JP2006176716A - Adhesive for connecting circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an adhesive for connecting circuits having excellent adhesiveness to circuit electrodes, a low water absorption coefficient and high heat and moisture resistances and making quick curability compatible with preservation stability. <P>SOLUTION: The adhesive consists essentially of an epoxy resin, an episulfide resin, a latent curing agent and electroconductive particles. The amount of the compounded episulfide resin is preferably ≥1 to <50 wt.% based on the total weight of the epoxy resin. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an adhesive for circuit connection for bonding and electrically connecting a substrate or an electronic component provided with electrodes, circuits and the like.

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

  The adhesive for circuit connection is a film or paste adhesive in which conductive particles are dispersed in an insulating resin composition. It is sandwiched between the objects to be connected and heated and pressurized to bond the objects to be connected. To do. That is, the resin in the adhesive flows by heating and pressurizing, sealing the gap between the electrodes facing each other on the connection object, and at the same time, a part of the conductive particles are caught between the facing electrodes. An electrical connection is achieved. In the adhesive for circuit connection, there is a conduction performance that lowers the resistance (conduction resistance) between the electrodes facing each other in the thickness direction and an insulation performance that raises the resistance (insulation resistance) between the electrodes adjacent in the plane direction. is needed.

  As the insulating resin composition constituting the adhesive for circuit connection, an epoxy thermosetting resin composition is mainly used. For example, a composition in which a thermosetting resin such as an epoxy resin or a phenoxy resin and a curing agent are combined is widely used.

  Since the adhesive for circuit connection is used for connection around a precision instrument such as a liquid crystal display (LCD), high reliability is required. 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 composition used for the adhesive for circuit connection contains a hydroxyl group in the molecule, so it has high water absorption and may cause poor connection in a high-temperature and high-humidity test, improving heat resistance and moisture resistance. It has become a challenge.

  In order to improve the heat resistance and moisture resistance of such an adhesive composition for circuit connection, various proposals have been made. For example, Patent Document 1 discloses a circuit connecting material comprising (1) a phenoxy resin, (2) a naphthalene type epoxy resin, (3) an adhesive composition essentially including a latent curing agent, and conductive particles. Yes. It is described that naphthalene-based epoxy resins have a rigid skeleton, so that the Tg of the cured product of the adhesive composition can be increased and the heat resistance and moisture resistance can be improved.

Further, Patent Document 2 discloses (1) a phenoxy resin, (2) a polyfunctional glycidyl ether type epoxy resin, and (3) a cured product that essentially requires a catalytic activity latent curing agent at 100 ° C. after 10 hours. An adhesive composition having a Na ⁺ and Cl ⁻ ion concentration of 300 ppm or less is disclosed. The use of a polyfunctional epoxy resin increases the cross-link density of the epoxy resin to increase the Tg of the cured product to improve the heat resistance, and it uses a catalyst-type latent curing agent with temperature activity to ensure long-term storage and fast curing. Both sexes are compatible.

  On the other hand, in order to improve the heat resistance and moisture resistance of the adhesive for circuit connection, not only the performance of the resin composition exemplified by Tg, water absorption rate, thermal expansion coefficient, etc. is improved, but also the resin composition and the conductive property are improved. It is effective to increase the adhesion with the conductive particles. That is, after the mounting, if the adhesion between the resin composition and the conductive particles is high, it is possible to firmly hold the conductive particles located between the counter electrodes, such as heat resistance, moisture resistance test and heat cycle test. Connection failure is less likely to occur during reliability evaluation. Furthermore, as the conductive particles, many metal powders and particles whose surfaces are coated with a metal are used, and the adhesion with the circuit electrodes can be improved by improving the adhesion with the conductive particles. However, those satisfying all these characteristics have not been obtained, and further improvement in performance of the adhesive for circuit connection is desired.

