JP2007035743A - Circuit connection method and connection structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a circuit connection method that has excellent conductivity between connection electrodes having a minute area and prevents insulation failure, such as short-circuit at the space section between fine adjacent electrodes and ion migration from occurring easily in the electrical connection of a fine circuit using an anisotropic conductive adhesive, and to provide a connection structure obtained by the circuit connection method. <P>SOLUTION: In the circuit connection method for connecting circuit electrodes that oppose each other by the anisotropic conductive adhesive with conductive particles and an insulating adhesive as main constituents, the circuit electrodes are connected so that the conductive particle capture rate between the connection electrodes becomes three times larger than the conductive particle retention rate of the space section between adjacent electrodes. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a connection method and a connection structure for electrically connecting fine pattern circuit electrodes to each other using an anisotropic conductive adhesive.

  Insulating as a connection material for easy connection between liquid crystal display and IC chip or TCP (Tape Carrier Package), FPC (Flexible Printed Circuit) and TCP, or TCP and printed wiring board An anisotropic conductive adhesive in which conductive particles are dispersed in an adhesive is used. For example, anisotropic conductive adhesives are widely used to connect liquid crystal displays of notebook computers and mobile phones to control ICs. Recently, flip chips that mount IC chips directly on printed circuit boards or flexible wiring boards. It is also used for mounting (Patent Documents 1, 2, and 3).

  In recent years, in this field, the size of wiring patterns and bump patterns to be connected has been increasingly miniaturized, and connection with high connection reliability has become difficult with the conventional anisotropic conductive adhesive in which conductive particles are randomly dispersed. . That is, when the density of the conductive particles is increased to connect electrodes having a small area, the conductive particles are aggregated and the insulation between adjacent electrodes cannot be maintained. On the contrary, if the density of the conductive particles is lowered in order to maintain insulation, an electrode that is not connected is generated this time, and it has been difficult to cope with miniaturization while maintaining connection reliability (Patent Document 4). .

On the other hand, attempts have been made to deal with the connection of fine patterns by arranging conductive particles in an insulating adhesive (Patent Document 5). However, in order to ensure adhesion and sealing against oxygen and moisture in the connection of fine patterns, it is necessary to flow the insulating adhesive during connection to fill the space between adjacent electrodes with the insulating adhesive. In this case, there is a problem that the conductive particles arranged at an angle flow together with the insulating adhesive.
On the other hand, in order to suppress the flow of particles at the time of connection and connect a fine pattern, a method of arranging conductive particles in a film that does not substantially flow (Patent Documents 6 and 7) has been studied.

Japanese Patent Laid-Open No. 03-107888 Japanese Patent Laid-Open No. 04-366630 JP-A-61-195179 JP 09-31176 A JP 2000-151084 A JP 2001-52778 A JP 2003-64324 A

  The present invention has excellent electrical conductivity between connection electrodes in a small area in electrical connection of a microcircuit using an anisotropic conductive adhesive, and also has poor insulation such as a short in a space between adjacent electrodes and ion migration. An object of the present invention is to provide a circuit connection method in which the occurrence of the problem is difficult to occur and a connection structure obtained thereby.

As a result of intensive studies to solve the above-mentioned problems, the present inventors have made a circuit connection for connecting the conductive particles so that the conductive particle trapping rate between the connecting electrodes is at least three times the conductive particle retention rate of the space between adjacent electrodes. It has been found that the method can meet the above objectives, and has led to the present invention.
In the technique of the above disclosure performed before the filing of the present application in order to solve the above problem, for example, in Patent Document 5, the conductive particles arranged at the corner flow at the time of connection, and the effect of the arrangement is limited. It was. On the other hand, in the case of Reference 6 and Reference 7, particles between connection electrodes do not flow at the time of connection, and a high capture rate is obtained and good conductivity is obtained, but the conductive particles in the space between adjacent electrodes do not flow in the same manner. For this reason, since the connection is made in a state where a large number of conductive particles stay in the space portion, it is a cause of insulation failure such as ion migration, and a satisfactory one has not been obtained.

  As in the present application, the conductive particle capture rate between the connection electrodes and the conductive particle retention rate in the space between adjacent electrodes are controlled separately to make the conductive particle capture rate a specific multiple or more of the conductive particle retention rate. In view of the above technical disclosure, it was a surprising discovery that could not be anticipated by those skilled in the art that the method could be used to solve the above problems.

That is, the present invention is as follows.
1) In a circuit connection method in which circuit electrodes facing each other are connected using an anisotropic conductive adhesive mainly composed of conductive particles and an insulating adhesive, the conductive particle capture rate between the connection electrodes is between adjacent electrodes. A circuit connection method in which connection is performed so that the conductive particle retention rate of the space portion is three times or more.
2) One of the circuits is an IC chip, and the anisotropic conductive adhesive is an anisotropic conductive adhesive film in which conductive particles are dispersed substantially evenly in the plane direction and arranged in a single layer in the thickness direction. The circuit connection method according to 1), wherein the connection is made so that the fluidity of the conductive particles existing in the space between adjacent electrodes at the time of connection is higher than the fluidity of the conductive particles existing between the connection electrodes.
3) A connection structure in which a circuit board and an IC chip are connected with an anisotropic conductive adhesive, and the conductive particle density between connection electrodes is q / mm ² and the conductive particle density is r in the space between adjacent electrodes. / Mm ² has a relationship of q> r × 3.
4) A connection structure in which a circuit board and an IC chip are connected with an anisotropic conductive adhesive, and the conductive particle density p / mm ^{2 in the} center portion having no IC chip electrode and the space portion between adjacent electrodes A connection structure characterized by having a relationship of p> r × 3 between the conductive particle density of r particles / mm ² .

