WO2016039089A1 - 錫めっき銅合金端子材及びその製造方法 - Google Patents

錫めっき銅合金端子材及びその製造方法 Download PDF

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Publication number
WO2016039089A1
WO2016039089A1 PCT/JP2015/073132 JP2015073132W WO2016039089A1 WO 2016039089 A1 WO2016039089 A1 WO 2016039089A1 JP 2015073132 W JP2015073132 W JP 2015073132W WO 2016039089 A1 WO2016039089 A1 WO 2016039089A1
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Prior art keywords
layer
alloy
plating
tin
less
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PCT/JP2015/073132
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English (en)
French (fr)
Inventor
加藤　直樹
雄基 井上
中矢　清隆
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三菱マテリアル株式会社
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Priority to CN201580044549.3A priority Critical patent/CN106795642B/zh
Priority to US15/505,174 priority patent/US10047448B2/en
Priority to KR1020177007699A priority patent/KR102355331B1/ko
Priority to MX2017002396A priority patent/MX2017002396A/es
Priority to EP15840443.4A priority patent/EP3192896B1/en
Publication of WO2016039089A1 publication Critical patent/WO2016039089A1/ja

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    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
    • C25D5/10—Electroplating with more than one layer of the same or of different metals
    • C25D5/12—Electroplating with more than one layer of the same or of different metals at least one layer being of nickel or chromium
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    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
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    • B32B15/01—Layered products comprising a layer of metal all layers being exclusively metallic
    • B—PERFORMING OPERATIONS; TRANSPORTING
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    • Y10T428/26—Web or sheet containing structurally defined element or component, the element or component having a specified physical dimension
    • Y10T428/263—Coating layer not in excess of 5 mils thick or equivalent
    • Y10T428/264—Up to 3 mils
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T428/00—Stock material or miscellaneous articles
    • Y10T428/26—Web or sheet containing structurally defined element or component, the element or component having a specified physical dimension
    • Y10T428/263—Coating layer not in excess of 5 mils thick or equivalent
    • Y10T428/264—Up to 3 mils
    • Y10T428/265—1 mil or less
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T428/00—Stock material or miscellaneous articles
    • Y10T428/27—Web or sheet containing structurally defined element or component, the element or component having a specified weight per unit area [e.g., gms/sq cm, lbs/sq ft, etc.]
    • Y10T428/273—Web or sheet containing structurally defined element or component, the element or component having a specified weight per unit area [e.g., gms/sq cm, lbs/sq ft, etc.] of coating

Definitions

  • the present invention relates to a tin-plated copper alloy terminal material useful as a connector terminal, particularly a multi-pin connector terminal used for connecting electrical wiring of automobiles and consumer devices, and a method for manufacturing the same.
  • the tin-plated copper alloy terminal material was subjected to copper plating and tin plating on a copper alloy base material and then reflowed to form a Cu—Sn alloy layer under the Sn-based surface layer of the surface layer. It is widely used as a terminal material.
  • Patent Document 1 there is a material (Patent Document 1) in which the surface of the Cu—Sn alloy layer is defined by roughening the base material (Patent Document 1), but there are problems that the contact resistance increases and the solder wettability decreases.
  • Patent Document 2 there is one that defines the average roughness of the Cu—Sn alloy layer (Patent Document 2), but there is a problem that, for example, the dynamic friction coefficient cannot be reduced to 0.3 or less in order to further improve the insertability.
  • Patent Document 3 there is a layer structure (Patent Document 3) in which nickel plating, copper plating, and tin plating are sequentially applied on a base material and reflow treatment is performed to form a base material / Ni / CuSn / Sn layer structure.
  • the purpose was to prevent contact resistance deterioration, and the dynamic friction coefficient could not be reduced to 0.3 or less.
  • the insertion force F of the connector is such that the force (contact pressure) by which the female terminal presses the male terminal is P, and the dynamic friction coefficient is ⁇ . 2 ⁇ ⁇ ⁇ P.
  • the contact pressure P can be reduced unnecessarily.
  • about 3N is required.
  • Some multi-pin connectors exceed 50 pins / connector, but the insertion force F of the entire connector is preferably 100 N or less, preferably 80 N or less, or 70 N or less, so that the dynamic friction coefficient ⁇ needs to be 0.3 or less. Is done.
  • terminal materials with lower surface frictional resistance have been developed, but in the case of connection terminals that fit male and female terminals, the same material type is rarely used for both, and male terminals are based on brass.
  • a general-purpose tin-plated terminal material is widely used as a material. Therefore, even if a low insertion force terminal material is used only for the female terminal, there is a problem that the effect of reducing the insertion force is small.
  • the present invention has been made in view of the above-described problems, and an object of the present invention is to provide a tin-plated copper alloy terminal material that can reduce the insertion force at the time of fitting even to a terminal using a general-purpose tin-plated terminal material.
  • the present inventors have found that the surface Sn layer is thin and that a part of the lower Cu—Sn alloy layer is exposed on the surface is advantageous in reducing the dynamic friction coefficient. Recognized. However, as the Sn layer becomes thinner, the electrical connection characteristics deteriorate. Therefore, if the Cu-Sn alloy layer has a steep rugged shape and the surface layer has a composite structure of Sn and Cu-Sn alloy layers, the exposure of the Cu-Sn alloy layer is controlled to a limited range, and the electrical connection characteristics It has been found that soft Sn between hard Cu—Sn alloy layers acts as a lubricant to reduce the coefficient of dynamic friction and obtain a low insertion force terminal material.
  • an Sn-based surface layer is formed on the surface of a substrate made of copper or a copper alloy, and the Sn-based surface layer is interposed between the Sn-based surface layer and the substrate.
  • the average thickness is 0.2 ⁇ m or more and 0.6 ⁇ m or less, and the area ratio of the exposed portion of the Cu—Sn alloy layer to the surface area of the surface layer of the tin-plated copper alloy terminal material is 1% or more and 40% or less,
  • the average value of equivalent circle diameters of the exposed portions of the Cu—Sn alloy layer is 0.1 ⁇ m. Above 1.5 ⁇ m or less, height of the projecting peak portions Rpk of the surface of the tin-plated copper alloy material for terminal is less 0.03 ⁇ m least 0.005 .mu.m, dynamic friction coefficient is 0.3 or less.
  • the protruding peak height Rpk of the surface of the tin-plated copper alloy terminal material is 0.005 ⁇ m or more and 0.03 ⁇ m or less, the average thickness of the Sn-based surface layer is 0.2 ⁇ m or more and 0.6 ⁇ m or less, and the surface layer of the tin-plated copper alloy terminal material
  • the area ratio of the exposed portion of the Cu—Sn alloy layer to the surface area of 1 to 40%, and the average value of the equivalent circle diameter of each exposed portion of the Cu—Sn alloy layer is 0.1 ⁇ m or more and 1.5 ⁇ m or less, A dynamic friction coefficient of 0.3 or less of the tin-plated copper alloy terminal material can be realized.
  • the surface of the Cu—Sn alloy layer becomes a fine uneven shape, and the height of the protruding peak portion of the tin-plated copper alloy terminal material is high.
  • the area ratio of the exposed portion of the Rpk and the Cu—Sn alloy layer is suppressed to a limited range.
  • the protrusion peak height Rpk on the surface of the tin-plated copper alloy terminal material is set to 0.03 ⁇ m or less because when it exceeds 0.03 ⁇ m, the hard Cu—Sn alloy layer scrapes off the soft Sn layer of the sliding counterpart. This is because abrasive wear occurs and the frictional resistance increases.
  • the protrusion peak height Rpk of the tin-plated copper alloy terminal material is set to 0.005 ⁇ m or more when the Sn-based surface layer and the Cu-Sn alloy layer are exposed when the Cu-Sn alloy layer is exposed on the surface of the Sn-based surface layer. This is because a step is generated between the exposed portion and the exposed portion.
  • the 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, solder wettability and electrical connection reliability are deteriorated. This is because the composite structure of the Sn layer and the Cu—Sn alloy layer cannot be formed and is occupied only by Sn, so that the dynamic friction coefficient increases.
  • the average thickness of the Sn-based surface layer is more preferably 0.3 ⁇ m to 0.5 ⁇ m.
  • the area ratio of the exposed portion of the Cu-Sn alloy layer to the surface area of the tin-plated copper alloy terminal material is less than 1%, the dynamic friction coefficient cannot be less than 0.3, and if it exceeds 40%, the electrical connection characteristics such as solder wettability Decreases.
  • a more preferable area ratio is 2% to 20%.
  • the average value of the equivalent circle diameter of each exposed portion of the Cu—Sn alloy layer is less than 0.1 ⁇ m, the area ratio of the exposed portion of the Cu—Sn alloy layer cannot be 1% or more, and if it exceeds 1.5 ⁇ m, it is hard.
  • the soft Sn between the Cu—Sn alloy layers cannot sufficiently function as a lubricant, and the dynamic friction coefficient cannot be 0.3 or less.
  • a more preferable equivalent circle diameter is 0.2 ⁇ m to 1.0 ⁇ m.
