JPS61123507A - Manufacture of anisotropically conductive sheet - Google Patents

Abstract

PURPOSE:To obtain the title sheet wherein a conductive powder is uniformly dispersed, and insulating property in the londgitudinal direction is secured, by mixing a conductive powder and a polytetrafluoroethylene, and rolling the mixture into a specified thickness. CONSTITUTION:A conductive powder for example of copper or ion and a polytetrafluoroethylene are mixed in a stirrer in the presence of a processing aid such as kerosine or the like. The mixture is filtered to remove the processing aid, and is rolled by even speed rolls into a sheet wherein the fibrillation of said polytetrafluoroethylene is facilitated. The rolling of the sheet is continued to have a thickness approximately equal to the particle diameter of the conductive powder so that the surfaces of each particle of the conductive powder are exposed on opposite sides of the sheet to obtain the intended sheet having conductivity in the direction of the thickness of the sheet.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for manufacturing an anisotropically conductive sheet.

Prior Art and Problems Anisotropic conductive sheets, which are conductive in the thickness direction but insulating in the horizontal and vertical directions, can be used for high-density connectors,
For example, it is useful for connecting a printed wiring board and a flat cable, and connecting a printed wiring board and an LSI package.

As such anisotropically conductive sheets, those in which conductive metal powder is dispersed in an insulating material such as rubber or synthetic resin, and those in which conductive fibers are embedded are known. 1 of the latter anisotropic conductive sheet! In this process, conductive fibers are dispersed in a rubber gelastic insulation material, the fibers are oriented, the rubber/glasstic material is cured, and the cured material is spread along a plane almost perpendicular to the direction in which the conductive fibers are oriented. This method requires tangle-free dispersion of conductive fibers, orientation of conductive fibers, curing reaction of rubber/glass materials, and slicing, which makes the manufacturing equipment complicated. Inevitable.

On the other hand, an anisotropic conductive sheet in which conductive powder is dispersed has an advantage in terms of equipment, but it is difficult to disperse the conductive powder at a high density (higher density reduces lateral contact of the conductive powder). There are disadvantages such as the resistance value variation in the sheet thickness direction due to contact pressure is significant. Regarding the latter cause, one possible cause is that the conductive powders are in chain contact in the sheet thickness direction, and the contact resistance between the conductive powders changes due to pressure.Therefore, theoretically, The above problem of contact resistance can be eliminated by dispersing the metal powder in a single manner (one location within the thickness of the sheet), but in order to do so, it is necessary to make the sheet thin to K, which is close to the diameter of the conductive powder. Such molding is extremely difficult with conventional techniques.

OBJECTS OF THE INVENTION The object of the present invention is to make it possible to monodisperse conductive powder, and to maintain sufficient insulation properties in the longitudinal and lateral directions of the sheet (1 fp: anisotropic The object of the present invention is to provide a method for easily manufacturing a conductive sheet.

Structure of the Invention The method for manufacturing an anisotropically conductive sheet according to the present invention involves mixing conductive powder and polytetrafluoroethylene in the presence of a processing aid, rolling the mixture into a sheet, and rolling the mixture into a sheet. Promotes fibrillation of fluoroethylene,
What is the conductive powder diameter for sheet rolling and sheet thickness? 7f%
This method is characterized by imparting conductivity in the thickness direction of the sheet by penetrating the sheet 1c with conductive powder until the sheet 1c reaches 10%.

Polytetrafluoroethylene (hereinafter referred to as pTrE)
It is common knowledge that fibrillation occurs under mechanical stress. However, the non-exploding cases are caused by conductive powder and PTF.
It has been found that when a mixture with 'g is rolled to form fibrils, fibers grow in the shape of root hairs between the conductive powders, thereby effectively eliminating contact between the conductive powders. This is an unexpected phenomenon in contrast to the common knowledge mentioned above. In this case, the sheet is subjected to tensile forces, but the tensile strength increases due to fibrillation, thus making it possible to roll the sheet to a thickness approximately equal to the diameter of the conductive powder, and thus easily The conductive powder can be passed through the sheet in a single state.

