Preparation method of copper-based conductive adhesive with resistance to wet heat oxidation and low resistance instability

Abstract

This invention relates to a method for preparing a copper-based conductive adhesive that is resistant to humid heat oxidation and exhibits low resistance instability. The invention belongs to the field of electronic packaging interconnect materials technology. The present invention addresses the problem that existing copper-based conductive adhesives are prone to copper powder oxidation, interfacial contact degradation, and conductive network damage under humid heat, high temperature, and high current pulse operating conditions, leading to increased volume resistivity change rate and high resistance instability. The method includes: 1. Preparing an epoxy resin solution; 2. Preparing surface-activated copper powder; 3. Preparing a ternary silane hydrolysate; 4. Preparing ternary silane-modified copper powder; 5. Preparing the copper-based conductive adhesive. This invention is used for preparing a copper-based conductive adhesive that is resistant to humid heat oxidation and exhibits low resistance instability.

Description

Technical Field

[0001] This invention belongs to the field of electronic packaging interconnect materials technology. Background Technology

[0002] As aerospace equipment, power electronic devices, and high-density electronic packaging technologies develop towards higher power density, higher integration, and longer service life, chip-substrate interconnects, electrode connections, and conductive adhesives not only need to possess good initial conductivity but also need to maintain stable conductive paths under complex service environments such as damp heat, high temperature, thermal shock, and high-current pulses. Copper-based conductive adhesives, as a low-temperature interconnect material, have advantages such as low processing temperature, strong process adaptability, and the ability to connect dissimilar materials, and have been widely used in electronic packaging and interconnect bonding.

[0003] Traditional silver-based conductive adhesives possess excellent conductivity and environmental adaptability, but silver fillers are costly and prone to silver ion migration under high humidity and electric fields, potentially leading to insulation failure, short circuits, or decreased device reliability. In contrast, metallic copper exhibits intrinsic conductivity close to that of silver, lower raw material costs, and better anti-electromigration potential, thus being considered an important candidate material to replace silver-based conductive fillers. Developing highly reliable copper-based conductive adhesives is crucial for reducing the cost of electronic packaging materials and improving the long-term service stability of interconnect systems. However, the practical application of copper-based conductive adhesives is still limited by copper powder surface oxidation and service resistance instability. Copper powder surfaces are easily oxidized in air, humid and hot environments to form low-conductivity oxide layers such as Cu2O and CuO, leading to increased contact resistance between copper powder particles. Simultaneously, nano-copper powder has high surface energy and is prone to agglomeration, while micron-sized copper powders are prone to contact gaps and resin isolation layers, causing localized breakage or contact degradation of the conductive network during long-term service.

[0004] The resistivity instability of copper-based conductive adhesives, i.e., the change rate of volume resistivity, is usually not caused by a single factor, but by the combined effects of copper powder oxide layer growth, changes in particle contact area, thermal aging of the resin matrix, debonding of the copper powder / resin interface, local void expansion, and Joule heat accumulation under high-current pulses. Under conditions of humid heat aging, high-temperature aging, and high-current pulse cycling, local high contact resistance areas in the conductive path will further induce local temperature rise, which in turn accelerates copper powder oxidation and interface degradation, forming a positive feedback failure process of "increased contact resistance—enhanced Joule heat—aggravated interface degradation—further increased resistance".

[0005] To address the issues of easy oxidation and insufficient interfacial stability of copper powder, existing technologies typically employ methods such as precious metal coating, organic acid treatment, inorganic oxide coating, or silane coupling agent modification to improve the oxidation resistance of copper powder. Among these, organic acid treatment can remove part of the surface oxide layer and activate the copper powder surface, but single organic acid treatment is insufficient to form a stable protective layer under long-term humid and hot conditions. Traditional monosilane coupling agents can improve the interfacial compatibility between copper powder and resin, but their interfacial anchoring and barrier effects are limited, making it difficult to simultaneously meet the requirements for oxidation resistance, moisture intrusion resistance, enhanced interfacial bonding, and electrical resistance stability.

[0006] Therefore, there is an urgent need to develop a new method for preparing copper-based conductive adhesives to construct a stable conductive network and a moisture- and heat-resistant interface layer, reduce the rate of change in volume resistivity during humid heat, high temperature and high current pulse service, thereby improving the resistance to electrical instability and long-term service reliability of copper-based conductive adhesives. Summary of the Invention

[0007] This invention aims to address the problem that existing copper-based conductive adhesives are prone to copper powder oxidation, interfacial contact degradation, and conductive network damage under humid heat, high temperature, and high current pulse service conditions, which leads to increased volume resistivity change rate and high resistance instability rate. Therefore, this invention provides a method for preparing a copper-based conductive adhesive that is resistant to humid heat oxidation and has low resistance instability.

[0008] A method for preparing a copper-based conductive adhesive resistant to damp heat oxidation and exhibiting low electrical resistance instability, comprising the following steps:

[0009] I. Preparation of epoxy resin solution:

[0010] Under stirring conditions, bisphenol A type epoxy resin and reactive diluent are premixed, and then bisphenol F type epoxy resin is added and heated and stirred until the mixture is uniform to obtain an epoxy resin solution.

[0011] The mass ratio of bisphenol A type epoxy resin to bisphenol F type epoxy resin is 1:(1~4);

[0012] II. Preparation of surface-activated copper powder:

[0013] The compounded copper powder was added to the surface activation system for treatment, and then subjected to standing, centrifugation, filtration, washing and vacuum drying in sequence to obtain surface activated copper powder.

[0014] The compounded copper powder is a mixture of flake-shaped micron copper powder and spherical nano copper powder; the mass ratio of the spherical nano copper powder to the flake-shaped micron copper powder is 1:(4~7); the average particle size of the flake-shaped micron copper powder is 5μm~10μm; the average particle size of the spherical nano copper powder is 20nm~50nm.

[0015] The surface activation system is composed of an aqueous ethanol solution and an organic acid;

[0016] III. Preparation of ternary silane hydrolysate:

[0017] The silane coupling agent complex was added to an aqueous ethanol solution and pre-hydrolyzed by stirring at room temperature to obtain a ternary silane hydrolysate.

[0018] The silane coupling agent complex is a mixture of bipedal silane coupling agents, nitrogen-containing heterocyclic silane coupling agents, and aromatic silane coupling agents;

[0019] IV. Preparation of ternary silane-modified copper powder:

[0020] Surface-activated copper powder was added to a ternary silane hydrolysate for interface modification, and then filtered, washed and vacuum dried sequentially to obtain ternary silane-modified copper powder.

[0021] V. Preparation of copper-based conductive adhesive:

[0022] An epoxy resin solution, a curing agent, and ternary silane-modified copper powder were sequentially subjected to planetary stirring, three-roll milling, and vacuum degassing to obtain a copper-based conductive adhesive that is resistant to humid heat oxidation and has a low electrical instability rate.

[0023] The beneficial effects of this invention are:

[0024] (1) This invention provides a method for preparing a copper-based conductive adhesive that is resistant to damp heat aging and has low electrical resistance instability. A ternary synergistic compound is used, consisting of a dipodysilicon, a nitrogen-containing heterocyclic coordination silane, and a phenylsilane. The dipodysilicon, through hydrolysis of its two-terminal -Si(OR)3, covalently bridges copper powder and resin in both directions, constructing a high-density three-dimensional "arch-shaped" crosslinking network, providing elastic stress relaxation and improving interfacial bonding. The electron-rich nitrogen-containing heterocyclic structure in the nitrogen-containing heterocyclic coordination silane molecule forms high-bond-energy Cu-N coordination bonds with unsaturated copper atoms on the copper surface, achieving strong coordination anchoring of the copper powder surface. The rigid planar benzene ring of the phenylsilane interpenetrates with the above-mentioned asymmetric coordination chain, optimizing the spatial configuration. Three silanes combine rigidity and flexibility, and in situ self-assemble at the copper powder-resin interface to form a nanoscale composite protective layer with a chemical bond energy gradient. This micro-network can effectively buffer local thermal stress and suppress stress concentration and fatigue cracking under extreme thermal shock, laying a stable structural foundation for the material's high mechanical retention and high thermal stability.

