JP2001049448A - Electroless nickel plating method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method capable of semipermanently using an electroless nickel plating soln. SOLUTION: Among eletroless nickel plating solns. contg. phosphite formed by the oxidation of hypophosphite in the range 0.2 to 2.5 mol/L, an electroless nickel plating soln. compsn. giving a prescribed precipitating rate and a prescribed Ni-P precipitation film compsn. is selected. An electroless nickel plating soln. having the concns. and pH value of nickel ions, a complexing agent, hypophosphite and phosphite and pH value corresponding to the compsn. and pH value of the plating soln. is prepared as the initial make-up of electrolytic bath, while plating is executed by using the plating soln., a part of the plating soln. is extracted continuously or at prescribed intervals, and, moreover, in such a manner that the concns. of the components and the pH value are retained in accordance with the above extracting amt., a replenishment soln. contg. the components is replenished continuously or at prescribed intervals.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electroless nickel plating method using hypophosphite as a reducing agent, and more particularly, to an electroless nickel plating method capable of semipermanently using an electroless nickel plating solution. It relates to a plating method.

[0002]

2. Description of the Related Art Conventionally, electroless nickel plating (electroless nickel plating) using sodium hypophosphite as a reducing agent has been widely used in various fields. In this type of electroless nickel plating, plating is performed by reducing nickel ions by the reducing action of hypophosphite ions and depositing them on the object to be plated.

Accordingly, as the plating proceeds, nickel ions and hypophosphite ions in the plating solution decrease, and the deposition rate decreases or the composition of the precipitate (the alloy composition of Ni and P).
Changes. For this reason, it has been practiced to appropriately replenish the insufficient nickel ions and hypophosphite ions, return the concentrations of these ions to the initial levels, and continue plating.

However, as described above, when nickel ions are reduced by the action of hypophosphite ions, hypophosphite ions are simultaneously oxidized and phosphite ions (H ₂ PO ₃ ⁻ ) are oxidized.
Are generated and are gradually accumulated in the plating solution.

[0005] The phosphite ion (H ₂ PO ₃ ^-), which hardly affects the plating if small, occurred affect the plating and large quantities to accumulate, for example, plating the object to be plated film Causes a problem with the adhesion to the coating, or causes eutectoids in the plating film to adversely affect its uniformity and corrosion resistance.
In extreme cases, the plating solution may be decomposed.

In this case, the conventional management of the electroless nickel plating solution mainly includes nickel ion management in the plating solution,
The fact was that the pH was controlled and the specific gravity of the plating solution was controlled.

That is, in electroless nickel plating,
Nickel ions are reduced to hypophosphite ions to form Ni-
In this case, the P film is deposited. In this case, the consumption of nickel ions, the consumption of hypophosphite ions,
The deposition amount of the P film or the treatment amount of the object to be plated (surface area of the object to be plated × plating time), and the degree of pH decrease of the plating solution have a substantially constant relationship, and the nickel calculated from the analysis of nickel ions When replenishing the shortage of ions,
According to the shortage, a predetermined hypophosphite and a pH adjuster (mainly caustic alkali) are also replenished to normalize the plating solution composition.
It has been practiced to measure the pH of the plating solution to check the pH of the plating solution. Further, by estimating the amount of phosphite accumulated from the total replenishment amount of the nickel ions or the total deposition amount of the plating film and estimating the degree of aging of the plating solution, by measuring the specific gravity of the plating solution at this time, Checking the degree of aging was done.

In the electroless nickel plating solution,
Complexing agents (mainly organic carboxylic acids) that complex nickel ions are also important components, but complexing agents are empirically used because they are not consumed by plating but are consumed by pumping. Only a small amount was supplied at appropriate intervals.

In the case of performing electroless nickel plating, 3 to 10 turns (1 turn is the total amount of nickel ions contained or consumed in the first electroless nickel plating solution, for example, Assuming that 6 g / L of nickel ions are present in the electrolytic nickel plating solution, one turn is a case where 6 g / L of nickel ions are consumed or precipitated, so that in this case, 3 to 10 turns of nickel ions are 18 times. It means that the electroless nickel plating solution was discarded after use, and from this point, even the above-mentioned management method caused a great trouble. There was nothing.

