JPS59232288A - High speed silver plating liquid - Google Patents

Abstract

PURPOSE:To provide a titled plating liquid which prevents replacement deposition of silver and to form a silver plating film having good adhesion by adding a cyclic compd. contg. an adequate amt. of a thioureylene group in the ring to said liquid in order to electroplate silver on a metallic base plate baser than silver. CONSTITUTION:A cyclic compd. contg. the thioureylene group expressed by the constitutional formula (R1, R2 are hydrogen or alkyl group or aryl group) is added at the amt. enough to prevent the replacement deposition of silver to a silver plating liquid for the purpose of electroplating silver on a copper, copper alloy or copper plating base or a base material consisting of a metal baser than silver such as iron, iron alloy, nickel, nickel alloy or the like, by which the high speed silver plating liquid to prevent the replacement deposition of silver on the above-mentioned base material by immersion is obtd. A cyclic compd. contg. a thioureylene group and a 5-6-membered ring consisting of C or N such as 2-thiobarbituric acid, 2-imidazolidinethion,1-phenyl-2-tetrazoline-5- thion or the deriv. or the like thereof is adequately usable as the above-mentioned cyclic compd.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a high-speed silver plating solution, and in particular,
Copper, copper alloys, iron, iron alloys, nickel.

Even if a base material made of a metal less base than silver, such as a nickel alloy, is immersed, no substitutional precipitation of silver will occur.

(I(,, R2 is hydrogen or alkyl group size Al)-
It is a high-speed silver plating process containing a cyclic compound containing a thioureylene group (2) in the ring.

Recently, high-speed plating methods have been widely adopted from an economic standpoint when silver plating electronic component materials. In this method, in order to increase the silver plating speed, the plating solution is heated under high temperature pressure. This is done by increasing the silver content in the plating solution and increasing the flow rate of the plating solution. No. 1 used in this method. The high-speed silver plating solution has free cyanide t” = D￥
It won't work unless '- is kept sufficiently low. This is because when the concentration of free cyanide is high, the free cyanide decomposes violently at high temperatures and generates a large amount of cyanide gas, which is dangerous. Therefore, silver salt is introduced into the high-speed silver plating solution in the form of alkali silver cyanide, and in order to gradually decompose and remove free cyanide generated from the cathode during electrolysis and prevent it from accumulating. It is characterized by the formation of a pH buffer system that maintains the pH of the liquid at about 5 to 90.

Additionally, in order to make more effective use of silver, which is expensive, a high-speed selective plating method is currently being used in which only the areas that require plating are plated at high speed. The main jet plating method is to apply plating by spraying a silver plating solution onto the part to be plated using a pump at high speed and passing an electric current between the substrate to be plated and an insoluble anode.

The biggest problem with conventional high-speed selective silver plating is that silver is precipitated by displacement just by immersing it in a silver plating solution on the base metal base material other than silver. That's true. This substitutional precipitation of silver is performed on copper and copper alloys as a total bending substrate.

This is noticeable when iron, iron alloys, and nickel alloys are used. This displacement-precipitated silver usually has poor adhesion to the base material, and when silver plating is applied electrolytically on it, the plating film peels off and blisters or discolors when heated, resulting in poor plating. This plating defect is especially fatal when it comes to silver plating of electronic parts. In addition, if one part is plated without applying this force, deposits will also be deposited on areas where plating is not required.
High price silver will be lost.

In conventional plating methods, in order to prevent such substitutional precipitation of silver with poor adhesion, a thin silver plating called strike plating is applied using a plating solution with a low silver concentration, and then regular plating is applied on top. It is given to However, in the case of single-part plating, strike plating can improve the adhesion of the plating, but it results in a loss of silver because strike plating must also be performed on areas where no plating is required. For the purpose of preventing silver displacement precipitation during high-speed partial plating such as.

Silver plating solutions containing mercapto compounds have also been proposed. (Japanese Patent Application Laid-Open No. 55-34699) However, the particularly recommended thiolactic acid and thiomalic acid have a bad odor and also have the drawback that their effect of preventing silver substitutional precipitation is easily lost in the presence of @ ions. have.