[0025] (2) Traditional copper-based conductive adhesives are modified with single-leg silanes such as KH-550 and KH-560. Due to single-point bonding, weak interfacial bonding force, and mismatch of adsorption site reaction rates, the grafted layer is often uneven and free polar hydrophilic groups remain, making the material prone to water molecule intrusion and hydrolysis debonding under high humidity and heat environment; at the same time, under high flux electron wind collision, copper atoms can easily overcome the low energy barrier and migrate in the direction of current, which aggravates local Joule heating, resulting in electromigration ablation and a surge in resistivity.

[0026] This invention fundamentally solves the problem of resistance instability under extreme service conditions by regulating interfacial reaction kinetics through a ternary modification system. In this system, the hydrolysis of the terminal silanes of the di-rooted silanes creates a high-density three-dimensional interpenetrating network at the copper powder-resin interface. The rigid planar benzene ring structure in the phenylsilane molecule has a large spatial spacing, which precisely fills the microscopic gaps in the cross-linked network, physically sealing the water vapor diffusion channels and preventing water molecules from penetrating under high temperature and humidity conditions, thus significantly improving the long-term stability of the interface against hydrolysis and debonding. Faced with high current impact, the lone pair electrons of the nitrogen atoms on the nitrogen heterocyclic silane form high-bond-energy Cu-N coordination bonds with the copper surface, achieving strong anchoring of the coupling agent on the copper powder surface. Combined with the "molecular fence" network constructed by the di-rooted silane, this doubly inhibits electromigration behavior, effectively solving the industry problem of significant resistance instability in copper-based conductive adhesives under extreme service conditions. This strategy provides key technical support for the preparation of high-reliability electronic packaging materials; these characteristics are not disclosed elsewhere. Attached Figure Description

[0027] Figure 1 The initial dynamic thermomechanical curve of the copper-based conductive adhesive prepared in Example 1;

[0028] Figure 2 The initial air atmosphere TGA mass change curve of the copper-based conductive adhesive prepared in Example 1;

[0029] Figure 3 The initial XPS pattern (Cu 2p spectrum) of the copper-based conductive adhesive prepared in Example 1. Detailed Implementation

[0030] The technical solution of the present invention is not limited to the specific embodiments listed below, but also includes any combination of the specific embodiments.

[0031] Specific Implementation Method 1: This implementation method provides a method for preparing a copper-based conductive adhesive that is resistant to damp heat oxidation and has low electrical resistance instability. It is carried out according to the following steps:

[0032] I. Preparation of epoxy resin solution:

[0033] Under stirring conditions, bisphenol A type epoxy resin and reactive diluent are premixed, and then bisphenol F type epoxy resin is added and heated and stirred until the mixture is uniform to obtain an epoxy resin solution.

[0034] The mass ratio of bisphenol A type epoxy resin to bisphenol F type epoxy resin is 1:(1~4);

[0035] II. Preparation of surface-activated copper powder:

[0036] The compounded copper powder was added to the surface activation system for treatment, and then subjected to standing, centrifugation, filtration, washing and vacuum drying in sequence to obtain surface activated copper powder.

[0037] The compounded copper powder is a mixture of flake-shaped micron copper powder and spherical nano copper powder; the mass ratio of the spherical nano copper powder to the flake-shaped micron copper powder is 1:(4~7); the average particle size of the flake-shaped micron copper powder is 5μm~10μm; the average particle size of the spherical nano copper powder is 20nm~50nm.

[0038] The surface activation system is composed of an aqueous ethanol solution and an organic acid;

[0039] III. Preparation of ternary silane hydrolysate:

[0040] The silane coupling agent complex was added to an aqueous ethanol solution and pre-hydrolyzed by stirring at room temperature to obtain a ternary silane hydrolysate.

[0041] The silane coupling agent complex is a mixture of bipedal silane coupling agents, nitrogen-containing heterocyclic silane coupling agents, and aromatic silane coupling agents;

[0042] IV. Preparation of ternary silane-modified copper powder:

[0043] Surface-activated copper powder was added to a ternary silane hydrolysate for interface modification, and then filtered, washed and vacuum dried sequentially to obtain ternary silane-modified copper powder.

[0044] V. Preparation of copper-based conductive adhesive:

[0045] An epoxy resin solution, a curing agent, and ternary silane-modified copper powder were sequentially subjected to planetary stirring, three-roll milling, and vacuum degassing to obtain a copper-based conductive adhesive that is resistant to humid heat oxidation and has a low electrical instability rate.

[0046] The copper-based conductive adhesive described in this embodiment uses an epoxy resin system as the matrix and a composite of flake-shaped micron-sized copper powder and spherical nano-sized copper powder as conductive fillers. A loose oxide layer on the copper powder surface is removed through surface activation with organic acid. A ternary synergistic interface modification layer is constructed using a bipedal silane coupling agent, a nitrogen-containing heterocyclic silane coupling agent, and an aromatic silane coupling agent. This ternary silane interface layer can form a multi-point anchoring, coordination-stabilized, and rigid hydrophobic barrier structure on the copper powder surface, reducing the risk of copper powder oxidation, interfacial contact degradation, and conductive network reconstruction under humid heat, high temperature, and high-current pulse conditions.

[0047] Compared with traditional single-silane modified or single-particle-size copper powder systems, this embodiment utilizes the combined effects of micro-nano copper powder composite conductive network, organic acid surface activation, and ternary silane synergistic interface modification to enable copper-based conductive adhesive to maintain a low volume resistivity change rate, low interface temperature rise, and high adhesive strength even after thermal aging, damp heat aging, and stepped high current pulse cycling. It is suitable for high-power electronic devices, aerospace electronic packaging, chip-substrate interconnection, and electrode conductive bonding.

[0048] The beneficial effects of this embodiment are:

[0049] (1) This embodiment provides a method for preparing a copper-based conductive adhesive that is resistant to damp heat aging and has low resistance instability. A ternary synergistic compound is used, consisting of a dipodysilicon, a nitrogen-containing heterocyclic coordination silane, and a phenylsilane. The dipodysilicon, through hydrolysis of its two-terminal -Si(OR)3, covalently bridges copper powder and resin in both directions, constructing a high-density three-dimensional "arch-shaped" crosslinking network, providing elastic stress relaxation and improving interfacial bonding. The electron-rich nitrogen-containing heterocyclic structure in the nitrogen-containing heterocyclic coordination silane molecule forms high-bond-energy Cu-N coordination bonds with unsaturated copper atoms on the copper surface, achieving strong coordination anchoring of the copper powder surface. The rigid planar benzene ring of the phenylsilane interpenetrates with the above-mentioned asymmetric coordination chain, optimizing the spatial configuration. Three silanes combine rigidity and flexibility, and in situ self-assemble at the copper powder-resin interface to form a nanoscale composite protective layer with a chemical bond energy gradient. This micro-network can effectively buffer local thermal stress and suppress stress concentration and fatigue cracking under extreme thermal shock, laying a stable structural foundation for the material's high mechanical retention and high thermal stability.

[0050] (2) Traditional copper-based conductive adhesives are modified with single-leg silanes such as KH-550 and KH-560. Due to single-point bonding, weak interfacial bonding force, and mismatch of adsorption site reaction rates, the grafted layer is often uneven and free polar hydrophilic groups remain, making the material prone to water molecule intrusion and hydrolysis debonding under high humidity and heat environment; at the same time, under high flux electron wind collision, copper atoms can easily overcome the low energy barrier and migrate in the direction of current, which aggravates local Joule heating, resulting in electromigration ablation and a surge in resistivity.

