TWI778132B - Flux and Solder Paste - Google Patents

Abstract

Flux and solder paste are available. To provide a flux and a solder paste, which can suppress the generation of voids in the formed solder joints and solder bumps by suppressing the decrease in the fluidity of the flux during the reflow of the solder paste, and can The occurrence of bump loss during solder bump formation is suppressed.

A flux comprising a rosin-based resin, an activator, a thixotropic agent, and a solvent, and a monohydric alcohol having a carbon number of 18 or more and 24 or less contained in 1 molecule as the solvent, and the monohydric alcohol The compounding amount is 30 mass % or more and 60 mass % or less with respect to the total amount of the flux.

Description

Flux and Solder Paste

The present invention relates to fluxes and solder pastes using the same.

Solder alloys are mainly used as bonding materials for bonding electronic components to electronic circuits formed on substrates such as printed circuit boards and silicon wafers.

As a joining method using this solder alloy, there are, for example, a method of printing a solder paste obtained by mixing solder alloy powder and flux onto a substrate, or a method of using solder bumps formed of a solder alloy formed on the substrate method to proceed. In addition, solder paste is sometimes used for the formation of the aforementioned solder bumps.

A general flux used in a solder paste is produced by melting an activator, a thixotropic agent, and the like in a solvent, using a resin such as rosin as a main component. However, in the case of using the solder paste of the conventional flux, there is a problem that voids are generated in the formed solder joints during the reflow process after the solder paste is printed on the electrodes. This void reduces the bonding property between the bonding portion and a portion to be bonded such as a substrate or an electronic component, and reduces heat dissipation, thereby causing a decrease in reliability of electronic devices and semiconductors.

In addition, in recent years, as a method of forming solder bumps using solder paste, a dry film process has been used. In this process, first, a dry film is attached to a substrate on which a predetermined electronic circuit, or a predetermined electronic circuit and an insulating layer are formed, and exposure and development of a predetermined pattern are performed. In this way, among the resist components of the dry film, the resist component of the portion where the solder bumps are to be formed (on the electrode portion) is removed, and a dry film layer of a predetermined pattern is formed on the substrate. A region (opening) surrounded by the dry film layer. then, Printing is performed to fill the openings with solder paste, and reflow is performed in this state to form solder bumps. Also thereafter, the dry film layer and the flux residue formed in the vicinity of the solder bumps are removed.

When the solder bumps are formed using this dry film process, compared with other bump formation methods, the following phenomena are likely to occur: the phenomenon that voids in the solder bumps are easily generated, and the solder bumps are easily removed from the solder bumps when the flux residue is removed. The missing bump phenomenon that disappears on the substrate.

The voids in the solder bumps are believed to be caused by flux components that enter into the molten solder alloy during reflow and are not expelled. The missing bump is considered to be caused by the decrease in the fluidity of the flux during reflow, so that the molten solder alloy did not reach the bottom of the opening sufficiently, and the flux accumulated at the bottom and became a residue. This is because the solvent contained in the flux volatilizes during reflow, so that the viscosity of the flux increases and the fluidity of the flux decreases.

In addition, when the solder bump is formed by a dry film process, the film thickness of the dry film layer forming the opening is likely to be thicker than that of a mask used in other methods. Therefore, in this case, it is considered that the height from the surface of the dry film layer to the bottom surface of the opening (the depth of the opening) becomes higher, which makes it difficult for the molten solder alloy to flow to the bottom of the opening, and the flux becomes difficult to flow. It is easy to accumulate on the bottom, and thus it becomes more likely to generate missing bumps.

As a method of suppressing the generation of missing bumps, for example, it is disclosed that a solvent having a boiling point of 240° C. or higher is used which has a viscosity that is supplied to an opening under reduced pressure and is filled in the opening under atmospheric pressure, adjusts the viscosity and thixotropic ratio solder paste (refer to Patent Document 1).

