Low-temperature-coefficient resistance paste for potentiometer and preparation method of low-temperature-coefficient resistance paste

Abstract

The invention belongs to the technical field of electronic paste, and discloses low-temperature-coefficient resistance paste for a potentiometer and a preparation method of the low-temperature-coefficient resistance paste. The resistance paste is composed of a conductive phase, a glass phase and an organic carrier, the conductive phase is bismuth ruthenate nanowires and carbon-coated copper nanowires, the glass phase comprises Bi2O3, B2O3, SiO2 and La2O3, and the organic carrier is composed of ethyl cellulose and terpilenol. The preparation method comprises the following steps: respectively preparing the components, mixing in proportion, and rolling by a three-roller mill. The TCR value of a resistive layer formed by the paste is controlled to be + / -50 ppm / DEG C, the resistance change is lower than 0.8% after 1000 times of-55-125 DEG C cold and hot cycles, low-temperature sintering can be achieved, the silver migration resistance is excellent, the high-frequency insertion loss of the 3GHz frequency band is low, the sheet resistance uniformity is good, and the paste is suitable for the miniaturization, high precision and high-frequency scene requirements of high-end potentiometers.

Description

Technical Field

[0001] This invention belongs to the field of electronic paste technology, and particularly relates to a low temperature coefficient resistive paste for potentiometers and its preparation method. Background Technology

[0002] With the trend towards miniaturization and high precision in electronic components, potentiometer resistive pastes, as functional materials that determine the core performance of devices, are facing increasingly prominent technological bottlenecks. While current mainstream ruthenium-based resistive pastes achieve basic electrical properties through the classic combination of the RuO2 conductive phase and the lead-boron glass phase, they are failing to meet the application requirements of emerging fields in key dimensions such as temperature stability, interface reliability, and high-frequency adaptability. There is an urgent need to break through existing technologies at the material system design level to solve performance defects caused by microstructural flaws.

[0003] Traditional RuO2-based slurries use micron-sized particles (1~3μm) as the conductive phase, requiring high-temperature sintering (typically >850℃) to form a conductive network. Under thermodynamic equilibrium, this structure exhibits a grain boundary-dominated conduction mechanism, resulting in a temperature coefficient of resistance (TCR) generally ranging from ±150 to ±200 ppm / ℃. When the ambient temperature exceeds 85℃, the decrease in viscosity of the glass phase triggers the migration and reorganization of conductive particles, causing a nonlinear shift in resistance. Although some studies have lowered the sintering temperature to below 600℃ by incorporating fluxes such as Bi2O3, such modifications often come at the cost of sacrificing TCR performance and increasing interfacial contact resistance.

[0004] A more serious problem lies in the electrode-resistivity interface reaction: during sintering, the silver electrode undergoes a redox reaction with RuO2, generating an insulating Ag2O diffusion layer, which leads to an increase in contact resistance. Existing technologies attempt to suppress silver diffusion by adding transition metals such as Ni and Cr, but these alloying components easily form high-melting-point compounds (such as NiAl2O4) with the glass phase, which in turn requires increasing the sintering temperature, resulting in a paradoxical cycle of technological improvement.

[0005] To comply with environmental regulations, lead-free glass phase systems have become the inevitable choice. However, their sintering activity is reduced by about 30% compared to the traditional PbO-B2O3 system, resulting in a narrower process window. Two typical failure modes emerge in actual production: First, insufficient sintering leads to incomplete melting of the glass phase, failing to effectively wet the conductive phase and substrate, resulting in increased gaps between conductive particles, higher porosity, and conductive network defects. Second, over-sintering causes excessive flow or volatilization of the glass phase, encapsulating conductive particles and blocking conductive pathways, leading to an abnormally high resistivity.

