JP7809566B2 - Sn-plated brass sheet material and its manufacturing method - Google Patents
Sn-plated brass sheet material and its manufacturing methodInfo
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Description
本発明は、黄銅板の表面がＳｎめっき層で被覆されたＳｎめっき黄銅板材、およびその製造方法に関するものである。 The present invention relates to a Sn-plated brass sheet material in which the surface of the brass sheet is coated with a Sn-plated layer, and a method for manufacturing the same.
電子部品の導電部材やコネクタなどの通電部品にはＳｎめっきを施した銅系材料が多用されている。銅系材料にＳｎめっきを施す場合、めっき密着性を確保する等の理由により、予め下地めっきとしてＣｕめっき層を形成させておくことが多い。めっき表面の光沢性を重視する用途などではＳｎめっき後にリフロー処理を行う場合がある。一方、リフロー処理は行わず、Ｓｎめっきが形成された銅系材料で作製されたコネクタなどの電子部品を樹脂に埋め込む際に、Ｓｎが溶融しない温度域で熱処理（インサート成形）するだけで十分な用途も多い。 Sn-plated copper-based materials are often used for current-carrying components such as conductive members and connectors in electronic components. When Sn-plating copper-based materials, a Cu plating layer is often formed first as an undercoat to ensure plating adhesion, etc. In applications where the gloss of the plated surface is important, a reflow process may be performed after Sn plating. However, there are also many applications where reflow processing is not performed, and when electronic components such as connectors made from Sn-plated copper-based materials are embedded in resin, heat treatment (insert molding) in a temperature range where Sn does not melt is sufficient.
特許文献１には、黄銅材（基材Ｎｏ.４）の表面に厚さ０.２μｍの下地Ｃｕめっきと、厚さ１μｍのＳｎめっきを施し、その後５００℃でリフロー処理を行った例（表２のＮｏ.３１）が示されている。 Patent Document 1 shows an example (No. 31 in Table 2) in which a 0.2 μm thick Cu undercoat and a 1 μm thick Sn plating are applied to the surface of a brass material (substrate No. 4), followed by a reflow treatment at 500°C.
特許文献２には、黄銅材（基材ｍ）の表面に厚さ０.４５μｍあるいは０.４１μｍの下地Ｃｕめっきと、厚さ０.８５μｍあるいは０.９３μｍのＳｎめっきを施し、さらにその上にＮｉやＡｇの金属膜を形成した例（表３のＮｏ.２７、２８）が示されている。 Patent Document 2 shows an example (Nos. 27 and 28 in Table 3) in which a 0.45 μm or 0.41 μm thick Cu underlayer is applied to the surface of a brass material (substrate m), followed by a 0.85 μm or 0.93 μm thick Sn plating, on which a Ni or Ag metal film is then formed.
特許文献３には、黄銅材の表面に下地のＮｉめっき層とＣｕめっき層を介して、Ｓｎめっきを施すことが記載されている。また、１５０～１７０℃で熱処理してＣｕめっき層とＳｎめっき層の界面にＣｕ６Ｓｎ５を生成させ、端子の挿入力を低減することが記載されている。Ｎｉめっき層が無い場合、Ｃｕめっき層はＳｎとの反応速度が速く、亜鉛の拡散防止層としての役割を果たせなくなると教示されている（段落００３５）。 Patent Document 3 describes applying Sn plating to the surface of a brass material via an underlying Ni plating layer and Cu plating layer. It also describes heat treatment at 150 to 170°C to generate Cu6Sn5 at the interface between the Cu plating layer and the Sn plating layer, thereby reducing the insertion force of the terminal. It teaches that without the Ni plating layer, the Cu plating layer reacts quickly with Sn, and therefore cannot function as a zinc diffusion barrier (paragraph 0035).
