JP3201269B2 - Regeneration method of electroless plating bath - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a regeneration of an electroless plating bath which enables repeated use of an electroless plating bath such as an electroless nickel or nickel alloy plating bath using sodium hypophosphite as a reducing agent. About the method.

[0002]

2. Description of the Related Art Electroless plating using sodium hypophosphite as a reducing agent, particularly electroless nickel plating (electroless Ni-P plating), has been widely used in various fields. ing. In this type of electroless plating, plating is performed by reducing metal ions by the reducing action of hypophosphite ions and precipitating them on an object to be plated.

Accordingly, as the plating proceeds, the metal ions and hypophosphite ions in the plating bath decrease, and the deposition rate decreases and the composition of the precipitate (for example, Ni and P in a Ni-P plating bath). Alloy composition) changes. For this reason,
Insufficient metal ions and hypophosphite ions are appropriately replenished, the concentration of these ions is returned to the initial level, and plating is continued.

However, as described above, hypophosphite ion
When reducing metal ions by reduction,
The ions are oxidized to phosphite ions (H_TwoPO _Three ^-)But
It forms and accumulates gradually in the plating bath.

This phosphite ion (H_TwoPO _Three ^-)
A small amount has little effect on plating, but a large amount
For example, 50 to 100 g / L or more, especially 150 g /
If it exceeds L, the plating may be affected.
Problems with the adhesion between the plating object and the plating film
Deposits in the plating film and adversely affects its uniformity and corrosion resistance.
To dissolve the plating bath,
There is a case.

Therefore, when performing electroless Ni-P plating, three to ten turns (one turn is the first electroless Ni-P plating)
-The total amount of nickel ions contained in the P bath was consumed or precipitated. For example, if 6 g / L of nickel ions were present in the first electroless Ni-P bath, 6 g / L
The case where the L nickel ions are consumed or precipitated is defined as one turn. Therefore, in this case, 3 to 10 turns mean that the nickel ions have been consumed or precipitated at 18 to 60 g / L. ) After use, the fact is that the electroless Ni-P bath was discarded.

[0007] Accordingly, the life of the electroless Ni-P bath is relatively short, and the waste liquid treatment accompanying the disposal of the electroless Ni-P bath has become an industrial problem. Although a regenerating method of the -P bath has been proposed, the conventional regenerating method involves a complicated processing method, impurity ions harmful to plating mixed in the regenerated plating bath, and high equipment cost. Due to problems, it has not been widely implemented.

[0008] From such a point, the present inventors have previously included hypophosphorous acid or a salt thereof as a water-soluble nickel salt, a complexing agent and a reducing agent, and reduced the concentration of hypophosphorous acid or a salt thereof by plating. A water-soluble nickel salt was added to the aging solution of an electroless nickel plating bath containing 100 g / L or more of phosphite ions generated by oxidation in an amount of 0.5 to 1 mol of the phosphite ions.
A method for regenerating an electroless nickel plating bath, characterized in that nickel phosphite is formed and precipitated by adding it in a molar ratio of not less than 1 mole and the precipitate is removed (Japanese Patent Laid-Open No. 5-2 / 1993).
No. 47660).

Further, the present inventors have conducted plating for a long period of time.
Electroless nickel with phosphite accumulated over 100 g / L
Effective from electroless plating baths such as metal or nickel alloy plating baths
Efficiently and bring in plating impurities into the plating bath.
After intensive studies on a simple and easy removal method,
As a result, one of the following (i), (ii) and (iii) or
Means two or more treatments: (i) from the electroless plating bath
Same as or the same as the constituent metal of the electroless plating film to be deposited
When there are two or more constituent metals, at least one of them
Sulfates, chlorides, carbonates, hydroxides or
These double salts were added to the metal
Add so that the concentration is higher than the ON concentration.
The addition treatment of the metal sulfate or chloride is (ii) and / or
Or with the treatment of (iii)), (ii)
The bath temperature to a temperature higher than the plating operation temperature, (i
ii) The above electroless plating bath is used in the plating operation.
By performing the treatment of raising the pH to a value higher than H,
Soluble phosphite is definitely formed and precipitates,
By removing the substances, the sub-electrode in the electroless plating bath is removed.
Phosphate (H_TwoPO _Three ^-Ion) is reduced,
Appearance of plating film when plating using plating bath
And the deposition rate returns to the level of the initial plating bath.
And proposed such a regenerating method first (Japanese Patent Application No. Hei 8
-51077).

