CN117612816A

CN117612816A - Thermal expansion protection piezoresistor, filler and preparation method thereof

Info

Publication number: CN117612816A
Application number: CN202311489127.XA
Authority: CN
Inventors: 罗有福
Original assignee: Chengdu Tieda Electronics Corp
Current assignee: Chengdu Tieda Electronics Corp
Priority date: 2023-11-09
Filing date: 2023-11-09
Publication date: 2024-02-27

Abstract

The invention belongs to the technical field of circuit protection devices, and discloses a thermal expansion protection piezoresistor which is arranged on a circuit board as an insert type piezoresistor to form a bleeder circuit, and the thermal expansion protection piezoresistor comprises a shell and a pressure sensitive module arranged in the shell, wherein the pressure sensitive module is provided with two pins, the pins penetrate out of the shell from an opening arranged at the lower part of the shell and are connected with an external circuit structure to form the bleeder circuit, an expansion part and an expansion extrusion part are further arranged in the shell, any part of the bleeder circuit which is connected in series on the pressure sensitive module is provided with an easily-broken part, the expansion part and the expansion extrusion part are respectively arranged at two sides of the easily-broken part, and the expansion part is heated to expand to push the expansion extrusion part to stretch the easily-broken part to form an open circuit.

Description

Thermal expansion protection piezoresistor, filler and preparation method thereof

Technical Field

The invention belongs to the technical field of circuit protection devices, relates to a piezoresistor, and in particular relates to a piezoresistor and a filler with thermal expansion protection and a preparation method thereof.

Background

The piezoresistor is a voltage limiting type protection device. By utilizing the nonlinear characteristic of the piezoresistor, when the overvoltage occurs between two poles of the piezoresistor, the piezoresistor can clamp the voltage to a relatively fixed voltage value, so that the protection of a subsequent circuit is realized. The main parameters of the piezoresistor are as follows: voltage-sensitive voltage, current capacity, junction capacitance, response time, etc. The response time of the piezoresistor is ns-level, is faster than that of the gas discharge tube and is slightly slower than that of the TVS tube, and the response speed of the overvoltage protection for the electronic circuit can meet the requirement under the general condition. The junction capacitance of the piezoresistor is generally in the order of magnitude of hundreds to thousands of Pf, and is not suitable for being directly applied to the protection of a high-frequency signal line in many cases, and when the piezoresistor is applied to the protection of an alternating current circuit, leakage current is increased due to the fact that the junction capacitance is large, and the leakage current needs to be fully considered when designing a protection circuit. The varistor has a larger current capacity but smaller than the gas discharge tube. The varistor is simply referred to as VDR, which is a voltage-sensitive nonlinear overvoltage protection semiconductor element.

For the on-board plug-in piezoresistor, the conventional form is an inner core and two pins, resin or other high polymer materials are wrapped outside, and the outer circuit is connected through the pins. The voltage dependent resistor has degradation, namely, the leakage current branch formed originally in the use process can cause short circuit due to the degradation, so that the problems of heating, ignition and the like are solved. In the prior art, in order to avoid the failure of external equipment caused by the deterioration short circuit fire, an explosion-proof shell is sleeved outside the explosion-proof shell, and a filler layer mainly comprising quartz sand is filled to form the filler layer, so that arc extinction can be realized, and meanwhile, the explosion-proof shell can also be insulated, so that the deterioration fire is prevented. However, although this structure prevents knocking, if it is not replaced in time, it always comes in a short-circuit state, and the external circuit is greatly affected. Even if the external circuit is provided with a safety structure, if the current cannot reach the threshold value of the action of the safety structure of the external circuit due to different degradation degrees, the hidden danger also exists.

In the prior art, there is a scheme that protection devices such as a built-in fuse and the like form extra protection measures, but for the smaller plug-in piezoresistor, the manufacturing difficulty is higher, the cost is higher, the internal structure needs to be changed, and for the explosion-proof piezoresistor with a filler layer, the filling effect of the filler needs to be considered, otherwise, the uniformity of the filler layer is influenced due to the arranged protection devices, and the effect of arc extinction and heat conduction cannot be achieved.

Disclosure of Invention

In order to solve the problems in the prior art, the invention provides the piezoresistor and the filler with thermal expansion protection and the preparation method thereof, and the expansion part and the expansion extrusion part are arranged in the piezoresistor and the filler, so that the structure with the easily-broken part is broken to form an open circuit by rapid expansion after being heated, the manufacturing cost is low, and the better protection effect can be achieved.

