Preparation method of gold electrode NTC thermosensitive ceramic chip and gold electrode NTC thermosensitive ceramic chip

Abstract

This application relates to the field of electronic component materials technology, and discloses a method for preparing a gold electrode NTC thermistor ceramic chip and the gold electrode NTC thermistor ceramic chip thereof. The method for preparing the gold electrode NTC thermistor ceramic chip in this application uses Mn3O4, Co2O3, NiO, and Cr2O3 as ceramic substrate raw materials. Through steps such as raw material pretreatment, batching and primary ball milling, discharge drying, sieving and pre-firing, and secondary ball milling and drying, the prepared gold electrode NTC thermistor ceramic chip exhibits a resistance value accuracy ≤ ±1% and a thermistor index B value accuracy ≤ ±1% at 25℃, and a resistance change rate ≤ 0.5% after aging at 125℃ for 1000 hours. This solves the technical problems of low raw material precision, poor powder uniformity, weak electrode bonding, and poor chip edge quality in existing technologies.

Description

Technical Field

[0001] This application relates to the field of electronic component materials technology, and in particular to a method for preparing a gold electrode NTC thermistor ceramic chip and the gold electrode NTC thermistor ceramic chip thereof. Background Technology

[0002] Negative Temperature Coefficient (NTC) thermistor ceramics are functional ceramic materials whose resistance decreases precisely with increasing temperature. Due to their high sensitivity, fast response speed, and low cost, they are widely used in temperature sensing and temperature compensation. As modern electronic devices develop towards higher precision and reliability, the performance requirements for NTC thermistor chips are also increasing, especially in applications such as automotive electronics, industrial control, and medical equipment where high temperature measurement accuracy is required. These applications demand chips with excellent resistance consistency, long-term stability, and environmental adaptability. Gold electrodes, due to their excellent chemical inertness and anti-migration properties, are widely used in high-reliability NTC thermistor chips.

[0003] Currently, the preparation of gold electrode NTC thermistor ceramic chips usually adopts the solid-state reaction method. The basic process steps include: first, the raw materials are prepared and then directly subjected to ball milling, sintering and other treatments; the sintered ceramic block is cut into thin slices, gold paste is coated on the surface of the thin slices, and gold electrodes are formed after drying and sintering; finally, the thin slices with electrodes are cut into chips of the required size to obtain gold electrode NTC thermistor chips.

[0004] However, the aforementioned existing technologies still have the following technical problems in practical applications: First, during the ball milling process, the dispersion and uniformity of the powder directly affect the sufficiency of the subsequent reaction. The existing ball milling process is difficult to effectively solve the problem of powder agglomeration, resulting in uneven microstructure of the ceramic body after sintering, manifested as wide grain size distribution, pores, or microcracks and other defects; Second, improper control of the drying process after gold paste coating can easily lead to insufficient bonding force, blistering, and detachment between the electrode and the ceramic substrate, affecting the lifespan and reliability of the chip; In addition, the chip edges after dicing often have micro-defects such as burrs and chipping, affecting the subsequent packaging yield and reliability. Summary of the Invention

[0005] To at least overcome one of the problems existing in the prior art, one objective of this application is to provide a method for preparing a gold electrode NTC thermistor ceramic chip. This method uses Mn3O4, Co2O3, NiO, and Cr2O3 as ceramic substrate raw materials. Through steps such as raw material pretreatment, batching and primary ball milling, discharge drying, sieving and pre-firing, and secondary ball milling and drying, the prepared gold electrode NTC thermistor ceramic chip exhibits a resistance value accuracy of ≤±0.82% at 25℃, a thermistor index B value accuracy of ≤±0.74%, a resistance change rate of ≤0.35% after aging at 125℃ for 1000 hours, qualified gold electrode bonding, and excellent chip edge appearance. This solves the technical problems of low raw material precision, poor powder uniformity, weak electrode bonding, and poor chip edge quality in the prior art. A second objective of this application is to provide the aforementioned gold electrode NTC thermistor ceramic chip.

[0006] Therefore, this application adopts the following technical solution: The first aspect of this application provides a method for preparing a gold electrode NTC thermistor ceramic chip, comprising the following steps: S1: Raw material pretreatment: Mn3O4, Co2O3, NiO and Cr2O3 of each component raw material are placed in a constant temperature and humidity chamber for static treatment. The static treatment temperature is 45~55℃, the relative humidity is 25~35%, and the time is 10~14h. S2: Batching and primary ball milling: Weigh the raw materials of each component after S1 treatment according to the formula, add them to the ball mill jar, then add grinding balls and ball milling solvent for primary ball milling to obtain primary slurry; the ball milling solvent is a mixed solvent of water and anhydrous ethanol, and the volume ratio of water to anhydrous ethanol is (12~14):1; the rotation speed of the primary ball mill is 170~190 r / min, and the time is 5~6 h; S3: Discharge and drying: Dry the primary slurry to obtain powder; S4: Sieving and pre-firing: The powder is sieved and then pre-firing to obtain pre-fired powder; the pre-firing temperature is 880~920℃ and the holding time is 4~6h; S5: Secondary ball milling and drying: The pre-calcined powder is added back into the ball mill jar, along with grinding balls and a ball milling solvent for secondary ball milling; the ball milling solvent is a mixture of water and anhydrous ethanol, with a volume ratio of water to anhydrous ethanol of (12~14):1; the rotation speed of the secondary ball milling is 170~190 r / min, and the time is 7~9 h, to obtain a secondary ball milling slurry; the secondary ball milling slurry is dried to obtain secondary ball milling powder; S6: Molding and Isostatic Pressing: The secondary ball-milled powder is pressed into shape and then subjected to isostatic pressing to obtain ceramic green body; S7: Sintering: The ceramic green body is sintered at a temperature of 1180~1220℃ and a holding time of 5~7h to obtain a ceramic core ingot; S8: Slicing and Cleaning: The ceramic core ingot is sliced ​​into ceramic substrates, ultrasonically cleaned, and then dried. S9: Coating gold electrodes: Gold paste is coated on both sides of the ceramic substrate, dried, and then the electrodes are sintered; the drying after coating the gold paste includes a first drying and a second drying, the first drying temperature is 140~160℃ and the time is 2~5min, the second drying temperature is 160~180℃ and the time is 8~12min; the electrode sintering temperature is 830~870℃, to obtain a ceramic substrate coated with gold electrodes; S10: Slicing: Cutting the ceramic substrate covered with gold electrodes into chips of a predetermined size; S11: Grinding and Cleaning: Grind the chip to remove edge burrs, and clean it to obtain a gold electrode NTC thermistor ceramic chip.

