Power type negative temperature coefficient thermistor for suppressing surge current and method

Abstract

The invention discloses a power type negative temperature coefficient thermistor and method for suppressing surge current, and relates to the technical field of negative temperature coefficient thermistors, the thermistor comprises a core body and pins, the pins are respectively arranged on electrodes on two sides of the core body by adopting a multi-contact-surface structure, and the pins are arranged on the two sides of the core body. The core body is made of a Mn-Co-Ni-La oxide with a nano composite gradient structure; the Mn-Co-Ni-La oxide with the nano-composite gradient structure determines the upper limits of core capabilities such as surge suppression, wide temperature stability and low power consumption of the thermistor, and the redesign of the pin is the key of performance transfer, so that the electrical properties (low contact resistance and high surge tolerance) of the Mn-Co-Ni-La oxide with the nano-composite gradient structure are not counteracted by structural defects; the arrangement of the bracket prevents the Mn-Co-Ni-La oxide with the nano-composite gradient structure from losing the effect due to heat accumulation and physical damage through thermal management and mechanical protection, and the three components supplement one another and cooperate with one another, so that the performance of the thermistor of the Mn-Co-Ni-La oxide with the nano-composite gradient structure is guaranteed.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of negative temperature coefficient thermistor, in particular, to a power type negative temperature coefficient thermistor for suppressing surge current. BACKGROUND

[0002] NTC thermistor is a kind of thermistor element with negative temperature coefficient, whose resistance decreases exponentially with temperature rise. The core characteristic of NTC thermistor is derived from the electron conduction mechanism of semiconductor material. When the temperature rises, the concentration of carriers (electrons or holes) in the material increases significantly, which leads to an exponential decrease in resistance. As an important branch of semiconductor ceramic elements, NTC thermistor is usually made of two or more transition metal oxides such as manganese, copper, cobalt, and nickel. The key performance such as resistivity and material constant (B value, a core parameter representing temperature coefficient) will change significantly with the difference in material composition ratio (such as the difference in manganese-cobalt-nickel oxide ratio), sintering atmosphere (air, inert gas, etc.), sintering temperature (usually 800-1200℃), and microstructure state (grain size, porosity, and grain boundary characteristics). Therefore, different application scenarios can be adapted through process control. NTC thermistor is currently widely used in surge suppression, temperature compensation, temperature measurement, and other fields.

[0003] In the field of electronic circuits, surge current far exceeding the rated current by several times to dozens of times is easily generated during the startup moment due to effects such as capacitor charging and inductance excitation. This current can cause instantaneous impact on elements such as backend chips, capacitors, and rectifier bridges, and can directly lead to element burnout or significantly shorten the service life. To solve this problem, power type NTC thermistors are generally connected in series in the power circuit. The core principle of surge suppression is based on the dynamic adaptation of the negative temperature coefficient characteristics and working state of the NTC thermistor:

[0004] Surge suppression stage during startup: Before startup, the NTC thermistor is in a room temperature (or low temperature) environment. According to the negative temperature coefficient characteristics, the resistance value is maintained at a high level at this time (i.e., "room temperature high resistance state"). When the circuit is powered on, the high resistance value of the NTC can limit the loop current through voltage division, effectively intercepting the surge current and preventing damage to the backend devices.

[0005] Steady state working stage: After completing surge suppression, the circuit enters a stable running state. The continuous working current through the NTC generates Joule heat, causing the temperature of the NTC to gradually rise. Based on the negative temperature coefficient characteristics, the resistance value of the NTC rapidly decreases from the room temperature high resistance state to a very low "high temperature low resistance state". At this time, the power consumption of the NTC is negligible compared to the total power consumption of the circuit, and the power voltage is almost entirely loaded to the backend devices, ensuring normal operation of the circuit.

[0006] Therefore, applying the power type NTC thermistor in the power supply circuit is a simple and efficient technical solution to realize the compatibility of "power-on surge suppression-steady-state low power consumption" and protect electronic devices.

[0007] However, the traditional power type NTC thermistor material has been limited by the inherent contradiction between "surge suppression capability" and "temperature stability" for a long time, and it is difficult to meet the stringent requirements of high-end electronic devices (such as new energy inverters, automotive electronics, and industrial high-power power supplies) for reliability. The specific pain points are reflected in two aspects:

[0008] Conflict between room temperature resistance (25℃) and functional requirements: If a higher room temperature resistance is designed to strengthen the surge suppression capability, although it can effectively limit the current during power-on, the "high-temperature residual resistance" of the NTC will also increase (the room temperature resistance and the high-temperature residual resistance are positively correlated in traditional materials) during steady-state operation of the circuit, resulting in a significant increase in its own power consumption, not only causing waste of electrical energy, but also causing the NTC to run at high temperature for a long time, accelerating material aging and pin loosening; if a lower room temperature resistance is designed to reduce high-temperature power consumption, although it can reduce steady-state loss, it cannot provide sufficient current limiting capability during power-on, and the surge current is easy to break through the safety threshold, resulting in damage to the downstream equipment;

[0009] High-temperature B value drift destroys performance stability: B value (temperature coefficient) is a core parameter that characterizes the NTC resistance-temperature relationship, and its stability directly determines the performance reliability of the NTC in a wide temperature range. In a high-temperature environment (> 150℃), the traditional NTC material (such as single manganese-cobalt-nickel spinel system) is prone to B value drift (usually fluctuates by ±15% or more) due to problems such as cation migration and increased lattice defects (vacancies, dislocations), which makes the resistance-temperature curve deviate from the design expectation, resulting in attenuation of surge suppression effect, decrease of temperature compensation accuracy, and even causing circuit overcurrent protection failure and safety hazards.