However, the life of the electroless nickel plating solution is relatively short, and the disposal of the electroless nickel plating solution has become an industrial problem. A regenerating method has also been proposed, and the applicant has previously included hypophosphorous acid or a salt thereof as a water-soluble nickel salt, a complexing agent and a reducing agent, and oxidized hypophosphorous acid or a salt thereof by plating. A water-soluble nickel salt was added to the aging solution of the electroless nickel plating solution containing 100 g / L or more of the generated phosphite ions at a ratio of 0.5 mol or more based on 1 mol of the phosphite ions. A method for regenerating an electroless nickel plating solution characterized by generating and precipitating nickel phosphate and removing the precipitate has been proposed (JP-A-5-247660, JP-A-10-247660).
183359).

With such a regenerating method, it is possible to extend the life of the electroless nickel plating solution. However, if the Ni-P plating solution exceeds 10 turns, the deposition rate is reduced, or the Ni-P coating Problems such as fluctuations in the composition occur, and even when used frequently, the electroless nickel plating solution must be discarded while containing useful components in about 15 to 20 turns.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an electroless nickel plating method that can use an electroless nickel plating solution for a longer period of time.

[0013]

Means for Solving the Problems The present inventors have conducted intensive studies to achieve the above object. As a result, when using an electroless nickel plating solution in which phosphite ions are accumulated to some extent, the deposition rate and Ni-P As a result of finding that the composition of the deposited film is relatively stable, and further focusing on this point, the phosphite was added in an amount of 0.2 to 2.5 mol / mol.
The electroless nickel plating solution which gives a predetermined deposition rate and a Ni-P deposition film composition is selected from the electroless nickel plating solutions included in the range of L, and nickel which matches the plating solution composition and pH value of this plating solution is selected. Use of an electroless nickel plating solution having ions, complexing agents, hypophosphite and phosphite concentrations and pH values, that is, conventionally regarded as rather impurities and not usually used in building baths The phosphite which was considered to be positively added to the construction bath solution, that is, an electroless nickel plating solution containing 0.2 to 2.5 mol / L of phosphite ions from the beginning of the construction bath was used. And withdrawing a portion of the plating solution in accordance with the amount of reduction of hypophosphite ion (the amount of oxidation to phosphite ion) calculated from the above deposition rate, and in accordance with this amount of extraction. Replenish the supply, in this case, as the replenisher, the nickel consumption, hypophosphite ion consumption, pH increase calculated from the deposition rate, and the amount of the plating solution withdrawn and replenishment of the replenisher. Using a replenisher containing a predetermined concentration of each of the above components according to the dilution amount of the plating solution, that is, using a replenisher containing also phosphite ions, the concentration of each of the above components in the plating solution and the pH are established. By maintaining the component concentration and pH in the plating solution at the time of bathing, continuous use of the plating solution of 20 turns or more, especially 50 turns or more becomes possible, and a constant deposition rate, Ni-P It has been found that the composition of the deposited film can be maintained.

Accordingly, the present invention provides an electroless nickel plating method in which plating is continued for at least 20 turns using an electroless nickel plating solution containing nickel ions, a complexing agent for the nickel ions, and hypophosphite. Wherein the phosphite generated by the oxidation of hypophosphite is 0.2 to 2.5
An electroless nickel plating solution that gives a predetermined deposition rate and a Ni-P deposition film composition is selected from the electroless nickel plating solutions contained in the range of mol / L, and nickel ions that match the plating solution composition and pH value are selected. , A complexing agent, hypophosphite and an electroless nickel plating solution having a phosphite concentration and a pH value are bathed, and while plating is performed using this plating solution, a part of the plating solution is continuously applied. A replenisher containing the above components is continuously or replenished at predetermined intervals so as to maintain the concentration and the pH value of the above components in accordance with the amount of the extracted components. A nickel plating method is provided.

