A three-terminal fuse and method of manufacture

Abstract

The application belongs to the technical field of circuit protection elements, and discloses a three-terminal fuse and a preparation method. The three-terminal fuse comprises a substrate, electrodes and a heating resistor on the substrate, the electrodes are prepared from conductive paste, a fusible metal sheet is arranged on the heating resistor, and a flux layer is coated on the upper surface of the fusible metal sheet. The flux layer comprises rosin, microcrystalline paraffin powder, fusible metal powder and sodium dodecyl sulfonate; and the conductive paste comprises micron silver powder, graphite powder, polyaniline, ceramic powder, dimethyl sulfoxide and organic resin. The preparation method of the three-terminal fuse comprises the following steps: (1) preparation of the flux and the conductive paste; (2) preparation of the substrate, the heating resistor and the fusible metal sheet; and (3) synthesis of the three-terminal fuse. The three-terminal fuse prepared by the application has a short melting time, a longer service life, a low production cost and is suitable for wide use in circuits.

Description

Technical Field

[0001] This application relates to the field of circuit protection element technology, and in particular to a three-terminal fuse and its preparation method. Background Technology

[0002] Three-terminal fuses are mainly used in built-in resistor protection devices. Also called heated fuses, they are fuses with a heating end. The other two ends of the three-terminal fuse are the electrode terminals. The working principle of a three-terminal fuse is that when the charging current is too high, the fuse will directly melt. When there is an overcharge and the voltage is too high, the heating end of the fuse will heat up, causing the fuse to melt, thus achieving overcurrent and overvoltage protection. In existing technology, the melting time of a three-terminal fuse under overcurrent or overvoltage conditions is the main characteristic for evaluating its performance. This performance characteristic is directly related to the alloy composition ratio of the fusible wire in the device. Therefore, current improvements to three-terminal fuse devices mainly focus on improving the alloy composition ratio of the fusible wire to shorten its melting time. Few improvements have been made to the electrodes directly connected to the fusible wire or the flux surrounding the fusible wire to shorten its melting time. Therefore, a technical solution is needed to minimize the melting time of the fusible wire. Summary of the Invention

[0003] In order to solve at least one of the above-mentioned technical problems and to develop a three-terminal fuse with better fusing performance, this application provides a three-terminal fuse and a method for its preparation.

[0004] On one hand, this application provides a three-terminal fuse, including a substrate, on which electrodes and a heating resistor are disposed. The electrodes are made of conductive paste, and a fusible metal sheet is disposed on the heating resistor. A flux layer is disposed on the upper surface of the fusible metal sheet, in parts by weight.

[0005] The raw materials for the flux layer include 30-40 parts of rosin, 7-20 parts of microcrystalline wax powder, 20-30 parts of fusible metal powder, and 10-25 parts of sodium dodecyl sulfonate.

[0006] The conductive paste contains 30-40 parts of micron-sized silver powder, 20-30 parts of graphite powder, 5-13 parts of polyaniline, 10-15 parts of ceramic powder, 15-25 parts of dimethyl sulfoxide, and 10-15 parts of organic resin.

[0007] Optionally, by weight, the flux includes 35-40 parts rosin, 10-13 parts microcrystalline wax powder, 20-25 parts fusible metal powder, and 14-19 parts sodium dodecyl sulfonate; the conductive paste includes 30-40 parts micron-sized silver powder, 20-23 parts graphite powder, 10-15 parts polyaniline, 13-15 parts ceramic powder, 15-25 parts dimethyl sulfoxide, and 10-15 parts organic resin.

[0008] By adopting the above technical solution, the use of microcrystalline wax powder in the flux can adjust the overall viscosity of the flux. When the flux is applied to the fusible metal sheet through a dispensing machine, it can spread rapidly with a suitable distribution thickness. Furthermore, the flux does not crack after drying. In subsequent processes, the microcrystalline wax precipitates from the flux surface to form a waterproof layer, enhancing the flux's water resistance. The fusible metal powder mainly uses bismuth alloy or tin alloy, ensuring that the fusible metal sheet can quickly melt and break when the current exceeds the voltage, relying solely on the heat from the heating resistor to reach a certain temperature. Sodium dodecyl sulfate has good thermal conductivity and heat resistance, allowing it to operate continuously at temperatures ranging from -50℃ to 200℃. Its low surface tension and polarity allow for good wetting of the fusible metal sheet and maintain good interfacial properties. During the melting process of the thermal fuse, it effectively drags the fusible metal sheet, thus fully utilizing the flux's role and improving the thermal fuse's melting performance. The amount of sodium dodecyl sulfonate used needs to be strictly controlled. If the amount is too large, the viscosity of the system will be low, the flux will flow easily, making it difficult to encapsulate and affecting the sealing of the temperature fuse element. If the amount is too small, the viscosity of the system will be too large, making it difficult to form a paste, which is not conducive to coating on fusible metal sheets.

