JP3910853B2 - Surface-treated steel sheet for electronic parts and manufacturing method thereof - Google Patents
Surface-treated steel sheet for electronic parts and manufacturing method thereof Download PDFInfo
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- JP3910853B2 JP3910853B2 JP2002009688A JP2002009688A JP3910853B2 JP 3910853 B2 JP3910853 B2 JP 3910853B2 JP 2002009688 A JP2002009688 A JP 2002009688A JP 2002009688 A JP2002009688 A JP 2002009688A JP 3910853 B2 JP3910853 B2 JP 3910853B2
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C28/00—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D
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Description
【０００１】
【発明の属する技術分野】
本発明は電子部品用表面処理鋼板およびその製造方法に関する。より詳細には、下地の鋼板の耐錆性およびホィスカー成長の抑制に優れるとともに、高温高湿の雰囲気中で長時間経時しても良好なハンダ濡れ性を示す電子部品用表面処理鋼板およびその製造方法に関する。
【０００２】
【従来の技術】
電子部品においては部品と基板、部品と他の部品、または同一部品同士をハンダ付けして電気的に接合することが行われている。そのため、電子部品の表面にはハンダとの濡れ性および耐ホィスカー性が良好なＳｎ−Ｚｎ合金層を形成させることが一般的に行われている。Ｓｎ−Ｚｎ合金めっきとしては従来、シアン浴、ピロリン酸浴、ホウフッ化物浴、スルホン酸浴、グルコン酸浴、クエン酸浴、酒石酸浴などが用いられているが、均一な組成のめっき皮膜が得られ難いこと、錯化剤を用いるため、排水処理に費用がかかるなどの欠点を有している。
【０００３】
これらの欠点を克服するため、カルボキシル基とスルホン基、またはカルボキシル基と１価の水酸基を含む錯化剤を用いるめっき浴を用いる方法（特開平１０−１６８５９２号公報）、ヒドロキシカルボン酸またはその塩を含むめっき浴を用いる方法（特開平６−２２８７８６号公報）などが試みられている。
【０００４】
【発明が解決しようとする課題】
しかし、これらの方法においては、均一な組成で平滑・緻密なＳｎ−Ｚｎ合金めっき層が得られるものの、めっき後に高温高湿の条件下で長時間放置した場合、ハンダとの濡れ性が劣化してしまう欠点を有している。
【０００５】
本発明はこれらの点に鑑みてなされたものであり、耐錆性および耐ホィスカー性に優れるとともに、高温高湿の条件下で長時間放置しても、良好なハンダとの濡れ性示す電子部品用表面処理鋼板およびその製造方法を提供することを目的とする。
【０００６】
【課題を解決するための手段】
本発明者らは、Ｓｎ２＋イオンとＺｎ２＋イオンを一定範囲の重量比で含有する合金めっき浴を用いて、鋼板に一定範囲の組成のＳｎとＺｎとからなるＳｎ−Ｚｎ合金層を電気めっきし、その後電気めっき鋼板をＳｎ−Ｚｎ合金の融点以上に加熱してＳｎ−Ｚｎ合金を溶融する加熱溶融処理を施した後、または加熱溶融処理を施さずに直接、前記電気めっき鋼板のＳｎ−Ｚｎ合金層上にウレタン樹脂または／およびエポキシ樹脂を塗布して有機樹脂皮膜を形成することにより、耐錆性および耐ホィスカー性に優れるとともに、高温高湿の条件下で長時間放置しても良好なハンダとの濡れ性を示す無塩素系の超非活性フラックスを用いて半田つけする電子部品用表面処理鋼板が得られることを発見し、本発明を完成させた。
【０００７】
