JP7474029B2 - Conductive material, connection structure, and method for manufacturing the connection structure - Google Patents

Description

The present invention relates to a conductive material containing a thermosetting component and solder particles. The present invention also relates to a connection structure using the conductive material and a method for manufacturing the connection structure.

Anisotropic conductive materials such as anisotropic conductive pastes and anisotropic conductive films are widely known. In the above anisotropic conductive materials, conductive particles are dispersed in a binder resin.

The anisotropic conductive material is used to obtain various connection structures. Examples of connections using the anisotropic conductive material include connections between a flexible printed circuit board and a glass substrate (FOG (Film on Glass)), between a semiconductor chip and a flexible printed circuit board (COF (Chip on Film)), between a semiconductor chip and a glass substrate (COG (Chip on Glass)), and between a flexible printed circuit board and a glass epoxy substrate (FOB (Film on Board)).

When electrically connecting, for example, an electrode of a flexible printed circuit board and an electrode of a glass epoxy board using the above-mentioned anisotropic conductive material, the anisotropic conductive material containing conductive particles is placed on the glass epoxy board. Next, the flexible printed circuit board is laminated, and heated and pressurized. This causes the anisotropic conductive material to harden, electrically connecting the electrodes via the conductive particles, and obtaining a connection structure.

The following Patent Document 1 discloses an anisotropic conductive material containing a large number of conductive particles in a thermosetting resin. The solidus temperature of the conductive particles is 125°C or higher, and the peak temperature is 200°C or lower. The temperature difference between the solidus temperature of the conductive particles and the peak temperature of the conductive particles is 15°C or higher.

The following Patent Document 2 discloses a thermosetting resin composition containing solder particles, a thermosetting resin binder, and a flux component. The solder particles are composed of an alloy of Sn and a metal selected from Ag, Cu, Bi, Zn, or In. The melting point of the solder particles is 240°C or lower. The thermosetting resin binder contains a liquid epoxy resin and a liquid phenolic resin curing agent. In the thermosetting resin composition, the content of the solder particles is in the range of 70% by mass to 95% by mass. The solder particles are dispersed in the thermosetting resin composition. The thermosetting resin composition can be applied to the surface of a wiring board.

WO2008/111615A1 JP 2014-98168 A

When a conductive connection is made using a conductive material containing solder particles, multiple upper electrodes are electrically connected to multiple lower electrodes to make a conductive connection. It is preferable that the solder is disposed between the upper and lower electrodes, and is not disposed between adjacent lateral electrodes. It is preferable that adjacent lateral electrodes are not electrically connected.

Generally, a conductive material containing solder particles is placed on a substrate and then heated by reflow or other methods before use. When the conductive material is heated above the melting point of the solder particles, the solder particles melt and the solder condenses between the electrodes, electrically connecting the upper and lower electrodes.

In a conventional conductive material containing solder particles, when the conductive material is heated, the solder particles may melt and the solder may become too fluid. If the solder becomes too fluid, the solder may coagulate too quickly. In a conventional conductive material containing solder particles, the solder may remain between adjacent lateral electrodes because the coagulation speed is too fast, and not all of the solder may coagulate on the electrodes, making it impossible to efficiently place the solder between the upper and lower electrodes to be connected. As a result, the amount of solder placed between the upper and lower electrodes to be connected may decrease, and the reliability of the electrical continuity between the upper and lower electrodes to be connected may decrease, or the reliability of the insulation between the adjacent lateral electrodes may decrease. In a conventional conductive material, it is difficult to adjust the cohesive force of the solder.

In addition, the anisotropic conductive material described in Patent Document 1 contains a small amount of the conductive particles, making it difficult to electrically connect the electrodes.

The object of the present invention is to provide a conductive material that allows solder to be efficiently placed on an electrode and effectively improves the reliability of electrical continuity between upper and lower electrodes to be connected. It is also an object of the present invention to provide a connection structure using the conductive material and a method for manufacturing the connection structure.

According to a broad aspect of the present invention, there is provided a conductive material that includes a thermosetting component and solder particles, the absolute value of the difference between the solidus temperature of the solder particles and the liquidus temperature of the solder particles is 5°C or more, and the content of the solder particles in 100% by weight of the conductive material is 15% by weight or more.

In a particular aspect of the conductive material according to the present invention, the viscosity of the conductive material at the solidus temperature of the solder particles is 0.1 Pa·s or more and 50 Pa·s or less.

In a particular aspect of the conductive material of the present invention, the solder particles include bismuth, indium, silver, copper, or tin.

In a particular aspect of the conductive material according to the present invention, the bismuth content is 1% by weight or more and 58% by weight or less out of 100% by weight of the metal contained in the solder particles.

In a particular aspect of the conductive material according to the present invention, the indium content is 1% by weight or more and 52% by weight or less out of 100% by weight of the metal contained in the solder particles.

In a particular aspect of the conductive material according to the present invention, the solidus temperature of the solder particles is 115°C or higher and 220°C or lower.

In a particular aspect of the conductive material according to the present invention, the particle diameter of the solder particles is 0.01 μm or more and 30 μm or less.

In a particular aspect of the conductive material according to the present invention, the conductive material is a conductive paste.

According to a broad aspect of the present invention, there is provided a connection structure comprising a first connection target member having a first electrode on its surface, a second connection target member having a second electrode on its surface, and a connection part connecting the first connection target member and the second connection target member, the material of the connection part being the conductive material described above, and the first electrode and the second electrode being electrically connected by a solder part in the connection part.

In a particular aspect of the connection structure according to the present invention, when the portion where the first electrode and the second electrode face each other is viewed in the stacking direction of the first electrode, the connection portion, and the second electrode, the solder portion in the connection portion is disposed in 50% or more of the 100% area of the portion where the first electrode and the second electrode face each other.

According to a broad aspect of the present invention, a method for manufacturing a connection structure is provided, comprising the steps of: using the above-mentioned conductive material to place the conductive material on the surface of a first connection target member having a first electrode on its surface; placing a second connection target member having a second electrode on the surface of the conductive material opposite the first connection target member side, such that the first electrode and the second electrode face each other; and heating the conductive material to a temperature equal to or higher than the liquidus temperature of the solder particles to form a connection part connecting the first connection target member and the second connection target member using the conductive material, and electrically connecting the first electrode and the second electrode with a solder part in the connection part.

In a particular aspect of the method for manufacturing a connection structure according to the present invention, when the portion where the first electrode and the second electrode face each other is viewed in the stacking direction of the first electrode, the connection portion, and the second electrode, a connection structure is obtained in which the solder portion in the connection portion is disposed in 50% or more of the 100% area of the portion where the first electrode and the second electrode face each other.

The conductive material according to the present invention includes a thermosetting component and solder particles. In the conductive material according to the present invention, the absolute value of the difference between the solidus temperature of the solder particles and the liquidus temperature of the solder particles is 5°C or more. In the conductive material according to the present invention, the content of the solder particles in 100% by weight of the conductive material is 15% by weight or more. Since the conductive material according to the present invention has the above configuration, the solder can be efficiently arranged on the electrodes, and the reliability of the conduction between the upper and lower electrodes to be connected can be effectively improved.

FIG. 1 is a cross-sectional view that illustrates a connection structure obtained by using a conductive material according to one embodiment of the present invention. 2(a) to 2(c) are cross-sectional views illustrating the steps of an example of a method for manufacturing a connection structure using a conductive material according to one embodiment of the present invention. FIG. 3 is a cross-sectional view showing a modified example of the connection structure.

The details of the present invention are explained below.

(Conductive materials)
The conductive material according to the present invention includes a thermosetting component and solder particles. In the conductive material according to the present invention, the absolute value of the difference between the solidus temperature of the solder particles and the liquidus temperature of the solder particles is 5° C. or more. In the conductive material according to the present invention, the content of the solder particles in 100% by weight of the conductive material is 15% by weight or more.

The conductive material according to the present invention has the above-mentioned configuration, so that the solder can be efficiently placed on the electrodes, and the reliability of the electrical connection between the upper and lower electrodes to be connected can be effectively improved.

In the conductive material according to the present invention, the content of the solder particles in 100% by weight of the conductive material is 15% by weight or more, so that the solder can be agglomerated on the electrodes and efficiently arranged between the upper and lower electrodes to be connected. In the present invention, it is important for obtaining the effects of the present invention that the content of the solder particles satisfies the above range.

The conductive material containing solder particles is placed on a substrate and then heated by reflow or other methods before use. When the conductive material is heated above the melting point of the solder particles, the solder particles melt and the solder condenses between the electrodes, electrically connecting the upper and lower electrodes.

In conventional conductive materials containing solder particles, when the conductive material is heated, the solder particles melt and the solder may become too fluid. When the solder becomes too fluid, the solder may agglomerate too quickly. In conventional conductive materials containing solder particles, the solder may agglomerate too quickly, resulting in solder remaining between adjacent lateral electrodes and not all of the solder being able to agglomerate on the electrodes, making it impossible to efficiently place the solder between the upper and lower electrodes to be connected.

The inventors focused on the absolute value of the difference between the solidus temperature of the solder particles and the liquidus temperature of the solder particles, and discovered that by using specific solder particles, it is possible to adjust the fluidity of the solder and adjust the rate at which the solder coheses. In the present invention, by appropriately adjusting the fluidity and cohesive force of the solder, the solder can be efficiently placed between the electrodes to be connected, and the reliability of the electrical connection between the upper and lower electrodes to be connected can be effectively improved.

