Antioxidant copper-based chip bonding material for metal connection in semiconductor device

Abstract

The invention provides a copper chip bonding material for packaging a third-generation semiconductor device. The bonding material is made of antioxidant copper paste, and the copper paste is specially designed to reduce oxidation and optimize the copper sintering density to the greatest extent, so that compact bonding with high shear strength can be formed. The antioxidant copper paste comprises copper metal particles and copper nanoparticles, and the copper nanoparticles have double-peak size distribution through special design. The invention provides a composition which does not need to be mixed in advance, can be directly applied to a metal substrate to simplify the sintering process, and also provides high shear and reliable bonding strength.

Description

Technical Field

[0001] This invention relates to general chip bonding compositions, and more specifically, to copper-based chip bonding compositions that are protected from oxidation during sintering. Background Technology

[0002] Traditional lead-based solders present numerous challenges when connecting third-generation semiconductors (such as silicon carbide (SiC) and gallium nitride (GaN)-based semiconductors) to electronic packages. These materials are designed for high-power and high-temperature applications, typically operating at temperatures well above 300°C, while traditional lead-based solders (such as eutectic lead-tin alloy solders) generally have a melting point around 183°C. Consequently, lead-based solders may soften or melt at high temperatures, leading to mechanical instability, poor contact, and even device failure.

[0003] Furthermore, silicon carbide and gallium nitride have high thermal conductivity and high coefficients of thermal expansion. The coefficient of thermal expansion of lead-containing solder is mismatched with these materials, leading to thermal stress. Over time, repeated thermal cycling (heating and cooling) can cause solder joint cracking or performance degradation, thus reducing device stability.

[0004] Furthermore, lead-containing solder also presents problems from an environmental and regulatory perspective. Due to the toxicity of lead, regulations such as the EU's Restriction of Hazardous Substances Directive (RoHS) restrict the use of lead, thereby promoting the adoption of lead-free alternatives in the electronics industry.

[0005] To address these issues, several alternative adhesives and technologies have been employed in third-generation semiconductor circuit connections. Here are a few relevant examples:

[0006] Silver-based solder paste: Silver-based substrates can be used as an alternative to traditional solders. Silver-based solder pastes, especially those using micron or nano-sized particles, can sinter at relatively low temperatures. For example, nano-silver solder paste has a sintering temperature of approximately 150-250°C, but forms stable high-temperature bonds. This sintered bond has a higher melting point (approximately 960°C, the melting point of silver). Silver also has excellent thermal conductivity and high electrical conductivity, making it suitable for high-temperature and high-power applications. Furthermore, silver has good mechanical properties, minimizing problems associated with mismatched coefficients of thermal expansion. However, silver paste is expensive, thus limiting its applications.

[0007] Gold-tin (AuSn) solder: Gold-tin alloys are commonly used in high-temperature semiconductor applications. With a melting point of approximately 280°C, gold-tin solder is particularly suitable for connecting silicon carbide and gallium nitride devices operating at higher temperatures. Gold-tin also possesses good electrical conductivity and thermal stability. However, gold-tin alloys are also very expensive.

[0008] Transient liquid phase bonding (TLP): TLP uses a low-melting-point alloy to form a high-melting-point intermetallic compound at the bonding interface during heating. Once the intermetallic compound is formed, this technology produces a stable bond that can withstand higher temperatures. TLP is suitable for high-temperature and power electronics applications. However, although the bonding temperature of TLP is relatively lower than that of conventional diffusion bonding, it still requires a relatively high bonding temperature (typically 60-80% of the substrate melting point). Furthermore, considering the diffusion of melting point inhibitors from the liquid interlayer into the substrate, the bonding process may need to be maintained at high temperatures for extended periods. Combined with the requirements of vacuum furnaces or controlled atmosphere chambers, the energy consumption and cost of this process remain quite high.

[0009] Conductive epoxy resins: Although their conductivity is not as high as that of metal solders, conductive epoxy resins are sometimes used in less demanding applications. They can withstand higher operating temperatures and provide flexible bonding, thereby reducing stress on semiconductors. However, their thermal and electrical conductivity are generally lower compared to metal bonding.

[0010] Although these alternatives demonstrate sufficient reliability in the interconnection of third-generation semiconductor devices operating at high temperatures, they are typically expensive (silver and gold) or lack sufficient thermal and electrical conductivity (epoxy resin).

[0011] Due to the excellent conductivity and cost-effectiveness of copper-based particle solder paste, it has become increasingly popular for bonding silicon carbide and gallium nitride components, thereby connecting microelectronic devices. However, copper (especially at the nanoscale) is prone to rapid oxidation in air. To address these challenges and optimize the performance of copper paste, various additives and strategies have been employed.

[0012] Of particular note is the addition of various metal complexes to enhance the oxidation resistance of copper particles. For example, adding a small amount of silver complex can improve the oxidation resistance of copper. Silver forms an alloy with copper, thereby stabilizing the copper surface and reducing oxidation. Similarly, adding a very small amount of palladium complex can also enhance the oxidation resistance of copper by forming a stable metal complex.

[0013] Using additional metal complexes can prevent oxidation, but it significantly increases the cost of copper-based pastes. Therefore, there is a need in the art for improved copper-based pastes that exhibit lower oxidation levels in sintering environments. Such copper pastes can be used to connect high-temperature semiconductors (e.g., silicon carbide and gallium nitride devices) to microelectronic packages and circuits. This invention addresses this need. Summary of the Invention

[0014] To address the aforementioned needs of the prior art, one aspect of the present invention provides an antioxidant copper chip bonding material for third-generation semiconductor device packaging. This chip bonding material is made from an antioxidant copper paste and formed under conditions that minimize oxidation and achieve high density. Therefore, dense bonds with high shear strength can be formed. The antioxidant copper paste comprises copper metal particles and uncoated copper nanoparticles. The solvent is configured to create a reducing environment, thereby enabling an oxidation-free sintering process.