[0006] With the expansion of millimeter-wave communication applications, the demand for low-loss potentiometers in the high-frequency band (3GHz) is becoming increasingly urgent. Traditional RuO2-based slurries are prone to significant dielectric losses due to the eddy current effect and interfacial polarization of micron-sized particles, resulting in aggravated signal attenuation. Related technologies have attempted to construct high-frequency adaptive conductive networks using one-dimensional materials such as carbon nanotubes to mitigate the eddy current effect. However, these one-dimensional materials have poor interfacial compatibility with the glass phase, easily agglomerating to form localized conductive inhomogeneities, leading to deterioration of resistance uniformity. At the same time, the TCR fluctuation of a single one-dimensional conductive phase is large, which cannot meet the stability requirements of high-precision potentiometers.

[0007] To address the aforementioned issues, this invention starts with material properties, designs a ruthenium salt-metal core-shell composite conductive phase, achieves TCR regulation at the nanoscale, and develops a glass system with gradient thermal expansion characteristics, taking into account both low-temperature sintering and interface stability, ultimately forming a low temperature coefficient resistive paste technology solution that meets the needs of high-end potentiometers. Summary of the Invention

[0008] To meet the performance requirements of potentiometers for low temperature coefficients, this invention provides a low temperature coefficient resistive paste for potentiometers and its preparation method. The specific technical solution provided by this invention is as follows.

[0009] Firstly, this invention provides a low temperature coefficient resistive paste for potentiometers, the components of which include a conductive phase, a glass phase, and an organic carrier; The conductive phase includes: bismuth ruthenate nanowires and carbon-coated copper nanowires; The glass phase includes: Bi2O3, B2O3, SiO2, and La2O3.

[0010] Furthermore, by mass percentage, the resistive paste comprises: 15-25% bismuth ruthenate nanowires, 5-10% carbon-coated copper nanowires, 30-50% glass phase, and 30-40% organic carrier.

[0011] Furthermore, the bismuth ruthenate nanowires have a diameter of 5±1 nm and a length of 30~40 nm.

[0012] Furthermore, the copper nanowires used to prepare carbon-coated copper nanowires have a diameter of 30±5 nm and a length of 3~5 μm.

[0013] Furthermore, the glass phase comprises, by mass percentage: 50% Bi2O3, 30% B2O3, 17% SiO2, and 3% La2O3.

[0014] Furthermore, the components of the organic carrier include, by mass percentage, 10-20% ethyl cellulose and 80-90% terpineol.

[0015] Secondly, the present invention provides a method for preparing the low temperature coefficient resistive paste for potentiometers, the method comprising: preparing bismuth ruthenate nanowires, preparing carbon-coated copper nanowires, preparing a glass phase, and preparing the resistive paste.

[0016] Furthermore, in the above preparation method, the preparation of bismuth ruthenate nanowires includes: preparing Bi(NO3)3·5H2O and RuCl3·3H2O by hydrothermal reaction combined with magnetic field directional drying; The preparation of the carbon-coated copper nanowires includes: preparing copper nanowires by liquid-phase reduction, and after surface activation treatment, using glucose as a carbon source, and performing carbon coating through hydrothermal reaction. The preparation of the glass phase includes: weighing 50% Bi2O3, 30% B2O3, 17% SiO2 and 3% La2O3 by mass percentage, and sequentially ball milling, high-temperature melting, quenching, pulverizing and sieving the raw materials to obtain the glass phase; The preparation of the resistive paste includes: mixing the prepared bismuth ruthenate nanowires, carbon-coated copper nanowires, glass phase and organic carrier in a certain proportion, and then rolling them on a three-roll mill to a fineness of ≤5μm.

[0017] Thirdly, the present invention claims protection for a potentiometer comprising: The substrate has arc-shaped or straight grooves on its surface; A resistive paste layer is coated into the groove; The sliding contact dynamically contacts the resistive slurry layer and changes the output resistance value through displacement; Pin terminals are used for circuit signal input and output; The resistive paste layer is obtained by screen printing the aforementioned resistive paste.

