JP2004253430A

JP2004253430A - Method for manufacturing planar coil

Info

Publication number: JP2004253430A
Application number: JP2003039326A
Authority: JP
Inventors: Takashi Ida; 隆伊田; Toshio Sugawa; 俊夫須川; 喜久 ▲高▼瀬; Yoshihisa Takase
Original assignee: Matsushita Electric Industrial Co Ltd
Current assignee: Panasonic Holdings Corp
Priority date: 2003-02-18
Filing date: 2003-02-18
Publication date: 2004-09-09

Abstract

<P>PROBLEM TO BE SOLVED: To produce a high space factor coil in which a part between wires is narrow and dead space is little for miniaturization and the thinning of a planar coil. <P>SOLUTION: The method is constituted of a step for forming resist 5 covering a coil on a surface of an underlying conductor layer 2 which is formed previously at least on one surface of an insulating substrate 1, a step for eliminating the conductor layer 2 in a part except the part where the resist 5 is formed by etching, a step for eliminating the resist 5, and a step wherein a conductor is formed by electroplating and a surface conductor layer 6 is laminated while local etching is repeated on the conductor layer 2 whose cross section shape is made nearly rectangular by etching. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
本発明はスピーカのボイスコイルや電気回路のインダクタンス、トランス等に広く利用可能である高占積率の平面コイルの製造方法に関するものである。
【０００２】
【従来の技術】
従来、電子機器の全般的な小型・薄型化に伴い、これらに用いられる平面コイルについても小型化、薄型化することが強く求められている。そのためには、線間が狭くデッドスペースの少ない、つまり高占積率の平面コイルを製造する必要がある。
【０００３】
ここで、占積率について説明しておく。ここで言う占積率とは、平面コイルのコイル導体線条が延びる方向に垂直な断面において、コイル導体線条の配列ピッチを幅とし、コイル導体線条の厚さを高さとする矩形領域に対するコイル導体線条の断面積の比率を意味する。従って、高占積率の平面コイルとするためには、コイル導体線条の断面形状を矩形にしかつ線間を狭くすれば良い。
【０００４】
この高占積率の平面コイルの製造のために、従来からプリント配線技術を応用した製造方法が提案されている。その代表的な技術に、サブトラ法とめっきを組み合わせた方法が良く知られている。この方法は、絶縁基板上に予め形成した下地導体層の表面にコイルパターンのレジストを形成した後、レジスト形成部以外の下地導体層をエッチングによって除去し、さらに、レジストを除去した後に残った下地導体層を核にして電気めっきを行うことにより、下地導体層をめっき導体にて補強し、コイル導体線条を作製する。
【０００５】
なお、この出願の発明に関する先行技術文献情報としては、例えば、特許文献１が知られている。
【０００６】
【特許文献１】
特開平７−１４２２５４号公報
【０００７】
【発明が解決しようとする課題】
このサブトラ法とめっきを組み合わせた方法は、高占積率の平面コイル製造のための有力な方法ではあるが、直流電流を印加して電気めっきを行うため、下地導体層の上面や側面に比較してコーナーやエッジ部などの電流集中部にめっき導体が厚く形成され、コイル導体線条の断面形状を矩形にするのが困難である。また、コーナーやエッジ部に厚く付いためっき導体が隣接するコイル導体線条と接触しないようにするために、コイルの線間を広くする必要がある。そのため、上述した方法では占積率の向上という点では不十分であった。
【０００８】
そこで、本発明は、コイル導体線条の断面形状が正確な矩形で、かつ、線間が狭い高占積率の平面コイルの製造方法を提供することを目的とするものである。
【０００９】
【課題を解決するための手段】
上記課題を解決するために本発明は、絶縁基板に形成した下地導体層にレジストを形成してエッチングを行い、レジストを除去した後、この下地導体層上に正電流の印加によるめっきとこの正電流より大きい電流密度の逆電流を印加してめっきの一部を局部エッチングすることを同一めっき液中で繰り返して表面導体層を形成して断面形状が矩形のコイル導体線条を形成する方法であり、線間の狭い高占積率の平面コイルを得ることができる。
【００１０】
【発明の実施の形態】
本発明の請求項１に記載の発明は、絶縁基板の少なくとも一方の面に予め形成した下地導体層の表面にコイルとなる部分を被覆するようにレジストを形成する工程と、レジストを形成した以外の部分の下地導体層をエッチングにより除去する工程と、前記レジストを除去し前記エッチングによって断面形状がほぼ矩形となった下地導体層を露出させる工程と、前記下地導体層上に表面導体層を形成するにあたり、正電流の印加によってめっき導体を形成するステップと正電流よりも大きい電流密度の逆電流を印加して前記正電流の印加で形成しためっき導体の一部を局部エッチングするステップとを同一めっき液中で繰り返し、前記下地導体層と前記表面導体層からなる断面形状が矩形のコイル導体線条を形成する工程を有する平面コイルの製造方法である。
【００１１】
ここで、本発明の表面導体層の成長のメカニズムを簡単に説明する。まず、下地導体層の上に正電流を印加してめっき導体を形成する。この時、電流集中部にめっき導体が厚く形成されるため、断面形状は、上面の両端のエッジ部が上面や側面よりも盛り上がった形状となる。この盛り上がるめっき導体の大きさは電流密度の大きさと印加時間に比例し、電流密度が大きく印加時間が長くなるほど盛り上がるめっき導体も大きくなる。また、盛り上がるめっき導体の大きさは、下地導体層の幅や高さおよび線間の距離とも相関があり、特に、線間が狭くなるほど顕著に現れる。次に、逆電流を印加して局部エッチングを行うが、この時、逆電流の電流密度を正電流の電流密度よりも大きくすると、電流集中部のめっき導体から優先的にエッチングされるため、上面や側面のめっき導体はほとんど研削されずに、上面の両端のエッジ部の盛り上がっためっき導体が集中的に研削される。従って、盛り上がっためっき導体を集中的に研削するように局部エッチングの条件を設定すれば、下地導体層の断面形状の矩形を相似形で維持したまま表面導体層を積層できることになる。
【００１２】
また、直流電流による表面導体層の形成では、線間を狭くすると上面の両端の盛り上がっためっき導体が隣接するコイル線条と接続してショートするため、線間を狭くすることは困難である。しかし、めっき導体の形成と局部エッチングを交互に行って表面導体層を形成すると、下地導体層の断面形状の矩形を維持したまま表面導体層を形成することができるので、直流電流によって表面導体層を形成する場合に比べて、線間を狭くすることができる。
【００１３】
このように、断面形状がほぼ矩形の下地導体層の上に表面導体層を形成する際、通常の直流電流による電気めっきではコーナーやエッジ部に電流が集中するため下地導体層の形状を維持したまま表面導体層を形成することは困難であるのに対して、本発明のように電気めっきによるめっき導体の形成と局部エッチングを繰り返して表面導体層を形成すると、電流集中部に形成された余分なめっき導体を局部エッチングによって除去しながら電気めっきによってめっき導体を成長させていくので、核となる下地導体層の断面形状の矩形を相似形で維持したまま表面導体層を形成でき、その結果、コイル導体線条の断面形状が正確な矩形で、かつ、線間の狭い高占積の平面コイルを提供することができる。
【００１４】
請求項２に記載の発明は、下地導体層の厚さを２０μｍ〜２００μｍとする請求項１に記載の平面コイルの製造方法であって、下地導体層の厚さを２０μｍ〜２００μｍにしているため、断面形状が矩形となった下地導体層の電気抵抗は低く、給電部から離れた部分でも均一な厚さの表面導体層が形成できる。
【００１５】
請求項３に記載の発明は、表面導体層のめっき導体の形成のために流す正電流の電流密度を３〜６Ａ／ｄｍ^２とする請求項１に記載の平面コイルの製造方法であって、下地導体層の矩形を維持したまま、短時間で表面導体層を形成する最適の電流密度である。つまり、電流密度を小さくすると下地導体層の矩形を維持したまま表面導体層を形成しやすいが所定の厚さにするのに時間がかかり、一方、電流密度を大きくしすぎると、局部エッチングによって除去すべき不要な部分が厚く付くため、矩形の維持が困難になってしまう。
