JP2697544B2 - Analysis method for electroless tin, lead or their alloy plating bath - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention determines the amount of reduction of each component in a plating bath due to pumping of a plating solution during a plating operation when electroless tin, lead or an alloy thereof is plated on copper or a copper alloy. In more detail, the analysis method
Electroless tin which can easily and accurately quantify the decrease due to the pumping out of each component in the plating bath, and which can reliably maintain a constant component composition by replenishing each component according to this quantitative value, The present invention relates to a method for analyzing a plating bath of lead or an alloy thereof.

[0002]

2. Description of the Related Art Conventionally, in order to impart solderability to copper or copper alloy parts of electronic industrial parts, circuits, etc., tin, lead or tin-lead alloy plating is carried out by electroplating. Although a film is formed, components and circuits are miniaturized or complicated with the miniaturization of electronic devices, and some parts cannot be plated by electroplating.

[0003] Therefore, an electroless tin, lead or tin-lead alloy plating method capable of plating even a portion where application of the electroplating method is difficult has been studied. For example, Japanese Patent Application Laid-Open No. 1-1842
No. 79 discloses an electroless tin-lead alloy plating containing a specific organic sulfonic acid, tin and lead salts of the organic sulfonic acid, sodium hypophosphite (reducing agent) and thiourea (complexing agent) as main components. A method using a bath has been proposed.

[0004] However, the conventional electroless tin, lead or tin-lead alloy plating method is often a disposable batch method in which the metal concentration in the plating bath is reduced to a deposition limit or less without replenishing the metal, and the metal is discarded as it is. Therefore, there is almost no proposal to use a plating bath continuously for the purpose of obtaining a thick plating film, and therefore a constant and constant deposition amount required for continuous use can be maintained. As for the replenishment management method of the plating bath, there is no practically effective proposal at present.

On the other hand, in a normal electroless plating method,
Replenishing the plating bath with a chemical corresponding to the consumed metal content enables thickening. More specifically, solution management is performed by analyzing the plating solution used, measuring the metal concentration, calculating the insufficient metal component from the measurement result, and replenishing the amount of the chemical according to the calculation result. I have.

However, according to the study of the present inventors, in the case of electroless tin, lead or a tin-lead alloy plating bath, the metal components tin and lead are elements which are originally difficult to analyze easily, and the In the electrolytic plating solution, the copper eluted from the object to be plated dissolves and accumulates in the plating bath as the plating proceeds, so that it is difficult to easily and accurately analyze tin and lead components. Plating bath management method is electroless tin,
It was difficult to apply to a lead or tin / lead alloy plating bath.

Therefore, the present inventors can relatively easily analyze the tin and lead consumption of the electroless tin, lead or tin-lead alloy plating bath, and can analyze the electroless tin, lead or tin-lead alloy plating bath. As a result of repeating various tests in order to develop a method for effectively performing bath management, the amount of copper eluted into the plating bath as the plating progresses and the amount of metal consumed is reduced. The inventors have found that there is a proportional relationship, and have previously proposed a method of measuring the copper ion concentration in a plating bath and replenishing metal components in accordance with the measured value (Japanese Patent Application Laid-Open No. 4-276081).

However, subsequent studies have revealed that the analysis of the copper concentration in the plating bath alone may not be able to maintain an appropriate concentration composition. That is, the reduction of the metal component due to the dilution of the plating solution due to the pumping out of the plating solution during the plating operation is not supplied, and even if the copper elutes into the plating bath due to the progress of plating, the copper in the plating bath is In some cases, the concentration of the eluted copper may not be increased enough to be pumped out, so that accurate metal replenishment may not be possible.

Here, in order to correct the decrease of each component due to pumping out of the electroless plating bath or the like, the concentration of each component is measured by atomic absorption spectrometry or the like, and each component is measured according to the measurement result. However, it is extremely difficult to perform such concentration measurement at any time during continuous plating due to processing efficiency.Therefore, at the plating factory site, each component can be easily extracted by pumping without interrupting the plating operation. Development of an electroless tin, lead or alloy plating bath analysis method that can quantify the amount of decrease in amount and can perform automatic analysis and can perform liquid replenishment at any time by combining with an automatic management device Is desired.

The present invention has been made in view of the above circumstances, and it is possible to easily and accurately quantitatively analyze the reduction amount of components in a plating bath by pumping, and to perform automatic analysis.
An object of the present invention is to provide a method for analyzing an electroless tin, lead or tin-lead alloy plating bath that can reliably maintain a constant component composition by replenishing each component as needed according to this quantitative value. .

