Halogen-free soldering material and method for producing the same

Abstract

This invention relates to the field of welding materials technology, specifically disclosing a halogen-free solder material and its preparation method. The solder material comprises solder alloy powder and a halogen-free flux; the solder alloy powder includes Bi, In, Ag, Cu, rare earth element Y, and Sn; the halogen-free flux includes hydrogenated rosin, a thixotropic agent, a corrosion inhibitor, a catalytic adsorbent, a composite organic acid activator, and a balance solvent. The preparation method includes surface grafting synthesis of the catalytic adsorbent, flux formulation, alloy powder atomization, and vacuum mixing. This method, through a novel adsorption-catalysis-slow release mechanism, simultaneously achieves excellent wettability, extremely low solder joint void ratio, high-strength interfacial bonding, and outstanding resistance to thermal fatigue and corrosion, all while ensuring complete halogen-free soldering. The resulting solder joints are full, bright, and free of solder beads, comprehensively solving the balance problem between activity, reliability, and processability in halogen-free soldering.

Description

Technical Field

[0001] This invention relates to the field of welding materials technology, and more specifically to a halogen-free solder material and its preparation method. Background Technology

[0002] With increasingly stringent global environmental regulations (such as the EU RoHS and the Halogen-Free Directive), the complete halogen-free transformation of electronic soldering materials has become an irreversible trend. In soldering materials, halogens (mainly chlorine and bromine) act as activators, effectively breaking down the oxide film on metal surfaces and significantly improving wettability. However, residual halogen compounds can severely corrode solder joints and substrates, leading to decreased circuit insulation resistance, ion migration, and even short-circuit failure, seriously threatening the long-term reliability of electronic products. Therefore, developing high-performance halogen-free soldering materials is a core challenge in this field.

[0003] Current halogen-free technologies primarily utilize organic acids (such as succinic acid and sebacic acid) and their derivatives to replace halogen reactivity. However, this approach has inherent contradictions: to achieve sufficient film removal capability, the organic acid content often needs to be increased, which in turn increases the corrosiveness of post-soldering residues, reduces surface insulation resistance (SIR), and generates more spatter and fumes during reflow soldering. Furthermore, pure organic acid systems are prone to decomposition and deactivation at high temperatures, resulting in limited ability to remove stubborn oxide layers and easily leading to defects such as poor wetting, incomplete soldering, and high void ratios. Although some studies have attempted to enhance activity by compounding multiple organic acids or adding amine compounds to low-temperature alloys such as Sn-Bi, it remains difficult to balance the relationship between activity, stability, and reliability.

[0004] On the other hand, to improve the mechanical properties of the solder joint itself, existing technologies often add trace amounts of metallic elements (such as Ag, Cu, rare earth elements, etc.) to the solder alloy to refine the grain size. However, these improvements focus on the solder interior and fail to fundamentally optimize the most critical "solder / substrate" interface reaction during the soldering process. The morphology and thickness of the intermetallic compound (IMC) layer formed at this interface directly determine the mechanical strength and long-term thermal fatigue resistance of the solder joint. Under halogen-free conditions, insufficient interface cleaning often leads to uneven and excessive growth of the IMC layer, becoming a weak point in the solder joint.

[0005] Therefore, there is an urgent need in this field for a completely new technical solution that not only completely eliminates halogens, but also goes beyond the traditional approach of simply adjusting the type and content of surfactants. It should start from the level of intervening in and optimizing the interface reaction process, and provide a halogen-free welding solution that can simultaneously achieve efficient interface cleaning, inhibit harmful IMC growth, and ensure long-term reliability. Summary of the Invention

[0006] The purpose of this invention is to provide a halogen-free solder material and its preparation method to solve the problems mentioned in the background art.

[0007] To achieve the above objectives, in one aspect, the present invention provides a halogen-free solder material, comprising, by weight percentage: 88.0-91.5% solder alloy powder and 8.5-12.0% halogen-free flux;

[0008] The solder alloy powder comprises, by weight percentage: Bi 10.0-18.0%, In 0.5-2.0%, Ag 0.3-0.7%, Cu 0.5-1.0%, rare earth element Y 0.01-0.05%, and Sn balance;

[0009] The halogen-free flux comprises, by weight percentage: 35-50% hydrogenated rosin, 1.0-2.5% thixotropic agent, 0.05-0.3% corrosion inhibitor, 1.0-3.0% catalytic adsorbent, 3.0-5.0% composite organic acid activator, and the balance being solvent;

[0010] The catalytic adsorbent is a mesoporous cerium-zirconium composite oxide with sebacic acid molecules grafted onto its surface, and its chemical formula is Ce. x Zr 1-x O2, where 0.5≤x≤0.8.

[0011] Preferably, the composite organic acid activator is composed of succinic acid and sebacic acid in a weight ratio of (1-3):1.

[0012] On the other hand, the present invention also provides a method for preparing the above-mentioned halogen-free solder material, comprising the following steps:

[0013] S1: Preparation of mesoporous Ce x Zr 1-x O2 powder was surface-treated and then dispersed in an organic solvent containing sebacic acid. The surface grafting reaction was carried out under reflux conditions. After the reaction was completed, the powder was separated and dried to obtain a catalytic adsorbent with surface-bonded sebacic acid.

[0014] S2: Heat and melt hydrogenated rosin, then add composite organic acid activator, corrosion inhibitor, solvent and catalytic adsorbent obtained in step S1 in sequence. After dispersing evenly, cool down and add thixotropic agent to form flux paste.

[0015] S3: Weigh each metal raw material according to the ratio, melt and stir evenly under a protective atmosphere, and then prepare solder alloy powder by gas atomization method;

[0016] S4: The solder alloy powder obtained in step S3 and the flux paste obtained in step S2 are mixed evenly under vacuum conditions in proportion to obtain the halogen-free solder material.

