TW202418301A - Conductive paste and connecting structure - Google Patents

Abstract

The present invention provides a conductive paste that can improve screen printing properties, maintain viscosity, and efficiently arrange solder particles on electrodes. The conductive paste of the present invention comprises a thermosetting component, a plurality of solder particles, a flux, and a tactile agent, wherein the average particle size of the solder particles is 5.0 μm or less, the flux is solid at 25°C, and the tactile agent is a tactile agent that is liquid at 25°C and has a hydroxyl group, or a tactile agent that is solid at 25°C and has a weight increase rate of 0.2% by weight or more when the tactile agent is placed at 25°C and 50% RH for 24 hours.

Description

Conductive paste and connecting structure

The present invention relates to a conductive paste containing solder particles and a connection structure using the conductive paste.

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

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

In recent years, in conductive materials including conductive particles such as solder particles, the particle size of conductive particles has been reduced due to the fine pitch of wiring and connectors in printed wiring boards.

The following patent document 1 discloses a conductive paste containing metal particles with an average particle size of 0.4 μm to 2.0 μm as a main component. In the conductive paste, the number of metal particles with a particle size of 0.2 μm or less is less than 5% out of the total number of the metal particles (100%). [Prior art document] [Patent document]

[Patent Document 1] Japanese Patent Publication No. 10-134637

[The problem the invention is trying to solve]

When the conductive paste containing solder particles is used for conductive connection, the plurality of electrodes on the upper side are electrically connected to the plurality of electrodes on the lower side to conduct the conductive connection. The solder particles are preferably arranged between the upper and lower electrodes, and are preferably not arranged between adjacent lateral electrodes. The adjacent lateral electrodes are preferably not electrically connected.

Generally speaking, conductive paste containing solder particles is placed at a specific position on the substrate by screen printing, etc., and then used by heating such as reflow. By heating the conductive paste to a temperature above the melting point of the solder particles, the solder particles melt and the solder condenses between the electrodes, thereby electrically connecting the upper and lower electrodes.

However, when the conductive paste is screen-printed on a fine-pitch printed wiring board as in Patent Document 1, the conductive paste has a larger surface area, so there is a possibility that a skin will form on the surface of the conductive paste. If a skin forms on the surface of the conductive paste, the viscosity of the conductive paste will decrease. A conductive paste with a low viscosity has a problem of positional displacement of the electrode during conductive connection.

Furthermore, if there is a skin on the surface of the conductive paste, the aggregation of solder particles is hindered, and the solder particles cannot be efficiently arranged between the upper and lower electrodes to be connected. As a result, the solder particles contained in the conductive paste are arranged in the area where no electrode is formed, and the amount of solder particles arranged between the upper and lower electrodes to be connected is reduced. Therefore, the conduction reliability between the upper and lower electrodes to be connected is reduced, or the insulation reliability between adjacent lateral electrodes is reduced.

In addition, due to the high volatility of conventional conductive pastes, the viscosity of the conductive paste during printing may increase depending on the storage environment or usage conditions, making it difficult to evenly apply the conductive paste to a printed wiring board or the like.

The purpose of the present invention is to provide a conductive paste that can improve screen printing properties, maintain viscosity, and efficiently arrange solder particles on electrodes. In addition, the purpose of the present invention is to provide a connection structure using the above conductive paste. [Technical means to solve the problem]

According to a broader aspect of the present invention, a conductive paste is provided, which includes a thermosetting component, a plurality of solder particles, a flux, and a thiotropy agent, wherein the average particle size of the solder particles is less than 5.0 μm, the flux is solid at 25°C, the thiotropy agent is a liquid at 25°C and has a hydroxyl group, or is a solid at 25°C and has a weight increase rate of more than 0.2 wt% when the thiotropy agent is placed at 25°C and 50% RH (relative humidity) for 24 hours.

Weight increase rate (weight %) = (W2-W1) × 100/W1 W1: The weight of the above-mentioned activator before placement W2: The weight of the above-mentioned activator after placement

In a specific embodiment of the conductive paste of the present invention, the content of the above-mentioned activator is greater than 0.005 wt % and less than 2 wt % in 100 wt % of the above-mentioned conductive paste.

In a specific embodiment of the conductive paste of the present invention, the content of the above-mentioned switching agent is not less than 0.003 parts by weight and not more than 2 parts by weight relative to 100 parts by weight of the above-mentioned solder particles.

In a specific embodiment of the conductive paste of the present invention, the above-mentioned thiotropy agent is a hydroxyl group-containing thiotropy agent that is liquid at 25°C.

In a specific embodiment of the conductive paste of the present invention, the above-mentioned thiotropy agent is a liquid at 25°C, has a hydroxyl group and has a boiling point of 80°C or above.

In a specific embodiment of the conductive paste of the present invention, the above-mentioned thiotropy agent is a thiotropy agent which is solid at 25° C. and has the above-mentioned weight gain rate of 1 wt % or more.

According to a broader aspect of the present invention, a connection structure is provided, which comprises: a first connection target component having a first electrode on its surface; a second connection target component having a second electrode on its surface; and a connection portion, which connects the first connection target component with the second connection target component; and the material of the connection portion is the conductive paste, and the first electrode and the second electrode are electrically connected via a solder portion in the connection portion. [Effect of the invention]

The conductive paste of the present invention comprises a thermosetting component, a plurality of solder particles, a flux, and a terminating agent. In the conductive paste of the present invention, the average particle size of the solder particles is 5.0 μm or less. In the conductive paste of the present invention, the flux is solid at 25°C. In the conductive paste of the present invention, the terminating agent is a terminating agent that is liquid at 25°C and has a hydroxyl group, or a terminating agent that is solid at 25°C and has a weight increase rate of 0.2% by weight or more when the terminating agent is placed at 25°C and 50% RH for 24 hours. Since the conductive paste of the present invention has the above-mentioned structure, it can improve screen printing properties, maintain viscosity, and efficiently arrange solder particles on the electrode.

The following is a detailed description of the present invention.

(Conductive paste) The conductive paste of the present invention comprises a thermosetting component, a plurality of solder particles, a flux, and a thiotropy agent. In the conductive paste of the present invention, the average particle size of the solder particles is 5.0 μm or less. In the conductive paste of the present invention, the flux is solid at 25°C. In the conductive paste of the present invention, the thiotropy agent is (A) a thiotropy agent that is liquid at 25°C and has a hydroxyl group, or (B) a thiotropy agent that is solid at 25°C and has the following weight increase rate of 0.2% by weight or more when the thiotropy agent is placed at 25°C and 50% RH for 24 hours.

Weight increase rate (weight %) = (W2-W1) × 100/W1 W1: The weight of the above-mentioned activator before placement W2: The weight of the above-mentioned activator after placement

Since the conductive paste of the present invention has the above-mentioned structure, it can improve screen printing performance, maintain viscosity, and efficiently arrange solder particles on the electrode.

Furthermore, in the conductive paste of the present invention, when the electrodes are electrically connected, a plurality of solder particles are easily gathered between the upper and lower electrodes facing each other, and a plurality of solder particles can be arranged on the electrode (pipeline). Furthermore, a part of the plurality of solder particles is not easily arranged between the lateral electrodes that should not be connected, and the amount of solder particles arranged between the lateral electrodes that should not be connected can be made very small. As a result, in the present invention, the conduction reliability between the upper and lower electrodes that should be connected can be effectively improved, and the insulation reliability between the adjacent lateral electrodes that should not be connected can be effectively improved.

Furthermore, in the present invention, the positional deviation between electrodes can be prevented. In the present invention, when the second connection target component is overlapped on the first connection target component with the conductive paste disposed on the upper surface, even if the alignment between the electrode of the first connection target component and the electrode of the second connection target component is deviated, the deviation can be corrected and the electrodes can be connected to each other (automatic alignment effect).

From the viewpoint of more efficiently disposing solder particles on the electrode, the viscosity (η25) of the conductive paste at 25°C is preferably 30 Pa·s or more, more preferably 50 Pa·s or more, and preferably 250 Pa·s or less, more preferably 200 Pa·s or less. The viscosity (η25) can be appropriately adjusted according to the type and amount of the formulated components.

The viscosity (η25) can be measured, for example, using an E-type viscometer at 25° C. and 5 rpm. Examples of the E-type viscometer include “TVE22L” manufactured by Toki Sangyo Co., Ltd.

The conductive paste is preferably an anisotropic conductive paste. The conductive paste is suitable for electrical connection of electrodes. The conductive paste is preferably a circuit connection paste.

The use environment of the conductive paste is not particularly limited. The conductive paste can be used in an environment of 25°C and 50%RH, and can also be used in other environments.

