Thermistor silver-coated nickel paste and preparation method thereof
By using silver-coated nickel powder with a silver content of 10-30wt% and glass powder with specific components, the problems of poor adhesion and high cost of thermistors have been solved, achieving low resistance change rate and stable welding pull force, and reducing production costs.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- GUANGDONG NANHAI ETETB TECH CO LTD
- Filing Date
- 2026-04-28
- Publication Date
- 2026-06-26
AI Technical Summary
Existing silver-coated nickel pastes are unsuitable for use with thermistors, exhibiting poor adhesion and high cost, and are unable to effectively reduce the rate of resistance change.
Silver-coated nickel powder with a silver content of 10-30wt% is used, combined with glass powder and carrier solution of specific components, to suppress thermal stress concentration through the three-phase interface, forming a silver-coated nickel paste with excellent adhesion and low resistance change.
It achieves excellent adhesion to thermistors, reduces production costs, and suppresses thermal expansion mismatch at high temperatures, maintaining stable welding pull and low resistance change rate.
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Abstract
Description
Technical Field
[0001] This invention relates to the field of conductive materials containing metals or alloys, and specifically to a silver-coated nickel paste for a thermistor and its preparation method. Background Technology
[0002] Thermistors are semiconductor ceramics. After the paste is printed onto the surface of the thermistor, a sintering process is required. The paste needs to form an extremely low contact resistance with the semiconductor ceramic to ensure accurate signal transmission and maintain a stable current change rate. Currently used pastes are mostly silver pastes, which are expensive due to their high silver content. Preparing silver-coated nickel paste can reduce the production cost of the paste; however, existing silver-coated nickel pastes are not suitable for thermistor applications due to poor adhesion and tensile strength. Therefore, developing a silver-coated nickel paste with a low resistance change rate and excellent adhesion to thermistors is crucial.
[0003] Chinese invention patent CN107945909A discloses an electrode silver paste for strontium titanate ring varistors and its preparation method. It utilizes chemical deposition to obtain silver-coated nickel alloy powder, which avoids the conductivity decrease problem caused by oxidation and maintains the same good conductivity as pure silver powder, while also significantly reducing costs. However, its adhesion to thermistors is poor, making it unsuitable for thermistor applications. Chinese invention patent CN119626626B discloses a silver-coated nickel paste and its preparation method, as well as a method for metallizing high-temperature sintered silicon solar cells. It uses a dense, high-reliability silver-coated nickel powder without nickel dispersants for single-back printing of high-temperature sintered silicon solar cells. Compared to pure silver paste, the contact resistance and printing wet weight are essentially the same, while costs are reduced. However, it cannot solve the technical problem of resistance change rate. Summary of the Invention
[0004] In order to develop a silver-coated nickel paste with a small resistance change rate and excellent adhesion to thermistors, the first aspect of the present invention provides a thermistor silver-coated nickel paste, the raw materials for which are prepared by weight percentage include 5-10% carrier solution, 30-50% silver powder, 3-5% glass powder, 10-20% silver-coated nickel powder, and 2-30% organic solvent, the total weight percentage being 100%, wherein the silver in the silver-coated nickel powder accounts for 10-30 wt% of the mass of the silver-coated nickel powder.
[0005] In this invention, silver-coated nickel powder with a silver content of 10-30 wt% is used in silver-coated nickel slurry to maintain stable welding pull force and exhibit low surge resistance and steady-state current resistance changes. When the silver content is <10%, insufficient conductivity leads to increased contact resistance; when the silver content is >30%, the effect of the nickel core weakens, and thermal stability decreases. A silver content of 10-30% provides a suitable silver shell thickness: it forms a good conductive path while ensuring sufficient thermal expansion buffering for the nickel core. At this ratio, the silver-coated nickel powder forms a "silver-nickel-glass" three-phase interface during sintering, effectively suppressing thermal stress concentration, making it suitable for thermistors.
[0006] In one embodiment, the raw materials for preparing the carrier solution include 80-90% resin solution, 6-10% dispersant and 4-10% leveling agent by weight percentage, with the total weight percentage being 100%.
