JP4687042B2 - Method for producing conductive paste - Google Patents
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本発明は、エレクトロニクス分野で使用される導電性ペーストとその製造方法に関し、例えば電子回路などの厚膜導体形成に用いられる導電性ペースト、及びそれを用いてなる電気回路に関する。 The present invention relates to a conductive paste used in the field of electronics and a method for manufacturing the same, and relates to a conductive paste used for forming a thick film conductor such as an electronic circuit, and an electric circuit using the same.
従来、厚膜形成用の導電性ペーストとして、金属粉末を有機ビヒクル中に分散させたものが広く使用されている。これらの導電性ペーストは、その用途に応じて、金属粉末等の固形成分と有機ビヒクル等の液体成分およびその他の成分を、３本ロール等の混合機によって混練することで製造している。例えば、特許文献１に金属粉末、ガラス粉末、及び有機ビヒクルを含有する厚膜導体ペーストが開示されている。金属粉末には貴金属粉末が用いられ、形状は球状が好ましく、粒径が０．１〜３．０μｍとの記載がある。ガラス粉末は従来から公知のＳｉＯ２、Ａｌ２Ｏ３、ＰｂＯ、ＣａＯ、Ｂ２Ｏ３等を主成分とした４５０〜６５０℃に軟化点を有するガラス粉末と記載されている。有機ビヒクルは、金属粉末と結合材とを混合し、塗布する際に適した材料とするために用いられる分散剤であり、溶剤成分と樹脂成分及び添加剤成分を含んでいる。 Conventionally, as a conductive paste for forming a thick film, a metal powder dispersed in an organic vehicle has been widely used. These conductive pastes are produced by kneading a solid component such as metal powder, a liquid component such as an organic vehicle, and other components with a mixer such as a three roll depending on the application. For example, Patent Document 1 discloses a thick film conductor paste containing metal powder, glass powder, and an organic vehicle. Noble metal powder is used for the metal powder, and the shape is preferably spherical, and the particle size is described as 0.1 to 3.0 μm. The glass powder is described as a glass powder having a softening point at 450 to 650 ° C. mainly composed of conventionally known SiO 2 , Al 2 O 3 , PbO, CaO, B 2 O 3 and the like. The organic vehicle is a dispersant used for mixing a metal powder and a binder and forming a material suitable for application, and includes a solvent component, a resin component, and an additive component.
これらの導電性ペーストは、スクリーン印刷等の方法によってパターン形成し、焼成して電気回路として使用する。例えばフラットディスプレイパネル基板の電極形成等の用途においては、高精細な電極形成が求められており、ファインパターン形成可能な導電性ペーストが要求されている。 These conductive pastes are formed into a pattern by a method such as screen printing, fired, and used as an electric circuit. For example, in applications such as electrode formation for flat display panel substrates, high-definition electrode formation is required, and a conductive paste capable of forming a fine pattern is required.
しかしながら、従来の厚膜形成用導電性ペーストの製造方法では導電性ペースト中に残存する不純物を取り除くことができず、スクリーン印刷法等によるファインパターン形成において、これに起因するパターンの断線や欠け、ピンホール等の印刷欠陥が生じるという問題が生じていた。この不純物としては、原料中に微量に存在する異物、又は作製工程で混入する埃、糸くず等の異物、有機ビヒクル由来の樹脂の不溶解物などが挙げられる。 However, the conventional method for producing a conductive paste for forming a thick film cannot remove impurities remaining in the conductive paste. In fine pattern formation by a screen printing method or the like, pattern disconnection or chipping due to this, There has been a problem that printing defects such as pinholes occur. Examples of the impurities include a foreign substance present in a minute amount in the raw material, a foreign substance such as dust and lint mixed in the production process, and an insoluble resin derived from an organic vehicle.
そこで、これらの不純物を取り除くために、特許文献２には作製したペーストを目開き１〜２０μｍのフィルタで濾過する方法が提案されている。しかし、一般に用いられる厚膜形成用の導電性ペーストは高粘度であるため、実質このような微細孔径のフィルタでは濾過できない。このため、一旦ペーストを加熱するか、あるいはペースト中に溶媒を添加して粘度を低下させた状態で目開き１〜２０μｍで濾過すると記載されているが、このような工程を加えるとペーストの組成が変わってしまい、ファインパターンの印刷性に必要不可欠なペーストのレオロジーが安定しないという問題がある。更に、導電性ペーストに含まれる金属粉末やガラス粉末等の固形物の粒径がフィルタの目開きよりも大きい場合は、必要な固形物まで除かれてしまい、ペーストの組成が変わり所望の特性が得られないという問題もある。 Therefore, in order to remove these impurities, Patent Document 2 proposes a method of filtering the prepared paste with a filter having an opening of 1 to 20 μm. However, since the conductive paste for forming a thick film generally used has a high viscosity, it cannot be substantially filtered with a filter having such a fine pore diameter. For this reason, it is described that the paste is heated once or filtered with an opening of 1 to 20 μm in a state where the viscosity is lowered by adding a solvent to the paste. Changes, and there is a problem that the rheology of the paste that is indispensable for the printability of the fine pattern is not stable. Furthermore, if the particle size of the solid matter such as metal powder or glass powder contained in the conductive paste is larger than the aperture of the filter, the required solid matter will be removed, the composition of the paste will change and the desired characteristics will be There is also a problem that it cannot be obtained.
