JPH0646527B2 - Method for producing anisotropically conductive rubber sheet - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing an anisotropically conductive rubber sheet for electrically connecting electronic parts by interposing them between electrodes of electronic parts facing each other.

[Prior art and its problems]

For example, when electrically connecting an integrated circuit element having a high integration density or a multi-contact electrical connector to each other, the soldering method which has been most commonly used for a long time has been intervened between electronic components in recent years. Conductive rubber sheets, especially anisotropic conductive rubber sheets, whose conductivity is maintained by simply tightening them, are now widely used.

The anisotropic conductive rubber sheet is a special conductive material that has conductivity only in the thickness direction of the sheet, and does not have conductivity in the plane direction. It is easy to electrically connect and improves contact reliability. It has a great effect on.

FIG. 6 is a partial cross-sectional view showing the simplest case of an electronic component in a state of being connected with an anisotropic conductive rubber sheet interposed, and a large number of electrodes provided on each of two basic elements 1 and 1a. This shows a state in which an anisotropically conductive rubber sheet 3 which has conductivity only in the thickness direction and has no conductivity in the plane direction is sandwiched between 2 and 2a. In this way, in FIG. 6, the electrodes 2 and 2a of each pair facing each other are electrically connected to each other, and the adjacent electrodes 2 or 2a have a high insulating property. The sheet 3 can easily electrically connect many counter electrodes with one rubber sheet.

In order to impart the above anisotropic conductivity to the conductive rubber sheet, it is necessary to arrange the conductive particles contained in the rubber sheet in the thickness direction of the rubber sheet.
Figures and 8 show the behavior as a model cross-sectional view of the seat. First, the conductive particles 4 uniformly dispersed in the rubber binder 5a as shown in FIG. 7 are arranged as shown in FIG. 8 by applying a magnetic field in the thickness direction, and after curing the rubber, It becomes anisotropically conductive, that is, locally conductive only in the thickness direction of the sheet 5.

The method for producing the anisotropic conductive rubber sheet in which the conductive particles are oriented in this manner is described in, for example, JP-A-55-159578, and as is well known, the conductive magnetic powder is uniformly dispersed. By adding a cross-linking agent to liquid rubber dispersed and mixed in, a magnetic field is applied in a mold at high temperature to locally collect conductive magnetic powder for particle orientation and pressure heating to form a sheet. It is what is molded.

However, this conventional method is difficult to uniformly disperse the conductive particles due to the high viscosity of the crosslinkable liquid rubber used as a rubber binder, and in addition to the long magnetic field treatment time required for the orientation of the conductive particles, Since heating is performed during the sheet forming, there is a problem that the flow of the uncured rubber mixture occurs in the mold to prevent the orientation of the conductive particles, and as a result, the anisotropy of the formed conductive rubber sheet is impaired. . Furthermore, in order to perform the magnetic field treatment, an appropriate magnetic field generation source must be installed in the mold, which increases the manufacturing cost of the molding mold and also affects the price of the anisotropic conductive rubber sheet obtained. Occurs.

On the other hand, the present inventor has noticed that a resin that is cured by UV irradiation is cured at room temperature in a short time, and uses this as a rubber binder of an anisotropic conductive rubber sheet to uniformly mix conductive magnetic powder. Disperse and fill a container that has at least one surface that allows light to pass through, orient the particles between two permanent magnet plates, and then irradiate ultraviolet rays from the light-transmitting surface of the container to cure the rubber binder. Patent pending for a method of producing an anisotropically conductive rubber sheet by carrying out the above.

