Tin-plated copper-alloy material for terminal having excellent insertion/extraction performance

Abstract

Tin-plated copper-alloy material for terminal in which: a Sn-based surface layer is formed on a surface of a substrate made of Cu alloy, and a CuSn alloy layer is formed between the Sn-based surface layer and the substrate; the CuSn alloy layer is an alloy layer containing Cu.sub.6Sn.sub.5 as a major proportion and having a compound in which a part of Cu in the Cu.sub.6Sn.sub.5 is substituted by Ni and Si in the vicinity of a boundary face at the substrate side; an average thickness of the Sn-based surface layer is 0.2 m or more and 0.6 m or less; an oil-sump depth Rvk of the CuSn alloy layer is 0.2 m or more; an area rate of the CuSn alloy layer exposed at a surface of the Sn-based surface layer is 10% or more and 40% or less; and dynamic friction coefficient is 0.3 or less.

Claims

1. A tin-plated copper-alloy material for terminal comprising a Sn-based surface layer is formed on a surface of a substrate made of Cu alloy, and a CuSn alloy layer is formed between the Sn-based surface layer and the substrate, wherein: the CuSn alloy layer is an alloy layer containing Cu.sub.6Sn.sub.5 as a major proportion and having a compound in which a part of Cu in the Cu.sub.6Sn.sub.5 is substituted by Ni and Si in the vicinity of a boundary face at the substrate side; an oil-sump depth Rvk of the CuSn alloy layer is 0.2 m or more; an average thickness of the Sn-based surface layer is 0.2 m or more and 0.6 m or less; an area rate of the CuSn alloy layer exposed at a top surface of the tin-plated copper-alloy material for terminal is 10% or more and 40% or less of the top surface of the tin-plated copper-alloy material for terminal; the CuSn alloy layer exposed at the top surface of the tin-plated copper-alloy material for terminal is exposed in equivalent-circle diameters; and a dynamic friction coefficient of the tin-plated copper-alloy material for terminal is 0.3 or less; wherein the tin-plated copper-alloy material for terminal is prepared by a method in which a Sn-based surface layer is formed through a medium of a CuSn alloy layer on a substrate by reflowing after forming a Cu-plating layer and a Sn-plating layer in sequence on the substrate made of Cu alloy, comprising steps of: using the substrate containing 0.5% or more and 5% or less by mass of Ni and 0.1% or more and 1.5% or less by mass of Si; furthermore 5% or less by mass in total of one or more selected from a group consisting of Zn, Sn, Fe and Mg if necessary; and a balance which is composed of Cu and unavoidable impurities; setting a thickness of the Cu-plating layer to 0.03 m or more and 0.14 m or less; setting a thickness of the Sn-plating layer to 0.6 m or more and 1.3 m or less; and reflowing by rapid-cooling surface temperature of the substrate after rising to 240 C. or more and 360 C. or less and holding the temperature for a time indicated below (1) to (3): (1) in a case in which the thickness of the Sn-plating layer is 0.6 m or more and less than 0.8 m: for 1 second or more and 3 seconds or less when the thickness of the Cu-plating layer is 0.03 or more and less than 0.05 m; for 1 second or more and 6 seconds or less when the thickness of the Cu-plating layer is 0.05 m or more and less than 0.08 m; and for 6 seconds or more and 9 seconds or less when the thickness of the Cu-plating layer is 0.08 m or more and 0.14 m or less (2) in a case in which the thickness of the Sn-plating layer is 0.8 m or more and less than 1.0 m: for 3 seconds or more and 6 seconds or less when the thickness of the Cu-plating layer is 0.03 or more and less than 0.05 m; for 3 seconds or more and 9 seconds or less when the thickness of the Cu-plating layer is 0.05 m or more and less than 0.08 m; and for 6 seconds or more and 12 seconds or less when the thickness of the Cu-plating layer is 0.08 m or more and 0.14 m or less (3) in a case in which the thickness of the Sn-plating layer is 1.0 m or more and 1.3 m or less: for 6 seconds or more and 9 seconds or less when the thickness of the Cu-plating layer is 0.03 or more and less than 0.05 m; for 6 seconds or more and 12 seconds or less when the thickness of the Cu-plating layer is 0.05 m or more and less than 0.08 m; and for 9 seconds or more and 12 seconds or less when the thickness of the Cu-plating layer is 0.08 m or more and 0.14 m or less.

