JP3774101B2

JP3774101B2 - Copper clad laminate

Info

Publication number: JP3774101B2
Application number: JP2000066979A
Authority: JP
Inventors: 紳月山田; 礼郎黒崎; 雄二中村
Original assignee: Mitsubishi Plastics Inc
Current assignee: Mitsubishi Plastics Inc
Priority date: 2000-03-10
Filing date: 2000-03-10
Publication date: 2006-05-10
Anticipated expiration: 2020-03-10
Also published as: JP2001253011A

Description

【０００１】
【発明の属する技術分野】
この発明は、フレキシブルプリント配線基板などの配線基板を製造する素材である銅張積層板に関する。
【０００２】
【従来の技術】
近年、電気機器や電気通信機器の産業分野においては、機器の小型軽量化および低コスト化が進められ、プリント配線基板にも高密度実装に対応するという課題を担うことが求められ、その結果、配線基板材料にも、高耐熱性、難燃性、寸法安定性などの向上がより高い基準に要求されるようになった。
【０００３】
また、資源再利用の機運の高まりに応じて、前述のような機器構成材料は、再利用（リサイクル）可能な材料であることが好ましく、そのような絶縁材料としてポリエステル樹脂や熱可塑性ポリイミド樹脂などのＦＰＣ材料が利用されている。
【０００４】
しかし、ポリエステル樹脂材料は、耐熱性が充分ではないので、配線基板の用途を充分に広げられない。また、熱可塑性ポリイミド樹脂は、これを銅箔の下地層に使用する際に、２８０℃を越える高温に加熱して接着する必要があって製造効率または製品の品質安定性を高めることが容易ではなく、また熱可塑性ポリイミド樹脂は、強塩基に対して弱く耐薬品性に難点があり、また吸水率が高いので寸法安定性が悪いという欠点もある。
【０００５】
【発明が解決しようとする課題】
ところで、配線基板における絶縁層は、銅箔などの金属箔を直接に重ねて設けられるものであり、配線板の製造工程において金属箔の積層時には高温に加熱されると同時に加圧され、また腐食性のエッチング用液剤にも接触するので、耐熱性および耐薬品性に優れた特性を有すると共に寸法安定性が良好な特性を有する必要があり、これが充分になければ、配線基板に「反り」が発生する。
【０００６】
このような「反り」が発生する主な原因を図面を参照しながら説明すると、図１に示すように、回路を形成するエッチング工程で絶縁層（絶縁フィルム）１の表裏両面において回路部分等として残る金属箔２の面積が各所で異なるようになり、金属箔２に接する絶縁層１と金属箔２に接しない絶縁層１との間で熱膨張（収縮）率差による界面をずらす方向の力が生じ、次いで図２に示すように、部品を表面に実装する工程において、ハンダがコーティングされた実装部品の端子や電極を金属箔に密着させた状態で加熱炉に入れハンダを再溶融させた際、そのような再溶融工程（リフローソルダリング：Reflow soldering、または単に、リフロー工程とも称される。）および冷却工程（図３）において、前記した配線基板内部に絶縁フィルム１と金属箔２との熱膨張差および熱収縮差による応力が発現し、反りを助長しているものと考えられる。
【０００７】
そこで、この発明の課題は上記した問題点を解決し、配線板に加工される素材である銅張積層板が、配線板製造工程における２度以上の被加熱時に「反り」を発生させないものとし、特にハンダ溶接温度にまで再加熱されても、その後に「反り」を発生させない銅張積層板とすることである。
【０００８】
【課題を解決するための手段】
