JP2005146043A - Anisotropic conductive adhesive - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an anisotropic conductive adhesive capable of highly reliable connection of electrodes of IC chips and circuit boards to be miniaturized.
SOLUTION: An epoxy resin, a curing agent, conductive particles, and a cured epoxy resin that has undergone a partial curing reaction, and a minimum melt viscosity of 400 Pa · s or more and 50000 Pa within a range of 50 ° C. to 200 ° C. A conductive layer that is less than or equal to s, and is laminated on at least one side of the conductive layer, and the minimum value of the melt viscosity is not more than 1/2 of the value that the conductive layer exhibits in the range of 50 ° C. to 200 ° C. An anisotropic conductive adhesive characterized by having an insulating layer. The conductive particles used are preferably linear or needle-shaped.
[Selection figure] None

Description

  The present invention relates to an anisotropic conductive adhesive that is used for connecting a circuit board and an IC chip to be mounted at high density, and that is less likely to cause a short circuit between electrodes even in a fine pitch circuit.

  As electronic devices become lighter and smaller, component parts are rapidly becoming smaller. As a result, the circuit (pitch) of each part and the distance between the electrodes are reduced, and recently, they are close to a few tens of μm. In order to join such circuits and electrodes without causing a short circuit, it is becoming difficult to use an anisotropic conductive film conventionally used.

  As the anisotropic conductive adhesive, one that is once bonded and then fixed by hardening or the like of the adhesive is used. For example, in an operation such as connecting the circuit board and the electrode of the IC chip, an anisotropic conductive adhesive is interposed between the circuit board and the IC chip, and the circuit board and the IC chip are connected by heating and pressing. At this time, the anisotropic conductive adhesive flows, but at the same time, the conductive substance contained in the adhesive may flow, and the conductive substance that should remain between the electrodes of the IC and the circuit board. May flow with the adhesive. If it becomes such a situation, it will become poor conduction between the electrodes, and the role of an anisotropic conductive adhesive cannot be fulfilled.

As a means for solving this problem, a layer containing a conductive substance and an insulating adhesive layer on the outside thereof are provided, and the melt viscosity at 150 ° C. of the layer containing the conductive substance is 100 poise or more. There is a disclosure of a multilayer anisotropic conductive adhesive having a multilayer structure having a melt viscosity at 100 ° C. of less than 100 poise (see Patent Document 1). In this way, when the temperature rises, the insulating adhesive layer first melts and flows, and by filling the gap around the electrodes of the IC and the circuit board, the layer containing the conductive particles flows due to further temperature rise. Therefore, the conductive particles can prevent the conductive particles from flowing out.
JP 2000-178511 A, (0012)

  However, even the means of Patent Document 1 cannot be said to be sufficient, and further solution means is required in terms of fluidity. In particular, if the fluidity is too high, when using anisotropic conductive adhesive at the desired bonding temperature, the adhesive may flow out to the surroundings and affect adjacent electrodes or circuits. It is considered necessary to control the fluidity of the resin. In addition, a certain balance is required between the fluidity of the layer containing a conductive substance and the fluidity of the insulating layer.

  The present invention embodies the above concept. That is, it includes an epoxy resin, a curing agent, conductive particles, and a cured epoxy resin that has undergone a partial curing reaction, and the minimum value of the melt viscosity is within a range of 50 ° C. to 200 ° C. The conductive layer is laminated on at least one side of the conductive layer, and the minimum value of the melt viscosity is not more than ½ of the value indicated by the conductive layer in the range of 50 ° C. to 200 ° C. An anisotropic conductive adhesive comprising an insulating layer. Thus, if the relationship between the fluidity of the conductive layer, which is a conductive layer containing conductive particles, and the flow conductivity of the insulating layer containing no conductive substance are within the above range, the anisotropic conductive adhesive is At the time of heating and flowing, the insulating layer first flows to fill the space between the electrodes, and the subsequent heating causes the conductive layer containing the conductive material to flow. At this time, the insulating layer already fills the space between the electrodes and is in the curing process, and even if the conductive layer flows, no large flow occurs. The balance is that the minimum value of the melt viscosity of the insulating layer at 50 ° C. to 200 ° C. is ½ or less of the minimum value of the melt viscosity of the conductive layer at 50 ° C. to 200 ° C.