The technical scheme adopted by the invention is as follows:

the invention provides a thermal expansion protection varistor, which is arranged on a circuit board as an insert varistor to form a bleeder branch, and comprises a shell and a pressure-sensitive module arranged in the shell, wherein the pressure-sensitive module is provided with two pins, the pins penetrate out of the shell from an opening formed in the lower part of the shell and are connected with an external circuit structure to form the bleeder branch, an expansion part and an expansion extrusion part are also arranged in the shell, any part of the bleeder branch which is formed in series on the pressure-sensitive module is provided with a frangible part, the expansion part and the expansion extrusion part are respectively arranged on two sides of the frangible part, and the expansion part is heated to expand to push the expansion extrusion part to break the frangible part to form a break.

With reference to the first aspect, the present invention provides a first implementation manner of the first aspect, where the pressure sensitive module has an inner core, and the pins are connected at two ends of the inner core;

the expansion extrusion part is a sheet body arranged on any pin, the breakable part is arranged on the pin with the expansion extrusion part, the breakable part and the expansion part are both arranged between the expansion extrusion part and the inner core, the inner core is pushed to separate from the breakable part when the expansion part is heated and expanded, and the expansion extrusion part is pressed to displace towards the opening of the shell.

With reference to the first embodiment of the first aspect, the present invention provides a second embodiment of the first aspect, wherein the expansion portion is made of a thermal expansion material having an expansion pressure of not less than 1.0N/mm2, and a minimum thickness of not less than 1.5mm.

With reference to the first implementation manner of the first aspect, the present invention provides a third implementation manner of the first aspect, wherein the two pins are provided with frangible portions, and a single expansion extrusion portion is connected to the two pins at the same time. It should be noted that this method may be a preferable method, as long as it is ensured that a short circuit state is formed when one of the pins is disconnected.

With reference to the first implementation manner of the first aspect, the present invention provides a fourth implementation manner of the first aspect, wherein the two inner cores are wrapped with a filler layer, and the expansion part and the frangible part are both disposed between the filler layer and the expansion extrusion part.

With reference to the first implementation manner of the first aspect, the present invention provides a fifth implementation manner of the first aspect, two inner cores are wrapped with a filler layer, the expansion portion is disposed between the inner core and the filler layer, and the frangible portions are both disposed between the filler layer and the expansion extrusion portion.

With reference to the first aspect, the present invention provides a sixth implementation manner of the first aspect, where two pressure-sensitive modules have an inner core, and the pins have bonding conductive parts, and are connected to two ends of the inner core through the bonding conductive parts;

the two sides of the inner core are respectively attached with expansion extrusion parts which are independently formed or combined with the packaging layer for blocking the packaging shell into a whole, and the electric conductor with fastening pins is connected with the inner core and the attached electric conductor part through the electric conductor;

the expansion extrusion part is also provided with a bulge part with a gap with the surface for attaching the inner core, and the bulge part is filled in the bulge part and separates the whole expansion extrusion part from the inner core when being heated;

the shell is made of flame-retardant materials, and the shell expands and deforms when the expansion part expands under heating;

the packaging layer is formed by filling and sealing a block solid structure, a particle solid filler or a liquid material,the adhesive force between the adhesive and the shell is 0.3-1.2N/mm ² In the range, when the expansion part is heated and expanded, the packaging layer expands and deforms or is separated from the shell.

With reference to the first embodiment of the first aspect, the present invention provides a seventh embodiment of the first aspect, where the frangible portion is a portion with a thickness or a connection area smaller than 50% of a pin cross section;

or as a detachable connection of two sub-parts of the detachably connected pins;

or as a connection structure of two sub-portions of the pins connected by low temperature soldering.

In a second aspect, the present invention further discloses a filler, which is disposed in the casing of the thermal expansion protection varistor to form a filler layer, and includes, in parts by mass:

100 parts of 10-30 mesh quartz sand, 3-6 parts of ammonium polyphosphate, 2-5 parts of aluminum hydroxide and 0.2-2 parts of packed red phosphorus, and uniformly mixing the materials with 1-3 parts of adhesive to prepare the filler.

In a third aspect, the present invention also discloses a preparation method, which is used for preparing the piezoresistor with thermal expansion protection, and the specific steps are as follows:

after the inner core is connected with the pins to form the pressure-sensitive module, the pins of the pressure-sensitive module are processed to form the breakable parts and then are put into the shell together, the filling material is filled to form the filling layer, and the expansion part and the expansion extrusion part are arranged at the lower part of the filling layer, and then the filling layer is injected with glue, fixed and sealed to form the product.

