High-temperature antioxidant electronic packaging soldering paste and preparation method thereof

Abstract

This invention relates to the field of microelectronic soldering materials, and discloses a high-temperature antioxidant electronic packaging solder paste and its preparation method. The method includes a modified composite alloy solder powder and a flux carrier. The solder powder consists of a core alloy powder and a composite modified layer covering its surface. The modified layer contains modified graphene oxide and in-situ reduced nano-metals, which are covalently bonded to the core powder via a silane coupling agent. This invention constructs a graphene / nano-metal composite self-reducing system, utilizing the synergistic effect of graphene's physical barrier and chemical reduction to achieve in-situ deoxygenation and microstructure strengthening during the soldering process. This improves solder wettability, reduces solder joint void ratio, and enhances the solder joint's creep resistance, thermal conductivity, and mechanical fatigue strength.

Description

Technical Field

[0001] This invention belongs to the field of microelectronic welding materials, specifically relating to a high-temperature antioxidant electronic packaging solder paste and its preparation method. Background Technology

[0002] In existing technologies, high-melting-point alloy solders, such as bismuth-based and zinc-based alloys, are traditionally used to meet the requirements of high-temperature bonding. These materials, due to their high melting points, can meet the service requirements under specific high-temperature conditions. However, these high-melting-point alloys have an extremely high tendency to oxidize at high temperatures, especially during reflow soldering, where a dense oxide film easily and rapidly forms on the surface of the solder powder. This oxide film not only alters the wetting characteristics of the metal surface, leading to severely deteriorated wettability, but also hinders the full spread and fusion of alloy droplets in the molten state, thereby inducing numerous void defects within the solder joint.

[0003] Nanometal solder pastes (such as nanosilver paste and nanocopper paste) utilize the small size effect of nanoparticles to achieve a bonding layer with high-temperature creep resistance through a relatively low-temperature sintering process. However, in practical engineering applications, nanometal systems exhibit thermodynamic instability. Due to the huge specific surface area and extremely high surface energy of nanoparticles, there are extremely strong van der Waals forces between the particles, which makes them prone to spontaneous aggregation during storage and stirring.

[0004] This uneven agglomeration directly leads to uneven mass transfer during sintering, making it difficult for the sintered layer to achieve the ideal density. The numerous microcracks and micropores present in the low-density sintered structure not only reduce the material's bulk thermal conductivity but also accelerate the penetration of ambient oxygen into the material's interior under long-term high-temperature service conditions, triggering internal oxidation.

[0005] Traditional fluxes primarily reduce oxides by adding volatile organic acids. However, these organic components rapidly decompose and volatilize at high temperatures, failing to provide sustained antioxidant protection during extended high-temperature service life. Simply adding an antioxidant coating often introduces non-conductive or low-strength impurity phases, impairing the electrical properties and interfacial bonding strength of the solder joint. Summary of the Invention

[0006] To address the technical bottlenecks in existing high-melting-point alloy solders, such as deteriorated wettability and excessive void ratio due to high oxidation tendency, and the low density caused by agglomeration and sintering due to thermodynamic instability in nano-metal solder pastes, this invention provides a high-temperature antioxidant electronic packaging solder paste and its preparation method. This invention constructs a graphene / nano-metal composite self-reducing system, utilizing the synergistic effect of graphene's physical barrier and chemical reduction to achieve in-situ deoxidation and strengthening of the solder joint microstructure during the soldering process.

[0007] The present invention provides a high-temperature oxidation-resistant electronic packaging solder paste, which, by mass percentage, comprises: 85% to 92% modified composite alloy solder powder and 8% to 15% flux carrier.

[0008] The modified composite alloy welding powder consists of a core alloy powder and a composite modification layer coating the surface of the core alloy powder. The core alloy powder is a high-melting-point bismuth-based alloy powder or a zinc-based alloy powder. Specifically, the bismuth-based alloy powder comprises bismuth and antimony, with bismuth accounting for 85% to 95% by mass and antimony accounting for 5% to 15% by mass, and has a melting point range of 271°C to 320°C. The zinc-based alloy powder comprises zinc and aluminum, with zinc accounting for 94% to 96% by mass and aluminum accounting for 4% to 6% by mass, and has a melting point range of 380°C to 400°C. The particle size distribution of the core alloy powder follows a normal distribution, with an average particle size D50 of 15 μm to 25 μm, and particles smaller than 5 μm accounting for less than 3% by mass, and particles larger than 45 μm accounting for less than 1% by mass.