[0007] In the preparation method of the gold electrode NTC thermistor ceramic chip of this application, step S1 involves pre-treatment of the raw materials by constant temperature and humidity to effectively control the moisture absorption rate of the raw materials, avoid raw material agglomeration or powder dispersion, and ensure the initial dispersibility of the raw materials; steps S2 and S5 use a mixed ball milling solvent of water and anhydrous ethanol with a volume ratio of (12~14):1, and ball milling is carried out at a ball milling speed of 170~190 r / min for one ball milling and two ball milling, which takes into account both the wettability and dispersibility of the powder, realizes the mixing and deep dispersion of the raw materials, and improves the sintering activity of the powder; in step S4, the pre-firing temperature of 880~920℃ and the holding time of 4~6h reduce the shrinkage rate of subsequent sintering and avoid cracking of the green body; step S6 adds isostatic pressing treatment after molding to improve the density of the ceramic green body and reduce internal porosity; in step S7, 1180 The sintering process at ~1220℃ for 5~7h is conducive to complete sintering in the ceramic green body and the formation of a dense ceramic crystalline phase structure. The step-by-step drying process in step S9, through the synergistic effect of surface shaping followed by deep curing, avoids solvent boiling and pinhole defects caused by single long-term drying, and significantly enhances the bonding force between the gold electrode and the ceramic substrate. Electrode sintering at 830~870℃ forms a strong bonding interface between the gold paste and the ceramic substrate, improving the electrode bonding strength. After dicing, the wafer is successively ground to remove burrs and cleaned, which effectively improves the dimensional accuracy of the chip and avoids electrostatic discharge and resistance drift problems caused by burrs. At the same time, the process parameters of the whole process are matched with each other to form a complete process control system for the preparation process, which can be used for industrial production. The prepared chip has excellent thermal stability, electrode bonding force and dimensional accuracy.

[0008] Preferably, in step S1, the temperature for the settling treatment is 48-52°C, the relative humidity is 28-32%, and the settling time is 11-13 hours. More preferably, in step S1, the temperature for the settling treatment is 50-52°C, the relative humidity is 30-32%, and the settling time is 12 hours. Even more preferably, in step S1, the temperature for the settling treatment is 50°C, the relative humidity is 30%, and the settling time is 13 hours.

[0009] Step S1 helps the raw materials reach a moisture balance, making the raw material powder more uniformly dispersed and avoiding agglomeration or scattering. It also prevents the raw material surface from becoming too dry or even clumping due to excessively high temperature, or the problem of incomplete moisture removal due to excessively low temperature. This improves the repeatability of subsequent processes such as batching and ball milling, and reduces product performance deviations between batches.

[0010] Preferably, in steps S2 and S5, the volume ratio of water to anhydrous ethanol is 13.3:1, and the rotation speed of the first and second ball milling is 175 r / min.

[0011] Preferably, in steps S2 and S5, the weight ratio of the grinding balls, raw materials, and milling solvent is (2~4):1:(0.6~1). More preferably, in steps S2 and S5, the weight ratio of the grinding balls, raw materials, and milling solvent is 3:1:0.7.

[0012] In the ball milling solvent, the dispersing effect of water and the surface tension-reducing effect of ethanol reach a good balance, which is conducive to further dispersion and refinement of powder. The rotation speed of 175 r / min ensures sufficient ball milling energy input while avoiding excessive heat generation and increased energy consumption caused by excessive rotation speed.

[0013] Preferably, in step S2, the raw materials of each component are weighed according to the following weight ratios: Mn3O4 41~47 parts; Co2O3 32-34 parts; NiO 15-18 parts; Cr2O3 6~13 parts.

[0014] More preferably, in step S2, the raw materials of each component are weighed according to the following weight ratios: Mn3O4 45~47 parts; Co2O3 32-33 parts; NiO 15-17 parts; Cr2O3 8~13 parts.

[0015] When the raw materials are within the above-mentioned range, the Mn-Ni-Co-Cr quaternary crystal phase structure of the ceramic matrix formed after sintering is more stable. This crystal phase is the core thermistor phase of the NTC thermistor ceramic chip, giving the ceramic matrix excellent negative temperature coefficient thermistor properties, avoiding crystal phase distortion caused by imbalance of raw material composition, and at the same time, the limited amount of Cr2O3 helps to stabilize the crystal phase structure, inhibit abnormal grain growth under high temperature sintering, and can further improve the thermal stability and resistance consistency of the ceramic matrix, and reduce resistance drift under high and low temperature cycling.

