JP2004265617A - Protective element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To eliminate bad fusion of a fuse element by securing a sufficient wetting area for the melted fuse element. <P>SOLUTION: In a protective element, a low-melting point metallic body 2 is disposed among a plurality of electrodes 4, 5 formed on a base substrate 1, and a current is intercepted by fusing the metallic body 2 with low melting point. An insulating cover plate 13 is disposed so as to face the base plate 1, and a metallic pattern 15 is formed on the cover plate 13 so as to face at least one electrode. By forming the metallic pattern 15 on the cover plate 13, an area having a wettability to the melted metallic body 2 is substantially enlarged, the melted metallic body 2 is quickly drawn into the gap between the electrodes 4, 5 and the metallic pattern 15. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
TECHNICAL FIELD The present invention relates to a protection element for interrupting an electric current due to fusing of a low-melting metal body when an abnormality occurs.
[0002]
[Prior art]
As a protection element that can be used to prevent not only an overcurrent but also an overvoltage, a protection element in which a heating element and a low-melting-point metal body are laminated on a substrate is known (for example, see Patent Documents 1 and 2). ). In the protection elements described in these patent documents, current is applied to the heating element when an abnormality occurs, and the heating element generates heat, so that the low-melting metal body is melted. The molten low-melting metal body is attracted to the electrode due to the good wettability to the electrode surface on which the low-melting metal body is placed, and as a result, the low-melting metal body is melted and the current is interrupted. You.
[0003]
As a connection mode between the low-melting point metal body and the heating element of this type of protection element, as described in Patent Documents 3 and 4, etc., without stacking the low-melting point metal body on the heating element, There is also known a mode in which a low-melting metal body and a heating element are arranged in a plane on a substrate and connected to each other, but the power supply to the heating element is cut off simultaneously with the fusing of the low-melting metal body. The effect is the same.
[0004]
By the way, with the miniaturization of portable devices and the like, this type of protection element is also required to be thinner. As one means for achieving the purpose, a fuse (low melting point metal body) is provided on an insulating substrate. A method of arranging and sealing this with an insulating cover plate and a resin to reduce the thickness has been proposed (for example, see Patent Document 5). In the substrate type thermal fuse described in Patent Document 5, a fuse mounting membrane electrode is formed on one surface of an insulating substrate, a low melting point fusible alloy piece is bridged between the membrane electrodes, and flux is applied to the low melting point fusible alloy piece. Applying, disposing an outer insulating cover plate smaller than the insulating substrate on one surface of the insulating substrate, filling a gap between a peripheral edge of the insulating cover plate and a peripheral edge of the insulating substrate with a sealing resin, The outer surface between the peripheral edge of the insulating cover plate of the sealing resin and the peripheral edge of the insulating substrate is formed as a concave curved inclined surface or a linear inclined surface.
[0005]
[Patent Document 1]
Japanese Patent No. 2790433 [0006]
[Patent Document 2]
Japanese Patent Laid-Open Publication No. Hei 8-161990
[Patent Document 3]
Japanese Patent Application Laid-Open No. 10-116549
[Patent Document 4]
JP 10-116550 A
[Patent Document 5]
JP-A-11-111138
[Problems to be solved by the invention]
However, in the method of sealing and thinning with an insulating cover plate and a resin as in the invention described in Patent Document 5, the space for accommodating the low-melting-point metal body is reduced, and the electrode area is reduced due to the downsizing. Since it tends to be smaller, there is a possibility that a fusing defect may occur. That is, as described above, the above-described substrate-type fuse is blown by the molten fuse element (low-melting metal body) flowing into the membrane electrode on the substrate. At this time, if the electrode area is sufficiently large and the volume on the electrode is secured, there is not much problem. However, if it is not, the fuse element cannot be blown even if it is melted. This is because, when the molten fuse element flows into the electrode, a phenomenon occurs in which it rises in the height direction. In the above case, the electrode alone cannot sufficiently draw the molten fuse element, and This is because a phenomenon such as contact between the fuse elements occurs.
[0011]
In recent years, the size and thickness of devices have been increasingly reduced, and the problem has become more serious as the protection elements have been required to be further reduced in size and thickness. In addition, the cross-sectional area of the fuse element has been increasing due to the high current rating. From this point, the problem has been further increased, and it is desired to solve the problem.
[0012]
The present invention has been proposed in view of such a conventional situation, and it is possible to secure a sufficient wet area with respect to a molten fuse element (a low-melting metal body), and to reduce a fusing defect of the fuse element. An object of the present invention is to provide a protection element which does not occur, can reliably cut off current when an abnormality occurs, and has stable operation characteristics.
