JP2008218285A - Method for forming anisotropic conductive sheet - Google Patents

Abstract

A method for manufacturing an anisotropic conductive sheet at low cost is provided.
A laminate 14 is formed by sandwiching a frame plate 2 made of a porous PTFE membrane between mask membranes 11 and 12, and then a plurality of punch needles in a state where the porous PTFE resin is impregnated with a resin other than PTFE. A large number of through holes are formed at once using a press die 40 having 41. After the formation of the through hole, the impregnated resin is dissolved and removed, and then the colloidal particle adhesion region is formed by immersion in the catalyst solution, and electroless plating using the catalyst particle as a nucleus is performed on the inner wall portion of the through hole 5. Then, the cylindrical electrode film 6 is formed.
[Selection] Figure 4

Description

  The present invention relates to a method for forming an anisotropic conductive sheet used for inspection of a semiconductor integrated circuit.

  Conventionally, a burn-in test has been performed as one of screening methods for removing an initial failure of a semiconductor device. In the burn-in test, accelerated stress higher than the operating conditions of the semiconductor device is applied to accelerate failure occurrence and remove defective products in a short time. For example, a large number of packaged semiconductor devices are arranged on a burn-in board, and a power supply voltage and an input signal that cause acceleration stress are applied from outside in a high-temperature bath for a certain period of time. Thereafter, the semiconductor device is taken out and a determination test for a non-defective product and a defective product is performed. In the determination test, an increase in leakage current due to a semiconductor device defect, a defective product due to a multilayer wiring defect, a contact defect, and the like are determined. The semiconductor device is generally a surface mount LSI such as a BGA (Ball Grid Array), an LGA (Land Grid Array), or a PLCC (Plastic Leaded Chip Carrier).

  For example, when a burn-in test of a semiconductor device is performed, the test is performed via an electrode pad on the surface of a surface-mounted LSI such as a BGA (Ball Grid Array), an LGA (Land Grid Array), or a PLCC (Plastic Leaded Chip Carrier). At that time, in order to compensate for the contact failure due to the variation in the electrode height between the electrode pad of the semiconductor device and the head electrode of the inspection jig, the conductivity difference between these electrodes is usually only in the film thickness direction. The test is performed with a conductive sheet (interposer) sandwiched in between. This anisotropic conductive sheet exhibits conductivity only in the plate thickness direction in the conductive portion arranged according to the pattern corresponding to the surface electrode.

  The anisotropically conductive sheet is not only used as a component for inspection tools for burn-in testing, but also for connecting sockets and electrical connectors between LSIs and printed circuit boards (PCBs), and for connecting printed circuit boards. It is used as an electrical connector.

  As the anisotropic conductive sheet, Patent Documents 1 and 2 describe a conductive plate in which a large number of holes serving as conductive portions are formed in a frame plate made of an elastic polymer sheet, and a wire or conductive paste is embedded in each hole. Providing is disclosed. Patent Document 3 discloses that a frame plate made of a high-strength resin or the like is used, and a hole is filled with a conductive part in which an elastic polymer is filled with conductive magnetic particles. Patent Document 4 discloses a technique in which porous PTFE is used as a frame plate, a cylindrical electrode film is formed on the inner wall surface of each hole by electroless plating, and this cylindrical electrode film is used as a conductive portion. Yes.

JP 9-35789 A JP 2002-216868 A Japanese Patent Laid-Open No. 9-320667 JP 2004-265844 A

  By the way, for anisotropic conductive sheets used as burn-in test interposers for semiconductor devices, etc., the surface electrode of the semiconductor device is connected to the head electrode of the measuring device, or the signal from the inspection device is connected to the terminal of the semiconductor package. In addition to the above, stress relaxation is also required. Therefore, the anisotropic conductive sheet is elastic in the film thickness direction, can conduct in the film thickness direction with a low compressive load, and can be elastically restored, making it suitable for frequent use. It is required to be. In addition, along with high-density mounting of semiconductor packages and the like, there is a demand for miniaturization (fine pitch) of patterns such as the size and pitch of each conductive portion of an anisotropic conductive sheet used for inspection.