特許文献４には、筒型ヒューズに用いる黄銅製のキャップの応力腐食割れを防止するために、黄銅材の表面に厚さ５μｍ以上の下地Ｃｕめっきを施し、その上にＳｎめっきを施して、それら２層の全厚さを７～２０μｍとすることが記載されている。 Patent Document 4 describes a method for preventing stress corrosion cracking in brass caps used in cylindrical fuses by applying a Cu undercoat of 5 μm or more to the surface of the brass material, followed by an Sn plating on top of that, with the total thickness of the two layers being 7 to 20 μm.
黄銅材の表面に下地のＣｕめっき層を介してＳｎめっき層が形成されている従来のＳｎめっき黄銅材では、そのＳｎめっき黄銅材を成形したコネクタなどの電子部品を樹脂に埋め込む際に、Ｓｎめっき層が溶融しない温度域での熱処理（インサート成形、例えば１５０℃前後）を施すと、その熱処理後にＳｎめっき層の表面が変色するという事象が見られることがある。また、必ずしも熱処理を施さなくても、部品加工に供するまでの保管期間や部品として使用されている期間に上記と同様の変色が生じることもある。変色が生じたＳｎめっき層では表面抵抗が大きくなる場合もある。発明者の調査によれば、この種の変色が生じる主たる原因は、基材中のＺｎが表層まで拡散して、めっき金属で被覆された材料の表面にＺｎを含む酸化物が形成されることにある。したがって、基材として黄銅を用いた場合に特有の上記問題（変色や表面抵抗の増大）を解消するには、基材中のＺｎが表層まで拡散することを防止する対策が必要となる。 In conventional Sn-plated brass materials, in which a Sn-plated layer is formed on the surface of a brass material via an underlying Cu-plated layer, discoloration of the surface of the Sn-plated layer can occur when the Sn-plated brass material is molded into an electronic component, such as a connector, and then embedded in resin. If the Sn-plated brass material is subjected to heat treatment at a temperature range that does not melt the Sn-plated layer (insert molding, for example, around 150°C), the Sn-plated layer may discolor after the heat treatment. Furthermore, even without heat treatment, similar discoloration can occur during storage before component processing or during use as a component. A discolored Sn-plated layer can also increase surface resistance. According to the inventor's research, the primary cause of this type of discoloration is the diffusion of Zn from the substrate to the surface, resulting in the formation of a Zn-containing oxide on the surface of the material coated with the plated metal. Therefore, to resolve the above-mentioned problems (discoloration and increased surface resistance) specific to using brass as a substrate, measures are needed to prevent Zn from diffusing to the surface.
特許文献１に具体的に示されているＳｎめっき黄銅材の例（上述のＮｏ.３１）ではリフロー処理が行われている。しかし発明者の検討によれば、そのＳｎめっき黄銅材（リフロー処理前のもの）にＳｎが溶融しない温度（例えば１５０℃前後）の熱処理を施した場合、上記の変色の問題は解消できない。 In the example of Sn-plated brass material specifically shown in Patent Document 1 (No. 31 above), a reflow process is performed. However, according to the inventors' research, if this Sn-plated brass material (before the reflow process) is subjected to heat treatment at a temperature at which Sn does not melt (for example, around 150°C), the discoloration problem described above cannot be resolved.
特許文献２に具体的に示されているＳｎめっき黄銅材の例（上述のＮｏ.２７、２８）は表層にＮｉやＡｇの金属膜が形成されている。しかし発明者の検討によれば、そのＳｎめっき黄銅材にＮｉやＡｇの金属膜を形成することなく、Ｓｎが溶融しない温度（例えば１５０℃前後）の熱処理を施した場合、上記の変色の問題はやはり解消できない。 The examples of Sn-plated brass materials specifically shown in Patent Document 2 (Nos. 27 and 28 mentioned above) have a metal film of Ni or Ag formed on the surface. However, according to the inventors' research, if the Sn-plated brass material is subjected to heat treatment at a temperature at which Sn does not melt (for example, around 150°C) without forming a metal film of Ni or Ag, the discoloration problem described above cannot be resolved.
