High-reliability flux for semiconductor bumping process

Abstract

The application discloses a kind of high reliability fluxes of semiconductor Bumping process, it is related to the field of fluxing material, by mass percentage, the flux includes the following synergistic components: film forming agent 18-28%, the film forming agent is made of modified rosin resin and epoxy-modified cardanol by quality 4:1-6:1 Compound is formed;Temperature trigger type double-layer core-shell microencapsulated active agent 10-18%;Hollow polymer microspheres 0.8-3%;Composite antioxidant 0.2-0.6%;The rest is storage stable type environmental protection composite solvent.The application realizes the long-term storage stability of microcapsule zero broken capsule, no settlement at room temperature by the synergistic effect of film forming agent, temperature trigger type double-layer core-shell microencapsulated active agent, hollow polymer microspheres and storage stable type environmental protection composite solvent;The melting point gradient of double-layer core-shell structure is accurately matched with reflow temperature zone, active component and corrosion inhibitor are completely released in activation section and reflow section, and oxidation film removal and UBM layer anti-overcorrosion are simultaneously completed.

Description

Technical Field

[0001] This invention relates to the field of flux materials, specifically a high-reliability flux for semiconductor bumping processes. Background Technology

[0002] In the semiconductor packaging field, wafer-level bumping is one of the key technologies for achieving high-density, high-reliability chip interconnection. With the continuous improvement of chip performance requirements for high-end applications such as 5G, artificial intelligence, and automotive-grade electronics, 8-inch and 12-inch wafer-level solder bumping processes have become the mainstream technology. Among them, flux, as the core auxiliary material in the bumping process, directly determines the forming quality, void ratio, bridging defects, and long-term reliability of subsequent packaging of solder bumps.

[0003] At the specific process level, currently widely used fluxes need to be compatible with lead-free Sn-Ag-Cu solder and reflow soldering of Ti / Cu / Ni structure UBM layers. However, existing flux systems generally have the following technical defects: First, insufficient storage stability. The active ingredients in traditional solvent-based fluxes are prone to react with film-forming agents at room temperature or cause microcapsule rupture and delamination, failing to meet the stringent requirements of semiconductor production lines for long-term material stability. Second, during reflow soldering, the release temperature range of the active components is poorly matched with the solder melting window, easily causing premature release that corrodes the UBM layer or delayed release that leads to insufficient activation, resulting in problems such as cold solder joints and high void ratios. Third, as the bump spacing continues to shrink, bridging defects are very likely to occur after the solder melts, and existing fluxes lack effective physical isolation methods. Fourth, cleaning post-soldering residues is difficult. Conventional fluxes require cleaning with organic solvents, which not only damages the wafer passivation layer but also makes it difficult to meet the automotive-grade high-temperature and high-humidity reliability requirements for ionic residues. Summary of the Invention

[0004] Based on this, the purpose of this invention is to provide a high-reliability flux for semiconductor bumping processes, in order to solve the technical problems of poor storage stability, high void ratio and UBM corrosion caused by the mismatch between the active release temperature range and the solder melting window of general fluxes.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a high-reliability flux for semiconductor bumping processes, applied to 8-inch or 12-inch wafer-level solder bump fabrication processes, adapted for reflow soldering of lead-free Sn-Ag-Cu solder and Ti / Cu / Ni structure UBM layers, characterized in that, by mass percentage, the flux comprises the following synergistic components:

[0006] Film-forming agent 18-28%, wherein the film-forming agent is compounded from modified rosin resin and terminal epoxy modified cashew phenol in a mass ratio of 4:1-6:1;

[0007] The temperature-triggered double-core-shell microencapsulated activator is 10-18%, and the melting point window of the encapsulation layer of the temperature-triggered double-core-shell microencapsulated activator is matched with the activation and reflow temperature range of Bumping reflow soldering.

[0008] Hollow polymer microspheres, 0.8-3%, wherein the melting point of the microspheres is higher than the peak temperature of reflow soldering;

[0009] Compound antioxidant 0.2-0.6%;

[0010] The remainder is a storage-stable environmentally friendly composite solvent, the solubility of which is matched with the compatibility of the film-forming agent and the micro-encapsulated surfactant coating layer.

[0011] The modified rosin resin is maleic anhydride addition-modified hydrogenated rosin with an acid value of 120-160 mgKOH / g and a softening point of 245-250℃. Its softening point is 5-15℃ higher than the melting point of the outer coating layer of the temperature-triggered double-layer core-shell micro-encapsulated surfactant. During the reflux preheating stage, the modified rosin resin forms a continuous protective film before the micro-encapsulated surfactant to avoid splashing or system stratification after the surfactant is released.

[0012] The terminal epoxy modified cashew phenol is a product of cashew phenol by addition to ethylene oxide followed by terminal epoxy capping, with a hydroxyl value of 80-120 mgKOH / g. Its terminal epoxy groups can form hydrogen bonds with the amino groups on the surface of hollow polymer microspheres, stably dispersing the microspheres in the flux system. It does not settle or separate after 6 months of storage at room temperature.

[0013] The temperature-triggered double-core-shell microencapsulated activator has a double-core-shell structure. The inner encapsulation layer is a food-grade microcrystalline wax with a melting point of 230-235℃, and the outer encapsulation layer is a modified rosin homologous to the film-forming agent with a melting point of 235-240℃. The core material is the active component, and the total mass ratio of the core material to the double-layer encapsulation layer is 3:1.

