JP2005146044A - Anisotropic conductive adhesive - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an anisotropic conductive adhesive which can connect electrodes to fine IC chips and circuit boards in high reliability. <P>SOLUTION: This anisotropic conductive adhesive is characterized by having a conductive layer which is obtained by reacting a composition comprising an epoxy resin, conductive particles, and two kinds of curing agents having different curing-initiating temperatures, at a temperature near to the reaction temperature of the curing agent reacting at the lower temperature among the curing agents, and has the lowest melt viscosity of 400 to 50,000 Pa×s in a range of 50 to 200°C, and an insulating layer which is laminated to at least one side of the conductive layer and has the lowest melt viscosity of one half or lower based on that of the conductive layer in a range of 50 to 200°C. The conductive particles have preferably a linear shape or a needle-like shape. <P>COPYRIGHT: (C)2005,JPO&NCIPI

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 solution to this problem, a layer containing a conductive substance and an insulating adhesive layer are provided on the outside thereof, 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 is an invention that provides a solution to the fluidity. The content is an anisotropic conductive adhesive comprising a conductive layer and an insulating layer laminated on at least one side of the conductive layer, the conductive layer comprising an epoxy resin, conductive particles, and curing initiation The minimum value of the melt viscosity obtained by reacting a composition containing two types of curing agents having different temperatures near the reaction temperature of the curing agent that reacts on the low temperature side among the curing agents is 50 ° C to 200 ° C. In the range of 400 Pa · s to 50000 Pa · s, the insulating layer has a minimum melt viscosity of the value indicated by the conductive layer in the range of 50 ° C. to 200 ° C. An anisotropic conductive adhesive characterized by being 1/2 or less.

  That is, by containing two kinds of curing agents having different curing temperatures in the epoxy resin used for the conductive layer, and reacting with a curing agent that cures on the low temperature side among the curing agents when the anisotropic conductive film is formed. The minimum value of the melt viscosity is increased in the range of 50 ° C to 200 ° C. When the melt viscosity is less than 400 Pa · s, the resin flows faster when used as an anisotropic conductive adhesive, and accordingly, the conductive particles contained in the composition also flow and remain between the electrodes. The amount of conductive particles is reduced. On the other hand, if the melt viscosity exceeds 50000 Pa · s, the resin does not flow at all even if pressure is applied, and the particles remain embedded in the resin, resulting in poor conduction.

  Moreover, if the fluidity of the insulating layer is too large in the range of 50 ° C. to 200 ° C., the fluid may flow out of the parts as soon as possible. Cannot be secured. Then, in order to make the flow proceed according to the fluidity of the conductive layer containing the conductive particles, it is preferable to set it to ½ or less of the minimum value of the melt viscosity in the conductive layer. If it exceeds 1/2, the flow of the conductive layer starts to flow before the insulating layer sufficiently flows, so that the adhesive force as the insulating layer cannot be sufficiently exhibited.

  The insulating layer preferably has a minimum melt viscosity of 10 Pa · s or more in the range of 50 ° C. to 200 ° C. If it is less than 10 Pa · s, it is difficult to balance the fluidity of the conductive layer, and the possibility of outflow from the circuit board or IC chip to be bonded increases. And also in an insulating layer, it is preferable to use an epoxy resin from a compatible viewpoint with adhesiveness, heat resistance, and an electroconductive layer.

  The epoxy resin is a bisphenol A type, F type or S type epoxy resin, and the curing agent that reacts on the low temperature side is an imidazole type, an amine type, a dicyandiamide type, a melamine type, a ketimine type, an acid anhydride type, and It is more preferable that it is at least one curing agent selected from the group consisting of phenols. In general, the alicyclic epoxy resin is insufficient in heat exploration, 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.
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.

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 has a curing temperature in the epoxy resin used for the conductive layer in order to increase the minimum value of the melt viscosity at the time of use of the epoxy resin used in the conductive layer containing the conductive particles. One characteristic is that two different kinds of curing agents are added. And the hardening | curing agent which raise | generates hardening reaction on the low temperature side among this hardening | curing agent makes 50 degreeC-200 of an electroconductive layer by advancing hardening reaction, when extending and drying an electroconductive layer in a film form. The minimum value of the melt viscosity in the range of ° C. can be set to 400 Pa · s or more and 50000 Pa · s or less. By having such characteristics, when the conductive layer is used as an anisotropic conductive adhesive, it is suppressed to flow quickly, and the fluidity that can fully exhibit the adhesive effect after flowing is assumed. is there.

  In addition, the insulating layer flows before the conductive layer flows, and has a role of filling between adjacent electrodes arranged on a circuit board, an IC chip, etc., and is strong by filling the gap. Gives an adhesive force. Therefore, it is necessary to make the minimum value of the melt viscosity smaller than that of the conductive layer in the temperature range of 50 ° C. to 200 ° C. at the time of bonding. It has been found that good results can be obtained if it is 1/2 or less of the minimum value.

If the minimum value of the melt viscosity in 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 one having 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.

  The epoxy resin used here is preferably 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.

  As the curing agent used in the present invention, the above-described curing agent for epoxy resin can be used. In the conductive layer, after mixing the conductive particles, the temperature is low among the two types of curing agents. Since the curing agent that reacts on the side needs to react, it is preferable to use a curing agent that reacts near the drying temperature of 100 ° C. As the curing agent that reacts on the high temperature side, a microencapsulated curing agent can be suitably used for the purpose of reacting near the use temperature as an adhesive.