特許文献３には上述のように、下地のＮｉめっき層とＣｕめっき層を介してＳｎめっきを施したＳｎめっき黄銅材において、Ｎｉめっき層が無い場合、Ｃｕめっき層は亜鉛の拡散防止層としての役割を果たせなくなると教示されている。したがって、特許文献３に開示される技術において、Ｎｉめっき層とＣｕめっき層からなる下地の２層構造を、Ｃｕめっき層からなる１層構造に変えても、上記の変色の問題の解消は期待できない。一方、下地をＮｉめっき層のみの１層構造とした場合にはＺｎの拡散を抑制する効果はある程度得られると考えられる。しかし、Ｎｉめっき層は材料を硬質化させ曲げ加工性等を低下させる傾向が大きいので、硬質なＳｎめっき黄銅材を望まない用途を含めた汎用性の高いＳｎめっき黄銅材を提供するためには、下地にＮｉめっき層を適用しない手法により上記変色の問題の解決を図ることが望まれる。 As mentioned above, Patent Document 3 teaches that in a Sn-plated brass material in which Sn plating is applied via an underlying Ni and Cu plating layer, if the Ni plating layer is absent, the Cu plating layer will no longer function as a zinc diffusion barrier. Therefore, even if the two-layer base structure consisting of Ni and Cu plating layers is changed to a single-layer structure consisting of a Cu plating layer in the technology disclosed in Patent Document 3, the discoloration problem described above cannot be expected to be resolved. On the other hand, if the base structure is a single-layer structure consisting of only a Ni plating layer, it is believed that the effect of suppressing Zn diffusion can be achieved to some extent. However, since the Ni plating layer tends to harden the material and reduce bending workability, etc., in order to provide a highly versatile Sn-plated brass material, including for applications where a hard Sn-plated brass material is not desired, it is desirable to solve the discoloration problem described above by using a method that does not apply a Ni plating layer to the base.
特許文献４に開示の技術では、筒型ヒューズの黄銅キャップにおける耐応力腐食割れ性を改善する目的で５μｍ以上といった厚い下地Ｃｕめっき層を形成させている。しかし、汎用性の高いＳｎめっき黄銅板材において、そのような厚い下地めっき層を形成させる手法はコスト上昇を招き、採用し難い。 The technology disclosed in Patent Document 4 involves forming a thick Cu undercoat layer of 5 μm or more in order to improve the stress corrosion cracking resistance of the brass cap of a cylindrical fuse. However, with the highly versatile Sn-plated brass sheet material, forming such a thick undercoat layer increases costs and is difficult to adopt.
発明者の研究によれば、基材である黄銅と直接接合しているＣｕ層は、黄銅からのＺｎの拡散を阻止するバリア層として機能することが確かめられた。本発明は、Ｓｎの溶融が生じない温度での熱処理に供したときに、黄銅と直接接しているＣｕ層が存在する構造の表層部が低コストで容易に構築されるＳｎめっき黄銅板材を提供することを目的とする。 The inventor's research has confirmed that the Cu layer directly bonded to the brass substrate functions as a barrier layer that prevents Zn from diffusing from the brass. The objective of the present invention is to provide a Sn-plated brass sheet material that, when subjected to heat treatment at a temperature that does not cause Sn to melt, can easily and inexpensively form a surface layer structure in which a Cu layer is in direct contact with the brass.
上記目的は、黄銅板からなる基材の表面上に、厚さ０.２８～０.８０μｍのＣｕめっき層を有し、前記Ｃｕめっき層の上に厚さ２.８～５.０μｍのＳｎめっき層を有するＳｎめっき黄銅板材によって達成される。 The above objective is achieved by a Sn-plated brass sheet material having a 0.28-0.80 μm thick Cu-plated layer on the surface of a brass plate substrate, and a 2.8-5.0 μm thick Sn-plated layer on top of the Cu-plated layer.
