Electrode for low-cost high-surge-resistance thermistor chip and preparation method thereof

Abstract

The invention discloses an electrode for a low-cost high-surge-resistance thermistor chip and a preparation method thereof, the electrode comprises a substrate, a composite barrier layer, a silver seed layer, a thick film electrode layer and an anti-oxidation layer, and the thick film electrode layer is made of copper. The NTC thermistor is manufactured through substrate pretreatment, composite barrier layer sputtering, silver seed layer sputtering, thick film electrode preparation, surface activation treatment and anti-oxidation treatment, and has the advantages that a high-resistance transition layer is eliminated, the contact resistance is stable, and the circulation requirement of the power type NTC thermistor is completely met; the copper paste is low in cost, low in electrode porosity, high in through-flow density, capable of bearing surge current, free of ablation, capable of working for more than 1000 hours under steady-state through-flow and low in contact resistance amplification, reducing atmosphere sintering can adapt to transformation of an existing thick film production line, the magnetron sputtering process is free of extra equipment investment, and direct large-scale mass production can be achieved.

Description

Technical Field

[0001] This invention belongs to the field of thermistor material technology, and relates to the manufacturing technology of high-performance NTC thermistors, specifically to an electrode for a low-cost, high-surge-resistance thermistor chip and its preparation method. Background Technology

[0002] The ceramic substrate of power-type NTC thermistors is a metal oxide (manganese, cobalt, copper, nickel, etc.) spinel semiconductor ceramic, and its core applications are power circuit surge suppression and steady-state high current operation. In existing technologies, thick-film silver electrodes are the mainstream solution, but the continuously soaring price of silver has led to high costs—5-8μm thick silver electrodes already significantly increase product cost pressure, and 10μm thick silver electrodes adapted to larger surge / steady-state currents further increase costs. Therefore, selecting an ideal alternative material for power-type NTC thermistors is an urgent priority. Among them, copper paste is the preferred alternative material due to its low price and excellent conductivity.

[0003] However, direct sintering of copper paste NTC spinel ceramics presents several problems: interfacial reactions easily occur, forming a high-resistance oxide transition layer, resulting in non-ohmic contacts (contact resistance > 50 mΩ). This leads to obstructed current flow, susceptibility to ablation under surge impact, weak interlayer bonding, and easy detachment after thermal cycling, making it unsuitable as a direct replacement for silver electrodes. Therefore, developing an electrode fabrication method that solves the ohmic contact problem while simultaneously reducing costs and achieving surge resistance and long-term stable performance has become a pressing technical challenge for the industry. Summary of the Invention

[0004] To address the aforementioned problems, the main objective of this invention is to design an electrode fabrication method that can solve the ohmic contact problem while also reducing costs, providing surge resistance, and maintaining long-term steady-state performance.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: An electrode for a low-cost, high-surge-resistance thermistor chip includes a substrate, a composite barrier layer, a silver seed layer, a thick-film electrode layer, and an anti-oxidation layer. The upper and lower surfaces of the substrate are covered with a 30-50 nm composite barrier layer. The bottom of the composite barrier layer is a 20-30 nm Ti layer, and the Ti layer is covered with a 30-50 nm Ta layer. The composite barrier layer is covered with a 20-30 nm silver seed layer, and the silver seed layer is covered with an 8-10 μm thick-film electrode layer. An anti-oxidation layer is sputtered on the surface of the thick-film electrode layer. The anti-oxidation layer is made of silver, and the thick-film electrode layer is made of copper. A glass glaze protective layer is disposed around the perimeter of the substrate and covers the sides of the composite barrier layer, the silver seed layer, the thick-film electrode layer, and the anti-oxidation layer.

[0006] As a further description of the present invention, the substrate is a spinel ceramic substrate of metal oxide (manganese, cobalt, copper, nickel, etc.), and the thickness of the anti-oxidation layer is 50nm.