  • the Sn-based surface layer is known to increase the dynamic friction coefficient when the vertical load at the time of measuring the dynamic friction coefficient decreases, but the product of the present invention hardly changes even when the vertical load is lowered. The effect can be exhibited even if it is used for small terminals.
  • the Ni content in the Cu—Sn alloy layer is preferably 1 at% or more and 25 at% or less.
  • the reason why the Ni content is defined as 1 at% or more is that if it is less than 1 at%, an intermetallic compound alloy in which a part of Cu of the Cu 6 Sn 5 alloy is replaced with Ni is not formed, and a steep uneven shape is not formed.
  • the reason why it is defined as 25 at% or less is that when it exceeds 25 at%, the shape of the Cu—Sn alloy layer tends to become too fine, and when the Cu—Sn alloy layer becomes too fine, the dynamic friction coefficient is reduced to 0.3 or less. This is because there are cases where it cannot be done.
  • the method for producing a tin-plated copper alloy terminal material according to the present invention includes the steps of performing reflow treatment after performing nickel plating or nickel alloy plating, copper plating and tin plating in this order on a base material made of a copper alloy.
  • the layer thickness is 0.05 ⁇ m or more and 1.0 ⁇ m
  • the second plating layer thickness by the copper plating is 0.05 ⁇ m or more and 0.20 ⁇ m or less
  • the third plating layer thickness by the tin plating is 0.5 ⁇ m or more and 1.0 ⁇ m or less.
  • the reflow treatment includes a heating step of heating each plating layer to a peak temperature of 240 to 300 ° C. at a temperature rising rate of 20 to 75 ° C./second, and reaching the peak temperature. It was followed, with a primary cooling step of cooling 2-15 seconds following cooling rate 30 ° C. / sec, and a secondary cooling step of cooling at a cooling rate of 100 ⁇ 300 ° C. / sec after the primary cooling.
  • the substrate is nickel-plated or nickel alloy-plated to form (Cu, Ni) 6 Sn 5 alloy after reflow treatment, and the unevenness of the Cu—Sn alloy layer becomes steep, thereby increasing the dynamic friction coefficient. It can be 0.3 or less.
  • the thickness of the first plating layer by nickel plating or nickel alloy plating is less than 0.05 ⁇ m, the Ni content contained in the (Cu, Ni) 6 Sn 5 alloy is reduced, and a steep uneven Cu-Sn alloy layer is formed. When the thickness exceeds 1.0 ⁇ m, bending or the like becomes difficult.
  • the thickness of the first plating layer by nickel plating or nickel alloy plating is 0.1 ⁇ m. It is desirable to set it above.
  • the metal used for nickel plating or nickel alloy plating is not limited to pure Ni, but may be Ni alloy such as Ni—Co or Ni—W.
  • the thickness of the second plating layer by copper plating is less than 0.05 ⁇ m, the Ni content contained in the (Cu, Ni) 6 Sn 5 alloy increases, and the shape of the Cu—Sn alloy layer becomes too fine.
  • the thickness exceeds 20 ⁇ m, the Ni content in the (Cu, Ni) 6 Sn 5 alloy becomes small, and a steep uneven Cu—Sn alloy layer is not formed.
  • the thickness of the third plating layer by tin plating is less than 0.5 ⁇ m, the Sn-based surface layer after reflow is thinned and the electrical connection characteristics are impaired, and when it exceeds 1.0 ⁇ m, the surface of the Sn-based surface layer is reached.
  • the area ratio of the exposed portion of the Cu—Sn alloy layer becomes small, and it is difficult to make the dynamic friction coefficient 0.3 or less.
  • the temperature increase rate in the heating process is less than 20 ° C./second, Cu atoms preferentially diffuse in the Sn grain boundary until the tin plating is melted, and the metal in the vicinity of the grain boundary. Since the compound grows abnormally, a steep uneven Cu—Sn alloy layer is not formed. On the other hand, if the rate of temperature rise exceeds 75 ° C./second, the growth of the intermetallic compound becomes insufficient, and a desired intermetallic compound alloy cannot be obtained in the subsequent cooling.
  • the peak temperature in the heating process is less than 240 ° C.
  • Sn does not melt uniformly
  • the peak temperature exceeds 300 ° C.
  • the intermetallic compound grows rapidly and the unevenness of the Cu—Sn alloy layer is large. This is not preferable.
  • the cooling step by providing a primary cooling step with a low cooling rate, Cu atoms diffuse gently in the Sn grains and grow with a desired intermetallic compound structure.
  • the cooling rate in the primary cooling step exceeds 30 ° C./second, the intermetallic compound cannot be sufficiently grown due to the rapid cooling, and the Cu—Sn alloy layer is not exposed on the surface.
  • an intermetallic compound cannot grow.
  • the cooling time exceeds 15 seconds, the Cu 6 Sn 5 alloy grows excessively and becomes coarse, and depending on the thickness of the copper plating layer, a Ni—Sn compound layer is formed under the Cu—Sn alloy layer. The barrier property is reduced. Air cooling is appropriate for this primary cooling step.
  • the secondary cooling step is rapidly cooled to complete the growth of the intermetallic alloy with a desired structure.
  • the cooling rate in the secondary cooling step is less than 100 ° C./second, the intermetallic compound further proceeds, and a desired intermetallic compound shape cannot be obtained.
  • the coefficient of dynamic friction is small, it is possible to achieve both low contact resistance, good solder wettability and low insertion / extraction, and it is effective even at low loads and is optimal for small terminals.
  • terminals used in automobiles and electronic components have superiority in parts that require low insertion force, stable contact resistance, and good solder wettability during bonding.
  • Example 4 is a graph showing X-ray diffraction patterns of Example 3, Comparative Example 4, and Comparative Example 10. It is a STEM image of the cross section of the tin plating copper alloy terminal material of Example 3. It is an EDS analysis figure along the white line part of FIG. It is a STEM image of the cross section of the tin plating copper alloy terminal material of the comparative example 4. It is an EDS analysis figure which follows the white line part of FIG. It is a STEM image of the cross section of the tin plating copper alloy terminal material of the comparative example 10. It is an EDS analysis figure which follows the white line part of FIG. It is a front view which shows notionally the apparatus for measuring a dynamic friction coefficient.
  • an Sn-based surface layer is formed on the surface of a base material made of copper or a copper alloy, and a Cu—Sn alloy is interposed between the Sn-based surface layer and the base material.
  • Layer / Ni layer or Ni alloy layer is formed in order from the Sn-based surface layer.
  • the base material is not particularly limited as long as it is made of copper or a copper alloy.
  • the Ni layer or the Ni alloy layer is a layer made of a Ni alloy such as pure Ni, Ni—Co, or Ni—W.
  • the Cu—Sn alloy layer is a layer made of only an intermetallic compound alloy in which a part of Cu of the Cu 6 Sn 5 alloy is replaced with Ni, and a part of the Cu—Sn alloy layer is exposed on the surface of the Sn-based surface layer, and a plurality of Forming part.
  • These layers are formed by applying a nickel plating, a copper plating, and a tin plating on the base material in order, as will be described later, and performing a reflow treatment. On the Ni layer or the Ni alloy layer, Cu— An Sn alloy layer is formed.
  • the protrusion peak part height Rpk of the surface of the tin plating copper alloy terminal material formed of Sn system surface layer shall be 0.005 micrometer or more and 0.03 micrometer or less.
  • the protruding peak height Rpk is an average height of the protruding peaks above the core portion of the roughness curve defined by JIS B0671-2, and is obtained by measuring with a laser microscope.
  • the average thickness of the Sn-based surface layer is 0.2 ⁇ m or more and 0.6 ⁇ m or less, and a part (exposed portion) of the Cu—Sn alloy layer is exposed on the surface of the Sn-based surface layer.
  • the area ratio of the exposed portion with respect to the surface area of the tin-plated copper alloy terminal material is 1% or more and 40% or less, and the average value of the equivalent circle diameter of each exposed portion of the Cu—Sn alloy layer is 0.1 ⁇ m or more and 1.5 ⁇ m. Formed below.
  • a Cu—Sn alloy layer made of only (Cu, Ni) 6 Sn 5 alloy in which a part of Cu is replaced with Ni is present, so that the surface layer has a hard Cu—
  • a composite structure of an Sn alloy layer and a soft Sn-based surface layer is formed, and a part (exposed portion) of the hard Cu-Sn alloy layer is slightly exposed on the Sn-based surface layer to form a plurality of exposed portions.
  • the soft Sn existing around each exposed portion acts as a lubricant, and a low dynamic friction coefficient of 0.3 or less is realized.
  • the area ratio of each exposed portion of the Cu—Sn alloy layer is in a limited range of 1% to 40% with respect to the surface area of the tin-plated copper alloy terminal material. There is no loss of properties.
  • the Ni content in the Cu—Sn alloy layer is 1 at% or more and 25 at% or less.
  • the reason why the Ni content is defined as 1 at% or more is that if it is less than 1 at%, an intermetallic compound alloy in which a part of Cu of the Cu 6 Sn 5 alloy is replaced with Ni is not formed, and a steep uneven shape is not formed.
  • the reason why it is defined as 25 at% or less is that when it exceeds 25 at%, the shape of the Cu—Sn alloy layer tends to become too fine, and when the Cu—Sn alloy layer becomes too fine, the dynamic friction coefficient is reduced to 0.3 or less. This is because there are cases where it cannot be done.