[0009] While micron-sized silver powder is used in conductive pastes, although the contact area formed between micron-sized silver powder particles is not as large as that formed by nano-sized silver powder, the smaller particle size of nano-sized silver powder leads to spontaneous attraction between particles, resulting in agglomeration and low-temperature non-dense diffusion problems. Although these problems can be resolved by external energy or ultrasonic vibration, the process is more complex and increases costs. Furthermore, the conductive layer of a paste mixed with nano-sized silver powder and organic materials is prone to cracking after printing and drying, affecting the conductivity of the electrode. Polyaniline is physically stirred and loaded onto ceramic powder. The porous structure of the ceramic powder promotes the uniform distribution of polyaniline in the conductive paste, compensating for the poor conductivity of the ceramic powder. Simultaneously, the good thermal insulation properties of ceramic powder and polyaniline reduce the heat conduction efficiency of the fusible metal sheet to the directly connected electrode material as the temperature rises, thus allowing the fusible metal sheet to heat up faster and reducing the melting reaction time.

[0010] Optionally, the particle size of the micron-sized silver powder is 10-50 μm.

[0011] Optionally, the molecular weight of the microcrystalline wax powder is 400-600, and the weight ratio of the microcrystalline wax powder to the rosin is 1:3-4.

[0012] By adopting the above technical solution, microcrystalline wax powder with a molecular weight of 400-600 will migrate and precipitate on the surface of the flux after the flux is dried. Since the microcrystalline wax powder has a low surface energy, it will migrate out of the flux layer to form a waterproof layer.

[0013] Optionally, the fusible metal powder is one or more of bismuth-tin alloy powder, bismuth-tin-silver alloy powder, and tin-magnesium alloy powder, and the fusible metal powder is alloy microspheres with a particle size of 2-10 μm.

[0014] Optionally, the ceramic powder is magnesium zirconium or zirconium yttrium ceramic powder, and the particle size of the ceramic powder is 10-80 μm.

[0015] Secondly, this application provides a method for preparing the aforementioned three-terminal fuse, comprising the following steps:

[0016] S1. Mix organic resin and dimethyl sulfoxide, and centrifuge to disperse to obtain material A; mix micron-sized silver powder, graphite powder, polyaniline and ceramic powder, and add the mixture to material A one by one while ultrasonic stirring to obtain material B; disperse material B by high-speed shear grinding, then sieve, and take the sieve material to obtain conductive paste for later use.

[0017] S2. Dissolve rosin in anhydrous ethanol, add sodium dodecyl sulfonate and microcrystalline wax powder, stir, heat in an oven to evaporate the ethanol, remove, add fusible metal powder to adjust into a paste mixture, and prepare a flux for later use; the weight ratio of rosin to anhydrous ethanol is 1:5-8.

[0018] S3. At the center of one side of the substrate, a resistive paste is screen-printed, and after standing and leveling, the substrate is placed in an oven for baking. Then, the substrate is placed in a mesh belt furnace for sintering to form a heating resistor. A glass paste is screen-printed on the heating resistor, and after standing and leveling, the glass paste covers the heating resistor. Then, the substrate is placed in an oven for baking. After baking, the substrate is placed in a mesh belt furnace for sintering to form a glass insulating layer.

[0019] S4. Electrode paste is screen-printed on the substrates on both sides of the heating resistor. After standing and leveling, the substrates are placed in an oven to bake to obtain the electrode.

[0020] S5. The fusible metal sheet is welded onto the electrode, and the flux is applied to the middle part of the fusible metal sheet through a dispensing machine. After heating and cooling, the flux forms a flux layer, thus producing a three-terminal fuse.

[0021] Optionally, in step S1, the mixing method of the micron-sized silver powder, graphite powder, polyaniline and ceramic powder is as follows: the micron-sized silver powder and graphite powder are mixed and stirred to obtain material C, the polyaniline and ceramic powder are mixed and stirred to obtain material D, and the materials C and D are mixed and stirred and then evenly divided and added to material A in 3-5 batches to obtain material B.

[0022] Optionally, in step S4, the baking temperature of the electrode slurry is 160-190℃.

[0023] By adopting the above technical solution, the heating resistor, glass insulation layer and electrodes can be firmly adsorbed on the substrate surface, thereby making the structure of the three-terminal fuse more stable.