[0010] Therefore, the traditional power type NTC thermistor has a technical bottleneck in the balance of "surge suppression-temperature stability-low power consumption", and it is necessary to break through the above inherent contradictions through material composition optimization and structural innovation to meet the application requirements of high-end electronic devices for high reliability and wide temperature adaptability. SUMMARY

[0011] The technical problem to be solved by the present application is to overcome the shortcomings of the prior art and provide a power type negative temperature coefficient thermistor that can overcome the above problems or at least partially solve the above problems.

[0012] To solve the above technical problems, the basic idea of the technical scheme of the present application is: a power type negative temperature coefficient thermistor for suppressing inrush current, comprising a core body and a pin, the pin is arranged on the electrodes on both sides of the core body in a multi-contact surface structure, the core body is an Mn-Co-Ni-La oxide with a nano-composite gradient structure, composed of a core layer, an intermediate layer and an outer layer, the composition and weight percentage range of each layer are:

[0013] The core layer: Mn3O440-50wt%, Co3O420-30wt%, NiO 15-25wt%, La2O33-7wt%, ZnO 1-5wt%, Nb2O51-3wt%;

[0014] The intermediate layer: Mn3O435-45wt%, Co3O425-35wt%, NiO 10-20wt%, CuO 5-10wt%, ZrO25-10wt%;

[0015] The outer layer: Mn3O430-40wt%, Co3O425-35wt%, NiO 5-15wt%, Al2O33-7wt%, SiO215-25wt%;

[0016] The preparation method of the core body comprises the following steps:

[0017] S1, the raw materials of the core layer, the intermediate layer and the outer layer are prepared into sols by sol-gel method at 60-80℃ and PH 6-7, dried at 80-100℃ and calcined at 400-500℃, to obtain core layer, intermediate layer and outer layer nano precursors with a particle size of 20-50nm;

[0018] S2, the core layer, the intermediate layer and the outer layer nano precursors are stacked and pressure formed in sequence to obtain a gradient structure blank;

[0019] S3, pulse field assisted sintering process is adopted to sinter at 1000-1100℃ in air atmosphere for 8-12 minutes.

[0020] Preferably, the composition of the core layer has a weight percentage range of: Mn3O445wt%, Co3O425wt%, NiO 20wt%, La2O35wt%, ZnO 3wt%, Nb2O52wt%;

[0021] The composition of the intermediate layer has a weight percentage range of: Mn3O440wt%, Co3O430wt%, NiO 15wt%, CuO 8wt%, ZrO27wt%;

[0022] The outer layer component ranges from 35wt% Mn3O4, 30wt% Co3O4, 10wt% NiO, 5wt% Al2O3, 20wt% SiO2.

[0023] Preferably, the inner core layer component ranges from 42wt% Mn3O4, 28wt% Co3O4, 22wt% NiO, 6wt% La2O3, 2wt% ZnO, 2wt% Nb2O5;

[0024] The intermediate layer component ranges from 38wt% Mn3O4, 32wt% Co3O4, 17wt% NiO, 7wt% CuO, 8wt% ZrO2;

[0025] The outer layer component ranges from 33wt% Mn3O4, 32wt% Co3O4, 12wt% NiO, 6wt% Al2O3, 18wt% SiO2.

[0026] Preferably, the inner core layer component ranges from 48wt% Mn3O4, 22wt% Co3O4, 18wt% NiO, 4wt% La2O3, 4wt% ZnO, 2wt% Nb2O5;

[0027] The intermediate layer component ranges from 43wt% Mn3O4, 27wt% Co3O4, 13wt% NiO, 9wt% CuO, 8wt% ZrO2;

[0028] The outer layer component ranges from 38wt% Mn3O4, 26wt% Co3O4, 8wt% NiO, 4wt% Al2O3, 24wt% SiO2.

[0029] Preferably, the multi-contact surface structure includes a continuous zigzag contact section between the pin and the contact section of the core electrode, and the zigzag contact section forms a triangular area on both sides of the core electrode.

[0030] Preferably, the multi-contact surface structure includes a semicircular arc contact section between the pin and the contact section of the core electrode, and the semicircular area of the semicircular arc contact section faces the core axis.

[0031] Preferably, the semicircular area of the semicircular arc contact section faces the outside.

[0032] Preferably, a bracket is further arranged on the core, the bracket includes two symmetrical legs, the core is located between the two legs, the bracket is provided with two arms on both sides, the arms are provided with clamping grooves, the pin is located in the clamping grooves, and the two arms and the two legs form a package for the core.

[0033] Further, a heat dissipation channel is arranged in the leg, and the heat dissipation channel is communicated with the opening section on the support.

[0034] Preferably, the two legs are provided with heat conduction blocks on the opposite sides, and the heat conduction blocks form an arch-shaped area on the leg.