[Prior Art Literature]

[Patent Literature]

[Patent Document 1] International Publication WO2012/173059

The solder paste disclosed in Patent Document 1 suppresses the occurrence of missing bumps due to insufficient filling of the solder paste when the openings are fine. In addition, in order to sufficiently fill the openings with solder paste, it is premised that the environment in which the substrate is placed is switched between reduced pressure and atmospheric pressure during printing of the solder paste, and further, the void suppression effect during reflow is neither disclosed nor disclosed. No hint.

An object of the present invention is to solve these problems, and by suppressing the decrease in the fluidity of the flux during reflow of the solder paste, it is possible to suppress the generation of voids in the formed solder joints and solder bumps, and to suppress the solder It is related to the flux and the solder paste used for the occurrence of missing bumps at the time of bump formation.

In order to achieve the above-mentioned object, the present invention has the following structures as its features.

(1) The flux of the present invention is characterized in that it contains a rosin-based resin, an activator, a thixotropic agent, and a solvent, and contains, as the solvent, a monohydric alcohol having a carbon number of 18 or more and 24 or less contained in 1 molecule. , the compounding amount of the monohydric alcohol is 30% by mass or more and 60% by mass or less with respect to the total amount of the flux.

(2) The structure according to the above (1), wherein the number of carbon atoms contained in one molecule of the monohydric alcohol is 18 or more and 20 or less.

(3) The structure according to the above (1) or (2), wherein the monohydric alcohol is a branched alcohol or an unsaturated alcohol.

(4) The structure according to any one of (1) to (3) above, wherein the monohydric alcohol is selected from the group consisting of oleyl alcohol, isostearyl alcohol, isoeicosanol, and 2-octyldodecanol or at least one of 2-decyltetradecanol.

(5) The configuration according to any one of (1) to (4) above, wherein the flux of the present invention is heated from room temperature to a peak temperature of 260° C. at a temperature increase rate of 2° C./sec. After the peak temperature, the viscosity was 30Pa after heating under reflow soldering conditions with a cooling rate of 2°C/sec. s or less.

(6) The solder paste of the present invention is characterized by containing the flux described in any one of (1) to (5) above, and a solder alloy powder.

(7) The method for forming a solder bump of the present invention is characterized in that an electrode portion and a first insulating layer are formed on a substrate, a second insulating layer is formed on the first insulating layer, and an opening region is formed on the electrode portion. In the method of printing the solder paste described in the above (6) to fill the opening region on the electrode portion, the opening region of the electrode portion is heated to the substrate filled with the solder paste to form on the substrate Solder bumps are formed by removing the flux residue and the second insulating layer.

The flux of the present invention and the solder paste using the same can suppress the occurrence of voids in the formed solder joints and solder bumps by suppressing the decrease in the fluidity of the flux during reflow of the solder paste, and can also suppress the Generation of missing bumps during solder bump formation.

1‧‧‧Substrate

2‧‧‧Electrode

3‧‧‧Insulation layer

4‧‧‧Dry film layer

5‧‧‧Opening

1 is a graph showing temperature profiles in a void test and a missing bump test of the solder pastes of Examples and Comparative Examples, and the viscosity measurement after heating (reflow) of the fluxes of Examples and Comparative Examples of the present invention.

2 is a schematic diagram of a substrate on which solder bumps are formed during a void test and a missing bump test of the solder pastes of Examples and Comparative Examples.

Hereinafter, one embodiment of the flux and solder paste of the present invention will be described in detail. In addition, this invention is not limited to this embodiment at all.

1. Flux

The flux of the present embodiment contains a rosin-based resin, an activator, a thixotropic agent, and a solvent.

Examples of the rosin-based resin include rosins such as tall oil rosin, gum rosin, and wood rosin; Derivatives etc.

In addition, among these rosin-based resins, it is preferable to use a rosin-based resin having a softening point of 100° C. or lower. By using a rosin-based resin with a low softening point, the fluidity of the flux during heating (reflow soldering) can be improved, so that the solder alloy (powder) tends to settle, thereby enhancing the effect of suppressing the occurrence of missing bumps.

