Flux composition, connection structure, and method for manufacturing connection structure

Abstract

Provided is a flux composition that can suppress the production of voids and increase conduction reliability in an obtained connection structure.　This flux composition includes an epoxy compound, and an organic acid or a neutralized product thereof, said organic acid including a releasable proton. After the flux composition has been heated at 250°C for 90 seconds, the condition of the heated product is a solid. When differential scanning calorimetry is performed by heating the flux composition in a nitrogen atmosphere from 30°C to 360°C at a temperature increase speed of 60°C / min, the temperature range of an exothermic peak includes 220°C, and the area of the exothermic peak in a temperature range of less than or equal to 220°C is less than 95% of the 100% total area of the exothermic peak.

Description

Flux composition, connection structure, and method for manufacturing the connection structure

[0001] The present invention relates to a flux composition and use of the flux composition. The present invention also relates to a connection structure using the flux composition and a method for manufacturing a connection structure using the flux composition.

[0002] In recent years, as electronic devices such as data servers, personal computers (PCs), and mobile terminals have become smaller, lighter, and more functional, finer pitch wiring has become increasingly common on printed wiring boards, etc. As a result, surface-mount packages such as ball grid arrays (BGAs), in which the wiring extends directly below the chip, and ultra-small chip-scale packages (CSPs) have been attracting attention.

[0003] However, in surface mount packages such as BGA, unlike conventional pin insertion packages, the electrodes on the surface of the wiring board are connected to each other by solder particles, which results in low adhesion and makes them susceptible to damage due to impacts such as being dropped (low impact resistance).

[0004] Therefore, an underfill material is sometimes filled between the semiconductor chip and the semiconductor package substrate and cured to reinforce the joint.

[0005] Patent Document 1 listed below discloses a thermosetting resin composition for reinforcing electronic components, which has a viscosity of 5 Pa·s or less at 140° C. In this resin composition, the temperature corresponding to the top of the exothermic peak generated by the curing reaction is 150° C. or more and 170° C. or less, and the difference between the temperature corresponding to the top and the temperature corresponding to half the height of the top of the rising part of the exothermic peak is 20° C. or less.

[0006] WO2019 / 225733A1

[0007] When an underfill material such as that described in Patent Document 1 is used as a sealant, it is possible to improve the adhesion between the semiconductor chip and the semiconductor package substrate and to improve the impact resistance of the resulting connection structure (semiconductor package).

[0008] However, in the production process of conventional connection structures, after a reflow process (heating process) is performed to connect electrodes, an underfill material must be allowed to penetrate and fill the gap between the semiconductor chip and the semiconductor package substrate by capillary action, and a heating process must be performed again to harden the underfill material. In other words, the conventional method of manufacturing a connection structure using an underfill material as described in Patent Document 1 requires two heating processes, resulting in low productivity.

[0009] Furthermore, when a connection structure is produced using a conventional underfill material as a flux composition, the flux composition hardens before the solder melts due to heating, preventing the solder from sufficiently wetting and spreading over the surface of the electrode, which can result in poor connection in the resulting connection structure. In other words, it is difficult to improve the electrical conductivity reliability of the resulting connection structure using a conventional flux composition.

[0010] Furthermore, when a connection structure is produced using a conventional flux composition, the flux composition may boil due to heating in the reflow process, causing bubbles to form, which may result in voids in the resulting connection structure.

[0011] An object of the present invention is to provide a flux composition and use of the flux composition that can suppress the generation of voids and improve the electrical conductivity reliability in the resulting connection structure. Another object of the present invention is to provide a connection structure using the flux composition, and a method for manufacturing a connection structure using the flux composition.

[0012] Disclosed herein are the following flux compositions, uses of the flux compositions, connection structures, and methods for manufacturing the connection structures.

[0013] Item 1. A flux composition comprising an epoxy compound and an organic acid having a liberable proton or a neutralized product thereof, wherein the flux composition is heated at 250°C for 90 seconds and then the heated product is in a solid state at 250°C, and when the flux composition is heated from 30°C to 360°C at a heating rate of 60°C / min in a nitrogen atmosphere and subjected to differential scanning calorimetry, the temperature range of an exothermic peak includes 220°C, and the area of ​​the exothermic peak in a temperature range of 220°C or less accounts for less than 95% of the total area of ​​the exothermic peaks (100%).

[0014] Item 2. The flux composition according to Item 1, further comprising a curing agent, the curing agent comprising an acid anhydride and a phenol compound.

[0015] Item 3. A flux composition according to Item 2, wherein the amount of substance of acid anhydride groups in the flux composition is 16 mol or more and 60 mol or less per 100 mol of the amount of substance of epoxy groups in the flux composition.

[0016] Item 4. The flux composition according to any one of Items 1 to 3, wherein the organic acid having a liberable proton or a neutralized product thereof is contained in an amount of 2.0% by weight or less relative to 100% by weight of the flux composition.

[0017] Item 5. The flux composition according to any one of Items 1 to 4, wherein the flux composition is a non-conductive flux composition.

[0018] Item 6. The flux composition according to any one of Items 1 to 5, wherein the flux composition is a first-in-place underfill material used in a first-in-place underfill process.

[0019] Item 7. The flux composition according to any one of Items 1 to 6, wherein the flux composition is used to contact a tin-silver-copper alloy solder.

[0020] Item 8. Use of the flux composition according to any one of Items 1 to 7 as a first-in-place underfill material in a first-in-place underfill process.

[0021] Item 9. Use of the flux composition according to any one of Items 1 to 7 as a flux for the surface of a tin-silver-copper alloy solder.

[0022] Item 10. 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 resin part connecting the first connection-target member and the second connection-target member, wherein the first electrode comprises a first electrode body and solder particles on the surface of the first electrode body, the first electrode body and the second electrode are electrically connected, and the material of the resin part is the flux composition according to any one of Items 1 to 7.

[0023] Item 11. A method for manufacturing a connection structure, comprising: using a first connection target member having a first electrode on a surface thereof, the first electrode comprising a first electrode body and solder particles on the surface of the first electrode body, or a second connection target member having a second electrode on a surface thereof, and using the flux composition according to any one of Items 1 to 7, a first arrangement step of arranging the flux composition on the surface of the solder particles in the first connection target member or on the surface of the second electrode in the second connection target member; a second arrangement step of arranging the first connection target member and the second connection target member so that the first electrode and the second electrode face each other; and a step of heating the solder particles and the flux composition to electrically connect the first electrode body and the second electrode and to form, from the flux composition, a resin part that connects the first connection target member and the second connection target member.

[0024] The flux composition according to the present invention is a flux composition containing an epoxy compound and an organic acid or a neutralized product thereof containing a liberable proton. After heating the flux composition according to the present invention at 250°C for 90 seconds, the heated product is in a solid state at 250°C. When the flux composition according to the present invention is heated from 30°C to 360°C at a heating rate of 60°C / min in a nitrogen atmosphere and subjected to differential scanning calorimetry, the temperature range of the exothermic peak includes 220°C, and the area of ​​the exothermic peak in the temperature range of 220°C or less accounts for less than 95% of the total area of ​​the exothermic peaks (100%). Because the flux composition according to the present invention has the above-described configuration, the generation of voids can be suppressed and the electrical conductivity reliability can be improved in the resulting connection structure.

[0025] FIG. 1 is a cross-sectional view schematically illustrating a connection structure obtained using a flux composition according to an embodiment of the present invention. FIG. 2( a) is a cross-sectional view illustrating each step of an example of a method for manufacturing a connection structure using a flux composition according to an embodiment of the present invention. FIG. 3( b1) is a cross-sectional view illustrating each step of an example of a method for manufacturing a connection structure using a flux composition according to an embodiment of the present invention. FIG. 4( c) is a cross-sectional view illustrating each step of an example of a method for manufacturing a connection structure using a flux composition according to an embodiment of the present invention. FIG. 5( d) is a cross-sectional view illustrating each step of an example of a method for manufacturing a connection structure using a flux composition according to an embodiment of the present invention. FIG. 6( b2) is a cross-sectional view illustrating a modified example of a method for manufacturing a connection structure using a flux composition according to an embodiment of the present invention. FIG. 7( b3) is a cross-sectional view illustrating a modified example of a method for manufacturing a connection structure using a flux composition according to an embodiment of the present invention. FIG. 8( b4) is a cross-sectional view illustrating a modified example of a method for manufacturing a connection structure using a flux composition according to an embodiment of the present invention.

