JP3241276B2 - Conductive microsphere and liquid crystal display device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conductive fine sphere and a liquid crystal display device using the same.

[0002]

2. Description of the Related Art In the field of electronics, conductive microspheres are used as conductors for connecting fine electrodes.

FIG. 5 shows a typical example of a TN (twisted nematic) mode liquid crystal display device. This liquid crystal display element includes a pair of substrates 37 and 39, and the pair of substrates 37 and 39.
In order to keep the gap 39 constant, a pair of substrates 3
The spacer 38 and the nematic liquid crystal 41 disposed between the pair of substrates 7 and 39, the sealing member 30 filled around the pair of substrates 37 and 39, and the polarizing sheet 42 coated on the surfaces of the substrates 37 and 39. , 43. The above substrate 3
In reference numerals 7 and 39, transparent electrodes 32 and 35 made of an ITO (Indium-Tin-Oxide) film or the like are pattern-formed on one surface of transparent substrates 31 and 34 made of glass. Are coated with alignment control films 33 and 36 made of a polyimide film or the like. The alignment control films 33 and 36 are subjected to an alignment control process by rubbing.

[0004] The liquid crystal display device having the above configuration is usually manufactured as follows. Spacers 38 are scattered on the orientation control film 33 of the one substrate 37, and a sealing resin is applied to the periphery of the substrate 37 by printing. Next, a pair of substrates 37 and 39 are overlapped and pressed so that the alignment control films 33 and 36 face each other. Next, the sealing resin is heated and cured to form a sealing member, and the pair of substrates 37 and 39 are fixed to each other. Next, the gap between the pair of substrates 37 and 39 is filled with the nematic liquid crystal 41 from the hole provided in the sealing member, and then the hole is closed. Then, the polarizing sheets 42 and 43 are laminated on the outer surfaces of the transparent substrates 31 and 34, respectively.

In the field of electronic packaging, in order to connect a pair of fine electrodes, a conductive paste is prepared by mixing metal particles such as gold, silver, and nickel and a binder resin. Is filled to connect the fine electrodes. However, such metal particles are non-uniform in shape, and
Since the specific gravity is larger than that of the binder resin, it is difficult to uniformly disperse the binder resin in the binder resin.

Japanese Patent Application Laid-Open No. 59-28185 discloses a method of forming conductive microspheres by providing a metal plating layer on the surface of particles such as glass beads, silica beads, and glass fibers having relatively uniform particle diameters. Is disclosed. However, the conductive microspheres disclosed in the above publication are difficult to compressively deform because the base microspheres are too hard. Therefore, if an attempt is made to connect the electrodes using the conductive microspheres, the contact area between the conductive microspheres and the electrode surface does not increase, and it becomes difficult to reduce the contact resistance value.

JP-A-62-185749 and JP-A-1-225776 disclose conductive fine spheres using polyphenylene sulfide particles, phenol resin particles or the like as base fine spheres. However, conductive microspheres using such synthetic resin particles as base microspheres have poor deformation recovery after compression deformation. Therefore, when the connection between the electrodes is performed using the conductive microspheres, when a compressive load acting on both electrodes is removed, a slight gap is formed at the interface between the conductive microspheres and the electrode surface, As a result, poor contact occurs.

[0008]

SUMMARY OF THE INVENTION In view of the above, the present invention provides a conductive fine sphere having appropriate compressive deformation and deformation recovery properties and excellent connection reliability, and a liquid crystal display using the same. It is intended to provide an element.

[0009]

The object of the present invention is to obtain K = (3 / √2) ・^FS -3 / 2 ・ R- ^{1 / 2} (where F is the 10% compressive deformation of the ^microsphere ) , S represents the compression displacement (mm), and R
Represents the radius (mm) of the microsphere. ) Is 50 kgf / mm ² or more and 250 k at 20 ° C.
gf / mm ² and the recovery rate after compression deformation is 20
Microspheres that are between 15 and 100% at
And a conductive layer provided on the surface.
This can be achieved by the use of the conductive microspheres and the liquid crystal display device using the same . Hereinafter, the present invention will be described in detail.

