JP2006249342A - Adhesive composition and anisotropic conductive adhesive using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an adhesive composition capable of suppressing thermal expansion under a high temperature and high humidity condition, and enhancing humidity resistance without deterioration of fundamental characteristics such as adhesiveness and conductivity/insulating property, etc. <P>SOLUTION: This adhesive composition comprises an epoxy resin, a silane-modified epoxy resin containing an alkoxy group, an inorganic filler and a latent hardener as essential ingredients, wherein an amount of formulation of the silane-modified epoxy resin containing the alkoxy group is ≥0.01 wt% and ≤20 wt% based on the total amount of the epoxy resin. The adhesive can be applied for use requiring high reliability because of less changes in characteristics when used under the high temperature and high humidity condition for a long period of time due to a low thermal expansion coefficient and a low humidity expansion coefficient. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an adhesive composition suitable for use in electronic materials, and specifically used as an anisotropic conductive adhesive, a sealant for electronic parts and semiconductor chips, a cured underfill resin, and the like. The present invention relates to an adhesive composition that can be used and an anisotropic conductive adhesive using the same.

  In recent years, electronic devices have been miniaturized and highly functionalized, and connection terminals in components have been miniaturized. For this reason, in the field of electronics mounting, various adhesives that can easily connect such terminals are used. For example, an anisotropic conductive adhesive is used as an adhesive for circuit connection to the bonding of an IC chip and a flexible printed wiring board (FPC), a glass substrate on which an IC chip and an ITO (Indium-Tin-Oxide) electrode circuit are formed. in use.

  An anisotropic conductive adhesive is a film-like or paste-like adhesive in which conductive particles are dispersed in an insulating adhesive composition, and is sandwiched between connection targets, heated and pressurized to be connected. Glue. That is, the adhesive composition in the anisotropic conductive adhesive flows by heating and pressurizing, sealing the gaps between the electrodes facing each other on the connection object, and at the same time, part of the conductive particles oppose each other. An electrical connection is achieved by biting between the electrodes. In anisotropic conductive adhesives, the conduction performance that lowers the resistance (conduction resistance) between the electrodes facing each other in the thickness direction and the insulation performance that raises the resistance (insulation resistance) between adjacent electrodes in the plane direction. Is needed.

  As an insulating adhesive composition constituting such an anisotropic conductive adhesive, an epoxy-based thermosetting resin composition is mainly used. For example, a combination of a thermosetting resin such as an epoxy resin and a curing agent is widely used.

  In addition, anisotropic conductive adhesives are required to have high reliability because they are used for connection around precision equipment such as a liquid crystal display (LCD). Therefore, environmental resistance is required in addition to conduction / insulation performance, and the performance is evaluated by, for example, a high-temperature and high-humidity test or a heat cycle test. Here, the epoxy resin-based adhesive composition used for the anisotropic conductive adhesive has high water absorption because it contains a hydroxyl group in the molecule, and may cause poor connection in a high temperature and high humidity test. There are challenges. Also, since the adhesive composition has a higher coefficient of thermal expansion than the substrate material, stress based on the difference in thermal expansion coefficient between the substrate and the adhesive is generated in the connection part under the heat cycle test, and the connection resistance at the connection part is reduced. May increase.

  Therefore, a method of adding an inorganic filler to the adhesive composition has been proposed in order to reduce the coefficient of thermal expansion and improve the moisture resistance. Patent Document 1 discloses an adhesive for connecting circuit members, wherein 100 parts by weight of the adhesive resin composition contains 5 to 200 parts by weight of an inorganic filler. Patent Document 2 includes an epoxy resin, a latent curing agent, an inorganic filler, and a polyethersulfone. The total content of the epoxy resin, the latent curing agent, and the polyethersulfone contains 100 parts of the inorganic filler. An epoxy resin sheet adhesive composition whose amount is 5 to 900 parts by weight is disclosed.

  On the other hand, in order to improve the heat resistance of an epoxy resin, a silane-modified epoxy resin composition characterized by containing an alkoxy group-containing silane-modified epoxy resin and a curing agent for epoxy resin has been proposed (Patent Document 3). ). An alkoxy group-containing silane-modified epoxy resin is a resin obtained by subjecting a bisphenol-type epoxy resin and an alkoxysilane partial condensate to a dealcoholization condensation reaction, an epoxy curing site that undergoes ring-opening / crosslinking reaction with a curing agent, and hydrolysis. -It has a sol-gel curing site that undergoes a condensation reaction. An epoxy-silica hybrid cured product is obtained by mixing and reacting with a curing agent for epoxy resin.