[0015] The copper paste comprises 10-60% by weight copper metal particles and 30-80% by weight copper nanoparticles. In addition, the copper paste contains 10-20% by weight solvent and 0.1-5% by weight additives to impart specific rheological properties, enabling its use in existing automated packaging equipment.

[0016] In one embodiment, the copper metal particles include flake-shaped copper particles, spherical copper particles, plate-shaped copper particles, or combinations thereof. The copper nanoparticles are divided into two groups: the first group contains copper nanoparticles with a particle size in the range of 10-80 nanometers and a grain size in the range of 15-40 nanometers; the second group contains copper nanoparticles with a particle size in the range of 100-200 nanometers and a grain size in the range of 90-130 nanometers. The solvent contains amino and hydroxyl functional groups, acting as an anti-agglomeration agent and reducing agent to prevent oxidation of the copper nanoparticles.

[0017] In one embodiment of the present invention, the copper metal particles have a particle size ranging from 0.3 to 10 micrometers.

[0018] In another embodiment, the copper metal particles are thin sheets of copper metal with an aspect ratio of 2 or greater.

[0019] In yet another embodiment, the copper metal particles have a particle size ranging from 1 to 3 micrometers.

[0020] In another embodiment, the solvent for the copper paste is selected from ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, 1,3-butanediol, dipropylene glycol methyl ether acetate, dipropylene glycol monobutyl ether, dipropylene glycol, diethylene glycol monobutyl ether acetate, triacetin, terpineol, triethanolamine, monoethanolamine, monoisopropanolamine, 2-amino-2-methyl-1-propanol, diethylene glycolamine, diethanolamine, N-methylethanolamine, diisopropanolamine, 2-(tert-butylamino)ethanol, methyldiethanolamine, N-butyldiethanolamine, dimethylethanolamine, triisopropanolamine, diethylethanolamine, or combinations thereof.

[0021] In another embodiment, the additive is selected from polyether-modified dimethyl polysiloxane copolymer, polyamide-based rheology modifier or modified urea-based rheology modifier, hexanoic acid, citric acid, malonic acid, ascorbic acid, 3-glycidoxypropyltrimethoxysilane or combinations thereof.

[0022] According to another aspect of the present invention, a two-step sintering method using the above-described antioxidant microelectronic bonding paste is provided. The method includes: coating the copper paste onto a substrate; placing microelectronic components at least partially on the copper paste coated onto the substrate; and heating to a temperature range of 250°C to 280°C under a nitrogen atmosphere to sinter copper metal particles and copper salt nanoparticles, thereby bonding the microelectronic components to the substrate.

[0023] In one embodiment, the substrate is selected from copper plating, silver plating, gold plating, platinum plating, or nickel plating.

[0024] In other embodiments, the microelectronic component or chip may be selected to have a copper plating, a silver plating, or a gold plating.

[0025] In another embodiment, the thickness of the bonding layer between the copper metal particles and the copper nanoparticles is 30-50 micrometers.

[0026] In another embodiment, the porosity of the slurry after sintering is not higher than 10%.

[0027] In another embodiment, sintering can be carried out under the following two conditions: (i) a pressure of 1 atm and a sintering time of about 60-90 minutes; or (ii) sintering under a pressure of 10-25 MPa and a sintering time of about 10 minutes.

[0028] In another embodiment, after sintering according to condition (i) above, the average shear strength of the bond is not less than 30 MPa; and after sintering according to condition (ii) above, the average shear strength of the bond is not less than 50 MPa. Attached Figure Description

[0029] Embodiments of the invention are described in more detail below with reference to the accompanying drawings, in which:

[0030] Figures 1A to 1C Scanning electron microscope (SEM) images of copper nanoparticles synthesized using the exemplary method described below are shown. Figure 1A SEM images of copper nanoparticles synthesized using synthetic route 1 are shown. Figure 1B SEM images of copper nanoparticles synthesized using synthetic route 2 are shown. Figure 1C SEM images of copper nanoparticles synthesized using synthetic route 3 are shown. The synthetic route described above will be described in detail below.

[0031] Figure 2A and 2B The image shows an SEM image of an exemplary copper microelectronic bonding paste of the present invention, highlighting its low porosity after sintering. Figure 2A The image shows an SEM image of the copper microelectronic bonding paste after pressure-assisted sintering. Figure 2BSEM images of the copper microelectronic interconnect paste after pressureless sintering are shown.

[0032] Figure 3 The X-ray diffraction (XRD) spectra of copper nanoparticles in an exemplary microelectronic interconnect paste embodiment are shown.

[0033] Figure 4 The XRD spectrum of copper metal particles is shown. Detailed Implementation

[0034] According to embodiments of the present invention, the antioxidant copper chip bonding material is made of antioxidant copper paste, which comprises four components: (i) 10-60 wt% copper metal particles; (ii) 30-80 wt% copper nanoparticles; (iii) 10-20 wt% solvent; and (iv) 0.1-5 wt% additives. Each component will be discussed in detail below. After describing the components, the sintering conditions for connecting third-generation semiconductors to microelectronic packages and circuits will be described. Examples illustrate specific components and tests on the resulting sintered bonds.

[0035] I. Copper metal particles

[0036] Copper metal particles account for 70-85% of the weight of the copper paste in this invention. In order to form a dense bonding layer with high shear strength and good electrical and thermal conductivity, the size and shape of the particles must be carefully selected to ensure the highest particle packing density.

