Electroless plating solution

Abstract

Noble metal and single metal plating films such as silver plating and tin plating films are widely used for contact and terminal parts such as connectors, switches, and relays in electronic devices because of their high conductivity. However, terminals using such noble metals and single metals have problems with durability. 【Solution means】The above problems were solved by an electroless plating solution containing a metal ion source in which intermetallic compound crystals containing Sn, Cu, Cr, and Al are dispersed in a matrix phase containing Sn and an Sn-Cu alloy.

Description

Technical Field

[0001] The present invention relates to an electroless plating solution.

Background Art

[0002] Plating films of noble metals and single metals such as silver plating and tin plating films are widely used for contacts, terminals, component coats, etc. such as connectors, switches, relays, semiconductor bumps, and substrate wiring coats of electronic devices because of their high conductivity. However, terminals using such noble metals and single metals have problems in durability over time.

[0003] In addition, Patent Document 1 below discloses a tin-copper intermetallic compound-dispersed tin contact terminal characterized in that a tin plating layer in which tin-copper intermetallic compounds are dispersed is formed on the surface of a base material made of copper or a copper alloy.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] An object of the present invention is to provide an electroless plating solution capable of obtaining a plating film with improved durability over time.

Means for Solving the Problems

[0006] The present invention provides an electroless plating solution containing a metal ion source in which intermetallic compound crystals containing Sn, Cu, Cr, and Al are dispersed in a matrix phase containing Sn and an Sn-Cu alloy. The present invention also provides an electroless plating solution containing a metal ion source in which intermetallic compound crystals containing Sn, Cu, Cr, Al, and Ni are dispersed in a matrix phase containing Sn and an Sn-Cu alloy.

Advantages of the Invention

[0007] According to the present invention, it is possible to provide an electroless plating solution capable of obtaining a plating film with improved durability over time.

Brief Description of the Drawings

[0008]

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[0009] Hereinafter, the embodiments of the present invention will be described in more detail. First, the terminology in this specification is as follows even in the case where there is no particular explanation. (1) When referring to a metal, it may include not only a single metal element but also an alloy containing a plurality of metal elements and an intermetallic compound crystal. (2) When referring to a single metal element, it does not mean only a substance consisting entirely of the metal element, but also includes cases where a minute amount of other substances is included. That is, it is not meant to exclude those containing trace amounts of impurities that hardly affect the properties of the metal element. Of course, for example, in the case of a matrix phase, it is not meant to exclude those in which some of the atoms in the Sn crystal are replaced by other elements (for example, Cu). For example, the other substances or other elements may be contained in the following electrodes in an amount of 0 to 0.1% by mass.

[0010] The electroless plating solution of the present invention exists in the following two forms. (1) It contains a metal ion source in which intermetallic compound crystals containing Sn, Cu, Cr, and Al are dispersed in a matrix phase containing Sn and an Sn-Cu alloy. (2) It contains a metal ion source in which intermetallic compound crystals containing Sn, Cu, Cr, Al, and Ni are dispersed in a matrix phase containing Sn and an Sn-Cu alloy.

[0011] The metal ion source in the present invention can be manufactured as follows.

[0012] First, metal particles described below (hereinafter sometimes referred to as the metal particles of the present invention) are manufactured. Subsequently, the obtained metal particles of the present invention are melted by high-frequency induction heating under vacuum, and this is cast into a mold under atmospheric pressure in a nitrogen gas atmosphere, cooled and solidified to form a rolled sheet, and if necessary, a plurality of these are laminated (hereinafter sometimes referred to as a bulk), and obtained by pulverizing.

[0013] The metal particles of the present invention can be manufactured from a raw material having a composition of, for example, 8% by mass of Cu, 0.5% by mass of Cr, 0.2% by mass of Al, and the balance being Sn in the form of (1). Also, in the form of (2), it can be manufactured from a raw material having a composition of, for example, 8% by mass of Cu, 0.5% by mass of Cr, 0.5% by mass of Al, 0.5% by mass of Ni, and the balance being Sn. For example, the raw material is melted, supplied onto a dish-shaped disk that rotates at high speed in a nitrogen gas atmosphere, the molten metal is scattered as droplets by centrifugal force, and the metal particles of the present invention are obtained by cooling and solidifying under reduced pressure.

