An ultra-thin positive temperature coefficient surface mount device

Abstract

The present invention discloses an ultra-thin positive temperature coefficient surface mount device (PTC-SMD), wherein the PTC-SMD comprises a PTC black material layer, an electrode layer and a solder resist layer. The present invention is prepared by an additive process, mainly comprising: screen printing, scraping, dispensing and inkjet printing, and comprises the following steps: (1) printing and preparing a PTC black material film and an electrode layer to obtain a core layer; (2) laminating different core layers to obtain a sheet; (3) printing a solder resist ink on the surface of the sheet, and cutting, silver immersion, nickel plating and tin plating to obtain a PTC-SMD. Compared with traditional subtractive manufacturing, the electrode layer prepared by printing can effectively replace copper foil, greatly reduce the thickness of the PTC-SMD, that is, more core layers can be included at the same thickness, effectively reduce its room temperature resistance, and increase the holding current. At the same time, the additive manufacturing process is energy-saving and environmentally friendly, and can greatly reduce costs.

Description

Technical Field

[0001] The invention relates to the field of surface mount devices (SMD), and in particular to an ultra-thin positive temperature coefficient (PTC) surface mount device (PTC-SMD). Background Art

[0002] SMD is a surface mount device, which has the advantages of high assembly density, small size and light weight of electronic products, high reliability and strong vibration resistance. PTC-SMD is a surface mount device with a positive temperature coefficient effect, and its resistivity shows a nonlinear change with temperature. When PTC-SMD is mounted in the circuit, when the circuit generates a large current or the temperature is too high, the temperature of PTC-SMD rises, and its resistance value increases instantly, cutting off the current in the circuit, thereby protecting the circuit; then as the temperature decreases, its resistance value can return to normal value, and the circuit operates normally, with self-recovery characteristics.

[0003] For PTC-SMD, the room temperature resistance is large, the holding current is low, it is difficult to meet the use requirements of high-power equipment, and the power loss in the circuit is large. At the same time, PTC-SMD adopts a subtractive manufacturing process, which is highly polluting, wasteful, and difficult to reduce its thickness. Advanced Electronic Materials (Advanced Electronic Materials, 2020, Vol. 6, No. 10) reported a method for preparing PTC thermistors by subtractive materials, which can effectively reduce its room temperature resistance, but it is highly polluting, wasteful, and has high manufacturing costs, and the preparation method cannot obtain a PTC-SMD with both thin thickness and low room temperature resistance. Therefore, it is of great significance to develop a method for preparing a PTC-SMD with both ultra-thin and low room temperature resistance and high holding current, which is green, environmentally friendly, and low-cost. Summary of the invention

[0004] The purpose of the present invention is to solve the problems of large thickness, high room temperature resistance and low holding current of PTC-SMD by developing a novel ultra-thin positive temperature coefficient surface mount device (PTC-SMD) preparation method, while reducing manufacturing costs, reducing waste and pollution, and realizing green manufacturing.

[0005] To achieve the above object, the present invention provides an ultra-thin positive temperature coefficient surface mount device (PTC-SMD).

[0006] The present invention is achieved through the following technical solutions:

[0007] An ultra-thin positive temperature coefficient surface mount device, characterized in that the PTC-SMD is prepared by an additive printing method, comprising the following steps:

[0008] 1) Printing preparation of PTC black material film and electrode layer to obtain core layer:

[0009] 1.1) preparing a black material film by screen printing or doctor blade coating of black material ink and drying, or by melt extrusion;

[0010] 1.2) Printing the electrode layer on the surface of the PTC black material film by screen printing, dispensing or inkjet printing the electrode ink and drying it to obtain the core layer:

[0011] The core layer is a PTC black material film with a width of L and has electrode layers with different arrangements printed on the surface thereof, and is obtained by three types of core layers: A stacking, B stacking, and C stacking.