Hereinafter, each component contained in the above conductive paste will be described. In addition, in this specification, "(meth)acrylic acid" means one or both of "acrylic acid" and "methacrylic acid".

(Thermosetting component) The conductive paste of the present invention contains a thermosetting component. The conductive paste preferably contains a thermosetting compound as the thermosetting component. The conductive paste may contain a thermosetting agent or may not contain a thermosetting agent. The conductive paste may contain a thermosetting compound and a thermosetting agent as the thermosetting component. When the conductive paste contains a thermosetting compound and a thermosetting agent, the conductive paste can be cured more effectively.

(Thermosetting component: thermosetting compound) The thermosetting compound is not particularly limited. Examples of the thermosetting compound include cyclohexane compounds, epoxy compounds, epoxy sulfide compounds, (meth) acrylic compounds, phenolic compounds, amino compounds, unsaturated polyester compounds, polyurethane compounds, polysiloxane compounds, and polyimide compounds. From the viewpoint of making the curability and viscosity of the conductive paste better, further improving the conduction reliability, and further improving the insulation reliability, the thermosetting compound is preferably an epoxy compound or an epoxy sulfide compound, and more preferably an epoxy compound. From the viewpoint of making the curability and viscosity of the conductive paste better, further improving the conduction reliability, and further improving the insulation reliability, the thermosetting compound preferably includes an epoxy compound. The above-mentioned thermosetting compounds 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 epoxy compounds, bisphenol F epoxy compounds, bisphenol S epoxy compounds, phenol novolac epoxy compounds, biphenyl epoxy compounds, biphenyl novolac epoxy compounds, biphenol epoxy compounds, naphthalene epoxy compounds, fluorene epoxy compounds, phenol aralkyl epoxy compounds, naphthol aralkyl epoxy compounds, dicyclopentadiene epoxy compounds, anthracene epoxy compounds, epoxy compounds having an adamantane skeleton, epoxy compounds having a tricyclodecane skeleton, naphthyl ether epoxy compounds, and epoxy compounds having a trioxane nucleus in the skeleton. The above epoxy compounds may be used alone or in combination of two or more.

The epoxy compound is liquid or solid at room temperature (25°C). When the epoxy compound is solid at room temperature, the melting temperature of the epoxy compound is preferably below the melting point of the solder particles. By using the preferred epoxy compound, the viscosity is higher at the stage of bonding the connecting components, and when acceleration is applied due to impact such as transportation, the positional displacement of the first connecting component and the second connecting component can be suppressed. Furthermore, the heat during curing can greatly reduce the viscosity of the conductive paste, and the solder particles can be efficiently condensed.

From the viewpoint of improving connection reliability, the epoxy compound preferably includes a phenolic novolac type epoxy compound or a bisphenol F type epoxy compound.

In 100 wt % of the conductive paste, the content of the thermosetting component is preferably 10 wt % or more, more preferably 15 wt % or more, further preferably 20 wt % or more, and preferably 90 wt % or less, more preferably 85 wt % or less, further preferably 80 wt % or less, and particularly preferably 75 wt % or less. If the content of the thermosetting component is above the lower limit and below the upper limit, the solder particles can be more efficiently arranged on the electrode, the insulation reliability between the electrodes can be further improved, and the conduction reliability between the electrodes can be further improved. From the viewpoint of effectively improving the impact resistance, it is preferred that the content of the thermosetting component is larger.

In 100 wt % of the conductive paste, the content of the thermosetting compound is preferably 5 wt % or more, more preferably 10 wt % or more, further preferably 15 wt % or more, and preferably 90 wt % or less, more preferably 85 wt % or less, further preferably 80 wt % or less, and particularly preferably 75 wt % or less. If the content of the thermosetting compound is above the lower limit and below the upper limit, the solder particles can be more efficiently arranged on the electrode, the insulation reliability between the electrodes can be further improved, and the conduction reliability between the electrodes can be further improved. From the viewpoint of effectively improving the impact resistance, it is preferred that the content of the thermosetting compound is larger.

In 100 wt % of the conductive paste, the content of the epoxy compound is preferably 5 wt % or more, more preferably 10 wt % or more, further preferably 15 wt % or more, and preferably 90 wt % or less, more preferably 85 wt % or less, further preferably 80 wt % or less, and particularly preferably 75 wt % or less. If the content of the epoxy compound is above the lower limit and below the upper limit, the solder particles can be more efficiently arranged on the electrode, the insulation reliability between the electrodes can be further improved, and the conduction reliability between the electrodes can be further improved. From the viewpoint of effectively improving the impact resistance, it is preferred that the content of the epoxy compound is larger.

(Thermosetting component: thermosetting agent) The thermosetting agent is not particularly limited. The thermosetting agent is used to thermoset the thermosetting compound. Examples of the thermosetting 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 free radical generator. The thermosetting agent may be used alone or in combination of two or more.

From the viewpoint of enabling the conductive paste to cure more quickly at low temperatures, the above-mentioned thermosetting agent is preferably an imidazole curing agent, a thiol curing agent, or an amine curing agent. Furthermore, from the viewpoint of improving the storage stability when the above-mentioned thermosetting compound is mixed with the above-mentioned thermosetting agent, the above-mentioned thermosetting 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. Furthermore, the above-mentioned thermosetting agent may be coated with a polymer 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-symmetric trisinium, and 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-symmetric trisinium isocyanuric acid adduct, 2-phenyl-4,5-dihydroxymethylimidazole, 2-phenyl- imidazole compounds in which the hydrogen at the 5-position of 1H-imidazole is substituted with a hydroxymethyl group and the hydrogen at the 2-position is substituted with a phenyl group or a toluyl group, such as 4-methyl-5-hydroxymethylimidazole, 2-phenyl-4-benzyl-5-hydroxymethylimidazole, 2-p-toluoyl-4-methyl-5-hydroxymethylimidazole, 2-m-toluoyl-4,5-dihydroxymethylimidazole and 2-p-toluoyl-4,5-dihydroxymethylimidazole.

The thiol curing agent is not particularly limited. Examples of the thiol curing agent include trihydroxymethylpropane tri-3-butyl propionate, pentaerythritol tetra-3-butyl propionate, and dipentaerythritol hexa-3-butyl propionate.

The amine curing agent is not particularly limited, and 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 hardener is not particularly limited. As the acid anhydride hardener, an acid anhydride used as a hardener for thermosetting compounds such as epoxy compounds can be widely used. Examples of the acid anhydride hardener include phthalic anhydride, tetrahydrophthalic anhydride, trialkyltetrahydrophthalic anhydride, hexahydrophthalic anhydride, methylhexahydrophthalic anhydride, methyltetrahydrophthalic anhydride, methylbutyltetrahydrophthalic anhydride, anhydride of phthalic acid derivatives, maleic anhydride, nalidic anhydride, methylnalidic anhydride, and methylnalidic anhydride. Bifunctional acid anhydride hardeners such as ethylene glycol ditrimellitic anhydride, succinic anhydride, glycerol ditrimellitic anhydride monoacetate, and ethylene glycol ditrimellitic anhydride, trifunctional acid anhydride hardeners such as trimellitic anhydride, and tetrafunctional or higher acid anhydride hardeners such as pyromellitic dianhydride, benzophenone tetracarboxylic dianhydride, methylcyclohexene tetracarboxylic dianhydride, and polyazelaic anhydride.

The above-mentioned thermal cationic initiator is not particularly limited. Examples of the above-mentioned thermal cationic initiator include iodine-based cationic curing agents, oxonium-based cationic curing agents, and cobalt-based cationic curing agents. Examples of the above-mentioned iodine-based cationic curing agents include bis(4-tert-butylphenyl)iodine hexafluorophosphate. Examples of the above-mentioned oxonium-based cationic curing agents include trimethyloxonium tetrafluoroborate. Examples of the above-mentioned cobalt-based cationic curing agents include tri-p-tolylcobaltium 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 compound include azobisisobutyronitrile (AIBN). Examples of the organic peroxide include di-tert-butyl peroxide and methyl ethyl ketone peroxide.

The reaction starting temperature of the thermosetting agent is preferably 50°C or higher, more preferably 60°C or higher, further preferably 70°C or higher, and preferably 250°C or lower, more preferably 200°C or lower, further preferably 175°C or lower, and particularly preferably 150°C or lower. If the reaction starting temperature of the thermosetting agent is above the lower limit and below the upper limit, the solder particles can be more efficiently arranged on the electrode. The reaction starting temperature of the thermosetting agent is particularly preferably 70°C or higher and 150°C or lower.

The reaction initiation temperature of the above-mentioned thermosetting agent means the rising start temperature of the exothermic peak in differential scanning calorimetry (DSC).