[0037] As used in this article, "bulk density" refers to the efficiency with which copper particles fill the available space in the slurry. Higher bulk density results in a larger contact area between particles and a denser bond layer after sintering. Different particle shapes exhibit differences in packing and sintering efficiency. For example, spherical particles typically have a lower bulk density than other shapes because they naturally form a looser packing structure (e.g., face-centered cubic or hexagonal close packing). Spheres cannot effectively fill all the voids between them. The ideal bulk density for spheres is approximately 64%, meaning that 36% of the volume is void. This leaves more space to be filled during sintering. However, despite the lower bulk density of spherical particles, they have a higher surface area to volume ratio at the contact points, which is beneficial for sintering at those points. However, due to the greater voids between particles, significant diffusion is required during sintering to eliminate these voids, typically necessitating higher sintering temperatures to achieve complete densification.

[0038] Compared to spherical particles, plate-like or sheet-like particles typically have a higher packing density because their flat surfaces can be stacked or overlapped, reducing interparticle voids. Furthermore, the larger contact surface area between plate-like particles enhances their physical interactions, promoting better bonding during sintering. Therefore, higher bonding density can be achieved, resulting in higher electrical and thermal conductivity. Due to the larger contact area, the amount of diffusion required during sintering can be reduced, thus requiring lower sintering temperatures. However, if all selected particles are plate-like, the resulting bond may be highly anisotropic, meaning the bonding strength or conductivity along the semiconductor and substrate directions is significantly enhanced.

[0039] Because microparticles (e.g., particles with a diameter of less than 10 micrometers) and nanoparticles have extremely high surface area-to-volume ratios, their diffusion rate accelerates rapidly during sintering. Furthermore, nanoparticles can fill the voids between larger particles, thereby increasing the bonding density of the sintered bonding layer.

[0040] Based on the above characteristics, this invention determines that a mixture of flake-like and spherical particles can improve the bonding density of copper paste and reduce its agglomeration, thereby ensuring good copper paste rheology and processing performance. This invention also determines that a mixed particle size distribution with multiple particle shapes and sizes can achieve the highest bonding strength and bonding density. For example, flake-like particles can provide a higher packing density, while smaller spherical particles can fill the remaining voids. Smaller particles (e.g., nanoparticles) can fill the voids between larger particles (e.g., spherical or flake-like particles).

[0041] In one embodiment, the copper metal particles are flake-shaped copper particles with a particle size ranging from 1 to 10 micrometers and an aspect ratio of 2 or greater; or spherical submicron or nano-sized copper particles with a particle size ranging from 0.3 to 1.5 micrometers and a grain size ranging from 15 to 40 nanometers. The copper metal particles can be flake-shaped, spherical, or a combination of both. Depending on the desired application, the copper metal particle mixture may also contain other shapes or only some other shapes of particles.

[0042] The sub-40 nm grain size of the copper material in this invention is crucial for low-temperature sintering. This nanostructure forms high-density grain boundaries, significantly enhancing the thermodynamic driving force for densification while providing rapid atomic diffusion pathways. Therefore, compared to conventional copper, this material can achieve complete densification and form a robust intergranular neck structure at significantly lower temperatures and in a shorter time.

[0043] The aforementioned mixture of specially formulated copper metal particles can form a more uniform structure, reduce voids, increase packing density, and ultimately lower the sintering temperature because fewer voids need to be filled during the sintering process.

[0044] II. Copper Nanoparticles

[0045] Copper nanoparticles are used to fill voids and increase packing density, thereby lowering the sintering temperature and reducing the porosity of the final copper bonds.

[0046] Specifically, according to various embodiments of the present invention, the copper nanoparticles are designed to be composed of two groups, each with a different particle size. The first group of copper nanoparticles has a particle size range of 10-80 nm and a grain size range of 15-40 nm; the second group of copper nanoparticles has a particle size range of 100-200 nm and a grain size range of 90-130 nm. This mixture with a bimodal size distribution optimizes the packing density and improves conductivity.

[0047] After copper paste is deposited onto a metal substrate, a first group of smaller copper nanoparticles fills the voids between a second group of larger copper nanoparticles, thereby forming a dense particle network. Specifically, compared to existing sintering pastes, which typically employ copper nanoparticles with continuously distributed sizes, making it difficult to form a "void-filling" stacked structure, the bimodal stacking structure used in this invention can minimize void volume and ensure sufficient contact between particles within the paste layer before sintering.

[0048] During heat treatment, smaller nanoparticles typically have lower sintering initiation temperatures, allowing them to form necking at relatively low temperatures, which in turn connects adjacent larger nanoparticles, promoting local densification.

[0049] As the sintering temperature increases, the diffusion path extends from smaller nanoparticles to larger nanoparticles, ultimately forming a progressive metallurgical bond. The bimodal size distribution thus facilitates the staged sintering process, combining the rapid diffusion kinetics of smaller nanoparticles with the electrical continuity and mechanical strength of larger nanoparticles. This results in a sintered copper layer with high bulk density, low residual porosity, and enhanced conductivity to the underlying substrate. Furthermore, as indicated by increased shear strength and reduced bonding layer thickness, adhesion to the underlying substrate is also enhanced.

[0050] III. Solvents

[0051] The choice of solvent affects the viscosity, printability, drying properties, and sintering behavior of copper paste particles. In copper paste, the solvent plays a role in dissolving or dispersing copper precursor complexes, binders, and additives to ensure a smooth and uniform distribution during coating. Furthermore, the solvent evaporates at different stages of the sintering process, thus influencing drying rate, particle alignment, and the overall quality of the final bond. In the early stages of sintering, the solvent remains in the copper paste, helping the copper particles to distribute uniformly before complete evaporation. This facilitates the formation of dense, defect-free copper bonds at lower sintering temperatures. Typically, the choice of solvent for a specific application depends on the specific coating technology used for microelectronic interconnects.

