JP3874911B2

JP3874911B2 - Plating method for micro plastic balls

Info

Publication number: JP3874911B2
Application number: JP29950297A
Authority: JP
Inventors: 武司西内; 文秋菊井; 吉村　　公志
Original assignee: Neomax Materials Co Ltd
Current assignee: Proterial Metals Ltd
Priority date: 1997-10-15
Filing date: 1997-10-15
Publication date: 2007-01-31
Anticipated expiration: 2017-10-15
Also published as: JPH11124682A

Description

【０００１】
【発明の属する技術分野】
この発明は、外径１ｍｍ以下の微小プラスチック球を使用して半導体パッケージのバンプ芯材として用いられる微小球を効率よく製造するためのめっき方法に係り、水平回転可能なめっき槽を用い、これを高速で正転反転を周期的に繰り返すことにより、無電解めっきによる導電性金属膜を有した微小プラスチック球に凝集を生じたり、組成や膜厚みの不均一などの膜質の不良を発生することなく、高効率ではんだなどの合金や金属のめっきを成膜することが可能な微小プラスチック球へのめっき方法に関する。
【０００２】
【従来の技術】
従来、ＢＧＡ（ＢａｌｌＧｒｉｄＡｒｒａｙ）タイプの半導体パッケージのバンプ芯材として用いられる微小球は、直径が０．１ｍｍ〜１．０ｍｍ程度で、材質としては所定組成のハンダの他、最近では、電気特性や機械的特性を考慮して、コバール（Ｎｉ−Ｃｏ−Ｆｅ合金）、Ｃｕ、４２Ｎｉ−Ｆｅ合金などの金属球を芯材としてろう材を被覆したチップキャリアーが提案（特開昭６２−１１２３５５号）されている。
【０００３】
前記微小球の製造方法として、溶融金属を所定温度の液体中に滴下し、溶融金属自体の表面張力にて球形化してそのまま凝固するいわゆる液体中滴下方法（特開平７−２５２５１０号）、金型によるフォーミング等のいわゆる機械的塑性加工方法（特開平４−３５４８０８号）、金属粒又は金属片を非酸化性雰囲気中で平板上に載置して振動を加えながら加熱溶融してその表面張力で球形化してそのまま凝固する振動加熱方法（特公平２−５０９６１号）などが提案されている。
【０００４】
このように製造された微小球の外周面のろう材としては、要求される寸法精度や半導体パッケージとプリント基板との固着強度などにより適宜選定される。例えば、厚み５〜５０μｍの種々の組成からなるハンダ（Ｐｂ−Ｓｎ系）が被覆され、必要に応じてＮｉなどの下地層を形成することもある。
【０００５】
従来、外径が０．６７〜０．７５ｍｍのＣｕボールについては、一般に、陽電極をめっき槽外に配設したバレルを水平軸による垂直方向回転あるいは傾斜軸による傾斜回転させ、５〜１５ｒｐｍ程度の回転数にて通電しながらめっきするバレルめっき法が行われていた。
【０００６】
【発明が解決しようとする課題】
今日の半導体パッケージの高密度化に伴い、チップキャリアーとしてのボール径はさらに小さくなり、径０．２５ｍｍや０．１５ｍｍＣｕボールが要求され、さらにＢＧＡ用Ｃｕボールの軽量化、パッケージへの二次実装時の信頼性向上を目的として、ＢＧＡ用プラスチック球表面に金属めっき膜を被覆した弾性変形可能な軽量化ボールが提案されている。
【０００７】
微小プラスチック球は非導電性のため、該球表面に生産性の良好な電気めっき法にてはんだめっき膜を被覆することはできず、はんだめっき膜を微小プラスチック球表面に設けるには、まず予め該球表面に無電解めっき法にて導電性金属膜を被覆する必要がある。
【０００８】
次に、無電解めっき法による導電性金属膜を設けた微小プラスチック球に、バレルめっき法にてはんだめっき膜を設けるが、外径が１ｍｍ以下の微小球をバレルにて低速回転でいずれの方向に回転させても、比重が小さなプラスチック球は十分に撹拌されずに球同士の凝集を生じやすく、その上にめっき被膜が生成されて２個付きや３個付き等を生じたり、また、陰極との接触が不十分なためにめっき膜質の不良を発生する問題があった。
【０００９】
