JP2003297605A - Chip-type overcurrent protective element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a chip-type overcurrent protective element, which can suppress the increase of its resistance value due to its thermal deformation generated, when the heat of a temperature exceeding the melting point of a thermoplastic resin constituting its resistance layer is applied to it, when the repeat of its ON-OFF and its reflow. <P>SOLUTION: The chip-type overcurrent protective element has a positive resistance-temperature characteristic bearing resistance layer 1, wherein the conductive substances are dispersed in a thermoplastic resin and has at least one positive temperature coefficient thermistor 3, having a pair of electrodes 2 wherebetween the resistance layer 1, is interposed. Further, each bonding layer 3, made of a thermoplastic resin which has no PTC characteristics and contains conductive substances, is interposed in between each principal surface of the resistance layer 1 and each electrode 2. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chip type overcurrent protection device composed of a thermistor having a positive resistance temperature characteristic (PTC characteristic) obtained by dispersing and mixing a conductive material in a thermoplastic resin.

[0002]

2. Description of the Related Art With the recent trend toward digital home appliances, multimedia, etc., there is a tendency that many devices are connected mainly to personal computers. In particular, interfaces such as USB and IEEE 1394 have been attracting attention as main interfaces in the future. In these interfaces, not only signals but also power are supplied to peripheral devices. Generally, a pair of signal lines, a power supply line, and a ground line are connected to the interface. Therefore, in these systems, in addition to the conventional measures against noise propagation and radiation, measures against overcurrent due to various malfunctions are required. Therefore, an overcurrent protection element is provided to take measures. The shape of such an overcurrent protection element is generally a chip type so that surface mounting is possible, and is mounted on the substrate by reflow soldering.

[0003]

As described above, when the overcurrent protection element is surface-mounted on the substrate by reflow, the overcurrent protection element is exposed to a temperature of about 230 to 250 ° C. Therefore, the overcurrent protection element is exposed to a temperature equal to or higher than the melting point of the thermoplastic resin, and as a result, thermal deformation occurs to increase the resistance value, degrading the original performance. is there. In the recent trend of lead-free, solder reflow temperature rises,
There is a possibility that the resistance value will increase more than ever. Although heat resistance is improved by subjecting the resin to a crosslinking treatment in order to prevent such an increase in resistance value, it is not yet complete.

Further, in Japanese Patent Laid-Open No. 2-281707, an electrically conductive substance such as an epoxy resin is used between a resistance layer in which an electrically conductive substance is dispersed in a thermoplastic resin and having a positive resistance temperature characteristic and an electrode. It is disclosed that an adhesive contained in a thermosetting resin such as an amide resin is interposed. However, when an adhesive layer made of such a thermosetting resin is used, the adhesive strength with the thermoplastic resin used for the resistance layer is low, cracks easily occur, and resistance increases due to repeated on / off and reflow. There is a problem that occurs.

In view of the problems of the prior art as described above, the present invention provides a resistance value generated by thermal deformation that occurs when a temperature exceeding the melting point of the thermoplastic resin forming the resistance layer is applied during repeated on / off and reflow. It is an object of the present invention to provide a chip-type overcurrent protection device that can suppress the rise of the current.

[0006]

Means for Solving the Problems A chip-type overcurrent protection device of the present invention comprises a resistance layer having a positive resistance temperature characteristic in which a conductive substance is dispersed in a thermoplastic resin, and a pair of resistance layers sandwiching the resistance layer. A chip-type overcurrent protection device having at least one positive temperature coefficient thermistor layer having an electrode, wherein the thermoplastic layer does not have a PTC property and contains a conductive material between both main surfaces of the resistance layer and the electrode. It is characterized in that a resin is interposed.

As described above, by interposing the adhesive layer containing the conductive material in the thermoplastic resin between the both surfaces of the resistance layer and the electrode, the resistance is increased when the temperature is increased by repeated on / off and reflow. It is possible to suppress an increase in the resistance value without changing the adhesion state between the layer and the adhesive layer.

Further, since the adhesive layer having high conductivity is formed between the resistance layer and the electrode, the interface resistance becomes small and the specific resistance as the overcurrent protection element can be made small.

In the present invention, by setting the melting point of the thermoplastic resin to be equal to or higher than the melting point of the thermoplastic resin forming the resistance layer, it is possible to better prevent the deformation of the adhesive layer when the temperature rises, and to repeatedly turn on and off. It is possible to better suppress an increase in resistance value due to reflow or reflow.

