JP3995942B2 - Method for producing conductive adhesive sheet having anisotropy - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a conductive adhesive sheet in which conductivity is imparted only in the thickness direction of a sheet by conductive fine particles dispersed and arranged in the sheet surface.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, a conductive adhesive sheet that imparts conductivity only in the thickness direction has been used at the time of connection between a liquid crystal display wiring and a flexible substrate, high density mounting of an integrated circuit component on a substrate, or the like. An example of a conventional conductive adhesive sheet is shown in FIG . In this example, the conductive fine particles 4 are randomly arranged in the sheet 20 made of an adhesive layer. This sheet has the following problems.
In recent years, the dimensions of connected wiring patterns and land patterns have been increasingly miniaturized. When the dimension of the connected pattern is reduced, in the sheet in which the conductive fine particles are randomly dispersed and arranged, the connected pattern is arranged at the position A where the conductive fine particles do not exist as shown in FIG. 7B. The probability that As a result, the connected patterns may not be electrically connected.
[0003]
In order to solve this problem, it is effective to disperse smaller conductive fine particles in the sheet at a high density. However, when the size of the conductive fine particles is reduced, as shown in FIG. There is a problem that variations in the protruding height of the connection patterns P1, P2 from the surfaces of the substrates B1, B2 cannot be absorbed. Further, when the density of the conductive particles 4 in the sheet 20 is increased, as shown in FIG. 8B , when the patterns P1 and P2 are arranged at a fine pitch, a short (short circuit) occurs between adjacent patterns. ) Is likely to occur. That is, in these methods, the connection reliability of a conductive adhesive sheet in which conductive fine particles are randomly dispersed and arranged is not improved.
[0004]
On the other hand, Japanese Patent Application Laid-Open Nos. 5-67480 and 10-256701 describe that conductive fine particles are dispersed in a predetermined arrangement in a sheet.
In the method described in Japanese Patent Laid-Open No. 5-67480, the conductive fine particles are charged before being dispersed in the sheet (adhesive layer), and the repulsive force between the conductive fine particles is utilized to make the conductive fine particles in the sheet. Are uniformly dispersed. In addition, each position of the conductive fine particles and the support is charged with different charges, and after the conductive fine particles are arranged on the support in a predetermined arrangement, the conductive fine particles are transferred to the adhesive layer while maintaining this arrangement. It is described to do.
[0005]
However, in this method, since the arrangement is maintained by the repulsive force between the charged conductive fine particles, it is impossible to bring the distance between the adjacent conductive fine particles within the sheet surface closer to 20 μm or less.
In JP-A-10-256701, a composition comprising a rubber material and conductive particles is formed into a sheet using conductive particles having magnetism, and a magnetic field is applied in the thickness direction of the sheet. It is described that the conductive particles are oriented to cure the rubber in this state.
However, this method has the following problems. Since it is difficult to concentrate the magnetic field in a very narrow region, the distance between adjacent conductive fine particles in the sheet surface cannot be brought close to 20 μm or less. In some cases, the conductive particles are arranged so as to overlap in the thickness direction of the rubber sheet. It is difficult to arrange the conductive particles regularly (while maintaining a predetermined interval between adjacent particles). The conductive particles that can be used are limited to magnetic materials.
[0006]
[Problems to be solved by the invention]
The present invention has been made paying attention to such problems of the prior art, and conductive adhesion imparting conductivity only in the thickness direction of the sheet by conductive fine particles dispersed in the sheet surface. To provide a method for producing a conductive adhesive sheet in which conductive fine particles are regularly and densely arranged in a sheet surface so that the distance between adjacent conductive fine particles is 20 μm or less. Is an issue.
[0007]
[Means for Solving the Problems]
This invention is a manufacturing method of the electroconductive adhesive sheet which solved the said subject.
That is,
1. In the adhesive sheet that imparts conductivity only in the thickness direction of the sheet by the conductive fine particles dispersed and arranged in the sheet surface, an adhesive layer is disposed on both surfaces of the core film disposed in the center in the thickness direction, The core film and the adhesive layer are insulative, and the core film is formed of a resin having a softening temperature that is 20 ° C. or higher than the resin constituting the adhesive layer, and part or all of the individual conductive fine particles are formed. In the method for producing a conductive adhesive sheet having anisotropy that is present in the core film and the conductive fine particles are arranged in a predetermined arrangement in the core film surface,
A mold having a convex portion arranged in a predetermined arrangement on a surface formed of metal, ceramics, or resin and a sheet-like core film are heat-pressed, and then the core film is peeled off from the mold to thereby remove the convex in the core film plane. Forming a concave portion corresponding to the portion, placing conductive fine particles in the predetermined concave portion in the film surface, and then forming an adhesive layer on both sides with the core film having the conductive fine particles placed in the center A method for producing a conductive adhesive sheet.
2.1. In the method for producing a conductive adhesive sheet described in 1., between the step of thermocompression bonding the mold having the convex portion and the sheet-like core film and the step of peeling the core film from the die after thermocompression bonding, 1. A step of adhering an adhesive layer formed on the material from the core film side is added. The manufacturing method of the electroconductive adhesive sheet of description.
3. In the adhesive sheet that imparts conductivity only in the thickness direction of the sheet by the conductive fine particles dispersed and arranged in the sheet surface, an adhesive layer is disposed on both surfaces of the core film disposed in the center in the thickness direction, The core film and the adhesive layer are insulative, and the core film is formed of a resin having a softening temperature that is 20 ° C. or higher than the resin constituting the adhesive layer, and part or all of the individual conductive fine particles are formed. In the method for producing a conductive adhesive sheet having anisotropy that is present in the core film and the conductive fine particles are arranged in a predetermined arrangement in the core film surface,
A resin solution in which a resin component for forming a core film is dissolved is applied to the surface of a mold having a convex portion arranged in a predetermined arrangement on a surface formed of metal, ceramics or resin, and a solvent. After removing the components by drying, a step of peeling the core film from the mold is performed to form a concave portion corresponding to the convex portion of the mold in the core film surface, and the conductive fine particles are disposed in the concave portion predetermined in the film surface. A method for producing a conductive adhesive sheet, comprising forming an adhesive layer on both sides of a core film in which conductive fine particles are disposed, with a core film disposed in the center.