9 and 10 are schematic sectional views for explaining the principle of this method. FIG. 9 shows a container 6 filled with a mixture 6 in which conductive magnetic powder is uniformly dispersed in a low-viscosity UV-curable resin, and a transparent glass or plastic lid 9 is placed on the support 8 for positioning, It is shown that conductive particles are oriented in the thickness direction by sandwiching the entire container including 9 between the upper permanent magnet plate 10 and the lower permanent magnet plate 10a. After that, except for the upper magnet plate 10, a lamp (not shown) is used to irradiate ultraviolet rays from above the lid 9 to cure the rubber binder and form an anisotropic conductive rubber sheet. FIG. 10 is a schematic cross-sectional view shown in FIG. 9, but in the case of FIG. 10, as a container to be filled with the mixture 6, for example, a bag sewn with a transparent film such as polyethylene is sewn.
11 is used, which is arranged between the upper permanent magnet plate 10 and the lower permanent magnet plate 10a. The procedure for forming the anisotropic conductive rubber sheet is similar to that shown in FIG.

In the above method, since the rubber binder having a low viscosity is used, the dispersibility of the conductive particles is good, and the particle orientation can be performed in a short time with a relatively small magnetic field using a permanent magnet plate. Since there is no need to heat the binder during curing, it has various advantages such as ensuring the anisotropy imparted by the orientation of the conductive particles and simplifying and facilitating the manufacturing method.

However, subsequent studies by the present inventor have revealed that there are some problems in the following points. That is, the conductive particles are not affected by the magnetic field after the mixture of the ultraviolet curable resin and the conductive particles is placed between the two permanent magnet plates and the conductive particles are oriented and then irradiated with ultraviolet rays. There is a short time, and at this time, the conductive particles once arranged in the thickness direction tend to return to the initial dispersion state in the mixture, and the conductive particles in the mixture with a rubber binder having a low viscosity are originally It is easy to move and has good dispersibility and orientation, but on the contrary, its orientation is likely to be lost when the magnetic field is removed.

Therefore, in order to further improve the anisotropy of the conductive rubber sheet, it is necessary to cure the rubber binder while completely maintaining the orientation of the conductive particles due to the magnetic field.

[Object of the Invention]

The present invention has been made in view of the above points, and its object is to increase the dispersibility of a mixture of conductive magnetic powder and a rubber binder in producing an anisotropic conductive rubber sheet, and to use this mixture in a mold. It is an object of the present invention to provide a method for producing a rubber sheet, which is capable of forming a sheet at room temperature while further improving anisotropic conductivity, while maintaining a state in which particles are oriented by applying a magnetic field without using.

[Main points of the invention]

The present invention focuses on that, among radiation curable resins, a resin that is cured by irradiation of ultraviolet rays is cured at room temperature in a short time, and this is used as a rubber binder of an anisotropic conductive rubber sheet to uniformly disperse conductive magnetic powder. After mixing and dispersing, at least one surface is filled in a container that transmits light, and the particles are oriented by using a magnetic field generating means that allows a magnetic flux to pass through in the thickness direction. By curing the rubber binder by transmitting ultraviolet rays from the light-permeable surface, a conductive rubber sheet having excellent anisotropy is manufactured.

Example of Invention

 The present invention will be described below based on examples.

The ultraviolet curable resin used in the present invention may be any one as long as it has a rubber-like shape after curing, but it is most preferable to use a silicone or polyurethane type ultraviolet curable resin. One of the conductive particles may be one having magnetism, and a ferromagnetic metal powder such as Fe or Ni can be used.

In the present invention, to prepare a mixture in which the conductive magnetic powder is uniformly dispersed in the ultraviolet curable resin, in order to make it a sheet,
At least one surface is filled in a container that transmits light, and the conductive magnetic powder is magnetized by using a magnetic field generating means that allows a magnetic flux to pass in the thickness direction of the entire container, and the particles are oriented in the thickness direction. While continuing, ultraviolet irradiation is performed to cure the resin.

FIG. 1 is a schematic cross-sectional view of the main parts of each member for explaining the situation, and for convenience, the same parts as those in FIGS. 9 and 10 are designated by the same reference numerals. The same applies to FIGS. 2 to 5 described later.

