PH12016500567B1 - Reductive electroless gold plating solution, and electroless gold plating method using said plating solution - Google Patents

Abstract

The purpose of the present invention is to provide an electroless gold plating solution which does not contain harmful substances and is capable of achieving good wire bonding performance, while suppressing corrosion of a base metal. In order to achieve this purpose, an electroless plating solution that contains a water-soluble gold compound, citric acid or a citrate, ethylenediaminetetraacetic acid or an ethylenediaminetetraacetate, hexamethylenetetramine and a chain polyamine containing three or more amino groups and an alkyl group having three or more carbon atoms is employed as a reduction-type electroless gold plating solution which is used for the purpose of forming an electroless gold plating film on the surface of an object to be plated by means of electroless plating.

Description

- 1 - 2 Ra : GT = 3g : [Document Name] Description wo CE : : 2/4 “® \el [Title of Invention] : of iF -- {+ Sel ana . REDUCTIVE ELECTROLESS GOLD PLATING SOLUTION, AND Tn . . LI

ELECTROLESS GOLD PLATING METHOD USING THE PLATING SOLUTION " - [Technical Field] = - . Joa : The invention disclosed in the present filing relates to an electroless gold plating solution, an electroless gold plating method using the electroless gold plating solution, and a plated product obtained by plating by the electroless gold plating method. More specifically, the invention relates to reductive electroless gold plating technology capable of plating directly a surface of a plating target. [Background Art] : = 20 In recent years, while requirements for higher ~ performance and higher multi-function of electronic devices x } have been raised, further downsizing has been demanded on

La wr printed wiring boards used in these electronic devices. In @ order to cope with the downsizing, micronization of circuit on 25 patterns is progressing and along with the micronization of wel Co - '

Le circuit patterns, advanced mounting technologies have been . £m) . =o demanded. Generally in the. field of printed wiring boards, nd “, as technologies of joining mounting components and terminal &

- 2 - | Ce oo . components, technologies using soldering and wire bonding on have been established. . a

ST ‘For the purpose of securing the. connection reliability of these junctions using soldering and wire bonding, | ~ plating is undergone as the surface treatment for wiring pads that are mounting portions and terminal portions of = circuits on printed wiring boards. The plating includes a = technology of carrying out nickel plating, palladium - plating and gold plating in order on a circuit pattern formed of a metal having a low electric resistance such as copper. A plated nickel film is to prevent the erosion of a - copper circuit by soldering; and a plated palladium film is oo to prevent the diffusion of nickel constituting the plated nickel film to a plated gold film. Then, the plated gold film is formed in order to provide excellent wetting performance of a solder, realizing a low electric resistance. oo : =. 20 As conventional technologies of the above-mentioned ” plating technology, there are, for example, Patent . Literature 1 to Patent Literature 3 described below. An - electroless gold plating method described in Patent © | Literature 1 is a method of forming a plated gold film on = ei 25 nickel by using an electroless gold plating solution : 2 containing a reducing agent, and involves formation of an immersion plated gold film as a catalyst for electroless ~ gold plating on nickel.

CE

: , | ~

Further an electroless gold plating method described oo in Patent Literature 2 is a method of forming an = .. . electroless plated gold film of a plated film laminate in fo which an electroless plated nickel film is formed on a - surface to be plated of an electronic component through a catalyst; an electroless plated palladium film is formed on = the electroless plated nickel film; and the electroless iy ~ plated gold film is further formed on the electroless ” plated palladium film, and involves the formation of the electroless plated gold film by first electroless gold plating using an electroless gold plating bath containing a water-soluble gold compound, a complexing agent, formaldehyde and/or a formaldehyde bisulfite salt adduct, and a specific amine compound. :

Further a reductive deposition-type electroless gold plating solution for a palladium film described in Patent

Literature 3 is an electroless gold plating solution wo 20 enabling the direct formation of a plated gold film on the — palladium film, and is composed of an aqueous solution = containing a water-soluble gold compound, a reducing agent and a complexing agent, wherein at least one compound © selected from the group consisting of formaldehyde . 25 bisulfites, Rongalite and hydrazines is contained as the : o reducing agent. - : nd [Citation List]

: C-4 - fo ~ | pn [Patent Literature] oo = , gd ed CATED SR [Patent Literature 1] 3 2

I Japanese Patent Laid-Open No. 05-222541 So A ~ 5 [Patent Literature 2] =, Vid oo Co @ SN wen

Japanese Patent Laid-Open No. 2008-266668 > Nhl [Patent Literature 3] : | o " Japanese Patent Laid-Open No. 2008-174774 5 : : od [Summary of Invention] [Technical Problem]

The electroless gold plating method of the Patent . Literature 1 has such a problem gold dissolves and corrodes substrate nickel, and nickel thereby diffuses in a plated gold film, however, since the immersion plated gold film is formed by depositing gold by utilizing the difference in redox potential between nickel that is a substrate and gold ions in the plating bath. When nickel diffuses in the fy 20 plated gold film, there arises a problem that the gold-gold junction strength in wire bonding decreases. In order to - | prevent such disadvantages, Patent Literature 1 forms an electroless plated gold film on an immersion plated gold = film to make the gold film thickness large to thereby © 25 suppress a decrease in wire bondability. The technology @ poses a problem of causing a rise in cost and poor : wo productivity, however, since formation of the immersion ~ plated gold film is essentially needed.

oo | so | J oF .

Further in the cases of the electroless gold plating ey ps ~ method described in Patent Literature 2 described above and

Lo iB ) of using a reductive deposition-type electroless gold. PET plating solution for a palladium film described in Patent ol

Literature 3 described above, although the corrosion of = nickel that is a substrate metal is enabled to be = suppressed, since the electroless gold plating bath a ~ contains formaldehyde or a formaldehyde bisulfite salt adduct, which is strongly toxic, it becomes difficult for the safety in plating work to be secured.

Hence, in markets, there has been raised the requirement for an electroless gold plating solution capable of suppressing the corrosion of a substrate metal and realizing excellent wire bondability and containing no hazardous substances. [Solution to Problem] : i” | As a result of diligent studies in order to solve the . above-mentioned problem, the present inventors have arrived - at providing an electroless gold plating solution, an = electroless gold plating method and a plated product, which £0 25 are shown below. : ed : - The reductive electroless gold plating solution = according to the present invention is used for the hi

: | - 6 - | = formation of an electroless plated gold film on a surface = oo of a plating target, and contains a water-soluble gold . - compound, citric acid or a citrate salt, -

Co ethylenediaminetetraacetic acid or an. .. - . Ce ethylenediaminetetraacetate salt, hexamethylenetetramine, : and a chain polyamine having an alkyl group having 3 or cr more carbon atoms and 3 or more amino groups. | =

The reductive electroless gold plating solution oY according to the present invention has preferably a pH of 7.0 to a pH of 9.0. | )

In the reductive electroless gold plating solution according to the present invention, the chain polyamine is preferably 3,3" -diamino-N-methyldipropylamine or N,N'- - bis (3-aminopropyl) ethylenediamine.