【００１６】
請求項４に記載の発明は、局部エッチングのために流す負電流の電流密度を表面導体層のめっき導体の形成のために流す正電流の電流密度の２〜３倍とする請求項１に記載の平面コイルの製造方法であって、局部エッチングのために流す負電流の電流密度をめっき導体の形成のために流す正電流の電流密度の２〜３倍としているために、導体形成時にコーナーやエッジ部などの電流集中部に形成されためっき導体を優先的にエッチングすることができ、核となる下地導体層の矩形となった形状を維持したまま表面導体層を形成することができる。つまり、逆電流の電流密度が正電流の電流密度に近いと、電流集中部のエッチングが不十分となって電流集中部に突起が発生し、一方、逆電流の電流密度が大きすぎると、電流集中部のエッチングが進みすぎるため、コーナーやエッジ部分が丸くなってしまう。
【００１７】
請求項５に記載の発明は、正電流の印加時間と逆電流の印加時間の比を１０：１〜１５：１の範囲とする請求項１に記載の平面コイルの製造方法であって、下地導体層の矩形を維持したまま、短時間で表面導体層を形成する最適の印加時間の比である。つまり、正電流の印加時間を短くすると下地導体層の矩形を維持したまま表面導体層を形成しやすいが所定の厚さにするのに時間がかかり、一方、正電流の印加時間を長くしすぎると、電流集中部に不要なめっき導体が厚く付きすぎ矩形を維持するのが困難になる。
【００１８】
請求項６に記載の発明は、めっき導体の形成と局部エッチングを繰り返す際の１サイクルの所要時間を０．１秒以下とする請求項１に記載の平面コイルの製造方法であって、１サイクルの所要時間を短くして頻繁にめっき導体の形成とエッチングを繰り返すことにより、核となる下地導体層の矩形となった形状を維持したまま表面導体層を形成することができる。
【００１９】
請求項７に記載の発明は、コイル導体線条の表面上に直流電流による電気めっきで平滑導体層を形成する請求項１に記載の平面コイルの製造方法であって、正電流と逆電流を交互に印加しながら形成した表面導体層の粗い表面上に、直流電流による電気めっきで平滑導体層を形成しているため、表面導体層の表面が酸化しにくくなり、コイル導体の電気抵抗の経時変化を防ぐことができる。
【００２０】
請求項８に記載の発明は、平滑導体層を形成するための直流電流の電流密度を３Ａ／ｄｍ^２以下とする請求項７に記載の平面コイルの製造方法であって、直流電流の電流密度を３Ａ／ｄｍ^２以下にすることによって、給電部近傍と離れた部分との電気めっきバラツキを無くし、かつ核となる下地導体層の矩形を維持したまま平滑導体層を形成することができる。
【００２１】
請求項９に記載の発明は、平滑導体層の厚さを表面導体層の厚さよりも薄くする請求項７に記載の平面コイルの製造方法であって、直流電流印加の電気めっきによって形成する平滑導体層の厚さが薄いために、核となる下地導体層の矩形となった形状を維持することができる。
【００２２】
請求項１０に記載の発明は、表面導体層および／または平滑導体層の形成に用いるめっき液を硫酸銅濃度６０〜１２０ｇ／ｌの硫酸銅めっき液とする請求項１または７に記載の平面コイルの製造方法であって、この濃度範囲のめっき液を用いると、局部エッチングを効率良く実施できるため、矩形を維持しやすいというだけでなく、経済的かつ液の管理も容易である。
【００２３】
以下、本発明の実施の形態における平面コイルの製造方法について、添付図面に従って説明する。
【００２４】
（実施の形態１）
図１（Ａ）〜（Ｆ）は、本発明の実施の形態１の平面コイル製造プロセスを説明するための概略図である。
【００２５】
まず、図１（Ａ）に示すように両面に３５μｍの下地導体層を形成した厚さ２０μｍの絶縁基板１を用意した。下地導体層２と絶縁基板１の構成材料は、各々、Ｃｕとポリイミドフィルムである。次に、図１（Ｂ）に示すように両面の下地導体層２および絶縁基板１を貫通するように、直径１０μｍのスルーホール３を設けた。次に、図１（Ｃ）に示すように両面の下地導体層の表面にレジスト５でパターンニングした。パターンニングには、１０μｍのドライフィルムを用い、レジスト幅６０μｍ、レジスト間スペース２０μｍの螺旋状のパターンを形成した。この際、パターンニングしたレジスト５がスルーホール３を被覆するようにしている。
【００２６】
次に図１（Ｄ）に示すようにレジスト５で被覆していない部分の下地導体層３を、塩化第２鉄水溶液を用いてエッチング除去した。この際、通常のエッチング時間よりも長くしてオーバーエッチングさせることにより、残った下地導体層２の断面形状を矩形にすることができる。次に、図１（Ｅ）に示すようにレジスト５を剥離させた。
【００２７】
その後、図１（Ｆ）に示すように硫酸銅濃度８０ｇ／ｌの硫酸銅めっき液を用いて、電流密度６Ａ／ｄｍ^２で印加時間３０ｍＳの正電流と、電流密度１８Ａ／ｄｍ^２で印加時間２ｍＳの負電流を交互に印加して、１０μｍの表面導体層６を形成し、コイル導体線条８を作製した。
【００２８】
（実施の形態２）
図２（Ａ）〜（Ｆ）は、本発明の実施の形態２の平面コイルの製造プロセスを説明するための概略図である。図２（Ａ）〜（Ｅ）までは上述の実施の形態１と全く同じプロセスであり、異なる点は図２（Ｆ）に示すプロセスのみである。
【００２９】
本発明の実施の形態１では、電流密度６Ａ／ｄｍ^２で印加時間３０ｍＳの正電流と、電流密度１８Ａ／ｄｍ^２で印加時間２ｍＳの負電流を交互に印加して、１０μｍの表面導体層を形成したが、本発明の実施の形態２では、電流密度６Ａ／ｄｍ^２で印加時間３０ｍＳの正電流と、電流密度１８Ａ／ｄｍ^２で印加時間２ｍＳの負電流を交互に印加して、８μｍの表面導体層６を形成した後、図２（Ｆ）に示すように電流密度２Ａ／ｄｍ^２の正電流を印加して２μｍの平滑導体層７を形成した。その他の条件は、実施の形態１と同様にしてコイルを形成した。
【００３０】
（比較例）
図３（Ａ）〜（Ｆ）は、比較技術の平面コイルの製造プロセスを説明するための概略図である。図３（Ａ）〜（Ｅ）に示すプロセスは本発明の実施の形態１のプロセスと同じであり、図３（Ｆ）のプロセスのみが本発明と異なる。
【００３１】
本発明の実施の形態１では、電流密度６Ａ／ｄｍ^２で印加時間３０ｍＳの正電流と、電流密度１８Ａ／ｄｍ^２で印加時間２ｍＳの負電流を交互に印加して、１０μｍの表面導体層を形成したが、比較例では、電流密度６Ａ／ｄｍ^２の正電流だけを印加し１０μｍの表面導体層６を形成した。その他の条件は、実施の形態１と同様にしてコイルを形成した。
【００３２】
以上のようにして作製した本実施の形態１，２および比較例の平面コイルの導体線条断面を図４（Ａ）、（Ｂ）に示す。図４（Ａ）に示したように、正電流と負電流を交互に印加して表面導体層６を形成した方が、図４（Ｂ）に示すように直流電流だけで表面導体層６を形成したものに比べて完全な矩形に近い形状をしている。比較例のものはコーナー部に表面導体層６が厚くめっき形成され矩形とは言いがたい形状となっている。以上のように、本発明の方法によれば、コイル断面がほぼ矩形に近い形状となるため、占積率の高いコイルを得ることができる。
【００３３】
なお、本発明の実施の形態１，２では、基板として両面に下地導体層として３５μｍのＣｕを形成した厚さ２０μｍのポリイミドフィルムを用い、スルーホール〜電気めっき工程を経て平面コイルを形成していったが、基板としては下地導体層を片面だけに形成しているものでも良く、また、下地導体層としてはＣｕに限定されるものではなく、導電性がありかつその後のエッチング工程によって断面形状を矩形にできる材料であれば問題はない。また、基板材料としてはポリイミドフィルムに限定されるものではなく、絶縁性を有しかつ電気めっき液に浸されないものであれば特に制限はない。また、レジストにはドライフィルムを用いたが、エッチング液に対する耐性があれば液状レジストでも可能で、パターンニングの方法についても特に限定するものではない。
【００３４】
【発明の効果】
本発明の実施の形態からもわかるように本発明の平面コイルの製造方法は、下地導体層上に表面導体層を形成するにあたり、正電流の印加によってめっき導体を形成するステップと正電流よりも大きい電流密度の逆電流を印加して前記正電流の印加で形成しためっき導体の一部を局部エッチングするステップとを同一めっき液中で繰り返し、下地導体層と表面導体層からなる断面形状が矩形のコイル導体線条を形成するため、核となる下地導体層の矩形を維持したまま表面導体層を形成でき、その結果、高占積率のコイル導体線条を有した平面コイルを提供することができる。
【図面の簡単な説明】
【図１】（Ａ）〜（Ｆ）本発明の実施の形態１の平面コイルの製造プロセスを示す概略図
【図２】（Ａ）〜（Ｆ）本発明の実施の形態２の平面コイルの製造プロセスを示す概略図
【図３】（Ａ）〜（Ｆ）比較例の平面コイルの製造プロセスを示す概略図
【図４】（Ａ）本発明の実施の形態１により形成した平面コイルの断面図
（Ｂ）比較例の平面コイルの断面図
【符号の説明】
１絶縁基板
２下地導体層
３スルーホール
４めっき層
５レジスト
６表面導体層
７平滑導体層