In the present invention, the basic requirement governing the high density of the conductive powder is the mixed state of the conductive powder and polytetrafluoroethylene, and the above fibrillation is an unavoidable part of the conductive powder under this mixing. The purpose is to separate the chain contact of powder. Conventionally, as a method for manufacturing fuel cell electrode materials, P'r
It is known to make F'B into a porous microstructure consisting of fibers and nodes interconnected by the fibers by stretching, impregnating the pores with conductive powder (e.g. carbon black), and further rolling. (Patent application published 1982-1)
21202), there is a limit to the uniform dispersibility of pores, and the amount of conductive powder impregnated cannot be increased so much.
Since the conductive powder constitutes a conductive path in a chain, it is difficult to expect the present invention to achieve higher density of the conductive powder, stability of resistance value against contact pressure in the thickness direction of the sheet, etc.

In the present invention, in order to mix the conductive powder and PTFF more uniformly, the PTFE fine powder is pre-stirred with a stirrer in the presence of a processing aid to advance fibrillation. PTFIEV
It is desirable to mix c4 conductive powder.

In the present invention, metal powder obtained by general metal powderization methods such as mechanical crushing or atomization can be used as the conductive powder, and it is preferable to use spherical powder, but angular or acicular powder can also be used. The size is 5μ to 5μr, preferably 1oμr.
It is about n~0.3.

To carry out the present invention, (a) first, fine powder of PTF I or fibrillated PTFE and conductive particles are mixed in the presence of a processing aid (crocin, white oil, etc.);
Mix with a stirrer.

Stirring progresses fibrillation of j7PTFE and promotes dispersion of the conductive powder. An autohomo mixer can be used as the stirrer, and a homodisper with stirring blades bent at 90° vertically around a disk is sufficient. It is appropriate that the amount of processing aid during this stirring be the minimum amount that can soak the entire mixture; if it is more than this, the conductive powder is likely to separate. The stirring time for the preliminary stirring and mixing described above was set at a blade rotation speed of 2000 to 5oooR/m.
2 to 3 minutes is sufficient.

The conductive powder can be copper, aluminum, zinc, tin or iron. Since the powder is passed through the PTWE sheet in a single state, the powder diameter is determined by the sheet thickness (rolling limit thickness O, OO5
In addition to being regulated by the relationship between O, Ol tm and
．． It is 3M. It is desirable to increase the amount of conductive powder added to PTPEi in order to increase the density of the connector, but if the amount is too large, it is difficult to ensure the mechanical strength (tensile strength) of the anisotropic conductive sheet, and the weight of PTFEilOO is usually increased. 100 to 2000 parts by weight per part is appropriate.

(b) Once the mixture of conductive powder and p'rp'g is obtained in this way, the liquid component (processing aid) is removed by p-filtration,
Roll rolling is performed at a constant speed. In this case, in order to ensure workability, it is appropriate that the roll temperature be 20 to 80°C. In order to efficiently promote fibrillation in this roll rolling, it is necessary to gradually reduce the thickness to a predetermined thickness by rolling in several or more stages. In addition, in order to further improve the dispersion of the conductive powder, sheets that have been rolled to a predetermined thickness are piled up and then re-rolled to the predetermined thickness several times until the sheets are uniform in color. It is desirable to repeat the procedure (for example, 3 to 5 times).

During this rolling, it is possible to replenish the conductive powder separated during the stirring and rolling.

The above-mentioned predetermined rolling thickness refers to a thickness that allows the conductive powder to be monodispersed in the rolled sheet, and is usually larger than the maximum diameter of the conductive powder, but smaller than 1.8 times the maximum diameter. The dimensions are as follows.

