KR102502530B1 - Non-cyanide electroless gold plating bath and electroless gold plating method - Google Patents

Abstract

(Problem) To provide a gold plating bath that can be used for gold plating formation in both the ENIG process and the ENEPIG process.
(Solution) An electroless gold plating bath containing a water-soluble gold salt, a reducing agent, and a complexing agent, and not containing cyan, wherein the reducing agent includes formic acid or a salt thereof, and hydrazines. Non-cyanide electroless gold plating bath.

Description

Non-cyanide electroless gold plating bath and electroless gold plating method {NON-CYANIDE ELECTROLESS GOLD PLATING BATH AND ELECTROLESS GOLD PLATING METHOD}

The present invention relates to a non-cyanide electroless gold plating bath and an electroless gold plating method.

BACKGROUND ART Conventionally, there is an ENIG (Electroless Nickel Immersion Gold) process for forming substitution type gold plating on electroless nickel plating as a final surface treatment in a mounting process of a printed wiring board or electronic component. This process can be used for solder bonding. It can also be used for wire bonding by applying gold to give thickness after the ENIG process.

On the other hand, the ENEPIG (Electroless Nickel Electroless Palladium Immersion Gold) process, in which gold plating is formed on the underlying electroless nickel plating via electroless palladium plating, is also employed as the final surface treatment. This process is optimal for lead-free solder bonding. It is also suitable for wire bonding.

The ENIG process and the ENEPIG process are selected according to the purpose of the plated object, and gold plating is finally performed in either process. However, in forming the gold plating, the former uses nickel with a high ionization tendency (low redox potential) as a base, while the latter uses palladium with a low ionization tendency (high redox potential) as a base. differ in that Therefore, until now, a gold plating bath according to each process has been used.

Further, as the gold plating bath, a cyan gold plating bath has conventionally been widely used, but in view of the toxicity of cyanide, a non-cyanide type gold plating bath has been demanded.

For example, as a non-cyanide type gold plating bath used in the ENEPIG process, Patent Document 1 sequentially applies an electroless nickel plating film, an electroless palladium plating film, and an electroless gold plating film to a conductor portion of a printed wiring board. In the formation, the gold plating solution used for forming the electroless gold plating film is composed of an aqueous solution containing a water-soluble gold compound, a reducing agent and a complexing agent, and the reducing agent is formaldehyde bisulfite, longalite and It is shown that it is at least 1 sort(s) selected from the group which consists of hydrazines. Further, in Patent Document 2, as an electroless gold plating solution capable of depositing a gold film directly on an electroless palladium plating film by an autocatalytic reduction reaction, non-cyanide gold sulfite, sulfite, thiosulfate, water-soluble polyaminocarboxylic acid , a plating solution containing a benzotriazole compound, a sulfur-containing amino acid compound, and hydroquinone at predetermined concentrations.

However, preparing a plating bath for each process or replacing the plating bath depending on the use of the plating object requires a number of steps and costs, and is not practical in terms of workability or economy. Therefore, a gold plating bath that can be used for both ENIG process and ENEPIG process gold plating formation has been demanded.

Further, in the non-cyanide type gold plating bath, a decrease in bath stability and plating reactivity tends to occur more easily than a cyan gold plating bath. Therefore, a combination of bath stability and plating reactivity is required as desirable characteristics of a non-cyanide type gold plating bath.

Japanese Patent Publication No. 5526440 Japanese Unexamined Patent Publication No. 2010-180467

The present invention has been made in view of the above circumstances, and its object is a non-cyanide electroless gold plating bath that can be used in both the ENIG process and the ENEPIG process, and the electroless using the non-cyanide electroless gold plating bath. It is to realize the gold plating method.

The non-cyanide electroless gold plating bath of the present invention that has been able to solve the above problems is an electroless gold plating bath containing water-soluble gold salt, a reducing agent, and a complexing agent, but not containing cyan, wherein the reducing agent is formic acid or a salt thereof; and hydrazines.

It is preferable that the non-cyanide electroless gold plating bath further contains a compound having a nitro group.