According to the above proposal, it is possible to easily and reliably regenerate and reuse an electroless plating bath using hypophosphorous acid or a salt thereof as a reducing agent without inconvenience of mixing harmful impurity ions. Although possible, this has created a new problem.

That is, in the case of an electroless nickel plating bath, those containing nickel sulfate, a complexing agent, and sodium hypophosphite as main components are widely used. Phosphite ion, p
In order to replenish and adjust H, nickel sulfate, sodium hypophosphite and sodium hydroxide as a pH adjuster are continuously used while being replenished. Therefore, as described above, phosphite ions accumulate in the plating bath, and sodium ions and sulfate ions also accumulate. In this case, since sodium sulfate has high solubility, it does not particularly affect the plating film.

However, the phosphite ions accumulated in accordance with the above-mentioned proposal are precipitated as nickel phosphite by adding nickel sulfate, and are removed to regenerate the electroless nickel plating bath and to repeat reuse. Finally, the solubility exceeds the solubility limit of sodium sulfate, and its crystals precipitate, which adversely affects the properties of the plating film.

For this reason, it has been desired to remove sodium sulfate accumulated during regeneration and reuse of the plating bath without inconvenience such as mixing of harmful impurity ions.

The present invention has been made in view of the above circumstances, and removes sodium sulfate accumulated as described above reliably and without mixing harmful impurity ions, and uses sodium hypophosphite as a reducing agent. An object of the present invention is to provide a method for regenerating an electroless plating bath which can recycle a used electroless plating bath and reuse it.

[0015]

In order to achieve the above object, the present invention provides a water-soluble sulfate of a metal to be electrolessly deposited, a complexing agent thereof and a hypophosphorous acid as a reducing agent. Including sodium, the electroless plating bath in which sodium phosphite has been accumulated, the same as the constituent metal of the electroless plating film deposited from the electroless plating bath or when the constituent metal is two or more, at least the A sulfate, chloride, carbonate, hydroxide or a double salt thereof of the same metal is added so as to have a concentration higher than the metal ion concentration in the plating operation of the plating bath, so that the metal is hardly soluble. Phosphite is generated and precipitated, and the poorly soluble phosphite is removed to regenerate the electroless plating bath and reuse is repeated. Natori The present invention provides a method for regenerating an electroless plating bath, comprising cooling a plating bath to 0 to 15 ° C. to precipitate and precipitate sodium sulfate when the amount of accumulated water exceeds 200 g / l. .

In this case, the present invention can be suitably used especially for an electroless nickel plating bath. In view of such a point, the present invention provides nickel sulfate, a complexing agent and a reducing agent thereof as preferred embodiments. And adding sodium sulfate to the electroless nickel plating bath containing sodium phosphite so as to have a concentration higher than the nickel ion concentration in the plating operation of the plating bath. Nickel is generated and precipitated, the nickel phosphite is removed, the electroless nickel plating bath is regenerated, and reuse is repeated. At the same time, 200 g of sodium sulfate in the electroless nickel plating bath is reused. / L or more, the plating bath is changed from 0 to 15
The present invention provides a method for regenerating an electroless nickel plating bath, wherein sodium sulfate is precipitated and precipitated by cooling to a temperature of ℃.

According to the present invention, by the above-described method, the phosphite ions accumulated in the plating bath can be effectively removed, and the plating bath can be regenerated and reused. A large amount of sodium sulfate accumulated by repetition can be easily and reliably removed without mixing in impurity ions, so that the plating bath has a longer life and the electroless plating bath can be used repeatedly for a longer period of time. Is possible.

Therefore, the above method is particularly advantageous in that the electroless plating bath is continuously supplied with a water-soluble sulfate of a metal to be electrolessly deposited such as nickel sulfate, sodium hypophosphite, and sodium hydroxide as a pH adjuster. This is effective when the type of sulfate ion and sodium ion used accumulates and increases as plating proceeds.

In the above-mentioned method, when producing and precipitating a sparingly soluble phosphite, the operation of raising the electroless plating bath to a temperature higher than the plating operation temperature and raising the pH to a higher pH than the plating operation. By performing one or both of the operations simultaneously, the poorly soluble phosphite can be more effectively removed.