[0014] An example of a manufacturing apparatus suitable for manufacturing the metal particles of the present invention will be described with reference to FIG. 17. The granulation chamber 1 has a cylindrical upper part and a conical lower part, and has a lid 2 at the upper part. A nozzle 3 is vertically inserted into the center of the lid 2, and a dish-shaped rotating disk 4 is provided immediately below the nozzle 3. Reference numeral 5 is a mechanism for supporting the dish-shaped rotating disk 4 so as to be movable up and down. Further, a discharge pipe 6 for the generated particles is connected to the lower end of the conical portion of the granulation chamber 1. The upper part of the nozzle 3 is connected to an electric furnace (high-frequency furnace: conventionally, a ceramic crucible was used, but in the present invention, a carbon crucible is used) 7 for melting the metal to be granulated. The atmosphere gas adjusted to a predetermined component in the mixed gas tank 8 is supplied to the inside of the granulation chamber 1 and the upper part of the electric furnace 7 through pipes 9 and 10, respectively. The pressure in the granulation chamber 1 is controlled by a valve 11 and an exhaust device 12, and the pressure in the electric furnace 7 is controlled by a valve 13 and an exhaust device 14. The molten metal supplied from the nozzle 3 onto the dish-shaped rotating disk 4 is scattered in the form of fine droplets by the centrifugal force of the dish-shaped rotating disk 4 and is cooled under reduced pressure to become solid particles. The generated solid particles are supplied from the discharge pipe 6 to an automatic filter 15 and separated. Reference numeral 16 is a fine particle recovery device.

[0015] The process of cooling and solidifying the molten metal from high-temperature melting is important for forming the metal particles of the present invention. For example, the following conditions can be mentioned. Set the melting temperature of the metal in the melting furnace 7 to 800°C to 1000°C, and while maintaining that temperature, supply the molten metal from the nozzle 3 onto the dish-shaped rotating disk 4. As the dish-shaped rotating disk 4, use a dish-shaped disk with an inner diameter of 35 mm and a rotating body thickness of 5 mm, and rotate it at 80,000 to 100,000 revolutions per minute. As the granulation chamber 1, after depressurizing using a vacuum chamber having a performance of depressurizing to about 9×10 -2 Pa, while supplying nitrogen gas at 15 to 50°C and exhausting at the same time, set the atmospheric pressure in the granulation chamber 1 to 1×10 -1 Pa or less.

[0016] The metal particles of the present invention in the above forms (1) and (2) are obtained as described above. The particle diameter of the metal particles of the present invention is approximately 5 μm, but the particle diameter of the metal particles of the present invention is preferably in the range of 1 μm to 50 μm, for example.

[0017] Subsequently, the obtained metal particles of the present invention are melted by high-frequency induction heating under vacuum, and this is subjected to die casting under atmospheric pressure in a nitrogen gas atmosphere, cooled and solidified to obtain a rolled sheet, and a bulk is obtained by laminating a plurality of sheets as necessary. Examples of the high-frequency induction heating and cooling and solidification conditions are as follows. High-frequency induction heating: 9×10 -2 Install a high-frequency melting crucible in a vacuum chamber having a performance capable of reducing the pressure to about 9×10 Cooling and solidification: Subsequently, while flowing nitrogen gas at 15 to 50 °C into the tank, set the heating temperature to about 400 °C or higher under atmospheric pressure, perform die casting, and cool and solidify at 30 °C or lower.

[0018] In the present invention, the composition of the bulk in the form (1), for example, is Cu 0.7 to 15% by mass, Cr 2 to 0.02% by mass, Al 3 to 0.02% by mass, with the balance being Sn (however, it may contain unavoidable impurities of 0.1% by mass or less). In the present invention, the composition of the bulk in the form (2), for example, is Cu 0.7 to 15% by mass, Cr 2 to 0.02% by mass, Al 3 to 0.02% by mass, Ni 1 to 0.02% by mass, with the balance being Sn (however, it may contain unavoidable impurities of 0.1% by mass or less). The composition is the same as that of the metal particles of the present invention.