The present invention also includes an electroless gold plating method characterized by performing electroless gold plating on the surface of an object to be plated using the non-cyanide electroless gold plating bath. In the electroless gold plating method, the surface of the plated object may be nickel or nickel alloy, ie ENIG process, or the plated object surface may be palladium or palladium alloy, ie ENEPIG process.

ADVANTAGE OF THE INVENTION According to this invention, the non-cyanide electroless gold plating bath which can be used for both ENIG process and ENEPIG process can be provided. Specifically, in the ENIG process, corrosion of the nickel plating is suppressed when gold plating is formed on the nickel plating. Also, in both the ENIG process and the ENEPIG process, gold deposition reactivity is improved, and gold plating can be made thicker. For example, in the ENIG process, precipitation of 0.07 μm or more is possible on nickel plating in about 20 minutes, and in the ENEPIG process, precipitation of 0.05 μm or more is possible on about 30 minutes on palladium plating.

1 is a SEM (Scanning Electron Microscope) observation photograph showing the presence or absence of corrosion on the nickel plating surface in Examples.

The present inventors repeated earnest research in order to solve the said subject. As a result, if a substitution reduction type non-cyanide electroless gold plating bath containing formic acid or a salt thereof and hydrazines as a reducing agent does not cause excessive corrosion such as nickel plating as a base material, the gold precipitation reactivity is increased. It was found that it can be used for both the ENIG process and the ENEPIG process, and the present invention was completed. Hereinafter, the non-cyanide electroless gold plating bath of the present invention is sometimes referred to as "electroless gold plating bath" or "gold plating bath". Below, each compound contained in the non-cyanide electroless gold plating bath of this invention is demonstrated.

(A) hydrazines

Hydrazines are compounds that contribute to the improvement of plating precipitation properties for palladium phases, in particular, and promote the formation of gold plating for palladium plating phases in the ENEPIG process. In addition, hydrazines are compounds that also contribute to ensuring a good plating appearance, and as a result, also contribute to ensuring good solder jointability and wire bonding jointability (W/B jointability). On the other hand, in the ENIG process, it is thought that hydrazines accelerate the substitution reaction on the nickel plating more than necessary and cause excessive corrosion of the nickel plating. However, as will be described later, excessive corrosion of the nickel plating can be suppressed by using it in combination with formic acid or a salt thereof.

Examples of the hydrazines include hydrazine; catcher hydrazine such as hydrazine monohydrate; hydrazine salts such as hydrazine carbonate, hydrazine sulfate, neutral hydrazine sulfate, and hydrazine hydrochloride; hydrazine organic derivatives such as pyrazoles, triazoles, and hydrazides; etc. can be used. As the pyrazoles, other than pyrazole, pyrazole derivatives such as 3,5-dimethylpyrazole and 3-methyl-5-pyrazolone can be used. As said triazoles, 4-amino-1,2,4-triazole, 1,2,3-triazole, etc. can be used. As hydrazides, adipic acid dihydrazide, maleic acid hydrazide, carbohydrazide, etc. can be used. Preferably, it is catcher hydrazine, such as hydrazine monohydrate, and hydrazine sulfate. These can be used individually or in combination of 2 or more types.

The total concentration of the hydrazines is preferably 0.1 to 5 g/L. More preferably, it is 0.3-3 g/L.

(B) Formic acid or its salt

Formic acid or a salt thereof is thought to have an effect of suppressing an excessive substitution reaction by the above hydrazines. Hereinafter, "formic acid or salts thereof" are collectively referred to as formic acids in some cases. In particular, in the case of gold plating in the ENIG process, excessive corrosion of the underlying Ni film can be suppressed. On the other hand, when only formic acids are used without combined use with the above hydrazines, gold precipitation reactivity tends to decrease, particularly in the ENEPIG process. Specifically, the gold deposition reactivity to the palladium plating phase as the base is poor, and it becomes difficult to secure the film thickness of the gold plating. Therefore, combined use with the above-mentioned hydrazines is required. The combined use of hydrazines and formic acids suppresses excessive corrosion of the nickel plating and contributes to ensuring solder jointability and W/B bondability.