[0014] The core active component of the temperature-triggered double-layer core-shell microencapsulated surfactant is composed of tetradecanoic acid, hydroxyethyl imidazoline and benzotriazole corrosion inhibitor in a mass ratio of 5:3:1. During the reflux process, the active component and the corrosion inhibitor are released simultaneously, and the removal of the oxide film of the UBM layer and the corrosion protection of the metal layer are completed simultaneously to avoid over-corrosion.

[0015] The hollow polymer microspheres are surface-amino-modified polystyrene-divinylbenzene hollow microspheres with a melting point of 265-275℃, a particle size of 15-25μm, and a hollow cavity ratio of 45-55%. During reflow, the microspheres physically isolate adjacent solder bumps in a solid state, completely avoiding small-pitch bump bridging defects.

[0016] The hollow polymer microspheres are loaded with a composite antioxidant homologous to the system, with a loading amount of 8-12% of the microsphere mass. The release temperature of the composite antioxidant is perfectly matched with the release temperature of the microencapsulated activator. At the reflow peak temperature, the microsphere cavity ruptures due to the surface tension of the molten solder, and the antioxidant is released simultaneously.

[0017] The storage-stable environmentally friendly composite solvent is composed of diethylene glycol butyl ether acetate and propylene glycol methyl ether acetate in a mass ratio of 2.5:1. It has a boiling point of 190-230℃ at normal pressure and a solubility parameter of 18-20 (J / cm³) at 25℃. 0.5 The difference in solubility parameters between the solvent and the film-forming agent is ≤2, and the difference in solubility parameters between the solvent and the temperature-triggered double-layer core-shell microencapsulated surfactant is ≥5. At room temperature, the solvent can completely dissolve the film-forming agent but not the microencapsulated layer.

[0018] The flux comprises, by weight percentage: 20% maleic anhydride-modified hydrogenated rosin, 4% terminal epoxy-modified cashew nut shell phenol, 15% temperature-triggered double-layer core-shell microencapsulated activator, 2% surface amino-modified hollow polymer microspheres loaded with antioxidants, 0.4% composite antioxidant, 38% diethylene glycol butyl ether acetate, and 20.6% propylene glycol methyl ether acetate.

[0019] An application of a high-reliability flux in semiconductor bumping processes, characterized in that the flux is applied to the preparation of wafer solder bumps, and the reflow soldering process is divided into four stages matched with the component properties:

[0020] Preheating section: 150-180℃, hold for 60-90s, during which the film-forming agent forms a continuous preliminary protective film;

[0021] Activation stage: 180-230℃, heat preservation for 40-60s, the outer coating of the micro-encapsulated surfactant softens, while the inner layer remains intact and locked in activation;

[0022] Reflux section: 230-250℃, peak temperature 245-250℃, residence time 50-70s, the double-layer coating of micro-encapsulated surfactants completely melts and releases active components, while the hollow microspheres rupture and release antioxidants.

[0023] Cooling section: rapidly cools to room temperature to complete the protrusion molding.

[0024] In summary, the present invention has the following main advantages: Through the synergistic effect of film-forming agents, temperature-triggered double-layer core-shell microencapsulated activators, hollow polymer microspheres, and storage-stable environmentally friendly composite solvents, the present invention achieves long-term storage stability with zero microcapsule rupture and no sedimentation at room temperature; by utilizing the melting point gradient of the double-layer core-shell structure to precisely match the reflux temperature zone, the active components and corrosion inhibitors are locked in the activation section and completely released in the reflux section, simultaneously completing oxide film removal and UBM layer over-corrosion prevention; the hollow polymer microspheres remain solid throughout the reflux process, physically eliminating small-pitch bump bridging defects, and the antioxidants loaded in their cavities are released simultaneously at the peak temperature, controlling the average void ratio of bumps to below 0.25%; simultaneously, the introduction of terminal epoxy-modified cashew phenol reduces post-weld pure water rinsing residue to as low as 42-58 ppm, and the hydrogen bond crosslinking with the amino groups on the microsphere surface further enhances the dispersion stability of the system. Tests show that the flux of this invention exhibits a bump shear strength reduction rate of ≤3.5% after 10 reflows and a leakage current change rate of ≤8.5% under 1000h high temperature and high humidity conditions, which can meet the high reliability mass production requirements of automotive-grade and advanced process wafer-level bumping processes. Attached Figure Description

[0025] Figure 1 This is a flowchart illustrating the preparation process of the base liquid in this invention.

[0026] Figure 2 This is a flowchart illustrating the dispersion process of the functional components of the present invention. Detailed Implementation

[0027] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0028] This invention relates to a high-reliability flux for semiconductor bumping processes, primarily suitable for 8-inch / 12-inch wafer-level solder bump fabrication processes. It can be matched with reflow soldering scenarios for lead-free Sn-Ag-Cu solder and Ti / Cu / Ni structure UBM layers. By mass percentage, the core components are: 18-28% film-forming agent, 10-18% temperature-triggered double-layer core-shell micro-encapsulation activator, 0.8-3% hollow polymer microspheres, 0.2-0.6% composite antioxidant, and the balance being a storage-stable environmentally friendly composite solvent.

[0029] The film-forming agent of the present invention is composed of modified rosin resin and terminal epoxy modified cashew phenol in a mass ratio of 4:1-6:1. The two components achieve the functions of high-temperature film formation protection, system compatibility and stability, and post-weld washability with pure water.

[0030] The modified rosin resin is a maleic anhydride-modified hydrogenated rosin. The preparation method is as follows: hydrogenated rosin is put into a stainless steel reactor under nitrogen protection, heated to 180°C until completely melted, and maleic anhydride is added at a molar ratio of 1:0.8 between hydrogenated rosin and maleic anhydride. The reaction is carried out at the temperature and stirred for 3 hours to complete the addition reaction. The product is then discharged at 120°C to obtain the target product. The product has an acid value of 120-160 mgKOH / g and a ring and ball softening point of 245-250°C, which is 5-15°C higher than the melting point of the outer coating layer of the subsequent micro-encapsulated activator.

