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

Abstract

Provided is a flux composition with which it is possible to enhance the cooling / heating cycle resistance of a resulting connection structure.　A flux composition according to the present invention contains an epoxy compound, an acid anhydride, a bifunctional phenol compound, and a curing accelerator. In 100 wt% of the flux composition, the acid anhydride content is 5.0-32.0 wt%.

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 more susceptible to breakage when 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, connection structures are sometimes repeatedly heated and cooled during use, and the connection portions are sometimes exposed to heating and cooling. When a connection structure is produced using a conventional underfill material as a flux composition, cracks may occur in the solder when the connection structure is repeatedly heated and cooled, and the connection resistance between the upper and lower electrodes to be connected may not be sufficiently low. In other words, it is difficult to improve the thermal cycle resistance of the resulting connection structure using a conventional flux composition.

[0010] An object of the present invention is to provide a flux composition and use of the flux composition that can improve the thermal cycle resistance of the resulting connection structure. Another object of the present invention is to provide a connection structure using the flux composition, and a method for producing a connection structure using the flux composition.

[0011] Disclosed herein are the following flux compositions, uses of the flux compositions, connection structures, and methods for manufacturing the connection structures.

[0012] Item 1. A flux composition comprising an epoxy compound, an acid anhydride, a bifunctional phenol compound, and a curing accelerator, wherein the content of the acid anhydride is 5.0% by weight or more and 32.0% by weight or less based on 100% by weight of the flux composition.

[0013] Item 2. The flux composition according to Item 1, wherein the content of the bifunctional phenol compound is 15.0% by weight or more and 42.0% by weight or less, based on 100% by weight of the flux composition.

[0014] Item 3. The flux composition according to Item 1 or 2, wherein the content of the curing accelerator is 0.1% by weight or more and 1.0% by weight or less, based on 100% by weight of the flux composition.

[0015] Item 4. The flux composition according to any one of Items 1 to 3, wherein a weight ratio of the content of the bifunctional phenol compound in the flux composition to the content of the acid anhydride in the flux composition is 0.5 or more and 7.9 or less.

[0016] Item 5. The flux composition according to any one of Items 1 to 4, wherein the flux composition is a non-conductive flux composition.

[0017] 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.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] The flux composition according to the present invention is a flux composition containing an epoxy compound, an acid anhydride, a bifunctional phenol compound, and a curing accelerator, and the content of the acid anhydride is 5.0% by weight or more and 32.0% by weight or less based on 100% by weight of the flux composition. Since the flux composition according to the present invention has the above-mentioned configuration, it is possible to improve the thermal cycle resistance of the resulting connection structure.

[0024] 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.

[0025] The present invention will be described in detail below.

[0026] (Flux Composition) The flux composition according to the present invention is a flux composition containing an epoxy compound, an acid anhydride, a bifunctional phenol compound, and a curing accelerator. In the flux composition according to the present invention, the content of the acid anhydride is 5.0 wt % or more and 32.0 wt % or less based on 100 wt % of the flux composition.

[0027] The flux composition is heat-curable. The flux composition has the property of being cured by heating.

[0028] 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.

[0029] 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).

[0030] 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.

[0031] Furthermore, connection structures are sometimes repeatedly heated and cooled during use, and the connection portions are sometimes exposed to heating and cooling. When a connection structure is produced using a conventional flux composition and the connection structure is repeatedly heated and cooled, cracks may occur in the solder, resulting in poor connection. That is, it is difficult to improve the thermal cycle resistance of the resulting connection structure using a conventional flux composition. In particular, when the solder does not sufficiently wet and spread on the surface of the electrode or when voids occur in the connection structure, cracks are likely to occur in the solder, and the above-mentioned problem becomes more pronounced.

[0032] 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.

[0033] Furthermore, since the flux composition according to the present invention has the above-mentioned configuration, it is possible to suppress the occurrence of cracks in the solder and the resulting connection failure when the connection structure is repeatedly heated and cooled. That is, the flux composition according to the present invention can improve the thermal cycle resistance of the connection structure obtained.

[0034] In order to achieve the effects of the present invention, it is necessary to use a bifunctional phenolic compound as the phenolic compound. If a trifunctional or higher functional phenolic compound is used, the solder wettability will be reduced. If a monofunctional phenolic compound is used, the thermal cycle resistance of the resulting connection structure will be reduced. The present inventors have found that in order to achieve the effects of the present invention, it is important to select and use a bifunctional phenolic compound from among phenolic compounds.

[0035] In general, increasing the curability of an adhesive (conductive paste) can result in poor storage stability and an increase in viscosity during storage, resulting in a problem of a shortened pot life (usable time).

