JP3608214B2 - Method for producing anisotropic conductive sheet - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a method for producing an anisotropic conductive sheet having conductive particles exposed on the front or back or one side, which is useful for electrical connection and inspection of high-density electrodes.
[0002]
[Prior art]
An anisotropic conductive sheet, which is conductive only in the thickness direction of a sheet made of rubber or synthetic resin, is a high-density electrode electrical circuit between circuit boards such as printed wiring boards and electronic components such as semiconductor chips. Used for connection and inspection. In these, conductivity is obtained between the counter electrodes by contact by pressurization or heating and pressurization, and the conductor is generally exposed or protruded on the front or back or one surface. As a conductor of such an anisotropic conductive sheet, conductive particles such as conductive fibers and conductive metal particles are embedded in the thickness direction of the sheet, or through holes are provided in the sheet, and conductive by plating or the like. What formed the body is known.
[0003]
[Problems to be solved by the invention]
In the case where the conductive material of the anisotropic conductive sheet is the former conductive particles, there are disadvantages in that the resolution is insufficient due to inability to cope with the recent increase in the density of electrodes and the reliability is insufficient. The reason for this is that when the conductive particles dispersed in the sheet are present at a high concentration, there is no insulation between adjacent electrodes due to contact in the surface direction, and the contact point decreases at a low concentration. This is because the lateral conductivity is insufficient. Moreover, since the height and area of the exposed portion of the conductive particles from the sheet cannot be sufficiently controlled, the conductivity varies, and in addition, when a component in which the conductive particles protrude from the sheet is used for repeated inspections. The reliability is still insufficient due to the conductive particles falling off the sheet.
[0004]
In the latter case, a fine through hole is provided in the sheet with a laser beam or the like, and a conductor is formed there by, for example, plating, so the process is complicated and it is difficult to obtain a large-area product. The resulting product is expensive to manufacture and has disadvantages that are 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 manufacturing an anisotropic conductive sheet useful for electrical connection and inspection of high-density electrodes.
[0005]
[Means for Solving the Problems]
The present invention includes (a) a step of applying an insulating coating containing a plating catalyst on the surface of conductive particles having a uniform particle diameter, (b) dispersing the conductive particles coated with the insulating coating in an insulating material, A step of forming a sheet-like material in which the thickness of the insulating material is equal to or less than the particle size of the conductive particles, and (c) a step of heating and pressing the sheet-like material to expose the insulating coating from the surface of the sheet-like material. And (d) relates to a method for producing an anisotropic conductive sheet comprising a step of electroless plating on an exposed portion of the sheet-like material. As shown in FIGS. 1 and 2, the particles used in the present invention are obtained by applying an insulating coating 2 made of an insulating material containing a plating catalyst on the surface of conductive particles 1 having a uniform particle diameter. Here, the uniform particle size preferably has a particle size range of ± 10% or less if it can be ± 20% of the center particle size. A narrower range is preferable because the height of protrusion from the sheet can be made uniform and stable contact resistance can be obtained.
[0006]
The center particle size is preferably about 2 to 5000 μm, more preferably 5 to 100 μm, and particularly preferably 10 to 80 μm. These are selected according to the desired resolution. In other words, it is necessary to make the particle size of the conductive particles smaller than the minimum width of the distance between adjacent electrodes and wiring patterns in order to prevent short-circuiting and cope with thinning of the wiring. On the other hand, if the particle size is too small, the sheet thickness is reduced, resulting in insufficient strength and difficult handling.
The conductive particles 1 can employ various metals, alloys, oxides, and the like having conductivity. Materials that are preferably used in consideration of conductivity and corrosion resistance are particles such as Ni, Cu, Al, Sn, Zn, Au, Pd, Ag, Co, and Pb. The particle shape is preferably approximately spherical, but may be any shape such as providing a large number of protrusions on the surface.
