JP4010717B2 - Electrical contact joining method - Google Patents

Description

表１に示した不具合現象は、いずれもＳｎ−Ｐｂソルダを用いた場合に、その被接合部材の材質との相互作用に伴って必然的に発生するものであって、その発生機構は、金属物理・化学の基本現象に起因する。ここで、上記表１中における不具合現象Ｎｏ．▲１▼の金属間化合物の形成機構と、不具合現象Ｎo.▲３▼のソルダによる被接合材料の侵食を検討する。
【０００９】
図４は、Ｃｕ−Ｓｎ系の平衡状態図を示す。図４から明らかなように、銅（Ｃｕ）とＳｎ−Ｐｂソルダの接触を考えると、Ｃｕ−Ｓｎそれぞれの組成比によって種々の平衡相が存在しうることが判る。特に、２４％Ｃｕと４４％Ｃｕのそれぞれの場合に、金属間化合物Ｃｕ_３ＳｎとＣｕ_６Ｓｎ_５が安定に存在し、これらは共にセラミックに近い性質を持つと考えられ、硬くて脆く、しかも高電気抵抗率の部分を形成するので、接合継手としては極めて由々しいものとなる。
【００１０】
一方、図５は、各種金属原子が溶融状態の６０％Ｓｎ−４０％Ｐｂソルダ中へ溶解していく速度を示す。図５の関係は次式（１）で表される。
【数１】

【００１１】
図５から明らかなように、一定温度で元素毎の比較をすると、錫は最も溶解が速く、金、銀の溶解は比較的速く、他の元素の溶解速度は相対的に低くなっていることが判る。一方、温度との関係では、各元素共に式（１）の指数関数型の依存性を示し、温度が高くなると、溶解速度が急激に増大する。
【００１２】
表１に示す不具合は、いずれもＳｎ−Ｐｂソルダと被接合部材との間の物理・化学的相互反応によって生じるので、これらを１００％解消できる方策はない。したがって、これらの不具合を根本的に回避するためには、従来のＳｎ−Ｐｂソルダを用いた接合法に替わる全く違う原理による接合手段を採用する必要がある。
【００１３】
このため、従来のソルダリング接合法の欠点から解放された、全く異なる接合手段に基づくバンプ−電極等の接合法の一つとして、導電接着剤を使用するものが開発されている。導電接着剤は、導電性を有する充填材（導電フィラー）としての銀や炭素等の粒子を、接着性を有する有機高分子中に混入分散したものであって、これを使用することによって、接着性と導電性を同時に実現することが出来る。この導電接着剤の主成分である高分子材料としては、接着性や耐久性が優れているエポキシ樹脂が一般に使用されている。
【００１４】
しかしながら、導電接着剤を使用した接合法とＳｎ−Ｐｂソルダを用いた接合法（ソルダリング）とを比較すると、導電接着剤を使用した接合法では、接続部の電気抵抗率がソルダに比べて遙かに高くなるという難点がある。表２は、導電フィラーとして銀を使用した導電接着剤とニッケルを使用した導電接着剤の電気抵抗率と接着強度を示すものである。
【表２】

この表２から、銀を導電フィラーとした導電接着剤であっても、電気抵抗率がソルダに比較して、１桁大きなレベルになっていることが判る。
【００１５】
このように、電気抵抗率が高くなる原因としては、主として、本来十分均一に分散すべき金属粒子の寸法が大きく、しかも高分子材料中で凝集して分散の均一度が低下することによると考えられる。そこで、ソルダと同程度の電気抵抗率を持った導電接着剤の実現と、それを用いたバンプ−電極等の電気接点の接合技術の確立に対するニーズが非常に高くなっている。
【００１６】
本発明は上記事情に鑑みて為されたもので、従来のソルダリングに代替え可能で該ソルダリング特有の不具合を悉く解消した電気接点の接合方法を提供することを目的とする。
【００１７】
【課題を解決するための手段】
請求項１に記載の発明は、２つの電気接点を電気的に接合するにあたり、接着性を有する液状の高分子材料の内部に、周囲をアルキル鎖殻で被覆した、大きさが約５ｎｍのクラスタ状の銀超微粒子を混入分散した導電接着剤を２つの電気接点間に介在させて仮止めし、しかる後、前記導電性接着剤を焼成して、前記銀超微粒子の周囲を被覆していたアルキル鎖殻を消失させ、前記高分子材料の収縮・硬化に伴って前記銀超微粒子同士を直接接触させて該接触部を焼結させることを特徴とする電気接点の接合方法である。
