ELECTROLESS PLATING SOLUTION

Abstract

According to this invention, disclosed is an electroless plating solution containing a metal ion source having a parent phase that contains Sn and a Sn-Cu alloy, and an intermetallic compound crystal that contains Sn, Cu, Cr and Al, dispersed in the parent phase.

Claims

1. An electroless plating solution containing a metal ion source having a parent phase that contains Sn and a Sn-Cu alloy, and an intermetallic compound crystal that contains Sn, Cu, Cr and Al, dispersed in the parent phase, the parent phase in the metal ion source having a composition represented by: Cu: 5 to 0.02% by mass; Cr: 0.001 to 18% by mass; Al: 3 to 0.02% by mass; and the balance of Sn, the intermetallic compound crystal having a composition represented by: Cu: 5 to 50% by mass; Cr: 0.001 to 10% by mass; Al: 0.1 to 20% by mass; and the balance of Sn, and a proportion of the intermetallic compound crystal being 20 to 60% by mass.

2. An electroless plating solution containing a metal ion source having a parent phase that contains Sn and a Sn-Cu alloy, and an intermetallic compound crystal that contains Sn, Cu, Cr, Al and Ni, dispersed in the parent phase, the parent phase in the metal ion source having a composition represented by: 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 of Sn, the intermetallic compound crystal having a composition represented by: 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 of Sn, and proportion of the intermetallic compound crystal being 20 to 60% by mass.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] FIG. 1 is a cross-section SEM image of a bulk 1 in Example 1.

[0011] FIG. 2 is a chart illustrating results of EDS elemental mapping on a cross section of the bulk 1.

[0012] FIG. 3 is a chart illustrating results of EDS elemental mapping on a specific point of the cross section of the bulk 1.

[0013] FIG. 4 is a chart illustrating results of EDS elemental mapping on a specific point of the cross section of the bulk 1.

[0014] FIG. 5 is a chart illustrating results of EDS elemental mapping on a specific point of the cross section of the bulk 1.

[0015] FIG. 6 is a chart illustrating results of EDS elemental mapping on a specific point of the cross section of the bulk 1.

[0016] FIG. 7 is a chart illustrating results of EDS elemental mapping on a specific point of the cross section of the bulk 1.

[0017] FIG. 8 is a chart illustrating results of EDS elemental mapping on a specific point of the cross section of the bulk 1.

[0018] FIG. 9 is a cross-section SEM image of a bulk 2 in Example 2. FIG. 10 is a chart illustrating results of EDS elemental mapping on a cross section of the bulk 2.

[0019] FIG. 11 is a chart illustrating results of EDS elemental mapping on a specific point of the cross section of the bulk 2.

[0020] FIG. 12 is a chart illustrating results of EDS elemental mapping on a specific point of the cross section of the bulk 2.

[0021] FIG. 13 is a chart illustrating results of EDS elemental mapping on a specific point of the cross section of the bulk 2.

[0022] FIG. 14 is a chart illustrating results of EDS elemental mapping on a specific point of the cross section of the bulk 2.

[0023] FIG. 15 is a chart illustrating results of EDS elemental mapping on a specific point of the cross section of the bulk 2.

[0024] FIG. 16 is a chart illustrating results of EDS elemental mapping on a specific point of the cross section of the bulk 2.

[0025] FIG. 17 is a drawing explaining an exemplary manufacturing apparatus suitable for manufacturing a metal particle in this invention.

[0026] FIGS. 18A and 18B are photographs illustrating durability of articles in Examples 1 and 2.

DESCRIPTION OF THE EMBODIMENTS

[0027] This invention will further be detailed below.

[0028] Terminology herein will be defined as follows, unless otherwise specifically noted.

[0029] (1) The term metal is used not only to encompass metal element as a simple substance, but also occasionally to encompass alloy and intermetallic compound composed of two or more metal elements.

