KR20080066570A - Method for maintaining plating capacity in electroless gold plating bath - Google Patents

Abstract

A method for stably maintaining and managing the plating capacity of an electroless gold plating bath for a long time is provided to obtain gold plating film with good external appearance without causing flaws in the external appearance according to the progress of intergranular corrosion on a nickel surface, and a method for maintaining and managing, stably for a long time, an electroless gold plating bath in which gold cyanide salt has been consumed by plating treatment is provided. As a method for maintaining and managing the plating capacity of the electroless gold plating bath in a state that an electroless gold plating bath is maintained at a temperature of 70 to 90 deg.C, the electroless gold plating bath containing gold cyanide salt, complexing agent, formaldehyde-sodium bisulfite adduct, and amine compound represented by a formula 1, R1-NH-C2H4-NH-R2, or formula 2, R3-(CH2-NH-C2H4-NH-CH2)n-R4, where R1, R2, R3 and R4 denote -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, the R1, R2, R3 and R4 being the same as or different from each other, and n is an integer of 1 to 4, the method for maintaining and managing the plating capacity of the electroless gold plating bath comprises regularly supplying alkali cyanide, formaldehyde-sodium bisulfite adduct, and an amine compound as first supply components.

Description

METHOD FOR MAINTAINING PLATING CAPACITY IN ELECTROLESS GOLD PLATING BATH}

The present invention relates to a method for maintaining the plating ability of an electroless gold plating bath.

Gold has the least ionization tendency among metals, that is, it is the most stable and hard to rust. In addition, it is also widely used in the electronics industry because of its excellent electrical conductivity. Substituted gold plating is widely used as final surface treatment of printed circuit boards, IC package mounting portions, and terminal portions. Specifically, for example, there are the following methods, and each has the following characteristics.

(1) ENIG (Electroless Nickel Immersion Gold: Electroless Nickel / Replacement Gold)

It is a method of forming a substituted gold plating film on a base electroless nickel plating film.

-It can prevent the diffusion of copper, prevent oxidation of nickel, and improve the corrosion resistance of circuits and terminals.

Can be used for solder joints.

· After ENIG treatment, thick gold plating can be used for wire bonding.

In the case of wire bonding, heat treatment is performed after the plating treatment, whereby nickel is diffused onto the gold film. In order to prevent it, electroless gold plating is performed on the nickel / substituted gold film to increase the film thickness of gold, thereby counteracting the diffusion of nickel.

(2) DIG (Direct Immersion Gold)

A method of forming a substitution gold plating film directly on copper.

Prevents oxidation of copper, prevents diffusion of copper, and improves corrosion resistance of circuits and terminals.

Can also be used for solder bonding and wire bonding.

• Compared to nickel / gold or nickel / palladium / gold, the long-term reliability is slightly inferior, but it can be used sufficiently under the condition that the heat load is not very low (such as low heat treatment temperature and low reflow number).

Low cost because of simple process

(3) ENEPIG (Electroless Nickel Electroless Palladium Immersion Gold: Electroless Nickel / Electroless Palladium / Replacement Gold)

A method of providing an electroless palladium plating film between an electroless nickel plating film and a substituted gold plating film.

-Prevents diffusion of copper, prevents oxidation and diffusion of nickel, and improves corrosion resistance of circuits and terminals.

-It is most suitable for the lead-free solder joining which is being promoted in recent years (lead-free solder has a heat load during solder joining compared with tin solder process solder, and the joining property is deteriorated in nickel / gold).

Suitable for wire bonding

Nickel diffusion does not occur even if the gold film thickness is not increased.

Even if it is possible to use nickel / gold, it is suitable for the case where it is desired to improve the reliability.

Substituted gold plating causes gold to precipitate by using a difference in redox potential in a plating bath with a base such as nickel, so that corrosion points due to oxidation (elution) are generated when gold erodes nickel. The corrosion point by this oxidation becomes a inhibitory factor when connecting tin and nickel of a solder layer at the time of subsequent solder reflow, and there exists a problem that a joining characteristic, such as strength, is reduced.

In order to solve this problem, the electroless gold plating bath containing the sulfite adduct of aldehyde is disclosed in Japanese Patent Application Laid-Open No. 2004-137589 (Patent Document 1), and a gold plating bath containing hydroxyalkyl sulfonic acid is disclosed in International Publication. It is disclosed in the 2004/111287 pamphlet (patent document 2), respectively. These techniques are aimed at suppressing the corrosion of the underlying metal.

