Conductive sheet, connection structure, and method for manufacturing connection structure

Abstract

This invention provides a conductive sheet, the shape of which does not easily become uneven even when stored for a long period of time on a release liner. A conductive sheet according to an embodiment of the present invention includes solder particles, epoxy resin, and polymer resin having a weight average molecular weight of ten thousand or more. At 50°C, the complex viscosity V1 of the conductive sheet is 500 Pa·s or more. At a melting point T0 of the solder particles, the complex viscosity V2 of the conductive sheet excluding the solder particles is 15.0 Pa·s or less.

Description

Conductive Sheet, Connection Structure, and Method for Producing Connection Structure

[0001] The present invention relates to a conductive sheet, a connection structure, and a method for producing a connection structure.

[0002] Conventionally, anisotropic conductive sheets have been used for connecting two wired circuit boards. An anisotropic conductive sheet, when heated while being disposed between two wired circuit boards, develops conductivity in the stacking direction of the two wired circuit boards, while ensuring insulation in the direction perpendicular to the stacking direction (plane direction).

[0003] As an anisotropic conductive sheet, one obtained by combining solder particles and a thermosetting resin is known (for example, Patent Document 1). When this anisotropic conductive sheet is heated, the solder particles melt and aggregate between an electrode of one wired circuit board and an electrode of the other wired circuit board. Thereafter, the molten solder is cooled and solidified, whereby these electrodes are electrically connected to each other. In regions where no electrodes are present, aggregation of the solder particles does not proceed, and insulation provided by the resin is maintained. By such a mechanism, anisotropy in which electrical characteristics differ between the stacking direction and the plane direction of the two wired circuit boards is developed.

[0004] International Publication No. 2023 / 145487

[0005] A conductive sheet can be produced, for example, by applying a conductive composition containing a conductive sheet material onto a release liner, and drying the obtained coating film. According to studies by the present inventors, conventional conductive sheets tend to have uneven shape when stored for a long period of time in a state disposed on a release liner.

[0006] An object of the present invention is to provide a conductive sheet that is less prone to uneven shape even when stored for a long period of time in a state disposed on a release liner.

[0007] [1] The conductive sheet according to an embodiment of the present invention is a conductive sheet comprising solder particles, epoxy resin, and a polymer resin having a weight-average molecular weight of 10,000 or more, wherein the complex viscosity V1 of the conductive sheet is 500 Pa·s or more at 50°C, and the complex viscosity V2 of the conductive sheet excluding the solder particles is 15.0 Pa·s or less at the melting point T0 of the solder particles. [2] In the conductive sheet described in [1] above, the storage modulus of the conductive sheet may be 22,000 Pa or more at a temperature 40°C higher than the melting point T0 (T0 + 40°C). [3] The conductive sheet described in [1] or [2] above may have a water absorption rate of 0.40% or less as determined by the following test. Test: The conductive sheet is cured to obtain a cured sheet. The cured sheet is left standing for 24 hours in an atmosphere of 85°C and 85% RH. The ratio of the weight W1 of the cured sheet before standing to the weight W2 of the water absorbed by the cured sheet during standing is defined as the water absorption rate. [4] In the conductive sheet according to any of [1] to [3] above, the solder particles may contain Sn. [5] In the conductive sheet according to any of [1] to [4] above, the weight-average molecular weight of the epoxy resin may be less than 10,000. [6] In the conductive sheet according to any of [1] to [5] above, the epoxy resin may contain repeating units having a glycidyl group. [7] In the conductive sheet according to any of [1] to [6] above, the epoxy resin may have at least one selected from the group consisting of a dicyclopentadiene skeleton, a biphenyl skeleton, a naphthalene skeleton, a phenol skeleton, and a cresol skeleton. [8] In the conductive sheet according to any of [1] to [7] above, the conductive sheet may contain both a liquid epoxy resin and a solid epoxy resin. [9] In the conductive sheet described in any of [1] to [8] above, the ratio of the solid epoxy resin content (weight%) to the sum of the epoxy resin content (weight%) and the polymer resin content (weight%) may be 50% or more.

[10] In the conductive sheet according to any of [1] to [9] above, the ratio of the polymer resin content (weight%) to the sum of the epoxy resin content (weight%) and the polymer resin content (weight%) may be 20% or less.

[11] The conductive sheet according to any of [1] to

[10] above may further contain flux.

[12] A connection structure according to an embodiment of the present invention comprises: a first substrate on which a first electrode is disposed; a second substrate on which a second electrode is disposed; and a connecting member connecting the first substrate and the second substrate, wherein the connecting member is formed from the conductive sheet according to any of [1] to

[11] above.

[13] A method for manufacturing a connection structure according to an embodiment of the present invention is a method for manufacturing a connection structure according to

[12] above, comprising: arranging the conductive sheet between the first substrate and the second substrate; and heating the conductive sheet to form the connecting member.

[0008] According to embodiments of the present invention, it is possible to provide a conductive sheet that is less prone to irregularities in its shape even when stored for a long period of time while placed on a release liner.

[0009] This graph illustrates the relationship between temperature and complex viscosity for a conductive sheet with solder particles removed. This is a schematic cross-sectional view of a conductive sheet according to one embodiment of the present invention. This is a schematic cross-sectional view of a connecting structure according to one embodiment of the present invention. This is a diagram illustrating the manufacturing method of the connecting structure shown in Figure 3. This is a diagram illustrating the manufacturing method of the connecting structure shown in Figure 3.

[0010] ≪1. Conductive Sheet≫ The conductive sheet according to the embodiment of the present invention contains solder particles, epoxy resin, and a polymer resin having a weight-average molecular weight of 10,000 or more. At 50°C, the complex viscosity V1 of the conductive sheet is 500 Pa·s or more. Furthermore, at the melting point T0 of the solder particles, the complex viscosity V2 of the conductive sheet excluding the solder particles is 15.0 Pa·s or less. The conductive sheet of this embodiment can typically function as an anisotropic conductive sheet.

[0011] The complex viscosity V1 can be measured by the following method. First, prepare the conductive sheet to be measured (measurement sample S1). The measurement sample S1 is disc-shaped, with a base diameter of 25.0 mm and a thickness of 400 ± 50 μm. The measurement sample S1 may also be obtained by punching out a disc shape from a laminate of multiple conductive sheets made using the conductive composition described in section <1-8. Method for manufacturing conductive sheets>. Next, perform dynamic viscoelasticity measurement on the measurement sample S1 under the following measurement conditions. From the results of the dynamic viscoelasticity measurement, determine the complex viscosity of the measurement sample S1 at 50°C, and consider the obtained value as the complex viscosity V1 of the conductive sheet. Measurement conditions Measurement environment: atmospheric atmosphere Strain value: 0.5% Measurement frequency: 1 Hz Temperature range: 25°C to 300°C Heating rate: 10°C / min Shape: parallel plate 25.0 mmφ

[0012] The complex viscosity V1 is 500 Pa·s or more, as described above, and may be 800 Pa·s or more, 1000 Pa·s or more, 3000 Pa·s or more, 5000 Pa·s or more, 8000 Pa·s or more, 10000 Pa·s or more, 13000 Pa·s or more, 15000 Pa·s or more, 20000 Pa·s or more, and even 25000 Pa·s or more. The complex viscosity V1 may be, for example, 50000 Pa·s or less, and even 30000 Pa·s or less. The complex viscosity V1 is preferably between 10000 Pa·s and 30000 Pa·s.

[0013] As described above, conventional conductive sheets tend to develop irregularities in their shape when stored for a long period of time on a release liner. These irregularities can be observed as depressions on the surface of the conductive sheet. The occurrence of these irregularities is thought to be due to the material in the conductive sheet not adhering sufficiently to the surface of the release liner, resulting in repulsion. According to our research, by adjusting the complex viscosity V1 of the conductive sheet at 50°C to 500 Pa·s or higher, the above-mentioned repulsion is suppressed, and irregularities in the shape of the conductive sheet tend to occur less easily.

[0014] The complex viscosity V2 can be measured by the following method. First, a conductive sheet from which solder particles have been removed is prepared. Note that a conductive sheet from which solder particles have been removed is simply a resin sheet and does not strictly exhibit conductivity, but for convenience, it is referred to as a "conductive sheet" in this specification. In this specification, the conductive sheet (conductive sheet from which solder particles have been removed) used to measure the complex viscosity V2 is sometimes referred to as the measurement sample S2. The measurement sample S2 is disc-shaped, with a base diameter of 25.0 mm and a thickness of 400 ± 50 μm. The measurement sample S2 may also be obtained by punching out a disc-shaped laminate of multiple conductive sheets made using a resin composition from which solder particles have been removed, as described in section <1-8. Method for manufacturing a conductive sheet>. Note that the above resin composition can be prepared by the same method as the conductive composition, except that solder particles are not added. Next, dynamic viscoelasticity measurement is performed on the measurement sample S2 for the complex viscosity V1 under the measurement conditions described above. Based on the results of the dynamic viscoelasticity measurement, the complex viscosity of the measurement sample S2 at the melting point T0 of the solder particles is determined, and the obtained value is considered to be the complex viscosity V2 mentioned above.