2. The tin-plated copper-alloy material for terminal according to claim 1, wherein equivalent-circle diameters of exposed portions of the CuSn alloy layer exposed at the surface of the Sn-based surface layer are 0.6 m or more to 2.0 m or less.

3. The tin-plated copper-alloy material for terminal according to claim 1, wherein an average thickness of the CuSn alloy layer is 0.6 m or more and 1 m or less.

4. The tin-plated copper-alloy material for terminal according to claim 1, wherein the substrate contains: 0.5% or more and 5% or less by mass of Ni and 0.1% or more and 1.5% or less by mass of Si; furthermore 5% or less by mass in total of one or more selected from a group consisting of Zn, Sn, Fe and Mg if necessary; and a balance which is composed of Cu and unavoidable impurities.

5. The tin-plated copper-alloy material for terminal according to claim 3, wherein the substrate contains: 0.5% or more and 5% or less by mass of Ni and 0.1% or more and 1.5% or less by mass of Si; furthermore 5% or less by mass in total of one or more selected from a group consisting of Zn, Sn, Fe and Mg if necessary; and a balance which is composed of Cu and unavoidable impurities.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a photograph by a scanning ion microscope (SIM) of copper-alloy material for terminal of an Example, including a part (a) showing a vertical section and a part (b) showing a surface-state.

(2) FIG. 2 is a sectional photograph by a scanning-transmission electron microscope (STEM) showing a boundary face between a substrate and a CuSn alloy layer of the copper-alloy material for terminal of the Example.

(3) FIG. 3 is a composition profile analyzed by EDS along the arrow in FIG. 2.

(4) FIG. 4 is a photograph by a scanning ion microscope (SIM) of copper-alloy material for terminal of a Comparative Example, showing a part (a) of a vertical section and a part (b) of a surface-state.

(5) FIG. 5 is a sectional photograph by a scanning-transmission electron microscope (STEM) showing a boundary face between a substrate and a CuSn alloy layer of the copper-alloy material for terminal of the Comparative Example.

(6) FIG. 6 is a photograph by a scanning ion microscope (SIM) showing a surface-state of the copper-alloy material for terminal of the Comparative Example.

(7) FIG. 7 is a front view conceptually showing an apparatus for measuring a dynamic friction coefficient of conductive members.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(8) An embodiment of tin-plated copper-alloy material for terminal according to the present invention will be explained.

(9) The tin-plated copper-alloy material for terminal of the present embodiment is constructed as: a Sn-based surface layer is formed on a substrate made of Cu alloy; and a CuSn alloy layer is formed between the Sn-based surface layer and the substrate.

(10) The substrate is copper alloy containing Ni and Si such as CuNiSi based-alloy, CuNiSiZn based-alloy and the like, furthermore 5% or less by mass in total of one or more selected from a group consisting of Zn, Sn, Fe and Mg if necessary, and a balance which is composed of Cu and unavoidable impurities. Ni and Si are essential components for the reason that Ni and Si are supplied from the substrate in reflowing so that Ni and Si are dissolved in the CuSn alloy layer in order to make an oil-sump depth Rvk of the CuSn alloy layer to 0.2 m or more by below-mentioned reflow treatment. Appropriate containing amount in the substrate is: 0.5% or more and 5% or less by mass for Ni, and 0.1% or more and 1.5% or less by mass for Si: because if Ni is contained less than 0.5% by mass, an effect of Ni cannot be obtained; and if Si is contained less than 0.1% by mass, an effect of Si cannot be obtained. If Ni is contained more than 5% by mass, cracking may be occurred when casting or hot-rolling; and if Si is contained more than 1.5% by mass, conductivity may be deteriorated.

(11) Zn and Sn improve strength and heat resistance. Fe and Mg improve stress-relief property. In a case in which one or more of Zn, Sn, Fe and Mg is added, it is undesirable that the containing amount exceed 5% by mass in total because the electrical conductivity is deteriorated. Especially, it is desirable to contain all of Zn, Sn, Fe and Mg.