[0018] Compared with the prior art, the present invention, "a low temperature coefficient resistive paste for potentiometers and its preparation method," has at least the following beneficial effects or advantages: This invention employs a bismuth ruthenate / carbon-coated copper dual-conductive phase. The negative TCR (-80ppm / ℃) of bismuth ruthenate and the positive TCR (+60ppm / ℃) of carbon-coated copper form a self-compensating effect, controlling the TCR value within ±50ppm / ℃ and the sheet resistance within approximately 2.00Ω / □ with excellent uniformity (coefficient of variation 1.08%). The high-frequency insertion loss in the 3GHz band is as low as 0.28~0.31dB, making it suitable for high-density packaging and high-frequency applications, and helping to extend the service life of equipment.

[0019] On the other hand, this invention introduces the lanthanum stabilizer La2O3 into the lead-free glass system to improve the oxidation resistance of the glass phase, and reduces environmental pollution when combined with the lead-free formula; in the accelerated aging 1000h test, silver migration is completely suppressed and the leakage current change is ≤7%, which can ensure the safe operation of medical or industrial equipment.

[0020] This invention employs low-temperature sintering of the glass phase, significantly reducing sintering energy consumption. While achieving densification sintering at low temperatures, the resistance change is only 0.73% after 1000 thermal cycles (-55~125℃), achieving a balance between low-temperature sintering and high stability. Detailed Implementation

[0021] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0022] Example 1 This embodiment describes the preparation of the glass phase.

[0023] 1. Raw material pretreatment 1) Weighing and mixing ratio: Using an electronic balance (accuracy 0.1mg), weigh out the following: 50g Bi2O3, 30g B2O3, 17g SiO2, and 3g La2O3.

[0024] 2) Ball milling: Load the raw materials into a zirconia ball mill jar (500mL volume) and mix using dry ball milling (ball-to-material ratio 5:1) for 2 hours at a speed of 300rpm to ensure uniform mixing of components. Pause for 10 minutes every 0.5 hours to prevent overheating.

[0025] 2. High-temperature melting 1) Charging and melting: Transfer the mixed powder to a platinum crucible (99.9% Pt), place it in a box-type resistance furnace, raise the temperature to 500℃ at 5℃ / min and hold for 60min to remove adsorbed water and organic residues; then raise the temperature to 900℃ at 3℃ / min and hold for 1h to melt the low melting point components to form the melt matrix; then raise the temperature to 1120℃ at 2℃ / min and hold for 2h to ensure complete melting; maintain the temperature at 1120℃ for 30min.

[0026] 2) Quenching treatment: The melt is quickly poured into deionized water for quenching, and the deionized water is stirred at high speed. The water bath volume is 50 times that of the melt to obtain amorphous glass slag.

[0027] 3. Crushing and Grading 1) Primary crushing: Crush glass fragments to a particle size of <1mm.

[0028] 2) Ultrafine grinding: An air jet mill (pressure 0.8MPa, classifier speed 8000rpm) is used. The airflow speed is adjusted to D50=2~3μm (particle size distribution Span value ≤1.0) by online monitoring with a laser particle size analyzer.

[0029] 3) Post-processing: After the powder is filtered through a 200-mesh sieve, it is vacuum-packed (-0.1MPa, aluminum foil bag) and stored in a drying oven (humidity <10% RH, 25℃) for later use.

[0030] Example 2 This embodiment describes the preparation of bismuth ruthenate (Bi2Ru2O7) nanowires.

[0031] 1. Raw material preparation 1) Preparation of precursor solutions (operated in a nitrogen glove box): Solution A (bismuth source): Dissolve Bi(NO3)3·5H2O (4.85g, 10mmol) in 20mL dilute nitric acid (5wt%) and stir magnetically until transparent; Solution B (ruthenium source): Dissolve RuCl3·3H2O (2.61g, 10mmol) in 30mL ethylene glycol and sonicate for 30min (300W).

[0032] 2) pH adjuster: Prepare 200 mL of 0.5 mol / L NaOH solution for later use.

