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

Technical Field

[0001] The present invention relates to a flux composition and the 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.

Background Art

[0002] In recent years, with the miniaturization, weight reduction, and high functionality of electronic devices such as data servers, personal computers (PCs), and mobile terminals, the wiring pitch in printed wiring boards and the like has been becoming finer. Therefore, surface mount packages such as ball grid arrays (BGAs) in which wiring extends directly under a chip and ultra-small chip scale packages (CSPs) have attracted attention.

[0003] However, in surface mount packages such as BGAs, unlike conventional pin insertion type packages, electrodes on the surface of a wiring board are connected by solder particles, so there is a problem that the adhesiveness is low and it is easily damaged (low impact resistance) when dropped.

[0004] Therefore, an underfill material may be filled and cured between a semiconductor chip and a semiconductor package substrate to reinforce the bonding portion.

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

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

[0007] When an underfill material as described in Patent Document 1 is used as a encapsulant, 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 conventional production process for connection structures, after a reflow process (heating process) is performed to connect the electrodes, an underfill material is permeated and filled between the semiconductor chip and the semiconductor package substrate by capillary action, and another heating process is required to harden the underfill material. In other words, the conventional method of manufacturing a connection structure using underfill material, as described in Patent Document 1, has the problem of low productivity because the heating process must be performed twice.

[0009] Furthermore, connection structures are repeatedly heated and cooled during use, and the connection points may be exposed to heating and cooling. When conventional underfill materials are used as the flux composition to fabricate connection structures, cracks may occur in the solder when the connection structure is repeatedly heated and cooled, making it impossible to sufficiently reduce the connection resistance between the upper and lower electrodes to be connected. In other words, it is difficult to improve the thermal cycling resistance of the resulting connection structure with conventional flux compositions.

[0010] An object of the present invention is to provide a flux composition and a use of the flux composition that can improve the thermal cycling resistance of the resulting connection structure. Another object of the present invention is to provide a connection structure using the above flux composition and a method for manufacturing the connection structure using the above flux composition. [Means for solving the problem]

[0011] This specification discloses the following flux compositions, uses of the flux compositions, connecting structures, and methods for manufacturing the connecting structures.

[0012] Item 1. A flux composition comprising an epoxy compound, an acid anhydride, a difunctional 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 of 100% by weight of the flux composition.

[0013] Item 2. The flux composition according to Item 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.

[0014] Item 3. The flux composition according to item 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.

[0015] Item 4. The flux composition according to any one of items 1 to 3, 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.

[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 underfill material used in a first-in underfill process.

[0018] Item 7. The flux composition according to any one of items 1 to 6, which is used in contact with a tin-silver-copper alloy solder.

[0019] Item 8. Use of any one of the flux compositions described in items 1 to 7 as a first-in underfill material in a first-in underfill process.

[0020] Item 9. Use of any one of the flux compositions described in items 1 to 7 as a flux for the surface of 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 portion 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 portion is the flux composition described in any one of items 1 to 7.

[0022] Item 11. A method for manufacturing a connection structure, comprising: a first placement step of placing the flux composition on the surface of the solder particles on the first connection structure or on the surface of the second connection structure, 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 items 1 to 7; a second placement 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 a resin portion connecting the first connection target member and the second connection target member using the flux composition. [Effects of the Invention]

[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. In 100% by weight of the flux composition, the content of the acid anhydride is 5.0% by weight or more and 32.0% by weight or less. In the flux composition according to the present invention, since the above configuration is provided, the thermal cycle resistance of the obtained connection structure can be enhanced.

Brief Description of Drawings

[0024] [Figure 1] FIG. 1 is a cross-sectional view schematically showing a connection structure obtained using the flux composition according to an embodiment of the present invention. [Figure 2] FIG. 2(a) is a cross-sectional view for explaining each step of an example of a method for manufacturing a connection structure using the flux composition according to an embodiment of the present invention. [Figure 3] FIG. 3(b1) is a cross-sectional view for explaining each step of an example of a method for manufacturing a connection structure using the flux composition according to an embodiment of the present invention. [Figure 4] FIG. 4(c) is a cross-sectional view for explaining each step of an example of a method for manufacturing a connection structure using the flux composition according to an embodiment of the present invention. [Figure 5] FIG. 5(d) is a cross-sectional view for explaining each step of an example of a method for manufacturing a connection structure using the flux composition according to an embodiment of the present invention. [Figure 6] FIG. 6(b2) is a cross-sectional view for explaining a modified example of a method for manufacturing a connection structure using the flux composition according to an embodiment of the present invention. [Figure 7] FIG. 7(b3) is a cross-sectional view for explaining a modified example of a method for manufacturing a connection structure using the flux composition according to an embodiment of the present invention. [Figure 8] FIG. 8(b4) is a cross-sectional view for explaining a modified example of a method for manufacturing a connection structure using the flux composition according to an embodiment of the present invention.

Embodiments for Carrying Out the Invention

[0025] The details of the present invention will be described below.

[0026] (Flux composition) The flux composition according to the present invention is a flux composition comprising an epoxy compound, an acid anhydride, a difunctional phenol compound, and a curing accelerator. In the flux composition according to the present invention, the content of the acid anhydride is 5.0% by weight or more and 32.0% by weight or less of the flux composition by 100% by weight.

[0027] The above flux composition is thermocurable. The above flux composition has the property of curing upon heating.

[0028] In conventional methods, where a reflow process (heating process) is performed to connect electrodes, followed by sealing with an underfill material, the heating process is repeated twice—once for soldering and once for curing the underfill material—which results in low productivity.

[0029] The flux composition according to the present invention has the above configuration, so when manufacturing a connection structure using the flux composition, the solder can be melted and the electrodes joined together in a single heating step (reflow step), and the flux composition can be cured. For this reason, it is not necessary to perform the heating step twice. In other words, with the flux composition of the present invention, batch mounting is possible when manufacturing a connection structure, so productivity can be increased. Since it can be used as a flux composition that does not require cleaning, the flux composition according to the present invention can be used to manufacture connection structures with small distances between electrodes well (it is suitably used for manufacturing connection structures with small distances between electrodes). Furthermore, with semiconductor chips or semiconductor package substrates with large surface areas, penetration of general underfill materials is difficult or impossible. The flux composition according to the present invention can be used to manufacture connection structures using semiconductor chips or semiconductor package substrates with large surface areas well (it is suitably used for manufacturing connection structures using semiconductor chips or semiconductor package substrates with large surface areas). The flux composition according to the present invention is suitably used as a first-in underfill material. From the viewpoint of effectively exhibiting the effects of the present invention, the flux composition is preferably a first-in underfill material used in a first-in underfill process (use of the flux composition as a first-in underfill material used in a first-in underfill process). From the viewpoint of effectively exhibiting 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 fabricated using a conventional flux composition, the flux composition hardens before the solder melts due to heating, preventing the solder from adequately wetting and spreading across the electrode surface. This can result in connection failures in the resulting connection structure. In other words, it is difficult to improve the conductivity reliability of the resulting connection structure using conventional flux compositions.

