JP3944849B2

JP3944849B2 - Connecting member

Info

Publication number: JP3944849B2
Application number: JP2003047433A
Authority: JP
Inventors: 功塚越; 貢藤繩; 直行塩沢; 泰史後藤; 共久太田
Original assignee: Hitachi Chemical Co Ltd; Showa Denko Materials Co Ltd
Current assignee: Showa Denko Materials Co Ltd
Priority date: 2003-02-25
Filing date: 2003-02-25
Publication date: 2007-07-18
Anticipated expiration: 2022-07-18
Also published as: JP2003272445A

Description

【０００１】
【発明の属する技術分野】
本発明は例えば電極の接続などに好適な、変形度の制御が可能な導電性粒子を用いた接続部材に関する。
【０００２】
【従来の技術】
回路素子と回路基板、回路基板同士を、エポキシ樹脂などの接着成分中に導電性粒子を分散した接続部材で接着し、回路素子と回路基板、回路基板同士を加圧方向にのみ電気的に接続する異方導電性接続部材がある。
この接続部材において、接着成分中に分散させる導電性粒子として、高分子重合体を核体（高分子核体）とし、その表面を金属薄層で被覆してなる導電性粒子が知られている。この粒子は、比重が小さいため、接着成分が液状であるとき、沈降しにくい。またこのような接続部材を用いて、例えば電子部品の微小電極などを接続するときに、接続時の温度や圧力で高分子核体が変形、導電性粒子と電極との接触面積を大きくすることができるなどの特徴がある。この場合、上記導電性粒子が変形しすぎないようにするため、硬質のスペーサ粒子を混合することも提案されている。
【０００３】
【発明が解決しようとする課題】
高分子核体の表面を金属薄層で被覆してなる導電性粒子は、接続時の温度や圧力が高くなると、高分子核体の変形が大きくなり、金属薄層が高分子核体から剥離したり、部分的に破壊したりして離散し、離散した金属片が接続電極と接触して隣接電極間の絶縁性を損なうことがあった。このため、接続条件を厳密にコントロールする必要があり、条件の変動を考慮し接続後の検査工程が必須な状況であった。
【０００４】
また、硬質のスペーサ粒子を混合する場合、これら混合粒子を均一に分散させる必要があるが、比重の差や表面電荷の相違により微小部分における均一分散性が困難である。特に最近では、この種の接着剤の適用分野が、ＩＣ、ＬＳＩなどの集積回路類や液晶やＥＬ、プラズマなどの表示素子類と電子回路類との接続といった、微細な電極や回路の接続用途に接続部材として多用され、そのため、広い接続条件で安定した接続信頼性が得られることや、大量生産における接続後の検査工程を不要にしたいといった要望が強く、一層使いやすい接続部材が求められるようになっている。
【０００５】
【課題を解決するための手段】
本発明は、ニッケル核１の表面にニッケル核の粒径の１／２以下の厚みの高分子の架橋体からなる軟質層２を形成し、その外側にニッケルを含む導電層３を接着成分中に０．１〜１５体積％含有してなる接続部材である。
【０００６】
本発明を以下図面を用いて説明する。
図１（ａ）は、本発明の一実施例を示す断面模式図である。
ニッケル核１の材料は、ニッケルおよびその合金である。このニッケル核の表面に軟質層を形成する。ここで、軟質層の意味は、導電性粒子の使用環境下例えば電極や回路の接続用途の場合の接続条件下で、ニッケル核と軟質層２を比べての相対的な硬さの関係を意味する。一定温度における弾性率や硬度などの一般的な硬さの指標や、例えば融点やガラス転移温度及び軟化点などの熱的変態点の差を目安とすることができる。
【０００７】
ニッケル核１の粒径は、平均して、０．１〜２０μｍ、好ましくは０．３〜１０μｍ、より好ましくは０．５〜６μｍとすることが、接続後の電極間距離を狭めて接続信頼性を向上する点から好ましい。ニッケル核１の粒径は均一とすることが好ましい。またニッケル核１の粒形は略球状が好ましいが、（ｂ）に示すように、表面に多数の凹凸があるなどの任意の形でよい。