[0011]

Means and Action for Solving the Problems The present inventors have
As a result of intensive studies to achieve the above object, a water-soluble tin salt and / or a water-soluble lead salt, an acid dissolving these salts, and an electroless plating bath containing thioamides as a complexing agent, A plating solution was taken out from the plating bath as an analysis sample, and the sample was adjusted to be acidic, bismuth ions were added to develop a color, and colorimetric analysis was performed to add the plating solution as a complexing agent. By measuring the concentration of thioamides in the plating bath and calculating the amount of reduction of each of the other components from the decrease in the concentration of thioamides, it is possible to accurately and easily quantify the amount of reduction of each component in the plating bath by pumping. I found it.

That is, the amount of reduction in the concentration of each component due to pumping out of the plating solution is expected to be proportional to the concentration of each component.
This can be confirmed by pumping experiments. Therefore, it is considered that any one component in the plating solution can be quantitatively analyzed, and the reduction amount of the other component can be proportionally calculated from the content ratio based on the reduction amount. However,
The analysis of the metal ions in the plating bath is difficult because the concentration changes due to the plating operation as the concentration decreases due to pumping. Therefore, the present inventors quantitatively analyze thioamides such as thiourea which complex metal components in the plating solution, and calculate the amount of reduction of other components from the amount of reduction of the thioamides in the plating solution. We investigated the method for quantitative analysis of thioamides by simple colorimetry suitable for automatic analysis.

As a result, they found a method of adding bismuth ions to a plating solution to form a color. That is, conventionally, a method is known in which thiourea is added to quantitative analysis of bismuth and measurement is performed by a colorimetric method. In this method, bismuth ions and thiourea and a derivative thereof form a complex to develop a yellow color. In this analysis method, the inventors of the present invention thought that coloration could be achieved by adding bismuth ions to thioamides, and the thioamides could be quantified by colorimetry. However, even if bismuth ions are simply added to the plating solution separated from the tin, lead or tin-lead alloy plating bath, stable color formation cannot be obtained. After acidification by adding an acid to the mixture, particularly after adjusting the pH to 2.0 or less, stable color development is obtained by adding bismuth ions.
The inventors have found that the concentration of thioamides can be quantitatively analyzed easily and accurately by a colorimetric method, thereby completing the present invention.

Accordingly, the present invention provides an electroless plating bath containing a water-soluble tin salt and / or a water-soluble lead salt, an acid dissolving these salts, and a thioamide as a complexing agent. When performing electroless tin, lead or alloy plating thereof, an analysis method for quantifying the amount of reduction of each component in the plating bath by pumping out with the plating operation, wherein a small amount of the plating solution is removed from the plating bath. After the mixture was adjusted to be acidic, bismuth ions were added to form a color, and the concentration of thioamides in the plating solution was measured by a colorimetric method to determine the amount of reduction, and the amount of reduction of this thioamide was determined. The present invention provides a method for analyzing electroless tin, lead or alloy plating baths thereof, wherein the amount of reduction of other components is determined from the following.

Hereinafter, the present invention will be described in more detail.
The plating bath used in the present invention contains a metal salt component composed of a water-soluble tin salt, a water-soluble lead salt or a mixture thereof, an acid component that dissolves these metal salts, and a complexing agent as main components. Things.

The water-soluble tin salt includes, for example, stannous sulfate, stannous alkanesulfonate, stannous chloride, stannous alkanolsulfonate, stannous sulfosuccinate and the like. Examples of the water-soluble lead salts include, for example, lead chloride, lead methanesulfonate, lead acetate, lead alkanolsulfonate, and lead sulfosuccinate.Also, examples of the acid component that dissolves these metal salts include alkanesulfonic acid, Examples include hydrochloric acid, alkanolsulfonic acid, perchloric acid, sulfosuccinic acid, and borofluoric acid.

The alkanesulfonic acid and alkanolsulfonic acid include, for example, methanesulfonic acid, ethanesulfonic acid, propanesulfonic acid, 2-propanesulfonic acid, butanesulfonic acid, pentanesulfonic acid, hexanesulfonic acid, and decanesulfonic acid. , Dodecanesulfonic acid, isethionic acid (2-hydroxyethane-1-sulfonic acid), 2-hydroxypropane-1-sulfonic acid,
1-hydroxypropane-2-sulfonic acid, 3-hydroxypropane-1-sulfonic acid, 2-hydroxybutane-1-sulfonic acid, 4-hydroxybutane-1-sulfonic acid, 2-hydroxypentane-1-sulfonic acid, 2-
Hydroxyhexane-1-sulfonic acid, 2-hydroxydecane-1-sulfonic acid, 2-hydroxydodecane-1
-Sulfonic acid and the like.

As the complexing agent, thioamides are used, and specific examples thereof include thiourea and thiourea derivatives such as thioformamide and thioacetamide. Among these, thiourea is generally used. Used for Further, a reducing agent such as hypophosphorous acid or hypophosphite can be added to the plating bath.