(12) The CuSn alloy layer is formed by the reflow treatment after forming a Cu-plating layer and an Sn-plating layer on the substrate as below-mentioned. Most part of the CuSn alloy layer is Cu.sub.6Sn.sub.5. (Cu, Ni, Si).sub.6Sn.sub.5 alloy in which a part of Cu is substituted by Ni and Si in the substrate is thinly formed in the vicinity of a boundary face between the CuSn alloy layer and the substrate. The boundary face between the CuSn alloy layer and the Sn-based surface layer is formed unevenly, so that a part of the CuSn alloy layer (Cu.sub.6Sn.sub.5) is exposed at the Sn-based surface layer so as to have 10% or more of an exposed-area rate and 0.2 m or more in an oil-sump depth Rvk of the CuSn alloy layer. Equivalent-circle diameters of exposed portions are 0.6 m or more and 2.0 m or less.

(13) The oil-sump depth Rvk is an average depth of prominent troughs in a surface roughness curve regulated by JIS B0671-2, which is an index indicating an extent of deeper parts than average unevenness. If the value is large, it is indicated that the unevenness is steep by existence of very deep trough.

(14) An average thickness of the CuSn alloy layer is preferably 0.6 m or more and 1 m or less. If it is less than 0.6 m, it is difficult to make the oil-sump depth Rvk of the CuSn alloy layer to 0.2 m or more. It is set to 1 m or less because it is wasteful if it is formed to have thickness of 1 m or more because the Sn-based surface layer should be formed thicker than necessary.

(15) An average thickness of the Sn-based surface layer is set to 0.2 m or more and 0.6 m or less. If the thickness is less than 0.2 m, soldering wettability and electrical-connection reliability may be deteriorated; and if it exceeds 0.6 m, a surface layer cannot be composite construction of Sn and CuSn and may be filled only by Sn, so that the dynamic friction coefficient is increased. More preferred average thickness of the Sn-based surface layer is 0.25 m or more and 0.5 m or less.

(16) At a surface of the Sn-based surface layer, the lower CuSn alloy layer is partially exposed so that an area rate of the exposed part is 10% or more and 40% or less. If the exposed-area rate is less than 10%, the dynamic friction coefficient cannot be suppressed to 0.3 or less; and if it exceeds 40%, the electrical-connection characteristic such as the soldering wettability and the like is deteriorated. More preferred area rate is 10% or more and 30% or less. In this case, the equivalent-circle diameters of the exposed portions are 0.6 m or more and 2.0 m or less. If the equivalent-circle diameters of the exposed portions are less than 0.6 m, it is difficult to set the exposed-area rate of the CuSn alloy layer to 10% or more with the thickness of the Sn-based surface layer satisfying a desired range; and if it exceeds 2.0 m, the soft Sn between the hard CuSn alloy layer cannot lubricate enough, so that it is difficult to set the dynamic friction coefficient to 0.3 or less. More preferably, it is 0.6 m or more and 1.3 m or less.

(17) In the material for terminal having such composition, the boundary face between the CuSn alloy layer and the Sn-based surface layer is formed to have steep uneven shape, so that: soft Sn exists in the steep troughs of the hard CuSn alloy layer in a depth range of hundreds nm from the surface of the Sn-based surface layer, and a part of the hard CuSn alloy layer is slightly exposed at the Sn-based surface layer at the surface; the soft Sn existing in the troughs acts as lubricant; and the dynamic friction coefficient is 0.3 or less. Furthermore, since the exposed-area rate of the CuSn alloy layer is in a limited range of 10% or more and 40% or less, the excellent electrical-connection characteristic of the Sn-based surface layer is not deteriorated.

(18) Next, a method of producing the material for terminal will be explained.

(19) A plate made of copper alloy such as CuNiSi based-alloy, CuNiSiZn based-alloy or the like containing Ni and Si, furthermore 5% or less by mass in total of one or more selected from a group consisting of Zn, Sn, Fe and Mg if necessary, and a balance which is composed of Cu and unavoidable impurities is prepared for a substrate. Surfaces of the plate are cleaned by treatments of degreasing, pickling and the like, then Cu-plating and Sn-plating are operated in sequence.

(20) In Cu-plating, an ordinary Cu-plating bath can be used; for example, a copper-sulfate plating bath or the like containing copper sulfate (CuSO.sub.4) and sulfuric acid (H.sub.2SO.sub.4) as major ingredients can be used. Temperature of the plating bath is set to 20 C. or more to 50 C. or less; and current density is set to 1 A/dm.sup.2 or more and 20 A/dm.sup.2 or less. A film thickness of the Cu-plating layer made by the Cu-plating is set to 0.03 m or more and 0.14 m or less. If it is less than 0.03 m, the alloy substrate has a significant influence, so that the CuSn alloy layer grows to the surface layer, glossiness and the soldering wettability are deteriorated; or if it exceeds 0.14 m, Ni cannot be supplied enough from the substrate while reflowing, so that the desired uneven shape of the CuSn alloy layer cannot be made.

