JPH0340899B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a circuit connection structure. (Prior art) Connecting terminals have traditionally been arranged facing each other at a fine pitch for connecting integrated circuits to wiring boards, connecting surface elements to wiring boards, connecting electrical circuits to leads, etc. In this case, methods using connecting members such as soldering and conductive adhesive are widely used. However, in these methods, the connection member must be formed only in the conductive circuit portion, making it difficult to connect fine circuits that are becoming increasingly dense and fine. Recently, consideration has been given to connection materials for circuits.
For example, JP-A-51-20941, JP-A-51-21192.
Publication No. 135938, Japanese Patent Application Laid-Open No. 1983-135938, Japanese Patent Publication No. 1983-
Publication No. 104007, Japanese Patent Application Publication No. 1983-122193, Japanese Patent Application Publication No. 1987-122193
57-111366, Japanese Patent Application Laid-open No. 58-111202, etc., an anisotropically conductive connecting member layer containing conductive particles such as metal particles and an adhesive component is provided between opposing circuits, and a pressure or It has been proposed to provide electrical connection between circuits and at the same time provide insulation between adjacent circuits by providing heating and pressing means to adhesively fix opposing circuits. However, in these methods, continuity between circuits is primarily achieved through contact between multiple conductive materials, often metal particles;
Because the metal particles are rigid, there is not enough contact area between particles or between particles and circuits, and because the coefficient of thermal expansion of the adhesive component and the metal particles are different,
This had the disadvantage that the resistance value changed significantly with respect to temperature changes, and the reliability of the connection part was poor. In order to reduce the temperature coefficient, it is effective to reduce the contact resistance of the connection part.
As seen in Japanese Patent No. 60-140790, there has been an attempt to obtain a good connection by melting and connecting heat-fusible metal particles dispersed in an insulating adhesive between circuits. However, since the metal particles are heat-fusible, this method has the disadvantage that the range of conditions required for connection work is narrow. In other words, at temperatures above the melting point, the metal particles melt and flow across tiny adjacent circuits, resulting in leakage, which makes it impossible to connect circuits with fine pitches. Since the particles do not melt at temperatures below the melting point of the metal, only rigid metal particles exist between the circuits, and as described above, the resistance change of the connection becomes large with respect to the change in ambient temperature.
It had the drawback of having a large so-called temperature coefficient. In addition, in display circuit connections, which is one of the main application fields for these anisotropic conductive connection materials, oxides such as tin oxide, indium oxide, titanium oxide, etc. are used on transparent substrates such as glass and plastic. Transparent conductive films, in which conductive circuits are formed using thin films of aluminum, chromium, etc., are often used, but heat-fusible metal particles, such as solder, have extremely high surface tension on these circuit surfaces. Due to the lack of wettability to the circuit surface and the fact that it does not form an alloy with the oxidized surface of aluminum or other oxide circuits, the wettability with the circuit surface is insufficient, and the rate of change in resistance with respect to temperature changes at the connection part also decreases. It had the disadvantage of being large. Therefore, in display applications such as liquid crystals (LCDs), electroluminescent (EL) plasmas, or fluorescent display tubes, there are practical problems such as the display becoming unclear or not being able to display at high temperatures. was. As an improvement method, Au or
The solution has been to increase the surface tension of the circuit by forming a thin layer of Ni or other materials by plating or sputtering, but this method requires complicated processes and advanced processing technology, resulting in high product costs. It had some drawbacks such as: (Problems to be Solved by the Invention) The present invention has been made in view of the above-mentioned drawbacks of the prior art, and provides a fine circuit connection structure in which the temperature coefficient of resistance of the circuit connection portion is small. (Means for Solving the Problems) That is, the present invention provides a circuit connection structure in which a plurality of conductive patterns and opposing circuits are electrically connected by a connection member, in which a polymer is placed between the circuits to be connected. Conductive particles in which almost the entire surface of a core material made of a polymer is substantially covered with a conductive metal thin layer, and a connecting member layer made of highly rigid spacer particles and an insulating adhesive are interposed; The present invention relates to a circuit connection structure characterized in that the core material is fixed in a deformed state so as to be pressed against the circuit surface, and the thickness between the opposing circuits is approximately equal to the diameter of the space particle. The constituent materials according to the present invention will be explained in detail below. First, the conductive particles have a thin metal layer on almost the entire surface of a core material made of a polymer (hereinafter referred to as a polymer core material). The structure of the polymer core material may be a completely solid body, a hollow body made of gas inside, a foam body with bubbles inside, an aggregate that is a collection of small particles, etc., and these can be used alone or in combination. It is possible to use it as The shape of the polymer core material 9 is typically approximately spherical, but the shape is not particularly limited. The materials include various plastics, rubbers, and natural polymers, and these are the main ingredients, and additives such as crosslinking agents and curing agents can be used as necessary. Examples of these polymers include polyethylene, polypropylene, polystyrene, acrylonitrile-styrene copolymer, and acrylonitrile-styrene copolymer.
