JP6594077B2 - Non-cyanide electroless gold plating bath and electroless gold plating method - Google Patents

Description

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

  Conventionally, there is an ENIG (Electroless Nickel Immersion Gold) process for forming substitutional gold plating on electroless nickel plating as a final surface treatment in the mounting process of printed wiring boards and electronic components. This process can be used for solder joints. Moreover, it can also be used for wire bonding by applying thickening after the ENIG process.

  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. This process is ideal for lead-free solder joints. It is also suitable for wire bonding.

  The ENIG process and the ENEPIG process are selected according to the use of the workpiece to be plated, and both processes are finally subjected to gold plating. However, in forming the gold plating, the former is based on nickel having a high ionization tendency (low oxidation-reduction potential), whereas the latter is based on palladium having a low ionization tendency (high oxidation-reduction potential). Is different. Therefore, until now, a gold plating bath corresponding to each process has been used.

  As the gold plating bath, a cyan gold plating bath has been widely used. However, in view of the toxicity of cyan, a non-cyanide type gold plating bath is required.

  For example, as a non-cyanide type gold plating bath used in the above ENEPIG process, Patent Document 1 discloses an electroless nickel plating film, an electroless palladium plating film, and an electroless gold plating film sequentially on a conductor portion of a printed wiring board. In forming, the gold plating solution used for forming the electroless gold plating film is an aqueous solution containing a water-soluble gold compound, a reducing agent, and a complexing agent, and the reducing agent includes formaldehyde bisulfite, longgarit, and hydrazine. It is shown to be at least one selected from the group consisting of genus. Patent Document 2 discloses a non-cyanide gold sulfite, a sulfite, a thiosulfate, as an electroless gold plating solution capable of depositing a gold film directly on an electroless palladium plating film by an autocatalytic reduction reaction. A plating solution containing water-soluble polyaminocarboxylic acid, benzotriazole compound, sulfur-containing amino acid compound, and hydroquinone at a predetermined concentration is shown.

  However, it is not practical to prepare a plating bath for each process or replace the plating bath depending on the use of the object to be plated. Therefore, there has been a demand for a gold plating bath that can be used for either the ENIG process or the ENEPIG process.

  Further, the non-cyanide type gold plating bath tends to cause a decrease in bath stability and plating reactivity as compared with a cyan gold plating bath. Therefore, the non-cyanide type gold plating bath is required to have both bath stability and plating reactivity as preferable characteristics.

Japanese Patent No. 5526440 JP 2010-180467 A

  The present invention has been made paying attention to the circumstances as described above, and its object is to provide a non-cyanide electroless gold plating bath that can be used in either the ENIG process or the ENEPIG process, and the non-cyanide electroless gold. The object is to realize an electroless gold plating method using a plating bath.

  The non-cyanide electroless gold plating bath of the present invention that has solved the above problems is an electroless gold plating bath that contains a water-soluble gold salt, a reducing agent, and a complexing agent, and does not contain cyan. , Formic acid or a salt thereof, and hydrazines.

  It is preferable that the non-cyanide electroless gold plating bath further contains a compound having a nitro group.

  The present invention also includes an electroless gold plating method characterized in that electroless gold plating is performed on the surface of the object to be plated using the non-cyanide electroless gold plating bath. In the electroless gold plating method, the surface of the plating object may be nickel or a nickel alloy, that is, an ENIG process, or the surface of the plating object is palladium or a palladium alloy, that is, an ENEPIG process. It may be.

  ADVANTAGE OF THE INVENTION According to this invention, the non-cyanide electroless gold plating bath which can be used for both an ENIG process and an ENEPIG process can be provided. Specifically, in the ENIG process, corrosion of nickel plating when forming gold plating on nickel plating is suppressed. Further, in both the ENEPIG process and the ENIG process, the gold deposition reactivity is improved, and the gold plating can be made thicker. 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 deposited on palladium plating in about 30 minutes.

FIG. 1 is a SEM (Scanning Electron Microscope) observation photograph showing the presence or absence of corrosion on the nickel plating surface in the examples.