In this case, the nickel ion concentration and the pH of the plating solution are measured continuously or intermittently, and the concentrations of the complexing agent, hypophosphite ion and phosphite ion of the plating solution are continuously measured. Or intermittently quantitative analysis, nickel ion, complexing agent according to the above analysis value and pH measurement value,
It is preferable to adjust the plating solution so that hypophosphite, phosphite, and a pH adjuster are replenished with a predetermined component so as to be included in a predetermined management range or the plating solution is withdrawn,
Thus, even when the plating solution fluctuates due to the withdrawal and replenishment of the plating solution, the plating solution composition and pH can be quickly and reliably maintained at a constant level.

Further, it is preferable to employ a capillary electrophoresis analysis method, an ion chromatography analysis method or an isotachophoresis analysis method for controlling the plating solution, whereby the hypophosphite ion, the phosphite ion The complexing agent concentration can be accurately and easily determined in about 3 to 10 minutes.
That is, it takes 2 to 3 hours for chemical analysis of hypophosphite ions and phosphite ions, and it is difficult to incorporate such a long-term analysis into the plating solution management system. As a complexing agent, usually, two to three kinds of organic carboxylic acids (for example, two to three kinds of citric acid, succinic acid, malic acid, tartaric acid, lactic acid, acetic acid, and salts thereof) are used. Since it was difficult to accurately quantify each of these carboxylic acids, the quantitative analysis of hypophosphite ions, phosphite ions, and complexing agents (organic carboxylic acids) was performed by the plating management system. Although it was not incorporated, in order to accurately and quickly manage the plating solution, it is necessary to accurately detect the concentration of these components and adjust the plating solution composition,
Then, the above components can be accurately and quickly quantified in about 3 to 10 minutes by using capillary electrophoresis analysis, ion chromatography analysis, or isotachophoresis analysis. By incorporating into the control and controlling the concentration of hypophosphite ion, phosphite ion, and complexing agent, a constant plating rate, even in the use of more than 20 turns, especially more than 50 turns,
Electroless nickel plating can be performed with a plating film composition.

Further, the extracted plating solution is used in the above-mentioned JP-A-5-247660 and JP-A-10-18335.
No. 9, phosphite ions can be removed and reduced by the method described in JP-A No. 9 to be easily regenerated, and the composition is further adjusted to be used as the replenishing solution, so that there is no waste of the extracted plating solution. All possible plating useful components can be used.

[0018]

DETAILED DESCRIPTION OF THE INVENTION The electroless nickel plating solution to be treated according to the present invention contains a water-soluble salt of nickel to be electrolessly deposited, a complexing agent thereof, and a hypophosphite as a reducing agent as a main component. Preferably, any type of nickel sulfate, sodium hypophosphite, and sodium hydroxide as a pH adjuster may be used as long as they can be continuously used. In this case, the electroless nickel plating solution is an acidic type. , Neutral type or alkaline type,
The composition may be a known one, and an acidic bath having a pH of 3.5 to 6.5 is particularly preferably applied.

Specifically, examples of the electroless nickel plating solution include nickel sulfate as a water-soluble salt of nickel, and carboxylic acids such as citric acid, succinic acid, tartaric acid, malic acid, acetic acid, lactic acid and the like as complexing agents. And other known nickel complexing agents and reducing agents containing sodium hypophosphite as a main component. The concentrations of these components are in the usual range, for example, nickel sulfate is 0.02
0.3 mol / L, complexing agent is in the range of 1 to 7 mol / L with respect to 1 mol / L of nickel sulfate, and sodium hypophosphite is 10 mol / L.
９０90 g / L. In addition, a stabilizer, a pH adjuster, and the like can be added to this plating solution, and the pH of the electroless nickel plating solution can be alkaline or acidic. However, the pH of the plating solution for continuous use is 3. 5
It is usually from 6.5 to 6, especially from 4 to 6.

In the present invention, in such an electroless nickel plating solution, a plating solution aged to a certain extent by using the electroless nickel plating solution based on a known replenishing method or the like, that is, phosphorous acid generated by oxidation of hypophosphite. 0.2 salt
~ 2.5 mol / L, preferably 0.6-1.5 mol / L
L, more preferably from 0.6 to 1.1 mol / L, still more preferably from 0.7 to 1.0 mol / L, a plating solution giving a predetermined deposition rate and a Ni-P deposition film composition. And a component analysis is performed to use a plating solution having a nickel ion, a complexing agent, hypophosphite and a phosphite concentration and a pH value that match the composition and pH value of the plating solution. Plating.

