HK1156963B - Anisotropic electroconductive adhesive and method for manufacturing connected structure using the anisotropic electroconductive adhesive - Google Patents

Description

Anisotropic conductive adhesive and method for producing connection structure using the same

Technical Field

The present invention relates to an anisotropic conductive adhesive in which conductive particles are dispersed in an insulating adhesive component, and a method for producing a connection structure using the same.

Background

Conventionally, in the fog (film on glass) bonding of bonding a glass substrate and a Flexible Printed circuit board (FPC), a terminal electrode of the glass substrate and a terminal electrode of the Flexible Printed circuit board are arranged to face each other via an anisotropic conductive adhesive, and the anisotropic conductive adhesive is heated and cured by a heating device (heating ツ - ル) while pressing the terminal electrodes to electrically connect the two terminal electrodes (terminals) together (patent document 1).

However, the linear expansion coefficient of the polyimide resin (10 to 40X 10) is generally used as a substrate for a flexible printed circuit board^-6/° c) is greater than the linear expansion coefficient of glass (about 8.5 x 10)^-6/° c), the degree of expansion (expansion) of the flexible printed circuit board due to heat of a heating device at the time of FOG bonding is larger than that of the glass substrate, so that dimensional variations occur in the terminal electrodes of the two substrates, and sufficient electrical connection tends to be difficult if the pitch of the terminal electrodes is reduced.

Therefore, it is practical to form the designed intervals of the terminal electrodes of the flexible printed circuit board at intervals smaller than the designed intervals (sometimes referred to as prescribed intervals) of the corresponding terminal electrodes of the glass substrate in advance, and then expand the specified intervals by heat emitted from a heating device at the time of curing the anisotropic conductive adhesive by heating, thereby suppressing dimensional deviation between the terminal electrodes of the flexible circuit and the glass substrate.

Documents of the prior art

Patent document

Patent document 1: japanese patent No. 3477367

Disclosure of Invention

Problems to be solved by the invention

However, when the design interval of the post electrodes of the flexible printed circuit board is formed narrower than the prescribed interval, if the operating conditions of the heating equipment at the time of FOG bonding are slightly deviated in each FOG bonding or the operating conditions of the heating equipment are slightly changed according to the need in the production, there is a case where good electrical connection cannot be achieved by the anisotropic conductive adhesive.

In this case, it is conceivable that in order to prevent or suppress the post of the anisotropic conductive adhesive on the printed circuit board from being cured before reaching the post of the glass substrate, thereby achieving sufficient contact of the two post electrodes of the glass substrate and the flexible printed circuit board with the conductive particles, it is necessary to contact/press the heating device against the flexible printed circuit board at a relatively fast speed, but there is a fear that a sufficient time required to expand the interval formed at the narrow portion of the post electrode of the flexible printed circuit board to the post electrode interval of the glass substrate cannot be secured.

Therefore, it is considered to contact and press the heating device with respect to the flexible printed circuit board at a relatively slow speed. Thereby ensuring a sufficient time required for the interval formed at the narrow portion of the post electrode of the flexible printed circuit board to expand to the interval of the post electrodes of the glass substrate. However, in this case, there is a fear that the anisotropic conductive adhesive is thermally cured before being sufficiently pressed, and thus sufficient contact between the two terminal electrodes of the glass substrate and the flexible printed circuit board and the conductive particles cannot be achieved.

In addition, when the heating device is contacted and pressed against the flexible printed circuit board, no matter how fast the speed is, internal stress is generated in the flexible printed circuit board due to cooling shrinkage after the pressing of the heating device is completed. In particular, the more the flexible printed circuit board is expanded to a sufficient distance between the terminal electrodes, the more the shrinkage is increased, the greater the internal stress is, and there is a fear that the connection reliability is lowered. Therefore, development of an anisotropic conductive adhesive having high stress relaxation ability is desired at present.

The present invention has been made to solve the above conventional problems, and an object of the present invention is to provide an anisotropic conductive adhesive that can achieve high electrical connection reliability even when a heating device is contacted and pressed at a slow speed, and a method for producing a connection structure using the adhesive.