[0012] The arrangement of the electrode layer in the A stacking layer is as follows: starting from one side of the PTC black material film, an electrode with a width of D is printed, and at every interval of d, an electrode with a width of 2D is printed;

[0013] The electrode layer arrangement in the B stacking layer is as follows: starting from one side of the PTC black material film, an electrode with a width of 2D is printed at a distance of d / 2, and an electrode with a width of 2D is printed at a distance of d;

[0014] The electrode layer arrangement in the C stacking layer is as follows: the upper surface of the PTC black material film adopts the A stacking layer electrode arrangement, and the lower surface adopts the B stacking layer electrode arrangement;

[0015] 2) Pressing different types of core layers together to obtain a sheet, that is, taking the C stacking layer as the base, stacking different numbers of B stacking layers and A stacking layers on the upper and lower surfaces of the C stacking layer in the positive or negative order to obtain a sheet. When pressing different core layers together, the electrode layer should be in contact with the black material layer. According to the number of black material layers, it is defined as a sheet with corresponding layers;

[0016] 3) Print solder resist ink on the surface of the sheet, and then cut, silver-dip, nickel-plate and tin-plate; that is, print solder resist ink on the upper and lower surfaces of the sheet, cut and divide it into single sheets along the first cutting path, dip the electrodes on both sides of each sheet into silver paste and solidify them to form silver electrodes at both ends, so that the core layer is conductive in the vertical direction; put the single sheet after silver dipping into the electroplating line, first nickel-plate and then tin-plate the silver electrodes at both ends, and continue to cut and divide the single sheet after electroplating along the second cutting path to obtain an ultra-thin positive temperature coefficient surface mount device.

[0017] The black ink in step 1.1) is obtained by stirring or ball-milling 50 parts of resin, 2 to 20 parts of filler powder, and 5 to 50 parts of solvent; the resin is one or more selected from polyethylene, polypropylene, polyvinylidene fluoride, polyhexafluoropropylene, polyamide, polyurethane, fluororubber and copolymers thereof; the filler powder is one of ceramic conductive fillers, carbon conductive fillers or metal conductive fillers; the solvent is a mixture of one or more selected from N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, diphenylamine, toluene, xylene, diethylene glycol ethyl ether, m-cresol and phenol.

[0018] The ceramic conductive filler is one or more selected from titanium carbide, tungsten carbide, tantalum carbide, titanium nitride, titanium diboride, aluminum nitride, magnesium nitride, and boron nitride; the carbon conductive filler is one or more selected from carbon black, acetylene black, chopped carbon fiber, chopped carbon fiber, single-walled carbon nanotube, multi-walled carbon nanotube, and graphite; and the metal conductive filler is one or more selected from nickel powder, copper powder, and silver powder.

[0019] In the step 1.2), the electrode ink is one selected from the group consisting of silver glue, silver paste, silver ink, copper glue, copper paste, and copper ink in the conductive paste.

[0020] The material sheet in step 2) includes three structures:

[0021] (1) "CBA...BA" type;

[0022] (2) “CBAB…AB” type;

[0023] (3) "AB...ABACBA...BA" type.

[0024] Among them, the "CBA...BA" type has C stacking layer as the bottom, B stacking layer and A stacking layer stacked in sequence, and A stacking layer as the upper surface of the sheet, such as "CBA", "CBABA";

[0025] Among them, the "CBAB...AB" type has C stacking layer as the bottom, B stacking layer and A stacking layer stacked in sequence, and B stacking layer as the upper surface of the sheet, such as "CBAB", "CBABAB";

[0026] Among them, the "AB...ABACBA...BA" type is that the stacking layer B and the stacking layer A are stacked in sequence in a positive direction on the upper surface of the stacking layer C, and the stacking layer A is the upper surface of the material sheet; the stacking layer A and the stacking layer B are stacked in sequence in a negative direction on the lower surface of the stacking layer C, and the stacking layer A is the lower surface of the material sheet, such as "ACBA" and "ABACBA".

[0027] In the step 2), the pressing is completed by hot pressing in a press, and the temperature of the hot pressing is 100-200°C.