That is, the phosphite is added at an amount of 0.2 from the beginning.
A bath containing a plating solution containing the plating solution in the range of ~ 2.5 mol / L and plating an object to be plated with the plating solution while continuously plating a part of the plating solution continuously or at predetermined intervals (preferably 10 minutes or less) A part of the plating solution is extracted (especially at intervals of 5 minutes or less) (preferably 5 to 20%, particularly 7 to 15% of the plating solution per hour). The replenishment is performed continuously or at predetermined intervals (preferably at intervals of 10 minutes or less, particularly at intervals of 5 minutes or less) so that the plating solution component concentration and the pH value at the time of the bathing are the same.

Here, the components and concentrations of the plating solution are as described above, and the concentrations and the control ranges (permissible increase / decrease ranges from the set concentrations) of the respective components which are more preferable for the purpose of the present invention are as follows. It is on the street. Water-soluble nickel salt (particularly nickel sulfate) concentration: 0.03 to 0.14 mol / L, particularly 0.07 to
0.1 mol / L (2-8 g / L as nickel, especially 4
-6 g / L) Control range: ± 0.02 mol / L, especially ± 0.01 mol / L
L (± 0.5 g / L as nickel, especially ± 0.1 g / L
L) If the nickel concentration is too high, the plating rate is increased and the plating solution is easily decomposed. On the other hand, if it is too low, the plating rate will be slow. Hypophosphite (especially sodium hypophosphite) concentration: 10 to 40 g / L, especially 20 to 30 g / L Control range: ± 1 to 5 g / L, especially ± 1 g / L High hypophosphite concentration If too much, the plating speed will increase,
The plating solution is easily decomposed. Also, the phosphorus content in the coating increases. On the other hand, if it is too low, the plating rate will be slow. Phosphite (especially monosodium phosphite) concentration: 0.2 to 2.5 mol / L (20 to 260 g / L) Control range: ± 0.1 to 1 mol / L (± 10 to 100 g / L)
L) If the phosphite concentration is too high, the plating rate becomes slow, and the plating solution is easily decomposed. Further, if the phosphorus content in the film increases and the increase is too large, the stability of the film properties decreases. Complexing agent (especially carboxylic acids) concentration: 50 to 500 mol% per 1 mol / L of nickel,
Especially 100 to 300 mol% (10 to 100 g / L, especially 20 to 60 g / L) Management range: ± 0.01 to 0.04 mol / L, especially ± 0.
01 to 0.02 mol / L (± 1 to 5 g / L, especially ± 1 to
(2 g / L) If the concentration of the complexing agent is too high, the plating rate is reduced. If it is too low, the plating rate will be high and the plating solution will be easily decomposed. On the other hand, if the control range is too large, the properties of the bath change, and the stability of the film properties decreases. pH (hydrogen ion concentration) pH value: 3.5 to 6.5, especially 4 to 6 Management concentration: ± 0.1, especially ± 0.05 If the pH is too high, the plating rate becomes high, and the plating solution is decomposed. It will be easier. If it is too low, the plating rate will be slow and the phosphorus content in the film will increase.

In this case, the phosphite ions in the plating solution do not gradually increase and the phosphite ions are maintained or slightly decreased in accordance with the deposition rate with respect to the amount of withdrawal, the amount of replenishment, and the concentration of each component of the replenisher. In addition to setting the amount of extraction so that the amount of the extraction solution, the amount of the evaporation by heating the plating solution, and the amount of the object to be plated are appropriately taken into consideration, the replenisher may be set so that the amount of the plating solution is maintained. it can.

Further, the concentration of each component in the replenishing solution is such that the complexing agent and the phosphite ion are maintained at a constant concentration in consideration of the extraction amount and the degree of dilution by the replenishing amount of the replenishing solution. It is preferable that nickel ions, hypophosphite ions and a pH increasing agent (caustic alkali such as NaOH or ammonia water) are extracted and replenished at the same time.
It can be set by considering the amount of consumption from the deposition rate. For example, a phosphite ion and a complexing agent are contained in the same concentration as the plating solution at the time of building bath, and the first concentration containing nickel ions in a high concentration in consideration of the consumption from the deposition rate.
And the same amount as the withdrawal amount, and a second solution containing hypophosphite and a pH increasing agent at a predetermined concentration.
And the replenishing solution can be supplied according to the evaporation rate of the plating solution during plating.