JP-A-11-61088 JP 2000-204324 A JP 2002-179762 A

  In the method of adding an inorganic filler in the adhesive composition, the adhesiveness at the interface between the resin component and the inorganic filler in the adhesive composition is insufficient, so the effect of suppressing thermal expansion and humidity expansion is sufficient. There is a problem that it cannot be obtained. As a countermeasure against this, the surface of the inorganic filler is generally treated with a silane coupling agent. However, when the particle size of the inorganic filler is reduced, it is difficult to uniformly treat the filler surface and secondary aggregation occurs. There are many. For example, in an anisotropic conductive adhesive, if a coarse inorganic filler is used, coarse particles may be caught between the counter electrodes, resulting in poor connection, and it is necessary to use an inorganic filler with a small particle size, It was difficult to satisfy both heat resistance and moisture resistance improvement and connection performance.

  In the epoxy-silica hybrid cured product using the alkoxy group-containing silane-modified epoxy resin, the problem of the filler-resin interface as described above does not occur. However, it is necessary to add a metal catalyst such as tin octylate as a sol-gel curing catalyst, which may cause problems such as migration when used for electronic materials. In order to advance the sol-gel curing reaction, heating at a relatively high temperature of 80 ° C. to 120 ° C. is required. However, at this temperature, the reaction between the epoxy curing agent and the epoxy group proceeds, and the necessary adhesive properties cannot be obtained. In order to prevent this, it is conceivable to use a so-called high-temperature curing type epoxy curing agent with a high reaction temperature. However, if a high-temperature curing type curing agent is used, the bonding process cannot be performed at a low temperature and in a short time. The cost at is high. Furthermore, since the sol-gel curing site of the alkoxy group-containing silane-modified epoxy resin is easily gelled, the blending amount in the adhesive composition cannot be increased. For this reason, the silica content required for the effect of improving heat resistance and moisture resistance cannot be obtained with only the epoxy-silica hybrid cured product.

  The present invention solves the above-mentioned problems, suppresses thermal expansion under high-temperature and high-humidity conditions, and improves moisture resistance without impairing basic properties such as adhesion and conduction / insulation performance. It is an object to provide an agent composition.

  The present inventor has paid attention to the characteristics of the alkoxy group-containing silane-modified epoxy resin and found that the above problems can be achieved by combining this with an inorganic filler, thereby completing the present invention.

  The present invention is an adhesive composition comprising (1) an epoxy resin, (2) an alkoxy group-containing silane-modified epoxy resin, (3) an inorganic filler, and (4) a latent curing agent as essential components, the alkoxy group The adhesive composition is characterized in that the amount of the silane-modified resin is 0.01% by weight or more and 20% by weight or less of the total weight of the epoxy resin (Claim 1).

  Moreover, this invention is an anisotropic conductive adhesive characterized by mixing said adhesive composition and electroconductive particle (Claim 6).

As described above, the alkoxy group-containing silane-modified epoxy resin has an epoxy curing site and a sol-gel curing site. Here, the sol-gel curing site has a structure represented by the general formula (a). (In the formula, R represents an alkyl group, and the average number of repeating units of n is 1 to 10.)

  The alkoxy group at the sol-gel curing site has a property of being easily dehydrated and condensed with a hydroxyl group on the surface of the inorganic filler by hydrolysis, and has a strong bonding force with the inorganic filler. For this reason, the adhesive force at the interface between the resin component and the inorganic filler is improved by adding the alkoxy group-containing silane-modified epoxy resin to the adhesive composition containing the epoxy resin, the inorganic filler, and the latent curing agent as essential components. As a result, an adhesive composition that can achieve both the dispersibility of the inorganic filler and the heat and humidity resistance properties can be obtained.

  As such an alkoxy group-containing silane-modified epoxy resin, a trimethoxysilane-modified bisphenol A-type epoxy resin, a triethoxysilane-modified bisphenol A-type epoxy resin, or the like can be used. Examples of the epoxy skeleton include bisphenol A type, F type, and S type.

