A low temperature cure paste with enhanced temperature cycle resistance and a method of making the same

Abstract

The application discloses a kind of low-temperature curing paste of enhanced temperature cycle resistance and preparation method thereof, it is related to chip packaging field, low-temperature curing paste includes by mass percentage: 1-20% thermoplastic resin particles, 0.1-5.0% thermosetting resin, 0.1-1.5% solvent and remaining silver powder;Silver powder includes by mass percentage: 10-45% spherical nanometer silver particles a, 1-5% spherical nanometer silver particles b and remaining micron silver flake;The particle size of micron silver flake is 1-10 μm, the particle size of spherical nanometer silver particles a is 50-100 nm, the particle size of spherical nanometer silver particles b is 5-50 nm, the particle size of thermoplastic resin particles is 1-15 μm.The paste of component allocation of the present application by thermoplastic resin particles and silver powder etc., when joint structure formed by paste solidification experiences temperature cycle, thermoplastic resin particles can melt at high temperature and dynamically fill the pore between silver powder particles, to hinder the migration path of silver atom, inhibit the metal grain growth caused by temperature fluctuation, reduce the internal stress generated by grain coarsening.

Description

Technical Field

[0001] This invention relates to the field of chip packaging, and more particularly to a low-temperature curing paste with enhanced temperature cycling resistance and its preparation method. Background Technology

[0002] As chips become increasingly smaller, their integration and power density are also increasing. Consequently, chip operating temperatures are rising, making the high-temperature performance of packaging structures increasingly crucial. Traditional conductive adhesives, due to their low melting points, are prone to failure at high temperatures, potentially damaging the chip and thus unsuitable for high-density packaging. Gold-based solders offer excellent electrical and thermal conductivity and a high melting point, but their high cost limits their widespread adoption in production. Silver, with a melting point of 961°C and excellent electrical and thermal conductivity, coupled with the size effect of nanoscale silver particles, exhibits low-temperature sintering and high-temperature operation characteristics, making it a promising candidate for high-power electronic device packaging.

[0003] Currently available silver pastes on the market are mainly composed of silver powder, solvent, and thermosetting resin. Silver powder is used for electrical and thermal conductivity and interface sintering. Thermosetting resin is used to uniformly disperse the silver powder to prevent it from precipitating and accumulating, and at the same time to achieve interface-assisted bonding. Solvent is used to adjust the viscosity of the paste and improve its workability. However, when the interconnect structure formed by this conductive paste experiences temperature fluctuations during service, the metal grain growth caused by high temperature will generate large stress, eventually leading to the separation between the connector and the substrate.

[0004] Therefore, a low-temperature curing slurry with enhanced temperature cycling resistance and its preparation method are proposed to solve the problem of large stress caused by metal grain growth in the joint structure due to temperature fluctuations. Summary of the Invention

[0005] The purpose of this invention is to provide a low-temperature curing slurry with enhanced temperature cycling resistance and its preparation method, thereby solving the problem of metal grain growth and large stress caused by temperature fluctuations in the joint structure.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] A low-temperature curing slurry with enhanced temperature cycling resistance, wherein the low-temperature curing slurry comprises, by weight percentage: 1-20% thermoplastic resin particles, 0.1-5.0% thermosetting resin, 0.1-1.5% solvent, and the remainder silver powder;

[0008] The silver powder comprises, by mass percentage: 10-45% spherical silver nanoparticles a, 1-5% spherical silver nanoparticles b, and the remainder being micron-sized silver flakes.

[0009] The micron-sized silver flakes have a particle size of 1-10 μm, the spherical silver nanoparticles a have a particle size of 50-100 nm, the spherical silver nanoparticles b have a particle size of 5-50 nm, and the thermoplastic resin particles have a particle size of 1-15 μm.

[0010] The thermoplastic resin particles are any one of polyvinyl chloride, polyvinyl acetate, polyamide, polymethyl methacrylate, and natural rubber.

[0011] The thermosetting resin is any one or more of epoxy resin, polyurethane resin, vinyl resin, and silicone resin.

[0012] The solvent is any one of alcohol-based solvents, acetic acid solvents, hydrocarbon solvents, or mixtures thereof.

[0013] The low-temperature curing slurry further includes less than 1.5% curing agent and less than 0.5% curing accelerator by mass percentage. The curing agent is any one or more of dicyandiamide, acid anhydride and phenol resin, and the curing accelerator is any one or more of imidazole curing accelerator, amine curing accelerator, diazabicyclol curing accelerator and urea curing accelerator.