[0017] Preferably, in step S1, the surface grafting reaction temperature is 80-120℃ and the reaction time is 4-8h.

[0018] Preferably, in step S1, the mesoporous Ce x Zr 1-x O2 powder needs to undergo vacuum dehydration and activation treatment at 200-300℃ before the reaction.

[0019] Preferably, in step S1, the mesoporous Ce x Zr 1-x Methods for preparing O2 powder include:

[0020] Weigh out the appropriate molar amounts of cerium source and zirconium source, dissolve them together in deionized water, and prepare a transparent solution A with a total metal ion concentration of 0.1-0.5 mol / L;

[0021] Dissolve the template agent in another part of deionized water to prepare solution B, wherein the molar ratio of the template agent to the total metal ions is (0.1-0.5):1;

[0022] Under continuous stirring, solution B is slowly added dropwise to solution A, the pH value is adjusted to 8-11, and the mixture is stirred at a constant temperature of 40-60℃ for 2-6 hours to obtain a mixed sol.

[0023] The mixed sol was subjected to hydrothermal aging treatment to obtain a mesoporous precursor.

[0024] The mesoporous precursor was cooled, filtered, the filter cake was washed and dried to obtain a fluffy dry gel.

[0025] The dry gel was subjected to programmed temperature calcination, and the calcined dry gel was then ground and sieved to obtain the mesoporous Ce. x Zr 1-x O2 powder.

[0026] Preferably, the programmed temperature rise calcination includes:

[0027] Increase the temperature to 350-450℃ at a rate of 1-5℃ / min and hold for 2-4 hours; then continue to increase the temperature to 500-600℃ at the same rate and hold for 3-6 hours.

[0028] Preferably, in step S2, uniform dispersion is achieved by high-speed shear dispersion, with a rotation speed of 3000-6000 rpm, a time of 20-40 min, and a temperature of 70-85℃.

[0029] Preferably, the gas atomization method is ultrasonic gas atomization, the atomizing gas pressure is 4.0-5.5 MPa, and the atomization temperature is set to be 15-25°C lower than the liquidus temperature of the alloy melt.

[0030] Preferably, in step S4, the mixing is carried out in a double planetary mixer with a vacuum of -0.09 to -0.1 MPa and a mixing temperature of 25±5℃. The mixer first revolves at a speed of 10-20 rpm for 2-3 minutes, and then rotates at a speed of 500-700 rpm for 7-9 minutes.

[0031] The beneficial effects of this invention are as follows:

[0032] 1. Superior Welding Performance: Utilizing a synergistic "catalysis-adsorption-slow release" system, it achieves wetting capabilities surpassing traditional high-organic-acid formulations with extremely low total acid content. High wetting power and short zero-interaction time effectively prevent incomplete and cold welds. The weld joints are full and the void ratio is significantly reduced.

[0033] 2. Excellent solder joint reliability: Clean and efficient interfacial reaction promotes the formation of a thin and uniform IMC layer. Combined with the grain refinement and IMC growth inhibition effect of rare earth Y in the alloy, the solder joint has higher shear strength, tensile strength and excellent thermal fatigue resistance.

[0034] 3. Outstanding long-term chemical stability: There are very few residues after soldering, and due to the effective utilization and bonding of active ingredients, the content of free corrosive ions is extremely low, which has excellent corrosion resistance and migration resistance, meeting the stringent requirements of high-reliability electronic products.

[0035] 4. Excellent process adaptability and environmental friendliness: The solder paste has stable viscosity, good printability, and is resistant to slumping, making it suitable for assembling fine-pitch components. The entire system is halogen-free and has low volatile organic compounds, complying with environmental regulations. Attached Figure Description

[0036] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the following detailed description to explain the invention, but do not constitute a limitation thereof. In the drawings:

[0037] Figure 1 A schematic diagram of the solder joint after soldering using the solder material of Embodiment 1 of the present invention is shown. Detailed Implementation

[0038] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0039] It should be noted that all reagents and raw materials used in this invention are commercially available, and the reagents are of analytical grade.

[0040] Succinic acid is sourced from Shandong Landian Biotechnology Co., Ltd., and its product name is bio-based succinic acid.

[0041] Sebacic acid is sourced from Shanghai Kaisai Biotechnology Co., Ltd., and its product name is DC10.

[0042] Hydrogenated castor oil is sourced from the French Arkema Group and is marketed as CRAYVALLAC MT.

[0043] The poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer (P123) is from BASF AG, Germany, and is designated as Pluronic P123.

[0044] This invention provides a halogen-free solder material, comprising, by weight percentage: 88.0-91.5% solder alloy powder and 8.5-12.0% halogen-free flux;

[0045] The solder alloy powder comprises, by weight percentage: Bi 10.0-18.0%, In 0.5-2.0%, Ag 0.3-0.7%, Cu 0.5-1.0%, rare earth element Y 0.01-0.05%, and Sn balance;

[0046] The halogen-free flux comprises, by weight percentage: 35-50% hydrogenated rosin, 1.0-2.5% thixotropic agent, 0.05-0.3% corrosion inhibitor, 1.0-3.0% catalytic adsorbent, 3.0-5.0% composite organic acid activator, and the balance being solvent;

[0047] The catalytic adsorbent is a mesoporous cerium-zirconium composite oxide with sebacic acid molecules grafted onto its surface, with the chemical formula Ce. x Zr 1- x O2, where 0.5 ≤ x ≤ 0.8, the carboxyl group of sebacic acid molecule and the mesoporous Ce x Zr 1-x Hydroxyl groups or oxygen vacancies on the O2 surface are chemically bonded together to form oxide-organic acid complexes. Sebacic acid forms chemical bonds with hydroxyl / oxygen vacancies on the oxide surface through its carboxyl groups. This ensures that the organic acid molecules are firmly and uniformly anchored to the support surface, avoiding the problem of detachment caused by simple physical mixing. This stable "bonded state" of organic acid releases more gradually upon heating, and the unique local environment formed by its carboxyl groups and the support is believed to catalyze a reduction in the activation energy of reactions between organic acids and metal oxides (such as esterification), thereby improving the efficiency of film removal.