As a salt of the said formic acid, For example, alkali metal salts of formic acid, such as potassium formate and sodium formate; alkaline earth metal salts of formic acid, such as magnesium formate and calcium formate; amine salts containing formic acid ammonium salts, quaternary ammonium salts, and primary to tertiary amines; etc. can be mentioned. In this invention, formic acid or its salt can be used individually or in combination of 2 or more types.

The total concentration of the formic acids is preferably contained within the range of 1 to 100 g/L. In order to fully exhibit the above effect, it is preferably 1 g/L or more, more preferably 5 g/L or more, and still more preferably 10 g/L or more. On the other hand, if it is contained excessively, the bath tends to become unstable, so it is preferable to set it to 100 g/L or less as described above.

In short, in the present invention, by using hydrazines and formic acids together as reducing agents, in the gold plating treatment of the ENIG process, nickel corrosion (substitution reaction) by hydrazines is suppressed by formic acids, and nickel plating, which is the base of gold plating, corrosion can be inhibited. On the other hand, in the gold plating treatment of the ENEPIG process, the high reactivity of hydrazines to the palladium plating phase accelerates the formation of gold plating compared to the case where formic acid alone is used, and it is possible to make the gold plating thicker. This is considered to be because the reduction reaction was promoted.

The gold plating bath of the present invention is an electroless gold plating bath that does not contain cyan and requires, in addition to the above hydrazines and formic acids, a water-soluble gold salt and a complexing agent. Also, as described later, reducing agents other than hydrazines and formic acids may be used. Hereinafter, the water-soluble gold salt will be described in order.

First, the electroless gold plating bath of the present invention contains a water-soluble gold salt as a gold source. As described above, the water-soluble gold salt is noncyanide, specifically, gold sulfite, thiosulfate, thiocyanate, sulfate, nitrate, methanesulfonate, tetraammine complex, chloride, bromide, iodide, hydroxide, oxide of gold etc. can be mentioned. These can be used individually or in combination of 2 or more types. The total concentration of the water-soluble gold salt in the plating bath is 0.3 to 5 g/L, particularly preferably 0.5 to 4 g/L as the gold (Au) concentration. If it is less than 0.3 g/L, the precipitation rate may be slow. On the other hand, when it exceeds 5 g/L, stability may fall, and even if it increases, the effect will hardly change and cost will also increase.

The electroless gold plating bath of the present invention may further have the following reducing agent as a reducing agent in addition to the above hydrazines and formic acids. That is, ascorbic acid compounds such as ascorbic acid and isoascorbic acid (erythorbic acid) or salts thereof (sodium salt, potassium salt, ammonium salt, etc.); Hydroquinone or its derivative(s), such as hydroquinone and methyl hydroquinone; pyrogallol or derivatives thereof such as pyrogallol, pyrogallol monomethyl ether, pyrogallol-4-carboxylic acid, pyrogallol-4,6-dicarboxylic acid, and gallic acid; can be heard These can be used individually or in combination of 2 or more types. In the present invention, as a reducing agent, the combined use of hydrazines and formic acids is essential, and as a reducing agent other than the hydrazines and formic acids, for example, ascorbic acid is used in combination with formic acids, the desired characteristics are not obtained. It is shown by No. 10 of the Example mentioned later.

The total concentration of the reducing agents other than hydrazines and formic acids in the gold plating bath is preferably 0.5 to 50 g/L, particularly 1 to 10 g/L.

The electroless gold plating bath of the present invention contains a complexing agent. As the complexing agent, a complexing agent having a complexing action of an eluted metal (eg, nickel, palladium, etc.) and a complexing agent having a complexing action of gold are preferable. It is a complexing agent having a complexing action of the metal to be eluted, and preferably, hydroxycarboxylic acids or salts thereof (sodium salt, potassium salt, ammonium salt, etc.); Aminocarboxylic acids such as glycine, aminodicarboxylic acid, nitrilotriacetic acid, EDTA, hydroxyethylethylenediaminetriacetic acid, diethylenetriaminepentaacetic acid, and polyaminocarboxylic acid or their salts (sodium salt, potassium salts, ammonium salts, hydrochlorides, sulfates, etc.); phosphorous acid-based chelating agents such as HEDP (hydroxyethane-1,1-diphosphonic acid), aminotrimethylsulfonic acid, and ethylenediaminetetramethylsulfonic acid, or salts thereof (sodium salt, potassium salt, ammonium salt, hydrochloride salt, sulfate salt, etc.); amine-based chelating agents such as ethylenediamine, diethylenetriamine, and triethylenetetramine, and salts thereof (such as hydrochloride and sulfate); etc. can be mentioned. These can be used individually or in combination of 2 or more types.