In carrying out the method of the present invention, it is effective to consider the utilization efficiency of the reducing agent (hypophosphite) in setting the composition of the plating solution and the composition of the replenishing solution. That is, the concept of the use efficiency of the reducing agent has been conventionally used, but this is economical if the use efficiency is high, and is uneconomical if the use efficiency is low, and is merely used as an index to some extent. However, in the conventional operation method in which the life until disposal is relatively short, the difference in efficiency of at most 10% is not a problem. On the other hand, in the present invention, it is effective to use it as an important technical factor in operation. For example, in the case of a bath having a hypophosphite reduction efficiency of 40%, when 1 mol of nickel is precipitated, 2.5 mol of phosphite ions are generated. If the nickel concentration of the replenisher is set in accordance with, the concentration management can be relatively easily performed, and the apparatus does not need to be complicated. The relationship between the reduction efficiency of hypophosphorous acid and the number of moles of phosphite ions generated when 1 mole of nickel is precipitated is as follows. Hypophosphite reduction efficiency Number of moles of formed phosphite (per mole of Ni) 40% 2.5 33% 3.0 25% 4.0 This value is based on the plating bath system (type of complexing agent, pH, etc.), and the reduction efficiency of hypophosphorous acid should be considered for the plating solution used.

Also, in the present invention, the above extraction,
While performing replenishment, quantitatively analyze nickel ions continuously or intermittently, confirm that the nickel ion concentration is within a predetermined control range at appropriate intervals, or replenish nickel ions so that they are within this control range. It is recommended to adjust. It should be noted that quantitative analysis of nickel ions can be performed continuously by using a spectrophotometer because analysis data can be continuously taken out by a spectrophotometric method.

In the present invention, the pH of the plating solution is
Is measured continuously or intermittently using a pH meter and p
It is recommended to confirm that H is within a predetermined control range, or to adjust the pH so that it is within this control range.

Furthermore, in the present invention, it is recommended to continuously or intermittently determine hypophosphite ion, phosphite ion, and complexing agent (usually, two or three or more organic carboxylic acids). Is done. In this case, it is preferable to employ a capillary electrophoresis (CE) method, an ion chromatography (IC) method or an isotachophoresis (ITP) method for the quantitative analysis. In particular, the capillary electrophoresis method requires a short analysis time. It is preferable because analysis can be performed even when an organic acid (salt) and an inorganic acid (salt) are mixed, and simultaneous quantification of anions and cations can be performed.

In the present invention, it is confirmed from the hypophosphite ion concentration value, the phosphite ion concentration value and the complexing agent concentration value obtained by the above method that these are within a predetermined control range, or It is recommended that hypophosphite, phosphite, and complexing agent be supplied or the plating solution is extracted and adjusted so as to be within this control range.

Further, in the present invention, the extracted plating solution is preferably subjected to a regenerating treatment by the following method.

That is, with respect to the extracted plating solution,
First, nickel sulfate is added, and phosphite ions in the plating solution are precipitated and removed as nickel phosphite.

In this case, the amount added in this treatment may be higher than the nickel ion concentration (normal plating control nickel ion concentration) in the normal plating operation of the plating solution, but is preferably the plating control nickel ion concentration. The concentration is more than 1 and not more than 10 times by weight, preferably 1.
It is preferable to add the phosphite in an amount of 2 to 10 times by weight, particularly 1.5 to 6 times by weight, from the viewpoint of the formation and precipitation of the hardly soluble phosphite. Further, it is preferable that the addition of the nickel sulfate is in 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 plating solution to a temperature higher than the plating operation temperature (normal plating management temperature) together with the addition of the nickel sulfate, and the operation of increasing the plating solution pH in the plating operation (normal plating management pH). It is preferable to perform one or both of the operations of raising the pH to a higher pH in order to more effectively generate and precipitate the hardly soluble nickel phosphite.