However, when a primary amine compound having an amino group (-NH ₂ ) is present, such as triethylenetetramine described in International Publication No. 2004/111287 pamphlet (Patent Document 2), grain boundary erosion of nickel surface proceeds. This causes a problem that the coating power of gold is lowered and the appearance of the film becomes red.

Patent Document 1: Japanese Patent Application Laid-Open No. 2004-137589

Patent Document 2: International Publication No. 2004/111287 Pamphlet

Patent Document 3: Japanese Patent Application Laid-Open No. 2002-226975

Patent Document 4: Japanese Patent No. 2538461

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and it is possible to stably maintain the plating ability of an electroless gold plating bath in which a gold plating film having a good coating appearance is obtained without causing appearance defects as grain boundary erosion of the nickel surface proceeds. In addition, it aims at providing the method of maintaining the electroless gold plating bath in which the gold cyanide salt was consumed by the plating process for a long time and stable.

The inventors of the present invention have gold cyanide salt as a gold component, formaldehyde bisulfite adduct as a reducing component and the following general formula (1) or (2).

R ₁ -NH-C ₂ H ₄ -NH-R ₂

R _3- (CH ₂ -NH-C ₂ H ₄ -NH-CH ₂ ) _n -R ₄

(In formulas 1 and 2, R ₁ , R ₂ , R ₃ and R ₄ are —OH, —CH ₃ , —CH ₂ OH, —C ₂ H ₄ OH, —CH ₂ N (CH ₃ ) ₂ , —CH ₂ NH (CH ₂ OH), -CH ₂ NH (C ₂ H ₄ OH), -C ₂ H ₄ NH (CH ₂ OH), -C ₂ H ₄ NH (C ₂ H ₄ OH), -CH ₂ N (CH ₂ OH) ₂ , -CH ₂ N (C ₂ H ₄ OH) ₂ , -C ₂ H ₄ N (CH ₂ OH) ₂ or -C ₂ H ₄ N (C ₂ H ₄ OH) ₂ , and It may be the same or different, where n is an integer of 1 to 4. By using an electroless gold plating bath containing an amine compound, it is found that grain boundary corrosion of the nickel surface as described above is less likely to occur. However, these plating baths, regardless of the plating operation, form the cyanide and the reducing agent component bisulfite adduct and the amine compound represented by the formula (1) or (2) are gradually lost in the plating bath, causing bath decomposition. I knew there was a problem. Thus, it has been found that the above problem can be solved by dispensing these missing components little by little at an appropriate concentration ratio.

That is, the present invention provides a plating capability maintenance method of the following electroless gold plating bath.

[1] gold cyanide salt, complexing agent, formaldehyde bisulfite adduct, and the following general formula (1) or (2)

(Formula 1)

R ₁ -NH-C ₂ H ₄ -NH-R ₂

(Formula 2)

R _3- (CH ₂ -NH-C ₂ H ₄ -NH-CH ₂ ) _n -R ₄

(In formulas 1 and 2, R ₁ , R ₂ , R ₃ and R ₄ are —OH, —CH ₃ , —CH ₂ OH, —C ₂ H ₄ OH, —CH ₂ N (CH ₃ ) ₂ , —CH ₂ NH (CH ₂ OH), -CH ₂ NH (C ₂ H ₄ OH), -C ₂ H ₄ NH (CH ₂ OH), -C ₂ H ₄ NH (C ₂ H ₄ OH), -CH ₂ N (CH ₂ OH) ₂ , -CH ₂ N (C ₂ H ₄ OH) ₂ , -C ₂ H ₄ N (CH ₂ OH) ₂ or -C ₂ H ₄ N (C ₂ H ₄ OH) ₂ , and May be the same as or different from each other, n is an integer of 1 to 4). n is an integer of 1 to 4. As a method of stably maintaining the plating ability of the electroless gold plating bath in a state where the electroless gold plating bath containing the amine compound represented by () is maintained at 70 to 90 ° C. And plating method of the electroless gold plating bath, wherein the alkali cyanide and the formaldehyde bisulfite adduct and the amine compound are periodically replenished as the first replenishment component.

[2] The replenishment is performed such that the proportion of the alkali cyanide, formaldehyde bisulfite adduct and amine compound is in the range of alkali cyanide: formaldehyde bisulfite adduct: amine compound = 0.5 to 5: 1: 0.1 to 5 (molar ratio). Plating ability maintenance method of the electroless gold plating bath as described in [1] characterized by the above-mentioned.