The blending amount of the rosin-based resin is preferably 25% by mass or more and 50% by mass or less, and more preferably 30% by mass or more and 40% by mass or less with respect to the total amount of the flux.

Examples of the activating agent include amine salts (inorganic acid salts, organic acid salts) such as hydrogen halide salts of organic amines, organic acids, organic acid salts, organic amine salts, and brominated halogen compounds. Specifically, for example, diethylamine salt, acid salt, succinic acid, adipic acid, sebacic acid, glutaric acid, diphenylguanidine hydrobromide, cyclohexylamine hydrobromide, tribromide Allyl isocyanurate, tris(2,3-dibromopropyl) isocyanurate, poly-8,13-dimethyl-8,12-eicosanedioic anhydride, etc. Among these, poly8,13- Dimethyl-8,12-eicosadioic anhydride serves as the aforementioned active agent. Poly-8,13-dimethyl-8,12-eicosanedioic anhydride is liquid at room temperature and is a long-chain compound, so it has excellent stability at high temperature, and can improve the effect of suppressing the generation of voids and suppressing The effect of missing bumps. In addition, these may be used alone or in combination of two or more.

The compounding quantity of the said activator differs depending on other components and the lead-free solder alloy used, and is generally 20 mass % or less with respect to the total amount of flux.

Examples of the thixotropic agent include hydrogenated castor oil, bisamide-based thixotropic agents (saturated fatty acid bisamide, unsaturated fatty acid bisamide, aromatic bisamide, etc.), dimethyldibenzylidene, and the like. Sorbitol, etc.

Among them, hydrogenated castor oil is particularly preferably used as the aforementioned thixotropic agent. Hydrogenated castor oil has a low softening point compared to other thixotropic agents, so it can improve the fluidity of the flux during heating (reflow). Therefore, the solder alloy (powder) tends to settle, and thereby the effect of suppressing the occurrence of missing bumps can be enhanced.

In addition, these may be used alone or in combination of two or more.

The blending amount of the thixotropic agent is preferably 3% by mass or more and 10% by mass or less, more preferably 5% by mass or more and 8% by mass or less, based on the total amount of the flux.

Examples of the solvent include alcohols, ethanols, acetones, toluenes, xylenes, ethyl acetates, ethyl cellosolves, butyl cellosolves, glycol ethers, esters, and the like. These can be used alone or in combination.

The flux of the present embodiment preferably contains, as the solvent, a monohydric alcohol having a carbon number of 18 or more and 24 or less contained in one molecule.

This monohydric alcohol has the property of being hard to volatilize even when the heating (reflow) temperature is high. Therefore, the volatilization amount of the solvent during heating (reflow soldering) is suppressed, and the flowability of the flux is suppressed from decreasing. As a result, it becomes difficult for the components of the flux to enter into the solder alloy melted during heating (reflow), and the generation of voids can be suppressed.

In addition, in the formation of the solder bumps, the molten solder alloy also easily flows to the bottom of the opening during heating (reflow), and the occurrence of missing bumps can also be suppressed. The same is true when the solder bumps are formed by the dry film process in which the depth of the opening is deeper, and the generation of missing bumps can be suppressed also in this process.

In addition, as a method of suppressing the decrease in the fluidity of the flux at the time of heating (reflow), the use of an ester-based solvent having a high boiling point (with a small amount of volatilization at a high temperature) is also considered.

However, such ester-based solvents are likely to have poor solubility with other flux components such as activators and thixotropic agents. Therefore, it is usually necessary to use another solvent with high solubility and a low boiling point together with this ester-based solvent, and it is often used as a flux.

However, the flux of the present embodiment contains, as the solvent, a monohydric alcohol having a carbon number of 18 or more and 24 or less contained in one molecule, and does not need to be used together with another solvent with a low boiling point, and can suppress heating even when used alone. The fluidity of the flux at the time of (reflow soldering) decreased. However, it is not excluded that the monohydric alcohol is used together with other solvents, and it can be used in combination as appropriate.

