JPH09176864A - Electroless gold plating thickening method - Google Patents

Abstract

(57) Abstract: After performing nickel plating using an electroless nickel plating solution to which a compound having an S-S sulfur bond is added, a plated object having a nickel plating film formed by this nickel plating A method for thickening electroless gold plating, which comprises immersing an object in an electroless gold plating bath to perform electroless gold plating. According to the thickening method of electroless gold plating of the present invention, the gold plating film can be made sufficiently thick in a short time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electroless gold plating thickening method which is preferably used when a gold plating film is formed on a printed wiring board, electronic industrial parts, etc. The present invention relates to an industrially useful electroless gold plating thickening method capable of sufficiently thickening an electroless gold plating film on a surface of an object to be plated plated with electroless nickel in a short time.

[0002]

2. Description of the Related Art Electroless gold plating has hitherto been used in view of physical properties such as electrical conductivity of gold, connectivity by thermocompression bonding, oxidation resistance and chemical resistance. Printed wiring board, ceramic IC package, IT
It is applied to the surface of electronic industrial parts such as O substrates and IC cards, and efficient thickening of electroless gold plating is an important issue in the printed circuit board industry and the like.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide an industrially useful electroless gold plating thickening method capable of sufficiently thickening electroless gold plating in a short time. To aim.

[0004]

Means for Solving the Problems and Modes for Carrying Out the Invention As a result of intensive studies to achieve the above-mentioned object, the present inventor has focused on an object to be plated when performing electroless gold plating, When the object to be plated is nickel-plated with an electroless nickel plating solution to which a compound having an S--S sulfur bond is added, and the object to be plated having this nickel plating film is subjected to electroless gold plating, the gold plating film is , And found that it is formed sufficiently thick in a short time.

In this case, after electroless nickel plating is performed on the object to be plated using an electroless nickel plating solution that does not contain a compound having an S--S sulfur bond, the film has an S--S sulfur bond. Electroless nickel plating is performed using an electroless nickel plating solution containing a compound, and by applying electroless gold plating on it, a gold plating film is formed to be sufficiently thick in a short time and discoloration over time It was found that a gold-plated film having a good appearance without
The present invention has been accomplished.

Therefore, according to the present invention, an object to be plated having a nickel plating film formed by this nickel plating after performing nickel plating using an electroless nickel plating solution to which a compound having an S--S sulfur bond is added The present invention provides a method for thickening electroless gold plating, which comprises immersing the above in an electroless gold plating bath to perform electroless gold plating. Also,
According to the present invention, electroless nickel plating is performed on an object to be plated using an electroless nickel plating solution containing no compound having an S-S sulfur bond, and then electroless nickel containing a compound having an S-S sulfur bond. Provided is a method of thickening electroless gold plating, which comprises performing plating and then performing electroless gold plating.

The present invention will be described in more detail below. The electroless gold plating thickening method of the present invention uses an electroless nickel plating solution to which a compound having an S--S sulfur bond is added, as described above. After performing nickel plating, electroless gold plating is performed.

The electroless nickel plating solution used in the present invention contains a water-soluble nickel salt, a reducing agent and a complexing agent.

Here, as the water-soluble nickel salt, nickel sulfate, nickel chloride or the like is used, and the amount used is 0.01 to 1 mol / L, particularly 0.05 to 0.2 mol / L.
It is preferable that

As the reducing agent, hypophosphite, hypophosphite such as sodium hypophosphite, dimethylamine borane, trimethylamine borane, hydrazine and the like are used. The amount used is 0.01 to 1 mol / L, especially 0.0
It is preferably 5 to 0.5 mol / L.

Examples of complexing agents include carboxylic acids such as malic acid, succinic acid, lactic acid, citric acid and sodium salts thereof, glycine, alanine, iminodiacetic acid, arginine,
Known complexing agents such as amino acids such as glutamic acid are used. The amount used is 0.01 to 2 mol / L, especially 0.0
It is preferably 5 to 1 mol / L.

To the electroless nickel plating solution, a water-soluble lead salt such as lead acetate and a sulfur compound such as thiodiglycolic acid can be added as stabilizers. The added amount is preferably 0.1 to 100 mg / L.

In the present invention, in addition to the above components, S-
A compound having an S-sulfur bond is added, which makes it possible to form an electroless nickel plating film that solves the problems of shoulder thinning and nickel squeezing out when plating is applied to a fine pattern.

