CN106399983B

CN106399983B - Cyanide-free electroless gold plating bath and electroless gold plating method

Info

Publication number: CN106399983B
Application number: CN201610584745.6A
Authority: CN
Inventors: 柴田利明; 田中小百合; 小田幸典
Original assignee: C Uyemura and Co Ltd
Current assignee: C Uyemura and Co Ltd
Priority date: 2015-07-28
Filing date: 2016-07-22
Publication date: 2020-07-21
Anticipated expiration: 2036-07-22
Also published as: JP6594077B2; TWI688672B; TW201715081A; KR102502530B1; CN106399983A; KR20170013814A; JP2017025399A

Abstract

The present invention provides a gold plating bath that can be used for gold plating in both an ENIG process and an ENEPIG process. The cyanide-free electroless gold plating bath is an electroless gold plating bath which contains a water-soluble gold salt, a reducing agent and a complexing agent and does not contain cyanide, and is characterized in that the reducing agent contains formic acid or a salt thereof and hydrazine.

Description

Cyanide-free electroless gold plating bath and electroless gold plating method

Technical Field

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

Background

Conventionally, in a mounting process of a printed circuit board or an electronic component, as a final surface treatment, ENIG (Electroless Nickel Immersion Gold) process of forming displacement type Gold plating on Electroless Nickel plating has been known. This procedure can be used in welding. Further, the ENIG process may be followed by thick gold plating to be used for wire bonding.

On the other hand, the final surface treatment described above is also used in the ENEPIG (Electroless nickel Palladium Immersion Gold) step of forming Gold plating by Electroless Palladium plating on a substrate by Electroless nickel plating. This procedure is particularly suitable for use in lead-free soldering. And is also applicable to wire bonding.

The ENIG step and the ENEPIG step may be selected according to the intended use of the object to be plated, and both steps are finally plated with gold. However, in the case of forming the gold plating, nickel having a large ionization tendency (low oxidation-reduction potential) is used as a substrate, and palladium having a small ionization tendency (high oxidation-reduction potential) is used as a substrate. Thus, gold plating baths suitable for various steps have been used.

Further, while cyanide-containing gold plating baths have been widely used conventionally as the gold plating bath, it is necessary to find non-cyanide type gold plating baths in consideration of the toxicity of cyanide.

For example, as a non-cyanide type gold plating bath used in the ENEPIG process, patent document 1 discloses that when an electroless nickel plating film, an electroless palladium plating film, and an electroless gold plating film are sequentially formed on a conductor portion of a printed wiring board, a gold plating solution used for forming the electroless gold plating film is composed of an aqueous solution containing a water-soluble gold compound, a reducing agent and a complexing agent, and the reducing agent is at least one selected from formaldehyde hydrogensulfite, rongalite, and hydrazine. Patent document 2 discloses a plating solution containing a non-cyanide gold sulfite salt, a thiosulfate salt, a water-soluble polyaminocarboxylic acid, a benzotriazole compound, a sulfur-containing amino acid compound and hydroquinone at a predetermined concentration as an electroless gold plating solution capable of directly depositing a gold film on an electroless palladium plating film by an autocatalytic reduction reaction.

However, depending on the application of the object to be plated, it is not practical from the viewpoints of operability and economy because it takes a number of steps and costs to prepare and replace the plating bath for each step. Therefore, a gold plating bath that can be used for forming gold plating in both the ENIG step and the ENEPIG step is required.

Further, the non-cyanide gold plating bath tends to be more susceptible to a decrease in plating bath stability and plating reactivity than cyanide gold plating baths. Therefore, the non-cyanide gold plating bath is expected to have preferable characteristics of both plating bath stability and plating reactivity.

Documents of the prior art

Patent document

Patent document 1: japanese patent No. 5526440

Patent document 2: japanese unexamined patent application publication No. 2010-180467

Disclosure of Invention

The present invention has been made in view of the above-mentioned problems, and an object thereof is to provide a cyanide-free electroless gold plating bath that can be used in both the ENIG step and the ENEPIG step, and an electroless gold plating method using the same.