８コイル導体線条[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for manufacturing a planar coil having a high space factor which can be widely used for a voice coil of a speaker, an inductance of an electric circuit, a transformer, and the like.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, as electronic devices are generally reduced in size and thickness, there is a strong demand for planar coils used in these devices to be reduced in size and thickness. For that purpose, it is necessary to manufacture a planar coil having a narrow space and a small dead space, that is, a high space factor.
[0003]
Here, the space factor will be described. Here, the space factor refers to a rectangular area having a width equal to the arrangement pitch of the coil conductors and a height equal to the thickness of the coil conductors in a cross section perpendicular to the direction in which the coil conductors of the planar coil extend. It means the ratio of the sectional area of the coil conductor wire. Therefore, in order to obtain a planar coil with a high space factor, the cross-sectional shape of the coil conductor should be rectangular and the distance between the lines should be narrow.
[0004]
In order to manufacture a planar coil having a high space factor, a manufacturing method using a printed wiring technology has been conventionally proposed. As a typical technique, a method in which a subtra method and plating are combined is well known. In this method, a resist of a coil pattern is formed on the surface of a base conductor layer previously formed on an insulating substrate, and then the base conductor layer other than the resist-formed portion is removed by etching, and the base remaining after removing the resist is further removed. By performing electroplating with the conductor layer as a nucleus, the underlying conductor layer is reinforced with a plated conductor to produce a coil conductor wire.
[0005]
As prior art document information relating to the invention of this application, for example, Patent Document 1 is known.
[0006]
[Patent Document 1]
JP-A-7-142254
[Problems to be solved by the invention]
The method combining this subtra method and plating is a promising method for manufacturing a planar coil with a high space factor.However, since DC plating is applied to perform electroplating, the method can be applied to the top and side surfaces of the underlying conductor layer. As a result, a thick plated conductor is formed in a current concentrated portion such as a corner or an edge portion, and it is difficult to make the cross-sectional shape of the coil conductor wire rectangular. Further, in order to prevent the plated conductor thickly attached to the corner or the edge from coming into contact with the adjacent coil conductor, it is necessary to widen the space between the coils. For this reason, the above-described method is insufficient in terms of improving the space factor.
[0008]
Accordingly, an object of the present invention is to provide a method of manufacturing a flat coil having a high space factor with a rectangular cross-section of a coil conductor wire having an accurate cross section and a narrow space between the wires.
[0009]
[Means for Solving the Problems]
In order to solve the above problems, the present invention provides a method for forming a resist on a base conductor layer formed on an insulating substrate, etching the resist, removing the resist, plating the base conductor layer by applying a positive current, A method of forming a surface conductor layer by applying a reverse current having a current density larger than the current and locally etching a portion of the plating in the same plating solution to form a coil conductor wire having a rectangular cross section. Yes, it is possible to obtain a flat coil having a high space factor with a narrow space between wires.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
The invention according to claim 1 of the present invention includes a step of forming a resist so as to cover a portion to be a coil on a surface of a base conductor layer previously formed on at least one surface of an insulating substrate; Removing the underlying conductive layer by etching, removing the resist and exposing the underlying conductive layer having a substantially rectangular cross-sectional shape by the etching, and forming a surface conductive layer on the underlying conductive layer. In doing so, the step of forming a plated conductor by applying a positive current and the step of applying a reverse current having a current density larger than the positive current and locally etching a part of the plated conductor formed by applying the positive current are the same. A planar coil having a step of forming a coil conductor wire having a rectangular cross-sectional shape composed of the base conductor layer and the surface conductor layer repeatedly in a plating solution. It is a production method.