[0015] The complex viscosity V2 is 15.0 Pa·s or less as described above, and may be 13.0 Pa·s or less, 10.0 Pa·s or less, 8.0 Pa·s or less, 5.0 Pa·s or less, 3.0 Pa·s or less, 2.0 Pa·s or less, 1.5 Pa·s or less, 1.0 Pa·s or less, 0.8 Pa·s or less, and even 0.5 Pa·s or less. The complex viscosity V2 is, for example, 0.01 Pa·s or more, and may be 0.05 Pa·s or more, and even 0.1 Pa·s or more. Preferably, the complex viscosity V2 is between 0.1 Pa·s and 15.0 Pa·s.

[0016] When a conductive sheet containing solder particles is heated to the melting point T0 of the solder particles, the solder particles melt within the conductive sheet. In this embodiment, since the complex viscosity V2 is 15.0 Pa·s or less, the molten solder easily moves within the conductive sheet at the melting point T0 of the solder particles. Therefore, when a conductive sheet is used to connect two wiring circuit boards, for example, the molten solder easily aggregates between the electrodes of one wiring circuit board and the electrodes of the other wiring circuit board, thereby providing a connection structure with high electrical connection reliability.

[0017] Furthermore, in this embodiment, it is preferable that the complex viscosity V3 of the conductive sheet excluding the solder particles is higher than 15.0 Pa·s at a temperature 40°C higher than the melting point T0 of the solder particles (T0 + 40°C). The complex viscosity V3 is, for example, 50 Pa·s or more, and may be 100 Pa·s or more, 500 Pa·s or more, 1000 Pa·s or more, 3000 Pa·s or more, 5000 Pa·s or more, 8000 Pa·s or more, 10000 Pa·s or more, 15000 Pa·s or more, and even 20000 Pa·s or more. The complex viscosity V3 is, for example, 500000 Pa·s or less, and may be 100000 Pa·s or less. The complex viscosity V3 can be determined by performing dynamic viscoelasticity measurement on the complex viscosity V2 using the method described above. In detail, the complex viscosity of the measurement sample S2 at a temperature of T0 + 40°C can be determined from the results of dynamic viscoelasticity measurements, and the obtained value can be considered as the complex viscosity V3 mentioned above.

[0018] A complex viscosity V3 higher than 15.0 Pa·s is typically due to the hardening of the resin (especially epoxy resin) in the conductive sheet. In other words, in this embodiment, when a conductive sheet is used to connect two wiring circuit boards, it is preferable that the resin in the conductive sheet hardens after the molten solder aggregates between the electrodes at the melting point T0 of the solder particles by further heating the conductive sheet. The hardening of the resin around the aggregated solder can form a connection structure with a stable structure.

[0019] In this embodiment, the ratio V3 / V2 of the complex viscosity V3 (Pa·s) to the complex viscosity V2 (Pa·s) is preferably 10 or more, and may be 50 or more, 100 or more, 1000 or more, 10000 or more, 30000 or more, or even 50000 or more. The ratio V3 / V2 may be, for example, 1,000,000 or less, or 100,000 or less.

[0020] Figure 1 is a graph (temperature-complex viscosity profile) illustrating the relationship between temperature and complex viscosity for a conductive sheet with solder particles removed (i.e., the measurement sample S2 described above). Note that this graph schematically shows the relationship between temperature and complex viscosity and does not limit the physical properties of the conductive sheet.

[0021] As can be seen from the graph in Figure 1, when the above-mentioned measurement sample S2 is heated and its temperature rises, the complex viscosity gradually decreases. At the melting point T0 of the solder particles, the complex viscosity V2 is 15.0 Pa·s or less. Furthermore, when the measurement sample S2 is heated to a temperature higher than the melting point T0, it is preferable that its complex viscosity increases. As described above, at a temperature 40°C higher than the melting point T0 of the solder particles (T0 + 40°C), it is preferable that the complex viscosity (complex viscosity V3) of the measurement sample S2 is higher than 15.0 Pa·s.

[0022] <1-1. Structure of the Conductive Sheet> An example of a conductive sheet according to an embodiment of the present invention is shown in Figure 2. Figure 2 shows the conductive sheet 1 placed on the release liner 15. Another aspect of the present invention is to provide a laminate 150 comprising the conductive sheet 1 and the release liner 15. When the conductive sheet 1 is used, the release liner 15 is peeled off from the conductive sheet 1.

[0023] As shown in Figure 2, the conductive sheet 1 has, for example, a matrix 3 and solder particles 5 dispersed in the matrix 3. More specifically, the matrix 3 surrounds the solder particles 5. In the matrix 3, the solder particles 5 may be spaced apart from each other or partially aggregated. In this embodiment, it is preferable that the matrix 3 contains the epoxy resin and polymer resin described above.

[0024] As the release liner 15, the release liner described in section <1-8. Method for Manufacturing Conductive Sheets> can be used. In the example in Figure 2, the conductive sheet 1 is placed on one release liner 15. However, the conductive sheet 1 may be placed between two release liners 15.

[0025] The components of the conductive sheet 1 will be described below.

[0026] <1-2. Solder Particles> As described above, the conductive sheet contains solder particles. There may be only one type of solder particle, or there may be two or more types. From the viewpoint of environmental protection, it is preferable that the solder particle material be lead-free solder material that does not contain lead.

[0027] The solder particles preferably contain tin (Sn). Solder particles containing tin tend to accelerate the hardening of the resin through metal catalytic action. In the solder particles, tin may exist in elemental form or form an alloy with other metals. Examples of tin alloys include tin-bismuth alloy (Sn-Bi), tin-silver-copper alloy (Sn-Ag-Cu), tin-silver alloy (Sn-Ag), and tin-bismuth-indium alloy (Sn-Bi-In).

[0028] When solder particles contain a tin-silver-copper alloy, the tin content in the tin-silver-copper alloy may be, for example, 90% by weight or more, and may be 95% by weight or more. The silver content in the tin-silver-copper alloy may be, for example, 10% by weight or less, and may be 5% by weight or less. The copper content in the tin-silver-copper alloy may be, for example, 1% by weight or less, and may be 0.5% by weight or less.

[0029] When the solder particles contain a tin-bismuth alloy, the tin content in the tin-bismuth alloy may be, for example, 80% by weight or less, or 50% by weight or less. The bismuth content in the tin-bismuth alloy may be, for example, 20% by weight or more, or 50% by weight or more.

[0030] The shape of the solder particles is not particularly limited as long as they are particulate, and examples include spherical, ellipsoidal, flaky, and fibrous shapes. Spherical solder particles are preferred. The average particle diameter (average primary particle diameter) of the solder particles is, for example, 20 μm or less, and may be 10 μm or less, 8 μm or less, 5 μm or less, or even 3 μm or less. Solder particles with a small average particle diameter are suitable for fabricating miniaturized, low-profile connection structures. The average particle diameter of the solder particles may be, for example, 0.1 μm or more, or 0.5 μm or more. In this specification, the average particle diameter can be specified as the median diameter (D50) in the particle size distribution measured by a laser diffraction particle size distribution analyzer or the like.

[0031] The melting point T0 of solder particles is, for example, 70°C or higher, and may be 100°C or higher, 120°C or higher, 150°C or higher, 180°C or higher, or even 200°C or higher. The melting point T0 of solder particles is, for example, 280°C or lower, and may be 260°C or lower, or even 240°C or lower. The melting point can be measured by differential scanning calorimetry (DSC).

[0032] The solder particle content in the conductive sheet is, for example, 20% by weight or more, and may be 30% by weight or more, 40% by weight or more, 50% by weight or more, or even 60% by weight or more. The above content may be, for example, 80% by weight or less, and may be 70% by weight or less.

[0033] Note that solder particles may have an oxide film formed on their surface, but it is preferable that no oxide film is formed. The oxide film on the solder particles can be removed, for example, by performing an acid treatment on the solder particles before manufacturing the conductive sheet. Details of the method for removing the oxide film will be explained in section 1-8. Method for manufacturing a conductive sheet.

[0034] <1-3. Epoxy Resin> As described above, the conductive sheet contains epoxy resin. More specifically, the epoxy resin is contained in the matrix of the conductive sheet. There may be only one type of epoxy resin or two or more types. Note that the epoxy resin described in section <1-3. Epoxy Resin> typically has a weight-average molecular weight of less than 10,000 and is not classified as a polymer resin.

[0035] Epoxy resins are typically thermosetting. In other words, epoxy resins typically have at least one epoxy group (particularly a glycidyl group) in one molecule. The epoxy equivalent of an epoxy resin is, for example, 100 g / eq. or more, and may be 150 g / eq. or more, 180 g / eq. or more, 200 g / eq. or more, 225 g / eq. or more, 230 g / eq. or more, 250 g / eq. or more, and even 280 g / eq. or more. The above epoxy equivalent is, for example, 3000 g / eq. or less, and may be 2000 g / eq. or less, 1000 g / eq. or less, 800 g / eq. or less, 500 g / eq. or less, 400 g / eq. or less, and even 300 g / eq. or less. Note that epoxy equivalent refers to the molecular weight of the epoxy resin per equivalent of epoxy groups contained in the epoxy resin. If the conductive sheet contains two or more types of epoxy resin, the average value of the epoxy equivalents may satisfy the above numerical range.

