A phase change toughener for epoxy molding compounds, its method of preparation and use

Abstract

This invention provides a phase change toughening agent for epoxy molding materials, its preparation method, and its uses. The phase change toughening agent is a microsphere with a core-shell structure. The microsphere has a cerium oxide core doped with rare earth elements and / or zirconium as the core and a doped zirconium oxide shell, wherein the molar ratio of cerium oxide to zirconium oxide is 1~100. This phase change toughening agent can be uniformly dispersed in an epoxy resin matrix. When the material is subjected to impact or stress, its particles can undergo phase change in a timely and appropriate manner, inducing a large number of controllable microcracks and volume effects, efficiently absorbing and dissipating energy, thereby greatly improving the toughness of the epoxy molding material while basically maintaining its strength and modulus.

Description

Technical Field

[0001] This invention relates to the field of chip packaging, and more specifically, to a phase change toughening agent for epoxy molding materials, its preparation method, and its uses. Background Technology

[0002] As electronic devices continue to evolve towards higher performance, smaller size, and higher reliability, the thermomechanical stress challenges faced by semiconductor packaging are becoming increasingly severe. Among various packaging forms, the Thin Quad Flat Package (LQFP) is widely used in microcontrollers, communication modules, and various medium- and high-density integrated circuits due to its good pin scalability, mature process technology, and excellent overall performance. In this packaging structure, epoxy molding compound encapsulates the chip, bonding wires, and lead frame into a single unit through a transfer molding process, playing a crucial role in electrical insulation, mechanical support, and environmental protection.

[0003] However, during temperature cycling, reflow soldering, and power cycling during device operation, significant thermal stress accumulates within the package due to the mismatch in the coefficients of thermal expansion between the chip (silicon, CTE≈2.5 ppm / °C), leadframe (copper alloy, CTE≈17 ppm / °C), and epoxy molding compound (typical CTE approximately 8–20 ppm / °C). This leads to a series of reliability issues, primarily including: Interface delamination: The bonding interface between the molding compound and the chip surface and lead frame peels off due to stress; Leadframe warping and decreased pin coplanarity: Thermal stress causes package structure deformation, affecting soldering quality; Chip cracking: Stress concentration causes microcracks in silicon chips, leading to circuit malfunction. Cracking of the molding compound itself: Cracks appear in the molding compound itself under low temperature or thermal shock, especially at the edges or in areas of stress concentration.

[0004] Currently, the industry mainly reduces the coefficient of thermal expansion of molding compounds by adding large amounts of inorganic fillers (such as fused silica) to epoxy resins. However, this method faces significant limitations in thin, large-size packages like LQFPs: high filler content leads to increased melt viscosity and decreased fluidity, easily causing incomplete filling and porosity defects; at the same time, excessive filler can impair material toughness, flexural strength, and interfacial adhesion, and exacerbate package warpage, potentially introducing new failure risks.

[0005] In addition, CN116670821A discloses several low-stress agents, such as low-stress agent 1: silicone oil, FZ-3730; low-stress agent 3: acrylonitrile butadiene rubber, CTBN 1 0 0 8 SP; low-stress agent 4: silicone resin, KR-480; and low-stress agent 5: epoxidized polybutadiene. These low-stress agents are all high-molecular-weight organic compounds. Silicone oil is prone to seepage during actual use, forming flow marks and pitting on the chip surface, while CTBN has a high energy storage modulus and is prone to cracking after being applied in a blister pack.

[0006] To fundamentally alleviate the thermal stress problem caused by CTE mismatch, this invention provides a novel low-stress epoxy molding material solution. This solution effectively regulates the stress response behavior of the material during thermal cycling by introducing a special low-stress additive into the epoxy resin matrix. This low-stress additive can absorb and dissipate some of the energy generated by differences in thermal expansion, significantly reducing stress accumulation at the interface and within the matrix, thereby inhibiting crack initiation and propagation, and reducing failure modes such as interface delamination, chip damage, and molding compound cracking.