It is also a complexing agent having a complexing action of gold, and preferably, sodium sulfite, potassium sulfite, ammonium sulfite, sodium bisulfite, potassium bisulfite, ammonium bisulfite, sodium bisulfite, potassium bisulfite, ammonium bisulfite, sodium thiosulfate, thiosulfate Potassium, ammonium thiosulfate, a hydantoin compound, an imide compound, etc. are mentioned. These can be used individually or in combination of 2 or more types. More preferably, sodium sulfite, ammonium sulfite, etc. are used.

The total concentration of the complexing agent having a complexing action for the metal to be eluted and the complexing agent having a complexing action for gold in the gold plating bath is preferably 1 to 200 g/L, particularly 10 to 150 g/L.

The electroless gold plating bath of the present invention preferably further contains a compound having a nitro group. By including the compound having a nitro group, even if cyan is not included, plating reactivity, that is, gold precipitation reactivity is not impaired, and bath stability can be sufficiently secured. As this action mechanism, it is conceivable that the nitro group captures gold and is stabilized. On the other hand, simple catechol or benzoic acid, which does not contain a nitro group, does not show a stability effect.

As a compound which has the said nitro group, the aromatic compound which has a nitro group is mentioned, for example. As an aromatic compound which has the nitro group, For example, Nitrobenzene; aromatic compounds having a nitro group and a hydroxyl group, such as nitrophenol and 4-nitrocatechol; Aromatic compounds which have a nitro group and an alkyl group, such as nitrotoluene, nitro xylene, and nitro styrene; aromatic compounds having a nitro group and an amino group, such as nitroaniline and 4-nitro-1,2-phenylenediamine; aromatic compounds having nitro groups and sulfur-containing groups, such as nitrobenzenesulfonic acids such as nitrothiophenol and 2,4-dinitrobenzenesulfonic acid; can be heard Furthermore, examples of the nitrobenzoic acid having a nitro group and a carboxyl group include 2-nitrobenzoic acid, 3,5-dinitrobenzoic acid, 3,4-dinitrobenzoic acid, and 5-amino-2-nitrobenzoic acid further having an amino group. there is. In addition, aromatic compounds having a halogen group, an ester group, an ether group, a carbonyl group, an aldehyde group and the like in addition to a nitro group may be mentioned. Alternatively, as salts of aromatic compounds having a nitro group, ammonium salts, sodium salts, potassium salts and the like can also be used.

For example, in the case of the nitrobenzoic acid, when the nitro group is adjacent to the carboxyl group, the stability effect is increased, so it is preferable. That is, the magnitude of the effect of stability is in the order of 2-nitrobenzoic acid > 3-nitrobenzoic acid > 4-nitrobenzoic acid.

As the compound having a nitro group, an aliphatic compound having a nitro group can also be used in addition to the above-mentioned aromatic compound having a nitro group.

More preferably, it is a compound having an electron-donating group together with a nitro group, particularly an aromatic compound having an electron-donating group together with a nitro group. When it has an electron-donating group, the effect of stabilizing a nitro group becomes large. Even in the case of dinitro with two adjacent nitro groups, it is considered that the effect on stability increases due to the form of trapping with two nitro groups. As said electron-donating group, a hydroxyl group, an alkyl group, an amino group, a sulfur-containing group, a carboxyl group, an ester group, a halogen group, an ether group etc. are mentioned, for example. It is preferable to have one or more of these.

The compound which has the said nitro group can use the compound as mentioned above individually or in combination of 2 or more types. The total concentration of the compounds having a nitro group is preferably in the range of, for example, 0.0010 to 5 g/L. It is because it is difficult to obtain the said effect when the said total concentration is less than 0.0010 g/L. The total concentration is more preferably 0.005 g/L or more, and still more preferably 0.010 g/L or more. On the other hand, if the concentration of the compound having a nitro group is too high, the surface of the underlying nickel plating is easily corroded. Therefore, the total concentration is preferably 5 g/L or less as described above, more preferably 4 g/L or less, still more preferably 3 g/L or less.