First, the K value defined in the present invention will be described. According to Landau-Orifsitz's theoretical physics course "Elasticity" (published by Tokyo Book, 1972), page 42, when two elastic spheres having radii R and R 'respectively come into contact, h
Is given by: h = F ^2/3 [D ² (1 / R + 1 / R ′)] ^1/3 (1) D = (3/4) [(1−σ ² ) / E + (1−σ ′ ² ) / E ′ (2) (where h represents the difference between R + R ′ and the distance between the centers of the two spheres, F represents the compressive force, E and E ′ represent the elastic moduli of the two elastic spheres, σ and σ ′ represent the Boisson's ratio of the elastic sphere.)

On the other hand, the ball is placed on a rigid plate, and
When compressing from both sides, if R '→ ∞, E) E', then
The following equation is approximately obtained. F = (2 ^1/2/3 ) (S ^3/2 ) (E · R ^1/2 ) (1−σ ² ) (3) (where S represents the amount of compressive deformation). Then, the following equation is easily obtained. K = E / (1−σ ² ) (4) Accordingly, an expression representing the K value: K = (3 / √2) ・^FS -3 / 2 ・ R- ^{1 / 2} (5) is obtained. The K value represents the hardness of a sphere universally and quantitatively. By using the above K value, it is possible to quantitatively and uniquely express the suitable hardness of the microsphere.

In the microspheres used in the present invention , the K value at 10% compressive strain is 50 kgf / mm ² or more and 250
It is less than kgf / mm ² . If it is less than 50 kgf / mm ² , the mechanical strength is insufficient, and if it is more than 250 kgf / mm ² , especially in the case of conductive fine spheres, the contact area becomes too small and the contact resistance becomes high. It is limited to the above range. Preferably, 100 kgf / mm ²
It is less than 250 kgf / mm ² .

By the way, it is not possible to completely express the material mechanical properties of a suitable microsphere simply by defining a suitable hardness of the microsphere. Another important property is that the recovery rate after compression deformation, which is a value indicating the elasticity of the microsphere, is within a predetermined range. By defining the recovery rate after compression deformation, the elasticity or plasticity of the microsphere can be quantitatively and uniquely expressed.

In the microspheres used in the present invention , the recovery rate after compression deformation of the microspheres is 15 to 100% at 20 ° C.
It is. If the recovery rate is less than 15%, the microspheres remain in a state of being compressed and deformed when the pressure is locally applied excessively when the gap is formed between the two substrates by the pressure press. Since the gap does not return to the original position at that point, which causes gap unevenness, the gap is limited to the above range. The preferred recovery rate after compression deformation is 20 to 95%.

Next, a method of measuring the K value and the recovery rate after compression deformation will be described. (A) Measurement method and conditions of K value (i) Measurement method At room temperature, microspheres are sprayed on a steel plate having a smooth surface, and one microsphere is selected from the microspheres. Next, using a micro compression tester (PCT-200 type, manufactured by Shimadzu Corporation), the microspheres are compressed on the smooth end face of a diamond cylinder having a diameter of 50 μm. At this time, the compression load is electrically detected as an electromagnetic force, and the compression displacement is electrically detected as a displacement by the operation transformer.

Thus, the compression displacement as shown in FIG.
A load relationship is required. From FIG. 2, the load value and the compressive displacement at 10% compressive deformation of the microsphere are obtained, respectively.
From these values and equation (5), the relationship between the K value and the compression distortion as shown in FIG. 3 is obtained. Here, the compressive strain is a value obtained by dividing a value obtained by dividing a compressive displacement by a particle diameter of a microsphere in%. (Ii) Compression speed This is performed by a constant load speed compression method. 0.27 grams weight per second (g
The load is increased at the rate of rf). (Iii) Test load The maximum load is 10 grf.

(B) Measurement method and condition of recovery rate after compressive deformation (i) Measurement method At room temperature, microspheres are scattered on a steel plate having a smooth surface, and one microsphere is selected from them. Next, using a micro compression tester (PCT-200 type, manufactured by Shimadzu Corporation), the microspheres are compressed on the smooth end face of a diamond cylinder having a diameter of 50 μm. At this time, the compression load is electrically detected as an electromagnetic force, and the compression displacement is electrically detected as a displacement by the operation transformer.