Therefore, for example, when silver plating is performed on a copper substrate, copper ions accumulate in the solution due to silver substitutional precipitation7, or copper ions are mixed in from the outside.
When the concentration of copper ions in the liquid increases, even if the same mercaptan compound is added to prevent displacement precipitation, the effect of preventing displacement precipitation immediately disappears.

This makes liquid management difficult.

In addition, for the purpose of preventing substitutional precipitation of silver, "silver plating solution containing an aromatic or aerocyclic compound having a mercapto group directly bonded to a cyclic nucleus" (Japanese Patent Application Laid-Open No. 57-4599
No. 5) and “dithiocarbamic acid or its salt and/or
Alternatively, a silver plating solution containing thiosemicarbazide or a salt thereof (Japanese Patent Application Laid-open No. 131382/1982) has also been proposed. However, these proposed compounds are
By adding cyanide to a silver plating solution with a high concentration, it is possible to prevent the displacement precipitation of silver due to total immersion, which is less noble than silver, but free cyanide used in high-speed plating is In a silver plating solution at a sufficiently low temperature, a precipitate is formed and there is no effect of preventing displacement precipitation.

As described above, in high-speed partial plating, the existing technology to date is not necessarily sufficient to prevent silver displacement precipitation, obtain a silver plating film with good adhesion, and prevent silver loss.

The present invention aims to solve the drawbacks of existing technologies as mentioned above.

(R,, R2 is hydrogen or an alkyl group) Using a cyclic compound containing a thioureylene group in the ring,
Prevents silver displacement precipitation in high-speed silver plating solutions with sufficiently low free cyanide concentrations.

The purpose of this method is to perform silver plating with good adhesion on the substrate without silver strike plating. This RlS R.

(R□, R2 are hydrogen, an alkyl group, or an aryl group) A cyclic compound containing a thioureylene group in the ring is extremely effective in preventing substitutional precipitation of silver.

Furthermore, the effect is unlikely to disappear even in the presence of Ou ions, which have a bad odor. Furthermore, no precipitation occurs even when added to a high-speed silver plating solution where the free cyanide concentration is sufficiently low.

These compounds can completely prevent substitutional precipitation by (1) adding 0.05 f/L to a high-speed silver plating solution with a sufficiently low free cyanide concentration; and (2) depending on the conditions, even 0.02 f/L can be used. A sufficient effect can be obtained.

The cyclic compound containing a thioureylene group such as R, S (R8, argyl group'!!: aryl group) used in the present invention has N atoms attached to both sides of the thione group.

Furthermore, the annular shape makes it stable and resistant to decomposition even under the harsh conditions of high temperature, high flow rate, and high current density during high-speed plating. Against this.

(R, , R2 are hydrogen, alkyl groups, or aryl groups) Compounds that are not cyclic even if they have a thioureylene group, or compounds that are cyclic but do not have N atoms on both sides of the thione group cannot be plated at high speed. It is easy to decompose under the conditions in which it is carried out. Such a cyclic compound containing a ureylene group,
In addition, compounds in which the ring is a 5-membered ring and a 6-membered Fi ring, and other constituent atoms of the ring are C or N, are particularly stable.

Examples of the cyclic compound containing a thioureylene group in the ring RlS R2 (R□, R2 is hydrogen, an alkyl group, or an aryl group) used in the present invention include 2-thiobarbic acid, 2-imidazolidinethione,
Preferred are 1-phenyl-2-tetrazoline-5-thione or derivatives thereof. These cyclic compounds may be added in an amount necessary and sufficient to prevent substitutional precipitation of silver, but generally 10 to 300 q//!
The amount of addition is suitable.

The high-speed silver plating solution of the present invention contains alkali silver cyanide as a silver salt. Although sodium silver cyanide can also be used as the alkali silver cyanide, potassium silver cyanide is generally best.