より具体的には、上記のＳｎめっき黄銅板材は、大気雰囲気中、１５０℃で９０分保持する熱処理を施したとき、その熱処理後に、Ｃｕめっき層とＳｎめっき層が形成されていた前記基材上の領域の全面にＣｕめっき層に由来するＣｕ層が残存する性質を有するものである。 More specifically, when the above-mentioned Sn-plated brass sheet material is subjected to heat treatment in an air atmosphere at 150°C for 90 minutes, a Cu layer derived from the Cu plating layer remains over the entire surface of the base material area where the Cu plating layer and Sn plating layer had been formed.
また本発明では上記Ｓｎめっき黄銅板材の製造方法として、 黄銅板からなる基材の表面上に、平均膜厚０.２８～０.８０μｍのＣｕめっき層が形成される条件で電気Ｃｕめっきを施し、前記電気Ｃｕめっきにより形成されたＣｕめっき層の上に平均膜厚２.８～５.０μｍのＳｎめっき層が形成される条件で電気Ｓｎめっきを施すＳｎめっき黄銅板材の製造方法が提供される。 The present invention also provides a method for manufacturing the above-mentioned Sn-plated brass sheet material, which involves electroplating the surface of a base material made of brass plate with Cu under conditions that form a Cu plating layer with an average thickness of 0.28 to 0.80 μm, and then electroplating the Sn under conditions that form a Sn plating layer with an average thickness of 2.8 to 5.0 μm on the Cu plating layer formed by the electroplating with Cu.
より具体的には、上記条件で電気Ｃｕめっきおよび電気Ｓｎめっきを施すことによって、大気雰囲気中、１５０℃で９０分保持する熱処理を施したとき、その熱処理後に、Ｃｕめっき層とＳｎめっき層が形成されていた前記基材上の領域の全面にＣｕめっき層に由来するＣｕ層が残存する性能を、前記Ｃｕめっき層と前記Ｓｎめっき層からなる金属被覆層に付与する、Ｓｎめっき黄銅板材の製造方法が提供される。 More specifically, by performing Cu electroplating and Sn electroplating under the above conditions, a method for producing a Sn-plated brass sheet material is provided in which, when heat-treated in an air atmosphere at 150°C for 90 minutes, a Cu layer derived from the Cu plating layer remains over the entire surface of the area on the base material where the Cu plating layer and Sn plating layer had been formed, imparting to the metal coating layer consisting of the Cu plating layer and the Sn plating layer the following performance.
本明細書において、「板材」とは金属の展性を利用して成形されたシート状の金属材料を意味する。薄いシート状の金属材料は「箔」と呼ばれることもあるが、そのような「箔」もここでいう「板材」に含まれる。コイル状に巻き取られた長尺のシート状金属材料も「板材」に含まれる。 In this specification, "plate material" refers to a sheet-like metal material formed by utilizing the malleability of metal. Thin sheet-like metal material is sometimes called "foil," and such "foil" is also included in the "plate material" referred to here. Long sheet-like metal material wound into a coil is also included in the "plate material."
本発明のＳｎめっき黄銅板材は、Ｓｎの溶融が生じない温度域（例えば１５０℃±３０℃）に加熱する熱処理を受けた後に、基材である黄銅と直接接しているＣｕ層が存在する表層構造が構築される。このような熱処理を受けたＳｎめっき黄銅部品は、前記のＣｕ層がバリア層として機能し、基材の黄銅から材料表面へのＺｎの拡散が顕著に抑制され、Ｓｎめっき黄銅部品のインサート処理で問題となりやすかった表面変色が防止できる。また、本発明のＳｎめっき黄銅板材は、熱処理を施さずに長期間保管した場合の耐変色性にも優れる。本発明のＳｎめっき黄銅は従来品と大差ない低コストで製造できる。 After the Sn-plated brass sheet material of the present invention is subjected to heat treatment in a temperature range where Sn does not melt (e.g., 150°C ± 30°C), a surface layer structure is developed in which a Cu layer is in direct contact with the brass substrate. In Sn-plated brass parts that have undergone such heat treatment, the Cu layer functions as a barrier layer, significantly suppressing the diffusion of Zn from the brass substrate to the material surface, preventing surface discoloration, which is a common problem with insert processing of Sn-plated brass parts. Furthermore, the Sn-plated brass sheet material of the present invention also exhibits excellent discoloration resistance when stored for long periods without heat treatment. The Sn-plated brass of the present invention can be manufactured at a cost not significantly different from that of conventional products.
