JP3830680B2

JP3830680B2 - Rolled copper foil for flexible printed circuit board and method for producing the same

Info

Publication number: JP3830680B2
Application number: JP37189298A
Authority: JP
Inventors: 隆紹波多野; 善雄黒沢
Original assignee: Nippon Mining and Metals Co Ltd
Current assignee: Nippon Mining Holdings Inc
Priority date: 1998-12-28
Filing date: 1998-12-28
Publication date: 2006-10-04
Anticipated expiration: 2018-12-28
Also published as: JP2000192172A

Description

【０００１】
【産業上の利用分野】
本発明は，フレキシブルプリント回路基板（Flexible printed circuit）等の可撓性配線部材の用途として好適な軟化特性を有する圧延銅箔に関するものである。
【０００２】
【従来の技術】
有機物を基材としたプリント配線基板は，ガラスエポキシおよび紙フェノール基板を構成材料とする硬質銅張積層板（リジット）と，ポリイミドおよびポリエステル基板を構成材料とする可撓性銅張積層基板（フレキシブル）とに大別され，プリント配線基板の導電材としては主として銅箔が使用されている。銅箔はその製造方法の違いにより電解銅箔と圧延銅箔に分類される。
【０００３】
上記プリント配線基板のうち，フレキシブルプリント回路基板（FPC）は，樹脂基板に銅箔をラミネートし，接着剤あるいは加熱加圧により一体化して形成される。近年では高密度実装の有効な手段として，ビルドアップ基板と呼ばれる多層配線基板が多く用いられている。このFPCの構成部材となる銅箔には，主に圧延銅箔が用いられている。
【０００４】
FPCは，プリンターのヘッド部やハードディスク内の駆動部等の可動部分への配線が必要とされる場所に広く使用され，100万回以上の屈曲が繰り返される。近年の装置の小型化や高水準化に伴い，この屈曲性への要求はより高度化している。
【０００５】
FPCに使用される銅箔の素材には，主にタフピッチ銅（酸素含有量100〜500 ppm）が用いられる。このタフピッチ銅箔は，インゴットを熱間圧延した後，所定の厚さまで冷間圧延と焼鈍とを繰り返して製造される。その後，樹脂基板との接着性を向上させるため，銅箔には表面に粗化めっきが施される。粗化めっき後の銅箔は，裁断された後，樹脂基板と貼り合わせられる。銅箔と樹脂との貼りあわせには，例えばエポキシ等の熱硬化性樹脂からなる接着剤が用いられ，張り合わせ後130〜170℃の温度で1〜2時間加熱して硬化させる。つぎに，銅箔をエッチングして種々の配線パターンを形成する。
【０００６】
銅箔の屈曲性は再結晶焼鈍を行うことにより圧延上がりよりも著しく向上する。そこで銅箔は焼鈍状態でFPCの構成部材として使用されるが，この焼鈍は粗化めっきして裁断した後に加熱処理を行うか，銅箔を樹脂基板と接着する際の加熱で兼ねる。このように，焼鈍状態の銅箔を最初から用いず製造工程の中間で焼鈍を行う理由は，焼鈍後の軟質状態では裁断や樹脂基盤との貼りあわせの際に銅箔が変形したり，銅箔にしわが生じたりするためであり，圧延上がりの硬質の状態の方がFPCの製造性の点からは有利なためである。
【０００７】
FPCの屈曲性を高めるためには，その素材となる圧延銅箔の屈曲性を高めることが有効である。焼鈍後の銅箔の屈曲性は，立方体集合組織が発達するほど向上する。また，この立方体集合組織を発達させるためには，銅箔の製造プロセスにおいて，最終圧延での加工度を高くすること，および最終圧延直前の焼鈍での結晶粒径を小さくすることが効果的である（特願平10-101858)。
【０００８】
ところが，このようなプロセスで製造した銅箔は，圧延で蓄積される塑性歪みが増大するため軟化温度が著しく低下し，場合によっては，室温で保管していても保管期間が長期に及ぶと軟化することがある。上述したように，すでに軟化した銅箔を用いてFPCを製造すると，銅箔が変形する等の問題が生じ，FPCの製造性が著しく低下する。したがって，上記の製造プロセスを選択して銅箔の屈曲性を向上させる場合，同時に銅箔の軟化温度を適度に高くする必要がある。
【０００９】
このように圧延銅箔が室温で保管中に軟化する問題は特開平10-230303でも指摘されていが，この発明では室温軟化の問題を回避する手段として50〜90%と低い圧延加工度で銅箔を製造することを提唱している。しかし，このような低い圧延加工度で銅箔を製造すると銅箔の屈曲性は著しく低下するため，屈曲性が優れた銅箔を製造する場合に，この手段を用いることはできない。
【００１０】
【発明が解決しようとする課題】
本発明の目的は，高屈曲性圧延銅箔の軟化温度を適度に高めて保管中の軟化に伴うトラブルを解消することにより，優れた屈曲性と適度な軟化特性を併せ持つFPC用圧延銅箔を提供することである。
【００１１】
【課題を改善するための手段】
すなわち本発明は，上記の問題点を解決したものであり，（１）S濃度が0.0005〜0.0020重量%，Ag，As，Sb，Bi，Se，Te，PbおよびSnの各成分の内一種以上の合計量が0.004 0重量%以下，酸素濃度が0.0100〜0.0500重量%，厚さが5〜50μm，200℃で30分間の焼鈍後の圧延面のX線回折で求めた200面の強度（I）が微粉末銅のX線回折で求めた200面の強度（I₀）に対しI／I₀＞20.0であり，120〜150℃の半軟化温度を有し，室温において継続して300 N／mm^２以上の引張り強さを保持し優れた屈曲性と適度な軟化特性を有することを特徴とする，フレキシブルプリント回路基板用圧延銅箔。
【００１２】
