JP3588227B2

JP3588227B2 - Ceramic heater

Info

Publication number: JP3588227B2
Application number: JP13893097A
Authority: JP
Inventors: 恵美子濱田; 潤福田; 広治坂元; 英徳中間
Original assignee: Kyocera Corp
Current assignee: Kyocera Corp
Priority date: 1997-05-28
Filing date: 1997-05-28
Publication date: 2004-11-10
Anticipated expiration: 2017-05-28
Also published as: JPH10335049A

Description

【０００１】
【発明の属する技術分野】
本発明は耐熱衝撃性、高温安定性に優れ、昇温特性及び耐久性の良好な石油ファンヒータ等の各種燃焼機器の点火用又は気化用ヒータや、酸素センサー等の各種センサーや測定機器、電子部品、産業機器、あるいは温水ヒータ、半田ごて等の一般家庭用電気製品等の加熱用ヒータ、更にはディーゼルエンジン等の始動時やアイドリング時に副燃焼室内を急速に予熱する内燃機関用グロープラグ等に適用される直流あるいは交流電源で使用される高温用のセラミックヒータに関するものである。
【０００２】
【従来の技術】
従来より、ディーゼルエンジンの始動促進に用いられるグロープラグをはじめとする各種点火用並びに加熱用ヒータとしては、耐熱金属製のシース内に高融点金属線等から成る発熱抵抗体を埋設した各種シーズヒータや、火花放電を利用した各種点火装置が多用されていたが、それらはいずれも急速昇温が困難であり、その上、耐摩耗性や耐久性に劣り、とりわけ前記各種点火装置においては、点火時に雑音等の電波障害が発生し易い他、確実な点火という点からの信頼性に欠ける等の欠点があった。
【０００３】
そこで熱伝達効率が優れ、急速昇温が可能で電波障害が発生せず、しかも確実に点火して安全性も高く、耐摩耗性や耐久性に優れた信頼性の高い発熱体として、セラミック焼結体と高融点金属やその化合物、及びそれらを主成分とする各種無機導電材から成る発熱部を担持または接合、あるいは埋設したセラミック発熱体が、内燃機関のグロープラグをはじめ、各種加熱用ヒータとして広く利用されるようになってきた。
【０００４】
一般に、セラミック発熱体としては、アルミナセラミックスの表面や内部に高融点金属の発熱部を設けたセラミックヒータが知られているが、電気絶縁材料として用いられるアルミナ（Ａｌ_２Ｏ_３）は耐熱衝撃性や高温強度に劣ることから、セラミック発熱体の絶縁部材には耐熱性や耐熱衝撃性、耐酸化性に優れた非酸化物系セラミックス、とりわけ耐熱性に優れ、高温強度も高く、熱容量が小さく、電気絶縁性が良好な窒化珪素質セラミックスが、急速昇温可能な高温用のセラミック発熱体の絶縁部材として広く採用されている。
【０００５】
かかるセラミック発熱体の端部側面には、無機導電材から成る発熱部と接続したリード部材がそれぞれ導出されて電極取り出し部が形成され、必要に応じて該電極取り出し部にニッケル（Ｎｉ）等の金属が被覆され、その上からメタライズ金属層を被着形成し、該メタライズ金属層から成る接合パッド部を介して外部電源に接続されるリード線がろう付け接合されてセラミックヒータが構成されている。
【０００６】
しかしながら、前記ろう付けに使用されるろう材は耐熱性を必要とするため、銀ろう等の高温用のろう材が用いられており、従ってろう付け接合する際には高温加熱されることから、冷却過程で絶縁部材のセラミックスとリード線の金属との熱膨張差により残留応力が生じてセラミックスとリード線との接合強度が低下するという欠点があった。
【０００７】
そこで、かかる欠点を解消するために、セラミックスと金属との間に接合応力緩和材としてＮｉ板を用いてろう付け接合することが提案されている（特開平７−２５６７４号公報）。
【０００８】
【発明が解決しようとする課題】
しかしながら、前記接合応力緩和材を介してセラミックスと金属を接合する技術をセラミックヒータのリード線の接合に適用し、接合強度が高い活性金属を含有するろう材を用いて前記同様に接合したとしても、従来例と同様、電極取り出し部の温度を想定した４０℃と４５０℃の温度に繰り返し加熱冷却する耐久試験では、短期的な試験には耐えるものの、５００サイクルを越える長期的な加熱冷却の反復に対しては、セラミックスと接合応力緩和材のＮｉとの９．４〜１１．８×１０^−６／℃にも及ぶ熱膨張差から、セラミックヒータのろう付け部周辺に残留応力が発生し、前記加熱冷却の繰り返しによりクラックが成長して接合強度が低下し、その結果、接合応力緩和材の剥離や、前記クラックから発熱部が酸化してセラミックヒータ自体の抵抗変化等を生じて耐久性が劣化し、長期的な信頼性に欠けるという課題があった。
【０００９】
【発明の目的】
本発明は前記課題に鑑み成されたもので、その目的は、リード線を接合した電極取り出し金属板の接合部が長期的な加熱冷却の反復に耐える強度を有し、クラック等が発生せず、かつ耐熱衝撃性、高温安定性に優れ、昇温特性の良好な各種燃焼機器の点火用又は気化用ヒータや、各種センサーや測定機器、電子部品、産業機器、一般家庭用電気製品等の加熱用ヒータ、更には内燃機関用グロープラグ等に好適な高温用のセラミックヒータを提供することにある。
【００１０】
【課題を解決するための手段】
本発明者等は前記課題について種々検討した結果、非酸化物系セラミック焼結体から成る絶縁部材と発熱部に接続する電極取り出し金属板との熱膨張の相関関係から、電極取り出し部と電極取り出し金属板とを電気的に接続する活性金属を含有した金属層から成る接合パッド部において、該接合パッド部の表面積とそれに接着する電極取り出し金属板の接合面積が、接続部周辺の残留応力に重大な影響を及ぼし、リード線を接合した電極取り出し金属板の絶縁部材との接合強度を左右していることを突き止めた。