[0033] 2. Hydrothermal reaction 1) Coprecipitation reaction: Slowly add solution A to solution B (dropping rate approximately 1 mL / min), simultaneously adding NaOH to maintain pH = 10.5 ± 0.2. The solution gradually changes from dark green to brownish-red, indicating that Bi... 3+ / Ru 3+ Co-precipitation forms.

[0034] 2) Filling and sealing: Transfer the mixture to a 100mL PTFE-lined stainless steel reactor, with the filling degree controlled at 70%. Tighten the reactor with a torque wrench (25N·m) and perform 3 cycles of vacuuming and nitrogen replacement.

[0035] 3) Step temperature ramping program: The temperature is ramped up in a step-by-step manner according to the following steps: 80℃, 2h (to eliminate thermal stress), 120℃, 1h (to form crystal nuclei), and 200℃, 12h (to grow nanowires).

[0036] 3. Post-processing 1) Product collection: After naturally cooling to 60℃, open the vessel and centrifuge (8000rpm, 10min). Wash with deionized water and anhydrous ethanol alternately 5 times (centrifuge for 5min each time).

[0037] 2) Directional drying: The precipitate was dispersed in 50 mL of n-hexane and placed in a uniform magnetic field with a magnetic field strength of 0.5 T parallel to the growth direction of the nanowires. The solvent was slowly evaporated at a rate of 5 mL / h at 60 °C and vacuum dried for 6 h to obtain oriented bismuth ruthenate (Bi2Ru2O7) nanowire bundles.

[0038] The bismuth ruthenate (Bi₂Ru₂O₇) nanowires were found to have a diameter of 5±1 nm and a length of 30~40 nm. X-ray diffraction (XRD) was used to measure the (111) crystal plane orientation of the bismuth ruthenate nanowires after directional drying. The preferred orientation was ≥85% (calculated using the Harris method).

[0039] This embodiment successfully prepared bismuth ruthenate nanowires with high crystallinity and specific exposed crystal faces through an ethylene glycol-mediated orientation growth mechanism combined with magnetic field-assisted drying. Compared with the traditional solid-state method, the hydrothermal synthesis temperature is reduced by approximately 200°C, and the product exhibits excellent conductivity without subsequent annealing. The abundant oxygen vacancies on the surface of the bismuth ruthenate nanowires can further enhance the TCR compensation effect of the resistive slurry.

[0040] Example 3 This embodiment describes the preparation of carbon-coated copper nanowires (Cu@C).

[0041] 1. Raw material pretreatment 1) Copper nanowire synthesis: High aspect ratio copper nanowires were prepared by liquid-phase reduction method: CuCl2·2H2O (1.70 g, 10 mmol) was dissolved in 50 mL of ethylenediamine / water mixed solvent (volume ratio 1:4), 20 mL of 0.1 M ascorbic acid solution was added, and the reaction was carried out at 80 °C for 3 h. After centrifugation, copper nanowires with a diameter of 30 ± 5 nm and a length of 3 ~ 5 μm were obtained.

[0042] 2) Surface activation treatment: Copper nanowires were immersed in 0.1M sodium citrate solution, sonicated at 150W for 30 minutes, and dried at 60℃ under nitrogen protection. After activation, the surface zeta potential was measured by a zeta potential meter, and the zeta potential was -30~-40mV, indicating the formation of a hydrophilic surface active layer.

[0043] 2. Carbon coating process 1) Preparation of glucose carbon source solution: Prepare a 0.8M glucose solution using deionized water as solvent, and add 0.05wt% cetyltrimethylammonium bromide (CTAB) as a dispersant.

[0044] 2) Hydrothermal coating reaction: Copper nanowires: glucose solution = 1:20 by mass, and transfer to a stainless steel reactor lined with polytetrafluoroethylene. Set a step heating program: 80℃, 1h, 120℃, 1h, 180℃, 16h.