【００１８】
これを用いれば、液状の高分子材料の内部に金属超微粒子を凝集を起こすことなく均一に混入分散させ、その後の焼成の際の高分子材料の収縮・硬化に伴って金属超微粒子同士を強固に接触させることによって、ソルダとほぼ同等な電気抵抗率を得ることができる。
【００１９】
請求項２に記載の発明は、前記銀超微粒子は、銀を含む有機錯体を熱分解して製造したものであることを特徴とする請求項１記載の電気接点の接合方法である。この銀超微粒子は、例えばステアリン酸銀を２５０℃程度の窒素雰囲気で４時間加熱し、精製することによって製造する。
【００２１】
【発明の実施の形態】
以下、本発明の実施の形態を図面を参照して説明する。
図１は、ＱＦＣ（quad flat package）タイプのＩＣパッケージをプリント配線板の両面に装着する表面実装工程に適用した本発明の一つの実施の形態の電気接点の接合方法を示す。
【００２２】
先ず、図１（ａ）に示すように、プリント配線板１０の表面（上面）の所定の位置に導電接着剤３０ａを印刷する。そして、図１（ｂ）に示すように、ＩＣパッケージ２０ａの各リード２２ａを前記各導電接着剤３０ａに付着させて仮止めし、しかる後、例えば２００℃程度に加熱して導電接着剤３０ａを焼成する。
【００２３】
次に、図１（ｃ）に示すように、プリント配線板１０を反転させた後、プリント配線板１０の裏面（上面）の所定の位置に導電接着剤３０ｂを印刷し、図１（ｄ）に示すように、ＩＣパッケージ２０ｂの各リード２２ｂを前記各導電接着剤３０ｂに付着させて仮止めした後、例えば２００℃程度に加熱して導電接着剤３０ｂを焼成する。
【００２４】
この実施の形態によれば、ソルダを使用していないので、図３に示す従来例における接着剤１４の塗布及びその乾燥・硬化工程を省略して、工程の簡素化を図ることができる。
【００２５】
図２（ａ）は、導電接着剤３０をプリント配線板１０の表面に塗布した直後の状態を、図２（ｂ）は、導電接着剤３０の焼成後の状態をそれぞれ概念的に示すものである。
【００２６】
前記導電接着剤３０は、その導電要素として、導電性の良い、例えば単体の銀で構成された銀超微粒子４０を利用し、その周囲をアルキル鎖殻４２で被覆したものを、接着剤と有機溶媒の混合液である液状の高分子材料４４内に混入分散させたものである。この銀超微粒子（金属超微粒子）４０は、その寸法が約５ｎｍ程度と極小クラスタ状をなしている。
【００２７】
ここで、周囲をアルキル鎖殻４２で被覆した、約５ｎｍ程度の極小クラクタ状の銀超微粒子４０は、例えばミリスチン酸、ステアリン酸またはオレイン酸を水酸化ナトリウムによって鹸化し、しかる後、硝酸銀と反応させることによって作製した直鎖型脂肪酸銀塩（アルキル鎖の炭素数＝１４，１８，１８ω）を、２５０℃程度の窒素雰囲気で４時間加熱し、精製することによって製造する。そして、このような、５ｎｍとクラスターレベルの極小な粒径をなした銀超微粒子４０を、例えばシクロヘキサン等の有機溶媒に溶解した状態で、液状の高分子材料４４内に供給し分散させると、極めて分散性が良好で、互いに凝集することなく、銀超微粒子４０が安定した状態で媒質中に均一に混じり合う。すなわち、高分子材料４４が液状の場合は、図２（ａ）に示すように、銀超微粒子４０同士は、互いに非接触状態で、高分子材料４４中に均一に分散する。
【００２８】
前記高分子材料４４の接着剤の主成分としては、例えば、エポキシ系やフェノール系等のような熱硬化性樹脂を用いている。この種の熱硬化性樹脂は、例えば、１７０℃以上の昇温・保持の操作で乾燥・硬化し、その際に一定の体積収縮を起こす。一方、銀超微粒子４０を被覆しているアルキル鎖殻４２は、２００℃程度の加熱で消滅することが知られている。
【００２９】
つまり、前述のように、導電接着剤３０を２００℃で焼成すると、図２（ｂ）に示すように、銀超微粒子４０の周囲を覆っていたアルキル鎖殻４２は消失し、更に、高分子材料４４の収縮・硬化に伴って銀超微粒子４０同士が直接接触し、更に接触部で焼結が起こる。その結果、銀粒子部分が全体として導電性を帯びると同時に高分子材料４４は硬化して接着が完了する。以上の過程を経てこの導電接着剤の電気抵抗率は、表２に示す導電フィラーとして銀を使用した従来の導電接着剤の１／９程度に低減でき、現状の６０％Ｓｎ−４０％Ｐｂソルダとほとんど同じレベルの値に改善できる。