In this case, the former operation is preferably performed at 5 ° C. or higher than the normal plating control temperature. For example, a common acidic electroless nickel plating solution 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 acid type electroless nickel plating solution having a pH of 4 to 6, the pH is 4.5 to 12, preferably a pH of 7 to 1.
0, especially high pH as described above in the range of pH 8-9
Is preferable.

The pH adjustment is important from the viewpoint of effectively producing and precipitating hardly soluble nickel phosphite. That is, when performing electroless nickel plating, hypophosphite as follows ion H ₂ PO ₂ ^- phosphite ion H ₂ PO ₃ by oxidation of ^- but is produced which H ₃ PO by the pH of the bath ₃ or HPO ₃ ^2- . In this case, N
i ^{2 +} react with make phosphite nickel salt sparingly soluble, to precipitate for HPO ₃ ^2-one in which adjusting pH as described above. H ₂ PO ₂ ⁻ + H ₂ O = H ₂ PO ₃ ⁻ + 2H ⁺ + 2e NaH ₂ PO ₃ + NaOH = Na ₂ HPO ₃ + H ₂ O

As a method of increasing the pH of the plating solution, a method of adding an alkali hydroxide such as sodium hydroxide or ammonia water and a method of adding a hydroxide or carbonate of nickel can be used. . In the latter case, in the treatment for increasing the pH, the addition increases the pH, so that the amount of nickel ions added may be smaller than in the above-described treatment for adding the additive.

When carrying out this method of raising the pH, the plating solution may be at room temperature, but it is preferable to keep and leave it at about 40 ° C.

In each of the above treatments, if necessary, the mixture is allowed to stand with stirring to form and precipitate a poorly soluble nickel phosphite salt. In this case, the standing time is 30 minutes to 24 hours, particularly 1 minute.
It is preferably set to 5 hours.

Separation and removal of the formed precipitate can be carried out by a conventional method such as filtration. In this case, it is preferable to separate by filtration at a high temperature.

The regenerated plating solution can be used for plating again after adjusting the nickel ion concentration, hypophosphite ion concentration, pH, etc., and thus can be used as the replenisher. . It should be noted that a new electroless nickel plating can be used as the replenishing agent.

The separated nickel phosphite N
iHPO ₃ can be treated by adding sulfuric acid or sulfuric acid and sodium sulfate thereto, whereby nickel sulfate and phosphorous acid or monosodium phosphite are formed from nickel phosphite according to the following reaction i or ii. . In _{NiHPO 3 + H 2 SO 4 =} NiSO 4 + H 3 PO 3 ... i NiHPO 3 + 1 / 2H 2 SO 4 + 1 / 2Na 2 SO 4 = NiSO 4 + NaH 2 PO 3 ... ii this process, in the case of the reaction of i sulfuric acid The amount used is
It is preferably from 0.5 to 1.2 mol, particularly preferably from 0.7 to 1.0 mol, per mol of nickel phosphite. When the amount of sulfuric acid is too small, there is a disadvantage that dissolution of nickel phosphite is delayed.When the amount is too large, after separating nickel sulfate and phosphorous acid, a large amount of a pH adjuster is required when reused. Occurs.

The sulfuric acid used in this treatment is 5
It is desirable to use 硫酸 20% by weight, especially 10-15% by weight of dilute sulfuric acid.

On the other hand, in the case of the reaction (ii), sulfuric acid and sodium sulfate are used in an equivalent amount, and the total amount thereof is 0.5 to 1.2 mol, particularly 0.7 to 0.7 mol per mol of nickel phosphite. It is preferable to make it 1.0 mol.
Sodium sulfate is 2 to 20% by weight, especially 5 to 1%.
It can be used by dissolving it in 5% by weight of dilute sulfuric acid.

Sulfuric acid or sulfuric acid and sodium sulphate are added to nickel phosphite to form nickel sulphate and phosphorous acid or monosodium phosphite, and the resulting nickel sulphate and phosphorous acid or monosodium phosphite are converted. Specific methods for separation include a conventional crystallization treatment utilizing the difference in solubility between nickel sulfate and phosphorous acid or monosodium phosphite in water, or nickel sulphate by electrodialysis using an ion exchange membrane. A method for obtaining a concentrate can be employed.

