A high resistance and low B value chip thermistor and preparation method thereof

Abstract

The present invention discloses a high-resistance, low-B-value chip thermistor and a preparation method thereof. The high-resistance, low-B-value chip thermistor comprises a thermistor ceramic layer, an insulating ceramic core and a terminal electrode; the thermistor ceramic layer is a hollow cylinder with a rectangular cross-section, the insulating ceramic core is a core filled in the hollow of the thermistor ceramic layer, the insulating ceramic core and the thermistor ceramic layer constitute a co-molded, one-piece thermistor monomer; the two ends of the co-molded, one-piece thermistor monomer are respectively provided with the terminal electrode plating layer. With the help of the specific structure of the co-molded, one-piece thermistor monomer, the chip thermistor of the present application can achieve high resistance and low B value, and has a simple structure and is easy to implement. In addition, the resistance of the product can be conveniently adjusted by simply changing the proportional relationship between the cross-sectional areas of the insulating ceramic core and the thermistor ceramic layer, and has a wide range of adaptability.

Description

Technical Field

[0001] The present invention relates to the technical field of resistor components, and in particular to a high-resistance and low-B-value chip thermistor and a preparation method thereof. Background Art

[0002] Electronic components are developing towards miniaturization and comprehensiveness. In particular, the complexity of the product application environment has put forward higher requirements on the size, structure and performance of the devices.

[0003] In the current industry, there is a chip NTC (negative temperature coefficient) thermistor that can be used for mass precision mounting. This NTC thermistor is easily limited by thermistor materials and cannot achieve high resistance values ​​under the condition of low B values. Therefore, in the entire system, thermistor components with high resistance and low B values ​​have become a vacancy in the series of products. In order to meet the needs of applications in high temperature environments, it is urgent to develop chip thermistors with high resistance and low B values ​​of the same size. Summary of the invention

[0004] In order to overcome the defects of the aforementioned prior art, the embodiment of the present application provides a high-resistance and low-B-value chip thermistor, comprising a thermistor ceramic layer, an insulating ceramic core and a terminal electrode; the thermistor ceramic layer is a hollow cylinder with a rectangular cross-section, the insulating ceramic core is a core filled in the hollow of the thermistor ceramic layer, the insulating ceramic core and the thermistor ceramic layer constitute a co-molded integrated thermistor monomer; the terminal electrodes are respectively provided at both ends of the co-molded integrated thermistor monomer.

[0005] The present invention can also adopt the following optional / preferred solutions:

[0006] The terminal electrode includes an inner terminal electrode layer, an intermediate terminal electrode layer and an outer terminal electrode layer which are tightly attached from the inside to the outside. The inner terminal electrode layer is in a cap shape and includes a bottom wall and a peripheral wall. The bottom wall of the inner terminal electrode layer is attached to the end of the co-molded integrated thermistor monomer. The peripheral wall of the inner terminal electrode layer extends a predetermined distance along the axial direction of the co-molded integrated thermistor monomer and is coated on the wall surface of the outer peripheral wall of the co-molded integrated thermistor monomer.

[0007] The length of the insulating ceramic core is equal to the length of the thermosensitive ceramic layer.

[0008] The cross-sectional width of the insulating ceramic core is less than or equal to 99% of the cross-sectional width of the thermosensitive ceramic layer, and the cross-sectional height of the insulating ceramic core is less than or equal to 99% of the cross-sectional height of the thermosensitive ceramic layer.

[0009] The thermosensitive ceramic layer has a rounded rectangular parallelepiped shape and a rounded rectangular or square cross section.

[0010] The insulating ceramic core is made of aluminum oxide, aluminum nitride or zirconium oxide ceramic material, and the thermistor ceramic layer is made of NTC thermistor ceramic material, PTC thermistor ceramic material or fixed value resistor material.