[0048] The solder alloy employs an optimized Sn-Bi-In-Ag-Cu-Y system, with Bi content controlled at 10-18% to balance low-temperature melting point and mechanical properties. In and trace amounts of rare earth Y are used to improve wettability and refine microstructure, respectively. The innovative catalytic adsorbent and composite organic acid activator in the halogen-free flux constitute a dual-active-source system. The catalytic adsorbent, as the core function, uses its high specific surface area and mesoporous structure to physically adsorb oxide film debris. Simultaneously, the surface-bonded organic acid provides precise and long-lasting cleaning capabilities at the interface through catalysis and controlled release, which is fundamental to achieving highly reliable soldering.

[0049] Rare earth element Y is used to refine the β-Sn grains of solder alloys and suppress the excessive growth of Cu6Sn5 intermetallic compounds. The addition of trace amounts of rare earth Y can, on the one hand, act as heterogeneous nucleation sites to refine the β-Sn grains and improve the toughness of the solder joint; on the other hand, Y atoms can segregate at the growth front of Cu6Sn5 IMC, inhibiting its excessive growth and coarsening, thereby obtaining a thin and uniform interfacial IMC layer, which greatly improves the thermal fatigue resistance of the solder joint.

[0050] Preferably, the composite organic acid activator is composed of succinic acid and sebacic acid in a weight ratio of (1-3):1. Succinic acid (a strong acid) provides rapid and effective initial film removal capability, while sebacic acid (a weak acid with good thermal stability) provides sustained activity and a wider process window. This ratio of succinic acid and sebacic acid, in synergy with the bonded acid on the catalytic adsorbent, ensures activity coverage throughout the entire process from the preheating zone to the reflux peak temperature, effectively avoiding welding defects caused by premature depletion or delayed activation of the activator.

[0051] On the other hand, the present invention also provides a method for preparing the above-mentioned halogen-free solder material, comprising the following steps:

[0052] S1: Preparation of mesoporous Ce x Zr 1-x O2 powder was surface-treated and then dispersed in an organic solvent containing sebacic acid. The surface grafting reaction was carried out under reflux conditions. After the reaction was completed, the powder was separated and dried to obtain a catalytic adsorbent with surface-bonded sebacic acid.

[0053] S2: Heat and melt hydrogenated rosin, then add composite organic acid activator, corrosion inhibitor, solvent and catalytic adsorbent obtained in step S1 in sequence. After dispersing evenly, cool down and add thixotropic agent to form flux paste.

[0054] S3: Weigh each metal raw material according to the ratio, melt and stir evenly under a protective atmosphere, and then prepare solder alloy powder by gas atomization method;

[0055] S4: Mix the solder alloy powder obtained in step S3 with the flux paste obtained in step S2 in a certain proportion under vacuum conditions to obtain halogen-free solder material.

[0056] In step S1, surface treatment can be performed using KH-550 silane coupling agent. After hydrolysis, the silanol groups of the silane coupling agent combine with the oxide surface, while the organic long chains extend to the outside, changing the powder surface from hydrophilic to oleophilic (hydrophobic), which greatly improves the compatibility with organic phases such as hydrogenated rosin.

[0057] Preferably, in step S1, the surface grafting reaction temperature is 80-120℃, and the reaction time is 4-8h. This condition ensures effective condensation reaction between carboxyl and hydroxyl groups while avoiding excessively high temperatures that could lead to organic acid decomposition or collapse of the support pore structure. This is key to obtaining a high grafting rate and highly active catalytic adsorbent.

[0058] Preferably, in step S1, mesoporous Ce x Zr 1-x The O2 powder needs to undergo vacuum dehydration and activation treatment at 200-300℃ before the reaction. Vacuum dehydration and activation can maximize the hydroxyl density on the carrier surface, creating conditions for the subsequent grafting reaction.

[0059] Preferably, in step S1, mesoporous Ce x Zr 1-x Methods for preparing O2 powder include:

[0060] Weigh out the appropriate molar amounts of cerium source and zirconium source, dissolve them together in deionized water, and prepare a transparent solution A with a total metal ion concentration of 0.1-0.5 mol / L;

[0061] Dissolve the template agent in another portion of deionized water to prepare solution B. The molar ratio of the template agent to the total metal ions is (0.1-0.5):1. The template agent can be hexadecyltrimethylammonium bromide (CTAB) or polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer (P123).

[0062] Under continuous stirring, solution B is slowly added dropwise to solution A, and the pH value is adjusted to 8-11 (dilute ammonia or dilute nitric acid can be used for adjustment). The mixture is stirred at a constant temperature of 40-60℃ for 2-6 hours. During this process, slow hydrolysis and condensation reactions occur, and the system gradually transforms into a transparent sol, resulting in a mixed sol.

[0063] The mixed sol is subjected to hydrothermal aging treatment, during which the template agent micelles guide inorganic species to self-assemble around it, forming a stable mesoporous precursor.

[0064] The mesoporous precursor was cooled, filtered, the filter cake was washed and dried to obtain a fluffy dry gel.

[0065] The dried gel was calcined at a programmed temperature, and the calcined dried gel was then ground and sieved to obtain mesoporous Ce. xZr 1-x O2 powder.