  The circuit connection method and the connection structure of the present invention are capable of electrical connection of a fine circuit using an anisotropic conductive adhesive, have excellent electrical conductivity between connection electrodes having a small area, and have a fine inter-electrode space portion. This provides a connection structure that is less prone to insulation defects such as short circuiting and ion migration, and is usefully used as a component of electronic equipment.

The present invention will be specifically described below.
In the circuit connection method of the present invention, the circuit electrodes facing each other are connected with an anisotropic conductive adhesive.
As a combination of circuits to be connected, a combination of an IC chip and a circuit board is preferable. As the circuit substrate, a glass substrate used in a liquid crystal panel or the like, an inorganic substrate such as ceramics, or a circuit substrate such as a polyimide, polyester, polyethersulfone, or polyethylene naphthalate film substrate is preferable. These circuit board circuits are made by vacuuming metal materials such as aluminum, copper, silver, tin, lead, indium, chromium, nickel, silicon, and thin films such as ITO (Indium Tin Oxide) and IZO (Indium Zinc Oxide) on the substrate. After forming by vapor deposition, sputtering, ion plating, or the like, the thin film can be formed by performing precision etching, laser beam cutting, or the like. Alternatively, it is called a method of forming a circuit using a conductive paste by screen printing or an inkjet method, a method of forming a circuit by etching a conductive foil such as a copper foil on a substrate, and an additive method of forming a circuit by plating on a substrate. It can be formed by a method or the like. Part of the circuit is an electrode for connection.

The IC chip may have a large aspect ratio, or may be a square or a similar one. When used for a liquid crystal panel, one having a large aspect ratio is preferable because the frame can be narrowed.
The electrodes of the IC chip may be only a base electrode called an under bump metal made of titanium, copper, gold, nickel or the like, and may have a protruding electrode made of a metal such as gold or nickel called a bump thereon. is there. It is preferable to have a protruding electrode because of high connection reliability. The IC chip has an electrode arrangement on the entire front surface of the lower surface of the chip with an electrode on the entire surface, a peripheral surface with an electrode on the portion other than the center of the lower surface of the chip, and a row of electrodes on two or four sides of the lower surface edge. Two-sided arrangement or four-sided arrangement may be used. Further, in the two-sided arrangement or the four-sided arrangement, a zigzag arrangement in which a part or all of the electrodes are arranged in two rows can be used.

The electrode size of the IC chip is preferably 500 μm ² or more and 10,000 μm ² or less from the viewpoint of connection stability and a reduction in the area of the IC chip. More preferably 550 .mu.m ² or more 5000 .mu.m ² or less, more preferably 600 .mu.m ² or more 2000 .mu.m ² or less, even more preferably, at 650 .mu.m ² or more 1500 .mu.m ² or less. The electrode pitch of the IC chip is preferably 15 μm or more and 100 μm or less from the viewpoint of ensuring insulation between adjacent electrodes and reducing the area of the IC chip. More preferably, they are 16 micrometers or more and 50 micrometers or less, More preferably, they are 17 micrometers or more and 30 micrometers or less, More preferably, they are 18 micrometers or more and 25 micrometers or less.
A combination of the circuit board, TCP, COF (Chip on Flex), and FPC can be used as a combination of circuits to be connected.

The anisotropic conductive adhesive used in the present invention is mainly composed of conductive particles and an insulating adhesive.
As the conductive particles used in the present invention, metal particles, particles made of carbon, particles obtained by coating a polymer thin film with a metal thin film, and the like can be used.
As the metal particles, for example, a simple substance such as gold, silver, copper, nickel, aluminum, zinc, tin, lead, solder, indium, palladium, etc., or two or more of these metals are combined in a layered or inclined manner. Particles are exemplified.

  Particles in which a polymer thin film is coated on a polymer core material include epoxy resin, styrene resin, silicone resin, acrylic resin, polyolefin resin, melamine resin, benzoguanamine resin, urethane resin, phenol resin, polyester resin, divinylbenzene crosslinked product, NBR , SBR and other polymer core materials combined with one or more polymers, gold, silver, copper, nickel, aluminum, zinc, tin, lead, solder, indium, palladium, etc. The particle | grains which metal-coated by plating etc. in combination of 2 or more types are illustrated. The thickness of the metal thin film is preferably in the range of 0.005 μm to 1 μm from the viewpoint of connection stability and particle cohesion. It is preferable in terms of connection stability that the metal thin film is uniformly coated. Particles obtained by further insulatingly coating the surface of these conductive particles and complex sugar type particles having fine particles attached to the surface can also be used.

