Electroless gold plating bath

Electroless gold plating bath technology field

[0001] The present invention relates to an electroless gold plating bath.

Background technique

[0002] Gold plating is widely used as a surface treatment method for applications requiring high reliability in the mounting process of printed circuit boards, electronic components, and the like. As a representative electroless plating method for forming a gold plating film, substitution type gold plating and substitution reduction type gold plating can be cited. Among these methods, the former displacement gold plating is a method of using the difference between the oxidation-reduction potential of a base metal such as silver and the plating bath to precipitate gold. However, due to the substitution reaction, gold oxidizes (dissolves) the base metal and corrodes, so it is difficult to thicken the gold plating film, and the type of base metal is also restricted. In addition, in the replacement gold plating, since the base metal diffuses on the gold plating film, there is also a problem that the wire bonding (W/B) bondability is reduced.

[0003] In contrast, the latter displacement reduction type gold plating is a method in which both the displacement reaction and the reduction reaction are carried out in the same plating bath, and the gold plating bath contains a reducing agent. As an example of the above-mentioned substitution reduction type gold plating, for example, there are: electroless silver plating/replacement gold (ENIG: Electroless Nickel Immersion Gold) in which a substitution gold plating film is formed on a base electroless silver plating film; Electroless Nickel Electroless Palladium Immersion Gold (ENEPIG: Electroless Nickel Electroless Palladium Immersion Gold) with an electroless palladium film, electroless palladium plating/replacement gold on the electroless palladium film, and copper Direct Immersion Gold (DIG: Direct Immersion Gold), etc., which directly replace the gold-plated film. According to the replacement reduction type gold plating, the corrosion of the base metal caused by the replacement type gold plating can be eliminated, and a gold plating film with excellent coating properties can be obtained. In addition, it is possible to increase the thickness of the gold plating film, and it can also be used for solder bonding and wire bonding.

[0004] As a technique for improving the corrosion of the base metal by substitution reduction type gold plating, for example, Patent Documents 1 and 2 can be cited. Examples of these reducing agents include formaldehyde and/or formaldehyde bisulfite adducts, predetermined amine compounds (Patent Document 1); aldehyde compounds and predetermined amine compounds (Patent Document 2).

[0005] In addition, Patent Document 3 was completed in view of the problem of "the bath stability of the aforementioned Patent Document 2 is poor, and gold also precipitates and decomposes after heating for several hours", and discloses that sodium cyanide and the like are replenished during the heating of the electroless gold plating solution. The cyanide compound is a method to stably maintain the solubility of gold in the gold plating solution. Patent Document 4 also adds a cyanide ion source such as potassium cyanide as a stabilizer, similarly to Patent Document 3 described above.

[0006] Prior Art Documents

[0007] Patent Literature

[0008] Patent Document 1: Japanese Patent Publication No. 2008-266668

[0009] Patent Document 2: Japanese Patent Publication No. 2008-144188

[0010] Patent Document 3: International Publication No. 2016/174780 Pamphlet

[0011] Patent Document 4: International Publication No. 2017/050662 Pamphlet Invention Contents

[0012] However, in Patent Documents 3 and 4, since a highly toxic cyanide compound is used, it is necessary to strictly manage the working environment in order to safely perform the plating process. Therefore, it is necessary to provide a gold plating bath that does not use cyanide

The compound can also prevent the decomposition of the plating bath.

[0013] The present invention is made in view of the above circumstances, and its object is to provide an electroless gold plating bath with excellent plating bath stability, which can eliminate the use of mice even when the plating heating time reaches a long time. The compound prevents the decomposition of the plating bath due to the precipitation of gold.

[0014] The composition of the electroless gold plating bath according to the present invention that solves the above-mentioned problems is as follows.

[0015] 1. An electroless gold plating bath, characterized in that the electroless gold plating bath contains a water-soluble gold salt, a reducing agent, and an instant compound represented by the following formula.

[0016]

[Chemical formula 1] In the regional production one-network formula, R1, R2, and R3 are each the same or different, and are phenyl groups or alkyl groups with 1-5 carbon atoms.

[0017]

[0018] At least one is substituted with a sulfonic acid group or a salt thereof, a murine group, or a carboxyl group or a salt thereof.

[0019] 2. The electroless gold plating bath according to 1 above, wherein the electroless gold plating bath is a gold plating bath that does not contain a rat compound as an additive.

[0020] According to the present invention, it is possible to provide an electroless gold plating bath with excellent plating bath stability. Even when the plating heating time reaches a long time, the electroless gold plating bath can prevent the precipitation of gold without using rat compounds. The resulting decomposition of the plating bath.

Description of the drawings

[0021] FIG. 1 is a SEM (Scanning Electron Microscope) observation photograph showing the presence or absence of corrosion on the silver coating surface. It is No. 16 (corrosion) in Table 1, No. 1 (no corrosion) in Table 1 Respective photos.

Detailed ways

[0022] In order to solve the above-mentioned problems, the inventors of the present invention have conducted various studies on the composition of the gold plating bath. As a result, it was found that if a predetermined transient compound is used as a stabilizer, the desired object can be achieved, and the present invention has been completed.

[0023] Instant compound

[0024] First, the transient compound of the above formula that is the most characteristic of the present invention will be described.

[0025] The above-mentioned transient compound as a stabilizer capable of preventing the decomposition of gold even if heated for a long time among water-soluble transient compounds was selected through basic experiments of the inventors of the present invention. By adding the above-mentioned transient compound, for example, In the case of heating the plating solution at 80C for a long time for 5 days as in Example 2 described later, there is no need to replenish rat compound during plating, which can suppress the occurrence of decomposition of the plating bath and maintain a good plating precipitation rate (refer to the following Table 5).

[0026] In the above formula, at least one of the phenyl group and the C5 alkyl group constituting Ri, R2, and R3 is substituted with a sulfonic acid group or a salt thereof, a murine group, or a substituent of a carboxyl group or a salt thereof Here, "the salt" includes, for example, alkali metal salts such as sodium salt and potassium salt; amine salt such as triethylamine salt; hydrochloride, etc. The instant compound used in the present invention is the above-mentioned R1, R2, and R3. At least one may be substituted, or all of two or three may be substituted. The above-mentioned transient compound may have the form of a hydrate.