黄銅（Ｃｕ－Ｚｎ系銅合金）は電子機器部品や通電部品などに広く使用され、汎用性の高い材料である。本発明は黄銅の板材を基材とするＳｎめっき黄銅板材を対象とする。具体的には、例えば、Ｚｎ：２８.５～４０.８質量％、ＣｕとＺｎの合計：９９.０質量％以上である組成範囲のＣｕ－Ｚｎ系銅合金が対象となる。これは、ＪＩＳ Ｈ３１００：２０００に「黄銅」として規定される合金記号Ｃ２６００、Ｃ２６８０、Ｃ２７２０、Ｃ２８０１を含むものである。また、より代表的な組成範囲として、Ｚｎ：２８.５～３１.５質量％、ＣｕとＺｎの合計：９９.０質量％以上であるＣｕ－Ｚｎ系銅合金を挙げることができる。これは、上記の合金記号Ｃ２６００に相当するものである。 Brass (Cu-Zn-based copper alloy) is a highly versatile material widely used in electronic components and electrical components. The present invention focuses on Sn-plated brass sheet materials using brass sheet materials as the base material. Specifically, the subject is a Cu-Zn-based copper alloy with a composition range of Zn: 28.5 to 40.8% by mass, and a total of Cu and Zn: 99.0% by mass or more. This includes alloys designated C2600, C2680, C2720, and C2801, which are specified as "brass" in JIS H3100:2000. A more representative composition range is a Cu-Zn-based copper alloy with Zn: 28.5 to 31.5% by mass, and a total of Cu and Zn: 99.0% by mass or more. This corresponds to the alloy designated C2600.
図１に、本発明のＳｎめっき黄銅板材について、熱処理前および熱処理後の表層部の断面構造を模式的に示す。図１上段の「熱処理前」が本発明に係るＳｎめっき黄銅板材である。黄銅板からなる基材（黄銅基材）の表面上に、下地めっきであるＣｕめっき層を有し、そのＣｕめっき層の上にＳｎめっき層を有する。Ｃｕめっき層、およびＳｎめっき層は、それぞれ公知の電気めっき法によって形成することができる。ここで、下地のＣｕめっき層の厚さは０.２８～０.８０μｍ、Ｓｎめっき層の厚さは２.８～５.０μｍに調整されていることが重要である。これらのめっき層厚さに調整するには、電気めっき条件および金属Ｃｕあるいは金属Ｓｎの密度（比重）に基づいて算出されるめっき金属の平均付着厚さ（平均膜厚）が上記の数値範囲となるように、めっき条件をコントロールすればよい。 Figure 1 shows a schematic cross-sectional structure of the surface layer of the Sn-plated brass sheet material of the present invention before and after heat treatment. The "Before Heat Treatment" section in the upper part of Figure 1 represents the Sn-plated brass sheet material of the present invention. A Cu plating layer is applied as an undercoat on the surface of a brass substrate (brass substrate), and a Sn plating layer is applied on top of the Cu plating layer. The Cu plating layer and Sn plating layer can be formed by known electroplating methods. It is important to adjust the thickness of the Cu plating layer to 0.28 to 0.80 μm and the Sn plating layer to 2.8 to 5.0 μm. These plating layer thicknesses can be achieved by controlling the plating conditions so that the average deposition thickness (average film thickness) of the plated metal, calculated based on the electroplating conditions and the density (specific gravity) of the metallic Cu or metallic Sn, falls within the above numerical range.
