An antioxidant soldering material and a soldering process for surface mount light emitting diodes

Abstract

This invention relates to an antioxidant solder material and a welding process for surface-mount LEDs, belonging to the field of LED welding technology. It achieves homogenization of composition through a combination of step-by-step melting and microstructure control. First, a tin-copper-bismuth master alloy is prepared by pre-melting in a pit furnace, pre-dispersing the bismuth element. Then, vacuum induction melting combined with electromagnetic stirring, along with an intermediate alloy feeding method, promotes the uniform dispersion of high-melting-point / active elements such as nickel and rare earth elements. Ni and rare earth elements can play a role in grain refinement and grain boundary purification, effectively suppressing the gravitational segregation and coarsening of the bismuth phase, avoiding the formation of brittle enrichment zones in the solder joints. The resulting solder joints have uniform grains, a moderate thickness of the intermetallic compound layer, and a smooth morphology, significantly improving the shear strength and thermal fatigue resistance of the solder joints and reducing the risk of brittle fracture failure of micro-solder joints.

Description

Technical Field

[0001] This invention belongs to the field of light-emitting diode (LED) welding technology, and relates to an anti-oxidation solder material and a welding process for surface-mount LEDs. Background Technology

[0002] Surface mount LEDs (SMD LEDs) are widely used in display backlighting, automotive electronics, and outdoor lighting due to their miniaturization, high luminous efficiency, and ease of integration. The connection quality between their electrodes and PCB pads directly determines the device's performance and lifespan, and is highly dependent on the solder materials used in the surface mount process. With the increasing adoption of lead-free technology in the electronics industry, tin-silver-copper lead-free solders have become mainstream. However, these solders have a significant drawback: they are prone to oxidation at high temperatures. During reflow soldering, oxides rapidly form on the surface of the liquid solder, which reduces wettability, leading to soldering defects such as cold solder joints, bridging, and solder balls. It also degrades the mechanical, electrical, and thermal properties of the solder joints, exacerbating LED light decay over long-term service, with the problem becoming even more pronounced under high temperature and humidity conditions.

[0003] Chinese invention patent application CN104476018A discloses a solder paste for surface mount diodes. Based on the weight of the solder paste, it is composed of 8-10% flux, 10-20% tin-bismuth alloy solder powder, and 72-80% Sn-Ag-Cu series solder powder. Tests have shown that this composition and appropriate ratio enable the solder paste to effectively guarantee the soldering quality and thus be effectively applied to electronic components. It can effectively maintain the high activity of the flux throughout the soldering process. In addition, the activation temperature of the flux is compatible with the melting point of lead-free solder, which greatly improves the wettability, oxidation resistance, and soldering performance of lead-free solder.

[0004] The solder paste in the above technical solution uses a physical blend of two alloy powders. During the reflow process, the high-melting-point SAC powder is difficult to fully melt and diffuse evenly, which easily causes local Bi phase enrichment at the solder joint. Since the surface mount diode is a micro-sized solder joint, Bi itself is brittle. The enrichment area will significantly reduce the toughness and thermal fatigue resistance of the solder joint. Under the conditions of device thermal cycling and mechanical vibration, microcracks are easily generated along the Bi enrichment zone, which will eventually lead to brittle fracture failure of the solder joint, seriously affecting the yield and long-term reliability of LED products. Summary of the Invention

[0005] The purpose of this invention is to provide an antioxidant solder material and a surface-mount light-emitting diode (LED) welding process. By combining body alloying control and surface composite film modification, along with a suitable reflow soldering process, the invention achieves the effects of improving the solder's oxidation resistance, optimizing solder joint performance, and increasing welding yield and service reliability.

[0006] The objective of this invention can be achieved through the following technical solutions: This invention provides an antioxidant solder material, comprising the following components by weight percentage: Ag 0.35-0.6%, Cu 0.5-0.8%, Bi 1.0-4.0%, Ni 0.05-0.08%, Dy 0.02-0.1%, In 0.2-0.9%, Ge 0.02%-0.1%, Si 0.03-0.05%, Gd 0.02-0.1%, Pr 0.02-0.1%, P 0.002-0.008%, with the balance being Sn.