[0011] The present invention also provides a method for preparing a high-resistance and low-B-value chip thermistor, comprising the following steps:

[0012] Thermosensitive ceramic sheet production: Thermosensitive ceramic powder, plasticizer, binder and dispersant are made into a fluid slurry according to a predetermined ratio, and then made into a sheet through a casting process;

[0013] BAR block green body production, the sheet is stacked to a predetermined thickness, and a dense BAR block green body is formed by an isostatic pressing process;

[0014] Groove processing: processing a groove of a predetermined width and depth on the BAR block green body along the length direction;

[0015] Insulating ceramic core green body production, after the insulating ceramic powder is pressed and bonded, a dense insulating ceramic green body is obtained through an isostatic pressing molding process;

[0016] Strip-shaped ceramic body manufacturing, sintering the insulating ceramic core green body to obtain a polycrystalline sintered body, and cutting the sintered body to obtain a strip-shaped ceramic body;

[0017] One-piece green body manufacturing, filling the strip-shaped ceramic body into the groove of the BAR block green body, and covering the BAR block green body on the upper layer, and pressing through an isostatic pressing process to obtain an one-piece green body;

[0018] The green body of the common integrated thermistor is manufactured by cutting the green body in one direction to form a green body of the common integrated thermistor with the strip-shaped ceramic body as the core and the BAR block green body as the shell;

[0019] Co-firing, co-firing the green body of the co-molded integrated thermistor body to obtain a green body of the co-molded integrated thermistor body;

[0020] Cutting, cutting the co-molded integrated thermistor body into a plurality of co-molded integrated thermistor monomers of a predetermined length;

[0021] Terminal electrodes are plated at two ends of the co-molded integrated thermistor monomer.

[0022] Preferably, in the BAR block green body manufacturing step, the predetermined thickness is 1 / 3 to 2 / 3 of the green body thickness of the high resistance and low B value chip thermistor product.

[0023] Preferably, the thickness of the BAR block green body covering the upper layer is smaller than the thickness of the BAR block green body provided with the groove.

[0024] Preferably, after the co-firing step and before the terminal electrodes are plated, the co-molded integrated thermistor monomer is chamfered.

[0025] One or more technical solutions provided in the embodiments of the present application have at least the following beneficial effects compared with the prior art:

[0026] Through the co-molded integrated thermistor monomer, the chip thermistor of the present application can achieve high resistance and low B value, and has a simple structure and is easy to implement. In addition, the resistance of the product can be easily adjusted by simply changing the cross-sectional area ratio of the insulating ceramic core and the thermistor ceramic layer, and has a wide range of adaptability. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1A This is a main structural cross-sectional view of the high-resistance and low-B-value chip NTC thermistor according to the first embodiment of the present application;

[0028] Figure 1B A schematic diagram of the top view of the high resistance and low B value chip NTC thermistor of the first embodiment of the present application;

[0029] Figure 1C for Figure 1B Schematic diagram of the cross-sectional structure along the AA direction;

[0030] Figure 2 This is a process flow chart of Example 2 of the present application;

[0031] Figure 3 It is a line graph comparing the electrical properties of conventional design products and the embodiment products of the present application. DETAILED DESCRIPTION

[0032] High-resistance devices consume less power, but due to material properties, high-resistance materials will also have high B values, that is, due to the development limitations of the material itself, it is impossible to make high-resistance and low-B-value materials. Therefore, under given size limitations, high-resistance chip thermistors with low B-value characteristics cannot be achieved. In addition, under the condition of meeting a specific B value, its resistivity cannot be adjusted to a large extent from the perspective of material development.

[0033] The present invention proposes a structure of a chip thermistor with high resistance and low B value. The thermistor adopts a process of co-firing insulating ceramic and thermistor green body. By replacing part of the thermistor with insulating ceramic, it is equivalent to reducing the cross-sectional area of ​​the thermistor body, thereby realizing the design of the electrical properties of the device, thereby breaking through the limitations caused by material properties.

[0034] Terminology Note:

[0035] In the present application, green tape refers to a semi-finished product after a uniformly ball-milled slurry is cast on a release film and dried; BAR block refers to a semi-finished product after multiple layers of green tapes are stacked and pressed together; a co-molded integrated thermistor body refers to a co-molded integrated structure formed by a strip-shaped thermistor ceramic core as a core and an insulating ceramic skeleton composed of a BAR block of a first thickness and a BAR block of a second thickness as a shell, which is the main structure of multiple thermistors; a co-molded integrated thermistor monomer refers to a main structure of a single thermistor obtained by cutting the co-molded integrated thermistor body according to a predetermined size.

[0036] In order to better understand the above technical solution, the following is combined with the accompanying drawings Figure 1A , Figure 1B , Figure 1C , Figure 2 and Figure 3 The present invention is further described in detail with specific embodiments, wherein the same reference numerals represent the same components unless otherwise specifically stated. It should be emphasized that the following description is merely exemplary and is not intended to limit the scope of the present invention and its application. The background section of the present invention may contain background information about the problem or environment of the present invention, but does not necessarily describe the prior art. Therefore, the content contained in the background technology section is not an admission of the applicant to the prior art.

