【０００１】
【発明の属する技術分野】
本発明は、導電性接着剤などの代替に使用されるフィルム付熱伝導シートに関する。
【０００２】
【従来の技術】
ＩＣチップを熱伝導性又は電気伝導性を有する材料で接着するダイボンディング材料としては、銀粉を充填材として使用したエポキシ樹脂系接着剤がある（非特許文献１参照）。これらは各種条件で乾燥、硬化して使用され、接着性及び熱伝導性は良好であるが、一度接着してしまうと剥離は困難であるという欠点があった。また、樹脂封止したＩＣパッケージの上面と筐体等を接触させて放熱させる用途には、筐体とＩＣパッケージを接着してしまうため、適用が困難である欠点があった。
【０００３】
【非特許文献１】
エポキシ テクノロジー（Ｅｐｏｘｙ Ｔｅｃｈｎｏｌｏｇｙ） 社（米国）のカタログ、テクニカル ペーパー（Ｔｅｃｈｎｉｃａｌ Ｐａｐｅｒ） ＧＢ４８
【０００４】
また、５０℃の低温で溶融するタイプの熱伝導シート材料がある（非特許文献２参照）。この材料は低温で溶融し、剥離も可能であるが、溶融する為、きつく締め付けている間隙に挿入された場合には、材料のしみ出しなども起こりうる。
【０００５】
【非特許文献２】
ロード ケミカル プロダクツ（Ｌｏｒｄ Ｃｈｅｍｉｃａｌ Ｐｒｏｄｕｃｔｓ） 社（米国）のサーモセット（Ｔｈｅｒｍｏｓｅｔ） に関するカタログ、アドバンスト サーマルマネージメント マテリアルズ（Ａｄｖａｎｃｅｄ Ｔｈｅｒｍａｌ Ｍａｎａｇｅｍｅｎｔ Ｍａｔｅｒｉａｌｓ）
【０００６】
銀粉のみを含有する導電接着剤は、導電性が良好であり、含有率を高くすれば熱伝導性も高くなるが、銀の価格が高いことからこの接着剤は高価になり易い欠点を有していた。さらに略球状銀粉を生産する場合、その平均粒径を大きくすると充填密度を高くすることが困難になる欠点もある。特に銀は銅に比べて柔らかいため、樹脂と混合する際に、らいかい機を使用すると、混合、分散中に略球状銀粉の形状が変形し、充填性が低下するため、そのタップ密度が低下する欠点を有していた。
【０００７】
また、銀は導電性が良好であり、大気中で取り扱っても銅粉のように表面酸化に伴う抵抗値の増加が起きないことから印刷配線板、電子部品等の配線層（導電層）又は電子部品の電気回路や電極の形成に使用されているが、これらは高温多湿の雰囲気下で電界が印加されると、電気回路や電極間にマイグレーションと称する銀の電析が生じ電極間又は配線間が短絡するという欠点が生じる。
【０００８】
上記のマイグレーションを防止するための方策はいくつか行われており、導体の表面に防湿塗料を塗布するか又は導電ペーストに含窒素化合物などの腐食抑制剤を添加する方策が検討されているが十分な効果の得られるものではなかった。銀粉に替えて銀−パラジウム合金粉を使用すれば耐マイグレーション性は改善できるが、銀及びパラジウムが高価なため銀−パラジウム合金粉も高価になる欠点を有していた。
【０００９】
一方、銅粉を使用した導電ペーストは、加熱硬化後の銅の被酸化性が大きいため、空気中及びバインダ中に含まれる酸素と銅粉が反応し、その表面に酸化膜を形成し、導電性を著しく低下させ、また熱伝導性も損ねる。そのため、各種還元剤を加えて、銅粉表面の酸化を防止し、導電性が安定した銅ペーストが開示されているが、導電性及び導電性の安定性は銀ペーストには及ばず、高温高湿試験などで導通抵抗値が増大するなどの欠点があった。
【００１０】
また、導電ペースト中の、銅粉の含有率を高くしなければ安定した導電性を得られない。しかし、銅粉の含有率を高くすると、この影響で接着性が悪くなったり、保存安定性が悪くなるなどの欠点があった。
【００１１】
銀粉に銅粉を添加して併用することで、耐マイグレーション性を改善する方法も検討されているが、銀粉を使用した場合と比較すると改善の効果は小さく、要求される耐マイグレーション性を満足するものではなかった。
このため、接着剤を用いずシート自体が熱伝導性及び密着性を有し、かつ耐マイグレーション性に優れるシート状の熱伝導シートが要求されている。
【００１２】
【発明が解決しようとする課題】
請求項１記載の発明は熱伝導性及び密着性の良好な熱伝導シートを有するフィルム付熱伝導シートを提供するものである。
請求項２及び３記載の発明は、請求項１記載の発明のうち、特に熱伝導性に優れ、また請求項１記載の発明に加えて、作業性に優れる熱伝導シートを有するフィルム付熱伝導シートを提供するものである。
請求項４、５及び６記載の発明は、請求項１記載の発明に加えて高充填性に優れ、熱伝導性が安定している熱伝導シートを有するフィルム付熱伝導シートを提供するものである。
【００１３】
【課題を解決するための手段】
本発明は、導電粉及びシリコーン樹脂を含有する熱伝導シートの両面が平滑面を有し、かつ少なくともその片側の面にフィルムを張り合わせてなるフィルム付熱伝導シートに関する。
また、本発明は、導電粉が、銅粉又は銅合金粉の一部を露出して表面が大略銀で被覆され、該銀の被覆量が５〜２５重量％の略球状銀被覆銅粉及び銀粉の混合物である前記のフィルム付熱伝導シートに関する。
また、本発明は、略球状銀被覆銅粉が、平均粒径が２〜１０μｍである前記のフィルム付熱伝導シートに関する。
【００１４】
また、本発明は、略球状銀被覆銅粉が、タップ密度が相対値で５５〜７５％であり、かつその表面が平滑化されたものである前記のフィルム付熱伝導シートに関する。
また、本発明は、略球状銀被覆銅粉と銀粉の配合割合が、重量比で略球状銀被覆銅粉：銀粉が９５：５〜９９．９：０．１である前記のフィルム付熱伝導シートに関する。
さらに、本発明は、導電粉とシリコーン樹脂の配合割合が、該混合物の固形分に対して重量比で導電粉：シリコーン樹脂が８７：１３〜９４：６である前記のフィルム付熱伝導シートに関する。
【００１５】
【発明の実施形態】
本発明で用いられる導電粉としては、銅粉又は銅合金粉の一部を露出して表面が大略銀で被覆された略球状銀被覆銅粉や銀粉を用いることが好ましい。
該略球状銀被覆銅粉において、銅粉の表面への銀の被覆量は特に制限はないが、銅粉に対して５〜２５重量％の範囲であることが好ましく、５〜２０重量％の範囲であることがさらに好ましい。銀の被覆量が２５重量％を超えると銀被覆工程での凝集割合が高くなり、タップ密度が低下する傾向があると共にコストアップとなり、一方、５重量％未満であると銅の露出割合が高くなり、導電性の信頼性が低くなり易くなる傾向がある。
