JP2004362950A - Conductive paste mainly composed of silver powder, and its manufacturing method - Google Patents
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【０００１】
【発明の属する技術分野】本発明は、セラミック基板その他の基材に電極、回路等の膜状導体（以下「導体膜」という。）を形成する用途に用いられる導体ペーストに関する。
【０００２】
【従来の技術】セラミック基板に電極を形成する導体ペーストとして典型的なものに、導電性粉末（金属粉末）として銀（Ａｇ）を主体に構成されたもの（以下「Ａｇペースト」と略称する場合がある。）が知られている（例えば特許文献１〜１６参照）。銀粉末は金（Ａｕ）粉末、白金（Ｐｔ）粉末等と比較して安価に入手できるものであり、さらに電気的抵抗度も低い。このため、Ａｇペーストはセラミック基板等の各種電子部品に電極その他の導体膜を形成する用途に広く使用されている。
【０００３】
Ａｇペーストに求められる性能の一つに、該ペーストから形成される導体膜の緻密性を向上させるとともに、所謂「半田喰われ（典型的には導体膜に含まれる銀の半田への溶解）」を防止することが挙げられる。顕著な半田喰われの発生は、導体膜から成る回路（電極）と各種素子との接合性を劣化させ、延いては断線その他の導通不良の原因ともなるため好ましくない。
かかる要求を満足させるべく、従来、半田喰われ防止能力、換言すれば半田耐熱性に優れるパラジウム（Ｐｄ）が添加されたことを特徴とするＡｇペーストが使用されている。例えば特許文献６や特許文献１１には、銀粉末を主体としつつ所定の割合でパラジウム粉末を含有する導体ペーストが記載されている。
【０００４】
しかしながら、パラジウムは銀に比べて高価であるため、パラジウムの含有量が多くなるほどコスト高になってしまう。そこで、パラジウムを使用せずに耐半田喰われ性（半田耐熱性）に優れるＡｇペーストの開発が望まれている。
なお、ペーストを塗布して形成された膜の焼成時の焼結収縮防止を向上させるために、球状の銀粉末とフレーク状の銀粉末とを併用した導体ペーストが知られている（例えば特許文献１７〜２２参照）。しかしながら、これら導体ペーストでも耐半田喰われ性（半田耐熱性）は充分ではなかった。
【０００５】
【特許文献１】特開平５−１２８９０８号公報
【特許文献２】特開平５−１４４３１７号公報
【特許文献３】特開平５−２１９１９号公報
【特許文献４】特開平５−８９７１８号公報
【特許文献５】特開２００１−２６６６４１号公報
【特許文献６】特開２００１−４３７３３号公報
【特許文献７】特開平１１−１１１０５２号公報
【特許文献８】特開平１１−３０６８６２号公報
【特許文献９】特開平９−１７２３２号公報
【特許文献１０】特開平１０−３４０６２２号公報
【特許文献１１】特開平８−２９８０１８号公報
【特許文献１２】特開平７−１７６４４８号公報
【特許文献１３】特開平５−２２１６８６号公報
【特許文献１４】特開平６−２３５００６号公報
【特許文献１５】特開平５−１８２５１４号公報
【特許文献１６】特開平５−１５１８１８号公報
【特許文献１７】特開平７−３０２５１０号公報
【特許文献１８】特許第３０６３５４９号公報
【特許文献１９】特開平８−９７５２７号公報
【特許文献２０】特開平１１−６６９５６号公報
【特許文献２１】特開２００２−２９８６４９号公報
【特許文献２２】特開２００１−３３８８３０号公報
【０００６】
【発明が解決しようとする課題】そこで本発明は、Ａｇペーストに関する上記従来の課題を解決すべく創出されたものであり、その目的とするところは、高価なパラジウムを使用することなく耐半田喰われ性（半田耐熱性）に優れ、良好な導電性を有する導体膜を形成し得るＡｇペースト及びその製造方法を提供することである。
【０００７】
【課題を解決するための手段、作用および効果】本発明者は、導電性粉末として、粒径及び形態の異なる球状銀粉末及びフレーク状銀粉末を合計４種以上併用することによって、パラジウムを使用せずに耐半田喰われ性（半田耐熱性）に優れるＡｇペーストを製造し得ることを見出し、本発明を完成するに至った。
すなわち、本発明によって提供される銀粉末を主体とする導体ペーストの製造方法は、相互に平均粒径が異なる少なくとも２種の球状銀粉末と、相互に平均粒径が異なる少なくとも２種のフレーク状銀粉末とが混合されて成る導電性粉末を用意する工程と、上記導電性粉末を有機媒質中に分散させる工程とを包含する方法である。
【０００８】
また、本発明によって提供される導体ペーストは、球状銀粉末とフレーク状銀粉末とから実質的に構成される導電性粉末と、有機媒質とを含む導電ペースト（Ａｇペースト）であって、その導電性粉末は相互に平均粒径が異なる少なくとも２種の球状銀粉末と、相互に平均粒径が異なる少なくとも２種のフレーク状銀粉末とが混合されて形成されている。
本発明によると、上記４種以上の粒径及び形態の異なる銀粉末を併用することによって、セラミック基板等の基材上に半田喰われの少ない（従って導電性と成形性に優れた）緻密な導体膜（電極等）を形成し得るＡｇペーストを製造することができる。本発明の導体ペーストによれば、パラジウムを含有しなくても、顕著な半田喰われが生じない実用上充分なレベルの半田耐熱性を備えた導体膜を基材上に形成する（焼き付ける）ことができる。かかる導体膜は、良好な形状（外観及び緻密性）と導電性を有する。このため、本発明の導体ペーストを用いると、電極等の導体膜形成に係るコストを抑えつつ、良好な性能の導体膜（電極等）が形成された基板その他の電子部品を製造することができる。
【０００９】
好ましくは、上記導電性粉末を構成する球状銀粉末として、少なくとも平均粒径０．１〜０．８μｍの球状銀粉末及び平均粒径１．０〜２．０μｍの球状銀粉末が用いられる。これらの粉末を用いることによって、上記導電性粉末を構成する球状銀粉末であって、粒径０．１〜０．８μｍの範囲及び１．０〜２．０μｍの範囲にそれぞれ粒度分布のピークがある球状銀粉末を含むことを特徴とする導体ペースト（Ａｇペースト）を製造することができる。
このような組成（粒度分布）の球状銀粉末を含有する導体ペーストによると、特に半田喰われ防止効果を向上させることができる。
【００１０】
また、好ましくは、少なくとも平均粒径５〜１５μｍのフレーク状銀粉末が用いられる。さらに好ましくは、平均粒径１〜４μｍのフレーク状銀粉末が用いられる。これらの粉末を用いることによって、半田喰われ防止効果を向上させ得るとともに、優れた成形性を実現する導体ペースト（Ａｇペースト）を製造することができる。
【００１１】
特に好ましい方法では、使用する導電性粉末が、その全体を１００質量％として、４０〜８０質量％の平均粒径０．１〜０．８μｍの球状銀粉末と、３〜４０質量％の平均粒径１．０〜２．０μｍの球状銀粉末と、３〜３０質量％の平均粒径１〜４μｍのフレーク状銀粉末と、５〜４０質量％の平均粒径５〜１５μｍのフレーク状銀粉末とから実質的に構成されていることを特徴とする。このような組成の導電性粉末を使用することにより、特に耐半田喰われ性能に優れる導体ペースト（Ａｇペースト）を製造することができる。
【００１２】
好ましくは、本発明の製造方法において、上記導電性粉末の含有率はペースト全体の８５質量％以上となるように設定される。このような含有率で導電性粉末を含むＡｇペーストは、緻密性が向上して特に高温での耐半田喰われ性能の高い導体膜を形成するのに好適である。
【００１３】
【発明の実施の形態】以下、本発明の好適な実施形態を説明する。なお、本明細書において特に言及している事項以外の事柄であって本発明の実施に必要な事柄は、いずれも従来技術に基づく当業者の設計事項として把握され得る。本発明は、本明細書及び図面によって開示されている事項と当該分野における技術常識とに基づいて実施することができる。
【００１４】
本発明の導体ペーストは、銀粉末を主体とする導体ペースト（Ａｇペースト）であり、相互に粒径の異なる２種以上の球状銀粉末と、相互に粒径の異なる２種以上のフレーク状銀粉末とから構成され、上記目的を達成し得る限りにおいて他の副成分の内容や組成に特に制限はない。
本明細書において銀粉末とは、銀（Ａｇ）を主体とする粒子の集合体をいい、典型的にはＡｇ単体から成る粒子の集合体であるが、Ａｇ以外の不純物やＡｇ主体の合金を若干量含むものも、全体としてＡｇ主体の粒子の集合体である限り、ここでいう「銀粉末」に包含され得る。なお、銀粉末自体は、従来公知の製造方法によって製造されたものでよく、特別な製造手段を要求するものではない。例えば、周知の還元析出法、気相反応法、ガス還元法等によって製造された球状銀粉末及びフレーク状銀粉末を使用することができる。