[0036] Epoxy resins preferably contain repeating units having epoxy groups (particularly glycidyl groups) in their molecules. Repeating units having epoxy groups are represented, for example, by the following formula (1).

[0037] In formula (1) above, A is a divalent linking group. Preferably, A includes a ring structure. Examples of ring structures include aliphatic rings such as dicyclopentadiene rings; aromatic rings such as benzene rings, biphenyl rings, and naphthalene rings. The ring structure may or may not have further substituents. The ring structure may be directly bonded to the benzene ring adjacent to A in formula (1), or it may be bonded via a linking group such as an alkylene group.

[0038] As shown in formula (1), the benzene ring adjacent to A has a glycidyl group. This benzene ring may further have other substituents besides the glycidyl group. Examples of other substituents include alkyl groups such as methyl groups.

[0039] Preferably, the epoxy resin has at least one selected from the group consisting of a dicyclopentadiene skeleton, a biphenyl skeleton, a naphthalene skeleton, a phenol skeleton, and a cresol skeleton in its molecule, more preferably has at least one selected from the group consisting of a dicyclopentadiene skeleton, a biphenyl skeleton, and a naphthalene skeleton, and particularly preferably has a dicyclopentadiene skeleton. Epoxy resins having skeletons such as a dicyclopentadiene skeleton, a biphenyl skeleton, and a naphthalene skeleton are suitable for increasing the complex viscosity V1 of the conductive sheet. This epoxy resin is also suitable for increasing the storage modulus E described later. Furthermore, this epoxy resin also tends to reduce the water absorption of the conductive sheet.

[0040] The dicyclopentadiene skeleton is represented, for example, by the following formula (2).

[0041] In the above formula (2), * indicates a bonding site to another structure. Specifically, formula (2) represents a dicyclopentadiene ring that functions as a divalent linking group. This dicyclopentadiene ring may or may not have a substituent. Examples of the epoxy resin having a dicyclopentadiene skeleton include those in which A is represented by formula (2) in the repeating unit of the above formula (1).

[0042] Furthermore, examples of the epoxy resin having a biphenyl skeleton include those in which A has a biphenyl ring in the repeating unit of the above formula (1). Examples of the epoxy resin having a naphthalene skeleton include those in which A has a naphthalene ring in the repeating unit of the above formula (1).

[0043] Note that the epoxy resin contained in the conductive sheet of the present embodiment is not limited to those described above. For example, the conductive sheet may contain an epoxy resin other than the epoxy resin having the repeating unit of the above formula (1).

[0044] Specific examples of epoxy resins (thermosetting epoxy resins) include bisphenol-type epoxy resins (e.g., bisphenol A-type epoxy resin, bisphenol F-type epoxy resin, and bisphenol S-type epoxy resin), novolac-type epoxy resins (e.g., phenol novolac-type epoxy resin, cresol novolac-type epoxy resin, and biphenyl-type epoxy resin), naphthalene-type epoxy resin, fluorene-type epoxy resin (e.g., bisarylfluorene-type epoxy resin), triphenylmethane-type epoxy resin (e.g., trishydroxyphenylmethane-type epoxy resin), and dicyclopentadiene-type epoxy resin.

[0045] The conductive sheet preferably contains at least one epoxy resin selected from the group consisting of dicyclopentadiene-type epoxy resin, biphenyl-type epoxy resin, and naphthalene-type epoxy resin, and is particularly preferably a dicyclopentadiene-type epoxy resin. However, the conductive sheet may also contain other epoxy resins (for example, bisphenol A-type epoxy resin, cresol novolac-type epoxy resin, phenol novolac-type epoxy resin, etc.).

[0046] Commercially available dicyclopentadiene-type epoxy resins include "EPICLON HP-7200HHH" from DIC Corporation and "XD-1000" from Nippon Kayaku Co., Ltd. Commercially available biphenyl-type epoxy resins include "NC-3000" and "NC-3500" from Nippon Kayaku Co., Ltd. Commercially available naphthalene-type epoxy resins include "NC-7000H" from Nippon Kayaku Co., Ltd. Commercially available bisphenol-type epoxy resins include "jER828" from Mitsubishi Chemical Corporation and "NPES907" from Nanya Plastics Co., Ltd. Commercially available cresol novolac-type epoxy resins include "EOCN-1020-70" from Nippon Kayaku Co., Ltd. Commercially available phenol novolac-type epoxy resins include "EPPN-502H" from Nippon Kayaku Co., Ltd.

[0047] The weight-average molecular weight of the epoxy resin is, for example, less than 10,000, and may be 9000 or less, 8000 or less, 7000 or less, 6000 or less, 5000 or less, or even 4000 or less. The above-mentioned weight-average molecular weight is, for example, 100 or more, and may be 300 or more, 500 or more, 800 or more, or even 1000 or more. The weight-average molecular weight can be measured by GPC (gel permeation chromatography).

[0048] The curing temperature of the epoxy resin is preferably not lower than the melting point T0 of the solder particles, and is, for example, 150°C to 280°C, may be 160°C to 260°C, or even 170°C to 250°C.

[0049] It should be noted that in the conductive sheet, the epoxy resin may be either liquid or solid. The conductive sheet of the present embodiment preferably contains both a liquid epoxy resin and a solid epoxy resin. However, the conductive sheet may contain only one of the liquid epoxy resin and the solid epoxy resin (for example, only a solid epoxy resin). In the present specification, the term "liquid" refers to a substance in a liquid state that is flowable at 25°C under atmospheric pressure (101.325 kPa), and the term "solid" refers to a substance in a solid state that does not flow at 25°C under atmospheric pressure.

[0050] The softening point of the solid epoxy resin is preferably lower than the melting point T0 of the solder particles. The above-mentioned softening point is, for example, 40°C or higher, and may be 60°C or higher, or even 80°C or higher. The above-mentioned softening point is, for example, 200°C or lower, and may be 180°C or lower, 150°C or lower, or even 140°C or lower. The softening point can be measured by a thermomechanical analyzer.

[0051] The content of the epoxy resin in the conductive sheet is, for example, 10% by weight or more, and may be 20% by weight or more, 25% by weight or more, or even 30% by weight or more. The above-mentioned content is, for example, 60% by weight or less, and may be 50% by weight or less, or even 40% by weight or less.

[0052] In the conductive sheet, the ratio R1 of the solid epoxy resin content (weight%) to the sum of the epoxy resin content (weight%) and polymer resin content (weight%) is, for example, 40% or more, and may be 50% or more, 60% or more, 65% or more, or even 70% or more. The ratio R1 is, for example, 95% or less, and may be 90% or less, 85% or less, or even 80% or less.

[0053] <1-4. Polymer Resin> As described above, the conductive sheet contains a polymer resin having a weight-average molecular weight of 10,000 or more. More specifically, the polymer resin is contained in the matrix of the conductive sheet. According to the inventors' studies, the polymer resin is suitable for increasing the complex viscosity V1 of the conductive sheet. The polymer resin may be one type or two or more types.

[0054] Examples of polymeric resins include epoxy resins and (meth)acrylic resins, which have a weight-average molecular weight of 10,000 or more. Epoxy resins with a weight-average molecular weight of 10,000 or more are sometimes called phenoxy resins. In this specification, "(meth)acrylic" means "acrylic and / or methacrylic".

[0055] The epoxy resin used as a polymer resin may be thermosetting or thermoplastic. A thermosetting epoxy resin typically has at least one epoxy group (particularly a glycidyl group) in one molecule. In this case, the epoxy equivalent of the epoxy resin may be, for example, 3000 g / eq. or more, 5000 g / eq. or more, and even 8000 g / eq. or more. The epoxy equivalent may also be, for example, 50000 g / eq. or less, and 10000 g / eq. or less.

[0056] Specific examples of epoxy resins are those exemplified in section <1-3. Epoxy Resins>. The epoxy resin used as the polymer resin is preferably a bisphenol-type epoxy resin (particularly bisphenol A-type epoxy resin or bisphenol F-type epoxy resin). Examples of commercially available bisphenol-type epoxy resins used as polymer resins include the product names "jER1256" and "jER4250" manufactured by Mitsubishi Chemical Corporation.

[0057] The (meth)acrylic resin used as the polymer resin is preferably thermoplastic. Examples of commercially available (meth)acrylic resins include "Teisan Resin SG-70L" manufactured by Nagase ChemteX Corporation and "ARUFON UH-2170" manufactured by Toagosei Co., Ltd.

[0058] The weight-average molecular weight of the polymer resin is 10,000 or more, as described above, but may be 20,000 or more, 30,000 or more, or even 40,000 or more. The above weight-average molecular weight may be, for example, 2 million or less, but may be 1 million or less, 500,000 or less, 300,000 or less, or even 100,000 or less.

