JP3948737B2 - Replacement type electroless gold plating solution - Google Patents

Description

  The present invention relates to a substitutional electroless gold plating solution, and more particularly to a substitutional electroless gold plating solution for uniformly forming a gold plating film on a nickel plating film such as a terminal portion of an electronic component. It is.

  Electroless Nickel Immersion Gold on the electroless nickel plating film in order to prevent corrosion of the terminals, wire bonding, solder bonding, etc. in the plating process used for the connection terminals of electronic components (Hereinafter abbreviated as “ENIG”) is widely used.

  In ENIG, when the nickel metal on the surface of the electroless nickel plating film, which is the base, becomes nickel ions and is eluted into the gold plating solution, the electrons emitted are given to the gold ions, and the gold ions become neutral gold. It is deposited on the surface of the nickel coating to form a gold coating.

  In recent years, as the terminal portion is miniaturized and the solder is replaced with lead-free solder, the lack of solder joint strength has become a problem in the mounting technology field.

  As a means of improving such a lack of solder joint strength, a reducing agent is added to the substitutional electroless gold plating solution, and a gold reduction film is formed in the electroless gold plating solution to form a gold plating film. A method of reducing the rate of gold film formation by substitution reaction is known (see Patent Document 1). Such an electroless gold plating solution is said to be a substitution reduction type, and since there is little elution of the underlying nickel, it is possible to reduce the roughness of the nickel surface and improve the decrease in solder joint strength.

  However, in this method, electrons generated by decomposition of the reducing agent react with gold ions to easily form a gold colloid in the plating solution, and gold is likely to be deposited in the gold plating bath and filter. . In addition, the management and replenishment of the gold plating solution also has a problem that the substitution reduction gold plating solution becomes complicated as compared with the substitution gold plating solution.

  For this reason, improving the solder joint strength while using a substitution reaction has been an important problem for technical improvement in the ENIG process.

  In order to solve this, it has been proposed to contain various nitrogen-containing compounds as gold precipitation inhibitors (see Patent Document 2), and organic compounds having two or more nitrogen atoms as nickel surface oxidation inhibitors. (See Patent Document 3), however, it may not be possible to obtain sufficient solder joint strength.

  Accordingly, there has been a demand for a substitutional electroless gold plating solution for ENIG that is unlikely to deposit gold in a gold plating bath, a filter, or the like and has excellent solder joint strength.

JP 2001-107259 A JP 2001-144441 A WO2004 / 038063

  The present inventor has been made in view of the background art, and the problem is that the substitutional electroless for ENIG, in which gold is difficult to deposit in a gold plating bath, a filter, etc., and excellent solder joint strength is obtained. It is to provide a gold plating solution.

  As a cause of the above insufficient strength, the present inventor has intensively studied to solve the above problems, and there is local erosion of the electroless nickel plating film as a base during substitutional electroless gold plating. I found out. The base electroless nickel plating film may contain several percent of elements such as phosphorus and sulfur in addition to nickel, and these elements are locally and unevenly dispersed in the nickel film. . In addition, when the electroless nickel plating film is observed with an electron microscope, it can be observed that it is composed of a collection of fine nickel particles in units of microns, but the composition of phosphorus, sulfur, etc. is inside and inside the grain boundary. It was also found that the grain boundary part is easily eroded by the displacement gold plating solution.

  In any case, the electroless nickel plating film is not homogeneous, and the elution of nickel into the gold plating solution is non-uniform, resulting in the occurrence of fine local erosion on the nickel film. It has been found that the formation of a gold plating film on a locally eroded nickel film may cause insufficient strength in wire connection or solder connection.

  And, in the gold plating solution containing a specific component and using a substitutional electroless gold plating solution whose oxidation-reduction potential is adjusted to a specific range, local erosion of the underlying electroless nickel coating is greatly increased. The present invention has been found to solve the above-mentioned problems.