また、本明細書において「銀粉末の平均粒径」は、当該粉末の粒度分布におけるＤ５０（メジアン径）をいう。かかるＤ５０は、例えばレーザー回折方式、光散乱方式等に基づく粒度分布測定装置によって容易に測定することができる。同様に、導電性粉末の粒度分布におけるピークの位置（典型的には含有率が際だって高い粒径範囲として把握される）を容易に同定することができる。
【００１５】
使用する球状銀粉末を構成する粒子は、いわゆる真球状のものに限られず、顕微鏡下で球と判断し得る程度であればよい。典型的には、当該粉末を構成する粒子（一次粒子）の７０質量％以上が球又はそれに類似する形状を有していることをいう。例えば銀粉末を構成する粒子の７０質量％以上がアスペクト比（即ち長径／短径比）１〜１．３であるものは本明細書における「球状銀粉末」に包含される典型例である。
球状銀粉末として相互に平均粒径が異なる少なくとも２種の粉末を混合する場合、特に限定するものではないが、平均粒径が０．１〜２．０μｍの範囲にあるものを使用することが好ましい。平均粒径０．１μｍ未満の球状粉末は凝集を起こし易く、ペーストに含まれる粉末の分散性を低下させる虞がある。一方、平均粒径が２．０μｍよりも大きすぎる球状粉末を使用し過ぎると、製造されたＡｇペーストから形成される導体膜の緻密性を低下させる虞があり好ましくない。
【００１６】
２種の球状銀粉末を混合する場合、平均粒径が概ね０．１〜０．８μｍの範囲にある球状銀粉末と、平均粒径が概ね１．０〜２．０μｍの範囲にある球状銀粉末とを少なくとも混合することが好ましい。
また、２種の球状銀粉末を混合する場合、一方の粉末の平均粒径が他方の粉末の平均粒径の概ね２〜５倍であることが好ましく、粒径の組み合わせにもよるが、３〜４倍であることが特に好ましい。例えば、一方の球状銀粉末の平均粒径が０．２〜０．７μｍ（特に０．３〜０．５μｍ）の範囲にある場合、他方の球状銀粉末の平均粒径は１．０〜２．０μｍ（特に１．２〜１．５μｍ）の範囲にあることが好ましい。このような平均粒径の球状銀粉末を組み合わせることによって、緻密な導体膜を形成し得るＡｇペースト（典型的には、粒度分布曲線において、混合した球状銀粉末の各平均粒径に対応した位置にそれぞれピークを有することで特徴付けられる。）を製造することができる。
なお、球状銀粉末は上述した２種に限定されず、相互に平均粒径の異なる３種又はそれ以上を用いることもできる。この場合にも平均粒径の範囲が０．１〜２．０μｍの範囲にある球状銀粉末を採用することが好ましい。
【００１７】
一方、使用するフレーク状銀粉末は、それを構成する粒子の過半数が顕微鏡下で薄片状と認められるものであればよく、典型的には、当該粉末を構成する粒子（一次粒子）の７０質量％以上がフレーク（薄片）又はそれに類似する形状を有していることをいう。例えば銀粉末を構成する粒子の７０質量％以上がアスペクト比（長径／短径比）１．５以上（例えば１．５〜２０）であるものは本明細書における「フレーク状銀粉末」に包含される典型例である。
【００１８】
使用するフレーク状銀粉末の平均厚さは０．１〜１．５μｍであることが望ましく、０．１〜１．０μｍであることがより好ましい。また、平均粒径が１〜２０μｍの範囲にあるものの使用が好ましい。平均粒径が上記範囲よりも大きすぎるものの使用は、導体膜の成形性が損なわれる虞があり好ましくない。また、平均粒径が上記範囲よりも小さすぎるものの使用は、フレーク状銀粉末を添加する効果が薄らぐため好ましくない。
【００１９】
フレーク状銀粉末として相互に平均粒径（典型的には長径における平均粒径をいう。以下同じ。）が異なる少なくとも２種の粉末を混合する場合、特に限定するものではないが、そのうちの一つは平均粒径が概ね５〜１５μｍの範囲にあるものの使用が好ましく、平均粒径が５〜１０μｍ（例えば６〜８μｍ）の範囲にあるフレーク状銀粉末の使用が特に好ましい。平均粒径５μｍ以上の比較的大きなフレーク状銀粉末を用いることによって、従来のＡｇペーストに比べて耐半田喰われ性能が向上したＡｇペーストを作成することができる。また、成形性及び導電性に優れた導体膜を形成することができる。
また、上記平均粒径が５〜１５μｍ（好ましくは５〜１０μｍ、特には６〜９μｍ）の範囲にあるフレーク状銀粉末とともに、平均粒径が１〜４μｍ（特に２〜３μｍ）の範囲にあるフレーク状銀粉末を使用することが好ましい。これら平均粒径（Ｄ５０）の異なる（換言すれば粒度分布の異なる）２種のフレーク状銀粉末を上述した２種又はそれ以上の球状銀粉末と組み合わせて用いることにより、緻密性及び耐半田喰われ性がより向上し、成形性に優れる導体膜を形成し得るＡｇペーストを製造することができる。なお、フレーク状銀粉末は上記２種に限定されず、平均粒径の異なる３種以上を用いることもできる。この場合にも平均粒径が１〜２０μｍの範囲にあるフレーク状銀粉末を採用することが好ましい。
【００２０】
また、２種のフレーク状銀粉末を混合する場合、一方の粉末の平均粒径が他方の粉末の平均粒径の概ね２〜５倍であることが好ましく、粒径の組み合わせにもよるが、３〜４倍であることが特に好ましい。例えば、一方のフレーク状銀粉末の平均粒径が１〜４μｍ（特に２〜３μｍ）である場合、他方のフレーク状銀粉末の平均粒径は５〜１５μｍ（特に８〜１２μｍ）であることが好ましい。このような平均粒径のフレーク状銀粉末を組み合わせることによって、緻密な導体膜を形成し得るＡｇペースト（典型的には、粒度分布曲線において、混合したフレーク状銀粉末の各平均粒径に対応した位置にそれぞれピークを有することで特徴付けられる。）を製造することができる。
【００２１】
導電性粉末を構成する球状銀粉末、フレーク状銀粉末の配合割合は、製造した導体ペーストをどのような用途に用いるか或いはどのような形状の導体膜を形成するか等に応じて適宜変更し得るものであり特に限定されない。例えば積層型セラミック基板における端子電極（側面電極）を形成する場合には、半田喰われを防止して所定の電極厚みや所望する導電性を確保すべく、好ましくは、導電性粉末の全量を１００質量％として、平均粒径０．１〜０．８μｍの球状銀粉末４０〜８０質量％、平均粒径１．０〜２．０μｍの球状銀粉末３〜４０質量％、平均粒径１〜４μｍのフレーク状銀粉末３〜３０質量％及び平均粒径５〜１５μｍのフレーク状銀粉末５〜４０質量％、となるように各粉末を混合するとよい。さらに好ましくは、導電性粉末の全量を１００質量％として、平均粒径０．１〜０．８μｍの球状銀粉末５０〜７０質量％、平均粒径１．０〜２．０μｍの球状銀粉末１０〜２０質量％、平均粒径１〜４μｍのフレーク状銀粉末５〜２０質量％及び平均粒径５〜１５μｍのフレーク状銀粉末１０〜２５質量％、となるように各粉末を混合する。このような組成の導電性粉末を含むＡｇペースト（例えば端子電極形成用Ａｇペースト）によれば、緻密性が高く半田喰われの生じ難い、導電性と成形性に優れた導体膜（例えば端子電極）を形成することができる。
【００２２】
本発明の実施に際し、導電性粉末（各種銀粉末の混合体）の含有量は特に制限されないが、ペースト全体を１００質量％として、その８５質量％以上（特に８６質量％以上、更には８７質量％以上、例えば８５〜９５質量％あるいは８６〜９３質量％あるいは８７〜９０質量％）が導電性粉末となるように含有率を調整することが好ましい。製造されたＡｇペースト中の導電性粉末含有量が上記のような場合には緻密性がより向上し、特に高温条件下における耐半田喰われ性能がより向上した導体膜を形成することができる。
【００２３】
次に、本発明の導体ペースト（Ａｇペースト）を製造する場合に使用する導電性粉末以外の材料について説明する。
【００２４】
本発明のＡｇペーストの副成分として、導電性粉末を分散させておく有機媒質（ビヒクル）が挙げられる。かかるビヒクルは、導電性粉末を良好に分散させ得るものであればよく、従来の導体ペーストに用いられているものを特に制限なく使用することができる。例えば、ミネラルスピリット等の石油系炭化水素（特に脂肪族炭化水素）、エチルセルロース等のセルロース系高分子、エチレングリコール及びジエチレングリコール誘導体、トルエン、キシレン、ブチルカルビトール（ＢＣ）、ターピネオール等の高沸点有機溶媒を一種類又は複数種組み合わせて使用することができる。特に限定しないが、ビヒクルの含有量はペースト全体のほぼ１〜１５質量％となる量が適当であり、ペースト全体の５〜１０質量％となる量が好ましい。
【００２５】