[0026] The present invention will be described in detail below.

[0027] (Flux Composition) The flux composition according to the present invention is a flux composition containing an epoxy compound and an organic acid having a liberable proton or a neutralized product thereof. After heating the flux composition according to the present invention at 250°C for 90 seconds, the heated product is in a solid state at 250°C. When the flux composition according to the present invention is heated from 30°C to 360°C at a heating rate of 60°C / min in a nitrogen atmosphere and subjected to differential scanning calorimetry, the temperature range of the exothermic peak includes 220°C, and the area of ​​the exothermic peak in a temperature range of 220°C or less accounts for less than 95% of the total area of ​​the exothermic peaks (100%).

[0028] The flux composition is heat-curable. The flux composition has the property of being cured by heating.

[0029] Conventionally, if a reflow process (heating process) is performed to connect the electrodes together and then sealing is performed with an underfill material, the heating process must be performed twice, once for solder bonding and once for hardening the underfill material, which poses a problem of low productivity.

[0030] The flux composition according to the present invention has the above-described features. When a connection structure is fabricated using the flux composition, a single heating step (reflow step) can melt the solder, bond the electrodes, and harden the flux composition. This eliminates the need for a second heating step. In other words, the flux composition according to the present invention allows for simultaneous mounting when fabricating a connection structure, thereby improving productivity. Because the flux composition according to the present invention can be used as a cleaning-free flux composition, it can successfully fabricate connection structures with short inter-electrode distances (i.e., it is suitable for use in fabricating connection structures with short inter-electrode distances). Furthermore, penetration of common underfill materials into semiconductor chips or semiconductor package substrates with large surface areas is difficult or impossible. The flux composition according to the present invention can successfully fabricate connection structures using large surface area semiconductor chips or semiconductor package substrates (i.e., it is suitable for use in fabricating connection structures using large surface area semiconductor chips or semiconductor package substrates). The flux composition according to the present invention is suitable for use as a first-in-place underfill material. From the viewpoint of effectively achieving the effects of the present invention, the flux composition is preferably a first-in-place underfill material used in a first-in-place underfill process (use of the flux composition as a first-in-place underfill material used in a first-in-place underfill process). From the viewpoint of effectively achieving the effects of the present invention, the flux composition according to the present invention is preferably used in contact with solder (use of the flux composition as a flux on the surface of solder).

[0031] Furthermore, when a connection structure is produced using a conventional flux composition, the flux composition hardens before the solder melts due to heating, preventing the solder from sufficiently wetting and spreading on the surface of the electrode, which can result in poor connection in the resulting connection structure. In other words, it is difficult to improve the electrical conductivity reliability of the resulting connection structure using a conventional flux composition.

[0032] Furthermore, when a connection structure is produced using a conventional flux composition, the flux composition may liquefy and boil due to heating in the reflow process (heating step), resulting in the generation of bubbles. As a result, voids may occur in the resulting connection structure. When voids occur in the connection structure, there is a problem that the impact resistance of the connection structure decreases. In other words, it is difficult to improve reflow resistance with conventional flux compositions.

[0033] The flux composition according to the present invention has the above-mentioned features, which allows the solder to sufficiently wet and spread on the surface of the electrodes, thereby reducing the connection resistance between the upper and lower electrodes in the resulting connection structure, thereby improving the electrical conductivity reliability of the resulting connection structure.

[0034] Furthermore, since the flux composition according to the present invention has the above-described configuration, it is possible to prevent the flux composition from boiling due to heating in the reflow process (heating process), and to suppress the generation of voids in the resulting connection structure. As a result, when a connection structure using the flux composition is subjected to an impact such as being dropped, the probability of the connection structure failing due to poor connection or the like can be reduced (the impact resistance of the resulting connection structure can be increased). In other words, the flux composition according to the present invention can improve reflow resistance.

[0035] After heating the flux composition at 250° C. for 90 seconds, the heated product is in a solid state at 250° C. The above-described configuration can suppress the incorporation of outgassing released from the substrate due to heating in the heating step, and can suppress the generation of voids in the resulting connection structure.

[0036] The properties of the flux composition at 250°C after heating for 90 seconds can be confirmed, for example, by the following method. A test specimen is obtained by applying 0.05 g of the flux composition to the surface of a copper plate (phosphorus-deoxidized copper plate, "C1220" manufactured by Engineering Test Services, Inc., thickness 0.3 mm) placed on a glass plate ("Large Glass Slide" manufactured by Matsunami Glass Co., Ltd., thickness 1.0 mm). The obtained test specimen is placed on a hot plate heated to 250°C from the glass plate side. After heating the test specimen for 90 seconds, the properties of the heated flux composition at 250°C on the hot plate are confirmed by touching with a toothpick.

[0037] The flux composition is heated from 30°C to 360°C at a temperature increase rate of 60°C / min in a nitrogen atmosphere and subjected to differential scanning calorimetry (DSC). In the differential scanning calorimetry, the temperature range of the exothermic peak includes 220°C, and the area of ​​the exothermic peak in the temperature range of 220°C or less accounts for less than 95% of the total area of ​​the exothermic peaks (100%). This configuration prevents the flux composition from completing hardening before the solder melts due to heating, allowing the solder to sufficiently wet and spread on the surface of the electrodes. As a result, the electrical conductivity reliability of the resulting connection structure can be improved.

[0038] The differential scanning calorimetry (DSC) can be performed as follows. A differential scanning calorimeter is prepared. 5 mg of the flux composition is placed in a dedicated aluminum pan (aluminum container). This dedicated aluminum pan and an empty aluminum pan (reference) are placed in a heating unit, and heating is performed under conditions of a nitrogen flow rate of 50 mL / min and a temperature increase rate of 60°C / min from 30°C to 360°C, and reverse heat flow and non-reverse heat flow are observed. The exothermic peak observed in the non-reverse heat flow is taken as the exothermic peak of the flux composition. Examples of the differential scanning calorimeter include the "EXSTAR DSC7020" manufactured by SII Corporation and the "DSC7020" manufactured by Hitachi High-Tech Science Corporation.

[0039] In the differential scanning calorimetry measurement of the flux composition, the temperature range of the exothermic peak includes 220°C. That is, the temperature range of the exothermic peak is a temperature range including 220°C. In the differential scanning calorimetry measurement of the flux composition, the exothermic start temperature is 220°C or less and the exothermic end temperature is 220°C or more. In the differential scanning calorimetry measurement of the flux composition, the reactivity at 220°C of the flux composition described below is greater than 0% and less than 100%.

[0040] In this specification, the term "exotherm onset temperature" refers to the temperature at which the amount of heat generated begins to increase from the baseline. Specifically, the exotherm onset temperature is defined as the temperature at which the DDSC or the DDDSC obtained by differentiating the DDSC with respect to temperature becomes 0. In this specification, the term "exotherm end temperature" refers to the temperature at which the amount of heat generated, after reaching the exotherm peak top, decreases to 1% of the amount of heat generated at the exotherm peak top.

[0041] In the differential scanning calorimetry, the area of ​​the exothermic peak in the temperature range of 220°C or less out of the total area of ​​the exothermic peaks (100%) is defined as the reactivity of the flux composition at 220°C. The reactivity of the flux composition at 220°C is less than 95%. If the reactivity of the flux composition at 220°C is less than 95%, the solder wettability will be reduced, and the electrical connection reliability of the resulting connection structure will be reduced. The reactivity of the flux composition at 220°C is preferably 1% or more, more preferably 5% or more, even more preferably 10% or more, particularly preferably 15% or more, and is preferably 94.5% or less, more preferably 94% or less, even more preferably 93% or less, even more preferably 85% or less, particularly preferably 80% or less, and most preferably 75% or less. If the reactivity of the flux composition at 220°C is equal to or greater than the lower limit, the release of outgassing due to boiling and thermal decomposition of the flux composition during the reflow process can be suppressed, thereby further suppressing the generation of voids. When the reactivity of the flux composition at 220° C. is equal to or less than the upper limit, the wettability of the solder can be further improved, and the electrical conductivity reliability of the resulting connection structure can be further improved.