【００１１】
そこで、かかる接合面積の関係を制御した結果、前述のような加熱冷却の厳しい長期間の熱履歴を受けても電極取り出し金属板が剥離したり、絶縁部材にクラックが発生したりせず、前記課題が解消できることを見いだし、優れた耐久性が得られることが明らかとなった。
【００１２】
即ち、本発明のセラミックヒータは、通電により発熱する無機導電材から成る発熱部を、窒化珪素、炭化珪素、又はサイアロン等の非酸化物系セラミック焼結体から成る絶縁部材に担持、あるいは該絶縁部材と接合、あるいは該絶縁部材中に埋設する等してセラミック発熱体を構成し、該セラミック発熱体の一端に導出された電極取り出し部に、活性金属を含有した貴金属から成る金属層を介して、電極取り出し金属板を接合する前記金属層から成る接合パッド部の表面積に対して、２０〜８０％の接合面積となるようにリード線を接合した電極取り出し金属板を電気的に接続して成ることを特徴とするものである。
【００１３】
また、前記金属層としては、活性金属としてＶ又はＴｉを含有し、貴金属としてＡｕを主成分とするものがより望ましいものである。
【００１４】
【作用】
本発明のセラミックヒータは、通電により発熱する無機導電材から成る発熱部と非酸化物系セラミック焼結体から成る絶縁部材とで構成されるセラミック発熱体の電極取り出し部に、活性金属を含有した貴金属から成る金属層を介して、該金属層から成る接合パッド部の表面積に対して２０〜８０％の接合面積となるようにリード線を接合した電極取り出し金属板を電気的に接続したことから、稼働時の加熱冷却の反復によるセラミック発熱体の絶縁部材と、前記電極取り出し金属板との熱膨張差で発生する応力は、活性金属を含有した金属層と電極取り出し部及び絶縁部材、電極取り出し金属板等との接合強度を損なうことなく、前記電極取り出し金属板に作用して該金属板自体が塑性変形し、前記応力を緩和してセラミックヒータを構成するセラミック発熱体のろう付け部周辺、即ち接合パッド部周囲のクラック発生を防止して耐久性が向上することになる。
【００１５】
【発明の実施の形態】
以下、本発明のセラミックヒータについて詳述する。
本発明において、前記発熱部の無機導電材は、Ｗ、Ｍｏ、Ｔｉ等の高融点金属、あるいはＷＣやＭｏＳｉ_２、ＴｉＮ等の高融点金属の炭化物や珪化物、窒化物等を主成分とする抵抗体が挙げられ、望ましくは絶縁部材の非酸化物系セラミック焼結体との熱膨張差、及び高温度下でもそれらと反応し難いという点からは、ＷＣあるいはＷを主成分とするものが好適である。
【００１６】
尚、前記発熱部を成す無機導電材の構成成分は、逆に絶縁部材である非酸化物系セラミック焼結体に添加して熱膨張差や反応性を調整しても良いことは言うまでもない。
【００１７】
また、前記無機導電材の主成分に対して、その粒成長を制御して絶縁部材との熱膨張差によるクラックを防止し、かつ抵抗を増大させないようにするために、分散材として窒化珪素、窒化硼素、窒化アルミニウムあるいは炭化珪素の一種以上を含有させても良く、その量は主成分１００重量部に対して、例えば、窒化珪素は５〜３０重量部、窒化硼素は１〜２０重量部、窒化アルミニウムは１〜１５重量部、炭化珪素は３〜１５重量部の割合であることが望ましい。
【００１８】
一方、本発明におけるセラミックヒータを構成する発熱部は、ブロック状や線状、又は層状のいずれでも良く、前記絶縁部材をその間に介してＵ字状に曲げたり、コイル状に巻回したり、平面にジグザグに折り曲げたりして、前記発熱部を平面視した時にＵ字状やＷ字状等、任意の形状を成すものとし、絶縁部材に担持したり、接合したり、あるいは埋設したりできる他、前記各種形状で絶縁体を介して２層以上の積層構造とする等、各種形状形態で適用でき、その両端にはＷ材等から成るリード部を電気的に接続したものでも良い。
【００１９】
また、非酸化物系セラミック焼結体から成る絶縁部材は、窒化珪素、炭化珪素、又はサイアロン等が適用可能だが、強度や耐熱衝撃性、高温時の粒界相における金属イオンの電界移動による電気絶縁性の低下の防止、耐久性の点からは窒化珪素質焼結体が最適である。
【００２０】
一方、本発明のリード線を接合した電極取り出し金属板は、活性金属を含有した金属層で加熱接合した後の冷却過程や、稼働時の加熱冷却で発生するセラミック発熱体の絶縁部材との熱膨張差を緩和するものであれば、いずれの材質でも適用可能だが、前記絶縁部材の３．０〜５．４×１０^−６／℃の熱膨張率に近似した３．０〜７．５×１０^−６／℃の金属板が望ましい。
【００２１】
また、前記金属板は、塑性変形し易いという点からは、ヤング率が１４〜１５×１０^３ｋｇ／ｍｍ^２を示すＦｅ−Ｎｉ−Ｃｏ合金やＦｅ−Ｎｉ合金等の鉄（Ｆｅ）基合金が最適であり、前記金属板自体の塑性変形で前記熱膨張差により発生する応力を十分吸収できるという点からは、該金属板の厚さを薄くして０．１〜０．５ｍｍ程度とすることが望ましく、周知の如く金属板の角部は応力集中を回避するために面取りや丸く曲面加工を施しておくことはより好ましい。
【００２２】
一方、前記電極取り出し部は削り出した露出面のままでも良いが、Ｎｉ等の金属被覆を施し、更に電極取り出し金属板に接続するリード線は低熱膨張率のＮｉ線等も適用できる。
【００２３】
次に、本発明における活性金属を含有した貴金属から成る金属層としては、Ａｕ及び／又はＡｇと、Ｎｉ又はＰｄのいずれか一種以上あるいはＣｕ、Ｃｏ、Ｓｉのいずれか一種の合計量が９０〜９９重量％で、残部１〜１０重量％がＶ、Ｍｏ、Ｔｉ、Ｚｒ、Ｈｆ、Ｍｎのいずれか一種以上の活性金属を含有するもの等が挙げられ、前記活性金属は窒化物や炭化物、水素化物等の形態で含有させても良い。