[0007] The low-stress epoxy molding material provided by this invention maintains good flowability and processability while also possessing a low coefficient of thermal expansion and high stress buffering capacity. It can significantly improve the structural integrity and long-term reliability of LQFP packages under temperature alternating environments, providing an important material solution for high-reliability electronic devices. Summary of the Invention

[0008] To address the problems existing in the prior art, this invention provides a phase change toughening agent for epoxy molding materials, its preparation method, and an epoxy molding material containing the phase change toughening agent. The phase change toughening agent is a core-shell structured doped cerium-based oxide microsphere. The microsphere has a doped cerium oxide (CeO2) core and a doped zirconium oxide (ZrO2) shell. Through synergistic design of components and structure, precise control of phase change temperature, phase change driving force, and toughening behavior is achieved. Doping stabilizes the metastable phase at room temperature, causing it to undergo a stress-induced phase change under stress, consuming energy. The interface between the particles and epoxy is optimized: certain doping elements can improve the interfacial bonding between the CeO2 and ZrO2 core-shell structured microspheres and the epoxy resin, improving stress transfer efficiency. The ultimate goal is to prepare a doped microsphere that is uniformly dispersed in an epoxy resin matrix. When the material is subjected to impact or stress, its particles can undergo phase transformation in a timely and appropriate manner, inducing a large number of controllable microcracks and volume effects, efficiently absorbing and dissipating energy, thereby greatly improving the toughness of epoxy molding materials while basically maintaining strength and modulus.

[0009] According to a first aspect of the present invention, a phase change toughening agent for epoxy molding materials is provided, which is a microsphere having a core-shell structure, wherein the microsphere has a core of cerium oxide (CeO2) doped with rare earth elements and / or zirconium elements and a shell of doped zirconium oxide (ZrO2), wherein the molar ratio of cerium oxide to zirconium oxide is 1 to 100, preferably 5 to 40, more preferably 10 to 40.

[0010] Preferably, based on the total weight of the core layer, the molar content of cerium oxide in the core layer is 50% to 99.5%, more preferably 60% to 99.5%, and even more preferably 65% ​​to 99.5%, with the balance being dopant.

[0011] Preferably, the dopant in the core layer is an oxide of a rare earth element and / or an oxide of zirconium, wherein the rare earth element is one or more selected from Y, Gd, Sm and La.

[0012] Preferably, in the core layer, the amount of rare earth element doping is 0.5% to 50% of the molar amount of CeO2.

[0013] Preferably, in the core layer, the doping amount of element Zr is 0.5% to 50% of the molar amount of CeO2.

[0014] The purpose of doping the core layer is to introduce oxygen vacancies, lower the phase transition energy barrier, stabilize the metastable phase, and regulate its phase transition initiation temperature to the target range of -55°C to 125°C.

[0015] Preferably, the molar content of zirconium oxide (ZrO2) in the shell is 70%~99.5%, with the remainder being dopants.

[0016] Preferably, the dopant in the shell is one or more selected from oxides of Y, oxides of Gd, and oxides of Sm.

[0017] The purpose of doping in the shell is to induce a reversible martensitic phase transformation (t→m) in the tetragonal phase (t-ZrO2) of stable zirconium oxide under stress or temperature triggering, resulting in a significant volume expansion effect and a synergistic or sequential response with the core phase transformation.

[0018] Preferably, the phase change toughening agent is in the form of regular spherical or near-spherical particles.

[0019] Preferably, the D50 particle size of the phase change toughening agent is 8~30μm.

[0020] According to a second aspect of the present invention, a method for preparing the phase change toughening agent is provided, comprising the following steps: 1) Synthesis of the nucleus: Cerium salt and the first dopant precursor were dissolved in deionized water, the first precipitant was added, and the mixture was subjected to hydrothermal reaction at 120~180°C. After centrifugation, washing and drying, the doped CeO2 nucleus microspheres were obtained. 2) Shell coating: The doped CeO2 core microspheres obtained in step 1) are ultrasonically dispersed in a medium, zirconium salt and the second dopant precursor are added, and the second precipitant is slowly added dropwise under continuous stirring, controlling the pH value between 8 and 10, and reacting at 40 to 80°C to uniformly deposit the doped Zr(OH)4 on the core surface; after the reaction is completed, the microspheres are centrifuged, washed, dried, and calcined in air at 400 to 600°C for 2 to 4 hours to obtain crystallized core-shell structured microspheres.

