Multi-layer plating film

Abstract

To provide a plating film capable of improving the connection reliability of solder joints due to the accumulation of heat history after solder mounting.SOLUTION: A multilayer plating film has an electroless nickel-germanium alloy plating film, an electroless palladium plating film, and an electroless gold plating film laminated in this order.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a multilayer plating film, and more particularly to a multilayer plating film having excellent characteristics in solder joint reliability.

Background Art

[0002] Conventionally, when connecting a circuit board and an electronic component, after electroless nickel plating is applied as a barrier metal on a conductor pattern such as a copper pattern provided on the circuit board, ENIG (Electroless Nickel Immersion Gold) in which gold plating is performed for the purpose of improving connection reliability, or after electroless nickel plating is applied as a barrier metal on the conductor pattern, electroless palladium is formed on the nickel plating, and ENEPIG (Electroless Nickel Electroless Palladium Immersion Gold) in which gold plating is performed for the purpose of improving connection reliability thereon is performed.

[0003] In recent years, with the increase in density and functionality of electronic components mounted on printed circuit boards, the load on solder joints has been increasing, but it is required to operate without problems such as breakage and deterioration in the solder joints. For example, higher reliability is required for the solder joints of output control devices such as traffic control devices and engines.

[0004] As a technique for enhancing the reliability of solder joints, for example, Patent Document 1 discloses a technique in which the average value of nickel crystal sizes in a nickel plating layer is 2 μm or more. Further, Patent Document 2 discloses a technique of laminating two electroless palladium plating films having different purities in a laminated film of an electroless nickel plating film, an electroless palladium plating film, and a displacement gold plating film.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

[0006] It has been pointed out that one of the causes of the failure of solder joints is thermal fatigue failure due to the accumulation of thermal history. For example, in in-vehicle electronic components, not only the ambient temperature changes, but also the radiant heat around the engine and the self-heating of the electronic components repeatedly apply temperature changes with a large temperature difference to the solder joints. When thermal fatigue accumulates in the solder joints due to such a thermal history, the solder joints may eventually break.

[0007] The present invention has been made in view of the above circumstances, and an object thereof is to provide a plating film capable of improving the connection reliability (hereinafter sometimes referred to as joint reliability) of solder joints due to the accumulation of thermal history. [Means for Solving the Problems]

[0008] The present invention that has solved the above problems has the following configuration. [1] A multilayer plating film in which an electroless nickel-germanium alloy plating film, an electroless palladium plating film, and an electroless gold plating film are laminated in this order.

[0009] [2] The multilayer plating film according to [1] above, wherein the germanium content contained in the electroless nickel-germanium alloy plating film is 0.01 to 25% by mass.

[0010] [3] A wiring board in which the electroless nickel-germanium alloy plating film, the electroless palladium plating film, and the electroless gold plating film according to [1] or [2] above are laminated in this order on the conductor surface of the substrate. [Effects of the Invention]

[0011] According to the multi-layer plating film of the present invention, the connection reliability of solder joints can be improved by the accumulation of thermal history.

Brief Description of the Drawings

[0012]

Figure 1

Embodiments for Carrying Out the Invention

[0013] The ENEPIG film (electroless nickel plating film / electroless palladium plating film / immersion gold plating film) has excellent bonding reliability and wire bonding properties at room temperature, but the plating film at the solder joint is likely to break due to thermal history. As a result of the inventors' investigation into the cause of the breakage, it was found that when a temperature change with a large temperature difference is repeatedly applied to the solder joint, for example, stress caused by the difference in the coefficient of thermal expansion between the electronic component and the substrate is repeatedly applied to the solder joint, and finally the solder joint breaks. As a result of a detailed investigation of the breakage location of the solder joint, it was found that the electroless nickel plating film is likely to break due to thermal deterioration. It was also found that the intermetallic compound between the solder material and the plating film grows due to thermal history, resulting in a decrease in bonding reliability. As a result of the inventors' intensive research, it was found that the bonding reliability can be significantly improved by including a specific alloy component in the electroless nickel plating film, leading to the present invention.