The content of the thermosetting agent is not particularly limited. The content of the thermosetting 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 further preferably 75 parts by weight or less, relative to 100 parts by weight of the thermosetting compound. If the content of the thermosetting agent is above the lower limit, it is easy to fully cure the conductive paste. If the content of the thermosetting agent is below the upper limit, the residual thermosetting agent that does not participate in the curing is unlikely to remain after curing, and the heat resistance of the cured product becomes higher.

(Solder particles) The above-mentioned solder particles are particles whose central part and outer surface are both made of solder. The above-mentioned solder particles are particles whose central part and outer surface are both made of solder. When a conductive particle having a base particle formed of a material other than solder and a solder portion arranged on the surface of the base particle is used instead of the above-mentioned solder particles, the conductive particles are difficult to gather on the electrode. In addition, among the above-mentioned conductive particles, since the solderability between the conductive particles is relatively low, there is a tendency for the conductive particles that have moved to the electrode to easily move outside the electrode, and there is a tendency for the effect of suppressing the positional deviation between the electrodes to become low.

The average particle size of the solder particles is 5.0 μm or less. The average particle size of the solder particles is preferably 0.1 μm or more, more preferably 0.5 μm or more, further preferably 1.0 μm or more, and preferably 4.9 μm or less, more preferably 4.5 μm or less, further preferably 4.0 μm or less. If the average particle size of the solder particles is above the lower limit and below the upper limit, the solder particles can be more efficiently arranged on the electrode. If the average particle size of the solder particles is below the upper limit, the screen printing property on a micro-spaced substrate can be further improved. In the conductive paste of the present invention, the smaller the average particle size of the solder particles is, the more effectively the above-mentioned effect of the present invention can be exerted. That is, in the conductive paste of the present invention, the smaller the average particle size of the solder particles, the more efficiently the solder particles can be arranged on the electrodes, the more effectively the conduction reliability between the upper and lower electrodes to be connected can be improved, and the more effectively the insulation reliability between adjacent lateral electrodes that should not be connected can be improved.

The average particle size of the solder particles is preferably a number average particle size. The average particle size of the solder particles can be obtained, for example, by observing 50 random solder particles using an electron microscope or an optical microscope and calculating the average particle size of each solder particle; or by performing laser diffraction particle size distribution measurement. In the observation using an electron microscope or an optical microscope, the particle size of each solder particle is obtained in the form of a particle size measured by a circle equivalent diameter. In the observation using an electron microscope or an optical microscope, the average particle size of 50 random solder particles measured by a circle equivalent diameter is approximately equal to the average particle size measured by an equivalent spherical diameter. In laser diffraction particle size distribution measurement, the particle size of each solder particle is obtained as a particle size measured by an equivalent spherical diameter. The average particle size of the solder particles is preferably calculated by laser diffraction particle size distribution measurement.

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

The above-mentioned coefficient of variation (CV value) can be measured as follows.

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

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

From the viewpoint of more efficiently arranging the solder particles on the electrode, the specific gravity of the solder particles is preferably 4 or more, more preferably 5 or more, and further preferably 6 or more.

The specific gravity of the solder particles can be determined, for example, by using "AccuPyc II 1340" manufactured by Shimadzu Corporation.

The above solder is preferably a metal having a melting point of 450°C or less (low melting point metal). The above solder particles are preferably metal particles having a melting point of 450°C or less (low melting point metal particles). The above low melting point metal particles are particles containing low melting point metal. The low melting point metal means a metal having a melting point of 450°C or less. The melting point of the low melting point metal is preferably 300°C or less, more preferably 260°C or less. The above solder is preferably a low melting point solder having a melting point of less than 250°C.

From the viewpoint of further improving connection reliability, the melting point of the solder particles is preferably 100°C or higher, more preferably 150°C or higher, further preferably 200°C or higher, and is preferably 400°C or lower, more preferably 350°C or lower, further preferably 300°C or lower.

The melting point of the solder particles can be determined by differential scanning calorimetry (DSC). Examples of the differential scanning calorimetry (DSC) apparatus include "EXSTAR DSC7020" manufactured by SII Corporation.

Furthermore, the solder particles preferably contain tin. The content of tin in 100 wt% of the metal contained in the solder particles is preferably 30 wt% or more, more preferably 40 wt% or more, further preferably 70 wt% or more, and particularly preferably 90 wt% or more. If the content of tin in the solder particles is above the lower limit, the conduction reliability and connection reliability between the solder portion and the electrode become higher.

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

By using the above solder particles, the solder melts and joins with the electrode, and the solder portion makes the electrodes conductive. For example, the solder portion and the electrode are easily in surface contact rather than point contact, so the connection resistance becomes lower. In addition, by using the above solder particles, the bonding strength between the solder portion and the electrode becomes higher, and as a result, the solder portion and the electrode are less likely to be separated, and the conduction reliability and connection reliability become higher.

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 the alloy include tin-silver alloy, tin-copper alloy, tin-silver-copper alloy, tin-bismuth alloy, tin-zinc alloy, tin-indium alloy, and tin-antimony alloy. In terms of excellent wettability to the electrode, the low melting point metal is preferably tin, tin-silver alloy, tin-silver-copper alloy, tin-bismuth alloy, tin-indium alloy, or tin-antimony alloy, and more preferably tin-silver-copper alloy, tin-bismuth alloy, tin-indium alloy, or tin-antimony alloy.

The solder particles are preferably filler materials with a liquidus of 450°C or less based on JIS Z3001: Soldering Terminology. Examples of the composition of the solder particles include metal compositions including zinc, gold, silver, lead, copper, tin, bismuth, and indium. Preferably, the solder particles are low-melting-point, lead-free tin-indium system (117°C eutectic) or tin-bismuth system (139°C eutectic). That is, the solder particles preferably do not contain lead, preferably contain tin and indium, or contain tin and bismuth.

In order to further improve the bonding strength between the solder portion and the electrode, the solder particles may also contain metals such as nickel, copper, antimony, aluminum, zinc, iron, gold, titanium, phosphorus, germanium, tellurium, cobalt, bismuth, manganese, chromium, molybdenum, and palladium. In addition, from the perspective of further improving the bonding strength between the solder portion and the electrode, the solder particles preferably contain nickel, copper, antimony, aluminum, or zinc. From the perspective of further improving the bonding strength between the solder portion and the electrode, the content of the metals used to improve the bonding strength is preferably 0.0001% by weight or more and preferably 1% by weight or less in 100% by weight of the metals contained in the solder particles.

In the above-mentioned conductive paste 100 weight %, the content of the above-mentioned solder particles is preferably 50 weight % or more, more preferably 55 weight % or more, further preferably 60 weight % or more, particularly preferably 65 weight % or more, and most preferably 70 weight % or more. In the above-mentioned conductive paste 100 weight %, the content of the above-mentioned solder particles is preferably 90 weight % or less, more preferably 85 weight % or less, further preferably 80 weight % or less, and particularly preferably 75 weight % or less. If the content of the above-mentioned solder particles is above the above-mentioned lower limit and below the above-mentioned upper limit, the solder particles can be more efficiently arranged on the electrode, and it is easy to arrange more solder between the electrodes, and the conduction reliability becomes higher. From the viewpoint of further improving the conduction reliability, it is better to have a larger content of the above-mentioned solder particles.

(Flux) The conductive paste of the present invention contains flux. The flux is solid at 25°C. Specifically, the flux (flux alone) is solid at 25°C when not mixed with the thermosetting component, the plurality of solder particles, and the tactile agent.

In the conductive paste, the flux is preferably solid at 25° C. In the conductive paste, the flux is preferably solid at 25° C.

Furthermore, whether the above-mentioned flux (flux alone) is solid at 25°C can be judged as follows. In this specification, for a flux that is not liquid at 25°C, a flux that maintains its shape when left alone at 25°C and 50% RH for 5 minutes is defined as a flux that is solid at 25°C. Moreover, a flux that does not maintain its shape when left alone at 25°C and 50% RH for 5 minutes is defined as a flux that is semi-solid at 25°C. Moreover, a flux that is semi-solid at 25°C is not included in a flux that is solid at 25°C.

Furthermore, whether the above-mentioned flux is solid in the conductive paste at 25°C can be judged as follows. In this specification, for a flux that is not liquid at 25°C, a flux that maintains its shape when the conductive paste containing the flux is left at 25°C and 50% RH for 5 minutes is defined as a flux that is solid at 25°C. Moreover, a flux that does not maintain its shape when the conductive paste containing the flux is left at 25°C and 50% RH for 5 minutes is defined as a flux that is semi-solid at 25°C. Moreover, a flux that is semi-solid at 25°C is not included in a flux that is solid at 25°C.