In this case, the compound having a sulfur bond may be an organic sulfur compound, but an inorganic sulfur compound,
Particularly, thiosulfates, dithionates, polythionates (for example, n = 1 to 4 in O ₃ S—Sn—SO ₃ ) and dithionite are preferable. As the salt, a water-soluble salt of an alkali metal such as sodium salt is used.

The addition amount of the above-mentioned compound having a sulfur bond is
0.01-100 mg / L, especially 0.05-50 mg / L
It is preferably L. If it is less than 0.01 mg / L, the above-mentioned object of the present invention cannot be sufficiently achieved, and 100 mg
If it is more than / L, the phenomenon that plating does not adhere at all occurs.

The pH of the electroless nickel plating solution of the present invention is preferably 4 to 7, and more preferably 4 to 6.

The method of performing electroless nickel plating on a fine pattern or the like using the above electroless nickel plating solution can be carried out by an ordinary method, and an object to be plated may be immersed in the plating solution. Examples of the material of the liquid to be plated include metals such as iron, cobalt, nickel, and palladium, and alloys thereof, which are catalytic in reducing and depositing the electroless nickel plating film. If the metal has no catalytic property, so-called galvanic initiation is performed (electricity is applied to the object to be plated until reduction precipitation occurs), or plating is performed after forming a plating film of the above-mentioned catalytically active metal. It suffices to carry out, and for glass, ceramics, plastics, or the like, or metals having no catalytic activity as described above, plating can be carried out after attaching metal catalyst nuclei such as palladium nuclei according to a conventional method. In this case, the plating temperature is preferably 40 to 95 ° C., particularly 60 to 95 ° C., and if necessary, stirring can be performed during plating.

The present invention is to perform electroless gold plating on an object to be plated, which has been subjected to such electroless nickel plating. Electroless nickel plating to which the above-mentioned compound having an S--S sulfur bond is added. When electroless gold plating is applied to the electroless nickel plating film formed by using the solution, the electroless nickel plating film from the electroless nickel plating solution containing no compound having such S—S sulfur bond is not formed. Surprisingly, compared to the case where electrolytic gold plating is applied, it is possible to perform thickening in a short time.

The electroless gold plating bath contains a gold raw material, a complexing agent and the like, and these may be the gold raw materials used in ordinary gold plating baths, for example, gold cyanide salt, gold sulfite salt,
Gold thiosulfate and the like can be used, and particularly water-soluble gold cyanide salt such as potassium gold cyanide can be preferably used. The amount of the gold raw material is not particularly limited, but the gold concentration is 0.5 to 10 g / L, particularly 1 to 5
g / L is preferable. In this case, the plating rate increases almost in proportion to the amount of the gold raw material mixed, that is, the concentration of gold ions in the plating bath. If the plating rate exceeds 10 g / L, the plating rate increases but the stability of the plating bath is poor. There is. On the other hand, if the gold concentration is less than 0.5 g / L, the plating rate may be extremely low.

Next, as the complexing agent to be blended with the electroless gold plating bath, known compounds can be used. Specifically, ammonium sulfate, aminocarboxylate, carboxylate, hydroxycarboxylate and the like can be used, and it is usually preferable to add 5 to 300 g / L, particularly 10 to 200 g / L, If it is less than 5 g / L, the effect as a complexing agent may be insufficient and the liquid stability may be insufficient, and if the amount exceeds 300 g / L, the effect may not be improved so much and it is uneconomical.

As the reducing agent, thiosulfate, hydrazine, ascorbate and the like can be added. In this case, as the thiosulfate, ammonium thiosulfate,
Sodium thiosulfate, potassium thiosulfate and the like are preferably used. The reducing agents may be used alone or in combination of two or more.

The compounding amount of the reducing agent is not particularly limited, but it is usually 0 to 10 g / L, preferably 0 to 5 g / L. In this case, the plating rate increases almost in proportion to the concentration of the reducing agent, but even if the amount exceeds 10 g / L, the plating rate does not increase so much, and rather the liquid stability may deteriorate. On the other hand, even if the reducing agent is not blended, gold is deposited by the substitution reaction with the underlying nickel.