更に、特許文献３においては、あらかじめバインダに溶解可能な成分を溶解させ有機ビヒクルを製造した後、この有機ビヒクルを目開き５μｍ以下のフィルタで濾過し、さらに固形成分を加える方法が提案されている。この方法ではペースト組成が変わるという問題はないが、固形成分を加えた後の工程で混入する不純物を取り除くことができない。よって混練工程中に混入する異物や金属粉末中の分散不良物などが混入する可能性がある。 Further, Patent Document 3 proposes a method in which an organic vehicle is prepared by dissolving components that can be dissolved in a binder in advance, and then the organic vehicle is filtered through a filter having an opening of 5 μm or less, and further a solid component is added. . In this method, there is no problem that the paste composition changes, but it is not possible to remove impurities mixed in the process after adding the solid component. Therefore, there is a possibility that foreign matters mixed in the kneading step, poor dispersion in the metal powder, and the like are mixed.
本発明の目的は、上記のようなペースト組成やレオロジーの変化を伴わず、簡易な工程で糸くずや塊状の異物等の不純物を取り除き、パターンの欠けや断線、ピンホール等の印刷欠陥を生じない厚膜形成用の導電性ペースト及びその製造方法を提供することにある。更にこの導電ペーストを基板上に印刷して作製した電気回路を提供することを目的とする。 The object of the present invention is not accompanied by changes in the paste composition and rheology as described above, and removes impurities such as lint and lump-like foreign matters in a simple process, resulting in print defects such as chipping, disconnection, and pinholes. It is an object to provide a conductive paste for forming a thick film and a method for manufacturing the same. It is another object of the present invention to provide an electric circuit produced by printing this conductive paste on a substrate.
本発明者は、金属粉末と有機ビヒクルを主成分とする導電性ペースト中に混入する塊状の不純物の粒径に着目した。このような導電性ペーストを印刷し、ファインパターン形成した場合に、パターンの欠けや断線、ピンホール等の印刷欠陥の原因となる不純物の粒径は５０μｍ以上であり、この粒径以下の不純物は印刷性に影響を及ぼさないことを見出した。 The inventor paid attention to the particle size of massive impurities mixed in a conductive paste mainly composed of metal powder and an organic vehicle. When such a conductive paste is printed and a fine pattern is formed, the particle size of impurities that cause printing defects such as chipping, disconnection, and pinholes in the pattern is 50 μm or more. It was found that printability is not affected.
例えば、スクリーン印刷によるパターン形成を考える。印刷時に使用するスクリーンマスクは印刷パターンの精細度に応じて選択し、通常、パターンが高精細になるほど高メッシュ数のスクリーンマスクが使用される。現在、最もファインパターン形成可能なスクリーンマスクとしてステンレス製５００メッシュのスクリーンマスクが使用されており、このスクリーンマスクの開口径は３３μｍである。たとえ粒径が小さくても、導電性ペースト中の不純物は少ない方が好ましいが、スクリーンマスクの開口径以下の粒径の不純物であれば、実際問題として印刷欠陥は生じない。また逆に２０μｍ以下の細かい不純物を除去するために、細かいフィルタを用いて導電ペーストを濾過しようとすると、ペースト中に必要な金属粉末等の固形分までが濾過されてしまい、ペーストの組成が安定しないという問題が生ずる。更に細かいフィルタを用いて濾過するためには濾過に長時間を必要とし、製造コストがかかるという問題もある。 For example, consider pattern formation by screen printing. The screen mask used at the time of printing is selected according to the definition of the print pattern. Usually, the screen mask having a higher mesh number is used as the pattern becomes higher in definition. At present, a stainless steel 500 mesh screen mask is used as the screen mask capable of forming the finest pattern, and the opening diameter of this screen mask is 33 μm. Even if the particle size is small, it is preferable that the conductive paste has few impurities. However, if the impurity has a particle size equal to or smaller than the opening diameter of the screen mask, a printing defect does not actually occur. Conversely, if the conductive paste is filtered using a fine filter in order to remove fine impurities of 20 μm or less, solids such as metal powder necessary for the paste are filtered, and the paste composition is stable. The problem of not doing arises. Furthermore, in order to filter using a finer filter, there is a problem that a long time is required for the filtration and manufacturing cost is increased.