Means for solving the problems

The present inventors have conducted extensive studies and as a result, have found that a cured component of an anisotropic conductive adhesive is mainly composed of a radical polymerizable compound, and that a satisfactory anisotropic conductive connection can be achieved even at a low heating equipment speed by setting the minimum melt viscosity to a very narrow range of 100 to 800Pa · s and the temperature to the minimum melt viscosity to a range of 90 to 115 ℃.

That is, the present invention provides an anisotropic conductive adhesive comprising conductive particles dispersed in an insulating adhesive component comprising a radical polymerizable compound, a radical initiator and a film-forming resin, wherein the anisotropic conductive adhesive has a minimum melt viscosity in the range of 100 to 800Pa · s and a temperature at which the minimum melt viscosity is in the range of 90 to 115 ℃.

The present invention also provides a method for producing a connection structure formed by connecting a glass substrate on which terminal electrodes are formed at a predetermined interval and a flexible printed circuit board on which terminal electrodes are formed at an interval narrower than the predetermined interval, using an anisotropic conductive adhesive, the method comprising the steps (a) and (B):

(A) a disposing step of disposing the anisotropic conductive adhesive of the present invention between the terminal electrode of the glass electrode and the terminal electrode of the flexible printed circuit board, and

(B) and a connection step of pressing the heating means from the side of the flexible printed circuit board and heating and pressing the means at a temperature higher than the minimum melt viscosity to electrically connect the terminal electrodes to each other.

Effects of the invention

The anisotropic conductive adhesive has the characteristics that the minimum melt viscosity is 100-800 Pa.s, and the temperature of the minimum viscosity range is 90-115 ℃. Therefore, when the glass substrate on which the terminal electrodes are formed at a predetermined interval and the flexible printed circuit board on which the terminal electrodes are formed at an interval narrower than the predetermined interval are connected using the anisotropic conductive adhesive of the present invention, it is possible to secure high fluidity even in a state of being sandwiched between the glass substrate and the flexible printed circuit board while sufficiently expanding the terminal electrode interval of the flexible printed circuit board. As a result, even if the speed of pressing the heating device is slightly deviated in production, or even at a low speed, a connection structure having high connection reliability can be provided.

Drawings

Fig. 1A is a schematic view of a method of bonding a glass substrate and a flexible printed circuit board.

Fig. 1B is a continuation of fig. 1A, and is a schematic view of a method of bonding a glass substrate and a flexible printed circuit board.

Best Mode for Carrying Out The Invention

Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the present specification, unless otherwise specified, the numerical range "X to Y" means X.ltoreq.Y.

The anisotropic conductive adhesive is formed by dispersing conductive particles in an insulating adhesive component containing a radical polymerizable compound, a radical initiator and a film-forming resin, and is characterized in that the minimum melt viscosity is 100-800 Pa.s, preferably 100-400 Pa.s, and the temperature for displaying the minimum melt viscosity is 90-115 ℃, preferably 95-110 ℃.

In the present invention, the reason for setting the minimum melt viscosity to 100 to 800Pa · s is that if it is 100Pa · s or more, excessive flow when the anisotropic conductive adhesive is heated and pressed can be avoided, and as a result, the amount of the adhesive necessary between the terminal electrodes can be secured. When the minimum melt viscosity exceeds 800Pa · s, the fluidity of the anisotropic conductive adhesive decreases when heated and pressed, and the connection thickness becomes larger than the diameter of the conductive particles, which results in a decrease in connection reliability.

The reason why the temperature at which the minimum melt viscosity is exhibited is set to 90 to 115 ℃ will be described below. First, since the anisotropic conductive adhesive having a minimum melting temperature of less than 90 ℃ rapidly reaches an increase region of melt viscosity under subsequent heating and pressing, and the fluidity rapidly decreases, in a flexible printed circuit board in which terminal electrodes are formed at a predetermined interval in advance at a narrower interval, excessive curing of the anisotropic conductive adhesive occurs before the interval is sufficiently expanded, and contact between the terminal electrodes and conductive particles of both of the glass substrate and the flexible printed circuit board is insufficient.