上記の課題を解決するため、本願の銅張積層板に係る発明においては、ガラス転移温度以上でゴム状弾性を示す温度領域を有する熱可塑性樹脂からなる絶縁フィルムにプリント配線用銅箔を重ねて一体化してなる銅張積層板において、前記銅箔は、１８０〜２４０℃で２０×１０^-6以上の平均線膨張係数を示す高温高膨張性の電解銅箔であり、前記絶縁フィルムは、そのガラス転移温度（Ｔｇ）以上で融点（Ｔｍ）未満の所定温度（Ｔｓ）に加熱された際、温度範囲（Ｔｓ−Ｔｇ）での平均線膨張係数が同温度範囲での前記電解銅箔の平均線膨張係数とほぼ等しくなるよう調製された熱可塑性樹脂からなる絶縁フィルムである銅張積層板としたのである。
【０００９】
上記したように構成される銅張積層板における絶縁フィルムは、その温度範囲（Ｔｓ−Ｔｇ）での絶縁フィルムの平均線膨張係数が同温度範囲での銅箔の平均線膨張係数とほぼ等しくなるよう調製されているので、温度（Ｔｓ）に加熱されたとき、およびその後に冷却されたときに、絶縁フィルムおよび銅箔が所定の割合で熱膨張および熱収縮し、絶縁フィルム内の内部応力が小さくなって配線基板が反らない。
【００１０】
また、上記の絶縁フィルムにおいて、温度範囲（Ｔｓ−Ｔｇ）における絶縁フィルムの平均線膨張係数（α₁）が、同温度範囲での銅箔の平均線膨張係数（α₂）に対して、α₂−９×１０^-6≦α₁≦α₂＋１６×１０^-6の関係を満たすように調製されている銅張積層板に係る発明では、所定温度範囲における絶縁フィルムの平均線膨張係数（α₁）が、同温度範囲での銅箔の平均線膨張係数と確実にほぼ等しいため、温度（Ｔｓ）に加熱され、そのあとに冷却された際に、絶縁フィルムの内部応力を小さくするように絶縁フィルムおよび銅箔が熱膨張および熱収縮し、配線基板はより確実に反らないものになる。
【００１１】
この発明で用いる銅箔は、１８０〜２４０℃で２０×１０^-6以上、好ましくは２０×１０^-6〜２５×１０^-6の平均線膨張係数を示す高温高膨張性の電解銅箔であり、１７×１０^-6の平均線膨張係数を示す通常の電解銅箔に比べて高い平均線膨張係数を示すものである。そのため、熱可塑性樹脂からなる絶縁フィルムの平均線膨張係数の調整が容易に行える。特に、熱可塑性樹脂に対して充填剤を添加することにより平均線膨張係数を低下させる場合には、充填剤の添加割合を通常の電解銅箔を使用した場合に比べて２〜５％以上低下させることができる。
【００１２】
このように本願の銅張積層板に係る発明では、温度範囲（Ｔｓ−Ｔｇ）での絶縁フィルムの平均線膨張係数が同温度範囲での銅箔の平均線膨張係数とほぼ等しくなるよう調製されている。そのため、ハンダ溶接温度（Ｔｓ）に加熱され、そのあとに冷却された際に絶縁フィルムおよび銅箔が同じ割合で熱膨張および熱収縮するものになり、部品実装工程でハンダ溶接後に反りが起こらない銅張積層板になる。
【００１３】
【発明の実施の形態】
この発明に用いる熱可塑性樹脂は、ガラス転移温度以上でゴム状弾性を示す温度領域を有し、銅箔に対して熱接着可能な熱可塑性樹脂であり、このような熱可塑性樹脂としては結晶性熱可塑性樹脂または非晶性熱可塑性樹脂のいずれであってもよく、またこのような一種以上の樹脂を混合した熱可塑性樹脂組成物であってもよい。なお、所要のゴム状弾性は、銅箔との熱接着性を良好にするために弾性率１０⁷〜１０¹⁰ｄｙｎ／ｃｍ²の範囲が好ましい。
【００１４】
また、この発明に用いる熱可塑性樹脂は、例えば７５μｍ程度の厚さのフィルム化された状態で配線板の製造時に耐える耐熱性を有するものであり、少なくともフロー工程またはリフロー工程におけるハンダ溶接時に回路形成された銅箔に圧接する状態で２３０〜２４０℃に加熱され、そのまま６０〜１８０秒程度耐えた場合に溶融せず、ゴム状弾性を有するという耐熱性があるものである。
【００１５】
結晶性の熱可塑性樹脂の具体例としては、ポリエーテルケトン（ＰＥＫ）、ポリエーテルエーテルケトン（ＰＥＥＫ）、ポリフェニレンサルファイド（ＰＰＳ）、シンジオタクチックポリスチレン（ＳＰＳ）などが挙げられる。
【００１６】
また、非晶性の熱可塑性樹脂の具体例としては、ポリエーテルイミド（ＰＥＩ）、ポリエーテルサルフォン（ＰＥＳ）、ポリアリルサルフォン（ＰＡｒＳ）、変性ポリフェニレンエーテル（変性ＰＰＥ）などが挙げられる。