That is, the present invention is, at least, gold cyanide salt, [pi electron rich aromatic having three or more nitrogen atoms in the molecule heterocyclic compound, and at least one selected from sulfite and phosphorous acid, as well as the group consisting of salts thereof An electroless plating solution containing a seed buffer, the oxidation-reduction potential at 25 ° C. being in the range of −150 mV to +10 mV, for producing an electroless gold plating film on the electroless nickel plating film A substitutional electroless gold plating solution is provided.

  The present invention also provides a method for producing an electroless gold plating film by suppressing local erosion of the grain boundary part of the electroless nickel plating film, characterized by using such a substitutional electroless gold plating solution. To do.

  Furthermore, the present invention provides a method for producing a gold plating film in which electroless gold plating is applied to a thickness in the range of 0.01 μm to 0.3 μm on an electroless nickel plating film using a substitution type electroless gold plating solution. It is to provide.

  Moreover, this invention provides the electronic component terminal by which the electroless gold plating film was given using this substitution type electroless gold plating solution.

  According to the present invention, gold does not easily deposit in a gold plating bath, a filter, etc., and it causes local erosion of the underlying electroless nickel plating film, and does not oxidize the underlying nickel plating film, and is an excellent solder An object of the present invention is to provide a substitutional electroless gold plating solution for ENIG from which a gold plating film having bonding strength can be obtained.

  The substitutional electroless gold plating solution of the present invention must contain at least a water-soluble gold salt, a heterocyclic compound having 3 or more nitrogen atoms in the molecule, and a buffer.

  Among these, the water-soluble gold salt is a gold source for the substitutional electroless gold plating solution of the present invention, is sufficiently stable in the plating solution, and is easily dissolved in water. Although it will not specifically limit if it is suitable as a source, Gold cyanide salt, gold sulfite, gold thiosulfate, etc. are mentioned. Preferred is a gold cyanide salt, and specific examples include a first gold cyanide salt and a second gold cyanide salt. Of these, particularly preferred is a first gold cyanide salt. Further, the counter cation forming the salt is not particularly limited, and examples thereof include alkali metal ions and ammonium ions. Among them, preferred is an alkali metal ion, and particularly preferred is a potassium ion. As the water-soluble gold salt, potassium primary cyanide is particularly preferable.

  The concentration of the water-soluble gold salt in the substitutional electroless gold plating solution is not particularly limited, but is preferably 0.1 g / L or more, particularly preferably 0.5 g / L or more, and preferably 5 g in terms of gold. / L or less, particularly preferably 4 g / L or less. If the concentration of the water-soluble gold salt is too high, the stability of the plating solution may be reduced, and if it is too low, the plating rate may be reduced.

  A heterocyclic compound having three or more nitrogen atoms in the molecule is a compound having an aromatic ring (hereinafter abbreviated as “heterocycle”) having one or more elements other than carbon, A compound in which the total number of nitrogen atoms forming a heterocycle and nitrogen atoms not forming a heterocycle in the compound molecule is 3 or more.

  The element other than carbon constituting the heterocycle (hereinafter abbreviated as “heteroelement”) is not particularly limited, and examples thereof include nitrogen, oxygen, and sulfur.

  The heterocyclic ring in the heterocyclic compound having 3 or more nitrogen atoms in the molecule of the present invention is not particularly limited. For example, a pyrrole ring, a furan ring, a thiophene ring, an imidazole ring, an oxazole ring, a thiazole ring, a pyrazole ring, Pyridine ring, pyrimidine ring, purine ring, quinoline ring, isoquinoline ring, carbazole ring, 1,2,3-triazole ring, 1,2,4-triazole ring, tetrazole ring, indole ring, benzimidazole ring, benzoxazole ring, Examples thereof include a benzthiazole ring and a benztriazole ring.

  The hetero element is preferably nitrogen. Further, those having two or more nitrogen atoms in the heterocycle are preferred, and those having three or more nitrogen atoms are particularly preferred.