本発明の電子部品用表面処理鋼板は、鋼板の少なくとも片面に、Ｓｎ：１〜２０ｇ／ｍ２ とＺｎ：０．０５〜１ｇ／ｍ２ とからなるＳｎ−Ｚｎ合金層と、Ｓｎ−Ｚｎ合金層上に０．１〜２μｍの厚さのウレタン樹脂または／およびエポキシ樹脂皮膜を形成させてなる無塩素系の超非活性フラックスを用いて半田つけする電子部品用表面処理鋼板であり、合金層中のＳｎ：Ｚｎの重量比が１５：１〜２０：１であることを特徴とする。
【０００８】
また、本発明の電子部品用表面処理鋼板の製造方法は、Ｓｎ２＋イオンとＺｎ２＋イオンを、重量比が１：５〜１：１０で含有してなる合金めっき浴を用いて、鋼板の少なくとも片面にＳｎ：１〜２０ｇ／ｍ２ とＺｎ：０．０５〜１ｇ／ｍ２ とからなるＳｎ−Ｚｎ合金層を電気めっきし、その後電気めっき鋼板をＳｎ−Ｚｎ合金の融点以上に加熱してＳｎ−Ｚｎ合金を溶融する加熱溶融処理を施した後、または加熱溶融処理を施さずに直接、前記電気めっき鋼板のＳｎ−Ｚｎ合金層上にウレタン樹脂または／およびエポキシ樹脂を乾燥後の皮膜厚さが０．１〜２μｍとなるように塗布し乾燥することを特徴とする無塩素系の超非活性フラックスを用いて半田つけする電子部品用表面処理鋼板の製造方法であり、合金めっき浴のｐＨが３．０以下であること、より好ましくは１．０〜２．０であることを特徴とする。
【０００９】
【発明の実施の形態】
以下に本発明を詳細に説明する。
【００１０】
ハンダとの濡れ性および耐ホィスカー性を示すＳｎ−Ｚｎ合金層においては、Ｚｎ含有量が３〜１０％であることが好ましく、更に５〜６％であることがより好ましい。ＳｎとＺｎを電気めっき法を用いてめっき浴から電析させる場合、ＳｎとＺｎの析出電位が大きく離れており、Ｓｎが極めて析出し易くＺｎは析出し難いために、上記のようなＺｎ含有量が少ない範囲で均一な合金組成を有するＳｎ−Ｚｎ合金めっきを得るには、Ｓｎの析出を抑制し、Ｚｎの析出を促進させる必要がある。そのため、本発明のめっき浴においては、Ｓｎ2+イオンとＺｎ2+イオンの重量比を１：５〜１：１０とし、めっき浴中のＺｎ2+イオン量をＳｎ2+イオン量より遥かに多く存在させることを特徴としている。
【００１１】
Ｓｎ2+イオンとＺｎ2+イオンの供給源としては、硫酸塩やハロゲン化物を用いることが好ましい。めっき浴のｐＨは３．０以下であることが好ましく、より好ましくは１．０〜２．０である。ｐＨが３．０を超えると均一な上記範囲のＳｎ−Ｚｎ合金組成が得られ難くなる。安定した合金組成のＳｎ−Ｚｎ合金組成を得るにはｐＨが１．０〜２．０であるめっき浴を用いることがより好ましい。
【００１２】
本発明においては、このように形成されている合金めっき浴を用いて鋼板にＳｎ−Ｚｎ合金をめっきする。めっき量としてはＳｎ：１〜２０ｇ／ｍ2 とＺｎ：０．０５〜１ｇ／ｍ2 の範囲であることが好ましい。Ｓｎ量が１ｇ／ｍ2 未満である場合はハンダ濡れ性が十分ではない、またＺｎ量が０．０５ｇ／ｍ2 未満である場合は耐錆性および耐ホィスカー性が十分ではなく、合金めっきが施されない鋼板の切断端面に錆が発生しやすくなる。Ｓｎ量が２０ｇ／ｍ2 を超えても耐錆性の向上効果は飽和する。また、Ｓｎ量の好適範囲の上限の２０ｇ／ｍ2 に対してＺｎ量が１ｇ／ｍ2 を超えるとハンダ濡れ性が不十分になる。
【００１３】
また、上記のめっき量範囲において、合金めっき中のＳｎ：Ｚｎの重量比は１５：１〜２０：１であることが好ましい。Ｚｎの重量がＳｎの重量の１／１５を超えるとハンダ濡れ性が十分ではなくなる。一方、Ｚｎの重量がＳｎの重量の１／２０未満では十分な耐ホィスカー性が得られない。
【００１４】
以上のようにして鋼板上にＳｎ−Ｚｎ合金めっき層を形成させた後、めっき鋼板をＳｎ−Ｚｎ合金の融点以上の温度に加熱してＳｎ−Ｚｎ合金を溶融させ、Ｓｎ−Ｚｎ合金のＳｎおよびＺｎと鋼板の鉄を拡散させてもよい。この拡散処理により、Ｓｎ−Ｚｎ合金めっき層と鋼板との密着性が向上する。
【００１５】
上記のようにして得られるＳｎ−Ｚｎ合金めっき鋼板は、めっき直後においては良好なハンダ濡れ性を有しているが、倉庫中に保管する場合など、大気中に長時間放置するとＳｎ−Ｚｎ合金表面にＳｎおよびＺｎの酸化物皮膜が成長し、ハンダ濡れ性が阻害されるようになる。この傾向は高温高湿の環境下では特に著しく、高温高湿の倉庫中で長期間にわたって放置しても良好なハンダ濡れ性を示すＳｎ−Ｚｎ合金めっき鋼板が求められていた。本実施の形態によれば、Ｓｎ−Ｚｎ合金めっき鋼板のＳｎ−Ｚｎ合金めっき層上に、有機樹脂皮膜を設けることにより、高温高湿の雰囲気中で長時間放置しても良好なハンダ濡れ性を維持することが可能であることが判明した。