It also contains alkali metal salts of phosphoric acid, pyrophosphoric acid, and citric acid to impart pH buffering properties and electrical conductivity to the solution. Additionally, a pH buffering salt such as boric acid may be further added.

The high-speed silver plating solution of the present invention is produced using conventional equipment.

It can be used under normal high-speed plating conditions. For example, the concentration of silver salt is 50 to 80 f/l as silver,
Liquid temperature is 40-80℃, current density is 20-200 A/d
i, pH can be used between 7.5 and 9.0. When high-speed plating is carried out at an appropriate flow rate under these conditions, the resulting silver plating film has good adhesion, is uniform, smooth, and has low hardness, making it ideal for silver plating for electronic components. However, the gloss is low, but if you want to obtain a high gloss plating film, you can add a selenium compound. Depending on the purpose of the user, antimony compounds, EDTA,
It is possible to add other ingredients known to those skilled in the art, such as surfactants, to modify the plating film and plating conditions.

As described above, the high speed silver plating solution of the present invention is as follows.

When performing high-speed plating on metal substrates baser than silver such as copper, copper alloys, iron, iron alloys, nickel, and nickel alloys, the adhesion of the plating film is It can be increased and the elimination of silver can be reduced. Moreover,
This effect is not lost due to impurities such as copper ions, and it is extremely easy to manage the liquid.Semi-permanent use is possible if consumable components are replenished as needed and activated carbon filtration is performed periodically.

Examples of the present invention will be described below.

Example 1 A high-speed silver plating solution with the following composition was prepared.

Adjust this to pH 3 and degrease with alkaline in the usual way.
When the pickled phosphor bronze plate was immersed, no substitutional precipitation of silver occurred on the phosphor bronze plate. Furthermore, using this solution, high-speed partial plating was performed using a jet plating method on a phosphor bronze plate that had been subjected to the same treatment. Current density is 100 A/d
rr? The liquid temperature was 65°C. The silver plating film obtained was uniform, smooth, and had low hardness. Adhesion was good, and when this was heated at 350° C. for 2 minutes, no change in appearance such as blistering occurred.

Example 2 In place of 2-thiobarbic acid in Example 1, 30 WV' of 2-imidazolidinethione was added.

When we conducted a similar experiment, we obtained almost the same results.

Example 3 A high-speed silver plating solution with the following composition was prepared.

When this solution was adjusted to pHEL 3 and a phosphor bronze plate that had been subjected to alkali degreasing and pickling in a conventional manner was immersed, no substitutional precipitation of silver occurred on the phosphor bronze plate.

Next, using a high-speed silver plating solution with this composition, apply 100A/dtr to a phosphor bronze plate that has undergone the same pretreatment. 65℃ at a current density of
High-speed partial plating was performed using the jet plating method. The obtained silver plating film was uniform, smooth, and had good adhesion, and no change in appearance such as blistering occurred even when it was heated at 350° C. for 2 minutes.

In Examples 1 to 3, 2-thiobarbic acid, 2-imidazolidine t-one, 21-phenyl-2,
When similar experiments were conducted using solutions not containing -tetrasoline-s-f;A-, displacement precipitation of silver with poor adhesion occurred in all cases.

Comparative experiment results 1 A high-speed silver plating solution with the following composition was prepared.

After adjusting the pH to 3, the compounds shown in Table 1 were added at a concentration of 100 .mu./l, and high-speed partial plating was carried out using the jet plating method.

Table 1 The negative sign of the effect of preventing refinancing precipitation indicates the following.

o: No substitutional precipitation of silver occurred, and the color of the phosphorus W@ plate changed significantly.

Δ: Substitutional precipitation of silver occurs partially, and the phosphor bronze plate becomes partially white.

X: Substitutional precipitation of silver occurs over the entire surface, and the phosphor bronze plate becomes completely white.

As shown in Table 1, additives of the present invention, such as 2-thiobarbic acid, 2-imidazolidinethione, and 1-phenyl-
2-tetrazoline-5-thione did not cause any precipitation. However, some of the comparative examples produced precipitation.