Further, in the present invention, by roughening the interface between the electrode and the adhesive layer, the electrode and the adhesive layer,
As a result, the adhesive strength between the electrode and the resistance layer can be increased, and deformation that causes peeling or the like due to reflow of the adhesive layer can be further suppressed. In particular, the use of the aluminum surface-expansion foil deepens the unevenness of the rough surface, and the adhesive strength between the adhesive layer and the electrode is further increased.

The structure of the present invention can also be applied to an overcurrent protection device having a multilayer structure having a plurality of the resistance layers and electrodes interposed therebetween.

[0012]

1A and 1B are a perspective view and a plan view showing an embodiment of an overcurrent protection element according to the present invention, respectively. Reference numeral 1 is a resistance layer having a positive resistance temperature characteristic in which a conductive substance is dispersed in a thermoplastic resin, and 2 is an electrode fixed to both main surfaces of the resistance layer via adhesive layers 3. The adhesive layer 3 is a layer that does not have PTC characteristics, and is formed by mixing a conductive material in a thermoplastic resin that is the same as or different from the resin that forms the resistance layer 1.

The electrode 2 is mainly composed of copper, nickel, aluminum or a metal such as these, and is subjected to a soldering treatment if necessary, and the adhesive surface with the adhesive layer 3 is formed on the rough surface 2a. To be done. As the electrode 2, an ordinary metal foil roughened by etching, an electrolytic metal foil whose surface is roughened, or an aluminum foil surface-enlarged is used. In particular, the aluminum surface-expanded is more preferable because the unevenness is deep and therefore the adhesive strength with the adhesive layer 3 is increased. The adhesive surface 3a of the adhesive layer 3 with the resistance layer 1 is also formed on the rough surface 3a.

The resistance layer 1 and the adhesive layer 3 are made of, for example, polyethylene resin, polyvinylidene fluoride (PVDF) resin,
Any one of polypropylene resin, polyvinyl acetate resin, ionomer, or a crystalline resin which is a copolymer thereof may be used. In particular, PVDF is suitable for use in a place where ignition is likely because PVDF is self-extinguishing. The thickness of the resistance layer 1 is preferably 50 μm to 2000 μm, more preferably 100 μm.
It is μm to 500 μm. The thickness of the adhesive layer 3 is preferably 5 μm to 30 μm, more preferably 10 μm to 2
It is 0 μm.

As the conductive material used for the resistance layer 1 and the adhesive layer 3, for example, copper, nickel, aluminum,
Metals such as silver, palladium, titanium and tungsten, alloys thereof, electrically conductive borides, nitrides, carbides and carbon black are used. The mixing ratio of the conductive material is preferably 20% by volume or more in order to obtain conductivity of a predetermined value or more, and 50% in order to obtain PTC characteristics. It is preferably not more than volume%. The thickness of the electrode layers 2a and 2b is preferably 5 μm to 70 μm, more preferably 18 μm.
It is m-35 micrometers.

FIG. 2 is a diagram showing a process of manufacturing the overcurrent protection element. As shown, powdery conductive material 4
And resin 5 are weighed and, for example, 100 to 2 by a kneader.
The mixture 6 is mixed at 00 ° C. for 0.5 to 1 hour, and the mixture 6 is heated and pressed at 100 to 200 ° C. and 1 to 10 MPa to prepare a sheet 1A for the resistance layer 1. FIG. 2 shows only one overcurrent protection element of the sheet.

In the case of embedding a glass cloth in the resistance layer 1, the conductive substance 4, the resin 5 and the solvent are weighed and mixed by a ball mill to form a coating material, and the belt-shaped glass cloth is dipped in the coating material and rolled. And then dried, and then a sheet 1A is prepared by hot pressing.

On the other hand, in order to form the adhesive layer 3 on the rough surface 2a of the electrode 2, the powdery conductive substance 7, the resin 8 and the solvent are weighed and mixed by a ball mill to form a paint 9.
Is applied to the rough surface 2a of the metal foil 2A to be an electrode by the spray device 10 and dried.