  • the 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, solder wettability and electrical connection reliability are deteriorated. This is because the composite structure of the Sn layer and the Cu—Sn alloy layer cannot be formed and is occupied only by tin, so that the dynamic friction coefficient increases.
  • the average thickness of the Sn-based surface layer is more preferably 0.3 ⁇ m to 0.5 ⁇ m.
  • the dynamic friction coefficient cannot be 0.3 or less, and when it exceeds 40%, the electrical connection characteristics such as solder wettability are deteriorated.
  • a more preferable area ratio is 2% to 20%.
  • the average value of the equivalent circle diameter of each exposed portion of the Cu—Sn alloy layer is less than 0.1 ⁇ m, the area ratio of the exposed portion cannot be 1% or more, and if it exceeds 1.5 ⁇ m, the area between the hard Cu—Sn alloy layers Therefore, the soft tin cannot sufficiently function as a lubricant, and the dynamic friction coefficient cannot be 0.3 or less.
  • a more preferable equivalent circle diameter is 0.2 ⁇ m to 1.0 ⁇ m.
  • the Sn-based surface layer is known to increase the dynamic friction coefficient when the vertical load at the time of measuring the dynamic friction coefficient decreases, but the product of the present invention hardly changes even when the vertical load is lowered. The effect can be exhibited even if it is used for small terminals.
  • a plate material made of copper or a copper alloy such as Cu—Ni—Si is prepared. After the surface of the plate material is cleaned by degreasing, pickling, etc., nickel plating, copper plating, and tin plating are performed in this order.
  • a general nickel plating bath may be used.
  • a sulfuric acid bath containing sulfuric acid (H 2 SO 4 ) and nickel sulfate (NiSO 4 ) as main components can be used.
  • the temperature of the plating bath is 20 to 50 ° C., and the current density is 1 to 30 A / dm 2 or less.
  • the thickness of the nickel plating layer (first plating layer thickness) formed by this nickel plating is 0.05 ⁇ m or more and 1.0 ⁇ m or less.
  • the thickness of the first plating layer is less than 0.05 ⁇ m, the Ni content contained in the (Cu, Ni) 6 Sn 5 alloy becomes small, and a sharp uneven Cu—Sn alloy layer is not formed. This is because if the thickness exceeds 1.0 ⁇ m, bending or the like becomes difficult.
  • a general copper plating bath may be used.
  • a copper sulfate bath mainly composed of copper sulfate (CuSO 4 ) and sulfuric acid (H 2 SO 4 ) may be used.
  • the temperature of the plating bath is 20 to 50 ° C., and the current density is 1 to 30 A / dm 2 .
  • the film thickness (second plating layer thickness) of the copper plating layer formed by this copper plating is 0.05 ⁇ m or more and 0.20 ⁇ m or less.
  • the thickness of the second plating layer is less than 0.05 ⁇ m, the Ni content contained in the (Cu, Ni) 6 Sn 5 alloy becomes large, the shape of the Cu—Sn alloy layer becomes too fine, and the second plating layer This is because if the thickness exceeds 0.20 ⁇ m, the Ni content contained in the (Cu, Ni) 6 Sn 5 alloy becomes small, and a steep uneven Cu—Sn alloy layer is not formed.
  • a general tin plating bath may be used.
  • a sulfuric acid bath mainly composed of sulfuric acid (H 2 SO 4 ) and stannous sulfate (SnSO 4 ) is used. Can do.
  • the temperature of the plating bath is 15 to 35 ° C., and the current density is 1 to 30 A / dm 2 .
  • the film thickness of the tin plating layer (third plating layer thickness) formed by this tin plating is 0.5 ⁇ m or more and 1.0 ⁇ m or less.
  • the thickness of the third plating layer is less than 0.5 ⁇ m, the Sn-based surface layer after reflow is thinned and the electrical connection characteristics are impaired.
  • the thickness of the third plating layer exceeds 1.0 ⁇ m, the surface of the terminal material is reached.
  • the area ratio of the exposed portion of the Cu—Sn alloy layer becomes small, and it is difficult to make the dynamic friction coefficient 0.3 or less.
  • the treated material (base material) after plating is heated to a peak temperature of 240 to 300 ° C. for 3 to 15 seconds at a temperature rising rate of 20 to 75 ° C./second in a heating furnace having a CO reducing atmosphere.
  • a heating step a primary cooling step of cooling for 2 to 15 seconds at a cooling rate of 30 ° C./second or less after reaching its peak temperature, and 0.5 to 5 at a cooling rate of 100 to 300 ° C./disease after the primary cooling.
  • a secondary cooling step of cooling for 2 seconds The primary cooling step is performed by air cooling, and the secondary cooling step is performed by water cooling using 10 to 90 ° C. water.
  • Cu and Sn electrodeposited at a high current density have low stability, and alloying and grain enlargement occur even at room temperature, making it difficult to produce a desired intermetallic compound structure by reflow treatment. For this reason, it is desirable to perform the reflow process immediately after the plating process. Specifically, it is necessary to perform reflow within 15 minutes, preferably within 5 minutes. A short standing time after plating does not cause a problem, but in a normal processing line, it is about one minute after construction.
  • the reflow treatment after the plating treatment was performed 1 minute after the final tin plating treatment, and the heating step, the primary cooling step, and the secondary cooling step were performed under various conditions.
  • Table 2 summarizes the test conditions and the thickness of the plating layer of each sample obtained.
  • the average thickness of the Sn-based surface layer, the Ni content in the (Cu, Ni) 6 Sn 5 alloy, the presence of an alloy layer other than the Cu 6 Sn 5 alloy, the protruding ridge height Rpk, In addition to measuring the area ratio of the exposed portion of the Cu-Sn alloy layer on the Sn-based surface, the average value of the equivalent circle diameter of the exposed portion, the coefficient of dynamic friction, solder wettability, glossiness, and electrical reliability (contact resistance) evaluated.
  • the thickness of the Sn-based surface layer was measured with a fluorescent X-ray film thickness meter (SFT 9400) manufactured by SII Nano Technology.
  • SFT 9400 fluorescent X-ray film thickness meter
  • the Sn-based surface layer is removed by immersing in an etching solution for several minutes, the underlying Cu—Sn alloy layer is exposed, and the thickness of the Cu—Sn alloy layer in terms of pure Sn is measured.
  • the thickness of the Sn-based surface layer was defined as the thickness of the Sn-based surface layer.
  • the position of the alloy is specified by observation of a cross-sectional STEM image and surface analysis by EDS analysis, and (Cu, Ni) by point analysis. ) The content of Ni in the 6 Sn 5 alloy was determined.
  • the position of the alloy is specified by observation of a cross-sectional STEM image and surface analysis by EDS analysis, and by line analysis in the depth direction of the alloy layer other than Cu 6 Sn 5 alloy. The presence or absence was sought.
  • the Sn-based surface layer is removed by immersing in an etching solution for stripping the tin plating film, and the underlying Cu—Sn After the alloy layer was exposed, it was determined by measuring an X-ray diffraction pattern by CuK ⁇ rays.
  • the measurement conditions are as follows. Made by PANalytical: MPD1880HR Tube used: Cu K ⁇ line Voltage: 45 kV Current: 40 mA
  • the protrusion peak height Rpk on the surface is 5 points in the longitudinal direction and 5 in the short direction under the condition of 150 times objective lens (measuring field of view 96 ⁇ m ⁇ 72 ⁇ m) using a Keyence Corporation laser microscope (VK-X200). It calculated
  • the area ratio and equivalent circle diameter of the exposed portion of the Cu—Sn alloy layer were determined by observing a 100 ⁇ 100 ⁇ m region with a scanning ion microscope after removing the surface oxide film.
  • Cu 6 Sn 5 alloy existing in the depth region from the outermost surface to about 20 nm is imaged in white. Therefore, using the image processing software, the area of each white region is calculated, The ratio of the area of the white area to the total area was calculated as the area ratio of the exposed portion of the Cu—Sn alloy layer.
  • the average value was calculated by taking the diameter of a circle having an area equivalent to the area of each exposed portion (white region) as the equivalent circle diameter of each exposed portion.
  • the equivalent circle diameter is a value obtained by converting a particle having an irregular particle shape in the particle size distribution measurement into a diameter of a circle having an area equivalent to the observed area of the particle. It is what you have seen.
  • a copper alloy plate (C2600, Cu: 70% by mass—Zn: 30% by mass) with a plate thickness of 0.25 mm is used as a base material, followed by copper plating and tin plating, followed by reflow treatment to prepare a sample for a male terminal specimen. Produced. The thickness of the Sn-based surface layer after reflowing was 0.6 ⁇ m, and the Cu—Sn alloy layer was not exposed.
  • the dynamic friction coefficient was measured using this male terminal test piece and each female terminal test piece prepared under the conditions shown in Table 2. For each sample, a plate-shaped male terminal test piece and a hemispherical female terminal test piece having an inner diameter of 1.5 mm were prepared, and the contact portion of the male terminal and female terminal of the fitting connector was simulated. Using a friction measuring machine ( ⁇ V1000) manufactured by Trinity Lab, the frictional force between both specimens was measured to obtain the dynamic friction coefficient.