[0031] Furthermore, connection structures are repeatedly heated and cooled during use, and the connection points may be exposed to heating and cooling. When connection structures are made using conventional flux compositions and are repeatedly heated and cooled, cracks may occur in the solder, leading to connection failure. In other words, it is difficult to improve the thermal cycling resistance of the resulting connection structures with conventional flux compositions. In particular, if the solder does not sufficiently wet and spread over the electrode surface, or if voids are present in the connection structure, cracks are more likely to occur in the solder, and the above problems become even more pronounced.

[0032] The flux composition according to the present invention has the above configuration, which allows the solder to sufficiently wet and spread across the electrode surface, thereby reducing the connection resistance between the upper and lower electrodes in the resulting connection structure. As a result, the conductivity reliability of the resulting connection structure can be improved.

[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 connection failures when the connection structure is repeatedly heated and cooled. In other words, the flux composition according to the present invention can improve the thermal cycling resistance of the resulting connection structure.

[0034] In order to achieve the effects of the present invention, it is necessary to use a difunctional phenol compound. Using a trifunctional or more functional phenol compound results in low solder wettability. Using a monofunctional phenol compound results in low thermal cycling resistance of the resulting connection structure. The inventors have found that in order to achieve the effects of the present invention, it is important to select and use a difunctional phenol compound from among phenol compounds.

[0035] Furthermore, generally speaking, increasing the curing properties of adhesives (conductive pastes) can lead to lower storage stability and increased viscosity during storage. As a result, there is a problem of a shorter pot life (working time).

[0036] The flux composition according to the present invention has the above-described configuration, and therefore its storage stability can be improved.

[0037] The viscosity (η25) of the above flux composition at 25°C is preferably 1.0 Pa·s or higher, more preferably 1.5 Pa·s or higher, even more preferably 6.0 Pa·s or higher, preferably 10.0 Pa·s or lower, and more preferably 6.5 Pa·s or lower. When the viscosity (η25) is above the lower limit, it is possible to suppress excessive wetting and spreading of the flux composition when it is placed, and to place the flux composition in an appropriate amount. As a result, the generation of voids in the resulting connection structure can be suppressed. Furthermore, when the viscosity (η25) is below the upper limit, the storage stability is further enhanced, and a sufficient amount of the flux composition can be placed. The viscosity (η25) can be appropriately adjusted depending on the type and amount of the components being blended.

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

[0039] From the viewpoint of further improving the applicability of the above flux composition, it is preferable that the flux composition be liquid at 25°C. Note that paste-like forms are included in the category of liquid.

[0040] The flux composition may be placed by dispensing, screen printing, inkjet dispensing, or dipping. From the viewpoint of suppressing the generation of voids in the resulting connection structure, it is preferable to place the flux composition by dispensing.

[0041] The properties of the heated material after heating the above flux composition at 250°C for 90 seconds are preferably solid. With the above configuration, the incorporation of outgassing released from the substrate due to heating during the heating process can be suppressed, and the generation of voids in the resulting connection structure can be suppressed.

[0042] The properties of the heated object at 250°C after heating the above flux composition at 250°C for 90 seconds can be confirmed, for example, by the following method: 0.05 g of the above flux composition is applied to the surface of a copper plate (phosphorus deoxidized copper plate, "C1220" manufactured by Engineering Test Service Co., Ltd., 0.3 mm thick) placed on a glass plate ("Large Slide Glass" manufactured by Matsunami Glass Co., Ltd., 1.0 mm thick), and the plate is placed on a hot plate heated to 250°C. After heating for 90 seconds, the properties of the heated object on the 250°C hot plate at 250°C are checked by touching it with a bamboo skewer.

[0043] Differential scanning calorimetry (DSC) is performed on the flux composition under a nitrogen atmosphere, heated from 30°C to 360°C at a heating rate of 60°C / min. In the flux composition, it is preferable that the temperature range of the exothermic peak in the differential scanning calorimetry includes 220°C. That is, in the flux composition, it is preferable that the exothermic start temperature is 220°C or lower, and the exothermic end temperature is 220°C or higher. Furthermore, in the flux composition, it is preferable that the reaction rate of the flux composition at 220°C, as described later, is greater than 0% and less than or equal to 100%. These preferred embodiments prevent the flux composition from curing before the solder melts due to heating, allowing the solder to wet and spread more sufficiently on the electrode surface. As a result, the conductivity reliability and thermal cycling resistance of the resulting connection structure can be further improved.

[0044] The differential scanning calorimetry (DSC) described above can be performed using the following method: Prepare a differential scanning calorimetry device. Place 5 mg of the flux composition in a dedicated aluminum pan (aluminum container). Place this dedicated aluminum pan and an empty aluminum pan (reference) in a heating unit and heat under conditions from 30°C to 360°C with a nitrogen flow rate of 50 mL / min and a heating rate of 60°C / min, and observe the reverse heat flow and non-reverse heat flow. 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 calorimetry devices described above include the "EXSTAR DSC7020" manufactured by SII Corporation and the "DSC7020" manufactured by Hitachi High-Tech Science Corporation.

[0045] In this specification, the exothermic onset temperature refers to the temperature at which the amount of heat generated begins to rise from the baseline. Specifically, the exothermic 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 exothermic termination temperature refers to the temperature at which the amount of heat generated decreases to 1% of the amount of heat generated at the exothermic peak after reaching the exothermic peak top.

[0046] In the differential scanning calorimetry described above, the exothermic onset temperature is preferably 100°C or higher, more preferably 120°C or higher, even more preferably 140°C or higher, preferably 220°C or lower, more preferably 200°C or lower, and even more preferably 180°C or lower. When the exothermic onset temperature is above the lower limit and below the upper limit, the storage stability and applicability of the flux composition can be improved, and the conductivity reliability can be increased when the device is mounted in a relatively short time.

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

[0048] From the viewpoint of improving conductivity reliability when implemented in a relatively short time, in the differential scanning calorimetry described above, the exothermic termination temperature is preferably 180°C or higher, more preferably 200°C or higher, even more preferably 220°C or higher, preferably 260°C or lower, more preferably 250°C or lower, and even more preferably 240°C or lower.