[0011]
Here, the mechanism of the growth of the surface conductor layer of the present invention will be briefly described. First, a positive current is applied on the underlying conductor layer to form a plated conductor. At this time, since the plated conductor is formed thick in the current concentrating portion, the cross-sectional shape is such that the edges at both ends of the upper surface are raised more than the upper surface and the side surfaces. The size of the raised plating conductor is proportional to the magnitude of the current density and the application time. The larger the current density is and the longer the application time, the larger the raised plating conductor becomes. Further, the size of the swelling plated conductor is also correlated with the width and height of the underlying conductor layer and the distance between the lines, and in particular, appears more remarkably as the distance between the lines becomes narrower. Next, local etching is performed by applying a reverse current. At this time, if the current density of the reverse current is larger than the current density of the positive current, etching is performed preferentially from the plating conductor in the current concentrated portion. The plated conductors on the edges at both ends of the upper surface are intensively ground without hardly grinding the plated conductors on the side surfaces. Therefore, if the conditions of the local etching are set so that the raised plated conductor is intensively ground, the surface conductor layer can be laminated while the rectangular shape of the cross-sectional shape of the base conductor layer is kept similar.
[0012]
Further, in the formation of the surface conductor layer by direct current, when the space between the lines is reduced, the raised plated conductors at both ends of the upper surface are connected to adjacent coil wires and short-circuited, so that it is difficult to reduce the space between the lines. However, if the surface conductor layer is formed by alternately performing the formation of the plated conductor and the local etching, the surface conductor layer can be formed while maintaining the rectangular shape of the cross-sectional shape of the base conductor layer. Can be narrowed as compared with the case of forming.
[0013]
As described above, when the surface conductor layer is formed on the base conductor layer having a substantially rectangular cross-section, the shape of the base conductor layer is maintained because the current is concentrated at the corners and edges in the usual electroplating using a direct current. While it is difficult to form the surface conductor layer as it is, if the surface conductor layer is formed by repeating the formation of the plated conductor by electroplating and local etching as in the present invention, the excess formed in the current concentration portion Since the plated conductor is grown by electroplating while removing the plated conductor by local etching, the surface conductor layer can be formed while maintaining the rectangular shape of the cross-sectional shape of the base conductor layer serving as the core in a similar shape, and as a result, It is possible to provide a planar coil having a rectangular shape in which the cross-sectional shape of the coil conductor wire is accurate and a narrow space between the wires.
[0014]
The invention according to claim 2 is the method for manufacturing a planar coil according to claim 1, wherein the thickness of the underlying conductor layer is 20 μm to 200 μm, and the thickness of the underlying conductor layer is 20 μm to 200 μm. The electric resistance of the base conductor layer having a rectangular cross-sectional shape is low, and a surface conductor layer having a uniform thickness can be formed even in a portion away from the power supply portion.