すなわち本発明は、金属粉末と有機ビヒクルを主成分とする導電性ペーストを、目開き３０μｍ以上、５０μｍ以下のフィルタで濾過する導電性ペーストの製造方法である。目開き５０μｍ以下のメッシュで濾過すれば、印刷時に問題となる５０μｍ以上の不純物を完全に除去することができる。またメッシュの目開きを３０μｍ以上とすることで、高粘度の導電性ペーストを濾過することが可能となり、導電性ペーストの組成やレオロジーの変化を起こすことが無い。 That is, the present invention is a method for producing a conductive paste in which a conductive paste mainly composed of a metal powder and an organic vehicle is filtered with a filter having an opening of 30 μm or more and 50 μm or less . If filtration is performed with a mesh having an opening of 50 μm or less, impurities having a size of 50 μm or more, which becomes a problem during printing, can be completely removed. Further, by setting the mesh opening to 30 μm or more, it becomes possible to filter the conductive paste having high viscosity, and the composition and rheology of the conductive paste are not changed.
フィルタ濾過時の導電性ペーストの粘度は４００Ｐａ・ｓ以下であることが好ましい（請求項１）。濾過時の粘度が４００Ｐａ・ｓより大きいと濾過工程に時間がかかり、作業性が悪くなるからである。しかし一般的に、微細なパターンを形成するためには４００Ｐａ・ｓ以上の粘度の導電性ペーストが使用される。これは、導電性ペーストの粘度が低いとラインのにじみ等の問題が起こるからである。このような高粘度の導電性ペーストの組成を変更すること無く、効率良く濾過するために、導電性ペーストのチクソトロピー性に着目した。 The viscosity of the conductive paste during filter filtration is preferably 400 Pa · s or less (Claim 1 ). This is because if the viscosity at the time of filtration is larger than 400 Pa · s, it takes a long time for the filtration step and the workability is deteriorated. However, generally, in order to form a fine pattern, a conductive paste having a viscosity of 400 Pa · s or more is used. This is because problems such as line bleeding occur when the viscosity of the conductive paste is low. In order to efficiently filter without changing the composition of such a high-viscosity conductive paste, attention was paid to the thixotropy of the conductive paste.
チクソトロピー性とは、粘度の剪断応力依存性である。すなわち剪断応力が大きい領域では低粘度であり、剪断応力が小さい領域では高粘度となる。このような導電性ペーストのチクソトロピー性を利用して、フィルタでの濾過時に剪断応力を負荷することでペーストの粘度４００Ｐａ・ｓ以下に低下させ、濾過工程の作業時間を短縮することができる（請求項２）。 The thixotropy is the shear stress dependence of viscosity. That is, the viscosity is low in a region where the shear stress is large, and the viscosity is high in a region where the shear stress is small. By utilizing the thixotropy of such conductive paste, by applying a shear stress during filtration with a filter, the viscosity of the paste can be reduced to 400 Pa · s or less, and the working time of the filtration process can be shortened (claims) Item 2 ).
導電性ペーストの粘度は回転粘度計等で測定できる。導電性ペーストのチクソトロピー性により、測定時の回転速度によって粘度の値は異なるため、Ｅ型回転粘度計で１回転で測定した粘度を剪断応力をかけないときの粘度と定義する。また、１回転での粘度と１０回転での粘度の比をチクソトロピー性の指標とする。チクソトロピー性は３以上であると好ましい。 The viscosity of the conductive paste can be measured with a rotational viscometer or the like. Since the value of the viscosity varies depending on the rotational speed at the time of measurement due to the thixotropy of the conductive paste, the viscosity measured in one rotation with an E-type rotational viscometer is defined as the viscosity when no shear stress is applied. The ratio of the viscosity at one rotation to the viscosity at 10 rotations is used as an index of thixotropy. The thixotropic property is preferably 3 or more.
本発明により得られる導電性ペーストは、金属粉末と有機ビヒクルを主成分とする導電性ペーストであり、導電性ペースト中に含まれる固形物の最大粒径が５０μｍ以下である導電性ペーストである。導電性ペースト中に含まれる固形物の最大粒径は、粒ゲージにより測定できる。導電性ペーストに混合する金属粉末等の固形物の平均粒径は最大でも１０μｍ程度であるため、粒ゲージ測定で測定される粒子は、これらの固形物の凝集塊や、有機ビヒクル中の不溶解物、混合中に混入するゴミ、等の不純物と考えられる。よって粒ゲージ測定での最大粒径は不純物の最大粒径であり、５０μｍ以下であることが好ましい。更に好ましくは３０μｍ以下である。 The electrically conductive paste obtained by this invention is an electrically conductive paste which has a metal powder and an organic vehicle as a main component, and is a electrically conductive paste with the largest particle size of the solid substance contained in an electrically conductive paste being 50 micrometers or less . The maximum particle size of the solid contained in the conductive paste can be measured with a particle gauge. Since the average particle size of solids such as metal powder mixed in the conductive paste is about 10 μm at maximum, the particles measured by the particle gauge measurement are insoluble in these solids and insoluble in organic vehicles. It is considered to be impurities such as waste and dust mixed during mixing. Therefore, the maximum particle size in the particle gauge measurement is the maximum particle size of impurities, and is preferably 50 μm or less. More preferably, it is 30 μm or less .