[0016] Preferably, in step S4, the pre-firing temperature is 880~920℃, and the holding time is 5~6h; in step S7, the sintering temperature is 1200~1220℃, and the holding time is 6h. More preferably, in step S4, the pre-firing temperature is 890~920℃, and the holding time is 5.5h; in step S7, the sintering temperature is 1210℃, and the holding time is 6h.

[0017] Preferably, in step S6, the isostatic pressing pressure is 220~250MPa, and the holding time is 1~5min. More preferably, in step S6, the isostatic pressing pressure is 230~245MPa, and the holding time is 1~5min.

[0018] The pre-firing process ensures the initial solid-state reaction proceeds, avoiding incomplete reactions due to insufficient time. At a sintering temperature of 1200–1220℃ and a holding time of 6 hours, the grains grow fully and are evenly distributed, ensuring sufficient grain boundary resistance while preventing abnormal grain growth caused by excessively high temperatures or times. This results in a ceramic body with low porosity and high density. The isostatic pressing treatment at 220–250 MPa effectively eliminates the density gradient generated during dry pressing, ensuring uniform density throughout the green body. The uniform and dense green body shrinks evenly during sintering, reducing defects such as warping and cracking.

[0019] Preferably, in step S9, the gold paste is prepared from gold powder, glass powder, triethanolamine, ethyl cellulose resin, and terpineol in a weight ratio of (70~74):(1~8):(3~9):(5~8):(7~12). More preferably, in step S9, the gold paste is prepared from gold powder, glass powder, triethanolamine, ethyl cellulose resin, and terpineol in a weight ratio of (72~74):(3~8):(5~9):(6~8):(10~12). Even more preferably, in step S9, the gold paste is prepared from gold powder, glass powder, triethanolamine, ethyl cellulose resin, and terpineol in a weight ratio of 73:5:8:6:11.

[0020] Preferably, in step S9, the first drying temperature is 150~160℃ and the time is 2~5 min, the second drying temperature is 165~180℃ and the time is 8~12 min; the electrode sintering temperature is 850~860℃. More preferably, in step S9, the first drying temperature is 155~160℃ and the time is 2~5 min, the second drying temperature is 165~175℃ and the time is 8~12 min; the electrode sintering temperature is 850~860℃.

[0021] The drying process of the gold paste is divided into two stages. The first drying stage is the surface setting stage, which uses a lower temperature to allow the surface solvent to evaporate at a moderate rate, forming a uniform semi-cured protective layer. This avoids excessively rapid surface evaporation and skin formation, which would lead to incomplete evaporation of the internal solvent. The second drying stage is the deep curing stage, which uses a higher temperature to provide sufficient heat energy, allowing heat to be quickly conducted to the interior of the electrode, driving the complete evaporation of the deep solvent while simultaneously causing deep curing inside. Through two-stage temperature gradient drying, solvent boiling and pinhole defects caused by single-stage constant-temperature drying are avoided, significantly improving the density and adhesion of the gold electrode.

[0022] Preferably, in step S11, the grinding disc treatment uses a rolling ball mill with zirconium balls as the grinding medium, and the grinding time is 20-40 minutes; the cleaning is performed using ultrasonic cleaning with alcohol. More preferably, in step S11, the grinding disc treatment uses a rolling ball mill with zirconium balls as the grinding medium, and the grinding time is 30-40 minutes; the cleaning is performed using ultrasonic cleaning with alcohol.

[0023] In step S11, the high hardness and low wear of the zirconium balls, combined with the rolling ball mill, help to efficiently remove burrs and cutting debris from the chip edges, avoiding chip corner breakage caused by hard grinding, and improving the chip's dimensional accuracy and appearance quality. The grinding time of 20-40 minutes can completely remove burrs while avoiding chip size irregularities caused by excessive grinding time. Alcohol ultrasonic cleaning can quickly dissolve the powder debris generated during the grinding process, and ultrasonic vibration can penetrate deep into the chip edges to remove impurities, resulting in a more thorough cleaning. In addition, alcohol is volatile and can quickly dry the chip, avoiding chip oxidation caused by insufficient drying after water washing, further ensuring the chip's surface cleanliness and performance.

[0024] The second aspect of this application provides a gold electrode NTC thermistor ceramic chip prepared according to the preparation method of the gold electrode NTC thermistor ceramic chip according to the first aspect of this application, wherein the gold electrode NTC thermistor ceramic chip includes a ceramic substrate and gold electrodes covering both sides of the ceramic substrate, wherein the ceramic substrate is formed of oxides of Mn, Co, Ni and Cr.

[0025] Compared with the prior art, this application has at least the following beneficial effects: 1) In the preparation method of the gold electrode NTC thermistor ceramic chip of this application, the moisture absorption rate of the raw materials is effectively controlled by the constant temperature and humidity pretreatment of the raw materials in step S1, which avoids the agglomeration of raw materials or the dispersion of powder. Steps S2 and S5 use a ball milling solvent of water and anhydrous ethanol with a volume ratio of (12~14):1, and a ball milling speed of 170~190 r / min, which takes into account both the wettability and dispersibility of the powder, realizes the deep dispersion of the raw materials, and thus improves the sintering activity of the powder. The pre-firing at 880~920℃ in step S4 and the sintering at 1180~1220℃ in step S7 work together to make the obtained ceramic matrix uniform in grain size, low in porosity and high in density. The gold electrode NTC thermistor ceramic chip prepared by the preparation method of this application has a resistance value accuracy of ≤±0.82% and a thermistor index B value accuracy of ≤±0.74% at 25℃, which solves the technical problems of poor powder uniformity and uneven ceramic microstructure in the prior art.