The method for analyzing a plating bath of tin, lead or their alloys according to the present invention is characterized in that an object to be plated having at least a part of its surface formed of copper or a copper alloy is immersed in the plating bath. In forming tin, lead or tin-lead alloy plating film on copper or copper alloy, in order to replenish each component in the plating bath reduced by pumping out with plating operation,
The quantitative analysis of the decrease in each component is performed by measuring the concentration of thioamides incorporated as a complexing agent in a plating bath by a colorimetric method, and obtaining each component in proportion to the decrease. In this case, in the present invention, a plating solution is taken out from the plating bath as an analysis sample, and the sample is made acidic,
Preferably, after adjusting the pH to 2 or less, bismuth ions are added to develop a color, and the color is determined by a colorimetric method.

The acid for adjusting the sample to be acidic includes inorganic acids such as sulfuric acid, perchloric acid and pyrophosphoric acid, and organic sulfonic acids such as methanesulfonic acid and ethanesulfonic acid. The addition concentration can be 10 to 900 g / L. In addition, this quantitative analysis method utilizes a coloration of the complex by forming a complex between the bismuth ion and the thioamides. Therefore, by adding a complexing agent for analysis at the time of analysis, it is more accurate. Colorimetric analysis. In this case, as a complexing agent for analysis, carboxylic acids such as oxalic acid, tartaric acid and citric acid, EDTA,
Aminocarboxylic acids such as CyDTA, EDTA-OH, NTA, IDA, HEDP (hydroxyethanediphosphonic acid), NTPO (nitrilotrismethylenesulfonic acid)
And the like, and salts thereof, and the like, and these can be used alone or in combination of plural kinds. The concentration of the complexing agent for analysis is not particularly limited, but is usually in the range of 5 to 200 g / L.

The bismuth ion can be added to the sample as the above-mentioned acid salt, nitrate, chloride or a basic salt or oxide thereof. The concentration of the bismuth ion is not particularly limited. Suitably, it is about 20 g / L. The colorimetric analysis method uses a wavelength of 480.
The method of measuring the absorbance around nm is recommended because it can easily and accurately quantify the concentration of thioamides and is suitable for automatic analysis.

As described above, the concentration of thioamides in the plating bath is measured, and the reduced amount of other components is determined in proportion to the reduced amount and the content ratio of other components. As a result, it is possible to obtain a reduced amount due to the pumping out of all components in the plating bath.This analysis operation is performed at any time during the plating operation, and each component is replenished to the plating bath so as to compensate for the shortage according to the result. By doing so, it becomes possible to correct the composition change of the plating bath due to pumping out and to stably perform plating with the always set component composition. At this time, each component may be independently replenished according to the reduced amount of each component, but a replenisher prepared to an appropriate composition is plated so as to replenish the reduced amount of thioamides obtained by analysis. By adding to the solution, all components can be replenished at once and accurately, and it is not necessary to calculate the reduction amount of other components one by one,
It is possible to easily and accurately perform bath management.

According to the analysis method of the present invention, a small amount of a plating solution is separated from a plating bath, an acid and a bismuth ion are added thereto, and each component is accurately analyzed by a simple operation of simply performing a quantitative analysis by a colorimetric method. Since the amount reduced by pumping can be quantified, strict bath control can be performed by performing analysis at any time during the plating operation, and a colorimetric method suitable for automatic analysis is used, and as described above Since the bath composition can be easily corrected by replenishing a replenisher having a predetermined composition, automatic management of the plating bath can be easily performed by combining with a plating solution replenisher.

Here, what can be analyzed by the method of the present invention is the amount of reduction of each component due to pumping out, and the amount of reduction of tin and lead due to deposition on the object to be plated cannot be analyzed. Therefore, it is preferable to separately analyze the amount of reduction of these components due to precipitation, and to replenish the amount. In this case, the amount of reduction of tin and lead is determined by the concentration of copper eluted from the plating object as plating proceeds. Can be easily analyzed by quantifying.

When the metal component is replenished in accordance with the increase in the copper concentration, it is preferable to increase and replenish the thioamides as the complexing agent in accordance with the increase in the copper concentration. Unless such thioamides are replenished in an increased amount, the complexing agent in the plating solution is consumed to complex the copper ions due to the increase of the copper ions, and the deterioration of the plating performance such as a decrease in the deposition rate occurs. May be invited.

[0026]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to the following examples. [Examples] Four types of electroless tin-lead alloy plating baths having the following composition with varied amounts of thiourea were prepared, and the thiourea concentrations in these plating baths were analyzed by the following method. Table 1 shows the results.