In the present invention, the heterocyclic compound is preferably a π-electron rich aromatic heterocyclic compound. That is, the heterocycle is preferably a π-electron rich aromatic heterocycle. For the definition of π-electron rich aromatic heterocycles, see the book “Heterocyclic Chemistry, by
Adrien Albert, The Anthon Press University of London, 1959 ”, and the“ π electron-rich aromatic heterocycle ”in the present invention is defined in the description of this book.

  Preferred examples of the hetero ring include a pyrazole ring, an imidazole ring, a 1,2,3-triazole ring, a 1,2,4-triazole ring, a tetrazole ring, a benzimidazole ring, and a benztriazole ring.

  In the heterocyclic compound having 3 or more nitrogen atoms in the molecule of the present invention, the substituent bonded to the ring is not particularly limited, but an amino group, an alkyl group, an alkylamino group and the like are preferable. Of these, an amino group is particularly preferred. When the substituent is an amino group, the total of the number of nitrogen atoms contained in the substituent group and the number of nitrogen atoms constituting the heterocyclic ring may be three or more. Further, nitrogen atoms may be concentrated on the heterocycle.

  In the present invention, the heterocyclic compound having 3 or more nitrogen atoms in the molecule is preferably, for example, 3-aminopyrazole, 4-aminopyrazole, 5-aminopyrazole, 2-aminoimidazole, 4-aminoimidazole, 5- Aminoimidazole, 1,2,3-triazole, 4-amino-1,2,3-triazole, 5-amino-1,2,3-triazole, 1,2,4-triazole, 3-amino-1,2 , 4-triazole, 5-amino-1,2,4-triazole, tetrazole, 5-aminotetrazole, 2-aminobenzimidazole, benztriazole, etc., or alkyl substituted products thereof. These are used alone or in combination of two or more.

  Particularly preferred are 1,2,4-triazole, 3-amino-1,2,4-triazole, tetrazole, 5-aminotetrazole and the like.

  The concentration of the heterocyclic compound having 3 or more nitrogen atoms in the molecule in the substitutional electroless gold plating solution is not particularly limited, but is preferably 5 ppm, particularly preferably 50 ppm or more, preferably 10,000 ppm or less, particularly preferably. Is 2000 ppm or less. When the concentration of the heterocyclic compound is too large, it may be precipitated in the plating solution. When it is too small, the oxidation suppression of the nickel plating film surface is insufficient, resulting in a decrease in solder joint strength. There is.

  The above heterocyclic compound having 3 or more nitrogen atoms in the molecule has an effect of preventing the surface of the nickel coating in contact with the substitutional electroless gold plating solution from being oxidized. When solder bonding is performed on an ENIG terminal whose nickel surface is oxidized, sufficient solder bonding strength may not be obtained, and this is an essential component of the substitutional electroless gold plating solution of the present invention.

  The substitutional electroless gold plating solution of the present invention contains a buffer as an essential component. The buffering agent is not particularly limited as long as it stabilizes the pH of the substitutional electroless gold plating solution, and an acid, a base, or a salt is appropriately mixed and used regardless of an organic compound or an inorganic compound.

  Specifically, for example, adipic acid, benzoic acid, citric acid, malic acid, succinic acid, formic acid, acetic acid, lactic acid, malonic acid, phthalic acid, succinic acid, tartaric acid, glycine, glutamic acid, glutaric acid, iminodiacetic acid, dehydro Carboxylic acids such as acetic acid and maleic acid or salts thereof; amine compounds such as ethylenediamine, hydroxyamine, ethanolamine, diethanolamine, triethanolamine or salts thereof, boric acid, phosphoric acid, pyrophosphoric acid, phosphorous acid, thiosulfuric acid Inorganic acids such as sulfurous acid, nitric acid, sulfuric acid, hydrochloric acid and thiocyanic acid or salts thereof. These are used singly or as a mixture of two or more, but are preferably used as a mixture of two or more.

  Preferable buffering agents include acids containing an atom having an oxidation number in an intermediate state or salts thereof. Moreover, the compound which exists in the intermediate potential of an oxidizing agent and a reducing agent is mentioned.