[0036] The flux composition according to the present invention has the above-mentioned features, and therefore can have improved storage stability.

[0037] The viscosity (η25) of the flux composition at 25°C is preferably 1.0 Pa·s or more, more preferably 1.5 Pa·s or more, even more preferably 6.0 Pa·s or more, and preferably 10.0 Pa·s or less, more preferably 6.5 Pa·s or less. When the viscosity (η25) is equal to or greater than the lower limit, excessive spreading of the flux composition can be suppressed when the flux composition is applied, allowing an appropriate amount of the flux composition to be applied. As a result, the generation of voids in the resulting connection structure can be suppressed. Furthermore, when the viscosity (η25) is equal to or less than the upper limit, storage stability is further improved and a sufficient amount of the flux composition can be applied. The viscosity (η25) can be appropriately adjusted by the type and amount of the components.

[0038] The viscosity (η25) can be measured, for example, using an E-type viscometer ("VISCOMETER TV-22" manufactured by Toki Sangyo Co., Ltd., rotor diameter 15 mm) under conditions of 25° C. and 5 rpm.

[0039] From the viewpoint of further improving the applicability of the flux composition, the flux composition is preferably in a liquid state at 25° C. Note that a paste state is included in the liquid state.

[0040] The flux composition may be applied by a dispensing method, a screen printing method, a dispensing method using an inkjet device, or a dipping method. From the viewpoint of suppressing the generation of voids in the resulting connection structure, the flux composition is preferably applied by a dispensing method.

[0041] The flux composition is preferably in a solid state at 250° C. after being heated for 90 seconds 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.

[0042] The properties of the heated product at 250°C after heating the flux composition at 250°C for 90 seconds can be confirmed, for example, by the following method. 0.05 g of the flux composition is 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 Glass Slide" manufactured by Matsunami Glass Co., Ltd., thickness 1.0 mm), and the plate is placed on a hot plate heated to 250°C. After heating for 90 seconds, the properties of the heated product at 250°C on the hot plate are confirmed by touching it with a toothpick.

[0043] 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 (DSC). For the flux composition, the temperature range of the exothermic peak preferably includes 220°C. That is, for the flux composition, the exothermic start temperature is preferably 220°C or lower and the exothermic end temperature is preferably 220°C or higher. Furthermore, for the flux composition, the reactivity at 220°C, as described below, is preferably greater than 0% and less than 100%. These preferred aspects prevent the flux composition from curing completely before the solder melts due to heating, allowing the solder to more thoroughly wet and spread on the surface of the electrodes. As a result, the electrical continuity reliability and thermal cycle resistance of the resulting connection structure can be further improved.

[0044] 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.

[0045] 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 DDSC or DDDSC obtained by differentiating 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 decreases to 1% of the amount of heat generated at the exotherm peak top after reaching the exotherm peak top.

[0046] In the differential scanning calorimetry, the heat generation initiation temperature is preferably 100° C. or higher, more preferably 120° C. or higher, and even more preferably 140° C. or higher, and is preferably 220° C. or lower, more preferably 200° C. or lower, and even more preferably 180° C. or lower. When the heat generation initiation temperature is equal to or higher than the lower limit and equal to or lower than the upper limit, the storage stability and applicability of the flux composition can be improved, and the electrical conductivity reliability can be improved when the flux composition is mounted in a relatively short time.

[0047] From the viewpoint of improving the conduction reliability when mounted in a relatively short time, the exothermic peak top temperature in the differential scanning calorimetry measurement is preferably 180°C or higher, more preferably 200°C or higher, even more preferably 220°C or higher, and is preferably 250°C or lower, more preferably 240°C or lower, even more preferably 230°C or lower.

[0048] From the viewpoint of improving the conductivity reliability when mounted in a relatively short time, the heat generation end temperature in the differential scanning calorimetry measurement is preferably 180°C or higher, more preferably 200°C or higher, even more preferably 220°C or higher, and is preferably 260°C or lower, more preferably 250°C or lower, even more preferably 240°C or lower.

[0049] 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 preferably 80% or more, more preferably 85% or more, even more preferably 87% or more, particularly preferably 90% or more, and preferably 95% or less, more preferably 94.5% or less, even more preferably 94% or less, even more preferably 93% or less, particularly preferably 92% or less, and most preferably 91% or less. When the reactivity of the flux composition at 220°C is equal to or greater than the lower limit, the curability of the flux composition can be further improved, and the generation of voids in the resulting connection structure can be suppressed. 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 and thermal cycle resistance of the resulting connection structure can be further improved.

[0050] 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.