[0052] In one embodiment of the present invention, the specific solvent includes ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, 1,3-butanediol, dipropylene glycol methyl ether acetate, dipropylene glycol monobutyl ether, dipropylene glycol, diethylene glycol monobutyl ether acetate, triacetin, terpineol, triethanolamine, monoethanolamine, monoisopropanolamine, 2-amino-2-methyl-1-propanol, diethylene glycolamine, diethanolamine, N-methylethanolamine, diisopropanolamine, 2-(tert-butylamino)ethanol, methyldiethanolamine, N-butyldiethanolamine, dimethylethanolamine, triisopropanolamine, diethylethanolamine, or combinations thereof.

[0053] Terpineol is a cyclic monoterpene alcohol, usually used in the form of α-terpineol. It is a viscous, oily liquid with a high boiling point (approximately 219°C). Terpineol can control the viscosity of formulations because its higher viscosity makes the copper paste more stable and reduces the risk of copper particle precipitation during storage or processing. Due to its rheological properties and slow evaporation rate caused by its high boiling point, terpineol can be used in screen printing.

[0054] Triethanolamine (TEA) is a tertiary amine and triol, thus acting as both a solvent and a complexing agent. With a boiling point of approximately 335°C, it is a high-boiling-point solvent. TEA can act as a chelating agent for copper ions, stabilizing copper precursor complexes such as copper formate or copper acetate, and preventing premature reduction or aggregation of copper particles. This stabilizing effect extends the shelf life of the copper paste. TEA also acts as a weak base, providing a reducing environment during sintering. It mitigates oxidation by stabilizing copper ions, preventing the formation of copper oxide during precursor decomposition. TEA can also improve the wettability of the paste on the substrate, ensuring good adhesion and uniform distribution of copper particles before sintering.

[0055] Tetraethylene glycol (TEG) is a linear ether containing four ethylene glycol units with a high boiling point (approximately 330°C) and moderate viscosity. Therefore, it helps the particles to align and distribute better before the solvent evaporates. TEG also acts as a plasticizer, softening the binder matrix during drying and sintering, thereby reducing the risk of slurry cracking or shrinkage.

[0056] Diethylene glycol (DEG) is a short-chain polyether glycol with a boiling point of approximately 245°C. Similar to TEG mentioned above, DEG can act as a co-solvent to help disperse copper nanoparticles, while maintaining its reducing properties through its hydroxyl groups, thereby providing antioxidant properties to the copper nanoparticles.

[0057] Triethylene glycol (TriEG) is a linear ether containing three ethylene glycol units. Its boiling point is between that of triethylene glycol (TEG) and diethylene glycol (DEG) (approximately 285°C). It is characterized by its strong solubility for metal ions and nanoparticles. It exhibits high thermal stability and, in addition to its reducing properties through its hydroxyl groups, can also act as a stabilizer for slurries and improve the uniformity of films after drying.

[0058] 1,3-Butanediol (1,3-BG) is a diol containing primary and secondary hydroxyl groups. Although its boiling point (approximately 205°C) is lower than that of other substances with weak reducing properties, it can improve the dispersibility of copper nanoparticles, thereby enhancing the wettability and adhesion of the slurry on various metal substrates.

[0059] Diethylene glycol monobutyl ether acetate (DGBEA) is an esterified glycol ether with a high boiling point (approximately 230°C) and moderate volatility. DGBEA improves the wettability and spreadability of copper paste on various substrates, enhances adhesion, and achieves uniform deposition.

[0060] Dipropylene glycol monobutyl ether (DPnB) is a moderately volatile ethylene glycol ether with a boiling point of approximately 230°C. DPnB can be used in copper pastes to adjust the viscosity and rheological properties of the formulation. Its moderate volatility ensures that it remains in the copper paste for a sufficient time, thereby promoting smooth deposition and flow during printing or dispensing processes. DPnB can also dissolve various additives used in copper pastes, such as dispersants, stabilizers, and binders, ensuring that all components are uniformly distributed in the copper paste.

[0061] Dipropylene glycol methyl ether acetate (DPGMEA) is a mixed ether-ester isomer solvent. DPGMEA has a boiling point of approximately 190°C, moderate polarity, good solubility in organic substances and resins, and excellent dispersibility, which is beneficial for forming uniform films. Therefore, DPGMEA is a good reagent for fine-tuning drying properties and film smoothness.

[0062] Dipropylene glycol (DPG) is a branched diol with a boiling point of approximately 230°C. Its hydroxyl functional groups help maintain a reducing environment and stabilize copper nanoparticles through hydrogen bonding. Its branched structure particularly improves dispersion uniformity and reduces aggregation.

[0063] Triacetin, also known as glyceryl triacetate, is a triester of glycerol and acetic acid with a boiling point of approximately 260°C. Although it does not contain free hydroxyl groups, its viscosity and plasticizing properties help control solvent evaporation and impart mechanical flexibility to the deposited layer, thereby improving the integrity of the sintered film.

[0064] In addition to the solvents mentioned above, other feasible solvents suitable for copper-based microelectronic sintering slurries include, but are not limited to: monoethanolamine, monoisopropanolamine, 2-amino-2-methyl-1-propanol, diethylene glycolamine, diethanolamine, N-methylethanolamine, diisopropanolamine, 2-(tert-butylamino)ethanol, methyldiethanolamine, N-butyldiethanolamine, dimethylethanolamine, triisopropanolamine, and diethylethanolamine.

[0065] These solvents are all primary, secondary, and tertiary amines containing hydroxyl groups. The presence of groups such as -NH2, -N-, -OH-, and / or -O- can effectively protect copper nanoparticles from oxidation, while also ensuring good rheological properties and overall thermal and chemical stability.

[0066] IV. Additives

[0067] Copper paste additives include additional reducing agents, optional rheology control agents, and optional sintering aids.

[0068] Reducing agents include acids such as ascorbic acid and citric acid, as well as other organic acids. These additives help prevent oxidation, maintain the metallic state of copper metal particles and copper nanoparticles, or remove existing surface oxides.