  The addition amount of the alkoxy group-containing silane-modified epoxy resin needs to be 0.01 wt% or more and 20 wt% or less of the total weight of the epoxy resin. If it is 0.01% by weight or less, the effect of improving the adhesion between the resin component and the inorganic filler cannot be obtained. On the other hand, if it is 20% by weight or more, gelation tends to occur, and the storage stability of the adhesive composition is poor. A more preferable range is 0.5 wt% or more and 10 wt% or less. The total weight of the epoxy resin is the total amount of the entire epoxy resin including the alkoxy group-containing silane-modified epoxy resin.

  The greater the blending amount of the inorganic filler, the lower the water absorption of the adhesive composition, and the moisture resistance can be improved. However, if the amount of the inorganic filler is too large, the adhesiveness is lowered, and the amount of the inorganic filler bitten between the terminals is increased, resulting in a problem that the conduction resistance is increased. For this reason, it is preferable that the compounding quantity of an inorganic filler is 0.5 to 30 weight% of the total weight of an epoxy resin. Claim 2 corresponds to this preferred embodiment. A more preferable blending amount of the inorganic filler is 5% by weight or more and 20% by weight or less of the total weight of the epoxy resin.

  Furthermore, in order to connect between narrow pitch electrodes, it is effective to orient the conductive particles in the circuit connecting adhesive. However, when an inorganic filler is mixed in the adhesive, the conductive particles are oriented. May be hindered. However, by selecting an inorganic filler having an average particle size of 500 nm or less, an inorganic filler in an amount necessary for improving moisture resistance can be blended without causing such a problem of inhibition of orientation.

  The greater the blending amount of the inorganic filler, the lower the water absorption rate of the adhesive, and the moisture resistance can be improved. However, if the amount of the inorganic filler is too large, the adhesiveness is lowered, and the amount of the inorganic filler bitten between the terminals is increased, resulting in a problem that the conduction resistance is increased. For this reason, it is preferable that the compounding quantity of an inorganic filler is 0.5 to 30 weight% of the total weight of an epoxy resin. Claim 2 corresponds to this preferred embodiment. A more preferable blending amount of the inorganic filler is 5% by weight or more and 20% by weight or less of the total weight of the epoxy resin.

  Although the particle size of the inorganic filler is not particularly limited, it is preferable that the average particle size is 1 μm or less and the maximum particle size is 3 μm or less in consideration of use in electronic materials such as anisotropic conductive adhesives. . As the average particle size decreases, the surface area of the inorganic filler increases and the interaction with the epoxy resin can be increased. As a result, the effect of improving moisture resistance and reducing the thermal expansion coefficient can be obtained with a small amount of blending. is there. If the maximum particle size is 3 μm or less, connection can be made stably without causing connection failure due to coarse particles. Claim 3 corresponds to this preferred embodiment. Furthermore, it is excellent in the moisture resistance improvement effect that the average particle diameter of an inorganic filler is 500 nm or less, and is preferable. The lower limit of the average particle size is not particularly limited, but is preferably 3 nm or more in consideration of workability.

  As the inorganic filler of the present invention, known ones such as metal oxides such as silica, alumina and titanium oxide, hydroxides such as aluminum hydroxide, magnesium hydroxide and calcium hydroxide, and complex oxides may be used. it can. When silica filler or alumina filler is used as the inorganic filler, the effect of reducing the coefficient of thermal expansion and the effect of improving insulation are excellent, which is preferable. Claim 4 corresponds to this preferred embodiment.

  The epoxy resin used in the present invention is not particularly limited, but other than bisphenol type epoxy resins having skeletons of bisphenol A, F, S, AD, etc., naphthalene type epoxy resins, novolac type epoxy resins, biphenyl type epoxy resins, Examples include dicyclopentadiene type epoxy resins. A phenoxy resin which is a high molecular weight epoxy resin can also be used.

