Copper sintering paste composition and method of making same

Abstract

The present invention relates to a copper sintering paste composition and a method for manufacturing the same, and provides a joining material which can replace existing solders and lead-free solders, and has excellent heat resistance, heat dissipation, thermal conductivity and joining strength.

Description

Technical Field

[0001] This invention relates to a copper sintering paste composition for forming copper sintering bonds and a method for preparing the same, and provides copper sintering bonds formed therefrom. Background Technology

[0002] Previously, various bonding materials were used to bond semiconductor devices to support members. As such bonding materials, lead-containing solders containing lead (Pb) and lead-free solders that have removed lead were used. Due to the harmful effects of lead in solders, the use of lead-free solders is constantly increasing.

[0003] However, most lead-free solders inevitably contain tin, which generally contains a small amount of lead. Furthermore, tin itself is more expensive than lead-containing solders, has a high melting point above 200°C, and presents challenges in controlling the shape and size of the joint. Additionally, bismuth or indium, added to address these issues, are rare elements and therefore expensive.

[0004] Therefore, the present invention aims to provide a copper sintering paste that forms a bond by sintering copper particles, which is less harmful than existing solder materials and can form a sintered bond with high shear strength at low cost.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Publication No. 2021-073639 (May 13, 2021)

[0008] Patent Document 2: Japanese Patent Publication No. 2021-064612 (April 22, 2021)

[0009] Patent Document 3: Japanese Patent Application Publication No. 2021-048396 (March 25, 2021)

[0010] Non-patent literature

[0011] Non-patent literature 1 R. Khazaka, L. Mendizabal, D. Henry, Characterization of Nano-silver Dry films for High Temperature Applications, J. ElecTron. Mater. 43(7), 2014, 2459-2466. Summary of the Invention

[0012] Technical issues

[0013] This invention relates to a copper sintering paste composition for forming copper sintered bonds, providing copper nanoparticles coated with a polymer for chemically protecting copper nanoparticles. By preparing a copper sintering paste composition containing the aforementioned copper nanoparticles coated with a polymer, a bonding material that can replace existing solders and lead-free solders is provided, while also providing a bonding material with excellent heat resistance, heat dissipation, thermal conductivity, and bond strength.

[0014] Solution to the problem

[0015] This invention relates to a copper sintering paste composition comprising copper nanoparticles coated with a polymer.

[0016] The copper sintering paste composition described above may include: copper nanoparticles coated with a polymer; a solvent; a reducing agent; a defoamer; and a viscosity modifier.

[0017] The aforementioned polymer-coated copper nanoparticles can refer to those prepared by coating the surface of copper nanoparticles with a polymer after removing the oxide film from the copper nanoparticles. In this case, the average particle size of the polymer-coated copper nanoparticles can be from 0.5 μm to 5 μm.

[0018] The polymers mentioned above may be one or more mixtures or copolymers selected from the group consisting of polyvinylpyrrolidone, polyethylene oxide, polyamide, polymethacrylate, polyacrylate, polyester and polyurethane.

[0019] The oxide film on the copper nanoparticles can be removed using an oxide film removal agent. This oxide film removal agent can be a material that reacts with the copper oxide film (CuO) to generate a copper salt. Copper nanoparticles coated with the polymer can be prepared by attaching a polymerization initiator to the surface of the copper nanoparticles after oxide film removal and forming a polymer.

[0020] The aforementioned oxide film removal agent may be an aqueous solution containing at least one selected from NH4Cl, NH4NO3 and (NH4)2SO4.

[0021] The polymerization initiator mentioned above can be a disulfide.

[0022] The solvents, reducing agents, defoamers, and viscosity modifiers mentioned above can vaporize or decompose when exposed to temperatures ranging from 200°C to 300°C.

[0023] The solid content of the aforementioned polymer-coated copper nanoparticles is 60% to 70% by weight.

[0024] The solvents mentioned above can be one or a mixture of two or more selected from the group consisting of methyl carbitol, butyl carbitol, dimethyl succinate, dipropylene glycol, 2-(2-hexyloxyethoxy)ethanol, diethylene glycol monobutyl ether acetate, and ethylene glycol monohexyl ether.

[0025] The reducing agent mentioned above may include one or more of the following groups: oxalic acid, malonic acid, oleic acid, pimelic acid, octanoic acid, sebacic acid, fumaric acid, myristic acid, palmitic acid, stearic acid, glutaric acid, maleic acid, azelaic acid, rosin acid, adipic acid, ascorbic acid, acrylic acid, and citric acid.