[0028] In the step 3), the solder resist ink is a mixture of the following components: 1 part of a leveling agent, 10 to 25 parts of an epoxy resin, 15 to 25 parts of an acrylic resin, 5 to 15 parts of polyamide, and 5 to 10 parts of barium sulfate.

[0029] In the step 3), the first scribing path refers to the center position between all core layer electrodes and is parallel to the electrodes; the second scribing path is perpendicular to the first scribing path, and the spacing distance is determined according to the SMD size; the silver immersion is to immerse the two side end electrodes of each sheet in silver paste and solidify it to form silver electrodes at both ends, so that the core layer is conductive in the vertical direction, and the silver immersion depth is 0.3 to 0.7 mm.

[0030] Beneficial Effects

[0031] The PTC-SMD of the present invention has the characteristics of ultra-thinness, low room temperature resistance and high holding current. The core layer is printed by additive manufacturing, and the PTC black material film is used as the substrate. The electrode layers are printed on the upper and lower surfaces according to three stacking methods to form core layers with different stacking. Different numbers of different core layers are pressed together in a certain arrangement order to obtain a sheet, and solder resist ink is printed on the upper and lower surfaces of the sheet, and the sheet is cut, silver-impregnated, nickel-plated and tin-plated to obtain the PTC-SMD, which solves the problems of the existing PTC-SMD with thick thickness, high room temperature resistance, low holding current, large pollution in the manufacturing process and serious waste.

[0032] Compared with traditional subtractive manufacturing, the additive manufacturing method adopted in the present invention can effectively reduce the thickness of PTC-SMD. Within a limited thickness, more PTC black material layers can be stacked to improve the performance of PTC-SMD. The process is simple, the cost is reduced, the production cycle is short, and the quality of PTC-SMD is guaranteed. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 The schematic diagram of the structure of the PTC-SMD prepared by the present invention. Among them, 01 is the solder mask layer, 02 is the electrode layer, 03 is the black material layer, and 04 is the electrodes at both ends;

[0034] Figure 2a A side view of the stacked core layer of the present invention;

[0035] Figure 2b A top view of the stacked core layer of the present invention;

[0036] Figure 3a This is a side view of the stacked core layer B of the present invention;

[0037] Figure 3b A top view of the stacked core layer B of the present invention;

[0038] Figure 4 It is a side view of the C stacking core layer of the present invention;

[0039] Figure 5 The "CBA" type stacked sheet prepared in Example 1 of the present invention;

[0040] Figure 6 The "ACBA" type stacked sheet prepared in Example 2 of the present invention;

[0041] Figure 7 The "CBAB" type stacked sheet prepared in Example 3 of the present invention;

[0042] Figure 8 This is a schematic diagram of the process of step (3) of the present invention;

[0043] Fig. 9 Schematic diagram of the structure of the PTC-SMD prepared in comparative example 1 (subtractive manufacturing), wherein 01 is a solder resist layer, 02 is an electrode layer, 03 is a black material layer, 04 is electrodes at both ends, and 05 is an adhesive layer. DETAILED DESCRIPTION

[0044] The present invention provides an ultra-thin positive temperature coefficient surface mount device (PTC-SMD) and a preparation method and application thereof. In order to more clearly illustrate the present invention, the present invention is further described below in conjunction with a preferred embodiment. Those skilled in the art should understand that the content described below is illustrative rather than restrictive, and should not be used to limit the scope of protection of the present invention. It mainly includes the following steps:

[0045] Example 1

[0046] (1) 25cm 3 Polyvinylidene fluoride (resin) was dissolved in 50 mL of N,N-dimethylformamide (solvent), and then 20 cm 3 Titanium carbide (conductive filler) is fully mixed to obtain PTC black ink, which is then scraped onto a glass plate and placed in a drying oven to completely evaporate the solvent to obtain a PTC black film.

[0047] (2) A PTC black material film A with a length of 500 mm, a width of 135 mm, and a thickness of 0.15 mm was fixed on a screen printer, and a silver paste electrode was printed on the PTC black material film as a substrate to obtain a stacking layer A (Figure 2). The electrode width D = 2.673 mm, the length is 135 mm, and the interval between the electrodes is d = 0.75 mm.