In the electroless gold plating bath, if necessary, in addition to the above components, a pH adjusting agent such as a phosphate, a phosphite or a carboxylate, a crystal such as Tl, As, Pb or the like. A regulator and other various additives can be appropriately mixed and used.

The above-mentioned plating bath is preferably used in the vicinity of neutrality, usually pH 3.5 to 9, more preferably pH.
It is recommended to use in the range of 4-9.

Here, the electroless gold plating bath is used for thickening, but the electroless gold plating method of the present invention is carried out according to a conventional method except that the electroless gold plating bath is used. It is also possible to form a film directly on the object to be plated on which the above electroless nickel plating film is formed, but especially when performing thick plating, after performing strike electroless gold plating, thick electroless plating is performed. It is preferable to perform gold plating, and by performing strike electroless gold plating, it is possible to perform thickening gold plating undercoat adjustment on the object to be plated, and when thickening, adhere to the object to be plated,
The film thickness can be made uniform, and the film can be formed well.

In this case, the composition of this strike electroless gold plating bath is 0.5 to 10 g with the above-mentioned gold raw material as the gold concentration.
/ L, especially 1 to 5 g / L, and EDTA and its alkali metal salt and the above-mentioned complexing agent 5 to 300 g / L,
Particularly, 10 to 200 g / L may be blended to adjust the pH to 3.5 to 9.

When gold plating is performed using the above electroless gold plating bath, the plating temperature (solution temperature) is 20 to 95 ° C., especially 30 to 90 ° C. in the strike electroless gold plating bath, and usually 0.5. -30 minutes, especially 1-15 minutes is preferable, and 20-95 in the thick electroless gold plating bath to be performed next.
℃, especially 50-90 ℃, usually 1-60 minutes, especially 5-4
It is preferable to set it to 0 minutes, and if the temperature of the plating solution is less than 20 ° C, the plating rate is slow, and in the case of thick coating, productivity is poor and it is uneconomical. If it exceeds 95 ° C, the plating solution may decompose. There is.

Further, in the case of directly carrying out thick electroless gold plating on the object to be plated, the temperature of the plating bath is 50 to 95 ° C.
In particular, the temperature is preferably 70 to 90 ° C., and if it is lower than 50 ° C., the plating rate may be extremely low, and if it exceeds 95 ° C., the plating rate may be high, but the stability of the gold deposition film characteristics may be poor. is there.

The present invention enables thickening of gold plating by performing electroless gold plating on the electroless nickel plating film containing the compound having an S--S sulfur bond as described above. In this case, before performing electroless nickel plating containing the compound having the S—S sulfur bond,
The electroless nickel plating not containing the S—S sulfur bond is applied to the object to be plated to form the electroless nickel plating film of the first layer, and the electroless nickel plating containing the S—S sulfur bond is applied thereon. It is recommended to perform electroless gold plating after forming the second layer of electroless nickel plating film.

That is, in the above electroless gold plating, even if a reducing agent is contained in the plating solution, the electroless gold containing essentially S--S sulfur bond is essentially contained when the gold raw material is a gold cyanide salt. It is carried out by a substitution reaction with the nickel plating film, that is, a mechanism in which the nickel plating film is dissolved in the electroless gold plating solution and gold ions Au ⁺ are reduced. Ni ⁰ → Ni ²⁺ + 2e 2Au ⁺ + 2e → 2Au ⁰

In this case, as shown in FIG. 2, the plating film obtained from the electroless nickel plating solution containing the compound having the S--S sulfur bond is locally dissolved to reach the substrate of the object to be plated. There is a risk of reaching pinholes. In the figure, 1 is an object to be plated, 2 is a nickel plating film obtained from an electroless nickel plating solution containing a compound having an S—S sulfur bond, 3 is an electroless gold plating film, and 4 is a pinhole. When the pinhole reaches the base material to be plated in this way, particularly when the base material to be plated is a metal such as copper that is easily corroded, corrosive metals such as copper in the base material to be plated are dissolved, Contaminate the electroless gold plating solution through the hole, or the electroless gold plating film,
This may cause discoloration.