[0007] The method for fabricating electrodes for low-cost, high-surge-resistance thermistor chips mainly includes the following steps: Step 1: Substrate pretreatment: Select a spinel ceramic substrate and perform ultrasonic cleaning and plasma cleaning to remove surface impurities and oxide layers. Step 2, composite barrier layer sputtering: a Ti-Ta composite barrier layer is deposited on the upper and lower surfaces of the pretreated substrate using magnetron sputtering. Step 3, Silver seed layer sputtering: Continue magnetron sputtering of a silver seed layer on the surface of the sputtered Ta layer, with the thickness uniformity deviation of the sputtered silver seed layer being less than ±5%; Step 4: Thick film electrode preparation: Copper paste is selected as the thick film electrode material, and high-density copper paste is printed on the surface of the silver seed layer using a thick film printing process; after printing, the thick film electrode is sintered in a nitrogen-protected furnace. Step 5, Surface activation treatment: After the electrode is sintered, plasma cleaning is used to remove the trace oxide layer on the surface and form a rough structure on the surface; Step 6, Antioxidant treatment: A thick silver layer is magnetron sputtered onto the surface of the surface-activated thick film electrode to form an antioxidant layer.

[0008] As a further description of the present invention, in step four, a nitrogen-protected furnace is used for electrode sintering. The thick film electrode is sintered under nitrogen protection for 40-60 minutes, of which the high-temperature sintering time is 3-8 minutes. The high-temperature sintering temperature is 500-600℃. After sintering, the temperature is lowered to below 100℃ and the electrode is removed from the furnace to complete the sintering of the thick film electrode.

[0009] As a further description of the present invention, in step five, the plasma cleaning is Ar plasma cleaning; the cleaning power is 180W, the time is 6min, the processing temperature is 130℃, the thickness of the removed oxide layer is less than 5nm, and the roughness Ra is about 0.25μm.

[0010] As a further description of the present invention, in step one, ultrasonic cleaning uses a neutral cleaning agent, with a cleaning time of 8 minutes and a temperature of 45°C; plasma cleaning has a power of 100W, a time of 3 minutes, and an argon flow rate of 15 sccm; and low-temperature annealing is performed at 300°C for 30 minutes.

[0011] As a further description of the present invention, in step two, the argon pressure of the Ti layer magnetron sputtering is 0.6 Pa, the sputtering power is 220 W, and the target-substrate distance is 90 mm; the argon pressure of the Ta layer is 0.7 Pa, the sputtering power is 240 W, and the target-substrate distance is 90 mm.

[0012] As a further description of the present invention, in step three, the argon gas pressure for magnetron sputtering of the silver seed layer is 0.4 Pa, the sputtering power is 200 W, and the sputtering rate is 6 nm / min.

[0013] As a further description of the present invention, in step four, the screen mesh count is 250, the squeegee pressure is 0.45 MPa, and the printing speed is 40 mm / s during thick film printing.

[0014] As a further description of the present invention, in step six, the sputtering temperature of the anti-oxidation thick silver layer is 160°C, the argon pressure is 0.4Pa, and the sputtering power is 190W.

[0015] Compared with the prior art, the technical advantages of the present invention are as follows: This invention provides an electrode for a low-cost, high-surge-resistance thermistor chip, which has the following main advantages: 1. Through the synergistic effect of the Ti-Ta composite barrier layer and the silver seed layer, the high-resistivity transition layer is eliminated, the contact resistance is stable, and the flow requirements of power-type NTC thermistors are fully met. 2. Copper paste has low cost, and the overall material cost is significantly lower compared to using a 10μm thick film silver electrode; 3. The electrode has low porosity and high current density, can withstand surge current and has no ablation, fully meeting the working requirements of NTC thermistors. 4. After working for more than 1000 hours under steady-state current, the increase in contact resistance, atomic diffusion, and transition metal atomic migration all meet the requirements and can satisfy long-term working needs.

[0016] 5. Reducing atmosphere sintering can be adapted to the transformation of existing thick film production lines, and magnetron sputtering process requires no additional equipment investment and can be directly mass-produced. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the overall structure of the present invention; Figure 2 This is a data table showing the results of the welding heat resistance test; Figure 3 This is a data table showing the results of a constant temperature and humidity experiment; Figure 4 This is a data table showing the results of high and low temperature impact tests; Figure 5 This is a data table showing the results of a high-temperature storage test; Figure 6 This is a data table showing the results of the maximum steady-state current test; Figure 7 This is a data table showing the results of the maximum capacitance test.