  Particularly preferred is phosphorous acid or a salt thereof, sulfurous acid or a salt thereof, and the like.

  In the present invention, the concentration of the buffer in the substitutional electroless gold plating solution is not particularly limited, but is preferably 1 g / L or more, particularly preferably 5 g / L or more, preferably 300 g / L or less, particularly preferably. Is 200 g / L or less. When the concentration of the buffering agent is too large, it may be easily deposited in the plating solution, and when it is too small, the buffering effect may be insufficient.

  The substitution-type electroless gold plating solution of the present invention is maintained at a stable pH mainly by the above-mentioned buffer, but the preferred range of the pH is 4-9, and the particularly preferred range is 4.5-8. It is. If the pH is too high, the resist on the substrate may be easily affected, and if it is too low, the water-soluble gold salt may become unstable.

The substitutional electroless gold plating solution of the present invention must have an oxidation-reduction potential in the range of −150 mV to +10 mV . The oxidation-reduction potential of the present invention is a value measured with an ORP (Oxidation Reduction Potential) meter in a plating solution at 25 ° C. Examples of the ORP meter include a pH / ORP meter TP-94 electrode PCM90 (manufactured by Toko Chemical Laboratory Co., Ltd.), and the oxidation-reduction potential of the present invention is a value measured by this.

The ORP meter uses a platinum electrode as a measurement electrode and a silver chloride electrode having 3.33 mol / L potassium chloride as an internal solution as a reference electrode, where V represents the measured oxidation-reduction potential. There is a relationship of approximately V = V _h −206 + 0.7 (t−25) with respect to the oxidation-reduction potential V _h using a platinum electrode as a measurement electrode and a standard hydrogen electrode as a reference electrode. t is the temperature of the measurement liquid. In the present invention, since it is specified by the measured value at 25 ° C., when it is fixed at 25 ° C. and converted to V _h, there is almost a relationship of V _h = V + 206.

  As in the present invention, when the oxidation-reduction potential (measured with an ORP meter) at a liquid temperature of 25 ° C. is in the range of −150 mV to +50 mV, the substitutional electroless gold plating solution is used for the underlying electroless nickel coating. It becomes possible to form a gold plating layer while suppressing local erosion, and there is no deposition of gold and the stability of the liquid is also good.

  When the electroless nickel plating film used as a base is obtained using an electroless nickel plating solution containing phosphorus and / or sulfur as an element, the grain boundary portion of the electroless nickel plating film is replaced. Since it is easy to be eroded locally at the time of type electroless gold plating, the effect of using the substitution type electroless gold plating solution of the present invention can be further enhanced, which is preferable.

  When the oxidation-reduction potential of the substitutional electroless gold plating solution exceeds +50 mV, the substitutional electroless gold plating solution becomes too noble and excessively promotes the substitution reaction, and as a result, local erosion of the nickel base tends to occur. . On the other hand, if it is lower than −150 mV, the substitutional electroless gold plating solution becomes too base and the substitution reaction is difficult to occur. Gold ions easily receive electrons from the plating solution without elution of nickel, and the plating solution medium acts as a kind of reducing agent, and gold is likely to precipitate. The environment of such a solution is similar to that of a reduced gold plating solution, which reduces the stability of the solution, makes it easier for gold to deposit in a gold plating bath or filter, or deposits gold on the insulating part of the substrate. It may be easier.

  Preferably, it is +30 mV or less, and particularly preferably +10 mV or less. Further, it is preferably −130 mV or more, particularly preferably −110 mV or more.

  There is no particular limitation as to which plating solution component is used to adjust the oxidation-reduction potential, but it may be added in a large amount, and is preferably adjusted with a buffering agent in the plating solution or a chelating agent described later.

  The substitutional electroless gold plating solution of the present invention preferably further contains a chelating agent.

