JP2006060145A - Manufacturing method of ptc thermister - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a PTC thermister capable of suppressing the formation of voids so as to be capable of reducing a variation in electric resistance characteristic. <P>SOLUTION: The manufacturing method of the PTC thermister includes a lamination step (S113), a first thermocompression bonding step (S115), and a second thermocompression bonding step (S117). In the lamination step (S113), a laminating body is obtained which includes a resistance raw material sheet wherein conductive particles are dispersed in a crystalline high polymer resin and a conductive sheet for an internal electrode. In the first thermocompression bonding step (S115), the laminating body is heated at a first temperature higher than the softening point of the crystalline high polymer resin and pressed by first pressure to apply thermocompression bonding to the laminating body. In the second thermocompression bonding step (S117), the laminating body subjected to the thermocompression bonding by the second thermocompression bonding step is heated at a second temperature higher than the softening point of the crystalline high polymer resin and pressed by second pressure lower than the first pressure to apply thermocompression bonding to the laminating body. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for manufacturing a PTC thermistor.

  As a PTC (Positive Temperature Coefficient) thermistor, a PTC thermistor (hereinafter referred to as “thermistor”) having a resistor layer in which conductive particles are dispersed in a crystalline polymer resin and internal electrodes positioned so as to face each other with the resistor layer interposed therebetween. , Which are referred to as “P-PTC thermistors” as necessary) (see, for example, Patent Document 1).

Patent Document 1 discloses the following method for manufacturing a PTC thermistor. First, a resistor base sheet in which conductive particles are dispersed in a crystalline polymer resin and a metal foil for internal electrodes are laminated and thermocompression bonded. Next, the sheet-like pressure-bonded body is cut into chips so that the metal foil is exposed to obtain a thermistor element. Next, external electrodes are formed at both ends of the thermistor element so as to be electrically connected to the metal foil.
JP 2000-31801 A

  However, the manufacturing method of the PTC thermistor described in Patent Document 1 has the following problems.

  In recent years, so-called lead-free solder that does not contain lead is becoming mainstream in the electronic equipment field. When lead-free solder is used, the temperature required for the reflow process is higher than in the case of conventional lead solder, and may reach about 260 ° C. Therefore, in an electronic device using lead-free solder, the PTC thermistor tends to be exposed to a high temperature.

  If even a small amount of air remains inside the sheet-like crimped body (thermistor element) obtained by thermocompression bonding of the resistor element base sheet and the metal foil, voids are generated when the PTC thermistor is exposed to high temperatures. Resulting in. When voids are generated in this way, the electrical resistance value of the PTC thermistor changes, resulting in variations in its characteristics. In particular, a method of drying a resistor base sheet after forming a slurry obtained by adding a solvent to a crystalline polymer resin and conductive particles and mixing them into a sheet (hereinafter referred to as “wet method” if necessary) In this case, the resistor base sheet has innumerable pores due to evaporation of the solvent, and air tends to remain in the pores. Possible causes of voids include expansion of air remaining inside the crimped body (thermistor element), or movement and collection of dispersed air due to softening of the resistor layer. .

  An object of the present invention is to provide a method for manufacturing a PTC thermistor capable of suppressing the generation of voids and reducing the variation in characteristics.

  A method for producing a PTC thermistor according to the present invention includes a lamination step of obtaining a laminate including a resistor base sheet in which conductive particles are dispersed in a crystalline polymer resin, and a conductive sheet for internal electrodes, and a laminate. Is heated at a first temperature lower than the softening point of the crystalline polymer resin, and is thermocompression-bonded in a first thermocompression process in which the pressure is applied at a first pressure and thermocompression is applied. A second thermocompression bonding step in which the laminated body is heated at a second temperature higher than the softening point of the crystalline polymer resin and pressurized at a second pressure lower than the first pressure to perform thermocompression bonding; It is characterized by providing.