[0026] The aforementioned defoamer may include one or two selected from the group consisting of polypropylene glycol and polyethylene glycol.

[0027] The method for preparing the copper sintering paste composition provided by the present invention may include the following steps: removing the oxide film on the surface of copper nanoparticles with an oxide film removal agent; bonding a polymerization initiator to the surface of the copper nanoparticles after removing the oxide film; preparing polymer-coated copper nanoparticles by polymerizing polymer monomers on the surface of the copper nanoparticles bonded with the polymerization initiator; and mixing the polymer-coated copper nanoparticles into a mixed solution.

[0028] As described above, the oxide film removal agent can be an aqueous solution containing at least one selected from NH4Cl, NH4NO3 and (NH4)2SO4, and the polymerization initiator can be a disulfide.

[0029] In addition, the above-mentioned mixed solution may include high-boiling-point solvents, reducing agents, defoamers, and viscosity modifiers.

[0030] Furthermore, copper sintering bonding can be formed by applying the copper sintering paste composition to a substrate, positioning the device on the copper sintering paste composition, and then holding it at a temperature of 200°C to 400°C for 1 to 10 minutes.

[0031] The effects of the invention

[0032] The copper sintering paste composition according to the present invention has excellent heat dissipation, thermal conductivity, bonding strength and electrical conductivity while being lead-free, thus providing a device bonding technology that can replace existing lead-free solders. Attached Figure Description

[0033] Figure 1 A graph showing the measured values ​​of the shear strength of a copper sintered bond formed according to an embodiment of the present invention. Detailed Implementation

[0034] The copper sintering paste, copper sintering paste composition, and preparation method thereof for forming copper sintered bonds according to the present invention will be described in detail below. The accompanying drawings are provided as examples to fully convey the spirit of the invention to those skilled in the art. Therefore, the invention is not limited to the drawings shown below and can be embodied in different forms; the drawings shown below may be exaggerated to more clearly illustrate the spirit of the invention. In this context, technical and scientific terms used in the invention, unless otherwise defined, have the meaning commonly understood by those skilled in the art to which this invention pertains, and explanations of well-known functions and structures that may unnecessarily obscure the spirit of the invention are omitted in the following description and drawings.

[0035] This invention relates to a copper sintering paste composition, which may include: copper nanoparticles coated with a polymer; a solvent; a reducing agent; a defoamer; and a viscosity modifier.

[0036] In this context, the aforementioned polymer-coated copper nanoparticles refer to copper nanoparticles prepared by coating their surface with a polymer after removing the oxide film from the copper nanoparticles. The average particle size of these copper nanoparticles can be from 0.5 μm to 5 μm, preferably from 1 μm to 3 μm. By using copper nanoparticles of this size, excellent bonding strength of 15 MPa or higher can be achieved when copper bonding is formed in the future.

[0037] The polymer can be one or more mixtures or copolymers selected from the group consisting of polyvinylpyrrolidone and polyethylene oxide. In this case, based on 100 parts by weight of the copper nanoparticles, the content of the polymer can be from 1 part by weight to 5 parts by weight.

[0038] The oxide film on the copper nanoparticles can be removed using an oxide film removal agent. Specifically, the oxide film removal agent can be any material capable of reacting with the copper oxide film (CuO) to form a copper salt, preferably an ammonium salt, and there are no particular limitations. Specifically, the oxide film removal agent can be an aqueous solution containing an ammonium salt selected from NH4Cl, NH4NO3, and (NH4)2SO4. When the oxide film removal agent and the ammonium aqueous solution are mixed, the copper oxide film can be easily removed, which is therefore preferred.

[0039] The oxide film removal agent and ammonia solution can be mixed in a weight ratio of 1:0.5 to 1:2. If the amount of oxide film removal agent added is less than the amount of ammonia solution added, the oxide film may not be completely removed, making the polymer coating reaction difficult. If an excessive amount of oxide film removal agent is added, copper may be over-dissolved, leading to an increase in the consumption of copper nanoparticles.

[0040] The aforementioned copper nanoparticles coated with polymer can be obtained by removing the oxide film on the surface of the copper nanoparticles with an oxide film remover, then binding a polymerization initiator to the surface of the copper nanoparticles with the oxide film removed, and then polymerizing polymer monomers on the surface of the copper nanoparticles with the polymerization initiator bound thereto.