[0035] Compared with the prior art, the application has the following beneficial effects:

[0036] 1. The power type negative temperature coefficient thermistor for suppressing surge current, the "pinning effect" of the intermediate layer ZrO2 enables the thermistor to withstand 8-9A surge current, and the fold line / semicircular arc structure of the pin increases the contact area, the triangular area / semicircular area stores solder, and mechanical engagement + solder anchoring is formed to avoid pin soldering from the surge impact.

[0037] 2. The power type negative temperature coefficient thermistor for suppressing surge current, the La-O bond of the core layer enables the resistance drift of the thermistor to be less than ±10% at a wide temperature of-40-200℃, the bending area of the pin can absorb thermal stress to avoid the soldering crack caused by the difference in thermal expansion between the pin and the core body when the temperature changes suddenly; and the high-temperature resistant epoxy resin material (temperature resistance > 150℃) of the support is suitable for a wide temperature environment, the heat conduction block and the heat dissipation channel can reduce the steady-state temperature of the core body, prevent the local overheating from breaking through the upper limit of 200℃, and avoid the B value drift.

[0038] 3. The power type negative temperature coefficient thermistor for suppressing surge current, the arch-shaped heat conduction block of the support is attached to the core body to accelerate heat transfer and avoid heat concentration of the core body, and the close attachment design of the pin also assists heat conduction to the outside, and the two together guarantee that the rapid thermal response is not weakened by heat accumulation and ensure that the surge suppression state is quickly entered at the moment of starting.

[0039] 4. The power type negative temperature coefficient thermistor for suppressing surge current, the nano-composite gradient structure Mn-Co-Ni-La oxide determines the upper limit of the core capabilities of the thermistor such as surge suppression, wide temperature stability, and low power consumption, and the redesign of the pin is the "key to performance transmission", which ensures that the electrical properties (low contact resistance and high surge withstand) of the nano-composite gradient structure Mn-Co-Ni-La oxide are not offset by structural defects; the support is provided to avoid the nano-composite gradient structure Mn-Co-Ni-La oxide from losing effect due to heat accumulation and physical damage through heat management and mechanical protection, and the three complement each other and cooperate to guarantee the performance of the nano-composite gradient structure Mn-Co-Ni-La oxide thermistor. BRIEF DESCRIPTION OF DRAWINGS

[0040] In the drawings:

[0041] Figure 1 Perspective view of the pin with straight contact portion;

[0042] Figure 2 Schematic view of the pin with straight contact portion on the holder;

[0043] Figure 3 Schematic view of the bending area of the pin with straight contact portion;

[0044] Figure 4 Schematic view of the pin with broken line contact portion;

[0045] Figure 5 Schematic view of the pin with broken line contact portion on the holder Figure 1 ;

[0046] Figure 6 Schematic view of the pin with broken line contact portion on the holder Figure 2 ;

[0047] Figure 7 Schematic view of the bending area of the pin with broken line contact portion;

[0048] Figure 8 Schematic view of the semicircular area of the pin with semicircular contact portion facing the axis of the core;

[0049] Figure 9 Schematic view of the pin with semicircular contact portion on the holder Figure 1 ;

[0050] Figure 10 Schematic view of the pin with semicircular contact portion on the holder Figure 2 ;

[0051] Figure 11 Schematic view of the bending area of the pin with semicircular contact portion;

[0052] Figure 12 Schematic view of the semicircular area of the pin with semicircular contact portion facing outward;

[0053] Figure 13 Schematic view of the structure of the leg, arm, clamping groove and arch-shaped area;

[0054] Figure 14 Perspective view of the holder;

[0055] Figure 15 Schematic view of the structure of the heat dissipation channel and opening section.

[0056] In the figure: 1, core; 11, pin; 111, straight contact portion;

[0057] 112, broken line contact portion; 1121, triangular area;

[0058] 113, semicircular contact portion; 1131, semicircular area;

[0059] 12, bending area;

[0060] 2, support; 21, leg; 22, arm; 23, clamping groove; 24, buckle; 25, heat-conducting bump; 26, arch-shaped area; 27, heat dissipation channel; 28, opening section. DETAILED DESCRIPTION

[0061] In order to make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme in the embodiments will be described clearly and completely below with reference to the drawings in the embodiments of the present application. The following embodiments are used to illustrate the present application but not to limit the scope of the present application.

[0062] Embodiment 1: A power type negative temperature coefficient thermistor for suppressing inrush current, the core 1 adopts Mn-Co-Ni-La oxide with nano-composite gradient structure, which is composed of a core layer, an intermediate layer and an outer layer, and the composition and weight percentage of each layer are as follows:

[0063] The composition and weight percentage of the core layer are as follows: Mn3O445wt%, Co3O425wt%, NiO 20wt%, La2O35wt%, ZnO 3wt%, Nb2O52wt%;

[0064] The composition and weight percentage of the intermediate layer are as follows: Mn3O440wt%, Co3O430wt%, NiO 15wt%, CuO 8wt%, ZrO27wt%;

[0065] The composition and weight percentage of the outer layer are as follows: Mn3O435wt%, Co3O430wt%, NiO 10wt%, Al2O35wt%, SiO220wt%.