[3] The electroless gold described in [2], wherein the first replenishment component is supplied by dividing 0.1 to 5 mol% of the concentration at the time of drying in 1 to 20 times per hour on the basis of the formaldehyde bisulfite adduct. How to maintain the plating ability of the plating bath.

[4] The plating bath in which gold is consumed by the plating treatment, wherein the gold cyanide salt, formaldehyde bisulfite adduct, and the amine compound are further replenished as a second replenishment component. Plating ability maintenance method of the electroless gold plating bath in any one of them.

[5] Replenishing the diffusion rate of the gold cyanide salt, formaldehyde bisulfite adduct and the amine compound to be the gold cyanide salt: formaldehyde bisulfite adduct: amine compound = 1: 0.1 to 5: 0.5 to 5 (molar ratio) Plating ability maintenance method of the electroless gold plating bath as described in [4] characterized by the above-mentioned.

[6] The electroless gold according to [5], wherein the second replenishment component is replenished by dividing 0.1 to 5 mol% of the concentration at the time of drying in 1 to 20 times per hour based on the formaldehyde bisulfite adduct. How to maintain the plating ability of the plating bath.

[7] The plating capacity maintenance method of the electroless gold plating bath according to [3] or [6], wherein a single supply amount of the formaldehyde bisulfite adduct is 2 millimoles or less per 1 L of the plating bath.

[8] The radioactive apparatus according to any one of [1] to [7], wherein a part or all of the supplemented formaldehyde bisulfite adduct is supplied in an equal molar amount of formaldehyde in place of the formaldehyde bisulfite adduct. How to maintain the plating ability of the gold plating bath.

According to the present invention, the plating ability of the electroless gold plating bath which forms a gold plating film having a good coating appearance without long causing appearance defects as the grain boundary erosion of the nickel surface proceeds can be maintained for a long time and stably. The electroless gold plating bath in which the gold cyanide salt is consumed by the plating treatment can be stably maintained for a long time.

(The best mode for carrying out the invention)

Hereinafter, the present invention will be described in more detail.

The electroless gold plating bath of the present invention comprises a gold cyanide salt, a complexing agent, formaldehyde bisulfite adduct, and the following Chemical Formula 1 or 2

(Formula 1)

R ₁ -NH-C ₂ H ₄ -NH-R ₂

(Formula 2)

R _3- (CH ₂ -NH-C ₂ H ₄ -NH-CH ₂ ) _n -R ₄

(In formulas 1 and 2, R ₁ , R ₂ , R ₃ and R ₄ are —OH, —CH ₃ , —CH ₂ OH, —C ₂ H ₄ OH, —CH ₂ N (CH ₃ ) ₂ , —CH ₂ NH (CH ₂ OH), -CH ₂ NH (C ₂ H ₄ OH), -C ₂ H ₄ NH (CH ₂ OH), -C ₂ H ₄ NH (C ₂ H ₄ OH), -CH ₂ N (CH ₂ OH) ₂ , -CH ₂ N (C ₂ H ₄ OH) ₂ , -C ₂ H ₄ N (CH ₂ OH) ₂ or -C ₂ H ₄ N (C ₂ H ₄ OH) ₂ , and It may be same or different, n is an integer of 1-4.

The electroless gold plating bath of the present invention is a substitution-reduction type electroless gold plating bath in which both the substitution reaction and the reduction reaction proceed in the same plating bath, unlike the conventional substitution gold plating bath. By including formaldehyde bisulfite adduct in the gold plating bath and an amine compound having a unique structure represented by the above formula (1) or (2), the electroless gold plating bath of the present invention is subjected to substitution reaction on a base metal such as copper or nickel. As a result, gold is precipitated, and gold is precipitated by a reducing agent using the precipitated gold as a catalyst.

In the electroless gold plating bath of the present invention, since the erosion of the underlying metal is minimized, elution of the underlying metal ions into the plating bath is small, and a stable deposition rate is maintained even when used over a long period of time. For example, in the case of normal substitution plating, the amounts of precipitated gold and eluted base metal (for example, copper or nickel) become equivalent in accordance with stoichiometry. In the plating bath of the present invention, for example, an ENIG process is performed. In this case, since most of the precipitation of gold is converted from substitution plating to reduction plating, the elution of base nickel eluted with respect to the precipitated gold is very small, and in this case, it is suppressed to about 1/8 of the conventional replacement gold plating. .