[0007]
Further, the conductive particles 1 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 diameter can be easily obtained. Examples of the organic material of the core material 3 include polymers such as polystyrene, nylon, and various rubbers. Since these are cross-linked bodies, the solvent resistance is improved. For example, the sheet raw material contains a solvent. In this case, there is no elution, and the influence on the sheet characteristics is small. When the core material 3 is a deformable particle such as a polymer, it is possible to flatten the protruding portion from the sheet or to provide elasticity by heating and pressurization during production. This is effective in improving the reliability by increasing the contact area.
The core material 3 may be inorganic particles such as glass, ceramic, silica, and in this case, the heat resistance can be further improved as compared with the polymer core material.
[0008]
The metal thin layer 4 can employ various metals, alloys, oxides and the like having conductivity. These can be made of the same material as that of the conductive particles described above, and they can also have a single-layer or multi-layer structure. As a means for forming the metal thin layer 4, a general method such as a vapor deposition method, a sputtering method, an ion plating method, a thermal spraying method, or a plating method may be used, but the electroless plating method provides a coating layer having a uniform thickness. preferable.
As shown in FIGS. 1 and 2, an insulating coating 2 in which a plating catalyst is mixed with an insulating material is formed on the surface of the conductive particles 1. The insulating coating 2 may be a curable material by heat or the like, or may be a material that exhibits heat softening property under heat and pressure, but the latter is preferable because it is easily exposed from the sheet. As a measure of thermal softening properties, general indices such as elastic modulus and hardness, and thermal transformation points such as melting point, glass transition temperature and softening point can be used as a guide.
[0009]
As the plating catalyst, palladium, platinum, gold, or a salt thereof can be applied. Among these, metal palladium, palladium salts, or a mixture of metal palladium and palladium salts is preferable from the viewpoint of precipitation and economical efficiency. The addition amount of the plating catalyst is preferably 1 to 20% by weight and more preferably 3 to 10% by weight with respect to the insulating material. When the addition amount is small, the deposition property of the plating is lowered, and when it is large, the insulation in the surface direction is lowered.
The insulating coating 2 may be present in the form of particles, and may be a single layer or a multilayer. 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 restriction | limiting in the formation means of the insulating coating 2, For example, there exist a solvent drying method, a spray method, a high-speed stirring method, a spray dryer method etc.
[0010]
Next, as shown in FIG. 3, particles having an insulating coating 2 on the surface of the conductive particles 1 are dispersed in the insulating material 5, and the thickness of the insulating material 5 is equal to or smaller than the particle size of the conductive particles 1. This forms a sheet-like material in which the particles are present in a single layer. As a dispersion method, the layers of the insulating material 5 and the conductive particles 1 can be integrated after being separately formed.
The insulating material in this case may be a thermoplastic resin such as polyethylene or polypropylene, but a curable insulating material by heat, light, electron beam or other energy such as epoxy resin or polyimide is heat resistant, moisture resistant and mechanical. It is preferably applicable because of its excellent characteristics. Since the present invention is a production method under heat and pressure, a system of epoxy resin and latent curing agent, a combination system of acrylic, urethane, epoxy resin and photoactivator reacts at a relatively low temperature. Since it is easy, it is more preferable.
[0011]
The proportion of the conductive particles in the sheet is preferably 2 to 70% by volume, more preferably 5 to 50% by volume, and particularly preferably 10 to 40% by volume. Even if the addition amount is excessive, the surface of the conductive particles has an insulating coating, so that the insulation of the adjacent electrode is difficult to decrease. If the addition amount is small, the number of conductive particles on the electrode to be connected decreases. Since the reliability is lowered, the addition amount can be set relatively excessively as long as the mechanical strength of the sheet is allowed.
When forming into a sheet-like material, it can be formed by rolling, for example, between rolls or by melt extrusion without using a substrate as shown in FIG. Moreover, it can also form on the base material 6 like FIG. The substrate 6 may be a peelable substrate such as a separator, or a wiring board as a substrate. Thus, when formed on the substrate 6, volume shrinkage due to solvent volatilization can be used at the time of forming a sheet, and for example, a continuous sheet-like material in which the thickness of the insulating material is equal to or less than the particle size of the conductive particles can be easily obtained can get. The peelable substrate can be removed if necessary after the cohesive strength of the insulating material described later has increased.