[0059] The polymer resin may be thermosetting or thermoplastic. If the polymer resin is thermosetting, the curing temperature of the polymer resin is preferably above the melting point T0 of the solder particles, for example, 120°C to 280°C, and may also be 160°C to 260°C, or even 170°C to 250°C.

[0060] In the conductive sheet, the polymer resin may be liquid, but it is preferably solid. The glass transition temperature of the solid polymer resin is preferably lower than the melting point T0 of the solder particles. The glass transition temperature is, for example, 50°C to 150°C, and may also be 80°C to 120°C.

[0061] The polymer resin content in the conductive sheet is, for example, 0.1% by weight or more, and may be 0.5% by weight or more, 1.0% by weight or more, 2.0% by weight or more, or even 3.0% by weight or more. The above content is, for example, 20% by weight or less, and may be 15% by weight or less, 10% by weight or less, or even 5.0% by weight or less.

[0062] In the conductive sheet, the ratio R2 of the polymer resin content (weight %) to the sum of the epoxy resin content (weight %) and the polymer resin content (weight %) is, for example, 30% or less, and may be 25% or less, 20% or less, 15% or less, or even 10% or less. The ratio R2 is, for example, 0.1% or more, and may be 0.5% or more, 1.0% or more, 5.0% or more, or even 8.0% or more.

[0063] <1-5. Flux> The conductive sheet preferably further contains flux. Flux tends to remove oxide films that may be present on the surface of solder particles. Flux also tends to remove oxide films that may be present on the surface of electrodes that the conductive sheet contacts when the conductive sheet is used to connect two wiring circuit boards. Furthermore, flux is also a component that can appropriately adjust the complex viscosity V1 to V3 of the conductive sheet. There may be only one type of flux or two or more types.

[0064] The flux is preferably an organic acid, and more preferably a carboxylic acid compound. Examples of carboxylic acid compounds include monocarboxylic acid compounds, dicarboxylic acid compounds, and tricarboxylic acid compounds, with dicarboxylic acid compounds being preferred.

[0065] Examples of monocarboxylic acid compounds include aliphatic monocarboxylic acids and aromatic monocarboxylic acids. Examples of aromatic monocarboxylic acids include 2-phenoxybenzoic acid.

[0066] Examples of dicarboxylic acid compounds include aliphatic dicarboxylic acids and aromatic dicarboxylic acids. Aliphatic dicarboxylic acids include linear saturated dicarboxylic acids, branched saturated dicarboxylic acids, linear unsaturated dicarboxylic acids, and branched unsaturated dicarboxylic acids.

[0067] Examples of linear saturated dicarboxylic acids include succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, and sebacic acid. Examples of branched saturated dicarboxylic acids include 3,3-dimethylglutaric acid and 3-methyladipic acid. Examples of linear unsaturated dicarboxylic acids include fumaric acid.

[0068] Examples of tricarboxylic acid compounds include 1,3,5-pentanetricarboxylic acid and tricarbaryl acid.

[0069] From the viewpoint of improving connection reliability, the flux is preferably an aliphatic dicarboxylic acid (especially a linear saturated dicarboxylic acid or a branched saturated dicarboxylic acid), more preferably glutaric acid, adipic acid, pimelic acid, 3-methyladipic acid, or 3,3-dimethylglutaric acid, and particularly preferably 3,3-dimethylglutaric acid.

[0070] The flux may also be a salt of an organic acid (especially a dicarboxylic acid compound).

[0071] The flux content in the conductive sheet is, for example, 1% to 10% by weight, and may also be 3% to 7% by weight.

[0072] The flux content in the conductive sheet is, for example, 1 part by weight or more, and may be 5 parts by weight or more, per 100 parts by weight of solder particles. The above content is, for example, 20 parts by weight or less, and may be 10 parts by weight or less, per 100 parts by weight of solder particles.

[0073] <1-6. Curing Agent> The conductive sheet may further contain a curing agent. The curing agent can react with a resin component, such as epoxy resin, to accelerate its curing. There may be only one type of curing agent, or there may be two or more types.

[0074] Examples of curing agents include acid anhydride-based curing agents, amine-based curing agents, phenol-based curing agents, cationic initiators, imidazole catalysts, and DICY (dicyandiamide).

[0075] The amount of curing agent in the conductive sheet is, for example, less than 20 parts by weight per 100 parts by weight of the resin component, and may be less than 10 parts by weight, less than 5 parts by weight, less than 3 parts by weight, or even less than 1 part by weight. The conductive sheet does not need to contain a curing agent.

[0076] <1-7. Other Additives> The conductive sheet may further contain other additives in addition to the components described above. Examples of other additives include resins other than the epoxy resin and polymer resin described above, solvents, curing aids, etc.

[0077] Other resins include urea resin, melamine resin, diallyl phthalate resin, silicone resin, phenolic resin, polyester resin (e.g., polyethylene terephthalate), polyimide resin, polyurethane resin, polyolefin (e.g., polyethylene, polypropylene, ethylene-propylene copolymer), polyvinyl acetate, ethylene-vinyl acetate copolymer, polyvinyl chloride, polystyrene, polyacrylonitrile, polyamide, polycarbonate, polyacetal, polyphenylene oxide, polyphenylene sulfide, polysulfone, polyethersulfone, polyetheretherketone, polyallylsulfone, polyaminobismaleimide, polyamideimide, polyetherimide, bismaleimide triazine resin, polymethylpentene, fluorinated resin, liquid crystal polymer, olefin-vinyl alcohol copolymer, ionomer, polyarylate, acrylonitrile-ethylene-styrene copolymer, acrylonitrile-butadiene-styrene copolymer, acrylonitrile-styrene copolymer, and butadiene-styrene copolymer.

[0078] The content of other additives in the conductive sheet may be, for example, 10% by weight or less, 5% by weight or less, 1% by weight or less, or even 0.1% by weight or less. The conductive sheet may be substantially free of other additives.

[0079] <1-8. Method for Manufacturing a Conductive Sheet> A conductive sheet according to an embodiment of the present invention can be manufactured, for example, by the following method. First, a conductive composition containing the material for the conductive sheet is prepared. The conductive composition can be prepared in detail by stirring and mixing the conductive sheet material, such as solder particles, epoxy resin, or polymer resin, with a solvent. An organic solvent such as methyl ethyl ketone can be used as the solvent. The composition of the conductive composition may be the same as the composition of the conductive sheet, except that it contains a solvent (or has a high solvent content). The solid content concentration of the conductive composition is, for example, 50% to 80% by weight, and may be 60% to 75% by weight.

[0080] Furthermore, before preparing the conductive composition, the oxide film formed on the surface of the solder particles may be removed beforehand. The oxide film can be removed, for example, by acid treatment, in which the solder particles are brought into contact with an acid treatment agent. The acid treatment agent may be one type or two or more types.

[0081] The acid treatment agent is preferably a carboxylic acid treatment agent having a carboxyl group. Examples of carboxylic acid treatment agents include monocarboxylic acid treatment agents, dicarboxylic acid treatment agents, and trifunctional or more carboxylic acid treatment agents, with dicarboxylic acid treatment agents being preferred. The dicarboxylic acid treatment agent is preferably an aliphatic dicarboxylic acid treatment agent, and is particularly preferably malic acid.

[0082] Next, the conductive composition is applied to the release liner to form a coating film. A conductive sheet can be formed by drying the coating film. The drying conditions for the coating film are not particularly limited, for example, the drying temperature is 40°C to 100°C and the drying time is 1 minute to 60 minutes.

[0083] Known materials can be used as the release liner. Examples of the base material for the release liner (hereinafter referred to as "liner base material") include resin films. Examples of resins that make up the resin film include polyester such as polyethylene terephthalate, acetate resin, polyethersulfone, polycarbonate, polyamide, polyimide, polyolefin, (meth)acrylic resin, polyvinyl chloride, polyvinylidene chloride, polystyrene, polyvinyl alcohol, polyarylate, and polyphenylene sulfide. Preferably, the resin that makes up the resin film is polyester such as polyethylene terephthalate. The thickness of the release liner is, for example, 1 μm to 100 μm.

[0084] The peel-off liner may include layers other than the liner substrate. The peel-off liner may include a release layer. For example, the peel-off liner includes a liner substrate and a release layer formed on one side of the liner substrate. In the peel-off liner, the release layer may be on the side of the coating film.

[0085] <1-9. Physical Properties of Conductive Sheets> The thickness of the conductive sheet is, for example, 50 μm or less, and may be 25 μm or less, 15 μm or less, or even 10 μm or less. The thickness of the conductive sheet is, for example, 1 μm or more.

[0086] It is preferable that the conductive sheet has a high storage modulus E at a temperature 40°C higher than the melting point T0 of the solder particles (T0 + 40°C). In this case, even if some of the components of the conductive sheet volatilize at a temperature around T0 + 40°C, voids (bubbles) tend to be less likely to form. The storage modulus E of the conductive sheet at T0 + 40°C is, for example, 22,000 Pa or more, and may be 30,000 Pa or more, 50,000 Pa or more, 80,000 Pa or more, 100,000 Pa or more, 130,000 Pa or more, 150,000 Pa or more, and even 300,000 Pa or more. The above storage modulus E is, for example, 2,000,000 Pa or less, and may be 1,000,000 Pa or less.