[0024] In summary, the present invention has at least one of the following beneficial technical effects:

[0025] 1. The three-terminal fuse prepared by the method of the present invention can be used in specific protection circuits. When an overcurrent occurs, the metal strip can melt; when an overcharge occurs, the metal strip of the three-terminal fuse can also be heated and melted, thus realizing both overcharge voltage protection and overcurrent protection. Moreover, the present invention improves both the flux layer and the electrode paste. Microcrystalline wax powder and sodium dodecyl sulfonate are added to the flux layer to enhance the weather resistance and moisture resistance of the flux, ensuring that the three-terminal resistance wire can melt in time even in humid conditions. Polyaniline and ceramic powder are added to the electrode paste to enhance the conductivity of the electrode and improve the heat insulation capacity of the electrode, thereby slowing down the transfer of heat from the soluble metal strip to the electrode. This allows the soluble metal strip to heat up rapidly and melt when the heating resistor releases a large amount of heat due to overvoltage.

[0026] 2. This invention uses fusible metal sheets that have been rolled by a roller press instead of fusible metal wires, resulting in a larger contact area with the flux and electrodes, faster heat absorption for the same volume, and a faster fluxing time to take effect.

[0027] 3. The metal sheet has a conventional formula, simple components in the flux and electrode paste, fewer manufacturing steps, less use of rare metal components, and lower raw material costs, making it suitable for use in most electronic products. Attached Figure Description

[0028] Figure 1 This is a longitudinal cross-sectional view of the three-terminal fuse prepared in Embodiment 1 of the present invention;

[0029] Figure 2 This is a schematic diagram of the overall structure of the three-terminal fuse obtained in Embodiment 1 of the present invention;

[0030] The following are the reference numerals in the attached diagram: 1. Insulating cover; 2. Substrate; 3. Electrode; 4. Heating element; 5. Fusible metal sheet; 6. Flux layer; 7. Curved insulating sheet. Detailed Implementation

[0031] The present application will be further described in detail below with reference to the accompanying drawings and embodiments.

[0032] This application provides a three-terminal fuse, including a substrate, on which electrodes and a heating resistor are disposed. The electrodes are made of conductive paste, and a fusible metal sheet is disposed on the heating resistor. A flux layer is disposed on the upper surface of the fusible metal sheet. By weight, the flux layer comprises 30-40 parts of rosin, 7-20 parts of microcrystalline wax powder, 20-30 parts of fusible metal powder, and 10-25 parts of sodium dodecyl sulfonate. The conductive paste comprises 30-40 parts of micron-sized silver powder, 20-30 parts of graphite powder, 5-13 parts of polyaniline, 10-15 parts of ceramic powder, 15-25 parts of dimethyl sulfoxide, and 10-15 parts of organic resin.

[0033] The fusible metal powder is one or more of bismuth-tin alloy powder, bismuth-tin-silver alloy powder, and tin-magnesium alloy powder, and the fusible metal powder is alloy microspheres with a particle size of 2-10 μm. The ceramic powder is magnesium-zirconium or zirconium-yttrium ceramic powder, and the particle size of the ceramic powder is 10-80 μm.

[0034] The three-terminal fuse provided in this application is prepared by the following method, including the following steps:

[0035] S1. Mix organic resin and dimethyl sulfoxide, and centrifuge to disperse to obtain material A; mix micron-sized silver powder, graphite powder, polyaniline and ceramic powder, and add the mixture to material A one by one while ultrasonic stirring to obtain material B; disperse material B by high-speed shear grinding, then sieve, and take the sieve material to obtain conductive paste for later use.

[0036] S2. Dissolve rosin in anhydrous ethanol, add sodium dodecyl sulfonate and microcrystalline wax powder, stir, place in an oven for heating treatment to evaporate the ethanol, take it out, add fusible metal powder to adjust into a paste mixture, and prepare a flux for later use; the weight ratio of rosin to anhydrous ethanol is 1:5-8.

[0037] S3. At the center of one side of the substrate, a resistive paste is screen-printed, and after standing and leveling, the substrate is placed in an oven for baking. Then, the substrate is placed in a mesh belt furnace for sintering to form a heating resistor. A glass paste is screen-printed on the heating resistor, and after standing and leveling, the glass paste covers the heating resistor. Then, the substrate is placed in an oven for baking. After baking, the substrate is placed in a mesh belt furnace for sintering to form a glass insulating layer.

[0038] S4. Electrode paste is screen-printed on the substrates on both sides of the heating resistor. After standing and leveling, the substrates are placed in an oven to bake to obtain the electrode.

[0039] S5. The fusible metal sheet is welded onto the electrode, and the flux is applied to the middle part of the fusible metal sheet through a dispensing machine. After heating and cooling, the flux forms a flux layer, thus producing a three-terminal fuse.