図１上段の本発明に係るＳｎめっき黄銅板材に、Ｓｎが溶融しない温度域（例えば１５０℃±３０℃）での熱処理を施すと、Ｃｕめっき層のＣｕ原子とＳｎめっき層のＳｎ原子とが相互拡散することにより、両層の界面にＣｕ－Ｓｎ合金層が形成される。コネクタ等の部品を樹脂に埋め込む際に行われるインサート成形などによって、上記温度域付近の熱処理が付与された場合、図１下段の「熱処理後」の図に示すようにＣｕめっき層に由来するＣｕ層が残存していれば、そのＣｕ層がＺｎの拡散を阻害するバリア層として機能し、黄銅基材中のＺｎがＳｎ層の中に侵入することが顕著に抑制されることがわかった。種々検討の結果、大気雰囲気中、１５０℃で９０分保持する条件での熱処理実験に供したときに、黄銅基材上のＣｕめっき層とＳｎめっき層が形成されていた領域の全面にＣｕめっき層に由来するＣｕ層が残存する性質を呈するＳｎめっき黄銅板材であれば、上記のインサート成形など、Ｓｎが溶融しない温度域に加熱して電子部品を製造する際に工業的に行われている通常の熱処理過程で、Ｃｕ層を残存させることが可能である。また、前記の性質を呈するＳｎめっき黄銅板材であれば、熱処理を施さずに長期間保管した場合や、熱処理を施さない工程で作製した部品を長期間使用した場合の耐変色性にも優れる。
なお、図１において、Ｃｕめっき層、Ｃｕ層の厚さは誇張して描いてある。
When the Sn-plated brass sheet material according to the present invention shown in the upper part of Figure 1 is subjected to heat treatment in a temperature range where Sn does not melt (for example, 150°C ± 30°C), the Cu atoms in the Cu plating layer and the Sn atoms in the Sn plating layer interdiffuse to form a Cu-Sn alloy layer at the interface between the two layers. When heat treatment is applied near the above temperature range, for example, by insert molding, which is performed when embedding parts such as connectors in resin, if a Cu layer derived from the Cu plating layer remains, as shown in the "After Heat Treatment" diagram in the lower part of Figure 1, it has been found that this Cu layer functions as a barrier layer that inhibits the diffusion of Zn, and the penetration of Zn in the brass base material into the Sn layer is significantly suppressed. As a result of various investigations, it was found that when a Sn-plated brass sheet material is subjected to a heat treatment experiment in which it is held in an air atmosphere at 150°C for 90 minutes, a Cu layer derived from the Cu plating layer remains on the entire surface of the area where the Cu plating layer and the Sn plating layer were formed on the brass substrate, so that the Cu layer can be left in the usual heat treatment process that is industrially performed when manufacturing electronic components by heating to a temperature range where Sn does not melt, such as the above-mentioned insert molding. Furthermore, a Sn-plated brass sheet material that exhibits the above-mentioned properties also has excellent discoloration resistance when stored for a long period of time without heat treatment, or when a component manufactured in a process without heat treatment is used for a long period of time.
In FIG. 1, the thickness of the Cu plating layer and the Cu layer is exaggerated.
Ｃｕ層の残存量は、素地の黄銅とＣｕ－Ｓｎ合金層とが直接接触している部分が存在しない限り、非常に薄くても有効である。例えばＳｎ層やＣｕ－Ｓｎ合金層は溶解するがＣｕ層は溶解しないフッ素系の酸性薬液（Ｓｎ剥離剤）でＳｎ層およびＣｕ－Ｓｎ層を剥離させた試料を作製したとき、黄銅基材の露出が観察されなければ、その試料は表面にＣｕ層が残存しているとみなすことができる。黄銅は表面の色調が銅と明らかに異なるので、Ｓｎ層およびＣｕ－Ｓｎ層を剥離させた試料においてＣｕ層の存在を目視で確認することができる。 A very thin remaining Cu layer is effective, as long as there are no areas where the base brass and the Cu-Sn alloy layer are in direct contact. For example, when a sample is prepared in which the Sn and Cu-Sn layers have been stripped using a fluorine-based acidic chemical (Sn stripper), which dissolves Sn and Cu-Sn alloy layers but not Cu layers, if no exposed brass substrate is observed, the sample can be considered to have a Cu layer remaining on its surface. Because the surface color of brass is clearly different from that of copper, the presence of the Cu layer can be visually confirmed in samples from which the Sn and Cu-Sn layers have been stripped.