(21) As a plating bath for making the Sn-plating layer, an ordinary Sn-plating bath can be used; for example, a sulfate bath containing sulfuric acid (H.sub.2SO.sub.4) and stannous sulfate (SnSo.sub.4) as major ingredients can be used. Temperature of the plating bath is set to 15 C. or more to 35 C. or less; and current density is set to 1 A/dm.sup.2 or more to 30 A/dm.sup.2 or less. A film thickness of the Sn-plating layer is set to 0.6 m or more and 1.3 m or less. If the thickness of the Sn-plating layer is less than 0.6 m, the Sn-based surface layer is thin after reflowing, so that the electrical-connection characteristic is deteriorated; or if it exceeds 1.3 m, the exposure of the CuSn alloy layer at the surface is reduced, so that it is difficult to suppress the dynamic friction coefficient to 0.3 or less.

(22) As the condition for the reflow treatment, the substrate is heated for 1 second or more and 12 seconds or less in a reduction atmosphere under a condition of a surface temperature is 240 C. or higher and 360 C. or lower, and then the substrate is rapidly cooled. More preferably, the substrate is heated to 260 C. or more to 300 C. or less at the surface temperature for 5 seconds or more to 10 seconds or less, and then rapidly cooled. In this case, a holding time is adequate in a range of 1 second or more to 12 seconds or less in accordance with the thickness of the Cu-plating layer and the thickness of the Sn-plating layer as below; so that the holding time is short when the plating thickness is thin, and the long holding time is necessary when the plating thickness is thick.

(23) <Holding Time after Increasing Substrate Temperature to 240 C. or More and 360 C. or Less>

(24) (1) In a case in which the thickness of the Sn-plating layer is 0.6 m or more and less than 0.8 m: for 1 second or more and 3 seconds or less when the thickness of the Cu-plating layer is 0.03 or more and less than 0.05 m; for 1 second or more and 6 seconds or less when the thickness of the Cu-plating layer is 0.05 m or more and less than 0.08 m; and for 6 seconds or more and 9 seconds or less when the thickness of the Cu-plating layer is 0.08 m or more and 0.14 m or less.
(2) In a case in which the thickness of the Sn-plating layer is 0.8 m or more and less than 1.0 m: for 3 seconds or more and 6 seconds or less when the thickness of the Cu-plating layer is 0.03 or more and less than 0.05 m; for 3 seconds or more and 9 seconds or less when the thickness of the Cu-plating layer is 0.05 m or more and less than 0.08 m; and for 6 seconds or more and 12 seconds or less when the thickness of the Cu-plating layer is 0.08 m or more and 0.14 m or less.
(3) In a case in which the thickness of the Sn-plating layer is 1.0 m or more and 1.3 m or less: for 6 seconds or more and 9 seconds or less when the thickness of the Cu-plating layer is 0.03 or more and less than 0.05 m; for 6 seconds or more and 12 seconds or less when the thickness of the Cu-plating layer is 0.05 m or more and less than 0.08 m; and for 9 seconds or more and 12 seconds or less when the thickness of the Cu-plating layer is 0.08 m or more and 0.14 m or less.

(25) If it is heated in a state in which the temperature is lower than 240 C. and the holding time is shorter than the time shown in the above (1) to (3), fusion of Sn is not proceeded; or if it is heated in a state in which the temperature is higher than 360 C. and the holding time is longer than the time shown in the above (1) to (3), crystal of CuSn alloy is largely grown so that the desired shape cannot be obtained, and the Sn-based surface layer which remains at the surface is too small (the exposed rate of the CuSn alloy layer to the surface is too large) because the CuSn alloy layer reaches to the surface. Furthermore, if a heating condition is high, it is not desirable because oxidation of the Sn-based surface layer is proceeded.

