Solder composition

Abstract

To provide a solder composition that achieves improved moisture-resistant insulation properties.SOLUTION: A solder composition contains solder powder and flux. The flux contains an epoxy resin, a curing agent, and an organic acid. The organic acid has a water solubility of 10 g / L or less. The content of the organic acid is 2-20 mass% relative to the total mass of the solid content of the flux. The flux further contains an imidazole compound, with the content of the imidazole compound being 0-10 pts.mass relative to 100 pts.mass of the total of the epoxy resin and the curing agent.SELECTED DRAWING: None

Description

Technical Field

[0001] The present disclosure generally relates to solder compositions, and more particularly to solder compositions containing a flux.

Background Art

[0002] Patent Document 1 discloses a solder paste. This solder paste is composed of solder powder and a flux. The flux contains an epoxy resin, a curing agent, a rubber-modified epoxy resin, and an organic acid. The rubber-modified epoxy resin is contained in a proportion of 3% by weight to 35% by weight based on the total weight of the flux.

[0003] Patent Document 1 also discloses a mounting structure. This mounting structure is a circuit board on which components are mounted using the above solder paste. This mounting structure includes a conductive portion in which the components and the circuit board are metallically joined, and a reinforcing portion formed by covering the periphery of the conductive portion with a cured product of the flux.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, the mounting structure using the solder paste of Patent Document 1 has room for improvement in moisture resistance insulation.

[0006] An object of the present disclosure is to provide a solder composition capable of improving moisture resistance insulation.

Means for Solving the Problems

[0007] The solder composition according to one aspect of the present disclosure contains solder powder and a flux. The flux includes an epoxy resin, a curing agent, and an organic acid. The solubility of the organic acid in water is 10 g / L or less.

Advantages of the Invention

[0008] According to the present disclosure, moisture resistance insulation can be improved.

Brief Description of the Drawings

[0009]

Figure 1

Modes for Carrying Out the Invention

[0010] 1. Overview As described above, there is room for improvement in the moisture resistance insulation of the mounting structure using the solder paste of Patent Document 1. One of the reasons is that the inventors consider that there is a possibility that an organic acid remains in the resin forming the reinforcing portion of the mounting structure. When such a mounting structure is placed in a high-temperature and high-humidity environment, when the resin in the reinforcing portion absorbs moisture, the organic acid remaining in the resin in the reinforcing portion can be ionized by this moisture. It is presumed that this causes migration and reduces the moisture resistance insulation.

[0011] Therefore, the inventors have continued intensive research to improve the moisture resistance insulation while using a solder paste containing an epoxy resin or the like, and as a result, have developed the following solder composition.

[0012] That is, the solder composition according to the present embodiment contains solder powder and a flux. The flux includes an epoxy resin, a curing agent, and an organic acid. The solubility of the organic acid in water is 10 g / L or less. In this way, since the organic acid is hardly soluble in water, ionization is suppressed. Therefore, migration is less likely to occur and insulation degradation is suppressed.

[0013] Therefore, according to this embodiment, the moisture resistance insulation can be improved. Furthermore, flux cleaning after soldering becomes unnecessary.

[0014] 2. Details (1) Solder composition The solder composition according to this embodiment is used, for example, to fix component 4 to substrate 3 by a surface mounting method (see FIG. 1). The solder composition becomes a joint portion 2 that joins component 4 and substrate 3, for example, after reflow. The joint portion 2 has a conductive portion 21 and a reinforcing portion 22. The conductive portion 21 is a portion that electrically joins the solder bump 7 provided on the electrode 6 of component 4 and the electrode 5 of substrate 3. The reinforcing portion 22 has electrical insulation and is a portion that reinforces the periphery of the conductive portion.

[0015] The solder composition according to this embodiment contains solder powder and flux. The solder composition is preferably in paste form. The solder composition may further contain a solvent. The viscosity of the solder composition can be adjusted by the solvent. The solvent is not particularly limited, and examples thereof include dibutyl diglycol (DBDG).

[0016] (1.1) Solder powder The solder powder is a material that can form the conductive portion 21 of the joint portion 2 (see FIG. 1). The solder powder is not particularly limited. The chemical composition of the solder powder includes lead-free solder and lead-containing solder. From the viewpoint of environmental protection, the chemical composition of the solder powder is preferably lead-free solder.

