WO2006080805A1

WO2006080805A1 - Surface-mounting type thermistor having multi layers and method for manufacturing the same

Info

Publication number: WO2006080805A1
Application number: PCT/KR2006/000293
Authority: WO
Inventors: Jong-Hwan Lee; Jun-Ku Han; Anna Lee; Ju-Dam Kim; Young-Jun Lee; Su-An Choi
Original assignee: Ls Cable Ltd.
Priority date: 2005-01-27
Filing date: 2006-01-25
Publication date: 2006-08-03
Also published as: KR100685088B1; KR20060086869A

Abstract

A surface-mounting thermistor with multi layers is configured so that at least two film resistance elements having electrodes patterned to symmetrically engage with each other with a non-conductive gap interposed therebetween are connected in parallel. Thus, a resistance is reduced without increasing a surface size of the film resistance element, so a resistance characteristic of the thermistor at a normal temperature is improved, and Tombstone phenomenon caused by an asymmetric structure is prevented. In addition, an intermediate insulation layer having a thermal expansion coefficient of 0.001/°C or below, a volume resistance of 5000 Ωcm or above, a dielectric strength of 1 KV/mm or above, and a coating adhesion of 0.5 kg/cm or above is interposed between the film resistance elements laminated in parallel. Thus, the thermistor has excellent durability, thermal resistance and dielectric strength and also is capable of preventing current leakage.

Description

SURFACE-MOUNTING TYPE THERMISTOR HAVING MULTI LAYERS AND METHOD FOR MANUFACTURING THE SAME

Technical Field

[1] The present invention relates to a thermistor and its manufacturing method, and more particularly to a thermistor surface-mounted to a printed circuit board (PCB) for protecting a circuit from overcurrent and its manufacturing method. Background Art

[2] A certain conductive material changes its inherent resistance depending on temperature. A resistance element using such a conductive material is commonly called a thermistor, which is representatively classified into a NTC (Negative Temperature Coefficient) element whose resistance is reduced as temperature rises and a PTC (Positive Temperature Coefficient) element whose resistance is increased as temperature rises.

[3] In particular, the PTC element allows current to pass through it at a low temperature such as a normal temperature since its resistance is low, while its resistance is increased 10 to 10 times when surrounding temperature rises or temperature of a material is increased due to overcurrent, thereby intercepting a current.

[4] Such a PTC element may be applied as various kinds of electric devices in connection with metal electrodes, and it is mainly used for intercepting overcurrent or protecting a circuit in an electric circuit. In particular, a device using the PTC element is generally mounted and used on a PCB. Recently, demands for decreasing size and weight of parts on the PCB due to high integration of a circuit design, so there are many limits to the shape of PTC element.

[5] In order to cope with the above, many techniques have been proposed up to now.

For example, manufacturing techniques of a PCT device are disclosed in US 6,020,808, US 6,157,289, US 6,172,591, US 6,188,308, US 6,223,423, US 6,236,302, US 6,242,997, US 6,377,467, US 6,348,852, US 6,380,839 and so on.

[6] Now, a general thermistor will be described in brief. A thermistor is generally configured so that electrodes are laminated on upper and lower surfaces of a film- shaped PCT material layer. The thermistor configured as above is mounted by soldering an electrode formed on a lower surface of the thermistor to an electrode pad already formed on the PCB surface. At this time, in order to connect the electrode formed on the upper surface of the thermistor to the electrode on the PCB, a separated wire is required and also processes and spare on the PCB are also required as much. Thus, in order to escape the above problems, an electrode formed on a lower surface of the thermistor is formed on a partial region of the lower surface of the thermistor, not on the entire region thereof, and a metal pattern separated from the electrode is formed on a remained region. The metal pattern and the upper electrode are electrically connected via a side of the PTC material layer. Then, when the thermistor is mounted on the PCB, the electrode and the metal pattern on the lower surface of the thermistor may be respectively soldered to corresponding electrode pads, so a separate wire or space is not required.

[7] However, the thermistor configured as above has the following problems.

[8] First, there arise so-called Tombstone phenomenon or Manhattan phenomenon.

When the thermistor is mounted to the PCB, a thermistor already having a solder coating on a lower electrode and a metal pattern on the lower surface of the thermistor is usually arranged on an electrode pad of the PCB, and then heat is applied thereto so the solder is reflowed. However, the heat applied at this time makes the PTC material and the electrode material of the thermistor be expanded with different coefficients of thermal expansion. In particular, since the above thermistor configured so that the metal pattern on the lower surface and the upper electrode are connected via a side of the PTC material layer structurally has an asymmetric shape, stress distribution is not regular in right and left portions and thus the PCB thermistor is inclined. As a result, physical and electrical reliability of the soldering is remarkably deteriorated. In order to decrease the above problem, US 6,380,839 proposes a structure that a thermal stress relief area is formed on the upper and lower electrodes, but it cannot give a fundamental solution.

[9] In addition, the connection between the upper electrode and the metal pattern on the lower surface through the side of the PTC material layer deteriorates physical and electric reliability. That is to say, the side of the PTC material layer receives much expansion pressure of the PTC material due to the heat applied at the solder reflow or the temperature rise while the thermistor is used. If the stress caused by the expansion pressure makes a crack in a connection portion formed in the side of the PTC material layer, this crack is propagated along the side of the PTC material, which may result in electric disconnection.

[10] Meanwhile, in the prior art including the above US patents, the thermistor is manufactured as follows. That is to say, a plurality of long slits are formed in parallel in a sheet having a PTC material layer on both surfaces of which is coated with a metal film such as aluminum foil, and the electrodes or metal patterns on the upper and lower surfaces are electrically connected through the slits. Namely, the slit becomes the side of the PTC material layer described above. A desired electrode pattern is formed between the slits, and then following processes such as solder resist coating and solder coating are conducted to successively form a plurality thermistors between the slits. Finally, the sheet is cut in a direction perpendicular to the slit, which allows mass production of the same thermistors.

[11] However, if long slits are formed in the sheet as mentioned above, a center portion of the slit may be drooped down due to the gravity or twisted due to heat during the manufacturing process. It may cause inexact formation of patterns during electrode patterning or solder resist coating, which results in increase of an error rate.