In FIG. 1, first, a container 6 is filled with a predetermined amount of a mixture 6 in which a conductive binder is uniformly dispersed in advance by using an ultraviolet curable resin having a low viscosity of about 1000 to 2000 CPS as a rubber binder. The container 7 is preferably made of a non-magnetic material such as Al or brass. When injecting the mixture 6 into the container 7, the mixture is filled up to the height of a support 8 provided along the periphery of the inner wall of the container 7, and a lid 9 is placed on the support 8 to cover the opening surface of the container 7 and the lid. Arrangement of the container 7, the support 8 and the lid 9 so that the upper surface of the sheet 9 becomes the same plane and the sheet has a desired thickness in consideration of shrinkage when the rubber binder in the mixture 6 is subsequently cured to form a sheet. Establish a relationship. The lid 9 is made of transparent glass or plastic to allow transmission of ultraviolet rays.

In FIG. 1, the upper permanent magnet plate 10 is used as the magnetic field generating means.
Using the two permanent magnet plates facing each other and the lower permanent magnet plate 10a, the mixture 6 is put between them and the entire container on which the lid 9 is placed is arranged. The difference between FIG. 1 and FIG. 9 is that FIG.
The magnet plates 10 and 10a are placed facing each other with an appropriate interval from the beginning, and the ultraviolet light source 11, 11a is used by utilizing the interval.
That is, the container was irradiated with ultraviolet rays.

That is, according to FIG. 1, by placing the container prepared as described above on the lower magnet plate 10a, the upper magnet plate 1
0 and the magnetic flux in the direction perpendicular to the parallel plane of the lower magnet plate 10a
The mixture is filled with the mixture 6 and the conductive magnetic powder contained therein is locally aligned in the direction of the magnetic flux so that the conductive magnetic powder is in the state shown in FIG. 8 described above. UV light source arranged to cure the rubber binder at 1
It becomes possible to irradiate the ultraviolet rays from the upper surface of the lid 9 with 1, 11a. By doing this, it is possible to cure the rubber binder by irradiating ultraviolet rays while maintaining the preferable arrangement state of the conductive particles without moving the upper magnet plate 10 to irradiate the ultraviolet rays after magnetizing and orienting the conductive particles. Thereby continuously treating particle orientation and rubber curing. In this process, once the conductive particles are oriented, there is no possibility of returning to the original dispersion state, so that the obtained conductive rubber sheet is given a large anisotropy. The permanent magnet plates 10 and 10a used at this time are magnetized so as to have magnetic poles in the thickness direction, and the residual magnetic flux density decreases after the magnetization.For example, if a rare earth cobalt magnet is used, the residual magnetic flux density of several KG is obtained. It is retained and is sufficient for the purposes of the invention. The anisotropic conductive rubber sheet sample thus obtained was No. 1,
It is used for the characteristic comparison described later.

Further, in order to simplify the above method, a bag-shaped container that transmits light can be used as a container for filling the mixture of the ultraviolet curable resin and the conductive magnetic particles. FIG. 2 is a schematic cross-sectional view shown in FIG. 1 and shows a case where a bag-shaped container 12 sewn with a transparent film such as polyethylene or polypropylene is used as a container for filling the mixture 6. . In FIG. 2, a bag-shaped container 12 filled with the mixture 6 is placed on the lower magnet plate 10a, and a pressing plate 13 such as transparent glass or plastic is lightly pressed from above to adjust the surface shape and thickness. . Since the magnetization orientation of the conductive particles and the curing process of the rubber binder are the same as those in FIG. 1, their description will be omitted. The sample of the anisotropic conductive rubber sheet obtained here is No. 2.