[0017] The lead-free solder is not particularly limited. For example, it contains Sn and further contains one or more elements selected from the group consisting of Bi, Sb, Cu, Ag, Zn, In, Ni, P, Ga, and Ge. That is, as the lead-free solder, for example, Sn-Bi-based solder, Sn-Sb-based solder, Sn-Cu-based solder, Sn-Ag-based solder, Sn-Zn-based solder, Sn-In-based solder, Sn-Ag-Cu-based solder, Sn-Cu-Ni-based solder, Sn-Zn-Bi-based solder, Sn-Ag-Cu-In-based solder, Sn-Bi-Cu-In-based solder, Sn-Ag-Bi-Cu-based solder, Sn-In-Ag-Bi-based solder, Sn-Cu-Ag-P-Ga-based solder, Sn-Cu-Ni-P-Ga-based solder, Sn-Ag-Cu-Ni-Ge-based solder, and Sn-Bi-Ag-Cu-In-based solder, etc. can be mentioned. In particular, the Sn-Bi-based solder is preferable because it has a low melting point and good wettability. Also, the Sn-Ag-Cu-based solder is preferable because it has high reliability and good wettability.

[0018] The melting point of the solder powder is preferably 80 °C or higher. Thereby, various solder powders can be used. The upper limit value of the melting point of the solder powder is not particularly limited. For example, it is the heat-resistant temperature of the component 4 (surface-mounted component). Specifically, the upper limit value of the melting point of the solder powder is, for example, 300 °C.

[0019] The content of the solder powder is preferably 75 parts by mass or more and 90 parts by mass or less, more preferably 77 parts by mass or more and 88 parts by mass or less, and still more preferably 80 parts by mass or more and 85 parts by mass or less with respect to a total of 100 parts by mass of the epoxy resin and the curing agent. When the content of the solder powder is 75 parts by mass or more, the conductivity of the conductive portion 21 can be improved. When the content of the solder powder is 90 parts by mass or less, the reinforcing effect of the conductive portion 21 by the reinforcing portion 22 can be improved.

[0020] (1.2) Flux The flux is a material that has a fluxing action and can form the reinforcing portion 22 of the joint portion 2 (see FIG. 1). The flux contains an epoxy resin, a curing agent, and an organic acid. Preferably, the flux further contains an imidazole compound.

[0021] Mainly, an epoxy resin and a curing agent form the reinforcing portion 22, and an organic acid can exhibit a fluxing action as an activator. An imidazole compound can function as a curing accelerator.

[0022] <Epoxy resin> The epoxy resin can impart thermosetting properties to the solder composition. The epoxy resin becomes a cured product and forms the reinforcing portion 22 around the conductive portion 21 (see FIG. 1).

[0023] The epoxy resin is not particularly limited, and examples thereof include bisphenol F type epoxy resin, bisphenol A type epoxy resin, and biphenyl type epoxy resin. Preferably, the epoxy resin is liquid at room temperature. This makes it easier to make the solder composition into a paste form at room temperature.

[0024] <Curing agent> The curing agent reacts with the epoxy resin to form the reinforcing portion 22 (see FIG. 1). The curing agent is not particularly limited, and examples thereof include phenolic resins. When the curing agent contains a phenolic resin, Phenolic resin and epoxy resin the equivalent ratio is preferably 0.02 or more and 0.5 or less, more preferably 0.05 or more and 0.3 or less.

[0025] Preferably, the curing agent is liquid at room temperature. This makes it easier to make the solder composition into a paste form at room temperature.

[0026] <Organic acid> As described above, the organic acid can exhibit a fluxing action as an activator. Examples of the fluxing action include a cleaning action, an antioxidant action, and a surface tension reducing action.

[0027] The cleaning action is an action of removing the oxide film of the solder powder or removing foreign substances on the surface of the electrode 5 of the substrate 3. The solder composition is printed on the electrode 5 of the substrate 3.

[0028] The antioxidant effect is the effect of preventing oxidation of the conductive part 21.

[0029] The surface tension reduction effect is the effect of suppressing the melting solder powder from becoming round. By reducing the surface tension of the solder, the wettability of the solder becomes good.