[0007] This antioxidant solder material is prepared through the following steps: Step 1: Place Sn-0.7Cu alloy and Bi particles in a well-type resistance furnace under argon protection and heat until melted. Then add Sn-5P master alloy, stir and mix, and cool to form Sn-Cu-Bi alloy. Next, place Sn, In and Ag at the bottom of a high-purity graphite crucible, and add Sn-Cu-Bi alloy, Sn-Ni alloy, Sn-Dy alloy, Sn-Ge alloy, Sn-Si alloy, Sn-Gd alloy and Sn-Pr alloy. Vacuum melt using a high-frequency vacuum induction furnace, and then cast to form solder alloy.

[0008] Step 2: Mix tetraethylammonium hydroxide, polyethylene glycol 4000, OP-10, ammonium molybdate, 2-aminobenzimidazole and deionized water evenly to obtain the surface treatment agent.

[0009] Step 2: Mix tetraethylammonium hydroxide, polyethylene glycol 4000, OP-10, ammonium molybdate, 2-aminobenzimidazole and deionized water evenly to obtain the surface treatment agent.

[0010] Furthermore, the specific preparation process of the Sn-Cu-Bi alloy is as follows: Soak Sn-0.7Cu alloy and Bi particles in 1 mol / L hydrochloric acid for 5-10 minutes, rinse, dry, place in a porcelain crucible, and then place in a pit-type resistance furnace with protective gas. Heat to molten at 350-360℃, press the particles into the molten alloy, and evenly sprinkle a covering agent accounting for 1-2% of the total mass of the melt on the surface. Hold for 1-2 hours, add Sn-5P master alloy at 30% of the target P content for pre-deoxidation, hold for 10-15 minutes, and stir with a graphite rod every 20-30 minutes under argon protection. Finally, pour the metal mixture into a graphite mold preheated at 150-160℃ and cool to room temperature to form the Sn-Cu-Bi alloy.

[0011] Furthermore, the mass ratio of Sn-0.7Cu alloy to Bi particles is 900-960:10-40.

[0012] Furthermore, the vacuum degree of vacuum melting is ≤5×10 -3 Pa, set the melting temperature to 500-520℃, and maintain the temperature for 45-60 minutes.

[0013] Furthermore, the ratio of tetraethylammonium hydroxide, polyethylene glycol 4000, OP-10, ammonium molybdate, 2-aminobenzimidazole, and deionized water is 0.6-1.0g: 0.6-1.0g: 0.2-0.3g: 0.02-0.03g: 0.05-0.07g: 96-110mL.

[0014] Furthermore, the ratio of solder alloy to surface treatment agent is 8-10g:90-100mL.

[0015] Furthermore, the soaking temperature is 25-30℃, and the soaking time is 10-15 minutes.

[0016] Furthermore, the drying temperature is 110-120℃, and the time is 15-20 minutes.

[0017] The present invention also provides a soldering process for surface-mount light-emitting diodes, comprising the following steps: Step 1: Mix the antioxidant solder material and flux in the specified proportions to form a solder paste. Then, evenly print the solder paste onto the pads of the LED circuit board.

[0018] Step 2: Precisely align and mount the surface-mount LEDs onto the pads coated with solder paste.

[0019] Step 3: The mounted circuit board is sent into the reflow oven and goes through three heating stages in sequence: preheating, heat preservation and reflow. During the soldering process, the temperature data of the soldering area is monitored by the temperature monitoring system.

[0020] Step 4: After reflow soldering is completed, the circuit board enters the cooling zone with the furnace to obtain the finished surface-mount LED.

[0021] Furthermore, the heating rate during the preheating stage is 3℃ / s.

[0022] Furthermore, the temperature during the heat preservation stage is 100-110℃, and the heat preservation time is 110-120s.

[0023] Furthermore, the peak reflux temperature during the reflux stage is 195-200℃, and the reflux time is 60-70s.

[0024] The beneficial effects of this invention are: 1. This invention addresses the problem of bismuth phase segregation and solder joint embrittlement that often occur in existing physically blended solders. It achieves compositional homogenization through the synergistic effect of step-by-step melting and microstructure control. First, a tin-copper-bismuth master alloy is prepared by pre-melting in a pit furnace to pre-dispersettle the bismuth element. Then, vacuum induction melting combined with electromagnetic stirring and intermediate alloy feeding promotes the uniform dispersion of high-melting-point / active elements such as nickel and rare earth elements. Ni and rare earth elements can play a role in grain refinement and grain boundary purification, effectively suppressing the gravity segregation and coarsening of the bismuth phase and avoiding the formation of brittle enrichment zones in the solder joint. The final solder joint has uniform grains, a moderate thickness of the intermetallic compound layer, and a smooth morphology, which greatly improves the shear strength and thermal fatigue resistance of the solder joint and reduces the risk of brittle fracture failure of micro solder joints.