JP-A-8-315885 JP 2002-265916 A

  In order to solve the above-mentioned problems, the present inventor studied the use of an episulfide resin in which the oxygen atom (O) of the epoxy resin is substituted with a sulfur atom (S). The episulfide resin is a resin having a thiirane ring in the molecule, and the thiirane ring has a property of causing a ring-opening reaction to form a cured product in the same manner as the oxirane ring of the epoxy resin. Here, the sulfur atom (S) has a lower electronegativity than the oxygen atom (O), and the polarity of the resin is lowered, so that the water absorption is lowered and the moisture resistance can be improved.

  Furthermore, it is generally known that sulfur atoms (S) are strongly bonded to metals and metal oxides, and can improve the adhesion between the conductive particles in the circuit connection adhesive and the resin composition. It is possible to increase the adhesive force with an electrode circuit made of gold, copper, nickel, ITO or the like and to obtain a stable connection performance.

  It is known that such an episulfide resin can be used as a curing agent for a sealant, but the thiirane ring of an episulfide compound has a high reactivity and excellent fast curing property, but has a disadvantage of poor storage stability. Yes, it was not used for adhesives for circuit connection.

  The present invention provides an adhesive for circuit connection that solves the above-mentioned problems, has excellent adhesion to circuit electrodes, has low water absorption, high heat resistance and moisture resistance, and can achieve both fast curing and storage stability. The task is to do.

  The present invention is an adhesive for circuit connection comprising (1) an epoxy resin, (2) an episulfide resin, (3) a latent curing agent, and (4) conductive particles as essential components (claim 1).

  The resin composition used for the adhesive for circuit connection of the present invention uses an episulfide resin having a low water absorption rate and excellent reactivity, an epoxy resin and a latent curing agent, thereby providing heat resistance, moisture resistance, and adhesion. It is possible to improve and satisfy both conflicting characteristics of fast curability and storage stability.

  Furthermore, due to the effect of sulfur atoms (S) present in the episulfide resin, the adhesive force between the conductive particles in the circuit connecting adhesive and the resin composition can be improved, and it consists of gold, copper, nickel, ITO, etc. Adhesive strength with the electrode circuit can be increased, and connection reliability can be improved.

  The compounding amount of the episulfide resin is preferably 1% by weight or more and less than 50% by weight of the total weight of the epoxy resin. This is because when the episulfide resin is 50% by weight or more of the total weight of the epoxy resin, the reactivity of the resin becomes too high and the storage stability is lowered. On the other hand, when the episulfide resin is less than 1% by weight, characteristics such as reduction in water absorption and improvement in adhesion to metal cannot be obtained. Claim 2 corresponds to this preferred embodiment. Furthermore, when the blending amount of the episulfide resin is 5% by weight or more and 30% by weight or less of the total weight of the epoxy resin, it is preferable because the balance of characteristics can be achieved.

  The episulfide resin used in the present invention is not particularly limited as long as it has two or more episulfide groups in one molecule. In addition to bisphenol episulfide resins having a skeleton of bisphenol A, F, S, AD, etc., episulfide resins having a skeleton of naphthalene type, novolak type, biphenyl type, etc. are exemplified.

  It is preferable to use a bisphenol type episulfide resin as the episulfide resin in terms of excellent adhesion to a metal circuit. Claim 3 corresponds to this preferred embodiment.

  The molecular weight of the episulfide resin is not particularly limited, and can be appropriately selected in consideration of the performance required for the adhesive for circuit connection. It is also necessary to consider the balance with the molecular weight of the epoxy resin used at the same time.

  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 for circuit connection. When the molecular weight is increased, the film formability is high, the melt viscosity of the resin at the connection temperature can be increased, and 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.

  Examples of the conductive particles used in the present invention include metal particles such as gold, silver, copper, nickel, and alloys thereof. Further, the surface of particles such as non-conductive glass, ceramic, plastic, or metal oxide may be coated with metal or ITO 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 4). 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 metal containing ferromagnetism. 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.