[0019] Also, the composition of the matrix phase of the bulk in the form (1) in the present invention is Cu 5 to 0.02% by mass, Cr 0.001 to 18% by mass, Al 3 to 0.02% by mass, and the balance can be Sn. The composition of the matrix phase is the same as that of the metal particles of the present invention.

[0020] Also, the composition of the matrix phase of the bulk in the form (2) in the present invention is Cu 5 to 0.02% by mass, Cr 0.001 to 18% by mass, Al 3 to 0.02% by mass Ni 1 to 0.02% by mass, and the balance can be Sn. The composition of the matrix phase is the same as that of the metal particles of the present invention.

[0021] Also, the composition of the intermetallic compound crystal of the bulk in the form (1) in the present invention is Cu 5 to 50% by mass, Cr 0.001 to 10% by mass, Al 0.1 to 20% by mass, and the balance can be Sn.

[0022] Also, the composition of the intermetallic compound crystal of the bulk in the form (2) in the present invention is Cu 5 to 50% by mass, Cr 0.001 to 18% by mass, Al 0.1 to 20% by mass, Ni 0.1 to 6.5% by mass, and the balance can be Sn.

[0023] Also, in the bulk of the forms (1) and (2), the proportion of the intermetallic compound crystal is, for example, 20 to 60% by mass, and preferably 30 to 40% by mass. The intermetallic compound crystal exists included in the matrix phase.

[0024] The composition and ratio of the matrix phase and intermetallic compound crystals of the present invention can be satisfied by following the manufacturing conditions of the bulk. The inventors have confirmed that the structure of the bulk is the same as that of the metal particles of the present invention.

[0025] Also, in the plating method using the electroless plating solution of the present invention, the intermetallic compound crystals and matrix phase contained in the bulk pulverized in the plating bath dissolve as a metal ion source, and these are plated on the surface of the base material to form a plating layer. The formed plating layer has a structure in which intermetallic compound crystals containing Sn, Cu, Cr, and Al or Sn, Cu, Cr, Al, and Ni are dispersed in a matrix phase composed of an Sn-Cu alloy.

[0026] The electroless plating solution of the present invention can contain various additives conventionally known as, for example, reducing plating solutions. For example, examples of the reducing agent include hypophosphite, formaldehyde, paraformaldehyde, ammonium borohydride, dimethylamine borane, and the like. Examples of the complexing agent include acetic acid, lactic acid, glycine, citric acid, malonic acid, malic acid, oxalic acid, succinic acid, tartaric acid, thioglycolic acid, ammonia, alanine, glutamic acid, ethylenediamine, and the like. As the pH adjuster, as the alkali, hydroxide solutions of alkali metals and alkaline earth metals such as sodium hydroxide, potassium hydroxide, sodium carbonate, and aqueous ammonia can be used. As the acid, hydrochloric acid, sulfuric acid, nitric acid, and the like can be used. Examples of the stabilizer include nitrates such as lead, bismuth, and thallium.

[0027] In the electroless plating solution of the present invention, the metal ion source concentration is preferably, for example, 10 to 200 g / liter, and the plating temperature is preferably 25 to 65°C.

[0028] The composition of the intermetallic compound crystals contained in the obtained plating layer is the same as that of the bulk used. In addition, the amount of the intermetallic compound crystals contained in the plating layer is, for example, 20 to 60% by mass. The composition of the matrix phase is also the same as that of the bulk used. The composition and structure of the entire plating layer, the matrix phase, and the intermetallic compound can be formed under the plating conditions.

[0029] The substrate after plating is heat-treated as necessary. As the heat treatment conditions, for example, the temperature is 100 to 300 °C, and the heating time is, for example, about 5 to 300 seconds.

[0030] By the above operations, a plating layer is formed on the surface of the substrate. The thickness of the plating layer is, for example, 2 μm to 10 μm.

[0031] Examples of the substrate include metals such as aluminum, aluminum alloys, copper, copper alloys, or stainless steel, and resins such as glass epoxy. These can be selected without particular limitation from known materials. For example, examples of copper alloys include brass and phosphor bronze.

[0032] Note that a titanium, nickel, or nickel alloy layer can be formed as an underlayer of the plating layer, and the heat resistance can be further enhanced. As the nickel alloy, those containing one or two of iron, tin, zinc, copper, cobalt, phosphorus, silver, boron, etc. can be used. The thickness of this underlayer is preferably about 0.1 μm to 1.5 μm, for example.