[0051] The area of ​​the exothermic peak in the temperature range of 220°C or less (the reactivity of the flux composition at 220°C) out of the total area of ​​the exothermic peaks (100%) can be calculated using, for example, spreadsheet software such as EXCEL or NEXTA standard analysis software ("Standard Analysis" manufactured by Hitachi High-Tech Corporation).

[0052] 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 later); a method of adjusting the content of curing agents; a method of adjusting the type and combination of curing accelerators (described later); and a method of adjusting the content of curing accelerators.

[0053] In the differential scanning calorimetry, the absolute value of the difference between the heat generation start temperature and the heat generation end temperature is preferably 5° C. or more, more preferably 10° C. or more, even more preferably 15° C. or more, particularly preferably 20° C. or more, and is preferably 100° C. or less, more preferably 95° C. or less, even more preferably 90° C. or less, particularly preferably 85° C. or less, and most preferably 80° C. or less. When the absolute value of the difference between the heat generation start temperature and the heat generation end temperature is equal to or greater than the above lower limit and equal to or less than the above upper limit, the storage stability of the flux composition can be improved, and the electrical conductivity reliability can be improved when the flux composition is mounted in a relatively short time.

[0054] In the differential scanning calorimetry, it is preferable that only one exothermic peak is observed. In the differential scanning calorimetry, it is preferable that only one exothermic peak is observed. In the differential scanning calorimetry, it is preferable that two or more exothermic peaks are not observed.

[0055] 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).

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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).

[0060] 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.

[0061] 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.

[0062] 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 and thermal cycle resistance 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 1.0×10 ８ This indicates a flux composition having a resistivity of Ω·cm or more.

[0063] 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).

[0064] <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.

[0065] 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.

[0066] 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.

[0067] From the viewpoint of further improving the applicability of the flux composition, the epoxy compound preferably contains an epoxy compound that is solid at 25° C. Only one type of the epoxy compound that is solid at 25° C. may be used, or two or more types may be used in combination.

[0068] From the viewpoint of further improving the applicability of the flux composition, the epoxy compound that is solid at 25° C. is preferably a crystalline resin. From the viewpoint of further improving the applicability of the flux composition, the epoxy compound that is solid at 25° C. is preferably a powder.

[0069] 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, and even more preferably 60.0% by weight or less. When the content of the epoxy compound is equal to or more than the above-mentioned lower limit and equal to or less than the above-mentioned upper limit, the viscosity stability can be further improved, the wettability of the solder can be further improved, and the thermal cycle resistance of the resulting connection structure can be further improved.

[0070] The content of the epoxy compound that is solid at 25° C. 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, and even more preferably 60.0% by weight or less. When the content of the epoxy compound that is solid at 25° C. is equal to or more than the above lower limit and equal to or less than the above upper limit, the viscosity stability can be further improved, the solder wettability can be further improved, and the thermal cycle resistance of the resulting connection structure can be further improved.

[0071] The content of the epoxy compound that is solid at 25° C., relative to 100% by weight of the epoxy compound, is preferably 80.0% by weight or more, more preferably 85.0% by weight or more, and even more preferably 90.0% by weight or more, and is preferably 100.0% by weight or less, and more preferably 95.0% by weight or less. When the content of the epoxy compound that is solid at 25° C. is equal to or more than the lower limit and equal to or less than the upper limit, the viscosity stability can be further improved, the solder wettability can be further improved, and the thermal cycle resistance of the resulting connection structure can be further improved.

[0072] <Curing Agent> The flux composition contains a curing agent, which thermally cures the epoxy compound.

[0073] 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.

[0074] The flux composition contains an acid anhydride and a bifunctional phenolic compound. In the flux composition, the acid anhydride and the bifunctional phenolic compound preferably act as curing agents for the epoxy compound. Because the flux composition contains a bifunctional phenolic compound, the curing properties of the flux composition are further enhanced, thereby suppressing the generation of voids in the resulting connection structure. Because the flux composition contains an acid anhydride, the flux composition is prevented from boiling due to heating in the reflow process (heating process), thereby suppressing the generation of voids in the resulting connection structure. Because the flux composition contains an acid anhydride and a bifunctional phenolic compound, the curing properties of the flux composition are further enhanced, thereby suppressing the generation of voids in the resulting connection structure. As a result, the thermal cycle resistance of the resulting connection structure is improved.

[0075] (Acid Anhydride) The flux composition contains the acid anhydride. The acid anhydride thermally cures the epoxy compound. By using the acid anhydride in combination with a curing accelerator (especially an organic phosphorus compound), the flux effect of the flux composition can be significantly enhanced. As a result, oxide films on the surfaces of electrodes and solder in the resulting connection structure can be effectively removed. Furthermore, by using the acid anhydride in combination with the bifunctional phenol compound, the curing properties of the flux composition can be further enhanced and the flux composition can be prevented from boiling due to heating in the reflow process (heating process). As a result, the generation of voids in the resulting connection structure can be suppressed, and the thermal cycle resistance of the resulting connection structure can be improved.