[0045] 3) Post-treatment: The product after the reaction was washed alternately with ethanol and deionized water and centrifuged (8000 rpm, 5 min, 5 cycles). It was then annealed at 300 °C for 2 h in a mixed atmosphere of 5% H2 and 95% Ar to enhance the graphitization of the carbon layer and obtain carbon-coated copper nanowires.

[0046] Transmission electron microscopy (TEM) revealed that the carbon coating of the carbon-coated copper nanowires was 100%, with no exposed copper surface. Thermogravimetric analysis (TGA) was used to measure the weight loss at 500℃ in air at a heating rate of 10℃ / min, corresponding to the carbon layer mass fraction. Combined with TEM observation, this confirmed a 100% carbon coating rate.

[0047] In this embodiment, a continuous carbon layer is constructed on the surface of copper nanowires using a hydrothermal method. The advantages are that the carbon shell effectively blocks the interdiffusion between copper and silver and inhibits dendrite formation; the graphitized carbon layer reduces high-frequency losses caused by the skin effect; and the addition of a small amount of carbon to coat the copper nanowires can form a three-dimensional conductive network in the silver paste, balancing cost and performance.

[0048] Example 4 This embodiment describes the preparation of the resistive paste.

[0049] 1. Preparation of glass phase: Prepared according to the method in Example 1.

[0050] 2. Conductive phase treatment: Bismuth ruthenate (Bi2Ru2O7) nanowires were prepared by the method in Example 2, and carbon-coated copper nanowires (Cu@C) were prepared by the method in Example 3.

[0051] 3. Slurry preparation: Take 15g of the prepared Bi2Ru2O7 nanowires, 5g of Cu@C nanowires, 50g of glass phase, 3g of ethyl cellulose, and 27g of terpineol (the sum of the mass percentages of each component is 100%), mix them, and roll them on a three-roll mill until the fineness is ≤5μm.

[0052] Example 5 This embodiment describes the preparation of the resistive paste.

[0053] 1. Preparation of glass phase: Prepared according to the method in Example 1.

[0054] 2. Conductive phase treatment: Bismuth ruthenate (Bi2Ru2O7) nanowires were prepared by the method in Example 2, and carbon-coated copper nanowires (Cu@C) were prepared by the method in Example 3.

[0055] 3. Slurry preparation: Take 20g of the prepared Bi2Ru2O7 nanowires, 10g of Cu@C nanowires, 40g of glass phase, 6g of ethyl cellulose, and 24g of terpineol (the sum of the mass percentages of each component is 100%), mix them, and roll them on a three-roll mill to a fineness of ≤5μm to obtain the slurry.

[0056] Example 6 This embodiment describes the preparation of the resistive paste.

[0057] 1. Preparation of glass phase: Prepared according to the method in Example 1.

[0058] 2. Conductive phase treatment: Bismuth ruthenate (Bi2Ru2O7) nanowires were prepared by the method in Example 2, and carbon-coated copper nanowires (Cu@C) were prepared by the method in Example 3.

[0059] 3. Slurry preparation: Take 25g of the prepared Bi2Ru2O7 nanowires, 5g of Cu@C nanowires, 30g of glass phase, 8g of ethyl cellulose, and 32g of terpineol (the sum of the mass percentages of each component is 100%), mix them, and roll them on a three-roll mill to a fineness of ≤5μm to obtain the slurry.

[0060] Comparative Example 1 This comparative example provides a resistive paste without Cu@C nanowires.

[0061] Conductive phase: Bi2Ru2O7 nanowires, 30g (30%); Glass phase: 40g (40%), prepared according to the method of Example 1; Organic carrier: 30g (30%), of which: ethyl cellulose 20% and terpineol 80%.

[0062] Preparation method: The conductive phase, glass phase and organic carrier are mixed and rolled to a fineness of ≤10μm using a three-roll mill.

[0063] Comparative Example 2 This comparative example provides a resistive paste without the addition of La2O3.