[0009] The composite modified layer comprises modified graphene oxide sheets and in-situ reduced nano-metal particles onto the modified graphene oxide sheets. The modified graphene oxide sheets have a thickness of 0.8 nm to 3.5 nm and a radial dimension of 0.5 μm to 2.0 μm, and their surface contains carboxyl, hydroxyl, and epoxy functional groups. The nano-metal particles are silver nanoparticles or copper nanoparticles with an average particle size of 10 nm to 50 nm. The modified graphene oxide sheets are covalently bonded to the surface hydroxyl groups of the core alloy powder via silane coupling agent molecular chains. The silane coupling agent is 3-aminopropyltriethoxysilane, whose hydrolysis product silanol group at one end undergoes a condensation reaction with the metal oxide on the surface of the alloy powder to form MO-Si bonds, and the amino group at the other end undergoes an amidation reaction with the carboxyl groups on the surface of the graphene oxide, constructing a stable organic-inorganic hybrid coating interface on the surface of the alloy powder.

[0010] The flux carrier comprises, by weight percentage, the following components: 35% to 50% modified resin, 30% to 45% solvent, 5% to 12% activator, 2% to 5% rheology modifier, and 1% to 3% antioxidant.

[0011] The modified resin is a mixture of hydrogenated rosin glycerol ester and maleic acid-modified rosin in a mass ratio of 3:1. The hydrogenated rosin glycerol ester has an acid value of 160 mg KOH / g to 170 mg KOH / g and a softening point of 80°C to 90°C, serving to provide initial viscous support and maintain thermal stability at high temperatures. The maleic acid-modified rosin has an acid value of 200 mg KOH / g to 230 mg KOH / g and is used to enhance the wetting and spreading ability of the carrier on metal surfaces.

[0012] The solvent is a high-boiling-point alcohol ether solvent, specifically a mixture of diethylene glycol monobutyl ether and triethylene glycol monobutyl ether in equal mass ratios. The solvent has a boiling point range of 230°C to 280°C, a flash point greater than 110°C, and a vapor pressure below 0.01 mmHg at 25°C. This solvent selection ensures that the solder paste has a stable working life of up to 12 hours during stencil printing, avoiding drastic viscosity fluctuations caused by rapid solvent evaporation.

[0013] The activator is composed of organic acid activators and organic amine activators. The organic acid activator is a composite system of succinic acid, glutaric acid, and azelaic acid, with a total mass percentage of 8%. The organic amine activator is triethanolamine and benzotriazole, with a mass percentage of 2%. This composite activator system undergoes synergistic dissociation in the temperature range of 150°C to 200°C, and the released hydrogen protons are used to pretreat the slight oxide layer on the surface of the solder pads and alloy powder.

[0014] The rheology modifier is a mixed powder of hydrogenated castor oil and polyamide wax, with a particle size of less than 10 μm. The rheology modifier constructs a thixotropic network structure in the carrier, maintaining the thixotropic index of the solder paste between 0.55 and 0.65, ensuring high shape retention of the printed solder paste pattern and preventing collapse.

[0015] The antioxidant is a hindered phenolic antioxidant, specifically tetrakis(β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate pentacarotene, which can capture free radicals generated by the carrier during high-temperature heating, prevent the resin from undergoing thermal oxidative degradation, and maintain the hydrodynamic characteristics of the carrier during the reflux process.

[0016] The evolution mechanism of the graphene / nanometal composite self-reducing system described in this invention during reflow soldering is as follows: In the heating stage, from room temperature to 150°C, the modified graphene oxide layer coating the alloy powder surface acts as a physical barrier, preventing oxygen from the external environment from penetrating into the alloy. When the temperature rises to the range of 180°C to 250°C, the oxygen-containing functional groups on the surface of the graphene oxide begin to undergo thermal decomposition, generating a reducing atmosphere; simultaneously, the nanometal particles embedded between the graphene sheets, due to their extremely high surface activity, begin to migrate to the surface of the alloy powder and undergo interfacial diffusion. This process induces an in-situ reduction reaction, reducing the residual metal oxides on the surface of the alloy powder to a metallic state, reducing the interfacial tension between the liquid solder and the substrate to be soldered, thus reducing the wetting angle.