[12] Meanwhile, in order to use the thermistor even in a high current power system, it is required to lower an initial resistance of the PTC element so that the power system may allow sufficient electric flow even in a high current that is an ordinary current. In case the PTC element is made of the same material, it may be considered to decrease a thickness of the PTC element or increase a size of the PTC element so as to lower a resistance of the PTC element. However, if the thickness of the PTC element is decreased, dielectric breakdown of the PTC element may occur when a high voltage is applied thereto. In addition, since surface-mounting products are generally classified depending on an area size and their technique pursues a smaller size, it is not desirable to increase an area of the PTC element in case a thermistor is used as a surface- mounting device. Disclosure of Invention Technical Problem

[13] The present invention is designed in consideration of the above problems, and therefore it is an object of the invention to provide a thermistor, which lowers its initial resistance without increasing area or thickness of the thermistor used as a surface- mounting device, and also does not generate current leakage due to excellent thermal resistance, durability and dielectric strength.

[14] In addition, an object of the present invention is to provide a thermistor, which may solve Tombstone phenomenon described above and also have a configuration in which connection portions of upper and lower electrode along a side of a thermistor material layer may ensure a crack well.

[15] In addition, an object of the present invention is to provide a method for manufacturing a thermistor, which may be mass-produced without causing twist or error.

Technical Solution

[16] In order to accomplish the above object, the present invention provides a thermistor configured with multi layers to have at least two film resistance elements arranged so that both surfaces face each other, thereby capable of lowering an initial resistance of the thermistor.

[17] In addition, the electrode patterns separately formed on both surfaces of the film resistance element have a symmetrically engaged shape with a non-conductive gap interposed between them, so it is possible to fundamentally prevent Tombstone phenomenon caused by an asymmetric structure.

[18] That is to say, in one aspect of the present invention, there is provided a thermistor, which includes at least two film resistance elements laminated and changing a resistance depending on temperature; first and second upper electrodes laminated on an upper surface of each film resistance element to be symmetrically engaged with each other with a non-conductive gap interposed therebetween; first and second lower electrodes laminated on a lower surface of each film resistance element to be symmetrically engaged with each other with a non-conductive gap interposed therebetween; an intermediate insulation layer interposed between the film resistance elements respectively; a first connection portion for electrically connecting the first upper electrode to the first lower electrode respectively; a second connection portion for electrically connecting the second upper electrode to the second lower electrode respectively; a first insulation layer prepared on upper surfaces of the first and second upper electrodes of the film resistance element positioned at a top layer of the film resistance elements; and a second insulation layer prepared on lower surfaces of the first and second lower electrodes of the film resistance element positioned at a lowest layer of the film resistance elements.

[19] At this time, a pattern of the first and second electrodes of each of the at least two film resistance elements is rotationally symmetric with a pattern of the first and second electrodes, and a pattern of the first and second electrodes of the top-layer film resistance element is symmetric with a pattern of the first and second lower electrodes of the lowest-layer film resistance element so that the same electrode pattern is shown on a surface when the thermistor is turned over.

[20] In addition, the non-conductive gap may have a crank shape, a rectangular uneven pattern, a zigzag shape or a waved shape.

[21] According to one embodiment of the present invention, the first connection portion electrically connects the first upper electrode and the first lower electrode of each film resistance element with surrounding one side of the at least two film resistance elements, and the second connection portion electrically connects the second upper electrode and the second lower electrode of each film resistance element with surrounding the other side of the at least two film resistance element, opposite to the above one side.

[22] In addition, in order to accomplish the above object, the thermistor of the present invention includes a plurality of film resistance elements connected in parallel, and an intermediate insulation layer having predetermined properties is interposed between them to lower the entire resistance of the thermistor.

[23] That is to say, in another aspect of the present invention, there is also provided a thermistor, which includes at least two film resistance elements prepared to face each other and changing a resistance depending on temperature; upper and lower electrodes laminated on both sides of each film resistance element; an intermediate insulation layers interposed between the film resistance elements respectively and having a thermal expansion coefficient of 0.001/°C or below, a volume resistance of 5000 Ωcm or above, a dielectric strength of 1 KV/mm or above, and a coating adhesion of 0.5 kg/ cm or above; a first connection portion for selectively electrically connecting the upper and lower electrodes of each film resistance element with surrounding one side of the at least two film resistance elements; a second connection portion for selectively electrically connecting the upper and lower electrodes of each film resistance element with surrounding the other side of the at least two film resistance element; a first insulation layer prepared on an upper surface of the upper electrode of the film resistance element position in a top layer of the film resistance elements; and a second insulation layer prepared on a lower surface of the lower electrode of the film resistance element positioned in a lowest layer of the film resistance elements.

[24] Meanwhile, in order to accomplish the above object, the present invention provides a thermistor manufacturing method, which manufactures a thermistor by forming a plurality of oval or circular through holes in a film resistance sheet in a matrix pattern. Thus, twist or interiority of the sheet occurring when long slits are formed may be remarkably decreased.

[25] That is to say, in still another aspect of the present invention, there is also provided a method for manufacturing a thermistor, which includes preparing at least two sheets in which metal films are laminated on both sides of a film resistance element whose resistance is changed depending on temperature; patterning both sides of each metal film of the sheet to form an electric pattern; preparing insulation material layers between the sheets, on an upper surface of a top-layer sheet, and on a lower surface of a lowest-layer sheet respectively and then uniting the sheets; forming a plurality of through holes having a predetermined shape in the united sheets in a matrix shape; connecting the metal films formed on both sides of the sheets through sidewalls of the through holes; and cutting the sheets having the electrode pattern in a width direction of the through holes so that a region between adjacent through holes becomes one unit.

[26] According to this embodiment, the thermistor manufacturing method may further include, between the metal film electrically connecting step and the sheet cutting step: coating solder resists on both sides of the sheet on which the electrode pattern is formed, except a portion in and around the through hole; and forming a solder to the electrode pattern in and around the through hole on which the solder resist is not coated.

[27] In addition, according to one embodiment, the intermediate insulation layer preferably has a thermal expansion coefficient of 0.001/°C or below, a volume resistance of 5000 Ωcm or above, a dielectric strength of 1 KV/mm or above, and a coating adhesion of 0.5 kg/cm or above.