[0042] From the viewpoint of more appropriate wetting and spreading of the solder, the reactivity of the flux composition at 220°C is preferably 70% or more, more preferably 75% or more, even more preferably 80% or more, particularly preferably 85% or more, and most preferably 90% or more.

[0043] The area of ​​the exothermic peak in the temperature range of 220°C or less (reaction rate of the flux composition at 220°C) out of the total area of ​​the exothermic peaks (100%) can be calculated by the quadrature method by division using, for example, spreadsheet software such as EXCEL or NEXTA standard analysis software ("Standard Analysis" manufactured by Hitachi High-Tech Corporation).

[0044] In the differential scanning calorimetry, the following methods can be used to adjust the exothermic peak temperature region, exothermic onset temperature, exothermic peak top temperature, exothermic end temperature, and the reactivity of the flux composition at 220°C within the preferred ranges: a method of adjusting the type and combination of epoxy compounds; a method of adjusting the content of epoxy compounds; a method of adjusting the type and combination of curing agents described below; and a method of adjusting the content of curing agents.

[0045] The flux composition has good adhesive properties. The flux composition is suitable for use as an adhesive. The flux composition is particularly suitable for use in bonding a semiconductor chip to a semiconductor package substrate (use of the flux composition for bonding a semiconductor chip to a semiconductor package substrate).

[0046] The flux composition is preferably used to obtain a connection structure. The flux composition is preferably used to obtain an electronic component. The flux composition is preferably used to bond and connect a surface mount package to a wiring board (use of the flux composition to bond and connect a surface mount package to a wiring board). Examples of the surface mount package include BGA and CSP.

[0047] The flux composition has good fluxing properties for solder. The flux composition can effectively remove oxide films on the surfaces of electrodes and solder in the resulting connection structure. The solder to which the flux composition can be applied is not particularly limited. The solder is preferably a filler metal having a liquidus of 450°C or less, based on JIS Z3001: Welding Terminology. The solder is preferably a metal (low-melting-point metal) having a melting point of 450°C or less. The solder may be solder particles. The solder particles are preferably metal particles (low-melting-point metal particles) having a 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 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 solder is preferably a low-melting-point solder having a melting point of less than 250°C.

[0048] The low-melting point metal constituting the solder 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, a tin-indium alloy, and a tin-antimony alloy. Because of their 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, a tin-indium alloy, or a tin-antimony alloy, more preferably a tin-silver-copper alloy, a tin-bismuth alloy, a tin-indium alloy, or a tin-antimony alloy, and particularly preferably a tin-silver-copper alloy.

[0049] From the viewpoint of effectively achieving the effects of the present invention, the flux composition is preferably used so as to come into contact with solder (use of the flux composition as a flux on the surface of solder). The flux composition has particularly good fluxing properties for tin-silver-copper alloy solder (SnAgCu solder). From the viewpoint of effectively achieving the effects of the present invention, the flux composition is preferably used so as to come into contact with tin-silver-copper alloy solder (SnAgCu solder) (use of the flux composition as a flux on the surface of tin-silver-copper alloy solder (SnAgCu solder)). That is, from the viewpoint of effectively achieving the effects of the present invention, the flux composition is preferably used in the manufacture of a connection structure using tin-silver-copper alloy solder (SnAgCu solder) (use of the flux composition for the manufacture of a connection structure using tin-silver-copper alloy solder). From the viewpoint of effectively exerting the effects of the present invention, it is particularly preferable that the flux composition is used so as to be in contact with the Sn96.5Ag3.0Cu0.5 solder (use of the flux composition as a flux on the surface of the Sn96.5Ag3.0Cu0.5 solder).

[0050] From the viewpoint of further improving connection reliability, the melting point of the solder is preferably 100°C or higher, more preferably 150°C or higher, even more preferably 200°C or higher, and preferably 400°C or lower, more preferably 350°C or lower, even more preferably 300°C or lower.

[0051] The melting point of the solder can be determined by differential scanning calorimetry (DSC). Examples of a DSC device include the "EXSTAR DSC7020" manufactured by SII Corporation.

[0052] The flux composition is preferably not conductive. The flux composition is preferably free of conductive materials. The flux composition is preferably free of conductive particles. The flux composition is preferably free of metal particles. The flux composition is preferably a non-conductive flux composition. When the flux composition satisfies these preferred aspects, the electrical conductivity reliability of the resulting connection structure can be further improved. In this specification, a non-conductive flux composition is defined as a flux composition having a volume resistivity of 10 ８ This indicates a flux composition having a resistivity of Ω·cm or more.

[0053] The volume resistivity is the volume resistivity at 20 kN. The volume resistivity can be measured using a resistivity meter ("Powder Resistivity Measurement System" manufactured by Mitsubishi Chemical Corporation).

[0054] <Epoxy Compound> The flux composition contains an epoxy compound. The epoxy compound is preferably a thermosetting compound. The epoxy compound is a compound having at least one epoxy group.

[0055] Examples of the epoxy compound include bixylenol-type epoxy compounds, 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.

[0056] From the viewpoint of further improving the applicability of the flux composition, the epoxy compound preferably includes a biphenyl-type epoxy compound, a bisphenol F-type epoxy compound, or an epoxy compound having a triazine nucleus in its skeleton, and more preferably includes a bisphenol F-type epoxy compound. The epoxy compound is preferably a biphenyl-type epoxy compound, a bisphenol F-type epoxy compound, or an epoxy compound having a triazine nucleus in its skeleton, and more preferably a bisphenol F-type epoxy compound.

[0057] The content of the epoxy compound in 100% by weight of the flux composition is preferably 40.0% by weight or more, more preferably 45.0% by weight or more, even more preferably 50.0% by weight or more, and is preferably 70.0% by weight or less, more preferably 65.0% by weight or less, even more preferably 60.0% by weight or less. When the content of the epoxy compound is equal to or more than the above lower limit and equal to or less than the above upper limit, the curability of the flux composition can be further improved, and the generation of voids in the resulting connection structure can be further suppressed.

[0058] <Organic Acid Having a Livable Proton or Neutralized Product Thereof> The flux composition includes an organic acid having a liberable proton or a neutralized product thereof. The flux composition may include an organic acid having a liberable proton, a neutralized product of an organic acid having a liberable proton, or both an organic acid having a liberable proton and a neutralized product of an organic acid having a liberable proton. In the flux composition, the organic acid having a liberable proton or a neutralized product thereof preferably acts as a curing accelerator or a thickening inhibitor for the epoxy compound.

[0059] In this specification, a liberable proton refers to a proton having a pKa of 13 or less measured in an aqueous solution at room temperature (for example, three types of protons contained in phosphoric acid, a proton contained in carboxylic acid, and a proton contained in sulfonic acid). In this specification, a neutralized product of an organic acid containing a liberable proton refers to a neutralized product of an organic acid that can release a free proton.

[0060] The organic acid containing a releasable proton contains at least one releasable proton. The organic acid containing a releasable proton or its neutralized product may be an organic acid containing one releasable proton or its neutralized product, or may be an organic acid containing two releasable protons or its neutralized product. The organic acid containing a releasable proton or its neutralized product may be an organic acid containing two or more releasable protons or its neutralized product, or may be an organic acid containing three or more releasable protons or its neutralized product. The organic acid containing a releasable proton or its neutralized product may be an organic acid containing 10 or fewer releasable protons or its neutralized product, an organic acid containing 5 or fewer releasable protons or its neutralized product, or an organic acid containing 4 or fewer releasable protons or its neutralized product. The organic acid containing a releasable proton or its neutralized product may be an organic acid containing three or fewer releasable protons or its neutralized product. From the viewpoint of improving storage stability and conductivity reliability, the flux composition preferably contains an organic acid containing one or two liberable protons or a neutralized product thereof, and more preferably contains a neutralized product of an organic acid containing one or two liberable protons. The range of the number of liberable protons can be set by appropriately selecting the above-mentioned lower limit and upper limit.