The cyanide-free electroless gold plating bath of the present invention, which solves the above-mentioned problems, is an electroless gold plating bath containing a water-soluble gold salt, a reducing agent and a complexing agent, but not containing cyanide, and is characterized in that the reducing agent contains formic acid or a salt thereof, and hydrazines.

The cyanide-free electroless gold plating bath preferably further contains a compound having a nitro group.

The present invention also includes an electroless gold plating method characterized by performing electroless gold plating on the surface of an object to be plated using the above cyanide-free electroless gold plating bath. In the electroless gold plating method, the surface of the object to be plated may be nickel or a nickel alloy, that is, an ENIG step, or the surface of the object to be plated may be palladium or a palladium alloy, that is, an ENEPIG step.

According to the present invention, a cyanide-free electroless gold plating bath that can be used in either the ENIG step or the ENEPIG step can be provided. Specifically, in the ENIG step, when gold plating is formed on nickel plating, corrosion of the nickel plating is suppressed. In either the ENIG step or the ENEPIG step, the gold deposition reactivity is improved, and the gold plating can be made thicker. For example, in the ENIG step, the deposition of 0.07 μm or more can be obtained in about 20 minutes on nickel plating, and in the ENEPIG step, the deposition of 0.05 μm or more can be obtained in about 30 minutes on palladium plating.

Drawings

FIGS. 1 and 2 are SEM (scanning Electron microscope) observation photographs showing the presence or absence of corrosion of the nickel-plated surface in examples.

Detailed Description

The inventors of the present invention have conducted intensive studies in order to solve the above-mentioned technical problems. As a result, the present inventors have found that, in the case of a cyanide-free electroless gold plating bath of the substitution reduction type containing formic acid or a salt thereof and hydrazines as reducing agents, excessive corrosion such as nickel plating of the substrate does not occur, the precipitation reactivity of gold is improved, and the bath can be used in both the ENIG step and the ENEPIG step, and have completed the present invention. Hereinafter, the cyanide-free electroless gold plating bath of the present invention is also referred to as an "electroless gold plating bath" or a "gold plating bath". In the following, each compound contained in the cyanide-free electroless gold plating bath of the present invention will be described

(A) Hydrazines

Hydrazines are compounds that are particularly advantageous for improving the plating deposition on palladium and promote the formation of gold plating on palladium in the ENEPIG process. Furthermore, hydrazines also contribute to maintaining good plating appearance, and as a result, contribute to ensuring good solderability and wire bonding bondability (W/B bondability). On the other hand, hydrazines promote the progress of the substitution reaction on the nickel plating more than necessary in the ENIG process, resulting in excessive corrosion of the nickel plating. However, as described later, the excessive corrosion of the nickel plating can be suppressed by using formic acid or a salt thereof in combination.

As the hydrazine, hydrazine hydrate such as hydrazine monohydrate, hydrazine salts such as hydrazine carbonate, hydrazine sulfate, dihydrazine sulfate and hydrazine hydrochloride, organic derivatives of hydrazine such as pyrazole, triazole and hydrazide, and the like can be used. As the pyrazole, a pyrazole derivative such as 3, 5-dimethylpyrazole or 3-methyl-5-pyrazolone can be used in addition to pyrazole. As the triazole, 4-amino-1, 2, 4-triazole, 1,2, 3-triazole and the like can be used. As the hydrazide, adipic acid dihydrazide, maleic acid hydrazide, carbohydrazide and the like can be used. Hydrazine hydrate such as hydrazine monohydrate and hydrazine sulfate are preferable. These compounds can be used alone or in combination of 2 or more.

The total concentration of the above hydrazines is preferably 0.1 to 5 g/L, more preferably 0.3 to 3 g/L.