[0017] In the molten section, where the temperature exceeds the alloy's melting point, the core alloy liquefies. Driven by the buoyancy within the liquid metal, the graphene sheets that were originally covering the surface migrate towards the solder interface due to their lower density and non-wetting properties with the liquid metal. These graphene sheets intertwine at the interface to form a continuous two-dimensional thermally conductive network and are distributed as pinned phases at the metal grain boundaries.

[0018] The present invention also provides a method for preparing the above-mentioned high-temperature oxidation-resistant electronic packaging solder paste, the specific process steps of which are as follows: Step 1: Surface pretreatment of the core alloy powder. The bismuth-based or zinc-based alloy powder is placed in a plasma cleaner, and a mixture of argon and oxygen is introduced. The powder is treated for 5 to 15 minutes at a power of 300 W to 500 W and a pressure of 20 Pa to 50 Pa. Plasma bombardment removes organic impurities from the powder surface and increases the surface hydroxyl density.

[0019] Step 2: Preparation of the composite modification solution. 0.1% to 0.5% (w / w) of graphene oxide was dispersed in anhydrous ethanol and ultrasonically dispersed for 60 min at 400 W using an ultrasonic cell disruptor to obtain a homogeneous graphene oxide colloid. Then, 0.5% (calculated amount) of 3-aminopropyltriethoxysilane was added, and the mixture was stirred in a 60°C constant temperature water bath for 4 h to complete the pre-grafting of graphene oxide with the silane coupling agent.

[0020] Step 3: Composite Coating Modification. The core alloy powder treated in Step 1 is slowly added to the composite modification liquid from Step 2, adjusting the solid content of the slurry to 40% to 60%. The mixture is then stirred at a low speed of 30 rpm for 12 hours in a dual planetary mixer. During this process, the temperature inside the reactor is controlled at 70℃ to promote the hydrolysis and condensation of the silane coupling agent on the alloy surface, achieving chemical coating of the graphene sheets.

[0021] Step 4: In-situ growth of nano-metals. Silver nitrate or copper acetate solution is added to the mixed slurry obtained in Step 3, with the metal ion content relative to the alloy powder being 0.05% to 0.15% by mass. Subsequently, a 5% sodium borohydride reducing agent solution is added dropwise at a controlled dropping rate of 2 mL / min, and the reaction is carried out in an ice-water bath for 2 hours. After the reaction is complete, the mixture is washed five times alternately by centrifugation with deionized water and anhydrous ethanol, and finally dried in a vacuum drying oven at 45°C for 24 hours to obtain the modified composite alloy welding powder.

[0022] Step 5: Preparation of flux carrier. Modified resin, solvent, and antioxidant are added to a reaction vessel in the specified proportions. The mixture is heated to 140°C to 160°C, maintaining a vacuum of -0.09 MPa, and stirred until the solid components are completely dissolved. The temperature is then lowered to 80°C, and activator and rheology modifier are added. The mixture is then sheared at 5000 rpm for 30 minutes in a high-speed emulsifier to form a uniform, semi-transparent paste-like fluid.

[0023] Step Six: Preparation of the Finished Solder Paste. Add the modified composite alloy solder powder obtained in Step Four and the flux carrier obtained in Step Five to a vacuum planetary mixer according to the specified mass ratio. First, stir at low speed under normal pressure for 10 minutes to wet the powder. Then, turn on the vacuum pump to -0.1 MPa, set the revolution speed to 40 r / min and the rotation speed to 80 r / min, and stir for 45 to 60 minutes. During stirring, turn on the cooling water system to ensure the material temperature is below 35℃.

[0024] Step 7: Degassing and Dispensing. The stirred solder paste is centrifuged at 1000 rpm for 5 minutes to remove tiny air bubbles entrained during mixing. Finally, it is automatically dispensed into syringes under nitrogen atmosphere and stored at 0°C to 10°C.