[0027] In addition, none of R1, R2, R3 has a substituent, and a compound composed only of a phenyl group or an alkyl group having 5 carbon atoms is not water-soluble, and therefore does not belong to the instant compound used in the present invention.

[0028] In addition, transient compounds having substituents other than those described above do not belong to the transient compounds used in the present invention. For example, R1, R2, R3 are lower alkyl groups, and at least one of them is an instant compound substituted by a hydroxyl group or an amino group other than the substituents (sulfonic acid group or its salt, cyano group, carboxyl group or its salt) specified in the present invention It is not included in the scope of the present invention. For example, using tris(3-hydroxypropyl) instantaneously as in Comparative Example 18 described later, the desired effect could not be obtained (see Table 5).

[0029] In the above formula, the alkyl group having 1 to 5 carbon atoms may be linear, branched, or cyclic, for example: methyl, ethyl, propyl, isopropyl, cyclopropyl , Butyl, sec-butyl, tert-butyl, pentyl, etc. Among these groups, an alkyl group having 1 to 3 carbon atoms is preferable, and a methyl group, an ethyl group, a propyl group, and an isopropyl group are preferable.

[0030] In the above formula, the phenyl group and the above-mentioned alkyl group having 1 to 5 carbon atoms are preferably substituted with the same substituent. In addition, the above-mentioned phenyl group is preferably substituted with a sulfonic acid group, and the above-mentioned alkyl group is preferably substituted with a carboxyl group or a salt thereof.

[0031] As the instant compound used in the present invention, for example, triphenyl instant-3-sulfonate sodium, dihydrate bis(p-sulfonylphenyl) phenyl instant dipotassium, triphenyl instant- Trisodium 3,3',3-trisulfonate, di(tert-butyl)(3-sulfonylpropyl) quinone, (2-cyanophenyl) diphenyl quinone, tris(2-cyanoethyl) ) Instantaneous, tris (2-ethyl) instantaneous hydrochloride and so on. It is preferably triphenylphosphine 3-sodium sulfonate, triphenylinstant-3,3',3-trisulphonate, tris(2-cyanoethyl)instant, tris(2-ethyl)ins Hydrochloride. As the instant compound used in the present invention, commercially available products can be used.

[0032] The concentration of the instant compound in the electroless gold plating bath of the present invention is preferably 0.0001 to 1 mmol/L. More preferably, it is 0.001-0.1 mmol/L.

(2) Water-soluble gold salt

[0034] The electroless gold plating bath of the present invention contains a water-soluble gold salt as a gold source. Specifically, in addition to cyanide gold salts such as gold cyanide, potassium gold cyanide, sodium gold cyanide, gold ammonium cyanide, etc., gold sulfite, thiosulfate, and thiocyanate can also be cited. Salt, sulfate, nitrate, methanesulfonate, tetraamine complex, chloride, iodide, iodide, hydroxide, oxide, etc. These can be used individually or in combination of 2 or more types. Among them, gold cyanide salts are particularly preferred.

[0035] The concentration of the above-mentioned water-soluble gold salt in the electroless gold plating bath of the present invention (contained alone is a single concentration, when two or more kinds are used in combination, the total concentration), in terms of the concentration of gold (Au), is preferably 0.00001 -0.1mol/L, more preferably 0.001-0.05mol/L. If the concentration is lower than the above range, the plating precipitation rate may decrease. On the other hand, if it exceeds the above range, the stability of the plating bath may decrease, and the effect of increasing the amount will hardly change, which is economically wasteful.

[0036] Reducing agent

[0037] The reducing agent used in the present invention is not particularly limited as long as it has a reduction and precipitation effect of gold ions. For example, the reducing agent described in the aforementioned Patent Document 1 (formaldehyde and/or formaldehyde bisulfite adduct and a prescribed amine compound); the reducing agent described in Patent Document 2 (the aldehyde compound and the aforementioned patent document 1 The same prescribed amine compound); ascorbic acid; hydrazine; formic acid or its salt, etc. In addition, the prescribed amine compounds and formaldehyde precursors described in Patent Documents 1 and 2 may be used as reducing agents. The type of amine compound is not limited to the above. For example, the amine compound of formula (1) described in Patent Document 3 and the ethylenediamine derivative of formula (1) described in Patent Document 4 may be used. For the details of the amine compound described in Patent Document 3, refer to paragraphs 0048-0067 of the document 3. For the details of the ethylenediamine derivative of formula (1) described in Patent Document 4, refer to paragraphs 0014-0021 of the document 4. The above-mentioned reducing agents can be used alone or in combination of two or more kinds.

[0038] The concentration of the above-mentioned reducing agent in the electroless gold plating bath of the present invention (individual concentration when contained alone, and the total concentration when two or more are used in combination) is preferably about 0.00001-1 mol/L, more preferably 0.0001-0.1 mol/ L. If the concentration is lower than the above range, the plating precipitation rate may decrease. On the other hand, if it exceeds the above range, the stability of the plating bath can be

The energy will be reduced, and the effect will hardly change even if the amount is increased, which is economically wasteful.

[0039] Examples of the above-mentioned hydrazines include hydrazine; hydrazine hydrate such as hydrazine hydrate monohydrate; hydrazine salts such as hydrazine carbonate, hydrazine sulfate, neutral hydrazine sulfate, and hydrazine hydrochloride; pyrazoles, triazoles, hydrazine Organic derivatives of hydrazine such as hydrazine; etc. As the above-mentioned pyrazoles, in addition to pyrazole, pyrazole derivatives such as 3,5-dimethylpyrazole and 3-methyl-5-pyrazolone can also be used. As the above-mentioned 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. These can be used individually or in combination of 2 or more types. Preferably, they are hydrazine hydrate such as hydrazine hydrate monohydrate and hydrazine sulfate. These can be used individually or in combination of 2 or more types.

[0040] Examples of the salt of formic acid include: 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; ammonium salts, quaternary ammonium salts of formic acid, and primary Amine~Amine salt of tertiary amine; etc. These can be used individually or in combination of 2 or more types.