On the other hand, since the anisotropic conductive adhesive having the lowest melt viscosity exceeding 115 ℃ reaches a predetermined time of heating and pressing by a heating device when the curing reaction itself does not sufficiently proceed, contact between the terminal electrodes of both the glass substrate and the flexible printed circuit board and the conductive particles is also insufficient.

Thus, in the present invention, the optimum range of the minimum melt viscosity is 100 to 800Pa · s, and the optimum range of the temperature exhibiting the minimum melt viscosity is 90 to 115 ℃, and therefore the optimum range of the value [ (minimum melt viscosity)/(temperature exhibiting the minimum melt viscosity) ] obtained by dividing the minimum melt viscosity by the temperature exhibiting the minimum melt viscosity is 0.88 to 8.8.

Even if the value of [ (minimum melt viscosity)/(temperature at which minimum melt viscosity is exhibited) ] is within the above range, if at least one of the "minimum melt viscosity" and the "temperature at which minimum melt viscosity is exhibited" is out of the optimum range, it may cause a connection failure.

As the conductive particles of the anisotropic conductive adhesive of the present invention, for example, conductive particles obtained by plating resin particles with gold, conductive particles obtained by insulating-coating the outermost layer of particles obtained by plating resin particles with gold, and the like can be used. Here, the average particle diameter of the conductive particles is preferably 1 to 20 μm, and more preferably 2 to 10 μm, from the viewpoint of conduction reliability. In addition, from the viewpoint of conduction reliability and insulation reliability, the content of the conductive particles in the insulating binder component is preferably 2 to 50% by mass, and more preferably 3 to 20% by mass.

As described above, the insulating adhesive component contains at least the radical polymerizable compound, the radical initiator, and the film-forming resin.

As the radical polymerizable compound, there can be used (meth) acrylate monomers such as dicyclopentyl (meth) acrylate and phosphorus-containing (meth) acrylate, and (meth) acrylate oligomers such as urethane (meth) acrylate and polyester (meth) acrylate. Among these, at least either one of a dicyclopentyl (meth) acrylate monomer and a urethane (meth) acrylate oligomer is preferably contained from the viewpoint that the melt viscosity and the curing speed are preferably compatible with each other. The above-mentioned monomer or oligomer may be used in combination with another radically polymerizable compound which can be radically polymerized, within a range not impairing the effects of the present invention.

As the radical initiator, a known radical polymerization initiator can be used, and among them, a peroxide-based radical initiator is preferably used. Specific examples of the peroxide radical initiator include diacyl peroxides such as benzoyl peroxide, alkyl perester such as t-hexyl peroxypivalate and t-butyl peroxybenzoate, and peroxyketals such as 1, 1-bis (t-butylperoxy) cyclohexane. Commercially available products include ナイパ -BW (diacyl peroxide, Nichiyan oil Co., Ltd.), ナイパ -BMT-K40 (diacyl peroxide, Nichiyan oil Co., Ltd.), ナイパ -BO (diacyl peroxide, Nichiyan oil Co., Ltd.), ナイパ -FF (diacyl peroxide, Nichiyan oil Co., Ltd.), ナイパ -BS (diacyl peroxide, Nichiyan oil Co., Ltd.), ナイパ -E (diacyl peroxide, Nichiyan oil Co., Ltd.), ナイパ -NS (diacyl peroxide, Nichiyan oil Co., Ltd.), パ - ヘキシル O (perester, Nichiyan oil Co., Ltd.), パ - ブチル O (perester, Nichiyan oil Co., Ltd.), パ - テトラ A (peroxyketal, Nichiyan oil Co., Ltd.), パ - ヘキサ C-80(S) (peroxyketal, Nichiyan oil Co., Ltd.), パ - ヘキサ C-75(EB) (peroxyketal, Nichio oil Co., Ltd.), パ - ヘキサ C (C) (peroxyketal, Nichio oil Co., Ltd.), パ - ヘキサ C (S) (peroxyketal, Nichio oil Co., Ltd.), パ - ヘキサ C-40 (peroxyketal, Nichio oil Co., Ltd.), パ - ヘキサ C-40MB (S) (peroxyketal, Nichio oil Co., Ltd.), パ - ヘキシル I (perester, Nichio oil Co., Ltd.). The radical initiator may be used alone or in combination.