[0021] Preferably, the first dopant precursor is a water-soluble, particularly water-soluble salt; more preferably, the first dopant precursor is selected from one or more of the following: nitrates, halide salts, sulfates, acetates, perchlorates, trifluoromethanesulfonates, and oxy salts of Y, Gd, Sm, La, and Zr.

[0022] Preferably, the first precipitant is selected from urea or hexamethylenetetramine.

[0023] Preferably, the hydrothermal reaction in step 1) is carried out for 2 to 12 hours.

[0024] Preferably, the medium in step 2) is a mixture of ethanol and water; more preferably, the weight ratio of ethanol to water is 1 to 20.

[0025] Preferably, the second precipitant is one or more selected from ammonia water, NaOH aqueous solution and KOH aqueous solution, and its concentration is 0.2~0.7M.

[0026] Preferably, the precipitation reaction in step 2) is carried out for 1 to 6 hours.

[0027] According to a third aspect of the present invention, an epoxy molding material is provided, comprising an epoxy resin, a coupling agent, a curing agent, a curing accelerator, and a phase change toughening agent according to the present invention.

[0028] Preferably, the content of the phase change toughening agent is 70% to 85% based on the total weight of the epoxy molding material.

[0029] Preferably, the epoxy resin is o-cresol formaldehyde epoxy resin. For example, Shandong Shengquan SQCN700 series o-cresol formaldehyde epoxy resin.

[0030] Preferably, the amount of epoxy resin used is 8% to 20% based on the total weight of the epoxy molding material.

[0031] The curing agent is a conventionally used curing agent in the art, with phenolic curing agents used in the epoxy molding compound field. For example, linear phenol-formaldehyde resin produced by Shandong Shengquan.

[0032] Preferably, the amount of curing agent used is 4% to 7% based on the total weight of the epoxy molding material.

[0033] Preferably, the silane coupling agent is one or more selected from γ-aminopropyltriethoxysilane (KH-550), γ-glycidoxypropyltrimethoxysilane (KH-560), γ-mercaptopropyltriethoxysilane (KH-580) and γ-mercaptopropyltrimethoxysilane (KH-590).

[0034] Preferably, the amount of silane coupling agent used is 0.3% to 0.7% based on the total weight of the epoxy molding material.

[0035] Preferably, the curing accelerator is one or more selected from triphenylphosphine (TPP), 4-methyl-2-phenylimidazolium (2P4MZ), 2-phenylimidazolium (2PZ), 2-ethyl-4-methylimidazolium (2E4MZ), 2-methylimidazolium (2MZ), and 2-phenyl-4-hydroxyimidazolium (2PHZ).

[0036] Preferably, the amount of curing accelerator is 0.1% to 0.3% based on the total weight of the epoxy molding material.

[0037] According to a fourth aspect of the present invention, a method for preparing an epoxy molding material according to the present invention is provided, comprising the following steps: a) Powder surface treatment: Mix silane coupling agent and phase change toughening agent and react to modify the surface of phase change toughening agent to obtain a surface-modified phase change toughening agent; b) Mixing: Place epoxy resin, curing agent, surface-modified phase change toughening agent, and curing accelerator in a mixing device and mix thoroughly to obtain a mixture; c) Mixing: Place the mixture in a two-roll mill or extruder for mixing to fully plasticize it and ensure that the toughening agent is evenly dispersed; d) Cooling and crushing: Cool and crush the material from step c) to obtain epoxy molding material.

[0038] Beneficial effects High-performance composite materials can be prepared by dispersing doped core-shell structured microspheres according to the present invention in an epoxy molding compound matrix at an addition amount of 70wt%~85wt%. This microsphere toughening agent can achieve a dual toughening mechanism: the martensitic phase transformation of the shell ZrO2 under stress consumes energy, and the phase transformation of the core CeO2 initiates controllable microcracks; the two are coupled through the stress field at the core-shell interface to produce a synergistic toughening effect.