Brief Description of the Drawings

[28] These and other features, aspects, and advantages of preferred embodiments of the present invention will be more fully described in the following detailed description, taken accompanying drawings. In the drawings:

[29] FlG. 1 is a perspective view showing a thermistor according to a preferred embodiment of the present invention;

[30] FlGs. 2 to 8 are a plane view showing examples of electrode patterns adopted in the thermistor according to the present invention;

[31] FlGs. 9 and 10 are sectional views taken along the line πi-III of FlG. 3, showing a current flow in the thermistor according to the present invention;

[32] FlG. 11 is a perspective view schematically showing a thermistor according to another embodiment of the present invention;

[33] FlG. 12 is a sectional view taken along the line IV-IV of FlG. 11 showing the thermistor;

[34] FlG. 13 is a sectional view schematically showing a thermistor according to a modification of the present invention;

[35] FlGs. 14 to 21 are drawings illustrating a method for manufacturing a thermistor according to a preferred embodiment of the present invention;

[36] FlG. 22 is a plane view illustrating a method for manufacturing a thermistor according to another embodiment of the present invention; and

[37] FlG. 23 is a plane view illustrating a method for manufacturing a thermistor according to still another embodiment of the present invention. Best Mode for Carrying Out the Invention

[38] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Prior to the description, it should be understood that the terms used in the specification and the appended claims should not be construed as limited to general and dictionary meanings, but interpreted based on the meanings and concepts corresponding to technical aspects of the present invention on the basis of the principle that the inventor is allowed to define terms appropriately for the best explanation. Therefore, the description proposed herein is just a preferable example for the purpose of illustrations only, not intended to limit the scope of the invention, so it should be understood that other equivalents and modifications could be made thereto without departing from the spirit and scope of the invention.

[39] FlG. 1 is a perspective view showing a thermistor according to a preferred embodiment of the present invention.

[40] Referring to FlG. 1, the thermistor of this embodiment includes at least two film resistance elements 110 changing a resistance depending on temperature, upper and lower electrodes 120, 130 respectively laminated on upper and lower surfaces of the film resistance elements 110, an intermediate insulation layer 140 interposed between the film resistance elements 110, a connection portion 150 for electrically connecting the upper and lower electrodes 120, 130, and first and second insulation layers 141, 142 prepared on an upper surface of the upper electrode of a top-layer resistance element among the film resistance element 110 and on a lower surface of the lower electrode of a lowest-layer resistance element. Hereinafter, the thermistor having two film resistance elements will be described in detail as an example.

[41] The film resistance elements 110 has a film shape with both surfaces, and a first film resistance element 111 and a second film resistance element 112 are arranged and connected in parallel so that their one surfaces face each other. Thus, it is possible to reduce an entire resistance without increasing a thickness or increasing an area of the film resistance elements 110.

[42] In addition, the film resistance element 110 includes a polymer element containing conductive particles dispersed therein to have a PTC nature, or alternatively a NTC nature. The polymer element includes polymer, conductive particles and antioxidant. The polymer may use HDPE (high-density polyethylene), LDPE (low-density polyethylene), PVDF (polyvinylidene fluoride), polypropylene, or ethylene/propylene polymer. The conductive particles may use carbon, metal or metal oxide. In addition, the PTC polymer may a specific resistance of 0.1 to 0.2 Ωcm at a normal temperature. However, the present invention is not limited to such materials.

[43] Meanwhile, though this embodiment adopts the film resistance elements 110 having two laminated layers including the first and second film resistance elements 111, 112, the number of film resistance elements may be selected in a range that the thickness of the entire thermistor is not too great but the film resistance elements may be connected in parallel to reduce a whole resistance of the thermistor.

[44] The upper electrode 120 and the lower electrode 130 are made of metal such as aluminum, copper or copper alloys, and they may be configured in various ways.

[45] For example, the upper electrode 120 may be configured to be symmetrically engaged with a non-conductive gap interposed therebetween. More specifically, the upper electrode 120 is composed of first and second upper electrodes 121a, 122a formed on the upper surface of the first film resistance element 111 and first and second upper electrodes 121b, 122b formed on the upper surface of the second film resistance element 122.

[46] In addition, the lower electrode 130 may also be configured to be symmetrically engaged with a non-conductive gap interposed therebetween. The lower electrode 130 is composed of first and second lower electrodes 131a, 132a formed on the lower surface of the first film resistance element 111 and first and second lower electrodes 131b, 132b formed on the lower surface of the second film resistance element 112.

[47] FlGs. 2 to 8 are plane views showing examples of electrode patterns adopted in the present invention. Referring to FlG. 2, the electrode pattern is separated to be engaged in a crank shape with a non-conductive gap 20 interposed therebetween, and this shape is identically formed in the upper and lower electrodes 120, 130 of the film resistance element 110 so that the pattern of the first and second upper electrodes 120 of each film resistance element 110 is rotationally symmetric to the pattern of the first and second lower electrodes 130. Thus, the Tombstone phenomenon is fundamentally eliminated. In addition, in order that the same electrode pattern is shown on the surface when the thermistor is turned over, the pattern of the first and second upper electrodes 121a, 122a of the first film resistance element 111 is formed to be rotationally symmetric with the pattern of the first and second lower electrodes 131b, 132b of the second film resistance element 112.

[48] Such an electrode pattern is not limited to the shape of FlG. 2, but may have 'D' shape (or, a rectangular uneven pattern), a zigzag shape (or, a triangular wave shape), a waved shape or the like, as shown in FlGs. 3 to 5. These configurations generally have a structure that a plurality of resistors having alternating poles are connected in parallel, so an entire resistance is reduced.

[49] Preferably, the non-conductive gap 20 has a width narrower than a thickness of the film resistance element 110. More specifically, the non-conductive gap 20 preferably has a width of 0.15 to 0.6 mm. This dimension narrows the width of the non- conductive gap, which allows current Ig (see FlGs. 9 and 10) to flow well to an adjacent electrode pattern on the upper or lower surface of the film resistance element as described later, thereby making sufficient current flowing at a normal temperature.