It is preferable that the pH of the electroless gold plating bath of this invention is 5-10. This is because the gold precipitation rate tends to decrease when the content is below this range, while the bath tends to become unstable when it exceeds the above range. The pH is more preferably 6 to 9.

The electroless gold plating bath of the present invention may appropriately contain known pH adjusters, pH buffers, and other additives within a range that does not impair the object of the present invention. As said pH adjuster, hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, carboxylic acid etc. are mentioned as an acid, sodium hydroxide, potassium hydroxide, aqueous ammonia etc. as an alkali, for example. Further, examples of the pH buffering agent include carboxylic acids such as citric acid, tartaric acid, malic acid, and phthalic acid; Phosphate, such as phosphoric acid, such as orthophosphoric acid, phosphorous acid, hypophosphorous acid, and pyrophosphoric acid, or their potassium salt, sodium salt, and ammonium salt; boric acid, tetraboric acid; etc. can be mentioned. In addition, as a metal ion masking agent, azoles, such as benzotriazole and methylbenzotriazole, phenanthroline, bipyridyl, a salicylate, etc. are mentioned. Moreover, aminocarboxylic acids, ammonium salts, chlorides, etc., such as EDTA and EDTMP, are mentioned as an auxiliary complexing agent. As the stabilizer, for example, sulfur-containing hetero compounds (2-mercaptobenzothiazole, 2-mercaptobenzoxazole, etc.), nitrogen-containing hetero compounds (benzotriazole, N-hydroxybenzotriazole, etc.) can be heard

At least one of a thallium compound, an arsenic compound, and a lead compound may be further added to the electroless gold plating bath of the present invention. These compounds improve the gold plating speed and act as crystal conditioners. Specific examples of the compound include carbonates, acetates, nitrates, sulfates, hydrochlorides and the like of metals (arsenic, thallium, lead) constituting the compound. The concentration of the crystal regulator in the gold plating bath is preferably, for example, 0.1 to 100 mg/L in total as a metal concentration, more preferably 0.2 to 50 mg/L in total, still more preferably in total 0.2 to 20 mg/L.

The present invention also stipulates that an electroless gold plating method is performed using the non-cyanide electroless gold plating bath. Examples of the plating target object subjected to gold plating include those having a surface of nickel or a nickel alloy. In the ENIG process described above, there is a case where the surface of the plated object is electroless nickel plating or electroless nickel alloy plating (hereinafter referred to as "electroless nickel-based plating"). As said nickel alloy, a nickel- phosphorus alloy, a nickel- boron alloy, etc. are mentioned.

The surface of the plating target object subjected to gold plating may be palladium or a palladium alloy. In the ENEPIG process described above, a case in which the surface of the plated object is electroless palladium plating or electroless palladium alloy plating (hereinafter referred to as "electroless palladium-based plating") is exemplified. As said palladium alloy, a palladium phosphorus alloy etc. are mentioned.

In the ENIG process, for example, electroless nickel-based plating and then electroless gold plating are formed on Al or Al-based alloys constituting the electrode, Cu or Cu-based alloy, and then electroless gold plating thereon. In the ENEPIG process, for example, the electrode On Al or Al-based alloys constituting Cu or Cu-based alloys, electroless nickel-based plating, then electroless palladium-based plating, and then electroless gold plating are formed thereon, wherein the electroless nickel-based plating or electroless For the formation of the palladium-based plating, a method commonly used may be employed.

In either of the above ENIG process and ENEPIG process, the electroless gold plating may be formed under conditions normally performed, except for using the non-cyanide electroless gold plating bath of the present invention. For example, contacting the electroless gold plating bath of the present invention for about 3 to 20 minutes is exemplified. As the contact, conventionally known methods such as immersion can be employed. The use temperature of the electroless gold plating bath is preferably 40 to 90°C. If it is less than the above range, there is a possibility that the precipitation rate will decrease, while if it exceeds the above range, there is a possibility that the bath becomes unstable. The use temperature is preferably 50 to 80°C.