  The chelating agent is not particularly limited as long as it is coordinated to a metal such as nickel, copper, iron, chromium, lead, cobalt and can be stably dissolved in water, but the chelating property to nickel, copper, etc. is good. Is preferable.

  Particularly preferable chelating agents are those having an iminodiacetic acid structure and / or a methylenephosphonic acid structure in that chelating properties with respect to nickel, copper and the like are good.

  Specifically, for example, ethylenediaminetetraacetic acid, nitrilotriacetic acid, hydroxyethylethylenediaminetriacetic acid, diethylenetriaminepentaacetic acid, triethylenetetraminehexaacetic acid, dicarboxymethylglutamic acid, propanediaminetetraacetic acid, 1,3-diamino-2-hydroxylpropane Carboxylic acids such as tetraacetic acid or salts thereof; phosphonic acids such as aminotrimethylenephosphonic acid, hydroxyethylidene diphosphonic acid, ethylenediaminetetramethylenephosphonic acid, diethylenetriaminepentamethylenephosphonic acid, hexamethylenediaminetetramethylenephosphonic acid, or salts thereof Is mentioned. These may be used alone or in combination of two or more. Among these, ethylenediaminetetraacetic acid, nitrilotriacetic acid, aminotrimethylenephosphonic acid, ethylenediaminetetramethylenephosphonic acid and the like are particularly preferable.

  The chelating agent is used in the range of 1 g / L to 100 g / L with respect to the entire substitutional electroless gold plating solution. It is preferably 2 g / L or more, particularly preferably 3 g / L or more, preferably 60 g / L or less, particularly preferably 40 g / L or less. When the concentration of the chelating agent is too large, it may be precipitated in the plating solution, and when it is too small, the chelating effect may be insufficient.

  The chelating agent has an effect of preventing the deposition of metals such as nickel, copper, iron, chromium, lead, cobalt, and the like accumulated in the plating tank as the gold plating solution is operated, and stably dissolving the metal.

  It is also preferable that the gold plating solution of the present invention is used in combination with a surfactant that controls the wetting characteristics of the plating solution, a crystal adjusting agent that controls the crystal structure of the deposited gold plating film, and the like, if necessary.

  The substitutional electroless gold plating solution thus obtained is put in a plating bath and used at a predetermined pH and solution temperature. The pH is usually in the range of 4 to 9, and the liquid temperature is usually in the range of 60 ° C to 100 ° C.

  The material to be immersed in the substitutional electroless gold plating solution of the present invention is formed by applying electroless nickel plating on copper to a thickness of usually 0.2 μm to 10 μm, and is formed on this nickel coating. The thickness of the displacement gold plating layer is preferably in the range of 0.01 μm to 0.3 μm. If it is too thick, the solder adhesive strength may be reduced. If it is too thin, the coloring of the gold plating film may not be detected visually. Particularly preferably, it is 0.02 μm or more and 0.1 μm or less.

  Using the substitutional electroless gold plating solution of the present invention, an electronic component terminal having an electroless gold plating film is obtained as described above. Even if such an electronic component is lead-free solder or the terminal portion is miniaturized, the solder joint strength is sufficiently high, and highly reliable mounting is achieved.

  When the substitutional electroless gold plating solution of the present invention is used, electroless gold plating can be performed while suppressing local erosion of the grain boundary portion of the electroless nickel plating film. There is no known literature describing the relationship between the local erosion of the nickel base and the oxidation-reduction potential of the electroless gold plating solution, and such a discovery is unexpected and is a very important finding of the present invention. An electroless gold plating solution containing a specific component having an oxidation-reduction potential in the range of −150 mV to +50 mV is not clear in the effect of the above effect. However, if it exceeds +50 mV, the nickel coating dissolves. It is considered that the speed is increased and the erosion of the grain boundary portion of the nickel coating having a relatively large amount of elements such as phosphorus and sulfur is more likely to occur, and as a result, the strength of the solder joint is lowered.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further in detail, this invention is not limited to these, unless the summary is exceeded. In the examples, “parts” indicates “parts by weight” unless otherwise specified, and “%” indicates “mass%” unless otherwise specified.