[0066] Preferably, the programmed temperature calcination includes:

[0067] Increase the temperature to 350-450℃ at a rate of 1-5℃ / min and hold for 2-4 hours; then continue increasing the temperature to 500-600℃ at the same rate and hold for 3-6 hours. The final calcination temperature is key to controlling the specific surface area and crystal structure. Lower temperatures (approximately 500℃) are beneficial for obtaining a higher specific surface area (>120 m² / g), but the crystallinity may be slightly lower; higher temperatures (approximately 600℃) result in more complete crystallization, but the specific surface area will decrease (approximately 80 m² / g).

[0068] Preferably, in step S2, uniform dispersion is achieved using high-speed shear dispersion at a rotation speed of 3000-6000 rpm for 20-40 minutes at a temperature of 70-85℃. High-speed shear dispersion (3000-6000 rpm) provides sufficient shear force to break up the agglomeration of nanoparticles, allowing them to achieve uniform nanoscale dispersion within the rosin matrix. The temperature control of 70-85℃ ensures a suitable viscosity of the matrix for dispersion while preventing premature reaction of the activator or evaporation of the solvent due to excessively high temperatures.

[0069] Preferably, the gas atomization method is ultrasonic gas atomization, with an atomizing gas pressure of 4.0-5.5 MPa and an atomization temperature set 15-25°C lower than the liquidus temperature of the alloy melt. Setting the atomization temperature 15-25°C below the liquidus temperature ensures that the alloy melt is in a semi-solid state during atomization. Under these conditions, the nascent Sn-rich solid phase and Bi-rich liquid phase form specific micro-agglomerations during rapid cooling, which is beneficial for forming a better solder joint microstructure in subsequent reflow soldering.

[0070] Preferably, in step S4, mixing is carried out in a dual planetary mixer under a vacuum of -0.09 to -0.1 MPa and a mixing temperature of 25±5℃. The mixer is first stirred at a planetary speed of 10-20 rpm for 2-3 minutes, then at a rotation speed of 500-700 rpm for 7-9 minutes. The vacuum environment removes air bubbles introduced during mixing, preventing solder voids. The two-step method—slow planetary stirring for macroscopic homogenization followed by rapid rotation for high-shear homogenization—ensures a high degree of microscopic uniformity between the metal powder and the organic paste, while avoiding mechanical damage to the alloy powder surface. This is a necessary step to obtain a stable and printable solder paste.

[0071] Example 1

[0072] S1: Preparation of the catalytic adsorbent:

[0073] S11: Mesoporous Ce 0.7 Zr0.3 Preparation of O2 powder;

[0074] (1) According to the chemical formula Ce 0.7 Zr 0.3 For O2 calculation, weigh out the corresponding molar amounts of cerium source (cerium nitrate hexahydrate) and zirconium source (zirconium oxychloride), dissolve them together in deionized water, and prepare a transparent solution A with a total metal ion concentration of 0.3 mol / L;

[0075] (2) Dissolve the template agent hexadecyltrimethylammonium bromide in another part of deionized water (the mass ratio of hexadecyltrimethylammonium bromide to deionized water is 1:25) to prepare solution B. The molar ratio of template agent to total metal ions is 0.3:1.

[0076] (3) Under continuous stirring, solution B was slowly added dropwise to solution A, and the pH value was adjusted to 10 using dilute ammonia (concentration 1.0 mol / L). The mixture was stirred at 50°C for 4 hours to obtain a mixed sol.

[0077] (4) The obtained mixed sol was transferred to a stainless steel reactor lined with polytetrafluoroethylene and subjected to hydrothermal aging treatment at 100°C for 30 hours.

[0078] (5) After aging, allow the product to cool naturally. Filter the resulting gel product and wash the filter cake alternately with deionized water and ethanol until no chloride ions (Cl) are detected in the filtrate using AgNO3 solution. - The washed wet gel was dried at 90°C for 18 hours to obtain a fluffy dry gel.

[0079] (6) The dry gel was placed in a muffle furnace and heated to 400°C at a rate of 3°C / min, and held for 3 h to completely decompose the template agent; then the temperature was increased to 550°C at the same rate and held for 5 h to obtain mesoporous Ce. 0.7 Zr 0.3 O2 powder.

[0080] S12: Mesoporous Ce 0.7 Zr 0.3 Activation of O2 powder

[0081] Mesoporous Ce 0.7 Zr 0.3 Before use, the O2 powder is placed in a vacuum oven and dehydrated and activated at 250°C for 3 hours, and then stored in a desiccator for later use.

[0082] S13: Powder Surface Amination Pretreatment

[0083] Mesoporous Ce 0.7 Zr 0.3O2 powder was dispersed in 100 mL of 95% (v / v) ethanol aqueous solution containing 0.15 g KH-550 silane coupling agent, refluxed and stirred at 70 °C for 5 h, and then centrifuged, washed and dried to obtain aminated powder.

[0084] S14: Take 10g of the above-mentioned aminated powder and place it in a three-necked flask equipped with a reflux condenser. Add 200mL of anhydrous ethanol and 5g of sebacic acid. Under nitrogen protection, heat the mixture in an oil bath to 90℃ and stir magnetically under reflux for 6h. After the reaction is complete, centrifuge to separate the solid product, wash it three times with anhydrous ethanol, and dry it in a vacuum drying oven at 80℃ for 12h to obtain a catalytic adsorbent grafted with sebacic acid.

[0085] S2: Preparation of halogen-free flux

[0086] Composition (by weight percentage): hydrogenated rosin (softening point 85℃) 45.0%, compound organic acid activator (by weight, succinic acid: sebacic acid = 2:1) 4.0%, catalytic adsorbent 2.0%, thixotropic agent (hydrogenated castor oil) 1.8%, corrosion inhibitor (benzotriazole) 0.2%, solvent (dipropylene glycol butyl ether) 47.0%.

