JPH04276082A - Analysis of copper ion concentration in bath for electroless plating of tin, lead, or those alloy - Google Patents

Abstract

PURPOSE:To offer the method for analyzing the copper ion concn. in an electroless plating bath of tin, lead or alloy of these metals for copper or copper alloy in order to easily and surely control the electroless plating bath by easily and accurately analyze the copper ion in the plating bath. CONSTITUTION:The electroless plating of tin, lead or allay of these metals on copper or copper alloy contains water-soluble tin salt and/or water-soluble lead salt, an acid which dissolves these salts and thiourea. An oxidizer which can decompose the thiourea is added to this bath to oxidize and decompose thiourea in the bath as well as to oxidize univalent copper ion to bivalent copper ion. Then the concn. of whole bivalent copper ion including the oxidized copper ion is measured by colorimetry.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for analyzing copper ion concentration in a plating bath for electroless tin, lead, or alloy plating of copper or copper alloys.

0002

[Prior art and problems to be solved by the invention] 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 films are formed by electroplating. With miniaturization, components, circuits, etc. have also become smaller or more complex, and there are some areas that cannot be plated using electroplating. Therefore, electroless tin, lead or tin-lead alloy plating methods, which can also plate these parts, are being considered. For example, JP-A-1-184279 discloses a specific organic sulfonic acid, tin and lead salts of the organic sulfonic acid, sodium hypophosphite (reducing agent), and thiourea (complexing agent). A method using an electrolytic tin/lead alloy plating bath has been proposed. However, conventional electroless tin, lead or tin-lead alloy plating methods do not require metal replenishment in the plating bath, and are often disposable batch methods in which the metal concentration drops below the precipitation limit and is discarded as is. This is used when forming a thin plating film, and there are almost no proposals for continuous use of the plating bath for the purpose of obtaining a thick plating film, therefore, maintaining a constant amount of deposit continuously required for continuous use. No proposal has been made regarding a possible plating bath replenishment management method.

On the other hand, in the usual electroless plating method,
The plating bath is managed by analyzing the metal components in the plating bath from time to time and replenishing the metal components in proportion to the amount of metal consumed. In the case of electrolytic tin, lead, or tin-lead alloy plating baths, as the plating progresses, the copper eluted from the object to be plated dissolves and accumulates in the plating bath, so tin and lead components can be easily removed in the plating bath. Moreover, it is difficult to analyze accurately, and it has been found that the above-mentioned normal plating bath management method is difficult to apply to electroless tin, lead, or tin-lead alloy plating baths. Therefore, it is desired to establish an analysis method that can easily and reliably control electroless tin, lead, or tin-lead alloy plating baths.

[0004] The present invention has been made in view of the above circumstances.
The copper ion concentration in electroless tin, lead, or tin/lead alloy plating baths can be easily and accurately analyzed, and therefore electroless tin, lead, or their alloy plating baths can be easily and reliably managed. An object of the present invention is to provide a method for analyzing copper ion concentration in an electroless tin, lead or tin-lead alloy plating bath.

[0005]

[Means and effects for solving the problem] The present inventors have
As a result of various studies to achieve the above objective, we found that in electroless tin, lead or tin-lead alloy plating baths for copper or copper alloys, the copper content of the copper or copper alloy to be plated dissolves in the plating bath. At the same time, a tin, lead, or tin-lead alloy plating film is precipitated and formed, and therefore, as plating progresses, copper content accumulates and increases in the plating bath, but in this case, the above-mentioned amount of eluted copper ions Therefore, by replenishing water-soluble tin salt and/or water-soluble lead salt based on the analysis results of the eluted copper ion concentration, the above-mentioned substances can be reduced. It has been found that the electrolytic plating bath can be easily and reliably controlled. Therefore, as a result of studying a method for easily and accurately analyzing the copper ion concentration in such an electroless plating bath, we found that water-soluble tin salts and/or water-soluble lead salts, acids that dissolve these salts, and complexing When analyzing the concentration of eluted copper ions in an electroless plating bath for copper or copper alloys that contains thiourea as an agent, first thiourea in the bath is oxidized and decomposed, and monovalent copper ions are converted to divalent copper ions. It has been found that the concentration of copper ions in a plating bath can be accurately and easily quantified by oxidizing and analyzing the concentration of all divalent copper ions including the oxidized copper ions using a colorimetric method.

That is, as mentioned above, in electroless tin, lead or tin-lead alloy plating, copper is eluted from the object to be plated and accumulates as the plating progresses. According to studies, the copper in the plating bath is present in a complexed state with thiourea, and some of it is present as divalent copper ions, but most of it is present as monovalent copper ions. Although the concentration of copper ions in this state can be determined by atomic absorption spectrometry, etc., the total amount of copper can be determined, however, the present inventors have considered a colorimetric method for easy analysis at the plating factory site. , it was not possible to perform a good colorimetric analysis as it was, so after further investigation, we added an oxidizing agent that can decompose thiourea, such as hydrogen peroxide or zincate, to the above plating solution to decompose thiourea. and further add 2 monovalent copper ions.
It was discovered that by performing colorimetric analysis after oxidizing to valent copper ions, it was possible to accurately quantify total copper ions, and that this total copper ion could be used as a guide for replenishing tin and lead salts. This is what we have come to do.