【００１６】
有機樹脂としては特に制限するものではないが、汎用性、塗装し易さ、コスト等の観点からウレタン樹脂、エポキシ樹脂、アクリル樹脂のいずれかを用いることが好ましい。これらの樹脂を１種、または２種以上を有機溶媒に溶解し、乾燥後の皮膜厚さが０．１〜２μｍとなるようにＳｎ−Ｚｎ合金めっき層上に塗布する。皮膜厚さが０．１μｍ未満の場合には、長時間放置した際に良好なハンダ濡れ性を維持することが困難になる。一方、皮膜厚さが２μｍを超えると加熱した溶融ハンダが接触した際に、有機樹脂皮膜がハンダとＳｎ−Ｚｎ合金めっきとの接着界面から十分に除去されず、十分なハンダ接着強度が得られないことがある。塗布方法はロールコート法、スプレー法などの常法を用いることができる。塗布後オーブン中で加熱したり、熱風を吹き付けて乾燥固化させる。
【００１７】
以上のようにして本発明の電子部品用表面処理鋼板を得ることができる。
【００１８】
【実施例】
以下、実施例にて本発明を詳細に説明する。
【００１９】
まず、厚さ：０．５ｍｍの低炭素鋼板に、常法を用いて電解洗浄処理、酸洗処理を施し、その後、表１のめっき番号１〜５に示すＳｎ−Ｚｎ合金めっき浴を用いるとともに電流密度および通電時間を適宜選択して、前記低炭素鋼板上に表２の試料番号１１〜２１に示す組成のＳｎ−Ｚｎ合金めっき層を形成させることにより、Ｓｎ−Ｚｎ合金めっき鋼板を作成した。一部のめっき鋼板（資料番号１７〜２０参照）については、めっきしたＳｎ−Ｚｎ合金の融点以上の温度に抵抗加熱してめっき層を溶融させ、直ちに水中に急冷した。
【００２０】
次いで、これらの試料に、表２に示す有機樹脂を有機溶媒に溶解させてロールコートし、その後熱風乾燥することにより、表２に示す皮膜厚さの有機樹脂皮膜を形成させて、特性評価用試料とした。
【００２１】
【表１】
【表２】
このようにして得られた試料について、下記の特性を評価した。
【００２４】
[耐錆性]
ＪＩＳ Ｚ ２３７１に基づいて塩水噴霧試験を実施し耐錆性を評価した。すなわち、試料を３０ｍｍ角に切り出し、切断面の評価用には切り出したままの状態で２時間塩水噴霧し、めっき面の評価用には切断面をワックスでシールして１２時間塩水噴霧した後、目視観察により下記の５段階の評点で耐錆性を評価した。
【００２５】
評点５：赤錆の発生は認められない。
【００２６】
評点４：実用上問題とならない程度のわずかな赤錆の発生が認められる。
【００２７】
評点３：実用上問題となる程度の赤錆の発生が認められる。
【００２８】
評点２：評価面のかなりの部分で赤錆の発生が認められる。
【００２９】
評点１：評価面の殆ど全面にわたって赤錆の発生が認められる。
【００３０】
評点５および４を本発明の合格とした。
【００３１】
[耐ホィスカー性]
試料を３０ｍｍ角に切り出し、温度：８５℃、湿度：８５％ＲＨの高温高湿の雰囲気中で３０日間暴露した後のホィスカーの発生状況を走査電子顕微鏡を用い、１５００倍の倍率で観察し、下記の評で耐ホィスカー性を評価した。
【００３２】
◎：ホィスカーの発生は認められない。
【００３３】
○：１０μｍ未満の長さのホィスカーがわずかに発生しているのが認められる。
【００３４】
△：１０〜３０μｍ未満の長さのホィスカーが発生しているのが認められる。
【００３５】
×：３０μｍを超える長さのホィスカーが発生しているのが認められる。
【００３６】
評価基準◎および○を本発明の合格とした。
【００３７】
[ハンダ濡れ性]
１０ｍｍ×３０ｍｍの大きさに切り出した直後の試料と、切り出した後に温度：１０５℃、湿度：１００％ＲＨ、圧力：１．２２×１０5 Ｐａの高温高湿の雰囲気中で８時間暴露した後の試料とにそれぞれ無塩素系の超非活性フラックスを塗布し、加熱溶融した無鉛ハンダ（Ａｇ：２．５％、Ｃｕ：０．５％、Ｂｉ：１．０％、残部：Ｓｎ）浴中に深さ１０ｍｍまで浸漬し、ハンダ浴面上部にハンダで濡れた部分が発生するまでに要する時間（秒）でハンダ濡れ性を評価した。切り出し直後については３秒以下、高温高湿の雰囲気中で暴露後については６秒以下を本発明の合格とした。