FIG. 3 is a modification of the method of FIG. In FIG. 3, a glass reflector 14 is embedded in the surface of the upper magnet plate 10 facing the bag-shaped container 12, and the ultraviolet light source 11 is embedded in the glass reflector 14.
An optical fiber 15 which is guided from and penetrates the upper magnet plate 10 is connected. At this time, the contact surface of the upper permanent magnet plate 10 with the reflection plate 14 is mirror-polished to enhance the reflection efficiency of ultraviolet rays,
As the reflection plate 14, it is preferable to use a glass plate having a small bending rate. Since the upper magnet plate 10 having the reflection plate 14 and the optical fiber 15 connected thereto can be rotated by the optical fiber 15, first, the bag-shaped container 12 filled with the mixture 6 is placed on the lower magnet plate 10a. By aligning the upper magnet plate 10, the conductive particles in the mixture 6 can be cured and oriented in the thickness direction, and then ultraviolet rays are transmitted from the ultraviolet light source 11 to the reflecting plate 14 by the optical fiber 15. By doing so, the ultraviolet rays are diffusely reflected inside the reflection plate 14 and on the contact surface with the upper magnet plate 10, and finally the reflection plate 14 causes the bag-shaped container 12
The mixture 6 therein is irradiated with ultraviolet rays, and the rubber binder contained in the mixture 6 is cured in a short time. Also in this case, the orientation of the conductive particles and the curing treatment of the rubber binder are continuously performed, and the upper and lower magnet plates 10 and 1 are
This is advantageous in narrowing the gap between 0a, and the anisotropy of the obtained conductive rubber sheet can be sufficiently secured. The sample of this anisotropic conductive rubber sheet is No. 3.

Further, in the present invention, a magnetic flux generating coil can be used as the magnetic field generating means instead of the permanent magnet plate. FIG. 4 is a model cross-sectional view showing the positional relationship. In FIG. 4, the bag-shaped container 12 filled with the mixture 6 and the transparent pressing plate 13 are placed on the lower magnet plate 10a in the same manner as in FIG. 2, but the lower magnet plate 10a is an ordinary iron plate. May be used,
It also serves as a base. These are placed so as to be located between the magnetic flux generating coils 16 and 16a. Ie coil 1
The direction in which the magnetic flux generated when a current flows from a power source (not shown in FIGS. 6 and 6a) is shown by the dotted line, and the positional relationship is such that the magnetic flux can pass in the thickness direction of the bag-shaped container 12. To set. At this time, as a matter of course, the upper permanent magnet plate 10 shown in the drawings so far is not necessary, and the ultraviolet light source 11 can be installed at that position. By curing the rubber binder while the conductive particles are oriented, a rubber sheet having a large anisotropic conductivity can be obtained. Magnetic flux generating coil 16,1
6a needs to be set so that the magnetic flux such as the wire diameter, number of turns, and current value is sufficient for the conductive particles to be aligned in the thickness direction of the sheet, but be careful not to make the magnetic flux near the center of the sheet insufficient. There must be. The anisotropic conductive rubber sheet sample is No. 4.

On the other hand, it is effective to use a bag in which transparent films are sewn, when the anisotropically conductive rubber sheet is manufactured not as a single sheet but as a conductive strip. FIG. 5 is a model cross-sectional view showing a main part for explaining an apparatus and a method for continuously producing an anisotropic conductive rubber sheet. In FIG. 5, transparent films 17 and 17a made of polyethylene, for example, are respectively wound around unwinding rolls 18 and 18a, and are fed out from here. The movement of the transparent films 17 and 17a in the steady state determines the path by the intermediate rolls 19 and 19a, and the heat-sealing device 20 seams the edges of each other into a tubular shape, and then the adjusting rolls 21 and 21a.
After passing through the gap of, for example, the reflector having the configuration shown in FIG.
Passing between the upper magnet plate 10 having 14 and the lower magnet plate 10a,
Finally, it operates so as to be wound by a take-up roll (not shown). Transparent film 17,17a on the above route at the start
When the film is set and wound by a winding roll (not shown), the films 17 and 17a are sent from the unwinding rolls 18 and 18a. At this point, the feeding is temporarily stopped and then the state is changed to a steady state, and the mixture 6a of the ultraviolet curable resin and the conductive magnetic powder is put into the bag. The mixture 6a keeps a uniform mixed state in the tank 22, is dropped from the bottom into a bag made of transparent films 17, 17a, and after being filled with a predetermined amount, the unwinding of the films 17, 17a is started again, and after restarting the heat fusion. The seam formed by the attachment device 20 may be only the edge portion, and the films 17, 17a form a tubular shape. After adding the mixture 6a, adjust the thickness with the adjusting rolls 21 and 21a, and
It passes between the permanent magnet plates 10 and 10a, but here it is the third
As described in the figure, the reflection plate 14 provided on the upper permanent magnet plate is irradiated with the ultraviolet rays from the light source 11 guided by the optical fiber 15, and the mixture 6a is subjected to the alignment of the conductive particles and the curing of the rubber binder in a timely manner. . At this time, the outer periphery of the bag-shaped container composed of the transparent films 17 and 17a, the surface of the reflecting plate 14 embedded in the upper permanent magnet plate 10 and the lower permanent magnet plate 10
The gap with the surface of a should be as small as possible without hindering the passage of the bag-shaped container. After that, the anisotropic conductive rubber sheet formed in the transparent film container is taken up as it is on a take-up roll (not shown). The sample thus obtained is No. 5.

