A method for manufacturing a thermistor of a base metal electrode and a thermistor

Abstract

This invention discloses a method for fabricating a base metallized electrode thermistor and the thermistor itself, relating to the field of thermistor technology. The thermistor comprises, from the inside out, a thermistor core, a copper-based composite electrode layer, leads, a cover, and an outer encapsulating resin. The invention utilizes a copper-based composite electrode layer with a high proportion of copper, supplemented with silver and nickel. Silver significantly improves conductivity and solderability, while nickel enhances oxidation resistance through solid solution strengthening, making it more similar to the ceramic material of the thermistor core. This alleviates stress accumulation during temperature cycling. Combined with the triple conductive path of leads, cover, and electrode layer, this not only increases the solder contact area and improves soldering reliability but also ensures a stable electrical connection. Through this synergistic effect, the solution significantly improves the long-term reliability of the thermistor under repeated thermal cycling while maintaining its performance, and successfully replaces the silver electrode with a copper electrode.

Description

Technical Field

[0001] This invention belongs to the field of thermistor technology, specifically, it relates to a method for manufacturing a thermistor with a base metal electrode and the thermistor itself. Background Technology

[0002] In existing technologies, the electrodes of thermistors are generally made of silver or silver-containing paste. Silver has excellent conductivity and solderability, meeting the basic electrical performance requirements of devices. However, as a precious metal, silver is expensive and its price fluctuates wildly, directly leading to high production costs for thermistors. With increasingly fierce competition in the electronics market and the large-scale application of thermistors in cost-sensitive fields such as the Internet of Things and smart homes, there is a growing demand for an electrode material with comparable performance and lower cost to replace silver. Copper, as a base metal, has a conductivity similar to silver, but its cost is only one-tenth that of silver, making it an ideal candidate material to replace silver electrodes.

[0003] While replacing silver with copper offers significant cost advantages, its implementation faces substantial technical obstacles. The interfacial bonding strength between copper and the thermistor ceramic substrate is insufficient, making it prone to delamination due to accumulated interfacial stress under temperature cycling conditions. Furthermore, copper is highly susceptible to oxidation during high-temperature sintering and subsequent processing, forming a non-conductive oxide layer that severely compromises the electrode's conductivity and soldering quality. Secondly, the mismatch in coefficients of thermal expansion is particularly pronounced: the thermistor ceramic material has a coefficient of thermal expansion of approximately 10 ppm / ℃, while copper boasts a coefficient as high as 17 ppm / ℃. When the device undergoes repeated thermal cycling, this difference induces significant thermal stress at the interface, leading to microcrack propagation and even electrode detachment over time, ultimately causing device failure. Moreover, traditional structures employ silver electrodes with linear pin designs, achieving electrical connections through soldering. However, the introduction of copper electrodes further exacerbates the reliability risks due to the difference in thermal expansion coefficients between copper and the epoxy resin encapsulation material. Epoxy resins have a wide range of coefficients of thermal expansion (14-70 ppm / ℃), with the specific value depending on the material type. For example, the coefficient of thermal expansion for FR-4 substrates is 14-17 ppm / ℃ below Tg, while it can reach 50-70 ppm / ℃ in the Z-axis direction. Within the typical operating temperature range of thermistors (room temperature to 80-125℃), the difference in coefficients of thermal expansion between different materials causes the solder joint area to be continuously subjected to mechanical stress, leading to fatigue damage, crack initiation, and pin connection failure, which has become a key obstacle restricting the practical application of base metal electrodes. Summary of the Invention

[0004] The purpose of this invention is to provide a method for manufacturing a thermistor with a base metal electrode and a thermistor in order to solve the problems mentioned in the background art.

[0005] To solve the above-mentioned technical problems, the basic concept of the technical solution adopted by the present invention is: a method for manufacturing a base metallized electrode thermistor and the thermistor, comprising: a thermistor core, a copper-based composite electrode layer, leads, a cover, and an outer encapsulating resin arranged sequentially from the inside to the outside; the thermistor core is composed of the following components in the following mass percentages: MnO2 (45%-48%), NiO (25%-28%), Co2O3 (15%-17%), CuO (5%-7%), Cr (4%-6%), Ag (0.1%-0.3%), and C (0.05%-0.1%); the copper-based composite electrode layer is composed of the following components in the following mass percentages: Cu ≥ 95wt%, Ag 2–3wt%, Ni 1–2wt%;

[0006] Method for preparing copper-based composite electrode layers:

[0007] S1. Perform plasma cleaning on the thermistor core;

[0008] S2. Use Ti or Cr to sputter a 50-100nm transition layer on both sides of the thermistor core.

[0009] S3. Sputter the copper-based composite electrode layer onto the transition layer to a depth of 3-5 µm;

[0010] The cover and the pins are mechanically engaged on the thermistor core. The cover has a hollowed-out mesh structure. Solder penetrates the cover to form a plurality of columnar three-dimensional connecting meshes that connect with the thermistor core, the pins, and the cover.

[0011] A base metallized electrode thermistor, wherein the lead includes a lead pin that contacts a copper-based composite electrode layer on the thermistor core, the lead pin being straight; the cover has a perforated mesh structure consisting of a plurality of openings formed by a plurality of horizontal and vertical lines, the cover being placed on the lead pin and in contact with the copper-based composite electrode layer.

[0012] Preferably, the lead component includes a lead pin that contacts the copper-based composite electrode layer on the thermistor core, and the lead pin is straight; the perforated mesh structure of the cover is composed of several openings formed by several horizontal and vertical lines, and a straight slot is provided on the cover, with one end of the straight slot penetrating the outer periphery of the cover, and the lead pin is located in the straight slot.

[0013] Preferably, the lead component includes a lead pin that contacts the copper-based composite electrode layer on the thermistor core. The lead pin has an extension section at its front end, and the angle between the extension section and the lead pin is 45°-135°. The perforated mesh structure of the cover is composed of several openings formed by several horizontal and vertical lines. The cover has a straight slot, one end of which penetrates the outer periphery of the cover. The other end of the straight slot has a short slot. The angle between the short slot and the straight slot is the same as the angle between the extension section and the lead pin. The lead pin and the extension section are located in the straight slot and the short slot.