In addition, the number of carbon atoms contained in one molecule of the monohydric alcohol is preferably 18 or more and 20 or less.

In addition, the aforementioned monohydric alcohol is preferably a branched alcohol or an unsaturated alcohol.

As said monohydric alcohol, oleyl alcohol, isostearyl alcohol, isoeicosanol, 2-octyldodecanol, 2-decyltetradecanol, etc. are mentioned, for example. Among them, oleyl alcohol, isostearyl alcohol, isoeicosanol, and 2-octyldodecanol are preferably used, and 2-octyldodecanol is particularly preferably used. These can be used alone or in combination.

It is preferable that the compounding quantity of the said solvent is 30 mass % or more and 60 mass % or less with respect to the total amount of flux, and it is more preferable that it is 40 mass % or more and 50 mass % or less.

In addition, the compounding amount of the monohydric alcohol is preferably 30 mass % or more and 60 mass % or less, preferably 35 mass % or more and 55 mass % or less, more preferably 40 mass % or more and 50 mass %, with respect to the total amount of the flux. %the following. By making the compounding quantity of the said monohydric alcohol into this range, the void suppression effect of a solder bump can be improved comparatively.

In the flux of the present embodiment, an antioxidant may be blended for the purpose of suppressing oxidation of the solder alloy powder.

As said antioxidant, a hindered phenol type antioxidant, a phenol type antioxidant, a bisphenol type antioxidant, a polymer type antioxidant, etc. are mentioned, for example. Among them, hindered phenol-based antioxidants are particularly preferably used.

The aforementioned antioxidants are not limited to these, and the compounding amount thereof is not particularly limited. The usual compounding amount thereof is about 0.5 mass % to 5 mass % with respect to the total amount of the flux.

Additives such as halogens, matting agents, and antifoaming agents may be further added to the flux of the present embodiment. The blending amount of the aforementioned additives is preferably 10% by mass or less, and more preferably 5% by mass or less, based on the total amount of the flux.

The flux of this embodiment is heated from room temperature to a peak temperature of 260°C at a temperature increase rate of 2°C/sec, as shown in the temperature profile shown in Fig. 1, and then cooled at a temperature drop rate of 2°C/sec after reaching the peak temperature The viscosity after heating under reflow soldering conditions should be 30Pa. s or less. In addition, the viscosity is more preferably 25Pa. s or less.

In the measurement of this viscosity, first, 4 g of the flux of the present embodiment was put into an aluminum pan, placed on a metal mesh, and reflowed using a reflow soldering apparatus. The reflow soldering conditions were in accordance with the temperature profile shown in FIG. 1 (the above-mentioned reflow soldering conditions).

Return the flux after reflow to room temperature and measure it with an E-type viscometer. In addition, the viscosity measurement conditions were made into 10 rpm of rotation speed and a measurement temperature of 25 degreeC.

2. Solder Paste

The solder paste of the present embodiment can be produced by mixing the flux of the present embodiment and the solder alloy powder by a known method.

Examples of the solder alloy powder include Sn, Ag, Cu, Bi, Zn, In, Ga, Sb, Au, Pd, Ge, Ni, Cr, Al, P, In, Pb, etc., in combination substance. In addition, the alloy composition of the said solder alloy powder is not specifically limited, As long as the effect of the solder paste of this embodiment is not impaired, it can be used.

In addition, as typical solder alloy powders, lead-free solders such as Sn-Ag-based solder alloys, Sn-Ag-Cu-based solder alloys, Sn-Ag-Cu-In-based solder alloys, and Sn-Cu-based solder alloys can be used As the alloy powder, lead-containing solder alloy powder can also be used.