4). 3. In the method for producing a conductive adhesive sheet according to claim 1, a resin solution in which a resin component for forming a core film is dissolved is applied to the surface where the convex portion of the mold having the convex portion is present, and the solvent component is dried and removed. a step, between the step of separating the mold core film after said step, further, 3, characterized in that adding a step of adhering an adhesive layer formed on the substrate from the core film side. The manufacturing method of the electroconductive adhesive sheet of description.
5. The conductive fine particles are fine particles made of copper, gold, silver, nickel, palladium, indium, tin, lead, zinc, bismuth, an alloy of any of these metals, or carbon, or fine particles having a metal coating on the surface. It is characterized by the following. To 4. The manufacturing method of the electroconductive adhesive sheet in any one of.
[0008]
The core film used in the present invention needs to be formed from a resin having a softening temperature higher by 20 ° C. or more than the resin constituting the adhesive layer formed on both sides thereof. This is because the flow of resin occurs when the conductive adhesive sheet of the present invention is placed in the center and the components or substrates to be connected from above and below are heat-pressed, but the conductive fine particles arranged in advance are difficult to move. It is a device. That is, the adhesive layer needs to be fluidized before the core film is fluidized so that the adhesive layer moves following the unevenness of the connection bumps on the component or the substrate and no gap is generated. When the resin composing the core film is fluidized at the same time or before the adhesive layer is fluidized, it is difficult to connect the fine pitch because the conductive particles placed in a predetermined position move with the flow of the resin. It becomes. Therefore, the softening temperature of the core film is 20 ° C. or more, preferably 50 ° C. or more, more preferably 80 ° C. or more higher than the softening temperature of the adhesive resin forming the adhesive layer.
[0009]
Here, the softening temperature of the core film and the adhesive layer means that the viscosity decreases greatly when the temperature of the resin forming the core film and the adhesive forming the adhesive layer is increased from room temperature (the slope of the viscosity curve). Means the first temperature that changes. This softening temperature can be examined by measuring the viscosity using a viscoelasticity measuring device such as a rheometer while increasing the temperature of the resin and the adhesive from room temperature at a constant rate.
As the resin forming the core film used in the present invention, polyimide resin, polyamide resin, polyamideimide resin, polysulfone resin, polyethersulfone resin, polyester resin, unsaturated polyester resin, polyallyl resin, polyolefin resin, polycarbonate resin, polystyrene A resin such as a resin, a polyphenylene ether resin, a thermoplastic resin containing these resins as a main component, or a thermosetting resin containing a thermosetting component of a type that is cured after being plasticized with heat is preferable.
[0010]
The thickness of the core film greatly depends on the size of the conductive fine particles used. That is, in the conductive adhesive sheet of the present invention, it is necessary to bring conductive fine particles into contact with both patterns to be connected during use. There are no through-holes in the core film used in the present invention. That is, the conductive particles arranged in a predetermined manner are in the holes not penetrating formed in the core film, or some or all of the individual conductive particles are taken into the core film. After only the layer is fluidized in accordance with the shape of the connection pattern and then curing is started by heat, the core film is softened by heat, and the portion of the thin core film around the conductive fine particles is fluidized. Therefore, it is necessary to set the thickness so that the core film, which is an insulator around the conductive fine particles, does not hinder connection.
[0011]
The thickness of the core film is preferably not more than 3 times, more preferably not more than 2 times the average particle diameter of the conductive fine particles used in the conductive adhesive sheet. Further, the lower limit of the thickness is preferably 0.5 times or more, more preferably 0.75 times or more the average particle diameter of the conductive fine particles used in the conductive adhesive sheet. If the core film is thinner than this, the conductive fine particles contained in the holes or recesses will be removed together with the removal of the conductive fine particles adhering to places other than the holes or recesses formed in the core film. Further, with reference to FIG. 1 (a-1), the thickness of the core film present at the bottom of the hole not penetrating is preferably 0. The thickness of the core film in the portion where no conductive fine particles are present. 5 times or less, more preferably 0.25 times or less. Further, the lower limit of the thickness of the core film present at the bottom of the non-penetrating hole is preferably 0.05 times or more, more preferably 0.1 times the thickness of the core film in the portion where no conductive fine particles are present. That's it. If it is thinner than this, when forming a recess not penetrating into the core film, when the core film is peeled from a mold having a protrusion corresponding to the recess, a location where physical strength cannot be maintained and the portion is broken. Or a portion that becomes a hole through which the concave portion passes is not preferable.
[0012]
Further, in the method of the present invention, holes that do not penetrate are formed in the core film, and conductive fine particles are put only in these holes. Therefore, the conductive fine particles adsorbed at a place other than the holes must be blown away using compressed air or the like, or adhered and removed using an adhesive sheet or the like. In this step, when the hole depth is shallower than the particle diameter of the conductive fine particles used, the conductive fine particles entering the holes are removed together with unnecessary conductive fine particles. Therefore, the preferable depth of the hole is 0.5 times or more, more preferably 1 time or more of the average particle diameter of the conductive fine particles. Therefore, the preferable thickness of the core film in the part where the holes are not opened is 0.7 times or more, more preferably 1.2 times or more the average particle diameter of the conductive fine particles used.
[0013]
In the method of the present invention, the size of the non-penetrating holes formed in the core film depends on the size of the conductive fine particles used, but is preferably 1 to 1.5 times the average particle diameter of the conductive particles. To do. The arrangement of the holes depends on the arrangement pitch of the connection pattern and the wiring width, but it is preferable to arrange the holes at intervals of 0.3 to 1 times the arrangement pitch. Moreover, it is also possible to form a hole only in the pattern of the part to connect. However, in this case, it is necessary to align the connection pattern and the connection component.