  If the shape of the adhesive for circuit connection is a film shape, and the conductive particles having an aspect ratio of 5 or more are oriented in the thickness direction of the film, it is preferable because anisotropic conductivity is further improved (Claim 5). 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

  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 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 latent curing agent is preferably 5 to 40% by weight with respect to the total weight of the epoxy resin and the episulfide 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 addition to the essential components described above, other thermosetting resins, thermoplastic resins, and the like can be added to the adhesive for circuit connection of the present invention within a range that does not impair the spirit of the present invention. 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 for circuit connection of the present invention can be obtained by mixing the components described above. For example, a liquid circuit connection adhesive can be obtained by dispersing conductive particles in a solution obtained by dissolving the epoxy resin, episulfide resin, latent curing agent or the like in a solvent. The 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 for circuit connection is obtained. Although the thickness of a film | membrane is not specifically limited, Usually, it is 10-50 micrometers.

  The present invention provides an adhesive for circuit connection having excellent heat resistance and moisture resistance. The adhesive for circuit connection of the present invention has good conductivity / insulation performance when performing connection between electrodes and the like, and has little change in characteristics even when used for a long time in a high temperature and high humidity environment. It can be used for applications that require high reliability.

  Next, the best mode for carrying out the invention will be described by way of examples. However, the scope of the present invention is not limited to the examples.

Example 1
(Preparation of coating solution)
As insulating resins, bisphenol A type solid epoxy resin [Epicoat 1256, manufactured by Japan Epoxy Resin Co., Ltd.], bisphenol A type liquid epoxy resin [Epicron 850, manufactured by Dainippon Ink & Chemicals, Inc.], bisphenol A type episulfide Resin [manufactured by Japan Epoxy Resin Co., Ltd., Epicoat YL7000], microcapsule type imidazole-based curing agent [manufactured by Asahi Kasei Epoxy Co., Ltd., Novacure HX3941] is used at a weight ratio of 50/40/10/10, These were dissolved in cyclohexanone to prepare a resin composition solution having a solid content of 50%. Furthermore, as the conductive particles, acicular nickel particles having a chain length distribution of 5 μm to 22 μm (nickel fine particles having an average particle diameter of 200 nm connected in a needle shape, aspect ratio: 15 to 55) are added to the total amount of solids ( (Resin composition + inorganic filler + nickel powder) was added so as to be 1% by volume, and uniformly dispersed by stirring using a centrifugal mixer to prepare a coating solution for an adhesive.

(Production of adhesive for circuit connection)
The coating solution prepared above is applied onto a release-treated PET film using a doctor knife, and then dried and solidified at 60 ° C. for 30 minutes in a magnetic field with a magnetic flux density of 100 mT to form a film having a thickness of 25 μm. An adhesive for circuit connection was obtained.

(Connection resistance evaluation)
A flexible printed circuit board in which 240 gold-plated circuits having a width of 25 μm and a height of 9 μm were arranged at intervals of 25 μm and a glass substrate having an ITO film formed on the entire surface were prepared. The flexible printed circuit board is sandwiched between the flexible printed circuit board and the glass substrate, and heated and bonded at a pressure of 4 MPa for 15 seconds while being heated to 200 ° C. And a bonded body of the glass substrate were obtained. The resistance value between two adjacent circuits connected via the circuit connecting adhesive and the ITO film was measured, and 1/2 of the value was defined as the connection resistance in the thickness direction. 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 60 ° C. and a humidity of 90%, taken out after 100 hours, and the average value of connection resistance was obtained again in the same manner as described above. .