<Preparation of substitutional electroless gold plating solution>
1.0 g / L of gold potassium cyanide in terms of gold, 1000 ppm of the heterocyclic compound shown in Table 1 with respect to the entire electroless gold plating solution, 20 g / L of the buffering agent shown in Table 1, and the chelate shown in Table 1 Each substitution type electroless gold plating solution of Examples 1-5 and Comparative Examples 1-8 was prepared by dissolving the agent in water to 5 g / L and adjusting the pH to 7.5. For pH adjustment, an aqueous sodium hydroxide solution was used to raise the pH, and sulfuric acid was used to lower the pH. In Table 1, “EDTA” represents ethylenediaminetetraacetic acid. The composition of Table 1 is the composition of each electroless gold plating solution in which all the first gold potassium cyanide is blended.

<Preparation of solder joint evaluation substrate>
A solder joint evaluation substrate having the configuration shown in FIGS. 1 and 2 was produced as follows. Circular copper pads with a diameter of 0.76 mm are arranged in a grid pattern on a polyimide resin substrate 40 mm long x 40 mm wide x 1.0 mm thick, and each copper pad is surrounded by a photo solder resist. The one coated with is used. Each copper pad is formed of copper having a thickness of 12 μm, the thickness of the photo solder resist is 20 μm, and the diameter of the opening of the solder ball pad is 0.62 mm.

  An electroless nickel plating film was formed to 5 μm on the copper pad of the substrate by the process shown in Table 2.

  Next, by using each substitution-type electroless gold plating solution prepared with the above composition at 70 ° C. for 10 minutes, the electroless substitution gold-plated film (hereinafter, Abbreviated as “ENIG coating”). When evaluating the solder joint characteristics, it is necessary to strictly control the thickness of the gold plating film on the solder ball pad. Therefore, the thickness of the gold plating film is measured by a fluorescent X-ray film thickness meter (SEA5120). , Manufactured by Seiko Instruments Inc.).

<Evaluation of solder joint strength>
An Sn-Ag-Cu lead-free solder ball having a diameter of 0.76 mm is mounted on a solder ball pad having an opening diameter of 0.62 mm on the substrate on which the ENIG coating is formed, and this is mounted on a reflow furnace apparatus (RF-430-M2 Corporation). (Nippon Pulse Technology Laboratory). A cross-sectional view thereof is shown in FIG. The fused solder balls were peeled off at room temperature using a bond tester (manufactured by # 4000 Dage) (FIG. 4), and the soldered joint strength was evaluated by observing the broken state.

  As shown in FIG. 5, when the breakage occurs in the solder ball and when the copper pad itself is broken, the solder joint strength is high. On the other hand, as shown in FIG. 6, the breakage occurs near the plating interface. When a part of the gold plating layer and / or the nickel plating layer is exposed, it is determined that the solder joint strength is low. When the solder joint strength is low, the reliability of the solder joint is also low.

By the above method, the percentage of the number of copper pads judged to have high solder joint strength to the total number of copper pads used for solder joint strength evaluation was determined and determined as follows. The results are shown in Table 3.
100%: ○
Less than 100%, 80% or more: ×
Less than 80%, 60% or more: XX
Less than 60%: XXX

The oxidation-reduction potential and gold plating solution storage stability of the substitutional electroless gold plating solution were evaluated by the methods shown below. The results are shown in Table 3.
<Oxidation-reduction potential measurement method>
The measurement of the oxidation-reduction potential was performed with an ORP meter (pH / ORP meter TP-94 electrode PCM90 manufactured by Toko Chemical Laboratory Co., Ltd.). First, the electrode was immersed in a quinhydrone standard solution for 30 minutes, and it was confirmed that the potential was 260 ± 20 mV. If it confirmed that it was in the range, the electrode was carefully washed with pure water and immersed in each electroless gold plating solution adjusted to 25 ° C. The value of the ORP meter after 5 minutes from the start of immersion was read and used as the oxidation-reduction potential of the substitutional electroless gold plating solution. The results are shown in Table 3.