【０００８】
軟質層２はポリスチレンやナイロン、各種ゴム類などの高分子類が好ましく、これらは架橋体であると耐溶剤性が向上するので、接着成分中に溶剤が含まれている場合、溶出がなく、特性に影響が少ないことからより好ましい。
また軟質層２を高分子とすると変形性を得やすく、導電層や核体との接着性もよい。そのため接続部材とした時、低抵抗で信頼性に優れた接続が得られる。また、接続電極や基板の耐熱性や硬さに応じて、適宜組み合わせを設定可能である。
【０００９】
軟質層２の厚みは、０．１〜１０μｍ程度が好適である。０．１μｍ未満では変形量が十分に得られず信頼性が不足し、１０μｍを超えると変形量が過剰となり金属薄層の被覆が剥離し易くなる。このような理由から、０．３〜５μｍが好ましく０．５〜３μｍがより好ましい。
【００１０】
また、軟質層２の厚みは、ニッケル核１の粒径以下、より好ましくは１／２以下とすると、導電粒子の変形量が制御しやすく回路の接続部材料として好ましい。軟質層２は、図１（ｃ）に示すように粒子状で存在してもよく、単層又は複層以上の構成とすることもできる。複層以上の構成の場合、強度保持性、耐溶剤性、接着性、柔軟性、耐熱性、耐めっき液性などの機能を分担することも可能なため好適である。軟質層２は、例えば噴霧法、高速撹拌法、スプレードライヤーなど任意の方法で形成できる。
【００１１】
導電層３は導電性を有する各種の金属や合金、酸化物などである。導電性と耐腐食性を加味して好ましく用いられる材料としては、Ｎｉ、Ｃｕ、Ａｌ、Ｓｎ、Ｚｎ、Ａｕ、Ｐｄ、Ａｇ、Ｃｏ、Ｐｂ、などであり、これらは単層もしくは複層以上の構成とすることもできる。
【００１２】
導電層３の形成手段としては、蒸着法、スパッタリング法、イオンプレーティング法、溶射法、めっき法、などの一般的な方法でよいが、無電解めっき法が均一厚みの被覆層の得られることから好ましい。
【００１３】
図１（ｄ）に示すように、必要に応じて導電層３の表面に接続条件で溶融可能な樹脂層４を形成してもよい。この場合、前記した微細電極の接続用とした場合、加熱加圧下において電極との接触面においては樹脂層が溶融し接続が可能となるが、隣接電極方向は熱量が不十分なため樹脂層が溶融し難いので絶縁性の低下が少なく、より高密度の実装が可能となる。
【００１４】
上記した各層間には必要に応じて、密着性向上のためのカップリング剤などの補助層を形成できる。
【００１５】
本発明の導電性粒子を微細電極の接続用とするためには、その粒径を隣接配線パターン間距離の最小幅よりも小さくすることが、隣接配線パターンとのショートを防止し配線の細線化に対応する上で必要である。
【００１６】
この場合の接着成分としては、熱可塑性材料でもよいが、熱、光、電子線などのエネルギーによる硬化性材料が耐熱性や耐湿性に優れることから好ましく適用できる。形態は液状、ペースト状、フィルム状などの何れでもよい、それぞれの特徴を生かして使いわける。例えばフィルム状であると一定の厚みが得やすく塗布作業も不要であり、また液状やペースト状の場合、微小面積の必要部のみに形成できるなどの特徴がある。
【００１７】
接続部材中に占める導電性粒子の割合は、用途により任意に設定できる。厚み方向のみに導電性の必要な微細電極用の接続部材の場合、０．１〜１５体積％、好ましくは０．２〜１０体積％、より好ましくは０．５〜６体積％である。配合量が少ないと、接続すべき電極上の導電性粒子数が減少するため信頼性が低下し、過多であると隣接電極の絶縁性が低下し微細電極の接続が困難となる。
【００１８】
面方向にも導電性が必要な塗料用の場合１０〜３５体積％が用いられる。
【００１９】
本発明になる導電性粒子を用いた接続部材の電極接続構造を、図２に示す。
基板１２、１２に設けられた電極１３、１３間で、接続時の加熱加圧により導電性粒子１１は、核の粒径で制御させて接続部材１４で接続される。この時ニッケル核１上の軟質層２は変形性を有するので、導電層３の剥離がない。電極の横方向は、導電性粒子の添加量や粒径の制御により絶縁性を保てる。
【００２０】