It is preferable to use spherical particles as the conductive particles, in which case the closer to a true sphere is preferable, and the ratio of the short axis to the long axis is preferably 0.5 or more, more preferably 0.7, and 0.9 or more. Even more preferred. The maximum value of the ratio of the short axis to the long axis is 1.
The average diameter of the conductive particles needs to be smaller than the distance between adjacent electrodes to be connected, and is preferably larger than the variation in the electrode height of the electronic component to be connected. Therefore, the average diameter of the conductive particles is preferably in the range of 0.3 μm or more and less than 30 μm, more preferably 0.5 μm or more and less than 20 μm, further preferably 0.7 μm or more and less than 15 μm, more preferably 1 μm or more and less than 10 μm, and still more preferably. Is 2 μm or more and less than 7 μm. The standard deviation of the particle size distribution of the conductive particles is preferably 50% or less of the average particle size.

  The insulating adhesive used in the present invention contains one or more resins selected from thermosetting resins, thermoplastic resins, photocurable resins, and electron beam curable resins. Examples of these resins include epoxy resins, phenol resins, silicone resins, urethane resins, acrylic resins, polyimide resins, phenoxy resins, polyvinyl butyral resins, SBR, SBS, NBR, polyether sulfone resins, polyether terephthalate resins, polyphenylenes. Sulfide resin, polyamide resin, polyether oxide resin, polyacetal resin, polystyrene resin, polyethylene resin, polyisobutylene resin, alkylphenol resin, styrene butadiene resin, carboxyl-modified nitrile resin, polyphenylene ether resin, polycarbonate resin, polyether ketone resin, etc. Of the modified resin. In particular, when adhesiveness with a substrate is required, an epoxy resin is preferably contained.

  Examples of the epoxy resin used here include bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin, tetramethylbisphenol A type epoxy resin, biphenol type epoxy resin, naphthalene type epoxy resin, and fluorene type epoxy. Resin, phenol novolac epoxy resin, cresol novolac epoxy resin, bisphenol A novolac epoxy resin, glycidyl ether epoxy resin such as aliphatic ether epoxy resin, glycidyl ether ester epoxy resin, glycidyl ester epoxy resin, glycidyl amine Type epoxy resin, hydantoin type epoxy resin, alicyclic epoxide, etc., these epoxy resins may be halogenated or hydrogenated Further, it may urethane-modified, rubber-modified, even modified epoxy resins such as silicone-modified.

  As the curing agent for the epoxy resin, a latent curing agent is preferable. As the latent curing agent, curing agents such as boron compounds, hydrazides, tertiary amines, imidazoles, dicyandiamides, inorganic acids, carboxylic acid anhydrides, thiols, isocyanates, boron complex salts and derivatives thereof are preferable. Among latent curing agents, microcapsule type curing agents are preferred. The microcapsule-type curing agent is a material in which the surface of the curing agent is stabilized with a resin film, etc., and the resin film is destroyed by the temperature and pressure during connection work, the curing agent diffuses outside the microcapsule, and the epoxy resin react. Among the microcapsule type latent curing agents, a latent curing agent obtained by microencapsulating an adduct type curing agent such as an amine adduct or an imidazole adduct is preferable because of excellent balance between stability and curability. Generally these epoxy resin hardening | curing agents are used in the quantity of 2-100 mass parts with respect to 100 mass parts of epoxy resins.

  The insulating adhesive used in the present invention is a phenoxy resin, a polyester resin, an acrylic rubber, SBR, NBR, a silicone resin, a polyvinyl butyral resin for the purpose of imparting film formability, adhesiveness, stress relaxation during curing, etc. Polyurethane resin, polyacetal resin, urea resin, xylene resin, polyamide resin, polyimide resin, rubber containing functional groups such as carboxyl group, hydroxyl group, vinyl group, amino group, and polymer components such as elastomers Is preferred. These polymer components preferably have a molecular weight of 10,000 to 10,000,000. The content of the polymer component is preferably 2 to 80% by mass with respect to the insulating adhesive.

The insulating adhesive may further contain insulating particles, fillers, softeners, accelerators, anti-aging agents, colorants, flame retardants, thixotropic agents, coupling agents and the like. When the insulating particles and the filler are contained, the maximum diameter is preferably less than the average particle diameter of the conductive particles. As the coupling agent, ketimine group, vinyl group, acrylic group, amino group, epoxy group and / or isocyanate group-containing silane coupling agent is preferable from the viewpoint of improvement in adhesiveness.
When mixing each component of an insulating adhesive, a solvent can be used as needed. Examples of the solvent include methyl ethyl ketone, methyl isobutyl ketone, toluene, xylene, ethyl acetate, butyl acetate, ethylene glycol monoalkyl ether acetate, propylene glycol monoalkyl ether acetate, and the like.

Examples of the anisotropic conductive adhesive used in the present invention include a paste-like anisotropic conductive paste and a film-like anisotropic conductive adhesive film. An anisotropic conductive adhesive film is preferable because the fluidity of the conductive particles can be easily controlled.
In the anisotropic conductive adhesive used in the present invention, the conductive particles may be randomly dispersed in the insulating adhesive, but the anisotropic conductive particles are arranged as a single layer in the insulating adhesive. A conductive adhesive film is preferred. The conductive particles arranged in a single layer are more preferably in the surface layer of the insulating adhesive. Here, the conductive particles in the surface layer means that the center of the conductive particles is located in a thickness region 1.5 times as large as the average particle diameter of the conductive particles from the surface of the insulating adhesive.