The conductive fine particles used in the present invention preferably have an average particle size of 0.5 to 50 μm, more preferably 1 to 20 μm, and most preferably 2 to 10 μm. If the average particle size of the conductive fine particles is less than 0.5 μm, the variation in the height of the connection pattern may not be absorbed. On the other hand, when the size exceeds 50 μm, it is not suitable for connection of a fine pattern.
[0014]
The shape of the conductive fine particles used in the present invention is not particularly required to be spherical, and polyhedral and spherical particles may have a large number of protrusions. However, a flat shape is not preferable because it is difficult to put in a hole or to be adsorbed by an adsorption device. Conductive fine particles that are easily crushed during compression and that are easy to deform are preferable because they can increase the contact area with the connection pattern and absorb variations in the height of the connection pattern.
The particle size distribution of the conductive fine particles used in the present invention is preferably such that the standard deviation is 50% or less of the average particle size. More preferably, the standard deviation is 20% or less of the average particle diameter, and most preferably 10% or less. If the particle size distribution of the conductive fine particles is widely distributed with a standard deviation exceeding 50% of the average particle size, the conductive fine particles having a small particle size may cause clogging of the through-holes, or may be present in places other than the holes. It becomes difficult to remove small conductive fine particles. Further, it becomes difficult to absorb the variation in the height of the connection pattern. This leads to a decrease in electrical connection reliability between connection patterns. Moreover, it is preferable that one conductive fine particle is contained in one hole, that is, one conductive fine particle exists in the thickness direction of the core film.
[0015]
As a method for classifying the conductive fine particles, a usual method, for example, a centrifugal classifier such as cyclone or clacyclon, a gravity classifier, an inertia classifier, an airflow classifier, or a classifier by sieving can be used. In order to classify fine conductive fine particles having a particle diameter of 10 μm or less, first, coarse classification is performed using an airflow classifier or the like, and then a classification method is performed by sieving using a sieve in which through holes are precisely formed. Is preferred. When fine conductive fine particles having a particle diameter of 10 μm or less are classified by precision sieving, it is effective to use ultrasonic waves in a solvent such as alcohol that does not change the conductive fine particles.
[0016]
As the adhesive forming the adhesive layer constituting the conductive adhesive sheet , for example, a thermosetting adhesive, a thermoplastic adhesive, a pressure sensitive adhesive, or the like can be preferably used. In particular, it is preferable to use a type of adhesive containing a so-called latent curing agent in which a compound containing a curing agent is confined in a microcapsule and curing starts when the microcapsule is crushed by pressure or heat.
Examples of the material of the adhesive layer include epoxy resins, polyimide resins, urea resins, amino resins, melamine resins, phenol resins, xylene resins, furan resins, isocyanate resins, benzocyclobutene resins, polyphenylene ethers. Examples thereof include a resin, a polysulfone resin, and a polyethersulfone resin. In particular, from the viewpoint of dimensional stability, heat resistance, etc., the resin constituting the adhesive used is an aromatic compound such as benzene, naphthalene, anthracene, pyrene, biphenyl, phenylene ether, cyclohexane, cyclohexene, bicyclooctane, bicyclo It is preferably composed of a compound having a skeleton of an aliphatic cyclic compound such as octene or adamantane in the molecular chain.
[0017]
In addition, if an adhesive made of a resin soluble in a solvent is used, an adhesive layer can be obtained by applying the adhesive on a support in a state dissolved in a solvent and then drying. Preferably, the thickness of the adhesive layer after drying (solvent removal) is 1 μm to 50 μm, more preferably 5 μm to 20 μm. When the thickness is less than 1 μm, it is difficult to obtain adhesion strength after bonding. When the thickness of the adhesive layer exceeds 50 μm, the amount of the adhesive is too large and the electrical connection between the conductive fine particles and the connection pattern is hindered.
In the conductive adhesive sheet of the present invention, the first and second adhesive layers are formed on both sides of the core film, but these adhesive layers are different even if they have the same composition. It doesn't matter. The first and second adhesive layers may be a laminate of a plurality of adhesive layers having different functions.
When the conductive adhesive sheet obtained in the present invention is exposed to an acidic aqueous solution, water, or the like in the production process, it is preferable to use an adhesive layer that does not undergo alteration or reaction in the aqueous processing solution. Further, by using an adhesive layer having tackiness or tackiness, the conductive adhesive sheet of the present invention can be temporarily fixed to an object to be connected.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described.
One embodiment of a conductive adhesive sheet obtained by the production method of the present invention will be described with reference to FIG.
The conductive adhesive sheet shown in FIG. 1 (a-1) includes a core film 1 disposed in the center in the thickness direction, adhesive layers 2 and 3 disposed on both surfaces of the core film 1, and a spherical conductive property. It consists of fine particles 4. The core film 1 is made of a polysulfone thermosetting resin and has a thickness of 10 μm. The adhesive layers 2 and 3 are made of an epoxy thermosetting adhesive containing a latent hardener and have a thickness of 12 μm. The conductive fine particles 4 are powders made of an alloy of copper and silver, and have an average particle size of 6 μm and a standard deviation of particle size distribution of 0.5 μm. The softening temperature of the polysulfone thermosetting resin used as the core film is 160 ° C., and the softening temperature of the epoxy thermosetting adhesive used as the adhesive layer is 60 ° C. A large number of holes 10 that do not penetrate in the thickness direction are regularly arranged in the film surface in the core film 1.
[0019]
In this embodiment, as shown in FIG. 1 (b), holes 10 that do not pass through are located at the positions of lattice points (intersections between the vertical lines and horizontal lines of the lattice) and the center positions of the unit lattices in the film plane. Has been placed. The interval between adjacent lattice points along the vertical line is 15 μm, and the interval between adjacent lattice points along the horizontal line is 15 μm. The planar shape (cross-sectional shape along the film surface) of the hole 10 not penetrating is circular, and the diameter of this circle is 7.5 μm (1.25 times the average particle diameter of the conductive fine particles 4). In addition, one conductive fine particle 4 is disposed in every hole 10 of the core film 1.