In addition, by appropriately adjusting the solder fluidity and cohesive strength, the amount of solder remaining between adjacent lateral electrodes can be reduced. As a result, the insulation reliability between adjacent lateral electrodes that must not be connected can be effectively improved.

In addition, since the present invention is provided with the above-mentioned configuration, when the electrodes are electrically connected, the solder is likely to gather between the upper and lower opposing electrodes, and the solder can be placed on the electrodes (lines). In addition, it is difficult for part of the solder to be placed between horizontal electrodes that should not be connected, and the amount of solder placed between horizontal electrodes that should not be connected can be significantly reduced. As a result, in the present invention, the amount of remaining solder between horizontal electrodes that should not be connected can be reduced.

In the present invention, the conductive material containing specific solder particles plays a major role in achieving the above-mentioned effects.

Furthermore, the present invention can prevent misalignment between electrodes. In the present invention, when a second connection target member is superimposed on a first connection target member having a conductive material disposed on its upper surface, even if the alignment between the electrodes of the first connection target member and the electrodes of the second connection target member is misaligned, the misalignment can be corrected to connect the electrodes together (self-alignment effect).

From the viewpoint of disposing the solder on the electrodes more efficiently, the conductive material is preferably liquid at 25°C and is preferably a conductive paste. The conductive material is preferably a conductive paste at 25°C.

From the viewpoint of disposing the solder on the electrode more efficiently, the viscosity (η25) of the conductive material at 25°C is preferably 0.1 Pa·s or more, more preferably 30 Pa·s or more, even more preferably 50 Pa·s or more, and is preferably 400 Pa·s or less, more preferably 300 Pa·s or less. The viscosity (η25) can be appropriately adjusted by the types and amounts of the blended components.

The above viscosity (η25) can be measured, for example, using an E-type viscometer (Toki Sangyo Co., Ltd.'s "TVE22L") at 25°C and 5 rpm.

The viscosity (ηsp) of the conductive material at the solidus temperature of the solder particles is preferably 0.1 Pa·s or more, more preferably 0.2 Pa·s or more, and preferably 50 Pa·s or less, more preferably 10 Pa·s or less. When the viscosity (ηsp) is equal to or greater than the lower limit and equal to or less than the upper limit, the solder can be more efficiently placed on the electrodes, and the reliability of the electrical connection between the upper and lower electrodes to be connected can be more effectively improved.

The viscosity (ηsp) of the conductive material at the solidus temperature of the solder particles can be measured using a STRESSTECH (manufactured by REOLOGICA) or similar under the following conditions: strain control 1 rad, frequency 1 Hz, heating rate 20°C/min, and measurement temperature range 25°C to 200°C (however, if the solidus temperature of the solder particles exceeds 200°C, the upper temperature limit is set to the solidus temperature of the solder particles). From the measurement results, the viscosity at the solidus temperature (°C) of the solder particles is evaluated.

The viscosity (ηmp) of the conductive material at the liquidus temperature (melting point) of the solder particles is preferably 50 Pa·s or less, more preferably 10 Pa·s or less, even more preferably 1 Pa·s or less, and is preferably 0.1 Pa·s or more, more preferably 0.2 Pa·s or more. If the viscosity (ηmp) is equal to or less than the upper limit, the solder can be efficiently agglomerated on the electrode. If the viscosity is equal to or greater than the lower limit, voids at the connection portion can be suppressed, and the conductive material can be suppressed from spilling out of areas other than the connection portion.

The above viscosity (ηmp) can be measured using a STRESSTECH (manufactured by REOLOGICA) or similar under the following conditions: strain control 1 rad, frequency 1 Hz, heating rate 20°C/min, measurement temperature range 25°C to 200°C (however, if the liquidus temperature (melting point) of the solder particles exceeds 200°C, the upper temperature limit is the liquidus temperature (melting point) of the solder particles). From the measurement results, the viscosity at the liquidus temperature (melting point) (°C) of the solder particles is evaluated.

The conductive material can be used as a conductive paste, a conductive film, or the like. The conductive paste is preferably an anisotropic conductive paste, and the conductive film is preferably an anisotropic conductive film. From the viewpoint of more efficiently disposing the solder on the electrodes, the conductive material is preferably a conductive paste. The conductive material is preferably used for electrically connecting the electrodes. The conductive material is preferably a circuit connection material.

The components contained in the conductive material are explained below. In this specification, "(meth)acrylic" means either or both of "acrylic" and "methacrylic".

(solder particles)
The solder particles are formed of solder at both the center and the outer surface. The solder particles are particles in which both the center and the outer surface are solder. When conductive particles having a base particle formed of a material other than solder and a solder portion arranged on the surface of the base particle are used instead of the solder particles, the conductive particles are less likely to gather on the electrode. In addition, the conductive particles have low solder bonding between the conductive particles, so that the conductive particles that have moved onto the electrode tend to move out of the electrode, and the effect of suppressing positional deviation between the electrodes also tends to be low.

The solder is preferably a metal (low melting point metal) with a liquidus temperature (melting point) of 450°C or less. The solder particles are preferably metal particles (low melting point metal particles) with a liquidus temperature (melting point) of 450°C or less. The low melting point metal particles are particles containing a low melting point metal. The low melting point metal refers to a metal with a liquidus temperature (melting point) of 450°C or less. The liquidus temperature (melting point) of the low melting point metal is preferably 300°C or less, more preferably 220°C or less, and even more preferably 190°C or less.

The liquidus temperature of the solder particles is preferably 140°C or higher, more preferably 145°C or higher, and preferably 230°C or lower, more preferably 225°C or lower. When the liquidus temperature of the solder particles is equal to or higher than the lower limit and equal to or lower than the upper limit, the solder can be arranged on the electrodes more efficiently, and the reliability of the electrical connection between the upper and lower electrodes to be connected can be more effectively improved.

The solidus temperature of the solder particles is preferably 115°C or higher, more preferably 120°C or higher, and preferably 220°C or lower, more preferably 150°C or lower, and even more preferably 145°C or lower. When the solidus temperature of the solder particles is equal to or higher than the lower limit and equal to or lower than the upper limit, the solder can be arranged on the electrodes more efficiently, and the reliability of the electrical connection between the upper and lower electrodes to be connected can be more effectively improved.

In the conductive material, the absolute value of the difference between the solidus temperature of the solder particles and the liquidus temperature of the solder particles is 5°C or more. The absolute value of the difference between the solidus temperature of the solder particles and the liquidus temperature of the solder particles is preferably 5°C or more, more preferably 8°C or more, and preferably 100°C or less, more preferably 90°C or less. When the absolute value of the difference between the solidus temperature of the solder particles and the liquidus temperature of the solder particles is equal to or more than the lower limit and equal to or less than the upper limit, the solder can be arranged on the electrode more efficiently, and the reliability of the conductivity between the upper and lower electrodes to be connected can be more effectively improved.

The liquidus temperature and solidus temperature of the solder particles can be determined by differential scanning calorimetry (DSC). The differential scanning calorimetry (DSC) is preferably performed under the following conditions: temperature rise range: 30°C to 500°C, temperature rise rate: 5°C/min, and nitrogen purge amount: 5 ml/min. An example of a differential scanning calorimetry (DSC) device is the "EXSTAR DSC7020" manufactured by SII. For the obtained differential scanning calorimetry (DSC) curve, a straight line is drawn by extending the baseline on the low temperature side to the high temperature side, and a tangent (tangent 1) is drawn at the point where the gradient of the curve on the low temperature side of the melting peak is maximum. The temperature at the intersection of the straight line extended to the high temperature side and the tangent (tangent 1) is the solidus temperature. In addition, for the obtained differential scanning calorimetry (DSC) curve, a straight line is drawn by extending the baseline on the high temperature side to the low temperature side, and a tangent (tangent 2) is drawn at the point where the gradient of the curve on the high temperature side of the melting peak is maximum. The temperature at the intersection of the straight line extended to the lower temperature side and the tangent (tangent 2) is the liquidus temperature.

Methods for adjusting the solidus temperature of the solder particles, the liquidus temperature of the solder particles, and the absolute value of the difference between the solidus temperature of the solder particles and the liquidus temperature of the solder particles to the above preferred ranges include a method of adjusting the type and content of metal contained in the solder particles.

The solder particles preferably contain bismuth, indium, silver, copper, or tin, more preferably contain bismuth, indium, or tin, and even more preferably contain bismuth or indium. When the solder particles satisfy the above preferred aspects, the solder can be arranged on the electrodes more efficiently, and the reliability of the electrical connection between the upper and lower electrodes to be connected can be more effectively improved.

The tin content of the 100% by weight metal contained in the solder particles is preferably 30% by weight or more, more preferably 40% by weight or more, and preferably 90% by weight or less, more preferably 70% by weight or less. When the tin content in the solder particles is equal to or greater than the lower limit and equal to or less than the upper limit, the electrical continuity reliability and connection reliability between the solder portion and the electrode are further improved.