Examples of the flux include zinc chloride, a mixture of zinc chloride and an inorganic halide, a mixture of zinc chloride and an inorganic acid, molten salts, organic phosphorus compounds, organic halides, hydrazine, amine compounds, organic acids, salts of organic acids, and rosin. The flux may be used alone or in combination of two or more.

Examples of the molten salt include ammonium chloride and the like.

Examples of the organic phosphorus compound include organic phosphonium salts, organic phosphoric acids, organic phosphoric acid esters, organic phosphonic acids, organic phosphonic acid esters, organic phosphinic acids, and organic phosphinic acid esters.

Examples of the amine compound include cyclohexylamine, dicyclohexylamine, benzylamine, dibenzhydrylamine, imidazole, benzimidazole, phenylimidazole, carboxybenzimidazole, benzotriazole, and carboxybenzotriazole.

The above-mentioned rosin is a rosin type having abietic acid as a main component. Examples of the above-mentioned rosin type include abietic acid and acrylic acid-modified rosin.

As the salt of the organic acid, there can be exemplified a neutralization product (salt) of an organic acid and an alkaline compound. The salt of the organic acid is preferably a salt produced by a neutralization reaction of an organic acid and an alkaline compound. The conditions for the neutralization reaction are preferably a heating temperature of 25°C to 150°C and a heating time of 5 minutes to 30 minutes. The organic acid is preferably effective in cleaning the surface of metal, and the alkaline compound is preferably effective in neutralizing the organic acid.

The organic acid is preferably an organic compound (carboxylic acid) having a carboxyl group. Examples of the organic acid include aliphatic carboxylic acids, alicyclic carboxylic acids, and aromatic carboxylic acids. Examples of the aliphatic carboxylic acids include malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, citric acid, and apple acid. Examples of the alicyclic carboxylic acids include cyclohexylcarboxylic acid and 1,4-cyclohexyldicarboxylic acid. Examples of the aromatic carboxylic acids include isophthalic acid, terephthalic acid, trimellitic acid, and ethylenediaminetetraacetic acid. From the viewpoint of more efficiently disposing solder particles on the electrode, improving insulation reliability, and more effectively improving conduction reliability, the organic acid is preferably glutaric acid, cyclohexylcarboxylic acid, or adipic acid.

The alkali compound is preferably an organic compound having an amino group (amine compound). Examples of the alkali compound include diethanolamine, triethanolamine, methyldiethanolamine, ethyldiethanolamine, cyclohexylamine, dicyclohexylamine, benzylamine, dibenzhydrylamine, 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 perspective of more efficiently arranging solder particles on the electrode, improving insulation reliability, and more effectively improving conduction reliability, the alkali compound is preferably benzylamine.

Examples of the salt of the organic acid include benzylamine adipate, benzylamine glutarate, and cyclohexylamine succinate.

From the viewpoint of more effectively maintaining the adhesiveness and more efficiently disposing the solder particles on the electrode, the flux is preferably a salt of an organic acid, and more preferably benzylamine adipate.

The above-mentioned flux can be dispersed in the conductive paste or attached to the surface of the solder particles.

The shape of the flux is not particularly limited. The flux may be spherical, or may be in a shape other than a spherical shape, or may be flat. From the perspective of further improving screen printing properties, the flux is preferably spherical.

The particle size of the flux is preferably 0.1 μm or more, more preferably 0.5 μm or more, further preferably 1.0 μm or more, and is preferably 30 μm or less, more preferably 25 μm or less, further preferably 20 μm or less.

The particle size of the flux is preferably an average particle size, and more preferably a number average particle size. The average particle size of the flux is obtained, for example, by observing 50 random fluxes with an electron microscope or an optical microscope and calculating the average particle size of each flux; or by laser diffraction particle size distribution measurement. In the observation with an electron microscope or an optical microscope, the particle size of each flux is obtained in the form of a particle size measured by a circle equivalent diameter. In the observation with an electron microscope or an optical microscope, the average particle size measured by a circle equivalent diameter of 50 random fluxes is approximately equal to the average particle size measured by an equivalent spherical diameter. In the laser diffraction particle size distribution measurement, the particle size of each flux is obtained in the form of a particle size measured by an equivalent spherical diameter. The average particle size of the flux is preferably calculated by the laser diffraction particle size distribution measurement.

The ratio of the average particle size of the flux to the average particle size of the solder particles (average particle size of the flux/average particle size of the solder particles) is preferably 0.01 or more, more preferably 0.1 or more, further preferably 0.2 or more, and is preferably 15.0 or less, more preferably 10.0 or less, further preferably 5.0 or less. If the ratio (average particle size of the flux/average particle size of the solder particles) is above the lower limit and below the upper limit, the flux and the solder particles can be effectively contacted, and the performance of the flux during heating can be further improved.

From the viewpoint of more effectively exerting the effect of the present invention, the flux is preferably non-water-absorbent and preferably non-hygroscopic.

When the above-mentioned flux is placed at 25°C and 50%RH for 24 hours, the weight of the above-mentioned flux may increase, decrease, or remain unchanged. When the above-mentioned flux is placed at 25°C and 50%RH for 24 hours, the weight of the above-mentioned flux after placement may be greater than the weight of the above-mentioned flux before placement, or may be less than the weight of the above-mentioned flux before placement. When the above-mentioned flux is placed at 25°C and 50%RH for 24 hours, the weight of the above-mentioned flux after placement may be the same as the weight of the above-mentioned flux before placement.

From the viewpoint of more effectively exerting the effect of the present invention, the weight change rate F of the above-mentioned flux when placed at 25°C and 50% RH for 24 hours is preferably less than 1% by weight, more preferably 0.9% by weight or less, and further preferably 0.5% by weight or less. The above-mentioned weight change rate F may be 0% by weight or more, or 0.1% by weight or more. From the viewpoint of more effectively exerting the effect of the present invention, the above-mentioned weight change rate F is preferably 0% by weight (no weight change before and after placement).

Weight change rate F (weight %) = |W4-W3|×100/W3 W3: Weight of the above flux before placement W4: Weight of the above flux after placement

The weight change rate F of the above flux can be measured by the following method. Take out 10 g of flux (W3) from a desiccator at 25°C and 0% RH, place it at 25°C and 50% RH for 24 hours, and measure the weight of the flux after placement (W4). Calculate the weight change rate F based on W3 and W4.

The melting point (activation temperature) of the flux is preferably 50° C. or higher, more preferably 80° C. or higher, further preferably 100° C. or higher, and preferably 300° C. or lower, more preferably 250° C. or lower, further preferably 200° C. or lower. If the melting point of the flux is above the lower limit and below the upper limit, the solder particles can be more efficiently arranged on the electrode.

The melting point of the flux can be determined by differential scanning calorimetry (DSC). Examples of differential scanning calorimetry (DSC) devices include "EXSTAR DSC7020" manufactured by SII Corporation.

In 100 wt % of the conductive paste, the content of the flux is preferably 1 wt % or more, more preferably 5 wt % or more, and preferably 30 wt % or less, more preferably 25 wt % or less. If the content of the flux is above the lower limit and below the upper limit, it is more difficult to form an oxide film on the surface of the solder particles and the electrode, and the oxide film formed on the surface of the solder particles and the electrode can be removed more effectively.

The content of the flux is preferably 1 part by weight or more, more preferably 5 parts by weight or more, and preferably 30 parts by weight or less, more preferably 25 parts by weight or less, relative to 100 parts by weight of the thermosetting component. If the content of the flux is above the lower limit and below the upper limit, it is more difficult to form an oxide film on the surface of the solder particles and the electrode, and the oxide film formed on the surface of the solder particles and the electrode can be removed more effectively.

The content of the flux is preferably 1 part by weight or more, more preferably 5 parts by weight or more, and preferably 30 parts by weight or less, more preferably 25 parts by weight or less, relative to 100 parts by weight of the solder particles. If the content of the flux is above the lower limit and below the upper limit, it is more difficult to form an oxide film on the surface of the solder particles and the electrode, and the oxide film formed on the surface of the solder particles and the electrode can be removed more effectively.

(Tactotropic agent) The conductive paste of the present invention contains a tactotropic agent. The tactotropic agent is (A) a liquid tactotropic agent at 25°C and having a hydroxyl group, or (B) a solid tactotropic agent at 25°C and having the following weight increase rate of 0.2% by weight or more when the tactotropic agent is placed at 25°C and 50% RH for 24 hours.

Weight increase rate (weight %) = (W2-W1) × 100/W1 W1: The weight of the above-mentioned activator before placement W2: The weight of the above-mentioned activator after placement

The thiotropy agent may be (A) a thiotropy agent that is liquid at 25°C and has a hydroxyl group (hereinafter, sometimes referred to as "thiotropy agent A"). Alternatively, the thiotropy agent may be (B) a thiotropy agent that is solid at 25°C and has the above-mentioned weight gain rate of 0.2 wt% or more (hereinafter, sometimes referred to as "thiotropy agent B"). The thiotropy agent is the thiotropy agent A or the thiotropy agent B.