本発明になる導電性粒子は、導電層３が、軟質層２の上に形成されており、この軟質層２が接続時に変形追随する。そして、その最大変形量は、核１の粒径で制御されるので、過度の変形を生じない。このため、接続作業時に、導電層３が剥離しない。
【００２１】
核１は、電極接続時の加熱加圧の際に軟質な層に比べ硬質としたことにより変形がほとんど無いか、あっても僅かとすることができる。そのため、加熱加圧による接続後の電極間距離を硬質核の粒径に制御可能なので、接続条件の考慮が少なくても安定した接続が得られる。よく知られているように、電極間距離の制御が接続信頼性向上に大きく影響する。
【００２２】
【実施例】
以下実施例でさらに詳細に説明するが、本発明はこれに限定されない。
実施例１
核として平均粒径３μｍのカルボニル法で得た導電性のＮｉ粒子（融点１４５５℃）の表面に、被覆層としてポリスチレン／ジビニルベンゼン＝１００／０．５（ガラス転移点１１５℃）よりなる平均粒径１μｍの粒子を、アルコールを分散剤としてスプレイドライヤで被覆し、１２５℃に加熱し、固定化した。
【００２３】
この粒子を水中に分散し、塩化パラジウム系の活性化処理の後、無電解Ｎｉめっき液を用いてＮｉめっきを９０℃で行った後、Ａｕめっき液を用い置換めっきを７０℃で行った。この時Ｎｉ／Ａｕの厚さは０．２／０．０２μｍであった。このようにして、図１（ｂ）の構成の導電性粒子を得た。
【００２４】
高分子量エポキシを主成分とする接着成分に、前記導電性粒子を２体積％添加し、厚み５０μｍのポリテトラフルオロエチレンフィルム上に、厚み２０μｍとなるように塗布して接続部材を得た。得られた接続部材を、１００℃の純水で、１０時間抽出した後の抽出水のナトリウムイオン及び塩素イオンは、それぞれ１０ｐｐｍ以下であった。
【００２５】
厚み７５μｍのポリイミド基板上に、厚み１５μｍの接着剤層を介し厚み１８μｍで回路上にＳｎ／Ｐｂ＝１０／９０のはんだ薄層を有するＣｕ回路電極と、厚み１．１ｍｍのガラス上に形成した酸化インジウム（ＩＴＯ、表面抵抗２０Ω／□）の薄層電極との間に、前記接続部材を１．５ｍｍ幅で載置し両電極を位置合わせ後、接続した。
【００２６】
なお、回路ピッチ１００μｍ、電極幅５０μｍの平行回路の電極で、試験片１枚で３００本の電極接続部を有する。接続部の温度を、１５０℃、１７０℃、１９０℃、また、圧力を、０．５ＭＰａ、２ＭＰａ、１０ＭＰａと広く変動させた。このように広範囲の接続条件下で、電極間距離は、核体の平均粒径である３μｍに制御され、良好な接続信頼性を示した。ニッケル核を融点の高い金属粒子としたことで、電極の表面がはんだのような酸化物質であっても酸化層に食い込む形で良好な接続が得られた。
【００２７】
比較例１
平均粒径５μｍの硬化エポキシ粒子の表面に、直接Ｎｉ／Ａｕ層（厚さは０．２／０．０２μｍ）を形成した導電性粒子を用い以下実施例１と同様にして接続部材を得、同様に評価した（ただし、厚み７５μｍのポリイミド基板上に形成した回路上にはＳｎ薄層を有するＣｕ回路電極とした。）
接続条件の変動により電極間距離は４〜１５μｍと変動し接続抵抗のばらつき幅が大きく、実用化のためにはごく狭い温度圧力の範囲内で接続条件の厳密なコントロールが必要であった。
【００２８】
【発明の効果】
以上詳述したように、本発明によれば広い接続条件下で安定した接続信頼性が得られ、一層使いやすい導電性粒子及び接続部材を得ることが可能となる。
【図面の簡単な説明】
【図１】本発明の一実施例になる導電性粒子の断面図である。
【図２】本発明の一実施例を示す電極の接続構造の断面図である。
【符号の説明】
１ニッケル核
２軟質層
３導電層
４樹脂層
１１導電性粒子
１２基板
１３電極
１４接続部材[0001]
BACKGROUND OF THE INVENTION
The present invention is for example the electrodes connected, such as to suitable for, on the connection member using a conductive particle child capable of controlling deformation degree.