[0040] The main technical problem addressed in this application is that few improvements to three-terminal fuse devices on the market focus on modifying the electrode directly connected to the fusible metal wire or the flux surrounding the fusible metal wire to shorten its melting time. Therefore, a technical solution is needed to minimize the melting time of the fusible metal wire. The three-terminal fuse in this application improves both the flux layer and the electrode paste. Microcrystalline wax powder and sodium dodecyl sulfonate are added to the flux layer to enhance its weather resistance and moisture-proof properties, ensuring that the three-terminal resistance wire can melt promptly even in humid conditions. Polyaniline and ceramic powder are added to the electrode paste to enhance the electrode's conductivity and improve its thermal insulation, thereby slowing down the transfer of heat from the fusible metal sheet to the electrode. This allows the fusible metal sheet to heat up rapidly and melt when the heating resistor releases a large amount of heat due to overvoltage.

[0041] The sources of the raw materials used in the embodiments of this application are as follows:

[0042] Rosin, Shanghai E. En Chemical Technology Co., Ltd.

[0043] Microcrystalline wax powder, Shanghai Zhixin Chemical Co., Ltd.

[0044] Sodium dodecyl sulfonate, Guangdong Wengjiang Chemical Reagent Co., Ltd.

[0045] Micron-sized silver powder, Shaanxi Kangduopu Biotechnology Co., Ltd.

[0046] Graphite powder, Shanghai Myriel Biochemical Technology Co., Ltd.

[0047] Polyaniline, Shanghai E. En Chemical Technology Co., Ltd.

[0048] Ceramic powder, Asia Pacific (Shanghai) Trading Co., Ltd.

[0049] Dimethyl sulfoxide, Hunan Yunbang Biotechnology Co., Ltd.

[0050] Polyamide resin, Jinjinle Chemical Co., Ltd.

[0051] Zirconium dioxide, Wuhan Xinyang Ruihe Chemical Technology Co., Ltd.

[0052] Yttrium oxide, Shanghai Jizhi Biochemical Technology Co., Ltd.

[0053] Silica, Tianjin Xiens Biochemical Technology Co., Ltd.

[0054] Alumina, Haihaohong Biomedical Technology Co., Ltd.

[0055] Bismuth-tin alloy, Sichuan High Purity Materials Technology Co., Ltd.

[0056] Preparation Examples 1-10

[0057] Preparation Examples 1-10 correspond to fluxes prepared with different raw material ratios, and the specific raw material ratios are shown in Table 1.

[0058] The fusible metal powder used in Examples 1-10 is bismuth-tin alloy powder obtained by grinding bismuth-tin alloy, wherein the molar ratio of bismuth to tin is 1:3, and the particle size of the bismuth-tin alloy powder obtained by grinding is 2-10 μm.

[0059] The molecular weight of the microcrystalline wax used in Preparation Examples 1-10 was 400-450.

[0060] Table 1

[0061]

[0062]

[0063] The preparation process of the flux in Examples 1-10 is as follows:

[0064] Rosin was dissolved in anhydrous ethanol. After the rosin was dissolved, sodium dodecyl sulfonate and microcrystalline wax powder were added to the mixture of rosin and anhydrous ethanol. The mixture was then stirred at a speed of 20 r / min for 5 min to obtain a premix. After stirring, the premix was placed in an oven and heated to 120℃ until all the ethanol was evaporated. The mixture was then removed and fusible metal powder was added to adjust it into a paste-like mixture to obtain a flux for later use. The weight of anhydrous ethanol was 5 times that of rosin.

[0065] Preparation of Comparative Examples 1-4

[0066] Comparative Examples 1-4 were prepared based on Preparation Example 2, the difference being the different types or amounts of flux components.

[0067] The difference between Comparative Example 1 and Comparative Example 2 is that the microcrystalline wax powder in Comparative Example 1 was replaced with calcium carbonate powder of the same particle size.

[0068] The difference between Comparative Example 2 and Preparation Example 2 is that the fusible metal powder in Comparative Example 2 is an alloy microsphere with a particle size of 20-30 μm.

[0069] The difference between Comparative Example 3 and Comparative Example 2 is that the amount of microcrystalline wax powder used in Comparative Example 3 is changed to 2.3 kg.

[0070] The difference between Comparative Example 4 and Comparative Example 2 is that the amount of sodium dodecyl sulfonate used in Comparative Example 4 is changed to 0.8 kg.

[0071] Preparation Examples 11-21

[0072] Examples 11-21 show conductive pastes prepared with different raw material ratios, and the specific raw material ratios are shown in Table 2.