The conductive adhesive sheet of FIG. 1A-2 is an example in which conductive fine particles arranged in a predetermined arrangement are embedded in the core film 1 in an embedded state. The thickness of the core film 1 is 4 μm, the thickness of the adhesive layers 2 and 3 is 10 μm, and the average particle size of the conductive fine particles is 6 μm.
[0020]
These conductive adhesive sheets are pressed while being sandwiched between substrates to be connected during use. As a result, the adhesive layers 2 and 3 are deformed to start curing. Subsequently, the core film 1 is deformed with a time delay, and the conductive fine particles 4 are brought into contact with both patterns to be connected. At this time, the arrangement of the conductive fine particles 4 in the sheet surface is fixed by the core film 1. In this conductive adhesive sheet, as described above, the conductive fine particles 4 are regularly and densely arranged in the sheet surface (so that the distance between adjacent conductive fine particles is 20 μm or less). ing.
Therefore, according to the conductive adhesive sheet of this embodiment, even when the dimension of the pattern to be connected is small or when patterns arranged at a fine pitch are connected, a highly reliable connection can be made. In particular, by setting the pitch and size of the holes 10 corresponding to the arrangement pitch and wiring width of the pattern to be connected, the position where the conductive fine particles 4 do not exist (indicated by symbol A in FIG. 7 ). The fear of being placed in is eliminated.
[0021]
According to the conductive adhesive sheet of this embodiment, since the conductive fine particles are regularly arranged, the conductive fine particles are extremely small (for example, a diameter of 2 μm or less, as in the case of being randomly arranged). Even if it is not, the probability that the pattern to be connected is arranged at a position where the conductive fine particles do not exist (indicated by symbol A in FIG. 7 ) becomes zero in principle. Therefore, in the conductive adhesive sheet of this embodiment, the conductive fine particles are made to have a certain size so that the connection pattern protrudes from the substrate surface more than the conductive adhesive sheet in which the conductive fine particles are randomly arranged. It becomes easy to absorb the variation in height.
[0022]
FIG. 1C shows a conductive adhesive sheet in which the arrangement of the holes 10 in the plane of the core film 1 is different from the above. In this example, the holes 10 are arranged at the positions of lattice points in the film plane. In each of these holes 10, one conductive fine particle 4 is disposed.
An embodiment of a method for producing a conductive adhesive sheet of the present invention will be described with reference to FIG .
A method for forming a mold having convex portions arranged in a predetermined arrangement on the surface will be described with reference to FIG. First, a resin pattern is formed on a substrate. FIG. 2B shows this state. As a method for forming a resin pattern on a substrate, there are a method using photolithography of a photosensitive resin, and a method of ablation processing in which the resin is melted or cut using a laser beam. A conductor film 12 is formed on the formed resin pattern by sputter deposition or electroless plating (FIG. 2 (c) shows this state), and then a metal 13 is grown by electrolytic plating, and the metal mold thus formed is formed. Is peeled from the substrate. FIG. 2 (e) shows this state. Examples of the metal to be deposited by electrolytic plating used in the present invention include copper, nickel, chromium, or nickel plating in which polytetrafluoroethylene fine particles, silicon carbide fine particles, and boron nitride fine particles having a particle size of sub-μm are dispersed. it can. In some cases, a normal method such as a method of cleaning the resin adhering to the metal mold surface with a solvent or a method of removing in a high energy atmosphere such as plasma can be used. Further, the surface of a ceramic or resin plate or a cylindrical substrate can be patterned using laser light.
[0023]
In order to form a pattern of 10 μm or less, an excimer laser is preferable. For pattern formation of about 10 to 20 μm, an excimer laser, a third harmonic of a YAG laser, or a copper vapor laser can be used.
As a method of forming a concave pattern on the surface of the core film, a method of pressing the core film formed in a sheet shape on the prepared mold while heating and then peeling it from the mold ( the method of claim 1 ), and a core on the surface of the mold There is a method ( method of claim 3) in which a resin solution in which a resin component forming a film is dissolved is applied in a predetermined thickness, and then the solvent is dried and peeled off from the mold (FIG. 3 (a)).
[0024]
When the core film is thin, it becomes difficult to handle by itself, so that the adhesive layer formed on the substrate before peeling from the mold can be adhered and reinforced from the adhesive side.
For example, the first adhesive is obtained by applying an adhesive solution (a liquid obtained by dissolving an adhesive in a solvent) on the support 5 made of a plastic film or the like to a predetermined thickness, and then removing the solvent by drying. Layer 2 is formed, and an adhesive layer is adhered to the surface of the core film that has no recess. As a method for applying the adhesive solution, a usual method such as a blade coating method, a spray coating method, a spin coating method, a roll coating method, or the like can be employed.
This state is shown in FIG.
[0025]
Next, as shown in FIG. 3 (c), after spraying a powder made of a large number of conductive fine particles 4 from above the core film 1, the support 5, the first adhesive layer 2, the core film 1, The conductive sheet 4 is put into the hole 10 of the core film 1 by vibrating the entire sheet made of the above. The conductive fine particles 4a that do not enter the hole 10 and exist on the upper surface of the core film 1 are removed by pressing with a film with an adhesive or the like. By vibrating the entire sheet, the conductive fine particles 4 easily enter all the holes 10. Alternatively, the conductive fine particles 4 may be put into the holes 10 of the core film 1 by passing the entire sheet through the container a plurality of times in the conductive fine particles. In this way, as shown in FIG. 3D, the conductive particles 4 are put in each of the holes 10 one by one.