  The inventors of the present invention have made extensive studies to solve the above problems. As a result, if a substitution reduction type non-cyanide electroless gold plating bath containing formic acid or a salt thereof and hydrazine as a reducing agent is used, the gold precipitation reaction without causing excessive corrosion of the underlying nickel plating or the like. The present invention has been completed by finding that it can be used for both the ENIG process and the ENEPIG process. Hereinafter, the non-cyanide electroless gold plating bath of the present invention may be referred to as “electroless gold plating bath” or “gold plating bath”. Below, each compound contained in the non-cyanide electroless gold plating bath of this invention is demonstrated.

(A) Hydrazines Hydrazines are compounds that contribute particularly to the improvement of plating deposition on palladium, and promote the formation of gold plating on palladium plating in the ENEPIG process. Further, hydrazines are compounds that contribute to securing a good plating appearance, and as a result, contribute to securing good solderability and wire bonding properties (W / B bonding properties). On the other hand, in the ENIG process, hydrazines are considered to accelerate the substitution reaction on the nickel plating more than necessary and cause excessive corrosion of the nickel plating. However, as will be described later, excessive corrosion of the nickel plating can be suppressed by using it together with formic acid or a salt thereof.

  Examples of the hydrazines include hydrazine; hydrazine hydrates such as hydrazine monohydrate; hydrazine salts such as hydrazine carbonate, hydrazine sulfate, hydrazine sulfate, hydrazine hydrochloride; hydrazines such as pyrazoles, triazoles, hydrazides, etc. Organic derivatives; etc. can be used. As the pyrazoles, in addition to pyrazole, pyrazole derivatives such as 3,5-dimethylpyrazole and 3-methyl-5-pyrazolone can be used. As the triazoles, 4-amino-1,2,4-triazole, 1,2,3-triazole and the like can be used. As the hydrazides, adipic acid dihydrazide, maleic hydrazide, carbohydrazide and the like can be used. These can be used alone or in admixture of two or more. Preferred are hydrazine hydrate such as hydrazine monohydrate and hydrazine sulfate. These can be used alone or in combination of two or more.

  The total concentration of the hydrazines is preferably 0.1 to 5 g / L. More preferably, it is 0.3-3 g / L.

(B) Formic acid or a salt thereof Formic acid or a salt thereof is considered to have an effect of suppressing an excessive substitution reaction by the hydrazines. Hereinafter, “formic acid or a salt thereof” is sometimes collectively referred to as formic acid. In particular, excessive corrosion of the underlying Ni film can be suppressed during gold plating in the ENIG process. On the other hand, when only formic acids are used without being used in combination with the hydrazines, the gold precipitation reactivity tends to be lowered particularly in the ENEPIG process. Specifically, the gold deposition reactivity on the palladium plating as a base is poor, and it is difficult to ensure the thickness of the gold plating. Therefore, combined use with the hydrazines mentioned above is required. The combined use of hydrazines and formic acids suppresses excessive corrosion of the nickel plating, contributing to securing solderability and W / B connectivity.

  Examples of the formic acid salt 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, primary -Amine salts containing tertiary amines; and the like. In the present invention, formic acid or a salt thereof can be used alone or in combination of two or more.

  The total concentration of the formic acids is preferably contained within a range of 1 to 100 g / L. In order to exhibit the said effect fully, it is preferable to set it as 1 g / L or more, More preferably, it is 5 g / L or more, More preferably, it is 10 g / L or more. On the other hand, if it is contained excessively, the bath tends to become unstable, and therefore, it is preferably 100 g / L or less as described above.

  In other words, in the present invention, by using hydrazines and formic acids in combination as a reducing agent, nickel corrosivity (substitution reaction) by hydrazines is suppressed by formic acids in the gold plating process of the ENIG process. Corrosion of some nickel plating can be suppressed. On the other hand, in the gold plating process of the ENEPIG process, the high reactivity of hydrazines on palladium plating promoted the formation of gold plating compared to the case of using formic acid alone, and it became possible to increase the thickness of the gold plating. . This is probably because the reduction reaction was promoted.