As shown in FIG. 4, after the microspheres are compressed to the reversal load value (indicated by curve (a) in FIG. 4), the load is reduced (in curve (b) in FIG. 4). Shown). At this time, the relationship between the load and the compression displacement is measured. However, the end point in the unloading is not a load value of zero but an origin load value of 0.1 g or more. The recovery rate is defined as the ratio (L ₂ / L ₁ ) of the displacement L _{1 up} to the point of inversion and the displacement difference L ₂ from the point of inversion to the point where the origin load value is obtained, expressed as a percentage.

(Ii) Measurement conditions Reverse load value 1 grf Origin load value 0.1 grf Compression speed under load and unload 0.029 grf / sec Measurement chamber temperature 20 ° C.

The fine spheres used in the present invention are preferably synthetic resin particles because the K value and the recovery rate can be easily adjusted within the above ranges. The synthetic resin particles are not particularly limited, for example, polyethylene, polypropylene, polymethylpentene, polyvinyl chloride, polytetrafluoroethylene, polystyrene, polymethyl methacrylate, polyethylene terephthalate, polybutylene terephthalate, polyamide, polyimide, polysulfone, Linear or crosslinked polymers such as polyphenylene oxide and polyacetal; epoxy resins,
Phenol resin, melamine resin, unsaturated polyester resin, divinylbenzene polymer, divinylbenzene-styrene copolymer, divinylbenzene-acrylate copolymer, diallyl phthalate polymer, triallyl isocyanurate polymer, benzoguanamine polymer, etc. And the like having a network structure of

Among them, a network structure such as a crosslinked copolymer of a terminal urethane acrylate-modified polyol and a polyfunctional acrylate, a divinylbenzene polymer, a divinylbenzene-styrene copolymer, a divinylbenzene-acrylic acid copolymer, etc. Is preferred.

The diameter of the microsphere used in the present invention is from 0.1 to
5000 μm is preferred. If it is less than 0.1 μm, the microspheres tend to agglomerate and lack practicality, and if it exceeds 5000 μm, it is rarely used. More preferably, it is 0.1 to 1000 μm. The coefficient of variation of the diameter is
50% or less is preferable. If it exceeds 50%, the particle size distribution becomes too wide, causing a problem in performance as microspheres. More preferably, it is 35% or less, still more preferably, 20% or less.

The conductive microsphere of the present invention comprises the above microsphere,
A conductive layer provided on the surface of the microsphere. This conductive microsphere can be used for conductive connection between fine electrodes in the field of electronics packaging. In this conductive fine sphere, as described above, the K value at 10% compressive strain is 50 kgf / mm ² or more and 250 kgf / mm ^2.
By using the conductive microspheres that are less than ² and within this range, for example, in a manufacturing process of a liquid crystal display element in which a pair of electrodes are connected by the conductive microspheres, the opposing electrode surface is electrically conductive microspheres. The gap can be easily controlled when a gap is formed between the two electrodes by a pressure press. Preferably, 100 kgf / mm ² or more and 250 kgf / mm ²
Is less than.

If the K value is less than 50 kgf / mm ² , compressive deformation often occurs when the conductive microspheres are sandwiched between two electrodes and a compressive load is applied. The layer can no longer follow this deformation,
As a result, there is a risk that the conductive layer may be torn or peeled. Further, when the amount of compressive deformation is excessive and the conductive fine spheres are flattened, the electrodes are in direct contact with each other, and there is a problem that a sufficient fine connection cannot be made.

In the conductive microspheres of the present invention, the range of the recovery rate after compression deformation of the conductive microspheres is 1 at 20 ° C.
5 to 100%. If the recovery rate is less than 15%, an adhesive in which the conductive fine spheres are dispersed is filled between two electrodes and pressure-bonded, and the pressure is reduced after the adhesive is cured. The adhesive layer repeatedly shrinks and expands in an environment of repeated heat and cold, but the conductive microspheres remain compressed and deformed, so a gap is created between the adhesive layer and the electrode surface when the adhesive layer expands. However, this may cause poor contact, so that it is limited to the above range. Preferably,
20-95%.