  The molecular weight of the epoxy resin can be appropriately selected in consideration of the performance required for the adhesive composition. When the molecular weight is high, the film-forming property is high and the melt viscosity of the resin at the connection temperature can be increased. When used as an anisotropic conductive adhesive, there is an effect that the connection can be made without disturbing the orientation of the conductive particles. On the other hand, when a low molecular weight epoxy resin is used, the crosslink density is increased and the heat resistance is improved, and the cohesive force of the resin is increased, so that the adhesive strength is increased. Accordingly, it is preferable to use a combination of a high molecular weight epoxy resin having a molecular weight of 15000 or more and a low molecular weight epoxy resin having a molecular weight of 2000 or less in order to balance the performance. The mixing ratio of the high molecular weight epoxy resin and the low molecular weight epoxy resin can be appropriately selected.

  The latent curing agent used in the present invention is a curing agent that is excellent in storage stability at low temperatures and hardly undergoes a curing reaction at room temperature, but rapidly undergoes a curing reaction under predetermined conditions by heating or the like. Examples of latent curing agents include imidazoles, hydrazides, boron trifluoride-amine complexes, amine imides, polyamines, tertiary amines, alkyl ureas and other amines, dicyandiamide, and modified products thereof. These can be used alone or as a mixture of two or more.

Among the latent curing agents, an imidazole latent curing agent is preferably used. As the imidazole-based latent curing agent, a known imidazole-based latent curing agent can be used, and specifically, an adduct of an imidazole compound with an epoxy resin is exemplified. Examples of the imidazole compound include imidazole, 2-methylimidazole, 2-ethylimidazole, 2-propylimidazole, 2-dodecylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole, and 4-methylimidazole.

  Further, these latent curing agents are coated with a polymer material such as polyurethane or polyester, a metal thin film such as nickel or copper, and an inorganic material such as calcium silicate and microencapsulated. This is preferable in order to more fully achieve the contradictory properties of fast curability. Therefore, a microcapsule type imidazole-type latent curing agent is particularly preferable.

  The blending ratio of the epoxy resin and the latent curing agent is preferably 5 to 40% by weight with respect to the total weight of the epoxy resin. When the ratio of the latent curing agent is less than 5% by weight, the curing rate may decrease and curing may be insufficient. On the other hand, when the amount is more than 40% by weight, unreacted curing agent tends to remain, which may reduce heat resistance and moisture resistance.

  In the adhesive composition of the present invention, other thermosetting resins, thermoplastic resins, and the like can be added in addition to the essential components as long as the gist of the present invention is not impaired. Moreover, you may contain additives, such as a hardening accelerator, a polymerization inhibitor, a sensitizer, a silane coupling agent, a flame retardant, and a thixotropic agent.

  The adhesive composition of the present invention can be obtained by mixing the aforementioned components. For example, a liquid adhesive composition can be obtained by dispersing an inorganic filler in a solution obtained by dissolving the epoxy resin, alkoxy group-containing silane-modified epoxy resin, latent curing agent and the like in a solvent. Moreover, this dispersion solution is applied with a roll coater or the like to form a thin film, and then the solvent is removed by drying or the like, whereby a film-like adhesive is obtained. Although the thickness of a film | membrane is not specifically limited, Usually, it is 10-50 micrometers.

  The present invention further provides an anisotropic conductive adhesive, wherein the adhesive composition and conductive particles are mixed. Examples of the conductive particles include metal particles such as gold, silver, copper, nickel, and alloys thereof, and carbon. Also, a non-conductive glass, ceramic, plastic, metal oxide or other core surface may be formed by coating a metal, ITO, or the like to form a conductive layer.

  When conductive particles having a diameter to length ratio (aspect ratio) of 5 or more are used as the conductive particles, the conduction resistance can be lowered without increasing the blending amount of the conductive particles, and good electrical connection can be achieved. Can be achieved, and the insulation resistance in the surface direction can be kept higher, which is preferable. Claim 6 corresponds to this preferred embodiment. The aspect ratio of the conductive particles is directly measured by a method such as CCD microscope observation. In the case of particles having a non-circular cross section, the aspect ratio is obtained using the maximum length of the cross section as a diameter. In addition, the conductive particles do not necessarily have a straight shape, and can be used without any problem even if they are slightly bent or branched. In this case, the aspect ratio is obtained with the maximum length of the conductive particles as the length. Commercially available acicular conductive particles can be used as the conductive particles having an aspect ratio of 5 or more. In addition, it is also possible to preferably use those formed by connecting a large number of fine metal particles into a needle shape. More preferably, the aspect ratio is 10 to 100.