[0025] 2. This invention constructs an anti-oxidation system covering the entire cycle of room temperature storage and high-temperature welding through the synergistic effect of bulk alloying and surface composite film. On the one hand, the initial oxygen content of the alloy is reduced through pre-deoxidation and vacuum melting processes. Trace phosphorus elements complete pre-deoxidation during the melting stage. Germanium and rare earth elements in the matrix can be enriched on the surface of the melt at high welding temperatures, forming a dense solid oxide barrier that prevents oxygen from diffusing into the melt. On the other hand, a protective film composed of an organic directional adsorption layer and a molybdate passivation layer is formed on the alloy surface through surface treatment. During room temperature storage, it prevents oxygen and moisture from entering. During reflow welding, the organic components gradually decompose, and the residual molybdate passivation components and the oxides precipitated from the matrix synergistically maintain the oxidation barrier effect, achieving a seamless transition from room temperature protection to high temperature protection. Compared with single anti-oxidation technologies, this invention significantly improves the anti-oxidation effect throughout the entire process.

[0026] 3. This invention improves the corrosion resistance of solder joints under high temperature and high humidity environments through the synergistic effect of substrate corrosion resistance modification and surface passivation barrier. Nickel, germanium and rare earth elements in the substrate can synergistically enhance the passivation effect of the substrate. Rare earth elements form stable oxides at grain boundaries to inhibit intergranular corrosion. The surface composite film remains after reflow soldering to form a passivation protective layer, blocking the intrusion of corrosive media. The synergy of the two causes the solder joint corrosion potential to shift positively and the corrosion rate to decrease, alleviating the corrosion degradation of solder joints under harsh operating conditions and extending the service life of the device. At the same time, the combination of bismuth and indium regulates the melting point of the solder, and the surface activity of trace amounts of silicon and indium improves the wettability of the molten solder. It is precisely adapted to the optimized three-stage reflow soldering process, which can achieve good pad wetting at a lower peak temperature, reduce welding defects and improve yield. The uniform and dense solder joints have excellent electrical and thermal conductivity, which can reduce the contact resistance and thermal resistance of the solder joints, alleviate the long-term light decay of the device, and improve the stability and service life of optoelectronic performance. Detailed Implementation

[0027] To further illustrate the technical means and effects of the present invention in achieving the intended purpose, the following detailed description of the specific implementation methods, features and effects of the present invention, in conjunction with preferred embodiments, is provided below.

[0028] Example 1: This example provides an antioxidant solder material, which, by mass percentage, comprises the following components: The antioxidant solder material is prepared by the following steps: 0.35% silver (Ag), 0.5% copper (Cu), 1.0% bismuth (Bi), 0.05% nickel (Ni), 0.02% dysprosium (Dy), 0.2% indium (In), 0.02% germanium (Ge), 0.03% silicon (Si), 0.02% gadolinium (Gd), 0.02% praseodymium (Pr), 0.002% phosphorus (P), with the balance being tin (Sn). S1: Immerse 900g of Sn-0.7Cu alloy and Bi particles in 1mol / L hydrochloric acid for 5 minutes, rinse thoroughly, and dry. Place the dried Sn-0.7Cu alloy in a porcelain crucible and then place it in a pit-type resistance furnace with protective gas. Heat to 350℃ until melted. Press 10g of Bi particles into the molten alloy. Sprinkle 1% of the total mass of the melt with a covering agent (55wt.%KCl+45wt.%LiCl) evenly on the surface to prevent oxidation. Hold for 1 hour. Add Sn-5P master alloy at 30% of the target P content for pre-deoxidation. Hold for another 10 minutes. Stir with a graphite rod every 20 minutes under argon protection. Finally, pour the metal mixture into a graphite mold preheated at 150℃ and cool to room temperature to form the Sn-Cu-Bi alloy.