[0002]
[Prior art]
The circuit element and the circuit board, and the circuit boards are bonded to each other with a connecting member in which conductive particles are dispersed in an adhesive component such as an epoxy resin, and the circuit elements, the circuit board, and the circuit boards are electrically connected only in the pressing direction. There is an anisotropic conductive connecting member.
In this connection member, as the conductive particles dispersed in the adhesive component, there are known conductive particles in which a high molecular polymer is used as a core (polymer core) and the surface thereof is covered with a thin metal layer. . Since these particles have a small specific gravity, they are difficult to settle when the adhesive component is liquid. In addition, using such a connection member, for example, when connecting a microelectrode of an electronic component, the polymer core is deformed by the temperature and pressure at the time of connection, and the contact area between the conductive particles and the electrode is increased. There are features such as being able to. In this case, in order to prevent the conductive particles from being deformed excessively, it has also been proposed to mix hard spacer particles.
[0003]
[Problems to be solved by the invention]
Conductive particles made by coating the surface of the polymer core with a thin metal layer will cause large deformation of the polymer core when the temperature and pressure at the time of connection increase, and the thin metal layer will peel from the polymer core. In some cases, the metal pieces are separated by being broken or partially broken, and the discrete metal pieces come into contact with the connection electrodes to impair the insulation between the adjacent electrodes. For this reason, it is necessary to strictly control the connection conditions, and the inspection process after the connection is indispensable in consideration of variation in conditions.
[0004]
In addition, when mixing hard spacer particles, it is necessary to uniformly disperse these mixed particles, but it is difficult to uniformly disperse in a minute portion due to a difference in specific gravity and a difference in surface charge. In particular, this type of adhesive has recently been applied to the connection of fine electrodes and circuits, such as the connection of integrated circuits such as IC and LSI, and display elements such as liquid crystal, EL, and plasma with electronic circuits. Therefore, there is a strong demand for stable connection reliability over a wide range of connection conditions and for eliminating the need for post-connection inspection processes in mass production. It has become.
[0005]
[Means for Solving the Problems]
In the present invention, a soft layer 2 made of a crosslinked polymer having a thickness of ½ or less of the particle size of nickel nuclei is formed on the surface of nickel nuclei 1, and a conductive layer 3 containing nickel is placed on the outside of the adhesive layer. Is a connecting member containing 0.1 to 15% by volume .
[0006]
The present invention will be described below with reference to the drawings.
FIG. 1A is a schematic sectional view showing an embodiment of the present invention.
The material of the nickel core 1 is nickel and its alloy. A soft layer is formed on the surface of the nickel core. Here, the meaning of the soft layer means the relative hardness relationship between the nickel core and the soft layer 2 under the connection conditions in the use environment of the conductive particles, for example, in the case of connecting electrodes and circuits. To do. A general hardness index such as elastic modulus and hardness at a constant temperature, or a difference in thermal transformation point such as melting point, glass transition temperature, and softening point can be used as a guide.
[0007]
The average particle diameter of the nickel core 1 is 0.1 to 20 μm, preferably 0.3 to 10 μm, more preferably 0.5 to 6 μm. From the viewpoint of improving the properties. The particle diameter of the nickel core 1 is preferably uniform. The particle shape of the nickel core 1 is preferably substantially spherical, but may be any shape such as a large number of irregularities on the surface as shown in FIG.
[0008]
The soft layer 2 is preferably a polymer such as polystyrene, nylon, or various rubbers, and since these are cross-linked products, the solvent resistance is improved, so when the adhesive component contains a solvent, there is no elution, It is more preferable because it has little influence on characteristics.
Moreover, when the soft layer 2 is made of a polymer, it is easy to obtain deformability, and adhesion to the conductive layer and the nucleus is good. Therefore, when a connection member is used, a connection with low resistance and excellent reliability can be obtained. Moreover, a combination can be appropriately set according to the heat resistance and hardness of the connection electrode and the substrate.
[0009]
The thickness of the soft layer 2 is preferably about 0.1 to 10 μm. If the thickness is less than 0.1 μm, a sufficient amount of deformation cannot be obtained and the reliability is insufficient. If the thickness exceeds 10 μm, the amount of deformation becomes excessive and the coating of the thin metal layer is easily peeled off. For these reasons, 0.3 to 5 μm is preferable and 0.5 to 3 μm is more preferable.