The bismuth content of the 100% by weight metal contained in the solder particles is preferably 1% by weight or more, more preferably 2% by weight or more, and preferably 58% by weight or less, more preferably 55% by weight or less. When the bismuth content in the solder particles is equal to or more than the lower limit and equal to or less than the upper limit, the solder can be arranged on the electrodes more efficiently, and the reliability of the electrical connection between the upper and lower electrodes to be connected can be more effectively improved.

The indium content of the 100% by weight metal contained in the solder particles is preferably 1% by weight or more, more preferably 2% by weight or more, and preferably 52% by weight or less, more preferably 45% by weight or less. When the indium content in the solder particles is equal to or more than the lower limit and equal to or less than the upper limit, the solder can be arranged on the electrodes more efficiently, and the reliability of the electrical connection between the upper and lower electrodes to be connected can be more effectively improved.

The tin, bismuth, or indium content can be measured using a high-frequency inductively coupled plasma optical emission spectrometer ("ICP-AES" manufactured by Horiba, Ltd.) or a fluorescent X-ray analyzer ("EDX-800HS" manufactured by Shimadzu Corporation).

By using the above solder particles, the solder melts and bonds to the electrodes, and the solder portion provides electrical continuity between the electrodes. For example, the solder portion and the electrodes tend to have surface contact rather than point contact, which reduces the connection resistance. In addition, the use of the above solder particles increases the bonding strength between the solder portion and the electrodes, making it even more difficult for the solder portion and the electrodes to peel off, and thus improving the reliability of electrical continuity and connection.

The low melting point metal constituting the solder particles is not particularly limited. The low melting point metal is preferably tin or an alloy containing tin. Examples of such alloys include a tin-silver alloy, a tin-copper alloy, a tin-silver-copper alloy, a tin-bismuth alloy, a tin-zinc alloy, and a tin-indium alloy. Since they have excellent wettability with respect to electrodes, the low melting point metal is preferably tin, a tin-silver alloy, a tin-silver-copper alloy, a tin-bismuth alloy, or a tin-indium alloy. It is more preferable that the low melting point metal is a tin-bismuth alloy or a tin-indium alloy.

The solder particles are preferably filler metals with a liquidus temperature of 450°C or less based on JIS Z3001: Welding Terminology. Examples of the composition of the solder particles include metal compositions containing zinc, gold, silver, lead, copper, tin, bismuth, and indium. The solder particles preferably do not contain lead, and preferably contain tin and indium, or tin and bismuth. The solder particles may contain eutectic solder. When the solder particles contain eutectic solder, it is preferable to blend multiple solder particles so that the absolute value of the difference between the solidus temperature and the liquidus temperature is 5°C or more.

To further increase the bonding strength between the solder part and the electrode, the solder particles may contain metals such as nickel, copper, antimony, aluminum, zinc, iron, gold, titanium, phosphorus, germanium, tellurium, cobalt, bismuth, manganese, chromium, molybdenum, and palladium. From the viewpoint of further increasing the bonding strength between the solder part and the electrode, the solder particles preferably contain nickel, copper, antimony, aluminum, or zinc. From the viewpoint of further increasing the bonding strength between the solder part and the electrode, the content of these metals for increasing the bonding strength is preferably 0.0001% by weight or more, and preferably 1% by weight or less, based on 100% by weight of the metal contained in the solder particles.

The particle diameter of the solder particles is preferably 0.01 μm or more, more preferably 1 μm or more, even more preferably 2 μm or more, and particularly preferably 3 μm or more, and is preferably 30 μm or less, more preferably 20 μm or less, and even more preferably 10 μm or less. When the particle diameter of the solder particles is equal to or greater than the lower limit and equal to or less than the upper limit, the solder can be arranged on the electrode more efficiently. It is particularly preferable that the particle diameter of the solder particles is equal to or greater than 3 μm and equal to or less than 10 μm.

The particle diameter of the solder particles is preferably an average particle diameter, and more preferably a number average particle diameter. The particle diameter of the solder particles is obtained, for example, by observing 50 arbitrary solder particles with an electron microscope or optical microscope and calculating the average particle diameter of each solder particle, or by performing laser diffraction particle size distribution measurement. In the observation with an electron microscope or optical microscope, the particle diameter of each solder particle is obtained as the particle diameter of a circle equivalent diameter. In the observation with an electron microscope or optical microscope, the average particle diameter of 50 arbitrary solder particles with a circle equivalent diameter is almost equal to the average particle diameter of a sphere equivalent diameter. In the laser diffraction particle size distribution measurement, the particle diameter of each solder particle is obtained as the particle diameter of a sphere equivalent diameter. The average particle diameter of the solder particles is preferably calculated by laser diffraction particle size distribution measurement.

The coefficient of variation (CV value) of the particle diameter of the solder particles is preferably 5% or more, more preferably 10% or more, and is preferably 40% or less, more preferably 30% or less. When the coefficient of variation of the particle diameter of the solder particles is equal to or more than the lower limit and equal to or less than the upper limit, the solder can be arranged on the electrode more efficiently. However, the CV value of the particle diameter of the solder particles may be less than 5%.

The above coefficient of variation (CV value) can be measured as follows:

CV value (%) = (ρ/Dn) × 100
ρ: Standard deviation of solder particle diameter Dn: Average value of solder particle diameter

The shape of the solder particles is not particularly limited. The shape of the solder particles may be spherical or may be a shape other than spherical, such as flat.

In the conductive material, the content of the solder particles is 15% by weight or more in 100% by weight of the conductive material. In 100% by weight of the conductive material, the content of the solder particles is preferably 20% by weight or more, more preferably 30% by weight or more, even more preferably 40% by weight or more, and preferably 90% by weight or less, more preferably 85% by weight or less, and even more preferably 80% by weight or less. When the content of the solder particles is equal to or greater than the lower limit and equal to or less than the upper limit, the solder can be arranged on the electrodes more efficiently, it is easy to arrange a large amount of solder between the electrodes, and the electrical reliability is further improved. From the viewpoint of further improving the electrical reliability, it is preferable that the content of the solder particles is large.

(Thermosetting component)
The conductive material includes a thermosetting component. The conductive material may include a thermosetting compound and a thermosetting agent as the thermosetting components. In order to increase the degree of cure of the conductive material, it is preferable that the conductive material includes a thermosetting compound and a thermosetting agent as the thermosetting components. In order to increase the degree of cure of the conductive material, it is preferable that the conductive material includes a curing accelerator as the thermosetting components.

(Thermosetting component: thermosetting compound)
The thermosetting compound is not particularly limited. Examples of the thermosetting compound include oxetane compounds, epoxy compounds, episulfide compounds, (meth)acrylic compounds, phenolic compounds, amino compounds, unsaturated polyester compounds, polyurethane compounds, silicone compounds, and polyimide compounds. From the viewpoint of further improving the curability and viscosity of the conductive material, more effectively increasing the conduction reliability, and more effectively increasing the insulation reliability, the thermosetting compound is preferably an epoxy compound or an episulfide compound, and more preferably an epoxy compound. The thermosetting compound preferably contains an epoxy compound. The thermosetting compound may be used alone or in combination of two or more.

The epoxy compound is a compound having at least one epoxy group. Examples of the epoxy compound include bisphenol A type epoxy compounds, bisphenol F type epoxy compounds, bisphenol S type epoxy compounds, phenol novolac type epoxy compounds, biphenyl type epoxy compounds, biphenyl novolac type epoxy compounds, biphenol type epoxy compounds, naphthalene type epoxy compounds, fluorene type epoxy compounds, phenol aralkyl type epoxy compounds, naphthol aralkyl type epoxy compounds, dicyclopentadiene type epoxy compounds, anthracene type epoxy compounds, epoxy compounds having an adamantane skeleton, epoxy compounds having a tricyclodecane skeleton, naphthylene ether type epoxy compounds, and epoxy compounds having a triazine nucleus in the skeleton. The epoxy compounds may be used alone or in combination of two or more.

The epoxy compound is liquid or solid at room temperature (23°C). When the epoxy compound is solid at room temperature, the melting temperature of the epoxy compound is preferably equal to or lower than the liquidus temperature of the solder particles. By using the preferred epoxy compound, the viscosity is high at the stage where the connection target members are bonded together, and when acceleration is applied due to an impact from transportation, etc., the positional deviation between the first connection target member and the second connection target member can be suppressed. Furthermore, the viscosity of the conductive material can be significantly reduced by the heat during curing, allowing the solder to efficiently coagulate.

From the viewpoint of more effectively increasing the insulation reliability and more effectively increasing the conduction reliability, it is preferable that the thermosetting compound contains an epoxy compound.

From the viewpoint of disposing the solder on the electrodes more effectively, it is preferable that the thermosetting compound contains a thermosetting compound having a polyether skeleton.

The above-mentioned thermosetting compounds having a polyether skeleton include compounds having glycidyl ether groups at both ends of an alkyl chain having 3 to 12 carbon atoms, and polyether-type epoxy compounds having a polyether skeleton having 2 to 4 carbon atoms and having structural units in which 2 to 10 polyether skeletons are bonded in succession.

From the viewpoint of more effectively increasing the heat resistance of the cured product, it is preferable that the above-mentioned thermosetting compound contains a thermosetting compound having an isocyanuric skeleton.

The above-mentioned thermosetting compounds having an isocyanuric skeleton include triisocyanurate type epoxy compounds, such as the TEPIC series (TEPIC-G, TEPIC-S, TEPIC-SS, TEPIC-HP, TEPIC-L, TEPIC-PAS, TEPIC-VL, TEPIC-UC) manufactured by Nissan Chemical Industries, Ltd.