[0048] (3) A PTC black material film B with a length of 500 mm, a width of 135 mm, and a thickness of 0.15 mm was fixed on a screen printer, and the silver paste electrode was printed using the PTC black material film as a substrate to obtain a B stacking layer (Figure 3). D and d are the same as the A stacking layer.

[0049] (4) A PTC black material film C with a length of 500 mm, a width of 135 mm, and a thickness of 0.15 mm was fixed on a screen printer. The PTC black material film was used as a substrate, and the A stacking electrode and the B stacking electrode were printed on the upper and lower surfaces respectively to obtain a C stacking layer ( Figure 4 ).

[0050] (5) The stacked layers obtained in the above steps are stacked from bottom to top in the order of "CB", placed in a press, and hot-pressed at 150° C. and 1.5 MPa to obtain a two-layer sheet.

[0051] The stacked layers obtained in the above steps were stacked from bottom to top in the order of "CBA", placed in a press, and hot pressed at 150°C and 1.5MPa to obtain a 3-layer sheet ( Figure 5 ).

[0052] The stacked layers obtained in the above steps are stacked from bottom to top in the order of "CBABA", placed in a press, and hot-pressed at 150° C. and 1.5 MPa to obtain a 5-layer sheet.

[0053] (6) Use screen printing to print a solder mask ink layer on the upper and lower surfaces of the sheet.

[0054] (7) The sheet printed with solder resist ink is cut along the center position between the core layer electrode and the electrode (parallel to the electrode direction) to obtain a single sheet.

[0055] (8) The electrodes on both sides of each single strip after dicing are dipped in silver paste and solidified to form silver electrodes at both ends, so that the core layer is conductive in the vertical direction. The silver immersion depth is 0.5 mm.

[0056] (9) Place the single silver-impregnated sheet into the electroplating line, and first plate the silver electrodes at both ends with nickel and then with tin.

[0057] (10) The electroplated single sheet is further cut along the direction perpendicular to the electrode, and the cutting track spacing is 1.524 mm, and finally a 1206 type ultra-thin PTC-SMD ( Figure 1 ).

[0058] Comparative Example 1

[0059] A PTC-SMD prepared by a subtractive process, the preparation steps are:

[0060] (1) The first electrode foil, the PTC black material and the second electrode foil are formed into a conductive composite material core layer (a single-layer sheet) having a positive temperature coefficient effect by a hot pressing process. Different numbers of single-layer sheets are bonded by an adhesive layer to obtain sheets having two layers, three layers, four layers, etc.

[0061] (2) Drilling is performed on the surface of the conductive composite material core layer to achieve the purpose of positioning.

[0062] (3) The core layer of the conductive composite material is subjected to nickel stripping treatment in a nickel stripping machine, and it is checked whether the nickel stripping is complete.

[0063] (4) The conductive composite material core layer is placed in a circuit grinding machine and the inner circuit is marked with chemicals, and then placed in a film laminating machine to paste a photosensitive film and expose it.

[0064] (5) Etch the inner layer circuit with corrosive solution in an etching machine, control the copper ion content in the solution to 120-150 g / L, the acid ion content to 0.5-1.0 g / L, and the temperature to 47-55°C.

[0065] (6) The etched conductive composite material core layer is placed in a browning machine for browning to enhance the bonding force between the inner core plate and the prepreg. The concentration of the browning solution is controlled to be 10-20%, the browning temperature is 45-55°C, and the browning pressure is 1-2.5 kg / cm 2 , the browning speed is 3-3.2m / min.

[0066] (7) The browned conductive composite material core layer is placed in a vacuum press for pressing, then placed in a drilling machine for drilling, and subjected to plasma treatment.

[0067] (8) Copper deposition: A thin layer of chemical copper is deposited on the drilled hole wall substrate by chemical methods to serve as the base for subsequent electroplating of copper. The content of copper brightener is controlled to be 1.0-1.8g / L and the temperature is 28-32℃.

