TW201715081A - Non-cyanide electroless gold plating bath and electroless gold plating method which can be used to perform gold plating in both the ENIG process and the ENEPIG process - Google Patents

Abstract

To provide a gold plating bath, which can be used to perform gold plating in both the ENIG process and the ENEPIG process. A non-cyanide electroless gold plating bath, which is an electroless gold plating bath comprising a water-soluble gold salt, a reducing agent, and a complexing agent, characterized in that the above-mentioned reducing agent comprises formic acid or salts and hydrazines thereof.

Description

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

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

Conventionally, in the mounting step of a printed wiring board or an electronic component, as a final surface treatment, there is a process of forming an ENIG (Electroless Nickel Immersion Gold) replacement gold plating on electroless nickel plating. This process can be used for welding. Moreover, by applying thickening gold after the ENIG process, it can also be used for wire bonding.

On the other hand, an ENEPIG (Electroless Nickel Electroless Palladium Immersion Gold) process in which gold plating is formed on the base electroless nickel plating via electroless palladium plating is also employed as the final surface treatment described above. This process is best suited for lead-free soldering. Also, it is also suitable for wire bonding.

The above ENIG process and the ENEPIG process are selected according to the use of the plated material, and any process is finally applied with gold plating. However, when forming the gold plating, the difference is that the former is made of nickel having a large ionization tendency (low oxidation potential), and the latter is ionized. Palladium having a small tendency (high redox potential) is used as a substrate. Therefore, a gold plating bath corresponding to each process has been used so far.

Further, as the gold plating bath, a cyano gold plating bath has been widely used in the past, but a non-cyanide type gold plating bath is required in view of the toxicity of cyanide.

For example, in the non-cyanide type gold plating bath used in the above-described ENEPIG process, Patent Document 1 discloses that an electroless nickel plating film, an electroless palladium coating film, and an electroless gold plating film are sequentially formed on a conductor portion of a printed wiring board. The gold plating liquid used in the formation of the electroless gold plating film is composed of an aqueous solution containing a water-soluble gold compound, a reducing agent and a crosslinking agent, and the reducing agent is selected from the group consisting of formaldehyde hydrogen sulfite, insurance powder and hydrazine. At least one of the groups. Further, in Patent Document 2, an electroless gold plating solution capable of directly depositing a gold film by a self-catalytic reduction reaction on an electroless palladium film reveals a non-cyanide gold salt of sulfite and sulfurous acid at a specified concentration. A salt, a thiosulfate, a water-soluble polyaminocarboxylic acid, a benzotriazole compound, a sulfur-containing amino acid compound, and a hydroquinone plating solution.

However, in order to prepare a plating bath or an exchange plating bath for each process in accordance with the use of the material to be treated, it takes a number of steps and costs, which is not practical from the viewpoint of workability or economy. Therefore, it is desirable to use a gold-plated bath that can be used in any gold plating process of the ENIG process and the ENEPIG process.

Further, in comparison with the cyano gold plating bath, the non-cyanide type gold plating bath tends to have bath stability or plating reactivity. Therefore, in the non-cyanide type gold plating bath, it is required to have both bath stability and plating reactivity.

[Previous Technical Literature] [Patent Document]

[Patent Document 1] Japanese Invention Patent No. 5526440

[Patent Document 2] Japanese Patent Laid-Open Publication No. 2010-180467

The present invention has been made in view of the above circumstances, and the object thereof is to realize a cyanide-free electroless gold plating bath which can be used in both the ENIG process and the ENEPIG process, and the electroless gold plating using the cyanide-free electroless gold plating bath. method.

The cyanide-free electroless gold plating bath of the present invention which can solve the above problems is a non-cyanide-free electroless gold plating bath comprising a water-soluble gold salt, a reducing agent and a complexing agent, wherein the reducing agent comprises formic acid or Salt and mites.

The aforementioned cyano-free electroless gold plating bath preferably further comprises a compound having a nitro group.