さらに、これらの導電性ペーストを基板上に印刷した電気回路が得られる。印刷欠陥の原因となる５０μｍ以上の不純物を取り除くことで、スクリーン印刷等の方法により基板上に微細な電気回路を形成することができ、例えば線幅１００μｍ以下のファインパターンを形成することができる。 Furthermore , an electric circuit obtained by printing these conductive pastes on a substrate can be obtained. By removing impurities of 50 μm or more that cause printing defects, a fine electric circuit can be formed on the substrate by a method such as screen printing, and for example, a fine pattern with a line width of 100 μm or less can be formed.
本発明は、スクリーン印刷等の方法によりファインパターン形成が可能な導電性ペーストの製造方法及び導電性ペーストを提供する。本発明の製造方法は、金属粉末等の固形物と有機ビヒクルとを工程を分けることなく、混合した状態のペーストを濾過することで一定以上の大きさの不純物を除去でき、印刷欠陥の原因となる不純物を低減できる。更に、導電性ペーストに剪断応力を加えて導電性ペーストの粘度を下げるため、ファインパターン形成に必要な導電性ペーストの組成やレオロジーに影響を及ぼすこともない。 The present invention provides a method for producing a conductive paste capable of forming a fine pattern by a method such as screen printing, and a conductive paste. The manufacturing method of the present invention can remove impurities of a certain size or more by filtering the paste in a mixed state without separating the solid material such as metal powder and the organic vehicle, and causes printing defects. Impurities can be reduced. Furthermore, since the shearing stress is applied to the conductive paste to lower the viscosity of the conductive paste, the composition and rheology of the conductive paste necessary for fine pattern formation are not affected.
本発明における金属粉末は、金属単体、合金及び複合金属から選ばれるものであれば良い。特にその金属種類は白金、金、銀、銅、ニッケル、パラジウムから選ばれると優れた導電性を示すので好ましい（請求項６）。さらに銀を使用すると、導電性、耐酸化性等の信頼性、価格等の諸特性のバランスが優れており、より好ましい。 The metal powder in this invention should just be chosen from a metal simple substance, an alloy, and a composite metal. In particular, the metal type is preferably selected from platinum, gold, silver, copper, nickel, and palladium because excellent conductivity is exhibited (Claim 6). Furthermore, the use of silver is more preferable because it has a good balance of various properties such as reliability such as conductivity and oxidation resistance, and price.
金属粉末の形状は特に限定されないが、球状、鱗片状などのものが使用できる。金属粉末の粒径は、導電性ペーストにより形成するパターンの形状を考慮して選択する。金属粉末の最大粒径は、形成するパターンの線幅の１／２以下であれば良く、更に好ましくは１／３以下である。金属粉末の平均粒径は１０ｎｍ〜５μｍのものが好ましく使用できる。またこの範囲内で粒径の異なるものを組み合わせて使用しても良い。 The shape of the metal powder is not particularly limited, but a spherical shape or a scale shape can be used. The particle size of the metal powder is selected in consideration of the shape of the pattern formed by the conductive paste. The maximum particle size of the metal powder may be ½ or less of the line width of the pattern to be formed, more preferably １ ／ or less. The average particle size of the metal powder is preferably 10 nm to 5 μm. Moreover, you may use combining what differs in a particle size within this range.
導電性ペーストには、金属粉末の他にガラスフリット等の無機フィラーを固形分として加えることができる。使用するガラスフリットは、鉛を含有せず、かつ金属粉末として銀を用いる場合には、作業点が５００℃以下のガラスフリットであるのが好ましい。鉛を含まず、比較的低温で作業できるため作業性が向上する。さらに好ましくは作業点が４５０℃以下のガラスフリットを用いるのが良い。このようなガラスフリットとしてはビスマス系の材料が好ましく使用できる。 In addition to the metal powder, an inorganic filler such as glass frit can be added as a solid content to the conductive paste. When the glass frit to be used does not contain lead and silver is used as the metal powder, the glass frit having a working point of 500 ° C. or less is preferable. Because it does not contain lead and can be operated at a relatively low temperature, workability is improved. More preferably, a glass frit having a working point of 450 ° C. or lower is used. As such a glass frit, a bismuth-based material can be preferably used.
ガラスフリットの粒径は、金属粉末と同様、形成するパターンの形状を考慮して選択し、最大粒径は形成するパターン線幅の１／２以下、更に好ましくは１／３とする。また金属粉末に対してガラスフリットの粒径が大きいとペースト中の分散性が悪くなる。ガラスフリットの平均粒径は３μｍ以下であるとペースト中での分散性が向上し、好ましい。 The particle size of the glass frit is selected in consideration of the shape of the pattern to be formed as in the case of the metal powder, and the maximum particle size is ½ or less, more preferably １ ／ of the pattern line width to be formed. Further, when the particle size of the glass frit is large with respect to the metal powder, the dispersibility in the paste is deteriorated. The average particle size of the glass frit is preferably 3 μm or less because dispersibility in the paste is improved.