The film-forming resin is a component which imparts film-forming properties to an insulating adhesive component containing a radical polymerizable compound and an anisotropic conductive adhesive agent containing the component, facilitates film formation, and improves the cohesive force of the anisotropic conductive adhesive agent as a whole. As the film-forming resin, at least one of a phenoxy resin and a mixed resin of a phenoxy resin and an epoxy resin produced in the production process of the phenoxy resin can be particularly preferably used. The weight average molecular weight of the phenoxy resin or the mixed resin is preferably 20000 to 60000, more preferably 20000 to 40000, in view of the film strength and fluidity of the anisotropic conductive adhesive. This is because excessive flow during heating of the anisotropic conductive adhesive can be avoided if the weight average molecular weight is 20000 or more, and insufficient flow is not caused if the weight average molecular weight is 60000 or less.

In the present invention, the insulating adhesive component preferably contains a stress relaxation agent. By containing the stress relaxation agent, the strength of the internal stress generated at the interface portion between the anisotropic conductive adhesive and the glass substrate or the interface portion between the anisotropic conductive adhesive and the flexible printed circuit board can be relaxed.

As the stress relaxation agent, a rubber-based elastic material can be preferably used, and the stress relaxation agent is preferably used in the form of particles. Examples of the rubber-based elastic material include Butadiene Rubber (BR) containing polybutadiene, acrylic rubber (ACR), nitrile rubber (NBR), and the like. Among them, Butadiene Rubber (BR) containing polybutadiene is preferable because it absorbs internal stress more because it has higher rebound elasticity than acrylic rubber (ACR) and nitrile rubber (NBR). Therefore, in the present invention, polybutadiene particles are particularly preferably used as the stress relaxation agent.

As the polybutadiene particles used in the present invention, those having an elastic modulus smaller than that of the cured anisotropic conductive adhesive are preferably used, but if too small, the holding force tends to be low, and if too high, the internal stress of the cured product of the anisotropic conductive adhesive tends to be insufficiently reduced, so that it is preferable to use polybutadiene particles having an elastic modulus of 1 × 10⁸～1×10¹⁰dyn/cm²The substance of (1).

Further, as a factor necessary for sufficiently securing the electrical connection between the conductive particles and the connection electrode, from the viewpoint of an important average particle diameter, it is preferable that the polybutadiene particles to be observed have an average particle diameter smaller than that of the conductive particles, but if too small, the internal stress cannot be completely absorbed, and if too large, the sufficient electrical connection between the conductive particles and the connection electrode may not be formed, so that a material having an average particle diameter of preferably 0.01 to 0.5 μm is used.

The content ratio of the polybutadiene particles in the anisotropic conductive adhesive is preferably 10 to 30 parts by mass, and more preferably 15 to 25 parts by mass, relative to 75 parts by mass of the total of the radical polymerizable compound and the film-forming resin. When the content is 10 parts by mass or more, the internal stress generated in the anisotropic conductive adhesive can be sufficiently reduced, and when the content is 30 parts by mass or less, the film formation of the anisotropic conductive adhesive is not adversely affected and the heat resistance is not lowered.

Next, an example of the method for preparing the anisotropic conductive adhesive of the present invention will be described.

First, a radical polymerizable compound and a film-forming resin are dissolved in a solvent, and then, a radical initiator and conductive particles are added in predetermined amounts, and further, a stress relaxation agent (preferably polybutadiene particles) is added as needed, followed by mixing and stirring. The mixed solution is applied to a release film such as a polyester film, dried, and then laminated to form a cover film, thereby obtaining a filmed anisotropic conductive adhesive.

The anisotropic conductive adhesive of the present invention described above can be preferably used for anisotropic conductive connection between a glass substrate such as a liquid crystal panel and a flexible printed circuit board to produce a connection structure. A method for producing the above-described connection structure is described below with reference to fig. 1A and 1B (schematic diagrams of a method for bonding a glass substrate and a flexible printed circuit board).

The method for producing a connection structure of the present invention is a method for producing a connection structure formed by connecting a glass substrate on which terminal electrodes are formed at a predetermined interval and a flexible printed wiring board on which terminal electrodes are formed at an interval narrower than the predetermined interval, using an anisotropic conductive adhesive, and has the following steps (a) and (B).