[0015]
The invention according to claim 3 is the method for manufacturing a planar coil according to claim 1, wherein the current density of the positive current flowing for forming the plated conductor of the surface conductor layer is 3 to 6 A / dm ² . This is an optimum current density for forming the surface conductor layer in a short time while maintaining the rectangular shape of the underlying conductor layer. In other words, when the current density is reduced, the surface conductor layer is easily formed while maintaining the rectangular shape of the underlying conductor layer, but it takes time to obtain a predetermined thickness. On the other hand, when the current density is too large, it is removed by local etching. Unnecessary portions to be formed are thickened, so that it becomes difficult to maintain the rectangle.
[0016]
According to a fourth aspect of the present invention, the current density of the negative current flowing for local etching is set to be two to three times the current density of the positive current flowing for forming the plated conductor of the surface conductor layer. In the method of manufacturing a planar coil, the current density of a negative current flowing for local etching is set to be two to three times the current density of a positive current flowing for forming a plated conductor. The plated conductor formed in the current concentrating portion such as the edge portion can be preferentially etched, and the surface conductor layer can be formed while maintaining the rectangular shape of the base conductor layer serving as a nucleus. That is, if the current density of the reverse current is close to the current density of the positive current, the etching of the current concentrating portion becomes insufficient and a projection is generated at the current concentrating portion. On the other hand, if the current density of the reverse current is too high, the current Since the etching of the concentrated portion proceeds too much, the corners and edges become round.
[0017]
The invention according to claim 5 is the method for manufacturing a planar coil according to claim 1, wherein the ratio of the application time of the positive current to the application time of the reverse current is in the range of 10: 1 to 15: 1. This is an optimum application time ratio for forming the surface conductor layer in a short time while maintaining the rectangular shape of the conductor layer. That is, if the application time of the positive current is shortened, it is easy to form the surface conductor layer while maintaining the rectangular shape of the underlying conductor layer, but it takes time to obtain a predetermined thickness, while the application time of the positive current is too long. In such a case, an unnecessary plating conductor is excessively attached to the current concentration portion, and it is difficult to maintain a rectangular shape.
[0018]
The invention according to claim 6 is the method for manufacturing a planar coil according to claim 1, wherein the time required for one cycle when the formation of the plated conductor and the local etching are repeated is 0.1 second or less. By repeating the formation and etching of the plated conductor frequently by shortening the required time, it is possible to form the surface conductor layer while maintaining the rectangular shape of the base conductor layer serving as a nucleus.
[0019]
The invention according to claim 7 is the method for manufacturing a flat coil according to claim 1, wherein the smooth conductor layer is formed on the surface of the coil conductor wire by electroplating using a direct current. Since the smooth conductor layer is formed by electroplating with a direct current on the rough surface of the surface conductor layer formed while applying alternately, the surface of the surface conductor layer is hardly oxidized and the electric resistance of the coil conductor with time Change can be prevented.
[0020]