In 100% by weight of the conductive material, the content of the thermosetting compound is preferably 5% by weight or more, more preferably 10% by weight or more, and preferably 85% by weight or less, more preferably 75% by weight or less, even more preferably 65% by weight or less, and particularly preferably 55% by weight or less. When the content of the thermosetting compound is equal to or more than the above lower limit and equal to or less than the above upper limit, the solder can be arranged on the electrodes more efficiently, the insulation reliability between the electrodes can be more effectively improved, and the conduction reliability between the electrodes can be more effectively improved. From the viewpoint of more effectively improving the impact resistance, the content of the thermosetting compound is preferably large.

In 100% by weight of the conductive material, the content of the epoxy compound is preferably 5% by weight or more, more preferably 10% by weight or more, and preferably 85% by weight or less, more preferably 75% by weight or less, even more preferably 65% by weight or less, and particularly preferably 55% by weight or less. When the content of the epoxy compound is equal to or more than the lower limit and equal to or less than the upper limit, the solder can be arranged on the electrodes more efficiently, the insulation reliability between the electrodes can be more effectively improved, and the conduction reliability between the electrodes can be more effectively improved. From the viewpoint of further improving the impact resistance, the content of the epoxy compound is preferably high.

(Thermosetting component: thermosetting agent)
The heat curing agent is not particularly limited. The heat curing agent heat cures the heat curing compound. Examples of the heat curing agent include imidazole curing agent, amine curing agent, phenol curing agent, thiol curing agent such as polythiol curing agent, acid anhydride curing agent, thermal cationic initiator (thermal cationic curing agent) and thermal radical generator. The heat curing agent may be used alone or in combination of two or more.

From the viewpoint of enabling the conductive material to be cured more quickly at low temperatures, the heat curing agent is preferably an imidazole curing agent, a thiol curing agent, or an amine curing agent. Furthermore, from the viewpoint of improving storage stability when the heat curing compound and the heat curing agent are mixed, the heat curing agent is preferably a latent curing agent. The latent curing agent is preferably a latent imidazole curing agent, a latent thiol curing agent, or a latent amine curing agent. The heat curing agent may be coated with a polymeric substance such as a polyurethane resin or a polyester resin.

The imidazole curing agent is not particularly limited. Examples of the imidazole curing agent include 2-methylimidazole, 2-ethyl-4-methylimidazole, 1-cyanoethyl-2-phenylimidazole, 1-cyanoethyl-2-phenylimidazolium trimellitate, 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine and 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine isocyanuric acid adduct, 2-phenyl-4,5-dihydroxymethylimidazole, 2-phenyl-4-methyl-5-hydro Examples of imidazole compounds include 1H-imidazole in which the hydrogen at the 5th position of the 1H-imidazole is replaced with a hydroxymethyl group and the hydrogen at the 2nd position is replaced with a phenyl group or a toluyl group, such as 2-phenyl-4-benzyl-5-hydroxymethylimidazole, 2-para-toluyl-4-methyl-5-hydroxymethylimidazole, 2-meta-toluyl-4-methyl-5-hydroxymethylimidazole, 2-meta-toluyl-4,5-dihydroxymethylimidazole, and 2-para-toluyl-4,5-dihydroxymethylimidazole.

The thiol curing agent is not particularly limited. Examples of the thiol curing agent include trimethylolpropane tris-3-mercaptopropionate, pentaerythritol tetrakis-3-mercaptopropionate, and dipentaerythritol hexa-3-mercaptopropionate.

The amine curing agent is not particularly limited. Examples of the amine curing agent include hexamethylenediamine, octamethylenediamine, decamethylenediamine, 3,9-bis(3-aminopropyl)-2,4,8,10-tetraspiro[5.5]undecane, bis(4-aminocyclohexyl)methane, metaphenylenediamine, and diaminodiphenylsulfone.

The acid anhydride curing agent is not particularly limited, and any acid anhydride that is used as a curing agent for thermosetting compounds such as epoxy compounds can be widely used. Examples of the acid anhydride curing agent include bifunctional acid anhydride curing agents such as phthalic anhydride, tetrahydrophthalic anhydride, trialkyltetrahydrophthalic anhydride, hexahydrophthalic anhydride, methylhexahydrophthalic anhydride, methyltetrahydrophthalic anhydride, methylbutenyltetrahydrophthalic anhydride, anhydrides of phthalic acid derivatives, maleic anhydride, nadic anhydride, methylnadic anhydride, glutaric anhydride, succinic anhydride, glycerin bistrimellitic anhydride monoacetate, and ethylene glycol bistrimellitic anhydride, trifunctional acid anhydride curing agents such as trimellitic anhydride, and tetrafunctional or higher acid anhydride curing agents such as pyromellitic anhydride, benzophenone tetracarboxylic anhydride, methylcyclohexene tetracarboxylic anhydride, and polyazelaic anhydride.

The above-mentioned thermal cationic initiator is not particularly limited. Examples of the above-mentioned thermal cationic initiator include an iodonium cationic curing agent, an oxonium cationic curing agent, and a sulfonium cationic curing agent. Examples of the above-mentioned iodonium cationic curing agent include bis(4-tert-butylphenyl)iodonium hexafluorophosphate. Examples of the above-mentioned oxonium cationic curing agent include trimethyloxonium tetrafluoroborate. Examples of the above-mentioned sulfonium cationic curing agent include tri-p-tolylsulfonium hexafluorophosphate.

The thermal radical generator is not particularly limited. Examples of the thermal radical generator include azo compounds and organic peroxides. Examples of the azo compounds include azobisisobutyronitrile (AIBN). Examples of the organic peroxides include di-tert-butyl peroxide and methyl ethyl ketone peroxide.

The reaction initiation temperature of the heat curing agent is preferably 50°C or higher, more preferably 70°C or higher, even more preferably 80°C or higher, and is preferably 250°C or lower, more preferably 200°C or lower, even more preferably 150°C or lower, and particularly preferably 140°C or lower. When the reaction initiation temperature of the heat curing agent is equal to or higher than the lower limit and equal to or lower than the upper limit, the solder is more efficiently disposed on the electrode. It is particularly preferable that the reaction initiation temperature of the heat curing agent is 80°C or higher and 140°C or lower.

From the viewpoint of disposing the solder on the electrodes more efficiently, the reaction initiation temperature of the thermosetting agent is preferably higher than the liquidus temperature of the solder particles, more preferably 5°C or more higher, and even more preferably 10°C or more higher.

The reaction start temperature of the above heat curing agent means the temperature at which the exothermic peak begins to rise in DSC.

The content of the heat curing agent is not particularly limited. The content of the heat curing agent is preferably 0.01 parts by weight or more, more preferably 1 part by weight or more, and preferably 200 parts by weight or less, more preferably 100 parts by weight or less, and even more preferably 75 parts by weight or less, relative to 100 parts by weight of the heat curing compound. When the content of the heat curing agent is equal to or more than the lower limit, it is easy to sufficiently cure the conductive material. When the content of the heat curing agent is equal to or less than the upper limit, it is difficult for excess heat curing agent that is not involved in curing to remain after curing, and the heat resistance of the cured product is further improved.

(Thermosetting component: curing accelerator)
The conductive material may contain a curing accelerator. The curing accelerator is not particularly limited. The curing accelerator preferably acts as a curing catalyst in the reaction between the thermosetting compound and the thermosetting agent. The curing accelerator preferably acts as a curing catalyst in the reaction with the thermosetting compound. Only one type of the curing accelerator may be used, or two or more types may be used in combination.

Examples of the curing accelerator include phosphonium salts, tertiary amines, tertiary amine salts, quaternary onium salts, tertiary phosphines, crown ether complexes, and phosphonium ylides. Specific examples of the curing accelerator include imidazole compounds, isocyanurates of imidazole compounds, dicyandiamide, derivatives of dicyandiamide, melamine compounds, derivatives of melamine compounds, diaminomaleonitrile, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, bis(hexamethylene)triamine, triethanolamine, diaminodiphenylmethane, amine compounds such as organic acid dihydrazides, 1,8-diazabicyclo[5,4,0]undecene-7, 3,9-bis(3-aminopropyl)-2,4,8,10-tetraoxaspiro[5,5]undecane, boron trifluoride, and organic phosphorus compounds such as triphenylphosphine, tricyclohexylphosphine, tributylphosphine, and methyldiphenylphosphine.

The phosphonium salt is not particularly limited. Examples of the phosphonium salt include tetra-normal-butylphosphonium bromide, tetra-normal-butylphosphonium O,O-diethyldithiophosphate, methyltributylphosphonium dimethylphosphate, tetra-normal-butylphosphonium benzotriazole, tetra-normal-butylphosphonium tetrafluoroborate, and tetra-normal-butylphosphonium tetraphenylborate.

The content of the curing accelerator is appropriately selected so that the thermosetting compound is cured well. The content of the curing accelerator per 100 parts by weight of the thermosetting compound is preferably 0.5 parts by weight or more, more preferably 0.8 parts by weight or more, and preferably 10 parts by weight or less, more preferably 8 parts by weight or less. When the content of the curing accelerator is equal to or more than the lower limit and equal to or less than the upper limit, the thermosetting compound can be cured well.

