JP2003147542A - Electroless substitution type gold plating solution - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electroless substitution type gold plating solution which can form a uniform gold plated layer having no unevenness on a copper metal. SOLUTION: The electroless substitution type gold plating solution forming a gold plated layer on the surface of copper or a copper alloy consists of an aqueous solution containing gold salt, conductive salt and a complexing agent. As the conductive salt, an acidic compound whose acid dissociation constant (pKa) in water is <=2.0 is contained, and, as the complexing agent, the one whose complex forming constant (pK) with copper ions is >=13 is contained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gold plating solution, and more particularly to a substitution type electroless gold plating solution used for connecting terminals of electronic parts.

[0002]

2. Description of the Related Art Gold plating is widely used for protecting the surface of a terminal connecting portion of an electronic component because of its excellent corrosion resistance, heat resistance, mechanical properties, electrical properties, etc.
The applicable substrate materials are various such as plastic, ceramic, metal, and film.

[0003]

In recent years, with the miniaturization and high density of electronic parts, there is an increasing demand for electroless plating capable of plating even terminals isolated from an electric circuit. The electroless plating includes a substitution type and a reduction type. The substitution type is usually used for forming a thin plating layer of 0.1 μm or less, and the reduction type is used for forming a thicker plating layer.

The substitutional electroless gold plating according to the present invention relates to a plating method utilizing a difference in ionization tendency between a terminal metal and gold, in which the terminal metal which is easily ionized emits electrons to form ions. This is an electrochemical reaction in which gold ions dissolved in the plating solution and instead dissolved in the plating solution receive electrons and deposit on the surface of the terminal. M (terminal metal) + Au ⁺ = M ⁺ (elution) +
Copper (deposition) Copper is most widely used as a terminal metal, but since the displacement gold plating is performed after electroless nickel plating on the copper surface, the conventional electrochemical reaction of displacement gold plating is Ni + 2Au ⁺ = It will be described by the chemical formula of Ni ⁺² + 2Au.

Solder balls are mounted on the connection terminal portions covered by the displacement gold plating, and fusion of these solder balls enables connection with other electronic components. Recently, electronic components have been downsized. As the terminal area has become smaller, the lack of adhesion of solder balls has come to be pointed out. When solder is fused, gold diffuses into the solder ball, but nickel remains without diffusing, so the adhesive force between the solder and terminals is determined mainly by the adhesive force between the solder and the electroless nickel plated surface. Will be done. The electroless nickel plating is usually formed on the copper surface with a thickness of about 2 to 5 μm, and reduction type nickel plating is used. The most widely used reducing agent for nickel plating is sodium hypophosphite whose main reaction is NiCl ₂ + NaH ₂ PO ₂ + H ₂ O = Ni + Na.
H ₂ PO ₃ + 2HCl, but NaH as a side reaction
₂ PO ₂ + H = P + NaOH + H ₂ O, etc.,
As a result, the electroless nickel plating layer has a P content of 5 to 10%.
Are often mixed as impurities. Moreover, since nickel forms crystal grains during precipitation, there is a local variation in the P concentration in the nickel film (concentration difference between nickel particles and grain boundaries).
Will be even larger. For this reason, the composition of the nickel film becomes non-uniform and it is very difficult to eliminate this. This is the main reason why the solder ball adhesion on the terminal surface plated with electroless nickel + electroless gold is unstable.

As a means for solving such a problem, it may be considered to apply an electroless gold plating solution capable of displacement plating directly on the copper surface without interposing an electroless nickel plating layer. Since the copper of the plated substrate does not contain a large amount of impurities such as electroless nickel, its adhesive force is stable even if the solder balls are fused.

Then, it is not so true that the substitutional gold plating solution of the type which replaces nickel currently in practical use can be applied to copper. Since copper has a lower ionization tendency than nickel, it is difficult to elute into the plating solution as an ion, so it usually takes 3 to 10 times as long as nickel to perform displacement plating, and unevenness is uneven. It is normal to obtain only a plated film. Also, as the plating solution is used, the eluted copper ions are concentrated and re-deposited together with gold, but copper eutectoid on gold plating is more likely to cause defects in the bonding process than nickel eutectoid. .

The object of the present invention is to find a technical means capable of performing uniform displacement plating without any unevenness directly on the copper metal at the same speed as the conventional displacement plating (processing time is 10 minutes or less), and The obtained gold plating solution should be less susceptible to the influence of eluted copper ions (500 ppm or more) accumulated in the plating solution.

[0009]

The main constituent components of the displacement gold plating solution are a gold salt, a conducting salt and a complexing agent, and the present inventors have complexed the acid dissociation constant (pKa) of the conducting salt component with water. The present inventors have found that the desired target is achieved when the complexing constant (pK) of the agent with the copper ion satisfies a specific condition, and have reached the present invention.