  In the method for manufacturing a PTC thermistor according to the present invention, the laminate including the resistor base sheet and the conductive sheet is heated at a first temperature lower than the softening point of the crystalline polymer resin in the first thermocompression bonding step. And pressurizing with the first pressure and thermocompression bonding. Thereby, the air which exists in a laminated body will be expelled from the said laminated body. In the second thermocompression bonding step, the laminated body thermocompression bonded in the first thermocompression bonding step is pressurized at a second temperature higher than the softening point of the crystalline polymer resin and is higher than the first pressure. Pressurized with a low second pressure and thermocompression bonded. Thereby, a resistor base sheet and an electroconductive sheet are fully thermocompression-bonded, and it can prevent that a resistor base sheet and an electroconductive sheet peel. Therefore, since air present in the laminated body is expelled from the laminated body, even when the PTC thermistor is exposed to a high temperature, generation of voids can be suppressed and variation in characteristics can be reduced.

  The first temperature is preferably 20 to 60 ° C. lower than the softening point of the crystalline polymer resin. In this case, the effects as described above can be further exhibited.

  The second temperature is preferably 20 to 100 ° C. higher than the softening point of the crystalline polymer resin. In this case, the effects as described above can be further exhibited.

  Moreover, it is preferable that a 1st pressure is a pressure of 20-200 Mpa. In this case, the effects as described above can be further exhibited.

  The second pressure is preferably a pressure of 10 MPa or less. In this case, the effects as described above can be further exhibited.

  Further, the resistor base sheet is preferably obtained by applying a slurry prepared by adding a solvent to the crystalline polymer resin and the conductive particles and mixing them, and then drying the slurry.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the PTC thermistor which can suppress generation | occurrence | production of a void and can reduce the dispersion | variation in a characteristic can be provided.

  Hereinafter, a preferred embodiment of a method for manufacturing a PTC thermistor according to the present invention will be described in detail with reference to the accompanying drawings. In the description, the same reference numerals are used for the same elements or elements having the same function, and redundant description is omitted.

  First, based on FIG. 1, the structure of the PTC thermistor 1 which concerns on this embodiment is demonstrated. FIG. 1 is a diagram showing a cross-sectional configuration of a PTC thermistor according to the present embodiment.

  The PTC thermistor 1 includes a substantially rectangular parallelepiped element 10 and external electrodes 21 and 23. The element 10 has a pair of side surfaces 10a and 10b positioned so as to be parallel to and opposed to each other in the stacking direction of the element 10. The element 10 includes a plurality of resistor layers 11, a plurality of internal electrodes 13 and 15, and a plurality of insulator layers 17. The element 10 is configured such that the resistor layers 11 and the internal electrodes 13 and 15 are alternately stacked and further sandwiched between the insulator layers 17. Therefore, in the element 10, the internal electrodes 13 and 15 are positioned so as to face each other with the resistor layer 11 interposed therebetween. The element 10 is covered with an insulator layer 19 except for the pair of side surfaces 10a and 10b.

  The resistor layer 11 contains a crystalline polymer resin and conductive particles dispersed in the crystalline polymer resin. The resistor layer 11 has a so-called “positive resistance-temperature characteristic” in which, in a certain temperature range, its electric resistance value increases rapidly with an increase in temperature. Examples of the crystalline polymer resin include polyvinylidene fluoride (PVDF), vinylidene fluoride, tetrafluoroethylene, hexafluoropropylene copolymer, polyethylene oxide (PEO), and polystyrene. Examples of the conductive particles include metal carbides such as tungsten carbide (WC), metal powders such as nickel (Ni), and conductive carbon materials such as carbon black.

  One internal electrode 13 extends from the inside to the one side surface 10a so as to be exposed from the other side surface 10b. That is, the end on the other side surface 10b side of one internal electrode 13 is located a predetermined length away from the other side surface 10b. One internal electrode 13 is not exposed on the other side surface 10b. The other internal electrode 15 extends from the inner side to the other side surface 10b rather than the one side surface 10a. That is, the end on the side surface 10a side of the other internal electrode 15 is located a predetermined length away from the side surface 10a. The other internal electrode 15 is not exposed on one side surface 10a. The other internal electrode 15 is positioned so that a part thereof overlaps with one internal electrode 13 when viewed from the stacking direction in the element 10. Examples of the internal electrodes 13 and 15 include metal materials such as silver (Ag), nickel, copper (Cu), palladium (Pd), and gold (Au).