In the conductive paste, since the above-mentioned switching agent is the above-mentioned switching agent A or the above-mentioned switching agent B, the performance of the flux can be well assisted, and the solder particles can be more efficiently arranged on the electrode.

In 100 wt % of the conductive paste, the content of the above-mentioned activator is preferably 0.005 wt % or more, more preferably 0.01 wt % or more, further preferably 0.05 wt % or more, and preferably 2 wt % or less, more preferably 1 wt % or less, further preferably 0.5 wt % or less. If the content of the above-mentioned activator is above the above lower limit and below the above upper limit, the performance of the flux can be well assisted, and the solder particles can be more efficiently arranged on the electrode.

The content of the above-mentioned switching agent is preferably 0.003 parts by weight or more, more preferably 0.005 parts by weight or more, and further preferably 0.01 parts by weight or more, and is preferably 2 parts by weight or less, more preferably 1 part by weight or less, and further preferably 0.7 parts by weight or less, relative to 100 parts by weight of the above-mentioned solder particles. If the content of the above-mentioned switching agent is above the above-mentioned lower limit and below the above-mentioned upper limit, the performance of the flux can be well assisted, and the solder particles can be more efficiently arranged on the electrode.

The content of the above-mentioned switching agent is preferably 0.1 parts by weight or more, more preferably 0.3 parts by weight or more, and preferably 5 parts by weight or less, more preferably 3 parts by weight or less, relative to 100 parts by weight of the above-mentioned thermosetting component. If the content of the above-mentioned switching agent is above the above-mentioned lower limit and below the above-mentioned upper limit, the performance of the flux can be well assisted, and the solder particles can be more efficiently arranged on the electrode.

The content of the above-mentioned switching agent is preferably 0.1 parts by weight or more, more preferably 0.3 parts by weight or more, and preferably 5 parts by weight or less, more preferably 3 parts by weight or less, relative to 100 parts by weight of the above-mentioned thermosetting compound. If the content of the above-mentioned switching agent is above the above-mentioned lower limit and below the above-mentioned upper limit, the performance of the flux can be well assisted, and the solder particles can be more efficiently arranged on the electrode.

[Trigger A] The above-mentioned trigger A is liquid at 25°C and has a hydroxyl group (-OH group).

The above-mentioned activator A is liquid at 25° C. Specifically, the above-mentioned activator A (activator A alone) is liquid at 25° C. in a state where it is not mixed with the above-mentioned thermosetting component, the plurality of solder particles, and the flux.

In the conductive paste, the activating agent A is preferably in a liquid state at 25° C. In the conductive paste, the activating agent A is preferably in a liquid state at 25° C.

The above-mentioned activator A has at least one hydroxyl group. The above-mentioned activator A may have one hydroxyl group, or may have two, or may have more than two, or may have three, or may have more than three, or may have more than four. The above-mentioned activator A may be a monohydric alcohol or a polyhydric alcohol. The above-mentioned activator A may be a dihydric alcohol, or may be a trihydric alcohol, or may be a tetrahydric alcohol. From the viewpoint of preventing the volatility of the conductive paste and further improving the screen printability, the above-mentioned activator A preferably has two or more hydroxyl groups, and more preferably has three or more. From the viewpoint of preventing the volatility of the conductive paste and further improving the screen printability, the above-mentioned activator A is preferably a polyvalent alcohol compound (polyvalent alcohol). The above-mentioned activator A may have 10 or less hydroxyl groups, or may have 7 or less hydroxyl groups.

Examples of the activator having one hydroxyl group in the activator A include methanol, ethanol, propanol, and N-oleylsarcosine.

Examples of the activator having two hydroxyl groups in the activator A include propylene glycol, propanediol, and diethylene glycol.

Examples of the activator having three hydroxyl groups in the activator A include glycerol, trihydroxymethylpropane, and 1,2,4-butanetriol.

Examples of the activator having four or more hydroxyl groups in the activator A include diglycerol and polyglycerol.

From the viewpoint of preventing the volatilization of the conductive paste and further improving the screen printing property, the above-mentioned activator A is preferably glycerol, N-oleyl sarcosine, or 1,2,4-butanetriol, and more preferably glycerol.

From the viewpoint of more effectively maintaining viscosity, the boiling point of the above-mentioned activator A is preferably 80°C or higher, more preferably 100°C or higher, further preferably 150°C or higher, particularly preferably 200°C or higher, and preferably 450°C or lower, further preferably 400°C or lower, further preferably 350°C or lower. From the viewpoint of preventing volatility of the conductive paste and further improving screen printability, the above-mentioned activator A is preferably (A1) a activator that is liquid at 25°C, has a hydroxyl group, and has a boiling point of 80°C or higher.

In 100 wt % of the conductive paste, the content of the activator A is preferably 0.001 wt % or more, more preferably 0.005 wt % or more, and more preferably 0.05 wt % or more, and preferably 2 wt % or less, more preferably 1 wt % or less, and more preferably 0.5 wt % or less. If the content of the activator A is above the lower limit and below the upper limit, the flux performance can be well assisted, and the solder particles can be more efficiently arranged on the electrode.

The content of the above-mentioned activator A is preferably 0.003 parts by weight or more, more preferably 0.005 parts by weight or more, and further preferably 0.01 parts by weight or more, and is preferably 2 parts by weight or less, more preferably 1 part by weight or less, and further preferably 0.7 parts by weight or less, relative to 100 parts by weight of the above-mentioned solder particles. If the content of the above-mentioned activator A is above the above-mentioned lower limit and below the above-mentioned upper limit, the performance of the flux can be well assisted, and the solder particles can be more efficiently arranged on the electrode.

[Tactotropic agent B] The above-mentioned tactotropic agent B is solid at 25°C, and the following weight increase rate when the above-mentioned tactotropic agent is placed at 25°C and 50%RH for 24 hours is 0.2% by weight or more.

Weight increase rate (weight %) = (W2-W1) × 100/W1 W1: The weight of the above-mentioned activator before placement W2: The weight of the above-mentioned activator after placement

The above-mentioned activator B is solid at 25° C. Specifically, the above-mentioned activator B (activator B alone) is solid at 25° C. in a state where it is not mixed with the above-mentioned thermosetting component, the plurality of solder particles, and the flux.

In the conductive paste, the activator B is preferably solid at 25°C. In the conductive paste, the activator B is preferably solid at 25°C.

Furthermore, whether the above-mentioned thiotropy agent B (thiotropy agent B alone) is solid at 25°C can be judged as follows. In this specification, for thiotropy agent B that is not liquid at 25°C, thiotropy agent B that keeps its shape when left alone at 25°C and 50% RH for 5 minutes is defined as thiotropy agent B that is solid at 25°C. Moreover, thiotropy agent B that does not keep its shape when left alone at 25°C and 50% RH for 5 minutes is defined as thiotropy agent B that is semi-solid at 25°C. Furthermore, the semisolid thiotropy agent B at 25°C is not included in the solid thiotropy agent B at 25°C.

Furthermore, whether the above-mentioned tactile agent B is solid in the conductive paste at 25°C can be judged as follows. In this specification, for tactile agent B that is not liquid at 25°C, tactile agent B that maintains its shape when the conductive paste containing tactile agent B is left at 25°C and 50% RH for 5 minutes is defined as tactile agent B that is solid at 25°C. Moreover, tactile agent B that does not maintain its shape when the conductive paste containing tactile agent B is left at 25°C and 50% RH for 5 minutes is defined as tactile agent B that is semi-solid at 25°C. Furthermore, tactile agent B that is semi-solid at 25°C is not included in tactile agent B that is solid at 25°C.

The weight of the above-mentioned activator B increases when placed at 25°C and 50%RH for 24 hours. When the above-mentioned activator B is placed at 25°C and 50%RH for 24 hours, the weight of the above-mentioned activator B after placement is greater than the weight of the above-mentioned activator B before placement.

From the viewpoint of assisting the fluxing agent performance well and more efficiently arranging the solder particles on the electrode, the above-mentioned switching agent B is preferably water-absorbent or hygroscopic, and more preferably hygroscopic. From the viewpoint of assisting the fluxing agent performance well and more efficiently arranging the solder particles on the electrode, the above-mentioned switching agent B is further preferably hygroscopic at 25°C and 50%RH.