[50] Though specific shape and size of the electrode pattern are described above, the present invention is not limited thereto, but it should be understood that the present invention may adopt various modifications in which the electrodes are symmetric or rotationally symmetric.

[51] Meanwhile, the upper and lower electrodes may not be patterned with the non- conductive gap interposed therebetween but be extended in one direction with exposing a part of the film resistance element 110 as shown in FlG. 6. That is to say, the upper electrode 125 may be extended toward the first connection portion, and a lower electrode (not shown) may be extended toward the second connection portion.

[52] In addition, though it has been described in the former embodiments that the patterns the electrodes formed on the upper and lower surfaces of the film resistance element are identical to each other so that the same pattern is shown when the film resistance element is turned over, it also be possible that the patterns of the electrodes formed on the upper and lower surfaces are different from each other. In addition, the electrode formed on the lower surface to be mounted to the PCB may be configured in a way that right and left patterns are just facing each other as an example, not engaged with each other, so that it may be stably contacted with the electrode pad formed on the PCB in a wider area. That is to say, as shown in FlGs. 7 and 8, the patterns of the first and second electrodes may be formed with the same size with a non-conductive gap interposed therebetween (see FlG. 7) or to simply face each other with different sizes in an asymmetric way (see FlG. 8).

[53] The intermediate insulation layer 140 is interposed between the first and second lower electrodes 131a, 132a of the first film resistance element 111 and the first and second upper electrodes 121b, 122b of the second film resistance element 112, which directly face each other between the first and second film resistance elements 111, 112, so as to electrically separate the above electrodes. In addition, the intermediate insulation layer 140 fills in the non-conductive gaps 20 formed in the electrodes 121b, 122b, 131a, 132a so as to electrically separate the electrodes more surely. Such an intermediate insulation layer 140 may be made of non-conductive material such as epoxy, glass fiber, ceramic, polyethylene or polypropylene.

[54] In addition, the intermediate insulation layer 140 has a thermal expansion coefficient of 0.001/°C or below, a volume resistance of 5000 Ωcm or above, a dielectric strength of 1 KV/mm or above, and a coating adhesion of 0.5 kg/cm or above. Thus, the thermistor has excellent durability, thermal resistance and dielectric strength and also is capable of preventing current leakage.

[55] Hereinafter, properties of the intermediate insulation layer 140 will be explained based on experimental examples for better understanding of the present invention. [56] Thermistors were manufactured using the intermediate insulation layer 140 whose thermal expansion coefficient, volume resistance, dielectric strength and coating adhesion are changed, and specific dimensions for the experimental conditions are shown in the following table 1.

[57] [58] Table 1

[59]

[60] Performance of the thermistor according to each experimental example and comparative example under the conductions shown in FIG. 1 was evaluated, and its results are shown in the table 2. Here, the thermal resistance was evaluated on the fact that shrinkage or separation was caused within 10 seconds at 200 °C, and the durability was determined on the fact that the connection portion is cut to intercept a current flow while a rated voltage and a rated current (or, maximum allowable voltage and current values for a circuit) were applied for 1 hour. As for the current leakage, if a resistance of the element does not increase 1000 times within 5 seconds by applying a rated voltage and a rated current (or, maximum allowable voltage and current values for a circuit), it was determined as being failed. The dielectric breakdown was observed with the naked eye from the insulation layer after applying a rated voltage and a rated current (or, maximum allowable voltage and current values for a circuit) for 1 hour.

[61] [62] Table 2

[63] [64] Seeing the table 2, it would be understood that the thermistors of the experimental examples 1 and 2 satisfying the conditions of thermal expansion coefficient, volume resistance, dielectric strength and coating adhesion of the present invention have excellent thermal resistance and durability and do not cause current leakage or dielectric breakdown. However, it is found that the thermistors of the comparative examples 1 to 4 not satisfying the above conditions are deficient in thermal resistance or durability or cause current leakage or dielectric breakdown when their performance is evaluated.

[65] The connection portion 150 includes a first connection portion 151 for electrically connecting the first upper electrodes 121a, 121b and the first lower electrodes 131a, 131b of the first and second film resistance elements 111, 112, and a second connection portion 152 for electrically connecting the second upper electrodes 122a, 122b and the second lower electrodes 132a, 132b of the first and second resistance elements 111, 112. This connection portion 150 is made of metal such as copper or its alloy.

[66] Meanwhile, the connection portion 150 is formed through the side of the film resistance element 110. In more detail, there are a case of connecting electrodes on the right and left sides of the film resistance element 110 or a case of connecting electrodes on the upper and lower surfaces of the film resistance element 110. According to the above connection method of the connection portion 150 that electrically connects the electrodes 120, 130, an amount of current flowing through the thermistor at a normal temperature is also changed, as explained below.

[67] FIGs. 9 and 10 are sectional views taken along the line πi-III of FIG. 3, which show internal current flows of the thermistor with respect the electrode pattern shown in FIG. 3.

[68] In FIG. 9, the first connection portion 151 connects the first upper electrodes 123a, 123b and the first lower electrodes 133a, 133b on the left side of FTG. 3, and the second connection portion 152 connects the second upper electrodes 124a, 124b and the second lower electrodes 134a, 134b on the right side of FIG. 3. In this case, if a voltage is applied to the lower electrodes 133b, 134b formed on the lower surface of the thermistor loaded on PCB, a current Ig flows through a surface layer of the resistance element between adjacent electrodes (or, through the non-conductive gap) formed on the upper and lower surfaces of the first and second film resistance elements 111, 112 as shown in FlG. 9, and at the same time a current Ir flows between vertically facing electrodes of the first and second film resistance elements 111, 112 in a thickness direction of the film resistance element.