  The insulator layer 17 contains a crystalline polymer resin. The insulator layer 17 does not disperse conductive particles and has electrical insulation. The crystalline polymer resin contained in the insulator layer 17 may be the same as or different from the crystalline polymer resin contained in the resistor layer 11. The insulator layer 17 may be any layer having a sufficiently high insulation resistance even if a small amount of conductive particles are contained.

  The external electrodes 21 and 23 are provided on the pair of side surfaces 10 a and 10 b of the element 10, respectively. The external electrodes 21 and 23 are formed so as to cover the side surfaces 10a and 10b, respectively. The external electrodes 21 and 23 are electrically connected to the internal electrodes 13 and 15 exposed at the side surfaces 10a and 10b on the side surfaces 10a and 10b, respectively. As a result, the external electrodes 21 and 23 are electrically connected to the internal electrodes 13 and 15 alternately every other layer.

  Next, a method for manufacturing the PTC thermistor 1 having the above-described configuration will be described with reference to FIGS. FIG. 2 is a flowchart for explaining the manufacturing process of the PTC thermistor according to this embodiment. 3-7 is a figure for demonstrating the manufacturing process of the PTC thermistor based on this embodiment.

  First, a crystalline polymer resin, conductive particles, and a solvent are prepared, a solvent is added to and mixed with the crystalline polymer resin and conductive particles, and a first slurry is prepared (step S101). For example, a ball mill is used for mixing the crystalline polymer resin, the conductive particles, and the solvent. In this embodiment, polyvinylidene fluoride is used as the crystalline polymer resin, and tungsten carbide is used as the conductive particles. Examples of the solvent include organic solvents such as acetone, N-methyl-2-pyrrolidone, and methyl ethyl ketone (MEK). In this step, the prepared first slurry may be filtered (filtered).

  Next, the prepared first slurry is applied onto a substrate (for example, a film made of polyethylene terephthalate) B1 by a known method such as a doctor blade method, and then dried to form a film M1 having a thickness of about 20 μm or less. It forms (refer Fig.3 (a)). The film M1 thus obtained is peeled from the base B1, and cut into a desired shape to produce a resistor base sheet (step S103). The obtained resistor base sheet is in a state where conductive particles are dispersed in the crystalline polymer resin. Drying is preferably performed, for example, at 60 to 80 ° C. for about 1 minute.

  Also, a crystalline polymer resin and a solvent are prepared, and the solvent is added to the crystalline polymer resin and mixed to prepare a second slurry (step S105). For mixing the crystalline polymer resin and the solvent, for example, a ball mill or the like is used. As the solvent, an organic solvent such as acetone, N-methyl-2-pyrrolidone, or methyl ethyl ketone can be used. In this step, filtration (filtration) of the prepared second slurry may be performed.

  Next, the prepared second slurry is applied onto a substrate (for example, a film made of polyethylene terephthalate) B2 by a known method such as a doctor blade method, and then dried to form a film M2 having a thickness of about 20 μm or less. It forms (refer FIG.3 (b)). The film M2 thus obtained is peeled off from the base B2, and cut into a desired shape to produce an insulator base sheet (step S107).

  In addition, a metal material, a binder resin, a solvent, and the like are prepared, and the binder resin and the solvent are added to the metal material and mixed to prepare a conductive paste for producing a conductive sheet described later (step S109). Examples of the binder resin include organic binder resins (for example, acrylic resins and fluorine resins). Examples of the solvent include organic solvents (for example, acetone, N-methyl-2-pyrrolidone, methyl ethyl ketone, etc.).

  Next, the prepared conductive paste is applied onto a substrate (for example, a film made of polyethylene terephthalate) B3 by a known method such as a doctor blade method, and then dried to form a film M3 having a thickness of about 20 μm or less. (See FIG. 3C). The film M3 thus obtained is peeled off from the base B3 and cut into a desired shape to produce a conductive sheet for the internal electrodes 13 and 15 (step S111). Here, as shown in FIGS. 4A and 4B, the conductive sheets ES1 and ES2 are cut into the conductive sheet ES1 for the internal electrode 13 and the conductive sheet ES2 for the internal electrode 15, respectively. A plurality of slits SL are formed along the planned cutting position C for exposure to the surface.