The weight gain rate of the above-mentioned activator B is 0.2 wt% or more. The above-mentioned weight gain rate of the above-mentioned activator B is preferably 0.3 wt% or more, more preferably 0.5 wt% or more, and further preferably 1 wt% or more, and preferably less than 10 wt%, more preferably less than 8 wt%, and further preferably less than 5 wt%. If the weight gain rate of the above-mentioned activator B is above the above-mentioned lower limit, the performance of the flux can be well assisted, and the solder particles can be more efficiently arranged on the electrode. If the weight gain rate of the above-mentioned activator B is below the above-mentioned upper limit or does not reach the above-mentioned upper limit, the screen printing property can be further improved. From the viewpoint of assisting the flux performance well and more efficiently arranging the solder particles on the electrode, the above-mentioned activator B is preferably a activator that is solid at 25° C. and has the above-mentioned weight increase rate of 1% by weight or more.

The weight increase rate of the above-mentioned activator B can be measured by the following method: Take out 10 g of activator B (W1) from a desiccator at 25°C and 0% RH, place it at 25°C and 50% RH for 24 hours, and measure the weight of activator B after placement (W2).

Examples of the above-mentioned activator B include boron trifluoride-monoethylamine complex, pentaerythritol, sorbitol, mannitol, sorbitan, dipentaerythritol, sucrose, glucose, mannose, fructose, and methyl glucoside.

From the viewpoint of more efficiently disposing the solder particles on the electrode, the above-mentioned switching agent B is preferably a boron trifluoride-monoethylamine complex or glucose, and more preferably a boron trifluoride-monoethylamine complex.

The shape of the above-mentioned activator B is not particularly limited. The above-mentioned activator B may be spherical, may be a shape other than spherical, may be flat, etc. From the viewpoint of further improving the screen printing property, the shape of the above-mentioned activator B is preferably spherical.

The particle size of the above-mentioned activator B is preferably 0.1 μm or more, more preferably 0.5 μm or more, further preferably 1 μm or more, and is preferably 30 μm or less, more preferably 25 μm or less, further preferably 20 μm or less.

The particle size of the above-mentioned activator B is preferably an average particle size, and more preferably a number average particle size. The average particle size of the above-mentioned activator B can be obtained, for example, by observing any 50 activators B using an electron microscope or an optical microscope and calculating the average value of the particle size of each activator B; or by performing laser diffraction particle size distribution measurement. In the observation using an electron microscope or an optical microscope, the particle size of each activator B is obtained in the form of a particle size measured by a circle equivalent diameter. In observation using an electron microscope or an optical microscope, the average particle size of any 50 tropomyosin B measured by equivalent spherical diameter is approximately equal to the average particle size measured by equivalent spherical diameter. In laser diffraction particle size distribution measurement, the particle size of each tropomyosin B is obtained as the particle size measured by equivalent spherical diameter. The above average particle size of tropomyosin B is preferably calculated by laser diffraction particle size distribution measurement.

The melting point (activation temperature) of the above-mentioned activator B is preferably 50° C. or higher, more preferably 60° C. or higher, further preferably 70° C. or higher, and preferably 140° C. or lower, more preferably 120° C. or lower, further preferably 100° C. or lower. If the melting point of the above-mentioned activator B is above the above lower limit and below the above upper limit, the solder particles can be more efficiently arranged on the electrode.

The melting point of the above-mentioned activator B can be determined by differential scanning calorimetry (DSC). Examples of differential scanning calorimetry (DSC) apparatus include "EXSTAR DSC7020" manufactured by SII Corporation.

From the perspective of more efficiently placing solder particles on the electrode, the melting point of the activator B is preferably lower than the melting point of the solder particles. From the perspective of more efficiently placing solder particles on the electrode, the melting point of the activator B is preferably lower by 5°C or more, and further preferably lower by 10°C or more.

In 100 wt % of the conductive paste, the content of the above-mentioned activator B is preferably 0.001 wt % or more, more preferably 0.005 wt % or more, and preferably 2 wt % or less, more preferably 1 wt % or less, and further preferably 0.5 wt % or less. If the content of the above-mentioned activator B is above the above lower limit and below the above upper limit, the performance of the flux can be well assisted, and the solder particles can be more efficiently arranged on the electrode.

The content of the above-mentioned activator B is preferably 0.005 parts by weight or more, more preferably 0.01 parts by weight or more, and preferably 2 parts by weight or less, more preferably 1 part by weight or less, and further preferably 0.7 parts by weight or less relative to 100 parts by weight of the above-mentioned solder particles. If the content of the above-mentioned activator B is above the above-mentioned lower limit and below the above-mentioned upper limit, the performance of the flux can be well assisted, and the solder particles can be more efficiently arranged on the electrode.

(Other ingredients) The conductive paste may also contain various additives such as fillers, extenders, softeners, plasticizers, levelers, polymerizing catalysts, hardening catalysts, colorants, antioxidants, heat stabilizers, light stabilizers, ultraviolet absorbers, lubricants, antistatic agents and flame retardants as needed.

(Connection structure) The connection structure of the present invention comprises: 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 portion connecting the first connection target member and the second connection target member. In the connection structure of the present invention, the material of the connection portion is the conductive paste. In the connection structure of the present invention, the first electrode and the second electrode are electrically connected via the solder portion in the connection portion.

The thickness of the solder portion 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.

The manufacturing method of the above-mentioned connection structure is not particularly limited. As an example of the manufacturing method of the connection structure, the following method can be cited: the above-mentioned conductive paste is arranged between the first connection target component and the second connection target component, and after obtaining the laminate, the laminate is heated. The above-mentioned heating temperature is preferably above 230°C, more preferably above 250°C, and preferably below 350°C, more preferably below 300°C. If the above-mentioned heating temperature is above the above-mentioned lower limit and below the above-mentioned upper limit, the conduction reliability and insulation reliability between the electrodes can be further improved. During the above-mentioned heating, pressurization may or may not be performed.

Hereinafter, specific implementations of the present invention will be described with reference to the drawings.

FIG. 1 is a cross-sectional view schematically showing a connection structure obtained by using a conductive paste according to an embodiment of the present invention.

The connection structure 1 shown in FIG1 has 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 by the above-mentioned conductive paste. In this embodiment, the above-mentioned conductive paste contains a thermosetting component, solder particles, a flux, and a thermosetting agent. The above-mentioned thermosetting component contains a thermosetting compound and a thermosetting agent. The above-mentioned thermosetting agent is the above-mentioned thermosetting agent A or the above-mentioned thermosetting agent B.

The connection portion 4 includes a solder portion 4A formed by a plurality of solder particles being aggregated and bonded to each other, and a cured portion 4B formed by thermally curing a thermosetting compound.

The first connection object component 2 has a plurality of first electrodes 2a on the surface (upper surface). The second connection object component 3 has a plurality of second electrodes 3a on the surface (lower surface). The first electrode 2a and the second electrode 3a are electrically connected via the solder portion 4A. Therefore, the first connection object component 2 and the second connection object component 3 are electrically connected via the solder portion 4A. Furthermore, in the connection portion 4, solder particles do not exist in a region (hardened portion 4B portion) different from the solder portion 4A gathered between the first electrode 2a and the second electrode 3a. Solder particles separated from the solder portion 4A do not exist in a region (hardened portion 4B portion) different from the solder portion 4A. Furthermore, if the amount is small, solder particles may also exist in a region (hardened material portion 4B portion) different from 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. After the plurality of solder particles are melted, the molten material of the solder particles wets and diffuses on the surface of the electrode and then solidifies to form a solder portion 4A. Therefore, the contact area between the solder portion 4A and the first electrode 2a, and between the solder portion 4A and the second electrode 3a becomes larger. That is, 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 becomes larger than when using conductive particles whose outer surface is a metal such as nickel, gold or copper. Thereby, the conduction reliability and connection reliability in the connection structure 1 are also improved. Furthermore, the above-mentioned flux generally becomes inactivated gradually due to heating.

In the connection structure 1, when the mutually opposing portions of the first electrode 2a and the second electrode 3a are observed in the stacking direction of the first electrode 2a, the connection portion 4, and the second electrode 3a, preferably, the solder portion 4A in the connection portion 4 is disposed at more than 50% of 100% of the area of the mutually opposing portions of the first electrode 2a and the second electrode 3a. By satisfying the above-mentioned preferred state, the conduction reliability can be further improved.