また、Ａｇペースト本来の導電性や本発明の効果、即ち耐半田喰われ性等を著しく損なわない限りにおいて種々の無機添加剤を副成分として含ませることができる。例えば、かかる無機添加剤としては、ガラスフリット、その他種々のフィラー等が挙げられる。そのようなガラスフリットとして、鉛系、亜鉛系、ホウケイ酸系ガラス、及び酸化ビスマス等、又はこれら２種以上の組み合わせが挙げられ、特に酸化ビスマスが好適である。
【００２６】
上述したような無機添加剤は、基板上に付着したペースト成分を安定的に焼き付き・固着させること（即ち接着強度の向上）に寄与する無機成分（無機結合材）となり得る。また、使用する無機添加剤（ガラスフリット等）としては、その比表面積が概ね０．５〜５０ｍ２／ｇであるものが好ましく、平均粒径が２μｍ以下（特に１μｍ程度又はそれ以下）のものが良好な導電性を損なわないため特に好適である。
【００２７】
無機添加剤としてガラスフリットや酸化ビスマス等の酸化物を加える場合には、それらの含有率がＡｇペースト全体のほぼ０．０１〜５質量％となる量が適当であり、０．０５〜５質量％、特に０．１〜１．０質量％となる量が好ましい。かかる低率の添加量によると、Ａｇペーストの良好な導電率を実質的に損なうことなく、Ａｇペーストから得られる焼成物（電極等の導体）の基材に対する接着強度の向上を実現することができる。
【００２８】
また、ペーストには、有機バインダーとして種々の樹脂成分を含ませることができる。本発明の実施にあたっては、かかる樹脂成分はＡｇペーストに良好な粘性及び塗膜（基材に対する付着膜）形成能を付与し得るものであればよく、従来の導体ペーストに用いられているものを特に制限なく使用することができる。例えば、アクリル樹脂、エポキシ樹脂、フェノール樹脂、アルキド樹脂、セルロース系高分子、ポリビニルアルコール、ロジン樹脂等を主体とするものが挙げられる。このうち、特にエチルセルロース等のセルロース系高分子、ロジン樹脂、アルキド樹脂又はこれらの２種以上の組み合わせが好ましい。特に限定しないが、樹脂成分の含有量はペースト全体のほぼ０．５〜５質量％となる量が適当である。
【００２９】
なお、上記の他にも本発明のＡｇペーストには、必要に応じて界面活性剤、消泡剤、可塑剤（例えばフタル酸ジオクチル（ＤＯＰ）等のフタル酸エステル）、増粘剤、酸化防止剤、分散剤、重合禁止剤等を適宜添加することができる。これら添加剤は、従来の導体ペーストの調製に用いられ得るものであればよく、詳細な説明は省略する。また、Ａｇペーストに光硬化性（感光性）を付与したい場合には、種々の光重合性化合物及び光重合開始剤を適宜添加してもよい。
【００３０】
ここで開示されるＡｇペーストは、従来の導体ペーストと同様、典型的には導電性粉末（球状銀粉末及びフレーク状銀粉末）、有機媒質（ビヒクル）及びその他の添加物（必要に応じて添加すればよい。）を混合することによって容易に調製することができる。ここで、導電性粉末は、相互に平均粒径の異なる少なくとも２種の球状銀粉末と少なくとも２種のフレーク状銀粉末とを混合して有機媒質中に分散させる。例えば、三本ロールミルその他の混練機を用いて、所定の混合割合の導電性粉末及び各種の添加剤を有機媒質とともに所定の配合比で混合・撹拌するとよい。
【００３１】
得られたＡｇペーストは、基板上に配線、電極等の導体膜を形成するのに従来用いられてきた導体ペーストと同様に取り扱うことができ、従来公知の方法を特に制限なく採用することができる。典型的には、ディップ塗布法、スクリーン印刷法やディスペンサー塗布法等によって、所望する形状・厚みとなるようにしてＡｇペーストを基板に塗りつける。本発明のＡｇペーストは、ディップ塗布法に基づいて基板上に導体膜（例えば積層セラミック基板の側面電極）を形成する、所謂ディップタイプＡｇペーストとして特に好ましく使用することができる。
次いで、好ましくは乾燥後、加熱器中で適当な加熱条件で所定時間加熱することによって、その塗りつけられたペースト成分を焼成（焼き付け）し、硬化させる。この一連の処理を行うことによって、目的の導体膜（端子電極、配線等）が形成された電子部品（ＭＬＣＣ等）が得られる。而して、当該電子部品を組み立て材料として用いつつ従来公知の構築方法を適用することによってさらに高度な電子部品を得ることができる。なお、かかる構築方法自体は、特に本発明を特徴付けるものではないため、詳細な説明は省略する。
【００３２】
【実施例】以下、本発明に関するいくつかの実施例を説明するが、本発明をかかる実施例に示すものに限定することを意図したものではない。
【００３３】
＜材料＞
以下の実施例及び比較例において使用した各成分を以下に列挙する。
（１）銀粉末
▲１▼球状銀粉末１：平均粒径（Ｄ５０）０．４μｍ
▲２▼球状銀粉末２：平均粒径（Ｄ５０）０．７μｍ
▲３▼球状銀粉末３：平均粒径（Ｄ５０）１．２μｍ
▲４▼フレーク状銀粉末１：平均粒径（Ｄ５０）２〜３μｍ
▲５▼フレーク状銀粉末２：平均粒径（Ｄ５０）５〜１０μｍ
（２）樹脂成分
▲１▼エチルセルロース
▲２▼ロジン系樹脂
（３）溶剤成分
▲１▼石油系溶剤（ミネラルスピリット）
▲２▼ＢＣ
▲３▼ターピネオール
（４）無機添加剤
▲１▼酸化ビスマス粉末（平均粒径：１〜５μｍ）
（５）添加剤
▲１▼可塑剤（ＤＯＰ）
【００３４】
＜実施例１：Ａｇペーストの調製（１）＞
５６部の球状銀粉末１と、１５部の球状銀粉末３と、９部のフレーク状銀粉末１と、２０部のフレーク状銀粉末２とを混合した。
次いで、得られた導電性粉末８６部に、２．０部のエチルセルロース及び２．０部のロジン系樹脂、さらには４．５部の石油系溶剤、４．０部のＢＣ及び／又はターピネオールを加え、三本ロールミルを用いて混練した。さらに、０．５部の酸化ビスマス粉末及び１部の可塑剤を添加して混練した。これにより、本実施例に係るＡｇペースト（導電性粉末の含有率：８６質量％）を調製した。
【００３５】
＜実施例２：Ａｇペーストの調製（２）＞
実施例１で得られた導電性粉末８０部に、２．０部のエチルセルロース及び２．０部のロジン系樹脂、さらには７．５部の石油系溶剤、７．０部のＢＣ及び／又はターピネオールを加え、三本ロールミルを用いて混練した。さらに、０．５部の酸化ビスマス粉末及び１部の可塑剤を添加して混練した。これにより、本実施例に係るＡｇペースト（導電性粉末の含有率：８０質量％）を調製した。
【００３６】
＜実施例３：Ａｇペーストの調製（３）＞
実施例１で得られた導電性粉末８７部に、７．０部のエチルセルロース及び２．０部のロジン系樹脂、さらには４．０部の石油系溶剤、３．５部のＢＣ及び／又はターピネオールを加え、三本ロールミルを用いて混練した。さらに、０．５部の酸化ビスマス粉末及び１部の可塑剤を添加して混練した。これにより、本実施例に係るＡｇペースト（導電性粉末の含有率：８７質量％）を調製した。
【００３７】
＜実施例４：Ａｇペーストの調製（４）＞
６３部の球状銀粉末２と、１５部の球状銀粉末３と、９部のフレーク状銀粉末１と、１３部のフレーク状銀粉末２とを混合した。
次いで、得られた導電性粉末８７部に、２．０部のエチルセルロース及び２．０部のロジン系樹脂、さらには４．０部の石油系溶剤、３．５部のＢＣ及び／又はターピネオールを加え、三本ロールミルを用いて混練した。さらに、０．５部の酸化ビスマス粉末及び１部の可塑剤を添加して混練した。これにより、本実施例に係るＡｇペースト（導電性粉末の含有率：８７質量％）を調製した。
【００３８】
＜比較例１：パラジウム含有Ａｇペーストの調製＞
８５部の球状銀粉末１と、１５部の球状パラジウム粉末とを混合して導電性粉末（Ａｇ／Ｐｄ粉末）を得た。
次いで、得られたＡｇ／Ｐｄ粉末８０部に、２．０部のエチルセルロース及び２．０部のロジン系樹脂、１３．０部のＢＣ及び／又はターピネオールを加え、三本ロールミルを用いて混練した。さらに、２．０部の酸化ビスマス粉末及び１部の可塑剤を添加して混練した。これにより、本比較例に係るＡｇ／Ｐｄペースト（導電性粉末の含有率：８０質量％）を調製した。
【００３９】
＜比較例２：２種の銀粉末を用いたＡｇペーストの調製（１）＞
５０部の球状銀粉末２と、５０部のフレーク状銀粉末２とを混合した。
次いで、得られた導電性粉末８０部に、２．０部のエチルセルロース及び２．０部のロジン系樹脂、さらには７．５部の石油系溶剤、７．０部のＢＣ及び／又はターピネオールを加え、三本ロールミルを用いて混練した。さらに、０．５部の酸化ビスマス粉末及び１部の可塑剤を添加して混練した。これにより、本比較例に係るＡｇペースト（導電性粉末の含有率：８０質量％）を調製した。
【００４０】
＜比較例３：２種の銀粉末を用いたＡｇペーストの調製（２）＞