The invention according to claim 8 is the method for manufacturing a planar coil according to claim 7, wherein the current density of the direct current for forming the smooth conductor layer is 3 A / dm ² or less. Is set to 3 A / dm ² or less, it is possible to eliminate the variation in electroplating between the vicinity of the power supply portion and the distant portion, and to form the smooth conductor layer while maintaining the rectangular shape of the base conductor layer serving as a core.
[0021]
The invention according to claim 9 is the method for manufacturing a planar coil according to claim 7, wherein the thickness of the smooth conductor layer is smaller than the thickness of the surface conductor layer, wherein the flat coil is formed by electroplating with application of a direct current. Since the thickness of the conductor layer is thin, the rectangular shape of the core underlying conductor layer can be maintained.
[0022]
The planar coil according to claim 1 or 7, wherein the plating solution used for forming the surface conductor layer and / or the smooth conductor layer is a copper sulfate plating solution having a copper sulfate concentration of 60 to 120 g / l. When a plating solution having this concentration range is used, local etching can be carried out efficiently, so that not only is it easy to maintain a rectangular shape, but also economical and easy to manage the solution.
[0023]
Hereinafter, a method for manufacturing a planar coil according to an embodiment of the present invention will be described with reference to the accompanying drawings.
[0024]
(Embodiment 1)
1 (A) to 1 (F) are schematic diagrams for explaining a planar coil manufacturing process according to Embodiment 1 of the present invention.
[0025]
First, as shown in FIG. 1A, an insulating substrate 1 having a thickness of 20 μm and a 35 μm underlying conductor layer formed on both surfaces was prepared. The constituent materials of the base conductor layer 2 and the insulating substrate 1 are Cu and a polyimide film, respectively. Next, as shown in FIG. 1B, through holes 3 having a diameter of 10 μm were provided so as to penetrate the underlying conductor layers 2 and the insulating substrate 1 on both surfaces. Next, as shown in FIG. 1C, the surfaces of the underlying conductor layers on both sides were patterned with a resist 5. For the patterning, a spiral pattern having a resist width of 60 μm and a space between the resists of 20 μm was formed using a 10 μm dry film. At this time, the patterned resist 5 covers the through hole 3.
[0026]
Next, as shown in FIG. 1 (D), the portion of the underlying conductive layer 3 not covered with the resist 5 was removed by etching using an aqueous ferric chloride solution. At this time, by performing over-etching with a longer etching time than usual, the cross-sectional shape of the remaining underlying conductor layer 2 can be made rectangular. Next, the resist 5 was peeled off as shown in FIG.
[0027]
Thereafter, as shown in FIG. 1 (F), using a copper sulfate plating solution having a copper sulfate concentration of 80 g / l, a positive current of 30 mS for an application time of 6 A / dm ² and an application time of 18 A / dm ² for a current density of 18 A / dm ² By applying a negative current of 2 mS alternately, a surface conductor layer 6 of 10 μm was formed, and a coil conductor wire 8 was produced.
[0028]
(Embodiment 2)
FIGS. 2A to 2F are schematic diagrams for explaining a manufacturing process of the planar coil according to the second embodiment of the present invention. 2 (A) to 2 (E) are exactly the same processes as in the above-described first embodiment, and the only difference is the process shown in FIG. 2 (F).
[0029]
In the first embodiment of the present invention, a positive current with an application time of 30 ms at a current density of 6 A / dm ² and a negative current with an application time of 2 ms at a current density of 18 A / dm ² are alternately applied to form a 10 μm surface conductor layer. It was formed, in the second embodiment of the present invention, a positive current application time 30mS at a current density of 6A / dm ^2, by applying a negative current application time 2mS alternately at a current density of 18A / dm ^2, 8 [mu] m of After forming the surface conductor layer 6, as shown in FIG. 2 (F), a positive current having a current density of 2 A / dm ² was applied to form a 2 μm smooth conductor layer 7. Other conditions were the same as in the first embodiment to form a coil.