  However, when the techniques described in Patent Documents 1 and 2 are used, there is a limit to the technique for forming fine holes in the elastic polymer sheet, and thus forming a fine pattern with a pitch of about 50 to 100 μm or less is not possible. Have difficulty. Further, in the technique described in Patent Document 3, it is difficult to form a fine pattern having a pitch of about 50 to 100 μm or less because of the structure, and the amount of lateral deformation of the conducting portion due to the pressing force is large. It is difficult to avoid an electrical short between the parts. That is, it is difficult to make a fine pitch.

  On the other hand, in the technique described in Patent Document 4 by the present applicant, since the frame plate is made of high-strength polymer, it is sufficiently possible to make a minute and highly accurate through-hole, and push Since the amount of deformation in the lateral direction of the conducting portion (cylindrical electrode film) due to pressure is extremely small, it is possible to cope with fine pitches with a pitch of about 50 to 100 μm or less. In that case, a chemical etching method, a thermal decomposition method, an ablation method using laser light or soft X-ray irradiation, an ultrasonic method, or the like is used for forming the through hole.

  On the other hand, according to the technique of Patent Document 4, the manufacturing cost may be too high for the required quality level depending on the type of anisotropic conductive sheet, and there is still room for improvement.

  The objective of this invention is providing the formation method of the anisotropic conductive sheet which can form an anisotropic conductive sheet at low cost.

  In the method for forming the anisotropic conductive sheet of the present invention, a plurality of through holes are simultaneously formed on a base film made of a porous resin by pressing, and then electroless plating is performed on the inner wall portion of each through hole. This is a method of forming a cylindrical electrode film.

  By this method, many through holes conventionally formed individually can be collectively formed, thereby reducing the manufacturing cost.

  Formation of through-holes and electroplating are carried out with the base film sandwiched between the mask films from both sides, and after the electroless plating is finished, the mask film is peeled off to remove the mask film on both sides. The electroless plating can be avoided.

  When forming the through-hole, the through-hole is formed in a state in which the base film is impregnated with the resin, and the resin waste generated by pressing is removed by removing the impregnated resin before electroless plating. It is possible to avoid filling the fine holes of the quality resin.

  According to the method for forming an anisotropic conductive sheet of the present invention, an anisotropic conductive sheet having a cylindrical electrode film can be manufactured at low cost.

-Structure of anisotropic conductive sheet-
FIG. 1 is a perspective view showing a structure of an anisotropic conductive sheet 1 which is a porous resin material according to an embodiment. FIG. 2 is a cross-sectional view of the anisotropic conductive sheet 1 taken along the line II-II shown in FIG. As shown in FIGS. 1 and 2, the anisotropic conductive sheet 1 of the present embodiment is a rectangular flat frame plate 2 (thickness is, for example, a base material made of a porous resin having a large number of micropores. About 120 μm), a large number of through holes 5 penetrating between the first surface 3 and the second surface 4 of the frame plate 2 in the thickness direction, and conduction formed in the inner wall portion (surface region) of the through hole 5 And a cylindrical electrode film 6 to be a part. Thereby, the anisotropic conductive function of having conductivity in the plate thickness direction and no conductivity in the plate surface direction is provided. The anisotropic conductive sheet of the present embodiment can be used for a burn-in test interposer or a connection structure between printed wiring boards as disclosed in Japanese Patent Application Nos. 2006-275895 and 2006-275896. it can.

  The diameter d of the through holes 5 is about 50 μm, and the pitch p is about 100 μm. Since the anisotropic conductive sheet 1 is used for a burn-in test of a semiconductor device, the frame plate 2 needs to have high heat resistance. And in order to prevent the electrical short circuit between each cylindrical electrode film 6 used as a conduction | electrical_connection part, the frame board 2 needs to be an insulator. Moreover, as will be described later, in the present embodiment, the frame plate 2 is made of a synthetic resin of a porous film so that the anisotropic conductive sheet 1 has both elasticity and high strength. In a conductive sheet used for a burn-in test of a semiconductor device or the like, it is preferable that the diameter of the through hole 5 is 20 μm or less in order to obtain a fine pitch. Moreover, when using for the connection structure of printed wiring boards currently disclosed by Japanese Patent Application No. 2006-275895 and 2006-275896, it is preferable that it is the range of 10 micrometers-50 micrometers.