この発明は、上記の問題点を解決し、ＢＧＡ（ＢａｌｌＧｒｉｄＡｒｒａｙ）タイプの半導体パッケージ用バンプ等として有効な量産性に優れ、しかも寸法精度が高い微小プラスチック球を極めて効率よく製造することを目的とし、無電解めっき法による導電性金属膜を設けた微小プラスチック球に凝集を生じたり、組成や膜厚みの不均一などの膜質の不良を発生することなく、微小プラスチック球表面に高効率ではんだなどの合金や金属のめっきを成膜することが可能な微小プラスチック球へのめっき方法の提供を目的とする。
【００１０】
【課題を解決するための手段】
発明者らは、外径１ｍｍ以下の微小プラスチック球に均一で高品質の電気めっき膜を効率よく成膜できるめっき方法を目的に種々検討した結果、無電解めっき法による導電性金属膜を設けた微小プラスチック球に、水平回転可能なめっき槽を用い、これを高速で正転反転を周期的に繰り返して、表面にＣｕ等の金属やはんだなどの合金を電気めっきすることより、凝集を生じたり、膜質の不良を発生することなく均一に成膜できることを知見し、この発明を完成した。
【００１１】
すなわち、この発明は、外径1mm以下の微小プラスチック球に無電解めっき法にて膜厚0.5μm〜5μmの導電性金属膜を成膜した後、垂直軸で水平回転可能な槽内円周部に陰極、槽内中央部に陽極を配設しためっき槽内に送入されためっき液を回転円周部より排出する構成の水平回転めっき槽を用い、前記微小プラスチック球をめっき槽内に装入し、該めっき槽を回転数50〜800rpmから選定する定速回転数にて所要方向に正転次いで反転の定速運転する回転制御を周期的に繰り返しながら、正転と反転のいずれも前記定速運転中にのみ通電を行い、例えば、はんだめっきの場合は、イオン濃度5〜20g/l、電流密度0.1〜5A/dm²のめっき浴条件で、微小プラスチック球を槽内円周部の陰極に電気的に接触させて所要金属又は合金の電気めっきを施す微小プラスチック球へのめっき方法である。
【００１２】
【発明の実施の形態】
この発明方法で用いる水平回転型めっき装置の構造を図１に示す。めっき装置は、垂直軸１に支持されたテーブル２上に載置された円錐状のめっき槽３を主体とし、めっき槽３が垂直軸１の回転で水平回転するもので、めっき槽３の底部円周にリング状のカソード部（陰極）４、めっき槽３中央部にアノード部（陽極）６が設置されており、図に示すようにめっき液はホンプで薬液パイプ７よりめっき槽３内に送入されるとともに、カソード部４の下部に設けた通気性の良い多孔質板からなるポーラスリング５を通じて水平回転速度に応じた流速でめっき槽３の円周部外へ排出され、めっき槽３を覆うように配置された防滴槽８の排出口９よりめっき液を排出する構成からなる。
【００１３】
めっき槽３の回転時は、めっき槽３内に取り付けた液面センサー１０により、回転数に応じてポーラスリング５より流出するめっき液が補給されて、めっき液面が所定高さに維持される。
【００１４】
この発明によるめっき方法は、めっき槽３を特定の回転数で正転させ、その後反転させ、これを周期的に繰り返して行うもので、微小プラスチック球１１はめっき槽３の回転と停止の際に起こる遠心力と慣性力によって円周壁面への堆積と崩壊を繰り返し、徐々に位置を変えながらめっきされるため、凝集が起こり難くなることを特徴としている。
【００１５】
めっき槽３の回転を制御する基本制御パターンの一例を図２に示す。基本的には、加速回転→定速（高速）回転→減速回転→休止の動作からなっており、各パートの時間設定は自由にプログラミングできる。この発明において、所定の高速回転の定速運転時にのみ通電してめっきを行うもので、微小プラスチック球は回転による遠心力によって陰極と十分に接触されるため、均一で良質な金属皮膜が生成され、良質な微小金属球を得ることができる。
【００１６】
この発明において、微小プラスチック球の外径は、１．０ｍｍ以下とするが、これを越えると半導体パッケージのバンプ芯材として用いられるボール外径を越えてしまうためであり、材質としては、アクリル、ポリプロピレン、塩化ビニル、ポリフェニレンサルファイドなどの一般的なプラスチックで微小球化が可能なものであればいずれのものも適用できる。
【００１７】