[0014] A method for preparing a low-temperature curing slurry with enhanced temperature cycling resistance, the method being applied to the low-temperature curing slurry as described above, the method comprising the following steps:

[0015] Step S1: Mix silver powder, including micron-sized silver flakes, spherical nano-silver particles a and b, with thermoplastic resin particles to obtain a mixed powder after mixing.

[0016] Step S2: Perform surface-activation treatment on the mixed powder to obtain active powder;

[0017] Step S3: Mix the active powder, aliphatic hydrocarbon solvent, monomer mixture and AIBN to obtain a mixed solution, then filter the mixed solution to obtain a solid product, and wash and dry the solid product with ethanol to obtain a composite powder;

[0018] Step S4: Mix the composite powder with thermosetting resin and solvent to obtain a low-temperature curing slurry.

[0019] Step S2 specifically includes the following steps:

[0020] Step S21: First, place the mixed powder on a porous plate inside the plasma reactor and evacuate the plasma reactor chamber to below 10 Pa. Then, let the first gas pass through the porous plate with a pore size of 0.5-5 μm to make the mixed powder turbulent. At the same time, oxygen is introduced to perform preliminary treatment on the mixed powder. After the treatment is completed, the preliminary powder is obtained.

[0021] Step S22: Maintaining the state of step S21, allow the second gas to pass through the holes of the porous plate and mix with the powder for secondary treatment. After the treatment is completed, active powder is obtained.

[0022] In step S21, the preliminary treatment time is 5-15 minutes, the working gas pressure of the plasma reactor chamber is 20-100 Pa, the power is 100-200 W, the oxygen flow rate is 50-200 sccm, the first gas flow rate is 500-2000 sccm, and the first gas is argon.

[0023] In step S22, the secondary treatment time is 20-40 min, the temperature of the plasma reactor chamber is 70-90℃, the working pressure is 50-200 Pa, the flow rate of the second gas is 100-500 sccm, and the second gas is a mixture of vaporized VTES and argon, wherein the volume flow rate ratio of vaporized VTES to argon is 1:(1-5).

[0024] The mixed solution is obtained according to the following steps:

[0025] Step S31: The active powder, aliphatic hydrocarbon solvent and monomer mixture are initially mixed to obtain a preliminary mixture;

[0026] Step S32: Mix the preliminary mixture with AIBN again to obtain a mixed solution.

[0027] In step S31, the initial mixing speed is 100-300 rpm and the time is 30-60 minutes. The mass ratio of the monomer mixture, aliphatic hydrocarbon solvent, and active powder is (5-15):(30-60):100. The aliphatic hydrocarbon solvent is any one of n-hexane, n-heptane, and isooctane. The monomer mixture is a mixture of HEMA and EGDMA, wherein the mass ratio of HEMA to EGDMA is (95-98):(2-5).

[0028] In step S32, the amount of AIBN added is 0.5%-1.0% of the total mass of the monomer mixture in step S31, and the remixing temperature is 70-80℃, the rotation speed is 50-150rpm, the time is 6-12h, and the heating rate is 1-3℃ / min.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] This invention provides a low-temperature curing slurry with enhanced temperature cycling resistance and its preparation method. The slurry, prepared from thermoplastic resin particles and silver powder including micron-sized silver flakes, spherical nano-silver particles a, and spherical nano-silver particles b, allows the thermoplastic resin particles to distribute within the silver powder framework after curing. During temperature cycling, the thermoplastic resin particles melt at high temperatures and dynamically fill the pores between the silver powder particles, hindering the migration path of silver atoms and thus suppressing metal grain growth caused by temperature fluctuations. This fundamentally reduces the internal stress caused by grain coarsening. Simultaneously… As a viscoelastic phase, the molten thermoplastic resin particles can absorb and relax the thermal stress caused by the mismatch in the coefficients of thermal expansion between the chip, the connector structure, and the substrate, reducing the risk of stress concentration leading to interface delamination. In addition, in the solidified connector structure, the micron-sized silver flakes construct the dominant conductive pathway, and the spherical silver nanoparticles a and the smaller spherical silver nanoparticles b successively fill the macroscopic and microscopic pores, forming an extremely dense initial sintered structure. This highly dense structure not only provides excellent initial electrical and thermal conductivity, but also further enhances the resistance to grain growth due to its small initial pores and long atomic migration paths. Attached Figure Description

[0031] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0032] The structures, proportions, sizes, etc., shown in the accompanying drawings of this specification are only for the purpose of assisting those skilled in the art in understanding and reading the content disclosed in the specification, and are not intended to limit the conditions under which the present invention can be implemented. Therefore, they have no substantial technical significance. Any modifications to the structure, changes in the proportions, or adjustments to the size, without affecting the effects and objectives that the present invention can produce, should still fall within the scope of the technical content disclosed in the present invention.