[0066] The preparation method of the core 1 includes the following steps: weighing the raw material powders of the core layer, the intermediate layer and the outer layer respectively, and preparing nano-scale precursors respectively;

[0067] The weighed raw material powders of each layer are added into a “citric acid-ethylene glycol mixed solvent” (citric acid is a chelating agent and ethylene glycol is a cosolvent) in proportion, the solid-liquid ratio is controlled to be 1:6, stirring is carried out in a 65℃ constant temperature water bath for 2-4h, and ammonia water is added dropwise to adjust the PH to 6.5, so that the metal ions form stable chelates with citric acid to form a sol;

[0068] The sol of each layer is transferred to a constant temperature drying oven and dried at 85℃ for 10h to form a dry gel;

[0069] The dry gel of each layer after drying is placed in a muffle furnace and calcined at 450℃ for 4h (the heating rate is 2-5℃ / min, the holding time is 1h, and the cooling rate is 2-5℃ / min); , avoid temperature rise caused by particle agglomeration), after complete combustion of the organic components, each layer of nanometer oxide precursor powder with a particle size of 30 nm and a specific surface area of 32 m2 / g is obtained;

[0070] Each layer of the precursor is granulated by adding 5wt% PVA and sieved through an 80 mesh sieve;

[0071] The outer layer, the intermediate layer, and the core layer are sequentially laid in the mold, and the pressure is gradually increased to 25MPa in steps, and the pressure is maintained for 30s;

[0072] Process parameters: air atmosphere, 1050℃ for 10min, pressure 12MPa, pulse voltage 600V, frequency 80Hz;

[0073] Cooling rate: 50℃ / min to room temperature, to obtain a core 1 with a nanocomposite gradient structure with interlayer bonding.

[0074] In subsequent processing, silver paste is printed, sintered at 620℃ for 30min, forming an electrode with a contact resistance of 4mΩ; packaged with epoxy resin; final performance: B value 3450K, room temperature resistance (room temperature resistance refers to rated resistance, rated at 25℃) 45Ω, thermal response time 0.6s, inrush current 8.5A, 1000h / 200℃ resistance drift ±9.2%.

[0075] Example 2: A power type negative temperature coefficient thermistor that suppresses inrush current, the core 1 adopts a nanocomposite gradient structure of Mn-Co-Ni-La oxide, composed of a core layer, an intermediate layer, and an outer layer, the components and weight percentages of each layer are:

[0076] The core layer has the following weight percentages: Mn3O442wt%, Co3O428wt%, NiO 22wt%, La2O36wt%, ZnO 2wt%, Nb2O52wt%;

[0077] The intermediate layer has the following weight percentages: Mn3O438wt%, Co3O432wt%, NiO 17wt%, CuO 7wt%, ZrO28wt%;

[0078] The outer layer has the following weight percentages: Mn3O433wt%, Co3O432wt%, NiO 12wt%, Al2O36wt%, SiO218wt%;

[0079] The core 1 preparation method includes the following steps: additional addition of 0.5wt% citric acid (enhance La 3+ chelation) in the core layer, 70℃ water bath stirring for 4h, pH=6.0, to ensure uniform dispersion of La 3+ ;

[0080] 90℃ drying 8h, avoiding La segregation, forming xerogel;

[0081] 480℃ calcination 3.5h (heating rate 8℃ / min), obtaining 25nm particle size of the precursor, specific surface area 38m² / g;

[0082] Each layer of the precursor added 4wt% PVA (for reducing organic residues), over 100 mesh sieve;

[0083] Layered pressure 30MPa, pressure 40s, ensuring no gap between layers;

[0084] Pulsed field sintering process parameters: air atmosphere, 1080℃ for 9min (high temperature and short holding for densification), pressure 15MPa, pulse voltage 700V, frequency 100Hz;

[0085] Cooling rate: the first 200℃ at 30℃ / min, to reduce thermal stress, the subsequent recovery 50℃ / min, to obtain the core 1 of the interlayer bonding of the nano composite gradient structure;

[0086] In the subsequent processing, printing silver paste, silver content 90wt%, 650℃ sintering 25min, contact resistance 3mΩ; using high temperature resistant epoxy resin packaging, the final performance: B value 3550K, room temperature resistance 48Ω, thermal response time 0.5s, inrush current 9.0A, 1000h / 200℃ resistance drift ±8.8%.

[0087] Example 3: a power type negative temperature coefficient thermistor for suppressing inrush current, the core 1 of the Mn-Co-Ni-La oxide of the nano composite gradient structure, composed of the core layer, the intermediate layer and the outer layer, the composition and weight percentage of each layer are:

[0088] The composition and weight percentage of the core layer are: Mn3O448wt%, Co3O422wt%, NiO 18wt%, La2O34wt%, ZnO 4wt%, Nb2O52wt%;

[0089] The composition and weight percentage of the intermediate layer are: Mn3O443wt%, Co3O427wt%, NiO 13wt%, CuO 9wt%, ZrO28wt%;

[0090] The composition and weight percentage of the outer layer are: Mn3O438wt%, Co3O426wt%, NiO 8wt%, Al2O34wt%, SiO224wt%;

[0091] Using a single citric acid solvent, solid-liquid ratio 1:5, 60℃ water bath stirring 2h, PH=7.0;

[0092] 80℃ drying 12h, gelling;