[0041] In the present invention, it is preferable to use the reducing agent described in the aforementioned Patent Documents 1 and 2, and the reducing agent described in the aforementioned Patent Document 1 and 2 consisting of a combination of a predetermined amine compound and a formaldehyde precursor.

(3-1) Reducing agent described in Patent Document 1

[0043] The reducing agent described in Patent Document 1 is a formaldehyde and/or formaldehyde bisulfite adduct and an amine compound represented by the following general formula (1) or (2). Formaldehyde and/or formaldehyde bisulfite adduct alone does not function as a reducing agent, but can exhibit a reducing effect by using it in combination with the following amine compound.

[0044] R1-NH-C2H4-NH-R2 (1)

[0045] R3-(CH2-NH-C2H4-NH-CH2) n-R4 (2)

[0046] In formula (1) and formula (2), R1, R2, R3, and R4 represent -OH, -CH3, -CH2OH, -C2H4OH, -CH2N(CH3) 2, -CH2NH (CH2OH), -CH2NH(C2H4OH),- C2H4NH (CH2OH), -C2H4NH(C2H4OH), -CH2N(CH2OH) 2, -CH2N (C2H4OH) 2, -C2H4N (CH2OH) 2 or -C2H4N (C2H4OH) 2, and can be the same or different , N is an integer of 1-4.

[0047] Specific examples of the formaldehyde bisulfite adduct include: formaldehyde sodium bisulfite, formaldehyde potassium bisulfite, formaldehyde ammonium bisulfite, and the like.

[0048] The concentration of the aforementioned formaldehyde and/or formaldehyde bisulfite adduct in the electroless gold plating bath of the present invention is preferably 0.0001 to 0.5 mol/L, more preferably 0.001 to 0.3 mol/L. If the concentration is lower than the above range, the base metal may corrode. On the other hand, if it exceeds the above range, the plating bath may become unstable.

[0049] The concentration of the amine compound of the above formula (1) or (2) in the electroless gold plating bath of the present invention is preferably 0.001 1 mol/L, more preferably 0.01-0.5 mol/L. If the concentration is lower than the above range, the plating precipitation rate may decrease. On the other hand, if it exceeds the above range, the plating bath may become unstable.

[0050] In addition, the molar ratio of the above-mentioned formaldehyde and/or formaldehyde bisulfite adduct to each content of the amine compound of the above formula (1) or (2) is preferably formaldehyde and/or formaldehyde bisulfite plus Finished product: the amine compound of the above formula (1) or (2)=1:30-3:1, particularly preferably 1:10-1:1. When the adduct of formaldehyde and/or formaldehyde bisulfite exceeds the above range, the plating bath may become unstable. On the other hand, even if the amine compound of the above formula (1) or (2) is added in excess of the above range, the effect is only saturated and it is economically wasteful.

[0051] (3-2) Reducing agent described in Patent Document 2

[0052] The reducing agent described in the aforementioned Patent Document 2 is an aldehyde compound and an amine compound represented by the aforementioned general formula (1) or (2). The aldehyde compound alone does not act as a reducing agent, but it exhibits a reducing effect by using it in combination with the above-mentioned amine compound.

[0053] Examples of the above-mentioned aldehyde compounds include: formaldehyde, acetaldehyde, propionaldehyde, n-butyraldehyde, α-methylvaleraldehyde, β-methylpentanal

Aliphatic saturated aldehydes such as aldehydes and γ-methylvaleraldehyde; aliphatic dialdehydes such as glyoxal and succinaldehyde; aliphatic unsaturated aldehydes such as crotonaldehyde; benzaldehyde, o-nitrobenzaldehyde, m-nitrogen Aromatics such as methyl benzaldehyde, p-nitrobenzaldehyde, o-methylbenzaldehyde, m-methylbenzaldehyde, p-methylbenzaldehyde, o-hydroxybenzaldehyde, m-hydroxybenzaldehyde, p-hydroxybenzaldehyde, phenylacetaldehyde, etc. Aldehydes; glucose, galactose, mannose, ribose, maltose, lactose and other sugars with an aldehyde group (-CHO). Particularly preferred is formaldehyde.

[0054] The concentration of the above-mentioned aldehyde compound in the electroless gold plating bath of the present invention is preferably 0.0001-0.5 mol/L, more preferably 0.001-0.3 mol/L. If the concentration is lower than the above range, the plating precipitation rate may decrease. On the other hand, if it exceeds the above range, the plating bath may become unstable.

[0055] In addition, the molar ratio of the content of the aldehyde compound to the amine compound of the formula (1) or (2) is preferably aldehyde compound:amine compound = 1:30-3:1, particularly preferably 1:10 -1:1. If the aldehyde compound is less than the above range, the plating bath may become unstable. On the other hand, even if the amine compound of the above formula (1) or (2) is added beyond the above range, the effect is only saturated and it is economically wasteful.

[0056] (3-3) A reducing agent composed of a combination of an amine compound and a formaldehyde precursor described in Patent Documents 1 and 2

[0057] The reducing agent is composed of a formaldehyde precursor and an amine compound represented by the general formula (1) or (2). The formaldehyde precursor alone does not act as a reducing agent, but can exhibit a reducing effect by using it in combination with the above-mentioned amine compound.

[0058] Here, "formaldehyde precursor" refers to a compound that decomposes in an aqueous plating bath and thereby forms formaldehyde. As said formaldehyde precursor, acetal, hemiacetal, aminal, N, O-acetal, etc. are mentioned, for example.

[0059] Specifically, for example, acetals, hemiacetals, aminal and N,O-acetals can be, for example, dimethylol glycol, sodium hydroxymethylglycinate, 1,3-bis( Hydroxymethyl) 5,5-dimethylimidazolidine-2,4-dione, 1,3,5,7-tetraazatricyclic [3.3.1. 1^3,7] Decane, phenyl hemiformal, 2-Ao-2-nitropropane-1,3-diol, 5-Ao-5-nitro-1,3-dioxane, 1,3-bis( Hydroxymethyl)-1-(1,3,4-tris(hydroxymethyl)-2,5-dioxoimidazolidine-4-yl)urea, 1,1'-methylenebis(3[1 -(Hydroxymethyl)-2,5-dioxoimidazolidine-4-yl]urea}, 3,5,7-triaza-1-aza^tricyclic [3.3.1. 1³,⁷]-Decane-1-(3-chloro-2-propenyl)-chloro, tetramethylol glycoluril, 1,3-bis(hydroxymethyl)2-imidazolinone, 1,3-bis(hydroxy Methyl) urea, 2,2,2-trichloroethane-1,1-diol and 5,5-dimethyl-1,3-dioxane, etc. For details of the aforementioned formaldehyde precursor, for example, Japanese Patent No. 6066131 can be referred to.