(26) Examples

(27) The substrate was a plate of copper alloy (Ni; 0.5% or more and 5.0% or less by mass-Zn; 1.0%-Sn; 0% or more and 0.5% or less by mass-Si; 0.1% or more and 1.5% or less by mass-Fe; 0% or more and 0.03% or less by mass-Mg; 0.005% by mass) having a plate thickness of 0.25 mm, and Cu-plating and Sn-plating were performed in sequence. In this case, plating conditions of the Cu-plating and the Sn-plating were the same in Examples and Comparative Examples as shown in Table 1. In Table 1, Dk is an abbreviation for current density for a cathode; and ASD is an abbreviation for A/dm.sup.2.

(28) TABLE-US-00001 TABLE 1 Cu PLATING Sn PLATING COMPOSITION OF COPPER SULFATE 250 g/L TIN SULFATE 75 g/L PLATING SOLUTION SULFURIC ACID 50 g/L SULFURIC ACID 85 g/L ADDITIVE 10 g/L SOLUTION 25 C. 20 C. TEMPERATURE Dk 5 ASD 5 ASD

(29) After plating, in Examples and Comparative Examples, the surface temperatures of the substrates were risen to 240 C. or more and 360 C. or less in reduction atmosphere; and subsequently, the substrates were heated for the time shown in the aforementioned (1) to (3) in accordance with the plating thickness, and then water-cooled as reflow treatments.

(30) The holding time shown in (1) to (3) are tabled as Table 2.

(31) TABLE-US-00002 TABLE 2 HOLDING TIME (sec) OF SUBSTRATE TEMPERATURE AFTER RISING TO 240 C. OR MORE AND 360 C. OR LESS Cu-PLATING THICKNESS (m) 0.03 or 0.08 or Sn-PLATING more and 0.05 or more and more and THICKNESS (m) less than 0.05 less than 0.08 0.14 or less 0.6 or more and 1 or more and 1 or more and 6 or more and less than 0.8 3 or less 6 or less 9 or less 0.8 or more and 3 or more and 3 or more and 6 or more and less than 1.0 6 or less 9 or less 12 or less 1.0 or more and 6 or more and 6 or more and 9 or more and 1.3 or less 9 or less 12 or less 12 or less

(32) As Comparative Examples, the substrates in which Ni concentration, Si concentration, Cu-plating thickness and Sn-plating thickness were varied were made.

(33) The conditions for those samples were shown in Table 3.