【００１６】
略球状銀被覆銅粉の平均粒径は、印刷、吐出等の取扱い、価格の点で２〜１０μｍの範囲が好ましく、４〜８μｍの範囲がさらに好ましい。
また、略球状銀被覆銅粉は、アスペクト比が１〜１．５の範囲であることが好ましく、１〜１．３の範囲であることがさらに好ましい。
【００１７】
本発明におけるアスペクト比とは、導電粉の粒子の長径と短径の比率（長径／短径）をいう。本発明においては、粘度の低い硬化性樹脂中に導電粉の粒子をよく混合し、静置して粒子を沈降させると共にそのまま樹脂を硬化させ、得られた硬化物を垂直方向に切断し、その切断面に現れる粒子の形状を電子顕微鏡で拡大して観察し、少なくとも１００の粒子について一つ一つの粒子の長径／短径を求め、それらの平均値をもってアスペクト比とする。
【００１８】
ここで、短径とは、前記切断面に現れる粒子について、その粒子の外側に接する二つの平行線の組み合わせ粒子を挟むように選択し、それらの組み合わせのうち最短間隔になる二つの平行線の距離である。一方、長径とは、前記短径を決する平行線に直角方向の二つの平行線であって、粒子の外側に接する二つの平行線の組み合わせのうち、最長間隔になる二つの平行線の距離である。これらの四つの線で形成される長方形は、粒子がちょうどその中に納まる大きさとなる。
なお、本発明において行った具体的方法については後述する。
【００１９】
略球状銀被覆銅粉のタップ密度は相対値で５５〜７５％の範囲であることが好ましく、６０〜７５％の範囲であることがさらに好ましい。タップ密度が５５％未満の場合、充填密度が低いため導電粉の配合割合を高くすると導電ペーストの粘度が高くなり、反面導電粉の配合割合を低くすると、十分な導電性及び信頼性が得られなくなる傾向があると共に銅粉を銀めっき処理すると銀被覆銅粉が得られるが、めっき処理しただけの銀被覆銅粉の表面は、銀の微結晶が析出しており、表面は平滑ではなく、粒子同士の流動性も低くなる傾向がある。
【００２０】
また、銀微結晶間に粒界が存在するため、銀めっき層の導電性自体も低い場合があると言われる。
さらに、置換めっき等で銀めっき処理を行った場合、銀めっき層とコア材の銅粉との密着性が十分でない場合もある。このような場合でも、解粒処理を行う際に銀被覆層の平滑化を行い、この平滑化の作用で銀被覆層とコア材の接着性を高くすることができる。一方、タップ密度が上記の７５％を超える略球状銀被覆銅粉は、それ自体作製することが困難である。
【００２１】
上記の理由により、タップ密度が上記の範囲で、かつその表面が平滑化されている略球状銀被覆銅粉を使用すれば、充填性、導電性及びこれらの信頼性の高い熱伝導シートを得ることができる。
なお、タップ密度の相対値とは、２５ｍｍのストロークでタッピングを１０００回行い、体積と質量から算出したタップ密度をその粒子の真密度又は理論密度で除した値である。
【００２２】
略球状銀被覆銅粉と銀粉の配合割合は、重量比で略球状銀被覆銅粉：銀粉が９５：５〜９９．９：０．１が好ましく、９５：５〜９９．５：０．５がさらに好ましい。銀粉の含有率が上記の範囲を超えると、導電性の信頼性は問題ないが、コストアップになり、また銀粉の含有率が上記の範囲未満であると、導電性の信頼性が低下する場合がある。
【００２３】
銀粉の平均粒径は７μｍ以下が好ましく、６μｍ以下がより好ましく、５μｍ以下がさらに好ましい。平均粒径が７μｍを超えると、略球状銀被覆銅粉と混合した後の印刷、吐出等の際の流動性が悪くなるおそれがある。また銀粉と略球状銀被覆銅粉を混合した際に緻密な充填状態を得ることも困難になる傾向がある。
なお、上記でいう平均粒径は、レ−ザ−散乱型粒度分布測定装置により測定することができる。本発明においては、測定装置としてマスタ−サイザ−（マルバン社製）を用いて測定した。
【００２４】
本発明で用いられるバインダとしては、弾力性、柔軟性及び密着性に優れるものとしてシリコーン樹脂が用いられる。該シリコーン樹脂に硬化剤又は添加剤を併用しても差し支えない。特に、硬化剤を併用することにより付着性がよく、可撓性に優れた熱伝導シートが得られる。硬化剤としては、ジブチル錫などの有機金属化合物が使用される。硬化剤の添加量は、シリコーン樹脂１００重量部に対して０．０５〜５重量部の範囲であることが好ましく、０．１〜３重量部の範囲であることがさらに好ましい。この添加量は、導電粉の表面状態によって、適正量に調節される。
【００２５】
本発明に用いられるシリコーン樹脂には、上記の材料以外に必要に応じてチキソ剤、カップリング剤、消泡剤、粉末表面処理剤等を添加して均一に混合して得られる。必要に応じて添加されるチキソ剤、カップリング剤、消泡剤、粉末表面処理剤、沈降防止剤等の含有量は、導電ペ−ストに対して０．０１〜１重量％の範囲であることが好ましく、０．０３〜０．５重量％の範囲であることがさらに好ましい。
【００２６】
導電粉とシリコーン樹脂の配合割合は、重量比で導電粉：シリコーン樹脂が８７：１３〜９４：６が好ましく、８９：１１〜９４：６がさらに好ましい。導電粉が上記の範囲を超えると、熱伝導シートの柔軟性が低下する傾向があり、また導電粉が上記の範囲未満であると、熱伝導率が悪化する傾向がある。
【００２７】
本発明において、熱伝導シートは、両面が平滑面であることが必要とされ、両面が平滑面でない場合、金属板などを密着させることができないという問題点が生じる。
本発明におけるフィルム付熱伝導シートは、上記のバインダ、導電粉及び必要に応じて添加されるチキソ剤、カップリング剤、消泡剤、粉末表面処理剤、沈降防止剤、溶剤等と共に、らいかい機、ニ−ダ−、三本ロ−ル等で均一に混合、分散した後、フィルム上にキスコータ、リバースコータ、ドクターブレード法などのコーティング装置により所望の膜厚で熱伝導シートが形成され、少なくともその片側の面に空気を巻き込まないようにしてフィルムを密着して張り合わせて製造することができる。
【００２８】
本発明においては、上記に示すように熱伝導シートの少なくとも片側の面にフィルムを密着して張り合わせることが必要である。もし、フィルムを密着して張り合わせず熱伝導シート単体で用いると、熱伝導シートが薄いため接着作業において取扱い難く、また金型などで打ち抜く場合、作業性が悪いという問題点が生じる。本発明のフィルム付熱伝導シートは、使用するときはフィルムを剥離して発熱体であるＩＣチップと放熱板である金属板又は金属製のケースやシャーシーと密着させて使用される。