Butadiene-styrene copolymer, polycarbonate, various acrylates such as polymethyl methacrylate, polyvinyl butyral, polyvinyl formal, polyimide, polyamide, polyester, polyvinyl chloride, polyvinylidene chloride, fluororesin, polyphenylene oxide, polyphenylene Rensulfide, polymethylpentene, urea resin, melamine resin, benzoguanamine resin, phenol-formalin resin, xylene resin, furan resin, diallyl phthalate resin, epoxy resin,
Examples include polyisocyanate resin, phenoxy resin, and silicone resin, and these may be modified as appropriate. Further, these may be used alone or as a composite of two or more kinds. For thermosetting materials,
The degree of curing is not critical as long as it does not interfere with mixing with the adhesive component. These polymeric core materials must be able to be softened or deformed by pressure applied during circuit connection or by heating and pressure. The reason why softening or deformation is required by applying pressure or heating and pressing during connection is to increase the contact area between conductive particles or between conductive particles and the circuit when connecting the circuit. It is also possible to use a pressure-sensitive connection using a so-called pressure-sensitive adhesive or a heat-sensitive connection using heating up to 400°C. If the polymer core material has a molecular weight of 100 to 250, it is preferable that the polymer core material has a molecular weight of 100 to 250. It is preferable that the material can be softened or deformed at ℃. The pressure should preferably be as low as possible so as not to adversely affect the circuit parts that need to be connected, and the pressure should be 100Kg/cm ^2.
(preferably 50 kg/cm ² or less). As the metal used for the coating, various conductive metals, metal oxides, alloys, etc. are used. Examples of metal elements include Zn, Al, Sb, U,
Cd, Ga, Ca, Au, Ag, Co, Sn, Se, Fe,
There are Cu, Th, Pb, Ni, Pd, Be, Mg, Mn, etc., and these can be used alone or in combination, and other elements or compounds can be used for special purposes such as improving hardness or surface tension. etc. can also be added. Methods for forming metal on the surface of polymer core materials include physicochemical methods such as vapor deposition, sputtering, ion plating, plating, and thermal spraying, as well as methods for forming metal on the surface of polymer core materials. Chemical methods include dispersing metals in monomers and adsorbing metal powder onto the surface of polymer particles after polymerization, chemically bonding metals with core materials that have functional groups, and adsorbing them with surface activators, coupling agents, etc. Methods such as manual methods can be adopted. As a method for plating the polymer core material, general methods for forming metals by electroless plating can be applied. Add a catalyst such as palladium. Thereafter, the core material may be treated in an electroless plating solution at a predetermined temperature and time for a certain amount of time to prevent agglomeration of the core material by stirring or the like if necessary. The plating thickness can be controlled by controlling the plating liquid amount, time, temperature, etc. For example, in the case of nickel, the plating liquid may be nickel-phosphorus, nickel-boron, etc., and the reducing agent may be sodium hypophosphite,
Sodium borohydride is typical, and in the case of copper plating, Rothsiel's salt bath and EDTA bath are typical, and formaldehyde or the like is used as the reducing agent. Furthermore, a case where a metal composite layer is formed by the plating method will be explained. For example, regarding the case where metal is provided on the nickel layer mentioned above, the metal plating solution is generally gold cyanide, and both reduction and substitution types can be applied, but the substitution type gold plating method is easier to handle. It is preferable for the present invention in view of the desired thickness. By treating a nickel-plated product in a gold plating solution at a predetermined temperature for a predetermined period of time, conductive particles having a composite layer of polymer core material/Ni/Au can be obtained. The thickness of the metal coating layer is preferably about 0.01 to 5 μm.