[69] In FlG. 10, the first connection portion 151 connects the first upper electrodes 123a,

123b and the second lower electrodes 134a, 134b on the upper surface of FlG. 3, and the second connection portion 152 connects the second upper electrodes 124a, 124b and the first lower electrodes 133a, 133b on the lower surface of FlG. 3. In this case, if a voltage is applied to the lower electrodes 133b, 134b formed on the lower surface of the thermistor loaded on PCB, a current Ig flows through the surface layer of the resistance element between adjacent electrodes (or, through the non-conductive gap) formed on the upper and lower surfaces of the film resistance elements 111, 112 as shown in FlG. 10. However, since electrodes vertically facing with the resistance elements 111, 112 being interposed therebetween are already electrically connected through the connection portions 151, 152 to have the same polarity, a current does not flow in a thickness direction of the resistance elements 111, 112. Thus, paths for current flow are limited in comparison to the connection structure shown in FlG. 9.

[70] Referring to FlG. 1 again, the insulation layers 141, 142 include a first insulation layer 141 formed on an upper surface of the top-layer upper electrode 121a, 122a of the thermistor and a second insulation layer 142 formed on a lower surface of the lowest-layer lower electrode 131b, 132b. The insulation layers 141, 142 electrically separate the electrodes 121a, 122a, 131b, 132b from the connection portions 151, 152 extended on the upper surface of the thermistor, and fill in the non-conductive gap 20 between the electrodes or a region 22 where no electrode is formed as shown in FlG. 6 for better electric separation. In addition, the insulation layers 141, 142 electrically separate the first and second connection portions 151, 152 on the upper and lower surfaces of the thermistor during the process of forming the connection portions 150, explained later.

[71] Preferably, in the thermistor of this embodiment, the connection portions 151, 152 may be extended toward the upper surface of the first insulation layer 141 or the lower surface of the second insulation layer 142. In addition, the thermistor of this embodiment further includes metal foil layers 143, 144 interposed between the extensions of the connection portions 151, 152 and the first and second insulation layers 141, 142. The metal foil layers 143, 144 play a role of effectively contacting the first or second insulation layer 141, 142 to the connection portions 151, 152, and they may be made of copper foil.

[72] Preferably, the thermistor of this embodiment further includes upper and lower solder resists 161, 162 formed at center portions of the upper and lower surfaces of the thermistor, and solder layers 171, 172 selectively formed on both sides of the upper and lower solder resists 161, 162 to surround a side of the thermistor.

[73] The upper and lower solder resists 161, 162 are arranged between the first and second connection portions 151, 152 extended on the upper and lower surfaces of the thermistor, and in the following solder forming process, they plays a role that solders 171, 172 are not formed in a region where the solder resists 161, 162 are already formed. That is to say, the solder resists solder a terminal of the thermistor to the PCB, and the solder resists with low wettability due to the solders are positioned between terminals, thereby preventing a short circuit between both terminals.

[74] The solders 171, 172 are soldered in contact with electrode pads formed on PCB when the thermistor is mounted, and then play a role of terminal for supplying current to electrodes of the thermistor. Generally the solders 171, 172 are made of Sn/Pb plating.

[75] Meanwhile, approximate semi-circular grooves 180 are formed on both sides of the thermistor according to this embodiment, and the resistance element 110, the electrodes 120, 130, the connection portion 150, the intermediate insulation layer 140, the insulation layers 141, 142 and the metal foil layers 143, 144 are exposed through the grooves 180. That is to say, the connection portion 150 is formed only on a region except for the grooves 180, not formed on the entire side of the thermistor. Thus, though a crack occurs in the connection portion 150 on the side of the thermistor while heat is applied as in the solder reflow process or the thermistor is in use, it is possible to prevent the crack from being propagated along the entire side. In addition, this groove 180 may be usefully used for checking inferiority of the connection portion 150.

[76] FlG. 11 is a perspective view showing a thermistor according to another embodiment of the present invention, and FlG. 12 is a sectional view taken along the line IV-IV of FlG. 11. In FlGs. 11 and 12, the same reference numeral as in the former drawings designate the same component having the same function, and it is not described in detail here.

[77] Referring to FlGs. 11 and 12, the thermistor of this embodiment is configured so that connection portions 251, 252 connect the electrodes 120, 130 with each other only through a groove 280 formed in a side. Solders 271, 272 are also formed in the groove 280. Configuration and materials except for the side are identical to the former embodiment, and not described in detail.

[78] According to this embodiment, since the connection portion 250 is formed in the groove 280, a crack occurring in the connection portion 250 does not propagate along the entire area of the side. Thus, reliability of the thermistor is ensured though a crack occurs.

[79] Meanwhile, though the grooves 180, 280 formed in the side of the thermistor have a semi-circular shape in the former embodiments, the grooves 180, 280 may have various shapes such as a semi-spherical shape, a V shape, a rectangular shape and so on. In addition, though it has been described in the former embodiments that the connection portion 150, 250 surround a side of the thermistor, the present invention is not limited thereto. For example, it is possible that a through hole is formed in the thermistor to pass through the film resistance element 110, and then a connection portion is formed through the through hole.

[80] In brief, though the above description and drawings illustrate electrode patterns and specific configuration of the connection portions caused therefrom, there may be various modifications for the electrode patterns and specific configuration of the connection portions caused therefrom within the scope of the present invention. For example, FIG. 13 is a sectional view taken along the line IV-IV of FIG. 11, which shows a sectional structure of a thermistor according to a modification of the present invention, and in this modification the thermistor adopts the electrode pattern 125 configured as shown in FIG. 6. That is to say, in this modification, the upper electrodes 125 of each film resistance element 111, 112 are electrically connected with each other through the first connection portion 251 on the left in the drawing, and the lower electrodes 126 of each film resistance element 111, 112 are electrically connected with each other through the second connection portion 252 on the right in the drawing. In addition, though not shown in the drawing, in case the electrode pattern as shown in FIG. 7 or 8, a connection portion is configured similarly to the section structure shown in FIG. 12. Meanwhile, though these modifications are described based on the embodiment shown in FIG. 11 in which the connection portion is formed along the sidewall in the groove 280, it is also possible to apply these modifications to the embodiment shown in FIG. 1 in which the connection portion is formed on the sidewall except for the groove 180.

[81] Hereinafter, a method for manufacturing a thermistor configured as mentioned above will be described, and at this time the thermistor is assumed to have two film resistance elements for convenient explanation.

[82] FIGs. 14 to 21 illustrate a method for manufacturing a thermistor of FIG. 1, and right portions of FIGs. 17 to 20 are partially-sectioned perspective views taken along the line V-V.