(B) Formic acid or its salt

Formic acid or a salt thereof has an effect of suppressing the excessive substitution reaction by the hydrazine. Hereinafter, "formic acid or a salt thereof" is also collectively referred to as "formic acid". In particular, excessive corrosion of the Ni film as a base can be suppressed at the time of gold plating in the ENIG process. On the other hand, when only a formic acid is used without using the hydrazine compound, the reactivity of gold precipitation tends to be lowered particularly in the ENEPIG step. Specifically, the gold deposition reactivity on the palladium plating as the base is poor, and it is difficult to secure the gold plating film thickness. Therefore, it is necessary to use the hydrazine in combination. By using hydrazine and formic acid in combination, excessive corrosion of the above nickel plating is suppressed, and weldability and W/B weldability are also facilitated.

Examples of the salt of formic acid include alkali metal salts of formic acid such as potassium formate and sodium formate; alkaline earth metal salts of formic acid such as magnesium formate and calcium formate; ammonium salts of formic acid, quaternary ammonium salts, amine salts containing primary to tertiary amines, and the like. In the present invention, formic acid or a salt thereof may be used alone or in combination of 2 or more.

The total concentration of the above-mentioned formic acids is preferably in the range of 1 to 100 g/L, and in order to fully exert the above-mentioned effects, it is preferably 1 g/L or more, more preferably 5 g/L or more, and still more preferably 10 g/L or more, and on the other hand, the plating bath tends to become unstable when contained in excess, and is preferably 100 g/L or less as described above.

That is, in the present invention, hydrazine and formic acid are used together as a reducing agent, and in the gold plating treatment in the ENIG step, the corrosion (substitution reaction) of nickel by hydrazine is suppressed by the formic acid, and the corrosion of nickel plating as a gold plating base can be suppressed. On the other hand, in the gold plating treatment in the ENEPIG process, the hydrazine compounds are more reactive to palladium plating, and the formation of gold plating is promoted than in the case of using formic acid alone, thereby making it possible to increase the thickness of gold plating. This is due to the fact that the reduction reaction is promoted.

The gold plating bath of the present invention must contain a water-soluble gold salt and a complexing agent and not contain cyanogen, in addition to the above hydrazines and formic acids. Further, as described below, reducing agents other than hydrazines and formic acids may be used. The following description will proceed in order from the water-soluble gold salt.

The electroless gold plating bath of the present invention contains a water-soluble gold salt as a gold source, the water-soluble gold salt is non-cyanide, and specifically, there are sulfite, thiosulfate, thiocyanate, sulfate, nitrate, methanesulfonate, tetramine complex, chloride, bromide, iodide, hydroxide, oxide, and the like of gold, these compounds can be used alone or in combination of 2 or more, the total concentration of the water-soluble gold salt in the plating bath is preferably 0.3 to 5 g/L, particularly preferably 0.5 to 4 g/L, and when less than 0.3 g/L, the deposition rate may be reduced, and when more than 5 g/L, the stability may be reduced, the effect of the addition amount may not be substantially changed, and the cost may be increased.

The electroless gold plating bath of the present invention may contain, as the reducing agent, the following reducing agents in addition to the above hydrazines and formic acids. That is, ascorbic acid such as ascorbic acid and erythorbic acid (erythorbic acid) or a salt thereof (sodium salt, potassium salt, ammonium salt, etc.); hydroquinone, methyl hydroquinone, or the like, or derivatives thereof; pyrogallol or its derivatives such as pyrogallol, pyrogallol monomethyl ether, pyrogallol-4-formic acid, pyrogallol-4, 6-dicarboxylic acid, and gallic acid. These compounds can be used alone or in combination of 2 or more. In the present invention, the use of the hydrazine and the formic acid is essential as the reducing agent, and for example, in example No.10 described later, it is shown that even when ascorbic acid, which is a reducing agent other than the hydrazine and the formic acid, is used in combination with formic acid, desired characteristics cannot be obtained.

