JPS6031043B2 - Anisotropic conductive sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention provides a sheet having conductivity only in the thickness direction.
It relates to a so-called anisotropic conductive sheet.

A thin sheet that is electrically conductive only in the thickness direction and electrically insulated in the direction crossing that direction is called an anisotropically conductive sheet, and is used for example in electronic desk calculators, electronic cameras, electronic It is useful as a material for interconnecting circuit elements housed in extremely limited space, such as in digital wristwatches. FIG. 1 schematically shows the anisotropic conductive sheet as described above. In FIG. 1, an anisotropically conductive sheet 1 includes a sheet-like matrix 2 made of a material having electrically insulating properties, and a large number of linear conductors 3 of approximately equal length oriented in the thickness direction of this matrix 2. have.

As is clear, this linear conductor 3 acts to conduct electricity only in the thickness direction of the matrix 2. To use it as a subsequent material between the circuit elements, as shown in FIG. 2, it is inserted between the circuit elements 4 and fixed by applying some clamping pressure. By this clamping, the circuit elements 4, 4
A connection is made between the opposing terminals 5,5. Such an anisotropic conductive sheet is generally manufactured by the following steps. That is, A. Cutting a magnetic filament-like conductor to create short, linear conductors of approximately equal length.

B. Dispersing the linear conductor in a matrix liquid having electrically insulating properties.

C This mixed liquid is filled between two planes with an interval equal to the length of the linear conductor, and a uniform magnetic field in the thickness direction is applied to the mixed liquid held in a sheet shape in this way. ,
Orienting the linear conductor in the thickness direction of the sheet-like mixed liquid.

D. Solidifying the matrix liquid in a state where the linear conductors are oriented.

However, in anisotropic conductive sheets created using this method, the terminals of the linear conductors are often incompletely exposed from the sheet surface, and are often covered with a thin film of the matrix component. '1} Contact resistance is high and unstable.

[2-The pressure required for conduction is large. '3' When the temperature rises, the ends of the twilled conductor sink into the matrix by the amount of thermal expansion of the matrix, resulting in disadvantages such as connection failure. After completion of orientation, it is useful as an improvement method to solidify the matrix with the conductor end completely reaching the sheet surface by making the distance between the two planes smaller than the length of the linear conductor. The exposed part is still insufficient, and a new problem arises in that the linear conductor is buckled within the sheet. This invention was obtained as a result of Makoto Tsurumi's consideration of what should be done to fundamentally solve the above-mentioned drawbacks.
An object of the present invention is to provide an excellent anisotropically conductive sheet which exhibits conductivity close to the theoretical value under clamping pressure and whose conductivity does not decrease even when the temperature is increased.

That is, in the present invention, a large number of linear conductors are arranged in the thickness direction of a sheet made of a material having electrically insulating properties, and both ends of the linear conductors are arranged from both sides of the sheet. This sheet is characterized by having a protruding foundation that can conduct electricity in the thickness direction of the sheet in a static layer state.

In the present invention, a structure that can conduct electricity in the thickness direction of the sheet in a static layer state means that electricity can be applied by contacting the electrodes from above and below the sheet without applying a strong tensile force in the thickness direction of the sheet. This function is achieved by the fact that both ends of the linear conductor slightly protrude from both sides of the sheet.

Next, this invention will be explained using the drawings. FIG. 3 is a diagram schematically showing a cross-sectional view of the electrically conductive sheet of the present invention. In FIG. 3, the electrically conductive sheet 1 includes a sheet matrix 2 made of a material having electrically insulating properties and a large number of linear conductors 3 arranged in the thickness direction of the matrix 2. There is. The length of the linear conductor 3 is
It is larger than the thickness of the sheet made of matrix 2, and both end portions protrude from the sheet surface. The anisotropically conductive sheet as shown in FIG. 3 is manufactured generally through the following steps. That is, A. Cutting a magnetic filamentary conductor to create shortened linear conductors of approximately equal length. B. Dispersing the linear conductor in a matrix liquid having electrically insulating properties.

C This mixed liquid is filled between two opposing planes, the surfaces of which are in contact with the mixed liquid of the matrix and the linear body are made of an inert soft film, and the mixed liquid is held in a sheet-like form.

At this time, the thickness of the mixed liquid sheet is set to be equal to or greater than the length of the linear body. D The magnetic linear conductors are oriented in the thickness direction of the sheet by the action of the magnetic field.

Thereafter, while maintaining this orientation, the interplanar spacing is gradually narrowed until the interplanar spacing becomes smaller than the length of the twilled conductor. By this operation, the terminal portion of the linear body is exposed from the matrix layer, and the tip is thrust into the soft coating. E Solidify the matrix in this state.

The characteristic feature of the above operations is that the matrix is solidified with the tip of the linear guide crab inserted into the container wall surface made of softening agent. In the above embodiments, the matrix material must be a material with electrically insulating properties. Such materials include polyester resins, epoxy resins, urethane resins, polystyrene resins, polyethylene resins, polyamide resins, Amo resins, silicone resins, thermosets and thermoplastics, and other substantially Contains all kinds of synthetic resins. Further, the matrix material has sufficient fluidity to perform the above-mentioned dispersion and orientation operations of the linear conductor at a temperature below the Curie point of the linear conductor, and does not have a solid state at room temperature. It needs to be something that can be maintained.