[0014] The plating film of the present invention is a multi-layer plating film in which an electroless nickel-germanium alloy plating film 3, an electroless palladium plating film 4, and an electroless gold plating film 5 are laminated in this order as shown in FIG. 1. The multi-layer plating film of the present invention obtains an effect of improving bonding reliability due to the synergistic effect of these three layers. The present invention also includes a wiring board in which an electroless nickel-germanium alloy plating film 3, an electroless palladium plating film 4, and an electroless gold plating film 5 are laminated in this order on the surface of a conductor 2 formed on a substrate 1. The multilayer plating film of the present invention only needs to be formed on at least a part of the conductor surface, and is preferably formed on the conductor surface constituting the solder joint. The multilayer plating film of the present invention may be formed on the entire conductor surface on the substrate other than the solder joint. Hereinafter, each plating film configuration will be described.

[0015] Electroless nickel-germanium alloy plating film The electroless nickel-germanium alloy plating film of the present invention is a plating film in which germanium and nickel are alloyed, and by containing germanium, it has excellent joint reliability against thermal history compared to the conventional electroless Ni-P plating film. Joint reliability cannot be obtained with electroless nickel alloy plating films other than the electroless nickel-germanium alloy plating film, for example, the electroless Ni-Fe alloy plating film, the electroless Ni-Cu alloy plating film, the electroless Ni-Sn alloy plating film, etc. as shown in the examples.

[0016] Germanium is essential for the electroless nickel-germanium alloy plating film to exhibit joint reliability, and in order to obtain better joint reliability, it is desirable to increase the germanium content. On the other hand, if the germanium content becomes too high, the nickel content decreases, resulting in changes in conductivity, adhesion, etc., and the joint reliability may decrease. The germanium content in the electroless nickel-germanium alloy plating film is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, still more preferably 1.0% by mass or more, and preferably less than 50% by mass, more preferably 30% by mass or less, still more preferably 25% by mass or less, and even more preferably 20% by mass or less. The remainder of the electroless nickel-germanium alloy plating film excluding the above germanium content is nickel and inevitable impurities. The composition of the electroless nickel-germanium alloy plating film is measured using an ICP emission spectrometer under the measurement conditions of the examples.

[0017] The thicker the electroless nickel-germanium alloy plating film, the more desirable it is because the bonding reliability can be improved. On the other hand, if the film thickness is too thick, the effect of improving the bonding reliability will saturate and it will not be economical. The film thickness of the electroless nickel-germanium alloy plating film is preferably 0.01 μm or more, more preferably 1.0 μm or more, preferably 100 μm or less, and more preferably 10 μm or less.

[0018] Third component The electroless nickel-germanium alloy plating film preferably does not contain alloy components (third components) other than nickel and germanium and is composed of nickel and germanium. Note that the electroless nickel-germanium alloy plating film allows third components that are inevitably contained due to raw materials such as reducing agents, but the inevitable impurities derived from raw materials are preferably 15% by mass or less, more preferably 10% by mass or less, still more preferably 5% by mass or less, and even more preferably 0% by mass. If the electroless nickel-germanium alloy plating film contains a third component, the film quality changes, the above-mentioned thermal deterioration is likely to occur, intermetallic compounds are likely to be formed, and the bonding reliability decreases.

[0019] Electroless palladium plating film The electroless palladium plating film has an effect of preventing the thermal diffusion of nickel and also has an effect of improving heat resistance. In addition, by forming a laminated structure of electroless nickel-germanium alloy, electroless palladium plating film, and electroless gold plating film in this order from the substrate side, the bonding reliability can be improved.

[0020] The electroless palladium plating film may contain alloy components other than palladium (referred to as other alloy components). Examples of other alloy components include phosphorus, boron, and germanium, and one or two or more of other alloy components may be used in combination. The content of other alloy components in the electroless palladium plating film (the total amount in the case of two or more types) may be set so as to obtain a desired effect. However, if the content becomes too high, the film quality of the plating film may change and the above effect may decrease. Therefore, it is preferably 10% by mass or less, more preferably 8% by mass or less, and may be 0% by mass (not including). When the electroless palladium plating film does not contain other alloy components, the palladium content is preferably 99.9% by mass or more, and the balance allows inevitable impurities, but more preferably 100% by mass.

[0021] If the film thickness of the electroless palladium plating film is too thin, the effect of improving the bonding reliability or the effect of preventing diffusion of nickel etc. may not be improved. Also, if it is too thick, the bonding reliability deteriorates. The film thickness of the electroless palladium plating film is preferably 0.01 μm or more, more preferably 0.02 μm or more, preferably 1.0 μm or less, more preferably 0.5 μm or less, and even more preferably 0.3 μm or less.