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

The electroless gold plating bath of the present invention contains a complexing agent. The complexing agent is a complexing agent having a complexing action for dissolving out a metal (e.g., nickel, palladium, etc.), and is preferably a complexing agent having a complexing action for gold. Preferred examples of the complexing agent having a complexing action for dissolving out the metal include hydroxycarboxylic acids such as glycolic acid, diglycolic acid, lactic acid, malic acid, citric acid, gluconic acid, and glucoheptonic acid (ヘプトグルコン acid) and salts thereof (sodium salt, potassium salt, ammonium salt, etc.); aminocarboxylic acids such as glycine, aminodicarboxylic acid, aminotriacetic acid, EDTA, hydroxyethylethylenediaminetriacetic acid, diethylenetriaminepentaacetic acid, and polyaminocarboxylic acids, and salts thereof (sodium salt, potassium salt, ammonium salt, hydrochloride salt, sulfate salt, and the like); phosphorous acid chelating agents such as HEDP (hydroxyethane-1, 1-diphosphonic acid), aminotrimethylsulfonic acid, and ethylenediaminetetramethylsulfonic acid, and salts thereof (sodium salt, potassium salt, ammonium salt, hydrochloride, sulfate, etc.); amine chelating agents such as ethylenediamine, diethylenetriamine, and triethylenetetramine, and salts thereof (such as hydrochloride and sulfate). These compounds can be used alone or in combination of 2 or more.

Further, as a preferred complexing agent having a complexing action of gold, sodium sulfite, potassium sulfite, ammonium sulfite, sodium bisulfite, potassium bisulfite, ammonium bisulfite, sodium metabisulfite, potassium metabisulfite, ammonium metabisulfite, sodium thiosulfate, potassium thiosulfate, ammonium thiosulfate, a hydantoin compound, an imide compound, and the like can be given. These compounds can be used alone or in combination of 2 or more. More preferably, sodium sulfite, ammonium sulfite, or the like is used.

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

The electroless gold plating bath of the present invention preferably further contains a compound having a nitro group. By containing the compound having a nitro group, the plating reactivity, that is, the gold deposition reactivity is not impaired even if cyanogen is not contained, and the plating bath stability can be sufficiently ensured. The mechanism of this action is thought to be that the nitro group captures and stabilizes gold. In contrast, no stabilizing effect is shown in the case of, for example, catechol or benzoic acid which does not contain a nitro group.

Examples of the compound having a nitro group include aromatic compounds having a nitro group. Examples of the aromatic compound having a nitro group include nitrobenzene; aromatic compounds having a nitro group and a hydroxyl group such as nitrophenol and 4-nitrocatechol; aromatic compounds having a nitro group and an alkyl group such as nitrotoluene, nitroxylene, and nitrostyrene; aromatic compounds having a nitro group and an amine group such as nitroaniline and 4-nitro-1, 2-phenylenediamine; and aromatic compounds having a nitro group and a sulfur-containing group, such as nitrobenzene sulfonic acid, e.g., nitrobenzene thiol and 2, 4-dinitrobenzene sulfonic acid. Further, examples of nitrobenzoic acids having a nitro group and a carboxyl group include 2-nitrobenzoic acid, 3, 5-dinitrobenzoic acid, 3, 4-dinitrobenzoic acid, and 5-amino-2-nitrobenzoic acid having a further amino group. Further, there may be mentioned aromatic compounds having a nitro group, a halogen group, an ester group, an ether group, a carbonyl group, an aldehyde group, etc. As the salt of the aromatic compound having a nitro group, an ammonium salt, a sodium salt, a potassium salt, or the like can be used.

For example, in the case of the above nitrobenzoic acid, the nitro group is preferably used because the effect of stability is improved when the nitro group is located at the ortho position to the carboxyl group. That is, the effect of stability is in the order of magnitude of 2-nitrobenzoic acid > 3-nitrobenzoic acid > 4-nitrobenzoic acid.

As the compound having a nitro group, an aliphatic compound having a nitro group may be used in addition to the aromatic compound having a nitro group.