[0039] The epoxy molding material of the present invention exhibits excellent adhesive compatibility with interface materials such as chips, lead frames, and silver paste, maintaining high adhesive strength retention under high temperature and humidity conditions, effectively preventing interface delamination failure. During repeated thermal cycling (e.g., thermal shock testing from -65°C to 150°C), the phase transformation toughening mechanism continuously dissipates energy, effectively resisting microcrack propagation caused by thermal fatigue and extending the lifespan of packaged devices. The controllable microcrack network induced by the CeO2 core layer helps release accumulated thermal stress, preventing the propagation of fatigue cracks. Attached Figure Description

[0040] Figure 1 The particle size distribution diagram of the phase change toughening agent obtained according to Preparation Example 1 is shown.

[0041] Figure 2 The particle size distribution diagram of the phase change toughening agent obtained according to Preparation Example 2 is shown. Detailed Implementation

[0042] The present invention will now be described in detail with reference to embodiments. It should be noted that the embodiments described below are only for illustrating the present invention and are not intended to limit the scope of the present invention.

[0043] Test methods Particle size D50: Tested using a Baxter laser particle size analyzer.

[0044] Elemental analysis: The proportion of metal elements was determined by inductively coupled plasma optical emission spectroscopy (ICP-OES), with the sample diluted 100-fold before testing.

[0045] Preparation Example 1 Phase change toughening agents were prepared using a sequential solvent-gel method, consisting of Gd-doped CeO2@Y-doped ZrO2 core-shell microspheres, through the following steps. 1) Preparation of the core layer: Cerium nitrate hexahydrate (Ce(NO3)3·6H2O) and gadolinium nitrate hexahydrate (Gd(NO3)3·6H2O) were dissolved in deionized water at a molar ratio of Ce∶Gd = 85∶15. Urea was added in an amount twice the sum of the molar amounts of cerium and gadolinium. The mixture was hydrothermally reacted at 160℃ for 8 hours. After centrifugation, washing, and drying, the product was calcined at 500℃ for 2 hours to obtain Gd-doped CeO2 microspheres with an average particle size of approximately 16 μm.

[0046] 2) Preparation of the core-shell structure: The Gd-doped CeO2 microspheres obtained in step 1) were ultrasonically dispersed in an ethanol / water mixed solvent (ethanol to water weight ratio of 8:2). Zirconium oxychloride (ZrOCl2·8H2O) and yttrium nitrate (Y(NO3)3·6H2O) were added, controlling the molar ratio of Zr to Y to be 95:5, and the molar ratio of Ce to Zr to be 15. Ammonia was slowly added dropwise to adjust the pH to 9.5, and the reaction was stirred at 60℃ for 4 hours. After centrifugation, washing, and drying, the product was calcined at 550℃ for 3 hours to obtain the core-shell structured phase change toughening agent.

[0047] Figure 1 The particle size distribution of the phase change toughening agent obtained above is shown, where D50 = 16.6 μm.

[0048] Table 1 shows the elemental determination results of the phase change toughening agent using inductively coupled plasma optical emission spectroscopy (ICP-OES). According to the results in Table 1, the molar content of Ce in the core layer is 85.4%, the molar content of Zr in the shell layer is 95.1%, and the molar ratio of zirconium to cerium is approximately 1:18.1.

[0049] Table 1: Elemental determination results in phase change toughening agents by inductively coupled plasma optical emission spectroscopy (ICP-OES)

[0050] Preparation Example 2 Phase change toughening agents were prepared using a sequential solvent-gel method, consisting of Gd-doped CeO2@Y-doped ZrO2 core-shell microspheres, through the following steps. 1) Preparation of the core layer: Cerium nitrate hexahydrate (Ce(NO3)3·6H2O) and gadolinium nitrate hexahydrate (Gd(NO3)3·6H2O) were dissolved in deionized water at a molar ratio of Ce∶Gd = 99∶1. Urea was added in an amount twice the sum of the molar amounts of cerium and gadolinium. The mixture was hydrothermally reacted at 160℃ for 8 hours. After centrifugation, washing, and drying, the product was calcined at 500℃ for 2 hours to obtain Gd-doped CeO2 microspheres with a particle size D50 of approximately 13.5 μm.

[0051] 2) Preparation of the core-shell structure: The Gd-doped CeO2 microspheres obtained in step 1) were ultrasonically dispersed in an ethanol / water mixed solvent (ethanol to water weight ratio of 8:2). Zirconium oxychloride (ZrOCl2·8H2O) and yttrium nitrate (Y(NO3)3·6H2O) were added, controlling the molar ratio of Zr to Y to be 99:1, and the molar ratio of Ce to Zr to be 10. Ammonia was slowly added dropwise to adjust the pH to 9.5, and the reaction was stirred at 60℃ for 4 hours. After centrifugation, washing, and drying, the product was calcined at 550℃ for 3 hours to obtain a core-shell structured phase change toughening agent.