[0030] (2) When referring to a certain metal element as a simple substance, it means not only an absolutely pure substance solely composed of such metal element, but also a substance containing a trace amount of other substance. That is, the metal element of course does not mean to exclude a case where a trace impurity that hardly affects properties of that metal element is contained. For example, the parent phase does not mean to exclude a case where a part of atoms in Sn crystal is replaced by other element (Cu, for example). For example, such other substance or other element may occasionally account for 0 to 0.1% by mass of the electrode described later.

[0031] The electroless plating solution of this invention can exist in two modes below: [0032] (1) a mode containing a metal ion source having a parent phase that contains Sn and a Sn-Cu alloy, and an intermetallic compound crystal that contains Sn, Cu, Cr and Al, dispersed in the parent phase; and [0033] (2) a mode containing a metal ion source having a parent phase that contains Sn and a Sn-Cu alloy, and an intermetallic compound crystal that contains Sn, Cu, Cr, Al and Ni, dispersed in the parent phase.

[0034] The metal ion source in this invention may be manufactured as described next.

[0035] First, a metal particle explained below (may occasionally be referred to as metal particle of this invention, hereinafter) is manufactured.

[0036] Next, the thus obtained metal particle of this invention is melted in vacuo under high-frequency induction heating, the melt is cast in a mold in a nitrogen gas atmosphere under atmospheric pressure, cooled to solidify, rolled into sheets, a plurality of which are optionally stacked (occasionally referred to as bulk, hereinafter), and the bulk is then ground.

[0037] The metal particle of this invention in mode (1) may be manufactured from a raw material, typically having a composition represented by Cu: 8% by mass, Cr: 0.5% by mass, Al: 0.2% by mass, and the balance of Sn.

[0038] Meanwhile, the metal particle in mode (2) may be manufactured form a raw material, typically having a composition represented by Cu: 8% by mass, Cr: 0.5% by mass, Al: 0.5% by mass, Ni: 0.5% by mass, and the balance of Sn.

[0039] The metal particle is obtainable typically by melting the raw material, feeding the molten metal onto a dish-like disk which is kept under spinning at a high speed in a nitrogen atmosphere, so as to be centrifugally scattered in the form of fine droplets, and by cooling and solidifying the droplets under reduced pressure.

[0040] A preferred example of a manufacturing apparatus suitable for manufacture of the metal particle of this invention will be explained referring to FIG. 17. A granulation chamber 1 has a cylindrical top and a conical bottom, and has a lid 2 placed on the top.

[0041] The lid 2 has a nozzle 3 perpendicularly inserted at the center thereof, and just under the nozzle 3 arranged is a dish-like rotating disk 4. Reference sign 5 represents a mechanism that supports the dish-like rotating disk 4 so as to be movable up and down. At the lower end of the conical bottom of the granulation chamber 1, connected is a discharge pipe 6 through which the produced particles are output. The upper end of the nozzle 3 is connected to an electric furnace (high-frequency induction furnace: employed in this invention is a carbon crucible, in place of a ceramic crucible having formerly been used) 7 for melting a metal to be granulated. An atmospheric gas, whose chemical composition has been specifically adjusted in a mixed gas tank 8, is fed through a pipe 9 and a pipe 10, respectively into the granulation chamber 1 and to the top of the electric furnace 7. Inner pressure of the granulation chamber 1 is controlled by a valve 11 and a ventilator 12, and inner pressure of the electric furnace 7 is controlled by a valve 13 and a ventilator 14. The molten metal fed through the nozzle 3 onto the dish-like rotating disk 4 is scattered in the form of fine droplets with the aid of centrifugal force of the dish-like rotating disk 4, and then solidified after cooled under reduced pressure. The thus produced solid particles are fed through the discharge pipe 6 to an automatic filter 15, where the particles are classified. Reference sign 16 represents a particle collector.

[0042] A process of bringing the molten metal from the hot molten state down to the cold solidified state is the key for formation of the metal particle of this invention.

[0043] Exemplary conditions are as follows.