【００２９】
熱伝導シートの少なくとも片側の面に密着して張り合わせるフィルムの材質及び厚さについては特に制限はないが、取り扱うことが可能であれば、薄い物でも差し支えない。少なくとも熱伝導シートに接するその表面は平滑であり、熱伝導シートとの剥離性を高めるために離型剤が塗布されていてもよい
【００３０】
【実施例】
以下、本発明を実施例により説明する。
実施例１
シリコーン樹脂〔エマソン＆カミング（Ｅｍｅｒｓｏｎ＆ Ｃｕｍｉｎｇ ）（社）製、商品名エコシル（ＥＣＯＳＩＬ）ＣＮ〕１００重量部に対してジブチル錫（試薬）３重量部を加えて均一に混合してバインダとした。
【００３１】
次に、アトマイズ法で作製した平均粒径が５．１μｍの球状銅粉（日本アトマイズ加工（株）製、商品名ＳＦＲ−Ｃｕ）を希塩酸及び純水で洗浄した後、水１リットルあたりＡｇＣＮ ８０ｇ及びＮａＣＮ７５ｇ含むめっき溶液で球状銅粉に対して銀の被覆量が６重量％になるように置換めっきを行い、水洗、乾燥して銀めっき銅粉（銀被覆銅粉）を得た。なお、上記の乾燥の際に水分をエタノールで３回置換したが、特に３回目のエタノールには、使用した銅粉１ｋｇあたり０．５ｇ（銅粉に対して被覆量が０．０５重量％に相当）のステアリン酸を溶解し、このステアリン酸を溶解したエタノールで上記銀めっき銅粉に含む水分を置換した後乾燥してステアリン酸処理した銀めっき銅粉を得た。
【００３２】
この後、２リットルのボ−ルミル容器内に上記で得た銀めっき銅粉２５０ｇ及び直径が３ｍｍのジルコニアボ−ル２ｋｇを投入し、３時間回転させて、アスペクト比が平均１．１及び長径の平均粒径が５．２μｍの解粒及び表面平滑化処理した略球状銀被覆銅粉を得た。
該略球状銀被覆銅粉のタップ密度は相対値で６３％であった。
【００３３】
上記で得たバインダ９．５ｇに、上記で得た略球状銀被覆銅粉８６．０ｇ及び平均粒径が２．２μｍの鱗片状銀粉（徳力化学研究所製，商品名ＴＣＧ−１）４．５ｇを加えて撹拌らいかい機及び三本ロ−ルで均一に混合、分散してペ−ストを得た。
なお、バインダと導電粉の割合は、該混合物の固形分に対して重量比でバインダ：導電粉が９．５：９０．５であった。
また、略球状銀被覆銅粉と鱗片状銀粉の割合は、重量比で略球状銀被覆銅粉：鱗片状銀粉が９５：５であった。
【００３４】
次に、上記で得たペ−ストをドクターブレード法で表面を離型剤処理した厚さが０．１ｍｍのポリエチレンテレフタレートフィルム上に０．３ｍｍの厚さにコーティングした。その上面に空気を巻き込まないようにして離型剤処理した厚さが０．０３ｍｍのポリエチレンテレフタレートフィルムを密着して張り合わせた。これを８０℃の熟成炉中で２４時間保管して厚さが０．３ｍｍの熱伝導シートの両面にポリエチレンテレフタレートフィルムを張り合わせたポリエチレンテレフタレートフィルム付熱伝導シート（以下フィルム付熱伝導シートとする）を得た。
【００３５】
得られたフィルム付熱伝導シートのフィルムを剥がし熱伝導シートの特性を評価した。その結果、熱伝導率は厚さ方向が１．５Ｗ／ｍ・Ｋであり、層方向は３．１Ｗ／ｍ・Ｋであった。
また、熱伝導シートの両表面に厚さが１ｍｍで表面が防錆処理してある銅板を密着させることができた。さらに密着後、熱伝導シートと銅板の間にドライバーを差し込み銅板を引き離す作業をしたところ、容易に剥離することができた。
【００３６】
なお、本実施例におけるアスペクト比の具体的測定法を以下に示す。低粘度のエポキシ樹脂（ビュ−ラ−社製）の主剤（Ｎｏ．１０−８１３０）８ｇと硬化剤（Ｎｏ．１０−８１３２）２ｇを混合し、ここへ導電粉２ｇを混合してよく分散させ、そのまま３０℃で真空脱泡した後、１０時間３０℃で静置して粒子を沈降させ硬化させた。その後、得られた硬化物を垂直方向に切断し、切断面を電子顕微鏡で１０００倍に拡大して切断面に現れた１５０個の粒子について長径／短径を求め、それらの平均値をもって、アスペクト比とした。
【００３７】
実施例２
実施例１で得た銀めっき銅粉を実施例１と同様の方法でボールミルを２時間回転させて、タップ密度が相対値で６５％の略球状銀被覆銅粉を得た。
実施例１で得たバインダ９．５ｇに、上記で得た略球状銀被覆銅粉８８．０ｇ及び平均粒径が０．６μｍの鱗片状銀粉（田中貴金属工業製，商品名ＡＹ−６０８０）２．５ｇを加えて撹拌らいかい機及び三本ロ−ルで均一に混合、分散してペ−ストを得た。
なお、バインダと導電粉の割合は、該混合物の固形分に対して重量比でバインダ：導電粉が９．５：９０．５であった。
また、略球状銀被覆銅粉と鱗片状銀粉の割合は、重量比で略球状銀被覆銅粉：鱗片状銀粉が９７．２：２．８であった。
【００３８】
上記で得たペーストを０．２ｍｍの厚さにコーティングした以外は、実施例１と同様の工程を経て厚さが０．２ｍｍの熱伝導シートの両面にポリエチレンテレフタレートフィルムを張り合わせたフィルム付熱伝導シートを得た。
得られたフィルム付熱伝導シートのフィルムを剥がし熱伝導シートの特性を評価した。その結果、熱伝導率は厚さ方向が１．７Ｗ／ｍ・Ｋであり、層方向は３．４Ｗ／ｍ・Ｋであった。
また、熱伝導シートの両表面に厚さが１ｍｍで表面が防錆処理してある銅板を密着させることができた。さらに密着後、熱伝導シートと銅板の間にドライバーを差し込み銅板を引き離す作業をしたところ、容易に剥離することができた。
【００３９】
実施例３
実施例１で得たバインダ９．５ｇに、実施例２で得た略球状銀被覆銅粉９０．０ｇ及び平均粒径が０．６μｍの鱗片状銀粉（田中貴金属工業製，商品名ＡＹ−６０８０）０．５ｇを加えて撹拌らいかい機及び三本ロ−ルで均一に混合、分散してペ−ストを得た。
なお、バインダと導電粉の割合は、該混合物の固形分に対して重量比でバインダ：導電粉が９．５：９０．５であった。
また、略球状銀被覆銅粉と鱗片状銀粉の割合は、重量比で略球状銀被覆銅粉：鱗片状銀粉が９９．４：０．６であった。
【００４０】
以下、実施例２と同様の工程を経て厚さが０．２ｍｍの熱伝導シートの両面にポリエチレンテレフタレートフィルムを張り合わせたフィルム付熱伝導シートを得た。
得られたフィルム付熱伝導シートのフィルムを剥がし熱伝導シートの特性を評価した。その結果、熱伝導率は厚さ方向が１．８Ｗ／ｍ・Ｋであり、層方向は３．４Ｗ／ｍ・Ｋであった。