[0030] The solubility of the organic acid in water (especially the solubility of the organic acid in water at 20 °C) is 10 g / L or less, preferably 5 g / L hereinafter , more preferably 1 g / L hereinafter is. Thus, since the organic acid is hardly soluble in water, the ionization of the organic acid is suppressed. Therefore, it becomes difficult for the organic acid to remain in the reinforcing part 22 as a flux residue. Even if the organic acid remains in the reinforcing part 22 as a flux residue, migration is less likely to occur and insulation degradation is suppressed. Therefore, the moisture insulation property of the mounting structure 1 can be improved. Furthermore, flux cleaning after soldering becomes unnecessary. Note that the lower limit value of the solubility of the organic acid in water is, for example, more than 0 g / L.

[0031] The organic acid is not particularly limited as long as its solubility in water is 10 g / L or less. Preferably, the organic acid has at least one or more carboxyl groups. Preferably, the organic acid contains at least one compound selected from the group consisting of p-hydroxybenzoic acid (4-hydroxybenzoic acid), salicylic acid, eicosanedioic acid, dodecanedioic acid, 6-hydroxy-2-naphthalenecarboxylic acid, dimer acid, and sebacic acid.

[0032] Dimer acid is a liquid fatty acid mainly composed of dibasic acids of C36 dicarboxylic acids produced by dimerization of C18 unsaturated fatty acids using vegetable oils as raw materials, and contains monobasic acids and tribasic acids. The C18 unsaturated fatty acids are not particularly limited, and examples include oleic acid, linoleic acid, and linolenic acid. The structure of the C36 dicarboxylic acid is a long-chain fatty acid with two alkyl side chains, and various structural isomers can exist. The purity of the C36 dicarboxylic acid in the dimer acid is preferably 90% or more. The acid value of the dimer acid is preferably 193 mgKOH / g or more and 201 mgKOH / g or less. The saponification value of the dimer acid is preferably 196 mgKOH / g or more and 203 mgKOH / g or less.

[0033] The molecular weight of the organic acid is preferably 135 or more and 570 or less. The smaller the molecular weight, the stronger the activity of the organic acid and the better the solderability.

[0034] The organic acid preferably has a hydrophobic group (lipophilic group). This makes it easier to reduce the solubility of the organic acid in water to 10 g / L or less.

[0035] The hydrophobic group is not particularly limited, and examples include a phenyl group, a naphthalene group, and a long-chain alkyl group. The phenyl group and the naphthalene group are preferred compared to the long-chain alkyl group. That is, the hydrophobic group preferably contains at least one of a phenyl group and a naphthalene group, and more preferably contains a phenyl group. With such an organic acid having a hydrophobic group, it is easy to make the solubility in water 10 g / L or less while having a low molecular weight. In particular, p-hydroxybenzoic acid (4-hydroxybenzoic acid) and salicylic acid are preferred because they contain a phenyl group.

[0036] The content of the organic acid is preferably 2.0% by mass or more and 20.0% by mass or less, more preferably 2.5% by mass or more and 10.0% by mass or less, and still more preferably 3.0% by mass or more and 8.0% by mass or less, based on the total mass of the solid content of the flux. When the content of the organic acid is 2.0% by mass or more, the flux action can be ensured. When the content of the organic acid is 20.0% by mass or less, the moisture resistance insulation can be further improved.

[0037] <Imidazole compound> As described above, the imidazole compound can function as a curing accelerator. When the flux contains the imidazole compound, a cured product with high heat resistance can be obtained. That is, a cured product with a high glass transition temperature (Tg) can be obtained. Therefore, the reinforcing effect of the conductive part 21 by the reinforcing part 22 can be improved. The imidazole compound is not particularly limited, and examples thereof include 2-phenyl-4-methyl-5-hydroxymethylimidazole (2P4MHZ).

[0038] When the flux contains the imidazole compound, the content of the imidazole compound is preferably more than 0 part by mass and 10 parts by mass or less, more preferably 2.0 parts by mass or more and 8.0 parts by mass or less, based on 100 parts by mass in total of the epoxy resin and the curing agent. In other words, the content of the imidazole compound is preferably more than 0 phr and 10 phr or less, more preferably 2.0 phr or more and 8.0 phr or less. Thereby, a cured product with higher heat resistance can be obtained. Note that the unit phr means the ratio (parts by mass) with respect to 100 parts by mass in total of the epoxy resin and the curing agent.