[0025] In the technical solution of this invention, the structural design of the modified composite alloy welding powder is the core to resolving the contradiction between high-temperature oxidation and wettability. By introducing a graphene coating layer on the surface of the alloy powder, this invention constructs a smart response barrier at the microscale. During the room temperature and preheating stages, the highly dense hexagonal honeycomb lattice of the graphene sheets forms a physical barrier against oxygen molecules, ensuring that the surface oxygen content increase of the alloy powder is less than 100 ppm during a storage period of up to 12 months. During the high-temperature stage of reflow soldering, the residual oxygen-containing functional groups on the surface of the graphene oxide undergo a disproportionation reaction with the reducing gases in the environment, and the locally generated reducing microenvironment can rapidly remove the secondary oxide film on the alloy surface.

[0026] The distribution of the nano-metal particles (such as nano-silver) on the graphene sheets not only serves to separate the graphene sheets and prevent secondary agglomeration, but also acts as an ignition point in the early stages of sintering. The high surface free energy of the nanoparticles lowers the spreading barrier of the liquid alloy on the solid substrate. When the alloy melts, nano-silver atoms rapidly diffuse into the Cu atomic layer of the substrate, forming an Ag-Cu solid solution or intermetallic compound layer with extremely high bonding strength. Due to the presence of the graphene sheets, the growth of these intermetallic compounds is spatially restricted, transforming from traditional coarse dendrites to diffusely distributed equiaxed fine grains. This microstructural transformation improves the mechanical fatigue strength of the solder joints.

[0027] The chemical composition of the flux carrier also reflects precise engineering considerations. The acid value distribution of the modified resin has been rigorously calculated to provide multi-stage active coverage. At around 120°C, hydrogenated rosin glycerol esters begin to soften, forming a continuous liquid film that encapsulates the solder joint and prevents secondary oxidation. Upon reaching 200°C, the highly active carboxyl groups of maleic acid-modified rosin begin to dissociate, synergistically working with organic acid activators to convert the oxide layer on the substrate surface into metal salts that dissolve in the solvent. The polarity gradient design of the high-boiling-point alcohol ether solvent ensures that these metal salts can be stably suspended, preventing them from settling and forming voids inside the solder joint.

[0028] This invention solves the technical challenge of easy agglomeration of nano-metal components in conventional systems by leveraging the bridging effect of graphene. The large specific surface area of ​​graphene provides abundant loading sites for nano-silver or nano-copper. Through van der Waals forces and chemisorption, nanoparticles are uniformly fixed on the graphene plane, avoiding physical aggregation during stirring and printing. During the cooling and solidification process after reflow soldering, these graphene sheets, due to their extremely high axial thermal conductivity (greater than 3000 W / (m·K)), construct efficient heat conduction paths within the solder joints, which improves the heat dissipation performance of high-power semiconductor chips.

[0029] The plasma pretreatment step in the preparation method is a key process to ensure coating strength. Compared with traditional chemical pickling, plasma treatment not only achieves zero-emission green cleaning but also allows for precise control of surface energy changes. By adjusting the argon-oxygen ratio, the density of hydroxyl groups generated on the alloy surface can be controlled to 3 to 5 per square nanometer, providing uniformly distributed reaction sites for the subsequent dehydration condensation of the silane coupling agent. During vacuum planetary stirring, strict temperature control (below 35°C) is used to prevent premature reaction between the active components in the flux carrier and the alloy powder, ensuring excellent viscosity stability and post-printing release properties of the solder paste.

[0030] At the physical performance level, the solder paste obtained by this invention produces solder joints with a void ratio controlled below 3% after reflow soldering, far lower than the industry-accepted standard of 10%. In the creep resistance test at a high temperature of 250°C, its steady-state creep rate is reduced by an order of magnitude compared to traditional Bi-Sb alloys. This is because the graphene sheets distributed at the grain boundaries hinder dislocation movement and atomic diffusion, resulting in a grain boundary strengthening effect.

[0031] During the preparation of the modified composite alloy welding powder, by controlling the rate of adding the reducing agent and the ultrasonic power, a monolayer dispersion of nano-metal particles on the graphene surface was achieved. In this structure, during welding, the graphene sheets can freely slide with the flow of liquid metal, preventing excessive increase in solder viscosity that could affect wetting. After solidification, they are fixed within the metal matrix. This dynamic synergy and static strengthening mechanism is the fundamental reason why this invention can simultaneously achieve high-temperature oxidation resistance and high-reliability bonding.