【００２４】
また、前記活性金属の量は、１重量％未満では接合強度の向上効果が見られず、１０重量％を越えると前記金属層の焼き付け温度が高くなり、冷却時に大きな残留応力を生じてクラックの原因となるため前記範囲に限定され、１〜５重量％が最も望ましい。
【００２５】
また、マイグレーション等による短絡の防止という点からは、金属層としては貴金属の主成分としてＡｕにＶ又はＴｉを活性金属として含有するものが最も望ましい。
【００２６】
また、前記金属層と接着する電極取り出し金属板は、熱膨張差による応力が狭い範囲に集中するのを回避するため、電極取り出し金属板が接合される前記金属層から成る接合パッド部の表面積に対して２０％以上の接合面積で接合することが必要であるが、逆に、８０％を越えると電極取り出し金属板の外周部に応力が集中することから、前記接合面積は接合パッド部の表面積の２０〜８０％に限定され、しかも前記金属板の外周部は金属層の外周部のいずれの縁とも重ならないことが望ましい。
【００２７】
なお、前記接合パッド部は、電極取り出し部と電気的に接続しておれば、電極取り出し部より引き出して設けることも可能であり、該接合パッド部の表面積の２０〜８０％の範囲内に電極取り出し金属板が実質的に接着した面積を有しておれば良い。
【００２８】
【実施例】
以下、本発明のセラミックヒータの実施例を図面に基づき説明する。
図１は、本発明のセラミックヒータの一実施例を示す斜視図であり、１は通電により発熱する無機導電材から成る発熱部２と、非酸化物系セラミック焼結体から成る絶縁部材３で構成されるセラミック発熱体４の電極取り出し部５に被着形成された金属層６を成す接合パッド部７を介して、リード線９を接合した電極取り出し金属板８を電気的に接続したセラミックヒータである。
【００２９】
図１において、セラミックヒータ１は、棒状の窒化珪素質焼結体から成る絶縁部材３の一方の端部に埋設されたＷＣを主成分とする略Ｕ字状の発熱部２と、該発熱部２の両端部と電気的に接続されたリード部１０と、該リード部１０に接続し他端側面で露出した電極取り出し部５と、金属層６を成す接合パッド部７を介して電気的に接続されたリード線９を接合した電極取り出し金属板８で構成された略直方体形状を成すものであり、リード部１０は、ＷＣを主成分とする導電体、またはＷ線、あるいはそれらを組み合わせて構成されるもので、通電による発熱も発熱部２よりはるかに低い温度にしか到達しないものである。
【００３０】
図２は、図１のセラミックヒータ１のリード線９を接合した電極取り出し金属板８を含む要部断面図であり、以下、図中の符号は図１と同一内容である。
【００３１】
図３は、本発明のセラミックヒータの他の例を示す要部断面図であり、金属層６から成る接合パッド７が一端面からそれに続く両側面にまで延設されたものである。
【００３２】
図４は、本発明のセラミックヒータの他の例を示す要部断面図であり、セラミック発熱体４を構成する絶縁部材３の断面を円形とした円柱形状を成すものである。
【００３３】
図５は、本発明のセラミックヒータの他の例を示す要部側面図であり、金属層６を複数個の電極取り出し部５から延設し、リード線９を接合した電極取り出し金属板８を電極取り出し部５から離れた部分で接続したもので、金属層６の破線部が接合パッド部７であり、この場合、電極取り出し金属板８の接合面積は該接合パッド部７の表面積に対して２０〜８０％の範囲内となるものである。
【００３４】
尚、本発明のセラミックヒータを構成するセラミック発熱体は、ブロック状又は層状の発熱部を平面視した時にＵ字状やＷ字状等、任意の形状を成すもので、該発熱部を絶縁部材に担持したり、接合したり、または埋設したり、あるいは、線状の発熱部をコイル状に巻回したり、屈曲させたりしたものを絶縁部材に担持したり、接合したり、または絶縁部材中に埋設し、かかる発熱部の両端にはＷ材等から成るリード部を電気的に接続したものでも良い。
【００３５】
次に、本発明のセラミックヒータを以下に詳述するようにして評価した。
先ず、比表面積が７〜１５ｍ^２／ｇのＳｉ_３Ｎ_４粉末に、希土類元素の酸化物としてＹｂ_２Ｏ_３を１０〜１５重量％、及びＭｏＳｉ_２を５重量％未満と、Ａｌ_２Ｏ_３を適量、それぞれ焼結助剤として添加し、必要に応じて着色剤や熱膨張率調整剤としてＭｏＳｉ_２、Ｍｏ_２Ｃ、ＷＳｉ_２、ＷＯ_３、ＷＣ等を適宜含有させて２４時間ボールミルで湿式混合した。
【００３６】
その後、得られた前記泥漿をそれぞれ噴霧乾燥して造粒し、該造粒体を用いてプレス成形法により平板状の成形体を作製した。
【００３７】
次に、ＷＣの微粉末８５重量％とＢＮの微粉末１５重量％の混合粉末に溶媒を加えて調製したペーストを使用して、スクリーン印刷法等によりＵ字状のパターンで、最終的に焼結体の先端より約５ｍｍ以内に位置するように前記成形体表面に発熱部を形成する。
【００３８】
更に、８５重量％のＷＣと１５重量％のＳｉ_３Ｎ_４の各微粉末から成るペーストを使用して、前記発熱部の両端と一部が重なるようにしてリード部の一部を所定の位置に形成する。
【００３９】
その際、電極取り出し部を前記リード部と同一組成のペーストでセラミック成形体の他端表面に、前記同様にして矩形状のパターンを２か所、セラミック成形体の側面まで平行に所定の配置でそれぞれ形成した。
【００４０】
次に、前記発熱部及びリード部、電極取り出し部をそれぞれ印刷形成した各成形体に、直径０．２５ｍｍのＷ線を前記リード部及び電極取り出し部のパターンとそれぞれ電気的に接続するように載置し、その上に別の成形体を重ねた後、Ｓｉ／ＳｉＯ_２雰囲気を調整した炭素（Ｃ）を含む還元性の雰囲気下、１７００〜１９００℃の温度で１時間以上、加圧焼成して略直方体形状のセラミック発熱体を得た。