  The gold plating bath of the present invention is an electroless gold plating bath that does not contain cyan and essentially contains a water-soluble gold salt and a complexing agent in addition to the hydrazines and formic acids. Further, as described later, a reducing agent other than hydrazines and formic acids may be used. Hereinafter, the water-soluble gold salt will be described in order.

  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 non-cyanide. Specifically, gold sulfite, thiosulfate, thiocyanate, sulfate, nitrate, methanesulfonate, tetraammine complex, chloride, bromide, iodide , Hydroxide, oxide and the like. These can 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, particularly preferably 0.5 to 4 g / L as the gold (Au) concentration. If it is less than 0.3 g / L, the deposition rate may be slow. On the other hand, if it exceeds 5 g / L, the stability may decrease, and even if the amount is increased, the effect is hardly changed and the cost is increased.

  The electroless gold plating bath of the present invention may further include the following reducing agent in addition to the hydrazines and formic acids as reducing agents. That is, ascorbic acid, isoascorbic acid (erythorbic acid) and other ascorbic acid compounds or salts thereof (sodium salt, potassium salt, ammonium salt, etc.); hydroquinone, methylhydroquinone and other hydroquinone or derivatives thereof; pyrogallol, pyrogallol monomethyl ether, pyrogallol Pyrogallol such as -4-carboxylic acid, pyrogallol-4,6-dicarboxylic acid, gallic acid or derivatives thereof; These can be used alone or in combination of two or more. In the present invention, it is essential to use the hydrazines and formic acids in combination as a reducing agent. As a reducing agent other than the hydrazines and formic acids, for example, ascorbic acid may be used in combination with formic acids. No. in Examples described later. 10.

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

  The electroless gold plating bath of the present invention contains a complexing agent. As the complexing agent, a complexing agent having a complexing action of eluted metal (for example, nickel, palladium, etc.) and a complexing agent having a complexing action of gold are suitable. As a complexing agent having a complexing action of the eluting metal, glycolic acid, diglycolic acid, lactic acid, malic acid, citric acid, gluconic acid, heptogluconic acid, etc., hydroxycarboxylic acids or their Salts (sodium salt, potassium salt, ammonium salt, etc.); glycine, aminodicarboxylic acid, nitrilotriacetic acid, EDTA, hydroxyethylethylenediamine triacetic acid, diethylenetriaminepentaacetic acid, aminocarboxylic acid such as polyaminocarboxylic acid or salts thereof (sodium salt) , Potassium salts, ammonium salts, hydrochlorides, sulfates, etc.); phosphite chelating agents such as HEDP (hydroxyethane-1,1-diphosphonic acid), aminotrimethylsulfonic acid, ethylenediaminetetramethylsulfonic acid or their salts (Sodium salt, potassium salt, a Moniumu salt, hydrochloride, sulfate, etc.); ethylenediamine, diethylenetriamine, amine based chelating agents and their salts (hydrochloride salt and triethylene tetramine, sulfates, etc.); and the like. These can be used alone or in combination of two or more.

  Preferred complexing agents having a complexing action with gold include sodium sulfite, potassium sulfite, ammonium sulfite, sodium bisulfite, potassium bisulfite, ammonium bisulfite, sodium disulfite, potassium disulfite, disulfite Examples thereof include ammonium sulfate, sodium thiosulfate, potassium thiosulfate, ammonium thiosulfate, hydantoin compounds, and imide compounds. These can be used alone or in combination of two or more. More preferably, sodium sulfite, ammonium sulfite or the like is used.

  The total concentration of the complexing agent having a complexing action of the eluting metal and the complexing agent having a gold complexing action in the gold plating bath is 1 to 200 g / L, particularly 10 to 150 g / L. Preferably there is.

  The electroless gold plating bath of the present invention preferably further contains a compound having a nitro group. By including this compound having a nitro group, bath stability can be sufficiently ensured without impairing plating reactivity, that is, gold deposition reactivity, even without cyan. As this mechanism of action, it is conceivable that the nitro group captures and stabilizes gold. In contrast, catechol or benzoic acid that does not contain a nitro group, for example, does not show a stability effect.