The compounding amount of the aforementioned solder alloy powder is preferably 63% by mass to 93% by mass relative to the total amount of the solder paste. A preferable compounding amount is 84 to 92 mass %, and a more preferable compounding amount is 86 to 90 mass %.

3. Solder joint

The solder joint portion formed using the solder paste of the present embodiment is formed, for example, by the following method.

That is, the above-mentioned solder paste is printed on a predetermined predetermined position on the substrate, and electronic components are mounted on the predetermined position on the substrate, and are formed by reflow soldering. The solder joints formed in this way can be applied to semiconductors, electronic devices, and the like because they generate few voids and have high reliability.

4. Solder bumps

Solder bumps formed using the solder paste of the present embodiment are formed, for example, by the following method.

First, an electrode portion and an insulating layer having a predetermined pattern are formed on a substrate. The insulating layer may be produced by any method as long as it can form a layer formed of an insulating component having a predetermined film thickness, such as a liquid solder resist or a dry film.

Next, a metal mask (opening on the electrode portion) corresponding to the pattern is placed on the substrate to contact the insulating layer, and the opening region on the electrode portion is filled with the solder paste by printing using a squeegee or the like. Then, the board is put into a reflow soldering apparatus, and reflow soldering is performed according to a specified temperature profile. After reflow soldering, solder bumps are formed by removing the flux components (flux residues) remaining on the substrate.

In addition, the solder paste of this embodiment can also form solder bumps using a dry film process. The step of forming the solder bumps by the dry film process is as follows, for example.

First, an electrode portion and an insulating layer having a predetermined pattern are formed on a substrate. This insulating layer may be produced by any method as long as it can form a layer formed of an insulating component having a predetermined film thickness, such as a liquid solder resist or a dry film.

Next, a dry film layer is formed on the aforementioned insulating layer. The dry film layer is formed by sticking a dry film on a specified range of the aforementioned substrate to contact the insulating layer, and by exposing and developing it in a specified pattern. That is, among the resist components in the dry film, the resist component in the portion where the solder bumps are to be formed (on the electrode portion) is removed by exposure and development, and a dry film layer of a predetermined pattern is formed on the substrate. In addition, a region (opening) surrounded by the dry film layer is thus formed.

Then, the openings are filled with the solder paste by printing using a squeegee or the like. Then, the substrate is placed in a reflow soldering apparatus, and reflow soldering is performed according to a specified temperature profile. After reflow soldering, solder bumps are formed by removing the flux component (flux residue) and the dry film layer remaining on the substrate.

The solder bumps formed in this way can suppress the reduction in the fluidity of the flux during reflow of the solder paste, so that the generation of voids in the solder bumps can be suppressed, and the occurrence of missing bumps during the formation of the solder bumps can be suppressed.

[Example]

Hereinafter, the present invention will be described in detail with reference to Examples and Comparative Examples. In addition, this invention is not limited to these Examples.

The production of flux

Each component was kneaded according to the composition and formulation shown in Table 1, and each flux of Examples 1 to 8 and Comparative Examples 1 to 7 was produced. In addition, in Table 1, the unit of the numerical value which shows a composition is mass %, unless it mentions in particular.

Next, 12 mass % of the fluxes of Examples 1 to 8 and Comparative Examples 1 to 7 and 88 mass % of Sn-3Ag-0.5Cu solder alloy powder (powder particle size of 2 μm to 8 μm: IPC standard Type 8) were mixed to obtain Examples The solder pastes of 1 to 8 and Comparative Examples 1 to 7.