[0093] 420℃ calcination 5h, precursor with 40nm particle size, 31m² / g specific surface area;

[0094] Each layer precursor added 6wt% PVA, passed through 60 mesh sieve;

[0095] Layered pressurization 20MPa, pressure maintaining 20s;

[0096] Pulse electric field sintering process parameters: air atmosphere, 1020℃ for 11min, pressure 10MPa, pulse voltage 500V, frequency 50Hz;

[0097] Natural cooling as the main, auxiliary air cooling, interlayer bonding of the nanocomposite gradient structure core 1 is obtained;

[0098] In subsequent processing, using conventional silver paste, silver content 85wt%, 600℃ sintering 35min, contact resistance 5mΩ; using epoxy resin packaging; final performance: B value 3350K, room temperature resistance 42Ω, thermal response time 0.7s, inrush current 8.0A, 1000h / 200℃ resistance drift ±9.8%.

[0099] Table 1 is the B value, room temperature resistance, thermal response time, inrush current parameter comparison of examples 1-3:

[0100]

[0101] The core 1 adopts nanocomposite gradient structure Mn-Co-Ni-La oxide technology, solves the contradiction between surge suppression and temperature stability through three-layer gradient structure design; the inner core layer, the intermediate layer and the outer layer respectively adopt different proportion of metal oxides, realizing the optimization of resistance gradient and heat diffusion;

[0102] The inner core layer: anchoring basic NTC characteristics and high temperature stability, in component design, taking Mn3O4, Co3O4, NiO as spinel structure main body, ensuring the core carrier (Mn 3+ / Mn 2+ ) of NTC effect, providing electronic conduction by changing valence;

[0103] La2O3 as rare earth dopant, La 3+ (ion radius ) replaces part of the octahedral position of Mn 3+ , forming high bond energy La-O bond (bond energy ≈530kJ / mol), inhibiting the migration and diffusion of cations at high temperature , reducing lattice defects (such as vacancies, dislocations), and reducing resistance drift rate from the root;

[0104] Zn of ZnO 2+ ( ) fill tetrahedral gap, refine grain, inhibit overgrowth; Nb of Nb2O5 5+ ( ) stabilize lattice charge through electric compensation (balance low electric charge of La 3+ ), avoid carrier concentration fluctuation;

[0105] Therefore, it can provide stable B value basis and high temperature structural support, ensuring resistance drift <±10% during long-term work.

[0106] Intermediate layer: build resistance gradient buffer zone, solve the "inhibition-power consumption" mutation problem, in this component design, by reducing the proportion of Mn3O4, increasing Co3O4, introducing CuO and ZrO2, forming the performance transition zone of the inner core and the outer layer;

[0107] In the resistance gradient adjustment mechanism, Cu of CuO 2+ / Cu + variable valence characteristics can dynamically adjust the carrier concentration, so that the room temperature resistance of the intermediate layer is between the inner core (high resistance) and the outer layer (low resistance), avoiding the local electric field concentration caused by resistance mutation at the moment of starting; Co3O4 proportion increase enhances the structural stability at high temperature (Co 3+ / Co 2+ redox buffer effect);

[0108] Zr of ZrO2 4+ ( ) forms dispersed ZrO2 nanoparticles, which hinder grain boundary sliding through "pinning effect", and cooperates with the stress dispersion design of gradient structure, so that the material can withstand 8.5A surge current;

[0109] Therefore, the design of the intermediate layer realizes the smooth transition of resistance from the inner core to the outer layer, which not only ensures the surge suppression effect at startup, but also avoids the surge of power consumption caused by resistance mutation at high temperature.

[0110] Outer layer: in the component design, greatly reduce Mn3O4 and NiO, introduce high proportion of SiO2 and Al2O3, form a dense surface layer structure;

[0111] SiO2 and Al2O3 form a non-crystalline-microcrystalline composite layer with low thermal conductivity (k) ), on the one hand, accelerate the heat diffusion to the outside during surge impact (avoid overheating of the inner core), on the other hand, reduce heat accumulation during work;

[0112] The glass phase characteristics of SiO2 improve the wettability of the material and the silver electrode, so that the contact resistance is reduced to <5mΩ, and Al2O3 enhances the hardness of the surface layer, improves the resistance to mechanical wear and corrosion resistance;

[0113] Therefore, the outer layer effectively balances thermal management by building a "thermal barrier and protective layer".

[0114] The 20-50 nm precursor prepared by the sol-gel method has a high specific surface area (m2 / g) Pulse field sintering can retain the nanocrystalline structure, with a heat response time of <0.8 s, ensuring that the surge suppression state is entered quickly at the moment of starting.

[0115] Compared with traditional sintering (such as air atmosphere sintering), the pulse field sintering method has the problems of grain coarsening (>1 μm), loose interlayer bonding, and composition segregation. The pulse field assisted sintering method used in the above embodiments has the following advantages:

[0116] Short-time high-temperature sintering (traditional ), while inhibiting excessive grain growth (maintaining 50-100 nm grains), realizing interlayer atomic diffusion bonding, and avoiding interlayer cracking;

[0117] The directional effect of the pulse electric field can inhibit the excessive mixing of different interlayer components, ensuring the composition gradient of the core layer-intermediate layer-outer layer, and ensuring the effectiveness of the functional partition;

[0118] Compared with traditional sintering, the energy consumption is reduced, and there is no need for complex atmosphere control (air atmosphere can be used), greatly reducing the industrialization cost.