Hereinafter, the present invention will be described in more detail. The electroless plating bath to be regenerated according to the present invention is composed of a water-soluble sulfate of a metal to be electrolessly deposited, a complexing agent thereof, and phosphorous hypophosphite as a reducing agent. Any type may be used as long as it is a type mainly containing sodium acid, preferably, the above-mentioned sulfate, sodium hypophosphite, and a type that is continuously used by replenishing sodium hydroxide as a pH adjuster. Nickel, cobalt, copper and other single plating baths, and electroless nickel-cobalt, nickel-copper, nickel-tungsten, cobalt-tungsten and other alloy plating baths can be mentioned, and in particular, electroless nickel and nickel alloy plating baths are preferable. Applied to These electroless plating baths may be any of an acidic type, a neutral type, and an alkaline type.
The composition may be a known one, but is particularly preferably applied to an acidic bath having a pH of 4 to 6.

In this case, the electroless nickel plating bath contains a carboxylic acid such as nickel sulfate, citric acid, succinic acid, malic acid, acetic acid, lactic acid and salts thereof, other known complexing agents for nickel, and hypophosphorous acid. Those containing sodium as a main component are used. The concentration of these components is in a normal range, for example, nickel sulfate is 0.05 to 0.3 mol / L,
The complexing agent can be in the range of 1 to 5 mol / L per mol of nickel sulfate, and sodium hypophosphite can be in the range of 15 to 90 g / L. In addition, a stabilizer, a pH adjuster and the like can be added to this plating bath, and the pH of the electroless nickel plating bath can be made alkaline or acidic. However, the plating solution for continuous use has a pH of 3. It is usually 5 to 6.5.

The plating method using this electroless nickel plating bath can also employ a usual method, but as the plating reaction proceeds, the nickel ions and hypophosphite ions in the plating bath decrease and the pH decreases. . For this reason, nickel sulfate, as a supplement to the plating bath, continuously or intermittently,
At the same time as adding sodium hypophosphite, a pH increasing agent such as sodium hydroxide is added to maintain the nickel ion concentration, the hypophosphite ion concentration and the pH in the plating bath at predetermined concentrations. Thereby, good electroless plating can be performed over a long period of time. However, when phosphite ions generated by oxidation of hypophosphite ions accumulate in the plating bath, a treatment for removing the phosphite ions is performed.

That is, the reproducing method of the present invention has the following
By using a plating bath, hypophosphite ion H_TwoPO _Two ^-
Consumption (oxidation) of phosphite (phosphite ion H_TwoP
O _Three ^-) Accumulated plating bath (in this case, the regeneration time is
It is appropriately selected and is not limited, but usually 50 g /
L or more, preferably 100 g / L or more, especially 15 g / L or more.
0g / L or more, and sometimes 200g / L or more
Plating bath), and is deposited from the above electroless plating bath.
Or the same as the constituent metal of the electroless plating film
Is the same metal as at least one of them when two or more are
Sulfate, chloride, carbonate, hydroxide or
Metal ion concentration in the plating operation of the above plating bath with salt
Is added so as to have a higher concentration.

In this treatment, for example, in the case of an electroless nickel plating bath, nickel sulfate, nickel chloride, nickel carbonate, nickel hydroxide, basic nickel carbonate [NiCO ₃
Ni (OH) ₂ .nH ₂ O] or the like. For example, in the case of an electroless nickel-copper alloy plating bath, copper sulfate, chloride, carbonate, water Oxides and double salts thereof are added. Preferably, the additive added here is a water-soluble sulfate such as nickel sulfate, which is suitable for the present invention.

In this case, the amount added in this treatment may be higher than the metal ion concentration (normal plating control metal ion concentration) in the normal plating operation of the plating bath, but is preferably the plating control metal ion. It is preferable to add so that the concentration becomes more than 1 and 10 times by weight or less, preferably 1.2 to 10 times by weight, particularly 1.5 to 6 times by weight, in terms of formation and precipitation of poorly soluble phosphite. It is suitable.
It is preferable that the additive such as nickel sulfate is added at a ratio of 0.5 mol or more, preferably 1 mol or more, per 1 mol of phosphite ions.

In addition, the operation of raising the temperature of the electroless plating bath to a temperature higher than the plating operation temperature (normal plating control temperature) together with the addition of the additive, and the operation of raising the pH of the electroless plating bath during the plating operation (normal plating operation). Plating control pH)
It is preferable to perform one or both of the operations of raising the pH to a higher pH, since the formation and precipitation of the hardly soluble phosphite are more effectively performed.