[0087] Preparation method: Heat 65% hydrogenated rosin by mass to 130°C to melt, keep stirring, add composite organic acid activator and corrosion inhibitor in sequence, keep warm and stir for 20 minutes until completely dissolved and transparent to obtain high viscosity mother liquor;

[0088] The remaining 35% hydrogenated rosin was mixed with all the solvents and heated to 80°C to dissolve, resulting in a low-viscosity diluent. A catalytic adsorbent was added and dispersed at 5000 rpm for 30 minutes to obtain a pre-dispersed slurry.

[0089] Mix the pre-dispersed slurry with the high-viscosity mother liquor, and continue dispersing at 80°C and 5000 rpm for 30 minutes. Then, cool the system to 60°C, add the thixotropic agent, switch to paddle stirring, and stir at 300 rpm for 60 minutes until a uniform, fine, and glossy paste is formed. Cool to room temperature, seal and store to obtain the halogen-free flux.

[0090] S3: Preparation of solder alloy powder

[0091] Alloy composition (weight percentage): Sn 82.64%, Bi 15.0%, In 1.0%, Ag 0.5%, Cu 0.8%, Y 0.06%.

[0092] Preparation method: Weigh out high-purity (≥99.99%) metal according to the specified ratio, place it in a graphite crucible, put it into a vacuum induction melting furnace, and evacuate to... High-purity argon gas was then introduced to a slightly positive pressure, and the temperature was raised to 550°C. After melting, the mixture was electromagnetically stirred for 40 minutes and kept at 500°C. The melt was then introduced into an ultrasonic gas atomization device through a guide tube. The atomization medium was high-purity nitrogen gas, and the pressure was set to 5.0 MPa. The temperature of the atomization chamber was controlled to be 20°C lower than the liquidus line of the alloy (approximately 205°C), i.e., approximately 185°C. The powder was collected and sieved to obtain welding alloy powder with a particle size D50 of 30 μm.

[0093] S4: Preparation of solder materials

[0094] Take 90.0 wt% of welding alloy powder and 10.0 wt% of halogen-free flux, put them into the material cylinder of a double planetary vacuum mixer, close the material cylinder, evacuate to -0.095 MPa, and stir at 25℃ for 2.5 min at a revolution speed of 15 rpm to initially wet the powder. Then switch to rotation mode and stir at 600 rpm for 8 min to perform high shear homogenization. After stirring, break the vacuum and discharge the material to obtain solder material.

[0095] Example 2

[0096] S1: The preparation of the catalytic adsorbent is basically the same as that in Example 1 in terms of raw material components and preparation method, except that:

[0097] In step S11:

[0098] In step (1), the mesoporous cerium-zirconium composite oxide is Ce 0.5 Zr 0.5 O2, the total metal particle concentration of transparent solution A is 0.1 mol / L. In step (2), the template agent is P123, and the molar ratio of the template agent to the total metal ions is 0.1:1. In step (3), the pH is adjusted to 9 using 0.5 mol / L dilute nitric acid, and the solution is stirred at 40℃ for 6 h. In step (6), the temperature is increased to 350℃ at a rate of 1℃ / min and held for 4 h. Then, the temperature is increased to 500℃ at the same rate and held for 6 h to obtain mesoporous Ce. 0.5 Zr 0.5 O2 powder;

[0099] In step S12, the cells are dehydrated and activated at 200°C for 4 hours.

[0100] S2: Preparation of halogen-free flux:

[0101] Composition (by weight percentage): hydrogenated rosin (softening point 85℃) 42.0%, compound organic acid activator (weight ratio: succinic acid: sebacic acid = 3:1) 5.0%, catalytic adsorbent 1.0%, thixotropic agent (hydrogenated castor oil) 2.2%, corrosion inhibitor (benzotriazole) 0.15%, solvent (dipropylene glycol butyl ether) 49.65%.

[0102] Preparation method: The preparation method of the high viscosity mother liquor and the pre-dispersion is the same as in Example 1;

[0103] The pre-dispersed slurry was mixed with the high-viscosity mother liquor and dispersed at 3000 rpm for 40 minutes at 70°C using a high-speed homogenizer. The system was then cooled to 60°C, and the thixotropic agent and solvent were added. The mixture was then stirred with a paddle mixer at 300 rpm for 60 minutes until a uniform, fine, and glossy paste was formed. The paste was then cooled to room temperature, sealed, and stored to obtain the halogen-free flux.

[0104] S3: Preparation of solder alloy powder

[0105] Alloy composition (weight percentage): Sn 79.89%, Bi 18.0%, In 0.8%, Ag 0.3%, Cu 1.0%, Y 0.01%.

[0106] Preparation method: Weigh out high-purity (≥99.99%) metal according to the specified ratio, place it in a graphite crucible, put it into a vacuum induction melting furnace, and evacuate to... High-purity argon gas was then introduced to a slightly positive pressure, and the temperature was raised to 550°C. After melting, the mixture was electromagnetically stirred for 40 minutes and kept at 500°C. The melt was then introduced into an ultrasonic gas atomization device through a guide tube. The atomization medium was high-purity nitrogen gas, and the pressure was set to 4.5 MPa. The temperature of the atomization chamber was controlled to be 15°C lower than the liquidus line of the alloy (approximately 200°C), i.e., approximately 185°C. The powder was collected and sieved to obtain welding alloy powder with a particle size D50 of 30 μm.

[0107] S4: Preparation of solder materials

[0108] Take 89.0 wt% of welding alloy powder and 11.0 wt% of halogen-free flux, put them into the material cylinder of a double planetary vacuum mixer, close the material cylinder, evacuate to -0.09 MPa, stir at 20 rpm for 3 minutes at 20°C, then switch to rotation mode and stir at 500 rpm for 9 minutes to perform high shear homogenization. After stirring, break the vacuum, discharge the material to obtain solder material.