[0033] Figure 1 This is a flowchart of the preparation method in this invention. Detailed Implementation

[0034] To make the objectives, features, and advantages of this invention more apparent and understandable, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described below are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0035] In the description of this invention, it should be understood that the terms "upper," "lower," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. It should be noted that when a component is considered to be "connected" to another component, it can be directly connected to the other component or there may be a component positioned centrally in the connection.

[0036] Example 1:

[0037] This embodiment provides a low-temperature curing slurry with enhanced temperature cycling resistance. The low-temperature curing slurry comprises, by weight percentage: 1-20% thermoplastic resin particles, 0.1-5.0% thermosetting resin, 0.1-1.5% solvent, and the remainder silver powder. Specifically, the thermoplastic resin particles comprise 10% by weight, the thermosetting resin comprises 3.0% by weight, the solvent comprises 1% by weight, and the silver powder comprises more than 75% by weight, preferably 85% by weight.

[0038] The silver powder comprises, by mass percentage: 10-45% spherical silver nanoparticles a, 1-5% spherical silver nanoparticles b, and the remainder micron-sized silver flakes; specifically, the micron-sized silver flakes comprise 60% by mass, the spherical silver nanoparticles a comprise 35% by mass, and the spherical silver nanoparticles b comprise 5% by mass.

[0039] The particle size of the micron-sized silver flakes is 1-10 μm, the particle size of spherical silver nanoparticles a is 50-100 nm, the particle size of spherical silver nanoparticles b is 5-50 nm, and the particle size of the thermoplastic resin particles is 1-15 μm. It should be noted that the particle size of spherical silver nanoparticles b is less than 50 nm, and the particle size of spherical silver nanoparticles a is greater than 50 nm. Specifically, the particle size of the micron-sized silver flakes is 5.0 μm, the particle size of spherical silver nanoparticles a is 100 nm, and the particle size of spherical silver nanoparticles b is 20 nm.

[0040] It is understandable that the joint formed after the silver paste has solidified is essentially a porous structure composed of countless silver particles connected by sintering necks. In particular, due to their extremely small size, nano-silver particles have extremely high specific surface area and surface energy, and this porous structure is in a thermodynamically unstable state. When the temperature rises (such as when the chip generates heat during operation), the silver atoms gain enough energy to migrate. The atoms will migrate from the small particles or neck region with small radius of curvature and high energy to the surface of the coarse particles with large radius of curvature and low energy. This causes the small particles to gradually shrink or disappear, while the large particles continue to grow, i.e., grain growth.

[0041] Grain growth is accompanied by coarsening of the sintering neck and coagulation of pores, which increases the interface for electron and phonon scattering, leading to a decrease in the electrical and thermal conductivity of the joint. Furthermore, grain growth is a non-uniform volume change process. This non-uniform contraction and expansion will generate local stress inside the joint. When different materials with mismatched thermal expansion coefficients, such as the chip, joint, and substrate, repeatedly expand and contract during temperature cycling, the internal stress generated by grain growth will be superimposed with the thermal mismatch stress, increasing the overall stress level. When the accumulated stress exceeds the bonding strength between the joint and the chip or substrate, microcracks will be generated and eventually propagate, leading to delamination and complete joint failure.

[0042] It should be noted that silver powder acts as a functional framework in the joint structure (formed after the low-temperature curing slurry is cured), responsible for establishing the core pathways for electrical and thermal conductivity. Thermoplastic resin particles can dynamically buffer stress and stabilize the microstructure, while thermosetting resin can form a three-dimensional network after the low-temperature curing slurry is cured, providing initial strength and shape stability to the low-temperature curing slurry, and ensuring that the thermoplastic resin particles and silver powder particles are uniformly dispersed and do not settle. In addition, the solvent acts as a processing regulator to adjust the viscosity of the low-temperature curing slurry, making it suitable for coating processes such as screen printing.

[0043] It is known that when the low-temperature curing slurry is cured, the thermoplastic resin particles can fill the pores between the silver powder, increase the density of the joint structure, and improve the thermal conductivity of the joint structure. During the service process, the thermoplastic resin particles can remelt and fill the pores between the metal particles, reducing the stress between the joint structure and the substrate while also hindering the growth of metal grains. In addition, as a viscoelastic material, the thermoplastic resin particles can absorb and relax the thermal stress caused by the mismatch of the thermal expansion coefficients between the chip, the joint, and the substrate, as well as the internal stress generated by the grain growth itself, preventing stress concentration from causing interface delamination, thereby inhibiting the delamination of the packaging interconnect structure.