[0007] In one embodiment, the resin solution comprises a resin and an organic solvent; the resin comprises at least one of acrylic resin, ethyl cellulose, epoxy resin, phenolic resin, polyimide resin, or polyvinyl butyral resin.
[0008] In one embodiment, both organic solvent one and organic solvent two include at least one of triethylene glycol monobutyl ether, tripropylene glycol monobutyl ether, dimethyl phthalate, terpineol, diethylene glycol butyl ether acetate, alcohol ester-12, butyl carbiphenyl, butyl carbiphenyl acetate, and ethylene glycol phenyl ether.
[0009] In one embodiment, the dispersant includes at least one of polyvinylpyrrolidone, polyvinyl alcohol, tributyl phosphate, oleic acid, and polyhydroxystearic acid.
[0010] In one embodiment, the leveling agent includes at least one of polyether-modified silicone leveling agent, modified polyacrylate leveling agent, anionic water-soluble ester leveling agent, and polyester leveling agent.
[0011] In one embodiment, the weight ratio of the resin to the second organic solvent is (30-60):(40-70).
[0012] In one embodiment, the D50 particle size of the glass powder is 2-4 μm.
[0013] In one embodiment, the D50 particle size of the glass powder is 2-3 μm.
[0014] In one embodiment, the raw materials for preparing the glass powder include, by weight, 40-65 parts Bi2O3, 10-30 parts B2O3, 1-10 parts SiO2, 10-30 parts ZnO, 5-20 parts CuO, 5-20 parts MnO, 1-10 parts Al2O3, 1-10 parts TiO2, 0.5-5 parts Na2O, and 0.5-5 parts K2O.
[0015] As one embodiment, the preparation method of the glass powder includes the following steps: mixing Bi2O3, B2O3, SiO2, ZnO, CuO, MnO, Al2O3, TiO2, Na2O, and K2O, melting them into a uniform glass liquid at 1000-1200℃, quenching them in water to form glass sheets, and obtaining glass powder by ball milling and air jet pulverization.
[0016] In one embodiment, the D50 particle size of the silver powder is 0.4-0.9 μm; the D50 particle size of the silver-coated nickel powder is 2-6 μm.
[0017] As one embodiment, the method for preparing the carrier solution includes the following steps: Mix the resin with organic solvent II and stir at 80-100℃ for 20-150 min to form a resin solution; Mix the resin solution with the dispersant and leveling agent, and stir at 800-1200 rpm for 20-50 minutes to obtain the carrier solution.
[0018] A second aspect of the present invention provides a method for preparing a silver-coated nickel paste for a thermistor, comprising the following steps; Preparation of carrier solution; Preparation of glass powder; The carrier solution, silver powder, silver-coated nickel powder, glass powder and organic solvent are mixed and stirred evenly to obtain a slurry; The slurry is stirred at 500-2100 rpm for 30-60 minutes, then rolled and sieved to obtain the silver-coated nickel paste for the thermistors.
[0019] In one embodiment, the rolling is performed by rolling with a three-roll mill 5-7 times until the slurry fineness is ≤10μm.
[0020] In one embodiment, the pore size of the sieve is ≤10μm.
[0021] Compared with the prior art, the present invention has the following beneficial effects: (1) The silver-coated nickel paste of the thermistor described in this invention uses silver-coated nickel powder to replace part of the silver powder, which can provide excellent thermal stability, effectively suppress thermal expansion mismatch at high temperature, and is suitable for thermistors, reducing the cost of precious metals.
[0022] (2) The thermistor silver-coated nickel paste of the present invention uses silver-coated nickel powder with a D50 particle size of 2.0-6.0μm, which balances the efficiency of conductive path formation and sintering density, so that the silver-coated nickel powder can form a continuous conductive network during sintering, while avoiding oxidation problems caused by excessively fine particles.
[0023] (3) The thermistor silver-coated nickel paste of the present invention uses silver-coated nickel powder with a silver content of 10-30wt%, which can maintain stable welding pull force and has low surge impact resistance change rate and steady-state current resistance change rate.