Step (A) < disposing step >

First, the anisotropic conductive adhesive of the present invention described above is disposed between the terminal electrodes of the glass substrate and the terminal electrodes of the flexible printed circuit board. In this disposing step, a conventionally known method can be used in addition to the use of the anisotropic conductive adhesive of the present invention.

Here, as shown in fig. 1A, the post electrodes 11 are formed on the glass substrate 1 at a predetermined interval a, and the post electrodes 31 are formed on the flexible printed circuit board 3 at an interval B narrower than the predetermined interval a of the glass substrate 1.

The glass substrate 1 may be a glass substrate of a display panel such as a liquid crystal panel. The predetermined interval a is a pitch of the post electrodes 11 formed of ITO electrodes or the like, and basically does not mean an interval between adjacent electrodes, but may be a standard interval. The interval is usually 20 to 200 μm, and particularly, the interval for effectively achieving the effect of the present invention is 20 to 60 μm which is fine.

On the other hand, as the flexible printed wiring board 3, a flexible printed wiring board obtained by processing a copper foil of a flexible substrate in which a copper foil is laminated on a polyimide film base material (ポリイミドフイルムベ - ス) by etching or the like into the terminal electrode 31 is preferably used. The interval B narrower than the predetermined interval a is a pitch of the post electrodes 31, and basically does not mean an interval between adjacent electrodes, but may be a standard interval.

The interval B is narrower than the predetermined interval a, but the degree of the narrowing differs depending on the difference in linear expansion coefficient of the glass substrate 1 or the flexible printed circuit board 3, the heating temperature, the heating rate, the pressing force, and the like, and is usually 0.01 to 1% smaller, preferably 0.1 to 0.3% smaller than the predetermined interval a. Step (B) < connecting step >

Next, a heating device (not shown) is pressed from the flexible printed circuit board 3 side, and the anisotropic conductive adhesive 2 is cured by heating and pressing at a temperature equal to or higher than the minimum melt viscosity, whereby the glass substrate 1 and the two terminal electrodes of the flexible printed circuit board 3 are electrically connected. That is, in this connection step, the flexible printed circuit board 3 is expanded by heating, and as shown in fig. 1B, the interval B' between the terminal electrodes 31 of the flexible printed circuit board 3 and the interval a between the terminal electrodes 11 of the glass substrate 1 are substantially equal, and the terminal electrodes 11 and 31 are electrically connected by a cured product of the anisotropic conductive adhesive. Thereby, a connection structure can be obtained.

Preferable conditions for the heating and pressing in the step (B) include a condition in which a heating device adjusted so that the temperature of the anisotropic conductive adhesive reaches 150 to 200 ℃ after 4 seconds is brought into contact with the flexible printed wiring board at a speed of 1 to 50mm/sec, preferably 1 to 10mm/sec, and then the flexible printed wiring board is heated and pressed at the speed for 4 seconds or more. Specifically, the anisotropic conductive adhesive 2 is heated and pressed at a pressing speed of 1 to 50mm/sec, particularly at a pressing speed of 1 to 10mm/sec when the anisotropic conductive adhesive is intentionally low, for a heating device of 150 to 200 ℃ for 4 seconds or more, preferably 4 to 6 seconds. Under such conditions, the temperature range (90 to 115 ℃) of the anisotropic conductive adhesive 2 showing the lowest melt viscosity is higher than the temperature at the start of heating (e.g., room temperature) and lower than the heating temperature (150 to 200 ℃) for curing the anisotropic conductive adhesive 2. Therefore, under such heating and pressing conditions, the viscosity of the anisotropic conductive adhesive 2 decreases after the start of heating, and increases through the lowest melt viscosity (100 to 800Pa · s) to be cured. By such a change in viscosity, the glass substrate and the flexible printed circuit board can be connected with high reliability.