  Preferably, the conductive particles are arranged at a specific center distance, and the center distance is arranged with a specific coefficient of variation, so that both the conductivity of the connection electrode and the insulation between the adjacent electrodes can be achieved. preferable. The average distance between the centers of the conductive particles is preferably 2 μm or more and 20 μm or less, preferably 2.5 μm or more and 18 μm or less, more preferably 3 μm or more and 16 μm or less, further preferably 3.5 μm or more and 15 μm or less, and further preferably 4 μm. It is 13 μm or less. By setting it to 2 μm or more, the insulation in the plane direction, that is, the insulation between adjacent electrodes can be maintained at a high level. On the other hand, by setting the center-to-center distance to 20 μm or less, the conductivity in the thickness direction, that is, the conductivity between the connection electrodes can be maintained at a high level, and high performance is exhibited.

  It is preferable that the conductive particles are distributed substantially evenly in the plane direction, and the coefficient of variation of the distance between the centers of the conductive particles, which is an index thereof (value obtained by dividing the standard deviation of the distance between the centers of the conductive particles by the average value) Is preferably 0.5 or less. Preferably they are 0.03 or more and 0.45 or less, More preferably, they are 0.05 or more and 0.4 or less, More preferably, they are 0.07 or more and 0.35 or less, More preferably, they are 0.08 or more and 0.3 or less. By setting it to 0.5 or less, the number of conductive particles trapped between the connection electrodes is stabilized, variation in connection resistance between the electrodes is small, and stable connection is obtained.

  The circuit connection method of the present invention is a connection method in which the conductive particle capture rate between connection electrodes is three times or more the conductive particle retention rate in the space between adjacent electrodes. Here, the conductive particle capture rate between the connection electrodes is the ratio of the number of conductive particles captured between the connection electrodes after connection to the number of conductive particles included in the connection electrode equivalent area of the anisotropic conductive adhesive film before connection. It is preferable to use the average value of the capture rate of all connected electrodes. However, when the number of connected electrodes is large, the average value of the conductive particle capture rate of the electrode sampled arbitrarily can be substituted. When sampling, it is necessary to select a sampling location and number so as to suppress errors due to sampling as much as possible.

  On the other hand, the conductive particle retention rate is the ratio of the number of conductive particles staying in the space between adjacent electrodes after connection to the number of conductive particles included in the area corresponding to the space between adjacent electrodes of the anisotropic conductive adhesive film before connection. Yes, it is preferable to use the average value of the retention rate of the space portion between all adjacent electrodes, but when the number of connection electrodes is large, the average value of the conductive particle retention rate of the space portion between adjacent electrodes sampled arbitrarily is substituted. I can do things. When sampling, it is necessary to select a sampling location and number so as to suppress errors due to sampling as much as possible. The conductive particle capturing rate between the connection electrodes is preferably 25% or more in order to conduct all the connection electrodes with low resistance. More preferably, they are 30% or more and 85% or less, More preferably, they are 35% or more and 70% or less, More preferably, they are 40% or more and 65% or less. The conductive particle retention rate is preferably 30% or less in order to ensure insulation between all adjacent electrodes. More preferably, it is 20% or less, more preferably 10% or less, and still more preferably 7% or less. Most preferably, the conductive particles do not stay in the space portion between adjacent electrodes. It is preferable that two or more staying conductive particles are not aggregated.

  In the present invention, in order to achieve both the conductivity of the connection electrode and the insulation between the adjacent electrodes, the conductive particle capture rate is three times or more the conductive particle retention rate. Preferably it is 4 times or more, More preferably, it is 5 times or more, More preferably, it is 10 times or more.

  As a circuit connection method in which the capture rate of the conductive particles is 3 times or more of the retention rate of the conductive particles, the fluidity of the conductive particles existing in the space between adjacent electrodes at the time of connection is determined by the flow of the conductive particles existing between the connection electrodes. There is a method of connecting so as to be higher than the fluidity. In the circuit connection method using anisotropic conductive adhesive, in order to ensure adhesion and sealability of the electrode part, the insulating adhesive flows so as to fill the gap during connection. Conductive adhesives are designed. The fluidity of the conductive particles refers to the ease of flow of the conductive particles following the flow of the insulating adhesive. As a method for making the fluidity of the conductive particles existing in the space between adjacent electrodes at the time of connection higher than the fluidity of the conductive particles existing between the connection electrodes, for example, a portion corresponding to the space between the adjacent electrodes after connection There is a method in which the conductive particles of the anisotropic conductive adhesive other than the above are fixed with a fixing resin and do not substantially flow or are connected after the fluidity is lowered.

  As another method, for example, the flow rate of the insulating adhesive in the space between adjacent electrodes at the time of connection is faster than the flow rate between the connection electrodes or the flow rate of the IC chip center without the electrodes. In this way, the electrode arrangement of the IC chip is designed, or the connection conditions are selected, and the conductive particles flow following the flow rate of the insulating adhesive in the space between adjacent electrodes, but between the connection electrodes In contrast to the flow rate of the insulating adhesive in the center of the IC chip that does not have an electrode, the conductive particles are substantially non-flowing or have a fixing strength that suppresses the flowability. And a method of connecting using an anisotropic conductive adhesive in which conductive particles are fixed with a fixing resin. As such an electrode arrangement of the IC chip, for example, an arrangement in which rectangular electrodes having long sides in a direction perpendicular to the chip end surface are arranged in a single row or a staggered pattern at the end of the IC chip is preferable.