（２）200℃で30分間加熱した後の残留抵抗比が10〜140であることを特徴とする上記（１）の圧延銅箔。
（３）インゴットを熱間圧延した後，冷間圧延と焼鈍とを繰り返し，最後に冷間圧延で箔に仕上げる工程で製造し，最後の冷間圧延前の焼鈍を，加熱炉の温度が500℃以上で，この焼鈍で得られる再結晶粒の平均粒径が5〜20μmになる条件下で行ない，焼鈍後5℃／秒以上の冷却速度で材料を100℃以下の温度まで冷却し，最後の冷間圧延の加工度を90.0%を超える値とし，優れた屈曲性と適度な軟化特性を有する上記（１）及び又は（２）の圧延銅箔を得ることを特徴とするフレキシブル回路基板用圧延銅箔の製造方法に関するものである。
【００１３】
銅箔を高加工度または微細結晶粒のプロセスで製造して立方体集合組織を発達させれば，屈曲性は向上するが，軟化温度が低くなり過ぎる。しかし，素材の微量成分をコントロールすることにより軟化温度を高めると，適度な軟化温度を有する銅箔を得ることが可能となる。
【００１４】
ここでいう適度な軟化温度とは，
(1) 銅箔の圧延上がりの引張り強さは400〜500 N／mm^２であるが，30℃で１年間放置した場合であっても300 N／mm^２以上の引張り強さを保つこと，
(2) 粗化めっきして裁断した後の熱処理または樹脂基板と接着する際の熱処理で，銅箔が軟化すること，
の２つの条件によって規定され，30分間焼鈍の際の半軟化温度（引張強さが焼鈍前と完全に軟化したときの中間の値になるときの焼鈍温度）でいえば，120〜150℃の範囲に相当する。
【００１５】
微量成分をコントロールして軟化温度を高める手段としては，
▲１▼タフピッチ銅を溶製する際に，合金元素を微量に添加する方法
▲２▼インゴットを箔に加工する過程で，不純物元素を固溶状態にする方法（不純物は析出状態よりも固溶状態の方が軟化抑制効果が著しく大きい）
の2通りがあげられる。本発明は，タフピッチ銅に新たに合金元素を添加することなく，従来のタフピッチ銅中に含有されている不純物を利用し，▲２▼の手段により圧延銅箔の軟化温度を高めることを主旨とする。
【００１６】
銅中に比較的高濃度で含有され，軟化特性に極めて大きな影響を及ぼす不純物元素として硫黄があげられる。Cu₂S粒子として存在する場合の硫黄の軟化抑制効果は小さいが，銅中に溶解した状態の硫黄は軟化を著しく抑制する。本発明者らは，この硫黄を適度に固溶させれば，FPC用圧延銅箔として好適な軟化温度が得られることを見出した。
【００１７】
また，固溶硫黄濃度を調整するためには，最終圧延前の焼鈍（最終焼鈍）における硫黄の固溶／析出挙動を制御すればよいことを知見した。すなわち，固体銅中の硫黄の平衡溶解度は温度が高くなるほど増大するため，最終焼鈍での加熱温度を高くすると銅中の硫黄の固溶濃度が増加し，その後圧延加工を加えた後の材料の軟化温度が上昇する。
【００１８】
また，最終焼鈍での加熱時間も，Cu₂SがSとして固溶する反応の進行の程度を左右する重要な因子であった。さらに，加熱中にSを固溶させても，その後の冷却速度が遅いと冷却の過程でSがCu₂Sとして析出するため，所定の速度以上で加熱後の冷却を行う必要がある。
なお，不純物硫黄の固溶／析出で半軟化温度をコントロールする場合，タフピッチ銅に含有されている硫黄以外の不純物を所定のレベル以下に規制した方が，より正確に軟化温度を調整できる。
【００１９】
本発明に関わる圧延銅箔の限定理由を以下に説明する。
本発明では，圧延銅箔を室温において継続して300Ｎ／mm^２以上の引張り強さを保持することを目標とした。より望ましくは30℃において1年間保管した場合であっても300N／mm^２以上の引張り強さを保持できることである。
【００２０】
ここで，30℃とは日本国内の年間平均気温を超える温度に相当し，銅箔がFPCに加工されるまでの保管期間は長くても１年間である。また，引張り強さが300 N／mm^２以上であれば，銅箔を加工中にしわが生じる等のトラブルは発生しない。したがって，30℃で１年間放置しても300 N／mm^２以上の引張り強さを保持できれば実用上問題はない。このような軟化特性は，30分間焼鈍したときの半軟化温度に換算すると，120℃以上の温度に相当する。
【００２１】
一方，30分間焼鈍したときの半軟化温度が150℃を超えると，粗化めっきして裁断した後の熱処理または樹脂基板と接着する際の熱処理で銅箔が軟化しないことがある。そこで，30分間焼鈍したときの半軟化温度を120〜150℃に規定した。
【００２２】
FPCの屈曲性を高めるためには，銅箔の屈曲性を高める必要がある。銅箔は再結晶状態でFPC中に組み込まれるが，純Cuの再結晶集合組織である立方体集合組織を発達させれば，銅箔の屈曲性は向上する。満足できる屈曲性が得られるときの立方体集合組織の発達度は，X線回折で求めた（200）面の強度が微粉末銅のX線回折で求めた（200）面の強度（I₀）に対し I／I₀＞20.0の関係であることで規定される。ここで，200℃で30分間の焼鈍は，X線強度の測定に際し，銅箔を再結晶させるために行うものである。
【００２３】
銅中の全S量を分析することは容易であるが，固溶したSだけの濃度を分析することは不可能である。この固溶S濃度は，間接的に残留抵抗比（RRR値）を測定することで知ることができる。RRR値は，293 Kと4.2 Kでの比抵抗値の比（ρ(293K)／ρ(4.2 K)）で定義される。純銅の比抵抗ρは，ρ₀＋ρ_tで表される。
【００２４】
ここで，ρ₀は残留抵抗値とよばれ，温度に依存せず，不純物の固溶量が増えると増加する。また，ρ_tは格子振動による散乱の項であり，温度が高くなると増加する。室温でのρはρ_t支配で金属固有の値となり，極低温でのρはρ₀支配となる。したがって，Sの固溶濃度が高くなると，ρ_tすなわちρ(293K)は変化しないが，ρ₀すなわちρ(4.2 K)が大きくなるため，RRR値が小さくなる。なお，固溶不純物以外に圧延で生じた塑性歪みもρ₀の値に影響を及ぼすため，この歪みを熱処理で除去してからRRR値を測定する必要がある。