(34) TABLE-US-00003 TABLE 3 THICKNESS (m) OF REFLOW CONDITION PLATING TEMPERATURE LAYER ( C.) OF HOLDING COMPOSITION OF SUBSTRATE Cu Sn SUBSTRATE TIME (sec) EXAMPLES 1 Ni2.0Zn1.0Sn0.5Si0.5Fe0.03Mg0.005 mass % 0.03 0.72 245 3.0 2 Ni2.0Zn1.0Sn0.5Si0.5Fe0.03Mg0.005 mass % 0.05 0.92 270 3.0 3 Ni2.0Zn1.0Sn0.5Si0.5Fe0.03Mg0.005 mass % 0.05 0.90 270 6.0 4 Ni2.0Zn1.0Sn0.5Si0.5Fe0.03Mg0.005 mass % 0.05 0.90 270 9.0 5 Ni2.0Zn1.0Sn0.5Si0.5Fe0.03Mg0.005 mass % 0.05 0.92 250 6.0 6 Ni2.0Zn1.0Sn0.5Si0.5Fe0.03Mg0.005 mass % 0.05 0.91 350 6.0 7 Ni2.0Zn1.0Sn0.5Si0.5Fe0.03Mg0.005 mass % 0.10 0.89 270 9.0 8 Ni2.0Zn1.0Sn0.5Si0.5Fe0.03Mg0.005 mass % 0.14 0.94 270 12.0 9 Ni2.0Zn1.0Sn0.5Si0.5Fe0.03Mg0.005 mass % 0.10 0.64 245 6.0 10 Ni2.0Zn1.0Sn0.5Si0.5Fe0.03Mg0.005 mass % 0.03 1.25 360 12.0 11 Ni0.5Zn1.0Sn0.5Si0.5Fe0.03Mg0.005 mass % 0.05 0.92 270 6.0 12 Ni5.0Zn1.0Sn0.5Si0.5Fe0.03Mg0.005 mass % 0.05 0.90 270 6.0 13 Ni2.0Zn1.0Sn0.5Si0.1Fe0.03Mg0.005 mass % 0.05 0.89 270 6.0 14 Ni2.0Zn1.0Sn0.5Si1.5Fe0.03Mg0.005 mass % 0.05 0.91 270 6.0 15 Ni2.0Zn1.0Sn0.5Si0.5Fe0.03Mg0.005 mass % 0.03 1.02 360 9.0 16 Ni2.0Zn1.0Sn0.5Si0.5Fe0.03Mg0.005 mass % 0.14 0.63 245 9.0 COMPARATIVE 1 Ni2.0Zn1.0Sn0.5Si0.5Fe0.03Mg0.005 mass % 0.00 0.88 270 6.0 EXAMPLES 2 Ni2.0Zn1.0Sn0.5Si0.5Fe0.03Mg0.005 mass % 0.30 0.88 270 3.0 3 Ni2.0Zn1.0Sn0.5Si0.5Fe0.03Mg0.005 mass % 0.40 0.35 270 1.0 4 Ni2.0Zn1.0Sn0.5Si0.5Fe0.03Mg0.005 mass % 0.40 0.46 270 2.0 5 Ni2.0Zn1.0Sn0.5Si0.5Fe0.03Mg0.005 mass % 0.40 0.58 270 3.0 6 Ni2.0Zn1.0Sn0.5Si0.5Fe0.03Mg0.005 mass % 0.40 0.71 270 3.0 7 Ni0.3Zn1.0Sn0.5Si0.5Fe0.03Mg0.005 mass % 0.05 0.93 270 6.0 8 Ni2.0Zn1.0Sn0.5Si0.08Fe0.03Mg0.005 mass % 0.05 0.92 270 6.0 9 Ni2.0Zn1.0Sn0.5Si0.5Fe0.03Mg0.005 mass % 0.05 0.91 270 2.0 10 Ni2.0Zn1.0Sn0.5Si0.5Fe0.03Mg0.005 mass % 0.05 0.92 270 12.0 11 Ni2.0Zn1.0Sn0.5Si0.5Fe0.03Mg0.005 mass % 0.05 0.89 400 3.0 12 Ni2.0Zn1.0Sn0.5Si0.5Fe0.03Mg0.005 mass % 0.30 0.70 270 6.0

(35) With respect to those samples: the thickness of Sn-based surface layer, the thickness of CuSn alloy layer, the oil-sump depth Rvk of the CuSn alloy layer, the exposed-area rate and the equivalent-circle diameter of the exposed portions on the Sn-based surface of the CuSn alloy layer were measured after reflowing; and the dynamic friction coefficient, the soldering wettability, glossiness, and the electrical-connection reliability were evaluated.

(36) The thicknesses of the Sn-based surface layer and the CuSn alloy layer after reflowing were measured by an X-ray fluorescent analysis thickness meter (SFT9400) by SII Nanotechnology Inc. At first, all the thicknesses of the Sn-based surface layers of the samples after reflowing were measured, and then the Sn-based surface layers were removed by soaking for a few minutes in etchant for abrasion of the plate coatings made from components which do not corrode CuSn alloy but etch pure Sn, for example, by L80 or the like by Laybold Co., Ltd. so that the lower CuSn alloy layers were exposed. Then, the thicknesses of the CuSn alloy layers in pure Sn conversion were measured. Finally, (the thicknesses of all the Sn-based surface layers minus the thickness of the CuSn alloy layer in pure Sn conversion) was defined as the thickness of the Sn-based surface layer.

(37) The oil-sump depth Rvk of the CuSn alloy layer was obtained by: removing the Sn-based surface layer by soaking in etchant for abrasion of the Sn-plate coating so that the lower CuSn alloy layer was exposed; and then obtaining from an average of measured Rvk value measured at 10 points including 5 points along a longitudinal direction and 5 points along a short direction in a condition of an object lens of 150 magnifications (a measuring field of 94 m70 m) using a laser microscope (VK-9700) made by Keyence Corporation.

(38) The exposed-area rate and the equivalent-circle diameter of the exposed portions in the CuSn alloy layer were observed at an area of 100100 m by a scanning ion microscope after removing surface-oxide films. In accordance with a measurement principle, if Cu.sub.6Sn.sub.5 exists in a depth area of substantially 20 nm from an outermost surface, it is imaged by white; so that an area-rate of the white portions with respect to a whole area of the measuring portion was regarded as the exposed-area rate of the CuSn alloy using an image processing software, the equivalent-circle diameters were calculated from the white portions, and an average value of them was regarded as the equivalent-circle diameter of the exposed portions in CuSn alloy.