[0064] Conductive phase: 20g (20%) Bi2Ru2O7 nanowires + 10g (10%) Cu@C nanowires; Glass phase: 40g (40%), of which: Bi2O3 50%, B2O3 30%, SiO2 20%; Organic carrier: 30g (30%), of which: ethyl cellulose 20% and terpineol 80%.

[0065] Preparation method: The conductive phase, glass phase and organic carrier are mixed and rolled to a fineness of ≤10μm using a three-roll mill.

[0066] Comparative Example 3 This comparative example provides a conventional resistive paste without the addition of Cu@C nanowires and La2O3.

[0067] Conductive phase: Bismuth ruthenate micron particles (D50=2μm), 30g (30%); Glass phase: 40g (40%), of which: Bi2O3 50%, B2O3 30%, SiO2 20%; Organic carrier: 30g (30%), of which: ethyl cellulose 20% and terpineol 80%.

[0068] Preparation method: The conductive phase, glass phase and organic carrier are mixed and rolled to a fineness of ≤10μm using a three-roll mill.

[0069] Example 7 This embodiment describes the performance test of the slurry sample prepared in Example 5 (preferred embodiment) and the resistive slurry samples prepared in Comparative Examples 1 to 3.

[0070] I. Sample Preparation Sample specifications: 96% Al2O3 ceramic substrate (size 50mm×50mm×0.635mm) was selected, and the resistive paste of Example 5 and Comparative Examples 1~3 was printed into rectangular resistive strips of 2mm×10mm (film thickness controlled at 15±2μm) by screen printing process.

[0071] Sintering process: All samples were placed in a box-type resistance furnace and subjected to the same sintering regime: the temperature was increased to 480℃ at a rate of 5℃ / min, held for 30min, and then naturally cooled to room temperature.

[0072] Electrode preparation: The input / output electrodes of all samples were made with the same specification of silver paste (silver content 99.5%), and were printed and sintered using the same process (480℃ for 20 min) to ensure consistent electrode-resistor interface conditions.

[0073] II. Testing Methods 1. Sheet resistance and uniformity test: Sheet resistance is tested using a four-probe tester: Five test points are evenly selected on each sintered resistance pattern (avoiding the 1mm edge area), and the sheet resistance at each point is measured using the four-probe method. The average value (Rs_avg) of the five points is calculated. Then, the sheet resistance uniformity is evaluated by calculating the average value and coefficient of variation of all point data.

[0074] 2. Temperature Coefficient of Resistance (TCR) Test: The test was conducted using a high-low temperature chamber and a high-precision multimeter. The test temperature range was set to -55℃ to 125℃. The sample was held at three key temperature points—-55℃, 25℃, and 125℃—for 30 minutes each to ensure temperature stability. The resistance value at each temperature point was measured and calculated according to the formula. Calculate the temperature coefficient of resistance, where R 125 R is the resistance at 125℃. -55 R is the resistance at -55℃. 25 This is the resistance value at 25℃.

[0075] 3. Thermal Cycling Stability Test: A high and low temperature shock chamber was used for testing. The thermal cycling conditions were set as follows: after holding at -55℃ for 30 minutes, the temperature was quickly switched to 125℃ and held for 30 minutes. This constituted one complete cycle, and 1000 cycles were completed. The initial resistance R0 of the sample was recorded before the test, and the final resistance R was measured after 1000 cycles. 1000 According to the formula, the rate of change of resistance = (R 1000 -R0) / R0×100%, calculate the change in resistance of the sample after the cold and hot cycle.