[0051] This embodiment fundamentally solves the problem of resistance instability under extreme service conditions by regulating the interfacial reaction kinetics through a ternary modification system. In this system, the hydrolysis of the terminal silanes of the di-rooted silanes creates a high-density three-dimensional interpenetrating network between the copper powder and resin interface. The rigid planar benzene ring structure in the phenylsilane molecule has a large spatial spacing, which precisely fills the microscopic gaps in the cross-linking network, physically sealing the water vapor diffusion channels and preventing water molecules from penetrating under high temperature and humidity conditions, thus significantly improving the long-term stability of the interface against hydrolysis and debonding. Faced with high current impact, the lone pair electrons of the nitrogen atoms on the nitrogen heterocyclic silane form high-bond-energy Cu-N coordination bonds with the copper surface, achieving strong anchoring of the coupling agent on the copper powder surface. Combined with the "molecular fence" network constructed by the di-rooted silane, this doubly inhibits electromigration behavior, effectively solving the industry problem of significant resistance instability in copper-based conductive adhesives under extreme service conditions. This strategy provides key technical support for the preparation of high-reliability electronic packaging materials; these characteristics are not disclosed elsewhere.

[0052] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that: the bisphenol A type epoxy resin mentioned in step one is E-51 type epoxy resin; the bisphenol F type epoxy resin mentioned in step one is F-44 epoxy resin; the reactive diluent mentioned in step one is 1,4-butanediol diglycidyl ether; and the mass ratio of the bisphenol A type epoxy resin to the reactive diluent mentioned in step one is 1:(1~4). Everything else is the same as in Specific Implementation Method One.

[0053] Specific Implementation Method Three: This implementation method differs from Specific Implementation Method One or Two in that: in step one, under conditions of room temperature and a stirring speed of 200 r / min to 500 r / min, bisphenol A type epoxy resin and reactive diluent are premixed for 30 min to 120 min. Then, under conditions of a temperature of 60℃ to 80℃ and a stirring speed of 200 r / min to 500 r / min, bisphenol F type epoxy resin is added and heated and stirred for 30 min to 120 min until uniformly mixed to obtain an epoxy resin solution. The rest is the same as in Specific Implementation Method One or Two.

[0054] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that: the organic acid mentioned in step two is glacial acetic acid; the surface activation system mentioned in step two is specifically obtained by adjusting the pH of the ethanol aqueous solution to 4.0-5.5 using glacial acetic acid, and the mass fraction of ethanol in the ethanol aqueous solution is 90%-95%; the mass ratio of the compounded copper powder to the surface activation system mentioned in step two is 1:(0.15-0.40). Everything else is the same as in Specific Implementation Methods One to Three.

[0055] Specific Implementation Method Five: This implementation method differs from Specific Implementation Methods One to Four in that, in step two, the compounded copper powder is added to the surface activation system and treated for 30 to 120 minutes at room temperature and a stirring speed of 200 to 500 r / min. Everything else is the same as in Specific Implementation Methods One to Four.

[0056] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One to Five in that: the bipedal silane coupling agent in step three is bis[3-(triethoxysilane)propyl]amine; the nitrogen-containing heterocyclic silane coupling agent in step three is triethoxy-3-(2-imidazolin-1-yl)propylsilane; the aromatic silane coupling agent in step three is m-aminophenyltrimethoxysilane; the mass ratio of the bipedal silane coupling agent to the nitrogen-containing heterocyclic silane coupling agent in step three is 1:(0.1~0.5); the mass ratio of the bipedal silane coupling agent to the aromatic silane coupling agent in step three is 1:(0.1~0.3); the mass ratio of the silane coupling agent complex to the ethanol aqueous solution in step three is 1:(1~4); and the mass fraction of ethanol in the ethanol aqueous solution in step three is 90%~95%. Everything else is the same as in Specific Implementation Methods One to Five.

[0057] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Methods One to Six in that: in step three, pre-hydrolysis is performed for 60 to 120 minutes at room temperature and a stirring speed of 200 to 500 r / min. Everything else is the same as in Specific Implementation Methods One to Six.

[0058] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Methods One to Seven in that: the mass ratio of surface-activated copper powder to ternary silane hydrolysate in step four is 1:(0.1~0.5); in step four, under the conditions of room temperature and a stirring speed of 200r / min~500r / min, the surface-activated copper powder is added to the ternary silane hydrolysate for interface modification treatment for 60min~120min. Everything else is the same as in Specific Implementation Methods One to Seven.

[0059] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Methods One to Eight in that: the curing agent mentioned in step five is one or a combination of two of dicyandiamide and 4,4'-diaminodiphenyl sulfone; the mass ratio of the epoxy resin solution to the curing agent mentioned in step five is 1:(0.1~0.2); the mass ratio of the epoxy resin solution to the ternary silane-modified copper powder mentioned in step five is 1:(5~9). Everything else is the same as in Specific Implementation Methods One to Eight.

[0060] Specific Implementation Method Ten: This implementation method differs from Specific Implementation Methods One to Nine in the following ways: The planetary stirring described in step five is specifically performed at a rotation speed of 1500 r / min to 2000 r / min for 3 to 6 minutes; the three-roll milling described in step five is specifically performed as follows: passing the mill through the rollers three times with a roller spacing of 30 μm to 50 μm, then passing it through the rollers three times with a roller spacing of 10 μm to 30 μm, and finally passing it through the rollers three times with a roller spacing of 5 μm to 10 μm; the vacuum degassing treatment described in step five is specifically performed in a vacuum environment with a stirring speed of 1500 r / min to 2000 r / min for 3 to 6 minutes. All other aspects are the same as in Specific Implementation Methods One to Nine.

[0061] The beneficial effects of the present invention are verified using the following embodiments:

[0062] Example 1:

[0063] A method for preparing a copper-based conductive adhesive resistant to damp heat oxidation and exhibiting low electrical resistance instability, comprising the following steps:

[0064] I. Preparation of epoxy resin solution:

[0065] Bisphenol A epoxy resin and reactive diluent were premixed for 60 min at room temperature and stirring speed of 500 r / min. Then, bisphenol F epoxy resin was added at 65℃ and stirring speed of 500 r / min and heated and stirred for 90 min to mix evenly to obtain epoxy resin solution.

[0066] The bisphenol A type epoxy resin is E-51 type epoxy resin, and the bisphenol F type epoxy resin is F-44 type epoxy resin; the mass ratio of the bisphenol A type epoxy resin to the bisphenol F type epoxy resin is 1:2.

[0067] The reactive diluent is 1,4-butanediol diglycidyl ether; the mass ratio of the bisphenol A epoxy resin to the reactive diluent is 1:1.

[0068] II. Preparation of surface-activated copper powder:

[0069] At room temperature and a stirring speed of 500 r / min, the compounded copper powder was added to the surface activation system and treated for 100 min. Then, it was subjected to standing, centrifugation, filtration, ethanol washing and vacuum drying to obtain surface activated copper powder.

[0070] The compounded copper powder is a mixture of flake-shaped micron copper powder and spherical nano copper powder; the mass ratio of the spherical nano copper powder to the flake-shaped micron copper powder is 1:6; the average particle size of the flake-shaped micron copper powder is 8 μm; and the average particle size of the spherical nano copper powder is 30 nm.

[0071] The surface activation system is composed of an aqueous ethanol solution and an organic acid; the organic acid is glacial acetic acid; specifically, the surface activation system is obtained by adjusting the pH of the aqueous ethanol solution to 5.5 using glacial acetic acid, and the mass fraction of ethanol in the aqueous ethanol solution is 95%; the mass ratio of the compounded copper powder to the surface activation system is 1:0.3.

[0072] The vacuum drying process specifically involves drying in a vacuum oven at a temperature of 40°C for 180 minutes.

[0073] III. Preparation of ternary silane hydrolysate:

[0074] The silane coupling agent complex was added to an ethanol aqueous solution and pre-hydrolyzed for 60 min at room temperature and a stirring speed of 500 r / min to obtain a ternary silane hydrolysate.