【００２５】
本発明者らは，200℃で30分間加熱し塑性歪みを除去した後のRRR値を10〜140の範囲に調整すれば，このときの固溶S濃度に応じて好適な軟化特性が得られることを知見した。一方，RRR値が140を超える場合には半軟化温度が120℃を下回り，10未満の場合には半軟化温度が150℃を超える。
120℃以上の半軟化温度すなわち140以下のRRR値に相当する固溶S濃度を得るためには，全硫黄濃度を0.0005重量%以上とする必要がある。
【００２６】
一方，全硫黄濃度が0.0020重量%を超えると，硫黄の固溶濃度が高くなり過ぎ，RRR値が10未満となって半軟化温度が150℃を超える。また，平衡固溶度を超える過剰の硫黄はCu₂Sとして析出するため，全硫黄濃度が0.0020重量%を超えると，このCu₂S介在物による屈曲性の低下が著しくなる。そこで，硫黄濃度を0.0005〜0.0020重量%に規定した。
【００２７】
Ag，As，Sb，Bi，Se，Te，PbおよびSnは，通常のタフピッチ銅中に極微量含有されている不純物のうち，半軟化温度への影響が大きい元素である。したがって，硫黄の固溶濃度で半軟化温度をコントロールする場合，これら不純物の濃度を低レベルに抑えた方が，半軟化温度のコントロールが容易になる。
【００２８】
Ag，As，Sb，Bi，Se，Te，PbおよびSnはその各成分の内一種以上の合計で0.0040重量%以下にすることが望ましく，0.0040重量%を超えると，硫黄の固溶濃度が同じでも半軟化温度に大きなばらつきが生じたり，硫黄の固溶濃度によっては半軟化温度が150℃を超えたりする。
【００２９】
通常純度の無酸素銅は，酸素濃度が低い影響として，タフピッチ銅よりも軟化温度が著しく高いことが知られている。また，タフピッチ銅中に過剰に含有された酸素は，Cu₂Oの介在物を形成する。酸素濃度を0.0100〜0.0500重量%に規定した理由は，酸素濃度が0.0100重量%未満の状態で硫黄を固溶状態にすると半軟化温度が150℃を超え，酸素濃度が0.0500重量%を超えるとCu₂O介在物が増大し屈曲性が低下するためである。
【００３０】
銅箔の厚みについては，薄いほど曲げ部の外周に生じる歪みが減少するため，屈曲性が向上する。銅箔の厚さが50μmを超えると，立方体集合組織を発達させても所望の屈曲性は得られない。一方，銅箔の厚さを5μm未満にすると，箔の強度が低くなり過ぎ，破断などにより箔の取り扱いが困難となる。そこで銅箔の厚みを5〜50μmとした。
【００３１】
つぎに，優れた屈曲性と120〜150℃の半軟化特性を得るための製造プロセスを規定した理由について説明する。本発明に関わる圧延銅箔は，インゴットを熱間圧延した後，冷間圧延と焼鈍とを繰り返し，最後に加工度90 .0%以上の冷間圧延で仕上げられるが，90 .0%を超える値と高い圧延加工度が採用される理由は，優れた屈曲性を得るための指標となる20.0を超えるI／I₀値を得るためには90.0 %を超える値の加工度が必要なためである。
【００３２】
このプロセスにおいて硫黄の固溶量を決定するのは最終冷間圧延の直前の焼鈍（最終焼鈍）である。最終焼鈍は一般的に連続焼鈍ラインを用いて行われるが，この焼鈍において，目標とする硫黄の固溶濃度（RRR値）を得るためには，炉の温度を500℃以上とすることが必要条件となる。温度が500℃より低いと，加熱時間をいくら長くしても，十分な硫黄の固溶濃度が得られず，RRR値が140を超え，半軟化温度が120℃より低くなる。
【００３３】
また，硫黄の固溶濃度は温度だけではなく加熱時間の影響をも受ける。目標の硫黄固溶濃度を得るための加熱温度と時間には種々の組み合わせがあるが，最終焼鈍後の再結晶粒径を指標とし，その平均粒径が5μm以上になるように温度と時間を設定する。
【００３４】
平均粒径が5μm未満の場合はRRR値が140を超え，半軟化温度が120℃より低くなる。また，平均粒径が20μmを超えると，加工度を90.0 %を超える値としてもI／I₀値が20.0以下となり満足できる屈曲性が得られない。そこで，最終焼鈍を，加熱炉の温度が500℃以上で，結晶粒径が5〜20μmになる条件に規定した。
【００３５】
さらに，加熱後に徐冷すると固溶したSがCu₂Sとして析出するが，5℃／秒以上の冷却速度で100℃以下の温度まで冷却すると，このような固溶Sの析出を防止できる。
【００３６】
一方，100℃までの冷却速度が5℃／秒未満の場合，固溶S濃度が低下し，RRR値が140を超え，半軟化温度が120℃より低くなる。
なお，上記最終焼鈍を熱間圧延で兼ねることもできるが，この場合も圧延終了温度を500℃以上とすること，圧延後の結晶粒径を5〜20μmとすること，および5℃／秒以上で100℃以下まで冷却することが必要である。
【００３７】
【実施例】
以下，本発明の態様を実施例により説明する。
表１のＮo．１〜Ｎo．１６に示す成分の材料から厚さ200 mm，幅600 mmの銅インゴットを製造し，熱間圧延により10 mmまで圧延した。
【００３８】
【表１】

【００３９】
つぎに，焼鈍と冷間圧延を繰り返し，厚さtommの圧延上がりの板を得た。この板を焼鈍して再結晶させ，酸化スケールを除去した後，所定の厚みt mmまで冷間圧延した。ここで，最後の冷間圧延での加工度はRは，
【数１】
R = (to−t) / to × 100 (%)
で与えられる。また，最終冷間圧延前の焼鈍では，焼鈍後の結晶粒径を圧延方向に直角な断面において切断法で測定した。
【００４０】
このように種々の中間焼鈍条件および最終圧延加工度で製造した銅箔試料について以下の特性を評価した。
（１）立方体集合組織
試料を200℃で30分間加熱した後，圧延面のX線回折で求めた(200)面強度の積分値（I）求めた。この値をあらかじめ測定しておいた微粉末銅の(200)面強度の積分値（I₀）で割り，I／I₀の値を計算した。
【００４１】
（２）屈曲性