Therefore, the electroless displacement type gold plating solution according to the present invention is a gold plating solution for forming a gold plating layer on the surface of copper or a copper alloy, and is composed of an aqueous solution containing a gold salt, a conductive salt and a complexing agent, The conductive salt contains an acidic compound having an acid dissociation constant (pKa) of 2.0 or less in water, and the complexing agent has a complex formation constant (pK) with copper ion of 1 as the complexing agent.
It is characterized by containing 3 or more.

[0011] Normally, in the electroless substitute gold plating solution, conductive salt component is HA = ^H + + A in water ^- but dissociates as the equilibrium constant Ka for this reaction Ka = ^{(H +} concentration) (A ^- (Concentration) / (HA concentration) (1), which is usually expressed in logarithm (pKa) as an acid dissociation constant showing the strength of the acid.

On the other hand, the complexing agent (Y ^-1 ) reacts with the metal ion (M ^{+ n} ) in water to form a complex (MY ^n-1 ), but [M ^{+ n} + Y ^-1 = MY ^{n −1} ] (2) The equilibrium constant K of this reaction is K = (MY ^n-1 concentration) / (M ^{+ n} concentration) (Y ^-1 concentration), and as a complex formation constant showing the stability of the complex, It is usually displayed in logarithm (pK).

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The gold plating solution according to the present invention contains a gold salt and an acidic compound having an acid dissociation constant pKa of 2 or less as a conductive salt, and has a complex formation constant pK of 1 with copper ions.
It contains 3 or more complexing agents.

The gold salt of the gold plating solution according to the present invention includes:
Illustrative examples of potassium 1st gold potassium cyanide, 2nd gold potassium cyanide, 1st gold potassium chloride, 2nd gold potassium chloride, potassium gold sulfite, sodium gold gold sulfite, potassium gold thiosulfate, sodium gold thiosulfate, and mixtures thereof. You can do it. Of these, potassium gold cyanide and sodium gold sulfite are particularly preferable.

The concentration of these gold salts in the plating solution is 0.
Range of 1 g / L to 50 g / L, particularly preferably 0.2 g
/ L to 15 g / L. If the concentration of the gold salt in the plating solution is less than 0.1 g / L, the plating rate will decrease, while if it exceeds 50 g / L, the manufacturing cost will increase, which is not preferable.

The conductive salt of the present invention has a pKa of 2.0.
The following acidic compounds. In the present invention, pKa is 1.8.
The following are preferred, and those of 1.5 or less are particularly preferred. The lower limit of pKa is -0.5.

Specific examples of such preferred compounds include the following acidic organic compounds and salts thereof. For reference, the pKa value of each compound is also shown. The “acid dissociation constant (pKa) of water for the conductive salt in the present invention” is defined by the above-mentioned formula (1) and is obtained from pKa = log ₁₀ Ka.

Benzenesulfonic acid (pKa 0.7
0), trichloroacetic acid (pKa 0.70), oxalic acid (pKa
Ka 1.23), dichloroacetic acid (pKa 1.4
8), nitroacetic acid (pKa 1.46), nitroaniline (pKa 0.99), glycerin phosphoric acid (pKa
1.34), bipyridine (pKa -0.2), pyrazine (pKa 0.6), glucose phosphate (pKa)
1.46), picric acid (pKa 0.33), pyridinecarboxylic acid (pKa 1.03), histidine (pKa
1.7), aminoethylenephosphonic acid (pKa 1.
1), maleic acid (pKa 1.83), isonicotinic acid (pKa 1.79), and their sodium salts, potassium salts, ammonium salts and the like.

Of these, benzenesulfonic acid and ammonium oxalate are particularly preferable. These conductive salts may be used alone or in combination of two or more.

The concentration of the conductive salt in the plating solution is 1 g / L.
To 300 g / L, preferably 5 g / L to 150
It is in the range of g / L. Conductive salt concentration in plating solution is 1g
If it is less than / L, undeposited part of the plating may occur, while if it exceeds 300 g / L, the color tone of the gold plating may be poor.

The complexing agent in the present invention is a compound having a complex formation constant (pK) with copper ions of 13 or more. In the present invention, a pK of 15 or more is preferable, and a pK of 17 or more is particularly preferable. The upper limit of pK is 35.

Specific examples of such preferable compounds include the following. for reference,
The Ka value of each compound is also shown. The complex formation constant (pK) of the complexing agent with copper ions in the present invention is defined by the above-mentioned formula (2), and pK = log
_{It is} calculated from ₁₀ K.