【００３０】
この過程は、接着剤以外の導電性樹脂、導電性ゴム（エラストマ）、導電性塗布料等に導電性を付与する場合のそれと基本的に同じである。
なお、接着剤の主成分としてエポキシ系やフェノール系の合成樹脂を用い、この合成樹脂の硬化時間を適度に選ぶことにより、少なくとも上記ソルダの２０〜４０％の値の結合力を確保し、その他の電気特性や長期耐久性も上記ソルダと同程度若しくはそれ以上となるようにすることができる。
【００３１】
また、一般に、ソルダリング接合と比較して接着剤による結合では継手部分の機械的性質が相対的に脆いので、粘り強さやクラック抵抗性が劣ることが問題点として指摘されている。この点に関しては、例えば航空機用途の構造接着剤として、変性（フレキシビライズ又はタフ化）したフェノール系、エポキシ系、アクリル系、ポリイミド系の接着剤の充当実用化がなされており十分な使用実積がある。そこで、必要に応じてこれに倣うことによって、この種の問題への対応が可能になると考えられる。
【００３２】
因に、エポキシ系接着剤の変性を起こすため、具体的には特有のエラストマを液状樹脂中に溶解し、これを硬化することによって必要な機能を得ることができる。例えば、エラストマを添加して変性することによって、エポキシ接着剤の室温剥離強さを１．１ｋＮ／ｍから５．５ｋＮ／ｍ へと著しく（５倍も）改善した実績が報告されている。また、ポリイミド系接着剤は、２３２℃の高温に保持した状態でも、１９.３ＭＰａと極度に高いラップシアー強さを示す。
【００３３】
以上説明したように、本発明の電気接点の接合方法によれば、従来のソルダリングと異なり、錫−鉛系合金の溶融体と被接合部材表面が高温で直接接触して濡れることに起因して生じる弊害を回避することができると同時に、ソルダリングの持つ利点の大部分をカバーする電気・電子部品の接合が可能となる。したがって、従来のソルダリングに替わって、前述の金属物理・化学現象に伴って必然的に生じる、ソルダリング特有の不具合（表１参照）を悉く解消した健全な電気的結合が可能となる。
【００３４】
【発明の効果】
以上説明したように、本発明によれば、従来のソルダリングに代替え可能で該ソルダリング特有の不具合を悉く解消した電気接点の接合方法を提供することができる。
【図面の簡単な説明】
【図１】本発明の一つの実施の形態の電気接点の接合方法を工程順に示す図である。
【図２】（ａ）は導電接着剤を塗布した直後の状態を、（ｂ）は導電接着剤の焼成後の状態を概念的に示す図である。
【図３】従来の電気接点の接合方法の一例を工程順に示す図である。
【図４】Ｃｕ−Ｓｎ系二元状態図と銅とのソルダリング界面の構造を示す図である。
【図５】各種金属の溶融６０％Ｓｎ−４０％Ｐｂソルダへの各元素の溶解速度を示すグラフである。
【符号の説明】
１０ プリント配線板
２０ａ、２０ｂ ＩＣパッケージ
２２ａ，２２ｂ リード（接点）
３０，３０ａ，３０ｂ 導電接着剤
４０ 銀超微粒子（金属超微粒子）
４２ アルキル鎖殻
４４ 高分子材料[0001]
BACKGROUND OF THE INVENTION
In the present invention, for example, when a chip constituting an electronic component or a semiconductor device is mounted on a substrate or the like, an electrical bonding bump (contact) provided on the surface of the chip and an electrode (contact) on the substrate are electrically connected. The present invention relates to a method for joining electrical contacts.