Thereby, erosion of the base metal can be suppressed to the minimum and a uniform and dense gold plating film can be obtained. In addition, since gold is continuously deposited on the gold precipitated by containing a reducing agent, thick film formation is possible in one plating bath without performing gold plating for forming a separate thickness. In addition, the deposition rate of gold can be maintained stably, and even if the film is thickened, the plating film does not appear reddish and the lemon yellow color peculiar to gold can be maintained.

In the case of the base is palladium, unlike in the case of nickel or copper, palladium and gold have a small potential difference. Therefore, when gold plating is performed on palladium using the conventional substitution type gold plating bath, uniform film thickness cannot be obtained and sufficient film thickness cannot be obtained. In contrast, the electroless gold plating bath of the present invention activates the surface of palladium, can deposit gold with a reducing agent using palladium as a catalyst, and further deposit gold using the deposited gold as a catalyst. It is possible to thicken the gold plated film on the surface.

Examples of the gold cyanide salt contained in the electroless gold plating bath of the present invention include gold cyanide, gold potassium cyanide, gold sodium cyanide, gold ammonium cyanide, and the like, and particularly preferably gold cyanide and gold cyanide.

It is preferable that it is 0.0001-1 mol / L on the basis of gold, and, as for content after the dry bath of gold cyanide salt and replenishing, it is more preferable that it is 0.001-0.5 mol / L. If it is less than the said range, there exists a possibility that a precipitation rate may fall, and when it exceeds the said range, it may become economically disadvantageous.

As the complexing agent included in the electroless gold plating bath of the present invention, 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, ethylenediamine tetraacetic acid, nitrilo triacetic acid, diethylenetriamine pentaacetic acid, hydroxyethylethylenediamine triacetic acid, triethylenetetramine hexaacetic acid, 1,3-propanediamine tetraacetic acid, 1,3- Diamino-2-hydroxypropane tetraacetic acid, hydroxyethylimino diacetic acid, dihydroxyglycine, glycol etherdiamine tetraacetic acid, dicarboxymethylglutamic acid, hydroxyethylidene diphosphate, ethylenediaminetetra (methylene phosphoric acid) Or alkali metal (for example, sodium and potassium) salts, alkaline earth metal salts, ammonium salts and the like.

It is preferable that it is 0.001-1 mol / L, and, as for the complexing agent density | concentration at the time of dry bath and after replenishment, it is more preferable that it is 0.01-0.5 mol / L. If it is less than the said range, precipitation rate may fall by the eluted metal, and when it exceeds the said range, it may become economically disadvantageous.

In the electroless gold plating bath of the present invention, formaldehyde bisulfite adduct is included. Specific examples of the formaldehyde bisulfite adduct include formaldehyde sodium bisulfite, formaldehyde potassium bisulfite, formaldehyde ammonium bisulfite, and the like.

It is preferable that it is 0.0001-0.5 mol / L, and, as for the density | concentration at the time of drying and replenishing these formaldehyde bisulfite adducts, it is more preferable that it is 0.001-0.3 mol / L. If it is less than the above range, the underlying nickel may corrode, and if it exceeds the above range, the bath may become unstable.

The electroless gold plating bath of the present invention is represented by the following Chemical Formula 1 or 2

(Formula 1)

R ₁ -NH-C ₂ H ₄ -NH-R ₂

(Formula 2)

R _3- (CH ₂ -NH-C ₂ H ₄ -NH-CH ₂ ) _n -R ₄

(In formulas 1 and 2, R ₁ , R ₂ , R ₃ and R ₄ are —OH, —CH ₃ , —CH ₂ OH, —C ₂ H ₄ OH, —CH ₂ N (CH ₃ ) ₂ , —CH ₂ NH (CH ₂ OH), -CH ₂ NH (C ₂ H ₄ OH), -C ₂ H ₄ NH (CH ₂ OH), -C ₂ H ₄ NH (C ₂ H ₄ OH), -CH ₂ N (CH ₂ OH) ₂ , -CH ₂ N (C ₂ H ₄ OH) ₂ , -C ₂ H ₄ N (CH ₂ OH) ₂ or -C ₂ H ₄ N (C ₂ H ₄ OH) ₂ , and It may be same or different, n is an integer of 1-4. The formaldehyde bisulfite adduct of the present invention does not act as a reducing agent with only the formaldehyde bisulfite adduct, but coexists with this amine compound to produce a reducing action.