[0033] An article having a plating film formed by the electroless plating solution in the above form (1) is particularly useful as, for example, a bump or a millimeter-wave radar antenna. It has the effect of suppressing transmission loss by forming a film that does not contain the magnetic metal Ni that causes transmission loss. In addition, although the plating crystal roughness of the underlying plating on the substrate usually has irregularities of about 5 microns, it has been confirmed that by forming the plating film in the present invention, the surface roughness can be improved to about 100 nanometers with irregularities, and high-performance transmission can be expected without causing significant transmission loss, which is useful. Incidentally, an article having a plating film formed by the electroless plating solution in the above aspect (2) is particularly useful as, for example, a terminal.

Example

[0034] Hereinafter, the present invention will be further described with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0035] Example 1 Example 1 is an example for explaining one form of an electroless plating solution containing a metal ion source in which intermetallic compound crystals containing Sn, Cu, Cr, and Al are dispersed in a matrix phase containing Sn and an Sn-Cu alloy. As a raw material, a raw material having a composition of 8% by mass of Cu, 0.5% by mass of Cr, 0.2% by mass of Al, and the balance being Sn was used, and metal particles 1 having a diameter of about 3 to 50 μm were produced by the production apparatus shown in FIG. 17. At that time, the following conditions were adopted. A melting crucible was installed in the melting furnace 7, the above raw material was put therein, melted at 900 ° C., and while maintaining the temperature, the molten metal was supplied from the nozzle 3 onto the dish-shaped rotating disk 4. As the dish-shaped rotating disk 4, a dish-shaped disk having a diameter of 35 mm and a rotating disk thickness of 3 to 5 mm was used, and the rotation speed was 80,000 to 100,000 revolutions per minute. As the granulation chamber 1, after depressurizing using a vacuum chamber having a performance of depressurizing to about 9 × 10 -2 Pa, while supplying nitrogen gas at 15 to 50 ° C., exhaust was simultaneously performed to make the atmospheric pressure in the granulation chamber 1 1 × 10 -1 Pa or less. Using the obtained metal powder 1, a bulk was produced. At that time, the following conditions were adopted. High-frequency induction heating: 9 × 10 -2A crucible for high-frequency melting was installed in a vacuum chamber capable of being evacuated to a degree of vacuum up to the Pa level. The metal particles of the present invention were introduced into the crucible, and high-frequency induction heating was performed on the metal particles of the present invention while maintaining the degree of vacuum up to the above-mentioned degree of vacuum. The heating temperature was set to 900 °C to melt the metal particles of the present invention, and the temperature was maintained for 5 minutes. Cooling and solidification: Subsequently, while flowing nitrogen gas at 15 to 50 °C into the chamber for 10 minutes, the heating temperature of the raw material was set to about 400 °C under atmospheric pressure, and casting into a mold was performed, followed by cooling and solidification at room temperature. Using the obtained material, it was rolled into sheets, multiple sheets were stacked, and Bulk 1 was produced. Subsequently, Bulk 1 was heated to 150 °C and crushed into small pieces, and the obtained crushed material was placed in the following plating bath.

[0036] The cross-sectional SEM image of Bulk 1 of Example 1 obtained is shown in FIG. 1. According to FIG. 1, it was confirmed that intermetallic compound crystals (dark color) were included and present in the matrix phase (light color). In addition, when elemental mapping analysis by EDS was performed on one cross-section of the above-mentioned Bulk 1 (see FIG. 2), it was found that its composition was 6.9 mass% Cu, 0.59 mass% Cr, 0.15 mass% Al, and the balance Sn. In addition, regarding the composition of the matrix phase, when elemental mapping analysis by EDS was performed at points 005 to 006 in FIGS. 7 to 8, Sn 86 to 90.9 mass%, Cu 2.06 to 4.14 mass%, Al 1.1 mass% or less and the presence of Sn and Sn-Cu alloy was confirmed. In addition, regarding the composition of the intermetallic compound crystals, when elemental mapping analysis by EDS was performed at points 001 to 004 in FIGS. 3 to 6, Sn 62.69 to 74.72 mass%, Cu 5.35 to 33.17 mass%, Cr 7.8 mass% or less, Al 3.29 mass% or less, and it was found that this was the case. In addition, the intermetallic compound crystals in the above-mentioned Bulk 1 occupied 30 to 35 mass%.