[0044] It should also be noted that the sheet-like structure of the micron-sized silver flakes in the silver powder can overlap to form wide conductive and thermally conductive channels during the sintering of the low-temperature curing slurry. Due to its two-dimensional shape, it leaves pores that facilitate gas exhaust. Subsequently, during the sintering process, the spherical silver nanoparticles a can fill the large pores between the micron-sized silver flakes through their high surface energy, thereby improving the initial density and strength of the joint structure. Finally, the spherical silver nanoparticles b, with their smaller particle size, can fill the tiny gaps that the spherical silver nanoparticles a cannot enter, making the joint structure even denser, thus maximizing the initial performance. Moreover, the denser initial structure means fewer initial pores and shorter atomic migration paths, laying a good foundation for resisting subsequent grain growth.

[0045] Specifically, the low-temperature curing slurry constructs a high-performance initial metal skeleton using silver powder. With the introduction of thermoplastic resin particles, this skeleton has dynamic self-adaptive capabilities under temperature cycling. When the joint structure experiences high temperatures, the thermoplastic resin melts, filling the micropores that may be generated by the growth of silver grains and inhibiting their further development. On the other hand, through the viscoelastic deformation of the thermoplastic resin itself, it absorbs and releases thermal mismatch stress, thereby suppressing the delamination failure trend of the joint structure and solving the problem of large stress generated by the joint structure with temperature fluctuations.

[0046] Furthermore, the thermoplastic resin particles are any one of polyvinyl chloride, polyvinyl acetate, polyamide, polymethyl methacrylate, and natural rubber; specifically, the thermoplastic resin particles are polyvinyl chloride.

[0047] Furthermore, the thermosetting resin is any one or more of epoxy resin, polyurethane resin, vinyl resin, and silicone resin; specifically, the thermosetting resin is an epoxy resin that is liquid at 25°C.

[0048] Furthermore, the solvent is any one of alcohol-based solvents, acetic acid solvents, hydrocarbon solvents, and mixtures thereof; specifically, the solvent is an alcohol-based solvent.

[0049] Furthermore, the low-temperature curing slurry also includes less than 1.5% curing agent and less than 0.5% curing accelerator by mass percentage. The curing agent is any one or more of dicyandiamide, acid anhydride, and phenolic resin, and the curing accelerator is any one or more of imidazole-based curing accelerator, amino-based curing accelerator, diazabicyclo-based curing accelerator, and urea-based curing accelerator. Specifically, the curing agent is 0.8% dicyandiamide, and the curing accelerator is 0.2% imidazole-based curing accelerator.

[0050] Please see Figure 1 This embodiment describes a method for preparing a low-temperature curing slurry with enhanced temperature cycling resistance. The preparation method is applied to the low-temperature curing slurry described above and includes the following steps:

[0051] Step S1: Mix silver powder, including micron-sized silver flakes, spherical nano-silver particles a and b, with thermoplastic resin particles to obtain a mixed powder after mixing.

[0052] Step S2: Perform surface-activation treatment on the mixed powder to obtain active powder;

[0053] Step S3: Mix the active powder, aliphatic hydrocarbon solvent, monomer mixture and AIBN (azobisisobutyronitrile) to obtain a mixed solution, then filter the mixed solution to obtain a solid product, and wash and dry the solid product with ethanol to obtain a composite powder;

[0054] Step S4: Mix the composite powder with thermosetting resin and solvent to obtain a low-temperature curing slurry.

[0055] Specifically, step S2 involves surface-actively treating the mixed powder to obtain active powder;

[0056] Step S2 specifically includes the following steps:

[0057] Step S21: First, place the mixed powder on a porous plate inside the plasma reactor and evacuate the plasma reactor chamber to below 10 Pa. Then, let the first gas pass through the porous plate with a pore size of 0.5-5 μm to make the mixed powder turbulent. At the same time, oxygen is introduced to perform preliminary treatment on the mixed powder. After the treatment is completed, the preliminary powder is obtained.