[0026]
Next, after the adhesive solution is applied on the core film 1 at a predetermined thickness, the solvent is dried and removed, thereby forming the second adhesive layer 3 on the core film 1. Further, the cover film 6 is covered on the second adhesive layer 3. Thereby, as shown in FIG.3 (e), a conductive adhesive sheet is obtained in the state in which the support body 5 was joined to one surface, and the cover film 6 was joined to the other surface, respectively.
Instead of this, the cover film 6 on which the adhesive layer 3 is formed is heated by placing the adhesive layer 3 on the core film 1 with the adhesive layer 3 facing the core film 1 side, thereby heating the cover film 6 shown in FIG. It is good also as a state. However, the heating temperature in this case needs to be a temperature at which the adhesive forming the adhesive layer 3 is not cured.
[0027]
In addition, a conductive adhesive sheet is used in the state which peeled the support body 5 and the cover film 6. FIG. Therefore, it is preferable to apply a silicone-based release agent to the surface of the support 5 on which the first adhesive layer 2 is formed and the surface of the cover film 6 on the second adhesive layer 3 side. .
As described above, according to this method , by using a mold having fine protrusions arranged in a predetermined arrangement on the surface, a minute hole 10 having a diameter of 20 μm or less is easily formed in the core film 1. be able to.
[0028]
[Example 1]
[Preparation of conductive adhesive sheet]
In this embodiment, a conductive adhesive sheet is produced by a method corresponding to the embodiment of the method of the present invention . This embodiment will be described with reference to FIG.
First, a polyethylene terephthalate (PET) film having a thickness of 25 μm was prepared, and the surface of this PET film was coated with polydimethylsiloxane as a release agent to a thickness of about 50 nm. A thermoplastic polyimide solution was applied to the surface of the PET film (support) 5 coated with a release agent using a blade coater. Next, the solvent was dried and removed from the coating film to form a film made of thermoplastic polyimide having a thickness of 10 μm on the PET film 5.
[0029]
As the thermoplastic polyimide solution, a thermoplastic polyimide solution “UPA-N-221” manufactured by Ube Industries, Ltd. was used.
Next, cylindrical convex patterns having a diameter of 7.5 μm and a height of 8 μm are arranged on the surface in the same arrangement as the arrangement of the non-through holes 10 shown in FIG. Furthermore, a nickel plate-shaped mold 13 in which the same cylindrical convex pattern was regularly arranged at the center of the lattice was also produced.
A core film made of thermoplastic polyimide and having a thickness of 10 μm was placed on this mold, and a thermocompression treatment was performed at 180 ° C. and 1 MPa for 10 minutes using a hot press machine (FIG. 3A). After cooling, the core film was peeled from the mold to form a non-penetrating recess corresponding to the mold protrusion on one side of the core film.
[0030]
Next, as shown in FIG. 3 (b), a PET film 5 having an adhesive layer (first adhesive layer) 2 made of an epoxy adhesive on one surface is used, and the adhesive layer 2 is used as a core. The film 1 was placed on the core film 1 and heated toward the surface without a concave portion, and joined by heating.
The PET film 6 in which the adhesive layer 3 made of an epoxy adhesive is formed on one surface was produced as follows. First, a polyethylene terephthalate (PET) film having a thickness of 25 μm was prepared, and the surface of this PET film was coated with polydimethylsiloxane as a release agent to a thickness of about 50 nm. An epoxy adhesive solution was applied to the surface of the PET film (cover film) 6 coated with a release agent using a blade coater. Next, a layer 3 made of an epoxy adhesive having a thickness of 10 μm was formed on the PET film 6 by drying and removing the solvent from the coating film.
[0031]
The composition of the epoxy adhesive solution used was as follows: bisphenol A type liquid epoxy resin: 10 parts by weight, phenoxy resin: 10 parts by weight, latent hardener comprising microcapsule type imidazole derivative epoxy compound: 4.5 parts by weight, and Toluene / ethyl acetate mixture: 5 parts by weight.
Next, after spraying a powder made of a large number of conductive fine particles 4 on the core film 1, the conductive fine particles 4 are formed in all the holes 10 by applying vibration to the entire sheet using an ultrasonic vibration device. I put it in. Next, the adhesive film “SPV-363” manufactured by Nitto Denko Co., Ltd. is attached to the surface of the core film 1 using a roller and then peeled off, so that it does not enter the hole 10 and exists on the upper surface of the core film 1. The conductive fine particles 4a to be removed were removed.
[0032]
Examples of the powder composed of the conductive fine particles 4 include Ag _x Cu _(1-x) (0.008 ≦ x ≦ 0.4) described in JP-A-6-223633, and silver on the particle surface. Concentration is higher than 2.2 times the average silver concentration, and is composed of spherical conductive particles having a region where the silver concentration increases toward the particle surface near the surface, the average particle size is 6 μm, and the standard deviation of the particle size distribution A powder having a thickness of 0.5 μm was used.
Next, as shown in FIG. 3 (d), a PET film 6 having an adhesive layer (second adhesive layer) 3 made of an epoxy adhesive on one surface is used, and the adhesive layer 3 is used as a core. The film 1 was placed on the core film 1 and heated by heating toward the film 1 side.
[0033]
As described above, the adhesive layers 2 and 3 made of an epoxy adhesive are arranged on both surfaces of the core film 1 made of a thermoplastic polyimide resin, and the core film 1 has circular holes 10 having a diameter of 7.5 μm, A conductive adhesive sheet which is regularly formed at a pitch of 15 μm (lattice spacing) in the arrangement shown in FIG. 1B, and each conductive fine particle 4 made of copper-silver alloy is arranged in each hole 10. was gotten. PET films 5 and 6 are bonded to both surfaces of the conductive adhesive sheet.