[0026] 2) In the preparation method of the gold electrode NTC thermistor ceramic chip of this application, step S9 is carried out by step drying process. The first drying is carried out at 140~160℃ for 2~5min to evaporate the surface solvent and form a uniform semi-cured protective layer to avoid the surface from forming a skin too quickly. The second drying is carried out at 160~180℃ for 8~12min to provide sufficient heat energy so that the heat can be quickly conducted to the inside of the electrode and drive the deep solvent to evaporate completely. The two temperature gradient drying processes work together to help enhance the bonding force between the gold electrode and the ceramic substrate.

[0027] 3) In the preparation method of the gold electrode NTC thermistor ceramic chip of this application, the grinding and cleaning process in step S11 uses zirconium balls as grinding media and a rolling ball mill for 20 to 40 minutes to effectively remove the edge burrs and cutting debris generated during slicing; combined with ultrasonic cleaning with alcohol, the powder debris generated during the grinding process is quickly dissolved, avoiding chip oxidation caused by insufficient drying after water washing, and improving the dimensional accuracy and surface cleanliness of the chip.

[0028] 4) The gold electrode NTC thermistor ceramic chip prepared by the method of this application has a ceramic substrate formed by oxides of Mn, Co, Ni and Cr. The addition of Cr2O3 stabilizes the crystal phase structure and inhibits abnormal grain growth under high temperature sintering. The chip prepared by this method has a resistance change rate of ≤0.35% after aging at 125℃ for 1000h, and has excellent thermal stability and long-term reliability, which fully meets the application requirements of gold electrode NTC thermistor ceramic chips in industries such as automotive electronics, industrial control and medical equipment. Detailed Implementation

[0029] The following detailed description of the contents of this application is provided through specific embodiments, comparative examples, and tables, but is not limited to all the arguments and data.

[0030] The gold paste was prepared by mixing gold powder, glass powder, triethanolamine, ethyl cellulose resin and terpineol in a weight ratio of 73:5:8:6:11 and then heating and stirring at 80°C for 4.5 h. The average particle sizes of the gold powder and glass powder were 1.4±0.1 μm and 3±0.1 μm, respectively.

[0031] It is particularly important to emphasize that, unless otherwise specified, the raw materials, reagents or devices used in this application can be obtained from conventional commercial sources.

[0032] The method for preparing the gold electrode NTC thermistor ceramic chip in this application specifically includes the following steps: S1: Raw material pretreatment: Place each component raw material Mn3O4, Co2O3, NiO and Cr2O3 in a constant temperature and humidity chamber for static treatment. The static treatment temperature is 45~55℃, the relative humidity is 25~35%, and the time is 10~14h. After treatment, each component raw material is sealed and stored for later use. S2: Batching and primary ball milling: Weigh out the raw materials Mn3O4, Co2O3, NiO, and Cr2O3 after step S1 according to the weight ratio of (41~47):(32~34):(15~18):(6~13), add them to the ball mill jar, and then add grinding balls and ball milling solvent for primary ball milling. The weight ratio of grinding balls, raw materials and ball milling solvent is controlled to be (2~4):1:(0.6~1). The ball milling solvent is a mixed solvent of water and anhydrous ethanol with a volume ratio of (12~14):1. The ball milling speed is 170~190 r / min and the time is 5~6 h to obtain primary slurry. S3: Discharge and drying: Place the primary slurry in a tray and dry it in an oven at 70~80℃ until constant weight to obtain powder; S4: Sieving and pre-firing: Sieve the powder through a 200-mesh sieve, take the sieved powder and place it in a high-temperature bell furnace, heat it to 880~920℃ at a heating rate of 6℃ / min, hold it at the temperature for 4~6 hours for pre-firing, and obtain the pre-fired powder after natural cooling. S5: Secondary ball milling and drying: The pre-calcined powder is added back to the ball mill jar, along with grinding balls and ball milling solvent for secondary ball milling. The weight ratio of grinding balls, raw materials, and ball milling solvent is controlled to be (2~4):1:(0.6~1). The ball milling solvent is a mixture of water and anhydrous ethanol with a volume ratio of (12~14):1. The secondary ball milling speed is 170~190 r / min, and the time is 7~9 h, to obtain a secondary ball milling slurry. The secondary ball milling slurry is placed in a tray and dried in an oven at 70~80℃ until constant weight, to obtain secondary ball milling powder. S6: Molding and Isostatic Pressing: The secondary ball milled powder is filled into the mold, pre-pressed under a pressure of 15~20MPa, and then placed into a rubber mold sleeve. Isostatic pressing is performed under a pressure of 220~250MPa and a holding time of 1~5min to obtain ceramic green body. S7: Sintering: Place the ceramic green body in a high-temperature bell furnace and heat it to 1180~1220℃ at a heating rate of 3℃ / min. Hold it at that temperature for 5~7h for sintering. After natural cooling, the ceramic core ingot is obtained. S8: Slicing and cleaning: Cut the ceramic core ingot into ceramic substrates with a thickness of 0.25mm using an internal circular cutter. Place the ceramic substrates on a cleaning rack, put them in a beaker, add deionized water, and ultrasonically clean for 30 minutes. Pour out the wastewater and repeat the operation until there are no visible dirt. Place the cleaned ceramic substrates along with the cleaning rack into an oven and dry at 100℃ for 10 minutes. S9: Coating Gold Electrodes: Place the ceramic substrate on a screen printing machine, using a 350-mesh screen, and print gold paste on both sides of the ceramic substrate. The printing thickness is controlled at 5~8μm. After printing, perform step-by-step drying: the first drying temperature is 140~160℃, and the time is 2~5min; the second drying temperature is 160~180℃, and the time is 8~12min. After drying, place it in a high-temperature bell furnace and sinter the electrodes at 830~870℃ for 20min. After natural cooling, a ceramic substrate coated with gold electrodes is obtained. S10: Slicing: Cutting a ceramic substrate coated with gold electrodes into chips of a predetermined size using a dicing machine; S11: Grinding and Cleaning: Add the chip and zirconia balls together to a rolling ball mill. Control the amount of zirconia balls added to be 25%~35% of the effective volume of the rolling ball mill tank. Grind the chip at a speed of 55~70 r / min for 20~40 min to remove burrs from the chip edges. After grinding, place the chip in a beaker, add anhydrous ethanol, and ultrasonically clean for 10~20 min. After cleaning, dry the chip at 60~70℃ to obtain a gold electrode NTC thermistor ceramic chip.