本発明に用いる有機ビヒクルは、前記金属粉末とガラスフリットを均一に混合した状態を維持し、かつスクリーン印刷等の基材への塗布時に均一かつ印刷パターンのにじみや流れを抑える特性を必要とする。これらの特性を維持するには、セルロース系樹脂やアクリル系樹脂を溶剤に溶解したものが好適である。また、エポキシ樹脂、フェノール樹脂等の熱硬化性樹脂、ポリエステル樹脂等を溶剤に溶解したものも好ましく使用できる。溶剤としてはペーストを塗布する基材に対して非腐食性であり、また揮発性の低いものを用いると印刷作業性が良い。このような溶剤としてはブチルカルビトールアセテート、カルビトールアセテート、α−テルピネオール等が例示される。 The organic vehicle used in the present invention needs to maintain a state in which the metal powder and the glass frit are uniformly mixed, and have characteristics that suppress the bleeding and flow of the printing pattern uniformly when applied to a substrate such as screen printing. . In order to maintain these characteristics, a cellulose resin or an acrylic resin dissolved in a solvent is preferable. Moreover, what melt | dissolved the thermosetting resins, such as an epoxy resin and a phenol resin, a polyester resin, etc. in a solvent can also be used preferably. The solvent is non-corrosive with respect to the substrate to which the paste is applied, and if a low volatility is used, the printing workability is good. Examples of such a solvent include butyl carbitol acetate, carbitol acetate, α-terpineol and the like.
これらの金属粉末、ガラスフリット等の固形分と有機ビヒクルを混合して導電性ペーストを作製する。更に要求特性に応じて、硬化剤、可塑剤、チクソ剤、レベリング剤等の添加剤を更に添加しても良い。これらの材料は３本ロール、回転撹拌脱泡機などにより混合、分散して均一な状態とする。 These metal powders and solids such as glass frit are mixed with an organic vehicle to produce a conductive paste. Furthermore, additives such as a curing agent, a plasticizer, a thixotropic agent, and a leveling agent may be further added according to required characteristics. These materials are mixed and dispersed by a three roll, rotary stirring defoaming machine, etc. to make it uniform.
作製した導電性ペーストを目開き３０μｍ以上、５０μｍ以下のフィルタで濾過して、塊状の不純物を取り除く。フィルタは濾過精度の高いものであれば、どのような形状のものを使用しても良い。最も簡易に用いることができるものとしては、篩形状で、容器底面にメッシュを貼り付けたものが挙げられる。フィルタの材質については、ステンレス等の金属材料やポリエステル、ポリアミド等の樹脂材料を用いることができる。更に、これらフィルター材料の表面にフッ素樹脂等によるコーティングを施し、汚染防止効果を高めることもできる。 The produced conductive paste is filtered through a filter having an opening of 30 μm or more and 50 μm or less to remove massive impurities. Any filter may be used as long as it has high filtration accuracy. Examples of the simplest use include a sieve shape and a mesh attached to the bottom of the container. As for the material of the filter, a metal material such as stainless steel or a resin material such as polyester or polyamide can be used. Furthermore, the surface of these filter materials can be coated with a fluororesin or the like to enhance the contamination prevention effect.
濾過方法は、ペーストに剪断応力を加えペースト粘度を低下させることにより、メッシュを通すものであれば、いかなる方法でも用いることができる。例えば、最も単純な方法として、メッシュ上にペーストをのせて、へら等で擦ることによりペーストの粘度を低下させ、メッシュを通すという方法がある。他にも、底面にメッシュを貼り付けた容器にペーストをのせ、これを回転羽根を用いて、ペーストに剪断応力を加えることにより、ペーストを粘度を低下させ、メッシュを通すという方法がある。 As the filtration method, any method can be used as long as it passes through a mesh by applying a shear stress to the paste to lower the paste viscosity. For example, as the simplest method, there is a method in which a paste is placed on a mesh, the viscosity of the paste is lowered by rubbing with a spatula or the like, and the mesh is passed. In addition, there is a method in which the paste is put on a container having a mesh attached to the bottom surface, and a shearing stress is applied to the paste using a rotating blade to reduce the viscosity of the paste and pass the mesh.
このようにして作製した導電性ペーストを、スクリーン印刷等の方法で基板上に印刷した後、加熱焼結して電極回路を形成する。スクリーン印刷に使用するスクリーンマスクは、形成するパターン形状により選択する。高精細なパターン形成を行うためには、ステンレススクリーンマスクが好適に用いられる。 The conductive paste thus produced is printed on the substrate by a method such as screen printing, and then heated and sintered to form an electrode circuit. The screen mask used for screen printing is selected according to the pattern shape to be formed. In order to form a high-definition pattern, a stainless screen mask is preferably used.