The beneficial effects of the invention are as follows:

(1) According to the invention, the breakable part is arranged in the shell and matched with the expansion part, so that after the piezoresistor is invalid and deteriorated, the leakage branch can be disconnected by utilizing the heat generated by continuous short circuit to quickly react and expand, double protection is formed between the leakage branch and the pressure-sensitive module, and the possible ignition condition of the continuous short circuit can be avoided;

(2) According to the invention, the expansion part is matched with the expansion extrusion part in various modes, and the structures of various easily-broken parts are arranged, so that the production efficiency is improved, the production cost is reduced, and the connection can be disconnected when the expansion part is heated;

(3) According to the invention, through optimization of the type and the proportion of the filler, a better explosion-proof effect can be provided, and meanwhile, a better expansion heat conduction effect is realized by matching with the expansion part.

Drawings

FIG. 1 is a schematic view of an external axis of a varistor in an assembled state according to an embodiment of the present invention;

FIG. 2 is a schematic axial view of the internal structure of the first varistor with the casing cut away in accordance with the present invention;

FIG. 3 is a schematic plan view showing the internal structure of a first varistor according to an embodiment of the present invention after the casing is cut;

FIG. 4 is a schematic axial view of the internal structure of a second varistor according to the present invention with the casing cut away;

FIG. 5 is a schematic plan view showing the internal structure of a second varistor according to an embodiment of the present invention after the casing is cut away;

FIG. 6 is a schematic axial view of the internal structure of a third varistor according to the present invention with the housing cut away;

FIG. 7 is a schematic plan view showing the internal structure of a third varistor according to an embodiment of the present invention with a housing cut away;

FIG. 8 is a schematic diagram illustrating a first axial view of an internal structure of a fourth varistor according to an embodiment of the present invention with a housing cut away;

FIG. 9 is a second axial schematic view of the internal structure of a fourth varistor according to the present invention with the housing cut away;

FIG. 10 is a schematic illustration of an assembled axial view of a fifth varistor with a housing cut away according to an embodiment of the present invention;

FIG. 11 is a schematic axial view of a fifth varistor according to an embodiment of the present invention with the housing and internal portions of the varistor being cut away.

In the figure: 1-shell, 2-pin, 3-inner core, 4-expansion part, 5-breakable part, 6-expansion extrusion part, 7-glue sealing part, 8-laminating conductive part and 9-slot.

Detailed Description

The invention is further illustrated by the following description of specific embodiments in conjunction with the accompanying drawings.

For the purposes of making the objects, technical solutions and advantages of the embodiments of the present application more clear, the technical solutions of the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is apparent that the described embodiments are some embodiments of the present application, but not all embodiments. The components of the embodiments of the present application, which are generally described and illustrated in the figures herein, may be arranged and designed in a wide variety of different configurations.

Thus, the following detailed description of the embodiments of the present application, as provided in the accompanying drawings, is not intended to limit the scope of the application, as claimed, but is merely representative of selected embodiments of the application. All other embodiments, which can be made by one of ordinary skill in the art without undue burden from the present disclosure, are within the scope of the present disclosure.

It should be noted that: like reference numerals and letters denote like items in the following figures, and thus once an item is defined in one figure, no further definition or explanation thereof is necessary in the following figures.

In the description of the present application, it should be noted that, if the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," "outer," and the like indicate an azimuth or a positional relationship based on that shown in the drawings, or an azimuth or a positional relationship that a product of the application conventionally puts in use, it is merely for convenience of describing the present application and simplifying the description, and does not indicate or imply that the device or element to be referred to must have a specific azimuth, be configured and operated in a specific azimuth, and thus should not be construed as limiting the present application. Furthermore, the terms "first," "second," and the like in the description of the present application, if any, are used for distinguishing between the descriptions and not necessarily for indicating or implying a relative importance.

Furthermore, the terms "horizontal," "vertical," and the like in the description of the present application, if any, do not denote a requirement that the component be absolutely horizontal or overhang, but rather may be slightly inclined. As "horizontal" merely means that its direction is more horizontal than "vertical", and does not mean that the structure must be perfectly horizontal, but may be slightly inclined.

In the description of the present application, it should also be noted that, unless explicitly stated and limited otherwise, the terms "disposed," "mounted," "connected," and "connected" should be construed broadly, and may be, for example, fixedly connected, detachably connected, or integrally connected; can be mechanically or electrically connected; can be directly connected or indirectly connected through an intermediate medium, and can be communication between two elements. The specific meaning of the terms in this application will be understood by those of ordinary skill in the art in a specific context.