  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; aromatics having a nitro group and an alkyl group such as nitrotoluene, nitroxylene, and nitrostyrene. Compound: Aromatic compound having nitro group and amino group such as nitroaniline and 4-nitro-1,2-phenylenediamine; and nitro group such as nitrobenzene sulfonic acid such as nitrothiophenol and 2,4-dinitrobenzene sulfonic acid; And aromatic compounds having a sulfur-containing group. Furthermore, as the nitrobenzoic acid having a nitro group and a carboxyl group, 2-nitrobenzoic acid, 3,5-dinitrobenzoic acid, 3,4-dinitrobenzoic acid, and 5-amino-2-nitrobenzoic acid further having an amino group An acid etc. are mentioned. In addition, an aromatic compound having a halogen group, an ester group, an ether group, a carbonyl group, an aldehyde group, or the like together with a nitro group. Alternatively, ammonium salts, sodium salts, potassium salts and the like can also be used as salts of aromatic compounds having these nitro groups.

  For example, in the case of the above nitrobenzoic acid, it is preferable that the nitro group is located adjacent to the carboxyl group because the effect of stability is increased. That is, the magnitude of the stability effect is in the order of 2-nitrobenzoic acid> 3-nitrobenzoic acid> 4-nitrobenzoic acid.

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

  More preferred are compounds having an electron donating group together with a nitro group, particularly aromatic compounds having an electron donating group together with a nitro group. When it has an electron donating group, the effect of stabilizing the nitro group is increased. In the case of dinitro having two nitro groups adjacent to each other, it is considered that trapping is performed with two nitro groups and the effect on stability is increased. 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. It is preferable to have one or more of these.

  The compound which has the said nitro group can use the above compounds individually or in combination of 2 or more types. The total concentration of the compounds having a nitro group is preferably in the range of 0.0010 to 5 g / L, for example. This is because if the total concentration is less than 0.0010 g / L, it is difficult to obtain the above effect. The total concentration is more preferably 0.005 g / L or more, and still more 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 plating as a base is easily corroded. Therefore, the total concentration is preferably 5 g / L or less as described above, 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 5-10. This is because if the amount falls below this range, the deposition rate of gold tends to decrease, while if it exceeds the above range, the bath tends to become unstable. The pH is more preferably 6-9.

  The electroless gold plating bath of the present invention may appropriately contain a known pH adjusting agent, pH buffering agent, and other additives as long as the object of the present invention is not impaired. Examples of the pH adjuster include hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, carboxylic acid and the like as acids, and sodium hydroxide, potassium hydroxide, aqueous ammonia and the like as alkalis. 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, or potassium salts thereof. Examples thereof include phosphates such as sodium salts and ammonium salts; boric acid and tetraboric acid. Other examples of the metal ion masking agent include azoles such as benzotriazole and methylbenzotriazole, phenanthroline, bipyridyl, and salicylate. Examples of auxiliary complexing agents include aminocarboxylic acids such as EDTA and EDTMP, ammonium salts, and chlorides. Examples of the stabilizer include sulfur-containing hetero compounds (2-mercaptobenzothiazole, 2-mercaptobenzoxazole, etc.), nitrogen-containing hetero compounds (benzotriazole, N-hydroxybenzotriazole, etc.) and the like.

  One or more of thallium compounds, arsenic compounds, and lead compounds can be further added to the electroless gold plating bath of the present invention. These compounds act as an improvement in the gold plating rate and a crystal modifier. Specific examples of the compound include carbonates, acetates, nitrates, sulfates, and hydrochlorides of metals (arsenic, thallium, lead) constituting the compounds. The concentration of the crystal modifier in the gold plating bath is preferably 0.1 to 100 mg / L in total as the metal concentration, more preferably 0.2 to 50 mg / L, and even more preferably in total. 0.2 to 20 mg / L.

  The present invention also provides that the electroless gold plating method is performed using the non-cyanide electroless gold plating bath. The surface of the plating object to be gold plated is nickel or a nickel alloy. In the ENIG process described above, 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”). Examples of the nickel alloy include a nickel-phosphorus alloy and a nickel-boron alloy.