More preferred are compounds having both a nitro group and an electron-donating group, particularly aromatic compounds having both a nitro group and an electron-donating group. The effect of nitro group stability is improved when electron donating groups are present. In the case where the nitro group is two adjacent nitro groups, the two nitro groups are formed in a clip shape (トラップする shape), whereby the effect of stability is enhanced. Examples of the electron donating group include a hydroxyl group, an alkyl group, an amino group, a sulfur-containing group, a carboxyl group, an ester group, a halogen group, and an ether group. Preferably one or more of the above.

The total concentration of the compounds having a nitro group is preferably in the range of, for example, 0.0010 to 5 g/L, and when the total concentration is 0.0010 g/L or less, the above-described effects are hardly obtained, the total concentration is more preferably 0.005 g/L or more, and still more preferably 0.010 g/L or more, and on the other hand, when the concentration of the compounds having a nitro group is too high, the surface of the nickel plating as the base becomes susceptible to corrosion, and the total concentration is preferably 5 g/L or less, more preferably 4 g/L or less, and still more preferably 3 g/L or less.

The electroless gold plating bath of the present invention preferably has a pH of 5 to 10. If the concentration is less than this range, the deposition rate of gold tends to decrease, while if the concentration exceeds the above range, the plating bath tends to become unstable. The pH is more preferably 6 to 9.

The electroless gold plating bath of the present invention may contain a known pH adjuster, a pH buffer, and other additives as appropriate within a range not affecting the object of the present invention. Examples of the pH adjuster include acids such as hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, and carboxylic acid, and examples of the bases include sodium hydroxide, potassium hydroxide, and aqueous ammonia. Examples of the pH buffer include carboxylic acids such as citric acid, tartaric acid, malic acid, and phthalic acid; phosphoric acids such as orthophosphoric acid, phosphorous acid, hypophosphorous acid and pyrophosphoric acid, and phosphates such as potassium salts, sodium salts and ammonium salts thereof; boric acid, tetraboric acid, and the like. Examples of the metal cation masking agent include azoles such as benzotriazole and methylbenzotriazole, phenanthroline, bipyridine, and salicylate. Examples of the auxiliary complexing agent include aminocarboxylic acids such as EDTA and EDTMP, ammonium salts, and chlorides. Examples of the stabilizer include sulfur-containing heterocyclic compounds (e.g., 2-mercaptobenzothiazole and 2-mercaptobenzoxazole), nitrogen-containing heterocyclic compounds (e.g., benzotriazole and N-hydroxybenzotriazole), and the like.

The electroless gold plating bath of the present invention may further contain one or more of thallium compound, arsenic compound and lead compound, which have the effect of increasing the gold plating rate and acting as a crystal modifier, and specifically, the compound may be a carbonate, acetate, nitrate, sulfate, hydrochloride or the like of the metal (arsenic, thallium or lead) constituting the compound, and the concentration of the crystal modifier in the gold plating bath is, for example, preferably 0.1 to 100 mg/L in total, more preferably 0.2 to 50 mg/L in total, and still more preferably 0.2 to 20 mg/L in total, in terms of metal concentration.

The invention also provides a method for electroless gold plating using the cyanide-free electroless gold plating bath. The plated article to be plated with gold includes nickel or a nickel alloy on the surface thereof. In the ENIG step, the surface of the object to be plated may be electroless nickel plating or electroless nickel alloy plating (hereinafter referred to as "electroless nickel plating system"). Examples of the nickel alloy include a nickel-phosphorus alloy and a nickel-boron alloy.

The surface of the plated article to be plated with gold may be palladium or a palladium alloy. In the ENEPIG process, the surface of the object to be plated may be electroless palladium plating or electroless palladium plating alloy (hereinafter referred to as "electroless palladium plating system"). The palladium alloy may be a palladium-phosphorus alloy.

In the ENIG step, for example, an electroless nickel plating system is formed on Al or an Al-based alloy, Cu or a Cu-based alloy constituting the electrode, and then electroless gold plating is formed thereon, and in the ENEPIG step, for example, an electroless nickel plating system is formed on Al or an Al-based alloy, Cu or a Cu-based alloy constituting the electrode, then an electroless palladium plating system is formed, and then electroless gold plating is formed thereon.