The reductive electroless gold plating solution according to the present invention preferably further = 20 - contains a thallium compound as a deposition accelerator. : - The method of electroless gold plating according to - ~ the present invention includes forming an electroless = plated gold film on a surface of a plating target using the al 25 above-mentioned reductive electroless gold plating solution. al ! wo In the electroless gold plating method according to = the present invention, one of copper, palladium, gold and

CE :

. nickel is preferably present on the surface of the ping’ 3 oo target. oo a 2 LB cr Further in the electroless gold plating method = TZ. sa according to the present invention, the surface of oe 5 NA) . : plating target preferably includes an electroless plated / hE palladium film formed on a surface of an electroless plated = © nickel film. : - - ) 10 The plated product according to the present invention is obtained by electroless gold plating by the above- mentioned electroless gold plating method. ~ [Advantageous Effects of Invention]

: When the reductive electroless gold plating solution of the present invention contains a water-soluble gold compound, citric acid or a citrate salt, ethylenediaminetetraacetic acid or an : = 20 ethylenediaminetetraacetate salt, hexamethylenetetramine, - and a chain polyamine having an alkyl group having 3 or . more carbon atoms and 3 or more amino groups, it becomes ~ easy for a plated gold film to be thickly deposited on a = : surface of a plating target. = Further even in the case where a plated nickel & film/plated palladium film/plated gold film installed on an ~ electric connection site is formed by using the reductive

- 8 - : fs 2 electroless gold plating solution of the present invention, on the plated gold film can be formed quickly on the surface o of the plated palladium film without being influenced by - +» +. the film thickness of the plated palladium film. Further jo © 5 when the reductive electroless gold plating solution of the z present invention is used, even in the case where an : electroless plated gold film is formed on a surface of an = electroless plated palladium film formed on a surface of an oo electroless plated nickel film, the dissolution of nickel a. can greatly be suppressed as compared with the case where an immersion plated gold film is formed, and the diffusion of nickel in the plated gold film is enabled to be prevented. Hence, when the reductive electroless gold plating solution of the present invention is used, a plated gold film capable of realizing high junction reliability of wire bonding can be obtained. | SE

Further since the reductive electroless gold plating : solution of the present invention has higher stability as a - 20 solution as compared with conventional electroless gold plating solutions and contains neither formaldehyde nor ~ formaldehyde bisulfite salt adduct, which is strongly toxic, oo it becomes easy for the safety in plating work to be 2 ‘secured. @ Additionally, in the reductive electroless gold i» plating solution of the present invention, since the = deposition reaction of gold occurs only on the surface of gold, palladium, nickel, copper or the like, which can Bow become a catalytic nucleus, and does not occur on porBond 8 ~ having no catalytic nucleus, the selective aeposition ¥ hy ~. property is excellent. Therefore, the plating sotuiosar| Jig) '5 avoid the formation of a plated gold film on portions o oi having no need of the deposition of gold, and is benefic ie in that the raw material can be saved. = 3 [Brief Description of Drawings] 10 | oo oo oo oo [Figure 1] Figure 1 is a graph showing a relation between : the plating time and the plated film thickness of a reductive electroless plated gold film of an Example sample group 1A. 15 [Figure 2] Figure 2 is a graph showing a relation between the plating time and the plated film thickness of a reductive electroless plated gold film of Example 2. [Figure 3] Figure 3 is diagrams showing relations between the film thickness of a substrate plated palladium film and . 0 20 the deposition rate of a plated gold film in the case of using electroless gold plating solutions of Example 1 and

Le ~ Comparative Example 1. [Figure 4] Figure 4 shows electron microscope photographs

Eo i] (x10,000 and x30,000) of a reductive electroless plated “ 25 gold film of an Example sample 1A-2. - [Figure 51 Figure 5 shows electron microscope photographs 0 (x30,000) of reductive electroless plated gold films of an : Example sample 2-2 and Comparative Example 2.

- 10 - fo [Figure 6] Figure 6 shows an electron microscope photograph - (x5,000) of the surface of a plated nickel film after . peeling-off of a reductive electroless plated gold film and - an electroless plated palladium film from a plated film of - an Example sample 1A-2. ol ~ [Figure 7] Figure 7 shows electron microscope photographs > (x3,000) of surfaces of plated nickel films after peeling- = off of reductive electroless plated gold films from plated = : films of an Example sample 2-2 and Comparative Example 2. ~ [Figure 8] Figure 8 is a cross-sectional observation . photograph (x30,000) of a reductive electroless plated gold film of an Example sample 1A-6. [Figure 9] Figure 9 shows electron microscope photographs (x500) of an end portion and a central portion of a plated product in which a plated film was formed under the same condition as in an Example sample 1A-6. [Figure 10] Figure 10 is a diagram showing relations of nickel dissolution amounts in gold plating solutions in the case of using electroless gold plating solutions of Example ° 20 1 and Comparative Example 1. " [Figure 11] Figure 11 is a Alagren showing deviations of . the film thicknesses of electroless plated gold films of - Example 2 and Comparative Example 2. © [Figure 12] Figure 12 is a diagram showing the wire bonding =~ 25 performance of electroless plated gold films of Example 2 @ and Comparative Example 2. : - [Description of Embodiments]

. - 11 - froin

Cl

Hereinafter, embodiments of the reductive electroless = gold plating solution, the electroless gold plating method Ny . | using the plating solution, and the plated product plated + by the method, respectively, according to the present - invention will be described. Le 1. The reductive electroless gold plating solution o according to the present invencion =

The reductive electroless gold plating solution according to the present invention is used for the formation of an electroless plated gold film on a surface of a plating target, and contains "a water-soluble gold compound", "citric acid or a citrate salt", : 15 "ethylenediaminetetraacetic acid or an ethylenediaminetetraacetate salt", "hexamethylenetetramine", and "a chain polyamine having an alkyl group having 3 or more carbon atoms and 3 or more amino groups". Hereinafter, the respective components will be described. .