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 fine particles having a chain length distribution from 3 μm to 15 μm were used. As the resin for the conductive layer, there are two kinds of epoxy resins (manufactured by JER Corporation, trade name Epicoat 1010 (molecular weight about 5500) and trade name Epicoat 828 (molecular weight about 380)), and two kinds of curing agents [Ajinomoto Fine Co., Ltd. Techno Co., Ltd., trade name Amicure PN-23J and Asahi Kasei Epoxy Co., Ltd., trade name NovaCure HX3941] were used at a weight ratio of 70/30/1/9.

  These resins and curing agents were dissolved in a mixed solvent of butyl acetate, methyl isobutyl ketone, and toluene in a weight ratio of 55/25/20 and mixed with three rolls to obtain a solution having a resin concentration of 40% by weight. 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.

  In addition, the insulating layer solution includes 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)), and a microcapsule type curing agent [Asahi Kasei. A resin using a weight ratio of 70/30/10 with Epoxy Co., Ltd. trade name NOVACURE HX3941] was dissolved in a mixed solvent of butyl acetate, methyl isobutyl ketone and toluene in a weight ratio of 55/25/20. Made.

  (Preparation of anisotropic conductive adhesive) After applying the solution for the conductive layer prepared above onto a PET film subjected to a release treatment using a doctor knife, it was 30 at 80 ° C. in a magnetic field with a magnetic flux density of 100 mT. The thickness of the linear particles in the film oriented in the direction of the magnetic field by proceeding with the curing reaction only for the low temperature side curing agent Amicure by removing the solvent by drying for 1 minute and then heating at 100 ° C. for 1 hour. A 12 μm conductive layer was obtained. The insulating layer solution was applied to one side, and again dried and solidified at 80 ° C. for 30 minutes, thereby producing an anisotropic conductive adhesive having a target total thickness of 25 μm.

(Measurement of Melt Viscosity) For the two types of solutions described above, the solvent was removed under vacuum at 40 ° C. so that the curing reaction would not proceed. The melt viscosity was measured and the minimum value was determined. The results obtained, including the results of the solutions used in the comparative examples described below, are shown in Table 1.

(Comparative Example 1)
As the resin for the insulating layer, two kinds of epoxy resins [trade name Epicoat 1010 (molecular weight about 5500) and trade name Epicoat 828 (molecular weight about 380) manufactured by JER Ltd.] and a curing agent that reacts on the high temperature side as a curing agent The same as in the examples except that the weight ratio of the microcapsule type curing agent [trade name NovaCure HX3941 manufactured by Asahi Kasei Epoxy Co., Ltd.] is 95/5/5, and only one curing agent is used. An anisotropic conductive adhesive having a total thickness of 25 μm was prepared. 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)
As a resin for the conductive layer, it is a curing agent that reacts with 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) on the high temperature side. , Using a microcapsule type curing agent [trade name Novacure HX3941 manufactured by Asahi Kasei Epoxy Co., Ltd.] at a weight ratio of 70/30/10, and polymerizing the epoxy resin, and one type of curing agent. Except for this, an anisotropic conductive adhesive having a total thickness of 25 μm was prepared in the same manner as in the example.

(Comparative Example 3)
A microcapsule that is a curing agent that reacts with two types of epoxy resins (trade name Epicoat 1256 (molecular weight of about 50,000) and 828 (molecular weight of about 380) manufactured by JER Corporation) on the high temperature side as the resin of the conductive layer Mold curing agent [NOVACURE HX3941 manufactured by Asahi Kasei Epoxy Co., Ltd.] was used in a weight ratio of 70/30/10, that is, a high molecular weight epoxy resin was used, and one type of curing agent was used. In addition, an anisotropic conductive adhesive having a total thickness of 25 μm was prepared in the same manner as in the example except that gold-plated resin particles having a diameter of 5 μm were used as the conductive particles.

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. Comparative Example 2 which does not use two kinds of curing agents in the conductive layer uses a high molecular weight epoxy resin in order to increase the melt viscosity of the conductive layer. Decreases and the contact resistance also 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 anisotropic conductive adhesive comprising a conductive layer and an insulating layer laminated on at least one side of the conductive layer, wherein the conductive layer is different in epoxy resin, conductive particles, and curing start temperature 2 Within the range of the minimum value of the melt viscosity obtained by reacting a composition containing a kind of curing agent near the reaction temperature of the curing agent that reacts on the low temperature side among the curing agents, within a range of 50 ° C to 200 ° C The insulating layer has a characteristic of 400 Pa · s or more and 50000 Pa · s or less, and the insulating layer has a minimum melt viscosity within a range of 50 ° C. to 200 ° C. and is ½ or less of the value of the conductive layer. An anisotropic conductive adhesive, characterized in that   The epoxy resin is a bisphenol A type, F type or S type epoxy resin, and the curing agent that reacts on the low temperature side is an imidazole type, an amine type, a dicyandiamide type, a melamine type, a ketimine type, an acid anhydride type, and The anisotropic conductive adhesive according to claim 1, which is one or more curing agents selected from the group consisting of phenols.   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 1 or 2.   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.