In the invention, in order to control such adhesion, it is particularly preferable to use an epoxy resin, and as a means for adjusting fluidity, an epoxy resin that has already been cured is added. The cured epoxy resin is preferably added after the epoxy resin is once cured and then pulverized and powdered.
Further, with respect to the conductive layer, when the minimum value of the melt viscosity at 50 ° C. to 200 ° C. of the insulating layer is 1/2 or more, the flow of the conductive layer starts in a state where the insulating layer does not sufficiently flow, The flow range of the conductive layer is undesirably increased.
And it is preferable in the minimum value of the melt viscosity in 50 to 200 degreeC of the said insulating layer being 10 Pa.s or more. If it is less than 10 Pa · s, the fluidity at the time of melting is too good, so that the insulating layer material easily flows out to the surroundings. The resin used for the insulating layer is also preferably an epoxy resin from the viewpoint of adhesion and compatibility with the conductive layer.

  The epoxy resin cured product is selected from the group consisting of a bisphenol A type, F type or S type epoxy resin and an imidazole type, amine type, dicyandiamide type, melamine type, ketimine type, acid anhydride type and phenol type 1 It is more preferable that it is a partly cured reaction with at least one type of curing agent. In general, the alicyclic epoxy resin is insufficient in heat resistance, and the phenol novolac type epoxy is poor in solubility in a solvent. Therefore, in the present invention, the bisphenol-based epoxy resin is preferred.

It is very preferable that the conductive particles are oriented in the thickness direction of the conductive layer, because short circuit between adjacent electrodes hardly occurs.
It is preferable that the conductive particles have a shape in which a large number of fine metal particles are connected in a straight chain or a needle shape. In the case of such a shape, it becomes a preferable choice especially by combining the operations of the orientation.
When the conductive particles are selected from one of a simple metal having magnetism, two or more kinds of alloys having magnetism, an alloy of a metal having magnetism with another metal, and a composite containing a metal having magnetism ,preferable. This is because the metal having magnetism attracts each other so that the conductive material is likely to gather in the conductive material sandwiched between the electrodes during the melt flow. Further, it is preferable because an alignment operation by magnetic force can be performed.

The conductive particles have a shape in which a large number of fine metal particles are connected in a straight chain, the thickness of the chain is 50 nm or more and 1 μm or less, and the particles have an aspect ratio of 10 or more and include 50% or more. It is preferable. If the conductive layer is oriented in the thickness direction, a strong conductive circuit can be formed when it is sandwiched between electrodes in the conductive layer even if it is pressurized in the thickness direction.
Furthermore, when the thickness of the conductive layer is equal to or less than the length of the conductive particles, the conductive particles exist in a state of penetrating the conductive layer, and therefore, the state sandwiched between the electrodes when the insulating layer flows Thus, even when the conductive layer flows, it is preferable because the conductive particles remain without flowing.

  The anisotropic conductive adhesive according to the present invention has good conductivity for bonding fine pitch circuit boards, IC chips and the like, and suppresses leakage to adjacent electrodes due to moderately adjusted melt fluidity. The preferred anisotropic conductive adhesive.

  The anisotropic conductive adhesive according to the present invention is an epoxy resin cured product in which a curing reaction has partially progressed to an epoxy resin used for a conductive layer containing conductive particles in order to increase the minimum value of melt viscosity at the time of use. There is one feature in adding.

  Usually, in order to increase the minimum value of the melt viscosity of the resin in a certain temperature range, a curing agent that starts to react at a low temperature is used, but in this case, the storage stability is deteriorated. As another measure, a means for increasing the molecular weight of the resin is also conceivable. However, since the heat softening point after adhesion is lowered, a sufficient thickening effect cannot be obtained.

In the present invention, the epoxy resin as the main material of the conductive layer is reacted in advance with a curing agent, and the resin after the reaction is dissolved in a solvent, or the resin after the reaction is crushed and dissolved in the solvent, A polymerized resin solution is prepared, and an unreacted epoxy resin, a curing agent, and conductive particles are added thereto to prepare a solution, which is spread into a film and dried. The film-like conductive layer produced in this way has a high heat softening temperature of the epoxy resin cured product to be added, and the minimum melt viscosity value can be greatly increased with a small amount of addition, which also affects the adhesion. Does not affect.
That is, the minimum value of the melt viscosity at 50 ° C. to 200 ° C. of the conductive layer can be adjusted by the amount of the epoxy resin cured product used, so that the insulating layer used in combination as the anisotropic conductive adhesive has a temperature of 50 ° C. to 200 ° C. The minimum value of the melt viscosity at 0 ° C. can be selected as appropriate.

