JPS619578A - Method for chemically plating copper - Google Patents

Abstract

PURPOSE:To form a plated copper film having superior mechanical properties by deposition by adding a soluble inorg. silicon compound and an oxidizing agent to a chemical copper plating soln. contg. a copper salt, a complexing agent, a reducing agent and a pH adjusting agent. CONSTITUTION:A soluble inorg. silicate such as sodium silicate or sodium metasilicate is added to a chemical copper plating soln. contg. a copper salt such as copper sulfater or cupric chloride, a complexing agent of the copper salt such as EDTA having a chemical structure represeted by a formula >N-C-C-N<, formaldehyde as a reducing agent for copper ions and NaOH as a pH adjusting agent. The amount of the silicate added is >=10mg/l (expressed in terms of Si). The stability of the resulting chemical copper plating soln. is improved by blowing air or adding hydrogen peroxide, a persulfate or the like. When a body to be plated is imersed in the chemical copper plating soln. heated to >=50 deg.C, a plated copper film having superior mechanical properties is formed by deposition.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a chemical copper plating method for depositing a copper plating film with excellent mechanical properties, and in particular to a chemical copper plating method suitable for thick plating in the manufacture of printed circuit boards. Regarding the method.

[Background of the invention]

BACKGROUND ART Chemical copper plating solutions have been known that contain copper salts, complexing agents for copper salts, reducing agents for copper salts, and pH adjusters as basic components.

A chemical copper plating solution that provides a plating film with excellent mechanical properties is required for printed wiring boards that perform through-hole plating due to thick plating. Copper plating solution is known. For example, additives include cyanide compounds, 2,2'-bipyridyl, polyethylene glycol, and the like.

However, these additives are difficult to handle and are consumed during plating, making it necessary to replenish them for analysis.

A method for improving the mechanical properties of copper plating films obtained by chemical copper plating has been published. An example of this is JP-A-54-19
As shown in Japanese Patent No. 430, the above main components and 2.2'
- A chemical copper plating solution containing dipyridyl, polyethylene glycol, and an alkali-soluble inorganic silicon compound. In the chemical copper plating solution, the alkali-soluble inorganic silicon compound is converted to silicon dioxide and is 5 to 100 wq/L (8i,
Including te 0.08~1.7 m mot/L), the tensile strength of the chemical copper plating film is 50~581!4 W/
1111" and an elongation of 4.4 to 6.7%. However, when using this chemical copper plating solution, it could not be used due to the following drawbacks.

To prepare a chemical copper plating solution, ion-exchanged water obtained by ion-exchanging tap water is used. Waterworks contain a large amount of silicon compounds, which exist as nonionic silicon compounds or polymerized anions that are difficult to ion exchange. Therefore, even with ion exchange treatment, silicon compounds cannot be completely removed and are contained in ion exchange water.

According to measurements by the inventors, the silicon content in ion-exchanged water is 0.04 to 0.43 mmot/l (average 0.2 mmot/L) as 3i. Silicon-free water can be obtained by distillation. However, since the chemical copper plating solution is used on a scale of several hundred to several thousand tons, expensive distilled water cannot be used.

Since chemical copper plating is used repeatedly, silicon is introduced into the plating solution.

When plating is used repeatedly, the main component of the plating solution (
To maintain a constant concentration of copper ions, hydroxide ions, formaldehyde, etc., an aqueous solution containing sulfuric acid-containing sodium hydroxide and formalin is replenished. The replenishment amount of these compounds is 3 as Cu per plating area of 100
For 5 μm plating, copper sulfate: 0.05 m
ot/ As Sodium hydroxide: 0.2 moZ/
Z % Formaldehyde = 0.1 mot/L, total amount of aqueous solution: 1 t of plating solution is applied, 0.1 t. For example, according to the JIS standard (grade 1) for sodium hydroxide, hydroxide
The 8fCh content in IJium is said to be 0.04% or less, but it is not standardized for other compounds, and 8fCh content is
10* is regulated as a substance that does not precipitate as an ignition residue or sulfide, sulfuric acid steel 20.3%, formalin: 0.01
%. Therefore, by replenishment, Si is reduced by approximately 0.3 mm.
There is a possibility that ot/ may be brought in.