In either of the ENIG step and the ENEPIG step, electroless gold plating may be performed under ordinary conditions except for using the cyanide-free electroless gold plating bath of the present invention. For example, the electroless gold plating bath of the present invention is contacted for about 3 to 20 minutes. The contact may be performed by a conventionally known method such as dipping. The electroless gold plating bath is preferably used at a temperature of 40 to 90 ℃. If the amount is less than the above range, the deposition rate may be decreased, while if the amount is more than the above range, the plating bath may be unstable. The above-mentioned use temperature is preferably 50 to 80 ℃.

The electroless gold plating bath and the electroless gold plating method using the electroless gold plating bath according to the present invention are suitably used for performing gold plating treatment on a printed circuit board, a ceramic substrate, a semiconductor substrate, a wiring circuit mounting portion or a terminal portion of an electronic component such as an IC package. The method is particularly suitable for UBM (under Barrier Metal) forming technology for welding and wire bonding (W/B) of Al electrodes or Cu electrodes on wafers. By using the gold plating bath of the present invention, formation of electroless gold plating as part of the UBM formation technique can be stably performed, and as a result, stable film characteristics can be realized.

This application claims 2015-7-28 application of japanese patent application No. 2015-148523 as a basis for priority. The entire contents of the specification of Japanese patent application No. 2015-148523, applied on 7/28/2015, are incorporated herein by reference.

Examples

The present invention will be described specifically by way of examples, but the present invention is not limited to the following examples, and can be modified and implemented appropriately within the spirit and scope of the present invention, and all of them are included in the technical scope of the present invention.

[ measurement of film thickness for gold plating, confirmation of the presence or absence of nickel plating corrosion, and preparation of sample for appearance observation of gold plating ]

[ samples of the ENIG procedure ]

The samples in the ENIG step used for the measurement of the gold plating film thickness were obtained by the following method. That is, a TEG wafer of Al — Cu as an Al-based alloy as an electrode was prepared, nickel plating having a thickness of 5.0 μm was formed on the electrode by electroless plating using an electroless nickel plating bath (NPR-18, manufactured by seikura industries), and electroless gold plating was then performed using an electroless gold plating bath shown in table 1. This sample is hereinafter referred to as "sample I of the ENIG process".

[ samples of the ENEPIG procedure ]

The samples of the ENEPIG process used for the measurement of the gold plating film thickness were obtained by the following method. Specifically, a TEG wafer of Al — Cu as an Al-based alloy for an electrode was prepared, nickel plating having a thickness of 5.0 μm was formed on the electrode by electroless plating using an electroless nickel plating bath (NPR-18, manufactured by seikura industries), palladium plating having a thickness of 0.05 μm was formed on the nickel plating by electroless plating using an electroless palladium plating bath (TFP-30, manufactured by seikura industries), and electroless gold plating was further performed using an electroless gold plating bath shown in table 1. This sample is hereinafter referred to as "sample I of the ENEPIG process".

Further conditions of electroless gold plating performed in each of the samples of ENIG and ENEPIG processes are as follows, that is, a gold sodium sulfite solution (Au concentration 100 g/L) was used as a gold source in an electroless gold plating bath, and the Au concentration in the electroless gold plating bath is shown in table 1 below, and thallium carbonate was used as a thallium (Tl) compound, and the Tl concentration in the electroless gold plating bath is shown in table 1 below, the temperature of the electroless gold plating bath was 75 ℃, immersion in the electroless gold plating bath was performed for 20 minutes in the case of sample I of the ENIG process, and immersion in the sample I of the ENEPIG process was performed for 30 minutes to form gold plating, and immersion in the samples I of the ENEPIG process of nos. 1,2,4 and 6 in table 1 below was performed for 20 minutes because a film thickness of gold plating can be secured at an early stage.

[ measurement of gold plating film thickness in ENIG Process or ENEPIG Process ]

The film thickness of the gold plating formed on the sample I in the ENIG step and the sample I in the ENEPIG step was measured by a fluorescent X-ray film thickness meter. In particular, a case where the thickness of the gold plating on the palladium plating in the ENEPIG process is 0.05 μm or more was evaluated as a gold plating bath applicable to the ENEPIG process.