[0049] In the differential scanning calorimetry described above, the area of ​​the exothermic peak in the temperature range of 220°C or below, out of 100% of the total area of ​​the exothermic peak, is defined as the reaction rate of the flux composition at 220°C. The reaction rate 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, 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. If the reaction rate of the flux composition at 220°C is above the lower limit, the curability of the flux composition can be further enhanced, and the generation of voids in the resulting connection structure can be suppressed. If the reaction rate of the flux composition at 220°C is below the upper limit, the wettability of the solder can be further enhanced, and the conductivity reliability and thermal cycle resistance of the resulting connection structure can be further enhanced.

[0050] From the viewpoint of further wetting and spreading the solder appropriately, the reaction rate 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 below 220°C (reaction rate of the flux composition at 220°C) within 100% of the total area of ​​the exothermic peaks mentioned above can be calculated, for example, using spreadsheet software such as Excel or NEXTA standard analysis software ("Standard Analysis" manufactured by Hitachi High-Tech Corporation).

[0052] In the differential scanning calorimetry described above, the following methods can be used to adjust the temperature range of the exothermic peak, the exothermic start temperature, the exothermic peak top temperature, the exothermic end temperature, and the reaction rate of the flux composition at 220°C to the preferred range described above: 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 described above, 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, 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 above the lower limit and below the upper limit, the storage stability of the flux composition can be improved, and the conductivity reliability can be increased when it is mounted in a relatively short time.

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

[0055] Furthermore, the flux composition has good adhesive properties. The flux composition is suitably used as an adhesive. The flux composition is particularly suitable for bonding semiconductor chips to semiconductor package substrates (use of the flux composition for bonding semiconductor chips to semiconductor package substrates).

[0056] The above flux composition is suitably used to obtain a connection structure. The above flux composition is suitably used to obtain an electronic component. The above flux composition is suitably used for bonding and connecting a surface mount package to a wiring board (use of the above flux composition for bonding and connecting a surface mount package to a wiring board). Examples of the above surface mount package include BGA and CSP.

[0057] The above flux composition has good fluxing properties for solder. The above flux composition can effectively remove oxide films from the surface of electrodes and solder in the resulting connection structure. The solder to which the above flux composition can be applied is not particularly limited. The above solder is preferably a filler material with a liquidus temperature of 450°C or less, based on JIS Z3001: Welding Terminology. The above solder is preferably a metal (low melting point metal) with a melting point of 450°C or less. The above solder may be solder particles. The above solder particles are preferably metal particles (low melting point metal particles) with a melting point of 450°C or less. The above low melting point metal particles are particles containing a low melting point metal. The low melting point metal refers to a metal with a melting point of 450°C or less. The melting point of the low melting point metal is preferably 300°C or less, more preferably 260°C or less. The above solder is preferably a low melting point solder with a melting point of less than 250°C.

[0058] The low-melting-point metal constituting the solder described above is not particularly limited. The low-melting-point metal is preferably tin or an alloy containing tin. Examples of such alloys include tin-silver alloys, tin-copper alloys, tin-silver-copper alloys, tin-bismuth alloys, tin-zinc alloys, tin-indium alloys, and tin-antimony alloys. Due to their excellent wettability to electrodes, the low-melting-point metal is preferably tin, tin-silver alloys, tin-silver-copper alloys, tin-bismuth alloys, tin-indium alloys, and tin-antimony alloys, more preferably tin-silver-copper alloys, tin-bismuth alloys, tin-indium alloys, or tin-antimony alloys, and particularly preferably tin-silver-copper alloys.

[0059] From the viewpoint of effectively exhibiting the effects of the present invention, it is preferable that the flux composition be used in contact with the solder (use of the flux composition as a flux on the surface of the solder). The flux composition has particularly good fluxing properties with respect to tin-silver-copper alloy solder (SnAgCu solder). From the viewpoint of effectively exhibiting the effects of the present invention, it is preferable that the flux composition be used in 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)). In other words, from the viewpoint of effectively exhibiting the effects of the present invention, it is preferable that the flux composition be used in the manufacture of a connection structure using tin-silver-copper alloy solder (use of the flux composition for the manufacture of a connection structure using tin-silver-copper alloy solder). From the viewpoint of effectively exhibiting the effects of the present invention, it is particularly preferable that the flux composition be used 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, preferably 400°C or lower, more preferably 350°C or lower, and even more preferably 300°C or lower.

[0061] The melting point of the above solder can be determined by differential scanning calorimetry (DSC). Examples of differential scanning calorimetry (DSC) equipment include the "EXSTAR DSC7020" manufactured by SII Corporation.

[0062] The flux composition described above is preferably non-conductive. The flux composition described above is preferably free of conductive substances. The flux composition described above is preferably free of conductive particles. The flux composition described above is preferably free of metal particles. The flux composition described above is preferably a non-conductive flux composition. When the flux composition satisfies these preferred embodiments, the conductivity reliability and thermal cycling resistance of the resulting connection structure can be further improved. In this specification, a non-conductive flux composition is defined as having a volume resistivity of 1.0 × 10⁻⁶. 8 This shows a flux composition with a value of Ω·cm or greater.

[0063] The volume resistivity mentioned above is the volume resistivity at 20 kN. This volume resistivity can be measured using a resistivity meter (Mitsubishi Chemical Corporation's "Powder Resistivity Measurement System").

[0064] <Epoxy compounds> The above 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 compounds mentioned above 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 core as their skeleton. Only one of the epoxy compounds may be used, or two or more may be used in combination.

[0066] From the viewpoint of further improving the applicability of the above flux composition, the epoxy compound preferably contains a biphenyl-type epoxy compound, a bisphenol F-type epoxy compound, or an epoxy compound having a triazine core as its backbone, and more preferably contains a bisphenol F-type epoxy compound. The epoxy compound preferably contains a biphenyl-type epoxy compound, a bisphenol F-type epoxy compound, or an epoxy compound having a triazine core as its backbone, and more preferably a bisphenol F-type epoxy compound.

[0067] From the viewpoint of further improving the applicability of the above flux composition, it is preferable that the epoxy compound includes an epoxy compound that is solid at 25°C. The epoxy compound that is solid at 25°C may be used alone, or two or more may be used in combination.

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

[0069] In 100% by weight of the above flux composition, the content of the epoxy compound 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, 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 above the lower limit and below the upper limit, viscosity stability can be further enhanced, solder wettability can be further enhanced, and the thermal cycling resistance of the resulting connection structure can be further enhanced.