[0069] Rheology control agents include products under various trade names: WA7333, and Or a combination thereof. It is a polyether-modified dimethyl polysiloxane copolymer that can be used as a silicone-based surface additive in solvent-based, water-based, and UV-curable systems. ( (Produced by the company) is a polyether-modified polydimethylsiloxane that can be used as a surface additive to significantly reduce surface tension and aid in substrate wetting. ( (Produced by the company) is a modified urea-based liquid rheology additive that can produce highly thixotropic flow behavior in medium-polarity solvent-based and solvent-free systems. It is a polyamide-based rheology modifier.

[0070] Sintering aids include fluxes, which help remove oxides formed on the copper surface during sintering, thereby increasing bond density.

[0071] In addition to precisely controlling the composition of the copper paste, another aspect of this invention provides a two-step sintering method for antioxidant microelectronic interconnect materials. Specifically, this invention only requires coating the material onto a metal substrate and heating it in a nitrogen atmosphere at a temperature range of 260°C to 280°C to sinter copper metal particles and copper nanoparticles, thereby bonding microelectronic components to the substrate. This two-step method is applicable to bonding microelectronic components to various metal substrates, including copper-plated, silver-plated, gold-plated, platinum-plated, or nickel-plated substrates.

[0072] Nitrogen is an economical and efficient inert gas that reduces the risk of oxidation and has a relatively small environmental impact because it can be directly released into the atmosphere. Optionally, a small amount of hydrogen (approximately 5% to 10% H2) can be added. The mixture of nitrogen and hydrogen is sometimes referred to as a "forming gas" and is commercially available.

[0073] To ensure good bond density, this invention employs pressure sintering. By applying external pressure during heating, the contact and bonding between particles can be enhanced. Pressure helps promote densification, allowing copper particles to contact more closely, thereby reducing porosity and improving the diffusion process. Compared to pressureless sintering, pressure sintering can be performed at lower temperatures, which is particularly advantageous for temperature-sensitive components. Furthermore, due to the increased degree of densification, bonds formed by pressure sintering tend to have better mechanical strength.

[0074] Therefore, the above sintering method can be carried out in the following two ways: (i) sintering at a pressure of 1 atm for about 90 minutes; or (ii) sintering at a pressure of 10-25 MPa for about 10 minutes. The bonding temperature required in both cases is the same as above, i.e., 260℃ to 280℃.

[0075] By employing a carefully designed antioxidant microelectronic bonding paste and a simple two-step sintering method, the shear strength of the bond formed under pressureless sintering is at least 30 MPa, while the shear strength of the bond formed under pressure sintering is at least 50 MPa, highlighting the mechanical strength of the sintered joint.

[0076] In addition, the thickness of the bonding layer between copper metal particles and copper nanoparticles is kept to a minimum of less than 30 micrometers, which is particularly important for minimizing the bonding layer thickness to ensure optimal thermal and electrical conductivity.

[0077] Example

[0078] Example 1: Synthesis of Copper Nanoparticles

[0079] Nanoparticle synthesis pathway 1 :

[0080] Prepare a 2-liter round-bottom flask equipped with a magnetic stirrer. Add 94.2 g of copper acetate monohydrate as a copper source to the flask. Then, add 60 g of water and 425 g of isopropanol as organic solvents to obtain the reaction solution.

[0081] The temperature of the reaction solution was raised to 62°C under mechanical stirring at 1000 rpm. While continuing stirring, 11.82 g of a 55% hydrazine monohydrate solution was added to the reaction solution at a rate of 1.6 mL / min using a syringe pump. Stirring was continued for 30 minutes. Then, 106.4 g of a 55% hydrazine monohydrate solution was added to the reaction solution at a rate of 3.2 mL / min using a syringe pump. Stirring was continued for 15 minutes. Subsequently, 47.3 g of a 55% hydrazine hydrate solution was added to the reaction solution at a rate of 3.2 mL / min using a syringe pump. The reaction solution was then maintained at 60°C and stirred for 1.5 hours.

[0082] Figure 1A The SEM image of the obtained copper nanoparticles is shown.

[0083] Nanoparticle synthesis pathway 2 :

[0084] Prepare a 2-liter round-bottom flask equipped with a magnetic stirrer. Add 47.1 g of copper acetate monohydrate as a copper source to the flask. Then, add 30 g of water and 220 g of isopropanol as organic solvents to obtain the reaction solution.

[0085] The temperature of the reaction solution was raised to 60°C under mechanical stirring at 380 rpm. While continuing stirring, 47.2 g of a 55% hydrazine monohydrate solution was added to the reaction solution at a rate of 3.2 mL / min using a syringe pump. Stirring was continued for 15 minutes. Subsequently, 6.0 g of a 55% hydrazine hydrate solution was added to the reaction solution at a rate of 3.2 mL / min using a syringe pump. The reaction solution was then maintained at 60°C and stirred for 1.5 hours.

[0086] After the reaction was complete, the reaction solution was cooled in an ice-water bath for 1 hour, and then centrifuged (8000 rpm, 20 minutes). The resulting solid was washed three times with ethanol to obtain approximately 14 g (87% yield) of copper nanoparticles.

[0087] SEM images of the obtained copper nanoparticles are shown in [link to image]. Figure 1B .

[0088] Nanoparticle synthesis pathway 3 :

[0089] Prepare a 250 mL round-bottom flask equipped with a magnetic stirrer. Add 47.1 g of copper acetate monohydrate as a copper source to the flask. Then, under magnetic stirring (380 rpm), raise the liquid temperature of the reaction solution to 90 °C. Continue stirring, and add 5.91 g of 55% hydrazine monohydrate solution to the reaction solution using a dropping funnel. Continue stirring for 30 minutes. Afterward, add 47.2 g of 55% hydrazine monohydrate solution to the reaction solution using a syringe pump at a rate of 3.2 mL per minute. Continue stirring for 15 minutes. Subsequently, add 6.0 g of 55% hydrazine monohydrate solution to the reaction solution using a syringe pump at a rate of 3.2 mL per minute. Then, maintain the reaction solution at 90 °C and stir for 1.5 hours. Add 30 g of water and 220 g of isopropanol as an organic solvent to the flask to obtain the reaction solution.