  The surface of the plating object to be plated with gold may be palladium or a palladium alloy. In the above-described ENEPIG process, the surface of the plating object may be electroless palladium plating or electroless palladium alloy plating (hereinafter referred to as “electroless palladium 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 Al, Al-based alloy, Cu, or Cu-based alloy constituting the electrode, and then electroless gold plating is formed thereon. In the ENEPIG process, for example, the electrode is configured. Electroless nickel-based plating, then electroless palladium-based plating, and then electroless gold plating on the Al, Al-based alloy, Cu or Cu-based alloy, The formation of electroless palladium plating may be performed by a commonly used method.

  In any of the ENIG process and the ENEPIG process, the electroless gold plating may be performed under the usual conditions except that the non-cyanide electroless gold plating bath of the present invention is used. For example, it may be brought into contact with the electroless gold plating bath of the present invention for about 3 to 20 minutes. As the contact, a conventionally known method such as immersion can be employed. The operating temperature of the electroless gold plating bath is preferably 40 to 90 ° C. If it is less than the above range, the deposition rate may be reduced, whereas if it exceeds the above range, the bath may become unstable. The use temperature is preferably 50 to 80 ° C.

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

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, but may be appropriately modified within a range that can meet the purpose described above and below. Of course, it is possible to implement them, and they are all included in the technical scope of the present invention.

[Measurement of gold plating thickness, confirmation of nickel plating corrosion, and preparation of sample for observation of gold plating appearance]
[Sample of ENIG process]
A sample of the ENIG process used for measuring the thickness of the gold plating was obtained as follows. That is, a TEG wafer made of Al—Cu whose electrode is an Al-based alloy is prepared, and an electroless nickel plating bath (NPR-18 manufactured by Uemura Kogyo Co., Ltd.) is used on the electrode, and electroless plating is performed. A nickel plating having a thickness of 0 μm was formed, and then electroless gold plating was performed using an electroless gold plating bath shown in Table 1. Hereinafter, this sample is sometimes referred to as “Sample I of ENIG process”.

[Sample of ENEPIG process]
A sample of the ENEPIG process used for measuring the thickness of the gold plating was obtained as follows. That is, a TEG wafer made of Al—Cu whose electrode is an Al-based alloy is prepared, and an electroless nickel plating bath (NPR-18 manufactured by Uemura Kogyo Co., Ltd.) is used on the electrode, and electroless plating is performed. A nickel plating with a thickness of 0 μm is formed, and then a palladium plating with a thickness of 0.05 μm is formed on the nickel plating by an electroless plating method using an electroless palladium plating bath (TFP-30 manufactured by Uemura Kogyo Co., Ltd.) Furthermore, it obtained by performing electroless gold plating using the electroless gold plating bath shown in Table 1. Hereinafter, this sample may be referred to as “Sample I of ENEPIG process”.

  Further conditions of electroless gold plating performed in the preparation of each sample of the ENIG process and the ENEPIG process are as follows. That is, in the electroless gold plating bath, a gold gold sulfite solution (Au concentration = 100 g / L) is used as a gold source, and Table 1 below shows the Au concentration in the electroless gold plating bath. Further, thallium carbonate is used as the thallium (Tl) compound, and Table 1 below shows the Tl concentration in the electroless gold plating bath. The temperature of the electroless gold plating bath is 75 ° C., and immersion in the electroless gold plating bath is performed for 20 minutes for the ENIG process sample I and for 30 minutes for the ENEPIG process sample I. Formed. In addition, No. in Table 1 described later. In Sample I of the 1, 2, 4, and 6 ENEPIG processes, the film thickness of the gold plating could be secured early, so the immersion time was 20 minutes.

[Measurement of film thickness of gold plating in ENIG process or ENEPIG process]
The film thicknesses of the gold plating formed on Sample I of the ENIG process and Sample I of the ENEPIG process were measured with a fluorescent X-ray film thickness meter. In particular, the case where the film thickness of the gold plating on the palladium plating in the ENEPIG process was 0.05 μm or more was evaluated as a gold plating bath applicable to the ENEPIG process.