[0119] Therefore, the core 1 can adapt to the starting impact of new energy inverters and industrial power supplies (500-2000 W), solving the problem of easy burning of traditional power type NTCs in high-power scenarios; in wide temperature environment applications, combined with low resistance drift rate, it can meet the temperature compensation needs of extreme environments such as automotive electronics (engine compartment) and aerospace;

[0120] In summary, the core advantage of the thermistor is that it realizes functional partitioning through a gradient structure, solves parameter contradictions with multi-element doping, and enhances performance boundaries with nanotechnology, retaining the NTC basic characteristics of the Mn-Co-Ni spinel system, and breaking through the traditional material "surge suppression-temperature stability-response speed" triangle restriction through La / Cu / Zr doping and SiO2 / Al2O3 surface optimization. It is suitable for high-end electronic equipment fields with strict reliability requirements.

[0121] Example 4: Refer to Figure 1 , Figure 3 , Figure 4 , Figure 7, the thermistor includes a core 1, a pin 11, the pin 11 is arranged on the electrodes on both sides of the core 1 in a multi-contact surface structure, the multi-contact surface structure includes a continuous zigzag contact part 112 provided on the contact section of the pin 11 and the electrode of the core 1, and the zigzag contact part 112 is formed with a triangular area 1121 on both sides of the electrode of the core 1;

[0122] With reference to Figure 1 The linear contact part 111 of the pin 11 is a design structure of a traditional pin 11, and the linear design is in linear contact with the core 1, the contact area is small, and when the temperature of the core 1 suddenly changes, such as surge impact and environmental temperature fluctuation, the thermal shrinkage of the two is inconsistent, thermal stress is generated, and looseness or falling off is caused;

[0123] The zigzag contact part 112 designed in a continuous "Z" shape, the folding angle is 60-70°, preferably 65°, effectively improves the contact area of the pin 11 and the electrode of the core 1;

[0124] And a triangular area 1121 is naturally formed on one side of the electrode of the core 1, and then when the solder is filled, the triangular area 1121 can be filled, forming a double fixation of mechanical engagement and solder anchoring between the core 1 and the pin 11, avoiding the soldering caused by the insufficient amount of solder in the traditional linear contact;

[0125] At the same time, when the epoxy resin is encapsulated or immersed in the epoxy resin, the epoxy resin will also be filled into the triangular area 1121, further enhancing the bonding force between the core 1 and the pin 11, avoiding the looseness between the pin 11 and the core 1 caused by the pulling force generated by the cutting process in the subsequent cutting process of the pin 11, and further reducing the risk of looseness and falling off of the pin 11.

[0126] Embodiment 5, with reference to Figure 8 The multi-contact surface structure includes a semicircular arc contact part 113 provided on the contact section of the pin 11 and the electrode of the core 1, and the semicircular area 1131 of the semicircular arc contact part 113 faces the axis of the core 1;

[0127] With reference to Figure 12 The semicircular area 1131 of the semicircular arc contact part 113 faces the outside;

[0128] The design of the semicircular arc contact part 113 can increase the contact area with the electrode of the core 1 compared with the traditional linear contact part 111, and the semicircular arc contact part 113 can make the solder flow more easily during welding, completely cover the contact arc surface, avoid the problem of uneven solder accumulation in the traditional linear contact, and the design of the semicircular area 1131 facing the outside and the axis of the core 1 can store more solder and enhance the welding strength.

[0129] Therefore, by designing the pin 11, the soldering-off rate can be reduced, and under the impact of the surge current, the contact resistance fluctuation of the pin 11 can be reduced, and the current limiting failure caused by the sudden change of the contact resistance can be avoided.

[0130] In some embodiments, with reference to Figure 3 , Figure 7 , Figure 11 The straight line contact part 111, the broken line contact part 112, and the semicircular arc contact part 113 are bent to form a bending area 12 at the center of the core 1. This design can increase the contact area of the pin 11 with the core 1 while extending the pin 11. In addition, during subsequent packaging, the pin 11 covers the core 1 in a semi-enclosed manner, which increases the bonding force between the epoxy resin and the core 1 and the pin 11, further improving the tensile resistance of the pin 11 and preventing the pin 11 from loosening.

[0131] In example 6, with reference to Figure 2 , Figure 5 , Figure 6 , Figure 9 , Figure 10 , Figures 12-15 The support 2 is arranged on the core 1, and the support 2 includes two symmetrical legs 21. The core 1 is located between the two legs 21, and the support 2 is provided with an arm 22 on both sides. The arm 22 is provided with a clamping groove 23, and the pin 11 is located in the clamping groove 23. The two arms 22 and the two legs 21 form a package for the core 1.

[0132] The pin 11 is placed in the clamping groove 23 of the arm 22, which can limit the pin 11 and separate the pins 11. In addition, the clamping groove 23 is provided with a buckle 24 on the side wall, which can limit the position of the pin 11 in the clamping groove 23, and can prevent the pin 11 from separating from the clamping groove 23.