The electroless gold plating bath of the present invention and the electroless gold plating method using the same are suitable for gold-plating a printed wiring board, a ceramic board, a semiconductor board, and a wiring circuit mounting portion or terminal portion of electronic components such as an IC package. do. In particular, it is preferably used in UBM (Under Barrier Metal) formation technology for the purpose of solder bonding and wire bonding (W/B) bonding to Al electrodes or Cu electrodes on a wafer. By using the gold plating bath of the present invention, it is possible to stably form electroless gold plating, which is a part of UBM formation technology, and as a result, it becomes possible to realize stable film properties.

This application claims the benefit of priority based on Japanese Patent Application No. 2015-148523 for which it applied on July 28, 2015. The entire content of the specification of Japanese Patent Application No. 2015-148523 filed on July 28, 2015 is incorporated herein by reference.

(Example)

Hereinafter, the present invention will be described in more detail with examples, but the present invention is not limited from the beginning by the following examples, but it is also possible to make appropriate changes within the range suitable for the purpose of the foregoing and later. Of course, it is possible, and they are all included in the technical scope of the present invention.

[Measurement of film thickness of gold plating, confirmation of corrosion of nickel plating, and preparation of samples for observing the appearance of gold plating]

[Sample of ENIG process]

A sample of the ENIG process used for measuring the film thickness of the gold plating and the like was obtained as follows. That is, a TEG wafer whose electrodes are made of Al-Cu, which is an Al-based alloy, is prepared, and on this electrode, an electroless nickel plating bath (NPR-18 manufactured by Uemura Kogyo Co., Ltd.) is used, and a thickness of 5.0 μm is applied by an electroless plating method. Thick nickel plating was formed, and then, electroless gold plating was performed using the electroless gold plating bath shown in Table 1, and obtained. This sample may be referred to as "Sample I of the ENIG process" below.

[Sample of ENEPIG process]

A sample of the ENEPIG process used for measuring the film thickness of the gold plating and the like was obtained as follows. That is, a TEG wafer whose electrodes are made of Al-Cu, which is an Al-based alloy, is prepared, and on this electrode, an electroless nickel plating bath (NPR-18 manufactured by Uemura Kogyo Co., Ltd.) is used, and a thickness of 5.0 μm is applied by an electroless plating method. Thick nickel plating is formed, and then, 0.05 μm thick palladium plating is formed on the nickel plating by an electroless plating method using an electroless palladium plating bath (TFP-30 manufactured by Uemura Kogyo Co., Ltd.), and further , obtained by performing electroless gold plating using the electroless gold plating bath shown in Table 1. This sample may be referred to as "sample I of the ENEPIG process" below.

Additional conditions for electroless gold plating performed in the ENIG process and each sample preparation of the ENEPIG process are as follows. That is, in the electroless gold plating bath, a gold sodium sulfite solution (Au concentration = 100 g/L) was used as a gold source, and later Table 1 shows the Au concentration in the electroless gold plating bath. Further, thallium carbonate was used as the thallium (Tl) compound, and Table 1 shows the Tl concentration in the electroless gold plating bath. The temperature of the electroless gold plating bath is set to 75 ° C., and the electroless gold plating bath is immersed for 20 minutes in the case of sample I of the ENIG process and for 30 minutes in the case of sample I of the ENEPIG process, and gold plating was formed. In addition, in Sample I of the ENEPIG process of Nos. 1, 2, 4 and 6 in Table 1 described later, since the film thickness of the gold plating was able to be ensured at an early stage, the immersion time was set to 20 minutes.

[Measurement of film thickness of gold plating in ENIG process or ENEPIG process]

The film thickness of the formed gold plating of Sample I of the ENIG process and Sample I of the ENEPIG process was measured with a fluorescence X-ray thickness meter. And especially, the case where the film thickness of the gold plating with respect to the palladium plating phase in an ENEPIG process was 0.05 micrometer or more was evaluated as a gold plating bath applicable to an ENEPIG process.