[0052] Figure 2 The particle size distribution of the phase change toughening agent obtained above is shown, where D50 = 13.70 μm.

[0053] Table 2 shows the results of cerium and zirconium analysis using inductively coupled plasma optical emission spectroscopy (ICP-OES). According to the results in Table 2, the molar content of Ce in the core is 99.0%, the molar content of Zr in the shell is 98.9%, and the molar ratio of zirconium to cerium is approximately 1:11.1.

[0054] Table 2: Elemental determination results in phase change toughening agents by inductively coupled plasma optical emission spectroscopy (ICP-OES)

[0055] Preparation Example 3 Phase change toughening agents, consisting of Gd-doped CeO2@Gd-doped ZrO2 core-shell microspheres, were prepared using a sequential solvent-gel method via the following steps. 1) Preparation of the core layer: Cerium nitrate hexahydrate (Ce(NO3)3·6H2O) and gadolinium nitrate hexahydrate (Gd(NO3)3·6H2O) were dissolved in deionized water at a molar ratio of Ce∶Gd = 70∶30. Urea was added in an amount twice the sum of the molar amounts of cerium and gadolinium. The mixture was hydrothermally reacted at 160℃ for 8 hours. After centrifugation, washing, and drying, the product was calcined at 500℃ for 2 hours to obtain Gd-doped CeO2 microspheres with an average particle size of approximately 8.2 μm. The particle size was measured using a Baxter laser particle size analyzer.

[0056] 2) Preparation of the core-shell structure: The Gd-doped CeO2 microspheres obtained in step 1) were ultrasonically dispersed in an ethanol / water mixed solvent (ethanol to water weight ratio of 8:2). Zirconium oxychloride (ZrOCl2·8H2O) and gadolinium nitrate hexahydrate (Gd(NO3)3·6H2O) were added, controlling the molar ratio of Zr to Y to be 98:2, and the molar ratio of Ce to Zr to be 30. Ammonia was slowly added dropwise to adjust the pH to 9.5, and the reaction was stirred at 60℃ for 4 hours. After centrifugation, washing, and drying, the product was calcined at 550℃ for 3 hours to obtain a core-shell structured phase change toughening agent with D50 = 8.37 μm.

[0057] The molar content of Ce in the core layer is 70.4%, the molar content of Zr in the shell layer is 96.2%, and the molar ratio of zirconium to cerium is approximately 1:32.9.

[0058] Preparation Example 4 Phase change toughening agents were prepared using a sequential solvent-gel method, consisting of Sm-doped CeO2@Sm-doped ZrO2 core-shell microspheres, through the following steps. 1) Preparation of the core layer: Cerium nitrate hexahydrate (Ce(NO3)3·6H2O) and samarium nitrate hexahydrate (Sm(NO3)3·6H2O) were dissolved in deionized water at a molar ratio of Ce∶Sm = 90∶10. Urea was added in an amount twice the sum of the molar amounts of cerium and samarium, and the mixture was hydrothermally reacted at 160℃ for 8 hours. After centrifugation, washing, and drying, the product was calcined at 500℃ for 2 hours to obtain Sm-doped CeO2 microspheres with a particle size D50 of approximately 27.1 μm.

[0059] 2) Preparation of the core-shell structure: The Sm-doped CeO2 microspheres obtained in step 1) were ultrasonically dispersed in an ethanol / water mixed solvent (ethanol to water weight ratio of 8:2). Zirconium oxychloride (ZrOCl2·8H2O) and samarium nitrate hexahydrate (Sm(NO3)3·6H2O) were added, controlling the molar ratio of Zr to Sm to be 80:20 and the molar ratio of Ce to Zr to be 20. Ammonia was slowly added dropwise to adjust the pH to 9.5, and the reaction was stirred at 60℃ for 4 hours. After centrifugation, washing, and drying, the product was calcined at 550℃ for 3 hours to obtain a core-shell structured phase change toughening agent with D50 = 27.9 μm.