[0022] Electroless gold plating film The electroless gold plating film has an effect of improving solder wetting property and also has an effect of improving heat resistance. Also, the bonding reliability can be improved by forming a multilayer structure in which an electroless nickel-germanium alloy plating film, an electroless palladium plating film, and an electroless gold plating film are laminated in order from the substrate side.

[0023] If the electroless gold plating film contains alloy components other than gold, the film quality may change and the above effects such as bonding reliability may decrease. In the electroless gold plating film, the gold content is preferably 99.9% by mass or more, and the balance allows inevitable impurities, but more preferably 100% by mass.

[0024] The film thickness of the electroless gold plating film may be set according to the required characteristics. For example, if the film thickness is increased, the solder wetting property can be enhanced. The thickness of the electroless gold plating film is preferably 0.01 μm or more, more preferably 0.05 μm or more, and preferably 1.0 μm or less, more preferably 0.5 μm or less.

[0025] The electroless gold plating film of the present invention may be either a substitution-type gold plating film or a reduction-type gold plating film. The electroless gold plating film is preferably a substitution gold plating film, and by adopting the substitution gold plating film, the multilayer plating film of the present invention can be treated in the same manner as an ENEPIG film.

[0026] The multilayer plating film of the present invention is composed of the above three layers and is laminated in the order shown in FIG. 1. In the present invention, if there are other plating films (other plating films) other than the above, the bonding reliability will decrease, so other plating films are not included.

[0027] Hereinafter, a method for forming the multilayer plating film of the present invention will be described. In the present invention, after performing pretreatment such as degreasing and activation on the object to be plated as needed, an electroless nickel-germanium alloy plating film, then an electroless palladium plating film is formed, and then an electroless gold plating film is formed thereon.

[0028] The object to be plated is a metal material that constitutes a conductor such as an electrode or wiring formed on the surface of a substrate. The metal material may be any material on which an electroless nickel-germanium alloy plating film can be formed, and examples include various known metal materials such as Al and Al-based alloys, Cu and Cu-based alloys. Examples of the substrate include various known insulating substrates such as resin substrates, ceramic substrates, glass substrates, and wafer substrates.

[0029] Examples of the pretreatment include, but are not limited to, cleaner treatment, pickling, etching, predip, catalyst, etc., and various known pretreatments may be performed as needed.

[0030] Electroless nickel-germanium alloy plating treatment The electroless nickel-germanium alloy plating process involves immersing the object to be plated in an electroless nickel-germanium alloy plating solution to form an electroless nickel-germanium alloy plating film. The immersion time is not particularly limited, and it is sufficient if the desired electroless nickel-germanium alloy plating film can be formed with the desired film thickness. For example, it may be about 10 seconds to 50 minutes. In the electroless nickel-germanium alloy plating process, stirring of the plating solution and rocking of the object to be plated may be performed as necessary.

[0031] Electroless nickel-germanium alloy plating solution The electroless nickel-germanium alloy plating solution of the present invention contains a water-soluble nickel salt as a nickel source. Examples of the water-soluble nickel salt include inorganic water-soluble nickel salts such as nickel sulfate, nickel bromide, nickel chloride, and nickel sulfamate; and organic water-soluble nickel salts such as nickel carbonate and nickel acetate. Preferably, it is nickel sulfate hexahydrate. These can be used alone or in combination of two or more.

[0032] Considering the plating deposition rate, it is desirable to increase the concentration of the water-soluble nickel compound in the electroless nickel-germanium alloy plating solution (the concentration when included alone is the single concentration, and the total concentration when two or more are used in combination). However, if the concentration of the water-soluble nickel compound becomes too high, the deposition rate may become too fast or the stability of the plating solution may decrease. The concentration of the water-soluble nickel compound, as nickel concentration (in terms of Ni), is preferably 0.1 g / L or more, more preferably 1.0 g / L or more, and preferably 100 g / L or less, more preferably 25 g / L or less.

[0033] The electroless nickel-germanium alloy plating solution contains a water-soluble germanium compound as a germanium source. Examples of the water-soluble germanium compound include germanium oxide, germanium chloride, germanium bromide, germanium sulfide, etc. Preferably, it is germanium oxide. These can be used alone or in combination of two or more.

[0034] Regarding the concentration of the water-soluble germanium compound in the electroless nickel-germanium alloy plating solution (the concentration is the individual concentration when contained alone, and the total concentration when two or more are used in combination), it is desirable to increase the germanium concentration in consideration of the bonding reliability. On the other hand, if the concentration of the water-soluble germanium compound becomes too high, the stability of the plating solution may decrease. The concentration of the water-soluble germanium compound, as the germanium (Ge) concentration, is preferably 0.01 g / L or more, more preferably 0.02 g / L or more, still more preferably 0.1 g / L or more, and even more preferably 1.0 g / L or more, and is preferably 100 g / L or less, more preferably 25 g / L or less, still more preferably 23 g / L or less, and even more preferably 15 g / L or less.