  When the resistor base sheet RS, the insulator base sheet IS, and the conductive sheets ES1 and ES2 are obtained, a desired number of sheets RS, IS, ES1 and ES2 are placed in a predetermined order as shown in FIG. Lamination is performed to obtain a laminate L including the resistor substrate sheet RS, the insulator substrate sheet IS, and the conductive sheets ES1 and ES2 (step S113: lamination step). In the present embodiment, from the bottom in FIG. 5, the insulator base sheet IS, the resistor base sheet RS, the conductive sheet ES1, the resistor base sheet RS, the conductive sheet ES2, the resistor base sheet RS, the conductive sheet ES1, The resistor base sheet RS and the insulator base sheet IS are laminated in this order.

  Next, the laminate L is heated at a first temperature lower than the softening point of the crystalline polymer resin and is pressurized at a first pressure to be thermocompression bonded (step S115: first thermocompression bonding step). The first temperature is preferably 20 to 60 ° C. lower than the softening point of the crystalline polymer resin. The first pressure is preferably 20 to 200 MPa. The softening point of polyvinylidene fluoride is generally 120 to 160 ° C. Since the softening point of polyvinylidene fluoride used in the present embodiment is 126 ° C., in this embodiment, the laminate L is pressurized at 80 ° C. and pressurized at 40 MPa for 15 minutes for thermocompression bonding.

  Next, the thermocompression-bonded laminate L is heated at a second temperature higher than the softening point of the crystalline polymer resin and is pressurized at a second pressure lower than the first pressure to perform thermocompression bonding (step) S117: Second thermocompression bonding step). The second temperature is preferably 20 to 100 ° C. higher than the softening point of the crystalline polymer resin. The second pressure is preferably greater than 0 MPa and not more than 10 MPa. Since the softening point of polyvinylidene fluoride used in this embodiment is 126 ° C., in this embodiment, the laminate L is pressurized at 150 ° C. and pressurized at a pressure of 5 MPa for 1 hour for thermocompression bonding.

  Next, as shown in FIG. 6, the thermocompression-bonded laminate L is cut at a planned cutting position C and a planned cutting position (not shown) orthogonal to the planned cutting position C (step S119). Thereby, the element 10 cut into a chip shape is obtained. The resistor layer 11 is constituted by the resistor base sheet RS. The internal electrodes 13 and 15 are constituted by the conductive sheets ES1 and ES2. The insulator layer 17 is formed by the insulator base sheet IS. Cutting the laminated body L is performed by cutting the laminated body L with a cutter heated to a predetermined temperature (for example, about 120 ° C.) in a state in which the laminated body L is heated to a predetermined temperature (for example, heated at about 90 ° C.). Do. When the elements 10 obtained by cutting are reattached, a step of separating the elements 10 reattached to each other may be added.

  Next, the obtained element 10 is barrel-polished (step S121). Thereby, the corner | angular part of the element 10 will be rounded off. When the wet barrel polishing method is used, a step of drying the element 10 may be added. As a drying process of the element 10, for example, suction drying is used.

  Next, as shown in FIG. 7, the insulator layer 19 is formed on the side surface of the element 10 (step S123). In the present embodiment, in the element 10 cut from the laminated body L, the internal electrodes 13 and 15 are exposed on the side surfaces other than the side surfaces 10a and 10b forming the external electrodes 21 and 23. It is necessary to form the insulator layer 19 on the side surface. Examples of the material of the insulator layer 19 include a resin having electrical insulation (for example, a resist resin).

  Next, the external electrodes 21 and 23 are formed on the element 10 (step S125). As a result, the PTC thermistor 1 shown in FIG. 1 is obtained. The external electrodes 21 and 23 are formed by transferring an electrode paste mainly composed of silver to the side surfaces 10a and 10b of the element 10 and then baking at a predetermined temperature (for example, about 700 ° C.), followed by electroplating. The For example, Ni and Sn are used as the electroplating material.