【００４１】
その後、前記セラミック発熱体の電極取り出し部の露出部と接続するように、表１に示す各金属層組成物をそれぞれスクリーン印刷法で３ｍｍ角の正方形状に被着し、真空炉中で９００〜１２００℃の温度で金属層を焼き付けた。
【００４２】
【表１】

【００４３】
次いで、前記金属層上に表１に示すように接合面積を種々設定した直径０．６ｍｍのＮｉ製のリード線を溶接したＦｅ−Ｎｉ−Ｃｏ合金及びＦｅ−Ｎｉ合金から成る正方形状の電極取り出し金属板を載置し、真空炉中、９００〜１２００℃の温度で接続した。
【００４４】
かくして得られた評価用のセラミックヒータを用いて、６００℃の温度で１０００時間暴露する連続放置の耐久試験後、及び４０℃と４５０℃の両温度に暴露する工程を１サイクルとする冷熱サイクルを１００００サイクル実施する耐久試験後のそれぞれの電極取り出し金属板の接続状態を以下のような方法で評価した。
【００４５】
先ず、前記評価用セラミックヒータの前記耐久試験前後の抵抗値を測定し、抵抗変化率の最大値を求めると共に、冷熱サイクル耐久試験後の電極取り出し金属板の接続部周辺を浸透探傷試験法と顕微鏡による検査を行い、クラックの有無を確認した。
【００４６】
また、前記評価用セラミックヒータを長手方向に金属層を通り切断し、該切断面の金属層を挟んで、金属層外縁間の絶縁部材に残留する圧縮応力をＸ線応力解析装置により測定した。
【００４７】
【表２】

【００４８】
表から明らかなように、本発明の請求範囲外である試料番号１、９、１０、１５、１６、２４、２５、２９は、耐久試験前後の抵抗変化率が１３．３％以上と大きく、しかもいずれも耐久試験後には絶縁部材にクラックが認められ、残留応力も３７．８ｋｇ／ｍｍ^２以上であるのに対して、本発明のセラミックヒータはいずれも抵抗変化率が６．０％以下と小さく、絶縁部材にもクラックは認められず、残留応力も１０．２ｋｇ／ｍｍ^２以下と抵抗変化率及びクラックの有無の結果と良く一致しており、電極取り出し金属板の接合面積比が本発明の範囲内では応力の集中が回避されており、その結果、電極取り出し金属板の接続強度が大幅に改善されていることが確認できた。
【００４９】
尚、本発明のセラミックヒータは前記実施例に限定されるものではなく、前記接合パッド及び電極取り出し金属板の形状は、本発明の主旨を逸脱しないものであればいかなる形状でも良く、またセラミック発熱体の断面形状も用途に応じて種々の変更が可能であり、また発熱抵抗体を平行に複数配設して多層構造とし、各発熱抵抗体を直列にあるいは並列に接続した構造としたものに適用しても同様の効果を奏するものである。
【００５０】
【発明の効果】
叙上の如く、本発明のセラミックヒータは、非酸化物系セラミックスを絶縁部材とし、通電により発熱する無機導電材から成る発熱部を具備したセラミック発熱体の電極取り出し部に被着形成した金属層を介して、電極取り出し金属板の接合面積の比率を前記金属層から成る接合パッドの表面積に対して所定範囲内となるように接続したことから、常温付近から高温まで急速に昇温することを長時間にわたり反復したり、高温下で発熱させて飽和状態で長時間、連続稼働したりしても、リード線を接続した電極取り出し金属板との接合部が長期的な加熱冷却の反復に耐える強度を有し、かつ耐熱衝撃性、高温安定性に優れ、昇温特性の良好な耐久性に優れたセラミックヒータが得られる。
【図面の簡単な説明】
【図１】本発明のセラミックヒータが略直方体形状を成す一実施例を示す斜視図である。
【図２】図１のセラミックヒータのリード線を接合した電極取り出し金属板を含む要部断面図である。
【図３】本発明のセラミックヒータの他の例を示す要部断面図である。
【図４】本発明のセラミックヒータが略円柱状形状を成す他の例を示す要部断面図である。
【図５】本発明のセラミックヒータの他の例を示す要部側面図である。
【符号の説明】
１セラミックヒータ
２発熱部
３絶縁部材
４セラミック発熱体
５電極取り出し部
６金属層
７接合パッド部
８電極取り出し金属板
９リード線[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention has excellent thermal shock resistance, high-temperature stability, and a heater for igniting or vaporizing various kinds of combustion equipment such as a petroleum fan heater having good temperature rising characteristics and durability, various sensors and measuring devices such as an oxygen sensor, and an electronic device. Heaters for parts, industrial equipment, or general household electrical appliances such as hot water heaters and soldering irons, as well as glow plugs for internal combustion engines that rapidly preheat the sub-combustion chamber when starting or idling diesel engines, etc. The present invention relates to a high-temperature ceramic heater used in a DC or AC power supply.