[0060] The concentration of the aforementioned formaldehyde precursor in the electroless gold plating bath of the present invention is preferably 0.0001-0.5 mol/L, more preferably 0.001-0.3 mol/L. If the concentration is lower than the above range, the base metal may corrode. On the other hand, if it exceeds the above range, the plating bath may become unstable.

[0061] The preferred concentration of the amine compound of the above formula (1) or (2) in the electroless gold plating bath of the present invention is the same as that of Patent Documents 1 and 2.

[0062] In addition, the molar ratio of the content of the formaldehyde precursor to the amine compound of the formula (1) or (2) is preferably formaldehyde precursor: amine compound = 1:30-3:1, especially 1: 10-1:1. If the formaldehyde precursor is less than the above range, the plating bath may become unstable. On the other hand, even if the amine compound of the above formula (1) or (2) is added beyond the above range, the effect is only saturated and it is economically wasteful.

[0063] The electroless gold plating bath of the present invention contains the above-mentioned transient compound as a stabilizer, and does not contain a cyanide compound as an additive. Here, "not containing a cyanide compound as an additive" means that, in addition to the cyanide compound derived from a water-soluble gold compound such as gold potassium cyanide, no cyanide compound as a cyanide source is added separately. In the case of normal plating, cyanide compounds such as potassium cyanide added as a complexing agent for gold gradually disappear during plating, and the plating bath decomposes. Therefore, the cyanide compound is replenished in order to prevent decomposition. In contrast to this, in the present invention, since the above-mentioned transient compound capable of preventing the decomposition of gold is added to the plating bath, it is not necessary to periodically replenish the cyanide compound during plating as in Patent Documents 3 and 4 mentioned above.

[0064] (4) Other

[0065] The electroless gold plating bath of the present invention contains the above-mentioned transient compound, water-soluble gold salt and reducing agent, and does not contain cyanide compounds as additives. In addition, the electroless gold plating bath of the present invention may contain additives commonly used in electroless gold plating baths as optional components. Hereinafter, the additives preferably used are described.

[0066] (4-1) Complexing agent

[0067] As the complexing agent contained in the electroless gold plating bath of the present invention, well-known complexing agents used in the electroless plating bath can be used, for example, phosphoric acid, boric acid, citric acid, gluconic acid, Tartaric acid, lactic acid, malic acid, ethylenediamine, triethanolamine, ethylenediaminetetraacetic acid, nitrilotriacetic acid, diethylenetriaminepentaacetic acid, hydroxyethylethylenediaminetriacetic acid, triethylenetetramine hexa Acetic acid, 1,3-propanediaminetetraacetic acid, 1,3-diamino-2-hydroxypropanetetraacetic acid, hydroxyethyl iminodiacetic acid, dihydroxyglycine, glycol ether diamine tetraacetic acid, dimethicone Glutamic acid, hydroxyethylene dimorphic acid, ethylenediamine tetrakis (methylene phosphoric acid), or its alkali metal (such as sodium, potassium) salt, alkaline earth metal salt, ammonium salt, etc. These can be used individually or in combination of 2 or more types.

[0068] The concentration of the above-mentioned complexing agent in the electroless gold plating bath of the present invention (individual concentration when used alone, and the total concentration when used in combination of two or more) is preferably 0.001-1 mol/L, more preferably 0.01-0.5 mol /L. If the concentration is lower than the above range, the plating precipitation rate may decrease due to the eluted metal. On the other hand, even if the addition exceeds the above range, the effect is only saturated and it is economically wasteful.

[0069] (4-2) Stabilizer

[0070] In the electroless gold plating bath of the present invention, stabilizers used in known electroless plating can be added. As the above-mentioned stabilizer, sulfur compounds such as 2-mercaptobenzothiazole, 2-mercaptobenzimidazole, thioglycolic acid, mercaptosuccinic acid, thiosulfuric acid, mercaptoglycol, thiourea, thiomalic acid, etc. can be cited; Nitrogen compounds such as benzotriazole and 1,2,4-aminotriazole. These can be used individually or in combination of 2 or more types.

[0071] The concentration of the stabilizer in the electroless gold plating bath of the present invention (individual concentration when contained alone, and the total concentration when two or more are used in combination) is preferably 0.0000001-0.01 mol/L, more preferably 0.0000010 .005mol/L. If the concentration is lower than the above range, the plating bath may become unstable. On the other hand, if it exceeds the above range, the plating precipitation rate may decrease.

[0072] (4-3) Other

[0073] The electroless gold plating bath of the present invention may further add one or more selected from thallium, arsenic compounds, and lead compounds. These compounds function to increase the plating speed and the crystallization regulator. Specific examples of the compound include carbonate, acetate, nitrate, sulfate, hydrochloride, etc. of the metal (arsenic, thallium, lead) constituting the compound. The concentration of the crystal regulator in the gold plating bath is, in terms of the metal concentration, for example, a total of 0.0001 to 1 mmol/L is preferable, a total of 0.0050.1 mmol/L is more preferable, and a total of 0.01-0.05 mmol/L is still more preferable.

[0074] The pH of the electroless gold plating bath of the present invention is preferably 5-10. If the pH is lower than the above range, the plating precipitation rate may decrease. On the other hand, if it exceeds the above range, the plating bath may become unstable. The above-mentioned pH can be adjusted by a pH adjuster. The pH adjuster used in the present invention is not particularly limited as long as it is a pH adjuster used in a known plating bath, and examples thereof include sodium hydroxide, potassium hydroxide, ammonia, sulfuric acid, phosphoric acid, and boric acid.