In the present invention, there is also provided an electroless gold plating method characterized in that the surface of the plated material to be treated is subjected to electroless gold plating using the above-mentioned cyanide-free electroless gold plating bath. The electroless gold plating method may be that the surface of the plating object to be treated is nickel or a nickel alloy, that is, an ENIG process, or The surface of the above-mentioned plated material to be treated may be a palladium or palladium alloy, that is, an ENEPIG process.

According to the present invention, a cyanide-free electroless gold plating bath which can be used in both the ENIG process and the ENEPIG process can be provided. Specifically, in the ENIG process, corrosion of nickel plating when gold plating is formed on nickel plating is suppressed. Moreover, in the ENIG process and the ENEPIG process, the precipitation reactivity of gold is increased, and thick film formation of gold plating is possible. For example, in the ENIG process, 0.07 μm or more can be deposited on nickel plating in about 20 minutes, and in the ENEPIG process, 0.05 μm or more can be precipitated on palladium plating in about 30 minutes.

Fig. 1 is a SEM (Scanning Electron Microscope) observation photograph showing the presence or absence of corrosion of the nickel-plated surface in the examples.

[Formation of the Invention]

The present inventors have repeated intensive studies in order to solve the aforementioned problems. As a result, it has been found that a substitution-reduction type non-cyanide electroless gold plating bath containing formic acid or a salt thereof and a hydrazine as a reducing agent does not cause excessive corrosion of nickel plating or the like as a base, and can improve gold precipitation reactivity. Can be used for both ENIG process and ENEPIG process, and complete this issue Bright. Hereinafter, the cyanide-free electroless gold plating bath of the present invention is also referred to as "electroless gold plating bath" or "gold plating bath". Hereinafter, each compound contained in the cyanide-free electroless gold plating bath of the present invention will be described.

(A) mites

The hydrazine type is particularly useful for compounds which have improved plating precipitation on palladium and promotes gold plating on palladium plating in the ENEPIG process. Further, the oxime also contributes to the improvement of the appearance of a good plating, and as a result, a compound which contributes to good weldability or wire bondability (W/B bondability). On the other hand, bismuth is considered to promote the displacement reaction on nickel plating in the ENIG process, which is excessive, and causes excessive corrosion of nickel plating. However, as will be described later, by using formic acid or a salt thereof in combination, excessive corrosion of the nickel plating can be suppressed.

As the above-mentioned anthracene, hydrazine hydrate such as hydrazine; 肼1 hydrate; cesium carbonate, barium sulfate, neutral barium sulfate, barium hydrochloride and the like; pyrazoles, triazoles, anthracenes and the like can be used. Organic derivatives such as hydrazine. As the pyrazole, a pyrazole derivative such as 3,5-dimethylpyrazole or 3-methyl-5-pyrazolium can be used in addition to pyrazole. As the triazole, 4-amino-1,2,4-triazole, 1,2,3-triazole or the like can be used. As the hydrazine, diterpene adipate, strontium maleate, carbaryl or the like can be used. It is preferably hydrazine hydrate or barium sulfate of 肼‧1 hydrate or the like. These may be used alone or in combination of two or more.

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

(B) formic acid or its salt

Formic acid or a salt thereof is considered to have an effect of suppressing an excessive displacement reaction due to the above hydrazine. Hereinafter, "formic acid or a salt thereof" is also collectively referred to as formic acid. In particular, in the case of gold plating in the ENIG process, excessive corrosion of the Ni film as a substrate can be suppressed. On the other hand, when only the formic acid is used in combination with the above-mentioned anthracene, the precipitation reaction property of gold is liable to be lowered particularly in the ENEPIG process. Specifically, gold has poor precipitation reactivity on palladium plating as a substrate, and it is difficult to secure a film thickness of gold plating. Therefore, it must be used in combination with the above-mentioned cockroaches. The use of a combination of an anthracene and a formic acid to suppress excessive corrosion of the nickel plating described above also contributes to the securing of weldability or W/B bondability.