以下に実施例を示すが、本発明は以下の実施例に限定されるものではない。 Examples are shown below, but the present invention is not limited to the following examples.
（導電性ペーストの作製）
有機ビヒクルとして、ブチルカルビトールアセテートに分子量１８０００のエチルセルロースを溶解し、樹脂分濃度１４重量％の溶液とした。これに表１に示す種類と量の銀粉末を加え、回転撹拌脱泡機を用いて均一に混合した。尚、銀粉末Ａは平均粒径０．５μｍの球状粒子、銀粉末Ｂは平均粒径３μｍの球状粒子である。さらに平均粒径２μｍとなるようにビーズミルで粉砕したガラスフリット（旭硝子（株）製、商品名ガラスフリット１１００）を加えて混合を継続し、観察により均一と判断してから、この溶液を三本ロールミルに通した後、目開き３３μｍのステンレス製フィルタを用いて濾過して導電性ペーストを作製した。なお、フィルタ濾過には回転羽根を用い、導電性ペーストに剪断応力を加えることにより、粘度を低下させてフィルタを通した。濾過時の剪断速度は、回転羽根のサイズ(羽根の長さ)と回転数、フィルタ／羽根間のクリアランスから計算により求めることができ、５〜１００ｓｅｃ−１にて濾過を実施した。実施例１〜６全て常態における偏析・外観の異常等は観察されなかった。
(Preparation of conductive paste)
As an organic vehicle, ethyl cellulose having a molecular weight of 18000 was dissolved in butyl carbitol acetate to obtain a solution having a resin concentration of 14% by weight. The silver powder of the kind and quantity shown in Table 1 was added to this, and it mixed uniformly using the rotation stirring deaerator. Silver powder A is spherical particles having an average particle diameter of 0.5 μm, and silver powder B is spherical particles having an average particle diameter of 3 μm. Further, glass frit (trade name glass frit 1100, manufactured by Asahi Glass Co., Ltd.) pulverized with a bead mill so as to have an average particle diameter of 2 μm was added and mixing was continued. After passing through a roll mill, a conductive paste was prepared by filtering using a stainless steel filter having an opening of 33 μm. In addition, the rotary blade was used for filter filtration, and the viscosity was reduced by applying a shear stress to the conductive paste, and the filter was passed through. The shear rate at the time of filtration can be obtained by calculation from the size of the rotating blade (blade length), the number of rotations, and the clearance between the filter and the blade, and filtration was performed at 5 to 100 sec −1 . In all of Examples 1 to 6, no segregation or abnormal appearance was observed in the normal state.
（粒ゲージ測定）
得られた導電性ペースト中に含まれる固形物の最大粒径を、粒ゲージ（コーティングテスター工業（株）製）を使用して測定した。結果を表１に示す。
(Grain gauge measurement)
The maximum particle diameter of the solid contained in the obtained conductive paste was measured using a particle gauge (manufactured by Coating Tester Industry Co., Ltd.). The results are shown in Table 1.
（粘度測定）
得られた導電性ペーストの粘度を、ＴＶＥ−２０Ｈ型回転粘度計（東機産業（株）製）を使用して測定した。回転数を１ｒｐｍから１０ｒｐｍまで変化させて粘度を測定し、１ｒｐｍでの粘度と１０ｒｐｍでの粘度の比を計算してチクソトロピー性の指標とした。更に、測定結果から、濾過時の剪断応力における導電性ペーストの粘度を推定した。結果を表１に示す。
(Viscosity measurement)
The viscosity of the obtained conductive paste was measured using a TVE-20H type rotational viscometer (manufactured by Toki Sangyo Co., Ltd.). The viscosity was measured by changing the rotation speed from 1 rpm to 10 rpm, and the ratio of the viscosity at 1 rpm to the viscosity at 10 rpm was calculated as an index of thixotropy. Furthermore, from the measurement results, the viscosity of the conductive paste at the shear stress during filtration was estimated. The results are shown in Table 1.
（スクリーン印刷によるパターン形成）
４００メッシュステンレススクリーンマスク（開口径４１μｍ、乳剤厚み１０μｍ）を使用し、導電性ペーストを青板ガラス基材にスクリーン印刷した。パターン形状は、線幅１００μｍ、７５μｍ、５０μｍ、３０μｍの４種類を同時に印刷できるものとし、また線の長さは８０ｍｍとし、各１０本ずつ印刷した。
パターン形成後の基材を１５０℃で３０分加熱して溶剤を揮発させた後、５００℃で３０分間加熱焼成して、所望の線幅の電気回路を作製した。それぞれの導電性ペーストにつき１０枚の基板を作製した。１０サンプル、すなわち１００本の印刷ラインにつき顕微鏡観察と導電性評価を行い、各印刷ラインのショート不良率を評価した。結果を表１に示す。
(Pattern formation by screen printing)
Using a 400 mesh stainless screen mask (opening diameter 41 μm, emulsion thickness 10 μm), the conductive paste was screen-printed on a blue glass substrate. Four types of pattern shapes having a line width of 100 μm, 75 μm, 50 μm, and 30 μm can be printed at the same time, and the length of the line is 80 mm.