[0014] Preferably, the lead component includes a lead pin that contacts the copper-based composite electrode layer on the thermistor core. The lead pin has an extension section 1 at its front end, with an angle of 90° between the extension section 1 and the lead pin. An extension section 2 is provided on the extension section 1, with an angle of 90° between the extension section 2 and the extension section 1, forming a U-shaped hook area between the lead pin, extension section 1, and extension section 2. The opening of the U-shaped hook area faces the lead component. The perforated mesh structure of the cover is composed of several openings 1 formed by several horizontal and vertical lines. A straight slot is provided on the cover, with one end of the straight slot penetrating the outer periphery of the cover. A short slot 1 is provided at the other end of the straight slot. A short slot 2 is provided on the short slot 1. The lead pin, extension section 1, and extension section 2 are located in the straight slot, short slot 1, and short slot 2.

[0015] Preferably, the lead component includes a lead pin that contacts the copper-based composite electrode layer on the thermistor core. A ring is provided at the front end of the lead pin, and a hollow area is formed in the middle of the ring. The ring is located on one side of the lead pin. The perforated mesh structure of the cover is composed of a number of openings formed by a number of horizontal and vertical lines. A straight slot is provided on the cover, and one end of the straight slot penetrates the outer periphery of the cover. A circular slot is provided at the other end of the straight slot. The lead pin and the ring are located in the straight slot and the circular slot.

[0016] Preferably, the outer periphery of the cover has a flanged bend, the flanged bend and the outer periphery of the surface layer of the cover form a stacked layer, a sinking area is formed in the middle of the surface layer, and a descent zone is formed between the sinking area and the stacked layer.

[0017] Preferably, the transition between the surface layer and the flanged bend is provided with a flat edge area.

[0018] Preferably, the flanged bending portion has a second opening.

[0019] By adopting the above technical solution, the present invention has the following beneficial effects compared with the prior art:

[0020] 1. The base metallized electrode thermistor has a copper-based composite electrode layer with a high proportion of copper as the base and the addition of silver and nickel components. Silver significantly improves conductivity and solderability, while nickel improves oxidation resistance through solid solution strengthening, making it closer to the ceramic material of the thermistor core and alleviating stress accumulation during temperature cycling.

[0021] 2. In this base metallized electrode thermistor, the cover and the lead form a mechanical interlocking structure on the thermistor core. The hollow mesh structure of the cover is formed by horizontal and vertical lines to form an opening. When the solder penetrates through the mesh structure, it forms a columnar three-dimensional connecting network that connects with the thermistor core, the lead and the cover. This three-dimensional network disperses thermal stress to multiple anchor points, avoiding stress concentration at a single interface, thereby preventing the lead from loosening or failing during temperature cycling.

[0022] 3. The base metallized electrode thermistor features a perforated mesh structure in its cover, allowing solder to penetrate and firmly connect the leads, cover, and copper-based composite electrode layer. This forms a triple conductive path, increasing the solder contact area and improving soldering reliability while ensuring a stable electrical connection. Through this synergistic effect, the solution significantly improves the long-term reliability of the thermistor under repeated thermal cycling while maintaining its performance, and successfully replaces the silver electrode with a copper electrode.

[0023] 4. The thermistor with base metallized electrodes features a cover design that optimizes current distribution. When the thermistor experiences a surge and a large instantaneous current, the current first flows from the geometrically shaped leads through solder into the cover. Subsequently, the current penetrates the solder through the perforated mesh of the cover and the solid portion of the cover, entering the newly introduced microstructure current homogenization layer. This microstructure current homogenization layer, with its fine mesh or lattice structure and the excellent conductivity of high-purity copper, efficiently disperses and redistributes the locally concentrated current from the cover before it enters the optimized copper-based composite electrode layer below. This structural design results in a more uniform current distribution at the electrode layer-ceramic interface, effectively avoiding localized current congestion. By homogenizing the current distribution, Joule heating at the electrode layer-ceramic interface also becomes more uniform, significantly suppressing the formation of localized hot spots. This prevents the thermistor or electrode interface from aging rapidly due to overheating in localized areas, reducing the risk of resistance drift and performance degradation. The microstructure current homogenization layer and the copper-based composite electrode layer have the same coefficient of thermal expansion, avoiding new CTE mismatch issues. Its thin-layer microstructure design does not affect the solder penetration and mechanical engagement of the cover and lead, ensuring that the advantages of the original solution in terms of mechanical fixation and three-dimensional conductive path are retained.

[0024] 5. The base metallized electrode thermistor, through the design of extension section one, extension section two, U-shaped hook area, ring body, and void area, effectively limits the lateral displacement and loosening risk of the pin under thermal stress, and strengthens the mechanical engagement stability between the cover and the pin, thereby ensuring the structural integrity and electrical connection reliability of the thermistor during repeated temperature cycles.

[0025] 6. The thermistor of the base metallized electrode enhances the mechanical strength of the outer periphery of the cover through the flanged and bent portion, enabling the edge area to maintain deformation stability under thermal stress; the stacked layer, as a stress dispersion structure, uniformly transfers the interfacial stress caused by the difference in thermal expansion coefficients to the entire cover; the recessed area provides sufficient space for solder penetration, ensuring that the solder forms a continuous three-dimensional connection network in the hollow mesh structure; the descent area, through its smooth transition geometry, allows the stress to gradually decrease during the transmission from the recessed area to the stacked layer, avoiding the generation of stress concentration points; the above structures work together to maintain the tight adhesion between the cover, the pins, and the outer encapsulation resin during thermal cycling.

[0026] The specific embodiments of the present invention will now be described in further detail with reference to the accompanying drawings. Attached Figure Description

[0027] In the attached diagram:

[0028] Figure 1 This is a front view of a thermistor with a base metallized electrode proposed in this invention.