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

The total concentration of the above formic acids is preferably in the range of 1 to 100 g/L. In order to fully exhibit the above 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. On the other hand, if it is contained excessively, the bath tends to be unstable, and as described above, it is preferably 100 g/L or less.

That is, in the present invention, by using a combination of an anthracene and a formic acid as a reducing agent, in the gold plating treatment of the ENIG process, nickel corrosion resistance (displacement reaction) due to hydrazine is suppressed by formic acid, thereby suppressing gold plating. Nickel plating corrosion of the substrate. On the other hand, gold plating on the ENEPIG process Among them, by the high reactivity of the hydrazine on the palladium plating, the formation of gold plating is promoted more than when the formic acid is used alone, and thick film formation of gold plating is possible. This is judged because the reduction reaction is promoted.

In addition to the above-mentioned anthraquinones and formic acid, the gold-plated bath of the present invention requires a non-cyano-free electroless gold plating bath of a water-soluble gold salt and a complexing agent. Further, as described later, a reducing agent other than hydrazines and formic acid can also be used. Hereinafter, the description will be given in order from the above water-soluble gold salt.

First, the electroless gold plating bath of the present invention contains a water-soluble gold salt as a gold source. As described above, the water-soluble gold salt is a cyano group-free, specifically, a sulfite, a thiosulfate, a thiocyanate, a sulfate, a nitrate, a methanesulfonate, a tetraammine complex of gold. , chloride, bromide, iodide, hydroxide, oxide, etc. These may be used alone or in combination of two or more. The total concentration of the water-soluble gold salt in the plating bath is preferably 0.3 to 5 g/L, and particularly preferably 0.5 to 4 g/L, in terms of gold (Au) concentration. When it is less than 0.3 g/L, there is a case where the deposition rate becomes slow. On the other hand, if it exceeds 5 g/L, stability may be lowered, and even if the increment is increased, the effect is hardly changed, and the cost is also high.

The electroless gold plating bath of the present invention may further contain the following reducing agent as the reducing agent, in addition to the above-mentioned anthraquinones and formic acid. That is, ascorbic acid compounds such as ascorbic acid and isoascorbic acid (isovitamin C) or salts thereof (sodium salts, potassium salts, ammonium salts, etc.); hydroquinones such as hydroquinone or methylhydroquinone or derivatives thereof; pyrogallol, Pyrogallol monomethyl ether, pyrogallol-4-carboxylic acid, pyrogallol-4,6-dicarboxylic acid, gallic acid or the like of pyrogallol or a derivative thereof. These may be used alone or in combination of two or more. In the present invention, as The reducing agent is required to be used in combination with the above-mentioned hydrazines and formic acid, and No. 10 of the examples described later shows that even if a reducing agent other than the above-mentioned hydrazines and formic acid, for example, ascorbic acid and formic acid, is used together, characteristic.

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

The electroless gold plating bath of the present invention contains a binder. The compounding agent is preferably a mis-alignment agent having a miscible metal (for example, nickel, palladium, or the like) and a misalignment agent having a gold mismatch. Examples of the compounding agent which is suitable for the mismatching of the eluted metal include a hydroxycarboxylic acid such as glycolic acid, diglycolic acid, lactic acid, malic acid, citric acid, gluconic acid or heptagluconic acid or a salt thereof. (sodium salt, potassium salt, ammonium salt, etc.); glycine acid, amino dicarboxylic acid, nitrogen triacetic acid, EDTA, hydroxyethyl ethylenediamine triacetic acid, di-ethyltriamine pentaacetic acid, polyamine Aminocarboxylic acid such as carboxylic acid or a salt thereof (sodium salt, potassium salt, ammonium salt, hydrochloride salt, sulfate salt, etc.); HEDP (hydroxyethane-1,1-diphosphonic acid), amine group III a phosphite-based chelating agent such as methanesulfonic acid or ethylenediaminetetramethylsulfonic acid or a salt thereof (sodium salt, potassium salt, ammonium salt, hydrochloride salt, sulfate salt, etc.); ethylenediamine, diammine An amine-based chelating agent such as ethyltriamine or tri-ethylamine, and a salt thereof (hydrochloride, sulfate, etc.). These may be used alone or in combination of two or more.