[0068] (10) After pickling, electroplating is performed once. For copper-plated wire, the concentration of the pickling solution is controlled to be 3-5%, the concentration of sulfuric acid is 180-220 g / L during copper plating, and the concentration of copper sulfate is 60-90 g / L.

[0069] (11) Use chemicals to mark the outer circuit in the circuit grinding machine, and then put it into the film laminating machine to paste the photosensitive film and expose it.

[0070] (12) Using a corrosive solution in an etching machine to etch out the outer layer circuit to obtain a circuit board, the copper ion content in the solution is controlled to be 120-150 g / L, the chloride ion content is controlled to be 170-220 g / L, the temperature is controlled to be 47-55° C., and the pH value is controlled to be 7.9-8.8.

[0071] (13) Use a screen printer to print solder mask ink on the upper and lower surfaces of the circuit board.

[0072] (14) The circuit board printed with solder resist ink is subjected to surface treatment by copper plating, nickel plating, and tin plating in sequence. The concentration of copper sulfate is 60-90 g / L, the concentration of nickel chloride is 8-15 g / L, and the concentration of stannous sulfate is 30-40 g / L.

[0073] (15) Cutting the surface-treated circuit board to obtain the PTC-SMD ( Fig. 9 ).

[0074] Example 2

[0075] (1) The PTC film was prepared by a melting method. 50 g of polyvinylidene fluoride (resin) and 150 g of titanium carbide (conductive filler) were put into an extruder, and after high-temperature melting and mixing, they were extruded to obtain a PTC black material film.

[0076] (2) The screen printing screen is fixed on the screen printing machine, and a PTC black material film A with a length of 500 mm, a width of 135 mm, and a thickness of 0.15 mm is used as a substrate to print an electrode layer to obtain an A stacking layer with an electrode width of D = 4.197 mm and a length of 135 mm. The interval between the electrodes is d = 0.75 mm.

[0077] (3) A PTC black material film B with a length of 500 mm, a width of 135 mm, and a thickness of 0.15 mm was fixed on a screen printer, and a silver paste electrode was printed using the PTC black material film as a substrate to obtain a B stacking layer. D and d are the same as the A stacking layer.

[0078] (4) A PTC black material film with a length of 500 mm, a width of 135 mm, and a thickness of 0.15 mm is fixed on a screen printing machine. The PTC black material film is used as a substrate, and the A stacking electrode and the B stacking electrode are printed on the upper and lower surfaces respectively to obtain a C stacking layer.

[0079] (5) stacking the stacked layers obtained in the above step from bottom to top in the order of "ACB", placing them in a press, and hot pressing them at 150° C. and 1.5 MPa to obtain a three-layer sheet;

[0080] The stacked layers obtained in the above steps were stacked from bottom to top in the order of "ACBA", placed in a press, and hot pressed at 150°C and 1.5MPa to obtain a 4-layer sheet ( Figure 6 ).

[0081] (6) Use screen printing to print a solder mask ink layer on the upper and lower surfaces of the sheet.

[0082] (7) The sheet printed with solder resist ink is cut along the center position between the core layer electrode and the electrode (parallel to the electrode direction) to obtain a single sheet.

[0083] (8) The electrodes on both sides of each single strip after dicing are dipped in silver paste and solidified to form silver electrodes at both ends, so that the core layer is conductive in the vertical direction. The silver immersion depth is 0.6 mm.

[0084] (9) Place the single silver-impregnated sheet into the electroplating line, and first plate the silver electrodes at both ends with nickel and then with tin.

[0085] (10) The electroplated single sheet is further cut along the direction perpendicular to the electrode, and the cutting line spacing is 3.048 mm, and finally an 1812-type ultra-thin PTC-SMD is obtained.

[0086] Example 3

[0087] (1) 30cm 3 Polyamide (resin) was dissolved in 50 mL of m-cresol (solvent), and then 20 cm 3 Titanium carbide (conductive filler) is fully mixed to obtain PTC black ink, which is then scraped onto a glass plate and placed in a drying oven to completely evaporate the solvent to obtain a PTC black film.