(flux)
The conductive material may contain a flux. By using the flux, the solder can be arranged on the electrode more efficiently. The flux is not particularly limited. As the flux, a flux generally used for solder joints or the like can be used.

The above-mentioned fluxes include zinc chloride, a mixture of zinc chloride and an inorganic halide, a mixture of zinc chloride and an inorganic acid, a molten salt, phosphoric acid, a derivative of phosphoric acid, an organic halide, hydrazine, an amine compound, an organic acid, and rosin. Only one type of the above-mentioned fluxes may be used, or two or more types may be used in combination.

The molten salt may be ammonium chloride or the like. The organic acid may be lactic acid, citric acid, stearic acid, glutamic acid, glutaric acid, or the like. The rosin may be activated rosin or non-activated rosin. The flux is preferably an organic acid having two or more carboxyl groups, or rosin. The flux may be an organic acid having two or more carboxyl groups, or rosin. The use of an organic acid having two or more carboxyl groups, or rosin, further increases the reliability of electrical conduction between the electrodes.

Examples of organic acids having two or more carboxyl groups include succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, and sebacic acid.

The above amine compounds include cyclohexylamine, dicyclohexylamine, benzylamine, benzhydrylamine, imidazole, benzimidazole, phenylimidazole, carboxybenzimidazole, benzotriazole, and carboxybenzotriazole.

The rosin is a rosin containing abietic acid as the main component. Examples of the rosin include abietic acid and acrylic modified rosin. The flux is preferably a rosin, and more preferably abietic acid. The use of this preferred flux further increases the reliability of electrical continuity between the electrodes.

The activation temperature (melting point) of the flux is preferably 50°C or higher, more preferably 70°C or higher, and even more preferably 80°C or higher, and is preferably 200°C or lower, more preferably 190°C or lower, even more preferably 160°C or lower, even more preferably 150°C or lower, and even more preferably 140°C or lower. When the activation temperature of the flux is above the lower limit and below the upper limit, the flux effect is more effectively exerted, and the solder is more efficiently placed on the electrode. The activation temperature (melting point) of the flux is preferably 80°C or higher and 190°C or lower. It is particularly preferable that the activation temperature (melting point) of the flux is 80°C or higher and 140°C or lower.

Examples of the flux with an active temperature (melting point) of 80°C or higher and 190°C or lower include dicarboxylic acids such as succinic acid (melting point 186°C), glutaric acid (melting point 96°C), adipic acid (melting point 152°C), pimelic acid (melting point 104°C), and suberic acid (melting point 142°C), benzoic acid (melting point 122°C), and malic acid (melting point 130°C), etc.

The boiling point of the flux is preferably 200°C or less.

From the viewpoint of disposing the solder on the electrodes more efficiently, the melting point of the flux is preferably higher than the liquidus temperature of the solder particles, more preferably by 5°C or more, and even more preferably by 10°C or more.

From the viewpoint of disposing the solder on the electrodes more efficiently, the melting point of the flux is preferably higher than the reaction initiation temperature of the heat curing agent, more preferably 5°C or more higher, and even more preferably 10°C or more higher.

The flux may be dispersed in the conductive material or may be attached to the surface of the solder particles.

The melting point of the flux is higher than the liquidus temperature of the solder particles, so that the solder can be efficiently condensed on the electrode part. This is because when heat is applied during joining, the electrode part has a higher thermal conductivity than the part of the member to be connected around the electrode, so the temperature of the electrode part rises faster. When the temperature of the solder particles exceeds the liquidus temperature, the inside of the solder particles melts, but the oxide film formed on the surface is not removed because it has not yet reached the melting point (activation temperature) of the flux. In this state, the temperature of the electrode part reaches the melting point (activation temperature) of the flux first, so the oxide film on the surface of the solder particles that have moved to the electrode is preferentially removed, and the solder can wet and spread over the surface of the electrode. This allows the solder to be efficiently condensed on the electrode.

The flux is preferably one that releases cations when heated. By using a flux that releases cations when heated, the solder can be placed on the electrodes more efficiently.

The flux that releases cations when heated includes the thermal cationic initiator (thermal cationic curing agent).

From the viewpoint of more efficiently disposing the solder on the electrodes, more effectively increasing the insulation reliability, and more effectively increasing the conduction reliability, it is preferable that the flux is a salt of an acid compound and a base compound.

The acid compound is preferably an organic compound having a carboxyl group. Examples of the acid compound include aliphatic carboxylic acids such as malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, citric acid, and malic acid, cyclic aliphatic carboxylic acids such as cyclohexyl carboxylic acid and 1,4-cyclohexyl dicarboxylic acid, and aromatic carboxylic acids such as isophthalic acid, terephthalic acid, trimellitic acid, and ethylenediaminetetraacetic acid. From the viewpoint of more efficiently disposing the solder on the electrodes, more effectively increasing the insulation reliability, and more effectively increasing the conduction reliability, the acid compound is preferably glutaric acid, cyclohexyl carboxylic acid, or adipic acid.

The basic compound is preferably an organic compound having an amino group. Examples of the basic compound include diethanolamine, triethanolamine, methyldiethanolamine, ethyldiethanolamine, cyclohexylamine, dicyclohexylamine, benzylamine, benzhydrylamine, 2-methylbenzylamine, 3-methylbenzylamine, 4-tert-butylbenzylamine, N-methylbenzylamine, N-ethylbenzylamine, N-phenylbenzylamine, N-tert-butylbenzylamine, N-isopropylbenzylamine, N,N-dimethylbenzylamine, imidazole compounds, and triazole compounds. From the viewpoint of more efficiently disposing the solder on the electrodes, more effectively increasing the insulation reliability, and more effectively increasing the conduction reliability, the basic compound is preferably benzylamine.

In 100% by weight of the conductive material, the content of the flux is preferably 0.5% by weight or more, preferably 30% by weight or less, and more preferably 25% by weight or less. The conductive material may not contain flux. When the content of the flux is equal to or more than the lower limit and equal to or less than the upper limit, it becomes even more difficult for an oxide film to form on the surfaces of the solder and the electrodes, and further, the oxide film formed on the surfaces of the solder and the electrodes can be removed more effectively.

(Filler)
The conductive material according to the present invention may contain a filler. The filler may be an organic filler or an inorganic filler. When the conductive material contains a filler, the solder can be uniformly aggregated on all the electrodes of the substrate.

It is preferable that the conductive material does not contain the filler or contains 5% by weight or less of the filler. When the thermosetting compound is used, the lower the filler content, the easier it is for the solder to move onto the electrode.

In 100% by weight of the conductive material, the content of the filler is preferably 0% by weight (not contained) or more, and is preferably 5% by weight or less, more preferably 2% by weight or less, and even more preferably 1% by weight or less. When the content of the filler is equal to or more than the lower limit and equal to or less than the upper limit, the solder is more uniformly arranged on the electrode.

(Other ingredients)
The conductive material may contain various additives, as necessary, such as a filler, an extender, a softener, a plasticizer, a thixotropic agent, a leveling agent, a polymerization catalyst, a curing catalyst, a colorant, an antioxidant, a heat stabilizer, a light stabilizer, an ultraviolet absorber, a lubricant, an antistatic agent, and a flame retardant.

(Connection structure and method for manufacturing the connection structure)
The connection structure according to the present invention includes a first connection target member having a first electrode on its surface, a second connection target member having a second electrode on its surface, and a connection part connecting the first connection target member and the second connection target member. In the connection structure according to the present invention, the material of the connection part is the conductive material described above. In the connection structure according to the present invention, the first electrode and the second electrode are electrically connected by a solder part in the connection part.

The method for manufacturing a connection structure according to the present invention includes a step of using the conductive material described above to place the conductive material on the surface of a first connection target member having a first electrode on its surface. The method for manufacturing a connection structure according to the present invention includes a step of placing a second connection target member having a second electrode on its surface opposite to the first connection target member side of the conductive material so that the first electrode and the second electrode face each other. The method for manufacturing a connection structure according to the present invention includes a step of forming a connection part connecting the first connection target member and the second connection target member from the conductive material by heating the conductive material to a temperature equal to or higher than the liquidus temperature of the solder particles, and electrically connecting the first electrode and the second electrode with a solder part in the connection part.

The connection structure and the method for manufacturing the connection structure according to the present invention use a specific conductive material, so that the solder is likely to gather between the first electrode and the second electrode, and the solder can be efficiently arranged on the electrodes (lines). In addition, a portion of the solder is unlikely to be arranged in an area (space) where no electrodes are formed, and the amount of solder arranged in the area where no electrodes are formed can be significantly reduced. Therefore, the reliability of the conduction between the first electrode and the second electrode can be improved. Moreover, electrical connection between laterally adjacent electrodes that should not be connected can be prevented, and the reliability of the insulation can be improved.

In addition, in order to efficiently place the solder on the electrodes and significantly reduce the amount of solder placed in areas where no electrodes are formed, it is preferable to use a conductive paste rather than a conductive film as the conductive material.

The thickness of the solder between the electrodes is preferably 10 μm or more, more preferably 20 μm or more, and preferably 100 μm or less, more preferably 80 μm or less. The solder wetted area on the surface of the electrode (the area in contact with the solder out of 100% of the exposed area of the electrode) is preferably 50% or more, more preferably 70% or more, and preferably 100% or less.