[0035] Reducing agent The reducing agent used in the present invention only needs to have the reducing precipitation action of nickel ions and germanium ions, and various known reducing agents used in electroless nickel plating solutions can be used. Examples of the reducing agent include hypophosphorous acid; hypophosphites such as sodium hypophosphite, potassium hypophosphite, and ammonium hypophosphite; amine borane compounds such as dimethylamine borane and trimethylamine borane; boron hydride compounds such as sodium borohydride and potassium borohydride; hydrazines, etc. Examples of hydrazines include hydrazine; hydrated hydrazines such as hydrazine monohydrate; hydrazine salts such as hydrazine carbonate, hydrazine sulfate, neutral hydrazine sulfate, and hydrazine hydrochloride; organic derivatives of hydrazine such as pyrazoles, triazoles, and hydrazides; etc. can be used. The above reducing agents can be used alone or in combination of two or more.

[0036] The concentration of the reducing agent in the electroless nickel-germanium alloy plating solution (when included alone, it is the concentration of the single component, and when two or more components are used in combination, it is the total concentration) varies depending on the type of the reducing agent, but it is preferably adjusted to a concentration at which a sufficient reducing action can be obtained. Considering the plating deposition rate, it is desirable to increase the concentration of the reducing agent. However, if the concentration of the reducing agent becomes too high, the stability of the plating solution may decrease. The concentration of the reducing agent in the plating solution is preferably 0.5 g / L or more, more preferably 1.0 g / L or more, still more preferably 10 g / L or more, and preferably 100 g / L or less, more preferably 50 g / L or less.

[0037] Note that, due to the reducing agent, reducing agent components such as phosphorus (P) may be contained in the electroless nickel-germanium alloy plating film. In the present invention, since a reliable joint can be obtained with an alloy film of nickel and germanium, phosphorus or the like derived from the reducing agent may be contained, and these are allowed as inevitable impurities.

[0038] Complexing agent As the complexing agent contained in the electroless nickel-germanium alloy plating solution of the present invention, known complexing agents used in electroless nickel plating solutions can be used. Examples of the complexing agent include monocarboxylic acids such as acetic acid, formic acid, propionic acid, and butyric acid, or salts thereof; dicarboxylic acids such as malonic acid, succinic acid, adipic acid, maleic acid, oxalic acid, and fumaric acid, or salts thereof; oxycarboxylic acids such as malic acid, lactic acid, glycolic acid, gluconic acid, citric acid, and tartaric acid, or salts thereof; aminocarboxylic acids such as glycine, alanine, arginine, aspartic acid, and glutamic acid, or salts thereof. Examples of the salts include alkali metal salts such as sodium, potassium, and lithium; alkaline earth metal salts such as calcium; and soluble salts such as ammonium salts. The above complexing agents can be used alone or in combination of two or more.

[0039] Regarding the concentration of the complexing agent in the electroless nickel-germanium alloy plating solution (when included alone, it is the individual concentration, and when two or more are used in combination, it is the total concentration), considering the plating deposition rate, it is desirable to increase the concentration of the complexing agent. On the other hand, even if the concentration of the complexing agent is increased too much, the effect will saturate. The concentration of the complexing agent is preferably 5 g / L or more, more preferably 10 g / L or more, and preferably 200 g / L or less, more preferably 80 g / L or less.

[0040] In addition to the above-described components, the electroless nickel-germanium alloy plating solution may be blended with known additives used in electroless nickel plating solutions as necessary. Examples of the additives include stabilizers, pH adjusters, surfactants, and the like.

[0041] Stabilizer As the stabilizer, various known stabilizers having an effect on the stability of the plating solution can be used. Examples of the stabilizer include lead compounds such as lead nitrate and lead acetate; cadmium compounds such as cadmium nitrate and cadmium acetate; thallium compounds such as thallium nitrate and thallium nitrate; antimony compounds such as antimony chloride and potassium antimonyl tartrate; chromium compounds such as chromium oxide and chromium sulfate; divalent or trivalent iron ion sources such as iron sulfate, iron chloride, iron sulfide, iron nitrate, and iron oxide; iodine ion sources such as potassium iodide, iron iodide, nickel iodide, lithium iodide, and sodium iodide. Among these, it is preferable to use a combination of an iron ion source and an iodine ion source because it can suppress the decomposition of the plating solution and stabilize the plating solution. The stabilizer can be used alone or in combination of two or more.