[0044] With the melting temperature of metal in the electric furnace 7 preset to 800 C. to 1000 C., the molten metal kept at that temperature is fed through the nozzle 3 onto the dish-like rotating disk 4.

[0045] The dish-like rotating disk 4 used herein is a dish-like disk having an inner diameter of 35 mm and a rotor thickness of 5 mm, which is rotated at 80,000 to 100,000 rpm.

[0046] The granulation chamber 1 used herein is a vacuum chamber allowed for evacuation down to 910.sup.2 Pa or around, to which nitrogen gas conditioned at 15 to 50 C. is fed while concurrently discharged, so as to adjust the pressure in the granulation chamber 1 to 110.sup.1 Pa or below.

[0047] The metal particles of this invention in modes (1) and (2) are obtainable as described above. Particle size of the metal particles of this invention is approximately 5 m, and preferably falls within the range from 1 m to 50 m, for example.

[0048] Next, each of the thus obtained metal particles of this invention is melted in vacuo under high-frequency induction heating, the melt is cast in a mold in a nitrogen gas atmosphere under the atmospheric pressure, cooled to solidify, rolled into sheets, a plurality of which are then optionally stacked, to obtain a bulk.

[0049] Conditions for the high-frequency induction heating and solidification under cooling are typically as follows.

[0050] High-frequency induction heating: A crucible suited to high-frequency melting is placed in a vacuum chamber allowed for evacuation down to 910.sup.2 Pa or around, the metal particle of this invention is placed in the crucible, the metal particle of this invention is subjected to high-frequency induction heating while keeping the pressure at around the aforementioned degree of vacuum, allowed to melt at a heating temperature of 800 C. to 1000 C., and the melt is kept at that temperature for 5 to 15 minutes.

[0051] Solidification under cooling: Nitrogen gas conditioned at 15 to 50 C. is then fed into the vacuum chamber, the heating temperature is set to approximately 400 C. or above under the atmospheric pressure, the melt is cast into a mold, and cooled at 30 C. or below to solidify.

[0052] The bulk of this invention in mode (1) has a chemical composition represented by: [0053] Cu: 0.7 to 15% by mass; [0054] Cr: 2 to 0.02% by mass; [0055] Al: 3 to 0.02% by mass; and the balance of Sn (possibly contains 0.1% by mass or less of an inevitable impurity).

[0056] The bulk of this invention in mode (2) has a chemical composition represented by: [0057] Cu: 0.7 to 15% by mass; [0058] Cr: 2 to 0.02% by mass; [0059] Al: 3 to 0.02% by mass; [0060] Ni: 1 to 0.02% by mass; and [0061] the balance of Sn (possibly contains 0.1% by mass or less of an inevitable impurity).

[0062] The chemical compositions are same as those of the metal particles of this invention.

[0063] The parent phase in the bulk of this invention in mode (1) may have a chemical composition represented by: [0064] Cu: 5 to 0.02% by mass; [0065] Cr: 0.001 to 18% by mass; [0066] Al: 3 to 0.02% by mass; and [0067] the balance of Sn.

[0068] The chemical composition of the parent phase is same as that of the metal particle of this invention.

[0069] The parent phase in the bulk of this invention in mode (2) may have a chemical composition represented by: [0070] Cu: 5 to 0.02% by mass; [0071] Cr: 0.001 to 18% by mass; [0072] Al: 3 to 0.02% by mass; [0073] Ni: 1 to 0.02% by mass; and [0074] the balance of Sn.

[0075] The chemical composition of the parent phase is same as that of the metal particle of this invention.

[0076] The intermetallic compound crystal in the bulk of this invention in mode (1) may have a chemical composition represented by: [0077] Cu: 5 to 50% by mass; [0078] Cr: 0.001 to 10% by mass; [0079] Al: 0.1 to 20% by mass; and [0080] the balance of Sn.