６６部の球状銀粉末１と、３４部のフレーク状銀粉末１とを混合した。
次いで、得られた導電性粉末８５部に、２．０部のエチルセルロース及び２．０部のロジン系樹脂、さらには５．０部の石油系溶剤、４．５部のＢＣ及び／又はターピネオールを加え、三本ロールミルを用いて混練した。さらに、０．５部の酸化ビスマス粉末及び１部の可塑剤を添加して混練した。これにより、本比較例に係るＡｇペースト（導電性粉末の含有率：８５質量％）を調製した。
【００４１】
＜比較例４：３種の銀粉末を用いたＡｇペーストの調製（１）＞
６７部の球状銀粉末１と、１８部のフレーク状銀粉末１と、１５部のフレーク状銀粉末２とを混合した。
次いで、得られた導電性粉末８５部に、２．０部のエチルセルロース及び２．０部のロジン系樹脂、さらには５．０部の石油系溶剤、４．５部のＢＣ及び／又はターピネオールを加え、三本ロールミルを用いて混練した。さらに、０．５部の酸化ビスマス粉末及び１部の可塑剤を添加して混練した。これにより、本比較例に係るＡｇペースト（導電性粉末の含有率：８５質量％）を調製した。
【００４２】
＜比較例５：３種の銀粉末を用いたＡｇペーストの調製（２）＞
６９部の球状銀粉末１と、１８部のフレーク状銀粉末１と、１３部のフレーク状銀粉末２とを混合した。
次いで、得られた導電性粉末８７部に、２．０部のエチルセルロース及び２．０部のロジン系樹脂、さらには４．０部の石油系溶剤、３．５部のＢＣ及び／又はターピネオールを加え、三本ロールミルを用いて混練した。さらに、０．５部の酸化ビスマス粉末及び１部の可塑剤を添加して混練した。これにより、本比較例に係るＡｇペースト（導電性粉末の含有率：８７質量％）を調製した。
【００４３】
＜比較例６：３種の銀粉末を用いたＡｇペーストの調製（３）＞
７０部の球状銀粉末１と、１５部の球状銀粉末２と、１５部のフレーク状銀粉末１とを混合した。
次いで、得られた導電性粉末８７部に、２．０部のエチルセルロース及び２．０部のロジン系樹脂、さらには４．０部の石油系溶剤、３．５部のＢＣ及び／又はターピネオールを加え、三本ロールミルを用いて混練した。さらに、０．５部の酸化ビスマス粉末及び１部の可塑剤を添加して混練した。これにより、本比較例に係るＡｇペースト（導電性粉末の含有率：８７質量％）を調製した。
【００４４】
＜端子電極の形成＞
次に、実施例３〜４に係る導体ペースト及び比較例２〜６に係る導体ペーストを用いて、それぞれ、積層型セラミック基板の表面（端面）に電極（端子電極）を形成した。すなわち、アルミナ製の積層セラミック基板（サイズ：５．０ｍｍ×５．０ｍｍ×０．８ｍｍ）の端面に、各実施例及び比較例の導体ペーストをディップ塗布し、所定の厚み（平均厚み：１０〜３０μｍ）の端子電極を形成した。
次に、この端子電極をセラミック基板ごと焼成した。すなわち、電気炉中で８５０℃で１時間の焼成処理を行った。この焼成処理によって、所定の膜厚の導体膜（電極）を積層セラミック基板の端面に焼き付けた。以下、単に導体膜というときは当該焼成後のものを指す。
【００４５】
＜半田耐熱性の評価（１）＞
実施例３〜４に係る導体ペースト及び比較例２〜６に係る導体ペーストを使用して得られた上記端子電極（導体膜）のそれぞれについて以下のようにして半田耐熱性試験を行った。
すなわち、各積層セラミック基板の導体膜部分にロジンフラックスを塗布した後、当該基板を所定温度の半田（ここではＳｎ／Ｐｂ＝６０／４０（質量比）を用いたが、所謂Ｐｂフリー半田を適用しても同様の効果が得られ得る。）に所定時間浸漬した。ここでは、かかる半田温度条件及び浸漬時間を２３０℃×１５秒、及び２６０℃×１５秒の２通りとした。而して、浸漬後に「半田喰われ」されなかった部分、即ち浸漬前と比較して浸漬後にセラミック基板上に残存している導体膜の面積比率で半田耐熱性を評価した。結果を表１に示す。
具体的には、導体膜の略９５％以上が残存しているものは優れた耐半田喰われ性能即ち半田耐熱性を示すものと判断して表中において◎で示した。また、導体膜の略９０％以上９５％未満が残存しているものは良好な半田耐熱性を示すものと判断して表中において○で示した。また、導体膜の残存している部分が浸漬前の略７０％以上９０％未満のものは半田耐熱性がやや劣っているものと判断して表中において△で示した。また、導体膜の残存している部分が浸漬前の７０％未満のものは半田耐熱性を有していないものと判断して表中において×で示した。表１から明らかなように、各実施例の導体ペーストを使用して形成した導体膜は、各比較例の導体ペーストを使用して形成した導体膜よりも高い半田耐熱性を有していた。
【００４６】
【表１】
＜半田耐熱性の評価（２）＞
実施例１〜２及び比較例１の導体ペーストを用いて、それぞれ、アルミナ製セラミック基材（厚み約０．８ｍｍ）の表面に概ね５ｍｍ×５ｍｍの導体膜を形成した。すなわち、一般的なディップ塗布法に基づいてセラミック基板の表面に導体ペーストを塗布し、所定の膜厚（１０〜３０μｍ）の塗膜を形成した。
続いて、遠赤外線乾燥機を用いて１００℃で１５分間の乾燥処理を施した。この乾燥処理により、上記塗膜から溶剤が揮発していき、セラミック基板上に未焼成の導体膜が形成された。
次に、この導体膜をセラミック基板ごと焼成した。すなわち、電気炉中で８５０℃で１時間の焼成処理を行った。この焼成処理によって、所定の膜厚の導体膜をセラミック基板上に焼き付けた。
【００４８】
次に、実施例３〜４及び比較例２〜６の導体ペーストを用いた場合と同様の半田耐熱性試験を行った。その結果として、半田浸漬後のセラミック基板の表面写真を図１に示す。
これら表面写真から明らかなように、実施例１の導体ペーストから形成された導体膜は、いずれの条件でもいわゆる「半田喰われ」が実質的に生じなかった。また、実施例２の導体ペーストから形成された導体膜も、２３０℃の条件では半田喰われが実質的に生じておらず、２６０℃の条件でも半田喰われの程度は僅かであった。他方、比較例１の導体ペースト（Ａｇ／Ｐｄペースト）から形成された導体膜は、２３０℃の条件で半田喰われが生じており、２６０℃の条件では半田喰われが顕著であった。以上の結果から、導電性粉末の含有率が８５質量％以上（実施例１の導体ペーストでは８６質量％）の導体ペーストから形成された導体膜は特に高い半田耐熱性を有していることが確かめられた。
【００４９】
＜乾燥外観の評価＞
実施例３〜４及び比較例２〜６に係る導体ペーストを使用して得られた端子電極の半田浸漬後の乾燥外観を目視にて評価した。すなわち、２３０℃で１５秒間の半田浸漬処理を行ったものについて、乾燥後の端子電極の外観が全体に亘って均質な穹窿形状に形成されているものを優良（表１中◎にて示す）とし、略均質な穹窿形状と認められるものを良好（表１中○にて示す）とし、表面の一部に角状突起が形成されていたり穹窿形状の一部が崩れているものを不良（表１中×にて示す）として評価した。結果を表１の該当欄に示す。
表１から明らかなように、比較例２〜６の導体ペーストにより得られた端子電極は、半田浸漬後の外観が悪化しており、半田耐熱性の低さを裏付ける結果となった。これに対して、実施例３及び４の導体ペーストから得られた端子電極は、上述した半田耐熱性と同様、良好な乾燥外観を保持していることが確認された。特に、実施例３の導体ペーストにより得られた端子電極は、半田耐熱性及び乾燥外観のいずれも優良であった。
【００５０】
以上の実施例において、本発明の具体例を詳細に説明したが、これらは例示にすぎず、特許請求の範囲を限定するものではない。特許請求の範囲に記載の技術には、以上に例示した具体例を様々に変形、変更したものが含まれる。
また、本明細書または図面に説明した技術要素は、単独であるいは各種の組み合わせによって技術的有用性を発揮するものであり、出願時の請求項記載の組み合わせに限定されるものではない。また、本明細書または図面に例示した技術は複数目的を同時に達成するものであり、そのうちの一つの目的を達成すること自体で技術的有用性を持つものである。
【図面の簡単な説明】
【図１】実施例１、２及び比較例１に係る導体ペーストを使用してセラミック基板上にそれぞれ形成した導体膜の半田浸漬処理後の状態を示す写真である。[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conductor paste used for forming a film conductor (hereinafter, referred to as a "conductor film") such as an electrode or a circuit on a ceramic substrate or other base material.