[0075] The use temperature (heating temperature) of the electroless gold plating bath of the present invention is preferably 40-90°C. If the temperature is lower than the above range, the plating precipitation rate may decrease. On the other hand, if it exceeds the above range, the plating bath may become unstable.

[0076] Using the electroless gold plating bath of the present invention, by contacting the metal surface with the electroless gold plating bath, the gold of the substrate can be

The surface is chemically plated. In this case, for example, a gold plating film with a thickness of 0.01-2 μm can be formed with a contact time of 5-60 minutes, and a gold plating film with a deposition rate of 0.002-0.03um/min can be formed, for example.

[0077] As the material of the metal surface (surface to be plated) of the substrate, copper, copper alloy, silver alloy, palladium, palladium alloy, etc. can be targeted. Examples of the silver alloy include silver-phosphorus alloys, nickel-boron alloys, and the like. Examples of palladium alloys include palladium-phosphorus alloys. Such a metal surface may be a surface of a metal (alloy) on which a metal film is formed on the surface of the substrate in addition to the surface of the substrate itself. The metal film may be any one of a metal film formed by electroplating and a metal film formed by electroless plating. In the case of nickel, nickel alloy, palladium, and palladium alloy, it is generally a metal film formed by electroless plating. In addition, it is also preferable to perform electroless gold plating on the surface of the palladium or palladium alloy film formed on the substrate via the nickel or nickel alloy film.

[0078] The electroless gold plating bath of the present invention can be prepared by, for example, the following method: ENIG (Electroless Nickel Immersion Gold), a method of forming a gold plating film on a base electroless silver plating layer (formed on copper); DIG (Direct Immersion Gold), that is, the method of directly forming gold plating on copper; ENEPIG (ElectrolessNickel Electroless Palladium Immersion Gold), that is, the method of forming gold plating on the base electroless silver film (formed on copper) through the electroless palladium film Any of the gold plating films can be used in the formation of gold plating. In any case, by using the electroless gold plating bath of the present invention, it is possible to form gold with a predetermined thickness in the above range on the silver surface, the copper surface, and the palladium surface. Coating.

[0079] In addition, the electroless gold plating bath of the present invention can obtain a good film even when the metal surface (surface to be plated) is copper, and when the substrate is copper, the oxidation and diffusion of copper are suppressed, and it is possible to obtain Good solder joint properties. In addition, it can also be used for wire bonding by increasing the thickness of the film. In addition, the plating bath of the present invention can also deposit a good gold film on palladium, so it is most suitable for lead-free solder bonding or wire bonding.

[0080] The electroless gold plating bath of the present invention and the electroless gold plating method using the bath are suitable for the case where the wiring circuit mounting portion or terminal portion of electronic components such as printed circuit boards, ceramic substrates, semiconductor substrates, and IC packages are gold-plated . Especially for the Al electrode or Cu electrode on the wafer, it is suitable for UBM (Under Barrier Metal) formation technology for solder bonding and wire bonding (W/B) bonding. By using the gold plating bath of the present invention, it is possible to stably perform the formation of electroless gold plating, which is a part of the UBM formation technology, and as a result, it is possible to realize stable film characteristics.

[0081] Embodiment

[0082] Hereinafter, the present invention will be explained in more detail with examples. However, the present invention is not limited by the following examples, and can be modified and implemented within the scope that can conform to the spirit of the foregoing and later descriptions, and they are all included in the present invention. Within the scope of technology. In addition, as long as there is no special description below, "parts" means "parts by mass" and "%" means "mass%,

Example 1

[0084] In this example, the presence or absence of bath decomposition caused by the presence or absence of a reducing agent when the plating bath was heated for a short time was visually observed. As described above, the decomposition of the plating bath occurs in displacement reduction plating containing a reducing agent, but the decomposition of the plating bath does not occur in displacement plating containing no reducing agent. In addition, depending on the type of reducing agent, the degree of decomposition of the plating bath may also vary. This example is a so-called confirmation experiment for confirming this point.

[0085] In detail, after heating the various plating solutions described in Table 1 in a hot water bath at 80° C. for 8 hours, the presence or absence of decomposition of the plating solution was visually observed.

[0086] In Table 1, No. 1-10 is an example of the present invention using the instant compound 1 described in Table 2, No. 11 is an example of the present invention using the instant compound 2 described in Table 2, and No. 12 is used The present example of the instant compound 3 described in Table 3, No. 13 is the present example of the present invention using the instant compound 4 described in Table 2, and No. 20 is a comparative example using the instant compound 5 described in Table 2. In Table 2,

The brackets indicate substituents. The aforementioned instant compound 5 is not an instant compound defined in the present invention, but an example using tris(3-hydroxypropyl) instant. No. 14T9 contains no instant compound.

[0087] In addition, in Table 1, amine compounds 1 and 2 are amine compounds represented by formula (1) described in Patent Documents 1 and 2, and amine compound 3 is represented by formula (2) described in Patent Documents 1 and 2. Amine compound. The amine compound 4 is N-methyl T,3-diaminopropane contained in the amine compound represented by formula (1) described in Patent Document 3. The amine compound 5 is M,M-diisopropylethane-1,2-diamine contained in the ethylenediamine derivative amine compound represented by formula (1) described in Patent Document 4.

[0088] No. 17 of Table 1 is to replenish KCN so that the replenishment amount per 1 hour per 1 L of the plating solution was 15 mg/L after heating, and other examples were not replenishing KCN during heating.

[0089] These results are shown in Table 3.