この発明において、微小プラスチック球に無電解めっき法にて膜厚０．５μｍ〜５μｍの導電性金属膜を成膜するが、球自体が非導電性であるため、目的とする電気めっきを施すために不可欠であり、例えば、Ｎｉ、Ｃｕ、はんだ等の金属、合金を成膜でき、膜厚みは０．５μｍ未満では電気めっき処理時に必要な導電性が確保できず、また５μｍを越えると、めっき時間やめっき液のコストの観点から問題を生じるため、０．５μｍ〜５μｍが望ましく、好ましくは１μｍ〜３μｍである。
【００１８】
この発明において、陽極は、一般の電気めっきと同様、目的とする金属種、合金組成に応じた金属を用いるが、陰極にはチタン、白金等の不溶性電極を円周壁にリング状に取り付けて用いることができる。
【００１９】
この発明では、Ｃｕ、はんだ、コバール（Ｆｅ‐Ｎｉ‐Ｃｏ合金）など、電気めっきによる金属皮膜形成が可能な全ての金属において、微小プラスチック球へのめっきが可能であり、めっき液中のイオン濃度、陰極電流密度は、対象とする微小プラスチック球の導電性膜並びにめっき金属に応じて適宜選定され、めっき浴条件としては、イオン濃度１〜７０ｇ／ｌ、電流密度０．０５〜１０Ａ／ｄｍ²が望ましい。
【００２０】
例えば、Ｃｕ被覆微小プラスチック球の製造に際して、めっき液中のＣｕイオン濃度は、４０ｇ／ｌ未満では極間電圧が高くガスが発生し、７０ｇ／ｌを越えると不均化反応が起こり良質なめっき被膜が得られないため、４０〜７０ｇ／ｌが好ましく、さらに好ましい条件は５０〜６０ｇ／ｌである。電流密度は、１Ａ／ｄｍ²未満では生産性が悪く、被膜表面がざらつき良好な被膜が得られず、１０Ａ／ｄｍ²を越えるとめっき反応時のガス発生が多く、ピンホールの発生が懸念されるため、１〜１０Ａ／ｄｍ²が好ましく、さらに好ましくは３〜５Ａ／ｄｍ²である。
【００２１】
また、Ａｕ被覆微小プラスチック球の製造に際して、めっき液中のＡｕイオン濃度は、１〜１５ｇ／ｌが好ましく、さらに好ましい条件は２〜１２ｇ／ｌで、電流密度は、０．０５〜２Ａ／ｄｍ²が好ましく、さらに好ましくは０．１〜１Ａ／ｄｍ²である。
【００２２】
この発明において、はんだ被覆微小プラスチック球の製造に際して、めっき液中の錫と鉛の合計イオン濃度は、５ｇ／ｌ未満では極間電圧が高くガス発生が生じ、２０ｇ／ｌを超えるとはんだ被膜組成のコントロールが難しくなるため、５〜２０ｇ／ｌが好ましく、さらに好ましい範囲は７〜１５ｇ／ｌである。
【００２３】
また、はんだ被覆微小プラスチック球の製造に際して、陰極電流密度は、０．１Ａ／ｄｍ²未満では生産性が悪い上、被膜表面がザラつき良好なめっき被膜が得られず、５Ａ／ｄｍ²を超えるとめっき反応時にガス発生が多くなり、ピンホールの多いめっきとなり良好なめっき被膜が得られないため、陰極電流密度は０．１〜５Ａ／ｄｍ²が好ましく、さらに好ましい電流密度範囲は０．２〜２Ａ／ｄｍ²である。
【００２４】
この発明において、めっき槽の回転数については、５０ｒｐｍ未満では十分な遠心力が得られず、陰極との接触が十分でないため、めっき表面の突起が多くザラついて良好なめっき被膜が得られず、また８００ｒｐｍを超えると、めっき液の飛散が生じ、安定しためっきができないため、５０〜８００ｒｐｍが好ましい。
【００２５】
この発明において、正転、反転する周期については、３秒未満では通電時間の割合が少なく能率的でなく、８秒を超えると陰極との接触時間が長く、金属球が陰極部に一部被着するので正転、反転する周期は、３〜８秒が好ましく、通電する定速回転時間は２秒〜６秒が好ましく、また、正転時間と反転時間は同一でも異なっていても良い。
【００２６】
この発明において、使用するめっき液は金属種に応じて適宜選定するが、Cuめっきの場合、硫酸銅、ピロリン酸銅等、また、はんだめっきの場合、アルカノールスルホン酸錫、アルカノールスルホン酸鉛、フェノールスルホン酸錫、フェノールスルホン酸鉛等をふくむめっき液を使用することができる。
【００２７】
【実施例】
実施例１
無電解Ｎｉ−Ｂめっき法により、２μｍの導電性金属膜としてＮｉ膜を被覆した外径０．１ｍｍの架橋アクリル球を１０万個用い、はんだめっき浴として錫７．９ｇ／ｌ、鉛２．１ｇ／ｌを含んだアルカノールスルホン酸、半光沢剤を含むｐＨ＜１のめっき液を用い、陽極板にはＳｎ／Ｐｂ＝６／４のはんだ板、陰極リングとしてＴｉリングを用い、浴温２３℃にて、電気めっきを実施した。
【００２８】
めっき条件は、陰極のＴｉリングを用い、めっき槽の水平回転数が６００ｒｐｍ、電流密度が０．５Ａｄｍ²、正転、反転周期が６秒からなる電気めっきを６時間行い、導電性金属膜としてＮｉ膜を被覆したアクリル球表面に３５μｍ厚みのの共晶はんだめっき層を被覆した。