If the melt viscosity of the resin used for the insulating layer is too low, it will flow and spread on the substrate, and the resin layer will be formed to an unnecessary range. Therefore, it is preferable to select a resin having a viscosity of 10 Pa · s or more.
Preferably, the minimum value of the melt viscosity is selected according to the use temperature. Then, what is necessary is just to adjust the minimum value of the said melt viscosity of resin used for an electroconductive layer, and to make it the resin compound which has a melt viscosity 2 times or more than the melt viscosity of an insulating layer.

  In order to produce the cured epoxy resin used here, it is preferable to use a bisphenol A type, F type or S type epoxy resin as the epoxy resin. And as a hardening | curing agent to be used, it is good to select 1 or more types chosen from the group which consists of an imidazole type | system | group, an amine type, a dicyandiamide type | system | group, a melamine type | system | group, a ketimine type | system | group, an acid anhydride type | system | group, and a phenol type. In particular, an imidazole system is preferably used.

  Moreover, as an epoxy resin used for this invention, the bisphenol-type resin used for the above-mentioned epoxy resin hardened | cured material can be used suitably. Moreover, as a hardening | curing agent, although the hardening | curing agent used for the above-mentioned epoxy resin hardened | cured material can be used, since it does not make sense when it hardens while drying after mixing electroconductive particle, it is an adhesive agent. For the purpose of reacting in the vicinity of the use temperature, a microencapsulated curing agent can be preferably used. As the kind of the curing agent, an imidazole-based curing agent capsule used in the above-described epoxy cured product can be suitably used.

On the other hand, as the conductive particles, metal powder can be used, but preferably, a shape having a large number of fine metal particles, linearly connected, or a needle shape, a so-called aspect ratio large shape is preferable. .
These particles are preferably used by being oriented in the thickness direction by passing through a magnetic field applied in the thickness direction at the time of forming the conductive layer.
Accordingly, the metal powder to be used preferably contains a magnetic metal in part, and has a magnetic simple substance, two or more kinds of alloys having magnetism, an alloy of magnetism metal and another metal, and magnetism. It is preferably one of composites containing a metal.

Particularly preferably, the conductive particles have a shape in which a large number of fine metal particles are connected in a straight chain, the chain thickness is 50 nm or more and 1 μm or less, and the aspect ratio is 10 or more. What contains more than% is good. If the chain thickness is less than 50 nm, the length effect cannot be obtained if the chain is broken by an external force during the manufacturing process. On the other hand, when the thickness exceeds 1 μm, a large metal particle powder is produced, which affects the dispersibility. When the aspect ratio is less than 10, the orientation effect is small when the film is oriented in the film thickness direction.
More preferably, the thickness is adjusted so that the thickness of the conductive layer is equal to or less than the length of the conductive particles. Alternatively, a chain metal powder longer than the desired thickness of the conductive layer may be used.
The metal powder having a shape in which a number of fine metals are connected in a chain form is a wet reduction method using tetravalent titanium ions as a reducing agent in the presence of trivalent titanium ions and using citric acid or the like as a cluster. Can be obtained.

  By the above combination, the anisotropic conductive adhesive of the present invention has a large electric resistance between adjacent electrodes even when it is used between an electronic circuit having a circuit pitch of about a dozen μm or between electrodes, and an electrode to be bonded. The conduction resistance between them is sufficiently small.

Examples are given below, but the present invention is not limited to the examples.
(Example)
(Preparation of Solution) As the conductive particles, linear nickel powder having a length distribution from 3 μm to 15 μm was used. As the resin for the conductive layer, two types of epoxy resins [manufactured by JER Corporation, trade name Epicoat 1010 (molecular weight about 5500) and trade name Epicoat 828 (molecular weight about 380)] are used, and the microcapsule type is used as the curing agent. A curing agent [trade name NOVACURE HX3941 manufactured by Asahi Kasei Epoxy Co., Ltd.] was used. The above weight ratio was set to a ratio of 70/30/10. The epoxy resin cured product includes two types of epoxy resins (trade name Epicoat 1010 (molecular weight about 5500) and trade name Epicoat 1001 (molecular weight about 900) manufactured by JER Corporation), and an imidazole-based curing agent [Shikoku Chemicals Co., Ltd. Industrial Co., Ltd. trade name Curesol 2MA-OK] was mixed at a weight ratio of 50/50/5 and heated in a thermostatic bath at 200 ° C. for 1 hour.