[0042] The concentration of the stabilizer in the electroless nickel-germanium alloy plating solution is not particularly limited as long as the effect of improving stability can be obtained. The concentration of the stabilizer (the individual concentration when included alone, and the total concentration when two or more are used in combination) is preferably 0.01 mg / L or more, more preferably 0.1 mg / L or more, and preferably 100 mg / L or less, more preferably 10 mg / L or less. When an iron ion source and an iodine ion source are used in combination, it is preferable to adjust the iron ion source in the range of 0.1 to 100 mg / L and the iodine ion source in the range of 10 to 4000 mg / L.

[0043] pH adjuster As the pH adjuster, various known pH adjusters having the effect of adjusting the pH of the plating solution to a predetermined value can be used. As the pH adjuster, for example, acids such as hydrochloric acid, sulfuric acid, and phosphoric acid; alkalis such as sodium hydroxide, potassium hydroxide, and aqueous ammonia can be used.

[0044] If the pH of the electroless nickel-germanium alloy plating solution is too low, the deposition rates of nickel and germanium decrease, the film-forming property of the nickel-germanium alloy plating film deteriorates, and defects such as pores may occur on the film surface. On the other hand, if the pH is too high, the deposition rates of nickel and germanium may become excessively fast, making it difficult to control the film thickness. The pH of the electroless nickel-germanium alloy plating solution is preferably 2.0 or more, more preferably 4.0 or more, and preferably 12.0 or less, more preferably 10.0 or less.

[0045] Surfactant As the surfactant, for example, various known surfactants such as nonionic, anionic, cationic, and amphoteric surfactants can be used alone or in combination of two or more.

[0046] The concentration of the surfactant in the electroless nickel-germanium alloy plating solution is not particularly limited as long as the addition effect can be obtained. The concentration of the surfactant (the concentration alone when contained alone and the total concentration when two or more are used in combination) is preferably 0.01 mg / L or more, more preferably 0.1 mg / L or more, preferably 100 mg / L or less, and more preferably 10 mg / L or less.

[0047] Temperature The temperature during the treatment of the electroless nickel-germanium alloy plating solution is preferably in the range of 30°C to 90°C of the solution temperature. If the solution temperature is too low, the deposition rate may become slow. On the other hand, if the solution temperature is too high, the deposition rate may become excessive, or the amount of water evaporation from the plating solution may increase and the solution composition may vary. The solution temperature of the electroless nickel-germanium alloy plating solution is preferably 30°C or more, more preferably 40°C or more, preferably 90°C or less, and more preferably 80°C or less.

[0048] Electroless palladium plating The electroless palladium plating film is formed on the surface of the electroless nickel-germanium alloy plating film. When performing electroless palladium plating after electroless nickel plating, for example, after forming the electroless nickel-germanium alloy plating film, washing with water is performed, and then activation treatment is performed using the activation composition of the present invention. After performing a water washing treatment as necessary, electroless palladium plating treatment may be performed. By immersing the object to be plated on which the electroless nickel-germanium alloy plating film is formed in the electroless palladium plating solution, an electroless palladium plating film can be formed (laminated) on the surface of the electroless nickel-germanium alloy plating film. The immersion time is not particularly limited as long as the desired electroless palladium plating film can be formed with the desired film thickness, and for example, it may be about 1 minute to 20 minutes.

[0049] Electroless palladium plating solution The plating solution and plating method used for electroless palladium plating can adopt the known electroless palladium plating solution and electroless palladium plating method used for the formation of ENEPIG.

[0050] The electroless palladium plating solution is an aqueous solution containing a palladium compound, a reducing agent, and a complexing agent as essential components. It contains a water-soluble palladium compound as a palladium source. As the water-soluble palladium compound, for example, water-soluble palladium compounds such as palladium sulfate, palladium chloride, palladium acetate, dichlorodiethylenediamine palladium, and tetraammine palladium dichloride can be used. These can be used alone or in combination of two or more.