It is preferable that it is 0.001-3 mol / L, and, as for these amine compound density | concentration at the time of a dry bath and after replenishment, it is more preferable. If it is less than the above range, the precipitation rate may decrease, and if it exceeds the above range, the bath may become unstable.

The stabilizer used by the well-known electroless plating can be added to the electroless gold plating bath of this invention. Examples of the stabilizer include sulfur compounds such as 2-mercaptobenzothiazole, 2-mercaptobenzoimidazole, mercaptoacetic acid, mercaptosuccinic acid, thiosulfate, thioglycol, thiourea, thiomalic acid, benzotriazole, 1,2 Nitrogen compounds, such as a 4-amino triazole, are mentioned.

It is preferable that it is 0.0000001-0.01 mol / L, and, as for the stabilizer density | concentration at the time of a dry bath and after replenishment, it is more preferable that it is 0.000001-0.005 mol / L. If it is less than the above range, the bath may become unstable, and if it exceeds the above range, the precipitation rate may decrease.

It is preferable that pH of the electroless gold plating bath of this invention is 5-10. If it is less than the above range, the precipitation rate may decrease, and if it exceeds the above range, the bath may become unstable. As a pH adjuster, sodium hydroxide, potassium hydroxide, ammonia, sulfuric acid, phosphoric acid, boric acid, etc. which are used by the well-known plating bath can be used.

Moreover, it is preferable that the use temperature of the electroless gold plating bath of this invention is 70-90 degreeC. If it is less than the above range, the precipitation rate may decrease, and if it exceeds the above range, the bath may become unstable.

In the present invention, the above-mentioned electroless gold plating bath is composed of a cyanide alkali such as sodium cyanide and potassium cyanide and an electroless gold plating bath when the bath temperature is continuously maintained at 70 to 90 ° C, especially 80 ° C or higher. By regularly replenishing the above-mentioned formaldehyde bisulfite adduct and the amine compound as the first replenishment component, the plating ability of the electroless gold plating bath can be maintained.

In this case, these components are supplied so that the diffusion ratio of alkali cyanide, formaldehyde bisulfite adduct and amine compound becomes alkali cyanide: formaldehyde bisulfite adduct: amine compound = 0.5-5: 1: 0.1-5 (molar ratio). It is desirable to. If the diffusion ratio is out of this range, excessive alkali cyanide may lower the coating power of gold, and nickel may corrode, and if it is too small, it may accelerate the decomposition of the bath. Too much formaldehyde bisulfite adduct may accelerate bath decomposition, and when too little, reducing power may decrease, nickel may be corroded, and gold coating power may be lowered. When the amine compound is excessive, there is a possibility that the decomposition of the bath may be accelerated. When the amine compound is excessively reduced, the reducing power may decrease, nickel may be corroded, and the coating power of gold may decrease. In this case, the balance of formaldehyde bisulfite adduct and the amine compound is particularly important.

In the present invention, for the plating bath in which gold is consumed by the plating treatment, the above-mentioned gold cyanide salt, formaldehyde bisulfite adduct and amine compound can also be supplied as the second replenishment component as a component of the electroless gold plating bath. Can be.

In this case, these components are added so that the diffusion ratios of the gold cyanide salt, the formaldehyde bisulfite adduct and the amine compound are the gold cyanide salt: the formaldehyde bisulfite adduct: the amine compound = 1: 0.1-5: 0.5-5 (molar ratio). It is desirable to spread. If the diffusion rate is out of the range, excessive gold cyanide salt may be disadvantageously costly. If the gold cyanide salt is excessively used, the gold concentration may be lowered and the gold film characteristics may be deteriorated. Too much formaldehyde bisulfite adduct may accelerate bath decomposition, and when too little, reducing power may decrease, nickel may be corroded, and gold coating power may be lowered. When the amine compound is excessive, there is a possibility that the decomposition of the bath may be accelerated. When the amine compound is excessively reduced, the reducing power may decrease, nickel may be corroded, and the coating power of gold may decrease. Also in this case, the balance of formaldehyde bisulfite adduct and the amine compound is particularly important.

In each replenishment using these first and second replenishment components, 0.1 to 5 mole% of the concentration at the time of dry bath is divided into 1 to 20 times per hour on the basis of formaldehyde bisulfite adduct, preferably at equal intervals. It is preferable to replenish, and it is preferable to make one replenishment amount of a formaldehyde bisulfite adduct into 2 millimoles or less per 1 L of plating baths. If the replenishment interval is too long, the composition change in the plating bath is large, and there is a fear that variation in the film characteristics occurs. In addition, when the supply amount is excessively large, the composition change in the plating bath is large, and there is a possibility that variation in the film characteristics may occur.