[0061] Examples of the organic acid containing a liberable proton or a neutralized product thereof include an organic phosphorus compound, an organic carboxylic acid compound, an organic sulfonic acid compound, and an organic thiol compound. The organic acid containing a liberable proton or a neutralized product thereof may be used alone or in combination of two or more.

[0062] From the viewpoint of further suppressing the occurrence of voids and further improving the electrical conductivity reliability, the flux composition preferably contains an organic phosphorus compound. From the viewpoint of improving the electrical conductivity reliability and suppressing the occurrence of voids, the organic acid having a liberable proton or its neutralized product preferably contains an organic phosphorus compound.

[0063] 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. The organic phosphorus compounds may be used alone or in combination of two or more.

[0064] From the viewpoint of improving the conduction reliability of the resulting connection structure, the organophosphorus compound preferably contains an organophosphonium salt, organophosphoric acid or organophosphate ester, and more preferably contains an organophosphonium salt.

[0065] The organic phosphonium salt includes an organic phosphonium salt composed of a phosphonium ion and its counter ion.

[0066] From the viewpoint of improving the electrical conductivity reliability of the resulting connection structure, the organic phosphonium salt is preferably methyl tributyl phosphonium dimethyl phosphate or tributyl methyl phosphonium bis(2-ethylhexyl) phosphate, and more preferably methyl tributyl phosphonium dimethyl phosphate.

[0067] Commercially available organic phosphonium salts include "tetrabutylphosphonium bis(2-ethylhexyl)phosphate" manufactured by Johoku Chemical Industry Co., Ltd., and the "Hishicolin" series manufactured by Nippon Chemical Industry Co., Ltd.

[0068] The organic phosphoric acid, the organic phosphoric acid ester, the organic phosphonic acid, the organic phosphonic acid ester, the organic phosphinic acid, and the organic phosphinic acid ester are not particularly limited. As the organic phosphoric acid, the organic phosphoric acid ester, the organic phosphonic acid, the organic phosphonic acid ester, the organic phosphinic acid, and the organic phosphinic acid ester, conventionally known compounds or commercially available products can be used.

[0069] From the viewpoint of improving the electrical conductivity reliability and curability, the flux composition preferably contains a neutralized product of the organic acid containing the liberable proton.

[0070] The content of the organic acid containing a liberable proton or its neutralized product in 100% by weight of the flux composition is preferably 0.1% by weight or more, more preferably 0.2% by weight or more, even more preferably 0.5% by weight or more, and preferably 5.0% by weight or less, more preferably 2.0% by weight or less, and even more preferably 1.0% by weight or less. When the content of the organic acid containing a liberable proton or its neutralized product is equal to or greater than the above-mentioned lower limit and equal to or less than the above-mentioned upper limit, the generation of voids in the resulting connection structure can be further suppressed, and the electrical reliability can be further improved. Note that when the flux composition contains both the organic acid containing a liberable proton and its neutralized product, the content of the organic acid containing a liberable proton or its neutralized product refers to the total content of the organic acid containing a liberable proton and its neutralized product.

[0071] The content of the organophosphorus compound in 100% by weight of the flux composition is preferably 0.1% by weight or more, more preferably 0.2% by weight or more, even more preferably 0.5% by weight or more, and is preferably 5.0% by weight or less, more preferably 2.0% by weight or less, and even more preferably 1.0% by weight or less. When the content of the organophosphorus compound is equal to or more than the above-mentioned lower limit and equal to or less than the above-mentioned upper limit, the generation of voids in the resulting connection structure can be further suppressed, and the electrical conductivity reliability can be further improved.

[0072] The content of the organic phosphonium salt in 100% by weight of the flux composition is preferably 0.1% by weight or more, more preferably 0.2% by weight or more, and even more preferably 0.5% by weight or more, and is preferably 5.0% by weight or less, more preferably 2.0% by weight or less, and even more preferably 1.0% by weight or less. When the content of the organic phosphonium salt is equal to or more than the above lower limit and equal to or less than the above upper limit, the generation of voids in the resulting connection structure can be further suppressed, and the electrical conductivity reliability can be further improved.

[0073] The flux composition may or may not contain a curing accelerator other than the organic acid containing a liberable proton and its neutralized product (a curing accelerator other than both the organic acid containing a liberable proton and its neutralized product, hereinafter referred to as "other curing accelerator"). The flux composition optionally contains the other curing accelerator. When the flux composition contains the other curing accelerator, the total content of the curing accelerators in 100 wt% of the flux composition is preferably 0.1 wt% or more, more preferably 0.2 wt% or more, even more preferably 0.3 wt% or more, and preferably 4.0 wt% or less, more preferably 3.5 wt% or less, and even more preferably 3.0 wt% or less. When the total content of the curing accelerators is above the lower limit and below the upper limit, the generation of voids in the resulting connection structure can be further suppressed, thereby further improving the electrical conductivity reliability. Note that the total content of the curing accelerators refers to the combined content of the organic acid containing a liberable proton or its neutralized product and the other curing accelerators.

[0074] <Curing Agent> The flux composition may or may not contain a curing agent. The flux composition optionally contains the curing agent. The curing agent thermally cures the epoxy compound. From the viewpoint of further enhancing the curability of the flux composition and further suppressing the occurrence of voids in the resulting connection structure, it is preferable that the flux composition further contains a curing agent.

[0075] Examples of the curing agent include phenol compounds (phenol curing agents), active ester compounds, carbodiimide compounds (carbodiimide curing agents), amine compounds (amine curing agents), thiol compounds (thiol curing agents), phosphine compounds, dicyandiamide, and acid anhydrides. The curing agent preferably has a functional group capable of reacting with the epoxy group of the epoxy compound. Only one type of curing agent may be used, or two or more types may be used in combination.

[0076] From the viewpoint of preventing the flux composition from boiling due to heating in the reflow process and further suppressing the occurrence of voids in the resulting connection structure, it is preferable that the curing agent contains an acid anhydride. From the viewpoint of controlling the curing rate of the flux composition and improving the electrical conductivity reliability in the resulting connection structure, it is preferable that the curing agent contains a phenol compound. From the viewpoint of further improving the electrical conductivity reliability of the flux composition and further suppressing the occurrence of voids in the resulting connection structure, it is more preferable that the curing agent contains an acid anhydride and a phenol compound.

[0077] The content of the curing agent in 100% by weight of the flux composition is preferably 30% by weight or more, more preferably 35% by weight or more, even more preferably 40% by weight or more, and is preferably 60% by weight or less, more preferably 55% by weight or less, and even more preferably 50% by weight or less. When the content of the curing agent is equal to or more than the lower limit and equal to or less than the upper limit, the generation of voids in the resulting connection structure can be further suppressed, and the electrical conductivity reliability can be further improved.

[0078] The amount of curing agent functional groups in the flux composition relative to 100 mol of epoxy groups in the flux composition is preferably 50 mol or more, more preferably 60 mol or more, even more preferably 70 mol or more, and preferably 110 mol or less, more preferably 100 mol or less, and even more preferably 90 mol or less. When the amount of curing agent functional groups in the flux composition relative to 100 mol of epoxy groups in the flux composition is above the lower limit and below the upper limit, the glass transition temperature of the cured product in the resulting connection structure can be effectively increased, further improving reliability. The curing agent functional group is, for example, a functional group in the curing agent that reacts with epoxy groups. The curing agent functional group is, for example, an acid anhydride group when the curing agent is an acid anhydride, or a phenolic hydroxyl group when the curing agent is a phenolic compound. The amount of substance of the curing agent functional group is the amount of substance of the acid anhydride group when the curing agent is an acid anhydride, and is the amount of substance of the phenolic hydroxyl group when the curing agent is a phenol compound. The amount of substance of the curing agent functional group is the sum of the amount of substance of the acid anhydride group and the amount of substance of the phenolic hydroxyl group when the curing agent is two types of curing agents, an acid anhydride and a phenol compound.