[0087] The storage modulus E mentioned above can be measured by the following method. First, prepare the conductive sheet to be measured. As this conductive sheet, the measurement sample S1 described above for the complex viscosity V1 can be used. Next, perform dynamic viscoelasticity measurement for the complex viscosity V1 under the measurement conditions described above. From the results of the dynamic viscoelasticity measurement, determine the storage modulus of the measurement sample S1 at T0 + 40°C, and consider the obtained value as the storage modulus E mentioned above.

[0088] Furthermore, it is preferable that the conductive sheet of this embodiment has a low water absorption rate, as determined by the following test. In this case, when the cured conductive sheet (cured sheet) is reflowed after being left in a high-humidity environment, defects tend to be less likely to occur. Test: A conductive sheet is cured to obtain a cured sheet. The cured sheet is left to stand for 24 hours in an atmosphere of 85°C and 85% RH. The water absorption rate is determined by the ratio of the weight W2 of water absorbed by the cured sheet after standing to the weight W1 of the cured sheet before standing.

[0089] The above water absorption rate may be, for example, 1.0% or less, but may also be 0.50% or less, 0.45% or less, 0.40% or less, 0.35% or less, or even 0.30% or less. The above water absorption rate may be, for example, 0.01% or more, but may also be 0.10% or more.

[0090] The above water absorption rate can be measured in detail by the following method. First, the conductive sheet is heated to harden the resin (especially epoxy resin) in the conductive sheet. This yields a hardened sheet. This hardened sheet is usually substantially free of water and is in a dry state. However, if necessary, the hardened sheet may be dried. Next, the dry hardened sheet is left to stand for 24 hours in an atmosphere of 85°C and 85% RH. The weight W2 of water absorbed by the hardened sheet during standing is measured using a commercially available trace moisture meter or the like. The ratio W2 / W1 of the above weight W2 to the weight W1 of the hardened sheet before standing (i.e., the dry hardened sheet) is determined as the water absorption rate.

[0091] ≪2. Connection Structure≫ <2-1. Configuration of the Connection Structure> An example of a connection structure according to an embodiment of the present invention is shown in Figure 3. The connection structure 100 shown in Figure 3 comprises a first substrate 20, a second substrate 30, and a connecting member 10. A first electrode 21 is arranged on the first substrate 20, and a second electrode 31 is arranged on the second substrate 30. The connecting member 10 is formed from the conductive sheet described above and connects the first substrate 20 and the second substrate 30. The first substrate 20, the connecting member 10, and the second substrate 30 are arranged in this order in the stacking direction Y.

[0092] The first substrate 20 is typically a wiring circuit board. The first substrate 20 has, for example, a flat plate shape and a pair of main surfaces (the surfaces of the first substrate 20 that have the largest surface area). Of the pair of main surfaces, the first electrode 21 is arranged on the main surface facing the connecting member 10.

[0093] Examples of materials for the first substrate 20 include insulating materials and semiconductor materials. The thickness of the first substrate 20 is, for example, 5 μm to 1000 μm.

[0094] The first electrodes 21 are arranged in a pattern on the first substrate 20, for example. For example, the first electrodes 21 may be arranged in a dot pattern. In this case, the shape of the first electrodes 21 is typically columnar (such as cylindrical or prismatic). In this embodiment, a plurality of columnar first electrodes 21 may be arranged in an evenly aligned plane direction X perpendicular to the stacking direction Y. Figure 3 shows an example in which two first electrodes 21 are arranged on the first substrate 20.

[0095] Examples of materials for the first electrode 21 include metals such as gold, copper, and nickel.

[0096] The thickness of the first electrode 21 is, for example, 0 μm to 20 μm, and may be 0.001 μm to 5 μm. At least a portion of the first electrode 21 may be embedded in the first substrate 20. In this case, the thickness of the portion of the first electrode 21 that protrudes from the first substrate 20 is considered to be the thickness of the first electrode 21. That is, if the first electrode 21 does not protrude from the first substrate 20 and the surface of the first electrode 21 coincides with the surface of the first substrate 20, the thickness of the first electrode 21 is 0 μm.

[0097] When the first electrode 21 is cylindrical, the diameter of the first electrode 21 in plan view is, for example, 1 μm to 200 μm, and may be 1 μm to 100 μm, 1 μm to 50 μm, or even 1 μm to 20 μm.

[0098] The distance (pitch) between two adjacent first electrodes 21 in the planar direction X is, for example, 3 μm to 400 μm, and may be 5 μm to 200 μm, 7 μm to 100 μm, or even 10 μm to 40 μm.

[0099] The second substrate 30 is typically a wiring circuit board. However, the second substrate 30 may also be a chip component such as a mini / micro LED. The second substrate 30 has, for example, a flat plate shape and a pair of main surfaces. The second electrode 31 is placed on the main surface of the pair of main surfaces that faces the connecting member 10.

[0100] The material and thickness of the second substrate 30 are as described above for the first substrate 20.

[0101] The second electrodes 31 are arranged in a pattern on the second substrate 30, for example. For example, the second electrodes 31 may be arranged in a dot pattern. In this case, the shape of the second electrodes 31 is typically columnar (such as cylindrical or prismatic). In this embodiment, a plurality of columnar second electrodes 31 may be arranged evenly aligned in the planar direction X. Figure 3 shows an example in which two second electrodes 31 are arranged on the second substrate 30.

[0102] The material and dimensions, such as thickness, of the second electrode 31 are as described above for the first electrode 21.

[0103] Preferably, the distance (pitch) between two adjacent second electrodes 31 in the planar direction X is the same as the distance (pitch) between two adjacent first electrodes 21 in the planar direction X. In other words, it is preferable that the second electrodes 31 face the first electrodes 21, and that these electrodes 21 and 31 are aligned along the stacking direction Y. More specifically, it is preferable that the second electrodes 31 overlap the first electrodes 21 in a plan view.

[0104] The connecting member 10 has a conductive portion 6 and an insulating portion 7. The conductive portion 6 is in direct contact with the first electrode 21 arranged on the first substrate 20 and the second electrode 31 arranged on the second substrate 30, and electrically connects them. The conductive portion 6 makes it possible to exhibit conductivity in the stacking direction Y.

[0105] It is preferable that the conductive portion 6 overlaps the first electrode 21 and the second electrode 31 in a plan view. If the first electrode 21 and the second electrode 31 are arranged in a pattern, it is preferable that the conductive portion 6 is also arranged in a pattern. For example, the conductive portion 6 may be arranged in a dot pattern. In this case, the shape of the conductive portion 6 is typically columnar (such as cylindrical or prismatic). In this embodiment, a plurality of columnar conductive portions 6 may be arranged evenly aligned in the planar direction X. Figure 3 shows an example in which two conductive portions 6 are arranged within the connecting member 10.

[0106] The conductive portion 6 is formed by the melting and aggregation of solder particles, as described later. Therefore, the conductive portion 6 typically contains material derived from solder particles.

[0107] The insulating portion 7 surrounds the conductive portion 6 and fills the space between the first substrate 20 and the second substrate 30 where the conductive portion 6 is not present. The insulating portion 7 is in direct contact with the surface of the first substrate 20 where the first electrode 21 is not placed, and with the surface of the second substrate 30 where the second electrode 31 is not placed. The insulating portion 7 can function as an adhesive portion that adheres to the first substrate 20 and the second substrate 30, respectively. The insulating portion 7 ensures insulation in the plane direction X.

[0108] The insulating portion 7 is formed by the curing of a resin such as epoxy resin, as described later. Typically, the insulating portion 7 includes a material derived from the matrix of the conductive sheet.

[0109] The thickness of the connecting member 10 is, for example, 50 μm or less, and may be 25 μm or less, 15 μm or less, or even 5 μm or less. The thickness of the connecting member 10 is, for example, 1 μm or more.

[0110] <2-2. Method for Manufacturing a Connecting Structure> A method for manufacturing a connecting structure 100 according to an embodiment of the present invention includes, for example, placing a conductive sheet 1 between a first substrate 20 and a second substrate 30, and heating the conductive sheet 1 to form a connecting member 10.

[0111] The connecting structure 100 can be manufactured in detail by the following method. First, as shown in Figure 4A, a conductive sheet 1 is placed between the first substrate 20 and the second substrate 30. At this time, it is preferable that the conductive sheet 1 is in contact with both the first electrode 21 and the second electrode 31.

[0112] Next, the conductive sheet 1 is heated. It is preferable to heat the conductive sheet 1 by first heating and second heating. In the first heating, the conductive sheet 1 is heated to a temperature above the softening point of the resin in the conductive sheet 1 (for example, solid epoxy resin or solid polymer resin) and below the melting point T0 of the solder particles 5. With the first heating, the conductive sheet 1 softens and the first electrode 21 and the second electrode 31 each become embedded in the conductive sheet 1 (Figure 4B). As a result, the first electrode 21 and the second electrode 31 each become embedded in the conductive sheet 1. The conductive sheet 1 comes into contact with the surface of the first substrate 20 where the first electrode 21 is not placed and the surface of the second substrate 30 where the second electrode 31 is not placed.