[83] Referring to FIG. 14, at first, two film resistance element sheets 11, 12 cut into a suitable size are prepared. The film resistance element sheets 11, 12 are configured so that metal films 120, 130 (the metal films will be upper and lower electrodes) are laminated on both surfaces of NTC or PTC resistance elements 111, 112 whose resistance is changed depending on temperature. These sheets may be prepared by means of electrolytic or electroless plating of metal such as aluminum or copper on the upper and lower surfaces of a polymer sheet in which conductive particles are dispersed, or by means of pressing of metal foils onto both surfaces of a polymer sheet. The sheet prepared as above is cut into a suitable size and then cleaned for easy handling in the following procedure.

[84] After that, as shown in FlG. 15, the upper and lower metal films 120, 130 of each sheet 11, 12 are patterned to form a predetermined electrode pattern. Specifically, photo resist is coated on each sheet 11, 12, and then exposed to light and developed into a desired pattern so as to form a photo resist pattern (not shown). After that, the metal films 120, 130 are etched with using the photo resist pattern as an etching mask so that the film resistance elements 111, 112 are exposed in a crank shape as shown in FlG. 15. Subsequently, the photo resist pattern is removed to form a sheet in a state as shown in FlG. 15.

[85] The exposed region of the film resistance elements 111, 112 in this stage then forms the aforementioned non-conductive gap 20. At this time, though the non-conductive gap 20 has a crank shape in FlG. 15, there it may have various shapes such as a rectangular uneven pattern, a zigzag shape, and a waved shape as shown in FlGs. 3 to 8. In addition, the non-conductive gaps 20 on the upper and lower surfaces of the sheet are rotationally symmetric so as to show the same shape when the sheet is turned over.

[86] Subsequently, referring to FlG. 16, the patterned sheet is united together with an insulation material layer. In more detail, the insulation material layer 140 (it will become the intermediate insulation layer) is interposed between two sheets, and also the insulation material layers 141, 142 (they will be the first and second insulation layers) are prepared on the upper and lower surfaces of the sheet, and they are laminated. Then, the insulation material fills in the non-conductive gaps 20 formed in the patterned electrodes on the upper and lower surfaces of the sheets 11, 12. At this time, the metal foils 143, 144 may be further prepared on the insulation material layers arranged on the upper and lower surfaces of the sheet.

[87] At this time, the insulation material layer 140 prepared between the sheets 11, 12 has a thermal expansion coefficient of 0.001/°C or below, a volume resistance of 5000 Ωcm or above, a dielectric strength of 1 KV/mm or above, and a coating adhesion of 0.5 kg/cm or above. Thus, the thermistor ensures excellent thermal resistance, durability dielectric strength and also is capable of preventing current leakage.

[88] After that, as shown in FlG. 17, a plurality of through holes 30 having predetermined width and length are perforated in the united sheet to be arranged in up, down, right and left directions. A region between adjacent through holes in a width direction of the through holes 30 (or, in a transverse direction on the drawing) will become a thermistor. Meanwhile, the through holes 30 are formed at regular intervals in a length direction, differently from slits successively formed in one direction in the conventional sheet. Thus, the sheet is not drooped down or twisted along a length direction of the through holes in the following processes.

[89] Subsequently, as shown in FlG. 18, copper or copper alloy is plated on a front side of the sheet in which the through holes 30 are formed so that the metal films 120, 130 on the upper and lower surfaces are electrically connected through the through holes 30. The copper or copper alloy plating film 150 formed as mentioned above will become the connection portions 151, 152 mentioned above.

[90] After that, as shown in FlG. 19, the solder resists 160 are formed on the upper and lower surfaces except for the region in or around the through holes 30 of the sheet, specifically, the plating film 150 and the metal foils 143, 144 are removed fro the region where the solder resist 160 will be formed, by means of D/F process, namely exposure, development and etching, and then the solder resist 160 may be laminated on the region. In addition, various methods such as screen printing and liquid photo printing may be adopted.

[91] Subsequently, if Sn/Pb is plated on the sheet on which the solder resist 160 is formed, the solder layer 170 is formed on the inner circumference of the through holes 30 and around the through holes 30, except a region where the solder resist 160 is formed, as shown in FlG. 20. This solder layer 170 is a terminal that will be connected to an electrode pad on PCB by means of solder reflow or the like when the thermistor is mounted to the PCB.

[92] Finally, as shown in FlG. 21, the sheet is cut along a cut line 40 passing through the through holes 30 in a width direction of the through holes 30, so a region between adjacent through holes in a width direction of the through holes 30 is divided into one unit thermistor. At this time, if a sidewall of a center portion of the through hole 30 is cut in a circular or oval shape, a thermistor having the groove 180 in the side shown in FlG. 1 is completed. Meanwhile, if the circular or oval perforating process is excluded in FlG. 21, it is possible to manufacture a thermistor in which the upper and lower electrodes are connected through the entire side of the thermistor.

[93] Meanwhile, though the upper and lower electrodes are separated into two parts with the non-conductive gap interposed therebetween using etching in the above description, it is also possible that the upper and lower electrodes have a single part extended in one direction with exposing a part of the film resistance element. That is to say, it is possible to manufacture a thermistor so that one end of the upper portion of the metal film is etched to expose the film resistance element (see FlG. 6).

[94] FlG. 22 illustrates a method for manufacturing a thermistor (see FlG. 11) according to the above another embodiment, and it will be described on the basis of differences from the thermistor manufacturing method of the one embodiment mentioned above.

[95] As described above, the thermistor of FlG. 11 has a side structure in which the upper and lower electrodes are connected through the semi-circular or semi-oval groove 280, differently from the thermistor of FlG. 1. In order to manufacture such a thermistor, as for the united sheet as shown in FlG. 16, circular or oval through holes 31 shown in FlG. 22 are formed instead of the through holes 30 of FlG. 17, and the following processes for forming connection portions, solder resists and solders are conducted, and then the sheet is cut along cut lines 60 and 70 shown in FlG. 22. That is to say, the sheet is cut through the through holes 31.