[0018] In the figure, 1. substrate, 2. thick film electrode layer, 3. composite barrier layer, 4. silver seed layer, 5. antioxidant layer. Detailed Implementation

[0019] The present invention will now be described in detail with reference to the accompanying drawings: like Figure 1 As shown, an electrode for a low-cost, high-surge-resistance thermistor chip according to the present invention mainly consists of a substrate 1, a composite barrier layer 3, a silver seed layer 4, a thick film electrode layer 2, and an antioxidant layer 5. The upper and lower surfaces of the substrate 1 are covered with a 30-50 nm composite barrier layer 3. The bottom of the composite barrier layer 3 is 20-30 nm Ti, and the Ti is covered with a 30-50 nm Ta layer. The composite barrier layer 3 is covered with a 20-30 nm silver seed layer 4, and the silver seed layer 4 is covered with an 8-10 μm thick film electrode layer 2. The surface of the thick film electrode layer 2 is sputtered with an antioxidant layer 5. The antioxidant layer 5 is made of silver, and the thick film electrode layer 2 is made of copper.

[0020] Among them, substrate 1 is a spinel ceramic substrate of metal oxide (manganese, cobalt, copper, nickel, etc.), and the thickness of the anti-oxidation layer 5 is 50nm.

[0021] The present invention provides a method for fabricating electrodes for low-cost, high-surge-resistance thermistor chips, which mainly includes the following steps: Step 1: Substrate pretreatment: Select spinel ceramic substrates and perform ultrasonic cleaning and plasma cleaning in sequence to remove surface impurities and oxide layers; Step 2, composite barrier layer sputtering: On the pretreated substrate surface, a Ti-Ta composite barrier layer is deposited using magnetron sputtering. Step 3, Silver seed layer sputtering: Continue magnetron sputtering of a silver seed layer on the surface of the sputtered Ta layer, with the thickness uniformity deviation of the sputtered silver seed layer being less than ±5%; Step 4: Thick film electrode preparation: Copper paste is selected as the thick film electrode material, and high-density copper paste is printed on the surface of the silver seed layer using a thick film printing process; after printing, the thick film electrode is sintered in a nitrogen-protected furnace. Step 5, Surface activation treatment: After the electrode is sintered, plasma cleaning is used to remove the trace oxide layer on the surface and form a rough structure on the surface; Step 6, Antioxidant treatment: A thick silver layer is magnetron sputtered onto the surface of the surface-activated thick film electrode to form an antioxidant layer.

[0022] In step one, ultrasonic cleaning uses a neutral cleaning agent, with a cleaning time of 8 minutes and a temperature of 45°C; plasma cleaning has a power of 100W, a time of 3 minutes, and an argon flow rate of 15 sccm; and low-temperature annealing is performed at 300°C for 30 minutes.

[0023] In step two, the argon pressure for magnetron sputtering of the Ti layer is 0.6 Pa, the sputtering power is 220 W, and the target-substrate distance is 90 mm; the argon pressure for the Ta layer is 0.7 Pa, the sputtering power is 240 W, and the target-substrate distance is 90 mm.

[0024] In step three, the silver seed layer is magnetron sputtered with an argon gas pressure of 0.4 Pa, a sputtering power of 200 W, and a sputtering rate of 6 nm / min.

[0025] In step four, a nitrogen-protected furnace is used for electrode sintering. The thick film electrode is sintered under nitrogen protection for 40-60 minutes, of which the high-temperature sintering time is 3-8 minutes. The high-temperature sintering temperature is 500-600℃. After sintering, the temperature is lowered to below 100℃ before the electrode is removed from the furnace, thus completing the sintering of the thick film electrode.

[0026] In step four, the screen mesh count is 250, the squeegee pressure is 0.45MPa, and the printing speed is 40mm / s during thick film printing.

[0027] In step five, the plasma cleaning uses Ar plasma cleaning; the cleaning power is 180W, the time is 6min, the processing temperature is 130℃, the thickness of the removed oxide layer is less than 5nm, and the roughness Ra is about 0.25μm.