[0002]
[Prior art]
Conventionally, various types of heaters for ignition and heating, such as glow plugs, used for accelerating the starting of diesel engines, include various types of sheathed heaters in which a heating resistor made of a high melting point metal wire or the like is embedded in a heat-resistant metal sheath. In addition, various igniters using spark discharge have been frequently used, but all of them are difficult to rapidly raise the temperature, and furthermore, they are inferior in wear resistance and durability. At the same time, there are drawbacks in that radio interference such as noise is likely to occur, and the reliability of reliable ignition is lacking.
[0003]
Therefore, it has excellent heat transfer efficiency, is capable of rapid temperature rise, does not cause radio wave interference, and has reliable ignition and high safety, as well as a highly reliable heating element with excellent wear resistance and durability. A ceramic heating element that carries, joins, or embeds a heat-generating unit made of a sintered body, a high-melting-point metal or a compound thereof, and various inorganic conductive materials containing these as a main component is used for various types of heaters, including glow plugs for internal combustion engines. Has come to be widely used.
[0004]
Generally, as a ceramic heating element, a ceramic heater provided with a heating portion of a high melting point metal on the surface or inside of alumina ceramics is known, but alumina (Al ₂ O ₃ ) used as an electrical insulating material has thermal shock resistance. Insulation members of ceramic heating elements are non-oxide ceramics with excellent heat resistance, thermal shock resistance, and oxidation resistance, especially high heat resistance, high high temperature strength, and low heat capacity. Silicon nitride ceramics having good electrical insulation properties have been widely adopted as insulating members for ceramic heating elements for high temperatures that can be rapidly heated.
[0005]
A lead member connected to a heating portion made of an inorganic conductive material is led out from an end side surface of the ceramic heating element to form an electrode extraction portion. If necessary, the electrode extraction portion may be formed of nickel (Ni) or the like. A ceramic heater is formed by coating a metal, forming a metallized metal layer thereon, and brazing a lead wire connected to an external power supply via a bonding pad portion made of the metallized metal layer. .
[0006]
However, since the brazing material used for the brazing requires heat resistance, a high-temperature brazing material such as silver brazing is used. During the cooling process, a residual stress is generated due to a difference in thermal expansion between the ceramics of the insulating member and the metal of the lead wire, and the joint strength between the ceramics and the lead wire is reduced.
[0007]
Then, in order to solve such a drawback, it has been proposed to perform brazing joining between a ceramic and a metal using a Ni plate as a joining stress relieving material (Japanese Patent Application Laid-Open No. 7-25674).
[0008]
[Problems to be solved by the invention]
However, even if the technique of joining ceramics and metal via the joining stress relieving material is applied to the joining of lead wires of a ceramic heater, and joining is performed in the same manner as described above using a brazing material containing an active metal having a high joining strength. As in the conventional example, in a durability test in which heating and cooling are repeatedly performed at temperatures of 40 ° C. and 450 ° C. assuming the temperature of the electrode take-out portion, a long-term repetition of heating and cooling exceeding 500 cycles can be withstand a short-term test. , Residual stress is generated around the brazed portion of the ceramic heater due to a thermal expansion difference of 9.4 to 11.8 × 10 ⁻⁶ / ° C. between ceramics and Ni as a bonding stress relieving material, Cracks grow due to the repetition of the heating and cooling, and the bonding strength is reduced. As a result, the ceramic heater is peeled off from the bonding stress relieving material and the heat generating portion is oxidized from the cracks. There has been a problem that durability changes due to a change in resistance of the device itself and the like, and long-term reliability is lacking.
[0009]
[Object of the invention]
The present invention has been made in view of the above problems, and its object is to provide a joint portion of an electrode extraction metal plate to which a lead wire is joined, which has strength enough to withstand long-term repeated heating and cooling, and does not generate cracks or the like. It has excellent thermal shock resistance, high temperature stability, and excellent temperature rise characteristics, and is used to ignite or vaporize various types of combustion equipment, and to heat various sensors and measuring instruments, electronic components, industrial equipment, and general household electrical products. It is an object of the present invention to provide a high-temperature ceramic heater suitable for a heater for an internal combustion engine and a glow plug for an internal combustion engine.
[0010]
[Means for Solving the Problems]
As a result of various studies on the above problems, the inventors of the present invention have found that from the correlation of thermal expansion between an insulating member made of a non-oxide ceramic sintered body and an electrode extraction metal plate connected to a heating section, an electrode extraction section and an electrode extraction In a bonding pad portion made of a metal layer containing an active metal that electrically connects to a metal plate, the surface area of the bonding pad portion and the bonding area of the electrode extraction metal plate adhered to the bonding pad portion are critical for residual stress around the connection portion. It has been found that the influence of the above influences on the bonding strength between the electrode extraction metal plate to which the lead wire is bonded and the insulating member.
[0011]
Therefore, as a result of controlling the relationship between the joining areas, the electrode extraction metal plate does not peel off even when subjected to the severe long-term heat history of heating and cooling as described above, and cracks do not occur in the insulating member. It was found that the problem could be solved, and it became clear that excellent durability could be obtained.