[0031] In the reflow preheating section at 150-180℃, the modified rosin resin can soften in advance to form a continuous and dense protective film. At this time, the micro-encapsulated activator has not yet reached the release temperature, which can completely avoid the problems of splashing and system stratification when the active components are released later. At the same time, it can provide isolation protection for the solder and UBM layer throughout the reflow process, preventing external moisture and impurities from entering.

[0032] Terminally epoxy-modified cashew nut shell powder is a product obtained by adding cashew nut shell powder to ethylene oxide and then capping it with terminal epoxy groups. The preparation method is as follows: cashew nut shell powder and ethylene oxide are added to a high-pressure reactor at a molar ratio of 1:2, and 0.3% potassium hydroxide catalyst is added. The temperature is raised to 130℃, the reaction pressure is controlled at 0.2MPa, and the reaction is maintained for 2 hours to obtain hydroxyethyl cashew nut shell powder. After cooling to 80℃, epichlorohydrin is added at a molar ratio of 1.2:1 to hydroxyethyl cashew nut shell powder, and sodium hydroxide is added simultaneously. The reaction is maintained for 4 hours to complete the capping. After washing with water to separate the layers and removing excess epichlorohydrin by vacuum distillation, the target product is obtained. The hydroxyl value of the product is 80-120 mgKOH / g.

[0033] The terminal epoxy groups can form a stable hydrogen bond crosslinking network with the amino groups on the surface of the subsequent hollow polymer microspheres, uniformly anchoring the microspheres in the flux system. This fundamentally solves the problems of microsphere sedimentation and system stratification, achieving no sedimentation or stratification after 6 months of storage at room temperature. At the same time, the long carbon chain structure of cashew phenol can improve the wettability of the flux to the solder and UBM layer. Its non-polar structure allows for complete cleaning with pure water after soldering, leaving no ion residue and avoiding damage to the wafer passivation layer by organic solvents.

[0034] The temperature-triggered double-core-shell micro-encapsulated activator has a double-core-shell structure, and the melting point window of its encapsulation layer matches the activation and reflow temperature range of Bumping reflow soldering.

[0035] The inner coating layer is food-grade microcrystalline wax with a melting point of 230-235℃, and the outer coating layer is modified rosin homologous to the film-forming agent with a melting point of 235-240℃; the core material is the active component, and the total mass ratio of the core material to the double coating layer is 3:1.

[0036] The preparation method employs a melt dispersion and cooling solidification process, with the following steps:

[0037] Core material premixing: Tetradecanoic acid, hydroxyethyl imidazoline and benzotriazole corrosion inhibitor are added to a stirred tank at a mass ratio of 5:3:1, heated to 120℃ until completely melted, and stirred and mixed evenly to obtain the active components of the core material;

[0038] Inner layer encapsulation preparation: Food-grade microcrystalline wax is heated to 240℃ until completely melted, and the above-mentioned core material active components are added. The mixture is stirred and dispersed evenly at 500-800 r / min to form an oil phase. Separately, a 0.5% (w / w) Tween-80 emulsifier aqueous solution is prepared and heated to 240℃ to form an aqueous phase. The oil phase is slowly added to the aqueous phase, and high-speed shear emulsification is performed at 2000 r / min for 30 min to form a uniform emulsion. Then, the temperature is slowly lowered to 220℃ at a rate of 1℃ / min, and the microcrystalline wax is completely solidified to form a single-layer microcapsule encapsulated in the inner layer.

[0039] Outer layer coating preparation: Modified rosin homologous to the film-forming agent is heated to 245℃ until completely melted, and the above-mentioned monolayer microcapsule emulsion is added. The mixture is kept warm and stirred for 30 min to uniformly coat the surface of the monolayer microcapsules. Then, it is slowly cooled to room temperature at a rate of 2℃ / min. After filtration, washing with deionized water, and vacuum drying, a double-layer core-shell microencapsulated activator is obtained. The particle size of the product can be stably controlled within 5-20 μm, which can be directly adapted to semiconductor-grade coating processes.

[0040] The dual-core-shell structure enables gradient temperature control and precise release. In the reflow activation section at 180-230℃, the outer modified rosin only softens without melting, while the inner microcrystalline wax remains solid, completely locking in the internal active components and preventing premature release of active components that could corrode the wafer's UBM layer. When the temperature rises above 230℃ in the reflow section, the inner microcrystalline wax and outer modified rosin melt sequentially according to their melting point gradient, completely releasing the core material's active components. This matches the 217-240℃ melting temperature range of Sn-Ag-Cu solder, providing continuous activation capabilities during the critical solder melting window. Simultaneously, the activator and corrosion inhibitor in the core material are released, completing the removal of the UBM layer oxide film and the corrosion protection of the metal layer. This thoroughly avoids insufficient activation leading to poor soldering or excessive activation leading to over-corrosion of the UBM layer.

[0041] The hollow polymer microspheres have the dual functions of physical isolation to prevent bridging and precise release of antioxidants at high temperatures, and their melting point is higher than the peak temperature of reflow soldering.

[0042] The hollow polymer microspheres are surface-amino-modified polystyrene-divinylbenzene hollow microspheres with a melting point of 265-275℃, which is higher than the reflux peak temperature of 245-250℃, ensuring that they remain solid throughout the reflux process. The particle size is 15-25μm, and the hollow cavity ratio is 45-55%. The cavity is loaded with a composite antioxidant homologous to the system, with a loading amount of 8-12% of the microsphere mass.