[0029] Figure 2 This is a schematic diagram of the three-dimensional structure of a thermistor with a base metal electrode proposed in this invention. Figure 1 ;

[0030] Figure 3 This is a schematic diagram of the pin structure of a thermistor with a base metallized electrode proposed in this invention.

[0031] Figure 4 This is a schematic diagram showing the cover of a base metallized electrode thermistor located on the lead element, as proposed in this invention.

[0032] Figure 5 This is a schematic diagram of the straight slot structure of a thermistor with a base metal electrode proposed in this invention.

[0033] Figure 6 This is a three-dimensional structural diagram of a thermistor with a base metal electrode proposed in this invention, showing a straight slot.

[0034] Figure 7 This is a schematic diagram of the extension section 1 and short slot 1 of a thermistor with a base metallized electrode proposed in this invention.

[0035] Figure 8 This is a three-dimensional structural diagram of the extension section 1 and short slot 1 of the thermistor with a base metallized electrode proposed in this invention.

[0036] Figure 9 This is a schematic diagram of the extension section two and short slot two of the thermistor of the base metallized electrode proposed in this invention.

[0037] Figure 10 This is a three-dimensional structural diagram of the extension section two and the short slot two of the thermistor with a base metallized electrode proposed in this invention.

[0038] Figure 11 This is a schematic diagram of the coil and void region of a thermistor with a base metallized electrode proposed in this invention.

[0039] Figure 12 This is a three-dimensional structural diagram of the coil and void region of a thermistor with a base metallized electrode proposed in this invention.

[0040] Figure 13 This is a schematic diagram of the cover, horizontal lines, vertical lines, and opening of a thermistor with a base metal electrode proposed in this invention.

[0041] Figure 14 This is a schematic diagram of the structure of the flanged and bent portion of a thermistor with a base metallized electrode proposed in this invention. Figure 1 ;

[0042] Figure 15 This is a schematic diagram of the structure of the flanged and bent portion of a thermistor with a base metallized electrode proposed in this invention. Figure 2 ;

[0043] Figure 16 This is a schematic diagram of the surface layer, stacked layer, subsidence region, and sag region of a base metallized electrode thermistor proposed in this invention.

[0044] Figure 17 This is a schematic diagram of the second opening of a thermistor with a base metal electrode proposed in this invention.

[0045] Figure 18 It is a columnar three-dimensional connecting network.

[0046] In the diagram: 1. Thermistor core;

[0047] 2. Lead component; 21. Lead pin; 22. Extension section one; 23. Extension section two; 231. U-shaped hook area; 24. Ring body; 241. Hollow area;

[0048] 3. Copper-based composite electrode layer;

[0049] 4. Cover part; 41. Horizontal line; 42. Vertical line; 43. Opening one; 44. Flat edge area; 45. Flanged bend; 46. Opening two;

[0050] 401. Straight slot; 402. Short slot one; 403. Short slot two; 404. Circular slot;

[0051] 410, Surface layer; 4101, Stacked layer; 4102, Sinking zone; 4103, Descent zone. Detailed Implementation

[0052] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments will be clearly and completely described below with reference to the accompanying drawings. The following embodiments are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0053] The following is in conjunction with the appendix Figure 1 -Appendix Figure 18 The technical solutions provided in the various embodiments of the present invention will be described in detail.

[0054] Example: Refer to Figure 3 , Figure 4 A method for fabricating a base metallized electrode thermistor includes: a thermistor core 1, a copper-based composite electrode layer 3, leads 2, a cover 4, and an outer encapsulating resin arranged sequentially from the inside out; the thermistor core 1 is composed of the following components in the following mass percentages: MnO2 (45%-48%), NiO (25%-28%), Co2O3 (15%-17%), CuO (5%-7%), Cr (4%-6%), Ag (0.1%-0.3%), and C (0.05%-0.1%); the copper-based composite electrode layer 3 is composed of the following components in the following mass percentages: Cu ≥ 95wt%, Ag 2–3wt%, Ni 1–2wt%;

[0055] Method for preparing copper-based composite electrode layer 3:

[0056] S1. Perform plasma cleaning on the thermistor core 1;

[0057] S2. Use Ti or Cr to sputter a 50-100nm transition layer on both sides of the thermistor core 1.

[0058] S3. Sputter the copper-based composite electrode layer 3 onto the transition layer to a depth of 3-5µm;

[0059] Cover 4 and pin 2 are mechanically engaged on the thermistor core 1. Cover 4 has a perforated mesh structure. Solder penetrates cover 4 to form several columnar three-dimensional connecting meshes that connect to the thermistor core 1, pin 2, and cover 4 (see reference). Figure 18This formula, optimized for surge suppression applications, has a room temperature resistance R25 of 5-50Ω, a resistance temperature coefficient B25 / 50 of 2550-2750K, and a rated power ≥2W. All parameters remain unchanged compared to existing thermistors, and the operating temperature can be reduced by about 5 degrees.

[0060] The thermistor core 1 is composed of a copper-based composite electrode layer 3, leads 2, a cover 4, and an outer encapsulating resin, arranged sequentially from the inside out. Specifically, the thermistor core 1 is composed of components in specific mass percentages, including MnO2 (45%-48%), NiO (25%-28%), Co2O3 (15%-17%), CuO (5%-7%), Cr (4%-6%), Ag (0.1%-0.3%), and C (0.05%-0.1%). This composition is designed to optimize the sintering characteristics and interface stability of the ceramic matrix. In practical applications, the amount of Ag added can be selected from 0.1% to 0.3%, specifically 0.15% or 0.25%, and the C content can be an intermediate value of 0.06% or 0.08% to maintain a reducing atmosphere and inhibit oxidation.

[0061] Furthermore, the copper-based composite electrode layer 3 is composed of Cu≥95wt% (main conductive phase), Ag2–3wt% (to improve conductivity and oxidation resistance) and Ni1–2wt% (to enhance bonding strength and solderability) by mass percentage. The ratio of Ag to Ni can be adjusted to a combination of Ag2.5wt% and Ni1.5wt%, or a combination of Ag2.2wt% and Ni1.8wt%, to balance conductivity and thermal expansion coefficient matching.