[0032] In this invention, the rheology modifier in the flux carrier not only affects printing performance but also synergizes with the graphene sheets. Polyamide wax fibers and graphene sheets are spatially interwoven, forming a complex dynamic mechanical network. Under squeegee shear force, this network rapidly disintegrates, exhibiting extremely low shear viscosity, facilitating the solder paste's passage through the stencil pores. Upon removal of the shear force, the network rapidly rebuilds under hydrogen bonding, preventing the solder paste from spreading and collapsing on the pads. This precise rheological control is crucial for micro-pitch packaging with a spacing of less than 100 μm.

[0033] In another preferred embodiment of the present invention, for zinc-based alloy solder powder, nano-copper particles are used in the composite modified layer. Due to the more reactive chemical properties of zinc, the Cu-Zn diffusion layer formed at the interface between nano-copper and zinc can inhibit the excessively rapid diffusion of zinc, slowing down the thickness growth of the brittle intermetallic compound layer at the solder joint interface. Graphene in this system not only acts as a reducing agent but also as a diffusion barrier layer, reducing the growth rate of the interfacial IMC layer and improving the drop toughness of the solder joint during long-term high-temperature aging.

[0034] In summary, the core of the engineering logic of this invention lies in the deep coupling of the macroscopic alloy joining process with the microscopic evolution of two-dimensional material properties. By pre-placing graphene on the alloy surface through chemical bonding, the global challenge of uniformly dispersing two-dimensional materials in a metal matrix is ​​solved. Through the construction of an in-situ reduction system, the originally harmful oxide film is transformed into a favorable metallurgical bonding force, achieving a technological leap from passive oxygen protection to active oxygen inhibition and strengthening.

[0035] This systematic design ensures that the invention has extremely high application value in the field of microelectronic packaging, especially in the packaging processes of wide-bandgap semiconductor power devices such as silicon carbide and gallium nitride. Its combined characteristics of high melting point, high thermal conductivity, and high oxidation resistance meet the requirements for long-term service at temperatures above 200°C, providing crucial material support for the miniaturization and high-power applications of electronic devices.

[0036] Regarding the compounding logic of activators in the flux carrier, this invention employs a combination of succinic acid (melting point 185℃), glutaric acid (melting point 97℃), and azelaic acid (melting point 106℃) to construct a kinetic system with a step-like acid release characteristic. In the preheating stage of the reflow curve, glutaric acid and azelaic acid, with their lower melting points, melt and dissociate first, performing preliminary cleaning of the slight oxides on the alloy powder surface. As the temperature rises to the leading edge of the reflow zone, succinic acid begins to play its role. Due to its shorter molecular chain and higher proton concentration, it can deeply peel off thicker oxide layers. This step-like activation release strategy avoids premature depletion of the activators at low temperatures, ensuring that the metal surface maintains the highest chemical purity near the alloy melting point.

[0037] Furthermore, the control of vacuum level is crucial in the preparation process of this invention. Maintaining a vacuum level above -0.09 MPa during the flux carrier preparation and final solder paste mixing stages is essential to completely eliminate dissolved oxygen and microbubbles within the system. For systems containing high specific surface area components such as graphene, bubbles readily adhere to the edges of graphene sheets. If these bubbles cannot be expelled during reflow, they will become a source of voids. This invention, through a combination of vacuum planetary stirring and centrifugal degassing, ensures the density of the solder paste, reduces the deviation between measured and theoretically calculated densities, and solves the problem of high solder joint void rates at the source of the process.

[0038] The preparation method provided by this invention also exhibits a high degree of certainty in controlling the environment for in-situ growth of nano-metals. Sodium borohydride reduction is carried out in an ice-water bath (0°C to 5°C) to reduce the reduction reaction rate, thereby obtaining nanoparticles with finer diameters and more uniform distribution. The slower reaction rate favors nucleation rather than growth of metal atoms on the graphene surface, allowing nanoparticles to precisely occupy defect sites or oxygen-containing functional group positions on the graphene surface. This precise site control not only enhances the binding force between nanoparticles and graphene but also maximizes the catalytic reduction efficiency of the nanocomposition.