[0075] The silane coupling agent complex is a mixture of bipedal silane coupling agents, nitrogen-containing heterocyclic silane coupling agents, and aromatic silane coupling agents;

[0076] The bipod silane coupling agent is bis[3-(triethoxysilane)propyl]amine; the nitrogen-containing heterocyclic silane coupling agent is triethoxy-3-(2-imidazolin-1-yl)propylsilane; the aromatic silane coupling agent is m-aminophenyltrimethoxysilane; the mass ratio of the bipod silane coupling agent to the nitrogen-containing heterocyclic silane coupling agent is 1:0.3; the mass ratio of the bipod silane coupling agent to the aromatic silane coupling agent is 1:0.2; the mass ratio of the silane coupling agent complex to the ethanol aqueous solution is 1:4; and the ethanol aqueous solution contains 95% ethanol by mass.

[0077] IV. Preparation of ternary silane-modified copper powder:

[0078] At room temperature and a stirring speed of 500 r / min, surface-activated copper powder was added to a ternary silane hydrolysate for interfacial modification treatment for 120 min. Then, the mixture was filtered, washed with ethanol, and vacuum dried to obtain ternary silane-modified copper powder.

[0079] The mass ratio of the surface-activated copper powder to the ternary silane hydrolysate is 1:0.2;

[0080] The vacuum drying process specifically involves drying in a vacuum oven at a temperature of 40°C for 180 minutes.

[0081] V. Preparation of copper-based conductive adhesive:

[0082] An epoxy resin solution, a curing agent, and ternary silane-modified copper powder were sequentially subjected to planetary stirring, three-roll milling, and vacuum degassing to obtain a copper-based conductive adhesive that is resistant to humid heat oxidation and has a low electrical instability rate.

[0083] The curing agent is a combination of dicyandiamide and 4,4'-diaminodiphenyl sulfone, and the mass ratio of dicyandiamide to 4,4'-diaminodiphenyl sulfone is 1:1; the mass ratio of epoxy resin solution to curing agent is 1:0.15; the mass ratio of epoxy resin solution to ternary silane-modified copper powder is 1:7.

[0084] The planetary mixer is specifically operated at a speed of 1800 r / min for 5 minutes.

[0085] The three-roll grinding process is carried out in the following steps: passing the rollers 3 times with a roller spacing of 30μm, then passing the rollers 3 times with a roller spacing of 20μm, and finally passing the rollers 3 times with a roller spacing of 10μm.

[0086] The vacuum degassing process is specifically carried out in a vacuum environment with a stirring speed of 2000 r / min for 5 min.

[0087] The structural formula of bis[3-(triethoxysilyl)propyl]amine described in step three of this embodiment is:

[0088] ;

[0089] The structural formula of triethoxy-3-(2-imidazolin-1-yl)propylsilane described in step three of this embodiment is:

[0090] ;

[0091] The structural formula of the m-aminophenyltrimethoxysilane mentioned in step three of this embodiment is:

[0092] .

[0093] Example 2: This example differs from Example 1 in that the mass ratio of spherical nano-copper powder to flake-shaped micron-copper powder in step two is 1:4. Everything else is the same as in Example 1.

[0094] Example 3: This example differs from Example 1 in that the mass ratio of spherical nano-copper powder to flake-shaped micron-copper powder in step two is 1:5. Everything else is the same as in Example 1.

[0095] Example 4: This example differs from Example 1 in that the mass ratio of spherical nano-copper powder to flake-shaped micron-copper powder in step two is 1:7. Everything else is the same as in Example 1.

[0096] Example 5: This example differs from Example 1 in that the mass ratio of the bipedal silane coupling agent to the nitrogen-containing heterocyclic silane coupling agent in step three is 1:0.1. Everything else is the same as in Example 1.

[0097] Example 6: This example differs from Example 1 in that the mass ratio of the bipedal silane coupling agent to the aromatic silane coupling agent in step three is 1:0.1. Everything else is the same as in Example 1.

[0098] Comparative Example 1: This comparative example differs from Example 1 in that the silane coupling agent complex in step three is replaced with KH-550. Everything else is the same as in Example 1.

[0099] Comparative Example 2: This comparative example differs from Example 1 in that the silane coupling agent complex in step three is replaced with KH-560. Everything else is the same as in Example 1.

[0100] Comparative Example 3: This comparative example differs from Example 1 in that the silane coupling agent complex described in step three is a mixture of a bipedal silane coupling agent and a nitrogen-containing heterocyclic silane coupling agent; the mass ratio of the bipedal silane coupling agent to the nitrogen-containing heterocyclic silane coupling agent is 1:0.3. Everything else is the same as in Example 1.

[0101] Comparative Example 4: This comparative example differs from Example 1 in that the silane coupling agent complex described in step three is a mixture of a bipedal silane coupling agent and an aromatic silane coupling agent; the mass ratio of the bipedal silane coupling agent to the aromatic silane coupling agent is 1:0.2. Everything else is the same as in Example 1.

[0102] Comparative Example 5: This comparative example differs from Example 1 in that the silane coupling agent complex described in step three is a mixture of a nitrogen-containing heterocyclic silane coupling agent and an aromatic silane coupling agent; the mass ratio of the nitrogen-containing heterocyclic silane coupling agent to the aromatic silane coupling agent is 0.3:0.2. Everything else is the same as in Example 1.

[0103] The copper-based conductive adhesives prepared in Examples 1 to 6 and Comparative Examples 1 to 5 were subjected to dynamic thermomechanical tests, thermogravimetric and oxidation weight gain tests, chip shear strength tests, volume resistivity tests, aluminum-aluminum bond strength tests, thermal aging stability tests, damp heat aging stability tests, and XPS surface oxidation state tests. The curing process described in the following tests was performed according to the following steps: first, curing at 150°C for 60 min, then curing at 180°C for 30 min to obtain cured samples. The specific tests are as follows:

[0104] a. Dynamic Thermomechanical Analysis (DMA) Test: Copper-based conductive adhesive is poured into a mold measuring 1.0 cm long, 0.5 cm wide, and 0.2 cm thick and cured to obtain cured copper-based conductive adhesive. The cured sample is then placed in a dynamic thermomechanical analyzer to test its storage modulus and glass transition temperature T. g The peak temperature of tanδ is used as the glass transition temperature T. g The heating rate was 5℃ / min, and the test atmosphere was air.

[0105] b. Thermogravimetric analysis and oxidation weight gain test: 5mg~10mg of cured copper-based conductive adhesive was tested using a thermogravimetric analyzer at a heating rate of 10℃ / min in air. The oxidation weight gain initiation temperature was determined by the mass change curve, which characterizes the initiation temperature at which significant oxidation of copper powder occurs in air.

[0106] c. Chip shear strength test: Copper-based conductive adhesive was coated on the surfaces of a copper substrate and a gold-plated copper substrate, with a thickness of 50 μm. Then, a 2×2 mm copper sheet was bonded to the surface of the copper substrate, and a 2×2 mm gold sheet was bonded to the surface of the gold-plated copper substrate to form a chip shear test sample. After curing, the cured chip shear test sample was obtained. A chip push-pull force tester was used to perform compression shear test at a test temperature of 25℃ and a shearing speed of 100 μm / s.

[0107] d. Volume resistivity test: Copper-based conductive adhesive was coated onto the surface of a glass slide with a length of 5.0 cm, a width of 1.0 cm, and a thickness of 0.2 mm. After curing, the cured copper-based conductive adhesive was obtained. The resistance was measured using a micro-ohmmeter according to method 5011 of GJB548B-2005. The volume resistivity was calculated according to formula (1):

[0108] (1)

[0109] Where ρ is the volume resistivity in Ω·cm, R is the test resistance in Ω, w is the sample width in cm, d is the sample thickness in cm, and L is the effective length between the two electrodes in cm.