[0013]
[Means for Solving the Problems]
In order to achieve the above object, a protection element according to the present invention has a low melting point metal body disposed between a plurality of electrodes formed on a base substrate, and a current is cut off by fusing the low melting point metal body. In the device, an insulating cover plate is provided so as to face the base substrate, and a metal pattern is formed on the insulating cover plate so as to face at least one electrode.
[0014]
In the protective element of the present invention, since the metal pattern showing good wettability with respect to the molten low-melting metal is also formed on the insulating cover plate, when the low-melting metal body is abnormally melted, the electrode is In addition, the metal pattern also functions to attract the molten low melting point metal. Therefore, for example, even when the space for accommodating the low-melting-point metal body is small, the low-melting-point metal melted in a manner similar to a capillary phenomenon is quickly drawn into the gap between the electrode and the metal pattern, and the low-melting-point metal is reliably formed The body is blown.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a protection element to which the present invention is applied will be described in detail with reference to the drawings.
[0016]
FIG. 1 shows an example (first embodiment) of a protection element to which the present invention is applied. FIG. 1 is a plan view with the insulating cover plate removed. The protection element of this example is a so-called substrate-type protection element (substrate-type fuse), and a low-melting-point metal body 2 serving as a fuse for interrupting current by fusing on a base substrate 1 of a predetermined size. A heating element (heater) 3 for generating heat at the time of abnormality and melting the low-melting metal body 2 is disposed in parallel and close to each other.
[0017]
Here, the material of the base substrate 1 may be any material as long as it has an insulating property. For example, a substrate used for a printed wiring board such as a ceramic substrate or a glass epoxy substrate, a glass substrate, a resin A substrate, an insulated metal substrate, or the like can be used. Among them, a ceramic substrate which is an insulating substrate having excellent heat resistance and good thermal conductivity is preferable.
[0018]
Further, as a material for forming the low melting point metal body 2 having a function as a fuse, various low melting point metal bodies conventionally used as a fuse material can be used. For example, JP-A-8-161990 The alloys and the like described in Table 1 can be used. Specifically, BiSnPb alloy, BiPbSn alloy, BiPb alloy, BiSn alloy, SnPb alloy, SnAg alloy, PbIn alloy, ZnAl alloy, InSn alloy, PbAgSn alloy, and the like can be given. Further, the shape of the low melting point metal body 2 may be a flake shape or a rod shape.
[0019]
The heating element 3 is formed by applying a resistive paste made of a conductive material such as ruthenium oxide or carbon black and an inorganic binder such as water glass or an organic binder such as a thermosetting resin, and firing as necessary. Can be formed by Further, a thin film of ruthenium oxide, carbon black, or the like may be formed by printing, plating, vapor deposition, or sputtering, or may be formed by sticking, laminating, or the like of these films.
[0020]
On the surface of the base substrate 1, a pair of electrodes 4 and 5 for the low melting point metal body 2 and a pair of electrodes 6 and 7 for the heating element 3 are formed. The low melting point metal body 2 and the heating element 3 are formed so as to be connected to 6, 7. Leads 8, 9, 10, 11 are connected to the electrodes 4, 5, 6, 7, respectively, and serve as external terminals.
[0021]
The electrode into which the molten low-melting metal body 2 flows, that is, the constituent material of the electrodes 4 and 5 for the low-melting metal body 2 is also not particularly limited, and has good wettability with the low-melting metal body 2 in a molten state. Can be used. For example, a metal simple substance such as copper, or a material whose at least surface is formed of Ag, Ag-Pt, Ag-Pd, Au or the like is used. Although it is not necessary to consider the wettability of the electrodes 6 and 7 for the heating element 3 with the low melting point metal body 2 in the molten state, usually, the electrodes 6 and 7 are collectively provided with the electrodes 4 and 5 for the low melting point metal body 2. Since it is formed, it is formed of the same material as the electrodes 4 and 5 for the low melting point metal body 2.
[0022]
For the leads 8, 9, 10, and 11, a metal wire such as a flat processed wire or a round wire is used. When the wires are attached to the electrodes 4, 5, 6, and 7 by soldering or welding, they are electrically connected to the electrodes. Connected. In the case of adopting such a form with leads, by making the positions of the leads bilaterally symmetrical, the work can be performed without being conscious of the mounting surface during the mounting work.
[0023]
On the low melting point metal body 2, an inner sealing portion 12 made of flux or the like is provided in order to prevent surface oxidation. As the flux, any known flux such as a rosin-based flux can be used, and the viscosity and the like are also arbitrary.
