the general formula (1) is preferably about 0.1 to 100 mg / l, whereby a good silver plating film can be formed with excellent liquid stability. I understood.

Claims (4)

A reduced electroless silver plating solution comprising 0.1 to 100 mg / l of a water-soluble silver compound, a reducing agent, and a compound represented by the following general formula (1) as a liquid stabilizer.

(In the formula, R represents an alkyl group or an aryl group, and m and n are each an integer of 1 to 3.)   The reduced electroless silver plating solution according to claim 1, wherein the compound is a compound having a Cas number of 68603-67-8.   The reduced electroless silver plating solution according to claim 2, wherein the compound is benzyldiethylenetriamine chloride. The reduced electroless silver plating solution according to any one of claims 1 to 3 , further comprising a sulfur-containing compound and / or an iodine-containing compound.