In the present invention, it is also possible to supply part or all of the formaldehyde bisulfite adduct to be supplied in the same molar amount of formaldehyde as the formaldehyde bisulfite adduct instead of the formaldehyde bisulfite adduct. Formaldehyde bisulfite adduct produces sulfurous acid by the temperature rise of a plating bath or a plating process, and the produced sulfurous acid accumulates in a plating bath. In the plating bath, sulfurous acid inhibits the reaction by the reducing agent, and thus acts as a so-called stabilizer that prevents decomposition of the plating bath. However, when excessive, the sulfurous acid inhibits the reaction by the reducing agent, thereby increasing the proportion of the substitution reaction, thereby reducing the underlying nickel. It may cause corrosion. When the base nickel is corroded, problems such as deterioration in solder bondability occur, so that part or all of the formaldehyde bisulfite adducts to be supplied are replaced with the formaldehyde bisulfite adducts instead of the formaldehyde bisulfite adducts. By the above-mentioned formaldehyde, the above problems due to excessive sulfurous acid can be suppressed. In particular, by using formaldehyde bisulfite adduct in the first replenishment component and formaldehyde in the second replenishment component, the replenishment component can be easily managed, and the sulfuric acid concentration in the plating bath can be maintained appropriately, so that both the bath stability and the solder bonding property can be maintained. It is suitable because it becomes good.

In particular, in the replenishment of the second replenishment component, when the total replenishment amount of gold from the dry bath by the second replenishment component to the plating bath is 0.2 g / L or more, preferably 0.1 g / L or more, Instead of the formaldehyde bisulfite adduct, it is preferable to replenish the same molar amount of formaldehyde as the formaldehyde bisulfite adduct.

In the electroless gold plating bath of the present invention, the bisulfite adduct of formaldehyde and the amine compound coexist in the bath to form a formaldehyde-amine complex represented by the following formula, which is believed to act as a reducing agent component.

Bisulfite adduct + amine compound of formaldehyde

→ reducing agent component (formaldehyde-amine complex) + sulfite

This reducing agent component (formaldehyde-amine complex) is consumed in the bath, i.e. the bisulfite adduct of formaldehyde and the amine compound are consumed. At this time, although it is necessary to replenish the bisulfite adduct and the amine compound of the consumed formaldehyde, formaldehyde may be replenished in place of the bisulfite adduct of formaldehyde. At the time of replenishment, if the replenishment balance of each component is not taken into consideration, problems such as decomposition of the bath, corrosion of nickel, reduction of the coating power of gold, and the like will occur. That is, it is important to replenish the bisulfite adduct: amine compound of formaldehyde, the formaldehyde: amine compound, or the bisulfite adduct of formaldehyde and the formaldehyde: amine compound in a fixed ratio, respectively.

As a material of the metal surface (plated surface) of the substrate when plating using the electroless gold plating bath of the present invention, copper, copper alloy, nickel, nickel alloy, palladium, palladium alloy and the like can be used. As said nickel alloy, a nickel-phosphorus alloy, a nickel-boron alloy, etc. are mentioned, As a palladium alloy, a palladium-phosphorus alloy etc. are mentioned. Such a metal surface may be the surface of this film in which a metal film was formed on the surface of the base, in addition to the surface of which the base itself is a metal (alloy). The metal film may be either formed by electroplating or formed by electroless plating. In the case of nickel, nickel alloys, palladium and palladium alloys, those formed by electroless plating are common. It is also suitable for the case of electroless gold plating the palladium or palladium alloy coating surface formed on the substrate via a nickel or nickel alloy coating.

The electroless gold plating bath of the present invention is, for example, a method of forming a gold plating film on ENIG (Electroless Nickel Immersion Gold), that is, a base electroless nickel plating film (formed on copper), DIG (Direct Immersion). Gold), i.e., a method of forming a gold plated film directly on copper, ENEPIG (Electroless Nickel Electroless Palladium Immersion Gold), i.e., through an electroless palladium plated film on an underlying electroless nickel plated film (formed on copper) Any method of forming a gold plated film can be used for formation of a gold plated film.