[0076] 4. Silver Migration Resistance Test: Test Equipment: Constant temperature and humidity chamber, high-precision leakage current tester, DC regulated power supply, and optical microscope. Test Conditions: Environmental Conditions: Temperature 85±2℃, relative humidity 85±3% RH, test duration 1000h; Electrical Conditions: A constant voltage of 100V DC (electric field strength 20V / mm) was applied to the silver electrode of each sample, and the voltage was kept stable throughout the test. Electrical data acquisition: Record the initial leakage current (stable value 1 hour before testing) and the leakage current over 1000 hours, and calculate the leakage current variation. Microscopic morphology observation: Take out the sample every 200 hours, and after standing for 1 hour at room temperature (25℃) and normal humidity (50% RH), observe the surface of the resistive slurry layer, the electrode edge, and the area between the electrodes using an optical microscope. Record the formation of silver dendrites (length > 1 μm). Judgment criteria: No silver dendrites (length ≤ 1 μm), qualified; a small number of silver dendrites (1~10 μm), unqualified; silver dendrites ≥ 10 μm, failed.

[0077] 5. High-frequency insertion loss test: A vector network analyzer was used, employing a microstrip line test structure, with the test frequency set to 3 GHz. The scattering parameter S of the sample was measured. 21 The high-frequency insertion loss (in dB) of the sample in the 3 GHz band was calculated.

[0078] III. Test Result Analysis 1. Sheet resistance and uniformity test (unit: Ω / □) Table 1. Shear resistance and coefficient of variation of each group of samples

[0079] Example 5 showed an average sheet resistance of 2.00 Ω / □ and a coefficient of variation of only 1.08%, demonstrating excellent printing uniformity. Comparative Example 1, lacking the conductive network compensation of carbon-coated copper nanowires, had a higher sheet resistance and decreased uniformity; Comparative Example 3 used micron-sized bismuth ruthenate particles, but particle agglomeration led to uneven conductive pathways, with a coefficient of variation of 3.82%.

[0080] 2. Temperature coefficient of resistance (TCR) test (unit: ppm / ℃) Table 2. Temperature coefficient of resistance of each group of samples

[0081] Example 5 utilizes the TCR self-compensation effect of bismuth ruthenate (-80 ppm / ℃) and carbon-coated copper (+60 ppm / ℃), achieving an average TCR of 40.7 ppm / ℃, ≤±50 ppm / ℃. Comparative Example 1, without the positive TCR compensation of carbon-coated copper, exhibits a strong negative TCR deviation; Comparative Example 3 uses a traditional micron-scale conductive phase, where the grain boundary conduction mechanism results in a TCR as high as -185.2 ppm / ℃, leading to poor temperature stability.

[0082] 3. Resistance change rate test after hot and cold cycling (unit: %) Table 3. Resistance change rate of each group of samples after thermal cycling

[0083] In Example 5, the stabilizing effect of La2O3 in the glass phase suppressed conductive phase migration and interface cracking, resulting in an average resistance change rate of only 0.73% after thermal cycling, lower than 0.8%. Comparative Example 2, lacking La2O3, exhibited insufficient glass phase structural stability, with a resistance change rate reaching 3.00%. In Comparative Example 3, the weak bonding between the micron-sized particles and the glass phase exacerbated interface defects after cycling, leading to a resistance change rate as high as 3.71%.

[0084] 4. Anti-silver migration test (unit: %) Table 4. Results of silver migration resistance tests for each group of samples.

[0085] The results showed that Example 5 exhibited no silver dendrite formation and a leakage current variation of ≤7%, demonstrating satisfactory anti-silver migration performance. In contrast, the comparative examples lacking either carbon-coated copper nanowires or La2O3 showed silver dendrites of varying lengths and significantly increased leakage current variations (24-125%), thus being deemed unqualified or ineffective, respectively. The experiment demonstrates that the synergistic effect of the carbon shell of the carbon-coated copper nanowires and La2O3 is crucial for suppressing silver migration and ensuring stable electrical performance; both are indispensable.

[0086] 5. High-frequency insertion loss test (unit: dB) Table 5. High-frequency insertion loss of each group of samples

[0087] The nanowire conductive phase (bismuth ruthenate + carbon-coated copper) in Example 5 effectively reduces eddy current effects and interfacial polarization, with an average insertion loss of only 0.28~0.31dB in the 3GHz band, meeting the requirements of high-frequency communication scenarios. In contrast, the micron-scale conductive phase in Comparative Example 3 exhibits significant eddy current effects, resulting in an insertion loss of 0.82~0.86dB, making it unsuitable for high-frequency applications.