  Examples of the metal that forms fine metal particles include a single metal having ferromagnetism such as Fe, Ni, Co, or a composite containing a ferromagnetic metal. When a metal having ferromagnetism is used, it is oriented by its own magnetism, and the conductive particles can be oriented using a magnetic field as will be described later.

  It is preferable to make the anisotropic conductive adhesive into a film shape and to orient the conductive particles having an aspect ratio of 5 or more in the thickness direction of the film because the anisotropic conductivity is further improved. Claim 7 corresponds to this preferable mode. The method for orienting the conductive particles in the thickness direction of the film is not particularly limited, but when using the conductive particles having ferromagnetism as described above, the conductive particles are dispersed in the resin solution, and the obtained dispersion is obtained. A method of fixing the orientation by applying the solution on a base to which a magnetic field is applied in a direction crossing the base surface, orienting the conductive particles, solidifying and curing by removing the solvent on the base, and the like is preferably exemplified. The Although the thickness of a film is not specifically limited, Usually, it is 10-50 micrometers.

  The compounding quantity of electroconductive particle is selected from the range of 0.01-30 volume% with respect to the whole volume of the adhesive agent for circuit connection, and uses properly by use. In order to prevent a decrease in insulation performance in the surface direction due to excessive conductive particles, the content is more preferably 0.01 to 10% by volume.

  The present invention provides an adhesive composition having excellent heat resistance and moisture resistance. The adhesive composition of the present invention has little change in properties even when used for a long time in a high-temperature and high-humidity environment, and can be used for applications requiring high reliability.

  Next, the best mode for carrying out the invention will be described by way of examples. The examples are not intended to limit the scope of the invention.

Example 1
(Preparation of coating solution)
As an epoxy resin, a phenoxy resin having an average molecular weight of about 60000 [YP-50 manufactured by Toto Kasei Co., Ltd.], a bisphenol A type solid epoxy resin having an average molecular weight of about 2900 [Epicoat 1007 manufactured by Japan Epoxy Resin Co., Ltd.], an average molecular weight of about 400 Bisphenol A type liquid epoxy resin [Epiclon 850 manufactured by Dainippon Ink and Chemicals, Inc.] and trimethoxysilane modified bisphenol A type epoxy resin [composeran E201 manufactured by Arakawa Chemical Industries, Ltd.] as an alkoxy group-containing silane modified epoxy resin. As a latent curing agent, a microcapsule type imidazole curing agent [manufactured by Asahi Kasei Epoxy Co., Ltd., NovaCure HX3941] was used at a weight ratio of 40/20/39/1/35, and these were used as γ-butyrolactone Resin composition having a solid content of 60% To prepare a liquid. Here, spherical silica particles having an average particle diameter of 20 nm as an inorganic filler were added so as to be 15% by weight with respect to the total weight of the epoxy resin, and kneading with three rolls was performed to obtain a uniform solution. Further, as the conductive particles, linear nickel fine particles having a chain length distribution of 3 μm to 11 μm (in which nickel fine particles having an average particle diameter of 200 nm are connected in a linear form. Aspect ratio: 15 to 55) It added so that it might become 1 volume% with respect to the total amount (resin composition + inorganic filler + nickel powder), and uniformly disperse | distributed by stirring using a centrifugal mixer, and the coating solution for adhesive agents was prepared.

(Production of film-like anisotropic conductive adhesive)
The coating solution prepared above is applied onto a release-treated PET film using a doctor knife, and then dried and solidified in a magnetic field with a magnetic flux density of 100 mT at 60 ° C. for 30 minutes, whereby a linear chain in the film is obtained. A film-like anisotropic conductive adhesive having a thickness of 25 μm was prepared in which the shaped particles were oriented in the magnetic field direction (film thickness direction).