[0090] [Table 1]

<td rowspan="7"></td><td></td><td></td><td></td><td></td><td></td><td></td><td>§</td><td></td><td></td><td>1</td><td></td><td></td><td></td><td></td><td></td><td></td><td>§</td><td></td><td>1</td>

<td>E</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>number</td><td>lt-</td>

<td>W</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>If</td><td>Ξ</td><td>9</td>

<td>l·-</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>3</td><td></td><td>g</td><td>g</td>

<td>9</td><td>c</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>g</td><td>I</td><td>K</td>

<td>Vi</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>number</td><td>d</td>

<td>three</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>g</td><td></td><td>r-</td>

<td rowspan="13"></td><td></td><td>Ν</td><td></td><td></td><td></td><td>=</td><td></td><td>§</td><td></td><td>Purpose</td><td></td><td></td><td></td><td></td><td></td><td></td><td>§</td><td></td><td>g</td>

<td>Z</td><td></td><td></td><td></td><td>number</td><td></td><td></td><td></td><td></td><td>t</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>number</td><td>g</td>

<td>-</td><td>s</td><td></td><td></td><td></td><td></td><td></td><td>w</td><td></td><td>b</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>g</td>

<td>Ξ</td><td></td><td>s</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>§</td><td></td><td>§</td><td>GO</td>

<td></td><td>s</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>Kas</td><td></td><td>8</td>

<td>Β</td><td></td><td>g</td><td></td><td></td><td></td><td></td><td>§</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>§</td><td>a</td><td>e</td>

<td>t-</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>§</td><td></td><td></td><td></td><td></td><td>ear</td><td>c</td>

<td>0</td><td>a</td><td>=</td><td></td><td></td><td></td><td></td><td>=</td><td></td><td></td><td></td><td>=</td><td></td><td></td><td></td><td></td><td>=</td><td></td><td>9</td>

<td></td><td></td><td>§</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>Contain</td><td>w</td><td>9</td>

<td>-Τ</td><td>s</td><td></td><td></td><td></td><td></td><td></td><td></td><td>§</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>§</td><td></td><td>L</td>

<td>Ε</td><td></td><td>s</td><td></td><td></td><td></td><td></td><td>s</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>3</td><td>To</td><td>a</td>

<td>Z</td><td></td><td></td><td></td><td></td><td></td><td></td><td>I</td><td></td><td>*</td><td></td><td></td><td></td><td></td><td></td><td></td><td>I</td><td></td><td></td>

<td>-</td><td></td><td>s</td><td></td><td></td><td></td><td></td><td>S</td><td></td><td>12 $</td><td></td><td></td><td></td><td></td><td></td><td></td><td>ws</td><td>9</td><td>9</td>

<td colspan="2" rowspan="2"></td><td></td><td>i</td><td></td><td>Different 3 Q</td><td></td><td></td><td>bamboo grove</td><td></td><td>[110^ 1 &lt;1Ν/ 11\&gt;I ΙΝΊ K/H^: J "Shi U Lishan</td><td></td><td>Just change ίΐ state of matter tcc\ 1 I_rNH4 _:lirNlK JiiNlCH, M (mol·1]</td><td>112 Shan Ba also received/W same as $1J treatment with Z small plus</td><td>I i [wif v</td><td>Stem Yun</td><td></td><td></td><td></td><td rowspan="2">ft.</td>

<td></td><td colspan="5"></td><td colspan="9"></td><td colspan="2"></td>

[0092] [Table 2]

<td></td><td>Ri</td><td>Di</td><td>R3</td>

<td>Instant Compound 1</td><td>Phe(SC)₃Na)</td><td>Phe tSOsNa)</td><td>Phe(SO₃Na)</td>

<td>Instant Compound 2</td><td>Phe(SO₃Na)</td><td>Phe</td><td>Phe</td>

<td>Instant Compound 3</td><td>CILCIL· (CN)</td><td>CILCIL· (CN)</td><td>CILCIL· (CN)</td>

<td>Instant Compound 4</td><td>CILCIL·(COOH)</td><td>CILCIL·tCOOII)</td><td>CILCIL·CCOOII)</td>

<td>Instant Compound 5</td><td>CII2CII2CH2COH)</td><td>CII2CII2CH2 (Oil)</td><td>CII2CII2CH2 (ΟΠ)</td>

[0094] [Table 3]

<td>Evaluation item</td><td>!</td><td>2 3</td><td></td><td>5 6</td><td>Implement Iraq 7</td><td></td><td>9</td><td>IU u 12</td><td>13</td><td>N</td><td>15</td><td>ί16</td><td>ΕComparative Example 17</td><td>1 stroke</td><td>N 20</td>

<td>Heating temperature</td><td>«0</td><td>80 SO</td><td>80</td><td>SO SO</td><td>of</td><td>SO</td><td>SO</td><td>SO SO fio</td><td>double)</td><td>80</td><td>SO</td><td>80</td><td>80</td><td>so</td><td>Sfl SO</td>

<td>Heating time|hour]</td><td>8</td><td>8 8</td><td>8</td><td>8 8</td><td>8</td><td>⁸</td><td>,</td><td>a 8 s</td><td>8</td><td>8</td><td>8</td><td>8</td><td>⁸</td><td>^s</td><td>8 8</td>

<td>Is there any KCN thrown during heating?</td><td>no</td><td>No no</td><td>no</td><td>No no</td><td>no</td><td>no</td><td>no</td><td>Ίκ</td><td>no</td><td>no</td><td>no</td><td>no</td><td>no</td><td>no</td><td>With or without</td>

<td>The presence or absence of bath decomposition</td><td>no</td><td>No no</td><td>no</td><td>No no</td><td>no</td><td>no</td><td>no</td><td>No no no</td><td>no</td><td>Have</td><td>Have</td><td>no</td><td>no</td><td>no</td><td>None</td>

[0096] According to Table 3, it can be considered as follows.

[0097] First, No. 13 in Table 1 is an example of the present invention using a reducing agent and the instant compound used in the present invention. These reducing agents contain various reducing agents, but using any one of the reducing agents, due to the effect of the above-mentioned transient compound to prevent the decomposition of the plating solution, no decomposition of the plating solution occurs.

[0098] In contrast, Nos. 14 and 15 of Table 1 contain a reducing agent, and since the instant compound used in the present invention is not added, bath decomposition occurs.

[0099] Nos. 16 and 17 are examples of using lung (No. 16) and ascorbic acid (No. 17) with a small reducing effect. Under the short-time heating conditions as in this example, no bath decomposition occurred.

[0100] No. 18 is an example that does not contain a reducing agent, and no bath decomposition occurs.