【００１７】
この発明において用いられる銅箔は、高温高膨張性の電解銅箔であり、１８０〜２４０℃で２０×１０^-6以上、好ましくは２０×１０^-6〜２５×１０^-6の平均線膨張係数を示す電解銅箔である。
【００１８】
このような電解銅箔は、不溶性金属からなる陽極と、表面を鏡面研磨された金属製陰極との間に電解液を流通させ、両極間に直流電流を流して陰極表面に銅箔を電着させ、陰極に形成される銅箔を連続的に剥離することによって連続的に製造される。上記の高温高膨張性の電解銅箔を製造するには、所定成分の銅電解液を使用するのであるが、このような高温高膨張性の電解銅箔は、いわゆる「高々温伸び箔」と称される周知の電解銅箔を使用することができる。
【００１９】
なお、通常銅箔に比べて高い降伏強度と１８０℃雰囲気という熱間で高い伸び率を示す銅箔が、特許第２７５４１５７号公報に記載されており、このような銅箔をこの発明の銅箔として使用することもできる。因みに、同公報に記載の銅箔を製造する際に用いる電解液は、鉛イオン濃度３ｐｐｍ以下、スズイオン濃度６ｐｐｍ以下、塩素イオン濃度２ｐｐｍ以下、ケイ素イオン濃度１５ｐｐｍ以下、カルシウムイオン濃度３０ｐｐｍ以下およびヒ素イオン濃度７ｐｐｍ以下に制御した銅電解液である。
【００２０】
上述したような「高々温伸び箔」と称される電解銅箔は、通常の電解銅箔のデンドライト（樹枝状）結晶とは異なり、実質的に配向のない微細な結晶粒からなるものであり、例えば１８０〜２４０℃程度で再結晶化するまでの昇温状態で結晶粒が徐々に大きく成長するものであって、再結晶化するまでに高い線膨張係数を示すものである。
【００２１】
図４に、市販の「高々温伸び箔」と称される電解銅箔Ａ、Ｂまたは、通常の電解銅箔Ｃの昇温工程の線膨張係数と温度の関係を示し、図５には、同様に再結晶後（図４に示す加熱工程後）の銅箔Ａ、Ｂ、Ｃの降温工程での線膨張係数と温度の関係を示した。
【００２２】
図４および図５の結果からも明らかなように、市販の「高々温伸び箔」と称される電解銅箔Ａ、Ｂは、昇温工程で１８０〜２４０℃で２０×１０^-6以上、好ましくは２０×１０^-6〜２５×１０^-6の平均線膨張係数を示す電解銅箔であった。
【００２３】
この発明において所定温度範囲の絶縁フィルムの平均線膨張係数を同温度範囲の銅箔の平均線膨張係数とほぼ等しくなるよう調整するには、前述の熱可塑性樹脂を分子構造的に改善するか、もしくは適当な共重合成分を導入した共重合体に調製するか、または充填材を配合する方法が挙げられる。
【００２４】
このうち、フィルムに配向を起こさせることなく平均線膨張係数を低下させることのできる充填材としては、粒径１〜１５μｍ程度の板状（フレーク状）または球状の無機質充填材がある。そのうち、板状のマイカ、アルミナ、タルク、または球状のシリカ、アルミナ、またはチタン酸カリウムウィスカなどのウィスカなどは好ましい充填材である。
【００２５】
この発明に用いる充填材の粒径、厚さ、アスペクト比は、特に限定する必要はないが、例えばマイカ、アルミナ、タルクでは平均粒径５〜９μｍ、厚さ０．５〜２０μｍ、アスペクト比１０〜５０のものを使用し、シリカ、アルミナでは、平均粒径０．５〜１μｍ程度のものを使用して好ましい結果を得ている。
【００２６】
なお、これら充填材の配合割合は、充填材の種類に応じて変わるので、一定した範囲を特定することは困難であるが、敢えて例示すれば、マイカなどの板状充填材では１０〜３０重量％、種類を特定しない場合の充填材の配合割合は、２０〜５０重量％程度であり、これらは実際には後述する実施例や比較例のように実験的手法により各充填材毎に適当な割合を設定する。
【００２７】
【実施例および比較例】
〔実施例１〜２９、比較例１〜４３〕
表１または表２に示す配合割合で熱可塑性樹脂および充填材を混合し、得られた熱可塑性樹脂組成物の弾性率と温度の関係を測定値をプロットして調べ、これによってガラス転移温度（Ｔｇ）を決定した。
【００２８】