[0030]
(Comparative example)
FIGS. 3A to 3F are schematic diagrams for explaining a manufacturing process of a planar coil according to a comparative technique. The processes shown in FIGS. 3A to 3E are the same as those of the first embodiment of the present invention, and only the process of FIG. 3F is different from the present invention.
[0031]
In the first embodiment of the present invention, a positive current with an application time of 30 ms at a current density of 6 A / dm ² and a negative current with an application time of 2 ms at a current density of 18 A / dm ² are alternately applied to form a 10 μm surface conductor layer. However, in the comparative example, only a positive current having a current density of 6 A / dm ² was applied to form a 10 μm surface conductor layer 6. Other conditions were the same as in the first embodiment to form a coil.
[0032]
FIGS. 4A and 4B show cross sections of the conductor wires of the planar coils of the first and second embodiments and the comparative example manufactured as described above. As shown in FIG. 4A, forming the surface conductor layer 6 by applying a positive current and a negative current alternately, as shown in FIG. The shape is closer to a perfect rectangle than the one formed. In the case of the comparative example, the surface conductor layer 6 is formed by plating thick at the corners, and has a shape that cannot be said to be rectangular. As described above, according to the method of the present invention, since the coil cross section has a substantially rectangular shape, a coil having a high space factor can be obtained.
[0033]
In the first and second embodiments of the present invention, a 20-μm-thick polyimide film in which 35 μm Cu is formed as a base conductor layer on both sides as a substrate is used, and a planar coil is formed through a through-hole to an electroplating process. However, the substrate may be one in which the underlying conductor layer is formed on only one side, and the underlying conductor layer is not limited to Cu, but may be conductive and have a cross-sectional shape by a subsequent etching process. There is no problem as long as the material can be made rectangular. Further, the substrate material is not limited to a polyimide film, and is not particularly limited as long as it has insulating properties and is not immersed in an electroplating solution. Although a dry film is used as the resist, a liquid resist can be used as long as it has resistance to an etching solution, and the patterning method is not particularly limited.
[0034]
【The invention's effect】
As can be seen from the embodiments of the present invention, the method for manufacturing a planar coil of the present invention is based on forming a surface conductor layer on a base conductor layer, by forming a plated conductor by applying a positive current, and The step of applying a reverse current of a large current density and locally etching a portion of the plated conductor formed by the application of the positive current is repeated in the same plating solution, and the cross-sectional shape of the base conductor layer and the surface conductor layer is rectangular. In order to form a surface conductor layer while maintaining the rectangular shape of the underlying conductor layer serving as a core, a planar coil having a coil conductor filament with a high space factor is provided. Can be.
[Brief description of the drawings]
1A to 1F are schematic views showing a manufacturing process of a planar coil according to a first embodiment of the present invention; FIGS. 2A to 2F are schematic views of a planar coil according to a second embodiment of the present invention; FIGS. 3A to 3F are schematic views showing a manufacturing process of a planar coil of a comparative example. FIGS. 4A to 4F are cross-sectional views of a planar coil formed according to the first embodiment of the present invention. FIG. (B) Cross-sectional view of a planar coil of a comparative example.
DESCRIPTION OF SYMBOLS 1 Insulating substrate 2 Base conductor layer 3 Through hole 4 Plating layer 5 Resist 6 Surface conductor layer 7 Smooth conductor layer 8 Coil conductor wire