The substrate after pattern formation was heated at 150 ° C. for 30 minutes to volatilize the solvent, and then heated and fired at 500 ° C. for 30 minutes to produce an electric circuit having a desired line width. Ten substrates were prepared for each conductive paste. Microscopic observation and conductivity evaluation were performed on 10 samples, that is, 100 printing lines, and the short-circuit defect rate of each printing line was evaluated. The results are shown in Table 1.
（導電性評価）
各線幅の印刷ラインにつき、四端子法にてライン抵抗を測定した。更にラインの膜厚とライン幅をレーザ顕微鏡で測定して断面積を算出し、得られた印刷ラインの体積抵抗率を評価した。ショート不良率評価と同様に１００本の印刷ラインについて評価し、ショート不良となったラインのデータを除いて平均値を求めた。結果を表１に示す。
(Conductivity evaluation)
The line resistance was measured by a four-terminal method for each line width printed line. Furthermore, the film thickness and line width of the line were measured with a laser microscope, the cross-sectional area was calculated, and the volume resistivity of the obtained printing line was evaluated. 100 print lines were evaluated in the same manner as the short-circuit defect rate evaluation, and the average value was obtained by excluding the data of the lines that were short-circuit defects. The results are shown in Table 1.
フィルタの目開きを４１μｍに変えたこと以外は実施例１と同様の方法にて、導電性ペーストの作製から導電性評価までの一連の工程を行った。結果を表１に示す。 A series of steps from the production of the conductive paste to the evaluation of conductivity was performed in the same manner as in Example 1 except that the aperture of the filter was changed to 41 μm. The results are shown in Table 1.
フィルタの目開きを５０μｍに変えたこと以外は実施例１と同様の方法にて、導電性ペーストの作製から導電性評価までの一連の工程を行った。結果を表１に示す。 A series of steps from the production of the conductive paste to the evaluation of conductivity was performed in the same manner as in Example 1 except that the aperture of the filter was changed to 50 μm. The results are shown in Table 1.
銀粉末の種類を変えたこと以外は実施例１と同様の方法にて、導電性ペーストの作製から導電性評価までの一連の工程を行った。結果を表１に示す。 A series of steps from the production of the conductive paste to the evaluation of the conductivity was performed in the same manner as in Example 1 except that the type of the silver powder was changed. The results are shown in Table 1.
銀粉末の種類を変えたこと以外は実施例２と同様の方法にて、導電性ペーストの作製から導電性評価までの一連の工程を行った。結果を表１に示す。 A series of steps from the production of the conductive paste to the evaluation of conductivity was performed in the same manner as in Example 2 except that the type of silver powder was changed. The results are shown in Table 1.
銀粉末の種類を変えたこと以外は実施例３と同様の方法にて、導電性ペーストの作製から導電性評価までの一連の工程を行った。結果を表１に示す。 A series of steps from the production of the conductive paste to the evaluation of conductivity were performed in the same manner as in Example 3 except that the type of silver powder was changed. The results are shown in Table 1.
（比較例１〜３）
導電性ペーストのフィルタ濾過を行わなかったこと以外は実施例１〜６と同様の方法にて、導電性ペーストの作製から導電性評価までの一連の工程を行った。結果を表２に示す。なお、比較例３においては、得られた導電性ペーストの粘度が高すぎることより、スクリーン印刷において不良が多発し、評価を行うことができなかった。導電性ペーストの粘度が高すぎるとスクリーン印刷時の塗出性が悪いことがこの原因と考えられる。
(Comparative Examples 1-3)
A series of steps from the production of the conductive paste to the evaluation of the conductivity was performed in the same manner as in Examples 1 to 6, except that the conductive paste was not filtered. The results are shown in Table 2. In Comparative Example 3, the resulting conductive paste was too high in viscosity, resulting in frequent failures in screen printing and could not be evaluated. If the viscosity of the conductive paste is too high, this may be due to poor coating properties during screen printing.
（比較例４）
導電性ペーストのフィルタ濾過工程において、導電性ペーストに剪断応力をかけなかったこと以外は実施例１と同様に導電性ペーストを作製した。導電性ペーストに剪断応力をかけないと導電性ペーストの粘度が高く、良好にフィルタ濾過を行えず、評価できなかった。
(Comparative Example 4)
A conductive paste was produced in the same manner as in Example 1 except that no shear stress was applied to the conductive paste in the filter filtration step of the conductive paste. Unless shear stress was applied to the conductive paste, the viscosity of the conductive paste was high, filter filtration could not be performed well, and evaluation was not possible.