そして、各実施例または比較例の絶縁フィルムについて、リフロー工程でのＴｓまたはＴ₁を想定して２３０℃から上記のＴｇまでの温度範囲における平均線膨張係数（平均線膨張率に同じ。）＝α₁を調べると共に、絶縁フィルムの片面に銅箔を重ねて加熱加圧により接着し、得られた片面銅張積層板を２３０℃の加熱炉に１２０秒間で通過させ、片面銅張板のカール量からフィルムの収縮率を調べ、これらの結果を表１または表２に「リフロー収縮率」として示した。
【００２９】
また、「高々温伸び箔」と称される電解銅箔Ａ（市販品）のＴｓからＴｇまでの線膨張係数（α₂)を調べ、これを表１または表２中に併記した。
【００３０】
【表１】

【００３１】
【表２】

【００３２】
表１および表２の結果からも明らかなように、温度範囲（Ｔs −Ｔｇ）における絶縁フィルムの平均線膨張係数（α₁）が、同温度範囲での銅箔の平均線膨張係数（α₂）に対して、α₂−９×１０^-6≦α₁≦α₂＋１６×１０^-6の関係を満たさない熱可塑性樹脂の絶縁フィルムからなる片面配線板（電解銅箔Ａを使用）である比較例１〜４３は、２３０℃の加熱炉を１２０秒通過させた後のフィルムの収縮率（％）が、０．１１％以上に高く、片面配線板に反りが形成された。
【００３３】
これに対して、α₂−９×１０^-6≦α₁≦α₂＋１６×１０^-6の関係を満たす熱可塑性樹脂の絶縁フィルムからなる片面配線板である実施例１〜２９は、２３０℃の加熱炉を１２０秒間で通過させた後のフィルムの収縮率（％）が、０．１０％以下に低く、片面配線板に反りが形成されなかった。
【００３４】
【発明の効果】
本願の銅張積層板に係る発明は、以上説明したように、所定の電解銅箔を採用すると共に絶縁フィルムの所定温度範囲（Ｔs −Ｔｇ）での平均線膨張係数が同温度範囲での前記銅箔の平均線膨張係数とほぼ等しくなるよう調製した銅張積層板としたので、配線板に加工される素材である銅張積層板が、配線板製造工程における２度以上の被加熱時に「反り」を発生させないものとなり、特にハンダ溶接温度にまで再加熱されても、その後に「反り」を発生させない銅張積層板になるという利点がある。
【００３５】
また、上記の絶縁フィルムにおいて、α₂−９×１０^-6≦α₁≦α₂＋１６×１０^-6の関係を満たすように調製されている銅張積層板に係る発明では、温度（Ｔs ）に加熱され、その後に冷却された際に絶縁フィルムおよび銅箔が所定の割合で熱膨張および熱収縮するので、より確実に配線板を反らせない銅張積層板になる。
【図面の簡単な説明】
【図１】配線板のエッチング工程の説明図
【図２】配線板のリフロー工程の説明図
【図３】配線板の冷却工程の説明図
【図４】銅箔の昇温工程における温度と線膨張率の関係を示す図表
【図５】銅箔の降温工程における温度と線膨張率の関係を示す図表
【符号の説明】
１絶縁フィルム
２銅箔[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a copper clad laminate which is a material for manufacturing a wiring board such as a flexible printed wiring board.
[0002]
[Prior art]
In recent years, in the industrial field of electrical equipment and telecommunications equipment, miniaturization and weight reduction of equipment has been promoted, and it has been required to take up the challenge of dealing with high-density mounting on printed wiring boards. Higher heat resistance, flame retardancy, and dimensional stability have also been required for wiring board materials to higher standards.