[0012]
That is, in the ceramic heater of the present invention, the heat generating portion made of an inorganic conductive material that generates heat when energized is supported on an insulating member made of a non-oxide ceramic sintered body such as silicon nitride, silicon carbide, or sialon, or A ceramic heating element is formed by joining with a member or embedded in the insulating member, etc., and an electrode extraction portion led out at one end of the ceramic heating element is connected via a metal layer made of a noble metal containing an active metal. An electrode extraction metal plate to which a lead wire is joined is electrically connected so that a bonding area of 20 to 80% of a surface area of a bonding pad portion made of the metal layer for joining the electrode extraction metal plate. It is characterized by the following.
[0013]
Further, the metal layer preferably contains V or Ti as an active metal and has Au as a main component as a noble metal.
[0014]
[Action]
The ceramic heater of the present invention contains an active metal in an electrode extraction portion of a ceramic heating element composed of a heating section made of an inorganic conductive material that generates heat by energization and an insulating member made of a non-oxide ceramic sintered body. Since the metal plate made of the noble metal is electrically connected to the electrode extraction metal plate to which the lead wire is bonded so as to have a bonding area of 20 to 80% with respect to the surface area of the bonding pad portion made of the metal layer. The stress generated due to the difference in thermal expansion between the insulating member of the ceramic heating element and the metal plate for taking out the electrode due to the repetition of heating and cooling during operation is caused by the metal layer containing the active metal, the electrode taking out part, the insulating member, and the electrode taking out. A ceramic heater is formed by acting on the electrode extraction metal plate and plastically deforming the metal plate itself to reduce the stress without impairing the bonding strength with a metal plate or the like. Braze periphery of the ceramic heating element, i.e. the durability by preventing the generation of cracks around the bonding pad portion is improved that.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the ceramic heater of the present invention will be described in detail.
In the present invention, the inorganic conductive material of the heat generating portion is mainly composed of a refractory metal such as W, Mo, Ti, or a carbide, silicide, nitride, or the like of a refractory metal such as WC, MoSi ₂ , or TiN. From the viewpoint that the thermal expansion difference between the non-oxide ceramic sintered body of the insulating member and the non-oxide-based ceramic sintered body, and the fact that it is difficult to react with them even at a high temperature, those having WC or W as a main component are preferred. It is suitable.
[0016]
In addition, it goes without saying that the components of the inorganic conductive material forming the heat generating portion may be added to the non-oxide ceramic sintered body as the insulating member to adjust the thermal expansion difference and the reactivity.
[0017]
In addition, for the main component of the inorganic conductive material, silicon nitride as a dispersing material, in order to prevent the crack due to thermal expansion difference with the insulating member by controlling the grain growth thereof and not to increase the resistance, One or more of boron nitride, aluminum nitride or silicon carbide may be contained, and the amount is 100 parts by weight of the main component, for example, silicon nitride is 5 to 30 parts by weight, boron nitride is 1 to 20 parts by weight, It is desirable that the ratio of aluminum nitride is 1 to 15 parts by weight and that of silicon carbide is 3 to 15 parts by weight.
[0018]
On the other hand, the heat generating portion constituting the ceramic heater according to the present invention may be any of a block shape, a linear shape, and a layer shape, and the insulating member may be bent into a U shape with the insulating member interposed therebetween, wound in a coil shape, It can be bent in a zigzag to form an arbitrary shape such as a U-shape or a W-shape when the heat-generating portion is viewed in plan, and can be carried on an insulating member, joined, or embedded. The present invention can be applied in various shapes, such as a laminate structure of two or more layers via an insulator in the various shapes described above, and a lead portion made of W material or the like may be electrically connected to both ends.
[0019]
The insulating member made of a non-oxide ceramic sintered body can be made of silicon nitride, silicon carbide, sialon, or the like. However, strength, thermal shock resistance, and electric field due to the electric field movement of metal ions in the grain boundary phase at high temperatures. A silicon nitride based sintered body is most suitable from the viewpoint of preventing a decrease in insulation properties and durability.
[0020]
On the other hand, the electrode extraction metal plate to which the lead wire of the present invention is bonded is formed by a cooling process after heating and bonding with the metal layer containing the active metal, and a heat generation between the ceramic heating element and the insulating member generated by heating and cooling during operation. Any material can be used as long as it can reduce the difference in expansion, but it is 3.0 to 7.5 × which is close to the coefficient of thermal expansion of 3.0 to 5.4 × 10 ⁻⁶ / ° C. of the insulating member. A metal plate of 10 ⁻⁶ / ° C. is desirable.
[0021]
Further, from the viewpoint that the metal plate is easily plastically deformed, an iron (Fe) -based alloy such as an Fe—Ni—Co alloy or an Fe—Ni alloy having a Young's modulus of 14 to 15 × 10 ³ kg / mm ^2. Is optimal, and from the point that the stress generated due to the difference in thermal expansion can be sufficiently absorbed by plastic deformation of the metal plate itself, the thickness of the metal plate is reduced to about 0.1 to 0.5 mm. As is well known, it is more preferable that the corners of the metal plate be chamfered or rounded in order to avoid stress concentration.
[0022]
On the other hand, the electrode take-out portion may be a cut-out exposed surface, but a metal coating such as Ni may be applied, and a lead wire connected to the electrode take-out metal plate may be a Ni wire having a low coefficient of thermal expansion.
[0023]
Next, the metal layer made of a noble metal containing an active metal in the present invention has a total amount of Au and / or Ag and one or more of Ni or Pd or one of Cu, Co, and Si of 90 to 90%. 99% by weight, with the remaining 1 to 10% by weight containing any one or more active metals of V, Mo, Ti, Zr, Hf and Mn. The active metal may be nitride, carbide, hydrogen, or the like. May be contained in the form of a compound or the like.