The reason why the pressing speed of the heating device is set to 1 to 50mm/sec is that if the pressing speed is slower than this speed, the interval between the terminal electrodes of the flexible printed circuit board can be expanded to a predetermined interval, but on the other hand, the anisotropic conductive adhesive is cured before the pressing is sufficiently performed, and as a result, a good anisotropic conductive connection cannot be achieved. Another reason is that there is a fear that, if this speed is faster, the anisotropic conductive adhesive is cured before the interval of the post electrodes of the flexible printed circuit board is expanded to a prescribed interval.

Examples

The present invention will be described more specifically with reference to examples. The components used in the examples and comparative examples are as follows.

< radically polymerizable Compound >

Dicyclopentadienyl dimethacrylate (DCP, New Zhongcun chemical industry Co., Ltd.)

Urethane acrylate (M-1600, Toyasynthetic (strain))

Phosphorus-containing methacrylate (PM2, Nippon Chemicals (Co., Ltd.))

< free radical polymerization initiator >

Peroxydicarbonate type initiator (パ - ロイル L, Nizhi oil (Co., Ltd.))

Diacyl peroxide initiator (ナイバ -BW, Nizhi (strain))

Peroxyketal initiator (パ - テトラ A, Nizhi oil (Co., Ltd.))

Dialkyl peroxide initiator (パ - クミル D, Nizhi oil (Co., Ltd.))

< film Forming resin >

Bisphenol A/bisphenol F Mixed phenoxy resin (Bis-A/Bis-F Mixed phenoxy resin: weight average molecular weight 60000) (YP-50, Doudou Kabushiki Kaisha)

Bisphenol A/bisphenol F Mixed phenoxy resin (Bis-A/Bis-F Mixed phenoxy resin: weight average molecular weight 30000) (jER-4110, ジヤパンエポキシレジン Strain.)

Bisphenol F type phenoxy resin (Bis-F phenoxy resin: weight average molecular weight 20000) (jER-4007P, ジヤパンエポキシレジン (strain))

< stress relaxation agent >

Acrylic rubber (weight-average molecular weight 1200000) (SG-600LB, ナガセケムテツクス (Strain))

Polybutadiene particles (average particle diameter 0.1 μm)

< silane coupling agent >

Silane coupling agent (KBM-503, shin-Etsu chemical Co., Ltd.)

< conductive particles >

Conductive particles obtained by coating benzoguanamine particles with nickel-gold plating (average particle diameter 5 μm, Nippon chemical industry Co., Ltd.)

Examples 1 to 7 and comparative examples 1 to 4

Among the compounding ingredients shown in table 1, a radical polymerizable compound, a radical initiator, a film-forming resin, and a coupling agent were dissolved in toluene as a solvent to prepare an insulating adhesive component solution.

Then, 3 parts by mass of conductive particles were added to this insulating adhesive component solution (100 parts by mass of the components other than toluene) to prepare an anisotropic conductive adhesive liquid.

Then, this anisotropic conductive adhesive liquid was applied to a polyester film subjected to a peeling treatment so that the thickness after drying became 25 μm, and the film was dried at 80 ℃ for 5 minutes to obtain a film-formed anisotropic conductive adhesive. The anisotropic conductive adhesive was cut into a rectangular shape having a width of 2mm, and used as the anisotropic conductive film samples of examples 1 to 7 and comparative examples 1 to 4.

(evaluation)

As described below, the measurement and evaluation of the "conduction resistance value", "connection reliability", "minimum melt viscosity", "temperature at which the minimum melt viscosity was reached", and "inter-post gap" due to connection were performed on each of the anisotropic conductive film samples of examples 1 to 7 and comparative examples 1 to 4. The results obtained are shown in table 2.

< (1) conduction resistance value >

A sample of the anisotropic conductive film was heat-pressed under conditions of 180 ℃ and a pressure of 3.5MPa for a pressing time of 4 seconds by using a heating apparatus of a stainless steel plate to prepare a connection structure, and the conduction resistance value of the connection structure was measured. The preparation was carried out at 5 speeds such as 50, 30, 10, 1.0 and 0.1mm/sec of the heating equipment speed, and the conduction resistance value was measured for each heating equipment speed.

< 2) connection reliability >

The connection structure having the conductivity resistance value measured as described above was aged at 85 ℃ and 85% relative humidity for 500 hours, and then the conductivity resistance was measured.