The nickel sulfate separated as described above can be used as a component of the plating solution, but it is recommended to use it as a raw material nickel sulfate used for precipitation and formation of the above-mentioned nickel phosphite. You.
Phosphorous acid or monosodium phosphite is discharged out of the system.

On the other hand, the plating solution after the above-mentioned nickel phosphite has been separated can be reused as a regenerating and replenishing solution as described above. Sodium sulfate may gradually accumulate in the plating solution.

For this reason, the electroless nickel plating solution from which nickel phosphite has been removed as described above is cooled, if necessary, to a temperature lower than room temperature to precipitate and precipitate sodium sulfate. It is recommended that the phosphite ions accumulate in the plating solution can be effectively removed, and the plating solution can be regenerated and reused. Sodium sulfate can be easily and reliably removed without mixing impurity ions, so that the plating solution has a longer life and the electroless nickel plating solution can be used repeatedly over a longer period of time. .

Here, the amount of the accumulated sodium sulfate when the treatment is performed is appropriately selected.
At 200 g / L or more, especially at 400 g / L or more, before the solubility limit of sodium sulfate is reached. Although the cooling temperature is not particularly limited, it is -3 to 15C, particularly 0 to 5C. If it is too low, the entire plating solution will crystallize, and if it is too high, the amount that can be removed at one time will be small. Further, as a method for removing the precipitated sodium sulfate, an ordinary crystallization method can be used.

In this case, the sodium sulfate removed from the plating solution can be used in the above reaction ii when nickel sulfate is obtained from nickel phosphite.

The plating solution from which the sodium sulfate has been removed in this manner is adjusted in the same manner as described above, and is reused as a replenisher for the plating solution.

The extracted plating solution is regenerated as described above, and if necessary, the same treatment is applied to the entire plating solution to reduce the phosphite ions in the plating solution. The plating solution concentration and pH can be adjusted and regenerated by the plating solution concentration and pH management method based on the present invention described above.

According to the present invention, according to the management method,
The plating solution can be used for 20 turns or more, preferably 30 turns or more, more preferably 40 turns or more, particularly 50 turns or more, and plating of 100 turns or more is also possible. , Deposition rate,
The Ni-P coating composition can be kept substantially the same as the initial one.

In the present invention, the deposition rate, Ni-
The fact that the composition of the P deposited film is constant means that the total area S of the portion of the object to be plated with respect to the plating temperature and the bath ratio (the plating solution amount L, ie, S /
L) means a state in which plating is continuously performed with a constant value, and thus indicates characteristics of the plating solution managed in the present invention.

In the actual plating operation of the present invention, it is optional to appropriately change the plating temperature and the bath ratio, and even if the plating temperature and the bath ratio are changed, the above-described plating method (plating solution management) is adopted. Then, under these conditions, the composition of the Ni-P deposition film at a constant deposition rate is maintained. In the present invention, there is no particular limitation on the material and the like of the object to be plated.

[0055]

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 solution having the following composition having a deposition rate of 11.3 μm / h and a Ni—P coating composition of 93.0% by weight of Ni and 7.0% by weight of P was prepared.

Nickel sulfate 0.085 mol / L Sodium hypophosphite 0.31 mol / L Sodium acetate 0.23 mol / L Malic acid 0.30 mol / L Lead ion (Pb ²⁺ ) 0.3 mg / L L Sodium phosphite 0.70 mol / L pH 4.6 On the other hand, the following replenishers I and II were prepared. (Replenisher I) Nickel sulfate 0.317 mol / L Sodium hypophosphite 0.31 mol / L Sodium acetate 0.23 mol / L Malic acid 0.30 mol / L Lead ion (Pb ²⁺ ) 0.25 Mmol / L sodium phosphite 0.14 mol / L pH 4.6 (Replenisher II) Sodium hypophosphite 1.099 mol / L sodium hydroxide (NaOH) 0.825 mol / L An object to be plated (steel, surface area: ² dm ² ) was put per liter, and a plating test was performed at 80 ° C. for 100 hours. In this case, the replenishment liquid I is 0.1
The replenishing solution II was replenished at a rate of 0.069 liter / hour at an interval of 20 minutes at a rate of 27 liters / hour, and at the same time, the plating solution was withdrawn at a rate of 0.127 liters / hour. The amount of the solution corresponding to the replenishment of the replenishment solution II corresponded to the decrease in the solution due to evaporation, and the plating solution held 1 liter during plating.