[Presence or absence of corrosion of nickel plating by SEM observation]

The nickel-plated surface obtained by removing the gold plating of Sample I of the ENIG process with a gold stripper was observed by SEM at a magnification of 5000, and the presence or absence of corrosion traces was confirmed. Then, those in which traces of corrosion were confirmed were evaluated as "presence" of corrosion of nickel plating, and those in which traces of corrosion were not confirmed were evaluated as "no" of corrosion of nickel plating. For reference, Fig. 1 shows an SEM observation picture. 1 (a) is a photograph of an example of the present invention in which no traces of corrosion of nickel plating are observed, and FIG. 1 (b) is a photograph of a comparative example in which no traces of corrosion of nickel plating are confirmed.

[Observation of appearance of gold plating]

The surface of the gold plating of Sample I of the ENIG process and Sample I of the ENEPIG process was visually observed. And those exhibiting a uniform gold-colored plating appearance were evaluated as "good", and those having red discoloration instead of gold were evaluated as "defective".

[Preparation of samples for evaluation of solder bonding and wire bonding (W/B) properties]

[Sample of ENIG process]

As a sample of the ENIG process used for evaluation of solder jointability and W/B property, a BGA substrate (pat diameter φ 0.5 mm) manufactured by Uemura Kogyo Co., Ltd. was prepared, and on this substrate, in the same manner as Sample I of the ENIG process described above, , Using an electroless nickel plating bath (NPR-18 manufactured by Uemura Kogyo Co., Ltd.), a 5.0 μm thick nickel plating was formed by an electroless plating method, and then an electroless gold plating bath shown in Table 1 was used, It was obtained by performing electroless gold plating. This sample may be referred to as "Sample II of the ENIG process" below.

[Sample of ENEPIG process]

As a sample of the ENEPIG process used for evaluation of solder joint property and W/B property, a BGA substrate (pat diameter φ 0.5 mm) manufactured by Uemura Kogyo Co., Ltd. was prepared, and on this substrate, in the same manner as Sample I of the ENEPIG process described above, , Using an electroless nickel plating bath (NPR-18 manufactured by Uemura Industrial Co., Ltd.), a 5.0 μm thick nickel plating was formed by an electroless plating method, and then an electroless palladium plating bath (TFP-30 manufactured by Uemura Industrial Co., Ltd.) ) was used, and palladium plating having a thickness of 0.05 μm was formed on the nickel plating by an electroless plating method, and further, electroless gold plating was performed using the electroless gold plating bath shown in Table 1 to obtain the resultant. This sample may be referred to as "sample II of the ENEPIG process" below.

[Evaluation of Solder Bondability]

Using sample II of the above ENIG process and sample II of the ENEPIG process, 20 points were evaluated for one condition using a bond tester SERIES4000 manufactured by Dage. In detail, each No. of Table 1. About,

When sample II of the ENIG process is used and the number of reflows shown below is 1;

When sample II of the ENEPIG process is used and the number of reflows shown below is 1;

When sample II of the ENIG process is used and the number of reflows shown below is 5; and

When sample II of the ENEPIG process is used and the number of reflows shown below is 5;

A total of 4 conditions x 20 = 80 points of solder joint strength were measured. As the solder joint strength, the solder breakage rate in the fracture mode was determined. Conditions for solder formation and solder joint strength measurement are as follows. In this example, the solder jointability was evaluated as "good" when the solder breakage rate was 85% or more, and the solder jointability was evaluated as "poor" when the solder breakage rate was less than 85%.

[Conditions for Solder Formation and Solder Joint Strength Measurement]

Measurement method: ball pool test

Solder ball: Senju Metals φ 0.6 mm Sn - 3.0Ag - 0.5Cu

Reflow device: TMR-15-22LH manufactured by Tamra Manufacturing Co., Ltd.