【００２９】
得られたアクリル球のはんだめっきの凝集状態、組成のばらつき、膜厚精度、凝集状態を測定した。その結果を表１に示す。なお、組成ばらつき、膜厚精度は５０個をサンプリングして測定した平均値並びに最大値、最小値より求めた。
【００３０】
比較例１
実施例１と同様の導電性金属膜を有したアクリル球を用い、めっき装置に水平軸にて垂直方向に回転するバレルめっき装置を用い、回転数１０ｒｐｍで反転なしとした以外は、実施例と同じ条件でめっきを行い、はんだめっきの凝集状態、組成、膜厚精度を測定し、その結果を表１に示す。
【００３１】
【表１】

【００３２】
実施例２
無電解Ｎｉ−Ｂめっき法により、２μｍの導電性金属膜としてＮｉ膜を被覆した外径０．１ｍｍの架橋アクリル球を１０万個用い、Ｃｕめっき浴としてＣｕを５５ｇ／ｌ含んだ硫酸浴を用い、浴温３０℃にて、電気めっきを実施した。
【００３３】
めっき条件は、陰極リングとしてＴｉリングを用い、陽極板として含りん銅を用い、めっき槽の水平回転数が５００ｒｐｍ、電流密度が３Ａｄｍ²、正転、反転周期が６秒からなる電気めっきを１時間行い、導電性金属膜としてＮｉ膜を被覆したアクリル球表面に３０μｍ厚みのＣｕめっき層を被覆した。
【００３４】
得られたアクリル球の銅めっきの表面状態、膜厚精度、凝集状態を測定した。その結果を表２に示す。なお、表面状態、膜厚精度は５０個をサンプリングして測定した平均値並びに最大値、最小値より求めた。
【００３５】
比較例２
実施例１と同様の導電性金属膜を有したアクリル球を用い、めっき装置に水平軸にて垂直方向に回転するバレルめっき装置を用い、回転数１０ｒｐｍで反転なしとした以外は、実施例と同じ条件でめっきを行い、はんだめっきの凝集状態、組成、膜厚ばらつきを測定し、その結果を表２に示す。
【００３６】
【表２】

【００３７】
【発明の効果】
この発明は、実施例に示すごとく、無電解めっき法による導電性金属膜を有した微小プラスチック球表面に、水平回転可能なめっき槽を用い、これを高速で正転反転を周期的に繰り返すことにより、微小プラスチック球に凝集を生じたり、組成や膜厚みの不均一などの膜質の不良を発生することなく、高効率ではんだなどの合金や金属のめっきを成膜することが可能で、均一なはんだ膜などをめっきした高精度な所要の外径を有する微小プラスチック球を効率よく大量生産できる。
【図面の簡単な説明】
【図１】この発明に用いる水平回転型めっき装置の縦断説明図である。
【図２】めっき槽の回転を制御する基本制御パターンの一例を示す説明図である。
【符号の説明】
１垂直軸
２テーブル
３めっき槽
３ａめっき槽底部
４カソード部
５ポーラスリング
６アノード部
７薬液パイプ
８防滴槽
９排出口
１０液面センサー
１１微小プラスチック球[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a plating method for efficiently producing microspheres used as bump core materials for semiconductor packages using microplastic spheres having an outer diameter of 1 mm or less, and using a horizontally rotatable plating tank. By periodically repeating forward and reverse rotation at high speed, there is no agglomeration of fine plastic spheres with conductive metal films by electroless plating, and no film quality defects such as uneven composition and film thickness. Further, the present invention relates to a method for plating fine plastic spheres capable of depositing an alloy such as solder or metal with high efficiency.