Further, it is suitable as a miscible agent having a gold mismatch, and examples thereof include sodium sulfite, potassium sulfite, ammonium sulfite, sodium hydrogen sulfite, potassium hydrogen sulfite, ammonium hydrogen sulfite, sodium disulfite, and potassium disulfite. , ammonium disulfite, sodium thiosulfate, potassium thiosulfate, ammonium thiosulfate, carbendazim compound, quinone imine compound, and the like. Can be alone or combined 2 Use this above. More preferably, sodium sulfite, ammonium sulfite or the like is used.

The total concentration of the mismatching agent for the miscible metal in the gold plating bath and the above-mentioned mismatching agent having the gold mismatching ratio is preferably from 1 to 200 g/L, particularly preferably from 10 to 150 g/L.

The electroless gold plating bath of the present invention preferably further comprises a compound having a nitro group. By including the compound having a nitro group, the plating reactivity can be sufficiently ensured even if the cyano group is not contained, that is, the precipitation reactivity of gold is not impaired, and the bath stability can be sufficiently ensured. As this mechanism of action, it is considered that the nitro group captures gold and is stabilized. On the other hand, the nitro group is not contained, and for example, the effect of stability is exhibited only by catechol or benzoic acid.

The compound having a nitro group may, for example, be an aromatic compound having a nitro group. Examples of the aromatic compound having a nitro group include an aromatic compound having a nitro group and a hydroxyl group such as nitrobenzene, nitrophenol or 4-nitrocatechol; nitrotoluene and nitroxylene; An aromatic compound having a nitro group and an alkyl group such as nitrostyrene; an aromatic compound having a nitro group and an amine group such as nitroaniline or 4-nitro-1,2-phenylenediamine; An aromatic compound having a nitro group and a sulfur-containing group, such as nitrobenzenesulfonic acid such as 2,4-dinitrobenzenesulfonic acid. Further, examples of the nitrobenzoic acid having a nitro group and a carboxyl group include 2-nitrobenzoic acid, 3,5-dinitrobenzoic acid, 3,4-dinitrobenzoic acid, and an amine group. 5-amino-2-nitrobenzoic acid or the like. Further, an aromatic compound having a nitro group together with a halogen group, an ester group, an ether group, a carbonyl group, an aldehyde group or the like can be given. Alternatively, an ammonium salt, a sodium salt, a potassium salt or the like may be used as the salt of the aromatic compound having a nitro group.

For example, when it is the above nitrobenzoic acid, the nitro group is adjacent At the position of the carboxyl group, the effect of stability is increased and it is preferable. That is, the effect of the stability effect is the order of 2-nitrobenzoic acid > 3-nitrobenzoic acid > 4-nitrobenzoic acid.

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

More preferred are compounds having a nitro group together with an electron-donating group, especially an aromatic compound having a nitro group together with an electron-donating group. When the electron supply group is provided, the effect of stabilization of the nitro group becomes large. In the case where the nitro group is two adjacent dinitro groups, it is considered that the two nitro groups 2 form a trapping shape and the effect on the stability is increased. Examples of the electron-donating group include a hydroxyl group, an alkyl group, an amine group, a sulfur-containing group, a carboxyl group, an ester group, a halogen group, and an ether group. It is preferable to have one or more of these.