The thickness of the conductive layer of the conductive fine spheres is set to 0.1.
It is preferably from 2 to 5 μm. The thickness of the conductive layer is 0.02 μm
If it is less than 5 μm, it becomes difficult to obtain desired conductivity,
When the value exceeds, the conductive layer is easily peeled off from the surface of the microspheres due to the difference in the coefficient of thermal expansion between the microspheres and the conductive layer, and aggregation of the conductive microspheres easily occurs.

The metal used for the conductive layer is not particularly limited. For example, nickel, gold, silver, copper, cobalt,
Examples include tin, indium, and the like, or alloys containing these as a main component. Among them, nickel, gold, silver, and indium are preferable. The method for forming a metal layer on the surface of the microspheres is not particularly limited. For example, a method by electroless plating (also referred to as a chemical plating method); a paste obtained by mixing metal fine powder alone or mixed with a binder is used as a microsphere. A physical vapor deposition method such as vacuum vapor deposition, ion plating, and ion sputtering.

A method for forming a conductive layer by the above-described electroless plating method will be described below with reference to the case of gold displacement plating as an example. This method is divided into the following etching step, activation step, chemical nickel plating step, and gold displacement plating step. The etching step is a step of attaching a plating layer to the microspheres by forming irregularities on the surface of the microspheres. The etching solution includes, for example, an aqueous solution of sodium hydroxide, concentrated hydrochloric acid, concentrated sulfuric acid, or chromic anhydride.

The activation step is a step for forming a catalyst layer on the surface of the etched microspheres and activating the catalyst layer. The activation of the catalyst layer promotes the deposition of metallic nickel in a chemical nickel plating step described below. Pd ²⁺ and Sn on ^microsphere surface
^The catalyst layer containing ²⁺ is treated with concentrated sulfuric acid or concentrated hydrochloric acid, and only Sn ²⁺ is dissolved and removed to metallize Pd ²⁺ . The metallized palladium is activated and sensitized by a palladium activator such as a concentrated solution of sodium hydroxide.

The chemical nickel plating step is a step of forming a metal nickel layer on the surface of the fine sphere on which the catalyst layer is formed. For example, nickel chloride is reduced by sodium hypophosphite, and nickel is reduced to the fine sphere. Deposited on the surface of In the gold displacement plating step, the microspheres coated with nickel in this way are placed in an aqueous solution of potassium potassium cyanide, and while elevating the temperature, nickel is eluted to deposit gold on the surface of the microspheres.

An element can be manufactured using the conductive fine spheres thus obtained. This element can be manufactured, for example, as follows. As shown in FIG. 1, conductive fine spheres 29 are
Is uniformly applied on one electrode 24 by screen printing or a dispenser. Alternatively, only the conductive fine spheres 29 are arranged on the electrode 24 without using the binder 28. In the latter case, the conductive microspheres 29 may be sprayed from above the electrode 24, or the conductive microspheres 29 may be charged and electrostatically adhered to the electrode 24.

Next, the other electrode 25 is connected to the electrode 24.
On top of. In this state, both electrodes 24 and 25 are pressurized. Here, no particularly large pressing force is required.
The pressure may be such that the contact between the conductive microspheres 29 and the surfaces of the electrodes 24 and 25 is maintained. Next, a pair of electrodes 24 and 25
The laminate in which the conductive microspheres 29 are sandwiched is heated.
Press heating is preferred as the heating method. Thus, the element A as shown in FIG. 1 is obtained.

Examples of the electrodes used in the above element include an electrode having an ITO thin film formed on a glass plate, an electrode having an aluminum thin film formed on a glass plate,
The electrode includes an electrode manufactured by attaching a copper sheet on a plastic film and etching the copper sheet, and an electrode manufactured by printing a silver paste or carbon black on the film. As described above, by using the conductive microspheres, predetermined portions between electrodes of a liquid crystal display element or the like can be electrically connected.

The conductive microspheres of the present invention can be appropriately compressed and deformed. Therefore, when the conductive microspheres are used to connect the electrodes, the contact between the conductive microspheres and the electrode surface is prevented. The contact resistance value can be reduced by enlarging the area. Furthermore, since the deformation recovery after compression deformation is moderate,
In the step of connecting the electrodes using conductive microspheres, when removing the compressive load acting on both electrodes, without forming a gap at the interface between the conductive microspheres and the electrode surface, It does not cause poor contact.