  • the male terminal test piece 12 is fixed on the horizontal base 11, the hemispherical convex surface of the female terminal test piece 13 is placed thereon, the plated surfaces are brought into contact with each other, and the weight 14 is applied to the female terminal test piece 13.
  • the male terminal test piece 12 was pressed by applying a load P of 500 gf. With the load P applied, the frictional force F when the male test piece 12 was pulled 10 mm in the horizontal direction indicated by the arrow at a sliding speed of 80 mm / min was measured by the load cell 15.
  • each sample was cut into a width of 10 mm, and the zero cross time was measured by a meniscograph method using a rosin-based active flux. (Measured under the condition of immersion in Sn-37% Pb solder with a solder bath temperature of 230 ° C, immersion speed of 2 mm / sec, immersion depth of 2 mm, and immersion time of 10 sec.) And when it exceeded 3 second, it evaluated that it was inferior.
  • the glossiness was measured using a gloss meter (model number: PG-1M) manufactured by Nippon Denshoku Industries Co., Ltd. according to JIS Z 8741 at an incident angle of 60 degrees.
  • the measuring method is based on JIS-C-5402, 4 terminal contact resistance tester (manufactured by Yamazaki Seiki Laboratories: CRS-113-AU), sliding type (1mm) load change from 0 to 50g-contact resistance was evaluated by the contact resistance value when the load was 50 g.
  • Comparative Examples 1, 3, 5, 7, 9, and 12 have a dynamic friction coefficient of 0.3 or more because the area ratio of the exposed portion of the Cu—Sn alloy layer is less than 1%.
  • Comparative Examples 2 and 6 since the area ratio of the exposed portion exceeds 40%, the solder wettability and the glossiness are poor.
  • Comparative Example 4 does not contain Ni in the Cu 6 Sn 5 alloy and the presence of the Cu 3 Sn alloy can be confirmed, the average value of the equivalent circle diameter of the exposed portion exceeds 1.5 ⁇ m, and therefore The dynamic friction coefficient exceeds 0.3.
  • Comparative Examples 8 and 11 deviate from the reflow conditions, and Rpk exceeds 0.03 ⁇ m and causes abrasive wear. Therefore, the dynamic friction coefficient exceeds 0.3.
  • Comparative Example 10 since the Ni 3 Sn 4 alloy was formed because it deviated from the reflow condition, the barrier property of the Ni layer was lowered and the contact resistance exceeded 9 m ⁇ .
  • FIG. 1 shows X-ray diffraction patterns of Example 3 and Comparative Examples 4 and 10 from 25 degrees to 46 degrees.
  • Example 3 only the peaks of the base material Cu, the base plating layer Ni, and the Cu 6 Sn 5 alloy were detected, but in Comparative Example 10, the Ni 3 was about 31.7 degrees.
  • the peak of Sn 4 alloy was detected, and in Comparative Example 4, the peak of Cu 3 Sn alloy was detected around 37.8 degrees.
  • Example 3 and Comparative Example 10 since the peak of the Cu 6 Sn 5 alloy is shifted to the high angle side, a part of Cu in the Cu 6 Sn 5 alloy may be replaced with Ni. Recognize.
  • Example 2 and 3 are a cross-sectional STEM image and an EDS analysis result of the sample of Example 3, wherein (a) is a Ni layer, (b) is a Cu—Sn alloy layer made of (Cu, Ni) 6 Sn 5 alloy, (C) is a tin layer.
  • 6 and 7 are cross-sectional STEM images and EDS line analysis results of Comparative Example 10, in which (a) is a Ni layer, (b) is a (Ni, Cu) 3 Sn 4 alloy layer, and (c) is (Cu, Ni). ) 6 Sn 5 alloy layer, (d) is a tin layer.
  • the example is composed of only the Cu 6 Sn 5 alloy containing Ni ((Cu, Ni) 6 Sn 5 alloy) between the Ni layer and the tin layer. Only the Cu—Sn alloy layer is formed.