[0070] In 100% by weight of the above flux composition, the content of the epoxy compound that is solid at 25°C 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, 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 above the lower limit and below the upper limit, viscosity stability can be further enhanced, solder wettability can be further enhanced, and the thermal cycling resistance of the resulting connection structure can be further enhanced.

[0071] In 100% by weight of the above epoxy compound, the content of the epoxy compound that is solid at 25°C is preferably 80.0% by weight or more, more preferably 85.0% by weight or more, even more preferably 90.0% by weight or more, 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 above the lower limit and below the upper limit, viscosity stability can be further enhanced, solder wettability can be further enhanced, and the thermal cycling resistance of the resulting connection structure can be further enhanced.

[0072] <Hardening agent> The above flux composition contains a curing agent. The curing agent heat-cures the epoxy compound.

[0073] Examples of the curing agents 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, dicyandiamides, and acid anhydrides. It is preferable that the curing agent has a functional group that can react with the epoxy group of the epoxy compound. The curing agent may be used alone or in combination of two or more.

[0074] The above flux composition comprises an acid anhydride and a difunctional phenol compound. In the above flux composition, the acid anhydride and the difunctional phenol compound preferably act as curing agents for the epoxy compound. Because the above flux composition contains a difunctional phenol compound, the curability of the flux composition can be further enhanced, and the generation of voids in the resulting connection structure can be suppressed. Because the above flux composition contains an acid anhydride, the boiling of the flux composition due to heating in the reflow process (heating process) can be prevented, and the generation of voids in the resulting connection structure can be suppressed. Because the above flux composition contains an acid anhydride and a difunctional phenol compound, the curability of the flux composition can be further enhanced, and the generation of voids in the resulting connection structure can be suppressed. As a result, the thermal cycling resistance of the resulting connection structure can be improved.

[0075] (acid anhydride) The above flux composition contains the above acid anhydride. The above acid anhydride heat-cures the above epoxy compound. By using the above acid anhydride in combination with a curing accelerator (particularly an organophosphorus compound), the fluxing effect of the above 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 above acid anhydride in combination with the above difunctional phenol compound, the curability 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 enhanced.

[0076] Examples of the above-mentioned acid anhydrides include phthalic acid anhydride, tetrahydrophthalic anhydride, trialkyltetrahydrophthalic anhydride, hexahydrophthalic anhydride, methylhexahydrophthalic anhydride, methyltetrahydrophthalic anhydride, methylbutenyltetrahydrophthalic anhydride, phthalic acid derivative anhydrides, maleic anhydride, nadic anhydride, methylnadic anhydride, glutaric anhydride, succinic anhydride, glycerin bistrimellitic anhydride monoacetate, and difunctional acid anhydrides such as ethylene glycol bistrimellitic anhydride, trifunctional acid anhydrides such as trimellitic anhydride, and tetrafunctional or more acid anhydrides such as pyromellitic anhydride, benzophenone tetracarboxylic anhydride, methylcyclohexenetetracarboxylic anhydride, and polyazelaic anhydride. The above-mentioned acid anhydrides may be used individually or in combination of two or more.

[0077] From the viewpoint of further improving the applicability of the above flux composition, the above acid anhydride preferably contains tetrahydrophthalic anhydride, hexahydrophthalic anhydride, or methylhexahydrophthalic anhydride, and more preferably contains methylhexahydrophthalic anhydride.

[0078] From the viewpoint of further improving the applicability of the above flux composition, it is preferable that the above acid anhydride is liquid at 25°C.

[0079] From the viewpoint of further improving the applicability 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 upper limit values.

[0080] The content of the above acid anhydride in 100% by weight of the above flux composition is 5.0% by weight or more and 32.0% by weight or less. If the content of the above acid anhydride is less than 5.0% by weight, the thermal cyclic resistance of the resulting connection structure will be low. If the content of the above acid anhydride exceeds 32.0% by weight, the wettability of the solder will be low. The inventors have also found that in order to achieve the effects of the present invention, it is insufficient to simply select and use a difunctional phenol compound from among phenol compounds, and that it is important to set the content of the above acid anhydride used together with the difunctional phenol compound to 5.0% by weight or more and 32.0% by weight or less.

[0081] In 100% by weight of the above flux composition, the content of the above acid anhydride 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, 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. If the content of the above acid anhydride is above the lower limit, the generation of voids can be suppressed and the thermal cycling resistance of the resulting connection structure can be improved. If the content of the above acid anhydride is below the upper limit, the wettability of the solder can be further improved.

[0082] The content of the acid anhydride per 100 parts by weight of the epoxy compound is preferably 3 parts by weight or more, more preferably 5 parts by weight or more, even more preferably 7 parts by weight or more, 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. If the content of the acid anhydride is above the lower limit, the generation of voids can be suppressed and the thermal cycling resistance of the resulting connection structure can be improved. If 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 is preferably 10 mol or more, more preferably 16 mol or more, even more preferably 20 mol or more, preferably 60 mol or less, more preferably 55 mol or less, and 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 is above the lower limit and below the upper limit, viscosity stability can be further enhanced, solder wettability can be further enhanced, and the thermal cycle resistance of the resulting connection structure can be further enhanced. When the amount of acid anhydride groups in the flux composition is below the upper limit, solder wettability can be further enhanced.

[0084] For example, the amount of curing agent functional groups in the flux composition relative to 100 moles of epoxy groups in the flux composition can be calculated from the functional group equivalents (g / eq) disclosed by the raw material manufacturer.

[0085] Furthermore, the amount of acid anhydride groups in the flux composition relative to 100 moles 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 ¹H-NMR (JEOL's "JNM series") is measured, and the ratio of epoxy groups to acid anhydride groups is calculated from the obtained spectrum.

[0086] (Difunctional phenolic compound) The above flux composition contains a difunctional phenol compound. The difunctional phenol compound heat-cures the epoxy compound. By using the above acid anhydride and the above difunctional phenol compound in combination, the curability of the flux composition can be further enhanced, and boiling of the flux composition due to heating in the reflow process (heating process) can be prevented. As a result, the generation of voids in the resulting connection structure can be suppressed, and the thermal cycling resistance of the resulting connection structure can be improved.

[0087] The above-mentioned difunctional phenolic compounds are compounds having two or more structures derived from phenol groups.

[0088] Examples of the above-mentioned difunctional phenol compounds include diallylbisphenol A, diallylbisphenol F, bisphenol A, and hydrogenated bisphenol A.