[0088] (2) A PTC black material film A with a length of 500 mm, a width of 135 mm, and a thickness of 0.15 mm was fixed on a screen printer, and a silver paste electrode was printed on the PTC black material film as a substrate to obtain a stacking layer A. The electrode width D = 1.657 mm, the length is 135 mm, and the interval between the electrodes d = 0.75 mm.

[0089] (3) A PTC black material film B with a length of 500 mm, a width of 135 mm, and a thickness of 0.15 mm was fixed on a screen printer, and a silver paste electrode was printed using the PTC black material film as a substrate to obtain a B stacking layer. D and d are the same as the A stacking layer.

[0090] (4) A PTC black material film with a length of 500 mm, a width of 135 mm, and a thickness of 0.15 mm is fixed on a screen printing machine. The PTC black material film is used as a substrate, and the A stacking electrode and the B stacking electrode are printed on the upper and lower surfaces respectively to obtain a C stacking layer.

[0091] (5) The stacked layers obtained in the above steps are stacked from bottom to top in the order of "CBA", placed in a press, and hot pressed at 160°C and 1.5 MPa to obtain a 3-layer sheet;

[0092] The stacked layers obtained in the above steps are stacked from bottom to top in the order of "CBAB", placed in a press, and hot pressed at 160°C and 1.5MPa. A 4-layer sheet ( Figure 7 ).

[0093] (6) Use screen printing to print a solder mask ink layer on the upper and lower surfaces of the sheet.

[0094] (7) The sheet printed with solder resist ink is cut along the center position between the core layer electrode and the electrode (parallel to the electrode direction) to obtain a single sheet.

[0095] (8) The electrodes on both sides of each single strip after dicing are dipped in silver paste and solidified to form silver electrodes at both ends, so that the core layer is conductive in the vertical direction. The silver immersion depth is 0.5 mm.

[0096] (9) Place the single silver-impregnated sheet into the electroplating line, and first plate the silver electrodes at both ends with nickel and then with tin.

[0097] (10) The electroplated single sheet is further cut along the direction perpendicular to the electrode, and the cutting line spacing is 1.270 mm, and finally a 0805 type ultra-thin PTC-SMD is obtained.

[0098] Table 1 Comparison of PTC-SMD performance prepared by the subtractive manufacturing process (comparative example) and the manufacturing process of the present invention

[0099]

Claims

1. An ultra-thin positive temperature coefficient surface mount device, characterized in that: The positive temperature coefficient surface mount device is prepared by an additive printing method, comprising the following steps: 1) Printing preparation of PTC black material film and electrode layer to obtain core layer: 1.1) preparing a black material film by screen printing or doctor blade coating of black material ink and drying, or by melt extrusion; 1.2) Printing the electrode layer on the surface of the PTC black material film by screen printing, dispensing or inkjet printing the electrode ink and drying it to obtain the core layer: The core layer is a PTC black material film with a width of L and has electrode layers with different arrangements printed on the surface thereof, and is obtained by three types of core layers: A stacking, B stacking, and C stacking. The arrangement of the electrode layer in the A stacking layer is as follows: starting from one side of the PTC black material film, an electrode with a width of D is printed, and at every interval of d, an electrode with a width of 2D is printed; The electrode layer arrangement in the B stacking layer is as follows: starting from one side of the PTC black material film, an electrode with a width of 2D is printed at a distance of d / 2, and an electrode with a width of 2D is printed at a distance of d; The electrode layer arrangement in the C stacking layer is as follows: the upper surface of the PTC black material film adopts the A stacking layer electrode arrangement, and the lower surface adopts the B stacking layer electrode arrangement; 2) Pressing different types of core layers together to obtain a sheet, that is, taking the C stacking layer as the base, stacking different numbers of B stacking layers and A stacking layers on the upper and lower surfaces of the C stacking layer in the positive or negative order to obtain a sheet. When the different core layers are pressed together, the electrode layer is in contact with the black material layer, and the number of black material layers is defined as a sheet with the corresponding number of layers; 3) Print solder resist ink on the surface of the sheet, and then cut, silver-dip, nickel-plate and tin-plate; that is: print solder resist ink on the upper and lower surfaces of the sheet, and cut along the first cutting path to form single sheets, dip the two side end electrodes of each sheet in silver paste and solidify to form silver electrodes at both ends, so that the core layer is conductive in the vertical direction; put the single sheet after silver dipping into the electroplating line, first nickel-plate and then tin-plate the silver electrodes at both ends, and continue to cut and divide the single sheet after electroplating along the second cutting path to obtain an ultra-thin positive temperature coefficient surface mount device.