  • Comparative Example 4 a Cu 3 Sn alloy layer was formed at the interface between the Cu 6 Sn 5 alloy layer and the Ni layer, and the Cu 6 Sn 5 alloy did not contain Ni. It can be seen that the unevenness is rough and gentle.
  • Comparative Example 10 the interface between the Cu 6 Sn 5 alloy layer and the Ni layer containing Ni, it can be seen that the Ni 3 Sn 4 alloy layer containing Cu is formed.

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Abstract

　銅又は銅合金からなる基材表面にＳｎ系表面層が形成されており、Ｓｎ系表面層と基材との間に、Ｓｎ系表面層から順にＣｕ－Ｓｎ合金層／Ｎｉ層又はＮｉ合金層が形成された錫めっき銅合金端子材であって、Ｃｕ－Ｓｎ合金層は、Ｃｕ６Ｓｎ５合金のＣｕの一部がＮｉに置換した金属間化合物合金のみからなる層であり、Ｃｕ－Ｓｎ合金層の一部がＳｎ系表面層に露出して複数の露出部を形成しており、Ｓｎ系表面層の平均厚みが０．２μｍ以上０．６μｍ以下であり、表面積に対するＣｕ－Ｓｎ合金層の露出部の面積率が１％以上４０％以下であり、Ｃｕ－Ｓｎ合金層の各露出部の円相当直径の平均値が０．１μｍ以上１．５μｍ以下であり、表面の突出山部高さＲｐｋが０．００５μｍ以上０．０３μｍ以下であり、動摩擦係数が０．３以下である錫めっき銅合金端子材。

Description

錫めっき銅合金端子材及びその製造方法
　本発明は、自動車や民生機器等の電気配線の接続に使用されるコネクタ用端子、特に多ピンコネクタ用の端子として有用な錫めっき銅合金端子材及びその製造方法に関する。
　本願は、２０１４年９月１１日に出願された特願２０１４－１８５０３３に基づき優先権を主張し、その内容をここに援用する。
　錫めっき銅合金端子材は、銅合金からなる基材の上に銅めっき及び錫めっきを施した後にリフロー処理することにより、表層のＳｎ系表面層の下層にＣｕ－Ｓｎ合金層が形成されたものであり、端子材として広く用いられている。
　近年、例えば自動車においては急速に電装化が進行し、これに伴い電気機器の回路数が増加するため、使用するコネクタの小型・多ピン化が顕著になっている。コネクタが多ピン化すると、単ピンあたりの挿入力は小さくても、コネクタを挿着する際にコネクタ全体では大きな力が必要となり、生産性の低下が懸念されている。そこで、錫めっき銅合金材の摩擦係数を小さくして単ピンあたりの挿入力を低減することが試みられている。
　例えば、基材を粗らして、Ｃｕ－Ｓｎ合金層の表面露出度を規定したもの（特許文献１）があるが、接触抵抗が増大する、ハンダ濡れ性が低下するといった問題があった。また、Ｃｕ－Ｓｎ合金層の平均粗さを規定したもの（特許文献２）もあるが、さらなる挿抜性向上のため例えば動摩擦係数を０．３以下にできないといった問題があった。
　また、基材上にニッケルめっき、銅めっき、錫めっきを順に施して、リフロー処理して、基材／Ｎｉ／ＣｕＳｎ／Ｓｎの層構造としたもの（特許文献３）があるが、加熱時の接触抵抗劣化の防止を目的としており動摩擦係数を０．３以下にできなかった。
　ここで、コネクタの挿入力Ｆは、メス端子がオス端子を圧し付ける力（接圧）をＰ、動摩擦係数をμとすると、通常オス端子は上下２方向からメス端子に挟まれるので、Ｆ＝２×μ×Ｐとなる。この挿入力Ｆを小さくするには、接圧Ｐを小さくすることが有効だが、コネクタ嵌合時のオス・メス端子の電気的接続信頼性を確保するためにはいたずらに接圧Ｐを小さくできず、３Ｎ程度は必要とされる。多ピンコネクタでは、５０ピン／コネクタを超えるものもあるが、コネクタ全体の挿入力Ｆは１００Ｎ以下、できれば８０Ｎ以下、あるいは７０Ｎ以下が望ましいため、動摩擦係数μとしては、０．３以下が必要とされる。
特開２００７－１００２２０号公報 特開２００７－６３６３２４号公報 特許第４３１９２４７号公報
　従来より表面の摩擦抵抗を下げた端子材が開発されているが、オス、メス端子を嵌合する接続端子の場合、両者に同じ材種を用いることが少なく、特にオス端子は、黄銅を基材とした汎用の錫めっき付き端子材が広く用いられている。そのため、メス端子のみに低挿入力端子材を用いても、挿入力低減の効果が小さいといった問題があった。
　本発明は、前述の課題に鑑みてなされたものであって、汎用の錫めっき端子材を用いた端子に対しても嵌合時の挿入力を低減できる錫めっき銅合金端子材の提供を目的とする。
　本発明者らは鋭意研究した結果、表層のＳｎ層が薄く、その表面にわずかに下層のＣｕ－Ｓｎ合金層の一部が露出していることは、動摩擦係数の低下に有利であるとの認識に至った。しかしながら、Ｓｎ層が薄くなることにより電気接続特性が低下する。そこで、Ｃｕ－Ｓｎ合金層を急峻な凹凸形状とし、表層付近をＳｎ層とＣｕ－Ｓｎ合金層の複合構造とすると、Ｃｕ－Ｓｎ合金層の露出を限られた範囲に制御して電気接続特性の低下を抑制できるとともに、硬いＣｕ－Ｓｎ合金層の間にある軟らかいＳｎが潤滑剤の作用を果たして動摩擦係数が下がり、低挿入力端子材が得られることを見出した。但し、この低挿入力端子材を端子の一方にのみ用い、他方を汎用の錫めっき材とした場合、摩擦係数低減の効果が半減した。これは、Ｃｕ－Ｓｎ合金層の一部を表面に露出させた場合、表面に露出したＣｕ－Ｓｎ合金層とＳｎ層とに段差が生じ、硬いＣｕ－Ｓｎ合金層が凸部を形成するため、端子の一方のみに用いると、他方の汎用の錫めっき材の軟らかいＳｎ系表面層を削り取るいわゆるアブレシブ摩耗が生じるためである。これらの知見の下、以下の解決手段とした。
　本発明の錫めっき銅合金端子材は、銅又は銅合金からなる基材上の表面にＳｎ系表面層が形成され、該Ｓｎ系表面層と前記基材との間に、前記Ｓｎ系表面層から順にＣｕ－Ｓｎ合金層／Ｎｉ層又はＮｉ合金層とが形成された錫めっき銅合金端子材であって、前記Ｃｕ－Ｓｎ合金層は、Ｃｕ６Ｓｎ５合金のＣｕの一部がＮｉに置換した金属間化合物合金のみからなる層であり、前記Ｃｕ－Ｓｎ合金層の一部が前記Ｓｎ系表面層の表面に露出して複数の露出部を形成しており、前記Ｓｎ系表面層の平均厚みが０．２μｍ以上０．６μｍ以下であり、前記錫めっき銅合金端子材の表層の表面積に対する前記Ｃｕ－Ｓｎ合金層の前記露出部の面積率が１％以上４０％以下であり、前記Ｃｕ－Ｓｎ合金層の前記各露出部の円相当直径の平均値が０．１μｍ以上１．５μｍ以下であり、前記錫めっき銅合金端子材の表面の突出山部高さＲｐｋが０．００５μｍ以上０．０３μｍ以下であり、動摩擦係数が０．３以下である。
　錫めっき銅合金端子材の表面の突出山部高さＲｐｋが０．００５μｍ以上０．０３μｍ以下、Ｓｎ系表面層の平均厚みを０．２μｍ以上０．６μｍ以下、錫めっき銅合金端子材の表層の表面積に対するＣｕ－Ｓｎ合金層の露出部の面積率を１～４０％、Ｃｕ－Ｓｎ合金層の各露出部の円相当直径の平均値を０．１μｍ以上１．５μｍ以下とすることで、錫めっき銅合金端子材の動摩擦係数の０．３以下を実現できる。この場合、Ｃｕの一部がＮｉに置換した（Ｃｕ，Ｎｉ）６Ｓｎ５合金の存在により、Ｃｕ－Ｓｎ合金層の表面が微細な凹凸形状となり、錫めっき銅合金端子材の突出山部高さＲｐｋ及びＣｕ－Ｓｎ合金層の露出部の面積率を限られた範囲に抑制している。
　錫めっき銅合金端子材の表面の突出山部高さＲｐｋを０．０３μｍ以下としたのは、０．０３μｍを超えると硬いＣｕ－Ｓｎ合金層が摺動相手材の軟らかいＳｎ層を削り取る、いわゆるアブレシブ摩耗を生じ、摩擦抵抗が大きくなるためである。錫めっき銅合金端子材の突出山部高さＲｐｋを０．００５μｍ以上としたのは、Ｃｕ－Ｓｎ合金層がＳｎ系表面層の表面に露出した場合、Ｓｎ系表面層とＣｕ－Ｓｎ合金層の露出部との間に段差が発生するからである。
　Ｓｎ系表面層の平均厚みを０．２μｍ以上０．６μｍ以下としたのは、０．２μｍ未満でははんだ濡れ性の低下、電気的接続信頼性の低下を招き、０．６μｍを超えると表層をＳｎ層とＣｕ－Ｓｎ合金層の複合構造とできず、Ｓｎだけで占められるので動摩擦係数が増大するためである。より好ましいＳｎ系表面層の平均厚みは０．３μｍ～０．５μｍである。
　錫めっき銅合金端子材の表面積に対するＣｕ－Ｓｎ合金層の露出部の面積率が１％未満では動摩擦係数を０．３以下とできず、４０％を超えると、はんだ濡れ性等の電気接続特性が低下する。より好ましい面積率は２％～２０％である。