[Presence or absence of corrosion of nickel plating by SEM observation]
The nickel plating surface that appears by removing the gold plating of Sample I of the ENIG process with a gold stripper was observed with a SEM at a magnification of 5000 times to confirm the presence or absence of corrosion marks. The case where the corrosion mark was confirmed was evaluated as “existing” corrosion of the nickel plating, and the case where the corrosion mark was not confirmed was evaluated as “no” corrosion of the nickel plating. For reference, an SEM observation photograph is shown in FIG. FIG. 1A is a photograph of an example of the present invention in which no corrosion mark of nickel plating is confirmed, and FIG. 1B is a photograph of a comparative example in which corrosion marks of nickel plating are confirmed.

[Observation of gold plating]
The surface of the gold plating of Sample I of the ENIG process and Sample I of the ENEPIG process was visually observed. And the thing which showed the golden plating external appearance uniformly was evaluated as "good", and the thing discolored red instead of gold was evaluated as "bad".

[Preparation of samples for evaluation of solderability and wire bonding (W / B) properties]
[Sample of ENIG process]
As a sample of the ENIG process used for the evaluation of solderability and W / B property, a BGA substrate (pad diameter φ0.5 mm) made by Uemura Kogyo Co., Ltd. is prepared, and the same as the above-described sample I of the ENIG process Then, using an electroless nickel plating bath (NPR-18, manufactured by Uemura Kogyo Co., Ltd.), a nickel plating with a thickness of 5.0 μm is formed by an electroless plating method, and then using an electroless gold plating bath shown in Table 1, It was obtained by applying electroless gold plating. Hereinafter, this sample is sometimes referred to as “Sample II of ENIG process”.

[Sample of ENEPIG process]
The sample of the ENEPIG process used for the evaluation of solderability and W / B property is a BGA substrate (pad diameter φ0.5 mm) manufactured by Uemura Kogyo Co., Ltd. On this substrate, the same as the sample I of the above-mentioned ENEPIG process Then, using an electroless nickel plating bath (NPR-18, manufactured by Uemura Kogyo Co., Ltd.), nickel plating having a thickness of 5.0 μm is formed by an electroless plating method. 30), a 0.05 μm-thick palladium plating was formed on the nickel plating by an electroless plating method, and further electroless gold plating was performed using an electroless gold plating bath shown in Table 1. . Hereinafter, this sample may be referred to as “Sample II of ENEPIG process”.

[Evaluation of solderability]
Using the ENIG process sample II and the ENEPIG process sample II, 20 points were evaluated per condition using a Dage bond tester SERIES 4000. Specifically, each No. For every,
When ENIG process sample II is used and the following reflow count is 1;
When sample II of ENEPIG process is used and the following reflow is performed once;
When ENIG process sample II is used and the following reflow times are 5 times; and when ENEPIG process sample II is used and the following reflow times is 5 times;
A total of 4 conditions × 20 = 80 points of solder joint strength was measured. As the solder joint strength, the solder fracture rate in the fracture mode was determined. Conditions for solder formation and solder joint strength measurement are as follows. In this example, when the solder fracture rate was 85% or more, the solderability was evaluated as “good”, and when the solder fracture rate was less than 85%, the solderability was evaluated as “bad”.

[Conditions for solder formation and solder joint strength measurement]
Measuring method: Ball pull test Solder ball: Senju Metal φ0.6mm Sn-3.0Ag-0.5Cu
Reflow device: TMR-15-22LH manufactured by Tamura Corporation
Reflow conditions: Top 240 ° C
Reflow environment: Air
Number of reflows: 1 or 5 times Flux: 529D-1 (RMA type) made by Senju Metal
Test speed: 5000 μm / sec Aging after solder mounting: 1 hour