In the manufacturing method of the connection structure according to the present invention, it is preferable that in the process of arranging the second connection target member and the process of forming the connection portion, no pressure is applied, and the weight of the second connection target member is applied to the conductive material. In the manufacturing method of the connection structure according to the present invention, it is preferable that in the process of arranging the second connection target member and the process of forming the connection portion, no pressure exceeding the force of the weight of the second connection target member is applied to the conductive material. In these cases, the uniformity of the amount of solder can be further improved in the multiple solder parts. Furthermore, the thickness of the solder part can be made thicker more effectively, making it easier for more solder to gather between the electrodes, and the solder can be more efficiently arranged on the electrodes (lines). In addition, it is difficult for part of the solder to be arranged in the area (space) where the electrodes are not formed, and the amount of solder arranged in the area where the electrodes are not formed can be further reduced. Therefore, the reliability of the conduction between the electrodes can be further improved. Moreover, it is possible to further prevent electrical connection between laterally adjacent electrodes that should not be connected, and the reliability of insulation can be further improved.

Furthermore, if a conductive paste is used instead of a conductive film, it becomes easier to adjust the thickness of the connection and solder parts by changing the amount of conductive paste applied. On the other hand, with a conductive film, there is the problem that in order to change or adjust the thickness of the connection, it is necessary to prepare a conductive film of a different thickness or a conductive film of a specified thickness. Also, compared to a conductive paste, with a conductive film, it is not possible to sufficiently reduce the melt viscosity of the conductive film at the melting temperature of the solder, and there is a tendency for the cohesion of the solder to be inhibited.

Specific embodiments of the present invention will be described below with reference to the drawings.

Figure 1 is a cross-sectional view showing a schematic diagram of a connection structure obtained using a conductive material according to one embodiment of the present invention.

The connection structure 1 shown in FIG. 1 includes a first connection target member 2, a second connection target member 3, and a connection portion 4 connecting the first connection target member 2 and the second connection target member 3. The connection portion 4 is formed of the conductive material described above. In this embodiment, the conductive material includes a thermosetting component and solder particles. The thermosetting component includes a thermosetting compound and a thermosetting agent. In this embodiment, a conductive paste is used as the conductive material.

The connection portion 4 has a solder portion 4A in which multiple solder particles are gathered and joined together, and a hardened portion 4B in which a thermosetting compound is thermally hardened.

The first connection target member 2 has a plurality of first electrodes 2a on its surface (upper surface). The second connection target member 3 has a plurality of second electrodes 3a on its surface (lower surface). The first electrode 2a and the second electrode 3a are electrically connected by the solder portion 4A. Therefore, the first connection target member 2 and the second connection target member 3 are electrically connected by the solder portion 4A. In the connection portion 4, solder is not present in a region (hardened portion 4B) other than the solder portion 4A gathered between the first electrode 2a and the second electrode 3a. In a region (hardened portion 4B) other than the solder portion 4A, solder is not present apart from the solder portion 4A. In addition, if the amount is small, solder may be present in a region (hardened portion 4B) other than the solder portion 4A gathered between the first electrode 2a and the second electrode 3a.

As shown in FIG. 1, in the connection structure 1, a plurality of solder particles gather between the first electrode 2a and the second electrode 3a, and after the plurality of solder particles melt, the molten solder particles wet and spread over the surface of the electrode, and then solidify to form the solder portion 4A. Therefore, the connection area between the solder portion 4A and the first electrode 2a, and between the solder portion 4A and the second electrode 3a is large. In other words, by using solder particles, the contact area between the solder portion 4A and the first electrode 2a, and between the solder portion 4A and the second electrode 3a is large compared to the case where conductive particles whose conductive outer surface is a metal such as nickel, gold, or copper are used. This also increases the conduction reliability and connection reliability of the connection structure 1. In addition, when the conductive material contains flux, the flux is generally gradually deactivated by heating.

In the connection structure 1 shown in FIG. 1, all of the solder portion 4A is located in the opposing region between the first and second electrodes 2a and 3a. The connection structure 1X of the modified example shown in FIG. 3 differs from the connection structure 1 shown in FIG. 1 only in the connection portion 4X. The connection portion 4X has a solder portion 4XA and a hardened portion 4XB. Like the connection structure 1X, most of the solder portion 4XA is located in the opposing region of the first and second electrodes 2a and 3a, and a part of the solder portion 4XA may protrude laterally from the opposing region of the first and second electrodes 2a and 3a. The solder portion 4XA protruding laterally from the opposing region of the first and second electrodes 2a and 3a is a part of the solder portion 4XA, and is not solder separated from the solder portion 4XA. In this embodiment, the amount of solder separated from the solder portion can be reduced, but the solder separated from the solder portion may be present in the hardened portion.

By using fewer solder particles, it becomes easier to obtain connection structure 1. By using more solder particles, it becomes easier to obtain connection structure 1X.

In the connection structure 1, 1X, when the portion where the first electrode 2a and the second electrode 3a face each other is viewed in the stacking direction of the first electrode 2a, the connection portion 4, 4X, and the second electrode 3a, it is preferable that the solder portion 4A, 4XA in the connection portion 4, 4X is disposed in 50% or more of the 100% area of the portion where the first electrode 2a and the second electrode 3a face each other. By having the solder portion 4A, 4XA in the connection portion 4, 4X satisfy the above-mentioned preferable aspects, the reliability of the electrical continuity can be further improved.

When the first electrode and the second electrode are viewed in the stacking direction of the first electrode, the connection portion, and the second electrode, it is preferable that the solder portion in the connection portion is arranged in 50% or more of the 100% area of the portion where the first electrode and the second electrode are viewed. When the first electrode and the second electrode are viewed in the stacking direction of the first electrode, the connection portion, and the second electrode, it is more preferable that the solder portion in the connection portion is arranged in 60% or more of the 100% area of the portion where the first electrode and the second electrode are viewed. When the first electrode and the second electrode are viewed in the stacking direction of the first electrode, the connection portion, and the second electrode, it is even more preferable that the solder portion in the connection portion is arranged in 70% or more of the 100% area of the portion where the first electrode and the second electrode are viewed. It is particularly preferable that the solder portion in the connection portion is disposed in 80% or more of the 100% area of the portion where the first electrode and the second electrode face each other when viewed in the stacking direction of the first electrode, the connection portion, and the second electrode. It is most preferable that the solder portion in the connection portion is disposed in 90% or more of the 100% area of the portion where the first electrode and the second electrode face each other when viewed in the stacking direction of the first electrode, the connection portion, and the second electrode. When the solder portion in the connection portion satisfies the above-mentioned preferable aspects, the electrical connection reliability can be further improved.

When the portion where the first electrode and the second electrode face each other is viewed in a direction perpendicular to the stacking direction of the first electrode, the connection portion, and the second electrode, it is preferable that 60% or more of the solder portion in the connection portion is disposed in the portion where the first electrode and the second electrode face each other. When the portion where the first electrode and the second electrode face each other is viewed in a direction perpendicular to the stacking direction of the first electrode, the connection portion, and the second electrode, it is more preferable that 70% or more of the solder portion in the connection portion is disposed in the portion where the first electrode and the second electrode face each other. It is even more preferable that 90% or more of the solder portion in the connection portion is disposed in the portion where the first electrode and the second electrode face each other when the portion where the first electrode and the second electrode face each other is viewed in a direction perpendicular to the stacking direction of the first electrode, the connection portion, and the second electrode. It is particularly preferable that 95% or more of the solder in the connection part is disposed in the portion where the first electrode and the second electrode face each other when viewed in a direction perpendicular to the stacking direction of the first electrode, the connection part, and the second electrode. It is most preferable that 99% or more of the solder in the connection part is disposed in the portion where the first electrode and the second electrode face each other when viewed in a direction perpendicular to the stacking direction of the first electrode, the connection part, and the second electrode. When the solder in the connection part satisfies the above-mentioned preferable aspects, the electrical connection reliability can be further improved.

Next, FIG. 2 illustrates an example of a method for manufacturing a connection structure 1 using a conductive material according to one embodiment of the present invention.

First, a first connection target member 2 having a first electrode 2a on its surface (top surface) is prepared. Next, as shown in FIG. 2(a), a conductive material 11 containing a thermosetting component 11B and solder particles 11A is placed on the surface of the first connection target member 2 (first step). The conductive material 11 used contains a thermosetting compound and a thermosetting agent as the thermosetting component 11B.

A conductive material 11 is placed on the surface of the first connection target component 2 on which the first electrode 2a is provided. After placing the conductive material 11, solder particles 11A are placed both on the first electrode 2a (line) and on the area (space) where the first electrode 2a is not formed.

The method of disposing the conductive material 11 is not particularly limited, but examples include application with a dispenser, screen printing, and ejection with an inkjet device.

A second connection target member 3 having a second electrode 3a on its surface (lower surface) is prepared. Next, as shown in FIG. 2(b), a second connection target member 3 is placed on the surface of the conductive material 11 on the surface of the first connection target member 2 opposite the first connection target member 2 side of the conductive material 11 (second process). The second connection target member 3 is placed on the surface of the conductive material 11 from the second electrode 3a side. At this time, the first electrode 2a and the second electrode 3a are opposed to each other.