Nitrilotriacetic acid (pK 13.2), hydroxyethylethylenediamine triacetic acid (pK 17.2)
6), ethylenediamine tetraacetic acid (pK 18.8), diethylenetriamine pentaacetic acid (pK 21.1), triethylenetetramine 6 acetic acid (pK32.6), aminotrimethylenephosphonic acid (pK 13.8), ethylenediaminetetra (methylene). Phosphonic acid) (pK 14.
7), dimethylenetriaminepenta (methylenephosphonic acid) (pK 17.3), and their sodium, potassium, ammonium salts and the like.

Among these, potassium salt, ammonium salt and sodium salt of ethylenediaminetetraacetic acid are particularly preferable. These complexing agents can be used alone or in admixture of two or more.

The concentration of the complexing agent in the plating solution is 0.1 g /
L to 100 g / L range, preferably 1 g / L to 50 g
The range is / L. The concentration of the complexing agent in the plating solution is 0.1
If it is less than g / L, un-deposited part of the plating may occur, while if it exceeds 100 g / L, trouble may occur in the treatment of the plating waste liquid.

The substituted gold plating solution according to the present invention contains various optional components (eg, buffer, pH adjuster, antioxidant, brightener, dye, suspending agent, surfactant, etc.) in addition to the above essential components. , A crystal modifier, etc.).

The gold plating solution of the present invention comprising such essential components and optional components can be prepared and used according to a conventional method. For example, the gold plating solution according to the present invention can be prepared by adding the above-mentioned components to water (preferably ion-exchanged water) simultaneously or separately and dissolving them to form a uniform solution, and adjusting the pH according to the application. . Plating bath temperature is 30 ℃ to 90
The copper surface is gold-plated by the substitution reaction by heating in the range of ° C and immersing the plating material having the copper surface in the range of 1 to 10 minutes.

The gold salt and necessary components consumed by the plating operation are replenished periodically or continuously, and at the same time p
It is also possible to adjust H and specific gravity according to a conventional method.

[0029]

The following examples relate to preferred specific examples of the electroless gold plating solution according to the present invention. Therefore, it goes without saying that the present invention is not limited only to the scope disclosed in the following examples.

(Plating Treatment Conditions) In carrying out the following Examples and Comparative Examples, all substrates having a copper circuit were
After the following degreasing and etching treatments were performed, a displacement gold plating treatment was performed.

[0031] (1) Substrate preparation On a 0.6 mm thick glass epoxy substrate, BGA (Ball Gr id Array) circuit was formed with 35 μ thick electrolytic copper. (2) Degreasing PAC200 (Murata) 50 ° C x 5 minutes (3) Washing with water Ion-exchanged water at room temperature for 30 seconds (4) Etching MEOX (Murata) 50 ° C x 3 minutes (5) Washing with water Ion-exchanged water at room temperature for 30 seconds (6) Substitution gold plating

(Evaluation apparatus) Metal analysis in plating liquid ICPS-1000 Shimadzu plating film thickness measurement SFT-800 Seiko Instruments plating film surface observation S-8000 Hitachi Co. soldering measurement SAT-5000 Resco plating surface Elemental analysis AAS-200 Nidec Anerva reflow device RF-430-M2 Nippon Pulse Giken <Example 1> Prepare an aqueous solution having the following composition and adjust the pH to 5.
After adjusting to 0, degreased and etched substrate 90 ℃ ×
It was immersed under the condition of 5 minutes and plated.

Benzenesulfonic acid 15 g / L Tripotassium citrate 40 g / L Ethylenediaminetetraacetic acid 3 potassium 20 g / L Potassium first gold cyanide 6 g / L On the copper wiring of the obtained substrate, 0.06 micron lemon yellow Was uniformly formed, and the solder wet speed was measured to be as good as 0.5 seconds. next,
This substrate was heat-treated 10 times in a reflow oven at 230 ° C. for 30 seconds and then subjected to meniscograph (SAT500).
The solder wet time was measured in 0), but it was 0.5 seconds and no deterioration was observed.

Example 2 An aqueous solution having the following composition was prepared, the pH was adjusted to 5.0, and the degreased and etched substrate was immersed at 90 ° C. for 5 minutes for plating treatment. .

Ammonium oxalate 25 g / L Diammonium citrate 40 g / L Ethylenediaminetetraacetic acid diammonium 20 g / L Potassium primary gold cyanide 5 g / L On the copper wiring of the obtained substrate, 0.07 μm of lemon yellow The gold film was formed uniformly. The plating operation was repeated while supplementing the first potassium potassium cyanide until the concentration of copper ions in the plating solution reached 500 ppm. The lemon yellow gold film is stably formed,
Moreover, the deterioration of the soldering time was not observed, and it was always maintained at 1 second or less.

Comparative Example 1 An aqueous solution having the following composition was prepared, the pH was adjusted to 5.0, and the degreased and etched substrate was immersed at 90 ° C. for 5 minutes for plating treatment. .