[0051] Considering the above effects of the electroless palladium plating film, it is desirable to increase the concentration of the water-soluble palladium compound in the electroless palladium plating solution (the concentration when included alone is the single concentration, and the total concentration when two or more are used in combination). On the other hand, if the concentration of the palladium compound is too high, the stability of the plating solution may decrease. The concentration of the water-soluble palladium compound, as the palladium (Pd) concentration, is preferably 0.1 g / L or more, more preferably 0.5 g / L or more, and preferably 30 g / L or less, more preferably 10 g / L or less.

[0052] Reducing agent The reducing agent only needs to have the action of reducing and depositing palladium ions, and various known reducing agents used in electroless palladium plating solutions can be used. The reducing agent is, for example, at least one selected from the group consisting of formic acids, hydrazines, hypophosphorous acid compounds, phosphorous acid compounds, amine borane compounds, and borohydride compounds. Examples of formic acids include formic acid and formate salts. Examples of hydrazines include hydrazine; hydrated hydrazines such as hydrazine monohydrate; hydrazine salts such as carbohydrazide, hydrazine sulfate, neutral hydrazine sulfate, and hydrazine hydrochloride; and organic derivatives of hydrazine such as pyrazoles, triazoles, and hydrazides. Examples of hypophosphorous acid compounds include hypophosphorous acid and hypophosphite salts. Examples of phosphorous acid compounds include phosphorous acid and phosphite salts. Examples of amine borane compounds include dimethylamine borane (DMAB) and trimethylamine borane (TMAB). Examples of borohydride compounds include alkali metal borohydrides such as sodium borohydride (SBH) and potassium borohydride (KBH). Examples of salts include alkali metal salts such as sodium and potassium; alkaline earth metal salts such as magnesium and calcium; ammonium salts, quaternary ammonium salts, and amine salts containing primary to tertiary amines. The above reducing agents can be used alone or in combination of two or more.

[0053] The concentration of the reducing agent in the electroless palladium plating solution (the concentration alone when used alone and the total concentration when used in combination of two or more) varies depending on the type of the reducing agent, but it is desirable to adjust it to a concentration at which a sufficient reducing action can be obtained. Considering the plating deposition rate, it is desirable to increase the reducing agent concentration, but if the concentration of the reducing agent becomes too high, the stability of the plating solution may decrease. The concentration of the reducing agent in the plating solution is preferably 0.1 g / L or more, more preferably 1.0 g / L or more, and preferably 100 g / L or less, more preferably 50 g / L or less.

[0054] Complexing agent In the present invention, known complexing agents used in electroless palladium plating solutions can be used. Examples of the complexing agent include amines such as ethylenediamine and diethylenetriamine; aminopolycarboxylic acids such as ethylenediaminediacetic acid, ethylenediaminetetraacetic acid, and diethylenetriaminepentaacetic acid, and their salts; amino acids such as glycine, alanine, iminodiacetic acid, nitrilotriacetic acid, L-glutamic acid, L-glutamic acid diacetate, L-aspartic acid, and taurine, and their salts; aminotrimethylenephosphonic acid, 1-hydroxyethylidene-1,1-diphosphonic acid, ethylenediaminetetramethylenephosphonic acid, and their salts can be blended. Examples of the salts include alkali metal salts such as sodium and potassium; alkaline earth metal salts such as calcium; and ammonium salts. The above complexing agents can be used alone or in combination of two or more.

[0055] The concentration of the complexing agent (when included alone, it is the concentration of the single one, and when two or more are used in combination, it is the total concentration) is preferably 0.5 g / L or more, more preferably 5 g / L or more, and preferably 100 g / L or less, more preferably 50 g / L or less.

[0056] In addition to the above components, the electroless palladium plating solution may be blended with known additives used in the electroless palladium plating solution as needed. Examples of the additives include stabilizers, pH adjusters, surfactants, etc. Various known stabilizers, pH adjusters, and surfactants can be used. Specific examples include the examples of various additives of electroless nickel-germanium alloy plating solutions, and the contents are also of the same degree.

[0057] pH The pH of the electroless palladium plating solution is preferably 2 or more, more preferably 3 or more, and preferably 9 or less, more preferably 8 or less.

[0058] Temperature The temperature during the treatment of the electroless palladium plating solution is preferably 30°C or higher, more preferably 40°C or higher, and preferably 90°C or lower, more preferably 80°C or lower, for the same reason as the liquid temperature of the electroless nickel-germanium alloy plating solution.