[0073] The ceramic powders used in Preparation Examples 11-21 were all zirconium-yttrium ceramic powders. The zirconium-yttrium ceramic powders were prepared by calcining zirconium oxide, yttrium oxide, aluminum oxide and silicon dioxide at 1500℃ in a molar ratio of 3:1:4:5. The particle size of the zirconium-yttrium ceramic powders used in Preparation Examples 11-21 was 50-60 μm.

[0074] The micron-sized silver powder used in Preparation Examples 11-21 has a particle size of 70-90 μm.

[0075] The organic resin selected in Preparation Examples 11-21 is polyamide resin.

[0076] Table 2

[0077]

[0078] The preparation process of Examples 11-21 is as follows:

[0079] (1) Mix polyamide resin and dimethyl sulfoxide, and centrifuge to disperse them at a speed of 1500 r / min for 8 min to obtain material A for later use; mix and stir micron-sized silver powder and graphite powder at a speed of 30 r / min for 3 min to obtain material C for later use; mix and stir polyaniline and ceramic powder at a speed of 30 r / min for 5 min to obtain material D for later use; mix material C and material D evenly and divide them into equal portions, and add them to material A in three batches. After each addition, ultrasonically stir for 10 min at a frequency of 10 kHz. After all the materials have been added and stirred, material B is obtained.

[0080] (2) The premixed material B is sheared, ground and dispersed on a three-roll mill, and then sieved through a 300-500 mesh screen to obtain the undersize material, thus producing a conductive slurry.

[0081] Preparation Example 22

[0082] Preparation Example 22 was based on Preparation Example 12, except that the amount of polyaniline used in Preparation Example 22 was 0.75 kg.

[0083] Preparation Example 23

[0084] Preparation Example 23 is based on Preparation Example 12, except that the micron-sized silver powder in Preparation Example 23 has a particle size of 10-20 μm.

[0085] Preparation of Comparative Examples 5-7

[0086] Comparative Example 5 was prepared based on Preparation Example 12, except that the types or amounts of conductive paste components were different.

[0087] The difference between Comparative Example 5 and Example 12 is that in Comparative Example 5, 3.5 kg of micron-sized silver powder was replaced with 3.5 kg of nano-sized silver powder, and the particle size of the nano-sized silver powder was 70-90 nm.

[0088] The difference between Comparative Example 6 and Example 12 is that the amount of ceramic powder used in Comparative Example 6 is changed to 2 kg.

[0089] The difference between Comparative Example 7 and Comparative Example 12 is that polyaniline is not used in Comparative Example 7.

[0090] Examples 1-22

[0091] In the three-terminal fuses prepared in Examples 1-10, the fluxes are respectively the fluxes prepared in Examples 1-10, and the conductive pastes are all the conductive pastes prepared in Example 12; in the three-terminal fuses prepared in Example 11, the fluxes are the fluxes prepared in Example 2, and the conductive pastes are the conductive pastes prepared in Example 11; in the three-terminal fuses prepared in Examples 12-22, the fluxes are all the fluxes prepared in Example 2, and the conductive pastes are respectively the conductive pastes prepared in Examples 13-23.

[0092] Comparative Examples 1-7

[0093] In the three-terminal fuses prepared in Comparative Examples 1-4, the fluxes were respectively the fluxes prepared in Comparative Examples 1-4, and the conductive pastes were all the conductive pastes prepared in Preparation Example 12; in the three-terminal fuses prepared in Comparative Examples 5-7, the fluxes were all the fluxes prepared in Preparation Example 2, and the conductive pastes were respectively the conductive pastes prepared in Comparative Examples 5-7.

[0094] based on Figure 1Embodiment 1 of the present invention will be described. A pair of electrodes 3 are provided at both ends of the upper surface of the insulating substrate 2. A heating element 4 is provided on the substrate in the middle part of the pair of electrodes 3. The heating element 4 is formed by a heating resistor wrapped with a glass insulating layer. The heating resistor is solidified on the substrate 2 by sintering. The glass insulating layer covers its upper surface and all sides. At the same time, the heating resistor is also connected to the protected circuit. A fusible metal sheet 5 is provided above the heating element 4. The two ends of the fusible metal sheet 5 are respectively connected to the corresponding electrodes 3. The fusible metal sheet 5 is close to the heating element 4 but not connected. A flux layer 6 is coated on the upper surface of the fusible metal sheet 5. The flux layer 6 is stacked in a cone shape on the upper surface of the fusible metal sheet 5. The flux layer 6 is attached to an arc-shaped insulating sheet 7. When the flux layer melts, the arc-shaped insulating sheet 7 can accelerate the diffusion of the molten material to both sides, thereby accelerating the melting. The arc-shaped insulating sheet 7 does not contact the electrodes but is connected to both sides of the insulating cover 1 of the three-terminal fuse. The insulating cover 1 is connected to the substrate 2.