[0028] In step six, the sputtering temperature of the anti-oxidation thick silver layer is 160℃, the argon pressure is 0.4Pa, and the sputtering power is 190W. Example 1

[0029] The substrate is a spinel ceramic substrate made of metal oxides (manganese, cobalt, copper, nickel, etc.), and the thick film electrode material is copper.

[0030] Step 1: Substrate pretreatment. The substrate is ultrasonically cleaned with a neutral cleaning agent for 8 minutes at 45°C. Then, plasma cleaning is performed with a power of 100W for 3 minutes and an argon flow rate of 15 sccm. After cleaning, the substrate is annealed at 300°C for 30 minutes.

[0031] Step 2, Composite Barrier Layer Sputtering: A Ti-Ta composite barrier layer is deposited on the pretreated substrate surface using magnetron sputtering. First, the Ti layer is sputtered to a thickness of 25 nm, with an argon pressure of 0.6 Pa and a sputtering power of 220 W. Then, the Ta layer is sputtered to a thickness of 35 nm, with an argon pressure of 0.7 Pa and a sputtering power of 240 W. The target-substrate distance for magnetron sputtering is 90 mm.

[0032] Step 3: Silver Seed Layer Sputtering: A silver seed layer is then sputtered onto the already sputtered Ta layer using magnetron sputtering. The argon gas pressure during magnetron sputtering is 0.4 Pa, the sputtering power is 200 W, and the sputtering rate is 6 nm / min. The silver seed layer thickness is 25 nm, with a thickness uniformity deviation of less than ±5%. Step 4: Thick Film Electrode Preparation: Copper paste is selected as the thick film electrode material. High-density copper paste is printed on the surface of the silver seed layer using a thick film printing process. The printing screen mesh is 250 mesh, the squeegee pressure is 0.45 MPa, and the printing speed is 40 mm / s. After printing, the electrode is placed in a nitrogen-protected furnace and sintered under nitrogen protection for 40-60 minutes, including 3-8 minutes of high-temperature sintering. The high-temperature sintering temperature is 500-600℃. After sintering, the electrode is cooled to below 100℃ and removed from the furnace, completing the sintering of the thick film electrode. Step 5, Surface activation treatment: After the electrode is sintered, plasma cleaning is used to remove the trace oxide layer on the surface and form a rough structure on the surface; Step 6, Antioxidant treatment: A 50 nm thick silver layer is magnetron sputtered onto the surface of the surface-activated thick film electrode at a sputtering temperature of 160℃, an argon pressure of 0.4 Pa, and a sputtering power of 190 W. After sputtering, the electrode is annealed in nitrogen at 200℃ for 30 min to form an antioxidant layer.

[0033] The above steps complete the fabrication of the copper electrode for the low-cost, high-surge-resistance thermistor chip. The test results of the copper electrode are as follows: Contact resistance 3.8mΩ, IV characteristic linearity ≥0.995, current density 7.0A / mm²; It withstood a 2500A / ms surge current for 20 cycles without erosion; The interlayer peel strength is 3.0 N / mm, and there is no peeling after 4000 thermal cycles.

[0034] It fully meets the technical requirements of power-type NTC thermistors.

[0035] After 1000 hours of operation, the copper atom diffusion rate is <5×10⁻⁶. -11 cm² / s, transition metal atom migration < 2 × 10⁻⁶ - 10 cm² / s, steady-state current density ≥6.5A / mm²; meets the technical requirements for long-term operation.

[0036] Based on the test results above, it can be seen that using copper electrodes instead of silver electrodes to make thermistors fully meets the actual production requirements. Example 2

[0037] The resistance changes of thermistors made with silver and copper as electrode materials under different conditions were investigated. The experimental temperature was 25℃. Figures 2-7 |ΔR 25 / R 25 |, where R 25 The resistance before the experiment is ΔR. 25The difference between the resistance after the experiment and the resistance before the experiment is |ΔR|. 25 / R 25 | represents the rate of change of resistance.

[0038] Experimental product carrier: 5Ω power NTC thermistor Experiment 1: Welding Heat Resistance Test Experimental conditions and methods: temperature 260±5℃, immersion depth 6mm from the resistive element, time 10±1s; Experimental results: such as Figure 2 .