  Synthetic resin materials constituting the porous membrane frame plate 2 of the present embodiment include polytetrafluoroethylene (PTFE), tetrafluoroethylene / hexafluoropropylene copolymer (FEP), tetrafluoroethylene / perfluoroalkyl. Fluorine resins such as vinyl ether copolymer (PFA), polyvinylidene fluoride (PVDF), polyvinylidene fluoride copolymer, ethylene / tetrafluoroethylene copolymer (ETFE resin); polyimide (PI), polyamideimide (PAI) ), Polyamide (PA), modified polyphenylene ether (mPPE), polyphenylene sulfide (PPS), polyetheretherketone (PEEK), polysulfone (PSU), polyethersulfone (PES), liquid crystal polymer (LCP), etc. A ring of plastic, and the like. Among these, PTFE is preferable in consideration of heat resistance, workability, mechanical properties, dielectric properties, and the like. Therefore, in the present embodiment, a porous PTFE film (porous polytetrafluoroethylene film) is used as the frame plate 2. In this embodiment, as will be described later, since a porous PTFE membrane obtained by a stretching method is used, the frame plate 2 is composed of very thin fibers (fibrils) formed by PTFE and the fibers. It has a fine fibrous structure (porous structure) composed of nodes (nodes) connected to each other.

  In the present embodiment, the porous PTFE membrane used as the frame plate 2 preferably has a porosity of about 20 to 80%. The porous PTFE membrane preferably has an average pore diameter of 10 μm or less or a bubble point of 2 kPa or more from the viewpoint of fine pitching of the conducting part, and an average pore diameter of 1 μm or less or a bubble point of 10 kPa or more. It is more preferable. The film thickness of the porous PTFE membrane can be appropriately selected according to the purpose of use and the place of use, but is usually 0.05 mm to 3 mm.

  The tubular electrode film 6 has a multilayer metal plating layer (electroless plating layer) having a tube thickness t of 3 μm to 5 μm on the inner wall portion including the inner wall surface of the through hole 5 and the inside of the fine hole. That is, the cylindrical electrode film 6 is formed in the surface region including the fibers of the porous PTFE film by the catalyst particles and the metal that have entered the micropores from the inner wall surface during the electroless plating. In the present embodiment, the cylindrical electrode film 6 is composed of a Cu layer, a Ni alloy layer (Ni—P alloy layer), and an Au layer deposited using catalyst particles attached to the fiber surface as nuclei. The Cu layer is not necessarily required. The Ni alloy layer is a barrier layer that is necessary as an underlayer for performing displacement gold plating during electroless plating and prevents the formation of oxides caused by the movement of Cu atoms from the Cu layer to the Au layer. It is functioning as well.

  As described above, the cylindrical electrode film 6 is preferably coated with a noble metal or a noble metal alloy in order to improve oxidation prevention and electrical contact. As the noble metal, palladium, rhodium, gold, and silver are preferable from the viewpoint of low electric resistance.

  As described above, during electroless plating, the catalyst particles penetrate not only from the inner wall surface of the through-hole 5 but also from the micropores of the porous PTFE film and adhere to the fiber surface. The porous PTFE membrane is deposited by penetrating into the inside from the micropores. That is, not only the multilayer metal plating layer but also the fibers of the porous PTFE film are mixed in the surface region (inner wall portion) of the tube thickness t shown in FIG. Since this cylindrical electrode film 6 is formed by adhering to the surface of the resin portion having a porous structure, the cylindrical electrode film 6 itself has a characteristic of being porous. Then, by applying a compressive load in the thickness direction of the anisotropic conductive sheet 1, conductivity is maintained only in the thickness direction of the anisotropic conductive sheet 1 while maintaining insulation between the cylindrical electrode films 6. Imparted (anisotropic conductivity). Further, when the compressive load is removed, the entire anisotropic conductive sheet 1 including the cylindrical electrode film 6 is elastically recovered, so that the anisotropic conductive sheet 1 of the present embodiment can be used repeatedly.

  The amount of compression is normally set to about ¼ of the thickness of the frame plate 2. In the present embodiment, since the frame plate 2 having a thickness of about 120 μm is used, the amount of compression is set to 30 μm. Yes. However, since the required resistance value differs depending on the type of anisotropic conductive sheet 1 and the object to be inspected, the resistance value of each cylindrical electrode film 6 having a variation in contact degree is less than the desired resistance value. Any compression amount can be used.