<Evaluation of storage stability of gold plating solution>
The above-mentioned substitutional electroless gold plating solution was adjusted to a use state, a beaker was covered with a cover for preventing evaporation, and the beaker was left in a 90 ° C. air constant temperature bath. The time at which gold began to deposit on the side wall and bottom of the beaker was measured to evaluate the storage stability of the gold plating solution, and the following determination was made. The results are shown in Table 3.
No precipitation was observed after standing for 50 hours:
Precipitation was observed in 10 hours to 50 hours: ×
Precipitation was observed in less than 10 hours: XX

The erosion state of the electroless nickel plating film as a base was observed by the following method.
<Evaluation of grain boundary erosion>
In the gold plating solution storage stability evaluation, substitutional electroless gold plating was performed on the nickel coating using a substitutional electroless gold plating solution that was not deposited even after being allowed to stand for 50 hours. Here, the method of electroless nickel plating, substitutional electroless gold plating, film thickness, and the like were performed in the same manner as described in the section “Preparation of a substrate for solder joint evaluation”.

The substrate on which the ENIG film is formed in this manner is immersed in a gold release agent (stripper gold manufactured by Nippon Kogyo Kagaku Co., Ltd.) at room temperature for 1 minute to remove the gold film, and the exposed nickel surface is scanned with a scanning electron microscope ( S-4300 (manufactured by Hitachi, Ltd.), and the state of grain boundary erosion of the nickel plating film was observed and determined as follows. The results are shown in Table 3.
Grain boundary erosion was not confirmed: ○
Grain boundary erosion was confirmed: ×

  As a typical example of determination, FIG. 7 shows an SEM photograph in the case of Example 1, and FIG. 8 shows an SEM photograph in the case of Comparative Example 1 as a representative example of × determination. In the gold plating solution storage stability evaluation, a plating solution having an evaluation of x or less was regarded as incapable of measuring grain boundary erosion because plating itself was impossible.

<Depth Auger Spectrum Measurement>
The substrate on which the ENGI film was formed in the same manner as the evaluation of grain boundary erosion was analyzed by depth Auger measurement (Microlab 310-F, UK VG, electron source: field emission). If oxygen is detected from the interface between the gold coating and the nickel coating, it is determined that the underlying nickel is oxidized. The results are shown in Table 3.

  FIG. 9 shows the measurement results of Example 1 in which oxidation of the underlying nickel was not confirmed, and FIG. 10 shows the measurement results of Comparative Example 3 in which oxidation was confirmed.

  As can be seen from Table 3, a substitutional electroless gold plating solution containing a heterocyclic compound having a redox potential in the range of −150 mV to +50 mV and having 3 or more nitrogen atoms in the molecule (Example 1 and Example 1). In Example 2), all the above evaluations were excellent. On the other hand, when the oxidation-reduction potential was too high at +130 mV (Comparative Example 1), the solder joint strength was inferior, and erosion was observed at the grain boundaries of the nickel plating film. Conversely, when the oxidation-reduction potential was too low at −200 mV (Comparative Example 2), gold began to deposit on the side walls and bottom of the beaker in 8 hours, and the gold plating solution storage stability was poor.

  Further, in the substitutional electroless gold plating solution containing no heterocyclic compound (Comparative Example 3), even when the oxidation-reduction potential is within the above range of −10 mV, the solder joint strength is inferior, and the grain boundary of the nickel plating film Erosion was seen. From this, it is only by combining a specific range of oxidation-reduction potential and a heterocyclic compound having 3 or more nitrogen atoms in the molecule that the above-mentioned performance required for a substitutional electroless gold plating solution is excellent. It turns out that it is obtained.