[0002]
[Prior art]
For example, the electrical bonding between the bumps for electrical bonding arranged on the surface of a chip constituting an electronic component or a semiconductor device and the electrodes provided at positions corresponding to these bumps on the substrate is made of tin and lead. Micro soldering using a solder (hereinafter referred to as Sn-Pb solder or solder) is widely used. According to this type of solder bonding method, generally, a bonding strength of about 39.2 MPa is secured, the electrical resistivity of the solder bulk is about 17 μΩcm, and the melting temperature is about 180 ° C. This makes it possible to easily obtain balanced bonding characteristics.
[0003]
FIG. 3 shows an example of a surface mounting process for mounting a QFC (quad flat package) type IC package on both surfaces of a printed wiring board by conventional general reflow soldering using this type of solder. First, as shown in FIG. 3A, the solder paste 12a is printed at a predetermined position on the surface (upper surface) of the printed wiring board 10, and further sandwiched between the solder pastes 12a as shown in FIG. 3B. The adhesive 14 is applied to the predetermined position. Then, as shown in FIG. 3C, the IC package 20a is mounted on the surface of the printed wiring board 10 via the adhesive 14 while the leads 22a are pressed against the solder pastes 12a, and the adhesive 14 is attached. Dry and cure.
[0004]
Next, as shown in FIG. 3D, after the printed wiring board 10 is inverted, the solder paste 12b is printed at a predetermined position on the back surface (upper surface) of the printed wiring board 10, and FIG. As shown, the solder paste 12a, by pressing the IC package 20b on the back surface of the printed wiring board 10 while pressing each lead 22b against the solder paste 12b, and then heating to 200 to 300 ° C., for example. 12b is melted and solidified.
[0005]
Here, in consideration of the melting property of the solder, the IC package 20a is mounted on one surface (front surface) of the printed wiring board 10 using the adhesive 14.
[0006]
[Problems to be solved by the invention]
However, in recent years, for example, bumps for electrical bonding provided on the surface of a chip constituting a semiconductor device and electrodes provided on a substrate have been increasingly miniaturized and pitched, and accordingly, conventional micro soldering has been performed. In the joining method used, the following disadvantages (1) to (3) are strongly regarded as problems.
[0007]
(1) When the wettability of the interface is good, an interaction layer such as a solid solution or an intermetallic compound is formed between the material to be joined and the molten solder, which causes deterioration of mechanical and electrical characteristics.
(2) Joining operations and conditions become complicated when the soldering property is remarkably different due to the difference in material between members to be joined.
{Circle around (3)} Due to the severe erosion of the material to be joined by the solder, the composition of the solder and the ground treatment of the material to be joined may be troublesome.
Table 1 shows the problems of the joining method using micro soldering that are expressed in terms of the phenomenon, generation mechanism, and countermeasures.