[0024] (4) The thermistor silver-coated nickel paste of the present invention uses glass powder with a D50 particle size of 2-4μm, which can avoid premature melting in the early stage of sintering and cause the slurry flow to run out of control. It can also effectively coat the silver-coated nickel powder particles, so that the glass powder forms a uniform glass bridging layer during the sintering process, and promote the interface bonding between the silver-coated nickel powder and the matrix.
[0025] (5) The silver-coated nickel paste of the thermistor described in this invention uses glass powder with specific components to form a low melting point eutectic glass, which can quickly wet the surface of the silver-coated nickel powder during sintering, so that the glass phase matches the ceramic matrix and reduces thermal stress cracks. Detailed Implementation
[0026] Example 1 A thermistor silver-coated nickel paste, prepared by weight percentage, comprises a carrier solution of 10%, silver powder of 50%, glass powder of 4%, silver-coated nickel powder of 10%, and organic solvent of 26%; wherein the silver in the silver-coated nickel powder accounts for 10 wt% of the mass of the silver-coated nickel powder.
[0027] The raw materials for preparing the carrier solution include, by weight percentage, 85% resin solution, 7% dispersant and 8% leveling agent.
[0028] The resin solution comprises a resin and an organic solvent, wherein the resin is a combination of acrylic resin, ethyl cellulose, and epoxy resin, and the organic solvent is diethylene glycol butyl ether acetate.
[0029] The weight ratio of the acrylic resin, ethyl cellulose, epoxy resin, and diethylene glycol butyl ether acetate is 15:15:10:60. The acrylic resin was purchased from Mitsubishi and its grade is BR115; the ethyl cellulose was purchased from Dow and its grade is Std45; and the epoxy resin was purchased from Baling Petrochemical and its grade is E-44.
[0030] The dispersant was purchased from Lubrizol, brand name 2291; the leveling agent was purchased from METOLAT® 288 in Germany.
[0031] The method for preparing the carrier solution includes the following steps: Mix the resin with organic solvent II and stir at 80°C for 40 minutes to form a resin solution; The resin solution was mixed with the dispersant and leveling agent and stirred at 800 rpm for 30 minutes to obtain the carrier solution.
[0032] The silver powder has a D50 particle size of 0.4-0.9 μm and was purchased from Guizhou Research Institute, with the brand name Agf-6000.
[0033] The silver-coated nickel powder has a D50 particle size of 2-6 μm and was purchased from Yinrui, grade YRS-AN060-10.
[0034] The organic solvent is tripropylene glycol monobutyl ether.
[0035] The raw materials for preparing the glass powder include, by weight, 50 parts Bi2O3, 10 parts B2O3, 3 parts SiO2, 10 parts ZnO, 15 parts CuO, 5 parts MnO, 3 parts Al2O3, 2 parts TiO2, 1 part Na2O, and 1 part K2O.
[0036] The D50 particle size of the glass powder is 2-3 μm.
[0037] The preparation method of the glass powder includes the following steps: mixing Bi2O3, B2O3, SiO2, ZnO, CuO, MnO, Al2O3, TiO2, Na2O, and K2O, melting them into a uniform glass liquid at 1000-1200℃, quenching them in water to form glass sheets, and obtaining glass powder by ball milling and air jet pulverization.
[0038] A method for preparing a silver-coated nickel paste for a thermistor includes the following steps; Preparation of carrier solution; Preparation of glass powder; The carrier solution, silver powder, silver-coated nickel powder, glass powder and organic solvent are mixed and stirred evenly to obtain a slurry; The slurry was stirred at 800 rpm for 60 minutes and rolled 6 times using a three-roll mill until the fineness of the slurry was ≤10μm. The slurry was then sieved to obtain the silver-coated nickel slurry for the thermistors.
[0039] Example 2 A thermistor silver-coated nickel paste, prepared by weight percentage, comprises a carrier solution of 8%, silver powder of 45%, glass powder of 4.5%, silver-coated nickel powder of 15%, and organic solvent of 27.5%; wherein the silver in the silver-coated nickel powder accounts for 10 wt% of the mass of the silver-coated nickel powder.
[0040] The raw materials for preparing the carrier solution include, by weight percentage, 80% resin solution, 10% dispersant and 10% leveling agent.