  Examples of a method for producing an anisotropic conductive adhesive in which conductive particles are fixed with a fixing resin include the following methods. That is, a plurality of conductive particles arranged separately are connected to each other with a fixing resin, and a method of embedding the connected conductive particles in an insulating adhesive or a film-like fixing resin thinner than the diameter of the conductive particles Examples thereof include a method in which conductive particles are dispersed in a single layer and an insulating adhesive is laminated on at least one surface thereof by lamination or the like. The former is preferable because the conductive particle fixing force of the fixing resin can be easily controlled.

  The fixing resin used here is preferably a resin that can fix the conductive particles in the IC chip center portion between the connection electrodes and in the center of the IC chip that does not have the electrodes, although the space between adjacent electrodes cannot fix the conductive particles under the connection conditions. A crosslinked polymer or thermoplastic polymer cured by heat or light is preferred. Examples of the crosslinked polymer include a crosslinked acrylate resin, a crosslinked vinyl resin, a crosslinked polyester resin, a crosslinked polyurethane resin, a crosslinked melamine resin, a crosslinked siloxane resin, a crosslinked epoxy resin, and a crosslinked phenol resin. Examples of the heat-resistant thermoplastic polymer include polyimide resin, polyamide resin, polyester resin, polysulfone resin, phenoxy resin, and acrylic resin. These fixing resins can be used in combination of two or more.

  As a method of interconnecting the conductive particles with a fixing resin and embedding the connected conductive particles in an insulating adhesive, for example, the conductive particles are filled into a single layer in a fixing resin, and the fixing resin is agglomerated. The conductive particles can be connected with a fixing resin by stretching while causing the occurrence of the problem and balancing the cohesive force and the stretching force. When a crosslinked polymer is used as the fixing resin, it is preferable to stretch in an uncrosslinked state and then crosslink using heat or light. As a method of embedding the conductive particles connected with the fixing resin in the insulating adhesive, the conductive particles connected with the fixing resin are stacked on the insulating adhesive formed on the peelable base material, Examples of the method include embedding in an insulating adhesive using a roll or a laminator. Here, the fixing resin used for the connection is preferably a linear resin having a diameter less than that of the conductive particles, and preferably has a spider web shape with the conductive particles as vertices. It is preferable that the individual conductive particles are interconnected with two or more other conductive particles on average. More preferably, the average number is 3 or more.

  As a method for dispersing conductive particles in a single layer in a film-like fixing resin and laminating an insulating adhesive, for example, a cross-linked polymer is used as a fixing resin on a peelable substrate, and the final film The coating is applied so that the thickness is smaller than the conductive particle diameter, and the conductive particles are arranged on the surface. Conductive particles can be arranged by charging them with the same charge and dispersing them, supplying conductive particles through finely-arranged holes, or attracting conductive particles to through-holes smaller than the size of the arbitrarily arranged conductive particles. For example, a method of fixing and then transferring to a fixing resin may be used.

  Next, the conductive particles are embedded in the fixing resin so as to reach the peelable substrate, and the crosslinked polymer is crosslinked using heat or light energy. After peeling the base material which can be peeled as needed, it laminates to an insulating adhesive using a hot roll or a laminator. Here, the film thickness of the fixing resin is less than the particle size of the conductive particles, preferably 2/3 or less, and more preferably 1/2 or less. A thermoplastic polymer can be used in place of the crosslinked polymer. In this case, after heating the thermoplastic polymer in the softened state, the conductive particles are held in place, and then the temperature is lowered to fix the conductive particles, or the thermoplastic polymer is softened with a solvent or the like. There is a method of fixing the conductive particles by holding the particles in place and then drying.

  The anisotropic conductive adhesive used in the present invention is preferably in the form of a film having a thickness of 5 μm or more and 50 μm or less, more preferably 6 μm or more and 35 μm or less, further preferably 7 μm or more and 25 μm or less, and more preferably 8 μm or more. 20 μm or less.

  In the circuit connection method of the present invention, after an anisotropic conductive adhesive is applied to the connection portion of the circuit board, the IC chip or another circuit board is aligned and stacked, and after temporary pressing as necessary, heating is performed. Pressurized. The temperature at this time is preferably 100 ° C. or higher and 280 ° C. or lower. The temperature is preferably determined in consideration of the balance between the strength of the fixing resin and the melt viscosity of the insulating adhesive. That is, by connecting at a low temperature, the melt viscosity of the insulating adhesive increases, and the conductive particles tend to flow. When the temperature increases, the melt viscosity of the insulating adhesive decreases, and the conductive particles flow. It becomes difficult to do. The conductive particles existing in the space between the adjacent electrodes flow, but the conductive particles between the connection electrodes and the conductive particles existing in the center of the IC chip having no electrode are preferably connected at a temperature that does not substantially flow. If necessary, after the flow of the insulating adhesive is settled, the temperature can be raised to advance the curing reaction of the insulating adhesive.