[0024]
If the amount of the active metal is less than 1% by weight, the effect of improving the bonding strength is not seen, and if it exceeds 10% by weight, the baking temperature of the metal layer becomes high, and a large residual stress is generated upon cooling, resulting in cracks. It is limited to the above range because it causes a cause, and 1 to 5% by weight is most desirable.
[0025]
Further, from the viewpoint of preventing short circuit due to migration or the like, the metal layer most preferably contains Au or V or Ti as an active metal as a main component of a noble metal.
[0026]
Further, the electrode extraction metal plate bonded to the metal layer has a surface area of a bonding pad portion made of the metal layer to which the electrode extraction metal plate is bonded in order to avoid stress due to a difference in thermal expansion from being concentrated in a narrow range. On the other hand, it is necessary to join with a bonding area of 20% or more. Conversely, if it exceeds 80%, stress concentrates on the outer peripheral portion of the electrode extraction metal plate. It is desirable that the outer peripheral portion of the metal plate does not overlap any edge of the outer peripheral portion of the metal layer.
[0027]
If the bonding pad portion is electrically connected to the electrode take-out portion, it can be provided by being pulled out from the electrode take-out portion, and the electrode can be provided within a range of 20 to 80% of the surface area of the bonding pad portion. It suffices that the extracted metal plate has an area substantially adhered thereto.
[0028]
【Example】
Hereinafter, embodiments of the ceramic heater of the present invention will be described with reference to the drawings.
FIG. 1 is a perspective view showing an embodiment of a ceramic heater according to the present invention. Reference numeral 1 denotes a heat generating portion 2 made of an inorganic conductive material that generates heat when energized, and an insulating member 3 made of a non-oxide ceramic sintered body. A ceramic heater in which an electrode extraction metal plate 8 to which a lead wire 9 is joined is electrically connected via a joining pad portion 7 forming a metal layer 6 attached to an electrode extraction portion 5 of the ceramic heating element 4 to be constituted. It is.
[0029]
In FIG. 1, a ceramic heater 1 has a substantially U-shaped heat generating portion 2 mainly composed of WC embedded at one end of an insulating member 3 made of a rod-shaped silicon nitride sintered body, and the heat generating portion. 2, a lead portion 10 electrically connected to both end portions, an electrode lead-out portion 5 connected to the lead portion 10 and exposed at the other end side surface, and a bonding pad portion 7 forming a metal layer 6 electrically. The lead portion 10 has a substantially rectangular parallelepiped shape composed of an electrode extraction metal plate 8 to which the connected lead wires 9 are joined, and the lead portion 10 is made of a conductor mainly composed of WC, a W wire, or a combination thereof. With this configuration, the heat generated by energization also reaches a temperature much lower than that of the heat generating portion 2.
[0030]
FIG. 2 is a cross-sectional view of a main part including an electrode extraction metal plate 8 to which a lead wire 9 of the ceramic heater 1 of FIG. 1 is joined. In the following, reference numerals in the drawing are the same as those in FIG.
[0031]
FIG. 3 is a cross-sectional view of a principal part showing another example of the ceramic heater of the present invention, in which a bonding pad 7 made of a metal layer 6 extends from one end surface to both side surfaces following the bonding pad.
[0032]
FIG. 4 is a cross-sectional view of a principal part showing another example of the ceramic heater of the present invention, in which the insulating member 3 constituting the ceramic heating element 4 has a columnar shape with a circular cross section.
[0033]
FIG. 5 is a main part side view showing another example of the ceramic heater of the present invention, in which a metal layer 6 is extended from a plurality of electrode extraction portions 5 and an electrode extraction metal plate 8 to which lead wires 9 are joined is shown. The connection is made at a portion distant from the electrode take-out portion 5, and the broken line portion of the metal layer 6 is the bonding pad portion 7. In this case, the bonding area of the electrode take-out metal plate 8 is larger than the surface area of the bonding pad portion 7. It is in the range of 20 to 80%.
[0034]
The ceramic heating element that constitutes the ceramic heater of the present invention has an arbitrary shape such as a U-shape or a W-shape when the block-shaped or layer-shaped heating portion is viewed in a plan view. Supported, joined, or buried, or a linear heating portion wound in a coil shape or bent, supported on an insulating member, joined, or mounted in an insulating member. And a lead portion made of W material or the like may be electrically connected to both ends of the heat generating portion.
[0035]
Next, the ceramic heater of the present invention was evaluated as described in detail below.
First, a Si ₃ N ₄ powder having a specific surface area of 7 to 15 m ² / g, 10 to 15 wt% of Yb ₂ O ₃ as an oxide of a rare earth element, less than 5 wt% of MoSi ₂ , and Al ₂ O ₃ , Respectively, as a sintering aid, and if necessary, appropriately containing MoSi ₂ , Mo ₂ C, WSi ₂ , WO ₃ , WC, etc. as a colorant or a thermal expansion coefficient adjuster, and wet-process with a ball mill for 24 hours. Mixed.
[0036]
Thereafter, each of the obtained slurry was spray-dried and granulated, and a flat molded body was produced by using the granulated material by a press molding method.
[0037]
Next, a paste prepared by adding a solvent to a mixed powder of 85% by weight of WC fine powder and 15% by weight of BN fine powder is finally fired in a U-shaped pattern by a screen printing method or the like. A heat generating portion is formed on the surface of the molded body so as to be located within about 5 mm from the tip of the unit.