[0079] For example, the amount of the curing agent functional group in the flux composition relative to 100 mol of the epoxy group in the flux composition can be calculated from the functional group equivalent (g / eq) disclosed by the raw material manufacturer.

[0080] The amount of the curing agent functional group in the flux composition relative to 100 mol of the epoxy group in the flux composition can be measured, for example, by the following method: After dissolving the flux composition in a deuterated chloroform solution, １ H-NMR (JNM series manufactured by JEOL) is measured, and the ratio of epoxy groups to curing agent functional groups is calculated from the obtained spectrum.

[0081] <<Acid Anhydride>> The flux composition may or may not contain an acid anhydride. The flux composition optionally contains the acid anhydride. The acid anhydride thermally cures the epoxy compound. The use of the acid anhydride in combination with an organic acid or its neutralized product (especially an organic phosphorus compound) containing a liberable proton significantly enhances the fluxing effect of the flux composition. The carboxylate ions generated by ring-opening of the acid anhydride group during the curing reaction exhibit fluxing properties. As a result, oxide films on the surfaces of electrodes and solder in the resulting connection structure can be effectively removed. Furthermore, the use of the acid anhydride in combination with the phenolic compound further enhances the curability of the flux composition and prevents boiling of the flux composition due to heating during the reflow process. As a result, the generation of voids in the resulting connection structure can be further suppressed.

[0082] Examples of the acid anhydride include phthalic anhydride, tetrahydrophthalic anhydride, trialkyltetrahydrophthalic anhydride, hexahydrophthalic anhydride, methylhexahydrophthalic anhydride, methyltetrahydrophthalic anhydride, methylbutenyltetrahydrophthalic anhydride, anhydrides of phthalic acid derivatives, bifunctional acid anhydrides such as maleic anhydride, nadic anhydride, methylnadic anhydride, glutaric anhydride, succinic anhydride, glycerin bistrimellitic anhydride monoacetate, and ethylene glycol bistrimellitic anhydride, trifunctional acid anhydrides such as trimellitic anhydride, and tetrafunctional or higher acid anhydrides such as pyromellitic anhydride, benzophenonetetracarboxylic anhydride, methylcyclohexenetetracarboxylic anhydride, and polyazelaic anhydride. Only one of the above acid anhydrides may be used, or two or more may be used in combination.

[0083] From the viewpoint of further improving the applicability of the flux composition, the acid anhydride preferably includes tetrahydrophthalic anhydride, hexahydrophthalic anhydride, or methylhexahydrophthalic anhydride, and more preferably includes methylhexahydrophthalic anhydride.

[0084] From the viewpoint of further improving the applicability of the flux composition, the acid anhydride is preferably in a liquid state at 25°C.

[0085] The content of the acid anhydride in 100% by weight of the flux composition is preferably 1.0% by weight or more, more preferably 3.0% by weight or more, even more preferably 5.0% by weight or more, and preferably 40% by weight or less, more preferably 38% by weight or less, and even more preferably 35% by weight or less. When the content of the acid anhydride is above the lower limit and below the upper limit, the generation of voids in the resulting connection structure can be further suppressed, and the conductivity reliability can be further improved. When the content of the acid anhydride is below the upper limit, the wettability of the solder can be further improved.

[0086] The amount of acid anhydride groups in the flux composition relative to 100 mol of epoxy groups in the flux composition is preferably 10 mol or more, more preferably 16 mol or more, even more preferably 20 mol or more, and preferably 70 mol or less, more preferably 65 mol or less, even more preferably 60 mol or less. When the amount of acid anhydride groups in the flux composition relative to 100 mol of epoxy groups in the flux composition is above the above lower limit and below the above upper limit, the generation of voids in the resulting connection structure can be further suppressed and the conductivity reliability can be further improved. When the amount of acid anhydride groups in the flux composition is below the above upper limit, the solder wettability can be further improved.

[0087] <<Phenol Compound>> The flux composition may or may not contain a phenolic compound. The flux composition optionally contains the phenolic compound. The phenolic compound thermally cures the epoxy compound. By using the acid anhydride and the phenolic compound in combination, boiling of the flux composition due to heating in the reflow process can be prevented, and the occurrence of voids in the resulting connection structure can be further suppressed. Furthermore, the curability of the flux composition can be further enhanced, and the occurrence of voids in the resulting connection structure can be further suppressed.

[0088] Examples of the phenol compound include novolac type phenol, biphenyl type phenol, naphthalene type phenol, dicyclopentadiene type phenol, aralkyl type phenol, and dicyclopentadiene type phenol.

[0089] Commercially available phenol compounds include novolac phenol (manufactured by DIC Corporation under the trademark "TD-2131"), novolac phenol (manufactured by DIC Corporation under the trademark "TD-2091"), bisphenol (manufactured by Gun-ei Chemical Industry Co., Ltd. under the trademark "APG-LC"), biphenyl novolac phenol (manufactured by Meiwa Chemical Industry Co., Ltd. under the trademark "MEH-7851"), aralkyl phenol (manufactured by Meiwa Chemical Industry Co., Ltd. under the trademark "MEH-7800"), and phenols having an aminotriazine skeleton (manufactured by DIC Corporation under the trademark "LA-1356" and "LA-3018-50P"). The phenol compounds may be used alone or in combination of two or more.

[0090] The content of the phenol compound in 100% by weight of the flux composition is preferably 1.0% by weight or more, more preferably 3.0% by weight or more, even more preferably 5.0% by weight or more, and is preferably 35% by weight or less, more preferably 30% by weight or less, even more preferably 25% by weight or less. When the content of the phenol compound is equal to or more than the above lower limit and equal to or less than the above upper limit, the generation of voids in the resulting connection structure can be further suppressed, and the electrical conductivity reliability can be further improved.

[0091] The total content of the acid anhydride and the phenol compound in 100% by weight of the flux composition is preferably 20.0% by weight or more, more preferably 30.0% by weight or more, even more preferably 40.0% by weight or more, and is preferably 70.0% by weight or less, more preferably 60.0% by weight or less, and even more preferably 50.0% by weight or less. When the total content of the acid anhydride and the phenol compound is equal to or more than the above-mentioned lower limit and equal to or less than the above-mentioned upper limit, the generation of voids in the resulting connection structure can be further suppressed, and the electrical conductivity reliability can be further improved.

[0092] The sum of the amount of acid anhydride groups and the amount of phenolic hydroxyl groups in the flux composition relative to 100 mol of the amount of epoxy groups in the flux composition is preferably 50 mol or more, more preferably 60 mol or more, even more preferably 70 mol or more, and preferably 110 mol or less, more preferably 100 mol or less, even more preferably 90 mol or less. When the sum of the amount of acid anhydride groups and the amount of phenolic hydroxyl groups in the flux composition relative to 100 mol of the amount of epoxy groups in the flux composition is equal to or greater than the above lower limit and equal to or less than the above upper limit, the glass transition temperature of the cured product in the resulting connection structure can be effectively increased, and the conductivity reliability can be further improved.

[0093] <Other Components> The flux composition may contain various additives, 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, as needed.

[0094] (Connection Structure and Method for Producing Connection Structure) The flux composition according to the present invention is suitably used to obtain a connection structure.

[0095] The connection structure according to 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 resin portion connecting the first connection target member and the second connection target member. In the connection structure according to the present invention, the first electrode comprises a first electrode body and solder particles on the surface of the first electrode body. In the connection structure according to the present invention, the first electrode body and the second electrode are electrically connected. In the connection structure according to the present invention, the material of the resin portion is the flux composition described above.