On the other hand, as shown in FIG. 3, an electroless nickel plating solution containing no compound having an S--S sulfur bond is used for the object to be plated 1 to form a nickel plating film 5 of the first layer, When the second layer nickel plating film 2 is formed on this using an electroless nickel plating solution containing a compound having an S—S sulfur bond, the elution rate of the electroless nickel plating film in the electroless gold plating solution ( The rate of substitution of gold ions with metallic gold) is shown in FIG. 1, in which the plating film 2 from the electroless nickel plating solution containing a compound having an S—S sulfur bond has a compound having an S—S sulfur bond. Plating film 5 from electroless nickel plating solution containing no
Since the plating film 5 from the electroless nickel plating solution containing no compound having an S-S sulfur bond has a significantly slower elution rate than the above, the electroless nickel containing the compound having an S-S sulfur bond is significantly slower. Even if the second layer plating film 2 from the plating solution is locally dissolved to form a pinhole 4 penetrating the film 2, the pinhole 4 has electroless nickel plating having an S—S sulfur bond. The pinholes 4 do not form pinholes on the first-layer plating film 5 from the electroless nickel plating solution that stops at the second-layer plating film 2 from the solution and does not contain a compound having an S—S sulfur bond. Is newly generated at another location of the second layer plating film 2, or acts so that the pinhole 4 spreads laterally at the location.

Therefore, the first electroless nickel plating solution containing no compound having an S--S sulfur bond is used.
If the second layer plating film 2 is formed on the layer plating film 5 with an electroless nickel plating solution containing a compound having an S—S sulfur bond, and electroless gold plating is performed in this state, the electroless gold plating film is obtained. Is formed thick in a short time, and the electroless gold plating solution is contaminated by the metal eluted from the substrate to be plated,
The discoloration of the electroless gold plating film is reliably prevented. Therefore, this method can be suitably used when the base metal of the object to be plated is a corrosive metal such as copper, for example, when the object to be plated is a printed wiring board or the like.

The plating solution and the plating conditions used for the electroless nickel plating not containing the compound having the S--S sulfur bond are the electroless nickel plating solution composition containing the compound having the S--S sulfur bond as described above. , This S
The same plating solution composition can be used except that a compound having a -S sulfur bond is not added, and plating can be performed under the same plating conditions.

The thickness of the plating film of the first layer from the electroless nickel plating solution containing no compound having an S--S sulfur bond is preferably 0.5 to 5 .mu.m, particularly 1 to 3 .mu.m. The thickness of the second layer of the plating film formed from the electroless nickel plating solution containing the compound having an S—S sulfur bond formed above is preferably 0.5 to 5 μm, and particularly preferably 1 to 5 μm.

When the substrate of the object to be plated is not a corrosive metal, the plated film can be formed directly from the electroless nickel solution containing the compound having the S--S sulfur bond on the object to be plated. In this case, the thickness of this plating film can be 0.5 to 10 μm, and particularly 1 to 8 μm. If the plating film is sufficiently thick, the above-mentioned penetration of pinholes can be prevented or reduced.

The thickness of the electroless gold plating film is appropriately selected and is not particularly limited, but is usually 0.1 to 2 μm, and particularly 0.3 to 0.8 μm.

[0038]

As described above, according to the thickening method for electroless gold plating of the present invention, the gold plating film can be made sufficiently thick in a short time.

[0039]

EXAMPLES The present invention will be described below in detail with reference to examples and comparative examples, but the present invention is not limited to the following examples.

Comparative Example Nickel Sulfate 20 g / L Sodium Hypophosphite 20 g / L Malic Acid 10 g / L Sodium Succinate 20 g / L Lead Ion 1.0 mg / L pH 4.6 Temperature 85 ° C.

Example 1 Nickel sulfate 20 g / L Sodium hypophosphite 20 g / L Malic acid 10 g / L Sodium succinate 20 g / L Lead ion 1.0 mg / L Sodium thiosulfate 1.0 mg / L pH 4. 6 Temperature 85 ℃

Use the electroless plating solutions of the above Comparative Examples and Examples.
A 5 μm plating film was formed on the copper plate. Then
Using the following strike electroless gold plating bath under the following conditions
After performing the strike plating, the following thick electroless plating
Thick plating under the following conditions using a bath
FIG. 1 shows the result of measuring the film thickness of the gold plating film. Strike electroless gold plating KAu (CN)_Two 1.5 g / L (Au 1.0 g / L) EDTA ・ 2Na 5.0 g / L citric acid ・ 2K 30.0 g / L pH 7 Temperature 90 ° C. Time 7 minutesThick electroless gold plating KAu (CN)_Two 5.9 g / L (Au 4.0 g / L) Ammonium sulfate 200 g / L Sodium thiosulfate 0.5 g / L Ammonium phosphate 5.0 g / L pH 6 Temperature 90 ° C.