[0090] After the reaction was complete, the reaction solution was cooled in an ice-water bath for 1 hour, and then centrifuged (8000 rpm, 20 minutes). The resulting solid was washed three times with ethanol to obtain approximately 14 g (87% yield) of copper nanoparticles.

[0091] Figure 1C SEM images of the synthesized copper nanoparticles are shown.

[0092] Example 2: Synthesis of Microelectronic Connecting Paste

[0093] Synthesis and sintering process 1:

[0094] Copper nanoparticles (synthesized according to the method described in Example 1 above) have the following XRD pattern: Figure 3 Copper paste is obtained by mixing flaky copper metal particles with a particle size of 1-6 micrometers, triethanolamine and ethylene glycol in proportions of 10-60% by weight, 20-60% by weight, 3-10% by weight and 10-25% by weight, as shown.

[0095] Before sintering, the copper-clad active metal brazing (AMB) substrate is first cleaned in a 2% citric acid solution for 5-10 seconds, then cleaned with deionized water and ethanol, and dried at low temperature. Next, copper paste is screen-printed onto the copper AMB substrate. The copper AMB substrate is placed in an oven at 120°C and pre-cured at atmospheric pressure for 10 minutes. Then, a 3mm × 3mm silver-plated silicon carbide chip is placed on the copper paste and chip bonding is performed at room temperature under a pressure of 5-8 kg for 10 seconds. Finally, the copper paste is sintered at 260°C and 20 MPa under nitrogen atmosphere for 10 minutes.

[0096] Table 1 below lists samples with different weight ratios of copper nanoparticles to copper metal particles and their respective mechanical properties.

[0097] Table 1: (Note: ">" indicates chip damage.)

[0098] Synthesis and sintering process 2:

[0099] Copper nanoparticles (synthesized according to the method described in Example 1 above), spherical copper metal particles with a particle size of 0.5-3 micrometers, triethanolamine, ethylene glycol and malonic acid are mixed in proportions of 30-60 weight percentage, 20-50 weight percentage, 3-10 weight percentage, 5-10 weight percentage and 1-2 weight percentage to obtain copper paste.

[0100] Before sintering, the copper-clad active metal brazing (AMB) substrate is first cleaned in a 2% citric acid solution for 5-10 seconds, then cleaned with deionized water and ethanol, and dried at low temperature. Next, copper paste is screen-printed onto the copper AMB substrate. The copper AMB substrate is placed in an oven at 120°C and pre-cured at atmospheric pressure for 10 minutes. Then, a 3mm × 3mm silver-plated silicon carbide chip is placed on the copper paste and chip bonding is performed at room temperature under a pressure of 5-8 kg for 10 seconds. Finally, the copper paste is sintered at 260°C and 20 MPa under nitrogen atmosphere for 10 minutes.

[0101] Table 2 below lists samples with different weight ratios of copper nanoparticles to copper metal particles and their respective mechanical properties.

[0102] Table 2:

[0103] Comparative example:

[0104] This comparative example uses the same copper metal particles as in Example 2 above and is compared with Example 2.

[0105] The method for synthesizing copper paste is as follows: Spherical copper metal particles with a particle size of 0.5-3 micrometers, triethanolamine, ethylene glycol and malonic acid are mixed in proportions of 80-90% by weight, 3-10% by weight, 5-10% by weight and 1-2% by weight, respectively, to obtain copper paste.

[0106] Before sintering, the copper-clad active metal brazing (AMB) substrate is first cleaned in a 2% citric acid solution for 5-10 seconds, then cleaned with deionized water and ethanol, and dried at low temperature. Next, copper paste is screen-printed onto the copper AMB substrate. The copper AMB substrate is placed in an oven at 120°C and pre-cured at atmospheric pressure for 10 minutes. Then, a 3mm × 3mm silver-plated silicon carbide chip is placed on the copper paste and chip bonding is performed at room temperature under a pressure of 5-8 kg for 10 seconds. Finally, the copper paste is sintered at 260°C and 20 MPa under nitrogen atmosphere for 10 minutes.

[0107] Table 3 below lists the mechanical properties of the copper paste samples for comparison.

[0108] Table 3:

[0109] Example 3: Coatings on different microelectronic surfaces

[0110] Copper nanoparticles (synthesized according to the method described in Example 1 above), sheet-like copper metal particles with a particle size of 0.8-5 micrometers, triethanolamine, ethylene glycol and PEG-200 are mixed in proportions of 20-40 weight percentage, 10-40 weight percentage, 3-10 weight percentage, 5-10 weight percentage and 3-5 weight percentage to obtain copper paste.

[0111] Before sintering, the copper-clad active metal brazing (AMB) substrate is first cleaned in a 2% citric acid solution for 5-10 seconds, then cleaned with deionized water and ethanol, and dried at low temperature. Next, copper paste is screen-printed onto the copper AMB substrate. The copper AMB substrate is placed in an oven at 120°C and pre-cured at atmospheric pressure for 10 minutes. Then, 3mm × 3mm silver-plated silicon carbide chips, 3mm × 3mm gold-plated silicon carbide chips, and 3mm × 3mm copper sheets are placed on the copper paste and chip bonding is performed at room temperature under a pressure of 5-8 kg for 10 seconds. Finally, the copper paste is sintered at 260°C and 20 MPa under nitrogen atmosphere for 10 minutes.

[0112] Table 4 below lists the corresponding mechanical properties of two different microelectronic surface coatings after sintering.

[0113] Table 4: (Note: ">" indicates chip damage.)