[0008]
[Table 1]

All of the malfunctions shown in Table 1 are inevitably caused by the interaction with the material of the member to be joined when Sn-Pb solder is used. It originates from basic phenomena of physics and chemistry. Here, the defect phenomenon No. 1 in Table 1 above. Study the formation mechanism of the intermetallic compound (1) and the erosion of the material to be joined by the solder of the failure phenomenon No. (3).
[0009]
FIG. 4 shows an equilibrium diagram of the Cu—Sn system. As is apparent from FIG. 4, considering the contact between copper (Cu) and Sn—Pb solder, it can be seen that various equilibrium phases can exist depending on the composition ratio of Cu—Sn. In particular, in each of the cases of 24% Cu and 44% Cu, the intermetallic compounds Cu ₃ Sn and Cu ₆ Sn ₅ exist stably, both of which are considered to have properties close to ceramics, are hard and brittle, Since a portion having a high electrical resistivity is formed, it is extremely serious as a joint joint.
[0010]
On the other hand, FIG. 5 shows the speed at which various metal atoms are dissolved in the molten 60% Sn-40% Pb solder. The relationship of FIG. 5 is expressed by the following equation (1).
[Expression 1]

[0011]
As is clear from FIG. 5, when comparing each element at a constant temperature, tin is the fastest dissolving, gold and silver are relatively fast, and the dissolution rates of other elements are relatively low. I understand. On the other hand, in relation to temperature, each element shows exponential dependence of the formula (1), and the dissolution rate increases rapidly as the temperature increases.
[0012]
All of the defects shown in Table 1 are caused by a physical / chemical interaction between the Sn-Pb solder and the member to be joined, and there is no way to eliminate them 100%. Therefore, in order to fundamentally avoid these problems, it is necessary to employ joining means based on a completely different principle that replaces the joining method using the conventional Sn-Pb solder.
[0013]
For this reason, a method using a conductive adhesive has been developed as one of bonding methods such as bump-electrodes based on completely different bonding means, which is free from the drawbacks of the conventional soldering bonding method. The conductive adhesive is a mixture of particles such as silver and carbon as a conductive filler (conductive filler) mixed in an organic polymer having adhesive properties. And conductivity can be realized at the same time. As the polymer material that is the main component of the conductive adhesive, an epoxy resin having excellent adhesion and durability is generally used.
[0014]
However, when the joining method using a conductive adhesive and the joining method (soldering) using a Sn-Pb solder are compared, in the joining method using a conductive adhesive, the electrical resistivity of the connecting portion is higher than that of the solder. There is the difficulty of becoming much higher. Table 2 shows the electrical resistivity and adhesive strength of a conductive adhesive using silver as a conductive filler and a conductive adhesive using nickel.
[Table 2]

From Table 2, it can be seen that even in the case of a conductive adhesive using silver as a conductive filler, the electrical resistivity is one level larger than that of solder.
[0015]
As described above, the reason why the electrical resistivity is increased is mainly due to the fact that the size of the metal particles that should be dispersed sufficiently uniformly is large, and that the uniformity of the dispersion is reduced by aggregation in the polymer material. It is done. Therefore, there is a great need for realizing a conductive adhesive having an electrical resistivity comparable to that of solder and establishing a bonding technique for electrical contacts such as bump-electrodes using the same.
[0016]
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for joining electrical contacts which can be replaced with conventional soldering and which eliminates problems peculiar to the soldering.
[0017]
[Means for Solving the Problems]
According to the first aspect of the present invention, when electrically connecting two electrical contacts, a cluster having a size of about 5 nm and having an outer periphery covered with an alkyl chain shell inside an adhesive liquid polymer material. The conductive adhesive in which the silver ultrafine particles are mixed and dispersed is temporarily interposed between two electrical contacts, and then the conductive adhesive is baked to cover the periphery of the silver ultrafine particles. An electrical contact joining method characterized in that the alkyl chain shell disappears and the ultrafine silver particles are brought into direct contact with each other as the polymer material shrinks and hardens to sinter the contact portion .