[0101] In Table 1, when the same type of reducing agent was used to compare the results of Nos. 2, 14, 19, and 20 with the same pH=7, under the short-time heating conditions as in this example, the results were compared with those of the instant compound. Regardless of the kind, in Nos. 2 and 20 where the instant compound was added, no bath decomposition occurred. On the contrary, in No. 14 where no instant compound was added, bath decomposition occurred. In addition, in No. 19, since KCN was replenished during heating, no bath decomposition occurred.

Example 2

[0103] In this example, a part of the plating bath described in Table 1 was used for continuous plating under the following conditions, and various characteristics were evaluated.

(1) Evaluation of stability (presence or absence of bath decomposition)

[0105] First, a copper clad laminate (MCL-E-67 manufactured by Hitachi Chemical Co., Ltd.) was cut into a 5 cm square substrate. The plating process shown in Table 4 is sequentially implemented on the substrate, electroless silver plating and electroless tin plating are performed to form a Ni/Pd plating film,

It was immersed in the electroless gold plating solution of the composition described in Table 1 to continuously deposit gold. Wash with water between each process in Table 4. After heating, the presence or absence of decomposition of the bath for 1-5 days was visually observed.

[0106] In each of the gold plating baths shown in Table 1, during heating, the water-soluble gold salt and the reducing agent were replenished for every 0.1 g/L consumption in terms of gold. Replace the substrate every 20 minutes. During the plating process, the pH value was measured every day, and the pH was adjusted as necessary to maintain the pH described in Table 1.

(2) Evaluation of film characteristics

[0108] In the same manner as in the above [1], each sample having a 5um thick Ni film/0.1um thick Pd film/0.1um thick Au film was produced, and various film properties in each sample at the initial stage of bathing were evaluated. [Presence of Ni corrosion, solder bondability and wire bonding [W/B] property]. The film thickness of the film was measured using a fluorescent X-ray film thickness meter (XDV-u manufactured by Fisher Instruments).

[0109] (2-1) The presence or absence of corrosion of Ni plating film observed by cross-sectional SEM

[0110] For each of the samples No. 1 and No. 16 in Table 1, the Ni/Pd/Au plating film was processed by a focused ion beam device (manufactured by Hitachi High-Technologies), and then observed with a SEM with a 30um window. Check for corrosion. Fig. 1(a) is an SEM photograph of No. 16 (comparative example) where corrosion is observed, and Fig. 1(b) is an SEM photograph of No. 1 (invention example) where no corrosion is observed. [0111] (2-2) Evaluation of solder bondability

[0112] The solder bondability of each sample was evaluated under the following conditions. As the solder joint strength, the solder fracture rate in the failure mode was determined, and the case where the solder fracture rate was 85% or more was evaluated as "good" solder jointability, and less than 85% was evaluated as solder jointability "poor".

[0113] (Measurement conditions)

[0114] Measurement method: ball tensile test

[0115] Solder ball: SAC305 (Φ0.6mm) manufactured by Senju Metal Industry

[0116] Reflow soldering device: UNI-6116a manufactured by ANTO

[0117] Reflow conditions: Top 260Ό

[0118] Reflow environment: Air

[0119] Number of reflows: 5 times

[0120] Flux: Senju Metals 529D-1 (RMA type)

[0121] Test speed: 5000um/sec

[0122] Aging after welding setup: 1 hour

[0123] Evaluation substrate: BGA substrate (Ball Grid Array: Uemura Kogyo Co., Ltd., 5 cm×5 cm, 6 0.5 mm)

[0124] (2-3) Evaluation of Wire Bonding (W/B) Performance

[0125] For each sample at the initial stage of bathing, wire bonding was performed with a semi-automatic wire bonder HB16 manufactured by TPT Corporation, and 20 points were evaluated for each condition by Bondtester SERIES4000 manufactured by Dage Corporation. Specifically, a part of the gold plating bath in Table 1 was used to measure the wire bond strength (W/B strength) at 20 points, and calculate the W/B average strength and standard deviation as the average value. Furthermore, the coefficient of variation (=standard deviation+average value X 100) is obtained based on this. The wire bonding formation conditions and the wire bondability evaluation conditions are as follows. In addition, the case where the average W/B strength is 8gf or more and the coefficient of variation of 15% or less is evaluated as "good" wire bondability, and the case where at least one of the above-mentioned average strength of W/B and the coefficient of variation is outside the above range It was evaluated as "bad" wire bondability.

[0126] [Conditions for Wire Bonding Formation and Wire Bonding Evaluation]

[0127] Capillary: B1014-51-18-12 (PECO)

[0128] Lead: 1Mil-Gold

CN 111663123 A

[0129] Stage temperature: 150 °C

[0130] Heat treatment conditions: 175°C, 16h

[0131] Ultrasound (mW): 250 (1st), 250 (2nd)

[0132] Bonding time: (milliseconds): 200 (1st), 50 (2nd)

[0133] Tension (gf): 25 (1 st), 50 (2nd)

[0134] Step length (from first to second length): 0.700mm

[0135] Measurement method: pull wire test

[0136] Test speed: 170 μm/sec

(3) Measurement of precipitation rate

[0138] After preparing each sample with Ni/Pd/Au plating film in the same manner as above (1), it was measured by using a fluorescent X-ray film thickness meter (XDV-u manufactured by Fisher Instruments Co., Ltd.) to be plated at 80° C. The plating precipitation rate of the gold plating film formed in minutes (um/20min).

[0139] These results are shown in Table 5. Each No. in Table 5 corresponds to each No. in Table 1.