[0059] Electroless gold plating treatment The electroless gold plating film is formed on the surface of the electroless palladium plating film. By immersing the object to be plated with the electroless palladium plating film in the electroless gold plating solution, an electroless gold plating film can be formed (laminated) on the surface of the electroless palladium plating film. The immersion time is not particularly limited, and it is sufficient if the desired electroless gold plating film can be formed with the desired film thickness. For example, it may be about 2 minutes to 60 minutes.

[0060] Electroless gold plating solution As the electroless gold plating solution used for the electroless gold plating treatment, various known displacement-type gold plating solutions and reduction-type gold plating solutions can be used. Hereinafter, a displacement-type gold plating solution, which is a preferred example, will be described. In the present invention, a known displacement gold plating solution and displacement gold plating method used for the formation of ENEPIG can be adopted. The displacement gold plating solution is an aqueous solution containing a water-soluble gold compound and a complexing agent as essential components. Known water-soluble gold salts can be used as the water-soluble gold compound. For example, cyanide-containing gold plating solutions and cyanide-free gold plating solutions can be mentioned, and a cyanide-free gold plating solution is preferred. Examples of the cyanide-containing plating solution include gold thiocyanate, or gold thiocyanate salts such as potassium cyanide, sodium cyanide, and ammonium cyanide. Examples of the cyanide-free gold plating solution include gold sulfite, gold thiosulfate, chloroauric acid, or salts thereof. Examples of the salts include alkali metal salts such as sodium, potassium, and lithium; alkaline earth metal salts such as calcium; and soluble salts such as ammonium salts. These can be used alone or in combination of two or more.

[0061] The concentration of the water-soluble gold compound in the displacement gold plating solution (the concentration alone when contained alone, and the total concentration when two or more are used in combination) is desirably increased in consideration of the above effects of the displacement gold plating film. On the other hand, if the concentration of the water-soluble gold compound is increased too much, the stability of the plating solution may decrease. The concentration of the water-soluble gold compound (the concentration alone when contained alone as the gold (Au) concentration, and the total concentration when two or more are used in combination) is preferably 0.1 g / L or more, more preferably 0.5 g / L or more, and preferably 30 g / L or less, more preferably 10 g / L or less.

[0062] Complexing agent In the present invention, known complexing agents used in displacement gold plating solutions can be used. Examples of the complexing agent include amines such as ethylenediamine and diethylenetriamine; aminopolycarboxylic acids such as ethylenediaminediacetic acid, ethylenediaminetetraacetic acid, and diethylenetriaminepentaacetic acid, and salts thereof; amino acids such as glycine, alanine, iminodiacetic acid, nitrilotriacetic acid, L-glutamic acid, L-aspartic acid, and taurine, and salts thereof; alkylsulfonic acids such as aminotrimethylenephosphonic acid, ethylenediaminetetramethylenephosphonic acid, methanesulfonic acid, and ethanesulfonic acid, and salts thereof; alkanolsulfonic acids such as hydroxymethanesulfonic acid and hydroxyethanesulfonic acid, and salts thereof; aromatic sulfonic acids such as benzenesulfonic acid and p-phenolsulfonic acid, and salts thereof. Examples of the salts include alkali metal salts such as sodium and potassium; alkaline earth metal salts such as calcium; and ammonium salts. The above complexing agents can be used alone or in combination of two or more.

[0063] The concentration of the complexing agent (the concentration alone when contained alone, and the total concentration when two or more are used in combination) is preferably 0.5 g / L or more, more preferably 5 g / L or more, and preferably 100 g / L or less, more preferably 50 g / L or less.

[0064] In addition to the above-described components, the immersion gold plating solution may be blended with known additives used in immersion gold plating solutions as needed. Examples of the additives include stabilizers, pH adjusters, surfactants, etc. Various known stabilizers, pH adjusters, and surfactants can be used. Specific examples include the examples of various additives in electroless nickel-germanium alloy plating solutions, and the contents are also of the same degree.

[0065] pH The pH of the immersion gold plating solution is preferably 2 or more, more preferably 3 or more, and preferably 9 or less, 8 or less.

[0066] Temperature Considering the deposition rate and the stability of the plating composition, the temperature during the treatment of the immersion gold plating solution is preferably 50°C or more, more preferably 60°C or more, and preferably 90°C or less, more preferably 80°C or less.

Examples

[0067] Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, and it is of course possible to appropriately modify and implement it within the range that can conform to the gist of the foregoing and following descriptions, and all of them are included in the technical scope of the present invention.