　Ｃｕ－Ｓｎ合金層の各露出部の円相当直径の平均値が０．１μｍ未満では、Ｃｕ－Ｓｎ合金層の露出部の面積率を１％以上とできず、１．５μｍを超えると、硬いＣｕ－Ｓｎ合金層の間にある軟らかいＳｎが十分に潤滑剤としての作用を果たすことができず、動摩擦係数を０．３以下とできない。より好ましい円相当直径は０．２μｍ～１．０μｍである。
　なお、Ｓｎ系表面層は、動摩擦係数測定時の垂直荷重が小さくなると動摩擦係数が増大することが知られているが、本発明品は、垂直荷重を下げても動摩擦係数が殆ど変化せず、小型端子に用いても効果が発揮できる。
　本発明の錫めっき銅合金端子材において、前記Ｃｕ－Ｓｎ合金層中のＮｉ含有率が１ａｔ％以上２５ａｔ％以下であるとよい。Ｎｉ含有率を１ａｔ％以上と規定したのは、１ａｔ％未満ではＣｕ６Ｓｎ５合金のＣｕの一部がＮｉに置換した金属間化合物合金が形成されず、急峻な凹凸形状とならないためであり、２５ａｔ％以下と規定したのは、２５ａｔ％を超えるとＣｕ－Ｓｎ合金層の形状が微細になりすぎる傾向にあり、Ｃｕ－Ｓｎ合金層が微細になりすぎると動摩擦係数を０．３以下にできない場合があるためである。
　本発明の錫めっき銅合金端子材の製造方法は、銅合金からなる基材上に、ニッケルめっきまたはニッケル合金めっき、銅めっき及び錫めっきをこの順で施した後に、リフロー処理することにより、前記基材の上にＮｉ層またはＮｉ合金層／Ｃｕ－Ｓｎ合金層／Ｓｎ系表面層を形成した錫めっき銅合金端子材を製造する方法であって、前記ニッケルめっき又はニッケル合金めっきによる第１めっき層厚みを０．０５μｍ以上１．０μｍとし、前記銅めっきによる第２めっき層厚みを０．０５μｍ以上０．２０μｍ以下とし、前記錫めっきによる第３めっき層厚みを０．５μｍ以上１．０μｍ以下とし、前記リフロー処理は、各めっき層を２０～７５℃／秒の昇温速度で２４０～３００℃のピーク温度まで加熱する加熱工程と、前記ピーク温度に達した後、３０℃／秒以下の冷却速度で２～１５秒間冷却する一次冷却工程と、一次冷却後に１００～３００℃／秒の冷却速度で冷却する二次冷却工程とを有する。
　前述したように基材にニッケルめっきまたはニッケル合金めっきすることにより、リフロー処理後（Ｃｕ，Ｎｉ）６Ｓｎ５合金を形成させ、これによりＣｕ－Ｓｎ合金層の凹凸が急峻になって動摩擦係数を０．３以下とできる。
　ニッケルめっきまたはニッケル合金めっきによる第１めっき層厚みが０．０５μｍ未満では、（Ｃｕ，Ｎｉ）６Ｓｎ５合金に含有するＮｉ含有率が小さくなり、急峻な凹凸形状のＣｕ－Ｓｎ合金層が形成されなくなり、１．０μｍを超えると曲げ加工等が困難となる。なお、基材からのＣｕの拡散を防ぐ障壁層としての機能をＮｉ層又はＮｉ合金層にもたせ耐熱性を向上させる場合には、ニッケルめっきまたはニッケル合金めっきによる第１めっき層厚みは０．１μｍ以上とすることが望ましい。ニッケルめっきまたはニッケル合金めっきに用いる金属は、純Ｎｉに限定されず、Ｎｉ－ＣｏやＮｉ－Ｗ等のＮｉ合金でも良い。
　銅めっきによる第２めっき層厚みが０．０５μｍ未満では、（Ｃｕ，Ｎｉ）６Ｓｎ５合金に含有するＮｉ含有率が大きくなり、Ｃｕ－Ｓｎ合金層の形状が微細になりすぎてしまい、０．２０μｍを超えると、（Ｃｕ，Ｎｉ）６Ｓｎ５合金に含有するＮｉ含有率が小さくなり、急峻な凹凸形状のＣｕ－Ｓｎ合金層が形成されなくなる。
　錫めっきによる第３めっき層厚みが０．５μｍ未満であると、リフロー後のＳｎ系表面層が薄くなって電気接続特性が損なわれ、１．０μｍを超えると、前記Ｓｎ系表面層の表面へのＣｕ－Ｓｎ合金層の露出部の面積率が小さくなって動摩擦係数を０．３以下にすることが難しい。
　リフロー処理においては、加熱工程における昇温速度が２０℃／秒未満であると、錫めっきが溶融するまでの間にＣｕ原子がＳｎの粒界中を優先的に拡散し粒界近傍で金属間化合物が異常成長するため、急峻な凹凸形状のＣｕ－Ｓｎ合金層が形成されなくなる。一方、昇温速度が７５℃／秒を超えると、金属間化合物の成長が不十分となり、その後の冷却において所望の金属間化合物合金を得ることができない。
　また、加熱工程でのピーク温度が２４０℃未満であると、Ｓｎが均一に溶融せず、ピーク温度が３００℃を超えると、金属間化合物が急激に成長しＣｕ－Ｓｎ合金層の凹凸が大きくなるので好ましくない。
　さらに、冷却工程においては、冷却速度の小さい一次冷却工程を設けることにより、Ｃｕ原子がＳｎ粒内に穏やかに拡散し、所望の金属間化合物構造で成長する。この一次冷却工程の冷却速度が３０℃／秒を超えると、急激に冷却される影響で金属間化合物が十分に成長できなくなり、Ｃｕ－Ｓｎ合金層が表面に露出しなくなる。冷却時間が２秒未満であっても同様に金属間化合物が成長できない。冷却時間が１５秒を超えると、Ｃｕ６Ｓｎ５合金の成長が過度に進み粗大化し、銅めっき層の厚みによっては、Ｃｕ－Ｓｎ合金層の下にＮｉ－Ｓｎ化合物層が形成され、Ｎｉ層のバリア性が低下する。この一次冷却工程は空冷が適切である。
　この一次冷却工程の後、二次冷却工程によって急冷して金属間化合物合金の成長を所望の構造で完了させる。この二次冷却工程の冷却速度が１００℃／秒未満であると、金属間化合物がより進行し、所望の金属間化合物形状を得ることができない。
　本発明によれば、動摩擦係数が小さいので、低接触抵抗、良好なはんだ濡れ性と低挿抜性を両立させることができ、また低荷重でも効果があり小型端子に最適である錫めっき銅合金端子材を提供できる。特に、自動車および電子部品等に使用される端子において、接合時の低い挿入力、安定した接触抵抗、良好なはんだ濡れ性を必要とする部位において優位性を持つ。
実施例３、比較例４、比較例１０のＸ線回折パターンを示すグラフである。 実施例３の錫めっき銅合金端子材の断面のＳＴＥＭ像である。 図２の白線部分に沿うＥＤＳ分析図である。 比較例４の錫めっき銅合金端子材の断面のＳＴＥＭ像である。 図４の白線部分に沿うＥＤＳ分析図である。 比較例１０の錫めっき銅合金端子材の断面のＳＴＥＭ像である。 図６の白線部分に沿うＥＤＳ分析図である。 動摩擦係数を測定するための装置を概念的に示す正面図である。
　本発明の一実施形態の錫めっき銅合金端子材を説明する。
　本実施形態の錫めっき銅合金端子材は、銅又は銅合金からなる基材上の表面にＳｎ系表面層が形成されており、Ｓｎ系表面層と基材との間に、Ｃｕ－Ｓｎ合金層／Ｎｉ層又はＮｉ合金層がＳｎ系表面層から順に形成されている。
　基材は、銅又は銅合金からなるものであれば、特に、その組成が限定されるものではない。
　Ｎｉ層又はＮｉ合金層は、純Ｎｉ、Ｎｉ－ＣｏやＮｉ－Ｗ等のＮｉ合金からなる層である。
　Ｃｕ－Ｓｎ合金層は、Ｃｕ６Ｓｎ５合金のＣｕの一部がＮｉに置換した金属間化合物合金のみからなる層であり、その一部がＳｎ系表面層の表面に露出して複数の露出部を形成している。
　これらの層は、後述するように基材の上にニッケルめっき、銅めっき、錫めっきを順に施してリフロー処理することにより形成されたものであり、Ｎｉ層又はＮｉ合金層の上に、Ｃｕ－Ｓｎ合金層が形成されている。
　この錫めっき銅合金端子材においては、表面に露出したＣｕ－Ｓｎ合金層が微細でありかつＳｎ系表面層との段差が小さく滑らかであることが重要であり、Ｃｕ－Ｓｎ合金層の露出部及びＳｎ系表面層によって形成される錫めっき銅合金端子材の表面の突出山部高さＲｐｋが０．００５μｍ以上０．０３μｍ以下とされる。突出山部高さＲｐｋは、ＪＩＳＢ０６７１－２で定義される、粗さ曲線のコア部の上にある突出山部の平均高さであって、レーザ顕微鏡で測定することにより求められる。
　Ｓｎ系表面層の平均厚みは０．２μｍ以上０．６μｍ以下であり、このＳｎ系表面層の表面にＣｕ－Ｓｎ合金層の一部（露出部）が露出している。そして、錫めっき銅合金端子材の表面積に対する露出部の面積率が１％以上４０％以下であり、Ｃｕ－Ｓｎ合金層の各露出部の円相当直径の平均値が０．１μｍ以上１．５μｍ以下に形成される。
　このような構造の錫めっき銅合金端子材は、Ｃｕの一部がＮｉに置換した（Ｃｕ，Ｎｉ）６Ｓｎ５合金のみからなるＣｕ－Ｓｎ合金層が存在することにより、表層が硬いＣｕ－Ｓｎ合金層と軟らかいＳｎ系表面層との複合構造とされ、その硬いＣｕ－Ｓｎ合金層の一部（露出部）がＳｎ系表面層にわずかに露出して複数の露出部を形成しており、各露出部の周囲に存在する軟らかいＳｎが潤滑剤の作用を果たし、０．３以下の低い動摩擦係数が実現される。このＣｕ－Ｓｎ合金層の各露出部の面積率は錫めっき銅合金端子材の表面積に対して１％以上４０％以下の限られた範囲であるから、Ｓｎ系表面層の持つ優れた電気接続特性を損なうことはない。