[0039] After replacing silver with copper as the electrode material and conducting welding heat resistance tests, the resistance change rate of the silver electrode was approximately 1.48%, while that of the copper electrode was approximately 1.18%. The resistance change rate of the copper electrode is close to that of the existing silver electrode and meets the technical requirement of less than 20% in practical use.

[0040] Experiment 2: Constant Temperature and Humidity Experiment Experimental conditions and methods: Temperature 40±2℃, humidity 93±2%, time 1000h; Experimental results: such as Figure 3 .

[0041] After replacing silver with copper as the electrode material in the constant temperature and humidity experiment, the resistance change rate of the silver electrode was about 3.67%, and the resistance change rate of the copper electrode was about 3.75%. The resistance change rate of the copper electrode is close to that of the existing silver electrode, and both meet the technical requirement of less than 20% in actual use.

[0042] Experiment 3: High and Low Temperature Impact Test Experimental conditions and methods: -40℃ / 30min to 170℃ / 30min for 1000 cycles; Experimental results: such as Figure 4 .

[0043] After replacing silver with copper as the electrode material in high and low temperature impact tests, the resistance change rate of the silver electrode was about 5.26%, and that of the copper electrode was about 6.17%. The resistance change rate of the copper electrode was close to that of the existing silver electrode, and both met the technical requirement of less than 20% in actual use.

[0044] Experiment 4: High-Temperature Storage Experiment Experimental conditions and methods: Temperature 170±5℃, time 1000h; Experimental results: such as Figure 5 .

[0045] After replacing silver with copper as the electrode material in a high-temperature storage experiment, the resistance change rate of the silver electrode was approximately 8.58%, while that of the copper electrode was approximately 8.26%. The resistance change rate of the copper electrode was close to that of the existing silver electrode, and both met the technical requirement of less than 20% in practical use.

[0046] Experiment 5: Maximum Steady-State Current Experiment Experimental conditions and methods: The maximum steady-state current was continuously applied at room temperature for 1000±24h; Experimental results: such as Figure 6 .

[0047] After replacing silver with copper as the electrode material and conducting the maximum steady-state current experiment, the resistance change rate of the silver electrode was approximately 12.82%, while that of the copper electrode was approximately 12.28%. The resistance change rate of the copper electrode is close to that of the existing silver electrode, and both meet the technical requirement of less than 20% in practical use.

[0048] Experiment 6: Maximum Capacitance Experiment Experimental conditions and methods: Apply the maximum allowable capacitance, intermittently close for 50ms, and open for 5 times the thermal time constant as one cycle, continue for 1000 cycles; Experimental results: such as Figure 7 .

[0049] After replacing silver with copper as the electrode material and conducting the maximum steady-state current experiment, the resistance change rate of the silver electrode was approximately 2.31%, while that of the copper electrode was approximately 2.95%. The resistance change rate of the copper electrode is close to that of the existing silver electrode, and both meet the technical requirement of less than 20% in practical use.

[0050] As can be seen from Experiments 1 to 6, under different experimental conditions, the resistance change rate of the copper electrode is close to that of the existing silver electrode, and both meet the technical requirements for practical use. Therefore, the copper in this application can be used as a replacement material for silver in the electrodes of the thermistor, thereby reducing costs.

[0051] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Any other modifications or equivalent substitutions made by those skilled in the art to the technical solutions of the present invention, as long as they do not depart from the direction and scope of the technical solutions of the present invention, should be covered within the scope of the claims of the present invention.

Claims

1. An electrode for a low-cost, high-surge-resistance thermistor chip, characterized in that: The substrate comprises a substrate, a composite barrier layer, a silver seed layer, a thick film electrode layer, and an antioxidant layer. The upper and lower surfaces of the substrate are covered with a 30-50 nm composite barrier layer. The bottom of the composite barrier layer is composed of 20-30 nm Ti, and above the Ti is a 30-50 nm Ta layer. The composite barrier layer is covered with a 20-30 nm silver seed layer, and the silver seed layer is covered with an 8-10 μm thick film electrode layer. An antioxidant layer, made of silver, is sputtered onto the surface of the thick film electrode layer. The thick film electrode layer is made of copper. A glass glaze protective layer surrounds the substrate and covers the sides of the composite barrier layer, the silver seed layer, the thick film electrode layer, and the antioxidant layer.