[0076] 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, difunctional 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.

[0077] 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.

[0078] From the viewpoint of further improving the applicability of the flux composition, the acid anhydride is preferably in a liquid state at 25°C.

[0079] From the viewpoint of further improving the coatability of the flux composition, the melting point of the acid anhydride is preferably 25°C or lower, more preferably 0°C or lower, and even more preferably -15°C or lower. The lower limit of the melting point of the acid anhydride is not particularly limited. The melting point of the acid anhydride may be -100°C or higher, -70°C or higher, or -40°C or higher. The range of the melting point of the acid anhydride can be set by appropriately selecting the lower limit and the upper limit.

[0080] The content of the acid anhydride in 100% by weight of the flux composition is 5.0% by weight or more and 32.0% by weight or less. If the content of the acid anhydride is less than 5.0% by weight, the thermal cycle resistance of the resulting connection structure will be reduced. If the content of the acid anhydride is more than 32.0% by weight, the solder wettability will be reduced. The inventors have also found that, in order to achieve the effects of the present invention, it is not sufficient to simply select and use a bifunctional phenolic compound from among phenolic compounds, but it is important to ensure that the content of the acid anhydride used together with the bifunctional phenolic compound is 5.0% by weight or more and 32.0% by weight or less.

[0081] The content of the acid anhydride in 100% by weight of the flux composition is preferably 5.3% by weight or more, more preferably 7.0% by weight or more, even more preferably 10.0% by weight or more, and preferably 30.0% by weight or less, more preferably 25.0% by weight or less, and even more preferably 20.0% by weight or less. When the content of the acid anhydride is equal to or greater than the lower limit, the generation of voids can be suppressed and the thermal cycle resistance of the resulting connection structure can be improved. When the content of the acid anhydride is equal to or less than the upper limit, the wettability of the solder can be further improved.

[0082] The content of the acid anhydride is preferably 3 parts by weight or more, more preferably 5 parts by weight or more, and even more preferably 7 parts by weight or more, and is preferably 80 parts by weight or less, more preferably 65 parts by weight or less, and even more preferably 50 parts by weight or less, relative to 100 parts by weight of the epoxy compound. When the content of the acid anhydride is above the lower limit, the generation of voids can be suppressed and the thermal cycle resistance of the resulting connection structure can be improved. When the content of the acid anhydride is below the upper limit, the wettability of the solder can be further improved.

[0083] 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 60 mol or less, more preferably 55 mol or less, even more preferably 50 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 viscosity stability can be further improved, the solder wettability can be further improved, and the thermal cycle resistance of the resulting connection structure 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.

[0084] 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.

[0085] The amount of acid anhydride groups in the flux composition relative to 100 mol of epoxy groups 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 acid anhydride groups is calculated from the obtained spectrum.

[0086] (Bifunctional Phenol Compound) The flux composition contains a bifunctional phenol compound. The bifunctional phenol compound thermally cures the epoxy compound. By using the acid anhydride and the bifunctional phenol compound in combination, the curing properties of the flux composition can be further enhanced and the flux composition can be prevented from boiling due to heating in the reflow process (heating process). As a result, the generation of voids in the resulting connection structure can be suppressed and the thermal cycle resistance of the resulting connection structure can be improved.

[0087] The bifunctional phenol compound is a compound having two or more structures derived from a phenol group.

[0088] Examples of the bifunctional phenol compound include diallyl bisphenol A, diallyl bisphenol F, bisphenol A, and hydrogenated bisphenol A.

[0089] Commercially available bifunctional phenol compounds include diallyl bisphenol F ("APG-LC" manufactured by Gun-ei Chemical Co., Ltd.), diallyl bisphenol A ("DA-BPA" manufactured by Yokkaichi Chemical Co., Ltd.), and hydrogenated bisphenol A ("H-BPA" manufactured by Maruzen Oil Co., Ltd.). The bifunctional phenol compounds may be used alone or in combination of two or more.

[0090] From the viewpoint of further improving the applicability of the flux composition, the bifunctional phenol compound preferably contains diallyl bisphenol F or diallyl bisphenol A, and more preferably contains diallyl bisphenol F.

[0091] From the viewpoint of further improving the applicability of the flux composition, the bifunctional phenol compound is preferably liquid at 25°C.