In this case, the former operation is preferably performed at a temperature of 5 ° C. or higher than a normal plating control temperature. For example, a common acidic electroless nickel plating bath is often plated at 90 ° C.
The temperature is raised to 5 ° C. or higher, particularly 97 ° C. or higher, and in some cases, to the boiling point. In the latter operation, it is preferable to raise the pH by 0.1 or more, particularly 1 or more, from the normal plating management pH,
For example, in the case of an acidic electroless plating bath having a pH of 4 to 6, it is preferable that the pH be as high as described above in the range of pH 4.5 to 12, preferably pH 4.5 to 7, particularly pH 5 to 7.

As a method for increasing the pH of the plating bath, a method of adding an alkali hydroxide such as sodium hydroxide and the like, and a method of adding a hydroxide or a carbonate of a metal described above may be mentioned. Can be In the latter case,
In the treatment for increasing the pH, the addition increases the pH, so that the amount of addition of the metal ion may be smaller than in the above-described treatment for adding the additive.

When carrying out this method of raising the pH, the plating bath may be at room temperature, but at a temperature of 40 to 90 ° C., particularly 50 to 70 ° C.
It is preferred that the temperature be raised to 0 ° C. and left.

In each of the above treatments, if necessary, the mixture is left under stirring to produce and precipitate a sparingly soluble phosphite. In this case, the standing time is 30 minutes to 24 hours, particularly 1 to 5 hours. Is preferred.

Separation and removal of the formed precipitate can be carried out according to a conventional method such as filtration. In this case, it is preferable to perform filtration at a high temperature, and a separate tank and a plurality of filtration devices are installed near the plating tank, and precipitation can be performed and filtration can be performed while one of the tanks is stopped. Alternatively, filtration may be performed in a separate tank.

The regenerated electroless plating bath can be used for plating again after adjusting the metal ion concentration, hypophosphite ion concentration, pH, etc. When acid ions are accumulated, by performing the regeneration treatment as described above, the acid ions can be used repeatedly, and thus the life of the electroless plating bath can be extended.

In the present invention, sodium ions and sulfate ions accumulate in the plating bath due to repeated use of the plating bath, and a large amount of sodium sulfate is generated. In this case, the plating bath is cooled to a temperature lower than room temperature to precipitate and precipitate sodium sulfate and remove it.

Here, the amount of the accumulated sodium sulfate when the above treatment is to be performed is 200 g / L or more.
Particularly at 400 g / L or more, before reaching the solubility limit of sodium sulfate. Further, the cooling temperature is 0 to 15 ° C, especially 0 ° C.
５5 ° C. If it is too low, the entire plating bath will crystallize, and if it is too high, the amount that can be removed at one time will be small. Further, the method of removing the precipitated sodium sulfate is the same as the method of removing the hardly soluble phosphite.

The plating bath from which sodium sulfate has been removed is adjusted in the same manner as described above, and the plating bath is reused.

[0036]

According to the present invention, phosphite ions can be easily, reliably and inexpensively removed from an aged electroless plating bath in which a large amount of phosphite ions have accumulated without introducing impurities. At the same time, sodium sulfate accumulated in large quantities by repeated use of the plating bath can be similarly easily, reliably, and inexpensively removed, and the plating bath can be regenerated and repeatedly used for a long time.

[0037]

The present invention will be described below in more detail with reference to Examples, but the present invention is not limited to the following Examples.

An electroless nickel plating bath having the following composition was prepared. Nickel sulfate 5.0 g / L (as Ni ²⁺ ) NaH ₂ PO ₂ .H ₂ O 25.0 g / L Sodium acetate 18.0 g / L Malic acid 40.0 g / L Pb ²⁺ 0.3 mg / L (NaH ₂ PO ₃₀ g / L) pH 4.5

Using the above electroless nickel plating bath, nickel sulfate, NaH ₂ PO ₂ .H ₂ O, and NaOH (or H ₂ SO ₄ ) as a pH adjuster were added at predetermined intervals to the above Ni ²⁺ concentration, NaH ₂ PO ₂・ Plating is performed at 90 ° C. while replenishing so that the H ₂ O concentration and the pH become 4.5 and, if necessary, while replenishing sodium acetate, malic acid, and Pb ²⁺ appropriately.
Further, when the phosphite ion increases to a predetermined value or more, a nickel sulphate ion removal treatment similar to that described later is performed, a phosphite ion removal operation is performed, plating is performed in the same manner as above, and then a plating bath (comparison) The analysis of Example 1) was performed. The results are as follows.