(Measurement of water absorption)
With respect to the above-mentioned circuit connection adhesive that was completely cured by treatment at 200 ° C. for 1 hour, first, the initial weight (M1) was measured, and the weight (M2) after being left at 30 ° C. and 90% RH for 100 hours was measured. . From these measurement results, the water absorption was determined based on the following formula [1].
Water absorption rate (% by weight) = [(M2−M1) / M1] × 100 [1]

(Life assessment)
For the above-mentioned circuit connection adhesive from which the solvent was removed under vacuum at 40 ° C. so that the curing reaction does not proceed, the melt viscosity from 50 ° C. to 200 ° C. was measured using a viscoelasticity measuring device (ARES manufactured by Rheometric Co., Ltd.). The minimum value was obtained. Further, after the sample was stored at 4 ° C. for 1 month, the same evaluation was performed, and a sample having an increase rate of the minimum value of the melt viscosity of less than 1000% was judged as ◯, and a sample having 1000% or more was judged as ×.

(Example 2)
As an insulating resin, bisphenol A type solid epoxy resin [Japan Epoxy Resin Co., Ltd., Epicoat 1256], bisphenol A type liquid epoxy resin [Dainippon Ink Chemical Co., Ltd. Epicron 850], bisphenol A type episulfide Resin [manufactured by Japan Epoxy Resin Co., Ltd., Epicoat YL7000], microcapsule type imidazole curing agent [manufactured by Asahi Kasei Epoxy Co., Ltd., Novacure HX3941] is used at a weight ratio of 40/10/50/10, These were dissolved in cyclohexanone to prepare a resin composition solution having a solid content of 50%. Except for the above, a film-like adhesive for circuit connection having a thickness of 25 μm was prepared in the same manner as in the Examples, and connection resistance evaluation, heat and humidity resistance test, water absorption rate measurement, and life evaluation were performed.

(Comparative Example 1)
As insulating resins, bisphenol A type solid epoxy resin [Epicoat 1256, manufactured by Japan Epoxy Resin Co., Ltd.], bisphenol A type liquid epoxy resin [Epicron 850, manufactured by Dainippon Ink & Chemicals, Inc.] and microcapsule type imidazole type A film-like adhesive for circuit connection having a thickness of 25 μm in the same manner as in the Examples except that a curing agent [NOVACURE HX3941 manufactured by Asahi Kasei Epoxy Co., Ltd.] was used at a weight ratio of 50/50/10. The connection resistance evaluation, the heat and humidity resistance test, the water absorption rate measurement, and the life evaluation were performed. The results are shown in Table 1.

  The results in Table 1 show that the water absorption is low when bonded using the circuit connecting adhesive of the present invention (Example), and the connection resistance value is high even when placed in a high temperature and high humidity environment for a long time. The increase is small, indicating that excellent heat and moisture resistance can be achieved. In Example 2 in which the same amount of episulfide resin as that of the epoxy resin was blended, the water absorption rate and the resistance increase rate were good, but it was somewhat difficult in terms of storage stability. On the other hand, in Comparative Example 1 in which only the epoxy resin and the latent curing agent were used as the insulating resin without using the episulfide resin, the water absorption was about 1.3 times that of Example 1, and in the heat and humidity resistance test. The rate of increase in resistance is also large. As is apparent from this result, by using the circuit connecting adhesive of the present invention example, excellent heat and humidity resistance can be achieved, and high reliability can be obtained.

Claims (5)

(1) Epoxy resin (2) Episulfide resin (3) Latent curing agent (4) Adhesive for circuit connection containing conductive particles as essential components.   The adhesive for circuit connection according to claim 1, wherein the amount of the episulfide resin is 1 wt% or more and less than 50 wt% of the total weight of the epoxy resin.   The adhesive for circuit connection according to claim 1 or 2, wherein the episulfide resin is a bisphenol type episulfide resin.   The adhesive for circuit connection according to any one of claims 1 to 3, wherein the conductive particles are metal particles having a diameter to length ratio (aspect ratio) of 5 or more.   5. The adhesive for circuit connection according to claim 4, wherein the shape is a film shape, and the conductive particles are oriented in the thickness direction of the film.