[0029] S2: Accurately weigh all raw materials to a total mass of 1000±0.1g and place them in a high-purity graphite crucible. Place industrial pure metals (purity ≥99.99%) Sn, In, and Ag at the bottom, followed by Sn-Cu-Bi alloy, Sn-Ni alloy, Sn-Dy alloy, Sn-Ge alloy, Sn-Si alloy, Sn-Gd alloy, and Sn-Pr alloy. Perform vacuum melting using a high-frequency vacuum induction furnace, with a vacuum degree ≤5×10⁻⁶. -3 Pa, set the melting temperature to 500℃, maintain the temperature for 45 minutes, and use the spontaneous stirring effect of the induced electromagnetic field to make the molten metal fully convect and mix, ensuring that each element is evenly dispersed; the whole process is in a vacuum environment to isolate oxygen, and after the heat preservation melting is completed, the casting and molding process is completed in a vacuum environment. The furnace is cooled to room temperature in a vacuum environment, and the molded ingot is taken out to obtain the solder alloy.

[0030] S3: Mix 0.6g tetraethylammonium hydroxide (25% aqueous solution), 0.6g polyethylene glycol 4000, 0.2g OP-10, 0.02g ammonium molybdate, 0.05g 2-aminobenzimidazole and 96mL deionized water evenly to obtain the surface treatment agent.

[0031] S4: Immerse the cooled and shaped solder alloy in anhydrous ethanol, ultrasonically clean for 3 minutes, then ultrasonically clean with deionized water for 2 minutes, and dry. Add 8g of the cleaned solder alloy and 90mL of surface treatment agent to the reaction vessel and soak at 25℃ for 10 minutes. A protective layer is formed through the spontaneous and orderly arrangement of molecules. That is, specific functional groups (such as amino and carboxyl groups) in organic molecules form directional adsorption on the surface of the solder alloy. Then, the barrier effect of the organic molecular layer blocks the oxidation or corrosion reaction between the solder alloy and oxygen, water, etc. The treated solder alloy is placed in deionized water, rinsed 3 times, dried at 110℃ for 15 minutes, and cooled to room temperature to obtain the antioxidant solder material.

[0032] Example 2: This example provides an antioxidant solder material, which, by mass percentage, comprises the following components: The antioxidant solder material is prepared by the following steps: 0.48% silver (Ag), 0.65% copper (Cu), 2.5% bismuth (Bi), 0.065% nickel (Ni), 0.06% dysprosium (Dy), 0.55% indium (In), 0.06% germanium (Ge), 0.04% silicon (Si), 0.06% gadolinium (Gd), 0.06% praseodymium (Pr), 0.004% phosphorus (P), with the balance being tin (Sn). S1: Immerse 930g of Sn-0.7Cu alloy and Bi particles in 1mol / L hydrochloric acid for 7 minutes, rinse thoroughly, and dry. Place the dried Sn-0.7Cu alloy in a porcelain crucible and then place it in a pit-type resistance furnace with protective gas. Heat to 355℃ until melted. Press 25g of Bi particles into the molten alloy. Sprinkle 1.5% of the total mass of the melt (55wt.%KCl+45wt.%LiCl) evenly on the surface to prevent oxidation. Hold for 1.5h. Add Sn-5P master alloy at 30% of the target P content for pre-deoxidation. Hold for another 12min. Stir with a graphite rod every 25min under argon protection. Finally, pour the metal mixture into a graphite mold preheated at 155℃ and cool to room temperature to form the Sn-Cu-Bi alloy.

[0033] S2: Accurately weigh all raw materials to a total mass of 1000±0.1g and place them in a high-purity graphite crucible. Place industrial pure metals (purity ≥99.99%) Sn, In, and Ag at the bottom, followed by Sn-Cu-Bi alloy, Sn-Ni alloy, Sn-Dy alloy, Sn-Ge alloy, Sn-Si alloy, Sn-Gd alloy, and Sn-Pr alloy. Perform vacuum melting using a high-frequency vacuum induction furnace, with a vacuum degree ≤5×10⁻⁶. -3 Pa, set the melting temperature to 510℃, maintain the temperature for 52 minutes, and use the spontaneous stirring effect of the induced electromagnetic field to make the molten metal fully convect and mix, ensuring that each element is evenly dispersed; the whole process is in a vacuum environment to isolate oxygen. After the heat preservation melting is completed, the casting and molding process is completed in a vacuum environment. The furnace is cooled to room temperature in a vacuum environment, and the molded ingot is taken out to obtain the solder alloy.