[0039] During the cooling phase of reflow soldering, a small residual compressive stress field is generated around the graphene sheets due to the difference in thermal expansion coefficients between the graphene sheets and the metal substrate. This compressive stress field can counteract the thermal cycling tensile stress experienced by the solder joint during service, inhibiting the initiation of fatigue cracks. This strengthening mechanism from a physicomechanical perspective, combined with the chemical-level antioxidant mechanism, ensures the structural integrity of the solder joint under extreme operating conditions. Furthermore, due to the electromagnetic signal shielding and absorption properties of the graphene sheets, the solder paste described in this invention exhibits unexpected auxiliary functions in reducing electromagnetic interference and improving signal transmission integrity in the packaging of certain high-frequency communication devices, further expanding its application prospects in the 5G / 6G communication packaging field.

[0040] Compared with the prior art, the beneficial effects of the present invention are: 1. In the composite modified layer of the present invention, graphene constructs a physical oxygen barrier, which, together with the in-situ reduction effect of nano-metals, inhibits the oxidation of welding powder at high temperature, reduces the formation of oxide film, and ensures the stability of the welding process. 2. The graphene / nano-metal composite system reduces the interfacial tension of liquid solder, and with the step-release activator, it enhances the solder's ability to spread on the substrate, reduces voids and defects in the solder joint, and ensures a dense connection. 3. Graphene forms a heat-conducting network at the solder joint interface, improving heat transfer efficiency; at the same time, as a grain boundary pinning phase, it hinders dislocation movement, enhances the solder joint's resistance to creep and fatigue, and extends its service life. 4. The covalently bonded coating layer on the surface of the solder powder prevents oxidation and agglomeration during storage, and the thixotropic structure of the flux carrier ensures printability and release properties, making it suitable for micro-pitch packaging and providing excellent storage stability. 5. It is compatible with bismuth-based, zinc-based and other high-melting-point alloy systems to meet the high-temperature packaging requirements of wide-bandgap semiconductors; the preparation process is green and low-pollution, with no harmful residues, which is in line with the environmental protection development trend of electronic materials. Detailed Implementation

[0041] This invention provides a high-temperature oxidation-resistant electronic packaging solder paste and its preparation method. Its core technical architecture aims to solve the stringent oxidation control and thermomechanical reliability challenges in high-melting-point power semiconductor packaging through microscale interface engineering. The solder paste consists of two main parts: modified composite alloy solder powder and a flux carrier. The modified composite alloy solder powder accounts for 85% to 92% of the total mass, with the remainder being the flux carrier. This high powder loading design not only ensures sufficient density of the metal interconnect formed after soldering but also provides ample alloy pool volume during reflow.

[0042] The technical solution of the present invention will be described in detail below with reference to specific embodiments and comparative examples, so as to ensure that those skilled in the art can fully understand and implement the present invention.

[0043] Example 1: By mass percentage, the modified composite alloy welding powder is 88% (the core alloy powder is a bismuth-based alloy, 90% bismuth and 10% antimony, melting point 295℃, average particle size D50=20μm; the composite modification layer contains modified graphene oxide sheets (thickness 2.2nm, radial size 1.2μm) and silver nanoparticles (average particle size 30nm); silane coupling agent 3-aminopropyltriethoxysilane covalently bonded). 12% flux carrier (42% modified resin, hydrogenated rosin glycerol ester: maleic acid modified rosin = 3:1; 38% solvent, diethylene glycol monobutyl ether: triethylene glycol monobutyl ether = 1:1; 9% activator, succinic acid: glutaric acid: azelaic acid = 3:3:2, triethanolamine: benzotriazole = 1:1; 3% rheology modifier, hydrogenated castor oil: polyamide wax = 1:1; 2% antioxidant, hindered phenols). Preparation steps: S1: Pretreatment of core alloy powder. Bismuth-based alloy powder is placed in a plasma cleaner and treated with an argon-oxygen mixed gas to increase the surface hydroxyl density. S2: Preparation of composite modified solution: 0.3% graphene oxide is dispersed in anhydrous ethanol and sonicated at 400W for 60 min; 3-aminopropyltriethoxysilane is added and stirred at 60℃ for 4 h. S3: Composite coating modification, pretreated alloy powder is added to modification liquid, solid content 50%, stirred in a double planetary mixer at 30r / min and 70℃ for 12h; S4: In-situ growth of nano-metals, silver nitrate solution (metal ions account for 0.1% of alloy powder) is added, 5% sodium borohydride solution is added dropwise under ice-water bath, react for 2 h, centrifuge and wash, and then vacuum dry at 45℃ for 24 h. S5: Preparation of flux carrier: Modified resin, solvent, and antioxidant are stirred and dissolved at 150℃ and -0.09MPa; the temperature is lowered to 80℃, activator and rheology modifier are added, and shearing is performed at 5000r / min for 30min. S6: Solder paste preparation, modified solder powder and flux carrier are mixed in a vacuum planetary mixer, stirred at low speed under normal pressure for 10 min, and then stirred at -0.1 MPa, 40 r / min revolution and 80 r / min rotation for 50 min; S7: Degassing and dispensing, centrifuge at 1000r / min for 5min to degas, dispense under nitrogen protection, and refrigerate at 0-10℃.