During the plating, nickel ions and pH were continuously determined by a spectrophotometer and a pH meter, and hypophosphite ions, phosphite ions, and complexing agents (malic acid and acetic acid) were added. Quantification was performed by capillary electrophoresis, and these components were controlled within the control range. (The equipment used was a device that can control the analytical accuracy of each component in a range of ± 1 to 5%, although the analysis accuracy for each component is not constant. ) Was checked, and if it exceeded the control range, replenishment was stopped and at the same time the operation of extracting the plating solution was stopped. The total replenishment amounts of the components thus replenished were as follows (total during plating for 100 hours). Nickel sulfate 4.0 mol / L Sodium hypophosphite 11.5 mol / L Sodium acetate 2.9 mol / L Malic acid 3.8 mol / L Lead ion (Pb ²⁺ ) 3.2 mg / L Hydroxide Sodium (NaOH) 5.7 mol / L

When the phosphite ion analysis value exceeds the predetermined control range (in this embodiment, the control upper limit concentration of NaH ₂ PO ₃ was set to 0.70 mol / L), plating was performed in addition to the above extraction. The liquid was extracted, and the replenishing liquid I was replenished in a corresponding amount. The total extraction amount of plating time is 1
It was 2.7 L.

As a result, the composition of the plating solution after 100 hours of plating (about 50 turns) was as follows. Nickel sulfate 0.085 mol / L Sodium hypophosphite 0.31 mol / L Sodium acetate 0.23 mol / L Malic acid 0.30 mol / L Lead ion (Pb ²⁺ ) 0.3 mg / L Phosphorous Sodium acid 0.70 mol / L pH 4.6

The plating rate and Ni—P coating composition at the time of plating for 100 hours are as follows:
Even after plating for 100 hours, that is, after about 50 turns, the plating rate and the Ni-P coating composition were kept almost constant. After 1 turn After 30 turns After 50 turns Plating time 11.3 μm / h 11.3 μm / h 11.3 μm / h Phosphorus content in Ni-P coating 7.0 wt% 7.0 wt% 7.0 wt%

[0062]

According to the present invention, electroless nickel plating can be carried out over a long period of 20 turns or more, especially 50 turns or more, while keeping the deposition rate and Ni-P coating composition constant.

Claims (4)

[Claims] 1. An electroless nickel plating method in which plating is continued for 20 turns or more using an electroless nickel plating solution containing nickel ions, a complexing agent for the nickel ions, and hypophosphite, An electroless nickel plating solution containing a phosphite generated by the oxidation of hypophosphite in the range of 0.2 to 2.5 mol / L, which provides a predetermined deposition rate and Ni-P deposition film composition. The composition of the nickel plating solution is selected, and an electroless nickel plating solution having a nickel ion, a complexing agent, a hypophosphite and a phosphite concentration and a pH value that match the composition and the pH value of the plating solution is established. Then, while plating using this plating solution,
A part of the plating solution is withdrawn continuously or at predetermined intervals, and the concentration of the component and p
An electroless nickel plating method characterized by replenishing a replenisher containing the above components continuously or at predetermined intervals so as to maintain the H value. 2. The method according to claim 2, wherein the nickel ion concentration and the pH of the plating solution are continuously or intermittently measured, and the concentrations of the complexing agent, hypophosphite ion, and phosphite ion of the plating solution are continuously or intermittently measured. Quantitatively analyzed intermittently, and according to the above analysis value and the measured pH value, nickel ions, complexing agents, hypophosphites, phosphites, and pH adjusters were specified so as to be included in the specified control range. 2. The plating method according to claim 1, wherein the plating solution is adjusted so as to replenish the components or withdraw the plating solution. 3. The plating method according to claim 2, wherein capillary electrophoresis analysis, ion chromatography analysis or isotachophoresis analysis is used for plating solution management. 4. The plating method according to claim 1, wherein the replenishing solution is a regenerated product of the extracted plating solution.