-Manufacturing process of anisotropic conductive sheet-
3A to 3E are perspective views showing a manufacturing process of the anisotropic conductive sheet 1 according to the embodiment. Hereinafter, the manufacturing process of the anisotropic conductive sheet will be described with reference to FIGS. In the step shown in FIG. 3A, a frame plate 2 that is a porous PTFE membrane is prepared. Generally, methods for producing a porous film using a synthetic resin include a pore making method, a phase separation method, a solvent extraction method, a stretching method, a laser irradiation method, and the like. By forming a porous film using a synthetic resin, elasticity can be given in the plate thickness direction and the dielectric constant can be further lowered. In particular, the porous film obtained by the stretching method (porous PTFE film in the present embodiment) is excellent in heat resistance, processability, mechanical characteristics, dielectric characteristics, etc., and has a uniform pore size distribution. Therefore, it is an optimal material for the anisotropic conductive sheet substrate (frame plate 2).

  The porous PTFE membrane of the present embodiment can be produced by, for example, the method described in Japanese Patent Publication No. 42-13560. First, a liquid lubricant is mixed with the unsintered powder of PTFE, and extruded into a tube shape or a plate shape by ram extrusion. When a thin sheet is desired, the plate is rolled with a rolling roll. After the extrusion rolling process, the liquid lubricant is removed from the extruded product or the rolled product as necessary. When the extruded product or the rolled product thus obtained is stretched at least in a uniaxial direction, unsintered porous PTFE is obtained in the form of a film. An unsintered porous PTFE membrane is highly porous when heated and stretched to a temperature of 327 ° C. or higher, which is the melting point of PTFE, while being fixed so that shrinkage does not occur. A PTFE membrane is obtained. When the porous PTFE membrane is in a tube shape, a flat membrane can be obtained by opening the tube.

  Next, in the step shown in FIG. 3 (b), the mask films 11 and 12 are fused on both sides of the frame plate 2 which is a porous PTFE film obtained by the stretching method, and the laminate 14 having a three-layer structure is formed. The through-hole 5 is formed in the whole laminated body 14 (refer to a broken line). As the mask films 11 and 12, a PTFE film made of the same material as that of the frame plate 2, preferably a porous PTFE film is used. At this time, for example, three layers of porous PTFE membranes are fused to each other by sandwiching both surfaces of three laminated porous PTFE membranes with two stainless steel plates and heating each stainless steel plate to a high temperature. Can do. Then, after fusion, the frame plate 2 and the mask films 11 and 12 are impregnated with a resin other than PTFE.

  FIG. 4 is a perspective view showing a method for forming the through hole 5 in the present embodiment. As shown in the figure, in the present embodiment, a press die 40 in which a large number of punching needles 42 are arranged on a flat plate 41 and a cradle 43 made of an elastic material are used. And the laminated body 14 of the frame board 2 and the mask films | membranes 11 and 12 is installed between the press metal mold | die 40 and the receiving stand 43, and the laminated body 14 whole is lowered | hung at high speed. The through-hole 5 is formed in. At this time, by impregnating the frame plate 2 and the mask films 11 and 12 with a resin other than PTFE, it is possible to prevent the resin waste generated during the press processing from blocking the micropores of the porous PTFE film. Thereafter, only the impregnated resin is dissolved and removed. For example, when paraffin is used as the impregnating resin, it can be dissolved in a hexane / xylene solution. Alternatively, the resin impregnated under conditions where PTFE does not burn may be removed by burning.

  The cross-sectional shape of the through hole 5 is arbitrary such as a circle, a star, an octagon, a hexagon, a quadrangle, and a triangle. The diameter d of the through-hole 5 by this method can be usually 20 μm to 50 μm, preferably about 20 μm to 30 μm in a field of application where micro holes are suitable, while in the field where a relatively large diameter hole is suitable, Usually, it can be 50 μm to 100 μm, preferably about 50 μm to 70 μm.

  Next, in the step shown in FIG. 3C, the catalyst is applied through conditioning, washing with water, and pre-dip of the laminate 14. The purpose of conditioning is to make the surface of PTFE having water repellency as hydrophilic as possible, and to facilitate the adhesion of the catalyst (Pd) in a later step. For the porous PTFE membrane, a solution containing alcohol such as ethanol or a surfactant is used as a conditioner, and the conditioner is infiltrated to each fiber in the porous structure.