The compound having a nitro group may be used singly or in combination of two or more kinds of the above compounds. The total concentration of the compound having a nitro group is, for example, preferably in the range of 0.0010 to 5 g/L. In this case, if the total concentration is less than 0.0010 g/L, it is difficult to obtain the above effects. The total concentration is more preferably 0.005 g/L or more, and particularly preferably 0.010 g/L or more. On the other hand, if the concentration of the compound having a nitro group is too high, the surface of the nickel-plated surface as a base is easily corroded. Therefore, 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 pH of the electroless gold plating bath of the present invention is preferably from 5 to 10. This is because if it is below this range, the precipitation rate of gold is easily lowered, and the other is On the other hand, if it exceeds the above range, the bath tends to be unstable. The above pH is preferably from 6 to 9.

In the electroless gold plating bath of the present invention, a well-known pH adjuster, pH buffer, and other additives may be suitably contained within a range not impairing the object of the present invention. Examples of the acid adjusting agent include hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, and carboxylic acid. Examples of the alkali include sodium hydroxide, potassium hydroxide, and ammonia water. Further, examples of the pH buffering agent include carboxylic acids such as citric acid, tartaric acid, malic acid, and phthalic acid; phosphoric acid such as orthophosphoric acid, phosphorous acid, hypophosphorous acid, and pyrophosphoric acid; or potassium salts and sodium thereof. a phosphate such as a salt or an ammonium salt; boric acid, tetraboric acid or the like. Further, examples of the metal ion concealing agent include azoles such as benzotriazole and methylbenzotriazole, phenanthroline, bipyridine, and salicylate. Further, examples of the auxiliary coupling agent include aminocarboxylic acids such as EDTA and EDTMP, ammonium salts, and chlorides. Further, examples of the stabilizer include sulfur-containing heterocyclic compounds (2-mercaptobenzothiazole and 2-mercaptobenzoene). Azole or the like, a nitrogen-containing heterocyclic compound (benzotriazole, N-hydroxybenzotriazole, etc.), and the like.

In the electroless gold plating bath of the present invention, one or more of a ruthenium compound, an arsenic compound, and a lead compound may be further added. These compounds act as an increase in the rate of gold plating or as a crystal modifier. Specific examples of the compound include carbonates, acetates, nitrates, sulfates, and hydrochlorides of metals (arsenic, antimony, and lead) constituting the compound. The concentration of the above-mentioned crystal modifier in the gold plating bath is preferably 0.1 to 100 mg/L, and more preferably 0.2 to 50 mg/L, and more preferably 0.2 to 20 mg/L.

The present invention also provides a method for performing electroless gold plating using the above-described cyanide-free electroless gold plating bath. The surface of the gold-plated plating material to be treated is nickel or a nickel alloy. In the above ENIG process, the surface of the plated material to be treated is electroless nickel plating or electroless nickel plating (hereinafter referred to as "electroless nickel plating"). Examples of the nickel alloy include a nickel-phosphorus alloy and a nickel-boron alloy.

The gold-plated plating material to be treated may have a surface of palladium or a palladium alloy. In the above-mentioned ENEPIG process, the surface of the plated material to be treated is electroless palladium or electroless palladium-plated gold (hereinafter referred to as "electroless palladium-based plating"). Examples of the palladium alloy include a palladium-phosphorus alloy.

In the ENIG process, for example, an electroless nickel-based plating is formed on an Al or Al-based alloy, a Cu or a Cu-based alloy constituting an electrode, and then electroless gold plating is formed thereon, in an ENEPIG process, for example, in forming an electrode. On the Al or Al-based alloy, Cu or Cu-based alloy, electroless nickel-based plating is formed, followed by electroless palladium-based plating, and then electroless gold plating is formed thereon, and the above-mentioned electroless nickel-based plating or no The formation of the electrolytic palladium plating may be carried out by a usual method.