[0041] The polymers described above can be chemically bonded to metal surfaces, and coverage can be achieved by further adding materials that can be used as polymer initiators to the monomers and then polymerizing them. For example, preferably, [S-CH2CH2OCOC(CH3)2Br]2 or [S-(CH2)]2 containing thiol groups can be used. 11 Disulfide initiators such as [OCOC(CH3)2Br2]2. By using the initiators described above, monomers can be polymerized to achieve surface coating of copper nanoparticles with chemical bonds between the polymer and the surface.

[0042] At this point, the density of the polymer can be adjusted according to the treatment time of the initiator, and the density of the polymer can increase with the increase of the treatment time.

[0043] The monomers described above can be selected from monomers capable of forming the polymers described above, and vinylpyrrolidone is preferably used.

[0044] The solvents, reducing agents, defoamers, and viscosity modifiers mentioned above vaporize or decompose when exposed to temperatures ranging from 200°C to 300°C. By using these materials, no organic residue remains when forming the bond, thus maintaining a high level of shear strength in the bond.

[0045] The solid content of the polymer-coated copper nanoparticles is 60% to 70% by weight. If the content of polymer-coated copper nanoparticles is higher than this value, the viscosity of the paste may be too high; if the content of polymer-coated copper nanoparticles is lower than this value, the viscosity of the paste may be too low, making sintering bonding difficult.

[0046] Based on 100 parts by weight of polymer-coated copper nanoparticles, the copper sintering paste composition according to the present invention may contain 1 to 5 parts by weight of a reducing agent, 0.5 to 1.5 parts by weight of a viscosity modifier, 0.5 to 1.5 parts by weight of an additive, 0.5 to 1.5 parts by weight of a defoamer, and 40 to 60 parts by weight of a solvent. By preparing a composition within the above range, a suitable viscosity is achieved, which is beneficial for semiconductor processes.

[0047] Preferably, the solvent is a high-boiling-point organic solvent, specifically, an organic solvent with a boiling point of 150°C or higher can be used. For example, the solvent can be one or a mixture of two or more selected from the group consisting of methyl carbitol, butyl carbitol, dimethyl succinate, dipropylene glycol, 2-(2-hexyloxyethoxy)ethanol, diethylene glycol monobutyl ether acetate, and ethylene glycol monohexyl ether. When using the solvent described above, less solvent volatilization occurs in the paste composition at room temperature, while volatilization occurs at high temperatures during bonding, which is therefore preferable. However, when using organic solvents with a boiling point exceeding 240°C, volatilization as described above is difficult to occur, which is therefore not preferred.

[0048] The reducing agent described above may include one or more selected from the group consisting of oxalic acid, malonic acid, oleic acid, pimelic acid, octanoic acid, sebacic acid, fumaric acid, myristic acid, palmitic acid, stearic acid, glutaric acid, maleic acid, azelaic acid, rosin acid, adipic acid, ascorbic acid, acrylic acid, and citric acid. Oxalic acid is preferably used in this case. By using the organic acid-based material described above, thermal decomposition at high temperatures during copper bonding results in low residual amounts, which is preferable.

[0049] The aforementioned defoamer may include one or two selected from the group consisting of polypropylene glycol and polyethylene glycol. By using the defoamer described above, air bubbles can be prevented from forming in the paste, thereby further improving the bond strength of the sintered bond.

[0050] The aforementioned viscosity modifiers can be mixtures of cellulose-based or acrylic-based materials with amine-based materials. Specifically, materials such as hydroxypropyl methylcellulose or hydroxyethyl methylcellulose are suitable as cellulose-based viscosity modifiers. Furthermore, materials previously used as thickeners, such as Carbopol 940, are suitable as acrylics, while materials such as triethylamine are suitable as amine materials to be mixed with them. By adding such materials, a viscosity suitable for copper sintering pastes used in semiconductor processes can be maintained.

[0051] The aforementioned copper sintering paste may also include a silane coupling agent as an additive. Specifically, the silane coupling agent may refer to ethoxy or methoxysilane coupling agents such as vinyltrimethoxysilane, vinyltriethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, 3-methacryloyloxypropyltrimethoxysilane, and 3-mercaptopropyltrimethoxysilane. By including the additives described above, the dispersion of particles in the paste is increased, thus allowing for uniform bonding during sintering.

[0052] The method for preparing the copper sintering paste composition according to the present invention may include the following steps: removing the oxide film on the surface of copper nanoparticles with an oxide film removal agent; bonding a polymerization initiator to the surface of the copper nanoparticles after removing the oxide film; preparing polymer-coated copper nanoparticles by polymerizing polymer monomers on the surface of the copper nanoparticles bonded with the polymerization initiator; and mixing the polymer-coated copper nanoparticles into a mixed solution.

