JPH07220539A - Manufacture of anisotropic conductive sheet - Google Patents

Abstract

PURPOSE:To enable the economical manufacture of aniotropic conductive sheets which are useful for electric connection of electrodes at high density and for inspection of the electrodes. CONSTITUTION:Conductive particles 1 of a uniform particle size are dispersed in an insulating material and a sheet-like object is formed which has the thickness of the insulating material is less than or equal to the particle size of the conductive particles. Then, at least one side of the sheet-like object is heated and pressed in the condition in which the sheet is set to face to a plane-like body having uneven surface. After that, the plane-like body having uneven surface is removed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an anisotropic conductive sheet having conductive particles exposed on the front and back surfaces or one surface, which is useful for electrical connection and inspection of high density electrodes.

[0002]

2. Description of the Related Art An anisotropic conductive sheet having conductivity only in the thickness direction of a sheet made of rubber or synthetic resin is used, for example, between circuit boards such as printed wiring boards and between these and electronic parts such as semiconductor chips. It is used for electrical connection and inspection of high density electrodes. These are those that obtain electrical conductivity between the opposing electrodes by contact by pressure or heat and pressure, and generally the one in which the conductor is exposed or projected on the front or back surface or one surface.
As the conductor of such an anisotropic conductive sheet, conductive particles such as conductive fibers or conductive metal particles are embedded in the thickness direction of the sheet, or a through hole is provided in the sheet, and conductive by plating or the like. It is known that the body is formed.

[0003]

When the conductor of the anisotropic conductive sheet is the former conductive particles, the resolution is insufficient and reliability is unsatisfactory due to the inability to cope with the recent high density of electrodes. Has the drawback of being sufficient. The reason for this is that when the conductive particles dispersed in the sheet are present at a high concentration,
This is because contact is made in the surface direction, the insulating property between adjacent electrodes is lost, and the contact points are reduced when the concentration is low, so that the conductivity in the thickness direction is insufficient. In addition, since the height and area of the exposed portion of the conductive particles from the sheet cannot be controlled sufficiently, the conductivity varies, and in addition, when the component in which the conductive particles protrude from the sheet is repeatedly used for inspection. However, the reliability is still insufficient because the conductive particles fall off from the sheet.

In the latter case, since a fine through hole is formed in the sheet by a laser beam or the like, and a conductor is formed therein by plating, for example, the process is complicated and it is difficult to obtain a large area product. Although the disassembled product can be obtained, it has high manufacturing cost, and has the drawback that it is expensive and difficult to put into practical use. The present invention has been made to solve the above problems, and provides an inexpensive method for producing an anisotropically conductive sheet useful for electrical connection and inspection of high-density electrodes.

[0005]

According to the present invention, (a) a sheet-like material in which conductive particles having a uniform particle diameter are dispersed in an insulating material, and the thickness of the insulating material is equal to or less than the particle diameter of the conductive particles. From the step of (b) applying heat and pressure with at least one surface of the sheet-like material facing the sheet having irregularities, and (c) removing the sheet having irregularities. And a method for producing the anisotropic conductive sheet.

As shown in FIG. 1, the particles in the present invention are conductive particles 1 having a uniform particle size, and preferably have a substantially spherical shape, and the surface thereof has an insulating property exhibiting a heat softening property under heat and pressure, if necessary. The coating 2 can be applied. Here, the uniform particle diameter is preferably ± 20% of the central particle diameter, and if it is possible, it has a particle diameter range of ± 10% or less. A narrower range is preferable because the height of protrusion from the sheet can be made uniform and a stable contact resistance can be obtained. The central particle diameter is preferably about 2 to 5000 μm, more preferably 5 to 100 μm, and 1
It is particularly preferable that the thickness is 0 to 80 μm. These are selected according to the desired resolution. That is, it is necessary to make the particle diameter of the conductive particles smaller than the minimum width of the distance between adjacent electrodes or wiring patterns in order to prevent short circuits and cope with thinning of wiring. If the particle size is too small, the strength of the sheet tends to be insufficient.