[0037] Embodiment 1

[0038] This embodiment provides a high resistance and low B value chip NTC thermistor, such as Figure 1A , Figure 1B and Figure 1C As shown, it includes a thermistor ceramic layer 1, an insulating ceramic core 2 and terminal electrodes. The length, width and height of the high resistance and low B value chip NTC thermistor are L1, W1 and H1 respectively, the length, width and height of the thermistor ceramic layer 1 are L2, W2 and H2 respectively, the length, width and height of the insulating ceramic core 2 are L2, W3 and H3 respectively, and W3<W2, H3<H2.

[0039] The thermistor layer 1 is a hollow cylinder with a rounded rectangular shape and a rounded rectangular cross section. The insulating ceramic core 2 is a core filled in the hollow of the thermistor layer 1. The length of the insulating ceramic core 2 is equal to the length of the thermistor layer 1. The cross-sectional width of the insulating ceramic core 2 is less than or equal to 99% of the cross-sectional width of the thermistor layer 1, and the cross-sectional height of the insulating ceramic core 2 is less than or equal to 99% of the cross-sectional height of the thermistor layer 1. The insulating ceramic core 2 and the thermistor layer 1 constitute a co-molded integrated thermistor monomer. Preferably, the cross section of the insulating ceramic core 2 is located in the center of the cross section of the thermistor layer 1.

[0040] The terminal electrodes are respectively provided at both ends of the co-molded integrated thermistor monomer. Preferably, the terminal electrodes include an inner terminal electrode layer (3a, 3b), an intermediate terminal electrode layer (4a, 4b) and an outer terminal electrode layer (5a, 5b) which are tightly attached from the inside to the outside, the inner terminal electrode layer (3a, 3b) is in a cap shape, including a bottom wall and a peripheral wall, the bottom wall of the inner terminal electrode layer (3a, 3b) is attached to the end of the co-molded integrated thermistor monomer, the peripheral wall of the inner terminal electrode layer (3a, 3b) extends a predetermined distance along the axial direction of the co-molded integrated thermistor monomer, and is coated on the wall surface of the outer peripheral wall of the co-molded integrated thermistor monomer. Further preferably, the thickness decreases from the inner terminal electrode layer (3a, 3b) to the intermediate terminal electrode layer (4a, 4b) and then to the outer terminal electrode layer (5a, 5b). More preferably, the thickness of the ends of the terminal electrode inner layer (3a, 3b), the terminal electrode middle layer (4a, 4b) and the terminal electrode outer layer (5a, 5b) extending in the axial direction are gradually reduced.

[0041] The insulating ceramic core 2 can be made of alumina, aluminum nitride or zirconium oxide ceramic material. In addition, the structure of this embodiment is also applicable to high-resistance chip PTC thermistors and high-resistance chip fixed-value resistors, that is, the thermistor ceramic layer 1 can be made of NTC thermistor ceramic material, PTC thermistor ceramic material or fixed-value resistor material.

[0042] Embodiment 2

[0043] A method for preparing a high-resistance and low-B-value chip NTC thermistor, which is used to prepare the high-resistance and low-B-value chip NTC thermistor as described in the above embodiment, such as Figure 2 As shown, the following steps are included:

[0044] Thermosensitive ceramic tablets are made by preparing a fluid slurry with thermosensitive ceramic powder, plasticizer, binder and dispersant in a predetermined ratio, and then forming tablets through a tape casting process. The fluid slurry is made through a ball milling process, and the tablets are specifically made by transferring the slurry to a release film through tape casting, and then cutting into square tablets.

[0045] The BAR block green body is made by laminating the sheet to a predetermined thickness and forming a dense BAR block green body through an isostatic pressing process. In this embodiment, at least two types of BAR block green bodies are made. The first type is to laminate the sheet to about half of the product green body height as a BAR block green body for subsequent groove processing, but it is not limited to this. The predetermined thickness can be selected between 1 / 3 and 2 / 3 of the product green body height. The second type is to laminate the sheet to a relatively thin BAR block green body, such as a thickness less than 1 / 3 of the product green body height.