[0110] e. Aluminum-aluminum bond strength test: Copper-based conductive adhesive is uniformly coated on the surface of an aluminum sheet with a thickness of 50 μm and an overlap length of 1.5 cm. After curing, a cured aluminum-aluminum bond sample is obtained. The tensile shear strength is tested using a universal testing machine. The test method is in accordance with GB / T 7124-2008, the test rate is 1 mm / min, and the test continues until the sample fails.

[0111] f. Damp-heat aging stability test: The cured copper-based conductive adhesive, the cured chip shear test sample, and the cured aluminum-aluminum bonding sample were placed in a constant temperature and humidity chamber and aged for 500 hours at 85℃ and 85% relative humidity. After aging, they were equilibrated for 2 hours in an environment of 25±2℃ and 45%~60% relative humidity. Subsequently, the chip shear strength, Al-Al tensile shear strength, volume resistivity, and T were tested. g The energy storage modulus and the volume resistivity change rate are calculated to evaluate the copper-based conductive adhesive's resistance to oxidation, interfacial degradation, and resistivity instability in humid and hot environments.

[0112] g. Thermal aging stability test: The cured copper-based conductive adhesive, the cured chip shear test sample, and the cured aluminum-aluminum bonding sample were placed in a 150℃ air-blown oven for 500 hours. After aging, they were equilibrated for 2 hours in an environment of 25±2℃ and 45%-60% relative humidity. Subsequently, the chip shear strength, Al-Al tensile shear strength, volume resistivity, and T were tested. g And storage modulus, used to evaluate the conductivity stability and interface retention ability of copper-based conductive adhesives in high-temperature air environments.

[0113] h. XPS Surface Oxidation State Test: The cured aluminum-aluminum bonded samples were subjected to 500 hours of damp heat aging at 85℃ / 85% RH. After aging, the samples were cooled to room temperature, and X-ray photoelectron spectroscopy (XPS) was performed on the surface or exposed cross-section of the cured adhesive layer. An Al Kα ray source was used, with the binding energy calibrated at the C 1s peak (284.8 eV). High-resolution spectra of Cu 2p, CuLMM, O 1s, and N 1s were acquired. The XPS results were obtained through the analysis of the Cu 2p main peak, Cu... 2+ Satellite peaks and Cu LMM Auger spectra were used to comprehensively determine the valence state of copper surface, and the peak area normalization method was used to calculate Cu. 0 / Cu + and Cu 2+ The relative content. At least three test areas were selected for each sample, and the average value was taken.

[0114] i. High-current pulse cycle stability test: Copper-based conductive adhesive was coated between two 1060 aluminum alloy sheets to form an overlapping conductive structure with an overlap area of ​​5mm × 2mm. The adhesive layer thickness was controlled at 100μm~200μm and then cured. The test was conducted in an environment of 25±2℃ and relative humidity of 45%~60%. The sample was connected to a DC pulse power supply, and based on the effective conductive cross-sectional area of ​​the copper-based conductive adhesive, 10A / mm² was applied sequentially. 2 20A / mm 2 30A / mm 2 40A / mm 2 and 50A / mm 2A stepped rectangular pulse current was applied; each current density was applied for 10 seconds and then de-energized for 50 seconds, completing five levels of current loading, which was recorded as one cycle. After 100, 200, 500, and 1000 cycles, the sample resistance was measured using a Keithley 2450 source meter with a four-terminal method, and the highest temperature at the interface was recorded using an infrared thermal imager.

[0115] Furthermore, the rate of change of volume resistivity after the above-mentioned damp heat aging, high temperature aging, or high current pulse cycling is calculated according to formula (2):

[0116] (2)

[0117] In the formula, The rate of change of volume resistivity The initial volume resistivity of the copper-based conductive adhesive before aging or cycling, in Ω·cm. The volume resistivity of the copper-based conductive adhesive after aging or cycling is expressed in Ω·cm.

[0118] Table 1: Initial Performance Test Results of Copper-Based Conductive Adhesive

[0119]

[0120] Table 2: Performance Test Results of Copper-Based Conductive Adhesive after 500h Damp Heat Aging at 85℃ / 85% RH

[0121]

[0122] Table 3: Performance test results of copper-based conductive adhesive after 500h heat aging at 150℃

[0123]

[0124] Table 4: XPS surface oxidation state analysis results of copper-based conductive adhesive samples after 500h of damp heat aging at 85℃ / 85% RH

[0125]

[0126] Table 5: Changes in volume resistivity and interface temperature rise of copper-based conductive adhesive after stepped high-current pulse cycling

[0127]

[0128] Figure 1 The initial dynamic thermomechanical curve of the copper-based conductive adhesive prepared in Example 1; Figure 2 The initial air atmosphere TGA mass change curve of the copper-based conductive adhesive prepared in Example 1; Figure 3 The initial XPS pattern (Cu 2p spectrum) of the copper-based conductive adhesive prepared in Example 1.

[0129] (1) Analysis of adhesive properties and thermomechanical properties after 500h of damp heat aging at 85℃ / 85% RH:

[0130] As shown in Table 2, after 500 hours of humid heat aging at 85℃ / 85% RH, Example 1 still maintained good interfacial bonding strength and thermomechanical properties, indicating that its copper powder / resin interface has good stability under long-term humid heat conditions. The gold-gold chip bonding strength after humid heat aging in Example 1 was 27.6 MPa, the copper-copper chip bonding strength was 23.1 MPa, the Al-Al shear strength at room temperature was 18.9 MPa, and the Al-Al shear strength at 150℃ was 12.1 MPa, indicating that it could still maintain a relatively complete metal interface bonding structure after humid heat aging.

[0131] Compared to the comparative examples, Comparative Example 5, lacking the bipedal silane, showed the most significant decrease. After damp heat aging, the gold-gold chip bond strength of Comparative Example 5 was only 12.8 MPa, approximately 46% of that of Example 1; the copper-copper chip bond strength was 11.5 MPa, approximately half of that of Example 1; the Al-Al shear strength at room temperature was 4.8 MPa, approximately one-quarter of that of Example 1; and the Al-Al shear strength at 150°C was 3.2 MPa, also only approximately one-quarter of that of Example 1. This indicates that the multi-point anchoring and siloxane network coverage provided by the bipedal silane play a crucial role in maintaining the interface after damp heat aging.

[0132] From a thermomechanical perspective, after 500 hours of damp heat aging in Example 1, T... g The temperature remained at 151.8℃, and the storage modulus at 150℃ was 7.5 GPa, indicating that its cured network and copper powder / resin interface layer still maintained good structural integrity. In contrast, Comparative Example 5's T... g The temperature dropped to 92.4℃, and the energy storage modulus at 150℃ was only 1.2 GPa, which is about 6.3 times that of Example 1. This result shows that the complete ternary silane system can significantly slow down the interfacial relaxation and structural degradation under humid and hot conditions; while without bipedal silane, the interfacial layer is more prone to hydrolysis, debonding and modulus decay.

[0133] After reducing the proportions of nitrogen-containing heterocyclic silanes and aromatic silanes in Examples 5 and 6 respectively, the T after damp heat aging... g The energy storage modulus at 150°C is lower than that in Example 1, indicating that the coordination stabilization effect of the copper surface provided by the nitrogen-containing heterocyclic silane and the rigid hydrophobic barrier effect provided by the aromatic silane both help to improve the structural retention ability after hygrothermal aging.

[0134] (2) Analysis of volume resistivity change after 500h of damp heat aging at 85℃ / 85% RH:

[0135] As shown in Table 2, after 500 hours of damp heat aging at 85℃ / 85% RH in Example 1, the volume resistivity decreased from the initial 0.5 × 10⁻⁶. -3 Ω·cm increased to 0.9×10 -3 The Ω·cm value remains at a low level, indicating that its conductive network has not experienced serious instability under long-term humid and hot conditions.