[0062] The fabrication method of this copper-based composite electrode layer 3 includes three key steps:

[0063] In stage S1, plasma cleaning is performed on the thermistor core 1 to remove impurities from the ceramic surface and activate it, providing a cleaner and more active bonding interface for the subsequent sputtering of the Ti or Cr transition layer. This further enhances the adhesion between the transition layer and the ceramic substrate thermistor core 1, thereby indirectly improving the overall bonding strength and reliability between the copper-based composite electrode layer 3 and the ceramic substrate thermistor core 1, effectively preventing electrode peeling. Specifically, before magnetron sputtering to prepare the copper-based composite electrode layer 3, the ceramic substrate thermistor core 1 is placed in a plasma cleaning device, where argon plasma bombards the ceramic surface to remove adsorbed organic matter, oxides, and other impurities, and generates dangling bonds, increasing the surface energy and providing an ideal, highly active bonding interface for the subsequent deposition of the Ti or Cr transition layer.

[0064] In the S2 stage, Ti or Cr is used to sputter a transition layer of 50-100 nm thickness on both sides of the thermistor core 1. The thickness of the transition layer can be set to a specific value of 60 nm or 85 nm to ensure the interfacial chemical bonding strength and enhance the adhesion to the ceramic matrix.

[0065] In the S3 stage, the copper-based composite electrode layer 3 is sputtered onto the transition layer to form a thickness of 3-5 μm. The sputtering process can be completed in two steps: the first sputtering is 2 μm thick, followed by annealing, and then the remaining thickness is sputtered to control internal stress.

[0066] Furthermore, the cover 4 and the pin 2 form a mechanical interlocking structure on the thermistor core 1. The perforated mesh structure on the cover 4 can form a columnar three-dimensional connection network through solder penetration. In practical applications, this perforated mesh structure can be implemented using geometric shapes such as triangular array holes, rhomboid mesh, and rectangular mesh to ensure sufficient solder penetration and dispersion of thermal stress. Thus, this application effectively solves the problems of insufficient adhesion between copper electrodes and ceramic substrates, high-temperature oxidation, and thermal expansion coefficient mismatch through the synergistic effect of the composition optimization of the thermistor core 1, the composite material design of the copper-based composite electrode layer 3, and the transition layer process. Among them, the introduction of the transition layer bridges the interface between ceramic and copper electrodes, while the perforated mesh structure of the cover 4, combined with the three-dimensional connection network formed by solder penetration, evenly distributes the stress during thermal cycling to multiple anchor points, avoiding connection failure caused by stress concentration, thereby realizing the reliable application of base metal electrodes in thermistors.

[0067] This fabrication method utilizes a layered structure design consisting of a thermistor core 1, a copper-based composite electrode layer 3, leads 2, a cover 4, and an outer encapsulating resin. Combined with optimized material composition and specific process steps, it collaboratively addresses the issues of insufficient adhesion, oxidation risk, and thermal expansion coefficient mismatch associated with copper electrodes in thermistor applications. Specifically, the thermistor core 1 employs a specific ratio of oxide components with trace amounts of silver and carbon. Silver promotes grain boundary formation and inhibits copper electrode oxidation during sintering, while carbon acts as a reducing agent to maintain a reducing atmosphere during sintering, thereby stabilizing the ceramic structure and reducing the risk of interface oxidation. The copper-based composite electrode layer 3 is designed with a high proportion of copper as a base, incorporating silver and nickel. Silver significantly improves conductivity and solderability, while nickel enhances oxidation resistance through solid solution strengthening, making it more similar to the ceramic material of the thermistor core 1 and mitigating stress accumulation during temperature cycling. Furthermore, in the fabrication process, the thermistor core 1 is subjected to plasma cleaning to remove surface organic contaminants and weak bonding layers, providing a highly active and clean surface for subsequent interfaces. Subsequently, a transition layer of 50-100 nanometers is sputtered on both sides of the thermistor core 1 using titanium or chromium. This transition layer forms a strong chemical bond with the ceramic oxide, effectively bridging the ceramic substrate thermistor core 1 and the copper-based composite electrode layer 3, avoiding insufficient adhesion caused by direct contact, and acting as a barrier layer to inhibit the oxidation and diffusion of copper at high temperatures. On this basis, a copper-based composite electrode layer 3 with a thickness of 3-5 micrometers is sputtered. The uniformity and chemical compatibility of the transition layer ensure stable adhesion of the copper substrate, providing sufficient conductive cross-section while avoiding internal stress concentration caused by excessive thickness.

[0068] The cover 4 and the pin 2 form a mechanical interlocking structure on the thermistor core 1. The hollow mesh structure of the cover 4 is formed by horizontal lines 41 and vertical lines 42 to form an opening 43. When the solder penetrates through the mesh structure, it forms a columnar three-dimensional connection network that connects with the thermistor core 1, the pin 2 and the cover 4. This three-dimensional network disperses thermal stress to multiple anchor points, avoiding stress concentration on a single interface, thereby preventing the pin 2 from loosening or failing during temperature cycling.

[0069] Furthermore, the design of the cover 4 optimizes current distribution. When the thermistor experiences a surge of large instantaneous current, the current first flows into the cover 4 through the solder from the geometrically shaped pins. Subsequently, the current penetrates the solder through the perforated mesh of the cover 4 and the solid portion of the cover 4, entering the newly introduced microstructure current homogenization layer. This microstructure current homogenization layer, with its fine mesh or lattice structure and the excellent conductivity of high-purity copper, efficiently disperses and redistributes the locally concentrated current from the cover 4 before it enters the optimized copper-based composite electrode layer 3 below. This structural design makes the current distribution at the electrode layer-ceramic interface more uniform, effectively avoiding localized current congestion. By homogenizing the current distribution, the Joule heating at the electrode layer-ceramic interface also becomes more uniform, significantly suppressing the formation of localized hot spots. This prevents the thermistor or electrode interface from aging rapidly due to overheating in localized areas, reducing the risk of resistance drift and performance degradation. The microstructure current homogenization layer and the copper-based composite electrode layer 3 have the same coefficient of thermal expansion, avoiding new CTE mismatch issues. Its thin-layer microstructure design does not affect the penetration and mechanical engagement of solder on the cover 4 and the lead 2, ensuring that the advantages of the original solution in terms of mechanical fixation and three-dimensional conductive path are retained.