The connection structure of the present invention is a connection structure in which a circuit board and an IC chip are connected with an anisotropic conductive adhesive, and the density of conductive particles between connection electrodes q / mm ² and the space between adjacent electrodes. There is a relationship of q> r × 3 between the conductive particle density r / mm ² . Preferably q> r × 4, more preferably q> r × 5, and even more preferably q> r × 10. When q is larger than 3 times r, the conductivity of the connection electrode and the insulation between the adjacent electrodes can be made highly compatible.
Furthermore, it is preferable to have a relationship of p> r × 3 with the density of conductive particles p / mm ^{2 in the} central portion that does not have an IC chip electrode. More preferably, p> r × 4, more preferably p> r × 5, and still more preferably p> r × 10. When p is larger than 3 times r, high insulation between adjacent electrodes can be maintained.

The connection structure of the present invention can be obtained, for example, by connecting an IC chip and a circuit board by the circuit connection method of the present invention described above.
The number of conductive particles of the connection structure can be counted using an optical microscope, a microscope, an X-ray inspection apparatus, etc. after disassembling the connection portion as necessary.
When obtaining q and r, it is preferable to calculate from the number of conductive particles in the space part between all connected electrodes or between all adjacent electrodes. However, when the number of connection electrodes is large, between the connection electrodes or adjacent electrodes sampled arbitrarily A value obtained from the number of conductive particles in the interspace can be substituted. When sampling, it is necessary to select a sampling location and number so as to suppress errors due to sampling as much as possible.
When obtaining p, it is necessary to obtain it from an area of 0.01 mm ² or more including the center of the IC chip. However, when the area of the central portion that does not have the electrode is less than 0.01 mm ² , it is obtained from the entire central portion that does not have the electrode.

  The minimum number of conductive particles trapped between the connection electrodes of the connection structure of the present invention (hereinafter referred to as the minimum particle capture number) is preferably 2 or more in order to maintain a low connection resistance. More preferably, they are 3 or more and 30 or less, More preferably, they are 4 or more and 25 or less, More preferably, they are 5 or more and 20 or less. Here, the minimum particle trapping number is defined as a value obtained by subtracting three times the standard deviation from the average value of the number of conductive particles trapped between the connection electrodes.

The invention is explained in more detail by means of examples.
(Production Example 1) (Production of anisotropic conductive adhesive)
100 parts by mass of phenoxy resin (manufactured by Toto Kasei Co., Ltd., trade name: phenototo YP50), 50 parts by mass of bisphenol A type liquid epoxy resin (Japan Epoxy Resin Co., Ltd., trade name: Epicoat YL980), microcapsule type latent curing agent And a liquid epoxy resin mixture (Asahi Kasei Chemicals Corporation, trade name: Novacure HX-3941HP) 50 parts by mass and ethyl acetate 200 parts by mass were mixed to obtain an adhesive varnish. The adhesive varnish was applied onto a 50 μm PET film separator subjected to a release treatment using a blade coater, and the solvent was removed by drying to obtain a film-like insulating adhesive A having an average film thickness of 20 μm.
50 parts by mass of bisphenol A liquid epoxy resin (Japan Epoxy Resin Co., Ltd., trade name: Epicoat YL980), 50 parts by mass of bisphenol A novolac epoxy resin (Japan Epoxy Resin Co., Ltd., trade name: Epicoat 157), 4 parts by mass of dicyandiamide , 0.2 parts by mass of 2-ethyl-4-methylimidazole and 3000 parts by mass of methyl ethyl ketone were mixed, applied to a 50 μm PET film subjected to a release treatment using a blade coater, and dried at 80 ° C. for 5 minutes. An adhesive resin having a tackiness before crosslinking was formed with an average film thickness of 1.2 μm.

  Conductive particles having a diameter of 3 μm were embedded in the fixing resin before cross-linking in a lattice shape with an interval of 8 μm. Here, the conductive particle is a divinylbenzene resin core, a nickel layer of 0.07 μm is formed on the surface layer by electroless plating, and a gold layer of 0.04 μm is formed by electroplating. The thing of 0.15 micrometer was used. As a method of embedding conductive particles in a lattice shape, a 25 μm-thick polyimide film in which through-holes having a diameter of 2.0 μm formed by irradiating an excimer laser through a metal mask are formed in a lattice shape at intervals of 8 μm is used as a suction port. Using the suction device installed on the surface, the conductive particles are held in the through-holes by vacuum suction, and then the conductive particles sucked and held against the surface of the fixing resin before crosslinking are pressed until the conductive particles reach the PET film before crosslinking. A method was used in which the conductive particles were transferred to the fixing resin before crosslinking by embedding in the fixing resin and releasing the vacuum after releasing the vacuum.