[0039] (2) Preparation method The solder composition according to the present embodiment can be prepared, for example, as follows.

[0040] First, an epoxy resin, a curing agent, an organic acid, and an imidazole compound are mixed and kneaded with a kneader to obtain a flux.

[0041] Next, solder powder is added to this flux and kneaded continuously to obtain a solder composition. The kneader is not particularly limited, and examples thereof include a planetary mixer.

[0042] (3) Use The solder composition according to this embodiment is used, for example, in the manufacture of the mounting structure 1 shown in FIG. 1. That is, the solder composition is used to fix the component 4 to the substrate 3 by the surface mounting method. The process of the surface mounting method includes a printing process, a component mounting process, and a reflow soldering process.

[0043] In the printing process, the solder composition is printed on the electrodes 5 (lands, etc.) of the substrate 3 such as a printed wiring board by screen printing or the like.

[0044] In the component mounting process, the component 4 is mounted on the printed substrate 3. The solder bump 7 provided on the electrode 6 of the component 4 is placed on the electrode 5 of the substrate 3.

[0045] In the reflow soldering process, the substrate 3 on which the component 4 is mounted is placed in a furnace and heated. As a result, the component 4 and the substrate 3 are joined by the joint portion 2. Even if the conductive portion 21 that electrically joins the component 4 and the substrate 3 is temporarily fragile, the reinforcing portion 22 covers and reinforces the periphery of the conductive portion 21, so that the drop resistance performance of the mounting structure 1 can be improved.

[0046] Note that the solder composition can also be used as a thermal interface material (TIM).

[0047] 3. Aspect As is clear from the above embodiment, the present disclosure includes the following aspects. Below, signs are attached in parentheses only for the purpose of clarifying the correspondence with the embodiment.

[0048] The first aspect is a solder composition containing solder powder and flux. The flux includes an epoxy resin, a curing agent, and an organic acid. The solubility of the organic acid in water is 10 g / L or less.

[0049] According to this aspect, the moisture resistance insulation can be improved.

[0050] The second aspect is a solder composition based on the first aspect. In the second aspect, the content of the organic acid is 2% by mass or more and 20% by mass or less with respect to the total mass of the solid content of the flux.

[0051] According to this aspect, while ensuring the flux action, the moisture resistance insulation can be further improved.

[0052] The third aspect is a solder composition based on the first or second aspect. In the third aspect, the flux contains an imidazole compound.

[0053] According to this aspect, a cured product with high heat resistance can be obtained.

[0054] The fourth aspect is a solder composition based on the third aspect. In the fourth aspect, the content of the imidazole compound is more than 0 part by mass and 10 parts by mass or less with respect to 100 parts by mass in total of the epoxy resin and the curing agent.

[0055] According to this aspect, a cured product with even higher heat resistance can be obtained.

[0056] The fifth aspect is a solder composition based on any one of the first to fourth aspects. In the fifth aspect, the melting point of the solder powder is 80°C or higher.

[0057] According to this aspect, it is possible to use a wide variety of solder powders.

[0058] The sixth aspect is a solder composition based on any one of the first to fifth aspects. In the sixth aspect, the content of the solder powder is 75 parts by mass or more and 90 parts by mass or less with respect to 100 parts by mass in total of the epoxy resin and the curing agent.

[0059] According to this aspect, the conductivity of the conductive portion (21) can be improved. Further, the reinforcing effect of the reinforcing portion (22) on the conductive portion (21) can be improved.

Example

[0060] Hereinafter, the present disclosure will be specifically described by way of examples. However, the present disclosure is not limited to the examples.

[0061] (1) Sample (1.1) Solder composition The materials used for the preparation of the solder composition are as follows.

[0062] <Solder powder> Sn-Bi based solder (Sn42Bi58, melting point 139 °C).