[0092] From the viewpoint of further improving the applicability of the flux composition, the melting point of the bifunctional phenol compound is preferably 25°C or lower, more preferably 0°C or lower, and even more preferably -15°C or lower. The lower limit of the melting point of the bifunctional phenol compound is not particularly limited. The melting point of the bifunctional phenol compound may be -100°C or higher, -70°C or higher, or -40°C or higher. The range of the melting point of the bifunctional phenol compound can be set by appropriately selecting the lower limit and the upper limit.

[0093] The content of the bifunctional phenol compound in 100% by weight of the flux composition is preferably 15.0% by weight or more, more preferably 20.0% by weight or more, even more preferably 30.0% by weight or more, and preferably 60.0% by weight or less, more preferably 50.0% by weight or less, and even more preferably 42.0% by weight or less. When the content of the bifunctional phenol compound is above the lower limit, the wettability of the solder can be further improved. When the content of the bifunctional phenol compound is below the upper limit, the generation of voids can be suppressed, and the thermal cycle resistance of the resulting connection structure can be improved.

[0094] The content of the bifunctional phenol compound is preferably 30 parts by weight or more, more preferably 40 parts by weight or more, and even more preferably 45 parts by weight or more, relative to 100 parts by weight of the epoxy compound, and is preferably 100 parts by weight or less, more preferably 90 parts by weight or less, and even more preferably 80 parts by weight or less. When the content of the bifunctional phenol compound is above the lower limit, the wettability of the solder can be further improved. When the content of the bifunctional phenol compound is below the upper limit, the generation of voids can be suppressed, and the thermal cycle resistance of the resulting connection structure can be improved.

[0095] The total content of the acid anhydride and the bifunctional phenol compound in the flux composition (100% by weight) is preferably 20.0% by weight or more, more preferably 30.0% by weight or more, and 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 bifunctional phenol compound is equal to or more than the lower limit and equal to or less than the upper limit, the viscosity stability can be further improved, the solder wettability can be further improved, and the thermal cycle resistance of the resulting connection structure can be further improved.

[0096] The total content of the acid anhydride and the bifunctional phenol compound relative to 100 parts by weight of the epoxy compound is preferably 50 parts by weight or more, more preferably 60 parts by weight or more, even more preferably 80 parts by weight or more, and is preferably 120 parts by weight or less, more preferably 110 parts by weight or less, and even more preferably 95 parts by weight or less. When the total content of the acid anhydride and the bifunctional phenol compound is equal to or more than the above lower limit and equal to or less than the above upper limit, the viscosity stability can be further improved, the solder wettability can be further improved, and the thermal cycle resistance of the resulting connection structure can be further improved.

[0097] The weight ratio of the content of the bifunctional phenol compound in the flux composition to the content of the acid anhydride in the flux composition is defined as the ratio (content of bifunctional phenol compound / content of acid anhydride). This weight ratio (content of bifunctional phenol compound / content of acid anhydride) is preferably 0.1 or more, more preferably 0.5 or more, even more preferably 1.0 or more, and preferably 10.0 or less, more preferably 7.9 or less, and even more preferably 5.0 or less. When the weight ratio (content of bifunctional phenol compound / content of acid anhydride) is equal to or greater than the lower limit, the solder wettability can be further improved. When the weight ratio (content of bifunctional phenol compound / content of acid anhydride) is equal to or less than the upper limit, the generation of voids can be suppressed and the thermal cycle durability of the resulting connection structure can be improved. The content of the bifunctional phenol compound in the flux composition is the content (wt%) of the bifunctional phenol compound in 100 wt% of the flux composition. The content of the acid anhydride in the flux composition is the content (wt%) of the acid anhydride in 100 wt% of the flux composition.

[0098] <Curing Accelerator> The flux composition contains a curing accelerator.

[0099] Examples of the curing accelerator include an imidazole compound, a phosphorus compound, an amine compound, and an organometallic compound. The curing accelerator may be used alone or in combination of two or more.

[0100] Examples of the imidazole compound include 2-undecylimidazole, 2-heptadecylimidazole, 2-methylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole, 1-benzyl-2-methylimidazole, 1-benzyl-2-phenylimidazole, 1,2-dimethylimidazole, 1-cyanoethyl-2-methylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazole, 1-cyanoethyl-2-undecylimidazole, 1-cyanoethyl-2-phenylimidazole, 1-cyanoethyl-2-undecylimidazole, 1-cyanoethyl-2-phenylimidazole, 1-cyanoethyl-2-undecylimidazole trimellitate, and 1-cyanoethyl-2-phenylimidazolium trimethylolate. limeritate, 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine, 2,4-diamino-6-[2'-undecylimidazolyl-(1')]-ethyl-s-triazine, 2,4-diamino-6-[2'-ethyl-4'-methylimidazolyl-(1')]-ethyl-s-triazine, 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine isocyanuric acid adduct, 2-phenylimidazole isocyanuric acid adduct, 2-methylimidazole isocyanuric acid adduct, 2-phenyl-4,5-dihydroxymethylimidazole, and 2-phenyl-4-methyl-5-dihydroxymethylimidazole.