[0046] Groove processing: processing a groove of predetermined width and depth along the length direction on the first BAR block green body. This operation can be performed by using a grinding wheel cutter to perform complex cutting on a thicker BAR block with a certain blade height, thereby constructing a groove of width W3 on the BAR block green body.

[0047] Insulating ceramic core green body production, after the insulating ceramic powder is pressed and bonded, a dense insulating ceramic green body is obtained through an isostatic pressing process. Specifically, a certain amount of insulating ceramic powder is first loaded into a pressing mold for pressing, so that the powder is pre-bonded together, and then the powder is further pressed into a dense green body through an isostatic pressing process.

[0048] The strip-shaped ceramic body is made by sintering the insulating ceramic core green body to obtain a polycrystalline sintered body, and cutting the sintered body to obtain a strip-shaped ceramic body. Specifically, the insulating ceramic core green body is placed in a box-type sintering furnace for sintering to form a dense polycrystalline sintered body. Then, the sintered body is cut into circular ceramic pieces using an inner circle cutting process, and further made into a strip-shaped ceramic body with a width of W3 and a height of H3 using a grinding wheel cutting machine.

[0049] The one-piece green body is manufactured by filling the strip-shaped ceramic body into the groove of the first BAR block green body, and covering the second BAR block green body on the upper layer, and pressing them together through an isostatic pressing process to obtain an one-piece green body.

[0050] The green body of the common integrated thermistor is produced by cutting the green body in one direction to form a green body of the common integrated thermistor with the strip ceramic body as the core and the BAR block green body as the shell. The one-way cutting here is cutting along the direction of the insulating ceramic core between adjacent insulating ceramic cores to ensure that the structure after sintering meets the expectations, and not cutting may cause problems such as cracking.

[0051] Co-firing, co-firing the green body of the co-molded integrated thermistor body to obtain the green body of the co-molded integrated thermistor body. The co-firing step can be performed by a box-type sintering furnace.

[0052] Cutting: cutting the co-molded integrated thermistor body into a plurality of co-molded integrated thermistor monomers of a predetermined length. The cutting can preferably be performed using a grinding wheel cutter, and the product obtained by this processing method has uniform and stable dimensions.

[0053] The terminal electrode plating layer is to seal the terminal electrodes at both ends of the co-molded integrated thermistor monomer, and then electroplate the electrodes after high temperature sintering. The conventional nickel plating and then tin plating process can be adopted, and the finished chip NTC thermistor can be obtained after cleaning and drying.

[0054] In addition, the co-molded integrated thermistor monomer is chamfered, and the chamfering can be performed by using a planetary chamfering machine to chamfer the cut ceramic body at a predetermined frequency.

[0055] The processing method of this embodiment can be used to design different electrical properties by changing the groove size and the cross-sectional width W3 and height H3 of the insulating ceramic body. Taking the 1005 size product as an example, the cross-sectional dimensions W3×H3 of the insulating ceramic body are designed to be 0.1mm×0.1mm, 0.2mm×0.2mm and 0.3mm×0.3mm respectively. The obtained product is compared with a conventional product without an insulating layer. The electrical properties detected are as follows: Figure 3 As shown, according to the structure in the figure, it can be seen that the resistivity of components of conventional products without insulating layers is about 40kΩ, while the electrical properties of devices using insulating layers with a cross-section of 0.1mm×0.1mm are about 42kΩ, the electrical properties of devices using insulating layers with a cross-section of 0.2mm×0.2mm are about 49.85kΩ, and the electrical properties of devices using insulating layers with a cross-section of 0.3mm×0.3mm are about 72kΩ. It can be seen that by adding an insulating layer, the resistance value of the device can be designed and the resistance value of the device can be significantly improved.

[0056] The processing method of this embodiment is also applicable to high-resistance chip PTC thermistors and high-resistance chip fixed resistors. Moreover, the process steps are simple, the precision requirements are low, it is easy to mass produce, and the production efficiency is high. The traditional manufacturing process of isoelectric thin film thermistors includes high-precision processes such as sputtering and laser etching, and processes such as sputtering, etching, and laser resistance adjustment that need to be repeatedly operated, which is complex, inefficient, and costly.

[0057] Although the preferred embodiments of the present invention have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0058] Those skilled in the art may combine and associate different embodiments or examples and features of different embodiments or examples described in this specification without mutual contradiction.