　この場合、Ｃｕ－Ｓｎ合金層中のＮｉ含有率は、１ａｔ％以上２５ａｔ％以下とされる。Ｎｉ含有率を１ａｔ％以上と規定したのは、１ａｔ％未満ではＣｕ６Ｓｎ５合金のＣｕの一部がＮｉに置換した金属間化合物合金が形成されず、急峻な凹凸形状とならないためであり、２５ａｔ％以下と規定したのは、２５ａｔ％を超えるとＣｕ－Ｓｎ合金層の形状が微細になりすぎる傾向にあり、Ｃｕ－Ｓｎ合金層が微細になりすぎると動摩擦係数を０．３以下にできない場合があるためである。
　Ｓｎ系表面層の平均厚みを０．２μｍ以上０．６μｍ以下としたのは、０．２μｍ未満でははんだ濡れ性の低下、電気的接続信頼性の低下を招き、０．６μｍを超えると表層をＳｎ層とＣｕ－Ｓｎ合金層の複合構造とできず、錫だけで占められるので動摩擦係数が増大するためである。より好ましいＳｎ系表面層の平均厚みは０．３μｍ～０．５μｍである。
　端子材の表面におけるＣｕ－Ｓｎ合金層の露出部の面積率が１％未満では動摩擦係数を０．３以下とできず、４０％を超えると、はんだ濡れ性等の電気接続特性が低下する。より好ましい面積率は、２％～２０％である。
　Ｃｕ－Ｓｎ合金層の各露出部の円相当直径の平均値が０．１μｍ未満では露出部の面積率を１％以上とできず、１．５μｍを超えると、硬いＣｕ－Ｓｎ合金層の間にある軟らかい錫が十分に潤滑剤としての作用を果たすことができず、動摩擦係数を０．３以下とできない。より好ましい円相当直径は０．２μｍ～１．０μｍである。
　また、Ｓｎ系表面層は、動摩擦係数測定時の垂直荷重が小さくなると動摩擦係数が増大することが知られているが、本発明品は、垂直荷重を下げても動摩擦係数が殆ど変化せず、小型端子に用いても効果が発揮できる。
　次に、この端子材の製造方法について説明する。
　基材として、銅又はＣｕ－Ｎｉ－Ｓｉ系等の銅合金からなる板材を用意する。この板材に脱脂、酸洗等の処理をすることによって表面を清浄にした後、ニッケルめっき、銅めっき、錫めっきをこの順序で施す。
　ニッケルめっきは一般的なニッケルめっき浴を用いればよく、例えば硫酸（Ｈ２ＳＯ４）と硫酸ニッケル（ＮｉＳＯ４）を主成分とした硫酸浴を用いることができる。めっき浴の温度は２０℃以上５０℃以下、電流密度は１～３０Ａ/ｄｍ２以下とされる。このニッケルめっきにより形成されるニッケルめっき層の膜厚（第１めっき層厚み）は０．０５μｍ以上１．０μｍ以下とされる。第１めっき層厚みが０．０５μｍ未満では、（Ｃｕ，Ｎｉ）６Ｓｎ５合金に含有するＮｉ含有率が小さくなり、急峻な凹凸形状のＣｕ－Ｓｎ合金層が形成されなくなり、第１めっき層厚みが１．０μｍを超えると曲げ加工等が困難となるためである。
　銅めっきは一般的な銅めっき浴を用いればよく、例えば硫酸銅（ＣｕＳＯ４）及び硫酸（Ｈ２ＳＯ４）を主成分とした硫酸銅浴等を用いることができる。めっき浴の温度は２０～５０℃、電流密度は１～３０Ａ／ｄｍ２とされる。この銅めっきにより形成される銅めっき層の膜厚（第２めっき層厚み）は０．０５μｍ以上０．２０μｍ以下とされる。第２めっき層厚みが０．０５μｍ未満では、（Ｃｕ，Ｎｉ）６Ｓｎ５合金に含有するＮｉ含有率が大きくなり、Ｃｕ－Ｓｎ合金層の形状が微細になりすぎてしまい、第２めっき層厚みが０．２０μｍを超えると、（Ｃｕ，Ｎｉ）６Ｓｎ５合金に含有するＮｉ含有率が小さくなり、急峻な凹凸形状のＣｕ－Ｓｎ合金層が形成されなくなるためである。
　錫めっき層形成のためのめっき浴としては、一般的な錫めっき浴を用いればよく、例えば硫酸（Ｈ２ＳＯ４）と硫酸第一錫（ＳｎＳＯ４）を主成分とした硫酸浴を用いることができる。めっき浴の温度は１５～３５℃、電流密度は１～３０Ａ／ｄｍ２とされる。この錫めっきにより形成される錫めっき層の膜厚（第３めっき層厚み）は０．５μｍ以上１．０μｍ以下とされる。第３めっき層厚みが０．５μｍ未満であると、リフロー後のＳｎ系表面層が薄くなって電気接続特性が損なわれ、第３めっき層厚みが１．０μｍを超えると、端子材の表面へのＣｕ－Ｓｎ合金層の露出部の面積率が小さくなって動摩擦係数を０．３以下にすることが難しい。
　各めっき処理を施した後、加熱してリフロー処理を行う。
　リフロー処理は、ＣＯ還元性雰囲気にした加熱炉内で、めっき後の処理材（基材）を２０～７５℃／秒の昇温速度で２４０～３００℃のピーク温度まで３～１５秒間加熱する加熱工程と、そのピーク温度に達した後、３０℃／秒以下の冷却速度で２～１５秒間冷却する一次冷却工程と、一次冷却後に１００～３００℃／病の冷却速度で０．５～５秒間冷却する二次冷却工程とを有する処理とする。一次冷却工程は空冷により、二次冷却工程は１０～９０℃の水を用いた水冷により行われる。
　このリフロー処理を還元性雰囲気で行うことにより、錫めっき表面に溶融温度の高いすず酸化物皮膜が生成するのを防ぎ、より低い温度かつより短い時間でのリフロー処理が可能となり、所望の金属間化合物構造を作製することが容易となる。また、冷却工程を二段階とし、冷却速度の小さい一次冷却工程を設けることにより、Ｃｕ原子がＳｎ粒内に穏やかに拡散し、所望の金属間化合物構造で成長する。そして、その後に急冷を行うことにより金属間化合物合金の成長を止め、所望の構造で固定化できる。
　高電流密度で電析したＣｕとＳｎは安定性が低く、室温においても合金化や結晶粒肥大化が発生し、リフロー処理で所望の金属間化合物構造を作ることが困難になる。このため、めっき処理後速やかにリフロー処理を行うことが望ましい。具体的には１５分以内、望ましくは５分以内にリフローを行う必要がある。めっき後の放置時間が短いことは問題とならないが、通常の処理ラインでは構成上１分後程度となる。
（メス端子試験片）
　板厚０．２５ｍｍのコルソン系（Ｃｕ－Ｎｉ－Ｓｉ系）銅合金板を基材とし、ニッケルめっき、銅めっき、錫めっきを順に施し、リフロー処理して各メス端子試験片用の試料を作製した。ニッケルめっき、銅めっき及び錫めっきのめっき条件は実施例、比較例とも同じで、表１に示す通りとした。表１中、Ｄｋはカソードの電流密度、ＡＳＤはＡ／ｄｍ２の略である。
Figure JPOXMLDOC01-appb-T000001
　めっき処理を施した後のリフロー処理は、最後の錫めっき処理をしてから１分後に行い、加熱工程、一次冷却工程、二次冷却工程について種々の条件で行った。各試験条件および得られた各試料のめっき層の厚さを表２にまとめた。
Figure JPOXMLDOC01-appb-T000002
　リフロー後のこれらの試料について、Ｓｎ系表面層の平均厚み、（Ｃｕ，Ｎｉ）６Ｓｎ５合金中のＮｉ含有率、Ｃｕ６Ｓｎ５合金以外の合金層の存在、突出山部高さＲｐｋ、Ｃｕ－Ｓｎ合金層の露出部のＳｎ系表面上における面積率、露出部の円相当直径の平均値を測定するとともに、動摩擦係数、はんだ濡れ性、光沢度、電気的信頼性（接触抵抗）を評価した。
　Ｓｎ系表面層の厚みは、エスアイアイ・ナノテクノロジー株式会社製蛍光Ｘ線膜厚計（ＳＦＴ９４００）にて測定した。最初にリフロー後の試料の全Ｓｎ系表面層の厚みを測定した後、例えばレイボルド株式会社製のＬ８０等の、純ＳｎをエッチングしＣｕ－Ｓｎ合金層を腐食しない成分からなるめっき被膜剥離用のエッチング液に数分間浸漬することによりＳｎ系表面層を除去し、その下層のＣｕ－Ｓｎ合金層を露出させ純Ｓｎ換算におけるＣｕ－Ｓｎ合金層の厚みを測定した後、（全Ｓｎ系表面層の厚み－純Ｓｎ換算におけるＣｕ－Ｓｎ合金層の厚み）をＳｎ系表面層の厚みと定義した。
　Ｃｕ－Ｓｎ合金層において、（Ｃｕ，Ｎｉ）６Ｓｎ５合金中のＮｉ含有率については、断面ＳＴＥＭ像の観察及びＥＤＳ分析による面分析で合金の位置を特定し、点分析で（Ｃｕ，Ｎｉ）６Ｓｎ５合金中のＮｉの含有率を求めた。Ｃｕ６Ｓｎ５合金以外の合金層の有無については、断面ＳＴＥＭ像の観察及びＥＤＳ分析による面分析で合金の位置を特定し、深さ方向の線分析によりＣｕ６Ｓｎ５合金以外の合金層の有無を求めた。また、断面観察に加え、より広範囲におけるＣｕ６Ｓｎ５合金以外の合金層の有無については、錫めっき被膜剥離用のエッチング液に浸漬してＳｎ系表面層を除去し、その下層のＣｕ－Ｓｎ合金層を露出させた後、ＣｕＫα線によるＸ線回折パターンを測定することで判定した。測定条件は以下のとおりである。
　ＰＡＮａｌｙｔｉｃａｌ製：ＭＰＤ１８８０ＨＲ
　使用管球：Ｃｕ　Ｋα線
　電圧：４５　ｋＶ
　電流：４０　ｍＡ
　表面の突出山部高さＲｐｋは、株式会社キーエンス製レーザ顕微鏡(ＶＫ－Ｘ２００)を用い、対物レンズ１５０倍（測定視野９６μｍ×７２μｍ）の条件で、長手方向で５点、短手方向で５点、計１０点測定したＲｐｋの平均値より求めた。