[0018]
If this is used, the ultrafine metal particles are uniformly mixed and dispersed within the liquid polymer material without agglomeration, and the ultrafine metal particles are strengthened as the polymer material shrinks and cures during subsequent firing. It is possible to obtain an electrical resistivity substantially equal to that of solder.
[0019]
The invention according to claim 2, wherein the ultra-fine silver particles are joining method of the electrical contacts according to claim 1, wherein the organic complex containing silver are those produced by thermal decomposition. The silver ultrafine particles are produced, for example, by heating and purifying silver stearate in a nitrogen atmosphere at about 250 ° C. for 4 hours.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows an electrical contact joining method according to an embodiment of the present invention applied to a surface mounting process in which a QFC (quad flat package) type IC package is mounted on both sides of a printed wiring board.
[0022]
First, as shown in FIG. 1A, the conductive adhesive 30 a is printed at a predetermined position on the surface (upper surface) of the printed wiring board 10. Then, as shown in FIG. 1B, each lead 22a of the IC package 20a is temporarily attached to each of the conductive adhesives 30a, and then heated to, for example, about 200 ° C. to remove the conductive adhesive 30a. Bake.
[0023]
Next, as shown in FIG. 1C, after the printed wiring board 10 is inverted, the conductive adhesive 30b is printed at a predetermined position on the back surface (upper surface) of the printed wiring board 10, and FIG. As shown in FIG. 3, after each lead 22b of the IC package 20b is attached to each of the conductive adhesives 30b and temporarily fixed, the conductive adhesive 30b is baked by heating to about 200 ° C., for example.
[0024]
According to this embodiment, since no solder is used, the application of the adhesive 14 and the drying / curing process thereof in the conventional example shown in FIG. 3 can be omitted, and the process can be simplified.
[0025]
FIG. 2A conceptually shows a state immediately after the conductive adhesive 30 is applied to the surface of the printed wiring board 10, and FIG. 2B conceptually shows a state after the conductive adhesive 30 is baked. is there.
[0026]
The conductive adhesive 30 uses, as its conductive element, silver ultrafine particles 40 made of, for example, simple silver having good conductivity, and the periphery thereof is covered with an alkyl chain shell 42. It is mixed and dispersed in a liquid polymer material 44 which is a mixed solution of solvents. The silver ultrafine particles (metal ultrafine particles) 40 have a very small cluster shape with a dimension of about 5 nm.
[0027]
Here, the ultrafine silver particle 40 of about 5 nm, which is coated with an alkyl chain shell 42, is saponified with, for example, myristic acid, stearic acid or oleic acid with sodium hydroxide, and then reacted with silver nitrate. It is manufactured by heating and purifying a linear fatty acid silver salt (alkyl chain carbon number = 14,18,18ω) prepared by heating in a nitrogen atmosphere at about 250 ° C. for 4 hours. Then, when such silver ultrafine particles 40 having a minimum particle size of 5 nm and a cluster level are dissolved in an organic solvent such as cyclohexane and supplied into the liquid polymer material 44 and dispersed, It has extremely good dispersibility, and the silver ultrafine particles 40 are uniformly mixed in the medium in a stable state without aggregating with each other. That is, when the polymer material 44 is in a liquid state, the silver ultrafine particles 40 are uniformly dispersed in the polymer material 44 in a non-contact state with each other as shown in FIG.
[0028]
As a main component of the adhesive of the polymer material 44, for example, a thermosetting resin such as epoxy or phenol is used. This type of thermosetting resin, for example, is dried and cured by a temperature raising and holding operation at 170 ° C. or higher, and causes a certain volume shrinkage. On the other hand, it is known that the alkyl chain shell 42 covering the ultrafine silver particles 40 disappears by heating at about 200 ° C.
[0029]
That is, as described above, when the conductive adhesive 30 is baked at 200 ° C., as shown in FIG. 2B, the alkyl chain shell 42 covering the periphery of the silver ultrafine particles 40 disappears, and further, the polymer As the material 44 contracts and hardens, the silver ultrafine particles 40 come into direct contact with each other, and further sintering occurs at the contact portion. As a result, the silver particle portion becomes conductive as a whole, and at the same time, the polymer material 44 is cured and the adhesion is completed. Through the above process, the electrical resistivity of the conductive adhesive can be reduced to about 1/9 of the conventional conductive adhesive using silver as the conductive filler shown in Table 2, and the current 60% Sn-40% Pb solder. Can be improved to almost the same level.