[0113] The heating temperature in the first heating stage is, for example, 180°C or lower, and may be 100°C or lower, 80°C or lower, or even 70°C or lower. The above heating temperature is, for example, 40°C or higher.

[0114] In the first heating stage, pressure may be applied to the laminate of the first substrate 20, the conductive sheet 1, and the second substrate 30 in the stacking direction Y to cause them to be pressed together (thermocompressed). The pressure applied to the laminate in the first heating stage may be, for example, 0.001 MPa to 10 MPa, 0.005 MPa to 5 MPa, or even 0.01 MPa to 1 MPa.

[0115] The second heating is typically performed after the first heating. In the second heating, the conductive sheet 1 is heated to a temperature above the melting point T0 of the solder particles 5. Due to the second heating, the solder particles 5 in the conductive sheet 1 melt and aggregate (self-aggregate) between the first electrode 21 and the second electrode 31. This forms a conductive portion 6 that electrically connects the first electrode 21 and the second electrode 31. At this time, the resin constituting the matrix 3 of the conductive sheet 1 hardens while surrounding the conductive portion 6, thereby forming an insulating portion 7. In this way, the connecting member 10 is formed from the conductive sheet 1 by the first and second heating, and a connecting structure 100 (Figure 3) can be obtained.

[0116] The heating temperature for the second heating step is, for example, 70°C or higher, and may be 100°C or higher, 120°C or higher, 130°C or higher, 150°C or higher, or even 200°C or higher. The above heating temperature is, for example, 300°C or lower, and may be 280°C or lower, or even 270°C or lower.

[0117] The second heating step may be performed using a pressure oven. A pressure oven allows the conductive sheet 1 to be heated under pressure in a sealed space. This tends to suppress the volatilization of some of the components of the conductive sheet 1 and the generation of voids. Examples of pressure ovens include automatic heating and pressurizing equipment, pressurizing ovens, voidless pressurizing ovens, autoclaves, and vacuum pressurizing reflow apparatus.

[0118] The present invention will be specifically described below with reference to examples, but the present invention is not limited in any way to these examples. Where "parts" is mentioned, it means "parts by weight" unless otherwise specified, and where "%" is mentioned, it means "percent by weight" unless otherwise specified.

[0119] (Example 1) First, a varnish (solid content concentration 60% by weight) was prepared by dissolving a dicyclopentadiene type epoxy resin (DIC Corporation, trade name "EPICLON HP-7200HHH", epoxy equivalent 280-292 g / eq, solid (25°C)) as a solid epoxy resin in methyl ethyl ketone. Similarly, a flux solution (solid content concentration 20% by weight) was prepared by dissolving 3,3-dimethylglutaric acid (Changzhou Liren Medical Technology) as a flux in methyl ethyl ketone.

[0120] Next, 200 parts by weight of solder particles (manufactured by DUKSAN Hi-Metal, trade name "Aurora SAC305 EN (0-3 μm)", Sn 96.5% by weight, Ag 3.0% by weight, Cu 0.5% by weight, melting point 218°C, spherical shape, average primary particle diameter 1 μm), 20 parts by weight of bisphenol A type epoxy resin as a liquid epoxy resin (manufactured by Mitsubishi Chemical Corporation, trade name "jER828", epoxy equivalent 184-194 g / eq, liquid (25°C)), and 70 parts by weight of the above varnish as a solid epoxy resin (calculated on a solid content basis). A conductive composition was obtained by mixing 10 parts by weight (in terms of solid content) of a varnish (manufactured by Mitsubishi Chemical Corporation, trade name "jER1256B40", solid content concentration 40% by weight) obtained by dissolving bisphenol A type epoxy resin (weight-average molecular weight 45,000, epoxy equivalent 8,500 g / eq, solid (25°C)) as a polymer resin in methyl ethyl ketone with 15 parts by weight (in terms of solid content) of the above flux solution and stirring.

[0121] Next, the conductive composition was applied to the release liner using an applicator to form a coating film. The coating film was dried at 60°C for 5 minutes to obtain the conductive sheet (thickness 5 μm) of Example 1. For the measurement of complex viscosity V1, complex viscosity V2, storage modulus E, and water absorption rate, Mitsubishi Chemical Corporation's product name "MRA50" was used for the release liner. For the accumulation test, moisture absorption reflow test, long-term storage test, and connection evaluation, Toyobo Co., Ltd.'s product name "TN-200" was used.

[0122] (Examples 2-11 and Comparative Example 1) Conductive sheets for Examples 2-11 and Comparative Example 1 were obtained by the same method as in Example 1, except that the types and contents of the materials used were changed as shown in Tables 1-2. In Examples 2-11 and Comparative Example 1, solid epoxy resin, polymer resin, flux, etc. were dissolved in a solvent such as methyl ethyl ketone beforehand as needed to prepare a varnish, and the varnish was mixed with other materials to prepare the conductive composition. In Examples 2, 10 and 11, the thickness of the conductive sheet was adjusted to 20 μm, taking into consideration the average primary particle size of the solder particles.

[0123] <Measurement of Complex Viscosity> (Complex Viscosity V1) The complex viscosity V1 of the conductive sheets at 50°C was measured using the conductive compositions prepared in the examples and comparative examples by the following method. First, the conductive composition was applied to a release liner using an applicator to form a coating film. Multiple conductive sheets with a thickness of 50 μm were prepared by drying the coating film at 60°C for 5 minutes. Multiple conductive sheets were laminated to create a laminate with a thickness of 400 ± 50 μm, and a measurement sample S1 with a bottom diameter of 25.0 mm was obtained by punching out this laminate into a disc shape. This measurement sample S1 was set in a rheometer (manufactured by Anton Paar, product name "MCR302e"), and dynamic viscoelasticity measurement was performed under the following measurement conditions. From the results of the dynamic viscoelasticity measurement, the complex viscosity of the measurement sample S1 at 50°C was determined, and the obtained value was considered to be the complex viscosity V1 of the conductive sheet. Measurement conditions: Measurement environment: atmospheric atmosphere; Strain value: 0.5%; Measurement frequency: 1 Hz; Temperature range: 25°C to 300°C; Heating rate: 10°C / min; Shape: Parallel plate, 25.0 mm diameter

[0124] (Complex Viscosity V2) Using resin compositions obtained by removing solder particles from the conductive compositions prepared in the examples and comparative examples, the complex viscosity V2 of the conductive sheet with solder particles removed at the melting point T0 of the solder particles was measured by the following method. First, various resins and fluxes were mixed, and acetone was added to the resulting mixture and stirred until homogeneous. This prepared a resin composition with a solid content of 70% by weight. Next, the resin composition was applied onto a release liner using an applicator to form a coating film. Multiple conductive sheets (conductive sheets with solder particles removed) with a thickness of 50 μm were prepared by drying the coating film at 60°C for 5 minutes. Multiple conductive sheets were laminated to prepare a laminate with a thickness of 400 ± 50 μm, and a measurement sample S2 with a bottom diameter of 25.0 mm was obtained by punching out this laminate into a disc shape. The measurement sample S2 was placed in a rheometer (manufactured by Anton Paar, product name "MCR302e"), and dynamic viscoelasticity measurements were performed under the same measurement conditions as for the complex viscosity V1. From the results of the dynamic viscoelasticity measurements, the complex viscosity of the measurement sample S2 at the melting point T0 of the solder particles was determined, and the obtained value was considered to be the complex viscosity V2 mentioned above.

[0125] <Measurement of Storage Modulus> Using the conductive compositions prepared in the examples and comparative examples, the storage modulus E of the conductive sheet at a temperature 40°C higher than the melting point T0 of the solder particles (T0 + 40°C) was measured by the following method. First, a sample S1 for measurement was prepared for the complex viscosity V1 by the method described above. Next, this sample S1 was set in a rheometer (manufactured by Anton Paar, product name "MCR302e"), and dynamic viscoelasticity measurement was performed under the same measurement conditions as for the complex viscosity V1. From the results of the dynamic viscoelasticity measurement, the storage modulus of the sample S1 at T0 + 40°C was determined, and the obtained value was considered to be the storage modulus E described above.

[0126] <Measurement of Water Absorption Rate> The conductive sheets prepared in the examples and comparative examples were subjected to the tests described above to measure their water absorption rate. Specifically, first, two conductive sheets were placed on top of each other and subjected to a heat-pressure bonding treatment for 2 seconds at a temperature of 65°C and a pressure of 0.3 MPa. This resulted in a laminate in which two conductive sheets were pressed together. Next, the resulting laminate was heated to cure the resin (especially epoxy resin) in the laminate. This resulted in a cured sheet. For Examples 1, 3-9 and Comparative Example 1, which used SAC305 solder particles, the laminate was heated at 150°C for 60 minutes, and for Examples 2 and 10-11, which used SnBi58 solder particles, it was heated at 170°C for 5 minutes. The resulting cured sheet was in a dry state. Next, the dry cured sheet was placed in a constant temperature and humidity oven and left to stand for 24 hours in an atmosphere of 85°C and 85% RH. A trace moisture meter (manufactured by Hiranuma Sangyo Co., Ltd., product name "AQS-2210AS") was used to measure the weight W2 of water absorbed by the hardened sheet after standing. The measurement of weight W2 was performed at a temperature of 105°C and for a maximum measurement time of 30 minutes. The ratio of weight W2 to weight W1 of the hardened sheet before standing, W2 / W1, was identified as the water absorption rate.