  As described above, in the present embodiment, the laminated body L including the resistor base sheet RS and the conductive sheets ES1 and ES2 is the first lower than the softening point of the crystalline polymer resin in the first thermocompression bonding step. And is pressed at the first pressure and thermocompression-bonded. Thereby, the air which exists in the laminated body L will be expelled from the said laminated body L. FIG. In the second thermocompression bonding step, the laminate L that has been thermocompression bonded in the first thermocompression bonding step is pressurized at a second temperature that is higher than the softening point of the crystalline polymer resin and is higher than the first pressure. Is pressed at a low second pressure and thermocompression bonded. Thereby, the resistor base sheet RS and the conductive sheets ES1 and ES2 are sufficiently thermocompression bonded, and the resistor base sheet RS and the conductive sheets ES1 and ES2 can be prevented from peeling off. Therefore, since the air existing in the laminate L is expelled from the laminate L, even when the PTC thermistor 1 is exposed to a high temperature by a reflow process or the like, the generation of voids is suppressed and the variation in characteristics is reduced. Can be reduced.

  A method of drying a resistor base sheet RS after forming a slurry obtained by adding a solvent to a crystalline polymer resin and conductive particles and mixing them into a sheet (hereinafter referred to as “wet method” as necessary) )), Innumerable pores exist in the resistor base sheet RS due to evaporation of the solvent. Therefore, when the laminated body L is formed using the resistor base sheet RS obtained by the wet method, air remains in the pores, so that relatively large voids are easily generated. However, in this embodiment, since the air remaining in the pore is expelled in the first thermocompression bonding step as described above, voids are generated even when the resistor base sheet RS obtained by the wet method is used. Can be reliably suppressed.

  In the present embodiment, the first temperature is 20 to 60 ° C. lower than the softening point of the crystalline polymer resin. When the first temperature is higher than the temperature lower by 20 ° C. than the softening point of the crystalline polymer resin, the thermocompression bonding between the resistor base sheet RS and the conductive sheets ES1 and ES2 is substantially advanced, and the air Becomes difficult to kick out. When the first temperature is lower than a temperature that is 60 ° C. lower than the softening point of the crystalline polymer resin, the crystalline polymer resin is not moderately softened, making it difficult to expel air. Therefore, the effect as described above can be further exhibited by setting the first temperature to a temperature 20 to 60 ° C. lower than the softening point of the crystalline polymer resin.

  In the present embodiment, the second temperature is 20 to 100 ° C. higher than the softening point of the crystalline polymer resin. If the second temperature is lower than a temperature 20 ° C. higher than the softening point of the crystalline polymer resin, there is a possibility that the resistor base sheet RS and the conductive sheets ES1 and ES2 cannot be reliably thermocompression bonded. . When the second temperature is higher than the temperature 100 ° C. higher than the softening point of the crystalline polymer resin, the crystalline polymer resin is too soft to be sufficiently pressurized, and the resistor base sheet There is a possibility that the RS and the conductive sheets ES1 and ES2 cannot be reliably thermocompression bonded. Therefore, the effect as described above can be further exhibited by setting the second temperature to a temperature 20 to 100 ° C. higher than the softening point of the crystalline polymer resin.

  In the present embodiment, the first pressure is a pressure of 20 to 200 MPa. When the first pressure is lower than 20 MPa, there is a possibility that air cannot be sufficiently expelled. When the first pressure is higher than 200 MPa, the conductive particles move in the resistor base sheet RS, so that the electric resistance value at room temperature may increase. Therefore, the effect as described above can be further exhibited by setting the first pressure to 20 to 200 MPa.

  In the present embodiment, the second pressure is a pressure of 10 MPa or less. When the second pressure is higher than a pressure of 10 MPa or less, the laminate L is distorted, and the electric resistance value of the PTC thermistor 1 obtained from the laminate L may vary. Therefore, the effect as described above can be further exhibited by setting the second pressure to a pressure of 10 MPa or less.