[0070] As a specific embodiment, the thermistor core 1 can be specifically composed of the following mass percentage components: MnO2 46%, NiO 26%, Co2O3 16%, CuO 6%, Cr 5%, Ag 0.2%, and C 0.08%; the copper-based composite electrode layer 3 can specifically be composed of Cu 96wt%, Ag 2.5wt%, and Ni The composition ratio is 1.5wt%. During the preparation process, argon is used as the working gas for plasma cleaning. Titanium material is selected and the thickness is controlled to be 80 nanometers when sputtering the transition layer. The sputtering thickness of the copper-based composite electrode layer 3 is set to 4 micrometers. In the hollow mesh structure of the cover 4, the cover 4 is 1.5 mm thick, the line width of the horizontal line 41 and the vertical line 42 is 1.2 mm, and the opening 43 is square with a length and width of 3 mm. After the solder penetrates, a columnar three-dimensional connecting mesh is formed (when the cover 4 is placed on the pin 21 of the lead 2, a gap will be formed between the cover 4 and the surface of the thermistor core 1. When the solder penetrates from the cover 4 to the thermistor core 1, it will form columnar solder when passing through the opening 43. And due to the existence of the gap, a columnar three-dimensional connecting mesh is formed).

[0071] Therefore, this solution significantly improves the interfacial bonding strength between the copper-based composite electrode layer 3 and the ceramic thermistor core 1 through the synergistic effect of material composition control and process steps. It effectively suppresses the oxidation tendency of copper under high-temperature conditions and alleviates mechanical stress during thermal cycling through matching thermal expansion coefficients and stress dispersion mechanisms. Ultimately, this achieves structural stability and electrical reliability of the thermistor device under long-term temperature variations. Specifically, the composition design of the thermistor core 1 and the addition of nickel to the copper-based composite electrode layer 3 jointly optimize the interfacial thermal expansion characteristics. The application of the transition layer ensures the adhesion quality of the electrode layer, and the three-dimensional interconnection network of the cover 4 evenly distributes external thermal stress, thereby avoiding microcrack formation and electrode detachment, and ensuring the durability of the device in application scenarios.

[0072] In some of the above embodiments, a mechanical interlocking structure between the pin 2 and the cover 4 is proposed to achieve electrical connection and stress dispersion. However, the specific shape of the pin 2 and the hollow mesh structure of the cover 4 lack effective design, resulting in local stress concentration due to the difference in thermal expansion coefficients between the copper-based composite electrode layer 3 and the pin material during temperature cycling. This makes the pins prone to displacement or loosening, leading to solder joint fatigue and device failure. To address this, refer to... Figure 3 , Figure 4 Furthermore, a base metal electrode thermistor is proposed. The lead component 2 includes lead pins 21 that contact the copper-based composite electrode layer 3 on the thermistor core 1. The lead pins 21 are straight. The perforated mesh structure of the cover component 4 consists of several openings 43 formed by several horizontal lines 41 and vertical lines 42. The cover component 4 is placed on the lead pins 21 and contacts the copper-based composite electrode layer 3. The cover component 4 can be manufactured by stamping, chemical etching or laser cutting. All three processes are mature and the cost of manufacturing the cover component 4 is low.

[0073] Specifically, pin 21 refers to the conductive component that contacts the copper-based composite electrode layer 3 on the thermistor core 1. It can be implemented using a regular geometric shape such as a straight line, with the aim of providing a stable assembly positioning reference and ensuring uniform force on the contact interface. The hollow mesh structure of the cover 4 is formed by horizontal lines 41 and vertical lines 42 surrounding an opening 43. It can be implemented using a regular structure of orthogonal grid or parallel arrangement. Its purpose is to form a continuous three-dimensional connection path with pin 21 and copper-based composite electrode layer 3 through solder penetration to disperse thermal stress and increase the bonding between pin 2 and copper-based composite electrode layer 3. Therefore, the cover 4 is placed directly on pin 21 and contacts copper-based composite electrode layer 3. The mechanical interlocking strength is strengthened through physical pressing and solder penetration, so that pin 21 is firmly constrained between the thermistor core 1 and cover 4, which significantly improves the fatigue resistance and loosening resistance of the overall structure under thermal expansion coefficient mismatch environment.

[0074] The above solution effectively avoids local stress concentration caused by differences in thermal expansion coefficients, prevents pin 2 from shifting or loosening during repeated thermal cycles, and thus significantly improves the structural stability and electrical connection reliability of the thermistor under temperature cycling conditions.

[0075] In one embodiment, refer to Figure 5 , Figure 6 The lead component 2 includes a lead pin 21 that contacts the copper-based composite electrode layer 3 on the thermistor core 1. The lead pin 21 is straight. The hollow mesh structure of the cover component 4 is composed of several openings 43 formed by several horizontal lines 41 and vertical lines 42. A straight slot 401 is provided on the cover component 4, and one end of the straight slot 401 penetrates through the outer periphery of the cover component 4. The lead pin 21 is located in the straight slot 401.

[0076] Among them, pin 21 refers to the conductive component that realizes the electrical connection. It can be implemented by a straight metal conductor. The purpose is to simplify the structure and ensure basic contact with the copper-based composite electrode layer 3. The opening 43 is intended to support solder penetration to build a basic mechanical connection. The straight slot 401 refers to the straight guide channel opened on the cover 4. It can be designed as a through slot with a width slightly larger than the diameter of pin 21, with one end extending to the outer peripheral edge of the cover 4. The purpose is to provide a directional constraint channel to limit the lateral movement freedom of pin 21.