[0089] Commercially available examples of the above-mentioned difunctional phenol compounds include diallylbisphenol F (APG-LC, manufactured by Gun-ei Chemical Co., Ltd.), diallylbisphenol A (DA-BPA, manufactured by Yokkaichi Gosei Co., Ltd.), and hydrogenated bisphenol A (H-BPA, manufactured by Maruzen Petroleum Co., Ltd.). The above-mentioned difunctional phenol compounds may be used individually or in combination of two or more.

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

[0091] From the viewpoint of further improving the applicability of the above flux composition, it is preferable that the difunctional phenol compound is liquid at 25°C.

[0092] From the viewpoint of further improving the applicability of the above flux composition, the melting point of the difunctional 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 difunctional phenol compound is not particularly limited. The melting point of the difunctional 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 difunctional phenol compound can be set by appropriately selecting the above lower limit and upper limit.

[0093] In 100% by weight of the above flux composition, the content of the above difunctional phenol compound 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, 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. If the content of the above difunctional phenol compound is above the lower limit, the wettability of the solder can be further improved. If the content of the above difunctional phenol compound is below the upper limit, the generation of voids can be suppressed and the thermal cycling resistance of the resulting connection structure can be improved.

[0094] The content of the difunctional phenol compound per 100 parts by weight of the epoxy compound is preferably 30 parts by weight or more, more preferably 40 parts by weight or more, even more preferably 45 parts by weight or more, 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. If the content of the difunctional phenol compound is above the lower limit, the wettability of the solder can be further improved. If the content of the difunctional phenol compound is below the upper limit, the generation of voids can be suppressed and the thermal cycling resistance of the resulting connection structure can be improved.

[0095] In 100% by weight of the above flux composition, the total content of the above acid anhydride and the above difunctional phenol compound 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, 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 above acid anhydride and the above difunctional phenol compound is above the lower limit and below the upper limit, viscosity stability can be further enhanced, solder wettability can be further enhanced, and the thermal cycling resistance of the resulting connection structure can be further enhanced.

[0096] The total content of the acid anhydride and the difunctional phenol compound per 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, 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 difunctional phenol compound is above the lower limit and below the upper limit, viscosity stability can be further enhanced, solder wettability can be further enhanced, and the thermal cycling resistance of the resulting connection structure can be further enhanced.

[0097] 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 defined as the ratio (content of difunctional phenol compound / content of acid anhydride). The weight ratio (content of difunctional 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, preferably 10.0 or less, more preferably 7.9 or less, and even more preferably 5.0 or less. If the weight ratio (content of difunctional phenol compound / content of acid anhydride) is above the lower limit, the wettability of the solder can be further improved. If the weight ratio (content of difunctional phenol compound / content of acid anhydride) 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. The content of the difunctional phenol compound in the flux composition is the content of the difunctional phenol compound (weight %) in 100% by weight of the flux composition. The content of the acid anhydride in the flux composition is the content of the acid anhydride (weight %) in 100% by weight of the flux composition.

[0098] <Curing accelerator> The above flux composition includes a curing accelerator.

[0099] Examples of the curing accelerators mentioned above include imidazole compounds, phosphorus compounds, amine compounds, and organometallic compounds. One curing accelerator may be used alone, or two or more may be used in combination.

[0100] The above imidazole compounds 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 trimellitate, and 1-cyanoethyl-2-phenylimidazole. Examples include rimelite, 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 isocyanurate adduct, 2-phenylimidazole isocyanurate adduct, 2-methylimidazole isocyanurate adduct, 2-phenyl-4,5-dihydroxymethylimidazole, and 2-phenyl-4-methyl-5-dihydroxymethylimidazole.

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

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

[0103] From the viewpoint of further improving the wettability of the solder and further improving the thermal cycling resistance of the resulting connection structure, the curing accelerator preferably contains the phosphorus compound, and more preferably contains an organophosphorus compound.

[0104] Examples of the above-mentioned organophosphorus compounds include organophosphonium salts, organophosphoric acids, organophosphoric acid esters, organophosphonic acid esters, organophosphinic acids, and organophosphinic acid esters. The above-mentioned organophosphorus compounds may be used individually or in combination of two or more.

[0105] From the viewpoint of improving the conductivity reliability of the resulting connection structure, the organophosphorus compound preferably includes an organophosphonium salt, an organophosphoric acid, or an organophosphoric acid ester, and more preferably an organophosphonium salt.

[0106] Examples of the above-mentioned organic phosphonium salts include organic phosphonium salts composed of a phosphonium ion and its counterion.

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

[0108] Examples of 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 "Hishikorin" series manufactured by Nippon Chemical Industrial Co., Ltd.

[0109] The above-mentioned organic phosphoric acid, organic phosphoric acid ester, organic phosphonic acid, organic phosphonic acid ester, organic phosphinic acid, and organic phosphinic acid ester are not particularly limited. Conventional known compounds or commercially available products can be used as the above-mentioned organic phosphoric acid, organic phosphoric acid ester, organic phosphonic acid, organic phosphonic acid ester, organic phosphinic acid, and organic phosphinic acid ester.

[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 cycling resistance, the neutralized product of the monovalent or higher organic acid preferably does not have a carboxyl group.

[0111] In 100% by weight of the above flux composition, the content of the curing accelerator 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, 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 above the lower limit and below the upper limit, the wettability of the solder can be further improved, and the thermal cycling resistance of the resulting connection structure can be further enhanced.

[0112] In 100% by weight of the above flux composition, the content of the above organophosphorus compound 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, 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 above organophosphorus compound is above the lower limit and below the upper limit, the wettability of the solder can be further improved, and the thermal cycling resistance of the resulting connection structure can be further enhanced.

[0113] In 100% by weight of the above flux composition, the content of the above organic phosphonium salt 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, 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 above organic phosphonium salt is above the lower limit and below the upper limit, the wettability of the solder can be further improved, and the thermal cycling resistance of the resulting connection structure can be further enhanced.

[0114] The content of the organic phosphonium salt per 100 parts by weight of the epoxy compound is preferably 0.18 parts by weight or more, more preferably 0.54 parts by weight or more, even more preferably 0.57 parts by weight or more, 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 above the lower limit and below the upper limit, the wettability of the solder can be further improved, and the thermal cycling resistance of the resulting connection structure can be further enhanced.

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

[0116] <Other ingredients> The above flux composition may optionally contain various additives such as fillers, bulking agents, softeners, plasticizers, thixotropes, leveling agents, polymerization catalysts, curing catalysts, colorants, antioxidants, heat stabilizers, light stabilizers, UV absorbers, lubricants, antistatic agents, and flame retardants.