[0002]
2. Description of the Related Art A typical conductor paste for forming electrodes on a ceramic substrate is a conductor paste mainly composed of silver (Ag) as a conductive powder (metal powder) (hereinafter referred to as "Ag paste"). Are known (for example, see Patent Documents 1 to 16). Silver powder is available at a lower cost than gold (Au) powder, platinum (Pt) powder, and the like, and has a lower electrical resistance. For this reason, Ag paste is widely used for forming electrodes and other conductive films on various electronic components such as ceramic substrates.
[0003]
One of the performances required for the Ag paste is to improve the denseness of a conductor film formed from the paste and to achieve so-called “solder erosion (typically, dissolution of silver contained in the conductor film into solder)”. Prevention. The occurrence of remarkable solder erosion is not preferable because it deteriorates the bondability between a circuit (electrode) formed of a conductive film and various elements, and eventually causes disconnection and other conduction defects.
In order to satisfy such a demand, an Ag paste characterized by the addition of palladium (Pd) having excellent solder erosion prevention ability, in other words, excellent solder heat resistance, has been used. For example, Patent Literature 6 and Patent Literature 11 disclose a conductive paste mainly containing silver powder and containing a predetermined ratio of palladium powder.
[0004]
However, since palladium is more expensive than silver, the cost increases as the content of palladium increases. Therefore, development of an Ag paste having excellent solder erosion resistance (solder heat resistance) without using palladium is desired.
In order to improve the prevention of sintering shrinkage during baking of a film formed by applying a paste, a conductive paste using a combination of a spherical silver powder and a flaky silver powder is known (for example, Patent Document 1). 17-22). However, even with these conductor pastes, the solder erosion resistance (solder heat resistance) was not sufficient.
[0005]
[Patent Document 1] JP-A-5-128908
[Patent Document 2] JP-A-5-144317
[Patent Document 3] JP-A-5-21919
[Patent Document 4] JP-A-5-89718
[Patent Document 5] JP-A-2001-266641
[Patent Document 6] JP-A-2001-43733
[Patent Document 7] JP-A-11-111052
[Patent Document 8] Japanese Patent Application Laid-Open No. 11-306862
[Patent Document 9] JP-A-9-17232
[Patent Document 10] JP-A-10-340622
[Patent Document 11] JP-A-8-298018
[Patent Document 12] JP-A-7-176448
[Patent Document 13] JP-A-5-221686
[Patent Document 14] JP-A-6-235006
[Patent Document 15] JP-A-5-182514
[Patent Document 16] JP-A-5-151818
[Patent Document 17] JP-A-7-302510
[Patent Document 18] Japanese Patent No. 3063549
[Patent Document 19] JP-A-8-97527
[Patent Document 20] JP-A-11-66956
[Patent Document 21] JP-A-2002-298649
[Patent Document 22] JP-A-2001-388830
[0006]
SUMMARY OF THE INVENTION Accordingly, the present invention has been made to solve the above-mentioned conventional problems relating to Ag paste, and an object of the present invention is to eliminate the use of expensive palladium to prevent solder erosion. An object of the present invention is to provide an Ag paste capable of forming a conductive film having excellent brittleness (solder heat resistance) and good conductivity, and a method for producing the same.
[0007]
Means for Solving the Problems, Action and Effect The present inventors have used palladium as a conductive powder by using a total of four or more types of spherical silver powder and flake silver powder having different particle sizes and shapes. It has been found that an Ag paste having excellent solder erosion resistance (solder heat resistance) can be produced without using the same, and the present invention has been completed.
That is, the method for producing a conductive paste mainly composed of silver powder provided by the present invention comprises at least two kinds of spherical silver powders having mutually different average particle diameters and at least two kinds of flake-shaped powders having mutually different average particle diameters. This method includes a step of preparing a conductive powder obtained by mixing silver powder and a step of dispersing the conductive powder in an organic medium.
[0008]
Further, the conductive paste provided by the present invention is a conductive paste (Ag paste) containing a conductive powder substantially composed of spherical silver powder and flaky silver powder, and an organic medium. The conductive powder is formed by mixing at least two kinds of spherical silver powders having mutually different average particle diameters and at least two kinds of flake silver powders having mutually different average particle diameters.
According to the present invention, by using the above-mentioned four or more kinds of silver powders having different particle diameters and forms in combination, a fine powder with less solder erosion (and thus excellent conductivity and moldability) on a substrate such as a ceramic substrate. An Ag paste capable of forming a conductive film (such as an electrode) can be manufactured. ADVANTAGE OF THE INVENTION According to the conductor paste of this invention, even if it does not contain palladium, the conductor film which has the solder heat resistance of a practically sufficient level which does not generate remarkable solder erosion is formed on a base material (baking). Can be. Such a conductive film has a good shape (appearance and denseness) and conductivity. Therefore, when the conductor paste of the present invention is used, it is possible to manufacture a substrate and other electronic components on which a conductor film (such as an electrode) having good performance is formed, while suppressing the cost for forming a conductor film such as an electrode. .
[0009]
Preferably, spherical silver powder having an average particle diameter of at least 0.1 to 0.8 μm and spherical silver powder having an average particle diameter of 1.0 to 2.0 μm are used as the spherical silver powder constituting the conductive powder. By using these powders, it is a spherical silver powder constituting the conductive powder, the peak of the particle size distribution in the range of particle size 0.1-0.8μm and 1.0-2.0μm, respectively. A conductor paste (Ag paste) characterized by containing a certain spherical silver powder can be produced.
According to the conductor paste containing the spherical silver powder having such a composition (particle size distribution), the effect of preventing solder erosion can be particularly improved.
[0010]
Preferably, flake silver powder having an average particle size of at least 5 to 15 μm is used. More preferably, flake silver powder having an average particle size of 1 to 4 μm is used. By using these powders, a conductor paste (Ag paste) that can improve the effect of preventing solder erosion and achieve excellent moldability can be manufactured.
[0011]
In a particularly preferred method, the conductive powder to be used is a spherical silver powder having an average particle size of 40 to 80% by mass and a mean particle size of 0.1 to 0.8 μm and an average particle size of 3 to 40% by mass, with the whole being 100% by mass. Spherical silver powder having a diameter of 1.0 to 2.0 μm, flake silver powder having an average particle diameter of 3 to 30% by mass, and flake silver powder having an average particle size of 5 to 15 μm having a particle size of 5 to 40% by mass And is substantially composed of By using the conductive powder having such a composition, a conductive paste (Ag paste) having particularly excellent solder erosion resistance can be produced.
[0012]
Preferably, in the production method of the present invention, the content of the conductive powder is set to be 85% by mass or more of the entire paste. An Ag paste containing a conductive powder with such a content is suitable for forming a conductor film having improved denseness and particularly high resistance to solder erosion at high temperatures.
[0013]
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below. It should be noted that matters other than matters specifically referred to in the present specification and necessary for carrying out the present invention can be grasped as design matters of those skilled in the art based on the conventional technology. The present invention can be carried out based on the matters disclosed in the present specification and the drawings and common technical knowledge in the relevant field.
[0014]
The conductor paste of the present invention is a conductor paste (Ag paste) mainly composed of silver powder, and is composed of two or more kinds of spherical silver powder having different particle diameters and two or more kinds of flake silver having different particle diameters. The content and composition of the other subcomponents are not particularly limited, as long as the above components can be achieved from the powder.
In the present specification, silver powder refers to an aggregate of particles mainly composed of silver (Ag), and is typically an aggregate of particles composed of Ag alone. However, impurities other than Ag and alloys mainly composed of Ag are used. What contains a small amount can be included in the “silver powder” as long as it is an aggregate of particles mainly composed of Ag as a whole. The silver powder itself may be manufactured by a conventionally known manufacturing method, and does not require any special manufacturing means. For example, spherical silver powder and flake silver powder produced by a well-known reduction precipitation method, gas phase reaction method, gas reduction method, or the like can be used.
Further, in the present specification, the “average particle size of silver powder” refers to D in the particle size distribution of the powder. 50 (Median diameter). Such a D 50 Can be easily measured by, for example, a particle size distribution measuring device based on a laser diffraction method, a light scattering method or the like. Similarly, it is possible to easily identify the position of the peak in the particle size distribution of the conductive powder (typically, the content is grasped as a particle size range that is significantly higher).
[0015]
The particles constituting the spherical silver powder to be used are not limited to so-called true spherical particles, and may be any particles that can be judged as spheres under a microscope. Typically, it means that 70% by mass or more of particles (primary particles) constituting the powder have a sphere or a shape similar thereto. For example, those in which 70% by mass or more of the particles constituting the silver powder have an aspect ratio (that is, a ratio of major axis / minor axis) of 1 to 1.3 are typical examples included in the “spherical silver powder” in this specification.