[0095] The substrate 2 can also have several through holes. The through holes are perpendicular to the surface of the substrate and are connected to the electrodes of the three-terminal fuse located on the surface of the substrate, so that the three-terminal fuse can be connected to the circuits on the upper and lower surfaces of the substrate, thereby maximizing the protection of the circuit. The through holes are classified as follows: (1) Metal deposition type through holes, the processing method is: by electroplating copper on the metallized through holes, the copper metal fills the entire through hole. A copper layer and a tin layer are sequentially coated on the opening end of the through hole. The tin layer is coated on the surface of the copper layer. The thickness of the copper layer is about 0.5 mm, and the thickness of the tin layer is about 1 mm. After the through hole is electroplated with copper, it can conduct electricity and signals on both the upper and lower surfaces. The tin layer at the opening of the through hole can be used as a solder pad for welding electrodes. (2) Silver paste filling type through holes, the processing method is: conductive paste (silver paste) is screen printed on the through hole. The conductive paste (silver paste) contains micron-sized silver powder and other conductive materials, as well as fillers and binders. After the conductive paste (silver paste) fills the entire through hole, it can conduct electricity and signals on both the upper and lower surfaces. A tin layer with a thickness of about 1 mm is applied to the opening end of the through hole. The tin layer should completely cover the conductive paste (silver paste) inside the through hole. The tin layer at the opening of the through hole can be used as a solder pad for the welding electrode. After the conductive paste (silver paste) is filled into the through hole, the substrate needs to be placed in an oven at a temperature of 180℃ for 200 minutes to cure. Then, a tin layer is applied to the opening end of the through hole, and the fabrication is completed. (3) Rivet welding type through hole, processing method: copper pillars that match the inner diameter and height of the through hole are filled into the through hole. Then, a tin layer with a thickness of about 1 mm is applied to the opening end of the through hole. The copper pillars and the tin layer are melted and welded together using a laser, so that the through hole can be connected to the circuit on the upper and lower surfaces of the substrate.

[0096] The preparation process of Example 1 is as follows:

[0097] (1) Take an area of ​​approximately 10cm² 2A 3mm thick 96 alumina ceramic sheet is used as substrate 2. A resistor paste is screen-printed at the center of one side of substrate 2. The resistor paste is a ruthenium paste that can be sintered at high temperatures. After screen printing, the substrate is left to stand and level for 3 minutes to allow the resistor paste to cover the set position for forming the heating resistor. Then, the substrate is first placed in an oven at 150℃ and baked for 10 minutes. Finally, it is placed in a mesh belt furnace at 850℃ to sinter and form the heating resistor for 10 minutes.

[0098] (2) Prepare a glass layer on the heating resistor so that the glass layer covers the heating resistor and is connected to the substrate: screen print glass paste on the heating resistor, let it stand and level for 3 minutes so that the glass paste covers the heating resistor. The thickness of the heating resistor is about 1 mm and the thickness of the glass layer is about 0.5 mm. Then, the substrate is first placed in an oven at 150°C and baked for 10 minutes. Finally, it is placed in a mesh belt furnace at 850°C to sinter and form the glass layer. The sintering time is 10 minutes to obtain the heating element 4. The glass paste is an insulating glass paste. The glass layer has high thermal conductivity and a high thermal conductivity coefficient, which allows the heat of the heating resistor to be fully conducted upward to the fusible metal sheet 5.

[0099] (3) Electrode paste is screen printed on the substrates on both sides of the heating element 4. The electrode paste prepared in Preparation Example 12 is screen printed at the preset position on the substrate (both sides of the heating resistor). The thickness is about 2.5 mm. After standing and leveling for 3 min, it is placed in an oven at 180°C and baked for 200 min to obtain electrode 3.

[0100] (4) The alloy formula for the fusible metal sheet is selected from existing alloy formulas, with 3-20% silver, 70-94% lead, and 3-10% tin. The above materials are put into a boiler in proportion, heated to 1000℃ for 5 hours, and then cold-cast into alloy ingots. The melting point of the alloy is in the range of 230-260℃. 5mg is pressed into a metal sheet with a thickness of 0.2mm, which can be used as the fusible metal sheet 5 in this embodiment. The fusible metal sheet is welded onto the electrode 3. The flux prepared in Preparation Example 1 is applied to the middle part of the fusible metal sheet through a dispensing machine. It is heated to 100℃ for 3 seconds and then cooled. The flux forms a flux layer 6. After the flux layer 6 is cured, it is stacked in a cone shape on the upper surface of the fusible metal sheet with a height of about 3-4mm. Finally, an insulating cover 1 is put on. An arc-shaped insulating sheet 7 is also connected in the insulating cover 1. The arc-shaped insulating sheet 7 is attached to the upper surface of the flux layer 6 to obtain a three-terminal fuse. The fusible metal sheet 5 is connected to the power supply of the protected device through an electrode, and the heating element 4 is connected to the power supply of the protected device through another path. The fuse will melt when subjected to a specified abnormal power, thus achieving the technical effect of a three-terminal fuse protection circuit.