[0003]
In addition, according to the increase in the momentum of resource reuse, the above-described equipment constituent materials are preferably reusable (recyclable) materials such as polyester resins and thermoplastic polyimide resins. FPC materials are used.
[0004]
However, since the polyester resin material does not have sufficient heat resistance, the use of the wiring board cannot be sufficiently expanded. In addition, when a thermoplastic polyimide resin is used as a copper foil underlayer, it is necessary to heat and bond it to a high temperature exceeding 280 ° C., and it is not easy to improve production efficiency or product quality stability. In addition, the thermoplastic polyimide resin is weak against a strong base and has a problem in chemical resistance, and has a drawback that its dimensional stability is poor because of its high water absorption.
[0005]
[Problems to be solved by the invention]
By the way, the insulating layer in the wiring board is provided by directly overlapping a metal foil such as a copper foil, and when the metal foil is laminated in the manufacturing process of the wiring board, the insulating layer is heated at the same time as being pressurized and corroded. It must also have excellent heat resistance and chemical resistance and good dimensional stability. If this is not sufficient, the wiring board will be warped. appear.
[0006]
The main cause of such “warping” will be described with reference to the drawings. As shown in FIG. 1, as shown in FIG. The area of the remaining metal foil 2 is different in various places, and the force in the direction of shifting the interface due to the difference in thermal expansion (shrinkage) between the insulating layer 1 in contact with the metal foil 2 and the insulating layer 1 not in contact with the metal foil 2 Then, as shown in FIG. 2, in the step of mounting the component on the surface, the solder and the solder were re-melted by placing them in a heating furnace in a state where the terminals and electrodes of the mounting component were in close contact with the metal foil. In such a remelting process (also referred to as reflow soldering, or simply referred to as a reflow process) and a cooling process (FIG. 3), the insulating film 1 and the metal are formed inside the wiring board. It is considered that stress due to the thermal expansion difference and thermal contraction difference with the foil 2 is expressed and promotes the warpage.
[0007]
Therefore, the problem of the present invention is to solve the above-mentioned problems, and the copper-clad laminate, which is a material processed into a wiring board, does not cause “warping” when heated twice or more in the wiring board manufacturing process. In particular, a copper-clad laminate that does not generate “warping” even when reheated to the solder welding temperature.
[0008]
[Means for Solving the Problems]
In order to solve the above problems, in the invention relating to the copper-clad laminate of the present application, a copper foil for printed wiring is laminated on an insulating film made of a thermoplastic resin having a temperature region that exhibits a rubber-like elasticity above the glass transition temperature. In the copper clad laminate formed integrally, the copper foil is a high-temperature and high-expansion electrolytic copper foil that exhibits an average linear expansion coefficient of 20 × 10 ⁻⁶ or more at 180 to 240 ° C., and the insulating film includes When heated to a predetermined temperature (Ts) above the glass transition temperature (Tg) and below the melting point (Tm), the average coefficient of linear expansion in the temperature range (Ts-Tg) is the average of the electrolytic copper foil in the same temperature range The copper-clad laminate, which is an insulating film made of a thermoplastic resin prepared so as to be approximately equal to the linear expansion coefficient, was used.
[0009]
In the insulating film in the copper clad laminate configured as described above, the average linear expansion coefficient of the insulating film in the temperature range (Ts-Tg) is substantially equal to the average linear expansion coefficient of the copper foil in the same temperature range. Therefore, when heated to temperature (Ts) and then cooled, the insulating film and the copper foil thermally expand and contract at a predetermined rate, and the internal stress in the insulating film is reduced. It becomes smaller and the wiring board does not warp.
[0010]
Moreover, in said insulating film, the average linear expansion coefficient ((alpha) ₁ ) of the insulating film in temperature range (Ts-Tg) is (alpha) with respect to the average linear expansion coefficient ((alpha) ₂ ) of copper foil in the same temperature range. _{In the} invention relating to the copper clad laminate prepared so as to satisfy the relationship of 2-9 × 10 ⁻⁶ ≦ α ₁ ≦ α ₂ + 16 × 10 ⁻⁶ , the average linear expansion coefficient (α ₁ ) is almost equal to the average coefficient of linear expansion of the copper foil in the same temperature range, so that the internal stress of the insulating film is reduced when heated to temperature (Ts) and then cooled. The insulating film and the copper foil are thermally expanded and contracted, and the wiring board is more reliably not warped.