S20 oo (1) A water-soluble gold compound . As a water-soluble gold compound used for the ~ reductive electroless gold plating solution according to = the present invention, any water-soluble gold compound of ° 25 cyanide-based gold salts and non-cyanide-based gold salts as long as the compound is soluble in the plating solution - and can provide a specific concentration can be used. ‘As - specific water-soluble gold compounds of cyanide-based gold

: oo - 12 - ps salts, potassium gold cyanide, sodium gold cyanide and on ammonium gold cyanide can be exemplified. Further as : specific water-soluble gold compounds of non-cyanide-based -

Cee gold salts, chloroaurate salts, gold sulfite salts and gold .. pw - oo 5 thiosulfate salts can be exemplified. Among these, no — : potassium gold cyanide is especially preferable. Further oo the water-soluble gold compounds may be used singly or in a = : combination of two or more. Here, the water-soluble gold = compounds are not limited to the gold compounds exemplified oo here. oo : : The concentration of a water-soluble gold compound in the reductive electroless gold plating solution according to the present invention is preferably 0.0025 mol/L to 0.0075 mol/L. This is because when the concentration of a . water-soluble gold compound is lower than 0.0025 mol/L, the deposition rate of a plated gold film is slow and a desired-thickness plated gold film is hardly obtained. This is because when the concentration of a water-soluble gold — is higher than 0.0075 mol/L, there arises a risk on that the stability of the plating solution decreases, and the high concentration is an economical drawback. oe : = (2) Citric acid or a citrate salt © 25 The reductive electroless gold plating solution - © according to the present invention contains citric acid or - a citrate salt. These citric acid and citrate salt are used ~ as a complexing agent capable of forming a complex with

Sa - | ~ gold ions. The concentration of citric acid or a citrate - salt in the reductive electroless gold plating solution = according to the present invention is preferably 0.05 mol/L - to 0.15 mol/L. This is because when the concentration of - - 5 citric acid or a citrate salt used as a complexing agent is ~ lower than 0.05 mol/L, gold deposits in the plating we solution and the solution stability is inferior; and this & is because when being more than 0.15 mol/L, the complex o formation excessively progresses and the deposition rate of gold decreases, and a desired-thickness plated gold film is : : hardly obtained. (3) Ethylenediaminetetraacetic acid (EDTA) or an ~ ethylenediaminetetraacetate salt

The reductive electroless gold plating solution according to the present invention contains ethylenediaminetetraacetic acid (EDTA) or an ~ ethylenediaminetetraacetate salt. These ethylenediaminetetraacetic acid and «& 20 ethylenediaminetetraacetate salt are complexing agents used ot o by in combination with the above-mentioned citric acid or © citrate salt. The concentration of : ethylenediaminetetraacetic acid or an © ethylenediaminetetraacetate salt in the reductive . 25 electroless gold plating solution according to the present

Cr invention is preferably 0.03 mol/L to 0.1 mol/L. This is ~ because when the concentration of ~ ethylenediaminetetraacetic acid or an :

Co :

Ed

- 14 - . ~

Cg ~. ethylenediaminetetraacetate salt used as. a complexing agent ” "is lower than 0.03 mol/L, gold deposits in the plating = iE solution and the solution stability is inferior; and this = : .. 1s because when the concentration is more than 0.1 mol/L, = : 5 the complex formation excessively progresses and the | - deposition rate of gold decreases, and a desired-thickness. plated gold film is hardly obtained. | = oo (4) Hexamethylenetetramine

The reductive electroless gold plating solution

Er according to the present invention contains Co hexamethylenetetramine. The hexamethylenetetramine is used as a reducing agent which reduces gold ions in the plating solution and causes gold to deposit on a surface of a plating target. ~ The concentration of hexamethylenetetramine in the reductive electroless gold plating solution according to : the present invention is preferably 0.003 mol/L to 0.009 - 20 mol/L. This is because when the concentration of o hexamethylenetetramine is lower than 0.003 mol/L, the “ deposition rate of a plated gold film is slow and a = desired-thickness plated gold film is hardly obtained; and © this is because when the concentration of “en 25 hexamethylenetetramine is higher than 0.009 mol/L, the o reduction reaction rapidly progresses and the gold salt in o the plating solution may abnormally deposit, and the : i”

- 15 - : ey) fy "solution stability is inferior and the high concentration ~ ~ is an economical drawback. nif i (5) A chain polyamine Co EE

Co 5 Further the reductive electroless gold plating Co solution according to the present invention contains = VI chain polyamine having an alkyl group having 3 or more = : carbon atoms and 3 or more amino groups. The chain Coo polyamine is an amine compound which acts as a reduction © 10 auxiliary agent assisting the reduction of gold ions in the : plating solution. As the chain polyamine, specifically, there can be used 3,3'-diamino-N-methyldipropylamine, N,N'- oo bis (3-aminopropyl) ethylenediamine and the like. This is oo

BN because these are especially preferable from the viewpoint of the performance of an obtained plated film, and the economic efficiency.

The concentration of the chain polyamine in the reductive electroless gold plating solution according to - 20 the present invention is preferably 0.02 mol/L to 0.06 o mol/L. By making the concentration of a chain polyamine in . the range of 0.02 mol/L to 0.06 mol/L, a high deposition = | rate can be maintained without affecting the substrate © metal film thickness. Further the throwing power of a vx 25 plated gold film can be improved and the plated gold film ed : = can have a large thickness of 0.2 um or larger. Further the : Ca solution stability can be greatly enhanced.

To

Le

B 16 - . ~ (6) Other components - : The reductive electroless gold plating solution = according to the present invention, in addition to a water- . | soluble gold compound, citric acid or a citrate salt, - ethylenediaminetetraacetic acid or an - oo ethylenediaminetetraacetate salt, hexamethylenetetramine, ee : and a chain polyamine having an alkyl group having 3 or = oo more carbon atoms and 3 or more amino groups, as described = above, may contain a deposition accelerator. The deposition - accelerator used here includes thallium compounds and lead compounds. It is preferable to use a thallium compound from: : the viewpoint of making a thick plated gold film. : The concentration of a thallium compound as the deposition accelerator in the reductive electroless gold plating solution according to the present invention is preferably 1 mg/L to 10 mg/L. When the concentration of a thallium compound as the deposition accelerator is lower than 1 mg/L, it becomes difficult to make a plated gold z 20 film thick. Further when the concentration of a thallium n compound as the deposition accelerator is higher than 10 . mg/L, making the thickness larger than that cannot be ~ accomplished and the high concentration would be an = economical drawback. ed 25 ol = ~ The reductive electroless gold plating solution & according to the present invention, in addition to the ~ | above-mentioned essential components, may contain additives