[0101] Examples of the amine compound include diethylamine, triethylamine, diethylenetetramine, triethylenetetramine, and 4,4-dimethylaminopyridine.

[0102] Examples of the organometallic compound include zinc naphthenate, cobalt naphthenate, tin octoate, cobalt octoate, bisacetylacetonate cobalt (II), and trisacetylacetonate cobalt (III).

[0103] From the viewpoint of further increasing the wettability of the solder and further increasing the thermal cycle resistance of the resulting connection structure, it is preferable that the curing accelerator contains the phosphorus compound, and it is more preferable that it contains an organic phosphorus compound.

[0104] 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.

[0105] 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.

[0106] The organic phosphonium salt includes an organic phosphonium salt composed of a phosphonium ion and its counter ion.

[0107] From the viewpoint of improving the electrical conductivity reliability of the resulting connection structure, the organic phosphonium salt is preferably methyltributylphosphonium dimethylphosphate, tributylmethylphosphonium bis(2-ethylhexyl)phosphate, or tetrabutylphosphonium bromide, and more preferably methyltributylphosphonium dimethylphosphate.

[0108] Commercially available organic phosphonium salts include "JPB-659" manufactured by Johoku Chemical Industry Co., Ltd., "SYIL-02" manufactured by Sanyo Chemical Industries, Ltd., and the "Hishicolin" series manufactured by Nippon Chemical Industry Co., Ltd.

[0109] 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.

[0110] From the viewpoint of improving solder wettability, the flux composition preferably contains a neutralized product of a monovalent or higher organic acid. From the viewpoint of improving thermal cycle resistance, the neutralized product of the monovalent or higher organic acid preferably does not have a carboxy group.

[0111] The content of the curing accelerator 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 curing accelerator is equal to or more than the lower limit and equal to or less than the upper limit, the wettability of the solder can be further improved, and the thermal cycle resistance of the resulting connection structure can be further improved.

[0112] 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 lower limit and equal to or less than the above upper limit, the wettability of the solder can be further improved, and the thermal cycle resistance of the resulting connection structure can be further improved.

[0113] 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, 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 wettability of the solder can be further improved, and the thermal cycle resistance of the resulting connection structure can be further improved.

[0114] The content of the organic phosphonium salt is preferably 0.18 parts by weight or more, more preferably 0.54 parts by weight or more, and even more preferably 0.57 parts by weight or more, relative to 100 parts by weight of the epoxy compound, and is preferably 1.83 parts by weight or less, more preferably 0.91 parts by weight or less, and even more preferably 0.58 parts by weight or less. When the content of the organic phosphonium salt is equal to or more than the above-mentioned lower limit and equal to or less than the above-mentioned upper limit, the wettability of the solder can be further improved, and the thermal cycle resistance of the resulting connection structure can be further improved.

[0115] From the viewpoint of further improving the wettability of the solder and further increasing the thermal cycle resistance of the resulting connection structure, the content of the curing accelerator is preferably 0.5 parts by weight or more, more preferably 1 part by weight or more, and preferably 10 parts by weight or less, more preferably 5 parts by weight or less, per 100 parts by weight of acid anhydride.

[0116] <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.

[0117] (Connection Structure and Method for Producing Connection Structure) The flux composition according to the present invention is suitably used to obtain a connection structure.

[0118] 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.

[0119] 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.

[0120] 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.

[0121] 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.

[0122] 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 improving thermal cycle resistance, it is preferable to dispose the flux composition by a dispensing method in the first disposing step.

[0123] 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.

[0124] 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). This eliminates the need for a second heating step. 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 heating step, thereby suppressing the generation of voids in the connection structure. As a result, the probability of connection failure due to poor connection or the like when the connection structure is repeatedly heated and cooled can be reduced (the connection structure's thermal cycle resistance can be improved).

[0125] Hereinafter, specific embodiments of the present invention will be described with reference to the drawings.

[0126] 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.

[0127] The connection structure 1 shown in FIG. 1 includes a first connection target member 2, a second connection target member 3, and a resin portion 4 connecting the first connection target member 2 and the second connection target member 3. The resin portion 4 is formed of 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 portion 4 is the flux composition 4Xa. The flux composition 4Xa contains an epoxy compound, an acid anhydride, a bifunctional phenol compound, and a curing accelerator. In this embodiment, the flux composition 4Xa is preferably in a liquid form, and more preferably a solvent-free liquid.