From FIG. 1, it can be seen that the electroless gold plating applied to the electroless nickel plating film of the example is less than the electroless gold plating applied to the electroless nickel plating film of the comparative example in unit time. It can be seen that the gold plating film around this is significantly thick, and that a film thickness of 0.5 μm or more can be easily obtained in a short time.

Example 2 The following plating solution composition was applied on a copper plate:
Electroless nickel plating was performed for 15 minutes under the plating conditions to form a first layer of electroless nickel plating film of 2.5 μm. First layer Nickel sulfate 20 g / L Sodium hypophosphite 20 g / L Malic acid 10 g / L Sodium succinate 20 g / L Lead ion 1.0 mg / L pH 4.6 Temperature 85 ° C. Time 15 minutes

Next, electroless nickel plating was performed on this first layer nickel plating film for 15 minutes under the following plating composition and plating conditions to form a second layer electroless nickel plating film of 3.0 μm. Second layer Nickel sulfate 20 g / L Sodium hypophosphite 20 g / L Malic acid 10 g / L Sodium succinate 20 g / L Lead ion 1.0 mg / L Sodium thiosulfate 1.0 mg / L pH 4.6 Temperature 85 ° C. hours 15 minutes

Next, the same strike electroless gold plating solution as in Example 1 was used and strike plating was performed for 7 minutes under the same conditions, and then the same thick plating gold plating solution as in Example 1 was used under the same conditions. Gold plating for 20 minutes, 0.5μm
A gold plating film of

After heat treatment in air at 150 ° C. for 4 hours, the appearance was evaluated. No discoloration was observed and the same golden appearance as immediately after plating was maintained.

It should be noted that, in the case where the nickel plating film of the first layer is not formed, there is no problem in practical use by heat treatment at 150 ° C. for 4 hours, but a slight discoloration, especially a fine wiring pattern or a large wiring pattern. Discoloration was observed at the edge of the pad.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between plating time and gold film thickness when electroless gold plating is applied to an electroless nickel plating film.

FIG. 2 is a schematic view showing a pinhole formation state when one nickel plating film is formed from an electroless nickel plating solution containing a compound having an S—S sulfur bond.

FIG. 3 shows a case where a plating film is formed from an electroless nickel plating solution containing a compound having an S—S sulfur bond on a plating film formed from an electroless nickel plating solution not containing a compound having an S—S sulfur bond. It is a schematic diagram which shows a pinhole formation state.

[Explanation of symbols]

1 Plating object 2 Plating film from electroless nickel plating solution containing compound having S-S sulfur bond 3 Electroless gold plating film 4 Pinhole 5 Electroless nickel plating solution not containing compound having S-S sulfur bond Plating film from

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical display location C23C 28/02 C23C 28/02 H05K 3/24 7511-4E H05K 3/24 A (72) Inventor Rumiko Usu 1-5-1, Exit Hirakata, Osaka Prefecture Central Research Institute, Uemura Industrial Co., Ltd. (72) Masayuki Kiso 1-5-1, Exit Hirakata, Osaka Prefecture Central Research Institute, Uemura Industrial Co., Ltd.

Claims (4)

[Claims] 1. After electroplating nickel using an electroless nickel plating solution to which a compound having an S—S sulfur bond is added, an object to be plated having a nickel plating film formed by this nickel plating is applied to electroless gold. A method for thickening electroless gold plating, which comprises immersing in a plating bath to perform electroless gold plating. 2. An electroless nickel plating solution is applied to an object to be plated using an electroless nickel plating solution containing no compound having an S—S sulfur bond, and then an electroless material containing a compound having an S—S sulfur bond. The electroless gold plating thickening method according to claim 1, wherein nickel plating is performed and then electroless gold plating is performed. 3. The compound having an S—S sulfur bond added to the electroless nickel plating solution is thiosulfate, dithionate, polythionate or dithionite. Electroless gold plating thickening method. 4. The electroless gold plating thickening method according to claim 1, wherein the electroless gold plating bath contains a gold cyanide salt as a gold raw material and has a pH of 4 to 9.