Lo oo - 17 - | = such as a pH regulator, an antioxidant, a surfactant and a - brightening agent. = y

Ce | The pH regulator is not especially limited, but oT includes potassium hydroxide, sodium hydroxide, an ammonia _ water solution, sulfuric acid and phosphoric acid. In the > reductive electroless gold plating solution according to = the present invention, by using a pH regulator, the pH is © preferably maintained at 7.0 to 9.0. This is because when the pH of the reductive electroless gold plating solution ~ is lower than 7.0, it becomes easy for the plating solution to be ‘decomposed; and when the pH is higher than 9.0, the plating solution becomes too stable and the plating - deposition rate becomes slow, and it needs to take much time for a plated gold film to be made thick. Further by regulating the pH condition at 7.0 to 9.0, even a plating target constituted from a material weak to alkali can be - plated. Further as the additives such as an antioxidant, a ~ surfactant and a brightening agent, known ones can be used. a 20 So 0 | (7) The plating condition - The gold plating condition using the reductive electroless gold plating solution according to the present = invention is not especially limited, but the solution wo 25 temperature is preferably 40°C to 90°C, and especially = | preferably 75°C to 85°C. The plating time also is neither i" especially limited, but 1 min to 2 hours is preferable, and = 2 min to 1 hour is especially preferable. =

- 18 - | © . . (Fr oo

Since the reductive electroless gold plating solution = according to the present invention comprises, as essential ~ components, a water-soluble gold compound, citric acid or a on citrate salt, ethylenediaminetetraacetic acid or an - ethylenediaminetetraacetate salt, hexamethylenetetramine, ~ : and a chain polyamine having an alkyl group having 3 or more carbon atoms and 3 or more amino groups as described “ above, it becomes easy for a plated gold film to be thickly deposited on a surface of a plating target by the electroless plating method.

Further even in the case where a plated nickel

Co film/plated palladium film/plated gold film installed on an electric connection site is formed, the plated gold film can be formed quickly on the surface of the plated palladium film without being influenced by the film thickness of the plated palladium film by using the reductive electroless gold plating solution according to the present invention. Further even in the case where an electroless plated gold film is formed on a surface of an - electroless plated palladium film formed on a surface of an h = electroless plated nickel film, by using the reductive = electroless gold plating solution of the present invention, £0 25 the dissolution of nickel can greatly be suppressed as @ compared with the case where an immersion plated gold film : - is formed, and the diffusion of nickel in the plated gold ~ film can be prevented. Therefore, when the reductive oo - 19 - a. oo . : electroless gold plating solution of the present invention -

Co is used, a plated gold film capable of realizing high BE junction reliability of wire bonding can be provided. 2 id hE 5 Further the reductive electroless gold plating ola solution of the present invention is high in the solut Hn V3 stability as compared with conventional electroless gol@ , [il plating solutions. For example, in the case where wg continuous plating is carried out while a plating solution is being replenished, the metal turnover (MTO, in which the case where gold in a plating solution in making-up of an electrolytic bath is all deposited is taken as 1 turn) is y used as an index of outwearing of the plating solution.

Whereas MTO is 2.0 to 3.0 turns in the case of conventional +15 reductive electroless gold plating solutions, an MTO of 5.0 turns or more is enabled to be realized in the reductive electroless gold plating solution of the present invention.

Further since the reductive electroless gold plating solution of the present invention contains neither o formaldehyde nor a formaldehyde bisulfite salt adduct, ~ which is strongly toxic and which is contained in conventional reductive electroless gold plating solutions, : it becomes easy for the safety in plating work to be “© 25 secured. = | - & Additionally, with the reductive electroless gold ~ plating solution of the present invention, since the

- 20 - ~ oo . deposition reaction of gold occurs only on the surface of - gold, palladium, nickel, copper or the like, which can ut become a catalytic nucleus, and does not occur on portions having no catalytic nucleus, the selective deposition: - - property is excellent. Therefore, the plating solution can - avoid the formation of a plated gold film on portions we having no need of the deposition of gold, and is beneficial - oo in that the raw material can be saved. “ 2. The electroless gold plating method :

Then, the electroless gold plating method according to the present invention will be described. The electroless gold plating method according to the present invention uses one of the reductive electroless gold plating solutions described above and carries out electroless gold plating on a surface of a plating target to thereby form a plated gold film. The electroless gold plating method carries out plating by a method of immersing a plating target in an : electroless gold plating solution as in usual reductive = 20 electroless plating methods.

Pa [x] a In the electroless gold plating method according to the present invention, it is preferable that one of copper, = palladium, gold and nickel is present on a surface of a “ 25 plating target, which is an object of the treatment. The ® presence form thereof may be any one as long as one of i” copper, palladium, gold and nickel is present on a surface ~ of a plating target. It is more preferable to use

Co - 21 - - particularly a plating target itself constituted from ~ + copper or a plating target having any film composed of © copper, palladium, gold, nickel or an alloy containing - these metals on the surface of the plating target. The 5. alloy containing these metals may include, for example, — gold cobalt. Gold, palladium, nickel, copper or an alloy _ containing these metals becomes a substrate metal for | = electroless gold plating in the present invention, and x exhibits a catalytically active effect to : © 10 hexamethylenetetramine 28 a reducing agent contained in the above-mentioned reductive electroless gold plating solution.

It is preferable that as the film to be formed on a surface of a plating target, particularly an electroless plated palladium film, an immersion plated gold film or a plated copper film is used. For example, in the case where mounting portions and terminal portions of circuits of printed wiring boards have undergone electroless nickel : plating on their surfaces, it is preferable that an electroless plated palladium film is formed on the surface o 20 of the electroless plated nickel film. This is because when n the plated nickel film has a plated palladium film formed ~ on its surface, it is especially effective in that the oo plated nickel film is prevented from being diffused in the = ~~ plated gold film. | Co os oo © 3. The plated product © Then, the plated product according to the present ~ inventien will be described. The plated product according

- 22 - | ft v to the present invention is characterized in that a surface om of a plating target undergoes electroless gold plating by x using one of the above-mentioned electroless gold plating - rr solutions and by the above-mentioned electroless gold ep plating method.

It is preferable to make a surface of a wo a. plating target undergo electroless gold plating or particularly by using the reductive electroless gold | =z plating solution having a pH of 7.0 to 9.0. Further, the © presence form thereof may be any one as long as one of - copper, palladium, gold and nickel is present on a surface of a plating target.