[0012]
For example, when a wiring board having an inspection circuit is used as the substrate 6 and a sheet is formed thereon, the circuit board with the sheet can be easily obtained. In this case, since the conductive particles can be contacted on the circuit, they may be exposed or protruded on one surface of the sheet.
A sheet-like material having a thickness of the insulating material obtained as described above equal to or smaller than the particle size of the conductive particles is heated and pressed to expose the insulating coating from the sheet. At this time, the insulating coating is heat-softening, and it is preferable to sandwich the sheet between flexible materials such as rubber rolls during heating and pressurization.
The heating and pressing conditions are such that the insulating coating is softened and melted at a temperature equal to or higher than the thermal softening point of the insulating coating, and then the insulating material is cured. That is, the insulating coating 2 on the surface of the sheet is exposed in this step, and the conductive particles are fixed in the sheet in a state where the cohesive force is improved by the curing of the insulating material 5 or the progress of the curing reaction or solidification by cooling. I can do it. At this time, in the case where curing is involved, the curing may be performed after the reaction is partially advanced, not the final curing.
[0013]
Under heat and pressure, the resin layer melts at the contact surface with the flexible material, and the conductive particles are exposed, but the resin layer is difficult to melt because the amount of heat is insufficient in the adjacent direction. Therefore, higher resolution is possible.
Under heat and pressure, the insulating material has a reduced viscosity at the contact surface with the flexible material and is removed from the particle top, exposing the insulating coating. At this time, even if the insulating coating 2 on the top of the particles is flow-excluded and the conductive layer is exposed, plating can be performed by displacement plating, for example. In the adjacent direction, since the amount of heat is insufficient, the resin layer is hardly melted, so that there is little decrease in insulation, and higher resolution is possible.
[0014]
Thereafter, the exposed portion 7 of the insulating coating 2 is plated as shown in FIG. As the plating method, an electroless plating method capable of depositing a metal only at a contact portion with a plating solution by a plating catalyst is preferable. As the plating metal, the same kind of conductive particles as described above can be applied, and a multilayer structure of these can also be used. For example, after obtaining a base layer such as Cu or Ni having a high deposition rate, substitution plating may be performed with Au or the like.
FIG. 6 shows another example of the plating method of the exposed portion, in which the plating catalyst is present in a granular form, and this portion is used as the plating nucleus 8 to grow the plating to form the needle protrusion 9. In this case, even if an oxide layer is present on the electrode surface, the conductivity can be obtained by breaking through the oxide layer.
[0015]
[Action]
According to the present invention, particles made of conductive particles having a uniform particle size coated with an insulating coating containing a plating catalyst are dispersed in an insulating material, and the thickness of the insulating material is equal to or smaller than the particle size of the conductive particles. In the step of forming the sheet-like material, the conductive particles are present as a single layer, and the insulating coating is exposed from the sheet surface. Next, by plating on this insulating coating, the conductive metal plated in the thickness direction of the sheet protrudes from the sheet surface, and since there is no exposure of the plating catalyst in the surface direction of the sheet, it is not plated. Since there is no reduction, higher resolution is possible.
[0016]
【Example】
Next, examples will be described, but the present invention is not limited thereto.
Example 1
As the core material 3 in FIG. 2, cross-linked polystyrene particles having an average particle size of 30 μm (glass transition point 160 ° C.) are used, and the surface is subjected to palladium chloride activation treatment, and then at 90 ° C. using an electroless Ni plating solution. Ni plating was performed, and further, substitution plating was performed at 70 ° C. using an Au plating solution to coat the metal thin layer 4, thereby obtaining conductive particles 1. At this time, the thickness of Ni / Au was 0.2 / 0.02 μm (the central particle diameter of the conductive particles 1 was 30.4 μm, and the fluctuation range was within ± 0.5 μm). Next, as a material for the insulating coating 2, 10 parts by weight of PEC-8 (trade name, manufactured by Hitachi Chemical Co., Ltd.), which is a palladium chloride mixed epoxy resin, is added to and mixed with rubber-modified epoxy resin. Prepared in solution (non-volatile content: 15% by weight). This material was stirred in the conductive particles 1 and then dried at 70 ° C. with a spray dryer to obtain conductive particles having a uniform particle size with an insulating coating containing a plating catalyst coated on the surface.