[0059] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A method for preparing a high resistance and low B value chip thermistor, characterized in that The steps include: Thermosensitive ceramic sheet production: Thermosensitive ceramic powder, plasticizer, binder and dispersant are made into a fluid slurry according to a predetermined ratio, and then made into a sheet through a casting process; BAR block green body production, the sheet is stacked to a predetermined thickness, and a dense BAR block green body is formed by an isostatic pressing process; Groove processing: processing a groove of a predetermined width and depth on the BAR block green body along the length direction; Insulating ceramic core green body production, after the insulating ceramic powder is pressed and bonded, a dense insulating ceramic green body is obtained through an isostatic pressing molding process; Strip-shaped ceramic body manufacturing, sintering the insulating ceramic core green body to obtain a polycrystalline sintered body, and cutting the sintered body to obtain a strip-shaped ceramic body; One-piece green body manufacturing, filling the strip-shaped ceramic body into the groove of the BAR block green body, and covering the BAR block green body on the upper layer, and pressing through an isostatic pressing process to obtain an one-piece green body; The green body of the common integrated thermistor is manufactured by cutting the green body in one direction to form a green body of the common integrated thermistor with the strip-shaped ceramic body as the core and the BAR block green body as the shell; Co-firing, co-firing the green body of the co-molded integrated thermistor body to obtain a green body of the co-molded integrated thermistor body; Cutting, cutting the co-molded integrated thermistor body into a plurality of co-molded integrated thermistor monomers of a predetermined length; Terminal electrodes are plated at two ends of the co-molded integrated thermistor monomer.

2. The method for preparing a high resistance and low B value chip thermistor according to claim 1, characterized in that: In the BAR block green body manufacturing step, the predetermined thickness is 1 / 3 to 2 / 3 of the thickness of the green body of the co-molded integrated thermistor body.

3. The method for preparing a high resistance and low B value chip thermistor according to claim 1, characterized in that: The thickness of the BAR block green body covered on the upper layer is smaller than the thickness of the BAR block green body provided with the groove.

4. The method for preparing a high resistance and low B value chip thermistor according to claim 1, 2 or 3, characterized in that: After the co-firing step and before the terminal electrode plating step, the co-molded integrated thermistor monomer is chamfered.

5. A high resistance and low B value chip thermistor prepared by the preparation method according to any one of claims 1 to 4, characterized in that: It includes a thermal-sensitive ceramic layer, an insulating ceramic core and terminal electrodes; The thermistor ceramic layer is a hollow cylinder with a rectangular cross section, the insulating ceramic core is a core filled in the hollow of the thermistor ceramic layer, and the insulating ceramic core and the thermistor ceramic layer constitute a co-molded integrated thermistor monomer; The terminal electrodes are respectively disposed at both ends of the co-molded integrated thermistor monomer.

6. The high resistance and low B value chip thermistor as claimed in claim 5, characterized in that: The terminal electrode includes an inner terminal electrode layer, an intermediate terminal electrode layer and an outer terminal electrode layer which are tightly attached from the inside to the outside. The inner terminal electrode layer is in a cap shape and includes a bottom wall and a peripheral wall. The bottom wall of the inner terminal electrode layer is attached to the end of the co-molded integrated thermistor monomer. The peripheral wall of the inner terminal electrode layer extends a predetermined distance along the axial direction of the co-molded integrated thermistor monomer and is coated on the wall surface of the outer peripheral wall of the co-molded integrated thermistor monomer.

7. The high resistance and low B value chip thermistor as claimed in claim 5, characterized in that: The length of the insulating ceramic core is equal to the length of the thermosensitive ceramic layer.

8. The high resistance and low B value chip thermistor as claimed in claim 5, characterized in that: The cross-sectional width of the insulating ceramic core is less than or equal to 99% of the cross-sectional width of the thermistor ceramic layer, and the cross-sectional height of the insulating ceramic core is less than or equal to 99% of the cross-sectional height of the thermistor ceramic layer.

9. The high resistance and low B value chip thermistor according to claim 5, characterized in that: The thermosensitive ceramic layer has a rounded rectangular parallelepiped shape and a rounded rectangular or square cross section.

10. The high resistance and low B value chip thermistor according to any one of claims 5 to 9, characterized in that: The insulating ceramic core is made of alumina, aluminum nitride or zirconium oxide ceramic material, and the thermistor ceramic layer is made of NTC thermistor ceramic material or PTC thermistor ceramic material.

Images