Example 1:

the embodiment discloses thermal expansion protection's piezo-resistor, sets up as plug-in components piezo-resistor and forms the bleeder branch on the circuit board, referring to fig. 1, including casing 1 and the pressure sensitive module of setting in casing 1, the pressure sensitive module has two pins 2 just the pin 2 wears out casing 1 and connects external circuit structure from the opening that casing 1 lower part had and form the bleeder branch, still has expansion portion 4 and inflation extrusion portion 6 in the casing 1, the pressure sensitive module is last to form the serial on the bleeder branch any place have frangible portion 5, expansion portion 4 and inflation extrusion portion 6 set up in frangible portion 5 both sides respectively, expansion portion 4 is heated the inflation and is promoted inflation extrusion portion 6 and break frangible portion 5 and form the circuit.

Meanwhile, the preparation method is used for preparing the piezoresistor with thermal expansion protection, and comprises the following specific steps: after the inner core 3 is connected with the pin 2 to form a pressure-sensitive module, the pin 2 of the pressure-sensitive module is processed to form a breakable part 5, the breakable part 5 is put into the shell 1 together, filler is filled to form a filler layer, and an expansion part 4 and an expansion extrusion part 6 are arranged at the lower part of the filler layer, and then glue injection, fixation and sealing are carried out to form the product.

Further, an embodiment is provided, referring to fig. 2 and 3, the pressure sensitive module has an inner core 3, and pins 2 are connected to both ends of the inner core 3; the expansion extrusion part 6 is a sheet body arranged on any pin 2, the breakable part 5 is arranged on the pin 2 with the expansion extrusion part 6, the breakable part 5 and the expansion part 4 are both arranged between the expansion extrusion part 6 and the inner core 3, the inner core 3 and the expansion extrusion part 6 are pushed to be separated from the breakable part 5 when the expansion part 4 is heated and expanded, and the expansion extrusion part 6 is pressed to be displaced towards the opening of the shell 1.

The breakable portion 5 in this embodiment is a structure in which the cross-sectional dimension formed by directly cutting the groove on the pin 2 on one side is smaller than 50% of the cross-section of the pin 2 itself, and the thickness after cutting the groove is generally only about 30% of the normal thickness.

It should be noted that, only the effect diagram is shown in the figure, that is, only the single-side lead 2 is provided with the material of the expansion portion 4 wrapping the single-side lead 2, and the expansion portion 4 is represented by a relatively standard block in the figure. In the actual product, according to the requirements of the use and the manufacturing process, an expansion part 4 mainly composed of the expansion material can be formed locally by filling the expansion material, and the expansion part is not limited to only having the expansion material, or an expansion body is separately arranged. The expansion extrusion part 6 is matched with the expansion part 4, is fixedly connected with the part of the pin 2 close to the breakable part 5, and can be transmitted to the part of the pin 2 at the connection part after being stressed to pull the breakable part 5 to break, and the area and the thickness of the expansion extrusion part are not limited, and the expansion extrusion part can be any structure which is fixedly connected with the part of the pin 2 and has a force transmission function.

Further, referring to fig. 4 and 5, in order to improve the sensitivity of the expansion breaking, one or more frangible portions 5 may be provided on each of the two pins 2, and the frangible portions 5 in this embodiment are also formed by cutting in a manner of slot, and the structure may be formed by directly cutting the corresponding position of the pin 2 during manufacturing, so that the manufacturing method is simple and low in cost, and the structure is fixed by filling or injecting glue in the housing 1, so as to be stable against external force.

The expansion and extrusion part 6 is a thinner sheet material, the area of which is close to the opening area of the shell 1, after the expansion and extrusion part is directly fixed on the two pins 2, the expansion part 4 is fixed between the expansion and extrusion part and the inner core 3, then the expansion and extrusion part and the inner core 3 are put into the shell 1 together, and finally the glue is injected to form and fix the glue sealing part 7. At this time, the inner core 3 is degraded and heated, the expansion part 4 is heated and expanded to apply extrusion force to the inner core 3 and the expansion extrusion part 6, and the shell 1 is hard material and cannot deform, but the opening part provided with the glue sealing part 7 can deform or even be damaged when being subjected to external force, at this time, the inner core 3 is kept stable relative to the shell 1, the expansion extrusion part 6 can displace outwards, and the pins 2 at two sides are pulled to be broken at the breakable parts 5 at the same time, so that broken circuit is formed.