[0038]
Further, using a paste composed of fine powder of 85% by weight of WC and 15% by weight of Si ₃ N ₄ , a part of the lead part is positioned at a predetermined position so that both ends of the heat generating part are partially overlapped. Formed.
[0039]
At this time, the electrode take-out portion is made of a paste having the same composition as the lead portion on the other end surface of the ceramic molded body. Each was formed.
[0040]
Next, a W line having a diameter of 0.25 mm is placed on each of the molded bodies on which the heat-generating portion, the lead portion, and the electrode take-out portion are formed by printing so as to be electrically connected to the patterns of the lead portion and the electrode take-out portion, respectively. After laying another molded body thereon, it is baked under pressure at a temperature of 1700 to 1900 ° C. for 1 hour or more in a reducing atmosphere containing carbon (C) prepared by adjusting the Si / SiO ₂ atmosphere. Thus, a substantially rectangular parallelepiped ceramic heating element was obtained.
[0041]
Thereafter, each metal layer composition shown in Table 1 was applied in a square of 3 mm square by a screen printing method so as to be connected to an exposed portion of an electrode take-out portion of the ceramic heating element. The metal layer was baked at a temperature of 1200 ° C.
[0042]
[Table 1]

[0043]
Next, a square electrode made of an Fe-Ni-Co alloy and an Fe-Ni alloy obtained by welding a lead wire made of Ni having a diameter of 0.6 mm and having various bonding areas as shown in Table 1 on the metal layer was welded. The metal plate was placed and connected at a temperature of 900 to 1200 ° C. in a vacuum furnace.
[0044]
Using the ceramic heater for evaluation obtained in this way, after a durability test of continuous leaving exposed at a temperature of 600 ° C. for 1000 hours, and a cooling / heating cycle including a step of exposing to both temperatures of 40 ° C. and 450 ° C. as one cycle The connection state of each electrode extraction metal plate after a durability test performed for 10,000 cycles was evaluated by the following method.
[0045]
First, the resistance value of the ceramic heater for evaluation was measured before and after the durability test to determine the maximum value of the rate of change in resistance. And the presence or absence of cracks was confirmed.
[0046]
Further, the ceramic heater for evaluation was cut in the longitudinal direction through the metal layer, and the compressive stress remaining on the insulating member between the outer edges of the metal layer was measured by an X-ray stress analyzer with the metal layer on the cut surface interposed.
[0047]
[Table 2]

[0048]
As is clear from the table, Sample Nos. 1, 9, 10, 15, 16, 24, 25, and 29, which are outside the scope of the present invention, have a large resistance change rate before and after the durability test of 13.3% or more. In addition, cracks were observed in the insulating member after the durability test, and the residual stress was 37.8 kg / mm ² or more, whereas the ceramic heater of the present invention had a resistance change rate of 6.0% or less. Small, no cracks were observed in the insulating member, and the residual stress was 10.2 kg / mm ² or less, which is in good agreement with the results of the resistance change rate and the presence or absence of cracks. Within the range, stress concentration was avoided, and as a result, it was confirmed that the connection strength of the electrode extraction metal plate was significantly improved.
[0049]
Note that the ceramic heater of the present invention is not limited to the above embodiment, and the shape of the bonding pad and the metal plate for taking out electrodes may be any shape as long as it does not depart from the gist of the present invention. The cross-sectional shape of the body can be variously changed according to the application.Also, a plurality of heating resistors are arranged in parallel to form a multilayer structure, and each heating resistor is connected in series or in parallel. Even if applied, a similar effect is achieved.
[0050]
【The invention's effect】
As described above, the ceramic heater according to the present invention has a metal layer adhered to an electrode lead-out portion of a ceramic heating element having a non-oxide ceramic as an insulating member and having a heating portion made of an inorganic conductive material that generates heat when energized. Through the connection so that the ratio of the bonding area of the electrode extraction metal plate is within a predetermined range with respect to the surface area of the bonding pad made of the metal layer, it is possible to rapidly raise the temperature from around room temperature to a high temperature. Even if it is repeated for a long time, or if it generates heat at high temperature and operates continuously for a long time in a saturated state, the joint with the electrode extraction metal plate to which the lead wire is connected can withstand long-term repeated heating and cooling A ceramic heater having strength, excellent thermal shock resistance, high-temperature stability, excellent temperature-rise characteristics, and excellent durability can be obtained.
[Brief description of the drawings]
FIG. 1 is a perspective view showing an embodiment in which a ceramic heater of the present invention has a substantially rectangular parallelepiped shape.
FIG. 2 is a cross-sectional view of a main part including an electrode extraction metal plate to which lead wires of the ceramic heater of FIG. 1 are joined.
FIG. 3 is a sectional view of a main part showing another example of the ceramic heater of the present invention.
FIG. 4 is a sectional view of a main part showing another example in which the ceramic heater of the present invention has a substantially columnar shape.
FIG. 5 is a side view of a main part showing another example of the ceramic heater of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Ceramic heater 2 Heating part 3 Insulating member 4 Ceramic heating element 5 Electrode extraction part 6 Metal layer 7 Bonding pad part 8 Electrode extraction metal plate 9 Lead wire

Claims

An electrode extraction metal plate in which a lead wire is joined to an electrode extraction portion of a ceramic heating element composed of a heating section made of an inorganic conductive material that generates heat by energization and an insulating member made of a non-oxide ceramic sintered body is activated. A ceramic heater electrically connected via a metal layer made of a noble metal containing metal, wherein a bonding area of an electrode extraction metal plate adhered to the metal layer is larger than a surface area of a bonding pad portion made of the metal layer. 20 to 80% of the ceramic heater.

The ceramic heater according to claim 1, wherein the metal layer contains vanadium (V) or titanium (Ti) as an active metal, and mainly contains gold (Au) as a noble metal.