The softening temperature of the thermoplastic polyimide and epoxy adhesive forming the core film was measured using a rotary “rheometer” which is a viscoelasticity measuring device manufactured by Rheometrics Scientific F.E. The measurement conditions were a rotation speed: 10 rad / sec, a temperature rise start temperature: room temperature, a temperature rise speed: 10 ° C./min, and the first temperature at which the slope of the viscosity curve changed was determined as the softening temperature. As a result, the softening temperature of the epoxy adhesive was about 60 ° C., and the softening temperature of the thermoplastic polyimide was 170 ° C.
[0034]
[Mold making]
Zinc displacement plating was performed on the surface of aluminum, and a copper layer having a thickness of 3 μm was formed thereon using a copper pyrophosphate plating bath. Further, the copper surface was blackened to produce a conductive substrate having a low reflectance.
A photosensitive resin layer having a thickness of 10 μm was formed on the conductive substrate, and a resin pattern was obtained using photolithography through a glass chromium mask corresponding to the hole arrangement pattern shown in FIG.
The photosensitive resin used was an unsaturated polyester prepolymer having a number average molecular weight of 2000: 100 parts by weight, tetraethylene glycol dimethacrylate: 10.7 parts by weight, diethylene glycol dimethacrylate: 4.3 parts by weight, pentaerythritol tris Methacrylate: 15 parts by weight, phosphoric acid (monomethacryloyloxyethyl): 3.6 parts by weight, 2,2-dimethoxy-2-phenylacetophenone: 2 parts by weight, 2,6-di-tert-butyl-4-methylphenol : 0.04 parts by weight, and “OPLAS Yellow 140” manufactured by Orient Chemical Co., Ltd .: 0.11 parts by weight were added and mixed by stirring.
[0035]
The unsaturated polyester prepolymer having a number average molecular weight of 2,000 was obtained by dehydration polycondensation reaction by adjusting the charging ratio of adipic acid, isophthalic acid, itaconic acid, fumaric acid and diethylene glycol. The number average molecular weight was measured using a gel permeation chromatography apparatus manufactured by Shimadzu Corporation and calibrated with a polystyrene standard product.
Next, as an exposure mask M, a circular chrome pattern having a diameter of 7.5 μm has the same arrangement as the arrangement of the through holes 10 shown in FIG. A glass photomask regularly arranged in the center was prepared. This exposure mask M was placed on the photosensitive resin layer 11, and the light from the ultrahigh pressure mercury lamp was irradiated on the exposure mask M. This irradiation light is a parallel light beam obtained by collimating the light from the light source by the optical system. FIG. 2A shows this state. However, in this figure, a PET cover film having a thickness of 10 μm is omitted.
[0036]
Next, the PET cover film was peeled off and developed. As a result, the portion of the photosensitive resin layer 11 that was not exposed to light was removed, and the core film 1 having a large number of holes 10 was formed on the conductive substrate, as shown in FIG.
Next, the substrate surface on which the resin pattern was formed was subjected to a palladium catalyst application treatment, followed by electroless nickel plating to form a nickel layer having a thickness of several μm. Furthermore, electrolytic nickel plating was performed in a nickel sulfamate plating bath to form a nickel layer having a thickness of 70 μm. FIG. 2 (d) shows this state.
Thereafter, the formed nickel layer was peeled from the substrate to obtain a nickel mold in which cylindrical convex portions having a diameter of 7.5 μm and a height of 10 μm were regularly arranged on the surface. The surface of the obtained mold was treated with a silicone mold release agent (manufactured by Shin-Etsu Chemical Co., Ltd., SEPA-COAT SP).
[0037]
[Performance evaluation]
4 (a) is a plan view showing a part of a test substrate, FIG. 4 (b) is a line a-a sectional view of FIGS. 4 (a).
The test substrate 30 has 200 wirings 32 on an insulating substrate 31, and the wirings 32 have a thickness of 15 μm and are exposed on the insulating substrate 31 in a convex shape. The width of the wiring 32 is 15 μm, and the arrangement pitch p is 30 μm.
First, peel off the PET film 5, 6 from both sides of the conductive adhesive sheets obtained in the above manner, and all the wiring 32 portion of the test substrate 30, shows a plan view of the pattern in FIGS. 6 (a) A glass substrate is sandwiched between one convex linear pattern 22 and a substrate D having a convex circular pattern 21 and an inspection terminal 26, and heated to 230 ° C. under a pressure of 50 MPa for 5 minutes. Retained. All the patterns of the substrate D are made using copper plating, the width of the linear pattern 22 is 15 μm, and the thickness is 15 μm. The diameter of the circular pattern arranged on both sides of the linear pattern 22 is 15 μm, and the height is 15 μm. They are arranged with a pitch of 30 μm. A thin chromium layer is formed between the glass substrate and the copper plating film for the purpose of improving adhesion. The circular pattern 21 is a dummy pattern for ensuring stability during connection evaluation. At this time, the wiring 32 of the test substrate 30 and the linear pattern of the substrate D were arranged so as to be orthogonal to each other. As a result, the wiring 32 portion of the test substrate 30 and the substrate D were bonded by the conductive adhesive sheet.
[0038]
Figure 5 includes a substrate D which was formed a convex-shaped conductor pattern on the glass substrate shown a plan view of the pattern wiring 32 parts in FIG. 6 of the test substrate 30 (a) is bonded by a conductive adhesive sheet It is sectional drawing which shows the state. The sectional view corresponds to a line b-b sectional view of FIG. 4 (a). At the time of bonding, the core film 1 of the conductive adhesive sheet and the adhesive layers 2 and 3 on both sides thereof are deformed, and these are collectively shown by reference numeral 23 in FIG.
A connection confirmation test using the conductive adhesive sheet of Example 1 was performed using the two test pieces thus obtained. That is, for each test piece, the resistance between the 200 test pads 35 and the test pads on the substrate D was measured. As a result, it was found that none of the total of 400 connection points of the two test pieces is not electrically connected to the copper substrate D.