The electroless gold plating bath of the present invention and the electroless gold plating method using the same are suitable when, for example, gold plating the wiring circuit mounting portion or the terminal portion of an electronic component such as a printed wiring board or an IC package. In the gold plating treatment, the method for maintaining the plating ability of the electroless gold plating bath of the present invention can be suitably applied.

Further, in the plating bath of the present invention, even when the metal surface (coated surface) is copper, a good film is obtained. When the base is copper, oxidation and diffusion of copper are suppressed, and good solder bonding properties are obtained. Moreover, it can also be used for wire bonding by thickening. Moreover, since the plating bath of this invention can precipitate a favorable gold film also on palladium, it is suitable for use for lead-free solder joining and wire bonding.

When the base is palladium, unlike the case of nickel or copper, palladium and gold have a small potential difference. Therefore, when gold plating is performed on palladium using the conventional substitution type gold plating bath, uniform film thickness cannot be obtained and sufficient film thickness cannot be obtained. In contrast, the electroless gold plating bath of the present invention activates the surface of palladium, can deposit gold with a reducing agent using palladium as a catalyst, and further precipitate gold using the deposited gold as a catalyst. It is possible to thicken the gold plated film even on palladium.

(Example)

Hereinafter, although an Example and a comparative example are given and this invention is demonstrated concretely, this invention is not limited to the following Example.

[Examples 1 and 2 and Comparative Example 1]

The gold plating bath shown in Table 1 was made into the plating bath at the time of a dry bath, this is hold | maintained at 80 degreeC, and the 1st supply component of the ratio shown in Table 2 is replenished regularly (Examples 1 and 2) or it is not replenished. (Comparative example 1) It hold | maintained for 100 hours. On the copper-clad printed substrates which were subjected to the treatments shown in Table 6 as nickel / gold processes, the presence or absence of precipitation of gold into the container, which was a symptom of bath decomposition, was visually determined by the state of the plating liquid. Table 3 shows the results obtained by immersing in the gold plating bath to conduct gold plating to confirm the appearance of the plating. The replenishment was made into 15 mg / L of potassium cyanide per hour, and the replenishment component was divided into 5 times per hour at the above ratio and replenished every 12 minutes.

Potassium cyanide (g / L) 2 Potassium Phosphate (g / L) 10 Ethylenediaminetetraacetic acid (g / L) 10 Formaldehyde Sodium Bisulfite (g / L) 2 C ₂ H ₅ -NH-C ₂ H ₄ -NH-C ₂ H ₄ OH [amine compound] (g / L) 10 pH 7.1

Example Comparative example One 2 One Potassium Cyanide (mol) 2 2  No spread Formaldehyde Sodium Bisulfite (Mall) 1.5 0.75 Formaldehyde (Mall) - 0.75 C ₂ H ₅ -NH-C ₂ H ₄ -NH-C ₂ H ₄ OH [amine compound] (mol) 3 3

80 ° C holding time (hrs) Bathing 2 4 10 50 100 Example 1 ○ ○ ○ ○ ○ ○ Example 2 ○ ○ ○ ○ ○ ○ Comparative Example 1 ○ ○ decomposition

○: The bath is stable (no gold precipitation) and the film appearance is also good.

[Examples 3 and 4]

In addition to the 1st replenishment component shown in Example 1, and performing the operation of the conditions of Example 1, the 2nd replenishment component shown in Table 4 is used every time 0.1 g / L of gold is consumed gold cyanide The amount of potassium supplemented was 0.15 g / L, and it was supplied at the above ratio. Whenever 0.5 g / L of gold was replenished, it was immersed in each gold plating bath and subjected to gold plating on a copper clad printed substrate subjected to the treatment shown in Table 6 as a nickel / gold process. Gold is peeled off by the gold releasing agent Copkia lip (COPKIA RIP) made from Uemu Lago Co., Ltd., and the obtained gold plating film is shown in Table 5 whether there is corrosion in the nickel surface after gold peeling.