2. The electrode for a low-cost, high-surge-resistance thermistor chip according to claim 1, characterized in that: The substrate is a spinel ceramic substrate, and the thickness of the antioxidant layer is 50nm.

3. The method for fabricating electrodes for low-cost, high-surge-resistance thermistor chips according to claim 1, characterized in that: Includes the following steps, Step 1: Substrate pretreatment: Select spinel ceramic substrates and perform ultrasonic cleaning and plasma cleaning in sequence to remove surface impurities and oxide layers; Step 2, composite barrier layer sputtering: On the upper and lower surfaces of the pretreated substrate, a Ti-Ta composite barrier layer is deposited using magnetron sputtering. Step 3, Silver seed layer sputtering: Continue magnetron sputtering of a silver seed layer on the surface of the sputtered Ta layer, with the thickness uniformity deviation of the sputtered silver seed layer being less than ±5%; Step 4: Thick film electrode preparation: Copper paste is selected as the thick film electrode material, and high-density copper paste is printed on the surface of the silver seed layer using a thick film printing process; After printing, thick film electrodes are sintered in a nitrogen-protected furnace. Step 5, Surface activation treatment: After the electrode is sintered, plasma cleaning is used to remove the trace oxide layer on the surface and form a rough structure on the surface; Step 6, Antioxidant treatment: A thick silver layer is magnetron sputtered onto the surface of the surface-activated thick film electrode to form an antioxidant layer.

4. The copper electrode for a low-cost, high-surge-resistance thermistor chip according to claim 3, characterized in that: In step four, a nitrogen-protected furnace is used for electrode sintering. The thick film electrode is sintered under nitrogen protection for 40-60 minutes, of which the high-temperature sintering time is 3-8 minutes. The high-temperature sintering temperature is 500-600℃. After sintering, the temperature is lowered to below 100℃ and the electrode is removed from the furnace, thus completing the sintering of the thick film electrode.

5. The electrode fabrication method for a low-cost, high-surge-resistance thermistor chip according to claim 3, characterized in that: In step five, the plasma cleaning uses Ar plasma cleaning; the cleaning power is 180W, the time is 6min, the processing temperature is 130℃, the thickness of the removed oxide layer is less than 5nm, and the roughness Ra is about 0.25μm.

6. The electrode fabrication method for a low-cost, high-surge-resistance thermistor chip according to claim 3, characterized in that: In step one, ultrasonic cleaning uses a neutral cleaning agent, with a cleaning time of 8 minutes and a temperature of 45°C; plasma cleaning has a power of 100W, a time of 3 minutes, and an argon flow rate of 15 sccm; and low-temperature annealing is performed at 300°C for 30 minutes.

7. The electrode fabrication method for a low-cost, high-surge-resistance thermistor chip according to claim 3, characterized in that: In step two, the argon pressure for magnetron sputtering of the Ti layer is 0.6 Pa, the sputtering power is 220 W, and the target-substrate distance is 90 mm; the argon pressure for the Ta layer is 0.7 Pa, the sputtering power is 240 W, and the target-substrate distance is 90 mm.

8. The electrode fabrication method for a low-cost, high-surge-resistance thermistor chip according to claim 3, characterized in that: In step three, the silver seed layer is magnetron sputtered with an argon gas pressure of 0.4 Pa, a sputtering power of 200 W, and a sputtering rate of 6 nm / min.

9. The electrode fabrication method for a low-cost, high-surge-resistance thermistor chip according to claim 3, characterized in that: In step four, the screen mesh count is 250, the squeegee pressure is 0.45MPa, and the printing speed is 40mm / s during thick film printing.

10. The electrode fabrication method for a low-cost, high-surge-resistance thermistor chip according to claim 3, characterized in that: In step six, the sputtering temperature of the anti-oxidation thick silver layer is 160℃, the argon pressure is 0.4Pa, and the sputtering power is 190W.

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