When mixing at least two kinds of powders having mutually different average particle diameters as the spherical silver powder, there is no particular limitation, but those having an average particle diameter in the range of 0.1 to 2.0 μm may be used. preferable. Spherical powder having an average particle size of less than 0.1 μm is liable to cause aggregation, and may reduce the dispersibility of the powder contained in the paste. On the other hand, if the spherical powder having an average particle size that is too large than 2.0 μm is used too much, the denseness of the conductor film formed from the manufactured Ag paste may be undesirably reduced.
[0016]
When two types of spherical silver powders are mixed, a spherical silver powder having an average particle size of approximately 0.1 to 0.8 μm and a spherical silver powder having an average particle size of approximately 1.0 to 2.0 μm It is preferable to mix at least the powder.
When two types of spherical silver powders are mixed, the average particle size of one powder is preferably about 2 to 5 times the average particle size of the other powder. It is particularly preferred that the ratio be up to 4 times. For example, when one spherical silver powder has an average particle size of 0.2 to 0.7 μm (particularly 0.3 to 0.5 μm), the other spherical silver powder has an average particle size of 1.0 to 2 μm. It is preferably in the range of 2.0 μm (especially 1.2 to 1.5 μm). Ag paste capable of forming a dense conductor film by combining spherical silver powders having such an average particle size (typically, a position corresponding to each average particle size of the mixed spherical silver powder in the particle size distribution curve). Are each characterized by having a peak at the same time.)
In addition, the spherical silver powder is not limited to the above two kinds, and three or more kinds having different average particle diameters can be used. Also in this case, it is preferable to use a spherical silver powder having an average particle size in the range of 0.1 to 2.0 μm.
[0017]
On the other hand, the flaky silver powder to be used is not particularly limited as long as a majority of the particles constituting the powder are recognized as flakes under a microscope. Typically, 70 masses of the particles (primary particles) constituting the powder are used. % Or more has a flake (flake) or similar shape. For example, particles having an aspect ratio (major axis / minor axis ratio) of 1.5 or more (for example, 1.5 to 20) in 70% by mass or more of the particles constituting the silver powder are included in the “flake silver powder” in this specification. This is a typical example.
[0018]
The average thickness of the flake silver powder used is preferably 0.1 to 1.5 μm, more preferably 0.1 to 1.0 μm. Further, it is preferable to use those having an average particle size in the range of 1 to 20 μm. It is not preferable to use one having an average particle size larger than the above range because the moldability of the conductor film may be impaired. The use of a powder having an average particle size smaller than the above range is not preferable because the effect of adding the flake silver powder is weakened.
[0019]
When at least two kinds of powders having mutually different average particle diameters (typically, the average particle diameter in a long diameter; the same applies hereinafter) are mixed as flake silver powder, it is not particularly limited, but one of them is used. One having an average particle size of about 5 to 15 μm is preferable, and the use of flake silver powder having an average particle diameter of 5 to 10 μm (for example, 6 to 8 μm) is particularly preferable. By using a relatively large flake silver powder having an average particle size of 5 μm or more, an Ag paste having improved solder erosion resistance as compared with a conventional Ag paste can be prepared. In addition, a conductive film having excellent moldability and conductivity can be formed.
In addition, the flake silver powder having an average particle diameter in the range of 5 to 15 μm (preferably 5 to 10 μm, particularly 6 to 9 μm) is used, and the average particle diameter is in the range of 1 to 4 μm (in particular, 2 to 3 μm). It is preferred to use flake silver powder. These average particle sizes (D 50 By using two kinds of flake silver powders having different (in other words, different particle size distribution) in combination with the above two or more kinds of spherical silver powders, the denseness and solder erosion resistance are further improved. An Ag paste capable of forming a conductive film having excellent moldability can be manufactured. The flake silver powder is not limited to the above two types, and three or more types having different average particle diameters can be used. Also in this case, it is preferable to use flake silver powder having an average particle size in the range of 1 to 20 μm.
[0020]
When two kinds of flaky silver powders are mixed, the average particle diameter of one powder is preferably about 2 to 5 times the average particle diameter of the other powder, depending on the combination of particle diameters. It is particularly preferred that the ratio be 3 to 4 times. For example, when the average particle diameter of one flake silver powder is 1 to 4 μm (particularly 2 to 3 μm), the average particle diameter of the other flake silver powder is 5 to 15 μm (particularly 8 to 12 μm). preferable. Ag paste capable of forming a dense conductor film by combining flaky silver powders having such an average particle diameter (typically, corresponding to each average particle diameter of the mixed flake silver powder in a particle size distribution curve). Are characterized by having a peak at each of the specified positions.).
[0021]
The mixing ratio of the spherical silver powder and the flake silver powder constituting the conductive powder may be changed as appropriate according to the intended use of the produced conductor paste or the shape of the conductor film to be formed. It is not particularly limited. For example, when forming a terminal electrode (side electrode) on a laminated ceramic substrate, preferably, the total amount of the conductive powder is set to 100 to prevent solder erosion and ensure a predetermined electrode thickness and desired conductivity. As mass%, spherical silver powder having an average particle size of 0.1 to 0.8 μm is 40 to 80 mass%, spherical silver powder having an average particle size of 1.0 to 2.0 μm is 3 to 40 mass%, and average particle size is 1 to 4 μm. It is advisable to mix the respective powders so as to obtain 3 to 30% by mass of flake silver powder and 5 to 40% by mass of flake silver powder having an average particle size of 5 to 15 μm. More preferably, assuming that the total amount of the conductive powder is 100% by mass, 50 to 70% by mass of the spherical silver powder having an average particle size of 0.1 to 0.8 μm, and 10 to 2.0% by mass of the spherical silver powder 10 having an average particle size of 1.0 to 2.0 μm. The respective powders are mixed so as to obtain -20% by mass, 5-20% by mass of flake silver powder having an average particle size of 1-4 μm, and 10-25% by mass of flake silver powder having an average particle size of 5-15 μm. According to an Ag paste containing a conductive powder having such a composition (for example, an Ag paste for forming a terminal electrode), a conductive film (for example, a terminal electrode) having a high density, hardly causing solder erosion, and having excellent conductivity and moldability. ) Can be formed.
[0022]
In carrying out the present invention, the content of the conductive powder (mixture of various silver powders) is not particularly limited, but is 85% by mass or more (especially 86% by mass or more, particularly 87% by mass, with the whole paste being 100% by mass). % Or more, for example, 85 to 95% by mass, 86 to 93% by mass, or 87 to 90% by mass) of the conductive powder. In the case where the content of the conductive powder in the manufactured Ag paste is as described above, the denseness is further improved, and in particular, a conductor film having more improved resistance to solder erosion under high temperature conditions can be formed.
[0023]
Next, materials other than the conductive powder used for producing the conductor paste (Ag paste) of the present invention will be described.
[0024]
As an auxiliary component of the Ag paste of the present invention, an organic medium (vehicle) in which conductive powder is dispersed may be mentioned. Such a vehicle may be any vehicle as long as it can disperse the conductive powder satisfactorily, and those used in conventional conductor pastes can be used without any particular limitation. For example, petroleum hydrocarbons (especially aliphatic hydrocarbons) such as mineral spirits, cellulosic polymers such as ethyl cellulose, ethylene glycol and diethylene glycol derivatives, high boiling point organic solvents such as toluene, xylene, butyl carbitol (BC), and terpineol Can be used alone or in combination. Although not particularly limited, the content of the vehicle is suitably in an amount of about 1 to 15% by mass of the whole paste, and preferably 5 to 10% by mass of the whole paste.
[0025]
In addition, various inorganic additives can be included as sub-components as long as the intrinsic conductivity of the Ag paste and the effect of the present invention, that is, resistance to solder erosion, etc. are not significantly impaired. For example, such inorganic additives include glass frit and various other fillers. Examples of such a glass frit include lead-based, zinc-based, borosilicate-based glass, bismuth oxide, and the like, or a combination of two or more thereof, with bismuth oxide being particularly preferred.
[0026]
The inorganic additive as described above can be an inorganic component (inorganic binder) that contributes to stably sticking and fixing the paste component attached to the substrate (that is, improving the adhesive strength). The inorganic additive (glass frit or the like) used has a specific surface area of approximately 0.5 to 50 m. 2 / G is preferable, and those having an average particle size of 2 μm or less (particularly about 1 μm or less) are particularly preferable because good conductivity is not impaired.
[0027]
When an oxide such as glass frit or bismuth oxide is added as an inorganic additive, the content thereof is preferably about 0.01 to 5% by mass of the whole Ag paste, and 0.05 to 5% by mass. %, Particularly preferably 0.1 to 1.0% by mass. According to such a low addition amount, it is possible to improve the adhesive strength of the fired product (conductor such as an electrode) obtained from the Ag paste to the base material without substantially impairing the good conductivity of the Ag paste. it can.