  And after completion | finish of a pre-dip process, the laminated body 14 is immersed in the catalyst liquid (for example, a tin chloride-palladium chloride colloid liquid) containing Pd, and the surface of each fiber of PTFE constituting the laminated body 14 is made of a Pd compound. Colloidal particles are adhered to form a colloidal particle adhesion region 15 formed by adhering colloidal particles on the surface of each fiber in a surface region such as the inner wall of the through hole 5. In the colloidal particle adhesion region 15, the colloidal particles are rarely a continuous layer on the surface of the fiber, and are often island-like layers. At this time, the colloidal particle adhesion region 15 is also formed in the surface region of the exposed portions of the mask films 11 and 12 (the hatched region shown in FIG. 3C). Even if the pre-dip step is omitted, the effect of the present invention can be exhibited.

  In this process, in the subsequent process, Pd as the catalytic metal is uniformly dispersed and attached to the surface of each fiber of the porous PTFE film, so that the cylindrical electrode film 6 formed by electroless plating is used. The electrical resistance value can be suppressed. However, in this step, colloidal particles made of a Pd compound are attached to the surface of the PTFE fiber, and not Pd alone. When the catalyst application step is completed, the laminate 14 is washed with water, and the process proceeds to the next step.

  Next, in the step shown in FIG. 3D, the mask films 11 and 12 are peeled off from both surfaces of the frame plate 2. At this time, the colloidal particle formation region 15 is not formed on both surfaces of the frame plate 2. On the other hand, the colloidal particle adhesion region 15 is also formed on the side edge of the frame plate 2. The colloidal particle adhesion region 15 formed in this part is appropriately selected after the end of this step or after the end of electroless plating. To be removed.

  Next, in the step shown in FIG. 3 (e), electroless plating is performed to form the cylindrical electrode film 6. Before that, colloidal particles made of a Pd compound are attached using dilute hydrochloric acid, dilute sulfuric acid, or the like. A process of activating Pd in the region 15 is performed. Thereby, activated catalyst particles are formed. The catalyst particles generally contain a Pd compound (for example, palladium-tin chloride) and simple Pd, and Pd is exposed on the surface even if all the colloidal particles are not changed to simple Pd. If it does, the function as a catalyst of electroless plating can be exhibited. Thereafter, the treatment liquid adhering to the surface of the frame plate 2 is washed away with water.

  In the electroless plating step, Cu is deposited around the catalyst particles from a copper sulfate solution or the like by electroless Cu plating using a solution containing copper ions such as copper sulfate and a reducing agent such as formaldehyde. Since the deposited Cu also has catalytic activity, a Cu layer having a thickness corresponding to the plating time is formed. When the electroless plating of Cu is completed, the process proceeds to the next step after washing with water.

  Next, in order to adhere the catalyst to the surface of the Cu layer, the frame plate 2 is again immersed in the catalyst solution. Here, a palladium chloride solution is used as the catalyst solution. Pre-dip and conditioning are not performed, and the catalyst liquid does not contain tin chloride, so that the catalyst particles hardly adhere to the exposed portions of PTFE that are not covered with the Cu layer. Thereafter, washing with water is performed to remove the catalyst solution remaining on the surface.

  Next, an Ni alloy layer (actually Ni-P alloy plating) is used on the Cu layer by electroless Ni plating (actually Ni-P alloy plating) using a solution containing Ni ions such as nickel sulfate and a reducing agent containing phosphinate ions. Is deposited with a Ni-P alloy layer). Then, it is washed with water.

  Thereafter, an Au layer is formed by displacement gold plating. When an electrochemically noble metal (Ni) is immersed in a solution containing electrochemically noble metal (Au) ions, noble metal ions are reduced by electrons released by the dissolution of the noble metal, A noble metal (Au) coating is deposited on the base metal (Ni) surface. Through the above steps, the cylindrical electrode film 6 made of catalyst particles, a Cu layer, a Ni—P alloy layer, and an Au layer is formed. Note that the Au layer may be formed by autocatalytic electroless plating after displacement plating. Then, the electroless plating process is completed by drying through water washing and alcohol substitution.

  According to the present embodiment, as a method for forming the through holes 5 in the frame plate 2 made of a porous PTFE film, the through holes 5 are individually provided as in the conventional laser method, drilling method, ultrasonic method, and the like. Instead of forming a large number of holes, a large number of through-holes 5 are collectively opened by pressing, so that it is extremely efficient and an anisotropic conductive sheet can be manufactured at low cost.