[0034] S3: Mix 0.8g tetraethylammonium hydroxide (25% aqueous solution), 0.8g polyethylene glycol 4000, 0.25g OP-10, 0.025g ammonium molybdate, 0.06g 2-aminobenzimidazole and 103mL deionized water evenly to obtain the surface treatment agent.

[0035] S4: Immerse the cooled and shaped solder alloy in anhydrous ethanol, ultrasonically clean for 4 minutes, then ultrasonically clean with deionized water for 3 minutes, and dry. Add 9g of the cleaned solder alloy and 95mL of surface treatment agent to the reaction vessel and soak at 27℃ for 12 minutes. A protective layer is formed through the spontaneous and orderly arrangement of molecules. That is, specific functional groups in organic molecules (such as amino and carboxyl groups) are directionally adsorbed on the surface of the solder alloy. Then, the barrier effect of the organic molecular layer is used to block the oxidation or corrosion reaction between the solder alloy and oxygen, water, etc. The treated solder alloy is placed in deionized water, rinsed 4 times, dried at 115℃ for 17 minutes, and cooled to room temperature to obtain the antioxidant solder material.

[0036] Example 3: This example provides an antioxidant solder material, which, by mass percentage, comprises the following components: The antioxidant solder material is prepared by the following steps: 0.6% silver (Ag), 0.8% copper (Cu), 4.0% bismuth (Bi), 0.08% nickel (Ni), 0.1% dysprosium (Dy), 0.9% indium (In), 0.1% germanium (Ge), 0.05% silicon (Si), 0.1% gadolinium (Gd), 0.1% praseodymium (Pr), 0.008% phosphorus (P), with the balance being tin (Sn). S1: Immerse 960g of Sn-0.7Cu alloy and Bi particles in 1mol / L hydrochloric acid for 10min, rinse thoroughly, and dry. Place the dried Sn-0.7Cu alloy in a porcelain crucible and then in a pit-type resistance furnace with protective gas. Heat to 360℃ until melted. Press 40g of Bi particles into the molten alloy. Sprinkle 2% of the total mass of the melt with a covering agent (55wt.%KCl+45wt.%LiCl) evenly on the surface to prevent oxidation. Hold for 2h. Add Sn-5P master alloy at 30% of the target P content for pre-deoxidation. Hold for another 15min. Stir with a graphite rod every 30min under argon protection. Finally, pour the metal mixture into a graphite mold preheated at 160℃ and cool to room temperature to form the Sn-Cu-Bi alloy.

[0037] S2: Accurately weigh all raw materials to a total mass of 1000±0.1g and place them in a high-purity graphite crucible. Place industrial pure metals (purity ≥99.99%) Sn, In, and Ag at the bottom, followed by Sn-Cu-Bi alloy, Sn-Ni alloy, Sn-Dy alloy, Sn-Ge alloy, Sn-Si alloy, Sn-Gd alloy, and Sn-Pr alloy. Perform vacuum melting using a high-frequency vacuum induction furnace, with a vacuum degree ≤5×10⁻⁶. -3 Pa, set the melting temperature to 520℃, maintain the temperature for 60 minutes, and use the spontaneous stirring effect of the induced electromagnetic field to make the molten metal fully convect and mix, ensuring that each element is evenly dispersed; the whole process is in a vacuum environment to isolate oxygen. After the heat preservation melting is completed, the casting and molding process is completed in a vacuum environment. The furnace is cooled to room temperature in a vacuum environment, and the molded ingot is taken out to obtain the solder alloy.

[0038] S3: Mix 1.0g tetraethylammonium hydroxide (25% aqueous solution), 1.0g polyethylene glycol 4000, 0.3g OP-10, 0.03g ammonium molybdate, 0.07g 2-aminobenzimidazole and 110mL deionized water evenly to obtain the surface treatment agent.

[0039] S4: Immerse the cooled and shaped solder alloy in anhydrous ethanol, ultrasonically clean for 5 minutes, then ultrasonically clean with deionized water for 4 minutes, and dry. Add 10g of the cleaned solder alloy and 100mL of surface treatment agent to the reaction vessel and soak at 30℃ for 15 minutes. A protective layer is formed through the spontaneous and orderly arrangement of molecules. That is, specific functional groups in organic molecules (such as amino and carboxyl groups) form directional adsorption on the surface of the solder alloy. Then, the barrier effect of the organic molecular layer blocks the oxidation or corrosion reaction between the solder alloy and oxygen, water, etc. The treated solder alloy is placed in deionized water, rinsed 5 times, dried at 120℃ for 20 minutes, and cooled to room temperature to obtain the antioxidant solder material.