On the other hand, the main component of the plating solution is copper sulfate: 0.
．． 04 mot/t, sodium hydroxide: 0.4 mo
t/t, formalin: 0.04 mot/l,
Copper ion complexing agent: This is done by dissolving 0.12 mol/l in the ion-exchanged water.

As a representative copper ion complexing agent, EDTA-2Na has an ignition component of &8% according to the JIS standard (special grade). Therefore, the maximum content of St in the plating solution is s after just preparing the bath.
, i m mo4/l. Therefore, when plating is repeated, the content of Si in the plating solution increases according to the following equation.

S i (m mol/1) in plating solution iz = 5.1
+0.3n-(1) (where n is the number of times of plating) As is clear from the above, Si is introduced into the plating solution as an impurity.
contains an extremely large number of elements. Japanese Patent Publication No. 54-1943
According to Publication No. 0, according to formula (1), the first plating (n=
1), its optimum amount (0.08 to 1.7 as Si)
m mol/L), and that probability is also extremely large. Since using chemicals of high purity will significantly increase the plating cost, industrial chemicals that meet JIS standards or lower are used. Therefore, the content of Si as an impurity increases significantly compared to formula (1). Therefore,
According to the prior art, the objective could not be achieved from the first plating without using extremely expensive water and chemicals and strictly controlling the concentration of liquid components. Furthermore, even if plating were to be possible by chance, the properties of the plating film would be sensitively affected by the Si concentration, and it would not be possible to stabilize the properties, which is the most important industrially in terms of quality control.

Furthermore, even when plating is carried out using the most expensive pure water and chemicals, the following problem occurs. According to the prior art, the 19i concentration must be strictly controlled because the Si concentration in the plating solution acutely affects the characteristics of the plating film. Analysis of 3i is extremely difficult, especially when Na coexists as in chemical copper plating (Na in the liquid is 235 times as much as Si).
Analyzing SI is said to be difficult. The detection sensitivity of atomic absorption spectrometry is also said to be about 2 mmat/l.

Therefore, when the Si content was at the detection sensitivity plate f, it became impossible to conduct a rigorous analysis unless an inaccurate analysis sample concentration operation was also used. Also from this point of view, a plating solution with a low S3 content has not been industrially possible.

[Purpose of the invention]

An object of the present invention is to provide a chemical copper plating method that allows easy control of the plating solution and provides a mechanically excellent matted film.

[Summary of the invention]

The present invention is characterized by a method of performing chemical copper plating using a chemical copper plating solution containing a copper salt, a complexing agent for the copper salt, a reducing agent for the copper salt, and a pH adjuster. A soluble inorganic silicon compound is added as an additive, and at least one of blowing an oxygen-containing gas into the chemical copper plating solution or adding an oxidizing agent such as hydrogen peroxide or persulfate is applied. This is where chemical copper plating is performed.

The purpose can be achieved by using at least one of an element-containing gas and an oxidizing agent.

Traditionally, water glass, sodium metasilicate.

It is known that an inorganic silicon compound such as sodium orthosilicate is added to a chemical copper plating solution, but this alone does not provide sufficient stability for the chemical copper plating solution, and as in the present invention, chemical copper plating is used for thick plating. When plating is done halfway through plating, the plating solution becomes unstable and it becomes virtually impossible to plate to a sufficient thickness. Regarding this point, the Metal Surface Technology Magazine, Volume 16, November issue (1965) states that although it is effective in preventing the self-decomposition of the plating solution, copper is deposited at the bottom of the plating bath. It is clear from this.

Furthermore, physical properties of the plated film obtained from the chemical copper plating solution described in the above cited reference were measured, but the film was brittle and did not exhibit sufficient mechanical properties.

On the other hand, blowing an oxygen-containing gas such as air into the chemical copper plating solution is described in Japanese Patent Publication No. 36-9063, and is known to be effective in stabilizing the chemical copper plating solution. However, it is not possible to significantly improve the mechanical properties of the plated film simply by blowing in oxygen-containing gas.

The present invention is based on the discovery of a synergistic effect in which the mechanical properties of a plated film can be significantly improved by adding a soluble inorganic silicon compound and using at least one of an oxygen-containing gas or an oxidizing agent. be.