Further, another embodiment is provided, the two inner cores 3 are wrapped with a packing layer, and the expansion part 4 and the frangible part 5 are arranged between the packing layer and the expansion extrusion part 6.

In another scheme, referring to fig. 6 and 7, the packing layer is wrapped outside the inner core 3, the expansion part 4 is arranged between the inner core 3 and the packing layer, and the frangible parts 5 are arranged between the packing layer and the expansion extrusion part 6.

Wherein the filler layer comprises the following components in parts by mass: 100 parts of 10-30 mesh quartz sand, 3-6 parts of ammonium polyphosphate, 2-5 parts of aluminum hydroxide and 0.2-2 parts of packed red phosphorus, and uniformly mixing the materials with 1-3 parts of adhesive to prepare the filler.

Further, referring to fig. 8 and 9, there is provided another embodiment, two pressure-sensitive modules having an inner core 3, a lead 2 having a bonded conductive portion 8, and expansion-extruded portions 6 respectively attached to both sides of the inner core 3 by the bonded conductive portion 8 and both ends of the inner core 3, the expansion-extruded portions 6 having electrical conductors by which the inner core 3 and the bonded conductive portion 8 are connected; the expansion-extrusion part 6 also has a bulge part with a gap from the attaching surface of the inner core 3, and the expansion part 4 is filled in the bulge part and separates the whole expansion-extrusion part 6 from the inner core 3 when heated; the shell 1 is made of fireproof soft materials, and the shell 1 expands and deforms when the expansion part 4 expands under heating.

It should be noted that, in this embodiment, the frangible portion 5 is a portion with a thickness or a connection area smaller than 50% of the cross section of the pin 2;

or as a detachable connection of two sub-parts of the detachably connected pin 2; referring to fig. 10 and 11, there is shown a detachable connection structure in which one side pin 2 includes two mutually sleeved sub-parts, wherein the sub-part connecting the inner core 3 has a slot 9, and the other sub-part is inserted into the slot 9 and is fixedly covered by the expansion 4.

Or as a connection structure of two sub-portions of the pin 2 connected by low temperature soldering.

In this embodiment, the expansion portion 4 is made of a heat-expandable material having an expansion pressure of not less than 1.0N/mm2 and a minimum thickness of not less than 1.5mm.

In order to verify the technical effects of the piezoresistor in the embodiment, which are different from those of the prior art, the experiment verification of the comparative example group is added:

the experimental samples are all prepared by uniformly mixing 100 parts of 10-30 mesh quartz sand, 5 parts of ammonium polyphosphate, 3 parts of aluminum hydroxide and 1 part of coated red phosphorus with a filler according to the weight of the 10-30 mesh quartz sand, 3 parts of aluminum hydroxide and 1 part of coated red phosphorus, wherein the breakable part 5 is formed by breaking two pins 2 close to the position of a pressure-sensitive body by 3-4mm and then welding with conventional soldering tin, and the comparison test is carried out by adding the expansion difference.

The experimental method comprises the following steps: the product is connected into a power supply with power of 30KVA, 550V alternating voltage of test voltage and 15-16A of short-circuit current, an ammeter is connected in series in the circuit to indicate actual current and confirm whether the circuit is disconnected, and the power is continuously supplied for 550V until the product is disconnected.

Experimental comparative example group one:

wherein the expansion block has a size of 10x6mm, a thickness of 3mm and an expansion pressure of 0.5N/mm ²

Experimental comparative example group two:

wherein the expansion block has a size of 10x6mm and a thickness of 3mm, and an expansion pressure of 1N +.mm ²

Experimental comparative example group three:

wherein the expansion block has a size of 10x6mm, a thickness of 1.5mm and an expansion pressure of 1N/mm ²

It can be seen that when the expansion pressure of the embodiment group shows that the expansion speed is lower than the specified value, even if the product is short-circuited and heated, the pin 2 of the breakable part 5 cannot be effectively separated, so that an effective open circuit is formed. When the thickness of the material having reached the set value is not equal to the set value, the breakable portion 5 cannot be effectively broken.

The invention is not limited to the alternative embodiments described above, but any person may derive other various forms of products in the light of the present invention. The above detailed description should not be construed as limiting the scope of the invention, which is defined in the claims and the description may be used to interpret the claims.