[0109] Example 3

[0110] S1: The preparation of the catalytic adsorbent is basically the same as that in Example 1 in terms of raw material components and preparation method, except that:

[0111] In step S11:

[0112] In step (1), the mesoporous cerium-zirconium composite oxide is Ce 0.8 Zr 0.2O2, the total metal particle concentration of transparent solution A is 0.5 mol / L. In step (2), the template agent is CTAB, and the molar ratio of the template agent to the total metal ions is 0.5:1. In step (3), the pH is adjusted to 11 using 0.5 mol / L dilute nitric acid, and the solution is stirred at 60℃ for 4 h. In step (6), the temperature is increased to 450℃ at a rate of 5℃ / min and held for 2 h. Then, the temperature is increased to 600℃ at the same rate and held for 3 h to obtain mesoporous Ce. 0.8 Zr 0.2 O2 powder;

[0113] In step S12, the cells are dehydrated and activated at 300°C for 2 hours.

[0114] In step S14, the oil bath heating temperature is 100℃ and the reaction time is 8h;

[0115] S2: Preparation of halogen-free flux:

[0116] Composition (by weight percentage): hydrogenated rosin (softening point 85℃) 48.0%, compound organic acid activator (weight ratio: succinic acid: sebacic acid = 1:1) 3.0%, catalytic adsorbent 3.0%, thixotropic agent (hydrogenated castor oil) 1.5%, corrosion inhibitor (benzotriazole) 0.3%, solvent (dipropylene glycol butyl ether) 44.2%.

[0117] Preparation method: The preparation method of the high viscosity mother liquor and the pre-dispersion is the same as in Example 1;

[0118] The pre-dispersed slurry was mixed with the high-viscosity mother liquor and dispersed at 6000 rpm for 20 minutes at 85°C using a high-speed homogenizer. The system was then cooled to 60°C, and the thixotropic agent and solvent were added. The mixture was then stirred with a paddle mixer at 300 rpm for 60 minutes until a uniform, fine, and glossy paste was formed. The paste was then cooled to room temperature, sealed, and stored to obtain the halogen-free flux.

[0119] S3: Preparation of solder alloy powder

[0120] Alloy composition (weight percentage): Sn 86.75%, Bi 10.0%, In 2.0%, Ag 0.7%, Cu 0.5%, Y 0.05%.

[0121] Preparation method: Weigh out high-purity (≥99.99%) metal according to the specified ratio, place it in a graphite crucible, put it into a vacuum induction melting furnace, and evacuate to... High-purity argon gas was then introduced to a slightly positive pressure, and the temperature was raised to 550°C. After melting, the mixture was electromagnetically stirred for 40 minutes and kept at 500°C. The melt was then introduced into an ultrasonic gas atomization device through a guide tube. The atomization medium was high-purity nitrogen gas, and the pressure was set to 5.5 MPa. The temperature of the atomization chamber was controlled to be 25°C lower than the liquidus line of the alloy (approximately 210°C), i.e., approximately 185°C. The powder was collected and sieved to obtain welding alloy powder with a particle size D50 of 30 μm.

[0122] S4: Preparation of solder materials

[0123] Take 91.0 wt% of welding alloy powder and 9.0 wt% of halogen-free flux, put them into the material cylinder of a double planetary vacuum mixer, close the material cylinder, evacuate to -0.1 MPa, stir at 30℃ for 2 minutes at a revolution speed of 10 rpm, then switch to rotation mode and stir at 700 rpm for 7 minutes to perform high shear homogenization. After stirring, break the vacuum, discharge the material, and obtain solder material.

[0124] Example 4

[0125] S1: The preparation of the catalytic adsorbent is basically the same as that in Example 1 in terms of raw material components and preparation method, except that:

[0126] In step S14, the oil bath heating temperature is 80℃, and the reaction time is 4 hours.

[0127] S2: Preparation of halogen-free flux:

[0128] Composition (by weight percentage): hydrogenated rosin (softening point 85℃) 40.0%, compound organic acid activator (weight ratio: succinic acid: sebacic acid = 2.5:1) 3.0%, catalytic adsorbent 4.5%, thixotropic agent (hydrogenated castor oil) 2.0%, corrosion inhibitor (benzotriazole) 0.25%, solvent (dipropylene glycol butyl ether) 50.75%.

[0129] Preparation method: The preparation method of the high viscosity mother liquor and the pre-dispersion is the same as in Example 1;

[0130] The pre-dispersed slurry was mixed with the high-viscosity mother liquor and dispersed at 4000 rpm for 20 minutes at 70°C using a high-speed homogenizer. The system was then cooled to 60°C, and the thixotropic agent and solvent were added. The mixture was then stirred with a paddle mixer at 300 rpm for 60 minutes until a uniform, fine, and glossy paste was formed. The paste was then cooled to room temperature, sealed, and stored to obtain the halogen-free flux.

[0131] S3: Preparation of solder alloy powder

[0132] Alloy composition (weight percentage): Sn 86.15%, Bi 12.0%, In 0.5%, Ag 0.4%, Cu 0.9%, Y 0.05%.

[0133] Preparation method: Weigh out high-purity (≥99.99%) metal according to the specified ratio, place it in a graphite crucible, put it into a vacuum induction melting furnace, and evacuate to... High-purity argon gas was then introduced to a slightly positive pressure, and the temperature was raised to 550°C. After melting, the mixture was electromagnetically stirred for 40 minutes and kept at 500°C. The melt was then introduced into an ultrasonic gas atomization device through a guide tube. The atomization medium was high-purity nitrogen gas, and the pressure was set to 4.0 MPa. The temperature of the atomization chamber was controlled to be 18°C ​​lower than the liquidus line of the alloy (approximately 208°C), i.e., approximately 190°C. The powder was collected and sieved to obtain welding alloy powder with a particle size D50 of 30 μm.