試料を200℃で30分間加熱して再結晶させた後，図１に示す装置により，屈曲疲労寿命の測定を行った。この装置は，発振駆動体４に振動伝達部材３を結合した構造になっており，被試験銅箔は１は，矢印で示したねじ２の部分と３の先端部の計４点で装置に固定される。振動部３が上下に駆動すると，銅箔１の中間部は，所定の曲率半径rでヘアピン状に屈曲される。本試験では，以下の条件下で屈曲を繰り返した時の破断までの回数を求めた。
【００４２】
試験片幅12.7 mm，試験片長さ：200 mm，試験片採取方向：試験片の長さ方向が圧延方向と平行になるように採取，曲率半径r：2.5 mm，振動ストローク：25 mm，振動速度：1500回／分
なお，屈曲疲労寿命が3万回以上の場合に，優れた屈曲性を有していると判断した。また，この試験は加速試験であり，実際にFPCが使用させる条件よりも厳しい条件下で行っている。
【００４３】
（３）半軟化温度
種々の温度で30分間の焼鈍を行なった後の引張り強さを測定した。そして，焼鈍後の引張り強さが，圧延上がりの引張り強さと300℃で30分間焼鈍し完全に軟化させた後の引張り強さとの中間の値になるときの焼鈍温度を求めた。半軟化温度が120〜150℃の範囲であれば，適正な軟化特性を有していると判断した。
【００４４】
（４）室温での軟化挙動
圧延上がりの材料を30℃に調整した恒温槽中に保管し，保管開始から1ヶ月毎に引張り強さを測定し，引張り強さが300 N／mm^２以下の値になるまでの期間を求めた。この評価は12ヶ月間まで継続した。
【００４５】
（５）比抵抗（RRR値）
200℃で30分焼鈍後の試料について，液体ヘリウム中（4.2 K）および室温（293 K）で比抵抗ρを測定し，両者の比（ρ(293K)／ρ(4.2 K)）を求めた。
【００４６】
表２に評価した試料の加工履歴と特性を示す。
【００４７】
【表２】

本発明に関わる圧延銅箔のＮo．１〜Ｎo．１６は，焼鈍を行うと立方体集合組織が発達して（200）面のI／I₀が20.0を超え，その結果として3万回以上の優れた屈曲寿命を示している。また，RRR値が10〜140で，半軟化温度が目標の120〜150℃の範囲であり，室温（30℃）で1年間保管しても引張強さが300 N／mm^２以上の値を保っている。
【００４８】
一方，比較例のNo. 1および2はS濃度が0.0005重量 %より低いため，RRR値が140を超え，半軟化温度が120℃よりも低く，30℃の保管で1年以内に引張強さが300 N／mm^２以下に低下している。
No.３はS濃度が0.0020重量%を超えるため，RRR値が10未満であり，半軟化温度が150℃を超えている。また，過剰のSがCu₂S介在物として析出したため，（200）面のI／I₀が20.0を超えているにもかかわらず，屈曲回数は目標の3万回に満たない。
【００４９】
No.4は不純物であるAg，As，Sb，Bi，Se，Te，PbおよびSnの合計量が0.004重量%を超えているため，RRR値が10未満であり，半軟化温度が150℃を超えている。
No.5は酸素濃度が0.0100重量%より低いため，RRR値が20以上であるにもかかわらず，半軟化温度が150℃を超えている。
No.6は酸素濃度が500 ppmを超えているため，Cu₂O介在物が増大し，200面のI/I₀が20.0を超えているにもかかわらず，屈曲回数が3万回未満の低い値を示している。
【００５０】
No.7は圧延前の焼鈍における炉の温度が500℃より低いため，No.8はこの焼鈍で得られる結晶粒径が5μmより小さいため，RRR値が140を超え，半軟化温度が120℃よりも低く，30℃の保管で1年以内に引張強さが300 N／mm^２以下に低下している。
【００５１】
No.9は圧延前の焼鈍で得られる結晶粒径が20μmより大きいため，（200）面のI／I₀が20.0より小さく，屈曲回数が3万回より少ない。
No.10は厚さが50μmを超えているため，立方体集合組織が発達しているにもかかわらず，屈曲回数が3万回未満である。
No.11は圧延前の焼鈍における冷却速度が5℃/秒より遅いため，RRR値が140を超え，半軟化温度が120℃よりも低い。
【００５２】
【発明の効果】
本発明のフレキシブルプリント回路用圧延銅箔は優れた屈曲性を有する。また，適度な軟化温度を有し，かつ保管中に軟化したりあるいは焼鈍を行っても軟化しないといったトラブルが生じないため，フレキシブルプリント回路基板としての好ましい特性を有する。
【図面の簡単な説明】
【図１】屈曲疲労寿命の測定を行うために使用した屈曲試験装置の説明図である。
【符号の説明】
１銅箔
ねじ
振動伝達部材
発振駆動体[0001]
[Industrial application fields]
The present invention relates to a rolled copper foil having softening characteristics suitable for use as a flexible wiring member such as a flexible printed circuit board.
[0002]
[Prior art]
Printed circuit boards based on organic materials are rigid copper-clad laminates (rigid) composed of glass epoxy and paper phenolic substrates, and flexible copper-clad laminates (polyflexible) composed of polyimide and polyester substrates. Copper foil is mainly used as a conductive material for printed wiring boards. Copper foils are classified into electrolytic copper foils and rolled copper foils depending on the manufacturing method.