Tripotassium citrate (pKa 3.14) 25 g / L Ethylenediaminetetraacetic acid 3 potassium 20 g / L Cyanide 1st potassium potassium 6 g / L A gold film was formed only on 0.02 micron on the obtained plated substrate. , There was red unevenness, and it was not satisfactory as the plating appearance. P of citric acid as conductive salt
It is considered that Ka is insufficient.

Comparative Example 2 An aqueous solution having the following composition was prepared, the pH was adjusted to 5.0, and the degreased and etched substrate was immersed at 90 ° C. for 5 minutes for plating treatment. .

Maleic acid 15 g / L Tripotassium citrate 25 g / L Dihydroxyethylglycine (pK 8.2) 15 g / L Potassium first potassium cyanide 6 g / L The gold-plated film on the obtained plated substrate had a thickness of 0.05 μm. However, it was not satisfactory because of its reddish and uneven appearance. It is considered that the complexing agent pK was insufficient.

Comparative Example 3 An aqueous solution having the following composition was prepared, the pH was adjusted to 5.0, and the degreased and etched substrate was immersed at 90 ° C. for 5 minutes for plating treatment. .

Maleic acid 15 g / L Tripotassium citrate 25 g / L Potassium first gold cyanide 6 g / 1 The obtained plated substrate had an uneven appearance in which black spots remained, and the correct plating film thickness was measured. could not.
It is considered that the reason was that no complexing agent was added.

<Comparative Example 4> A substrate that had been degreased and etched using a commercially available substitutional gold plating solution (JH-GOLD, manufactured by Japan Kojundo Chemical Co., Ltd.) used for electroless plating was used.
Although the plating treatment was performed at 0 ° C., it took 12 minutes to reach the plating film thickness of 0.05 μ, and the central portion of the obtained plated product was blackened.

[0043]

According to the electroless displacement type gold plating solution of the present invention, it is possible to form a uniform displacement gold plating layer on copper metal without unevenness, and gold plating can be performed at a speed equivalent to that of the conventional displacement plating method. It is possible to form layers. Therefore, according to the present invention, the gold plating layer can be directly formed on the copper metal without using the undercoating of nickel or the like which has been conventionally performed. Therefore, it is derived from nickel or its reaction product. It is possible to efficiently perform the gold plating work while avoiding the problems caused by impurities.

Since the gold plating solution according to the present invention is not easily affected by the eluted copper ions accumulated in the solution, a gold plating layer having good characteristics can be formed stably and for a long time.

[Procedure amendment]

[Submission date] November 19, 2001 (2001.11.
19)

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0017

[Correction method] Change

[Correction content]

Specific examples of such preferred compounds include the following acidic organic compounds and salts thereof. For reference, the pKa value of each compound is also shown. The “acid dissociation constant (pKa) of water for the conductive salt in the present invention” is defined by the above-mentioned formula (1), and is obtained from pKa = −log ₁₀ Ka.

Claims (4)

[Claims] 1. A gold plating solution for forming a gold plating layer on the surface of copper or a copper alloy, which comprises an aqueous solution containing a gold salt, a conductive salt and a complexing agent, and as the conductive salt, an acid dissociation constant in water ( It contains an acidic compound having a pKa of 2.0 or less, and has a complex formation constant (p
An electroless substitution type gold plating solution, characterized in that K) contains 13 or more. 2. A gold salt is a first gold potassium cyanide, a second gold potassium cyanide, a first gold potassium chloride, a second gold potassium chloride, a gold gold sulfite, a sodium gold sulfite, a potassium gold thiosulfate, or a thiosulfate. 2. A sodium selected from the group consisting of gold and mixtures thereof.
The electroless displacement type gold plating solution according to. 3. The conductive salt is benzenesulfonic acid, trichloroacetic acid, oxalic acid, dichloroacetic acid, nitroacetic acid, nitroaniline, glycerin phosphoric acid, bipyridine, pyrazine, glucose phosphoric acid, picric acid, pyridinecarboxylic acid, histidine, aminoethylene. The electroless displacement type gold plating solution according to claim 1 or 2, which is selected from the group consisting of phosphonic acid, maleic acid, isonicotinic acid, their sodium salts, potassium salts, ammonium salts, and mixtures thereof. . 4. The complexing agent is nitrilotriacetic acid, hydroxyethylethylenediamine triacetic acid, ethylenediamine tetraacetic acid, diethylenetriamine pentaacetic acid, triethylenetetramine hexaacetic acid, aminotrimethylenephosphonic acid, ethylenediaminetetra (methylenephosphonic acid), dimethylene. 3. A compound selected from the group consisting of triamine penta (methylenephosphonic acid), sodium salt, potassium salt, ammonium salt thereof, and a mixture thereof.
4. The electroless displacement type gold plating solution according to any one of 3 to 3.