[0081] The intermetallic compound crystal in the bulk of this invention in mode (2) may have a chemical composition represented by: [0082] Cu: 5 to 50% by mass; [0083] Cr: 0.001 to 18% by mass; [0084] Al: 0.1 to 20% by mass; [0085] Ni: 0.1 to 6.5% by mass; and [0086] the balance of Sn.

[0087] Each of the intermetallic compound crystals in the bulks in modes (1) and (2) typically accounts for 20 to 60% by mass, and the percentage is preferably 30 to 40% by mass.

[0088] The intermetallic compound crystal resides in the parent phase so as to be embedded therein.

[0089] The chemical compositions and proportions of the parent phases and the intermetallic compound crystals of this invention may be met by following manufacturing conditions of the bulks. Note that the present inventors have confirmed that the structures of the bulks and the metal particles of this invention are the same.

[0090] In a plating method with use of the electroless plating solution of this invention, the intermetallic compound crystal and the parent phase contained in the ground bulk will dissolve as the metal ion source into the plating bath, and these components are plated over the surface of a base to form a plating layer. The thus formed plating layer has a structure in which the intermetallic compound crystal that contains a set of Sn, Cu, Cr and Al, or a set of Sn, Cu, Cr, Al and Ni, is dispersed in a parent phase composed of a Sn-Cu alloy.

[0091] The electroless plating solution of this invention, typically as a reductive plating solution, may contain any of various known additives.

[0092] For instance, reducing agent is exemplified by hydrophosphite, formaldehyde, paraformaldehyde, ammonium boron hydroxide, and dimethylamine borane.

[0093] Complexing agent is exemplified by acetic acid, lactic acid, glycine, citric acid, malonic acid, malic acid, oxalic acid, succinic acid, tartaric acid, thioglycolic acid, ammonia, alanine, glutamic acid, and ethylenediamine.

[0094] pH adjustor, usable as alkali, is exemplified by aqueous solution of hydroxide or carbonate of alkali metal or alkali earth metal, such as sodium hydroxide and potassium hydroxide; and ammonia water. pH adjustor, usable as acid, is exemplified by hydrochloric acid, sulfuric acid, and nitric acid.

[0095] Stabilizer is exemplified by nitrates of lead, bismuth, and thallium, for example.

[0096] In the electroless plating solution of this invention, the concentration of the metal ion source is preferably 10 to 200 g/L, and the plating temperature is preferably 25 to 65 C., for example.

[0097] The chemical compositions of the intermetallic compound crystals contained in the obtained plating layer are same as those of the bulks.

[0098] The contents of the intermetallic compound crystals in the plated layers are typically 20 to 60% by mass. Also the chemical compositions of the parent phases are same as those of the bulks.

[0099] The chemical compositions and structures of the whole plating layer, the parent phase, and the intermetallic compound are adjustable according to the plating conditions.

[0100] The base after the plating is subjected to heat treatment as necessary. Conditions for the heat treatment typically include a temperature of 100 to 300 C., and a heating time of 5 to 300 seconds or around.

[0101] The plating layer is thus formed on the surface of the base, by the operations described above. The plating layer typically has a thickness of 2 m to 10 m.

[0102] The base may be formed of any known material selectable without special limitation, including metals such as aluminum, aluminum alloy, copper, copper alloy and stainless steel; or resins such as glass-epoxy resin. The copper alloy is exemplified by brass and phosphor bronze.

[0103] It is also acceptable to form, under the plating layer, an underlying layer formed of titanium, nickel, or nickel alloy layer for enhanced heat resistance. The nickel alloy applicable herein contains one or two elements selected from iron, tin, zinc, copper, cobalt, phosphorus, silver and boron. The underlying layer preferably has a thickness of 0.1 m to 1.5 m or around, for example.

[0104] Articles having the plating film formed from the electroless plating solution in mode (1) is particularly useful as bump or millimeter-wave radar antenna. With the film formed without containing Ni, which is a magnetic metal that causes transmission loss, obtainable is an effect of suppressing the transmission loss.