As the conductive particles 1, various conductive metals, alloys and oxides can be used. Ni, Cu, and A are preferably used as the material in consideration of conductivity and corrosion resistance.
Particles of l, Sn, Zn, Au, Pd, Ag, Co, Pb and the like. The grain shape is preferably substantially spherical, but may be any shape such as providing a large number of protrusions on the surface. Further, as the conductive particles 1, those having a structure in which the thin metal layer 4 is provided on the surface of the core material 3 as shown in FIG. 2 are preferable because spherical products having a uniform particle size are easily available. Examples of the organic material for the core material 3 include polymers such as polystyrene, nylon, and various rubbers. When they are cross-linked, solvent resistance is improved. For example, a solvent is contained in the sheet raw material. In this case, there is no elution and the characteristics of the sheet are less affected, which is preferable. When the core material 3 is a deformable particle such as a polymer, it is possible to flatten the protruding portion from the sheet and impart elasticity by heating and pressing during manufacturing. It is effective for improving reliability by increasing the contact area of the.

The core material 3 may be particles of an inorganic material such as glass, ceramics, silica, etc. In this case, the heat resistance can be further improved as compared with the polymer core material. As the thin metal layer 4, various conductive metals, alloys, oxides and the like can be adopted. The same material as the above-mentioned conductive particles can be applied to these, and they can also have a single-layer or multi-layer structure. The thin metal layer 4 may be formed by a general method such as a vapor deposition method, a sputtering method, an ion plating method, a thermal spraying method, or a plating method. However, the electroless plating method provides a coating layer having a uniform thickness. preferable. As shown in FIGS. 1 and 2, it is also possible to form an insulating coating 2 on the surface of the conductive particles 1 that exhibits a thermal softening property under heating and pressurization. General indicators such as elastic modulus and hardness as a measure of heat softening property,
For example, thermal transformation points such as melting point, glass transition temperature and softening point can be used as a standard.

As the insulating coating 2, there are hot melt adhesives and base polymers thereof, such as polyethylene,
Ethylene-acetic acid copolymer, ethylene-acrylic acid copolymer, ethylene-acrylic acid ester copolymer, polyamide, polyester, polyurethane, polystyrene, styrene-divinylbenzene copolymer, styrene-isoprene copolymer, styrene-butadiene Examples thereof include copolymers, ethylene-propylene copolymers, acrylic ester rubbers, styrene-ethylene-butylene copolymers, phenoxy resins and solid epoxies. The insulating coating 2 may be present in the form of particles, and may have a single-layer or multi-layer structure. In the case of a multilayer structure, the functions of strength retention, solvent resistance, adhesiveness, flexibility, heat resistance, and plating solution resistance can be shared, which is preferable. There is no limitation on the means for forming the soft layer 2, and there are a spray method, a high-speed stirring method, a spray dryer method, and the like.

Next, the conductive particles are dispersed in the insulating material to form a sheet-like material having a single layer of particles having a thickness equal to or smaller than the particle diameter of the conductive particles. As a dispersion method, the conductive particles and the insulating material may be separately formed and then integrated. The insulating material in this case may be a thermoplastic resin such as polyethylene or polypropylene, but a curable insulating material such as epoxy resin or polyimide by heat, energy such as light or electron beam, heat resistance, moisture resistance and mechanical properties. It is preferably applied because it is excellent in Since the present invention is a manufacturing method under heat and pressure, a system of epoxy resins and a latent curing agent, or a combination system of acrylic or urethane, an epoxy resin and a photoactivator, is likely to react at a relatively low temperature. Therefore, it is more preferable.

The ratio of the conductive particles in the sheet is 2
˜70% by volume is preferably used, more preferably 5 to 50% by volume, and particularly preferably 10 to 40% by volume. Even if the addition amount is excessive, according to the present invention, particles can be arranged at a desired pitch, and since the conductive particle surface which is a preferable mode has an insulating coating, the insulating property of the adjacent electrode is unlikely to deteriorate. . When forming a sheet-like material, it can be formed by rolling between rolls without using a substrate or by melt extrusion. It can also be formed on a substrate. The base material may be a peelable base material such as a separator, or may be a wiring board. Thus, when formed on a substrate, volume contraction due to solvent volatilization can be utilized at the time of sheet formation, and the thickness of the insulating material is equal to or less than the particle diameter of the conductive particles,
For example, a continuous sheet material can be easily obtained. The releasable base material can be removed if necessary after the cohesive force of the insulating material described later has increased.

When a sheet is formed on the wiring board having the inspection circuit, the circuit board with sheet can be easily obtained. At this time, when contact between the wiring board and the conductive particles is obtained, the conductive particles may be exposed or projected only on the surface of the sheet. Next, at least one surface of the sheet is made to face a planar body having irregularities and heated and pressed to promote softening flow of the insulating material. Examples of the sheet having irregularities include a polishing sheet and an anisotropic conductive sheet. In the case of an anisotropic conductive sheet, as shown in the sectional view of FIG. 3, (a)
The projecting conductors 5, such as the circular shape of (c), the triangular shape of (b), and the square shape of (d), are present protruding from the front and back surfaces or one surface of the support 6. As shown in FIG. 4, the planar body having the irregularities is preferably formed with a predetermined pitch P and a space S (distance between the conductors 5). In addition, the conductor 5 in the planar body having the unevenness may be insulative.