[0039]
Next, the PET films 5 and 6 are peeled off from both surfaces of the conductive adhesive sheet obtained by the above method, and all the wiring 32 portions of the test substrate 30 and the glass whose cross-sectional structure is shown in FIG. The plate was sandwiched between the plates E, heated to 230 ° C. under a pressure of 50 MPa, and held for 5 minutes. This on the glass substrate E are given the irregularities on the surface in the same pattern as the pattern shown FIG. 6 (a). That is, the hatched portion in FIG. 6 (a) so as to project, and ablation processing using an excimer laser. The height of the convex portion was 15 μm. As a result, the wiring 32 portion of the test substrate 30 and the glass substrate were bonded by the conductive adhesive sheet. Similar to the connection confirmation test, both substrates were arranged so that the wiring 32 of the inspection substrate and the linear pattern on the glass substrate E were orthogonal.
[0040]
Using the two test pieces thus obtained, the insulation resistance between adjacent test pads 35 was measured. As a result, regarding the total of 398 test pads 35 of the two test pieces, all the insulation resistances were 10 ¹² Ω or more. As a result, it was found that no short circuit occurred at all the adjacent connection points for all the connection points of the total 398 sets of the two test pieces.
From these test results, with the conductive adhesive sheet of this example, as shown in FIG. 4 , the wiring 32 and the substrate D of the test substrate 30 are connected by the conductive fine particles 4 of the conductive adhesive sheet and are adjacent to each other. It can be seen that the wirings 32 are not connected by the conductive fine particles 4.
[0041]
[Example 2]
[Preparation of conductive adhesive sheet]
A conductive adhesive sheet having anisotropic conductivity was produced by the same method as in Example 1 except that the resin forming the core film was a polysulfone resin composition in which polysulfone and cyanate ester were dissolved in tetrahydrofuran.
The polysulfone-based thermosetting resin solution used was composed of 80 parts by weight of a polysulfone resin (Amoco Polymer, Udel P-1700), 20 parts by weight of a cyanate ester resin (Ciba-Geigy, B-30), and 400 parts by weight of THF. Obtained by stirring and mixing.
The softening temperature of the polysulfone-based thermosetting resin was determined by the same method as in Example 1. As a result, the softening temperature of the polysulfone-based thermosetting resin was 160 ° C.
[0042]
[Performance evaluation]
Using the conductive adhesive sheet produced in Example 2 and the same test substrate 30, substrate D, and glass substrate E as in Example 1, two test pieces were formed in the same manner as in Example 1. A connection confirmation test and a short confirmation test were performed in the same manner as in Example 1.
As a result, in the connection confirmation test, it was confirmed that none of the total 400 connection locations of the two test pieces was not electrically connected to the substrate D.
Further, in the short check test, all the insulation resistances were 10 ¹² Ω or more for a total of 400 test pads 35 of two test pieces. As a result, it was confirmed that no short circuit occurred between all the adjacent connection wirings 32 at all the connection points of the total 398 sets of the two test pieces.
[0043]
[Comparative Example 1]
[Preparation of conductive adhesive sheet]
The conductive fine particles 4 used in Example 1 were added to the epoxy adhesive solution used in Example 1 at a ratio of 1.2% by volume and mixed. This liquid was applied to the surface of a PET film coated with polydimethylsiloxane as a release agent using a blade coater. Next, by removing the solvent from the coating film by drying, a conductive adhesive sheet having a thickness of 28 μm was formed on the PET film. This conductive adhesive sheet is used after peeling off the PET film.
The addition rate of the conductive fine particles 4 to the epoxy adhesive solution was set so that the content of the conductive fine particles 4 in the conductive adhesive sheet was approximately the same as that in Example 2.
[0044]
[Performance evaluation]
Using the conductive adhesive sheet produced in Comparative Example 1 and the same test substrate 30, copper plate D, and glass substrate as in Example 1, two test pieces were produced in the same manner as in Example 1. Then, a connection confirmation test and a short confirmation test were performed in the same manner as in Example 1.
As a result, in the connection confirmation test, it was confirmed that four of the 400 connection pads 34 of the two test pieces were not electrically connected to the copper plate D.
Further, in the short check test, all the insulation resistances were 10 ¹² Ω or more for a total of 400 test pads 35 of two test pieces. As a result, it was confirmed that no short circuit occurred between all adjacent connection pads 34 for all 400 connection pads 34 of the two test pieces.
[0045]
[Comparative Example 2]
A conductive adhesive sheet having the same configuration was produced in the same manner as in Comparative Example 1 except that the addition ratio of the conductive fine particles 4 to the epoxy adhesive solution was 20% by volume.
Using the conductive adhesive sheet produced in Comparative Example 2 and the same test substrate 30, copper plate D, and glass substrate as in Example 1, two test pieces were produced in the same manner as in Example 1. Then, a connection confirmation test and a short confirmation test were performed in the same manner as in Example 1.
As a result, in the connection confirmation test, it was confirmed that all the 400 connection pads 34 of the two test pieces were electrically connected to the copper plate D.
In the short check test, the insulation resistance was 10 ⁸ Ω or less at 10 points out of a total of 400 test pads 35 of 2 test pieces. Thereby, it turned out that the short circuit has generate | occur | produced between the connection pads 34 adjacent in these 10 places.
[0046]
【The invention's effect】
As described above, according to the method for manufacturing a conductive adhesive sheet of the present invention, a plurality of through holes are formed in a predetermined arrangement in the core film surface, and conductive fine particles are arranged in the through holes. The pitch and size of the holes can be set corresponding to the arrangement pitch of the pattern to be connected, the wiring width, and the like. In use, the arrangement of the conductive fine particles in the sheet surface is fixed by the core film.
Therefore, by setting the pitch and size of the through holes corresponding to the arrangement pitch and wiring width of the pattern to be connected, even when connecting patterns arranged at a fine pitch, short-circuits between adjacent patterns. Can be prevented from occurring. Further, it is possible to eliminate the fear that the pattern to be connected is disposed at a position where no conductive fine particles are present.