[0040] Example 4: This example provides a soldering process for a surface-mount LED, including the following steps: Step 1: Mix the antioxidant solder material and flux prepared in Example 1 at a mass ratio of 88:12 to form a solder paste. Use a 0.2mm thick printing stencil and a scraper to evenly print the solder paste onto the pads of the LED circuit board.

[0041] Step 2: Use surface mount equipment to precisely align and mount the surface mount LEDs onto the pads coated with solder paste. Apply appropriate pressure during the mounting process to ensure that the device electrodes are in full contact with and adhere to the solder paste, thus fixing the relative position of the device. After mounting, check the alignment accuracy to ensure that the device is not offset or skewed.

[0042] Step 3: The mounted circuit board is placed into the reflow oven and goes through three heating stages in sequence: preheating, holding, and reflow. First, it is preheated at a heating rate of 3℃ / s, then it enters the holding stage, where the temperature is maintained at 100℃ for 110s. Finally, it enters the reflow stage, where the peak reflow temperature is controlled at 195℃ and the reflow time is 60s. During the soldering process, the temperature data of the soldering area is acquired in real time through the temperature monitoring system, and the deviation from the preset temperature curve is calculated. When an abnormal temperature is detected, the system automatically adjusts the heating power according to the degree of abnormality (low or high) to ensure that the solder melts and wets the pads within the optimal temperature window, avoiding severe oxidation of the solder due to excessively high temperature or cold soldering due to excessively low temperature.

[0043] Step 4: After reflow soldering is completed, the circuit board enters the cooling zone with the furnace. The cooling rate is controlled to ensure that the solder joints solidify quickly and evenly. This avoids thermal stress caused by excessively fast cooling and coarse grains caused by excessively slow cooling, resulting in anti-oxidation solder joints with a bright surface and dense internal structure, thus obtaining the finished surface mount LED.

[0044] Example 5: This example provides a surface mount LED welding process. The difference from Example 4 is that in Step 3, the temperature during the heat preservation stage is maintained at 105°C and the heat preservation time is 115s. During the reflow stage, the reflow peak temperature is controlled at 197°C and the reflow time is 65s.

[0045] Example 6: This example provides a surface mount LED welding process. The difference from Example 4 is that in Step 3, the temperature during the heat preservation stage is maintained at 110°C and the heat preservation time is 120s. During the reflow stage, the reflow peak temperature is controlled at 200°C and the reflow time is 70s.

[0046] Example 7: This example provides a soldering process for a surface-mount LED. The difference from Example 4 is that in Step 1, the antioxidant solder material prepared in Example 2 is used instead of the antioxidant solder material prepared in Example 1.

[0047] Example 8: This example provides a soldering process for a surface-mount LED. The difference from Example 4 is that in Step 1, the antioxidant solder material prepared in Example 3 is used instead of the antioxidant solder material prepared in Example 1.

[0048] Comparative Example 1: This comparative example provides an antioxidant solder material. The difference from Example 1 is that steps S3 and S4 are not performed. The solder alloy prepared in step S2 is the antioxidant solder material.

[0049] Comparative Example 2: This comparative example provides a soldering process for a surface-mount LED. The difference from Example 4 is that the antioxidant solder material prepared in Comparative Example 1 is used instead of the antioxidant solder material prepared in Example 1 in Step 1.

[0050] Comparative Example 3: This comparative example provides a soldering process for a surface-mount LED. The difference from Example 4 is that in Step 1, commercially available solder material (Yunnan Tin Brand 0.3% Silver Environmentally Friendly Lead-Free Solder Wire, purchased from Wuxi Fanchuan Tin Industry Co., Ltd.) is used instead of the antioxidant solder material prepared in Example 1.

[0051] The performance of the antioxidant solder materials prepared in Examples 1-3 and Comparative Example 2 was tested: Antioxidant properties: The sample was placed in an oven at 100℃ for 72 hours. After removal, the color difference of the antioxidant solder material was measured, and its surface morphology and elemental composition were analyzed to evaluate the degree of oxidation of the antioxidant solder material.

[0052] Wettability: The spread area method was used for testing. 0.1g of anti-oxidation solder material was placed on a pretreated copper-plated substrate and kept at 250℃ for 60s. After cooling, the spread area of ​​the solder after solidification was measured. The larger the spread area, the better the wettability of the molten solder.