【００３８】
これらの特性評価結果を表３に示す。
【００３９】
【表３】
表３に示すように、資料番号１２〜１５および１７〜１９の各製造条件に従って表面に有機皮膜を被覆したＳｎ−Ｚｎめっき鋼板は、それぞれ耐錆性および耐ホィスカー性に優れているとともに、高温高湿の雰囲気中に長時間放置しても優れたハンダ濡れ性を示すものであった。一方、資料番号１１、１６、２０および２１の各製造条件に従って表面に有機皮膜を被覆したＳｎ−Ｚｎめっき鋼板は、それぞれ切出直後および高温高湿暴露後のハンダ濡れ性（資料番号１１：Ｓｎ2+イオンとＺｎ2+イオンとの重量比が１：５〜１：１０以外のため）、耐錆性（資料番号１６：Ｚｎ量が０．０５ｇ／ｍ2 未満のため）、高温高湿暴露後のハンダ濡れ性（資料番号２０：有機樹脂皮膜がないため）および耐ホィスカー性（資料番号２１：Ｓｎ2+イオンとＺｎ2+イオンとの重量比が１：５〜１：１０以外のため）において不合格であった。
【００４１】
【発明の効果】
本発明は、Ｓｎ2+イオンとＺｎ2+イオンを一定範囲の重量比で含有する合金めっき浴を用いて、鋼板に一定範囲の組成のＳｎとＺｎとからなるＳｎ−Ｚｎ合金層を電気めっきし、その後電気めっき鋼板をＳｎ−Ｚｎ合金の融点以上に加熱してＳｎ−Ｚｎ合金を溶融する加熱溶融処理を施した後、または加熱溶融処理を施さずに直接、前記電気めっき鋼板のＳｎ−Ｚｎ合金層上に有機樹脂を塗布して有機樹脂皮膜を形成してなる表面処理鋼板であり、優れた耐錆性および耐ホィスカー性を有しているとともに、長時間高温高湿の条件下で長時間放置しても良好なハンダ濡れ性を示す。そのためハンダ付けを行う電子部品用に好適に適用することができる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a surface-treated steel sheet for electronic parts and a method for producing the same. More specifically, a surface-treated steel sheet for electronic parts that exhibits excellent rust resistance and suppression of whisker growth of the underlying steel sheet, and exhibits good solder wettability even after a long time in a high-temperature and high-humidity atmosphere, and its manufacture Regarding the method.
[0002]
[Prior art]
In an electronic component, a component and a board, a component and another component, or the same components are soldered and electrically joined. Therefore, it is a common practice to form a Sn—Zn alloy layer having good wettability with solder and whisker resistance on the surface of the electronic component. Conventionally, cyan bath, pyrophosphoric acid bath, borofluoride bath, sulfonic acid bath, gluconic acid bath, citric acid bath, tartaric acid bath, etc. have been used as Sn—Zn alloy plating. It is difficult to do so, and because it uses a complexing agent, it has disadvantages such as costly wastewater treatment.