[0028]
Further, the paste may contain various resin components as an organic binder. In the practice of the present invention, such a resin component may be any as long as it can impart good viscosity and the ability to form a coating film (adhesion film to a substrate) to the Ag paste. It can be used without particular limitation. For example, those mainly composed of acrylic resin, epoxy resin, phenol resin, alkyd resin, cellulosic polymer, polyvinyl alcohol, rosin resin and the like can be mentioned. Among them, a cellulose-based polymer such as ethyl cellulose, a rosin resin, an alkyd resin, or a combination of two or more thereof is particularly preferable. Although not particularly limited, it is appropriate that the content of the resin component is about 0.5 to 5% by mass of the whole paste.
[0029]
In addition to the above, the Ag paste of the present invention may further contain a surfactant, an antifoaming agent, a plasticizer (for example, phthalic acid ester such as dioctyl phthalate (DOP)), a thickener, an antioxidant, if necessary. An agent, a dispersant, a polymerization inhibitor and the like can be appropriately added. These additives may be any additives that can be used for preparing a conventional conductive paste, and a detailed description thereof will be omitted. When it is desired to impart photocurability (photosensitivity) to the Ag paste, various photopolymerizable compounds and photopolymerization initiators may be appropriately added.
[0030]
The Ag paste disclosed herein is typically a conductive powder (spherical silver powder and flaky silver powder), an organic medium (vehicle), and other additives (added as necessary), similar to conventional conductor pastes. Can be easily prepared by mixing Here, the conductive powder is obtained by mixing at least two types of spherical silver powders and at least two types of flake silver powders having mutually different average particle diameters and dispersing them in an organic medium. For example, using a three-roll mill or other kneading machine, a predetermined mixing ratio of the conductive powder and various additives may be mixed and stirred with the organic medium at a predetermined mixing ratio.
[0031]
The obtained Ag paste can be handled in the same manner as a conductor paste conventionally used for forming a conductor film such as a wiring and an electrode on a substrate, and a conventionally known method can be employed without any particular limitation. . Typically, an Ag paste is applied to a substrate in a desired shape and thickness by a dip coating method, a screen printing method, a dispenser coating method, or the like. The Ag paste of the present invention can be particularly preferably used as a so-called dip type Ag paste for forming a conductive film (for example, a side electrode of a laminated ceramic substrate) on a substrate based on a dip coating method.
Then, preferably after drying, the applied paste component is baked (baked) by heating in a heater under appropriate heating conditions for a predetermined period of time, and cured. By performing this series of processes, an electronic component (MLCC or the like) on which the target conductive film (terminal electrode, wiring, or the like) is formed can be obtained. Thus, a more sophisticated electronic component can be obtained by applying a conventionally known construction method while using the electronic component as an assembling material. Note that such a construction method itself does not particularly characterize the present invention, and a detailed description thereof will be omitted.
[0032]
EXAMPLES Some examples of the present invention will be described below, but it is not intended to limit the present invention to those shown in the examples.
[0033]
<Material>
Each component used in the following Examples and Comparative Examples is listed below.
(1) Silver powder
{Circle around (1)} Spherical silver powder 1: average particle diameter (D 50 ) 0.4 μm
(2) Spherical silver powder 2: average particle diameter (D 50 ) 0.7 μm
(3) Spherical silver powder 3: Average particle size (D 50 ) 1.2 μm
{Circle around (4)} Flaky silver powder 1: average particle size (D 50 ) 2-3 μm
(5) Flaky silver powder 2: Average particle size (D 50 ) 5-10 μm
(2) Resin component
(1) Ethyl cellulose
(2) Rosin resin
(3) Solvent component
(1) Petroleum solvent (mineral spirit)
(2) BC
(3) Terpineol
(4) Inorganic additives
(1) Bismuth oxide powder (average particle size: 1 to 5 μm)
(5) Additive
(1) Plasticizer (DOP)
[0034]
<Example 1: Preparation of Ag paste (1)>
56 parts of the spherical silver powder 1, 15 parts of the spherical silver powder 3, 9 parts of the flake silver powder 1, and 20 parts of the flake silver powder 2 were mixed.
Next, 2.0 parts of ethyl cellulose and 2.0 parts of a rosin-based resin, further 4.5 parts of a petroleum-based solvent, and 4.0 parts of BC and / or terpineol were added to 86 parts of the obtained conductive powder. In addition, the mixture was kneaded using a three-roll mill. Further, 0.5 part of bismuth oxide powder and 1 part of a plasticizer were added and kneaded. In this way, an Ag paste according to the present example (a conductive powder content: 86% by mass) was prepared.
[0035]
<Example 2: Preparation of Ag paste (2)>
To 80 parts of the conductive powder obtained in Example 1, 2.0 parts of ethylcellulose and 2.0 parts of a rosin-based resin, further 7.5 parts of a petroleum-based solvent, 7.0 parts of BC and / or Terpineol was added and kneaded using a three-roll mill. Further, 0.5 part of bismuth oxide powder and 1 part of a plasticizer were added and kneaded. In this way, an Ag paste (a conductive powder content: 80% by mass) according to the present example was prepared.
[0036]
<Example 3: Preparation of Ag paste (3)>
In 87 parts of the conductive powder obtained in Example 1, 7.0 parts of ethyl cellulose and 2.0 parts of a rosin-based resin, further 4.0 parts of a petroleum-based solvent, 3.5 parts of BC and / or Terpineol was added and kneaded using a three-roll mill. Further, 0.5 part of bismuth oxide powder and 1 part of a plasticizer were added and kneaded. In this way, an Ag paste (a conductive powder content: 87% by mass) according to the present example was prepared.
[0037]
<Example 4: Preparation of Ag paste (4)>
63 parts of spherical silver powder 2, 15 parts of spherical silver powder 3, 9 parts of flake silver powder 1, and 13 parts of flake silver powder 2 were mixed.
Next, 2.0 parts of ethyl cellulose and 2.0 parts of a rosin-based resin, further 4.0 parts of a petroleum solvent, and 3.5 parts of BC and / or terpineol were added to 87 parts of the obtained conductive powder. In addition, the mixture was kneaded using a three-roll mill. Further, 0.5 part of bismuth oxide powder and 1 part of a plasticizer were added and kneaded. In this way, an Ag paste (a conductive powder content: 87% by mass) according to the present example was prepared.
[0038]
<Comparative Example 1: Preparation of Ag paste containing palladium>
85 parts of spherical silver powder 1 and 15 parts of spherical palladium powder were mixed to obtain a conductive powder (Ag / Pd powder).
Next, 2.0 parts of ethyl cellulose, 2.0 parts of a rosin-based resin, 13.0 parts of BC and / or terpineol were added to 80 parts of the obtained Ag / Pd powder, and kneaded using a three-roll mill. . Further, 2.0 parts of bismuth oxide powder and 1 part of a plasticizer were added and kneaded. Thereby, an Ag / Pd paste (content of conductive powder: 80% by mass) according to this comparative example was prepared.
[0039]
<Comparative Example 2: Preparation of Ag paste using two types of silver powder (1)>
50 parts of spherical silver powder 2 and 50 parts of flake silver powder 2 were mixed.
Next, 2.0 parts of ethyl cellulose and 2.0 parts of a rosin-based resin, 7.5 parts of a petroleum solvent, and 7.0 parts of BC and / or terpineol were added to 80 parts of the obtained conductive powder. In addition, the mixture was kneaded using a three-roll mill. Further, 0.5 part of bismuth oxide powder and 1 part of a plasticizer were added and kneaded. In this way, an Ag paste (a conductive powder content: 80% by mass) according to this comparative example was prepared.
[0040]
<Comparative Example 3: Preparation of Ag paste using two types of silver powder (2)>
66 parts of spherical silver powder 1 and 34 parts of flake silver powder 1 were mixed.
Then, to 85 parts of the obtained conductive powder, 2.0 parts of ethyl cellulose and 2.0 parts of a rosin-based resin, further 5.0 parts of a petroleum-based solvent, 4.5 parts of BC and / or terpineol were added. In addition, the mixture was kneaded using a three-roll mill. Further, 0.5 part of bismuth oxide powder and 1 part of a plasticizer were added and kneaded. In this way, an Ag paste according to the present comparative example (a conductive powder content: 85% by mass) was prepared.
[0041]
<Comparative Example 4: Preparation of Ag paste using three types of silver powder (1)>
67 parts of spherical silver powder 1, 18 parts of flake silver powder 1, and 15 parts of flake silver powder 2 were mixed.
Then, to 85 parts of the obtained conductive powder, 2.0 parts of ethyl cellulose and 2.0 parts of a rosin-based resin, further 5.0 parts of a petroleum-based solvent, 4.5 parts of BC and / or terpineol were added. In addition, the mixture was kneaded using a three-roll mill. Further, 0.5 part of bismuth oxide powder and 1 part of a plasticizer were added and kneaded. In this way, an Ag paste according to the present comparative example (a conductive powder content: 85% by mass) was prepared.
[0042]
<Comparative Example 5: Preparation of Ag paste using three types of silver powder (2)>
69 parts of spherical silver powder 1, 18 parts of flake silver powder 1, and 13 parts of flake silver powder 2 were mixed.