[0134] S4: Preparation of solder materials

[0135] Take 88.5 wt% of welding alloy powder and 11.5 wt% of halogen-free flux, put them into the material cylinder of a double planetary vacuum mixer, close the material cylinder, evacuate to -0.095 MPa, stir at 30℃ for 3 minutes at a revolution speed of 20 rpm, then switch to rotation mode and stir at 500 rpm for 9 minutes to perform high shear homogenization. After stirring is finished, break the vacuum, discharge the material, and obtain solder material.

[0136] Comparative Example 1

[0137] Compared with Example 1, the catalyst adsorbent in the flux formulation was replaced with an equal amount of hydrogenated rosin, and the total content of the composite organic acid activator was increased from 4.0% to 7.0%.

[0138] Comparative Example 2

[0139] Compared to Example 1, the catalyst adsorbent in the flux formulation was replaced with an equal amount of untreated fumed silica of the same particle size. (Specific surface area approximately 200 m² / g).

[0140] Comparative Example 3

[0141] Compared to Example 1, the catalyst adsorbent in the flux formulation was replaced with an equal amount of nano-titanium dioxide treated using the same grafting process. Mesoporous Ce 0.7 Zr 0.3 O2 powder was replaced with nano-titanium dioxide.

[0142] Comparative Example 4

[0143] Compared to Example 1, the welding alloy powder used was conventional Sn-58Bi eutectic alloy powder (Sn 42wt%, Bi 58wt%).

[0144] The solder materials prepared in the above embodiments and comparative examples were subjected to relevant performance tests. The test items and methods are as follows:

[0145] 1. Wettability Test: A wetting balance tester was used, referring to IPC-TM-650 2.4.45-1998 "Solder Paste - Wetting Test". The copper sheet was immersed in a solder bath at 235℃, and the maximum wetting force and zero-crossing time were measured. Each sample was measured 5 times and the average value was taken.

[0146] 2. Solderability Test: Solder paste was printed onto OSP-treated copper pads (0.6mm × 0.6mm) using a 10-gauge stencil, with a printing thickness of 0.12mm. Reflow soldering was performed under nitrogen protection (oxygen concentration <1000ppm) at a peak temperature of 235℃, with the liquidus level maintained for 60 seconds. Samples were prepared after cooling.

[0147] 3. Solder joint void rate: Solder joints were inspected using an X-ray inspection system (2D AXI), and the percentage of void area to the total solder joint area was calculated. The average value was taken from 20 solder joints.

[0148] 4. Solder joint shear strength: Using a universal testing machine and a dedicated micro solder joint shear fixture, shear tests were performed at a speed of 0.5 mm / s, referring to IPC-TM-650 2.4.44-1998 "Solder Paste - Viscosity Test". Fifteen solder joints were tested in each group, and the average value was taken.

[0149] 5. Interface IMC Thickness: Metallographic samples of the solder joints after reflow soldering were prepared, polished, etched, and the interface morphology was observed using a scanning electron microscope (SEM). The IMC layer was then measured. The average thickness was measured at 5 different fields of view.

[0150] 6. Thermal cycling reliability: Place the welded test plate in a thermal cycling chamber and hold it at -40℃ for 15 minutes. The solder joints were subjected to 1000 cycles at 125°C (15 min residence time), with a heating / cooling rate of 10°C / min. After the cycles, the shear strength of the solder joints was tested, and the retention rate relative to the initial strength was calculated.

[0151] 7. Surface Insulation Resistance (SIR): Refer to IPC-TM-650 2.6.3.7-2007 "Surface Insulation Resistance Test Method", using a standard comb electrode test plate, measure the surface insulation resistance value after 168 hours at 85℃ / 85%RH. Requirements .

[0152] The test results are shown in Table 1.

[0153] Table 1 Performance Test Results

[0154]

[0155] Results analysis:

[0156] 1. Wettability and Welding Performance: The wetting force of all embodiments was significantly higher than that of Comparative Examples 1 and 4, with shorter zero-crossing times and much lower weld void rates. This indicates that the dual-active-source system of the catalytic adsorbent + appropriate amount of composite acid of the present invention achieves superior wetting efficiency and welding quality with lower total acid content. Comparative Example 2 showed the worst performance, proving that simple physical filling is ineffective or even harmful. Comparative Example 3 was better than Comparative Example 1 but not as good as the embodiments, indicating... Composite oxides have unique catalytic advantages.

[0157] 2. Solder Joint Strength and Interface: The example exhibited the highest initial shear strength and the thinnest interfacial IMC layer (approximately 1.1-1.4 μm). Comparative Example 1 showed a slightly thicker IMC layer due to incomplete interface cleaning; Comparative Example 4 had the lowest strength due to the inherent brittleness of the alloy and poor IMC control. This demonstrates that optimized alloy composition (especially trace amounts of Y) works synergistically with efficient interface cleaning to achieve the best initial bond strength.

[0158] 3. Long-term reliability: After a rigorous 1000 thermal cycles, the shear strength retention rate of the examples all exceeded 93%, significantly higher than all comparative examples. This is directly attributed to the thinner, more stable IMC layer and the stabilizing effect of rare earth Y on the microstructure of the solder joints. Comparative example 4 showed the lowest retention rate, highlighting the fragility of high-Bi alloys under thermal stress.

[0159] 4. Electrochemical reliability: SIR values ​​of the examples far exceeding The standard demonstrates that the post-weld residue exhibits excellent insulation and low corrosivity. Comparative Example 1, due to its high organic acid content, may have more residue and a lower SIR. This illustrates the excellent balance achieved by this invention between high reactivity and low corrosivity.