[0105] Roughness of plated crystal in the underlying layer on the base is usually expressed by an irregularity of 5 m or around. The present inventors confirmed that formation of the plating film of this invention successfully reduced the surface roughness down to 100 nanometers or around, which was advantageous in enabling high performance transmission without causing considerable transmission loss.

[0106] An article having the plating film formed from the electroless plating solution in mode (2) is particularly useful as terminals, for example.

EXAMPLES

[0107] This invention will further be explained below referring to Examples and Comparative Examples. This invention is, however, not limited to Examples below.

Example 1

[0108] Example 1 exemplifies a mode of electroless plating solution containing a metal ion source having a parent phase that contains Sn and a Sn-Cu alloy, and an intermetallic compound crystal that contains Sn, Cu, Cr and Al, dispersed in the parent phase.

[0109] A raw material used herein had a composition represented by Cu: 8% by mass, Cr: 0.5% by mass, Al: 0.2% by mass, and the balance of Sn, from which a metal particle 1 having a diameter of approximately 3 to 50 m was manufactured, with use of the manufacturing apparatus illustrated in FIG. 17.

[0110] In this process, conditions below were employed.

[0111] A melting crucible was placed in the melting furnace 7, into which the aforementioned raw material was placed, the content was melted at 900 C., and the melt was fed through the nozzle 3 onto the dish-like rotating disk 4 while keeping the temperature.

[0112] The dish-like rotating disk 4 used herein was a dish-like disk having a diameter of 35 mm and a rotor thickness of 3 to 5 mm, which was rotated at 80,000 to 100,000 rpm.

[0113] The granulation chamber 1 used herein was a vacuum chamber allowed for evacuation down to 910.sup.2 Pa or around, the chamber was evacuated, into which nitrogen gas conditioned at 15 to 50 C. was fed while concurrently discharged, so as to adjust the pressure in the granulation chamber 1 to 110.sup.1 Pa or below.

[0114] With use of the thus obtained metal particle 1, a bulk was manufactured.

[0115] In this process, conditions below were employed.

[0116] High-frequency induction heating: A crucible suited to high-frequency melting was placed in the vacuum chamber allowed for evacuation down to 910.sup.2 Pa or around, the metal particle of this invention was placed in the crucible, the metal particle of this invention was subjected to high-frequency induction heating while keeping the pressure at around the aforementioned degree of vacuum, allowed to melt at a heating temperature of 900 C., and the melt was kept at that temperature for 5 minutes.

[0117] Solidification under cooling: Nitrogen gas conditioned at 15 to 50 C. was then fed into the vacuum chamber for 10 minutes, during which the heating temperature was set to approximately 400 C. under the atmospheric pressure, the melt was cast into a mold, and cooled at room temperature to solidify.

[0118] The thus obtained material was rolled into sheets, a plurality of which were stacked, to manufacture a bulk 1. The bulk 1 was then heated to 150 C., cut into small pieces, and the thus obtained pieces were placed in a plating bath below.

[0119] A cross-sectional SEM image of the thus obtained bulk 1 in Example 1 is presented in FIG. 1. It was confirmed from FIG. 1 that the intermetallic compound crystal (dark-colored) presents in the parent phase (pale-colored) so as to be embedded therein.

[0120] EDS elemental mapping on a cross section of the bulk 1 (see FIG. 2) revealed that the chemical composition is represented by Cu: 6.9% by mass, Cr: 0.59% by mass, Al: 0.15% by mass, and the balance of Sn.

[0121] Also the parent phase was analyzed by EDS elemental mapping at points 005 and 006 as illustrated in FIGS. 7 and 8, respectively, revealing the chemical composition as: [0122] Sn: 86 to 90.9% by mass; [0123] Cu: 2.06 to 4.14% by mass; and [0124] Al: 1.1% by mass or less,
from which existence of Sn and Sn-Cu alloy was confirmed.