[0030]
This process is basically the same as that for imparting conductivity to conductive resins other than adhesives, conductive rubber (elastomer), conductive coating materials, and the like.
In addition, by using an epoxy-based or phenol-based synthetic resin as the main component of the adhesive, and by appropriately selecting the curing time of this synthetic resin, at least a binding force of 20 to 40% of the above-mentioned solder is secured, and the others The electrical characteristics and long-term durability of the solder can be the same as or higher than those of the solder.
[0031]
In general, it has been pointed out as a problem that the bond strength and crack resistance are inferior because the mechanical properties of the joint portion are relatively brittle in the bonding with an adhesive as compared with soldering bonding. In this regard, for example, as structural adhesives for aircraft applications, the use of modified (flexibilized or toughened) phenolic, epoxy, acrylic, and polyimide adhesives has been put into practical use. There is a product. Therefore, it is considered that this type of problem can be dealt with by following this as necessary.
[0032]
In order to cause modification of the epoxy adhesive, specifically, a specific function can be obtained by dissolving a specific elastomer in a liquid resin and curing it. For example, it has been reported that the room temperature peel strength of an epoxy adhesive is remarkably improved (from 5 times) from 1.1 kN / m to 5.5 kN / m by adding and modifying an elastomer. In addition, the polyimide-based adhesive exhibits an extremely high lap shear strength of 19.3 MPa even when held at a high temperature of 232 ° C.
[0033]
As described above, according to the electrical contact joining method of the present invention, unlike the conventional soldering, the molten tin-lead alloy and the surface of the member to be joined come into direct contact at high temperature and get wet. In addition to avoiding harmful effects caused by soldering, it is possible to join electric / electronic components that cover most of the advantages of soldering. Therefore, in place of the conventional soldering, it is possible to achieve a sound electrical coupling that eliminates the problems peculiar to soldering (see Table 1) that are inevitably caused by the above-described metal physics / chemical phenomenon.
[0034]
【The invention's effect】
As described above, according to the present invention, it is possible to provide a method for joining electrical contacts which can be replaced with conventional soldering and which eliminates problems peculiar to the soldering.
[Brief description of the drawings]
FIG. 1 is a diagram showing a method of joining electrical contacts according to an embodiment of the present invention in the order of steps.
2A is a diagram conceptually showing a state immediately after applying a conductive adhesive, and FIG. 2B is a diagram conceptually showing a state after firing the conductive adhesive.
FIG. 3 is a diagram showing an example of a conventional method for joining electrical contacts in the order of steps.
FIG. 4 is a diagram showing a structure of a soldering interface between a Cu—Sn based binary phase diagram and copper.
FIG. 5 is a graph showing the dissolution rate of each element in molten 60% Sn-40% Pb solder of various metals.
[Explanation of symbols]
10 Printed wiring boards 20a, 20b IC packages 22a, 22b Lead (contact point)
30, 30a, 30b Conductive adhesive 40 Silver ultrafine particles (metal ultrafine particles)
42 alkyl chain shell 44 polymer material

Claims (2)

In electrically joining two electrical contacts,
An electrically conductive adhesive in which cluster-like ultrafine silver particles having a size of about 5 nm are mixed and dispersed inside the liquid polymer material having adhesive properties is interposed between two electrical contacts. Temporarily
Thereafter, the conductive adhesive is baked to eliminate the alkyl chain shells that have covered the periphery of the silver ultrafine particles, and the silver ultrafine particles are brought into direct contact with each other as the polymer material shrinks and cures. And sintering the contact portion .   The method for joining electrical contacts according to claim 1, wherein the silver ultrafine particles are produced by thermally decomposing an organic complex containing silver.

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