As a result, according to the conductive adhesive sheet of the present invention, a highly reliable connection can be performed even when the dimension of the pattern to be connected is small or when patterns arranged at a fine pitch are connected.
Further, according to the method for producing a conductive adhesive sheet of the present invention, the conductive fine particles are regularly and densely arranged in the sheet surface (so that the distance between adjacent conductive fine particles is 20 μm or less). It is possible to easily manufacture the conductive adhesive sheet.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view (a-1, a-2) and a plan view (b, c) showing an embodiment of a conductive adhesive sheet obtained by the method for producing a conductive adhesive sheet of the present invention.
FIG. 2 is a diagram illustrating a method for producing a mold used in the method for producing a conductive adhesive sheet of the present invention .
FIG. 3 is a diagram illustrating an embodiment of a method for producing a conductive adhesive sheet of the present invention and Example 1.
FIG. 4 is a plan view (a) and a cross-sectional view (b) showing a test substrate used for performance evaluation in Examples 1 and 2 and Comparative Examples 1 and 2 of the present invention.
[5] and the wiring portion and the substrate D of the test substrate is a view showing a state of being adhered by a conductive adhesive sheets of Examples 1, 2, b-b line cross-sectional view of FIGS. 4 (a) It corresponds to.
6 is a plan view (a) showing patterns of the substrate D and the substrate E used in the performance evaluation, where (b) corresponds to a cross-sectional view of the substrate E taken along the line cc. FIG.
FIG. 7 is a cross-sectional view (a) and a plan view (b) showing an example of a conventional conductive adhesive sheet.
FIG. 8 is a cross-sectional view for explaining problems of a conventional conductive adhesive sheet.
[Explanation of symbols]
1 Core film 2 Adhesive layer (first adhesive layer)
3 Adhesive layer (second adhesive layer)
4 conductive fine particles 5 support 6 cover film 7 conductive substrate 8 photosensitive resin layer 10 through hole 11 photosensitive resin layer 12 electroless plating layer 13 metal layer 20 sheet made of adhesive layer 21 copper cylindrical convex portion 22 made of copper Linear convex portion 23 Core film and adhesive layer 24 Cylindrical convex portion made of glass 25 Glass plate 26 Electrical inspection pad 30 Test substrate 31 Insulating substrate 32 Wiring 35 Inspection pad A Position where conductive fine particles do not exist B1 Substrate B2 Substrate C Fig. 6 (b) Cross section line D substrate h Wiring height M Exposure mask P1 Connection pattern P2 Connection pattern p Wiring arrangement pitch p10 Cylindrical convex arrangement pitch W Wiring width W1 Copper straight line Width of convex part W2 Diameter of copper cylindrical convex part

Claims (5)

  In the adhesive sheet that imparts conductivity only in the thickness direction of the sheet by the conductive fine particles dispersed and arranged in the sheet surface, an adhesive layer is disposed on both surfaces of the core film disposed in the center in the thickness direction, The core film and the adhesive layer are insulative, and the core film is formed of a resin having a softening temperature that is 20 ° C. or higher than the resin constituting the adhesive layer, and part or all of the individual conductive fine particles are formed. In the method for producing a conductive adhesive sheet having anisotropy that is present in the core film and the conductive fine particles are arranged in a predetermined arrangement in the core film surface,
  A mold having a convex portion arranged in a predetermined arrangement on a surface formed of metal, ceramics, or resin and a sheet-like core film are heat-pressed, and then the core film is peeled off from the mold to thereby remove the convex in the core film plane. Forming a concave portion corresponding to the portion, placing conductive fine particles in the predetermined concave portion in the film surface, and then forming an adhesive layer on both sides with the core film having the conductive fine particles placed in the center A method for producing a conductive adhesive sheet.   In the manufacturing method of the conductive adhesive sheet according to claim 1, between the step of thermocompression bonding the mold having the convex portion and the sheet-like core film, and the step of peeling the core film from the die after thermocompression bonding, Furthermore, the process of adhere | attaching the adhesive bond layer formed on the base material from the core film side is added, The manufacturing method of the electroconductive adhesive sheet of Claim 1 characterized by the above-mentioned.   In the adhesive sheet that imparts conductivity only in the thickness direction of the sheet by the conductive fine particles dispersed and arranged in the sheet surface, an adhesive layer is disposed on both surfaces of the core film disposed in the center in the thickness direction, The core film and the adhesive layer are insulative, and the core film is formed of a resin having a softening temperature that is 20 ° C. or higher than the resin constituting the adhesive layer, and part or all of the individual conductive fine particles are formed. In the method for producing a conductive adhesive sheet having anisotropy that is present in the core film and the conductive fine particles are arranged in a predetermined arrangement in the core film surface,
  A resin solution in which a resin component for forming a core film is dissolved is applied to the surface of a mold having a convex portion arranged in a predetermined arrangement on a surface formed of metal, ceramics or resin, and a solvent. After removing the components by drying, a step of peeling the core film from the mold is performed to form a concave portion corresponding to the convex portion of the mold in the core film surface, and the conductive fine particles are disposed in the concave portion predetermined in the film surface. And then forming an adhesive layer on both sides with a core film on which conductive fine particles are arranged sandwiched in the center.   In the manufacturing method of the electroconductive adhesive sheet of Claim 3, the resin solution which melt | dissolved the resin component which forms a core film is apply | coated to the surface where the convex part of the type | mold which has this convex part exists, and a solvent component is used. Claims characterized in that a step of adhering the adhesive layer formed on the substrate from the core film side is further added between the step of drying and removing and the step of peeling the core film from the mold after the step. Item 4. A method for producing a conductive adhesive sheet according to Item 3.   The conductive fine particles are fine particles made of copper, gold, silver, nickel, palladium, indium, tin, lead, zinc, bismuth, an alloy of any of these metals, or carbon, or fine particles having a metal coating on the surface. The method for producing a conductive adhesive sheet according to any one of claims 1 to 4, wherein:

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