A thickness of 0.05 to 1 μm is more preferable, but it is desirable that the thickness falls within 1/5 to 1/1000 of the particle size of the conductive particles before circuit connection. This is because if the metal thin layer is thin, the conductivity will be reduced, and if the metal thin layer is thick, it will lose its ability to follow the softening and deformation of the polymer core material during circuit connection. Further, since the metal is a thin layer, it has sufficient deformation followability, but it is preferable to use a malleable material with good extensibility, for example. Conventionally, such conductive particles were made into glass spheres (beads) or glass hollow spheres (balloons).
Although there are products in which a thin layer of Ag or the like is formed, these are not suitable for carrying out the present invention because they cannot be softened and deformed when heated and pressed. The conductive particles obtained above have an average particle size of
Preferably, the particle size is 0.5 to 300 μm, and the ratio of the maximum particle size to the minimum particle size is 0.05 to 1.0. The particle size is
If the diameter is 0.5 μm or less, a large amount of conductive particles is required, and as a result, the number of filled particles increases, resulting in poor adhesion to the circuit. If the diameter is 300 μm or more, the particles are large, making it difficult to conduct between adjacent circuits on the same board. (leak), which is not desirable. In order to prevent the occurrence of leaks, it is necessary to select conductive particles whose particle size is smaller than the gap between the circuits to be connected. It is preferable to use 2 to 1/4 of conductive particles. The shape of the conductive particles preferably has a ratio of the maximum diameter to the minimum diameter (hereinafter referred to as particle size ratio) of 0.05 to 1.0. Outside this range, the particles will be too flat, making them unsuitable for achieving the electrical conductivity between circuits and the insulation between adjacent circuits, which are the objectives of the present invention, and there is also a strong tendency for adhesiveness with circuits to deteriorate. . A typical example that satisfies this range is one that is approximately spherical, but is not particularly limited as long as it satisfies the above conditions. Further, the particle surface may have some protrusions or irregularities, and the particle may not be limited to a single particle but may be an aggregate of fine particles. The particle size is the overall average particle size, and it is convenient to measure the particle shape and particle size using, for example, a scanning electron microscope. Average particle size D
is calculated using the following formula. P=Σnd/Σn where n indicates the number of particles with a particle size of d. When the conductive particles are spherical, it is easy to obtain contact between the particles or between the particles and the circuit surface by applying heat and pressure during connection, and it is easy to obtain high conductivity. The conductive particles may exist in a single layer in the thickness direction of the connection member, or may have a structure in which they are arranged in multiple rows or aggregated. Conductive particles account for 0.1-15% by volume in the adhesive
is appropriate. If it is less than 0.1 volume %, satisfactory conductivity cannot be obtained, and if it is more than 15 volume %, the chances of particles connecting in the lateral (width) direction increase, the insulation with adjacent circuits decreases, and transparency deteriorates. For the above reasons, a more preferable addition amount is 0.5 to 10% by volume. As the adhesive used in the present invention, basically any formulation used in conventional adhesive sheets exhibiting insulation properties can be used. The composition used for ordinary adhesive sheets includes polymers such as synthetic resins and rubbers to impart cohesive force, and tackifiers, tackiness modifiers, crosslinking agents, anti-aging agents, etc. used as necessary. It consists of dispersants, etc. As a method for manufacturing a connecting member according to the present invention,
An adhesive composition consisting of a polymer and other additives used as necessary is dispersed in a medium in a solvent or in a suspension state, or heated and melted to a liquid state, and then the conductive particles are processed using a conventional method such as a ball mill or stirring device. A conductive particle mixed adhesive composition is obtained. When using a solvent, it is possible to use a solvent because conductive particles with a metal layer formed on the polymer core material have almost no solubility in solvents, but it is possible to use a solvent to dissolve the adhesive and remove the polymer core material. It is further preferable to select a solvent that does not dissolve. A good method for this purpose is, for example, to emulse the adhesive and disperse the conductive particles in an aqueous medium. The above-mentioned conductive particle mixed adhesive composition may be used to form an adhesive layer directly on one or