JP2874088B2 - Electroless gold plating bath - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electroless gold plating bath suitably used for forming a gold plating film on a metal part of a printed wiring board, a ceramic IC package, an ITO substrate, an IC card, and the like. More specifically, an electroless gold plating film having excellent wire bonding properties and die bonding properties can be reliably formed, and the plating process is performed well without attacking the resist, aluminum nitride, glass, etc. of the printed wiring board. Electroless gold plating bath.

[0002]

2. Description of the Related Art Conventionally, electroless gold plating has been applied to physical properties of gold such as electrical conductivity, connectivity by thermocompression bonding, and chemical properties such as oxidation resistance and chemical resistance. Due to its properties, it is applied to terminals and circuit surfaces of electronic industrial parts such as printed wiring boards, ceramic IC packages, ITO substrates, and IC cards.

Conventionally, as an electroless gold plating bath, a strongly alkaline bath containing a cyanide aurate, a caustic alkali and a borohydride compound has been known. However, since the electroless gold plating bath is strongly alkaline, there is a problem in that the electroless gold plating bath attacks the resist of a printed wiring board and the aluminum nitride material or glass material of an IC package.
In addition, there is a problem of environmental preservation because it contains cyanide ions.

Conventionally, a neutral bath containing a sulfite and hydrazine is also known. However, the gold plating film obtained from this plating bath has a small crystal form and is angular, so that it cannot be visually observed. It appears that the plating tone is reddish and discolored. Furthermore, due to the above crystal form, there is a drawback that the surface cleaning property after plating is poor and the gold wire bonding property is sometimes deteriorated. In addition, it has been customarily recognized that a gold plating film having a good function has a beautiful color tone of lemon yellow. It is not easily accepted as a product, and its commercial value is low.

Further, in this neutral bath, a so-called plating spread is apt to occur, in which a film is deposited at a place other than the purpose, and bleeding or the like occurs. In particular, this tendency is remarkable when plating is performed on a metal portion formed on a ceramic material, and a plating film may protrude from the metal portion and deposit on the surface of the ceramic material.

The present invention has been made in view of the above circumstances, and provides a gold-plated film having a beautiful color of lemon yellow and excellent in wire bonding property and die bonding property, which can be used for resists on printed wiring boards and IC packages. Without attacking aluminum nitride or glass materials
An object of the present invention is to provide an electroless gold plating bath that can be formed reliably and can further solve the problem of plating spread.

[0007]

Means for Solving the Problems and Actions The present inventors have made intensive studies to achieve the above object, and as a result, have found that they do not attack the resist of a printed wiring board or the aluminum nitride material or glass material of an IC package. A neutral sulfonate containing a gold sulfite, a sulfite, and one or more selected from the group consisting of hydrazines, ascorbic acid, ascorbate, trimethylamine borane and dimethylamine borane as a reducing agent; By adding an organic phosphonic acid or a salt thereof and the following specific nitrogen-containing compound to the electrolytic gold plating bath, the crystal morphology of the resulting gold plating film is improved and has a beautiful color of lemon yellow,
The inventors have found that a gold plating film excellent in wire bonding property and die bonding property can be obtained and that the spread of plating can be effectively prevented, and the present invention has been completed.

[0008] Accordingly, the present invention relates to a method for preparing a gold sulfite, a sulfite, and one or more reductions selected from the group consisting of hydrazines, ascorbic acid, ascorbate, trimethylamine borane and dimethylamine borane. And an organic phosphonic acid or a salt thereof, and p-methylaminophenol, phenylenediamine, aminophenol, aminobenzoic acid, metanilic acid or anthranilic acid as a nitrogen-containing compound in an electroless gold plating bath containing And an electroless gold plating bath characterized in that the pH is 6 to 11.

Hereinafter, the present invention will be described in more detail.
As the gold sulfite compounded as a gold source in the electroless gold plating bath of the present invention, sodium gold sulfite, potassium potassium sulfite, gold ammonium sulfite and the like are preferably used. The amount of the gold sulfite is not particularly limited, but is preferably 1 to 20 g / L, particularly preferably 2 to 8 g / L as gold ions. In this case, the compounding amount of this gold sulfite,
That is, the plating rate increases almost in proportion to the concentration of gold ions in the plating bath. However, when the plating rate exceeds 20 g / L, the plating rate increases, but the stability of the plating bath may be poor. It is uneconomical because the pumping amount increases. On the other hand, if the gold ion concentration is less than 1 g / L, the plating rate becomes extremely low.