On both sides of the sheet 1A obtained as described above, the adhesive layer 3 is sandwiched between the metal foils 2A coated with rough surfaces, and 10
A material is prepared by heating and pressing at 0 to 200 ° C. and 1 to 10 MPa. Then, punch out the sheet-shaped material and
The overcurrent protection element shown in (A) and (B) is obtained. In addition,
The adhesive layer 3 may be integrated by heating and pressurizing it by interposing the sheet-shaped one between the metal foil 2A and the resistance layer sheet 1A.

In the present embodiment, the structure in which only one resistance layer 1 is provided has been described, but in the case of a multilayer structure, both surfaces of the intermediate layer electrode 2 are formed on the rough surface 2a, and the upper and lower electrodes are formed. In No. 2, the adhesive layer 3 is formed on the rough surface with only one surface being a rough surface, and the resistance layer 1 is sandwiched between the adhesive layers 3 and laminated by heating and pressing.

[0021]

Example 1 (1) Formation of Resistance Layer 1 An overcurrent protection device having the structure shown in FIG. 1 was obtained by the following steps. PVDF as a thermoplastic resin forming the resistance layer 1
A silane coupling agent (KBC1003, manufactured by Shin-Etsu Chemical Co., Ltd.) for improving the wettability between the resin and the conductive material is added to 100 parts by weight of PVDF for (Kiner 711, manufactured by Elf Atchem North America, USA). On the other hand, 2,5-dimethyl-2,5-di (t-butylperoxine) hexyne-3, which is an organic peroxide for adding 10 parts by weight, and promoting a crosslinking reaction to improve heat resistance. 1 part by weight was added and dissolved in an NMP (N-methyl-pyrrolidone) solution, and WC as a conductive substance was further added.
Powder (WC-F manufactured by Nippon Shinkin Co., Ltd., average particle size 0.65)
μm) in the mixture with the resin to a final content of 3
The mixture was weighed and mixed in a stirring tank so as to be 0% by volume, and was further made into a paint by a ball mill in which steel balls were mixed as a medium.

After the conductive substance is appropriately dispersed in the mixture by the above-mentioned steps, the coating mixture is put in a coating tank, and the glass cloth fed from the reel is dipped in the mixture, Then, the film thickness was controlled to be constant by passing through a film thickness control roller. After that, the NMP solution was blown through a drying furnace to dry PVDF to obtain a resistance layer sheet 1A having PTC characteristics. Then, after cooling this sheet 1A, it was wound up on a winding reel.

Next, the sheet 1A wound on the reel was cut out into a constant width by a cutter while being fed out. Next, the sheet thus obtained was pressed from above and below with a press plate heated to 200 ° C. at a pressure of 2 MPa for 15 minutes.
It was heated and formed into a sheet having a thickness of 0.2 mm.

(2) Formation of Electrode Metal Foil 2A and Adhesive Layer 3 Electrode copper foil having a roughened surface was used as the electrode metal foil 2A. The resin for forming the adhesive layer 3 is PVDF.
(Kainer 711: melting point 170 ° C.) was used. Carbon black (CB) (EC600 manufactured by Ketjen Black International) was used as the conductive material. Other additives and solvents were used in the same manner as in the production method for the resistance layer 1, and the mixture was mixed so that the addition amount of the carbon black resin and the carbon black was 20 VOL% with respect to the total amount, to form a paint. This paint was applied to a sheet which will be the electrode 2 and dried. The thickness of the metal foil 2A was 35 μm, and the thickness of the adhesive layer 3 was 15 μm.

(3) Lamination The resistance layer sheet 1A cut, heated and pressure-molded as described in (1) above is sandwiched between the electrode sheets 2A having the adhesive layer 3 provided on the rough surface, and 200 ° C. Then, it was fixed by pressurizing and heating at a pressure of 5 MPa for 10 minutes.

(4) Chip formation Next, it was cut out into a chip size by punching or dicing.

[0027]

Example 2 The amount of conductive material added to the resistance layer 1 is 25 VO.
A sample was prepared in the same manner as in Example 1 except that the content was changed to L%.

[0028]

Example 3 A sample was prepared in the same manner as in Example 1 except that a polychlorotrifluoroethylene resin having a melting point of 220 ° C. (Daiflon manufactured by Daikin Industries, Ltd.) was used as the resin for the adhesive layer 3.

[0029]

Example 4 A sample was produced in the same manner as in Example 1 except that carbon black (Tokai Black # 4500 manufactured by Tokai Carbon Co., Ltd.) was used as the conductive material of the resistance layer 1 and the addition amount was 25 VOL%.