[0043] The preparation method uses seed swelling polymerization, and the steps are as follows:

[0044] Preparation of polystyrene seed microspheres: Monodisperse polystyrene seed microspheres were prepared by dispersion polymerization, with the particle size controlled at 2-3 μm;

[0045] Preparation of hollow microspheres: Seed microspheres were dispersed in an ethanol aqueous solution, and styrene monomer, divinylbenzene crosslinking agent, toluene porogen, and azobisisobutyronitrile initiator were added. The mixture was heated to 70℃ and polymerized for 24 h to obtain porous polymer microspheres. Subsequently, the porogen was removed by ethanol extraction to obtain hollow polymer microspheres. The particle size was controlled to be 15-25 μm and the hollow cavity ratio was controlled to be 45-55% by adjusting the monomer ratio.

[0046] Surface amino modification: Hollow microspheres were dispersed in an ethanol solution, and aminosilane coupling agent KH550 was added. The temperature was raised to 60℃ and kept at the temperature for 4 hours. After filtration, washing with ethanol and vacuum drying, surface amino modified hollow polymer microspheres were obtained. The melting point of the product was 265-275℃ as determined by differential scanning calorimetry.

[0047] Antioxidant loading: The composite antioxidant (antioxidant 1010: antioxidant 168 = 1:1) is dissolved in dichloromethane, and the above-mentioned amino-modified hollow microspheres are added. The microspheres are then vacuum impregnated at room temperature for 2 hours, and then the dichloromethane is slowly evaporated to remove the antioxidants, so that the antioxidants are uniformly loaded in the cavity of the microspheres. The loading amount is controlled to be 8-12% of the mass of the microspheres, thus obtaining hollow polymer microspheres.

[0048] The microspheres have a melting point higher than the reflow peak temperature and remain solid throughout the reflow process. This allows them to form a stable physical barrier between adjacent small-pitch bumps, preventing bridging defects caused by solder melt and flow at the source. At the reflow peak temperature, the surface tension generated by the melting solder compresses the microspheres, causing the microsphere cavities to rupture and simultaneously releasing the internally loaded antioxidants. The release temperature of the antioxidants perfectly matches the release temperature of the micro-encapsulated activators, achieving precise protection in the high-temperature range where the solder is most prone to oxidation, further reducing the bump void rate. The amino groups on the surface of the microspheres can form hydrogen bonds with the epoxy groups of the terminal epoxy modified cashew phenol in the film-forming agent, achieving long-term stable dispersion of the microspheres in the system without sedimentation or agglomeration.

[0049] The composite antioxidant of this invention is composed of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (antioxidant 1010) as the main antioxidant and tris(2,4-di-tert-butylphenyl) phosphite (antioxidant 168) as the auxiliary antioxidant in a mass ratio of 1:1. It has the dual ability of free radical scavenging and peroxide decomposition. It is completely homologous to the antioxidant loaded in the cavity of the hollow microspheres, which can ensure the compatibility of the whole system and avoid the problems of layering and precipitation caused by incompatibility.

[0050] The solubility of the storage-stable environmentally friendly composite solvent described in this invention is matched with the compatibility of the film-forming agent and the micro-encapsulated surfactant coating layer.

[0051] The component is a compound of diethylene glycol butyl ether acetate (DBA) and propylene glycol methyl ether acetate (PMA) in a mass ratio of 2.5:1. The boiling point at normal pressure is 190-230℃, and the solubility parameter at 25℃ is 18-20 (J / cm³). 0.5 .

[0052] Selective dissolution is achieved by matching solubility parameters; the solubility parameter of the film-forming agent is 19-19.5 (J / cm³). 0.5 The solubility parameter difference between the composite solvent and the microencapsulated surfactant is ≤2, therefore the composite solvent can completely dissolve the film-forming agent at room temperature to form a uniform and transparent base liquid; while the solubility parameter of the modified rosin on the outer layer of the microencapsulated surfactant is 23.5-24 (J / cm³). 0.5 The solubility parameter difference between the composite solvent and the microcapsule is ≥5, so the composite solvent will not dissolve the outer coating layer of the microcapsule at room temperature. This avoids premature microcapsule rupture and premature precipitation of active components, fundamentally solving the industry pain point of unstable storage of microcapsule systems in solvent-based fluxes. At the same time, the boiling point of the composite solvent matches the reflow temperature zone. The preheating section will not evaporate a large amount of flux, causing it to dry out. The reflow section can completely evaporate without residue. It is also halogen-free and low in VOCs, meeting the environmental protection requirements of the semiconductor industry.

[0053] The solubility parameters of this invention are calculated using the Hildebrand solubility parameter formula, and the specific measurement method can be found in ASTM D3132 standard.

[0054] The preparation of the flux described in this invention is carried out entirely at room temperature and pressure, and the specific steps are as follows:

[0055] Base liquid preparation: According to the formula ratio, the composite solvent is put into a stainless steel stirred tank, and the film-forming agent, maleic anhydride modified hydrogenated rosin and terminal epoxy modified cashew phenol are added at room temperature and pressure. Stir at 300 r / min for 2 hours until the film-forming agent is completely dissolved to obtain a uniform and transparent base liquid.

[0056] Functional component dispersion: Add composite antioxidant, temperature-triggered double-layer core-shell micro-encapsulated activator and hollow polymer microspheres to the above base liquid in sequence. First, stir at high speed of 500 r / min for 1 h to make each component uniformly dispersed. Then stir at low speed of 100 r / min for 30 min to degas and avoid bubbles affecting the uniformity of subsequent coating.