[0053] The surface-mount LEDs prepared in Examples 4-8 and Comparative Examples 2-3 were subjected to performance testing: Shear strength test: The shear strength of the sealed joint was tested at room temperature using an IIC-MST-100 electronic universal tensile testing machine at a shear rate of 0.2 mm / min. The shear strength was calculated using the following formula: δ = F / S, where δ is the shear strength (MPa), F is the maximum shear force (N), and S is the overlap area of ​​the specimen (mm²). 2 ).

[0054] Electrochemical performance testing: The solder joints were cut using wire cutting, sanded and polished, ultrasonically cleaned, and then the wires were bonded to the solder joints with conductive tape. The non-corroded surfaces were sealed with epoxy resin. Electrochemical etching of the solder joints was performed using a Parstat 2273 electrochemical workstation. A standard three-electrode system was used: the counter electrode (CE) was connected to a platinum electrode, the reference electrode (RE) was connected to a saturated calomel electrode, and the working electrode (WE) was connected to the treated solder joint sample. The electrochemical etching solution was a 3.5% NaCl solution. Experimental data were imported into CS Studio 5 software for curve fitting to obtain the corrosion potential (Ecorr / V) and self-corrosion current density (icorr / A·cm). -2 ) and corrosion rate (mm / a).

[0055] The test results are shown in Table 1 and Table 2 respectively: Table 1. Summary of Performance Tests for Antioxidant Solder Materials

[0056] As shown in Table 1, the color difference change rate of Examples 1-3 after 72 hours at high temperature is less than that of Comparative Example 1, indicating that Examples 1-3 have better antioxidant properties. This may be because, based on the deoxidation and refinement of the bulk material, Examples 1-3 formed a protective layer of directionally adsorbed organic molecules and a molybdate passivation layer on the alloy surface through surface treatment. This can physically block the diffusion of oxygen and water vapor into the substrate, and the active elements in the bulk material and the surface film layer work together to exert a better antioxidant effect.

[0057] As shown in Table 1, the spreading area of ​​Examples 1-3 is greater than that of Comparative Example 1, indicating that the anti-oxidation solder materials of Examples 1-3 have better wettability. This may be because the trace amounts of Si and In in the matrix are surface-active elements, which agglomerate towards the surface of the melt in the molten state, reducing the surface tension of the liquid solder and improving the spreading ability. On the other hand, the pre-deoxidation process and vacuum melting reduce the oxidation inclusions inside the melt. The surface treatment film gradually decomposes during the heating process, and the residual molybdate components can inhibit the rapid oxidation of the solder during the melting process, avoiding the surface oxide film from hindering the solder spreading. The two work together to improve the wetting effect of the solder on the copper substrate.

[0058] Table 2. Overview of Performance Tests for Surface Mount LEDs

[0059] As shown in Table 2, the shear strength of Examples 4-8 is greater than that of Comparative Examples 2-3. This may be because the anti-oxidation solder materials used in Examples 4-8 are vacuum melted and pre-deoxidized, resulting in uniform composition and dense structure. Ni and rare earth elements can refine the solder grains and reduce the segregation of Bi brittle phase. At the same time, the surface composite anti-oxidation film can inhibit solder oxidation during reflow and reduce the content of interface oxidation inclusions. Combined with the optimized reflow soldering process, the interface IMC (intermetallic compound layer) layer grows uniformly, and the solder joints are more firmly bonded, thus resulting in higher shear strength.

[0060] As shown in Table 2, Examples 4-8 exhibit better corrosion resistance. This may be because the Ni, rare earth, and Ge elements in the antioxidant solder materials used in Examples 4-8 can enhance the passivation capability of the substrate. Rare earth elements form stable oxides at grain boundaries, hindering the diffusion of corrosive media along the grain boundaries. Simultaneously, the molybdate residues on the solder joint surface after soldering, together with the oxides of rare earth and germanium, constitute a dense passivation layer, physically blocking Cl... - When corrosive media penetrate, the body modification and surface protection work synergistically, resulting in superior corrosion resistance.

[0061] It should be noted that, in this document, terms such as “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus.

[0062] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention.