  About substitution type electroless gold plating solution of Examples 1-5 and Comparative Examples 1-8, (1) Relationship between oxidation-reduction potential and gold-plating solution storage stability, (2) Oxidation-reduction potential (with strong solder joint strength) The relationship with intergranular erosion was measured. The results are shown in Table 4.

  As can be seen from the results in Table 4, all of the redox potentials in the range of −150 mV to +50 mV except for Comparative Example 3 were not confirmed to have grain boundary erosion (Examples 1 to 5), and the redox potential was In all cases outside the above range, grain boundary erosion was confirmed, or gold was deposited during storage and plating was not performed normally. (Comparative Examples 1-8). In Comparative Example 3, since no heterocyclic compound was contained, grain boundary erosion was confirmed although the oxidation-reduction potential was within the above range.

  From this, the presence or absence of grain boundary erosion is clear depending on whether or not the redox potential is in the range of −150 mV to +50 mV, provided that a heterocyclic compound having 3 or more nitrogen atoms is contained in the molecule. That is, it was found that the magnitude of the solder joint strength (solder joint reliability) is clearly distinguished.

  The substitutional electroless gold plating solution of the present invention is widely used as a substitutional electroless gold plating solution for ENIG because it is difficult for gold to deposit in a gold plating bath or a filter, and an excellent solder joint strength is obtained. It is used for forming a gold plating film on a connection terminal portion of an electronic component.

It is a top view which shows the length etc. of each part of the board | substrate used for solder joint evaluation. It is sectional drawing which shows the length etc. of each part of the board | substrate used for solder joint evaluation. It is sectional drawing which shows the shape of the fused solder ball used for solder joint evaluation. It is a figure which shows the normal temperature pull system by a bond tester in solder joint evaluation. FIG. 5 is a cross-sectional view showing a state in which the solder joint strength is high and breakage occurs in the solder ball. FIG. 5 is a cross-sectional view showing a state in which a solder joint strength is low and fracture occurs near a plating interface, and a part of a gold plating layer and / or a nickel plating layer is exposed. It is a 2000 times SEM photograph of what the grain plating erosion was not confirmed on the nickel plating film surface which peeled and exposed the gold plating film. It is a 2000 times SEM photograph of what grain boundary erosion was confirmed on the nickel plating film surface which peeled and exposed the gold plating film. It is a depth Auger spectrum measurement result of the board | substrate which formed the ENGI film. When oxidation of the underlying nickel coating was not confirmed. It is a depth Auger spectrum measurement result of the board | substrate which formed the ENGI film. When oxidation of the underlying nickel coating is confirmed.

Claims (7)

At least a gold cyanide salt, a π-electron rich aromatic heterocyclic compound having 3 or more nitrogen atoms in the molecule , and at least one buffer selected from the group consisting of sulfurous acid, phosphorous acid and salts thereof A substitutional electroless gold for producing an electroless gold plating film on an electroless nickel plating film , the electroless plating solution being contained and having a redox potential at 25 ° C. in the range of −150 mV to +10 mV Plating solution.   The substitutional electroless gold plating solution according to claim 1, further comprising a chelating agent.   The substitutional electroless gold plating solution according to claim 2, wherein the chelating agent has an iminodiacetic acid structure and / or a methylenephosphonic acid structure in the molecule.   The electroless gold plating solution using the substitutional electroless gold plating solution according to any one of claims 1 to 3 while suppressing local erosion of the grain boundary portion of the electroless nickel plating film. A method for producing a plating film.   The electroless nickel plating film is obtained by using an electroless nickel plating solution containing phosphorus and / or sulfur, and suppresses local erosion of the grain boundary part of the electroless nickel plating film according to claim 4. To produce an electroless gold plating film.   An electroless gold plating solution having a thickness in the range of 0.01 μm to 0.3 μm on the electroless nickel plating film using the substitutional electroless gold plating solution according to claim 1. A method for producing a gold plating film to be plated.   An electronic component terminal provided with an electroless gold plating film using the substitutional electroless gold plating solution according to any one of claims 1 to 3.