[0114] Example 4: Different sintering pressures

[0115] Copper nanoparticles (synthesized according to the method described in Example 1 above), sheet-like copper metal particles with a particle size of 0.8-5 micrometers, triethanolamine, ethylene glycol and PEG-200 are mixed in proportions of 20-40 weight percentage, 10-40 weight percentage, 3-10 weight percentage, 5-10 weight percentage and 3-5 weight percentage to obtain copper paste.

[0116] Before sintering, the copper-clad active metal brazing (AMB) substrate is first cleaned in a 2% citric acid solution for 5-10 seconds, then cleaned with deionized water and ethanol, and dried at low temperature. Next, copper paste is screen-printed onto the copper AMB substrate. The copper AMB substrate is placed in an oven at 120°C and pre-cured at atmospheric pressure for 10 minutes. Then, 3mm × 3mm silver-plated or gold-plated silicon carbide chips are placed on the copper paste and chip bonding is performed at room temperature under a pressure of 5-8 kg for 10 seconds. Finally, the copper paste is sintered at 260°C and under varying pressures for 10 minutes under nitrogen atmosphere.

[0117] Table 5 below lists the corresponding mechanical properties after sintering under different sintering pressures.

[0118] Table 5:

[0119] like Figure 2A As shown in the figure, this is a SEM image of the sample synthesized by the above method under a sintering pressure of 20 MPa. The porosity after sintering is no more than 10%.

[0120] Example 5: Pressureless sintering

[0121] Copper nanoparticles (synthesized according to the method described in Example 1 above), sheet-like copper metal particles with a particle size of 0.8-5 micrometers, triethanolamine, ethylene glycol and diethylene glycol are mixed in proportions of 60-80% by weight, 10-30% by weight, 3-10% by weight, 3-10% by weight and 3-5% by weight to obtain copper paste.

[0122] Before sintering, the copper-clad active metal brazing (AMB) substrate is first cleaned in a 2% citric acid solution for 5-10 seconds, then cleaned with deionized water and ethanol, and dried at low temperature. Next, copper paste is screen-printed onto the copper AMB substrate. The copper AMB substrate is placed in an oven at 120°C and pre-cured at atmospheric pressure for 10 minutes. Then, a 3mm × 3mm gold-plated silicon carbide chip is placed on the copper paste and chip bonding is performed at room temperature under a pressure of 5-8 kg for 10 seconds. Finally, the copper paste is sintered at 260°C for 90 minutes under nitrogen atmosphere.

[0123] Table 6 below lists the mechanical properties after sintering without applying additional pressure.

[0124] Table 6:

[0125] Figure 2B SEM images of the pressureless sintered copper paste after sintering are shown. Similar to the pressure-sintered copper paste shown in Example 4 above, the porosity of this sintered copper paste is also less than 10%.

[0126] Example 6: Pressureless Sintering (II)

[0127] Copper nanoparticles (synthesized according to the method described in Example 1 above), sheet-like copper metal particles with a particle size of 0.8-5 micrometers, triethanolamine, ethylene glycol, diethylene glycol, and 3×glycidyl ether propyltrimethoxysilane are mixed in proportions of 70-80% by weight, 10-20% by weight, 3-10% by weight, 3-10% by weight, 3-5% by weight, and 0.5-2% by weight to obtain copper paste.

[0128] Before sintering, the copper-clad active metal brazing (AMB) substrate is first cleaned in a 2% citric acid solution for 5-10 seconds, then cleaned with deionized water and ethanol, and dried at low temperature. Next, copper paste is screen-printed onto the copper AMB substrate. The copper AMB substrate is placed in an oven at 120°C and pre-cured at atmospheric pressure for 10 minutes. Then, a 3mm × 3mm gold-plated silicon carbide chip is placed on the copper paste and chip bonding is performed at room temperature under a pressure of 5-8 kg for 10 seconds. Finally, the copper paste is sintered at 260°C for 30 minutes under nitrogen atmosphere.

[0129] Table 7 below lists the mechanical properties after sintering without applying additional pressure.

[0130] Table 7:

[0131] Example 7: Pressureless Sintering - Coating of Different Microelectronic Surfaces

[0132] Copper nanoparticles (synthesized according to the method described in Example 1 above), sheet-like copper metal particles with a particle size of 0.8-5 micrometers, triethanolamine, ethylene glycol and diethylene glycol are mixed in proportions of 70-80% by weight, 10-20% by weight, 3-10% by weight, 3-10% by weight and 1-3% by weight to obtain copper paste.

[0133] Before sintering, the copper-clad active metal brazing (AMB) substrate is first cleaned in a 2% citric acid solution for 5-10 seconds, then cleaned with deionized water and ethanol, and dried at low temperature. Next, copper paste is screen-printed onto the copper AMB substrate. Then, a 3mm × 3mm silver-plated or gold-plated silicon carbide chip or a 5mm × 5mm copper block is placed on the copper paste, and the copper paste is sintered at 260°C for 90 minutes under nitrogen atmosphere.

[0134] Table 8 below lists the mechanical properties after sintering using different microelectronic surface coating processes without applying additional pressure.

[0135] Table 8: (Note: ">" indicates that the chip shear strength tester has exceeded its limit.)

[0136] Example 8: Pressureless sintering - different sintering times

[0137] Copper nanoparticles (synthesized according to the method described in Example 1 above), sheet-like copper metal particles with a particle size of 0.8-5 micrometers, glycerol, triethanolamine and ethylene glycol are mixed in proportions of 70-80% by weight, 10-20% by weight, 3-10% by weight, 3-5% by weight and 3-5% by weight to obtain copper paste.

[0138] Before sintering, the copper-clad active metal brazing (AMB) substrate is first cleaned in a 2% citric acid solution for 5-10 seconds, then cleaned with deionized water and ethanol, and dried at low temperature. Next, copper paste is screen-printed onto the copper AMB substrate. Then, a 3mm × 3mm gold-plated silicon carbide chip is placed on the copper paste, and the copper paste is sintered at 260°C for 60 or 90 minutes under nitrogen atmosphere.