The above-mentioned sulfite acts as a complexing agent for gold ions. As the sulfite, sodium sulfite, potassium sulfite, ammonium sulfite and the like are preferably used. The amount of these sulfites is not particularly limited, but is usually 5 to 150 g / L, preferably 20 to 100 g / L, and more preferably 5 g / L.
If the amount is less than the above, the effect as a complexing agent becomes insufficient and the bath stability may be lacking. In addition, even if the amount exceeds 150 g / L, the effect does not increase so much and is uneconomical.

Next, hydrazines, ascorbic acid, ascorbate, trimethylamine borane (TMAB) and dimethylamine borane (D
MAB) is used. Here, examples of the hydrazines include hydrazine compounds such as hydrazine hydrate, hydrazine sulfate, neutral hydrazine sulfate, and hydrazine maleate, and salts thereof and hydrazine derivatives such as hydroxylamine. Ascorbate includes ascorbate Sodium, potassium and ammonium salts of acids are mentioned.

The action of these reducing agents causes gold ions in the plating bath to precipitate on the object to be plated. One of the above reducing agents may be used alone, or two or more thereof may be used in combination. In this case, although not particularly limited, it is preferable to use one or more hydrazines as at least a part of the reducing agent.

The amount of the reducing agent is appropriately selected according to the type of the reducing agent. Specifically, when using hydrazines or other reducing agents alone, usually 1 to 100
g / L, especially 5 to 70 g / L. When hydrazines and other reducing agents are used in combination, the hydrazines are usually blended in the same manner as in the case of the above-mentioned single use, and the other reducing agents are added in 0%. It is preferable to mix in the range of 0.1 to 20 g / L, particularly 0.3 to 30 g / L. In this case, the plating rate increases almost in proportion to the concentration of these reducing agents. However, even if an amount exceeding the above range is added, the plating rate does not become too large, and the liquid stability may be deteriorated. If it is less than the above range, the plating rate will be very low.

The electroless gold plating bath of the present invention improves the crystal morphology of a deposited film by adding an organic phosphonate to a plating bath containing the above-mentioned gold sulfite, a sulfite, and a reducing agent. Thus, a gold-plated film having a beautiful color tone of lemon yellow, excellent in wire bonding property and die bonding property is obtained, and the spread of plating can be effectively prevented.

The organic phosphonate is not particularly limited, but includes aminotri (methylene phosphonic acid) and salts thereof, 1-hydroxyethylidene-1.1-
Diphosphonic acid and its salts, ethylenediaminetetra (methylenephosphonic acid) and its salts, diethylenetriaminepenta (methylenephosphonic acid) and its salts, and the like. These salts include sodium salts, potassium salts,
Ammonium salts are preferred. Among these organic phosphonic acids, although not particularly limited, ethylenediaminetetra (methylenephosphonic acid) and its salts are particularly preferably used, and have particularly favorable effects on color tone and bath stability.

The amount of the organic phosphonic acid or salt thereof to be added is not particularly limited, but is preferably 1 to 200 g / g.
L, particularly preferably 10 to 150 g / L. In this case, if the added amount is less than 1 g / L, the effect may not be obtained, and if the added amount exceeds 200 g / L, the effect is not particularly increased.

The electroless gold plating bath of the present invention contains the above-mentioned gold sulfite, sulfite, reducing agent and organic phosphonic acid or a salt thereof, and has a beautiful yellow color tone and good bonding property. An electroless gold-plated film having the same is obtained, and the occurrence of plating spread is effectively prevented. However, in order to more reliably prevent the spread of plating, a nonionic surfactant and / or Alternatively, a non-ionic polymer can be added.