both of the circuits to be connected using means such as screen printing or a roll coater, or to form a continuous adhesive layer in the form of a film. It may be a long body. To obtain an adhesive film as a continuous length, a connecting member layer may be formed by the above method on a separator made of paper or plastic film, which has been subjected to peeling treatment as necessary, and then continuously rolled up. If the adhesive layer has no tackiness, it is possible to roll the adhesive layer without using a separator, and it is also possible to use a core material such as a non-woven fabric to reinforce the adhesive. A method for connecting a circuit using the obtained connecting member includes, for example, temporarily attaching a film-like connecting member to the circuit and peeling off the separator if there is a separator, or applying an adhesive composition to the circuit. If necessary, after the solvent has been removed, other circuits to be connected may be attached to that surface using a hot press or a heated roll. During heating and pressurization during connection, the coating metal is a thin layer, so it can fully follow the deformation of the polymer core material, and even if it cannot follow the deformation and defects such as cracks occur in the metal layer, The conductive path can be maintained by contact with circuits or other particles. In order to obtain an optimal connection state, it is preferable that the ratio of the thickness (T) of the connection member before connection to the circuit interval (t) after connection is within the range of t/T=0.02 to 0.95. At this time, if the conductive particles with a particle size D before connection exist in the form of a single particle in the thickness direction, the particle size after connection is d, and the ratio of d/D is t/
It can be used in the same way as T. If t/T is less than 0.02, the conductive particles will break and the metal flakes will easily fall off, and if this ratio is more than 0.95, sufficient surface contact with the circuit or conductive particles cannot be obtained, so it should be satisfied. Since it cannot be used as a connected structure, it is not preferable for implementing the present invention. For the above reasons, the more preferable range of t/T is
It is between 0.10 and 0.90. An easy way to obtain this optimal connection state is to insert a spacer with a desired thickness and rigidity between the circuits during the connection operation, or to mix spacer particles into the connection member. Since it can be deformed into a shape, it is possible to easily obtain a connection structure having a polymer core material spacing of a desired thickness. The spacer particles need to have higher rigidity than the conductive particles. In other words, it is necessary that the spacer particles show almost no change in particle shape due to pressurization or heating and pressurization during production of the circuit connection structure. Further, the spacer particles may be either conductive or insulating, and a combination of both may be used. There are no particular restrictions on the particle size, particle shape, and amount added of the spacer particles, but preferably the average particle size is 0.5 to 0.5, as in the case of conductive particles.
300 μm, the ratio of the maximum diameter to the minimum diameter as a particle shape is 0.05 to 1.0, and the amount added is 0.1 to 15% by volume. The ratio of the amount of conductive particles to spacer particles added is not particularly limited, and may be determined taking into consideration the characteristics of the connected structure. (Function) In the circuit connection structure according to the present invention,
The conductive particles come into contact with each other or with the conductive circuit section by applying pressure or heating and pressurizing during connection, thereby forming a conductive path. At this time, since the polymer core material can be softened or deformed during connection operations by pressurization or heating and pressurization, it can be appropriately deformed to press against the circuit surface or between the conductive particle phases and maintain a large contact area. , good conductivity and reliability can be obtained. On the other hand, particles in non-circuit areas are not subjected to as much pressure as particles between circuits, so they do not deform.Therefore, in addition to selecting the particle size and addition amount of conductive particles, insulation from adjacent circuits is Sufficiently maintained. Furthermore, since the softening deformation range of the polymer core material can be set arbitrarily by selecting or combining the thermal properties of the material, it becomes possible to obtain a connected structure under a wide range of work conditions. For example, when an amorphous polymer that does not exhibit a constant melting point or a broadly crosslinked rubber-like region is used as a core material, the softening flow range is particularly wide, and the conditions (temperature, pressure, time) during circuit connection It is also possible to have a wider width, which significantly improves reliability during