また、熱伝導シートの両表面に厚さが１ｍｍで表面が防錆処理してある銅板を密着させることができた。さらに密着後、熱伝導シートと銅板の間にドライバーを差し込み銅板を引き離す作業をしたところ、容易に剥離することができた。
【００４１】
実施例４
実施例１で得た銀めっき銅粉を実施例１と同様の方法でボールミルを２．５時間回転させて、タップ密度が相対値で６４％の略球状銀被覆銅粉を得た。
実施例１で得たバインダ９．５ｇに、上記で得た略球状銀被覆銅粉９０．３ｇ及び平均粒径が０．６μｍの鱗片状銀粉（田中貴金属工業製，商品名ＡＹ−６０８０）０．２ｇを加えて撹拌らいかい機及び三本ロ−ルで均一に混合、分散してペ−ストを得た。
なお、バインダと導電粉の割合は、該混合物の固形分に対して重量比でバインダ：導電粉が９．５：９０．５であった。
また、略球状銀被覆銅粉と鱗片状銀粉の割合は、重量比で略球状銀被覆銅粉：鱗片状銀粉が９９．８：０．２であった。
【００４２】
以下、実施例２と同様の工程を経て厚さが０．２ｍｍの熱伝導シートの両面にポリエチレンテレフタレートフィルムを張り合わせたフィルム付熱伝導シートを得た。
得られたフィルム付熱伝導シートのフィルムを剥がし熱伝導シートの特性を評価した。その結果、熱伝導率は厚さ方向が１．８Ｗ／ｍ・Ｋであり、層方向は３．６Ｗ／ｍ・Ｋであった。
また、熱伝導シートの両表面に厚さが１ｍｍで表面が防錆処理してある銅板を密着させることができた。さらに密着後、熱伝導シートと銅板の間にドライバーを差し込み銅板を引き離す作業をしたところ、容易に剥離することができた。
【００４３】
実施例５
実施例１で得たバインダ１４．５ｇに、実施例２で得た略球状銀被覆銅粉８３．０ｇ及び平均粒径が０．６μｍの鱗片状銀粉（田中貴金属工業製，商品名ＡＹ−６０８０）２．５ｇを加えて撹拌らいかい機及び三本ロ−ルで均一に混合、分散してペ−ストを得た。
なお、バインダと導電粉の割合は、該混合物の固形分に対して重量比でバインダ：導電粉が１４．５：８５．５であった。
また、略球状銀被覆銅粉と鱗片状銀粉の割合は、重量比で略球状銀被覆銅粉：鱗片状銀粉が９７．１：２．９であった。
【００４４】
以下、実施例１と同様の工程を経て厚さが０．３ｍｍの熱伝導シートの両面にポリエチレンテレフタレートフィルムを張り合わせたフィルム付熱伝導シートを得た。
得られたフィルム付熱伝導シートのフィルムを剥がし熱伝導シートの特性を評価した。その結果、熱伝導率は厚さ方向が０．０５Ｗ／ｍ・Ｋであり、層方向は０．０８Ｗ／ｍ・Ｋであった。
また、熱伝導シートの両表面に厚さが１ｍｍで表面が防錆処理してある銅板を密着させることができた。さらに密着後、熱伝導シートと銅板の間にドライバーを差し込み銅板を引き離す作業をしたところ、容易に剥離することができた。
【００４５】
実施例６
実施例１で得た銀めっき銅粉を実施例１と同様の方法でボールミルを２０時間回転させて、タップ密度が相対値で５８％の略球状銀被覆銅粉を得た。
実施例１で得たバインダ９．５ｇに、上記で得た略球状銀被覆銅粉９０．５ｇを加えて撹拌らいかい機及び三本ロ−ルで均一に混合、分散してペ−ストを得た。
なお、バインダと導電粉の割合は、該混合物の固形分に対して重量比でバインダ：導電粉が９．５：９０．５であった。
また、略球状銀被覆銅粉と鱗片状銀粉の割合は、重量比で略球状銀被覆銅粉：鱗片状銀粉が１００：０であった。
【００４６】
以下、実施例１と同様の工程を経て厚さが０．３ｍｍの熱伝導シートの両面にポリエチレンテレフタレートフィルムを張り合わせたフィルム付熱伝導シートを得た。
得られたフィルム付熱伝導シートのフィルムを剥がし熱伝導シートの特性を評価した。その結果、熱伝導率は厚さ方向が０．６Ｗ／ｍ・Ｋであり、層方向は１．４Ｗ／ｍ・Ｋであった。
また、熱伝導シートの両表面に厚さが１ｍｍで表面が防錆処理してある銅板を密着させることができた。さらに密着後、熱伝導シートと銅板の間にドライバーを差し込み銅板を引き離す作業をしたところ、容易に剥離することができた。
【００４７】
比較例１
実施例１で得たバインダ９．５ｇに、実施例２で得た略球状銀被覆銅粉８８．０ｇ及び平均粒径が０．６μｍの鱗片状銀粉（田中貴金属工業製，商品名ＡＹ−６０８０）２．５ｇを加えて撹拌らいかい機及び三本ロ−ルで均一に混合、分散してペ−ストを得た。
【００４８】
次に、上記で得たペ−ストをドクターブレード法で表面を離型剤処理した厚さが０．１ｍｍのポリエチレンテレフタレートフィルム上に０．３ｍｍの厚さにコーティングした。これを８０℃の熟成炉中で２４時間保管して厚さが０．３ｍｍの熱伝導シートの下面のみにポリエチレンテレフタレートフィルムを張り合わせたフィルム付熱伝導シートを得た。
なお、バインダと導電粉の割合は、該混合物の固形分に対して重量比でバインダ：導電粉が９．５：９０．５であった。
また、略球状銀被覆銅粉と鱗片状銀粉の割合は、重量比で略球状銀被覆銅粉：鱗片状銀粉が９７．２：２．８であった。
【００４９】
得られたフィルム付熱伝導シートのフィルムを剥がし熱伝導シートの特性を評価した。その結果、熱伝導率は厚さ方向が１．７Ｗ／ｍ・Ｋであり、層方向は３．４Ｗ／ｍ・Ｋであった。
また、熱伝導シートの両表面に厚さが１ｍｍで表面が防錆処理してある銅板を密着させることを試みたが、ポリエチレンテレフタレートフィルムを張り合わせた下面にのみに銅板は密着したが、ポリエチレンテレフタレートフィルムを張り合わせない上面は表面が平滑面でないため銅板は密着しなかった。
【００５０】
【発明の効果】
請求項１記載のフィルム付熱伝導シートは、熱伝導性及び付着性の良好な熱伝導シートを有するフィルム付熱伝導シートである。
請求項２及び３記載のフィルム付熱伝導シートは、請求項１記載の発明のうち、特に熱伝導性に優れ、また請求項１記載の発明に加えて、作業性に優れる熱伝導シートを有するフィルム付熱伝導シートである。
請求項４、５及び６記載のフィルム付熱伝導シートは、請求項１記載の発明に加えて、高充填性に優れ、熱伝導性が安定している熱伝導シートを有するフィルム付熱伝導シートである。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a heat conductive sheet with a film used as a substitute for a conductive adhesive or the like.