[0030]

[Example 5] A sample was prepared in the same manner as in Example 1 except that the electrode 2 of the resistance layer 1 was subjected to surface-expansion treatment of aluminum.

[0031]

Comparative Example 1 A sample was prepared in the same manner as in Example 1 except that the adhesive layer 3 was not provided.

[0032]

Comparative Example 2 As a resin used for the adhesive layer 3, Examples 1 to 1
PVDF with a melting point lower than 4 (US Elf Atchem.
Kainer ADS manufactured by North America (melting point: 93
A sample was prepared in the same manner as in Example 1 except that (.degree. C.)) was used.

[0033]

Comparative Example 3 A sample was prepared in the same manner as in Example 1 except that an epoxy resin which was a thermosetting resin was used as the adhesive layer 3.

[Evaluation] Examples 1 to 5 and Comparative Examples 1 to 3
The initial resistance value and the rate of resistance change due to reflow were obtained. The conditions for the reflow test are that the preheating temperature is 150 ° C. for 100 seconds,
The peak temperature was 230 ° C. for 50 seconds. The reflow resistance change rate r was calculated by the following equation (1). r = (R2-R1) / R1 (1) where R2: resistance after reflow, R1: initial resistance Table 1 shows the compositions in Examples 1 to 5 and Comparative Examples 1 to 3,
The initial resistance value and the resistance change rate due to reflow are shown.

[0035]

[Table 1]

As shown in Table 1, the adhesive layer 3 according to the present invention
In the case of Examples 1 to 5 provided with, the rate of change in resistance due to reflow is reduced as compared with the case where the adhesive layer 3 is not provided as in Comparative Example 1 (that is, increase in resistance value due to reflow is suppressed). I understand.

Further, the electrode 2 of Example 5 which has been subjected to the surface widening treatment of aluminum has a low initial resistance value and a small resistance change rate due to reflow.

Further, in the case of Comparative Example 2 in which the melting point lower than that of the resistance layer 1 is used as the resin of the adhesive layer 3, the resistance change rate due to the reflow becomes large. On the other hand, as the resin of the adhesive layer 3,
In the case of Examples 1 to 5 in which the melting point is the same as or higher than that of the resistance layer 1, the rate of resistance change due to reflow is small. In particular, in the case of Example 3 in which the melting point higher than that of the resistance layer 1 was used as the resin of the adhesive layer 3, the rate of resistance change due to reflow was small.

When a thermosetting resin is used as the resin forming the adhesive layer 3 as in Comparative Example 3, a change in resistance due to reflow is compared with the case where a thermoplastic resin is used as in Examples 1 to 5. The rate becomes very large.

[0040]

According to the present invention, since an adhesive layer made of a thermoplastic resin having no PTC characteristic and containing a conductive substance is interposed between both main surfaces of the resistance layer and the electrode, the on / off state is improved. It is possible to suppress an increase in resistance value caused by thermal deformation that occurs when heat having a temperature exceeding the melting point of the thermoplastic resin forming the resistance layer is applied during repetition or reflow.

[Brief description of drawings]

FIG. 1A is a perspective view showing an embodiment of an overcurrent protection element according to the present invention, and FIG. 1B is a sectional view thereof.

FIG. 2 is a process drawing showing an example of a manufacturing process of an overcurrent protection element of the present invention.

[Explanation of symbols]

1: Resistance layer, 1A: Resistance layer sheet, 2: Electrode, 2A:
Metal foil, 2a: rough surface, 3: adhesive layer, 3a: rough surface

Claims (3)

[Claims] 1. A chip type having a resistance layer having a positive resistance temperature characteristic in which a conductive material is dispersed in a thermoplastic resin, and at least one positive temperature coefficient thermistor layer having a pair of electrodes sandwiching the resistance layer. An overcurrent protection element, characterized in that an adhesive layer made of a thermoplastic resin having no PTC characteristic and containing a conductive substance is interposed between both main surfaces of the resistance layer and the electrode. Type overcurrent protection element. 2. The chip-type overcurrent protection device according to claim 1, wherein the melting point of the thermoplastic resin forming the adhesive layer is equal to or higher than the melting point of the thermoplastic resin forming the resistance layer. Chip type overcurrent protection device. 3. The chip-type overcurrent protection device according to claim 1, wherein the electrode is a surface-expansion foil of aluminum.