JP2964790B2 - Metal-coated novolak-epoxide spherical resin - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal-coated spherical resin useful as a conductive material for an anisotropic conductive film used for connection between a liquid crystal and a driving circuit and a conductive material used for bumpless bonding of a silicon chip. About.

[0002]

2. Description of the Related Art In a liquid crystal display device, an anisotropic conductive film is used as a connector for connecting a transparent electrode of a liquid crystal panel and a copper foil electrode of a liquid crystal drive circuit. This is obtained by uniformly dispersing a spherical conductive material in an adhesive, and thermocompression-bonded between electrodes. When the conductive material is compressed by the thickness of the copper foil of the electrode portion and comes into contact with the electrode, the conductive material has conductivity in the thickness direction and has no conductivity in the surface direction. That is, a film having anisotropy in conductivity is obtained, and high-density contact is possible. As the conductor material, conventionally, metal particles such as solder and nickel have been used. However, it is difficult to miniaturize and uniformize the particles and cannot cope with high-density connection. There was a problem that connection was not obtained and reliability was lacking. In order to solve these problems, attempts have been made to use a spherical resin coated with metal by wet plating as a conductive material. Resins that can be used for this purpose must have good adhesion to the coated metal and have suitable elasticity and hardness. However, most resins have poor adhesion to metal, and are crushed by thermocompression bonding to break or peel off the metal film, resulting in short-circuits or poor conductivity, which has a problem in reliability. A phenolic resin is considered as a resin suitable for such purpose. However, the phenol resin is slightly brittle, so that it is easily cracked and easily attacked by alkali. Further, a phenol resin containing a large number of phenolic hydroxyl groups in a molecule has a large water absorption rate, which may cause a problem because corrosion of a metal coating occurs after plating.

[0003]

SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to provide a highly reliable conductor material having appropriate elasticity and hardness, and excellent durability and moisture resistance.

[0004]

[Knowledge to Solve the Problem] The inventors have studied means for achieving the above object. Then, after producing a microspherical resin using phenol and formaldehyde, the present inventors have found that a metal-coated resin sphere which has been subjected to three-dimensional crosslinking treatment using epoxide and then metal-coated satisfies all the above-mentioned problems. Was completed.

[0005]

That is, according to the present invention,
The present invention provides a metal-coated novolak-epoxide spherical resin obtained by forming a spherical novolak-type condensate of phenol and formaldehyde and then coating the three-dimensional crosslinked structure obtained by reacting an epoxide with a metal. The novolak-type condensate can be obtained by, as is known, reacting phenol and formaldehyde by gently heating in the presence of an acid catalyst. Here, as the phenol, any compound having a phenolic hydroxyl group can be used. Formaldehyde can be used in any form of formalin and paraformaldehyde. Acid catalysts used for novolak formation include:
For example, hydrochloric acid, oxalic acid and the like can be mentioned.

In order to obtain a spherical novolak, phenol is added to a mixture of an acid catalyst and formaldehyde, preferably formalin, and the mixture is reacted with stirring. A typical reaction procedure for obtaining a spherical novolak is as follows. While the formaldehyde in the aqueous medium and the acid catalyst were being stirred and the phenol having a weight ratio of 1 to 20 was added dropwise to formaldehyde, the temperature was gradually raised to 80 to 90 ° C over 4 to 8 hours. Let react for ~ 2 hours.
At a reaction temperature of 80 ° C. or lower, fusion of the product is liable to occur, and 9
A temperature of 0 ° C. or higher is not preferable because it is difficult to obtain a suitable particle size distribution. In order to obtain a suitable particle size distribution, it is preferable to add additives such as polyvinyl alcohol, gelatin, gum arabic, and guar gum. These additives prevent the adhesion between the novolak particles. Further, the stirring speed may be adjusted to obtain a desired average particle size. Novolak having a softening point of about 60 to 70 ° C. is obtained by the above reaction.