[0160] Application examples

[0161] The solder material (solder paste) prepared in Example 1 was printed onto OSP-treated or gold-plated PCB pads using a stainless steel laser stencil. Subsequently, electronic components were precisely mounted onto the solder paste using a pick-and-place machine. The mounted PCB was then placed in a nitrogen-protected reflow oven for reflow soldering at a peak temperature of 235°C. After soldering, the soldered area was observed. Figure 1 As shown. By Figure 1As can be seen, after soldering, the PCB solder pads exhibit full and plump solder joints with no solder ball spatter, and a transparent and bright finish. The full solder joint formation demonstrates the flux system's extremely strong wetting activity and excellent alloy fluidity, ensuring the inherent high mechanical strength and reliable electrical connection of the solder joints. The absence of solder ball spatter indicates excellent rheological properties and thermal stability of the solder paste, providing a very wide process window that eliminates short-circuit risks from the source, significantly improving assembly yield. The transparent and bright solder joint surface reflects complete flux reaction, pure residues, high insulation, and a dense and uniform microstructure. This directly endows the product with excellent long-term corrosion resistance, resistance to electrochemical migration, and ease of optical inspection, fully meeting the stringent requirements of high reliability and high-quality appearance for high-end electronic products.

[0162] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details of the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, and these simple modifications all fall within the protection scope of the present invention. Furthermore, it should be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the present invention will not further describe the various possible combinations.

[0163] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A halogen-free solder material, characterized in that, By weight percentage: 88.0-91.5% solder alloy powder and 8.5-12.0% halogen-free flux; The solder alloy powder comprises, by weight percentage: Bi 10.0-18.0%, In 0.5-2.0%, Ag 0.3-0.7%, Cu 0.5-1.0%, rare earth element Y 0.01-0.05%, and Sn balance; The halogen-free flux comprises, by weight percentage: 35-50% hydrogenated rosin, 1.0-2.5% thixotropic agent, 0.05-0.3% corrosion inhibitor, 1.0-3.0% catalytic adsorbent, 3.0-5.0% composite organic acid activator, and the balance being solvent; The catalytic adsorbent is a mesoporous cerium-zirconium composite oxide with sebacic acid molecules grafted onto its surface, and its chemical formula is Ce. x Zr 1- x O2, where 0.5 ≤ x ≤ 0.8; The composite organic acid activator is composed of succinic acid and sebacic acid in a weight ratio of (1-3):

1.

2. A method for preparing halogen-free solder material according to claim 1, characterized in that, Includes the following steps: S1: Preparation of mesoporous Ce x Zr 1-x O2 powder was surface-treated and then dispersed in an organic solvent containing sebacic acid. The surface grafting reaction was carried out under reflux conditions. After the reaction was completed, the powder was separated and dried to obtain a catalytic adsorbent with surface-bonded sebacic acid. S2: Heat and melt hydrogenated rosin, then add composite organic acid activator, corrosion inhibitor, solvent and catalytic adsorbent obtained in step S1 in sequence. After dispersing evenly, cool down and add thixotropic agent to form flux paste. S3: Weigh each metal raw material according to the ratio, melt and stir evenly under a protective atmosphere, and then prepare solder alloy powder by gas atomization method; S4: The solder alloy powder obtained in step S3 and the flux paste obtained in step S2 are mixed evenly under vacuum conditions in proportion to obtain the halogen-free solder material.

3. The method for preparing halogen-free solder material according to claim 2, characterized in that, In step S1, the surface grafting reaction is carried out at a temperature of 80-120°C for 4-8 hours.

4. The method for preparing halogen-free solder material according to claim 2, characterized in that, In step S1, the mesoporous Ce x Zr 1-x O2 powder needs to undergo vacuum dehydration and activation treatment at 200-300℃ before the reaction.

5. The method for preparing halogen-free solder material according to claim 2, characterized in that, In step S1, the mesoporous Ce x Zr 1-x Methods for preparing O2 powder include: Weigh out the appropriate molar amounts of cerium source and zirconium source, dissolve them together in deionized water, and prepare a transparent solution A with a total metal ion concentration of 0.1-0.5 mol / L; Dissolve the template agent in another part of deionized water to prepare solution B, wherein the molar ratio of the template agent to the total metal ions is (0.1-0.5):1; Under continuous stirring, solution B is slowly added dropwise to solution A, the pH value is adjusted to 8-11, and the mixture is stirred at a constant temperature of 40-60℃ for 2-6 hours to obtain a mixed sol. The mixed sol was subjected to hydrothermal aging treatment to obtain a mesoporous precursor. The mesoporous precursor was cooled, filtered, the filter cake was washed and dried to obtain a fluffy dry gel. The dry gel was subjected to programmed temperature calcination, and the calcined dry gel was then ground and sieved to obtain the mesoporous Ce. x Zr 1-x O2 powder.

6. The method for preparing halogen-free solder material according to claim 5, characterized in that, The programmed heating and calcination includes: Increase the temperature to 350-450℃ at a rate of 1-5℃ / min and hold for 2-4 hours; then continue to increase the temperature to 500-600℃ at the same rate and hold for 3-6 hours.

7. The method for preparing halogen-free solder material according to claim 2, characterized in that, In step S2, uniform dispersion is achieved by high-speed shear dispersion, with a rotation speed of 3000-6000 rpm, a time of 20-40 min, and a temperature of 70-85℃.

8. The method for preparing halogen-free solder material according to claim 2, characterized in that, The atomization method is ultrasonic atomization, with an atomizing gas pressure of 4.0-5.5 MPa and an atomization temperature set to be 15-25°C lower than the liquidus temperature of the alloy melt.

9. The method for preparing halogen-free solder material according to claim 2, characterized in that, In step S4, the mixing is carried out in a double planetary mixer with a vacuum of -0.09 to -0.1 MPa and a mixing temperature of 25±5℃. The mixer first revolves at a speed of 10-20 rpm for 2-3 minutes, and then rotates at a speed of 500-700 rpm for 7-9 minutes.

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