Next, the fixing resin in which the conductive particles are embedded is heated at 160 ° C. for 2 minutes before crosslinking to crosslink the fixing resin, and then the film-like insulating adhesive A is stacked on the conductive particle side. By laminating, the conductive particles protruding from the fixing resin are embedded in the insulating adhesive A, and the fixing resin and the insulating adhesive A are laminated without any gaps, and the film-like anisotropic conductive adhesive A Got. As a result of observing the anisotropic conductive adhesive A with a microscope (manufactured by Keyence Corporation, trade name: VHX-100, the same shall apply hereinafter), the conductive particles are arranged separated from each other, and further obtained with a microscope. Using the image processing software (trade name: A image-kun, manufactured by Asahi Kasei Co., Ltd., hereinafter the same), the average value of the distance between the centers of the adjacent conductive particles and the coefficient of variation thereof was obtained from The average value was 8.7 μm, the coefficient of variation was 0.25, and the number of conductive particles was 15000 particles / mm ² . Note that the image processing was performed on five arbitrarily selected areas of 0.06 mm ² and the average value was used.

(Production Example 2) (Production of anisotropic conductive adhesive)
A film-like anisotropic conductive adhesive B was prepared in the same manner as in Production Example 1 except that the diameter of the conductive particles was 4 μm, the standard deviation was 0.2 μm, and the diameter of the through hole opened in the polyimide film was 2.5 μm. Obtained. As a result of observing the anisotropic conductive adhesive B with a microscope, the conductive particles are spaced apart from each other. Further, from the image obtained with the microscope, the proximity of the conductive particles is obtained using image processing software. As a result of obtaining the average value of the center-to-center distance from the particles and the coefficient of variation thereof, the average value was 8.2 μm, the coefficient of variation was 0.11, and the number of conductive particles was 17000 / mm ² . Note that the image processing was performed on five arbitrarily selected areas of 0.06 mm ² and the average value was used.

(Production Example 3) (Production of anisotropic conductive adhesive)
100 parts by mass of phenoxy resin (manufactured by Toto Kasei Co., Ltd., trade name: phenotote YP50), 90 parts by mass of bisphenol A type liquid epoxy resin (Japan Epoxy Resin Co., Ltd., trade name: Epicoat YL980), microcapsule type latent curing agent And 60 parts by mass of a mixture of epoxy resin and liquid epoxy resin (Asahi Kasei Chemicals Corporation, trade name: Novacure HX-3941HP) and 200 parts by mass of ethyl acetate were mixed to obtain an adhesive varnish. This adhesive varnish was applied onto a 50 μm PET film separator subjected to a release treatment using a blade coater, and the solvent was removed by drying to obtain a film-like insulating adhesive B having an average film thickness of 18 μm.

A 100 μm unstretched polypropylene film was coated with an acrylic polymer having a weight average molecular weight of 1.1 million and a glass transition temperature of −30 ° C. diluted to 4% by mass with ethyl acetate using a blade coater, and dried at 80 ° C. for 5 minutes. A tacky acrylic polymer was formed with a thickness of 5 μm.
After the conductive particles having a diameter of 4 μm are filled on this acrylic polymer, the conductive particles not reaching the acrylic polymer are eliminated by air blowing, and the filling rate defined by the filling area ratio of the conductive particles with respect to the total area is 73%. A single-layer conductive particle layer was formed. Here, the conductive particle is a divinylbenzene resin core, a nickel layer of 0.07 μm is formed on the surface layer by electroless plating, and a gold layer of 0.04 μm is formed by electroplating. A 0.2 μm one was used.

  Next, the polypropylene film in which the conductive particles are held in the acrylic polymer is stretched 1.5 times at a rate of 6% / second in both longitudinal and lateral directions at 130 ° C. using a test biaxial stretching apparatus. The ratio was lowered to 2% / second, the film was stretched to 2.5 times the initial value, and then cooled to room temperature. As a result of observing the obtained stretched film with a microscope, the conductive particles were separated from each other, and each conductive particle was an average of 4.3 other conductive particles connected with an acrylic polymer. The acrylic polymer had a thread-like structure with a diameter of about 2 μm.

Insulating adhesive B is laminated on the conductive particle side on the conductive particle linking structure using the acrylic polymer obtained here as a fixing resin, laminated at 50 ° C. under vacuum, and then peeled off the polypropylene film. The conductive particle linking structure used as the fixing resin was embedded in the surface layer of the insulating adhesive B to obtain a film-like anisotropic conductive adhesive C. As a result of observing the anisotropic conductive adhesive C with a microscope, the conductive particles are arranged to be separated from each other, and from the image obtained with the microscope, the proximity of the conductive particles is obtained using image processing software. As a result of obtaining the average value of the center-to-center distance from the particles and the coefficient of variation thereof, the average value was 10.6 μm, the coefficient of variation was 0.35, and the number of conductive particles was 9300 particles / mm ² . Note that the image processing was performed on five arbitrarily selected areas of 0.06 mm ² and the average value was used.
[Example 1]

15.1 mm × 1.6 mm size, 20 μm × 100 μm gold bump electrodes (height 15 μm) are arranged in a row at the end of 4 sides so that the long side is perpendicular to the end face of the IC chip TEG1 (Test Element Group) comprising a set of a total of 726 IC chips arranged at intervals of 30 μm and an ITO glass substrate having a connection pitch corresponding thereto was prepared.
The anisotropic conductive adhesive A cut to 16 mm × 1.8 mm was peeled off the PET film on the conductive particle side, and then attached to the connection part of the ITO glass substrate, heated at 80 ° C. for 3 seconds, and the separator was peeled off. Next, after aligning the ITO glass substrate on which the IC chip and the anisotropic conductive adhesive A are pasted using a flip chip bonder FC2000 manufactured by Toray Engineering Co., Ltd., the connection speed is 5 mm / second and the connection temperature is 200. The connection structure 1 was obtained by connecting the IC chip to the ITO glass substrate by heating and pressurizing under conditions of 20 ° C. and a connection pressure of 20 gf per electrode and a connection time of 10 seconds.