  In the wet method, since the crystalline polymer resin is dissolved in the solvent at around room temperature, it is not necessary to heat them. Therefore, the conductive particles are not easily oxidized, and the change in the characteristics of the PTC thermistor 1 is suppressed.

  By the way, the present inventors measured the peel strength of the adhesive surface between the resistor base sheet and the conductive sheet. The peel strength of the bonding surface between the resistor base sheet and the conductive sheet thermocompression bonded according to the present embodiment is 1.95 N, and no peeling occurs at the interface between the resistor base sheet and the conductive sheet. It broke like a fold. On the other hand, the peel strength of the bonding surface between the resistor base sheet and the conductive sheet that is thermocompression bonded at a temperature lower than the softening point of the crystalline polymer resin is 0.97 N, and the resistor base sheet and the conductive sheet are electrically conductive. Peeling occurred at the interface with the adhesive sheet. From this measurement result, it was confirmed that the resistor base sheet and the conductive sheet were sufficiently thermocompression bonded according to this embodiment.

  The preferred embodiment of the present invention has been described in detail above, but the present invention is not limited to the above embodiment. For example, the number of laminated layers, the laminated state, and the like of the resistor base sheet RS (resistor layer 11) and the conductive sheets ES1 and ES2 (internal electrodes 13 and 15) are not limited to the above-described embodiments. A plurality of resistor base sheets RS (resistor layers 11) may be laminated between the conductive sheets ES1 and ES2 (internal electrodes 13 and 15).

It is a figure which shows the cross-sectional structure of the PTC thermistor which concerns on this embodiment. It is a flowchart for demonstrating the manufacturing process of the PTC thermistor which concerns on this embodiment. (A)-(c) is a figure for demonstrating the manufacturing process of the PTC thermistor which concerns on this embodiment. (A) And (b) is a figure for demonstrating the manufacturing process of the PTC thermistor which concerns on this embodiment. It is a figure for demonstrating the manufacturing process of the PTC thermistor which concerns on this embodiment. It is a figure for demonstrating the manufacturing process of the PTC thermistor which concerns on this embodiment. It is a figure for demonstrating the manufacturing process of the PTC thermistor which concerns on this embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... PTC thermistor, 10 ... Element, 11 ... Resistor layer, 13, 15 ... Internal electrode, 21, 23 ... External electrode, B1-B3 ... Base | substrate, C ... Cutting position, ES1, ES2 ... Conductive sheet, IS ... insulator base sheet, L ... laminate, M1 to M3 ... film, RS ... resistor base sheet, S113 ... lamination step, S115 ... first thermocompression step, S117 ... second thermocompression step.

Claims (6)

A laminating step of obtaining a laminate including a resistor base sheet in which conductive particles are dispersed in a crystalline polymer resin and a conductive sheet for internal electrodes;
A first thermocompression bonding step of heating the laminated body at a first temperature lower than the softening point of the crystalline polymer resin and pressurizing and thermocompression bonding at a first pressure;
The laminated body thermocompression-bonded in the first thermocompression bonding step is heated at a second temperature higher than the softening point of the crystalline polymer resin and at a second pressure lower than the first pressure. And a second thermocompression bonding step of pressurizing and thermocompression bonding. A method for producing a PTC thermistor, comprising:   2. The method for producing a PTC thermistor according to claim 1, wherein the first temperature is 20 to 60 ° C. lower than a softening point of the crystalline polymer resin.   2. The method for producing a PTC thermistor according to claim 1, wherein the second temperature is 20 to 100 ° C. higher than the softening point of the crystalline polymer resin.   The method for manufacturing a PTC thermistor according to claim 1, wherein the first pressure is a pressure of 20 to 200 MPa.   The method for manufacturing a PTC thermistor according to claim 1, wherein the second pressure is a pressure of 10 MPa or less.   The said resistor base sheet is obtained by drying, after apply | coating to the base | substrate the slurry prepared by adding a solvent to the said crystalline polymer resin and the said electroconductive particle, and mixing. Manufacturing method of PTC thermistor.

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