(39) The dynamic friction coefficient was obtained by: preparing plate-shaped male test pieces and half-spherical female test pieces having an inner diameter of 1.5 mm of the samples so as to simulate a contact of a male terminal and a female terminal in an insertion-type connector; and measuring a friction force between the test pieces using a friction-measuring instrument (V1000) made by Trinity Lab INC. It is explained with reference to FIG. 7 that: the male test piece 12 was fixed on a horizontal table 11, a half-spherical convex of the female test piece 13 was deposited on the male test piece 12 so that plated surfaces were in contact with each other, and the male test piece 12 was pressed at a load P of 100 gf or more to 500 gf or less by the female test piece 13 with a weight 14. In a state in which the load P was applied, a friction force F was measured by a load cell 15 when the male test piece 12 was drawn in the horizontal direction shown by an arrow for 10 mm at a frictional speed of 80 mm/minute. The dynamic friction coefficient (=Fav/P) was obtained from an average value Fav of the friction force F and the load P. Both a case in which the load was 0.98 N (100 gf) and a case in which the load was 4.9 N (500 gf) were described in Table 3.

(40) With respect to the soldering wettability, the test pieces were cut out to have width of 10 mm; so that zero-cross time was measured by a meniscograph method using a rosin-based active flux. (The test pieces were soaked in Sn-37% Pb solder with solder-bath temperature of 230 C.; so that the soldering wettability was measured in a condition in which a soaking speed was 2 mm/sec, a soaking depth was 2 mm, and a soaking time was 10 seconds.) If the soldering zero-cross time was 3 seconds or less, it was evaluated as O; or it was more than 3 seconds, it was evaluated as X.

(41) The glossiness was measured using a gloss meter (model number: PG-1M) made by Nippon Denshoku Industries Co., Ltd. with an entry angle of 60 in accordance with JIS Z 8741.

(42) In order to evaluate the electrical-connection reliability, the contact resistance was measured with heating in the atmosphere at 150 C.500 hours. The measuring method was in accordance with JIS-C-5402, load variation from 0 to 50 gcontact resistance in sliding type (1 mm) was measured using a four-terminal contact-resistance test equipment (made by Yamasaki-Seiki Co., Ltd.: CRS-113-AU), so that a contact resistance value was evaluated when the load was 50 g.

(43) Those measurement results and the evaluation results are described in Table 4.

(44) TABLE-US-00004 TABLE 4 LAYER THICKNESS (m) AFTER OIL-SUMP EXPOSED RATE EQUIVALENT-CIRCLE DYNAMIC FRICTION REFLOWING DEPTH (%) DIAMETER (m) COEFFICIENT Sn CuSn Rvk (m) OF Cu.sub.6Sn.sub.5 OF EXPOSED Cu.sub.6Sn.sub.5 LOAD 500 gf EXAMPLES 1 0.27 0.65 0.32 30 0.96 0.20 2 0.43 0.71 0.27 15 0.68 0.25 3 0.36 0.78 0.31 24 0.81 0.23 4 0.26 0.92 0.36 37 1.04 0.21 5 0.42 0.72 0.32 14 0.65 0.22 6 0.28 0.91 0.32 28 0.91 0.23 7 0.23 0.95 0.35 31 1.25 0.21 8 0.32 0.90 0.24 10 0.85 0.25 9 0.22 0.60 0.22 20 1.04 0.26 10 0.57 0.98 0.39 15 0.79 0.19 11 0.42 0.72 0.30 18 0.71 0.24 12 0.31 0.85 0.31 27 0.83 0.23 13 0.40 0.71 0.30 16 0.81 0.24 14 0.34 0.81 0.32 26 0.85 0.22 15 0.22 1.1 0.28 36 1.91 0.27 16 0.20 0.60 0.20 39 2.08 0.28 COMPARATIVE 1 0.19 0.99 0.39 45 2.22 0.20 EXAMPLE 2 0.47 0.59 0.18 0.2 0.53 0.39 3 0.01 0.48 0.12 75 4.42 0.27 4 0.09 0.52 0.19 45 3.80 0.28 5 0.17 0.58 0.15 34 2.02 0.31 6 0.31 0.58 0.16 4 0.86 0.38 7 0.49 0.63 0.19 7 0.97 0.36 8 0.47 0.65 0.18 5 0.81 0.35 9 0.48 0.62 0.14 8 1.04 0.31 10 0.12 1.2 0.38 58 2.75 0.22 11 0.10 1.1 0.34 53 2.81 0.21 12 0.27 0.60 0.15 16 1.48 0.32 DYNAMIC FRICTION CONTACT COEFFICIENT SOLDERING GLOSSINESS RESISTANCE LOAD 100 gf WETTABILITY (10.sup.2 GU) (m) EXAMPLES 1 0.21 7.6 5.31 2 0.29 8.2 2.51 3 0.26 7.7 3.01 4 0.23 7.3 6.21 5 0.24 8.2 3.56 6 0.24 7.9 3.01 7 0.22 7.6 5.36 8 0.29 8.2 4.02 9 0.28 7.5 7.55 10 0.20 7.6 3.22 11 0.27 8.1 2.60 12 0.26 7.9 3.11 13 0.28 8.0 2.62 14 0.25 7.5 2.87 15 0.29 7.2 7.92 16 0.30 7.1 8.37 COMPARATIVE 1 0.21 X 6.6 11.27 EXAMPLE 2 0.51 8.6 2.18 3 0.28 X 6.1 18.30 4 0.30 X 6.7 14.59 5 0.36 X 6.9 9.21 6 0.48 8.5 3.62 7 0.46 8.3 2.90 8 0.43 8.3 2.73 9 0.35 8.5 2.78 10 0.23 X 6.3 11.08 11 0.22 X 6.4 10.03 12 0.39 8.0 4.75