[0002]
[Prior art]
Conventionally, a microsphere used as a bump core material of a BGA (Ball Grid Array) type semiconductor package has a diameter of about 0.1 mm to 1.0 mm, and the material is not only solder of a predetermined composition, but recently, electrical characteristics. In consideration of the mechanical properties, a chip carrier is proposed in which a metal ball such as Kovar (Ni—Co—Fe alloy), Cu, or 42Ni—Fe alloy is coated with a brazing material (Japanese Patent Laid-Open No. 62-112355). )
[0003]
As the method for producing the microspheres, a so-called liquid dropping method (Japanese Patent Laid-Open No. 7-252510), in which molten metal is dropped into a liquid at a predetermined temperature, spheroidized by the surface tension of the molten metal itself, and solidified as it is, mold A so-called mechanical plastic working method such as forming (Japanese Patent Laid-open No. 4-354808), placing metal particles or metal pieces on a flat plate in a non-oxidizing atmosphere, heating and melting them while applying vibrations, and using the surface tension A vibration heating method (Japanese Patent Publication No. 2-50961) that forms a sphere and solidifies as it is proposed.
[0004]
The brazing material on the outer peripheral surface of the microspheres manufactured in this way is appropriately selected depending on the required dimensional accuracy, the bonding strength between the semiconductor package and the printed circuit board, and the like. For example, solder (Pb—Sn series) having various compositions having a thickness of 5 to 50 μm is coated, and an underlayer such as Ni may be formed as necessary.
[0005]
Conventionally, for Cu balls having an outer diameter of 0.67 to 0.75 mm, generally, a barrel in which a positive electrode is disposed outside a plating tank is rotated in the vertical direction by a horizontal axis or inclined by an inclined axis, and is about 5 to 15 rpm. A barrel plating method in which plating is carried out while energizing at a rotational speed of is performed.
[0006]
[Problems to be solved by the invention]
With today's high-density semiconductor packages, the ball diameter as a chip carrier is further reduced, and 0.25 mm and 0.15 mm Cu balls are required. Further, the weight of Cu balls for BGA is reduced, and secondary mounting on the package. For the purpose of improving the reliability at the time, there has been proposed a weight-reducing ball that is elastically deformable and has a metal plating film on the surface of a BGA plastic ball.
[0007]
Since the micro plastic sphere is non-conductive, the surface of the sphere cannot be coated with a solder plating film by a highly productive electroplating method. It is necessary to coat the spherical surface with a conductive metal film by electroless plating.
[0008]
Next, a solder plating film is provided by a barrel plating method on a fine plastic sphere provided with a conductive metal film by an electroless plating method, but a microsphere having an outer diameter of 1 mm or less is rotated at any speed in the barrel in any direction. The plastic spheres with a small specific gravity are not sufficiently stirred even if they are rotated, and the spheres tend to agglomerate with each other, and a plating film is formed on the plastic spheres to form two or three pieces. There is a problem that the plating film quality is poor due to insufficient contact with the film.
[0009]
SUMMARY OF THE INVENTION An object of the present invention is to solve the above-described problems and to produce a micro plastic sphere having excellent mass productivity as a BGA (Ball Grid Array) type semiconductor package bump and the like and having a high dimensional accuracy extremely efficiently. Soldering with high efficiency on the surface of the micro plastic sphere without agglomeration in the micro plastic sphere provided with the conductive metal film by the electroless plating method and without causing poor film quality such as non-uniform composition and film thickness. An object of the present invention is to provide a method for plating fine plastic spheres capable of depositing an alloy or a metal plating.