[0011]
The copper foil used in the present invention is a high-temperature and high-expansion electrolytic copper foil that exhibits an average linear expansion coefficient of 20 × 10 ⁻⁶ or more, preferably 20 × 10 ^{−6 to} 25 × 10 ⁻⁶ at 180 to 240 ° C. The average linear expansion coefficient is higher than that of a normal electrolytic copper foil having an average linear expansion coefficient of 17 × 10 ⁻⁶ . Therefore, it is possible to easily adjust the average linear expansion coefficient of the insulating film made of the thermoplastic resin. In particular, when the average coefficient of linear expansion is reduced by adding a filler to the thermoplastic resin, the additive ratio of the filler is reduced by 2 to 5% or more compared to the case of using a normal electrolytic copper foil. Can be made.
[0012]
As described above, in the invention according to the copper clad laminate of the present application, the average linear expansion coefficient of the insulating film in the temperature range (Ts-Tg) is adjusted to be substantially equal to the average linear expansion coefficient of the copper foil in the same temperature range. ing. Therefore, when heated to the solder welding temperature (Ts) and then cooled, the insulating film and the copper foil thermally expand and contract at the same rate, and no warpage occurs after solder welding in the component mounting process. It becomes a copper clad laminate.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
The thermoplastic resin used in the present invention is a thermoplastic resin that has a temperature region that exhibits rubber-like elasticity above the glass transition temperature and can be thermally bonded to a copper foil. Such a thermoplastic resin is crystalline. Either a thermoplastic resin or an amorphous thermoplastic resin may be used, and a thermoplastic resin composition in which one or more of such resins are mixed may be used. The required rubber-like elasticity is preferably in the range of an elastic modulus of 10 ⁷ to 10 ¹⁰ dyn / cm ² in order to improve the thermal adhesiveness with the copper foil.
[0014]
In addition, the thermoplastic resin used in the present invention has heat resistance that can withstand the production of a wiring board in the form of a film having a thickness of about 75 μm, for example, and at least a circuit is formed at the time of solder welding in a flow process or a reflow process. It is heated to 230-240 ° C. in a state of being pressed against the copper foil, and has a heat resistance such that it does not melt and has rubber-like elasticity when it is endured for about 60-180 seconds.
[0015]
Specific examples of the crystalline thermoplastic resin include polyether ketone (PEK), polyether ether ketone (PEEK), polyphenylene sulfide (PPS), syndiotactic polystyrene (SPS), and the like.
[0016]
Specific examples of the amorphous thermoplastic resin include polyetherimide (PEI), polyethersulfone (PES), polyallylsulfone (PArS), and modified polyphenylene ether (modified PPE).
[0017]
The copper foil used in the present invention is a high-temperature and high-expansion electrolytic copper foil, and has an average linear expansion coefficient of 20 × 10 ⁻⁶ or more, preferably 20 × 10 ^{−6 to} 25 × 10 ⁻⁶ at 180 to 240 ° C. It is the electrolytic copper foil which shows.
[0018]
In such an electrolytic copper foil, an electrolytic solution is circulated between an anode made of an insoluble metal and a metal cathode whose surface is mirror-polished, and a direct current is passed between both electrodes to electrodeposit the copper foil on the cathode surface. And the copper foil formed on the cathode is continuously peeled off to be continuously manufactured. In order to produce the above-described high-temperature and high-expansion electrolytic copper foil, a copper electrolyte of a predetermined component is used. Such a high-temperature and high-expansion electrolytic copper foil is a so-called “highly hot-elongation foil”. The known electrolytic copper foil referred to can be used.