[0125] Also the intermetallic compound crystal was analyzed by EDS elemental mapping at points 001 to 004 as illustrated in FIGS. 3 to 6, respectively, revealing the chemical composition as: [0126] Sn: 62.69 to 74.72% by mass; [0127] Cu: 5.35 to 33.17% by mass; [0128] Cr: 7.8% by mass or less; and [0129] Al: 3.29% by mass or less.

[0130] The intermetallic compound crystal was also found to account for 30 to 35% by mass of the bulk 1.

[0131] The base used herein was a ceramic board having copper interconnects, a copper antenna and copper bumps formed thereon, and these copper components were then subjected to electroless plating. Details of the electroless plating bath are as follows.

[0132] Chemical composition of electroless plating (concentration/1 L water): [0133] metal ion source: intermetallic compound crystal and parent phase contained in the bulk 1 [0134] Sn concentration=10 g/L; [0135] Cu concentration=1 g/L; [0136] Cr concentration=0.1 g/L; and [0137] Al concentration=0.1 g/L.

[0138] Conditions for the electroless plating are as follows: [0139] plating temperature: 50 C.; [0140] plating time: 120 minutes; [0141] heat treatment temperature for base after plating: 200 C.; and [0142] heat treatment time for base after plating: 300 seconds (in nitrogen atmosphere).

[0143] The chemical composition of the plating layer on the thus obtained article was found to be same as that of the bulk 1. The plating layer was found to be 5 m thick.

[0144] The article thus obtained in Example 1 was immersed in a 5% aqueous NaCl solution for 120 hours, and the condition was observed. Results are presented in FIGS. 18A and 18B. FIG. 18A presents a result of Example 1, in which no corrosion was observed. FIG. 18B presents an article with conventional Sn-Cu plating, in which corrosion was observed on the surface.

Example 2

[0145] Example 2 exemplifies a mode of electroless plating solution containing a metal ion source having a parent phase that contains Sn and a Sn-Cu alloy, and an intermetallic compound crystal that contains Sn, Cu, Cr, Al, and Ni, dispersed in the parent phase.

[0146] A raw material used herein had a composition represented by Cu: 8% by mass, Cr: 0.5% by mass, Al: 0.5% by mass, Ni: 0.5% by mass, and the balance of Sn. A metal particle 2 having a diameter of approximately 3 to 50 m was manufactured, with use of the manufacturing apparatus illustrated in FIG. 17.

[0147] In this process, conditions below were employed.

[0148] A melting crucible was placed in the melting furnace 7, into which the aforementioned raw material was placed, the content was melted at 900 C., and the melt was fed through the nozzle 3 onto the dish-like rotating disk 4 while keeping the temperature.

[0149] The dish-like rotating disk 4 used herein was a dish-like disk having a diameter of 35 mm and a rotor thickness of 3 to 5 mm, which was rotated at 80,000 to 100,000 rpm.

[0150] The granulation chamber 1 used herein was a vacuum chamber allowed for evacuation down to 910.sup.2 Pa or around, the chamber was evacuated, into which nitrogen gas conditioned at 15 to 50 C. was fed while concurrently discharged, so as to adjust the pressure in the granulation chamber 1 to 110.sup.1 Pa or below.

[0151] With use of the thus obtained metal particle 2, a bulk was manufactured.

[0152] In this process, conditions below were employed.

[0153] High-frequency induction heating: A crucible suited to high-frequency melting was placed in the vacuum chamber allowed for evacuation down to 910.sup.2 Pa or around, the metal particle of this invention was placed in the crucible, the metal particle of this invention was subjected to high-frequency induction heating while keeping the pressure at around the aforementioned degree of vacuum, allowed to melt at a heating temperature of 900 C., and the melt was kept at that temperature for 5 minutes.

[0154] Solidification under cooling: Nitrogen gas conditioned at 15 to 50 C. was then fed into the vacuum chamber for 10 minutes, during which the heating temperature was set to approximately 400 C. under the atmospheric pressure, the melt was cast into a mold, and cooled at room temperature to solidify.