In FIG. 5, the direction of rotation of each roll is indicated by an arrow, and the thickness of the container made of the transparent film 17, 17a is shown in the same manner for convenience, but after the mixture 6a is charged, the thickness is adjusted by the adjusting rolls 21, 21a. However, the air mixed in the mixture 6a at this time is pushed upward because the viscosity of the rubber binder is low. Therefore, the adjusting rolls 21 and 21a are preferably arranged as close as possible to the heat-sealing device 20, and in order to continuously flow from the material feeding to the formation of the anisotropic conductive rubber sheet, the transparent film container is fed. In addition to the speed, thickness, magnetic field strength, etc., it is necessary to set the mutually related conditions so that the desired anisotropic conductive rubber sheet can be obtained.

Next, Table 1 shows the results of measuring the conductivity and anisotropy of the anisotropic conductive rubber sheets No. 1 to No. 5 samples obtained by the present invention as described above. Show. For comparison, Table 1 also shows conventional ones.

The conductivity in Table 1 is indicated by the resistance value when a rubber sheet is sandwiched between opposing electrodes of 1 cm ² and pressed with a pressure of 1 kg / mm ^{2 in} the thickness direction. A parallel electrode of 0.5 mm and 5 cm square is applied at a pressure of 1 kg / cm ² . It was pressed against a rubber sheet, and the presence or absence of conduction between the 50 conductors was examined, and those with no conduction were indicated as excellent, and those with conduction observed at one or two places were indicated as good. For example, if the magnetic field treatment is not performed, 5 or more conductions are recognized, which is acceptable in this comparison.

The magnitude of magnetization is 2,000 to 3,000 gauss, and the holding time is about 5 minutes. Since the ultraviolet curable urethane resin used in the present invention has a low viscosity of 1,000 to 2,000 CPS, the conductive particles can be easily and uniformly dispersed, and the conductive particles can be easily dispersed when placed in a magnetic field. The alignment in the directions can also be performed in a short time with a relatively small magnetic field. Moreover, the UV-curable resin does not need to be heated during curing, and instantaneously cures without disturbing the orientation of the conductive particles due to the flow and convection of the mixture, and in the present invention, the state after the orientation of the conductive particles is maintained. It is clear from the results in Table 1 that the conductive rubber sheet obtained can be excellently anisotropy because it can be irradiated with ultraviolet rays as it is.

Further, the mixture storage container used in the present invention can be set to a desired thickness of the anisotropic conductive rubber sheet, and a complicated and expensive mold having a built-in magnetic field generator unlike the prior art is unnecessary. However, it is economically advantageous that, for example, two permanent magnet plates can be used.