下地めっきであるＣｕめっき層の厚さが０.２８μｍを下回ると、大気雰囲気中、１５０℃で９０分保持する条件での熱処理実験に供したときに、Ｃｕを安定して残存させることが難しくなる。Ｃｕめっき層の厚さが０.８０μｍを超えるような厚い下地めっきを施すと、熱処理後にＣｕ層を残存させる機能が過剰となり、汎用性の高いＳｎめっき黄銅板材を製造する上ではコスト面で好ましくない。したがって、本発明では下地のＣｕめっき層の厚さを０.２８～０.８０μｍに規定する。０.３０～０.８０μｍとすることがより好ましく、０.４０～０.８０μｍとすることが更に好ましい。 If the thickness of the Cu plating layer (undercoat) is less than 0.28 μm, it becomes difficult to retain the Cu stably when subjected to heat treatment experiments in air at 150°C for 90 minutes. Applying a thick undercoat with a Cu plating layer thickness exceeding 0.80 μm results in excessive functionality of the Cu layer remaining after heat treatment, which is undesirable from a cost perspective when producing versatile Sn-plated brass sheet material. Therefore, in this invention, the thickness of the Cu plating layer undercoat is specified to be 0.28 to 0.80 μm. 0.30 to 0.80 μm is more preferable, and 0.40 to 0.80 μm is even more preferable.
Ｓｎめっき層の厚さが２.８μｍを下回ると、Ｃｕ－Ｓｎ合金層が形成されたときに上層として残存するＳｎ層が薄くなることに伴い、はんだ濡れ性の低下やウィスカの発生が顕著となる。一方、Ｓｎめっき層の厚さが５.０μｍを超えるとコストが高くなる。したがって、本発明では下地のＳｎめっき層の厚さを２.８～５.０μｍに規定する。２.８～４.０μｍとすることがより好ましい。 If the thickness of the Sn plating layer is less than 2.8 μm, the Sn layer remaining as the upper layer when the Cu-Sn alloy layer is formed will be thinner, resulting in a significant decrease in solder wettability and whisker formation. On the other hand, if the thickness of the Sn plating layer exceeds 5.0 μm, costs will increase. Therefore, in this invention, the thickness of the base Sn plating layer is specified to be 2.8 to 5.0 μm. A thickness of 2.8 to 4.0 μm is more preferable.
合金記号Ｃ２６００に相当する市販の黄銅板から長さ７５ｍｍ、幅２０ｍｍ、厚さ０.３ｍｍの短冊状の板材を切り出した。この板材を基材に用いて、従来公知の電気Ｃｕめっき法（シアン浴を使用）により種々の厚さの下地Ｃｕめっき層を形成し、その上に従来公知の電気Ｓｎめっき法（有機酸浴を使用）により厚さ３μｍのＳｎめっき層を形成し、Ｓｎめっき黄銅板材を得た。めっき浴の液温、電流密度、めっき時間、並びに使用しためっき装置およびめっき浴において前記液温、電流密度、めっき時間の条件で形成されるめっき層厚さ（平均膜厚）を表１に示してある。 Strip-shaped plate materials measuring 75 mm in length, 20 mm in width, and 0.3 mm in thickness were cut from commercially available brass plate corresponding to alloy designation C2600. Using these plates as substrates, Cu undercoat layers of various thicknesses were formed using a conventional Cu electroplating method (using a cyanide bath), and then a 3 μm thick Sn electroplating layer was formed on top of this using a conventional Sn electroplating method (using an organic acid bath), yielding Sn-plated brass plate materials. The plating bath liquid temperature, current density, plating time, and plating layer thickness (average film thickness) formed under the above conditions for the plating bath and plating equipment used are shown in Table 1.