[0101] Examples 1-23 and Comparative Examples

[0102] Performance testing

[0103] 1. The electric fuse performance was tested according to standard UL60691. The testing instruments included a constant current source and a stopwatch.

[0104] Test conditions: room temperature; relative humidity 60±20%. The fusible metal sheet was set as a control group, and the electro-fusion performance of Examples 1-23 and Comparative Examples 1-6 was tested.

[0105] 2. Internal Resistance Test: The resistance was measured using the Wheatstone Bridge Method. The testing instrument was a TH2511 low-resistance tester (Changzhou Tonghui Electronics Co., Ltd.); room temperature and relative humidity were 50±20%. A separate control group was set up for the fusible metal sheet. The resistance value of the fusible metal sheet of the three-terminal fuses in Examples 1-10 was tested to analyze the influence of changes in flux and electrode composition on the fuse's internal resistance.

[0106] 3. Fusible Fuse Temperature Test: At room temperature, silicone oil was used as the heating fluid for oil bath heating. The fusible metal strip was clamped in the ohm setting of a multimeter and placed in the heating fluid. Heating was carried out at a rate of 0.5-1℃ / min until the thermal fuse melted. The temperature of the bath fluid (water or silicone oil) at this point was recorded as the fuse melting temperature. The fusible metal strip was used as a separate control group to test the melting temperature of the fusible metal strip of the three-terminal fuses in Examples 1-10, and the effects of flux and electrodes on the fuse melting temperature were analyzed.

[0107] 4. Conductive paste performance test: The electrodes made of conductive paste in the three-terminal fuses prepared in Examples 11-23 and Comparative Examples 1-7 were subjected to performance tests respectively; (1) Resistance measurement, referring to the sheet resistance measurement method of GB17473.3-2008 "Test Method for Noble Metal Pastes for Microelectronics Technology"; (2) Adhesion measurement, referring to the adhesion measurement method of GB17473.3-2008 "Test Method for Noble Metal Pastes for Microelectronics Technology"; (3) Observe whether the appearance of the electrode after curing is cracked, powdered or has bubbles.

[0108] 5. Moisture resistance test of three-terminal fuses: The three-terminal fuses prepared in Examples 1-23 and Comparative Examples 5-7 were placed in an environment with room temperature and 80% humidity for one week, and the fusing temperature and fusing time at a fusing current of 5A were tested.

[0109] The test results of the electric fusing performance are shown in Table 3. The test results of the internal resistance and fusing temperature of the fusible metal sheet and flux layer are shown in Table 4. The test results of the conductive paste performance are shown in Table 5. The test results of the moisture resistance of the three-terminal fuse are shown in Table 6.

[0110] Table 3

[0111]

[0112]

[0113] Table 4

[0114]

[0115]

[0116] Table 5

[0117]

[0118]

[0119] Table 6

[0120]

[0121] Analysis of the data in the table above, based on the control group and examples, reveals that flux can significantly shorten the melting time and reduce the melting temperature of the fusible metal sheet. The difference in melting time between Comparative Examples 1-4 and the examples in Table 3 indicates that the amount of microcrystalline wax, the particle size of the molten metal powder, and the amount of sodium dodecyl sulfate significantly affect the melting time of the fusible metal sheet when the rosin amount remains constant. Comparison of the control group and Examples 1-10 in Table 4 shows that increasing the flux layer has no significant effect on the internal resistance of the metal sheet, and the flux can reduce the melting temperature. Comparative Examples 1-4 in Table 4 also indicate that the amount of microcrystalline wax, the particle size of the molten metal powder, and the amount of sodium dodecyl sulfate significantly affect the melting temperature of the fusible metal sheet when the rosin amount remains constant. As shown in Comparative Examples 5-7 in Table 5, using only nano-silver powder in the conductive paste leads to cracking or powdering on the surface of the cured electrode. This not only affects mechanical properties but also reduces the adhesion of the electrode to the substrate. Furthermore, the agglomeration effect of nano-silver powder results in uneven internal structure of the electrode material, affecting the internal resistance of the electrode and causing unnecessary heating of the fuse, thus hindering its normal operation. Data from the control group and examples in Table 6 show that the three-terminal fuse prepared in this application has certain moisture-proof properties. Even after being placed in a humid environment for a week, the fusing time and fusing temperature did not change significantly. In contrast, Comparative Example 1, which did not use microcrystalline wax, experienced a nearly 2-second longer fusing time in a humid environment. Therefore, microcrystalline wax is beneficial for enhancing the moisture-proof performance of the three-terminal fuse.