[0041] The resin solution comprises a resin and an organic solvent, wherein the resin is a combination of acrylic resin, ethyl cellulose, and polyvinyl butyral resin, and the organic solvent is butyl carbiphenyl acetate.
[0042] The weight ratio of the acrylic resin, ethyl cellulose, polyvinyl butyral resin, and butyl carbiphenyl acetate is 20:15:10:55. The acrylic resin was purchased from Disparon, brand name ER2602; the ethyl cellulose was purchased from Dow, brand name Std45; and the polyvinyl butyral resin was purchased from Kuraray, brand name 30H.
[0043] The dispersant was purchased from Rieter Resin, brand name LD-109; the leveling agent was purchased from Zyxel, brand name ADDITOL-VXL 4930.
[0044] The method for preparing the carrier solution includes the following steps: The resin was mixed with organic solvent II and stirred at 90°C for 60 min to form a resin solution. The resin solution was mixed with the dispersant and leveling agent and stirred at 1000 rpm for 30 minutes to obtain the carrier solution.
[0045] The silver powder has a D50 particle size of 0.4-0.9 μm and was purchased from Yinrui, brand name YRS 600.
[0046] The D50 particle size of the silver-coated nickel powder is 2-6 μm, and it was purchased from Yinrui, YRS-AN060-10.
[0047] The organic solvent is diethylene glycol butyl ether acetate.
[0048] The raw materials for preparing the glass powder include, by weight, 45 parts Bi2O3, 10 parts B2O3, 3 parts SiO2, 10 parts ZnO, 15 parts CuO, 10 parts MnO, 3 parts Al2O3, 2 parts TiO2, 1 part Na2O, and 1 part K2O.
[0049] The D50 particle size of the glass powder is 2-3 μm.
[0050] The preparation method of the glass powder includes the following steps: mixing Bi2O3, B2O3, SiO2, ZnO, CuO, MnO, Al2O3, TiO2, Na2O, and K2O, melting them into a uniform glass liquid at 1000-1200℃, quenching them in water to form glass sheets, and obtaining glass powder by ball milling and air jet pulverization.
[0051] A method for preparing a silver-coated nickel paste for a thermistor includes the following steps; Preparation of carrier solution; Preparation of glass powder; The carrier solution, silver powder, silver-coated nickel powder, glass powder and organic solvent are mixed and stirred evenly to obtain a slurry; The slurry was stirred at 800 rpm for 60 minutes and rolled 6 times using a three-roll mill until the fineness of the slurry was ≤10μm. The slurry was then sieved to obtain the silver-coated nickel slurry for the thermistors.
[0052] Example 3 A thermistor silver-coated nickel paste, the raw materials for preparation by weight percentage include 10% carrier solution, 40% silver powder, 5% glass powder, 20% silver-coated nickel powder, and 25% organic solvent; the silver in the silver-coated nickel powder accounts for 10 wt% of the mass of the silver-coated nickel powder.
[0053] The raw materials for preparing the carrier solution include, by weight percentage, 90% resin solution, 5% dispersant and 5% leveling agent.
[0054] The resin solution comprises a resin and an organic solvent, wherein the resin is a combination of acrylic resin and ethyl cellulose, and the organic solvent is diethylene glycol butyl ether acetate.
[0055] The acrylic resin, ethyl cellulose, and diethylene glycol butyl ether acetate are present in a weight ratio of 20:20:60. The acrylic resin is purchased from Mitsubishi and its grade is BR115; the ethyl cellulose is purchased from Eastman and its grade is CAB-381-20.
[0056] The dispersant was purchased from Lubrizol, brand name 2291; the leveling agent was purchased from METOLAT® 288 in Germany.
[0057] The method for preparing the carrier solution includes the following steps: Mix the resin with organic solvent II and stir at 80°C for 40 minutes to form a resin solution; The resin solution was mixed with the dispersant and leveling agent and stirred at 800 rpm for 30 minutes to obtain the carrier solution.
[0058] The silver powder has a D50 particle size of 0.4-0.9 μm and was purchased from Yinke, with the grade name YK-9.