< 3) minimum melt viscosity and temperature showing minimum melt viscosity >

The sample obtained by removing toluene without curing the anisotropic conductive adhesive liquid and then curing was charged into a rotary viscometer, and the melt viscosity was measured while the temperature was increased at a predetermined temperature increase rate (10 ℃/min).

< 4) gap between terminal electrodes >

The connection structures connected by the various anisotropic conductive film samples were visually observed from the glass substrate side using an optical microscope to see whether or not there was a void.

(evaluation results)

As is clear from the results in tables 1 and 2, the samples of the anisotropic conductive adhesives prepared by blending the examples 1 to 7 had the minimum melt viscosity adjusted to 100 to 800Pa · s, and therefore, even when the heating equipment speed was in the range of 1.0 to 50mm/sec, the connection structure using these examples had the conduction resistance value of 1 Ω or less, and the initial connection state was good. Further, it is understood from the results that the resistance value of these examples does not increase more than 5 Ω even after a predetermined aging, and the connection reliability is high.

On the other hand, the connection structure using the sample of comparative example 1 exhibited a low conduction resistance value in the case where the heating apparatus speed was relatively high, but reached 10 Ω at 1.0 mm/sec. The sample of comparative example 1 had a suitable temperature for attaining the minimum melt viscosity, but had a minimum melt viscosity of 1000 pas, a high viscosity and a poor flowability. Although this is not a problem when the heating device is at a high speed, if the pressurizing device is at a low speed, the interval between the terminal electrodes of the flexible printed circuit board reaches the region where the melt viscosity rises due to the lowest melt viscosity of the anisotropic conductive film before the interval between the terminal electrodes of the flexible printed circuit board is expanded to a predetermined interval between the terminal electrodes on the glass substrate, and therefore, the contact between the conductive particles and the two terminal electrodes of the glass substrate and the flexible printed circuit board is insufficient, resulting in a poor electrical connection of the connection structure.

Voids were generated in the connecting structure using the sample of comparative example 2 at all heating equipment speeds. The occurrence of voids does not directly cause electrical connection failure of the connection structure, but may cause the connection failure. The sample of comparative example 2 had a suitable temperature for achieving the lowest melt viscosity, but the lowest melt viscosity was 70 pas, the viscosity itself was low, and voids were generated due to excessive flow.

Even when the heating equipment speed was in the range of 1.0 to 50mm/sec, the connection structure using the sample of comparative example 3 had a conduction resistance value of 1 Ω or less, and the initial connection state was good. However, the conduction resistance value greatly increases after a predetermined aging. The sample of comparative example 3 had a minimum melt viscosity of 250 pas and a suitable viscosity, but the temperature at which the minimum melt viscosity was reached was 120 ℃ and the temperature was high. Therefore, time is required for final curing, which causes poor curing, resulting in poor electrical connection of the connection structure.

In the connection structure using the sample of comparative example 4, when the heating equipment speed entered the low speed region of 10mm/sec, the conduction resistance value increased. The sample of comparative example 4 had a minimum melt viscosity of 900 pas, a high viscosity, and a temperature of 88 ℃ and a low temperature at which the minimum melt viscosity was reached. Therefore, it is considered that the lowest melt viscosity of the anisotropic conductive adhesive reaches an increased region of the melt viscosity, and if the heating equipment speed is in a low speed region, the contact between the two posts and the conductive particles is insufficient, and as a result, the electrical connection of the connection structure is poor.

< expansion ratio of Flexible printed Circuit Board >

In the connection structures using the anisotropic conductive film samples of examples 1 to 7, the expansion and contraction ratios of the flexible printed wiring boards in the connection structures of examples 2 and 3 were measured. The results obtained are shown in table 3.

The length of the flexible printed circuit board before and after thermocompression bonding was measured using a 2-dimensional length measuring machine, and the concerned expansion and contraction rate was calculated. The thermal expansion coefficients of a glass substrate (product name コ - ニング 1737F, manufactured by コ - ニング) and a polyimide (product name カプトン EN, manufactured by envoy レ and デイポン) used in the connection structure were 3.7 × 10, respectively^-6/° C and 16 × 10^-6/℃。

[ Table 3]

As can be seen from table 3, in the temperature, pressure and time of the heating apparatus used in the embodiment, when the speed of the heating apparatus is relatively slow, the stretching of the flexible printed circuit board increases. It follows that even if the same actual installation equipment is used, the amount of extension should be taken into consideration when performing heating and pressing at a slow heating equipment speed.