[0002]
[Prior art]
As a die bonding material for bonding an IC chip with a material having thermal conductivity or electrical conductivity, there is an epoxy resin-based adhesive using silver powder as a filler (see Non-Patent Document 1). These are used after being dried and cured under various conditions, and have good adhesiveness and thermal conductivity, but have the disadvantage that once adhered, peeling is difficult. In addition, there is a drawback that the case is difficult to apply to an application in which heat is dissipated by bringing the upper surface of the resin-sealed IC package into contact with the housing or the like, since the housing and the IC package are bonded.
[0003]
[Non-patent document 1]
Catalog of Epoxy Technology (USA), Technical Paper GB48
[0004]
There is also a heat conductive sheet material of a type that melts at a low temperature of 50 ° C. (see Non-Patent Document 2). This material melts at a low temperature and can be peeled off, but if it is inserted into a tightly tightened gap, the material may exude.
[0005]
[Non-patent document 2]
A catalog of Thermoset from Lord Chemical Products (USA), Advanced Thermal Management Materials.
[0006]
A conductive adhesive containing only silver powder has good conductivity, and the higher the content, the higher the thermal conductivity.However, since the price of silver is high, this adhesive has a disadvantage that it is easily expensive. I was Furthermore, when producing substantially spherical silver powder, there is a disadvantage that it is difficult to increase the packing density if the average particle size is increased. In particular, silver is softer than copper, so if you use a grinder when mixing with resin, the shape of the roughly spherical silver powder will be deformed during mixing and dispersion, and the filling property will decrease, so the tap density will decrease. Had the disadvantage of
[0007]
In addition, silver has good conductivity, and does not cause an increase in resistance due to surface oxidation unlike copper powder even when handled in the air. Therefore, the wiring layer (conductive layer) of printed wiring boards, electronic components, etc. They are used to form electric circuits and electrodes of electronic components. When an electric field is applied in a high-temperature and high-humidity atmosphere, silver deposition called migration occurs between the electric circuits and the electrodes, and the electrodes or wirings are formed. There is a drawback that a short circuit occurs between them.
[0008]
Some measures have been taken to prevent the migration described above, and measures to apply a moisture-proof paint to the surface of the conductor or to add a corrosion inhibitor such as a nitrogen-containing compound to the conductive paste have been studied, but are sufficiently considered. Effect was not obtained. If silver-palladium alloy powder is used instead of silver powder, migration resistance can be improved, but silver and palladium are expensive, so that silver-palladium alloy powder has the disadvantage of being expensive.
[0009]
On the other hand, the conductive paste using copper powder has a high oxidizability of copper after heat curing, so that oxygen contained in air and in a binder reacts with copper powder to form an oxide film on the surface thereof, and the conductive paste becomes conductive. Properties are significantly reduced and the thermal conductivity is impaired. Therefore, a copper paste having a stable conductivity is disclosed by adding various reducing agents to prevent oxidation of the copper powder surface, but the conductivity and the stability of the conductivity are not as high as those of the silver paste, and the temperature is high. There were drawbacks such as an increase in conduction resistance in a humidity test or the like.
[0010]
Unless the content of copper powder in the conductive paste is increased, stable conductivity cannot be obtained. However, when the content of the copper powder is increased, there are drawbacks such as poor adhesion and poor storage stability due to this effect.
[0011]
A method of improving migration resistance by adding copper powder to silver powder and using it together has been studied, but the effect of the improvement is smaller than when silver powder is used, and the required migration resistance is satisfied. It was not something.
Therefore, there is a demand for a sheet-shaped heat conductive sheet which does not use an adhesive, has thermal conductivity and adhesiveness itself, and has excellent migration resistance.
[0012]
[Problems to be solved by the invention]
The invention described in claim 1 provides a heat conductive sheet with a film having a heat conductive sheet having good heat conductivity and adhesion.
The inventions according to claims 2 and 3 are, among the inventions according to claim 1, particularly excellent in heat conductivity, and in addition to the invention according to claim 1, a heat conduction with a film having a heat conduction sheet excellent in workability. A sheet is provided.
The inventions according to claims 4, 5 and 6 provide a heat conductive sheet with a film having a heat conductive sheet excellent in high filling property and stable in heat conductivity in addition to the invention according to claim 1. is there.
[0013]
[Means for Solving the Problems]
The present invention relates to a heat conductive sheet with a film in which both surfaces of a heat conductive sheet containing a conductive powder and a silicone resin have smooth surfaces, and a film is bonded to at least one surface thereof.
Further, according to the present invention, the conductive powder exposes a part of the copper powder or the copper alloy powder, and the surface thereof is substantially covered with silver, and the coating amount of the silver is approximately 25 to 25% by weight. The present invention relates to the heat-conductive sheet with a film, which is a mixture of silver powder.
Further, the present invention relates to the above-mentioned heat conductive sheet with a film, wherein the substantially spherical silver-coated copper powder has an average particle size of 2 to 10 μm.
[0014]
The present invention also relates to the above-mentioned heat conductive sheet with a film, wherein the substantially spherical silver-coated copper powder has a tap density of 55 to 75% in a relative value and a smoothed surface.
Further, in the present invention, the thermal conductivity with the film is such that the mixing ratio of the substantially spherical silver-coated copper powder and the silver powder is 95: 5 to 99.9: 0.1 in weight ratio of approximately spherical silver-coated copper powder: silver powder. Regarding the sheet.
Further, the present invention relates to the above-mentioned heat conductive sheet with a film, wherein the mixing ratio of the conductive powder and the silicone resin is 87:13 to 94: 6 by weight based on the solid content of the mixture. .
[0015]
DETAILED DESCRIPTION OF THE INVENTION
As the conductive powder used in the present invention, it is preferable to use a substantially spherical silver-coated copper powder or a silver powder in which a part of a copper powder or a copper alloy powder is exposed and the surface is substantially covered with silver.
In the substantially spherical silver-coated copper powder, the amount of silver coated on the surface of the copper powder is not particularly limited, but is preferably in the range of 5 to 25% by weight, and more preferably 5 to 20% by weight based on the copper powder. More preferably, it is within the range. When the silver coating amount exceeds 25% by weight, the agglomeration ratio in the silver coating step increases, the tap density tends to decrease, and the cost increases. On the other hand, when it is less than 5% by weight, the copper exposure ratio increases. And the reliability of the conductivity tends to be low.