Electroless tin-lead alloy plating bath composition Methanesulfonic acid 50 g / L Tin methanesulfonate 20 g / L Lead methanesulfonate 13 g / L Thiourea See Table 1 Sodium hypophosphite 80 g / L Citric acid 15 g / L Laurylpyridium chloride 5 g / L EDTA 3 g / L pH 2.0 Bath temperature 80 ° C. Plating rate 5 μm / 15 min Sn (wt%) in the deposited film 75

Analysis Method 1 mL of a plating solution was taken from a plating bath, and 40 mL of a solution containing 4 g / L of bismuth oxide, 10 g / L of EDTA.4H, and 500 g / L of methanesulfonic acid was added to the solution. Adjust to 50 mL with ion-exchanged water (pH 1 or less). After allowing this to stand for 5 minutes, the absorbance was measured at a wavelength of 480 n.
The thiourea concentration was measured using a spectrophotometer (U-3210, manufactured by Hitachi, Ltd.) in m.

[0029]

[Table 1]

From the results shown in Table 1, it was confirmed that the thiourea concentration in the plating bath can be accurately measured by this method.

[Application Example] The compounding amount of thiourea is 100 g /
Using the same electroless tin-lead alloy plating bath as in Example 1 above, the printed wiring board on which the copper pattern was formed was subjected to a running test. At this time, the plating solution is analyzed as needed, and each time the amount of thiourea is reduced by 2 g / L, the following replenishers (1), (2), and (3) are replenished in the amounts shown below, and the amount of copper is reduced to 0. Each time 2 g / L was increased, the following replenishers (1), (2), and (3) were replenished in the amounts shown below, and plating was performed while correcting each component in the plating bath. The quantification of thiourea was performed in the same manner as in the above example,
The quantity of copper was determined using a fluorescent X-ray analyzer.

Replenisher (1) Tin methanesulfonate 40 g / L Thiourea 200 g / L Replenisher (2) Lead methanesulfonate 50 g / L Replenisher (3) Methanesulfonic acid 100 g / L Sodium hypophosphite 215 g / L L Citric acid 40 g / L Laurylpyridinium chloride 13 g / L EDTA 50 g / L Replenishment amount Copper amount Replenishment with thiourea Replenisher (1) 10 ml / L 10 ml / L Replenisher (2) 2 ml / L 5.2 ml / L Replenisher (3)-10ml / L

As described above, the plating process for the printed wiring board was continuously repeated while performing the bath management. At this time, immediately after the components of the plating bath were corrected by the replenishment of the replenishers (1), (2) and (3), the concentrations of Sn and Pb in the plating bath were successively measured using a fluorescent X-ray analyzer. , The fluctuation width (deviation) was observed. Table 2 shows the results. In addition,
The printed wiring board used had a pattern ratio of 1.0% and a bath load of 0.5 m ² board / 100 L. A tin / lead alloy plating film having a thickness of 5 μm was formed on the copper pattern of the printed wiring board. Further, the quantification of the thiourea and the quantification of the copper amount were performed every 45 racks.

[0034]

[Table 2]

As is evident from the results in Table 2, according to the analysis method of the present invention, the amount of each component reduced by pumping can be quantitatively analyzed easily and accurately. It is confirmed that the composition of the plating bath can be well controlled over a long period of time and the plating can be stably performed while maintaining a constant plating performance by replenishing the solution by copper concentration analysis. Was.

[0036]

As described above, according to the method for analyzing an electroless tin, lead or tin-lead alloy plating bath of the present invention, the amount of each component reduced by pumping can be quantitatively analyzed simply and accurately. It is possible to easily and surely control the bath composition of the electroless tin, lead or tin-lead alloy plating bath by replenishing the solution according to the analysis result.

Continuation of the front page (72) Inventor Toru Kamitama 1-5-1, Hirakata Exit, Hirakata-shi, Osaka Uemura Industry Co., Ltd. Central Research Laboratory (56) References JP-A-4-276082 (JP, A) JP-A-3 -207898 (JP, A) JP-A-3-64482 (JP, A)

Claims (1)

(57) [Claims] 1. An electroless plating bath containing a water-soluble tin salt and / or a water-soluble lead salt, an acid for dissolving these salts, and a thioamide as a complexing agent. When performing plating of lead or an alloy thereof, it is an analysis method for quantifying the amount of reduction of each component in the plating bath due to pumping out of the plating operation, in which a small amount of plating solution is separated from the plating bath, After adjusting the acidity, the color is developed by adding bismuth ions, the concentration of thioamides in the plating solution is measured by a colorimetric method to determine the amount of reduction, and other components are determined from the amount of reduction of the thioamides. A method for analyzing a plating bath for electroless tin, lead or their alloys, characterized by determining the amount of reduction of the plating bath.