[0117] (Connection structure and method for manufacturing the connection structure) The flux composition according to the present invention is suitably used to obtain a connecting 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 the 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 comprises 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 using the flux composition described above to place the flux composition on the surface of the solder particles on the first connection target member or on the surface of the second electrode on the second connection target member. (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 step of electrically connecting the first electrode body and the second electrode by heating the solder particles and the flux composition, and forming a resin portion connecting the first connection target member and the second connection target member with the flux composition.

[0120] In the pre-fill underfill method, the flux composition is placed on at least one surface of the first and second connection target members before the first and second connection target members are brought into contact with each other. The method for manufacturing a connection structure according to the present invention is a method for manufacturing a connection structure using the pre-fill underfill method.

[0121] In the manufacturing method of the above-described connection structure, the following arrangement methods may be employed. In the first arrangement step, 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, may be used, and the flux composition described above may be used to arrange the flux composition on the surface of the solder particles in the first connection target member. In the first arrangement step, a second connection target member having a second electrode on its surface, may be used, and the flux composition described above may be used to arrange the flux composition on the surface of the second electrode in the second connection target member.

[0122] In the method for manufacturing a connecting structure according to the present invention, in the first placement step, the flux composition may be placed by dispensing, by screen printing, by ejection using an inkjet device, or by dipping. From the viewpoint of further improving thermal cycling resistance, it is preferable to place the flux composition by dispensing in the first placement step.

[0123] Conventional manufacturing methods for connection structures using underfill material require a reflow process (heating process) to connect electrodes, followed by the application of underfill material between the connection components via capillary action, and then another heating process to harden the underfill material. In other words, conventional manufacturing methods for connection structures using underfill material require two heating processes, resulting in low productivity. Furthermore, solder flash can occur in conventional connection structures using underfill material. Solder flash can lead to short circuits or open circuits.

[0124] The connection structure and method for manufacturing the connection structure according to the present invention use a specific flux composition, so that electrodes can be electrically connected and the flux composition can be cured in a single heating step (reflow step). Therefore, it is not necessary to perform the heating step twice. In other words, the connection structure and method for manufacturing the connection structure according to the present invention enable batch mounting, and as a result, productivity can be further increased. Furthermore, because the connection structure and method for manufacturing the connection structure according to the present invention use a specific flux composition, the solder in the solder particles can sufficiently wet and spread on the surface of the electrodes, and the connection resistance between the upper and lower electrodes in the connection structure can be reduced. As a result, the conductivity reliability of the connection structure can be improved. Furthermore, because the connection structure and method for manufacturing the connection structure according to the present invention use a specific flux composition, it is possible to prevent the flux composition from boiling due to heating in the heating step, and the generation of voids in the connection structure can be suppressed. As a result, the probability of connection failure or other problems occurring and the connection structure failing when the connection structure is repeatedly heated and cooled can be reduced (the thermal cycle resistance of the connection structure can be improved).

[0125] Specific embodiments of the present invention will be described below with reference to the drawings.

[0126] Figure 1 is a schematic cross-sectional view showing a connection structure obtained using a flux composition according to one embodiment of the present invention.

[0127] The connecting structure 1 shown in Figure 1 comprises a first connecting target member 2, a second connecting target member 3, and a resin part 4 connecting the first connecting target member 2 and the second connecting target member 3. The resin part 4 is formed from a flux composition 4Xa (see Figure 3(b1) (or Figure 6(b2) or Figure 7(b3) or Figure 8(b4)), Figure 4(c) and Figure 5(d)). The material of the resin part 4 is the flux composition 4Xa. The flux composition 4Xa contains an epoxy compound, an acid anhydride, a difunctional phenol compound, and a curing accelerator. In this embodiment, the flux composition 4Xa is preferably in liquid form, and more preferably a solvent-free liquid.

[0128] The resin part 4 is a cured product formed by heat curing of the flux composition 4Xa.

[0129] The first connection target member 2 has a plurality of first electrodes on its surface (bottom surface). The first electrode comprises a first electrode body 2a and a solder portion 2B (solder particles) on the surface of the first electrode body 2a. The first electrode is a composite electrode of the first electrode body 2a and the solder portion 2B. The second connection target member 3 has a plurality of second electrodes 3a on its surface (top 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 portion 2B.

[0130] As shown in Figure 1, in the connection structure 1, at least the portion of the solder particles in contact with the second electrode 3a melts between the first electrode body 2a and the second electrode 3a, and then the solder particles solidify to form a solder portion 2B. As a result, the contact area between the solder portion 2B and the second electrode 3a becomes larger.

[0131] Next, an example of a method for manufacturing a connecting structure will be specifically described using Figures 2(a), 3(b1) (or 6(b2), 7(b3), or 8(b4)), 4(c), and 5(d). Figures 2(a), 3(b1) (or 6(b2), 7(b3), or 8(b4)), 4(c), and 5(d) are cross-sectional views illustrating each step of an example of a method for manufacturing a connecting 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 (bottom surface) and a second connection target member 3 having a second electrode 3a on its surface (top surface) are prepared. The first electrode comprises 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 difunctional phenol compound, and a curing accelerator.

[0133] Next, as shown in Figure 3(b1), the flux composition 4Xa is placed on the surface of the solder particles 2b (first electrode) in the first connection target member 2 (first placement step). At this time, as shown in Figure 6(b2), the flux composition 4Xa may also be placed on the surface of the second electrode 3a in the second connection target member 3 (first placement step). That is, in the first placement step, the flux composition 4Xa is placed on the surface of the solder particles 2b in the first connection target member 2 or on the surface of the second electrode 3a in the second connection target member 3 by the dispensing method. The flux composition 4Xa is placed on the surface of the solder particles 2b in the first connection target member 2 or on the surface of the second electrode 3a in the second connection target member 3 using a dispenser.

[0134] In Figure 3(b1), the flux composition 4Xa is separately placed on each of the multiple solder particles 2b (first electrodes). As shown in Figure 7(b3), the flux composition 4Xa may be placed across the multiple solder particles 2b (first electrodes) (first placement step). In Figure 6(b2), the flux composition 4Xa is separately placed on each of the multiple second electrodes 3a. As shown in Figure 8(b4), the flux composition 4Xa may be placed across the multiple second electrodes 3a (first placement step). In the first placement step, the flux composition 4Xa may be placed on the surface of the second electrodes 3a of the second connection target member 3 by a dispensing method or the like, so as to span across the multiple second electrodes 3a.