[0037] A substrate with copper wiring, copper antennas, and copper bumps formed on a ceramic substrate as the base material was used, and electroless plating was performed on the copper plating. The details of the electroless plating bath are as follows.

[0038] Electroless plating bath composition (concentration per liter of water): Metal ion source: Intermetallic compound crystals and matrix phase contained in the bulk 1 Sn concentration = 10 g / L Cu concentration = 1 g / L Cr concentration = 0.1 g / L Al concentration = 0.1 g / L

[0039] The electroless plating conditions are as follows. Plating temperature: 50 °C Plating time: 120 minutes Heat treatment temperature of the substrate after plating: 200 °C Heat treatment time of the substrate after plating: 300 seconds (under nitrogen atmosphere)

[0040] The composition of the plating layer of the obtained article was the same as that of the bulk 1. Also, the thickness of the plating layer was 5 μm.

[0041] The article obtained in Example 1 above was immersed in a 5% NaCl aqueous solution for 120 hours, and the state was observed. The results are shown in Fig. 18. Fig. 18(a) shows the results of this Example 1, and no corrosion was observed on the surface. Fig. 18(b) shows an article by conventional Sn-Cu plating, and corrosion was observed on the surface.

[0042] Example 2 Example 2 is an example for explaining one form of an electroless plating solution containing a metal ion source in which intermetallic compound crystals containing Sn, Cu, Cr, Al, and Ni are dispersed in a matrix phase containing Sn and an Sn-Cu alloy. As a raw material, a raw material having a composition of 8% by mass of Cu, 0.5% by mass of Cr, 0.5% by mass of Al, 0.5% by mass of Ni, and the balance being Sn was used, and metal particles 2 having a diameter of about 3 to 50 μm were produced by the manufacturing apparatus shown in Fig. 17. At that time, the following conditions were adopted. A melting crucible was installed in the melting furnace 7, the above raw materials were put therein, melted at 900 °C, and while maintaining the temperature, the molten metal was supplied from the nozzle 3 onto the dish-shaped rotating disk 4. As the dish-shaped rotating disk 4, a dish-shaped disk with a diameter of 35 mm and a rotating disk thickness of 3 - 5 mm was used, and it was rotated at 80,000 - 100,000 revolutions per minute. As the granulation chamber 1, after depressurizing using a vacuum chamber having a performance of depressurizing to about 9×10 -2 Pa, while supplying nitrogen gas at 15 - 50 °C and exhausting simultaneously, the atmospheric pressure in the granulation chamber 1 was set to 1×10 -1 Pa or less. Using the obtained metal powder 1, a bulk was produced. At that time, the following conditions were adopted. High-frequency induction heating: A high-frequency melting crucible was installed in a vacuum chamber having a performance of depressurizing to about 9×10 -2 Pa, the metal particles of the present invention were introduced into the crucible, high-frequency induction heating was performed on the metal particles of the present invention while maintaining the degree of depressurization to the above-mentioned degree of depressurization, the heating temperature was set to 900 °C to melt the metal particles of the present invention, and the temperature was maintained for 5 minutes. Cooling and solidification: Subsequently, while flowing nitrogen gas at 15 - 50 °C into the tank for 10 minutes, the heating temperature of the raw materials was set to about 400 °C under atmospheric pressure, casting into a mold was performed, and it was cooled and solidified at room temperature. Using the obtained material, it was rolled into a sheet, multiple sheets were stacked, and a bulk 2 was produced. Subsequently, the bulk 2 was put into a cutting machine heated to 150 °C, crushed into a size of 1 cm - 3 cm × 1 mm - 5 mm, and the obtained crushed material was placed in the following plating bath.