These epoxy resin blends and epoxy cured products are blended at a ratio of 80/20, dissolved in a mixed solvent of butyl acetate, methyl isobutyl ketone and toluene in a weight ratio of 55/25/20, and mixed using a three-roll. A solution having a resin concentration of 40% by weight was obtained.
To this solution, the Ni powder was added so that the metal filling rate represented by the ratio of the total solid content (Ni powder + resin) was 0.5% by volume, and then stirred using a centrifugal stirring mixer. As a result, Ni powder was uniformly dispersed to prepare a solution for the conductive layer.
Separately, for the insulating layer, the cured epoxy resin and an epoxy resin solution to which Ni powder was not added were prepared.

  (Preparation of anisotropic conductive film) After applying the solution for the conductive layer prepared above onto a PET film subjected to a release treatment using a doctor knife, in a magnetic field with a magnetic flux density of 100 mT at 80 ° C for 30 minutes, After drying and solidifying, a conductive layer having a thickness of 12 μm in which the linear particles in the film were oriented in the magnetic field direction was obtained. The insulating layer solution was applied thereon, and again dried and solidified at 80 ° C. for 30 minutes to produce an anisotropic conductive adhesive having a target total thickness of 25 μm.

(Measurement of melt viscosity) The solvent of the solution for the conductive layer is removed under vacuum at 40 ° C. so that the curing reaction does not proceed, a 500 μm-thick film is produced, and a viscoelasticity measuring apparatus (ARES manufactured by Rheometric Co., Ltd.) is used. The melt viscosity from 50 ° C. to 200 ° C. was measured, and the minimum value was determined.
Similarly, the solvent of the solution for the insulating tank is removed under vacuum at 40 ° C. so that the curing reaction does not proceed, a film having a thickness of 500 μm is produced, and from 50 ° C. using a viscoelasticity measuring apparatus (ARES manufactured by Rheometric Co., Ltd.). The melt viscosity up to 200 ° C. was measured and the minimum value was determined.
Table 1 shows the lowest melt viscosity obtained.

(Comparative Example 1)
Two types of epoxy resins (trade name Epicoat 1010 (molecular weight about 5500) and trade name Epicoat 828 (molecular weight about 380) manufactured by JER) and microcapsule type curing agent [Asahi Kasei Epoxy Co., Ltd. An anisotropic conductive adhesive having a total thickness of 25 μm was produced in the same manner as in the example except that the weight ratio with the product name NOVACURE HX3941 manufactured by Co., Ltd. was used at a ratio of 95/5/5. In this insulating layer, the minimum value of the melt viscosity in the same temperature range exceeds 1/2 with respect to the minimum value of the melt viscosity at 50 ° C. to 200 ° C. of the conductive layer.

(Comparative Example 2)
Two types of epoxy resins (trade name Epicoat 1256 (molecular weight of about 50,000) and trade name Epicoat 828 (molecular weight of about 380) manufactured by JER Corporation) as a resin for the conductive layer, and a microcapsule type curing agent [ Asahi Kasei Epoxy Co., Ltd. product name Novacure HX3941] was used at a ratio of 70/30/10 in weight ratio (no epoxy cured product added), and the total thickness was 25 μm. An anisotropic conductive adhesive was prepared.

(Comparative Example 3)
As the resin for the conductive layer, two kinds of epoxy resins [Epicoat 1256 (molecular weight of about 50,000) and 828 (molecular weight of about 380) manufactured by JER Co., Ltd.] and a microcapsule type curing agent [Novacure HX3941 manufactured by Asahi Kasei Epoxy Co., Ltd.] ] At a ratio of 70/30/10 by weight (no epoxy cured product added), gold-plated resin particles having a diameter of 5 μm were used as the conductive particles, and the resin + conductive particles were taken as 100. An anisotropic conductive adhesive having a total thickness of 25 μm was prepared in the same manner as in the example except that 10% by volume was added.