[0010]
Further, if the thickness of the soft layer 2 is not more than the particle diameter of the nickel core 1, more preferably not more than ½, the deformation amount of the conductive particles can be easily controlled, which is preferable as a circuit connection material. The soft layer 2 may be present in the form of particles as shown in FIG. 1 (c), and may be configured as a single layer or multiple layers. In the case of a structure of multiple layers or more, functions such as strength retention, solvent resistance, adhesion, flexibility, heat resistance, and plating solution resistance can be shared, which is preferable. The soft layer 2 can be formed by an arbitrary method such as a spray method, a high-speed stirring method, or a spray dryer.
[0011]
The conductive layer 3 is made of various conductive metals, alloys, oxides, and the like. Materials that are preferably used in consideration of conductivity and corrosion resistance are Ni, Cu, Al, Sn, Zn, Au, Pd, Ag, Co, Pb, etc., which are single layer or multiple layers or more. It can also be configured.
[0012]
The conductive layer 3 may be formed by a general method such as a vapor deposition method, a sputtering method, an ion plating method, a thermal spraying method, or a plating method, but the electroless plating method should provide a coating layer having a uniform thickness. To preferred.
[0013]
As shown in FIG. 1D, a resin layer 4 that can be melted under connection conditions may be formed on the surface of the conductive layer 3 as necessary. In this case, when it is used for connection of the fine electrode described above, the resin layer melts and can be connected at the contact surface with the electrode under heating and pressure, but the resin layer is not sufficiently heated in the adjacent electrode direction. Since it is difficult to melt, there is little decrease in insulation, and higher-density mounting becomes possible.
[0014]
An auxiliary layer such as a coupling agent for improving adhesion can be formed between the above-described layers as necessary.
[0015]
In order to use the conductive particles of the present invention for connecting fine electrodes, it is possible to make the particle size smaller than the minimum width of the distance between adjacent wiring patterns to prevent a short circuit between adjacent wiring patterns and to reduce the thickness of the wiring. It is necessary to cope with.
[0016]
The adhesive component in this case may be a thermoplastic material, but is preferably applied because a curable material using energy such as heat, light, and electron beam is excellent in heat resistance and moisture resistance. The form may be any of liquid, paste, film, etc., and can be used by taking advantage of each feature. For example, when it is in the form of a film, it is easy to obtain a certain thickness, and an application operation is not necessary. In the case of a liquid or paste, it can be formed only in a necessary portion of a small area.
[0017]
The ratio of the electroconductive particle which occupies in a connection member can be arbitrarily set by a use. In the case of a connecting member for a fine electrode that requires electrical conductivity only in the thickness direction, it is 0.1 to 15% by volume, preferably 0.2 to 10% by volume, more preferably 0.5 to 6% by volume. When the blending amount is small, the number of conductive particles on the electrode to be connected is reduced, so that the reliability is lowered. When the blending amount is excessive, the insulating property of the adjacent electrode is lowered and the connection of the fine electrode becomes difficult.
[0018]
In the case of a coating material that requires conductivity also in the surface direction, 10 to 35% by volume is used.
[0019]
The electrode connection structure of the connection member using the electroconductive particle which becomes this invention is shown in FIG.
Between the electrodes 13 and 13 provided on the substrates 12 and 12, the conductive particles 11 are connected by the connection member 14 while being controlled by the particle diameter of the nucleus by heat and pressure at the time of connection. At this time, since the soft layer 2 on the nickel core 1 has deformability, the conductive layer 3 does not peel off. In the lateral direction of the electrode, insulation can be maintained by controlling the amount of conductive particles added and the particle size.
[0020]
In the conductive particles according to the present invention, the conductive layer 3 is formed on the soft layer 2, and the soft layer 2 follows deformation at the time of connection. And since the maximum deformation amount is controlled by the particle size of the core 1, excessive deformation does not occur. For this reason, the conductive layer 3 does not peel off during the connection work.