[0003]
In order to overcome these drawbacks, a method using a plating bath using a complexing agent containing a carboxyl group and a sulfone group, or a carboxyl group and a monovalent hydroxyl group (Japanese Patent Laid-Open No. 10-168592), hydroxycarboxylic acid or a salt thereof Attempts have been made to use a plating bath containing Ni (JP-A-6-228786).
[0004]
[Problems to be solved by the invention]
However, in these methods, although a smooth and dense Sn—Zn alloy plating layer with a uniform composition can be obtained, the wettability with solder deteriorates when left for a long time under high temperature and high humidity conditions after plating. Have the disadvantages.
[0005]
The present invention has been made in view of these points, and is excellent in rust resistance and whisker resistance, and exhibits good wettability with solder even when left for a long time under high temperature and high humidity conditions. An object of the present invention is to provide a surface-treated steel sheet and a method for producing the same.
[0006]
[Means for Solving the Problems]
The present inventors electroplated a Sn—Zn alloy layer composed of Sn and Zn having a certain range of composition on a steel sheet using an alloy plating bath containing Sn 2+ ions and Zn 2+ ions in a certain range of weight ratio, Thereafter, the electroplated steel sheet is heated to the melting point of the Sn-Zn alloy or higher to melt the Sn-Zn alloy, or directly or without being subjected to the heat-melting process. by forming an organic resin film by applying a urethane resin and / or epoxy resins on the layer, which is excellent in rust resistance and whisker resistance, even better to left for a long time under the conditions of high temperature and high humidity The present invention was completed by discovering that a surface-treated steel sheet for electronic parts to be soldered using a chlorine-free super-inactive flux showing wettability with solder can be obtained.
[0007]
The surface-treated steel sheet for electronic parts of the present invention has an Sn—Zn alloy layer composed of Sn: 1 to 20 g / m 2 and Zn: 0.05 to 1 g / m 2 on at least one surface of the steel sheet, and a Sn—Zn alloy layer. Is a surface-treated steel sheet for electronic parts that is soldered using a chlorine-free super-inactive flux formed by forming a urethane resin or / and epoxy resin film having a thickness of 0.1 to 2 μm in the alloy layer. The weight ratio of Sn: Zn is 15: 1 to 20: 1.
[0008]
Moreover, the manufacturing method of the surface-treated steel sheet for electronic components of this invention uses the alloy plating bath which contains Sn2 + ion and Zn2 + ion by weight ratio 1: 5 to 1:10, and at least one surface of a steel plate. An Sn—Zn alloy layer composed of Sn: 1 to 20 g / m 2 and Zn: 0.05 to 1 g / m 2 is electroplated, and then the electroplated steel sheet is heated to a melting point or higher of the Sn—Zn alloy to produce an Sn—Zn alloy. was subjected to heating and melting treatment for melting, or heat-melting treatment directly without performing, Sn-Zn alloy layer on the urethane resin and / or epoxy resins of the film thickness after drying of the electroplated steel sheet 0 A method for producing a surface-treated steel sheet for electronic parts to be soldered using a chlorine-free super-inactive flux , wherein the coating is dried to a thickness of 1 to 2 μm, and the pH of the alloy plating bath is 3 .0 or more It is below, More preferably, it is 1.0-2.0.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
The present invention is described in detail below.
[0010]
In the Sn—Zn alloy layer showing wettability with solder and whisker resistance, the Zn content is preferably 3 to 10%, and more preferably 5 to 6%. When Sn and Zn are electrodeposited from a plating bath using an electroplating method, the precipitation potential of Sn and Zn is greatly separated, and Sn is very easy to precipitate. In order to obtain Sn—Zn alloy plating having a uniform alloy composition in a small amount range, it is necessary to suppress the precipitation of Sn and promote the precipitation of Zn. Therefore, in the plating bath of the present invention, the weight ratio of Sn 2+ ions to Zn 2+ ions is set to 1: 5 to 1:10, and the amount of Zn 2+ ions in the plating bath is far greater than the amount of Sn 2+ ions. It is characterized by having many.
[0011]
As a supply source of Sn 2+ ions and Zn 2+ ions, it is preferable to use sulfates or halides. The pH of the plating bath is preferably 3.0 or less, more preferably 1.0 to 2.0. When the pH exceeds 3.0, it is difficult to obtain a uniform Sn—Zn alloy composition in the above range. In order to obtain a Sn—Zn alloy composition having a stable alloy composition, it is more preferable to use a plating bath having a pH of 1.0 to 2.0.