As shown in FIG. 4, when the particle diameter of the conductive particles 1 is set to be equal to or smaller than the distance of the pitch P, the conductive particles 1 can be arranged more efficiently. More preferably conductive particles 1
Is equal to or higher than the height of the conductor 5 having the projected particle diameter of
When the size is / 2 or more and the pitch is P or less, the single particle arrangement of the conductive particles 1 can be efficiently formed in the space 9 of the space portion of the planar body having irregularities. As illustrated in FIG. 4, when the protruding conductor 5 projects in a taper shape from the surface of the support 6 and the amount of the conductive particles 1 is added in accordance with the pitch P of the conductor 5, the base material 8 is formed. It is more preferable that the conductive particles 1 of the formed sheet 7 are fluidized and arranged in the sheet material at the time of heating and pressurization so that the particles can be efficiently arranged.

By heating and pressing between the sheet bodies having irregularities, the irregularities are transferred and formed on the surface of the sheet by the softening flow of the insulating material, and the cohesive force is caused by the curing of the insulating material or the progress of the curing reaction or the solidification by cooling. Is used as an insulating material, and irregularities are formed on the surface of the sheet while fixing the particles in the sheet. For example, an expensive anisotropic conductive sheet can be used sufficiently because it can be used repeatedly by providing a peelable film on a textured sheet or by subjecting the sheet to a peeling treatment such as silicone or fluorine. It will be possible. Due to this heating and pressing, even when the surface of the conductive particles has an insulating coating,
The insulating coating on the sheet surface can be removed by softening and melting.

Heating and pressurization is performed by applying soft plastic on the surface,
It can be performed between rolls and presses having a flexible material such as rubber, and for example, when a sheet is formed on the roll surface, a continuous long product is obtained. When the insulating coating is present, the heating and pressurizing conditions are set to a temperature equal to or higher than the thermal softening point of the insulating coating to soften and melt the insulating coating, and then the insulating material is cured. That is, in this step, the insulating layer on the surface of the sheet is removed, and in the state where the conductivity in the thickness direction is obtained, the cohesive force such as the curing of the insulating material 5 or the progress of the curing reaction and the solidification due to the cooling improves the particles 1. Can be fixed in the seat 7. Finally, the planar body having irregularities is removed to obtain an anisotropic conductive sheet. Under heating and pressurization, the resin layer melts on the contact surface with the flexible material and the conductive particles are exposed, but since the resin layer is difficult to melt due to insufficient heat in the adjacent direction, insulation deteriorates. Is less and higher resolution is possible. If necessary, a step of cleaning the protrusions on at least one surface of the sheet may be provided. As a cleaning means, various methods such as buffing, solvent, etching, polishing and laser can be adopted.

[0016]

According to the present invention, the conductive particles are easily exposed from the surface of the sheet in the step (a). Next, in the step (b), unevenness is transferred and formed on the surface of the sheet by softening flow of the sheet, and particles can be fixed in the sheet having improved cohesive force by hardening of the insulating material or progress of hardening reaction or solidification by cooling. . At this time, if the planar body having irregularities is formed at a predetermined pitch and the particle diameter of the conductive particles is equal to or less than the above pitch, the conductive particles can be efficiently formed in a single particle shape in accordance with the pitch. Finally, in the step (c), the planar body having irregularities is removed. Further, if necessary, by cleaning the projections on at least one surface of the sheet, the contact resistance with the electrodes can be further reduced.

[0017]

EXAMPLES Next, examples will be described, but the present invention is not limited to these examples. Example 1 Crosslinked polystyrene particles having an average particle size of 30 μm (glass transition point 160 ° C.) were used as the core material 3 in FIG. 2, and the surface was subjected to palladium chloride-based activation treatment and then electroless Ni.
Ni plating is performed at 90 ° C. using a plating solution, and displacement plating is performed at 70 ° C. using an Au plating solution to form a metal thin layer 4
Was formed. At this time, the thickness of Ni / Au is 0.2 / 0.0
2 μm (center particle size of conductive particles 1 is 30.4 μm, variation range is within ± 0.5 μm), and particle density is 2.0.
Met.