[0077] Specifically, this solution precisely embeds the pin 21 into the straight slot 401 of the cover 4, thereby applying a lateral constraint force to the pin 21 through the slot wall of the cover 4. During temperature cycling, when thermal stress is caused by differences in thermal expansion coefficients, the directional structure of the straight slot 401 effectively suppresses the lateral displacement tendency of the pin 21 in the plane, constraining its degree of freedom of movement within a one-dimensional range along the slot direction. Simultaneously, the perforated mesh structure of the cover 4 maintains solder penetration capability, forming a columnar three-dimensional connecting mesh to provide basic mechanical connections. This design significantly improves the stability of mechanical engagement under thermal stress environments through a physical constraint mechanism without compromising the penetration performance of the perforated mesh structure.

[0078] Therefore, this solution effectively limits the lateral displacement and loosening risk of the pin 21 under thermal stress, strengthens the mechanical engagement stability between the cover 4 and the pin 2, thereby ensuring the structural integrity and electrical connection reliability of the thermistor during repeated temperature cycles.

[0079] In some implementations, refer to Figure 7 , Figure 8The lead component 2 includes a lead pin 21 that contacts the copper-based composite electrode layer 3 on the thermistor core 1. The lead pin 21 has an extension section 22 at its front end. The angle between the extension section 22 and the lead pin 21 is 45°-135°. The perforated mesh structure of the cover component 4 is composed of several openings 43 formed by several horizontal lines 41 and vertical lines 42. The cover component 4 has a straight slot 401, one end of which penetrates the outer periphery of the cover component 4. The other end of the straight slot 401 has a short slot 402. The angle between the short slot 402 and the straight slot 401 is the same as the angle between the extension section 22 and the lead pin 21. The lead pin 21 and the extension section 22 are located in the straight slot 401 and the short slot 402.

[0080] Specifically, the angle between the extension section 22 and the pin 21 is preferably 90°. The extension section 22 refers to the curved extension structure provided at the front end of the pin 21. It can be implemented by arc bending, stepped bending or straight structure with different radii of curvature. Its purpose is to provide elastic deformation space to absorb the stress caused by the mismatch of thermal expansion coefficients, avoid stress concentration in the solder joint area, and further improve the interlocking strength between the pin 2 and the cover 4 through bending. The straight slot 401 refers to the through channel opened in the straight direction on the cover 4. It can be designed as a trapezoidal or rectangular cross-section slot structure. Its purpose is to provide a precise positioning channel for the pin 21 and accommodate the initial thermal expansion displacement. The short slot 402 refers to the directional constraint slot connected to the end of the straight slot 401. Its purpose is to match the bending direction of the extension section 22, guide the pin to bend controllably along the preset path, and strengthen the interlocking of the cover 4 when the pin 2 is pulled by external force.

[0081] Specifically, this solution achieves a dynamic thermal stress buffering mechanism through the structural cooperation between the pin 2 and the cover 4. The bending structure of the extension segment 22 undergoes elastic deformation during temperature cycling, effectively absorbing the displacement caused by the difference in thermal expansion coefficients between the thermistor ceramic material, the copper-based composite electrode layer 3, and the epoxy resin encapsulation material. One end of the straight slot 401 penetrates the outer periphery of the cover 4, ensuring precise insertion of the pin 21 and providing an initial displacement channel. The other end is connected to a short slot 402 that matches the bending angle of the extension segment 22, allowing the extension segment 22 to bend controllably along a preset path under thermal stress, avoiding damage caused by forced deformation. The perforated mesh structure of the cover 4 allows solder to fully penetrate and form a columnar three-dimensional connecting mesh (see reference). Figure 18 This connection network constrains the displacement amplitude through mechanical interlocking while maintaining the stability of the electrical connection, thereby achieving the dual functions of stress dispersion and dynamic buffering under thermal stress.

[0082] In some embodiments, refer to Figure 9 , Figure 10The lead component 2 includes a lead pin 21 that contacts the copper-based composite electrode layer 3 on the thermistor core 1. The lead pin 21 has a first extension section 22 at its front end, with an angle of 90° between the first extension section 22 and the lead pin 21. An second extension section 23 is provided on the first extension section 22, with an angle of 90° between the second extension section 23 and the first extension section 22, forming a U-shaped hook area 231 between the lead pin 21, the first extension section 22, and the second extension section 23. The opening of the U-shaped hook area 231 faces the lead pin. Part 2; The hollow mesh structure of the cover part 4 is composed of several openings 43 formed by several horizontal lines 41 and vertical lines 42. The cover part 4 has a straight slot 401, and one end of the straight slot 401 penetrates the outer periphery of the cover part 4. The other end of the straight slot 401 is provided with a short slot 402. The short slot 402 is provided with a short slot 403. The pin 21, the extension section 22, and the extension section 23 are located in the straight slot 401, the short slot 402, and the short slot 403.

[0083] Extension section 1 22 refers to the bent structure set at the front end of the pin 21, which can be implemented by right-angle bend or arc transition, with the purpose of changing the extension path of the pin to disperse thermal stress; among them, extension section 23 refers to the secondary bent structure set on extension section 1 22, which can be designed to form a continuous bent geometry with extension section 1 22, with the purpose of forming a mechanical locking area together with extension section 1 22; U-shaped hook area 231 refers to the hook-shaped area surrounded by pin 21, extension section 1 22 and extension section 23, which can be configured as an orientation structure with the opening facing the pin 2, with the purpose of generating an inward tightening biting force during thermal expansion and providing a stronger biting force with the cover 4; straight slot 401, short slot 1 402 and short slot 2 403 are intended to form multi-level mechanical interlocking points to disperse interface stress.