[0057] Filtration and discharge: The above dispersion is precisely filtered using a 10μm precision polypropylene filter to remove large particulate impurities, thus obtaining a high-reliability flux product for semiconductor bumping processes, which can be directly filled for use in semiconductor production lines.

[0058] Example 1

[0059] By weight percentage, the flux components are: 20% maleic anhydride-modified hydrogenated rosin, 4% terminal epoxy-modified cashew phenol (film-forming agent ratio 5:1), 15% temperature-triggered double-layer core-shell microencapsulated activator, 2% surface amino-modified hollow polymer microspheres loaded with antioxidants, 0.4% composite antioxidant, 38% diethylene glycol butyl ether acetate, and 20.6% propylene glycol methyl ether acetate.

[0060] The parameters of each component are as follows: modified rosin acid value 140 mg KOH / g, softening point 248℃; terminal epoxy-modified cashew phenol hydroxyl value 100 mg KOH / g; microencapsulated surfactant inner layer microcrystalline wax melting point 232℃, outer layer modified rosin melting point 238℃, core material ratio tetradecanoic acid: hydroxyethyl imidazoline: benzotriazole = 5:3:1, core material to encapsulation layer mass ratio 3:1, particle size 10μm; hollow microspheres melting point 270℃, particle size 20μm, cavity ratio 50%, antioxidant loading 10%; composite solvent solubility parameter 18.5 (J / cm³). 0.5 .

[0061] Example 2

[0062] By weight percentage, the flux components are: 15% maleic anhydride-modified hydrogenated rosin, 3.75% terminal epoxy-modified cashew phenol (film-forming agent ratio 4:1), 10% temperature-triggered double-layer core-shell microencapsulated activator, 0.8% surface amino-modified hollow polymer microspheres loaded with antioxidants, 0.2% composite antioxidant, 48% diethylene glycol butyl ether acetate, and 22.25% propylene glycol methyl ether acetate.

[0063] Example 3

[0064] By weight percentage, the flux components are: 24% maleic anhydride-modified hydrogenated rosin, 4% terminal epoxy-modified cashew phenol (film-forming agent ratio 6:1), 18% temperature-triggered double-layer core-shell microencapsulated activator, 3% surface amino-modified hollow polymer microspheres loaded with antioxidants, 0.6% composite antioxidant, 32% diethylene glycol butyl ether acetate, and 18.4% propylene glycol methyl ether acetate.

[0065] Example 4

[0066] By weight percentage, the flux components are: 18% maleic anhydride-modified hydrogenated rosin, 3.6% terminal epoxy-modified cashew phenol (film-forming agent ratio 5:1), 12% temperature-triggered double-layer core-shell microencapsulated activator, 1.5% surface amino-modified hollow polymer microspheres loaded with antioxidants, 0.3% composite antioxidant, 42% diethylene glycol butyl ether acetate, and 22.6% propylene glycol methyl ether acetate.

[0067] Example 5

[0068] By weight percentage, the flux components are: 22% maleic anhydride-modified hydrogenated rosin, 4.4% terminal epoxy-modified cashew phenol (film-forming agent ratio 5:1), 16% temperature-triggered double-layer core-shell microencapsulated activator, 2.5% surface amino-modified hollow polymer microspheres loaded with antioxidants, 0.5% composite antioxidant, 35% diethylene glycol butyl ether acetate, and 19.1% propylene glycol methyl ether acetate.

[0069] Comparative Example 1

[0070] The components are: 24% hydrogenated rosin, 8% sebacic acid, 55% diethylene glycol monobutyl ether, 2% fumed silica, and 10101% antioxidant.

[0071] Comparative Example 2

[0072] Except for replacing 15% of the double-layer core-shell microencapsulated activator with 11.25% of the core material active component (tetradecanoic acid: hydroxyethyl imidazoline: benzotriazole = 5:3:1) and 3.75% modified rosin, the other components, ratios, and parameters are completely consistent with those in Example 1.

[0073] Comparative Example 3

[0074] Except for replacing 2% of the functionalized hollow microspheres with 2% of hydrophobic fumed silica, the other components, ratios, and parameters are completely consistent with those in Example 1.

[0075] Comparative Example 4

[0076] Except for replacing 20% ​​modified rosin + 4% cashew phenol with 24% single modified rosin, the other components, proportions, and parameters are completely consistent with those in Example 1.

[0077] Comparative Example 5

[0078] Except for replacing the composite solvent with 100% diethylene glycol monobutyl ether (the difference in solubility parameter between the composite solvent and the outer layer of the microcapsule is 3.3 < 5), the other components, ratios, and parameters are completely consistent with those in Example 1.

[0079] All tests were conducted using standard semiconductor packaging industry testing methods. The test subjects were flux samples from Examples 1-5 and Comparative Examples 1-5, and the test conditions were completely consistent with industry mass production requirements.

[0080] Storage stability test: The sample was sealed and stored in a dry environment at 25°C for 6 months. The presence of stratification, sedimentation, and clumping was observed. The rupture rate of the microcapsules before and after storage was tested using an optical microscope.

[0081] Soldering performance test: 12-inch wafers were used, the UBM layer was a Ti / Cu / Ni structure, the solder was Sn-3.0Ag-0.5Cu lead-free solder, the bump spacing was 50μm, the flux was applied by ultrasonic spraying, and the reflow process adopted the four-segment temperature zone described in claim 10.