As described above, the conductive microspheres of the present invention
Since it has moderate compressive deformation and deformation recovery properties, when used between two electrodes, it can exhibit excellent anisotropic conductive performance and connection reliability performance, and is suitable for the following applications It is. A transfer material for electrical connection between upper and lower substrate electrodes in a liquid crystal display device. COG between LSI and glass wiring board in liquid crystal display device
(Chip-on-glass) connection material. Electrical connection material between glass wiring board and flexible printed circuit in liquid crystal display device. LS as plate or film substrate
Material for connecting COG (chip on glass) or COF (chip on film) with I.

[0036]

EXAMPLES The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

Evaluation items in Reference Examples, Examples and Comparative Examples are as follows. Evaluation: Compression characteristics of microspheres (i) Load at 10% compression deformation (grf) (ii) K value at 10% compression deformation (Kgf / mm ² ) (iii) Compression deformation recovery rate after 1 grf load (%) ) Micro compression tester (PCT-200 type, manufactured by Shimadzu Corporation)
Were used to evaluate (i) to (iii). Evaluation: Temporal change of connection resistance The test electrode was left at -40 ° C and 80 ° C every hour, and the connection resistance of the electrode was measured every 250 hours using a digital multimeter (manufactured by Takeda Riken).

Reference Examples 1-3 Oligoacrylates and acrylates having the compositions shown in Table 1 were mixed and dissolved. In this mixture, 2% by weight of benzoyl peroxide was dissolved as a radical polymerization initiator. This mixture was put into a 5.5% aqueous solution of Povar at 400% by weight based on the total amount, and mixed and stirred to prepare an aqueous suspension. This aqueous suspension is allowed to stand at 85 ° C. for 5 hours,
Further, the mixture was heated and reacted at 90 ° C. for 3 hours to obtain elastic microspheres as a crosslinked polymer. A sample obtained by separating and drying the obtained microspheres was subjected to the above evaluation. Table 1 shows the evaluation results.

REFERENCE EXAMPLE 4 The same evaluation as that of Reference Example 1 was carried out using commercially available microspheres having a particle size of 5 μm (manufactured by Sumitomo Chemical Co., Ltd., Fine Pearl, polystyrene, low crosslink density) which are generally called a soft type. . Table 1 shows the evaluation results.

Reference Example 5 A commercially available microsphere having a particle size of 5 μm (Micropearl SPA, manufactured by Sekisui Fine Chemical Co., Ltd.) which is generally called a hard type
Reference Example 1 using N, divinylbenzene, high crosslink density)
The same evaluation was performed. Table 1 shows the evaluation results.

[0041]

[Table 1]

In Table 1, M-1310 is a liquid polyol modified at both ends with urethane acrylate (bifunctional, Aronix M series M-1310 manufactured by Toagosei Co., Ltd.) and M-2310.
45 is polyethylene glycol diacrylate (bifunctional, manufactured by Toagosei Co., Ltd., Aronix M series M-24)
5), TEA-1000 is a 1, 6-terminal acrylic-modified butadiene oligomer (polyfunctional, manufactured by Nippon Soda Co., Ltd.)
HXA represents 1,6-hexanediol diacrylate (bifunctional, manufactured by Kyoeisha Chemical Co., Ltd.), and A-TMPT represents trimethylolpropane triacrylate (trifunctional).

Example 1 The surface of the elastic microspheres obtained in Reference Example 1 was plated with gold to a thickness of 100 mm to obtain conductive microspheres. 15 parts by weight of the conductive microspheres were mixed with 100 parts by weight of a 30% by weight toluene solution of a styrene-ethylene-butylene-styrene block copolymer to prepare an anisotropic conductive paste. This anisotropic conductive paste was coated with 3 gold-plated wires / m
A coating of 2.5 mm in width was applied to the joints of the 20 flexible printed circuit test electrodes formed at intervals of m so that the coating thickness after drying was 25 μm. This flexible printed circuit test electrode was heated and joined to a printed wiring board test electrode having the same wiring as this electrode. This bonded electrode was subjected to the above evaluation. Figure 6 shows the evaluation results.
It was shown to.