[0033] Regarding step S1, in some specific implementations, the temperature for static treatment can be 45°C, 48°C, 50°C, 52°C or 55°C, the relative humidity can be 25%, 28%, 30% or 35%, and the time can be 10h, 12h or 14h.

[0034] Regarding step S2, in some specific implementation schemes, the weight ratio of each component raw material Mn3O4, Co2O3, NiO, and Cr2O3 can be 43:33:17:7, 45:32:18:10, 47:33:16:8, or 47:34:15:13; the weight ratio of grinding balls, raw materials, and ball milling solvent can be 2:1:1, 3:1:0.6, 4:1:0.7, or 4:1:1; in the ball milling solvent, the volume ratio of water to anhydrous ethanol can be 12:1, 13:1, or 14:1; the rotation speed of one ball milling can be 170 r / min, 180 r / min, or 190 r / min, and the time can be 5 h, 5.5 h, or 6 h.

[0035] Regarding step S4, in some specific implementations, the preheating temperature can be 880℃, 890℃, 900℃ or 920℃, and the holding time can be 4h, 5h or 6h.

[0036] Regarding step S5, in some specific implementations, the weight ratio of grinding balls, raw materials, and ball milling solvent can be 2:1:1, 3:1:0.6, 4:1:0.7, or 4:1:1; the volume ratio of water to anhydrous ethanol in the ball milling solvent can be 12:1, 13:1, or 14:1; the rotation speed of the secondary ball mill can be 170 r / min, 180 r / min, or 190 r / min, and the time can be 7 h, 8 h, or 9 h.

[0037] Regarding step S6, in some specific implementations, the pre-compression pressure is 15MPa, 17MPa or 20MPa, the isostatic pressing pressure can be 220MPa, 235MPa or 250MPa, and the holding time can be 1min, 3min or 5min.

[0038] For step S7, in some specific implementations, the sintering temperature can be 1180℃, 1200℃, 1210℃ or 1220℃, and the holding time can be 5h, 6h or 7h.

[0039] Regarding step S9, in some specific embodiments, the temperature of the first drying can be 140℃, 150℃ or 160℃, and the time can be 2min, 3min or 5min; the temperature of the second drying can be 160℃, 170℃ or 180℃, and the time can be 8min, 10min or 12min; the temperature of electrode sintering can be 830℃, 840℃, 860℃ or 870℃.

[0040] Regarding step S11, in some specific embodiments, the amount of zirconia balls added is 25%, 30%, or 35% of the effective volume of the rolling ball mill tank; the rotation speed of the grinding discs can be 55 r / min, 60 r / min, or 70 r / min; the time can be 20 min, 30 min, or 40 min; the ultrasonic cleaning time can be 10 min, 15 min, or 20 min; and the drying temperature can be 60°C, 65°C, or 70°C.

[0041] Based on the method for preparing the gold electrode NTC thermistor ceramic chip of this application, the following examples and comparative examples are provided: Example 1

[0042] A method for fabricating a gold electrode NTC thermistor ceramic chip specifically includes the following steps: S1: Raw material pretreatment: Mn3O4, Co2O3, NiO and Cr2O3 of each component raw material were placed in a constant temperature and humidity chamber for static treatment. The static treatment temperature was 50℃, the relative humidity was 30% and the time was 11h. The treated raw materials of each component raw material were sealed and stored for later use. S2: Batching and primary ball milling: Weigh 86g Mn3O4, 66g Co2O3, 34g NiO, and 14g Cr2O3, add them to the ball mill jar, then add 100g zirconia balls and 100g of a mixed solvent of water and anhydrous ethanol in a volume ratio of 12:1. Set the speed to 180r / min and perform primary ball milling for 6 hours to obtain the primary slurry. S3: Discharge and drying: Place the primary slurry in a tray and dry it in a 75℃ oven until constant weight to obtain powder; S4: Sieving and pre-firing: The powder is sieved through a 200-mesh sieve, and the sieved powder is placed in a high-temperature bell furnace. The temperature is raised to 890°C at a rate of 6°C / min and held for 5.5 hours for pre-firing. After natural cooling, the pre-fired powder is obtained. S5: Secondary ball milling and drying: The pre-calcined powder is added back to the ball mill jar, along with 100g of zirconia balls and 100g of a mixed solvent of water and anhydrous ethanol in a volume ratio of 12:1. The milling speed is set to 180r / min, and the mixture is ball-milled for 8.5h to obtain a secondary ball mill slurry. The secondary ball mill slurry is placed in a tray and dried in an 80℃ oven until constant weight to obtain the secondary ball milled powder. S6: Molding and Isostatic Pressing: The secondary ball milled powder is filled into the mold, pre-pressed under a pressure of 20MPa, and then placed into a rubber mold sleeve. Isostatic pressing is performed under a pressure of 230MPa and a holding time of 5min to obtain a ceramic green body. S7: Sintering: The ceramic green body is placed in a high-temperature bell furnace and heated to 1180°C at a heating rate of 3°C / min. It is then held at that temperature for 7 hours for sintering. After natural cooling, the ceramic core ingot is obtained. S8: Slicing and cleaning: Cut the ceramic core ingot into ceramic substrates with a thickness of 0.25mm using an internal circular cutter. Place the ceramic substrates on a cleaning rack, put them in a beaker, add deionized water, and ultrasonically clean for 30 minutes. Pour out the wastewater and repeat the operation until there are no visible dirt. Place the cleaned ceramic substrates along with the cleaning rack into an oven and dry at 100℃ for 10 minutes. S9: Coating Gold Electrodes: Place the ceramic substrate on a screen printing machine, using a 350-mesh screen, and print gold paste on both sides of the ceramic substrate. The printing thickness is controlled at 6μm. After printing, perform step-by-step drying: the first drying temperature is 150℃ and the time is 3min; the second drying temperature is 170℃ and the time is 12min. After drying, place it in a high-temperature bell furnace and sinter the electrodes at 850℃ for 20min. After natural cooling, a ceramic substrate coated with gold electrodes is obtained. S10: Slicing: The ceramic substrate coated with gold electrodes is diced into chips of a predetermined size of 0.5mm × 0.5mm using a dicing machine; S11: Grinding and Cleaning: Add the chip and zirconia balls together to a rolling ball mill. Control the amount of zirconia balls added to be 25% of the effective volume of the rolling ball mill tank. Grind the chip at a speed of 60 r / min for 35 min to remove burrs from the chip edges. After grinding, place the chip in a beaker, add anhydrous ethanol, and ultrasonically clean for 15 min. After removal, dry at 60℃ to obtain a gold electrode NTC thermistor ceramic chip. Example 2