[0010]
[Means for Solving the Problems]
As a result of various studies for the purpose of plating methods capable of efficiently forming a uniform and high-quality electroplated film on fine plastic spheres having an outer diameter of 1 mm or less, the inventors have provided a conductive metal film by an electroless plating method. Using a plating vessel that can be rotated horizontally on a micro plastic sphere, and periodically reversing forward and reverse at high speed, and electroplating a metal such as Cu or an alloy such as solder on the surface, agglomeration may occur. The present invention was completed by discovering that a film can be uniformly formed without causing a defect in film quality.
[0011]
That is, the present invention provides a peripheral portion in the tank that can be rotated horizontally on a vertical axis after a conductive metal film having a film thickness of 0.5 μm to 5 μm is formed on a small plastic sphere having an outer diameter of 1 mm or less by an electroless plating method. The horizontal plastic plating tank is configured to discharge the plating solution fed into the plating tank having the cathode and the anode disposed in the center of the tank from the rotating circumferential part, and the fine plastic spheres are mounted in the plating tank. Type, while repeating rotation control periodically to constant speed operation of the forward and then reversed to the required direction at constant rotation speed to select the plating tank from the rotational speed 50～800Rpm, both a forward reversal of the Energize only during constant speed operation.For example, in the case of solder plating, micro plastic balls are placed around the circumference of the tank under plating bath conditions with an ion concentration of 5 to 20 g / l and a current density of 0.1 to 5 A / dm ² . Microplasty for electroplating the required metal or alloy in electrical contact with the cathode This is a plating method for the hook ball.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
The structure of a horizontal rotary plating apparatus used in the method of the present invention is shown in FIG. The plating apparatus mainly includes a conical plating tank 3 mounted on a table 2 supported by a vertical shaft 1, and the plating tank 3 rotates horizontally by the rotation of the vertical shaft 1. A ring-shaped cathode part (cathode) 4 is provided on the circumference, and an anode part (anode) 6 is provided in the central part of the plating tank 3. As shown in the figure, the plating solution is pumped into the plating tank 3 from the chemical solution pipe 7. In addition to being fed in, it is discharged out of the circumferential portion of the plating tank 3 at a flow rate according to the horizontal rotation speed through a porous ring 5 made of a porous plate having good air permeability provided at the lower part of the cathode part 4. The plating solution is discharged from the discharge port 9 of the drip-proof tank 8 arranged so as to cover the surface.
[0013]
When the plating tank 3 rotates, the plating solution flowing out from the porous ring 5 is replenished by the liquid level sensor 10 attached in the plating tank 3 according to the number of rotations, and the plating solution level is maintained at a predetermined height. .
[0014]
In the plating method according to the present invention, the plating tank 3 is normally rotated at a specific rotation number, and then inverted, and this is periodically repeated. The micro plastic ball 11 is rotated when the plating tank 3 is rotated and stopped. It is characterized by the fact that it is difficult to agglomerate because plating is performed while gradually changing the position by repeatedly depositing and collapsing on the circumferential wall surface by the centrifugal force and inertial force that occur.
[0015]
An example of a basic control pattern for controlling the rotation of the plating tank 3 is shown in FIG. Basically, it consists of acceleration rotation-> constant speed (high speed) rotation-> deceleration rotation-> pause operation, and the time setting of each part can be freely programmed. In the present invention, plating is performed by energizing only during a constant speed operation at a predetermined high speed rotation. Since the micro plastic sphere is sufficiently in contact with the cathode by the centrifugal force due to rotation, a uniform and high-quality metal film is produced. A fine metal sphere of good quality can be obtained.
[0016]
In this invention, the outer diameter of the micro plastic sphere is 1.0 mm or less, but if it exceeds this, it will exceed the outer diameter of the ball used as the bump core material of the semiconductor package. Any general plastics such as polypropylene, vinyl chloride, polyphenylene sulfide and the like that can be microsphered can be used.
[0017]
In this invention, a conductive metal film having a film thickness of 0.5 μm to 5 μm is formed on a small plastic sphere by electroless plating. However, since the sphere itself is non-conductive, the intended electroplating is performed. For example, metals such as Ni, Cu, and solder, and alloys can be formed. If the film thickness is less than 0.5 μm, the necessary conductivity cannot be ensured during the electroplating process. In order to raise a problem from the viewpoint of time and cost of the plating solution, 0.5 μm to 5 μm is desirable, and preferably 1 μm to 3 μm.