[0058] In step S21, the preliminary treatment time is 5-15 minutes, the working gas pressure of the plasma reactor chamber is 20-100 Pa, the power is 100-200 W, the oxygen flow rate is 50-200 sccm, the first gas flow rate is 500-2000 sccm, and the first gas is argon; preferably, the preliminary treatment time is 10 minutes, the working gas pressure of the plasma reactor chamber is 60 Pa, the power is 150 W, the oxygen flow rate is 125 sccm, and the first gas flow rate is 1250 sccm.

[0059] It should be noted that oxygen forms oxygen plasma in the plasma reactor chamber, which bombards the active particles: efficiently introducing active oxygen-containing functional groups such as hydroxyl and carboxyl groups onto the surface of the thermoplastic resin particles; removing all organic contaminants from the surface of the silver powder, and forming a thin active silver oxide layer rich in hydroxyl groups on its surface.

[0060] It should also be noted that after the initial treatment, the surface of all particles in the mixed powder changes from an inert low-energy state to a hydrophilic high-energy state, increasing the surface energy and creating the necessary conditions for subsequent chemical bonding.

[0061] It is worth noting that the pores on the porous plate can be uniformly distributed, sparsely distributed in the central region and densely distributed at the edges, or distributed in a fan-shaped pattern. Understandably, a uniformly distributed pore pattern provides uniform airflow distribution, suitable for situations with moderate powder loading and good fluidization. A non-uniform pore distribution, with sparse pores in the central region and dense pores at the edges, specifically involves dividing the porous plate into a central region and an edge region. The pore spacing in the central region is larger, while the pore spacing in the edge region is smaller. As gas flows in from the bottom center of the porous plate and diffuses outwards, its dynamic pressure naturally decreases. By increasing the porosity of the edge region, the pressure loss when the gas flows towards the edge can be compensated, thereby obtaining a more uniform airflow velocity across the entire porous plate surface. This eliminates existing channeling and dead zones, ensuring that all mixed powders, especially those near the plasma reactor wall, can be uniformly fluidized and processed. The fan-shaped pore distribution specifically involves dividing the porous plate into a central region and an edge region. From the central region to the edge region, the pore density of the fan-shaped partition increases in a stepwise manner. By dividing the porous plate surface into fan-shaped partitions, the gas flow rate at different radial positions can be more precisely controlled.

[0062] Step S22: Maintaining the state of step S21, allow the second gas to pass through the holes of the porous plate and mix with the powder for secondary treatment. After the treatment is completed, active powder is obtained.

[0063] In step S22, the secondary treatment time is 20-40 min, the temperature of the plasma reactor chamber is 70-90℃, the working pressure is 50-200 Pa, the flow rate of the second gas is 100-500 sccm, and the second gas is a mixture of vaporized VTES (vinyltriethoxysilane) and argon, wherein the volume flow rate ratio of vaporized VTES to argon is 1:(1-5); preferably, the secondary treatment time is 30 min, the temperature of the plasma reactor chamber is 80℃, the working pressure is 125 Pa, the flow rate of the second gas is 300 sccm, and the volume flow rate ratio of vaporized VTES to argon is 1:3.

[0064] It should be noted that when vaporized VTES is introduced into the plasma reactor chamber at 80°C, the ethoxy group at one end of the VTES molecule undergoes a hydrolysis reaction with the hydroxyl group on the surface of the mixed powder particles to generate active silanol groups. The silanol groups then undergo dehydration condensation with the hydroxyl groups on the surface of the mixed powder particles to form strong Si-O-Si or Si-OM covalent bonds. After the reaction is completed, a molecular layer with terminal vinyl groups will be formed on the surface of the mixed powder particles, thus giving the mixed powder particles a chemical interface that can undergo free radical polymerization.

[0065] It is important to emphasize that the gas introduced through the porous plate causes the mixed powder to tumble, allowing each particle in the mixed powder to be treated by oxygen plasma and vaporization VTES. This enables each particle to achieve a global and uniform surface treatment and functionalization. At the same time, the gas introduced by the porous plate can effectively remove the heat generated by the plasma, preventing local overheating that could cause the thermoplastic resin particles in the mixed powder to melt or the micron-sized silver flakes, spherical nano-silver particles a, and spherical nano-silver particles b to sinter. Furthermore, the tumbling of the mixed powder increases the gas-solid contact area, making vapor deposition faster and more thorough.

[0066] It is worth noting that treating various powder particles in the mixed powder with oxygen plasma can unify the surface activity of materials with different chemical properties, thus providing a unified basis for the grafting of vinyl functional groups in the subsequent vapor deposition process, thereby ensuring the quality of surface activity treatment. In addition, the preliminary and secondary treatments of the mixed powder are carried out in a solvent-free dry environment, which avoids problems such as solvent residue, wastewater treatment, and particle re-agglomeration that may occur during the drying process in wet chemistry. The product has high purity and the process is more environmentally friendly.