[0019]
In addition, the copper foil which shows high yield strength compared with normal copper foil and the high elongation rate in the hot of 180 degreeC atmosphere is described in patent 2754157, Such a copper foil is described in the copper foil of this invention. It can also be used as Incidentally, the electrolytic solution used in producing the copper foil described in the publication is a lead ion concentration of 3 ppm or less, a tin ion concentration of 6 ppm or less, a chlorine ion concentration of 2 ppm or less, a silicon ion concentration of 15 ppm or less, a calcium ion concentration of 30 ppm or less, and an arsenic ion. It is a copper electrolyte controlled to a concentration of 7 ppm or less.
[0020]
The electrolytic copper foil referred to as the “highly hot-elongated foil” as described above is composed of fine crystal grains having substantially no orientation, unlike the dendritic (dendritic) crystal of an ordinary electrolytic copper foil. For example, the crystal grains gradually grow large in a temperature rise state until recrystallization at about 180 to 240 ° C., and shows a high linear expansion coefficient before recrystallization.
[0021]
FIG. 4 shows the relationship between the linear expansion coefficient and the temperature in the heating step of the electrolytic copper foils A and B or the ordinary electrolytic copper foil C, which are referred to as commercially available “at most hot stretch foils”. Similarly, the relationship between the linear expansion coefficient and the temperature in the temperature lowering process of the copper foils A, B, and C after recrystallization (after the heating process shown in FIG. 4) is shown.
[0022]
As is clear from the results of FIGS. 4 and 5, the commercially available electrolytic copper foils A and B called “highly hot-elongated foils” are 20 × 10 ⁻⁶ or more at 180 to 240 ° C. in the temperature raising step, Preferably, it was an electrolytic copper foil exhibiting an average linear expansion coefficient of 20 × 10 ^{−6 to} 25 × 10 ⁻⁶ .
[0023]
In this invention, in order to adjust the average linear expansion coefficient of the insulating film in a predetermined temperature range to be substantially equal to the average linear expansion coefficient of the copper foil in the same temperature range, the above-described thermoplastic resin is improved in molecular structure, Alternatively, a method of preparing a copolymer into which an appropriate copolymer component has been introduced or a method of blending a filler can be mentioned.
[0024]
Among these, examples of the filler that can reduce the average linear expansion coefficient without causing orientation of the film include a plate-like (flakes) or spherical inorganic filler having a particle size of about 1 to 15 μm. Of these, plate-like mica, alumina, talc, or spherical silica, alumina, or whisker such as potassium titanate whisker are preferred fillers.
[0025]
The particle size, thickness, and aspect ratio of the filler used in the present invention need not be particularly limited. For example, mica, alumina, and talc have an average particle size of 5 to 9 μm, a thickness of 0.5 to 20 μm, and an aspect ratio of 10 ˜50 are used, and silica and alumina having an average particle size of about 0.5 to 1 μm are used to obtain preferable results.
[0026]
In addition, since the blending ratio of these fillers varies depending on the type of filler, it is difficult to specify a certain range, but for example, a plate-like filler such as mica is 10 to 30 weights. %, The blending ratio of the filler when the type is not specified is about 20 to 50% by weight. These are actually appropriate for each filler by an experimental method as in Examples and Comparative Examples described later. Set the percentage.
[0027]
Examples and Comparative Examples
[Examples 1 to 29, Comparative Examples 1 to 43]
The thermoplastic resin and the filler are mixed at the blending ratio shown in Table 1 or Table 2, and the relationship between the elastic modulus and the temperature of the obtained thermoplastic resin composition is examined by plotting the measured values, whereby the glass transition temperature ( Tg) was determined.
[0028]
Then, the insulating films of Examples and Comparative Examples, the average linear expansion coefficient in a temperature range of Ts or T ₁ of the at reflow process from to 230 ° C. assumed to above Tg (same in average coefficient of linear expansion.) = together determine the alpha _1, superimposed copper foil on one surface of the insulating film is adhered by heat and pressure, is passed through in 120 seconds sided copper-clad laminate obtained in the heating furnace of 230 ° C., curling of the single-sided copper clad laminate The shrinkage ratio of the film was examined from the amount, and these results are shown as “reflow shrinkage ratio” in Table 1 or Table 2.
[0029]
Further, the coefficient of linear expansion (α ₂ ) from Ts to Tg of electrolytic copper foil A (commercially available) called “at most warm-elongated foil” was examined, and this was also shown in Table 1 or Table 2.