[0060] The molar content of Ce in the core layer is 88.5%, the molar content of Zr in the shell layer is 78.7%, and the molar ratio of zirconium to cerium is approximately 1:19.7.

[0061] Comparative Preparation Example 1 CeO2@ZrO2 core-shell microspheres were prepared in the same manner as in Example 1, except that no doping was performed.

[0062] Comparative Preparation Example 2 Commercially available spherical silica (Lianrui): average particle size 20μm.

[0063] Examples 1 to 4, and Comparative Examples 1 to 3 Preparation and performance testing of epoxy molding compound compositions: a) The phase change toughening agents prepared in Preparation Examples 1 to 4 above, the microspheres obtained in Comparative Preparation Examples 1 and 2, and the silane coupling agent were mixed and reacted in a mixer to obtain a surface-modified phase change toughening agent. b) Epoxy resin, a phase change toughening agent with surface modification of the curing agent, and a curing accelerator are mixed in a mixer to obtain a premix. Then, the premix is ​​extruded through an extruder (extrusion conditions: the temperature of the test extruder is room temperature-room temperature-80℃-120℃, screw speed is 200 rpm, and feed rate is 6 kg / h) to fully plasticize the premix and ensure that the toughening agent is uniformly dispersed. c) Cool, crush, and sieve to obtain epoxy molding compound material.

[0064] The specific formula and performance test results are shown in Table 3 below.

[0065]

[0066] o-Cresol-formaldehyde epoxy resin: SQCN700 series o-cresol-formaldehyde epoxy resin produced by Shandong Shengquan; Phenolic curing agent: Linear phenol-formaldehyde resin produced by Shandong Shengquan.

[0067] Results analysis: 1. Processability: The flowability and gel time of Examples 1 to 4, as well as Comparative Examples 1 to 3, all meet the requirements of the molding process.

[0068] 2. Thermomechanical properties: Coefficient of linear expansion (CTE): The CTE1 and CTE2 of the epoxy molding compound materials prepared in Examples 1 to 4 were significantly lower than those in Comparative Examples 1 to 3. More importantly, the CTE2 (above the glass transition region) of the epoxy molding compound materials prepared in Examples 1 to 4 remained at a low level, indicating that the phase transition volume effect of the core-shell microspheres provided effective dimensional stability at high temperatures. The epoxy molding compound material prepared in Comparative Example 1 (undoped microspheres) had a higher CTE2, indicating that doping effectively suppressed excessive expansion.

[0069] Flexural strength and modulus: The flexural strength of the epoxy molding compounds prepared in Examples 1 to 4 was higher than that of Comparative Example 1 (undoped) and Comparative Example 3 (pure resin), demonstrating that the doped core-shell microspheres maintained a reinforcing effect while toughening the material. The retention rate of modulus at high temperature (260℃) was also better than that of Comparative Example 1, showing better thermal stability.

[0070] 3. Reliability: Ion purity: The electrical conductivity of the epoxy molding compound materials prepared in Examples 1 to 4 is far below the conventional standard of 5 μS / cm, which meets the stringent requirements of semiconductor packaging for ionic impurity content.

[0071] Thermal Shock Performance (TST): The epoxy molding compounds prepared in Examples 1 to 4 exhibited excellent thermal cycling reliability, with chip interface delamination area ratios significantly lower than the 1% threshold after 500 and 1000 TST cycles. In contrast, the epoxy molding compound prepared in Comparative Example 1 (using undoped microspheres) failed after 500 TST cycles, and the epoxy molding compound prepared in Comparative Example 2 (using commercially available SiO2) also failed prematurely. This directly demonstrates that core-shell structured microspheres with precisely controlled phase transition behavior through doping can more effectively buffer thermal stress and suppress interface delamination, exhibiting significantly superior performance compared to undoped similar materials and traditional fillers.

[0072] The CeO2@ZrO2 microspheres with a specific doped core-shell structure described in this invention, used as a toughening agent in epoxy molding compounds, can efficiently dissipate stress through tunable phase transition behavior under thermal cycling conditions ranging from -55°C to 125°C. This significantly improves the material's toughness and high-temperature dimensional stability without compromising its processability, strength, or ionic purity. Ultimately, this enables packaged devices to achieve unprecedented resistance to extreme temperature shocks, fully meeting the requirements of high-reliability electronic packaging.