[96] Meanwhile, as a result of forming non-conductive gaps having the same crank shape between the through holes 31, there arises a problem that the sheet is wasted as much as certain margins above and below the through holes. This problem is originated from the fact that, in the thermistor manufacturing process of the present invention, the through holes are formed at regular intervals instead of forming long slits successively formed in an up/down direction on the drawing, so as to prevent the sheet from being twisted.

[97] In this regards, it is possible that non-conductive gaps 21 are successively formed by alternately turning over a crank shape to the right and left in an up/down direction on the drawing and then cut the sheet along the cut lines 60 and 70 to manufacture a thermistor, not making the non-conductive gaps 21 have the same shape in all regions where each thermistor is formed. As a result, there is no wasted area between the cut lines 70, thereby reducing waste.

[98] The present invention has been described in detail. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. Industrial Applicability

[99] As described above, the thermistor of the present invention may lower an initial resistance without increasing a size of the thermistor used as a surface-mounting device, so it is possible to improve a resistance characteristic of the thermistor at a normal temperature. Furthermore, the thermistor of the present invention has excellent thermal resistance, durability and dielectric strength, so it may prevent generation of current leakage.

[100] In addition, the thermistor of the present invention structurally has a symmetric shape, so it may fundamentally prevent Tombstone phenomenon caused by an asymmetric structure. In addition, though a crack occurs in the side of the thermistor, the connection portions of the upper and lower electrodes through the side of the material layer may endure well against the crack. Furthermore, according to the thermistor manufacturing method of the present invention, since the elongated, circular or oval through holes are arranged in the sheet at regular intervals in up, down, right and left directions, it is possible to prevent the sheet from being twisted during the thermistor manufacturing process.

Claims

[ 1 ] A thermistor, comprising : at least two film resistance elements laminated and changing a resistance depending on temperature; first and second upper electrodes laminated on an upper surface of each film resistance element to be symmetrically engaged with each other with a non- conductive gap interposed therebetween; first and second lower electrodes laminated on a lower surface of each film resistance element to be symmetrically engaged with each other with a non- conductive gap interposed therebetween; an intermediate insulation layer interposed between the film resistance elements respectively; a first connection portion for electrically connecting the first upper electrode to the first lower electrode respectively; a second connection portion for electrically connecting the second upper electrode to the second lower electrode respectively; a first insulation layer prepared on upper surfaces of the first and second upper electrodes of the film resistance element positioned at a top layer of the film resistance elements; and a second insulation layer prepared on lower surfaces of the first and second lower electrodes of the film resistance element positioned at a lowest layer of the film resistance elements.

[2] The thermistor according to claim 1, wherein the first and second connection portions are partially extended to an upper surface of the first insulation layer and a lower surface of the second insulation layer, and wherein the thermistor further comprises a metal foil layer interposed between the extensions of the first and second connection portions and the first insulation layer or between the extensions of the first and second connection portions and the second insulation layer.

[3] The thermistor according to claim 1, further comprising: upper and lower solder resists formed in center portions of the upper and lower surfaces of the thermistor; and solder layers formed on both sides of the upper and lower solder resists to surround sides of the thermistor.

[4] The thermistor according to claim 1, wherein a pattern of the first and second electrodes of each of the at least two film resistance elements is rotationally symmetric with a pattern of the first and second electrodes, and wherein a pattern of the first and second electrodes of the top-layer film resistance element is symmetric with a pattern of the first and second lower electrodes of the lowest-layer film resistance element so that the same electrode pattern is shown on a surface when the thermistor is turned over.

[5] The thermistor according to claim 1, wherein the first connection portion electrically connects the first upper electrode and the first lower electrode of each film resistance element with surrounding one side of the at least two film resistance elements, and wherein the second connection portion electrically connects the second upper electrode and the second lower electrode of each film resistance element with surrounding the other side of the at least two film resistance element, opposite to the above one side.

[6] The thermistor according to claim 5, wherein grooves are respectively formed in both sides of the film resistance elements, and the first and second connection portions electrically connect the electrodes with surrounding both sides except for the grooves.

[7] The thermistor according to claim 5, wherein grooves are respectively formed in both sides of the film resistance elements, and the first and second connection portions electrically connect the electrodes with surrounding the grooves of both sides respectively.

[8] The thermistor according to claim 1, wherein the non-conductive gap has a crank shape, a rectangular uneven pattern, a zigzag shape or a waved shape.

[9] The thermistor according to claim 1, wherein the non-conductive gap has a width smaller than a thickness of the film resistance element.

[10] The thermistor according to claim 1, wherein the non-conductive gap has a width of 0.13 to 0.6 mm.

[11] The thermistor according to claim 1 , wherein the film resistance element is a PTC (Positive Temperature Coefficient) polymer element having a PTC characteristic.

[12] The thermistor according to claim 11, wherein the PTC polymer element includes polymer, conductive particles and antioxidant, and wherein the PTC polymer has a specific resistance of 0.1 to 2.0 Ωcm at a normal temperature.

[13] The thermistor according to claim 1, wherein the first and second upper electrodes and the first and second lower electrodes are made of copper or its alloy.

[14] The thermistor according to claim 1, wherein the intermediate insulation layer has a thermal expansion coefficient of 0.001/°C or below, a volume resistance of 5000 Ωcm or above, a dielectric strength of 1 KV/mm or above, and a coating adhesion of 0.5 kg/cm or above.

[15] A thermistor, comprising: at least two film resistance elements prepared to face each other and changing a resistance depending on temperature; upper and lower electrodes laminated on both sides of each film resistance element; an intermediate insulation layers interposed between the film resistance elements respectively and having a thermal expansion coefficient of 0.001/°C or below, a volume resistance of 5000 Ωcm or above, a dielectric strength of 1 KV/mm or above, and a coating adhesion of 0.5 kg/cm or above; a first connection portion for selectively electrically connecting the upper and lower electrodes of each film resistance element with surrounding one side of the at least two film resistance elements; a second connection portion for selectively electrically connecting the upper and lower electrodes of each film resistance element with surrounding the other side of the at least two film resistance element; a first insulation layer prepared on an upper surface of the upper electrode of the film resistance element position in a top layer of the film resistance elements; and a second insulation layer prepared on a lower surface of the lower electrode of the film resistance element positioned in a lowest layer of the film resistance elements.