[0043] The preparation method of a gold electrode NTC thermistor ceramic chip is the same as in Example 1, except that in Example 2, the temperature of the static treatment in step S1 is 48°C, the relative humidity is 28%, and the static time is 11h. Example 3

[0044] The preparation method of a gold electrode NTC thermistor ceramic chip is the same as in Example 1, except that in step S2 of Example 3, the masses of Mn3O4, Co2O3, NiO and Cr2O3 are 88g, 64g, 36g and 12g, respectively. Example 4

[0045] The preparation method of a gold electrode NTC thermistor ceramic chip is the same as in Example 1, except that in steps S2 and S5 of Example 4, the ball milling speed is 170 r / min. Example 5

[0046] The preparation method of a gold electrode NTC thermistor ceramic chip is the same as in Example 1, except that in step S9 of Example 5, the first drying temperature is 160°C and the time is 3 min; the second drying temperature is 170°C and the time is 12 min. Example 6

[0047] The preparation method of a gold electrode NTC thermistor ceramic chip is the same as in Example 1, except that in step S11 of Example 6, the grinding time is 25 min.

[0048] Comparative Example 1: A method for preparing a gold electrode NTC thermistor ceramic chip is the same as in Example 1, except that step S1 is omitted in Comparative Example 1, and the raw materials of each component are directly used for mixing without constant temperature and humidity settling treatment.

[0049] Comparative Example 2: A method for preparing a gold electrode NTC thermistor ceramic chip is the same as in Example 1, except that in step S2 of Comparative Example 2, the Cr2O3 in the raw material is replaced with an equal amount of Al2O3.

[0050] Comparative Example 3: The preparation method of a gold electrode NTC thermistor ceramic chip is the same as in Example 1, except that in step S2 of Comparative Example 3, the masses of Mn3O4, Co2O3, NiO and Cr2O3 are 86g, 62g, 40g and 12g, respectively.

[0051] Comparative Example 4: A method for preparing a gold electrode NTC thermistor ceramic chip is the same as in Example 1, except that in steps S2 and S5 of Comparative Example 4, the mixed solvent of water and anhydrous ethanol is replaced with water in equal amounts.

[0052] Comparative Example 5: The preparation method of a gold electrode NTC thermistor ceramic chip is the same as that in Example 1, except that the drying in step S9 of Comparative Example 5 is a one-time drying, the drying temperature is 170℃ and the time is 15min.

[0053] Material performance testing: The gold electrode NTC thermistor ceramic chips obtained in Examples 1-6 and Comparative Examples 1-5 were subjected to various performance tests, and the test methods are as follows: Resistance value and accuracy at 25℃: In accordance with GB / T 6663.1, the low-power resistance test method is adopted. A high-precision digital multimeter (6½ digits) is used to measure the zero-power resistance value of the sample in a constant temperature oil bath (temperature control accuracy ±0.01℃). The resistance value accuracy is then calculated based on the relative deviation between the measured resistance value and the design target resistance value (10.00 kΩ).

[0054] B value (25 / 85) and accuracy: Measure the zero-power resistance R at 25℃ and 85℃ respectively. 25 and R 85 Calculate the value of B using the following formula: B 25 / 85 =[(T) 25 ·T 85 ) / (T85 -T 25 )]·In(R 25 / R 85 ), where T 25 =298.15K ， T 85 =358.15K; then calculate the accuracy of the B value based on the relative deviation between the measured B value and the design target B value (3950 K).

[0055] Resistance change rate after 1000h aging at 125℃: The chip was placed in a high-temperature environment chamber and kept at 125℃±2℃ for 1000h. After aging, the temperature was restored to 25℃, and the zero-power resistance value before and after aging was tested. The resistance change rate before and after aging was calculated.

[0056] Gold electrode bonding strength: Use 3M tape to peel off at 90°, then observe under a microscope whether the electrode bubbles or falls off. Bubbles or falling off indicate that the electrode is unqualified.