The formation of electroless gold plating in the above ENIG process and the ENEPIG process is carried out by using the cyanide-free electroless gold plating bath of the present invention, and other conditions can be employed. For example, it is possible to contact the electroless gold plating bath of the present invention for about 3 to 20 minutes. As the contact, a conventional method such as dipping can be employed. The use temperature of the electroless gold plating bath is preferably 40 to 90 °C. If the above range is not reached, there is a drop in the rate of precipitation, and if it exceeds In the above range, there is a problem that the bath becomes unstable. The above use temperature is preferably from 50 to 80 °C.

The electroless gold plating bath of the present invention and the electroless gold plating method using the same are suitable for gold plating of a wiring circuit mounting portion or a terminal portion of an electronic component such as a printed wiring board, a ceramic substrate, a semiconductor substrate, or an IC package. In particular, it is suitable for UBM (Under Barrier Metal) forming technology for the purpose of soldering and wire bonding (W/B) bonding for an Al electrode or a Cu electrode on a wafer. By using the gold plating bath of the present invention, the formation of electroless gold plating which is a part of the UBM formation technique can be stably carried out, and as a result, stable film characteristics can be achieved.

This case is based on Japanese Patent Application No. 2015-148523 filed on July 28, 2015, and claims the benefit of priority. The entire contents of the specification of Japanese Patent Application No. 2015-148523, filed on Jul. 28, 2015, are hereby incorporated by reference.

[Examples]

The present invention is not limited by the following examples, but the present invention is of course not limited to the following examples, and it is of course possible to carry out appropriate modifications within the scope of the above-described embodiments. And the like are included in the technical scope of the present invention.

[Measurement of film thickness of gold plating, confirmation of corrosion by nickel plating, and preparation of sample for observation of gold plating] [Test sample of ENIG process]

The sample of the ENIG process used for the measurement of the film thickness of the above gold plating is obtained as follows. In other words, the preparation electrode is a TEG wafer made of Al-Cu of an Al-based alloy, and an electroless nickel plating bath (NPR-18 manufactured by Uemura Kogyo Co., Ltd.) is used for the electrode, and is formed by electroless plating. Nickel plating of a thickness of 5.0 μm was carried out by applying electroless gold plating using the electroless gold plating bath shown in Table 1. This sample is also referred to below as "Test Sample I of ENIG Process".

[sample of ENEPIG process]

The sample of the ENEPIG process used for the measurement of the film thickness of the above gold plating is obtained as follows. In other words, the preparation electrode is a TEG wafer made of Al-Cu of an Al-based alloy, and an electroless nickel plating bath (NPR-18 manufactured by Uemura Kogyo Co., Ltd.) is used for the electrode, and is formed by electroless plating. Nickel plating of a thickness of 5.0 μm, followed by electroless plating of a palladium bath (TFP-30 manufactured by Uemura Kogyo Co., Ltd.) on the nickel plating, and palladium plating having a thickness of 0.05 μm was formed by electroless plating, and further used. The electroless gold plating bath shown in Table 1 was obtained by electroless gold plating. This sample is also referred to below as "sample 1 of the ENEPIG process".

The further conditions of the electroless gold plating performed in the above ENIG process and the ENEPIG process are as follows. That is, in the electroless gold plating bath, a gold sodium sulfite solution (Au concentration = 100 g/L) was used as a gold source, and Table 1 below shows the Au concentration in the electroless gold plating bath. Further, cesium carbonate was used as the ruthenium (Tl) compound, and the following Table 1 shows no The concentration of T1 in the electrolytic gold plating bath. The temperature of the electroless gold plating bath was 75 ° C, and the immersion in the electroless gold plating bath was carried out for 20 minutes in the case of the sample I of the ENIG process, and in the case of the sample I of the ENEPIG process for 30 minutes to form gold plating. In the sample I of the ENEPIG process of Nos. 1, 2, 4, and 6 of Table 1, which will be described later, the immersion time was set to 20 minutes in order to ensure the film thickness of gold plating at an early stage.