It is more preferable to use particularly a plating target itself constituted from copper or a plating target having any film composed of copper, palladium, gold, nickel or an alloy containing these metals on the surface of the plating target.

It is preferable that as the film to be formed on a surface of a plating target, particularly an electroless plated palladium film, an immersion plated gold film or a plated copper £ilm is used.

It is preferable that a plating target - u 20 including an electroless plated palladium film on its - surface is particularly one having an electroless plated nickel film as an underlayer of the electroless plated - palladium film formed on its surface.

This is because the © plating using the above-mentioned reductive electroless «n 25 gold plating solution can especially suitably be used for = the formation of plated films of electric connection sites. —

CE

The embodiments according to the present inventiqy ey described hitherto are one aspect of the present inventgo Jy ) and it is natural that changes and modifications may 4

Lo suitably be made without departing from the gist of phef Lhd present invention. | -

The present invention will be described more Co = specifically hereinafter by referring to Example 1 and ©

Example 2 of plated gold films fabricated by using the ” 10. reductive electroless gold plating solution of the present invention, Comparative Example 1 of a plated gold film fabricated by using an immersion electroless gold plating

BE | solution, and Comparative Example 2 of a plated gold film fabricated by using a conventional reductive electroless B plating solution. Note that, it should be mentioned by way of caution that the present invention is not limited to

Examples described in the below. [Example 1] oo

In Example 1, by using a reductive electroless gold - plating solution to which the present invention was applied - and using a copper plate as a substrate, plated films © composed of an electroless plated nickel film/electroless tx 25 plated palladium film/electroless plated gold film were ol : = formed on the substrate. ti ‘

oo : Preparation of the reductive electroless gold plating > : solution: The composition of the reductive electroless gold = : plating solution used in the present Example is shown in .. ~. the below: The plating condition (pH, solution temperature) oo is shown together with the composition. ~

Potassium gold cyanide: 5 mmol/L we

Dipotassium ethylenediaminetetraacetate: 0.03 mol/L 5

Citric acid: 0.15 mol/L oo o

Hexamethylenetetramine: 3 mmol/L 3,3" -diamino-N-methyldipropylamine: 0.02 mol/L © Thallium acetate: 5 mg/L pH: 8 -5 : : solution temperature: 80°C

Fabrication of plated films: Samples with a plated film as

Example 1 were composed of an Example sample group 1A to an

Example sample group 1D. These Example sample group 1A to

Example sample group 1D were divided according to : differences in electroless plated palladium film thickness.

EEL a - The Example sample group 1A was composed of an Example “ sample 1A-1 to an Example sample 1A-6; and the each Example . sample was made by forming an electroless plated nickel = film of 5 um in film thickness on the surface of the copper wn 25 plate, and thereafter forming an electroless plated @ palladium film of 0.1 pm in film thickness on the surface ” of the electroless plated nickel film. Thereafter, a w reductive electroless plated gold film was formed on the

— : surface of the electroless plated palladium film by using ” the above-mentioned reductive electroless gold plating = solution according to the condition of a corresponding ~ +--+ plating time. -Specifically, in the Example sample 1A-1 to - the Example sample 1A-6, the plating time conditions in the reductive electroless plated gold film formation were made > ‘to be 10 min, 20 min, 30 min, 40 min, 50 min and 60 min, o “respectively, to thereby obtain samples with a plated gold @ film.

The Example sample group 1B was composed of an Example sample 1B-1 to an Example sample 1B-6, and fabricated as in - the Example sample group 1A, except that the film thickness of the electroless plated palladium film was 0.2 um. Here, in each of the Example sample 1B-1 to the Example sample 1B-6, the plating time conditions in the reductive : electroless plated gold film formation were made different, as in the Example sample 1A-1 to the Example sample 1A-6. o 20 The Example sample group 1C was composed of an Example i sample 1C-1 to an Example sample 1C-6, and fabricated as in ~ the Example sample group 1A, except that the film thickness - of the electroless plated palladium film was 0.4 um. Here, - in each of the Example sample 1C-1 to the Example sample = 25 1C-6, the plating time conditions in the reductive = electroless plated gold film formation were made different, © as in the Example sample 1A-1 to the Example sample 1A-6. wt

. - 26 - oe -

The Example sample group 1D was composed of an Example vr sample 1D-1 to an Example sample 1D-6, and fabricated as in = the Example sample group 1A, except that the film thickness ~~ of the electroless plated palladium film was 0.6 pm. Here, oo in each of the Example sample 1D-1 to the Example sample - 1D-6, the plating time conditions in the reductive ow electroless plated gold film formation were made different, 2 as in the Example sample 1A-1 to the Example sample 1A-6. pF

Te! [Example 2] oo

In Example 2, by using the reductive electroless gold plating solution as in Example 1 and using a copper plate. as a substrate, plated films composed of an electroless plated nickel film/immersion electroless plated gold film/reductive electroless plated gold film were formed on the substrate. Samples with a plated film as Example 2 were : composed of an Example sample 2-1 to an Example sample 2-6.

The Example sample 2-1 to the Example sample 2-6 were each 2 20 made by forming an electroless plated nickel film of 5 um — in film thickness on the surface of the copper plate, and = thereafter forming an immersion electroless plated gold 2 film of 0.07 um in film thickness on the surface of the © electroless plated nickel film. Thereafter, a reductive . 25 electroless plated gold film was formed on the surface of & the immersion electroless plated gold film by using the - above-mentioned reductive electroless gold plating solution - according to the condition of a corresponding plating time. ie :

- 27 - = .

Here, in each of the Example sample 2-1 to the Example - sample 2-6, the plating time conditions in the reductive - electroless plated gold film formation were made different, = as in the Example sample 1A-1 to the Example sample 1a-6. | oo so [Comparative Examples] . we = : [Comparative Example 1] =

In Comparative Example 1, by using an immersion oo ” electroless gold plating solution and using a copper plate as a substrate as in Example 1, plated films composed of an oo electroless plated nickel film/electroless plated palladium film/electroless plated gold film were fabricated on the oo substrate.