Therefore, the present invention provides electroless tin, lead or tin-lead alloy plating for copper or copper alloys containing water-soluble tin salts and/or water-soluble lead salts, acids that dissolve these salts, and thiourea. In the method of analyzing the copper ion concentration in a bath, an oxidizing agent capable of decomposing thiourea is added to the plating bath to oxidize and decompose the thiourea in the plating bath, and monovalent copper ions are converted to divalent copper. A method for analyzing the concentration of copper ions in an electroless tin, lead or alloy plating bath, characterized by oxidizing to ions and measuring the concentration of all divalent copper ions including the oxidized copper ions using a colorimetric method. I will provide a.

[0008] The present invention will be described in more detail below. In the present invention, the plating bath to be analyzed is an electroless tin, lead, or alloy plating bath thereof, and water-soluble tin salt and/or water-soluble lead salt. , acids that dissolve these salts, and thiourea as a complexing agent are used.

Examples of water-soluble tin salts used in the electroless plating bath include stannous sulfate, stannous alkanesulfonate, stannous chloride, stannous alkanolsulfonate, and stannous sulfosuccinate. Can be mentioned. Examples of water-soluble lead salts include lead chloride, lead alkanesulfonate, lead acetate, lead alkanolsulfonate, and the like. The content of these metal salt components is usually 0.5 to 30 g/l, particularly 1 to 20 g/l. Examples of the acid component include alkanesulfonic acid, hydrochloric acid, alkanolsulfonic acid, perchloric acid, borofluoric acid, and sulfosuccinic acid. The content of these acid components is usually 50 to 250 g/l, especially 10
It is 0 to 200 g/l. Further, the content of thiourea is usually 30 to 200 g/l, particularly 50 to 100 g/l.

[0010] The electroless plating bath usually contains 30 to 300% hypophosphorous acid or a water-soluble salt thereof as a reducing agent.
g/l, especially 50 to 200 g/l, and EDTA, citric acid, etc. may also be added. Note that the pH of the plating bath is usually 0 to 3, particularly 0.5 to 2.5.

[0011]The above-mentioned electroless plating bath can be used to produce electroless tin, lead or tin-lead alloy by immersing the object to be plated, which has a copper or copper alloy part on at least a part of its surface, into the plating bath. A plating film is deposited and formed on the copper or copper alloy part, but at this time, copper content is eluted from the copper or copper alloy part and accumulates in the plating bath.

[0012] The present invention relates to a method for quantifying the copper ion concentration in this plating bath, and the copper ions in this plating bath are complexed with thiourea and mostly exist as monovalent copper ions. (In fact, plating baths are usually colorless).

In the present invention, in order to measure the total copper ion concentration in the plating bath, an oxidizing agent capable of decomposing thiourea is first added to oxidize and decompose the thiourea, thereby removing the complexation of copper ions with the thiourea. At the same time, monovalent copper ions are oxidized to divalent copper ions.

In this case, any oxidizing agent may be used as long as it is colorless and can decompose thiourea and does not become colored by the oxidation reaction, but in particular peroxides such as hydrogen peroxide and chlorite or its salts are preferably used, with hydrogen peroxide being the most preferred. The amount added is the amount that can decompose thiourea and oxidize monovalent copper ions to divalent copper ions. For example, in the case of hydrogen peroxide solution, 0.1 to 2 g is usually added to 1 ml of plating bath. be done.

[0015] When thiourea is decomposed by adding the above-mentioned oxidizing agent, tin ions, especially Sn4+ and lead ions complexed by thiourea, may precipitate and the plating bath may become cloudy. To prevent the formation of this precipitate,
Oxalic acid, tartaric acid, citric acid, EDTA and their salts,
A complexing agent capable of complexing Sn4+ and Pb2+, such as triethanolamine, can be added. In this case, the amount added is usually 1 to 40 g per ml of plating bath.

Furthermore, in the analysis method of the present invention, colorless monovalent copper ions are oxidized into blue divalent copper ions by adding the oxidizing agent, so the plating bath is colored and the degree of coloring is compared. The amount is determined by a color method, but a coloring agent can be added in order to further clarify the coloring caused by divalent copper ions and increase the detection sensitivity of divalent copper ions. As the coloring agent, ammonia and amines such as ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, and aminoethylmonoethanolamine are preferably used. The amount of these coloring agents added can generally be 0.2 to 5 g per ml of the plating bath.