(c) If a rolled sheet of a predetermined thickness is obtained in this way,
Processing aids are finally removed by heat drying or solvent soaking. Next, this sheet is finally rolled to expose the monodispersed conductive powder from both sides of the sheet, so that the conductive powder passes through the sheet in a single state. The thickness of this final rolling is set depending on the powder diameter distribution of the conductive powder used, but is usually within the range of the maximum powder diameter to the average powder diameter.

b) Finally, PTF'Fi is fired. The firing temperature is usually 360° to 380°C. When the conductive powder is easily oxidized, especially copper powder, it is necessary to sinter it in an inert gas such as nitrogen gas.

Incidentally, when the anisotropically conductive sheet is attached to a substrate such as a connector main body and then fired, or when used unfired, the above step (2) can be omitted.

As in step (c) above, after removing the processing aid,
When final rolling (penetrating the sheet of conductive particles) is performed, pinholes and the like left after removal of the processing aid can be closed by rolling.

However, if the occurrence of pinholes is slight or not a problem, the final thickness (predetermined thickness) in the step (b) should be adjusted to the final rolling thickness (maximum diameter of conductive particles ~
The average diameter may be set as 1, and only the processing aid may be removed in step e9 above.

Furthermore, in the step (c) above, the thickness of the processing aid-removed sheet (degreased sheet) to be final rolled is made to be very slightly thicker than the thickness of the sheet through which the conductive powder penetrates, because The purpose is to minimize the processing of PTFE after degreasing. Therefore, even though PTFg solidifies due to degreasing, damage to PTFFi can be effectively prevented.

According to the method for manufacturing an anisotropically conductive sheet according to the present invention, P
By fibrillating TFEt, the conductive powder can be sufficiently non-contacted with each other, and conductivity in the thickness direction can be imparted by penetrating the sheet in a single state of the conductive powder. Due to its good dispersibility, it is possible to produce a high-density anisotropically conductive sheet with excellent conductivity against contact pressure in the thickness direction and insulation in the horizontal and vertical directions with only simple operations such as mixing and rolling.

Description of examples Examples of the present invention will be described below.

[Example 1] Kerosene was added to 100 parts by weight of PTFg fine powder (manufactured by Daikin Industries, Ltd., trade name FIOI), and PTF'lE was added.
immersed in kerosene, use a stirrer (manufactured by Tokushu Kika Kogyo, Auto Homo Mixer) with Homo Desper blades at 200 rpm.
Forced stirring was carried out for 2 minutes at 0=3000 V, and 300 weight of conductive metallic copper powder (manufactured by Shushu Metal Foil Powder Industries, 100 to 200 mesh sieve, maximum 150 μm, average 125 μm) was added thereto. Then, kerosene was added to the extent that the entire mixture was submerged, and the mixture was stirred for 3 minutes at the same rotation speed as before. As a result, the conductive metallic copper powder was almost uniformly dispersed. to remove excess kerosene, pass it through constant speed rolling rolls at a temperature of 60°C, make the first roll gear lug 5mm thick, successively thinner by 0.2m, and repeat rolling to achieve the desired thickness. When it became 0.5 tomo, Zara V-ko,
The sheet was folded four times and rolled again to a thickness of 0.5j+m. This was repeated three times. As a result, the color unevenness of the sheet was eliminated and the sheet became a uniform copper color. Further rolling was continued to obtain a sheet with a thickness of 0.15 mm. Since this sheet contains kerosene as a processing aid, it was stored in a hot air dryer at 80° C. for 4 hours to degrease it. As a result, the sheet becomes a sheet of PTFEi in which metallic copper powder is monodispersed. This sheet was further rolled by narrowing the rolling roll gear lugs to obtain a sheet thickness of 9011rrL and 60 μm.
I created two types of sheets. In this way, the metallic copper powder penetrated through the sheet in the thickness direction in a single state. Firing is performed for the purpose of improving the mechanical strength of this sheet and fixing the metallic copper powder.

In order to prevent the sheet from shrinking, the sheet was wrapped around an iron pipe together with aluminum foil and fired at 370'C in a nitrogen gas atmosphere.

[Example 2] The same PTFE and metal steel powder as in Example 1 were used. However, the blending ratio is PTFE 100. The amount of metallic copper powder was 1000 parts by weight based on the i-placed part. Two types of anisotropically conductive sheets with thicknesses of 90 μm and 60 μm were prepared in the same manner as in Example 1.