Claims

1. An antioxidant solder material, characterized in that, By mass percentage, it includes the following components: Ag 0.35-0.6%, Cu 0.5-0.8%, Bi 1.0-4.0%, Ni 0.05-0.08%, Dy 0.02-0.1%, In 0.2-0.9%, Ge 0.02%-0.1%, Si 0.03-0.05%, Gd 0.02-0.1%, Pr 0.02-0.1%, P 0.002-0.008%, balance Sn; This antioxidant solder material is prepared through the following steps: Step 1: Place Sn-0.7Cu alloy and Bi particles in a well-type resistance furnace under argon protection and heat until melted. Then add Sn-5P master alloy, stir and mix, and cool to form Sn-Cu-Bi alloy. Next, place Sn, In, and Ag at the bottom of a high-purity graphite crucible, and add Sn-Cu-Bi alloy, Sn-Ni alloy, Sn-Dy alloy, Sn-Ge alloy, Sn-Si alloy, Sn-Gd alloy, and Sn-Pr alloy. Vacuum melt using a high-frequency vacuum induction furnace, and then cast to form solder alloy. Step 2: Mix tetraethylammonium hydroxide, polyethylene glycol 4000, OP-10, ammonium molybdate, 2-aminobenzimidazole and deionized water evenly to obtain the surface treatment agent; Step 3: Immerse the cleaned solder alloy in a surface treatment agent, then rinse and dry to obtain an antioxidant solder material.

2. The antioxidant solder material according to claim 1, characterized in that, The specific preparation process of the Sn-Cu-Bi alloy described in step one is as follows: Soak Sn-0.7Cu alloy and Bi particles in 1 mol / L hydrochloric acid for 5-10 minutes, rinse, dry, place in a porcelain crucible, and then place in a pit-type resistance furnace with protective gas. Heat to molten at 350-360℃, press the particles into the molten alloy, and evenly sprinkle a covering agent accounting for 1-2% of the total mass of the melt on the surface. Hold for 1-2 hours, add Sn-5P master alloy at 30% of the target P content for pre-deoxidation, hold for 10-15 minutes, and stir with a graphite rod every 20-30 minutes under argon protection. Finally, pour the metal mixture into a graphite mold preheated at 150-160℃ and cool to room temperature to form the Sn-Cu-Bi alloy.

3. The antioxidant solder material according to claim 2, characterized in that, The mass ratio of the Sn-0.7Cu alloy to Bi particles is 900-960:10-40.

4. The antioxidant solder material according to claim 1, characterized in that, The vacuum degree of the vacuum melting in step one is ≤5×10 -3 Pa, set the melting temperature to 500-520℃, and maintain the temperature for 45-60 minutes.

5. The antioxidant solder material according to claim 1, characterized in that, In step two, the ratio of tetraethylammonium hydroxide, polyethylene glycol 4000, OP-10, ammonium molybdate, 2-aminobenzimidazole, and deionized water is 0.6-1.0g: 0.6-1.0g: 0.2-0.3g: 0.02-0.03g: 0.05-0.07g: 96-110mL.

6. The antioxidant solder material according to claim 1, characterized in that, The ratio of the solder alloy to the surface treatment agent is 8-10g:90-100mL.

7. The antioxidant solder material according to claim 1, characterized in that, The soaking temperature is 25-30℃ and the soaking time is 10-15 minutes.

8. The antioxidant solder material according to claim 1, characterized in that, The drying temperature is 110-120℃, and the time is 15-20 minutes.

9. A welding process for surface-mount light-emitting diodes, characterized in that, Includes the following steps: Step 1: Mix the antioxidant solder material and flux in the specified ratio to make solder paste, and then print the solder paste evenly on the pads of the LED circuit board. Step 2: Precisely align and mount the surface-mount LEDs onto the pads coated with solder paste; Step 3: The mounted circuit board is sent into the reflow oven and goes through three heating stages in sequence: preheating, heat preservation and reflow. During the soldering process, the temperature data of the soldering area is monitored by the temperature monitoring system. Step 4: After reflow soldering is completed, the circuit board enters the cooling zone with the furnace to obtain the finished surface-mount LED. The antioxidant solder material is one of the antioxidant solder materials according to any one of claims 1-8.

10. The welding process for a surface-mount light-emitting diode according to claim 9, characterized in that, The heating rate during the preheating stage is 3℃ / s; The temperature during the heat preservation stage is 100-110℃, and the heat preservation time is 110-120s; The peak reflux temperature during the reflux stage is 195-200℃, and the reflux time is 60-70s.

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