[0024]
The above is the internal structure of the protection element of the present embodiment. In the protection element of the present embodiment, as shown in FIG. 2, an insulating cover plate 13 is provided so as to cover the low melting point metal body 2 and the heating element 3. Have been. The insulating cover plate 13 is fixed at a predetermined distance to the base substrate 1 by arranging a resin 14 around the insulating cover plate 13, and the low-melting-point metal body is provided in a space between the insulating cover plate 13 and the base substrate 1. 2 and the heating element 3 are accommodated.
[0025]
By providing the insulating cover plate 13, for example, the rise of the sealing resin can be suppressed, and the overall thickness of the protection element can be reduced. Here, the material of the insulating cover plate 13 may be any material as long as it is an insulating material having heat resistance and mechanical strength enough to withstand fusing of the low melting point metal body 2, for example, glass, ceramics, plastic Various materials such as a substrate material used for a printed wiring board such as a glass epoxy substrate can be applied. Further, the insulating cover plate 13 may be formed by using a metal plate and forming an insulating material layer such as a resin or a resist on a surface facing the base substrate 1 to make the insulating cover plate 13. In particular, when a material having high mechanical strength such as a ceramic plate is used, the thickness of the insulating cover plate 13 itself can be reduced, which greatly contributes to a reduction in the thickness of the entire protection element.
[0026]
The insulating cover plate 13 is made of a material having excellent thermal conductivity, such as a ceramic plate, and is brought into contact with the base substrate 1 via a flux, so that heat from a portion other than a normal mounting contact surface (the base substrate 1 side) is obtained. , A fuse with good responsiveness can be obtained. In this case, the size of the insulating cover plate 13 is preferably equal to the size of the base substrate 1 from the viewpoint of detecting heat from both sides, but is not limited thereto, and one of the two may be smaller or larger. However, the same effect can be obtained.
[0027]
The insulating cover plate 13 may be a mere flat plate or a so-called cap having a rising wall around it. In the former case, it is necessary to seal the periphery with a resin. In the latter case, for example, the insulating cover plate 13 may be simply bonded to the base substrate 1.
[0028]
On the surface of the insulating cover plate 13 facing the base substrate 1, there is formed a metal pattern 15 exhibiting good wettability with respect to the molten low-melting-point metal body 2, which is a protective element of the present invention. This is the most characteristic matter. Hereinafter, the metal pattern 15 will be described in detail.
[0029]
As shown in FIG. 3, the metal pattern 15 formed on the surface of the insulating cover plate 13 facing the base substrate 1 substantially corresponds to the electrodes 4 and 5 for the low melting point metal body 2 on the base substrate 1. They are formed at substantially the same size at the same position. The material of the metal pattern 15 is not necessarily limited to metal as long as it has good wettability with respect to the low-melting metal body 2 that is more molten than the insulating cover plate 13. Since it is difficult to obtain the property, it is effective to use a metal material.
[0030]
The metal pattern 15 may be selected from a metal material having good wettability with respect to the molten low melting point metal body 2 from such a viewpoint, and may be variously selected from Ag, Ag-Pt, Ag-Pd, and Au. Various materials can be applied.
[0031]
For example, when the insulating cover plate 13 is made of a ceramic plate, the metal pattern 15 can be formed by printing a conductive paste containing the metal material and firing the conductive paste. When the insulating cover plate 13 is made of a material having poor heat resistance, such as plastic, for example, a metal film is formed on the insulating cover plate 13 by a method such as evaporation or sputtering, and is formed by patterning by etching. be able to. When a board material used for a printed wiring board such as a glass epoxy board is used for the insulating cover plate 13, for example, a copper-clad board to which a copper foil is adhered is used and the board is formed by patterning by wet etching or the like. Can be. Further, when a metal plate having an insulating material layer such as a resin or a resist formed on the surface facing the base substrate 1 is used as the insulating cover plate 13, the insulating material layer is selectively removed (for example, the resist layer is removed). It is also possible to use the exposed metal plate as the metal pattern 15 by patterning by a method such as printing.
[0032]
As described above, the insulating cover plate 13 and the base substrate 1 correspond to the electrodes 4 and 5 for the low melting point metal body 2 on the base substrate 1 into which the molten low melting point metal flows when the low melting point metal body 2 is melted. By forming the metal pattern 15 having such a property that the molten low melting point metal is easily wetted on the facing surface, it is possible to secure a sufficient molten low melting point metal wet area inside the element while making the protection element a thin element. Even at the rated current (the cross-sectional area of the low melting point metal body 2 is large), stable operation characteristics can be obtained.