As a result of observing the connection structure 1 with a microscope, the conductive particle density between the connection electrodes was 11250 particles / mm ² , the conductive particle density in the space between adjacent electrodes was 3200 particles / mm ² , The density of the conductive particles is 13000 / mm ² , the conductive particle capture rate between the connecting electrodes is 75%, the conductive particle retention rate in the space portion between the adjacent electrodes is 21%, and the fluidity of the conductive particles is determined by the space between the adjacent electrodes. It was found that the portion was higher than between the connection electrodes. The observation with a microscope was carried out for an area of 0.06 mm ² including 50 connection electrodes arbitrarily selected and 50 spaces and the center of the IC chip.

Next, the connection reliability of the connection structure 1 was evaluated. In the connection structure 1, a daisy chain circuit having 480 joint portions and a comb-shaped electrode having 20 pairs of combs were formed, and connection resistance was measured at the daisy chain portion and an ion migration test was performed at the comb-shaped electrode portion. The ion migration test was conducted with a temperature of 85 ° C., a relative humidity of 85%, and a voltage of 20V. As a result of the measurement, the daisy chain circuit was turned on, indicating that all connections were made. On the other hand, the ion migration test showed an insulation resistance of 5 × 10 ⁷ Ω or more over 500 hours and a high insulation reliability.
[Examples 2 to 6]

15.1 mm × 1.6 mm size, 16 μm × 90 μm gold bump electrodes (height 10 μm) are arranged in a row at the end of 4 sides so that the long side is perpendicular to the end face of the IC chip A TEG2 made of a set of a total of 870 IC chips arranged at intervals of 25 μm pitch and an ITO glass substrate having a connection pitch corresponding thereto was prepared. In the same manner as in Example 1, connection was performed under the conditions shown in Table 1 to obtain connection structures 2 to 6.
Table 1 shows the observation results of the connection structures 2 to 6 with a microscope. Furthermore, connection reliability evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.
[Comparative Examples 1-2]

In the same manner as in Example 1, connection was performed under the conditions shown in Table 1 to obtain connection structures 7 to 8.
Table 1 shows the observation results of the connection structures 7 to 8 with a microscope. Furthermore, connection reliability evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.
As shown in Table 1, in the circuit connection method of Comparative Example 1, both the conductive particle capture ratio between the connection electrodes and the conductive particle retention ratio in the space portion between adjacent electrodes are high, and the ratio is 1.3: 1. As a result, in connection resistance measurement, all the connections could be conducted and there was no problem. However, in the ion migration test, dielectric breakdown occurred in 120 hours, and the insulation reliability was low.
On the other hand, in the circuit connection method of Comparative Example 2, the conductive particle trapping rate between the connection electrodes and the conductive particle retention rate in the space portion between adjacent electrodes are both low, and the ratio is 1.9: 1, and no conductive particles are placed. The existence of a connection has been confirmed. As a result, a problem called daisy chain circuit connection failure occurred. Further, in the ion migration test, the conductive particles aggregated in the space portion, resulting in problems.

  The circuit connection method and the connection structure of the present invention are capable of electrical connection of a fine circuit using an anisotropic conductive adhesive, have excellent conductivity between connection electrodes having a small area, and have a fine space between adjacent electrodes. This provides a connection structure that is less prone to insulation failure such as shorting of parts and ion migration, and can be suitably used as a component of electronic equipment.

Claims (4)

In a circuit connection method for connecting circuit electrodes facing each other using an anisotropic conductive adhesive mainly composed of conductive particles and an insulating adhesive, the conductive particle capturing rate between the connection electrodes is a space portion between adjacent electrodes. Circuit connection method for connecting the conductive particles so as to be 3 times or more of the conductive particle retention rate. One of the circuits is an IC chip, and an anisotropic conductive adhesive is an anisotropic conductive adhesive film in which conductive particles are dispersed substantially evenly in the plane direction and arranged in a single layer in the thickness direction. The circuit connection method according to claim 1, wherein the connection is performed such that the fluidity of the conductive particles existing in the space between adjacent electrodes is higher than the fluidity of the conductive particles existing between the connection electrodes. A connection structure in which a circuit board and an IC chip are connected with an anisotropic conductive adhesive, and the conductive particle density between connection electrodes is q / mm ² and the conductive particle density is r / mm in the space between adjacent electrodes. ^2. A connection structure having a relationship of q> r × 3 between ² and ² . A connection structure in which a circuit board and an IC chip are connected with an anisotropic conductive adhesive, and the density of conductive particles in the central part, which does not have an electrode of the IC chip, p pieces / mm ^2, and the conductivity of the space part between adjacent electrodes A connection structure characterized by having a relationship of p> r × 3 between the particle density and r particles / mm ² .