(Connection resistance evaluation)
An IC chip in which 726 gold plated bumps having a width of 15 μm, a length of 100 μm, and a height of 16 μm were arranged at intervals of 15 μm, and a glass substrate on which the same number of ITO electrodes were formed with a width of 20 μm and a space of 10 μm were prepared. The anisotropic conductive adhesive film obtained above is sandwiched between the IC chip and the circuit board, and heated to 200 ° C. for 20 seconds with a pressure of 20 gf per bump for 20 seconds to thermally bond the IC and glass. A joined body with the substrate was obtained. Of the 726 electrodes of this bonded body, 32 consecutive resistance values connected via ITO electrode, anisotropic conductive adhesive, and gold bump are obtained by the four-terminal method, and the value is divided by 32. Thus, the connection resistance per electrode was obtained. This evaluation was repeated 10 times, and the average value of the connection resistance was obtained.

(Heat and humidity resistance test)
The joined body of the IC and the glass substrate was put into a constant temperature and humidity chamber set at a temperature of 85 ° C. and a humidity of 85%, taken out after 100 hours, and the average value of the connection resistance was obtained again in the same manner as described above. . The results are shown in Table 1.
(Storage stability evaluation)
About the anisotropic conductive adhesive produced above, the melt viscosity from 50 ° C. to 200 ° C. was measured using a viscoelasticity measuring device (ARES manufactured by Rheometric Co., Ltd.), and the minimum value was obtained. Furthermore, this sample was allowed to stand at room temperature of 25 ° C., and the time until the minimum value of the melt viscosity exceeded 10 times was examined.

(Example 2)
As conductive particles, spherical resin particles with an average particle diameter of 5 μm and coated with gold were used and dried and solidified without applying a magnetic field. An anisotropic conductive adhesive was prepared, and connection resistance evaluation, heat and humidity resistance test, and life evaluation were performed. The results are shown in Table 1.

(Comparative Example 1)
A film having a thickness of 25 μm in the same manner as in Example 1 except that the blending ratio of phenoxy resin, solid epoxy resin, liquid epoxy resin, silane-modified epoxy resin, and latent curing agent was 40/20/40/0/35. An anisotropic conductive adhesive was prepared, and connection resistance evaluation, heat / moisture resistance test and life evaluation were performed. The results are shown in Table 1.

(Comparative Example 2)
A film having a thickness of 25 μm in the same manner as in Example 1 except that the blending ratio of phenoxy resin, solid epoxy resin, liquid epoxy resin, silane-modified epoxy resin, and latent curing agent was 40/20/15/25/35 An anisotropic conductive adhesive was prepared, and connection resistance evaluation, heat / moisture resistance test, and life evaluation were performed. The results are shown in Table 1.

  The results of Table 1 show that when bonded using the anisotropic conductive adhesive of the present invention (Example), the increase in connection resistance value is small even when placed in a high temperature and high humidity environment for a long time. It shows that excellent heat and humidity resistance can be achieved. On the other hand, in Comparative Example 1 in which no alkoxy group-containing silane-modified epoxy resin was added, the increase rate of the resistance value after the high temperature and high humidity test was large. Further, in Comparative Example 2 in which the blending amount of the alkoxy group-containing silane-modified epoxy resin is 25% by weight of the total weight of the epoxy resin, the increase rate of the resistance value is increased and the life is shortened. As is apparent from this result, by using the adhesive composition of the present invention example, excellent heat and humidity resistance can be achieved, and high reliability can be obtained.

Claims (7)

  An adhesive composition comprising (1) an epoxy resin, (2) an alkoxy group-containing silane-modified epoxy resin, (3) an inorganic filler, and (4) a latent curing agent, the alkoxy group-containing silane-modified epoxy resin. The adhesive composition is characterized in that the blending amount is 0.01% by weight or more and 20% by weight or less of the total weight of the epoxy resin.   The adhesive composition according to claim 1, wherein the amount of the inorganic filler is 0.5 wt% or more and 30 wt% or less of the total weight of the epoxy resin.   The adhesive composition according to claim 1 or 2, wherein the inorganic filler has an average particle size of 1 µm or less and a maximum particle size of 3 µm or less.   The adhesive composition according to any one of claims 1 to 3, wherein the inorganic filler is a silica filler or an alumina filler.   An anisotropic conductive adhesive, wherein the adhesive composition according to claim 1 and conductive particles are mixed.   The anisotropic conductive adhesive according to claim 5, wherein the conductive particles are conductive particles having a diameter to length ratio (aspect ratio) of 5 or more. The anisotropic conductive adhesive according to claim 6, wherein the shape is a film, and the conductive particles are oriented in the thickness direction of the film.