[0057] Chip edge appearance: The chip cutting edge and surface morphology are observed using a 100x optical microscope to evaluate for defects such as burrs, chipping, cracks, and electrode blistering. Evaluation is based on the following criteria: no visible defects is excellent; slight burrs that do not affect performance are good; and obvious chipping or cracks are poor.

[0058] The test results are shown in Table 1: The test performance of the gold electrode NTC thermistor ceramic chips of Examples 1-6 and Comparative Examples 1-5 is shown in Table 1 below:

[0059] The preparation methods of gold electrode NTC thermistor ceramic chips in Examples 1-6 use Mn3O4, Co2O3, NiO, and Cr2O3 as ceramic substrate raw materials. The process involves raw material pretreatment, batching and primary ball milling, discharge drying, sieving and pre-firing, secondary ball milling and drying, molding and isostatic pressing, sintering, slicing and cleaning, gold electrode coating, slicing, grinding, and cleaning. The resulting gold electrode NTC thermistor ceramic chips exhibit resistance accuracy ≤ ±0.82% at 25°C, the thermistor index B value accuracy ≤ ±0.74%, and a resistance change rate ≤ 0.35% after aging at 125°C for 1000 hours. The gold electrode bonding strength is qualified, and the chip edge appearance is excellent. This demonstrates that the gold electrode NTC thermistor ceramic chips prepared by the method described in this application achieve excellent levels in resistance consistency, long-term stability, electrode bonding strength, and appearance quality, and their overall performance meets the requirements for high precision and high reliability.

[0060] Compared with Example 1, Comparative Example 1 omits step S1, the constant temperature and humidity settling treatment of raw materials, and the raw materials are used directly for batching without pretreatment. The results show that most of the performance of the gold electrode NTC thermistor ceramic chip in Comparative Example 1 is reduced: the resistance accuracy at 25℃ is ±1.57%, the B-value accuracy is ±1.41%, and the resistance change rate increases to 0.85% after aging at 125℃ for 1000 hours. This may be because the lack of raw material pretreatment leads to uneven moisture absorption, resulting in poor initial dispersion of the raw material powder. During ball milling, it is difficult to effectively break up agglomerates, leading to decreased powder uniformity. This non-uniformity continues into the subsequent pre-sintering and sintering processes, resulting in uneven microstructure of the ceramic substrate after sintering, poor grain size and density control, and ultimately, varying degrees of adverse effects on the resistance accuracy, B-value accuracy, and high-temperature aging stability of the prepared gold electrode NTC thermistor ceramic chip.

[0061] Compared with Example 1, Comparative Example 2 differs in that the Cr2O3 in the raw materials of step S2 is replaced by an equal amount of Al2O3. The results show that the resistance accuracy, B-value accuracy, and high-temperature aging stability of Comparative Example 2 are significantly reduced, with a resistance change rate as high as 1.60% after aging at 125℃ for 1000 hours. This may be because the system lacks the stabilizing effect of Cr2O3 on the crystal phase, making it impossible to form a stable Mn-Co-Ni-Cr quaternary thermistor crystal phase. At high temperatures, the crystal phase is prone to distortion, and abnormal grain growth cannot be effectively suppressed, resulting in significant resistance drift during long-term use of the chip, and a corresponding deterioration in resistance accuracy and B-value accuracy.

[0062] Compared with Example 1, Comparative Example 3 differs in that the proportions of Mn3O4, Co2O3, NiO, and Cr2O3 in step S2 of Comparative Example 3 are not within the scope of this application. The results show that the resistance value accuracy of Comparative Example 3 reaches ±2.16%, the B value accuracy is ±1.95%, and the resistance change rate increases to 1.33% after aging at 125℃ for 1000 hours. This may be because the imbalance in the raw material ratio disrupts the eutectic equilibrium in the quaternary system, and the distribution of oxygen ions in the sintered body may not be uniform enough, resulting in incomplete solid-phase reaction and insufficient crystal phase development in some areas. On the other hand, abnormal grain growth in local areas widens the grain size distribution, ultimately leading to a decrease in the consistency of the electrical performance of the prepared gold electrode NTC thermistor ceramic chip, insufficient crystal phase structure stability, and an increased resistance change rate under high-temperature aging.

[0063] Compared to Example 1, Comparative Example 4 differed in that the mixed solvent of water and anhydrous ethanol in steps S2 and S5 was replaced with water in equal amounts. The results showed that the resistance accuracy, B-value accuracy, and high-temperature aging stability of Comparative Example 4 all decreased. At 25°C, the resistance accuracy was ±1.87%, the B-value accuracy was ±1.72%, and the resistance change rate after 1000 hours of aging at 125°C reached 0.94%, with a good edge appearance. This may be because using only water as the ball milling solvent resulted in insufficient powder wetting and dispersion, exacerbating particle agglomeration. This led to a decrease in the density and microscopic uniformity of the sintered ceramic substrate, consequently reducing the consistency of the chip's electrical performance and its high-temperature aging stability. Furthermore, the uneven strength distribution caused by internal defects in the ceramic substrate made it more prone to slight edge chipping during cutting, thus reducing the edge appearance to "good."

[0064] Compared with Example 1, Comparative Example 5 differs in that step S9 in Comparative Example 5 uses a one-time drying process instead of the step-by-step drying method of this application. The results show that the gold electrode bonding force of Comparative Example 5 is unqualified, with blistering and detachment occurring. At the same time, the resistance change rate increases to 0.81% after aging at 125°C for 1000 hours. This may be because the one-time drying causes the solvent to evaporate too quickly and unevenly, which easily forms pinholes or bubbles at the interface between the electrode and the ceramic substrate, reducing the electrode bonding force. In addition, the internal stress generated by drying will also exacerbate the resistance drift after high-temperature aging of the chip, resulting in a decrease in the high-temperature aging performance of the chip.