The resulting spherical novolak is a two-dimensional crosslinked structure which is heat-soluble and soluble in a solvent, and is reacted with epoxide to form a three-dimensional crosslinked structure, thereby forming an insoluble and infusible resin. The reaction procedure between the spherical novolak and the epoxide can be performed as follows. Spherical novolak was added to the spherical novolak in an aqueous medium or a polar solvent such as ethanol while stirring epoxide (e.g., epichlorohydrin) at a weight ratio of 1 to 5;
React at ~ 90 ° C for 5-30 hours. At a reaction temperature of 40 ° C. or lower, the crosslinking reaction does not proceed, and at a temperature of 90 ° C. or higher, spherical novolaks are undesirably fused. In order to obtain suitable dispersibility, it is preferable to add additives such as polyvinyl alcohol, gelatin, gum arabic, and guar gum. The epoxide used for crosslinking the novolak may be any one having an epoxide group or a group equivalent thereto. For example, styrene oxide, octene oxide, epichlorohydrin and the like are used.

When a spherical resin is used in the anisotropic conductive film, the primary particles have an average particle size of 1 to 30 μm, and at least 70% or more of the primary particles have a particle size range of ± 30% of the average particle size. Must be present. Primary particle size is 1μm
If the particle size is smaller than the above range, the conductive film does not easily have sufficient anisotropy because it is easy to aggregate and hardly monodisperse. Further, if it is larger than 30 μm, it is not preferable because fine pitch cannot be coped with. Further, if at least 70% or more of the primary particles are not present in the particle size range of ± 30% of the average particle size, the particles are also likely to aggregate and hardly monodisperse, and thus are not suitable for applications such as conductive films.

The most suitable method for coating a metal is an electroless plating method, and a known general method used for electroless plating after imparting a catalytic property by a Sn / Pd system can be used. The amount of metal coating varies depending on the particle size of the spherical resin used as the core material and the specific gravity of the metal to be coated, but the amount of coating for obtaining sufficient conductivity is in the range of 10 to 90% by weight. When the coating amount is less than 10% by weight, the particle size of the specific surface area is small.
Even when a spherical resin having a thickness of μm is used, the film thickness of the metal coating is so small that sufficient conductivity cannot be obtained. When the content is more than 90% by weight, sufficient conductivity can be obtained even when a spherical resin having a large specific surface area and a particle diameter of 1 μm is used, and even if the thickness of the metal coating is further increased, not only does the conductivity level off. , The specific gravity is increased, and the dispersibility is deteriorated. The metal to be coated is a metal that can be electrolessly plated, Au, Pd, Ag, C
u, Co, or Ni. The metal layer may be a single layer or two or more layers, and the thickness of the metal coating is 0.05.
If not more than μm, sufficient conductivity cannot be obtained.
In the case of coating a noble metal such as u or Pd, it is recommended to provide a required film thickness in the lower layer as two or more layers in order to reduce the cost, and to coat only the outermost layer with the noble metal.

[0010]

According to the metal-coated novolak-epoxide spherical resin obtained by the present invention, the epoxide reacts with the novolak resin to form three-dimensional crosslinks. For this reason, the bending strength is improved and the generation of cracks is eliminated. Furthermore, the phenolic hydroxyl group in the novolak resin is etherified by the reaction with the epoxide, so that the thermal oxidation resistance and alkali chemical resistance are improved, and the number of hydroxyl groups per unit weight is reduced, so that the water absorption is reduced. ,
The occurrence of corrosion after metal coating is suppressed. Therefore, by using the metal-coated resin ball of the present invention as a conductor, a highly reliable conductive filler can be obtained.

Hereinafter, the present invention will be described specifically with reference to examples.