[0140] [Table 4]

<td>plating</td><td>Overlay</td><td>Temperature [°C]</td><td>Time [minutes]</td>

<td>Detergent cleaning</td><td>Uemura Industrial System ACL-007</td><td>50</td><td>5</td>

<td>Hot water cleaning</td><td>Warm ion exchange water</td><td>50</td><td>1</td>

<td>Soft etching</td><td>Sodium persulfate IQQg/L Sulfuric acid 20g/L</td><td>25</td><td>1</td>

<td>Pickling</td><td>Sulfuric acid 50g/L</td><td>25</td><td>1</td>

<td>Electroless plating</td><td>Uemura Industrial Co., Ltd. NPR-4</td><td>80</td><td>25</td>

<td>Electroless Plating Loquat</td><td>Uemura Industrial Co., Ltd. TPD-30</td><td>50</td><td>4</td>

<td>Electroless gold plating</td><td>See Table 1</td><td>80</td><td>See Table 5 (days)</td>

[0142] [Table 5]

<td colspan="2" rowspan="2">Evaluation item II</td><td colspan="6">Practical example</td><td colspan="7">Comparative example</td>

<td></td><td>4</td><td>9</td><td>1]</td><td>12</td><td>Ij</td><td>14</td><td>15</td><td>J6</td><td>17</td><td>18</td><td>19</td><td>20</td>

<td rowspan="5">Dingyou</td><td>Largest</td><td>no</td><td>no</td><td>no</td><td></td><td>no</td><td>no</td><td>Ϊ1</td><td>(1</td><td>no</td><td>no</td><td>ΑΪ</td><td>no</td><td>no</td>

<td>Daughter</td><td>no</td><td>no</td><td>especially</td><td>no</td><td>no</td><td>no</td><td>ΪΙ</td><td>Ding</td><td>no</td><td>no</td><td>no</td><td>no</td><td>Ding</td>

<td>*</td><td>no</td><td>ratio</td><td>no</td><td></td><td>no</td><td>ratio</td><td>ϊί</td><td>(1</td><td>Row</td><td>Ding</td><td>ratio</td><td>no</td><td>Jun</td>

<td>The fourth day</td><td>no</td><td>no</td><td>no</td><td>no</td><td>no</td><td>no</td><td>ϊί</td><td>Row</td><td>Ding</td><td>ΪΙ</td><td>no</td><td>ratio</td><td>ϊί</td>

<td></td><td>no</td><td>ratio</td><td>no</td><td>Ai</td><td>ratio</td><td>no</td><td>ϊί</td><td>Ding</td><td>Ding</td><td>Treatment</td><td>ratio</td><td>no</td><td>Μ</td>

<td colspan="2">No KCN supplies</td><td>no</td><td>ratio</td><td>no</td><td>no</td><td>ratio</td><td>no</td><td>no</td><td>no</td><td>no</td><td>no</td><td></td><td>Ding</td><td>no</td>

<td colspan="2">The ratio of Ni at the ladder</td><td>ratio</td><td>ratio</td><td>no</td><td></td><td>ratio</td><td>ratio</td><td>no</td><td>ratio</td><td>no</td><td>no</td><td></td><td>no</td><td>no</td>

<td rowspan="2">Solder bonding</td><td>determination</td><td></td><td>good</td><td></td><td></td><td>Yi</td><td>good</td><td>good</td><td>good</td><td></td><td></td><td>Koya</td><td>U</td><td></td>

<td>Thick material fracture rate</td><td>JOO</td><td>100</td><td>90</td><td>50</td><td>95</td><td>J0O</td><td>100</td><td>100</td><td>90</td><td>85</td><td>40</td><td>100</td><td></td>

<td rowspan="3">XV Tian Xing</td><td>determination</td><td>or</td><td>R</td><td>Stand up</td><td>ά</td><td>mouth</td><td>mouth</td><td>ii</td><td>good</td><td>To</td><td>ά</td><td>Should not</td><td>U</td><td>mouth</td>

<td>Average production intensity</td><td>9.5</td><td>SS</td><td>8 7</td><td>8.8</td><td>9.0</td><td>9.J</td><td>9 2</td><td>8.7</td><td>8 5</td><td>8.2</td><td>64</td><td>so</td><td>9.2</td>

<td>Coefficient of variation</td><td>9</td><td>12</td><td>9</td><td>Η</td><td>9</td><td>10</td><td>10</td><td>12</td><td>J1</td><td>\3</td><td>21</td><td>12</td><td>8</td>

<td colspan="2">Heating turbulence</td><td>80</td><td>80</td><td>80</td><td>SO</td><td>SO</td><td>SO</td><td>80</td><td>80</td><td>80</td><td>80</td><td>S0</td><td>80</td><td>80</td>

<td colspan="2">Beam out speed [um NOmin]</td><td>0.14</td><td>Q.12</td><td>007</td><td>0.07</td><td>υ,07</td><td>G.I2</td><td>0 14</td><td>0.13</td><td>0.07</td><td>0Ό7</td><td>0.07</td><td>0.14</td><td>0.02</td>

[0144] From Table 5, it can be considered as follows.

[0145] First, Preparations. 2, 4, 9, 11, 12, 13 are the present invention using a reducing agent and the instant compound used in the present invention

example. Due to the bath decomposition action of the transient compound, no bath decomposition occurs even when heated and used for a long period of time, and a good precipitation rate can be maintained. In addition, since Ni corrosion was not observed, the solder joint properties and W/B properties were also good.

[0146] In contrast, Nos. 14 and 15 contained a reducing agent and did not add the instant compound used in the present invention, so bath decomposition occurred. In addition, in the aforementioned Nos. 14 and 15 (and Nos. 16, 17, 19, and 20) containing a reducing agent, since Ni corrosion was not observed, the solder joint properties and W/B properties were also good.

[0147] Nos. 16 and 17 are examples of using hydrazine (No. 16) and ascorbic acid (No. 17) with a small reducing effect. Under the long-term heating conditions such as this example, bath decomposition occurred after the third day.

[0148] No. 18 is an example that does not contain a reducing agent. Although bath decomposition did not occur, Ni corrosion was confirmed. As a result, the solder bonding properties and W/B properties were also reduced.

[0149] No. 20 is an example of using an instant compound outside the scope of the present invention, and bath decomposition significantly occurs the next day after heating. Moreover, the plating precipitation rate is also significantly reduced.

[0150] In No. 19, since KCN was replenished during heating, bath decomposition did not occur.

[0151] From these results, it can be seen that the instant compound used in the present invention is particularly useful for preventing bath decomposition during continuous heating for a long time, and can maintain a high plating precipitation rate, and therefore can greatly contribute to Improved plating stability. In addition, according to the present invention, the above-mentioned effects can be obtained even if a highly toxic cyanide compound is not added as an additive, so it is extremely useful in terms of work efficiency and the environment.