実施例１〜３及び実施例４〜６はフィルタの目開きを３３μｍ、４１μｍ、５０μｍと変えて作製した導電性ペーストの評価結果である。表１に示すように、フィルタの目開きが大きくなるほど粒ゲージ測定での最大粒径は大きくなっているが、いずれの条件でも最大粒径は３０μｍ以下である。またこれらの導電性ペーストをガラス基板に印刷した電気回路のショート不良率においても、フィルタの目開きが大きくなるほどショート不良率が高くなっている。さらに、平均粒径０．５μｍの球状銀粉末Ａを使用した実施例１〜３よりも、平均粒径３μｍの銀粉末Ｂを使用した実施例４〜６の方がショート不良率が高い。これより、ファインパターンを形成するためには、導電性ペーストに使用する金属粉末の粒径が小さい方が好ましいと言える。 Examples 1 to 3 and Examples 4 to 6 are evaluation results of conductive pastes produced by changing the filter openings to 33 μm, 41 μm, and 50 μm. As shown in Table 1, the maximum particle size in the particle gauge measurement increases as the filter aperture increases, but the maximum particle size is 30 μm or less under any condition. Moreover, also in the short circuit defect rate of the electric circuit which printed these electrically conductive pastes on the glass substrate, the short circuit defect rate becomes high, so that the opening of a filter becomes large. Furthermore, Examples 4 to 6 using silver powder B having an average particle size of 3 μm have a higher short-circuit defect rate than Examples 1 to 3 using spherical silver powder A having an average particle size of 0.5 μm. From this, it can be said that in order to form a fine pattern, it is preferable that the particle size of the metal powder used for the conductive paste is smaller.
比較例１〜３はフィルタ濾過工程を行わずに作製した導電性ペーストの評価結果である。表２に示すように、フィルタ濾過工程を行わないと粒ゲージ測定での最大粒径が大きくなり、また導電性ペーストを印刷した電気回路のショート不良率も高くなっている。特に平均粒径３μｍの銀粉末Ｂを使用した比較例２の導電性ペーストではショート不良率が高い。また、有機ビヒクルの配合量を減らした比較例３の導電性ペーストは粘度が高いため、剪断応力を負荷しても粘度が下がりきらず、うまくフィルター濾過することができなかった。 Comparative Examples 1 to 3 are evaluation results of conductive pastes produced without performing the filter filtration step. As shown in Table 2, when the filter filtration step is not performed, the maximum particle size in the particle gauge measurement is increased, and the short circuit failure rate of the electric circuit printed with the conductive paste is also increased. In particular, the conductive paste of Comparative Example 2 using silver powder B having an average particle size of 3 μm has a high short-circuit defect rate. Moreover, since the conductive paste of Comparative Example 3 in which the blending amount of the organic vehicle was reduced had a high viscosity, the viscosity did not decrease even when a shear stress was applied, and the filter could not be filtered well.
比較例４は、実施例１と同様の配合で材料を混合して導電性ペーストを作製し、フィルタ濾過工程において導電性ペーストに剪断応力をかけなかったものである。剪断応力をかけない場合、導電性ペーストの粘度が下がらず、うまくフィルタ濾過できなかった。 In Comparative Example 4, a conductive paste was prepared by mixing materials with the same composition as in Example 1, and no shear stress was applied to the conductive paste in the filter filtration step. When no shear stress was applied, the viscosity of the conductive paste did not decrease, and the filter could not be filtered well.
Claims (2)
フィルタ濾過時に導電性ペーストに剪断応力を加え、該剪断応力がかかった状態でのフィルタ濾過時の導電性ペーストの粘度が４００Ｐａ・ｓ以下であることを特徴とする、導電性ペーストの製造方法。 A method for producing a conductive paste comprising filtering a conductive paste mainly composed of a metal powder and an organic vehicle with a filter having an opening of 30 μm or more and 50 μm or less,
A method for producing a conductive paste, wherein a shear stress is applied to the conductive paste during filter filtration, and the viscosity of the conductive paste during filter filtration in a state where the shear stress is applied is 400 Pa · s or less.
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| JP2001357719A (en) * | 2000-06-12 | 2001-12-26 | Murata Mfg Co Ltd | Manufacturing method of paste for thick film formation, paste for thick film formation, and filter device |
| JP2002270036A (en) * | 2001-03-14 | 2002-09-20 | Noritake Co Ltd | Solventless photo-curing conductor paste and manufacturing method for ceramic electronic component |
| WO2003017290A1 (en) * | 2001-08-09 | 2003-02-27 | Matsushita Electric Industrial Co., Ltd. | Production method for conductive paste and production method for printed circuit board |
| JP2003187638A (en) * | 2001-12-20 | 2003-07-04 | Murata Mfg Co Ltd | Conductive paste for gravure printing and its manufacturing method as well as laminated ceramic electronic component |
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| JP2006079912A (en) | 2006-03-23 |
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