[0155] The thus obtained material was rolled into sheets, a plurality of which were stacked, to manufacture a bulk 2. The bulk 2 was then put into a cutting machine preheated at 150 C., cut into a size of 1 cm to 3 cm1 mm to 5 mm, and the obtained piece was placed in a plating bath below.

[0156] A cross-sectional SEM image of the thus obtained bulk 2 in Example 2 is presented in FIG. 9. It was confirmed from FIG. 9 that the intermetallic compound crystal (dark-colored) presents in the parent phase (pale-colored) so as to be embedded therein.

[0157] EDS elemental mapping on a cross section of the bulk 2 (see FIG. 10) revealed that the chemical composition is represented by Cu: 7.22% by mass, Cr: 0.54% by mass, Al: 0.28% by mass, Ni: 0.24% by mass, and the balance of Sn.

[0158] Also the parent phase was analyzed by EDS elemental mapping at points 005 and 006 as illustrated in FIGS. 15 and 16, respectively, revealing the chemical composition as: [0159] Sn: 74.38% by mass to 85.74% by mass; [0160] Cu: 4.11% by mass to 4.49% by mass; [0161] Al: 0.78% by mass to 1.77% by mass; and [0162] Ni: 0.61% by mass to 0.86% by mass,
from which existence of Sn and Sn-Cu alloy was confirmed.

[0163] Also the intermetallic compound crystal was analyzed by EDS elemental mapping at points 001 to 004 as illustrated in FIGS. 11 to 14, respectively, revealing the chemical composition as: [0164] Sn: 30.61% by mass to 68.66% by mass; [0165] Cu: 7.48% by mass to 27.37% by mass; [0166] Cr: 15.67% by mass or less; [0167] Al: 7.38% by mass or less; and [0168] Ni: 10.74% by mass or less.

[0169] The intermetallic compound crystal was also found to account for 30 to 35% by mass of the bulk 2.

[0170] The base used herein was a copper spring, which was then subjected to electroless plating. Details of the electroless plating bath are as follows.

[0171] Chemical composition of electroless plating (concentration/1 L water): [0172] metal ion source: intermetallic compound crystal and parent phase contained in the bulk 2 [0173] Sn concentration in plating solution=10 g/L; [0174] Cu concentration in plating solution=1 g/L; [0175] Cr concentration in plating solution=0.1 g/L; [0176] Ni concentration in plating solution=0.1 g/L; and [0177] Al concentration in plating solution=0.1 g/L.

[0178] Conditions for the electroless plating are as follows: [0179] plating temperature: 50 C.; [0180] plating time: 120 minutes; [0181] heat treatment temperature for base after plating: 200 C.; and [0182] heat treatment time for base after plating: 300 seconds (in nitrogen atmosphere).

[0183] The chemical composition of the plating layer on the thus obtained article was found to be same as that of the bulk 2. The plating layer was found to be 5 m thick.

[0184] The article thus obtained in Example 2 was immersed in a 5% aqueous NaCl solution for 120 hours, and the condition was observed. A result same as that in Example 1 was obtained (see FIG. 18A).

[0185] Having detailed this invention referring to the attached drawings, this invention is not limited to these Examples. It is apparent that those skilled in the art will easily arrive at various modifications, on the basis of basic technical spirit and teaching of this invention.

REFERENCE SIGNS LIST

[0186] 1 granulation chamber [0187] 2 lid [0188] 3 nozzle [0189] 4 dish-like rotating disk [0190] 5 rotating disk support mechanism [0191] 6 particle discharge pipe [0192] 7 electric furnace [0193] 8 mixed gas tank [0194] 9 pipe [0195] 10 pipe [0196] 11 valve [0197] 12 ventilator [0198] 13 valve [0199] 14 ventilator [0200] 15 automatic filter [0201] 16 particle collector