[0012]
In the present invention, the Sn—Zn alloy is plated on the steel sheet using the alloy plating bath formed in this way. The plating amount is preferably in the range of Sn: 1 to 20 g / m 2 and Zn: 0.05 to 1 g / m 2 . If Sn content is less than 1 g / m 2 is not enough solder wettability and Zn weight 0.05 g / m when it is less than 2 and not have sufficient rust resistance and whisker resistance, alloy plating Rust tends to occur on the cut end face of the steel sheet that is not applied. Even if the Sn amount exceeds 20 g / m 2 , the effect of improving rust resistance is saturated. The solder wettability is insufficient when Zn content relative to 20 g / m 2 of an upper limit of the preferred range of Sn content is more than 1 g / m 2.
[0013]
In the above plating amount range, the Sn: Zn weight ratio during alloy plating is preferably 15: 1 to 20: 1. When the weight of Zn exceeds 1/15 of the weight of Sn, the solder wettability becomes insufficient. On the other hand, if the weight of Zn is less than 1/20 of the weight of Sn, sufficient whisker resistance cannot be obtained.
[0014]
After the Sn—Zn alloy plating layer is formed on the steel plate as described above, the plated steel plate is heated to a temperature equal to or higher than the melting point of the Sn—Zn alloy to melt the Sn—Zn alloy, and the Sn—Zn alloy Sn. Further, Zn and iron of the steel plate may be diffused. This diffusion treatment improves the adhesion between the Sn—Zn alloy plating layer and the steel sheet.
[0015]
The Sn—Zn alloy-plated steel sheet obtained as described above has good solder wettability immediately after plating. However, when it is stored in the warehouse for a long time, such as when stored in a warehouse, it is Sn—Zn alloy. An oxide film of Sn and Zn grows on the surface, and solder wettability is inhibited. This tendency is particularly remarkable in a high-temperature and high-humidity environment, and a Sn—Zn alloy-plated steel sheet that exhibits good solder wettability even when left in a high-temperature and high-humidity warehouse for a long period of time has been demanded. According to the present embodiment, by providing an organic resin film on the Sn—Zn alloy plating layer of the Sn—Zn alloy plated steel sheet, good solder wettability even if left in a high temperature and high humidity atmosphere for a long time. It was found that it was possible to maintain.
[0016]
Although it does not restrict | limit especially as an organic resin, It is preferable to use either urethane resin, an epoxy resin, and an acrylic resin from viewpoints of versatility, the ease of coating, cost, etc. One or two or more of these resins are dissolved in an organic solvent, and applied on the Sn—Zn alloy plating layer so that the film thickness after drying is 0.1 to 2 μm. When the film thickness is less than 0.1 μm, it is difficult to maintain good solder wettability when left for a long time. On the other hand, when the thickness of the coating exceeds 2 μm, when the heated molten solder comes into contact, the organic resin coating is not sufficiently removed from the bonding interface between the solder and the Sn—Zn alloy plating, and sufficient solder bonding strength is obtained. There may not be. As a coating method, conventional methods such as a roll coating method and a spray method can be used. After application, it is heated in an oven or blown with hot air to dry and solidify.
[0017]
As described above, the surface-treated steel sheet for electronic parts of the present invention can be obtained.
[0018]
【Example】
Hereinafter, the present invention will be described in detail with reference to examples.
[0019]
First, an electrolytic cleaning treatment and a pickling treatment are performed on a low carbon steel sheet having a thickness of 0.5 mm using a conventional method, and then a Sn—Zn alloy plating bath shown in plating numbers 1 to 5 in Table 1 is used. A Sn—Zn alloy-plated steel sheet was prepared by appropriately selecting a current density and energization time and forming a Sn—Zn alloy plating layer having the composition shown in Sample Nos. 11 to 21 in Table 2 on the low-carbon steel sheet. . Some of the plated steel sheets (see Document Nos. 17 to 20) were resistance-heated to a temperature equal to or higher than the melting point of the plated Sn—Zn alloy to melt the plated layer and immediately quenched into water.
[0020]
Next, the organic resin shown in Table 2 was dissolved in an organic solvent, roll-coated on these samples, and then dried with hot air to form an organic resin film having the film thickness shown in Table 2 for property evaluation. A sample was used.