[ Observation of the Presence or absence of Nickel plating Corrosion by SEM ]

The nickel-plated surface exposed by removing the gold-plating stripping solution of sample I in the ENIG step was observed with an SEM at a magnification of 5000 times, and the presence or absence of corrosion marks was confirmed. Then, the sample in which the corrosion mark was confirmed was evaluated as "having" the nickel-plating corrosion ", and the sample in which the corrosion mark was not confirmed was evaluated as" having "the nickel-plating corrosion". SEM observation photographs are shown in fig. 1 and 2 as references. Fig. 1 is a photograph of an example of the present invention in which no nickel-plated corrosion mark is observed, and fig. 2 is a photograph of a comparative example in which a nickel-plated corrosion mark is observed.

[ appearance Observation of gold plating ]

The gold-plated surfaces of the sample I in the ENIG step and the sample I in the ENEPIG step were visually observed. Then, the sample exhibiting the appearance of the plating layer of uniform gold color was evaluated as "good", and the appearance of the plating layer changed not to gold color but to red color was evaluated as "bad".

[ preparation of sample for evaluation of weldability and wire bonding (W/B) ]

[ samples of the ENIG procedure ]

Samples of the ENIG step used for evaluation of solderability and W/B Properties were prepared as BGA substrates (pad diameter)

) On this substrate, nickel plating having a thickness of 5.0 μm was formed by electroless plating using an electroless nickel plating bath (NPR-18, manufactured by NIPPON CORPORATION, KOKAI) in the same manner as in sample I of the ENIG step, and then electroless gold plating was performed using the electroless gold plating bath shown in Table 1. This sample is hereinafter referred to as "sample II of the ENIG step".

[ samples of the ENEPIG procedure ]

Samples of ENEPIG process used for evaluation of solderability and W/B performance were prepared by preparing a BGA substrate (pad diameter. phi.0.5 mm) manufactured by Korea Kabushiki Kaisha, forming a nickel plating having a thickness of 5.0 μm on the substrate by electroless plating using an electroless nickel plating bath (NPR-18 manufactured by Korea Kabushiki Kaisha) in the same manner as in sample I of the ENEPIG process, forming a palladium plating having a thickness of 0.05 μm on the nickel plating by electroless plating using an electroless palladium plating bath (TFP-30 manufactured by Korea Kabushiki Kaisha), and further performing electroless gold plating using the electroless gold plating bath shown in Table 1. This sample is hereinafter referred to as "sample II of the ENEPIG process".

[ evaluation of weldability ]

Using the sample II of the ENIG process and the sample II of the ENEPIG process, each of the conditions was evaluated to 20 minutes using the bondtester tools 4000 manufactured by Dage corporation, specifically, the welding strength was measured sequentially under 4 conditions × 20 in total of 80 minutes in each No. of table 1,

the following reflux number was 1 time using sample II from the ENIG step;

the following reflux number was 1 time using sample II from the ENEPIG step;

the following reflux number was 5 times in sample II obtained by ENIG step; and

the number of times of refluxing was 5 times as described below for sample II obtained in the ENEPIG step.

As the weld strength, the weld breakage rate in the breakage mode was obtained. The conditions for measuring the weld formation and the weld strength are as follows. In the present example, a case where the weld breakage rate was 85% or more was evaluated as "good" weldability, and a case where the weld breakage rate was less than 85% was evaluated as "poor" weldability.