[0122] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A three-terminal fuse comprising a substrate, an electrode and a heat-generating resistor provided on the substrate, the electrode being made of a conductive paste, and a fusible metal sheet provided on the heat-generating resistor, a flux layer being provided on the upper surface of the fusible metal sheet, characterized in that, By weight parts The raw materials for the flux layer include 30-40 parts of rosin, 7-20 parts of microcrystalline wax powder, 20-30 parts of fusible metal powder, and 10-25 parts of sodium dodecyl sulfonate. The conductive paste contains 30-40 parts of micron-sized silver powder, 20-30 parts of graphite powder, 5-13 parts of polyaniline, 10-15 parts of ceramic powder, 15-25 parts of dimethyl sulfoxide, and 10-15 parts of organic resin.

2. The three-terminal fuse according to claim 1, characterized in that, By weight, the flux layer comprises 35-40 parts rosin, 10-13 parts microcrystalline wax powder, 20-25 parts fusible metal powder, and 14-19 parts sodium dodecyl sulfonate; the conductive paste comprises 30-40 parts micron-sized silver powder, 20-23 parts graphite powder, 10-13 parts polyaniline, 13-15 parts ceramic powder, 15-25 parts dimethyl sulfoxide, and 10-15 parts organic resin.

3. The three-terminal fuse according to claim 1, characterized in that, The micron-sized silver powder has a particle size of 10-50 μm.

4. The three-terminal fuse according to claim 1, characterized in that, The molecular weight of the microcrystalline wax powder is 400-600, and the weight ratio of the microcrystalline wax powder to the rosin is 1:3-4.

5. The three-terminal fuse according to claim 1, characterized in that, The fusible metal powder is one or more of bismuth-tin alloy powder, bismuth-tin-silver alloy powder, and tin-magnesium alloy powder, and the fusible metal powder is alloy microspheres with a particle size of 2-10 μm.

6. The three-terminal fuse according to claim 1, characterized in that, The ceramic powder is magnesium zirconium powder or zirconium yttrium ceramic powder, and the particle size of the ceramic powder is 10-80 μm.

7. The three-terminal fuse according to claim 1, characterized in that, The weight ratio of the ceramic powder to the polyaniline is 2:

1.

8. A method for preparing a three-terminal fuse according to any one of claims 1-7, characterized in that, Includes the following steps: S1. Mix organic resin and dimethyl sulfoxide, and centrifuge to disperse to obtain material A; mix micron-sized silver powder, graphite powder, polyaniline and ceramic powder, and add the mixture to material A one by one while ultrasonic stirring to obtain material B; disperse material B by high-speed shear grinding, then sieve, and take the sieve material to obtain conductive paste for later use. S2. Dissolve rosin in anhydrous ethanol, add sodium dodecyl sulfonate and microcrystalline wax powder, stir, place in an oven for heating treatment to evaporate the anhydrous ethanol, take out, add fusible metal powder to adjust into a paste mixture, and prepare a flux for later use; the weight ratio of rosin to anhydrous ethanol is 1:5-8. S3. At the center of one side of the substrate, a resistive paste is screen-printed, and after standing and leveling, the substrate is placed in an oven for baking. Then, the substrate is placed in a mesh belt furnace for sintering to form a heating resistor. A glass paste is screen-printed on the heating resistor, and after standing and leveling, the glass paste covers the heating resistor. Then, the substrate is placed in an oven for baking. After baking, the substrate is placed in a mesh belt furnace for sintering to form a glass insulating layer. S4. Conductive paste is screen-printed on the substrates on both sides of the heating resistor. After standing and leveling, the substrates are placed in an oven to bake to obtain the electrode. S5. The fusible metal sheet is welded onto the electrode, and the flux is applied to the middle part of the fusible metal sheet through a dispensing machine. After heating and cooling, the flux forms a flux layer, thus producing a three-terminal fuse.

9. The method for preparing a three-terminal fuse according to claim 8, characterized in that, In step S1, the mixing method of the micron-sized silver powder, graphite powder, polyaniline and ceramic powder is as follows: the micron-sized silver powder and graphite powder are mixed and stirred to obtain material C, the polyaniline and ceramic powder are mixed and stirred to obtain material D, and the materials C and D are mixed and stirred and then evenly divided and added to material A in 3-5 batches to obtain material B.

10. The method for preparing a three-terminal fuse according to claim 8, characterized in that, In step S4, the baking temperature of the conductive paste is 160-190℃.

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