[0059] The D50 particle size of the silver-coated nickel powder is 2-6 μm, and it was purchased from Yinrui, YRS-AN060-10.
[0060] The organic solvent is butyl carbihydrol.
[0061] The raw materials for preparing the glass powder include, by weight, 55 parts Bi2O3, 10 parts B2O3, 3 parts SiO2, 10 parts ZnO, 10 parts CuO, 5 parts MnO, 3 parts Al2O3, 2 parts TiO2, 1 part Na2O, and 1 part K2O.
[0062] The D50 particle size of the glass powder is 2-3 μm.
[0063] The preparation method of the glass powder includes the following steps: mixing Bi2O3, B2O3, SiO2, ZnO, CuO, MnO, Al2O3, TiO2, Na2O, and K2O, melting them into a uniform glass liquid at 1000-1200℃, quenching them in water to form glass sheets, and obtaining glass powder by ball milling and air jet pulverization.
[0064] A method for preparing a silver-coated nickel paste for a thermistor includes the following steps; Preparation of carrier solution; Preparation of glass powder; The carrier solution, silver powder, silver-coated nickel powder, glass powder and organic solvent are mixed and stirred evenly to obtain a slurry; The slurry was stirred at 800 rpm for 60 minutes and rolled 6 times using a three-roll mill until the fineness of the slurry was ≤10μm. The slurry was then sieved to obtain the silver-coated nickel slurry for the thermistors.
[0065] Comparative Example 1 A thermistor silver paste is prepared by means of raw materials including 10% carrier solution, 60% silver powder, 4% glass powder, and 26% organic solvent by weight percentage. The remaining embodiments are the same as in Example 1.
[0066] The silver powder has a D50 particle size of 0.4-0.9 μm and was purchased from Guizhou Research Institute, with the brand name Agf-6000.
[0067] Comparative Example 2 A thermistor silver paste is prepared by means of raw materials including 8% carrier solution, 60% silver powder, 4.5% glass powder, and 27.5% organic solvent by weight percentage. The remaining embodiments are the same as in Example 2.
[0068] The silver powder has a D50 particle size of 0.4-0.9 μm and was purchased from Yinrui, brand name YRS 600.
[0069] Comparative Example 3 A thermistor silver paste is prepared by means of raw materials including 10% carrier solution, 60% silver powder, 5% glass powder, and 25% organic solvent by weight percentage. The remaining embodiments are the same as in Example 3.
[0070] The silver powder has a D50 particle size of 0.4-0.9 μm and was purchased from Yinke, with the grade name YK-9.
[0071] Comparative Example 4 A thermistor silver-coated nickel paste, the specific implementation method is the same as in Example 1, the difference being that the D50 particle size of the silver-coated nickel powder is 0.6-1.6μm, purchased from Yinrui, YRS-AN010-10.
[0072] Comparative Example 5 A silver-coated nickel paste for thermistors, the specific implementation is the same as that of Example 1, the difference is that the silver in the silver-coated nickel powder accounts for 30% of the mass of the silver-coated nickel powder, purchased from Yinrui, and the product number is YRS-AN060-30.
[0073] Comparative Example 6 A silver-coated nickel paste for thermistors, the specific implementation is the same as that of Example 1, the difference is that the composition of the glass powder is different, specifically 66 parts of Bi2O3, 10 parts of SiO2, 8 parts of B2O3, 0.1 part of ZnO, 5 parts of CuO, 7.9 parts of V2O5, 1.2 parts of Al2O3, 1 part of TiO2, 0.8 part of MnO2.
[0074] Performance Test The silver-coated nickel paste prepared in the examples and comparative examples was printed on a thermistor substrate (ceramic sheet) using a 230-mesh screen, dried at 200 °C for 1 min, and sintered at 820 °C for 10 min to form a dense silver film on the thermistor substrate.
[0075] 1. Tensile Test: Set the temperature of the soldering iron to 350 °C, paste a high-temperature sticker with a hole area of 3.14 mm 2 on the substrate with the sintered silver film; weld with a φ1.0 mm tin wire, wait for 10 s after welding to cool and solidify, and use a tensile machine for tensile test, tensile speed: 50 mm / min; test the welding tensile force, welding tensile force > 20 N / 3.14 mm 2 is qualified.