Next, 2.0 parts of ethyl cellulose and 2.0 parts of a rosin-based resin, further 4.0 parts of a petroleum solvent, and 3.5 parts of BC and / or terpineol were added to 87 parts of the obtained conductive powder. In addition, the mixture was kneaded using a three-roll mill. Further, 0.5 part of bismuth oxide powder and 1 part of a plasticizer were added and kneaded. Thus, an Ag paste (a conductive powder content: 87% by mass) according to this comparative example was prepared.
[0043]
<Comparative Example 6: Preparation of Ag paste using three types of silver powder (3)>
70 parts of spherical silver powder 1, 15 parts of spherical silver powder 2, and 15 parts of flake silver powder 1 were mixed.
Next, 2.0 parts of ethyl cellulose and 2.0 parts of a rosin-based resin, further 4.0 parts of a petroleum solvent, and 3.5 parts of BC and / or terpineol were added to 87 parts of the obtained conductive powder. In addition, the mixture was kneaded using a three-roll mill. Further, 0.5 part of bismuth oxide powder and 1 part of a plasticizer were added and kneaded. Thus, an Ag paste (a conductive powder content: 87% by mass) according to this comparative example was prepared.
[0044]
<Formation of terminal electrode>
Next, an electrode (terminal electrode) was formed on the surface (end face) of the multilayer ceramic substrate using the conductive paste according to Examples 3 and 4 and the conductive paste according to Comparative Examples 2 to 6, respectively. That is, the conductor pastes of the examples and the comparative examples were applied to the end face of a laminated ceramic substrate made of alumina (size: 5.0 mm × 5.0 mm × 0.8 mm) by dip coating to obtain a predetermined thickness (average thickness: 10 to 10 mm). 30 μm) was formed.
Next, this terminal electrode was fired together with the ceramic substrate. That is, firing treatment was performed at 850 ° C. for 1 hour in an electric furnace. By this firing treatment, a conductor film (electrode) having a predetermined thickness was baked on the end face of the multilayer ceramic substrate. Hereinafter, when simply referred to as a conductor film, it refers to the film after firing.
[0045]
<Evaluation of solder heat resistance (1)>
Each of the terminal electrodes (conductor films) obtained by using the conductor pastes according to Examples 3 and 4 and the conductor pastes according to Comparative Examples 2 to 6 was subjected to a solder heat resistance test as follows.
That is, after applying a rosin flux to the conductor film portion of each laminated ceramic substrate, the substrate is soldered at a predetermined temperature (here, Sn / Pb = 60/40 (mass ratio), but so-called Pb-free solder is applied). The same effect can be obtained even if the same is performed.). Here, the solder temperature conditions and the immersion time were set to 230 ° C. × 15 seconds and 260 ° C. × 15 seconds. Thus, the solder heat resistance was evaluated by the area ratio of the conductive film remaining on the ceramic substrate after the immersion as compared with the portion before the immersion, that is, the portion which was not “solder-eroded” after the immersion. Table 1 shows the results.
Specifically, those having about 95% or more of the conductor film remaining were judged to exhibit excellent solder erosion resistance performance, that is, solder heat resistance, and are indicated by ◎ in the table. Further, those in which about 90% or more and less than 95% of the conductor film remained were judged to show good soldering heat resistance, and are indicated by ○ in the table. Further, when the remaining portion of the conductive film was approximately 70% or more and less than 90% before immersion, it was judged that the solder heat resistance was slightly inferior, and was indicated by Δ in the table. Those having less than 70% of the conductor film remaining before immersion were judged to have no soldering heat resistance, and are indicated by x in the table. As is clear from Table 1, the conductor films formed using the conductor pastes of the respective examples had higher solder heat resistance than the conductor films formed using the conductor pastes of the respective comparative examples.
[0046]
[Table 1]
<Evaluation of solder heat resistance (2)>
Using the conductor pastes of Examples 1 and 2 and Comparative Example 1, a conductor film of approximately 5 mm × 5 mm was formed on the surface of an alumina ceramic substrate (about 0.8 mm thick). That is, the conductor paste was applied to the surface of the ceramic substrate based on a general dip coating method, and a coating film having a predetermined thickness (10 to 30 μm) was formed.
Subsequently, a drying treatment was performed at 100 ° C. for 15 minutes using a far-infrared dryer. By this drying treatment, the solvent volatilized from the coating film, and an unsintered conductor film was formed on the ceramic substrate.
Next, this conductor film was fired together with the ceramic substrate. That is, firing treatment was performed at 850 ° C. for 1 hour in an electric furnace. By this firing treatment, a conductor film having a predetermined thickness was baked on the ceramic substrate.
[0048]
Next, the same solder heat resistance test as in the case of using the conductor pastes of Examples 3 to 4 and Comparative Examples 2 to 6 was performed. As a result, FIG. 1 shows a photograph of the surface of the ceramic substrate after the solder immersion.
As is apparent from these surface photographs, the conductor film formed from the conductor paste of Example 1 did not substantially suffer from so-called "solder erosion" under any conditions. Also, the conductor film formed from the conductor paste of Example 2 did not substantially suffer from solder erosion at 230 ° C., and the degree of solder erosion was slight even at 260 ° C. On the other hand, in the conductor film formed from the conductor paste (Ag / Pd paste) of Comparative Example 1, solder erosion occurred at 230 ° C., and solder erosion was remarkable at 260 ° C. From the above results, it can be seen that the conductor film formed from the conductor paste having a conductive powder content of 85% by mass or more (86% by mass in the conductor paste of Example 1) has particularly high solder heat resistance. I was assured.
[0049]
<Evaluation of dry appearance>
The dried appearance of the terminal electrodes obtained by using the conductor pastes according to Examples 3 to 4 and Comparative Examples 2 to 6 after solder immersion was visually evaluated. That is, as for the one subjected to the solder immersion treatment at 230 ° C. for 15 seconds, the one in which the appearance of the terminal electrode after drying is formed in a uniform dome shape over the whole is excellent (shown by ◎ in Table 1). If the shape was recognized as a substantially uniform vault shape, it was regarded as good (shown by ○ in Table 1). (Indicated by x in Table 1). The results are shown in the corresponding column of Table 1.
As is clear from Table 1, the terminal electrodes obtained by using the conductor pastes of Comparative Examples 2 to 6 had deteriorated appearance after solder immersion, and proved to have low solder heat resistance. On the other hand, it was confirmed that the terminal electrodes obtained from the conductor pastes of Examples 3 and 4 had a good dry appearance, similarly to the solder heat resistance described above. In particular, the terminal electrode obtained from the conductor paste of Example 3 was excellent in both solder heat resistance and dry appearance.
[0050]
In the above embodiments, specific examples of the present invention have been described in detail. However, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and alterations of the specific examples illustrated above.
Further, the technical elements described in the present specification or the drawings exhibit technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. The technology illustrated in the present specification or the drawings achieves a plurality of objects at the same time, and has technical utility by achieving one of the objects.
[Brief description of the drawings]
FIG. 1 is a photograph showing a state after a solder immersion treatment of a conductor film formed on a ceramic substrate using the conductor paste according to Examples 1 and 2 and Comparative Example 1, respectively.
Claims (10)
相互に平均粒径が異なる少なくとも２種の球状銀粉末と、相互に平均粒径が異なる少なくとも２種のフレーク状銀粉末とが混合されて成る導電性粉末を用意する工程と、
前記導電性粉末を有機媒質中に分散させる工程と、
を包含する製造方法。A method for producing a conductor paste mainly composed of silver powder,
A step of preparing a conductive powder obtained by mixing at least two kinds of spherical silver powders having mutually different average particle diameters and at least two kinds of flaky silver powders having mutually different average particle diameters;
Dispersing the conductive powder in an organic medium,
A production method comprising:
４０〜８０質量％の平均粒径０．１〜０．８μｍの球状銀粉末と、
３〜４０質量％の平均粒径１．０〜２．０μｍの球状銀粉末と、
３〜３０質量％の平均粒径１〜４μｍのフレーク状銀粉末と、
５〜４０質量％の平均粒径５〜１５μｍのフレーク状銀粉末と、
から実質的に構成される、請求項４に記載の製造方法。The conductive powder, with the whole as 100% by mass,
40-80% by mass of spherical silver powder having an average particle size of 0.1-0.8 μm;
A spherical silver powder having an average particle size of 1.0 to 2.0 μm of 3 to 40% by mass,
Flake silver powder having an average particle size of 1 to 4 μm of 3 to 30% by mass;
Flake silver powder having an average particle size of 5 to 15 μm of 5 to 40% by mass;
The method according to claim 4, wherein the method substantially comprises:
その導電性粉末は、相互に平均粒径が異なる少なくとも２種の球状銀粉末と、相互に平均粒径が異なる少なくとも２種のフレーク状銀粉末とが混合されて形成されている、導電ペースト。A conductive powder substantially comprising spherical silver powder and flake silver powder, and a conductive paste containing an organic medium,
A conductive paste, wherein the conductive powder is formed by mixing at least two types of spherical silver powders having mutually different average particle sizes and at least two types of flake silver powder having mutually different average particle sizes.
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