[0082] Bump defect testing: The average void rate and bridging failure rate of bumps across the entire wafer are detected using an X-ray inspection instrument;

[0083] UBM layer corrosion test: Flux was applied to the wafer with the UBM layer, and after being left at room temperature for 7 days, the corrosion of the UBM layer was observed using a scanning electron microscope.

[0084] Cleanability test: After soldering, the wafer surface was ultrasonically cleaned with pure water for 5 minutes, and the amount of residue was detected by X-ray photoelectron spectroscopy (XPS).

[0085] Long-term reliability testing: The rate of decrease in shear strength of the bump after 10 reflows and the rate of change in leakage current after 1000 hours in an 85℃ / 85%RH environment were tested.

[0086] Test Results

[0087] Test Project Example 1 Example 2 Example 3 Example 4 Example 5 6-month storage stability No stratification, no sedimentation, and a rupture rate of <1%. No stratification, no sedimentation, and a rupture rate of <1%. No stratification, no sedimentation, and a rupture rate of <1%. No stratification, no sedimentation, and a rupture rate of <1%. No stratification, no sedimentation, and a rupture rate of <1%. Average porosity of convex points 0.18% 0.25% 0.22% 0.20% 0.21% Bump bridging failure rate 0% 0% 0% 0% 0% 7-day UBM layer corrosion status Non-corrosive Non-corrosive Non-corrosive Non-corrosive Non-corrosive Residual amount after rinsing with pure water 42ppm 58ppm 52ppm 48ppm 45ppm Shear strength reduction rate after 10 reflows 2.8% 3.5% 3.2% 3.0% 3.1% 1000h High Temperature and High Humidity Leakage Current Change Rate 7.2% 8.5% 8.1% 7.8% 7.5%

[0088] Test Project Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 6-month storage stability Slight stratification Severe stratification, activity group analysis Microsphere sedimentation and stratification Slight stratification The microcapsules were completely ruptured, and the bioactive components were analyzed. Average porosity of convex points 1.25% 0.82% 0.75% 0.35% 0.90% Bump bridging failure rate 2.35% 1.82% 2.10% 0% 1.75% 7-day UBM layer corrosion status Severe corrosion Severe corrosion Non-corrosive Non-corrosive Severe corrosion Residual amount after rinsing with pure water 320ppm 280ppm 65ppm 180ppm 260ppm Shear strength reduction rate after 10 reflows 12.5% 9.8% 8.5% 4.2% 10.2% 1000h High Temperature and High Humidity Leakage Current Change Rate 25.6% 22.3% 19.8% 10.5% 21.6%

[0089] All core indicators of the embodiments fully met the standards: no stratification or sedimentation after 6 months of storage, microcapsule breakage rate <1%; bump bridging failure rate was 0%; no corrosion of UBM layer after 7 days of room temperature storage; average bump void rate was stably controlled between 0.18% and 0.25%, far lower than the mass production control line of ≤0.5% for advanced processes.

[0090] Example 1 represents the optimal scenario. Examples 2-5 show slight fluctuations compared to the optimal Example 1 in minor indicators such as cleaning residue, the rate of decrease in shear strength after 10 reflow cycles, and the rate of change in leakage current under high temperature and humidity, but all are far superior to industry control standards, with no precipitous performance decline. For example, the pure water cleaning residue in boundary value Example 2 is 58 ppm, which is still far below the semiconductor industry's residue limit of ≤100 ppm; the rate of change in leakage current under high temperature and humidity for 1000 hours is 8.5%, only 1 / 3 of that in the prior art.

[0091] Comparative Example 1 uses a classic flux formulation framework commonly used in the industry. After 10 reflows, the bump shear strength decreased by 12.5%. After 1000 hours in a high-temperature and high-humidity environment of 85℃ / 85%RH, the change rate of bump leakage current reached 25.6%. This completely fails to meet the high reliability requirements of automotive-grade and advanced processes. Conventional fluxes only focus on the soldering effect of a single reflow and are not specifically designed for the stringent requirements of multiple reflows of wafer-level bumps and long-term service in a wide temperature range of -40℃ to 125℃ for automotive-grade products. They can only meet the minimum reliability requirements of consumer electronics and cannot be adapted to high-value-added automotive-grade, industrial-grade, and advanced process semiconductor packaging scenarios.

[0092] Compared with Example 1, Comparative Example 2 only replaced 15% of the double-layer core-shell microencapsulated surfactant with an equal proportion of directly mixed core active components and encapsulation layer materials, while all other conditions were completely the same.

[0093] Performance changes: Severe stratification and active group analysis after 6 months of storage; severe corrosion of UBM layer after 7 days at room temperature; bump void rate increased from 0.18% to 0.82%; shear strength reduction rate after 10 reflows increased from 2.8% to 9.8%.

[0094] The double-layer core-shell microencapsulated surfactant is not simply a surfactant package; it achieves the functions of room temperature activation and corrosion prevention, precise temperature-controlled release to ensure activation, and homologous outer layer design to ensure system compatibility.

[0095] Compared with Example 1, Comparative Example 3 only replaced 2% of functionalized hollow microspheres with an equal proportion of industry-standard rheology modulator hydrophobic fumed silica, while all other conditions were exactly the same.

[0096] Performance changes: the failure rate of bump bridging increased from 0 to 2.10%; the bump void rate increased from 0.18% to 0.75%; the rate of decrease in shear strength after 10 reflows increased from 2.8% to 8.5%; and the rate of change in leakage current after 1000 hours of high temperature and high humidity increased from 7.2% to 19.8%.

[0097] Hollow microspheres achieve high-melting-point solid-state physical isolation to eliminate bridging at the source, cavity-loaded antioxidants achieve precise high-temperature protection, and surface amino modification and film-forming agents form hydrogen bond crosslinks to improve storage stability.