  In particular, in the formation of the porous PTFE resin through-holes, there is a problem that the chips block the fine holes. As already described, the cylindrical electrode film 6 is composed of an electroless plating layer that penetrates into the fine hole from the inner wall surface of the through hole 5 and adheres to the fiber surface to a certain depth. With such a structure, an elastic force capable of withstanding repeated load is maintained. Therefore, if the fine holes are closed with chips, the basic function of the anisotropic conductive sheet may be impaired. For this reason, it has been difficult to perform batch hole punching by pressing, but by impregnating the porous PTFE membrane with other resin before the formation of the through hole, as in this embodiment, It is possible to prevent chips from entering the fine premises from the wall surface of the through hole.

In the above embodiment, not only the frame plate 2 but also the mask films 11 and 12 are impregnated with resin, but only the frame plate 2 or only the frame plate 2 and the upper mask film 12 are impregnated with resin. Also good. In that case, in the step shown in FIG. 3A, only the frame plate 2 or only the frame plate 2 and the upper mask film 12 is impregnated with resin other than PTFE, and the step shown in FIG. Before the step, the impregnated resin may be dissolved.
(Other embodiments)

  In the above-described embodiment, the frame plate 2 is sandwiched between the mask films 11 and 12 from both sides, and the laminated body 14 is formed. Then, the through holes are formed and immersed in the catalyst solution. There is no need to form. For example, the steps shown in FIGS. 3C to 3E, such as formation of through holes, application of a catalyst, activation treatment, and electroless plating, may be performed on the frame plate alone. In that case, an electroless plating layer is also formed on the plate surface of the frame plate, but may be removed by polishing or etching. However, by forming the through hole 5 in the laminate 14 as in the present embodiment, the highly accurate through hole 5 can be obtained.

  In Embodiment 1 above, Pd, which is catalyst particles, is attached to the PTFE fiber surface by conditioning, pre-dip, catalyst application, and activation treatment, but the method for fixing catalyst particles such as Pd is limited to this procedure. Any other method may be used. The catalyst particles are not limited to Pd, and may be other metals, inorganic materials other than metals, organic conductors, and the like.

  The structure of the embodiment of the present invention disclosed above is merely an example, and the scope of the present invention is not limited to the scope of these descriptions. The scope of the present invention is indicated by the description of the scope of claims, and further includes meanings equivalent to the description of the scope of claims and all modifications within the scope.

  The anisotropic conductive sheet of the present invention can be used for an interposer used for inspection of a semiconductor integrated circuit and various devices, or a connection structure between wirings of a flexible printed wiring board or a rigid printed wiring board.

It is a perspective view which shows the structure of the anisotropically conductive sheet which concerns on embodiment. It is sectional drawing of the anisotropically conductive sheet in the II-II line | wire shown in FIG. (A)-(e) is a perspective view which shows the manufacturing process of the anisotropically conductive sheet which concerns on embodiment. It is a perspective view for demonstrating the formation method of a through-hole.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Anisotropic conductive sheet 2 Frame board 3 1st surface 4 2nd surface 5 Through-hole 6 Cylindrical electrode film 11 Mask film 12 Mask film 14 Laminated body 15 Colloid particle adhesion area 40 Press die 41 Flat plate 42 Punching needle 43 Receiving Stand

Claims (3)

Preparing a base film comprising a porous resin having a plurality of micropores (a);
A step (b) of forming a plurality of through holes penetrating the base film in the thickness direction;
A step (c) of forming a cylindrical electrode film including an electroless plating layer on the inner wall portion of each through hole by electroless plating,
In the step (b), the anisotropic conductive sheet forming method, wherein the plurality of through holes are simultaneously formed by pressing. In the formation method of the anisotropically conductive sheet according to claim 1,
The steps (b) and (c) are performed in a state where the base film is sandwiched by mask films from both sides,
A method for forming an anisotropic conductive sheet, wherein the mask film is removed after the step (c). In the formation method of the anisotropic conductive sheet of Claim 1 or 2,
In the step (b), a through hole is formed in a state in which the base film is impregnated with a resin,
A method for forming an anisotropic conductive sheet, wherein the impregnated resin is removed before the step (c).

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