[0018]
In this invention, the anode uses a metal corresponding to the target metal type and alloy composition as in general electroplating, but the cathode is used with an insoluble electrode such as titanium or platinum attached to the circumferential wall in a ring shape. be able to.
[0019]
In this invention, it is possible to plate micro plastic spheres on all metals that can form a metal film by electroplating, such as Cu, solder, Kovar (Fe-Ni-Co alloy), and the ion concentration in the plating solution. The cathode current density is appropriately selected according to the conductive film of the target fine plastic sphere and the plating metal. The plating bath conditions include an ion concentration of 1 to 70 g / l and a current density of 0.05 to 10 A / dm ^2. Is desirable.
[0020]
For example, in the production of Cu-coated microplastic spheres, the Cu ion concentration in the plating solution is less than 40 g / l, and a high voltage is generated between the electrodes, and if it exceeds 70 g / l, disproportionation occurs and high quality plating occurs. Since a film cannot be obtained, 40-70 g / l is preferable, and more preferable conditions are 50-60 g / l. If the current density is less than 1 A / dm ² , the productivity is poor, and the coating surface is rough and a good coating cannot be obtained. If the current density exceeds 10 A / dm ² , there is a concern about the generation of pinholes due to the large amount of gas generated during the plating reaction. Therefore, 1-10 A / dm < ² > is preferable, More preferably, it is 3-5 A / dm < ² >.
[0021]
In the production of Au-coated microplastic spheres, the Au ion concentration in the plating solution is preferably 1 to 15 g / l, more preferably 2 to 12 g / l, and the current density is 0.05 to 2 A / dm. ² is preferable, and 0.1 to 1 A / dm ² is more preferable.
[0022]
In the present invention, when the solder-coated micro plastic sphere is produced, the total ion concentration of tin and lead in the plating solution is less than 5 g / l, and the interelectrode voltage is high and gas is generated. 5 to 20 g / l is preferable, and a more preferable range is 7 to 15 g / l.
[0023]
Further, in the production of solder-coated fine plastic spheres, the cathode current density is less than 0.1 A / dm ² , and the productivity is poor, and a good plating film with a rough surface cannot be obtained, and the cathode current density exceeds 5 A / dm ² . Gas generation at the time of plating reaction and plating with many pinholes, and a good plating film cannot be obtained. Therefore, the cathode current density is preferably 0.1 to 5 A / dm ² , and a more preferable current density range is 0.2. it is a ~2A / dm ^2.
[0024]
In this invention, with respect to the number of rotations of the plating tank, sufficient centrifugal force cannot be obtained at less than 50 rpm, and contact with the cathode is not sufficient, so that a good plating film cannot be obtained due to a lot of protrusions on the plating surface, On the other hand, if it exceeds 800 rpm, the plating solution is scattered and stable plating cannot be performed. Therefore, 50 to 800 rpm is preferable.
[0025]
In the present invention, the period of forward and reverse rotation is not efficient when the current passing time is less than 3 seconds, and when it exceeds 8 seconds, the contact time with the cathode is long, and the metal sphere partially covers the cathode portion. The period of forward rotation and reverse rotation is preferably 3 to 8 seconds, so that the constant speed rotation time for energization is preferably 2 seconds to 6 seconds. The normal rotation time and the reverse time may be the same or different.
[0026]
In this invention, the plating solution used is suitably selected according to the metal species in the case of Cu plating, copper sulfate, copper pyrophosphate and the like. In the case of solder plating, A Luke Nord sulfonic tin, alkanol sulfonic lead, A plating solution containing tin phenol sulfonate, lead phenol sulfonate, or the like can be used.
[0027]
【Example】
Example 1
By electroless Ni-B plating, 100,000 cross-linked acrylic spheres with an outer diameter of 0.1 mm coated with a Ni film were used as a 2 μm conductive metal film, tin 7.9 g / l, lead 2. A plating solution with an alkanol sulfonic acid containing 1 g / l and a pH <1 containing a semi-brightening agent is used, a Sn / Pb = 6/4 solder plate is used for the anode plate, a Ti ring is used as the cathode ring, and a bath temperature of 23 Electroplating was performed at ° C.
[0028]
Plating conditions were as follows: electroplating using a negative electrode Ti ring, horizontal rotation speed of plating tank of 600 rpm, current density of 0.5 Adm ² , forward rotation and inversion period of 6 seconds for 6 hours as a conductive metal film The surface of the acrylic sphere coated with the Ni film was coated with a eutectic solder plating layer having a thickness of 35 μm.