Examples of soluble inorganic silicon compounds that can be used in the present invention include water glass, metasilicates such as sodium metasilicate, orthosilicates such as sodium orthosilicate, silicates such as sodium silicate and potassium silicate, and sodium polysilicate. polysilicate, silicon dioxide,
Examples include silicon-containing gas. The amount of silicon added that is effective in improving the mechanical properties of the plating film is 1.
0 my/ or more is necessary; if it is less than that, no significant effect can be expected.

The soluble inorganic silicon compound used in the present invention causes no problems in handling. Furthermore, there are no BOD or CoDO problems, and almost no energy is consumed during plating. Furthermore, the fact that it is inexpensive is also a great industrial advantage.

In the present invention, air is generally used as the oxygen-containing gas, and the stability of the chemical copper plating solution is maintained by blowing the air into it. Naturally, pure oxygen can also be used as the oxygen-containing gas. Furthermore, persulfates such as hydrogen peroxide and potassium persulfate can be used as the oxidizing agent. The amount of these additives varies depending on the type of oxidizing agent, but it is necessary to add at least about 0.5 g/kg. If the amount is less than that, the stability of the chemical copper plating solution cannot be maintained sufficiently, and the thickness of the chemical copper plating solution will be substantially reduced. It is impossible to carry out additional plating.Hydrogen peroxide and persulfate are also relatively easy to handle and do not cause any problem on BOD-COD.

In the present invention, the plating temperature is preferably 50C or higher,
If it is less than 500, a plated film with sufficiently good mechanical properties cannot be obtained.

Furthermore, the basic components of the chemical copper plating solution used in the present invention are a copper salt, a complexing agent for the copper salt, a reducing agent for the copper salt, and a pH adjuster. Known materials such as copper can be used. 'The copper salt complexing agent is preferably one having a >N -C-C-k skeleton, ethylenediaminetetraacetic acid,
N-hydroxyethylethylenediaminetriacetic acid, 1,2
-Diaminopropanetetraacetic acid, diethylenetriaminepentaacetic acid, cyclohexanediaminetetraacetic acid, etc. are applicable.

When using monoamines such as triethanolamine, iminotriacetic acid, iminotriacetic acid, or Rossel's salt, it may not be possible to obtain a plated film with sufficient mechanical properties, or the stability of the plating solution may deteriorate. A problem arises in which plating is insufficient and substantially thick plating cannot be achieved. As the reducing agent for the copper salt, formalin, which is commonly used, is suitable;
Furthermore, sodium hydroxide can be used as a pH adjuster.

[Embodiments of the invention]

Next, the present invention will be specifically explained using examples.

Examples 1 to 13 A stainless steel plate whose surface was polished smoothly was degreased, and palladium, which is an initiator for a plating reaction, was attached to the surface. Next, chemical copper plating was performed using the chemical copper plating solution composition and plating conditions shown in Table 1, and the thickness was approximately 30 μm.
A plated film with a thickness of . This plating film was peeled off from a stainless steel plate and cut to a width of 105 m, and the elongation rate and tensile strength until break were measured using a tensile tester manufactured by Toyo Sokkyo Co., Ltd. with an initial tension interval of 50 cm. The results are shown in Table 2.

Comparative Examples 1 to 6 Under the conditions described in the Comparative Examples column of Table 1, Examples 1 to 13
It was plated and evaluated in the same manner as above. The results are also shown in Table 2.

〔Effect of the invention〕

As is clear from Table 2, which lists the results of Examples and Comparative Examples, the chemical copper plating method of the present invention makes it possible to obtain a laminated film with excellent mechanical properties.

In addition, the stability of the chemical copper plating solution is maintained well, and substantial thick plating is possible.

Claims (1)

[Claims] 1. A method of performing chemical copper plating using a chemical copper plating solution containing a copper salt, a complexing agent for the copper salt, a reducing agent for the copper salt, and a pH adjuster, wherein the chemical copper A chemical copper plating method characterized by adding a soluble inorganic silicon compound as an additive to a plating solution, blowing an oxygen-containing gas into the plating solution, and/or adding an oxidizing agent. 2. The chemical copper plating method according to claim 1, characterized in that the content of the additive is 10 mg/l or more as silicon content. 3. A chemical copper plating method according to claim 1, characterized in that the plating temperature is 50° C. or higher. 4. A chemical copper plating method as set forth in claim 1, wherein the copper salt complexing agent has a chemical structure of >N-C-C-N<.