[0098] Compared with Example 1, Comparative Example 4 only replaced the film-forming agent of 20% modified rosin and 4% modified cashew phenol with 24% single modified rosin, while all other conditions were exactly the same.

[0099] Performance changes: Slight stratification appeared after 6 months of storage; the residue after pure water rinsing increased from 42ppm to 180ppm; the rate of decrease in shear strength after 10 reflows increased from 2.8% to 4.2%; the rate of change in leakage current after 1000h high temperature and high humidity increased from 7.2% to 10.5%.

[0100] Terminal epoxy groups can anchor hollow microspheres to prevent sedimentation, long carbon chain structures can improve wettability and enable washing with pure water, and homologous structures can match the outer layer of microcapsules to ensure system compatibility.

[0101] Comparative Example 5 and Example 1 were identical except that the composite solvent with matching solubility was replaced with diethylene glycol monobutyl ether, a common single solvent in the industry.

[0102] Performance changes: Microcapsules were completely ruptured and active components were identified; the UBM layer was severely corroded after 7 days at room temperature; the bump void rate increased from 0.18% to 0.90%; and storage resulted in complete failure.

[0103] By precisely designing the solubility parameters, selective dissolution is achieved, completely dissolving the film-forming agent at room temperature without dissolving the outer coating layer of the microcapsules, thus fundamentally solving the problem of microcapsule rupture during storage in solvent-based systems.

[0104] Furthermore, a verification experiment was conducted to demonstrate the synergistic effect, with the following control samples set up:

[0105] Control A: Contains only 24% film-forming agent + the remainder of composite solvent (no microencapsulated surfactants, no hollow microspheres);

[0106] Control B: Contains only 15% microencapsulated surfactant + the remainder of composite solvent (no film-forming agent, no hollow microspheres).

[0107] Control C: Contains only 2% hollow microspheres + the remainder of composite solvent (no film-forming agent, no microencapsulated surfactant);

[0108] Control D: 24% film-forming agent + 15% microencapsulated surfactant + composite solvent (no hollow microspheres);

[0109] Control E: 24% film-forming agent + 2% hollow microspheres + composite solvent (no microencapsulated surfactant);

[0110] Control F: 15% microencapsulated surfactant + 2% hollow microspheres + composite solvent (no film-forming agent);

[0111] Example 1 (all three are present).

[0112] Test results: Control A: void rate 1.8%, bridging rate 3.2%; Control B: void rate 2.5%, bridging rate 2.8%; Control C: void rate 3.1%, bridging rate 0.5% (microspheres are effective in preventing bridging but have a high void rate); Control D: void rate 0.45%, bridging rate 2.1%; Control E: void rate 1.2%, bridging rate 0.3%; Control F: void rate 0.9%, bridging rate 0.2%; Example 1: void rate 0.18%, bridging rate 0%. It is evident that the combination of the three is not only optimal in each individual indicator, but also has significantly lower void rate and bridging rate than any pairwise combination, proving a synergistic effect.

[0113] The specific steps for the mass production application of the above-mentioned flux in the 12-inch wafer bumping process are as follows:

[0114] Wafer pretreatment: The 12-inch wafer with the Ti / Cu / Ni structure UBM layer is subjected to plasma cleaning to remove surface organic contaminants and native oxide layer;

[0115] Flux coating: The flux from Example 1 was uniformly coated onto the wafer surface using an ultrasonic spraying process. The coating thickness was 15 μm, and the coating uniformity deviation was ≤ ±2%.

[0116] Solder ball placement: Using a fully automatic ball placement machine, Sn-3.0Ag-0.5Cu lead-free solder balls are precisely placed on the corresponding pads of the UBM layer;

[0117] Reflow soldering: A four-stage reflow process matching the properties of the flux components is employed.

[0118] Preheating section: 150-180℃, hold for 75 seconds. During this stage, the film-forming agent softens and forms a continuous preliminary protective film.

[0119] Activation stage: 180-230℃, hold for 50 seconds, the outer coating of the micro-encapsulated surfactant softens while the inner layer remains intact and locked in activation.

[0120] Reflux section: 230-250℃, peak temperature 248℃, residence time 60s, the double-layer coating of micro-encapsulated surfactant completely melts and releases active components, while the hollow microsphere cavity breaks and releases antioxidants.

[0121] Cooling section: rapidly cools to room temperature at a rate of 4℃ / s to complete solder bump formation;

[0122] Post-soldering cleaning: Ultrasonic cleaning with pure water for 5 minutes to remove flux residue, followed by nitrogen drying to obtain wafer-level solder bump products.

[0123] According to mass production line testing, the solder bumps prepared in this application example have a void rate of ≤0.2%, a bridging failure rate of 0, a bump shear strength of ≥120MPa, and a shear strength decrease rate of ≤3% after 10 reflows, which fully meets the high reliability mass production requirements of advanced wafer-level bumping processes.

[0124] Although embodiments of the present invention have been shown and described, these specific embodiments are merely explanations of the invention and are not intended to limit it. The specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. After reading this specification, those skilled in the art may make modifications, substitutions, and variations to the embodiments as needed without departing from the principles and spirit of the invention, but such modifications, substitutions, and variations are protected by patent law as long as they are within the scope of the claims of the present invention.