Next, the conductive material 11 is heated to a temperature equal to or higher than the melting point of the solder particles 11A (third step). Preferably, the conductive material 11 is heated to a temperature equal to or higher than the hardening temperature of the thermosetting component 11B (thermosetting compound). During this heating, the solder particles 11A that existed in the area where no electrode is formed gather between the first electrode 2a and the second electrode 3a (self-aggregation effect). When a conductive paste is used instead of a conductive film, the solder particles 11A gather more effectively between the first electrode 2a and the second electrode 3a. In addition, the solder particles 11A melt and bond to each other. In addition, the thermosetting component 11B is thermally cured. As a result, as shown in FIG. 2(c), the connection portion 4 that connects the first connection target member 2 and the second connection target member 3 is formed by the conductive material 11. The connection portion 4 is formed by the conductive material 11, the solder portion 4A is formed by bonding the multiple solder particles 11A, and the hardened portion 4B is formed by thermally curing the thermosetting component 11B. If the solder particles 11A move sufficiently, it is not necessary to keep the temperature constant from the start of the movement of the solder particles 11A that are not located between the first electrode 2a and the second electrode 3a until the movement of the solder particles 11A to between the first electrode 2a and the second electrode 3a is completed.

In this embodiment, it is preferable not to apply pressure in the second and third steps. In this case, the weight of the second connection target member 3 is added to the conductive material 11. Therefore, when the connection portion 4 is formed, the solder particles 11A gather more effectively between the first electrode 2a and the second electrode 3a. Note that if pressure is applied in at least one of the second and third steps, the tendency of the solder particles 11A to gather between the first electrode 2a and the second electrode 3a tends to be hindered.

In addition, since no pressure is applied in this embodiment, even if the first connection target member 2 and the second connection target member 3 are overlapped with the first electrode 2a and the second electrode 3a misaligned, the misalignment can be corrected to connect the first electrode 2a and the second electrode 3a (self-alignment effect). This is because the molten solder that self-aggregates between the first electrode 2a and the second electrode 3a is energetically more stable when the contact area between the solder between the first electrode 2a and the second electrode 3a and the other components of the conductive material is minimized, and a force acts to make the connection structure with alignment, which is the connection structure with the minimum area. At this time, it is desirable that the conductive material is not hardened, and that the viscosity of the components of the conductive material other than the solder particles is sufficiently low at that temperature and time.

In this way, the connection structure 1 shown in FIG. 1 is obtained. The second step and the third step may be performed consecutively. After the second step, the resulting laminate of the first connection target member 2, the conductive material 11, and the second connection target member 3 may be moved to a heating section and the third step may be performed. To perform the heating, the laminate may be placed on a heating member, or the laminate may be placed in a heated space.

The heating temperature in the third step is preferably 140°C or higher, more preferably 160°C or higher, and preferably 450°C or lower, more preferably 250°C or lower, and even more preferably 200°C or lower.

The heating method in the third step can be a method of heating the entire connection structure using a reflow furnace or oven to a temperature above the liquidus temperature (melting point) of the solder particles and above the curing temperature of the thermosetting component, or a method of locally heating only the connection portion of the connection structure.

Tools used for localized heating include hot plates, heat guns that apply hot air, soldering irons, and infrared heaters.

When using a hot plate for localized heating, it is preferable to form the top surface of the hot plate from a metal with high thermal conductivity directly below the connection, and from a material with low thermal conductivity such as fluororesin for other areas where it is not desirable to heat the connection.

The first and second connection target members are not particularly limited. Specific examples of the first and second connection target members include electronic components such as semiconductor chips, semiconductor packages, LED chips, LED packages, capacitors, and diodes, as well as electronic components such as resin films, printed circuit boards, flexible printed circuit boards, flexible flat cables, rigid flexible boards, glass epoxy boards, and glass boards. It is preferable that the first and second connection target members are electronic components.

At least one of the first connection target member and the second connection target member is preferably a resin film, a flexible printed circuit board, a flexible flat cable, or a rigid flexible circuit board. The second connection target member is preferably a resin film, a flexible printed circuit board, a flexible flat cable, or a rigid flexible circuit board. Resin films, flexible printed circuit boards, flexible flat cables, and rigid flexible circuit boards have the properties of being highly flexible and relatively lightweight. When a conductive film is used to connect such connection target members, solder tends not to gather on the electrodes. In contrast, by using a conductive paste, even if a resin film, a flexible printed circuit board, a flexible flat cable, or a rigid flexible circuit board is used, the solder can be efficiently gathered on the electrodes, thereby sufficiently improving the conduction reliability between the electrodes. When a resin film, a flexible printed circuit board, a flexible flat cable, or a rigid flexible circuit board is used, the effect of improving the conduction reliability between the electrodes by not applying pressure can be obtained more effectively than when other connection target members such as semiconductor chips are used.

The electrodes provided on the connection target members include metal electrodes such as gold electrodes, nickel electrodes, tin electrodes, aluminum electrodes, copper electrodes, molybdenum electrodes, silver electrodes, SUS electrodes, and tungsten electrodes. When the connection target members are flexible printed circuit boards, the electrodes are preferably gold electrodes, nickel electrodes, tin electrodes, silver electrodes, or copper electrodes. When the connection target members are glass substrates, the electrodes are preferably aluminum electrodes, copper electrodes, molybdenum electrodes, silver electrodes, or tungsten electrodes. When the electrodes are aluminum electrodes, they may be electrodes made of aluminum only, or may be electrodes in which an aluminum layer is laminated on the surface of a metal oxide layer. Examples of materials for the metal oxide layer include indium oxide doped with a trivalent metal element and zinc oxide doped with a trivalent metal element. Examples of the trivalent metal element include Sn, Al, and Ga.

In the connection structure according to the present invention, the first electrode and the second electrode are preferably arranged in an area array or peripheral arrangement. When the first electrode and the second electrode are arranged in an area array or peripheral arrangement, the effect of the present invention is more effectively exerted. The area array is a structure in which the electrodes are arranged in a lattice on the surface on which the electrodes of the connection target member are arranged. The peripheral is a structure in which the electrodes are arranged on the outer periphery of the connection target member. In the case of a structure in which the electrodes are arranged in a comb shape, it is sufficient for the solder to aggregate along a direction perpendicular to the comb, whereas in the area array or peripheral structure, the solder needs to aggregate uniformly over the entire surface on which the electrodes are arranged. Therefore, while the amount of solder tends to be non-uniform in the conventional method, the effect of the present invention is more effectively exerted in the method of the present invention.

The present invention will be specifically described below with reference to examples and comparative examples. The present invention is not limited to the following examples.

Thermosetting components (thermosetting compounds):
Thermosetting compound 1: Bisphenol F type epoxy compound, "YDF-8170C" manufactured by Nippon Steel & Sumikin Chemical Co., Ltd.
Thermosetting compound 2: Bisphenol A type epoxy compound, "YD-8125" manufactured by Nippon Steel & Sumikin Chemical Co., Ltd.
Thermosetting compound 3: Phenol novolac type epoxy compound, "DEN431" manufactured by DOW
Thermosetting compound 4: Aliphatic epoxy compound, "Epolite 1600" manufactured by Kyoeisha Chemical Co., Ltd.
Thermosetting compound 5: isocyanuric skeleton-containing epoxy compound, "TEPIC-SP" manufactured by Nissan Chemical Industries, Ltd.

Thermosetting component (thermosetting agent):
Heat curing agent 1: Acid anhydride curing agent, "Rikacid TH" manufactured by New Japan Chemical Co., Ltd.
Heat curing agent 2: Acid anhydride curing agent, "Rikacid MH" manufactured by New Japan Chemical Co., Ltd.

Thermosetting component (curing accelerator):
Curing accelerator 1: organic phosphonium salt, "PX-4MP" manufactured by Nippon Chemical Industry Co., Ltd.

flux:
Flux 1: "Glutaric acid benzylamine salt", melting point 108°C
How to make Flux 1:
24 g of water as a reaction solvent and 13.212 g of glutaric acid (manufactured by Wako Pure Chemical Industries, Ltd.) were placed in a glass bottle and dissolved at room temperature until homogenous. Then, 10.715 g of benzylamine (manufactured by Wako Pure Chemical Industries, Ltd.) was added and stirred for about 5 minutes to obtain a mixed solution. The resulting mixed solution was placed in a refrigerator at 5°C to 10°C and left overnight. The precipitated crystals were separated by filtration, washed with water, and vacuum dried to obtain flux 1.

Solder particles:
Solder particle 1: Sn42Bi58 solder particle, average particle diameter 10 μm
Solder particles 2: Sn66Bi34 solder particles, average particle size 10 μm
Solder particles 3: Sn53Bi47 solder particles, average particle size 10 μm
Solder particles 4: Sn90In10 solder particles, average particle diameter 10 μm
Solder particles 5: SnIn8Ag3.5 solder particles, average particle diameter 10 μm
Solder particles 6: SnAg3Cu0.5 solder particles, average particle size 10 μm

(Examples 1 to 24 and Comparative Examples 1 to 12)
(1) Preparation of Conductive Material (Anisotropic Conductive Paste) The components shown in Tables 1 to 3 below were mixed in the amounts shown in Tables 1 to 3 below to obtain a conductive material (anisotropic conductive paste).