[0127] <Integration Test> Using the conductive sheets of the examples and comparative examples, connection structures were fabricated using the following method, and the solder integration ratio and voids were evaluated. The solder integration ratio is an indicator of the reliability of the electrical connection in the connection structure. The voids are an indicator of the adhesive reliability in the connection structure.

[0128] (Fabrication of the connection structure) First, a dummy wafer with Au electrodes (10 mm long x 10 mm wide) and alkali-free glass (10 mm long x 10 mm wide) were prepared. In Example 1 and Comparative Example 1, a dummy wafer with an electrode square of 10 μm and an electrode end-to-end distance of 10 μm was used. In Examples 2 to 11, a dummy wafer with an electrode square of 50 μm and an electrode end-to-end distance of 50 μm was used. Next, the release liner was peeled off from the conductive sheet prepared in the Examples and Comparative Examples, and the conductive sheet was placed between the dummy wafer and the alkali-free glass.

[0129] Next, a laminate of a dummy wafer, a conductive sheet, and alkali-free glass was subjected to a first heating (thermocompression bonding) for 2 seconds at a temperature of 60°C and a pressure of 0.3 MPa. After the first heating, the laminate was observed with an optical microscope (digital microscope, manufactured by Keyence Corporation, product name "VHX-8000") to confirm that there were no trapped air bubbles.

[0130] Next, the laminate was placed in a vacuum pressure reflow apparatus (SST Vacuum Reflow System, product name "Model1200 Table Top Furnace"), vacuuming was performed, and then a second heating was carried out. For Examples 1, 3-9 and Comparative Example 1, which used SAC305 solder particles, the second heating was performed under the following conditions: pressurized to 4.5 atmospheres with nitrogen, heating rate of 200°C / min, maximum temperature of 260°C, and holding time of 1 minute. For Examples 2 and 10-11, which used SnBi58 solder particles, the second heating was performed under the following conditions: pressurized to 4.5 atmospheres with nitrogen, heating rate of 100°C / min, maximum temperature of 170°C, and holding time of 1 minute. As a result, connecting members were formed from the conductive sheets, and a connecting structure was obtained.

[0131] (Evaluation of solder density and voids) The solder density and voids of the fabricated connection structure were evaluated using the following method. First, the connection structure was observed from the alkali-free glass side using an optical microscope (digital microscope, manufactured by Keyence Corporation, product name "VHX-8000"). The connection structure was observed at a magnification of 500x in four different field-of-view areas.

[0132] Next, for the 35 electrodes within the observation field, electrodes that were completely covered with solder were evaluated as pass, and those with part or all of their surface exposed were evaluated as fail. The ratio of electrodes evaluated as pass was considered the solder density, and evaluation was performed based on the following criteria: • Evaluation criteria for solder density 4: Solder density is 95% or higher. 3: Solder density is 90% or higher but less than 95%. 2: Solder density is 80% or higher but less than 90%. 1: Solder density is less than 80%.

[0133] Furthermore, voids (air bubbles) present within the field of view were identified. The area of ​​each identified void was calculated, and the total area (void area) was determined. Based on this result, the ratio of the void area to the area of ​​the field of view was calculated. Based on the ratio of the void area and the number of voids observed, the voids were evaluated according to the following criteria. In the evaluation criteria below, if the evaluation result differed between the ratio of the void area and the number of voids observed, the worse evaluation result was adopted. For example, if the ratio of the void area was 1% or more, while the number of voids was 5 or more but less than 10, the evaluation result was set to 1. ・Void evaluation criteria 4: The ratio of the void area is less than 0.5%, and the number of voids is less than 5. 3: The ratio of the void area is 0.5% or more but less than 0.8%, or the number of voids is 5 or more but less than 10. 2: The ratio of the void area is 0.8% or more but less than 1%, or the number of voids is 10 or more but less than 15. 1. The proportion of void area is 1% or more, or the number of voids is 15 or more.

[0134] <Moisture Absorption Reflow Test> The conductive sheets of Examples 1, 3, 4 and Comparative Example 1 were subjected to a moisture absorption reflow test using the following method. First, two electrode-equipped wafers (10 mm square, 50 μm thick) were prepared, and the electrode surfaces were cleaned by UV irradiation for 1 second. Next, the conductive sheet was placed on top of the UV-irradiated surface of one wafer (first wafer) and heat-pressed. The heat-pressure bonding with the first wafer was performed using a vacuum pressure laminator at a temperature of 65°C and a pressure of 0.3 MPa for 2 seconds. Furthermore, the conductive sheet was placed on top of the UV-irradiated surface of the other wafer (second wafer) and heat-pressed. The heat-pressure bonding with the second wafer was performed using a high-precision die bonding device (manufactured by Finetech Co., Ltd.) at a temperature of 60°C and a load of 0.5 N for 15 seconds.

[0135] Next, the laminate of the first wafer, conductive sheet, and second wafer was subjected to a first heating (thermocompression bonding) for 2 seconds using a vacuum pressure laminator at a temperature of 65°C and a pressure of 0.3 MPa. Then, the laminate after the first heating was placed in a vacuum pressure reflow apparatus (SST Vacuum Reflow System, product name "Model1200 Table Top Furnace") and a second heating was performed under the conditions of a pressure of 0.45 MPa, a heating rate of 200°C / min, a maximum temperature of 260°C, and a holding time of 30 minutes. As a result, a connecting member was formed from the conductive sheet, and a connecting structure was obtained.

[0136] Next, a die attach film (DAF, manufactured by Nitto Denko Corporation, product name "Elepmount EM-310") was laminated onto the wafer at a temperature of 80°C and bonded to a BGA (Ball Grid Array) substrate. Then, the DAF was heat-cured using a pressure oven. The heat curing of the DAF was performed by (1) raising the temperature from 50°C to 100°C in 6 minutes, (2) raising the temperature from 100°C to 150°C in 30 minutes, (3) maintaining at 150°C for 60 minutes, and (4) allowing it to cool naturally.

[0137] Next, plasma treatment was performed to improve the wettability of the wafer and BGA substrate. The plasma treatment was carried out using Ar gas at 100 W for 1.5 minutes. Next, molding was performed using epoxy encapsulating material (Sumitomo Bakelite Co., Ltd., product name "Sumicon EME") by transfer at 175°C for 90 seconds. Furthermore, post-molding cure (PMC) was performed at 175°C for 5 hours to cure the molding resin. Next, the samples were obtained by dicing them using a dicing saw (DISCO Corporation, product name "DFD6361").

[0138] Next, the sample was placed in a constant temperature and humidity chamber and left to stand for 24 hours in an atmosphere of 85°C and 85% RH. After standing, the sample was placed in an IR reflow apparatus (manufactured by Tamura Corporation, product name "TAP30-407PM") and reflowed three times at 260°C. Next, the sample after reflow was photographed using an ultrasonic imaging device (manufactured by Hitachi High-Tech Corporation, product name "FS200"). The obtained SAT images were evaluated based on the following criteria: Evaluation Criteria 4: No dark black areas are observed outside the wafer region in the SAT image. 1: Dark black areas are observed outside the wafer region in the SAT image.

[0139] <Long-Term Storage Test> The conductive sheets of the examples and comparative examples were stored for a long period of time on top of the release liner, and changes in their shape were observed. Specifically, the laminate of the conductive sheet and release liner immediately after preparation was placed in a constant temperature and humidity chamber and stored under conditions of 23°C and 50% RH. Three pre-specified areas (4 cm square) of the conductive sheet one day after preparation and the conductive sheet 28 days after preparation were observed with an optical microscope (digital microscope, manufactured by Keyence Corporation, product name "VHX-8000"), and evaluated based on the following criteria. ・Evaluation criteria 4: The number of depressions observed after one day is less than 5, and the number of depressions observed after 28 days is less than 5. 3: The number of depressions observed after one day is less than 5, and the number of depressions observed after 28 days is 5 or more but less than 10. 2: The number of depressions observed after 1 day is less than 5, and the number of depressions observed after 28 days is 10 or more. 1: The number of depressions observed after 1 day is 5 or more.

[0140] <Connection Evaluation> Using the conductive sheets of Examples 1 and 11, connection structures were fabricated using the following method, and connection evaluation was performed.

[0141] [Solder Connection Evaluation] (Example 1) First, two dummy wafers with Au electrodes (10 mm long x 10 mm wide, electrode square 10 μm, electrode end-to-end distance 10 μm) were prepared. Next, the release liner was peeled off the conductive sheet (thickness 5 μm) from Example 1, and the conductive sheet was placed between the two dummy wafers. At this time, a high-precision die bonding device (Finetech Co., Ltd., product name "FINEPLACER lambda 2") was used to adjust the electrodes of the opposing wafers so that they were aligned via the conductive sheet.