※1 完全氫化改性松香(軟化點80℃) Eastman Chemical公司製※2 甲醯化松香(軟化點85~95℃) Harima Chemicals(股)製※3 三(2,3-二溴丙基)異氰脲酸酯 日本化成(股)製※4 聚8,13-二甲基-8,12-二十碳二酸酐 岡村製油(股)製※5 2-癸基十四醇(碳數24：支鏈型) 新日本理化(股)製※6 2-辛基十二醇(碳數20：支鏈型) 新日本理化(股)製※7 異二十醇(碳數20：支鏈型) 日產化學工業(股)製※8 異十八醇(碳數18：支鏈型) 高級醇工業(股)製※9 2-十六醇(碳數16：支鏈型) 新日本理化(股)製※10 癸二酸雙(2-乙基己酯) 大八化學工業(股)製

※1 Fully hydrogenated modified rosin (softening point 80°C) Eastman Chemical Co. Ltd. ※2 Carboxylated rosin (softening point 85~95°C) Harima Chemicals Co., Ltd. ※3 Tris(2,3-dibromopropyl) Isocyanurate Nippon Chemical Co., Ltd. *4 Poly-8,13-dimethyl-8,12-eicosadioic anhydride Okamura Oil Co., Ltd. *5 2-decyltetradecanol (24 carbon atoms) : Branched type) Nippon RIKEN Co., Ltd. *6 2-Octyldodecanol (20 carbon atoms: branched) Nippon Rika Co., Ltd. *7 Isoeicosanol (20 carbon atoms: branched) Type) Nissan Chemical Industry Co., Ltd. ※8 Isostearyl alcohol (C 18: branched type) Advanced Alcohol Industry Co., Ltd. ※9 2-hexadecanol (C16: branched type) Nippon RIKEN Co., Ltd. ※10 Bis(2-ethylhexyl sebacate) Manufactured by Daihachi Chemical Industry Co., Ltd.

<weight loss rate>

For each solvent component, the weight loss rate at 220°C was measured.

The measurement of the weight loss rate was performed under the following conditions. That is, using a simultaneous differential thermogravimetric measuring apparatus (product name: STA7200RV, manufactured by Hitachi High-Technologies Corporation), 10 mg of the measurement sample was heated to 220° C. in a N2 (300 ml/min) environment at a heating rate of 10° C./min. weight loss rate. The results are shown in Table 2.

<void test>

As shown in FIG. 2 , electrodes 2 , insulating layers 3 , dry film layers 4 , and openings 5 are formed on the substrate 1 . The board|substrate 1 which has such a structure is manufactured by the following method, for example.

First, electrodes 2 and insulating layers 3 having a predetermined pattern were formed on a substrate 1 (dimension: 250 mm×75 mm). The insulating layer 3 may be produced by any method as long as a layer formed of an insulating component having a predetermined film thickness such as a liquid solder resist or a dry film can be formed. In addition, the opening diameter of the surface (upper surface) of the insulating layer 3 was set to be 85 μm in diameter.

Next, the dry film layer 4 is formed on the insulating layer 3 . The dry film layer 4 is formed by contacting the insulating layer 3 (product name: WB-5040, manufactured by DuPont) with a dry film on a predetermined area of the substrate 1, and exposing and developing it in a predetermined pattern. That is, among the resist components of the dry film described above, the resist component for forming the solder bump portion (on the electrode 2 ) is removed by exposure and development, and the dry film layer 4 of a predetermined pattern is formed on the substrate 1 . In addition, the height (thickness) of the dry film layer 4 was 38 μm and the width was 35 μm. The opening diameter of the surface (upper surface) was 115 μm in diameter, and the pitch width (the distance from A to B in FIG. 2 ) was 150 μm. Thereby, the area|region (opening part 5) surrounded by the dry film layer 4 is formed.

Then, each of the solder pastes of Examples 1 to 8 and Comparative Examples 1 to 7 was printed on each of the substrates 1 using a urethane squeegee, and the openings 5 were filled. In addition, the number of times of printing was 10 times in one direction.

Then, each substrate 1 on which each solder paste was printed was placed in a reflow soldering apparatus (product name: TNP25-538EM, manufactured by Tamura Co., Ltd.), followed by a temperature profile shown in FIG. 1 under a nitrogen atmosphere (oxygen concentration 100 ppm). Below) Reflow soldering is performed under the conditions of no preheating, peak temperature 260°C, heating rate and cooling rate 2°C/sec. Then, after the reflow soldering, the flux components (flux residues) and the dry film layer 4 remaining on the respective substrates 1 are removed to form solder bumps.