[0040] _{^{Ni 2+ 5.0 g / L NaH 2}} PO 2 · H 2 O 25.0 g / L NaH 2 PO 3 205 g / L Na 2 SO 4 · 7H 2 O 430 g / L Pb 2+ 0 0.3mg / L

Next, the plating bath according to Comparative Example 1
After leaving at room temperature for 1 hour and removing the crystallized sodium sulfate by filtration, the obtained plating bath (Comparative Example 2) was analyzed, and the following results were obtained.

[0042] _{^{Ni 2+ 5.0 g / L NaH 2}} PO 2 · H 2 O 24.3 g / L NaH 2 PO 3 203 g / L Na 2 SO 4 · 7H 2 O 110 g / L Pb 2+ 0 0.3mg / L

Further, nickel sulfate was added to the plating bath of Comparative Example 2 at a concentration of 30 g / L.
The mixture was kept for a while, and the resulting precipitate was removed. The analysis results of the obtained plating bath (Example 1) are as follows.

[0044] _{^{Ni 2+ 9.0 g / L NaH 2}} PO 2 · H 2 O 7.3 g / L NaH 2 PO 3 99 g / L Na 2 SO 4 · 7H 2 O 106 g / L Pb 2+ 0 .1 mg / L

For each of the above plating baths, Ni ²⁺ 5.0
_{g / L, NaH 2 PO 2} · H 2 O25.0g / L, pH
After adjusting to 4.5, plating was performed at 90 ° C. for 30 minutes. A 5 × 10 cm mild steel plate was used as the object to be plated.
The plating bath volume was 1 liter. The results of visual observation of the appearance of the obtained plating film were as follows.

Comparative Example 1: The surface had roughness, and brown iron rust was generated only after being left in the washing water for 30 minutes. Comparative Example 2: There was no roughness on the surface, but 3
When left for 0 minutes, generation of brown iron rust was observed. Example 1: There was no roughness on the surface, and there was no generation of iron rust even after being left in the washing water for 60 minutes.

Claims (4)

(57) [Claims] 1. An electroless plating bath containing sodium hypophosphite as a water-soluble sulfate of a metal to be electrolessly deposited, a complexing agent thereof and a reducing agent, wherein sodium phosphite is accumulated. When the constituent metal of the electroless plating film deposited from the plating bath is the same as the constituent metal or two or more constituent metals, sulfate, chloride, carbonate, hydroxide or the same of at least one of the same metals is used. A double salt is added so as to have a concentration higher than the metal ion concentration in the plating operation of the plating bath to generate and precipitate the hardly soluble phosphite of the metal, and the hardly soluble phosphite is removed. The electroless plating bath is regenerated and reused repeatedly. When the sodium sulfate in the electroless plating bath according to the reuse is accumulated at 200 g / l or more, the plating bath is cooled to 0 to 15 ° C. do it A method for regenerating an electroless plating bath, comprising depositing and precipitating sodium sulfate and removing the same. 2. An electroless nickel plating bath containing sodium hypophosphite as a nickel sulphite, a complexing agent and a reducing agent thereof, wherein nickel sulphate is accumulated in an electroless nickel plating bath in which sodium phosphite is accumulated. Nickel phosphite is generated and precipitated by adding so as to have a concentration higher than the concentration, and the nickel phosphite is removed, the electroless nickel plating bath is regenerated, and reuse is repeated. When sodium sulfate in the electroless nickel plating bath for reuse is accumulated at 200 g / l or more, the plating bath is cooled to 0 to 15 ° C. to precipitate and precipitate sodium sulfate, and the sodium sulfate is removed. To regenerate an electroless nickel plating bath. 3. An electroless plating bath comprising: a water-soluble sulfate of a metal to be electrolessly deposited; sodium hypophosphite;
3. The method according to claim 1, wherein the modifier is of a type which is reinforced and continuously used with sodium hydroxide. 4. When producing and precipitating a sparingly soluble phosphite, one or both of an operation of raising an electroless plating bath to a temperature higher than a plating operation temperature and an operation of raising a pH to a pH higher than a plating operation is performed. 4. The reproducing method according to claim 1, wherein the reproducing method is performed simultaneously.