2. The positive temperature coefficient surface mount device according to claim 1, characterized in that: The black ink in step 1.1) is obtained by stirring or ball-milling 50 parts of resin, 2 to 20 parts of filler powder, and 5 to 50 parts of solvent; the resin is one or more selected from polyethylene, polypropylene, polyvinylidene fluoride, polyhexafluoropropylene, polyamide, polyurethane, fluororubber and copolymers thereof; the filler powder is one of ceramic conductive fillers, carbon conductive fillers or metal conductive fillers; the solvent is a mixture of one or more selected from N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, diphenylamine, toluene, xylene, diethylene glycol ethyl ether, m-cresol and phenol.

3. The positive temperature coefficient surface mount device according to claim 2, characterized in that: The ceramic conductive filler is one or more selected from titanium carbide, tungsten carbide, tantalum carbide, titanium nitride, titanium diboride, aluminum nitride, magnesium nitride, and boron nitride; the carbon conductive filler is one or more selected from carbon black, acetylene black, chopped carbon fiber, chopped carbon fiber, single-walled carbon nanotube, multi-walled carbon nanotube, and graphite; and the metal conductive filler is one or more selected from nickel powder, copper powder, and silver powder.

4. The positive temperature coefficient surface mount device according to claim 1, characterized in that: In the step 1.2), the electrode ink is one selected from the group consisting of silver glue, silver paste, silver ink, copper glue, copper paste, and copper ink in the conductive paste.

5. The positive temperature coefficient surface mount device according to claim 1, characterized in that: The material sheet in step 2) includes three structures: (1) "CBA...BA" type; (2) "CBAB…AB" type; (3) "AB…ABACBA…BA" type; Wherein, the "CBA...BA" type has C stacking layer as the bottom, B stacking layer and A stacking layer stacked in the positive direction in sequence, and A stacking layer as the upper surface of the sheet; Wherein, the "CBAB...AB" type has C stacking layer as the bottom, B stacking layer and A stacking layer stacked in the positive direction in sequence, and B stacking layer as the upper surface of the sheet; Among them, the "AB...ABACBA...BA" type has stacking layers B and A stacking layers stacked in sequence in a positive direction on the upper surface of stacking layer C, with stacking layer A being the upper surface of the material sheet; and stacking layers A and B stacking layers stacked in sequence in a negative direction on the lower surface of stacking layer C, with stacking layer A being the lower surface of the material sheet.

6. The positive temperature coefficient surface mount device according to claim 1, characterized in that: In the step 2), the pressing is completed by hot pressing in a press, and the temperature of the hot pressing is 100-200°C.

7. The positive temperature coefficient surface mount device according to claim 1, characterized in that: In the step 3), the solder resist ink is a mixture of the following components: 1 part of a leveling agent, 10 to 25 parts of an epoxy resin, 15 to 25 parts of an acrylic resin, 5 to 15 parts of polyamide, and 5 to 10 parts of barium sulfate.

8. The positive temperature coefficient surface mount device according to claim 1, characterized in that In the step 3), the first scribing path refers to the center position between all core layer electrodes and is parallel to the electrodes; the second scribing path is perpendicular to the first scribing path, and the spacing distance is determined according to the SMD size; the silver immersion is to immerse the two side end electrodes of each sheet in silver paste and solidify it to form silver electrodes at both ends, so that the core layer is conductive in the vertical direction, and the silver immersion depth is 0.3 to 0.7 mm.

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