[0021]
[Table 1]
[Table 2]
The following characteristics were evaluated for the samples thus obtained.
[0024]
[Rust resistance]
A salt spray test was performed based on JIS Z 2371 to evaluate rust resistance. That is, the sample was cut into 30 mm squares, and sprayed with salt water for 2 hours in the state of being cut out for evaluation of the cut surface, and for evaluation of the plated surface, the cut surface was sealed with wax and sprayed with salt water for 12 hours, Rust resistance was evaluated with the following five grades by visual observation.
[0025]
Score 5: No occurrence of red rust.
[0026]
Score 4: Generation of slight red rust that is not a problem in practical use is observed.
[0027]
Score 3: Generation of red rust that is problematic in practice is observed.
[0028]
Score 2: Red rust is observed in a considerable part of the evaluation surface.
[0029]
Score 1: Red rust is observed on almost the entire evaluation surface.
[0030]
Scores 5 and 4 were accepted for the present invention.
[0031]
[Whisker resistance]
A sample was cut into a 30 mm square and the whisker generation state after exposure for 30 days in a high temperature and high humidity atmosphere of temperature: 85 ° C. and humidity: 85% RH was observed at a magnification of 1500 times using a scanning electron microscope. The whisker resistance was evaluated according to the following evaluation.
[0032]
A: No whisker is observed.
[0033]
○: It is recognized that whiskers having a length of less than 10 μm are slightly generated.
[0034]
Δ: Whisker having a length of less than 10 to 30 μm is observed.
[0035]
X: It is recognized that whiskers having a length exceeding 30 μm are generated.
[0036]
Evaluation criteria ◎ and ○ were regarded as acceptable for the present invention.
[0037]
[Solder wettability]
A sample immediately after being cut into a size of 10 mm × 30 mm, and after being cut out for 8 hours in a high temperature and high humidity atmosphere of temperature: 105 ° C., humidity: 100% RH, pressure: 1.22 × 10 5 Pa In a lead-free solder (Ag: 2.5%, Cu: 0.5%, Bi: 1.0%, balance: Sn) bath which is coated with a chlorine-free super-inactive flux and heated and melted. Then, the solder wettability was evaluated by the time (seconds) required until a portion wetted with solder was generated on the upper part of the solder bath surface. Immediately after cutting, 3 seconds or less, and after exposure in a high temperature and high humidity atmosphere, 6 seconds or less were considered acceptable.
[0038]
These characteristic evaluation results are shown in Table 3.
[0039]
[Table 3]
As shown in Table 3, the Sn-Zn plated steel sheet having the surface coated with an organic film according to the production conditions of Document Nos. 12 to 15 and 17 to 19 is excellent in rust resistance and whisker resistance, and at high temperature. Even when left in a high humidity atmosphere for a long time, it exhibited excellent solder wettability. On the other hand, the Sn—Zn plated steel sheet coated with an organic film on the surface in accordance with the production conditions of Document Nos. 11, 16, 20, and 21 is solder wettability immediately after cutting and after exposure to high temperature and high humidity (Document No. 11: Sn). 2+ ions and Zn 2+ ions are in a weight ratio other than 1: 5 to 1:10), rust resistance (material number 16: because Zn content is less than 0.05 g / m 2 ), high temperature and humidity Solder wettability after exposure (document number 20: no organic resin film) and whisker resistance (document number 21: weight ratio of Sn 2+ ion to Zn 2+ ion is other than 1: 5 to 1:10) )).
[0041]
【The invention's effect】
The present invention electroplates a Sn—Zn alloy layer composed of Sn and Zn having a composition in a certain range on a steel sheet using an alloy plating bath containing Sn 2+ ions and Zn 2+ ions in a certain range by weight ratio. Thereafter, the electroplated steel sheet is heated to the melting point of the Sn-Zn alloy or higher and subjected to a heat-melting process for melting the Sn-Zn alloy, or directly without the heat-melting process. It is a surface-treated steel sheet formed by coating an organic resin on a Zn alloy layer to form an organic resin film. It has excellent rust resistance and whisker resistance, and it can be used under conditions of high temperature and humidity for a long time. Good solder wettability even when left for a long time. Therefore, it can be suitably applied to an electronic component for soldering.
Claims (5)
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