[0096] In a method for manufacturing a connection structure according to the present invention, a first connection target member has a first electrode on its surface, the first electrode includes a first electrode body and solder particles on the surface of the first electrode body, and a second connection target member has a second electrode on its surface. The method for manufacturing the connection structure comprises the following steps: (1) a first arrangement step of using the first connection target member or the second connection target member and the above-described flux composition to arrange the flux composition on the surface of the solder particles in the first connection target member or on the surface of the second electrode in the second connection target member; and (2) a second arrangement step of arranging the first connection target member and the second connection target member so that the first electrode and the second electrode face each other. (3) A process of heating the solder particles and the flux composition to electrically connect the first electrode body and the second electrode, and to form a resin part using the flux composition that connects the first connection target member and the second connection target member.

[0097] In the first-in underfill method, the flux composition is placed on the surface of at least one of the first and second connection target members before the first and second connection target members are placed opposite each other. The method for manufacturing a connection structure according to the present invention is a method for manufacturing a connection structure using the first-in underfill method.

[0098] The method for manufacturing the connection structure may employ the following arrangement method. In the first arrangement step, a first connection target member having a first electrode on its surface, the first electrode comprising a first electrode body and solder particles on the surface of the first electrode body, may be used, and the above-described flux composition may be used to arrange the flux composition on the surfaces of the solder particles of the first connection target member. In the first arrangement step, a second connection target member having a second electrode on its surface, the above-described flux composition may be used to arrange the flux composition on the surfaces of the second electrode of the second connection target member.

[0099] In the method for manufacturing a connection structure according to the present invention, in the first disposing step, the flux composition may be disposed by a dispensing method, by screen printing, by ejection using an inkjet device, or by dipping. From the viewpoint of further suppressing the occurrence of voids, it is preferable to dispose the flux composition by a dispensing method in the first disposing step.

[0100] In a conventional method for manufacturing a connection structure using an underfill material, after a reflow process (heating process) for connecting electrodes, the underfill material must be allowed to penetrate and fill the spaces between the components to be connected by capillary action, and a heating process must be performed again to harden the underfill material. In other words, the conventional method for manufacturing a connection structure using an underfill material requires two heating processes, resulting in low productivity. Furthermore, in connection structures using conventional underfill materials, solder flash can occur. When solder flash occurs, short circuits or open circuits can occur.

[0101] The connection structure and the method for manufacturing the connection structure according to the present invention use a specific flux composition, which allows electrodes to be electrically connected and the flux composition to be cured in a single heating step (reflow step). Therefore, there is no need to perform the heating step twice. In other words, the connection structure and the method for manufacturing the connection structure according to the present invention enable simultaneous mounting, thereby further improving productivity. Furthermore, the connection structure and the method for manufacturing the connection structure according to the present invention use a specific flux composition, which allows the solder in the solder particles to sufficiently wet and spread over the surfaces of the electrodes, thereby reducing the connection resistance between the upper and lower electrodes in the connection structure. As a result, the electrical conductivity reliability of the connection structure can be improved. Furthermore, the connection structure and the method for manufacturing the connection structure according to the present invention use a specific flux composition, which prevents the flux composition from boiling due to heating in the reflow step (heating step), thereby suppressing the generation of voids in the connection structure. As a result, the probability of the connection structure failing due to poor connection or the like when the connection structure is subjected to an impact, such as being dropped, can be reduced (the impact resistance of the connection structure can be improved).

[0102] Hereinafter, specific embodiments of the present invention will be described with reference to the drawings.

[0103] FIG. 1 is a cross-sectional view that schematically shows a connection structure obtained using a flux composition according to one embodiment of the present invention.

[0104] The connection structure 1 shown in FIG. 1 includes a first connection target member 2, a second connection target member 3, and a resin part 4 connecting the first connection target member 2 and the second connection target member 3. The resin part 4 is formed from a flux composition 4Xa (see FIG. 3(b1) (or FIG. 6(b2) or FIG. 7(b3) or FIG. 8(b4)), FIG. 4(c) and FIG. 5(d)). The material of the resin part 4 is the flux composition 4Xa. The flux composition 4Xa includes an epoxy compound and an organic acid or a neutralized product thereof that contains a liberable proton. In this embodiment, the flux composition 4Xa is preferably in a liquid form, and more preferably a solvent-free liquid.

[0105] The resin portion 4 is a cured portion obtained by thermally curing the flux composition 4Xa.

[0106] The first connection target member 2 has a plurality of first electrodes on its surface (lower surface). The first electrodes include a first electrode body 2a and solder portions 2B (solder particles) on the surface of the first electrode body 2a. The first electrodes are composite electrodes of the first electrode body 2a and the solder portions 2B. The second connection target member 3 has a plurality of second electrodes 3a on its surface (upper surface). In the connection structure 1, the first electrode body 2a and the second electrode 3a are electrically connected. In the connection structure 1, the first electrode body 2a and the second electrode 3a are electrically connected by the solder portions 2B.

[0107] 1, in the connection structure 1, at least the portions of the solder particles that contact the second electrode 3a melt between the first electrode body 2a and the second electrode 3a, and then the solder particles solidify to form the solder portion 2B, which increases the connection area between the solder portion 2B and the second electrode 3a.

[0108] Next, an example of a method for manufacturing a connection structure will be specifically described with reference to Figure 2(a), Figure 3(b1) (or Figure 6(b2) or Figure 7(b3) or Figure 8(b4)), Figure 4(c) and Figure 5(d). Figure 2(a), Figure 3(b1) (or Figure 6(b2) or Figure 7(b3) or Figure 8(b4)), Figure 4(c) and Figure 5(d) are cross-sectional views for explaining each step of an example of a method for manufacturing a connection structure using a flux composition according to one embodiment of the present invention.

[0109] First, as shown in Figure 2(a), a first connection target member 2 having a first electrode on its surface (lower surface) and a second connection target member 3 having a second electrode 3a on its surface (upper surface) are prepared. The first electrode includes a first electrode body 2a and solder particles 2b on the surface of the first electrode body 2a. Furthermore, a flux composition 4Xa is prepared. The flux composition 4Xa includes an epoxy compound and an organic acid or its neutralized product containing a liberable proton.

[0110] Next, as shown in Fig. 3(b1), flux composition 4Xa is placed on the surfaces of solder particles 2b (first electrodes) of the first connection target member 2 (first placing step). At this time, as shown in Fig. 6(b2), flux composition 4Xa may also be placed on the surface of the second electrode 3a of the second connection target member 3 (first placing step). That is, in the first placing step, flux composition 4Xa is placed by a dispenser on the surfaces of solder particles 2b of the first connection target member 2 or on the surface of the second electrode 3a of the second connection target member 3. Flux composition 4Xa is placed on the surfaces of solder particles 2b of the first connection target member 2 or on the surface of the second electrode 3a of the second connection target member 3 using a dispenser.

[0111] In addition, in Fig. 3(b1), the flux composition 4Xa is separately disposed on each of the plurality of solder particles 2b (first electrodes). As shown in Fig. 7(b3), the flux composition 4Xa may be disposed so as to straddle the plurality of solder particles 2b (first electrodes) (first disposing step). In Fig. 6(b2), the flux composition 4Xa is separately disposed on each of the plurality of second electrodes 3a. As shown in Fig. 8(b4), the flux composition 4Xa may be disposed so as to straddle the plurality of second electrodes 3a (first disposing step). In the first disposing step, the flux composition 4Xa may be disposed by a dispensing method or the like on the surface of the second electrode 3a of the second connection target member 3 so as to straddle the plurality of second electrodes 3a.

[0112] The amount of flux composition placed on the surface of the solder particles is preferably an amount that can fill the gap between the first and second target components in the resulting connection structure.

[0113] Next, as shown in FIG. 3(b1) (or FIG. 6(b2) or FIG. 7(b3) or FIG. 8(b4)) and FIG. 4(c), the first connection target member 2 and the second connection target member 3 are arranged so that the first electrode (first electrode body 2a and solder particles 2b) faces the second electrode 3a (second arrangement step). The second connection target member 3 is arranged from the second electrode 3a side, facing the first electrode side of the first connection target member 2. At this time, the first electrode body 2a and the second electrode 3a face each other.