Examples of the nonionic surfactant include polyethylene glycol (PEG) and polypropylene glycol (PPG) having a molecular weight of 200 to 9000, especially 50.
0-4000 polyalkylene glycols such as PE
G-4000, PEG-1540, PPG-1000,
Polyalkylene glycol type surfactants such as PEG-600, for example, polyoxyethylene alkylphenol ether, polyoxyethylene alkyl ether, polyoxyethylene fatty acid ester, polyoxyethylene alkylamine, polyoxyethylene / oxypropylene block polymer, acetylene glycol (Specifically, an EO adduct of nonylphenol, an EO adduct of beta naphthol, an EO adduct of lauryl alcohol, an EO adduct of tallowamine, and the like). Further, as the nonionic polymer, polyvinyl alcohol (Gosenol NL-05, manufactured by Nippon Synthetic Chemical Co., Ltd.)
Etc.), polyvinylpyrrolidone (K-12, K-15, K
-30, K-60, K-90, etc.). The number of moles of ethylene oxide (EO) added is about 5 to
About 100 is preferable.

These nonionic surfactants and nonionic polymers may be used alone or in combination of two or more. The amount of the nonionic surfactant and the nonionic polymer is appropriately selected depending on the type of the stabilizer. However, it is usually preferably 0.1 to 100 mg / L, particularly preferably 0.3 to 30 mg / L. In this case, if the amount of these stabilizers is small, it may not be possible to reliably prevent the spread of plating, and if too large, the plating speed may be reduced.

By adding these stabilizers, it is possible to more reliably prevent the spread of plating from occurring and to form a good gold plating film only on the metal portion. It also has the effect of preventing. The mechanism of action of these effects is not clear, but can be considered as follows.

That is, the above-mentioned stabilizer is adsorbed on the gold plating film or on the gold colloid particles generated by the solution decomposition to prevent the deposition of gold, and the plating proceeds on the plating film by some mechanism. In this case, plating does not proceed, which is considered to prevent decomposition of the plating solution and plating spread. Alternatively, it can be considered that the stabilizer is adsorbed on the ceramic surface of the material, and acts to prevent gold from being deposited thereon. That is, it can be considered that the metal is selectively adsorbed on the ceramics rather than on the gold plating film to prevent the plating from spreading. In addition, the colloidal gold particles have a remarkably large surface area per the same volume as the plating surface, so that the stabilizer selectively prevents the growth of colloidal gold to prevent the plating solution from decomposing and is generated by the decomposition of the solution. It is also considered that the spread of the plating is prevented by preventing the colloidal gold particles adsorbed on the ceramic and forming a core to prevent the plating from growing.

The electroless gold plating bath of the present invention comprises the above-mentioned gold sulfite, sulfite, reducing agent, organic phosphonic acid or a salt thereof and, if necessary, the above stabilizer.
In addition to these components, a nitrogen-containing compound can be further added, whereby the plating rate can be increased.

As the nitrogen-containing compound, ammonia, aminocarboxylic acid, iminocarboxylic acid, other water-soluble nitrogen-containing organic compounds, and salts thereof are used. Ammonia and its salts include ammonia water, ammonium sulfate, ammonium chloride, ammonium acetate, ammonium nitrate, and the like. Aminocarboxylic acids and iminocarboxylic acids include aminocarboxylic acids such as essential amino acids, ethylenediaminetetraacetic acid, and nitrilo. And iminocarboxylic acids such as triacetic acid. Examples of other water-soluble nitrogen-containing organic compounds include amines such as ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, hexamethylenetetramine, and guanidine; and aminoalcohols such as monoethanolamine, diethanolamine, and triethanolamine. , Aromatic amines such as p-methylaminophenol, aminophenol, phenylenediamine and aminobenzoic acid; heterocyclic compounds such as imidazole, uracil, morpholine and pyrazine; bis (hydroxyethyl) aminoethanesulfonic acid and metanilic acid , Anthranilic acid, pyridinesulfonic acid, nitrogen-containing sulfonic acids such as 8-hydroxyquinoline-5-sulfonic acid, taurine, pyridinesulfonic acid, dipyridyls, picolinic acid, dihydroxy Examples include, but are not limited to, pyridines such as lysine. Among these water-soluble nitrogen-containing organic compounds, the present invention includes p-methylaminophenol, phenylenediamine, aminophenol, aminobenzoic acid, methanyl An acid or anthranilic acid is added as an essential component. The amount of the nitrogen-containing compound to be added is appropriately selected depending on the type of the nitrogen-containing compound and the like, and is not particularly limited, but is usually 1 to 200 g / L, particularly 5 to 15 g for ammonia.
It is preferably 0 g / L, and in the case of aminocarboxylic acid, iminocarboxylic acid, other water-soluble nitrogen-containing organic compounds and salts thereof, 0.05 to 100 g / L, particularly 0.05 to 50 g / L, Desirably 0.1 to 50 g
/ L is preferable.