[0068] Continuous plating was performed under the following conditions, and the solder jointability was evaluated. A substrate obtained by cutting a copper-clad laminate (MCL-E-67 manufactured by Hitachi Chemical Co., Ltd.) into a 5 cm square was prepared. On this substrate, the plating processes shown in Table 1 were sequentially performed to carry out electroless Ni plating treatment and electroless Pd plating treatment. After forming a laminated plating film of an electroless Ni plating film (film thickness: 6.0 μm) and an electroless Pd plating film (film thickness: 0.1 μm) shown in Table 1, immersion gold plating treatment was performed to form an immersion Au plating film (film thickness: 0.10 μm) on the electroless Pd plating film. Water washing was performed between each process. The solder jointability of each manufactured sample was evaluated under the following conditions.

[0069] The Ge content in the electroless Ni plating film (electroless Ni-Ge alloy plating film) was measured under the following conditions. After forming an electroless Ni plating film on a copper-clad laminate in the same manner as above, the Ni plating film was completely dissolved with nitric acid, and the nitric acid solution was measured using an ICP emission spectrometer.

[0070]

Table 1

[0071]

Table 2

[0072]

Table 3

[0073] Evaluation of solder jointability The joint reliability was evaluated on a 20-point scale for each condition by the ball pull test. After forming a film on a substrate provided with a solder resist (SR) opening with a diameter of 0.5 mm, a 0.6 mm solder ball (Sn-3Ag-0.5Cu, SAC305) was mounted in the SR opening under heat treatment conditions of 260 °C (TOP temperature) using a reflow apparatus (UNI-6116α manufactured by ANTOM Co., Ltd.), and a ball pull test was performed using a bond tester (bond tester SERIES4000 manufactured by Dage Co., Ltd.) to evaluate the fracture mode. Solder fracture was defined as the OK mode, and plating film fracture was defined as the NG mode. A solder fracture rate of 85% or more in the OK mode was rated as "excellent", 70% or more and less than 85% was rated as "acceptable", and less than 70% was rated as "defective". The evaluation conditions are summarized below. (Measurement conditions) Measurement method: Ball pull test Solder ball: SAC305 (φ0.6 mm) manufactured by Senju Metal Industry Co., Ltd. Reflow apparatus: UNI-6116α manufactured by ANTOM Co., Ltd. Reflow conditions: Top 260 °C Reflow environment: Air Number of reflows: 7 times Flux: 529D-1 (RMA type) manufactured by Senju Metal Industry Co., Ltd. Test speed: 1000 μm / second Aging after solder mounting: 1 hour Evaluation substrate: BGA substrate (Ball Grid Array: manufactured by Uemura Kogyo Co., Ltd., 5 cm × 5 cm, φ0.5 mm)

[0074] From the results of the experiment, the following considerations can be made. Examples 1 to 10 are inventive examples in which the electroless Ni plating film contains Ge (electroless Ni-Ge alloy plating film). All of these showed excellent bonding reliability. Example 8 is an example in which the germanium content is below the suitable range (0.01 mass%), and the bonding reliability was inferior compared to other inventive examples. Example 9 is an example in which the germanium content is more than that of other examples, and the bonding reliability was inferior compared to other inventive examples. Comparative Example 1 is a comparative example in which the electroless Ni plating film does not contain Ge. Comparative Example 1 had poor bonding reliability. Comparative Examples 2 to 4 are comparative examples in which the electroless Ni plating film does not contain Ge. Comparative Example 2 was an electroless Ni-Fe plating film, Comparative Example 3 was an electroless Ni-Cu plating film, and Comparative Example 4 was an electroless Ni-Sn plating film. Comparative Examples 2 to 4 had poor bonding reliability. From the above results, it can be seen that excellent bonding reliability is an effect obtained only when Ge is contained as an alloy component in the electroless Ni plating film (electroless Ni-Ge alloy plating film).

Explanation of symbols

[0075] 1 Substrate 2 Conductor 3 Electroless nickel-germanium alloy plating film 4 Electroless palladium plating film 5 Electroless gold plating film

Claims

1. A multi-layer plating film in which an electroless nickel-germanium alloy plating film, an electroless palladium plating film, and an electroless gold plating film are laminated in this order.

2. The multi-layer plating film according to claim 1, wherein the germanium content contained in the electroless nickel-germanium alloy plating film is 0.01 to 25% by mass.

3. A wiring board in which the electroless nickel-germanium alloy plating film, the electroless palladium plating film, and the electroless gold plating film according to claim 1 or 2 are laminated in this order on the conductor surface of a substrate.

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