Claims

1. A high-reliability flux for semiconductor bumping processes, applied to 8-inch or 12-inch wafer-level solder bump fabrication processes, compatible with reflow soldering of lead-free Sn-Ag-Cu solder and Ti / Cu / Ni structure UBM layers, characterized in that... By weight percentage, the flux comprises the following synergistic components: Film-forming agent 18-28%, wherein the film-forming agent is compounded from modified rosin resin and terminal epoxy modified cashew phenol in a mass ratio of 4:1-6:1; The temperature-triggered double-core-shell microencapsulated activator is 10-18%, and the melting point window of the encapsulation layer of the temperature-triggered double-core-shell microencapsulated activator is matched with the activation and reflow temperature range of Bumping reflow soldering. Hollow polymer microspheres, 0.8-3%, wherein the melting point of the microspheres is higher than the peak temperature of reflow soldering; Compound antioxidant 0.2-0.6%; The remainder is a storage-stable environmentally friendly composite solvent, the solubility of which is matched with the compatibility of the film-forming agent and the micro-encapsulated surfactant coating layer.

2. The high-reliability flux for semiconductor bumping process according to claim 1, characterized in that: The modified rosin resin is maleic anhydride addition-modified hydrogenated rosin with an acid value of 120-160 mgKOH / g and a softening point of 245-250℃. Its softening point is 5-15℃ higher than the melting point of the outer coating layer of the temperature-triggered double-layer core-shell micro-encapsulated surfactant. During the reflux preheating stage, the modified rosin resin forms a continuous protective film before the micro-encapsulated surfactant to avoid splashing or system stratification after the surfactant is released.

3. The high-reliability flux for semiconductor bumping process according to claim 1, characterized in that: The terminal epoxy modified cashew phenol is a product of cashew phenol by addition to ethylene oxide followed by terminal epoxy capping, with a hydroxyl value of 80-120 mgKOH / g. Its terminal epoxy groups can form hydrogen bonds with the amino groups on the surface of hollow polymer microspheres, stably dispersing the microspheres in the flux system. It does not settle or separate after 6 months of storage at room temperature.

4. The high-reliability flux for semiconductor bumping process according to claim 1, characterized in that: The temperature-triggered double-core-shell microencapsulated activator has a double-core-shell structure. The inner encapsulation layer is a food-grade microcrystalline wax with a melting point of 230-235℃, and the outer encapsulation layer is a modified rosin homologous to the film-forming agent with a melting point of 235-240℃. The core material is the active component, and the total mass ratio of the core material to the double-layer encapsulation layer is 3:

1.

5. The high-reliability flux for semiconductor bumping process according to claim 4, characterized in that: The core active component of the temperature-triggered double-layer core-shell microencapsulated surfactant is composed of tetradecanoic acid, hydroxyethyl imidazoline and benzotriazole corrosion inhibitor in a mass ratio of 5:3:

1. During the reflux process, the active component and the corrosion inhibitor are released simultaneously, and the removal of the oxide film of the UBM layer and the corrosion protection of the metal layer are completed simultaneously to avoid over-corrosion.

6. The high-reliability flux for semiconductor bumping process according to claim 1, characterized in that: The hollow polymer microspheres are surface-amino-modified polystyrene-divinylbenzene hollow microspheres with a melting point of 265-275℃, a particle size of 15-25μm, and a hollow cavity ratio of 45-55%. During reflow, the microspheres physically isolate adjacent solder bumps in a solid state, completely avoiding small-pitch bump bridging defects.

7. The high-reliability flux for semiconductor bumping process according to claim 6, characterized in that: The hollow polymer microspheres are loaded with a composite antioxidant homologous to the system, with a loading amount of 8-12% of the microsphere mass. The release temperature of the composite antioxidant is perfectly matched with the release temperature of the microencapsulated activator. At the reflow peak temperature, the microsphere cavity ruptures due to the surface tension of the molten solder, and the antioxidant is released simultaneously.

8. The high-reliability flux for semiconductor bumping process according to claim 1, characterized in that: The storage-stable environmentally friendly composite solvent is composed of diethylene glycol butyl ether acetate and propylene glycol methyl ether acetate in a mass ratio of 2.5:

1. It has a boiling point of 190-230℃ at normal pressure and a solubility parameter of 18-20 (J / cm³) at 25℃. 0.5 The difference in solubility parameters between the solvent and the film-forming agent is ≤2, and the difference in solubility parameters between the solvent and the temperature-triggered double-layer core-shell microencapsulated surfactant is ≥5. At room temperature, the solvent can completely dissolve the film-forming agent but not the microencapsulated layer.

9. A high-reliability flux for semiconductor bumping processes according to any one of claims 1-8, characterized in that: The flux comprises, by weight percentage: 20% maleic anhydride-modified hydrogenated rosin, 4% terminal epoxy-modified cashew nut shell phenol, 15% temperature-triggered double-layer core-shell microencapsulated activator, 2% surface amino-modified hollow polymer microspheres loaded with antioxidants, 0.4% composite antioxidant, 38% diethylene glycol butyl ether acetate, and 20.6% propylene glycol methyl ether acetate.

10. The application of a high-reliability flux for semiconductor bumping processes according to any one of claims 1 to 9, characterized in that, When the flux is applied to the preparation of wafer solder bumps, the reflow soldering process is divided into four stages that match the properties of the components: Preheating section: 150-180℃, hold for 60-90s, during which the film-forming agent forms a continuous preliminary protective film; Activation stage: 180-230℃, heat preservation for 40-60s, the outer coating of the micro-encapsulated surfactant softens, while the inner layer remains intact and locked in activation; Reflux section: 230-250℃, peak temperature 245-250℃, residence time 50-70s, the double-layer coating of micro-encapsulated surfactants completely melts and releases active components, while the hollow microspheres rupture and release antioxidants. Cooling section: rapidly cools to room temperature to complete the protrusion molding.

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