[0003]
Among the printed wiring boards, a flexible printed circuit board (FPC) is formed by laminating a copper foil on a resin board and integrating them with an adhesive or heat and pressure. In recent years, a multilayer wiring board called a build-up board is often used as an effective means for high-density mounting. A rolled copper foil is mainly used as a copper foil as a constituent member of this FPC.
[0004]
FPC is widely used in places where wiring to movable parts such as printer heads and drive units in hard disks is required, and it bends over 1 million times. With the recent miniaturization and higher level of equipment, the demand for this flexibility has become more sophisticated.
[0005]
The copper foil used for FPC is mainly made of tough pitch copper (oxygen content of 100 to 500 ppm). This tough pitch copper foil is manufactured by hot rolling an ingot and then repeatedly cold rolling and annealing to a predetermined thickness. Thereafter, the surface of the copper foil is roughened to improve the adhesion to the resin substrate. The copper foil after the rough plating is cut and then bonded to the resin substrate. For bonding the copper foil and the resin, for example, an adhesive made of a thermosetting resin such as epoxy is used. After the lamination, the adhesive is heated and cured at a temperature of 130 to 170 ° C. for 1 to 2 hours. Next, the copper foil is etched to form various wiring patterns.
[0006]
The bendability of the copper foil is remarkably improved over the rolling up by performing recrystallization annealing. Therefore, copper foil is used as an FPC component in the annealed state, but this annealing can be either heat treatment after rough plating and cutting, or heating when bonding the copper foil to the resin substrate. In this way, the reason for annealing in the middle of the manufacturing process without using the annealed copper foil from the beginning is that in the soft state after annealing, the copper foil is deformed during cutting and bonding to the resin substrate, This is because the foil is wrinkled, and the hard state after rolling is more advantageous in terms of manufacturability of FPC.
[0007]
In order to increase the flexibility of FPC, it is effective to increase the flexibility of the rolled copper foil used as the material. The flexibility of the copper foil after annealing improves as the cube texture develops. In order to develop this cubic texture, it is effective in the copper foil manufacturing process to increase the degree of processing in the final rolling and to reduce the crystal grain size in the annealing immediately before the final rolling. Yes (Japanese Patent Application No. 10-101858).
[0008]
However, the copper foil produced by such a process has a significantly reduced softening temperature due to an increase in plastic strain accumulated during rolling. In some cases, the copper foil softens when stored for a long time even at room temperature. There are things to do. As described above, when FPC is manufactured using already softened copper foil, problems such as deformation of the copper foil occur, and the productivity of FPC is significantly reduced. Therefore, when the above manufacturing process is selected to improve the flexibility of the copper foil, it is necessary to increase the softening temperature of the copper foil appropriately at the same time.
[0009]
The problem that the rolled copper foil softens during storage at room temperature is pointed out in Japanese Patent Application Laid-Open No. 10-230303. In the present invention, however, the copper with a rolling degree as low as 50 to 90% is a means for avoiding the problem of room temperature softening. Propose to produce foil. However, when a copper foil is manufactured at such a low degree of rolling, the flexibility of the copper foil is remarkably lowered. Therefore, this means cannot be used when manufacturing a copper foil having excellent flexibility.
[0010]
[Problems to be solved by the invention]
An object of the present invention is to provide a rolled copper foil for FPC that has both excellent flexibility and moderate softening characteristics by appropriately increasing the softening temperature of the highly flexible rolled copper foil to eliminate the problems associated with softening during storage. Is to provide.
[0011]
[Means for improving the problem]
That is, the present invention solves the above-mentioned problems. (1) One or more of the components of Ag, As, Sb, Bi, Se, Te, Pb, and Sn with an S concentration of 0.0005 to 0.0020% by weight. The strength of the 200 planes obtained by X-ray diffraction of the rolled surface after annealing for 30 minutes at 200 ° C, with a total amount of 0.0040 wt% or less, an oxygen concentration of 0.0100 to 0.0500 wt%, a thickness of 5 to 50μm (I ) Has an I / I ₀ > 20.0 with respect to the strength (I ₀ ) of 200 planes determined by X-ray diffraction of finely powdered copper, has a semi-softening temperature of 120 to 150 ° C, and is continuously 300 N A rolled copper foil for a flexible printed circuit board characterized by having a tensile strength of / mm ² or more and having excellent flexibility and moderate softening characteristics.
[0012]
(2) The rolled copper foil of (1) above, wherein the residual resistance ratio after heating at 200 ° C. for 30 minutes is 10 to 140.
(3) After the ingot is hot-rolled, cold rolling and annealing are repeated, and finally the foil is finished by cold rolling. The annealing before the final cold rolling is performed at a temperature of the heating furnace of 500 This is performed under the condition that the average grain size of the recrystallized grains obtained by this annealing is 5 to 20μm above ℃, and after annealing, the material is cooled to a temperature of 100 ℃ or less at a cooling rate of 5 ℃ / second For the flexible circuit board characterized by obtaining the rolled copper foil of the above (1) and (2) having a workability of cold rolling exceeding 90.0% and having excellent flexibility and moderate softening characteristics The present invention relates to a method for producing a rolled copper foil.
[0013]
If a copper foil is manufactured by a high degree of processing or a fine grain process to develop a cubic texture, the flexibility is improved, but the softening temperature becomes too low. However, if the softening temperature is increased by controlling the trace components of the material, a copper foil having an appropriate softening temperature can be obtained.
[0014]
The moderate softening temperature here is
(1) The tensile strength after rolling of copper foil is 400 to 500 N / mm ² , but it must maintain a tensile strength of 300 N / mm ² or more even when left at 30 ° C for 1 year.
(2) The copper foil is softened by heat treatment after rough plating and cutting, or heat treatment when bonding to a resin substrate.
The semi-softening temperature during annealing for 30 minutes (annealing temperature when the tensile strength is intermediate between that before annealing and completely softened) is 120 to 150 ° C. Corresponds to the range.