Reflow conditions: Top 240 ℃

Reflow Environment: Air

Number of reflows: 1 or 5 times

Flux: 529D-1 manufactured by Senju Metals (RMA type)

Test speed: 5000 μm/sec

Aging after solder mount: 1 hour

[Evaluation of Wire Bonding (W/B) Properties]

Using sample II of the above ENIG process and sample II of the ENEPIG process, wire bonding was performed with a semi-automatic wire bonder HB16 manufactured by TPT, and 20 points were evaluated for one condition by a bond tester SERIES4000 manufactured by Dage. In detail, each No. of Table 1. For , the wire bonding strength (W/B strength) of the case of using sample II of the ENIG process and the case of using sample II of the ENEPIG process, under the total of 2 conditions × 20 = 40 points, was measured, and the average value of W/B Average intensity and standard deviation were calculated. Further, based on them, a coefficient of variation (= standard deviation ÷ average value × 100) was determined. The conditions for forming wire bonding and the conditions for evaluating wire bonding properties are as follows. And, when the W/B average strength is 8 gf or more and the coefficient of variation is 15% or less, the wire bonding property is evaluated as "good", and at least either of the W/B average strength or the coefficient of variation is outside the above range. The case was evaluated as "defective" in wire bonding property.

[Conditions for Wire Bonding Formation and Wire Bondability Evaluation]

Capillary: B1014-51-18-12 (PECO)

Wire: 1 Mil-Gold

Stage temperature: 150 ℃

Ultrasound (mW): 250 (1st), 250 (2nd)

Bonding time (milliseconds): 200 (1st), 50 (2nd)

Tensile force (gf): 25 (1st), 50 (2nd)

Step (length from 1st to 2nd): 0.700 mm

Measurement method: wire pull test

Test speed: 170 μm/sec

In this embodiment, when both the solder bondability and the wire bondability are "good", the solder bondability and the W/B property are evaluated as "good", and at least one of the solder bondability and the wire bondability is "good". In the case of "defect", the solder jointability and W/B property were evaluated as "defective".

[Evaluation of Bath Stability]

The electroless gold plating bath of each bath composition shown in Table 1 was left to stand at a temperature of 70°C for one month, and the bath stability was evaluated. Those that did not decompose even after being left for one month were evaluated as "stable", and those that decomposed within one month were evaluated as "unstable".

These results are listed together in Table 1.

From Table 1, the following can be seen. In Nos. 1 to 6, gold plating was performed using a gold plating bath containing a combination of formic acid and hydrazine as prescribed, so that the gold plating film thickness can be sufficiently secured even in the case of the ENEPIG process, and ENIG Corrosion of the nickel plating was also suppressed in the process, and a good plating appearance was obtained. In addition, all of these examples were able to satisfactorily perform both solder bonding and wire bonding bonding. Further, from the comparison between Nos. 1 to 3 and No. 4, it can be seen that a gold plating bath further containing a compound having a nitro group is preferable from the viewpoint of ensuring sufficient bath stability. Further, from the comparison between No. 3 and No. 5, it can be seen that it is preferable to set the content of formic acids to the recommended upper limit or less (100 g/L or less).

On the other hand, Nos. 7 to 10 did not contain any of the prescribed formic acids and hydrazines, so a problem occurred. In detail, since No.7 and No.8 did not contain formic acid, corrosion of the nickel plating occurred. As a result, solder bonding properties and W/B properties became poor. Moreover, No. 9 is an example which does not contain hydrazines. In this example, in the ENEPIG process, the film thickness of gold plating became thin. No. 10 is an example in which ascorbic acid as a reducing agent is used in combination with formic acids instead of hydrazines. Also in this example, the film thickness of gold plating became thin in the ENEPIG process. Also, in Nos. 9 and 10, the appearance of the gold plating became reddish. Due to the occurrence of such a red discoloration defect, the solder joint property and W/B property were poor.

Claims (5)

An electroless gold plating bath containing water-soluble gold salt, a reducing agent, and a complexing agent, and not containing cyan, characterized in that the reducing agent includes formic acid or a salt thereof, and hydrazines, wherein the content of the formic acid or a salt thereof is 1 g/L or more and 100 g/L or less, and the content of the hydrazines is 0.1 g/L or more and 5 g/L or less. According to claim 1,
A non-cyanide electroless gold plating bath containing a compound having a nitro group. An electroless gold plating method characterized by performing electroless gold plating on the surface of an object to be plated using the non-cyanide electroless gold plating bath according to claim 1 or 2. According to claim 3,
The electroless gold plating method of claim 1, wherein the surface of the plated object is nickel or a nickel alloy. According to claim 3,
The electroless gold plating method of claim 1, wherein the surface of the plated object is palladium or a palladium alloy.

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