[0033]
FIG. 4 shows the difference in the flow of the molten low melting point metal onto the electrodes 4 and 5 depending on the presence or absence of the metal pattern 15. When only the electrodes 4 and 5 have good wettability with respect to the molten low melting point metal body 2, as shown in FIG. 4 (a), they are attracted onto the electrodes 4 and 5 in a swelling manner like water droplets. . At this time, if the amount of the molten low melting point metal body 2 is large or if the gap between the base substrate 1 and the insulating cover plate 13 is narrow and the top of the molten low melting point metal body 2 is pressed by the insulating cover plate 13, the electrode 4 , 5 on the electrode 4 and the low melting point metal body 2 on the electrode 5 may come into contact with each other. When the low-melting metal members 2 on the electrodes 4 and 5 come into contact with each other, the low-melting metal members 2 are electrically conducted, and the low-melting metal members 2 are not blown.
[0034]
On the other hand, when the metal pattern 15 is formed on the insulating cover plate 13, the area of the surface exhibiting wettability with respect to the molten low melting point metal body 2 is substantially enlarged, and FIG. As shown in FIG. 2B, the molten low-melting metal body 2 is quickly drawn into the gap between the electrodes 4 and 5 and the metal pattern 15. At this time, a state like a so-called capillary phenomenon occurs, and the molten low-melting metal body 2 is held in a state of forming a meniscus, and the protrusion in the lateral direction is suppressed. Therefore, the contact of the molten low melting point metal body 2 due to the protrusion is eliminated, and the low melting point metal body 2 is reliably blown.
[0035]
Here, the metal pattern 15 is formed at a position facing the electrodes 4 and 5 to have the same size as the electrodes 4 and 5, but is not limited thereto. However, the formation position of the metal pattern 15 is set so as to include the center of the effective area of the electrodes 4 and 5 on the base substrate 1 side for the molten low melting point metal body 2 (the top of the pool of the low melting point metal body 2 after melting). Preferably, it is formed.
[0036]
Further, by making the distance w1 between the metal patterns 15 closer to the distance w2 between the electrodes 4 and 5 on the base substrate 1, it is possible to improve the cutting characteristics when the low-melting metal body 2 is melted. However, it is necessary to secure a minimum distance (for example, 0.2 mm or more) that can guarantee complete fusing as the distance w1.
[0037]
On the other hand, although the distance t between the insulating cover plate 13 and the base substrate 1 is sufficient, if a sufficient wet area can be secured, the insulating cover plate 13 is in close contact with the low melting point metal body 2 (the low melting point metal body 2). The thickness t is preferably 1.2 to 4 times the thickness of the low melting point metal body 2. If the distance t is less than 1.2 times the thickness of the low-melting metal body 2, it is difficult to guarantee quick fusing by the melt flow of the low-melting metal body 2. On the other hand, if the distance t exceeds four times the thickness of the low-melting metal body 2, the distance may be too large and the metal pattern 15 may not be wet, and the thinning which is the original purpose may be achieved. Difficult to achieve.
[0038]
As described above, in the protection element of the present embodiment, the effective wetting area for the molten low-melting metal body 2 is increased by maximizing the space on the insulating cover plate 13 side. Even if the current is high (the cross-sectional area of the low-melting metal body 2 is large), the area of the melt flowing in can be secured by that amount, and stable fusing can be guaranteed.
[0039]
Next, another embodiment (second embodiment) of the protection element to which the present invention is applied will be described. Note that the protection element of the present embodiment is an example of a protection element in which a heating element and a low-melting metal body are not arranged in a plane, but are arranged in a state where they are overlapped.
[0040]
As shown in FIGS. 5A to 5C, the protection element of this embodiment is provided with low melting point metal body electrodes 22a, 22b, and 22c on a base substrate 21, and these electrodes 22a, 22b are provided. , 22c are provided so as to be bridged between the low-melting metal bodies 23 (23a, 23b). On the lower surface side of the central electrode 22c, a heating element 25 is provided via an insulating layer 24. The heating element 25 is electrically heated between the wirings 26x and 26y derived from the heating element electrode 26a and the heating element electrode 26b. The heating element electrode 26b is electrically connected to the low melting point metal element electrode 22c. Therefore, when the heating element 25 generates heat, the low-melting metal member 23a between the electrodes 22a and 22c and the low-melting metal member 23b between the electrodes 22b and 22c are melted, and the power supply to the protected device is cut off. 25 is also cut off. FIG. 6 shows a circuit diagram of the protection element configured as described above.