Comparative Example 1 An anisotropic conductive paste was prepared in the same manner as in Example 1 except that a commercially available hard conductive fine sphere having a particle size of 5 μm (Micropearl Au hard type, manufactured by Sekisui Fine Chemical Co., Ltd.) was used. Then, the same evaluation as in Example 1 was performed on this anisotropic conductive paste. The evaluation results are shown in FIG.

Comparative Example 2 An anisotropic conductive paste was prepared in the same manner as in Example 1 except that a commercially available soft conductive fine sphere having a particle size of 5 μm (Auropearl, manufactured by Okuno Pharmaceutical Co., Ltd.) was used. The same evaluation as in Example 1 was performed for the conductive paste. The evaluation results are shown in FIG.

As is clear from FIG. 6, the electrode bonded with the anisotropic conductive paste using the conductive microspheres of the present invention has excellent initial properties similar to those using the soft conductive microspheres. Connection resistance. Further, in the electrode of the conductive microsphere of the present invention, the connection resistance hardly changes over time, similarly to the electrode of the hard conductive microsphere. Therefore,
It can be seen that the conductive microspheres of the present invention are most excellent as a conductive material.

[0047]

Conductive fine spheres of the present invention, according to the present invention than the constitution described hereinabove, the connection reliability of the extremely high liquid crystal display device can be obtained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a main part of a liquid crystal display device obtained by using a conductive microsphere of the present invention.

FIG. 2 is a graph showing a relationship between a load and a compression displacement of a microsphere.

FIG. 3 is a graph showing a relationship between a K value and a compressive strain of a microsphere.

FIG. 4 is a diagram illustrating a method of measuring a recovery rate after compression deformation of a microsphere.

FIG. 5 is a sectional view showing a general liquid crystal display element.

FIG. 6 is a diagram showing a change over time in connection resistance in Example 1 and Comparative Examples 1 and 2 . The vertical axis represents connection resistance (Ω), and the horizontal axis represents elapsed time (time). ○ indicates Example 1
Represents the conductive fine spheres of Comparative Example 1 , X represents the hard conductive fine spheres of Comparative Example 1 , and Δ represents the soft conductive fine spheres of Comparative Example 2 .

[Explanation of symbols]

 21a electrode 22 electrode 24 electrode 25 electrode 26 transparent substrate 27 transparent electrode 28 binder 29 conductive microsphere 30 seal member 31 transparent substrate 32 transparent electrode 33 orientation control film 34 transparent substrate 35 transparent electrode 36 orientation control film 37 substrate 38 spacer 39 substrate 41 Nematic liquid crystal 42 Polarizing sheet 43 Polarizing sheet

Continuation of front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G02F 1/1339 500

Claims (6)

(57) [Claims] 1. K = (3 / √2) ・^FS -3 / 2 ・ R- ^{1 / 2} (where F represents a load value (kgf) at 10% compressive deformation of the microsphere; S represents the compression displacement (mm), and R
Represents the radius (mm) of the microsphere. ) Is 50 kgf / mm ² or more and 250 k at 20 ° C.
gf / mm ² and the recovery rate after compression deformation is 20
Microspheres that are between 15 and 100% at
And a conductive layer provided on the surface.
Electrostatic microspheres. Value of 2. A K is, 100 kgf / mm ² or more 2
^2. The conductive microsphere according to claim 1, which has a weight of less than 50 kgf / mm2. 3. The conductive microsphere according to claim 1, wherein a recovery rate after the compression deformation is 20 to 95%. 4. The microsphere has a diameter of 0.1 to 5000 μm.
Wherein the coefficient of variation of the diameter (a value obtained by dividing the standard deviation by the diameter in%) is 50% or less.
4. The conductive microsphere according to 2 or 3. 5. The microsphere has a diameter of 0.1 to 1000 μm.
5. The conductive microsphere according to claim 1, wherein the coefficient of variation of the diameter is 50% or less. 6. A liquid crystal display device using the conductive microspheres according to claim 5.