[Measurement of gold-plated film thickness in ENIG process or ENEPIG process]

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

[SEM observation of nickel plating for corrosion]

The nickel-plated surface which was formed by removing the gold plating of the sample I of the ENIG process with a gold stripping solution was observed by a SEM at a magnification of 5000 times to confirm the presence or absence of corrosion marks. Further, those who saw corrosion marks were evaluated for corrosion of "with" nickel plating, and those who did not see corrosion were evaluated as "no" nickel plating. For reference only, the SEM observation photograph is shown in FIG. Fig. 1(a) is a photograph of an example of the present invention in which no corrosion trace of nickel plating was observed, and Fig. 1(b) is a photograph showing a comparative example of corrosion traces of nickel plating.

[Gold-plated appearance observation]

Visual observation of the above-mentioned ENIG process sample I and ENEPIG process The gold-plated surface of sample I. Further, those who exhibited uniform gold plating appearance were evaluated as "good", and those who were not golden and red discolored were evaluated as "poor".

[Production of sample for evaluation of weldability and wire bonding (W/B)] [Test sample of ENIG process]

The sample of the ENIG process used for the evaluation of the weldability and the W/B property was prepared by preparing a BGA substrate (pad diameter Φ 0.5 mm) made by Uemura Industrial Co., Ltd., and the substrate was similar to the sample I of the ENIG process described above. An electroless nickel plating bath (NPR-18 manufactured by Uemura Kogyo Co., Ltd.) was used to form nickel plating having a thickness of 5.0 μm by electroless plating, followed by using an electroless gold plating bath as shown in Table 1, by applying It is obtained by electroless gold plating. This sample is also referred to below as "Test Sample II of ENIG Process".

[sample of ENEPIG process]

The sample of the ENEPIG process used for the evaluation of the weldability and the W/B property was prepared by preparing a BGA substrate (pad diameter Φ 0.5 mm) made by Uemura Kogyo Co., Ltd., and the substrate was the same as the sample I of the ENEPIG process. An electroless nickel plating bath (NPR-18 manufactured by Uemura Kogyo Co., Ltd.) was used to form a nickel plating layer having a thickness of 5.0 μm by electroless plating, followed by an electroless palladium plating bath (TFP-made by Uemura Kogyo Co., Ltd.). 30) Palladium plating having a thickness of 0.05 μm was formed on the nickel plating by electroless plating, and an electroless gold plating bath as shown in Table 1 was used, and electroless gold plating was applied. This sample is also referred to below as the "ENEPIG Process Test". Material II".

[Evaluation of weldability]

The sample II of the ENIG process and the sample II of the ENEPIG process were used, and the joint tester SERIES 4000 manufactured by Dage Co., Ltd. was used, and 20 points were evaluated for each condition. Specifically, for each No. of Table 1, the sample II using the ENIG process was measured, and the number of reflows was as follows: when the sample II of the ENEPIG process was used, the number of reflows was 1 time; and the sample using the ENIG process was used. II, when the number of reflowing times is 5 times; and when the sample II of the ENEPIG process is used, the following reflowing times are 5 times; the total of 4 conditions x 20 = 80 points of welding strength. As the welding strength, the welding fracture rate in the failure mode was obtained. The conditions for the formation of the weld and the measurement of the weld strength are as follows. In the present embodiment, the weld fracture ratio was 85% or more, and the weldability was "good", and the weld fracture rate was less than 85%, and the weldability was "poor".

[Welding conditions for welding formation and welding strength measurement]

Measuring method: pull ball test

Solder ball: Φ0.6mm Sn-3.0Ag-0.5Cu

Reflow soldering device: TMR-15-22LH manufactured by TAMURA

Reflow conditions: Top 240 ° C

Reflow environment: Air

Number of reflows: 1 or 5 times

Flux: 399D-1 (RMA type)

Test rate: 5000 μm / sec

Matured after welding: 1 hour

[Evaluation of wire bonding (W/B)]