〔The invention's effect〕

An anisotropic conductive rubber sheet that has conductivity only in the thickness direction and does not have conductivity in the plane direction causes a magnetic field to act on the conductive particles dispersed in the rubber binder to locally disperse the conductive particles. It is carried out by orienting in the thickness direction, but the thermosetting rubber binder conventionally used has a high viscosity,
In addition to the poor dispersion of the conductive particles, since the orientation of the conductive particles was disturbed by heating, sufficient anisotropic conductivity could not be obtained, while the method of the present invention was described in the examples. As described above, a low viscosity UV curable resin is used as a rubber binder to enhance the dispersibility of conductive particles, and a mixture of these particles is filled in a container having at least one surface to transmit light. It is placed between magnetic field generating means to locally orient the conductive particles locally in the thickness direction, and then ultraviolet rays are radiated from the light-transmitting surface of the container while the magnetic field that ensures the orientation is applied. By doing so, the rubber binder is instantaneously cured, so that the thickness of the rubber sheet can be easily and arbitrarily changed without the need for a complicated mold equipped with a magnetic field generator as in the past. It ’s possible, and Since there is no need to heat the binder for curing, it facilitates the orientation of the uniformly dispersed conductive particles by the magnetic field, and keeps the orientation state until the completion of the curing of the rubber binder, and as a result, it is extremely efficient and excellent. The conductive rubber sheet having anisotropy can be obtained.

[Brief description of drawings]

FIG. 1 is a model cross-sectional view for explaining the magnetization of conductive particles and the curing process of a rubber binder in the method of the present invention.
The figure is a model cross-sectional view when using a transparent bag-like container, FIG. 3 is the model cross-sectional view when using a reflector and an optical fiber, and FIG. 4 is the model cross-sectional view when using a magnetic flux generating coil. , FIG. 5 is a model cross-sectional view showing a process for continuous molding, FIG. 6 is a cross-sectional view of an essential part of a substrate with an anisotropic conductive rubber sheet interposed, and FIG. 7 is a conductive particle in a rubber binder. Fig. 8 is a model diagram showing the dispersed state of Fig. 8, Fig. 8 is a model diagram showing the orientation of conductive particles in a rubber sheet due to a magnetic field,
FIG. 9 is a model cross-sectional view of the magnetization process in which a mixture of rubber binder and conductive particles filled in a container is sandwiched between two magnet plates, and FIG. 10 is a model cross-sectional view when a transparent bag-shaped container is also used. Is. 3: anisotropic conductive rubber sheet, 4: conductive particles, 6: mixture, 7: container, 8: support, 10: upper permanent magnet plate, 11:
Ultraviolet light source, 12: bag-like container, 14: reflector, 16: magnetic flux generating coil, 17: transparent film, 18: unwind roll, 19: intermediate roll, 20: heat fusion device, 21: adjusting roll.

Claims (4)

[Claims] 1. A method for producing an anisotropic conductive rubber sheet having conductivity only in the thickness direction, wherein an ultraviolet curable resin is used as a rubber binder, and a predetermined amount of conductive magnetic powder is uniformly applied to the ultraviolet curable resin. The dispersed mixture is filled in a container having at least one surface that transmits light, and the container is arranged between a plurality of magnetic field generating means so as to pass a magnetic flux in a direction perpendicular to the light transmitting surface. An anisotropic conductive rubber, characterized in that the conductive magnetic powder is magnetized and oriented, and the rubber binder is cured by irradiating ultraviolet rays from the surface through which the light is transmitted while maintaining the orientation state by the magnetic field generating means. Sheet manufacturing method. 2. A method according to claim 1, wherein two upper and lower permanent magnet plates each having a magnetic pole in the thickness direction are used as the magnetic field generating means, and the light transmitting surface of the container is the upper permanent magnet. A method for producing an anisotropically conductive rubber sheet, characterized in that it is arranged so as to face a plate. 3. The method according to claim 1 or 2, wherein the ultraviolet irradiation is performed by ultraviolet rays transmitted from a light source to a transparent reflecting plate embedded in an upper permanent magnet plate by an optical fiber. Method for producing anisotropic conductive rubber sheet. 4. A method for manufacturing an anisotropic conductive rubber sheet according to claim 1, wherein a magnetic flux generating coil is used as the magnetic field generating means.