Further, the plating bath of the present invention contains thiosulfate,
Oxycarboxylic acids can be added. Thiosulfate shows a complexing action of gold ions and is effective for improving the plating rate and bath stability, and the added amount is 0.1 to 30 g.
/ L, particularly preferably 0.1 to 3 g / L, and the peak of the plating rate is around 1 g / L. If the amount is less than 0.1 g / L, good effects may not be obtained. If the amount is more than 30 g / L, no improvement is observed, and the plating rate and bath stability are reduced. There are cases. The oxycarboxylic acids have an effect of improving bath stability and color tone, and include oxycarboxylic acids, derivatives thereof, and salts thereof. Specific examples thereof include citric acid, tartaric acid, and sodium and potassium salts thereof. Salts, ammonium salts, glucono-δ-lactone, sodium gluconate, potassium gluconate and the like. The amount of the oxycarboxylic acid added is 5 to 100 g /
L, particularly preferably 10 to 70 g / L.

When plating a copper material using the plating bath of the present invention, copper ions may be eluted in the bath, and gold may be deposited where copper ions are eluted. . Therefore, benzotriazole and in the plating bath in order to prevent this / or CN ^- it can be added. Benzotriazole acts by adsorbing on Cu or forming a water-insoluble chelate with Cu ions to prevent elution of Cu ions. Furthermore, CN ^- the mechanism of action of is unknown, Cu ⁺ and CN ^- and may form a complex Cu ⁺
It is thought that this is due to the reduction of the reducing power.

The amount of the benzotriazole added is not particularly limited, but is 0.001 to 10 g / L.
In particular, it is preferably 0.01 to 1 g / L, and 0.0
If the amount is less than 01 g / L, an effective effect may not be obtained. Even if an amount exceeding 10 g / L is added, no significant increase in the effect is observed. May be invited. Furthermore, CN ^- amount of 1
The amount is preferably 0 to 2000 mg / L, particularly preferably 50 to 1000 mg / L, and if it is less than 10 mg / L, an effective effect may not be obtained. The aluminum nitride material or glass material of the IC package may be eroded. Incidentally, in the plating bath CN ^- C supplies
As the N ^- source, NaCN, KCN, Na [Au (C
N) ₂ ], K [Au (CN) ₂ ] and the like.

The electroless gold plating bath of the present invention comprises the above-mentioned gold sulfite, sulfite, reducing agent, organic phosphonate and, if necessary, the above stabilizer, nitrogen-containing compound, thiosulfate, oxycarboxylic acid, triazole, CN ^- and although those containing, can be added additives which are more usually used to lead ions, an electroless gold plating bath of thallium ions.

When plating is performed using the electroless gold plating bath of the present invention, an object to be plated such as a printed wiring board or a ceramic IC package is immersed in the bath. In this case, there is no particular limitation. Preferably, the printed wiring board and the ceramic IC package are formed by forming an electroless Ni / B plating film and / or an electroless Ni / P plating film, and further forming a replacement gold plating film thereon.

Next, the plating conditions will be described. First, the pH of the plating bath is preferably set to 6 to 11, particularly preferably 7 to 9. In this case, if the pH is 6 or less, the plating rate may decrease, and if the pH exceeds 11, the plating rate increases, but the bath stability decreases and the plating material having poor alkali resistance is eroded. There is.

The plating temperature (solution temperature) is preferably from 40 to 90 ° C., particularly preferably from 50 to 80 ° C. If it is less than 40 ° C., the plating rate may be very low. However, plating stability may be poor. In addition, it is no problem to stir,
Further, it is preferable to provide a mechanism for hitting the object to be plated with a hammer or the like in order to prevent the generation of gas pits.Furthermore, replacement filtration and circulating filtration can be performed. Thereby, it is possible to prevent unevenness in the temperature of the plating solution and to filter solid dust in the plating solution. In this case, if the plating solution is vigorously stirred, the plating rate tends to decrease, and
It is preferable that circulation of the plating solution by rocking and filtering the object to be plated is not performed too violently.