Claims

1. The utility model provides a thermal expansion protection's piezo-resistor, forms the bleeder branch as plug-in components piezo-resistor setting on the circuit board, includes casing (1) and sets up the pressure sensitive module in casing (1), pressure sensitive module has two pins (2) just pin (2) are worn out casing (1) and are connected external circuit structure from the opening that casing (1) lower part had and form bleeder branch, its characterized in that:

the shell (1) is internally provided with an expansion part (4) and an expansion extrusion part (6), any part on the pressure-sensitive module, which is connected in series, is provided with a frangible part (5), the expansion part (4) and the expansion extrusion part (6) are respectively arranged on two sides of the frangible part (5), and the expansion part (4) is heated to expand to push the expansion extrusion part (6) to break the frangible part (5) to form an open circuit.

2. A thermal expansion protected varistor according to claim 1, wherein: the pressure-sensitive module is provided with an inner core (3), and the pins (2) are connected to two ends of the inner core (3);

the expansion extrusion part (6) is a sheet body arranged on any pin (2), the breakable part (5) is arranged on the pin (2) with the expansion extrusion part (6), the breakable part (5) and the expansion part (4) are both arranged between the expansion extrusion part (6) and the inner core (3), the expansion part (4) pushes the inner core (3) and the expansion extrusion part (6) to separate from the breakable part (5) when being heated and expanded, and the expansion extrusion part (6) is pressed to displace towards the opening of the shell (1).

3. A thermal expansion protected varistor according to claim 2, wherein: the expansion part (4) adopts an expansion pressure not lower than 1.0N/mm ² Is made of a heat-expandable material having a minimum thickness of not less than 1.5mm.

4. A thermal expansion protected varistor according to claim 2, wherein: the two pins (2) are provided with frangible parts (5), and a single expansion extrusion part (6) is connected to the two pins (2) at the same time.

5. A thermal expansion protected varistor according to claim 2, wherein: the two inner cores (3) are externally wrapped with a packing layer, and the expansion part (4) and the frangible part (5) are both arranged between the packing layer and the expansion extrusion part (6).

6. A thermal expansion protected varistor according to claim 2, wherein: two outside parcel of inner core (3) has the packing layer, expansion portion (4) set up between inner core (3) and packing layer, frangible portion (5) all set up between packing layer and expansion extrusion portion (6).

7. A thermal expansion protected varistor according to claim 1, wherein: the two pressure-sensitive modules are provided with inner cores (3), the pins (2) are provided with attaching conductive parts (8), and the pins are connected with two ends of the inner cores (3) through the attaching conductive parts (8);

the two sides of the inner core (3) are respectively attached with expansion extrusion parts (6), the expansion extrusion parts (6) are independently formed or are combined with a packaging layer (7) for blocking the packaging shell (1) into a whole, the electric conductors with fastening pins (2) are connected with the inner core (3) and the attaching conductive parts (8) through the electric conductors;

the expansion extrusion part (6) is also provided with a bulge part with a gap with the attaching surface of the inner core (3), and the expansion part (4) is filled in the bulge part and separates the whole expansion extrusion part (6) from the inner core (3) when being heated;

the shell (1) is made of flame-retardant materials, and the shell (1) expands and deforms when the expansion part (4) is heated and expands;

the packaging layer (7) is formed by filling and sealing a block solid structure, a particle solid filler or a liquid material, and the adhesive force between the packaging layer and the shell (1) is 0.3-1.2N/mm ² In the range, when the expansion part (4) is heated and expanded, the packaging layer (7) expands and deforms or is separated from the shell (1).

8. A thermal expansion protected varistor according to claim 2, wherein: the frangible portion (5) is a portion with a thickness or a connection area smaller than 50% of the section of the pin (2);

or as a detachable connection of two sub-parts of the detachably connected pins (2);

or as a connection structure of two sub-portions of the pin (2) connected by low temperature soldering.

9. A filler, characterized in that: a filler layer formed in the casing (1) of the thermal expansion protected varistor according to claim 5 or 6, comprising, in parts by mass:

10. A method of preparation, characterized in that: a varistor for preparing a thermal expansion protection according to claim 7 or 8, comprising the steps of: after the inner core (3) is connected with the pins (2) to form a pressure-sensitive module, the pins (2) of the pressure-sensitive module are processed to form the frangible parts (5), the frangible parts are put into the shell (1) together, filler is filled to form a filler layer, and an expansion part (4) and an expansion extrusion part (6) are arranged at the lower part of the filler layer, and then glue injection, fixation and sealing are carried out to form a product.