[0135] The amount of flux composition placed on the surface of the solder particles is preferably such that it can fill the gap between the first member to be connected and the second member to be connected in the resulting connection structure.

[0136] Next, as shown in Figure 3(b1) (or Figure 6(b2) or Figure 7(b3) or Figure 8(b4)) and Figure 4(c), the first connection target member 2 and the second connection target member 3 are positioned so that the first electrode (first electrode body 2a and solder particles 2b) and the second electrode 3a face each other (second positioning step). The second connection target member 3 is positioned from the second electrode 3a side toward 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 Figures 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 above the melting temperature of the portion of the solder particles 2b that contacts the second electrode 3a. More preferably, the flux composition 4Xa is heated to a temperature above 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 undergoes thermal curing. As a result, as shown in Figure 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 curing of the flux composition 4Xa. Furthermore, as shown in Figure 5(d), a 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 higher, more preferably 0.2 Pa·s or higher, preferably 50 Pa·s or lower, more preferably 10 Pa·s or lower, and even more preferably 1 Pa·s or lower. When the viscosity (ηmp) is above the lower limit and below the upper limit, the conductivity reliability of the resulting connection structure can be improved.

[0139] The viscosity (ηmp) can be measured, for example, using a Thermo Fisher Scientific HAAKE MARS III rheometer under the following conditions: frequency 2 Hz, heating rate 0.11 °C / sec, and measurement temperature range 25 °C to 200 °C (however, if the melting point of the solder particles exceeds 200 °C, the upper temperature limit will be 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 can be evaluated.

[0140] In this way, the connection structure 1 shown in Figure 1 is obtained. Note that the second arrangement step and the third step may be performed consecutively. Alternatively, after performing 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 the heating section and the third step may be performed. To perform the heating, the laminate may be placed on a heating member, or the laminate may be placed in a heated space.

[0141] The heating temperature in the third step is preferably 140°C or higher, more preferably 160°C or higher, 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 above the melting point of the solder particles. The heating temperature in the third step is preferably above the curing temperature of the epoxy compound. The heating temperature in the third step is preferably above the melting temperature of the portion of the solder particles that is in contact with the second electrode, and more preferably above the curing temperature of the epoxy compound.

[0142] The heating method in the third step described above may include heating the entire laminate using a reflow oven or oven, or locally heating only the solder and resin parts of the laminate.

[0143] Examples of devices used for localized heating include hot plates, heat guns that apply hot air, soldering irons, and infrared heaters.

[0144] Furthermore, when heating locally with a hot plate, it is preferable to form the top surface of the hot plate with a metal that has high thermal conductivity directly beneath the soldered and resin parts, and with a material with low thermal conductivity, such as fluororesin, in other areas where heating is undesirable.

[0145] The thickness of the solder portion in the connecting structure is preferably 10 μm or more, more preferably 20 μm or more, preferably 100 μm or less, and more preferably 80 μm or less.

[0146] The thickness of the resin portion in the connecting structure is preferably 10 μm or more, more preferably 20 μm or more, preferably 100 μm or less, and more preferably 80 μm or less.

[0147] When the flux composition is a paste (liquid), it becomes easy to adjust the thickness of the resin portion by changing the amount of flux composition applied.

[0148] The first and second connection targets described above are not particularly limited. Specifically, the first and second connection targets 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 circuit boards, glass epoxy circuit boards and glass circuit boards. It is preferable that the first and second connection targets are electronic components.

[0149] Examples of electrodes provided on the above-mentioned connection target member 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 above-mentioned connection target member is a flexible printed circuit board, the electrodes are preferably gold electrodes, nickel electrodes, tin electrodes, silver electrodes, or copper electrodes. When the above-mentioned connection target member is a glass substrate, the electrodes are preferably aluminum electrodes, copper electrodes, molybdenum electrodes, silver electrodes, or tungsten electrodes. In the case of aluminum electrodes, the electrodes may be made solely of aluminum, or they 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 described above is preferably a metal with a melting point of 450°C or less (low melting point metal). The solder particles described above are preferably metal particles with a melting point of 450°C or less (low melting point metal particles). The low melting point metal particles described above are particles containing a low melting point metal. The low melting point metal refers to a metal with 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 described above is preferably a low melting point solder with a melting point of less than 250°C.

[0151] The low-melting-point metal constituting the solder particles described above is not particularly limited. The low-melting-point metal is preferably tin or an alloy containing tin. Examples of such alloys include tin-silver alloys, tin-copper alloys, tin-silver-copper alloys, tin-bismuth alloys, tin-zinc alloys, tin-indium alloys, and tin-antimony alloys. Due to their excellent wettability to electrodes, the low-melting-point metal is preferably tin, tin-silver alloys, tin-silver-copper alloys, tin-bismuth alloys, tin-indium alloys, and tin-antimony alloys, and more preferably tin-silver-copper alloys, tin-bismuth alloys, tin-indium alloys, or tin-antimony alloys.

[0152] The solder particles described above are preferably filler materials with a liquidus temperature of 450°C or lower, 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 preferably contain tin, silver, and copper. The solder particles are preferably tin-silver-copper alloy solder particles.

[0153] To further enhance the bonding strength between the solder 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 enhancing the bonding strength between the solder and the electrode, it is preferable that the solder particles contain nickel, copper, antimony, aluminum, or zinc. From the viewpoint of further enhancing the bonding strength between the solder and the electrode, the content of these metals for enhancing bonding strength is preferably 0.0001% by weight or more, and preferably 1% by weight or less, out of 100% by weight 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, preferably 400°C or lower, more preferably 350°C or lower, and even more preferably 300°C or lower.

[0155] The melting point of the solder particles mentioned above can be determined by differential scanning calorimetry (DSC). Examples of differential scanning calorimetry (DSC) equipment include the "EXSTAR DSC7020" manufactured by SII Corporation.

[0156] Furthermore, it is preferable that the solder particles contain tin. The tin content 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 above the lower limit, the conductivity reliability and connection reliability of the connection structure can be further improved. There is no particular upper limit to the tin content in the solder particles. 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 atomic emission spectrometer (for example, Horiba's "ICP-AES") or an X-ray fluorescence analyzer (for example, Shimadzu's "EDX-800HS").

[0158] The present invention will be specifically described below with reference to examples and comparative examples. The present invention is not limited to the following examples.

[0159] The following materials were prepared.