[ conditions for solder formation and solder Strength measurement ]

The measurement method comprises the following steps: solder ball pull test

Solder ball: phi 0.6mm Sn-3.0Ag-0.5Cu made of thousand metal

The reflux device is TMR-15-22L H manufactured by rural manufacturing

Refluxing conditions: top 240 ℃ C

And (3) refluxing environment: air (a)

The reflux times are as follows: 1 or 5 times

Flask: thousands of Metal 529D-1(RMA type)

Testing speed: 5000 μm/sec

Burn-in after solder mounting (half-Tian \12510; \12454 ント rear エージング): 1 hour

[ evaluation of wire bonding (W/B) Properties ]

Specifically, in each of nos. in table 1, the wire bonding strength (W/B strength) was measured sequentially under 2 conditions × ═ 40 minutes in total under the case of using sample II in the ENIG process and the sample II in the ENEPIG process, and the average value W/B average strength and standard deviation were calculated, and further, the coefficient of variation (standard deviation ÷ average value ×) was calculated based on the measured results, the conditions for forming the wire bonding and the evaluation of the wire bondability were as follows, and the case where the average strength W/B was 8gf or more and the coefficient of variation was 15% or less was evaluated as "good", and the case where at least one of the average strength W/B and the coefficient of variation was outside the above-described range was evaluated as "poor wire bondability".

[ conditions for wire-bonding formation and evaluation of wire-bonding Property ]

Capillary tube: b1014-51-18-12(PECO)

Leading wires: 1Mil-Gold

Stage temperature: 150 ℃ C

Ultrasonic wave (mW): 250(1st), 250(2nd)

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

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

Step size (length of first to second): 0.700mm

The measurement method comprises the following steps: pull wire test

Testing speed: 170 μm/sec

In the present example, when both the weldability and the wire bondability were "good", the weldability and the W/B property were evaluated as "good", and when one of the weldability and the wire bondability was "poor", the weldability and the W/B property were evaluated as "poor".

[ evaluation of plating bath stability ]

The electroless gold plating baths of the respective plating bath compositions shown in table 1 were left at a temperature of 70 ℃ for one month to evaluate the stability of the plating baths. The electroless gold plating bath which did not decompose even after one month was evaluated as "stable", and the electroless gold plating bath which did not decompose after one month was evaluated as "unstable".

The results are shown in Table 1.

TABLE 1

In addition, in these examples, soldering and wire bonding can be performed well, and from the comparison of Nos. 1-3 and 4, a gold plating bath further containing a compound having a nitro group is preferable from the viewpoint of ensuring sufficient plating bath stability, and from the comparison of Nos. 3 and 5, it is preferable that the content of formic acid is not more than the recommended upper limit (not more than 100 g/L).

On the other hand, Nos. 7 to 10 did not contain any of the specified formic acids and hydrazines, and had defects. Specifically, No.7 and No.8, since they do not contain formic acid, corrosion by nickel plating occurs. As a result, weldability and W/B property are deteriorated. No.9 shows an example in which no hydrazine is contained. In this example, the gold plating film thickness in the ENEPIG process is reduced. Further, No.10 shows an example in which ascorbic acid is used in place of hydrazine as a reducing agent, and formic acid is used in combination. In this example, the gold plating film thickness in the ENEPIG process is reduced. Further, the appearance of gold plating in Nos. 9 and 10 became red. Such reddening causes poor weldability and poor W/B properties.

Claims

1. A cyanide-free electroless gold plating bath containing a water-soluble gold salt, a reducing agent and a complexing agent, the cyanide-free electroless gold plating bath being cyanide-free, characterized in that the reducing agent contains formic acid or a salt thereof, and hydrazines.

2. The cyanide-free electroless gold plating bath according to claim 1, further containing a compound having a nitro group.

3. The cyanide-free electroless gold plating bath according to claim 1 or 2, wherein the complexing agent is at least one of a hydroxycarboxylic acid or salt thereof, an aminocarboxylic acid or salt thereof, a phosphorous acid-based chelating agent or salt thereof, and an amine-based chelating agent and salt thereof.

4. An electroless gold plating method characterized by using the cyanide-free electroless gold plating bath according to any one of claims 1 to 3 to perform electroless gold plating on the surface of an object to be plated.

5. The electroless gold plating method according to claim 4, wherein the surface of the plated object is nickel or a nickel alloy.

6. The electroless gold plating method according to claim 4, wherein the surface of the plating object is palladium or a palladium alloy.