Preparation of the immersion electroless gold plating solution: The composition of the immersion electroless gold plating solution used in Comparative Example 1 is shown in the below. The plating condition (pH, solution temperature) © 20 is shown together with the composi tion. o Potassium gold cyanide: 10 mmol/L ~

B Ethylenediaminetetraacetic acid: 0.03 mol/L

Citric acid: 0.15 mol/L © Thallium acetate: 50 mg/L ef 25 pH: 4.5 : = Solution temperature: 80°C

28 - : ~ . N

Fabrication of plated films: Samples with a plated film as 7

Comparative Example 1 are composed of a comparative sample - group 1A to a comparative sample group 1D. These ol comparative sample group 1A to comparative sample group 1D — wr are divided according to differences in electroless plated i .palladium film thickness. - | =e

The comparative sample group 1A was composed of a © comparative sample 1A-1 to a comparative sample 1A-6; and the each comparative sample was made by forming an electroless plated nickel film of 5 um in film thickness on the surface of the copper plate, and thereafter forming an electroless plated palladium film of 0.1 pm in film thickness on the surface of the electroless plated nickel film. Thereafter, an immersion electroless plated gold film was formed on the surface of the electroless plated palladium film by using the above-mentioned immersion electroless gold plating solution according to the condition of a corresponding plating time. Specifically, in - 20 the comparative sample 1A-1. to the comparative sample 1a-6, po the plating time conditions in the immersion electroless ‘plated gold film formation were made to be 10 min, 20 min, . 30 min, 40 min, 50 min and 60 min, respectively, to thereby ~ obtain samples with a plated gold film. - 25 “ The comparative sample group 1B was composed of a = comparative sample 1B-1 to a comparative sample 1B-6, and & fabricated as in the comparative sample group 1A, except wd

\ - | | 29 - - that the film thickness of the electroless plated palladium ” film was 0.2 pm. Here, in each of the comparative sample wo 1B-1 to the comparative sample 1B-6, the plating time

SO conditions in the immersion electroless plated gold film et formation were made different, as in the comparative sample = . 1A-1 to the comparative sample 1A-6. we : The comparative sample group 1C was composed of a IZ comparative sample 1C-1 to a comparative sample 1C-6, and - fabricated as in the comparative sample group 1A, except that the film thickness of the electroless plated palladium film was 0.4 pm. Here, in each of the comparative sample 1C-1 to the comparative sample 1C-6, the plating time conditions in the immersion electroless plated gold film formation were made different, as in the comparative sample 1A-1 to the comparative sample 1A-6.

The comparative sample group 1D was composed of a : comparative sample 1D-1 to a comparative sample 1D-6, and fabricated as in the comparative sample group 1A, except " "that the film thickness of the electroless plated palladium ~ film was 0.6 um. Here, in each of the comparative sample : 1D-1 to the comparative sample 1D-6, the plating time = conditions in the immersion electroless plated gold film wl 25 formation were made different, as in the comparative sample i = 1A-1 to the comparative sample 1A-6. ” ~ [Comparative Example 2] fu)

- 30 - =

N

In Comparative .Example 2, by using a conventional or reductive electroless gold plating solution and using a 2 copper plate as a substrate as in Example 2, plated films -

Co composed of an-electroless plated nickel film/immersion CP electroless plated gold £i1m/conventional reductive 2 1.3 electroless plated gold film were formed on the cielo § wy Al a | 3 . Preparation of the conventional reductive electroless gSld 3 plating solution: The composition of the reductive 2 electroless gold plating solution used in Comparative F ' Example 2 is shown in the below. The plating condition (pH, solution temperature) is shown together with the composition.

Potassium gold cyanide: 0.015 mol/L

Potassium cyanide: 0.03 mol/L

Sodium hydroxide: 0.8 mol/L

Dimethylamine borane: 0.2 mol/L

Lead compound: 5 mg/L (in terms of lead) pH: 13 fl 20 Solution temperature: 70°C

Lr ) Fabrication of a plated film: In Comparative Example 2, an electroless plated nickel film of 5 pm in film thickness was formed on the surface of a copper plate, and thereafter, =“ 25 an immersion electroless plated gold film of 0.05 um in © film thickness was formed on the surface of the electroless i” plated nickel film. Thereafter, by using the above- oo mentioned reductive electroless gold plating solution, a

- 31 - | ~ reductive electroless plated gold film of 0.20 pum in film - thickness was formed on the surface of the immersion electroless plated gold film. [Evaluations] : CO

Then, the plated gold films in Example 1 and Example 2 *° fabricated by using the reductive electroless gold plating = solution of the present invention were evaluated for the = deposition rate, the surface form and the like. Hereinafter, = these evaluations will be described specifically, if required, by comparing Example 1 and Example 2 with

Comparative Example 1 of the plated gold films fabricated by using the immersion electroless gold plating solution and Comparative Example 2 of the plated gold film : fabricated by using the conventional reductive electroless plating solution. :

Deposition rate: There is shown in Figure 1 a relation between the plating time and the plated film thickness of - 20 + the plated gold films of the Example sample group 1A (the - Example sample 1A-1 to the Example sample 1A-6) in Example = 1 using the reductive electroless gold plating solution - according to the present invention. There is similarly = shown in Figure 2 a relation between the plating time and ez 25 the plated film thickness of the plated gold films of ® Example 2 (the Example sample 2-1 to the Example sample 2- - 6) using the reductive electroless gold plating solution according to the present invention. Here, in Figure 2,

Ch vo - 32-0 oe there is shown an electron microscope photograph (x10,000) i of the plated gold film of the Example sample 2-2 obtained - by making the plating time to be 20 min. iy

Cee oo Ce or 5 It is confirmed from Figure 1 that the plated gold =o film formed on the surface of the electroless plated = : palladium film by using the above-mentioned reductive : 2 electroless gold plating solution was formed stably at a = rate of 0.15 pm/30 min without being influenced by the . thickness of the plated gold film formed. : It is confirmed from Figure 2 that the reductive plated gold film formed on the surface of the immersion + electroless plated gold film by using the above-mentioned reductive electroless gold plating solution was formed _ stably at a rate of 0.17 um/30 min without being influenced . by the thickness of the plated gold film formed.