[0128] The resin portion 4 is a cured portion obtained by thermally curing the flux composition 4Xa.

[0129] 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.

[0130] 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.

[0131] 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.

[0132] 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. A flux composition 4Xa is also prepared. The flux composition 4Xa contains an epoxy compound, an acid anhydride, a bifunctional phenol compound, and a curing accelerator.

[0133] 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.

[0134] 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.

[0135] 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.

[0136] 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.

[0137] 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.

[0138] 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.

[0139] 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.

[0140] 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.

[0141] 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.

[0142] 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.

[0143] 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.

[0144] 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.

[0145] 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.

[0146] 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.

[0147] 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.

[0148] 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.

[0149] 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.

[0150] 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.

[0151] 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.

[0152] 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.

[0153] 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.

[0154] 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.

[0155] 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.

[0156] 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.

[0157] 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).

[0158] 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.

[0159] The following materials were prepared:

[0160] Epoxy compounds: Bisphenol F type epoxy compound ("EXA-830CRP" manufactured by DIC Corporation) Biphenyl type epoxy compound ("YX-4000HK" manufactured by Mitsubishi Chemical Corporation)

[0161] Acid anhydride: Mixture of hexahydrophthalic anhydride and methylhexahydrophthalic anhydride ("Rikacid MH-700" manufactured by New Japan Chemical Co., Ltd.) 4-methylhexahydrophthalic anhydride ("Rikacid MH-T" manufactured by New Japan Chemical Co., Ltd.)

[0162] Bifunctional phenol compounds: Diallyl bisphenol F ("APG-LC" manufactured by Gunei Chemical Industry Co., Ltd.) Diallyl bisphenol A ("DA-BPA" manufactured by Yokkaichi Chemical Co., Ltd.)

[0163] Trifunctional phenol compound: 1,1,1-tris(4-hydroxyphenyl)ethane ("TrisP-HAP" manufactured by Honshu Chemical Industry Co., Ltd.)

[0164] Monofunctional phenolic compound: Phenol (Tokyo Chemical Industry Co., Ltd.)

[0165] Curing accelerator: Methyl tributylphosphonium dimethylphosphate (Nippon Chemical Industry Co., Ltd., "Hishicolin PX-4MP") Tetrabutylphosphonium benzotriazolate (Nippon Chemical Industry Co., Ltd., "Hishicolin PX-4BT") Tetrabutylphosphonium tetraphenylborate (Nippon Chemical Industry Co., Ltd., "Hishicolin PX-4PB")

[0166] Activator: Benzylamine adipate (Showa Chemical Co., Ltd.)

[0167] (Examples 1 to 12 and Comparative Examples 1 to 6) (1) Preparation of Flux Compositions The components shown in Tables 1 to 4 below were mixed in the amounts shown in Tables 1 to 4 below, and then kneaded with a three-roll mill (NR-42A manufactured by Noritake Co., Ltd.) at a roll gap of 30 μm, and filtered with a SUS mesh filter (opening size 100 μm) to obtain flux compositions.

[0168] (2) Preparation of Connection Structure: A BGA (0.8 mm pitch, 100 electrodes) was prepared as a first connection target component (package) having first electrodes on its surface. A printed circuit board (material: FR4, thickness: 1 mm) having gold electrodes on its surface corresponding to the first connection target component was prepared as a second connection target component. The flux composition immediately after preparation was dispensed onto the second electrodes of the second connection target component (first placement step, see FIG. 8(b4)). Next, the first connection target components were stacked so that their electrodes faced each other (second placement step). The weight of the first connection target component was added to the solder particles (Sn96.5Ag3.0Cu0.5 solder (melting point: 217°C), particle diameter: 0.5 mm) and flux composition in the BGA. From this state, the flux composition was cured by heating it from 35°C to 260°C at a temperature increase rate of 1°C / sec, for a total time of 90 seconds at or above 220°C, using a reflow simulator (Cores Corporation, "core9056a"). No pressure was applied during heating. Note that in all examples and comparative examples, the heating step (reflow step) was performed only once.

[0169] (Evaluation) (1) Viscosity at 25°C The viscosity of the obtained flux composition at 25°C immediately after preparation was measured using an E-type viscometer ("VISCOMETER TV-22" manufactured by Toki Sangyo Co., Ltd., rotor diameter 15 mm) under the conditions of 25°C and 5 rpm.