[0015]
As a means to increase the softening temperature by controlling trace components,
(1) A method of adding a small amount of alloy elements when melting tough pitch copper (2) A method of making an impurity element into a solid solution in the process of processing an ingot into a foil (impurities are dissolved in a solid solution rather than a precipitated state) The softening suppression effect is significantly greater in the state)
There are two ways. The purpose of the present invention is to increase the softening temperature of the rolled copper foil by means of (2) by using impurities contained in the conventional tough pitch copper without adding a new alloying element to the tough pitch copper. To do.
[0016]
Sulfur is an impurity element that is contained in copper at a relatively high concentration and has a great influence on the softening properties. Although the effect of suppressing sulfur softening when present as Cu ₂ S particles is small, sulfur dissolved in copper significantly suppresses softening. The present inventors have found that a softening temperature suitable as a rolled copper foil for FPC can be obtained if this sulfur is appropriately dissolved.
[0017]
In addition, in order to adjust the solid solution sulfur concentration, it was found that the solid solution / precipitation behavior of sulfur in the annealing before final rolling (final annealing) should be controlled. In other words, since the equilibrium solubility of sulfur in solid copper increases as the temperature increases, increasing the heating temperature in the final annealing increases the solid solution concentration of sulfur in the copper. Softening temperature increases.
[0018]
The heating time in the final annealing was also an important factor that affected the progress of the reaction in which Cu ₂ S was dissolved as S. In addition, even if S is dissolved during heating, if the subsequent cooling rate is slow, S precipitates as Cu ₂ S during the cooling process, so it is necessary to perform cooling after heating at a predetermined rate or higher.
When the semi-softening temperature is controlled by solid solution / precipitation of impurity sulfur, the softening temperature can be adjusted more accurately by regulating impurities other than sulfur contained in tough pitch copper to a predetermined level or less.
[0019]
The reasons for limiting the rolled copper foil according to the present invention will be described below.
In the present invention, it was aimed to maintain the tensile strength of 300 N / mm ² or more by continuously maintaining the rolled copper foil at room temperature. More desirably, it can maintain a tensile strength of 300 N / mm ² or more even when stored at 30 ° C. for one year.
[0020]
Here, 30 ° C corresponds to a temperature exceeding the average annual temperature in Japan, and the storage period until copper foil is processed into FPC is at most one year. If the tensile strength is 300 N / mm ² or more, troubles such as wrinkling will not occur during processing of copper foil. Therefore, there is no practical problem as long as the tensile strength of 300 N / mm ² or more can be maintained even if left at 30 ° C for one year. Such softening characteristics correspond to temperatures above 120 ° C when converted to the semisoftening temperature when annealed for 30 minutes.
[0021]
On the other hand, if the semi-softening temperature after annealing for 30 minutes exceeds 150 ° C, the copper foil may not be softened by the heat treatment after roughing plating and cutting or the heat treatment for bonding to the resin substrate. Therefore, the semi-softening temperature after annealing for 30 minutes was specified as 120-150 ℃.
[0022]
In order to increase the flexibility of FPC, it is necessary to increase the flexibility of copper foil. The copper foil is incorporated into the FPC in the recrystallized state, but if the cubic texture, which is the recrystallized texture of pure Cu, is developed, the flexibility of the copper foil can be improved. The degree of development of the cube texture when satisfactory flexibility is obtained is the strength of the (200) plane obtained by X-ray diffraction of (200) plane determined by X-ray diffraction (I ₀ ) Is defined as I / I ₀ > 20.0. Here, annealing at 200 ° C for 30 minutes is performed to recrystallize the copper foil when measuring the X-ray intensity.
[0023]
Although it is easy to analyze the total amount of S in copper, it is impossible to analyze the concentration of only the dissolved S. This solute S concentration can be known by indirectly measuring the residual resistance ratio (RRR value). The RRR value is defined as the ratio of resistivity values at 293 K and 4.2 K (ρ (293K) / ρ (4.2 K)). The specific resistance ρ of pure copper is represented by ρ ₀ + ρ _t .
[0024]
Here, ρ ₀ is called the residual resistance value and does not depend on the temperature, and increases as the amount of impurities in solution increases. Moreover, ρ _t is a term of scattering due to lattice vibration and increases as the temperature increases. Ρ at room temperature is a value peculiar to the metal under ρ _t , and ρ at the very low temperature is ρ ₀ . Therefore, the solid solution concentration of S is high, [rho _t i.e. [rho (293 K) does not change, because the [rho ₀ i.e. ρ (4.2 K) increases, RRR value decreases. In addition to the solid solution impurities, plastic strain caused by rolling also affects the value of ρ ₀ , so it is necessary to measure the RRR value after removing this strain by heat treatment.
[0025]
If the RRR value after removing the plastic strain by heating at 200 ° C. for 30 minutes is adjusted to a range of 10 to 140, the present inventors can obtain suitable softening characteristics according to the solid solution S concentration at this time. I found out. On the other hand, when the RRR value exceeds 140, the semi-softening temperature falls below 120 ° C, and when it is less than 10, the semi-softening temperature exceeds 150 ° C.
In order to obtain a solid solution S concentration corresponding to a semi-softening temperature of 120 ° C or higher, that is, an RRR value of 140 or lower, the total sulfur concentration must be 0.0005 wt% or more.
[0026]
On the other hand, when the total sulfur concentration exceeds 0.0020% by weight, the solid solution concentration of sulfur becomes too high, the RRR value is less than 10, and the semisoftening temperature exceeds 150 ° C. In addition, excess sulfur exceeding the equilibrium solid solubility is precipitated as Cu ₂ S. Therefore, when the total sulfur concentration exceeds 0.0020% by weight, the decrease in flexibility due to this Cu ₂ S inclusion becomes significant. Therefore, the sulfur concentration was specified to be 0.0005-0.0020% by weight.