[0142] Next, the laminate was placed in a vacuum pressure reflow apparatus (SST Vacuum Reflow System, product name "Model1200 Table Top Furnace"), and then vacuum was applied. Subsequently, it was pressurized to 4.5 atmospheres with nitrogen and heated under the conditions of a heating rate of 200°C / min, a maximum temperature of 260°C, and a holding time of 60 seconds. As a result, connecting members were formed from the conductive sheets, and a connecting structure was obtained.

[0143] The obtained connection structures were embedded in resin, and the laminated cross-section was exposed by mechanical polishing. The laminated cross-section was observed with an optical microscope (name "VHX-7000", manufactured by Keyence Corporation), and the solder connection between opposing electrodes was evaluated based on the following criteria: • Evaluation Criteria 2: Solder connection between opposing electrodes was observed. 1: Solder connection between opposing electrodes was not observed.

[0144] [Electrical Connection Evaluation] (Example 11) First, two FPC substrates (electrode □100 μm, electrode end-to-end distance 100 μm) were prepared. Next, the release liner was peeled off the conductive sheet (thickness 20 μm) of Example 11, and the conductive sheet was placed between the two FPC substrates. At this time, a high-precision die bonding device (Finetech Co., Ltd., product name "FINEPLACER lambda 2") was used to adjust the electrodes of the opposing FPC substrates so that they were aligned via the conductive sheet.

[0145] Next, the laminate was placed in a vacuum pressure reflow apparatus (SST Vacuum Reflow System, product name "Model1200 Table Top Furnace"), and then vacuum was applied. Subsequently, it was pressurized to 4.5 atmospheres with nitrogen and heated under the conditions of a heating rate of 100°C / min, a maximum temperature of 170°C, and a holding time of 60 seconds. As a result, connecting members were formed from the conductive sheets, and a connecting structure was obtained.

[0146] For this connection structure, the electrical resistance between the opposing electrodes was measured using a digital multimeter (name "PC500a", manufactured by Sanwa Electric Instruments Co., Ltd.), and the electrical connection (conductivity) of the opposing electrodes was evaluated based on the following criteria: 2: Electrical resistance could be measured (electrical resistance was measured as a positive value). 1: Electrical resistance could not be measured (the measurement range of the multimeter was overloaded).

[0147]

[0148]

[0149] The abbreviations in Tables 1 and 2 are as follows: SAC305: Manufactured by DUKSAN Hi-Metal, product name "Aurora SAC305 EN (0-3 μm)", Sn 96.5 wt%, Ag 3.0 wt%, Cu 0.5 wt%, melting point 218°C, spherical shape, average primary particle diameter 1 μm SnBi58 ST7: Manufactured by Mitsui Mining & Smelting Co., Ltd., product name "Sn42Bi58 ST-7", Sn 42 wt%, Bi 58 wt%, melting point 139°C, spherical shape, average primary particle diameter 7 μm SnBi58 STC7: Manufactured by Mitsui Mining & Smelting Co., Ltd., product name "Sn42Bi58 STC-7", Sn 42 wt%, Bi 58 wt%, melting point 139°C, spherical shape, average primary particle diameter 8 μm jER828: Bisphenol A type epoxy resin (manufactured by Mitsubishi Chemical Corporation, product name "jER828", epoxy equivalent weight 184-194 g / eq, liquid (25°C)) HP7200HHH: Dicyclopentadiene type epoxy resin (manufactured by DIC Corporation, product name "EPICLON HP-7200HHH", epoxy equivalent weight 280-292 g / eq, solid (25°C)) XD1000: Dicyclopentadiene type epoxy resin (manufactured by Nippon Kayaku Co., Ltd., product name "XD-1000", epoxy equivalent weight 245-260 g / eq, solid (25°C)) NC7000H: Naphthalene type epoxy resin (manufactured by Nippon Kayaku Co., Ltd., product name "NC-7000H", epoxy equivalent weight 223-238 g / eq, solid (25°C)) NC3000: Biphenyl-type epoxy resin (manufactured by Nippon Kayaku Co., Ltd., product name "NC-3000", epoxy equivalent 265-285 g / eq, solid (25°C)) EOCN102070: Cresol novolac-type epoxy resin (manufactured by Nippon Kayaku Co., Ltd., product name "EOCN-1020-70", epoxy equivalent 191-207 g / eq, solid (25°C)) NPES907: Bisphenol A-type epoxy resin (manufactured by Nanya Plastics Co., Ltd., product name "NPES907", epoxy equivalent 1500-1600 g / eq, solid (25°C), softening point 120-130°C) jER1256: A varnish (manufactured by Mitsubishi Chemical Corporation, product name "jER1256B40", solid content concentration 40% by weight) obtained by dissolving bisphenol A type epoxy resin (weight-average molecular weight 45,000, epoxy equivalent 8,500 g / eq, solid (25°C)) in methyl ethyl ketone.UH2170: (meth)acrylic resin (manufactured by Toagosei Co., Ltd., product name "ARUFON UH-2170", weight-average molecular weight 14,000, solid (25°C)) SG70L: (meth)acrylic resin (weight-average molecular weight 900,000, solid (25°C)) dissolved in toluene and methyl ethyl ketone varnish (manufactured by Nagase ChemteX Co., Ltd., product name "Teisan Resin SG-70L", solid content concentration 12.5% ​​by weight) jER4250: bisphenol F type epoxy resin (manufactured by Mitsubishi Chemical Corporation, product name "jER4250", weight-average molecular weight 60,000, epoxy equivalent 8,200 g / eq, solid (25°C)) HXA9382HP: curing agent (manufactured by Asahi Kasei Corporation, product name "NovaCure HXA9382HP") Note that the content of each component listed in Tables 1 and 2 is the value excluding the solvent (solid content equivalent).

[0150] As can be seen from Tables 1 and 2, the conductive sheets of the examples in which the complex viscosity V1 at 50°C was 500 Pa·s or higher showed fewer indentations and less unevenness in shape, even when stored for a long period of time while placed on a release liner.

[0151] Furthermore, in the conductive sheets of the examples, the complex viscosity V2 at the melting point T0 of the solder particles was 15.0 Pa·s or less, resulting in good results in the integration test (especially the solder integration rate). In addition, the conductive sheets of Examples 1, 3, and 4, which had low water absorption rates, also showed good results in the moisture absorption reflow test.

[0152] The conductive sheet of the present invention can be used for connecting wiring circuit boards.

Claims

1. A conductive sheet comprising solder particles, epoxy resin, and a polymer resin having a weight-average molecular weight of 10,000 or more, wherein the complex viscosity V1 of the conductive sheet is 500 Pa·s or more at 50°C, and the complex viscosity V2 of the conductive sheet excluding the solder particles is 15.0 Pa·s or less at the melting point T0 of the solder particles.

2. The conductive sheet according to claim 1, wherein the storage modulus of the conductive sheet is 22,000 Pa or more at a temperature 40°C higher than the melting point T0 (T0 + 40°C).

3. The conductive sheet according to claim 1, wherein the water absorption rate determined by the following test is 0.40% or less. Test: The conductive sheet is cured to obtain a cured sheet. The cured sheet is left standing for 24 hours in an atmosphere of 85°C and 85% RH. The water absorption rate is determined by the ratio of the weight W2 of water absorbed by the cured sheet during the standing period to the weight W1 of the cured sheet before the standing period.

4. The conductive sheet according to claim 1, wherein the solder particles contain Sn.

5. The conductive sheet according to claim 1, wherein the weight-average molecular weight of the epoxy resin is less than 10,000.

6. The conductive sheet according to claim 1, wherein the epoxy resin comprises repeating units having glycidyl groups.

7. The conductive sheet according to claim 1, wherein the epoxy resin has at least one selected from the group consisting of a dicyclopentadiene skeleton, a biphenyl skeleton, a naphthalene skeleton, a phenol skeleton, and a cresol skeleton.

8. The conductive sheet according to claim 1, wherein the conductive sheet comprises a liquid epoxy resin and a solid epoxy resin.

9. The conductive sheet according to claim 1, wherein the ratio of the solid epoxy resin content (weight%) to the sum of the epoxy resin content (weight%) and the polymer resin content (weight%) is 50% or more.

10. The conductive sheet according to claim 1, wherein the ratio of the content of the polymer resin (weight%) to the sum of the content of the epoxy resin (weight%) and the content of the polymer resin (weight%) is 20% or less.

11. The conductive sheet according to claim 1, further comprising flux.

12. A connecting structure comprising: a first substrate on which a first electrode is disposed; a second substrate on which a second electrode is disposed; and a connecting member connecting the first substrate and the second substrate, wherein the connecting member is formed from a conductive sheet according to any one of claims 1 to 11.

13. A method for manufacturing a connecting structure according to claim 12, comprising: arranging the conductive sheet between the first substrate and the second substrate; and heating the conductive sheet to form the connecting member.

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