Preferably, when the mutually opposing portion of the first electrode and the second electrode is observed in the stacking direction of the first electrode, the connecting portion, and the second electrode, the solder portion in the connecting portion is disposed on 50% or more of 100% of the area of the mutually opposing portion of the first electrode and the second electrode. More preferably, when the mutually opposing portion of the first electrode and the second electrode is observed in the stacking direction of the first electrode, the connecting portion, and the second electrode, the solder portion in the connecting portion is disposed on 60% or more of 100% of the area of the mutually opposing portion of the first electrode and the second electrode. Furthermore, it is preferred that when the mutually opposing portions of the first electrode and the second electrode are observed in the stacking direction of the first electrode, the connecting portion, and the second electrode, the solder portion in the connecting portion is disposed at 70% or more of 100% of the area of the mutually opposing portions of the first electrode and the second electrode. It is particularly preferred that when the mutually opposing portions of the first electrode and the second electrode are observed in the stacking direction of the first electrode, the connecting portion, and the second electrode, the solder portion in the connecting portion is disposed at 80% or more of 100% of the area of the mutually opposing portions of the first electrode and the second electrode. The best is that when the mutually opposing portions of the first electrode and the second electrode are observed in the stacking direction of the first electrode, the connecting portion, and the second electrode, the solder portion in the connecting portion is disposed at more than 90% of the 100% area of the mutually opposing portions of the first electrode and the second electrode. By satisfying the above-mentioned preferred state, the conduction reliability can be further improved.

Preferably, when the mutually opposing portions of the first electrode and the second electrode are observed in a direction perpendicular to the stacking direction of the first electrode, the connecting portion, and the second electrode, more than 60% of the solder portion in the connecting portion is disposed in the mutually opposing portions of the first electrode and the second electrode. More preferably, when the mutually opposing portions of the first electrode and the second electrode are observed in a direction perpendicular to the stacking direction of the first electrode, the connecting portion, and the second electrode, more than 70% of the solder portion in the connecting portion is disposed in the mutually opposing portions of the first electrode and the second electrode. It is further preferred that when the mutually opposing portions of the first electrode and the second electrode are observed in a direction perpendicular to the stacking direction of the first electrode, the connecting portion, and the second electrode, more than 90% of the solder portion in the connecting portion is disposed in the mutually opposing portions of the first electrode and the second electrode. It is particularly preferred that when the mutually opposing portions of the first electrode and the second electrode are observed in a direction perpendicular to the stacking direction of the first electrode, the connecting portion, and the second electrode, more than 95% of the solder portion in the connecting portion is disposed in the mutually opposing portions of the first electrode and the second electrode. The best is that when the mutually opposing portions of the first electrode and the second electrode are observed in a direction orthogonal to the stacking direction of the first electrode, the connecting portion, and the second electrode, more than 99% of the solder portion in the connecting portion is disposed in the mutually opposing portions of the first electrode and the second electrode. By satisfying the above-mentioned preferred state, the conduction reliability can be further improved.

The first and second connection target components are not particularly limited. Specifically, the first and second connection target components include electronic components such as semiconductor chips, semiconductor packages, LED (Light Emitting Diode) chips, LED packages, capacitors, and diodes; and electronic components such as circuit substrates such as resin films, printed circuit boards, flexible printed circuit boards, flexible flat cables, rigid flexible substrates, glass epoxy substrates, and glass substrates. The first and second connection target components are preferably 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 substrate. The second connection target member is preferably a resin film, a flexible printed circuit board, a flexible flat cable or a rigid flexible substrate. Resin films, flexible printed circuit boards, flexible flat cables and rigid flexible substrates have the properties of being highly flexible and relatively light. When such connection target members are connected using a conductive film, solder particles tend to be difficult to gather on the electrode. In contrast, by using conductive paste, solder particles can be efficiently gathered on the electrodes even when using resin films, flexible printed circuit boards, flexible flat cables, or rigid flexible substrates, thereby fully improving the reliability of conduction between the electrodes. When using resin films, flexible printed circuit boards, flexible flat cables, or rigid flexible substrates, the effect of improving the reliability of conduction between the electrodes without applying pressure can be more effectively obtained compared to when using other connection target components such as semiconductor chips.

Examples of the electrode disposed on the above-mentioned connecting object component include metal electrodes such as gold electrode, nickel electrode, tin electrode, aluminum electrode, copper electrode, molybdenum electrode, silver electrode, SUS (Steel Use Stainless, Japanese Stainless Steel Standard) electrode, and tungsten electrode. When the above-mentioned connecting object component is a flexible printed circuit board, the above-mentioned electrode is preferably a gold electrode, a tin electrode, a silver electrode, or a copper electrode. When the above-mentioned connecting object component is a glass substrate, the above-mentioned electrode is preferably a copper electrode or a silver electrode. Furthermore, when the electrode is an aluminum electrode, it may be an electrode formed of aluminum alone or an electrode in which an aluminum layer is layered on the surface of a metal oxide layer. Examples of the material of 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 of the present invention, the first electrode and the second electrode are preferably arranged in a surface array or a peripheral array. When the first electrode and the second electrode are arranged in a surface array or a peripheral array, the effect of the present invention can be more effectively exerted. The surface array is a structure in which electrodes are arranged in a grid shape on the surface of the connection object component on which the electrodes are arranged. The peripheral array is a structure in which electrodes are arranged on the periphery of the connection object component. In the case of a structure in which electrodes are arranged in a comb shape, it is sufficient for the solder particles to condense in a direction perpendicular to the comb. In contrast, in the surface array or peripheral array structure, it is necessary to uniformly condense the solder particles on the entire surface on which the electrodes are arranged. Therefore, in the previous method, the amount of solder tends to become uneven, whereas in the method of the present invention, the solder particles can be uniformly aggregated on the entire surface.

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

Thermosetting components (thermosetting compounds): Phenolic novolac type epoxy compound ("DEN431" manufactured by DOW) Bisphenol F type epoxy compound ("DER354" manufactured by DOW)

Solder particles: Solder particles 1 (SnAgCu solder particles, "Sn96.5Ag3.0Cu0.5 ST-3" manufactured by Mitsui Metals, average particle size: 3.0 μm, melting point: 219°C, specific gravity: 7.4) Solder particles 2 (SnBi solder particles, "Sn42Bi58 ST-3" manufactured by Mitsui Metals, average particle size: 3.0 μm, melting point: 138°C, specific gravity: 8.6) Solder particles 3 (SnAgCu solder particles, "Sn96.5Ag3.0Cu0.5 DS10" manufactured by Mitsui Metals, average particle size: 10.0 μm, melting point: 219°C, specific gravity: 7.4) Solder particles 4 (SnAgCu solder particles, "Sn96.5Ag3.0Cu0.5 ST-7" manufactured by Mitsui Metals, average particle size: 7.0 μm, melting point: 219°C, specific gravity: 7.4)

Flux: Benzylamine adipate ("Benzylamine adipate" manufactured by Showa Chemical Industry Co., Ltd., solid at 25°C, average particle size: 10 μm, melting point: 180°C) Oleic acid ("Oleic acid" manufactured by Fuji Film Co., Ltd., liquid at 25°C, boiling point: 223°C)

=Trigger: Glycerol ("Glycerol" manufactured by Nacalai Tesque, liquid at 25°C, hydroxyl number: 3, boiling point: 290°C) N-Oleyl Sarcosine ("N-Oleyl Sarcosine" manufactured by TCI, liquid at 25°C, hydroxyl number: 1, boiling point: 197°C) Boron trifluoride-monoethylamine complex ("Boron trifluoride-monoethylamine complex" manufactured by TCI, solid at 25°C, hygroscopic at 25°C and 50%RH, melting point: 85°C) N,N'-Ethylene bis(stearylamide) ("SLIPACKS E" manufactured by Mitsubishi Chemical, solid at 25°C, non-hygroscopic at 25°C and 50%RH (weight gain rate 0 weight%))

(Determination of weight gain rate) For the "boron trifluoride-monoethylamine complex" manufactured by TCI, the weight gain rate of the boron trifluoride-monoethylamine complex after being placed at 25°C and 50% RH for 24 hours was determined using the above method relative to the weight of the boron trifluoride-monoethylamine complex before being placed. The weight gain rate of the boron trifluoride-monoethylamine complex is 1.0% by weight to 2.0% by weight.

(Examples 1 to 6 and Comparative Examples 1 to 4) (1) Preparation of conductive paste (anisotropic conductive paste) The components shown in Tables 1 to 3 below are mixed in the amounts shown in Tables 1 to 3 below to obtain a conductive paste (anisotropic conductive paste).

(2) Preparation of connection structure A glass epoxy substrate (material: FR-4, thickness: 0.6 mm) with a copper electrode (electrode length: 3 mm, electrode thickness: 12 μm) with L/S = 50 μm/50 μm on the surface was prepared as the first connection target component.