[0139] Table 9 below lists the mechanical properties of the sintered material after different sintering times.

[0140] Table 9:

[0141] The foregoing briefly describes several embodiments and detailed features of this disclosure. The embodiments described in this disclosure can be readily used as the basis for designing or modifying other processes and structures to achieve the same or similar purposes and / or obtain the same or similar advantages as those described in the embodiments of this disclosure. Such equivalent constructions do not depart from the spirit and scope of this disclosure, and various changes, substitutions, and modifications can be made without departing from the spirit and scope of this disclosure.

[0142] As used herein, terms such as “approximately,” “substantially,” “essentially,” and “about” are used to describe and explain minute variations. When used in conjunction with an event or situation, the term can refer to a situation where the event or situation occurs precisely, or an situation where the event or situation occurs approximately. As used herein with respect to a given value or range, the term “about” generally means within ±10%, ±5%, ±1%, or ±0-5% of a given value or range. A range can be expressed herein as from one endpoint to another or between two endpoints. Unless otherwise stated, all ranges disclosed in this disclosure include endpoints. The term “substantially coplanar” can refer to two surfaces located within a few micrometers (μm) along the same plane, such as within 10 μm, 5 μm, 1 μm, or 0.5 μm along the same plane. When referring to “substantially” identical values ​​or characteristics, the term can refer to values ​​within ±10%, ±5%, ±1%, or ±0.5% of the average value.

Claims

1. An antioxidant copper-based microelectronic bonding paste, characterized in that, include: 10-60% by weight of copper metal particles; 30-80% by weight of copper nanoparticles; 10-20% by weight of solvent, and 0.1-5% by weight of additives; The copper metal particles include flake copper particles, spherical copper particles, plate-shaped copper particles, or combinations thereof. The copper nanoparticles are divided into a first group and a second group. The first group of copper nanoparticles has a particle size of 10 to 80 nanometers, and the second group of copper nanoparticles has a particle size of 100 to 200 nanometers. The solvent contains amino and hydroxyl functional groups, which are used as anti-agglomeration agents and reducing agents to prevent the oxidation of the copper nanoparticles.

2. The antioxidant copper-based microelectronic bonding paste according to claim 1, characterized in that, The copper metal particles have a particle size ranging from 0.3 micrometers to 10 micrometers.

3. The antioxidant copper-based microelectronic bonding paste according to claim 2, characterized in that, The copper metal particles are copper metal sheets with an aspect ratio of 2 or higher.

4. The antioxidant copper-based microelectronic bonding paste according to claim 2, characterized in that, The copper metal particles have a particle size range of 1 micrometer to 3 micrometers.

5. The antioxidant copper-based microelectronic bonding paste according to claim 1, characterized in that, The copper metal particles have a grain size of 90 nanometers to 130 nanometers.

6. The antioxidant copper-based microelectronic bonding paste according to claim 1, characterized in that, The first group of copper nanoparticles has a grain size of 15 nanometers to 40 nanometers, and the second group of copper nanoparticles has a grain size of 90 nanometers to 130 nanometers.

7. The antioxidant copper-based microelectronic bonding paste according to claim 1, characterized in that, The solvent is selected from ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, 1,3-butanediol, dipropylene glycol methyl ether acetate, dipropylene glycol monobutyl ether, dipropylene glycol, diethylene glycol monobutyl ether acetate, triacetin, terpineol, triethanolamine, monoethanolamine, monoisopropanolamine, 2-amino-2-methyl-1-propanol, diethylene glycolamine, diethanolamine, N-methylethanolamine, diisopropanolamine, 2-(tert-butylamino)ethanol, methyldiethanolamine, N-butyldiethanolamine, dimethylethanolamine, triisopropanolamine, diethylethanolamine, or combinations thereof.

8. The antioxidant copper-based microelectronic bonding paste according to claim 1, characterized in that, The additive is selected from polyether-modified dimethyl polysiloxane copolymer, polyamide-based rheology modifier or modified urea-based rheology modifier, hexanoic acid, citric acid, malonic acid, ascorbic acid, 3-glycidyl ether propyltrimethoxysilane or combinations thereof.

9. A two-step sintering method using the antioxidant copper-based microelectronic bonding paste according to claim 1, characterized in that, include: The slurry according to claim 1 is coated onto the substrate; At least a portion of the microelectronic components are placed on the paste coated on the substrate; as well as The substrate is heated to a temperature of 250°C to 280°C in a nitrogen atmosphere to sinter the copper metal particles with the copper nanoparticle slurry and to bond the microelectronic components to the substrate.

10. The two-step sintering method according to claim 9, characterized in that, The substrate is selected from copper plating, silver plating, gold plating, platinum plating, or nickel plating.

11. The two-step sintering method according to claim 9, characterized in that, The microelectronic components are selected from copper plating, silver plating, or gold plating.

12. The two-step sintering method according to claim 9, characterized in that, The thickness of the adhesive layer between the copper metal particles and the copper nanoparticles is 20-50 micrometers.

13. The two-step sintering method according to claim 9, characterized in that, The porosity of the slurry after sintering is no higher than 10%.

14. The two-step sintering method according to claim 9, characterized in that, The sintering is carried out under a pressure of 1 atm for a time of not less than 60 minutes.

15. The two-step sintering method according to claim 14, characterized in that, The average shear strength of the bond after sintering is not less than 30 MPa.

16. The two-step sintering method according to claim 9, characterized in that, The sintering is carried out under a pressure of 10 MPa to 25 MPa for 10 minutes.

17. The two-step sintering method according to claim 16, characterized in that, The average shear strength of the bond after sintering is not less than 50 MPa.

Images