[0133] In addition, during the manufacturing process of the thermistor, the core 1 is inserted between the front and back of the pin 11 by automatic equipment. Therefore, by limiting the pin 11 with the support 2, the position of the pin 11 can be fixed before the core 1 is inserted between the pins 11, which can prevent the core 1 from falling due to the excessive separation distance between the pins 11.

[0134] At the same time, the support 2 can prevent the position of the pin 11 on the core 1 from shifting greatly (because the two arms 22 on both sides form a package for the core 1 when the core 1 is inserted into the pin 11, and because the two arms 22 on both sides are arc-shaped, the insertion of the core 1 can be self-centered), which can prevent the pin 11 from being skewed or leaking outside the core 1 after welding, and further improve the welding quality of the pin 11.

[0135] Further, the setting of the support leg 21 on the support 2 can cooperate with the bending area 12 of the lead 11 to form a limit for the lead 11, which can further avoid the lead 11 from being pulled by external force and loosened from the core 1.

[0136] In some embodiments, with reference to Figure 13 、 Figure 14 、 Figure 15 , a heat dissipation channel 27 is arranged in the support leg 21, and the heat dissipation channel 27 is in communication with an opening section 28 on the support 2 (wherein it is understood that the length of the opening section 28 can be set according to the actual packaging requirements of the core 1, so as to avoid the packaging body from entering the opening section 28; further, a heat-conducting block with the same cross section as the opening section 28 can be inserted into the opening section 28 to fill and block the opening section 28, so as to avoid moisture from entering while not affecting heat dissipation);

[0137] A part of the core 1 is located between the two support legs 21, and the support legs 21 are close to the middle part of the core 1. The support legs 21 are integrated with the core 1 through packaging, and form a heat dissipation path of the core 1-support leg 21-opening section 28, so that when the core 1 is at high temperature, the core 1 can be promptly cooled through the heat dissipation channel 27;

[0138] The support 2 is made of high-temperature-resistant epoxy resin and is injection molded.

[0139] In some embodiments, with reference to Figure 13 、 Figure 14 、 Figure 15 , the two support legs 21 are each provided with a heat-conducting block 25 on the opposite side, and the heat-conducting block 25 forms an arch-shaped area 26 on the support leg 21;

[0140] The heat-conducting block 25 directly adheres to the side surface of the core, quickly conducts the heat generated by the core during operation (especially the instantaneous heat after surge impact) to the support leg 21, and then conducts the heat to the outside through the heat dissipation channel 27 and the opening section 28, thereby forming an efficient heat dissipation path of the core 1-heat-conducting block 25-heat dissipation channel 27;

[0141] The arch-shaped area 26 can increase the contact area and contact points of the heat-conducting block 25 and the core 1, so as to avoid too few contact surfaces between the support leg 21 and the core 1 due to deformation of the support leg 21;

[0142] In addition, the heat-conducting block 25 of the arch-shaped area 26 forms multi-point support for the core 1, which can limit the left-right and up-down displacement of the core 1 in the vibration or impact scene, avoid mechanical stress generated by the core 1 shaking at the welding position of the core 1 and the lead 11, and prevent the core 1 from being damaged due to direct friction between the core 1 and the inner wall of the support 2;

[0143] In one embodiment, the heat-conducting bump 25 protrudes 1-2mm from the surface of the foot 21, which leaves a gap between the core 1 and the foot 21, and when encapsulating, the epoxy resin fills into the gap, which can further improve the heat dissipation effect of the core 1 through the bracket 2, and improve the bonding force between the bracket 2 and the core 1 after encapsulation, avoid the bracket 2 loose, and further protect the stability of the pin 11, and the arch-shaped area 26 formed by the heat-conducting bump 25 can further improve the bonding force between the bracket 2 and the core 1.

[0144] In one embodiment, the heat-conducting bump 25 extends into the heat dissipation channel 27, further improving the conduction of heat.

[0145] The setting of the arch-shaped area 26 on the bracket 2 can avoid the destruction of the material structure of the core 1 due to heat accumulation.

[0146] In the present application, the nano-composite gradient Mn-Co-Ni-La oxide is the "performance core" of the thermistor, which determines the upper limit of surge suppression (8A-9A), wide temperature stability (-40~200℃), and fast thermal response (<0.8s); the redesigned pin 11 increases the welding area and buffers thermal stress, avoids the surge bearing force of the nano-composite gradient structure being offset by the disassembly, and at the same time guarantees low contact resistance and does not waste the low power consumption advantage of the nano-composite gradient structure;

[0147] And the bracket 2 not only strengthens the heat dissipation to make the nano-composite gradient structure immune to performance degradation caused by overheating, but also fixes the core 1 and the pin 11 to avoid damage to the nano-composite gradient structure due to mechanical impact, and the three work together to make the performance of the thermistor truly translate into reliable protection and stable work in actual application.

[0148] The above only describes the preferred embodiments of the present application, and does not limit the present application in any form, although the present application has been disclosed as above, however, it is not intended to limit the present application, any person skilled in the art can make some changes or modifications to the above-mentioned technical content without departing from the scope of the technical solution of the present application, as long as it does not depart from the technical solution of the present application, any simple modification, equivalent change and modification of the above embodiments according to the technical essence of the present application, all still belong to the scope of the present application.