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

The conductive paste (anisotropic conductive paste) just produced is applied to the upper surface of the glass epoxy substrate in a manner that the thickness becomes 100 μm to form a conductive paste (anisotropic conductive paste) layer. Then, a flexible printed circuit board is laminated on the upper surface of the conductive paste (anisotropic conductive paste) layer in a manner that the electrodes face each other. The weight of the flexible printed circuit board is applied to the conductive paste (anisotropic conductive paste) layer. From this state, the conductive paste (anisotropic conductive paste) layer is heated in a manner that the temperature becomes the melting point of the solder particles 10 seconds after the start of the temperature rise. Furthermore, the conductive paste (anisotropic conductive paste) layer was heated so that the temperature reached 250° C. 15 seconds after the start of the temperature rise, and the conductive paste (anisotropic conductive paste) layer was hardened to obtain a connection structure. During the heating, no pressure was applied.

(Evaluation) (1) Screen printing properties The obtained conductive paste (anisotropic conductive paste) was screen printed on a glass slide using a metal mask with an opening size of 80 μm × 80 μm and a thickness of 30 μm. The printed surface of the 50 patterns was observed under a laser microscope, and the volume of the conductive paste applied on the glass slide was calculated. The ratio X (%) of the volume of the conductive paste applied on the glass slide to the volume of the opening of the metal mask was calculated. The screen printing properties were determined according to the following criteria.

[Criteria for judging screen printability] ○○: Ratio X is 50% or more ○: Ratio X is 30% or more but less than 50% ×: Ratio X is less than 30%

(2) Adhesion The conductive paste (anisotropic conductive paste) just produced was applied to the upper surface of the above-mentioned slide in a manner that the thickness was 250 μm to form a conductive paste (anisotropic conductive paste) layer. A cylindrical probe with a diameter of 5 mm was pressed against the surface of the conductive paste layer just formed and 24 hours after formation at a pressure of 1 N/5 mmφ for 1 second, and then the probe was peeled off from the conductive paste layer at a speed of 125 mm/min. The peeling force value at the time of peeling was set as the adhesion. In addition, the "Adhesion Tester TAC-II" manufactured by RHESCA was used as a measuring device and the measurement was performed at 25°C. The viscosity was judged according to the following criteria.

[Stickness Criteria] ○○: Adhesion is 1 N or more immediately after formation and 24 hours later ○: Adhesion is 1 N or more immediately after formation and less than 1 N after 24 hours ×: Adhesion is less than 1 N immediately after formation and less than 1 N after 24 hours

(3) Solder particle placement accuracy In the obtained connection structure, when observing the mutually opposing portions of the first electrode and the second electrode in the stacking direction of the first electrode, the connection portion, and the second electrode, the ratio Y of the area of the solder portion in the connection portion to 100% of the area of the mutually opposing portions of the first electrode and the second electrode is evaluated. The solder particle placement accuracy is determined according to the following criteria.

[Judgment criteria for solder particle placement accuracy] ○○: Ratio Y is 70% or more ○: Ratio Y is 50% or more and less than 70% ×: Ratio Y is less than 50%

The results are shown in Tables 1 to 3 below.

[Table 1] Embodiment 1 Embodiment 2 Embodiment 3 Conductive paste Thermosetting ingredients Phenolic novolac type epoxy compound Weight 50 50 50 Bisphenol F Epoxide Weight 50 50 50 Solder particles Solder particles 1 (average particle size 3.0 μm) Weight 200 200 Solder particles 2 (average particle size 3.0 μm) Weight 200 Solder particles 3 (average particle size 10.0 μm) Weight Solder particles 4 (average particle size 7.0 μm) Weight Flux Benzylamine adipate Weight 25 25 25 Oleic acid Weight Trigger Glycerol Weight 1 1 N-Oleyl Sarcosine Weight 1 Boron trifluoride-monoethylamine complex Weight N,N'-Ethylene Bis(Stearylamide) Weight Content of the contact agent in 100% by weight of the conductive paste weight% 0.3 0.3 0.3 Content of flux relative to 100 parts by weight of solder particles Weight 0.5 0.5 0.5 Reviews Screen printability - ○○ ○○ ○ Viscosity Adhesion after formation N 1.5 1.5 1.2 Adhesion after 24 hours N 1.2 1.2 0.9 determination - ○○ ○○ ○ Solder particle placement accuracy - ○○ ○○ ○

[Table 2] Embodiment 4 Embodiment 5 Embodiment 6 Conductive paste Thermosetting ingredients Phenolic novolac type epoxy compound Weight 50 50 50 Bisphenol F Epoxide Weight 50 50 50 Solder particles Solder particles 1 (average particle size 3.0 μm) Weight 200 Solder particles 2 (average particle size 3.0 μm) Weight 200 200 Solder particles 3 (average particle size 10.0 μm) Weight Solder particles 4 (average particle size 7.0 μm) Weight Flux Benzylamine adipate Weight 25 25 25 Oleic acid Weight Trigger Glycerol Weight N-Oleyl Sarcosine Weight 1 Boron trifluoride-monoethylamine complex Weight 1 1 N,N'-Ethylene Bis(Stearylamide) Weight Content of the contact agent in 100% by weight of the conductive paste weight% 0.3 0.3 0.3 The content of the switching agent relative to 100 parts by weight of solder particles Weight 0.5 0.5 0.5 Reviews Screen printability - ○ ○○ ○○ Viscosity Adhesion after formation N 1.2 1.5 1.5 Adhesion after 24 hours N 0.9 1.3 1.3 determination - ○ ○○ ○○ Solder particle placement accuracy - ○ ○○ ○○

[table 3] Comparison Example 1 Comparison Example 2 Comparison Example 3 Comparison Example 4 Conductive paste Thermosetting ingredients Phenolic novolac type epoxy compound Weight 50 50 50 50 Bisphenol F Epoxide Weight 50 50 50 50 Solder particles Solder particles 1 (average particle size 3.0 μm) Weight 200 200 Solder particles 2 (average particle size 3.0 μm) Weight Solder particles 3 (average particle size 10.0 μm) Weight 200 Solder particles 4 (average particle size 7.0 μm) Weight 200 Flux Benzylamine adipate Weight 25 25 25 Oleic acid Weight 25 Trigger Glycerol Weight 1 1 1 N-Oleyl Sarcosine Weight Boron trifluoride-monoethylamine complex Weight N,N'-Ethylene Bis(Stearylamide) Weight 1 Content of the contact agent in 100% by weight of the conductive paste weight% 0.3 0.3 0.3 0.3 The content of the switching agent relative to 100 parts by weight of solder particles Weight 0.5 0.5 0.5 0.5 Reviews Screen printability - × ○ × × Viscosity Adhesion after formation N 1.2 0.8 1.1 1.0 Adhesion after 24 hours N 0.8 0.5 0.7 0.6 determination - ○ × ○ ○ Solder particle placement accuracy - × ○ ○ ○

1: Connecting structure 2: First connecting component 2a: First electrode 3: Second connecting component 3a: Second electrode 4: Connecting part 4A: Solder part 4B: Hardened part

FIG. 1 is a cross-sectional view schematically showing a connection structure obtained by using a conductive paste according to an embodiment of the present invention.

Claims (7)

A conductive paste comprising a thermosetting component, a plurality of solder particles, a flux, and a tactile agent, wherein the average particle size of the solder particles is 5.0 μm or less, the flux is solid at 25°C, the tactile agent is a hydroxyl group-containing tactile agent that is liquid at 25°C, or a tactile agent that is solid at 25°C and has a weight gain of 0.2% by weight or more when the tactile agent is placed at 25°C and 50% RH for 24 hours, weight gain (weight %) = (W2-W1) × 100/W1 W1: weight of the tactile agent before placement W2: weight of the tactile agent after placement. The conductive paste of claim 1, wherein the content of the above-mentioned activator is not less than 0.005 weight % and not more than 2 weight % in 100 weight % of the above-mentioned conductive paste. The conductive paste of claim 1 or 2, wherein the content of the above-mentioned switching agent is not less than 0.003 parts by weight and not more than 2 parts by weight relative to 100 parts by weight of the above-mentioned solder particles. The conductive paste of claim 1 or 2, wherein the above-mentioned thiotropic agent is a hydroxyl group-containing thiotropic agent that is liquid at 25°C. As in claim 4, the conductive paste, wherein the above-mentioned thiotropic agent is a liquid at 25°C, has a hydroxyl group and a boiling point of 80°C or above. The conductive paste of claim 1 or 2, wherein the above-mentioned thiotropy agent is a thiotropy agent which is solid at 25°C and has the above-mentioned weight gain rate of 1 wt % or more. A connection structure, comprising: a first connection target component having a first electrode on its surface; a second connection target component having a second electrode on its surface; and a connection portion connecting the first connection target component with the second connection target component; and the material of the connection portion is a conductive paste as described in any one of claims 1 to 6, the first electrode and the second electrode are electrically connected via a solder portion in the connection portion.