[0043] The cross-sectional SEM image of the bulk 2 of Example 2 obtained is shown in Fig. 9. According to Fig. 9, it was confirmed that intermetallic compound crystals (dark color) were included and present in the matrix phase (light color). In addition, when elemental mapping analysis by EDS of one cross-section of the above bulk 2 was performed (see Fig. 10), it was found that its composition was Cu 7.22 mass%, Cr 0.54 mass%, Al 0.28 mass%, Ni 0.24 mass%, and the balance was Sn. The composition of the mother phase was determined by elemental mapping analysis using EDS at points 005 - 006 in FIGS. 15 - 16. Sn: 74.38 mass% - 85.74 mass% Cu: 4.11 mass% - 4.49 mass% Al: 0.78 mass% - 1.77 mass% Ni: 0.61 mass% - 0.86 mass% and the presence of Sn and the Sn - Cu alloy was confirmed. The composition of the intermetallic compound crystals was determined by elemental mapping analysis using EDS at points 001 - 004 in FIGS. 11 - 14. Sn: 30.61 mass% - 68.66 mass% Cu: 7.48 mass% - 27.37 mass% Cr: 15.67 mass% or less Al: 7.38 mass% or less Ni: 10.74 mass% or less and it was found to be so. Also, the intermetallic compound crystals in the above - mentioned bulk 2 occupied 30 - 35 mass%.

[0044] A copper spring was used as the base material and electroless plating was carried out. The details of the electroless plating bath are as follows.

[0045] Electroless plating bath composition (concentration per liter of water): Metal ion source: The intermetallic compound crystals and the mother phase contained in the above - mentioned bulk 2 Sn concentration in the plating solution = 10 g / L Cu concentration in the plating solution = 1 g / L Cr concentration in the plating solution = 0.1 g / L Ni concentration in the plating solution = 0.1 g / L Al concentration in the plating solution = 0.1 g / L

[0046] The electroless plating conditions are as follows. Plating temperature: 50°C Plating time: 120 minutes Heat treatment temperature of the base material after plating: 200°C Heat treatment time of the substrate after plating: 300 seconds (in a nitrogen atmosphere)

[0047] The composition of the plating layer of the obtained article was the same as that of the bulk 2. Also, the thickness of the plating layer was 5 μm.

[0048] The article obtained in Example 2 above was immersed in a 5% concentration NaCl aqueous solution for 120 hours, and the state was observed. As a result, the same result as in Example 1 was obtained (see Fig. 18(a)).

[0049] The present invention has been described in detail with reference to the accompanying drawings, but the present invention is not limited thereto, and it is obvious that those skilled in the art can conceive various modifications based on its basic technical idea and teaching.

Explanation of reference numerals

[0050] 1 Granulation chamber 2 Lid 3 Nozzle 4 Dish-shaped rotating disk 5 Rotating disk support mechanism 6 Particle discharge pipe 7 Electric furnace 8 Mixed gas tank 9 Pipe 10 Pipe 11 Valve 12 Exhaust device 13 Valve 14 Exhaust device 15 Automatic filter 16 Fine particle recovery device

Claims

1. An electroless plating solution containing a metal ion source in which intermetallic compound crystals containing Sn, Cu, Cr and Al are dispersed in a matrix containing Sn and a Sn-Cu alloy, The electroless plating solution, wherein the composition of the parent phase, the composition of the intermetallic compound crystals, and the ratio of the intermetallic compound crystals in the metal ion source are as follows: The composition of the parent phase is Cu 5-0.02% by mass, Cr 0.001-18% by mass, Al 3-0.02% by mass, The balance is Sn. The composition of the intermetallic compound crystal is Cu 5-50% by mass, Cr 0.001-10% by mass, Al 0.1-20% by mass, The balance is Sn. The ratio of the intermetallic compound crystals is 20 to 60 mass %.

2. An electroless plating solution containing a metal ion source in which intermetallic compound crystals containing Sn, Cu, Cr, Al and Ni are dispersed in a matrix containing Sn and a Sn-Cu alloy, The electroless plating solution, wherein the composition of the parent phase, the composition of the intermetallic compound crystals, and the ratio of the intermetallic compound crystals in the metal ion source are as follows: The composition of the parent phase is Cu 5-0.02% by mass, Cr 0.001-18% by mass, Al 3-0.02% by mass Ni 1-0.02% by mass, The balance is Sn. The composition of the intermetallic compound crystal is Cu 5-50% by mass, Cr 0.001-18% by mass, Al 0.1-20% by mass, Ni 0.1-6.5% by mass, The balance is Sn. The ratio of the intermetallic compound crystals is 20 to 60 mass %.

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