Example 3 4 Gold Potassium Cyanide (mol) 0.5 0.5 Formaldehyde (Mall) 0.5 - Formaldehyde Sodium Bisulfite (Mall) - 0.5 C ₂ H ₅ -NH-C ₂ H ₄ -NH-C ₂ H ₄ OH [amine compound] (mol) One One

Gold supply total amount (g / L) Bathing 0.5 One 1.5 2 Example 3 ○ ○ ○ ○ ○ Example 4 ○ ○ △ × ×

(Circle): Nickel surface after gold peeling is favorable (no corrosion)

Δ: slightly corroded to the surface of nickel after peeling gold

X: There is clear corrosion on the nickel surface after gold peeling

In Example 3, since the sulfite is not produced excessively by replenishing with the same molar amount of formaldehyde instead of formaldehyde sodium bisulfite, the nickel surface after the gold peeling is good without corrosion, but in Example 4, gold From the vicinity of the total amount exceeding 1 g / L, corrosion of the nickel surface after peeling of gold, which is thought to be due to excessive generation of sulfurous acid, occurs.

Temperature (℃) Minutes Cleaner Uemurago dating ACL-009 50 5 Soft etching Persulfate Na 100g / L Sulfuric acid 20g / L 25 One Acid washing Sulfuric acid 50g / L 25 One Activator Uemurago fellowship MNK-4 30 2 Electroless nickel plating Uemurago fellowship NPR-4 80 30 Gold plated Baths presented in Table 1 80 10

Water washing between each process

Claims (8)

Gold cyanide salts, complexing agents, formaldehyde bisulfite adducts, and the formula (Formula 1) R ₁ -NH-C ₂ H ₄ -NH-R ₂ (Formula 2) R _3- (CH ₂ -NH-C ₂ H ₄ -NH-CH ₂ ) _n -R ₄ (In formulas 1 and 2, R ₁ , R ₂ , R ₃ and R ₄ are —OH, —CH ₃ , —CH ₂ OH, —C ₂ H ₄ OH, —CH ₂ N (CH ₃ ) ₂ , —CH ₂ NH (CH ₂ OH), -CH ₂ NH (C ₂ H ₄ OH), -C ₂ H ₄ NH (CH ₂ OH), -C ₂ H ₄ NH (C ₂ H ₄ OH), -CH ₂ N (CH ₂ OH) ₂ , -CH ₂ N (C ₂ H ₄ OH) ₂ , -C ₂ H ₄ N (CH ₂ OH) ₂ or -C ₂ H ₄ N (C ₂ H ₄ OH) ₂ , and May be the same as or different from each other, n is an integer of 1 to 4). n is an integer of 1 to 4. As a method of stably maintaining the plating ability of the electroless gold plating bath in the state where the electroless gold plating bath containing the amine compound represented by () is maintained at 70 to 90 ° C. , A plating capacity maintenance method for an electroless gold plating bath, wherein the alkali cyanide and the formaldehyde bisulfite adduct and the amine compound are periodically replenished as a first replenishment component. 2. The cyanide alkali, formaldehyde bisulfite adduct and amine compound diffusion ratio of alkali cyanide: formaldehyde bisulfite adduct: amine compound = 0.5 to 5: 1: 0.1 to 5 (molar ratio) Plating capacity maintenance method of the electroless gold plating bath, characterized in that the replenishment. 3. The electroless gold plating bath according to claim 2, wherein the first replenishment component is replenished by dividing 0.1 to 5 mole% of the concentration at the time of drying in 1 to 20 times per hour on the basis of the formaldehyde bisulfite adduct. To maintain plating capability The method according to any one of claims 1 to 3, wherein the gold cyanide salt, formaldehyde bisulfite adduct and amine compound are further supplied as a second replenishment component to the plating bath in which gold is consumed by the plating treatment. Plating ability maintenance method of the electroless gold plating bath characterized by the above-mentioned. The diffusion rate of the gold cyanide salt, formaldehyde bisulfite adduct and amine compound is set to be the gold cyanide salt: formaldehyde bisulfite adduct: amine compound = 1: 0.1 to 5: 0.5 to 5 (molar ratio). Plating capacity maintenance method of the electroless gold plating bath, characterized in that the replenishment. 6. The electroless gold plating bath according to claim 5, wherein the second replenishment component is replenished by dividing 0.1 to 5 mol% of the concentration at the time of drying in 1 to 20 times per hour on the basis of the formaldehyde bisulfite adduct. To maintain plating capability 7. The plating capacity maintenance method of an electroless gold plating bath according to claim 3 or 6, wherein a single supply amount of the formaldehyde bisulfite adduct is 2 millimoles or less per 1 L of the plating bath. 8. The electroless according to any one of claims 1 to 7, wherein some or all of the formaldehyde bisulfite adduct to be supplied is supplied with the same molar amount of formaldehyde in place of the formaldehyde bisulfite adduct. How to maintain the plating ability of the gold plating bath.