[0088] IV. Conclusion The performance tests above show that the resistive paste of Example 5 of the present invention, through the TCR self-compensation design of bismuth ruthenium / carbon-coated copper dual conductive phase and the stability enhancement design of La2O3 modified lead-free glass phase, is significantly better than comparative examples 1 to 3 in terms of key indicators such as sheet resistance accuracy, temperature stability, environmental reliability, high frequency adaptability and low temperature sintering performance. It can meet the application requirements of high-end potentiometers in miniaturization, high precision, wide temperature range and high frequency scenarios.

[0089] The above embodiments can well illustrate the technical solution of the present invention, but they are only describing preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, all kinds of changes and improvements made by those skilled in the art to the technical solution of the present invention should fall within the protection scope defined by the present invention.

Claims

1. A low temperature coefficient resistive paste for potentiometers, characterized in that, Its components include a conductive phase, a glassy phase, and an organic support; The conductive phase includes: bismuth ruthenate nanowires and carbon-coated copper nanowires; The glass phase includes: Bi2O3, B2O3, SiO2, and La2O3.

2. The low temperature coefficient resistive paste for potentiometers according to claim 1, characterized in that, The resistive paste comprises, by mass percentage: 15-25% bismuth ruthenate nanowires, 5-10% carbon-coated copper nanowires, 30-50% glass phase, and 30-40% organic carrier.

3. The low temperature coefficient resistive paste for potentiometers according to claim 1, characterized in that, The bismuth ruthenate nanowires have a diameter of 5±1 nm and a length of 30~40 nm.

4. The low temperature coefficient resistive paste for potentiometers according to claim 1, characterized in that, The copper nanowires used to prepare carbon-coated copper nanowires have a diameter of 30±5 nm and a length of 3~5 μm.

5. The low temperature coefficient resistive paste for potentiometers according to claim 1, characterized in that, The glass phase comprises, by mass percentage: 50% Bi2O3, 30% B2O3, 17% SiO2, and 3% La2O3.

6. The low temperature coefficient resistive paste for potentiometers according to claim 1, characterized in that, The components of the organic carrier include, by mass percentage, 10-20% ethyl cellulose and 80-90% terpineol.

7. The method for preparing the low temperature coefficient resistive paste for potentiometers according to claim 1, characterized in that, The preparation method includes: preparing bismuth ruthenate nanowires, preparing carbon-coated copper nanowires, preparing a glass phase, and preparing a resistive paste.

8. The preparation method according to claim 7, characterized in that, The preparation of bismuth ruthenate nanowires includes: preparing Bi(NO3)3·5H2O and RuCl3·3H2O through a hydrothermal reaction combined with magnetic field-directed drying; The preparation of the carbon-coated copper nanowires includes: preparing copper nanowires by liquid-phase reduction, and after surface activation treatment, using glucose as a carbon source, and performing carbon coating through hydrothermal reaction. The preparation of the glass phase includes: weighing 50% Bi2O3, 30% B2O3, 17% SiO2 and 3% La2O3 by mass percentage, and sequentially ball milling, high-temperature melting, quenching, pulverizing and sieving the raw materials to obtain the glass phase; The preparation of the resistive paste includes: mixing the prepared bismuth ruthenate nanowires, carbon-coated copper nanowires, glass phase and organic carrier in a certain proportion, and then rolling them on a three-roll mill to a fineness of ≤5μm.

9. A potentiometer, the potentiometer comprising: The substrate has arc-shaped or straight grooves on its surface; A resistive paste layer is coated into the groove; The sliding contact dynamically contacts the resistive slurry layer and changes the output resistance value through displacement. Pin terminals are used for circuit signal input and output; The resistive paste layer is characterized in that it is obtained by screen printing the resistive paste according to claim 1.

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