[Example 3] The same PTFEi as in Example 1 was used, and the metal powder had a maximum of 63 μm and an average of 45 μr IL (Fukuda Metal Foil & Powder Industry c.
Copper powder of U-Q-250) was used. PTF'EflO
An undegreased sheet with a thickness of 70 μm was obtained in the same manner as in Example 1 using 300 parts by weight of metallic copper powder per part by weight of O, and after degreasing, it was rolled to obtain two types of sheets, 60 μm and 30 μm, and fired. An anisotropically conductive sheet was prepared.

[Example 4] Same composition as Example 3, but with the amount of P T F' glo
.

Two types of anisotropically conductive sheets having sheet thicknesses of 60 μtn and 30 μm were prepared in the same manner as in Example 3 using 1000 parts by weight of metallic copper powder.

[Example 5] Same composition as Example 3, but with a blending amount of PTF''E10
0 parts by weight, the metallic copper powder was 1500 parts by weight, and sheet thicknesses of 60 μm and 30 μm were prepared in the same manner as in Example 3.
Two types of anisotropically conductive sheets were created.

[Example 6] The composition was the same as in Example 3, but the amount was PTFglo.

Two types of anisotropically conductive sheets with sheet thicknesses of 60 μm and 30 μm were prepared in the same manner as in Example 3 using 2000 parts by weight of metallic copper powder. The electrical conductivity in the sheet thickness direction and the electrical resistance across the surface of the electrically conductive sheet were measured, and the results were as shown in Table 1.

Therefore, even when 20oO parts by weight of copper powder is blended with 100 parts by weight of PTF'E, sufficient insulation in the vertical or lateral direction (electrical resistance between the sheet surfaces) can be ensured, and the copper powder It is clear that the situation is very dispersed.

It is also clear that the conductivity through the sheet thickness can be increased by reducing the sheet thickness.

For comparison with the present invention, 300 parts by weight of copper powder with a particle size of 0.151 uI was blended with 100 parts by weight of these insulating materials for each of soricone rubber and polyvinyl chloride, and this was rolled into a sheet with a thickness of 0. Although it was rolled to .1sm,
The sheet strength was so weak that it could not be used.

The above measurement procedure is as follows.

The anisotropic conductive sheet of each example was placed on a flat brass plate serving as a conductive electrode in the thickness direction of the sheet, and a 4-point groove (needle electrode thickness 0.75 sm, between needle electrodes) was placed on the surface of the sheet. Distance 3 dragons, series) contact,
Connect one needle electrode and the flat brass plate electrode to a digital multimeter (Takeda Riken (Kiku!'! T rl 6855) and read the resistance.

At some point, disconnect the needle electrode from the meter, connect the other needle electrode to the meter, and read the resistance. In this way, four points are measured for one sample. The number of samples was five for each example. An anisotropically conductive sheet of the same type was placed on it, a glass flat plate was placed on top of it under a load of 1 kg, and the resistance was measured by connecting to a digital multimeter.

Claims (3)

[Claims] (1) Conductive powder and polytetrafluoroethylene are mixed in the presence of a processing aid, this mixture is rolled into a sheet shape, and the fibrillation of the polytetrafluoroethylene is promoted, and the sheet rolling is adjusted to the sheet thickness. 1. A method for producing an anisotropic conductive sheet, characterized in that conductivity is imparted in the thickness direction of the sheet by penetrating the sheet with conductive powder until the diameter of the conductive powder becomes approximately equal to the diameter of the conductive powder. (2) An anisotropic conductive sheet according to claim 1, characterized in that the polytetrafluoroethylene to be mixed with the conductive powder is stirred in the presence of a processing aid to advance fibrillation. manufacturing method. (3) A method for producing an anisotropically conductive sheet according to claim 1 or 2, which comprises stacking a plurality of sheets with accelerated fibrillation and rolling the stacked sheets. .