Influence of the thickness of the electroless plated wn 20 palladium film on the deposition rate of the plated gold

Tn film: Then, comparing Example 1 with Comparative Example 1, © there will be described the influence of the thickness of - the electroless plated palladium film on the deposition = rate of the plated gold film. Figure 3 shows a relation ol 25 between the film thickness of the electroless plated = palladium film and the deposition rate of the plated gold - ~ film in the Example sample group 1A: (the Example sample 1A- oT 1 to the Example sample 1A-6) to the Example sample group

CE

) a | C33 - | | - oo 1p (the Example sample 1D-1 to the Example sample 1D-6) o ‘each in which the plated gold film was formed on the’ surface of the electroless plated palladium film by using 2 _ the reductive electroless gold plating solution. Figure 3 = also shows, together with the relation, a relation between - the film thickness of the electroless plated palladium film we "and the deposition rate of the plated gold film in the - comparative sample group 1A (the comparative sample 1A-1 to = the comparative sample 1A-6) to the comparative sample - group 1D (the comparative sample 1D-1 to the comparative sample 1D-6) each in which the plated gold film was formed : on the surface of the electroless plated palladium film by using the immersion electroless gold plating solution. . 15 It is found from Figure 3 that in the plated gold films formed by using the immersion electroless gold plating solution of the comparative sample group 1A to the comparative sample group 1D, the thicker the plated palladium film being the substrate metal, the more the

Hw 20 deposition rate of the plated gold film decreased. By ~ | contrast, it can be confirmed that the plated gold films = ~ formed by using the reductive electroless gold plating = solution of the Example sample group 1A to the Example © sample group 1D were formed at a stable rate irrespective .s 25 of the thickness of the plated palladium film being the = substrate metal. il wt

Tn!

oo | - 34 - | re

Co

Surface form of the plated gold film: Then, the surface Cn form of the plated gold film formed on the surface of the Cw electroless plated palladium film by using the reductive . cu : electroless gold plating solution of the present invention Po . 5 was observed. Figure 4 shows electron microscope - : photographs (x10,000 and x 30,000) of the plated gold film Ge surface of the Example sample 1A-2 in which the reductive = electroless plated gold film was formed in a film thickness . - of 0.1 um out of Example 1. The surface form of the -

Co 10 reductive electroless plated gold film formed on the surface of the immersion electroless plated gold film by using the reductive electroless gold plating solution of the present invention was further observed. Figure 5 shows an electron microscope photograph (x30,000) of the plated ' gold film surface of the Example sample 2-2 in which the reductive electroless plated gold film was formed in a film thickness of 0.13 um out of Example 2. As a comparison, there was observed the surface form of the reductive electroless plated gold film formed on the surface of the

I © 20 immersion electroless plated gold film by using the hn conventional reductive electroless gold plating solution. ~ Figure 5 shows an electron microscope photograph (x30,000) ~ of the plated gold film surface of Comparative Example 2 in © which the reductive electroless plated gold film was formed 0 . 25 in a film thickness of 0.13 um. “ It can be confirmed from Figure 4 and Figure 5 that 3 ~ the electroless plated gold film was densely formed not

Co - 35 - : oo | | oo only by using the reductive electroless gold plating ” : solution of the present invention, but by using the - conventional reductive electroless gold plating solution. ol

RU

5S. Surface form after peeling-off of the electroless plated oo gold film: Further there were observed the surface forms of °° the plated nickel films after the electroless plated gold = BN + film or the electroless plated gold film and the © electroless plated palladium film were peeled off from the ” 10 each plated film shown in Figure 4 and Figure 5. Figure 6 shows an electron microscope photograph (x5,000) of the ‘plated nickel film surface after the electroless plated gold film and the electroless plated palladium film were peeled off from the state of Figure :. Figure 7 shows . 15 electron microscope photographs (x3,000) of the plated - nickel film surfaces after the electroless plated gold film : was peeled off from the state of Figure 5.

As apparent from Figure 6 and Figure 7, in any of o 20 Examples and Comparative Examples formed by using the reductive electroless gold plating solutions, no local ~ corrosion of the plated nickel film was observed. wl : = Cross-sectional form of the plated film: Then, the cross- - 25 section of the plated film having the layer structure of = the electroless plated nickel film/electroless plated © palladium film/electroless plated gold film of Example 1, = in which the plated gold film was formed on the surface of

- 36 = oo > : ~ the electroless plated palladium film by using the oom reductive electroless gold plating solution of the present on invention was observed. ‘Figure 8 shows a cross-sectional . ~~~ photograph (x30,000) of the plated film of the Example = sample 1A-6, in which the reductive electroless plated gold - film was formed in a film thickness of 0.3 um. It can be we confirmed from Figure 8 that the electroless plated gold = : film formed by using the above-mentioned reductive | . electroless gold plating solution was formed uniformly on * the surface of the plated palladium: film.

Selective deposition property of the plated gold film: Then, there are shown in Figure 9 electron microscope photographs (x500) of an end portion and a central portion of a plated ~ 15 product whose plated film was formed under the same condition as in the Example sample 1A-6 out of Example 1, in which the plated gold film was formed on the surface of the electroless plated palladium film by using the reductive electroless gold plating solution of the present o 20 invention. It can be confirmed from Figure 5 that the hi electroless plated gold films were formed uniformly - | similarly in the end portion and the central portion of the - plated product. Hence, it can be said also from the = photograph of Figure 9 that the reductive electroless gold

Bl 25 plating solution of the present invention was excellent in ot = the selective deposition property of the electroless plated i” gold film. od

Co : - 37 - | ~ > . Influence of the nickel dissolution in the gold plating oo solution: Then, with respect to Example 1, in which the = plated gold film was formed on the surface of the 0 electroless plated palladium film by Using the reductive ~ electroless gold plating solution of the present invention, - there was investigated the influence of the dissolution of wo the electroless nickel into the reductive electroless gold = } plating solution. Specifically, there was examined the - dissolution amount of the substrate nickel into the To electroless gold plating solution in the case where 1 g of : ~ gold was deposited on the surface of the electroless plated ) palladium film, by using ICP. As a comparison, also oo

Comparative Example 1 using the immersion electroless gold plating solution was examined as in Example 1. Figure 10° shows a dissolution amount of the electroless nickel of

Example 1 using the reductive electroless gold plating solution and a dissolution amount of the substrate nickel of Comparative Example 1 using the immersion electroless gold plating solution. Figure 10 indicates, for the either = 20 case, a value when the dissolution amount of Ni into the - n gold plating solution in the case where 1 g of gold was . deposited was examined by using ICP. ot = From Figure 10, in Comparative Example 1 in which 1 g = 25 of the plated gold film was deposited by using the @ immersion electroless gold plating solution, Ni used as the “ substrate metal dissolved out in 162 ppm into the immersion ~ electroless gold plating solution. By contrast, in Example

} - - 38 - = > 1 in which 1 g of the plated gold film was deposited by wo! using the reductive electroless gold plating solution of . present application, Ni used as the substrate metal y dissolved out in 0.2 ppm only into the reductive | pot electroless gold plating solution. -

From the results of the evaluation tests, it can be © said that the reductive electroless gold plating solution ~ according to the present application could greatly suppress } : the dissolution of the substrate nickel through the plated ~~ palladium film as compared with the case of forming the immersion plated gold film, and nickel was enabled to be prevented from diffusing into the plated gold film. a 15 Deviation in film thickness of the plated gold film: Then, there was investigated the deviation in film thickness of the plated gold film formed by using the reductive electroless gold plating solution on the surface of the immersion electroless plated gold film. Here, there was = 20 examined the film thickness of the reductive electroless = plated gold film of the Example sample 2-2 of Example 2 as = an example using the reductive electroless gold plating solution according to the present invention. As a ® comparison, there was examined the film thickness of the wn 25 reductive electroless plated gold film of Comparative = Example 2 using the conventional reductive electroless gold ~ plating solution. For the each case, the results by the = examination of the film thickness of 20 points are

- 39 - = collectively shown in Table 1. Further Figure 11 shows the i ~~ deviation states. - - . ’ “uy [Table 1] ce Ca . : 1.