[Evaluation of wire bonding (W / B) properties]
Using the ENIG process sample II and the ENEPIG process sample II, wire bonding was performed using a semi-automatic wire bonder HB16 manufactured by TPT, and 20 points were evaluated per condition using a bond tester SERIES 4000 manufactured by Dage. Specifically, each No. In the case of using the ENIG process sample II and the ENEPIG process sample II, a total of 2 conditions × 20 = 40 points of wire bonding strength (W / B strength) is measured, and is an average value thereof. W / B average intensity and standard deviation were calculated. Furthermore, the coefficient of variation (= standard deviation ÷ average value × 100) was determined based on them. The conditions for forming the wire bonding and evaluating the wire bonding property are as follows. When the W / B average strength is 8 gf or more and the variation coefficient is 15% or less, the wire bonding property is evaluated as “good”, and at least one of the W / B average strength and the variation coefficient falls within the above range. When it came off, the wire bonding property was evaluated as “bad”.

[Conditions for wire bonding formation and wire bonding evaluation]
Capillary: B1014-51-18-12 (PECO)
Wire: 1 Mil-Gold
Stage temperature: 150 ° C
Ultrasound (mW): 250 (1st), 250 (2nd)
Bonding time: (milliseconds): 200 (1st), 50 (2nd)
Tensile force (gf): 25 (1st), 50 (2nd)
Step (length from 1st to 2nd): 0.700mm
Measurement method: Wire pull test Test speed: 170 μm / sec

  In this example, when both the solderability and the wire bonding property are “good”, the solderability and W / B property are evaluated as “good”, and the solderability and the wire are evaluated. When at least one of the bonding properties was “defective”, the solderability and W / B property were evaluated as “defective”.

[Evaluation of bath stability]
The electroless gold plating bath having each bath composition shown in Table 1 was allowed to stand at a temperature of 70 ° C. for 1 month to evaluate the stability of the bath. Those that did not decompose even after being allowed to stand for 1 month were evaluated as “stable”, and those that had decomposed within 1 month were evaluated as “unstable”.

  These results are also shown in Table 1.

  Table 1 shows the following. No. For Nos. 1 to 6, since gold plating was performed using a gold plating bath in which specified formic acids and hydrazines were used in combination, the film thickness of the gold plating could be sufficiently secured even in the ENEPIG process, and nickel plating in the ENIG process Corrosion was also suppressed, and a good plating appearance was obtained. Moreover, both of these examples were able to perform both solder bonding and wire bonding bonding satisfactorily. No. 1 to 3 and no. From the comparison of 4, it can be seen that a gold plating bath further containing a compound having a nitro group is preferable from the viewpoint of ensuring sufficient bath stability. No. 3 and no. From the comparison of 5, it is understood that the content of formic acid is preferably set to a recommended upper limit (100 g / L or less).

  In contrast, no. Since 7-10 did not contain any of the prescribed formic acids and hydrazines, problems occurred. Specifically, no. 7 and no. Since No. 8 contained no formic acid, corrosion of nickel plating occurred. As a result, the solderability and W / B property were poor. No. 9 is an example not containing hydrazines. In this example, the thickness of the gold plating was reduced in the ENEPIG process. No. 10 is an example in which ascorbic acid, which is a reducing agent, is used in combination with formic acids instead of hydrazines. Also in this example, the film thickness of the gold plating was reduced in the ENEPIG process. No. In 9 and 10, the appearance of the gold plating turned red. Due to the occurrence of such red discoloration defects, the solderability and W / B properties were poor.

Claims (5)

An electroless gold plating bath containing a water-soluble gold salt, a reducing agent, and a complexing agent and not containing cyan,
The reducing agent includes formic acid or a salt thereof, and hydrazines ,
Furthermore, the non-cyanide electroless gold plating bath characterized by including a thallium compound .   The non-cyanide electroless gold plating bath according to claim 1, further comprising a compound having a nitro group.   An electroless gold plating method, wherein electroless gold plating is performed on the surface of a plating object using the non-cyanide electroless gold plating bath according to claim 1.   The electroless gold plating method according to claim 3, wherein the surface of the plating object is nickel or a nickel alloy.   The electroless gold plating method according to claim 3, wherein the surface of the plating object is palladium or a palladium alloy.