[0114] Next, as shown in FIGS. 4(c) and 5(d), the solder particles 2b and the flux composition 4Xa are heated (third step). Preferably, the flux composition 4Xa is heated to a temperature equal to or higher than the melting point of the solder particles 2b in contact with the second electrode 3a. More preferably, the flux composition 4Xa is heated to a temperature equal to or higher than the curing temperature of the epoxy compound. This heating electrically connects the first electrode (first electrode body 2a and solder particles 2b or solder portion 2B) to the second electrode 3a. The flux composition 4Xa also thermally hardens. As a result, as shown in FIG. 5(d), the resin portion 4 connecting the first connection target member 2 and the second connection target member 3 is formed by the flux composition 4Xa. The resin portion 4 is formed by the thermal hardening of the flux composition 4Xa. As shown in FIG. 5(d), the solder portion 2B is formed by the solder particles 2b, and the first electrode body 2a and the second electrode 3a are electrically connected by the solder portion 2B.

[0115] The viscosity (ηmp) of the flux composition at the melting point 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, and even more preferably 1 Pa s or less. When the viscosity (ηmp) is equal to or greater than the lower limit and equal to or less than the upper limit, the electrical conductivity reliability of the resulting connection structure can be improved.

[0116] The viscosity (ηmp) can be measured, for example, using a rheometer "HAAKE MARS III" manufactured by Thermo Fisher Scientific under the conditions of a frequency of 2 Hz, a temperature rise rate of 0.11°C / sec, and a measurement temperature range of 25°C to 200°C (however, when the melting point of the solder particles exceeds 200°C, the upper temperature limit is set to the melting point of the solder particles). From the measurement results, the viscosity of the flux composition at the melting point (°C) of the solder particles is evaluated.

[0117] In this manner, the connection structure 1 shown in FIG. 1 is obtained. The second arrangement step and the third step may be performed consecutively. After the second arrangement step, the laminate of the first connection target member 2, the flux composition 4Xa, and the second connection target member 3 may be moved to a heating unit, 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.

[0118] 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 temperature in the third step is preferably higher than the melting point of the solder particles. The heating temperature in the third step is preferably higher than the curing temperature of the epoxy compound. The heating temperature in the third step is preferably higher than the temperature at which the portion of the solder particles in contact with the second electrode melts, and more preferably higher than the curing temperature of the epoxy compound.

[0119] The heating method in the third step may be a method of heating the entire laminate using a reflow furnace or oven, or a method of locally heating only the solder and resin portions of the laminate.

[0120] Examples of tools used for localized heating include a hot plate, a heat gun that applies hot air, a soldering iron, and an infrared heater.

[0121] Furthermore, when heating locally with a hot plate, it is preferable to form the top surface of the hot plate with a metal having high thermal conductivity directly below the solder and resin parts, and with a material having low thermal conductivity such as fluororesin for other areas where it is not desirable to heat.

[0122] The thickness of the solder portion in the connection structure is preferably 10 μm or more, more preferably 20 μm or more, and is preferably 100 μm or less, more preferably 80 μm or less.

[0123] The thickness of the resin portion in the connection structure is preferably 10 μm or more, more preferably 20 μm or more, and is preferably 100 μm or less, more preferably 80 μm or less.

[0124] When the flux composition is in the form of a paste (liquid), the thickness of the resin portion can be easily adjusted by adjusting the amount of the flux composition applied.

[0125] 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. The first and second connection target members are preferably electronic components.

[0126] Examples of 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 formed solely from aluminum, 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.

[0127] The solder is preferably a metal having a melting point of 450°C or less (low-melting-point metal). The solder particles are preferably metal particles having a melting point of 450°C or less (low-melting-point metal particles). The low-melting-point metal particles are particles containing a low-melting-point metal. The low-melting-point metal refers to 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 solder is preferably a low-melting-point solder having a melting point of less than 250°C.

[0128] 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, a tin-indium alloy, and a tin-antimony alloy. Because of their excellent wettability with electrodes, the low-melting point metal is preferably tin, a tin-silver alloy, a tin-silver-copper alloy, a tin-bismuth alloy, a tin-indium alloy, or a tin-antimony alloy, and more preferably a tin-silver-copper alloy, a tin-bismuth alloy, a tin-indium alloy, or a tin-antimony alloy.

[0129] The solder particles are preferably filler metals having 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 are preferably lead-free and contain tin, silver, and copper. The solder particles are preferably tin-silver-copper alloy solder particles.

[0130] In order to further increase the bonding strength between the solder portion 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. Furthermore, from the viewpoint of further increasing the bonding strength between the solder portion 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 portion and the electrode, the content of these metals to increase the bonding strength is preferably 0.0001 wt % or more and preferably 1 wt % or less based on 100 wt % of the metal contained in the solder particles.

[0131] 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, even more preferably 200°C or higher, and preferably 400°C or lower, more preferably 350°C or lower, even more preferably 300°C or lower.

[0132] The melting point of the solder particles can be determined by differential scanning calorimetry (DSC). Examples of DSC devices include the "EXSTAR DSC7020" manufactured by SII Corporation.

[0133] Furthermore, the solder particles preferably contain tin. The tin content of 100% by weight of the metal contained in the solder particles is preferably 30.0% by weight or more, more preferably 40.0% by weight or more, even more preferably 70.0% by weight or more, and particularly preferably 90.0% by weight or more. When the tin content in the solder particles is equal to or greater than the lower limit, the electrical continuity reliability and connection reliability of the connection structure can be further improved. The upper limit of the tin content in the solder particles is not particularly limited. The tin content in the solder particles may be 99.9% by weight or less, 99.0% by weight or less, or 98.0% by weight or less.

[0134] The tin content can be measured using a high-frequency inductively coupled plasma optical emission spectrometer (for example, "ICP-AES" manufactured by Horiba, Ltd.) or a fluorescent X-ray analyzer (for example, "EDX-800HS" manufactured by Shimadzu Corporation).

[0135] The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0136] The following materials were prepared:

[0137] Epoxy compounds: Bisphenol F type epoxy compound (DIC Corporation "EXA-830CRP") Bixylenol type epoxy compound (Mitsubishi Chemical Corporation "YX-4000HK") Amine type tetrafunctional epoxy compound (tetraglycidyldiaminodiphenylmethane, Sumitomo Chemical Co., Ltd. "ELM-434") Naphthalene type epoxy compound (DIC Corporation "HP-4710")

[0138] Curing agent: Acid anhydride (mixture of hexahydrophthalic anhydride and methylhexahydrophthalic anhydride, "Rikacid MH-700" manufactured by New Japan Chemical Co., Ltd.), Bisphenol compound ("APG-LC" manufactured by Gunei Chemical Industry Co., Ltd.), Novolac type phenol compound ("TD-2131" manufactured by DIC Corporation)

[0139] Curing accelerator (organic acid having a liberable proton or neutralized product thereof): Methyl tributylphosphonium dimethyl phosphate ("Hishicolin PX-4MP" manufactured by Nippon Chemical Industry Co., Ltd., number of free protons: 1) Phosphonium salt 1 (compound represented by the following formula (1), number of free protons: 1) Phosphonium salt 2 (compound represented by the following formula (2), number of free protons: 1) Phosphonium salt 3 (compound represented by the following formula (3), number of free protons: 1) Phosphonium salt 4 (mixture of compound represented by the following formula (4A) and compound represented by the following formula (4B) (semi-neutralized product), number of free protons: 1 to 2) Phosphonium salt 5 (mixture of compound represented by the following formula (5A) and compound represented by the following formula (5B) (fully neutralized product), number of free protons: 1 to 2) Phosphonium salt 6 (compound represented by the following formula (6), number of free protons: 1) Carboxylate ("SYIL-02" manufactured by Sanyo Chemical Industries, Ltd., number of free protons: 1)

[0140] Thickening inhibitor (organic acid containing a liberable proton or its neutralized product): 2-ethylhexyl acid phosphate ("JP-508" manufactured by Johoku Chemical Co., Ltd., number of free protons: 1 to 2) Tetracosyl acid phosphate ("JP-524R" manufactured by Johoku Chemical Co., Ltd., number of free protons: 1 to 2)

[0141]

[0142]

[0143]

[0144]

[0145]

[0146]

[0147]

[0148]

[0149] The compound represented by the formula (4A) is the same as the compound represented by the formula (5A). The compound represented by the formula (4B) is the same as the compound represented by the formula (5B).