Example 2

Comparative (Example Example 2 sample 2-2) p Lo

Plating Time =

Average Value (um) 0.199 0.206 Cm from

Maximum Value (um) 0.204 0.218 os

Film Minimum Value (um) 0.194 0.182 ht

Thickness | Maximum - Minimum 0.01 0.036 (pm)

Standard Deviation | 0.004 0.013

The average value of the film thickness of the electroless plated gold film of the Example sample 2-2 using the reductive electroless gold plating solution according to the present invention was 0.199 pm; the : difference between the maximum value and the minimum value was 0.01 pm; and the standard deviation was pretty much as low as 0.004. By contrast, the average value of the film od wr thickness of the electroless plated gold film of

Ce

Li 15 Comparative Example 2 using the conventional reductive

A electroless gold plating solution was 0.206 um; the ~ difference between the maximum value and the minimum value . was 0.036 um; and the standard deviation was 0.013. Hence, we it is found that by using the reductive electroless gold penn] = 20 plating solution according to the present invention, as : © compared with the case where the conventional reductive

Co electroless gold plating solution was used, there was ny oo - 40 - | ~ provided the electroless plated gold film having a low on deviation in a considerably high level, that is, being ~ uniform, across the entire region. From the results, by 7 : using the reductive electroless gold plating solution : fot 5 according to the present invention, the entire of the - surface of the plating target was enabled to undergo | Hw plating more uniformly and the quality could be improved. =

Further since the electroless plated gold film could be . formed in a required thickness, the formation of the ” electroless plated gold film exceeding the required thickness was suppressed and an excess burden of gold was enabled to be greatly reduced.

Wire bonding performance of the plated gold film: Then, there was investigated the wire bonding performance of the plated gold film formed by using the reductive electroless gold plating solution according to the present invention. a There was examined the strength of wire bonding of the reductive electroless plated gold film of the Example o 20 sample 2-2 of Example 2 as an example using the reductive oo on electroless gold plating solution according to the present ~ invention. As a comparison, there was examined the strength ~ of wire bonding of the reductive electroless plated gold z film of Comparative Example 2 using the conventional © 25 reductive electroless gold plating solution. Specifically, = a gold wire of 25 um in wire diameter was joined to the : @ reductive electroless plated film of the Example sample 2-2 ~ and Comparative Example 2 each by using a wire bonding eo

Lo apparatus; the wire was pulled by a pull tester and the ” strength of the wire bonding was examined. For the each o case, 20 points were examined and the maximum value, the -»-. minimum value and the average value of the wire bonding - strength were determined. The examination results are shown oo in Figure 12. | w

The maximum value of the wire bonding strength of the ~ ‘electroless plated gold film of Example 2 (the Example © sample 2-2) using the reductive electroless plating solution according to the present invention was 6.0 gf; the minimum value thereof was a.8 gf; and the average value thereof was 5.3 gf. Then, the maximum value of the wire bonding strength of the electroless plated gold film of

Comparative Example 2 using the conventional reductive electroless plating solution was 6.0 gf; the minimum value thereof was 4.8 gf; and the average value thereof was 5.3 gf. From these results, it is found that the electroless plated gold film obtained by using the reductive = 20 electroless plating solution according to the present i" invention provided an excellent wire bonding strength, ; almost the same as the case sing the conventional - reductive electroless plating solution. Hence, it can be = said that the reductive electroless gold plating solution el 25 of the present invention enables to provide a plated gold —- = film capable of realizing the high junction reliability of o wire bonding. wd : ox

= 42 = frome - - [Industrial Applicability] ao! ol Ww : The reductive electroless gold plating solution of the © present invention greatly suppresses the dissolution of the } Lr substrate metal such as nickel and palladium, and enables ” . . . fn the plated gold film to be deposited at a high deposition Le rate in a thick deposition on the surface of the substrate o : [2 metal. Hence, the present invention enables the plated gold film high in the wire bonding junction reliability to be provided. 2 1 i ie 5 & —- = & ~) “ By ~ YY - a - | 2 | /% o/f i#

Ki . po] : Co

LN . 17 we] . yma] . sporaif | . } a apenid ’ . :

Claims (1)

1. So | Nv Claims oo Ln 8 8 32

   - 1. A reductive electroless gold plating solution uged 3 f= So for formation of an electroless plated gold Film whegpind Er one of copper, palladium, gold and nickel is present-pn 4 g . surface of a plating target, comprising: - a oo a water-soluble gold compound; citric acid or JRE : citrate salt; ethylenediaminetetraacetic acid or an - ethylenediaminetetraacetate salt; hexamethylenetetramine; - and a chain polyamine having an alkyl group having 3 or - more carbon atoms and 3 or more amino groups. -

   2. The reductive electroless gold plating solution - Co according to claim 1, wherein the gold plating solution has a pH of 7.0 to a DH of 9.0. ‘15 3. The reductive electroless gold plating solution ~ according to claim 1 or 2, wherein the chain polyamine is | i 3,3'-diamino-N-methyldipropylamine or N,N'-bis(3- ~ aminopropyl) ethylenediamine.

   La. The reductive electroless gold plating solution = 20 according to claim 1, comprising a thallium compound as a o deposition accelerator. : : . 5. A method of electroless gold plating, comprising

   ~ . - forming an electroless plated gold 11m, wherein one of - copper, palladium, gold and nickel is present on a “ 25 surface of a plating target using the reductive = electroless gold plating solution according to claim 1. ~ oo - ®

   Co, nae | ~

   -

   6. The method of electroless gold plating according to oo claim 5, wherein the surface of the plating target | - : ft includes an electroless plated palladium film formed on a - Le surface of an electroless plated nickel film. Sl . : . II ‘ bei Le i o wf . : . } . [ia] ’ Cm . Ce | | | So - sano] . } wd