[0030]
[Table 1]

[0031]
[Table 2]

[0032]
Table 1 and as is clear from the results in Table 2, the average linear expansion coefficient of average linear expansion coefficient of the insulating film in the temperature range (Ts -Tg) (α ₁₎ is a copper foil at the same temperature range (alpha ₂ ) ^Is a single-sided wiring board (using electrolytic copper foil A) made of an insulating film of a thermoplastic resin that does not satisfy the relationship of α ₂ −9 × 10 ⁻⁶ ≦ α ₁ ≦ α ₂ + 16 × 10 ^−6. In Comparative Examples 1 to 43, the shrinkage rate (%) of the film after passing through a heating furnace at 230 ° C. for 120 seconds was as high as 0.11% or more, and warpage was formed on the single-sided wiring board.
[0033]
In contrast, a single-sided wiring board made of an insulating film of a thermoplastic resin which satisfies the _{^{α 2 -9 × 10 -6 ≦ α}} 1 ≦ α 2 + 16 × 10 -6 relationship Example 1-29 is, 230 ° C. The shrinkage rate (%) of the film after passing through the heating furnace for 120 seconds was as low as 0.10% or less, and no warpage was formed on the single-sided wiring board.
[0034]
【The invention's effect】
As described above, the invention related to the copper clad laminate of the present application employs a predetermined electrolytic copper foil and the insulating film has an average linear expansion coefficient in a predetermined temperature range (Ts-Tg) in the same temperature range. Since the copper clad laminate was prepared so as to be approximately equal to the average linear expansion coefficient of the copper foil, the copper clad laminate, which is a material processed into the wiring board, was heated when heated twice or more in the wiring board manufacturing process. There is an advantage that a copper-clad laminate that does not generate “warp” after that even when reheated to the solder welding temperature is obtained.
[0035]
In the invention relating to the copper clad laminate prepared so as to satisfy the relationship of α ₂ −9 × 10 ⁻⁶ ≦ α ₁ ≦ α ₂ + 16 × 10 ^{−6 in} the above insulating film, the temperature (Ts) When heated and then cooled, the insulating film and the copper foil thermally expand and contract at a predetermined rate, so that a copper-clad laminate that does not warp the wiring board more reliably is obtained.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of an etching process of a wiring board. FIG. 2 is an explanatory diagram of a reflow process of the wiring board. FIG. 3 is an explanatory diagram of a cooling process of the wiring board. Chart showing the relationship between expansion coefficients [Fig. 5] Chart showing the relationship between temperature and linear expansion coefficient in the temperature-falling process of copper foil [Explanation of symbols]
1 Insulating film 2 Copper foil

Claims

In a copper-clad laminate formed by superimposing a copper foil for printed wiring on a insulating film made of a thermoplastic resin having a temperature range that exhibits a rubbery elasticity above the glass transition temperature,
The copper foil is a high-temperature and high-expansion electrolytic copper foil that exhibits an average linear expansion coefficient of 20 × 10 ⁻⁶ or more at 180 to 240 ° C., and the insulating film has a melting point (Tg) that is higher than its glass transition temperature (Tg). When heated to a predetermined temperature (Ts) less than Tm), the average linear expansion coefficient in the temperature range (Ts-Tg) is adjusted to be approximately equal to the average linear expansion coefficient of the electrolytic copper foil in the same temperature range. A copper-clad laminate, which is an insulating film made of a thermoplastic resin.

The copper clad laminate according to claim 1, wherein the electrolytic copper foil is an electrolytic copper foil having an average linear expansion coefficient of 20 × 10 ^{−6 to} 25 × 10 ⁻⁶ at 180 to 240 ° C.

The average linear expansion coefficient (α ₁ ) of the insulating film in the temperature range (Ts−Tg) is α ₂ −9 × 10 ⁻⁶ ≦ the average linear expansion coefficient (α ₂ ) of the copper foil in the same temperature range. The copper-clad laminate according to claim 1 or 2, wherein the copper-clad laminate is prepared so as to satisfy a relationship of α ₁ ≦ α ₂ + 16 × 10 ⁻⁶ .