[0073] Test methods Gelation time determination method: Place 1.0g of epoxy molding compound material on a heating plate at 175±1℃. Start timing when the sample melts, and press continuously with a flat spatula. Stop timing when it becomes gelled.

[0074] Spiral flow length: At 175℃ and with the transmission pressure set to 6.9MPa, epoxy molding compound powder is injected into a spiral flow length test mold preheated to the same temperature through a transfer molding press, and the length of the longest continuous point is read.

[0075] Method for determining the coefficient of linear expansion (CTE): Using a transfer molding machine, the molding resin composition is injected and molded under the conditions of mold temperature 175°C, injection pressure 9.8 MPa, and curing time 120 seconds to obtain a test piece with a length of 15 mm × width of 4 mm × thickness of 4 mm. After curing the test piece at 175°C for 4 hours, the CTE is measured using a thermomechanical analysis device in compression mode under the conditions of a measurement temperature range of 0°C to 320°C and a heating rate of 5°C / min. Based on the measurement results, the average coefficient of linear expansion from 40°C to 80°C is calculated as CTE1, and the average coefficient of linear expansion from 190°C to 230°C is calculated as CTE2.

[0076] Bending strength test method: GB / T9341 is adopted, the load application speed is 2mm / min, and the load value is read when the cured epoxy molding compound sample breaks.

[0077] Flexural modulus determination method: The TA DMA850 dynamic thermomechanical analyzer was used for testing. The test mode was three-point bending mode with fixed amplitude oscillation, preload force of 0.5N, heating rate of 3℃ / min, 25~280℃, and sample size of 3*15*50mm. Modulus data were read at 25℃ and 260℃.

[0078] Measurement of ion content of powder: Weigh 5g of powder into 95ml of measured deionized water using a balance, stir with a magnetic stir bar for 30 minutes, and then measure the conductivity. Subtract the conductivity value of the deionized water to get the conductivity value of the powder sample, which is generally ≤5μS / cm.

[0079] LQFP chips were packaged using a high-temperature molding and curing method (curing at 175°C for 90 minutes, then at 175°C for 6-8 hours). The LQFP chips were then subjected to a thermal shock test (TST) repeatedly, with the chips maintained at -55°C for 10 minutes followed by a 10-minute maintenance period at 125°C. Ultrasonic images of the chips were obtained using an ultrasonic scanner (Nordson, D9650) after 500 (TST500) and 1000 (TST1000) cycles of this procedure. In areas of peeling (void, missing adhesive), the signal is very strong due to near total reflection of ultrasound in air / vacuum, typically appearing as a bright color. A threshold was set at a point that clearly distinguishes between "good adhesion" and "defects (peeling)". All pixels with signal strength exceeding this threshold were identified by the software as "defects" (i.e., peeling areas). Total peeling area...

Claims

1. A phase change toughening agent for epoxy molding materials, comprising microspheres with a core-shell structure, wherein the microspheres have cerium oxide doped with rare earth elements and / or zirconium as the core and doped zirconium oxide as the shell, wherein... The molar ratio of cerium oxide to zirconium oxide is 1 to 100.

2. The phase change toughening agent for epoxy molding materials according to claim 1, wherein, The molar ratio of cerium oxide to zirconium oxide is 5~40. And / or, based on the total weight of the core layer, the molar content of cerium oxide in the core layer is 50% to 99.5%, with the remainder being dopants; And / or, the dopants in the core layer are oxides of rare earth elements and / or oxides of zirconium, wherein the rare earth elements are one or more selected from Y, Gd, Sm and La.

3. The phase change toughening agent for epoxy molding materials according to claim 1, wherein, In the core layer, the doping amount of the rare earth element is 0.5% to 50% of the molar amount of CeO2; And / or, in the core layer, the amount of Zr doped is from 0.5% to 50% of the molar amount of CeO2; And / or, based on the total weight of the core layer, the molar content of cerium oxide in the core layer is 60% to 99.5%, with the remainder being dopants.