[0084] Therefore, this solution achieves mechanical interlocking between the pin 2 and the cover 4 through the coordinated design of the U-shaped hook area 231 and the matching groove structure on the cover 4. The extension section 22 at the front end of the pin 21 forms the first right-angle bend, changing the extension path of the pin and allowing the thermal stress generated during temperature cycling to be dispersed and absorbed by the bending structure, avoiding slippage caused by stress concentration. The extension section 23 on the extension section 22 forms the second right-angle bend, which together with the extension section 22 constitutes the U-shaped hook area 231. The opening of this hook area faces the pin 2, so that when the cover 4 is pressed, the U-shaped hook area 231 can be inserted into the corresponding short slots 402 and 403, forming a bidirectional mechanical lock and effectively resisting displacement caused by material expansion and contraction. The straight slot 401, short slot one 402, and short slot two 403 on the cover 4 precisely match the geometry of the U-shaped hook area 231, allowing the pin 21, extension section one 22, and extension section two 23 to be embedded in their respective slots, reducing stress concentration points at the interface. Simultaneously, the perforated mesh structure of the cover 4 allows solder to fully penetrate the slots and mesh area, forming a columnar three-dimensional interconnecting mesh (see reference). Figure 18 The thermistor core 1, pin 2 and cover 4 are firmly integrated, which improves the overall structure's resistance to thermal fatigue.

[0085] In one implementation, reference Figure 11 , Figure 12 The lead component 2 includes a lead pin 21 that contacts the copper-based composite electrode layer 3 on the thermistor core 1. A ring 24 is provided at the front end of the lead pin 21, and a hollow area 241 is formed in the middle of the ring 24. The ring 24 is located on one side of the lead pin 21. The hollow mesh structure of the cover component 4 is composed of a number of openings 43 formed by a number of horizontal lines 41 and vertical lines 42. A straight slot 401 is provided on the cover component 4, and one end of the straight slot 401 penetrates the outer periphery of the cover component 4. A circular slot 404 is provided at the other end of the straight slot 401. The lead pin 21 and the ring 24 are located in the straight slot 401 and the circular slot 404.

[0086] Among them, the ring body 24 refers to the annular curved structure formed at the front end of the pin 21, which can be realized by cold bending forming process. Its purpose is to provide elastic deformation space to absorb thermal stress. The hollow area 241 can be understood as the hollow area formed inside the ring body 24. Specifically, it can be elliptical or approximately circular. Its purpose is to accommodate solder and form a column with a larger diameter in the ring body 24 to enhance the bonding force between the cover 4 and the pin 2. The ring body 24 is located on one side of the pin 21, which means that the ring body 24 is offset relative to the axis of the pin 21. It can be realized by unilateral bending or asymmetrical layout. Its purpose is to optimize the transmission path of thermal expansion force, make the stress more evenly distributed, and enhance the interlocking force between the pin 2 and the cover 4. Together with the hollow mesh structure of the cover 4, a columnar three-dimensional connecting mesh is formed.

[0087] The above solution effectively alleviates the problem of thermal stress accumulation caused by thermal expansion coefficient mismatch, significantly improves the structural stability and connection reliability of the device under temperature cycling conditions, avoids solder joint fatigue failure and pin loosening, and extends the service life of the thermistor in application scenarios.

[0088] In one implementation, refer to Figure 15 , Figure 16 A flanged bending portion 45 is formed on the outer periphery of the cover 4, and a stacked layer 4101 is formed between the flanged bending portion 45 and the outer periphery of the surface layer 410 of the cover 4. A sunken area 4102 is formed in the middle of the surface layer 410, and a descent area 4103 is formed between the sunken area 4102 and the stacked layer 4101.

[0089] Among them, the flanged bending portion 45 refers to the edge reinforcement structure formed by bending the outer periphery of the cover 4 upward or downward, which aims to enhance the structural rigidity of the edge area and resist the deformation tendency caused by the mismatch of thermal expansion coefficients during thermal cycling; the stacked layer 4101 can be understood as a multi-layer material structure formed by the overlap of the flanged bending portion 45 and the outer periphery of the surface layer 410, which aims to expand the stress transfer area and disperse the interfacial thermal stress to a larger area; the sunken area 4102 specifically refers to the downward recessed accommodating area in the middle of the surface layer 410, which aims to provide extra space for solder and allow more solder to accumulate in the middle of the cover 4; the gradual descent area 4103 can be understood as the transition area between the sunken area 4102 and the stacked layer 4101, which can be achieved through a gradual curved surface or a ramp structure, with the aim of eliminating geometric abrupt points, making the stress transfer process smooth and continuous, and allowing the solder penetrating the cover 4 to quickly diffuse to the outer periphery;

[0090] Specifically, this solution enhances the mechanical strength of the outer periphery of the cover 4 through the flanged bending portion 45, enabling the edge area to maintain deformation stability under thermal stress; the stacked layer 4101 acts as a stress dispersion structure, uniformly transferring the interfacial stress caused by the difference in thermal expansion coefficients to the entire cover 4; the recessed area 4102 provides sufficient space for solder penetration, ensuring that the solder forms a continuous three-dimensional connection network in the hollow mesh structure; the descent area 4103, through its smooth transition geometry, gradually attenuates the stress during the transfer from the recessed area 4102 to the stacked layer 4101, avoiding the generation of stress concentration points; the above structures work together to maintain the tight adhesion between the cover 4, the pins 2, and the outer encapsulation resin during thermal cycling.

[0091] When the cover 4 does not use the flanged bending part 45, downward protrusions can be stamped at the outer peripheral edge of the cover 4. The purpose is to increase the gap between the cover 4 and the thermistor core 1, increase the penetration range of the solder, and improve the bonding force between the cover 4 and the thermistor core 1.

[0092] Reference Figure 15 A smooth edge area 44 is provided at the transition between the surface layer 410 and the flanged bending part 45;

[0093] Among them, the smooth edge area 44 refers to the smooth treatment structure of the transition area between the surface layer 410 and the flanged bending part 45. It can be achieved by using rounded corner transition, bevel transition or micro-arc transition, etc. The purpose is to strengthen the strength of the flanged bending part 45, avoid uneven stress distribution caused by the breakage of the cover part 4, and eliminate sharp edges to make the stress distribution more uniform and avoid the formation of local stress peaks.

[0094] Therefore, the flat edge area 44 makes the geometric transition between the surface layer 410 and the flanged bending part 45 continuous and smooth. When the cover 4 generates stress due to the difference in the thermal expansion coefficient of the material during thermal cycling, the smooth transition area effectively disperses the stress transmission path, prevents the local accumulation of stress at the micro level, thereby suppressing the initiation and propagation of microcracks and maintaining the structural integrity of the cover 4 and the pin 2.