The expansion and contraction rate generally relates to the temperature of the heating device, the speed of the heating device, and the linear expansion coefficient and thickness of the polyimide in the flexible printed circuit board, but in the low speed region (1.0 to 10mm/sec), the expansion and contraction rate is in the range of 0.1 to 0.25% as can be seen from table 3.

Industrial applicability

The anisotropic conductive adhesive of the present invention can realize high electrical connection reliability even when a heating device is contacted and pressed at a slow speed. Therefore, the anisotropic conductive film is useful for anisotropic conductive connection between a glass substrate of a display element such as a liquid crystal panel and a flexible printed circuit board.

Description of the symbols

1 glass substrate

2 Anisotropic conductive adhesive

3 Flexible printed Circuit Board

11. 31 terminal post electrode

Claims (9)

1. An anisotropic conductive adhesive comprising conductive particles dispersed in an insulating adhesive component comprising a radical polymerizable compound, a radical initiator and a film-forming resin, wherein the anisotropic conductive adhesive has a minimum melt viscosity in the range of 100 to 800Pa · s and a temperature at which the minimum melt viscosity is in the range of 95 to 110 ℃,

the film-forming resin contains at least one of a phenoxy resin having a weight-average molecular weight of 20000 to 60000 or a mixed resin having a weight-average molecular weight of 20000 to 60000 composed of a phenoxy resin and an epoxy resin,

the radical polymerizable compound contains at least one of a dicyclopentyl (meth) acrylate monomer and a urethane (meth) acrylate oligomer,

the anisotropic conductive adhesive further contains a stress relaxation agent,

as the stress relaxation agent, a rubber-based elastic material is used.

2. The anisotropic conductive adhesive of claim 1, wherein a ratio of the lowest melt viscosity/a temperature showing the lowest melt viscosity is 0.88 to 8.8.

3. The anisotropic conductive adhesive of claim 1, wherein the stress relaxation agent is polybutadiene particles.

4. The anisotropic conductive adhesive of claim 3, wherein the polybutadiene particles are contained in an amount of 10 to 30 parts by mass based on 75 parts by mass of the total of the radical polymerizable compound and the film-forming resin.

5. The anisotropically conductive adhesive according to claim 3 or 4, wherein the polybutadiene particles have a size of 1 x 10⁸～1×10¹⁰dyn/cm²The modulus of elasticity of (a).

6. The anisotropic conductive adhesive of claim 3 or 4, wherein the polybutadiene particles have a size of 0.01 to 5μm is the average particle diameter.

7. A method for producing a connection structure, wherein the connection structure is formed by connecting a glass substrate having terminal electrodes formed at predetermined intervals and a flexible printed wiring board having terminal electrodes formed at intervals narrower than the predetermined intervals, by using the anisotropic conductive adhesive according to any one of claims 1 to 6, the method comprising the steps (A) and (B):

(A) a disposing step of disposing the anisotropic conductive adhesive according to claim 1 between the terminal electrode of the glass substrate and the terminal electrode of the flexible printed circuit board, and

(B) and a connection step of pressing the heating means from the side of the flexible printed circuit board and heating and pressing the means at a temperature higher than the minimum melt viscosity to electrically connect the terminal electrodes to each other.

8. The manufacturing method of claim 7, wherein the heating device adjusted so that the temperature of the anisotropic conductive adhesive reaches 150 to 200 ℃ after 4 seconds is brought into contact with the flexible printed circuit board at a speed of 1 to 50mm/sec in the step (B), and then heated and pressed at the speed for 4 seconds or more.

9. The manufacturing method of claim 7, wherein the heating device adjusted so that the temperature of the anisotropic conductive adhesive reaches 150 to 200 ℃ after 4 seconds is brought into contact with the flexible printed circuit board at a speed of 1 to 10mm/sec in the step (B), and then heated and pressed at the speed for 4 seconds or more.