Rubber-modified flexible epoxy resin, microcapsule type latent curing agent (activation temperature 1
20 ° C) and toluene solvent as main components (nonvolatile content 50%)
22% by volume, which is the amount by which the above particles can be present as a single layer in an area of 50 μm square with a thickness of 20 μm.
Was added to form a roll gap of 40 μm, and then 100 ° C.
After drying for 10 minutes, a 20 μm thick adhesive (10
Na ions and Cl ions in the extracted water after extraction at 0 ° C. for 10 hours were each 10 ppm or less) were formed on a base tetrafluoroethylene film (separator, thickness 50 μm). It was possible to make a sheet thinner than the particle size due to volumetric shrinkage due to solvent drying.

As a planar body having irregularities, a surface of a component (FIG. 3A) (an anisotropic conductive sheet having a pitch of 50 μm, a space of 20 μm, and a protruding height of 10 μm) thinly coated with silicone release liquid is dried. Put the sheet in between, 150
℃ heating rubber rolls (100 mmφ iron roll with a rubber hardness of 70 is formed with a thickness of 2 mm) at a pressure of 20 kg / cm ² at a speed of 0.1 m / min, to cure the insulating material It was removed to obtain an anisotropic conductive sheet. The sheet-like body could be easily peeled off from the sheet with the silicone release liquid, and it was easy to handle as a sheet even after curing due to the flexibility of the rubber-modified epoxy resin. Further, the microcapsule type latent curing agent enabled curing in a short time.

Example 2 Both surfaces of the sheet of Example 1 were further buffed (abrasive powder particle size 0.3 μm) to obtain an anisotropic conductive sheet. Example 3 The surface of the conductive particles 1 in Example 1 is coated with an insulating coating 2
Polystyrene / divinylbenzene as 100/0.
Particles of 5 (glass transition point 115 ° C.) having an average particle size of 1 μm are formed by a spray dryer using alcohol as a dispersant, and heated at 125 ° C. by this device to be immobilized,
Particles with a coating thickness of 0.5 μm were obtained.

Example 4 Instead of the separator in Example 1, an FPC (flexible printed circuit board, distance between circuits and adjacent circuits was 50 μm) was used. Example 5 An anisotropic conductive sheet was obtained in the same manner as in Example 1 except that the conductive particles used in Example 1 were substantially spherical nickel (center particle size: 30 μm, variation range: within ± 2.9 μm). .

Evaluation The anisotropic conductive sheet obtained in each of the above examples was sandwiched with a width of 2 mm between FPCs similar to those used in Example 4, and the circuits of the FPC were aligned. 1kg / c
The connection resistance was measured between the opposing circuits of the FPC, and the insulation property was measured by the resistance between the adjacent circuits while being pressurized with m ² . The width of the FPC used for the measurement is 20 mm, and the number of circuits is 200. As a result, regarding the connection resistance of the sheet, 0.15, 0.11,
The resistance was 0.26, 0.30 and 0.23Ω, and the insulation resistance was 10 ⁹ Ω or more, showing good anisotropic conductivity.

[0023]

According to the present invention, it is possible to provide an inexpensive method for producing an anisotropic conductive sheet having high resolution, excellent reliability, and simple steps.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing a structure of particles in a production method of the present invention.

FIG. 2 is a schematic sectional view showing the structure of particles in the production method of the present invention.

FIG. 3 is a schematic cross-sectional view showing an example of a planar body having irregularities used in the present invention.

FIG. 4 is a schematic cross-sectional view showing a state in which the sheet-like article of the present invention and a sheet-like article are opposed to each other.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Conductive particle, 2 ... Insulating coating, 3 ... Core material, 4 ... Metal thin layer, 5 ... Conductor, 6 ... Support body, 7 ... Sheet, 8 ... Base material, 9 ... Space part

Claims (3)

[Claims] 1. A step of: (a) dispersing conductive particles having a uniform particle diameter in an insulating material to form a sheet-like material having a thickness of the insulating material equal to or smaller than the particle diameter of the conductive particles; An anisotropic method, characterized by comprising the step of heating and pressing with at least one surface of the sheet-like material facing the planar body having irregularities, and (c) the step of removing the planar body having irregularities. Manufacturing method of conductive sheet. 2. A planar body having irregularities is formed at a predetermined pitch, and the particle size of the conductive particles is equal to or smaller than the pitch.
A method for producing the anisotropic conductive sheet described. 3. The method for producing an anisotropically conductive sheet according to claim 1, further comprising a step of cleaning the projections on at least one surface of the sheet-shaped article after the step (c) is completed.