[0076] 2. Adhesion: Immerse the thermistor substrate with the sintered silver film in a flux (the main component is rosin), bake at 100 °C for 1 min, clamp the substrate with a conductive metal wire and immerse it in a tin pot for 3 - 4 S, and after cooling, place the substrate vertically on a tensile machine to test the adhesion. The combination effect of the silver film and the substrate is tight, and the pulled black film area > 98% is qualified. The black film refers to the material peeled off from the surface of the substrate and attached under the silver film when testing the adhesion.
[0077] 3. Surge Impact Resistance Change Rate: A thermistor, a series resistor, and a tested capacitor (capacitance value 330 μF) form a circuit, charge the capacitor with a 345 V DC voltage, discharge through the thermistor, and calculate the change rate after 1000 impacts. After recovery at 25 °C, the nominal resistance change ≤ ±20% is qualified.
[0078] 4. Steady-State Current Resistance Change Rate: Apply a steady-state current of 5 A to the thermistor for 1000 h, and after recovery at 25 °C, the nominal resistance change ≤ ±20% is qualified.
[0079] The test results are shown in Table 1.
[0080] Table 1
Claims
1. A silver-coated nickel paste for a thermistor, characterized in that, The raw materials prepared by weight percentage include 5-10% carrier solution, 30-50% silver powder, 3-5% glass powder, 10-20% silver-coated nickel powder, and 2-30% organic solvent, with a total weight percentage of 100%; the silver in the silver-coated nickel powder accounts for 10-30 wt% of the mass of the silver-coated nickel powder.
2. The thermistor silver-coated nickel paste according to claim 1, characterized in that, The raw materials for preparing the carrier solution include, by weight percentage, 80-90% resin solution, 6-10% dispersant and 4-10% leveling agent, with a total weight percentage of 100%.
3. The thermistor silver-coated nickel paste according to claim 2, characterized in that, The resin solution comprises a resin and an organic solvent; the resin comprises at least one of acrylic resin, ethyl cellulose, epoxy resin, phenolic resin, polyimide resin, or polyvinyl butyral resin.
4. The thermistor silver-coated nickel paste according to claim 3, characterized in that, The weight ratio of the resin to organic solvent II is (30-60):(40-70).
5. The thermistor silver-coated nickel paste according to claim 1, characterized in that, The D50 particle size of the glass powder is 2-4 μm.
6. The thermistor silver-coated nickel paste according to claim 1, characterized in that, The raw materials for preparing the glass powder include, by weight, 40-65 parts Bi2O3, 10-30 parts B2O3, 1-10 parts SiO2, 10-30 parts ZnO, 5-20 parts CuO, 5-20 parts MnO, 1-10 parts Al2O3, 1-10 parts TiO2, 0.5-5 parts Na2O, and 0.5-5 parts K2O.
7. The thermistor silver-coated nickel paste according to claim 1, characterized in that, The silver powder has a D50 particle size of 0.4-0.9 μm; the silver-coated nickel powder has a D50 particle size of 2-6 μm.
8. The thermistor silver-coated nickel paste according to claim 3, characterized in that, The method for preparing the carrier solution includes the following steps: Mix the resin with organic solvent II and stir at 80-100℃ for 20-150 min to form a resin solution; Mix the resin solution with the dispersant and leveling agent, and stir at 800-1200 rpm for 20-50 minutes to obtain the carrier solution.
9. A method for preparing silver-coated nickel paste for a thermistor according to any one of claims 1-8, characterized in that, Includes the following steps; Preparation of carrier solution; Preparation of glass powder; The carrier solution, silver powder, silver-coated nickel powder, glass powder and organic solvent are mixed and stirred evenly to obtain a slurry; The slurry is stirred at 500-2100 rpm for 30-60 minutes, then rolled and sieved to obtain the silver-coated nickel paste for the thermistors.
10. The method for preparing the silver-coated nickel paste for the thermistor according to claim 9, characterized in that, The sieve aperture is ≤10μm.