(45) Obviously from Table 4, in every Example, the dynamic friction coefficient was small as 0.3 or less, the soldering wettability was good, the glossiness was high, the exterior appearance was good and the contact resistance was 10 m or less. On the other hand, the oil-sump depth Rvk of the CuSn alloy layer is less than 0.2 m in Comparative Examples 2, 5, 6, 7, 8, 9 and 12; the soldering wettability and the glossiness of Comparative Example 1 were poor by being largely influenced by the alloy substrate; and in Comparative Examples 3, 4, 10 and 11, even though the dynamic friction coefficient was 0.3 or less, because the thickness of Sn is thin, the soldering wettability was poor, the glossiness was low, and the contact resistance exceeds 10 m so that the electrical reliability was deteriorated.

(46) FIG. 1 and FIG. 2 are photomicrographs of the sample of Example 2; and FIG. 3 is a composition profile in which a section of Example 2 is analyzed by an EDS (an Energy Dispersive X-ray Spectrometer). In FIG. 2 and FIG. 3; a part (i) is the substrate, a part (ii) is the (Cu, Ni, Si).sub.6Sn.sub.5 layer, and a part (iii) is the Cu.sub.6Sn.sub.5 layer. FIG. 4 and FIG. 5 are photomicrographs of Comparative Example 2. FIG. 6 is a photomicrograph of Comparative Example 3. As recognized by comparing those photographs, in the samples of Examples, the asperity of the CuSn alloy layer is precipitous; (Cu, Ni, Si).sub.6Sn.sub.5 which is a compound in which a part of Cu was substituted by Ni and Si was slightly found in the vicinity of the boundary face of the CuSn alloy layer at the substrate side (below the broken line in FIG. 2); and a part of the CuSn alloy layer was exposed with being scattered at the Sn-based surface layer and having small equivalent-circle diameters. The samples of the Comparative Examples, as shown in FIG. 5, has constitution in which: a relatively thick Cu.sub.3Sn layer was found at a lower part of the CuSn alloy layer; the Cu.sub.6Sn.sub.5 layer was laminated on the Cu.sub.3Sn layer; and the asperity of the CuSn alloy layer was rough and gentle so that the exposure at the surface was small. As shown in FIG. 6, the equivalent-circle diameter of the exposed portions of the CuSn alloy layer was large.

(47) Industrial Applicability

(48) The tin-plated copper-alloy material for terminal of the present invention is applicable to a terminal for a connector used for connecting electrical wiring of automobiles or personal products, in particular, to a terminal for a multi-pin connector.

DESCRIPTION OF THE REFERENCE SYMBOLS

(49) 11 Table 12 Male test piece 13 Female test piece 14 Weight 15 Load cell