Next, flux (product name: BF-30, manufactured by Tamura Co., Ltd.) was applied to the formed solder bumps, and reflow soldering was performed under the same conditions as the reflow soldering conditions at the time of forming the above-mentioned solder bumps to prepare each Test substrate. In addition, to remove the dry film layer 4, a peeling solution (product name: CLEANTHROUGH A-04: manufactured by Kao Co., Ltd.) was used, and vibration was applied for 1 minute using an ultrasonic cleaning apparatus (product name: ASU-3M, manufactured by AS ONE Co., Ltd.). and proceed. In addition, the number of pads provided on each substrate 1 was set to 7200.

About 500 of the formed solder bumps were visually observed for voids using an X-ray observation apparatus (product name: XD7600 Diamond, manufactured by Nordson Dage Corporation) for each of the produced test boards, and these solder bumps were measured. The maximum void diameter (%), average void diameter (%), and the proportion of generated solder bumps with a void diameter ratio of 10% or more (void generation rate (%)) were evaluated according to the following criteria. The results are shown in Table 3.

. Maximum void diameter (%)

◎: The maximum void diameter is 0% or more and 20% or less

○: Maximum void diameter exceeds 20% and is 25% or less

△: The maximum void diameter exceeds 25% and is 30% or less

×: The maximum void diameter exceeds 30%

. Average void diameter (%)

○: The average void diameter is 0% or more and 15% or less

△: Average void diameter exceeds 15%

． Void generation rate (%)

◎◎: The void generation rate is 0% or more and 25% or less

◎: The void generation rate exceeds 25% and is 35% or less

○: The void generation rate exceeds 35% and is 45% or less

△: The void generation rate exceeds 45% and is 50% or less

×: The void generation rate exceeds 50%

<Missing bump test>

Each test substrate was produced under the same conditions as the above-mentioned void test.

For each test substrate, the number of solder bumps with missing bumps was measured and evaluated according to the following criteria. The results are shown in Table 3.

○: No missing bumps (zero occurrence)

×: There are missing bumps

<Flux viscosity after reflow>

In the measurement of the viscosity, first, 4 g of each of the fluxes of Examples 1 to 8 and Comparative Examples 1 to 7 was put into an aluminum pan, placed on a metal mesh, and a reflow soldering apparatus (product name: TNP25- 538EM, manufactured by Tamura Manufacturing Co., Ltd.) for reflow soldering. In addition, the reflow soldering conditions are based on the temperature profile shown in FIG. 1 .

Each flux after reflow was returned to normal temperature, and was measured using an E-type viscometer (product name: RE150U, manufactured by Toki Sangyo Co., Ltd.). In addition, the viscosity measurement conditions were made into 10 rpm of rotation speed and a measurement temperature of 25 degreeC. Then, the measured viscosity was evaluated according to the following criteria. The results are shown in Table 3.

◎: 15Pa. s or less

○: More than 15Pa. s and is 25Pa. s or less

△: More than 25Pa. s and is 30Pa. s or less

×: More than 30Pa. s

As can be seen from the above, the results of the void test (maximum void diameter, average void diameter, and void generation rate) of the solder bumps formed using the solder pastes of the respective Examples were also good, and the suppression of the occurrence of missing bumps was also very good. . It can be seen that the compounding amount of the monohydric alcohol whose carbon number contained in 1 molecule is 18 or more and 24 or less, especially the carbon number contained in 1 molecule is 18 or more and 20 or less is 40% by mass or more and 50% by mass. In Examples 2 to 6 having a mass % or less, the effect of suppressing the generation of voids can be further enhanced.

On the other hand, in Comparative Example 1 using an ester-based solvent with a low weight loss rate at 220° C., the other flux components were not completely melted, and were in a state that could not be used as a flux. As described above, in Comparative Example 1, since it was in a state in which flux and solder paste could not be prepared, the evaluation results for each test were expressed as "unmeasurable".