　Ｃｕ－Ｓｎ合金層の露出部の面積率及び円相当直径は、表面酸化膜を除去後、１００×１００μｍの領域を走査イオン顕微鏡により観察して求めた。測定原理上、最表面から約２０ｎｍまでの深さ領域に存在するＣｕ６Ｓｎ５合金は白くイメージングされるので、画像処理ソフトを使用して、個々の白い領域の面積を計算し、測定領域の全面積に対する白い領域の面積の比率をＣｕ－Ｓｎ合金層の露出部の面積率として算出した
　また、各露出部(白い領域)の面積と同等の面積を持つ円の直径を各露出部の円相当直径として、その平均値を算出した。円相当直径とは、粒径分布の測定において粒の形状が不規則である粒子に対して、観察されたその粒子の面積と同等の面積を持つ円の直径に換算した値を粒子の直径とみなしたものである。
（動摩擦係数測定用オス端子試験片）
　板厚０．２５ｍｍの銅合金板（Ｃ２６００、Ｃｕ：７０質量％－Ｚｎ：３０質量％）を基材とし、銅めっき、錫めっきを順に施し、リフロー処理してオス端子試験片用の試料を作製した。リフロー後のＳｎ系表面層の厚みは０．６μｍであり、Ｃｕ－Ｓｎ合金層の露出は無かった。
　このオス端子試験片と、表２の各条件で作製した各メス端子試験片とを用いて動摩擦係数を測定した。各試料について板状のオス端子試験片と内径１．５ｍｍの半球状としたメス端子試験片とを作成して、嵌合型のコネクタのオス端子とメス端子の接点部を模擬し、株式会社トリニティーラボ製の摩擦測定機（μＶ１０００）を用い、両試験片間の摩擦力を測定して動摩擦係数を求めた。
　図８により説明すると、水平な台１１上にオス端子試験片１２を固定し、その上にメス端子試験片１３の半球凸面を置いてめっき面同士を接触させ、メス端子試験片１３に錘１４によって５００ｇｆの荷重Ｐをかけてオス端子試験片１２を押さえた。この荷重Ｐをかけた状態で、オス試験片１２を摺動速度８０ｍｍ／分で矢印により示した水平方向に１０ｍｍ引っ張ったときの摩擦力Ｆをロードセル１５によって測定した。その摩擦力Ｆの平均値Ｆａｖと荷重Ｐより動摩擦係数（＝Ｆａｖ／Ｐ）を求めた。
　はんだ濡れ性については、各試料を１０ｍｍ幅に切り出し、ロジン系活性フラックスを用いてメニスコグラフ法にてゼロクロスタイムを測定した。（はんだ浴温２３０℃のＳｎ－３７％Ｐｂはんだに浸漬させ、浸漬速度２ｍｍ／ｓｅｃ、浸漬深さ２ｍｍ、浸漬時間１０ｓｅｃの条件にて測定した。）はんだゼロクロスタイムが３秒以下を良と評価し、３秒を超えた場合を不良と評価した。
　光沢度は、日本電色工業株式会社製光沢度計（型番：ＰＧ－１Ｍ）を用いて、ＪＩＳ　Ｚ　８７４１に準拠し、入射角６０度にて測定した。
　電気的信頼性を評価するため、大気中で１６０℃×５００時間加熱し、接触抵抗を測定した。測定方法はＪＩＳ－Ｃ－５４０２に準拠し、４端子接触抵抗試験機（山崎精機研究所製：ＣＲＳ－１１３－ＡＵ）により、摺動式（１ｍｍ）で０から５０ｇまでの荷重変化－接触抵抗を測定し、荷重を５０ｇとしたときの接触抵抗値で評価した。
　これらの測定結果、評価結果を表３に示す。
Figure JPOXMLDOC01-appb-T000003
　この表３から明らかなように、実施例はいずれも動摩擦係数が０．３以下と小さく、はんだ濡れ性が良好で、光沢度も高く外観が良好で接触抵抗も１０ｍΩ以下を示した。特に、ニッケルめっきにより厚み０．１μｍ以上のニッケルめっき層を形成した実施例１から４及び７，８は、全て４ｍΩ以下の低い接触抵抗を示した。
　これに対し比較例１，３，５，７，９，１２は、Ｃｕ－Ｓｎ合金層の露出部の面積率が１％未満のため動摩擦係数が０．３以上ある。比較例２、６は露出部の面積率が４０％を超えるためはんだ濡れ性、光沢度が悪くい。比較例４はＣｕ６Ｓｎ５合金中にＮｉを含有しておらず、Ｃｕ３Ｓｎ合金の存在が確認できるため、露出部の円相当直径の平均値が１．５μｍを超えてしまい、このため、動摩擦係数が０．３を超えている。
　比較例８、１１は、リフロー条件を逸脱しており、Ｒｐｋが０．０３μｍを超えアブレシブ摩耗を生じるため、動摩擦係数が０．３を超えている。比較例１０は、リフロー条件を逸脱しているためＮｉ３Ｓｎ４合金が形成された結果、Ｎｉ層のバリア性が低下し接触抵抗が９ｍΩを超えている。
　図１は実施例３と比較例４，１０の２５度から４６度までのＸ線回折パターンである。これらパターンを比較してわかるように、実施例３は、基材のＣｕ、下地めっき層のＮｉ及びＣｕ６Ｓｎ５合金のピークしか検出されないが、比較例１０は３１．７度付近にＮｉ３Ｓｎ４合金のピークが検出され、比較例４は、３７．８度付近にＣｕ３Ｓｎ合金のピークが検出された。また、実施例３と比較例１０は、Ｃｕ６Ｓｎ５合金のピークが高角度側にシフトしていることから、Ｃｕ６Ｓｎ５合金中のＣｕの一部がＮｉに置換されていることがわかる。
　図２及び図３は実施例３の試料の断面ＳＴＥＭ像とＥＤＳ分析結果であり、（ａ）がＮｉ層、（ｂ）が（Ｃｕ，Ｎｉ）６Ｓｎ５合金からなるＣｕ－Ｓｎ合金層、（ｃ）が錫層である。
　図４、５は比較例４の断面ＳＴＥＭ像とＥＤＳ分析結果であり、（ａ）がＮｉ層、（ｂ）がＣｕ３Ｓｎ合金層、（ｃ）が（Ｃｕ，Ｎｉ）６Ｓｎ５合金層、（ｄ）が錫層である。
　図６、７は比較例１０の断面ＳＴＥＭ像とＥＤＳ線分析結果であり、（ａ）がＮｉ層、（ｂ）が（Ｎｉ，Ｃｕ）３Ｓｎ４合金層、（ｃ）が（Ｃｕ，Ｎｉ）６Ｓｎ５合金層、（ｄ）が錫層である。
　これらの写真およびグラフを比較してわかるように、実施例のものはＮｉ層と錫層の間に、Ｎｉを含有したＣｕ６Ｓｎ５合金（（Ｃｕ，Ｎｉ）６Ｓｎ５合金）のみからなるＣｕ－Ｓｎ合金層しか形成されていない。一方、比較例４は、Ｃｕ６Ｓｎ５合金層とＮｉ層との界面にＣｕ３Ｓｎ合金層が形成され、Ｃｕ６Ｓｎ５合金中にＮｉを含有しておらず、Ｃｕ－Ｓｎ合金層の凹凸も粗く緩やかなことがわかる。また、比較例１０は、Ｎｉを含有したＣｕ６Ｓｎ５合金層とＮｉ層との界面に、Ｃｕを含むＮｉ３Ｓｎ４合金層が形成されていることがわかる。
　動摩擦係数が小さいので、低接触抵抗、良好なはんだ濡れ性と低挿抜性を両立させることができ、また低荷重でも効果があり小型端子に最適である錫めっき銅合金端子材を提供できる。特に、自動車および電子部品等に使用される端子において、接合時の低い挿入力、安定した接触抵抗、良好なはんだ濡れ性を必要とする部位において優位性を持つ。
　１１　台
　１２　オス端子試験片
　１３　メス端子試験片
　１４　錘
　１５　ロードセル

 

Claims (3)

  1. 　銅又は銅合金からなる基材上の表面にＳｎ系表面層が形成されており、該Ｓｎ系表面層と前記基材との間に、前記Ｓｎ系表面層から順にＣｕ－Ｓｎ合金層／Ｎｉ層又はＮｉ合金層が形成された錫めっき銅合金端子材であって、
    　前記Ｃｕ－Ｓｎ合金層は、Ｃｕ６Ｓｎ５合金のＣｕの一部がＮｉに置換した金属間化合物合金のみからなる層であり、
    　前記Ｃｕ－Ｓｎ合金層の一部が前記Ｓｎ系表面層の表面に露出して複数の露出部を形成しており、
    　前記Ｓｎ系表面層の平均厚みが０．２μｍ以上０．６μｍ以下であり、
    　前記錫めっき銅合金端子材の表層の表面積に対する前記Ｃｕ－Ｓｎ合金層の前記露出部の面積率が１％以上４０％以下であり、
    　前記Ｃｕ－Ｓｎ合金層の前記各露出部の円相当直径の平均値が０．１μｍ以上１．５μｍ以下であり、
    　前記錫めっき銅合金端子材の表面の突出山部高さＲｐｋが０．００５μｍ以上０．０３μｍ以下であり、動摩擦係数が０．３以下である
    ことを特徴とする錫めっき銅合金端子材。
  2. 　前記Ｃｕ－Ｓｎ合金層中のＮｉ含有率が、１ａｔ％以上２５ａｔ％以下であることを特徴とする請求項１記載の錫めっき銅合金端子材。
  3. 　銅合金からなる基材上に、ニッケルめっきまたはニッケル合金めっき、銅めっき及び錫めっきをこの順に施した後に、リフロー処理することにより、前記基材の上にＮｉ層またはＮｉ合金層／Ｃｕ－Ｓｎ合金層／Ｓｎ系表面層を形成した錫めっき銅合金端子材を製造する方法であって、
    　前記ニッケルめっき又はニッケル合金めっきによる第１めっき層厚みを０．０５μｍ以上１．０μｍとし、
    　前記銅めっきによる第２めっき層厚みを０．０５μｍ以上０．２０μｍ以下とし、
    　前記錫めっきによる第３めっき層厚みを０．５μｍ以上１．０μｍ以下とし、
    　前記リフロー処理は、各めっき層を２０～７５℃／秒の昇温速度で２４０～３００℃のピーク温度まで加熱する加熱工程と、前記ピーク温度に達した後、３０℃／秒以下の冷却速度で２～１５秒間冷却する一次冷却工程と、一次冷却後に１００～３００℃／秒の冷却速度で冷却する二次冷却工程とを有する
    ことを特徴とする錫めっき銅合金端子材の製造方法。

     
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