[0017]
As an insulating material, a rubber-modified flexible epoxy resin, a microcapsule-type latent curing agent (activation temperature: 120 ° C.), and an adhesive mainly composed of a toluene solvent (nonvolatile content: 50%), and 20% by volume of the particles. After adding and forming at a roll interval of 40 μm, drying is performed at 100 ° C. for 10 minutes, and a 20 μm thick adhesive (Na ions and Cl ions in the extracted water after extraction with pure water at 100 ° C. for 10 hours is 10 ppm or less each) It was formed on a tetrafluoroethylene film (separator, thickness 50 μm) as a base material. A sheet thinner than the particle diameter could be created by volume shrinkage due to solvent drying.
The sheet was passed at a speed of 0.1 m / min at a pressure of 2 kg / cm ² between a silicone rubber roll heated to 150 ° C. (a rubber having a rubber hardness of 70 mm formed on a 100 mmφ iron roll with a thickness of 2 mm), The insulating coating was exposed from the sheet surface. Fast curing is possible by the action of the microcapsule-type latent curing agent, and it was easy to handle as a sheet due to the flexibility of the epoxy resin.
[0018]
This sheet was immersed in an electroless copper plating solution CC-41 (trade name, manufactured by Hitachi Chemical Co., Ltd.) at 50 ° C. for 5 minutes to obtain an anisotropic conductive sheet. The protrusion height in this case was 5 μm.
Between the evaluation FPC (flexible printed circuit board, the distance between the circuit and adjacent circuit is 50 μm each), the anisotropic conductive sheet obtained in each of the above examples is sandwiched with a width of 2 mm, and the FPC circuit is aligned. In a state where the portion was pressurized at 1 kg / cm ² , the connection resistance was measured between the opposing circuits of the FPC, and the insulation was measured by the resistance between adjacent circuits. The width of the FPC used for the measurement is 20 mm, and the number of circuits is 200. As a result, the connection resistance of the sheet was 0.13Ω, and the insulation resistance was 10 ⁹ Ω or more, indicating good anisotropic conductivity.
[0019]
【The invention's effect】
According to the present invention, an inexpensive method for manufacturing an anisotropic conductive sheet with high resolution, excellent reliability, and simple processes can be provided.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view showing the structure of particles in the production method of the present invention.
FIG. 2 is a schematic cross-sectional view showing the structure of particles in the production method of the present invention.
FIG. 3 is a diagram for explaining a method for forming a sheet-like material in the production method of the present invention.
FIG. 4 is a diagram for explaining a method for forming a sheet-like material in the production method of the present invention.
FIG. 5 is a diagram for explaining a plating state on an insulating coating in the production method of the present invention.
FIG. 6 is a diagram for explaining a plating state on an insulating coating in the production method of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Conductive particle, 2 ... Insulating coating, 3 ... Core material, 4 ... Metal thin layer, 5 ... Insulating material, 6 ... Base material, 7 ... Exposed part, 8 ... Plated nucleus, 9 ... Needle-like protrusion

Claims (1)

(A) a step of applying an insulating coating containing a plating catalyst to the surface of the conductive particles having a uniform particle size; (b) dispersing the conductive particles coated with the insulating coating in an insulating material; A step of forming a sheet-like material having a thickness equal to or smaller than the particle size of the conductive particles, (c) a step of heating and pressing the sheet-like material to expose the insulating coating from the surface of the sheet-like material, and (d) The manufacturing method of the anisotropically conductive sheet characterized by including the process of electroless- plating to the exposed part of this sheet-like material.

Images