In addition, it was found that in Comparative Examples 2 to 4 and 7 in which only a solvent other than a monohydric alcohol having a carbon number of 18 or more and 24 or less contained in one molecule was used, it was difficult to suppress the decrease in fluidity during reflow, and therefore the solder bumps The void generation rate in all of them exceeded 50%, and other void test results and/or missing bump test results were also worse than those of the solder pastes of the respective Examples.

Furthermore, it can be seen that in Comparative Example 5 in which the compounding amount of a monohydric alcohol having a carbon number of 18 or more and 24 or less contained in 1 molecule is less than 30 mass % with respect to the total amount of the flux, and in Comparative Example 6 in which it exceeds 60 mass %, The void generation rate exceeds 50%.

Claims (11)

A flux comprising a rosin-based resin, an activating agent, a thixotropic agent, and a solvent, wherein the flux contains a monohydric alcohol having a carbon number of 18 or more and 24 or less contained in one molecule as the solvent, The compounding quantity of the said monohydric alcohol is 40 mass % or more and 50 mass % or less with respect to the total amount of the flux, and poly-8,13-dimethyl-8,12-eicosanedioic anhydride is contained as the said activator system. The flux according to claim 1, wherein the number of carbon atoms contained in one molecule of the monohydric alcohol is 18 or more and 20 or less. The flux according to claim 1 or claim 2, wherein the monohydric alcohol is a branched alcohol or an unsaturated alcohol. The flux according to item 1 or item 2 of the claimed scope, wherein the monohydric alcohol is selected from oleyl alcohol, isostearyl alcohol, isoeicosanol, 2-octyldodecanol or 2- At least one of decyltetradecanol. The soldering flux according to item 3 of the claimed scope, wherein the monohydric alcohol is selected from oleyl alcohol, isostearyl alcohol, isoeicosanol, 2-octyldodecanol or 2-decyltetradecyl alcohol at least one of alcohols. The flux according to claim 1 or claim 2, characterized in that the flux is heated from room temperature to a peak temperature of 260°C at a temperature increase rate of 2°C/sec, and then decreases after reaching the peak temperature. The viscosity of the reflow soldering under the condition of cooling at a temperature rate of 2°C/sec after heating is 30Pa. s or less. The flux according to claim 3, wherein the flux is heated from room temperature to a peak temperature of 260°C at a temperature increase rate of 2°C/sec, and after reaching the peak temperature, the flux is cooled at a rate of 2°C The viscosity of the reflow soldering condition after cooling under the condition of / second was 30Pa after heating. s or less. The flux according to claim 4, wherein the flux is heated from room temperature to a peak temperature of 260°C at a temperature increase rate of 2°C/sec, and after reaching the peak temperature, the flux is cooled at a rate of 2°C The viscosity of the reflow soldering condition after cooling under the condition of / second was 30Pa after heating. s or less. The flux according to claim 5, wherein the flux is heated from room temperature to a peak temperature of 260°C at a temperature increase rate of 2°C/sec, and after reaching the peak temperature, the flux is cooled at a rate of 2°C The viscosity of the reflow soldering condition after cooling under the condition of / second was 30Pa after heating. s or less. A solder paste characterized by comprising the flux according to any one of the first to ninth claims and a solder alloy powder. A method of forming a solder bump, characterized in that an electrode portion and a first insulating layer are formed on a substrate, a second insulating layer is formed on the first insulating layer, an opening region is formed on the electrode portion, and printing is performed. The opening area of the electrode portion is filled with the solder paste according to claim 10, the substrate in which the solder paste is filled in the opening area of the electrode portion is heated, and the solder paste is filled in the opening area of the electrode portion. Soldering flux residues are formed on the substrate, and solder bumps are formed by removing the fluxing residues and the second insulating layer.

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