[0021]
Since the core 1 is harder than the soft layer at the time of heating and pressing at the time of electrode connection, there is little or no deformation. Therefore, since the distance between the electrodes after the connection by heating and pressing can be controlled to the particle size of the hard core, a stable connection can be obtained even if there is little consideration of the connection conditions. As is well known, the control of the distance between the electrodes greatly affects the improvement of connection reliability.
[0022]
【Example】
Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited thereto.
Example 1
An average particle of polystyrene / divinylbenzene = 100 / 0.5 (glass transition point 115 ° C.) as a coating layer on the surface of conductive Ni particles (melting point 1455 ° C.) obtained by a carbonyl method having an average particle size of 3 μm as a nucleus Particles having a diameter of 1 μm were coated with a spray dryer using alcohol as a dispersant, heated to 125 ° C. and fixed.
[0023]
The particles were dispersed in water, and after palladium chloride activation treatment, Ni plating was performed at 90 ° C. using an electroless Ni plating solution, and substitution plating was then performed at 70 ° C. using an Au plating solution. At this time, the thickness of Ni / Au was 0.2 / 0.02 μm. Thus, the electroconductive particle of the structure of FIG.1 (b) was obtained.
[0024]
2% by volume of the conductive particles were added to an adhesive component having a high molecular weight epoxy as a main component, and applied on a polytetrafluoroethylene film having a thickness of 50 μm to a thickness of 20 μm to obtain a connecting member. The sodium ion and the chlorine ion of the extracted water after extracting the obtained connection member for 10 hours with 100 degreeC pure water were 10 ppm or less, respectively.
[0025]
A Cu circuit electrode having a thin solder layer of Sn / Pb = 10/90 on a circuit having a thickness of 18 μm on a polyimide substrate having a thickness of 15 μm was formed on a polyimide substrate having a thickness of 15 μm and a glass having a thickness of 1.1 mm. The connecting member was placed with a width of 1.5 mm between a thin layer electrode of indium oxide (ITO, surface resistance 20Ω / □), and both electrodes were aligned and then connected.
[0026]
In addition, it is an electrode of a parallel circuit with a circuit pitch of 100 μm and an electrode width of 50 μm, and one test piece has 300 electrode connection portions. The temperature of the connection part was widely varied as 150 ° C., 170 ° C., 190 ° C., and the pressure was widely changed to 0.5 MPa, 2 MPa, and 10 MPa. Thus, under a wide range of connection conditions, the distance between the electrodes was controlled to 3 μm, which is the average particle diameter of the nuclei, and good connection reliability was exhibited. By using nickel nuclei as metal particles having a high melting point, even if the surface of the electrode is an oxide material such as solder, a good connection was obtained in the form of biting into the oxide layer.
[0027]
Comparative Example 1
Using conductive particles in which a Ni / Au layer (thickness: 0.2 / 0.02 μm) was directly formed on the surface of a cured epoxy particle having an average particle diameter of 5 μm, a connecting member was obtained in the same manner as in Example 1 below. Evaluation was made in the same manner (however, a Cu circuit electrode having a Sn thin layer was formed on a circuit formed on a polyimide substrate having a thickness of 75 μm.)
Due to variations in connection conditions, the distance between the electrodes varies from 4 to 15 μm and the variation range of the connection resistance is large. For practical use, it is necessary to strictly control the connection conditions within a very narrow temperature and pressure range.
[0028]
【The invention's effect】
As described above in detail, according to the present invention, stable connection reliability can be obtained under a wide range of connection conditions, and conductive particles and connection members that are easier to use can be obtained.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of conductive particles according to an embodiment of the present invention.
FIG. 2 is a sectional view of an electrode connection structure according to an embodiment of the present invention.
[Explanation of symbols]
1 Nickel Core 2 Soft Layer 3 Conductive Layer 4 Resin Layer 11 Conductive Particles 12 Substrate 13 Electrode 14 Connecting Member

Claims

ニッケル核の表面にニッケル核の粒径の１／２以下の厚みの高分子の架橋体からなる軟質層を形成し、その外側にニッケルを含む導電層を形成してなる導電性粒子を接着成分中に０．１〜１５体積％含有してなる接続部材。 1/2 or less of the soft layer comprising a crosslinked product of a polymer thickness formed, the adhesive component of the conductive particles obtained by forming a conductive layer comprising nickel on the outside of the particle size of nickel nuclei on the surface of the nickel nuclei A connecting member containing 0.1 to 15% by volume.