The above Examples and Comparative Examples 1 to 3 were evaluated as anisotropic conductive adhesives.
(Resistance evaluation)
An IC chip in which 700 Au 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 a transparent conductive circuit (ITO) was formed with the same line width were prepared. The anisotropic conductive adhesives produced in Examples and Comparative Examples were sandwiched between the IC chip and the circuit board, and were heated and bonded at a pressure of 30 gf per bump for 15 seconds while being heated to 200 ° C.
And the circuit resistance value including the conductor resistance between the continuous 480 electrodes conductively connected through the ITO electrode, the anisotropic conductive adhesive and the Au bump was measured. The results are shown in Table 1.

(Adhesive strength evaluation)
An IC chip in which 700 Au 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 an ITO glass plate on which no circuit was formed were prepared. The anisotropic conductive adhesives produced in Examples and Comparative Examples were sandwiched between the IC chip and the glass plate, and were heated and bonded at a pressure of 30 gf per bump for 15 seconds while being heated to 200 ° C. Thereafter, the adhesive strength was measured using a shear strength tester (2400PC manufactured by Daisy). The obtained results are shown in Table 1.

As shown in Table 1, when the example which is an example of the present invention is used as an anisotropic conductive adhesive, the adhesive strength is good and the connection resistance is also small. In Comparative Example 1, since the minimum value of the melt viscosity at the time of adhesion is that of the insulating layer is larger than ½ of the value of the conductive layer, the connection between the electrodes is not preferable, and the connection resistance is increased. In Comparative Example 2 in which the epoxy resin cured product is not blended in the conductive layer, the appearance at the time of adhesion is good as a result of using a polymer epoxy resin in order to increase the melt viscosity of the conductive layer. Decreases and the contact resistance increases. Further, in Comparative Example 3, in contrast to the result of Comparative Example 2, the conductive particles used in the conductive layer were replaced with linear nickel powder, and gold-plated resin particles having a diameter of 5 μm were used. is there. Although the minimum value of the melt viscosity of the conductive layer at 50 ° C. to 200 ° C. increases because it contains a large amount of conductive particles, the contribution to the adhesiveness decreases, so the adhesive strength decreases. In addition, since the minimum value of the melt viscosity is large, the fluidity of the conductive particles is not preferable, and it is difficult to contact each other, so that the connection resistance is increased.
As described above, the anisotropic conductive adhesive according to the present invention provides a reliable connection for the connection of fine pitch circuit boards and IC chips. In particular, the effect is improved by orienting the conductive particles contained in the conductive layer.

Claims (8)

  An epoxy resin, a curing agent, conductive particles, and a cured epoxy resin that has undergone a partial curing reaction, with a minimum melt viscosity of 400 Pa · s or more and 50000 Pa · s or less within a range of 50 ° C. to 200 ° C. A conductive layer and an insulating layer laminated on at least one side of the conductive layer, and having a minimum melt viscosity within a range of 50 ° C. to 200 ° C. and not more than ½ of the value indicated by the conductive layer An anisotropic conductive adhesive comprising:   The epoxy resin cured product is selected from the group consisting of a bisphenol A type, F type or S type epoxy resin and an imidazole type, amine type, dicyandiamide type, melamine type, ketimine type, acid anhydride type and phenol type 1 The anisotropic conductive adhesive according to claim 1, which is partially cured by a curing agent of at least one species.   The anisotropic conductive adhesive according to claim 1 or 2, wherein the conductive particles are oriented in the thickness direction of the conductive layer.   The anisotropic conductive adhesive according to any one of claims 1 to 3, wherein the conductive particles have a shape in which a large number of fine metal particles are connected in a straight chain or a needle shape.   The conductive particles are any one of a simple metal having magnetism, two or more kinds of alloys having magnetism, an alloy of a metal having magnetism with another metal, and a composite containing a metal having magnetism. 4. An anisotropic conductive adhesive according to any one of 4 above.   The conductive particles have a shape in which a large number of fine metal particles are connected in a straight chain, the thickness of the chain is 50 nm or more and 1 μm or less, and the particles have an aspect ratio of 10 or more and include 50% or more. The anisotropic conductive adhesive according to claim 5.   The anisotropic conductive adhesive according to claim 6, wherein a thickness of the conductive layer is equal to or less than a length of the conductive particles.   The anisotropic conductive adhesive according to claim 1, wherein a minimum value of melt viscosity at 50 ° C. to 200 ° C. of the insulating layer is 10 Pa · s or more.