[0063] <Flux> ≪Epoxy resin≫ · Epoxy resin 1: Bisphenol F type epoxy resin (manufactured by Nippon Steel Chemical & Material Co., Ltd., trade name "YDF-8170", epoxy equivalent 155 - 165 g / eq) · Epoxy resin 2: Bisphenol A type epoxy resin (manufactured by Nippon Steel Chemical & Material Co., Ltd., trade name "YD-8125", epoxy equivalent 168 - 178 g / eq) · Epoxy resin 3: Biphenyl type epoxy resin (manufactured by Nippon Kayaku Co., Ltd., trade name "NC-3000-L", epoxy equivalent 261 - 282 g / eq) ≪Hardener≫ · Phenolic resin: Liquid phenolic resin (manufactured by Meiwa Kasei Co., Ltd., trade name "MEH-8000H", OH equivalent 139 - 143 g / eq) ≪Imidazole compound≫ · 2-Phenyl-4-methyl-5-hydroxymethylimidazole (2P4MHZ) ≪Organic acid≫ · Organic acid 1: Eicosanedioic acid · Organic acid 2: Dodecanedioic acid · Organic acid 3: 6-Hydroxy-2-naphthalenecarboxylic acid · Organic acid 4: p-Hydroxybenzoic acid · Organic acid 5: Salicylic acid · Organic acid 6: Dimer acid (manufactured by Tsukino Food Industry Co., Ltd., trade name "Tsunodyme 395", acid value 196 mg KOH / g, saponification value 198 mg KOH / g, purity of C36 dicarboxylic acid 94.0%) · Organic acid 7: Sebacic acid · Organic acid 8: Adipic acid · Organic acid 9: Glutaric acid.

[0064] (1.2) Preparation method First, an epoxy resin, a curing agent, an organic acid, and an imidazole compound were mixed and kneaded with a planetary mixer to obtain a flux. Then, solder powder was added to this flux and continuously kneaded to obtain a solder composition. The formulation of the solder composition is as shown in Table 1.

[0065] (2) Evaluation items The following tests were conducted on the solder composition.

[0066] (2.1) Moisture resistance and insulation The solder composition was supplied to a JIS II type comb-shaped substrate by printing, and heat treatment was performed by reflow soldering with a predetermined temperature profile to obtain an evaluation substrate. This evaluation substrate was placed in a high-temperature and high-humidity chamber at 85°C and 85% RH for 1000 hours, and then a bias voltage of 50 V was applied to the evaluation substrate. The resistance value at this time was measured and converted to volume resistivity. The volume resistivity was classified according to the following evaluation criteria to evaluate the moisture resistance and insulation.

[0067] <Evaluation criteria> A: Volume resistivity is 1×10 8 Ω·cm or more C: Volume resistivity is less than 1×10 8 Ω·cm.

[0068] (2.2) Viscosity The viscosity (Pa·s) of the solder composition at 25°C and 5 rpm was measured. For the measurement of viscosity, an E-type viscometer (manufactured by Toki Sangyo Co., Ltd., model number "RE-215U") was used. The viscosity is preferably 50 Pa·s or more and 250 Pa·s or less, more preferably 100 Pa·s or more and 150 Pa·s or less.

[0069] (2.3) Thixotropy The thixotropy ratio of the solder composition at 25°C was measured. The thixotropy ratio was calculated as the ratio of the viscosity at 0.5 rpm and the viscosity at 5.0 rpm (viscosity at 0.5 rpm / viscosity at 5.0 rpm) using the above E-type viscometer. The thixotropy ratio is preferably 1.0 or more, more preferably 2.5 or more.

[0070] [Table 1]

Claims

1. containing solder powder and flux, wherein the flux contains an epoxy resin, a curing agent, and an organic acid, the curing agent is composed of a phenolic resin, the equivalent ratio of the phenolic resin to the epoxy resin is 0.02 or more and 0.3 or less, the solubility of the organic acid in water is 10 g / L or less, the content of the organic acid is 2% by mass or more and 20% by mass or less based on the total mass of the solid content of the flux, a solder composition.

2. the flux further contains an imidazole compound, the solder composition according to Claim 1.

3. the content of the imidazole compound is more than 0 part by mass and 10 parts by mass or less based on 100 parts by mass in total of the epoxy resin and the curing agent, the solder composition according to Claim 2.

4. the solder powder is a solder powder composed of a solder alloy having a melting point of 80°C or higher, the solder composition according to any one of Claims 1 to 3.

5. the content of the solder powder is 75 parts by mass or more and 90 parts by mass or less based on 100 parts by mass in total of the epoxy resin and the curing agent, the solder composition according to any one of Claims 1 to 4.

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