[0044] Example 2: 85% modified composite alloy welding powder, 15% welding flux carrier, and the remaining components and proportions are the same as in Example 1; Preparation steps: Same as in Example 1.

[0045] Example 3: 92% modified composite alloy welding powder, 8% welding carrier, and the remaining components and proportions are the same as in Example 1; Preparation steps: Same as in Example 1.

[0046] Example 4: The core alloy powder is a zinc-based alloy (95% zinc, 5% aluminum, melting point 390℃), the nano-metal particles are nano-copper particles (average particle size 25nm), and the remaining components and proportions are the same as in Example 1; Preparation steps: Same as in Example 1, except that in step S4, copper acetate solution is added instead of silver nitrate solution.

[0047] Example 5: The composite modified liquid contained 0.1% graphene oxide by mass, and the remaining components and proportions were the same as in Example 1; Preparation steps: Same as in Example 1.

[0048] Example 6: The composite modified liquid contains 0.5% graphene oxide by mass, and the remaining components and proportions are the same as in Example 1; Preparation steps: Same as in Example 1.

[0049] Example 7: The flux carrier contains 5% activator, and the remaining components and proportions are the same as in Example 1; Preparation steps: Same as in Example 1.

[0050] Example 8: The flux carrier contains 12% activator, and the remaining components and proportions are the same as in Example 1; Preparation steps: Same as in Example 1.

[0051] Comparative Example 1: No composite modification layer, the core alloy powder is not coated with graphene oxide and nano-metals, and the other components are the same as in Example 1; Preparation steps: Steps S2-S4 are omitted. The core alloy powder is only subjected to plasma pretreatment. The remaining process parameters and steps are the same as in Example 1.

[0052] Comparative Example 2: The composite modified liquid contained no 3-aminopropyltriethoxysilane, and the other components were the same as in Example 1; Preparation steps: No silane coupling agent is added in step S2, and the remaining process parameters and steps are the same as in Example 1.

[0053] Test method: High-temperature oxidation resistance test: The thickness of the oxide layer on the surface of the solder powder was measured after holding at 250℃ in air for 100 hours. Wetting performance test: The wetting angle of the alloy on a copper substrate was measured (250°C). Microscopic performance testing: The microstructure of the solder joints was observed using a scanning electron microscope, and the void ratio was determined. Mechanical property testing: The shear strength of the weld joint was measured, and the strength retention rate was tested after 500 thermal cycles from -55℃ to 150℃. Printing performance test: Determine the thixotropic index of solder paste; Thermal conductivity test: The radial thermal conductivity of the solder joint is measured.

[0054] The test data comparisons are shown in Table 1 and Table 2.

[0055] Table 1 Comparison of Wetting Angle, Solder Void Rate, Shear Strength, and Thermal Cycling Strength Retention Rate Table 2 Comparison of Oxide Layer Thickness, Thixotropic Index, and Thermal Conductivity at 250℃ Examples 1 to 8 utilize graphene to construct a physical oxygen barrier layer, nano-metals to reduce the oxide film in situ, and silane coupling agents to strengthen interfacial bonding. These three elements synergistically improve high-temperature stability and solder joint reliability. Comparative Example 1, lacking a composite modification layer, exhibits severe oxidation and high void ratio; Comparative Example 2, lacking a silane coupling agent, suffers from weak interfacial bonding and performance degradation.

[0056] When the solder powder ratio is 88% to 92%, the graphene oxide content is 0.3% to 0.5%, and the activator content is 9% to 12%, the overall performance is better. Among them, the graphene oxide content determines the oxygen barrier effect and the integrity of the thermal conductivity network, while the activator content balances the wetting ability and residual stability. The two work together to ensure the overall performance of the solder paste.