[0136] In contrast, the volume resistivity of Comparative Example 5 increased to 7.2 × 10⁻⁶ after damp heat aging. -3 The volume resistivity of Comparative Examples 1 and 3 after damp heat aging was 4.1 × 10⁻⁶ Ω·cm, approximately eight times that of Example 1; -3 Ω·cm and 4.5×10 -3 The Ω·cm values ​​were approximately 4.6 times and 5 times those of Example 1, respectively. These results indicate that in conventional monosilane systems or when key silane components are lacking, moisture more readily enters the copper powder / resin interface, causing copper powder oxidation, contact interface degradation, and deterioration of the conductive pathway.

[0137] From the perspective of the role of the ternary silane component, after reducing the proportion of nitrogen-containing heterocyclic silanes in Example 5, the volume resistivity after damp heat aging was 2.8 × 10⁻⁶. -3 Ω·cm; Example 6: After reducing the proportion of aromatic silanes, the volume resistivity was 2.9 × 10⁻⁶ Ω·cm; -3 The Ω·cm values ​​were significantly higher than those in Example 1. This indicates that the coordination stabilizing effect of nitrogen-containing heterocyclic silanes and the rigid hydrophobic barrier effect of aromatic silanes both contribute to reducing the risk of increased volume resistivity under humid and hot environments.

[0138] Furthermore, while the rate of change in volume resistivity of Example 1 was not the lowest among all samples, its absolute volume resistivity after damp heat aging remained at 0.9 × 10⁻⁶. -3 It has a low Ω·cm level, while also possessing high adhesive strength and high T. g The high energy storage modulus indicates that it is not the best in a single conductivity index, but rather achieves a better comprehensive balance between conductivity stability, interfacial bonding, and thermomechanical properties.

[0139] (3) Analysis of bonding performance and thermomechanical properties after heat aging at 150℃ for 500h:

[0140] As shown in Table 3, after 500 hours of heat aging in air at 150℃, Example 1 still maintains high bonding strength and thermomechanical properties, indicating that its copper powder / resin interface and resin-cured network have good structural retention capabilities under high-temperature conditions. The copper-copper chip bonding strength after heat aging in Example 1 is 23.6 MPa, the gold-gold chip bonding strength is 28.4 MPa, the Al-Al room temperature shear strength is 20.2 MPa, and the Al-Al shear strength at 150℃ is 13.9 MPa, indicating that it still has relatively stable metal interface bonding capabilities after high-temperature aging.

[0141] Compared to Comparative Example 5, the copper-copper chip bond strength after thermal aging in Example 1 was approximately 2.4 times stronger, the gold-gold chip bond strength was approximately 2.8 times stronger, the Al-Al room temperature shear strength was approximately 4.8 times stronger, and the Al-Al shear strength at 150°C was also approximately 4.8 times stronger. These results indicate that, in the absence of bipedal silane, the copper powder / resin interface and the metal lap interface are more prone to interfacial relaxation and decreased cohesive strength in high-temperature environments.

[0142] Comparative Examples 1 and 2 used a traditional monosilane system. The copper-copper chip bonding strengths after thermal aging were 14.7 MPa and 14.8 MPa, respectively, and the gold-gold chip bonding strengths were 16.6 MPa and 16.4 MPa, respectively. These were significantly lower than those in Example 1, indicating that the interface layer formed by the traditional monosilane system has limited retention capacity at high temperatures.

[0143] Regarding thermomechanical properties, after thermal aging in Example 1, T g The temperature was 146.1℃, and the energy storage modulus at 150℃ was 8.7 GPa; while the T in Comparative Example 5... g The temperature is only 68.2℃, and the energy storage modulus at 150℃ is 1.4 GPa, which is about 6.2 times that of Example 1. This difference indicates that the ternary silane synergistic interface layer can not only improve the initial interface bonding, but also maintain the interface rigidity and structural integrity during high-temperature aging.

[0144] Comparative Example 3 lacks aromatic silanes, and Comparative Example 4 lacks nitrogen-containing heterocyclic silanes; both exhibit varying degrees of T after thermal aging. g The decrease in energy storage modulus indicates that aromatic silanes contribute to the thermal rigidity of the interface layer, nitrogen-containing heterocyclic silanes play a role in the coordination stability of the copper surface, and bipedal silanes are most critical for forming a stable siloxane network and maintaining interface integrity.

[0145] (4) Analysis of volume resistivity change after 500h of thermal aging at 150℃:

[0146] As shown in Tables 1 and 3, the volume resistivity of Example 1 remained at 0.7 × 10⁻⁶ after 500 hours of thermal aging at 150°C. -3 Ω·cm, compared to the initial value of 0.5 × 10 -3 The minimal change in Ω·cm indicates that the conductive network did not experience significant resistance drift under high-temperature air conditions. This result demonstrates that the ternary silane interface layer can mitigate copper powder oxidation and interfacial contact degradation under high-temperature conditions, thereby maintaining a stable conductive pathway.

[0147] In contrast, the volume resistivity of Comparative Example 5 after thermal aging was 6.5 × 10⁻⁶. -3The volume resistivity of Comparative Examples 1 and 3 after thermal aging was 3.8 × 10⁻⁶ Ω·cm, approximately 9.3 times that of Example 1; -3 Ω·cm and 4.7×10 -3 The Ω·cm values ​​were approximately 5.4 times and 6.7 times those of Example 1, respectively. Although some comparative examples may have experienced a certain densification effect during the thermal aging process due to the post-curing of the resin, the absolute value of the volume resistivity of the comparative examples was still significantly higher than that of Example 1, indicating that the continuity of its conductive network and the stability of its interface protection were not as good as those of the ternary silane composite system.

[0148] Therefore, the volume resistivity results after thermal aging at 150℃ indicate that the micro-nano copper powder composite structure and the ternary silane interface layer in Example 1 can jointly maintain the stability of the conductive pathway under high temperature conditions and reduce the risk of resistance instability during high-temperature service.

[0149] (5) Effect of the ratio of micron-sized copper powder to nano-sized copper powder on conductivity stability:

[0150] As shown in Examples 1 to 4, the mixing ratio of micron-sized flake copper powder to spherical nano-copper powder directly affects the volume resistivity and conductive network stability of the copper-based conductive adhesive. In Example 1, the mass ratio of micron-sized copper powder to nano-copper powder was 6:1, and the initial volume resistivity was 0.5 × 10⁻⁶. -3 Ω·cm, the lowest value among Examples 1 to 4, indicates that at this ratio, the flake-shaped micron copper powder can form the main conductive framework, and the nano copper powder can effectively fill the gaps between particles, thereby forming a more continuous conductive path.

[0151] When the proportion of nano-copper powder was increased to 4:1 as in Example 2, the initial volume resistivity increased to 0.8 × 10⁻⁶. -3 The value of Ω·cm indicates that excessively high nano-copper powder content may cause agglomeration and increase the resin coating requirement, thus reducing effective conductive contact; when the proportion of nano-copper powder is reduced to 7:1 in Example 4, the initial volume resistivity increases to 0.9 × 10⁻⁶. -3 Ω·cm, after damp heat aging, the volume resistivity further increases to 1.6×10 Ω·cm. -3 The value of Ω·cm indicates that insufficient filling of the gaps by nano-copper powder will increase local breakpoints and resin isolation layer.

[0152] Therefore, there is a favorable blending window between micron-sized copper powder and nano-sized copper powder. The 6:1 ratio in Example 1 achieves a good balance between building a long-range conductive framework and filling interparticle gaps, which is an important reason for obtaining low initial volume resistivity and stable conductivity after aging.