The sample II of the ENIG process and the sample II of the ENEPIG process were used for wire bonding by a semi-automatic multi-wire bonding machine HB16 manufactured by TPT Corporation, and the joint tester SERIES 4000 manufactured by Dage Co., Ltd. was evaluated for 20 points per one condition. Specifically, for each No. in Table 1, the wire bonding strength (W/B intensity) of 2 conditions × 20 = 40 points when the sample II using the ENIG process and the sample II using the ENEPIG process were measured, and the average value was calculated. W/B average intensity and standard deviation. Furthermore, on the basis of these, the coefficient of variation (= standard deviation ÷ average value × 100) is obtained. The conditions for the wire bonding formation conditions and the wire bondability evaluation are as follows. In addition, when the average W/B intensity is 8 gf or more and the coefficient of variation is 15% or less, the wire bondability is "good", and at least one of the W/B average intensity and the coefficient of variation is outside the above range. The evaluation was "wire defect".

[Conditions for wire bonding formation and wire bondability evaluation]

Capillary: B1014-51-18-12 (PECO)

Line: 1Mil-Gold

Stage temperature: 150 ° C

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

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

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

Step distance (length from 1st to 2nd): 0.700mm

Measuring method: cable test

Test rate: 170 μm / sec

In the present embodiment, the weldability and the W/B property are evaluated as "good" in the case where both the weldability and the wire bondability are "good", and at least either of the weldability and the wire bondability are used. Weldability and W/B "bad" were evaluated for the "bad" situation.

[Evaluation of bath stability]

The electroless gold plating bath of each bath composition shown in Table 1 was allowed to stand at a temperature of 70 ° C for one month, and the stability of the bath was evaluated. If the person who is not decomposed for one month is evaluated as "safety", the person who decomposes within one month will be evaluated as "unstable."

The results of these are also listed in Table 1.

The following are known from Table 1. No.1~6 is used for gold plating with a gold plating bath of the specified formic acid and hydrazine. Therefore, the thickness of the gold plating film can be sufficiently ensured in the case of the ENEPIG process, and the corrosion of nickel plating is also suppressed in the ENIG process. , get a good plating appearance. Moreover, in all of these cases, welding and wire bonding can be performed well at the same time. Further, from the comparison of No. 1 to 3 and No. 4, it is preferable to further include a gold plating bath containing a compound having a nitro group from the viewpoint of sufficient bath stability. Further, as seen from the comparison between No. 3 and No. 5, it is preferred to set the content of the formic acid to be less than or equal to the recommended upper limit (100 g/L or less).

In contrast, No. 7 to 10 did not contain any of the predetermined formic acid and anthraquinone, and a problem occurred. In detail, No. 7 and No. 8 were corroded by nickel plating because they did not contain formic acid. As a result, weldability and W/B properties were poor. Further, No. 9 does not contain an anthraquinone. In this example, the thickness of the gold-plated film in the ENEPIG process is thin. Further, No. 10 is a substitute for an anthraquinone, and an ascorbic acid and a formic acid as a reducing agent are used. In this case, the film thickness of the gold plating is also thinned in the ENEPIG process. Further, the appearance of gold plating in Nos. 9 and 10 is red discoloration. The weldability and W/B properties are poor due to such red discoloration.

Claims (5)

A non-cyanide-based electroless gold plating bath comprising a water-free gold salt, a reducing agent and a complexing agent, and a cyano group-free electroless gold plating bath, characterized in that the reducing agent comprises formic acid or a salt thereof and a hydrazine. The cyano-free electroless gold plating bath of claim 1, which further comprises a compound having a nitro group. An electroless gold plating method characterized in that electroless gold plating is applied to the surface of a plated material to be treated using a cyanide-free electroless gold plating bath as claimed in claim 1 or 2. The electroless gold plating method according to claim 3, wherein the surface of the plating object to be treated is nickel or a nickel alloy. The electroless gold plating method according to claim 3, wherein the surface of the plating target is a palladium or a palladium alloy.