4. The phase change toughening agent for epoxy molding materials according to any one of claims 1 to 3, wherein, The molar content of zirconium oxide (ZrO2) in the shell is 70%~99.5%, with the remainder being dopants; And / or, the dopant in the shell is one or more selected from oxides of Y, oxides of Gd and oxides of Sm; And / or, the phase change toughening agent is in the form of regular spherical or near-spherical particles.

5. The phase change toughening agent for epoxy molding materials according to claim 1, wherein, The phase change toughening agent has a D50 particle size of 8~30μm.

6. A method for preparing a phase change toughening agent according to any one of claims 1 to 5, comprising the following steps: 1) Synthesis of the nucleus: Cerium salt and the first dopant precursor were dissolved in deionized water, the first precipitant was added, and the mixture was subjected to hydrothermal reaction at 120~180°C. After centrifugation, washing and drying, the doped CeO2 nucleus microspheres were obtained. 2) Shell coating: The doped CeO2 core microspheres obtained in step 1) are ultrasonically dispersed in a medium, zirconium salt and the second dopant precursor are added, and the second precipitant is slowly added dropwise under continuous stirring, controlling the pH value between 8 and 10, and reacting at 40 to 80°C to uniformly deposit the doped Zr(OH)4 on the core surface; after the reaction is completed, the microspheres are centrifuged, washed, dried, and calcined in air at 400 to 600°C for 2 to 4 hours to obtain crystallized core-shell structured microspheres.

7. The method for preparing a phase change toughening agent according to claim 6, wherein, The first dopant precursor is selected from one or more of the following: nitrates, halide salts, sulfates, acetates, perchlorates, trifluoromethanesulfonates, and oxy salts of Y, Gd, Sm, La, and Zr. And / or, the first precipitant is selected from urea or hexamethylenetetramine; And / or, the hydrothermal reaction in step 1) is carried out for 2 to 12 hours; And / or, the medium in step 2) is a mixture of ethanol and water; And / or, the second precipitant is one or more selected from ammonia water, NaOH aqueous solution and KOH aqueous solution, with a concentration of 0.2~0.7M; And / or, the precipitation reaction in step 2) is carried out for 1 to 6 hours.

8. An epoxy molding material comprising epoxy resin, coupling agent, curing agent, curing accelerator, and phase change toughening agent according to any one of claims 1 to 5.

9. The epoxy molding material according to claim 8, wherein, Based on the total weight of the epoxy molding material, the content of the phase change toughening agent is 70%~85%; And / or, the epoxy resin is o-cresol epoxy resin; And / or, based on the total weight of the epoxy molding material, the amount of epoxy resin used is 8% to 20%; And / or, the curing agent is a phenolic curing agent; And / or, based on the total weight of the epoxy molding material, the amount of the curing agent is 4% to 7%; And / or, the silane coupling agent is one or more selected from γ-aminopropyltriethoxysilane (KH-550), γ-glycidoxypropyltrimethoxysilane (KH-560), γ-mercaptopropyltriethoxysilane (KH-580) and γ-mercaptopropyltrimethoxysilane (KH-590); And / or, based on the total weight of the epoxy molding material, the amount of silane coupling agent is 0.3% to 0.7%; And / or, the curing accelerator is one or more selected from triphenylphosphine (TPP), 4-methyl-2-phenylimidazolium (2P4MZ), 2-phenylimidazolium (2PZ), 2-ethyl-4-methylimidazolium (2E4MZ), 2-methylimidazolium (2MZ) and 2-phenyl-4-hydroxyimidazolium (2PHZ); And / or, based on the total weight of the epoxy molding material, the amount of the curing accelerator is 0.1% to 0.3%.

10. A method for preparing the epoxy molding material according to claim 8 or 9, comprising the following steps: a) Powder surface treatment: Mix silane coupling agent and phase change toughening agent and react to modify the surface of phase change toughening agent to obtain a surface-modified phase change toughening agent; b) Mixing: Place epoxy resin, curing agent, surface-modified phase change toughening agent, and curing accelerator in a mixing device and mix thoroughly to obtain a mixture; c) Mixing: Place the mixture in a two-roll mill or extruder for mixing to fully plasticize it and ensure that the toughening agent is evenly dispersed; d) Cooling and crushing: Cool and crush the material from step c) to obtain epoxy molding material.

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