These high-speed silver plating solutions are alkaline degreased in the usual way,
When a pickled phosphor bronze plate was immersed for 30 seconds, Table 1 shows the effectiveness of each additive in preventing silver displacement precipitation.

When high-speed silver plating was performed on a pretreated phosphor bronze plate under the same conditions as in Example 1 using a high-speed silver plating solution that causes such substitutional precipitation, not only a large amount of silver was deposited on areas where no plating was required. The silver plating film obtained had a large unevenness in appearance.

Adhesion was poor, and discoloration and blistering occurred when heated at SSa°C for 2 minutes.

Comparative Experiment Result 2 A high-speed silver plating solution with the same composition as Comparative Experiment Result 1 was prepared,
A phosphor bronze plate was immersed to elute the can ions. To this solution were added 50' of the following compounds: 0 thiolactic acid, 0 thiomalic acid, 0 2-thiobarbital acid, 0 2-imidazolidinethione, 01-phenyl-2-tetrazoline-5-thione.

Using this solution, perform alkaline degreasing in the usual manner.

When the pickled phosphor bronze plate was immersed, no displacement precipitation occurred. Furthermore, when high-speed partial plating was performed using these silver plating solutions under the same conditions as in Example 1,
Good silver plating films were obtained in all cases.

This silver plating solution was then allowed to stand for 72 hours.

When a phosphor bronze plate that had been pretreated in the same way was immersed,
In the solution to which thiolactic acid and thiomalic acid were added, displacement precipitation of chlorine with poor adhesion occurred.

When high-speed plating was further performed, the resulting side-plated film had poor adhesion and was highly uneven in appearance.

On the other hand, 1 is the additive of the present invention, 2-thiobarbituric acid, 2
- In the solution containing imidazolidinethione and 1-phenyl-2-tetrazoline-5-thione, the precipitation of coins on the pretreated phosphorus M' plate was completely prevented even after standing for 72 hours. . When high-speed plating was performed, the silver plating film obtained was as good as before. Further, similar results were obtained after being left for 240 hours or more.

Patent applicant: Japan Mining Co., Ltd. Agent: Patent attorney (7569) Keishi Namikawa

Claims (1)

[Claims] (1) Electroplating of silver onto a substrate made of copper, a copper alloy, a galvanized base material, or a base material less noble than silver such as iron, an iron alloy, nickel, or a nickel alloy. In silver plating solution for. RIS R2 (R□l B is hydrogen, an alkyl group, or an ali?-
A high-speed silver film characterized by adding a cyclic compound containing a thioureylene group in the ring in an amount sufficient to prevent silver displacement precipitation on the substrate by immersion. Plating solution. A cyclic compound containing a thioureylene group in the ring to R, S (R□, R2 is hydrogen, an alkyl group, or an aryl group) has a 5- or 6-membered ring, and other constituent atoms of the ring The high-speed silver plating solution according to claim 1, wherein is C or )■. R, S R. (R1, R, is hydrogen, an alkyl group, or an aryl group) A cyclic compound containing a thioureylene group in the ring is 2-
The high-speed steel plating solution according to claim 2, which is thiobarbic acid, 2-imidazolidinethione, 1-phenyl-2-tetrazoline-5-thione, or a derivative thereof. (4) The high-speed silver plating solution uses cyanide 6u as a silver salt.
Contains alkali and. Horse SR. (R1 and R2 are hydrogen, an alkyl group, or an alkyl group) In the presence of a cyclic compound containing a thioureylene group in the ring, free cyanide is removed to prevent silver bonding and precipitation due to immersion. The high-speed silver plating solution according to claim 1, wherein the amount is sufficiently low. (5) High-speed silver plating solution is phosphoric acid or birophosphoric acid. Claim 1, which contains a salt selected from alkali metal salts of citric acid to impart electrical conductivity and pH buffering properties, and whose pH is adjusted within the range of 15 to 90. High speed silver plating solution.