[0153] (6) Analysis of the oxidation state of XPS surface:

[0154] As shown in Table 4, after 500 hours of damp heat aging at 85 / 85% RH, the Cu in Example 1...2+ The relative content was 29.2%, and the O / Cu atomic ratio was 0.55, both at relatively low levels, indicating a light degree of oxidation on the surface of the copper powder. In contrast, the Cu in Comparative Example 5... 2+ The relative content reached 56.2%, which is nearly twice that of Example 1, and the O / Cu atomic ratio also increased to 1.10, indicating that without bipedal silane, the copper powder surface is more likely to form low-conductivity oxide layers such as Cu2O / CuO in a humid and hot environment.

[0155] From the perspective of the role of the ternary silane component, after reducing the proportion of nitrogen-containing heterocyclic silanes in Example 5, Cu 2+ The relative content increased to 37.6%; in Example 6, after reducing the proportion of aromatic silanes, Cu 2+ The relative content was 35.9%, which was higher than that in Example 1. This indicates that nitrogen-containing heterocyclic silanes help reduce the oxidation activity of copper surfaces by forming coordination stabilization with the copper surface through nitrogen atoms; while the rigid and hydrophobic barrier structure provided by aromatic silanes helps to slow down the diffusion of humid and hot media to the copper powder surface.

[0156] In addition, Comparative Examples 1 and 2 used a traditional single silane system, and Cu was subjected to wet heat aging. 2+ The relative contents were 44.8% and 49.4%, respectively, significantly higher than in Example 1, indicating insufficient integrity of the monosilane interface layer and insufficient resistance to damp heat oxidation. XPS results, from the perspective of copper surface valence state, demonstrate that ternary silane synergistic modification can reduce the degree of oxidation on the copper powder surface after damp heat aging, thereby helping to maintain effective contact between particles and reduce the risk of resistive instability.

[0157] (7) Analysis of volume resistivity change rate and interface temperature rise under high current pulse cycling:

[0158] High-current pulse cycling is mainly used to evaluate the conductivity path stability and interface temperature rise behavior of copper-based conductive adhesive under repeated electro-thermal shocks. Table 5 shows that after 1000 stepped high-current pulse cycles, the volume resistivity of Example 1 decreased from 0.5 × 10⁻⁶ to 0.5 × 10⁻⁶. -3 Ω·cm increased to 0.8×10 -3 The Ω·cm and the interface temperature of 50.3℃ indicate that it maintains a relatively stable conductive path and low heat accumulation even after repeated electrothermal shocks.

[0159] In contrast, Comparative Example 5 showed a volume resistivity of 13.5 × 10⁻⁶ after 1000 cycles. -3 The Ω·cm resistance was approximately 16.9 times that of Example 1, and the interface temperature also rose to 99.3°C, nearly twice that of Example 1. This result indicates that in the absence of bipedal silane, the copper powder contact interface is more prone to loosening, oxidation, and increased contact resistance under repeated Joule thermal shocks, thereby inducing a stronger local temperature rise.

[0160] Furthermore, while the volume resistivity change rates of some comparative examples were not high, their initial volume resistivity or interface temperature rise after cycling was significantly higher than that of Example 1. Therefore, this alone cannot be used to determine whether their conductivity stability is superior. For example, the volume resistivity of Example 1 after 1000 cycles was 0.8 × 10⁻⁶. -3 The volume resistivity of Comparative Example 1 was 50.3℃, while the volume resistivity of Comparative Example 1 was lower. However, after 1000 cycles, its interface temperature reached 70.3℃, which was significantly higher than that of Example 1, indicating that its electrothermal stability was still inferior to that of Example 1.

[0161] The volume resistivity of Comparative Examples 2 and 4 after 1000 cycles was 4.2 × 10⁻⁶. -3 Ω·cm and 4.3×10 -3 The resistance and interface temperature were both more than five times that of Example 1, showing a significant increase. This indicates that in traditional monosilane systems or when nitrogen-containing heterocyclic silanes are lacking, the surface protection and coordination stabilization effects of copper powder are insufficient, making it difficult to maintain a stable conductive path under high-current pulse conditions.

[0162] (8) Analysis of the onset temperature of oxidative weight gain and antioxidant stability:

[0163] As shown in Table 1, the oxidation weight gain initiation temperature of Example 1 reached 520.1℃, the highest among all samples, indicating that its copper powder surface has better oxidation resistance. In contrast, the oxidation weight gain initiation temperature of Comparative Example 5 was only 427.3℃, about 93℃ lower than that of Example 1, indicating that the lack of bipedal silane reduced the integrity of the protective layer on the copper powder surface, making it more susceptible to oxidation weight gain in air.

[0164] The oxidation weight gain initiation temperatures of Examples 5 and 6 were 470.9℃ and 440.3℃, respectively, both lower than that of Example 1. This indicates that reducing the proportion of nitrogen-containing heterocyclic silanes or aromatic silanes weakens the coordination stabilization effect on the copper surface and the rigid hydrophobic barrier ability of the interface layer, thus reducing the antioxidant performance. The oxidation weight gain initiation temperatures of Comparative Examples 3 and 4 were also lower than that of Example 1, further demonstrating that all three silane components participate in improving the antioxidant protection ability of the copper powder surface.

[0165] Therefore, the results of the oxidation weight gain initiation temperature indicate that the ternary silane synergistic interface modification can delay the oxidation process of copper powder in air atmosphere, providing a basis for copper-based conductive adhesives to maintain a low volume resistivity change rate under thermal aging, damp heat aging and high current pulse environments.

[0166] In summary, the performance improvement of the copper-based conductive adhesive in the examples is not due to the action of a single component, but rather the combined result of micro / nano copper powder compounding, organic acid surface activation, and ternary silane synergistic interface modification. Specifically, the sheet-like micron-sized copper powder serves as the main conductive framework, providing a continuous long-range conductive pathway; the spherical nano-sized copper powder fills the contact gaps between the micron-sized copper powders, increasing the effective contact points between particles, thereby reducing the initial volume resistivity and improving the continuity of the conductive network. Organic acid surface activation removes some of the loose oxide layer on the copper powder surface, exposing more reactive sites and providing a foundation for subsequent silane interface modification.

[0167] Based on the results of the examples, Example 1 exhibited superior overall performance when the mass ratio of micron-sized copper powder to nano-sized copper powder was 6:1 and the mass ratio of ternary silane was 1:0.3:0.2. Its initial copper-copper chip adhesion strength was 25.2 MPa, and its gold-gold chip adhesion strength was 30.1 MPa, indicating that the system has good adhesion compatibility to different metal interfaces; its initial volume resistivity was 0.5 × 10⁻⁶. -3 The volume resistivity remains low even after 500 hours of damp heat aging (Ω·cm), and is 0.7 × 10⁻⁶ after 500 hours of heat aging at 150℃. -3 The Ω·cm value remained largely unchanged compared to the initial value, and it maintained a low interface temperature rise and a relatively stable conductive path even after 1000 cycles of stepped high-current pulse cycling. Simultaneously, its oxidation weight gain onset temperature reached 520.1℃, significantly higher than that of the traditional single-silane system and the comparative formulation lacking the key silane component. These results indicate that this formulation achieves a good overall balance between interfacial adhesion, conductive stability, thermal aging stability, damp heat reliability, and oxidation resistance.

[0168] The ternary silane system is key to improving long-term reliability. Bipedal silane coupling agents provide multi-point anchoring and a high-density siloxane network, enhancing the integrity of the interface layer on the copper powder surface. Nitrogen-containing heterocyclic silane coupling agents can reduce the oxidation activity of the copper surface by forming coordination stabilization with nitrogen atoms. Aromatic silane coupling agents introduce a rigid hydrophobic structure, improving the heat resistance and humid heat barrier properties of the interface layer. The synergistic effect of these three components forms a composite interface layer on the copper powder surface that combines anchoring, coordination, and barrier functions, thereby mitigating the formation of low-conductivity oxide layers such as Cu2O / CuO under humid and high-temperature environments.