[0053] If the materials are not evenly dispersed during mixing, the bonding strength may be reduced during the subsequent copper bonding process, leading to breakage of the joint.

[0054] The above-mentioned mixed solution includes the high-boiling-point solvent, reducing agent, defoamer and viscosity modifier. The oxide film remover and polymerization initiator are the same as those mentioned above, so they will not be described again.

[0055] Copper sintering can be formed by applying the copper sintering paste composition as described above onto a substrate, positioning the device on the copper sintering paste composition, and then holding it at a temperature of 200°C to 400°C for 1 to 10 minutes.

[0056] Furthermore, the above-described bonding method may include a preheating process of up to one minute. This preheating can be performed at 100°C to 200°C for up to two minutes. By further including the preheating process described above, rapid gas generation due to temperature changes during the bonding of small electrical components can be prevented, thereby enabling more precise processes.

[0057] The shear strength of copper sintered joints formed using the copper sintering paste described above can be from 10 MPa to 25 MPa.

[0058] The copper sintering paste according to the invention and the copper sintered joints formed therefrom will be described in more detail below by way of examples. However, the following examples are merely for the purpose of explaining the invention in detail, and the invention is not limited thereto, and the invention can be implemented in various forms.

[0059] Furthermore, unless otherwise defined, all technical and scientific terms have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein is intended only to effectively describe particular embodiments and not to limit the invention.

[0060] Removal of oxide film from copper nanoparticles

[0061] 1 L of a mixed solution consisting of 2 g of (NH4)2SO4 and 1 g of NH4OH as an oxide film removal agent was placed in a semi-batch isothermal reactor. 10 g of copper nanoparticles were added, and the mixture was heated to a reaction temperature of 40 °C while stirring. The reaction was carried out for 10 minutes to remove the oxide film from the copper nanoparticles. The solution was then filtered and the reactants were dried to obtain copper nanoparticles with the oxide film removed.

[0062] Preparation of polymer-coated copper nanoparticles

[0063] 150 μL of disulfide ([S-(CH2)) was added to a 500 mL round-bottom flask as a polymer initiator. 11 [OCOC(CH3)2Br]2) and 200 mL of tetrahydrofuran (THF; Sigma Aldrich) were added slowly with vigorous stirring to remove the oxide film from copper nanoparticles. After stirring at 20 °C for 24 hours, copper nanoparticles were obtained by centrifugation and then dispersed in N,N-dimethylformamide (DMF). Subsequently, 0.5 g of 4-vinylpyridine (4VP) and 0.5 mL of distilled water were added under a nitrogen atmosphere, and the mixture was then vigorously stirred at 40 °C for 48 hours to initiate polymerization, thereby coating the surface of the copper nanoparticles with PVP. The solution was then filtered to obtain copper nanoparticles coated with PVP.

[0064] Example 1

[0065] A copper sintering paste composition was prepared by mixing and stirring 65g of the above-mentioned PVP-coated copper nanoparticles with 30g of butylcarbidol, adding 2g of reducing agent, 0.5g of viscosity modifier and 0.5g of additive, and stirring.

[0066] Comparative Example 1

[0067] Except for the use of copper nanoparticles without PVP coating, the copper sintering paste composition was prepared in the same manner as in Example 1 above.

[0068] Characteristic evaluation methods

[0069] Shear strength determination

[0070] Copper sintering was performed using copper sintering paste, and the shear strength of the joint was measured.

[0071] Table 1

[0072]

[0073]

[0074] Reference Figure 1 The shear strength of the bonds formed in Example 1 and Comparative Example 1 can be visually confirmed. In Example 1, the shear strength increases proportionally with sintering time, and the shear strength is optimal when the bond is joined for 5 minutes. As the sintering time exceeds 5 minutes, the shear strength tends to gradually decrease, indicating that the optimal sintering time for Example 1 is approximately 3 to 8 minutes. In contrast, in Comparative Example 1, although the shear strength increases with sintering time, it is generally lower than that of Example 1.

[0075] Furthermore, in the case of Example 1 with PVP coverage, the shear strength deviation tends to be larger, but when bonding is performed within 10 minutes, the shear strength is generally excellent and has no significant impact on quality.

[0076] The present invention has been described above with specific details and limited embodiments, such as specific structural elements, but this is only provided to help to understand the invention more comprehensively. The embodiments of the present invention are not limited to the above embodiments, and those skilled in the art to which the present invention pertains can make various modifications and changes based on such description.