Claims

絶縁基板の少なくとも一方の面に予め形成した下地導体層の表面にコイルとなる部分を被覆するようにレジストを形成する工程と、レジストを形成した以外の部分の下地導体層をエッチングにより除去する工程と、前記レジストを除去し前記エッチングによって断面形状がほぼ矩形となった下地導体層を露出させる工程と、前記下地導体層上に表面導体層を形成するにあたり正電流の印加によってめっき導体を形成するステップと正電流よりも大きい電流密度の逆電流を印加して前記正電流の印加で形成しためっき導体の一部を局部エッチングするステップとを同一めっき液中で繰り返し、前記下地導体層と前記表面導体層からなる断面形状が矩形のコイル導体線条を形成する工程を有する平面コイルの製造方法。A step of forming a resist so as to cover a portion to be a coil on a surface of a base conductor layer formed in advance on at least one surface of the insulating substrate; Removing the resist and exposing a base conductor layer having a substantially rectangular cross-sectional shape by the etching, and forming a plated conductor by applying a positive current when forming a surface conductor layer on the base conductor layer. Repeating the step and the step of applying a reverse current having a current density greater than the positive current and locally etching a part of the plated conductor formed by the application of the positive current in the same plating solution, to obtain the base conductor layer and the surface A method for manufacturing a planar coil, comprising a step of forming a coil conductor wire having a rectangular cross section made of a conductor layer.

下地導体層の厚さを２０μｍ〜２００μｍとする請求項１に記載の平面コイルの製造方法。The method for manufacturing a planar coil according to claim 1, wherein the thickness of the base conductor layer is 20 μm to 200 μm.

表面導体層のめっき導体の形成のために流す正電流の電流密度を３〜６Ａ／ｄｍ^２とする請求項１に記載の平面コイルの製造方法。Manufacturing method of a flat coil according to claim 1 for the current density of the positive current flowing for the formation of the plating conductor surface conductive layer and 3~6A / dm ^2.

局部エッチングのために流す負電流の電流密度を表面導体層のめっき導体の形成のために流す正電流の電流密度の２〜３倍とする請求項１に記載の平面コイルの製造方法。2. The method for manufacturing a planar coil according to claim 1, wherein the current density of the negative current flowing for local etching is set to be two to three times the current density of the positive current flowing for forming the plated conductor of the surface conductor layer.

正電流の印加時間と逆電流の印加時間の比を１０：１〜１５：１の範囲とする請求項４に記載の平面コイルの製造方法。The method for manufacturing a planar coil according to claim 4, wherein the ratio of the application time of the positive current to the application time of the reverse current is in the range of 10: 1 to 15: 1.

めっき導体の形成と局部エッチングを繰り返す際の１サイクルの所要時間を０．１秒以下とする請求項１に記載の平面コイルの製造方法。2. The method for manufacturing a planar coil according to claim 1, wherein the time required for one cycle when the formation of the plated conductor and the local etching are repeated is set to 0.1 second or less.

コイル導体線条の表面上に直流電流による電気めっきで平滑導体層を形成する工程を付加した請求項１に記載の平面コイルの製造方法。2. The method for manufacturing a flat coil according to claim 1, further comprising a step of forming a smooth conductor layer on the surface of the coil conductor wire by electroplating using a direct current.

平滑導体層を形成するための直流電流の電流密度を３Ａ／ｄｍ^２以下とする請求項７に記載の平面コイルの製造方法。Manufacturing method of a flat coil according to claim 7, the current density of the direct current for forming a smooth conductor layer and 3A / dm ² or less.

平滑導体層の厚さを表面導体層の厚さよりも薄くする請求項７に記載の平面コイルの製造方法。The method for manufacturing a planar coil according to claim 7, wherein the thickness of the smooth conductor layer is smaller than the thickness of the surface conductor layer.

表面導体層および／または平滑導体層に用いるめっき液を硫酸銅濃度６０ｇ／ｌ〜１２０ｇ／ｌの硫酸銅めっき液とする請求項１または７に記載の平面コイルの製造方法。The method for manufacturing a planar coil according to claim 1 or 7, wherein the plating solution used for the surface conductor layer and / or the smooth conductor layer is a copper sulfate plating solution having a copper sulfate concentration of 60 g / l to 120 g / l.