[0067] Specifically, in step S3, the active powder, aliphatic hydrocarbon solvent, monomer mixture and AIBN are mixed to obtain a mixed solution, and then the mixed solution is filtered to obtain a solid product. The solid product is then washed and dried with ethanol to obtain a composite powder.

[0068] The mixed solution is obtained according to the following steps:

[0069] Step S31: The active powder, aliphatic hydrocarbon solvent and monomer mixture are initially mixed to obtain a preliminary mixture;

[0070] In step S31, the initial mixing speed is 100-300 rpm and the time is 30-60 min. The mass ratio of the monomer mixture, aliphatic hydrocarbon solvent, and active powder is (5-15):(30-60):100. The aliphatic hydrocarbon solvent is any one of n-hexane, n-heptane, and isooctane. The monomer mixture is a mixture of HEMA (hydroxyethyl methacrylate) and EGDMA (ethylene glycol dimethacrylate), wherein the mass ratio of HEMA to EGDMA is (95-98):(2-5). Preferably, the initial mixing speed is 200 rpm and the time is 45 min. The mass ratio of the monomer mixture, aliphatic hydrocarbon solvent, and active powder is 10:45:100. The aliphatic hydrocarbon solvent is n-hexane. The monomer mixture is a mixture of HEMA and EGDMA, wherein the mass ratio of HEMA to EGDMA is 96.5:3.5.

[0071] It should be noted that the initial mixing ensures that monomer molecules diffuse fully and adsorb onto the surface of the active powder particles, while maintaining the original morphology of the thermoplastic resin particles. In this process, the aliphatic hydrocarbon solvent prevents the thermoplastic resin particles from swelling or dissolving before polymerization, ensuring their existence as independent functional phases. HEMA and EGDMA can penetrate uniformly into the voids of the active powder during the initial mixing and come into close contact with the vinyl groups on the surface of the active powder particles.

[0072] Step S32: Mix the preliminary mixture with AIBN again to obtain a mixed solution.

[0073] In step S32, the amount of AIBN added is 0.5%-1.0% of the total mass of the monomer mixture in step S31, and the remixing temperature is 70-80℃, the rotation speed is 50-150rpm, the time is 6-12h, and the heating rate is 1-3℃ / min; preferably, the amount of AIBN added is 0.75% of the total mass of the monomer mixture in step S31, and the remixing temperature is 80℃, the rotation speed is 100rpm, the time is 8h, and the heating rate is 2℃ / min.

[0074] It should be noted that AIBN decomposes under heating to generate free radicals, which initiate the polymerization of HEMA and EGDMA. This polymerization reaction preferentially starts from the vinyl active sites on the surface of the active powder particles (graft polymerization). The grown polymer chains are interconnected through EGDMA, eventually forming a three-dimensional cross-linked polymer network that encapsulates and connects thermoplastic resin particles, micron-sized silver flakes, spherical silver nanoparticles a and b.

[0075] It is important to emphasize that HEMA, as the main monomer, has methacrylate groups in its molecular structure that are responsible for the polymerization reaction to form the main chain, while the hydroxyl groups in the side chains can endow the final polymer network with excellent hydrophilicity and toughness. EGDMA, as a crosslinking agent, has dimethacrylate functional groups that can establish covalent connection points between the growing polymer chains, transforming the linear polymer structure into a stable three-dimensional crosslinked network. This network is the structural skeleton that gives the composite powder macroscopic strength and locks all particles in it.

[0076] It should also be noted that after the solid product is cleaned, dried and pulverized, it becomes a composite powder with good flowability. The bonding force between the composite powder particles is upgraded from weak van der Waals forces to strong covalent bonds. The thermoplastic resin particles become tough nodes in the three-dimensional cross-linked polymer network, while the micron silver flakes, spherical silver nanoparticles a and b are firmly fixed in the three-dimensional cross-linked polymer network.

[0077] It is known that by preparing composite powder from mixed powder through steps S2 and S3, a strong covalent bond network is formed between the silver powder and thermoplastic resin particles in the mixed powder under the action of chemical methods. This gives each particle high interfacial bonding strength and structural integrity, further eliminating the risk of delamination caused by weak interfacial bonding. It can also more efficiently transfer and dissipate heat stress between the metal skeleton formed by silver powder and the thermoplastic resin phase, thereby giving the joint structure better resistance to temperature cycling fatigue. In addition, when the service temperature of the joint structure formed by composite powder increases, the thermoplastic resin bound by the chemical network cannot migrate after melting. It can continuously and accurately fill the pores caused by the growth of silver grains, dynamically inhibit grain coarsening, and stabilize the electrical and thermal properties of the joint structure. At the same time, the stability of the three-dimensional cross-linked polymer network of composite powder ensures that the low-temperature curing slurry prepared by composite powder has excellent storage stability and workability, and no sedimentation.