connection, and also provides good connection workability. Furthermore, the degree of softening and deformation of the polymer core material can be arbitrarily set depending on the connection conditions, making it possible to control the connection state. For example, even if the particle sizes of the conductive particles at the connection part do not match, by controlling the connection conditions, it is possible to connect the large conductive particles by crimping them until they are the same size as the small conductive particles or even smaller. is possible, and many conductive particles can effectively contribute to conduction. On the other hand, in the case of conventional metal particles, large metal particles act as spacers, and other small particles do not contribute to conduction, resulting in a decrease in the number of conduction points and low connection reliability. In order to effectively manage the connection state, it is preferable to add spacer particles, which are more rigid than conductive particles, to the connection member.In this case, since the conductive particles can be deformed arbitrarily, It becomes possible to obtain a connected structure with a desired thickness. As mentioned above, the circuit connection structure according to the present invention deforms appropriately so that the conductive particles are pressed along the circuit surface, and can maintain a large contact area, which is different from the conventional soldered structure. For example, it is possible to maintain an effective contact area even with a transparent conductive film, which was previously impossible. In addition, Au
No special surface treatment such as or Ni plating is required.
Connection structures can also be obtained for various other circuit surfaces. The contact area with the circuit can now be increased, and the expansion coefficient of the polymer core material is similar to that of the adhesive component, so even if the distance between connected circuits increases due to the thermal expansion of the adhesive, conductivity is maintained. Thermal expansion of the particles allows it to follow the expansion of the distance between the connected circuits, maintaining good contact between the particles and the circuits.
The resistance change with respect to temperature of the connection part is extremely small. Examples 1 to 3 (1) Preparation of connecting member In an adhesive solution consisting of 100 parts by weight of styrene-butadiene block copolymer (M12.6), 40 parts by weight of rosin-modified phenolic resin with a softening point of 130°C, and 200 parts by weight of toluene. A solution obtained by dispersing Ni-coated polystyrene particles and atomized i (average particle size 10 μm, almost spherical) was applied onto spacer particles (silicon-treated polyester film) using a bar coater, and heated at 110°C.
- Dry for 5 minutes and add 2% by volume of conductive particles.
A connecting member having a thickness of 35 μm was obtained. Here, the average particle size of the conductive particles was 30 μm, and the thickness of the Ni coating layer was about 0.5 μm. (2) Connecting the circuit Place the connection part cut to a length of 100 mm with an adhesive width of 3 mm on a flexible circuit board (FPC) with a total circuit width of 100 mm, which has a circuit with a line width of 0.1 mm, a pitch of 0.2 mm, and a thickness of 35 μm. At 150℃ - 10Kg/cm ² Temporarily pasted by heating and pressurizing for -5 seconds and attaching the connecting member.
Got FPC. Then peel off the separator and
Align the circuit with another transparent conductive glass (indium oxide circuit, glass thickness 1 mm) with the same pitch under a microscope, and conduct the test at 170℃ - 20Kg/cm ²
The circuit was connected by applying heat and pressure for −10 seconds. (3) Evaluation The circuit connection part was kept in a thermostatic chamber, and the connection resistance of the circuit at -20°C and 80°C was measured with a multimeter using a lead wire, and the insulation between adjacent circuits was also checked. Insulation was considered good if it was 10 ⁷ Ω or more. Resistance measurement result is -20℃
It is expressed as the rate of change in resistance at 80°C, with the value at 1.0 being the standard. The results are shown in Table 1, and the rate of change in resistance was good, and in Examples 1-2 and 1-3, the thickness after circuit connection was determined by the particle diameter of the conductive Ni particles used as spacer particles. The thickness was controlled to 10 μm. By using a conductive spacer with a particle size smaller than the conductive particles made of polymer core material, the conductive particles made of polymer core material are mixed with Ni between the connected circuits, and the conductive particles made of polymer core material are slightly crushed between the circuits. I was able to get a good connection. In the case of connection at 130°C in Example 1-1, the thickness between the circuits was 18 μm, which did not reach the spacer particle diameter of 10 μm, because the fluidity of the polymer core material and adhesive component was insufficient. Furthermore, the spacer thickness can be controlled by means such as increasing the temperature. The change in thickness in Table 1 is the ratio of the change in the thickness (T) of the connecting member before connection to the circuit interval (t) after connection (t/