[0016]
The average particle diameter of the substantially spherical silver-coated copper powder is preferably in the range of 2 to 10 μm, and more preferably in the range of 4 to 8 μm, in terms of handling such as printing and discharging, and price.
Further, the substantially spherical silver-coated copper powder preferably has an aspect ratio in the range of 1 to 1.5, and more preferably in the range of 1 to 1.3.
[0017]
The aspect ratio in the present invention refers to a ratio (major axis / minor axis) between the major axis and the minor axis of the particles of the conductive powder. In the present invention, the particles of the conductive powder are mixed well in a curable resin having a low viscosity, and the resin is cured as it is by allowing the particles to settle by standing, and the resulting cured product is cut in the vertical direction. The shape of the particles appearing on the cut surface is observed under magnification with an electron microscope, and the major axis / minor axis of each particle is obtained for at least 100 particles, and the average value thereof is defined as the aspect ratio.
[0018]
Here, the minor axis is a particle that appears on the cut surface, and is selected so as to sandwich a combination particle of two parallel lines that are in contact with the outside of the particle. Distance. On the other hand, the major axis is the two parallel lines perpendicular to the parallel line that determines the minor axis, and is the distance between the two parallel lines at the longest interval among the combination of the two parallel lines tangent to the outside of the particle. is there. The rectangle formed by these four lines is sized to fit the particle exactly inside it.
The specific method used in the present invention will be described later.
[0019]
The tap density of the substantially spherical silver-coated copper powder is preferably in the range of 55 to 75%, and more preferably in the range of 60 to 75%. When the tap density is less than 55%, the filling density is low, so that the mixing ratio of the conductive powder is increased, so that the viscosity of the conductive paste is increased. On the other hand, when the mixing ratio of the conductive powder is reduced, sufficient conductivity and reliability are obtained. Silver-coated copper powder can be obtained by subjecting the copper powder to silver plating with the tendency to disappear, but the surface of the silver-coated copper powder which has just been plated has silver microcrystals precipitated, and the surface is not smooth, The fluidity between particles also tends to be low.
[0020]
Further, it is said that the conductivity of the silver plating layer itself is sometimes low due to the existence of grain boundaries between silver microcrystals.
Furthermore, when silver plating is performed by displacement plating or the like, the adhesion between the silver plating layer and the copper powder of the core material may not be sufficient. Even in such a case, the silver coating layer is smoothed during the pulverization process, and the adhesion between the silver coating layer and the core material can be increased by the smoothing action. On the other hand, it is difficult to produce the substantially spherical silver-coated copper powder having a tap density exceeding 75% as described above.
[0021]
For the above-mentioned reason, if the tap density is in the above-mentioned range, and a substantially spherical silver-coated copper powder whose surface is smoothed is used, a heat conductive sheet having high filling property, conductivity and reliability thereof is obtained. be able to.
The relative value of the tap density is a value obtained by tapping 1000 times with a stroke of 25 mm and dividing the tap density calculated from the volume and the mass by the true density or the theoretical density of the particle.
[0022]
The mixing ratio of the substantially spherical silver-coated copper powder and the silver powder is preferably 95: 5 to 99.9: 0.1, more preferably 95: 5 to 99.5: 0.5. Is more preferred. When the content of silver powder exceeds the above range, the reliability of conductivity is not problematic, but the cost increases, and when the content of silver powder is less than the above range, the reliability of conductivity decreases. There is.
[0023]
The average particle size of the silver powder is preferably 7 μm or less, more preferably 6 μm or less, and still more preferably 5 μm or less. If the average particle size exceeds 7 μm, the fluidity during printing, discharging, and the like after mixing with the substantially spherical silver-coated copper powder may deteriorate. Also, it tends to be difficult to obtain a densely filled state when silver powder and substantially spherical silver-coated copper powder are mixed.
The above average particle size can be measured by a laser scattering type particle size distribution measuring device. In the present invention, the measurement was performed using a master sizer (manufactured by Malvern) as a measuring device.
[0024]
As the binder used in the present invention, a silicone resin having excellent elasticity, flexibility and adhesion is used. A curing agent or an additive may be used in combination with the silicone resin. In particular, by using a curing agent together, a heat conductive sheet having good adhesion and excellent flexibility can be obtained. As the curing agent, an organometallic compound such as dibutyltin is used. The amount of the curing agent added is preferably in the range of 0.05 to 5 parts by weight, more preferably 0.1 to 3 parts by weight, based on 100 parts by weight of the silicone resin. This addition amount is adjusted to an appropriate amount depending on the surface state of the conductive powder.
[0025]
The silicone resin used in the present invention can be obtained by adding a thixotropic agent, a coupling agent, an antifoaming agent, a powder surface treating agent, and the like, as necessary, in addition to the above-mentioned materials, and mixing them uniformly. The content of the thixotropic agent, coupling agent, defoaming agent, powder surface treating agent, anti-settling agent and the like added as necessary is in the range of 0.01 to 1% by weight based on the conductive paste. It is more preferable that the content be in the range of 0.03 to 0.5% by weight.
[0026]
The mixing ratio of the conductive powder and the silicone resin is preferably 87:13 to 94: 6, more preferably 89:11 to 94: 6, by weight ratio, of the conductive powder and the silicone resin. When the conductive powder exceeds the above range, the flexibility of the heat conductive sheet tends to decrease, and when the conductive powder is less than the above range, the thermal conductivity tends to deteriorate.
[0027]
In the present invention, the heat conductive sheet needs to have smooth surfaces on both sides, and when both surfaces are not smooth, there is a problem that a metal plate or the like cannot be adhered.
The heat-conducting sheet with a film in the present invention, together with the above-mentioned binder, conductive powder and thixo agent, coupling agent, defoaming agent, powder surface treatment agent, anti-settling agent, solvent, etc. After uniformly mixing and dispersing with a machine, kneader, three rolls, etc., a heat conductive sheet is formed on the film with a desired thickness by a coating apparatus such as a kiss coater, a reverse coater, a doctor blade method, It can be manufactured by adhering and adhering a film in such a manner that air is not entrapped at least on one side thereof.
[0028]
In the present invention, as described above, it is necessary to adhere a film to at least one surface of the heat conductive sheet in close contact. If the heat conductive sheet is used alone without closely adhering the films, the heat conductive sheet is so thin that it is difficult to handle in the bonding operation, and that the workability is poor when punching with a mold or the like. When the heat conductive sheet with a film of the present invention is used, the film is peeled off and used in close contact with an IC chip as a heating element and a metal plate or a metal case or chassis as a heat sink.
[0029]
There is no particular limitation on the material and thickness of the film adhered to at least one surface of the heat conductive sheet, but a thin material may be used as long as it can be handled. At least the surface in contact with the heat conductive sheet is smooth, and a release agent may be applied to enhance the releasability from the heat conductive sheet.
[0030]
【Example】
Hereinafter, the present invention will be described with reference to examples.