Claims

1. A power-type negative temperature coefficient thermistor for suppressing surge current, characterized in that, The thermistor includes a core (1) and pins (11). The pins (11) are arranged on the electrodes on both sides of the core (1) using a multi-contact surface structure. The core (1) is a Mn-Co-Ni-La oxide with a nanocomposite gradient structure, consisting of a core layer, an intermediate layer, and an outer layer. The composition and weight percentage range of each layer are as follows: Core layer: Mn3O4 40-50wt%, Co3O4 20-30wt%, NiO 15-25wt%, La2O3 3-7wt%, ZnO 1-5wt%, Nb2O5 1-3wt%; Intermediate layer: Mn3O4 35-45wt%, Co3O4 25-35wt%, NiO 10-20wt%, CuO 5-10wt%, ZrO 25-10wt%; Outer layer: Mn3O4 30-40wt%, Co3O4 25-35wt%, NiO 5-15wt%, Al2O3 3-7wt%, SiO2 15-25wt%; The preparation method of the core (1) includes the following steps: S1. The raw materials of the core layer, intermediate layer and outer layer are prepared into sols by sol-gel method at 60-80℃ and pH 6-7, and then dried at 80-100℃ and calcined at 400-500℃ to obtain core layer, intermediate layer and outer layer nano precursors with a particle size of 20-50nm. S2. The core layer, intermediate layer and outer layer of nano-precursor are stacked in sequence and pressed to form a gradient structure preform. S3. The pulse electric field assisted sintering process is adopted, and the sintering is carried out in air atmosphere at a temperature of 1000-1100℃ for 8-12 minutes.

2. The power-type negative temperature coefficient thermistor for suppressing surge current according to claim 1, characterized in that, The core layer components are as follows by weight percentage: Mn3O4 45wt%, Co3O4 25wt%, NiO 20wt%, La2O 35wt%, ZnO 3wt%, Nb2O 52wt%; The intermediate layer components are as follows by weight percentage: Mn3O4 40wt%, Co3O4 30wt%, NiO 15wt%, CuO 8wt%, ZrO 27wt%; The outer layer components are as follows by weight percentage: Mn3O4 35wt%, Co3O4 30wt%, NiO 10wt%, Al2O3 5wt%, SiO2 20wt%.

3. A power-type negative temperature coefficient thermistor for suppressing surge current according to claim 1, characterized in that, The core layer components are as follows by weight percentage: Mn3O4 42wt%, Co3O4 28wt%, NiO 22wt%, La2O3 6wt%, ZnO 2wt%, Nb2O5 2wt%; The intermediate layer components are as follows by weight percentage: Mn3O4 38wt%, Co3O4 32wt%, NiO 17wt%, CuO 7wt%, ZrO 28wt%; The outer layer components are as follows by weight percentage: Mn3O4 33wt%, Co3O4 32wt%, NiO 12wt%, Al2O3 6wt%, SiO2 18wt%.

4. A power-type negative temperature coefficient thermistor for suppressing surge current according to claim 1, characterized in that, The core layer components are as follows by weight percentage: Mn3O4 48wt%, Co3O4 22wt%, NiO 18wt%, La2O3 4wt%, ZnO 4wt%, Nb2O5 2wt%; The intermediate layer components are as follows by weight percentage: Mn3O4 43wt%, Co3O4 27wt%, NiO 13wt%, CuO 9wt%, ZrO 28wt%; The outer layer components are as follows by weight percentage: Mn3O4 38wt%, Co3O4 26wt%, NiO 8wt%, Al2O3 4wt%, SiO2 24wt%.

5. A power-type negative temperature coefficient thermistor for suppressing surge current according to claim 2, 3, or 4, characterized in that, The multi-contact surface structure includes a continuous zigzag contact portion (112) provided on the contact section between the pin (11) and the core (1) electrode. The zigzag contact portion (112) has a triangular region (1121) formed on both sides of the core (1) electrode.

6. A power-type negative temperature coefficient thermistor for suppressing surge current according to claim 2, 3, or 4, characterized in that, The multi-contact surface structure includes a semi-circular contact portion (113) provided on the contact section between the pin (11) and the electrode of the core (1), and the semi-circular area (1131) of the semi-circular contact portion (113) faces the axis of the core (1).

7. A power-type negative temperature coefficient thermistor for suppressing surge current according to claim 6, characterized in that, The semicircular area (1131) of the semicircular contact portion (113) faces outward.

8. A power-type negative temperature coefficient thermistor for suppressing surge current according to claim 1, characterized in that, It also includes a bracket (2) set on the core (1), the bracket (2) includes two symmetrical legs (21), the core (1) is located between the two legs (21), the bracket (2) has arms (22) on both sides, the arms (22) have slots (23) on them, the pin (11) is located in the slots (23), and the two arms (22) and the two legs (21) form a wrap around the core (1).

9. A power-type negative temperature coefficient thermistor for suppressing surge current according to claim 8, characterized in that, The support leg (21) has a heat dissipation channel (27) which is connected to the opening section (28) on the bracket (2).

10. A power-type negative temperature coefficient thermistor for suppressing surge current according to claim 9, characterized in that, Both of the legs (21) are provided with heat-conducting bumps (25) on their opposite surfaces, and the heat-conducting bumps (25) form an arch-shaped area (26) on the legs (21).

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