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

[0161] Acid anhydride: A mixture of hexahydrophthalic anhydride and methylhexahydrophthalic anhydride (Shin Nippon Rika Co., Ltd. "Ricacid MH-700") 4-Methylhexahydrophthalic anhydride (Shin Nippon Rika Co., Ltd. "Ricacid MH-T")

[0162] Difunctional phenolic compounds: Diallylbisphenol F (APG-LC, manufactured by Gun-ei Chemical Industry Co., Ltd.) Diallylbisphenol A (DA-BPA, manufactured by Yokkaichi Synthetic Co., Ltd.)

[0163] Trifunctional phenolic compounds: 1,1,1-Tris(4-hydroxyphenyl)ethane (manufactured by Honshu Chemical Industry Co., Ltd. as "TrisP-HAP")

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

[0165] Curing accelerator: Methyltributylphosphonium dimethyl phosphate (Hishi-Korin PX-4MP, manufactured by Nippon Chemical Industries, Ltd.) Tetrabutylphosphonium benzotriazolate (Hishikorin PX-4BT, manufactured by Nippon Chemical Industrial Co., Ltd.) Tetrabutylphosphonium tetraphenylborate (Hishi-Korin PX-4PB, manufactured by Nippon Chemical Industries, Ltd.)

[0166] Activating agent: Benzylamine adipate (manufactured by Showa Chemical Co., Ltd.)

[0167] (Examples 1-12 and Comparative Examples 1-6) (1) Preparation of flux composition The components shown in Tables 1-4 below were mixed in the amounts shown in Tables 1-4 below, then kneaded with a roll gap of 30 μm using a three-roll machine (Noritake "NR-42A"), and filtered through a SUS mesh filter (mesh opening 100 μm) to obtain the flux composition.

[0168] (2) Fabrication of the connecting structure A BGA (0.8 mm pitch, 100 electrodes) was prepared as the first connection target member (package) having a first electrode on its surface. A printed circuit board (material: FR4, thickness: 1 mm) having a gold electrode on its surface corresponding to the first connection target member was prepared as the second connection target member. The flux composition immediately after fabrication was placed on the second electrode of the second connection target member by the dispensing method (first placement step, see Figure 8(b4)). Next, the first connection target members were stacked so that the electrodes faced each other (second placement step). The weight of the first connection target member is added to the solder particles (Sn96.5Ag3.0Cu0.5 solder (melting point: 217°C), particle size 0.5 mm) and flux composition in the BGA. From that state, the flux composition was heated using a reflow simulator (Cores "core9056a") at a heating rate of 1°C / second from 35°C to 260°C, with a total time spent above 220°C for 90 seconds, thereby curing the flux composition and obtaining the connecting structure. No pressure was applied during heating. In all examples and comparative examples, the heating process (reflow process) was performed only once.

[0169] (evaluation) (1) Viscosity at 25°C The viscosity of the obtained 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) under the conditions of 25°C and 5 rpm, immediately after preparation.

[0170] (2) Wetting properties of solder A flux composition obtained was applied to a substrate (phosphorus deoxidized copper plate, "C1220" manufactured by Engineering Test Services Co., Ltd.) by screen printing to form a flux composition layer with a thickness of 0.2 mm. Next, solder particles (Sn96.5Ag3.0Cu0.5 solder (melting point: 217°C), particle size 0.5 mm) were placed on the surface of the flux composition layer to form a laminate comprising the substrate, the flux composition layer, and the solder particles. The obtained laminate was heated using a reflow simulator ("Core9056a" manufactured by Cores Corporation) at a heating rate of 1°C / second from 35°C to 260°C, with a total time above 220°C being 90 seconds, and then cooled to room temperature. After that, the solder was observed using an optical microscope (manufactured by Keyence Corporation), and the major axis (μm) of the solder in a plan view was measured. The wetting spreadability of the solder was determined according to the following criteria.

[0171] [Criteria for determining solder wetting spreadability] ○○: The longest diameter of the solder is 800 μm or more. ○: The longest diameter of the solder is 700 μm or more and less than 800 μm. ×: The longest diameter of the solder is less than 700 μm.

[0172] (3) Viscosity stability The obtained flux composition was allowed to stand at 25°C for 8 hours, and then 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° × R14) under the conditions of 25°C and 10 rpm. The viscosity ratio expressed by the following formula was calculated. Viscosity stability was determined according to the following criteria.

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

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

[0175] (4) Resistance to cold and heat cycling The obtained flux composition was applied to a transfer tray to a thickness of 0.15 mm. Then, using a chip mounter "SMT-64RH (Okuhara Electric Co., Ltd.)", the flux composition was transferred to the solder bumps of a dummy chip "WLP100T.3C-DC108D (Tpline Co., Ltd.)", and then mounted on a PCB in alignment to fabricate a connection structure. For the obtained connection structure (connection structure before the thermal cycling test), the connection resistance per connection point between the upper and lower electrodes was measured using the four-terminal method. Note that, from the relationship voltage = current × resistance, the connection resistance can be determined by measuring the voltage when a constant current is passed. Next, the connection structure was heated from 35°C to 260°C at a heating rate of 1°C / second, so that the total time at 220°C or higher was 90 seconds, and then cooled to room temperature. After that, the thermal cycling test was performed by repeating the cooling to -40°C cycle 1000 times, with each cycle being considered one cycle. Similarly, the average value of the connection resistance was calculated for the connection structure after the thermal cycling test. The rate of change in connection resistance, expressed by the following formula, was calculated. Thermal cycling resistance was determined according to the following criteria.

[0176] Percentage change in connection resistance (%) = ((Average value of connection resistance after the thermal cycling test) - (Average value of connection resistance before the thermal cycling test)) / (Average value of connection resistance before the thermal cycling test) × 100

[0177] [Criteria for determining resistance to thermal cycling] ○○: 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%. ×: Change rate of connection resistance is 10% or more

[0178] The composition and results are shown in Tables 1-4 below.

[0179] [Table 1]

[0180] [Table 2]

[0181] [Table 3]

[0182] [Table 4] [Explanation of Symbols]

[0183] 1…Connection structure 2…First connection target member 2a...First electrode body 2b... Solder particles 2B...Soldering section 3…Second connection target member 3a...Second electrode 4… Resin part 4Xa... Flux composition

Claims

1. A flux composition comprising an epoxy compound, an acid anhydride, a difunctional phenol compound, and a curing accelerator. The content of the epoxy compound in 100% by weight of the flux composition is 40.0% by weight or more and 70.0% by weight or less. 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. The content of the difunctional phenol compound in 100% by weight of the flux composition is 15.0% by weight or more and 60.0% by weight or less. 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 10.0 or less. A flux composition having a viscosity of 1.0 Pa·s or more and 10.0 Pa·s or less at 25°C.

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.

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