[0095] Reference Figure 17 The flanged bending portion 45 has a second opening 46. The second opening 46 can be understood as a through hole structure set on the flanged bending portion 45. Its purpose is to provide a solder penetration channel and enhance the bonding force between the cover 4 and the thermistor core 1.

[0096] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-described technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for fabricating a thermistor with a base metal electrode, characterized in that, include: The thermistor core (1), copper-based composite electrode layer (3), lead (2), cover (4) and outer encapsulation resin are arranged sequentially from the inside to the outside. The thermistor core (1) is composed of the following components in the indicated mass percentages: MnO2 45%-48%, NiO 25%-28%, Co2O3 15%-17%, CuO 5%-7%, Cr 4%-6%, Ag 0.1%-0.3%, C 0.05%-0.1%; The copper-based composite electrode layer (3) is composed of the following components by mass percentage: Cu ≥ 95 wt%, Ag 2–3 wt%, Ni 1–2 wt%; Preparation method of copper-based composite electrode layer (3): S1. Plasma cleaning is performed on the thermistor core (1); S2. Use Ti or Cr to sputter a 50-100nm transition layer on both sides of the thermistor core (1); S3. Sputter the copper-based composite electrode layer (3) onto the transition layer to a depth of 3-5 µm; The cover (4) and the pin (2) form a mechanical engagement on the thermistor core (1). The cover (4) has a hollow mesh structure. Solder penetrates the cover (4) to form a plurality of columnar three-dimensional connecting meshes that are connected to the thermistor core (1), the pin (2), and the cover (4). The outer periphery of the cover (4) has a flanged bending portion (45), and the flanged bending portion (45) and the outer periphery of the surface layer (410) of the cover (4) form a stacked layer (4101). A sinking area (4102) is formed in the middle of the surface layer (410), and a descent area (4103) is formed between the sinking area (4102) and the stacked layer (4101).

2. A thermistor with a base metallized electrode, comprising the method for manufacturing a thermistor with a base metallized electrode as described in claim 1, characterized in that, The lead element (2) includes a lead pin (21) that contacts the copper-based composite electrode layer (3) on the thermistor core (1), and the lead pin (21) is straight. The perforated mesh structure of the cover (4) consists of several openings (43) formed by several horizontal lines (41) and vertical lines (42). The cover (4) is placed on the pin (21) and in contact with the copper-based composite electrode layer (3).

3. A thermistor with a base metallized electrode, comprising the method for manufacturing a thermistor with a base metallized electrode as described in claim 1, characterized in that, The lead (2) includes a lead pin (21) that contacts the copper-based composite electrode layer (3) on the thermistor core (1), and the lead pin (21) is straight. The perforated mesh structure of the cover (4) consists of several openings (43) formed by several horizontal lines (41) and vertical lines (42). The cover (4) has a straight slot (401) with one end penetrating the outer periphery of the cover (4). The pin (21) is located in the straight slot (401).

4. A thermistor with a base metallized electrode, manufactured using the method for producing a thermistor with a base metallized electrode as described in claim 1, characterized in that, The pin (2) includes a pin (21) that contacts the copper-based composite electrode layer (3) on the thermistor core (1). The front end of the pin (21) is provided with an extension section (22), and the angle between the extension section (22) and the pin (21) is 45°-135°. The perforated mesh structure of the cover (4) is composed of several openings (43) formed by several horizontal lines (41) and vertical lines (42). A straight slot (401) is provided on the cover (4), and one end of the straight slot (401) penetrates the outer periphery of the cover (4). A short slot (402) is provided at the other end of the straight slot (401). The angle between the short slot (402) and the straight slot (401) is the same as the angle between the extension section (22) and the pin (21). The pin (21) and the extension section (22) are located in the straight slot (401) and the short slot (402).

5. A thermistor with a base metallized electrode, manufactured using the method for producing a thermistor with a base metallized electrode as described in claim 1, characterized in that, The lead component (2) includes a lead pin (21) that contacts the copper-based composite electrode layer (3) on the thermistor core (1). The lead pin (21) has an extension section 1 (22) at its front end. The angle between the extension section 1 (22) and the lead pin (21) is 90°. An extension section 2 (23) is provided on the extension section 1 (22). The angle between the extension section 2 (23) and the extension section 1 (22) is 90°, so that a U-shaped hook area (231) is formed between the lead pin (21), the extension section 1 (22), and the extension section 2 (23). The opening of the U-shaped hook area (231) faces the lead component (2). The perforated mesh structure of the cover (4) is composed of several openings (43) formed by several horizontal lines (41) and vertical lines (42). The cover (4) has a straight slot (401) with one end penetrating the outer periphery of the cover (4). The other end of the straight slot (401) is provided with a short slot (402). The short slot (402) is provided with a short slot (403). The pin (21), extension section one (22), and extension section two (23) are located in the straight slot (401), short slot one (402), and short slot two (403).

6. A thermistor with a base metallized electrode, manufactured using the method for producing a thermistor with a base metallized electrode as described in claim 1, characterized in that, The pin (2) includes a pin (21) that contacts the copper-based composite electrode layer (3) on the thermistor core (1). A ring (24) is provided at the front end of the pin (21). A cavity area (241) is formed in the middle of the ring (24). The ring (24) is located on one side of the pin (21). The perforated mesh structure of the cover (4) is composed of several openings (43) formed by several horizontal lines (41) and vertical lines (42). The cover (4) has a straight slot (401) with one end penetrating the outer periphery of the cover (4) and the other end of the straight slot (401) has a circular slot (404). The pin (21) and the ring (24) are located in the straight slot (401) and the circular slot (404).

7. A thermistor with a base metallized electrode according to any one of claims 2-6, characterized in that, The transition between the surface layer (410) and the flanged bend (45) is provided with a flat edge area (44).

8. A thermistor with a base metallized electrode according to any one of claims 2-6, characterized in that, The flanged bending part (45) has two openings (46).

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