[0057] Compared to Comparative Example 1 without the composite modification layer, the wettability angle is reduced by more than 65%, the void ratio is reduced by more than 82%, and the shear strength is increased by more than 46%. Compared to Comparative Example 2 without the silane coupling agent, the oxide layer thickness is reduced by more than 66%, the thermal cycling strength retention rate is increased by more than 26%, and the thermal conductivity is increased by more than 35%, thus meeting the high-temperature packaging requirements of wide bandgap semiconductors.

[0058] In summary, this invention achieves simultaneous improvement in high-temperature oxidation resistance, high wetting performance, and high reliability by coupling a graphene / nano-metal composite self-reducing system with process optimization. It solves the core pain points of traditional high-temperature solder paste, is suitable for high-end electronic packaging, and has good potential for industrialization.

[0059] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A high-temperature antioxidant electronic packaging solder paste, characterized in that, Its components, by mass percentage, include: Modified composite alloy welding powder 85% to 92%, welding carrier 8% to 15%; The modified composite alloy welding powder consists of a core alloy powder and a composite modification layer coated on the surface of the core alloy powder. The flux carrier includes a modified resin, a solvent, an activator, a rheology modifier, and an antioxidant, wherein the activator comprises a complex organic acid system with a stepwise acid release characteristic.

2. The high-temperature antioxidant electronic packaging solder paste according to claim 1, characterized in that, The composite modified layer forms a covalent bond between the silane coupling agent molecular chain and the surface hydroxyl groups of the core alloy powder, thus constructing an organic-inorganic hybrid coating interface.

3. The high-temperature antioxidant electronic packaging solder paste according to claim 1, characterized in that, The core alloy powder is selected from either high-melting-point bismuth-based alloy powder or zinc-based alloy powder.

4. The high-temperature antioxidant electronic packaging solder paste according to claim 3, characterized in that, When the core alloy powder is the bismuth-based alloy powder, its composition by mass percentage is 85% to 95% bismuth and 5% to 15% antimony; when the zinc-based alloy powder is used, its composition by mass percentage is 94% to 96% zinc and 4% to 6% aluminum.

5. The high-temperature antioxidant electronic packaging solder paste according to claim 1, characterized in that, The composite modified layer includes a modified graphene oxide sheet and nano-metal particles loaded on the modified graphene oxide sheet; the surface of the modified graphene oxide sheet contains carboxyl, hydroxyl and epoxy functional groups for chemical bonding and in-situ reduction reactions.

6. The high-temperature antioxidant electronic packaging solder paste according to claim 5, characterized in that, The nano-metal particles are generated by an in-situ reduction reaction; when the core alloy powder is a bismuth-based alloy powder, the nano-metal particles are silver nanoparticles; when the core alloy powder is a zinc-based alloy powder, the nano-metal particles are copper nanoparticles.

7. The high-temperature antioxidant electronic packaging solder paste according to claim 2, characterized in that, The silane coupling agent is 3-aminopropyltriethoxysilane.

8. The high-temperature antioxidant electronic packaging solder paste according to claim 1, characterized in that, The flux carrier, by weight percentage, consists of the following components: Modified resin: 35% to 50%; Solvent: 30% to 45%; Surfactant: 5% to 12%; Rheology modifier: 2% to 5%; Antioxidants: 1% to 3%.

9. The high-temperature antioxidant electronic packaging solder paste according to claim 8, characterized in that, The modified resin is a mixture of hydrogenated rosin glycerol ester and maleic acid modified rosin in a mass ratio of 3:1; the solvent is a mixture of diethylene glycol monobutyl ether and triethylene glycol monobutyl ether in a mass ratio of 1:

1.

10. The high-temperature antioxidant electronic packaging solder paste according to claim 8, characterized in that, The activator is composed of organic acid activator and organic amine activator, wherein the organic acid activator is a composite system composed of succinic acid, glutaric acid and azelaic acid, and the sum of the masses of succinic acid, glutaric acid and azelaic acid accounts for 8% of the total mass of the flux carrier; the organic amine activator is triethanolamine and benzotriazole, and the sum of the masses of triethanolamine and benzotriazole accounts for 2% of the total mass of the flux carrier.

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