T). Example 2 The same as Example 1, except that insulating silica powder (spherical with a particle size of 10 μm) was added instead of atomized Ni as spacer particles. As shown in Table 1, in this case as well, it was possible to control the rate of change in resistance and the thickness between the connecting circuits. The addition of insulating spacer particles seems to have the effect of preventing leakage between circuits, and the addition of so-called thermally resistant expansion materials such as silica reduces the coefficient of thermal expansion of the entire matrix (in this example, the adhesive). This is a known fact, and it seems that such an effect also occurs in this example. Example 3 The same as Example 2, except that the conductive particles contained 2% by volume of particles with an average particle diameter of 3 μm (the coating layer was made of Ni and had a thickness of 0.1 μm), and a film-like connecting member with a thickness of 15 μm was prepared. I got it. This case corresponds to using spacer particles larger than the conductive particles. The results showed a good rate of change in resistance as shown in Table 1, and the thickness between the circuits after connection could be obtained to match the particle diameter of the spacer particles. Furthermore, between the circuits, it was possible to observe with an electron microscope a cross section of the connection part that several conductive particles were aggregated and connected. Comparative example Solder particles with a particle size of 20 μm and a melting point of 170°C are mixed in a solution consisting of 100 parts by weight of thermoplastic polyester (molecular weight 20000, Tg 7°C), 20 parts by weight of alkylphenol resin (softening point 100°C), and 280 parts by weight of methyl ethyl ketone. A film-like adhesive member was used in the same manner as in the above embodiment. The results are shown in Table 1, and the rate of change was approximately twice that of Examples 1 to 3. Also, when I observed the circuit connection part, I found that the FPC side
The solder was wet on the Cu circuit surface and a good connection was made, but there was no solder wetting on the transparent conductive film surface and there was only point contact. Therefore, while the adhesive layer, which has large thermal expansion and contraction, fluctuates, the metal solder particles only slightly fluctuate, resulting in unstable contact between the solder particles and the glass circuit surface, resulting in a large rate of change in resistance. It is estimated that the [Effects of the Invention] As described in detail above, the circuit connection structure of the present invention uses conductive particles on the surface of a polymer core material that can be softened or deformed by applying pressure or heating and pressure during circuit connection. conductive material with a thin conductive metal layer

[Table] Due to the action of the electrically conductive particles, the circuit surface or spacer particles are appropriately deformed so as to press against each other, so it is possible to have a large contact area. In addition, the rigidity and thermal expansion/contraction properties of the polymer core material are extremely similar to those of adhesives, and even when the adhesive undergoes thermal expansion/contraction deformation due to temperature changes, the polymer core material follows the thermal expansion/contraction deformation, resulting in a change in resistance. It is possible to create a connected structure with fewer connections. Furthermore, because the thin layer of conductive metal is pressed against the circuit surface due to the elasticity of the polymer core material, it has the feature that there is no selectivity to the circuit material. It has become possible to obtain an effective structure with excellent reliability without any special surface treatment of the membrane. In addition, in the connected structure of the present invention, since the core of the conductive particles is a polymer, its softening or deformation range is wide, so it has a wide range of connection conditions, so stable connection with less variation can be achieved. It is possible to obtain a structure.

Claims (1)

[Scope of Claims] 1. In a circuit connection structure in which connection circuits formed facing each other are connected to each other by an electrical connection member, the connection member covers substantially the entire surface of a core material made of a high molecular weight polymer. consisting of conductive particles substantially covered with a thin layer of conductive metal, highly rigid spacer particles, and an insulating adhesive, said conductive particles being pressed by opposing circuits separated by said spacer particles. A circuit connection structure characterized by being fixed in a deformed state. 2. The circuit connection structure according to claim 1, wherein at least one of the opposing circuits is a transparent conductive film.