Example 1 30 g of oxalic acid was added to 37% formalin 500
650 mL of phenol and 80 g of gum arabic, and heated to 90 ° C. for 5 hours with stirring. When the temperature reached 90 ° C, 40 mL of 10% hydrochloric acid was added, and stirring was continued for 1 hour while maintaining the temperature at 90 ° C. The obtained spherical novolak resin was taken out of the system and washed with water. A mixed solution consisting of 75% by weight of epichlorohydrin and 25% by weight of water is azeotropically aggregated, and only 10 kg of the upper layer (7% by weight aqueous solution of epochlorohydrin) is prepared. To this, 120 g of gum arabic is added. Disperse the spherical novolak resin,
The mixture was heated to 80 ° C. with stirring and maintained for 8 hours. The obtained novolak-epoxide spherical resin was taken out of the system, washed with water and dried. The yield is 957 g and the particle size is 12 μm.
m and 22% were peaks and distributed in the range of 1 to 29 μm. This was put together with dummy glass beads in an ultrasonic classifier and classified to 10 ± 1 μm. The yield is 79 g, 10
92% or more of the spherical resin was present in the range of ± 1 μm. The obtained resin was treated with SnCl ₂ 10 g / L, HCl 2
To sensitize by immersing in 0 mL / L aqueous solution,
After activation by immersion in an aqueous solution of 1 g / L of PdCl _{2 and 2} mL / L of HCl, 50% by weight of Ni, 50% by weight of Ag and
After coating with 0% by weight, three kinds of metal-coated novolak-epoxide spherical resins of 20% by weight of Au were obtained. Ni plating (plating bath temperature: 70 ° C) Sodium citrate 20g / L Lactic acid 20mL / L Nickel sulfate 25g / L Sodium hyposulfite 30g / L Lead acetate 5mg / L Ag plating (plating bath temperature: 25 ° C) Ethylenediaminotetraacetic acid Tetrasodium 100g / L Sodium hydroxide 30g / L Formalin 50mL / L Silver nitrate ^* 15g / L Ammonia water ^* 50mL /
L *: Dilute in water and add dropwise Au plating (plating bath temperature: 70 ° C) Sodium cyanide 10g / L Sodium hydroxide 20g / L Ethylenediamine 20mL /
L Potassium gold cyanide 4g / L Sodium borohydride 20g / L

[0012]

[Comparative Example] Commercially available spherical phenol resin is 10 ± 1μm
(Existence rate: 91% or more), and N
i 50% by weight, Ag 50% by weight and Ni 40% by weight
% Coated phenol of 20% by weight Au after coating
A spherical resin was obtained. In both Examples and Comparative Examples, the relative humidity was 85.
% X 85 ° C for 24 hours.
When the surface of was observed with a scanning electron microscope,
No abnormalities such as spots and blisters were observed, but in Comparative Examples
Means that the liquid seeps from the pinhole
Dark spots due to protrusion were seen. Examples,
In both comparative examples, the relative humidity of
It was left in a constant temperature and humidity chamber of 85% × 85 ° C. for 120 hours. Release
Separate the sample by 1g before and after placing, and cross-sectional area 1cm^TwoNo electricity
Between the poles, 10kg / cm^TwoResistance while applying pressure
As a result of measurement, in the example, the change before and after
Not seen, any of 10^-FiveΩ · cm order
Was. On the other hand, in the comparative example, 10^-Five Oh
It was 10^-3Ω · cm order
ー, 10^-FourΩ ・ cm and one or two digits higher volume resistivity
Indicated. Furthermore, the pressure is 100 kg / cm^TwoThat was raised to
Of course, in the examples,^-FiveΩ · cm order volume resistance
No change was observed even if the pressure was increased while maintaining the drag rate
However, in the comparative example, the phenol resin cracked,
All 10^-3High volume resistivity up to the order of Ωcm
Was.

Claims (5)

(57) [Claims] 1. A metal-coated novolak-epoxide spherical resin, wherein a three-dimensional crosslinked structure obtained by converting phenol and formaldehyde into a spherical novolak-type condensate and then reacting with epoxide is coated with a metal. 2. The primary particles have an average particle size of 1 to 30 μm,
2. The metal-coated novolak-epoxide spherical resin according to claim 1, wherein at least 70% or more of the primary particles are present in a particle size range of ± 30% of the average particle size. 3. The metal-coated novolak-epoxide spherical resin according to claim 1, wherein the method of coating the metal is an electroless plating method. 4. The metal-coated novolak-epoxide spherical resin according to claim 1, wherein the coating amount of the metal is 10 to 90% by weight. 5. The metal to be coated is Au, Pd, Ag, C
The metal-coated novolak-epoxide spherical resin according to claim 1, wherein the metal-coated novolak-epoxide spherical resin is one or more layers of u, Co, and Ni.