[0077] Therefore, the concept of the present invention is not limited to the embodiments described above. Not only does the scope of the appended patent claims fall within the scope of the present invention, but all scopes that are equivalent to or have been modified therefrom also fall within the scope of the present invention.

Claims

1. A copper sintering paste composition characterized by comprising, comprises: copper nanoparticles coated with a polymer; a solvent; a reducing agent; an antifoaming agent; and a viscosity modifier, based on 100 parts by weight of the copper nanoparticles coated with a polymer, the copper sintering paste composition comprises 1 to 5 parts by weight of the reducing agent, 0.5 to 1.5 parts by weight of the viscosity modifier, 0.5 to 1.5 parts by weight of the additive, 0.5 to 1.5 parts by weight of the antifoaming agent, and 40 to 60 parts by weight of the solvent, the copper nanoparticles coated with a polymer are prepared by removing an oxide film on a surface of the copper nanoparticles with an oxide film remover, and forming a polymer by bonding a polymerization initiator to the surface of the copper nanoparticles after removing the oxide film, the reducing agent comprises one or more than two selected from the group consisting of oxalic acid, malonic acid, oleic acid, pimelic acid, suberic acid, sebacic acid, fumaric acid, myristic acid, palmitic acid, stearic acid, glutaric acid, maleic acid, azelaic acid, abietic acid, adipic acid, ascorbic acid, acrylic acid, and citric acid, the antifoaming agent comprises at least one selected from polypropylene glycol and polyethylene glycol.

2. The copper sintering paste composition according to claim 1, wherein the average particle diameter of the copper nanoparticles coated with a polymer is 0.5 to 5 μm.

3. The copper sintering paste composition according to claim 1, wherein the polymer is at least one selected from polyvinylpyrrolidone and polyethylene oxide.

4. The copper sintering paste composition according to claim 1, wherein the oxide film remover is an aqueous solution containing at least one selected from NH4Cl, NH4NO3, and (NH4)2SO4.

5. The copper sintering paste composition according to claim 1, wherein the polymerization initiator is a disulfide.

6. The copper sintering paste composition according to claim 1, wherein the solvent, the reducing agent, the antifoaming agent, and the viscosity modifier are vaporized or decomposed when exposed to a temperature range of 200 to 300°C.

7. The copper sintering paste composition according to claim 1, wherein the solid content of the copper nanoparticles coated with a polymer is 60 to 70% by weight.

8. The copper sintering paste composition according to claim 1, wherein the solvent is one or a mixture of two or more selected from the group consisting of methyl carbitol, butyl carbitol, dimethyl succinate, dipropylene glycol, 2-(2-hexyloxyethoxy)ethanol, diethylene glycol monobutyl ether acetate, and ethylene glycol monohexyl ether. comprises the steps of:

9. A method of preparing a copper sintering paste composition, characterized by, removing an oxide film on a surface of copper nanoparticles with an oxide film remover; bonding a polymerization initiator to the surface of the copper nanoparticles after removing the oxide film; preparing copper nanoparticles coated with a polymer by polymerizing a polymer monomer on the surface of the copper nanoparticles to which the polymerization initiator is bonded; and mixing the copper nanoparticles coated with a polymer into a mixed solution, ​ The copper sintering paste composition comprises 1 to 5 parts by weight of a reducing agent, 0.5 to 1.5 parts by weight of a viscosity modifier, 0.5 to 1.5 parts by weight of an additive, 0.5 to 1.5 parts by weight of an antifoaming agent, and 40 to 60 parts by weight of a solvent, based on 100 parts by weight of the polymer-coated copper nanoparticles, The reducing agent includes one or two or more selected from the group consisting of oxalic acid, malonic acid, oleic acid, pimelic acid, suberic acid, sebacic acid, fumaric acid, myristic acid, palmitic acid, stearic acid, glutaric acid, maleic acid, azelaic acid, abietic acid, adipic acid, ascorbic acid, acrylic acid, and citric acid, The antifoaming agent includes at least one selected from polypropylene glycol and polyethylene glycol.

10. The method of preparing a copper sinter paste composition according to claim 9, characterized in that, The oxidized film remover is an aqueous solution including at least one selected from NH4Cl, NH4NO3, and (NH4)2SO4.

11. The method of making a copper sinter paste composition according to claim 9, characterized in that, The polymerization initiator is a disulfide.

12. The method of making a copper sinter paste composition according to claim 9, wherein, The mixed solution includes a high-boiling solvent, a reducing agent, an antifoaming agent, and a viscosity modifier.

Images