Furthermore, in performing analysis according to the present invention, the pH of the analysis solution is preferably 4 to 11, particularly 5 to 10. If the pH is lower than 4, the color development of copper ions may be weakened, and if the pH is higher than 11, especially when hydrogen peroxide is used as an oxidizing agent, the hydrogen peroxide decomposes and bubbles are generated, causing light absorption. There is a risk that it will have an impact. In this case, acetic acid, a salt thereof, hexaethylenetetramine, etc. can be used as a pH adjuster or a pH buffering agent, and the pH can also be adjusted to the above range by adding the above-mentioned complexing agent or coloring agent.

[0018] There is no particular restriction on the order of addition of the oxidizing agent, complexing agent, coloring agent, and pH adjuster, and they can be added at the same time. It is preferable to add an oxidizing agent, and the coloring agent may be added last.

[0019] The analytical sample in which thiourea is decomposed and monovalent copper ions are oxidized to divalent copper ions to develop a color is quantified by a colorimetric method. As a colorimetric method, a method of visual comparison with a standard sample may be adopted, but in general, a method of measuring the absorbance at a wavelength of 500 to 800 nm and comparing it with a calibration value prepared in advance from a standard sample is suitable.

The analysis can be carried out by intermittently taking the plating bath as a sample solution and performing the above-mentioned operations individually, or by continuously sending the sample solution from the plating bath to the analyzer using a pump, and using this analyzer to perform the above-described operations. This can be carried out according to a conventional method, such as automatically performing a pretreatment operation and then flowing the sample through a flow cell to continuously measure the absorbance.

The copper ion concentration determined in this manner is used to control the tin and lead content in the electroless tin, lead or tin-lead alloy plating bath. In other words, since the copper ion concentration in the plating bath is proportional to the amount of metals consumed (tin, lead), the copper ion concentration serves as a guideline for replenishing these metals, and the increase in copper ion concentration By replenishing tin salt and lead salt, it is possible to control the tin salt and lead salt in the plating bath.

[0022]

As explained above, according to the method of the present invention, the copper ion concentration of an electroless tin, lead or tin-lead alloy plating bath can be easily and accurately analyzed. In this case, since a colorimetric method was adopted as the analysis method, it can be easily adapted to automatic analysis and can be effectively used for the management of electroless tin, lead or tin-lead alloy plating baths.

[0023]

[Examples] The present invention will be specifically explained below with reference to Examples, but the present invention is not limited to the following Examples.

[0024] While performing electroless plating on copper products using the following plating bath and under the following conditions, the throughput was 26 μm·d.
Sample 5 ml of the plating bath for every m2/l, and add 20 g/l of triethylenetetramine and 100 g/l of acetic acid.
, 200 ml of a solution of 100 g/l ammonium citrate
After adding 2 ml of 35% hydrogen peroxide solution, the absorbance was measured using an absorbance meter (U-321 manufactured by Hitachi, Ltd.) at a wavelength of 620 nm.
0) to quantify the total amount of copper. The results are shown in Table 1. For comparison, the results of atomic absorption spectrometry are also shown.

[0025] As the plating progresses, the following replenishing solutions (1) to (3) are added in the amounts shown below every time the amount of copper obtained by analysis increases by 0.5 g/l. I tried to replenish it. Plating solution composition and plating conditions Methanesulfonic acid
50g/l tin methanesulfonate
20g/l lead methanesulfonate 13
g/l thiourea
75g/l Sodium hypophosphite 80g/l
citric acid
15g/l laurylpyridinium chloride 5g/l EDTA

3g/lpH
2.0
bath temperature
80℃ replenishment liquid (1) 5
ml/l supplementary tin methanesulfonate 40
0g/l methanesulfonic acid
180g/l replenishment liquid (2) 5ml/l replenishment lead methanesulfonate 38
0g/l methanesulfonic acid
240g/l replenishment solution (3) 15ml/l replenishment thiourea
120g/l sodium hypophosphite
3g/l citric acid
25g/l

[
0026

[Table 1]

From the results shown in Table 1, the analytical values for copper according to the present invention almost coincided with the analytical values by atomic absorption spectrometry, and it was therefore confirmed that copper content could be easily analyzed according to the present invention.

Claims (1)

[Claims] Claim 1. Copper in an electroless tin, lead or tin-lead alloy plating bath for copper or copper alloys containing a water-soluble tin salt and/or a water-soluble lead salt, an acid that dissolves these salts, and thiourea. In the method of analyzing ion concentration, an oxidizing agent capable of decomposing thiourea is added to the plating bath to oxidize and decompose the thiourea in the plating bath, and monovalent copper ions are oxidized to divalent copper ions. A method for analyzing copper ion concentration in an electroless tin, lead or alloy plating bath, which comprises measuring the total divalent copper ion concentration including the oxidized divalent copper ions by a colorimetric method.