[0027]
Ag, As, Sb, Bi, Se, Te, Pb, and Sn are elements that have a large influence on the semi-softening temperature among impurities contained in trace amounts in ordinary tough pitch copper. Therefore, when the semisoftening temperature is controlled by the solid solution concentration of sulfur, it is easier to control the semisoftening temperature if the concentration of these impurities is suppressed to a low level.
[0028]
Ag, As, Sb, Bi, Se, Te, Pb, and Sn are preferably added in a total of at least one of the components to 0.0040% by weight or less, and if it exceeds 0.0040% by weight, the solid solution concentration of sulfur is the same. However, the semi-softening temperature varies greatly, and the semi-softening temperature exceeds 150 ° C depending on the solid solution concentration of sulfur.
[0029]
It is known that oxygen-free copper of normal purity has a significantly higher softening temperature than tough pitch copper due to the low oxygen concentration. In addition, oxygen excessively contained in tough pitch copper forms Cu ₂ O inclusions. The reason why the oxygen concentration is specified to be 0.0100 to 0.0500% by weight is that if the oxygen concentration is less than 0.0100% by weight and the sulfur is in a solid solution state, the semi-softening temperature exceeds 150 ° C, and if the oxygen concentration exceeds 0.0500% by weight, Cu _{This is because 2} O inclusions increase and flexibility decreases.
[0030]
As for the thickness of the copper foil, the thinner the bend, the less the distortion that occurs on the outer periphery of the bent part, so the flexibility is improved. If the thickness of the copper foil exceeds 50 μm, the desired flexibility cannot be obtained even if the cubic texture is developed. On the other hand, if the thickness of the copper foil is less than 5 μm, the strength of the foil becomes too low, and handling of the foil becomes difficult due to breakage or the like. Therefore, the thickness of the copper foil was set to 5 to 50 μm.
[0031]
Next, the reason why the manufacturing process for obtaining excellent flexibility and semi-softening property at 120 to 150 ° C. is specified will be described. The rolled copper foil according to the present invention is subjected to cold rolling and annealing after hot rolling of the ingot, and finally finished by cold rolling with a workability of 90.0% or more, exceeding 90.0% The reason why the value and high rolling workability are adopted is that a workability of more than 90.0% is required to obtain an I / I ₀ value exceeding 20.0, which is an index for obtaining excellent flexibility. is there.
[0032]
In this process, the solid solution amount of sulfur is determined by annealing (final annealing) immediately before the final cold rolling. Final annealing is generally performed using a continuous annealing line. In this annealing, the furnace temperature must be 500 ° C or higher in order to obtain the target sulfur solid solution concentration (RRR value). It becomes a condition. If the temperature is lower than 500 ° C, no sufficient sulfur solid solution concentration can be obtained no matter how long the heating time is, the RRR value exceeds 140 and the semi-softening temperature becomes lower than 120 ° C.
[0033]
In addition, the solid solution concentration of sulfur is affected not only by temperature but also by heating time. There are various combinations of heating temperature and time to obtain the target sulfur solid solution concentration, but the temperature and time are set so that the average grain size is 5μm or more using the recrystallized grain size after the final annealing as an index. Set.
[0034]
When the average particle size is less than 5μm, the RRR value exceeds 140 and the semi-softening temperature is lower than 120 ° C. On the other hand, if the average particle size exceeds 20 μm, even if the degree of work exceeds 90.0%, the I / I ₀ value is 20.0 or less and satisfactory flexibility cannot be obtained. Therefore, the final annealing was stipulated under conditions where the furnace temperature was 500 ° C or higher and the crystal grain size was 5-20 µm.
[0035]
Furthermore, when it is slowly cooled after heating, the solid solution S precipitates as Cu ₂ S. However, cooling to a temperature of 100 ° C. or less at a cooling rate of 5 ° C./second or more can prevent such precipitation of the solid solution S.
[0036]
On the other hand, when the cooling rate to 100 ° C is less than 5 ° C / second, the solid solution S concentration decreases, the RRR value exceeds 140, and the semisoftening temperature becomes lower than 120 ° C.
The final annealing can also be performed by hot rolling. In this case, the rolling end temperature is 500 ° C. or higher, the crystal grain size after rolling is 5 to 20 μm, and 5 ° C./second or higher. It is necessary to cool to below 100 ° C.
[0037]
【Example】
Hereinafter, embodiments of the present invention will be described by way of examples.
No. in Table 1. 1-No. A copper ingot having a thickness of 200 mm and a width of 600 mm was produced from the material of the component 16 and rolled to 10 mm by hot rolling.
[0038]
[Table 1]

[0039]
Next, annealing and cold rolling were repeated to obtain a rolled plate with a thickness of tomm. The plate was annealed and recrystallized to remove the oxide scale, and then cold-rolled to a predetermined thickness t mm. Here, the working degree in the last cold rolling is R,
[Expression 1]
R = (to−t) / to × 100 (%)
Given in. In the annealing before the final cold rolling, the crystal grain size after annealing was measured by a cutting method in a cross section perpendicular to the rolling direction.
[0040]
Thus, the following characteristics were evaluated about the copper foil sample manufactured by various intermediate annealing conditions and the final rolling workability.
(1) After heating the cube texture sample at 200 ° C. for 30 minutes, the integral value (I) of (200) plane strength obtained by X-ray diffraction of the rolled surface was obtained. This value was divided by the integral value (I ₀ ) of the (200) plane strength of finely pulverized copper that had been measured in advance, and the value of I / I ₀ was calculated.
[0041]
(2) The bendable specimen was recrystallized by heating at 200 ° C. for 30 minutes, and then the bending fatigue life was measured using the apparatus shown in FIG. This apparatus has a structure in which a vibration transmitting member 3 is coupled to an oscillation driver 4, and a copper foil to be tested 1 is connected to the apparatus at a total of four points including a screw 2 part indicated by an arrow and a tip part of 3. Fixed. When the vibration part 3 is driven up and down, the intermediate part of the copper foil 1 is bent into a hairpin shape with a predetermined radius of curvature r. In this test, the number of times to break when bending was repeated under the following conditions was obtained.