[0065] Obviously, the above embodiments of this application are merely examples for clearly illustrating this application, and are not intended to limit the implementation of this application. For those skilled in the art, other variations or modifications can be made based on the above description. Any obvious variations or modifications derived from the technical solutions of this application are still within the protection scope of this application.

Claims

1. A method for fabricating a gold electrode NTC thermistor ceramic chip, characterized in that, Includes the following steps: S1: Raw material pretreatment: Mn3O4, Co2O3, NiO and Cr2O3 of each component raw material are placed in a constant temperature and humidity chamber for static treatment. The static treatment temperature is 45~55℃, the relative humidity is 25~35%, and the time is 10~14h. S2: Batching and primary ball milling: Weigh the raw materials of each component after S1 treatment according to the formula, add them to the ball mill jar, then add grinding balls and ball milling solvent for primary ball milling to obtain primary slurry; the ball milling solvent is a mixed solvent of water and anhydrous ethanol, and the volume ratio of water to anhydrous ethanol is (12~14):1; the rotation speed of the primary ball mill is 170~190 r / min, and the time is 5~6 h; S3: Discharge and drying: Dry the primary slurry to obtain powder; S4: Sieving and pre-firing: The powder is sieved and then pre-firing to obtain pre-fired powder; the pre-firing temperature is 880~920℃ and the holding time is 4~6h; S5: Secondary ball milling and drying: The pre-calcined powder is added back into the ball mill jar, along with grinding balls and a ball milling solvent for secondary ball milling; the ball milling solvent is a mixture of water and anhydrous ethanol, with a volume ratio of water to anhydrous ethanol of (12~14):1; the rotation speed of the secondary ball milling is 170~190 r / min, and the time is 7~9 h, to obtain a secondary ball milling slurry; the secondary ball milling slurry is dried to obtain secondary ball milling powder; S6: Molding and Isostatic Pressing: The secondary ball-milled powder is pressed into shape and then subjected to isostatic pressing to obtain ceramic green body; S7: Sintering: The ceramic green body is sintered at a temperature of 1180~1220℃ and a holding time of 5~7h to obtain a ceramic core ingot; S8: Slicing and Cleaning: The ceramic core ingot is sliced ​​into ceramic substrates, ultrasonically cleaned, and then dried. S9: Coating gold electrodes: Gold paste is coated on both sides of the ceramic substrate, dried, and then the electrodes are sintered; the drying after coating the gold paste includes a first drying and a second drying, the first drying temperature is 140~160℃ and the time is 2~5min, the second drying temperature is 160~180℃ and the time is 8~12min; the electrode sintering temperature is 830~870℃, to obtain a ceramic substrate coated with gold electrodes; S10: Slicing: Cutting the ceramic substrate covered with gold electrodes into chips of a predetermined size; S11: Grinding and Cleaning: Grind the chip to remove edge burrs, and clean it to obtain a gold electrode NTC thermistor ceramic chip.

2. The method for preparing the gold electrode NTC thermistor ceramic chip according to claim 1, characterized in that, In step S1, the temperature for the static treatment is 48~52℃, the relative humidity is 28~32%, and the static time is 11~13h.

3. The method for preparing the gold electrode NTC thermistor ceramic chip according to claim 1, characterized in that, In steps S2 and S5, the volume ratio of water to anhydrous ethanol is 13.3:1, and the rotation speed of the first and second ball milling is 175 r / min.

4. The method for preparing the gold electrode NTC thermistor ceramic chip according to claim 1, characterized in that, In step S2, the raw materials of each component are weighed according to the following weight ratios: 41-47 parts of Mn3O4; Co2O3 32-34 parts; NiO 15-18 parts; Cr2O3 6~13 parts.

5. The method for preparing a gold electrode NTC thermistor ceramic chip according to claim 1, characterized in that, In step S4, the pre-firing temperature is 880~920℃ and the holding time is 5~6h; in step S7, the sintering temperature is 1200~1220℃ and the holding time is 6h.

6. The method for preparing the gold electrode NTC thermistor ceramic chip according to claim 1, characterized in that, In step S6, the pressure of the isostatic pressing treatment is 220~250MPa, and the holding time is 1~5min.

7. The method for preparing a gold electrode NTC thermistor ceramic chip according to claim 1, characterized in that, In step S9, the gold paste is prepared from gold powder, glass powder, triethanolamine, ethyl cellulose resin and terpineol in a weight ratio of (70~74):(1~8):(3~9):(5~8):(7~12).

8. The method for preparing a gold electrode NTC thermistor ceramic chip according to claim 1, characterized in that, In step S9, the temperature of the first drying is 150~160℃ and the time is 2~5 min; the temperature of the second drying is 165~180℃ and the time is 8~12 min; the temperature of the electrode sintering is 850~860℃.

9. The method for preparing a gold electrode NTC thermistor ceramic chip according to claim 1, characterized in that, In step S11, the grinding disc treatment uses a rolling ball mill with zirconium balls as the grinding medium, and the grinding time is 20-40 minutes; the cleaning is performed by ultrasonic cleaning with alcohol.

10. A gold electrode NTC thermistor ceramic chip, characterized in that, The gold electrode NTC thermistor ceramic chip, prepared by any one of claims 1 to 9, comprises a ceramic substrate and gold electrodes covering both sides of the ceramic substrate, wherein the ceramic substrate is formed of oxides of Mn, Co, Ni and Cr.

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