(2) Preparation of Connection Structure As a first connection target member, a glass epoxy substrate (material: FR-4, thickness: 0.6 mm) having copper electrodes (electrode length: 3 mm, electrode thickness: 12 μm) with L/S = 50 μm/50 μm on its surface was prepared.

As the second connection target member, a flexible printed circuit board (material: polyimide, thickness: 0.1 mm) with copper electrodes (electrode length: 3 mm, electrode thickness: 12 μm) with L/S = 50 μm/50 μm on its surface was prepared.

The conductive material (anisotropic conductive paste) immediately after preparation was applied to the upper surface of the glass epoxy substrate to a thickness of 100 μm to form a conductive material (anisotropic conductive paste) layer. Next, a flexible printed circuit board was laminated on the upper surface of the conductive material (anisotropic conductive paste) layer so that the electrodes face each other. The weight of the flexible printed circuit board is added to the conductive material (anisotropic conductive paste) layer. From this state, the conductive material (anisotropic conductive paste) layer was heated so that the temperature of the conductive material (anisotropic conductive paste) layer reached the solidus temperature of the solder particles 5 seconds after the start of the temperature rise. Furthermore, 15 seconds after the start of the temperature rise, the conductive material (anisotropic conductive paste) layer was heated so that the temperature of the conductive material (anisotropic conductive paste) layer reached 200° C., the conductive material (anisotropic conductive paste) layer was hardened, and a connection structure was obtained. No pressure was applied during heating.

(evaluation)
(1) Solder particle solidus temperature, solder particle liquidus temperature, and absolute value of difference between the solder particle solidus temperature and the solder particle liquidus temperature The solidus temperature and liquidus temperature of the solder particles were measured using differential scanning calorimetry (DSC) as follows. The differential scanning calorimetry (DSC) device used was an "EXSTAR DSC7020" manufactured by SII Corporation.

(Method of measuring the solidus temperature and liquidus temperature of solder particles)
About 10 mg of the solder particles were weighed, and the sample was placed in the approximate center of an aluminum container (sample container), and the aluminum lid of the container was placed and clamped. The obtained sample container was attached to one of the container holders of a differential scanning calorimetry (DSC) device. An empty aluminum container (sample container) with no sample and an aluminum lid clamped was attached to the other container holder. In addition, the nitrogen gas flow rate was set to an appropriate value in the range of 10 ml/min to 50 ml/min, and was allowed to flow until the end of the measurement. The temperature was increased at a rate of 10°C/min, and the measurement was performed while heating to a temperature about 30°C higher than the end of the melting peak. For the obtained differential scanning calorimetry (DSC) curve, a straight line was drawn by extending the baseline on the low temperature side to the high temperature side, and a tangent (tangent 1) was drawn at the point where the gradient of the curve on the low temperature side of the melting peak was maximum. The temperature at the intersection of the straight line extended to the high temperature side and the tangent (tangent 1) was taken as the solidus temperature. For the obtained differential scanning calorimetry (DSC) curve, a straight line was drawn by extending the high-temperature side baseline to the low-temperature side, and a tangent (tangent 2) was drawn at the point where the gradient of the curve on the high-temperature side of the melting peak was maximum. The temperature at the intersection of the straight line extended to the low-temperature side and the tangent (tangent 2) was determined as the liquidus temperature.

From the measurement results, the absolute value of the difference between the solidus temperature of the solder particles and the liquidus temperature of the solder particles was calculated.

(2) Content of tin, bismuth, and indium in 100% by weight of metal contained in solder particles The content of tin, bismuth, and indium in 100% by weight of metal contained in the solder particles was measured using a high-frequency inductively coupled plasma optical emission spectrometer ("ICP-AES" manufactured by HORIBA, Ltd.).

(3) Viscosity of the conductive material at the solidus temperature of the solder particles (ηsp)
The obtained conductive material was used to measure the viscosity (ηsp) of the conductive material at the solidus temperature of the solder particles. The viscosity (ηsp) of the conductive material at the solidus temperature of the solder particles was measured using STRESSTECH (manufactured by REOLOGICA) under the conditions of strain control 1 rad, frequency 1 Hz, heating rate 20°C/min, and measurement temperature range 25°C to 200°C (however, when the solidus temperature of the solder particles exceeds 200°C, the upper temperature limit is set to the solidus temperature of the solder particles).

(4) Placement Accuracy of Solder on Electrode In the obtained connection structure, when the portion where the first electrode and the second electrode face each other is viewed in the lamination direction of the first electrode, the connection portion, and the second electrode, the proportion X of the area where the solder portion in the connection portion is placed in 100% of the area where the first electrode and the second electrode face each other was evaluated. The placement accuracy of the solder on the electrode was evaluated according to the following criteria.

[Criteria for judging the accuracy of solder placement on electrodes]
〇〇〇: Percentage X is 90% or more. 〇〇: Percentage X is 80% or more but less than 90%. 〇: Percentage X is 70% or more but less than 80%. ×: Percentage X is less than 70%.

(5) Conduction reliability between upper and lower electrodes In the obtained connection structures (n = 15 pieces), the connection resistance per connection point between the upper and lower electrodes was measured by the four-terminal method. The average value of the connection resistance was calculated. Note that, based on the relationship of voltage = current x resistance, the connection resistance can be obtained by measuring the voltage when a constant current is passed. The conduction reliability was evaluated according to the following criteria.

[Conductivity reliability criteria]
○ ○ ○: The average connection resistance is 50 mΩ or less. ○ ○: The average connection resistance is more than 50 mΩ and less than 70 mΩ. ○: The average connection resistance is more than 70 mΩ and less than 100 mΩ. ×: The average connection resistance exceeds 100 mΩ, or a connection failure has occurred.

The results are shown in Tables 1 to 3 below.

Similar trends were observed when using resin film, flexible flat cable, and rigid-flexible boards.

REFERENCE SIGNS LIST 1, 1X... Connection structure 2... First connection target member 2a... First electrode 3... Second connection target member 3a... Second electrode 4, 4X... Connection portion 4A, 4XA... Solder portion 4B, 4XB... Hardened portion 11... Conductive material 11A... Solder particle 11B... Thermosetting component

Claims (14)

a thermosetting component and solder particles;
The conductive particles contained in the conductive material are only solder particles having a liquidus temperature of 300° C. or less,
the absolute value of the difference between the solidus temperature of the solder particles and the liquidus temperature of the solder particles is 5° C. or more;
A conductive material (excluding a transient liquid phase sintering composition), wherein the content of the solder particles is 15% by weight or more based on 100% by weight of the conductive material. The conductive material according to claim 1, wherein the viscosity of the conductive material at the solidus temperature of the solder particles is 0.1 Pa·s or more and 50 Pa·s or less. The conductive material according to claim 1 or 2, wherein the particles contained in the conductive material are only solder particles having a liquidus temperature of 230°C or less. The conductive material according to any one of claims 1 to 3, wherein the conductive particle powder contained in the conductive material is only solder particles containing tin and bismuth, only solder particles containing tin and indium, only solder particles containing tin, indium and silver, or only two types of solder particles, namely, solder particles containing tin and bismuth and solder particles containing tin, silver and copper. The conductive material according to any one of claims 1 to 3, wherein the solder particles contain bismuth, indium, silver, copper, or tin. The conductive material according to claim 5, wherein the bismuth content is 1% by weight or more and 58% by weight or less out of 100% by weight of the metal contained in the solder particles. The conductive material according to claim 5 or 6, wherein the indium content is 1% by weight or more and 52% by weight or less out of 100% by weight of the metal contained in the solder particles. The conductive material according to any one of claims 1 to 7, wherein the solidus temperature of the solder particles is 115°C or higher and 220°C or lower. The conductive material according to any one of claims 1 to 8, wherein the particle diameter of the solder particles is 0.01 μm or more and 30 μm or less. The conductive material according to any one of claims 1 to 9, which is a conductive paste. a first connection target member having a first electrode on a surface thereof;
a second connection target member having a second electrode on a surface thereof;
a connection portion that connects the first connection target member and the second connection target member,
The material of the connection portion is the conductive material according to any one of claims 1 to 10,
A connection structure, wherein the first electrode and the second electrode are electrically connected by a solder portion in the connection portion. The connection structure according to claim 11, wherein, when the portion where the first electrode and the second electrode face each other is viewed in the stacking direction of the first electrode, the connection portion, and the second electrode, the solder portion in the connection portion is disposed in 50% or more of the 100% area of the portion where the first electrode and the second electrode face each other. A step of disposing the conductive material according to any one of claims 1 to 10 on a surface of a first connection target member having a first electrode on a surface thereof;
A step of disposing a second connection target member having a second electrode on a surface of the conductive material opposite to the first connection target member side such that the first electrode and the second electrode face each other;
a step of forming a connection portion connecting the first connection target member and the second connection target member from the conductive material by heating the conductive material to a temperature equal to or higher than the liquidus temperature of the solder particles, and electrically connecting the first electrode and the second electrode by a solder portion in the connection portion. 14. The method for manufacturing a connection structure according to claim 13, wherein when the opposing portion of the first electrode and the second electrode is viewed in the stacking direction of the first electrode, the connection portion, and the second electrode, a connection structure is obtained in which the solder portion in the connection portion is arranged in more than 50% of the 100% area of the opposing portion of the first electrode and the second electrode.

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