[0170] (2) Solder Wetting and Spreading Properties: The resulting flux composition was applied by screen printing to a substrate (phosphorus-deoxidized copper plate, "C1220" manufactured by Engineering Test Services) to form a 0.2 mm thick flux composition layer. 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 using a reflow simulator ("Core9056a" manufactured by Cores Corporation) at a heating rate of 1°C / sec from 35°C to 260°C, with a total time of 220°C or higher for 90 seconds, and then cooled to room temperature. The solder was then observed using an optical microscope (manufactured by Keyence Corporation), and the major axis (μm) of the solder in plan view was measured. The solder wetting and spreading properties were evaluated according to the following criteria.

[0171] [Criteria for determining solder wetting and spreading properties] ○○: The major axis of the solder is 800 μm or more. ○: The major axis of the solder is 700 μm or more and less than 800 μm. ×: The major axis of the solder is less than 700 μm.

[0172] (3) Viscosity Stability After the obtained flux composition was allowed to stand at 25°C for 8 hours, the viscosity of the flux composition at 25°C was measured using an E-type viscometer ("VISCOMETER TV-22" manufactured by Toki Sangyo Co., Ltd., rotor diameter 15 mm, 3° x R14) at 25°C and 10 rpm. The viscosity ratio expressed by the following formula was calculated. The viscosity stability was evaluated according to the following criteria.

[0173] Viscosity ratio = (viscosity of the flux composition after standing at 25°C for 8 hours) / (viscosity of the flux composition immediately after preparation)

[0174] [Criteria for determining viscosity stability] ◯: Viscosity ratio is 1.0 or more and less than 1.1 ○: Viscosity ratio is 1.1 or more and less than 1.5 ×: Viscosity ratio is 1.5 or more

[0175] (4) Thermal Cycle Resistance: The resulting flux composition was applied to a transfer tray to a thickness of 0.15 mm, and then transferred to the solder bumps of a dummy chip, WLP100T.3C-DC108D (Tpline), using a chip mounter, SMT-64RH (Okuhara Electric Co., Ltd.). The resulting chip was then aligned and mounted on a PCB to produce a connection structure. The connection resistance per connection point between the upper and lower electrodes of the resulting connection structure (connection structure before thermal cycle testing) was measured using a four-terminal method. Note that, based on the relationship voltage = current × resistance, the connection resistance can be determined by measuring the voltage when a constant current is applied. The connection structure was then heated from 35°C to 260°C at a heating rate of 1°C / s, with the total time at 220°C or higher being 90 seconds, and then cooled to room temperature. A thermal cycle test was then performed, repeating 1,000 cycles, with each cycle consisting of cooling to -40°C. The average value of the connection resistance was calculated for the connection structure after the thermal cycle test in the same manner. The rate of change in connection resistance was calculated using the following formula. The thermal cycle resistance was evaluated according to the following criteria.

[0176] Change rate of connection resistance (%)=((average value of connection resistance after thermal cycle test)−(average value of connection resistance before thermal cycle test)) / (average value of connection resistance before thermal cycle test)×100

[0177] [Criteria for thermal cycle resistance] ○○: The rate of change in connection resistance is less than 5%. ○: The rate of change in connection resistance is 5% or more but less than 10%. ×: The rate of change in connection resistance is 10% or more.

[0178] The compositions and results are shown in Tables 1 to 4 below.

[0179]

[0180]

[0181]

[0182]

[0183] 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, an acid anhydride, a difunctional phenol compound, and a curing accelerator. A flux composition wherein the content of the acid anhydride is 5.0% by weight or more and 32.0% by weight or less in 100% by weight of the flux composition.

2. The flux composition according to claim 1, wherein the content of the difunctional phenol compound in 100% by weight of the flux composition is 15.0% by weight or more and 42.0% by weight or less.

3. The flux composition according to claim 1 or 2, wherein the content of the curing accelerator in 100% by weight of the flux composition is 0.1% by weight or more and 1.0% by weight or less.

4. The flux composition according to claim 1 or 2, wherein the weight ratio of the content of the difunctional phenol compound in the flux composition to the content of the acid anhydride in the flux composition is 0.5 or more and 7.9 or less.

5. The flux composition according to claim 1 or 2, wherein the flux composition is a non-conductive flux composition.

6. The flux composition according to claim 1 or 2, wherein the flux composition is a pre-fill underfill material used in a pre-fill underfill process.

7. The flux composition according to claim 1 or 2, wherein the flux composition is used in contact with a tin-silver-copper alloy solder.

8. Use of the flux composition according to claim 1 or 2 as a pre-fill underfill material used in a pre-fill underfill process.

9. Use of the flux composition according to claim 1 or 2 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 claim 1 or 2.

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 according to claim 1 or 2, 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.