Example 1
3 parts by weight of dibutyltin (reagent) was added to 100 parts by weight of a silicone resin (manufactured by Emerson & Cuming, Inc., trade name: ECOSIL CN) and uniformly mixed to form a binder.
[0031]
Next, after washing spherical copper powder (trade name: SFR-Cu, manufactured by Nippon Atomize Processing Co., Ltd.) with an average particle size of 5.1 μm prepared by an atomizing method with dilute hydrochloric acid and pure water, 80 g of AgCN per liter of water was used. And a plating solution containing 75 g of NaCN so that the spherical copper powder was subjected to displacement plating so that the silver coverage was 6% by weight, washed with water and dried to obtain a silver-plated copper powder (silver-coated copper powder). The water was replaced three times with ethanol during the above-mentioned drying. Particularly, the third ethanol contained 0.5 g per kg of the used copper powder (the coating amount was reduced to 0.05% by weight based on the copper powder). (Equivalent) was dissolved, and ethanol containing the dissolved stearic acid was used to replace the water contained in the silver-plated copper powder, followed by drying to obtain a stearic acid-treated silver-plated copper powder.
[0032]
Thereafter, 250 g of the silver-plated copper powder obtained above and 2 kg of a zirconia ball having a diameter of 3 mm were put into a 2 liter ball mill container, and the mixture was rotated for 3 hours to obtain an average aspect ratio of 1.1 and a long diameter. To obtain a substantially spherical silver-coated copper powder having an average particle size of 5.2 μm and subjected to pulverization and surface smoothing.
The tap density of the substantially spherical silver-coated copper powder was 63% as a relative value.
[0033]
3. 9.5 g of the binder obtained above, 86.0 g of the substantially spherical silver-coated copper powder obtained above, and flaky silver powder having an average particle size of 2.2 μm (trade name: TCG-1). 5 g was added, and the mixture was uniformly mixed and dispersed with a stirrer and a triple roll to obtain a paste.
The ratio of the binder and the conductive powder was 9.5: 90.5 in terms of weight ratio to the solid content of the mixture.
The ratio of the substantially spherical silver-coated copper powder to the flaky silver powder was 95: 5 in terms of a weight ratio of approximately spherical silver-coated copper powder: flaky silver powder.
[0034]
Next, the paste obtained above was coated on a polyethylene terephthalate film having a thickness of 0.1 mm, the surface of which was treated with a release agent by a doctor blade method to a thickness of 0.3 mm. A polyethylene terephthalate film having a thickness of 0.03 mm, which was treated with a release agent so that air was not entrapped on the upper surface thereof, was closely adhered. This is stored in an aging furnace at 80 ° C. for 24 hours, and a heat conductive sheet having a polyethylene terephthalate film in which a polyethylene terephthalate film is laminated on both sides of a heat conductive sheet having a thickness of 0.3 mm (hereinafter referred to as a heat conductive sheet with a film). Got.
[0035]
The film of the obtained heat conductive sheet with a film was peeled off, and the properties of the heat conductive sheet were evaluated. As a result, the thermal conductivity was 1.5 W / m · K in the thickness direction and 3.1 W / m · K in the layer direction.
Further, a copper plate having a thickness of 1 mm and having a rust-proofed surface could be adhered to both surfaces of the heat conductive sheet. Further, after the contact, a screwdriver was inserted between the heat conductive sheet and the copper plate to separate the copper plate. As a result, the copper plate could be easily separated.
[0036]
A specific method for measuring the aspect ratio in this embodiment is described below. 8 g of a base material (No. 10-8130) of a low-viscosity epoxy resin (manufactured by Viewer) and 2 g of a curing agent (No. 10-8132) are mixed, and 2 g of conductive powder is mixed and dispersed well. After vacuum defoaming at 30 ° C. as it was, the particles were allowed to stand at 30 ° C. for 10 hours to settle and harden the particles. Then, the obtained cured product was cut in the vertical direction, the cut surface was magnified 1000 times with an electron microscope, and the long diameter / short diameter of 150 particles appeared on the cut surface was obtained. Ratio.
[0037]
Example 2
The silver-plated copper powder obtained in Example 1 was rotated in a ball mill for 2 hours in the same manner as in Example 1 to obtain a substantially spherical silver-coated copper powder having a tap density of 65% as a relative value.
To 9.5 g of the binder obtained in Example 1, 88.0 g of the substantially spherical silver-coated copper powder obtained above and flaky silver powder having an average particle diameter of 0.6 μm (trade name: AY-6080, manufactured by Tanaka Kikinzoku Kogyo) 2 Then, the paste was uniformly mixed and dispersed with a stirrer and a triple roll to obtain a paste.
The ratio of the binder and the conductive powder was 9.5: 90.5 in terms of weight ratio to the solid content of the mixture.
The weight ratio of the substantially spherical silver-coated copper powder to the flaky silver powder was 97.2: 2.8 for the substantially spherical silver-coated copper powder: scale-like silver powder.
[0038]
Except that the paste obtained above was coated to a thickness of 0.2 mm, a heat conductive sheet having a thickness of 0.2 mm and a polyethylene terephthalate film attached to both surfaces of the heat conductive sheet through the same process as in Example 1 was used. I got a sheet.
The film of the obtained heat conductive sheet with a film was peeled off, and the properties of the heat conductive sheet were evaluated. As a result, the thermal conductivity was 1.7 W / m · K in the thickness direction and 3.4 W / m · K in the layer direction.
Further, a copper plate having a thickness of 1 mm and having a rust-proofed surface could be adhered to both surfaces of the heat conductive sheet. Further, after the contact, a driver was inserted between the heat conductive sheet and the copper plate to separate the copper plate. As a result, the copper plate was easily peeled off.
[0039]
Example 3
To the 9.5 g of the binder obtained in Example 1, 90.0 g of the substantially spherical silver-coated copper powder obtained in Example 2 and the flaky silver powder having an average particle diameter of 0.6 μm (trade name: AY-6080, manufactured by Tanaka Kikinzoku Kogyo Kogyo) ) 0.5 g was added, and the mixture was uniformly mixed and dispersed with a stirrer and a triple roll to obtain a paste.
The ratio of the binder and the conductive powder was 9.5: 90.5 in terms of weight ratio to the solid content of the mixture.
The ratio of the substantially spherical silver-coated copper powder to the flaky silver powder was 99.4: 0.6 in weight ratio of approximately spherical silver-coated copper powder: scale-like silver powder.
[0040]
Hereinafter, through the same steps as in Example 2, a heat conductive sheet with a film in which a polyethylene terephthalate film was adhered to both sides of a heat conductive sheet having a thickness of 0.2 mm was obtained.
The film of the obtained heat conductive sheet with a film was peeled off, and the properties of the heat conductive sheet were evaluated. As a result, the thermal conductivity was 1.8 W / m · K in the thickness direction and 3.4 W / m · K in the layer direction.