[0150] Curing accelerator (organic acid not containing a liberable proton or its neutralized product): Phosphonium salt A (compound represented by the following formula (A), number of free protons: 0) Phosphonium salt B (compound represented by the following formula (B), number of free protons: 0)

[0151]

[0152]

[0153] Curing accelerator (not applicable to organic acids or their neutralized products): Novacure HX-3088 (manufactured by Asahi Kasei Corporation)

[0154] The number of free protons of the organic acid or its neutralized product indicates the number of protons that can be released with a pKa of 13 or less.

[0155] (Examples 1 to 13 and Comparative Examples 1 to 7) (1) Preparation of Flux Compositions The components shown in Tables 1, 3, 5, and 7 below were mixed in the amounts shown in Tables 1, 3, 5, and 7 below, and the mixture was stirred at 2000 rpm for 2 minutes using a planetary centrifugal mixer (Thinky Corporation's "Awatori Rentaro ARE-310"), and then degassed at 2200 rpm for 3 minutes to obtain flux compositions.

[0156] (Evaluation) (1) Properties of the heated product after heating the flux composition at 250°C for 90 seconds: 0.05 g of the obtained flux composition was applied to the surface of a copper plate (phosphorus-deoxidized copper plate, "C1220" manufactured by Engineering Test Services, Inc., thickness 0.3 mm) placed on a glass plate ("Large slide glass" manufactured by Matsunami Glass Co., Ltd., thickness 1.0 mm) to obtain a test specimen. The obtained test specimen was placed on a hot plate heated to 250°C from the glass plate side. After heating the test specimen for 90 seconds, the properties of the heated product of the flux composition on the hot plate at 250°C were confirmed by touching with a toothpick.

[0157] (2) Reaction rate of the flux composition at 220°C Differential scanning calorimetry (DSC) was performed on the obtained flux composition using a differential scanning calorimetry (DSC) device (Hitachi High-Tech Science Corporation, "DSC7020") by heating the flux composition from 30°C to 360°C at a heating rate of 60°C / min. Using the method described above, the area of ​​the exothermic peak in the temperature range of 220°C or less (the reaction rate of the flux composition at 220°C) out of the total area of ​​the exothermic peaks (100%) was calculated. It was also confirmed that the temperature range of the exothermic peaks included 220°C in all of the examples and comparative examples.

[0158] (3) Solder Wetting and Spreading Properties: The obtained flux composition was applied to a substrate (phosphorus-deoxidized copper plate, "C1220" manufactured by Engineering Test Services) by a dispenser method. Next, solder particles (Sn96.5Ag3.0Cu0.5 solder (melting point: 217°C), particle diameter: 0.5 mm) were placed on the surface of the flux composition layer to form a laminate comprising the substrate, flux composition layer, and solder particles. The resulting laminate was heated in a nitrogen atmosphere using a reflow simulator ("Core9056a" manufactured by Cores Corporation) at a heating rate of 1°C / sec from 30°C to 255°C, with a total time of 90 seconds at or above 220°C, and then cooled to room temperature. The solder particles were then observed using a microscope (manufactured by Keyence Corporation), and the major axis (μm) of the solder particles in plan view was measured. The solder wetting and spreading properties were evaluated according to the following criteria.

[0159] [Criteria for determining solder wetting and spreading properties] ◯: The major axis of the solder particles is 800 μm or more. ○: The major axis of the solder particles is 700 μm or more and less than 800 μm. ×: The major axis of the solder particles is less than 700 μm.

[0160] (4) Void Suppression in Connection Structures: A printed circuit board (material: FR4, Sn42Bi58 solder particles, particle diameter 0.4 mm, 0.8 mm pitch, 100 electrodes, 10 mm length x 10 mm width) having solder particles on its surface was prepared. The printed circuit board was placed on the surface of a hot plate from the side opposite the solder particles and heated at 150°C for 10 minutes to dry. Next, 0.05 g of the immediately prepared flux composition was dispensed onto the surface of the solder particles of the printed circuit board. An 18 mm x 18 mm square cover glass (manufactured by Matsunami Glass Co., Ltd.) was placed on the surface of the applied flux composition opposite the printed circuit board to obtain a laminate. The resulting laminate was heated on a hot plate at 250°C for 90 seconds and then cooled to room temperature. After heating and cooling were repeated three times, the number of voids with a diameter of 100 μm or more was counted using a microscope. The void suppression in the connection structures was evaluated according to the following criteria.

[0161] [Criteria for evaluating the suppression of voids in connection structures] 〇〇: The number of voids generated is 1 or less. ○: The number of voids generated is 2 to 3. ×: The number of voids generated is 4 or more.

[0162] The compositions and results are shown in the following Tables 1 to 8. In Tables 1, 3, 5, and 7, the "content of the organic acid containing a liberable proton or its neutralized product in 100% by weight of the flux composition" is described as the "content of the organic acid-based additive containing a liberable proton in 100% by weight of the flux composition."

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[0164]

[0165]

[0166]

[0167]

[0168]

[0169]

[0170]

[0171] REFERENCE SIGNS LIST 1 Connection structure 2 First connection target member 2a First electrode body 2b Solder particles 2B Solder portion 3 Second connection target member 3a Second electrode 4 Resin portion 4Xa Flux composition

Claims

1. A flux composition comprising an epoxy compound and an organic acid containing a freeable proton or its neutralized form, The properties of the heated flux composition after heating it at 250°C for 90 seconds are that it is solid. The flux composition, when heated in a nitrogen atmosphere at a heating rate of 60°C / min from 30°C to 360°C and differential scanning calorimetry performed, has a temperature range of 220°C in the exothermic peak, and the area of ​​the exothermic peak in the temperature range of 220°C or below accounts for less than 95% of the total area of ​​the exothermic peak.

2. The flux composition further comprises a curing agent, The flux composition according to claim 1, wherein the curing agent comprises an acid anhydride and a phenol compound.

3. The flux composition according to claim 2, wherein the amount of acid anhydride groups in the flux composition is 16 mol or more and 60 mol or less relative to 100 mol of epoxy groups in the flux composition.

4. The flux composition according to any one of claims 1 to 3, wherein the flux composition contains, in an amount of 2.0% by weight or less, an organic acid containing the liberable proton or a neutralized product thereof, in 100% by weight of the flux composition.

5. The flux composition according to any one of claims 1 to 3, wherein the flux composition is a non-conductive flux composition.

6. The flux composition according to any one of claims 1 to 3, wherein the flux composition is a first-in underfill material used in a first-in underfill process.

7. The flux composition according to any one of claims 1 to 3, wherein the flux composition is used in contact with a tin-silver-copper alloy solder.

8. Use of the flux composition according to any one of claims 1 to 3 as a first-in underfill material used in a first-in underfill process.

9. Use of the flux composition according to any one of claims 1 to 3 as a flux on the surface of a tin-silver-copper alloy solder.

10. A first connection target member having a first electrode on its surface, A second connection target member having a second electrode on its surface, The device comprises a resin portion connecting the first connection target member and the second connection target member, The first electrode comprises a first electrode body and solder particles on the surface of the first electrode body. The first electrode body and the second electrode are electrically connected. A connecting structure wherein the material of the resin portion is the flux composition described in any one of claims 1 to 3.

11. A first arrangement step of placing the flux composition on the surface of the solder particles in the first connection target member or on the surface of the second electrode in the second connection target member, using a first connection target member having a first electrode on its surface, wherein the first electrode comprises a first electrode body and solder particles on the surface of the first electrode body, or a second connection target member having a second electrode on its surface, and using the flux composition described in any one of claims 1 to 3, A second arrangement step involves arranging the first connection target member and the second connection target member so that the first electrode and the second electrode face each other. A method for manufacturing a connection structure, comprising the steps of: heating the solder particles and the flux composition to electrically connect the first electrode body and the second electrode, and forming a resin portion connecting the first connection target member and the second connection target member using the flux composition.