It is also possible to introduce air into the plating bath.
This allows for gold colloid particles or gold in the plating bath.
The generation of particles can be more effectively prevented.
Although the effect of this air introduction is not clear, a known C
N^-+ O_Two+ Au → Au⁺O by the same mechanism as the reaction of_TwoExistence
SO in the presence_Three ^2-Good dissolution of Au
It is thought that it can be done. In addition, the base is copper.
In this case, the Cu melts out into the plating bath and Au⁺+
Cu⁺→ Au ↓ + Cu²⁺Reaction produces gold particles
However, in this case, Cu
⁺Is O_TwoIs harmless by being oxidized by Cu²⁺When
It is thought to be. The above Au⁺+ Cu⁺
→ Au ↓ + Cu²⁺It is unknown whether the reaction will progress
However, it was found that Au was precipitated where Cu was eluted.
Confirmed experimentally.

In this case, the introduction of air can be performed by blowing air into the plating bath. Even if air is introduced by employing air stirring as the stirring operation of the plating bath, the stirring operation is also performed. Alternatively, air may be blown. Further, it is preferable that the blown air does not directly hit the plating surface. Therefore, it is preferable to provide an air partition plate in the plating bath. When air directly hits the plating surface, the liquid flow increases and the liquid flow becomes uneven at the plating interface, which may cause inconveniences such as uneven color of the plating film, thickness variation, and reduced plating speed.

The electroless gold plating bath of the present invention can generally obtain a plating rate of about 0.1 to 5 μm / Hr, and a plating film is formed on a gold plate (gold plating film). It is considered to have autocatalytic properties, and by further replenishing the spent gold source and reducing agent, etc., about 5 MTO
(Turn) can be used.

[0034]

EXAMPLES Hereinafter, the present invention will be described specifically with reference to Reference Examples, Examples and Comparative Examples, but the present invention is not limited to the following Examples. [Reference Example 1] A 7 µm electroless Ni / P plating film was formed on a copper pattern partially printed with a permanent resist, and 0.1 µm was formed thereon.
Was subjected to electroless gold plating under the following plating conditions using a plating bath having the following composition. Plating speed is 0.6μm
/ Hr.

Plating bath composition Gold sodium sulfite 3 g / L sodium monosulfide ion 70 g / L Ethylenediaminetetra (disodium methylenephosphonate) 110 g / L Hydrazine hydrate 10 g / L pH 7 Plating conditions Liquid temperature 60 ° C. Volume 500mL liquid stirring Air stirring Plating time 60 minutes

When the test substrate after the plating treatment was examined, the appearance of the obtained gold plating film had a beautiful tone of lemon yellow, and no corrosion or plating spread of the substrate was observed. Also, the gold wire bonding property and the die bonding property were good.

Example 1 In the same plating bath as in Reference Example 1, Na 2 g / sulfur thiosulfate was further added.
L, phenylenediamine 2 g / L, EDTA 8 g / L,
35 g / L of monohydrogen citrate dipotassium salt was added, and the same test substrate was subjected to electroless gold plating in the same manner as in Reference Example 1. The plating rate was 0.8 μm / Hr.

When the test substrate after the plating treatment was examined, the appearance of the obtained gold plating film had a beautiful lemon yellow color tone, and no corrosion or plating spread of the substrate was observed. Also, the gold wire bonding property and the die bonding property were good.

Example 2 In the same plating bath as in Example 1, Gohsenol NL-05 was added.
Was added at 0.5 mg / L, and the same test substrate was subjected to electroless gold plating in the same manner as in Example 1. The plating rate was 0.6 μm / Hr.

When the test substrate after the plating treatment was examined, the appearance of the obtained gold plating film had a beautiful lemon yellow color tone, and no corrosion or plating spread of the substrate was observed. The gold wire bonding property and the die bonding property were also good.

Example 3 The pattern on the metallized aluminum nitride substrate was 1
μm electroless Ni / B plating film is formed, and
An electroless Ni / P plating film having a thickness of 0.1 μm was formed thereon, and a 0.1 μm replacement gold plating film was further formed thereon. Plating was applied.

The obtained gold plating film had a beautiful color tone of lemon yellow, and the plating spread was not observed at all. Also, the gold wire bonding property and the die bonding property were good.