"Solidification" here includes chemical reaction hardening and the cooling and solidification of materials that have been molten at relatively high temperatures.
Furthermore, the matrix material is preferably an elastomer. This is because elastomer allows for close contact with a slight clamping pressure even when the terminal is uneven or has dust attached to it when used as a conductive sheet as explained in Figure 2 above. . Therefore, connection failure will not occur. Such elastomers are typified by silicone resins such as silicone rubber, which are obtained as liquid monomers and polymers at room temperature, and which polymerize and solidify at relatively low temperatures, and urethane resins. It is desirable that the linear conductor has both magnetic and conductive properties at the same time, such as iron, nickel, cobalt metals, or alloys containing these metals as main components.

However, the surface of a non-magnetic material such as a copper wire, an aluminum wire, carbon fiber, or glass fiber may be plated with a magnetic metal such as nickel.
Furthermore, the outermost layer of the linear conductor may be plated with gold or wire in order to provide chemical stability against oxidation and the like.
One of the features of the conductive sheet according to the present invention is that plating with an expensive metal such as gold can be applied only to the exposed parts.

Since the anisotropic conductive sheet of the present invention is used as an electrical connection material, it is desirable that the electrical resistance of the linear conductor is low.

However, the degree of magnetism need only be sufficient to effect said orientation in the thickness direction of the matrix. The linear conductor is added to the matrix liquid in an amount of about 0.01 to 5.0% by volume, preferably about 0.05 to 1.0% by volume.

The coating applied to the surface that comes into contact with the liquid mixture is an inert coating that does not react with or adhere to the matrix.

The required rheological properties and thickness will vary depending on the temperature at which the above operation D is performed, the thickness, length, rigidity, etc. of the linear body, but the linear body will not buckle in operation D. It is necessary that the soft body has enough plastic viscoelasticity to penetrate into the film to a depth of at least lr. Particularly suitable are various elastomers such as polybutadiene rubber, nitrile butadiene rubber, styrene butadiene, etc., and polyethylene which softens at relatively low temperatures.

These soft films are usually used by coating or adhering onto a surface made of a hard material, but they can also be used by simply superimposing a film-like film on a surface of a hard material. As described above, the present invention can provide complete conductivity because the conductor protrudes from the sheet surface, but since there is a gap between the tip of the conductor and the sheet surface, it is difficult to use an insulating adhesive. Even when the sheet is fixed or temporarily fixed to a circuit electrode, the adhesive has the characteristic that conductivity is not hindered. Example 1 A thin steel wire with a diameter of 12r was cut to obtain a large number of short linear conductors having an average length of 0.4 and a standard deviation of 0.01 length.

Nickel was electrolessly plated to a thickness of 0.6 µm on the surface of this linear conductive body, and gold was electrolessly plated thereon to a thickness of 0.08 µm.

1.0% by weight of the thus obtained linear conductor was added to a transparent low-temperature curing silicone rubber stock solution having a specific gravity of 1.05, and the mixture was heated under vacuum to obtain a mixed solution.

Two composite films obtained by coating nitrile butadiene rubber to a thickness of 30 μm on a polyester film having a thickness of 100 μm are sandwiched between donut-shaped aluminum basers with a thickness of 0.47, and the rubber film is placed on the inside. The above mixed solution was injected into a space surrounded by the baser and the film, which were made to face each other. A pair of upper and lower flat molds was set in the gap of a solenoid coil with a gap to generate a uniform magnetic field perpendicular to the plane in the space between the upper and lower molds, and the molds were heated to 60 qo. The liquid mixture held in the form of a sheet by the film described above was set on the lower mold surface.

The mold surface spacing was set to 1.0 skin, and a magnetic field of 3000 Gauss was generated at the same time as 0.08 skin/min. The mold was closed at a speed of

After the mold was closed by the spacer, this state was maintained for 40 minutes, the mold was opened, and the cured sheet was taken out. Further, this was heated in an open environment at 150 dC for 15 minutes to completely cure it, and then the composite film on the surface was peeled off to obtain an anisotropically conductive sheet. Except for using polyester film without rubber coating,
A comparative conductive sheet 2 was prepared by performing exactly the same operation as above.

Table 1 shows the comparison results of the characteristics of the two types of anisotropically conductive sheets thus obtained.

The sheet is clearly superior, and the effect of making the ends of the linear conductors protrude from the sheet surface is remarkable. Table 1 Characteristic comparison

[Brief explanation of the drawing]

FIG. 1 is a partially cutaway schematic perspective view schematically showing a conventional anisotropically conductive sheet, and FIG. 2 is a partially cutaway schematic perspective view of a conventional anisotropically conductive sheet. This shows how it is used as a bushing material. FIG. 3 is a sectional view of the anisotropically conductive sheet of the present invention, schematically showing how the linear conductors protrude from the matrix surface. 1: Anisotropic conductive sheet, 2: Matrix, 3: Linear conductor, 4: Electric circuit element, 5: Terminal of electric circuit element. Figure 1 Figure 3 Figure 2

Claims (1)

[Claims] 1. A large number of linear conductors are oriented in the thickness direction of a sheet made of a material having electrically insulating properties, and both ends of the linear conductors are oriented from both sides of the sheet. An anisotropically conductive sheet characterized by having a structure in which the sheet protrudes and can conduct electricity in the thickness direction of the sheet in a stationary state. 2. The anisotropically conductive sheet according to claim 1, wherein the sheet has flexibility. 3. The anisotropically conductive sheet according to claim 1, wherein the rubber is silicone rubber. 4. The anisotropic conductive sheet according to claim 1, wherein the linear conductor is a thin metal wire. 5. The anisotropic conductive sheet according to claim 1, wherein the surface of the linear conductor is coated with gold or silver.