[0078] Specifically, in step S4, the composite powder is mixed with thermosetting resin and solvent to obtain a low-temperature curing slurry.

[0079] Furthermore, the prepared low-temperature curing slurry is coated onto the surface of the printed circuit board pads by screen printing, and cured at 200-250℃ and 10MPa for 30 minutes to form a joint structure; preferably, the curing is completed at 200℃ to form a joint structure.

[0080] Example 2:

[0081] The basic content is the same as in Example 1, except that:

[0082] The method for preparing a low-temperature curing slurry with enhanced temperature cycling resistance in this embodiment includes silver powder comprising, by mass percentage: 50% micron-sized silver flakes, 45% spherical nano-silver particles a, and 5% spherical nano-silver particles b.

[0083] The micron-sized silver flakes have a particle size of 5.0 μm, the spherical silver nanoparticles a have a particle size of 100 nm, and the spherical silver nanoparticles b have a particle size of 20 nm.

[0084] Example 3:

[0085] The basic content is the same as in Example 1, except that:

[0086] In this embodiment, a method for preparing a low-temperature curing slurry with enhanced temperature cycling resistance is described. Step S4 involves mixing the composite powder with a thermosetting resin and a solvent to obtain a low-temperature curing slurry. The prepared low-temperature curing slurry is then screen-printed onto the surface of the solder pads on a printed circuit board and cured at 250°C to form a joint structure.

[0087] Example 4:

[0088] The basic content is the same as in Example 1, except that:

[0089] This embodiment describes a method for preparing a low-temperature curing slurry with enhanced temperature cycling resistance, wherein the thermoplastic resin particles account for 12% of the mass of the low-temperature curing slurry, and the thermoplastic resin particles are polymethyl methacrylate particles.

[0090] Example 5:

[0091] The basic content is the same as in Example 1, except that:

[0092] This embodiment describes a method for preparing a low-temperature curing slurry with enhanced temperature cycling resistance, wherein the composite powder is silver nanoparticles with a particle size of 100 nm.

[0093] Example 6:

[0094] This embodiment describes a method for preparing a low-temperature curing slurry with enhanced temperature cycling resistance. The low-temperature curing slurry includes a thermosetting resin, a solvent, and a composite powder. After the thermosetting resin, solvent, and composite powder are mixed to form the low-temperature curing slurry, the low-temperature curing slurry is coated onto the surface of a printed circuit board using screen printing and cured at 200°C to form a joint structure.

[0095] Table 1 shows the performance tests of the joint structures formed by the low-temperature curing slurry in each embodiment:

[0096] Table 1

[0097]

[0098] In the above, ultrasonic testing was used to measure the weld ratio of the joint structure, the volume resistivity of the joint structure was measured according to GB / T15662-2019, the thermal conductivity of the joint structure was measured according to SJ / T 11725-2018, and the shear strength of the joint structure was measured according to YS / T 1009-2014. It is understood that the above measurement methods are well known to those skilled in the art, and will not be described in detail in this application.

[0099] It can be seen from the data in Table 1 that the electrical and thermal conductivity of the joint structure formed at 250℃ is significantly improved; compared with Example 5, the joint structure with silver particles of various shapes has better shear strength than the joint structure with a single silver particle; compared with Example 6, the joint structure formed by adding thermoplastic resin particles has less weld rate decay after temperature cycling, proving that thermoplastic resin particles can enhance the temperature cycling resistance of the joint.