Further, a copper plate having a thickness of 1 mm and having a rust-proofed surface could be adhered to both surfaces of the heat conductive sheet. Further, after the contact, a screwdriver was inserted between the heat conductive sheet and the copper plate to separate the copper plate. As a result, the copper plate could be easily separated.
[0041]
Example 4
The silver-plated copper powder obtained in Example 1 was rotated in a ball mill for 2.5 hours in the same manner as in Example 1 to obtain a substantially spherical silver-coated copper powder having a tap density of 64% as a relative value.
Into 9.5 g of the binder obtained in Example 1, 90.3 g of the substantially spherical silver-coated copper powder obtained above and flaky silver powder having an average particle diameter of 0.6 μm (trade name: AY-6080, manufactured by Tanaka Kikinzoku Kogyo) 0 Then, the mixture was uniformly mixed and dispersed with a stirrer and a triple roll to obtain a paste.
The ratio of the binder and the conductive powder was 9.5: 90.5 in terms of weight ratio to the solid content of the mixture.
The ratio of the substantially spherical silver-coated copper powder to the flaky silver powder was 99.8: 0.2 in weight ratio of approximately spherical silver-coated copper powder: flaky silver powder.
[0042]
Hereinafter, through the same steps as in Example 2, a heat conductive sheet with a film in which a polyethylene terephthalate film was adhered to both sides of a heat conductive sheet having a thickness of 0.2 mm was obtained.
The film of the obtained heat conductive sheet with a film was peeled off, and the properties of the heat conductive sheet were evaluated. As a result, the thermal conductivity was 1.8 W / m · K in the thickness direction and 3.6 W / m · K in the layer direction.
Further, a copper plate having a thickness of 1 mm and having a rust-proofed surface could be adhered to both surfaces of the heat conductive sheet. Further, after the contact, a driver was inserted between the heat conductive sheet and the copper plate to separate the copper plate. As a result, the copper plate was easily peeled off.
[0043]
Example 5
To 14.5 g of the binder obtained in Example 1, 83.0 g of the substantially spherical silver-coated copper powder obtained in Example 2 and flaky silver powder having an average particle diameter of 0.6 μm (trade name: AY-6080, manufactured by Tanaka Kikinzoku Kogyo Kogyo) ) 2.5 g was added, and the mixture was uniformly mixed and dispersed with a stirrer and a triple roll to obtain a paste.
The ratio of the binder to the conductive powder was 14.5: 85.5 in terms of weight ratio to the solid content of the mixture.
The weight ratio of the substantially spherical silver-coated copper powder to the flaky silver powder was 97.1: 2.9 for the substantially spherical silver-coated copper powder: scale-like silver powder.
[0044]
Thereafter, through the same steps as in Example 1, a heat conductive sheet with a film in which a polyethylene terephthalate film was adhered to both sides of a heat conductive sheet having a thickness of 0.3 mm was obtained.
The film of the obtained heat conductive sheet with a film was peeled off, and the properties of the heat conductive sheet were evaluated. As a result, the thermal conductivity was 0.05 W / m · K in the thickness direction and 0.08 W / m · K in the layer direction.
Further, a copper plate having a thickness of 1 mm and having a rust-proofed surface could be adhered to both surfaces of the heat conductive sheet. Further, after the contact, a driver was inserted between the heat conductive sheet and the copper plate to separate the copper plate. As a result, the copper plate was easily peeled off.
[0045]
Example 6
The silver-plated copper powder obtained in Example 1 was rotated in a ball mill for 20 hours in the same manner as in Example 1 to obtain a substantially spherical silver-coated copper powder having a relative density of 58% in tap density.
99.5 g of the substantially spherical silver-coated copper powder obtained above was added to 9.5 g of the binder obtained in Example 1, and the mixture was uniformly mixed and dispersed by a stirrer and a three-roll mill to disperse the paste. Obtained.
The ratio of the binder and the conductive powder was 9.5: 90.5 in terms of weight ratio to the solid content of the mixture.
The weight ratio of the substantially spherical silver-coated copper powder to the flaky silver powder was 100: 0 in terms of weight ratio.
[0046]
Thereafter, through the same steps as in Example 1, a heat conductive sheet with a film in which a polyethylene terephthalate film was adhered to both sides of a heat conductive sheet having a thickness of 0.3 mm was obtained.
The film of the obtained heat conductive sheet with a film was peeled off, and the properties of the heat conductive sheet were evaluated. As a result, the thermal conductivity was 0.6 W / m · K in the thickness direction and 1.4 W / m · K in the layer direction.
Further, a copper plate having a thickness of 1 mm and having a rust-proofed surface could be adhered to both surfaces of the heat conductive sheet. Further, after the contact, a driver was inserted between the heat conductive sheet and the copper plate to separate the copper plate. As a result, the copper plate was easily peeled off.
[0047]
Comparative Example 1
To the 9.5 g of the binder obtained in Example 1, 88.0 g of the substantially spherical silver-coated copper powder obtained in Example 2 and the flaky silver powder having an average particle diameter of 0.6 μm (trade name: AY-6080, manufactured by Tanaka Kikinzoku Kogyo Kogyo) ) 2.5 g was added, and the mixture was uniformly mixed and dispersed with a stirrer and a triple roll to obtain a paste.
[0048]
Next, the paste obtained above was coated on a polyethylene terephthalate film having a thickness of 0.1 mm, the surface of which was treated with a release agent by a doctor blade method to a thickness of 0.3 mm. This was stored in an aging furnace at 80 ° C. for 24 hours to obtain a heat conductive sheet with a film in which a polyethylene terephthalate film was adhered to only the lower surface of the heat conductive sheet having a thickness of 0.3 mm.
The ratio of the binder and the conductive powder was 9.5: 90.5 in terms of weight ratio to the solid content of the mixture.
The weight ratio of the substantially spherical silver-coated copper powder to the flaky silver powder was 97.2: 2.8 for the substantially spherical silver-coated copper powder: scale-like silver powder.
[0049]
The film of the obtained heat conductive sheet with a film was peeled off, and the properties of the heat conductive sheet were evaluated. As a result, the thermal conductivity was 1.7 W / m · K in the thickness direction and 3.4 W / m · K in the layer direction.
Also, an attempt was made to adhere a copper plate having a thickness of 1 mm and a rust-proof surface to both surfaces of the heat conductive sheet, but the copper plate adhered only to the lower surface where the polyethylene terephthalate film was adhered. The copper plate did not adhere to the upper surface where the film was not bonded because the surface was not smooth.
[0050]
【The invention's effect】
The heat conductive sheet with a film according to claim 1 is a heat conductive sheet with a film having a heat conductive sheet having good heat conductivity and adhesion.
The heat conductive sheet with a film according to claims 2 and 3 has a heat conductive sheet having excellent heat conductivity among the inventions according to claim 1 and excellent workability in addition to the invention according to claim 1. It is a heat conductive sheet with a film.
The heat conductive sheet with a film according to claims 4, 5 and 6 is a heat conductive sheet with a film having a heat conductive sheet which is excellent in high filling property and stable in heat conductivity in addition to the invention according to claim 1. It is.