[0169] Compared to the traditional KH-550 and KH-560 single silane systems, the ternary silane complex system in Example 1 exhibits superior advantages in interface coverage integrity, humid heat barrier properties, and maintenance of conductive pathways. Compared to the comparative examples lacking bipedal silanes, nitrogen-containing heterocyclic silanes, or aromatic silanes, Example 1 demonstrates greater stability in volume resistivity after humid heat aging, XPS surface oxidation state, interface temperature rise after high-current pulses, and energy storage modulus after thermal aging. This indicates a clear synergistic relationship among the three silane components, rather than a simple superposition of coupling agents. Therefore, the examples, through a synergistic technical route of "micro-nano copper powder complexation to construct a stable conductive network—organic acid activation to enhance the surface reactivity of copper powder—ternary silane construction of an antioxidant interface layer," effectively reduce the risks of copper powder oxidation, interface contact degradation, and conductive network instability in copper-based conductive adhesives under humid heat, high temperature, and high-current pulse service conditions. This copper-based conductive adhesive combines low volume resistivity, low volume resistivity change rate, good interfacial adhesion retention, and high oxidation stability, making it suitable for applications with high long-term reliability requirements, such as high-power electronic devices, chip-substrate interconnection, electrode conductive bonding, and aerospace electronic packaging.

Claims

1. A method for preparing a copper-based conductive adhesive resistant to damp heat oxidation and exhibiting low electrical resistance instability, characterized in that... It is done in the following steps: I. Preparation of epoxy resin solution: Under stirring conditions, bisphenol A type epoxy resin and reactive diluent are premixed, and then bisphenol F type epoxy resin is added and heated and stirred until the mixture is uniform to obtain an epoxy resin solution. The mass ratio of bisphenol A type epoxy resin to bisphenol F type epoxy resin is 1:(1~4); II. Preparation of surface-activated copper powder: The compounded copper powder was added to the surface activation system for treatment, and then subjected to standing, centrifugation, filtration, washing and vacuum drying in sequence to obtain surface activated copper powder. The compounded copper powder is a mixture of flake-shaped micron copper powder and spherical nano copper powder; the mass ratio of the spherical nano copper powder to the flake-shaped micron copper powder is 1:(4~7); the average particle size of the flake-shaped micron copper powder is 5μm~10μm; the average particle size of the spherical nano copper powder is 20nm~50nm. The surface activation system is composed of an aqueous ethanol solution and an organic acid; III. Preparation of ternary silane hydrolysate: The silane coupling agent complex was added to an aqueous ethanol solution and pre-hydrolyzed by stirring at room temperature to obtain a ternary silane hydrolysate. The silane coupling agent complex is a mixture of bipedal silane coupling agents, nitrogen-containing heterocyclic silane coupling agents, and aromatic silane coupling agents; IV. Preparation of ternary silane-modified copper powder: Surface-activated copper powder was added to a ternary silane hydrolysate for interface modification, and then filtered, washed and vacuum dried sequentially to obtain ternary silane-modified copper powder. V. Preparation of copper-based conductive adhesive: An epoxy resin solution, a curing agent, and ternary silane-modified copper powder were sequentially subjected to planetary stirring, three-roll milling, and vacuum degassing to obtain a copper-based conductive adhesive that is resistant to humid heat oxidation and has a low electrical instability rate.

2. The method for preparing a copper-based conductive adhesive with resistance to damp heat oxidation and low electrical resistance instability according to claim 1, characterized in that... The bisphenol A type epoxy resin mentioned in step one is E-51 type epoxy resin; the bisphenol F type epoxy resin mentioned in step one is F-44 epoxy resin; the reactive diluent mentioned in step one is 1,4-butanediol diglycidyl ether; the mass ratio of the bisphenol A type epoxy resin to the reactive diluent mentioned in step one is 1:(1~4).

3. The method for preparing a copper-based conductive adhesive with resistance to damp heat oxidation and low electrical resistance instability according to claim 1, characterized in that... In step one, under the conditions of room temperature and stirring speed of 200 r / min to 500 r / min, bisphenol A type epoxy resin and reactive diluent are premixed for 30 min to 120 min. Then, under the conditions of temperature of 60℃ to 80℃ and stirring speed of 200 r / min to 500 r / min, bisphenol F type epoxy resin is added and heated and stirred for 30 min to 120 min until it is mixed evenly to obtain an epoxy resin solution.

4. The method for preparing a copper-based conductive adhesive with resistance to damp heat oxidation and low electrical resistance instability according to claim 1, characterized in that... The organic acid mentioned in step two is glacial acetic acid; the surface activation system mentioned in step two is specifically obtained by adjusting the pH of the ethanol aqueous solution to 4.0~5.5 using glacial acetic acid, and the mass fraction of ethanol in the ethanol aqueous solution is 90%~95%; the mass ratio of the compounded copper powder to the surface activation system mentioned in step two is 1:(0.15~0.40).

5. The method for preparing a copper-based conductive adhesive with resistance to damp heat oxidation and low electrical resistance instability according to claim 1, characterized in that... In step two, under the conditions of room temperature and stirring speed of 200 r / min to 500 r / min, the compounded copper powder is added to the surface activation system and treated for 30 min to 120 min.

6. The method for preparing a copper-based conductive adhesive with resistance to damp heat oxidation and low electrical resistance instability according to claim 1, characterized in that... The bipedal silane coupling agent mentioned in step three is bis[3-(triethoxysilane)propyl]amine; the nitrogen-containing heterocyclic silane coupling agent mentioned in step three is triethoxy-3-(2-imidazolin-1-yl)propylsilane; the aromatic silane coupling agent mentioned in step three is m-aminophenyltrimethoxysilane; the mass ratio of the bipedal silane coupling agent to the nitrogen-containing heterocyclic silane coupling agent mentioned in step three is 1:(0.1~0.5); the mass ratio of the bipedal silane coupling agent to the aromatic silane coupling agent mentioned in step three is 1:(0.1~0.3); the mass ratio of the silane coupling agent complex to the ethanol aqueous solution mentioned in step three is 1:(1~4); the mass fraction of ethanol in the ethanol aqueous solution mentioned in step three is 90%~95%.

7. The method for preparing a copper-based conductive adhesive with resistance to damp heat oxidation and low electrical resistance instability according to claim 1, characterized in that... In step three, pre-hydrolyze for 60 min to 120 min at room temperature and a stirring speed of 200 r / min to 500 r / min.

8. The method for preparing a copper-based conductive adhesive with resistance to damp heat oxidation and low electrical resistance instability according to claim 1, characterized in that... The mass ratio of surface-activated copper powder to ternary silane hydrolysate in step four is 1:(0.1~0.5); in step four, under the conditions of room temperature and stirring speed of 200r / min~500r / min, surface-activated copper powder is added to ternary silane hydrolysate for interface modification treatment for 60min~120min.

9. The method for preparing a copper-based conductive adhesive with resistance to damp heat oxidation and low electrical resistance instability according to claim 1, characterized in that... The curing agent mentioned in step five is one or a combination of two of dicyandiamide and 4,4'-diaminodiphenyl sulfone; the mass ratio of the epoxy resin solution to the curing agent mentioned in step five is 1:(0.1~0.2); the mass ratio of the epoxy resin solution to the ternary silane modified copper powder mentioned in step five is 1:(5~9).

10. The method for preparing a copper-based conductive adhesive with resistance to damp heat oxidation and low electrical resistance instability according to claim 1, characterized in that... The planetary stirring described in step five is specifically carried out at a speed of 1500 r / min to 2000 r / min for 3 min to 6 min; the three-roll milling described in step five is specifically carried out according to the following steps: passing through the rollers 3 times with a roller spacing of 30 μm to 50 μm, then passing through the rollers 3 times with a roller spacing of 10 μm to 30 μm, and finally passing through the rollers 3 times with a roller spacing of 5 μm to 10 μm; the vacuum degassing treatment described in step five is specifically carried out in a vacuum environment and at a stirring speed of 1500 r / min to 2000 r / min for 3 min to 6 min.

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