[0100] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a low-temperature curing slurry with enhanced temperature cycling resistance, characterized in that, The low-temperature curing slurry comprises, by weight percentage: 1-20% thermoplastic resin particles, 0.1-5.0% thermosetting resin, 0.1-1.5% solvent, and the remainder silver powder; the preparation method of the low-temperature curing slurry with enhanced temperature cycling resistance includes the following steps: Step S1: Mix silver powder, including micron-sized silver flakes, spherical silver nanoparticles a and b, with thermoplastic resin particles to obtain a mixed powder. The silver powder comprises, by mass percentage: 10-45% spherical silver nanoparticles a, 1-5% spherical silver nanoparticles b, and the remainder micron-sized silver flakes. The micron-sized silver flakes have a particle size of 1-10 μm, the spherical silver nanoparticles a have a particle size of 50-100 nm, the spherical silver nanoparticles b have a particle size of 5-50 nm, and the thermoplastic resin particles have a particle size of 1-15 μm. Step S2: Perform surface-activation treatment on the mixed powder to obtain active powder; Step S3: Mix the active powder, aliphatic hydrocarbon solvent, monomer mixture and AIBN to obtain a mixed solution, then filter the mixed solution to obtain a solid product, and wash and dry the solid product with ethanol to obtain a composite powder; Step S4: Mix the composite powder with the thermosetting resin and solvent to obtain a low-temperature curing slurry after mixing. Step S2 specifically includes the following steps: Step S21: First, place the mixed powder on a porous plate inside the plasma reactor, and evacuate the plasma reactor chamber to below 10 Pa. Then, allow a first gas to pass through the porous plate with a pore size of 0.5-5 μm to agitate the mixed powder. Simultaneously, introduce oxygen to perform preliminary treatment on the mixed powder. After the treatment is completed, a preliminary powder is obtained. In step S21, the preliminary treatment time is 5-15 min, the working gas pressure of the plasma reactor chamber is 20-100 Pa, the power is 100-200 W, the oxygen flow rate is 50-200 sccm, the first gas flow rate is 500-2000 sccm, and the first gas is argon. Step S22: Maintaining the state of step S21, allow the second gas to pass through the holes of the porous plate and undergo secondary treatment with the mixed powder. After the treatment is completed, active powder is obtained. In step S22, the secondary treatment time is 20-40 min, the temperature of the plasma reactor chamber is 70-90℃, the working pressure is 50-200 Pa, the flow rate of the second gas is 100-500 sccm, and the second gas is a mixture of vaporized VTES and argon, wherein the volume flow rate ratio of vaporized VTES to argon is 1:(1-5).

2. The method for preparing the low-temperature curing slurry with enhanced temperature cycling resistance according to claim 1, characterized in that, The mixed solution is obtained according to the following steps: Step S31: The active powder, aliphatic hydrocarbon solvent and monomer mixture are initially mixed to obtain a preliminary mixture; Step S32: Mix the preliminary mixture with AIBN again to obtain a mixed solution.

3. The method for preparing the low-temperature curing slurry with enhanced temperature cycling resistance according to claim 2, characterized in that, In step S31, the initial mixing speed is 100-300 rpm and the time is 30-60 minutes. The mass ratio of the monomer mixture, aliphatic hydrocarbon solvent, and active powder is (5-15):(30-60):

100. The aliphatic hydrocarbon solvent is any one of n-hexane, n-heptane, and isooctane. The monomer mixture is a mixture of HEMA and EGDMA, wherein the mass ratio of HEMA to EGDMA is (95-98):(2-5). In step S32, the amount of AIBN added is 0.5%-1.0% of the total mass of the monomer mixture in step S31, and the remixing temperature is 70-80℃, the rotation speed is 50-150rpm, the time is 6-12h, and the heating rate is 1-3℃ / min.

4. The method for preparing the low-temperature curing slurry with enhanced temperature cycling resistance according to claim 1, characterized in that, The thermoplastic resin particles are any one of polyvinyl chloride, polyvinyl acetate, polyamide, polymethyl methacrylate, and natural rubber.

5. The method for preparing the low-temperature curing slurry with enhanced temperature cycling resistance according to claim 1, characterized in that, The thermosetting resin is any one or more of epoxy resin, polyurethane resin, vinyl resin, and silicone resin.

6. The method for preparing the low-temperature curing slurry with enhanced temperature cycling resistance according to claim 1, characterized in that, The solvent is any one of alcohol-based solvents, acetic acid solvents, hydrocarbon solvents, or mixtures thereof.

7. The method for preparing the low-temperature curing slurry with enhanced temperature cycling resistance according to claim 1, characterized in that, The low-temperature curing slurry further includes less than 1.5% curing agent and less than 0.5% curing accelerator by mass percentage. The curing agent is any one or more of dicyandiamide, acid anhydride and phenol resin, and the curing accelerator is any one or more of imidazole curing accelerator, amine curing accelerator, diazabicyclol curing accelerator and urea curing accelerator.

8. A low-temperature curing slurry with enhanced temperature cycling resistance, characterized in that, The low-temperature curing slurry is obtained using the preparation method described in claims 1-7.

Images