各Ｓｎめっき黄銅板材に、大気雰囲気中、１５０℃で９０分保持する熱処理を施した。この熱処理を施した試料の表面を、Ｓｎ層、Ｃｕ－Ｓｎ合金層などのＳｎ含有層は溶解するがＣｕ層は溶解しないフッ素系の酸性薬液（メルテックス株式会社製、ＴＬ－１０５）で処理することにより、表層部のＳｎ含有層を剥離させた。以下、この処理を「剥離処理」と呼ぶ。剥離処理後の試験片の表面を目視観察することによりＣｕ層の残存状態を調べ、以下の基準で熱処理後のＣｕ層残存性を評価した。
○：Ｃｕ層が全面に残存している。
△：Ｃｕ層の残存は認められるが、一部に基材の黄銅の露出が見られる。
×：Ｃｕ層の残存はほとんど認められず、ほぼ全面に基材の黄銅が露出している。
各Ｓｎめっき黄銅板材について試験数ｎ＝５で試験を行い、５本の試験片のなかで最も成績の悪かった試験片の評価結果を当該Ｓｎめっき黄銅板材の成績として採用した。○評価のものが合格と判定される。結果を表１に示す。
Each Sn-plated brass sheet material was subjected to a heat treatment in an air atmosphere at 150°C for 90 minutes. The surface of the heat-treated sample was treated with a fluorine-based acidic chemical solution (TL-105, manufactured by Meltex Inc.) that dissolves Sn-containing layers such as Sn layers and Cu-Sn alloy layers but not Cu layers, thereby peeling off the Sn-containing layer from the surface layer. Hereinafter, this treatment will be referred to as the "peeling treatment." The surface of the test piece after the peeling treatment was visually observed to examine the remaining state of the Cu layer, and the remaining Cu layer after the heat treatment was evaluated according to the following criteria.
◯: The Cu layer remains on the entire surface.
Δ: The Cu layer remains, but the brass of the substrate is partially exposed.
x: Almost no remaining Cu layer is observed, and the brass substrate is exposed over almost the entire surface.
Each Sn-plated brass sheet material was tested five times, and the evaluation result of the test piece with the worst performance among the five test pieces was adopted as the performance of that Sn-plated brass sheet material. Test pieces with an evaluation of ○ were judged to pass. The results are shown in Table 1.
下地Ｃｕめっき層を本発明の規定（０.２８～０.８０μｍ）を満たす厚さとなるように形成させた実施例のものはＣｕ層の残存が全面に認められ、Ｃｕ層残存性は○評価であった。これらはＣｕ層がＺｎの拡散を阻害するバリア層として機能し、高い耐変色性能を発揮する。 In the examples where the underlying Cu plating layer was formed to a thickness that met the specifications of the present invention (0.28 to 0.80 μm), the Cu layer remained over the entire surface, and the Cu layer remnant property was rated as ○. The Cu layer functions as a barrier layer that inhibits the diffusion of Zn, demonstrating high discoloration resistance.
図２に、各例の剥離処理後の試験片の表面外観写真を例示する。これはカラー写真をモノクロ化したものである。×評価の試験片表面はほぼ全面が黄銅の色調を呈し、○評価の試験片表面は全面が銅の色調を呈する。黄銅と銅の色調差は、目視により判別できる。 Figure 2 shows an example of a photograph of the surface appearance of the test specimens after the peeling treatment for each example. This is a monochrome version of a color photograph. The surface of test specimens rated × exhibits a brass color tone over almost the entire surface, while the surface of test specimens rated ○ exhibits a copper color tone over the entire surface. The difference in color tone between brass and copper can be distinguished visually.
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