[0029]
Aggregation state, composition variation, film thickness accuracy, and aggregation state of solder plating of the obtained acrylic sphere were measured. The results are shown in Table 1. The composition variation and film thickness accuracy were obtained from the average value, the maximum value, and the minimum value measured by sampling 50 samples.
[0030]
Comparative Example 1
Except for using an acrylic sphere having the same conductive metal film as in Example 1, using a barrel plating apparatus that rotates in the vertical direction on the horizontal axis in the plating apparatus, and without reversing at a rotation speed of 10 rpm, Plating was performed under the same conditions, and the agglomeration state, composition, and film thickness accuracy of the solder plating were measured, and the results are shown in Table 1.
[0031]
[Table 1]

[0032]
Example 2
Using an electroless Ni-B plating method, 100,000 cross-linked acrylic spheres having an outer diameter of 0.1 mm coated with a Ni film as a 2 μm conductive metal film were used, and a sulfuric acid bath containing 55 g / l of Cu was used as a Cu plating bath. The electroplating was performed at a bath temperature of 30 ° C.
[0033]
As for the plating conditions, a Ti ring is used as a cathode ring, phosphorous copper is used as an anode plate, a plating tank has a horizontal rotation speed of 500 rpm, a current density of 3 Adm ² , a forward rotation, and a reversal period of 6 seconds. After 30 hours, a 30 μm thick Cu plating layer was coated on the surface of an acrylic sphere coated with a Ni film as a conductive metal film.
[0034]
The surface state, film thickness accuracy, and aggregation state of the copper plating of the obtained acrylic sphere were measured. The results are shown in Table 2. The surface condition and film thickness accuracy were determined from the average value, the maximum value, and the minimum value obtained by sampling 50 samples.
[0035]
Comparative Example 2
Except for using an acrylic sphere having the same conductive metal film as in Example 1 and using a barrel plating apparatus that rotates in the vertical direction on the horizontal axis in the plating apparatus, and that there is no inversion at a rotational speed of 10 rpm, Plating was performed under the same conditions, and the agglomeration state, composition, and film thickness variation of the solder plating were measured, and the results are shown in Table 2.
[0036]
[Table 2]

[0037]
【The invention's effect】
As shown in the examples, the present invention uses a plating tank that can be rotated horizontally on the surface of a fine plastic sphere having a conductive metal film by an electroless plating method, and periodically repeats normal inversion at high speed. This makes it possible to deposit alloy and metal plating such as solder with high efficiency without causing agglomeration of fine plastic spheres or causing poor film quality such as non-uniform composition and film thickness. It is possible to efficiently mass-produce micro plastic balls having a required outer diameter with high accuracy plated with a solder film.
[Brief description of the drawings]
FIG. 1 is a longitudinal explanatory view of a horizontal rotary plating apparatus used in the present invention.
FIG. 2 is an explanatory diagram showing an example of a basic control pattern for controlling the rotation of the plating tank.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Vertical axis 2 Table 3 Plating tank 3a Plating tank bottom part 4 Cathode part 5 Porous ring 6 Anode part 7 Chemical solution pipe 8 Drip-proof tank 9 Outlet 10 Liquid level sensor 11 Micro plastic sphere

Claims

After a conductive metal film with a film thickness of 0.5 μm to 5 μm is formed on a small plastic sphere with an outer diameter of 1 mm or less by electroless plating, the cathode and the center of the tank are placed around the circumference of the tank that can be rotated horizontally around the vertical axis. Using a horizontal rotating plating tank configured to discharge the plating solution fed into the plating tank having an anode disposed at the part thereof from the rotating circumferential part, the fine plastic sphere is charged into the plating tank, and the plating tank the while the rotation control for constant speed operation of the forward and then reversed to the required direction at constant rotation speed to be selected from the rotation speed 50~800rpm periodically and repeatedly, both a forward reversal only during the constant speed operation A plating method for micro plastic spheres, in which energization is carried out and the required metal or alloy is electroplated by bringing the micro plastic spheres into electrical contact with the cathode in the circumferential part of the tank.

^{2. The} method for plating fine plastic spheres according to claim 1, wherein the plating bath conditions are an ion concentration of 1 to 70 g / l and a current density of 0.05 to 10 A / dm ² .