[0042]
Specimen width 12.7 mm, Specimen length: 200 mm, Specimen sampling direction: Specimen length direction is parallel to the rolling direction, Curvature radius r: 2.5 mm, Vibration stroke: 25 mm, Vibration speed : 1500 times / minute In addition, when the bending fatigue life was 30,000 times or more, it was judged to have excellent flexibility. This test is an accelerated test and is performed under conditions that are more severe than those actually used by the FPC.
[0043]
(3) Semi-softening temperature Tensile strength after annealing at various temperatures for 30 minutes was measured. Then, the annealing temperature was determined when the tensile strength after annealing reached an intermediate value between the tensile strength after rolling and the tensile strength after annealing at 300 ° C for 30 minutes and complete softening. If the semi-softening temperature was in the range of 120 to 150 ° C, it was judged that the film had appropriate softening characteristics.
[0044]
(4) Softening behavior at room temperature Rolled material is stored in a thermostat adjusted to 30 ° C, tensile strength is measured every month from the start of storage, and the tensile strength is 300 N / mm ² or less. The period until reaching the value was obtained. This evaluation continued for up to 12 months.
[0045]
(5) Specific resistance (RRR value)
The resistivity ρ of the sample after annealing at 200 ° C for 30 minutes was measured in liquid helium (4.2 K) and at room temperature (293 K), and the ratio between the two (ρ (293K) / ρ (4.2 K)) was obtained. .
[0046]
Table 2 shows the processing history and characteristics of the evaluated samples.
[0047]
[Table 2]

No. of rolled copper foil related to the present invention. 1-No. No. 16 shows that when annealing, the cubic texture develops and the (200) plane I / I ₀ exceeds 20.0, resulting in an excellent flex life of 30,000 times or more. In addition, the RRR value is 10 to 140, the semi-softening temperature is within the target range of 120 to 150 ° C, and the tensile strength is 300 N / mm ² or more even if stored for 1 year at room temperature (30 ° C). I keep it.
[0048]
On the other hand, in Comparative Examples No. 1 and 2, since the S concentration is lower than 0.0005% by weight, the RRR value exceeds 140, the semisoftening temperature is lower than 120 ° C, and the tensile strength is within one year when stored at 30 ° C. Is reduced to 300 N / mm ² or less.
In No. 3, the S concentration exceeds 0.0020 wt%, so the RRR value is less than 10 and the semi-softening temperature exceeds 150 ° C. In addition, because excessive S was precipitated as Cu ₂ S inclusions, the number of flexing was less than the target of 30,000 despite the (200) plane I / I ₀ exceeding 20.0.
[0049]
In No.4, the total amount of impurities Ag, As, Sb, Bi, Se, Te, Pb and Sn exceeds 0.004% by weight, so the RRR value is less than 10 and the semi-softening temperature is 150 ° C. Over.
No. 5 has an oxygen concentration lower than 0.0100% by weight, so its semi-softening temperature exceeds 150 ° C even though its RRR value is 20 or more.
In No.6, since the oxygen concentration exceeds 500 ppm, the inclusion of Cu ₂ O increases, and the number of bendings is less than 30,000 even though I / I ₀ on the 200 plane exceeds 20.0. It shows a low value.
[0050]
In No. 7, the furnace temperature in annealing before rolling is lower than 500 ° C. In No. 8, the crystal grain size obtained by this annealing is smaller than 5μm, so the RRR value exceeds 140 and the semi-softening temperature is 120 ° C. lower than, have dropped to 300 N / mm ² or less tensile strength within one year in storage 30 ° C..
[0051]
In No. 9, the crystal grain size obtained by annealing before rolling is larger than 20 μm, so the I / I ₀ on the (200) plane is smaller than 20.0 and the number of bendings is less than 30,000.
No. 10 has a thickness exceeding 50 μm, so the number of flexing is less than 30,000 despite the fact that the cubic texture has developed.
No. 11 has an RRR value exceeding 140 and a semi-softening temperature lower than 120 ° C because the cooling rate during annealing before rolling is slower than 5 ° C / sec.
[0052]
【The invention's effect】
The rolled copper foil for flexible printed circuits of the present invention has excellent flexibility. Further, since it has an appropriate softening temperature and does not cause troubles such as softening during storage or annealing, it has preferable characteristics as a flexible printed circuit board.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of a bending test apparatus used for measuring a bending fatigue life.
[Explanation of symbols]
1 Copper foil screw vibration transmission member Oscillation driver

Claims

S concentration is 0.0005 to 0.0020 wt%, Ag, As, Sb, Bi, Se, Te, Pb and Sn total amount of one or more of each component is 0.0040 wt% or less, oxygen concentration is 0.0100 to 0.0500 wt%, thickness The strength (I) of the (200) plane obtained by X-ray diffraction of the rolled surface after annealing for 30 minutes at 200 ° C for 5 to 50 µm is the strength of the (200) plane obtained by X-ray diffraction of fine copper powder I / I ₀ > 20.0 with respect to (I ₀ ), has a semi-softening temperature of 120 to 150 ° C, maintains a tensile strength of 300 N / mm ² or more at 30 ° C, and has excellent flexibility Rolled copper foil for flexible printed circuit boards, characterized by having moderate softening properties.

The rolled copper foil according to claim 1, wherein the residual resistance ratio after heating at 200 ° C for 30 minutes is 10 to 140.

After the ingot is hot-rolled, cold rolling and annealing are repeated, and finally the foil is finished by cold rolling. The annealing before the final cold rolling is performed at a heating furnace temperature of 500 ° C or higher. , Under the condition that the average grain size of recrystallized grains obtained by this annealing is 5 to 20 μm, after annealing, the material is cooled to a temperature of 100 ° C. or less at a cooling rate of 5 ° C./second or more, and the final cold A rolled copper foil for a flexible circuit board, characterized in that the rolled copper foil according to claim 1 or 2 having a degree of workability of rolling exceeding 90.0% and having excellent flexibility and moderate softening properties is obtained. Method.