[16] The thermistor according to claim 15, wherein each upper electrode of the at least two film resistance elements is formed on the upper surface of the film resistance elements with exposing a part of the upper surface of the film resistance elements toward the other side, wherein each lower electrode of the at least two film resistance element is formed on the lower surface of the film resistance elements with exposing a part of the lower surface of the film resistance element toward the one side, wherein the first connection portion electrically connects the upper electrodes of the at least two film resistance element, and wherein the second connection portion electrically connects the lower electrodes of the at least two film resistance elements.

[17] The thermistor according to claim 16, wherein each upper electrode of the at least two film resistance element includes a first upper electrode formed on the upper surface of the film resistance elements toward one side and a second upper electrode formed on the upper surface of the film electrode elements toward the other side, which are electrically separated with a non-conductive gap interposed therebetween, wherein each lower electrode of the at least two film resistance elements includes a first lower electrode formed on the lower surface of the film resistance elements toward the one side and a second lower electrode formed on the lower surface of the film resistance element toward the other side, which are electrically separated with a non-conductive gap interposed therebetween, wherein the first connection portion electrically connects the first upper electrode and the first lower electrode of each of the at least two film resistance elements, and wherein the second connection portion electrically connects the second upper electrode and the second lower electrode of each of the at least two film resistance elements.

[18] The thermistor according to claim 17, wherein the first upper electrode is asymmetrically formed to have a larger size than the second upper electrode, and wherein the first lower electrode is asymmetrically formed to have a smaller size than the second lower electrode.

[19] The thermistor according to claim 17, wherein the first and second upper electrodes or the first and second lower electrodes have the same size and are symmetrically formed so that the non- conductive gap is interposed therebetween.

[20] The thermistor according to claim 17, wherein the first and second upper electrodes and the first and second lower electrodes have the same size and are symmetrically engaged so that the non- conductive gap is interposed therebetween.

[21] The thermistor according to claim 15, wherein grooves are respectively formed in both sides of the film resistance elements, and the first and second connection portions electrically connect the electrodes with surrounding both sides except for the grooves.

[22] The thermistor according to claim 15, wherein grooves are respectively formed in both sides of the film resistance elements, and the first and second connection portions electrically connect the electrodes with surrounding the grooves in both sides.

[23] The thermistor according to claim 15, wherein the first and second connection portions are partially extended to an upper surface of the first insulation layer and a lower surface of the second insulation layer, and wherein the thermistor further comprises a metal foil layer interposed between the extensions of the first and second connection portions and the first insulation layer or between the extensions of the first and second connection portions and the second insulation layer.

[24] The thermistor according to claim 24, further comprising: upper and lower solder resists formed in center portions of the upper and lower surfaces of the thermistor; and solder layers formed on both sides of the upper and lower solder resists to surround a side of the thermistor.

[25] The thermistor according to claim 25, wherein the film resistance element is a PTC polymer element having a PTC characteristic.

[26] The thermistor according to claim 25, wherein the PTC polymer element includes polymer, conductive particles and antioxidant, and wherein the PTC polymer element has a specific resistance of 0.1 to 2.0 Ωcm at a normal temperature.

[27] The thermistor according to claim 15, wherein the first and second upper electrodes and the first and second lower electrodes are made of copper or its alloy.

[28] A method for manufacturing a thermistor, comprising: preparing at least two sheets in which metal films are laminated on both sides of a film resistance element whose resistance is changed depending on temperature; patterning both sides of each metal film of the sheet to form an electric pattern; preparing insulation material layers between the sheets, on an upper surface of a top-layer sheet, and on a lower surface of a lowest-layer sheet respectively and then uniting the sheets; forming a plurality of through holes having a predetermined shape in the united sheets in a matrix shape; connecting the metal films formed on both sides of the sheets through sidewalls of the through holes; and cutting the sheets having the electrode pattern in a width direction of the through holes so that a region between adjacent through holes becomes one unit.

[29] The method for manufacturing a thermistor according to claim 28, wherein metal foils are further provided to an upper surface of the insulation material layer prepared on the upper surface of the top-layer sheet and a lower surface of the insulation material layer prepared on the lower surface of the lowest-layer sheet, and then united each other.

[30] The method for manufacturing a thermistor according to claim 28, wherein, in the sheet cutting step, the sheet is cut in a transverse direction through upper and lower portions of the through holes in a length direction respectively.

[31] The method for manufacturing a thermistor according to claim 30, wherein, in the sheet cutting step, a sidewall of the through hole is partially cut to form a groove in the sidewall.

[32] The method for manufacturing a thermistor according to claim 28, wherein, in the sheet cutting step, the sheet is transversely cut without cutting through upper and lower portions of the through holes in a length direction, and the sheet is vertically cut through the through holes.

[33] The method for manufacturing a thermistor according to claim 28, wherein, in the electrode pattern forming step, as for the metal films formed on both sides of the sheet, the metal films are removed to be two electrode patterns separated but symmetrically engaged with each other in each region between adjacent through holes in a width direction of the through holes.

[34] The method for manufacturing a thermistor according to claim 28, wherein the metal films are removed so that the same pattern is shown when the sheet is turned over or the united sheets are turned over.

[35] The method for manufacturing a thermistor according to claim 33 or 34, wherein the metal films are removed so that a removed region of the metal film has a crank shape, a zigzag shape, a rectangular uneven pattern, or a waved shape.

[36] The method for manufacturing a thermistor according to claim 28, further comprising, between the metal film electrically connecting step and the sheet cutting step: coating solder resists on both sides of the sheet on which the electrode pattern is formed, except a portion in and around the through hole; and forming a solder to the electrode pattern in and around the through hole on which the solder resist is not coated.

[37] The method for manufacturing a thermistor according to claim 28, wherein the intermediate insulation layer has a thermal expansion coefficient of 0.001/°C or below, a volume resistance of 5000 Ωcm or above, a dielectric strength of 1 KV/mm or above, and a coating adhesion of 0.5 kg/cm or above. [38] The method for manufacturing a thermistor according to claim 28, wherein, in the electrode pattern forming step, the metal film is removed so that the film resistance element is partially exposed.