[0043]

[0044]

[0045]

[0046]

[0047]

[0048]

Example 4 In the same plating bath as in Reference Example 1, 4 g of Na thiosulfate /
L, citric acid 3Na 35 g / L, anthranilic acid 30 g
/ L and electroless gold plating was performed on the same test substrate as in Reference Example 1. Plating speed is 0.5 μm /
Hr.

Example 5 The same plating bath as in Reference Example 1 was further added with 2 g of Na thiosulfate /
L, glucono-δ-lactone 10 g / L, metanilic acid 3
0 g / L was added, and the same test substrate was subjected to electroless gold plating in the same manner as in Reference Example 1. Plating speed is 0.6μ
m / Hr.

When the test substrates after plating treatment obtained in Examples 4 and 5 were examined, the appearance of each of the gold plating films obtained had a beautiful color of lemon yellow, corrosion of the substrates and plating spread. Was not seen. Also, the gold wire bonding property and the die bonding property were good.

Example 6 In place of hydrazine hydrate in the plating bath of Example 1, 30 g / L of ascorbic acid was added, 20 ppm of polyvinylpyrrolidone K-30 and 100 p of benzotriazole.
pm and 2 ppm of thallium sulfate, and the pH was 7.5.
The same plating bath as in Example 1 was used, except that
Still at 0 ° C. without liquid agitation and on the same substrate as in Reference Example 4.
Plating was performed for 0 minutes. Plating speed is 1.2μm / Hr
Met.

When the test substrates obtained in Example 6 after the plating treatment were examined, the appearance of each of the obtained gold plating films had a beautiful lemon yellow color tone, and the corrosion and plating spread of the substrate were observed. I couldn't. Also, the gold wire bonding property and the die bonding property were good.

Comparative Example 1 110 g of EDTA-2Na was used instead of the organic phosphonic acid.
Using the same plating bath as in Reference Example 1 except that L was added, the same test substrate was subjected to electroless gold plating under the same conditions. The plating rate was 0.5 μm / Hr, which was slightly inferior to Reference Example 1.

The obtained gold-plated film had a slightly reddish appearance and spread of the plating, and was poor in commercial value. The wire bonding property was almost the same as the film of Reference Example 1.

Comparative Example 2 110 g / EDTA-2Na was used instead of the organic phosphonic acid.
Using the same plating bath as in Example 1 except that L was added, the same test substrate was subjected to electroless gold plating under the same conditions.

The obtained gold-plated film had a slightly reddish appearance and spread of plating, and was poor in commercial value. The wire bonding property was almost the same as that of the film of Example 1.

[0058]

As described above, according to the electroless gold plating bath of the present invention, it has a beautiful color of lemon yellow,
A gold plating film having excellent wire bonding properties and die bonding properties can be reliably formed without attacking the resist of a printed wiring board or the aluminum nitride material or glass material of an IC package, and without causing plating spread. .

Continuation of the front page (72) Inventor Toru Murakami 1-5-1, Exit Hirakata, Osaka Pref. Uemura Industry Co., Ltd. Central Research Laboratory (56) References JP-A-3-294484 (JP, A) JP-A-63- 137178 (JP, A) JP-A-52-111835 (JP, A) JP-A-51-126932 (JP, A) JP-A-3-215677 (JP, A) JP-A-4-350172 (JP, A) JP-A-1-117882 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C23C 18/44

Claims (3)

(57) [Claims] 1. A composition comprising a gold sulfite, a sulfite, and one or more reducing agents selected from the group consisting of hydrazines, ascorbic acid, ascorbate, trimethylamine borane and dimethylamine borane. In the resulting electroless gold plating bath, an organic phosphonic acid or a salt thereof is added, and p-methylaminophenol, phenylenediamine, aminophenol, aminobenzoic acid, metanilic acid or anthranilic acid is added as a nitrogen-containing compound. An electroless gold plating bath having a pH of 6 to 11. 2. The electroless device according to claim 1, wherein the organic phosphonic acid is selected from 1-hydroxyethylidene-1,1-diphosphonic acid, ethylenediaminetetra (methylenephosphonic acid) and diethylenetriaminepenta (methylenephosphonic acid). Gold plating bath. 3. One or two of a nonionic surfactant, a nonionic polymer, a thiosulfate and an oxycarboxylic acid.
The electroless gold plating bath according to claim 1, wherein at least one species is added.