[0041]
In the protection device of the present embodiment, similarly to the case of the protection device of the first embodiment, the insulating cover plate 27 is provided so that the entire protection device can be made thinner and the base of the insulating cover plate 27 can be formed. As shown in FIG. 7, a metal pattern showing good wettability with respect to the low melting point metal body 23 corresponding to each low melting point metal body electrode 22a, 22b, 22c is formed on the surface facing the substrate 21. 28a, 28b and 28c are formed.
[0042]
Here, it is ideal that the metal patterns 28a, 28b, 28c are formed in three places corresponding to the low melting point metal body electrodes 22a, 22b, 22c. However, the present invention is not limited to this. Only the metal pattern 28c may be formed in a form corresponding to only the melting point metal body electrode 22c. In the case of the protection element of the present embodiment, the heating element 25 is formed immediately below the central low-melting-point metal electrode 22c. Melting starts from a part of the low melting point metal body 23. Therefore, if the low-melting metal body 23 melted by the action of the metal pattern 28c is drawn in this portion, fusing occurs promptly and the power supply to the protected device is cut off.
[0043]
In the protection element of the present embodiment (second embodiment) as well, the formation of the metal patterns 28a, 28b, and 28c makes the effective element for the molten low melting point metal body 23 similar to the previous embodiment (first embodiment). The wet area can be enlarged, and stable melting of the low melting point metal body 23 can be guaranteed.
[0044]
【Example】
Next, specific examples to which the present invention is applied will be described based on experimental results.
[0045]
Example This example is an example in which a protection element is manufactured according to the configuration of the first embodiment. That is, a 0.5 mm-thick ceramic substrate having a size of 6 mm × 6 mm was used as a base substrate, and electrodes were formed thereon. As each electrode, an Ag-Pd electrode was formed by printing.
[0046]
Then, a heating resistor was formed by printing a ruthenium oxide-based heating resistor material between a pair of electrodes and baking it. The electric resistance of the formed heating resistor was 4Ω. A low-melting-point metal (width 1 mm, thickness 0.3 mm) was connected between the other pair of electrodes by welding and sealed with a rosin-based flux. In addition, a Ni-plated Cu lead wire (width 1 mm, thickness 0.5 mm) was connected to each electrode by soldering.
[0047]
Next, a two-liquid epoxy resin is applied to the outer periphery of the ceramic substrate, and an insulating cover plate (size: 6 mm × 6 mm, thickness: 0.5 mm) made of ceramic is placed and pushed until it comes into contact with the lead wire at 40 ° C. It was cured under the condition of 8 hours.
[0048]
A metal pattern having the same dimensions was formed on the insulating cover plate so as to face the electrode to which the low melting point metal was connected. The metal pattern was formed by printing and firing an Ag-Pd paste in the same manner as the electrodes.
[0049]
Comparative example [0050]
The basic configuration of the protection element is the same as in the previous embodiment. However, the difference from the embodiment is that no metal pattern is formed on the insulating cover plate.
[0051]
Evaluation result [0052]
With respect to the protection elements (10 pieces each) of the examples and the comparative examples produced as described above, 2 W of electric power was applied to the heating resistor, and the fusing of the low melting point metal body was confirmed. As a result, it was found that the low-melting-point metal body was blown out in an average of 30 seconds in all of the ten protection elements in the protection element of the example.
[0053]
On the other hand, in the protection element of the comparative example, even when a power of 2 W was similarly applied, it was found that the low-melting-point metal body did not flow into the electrode and was not blown out in three out of ten. When the protection element that caused the fusing failure was disassembled and the inside was observed, the molten low-melting metal body (fuse element) came into contact with the insulating cover plate side and was extruded. It was confirmed that there was not enough space.
[0054]
【The invention's effect】
As is clear from the above description, according to the present invention, since the metal pattern is formed on the insulating cover plate, it is necessary to secure a sufficient wet area for the fused fuse element (low-melting metal body). Therefore, the occurrence of a fusing defect of the fuse element can be suppressed. Therefore, it is possible to reliably shut off the current in the event of an abnormality and to provide a protection element having stable operation characteristics.
[Brief description of the drawings]
FIG. 1 is a plan view illustrating an internal structure of a protection element according to a first embodiment.
FIG. 2 is a schematic sectional view showing a state of sealing with an insulating cover plate.
FIG. 3 is a plan view showing a surface of the insulating cover plate facing the base substrate.
4A and 4B are schematic diagrams showing a state of a molten low-melting metal on an electrode, wherein FIG. 4A shows a case where a metal pattern is not formed on an insulating cover plate, and FIG. Each case is shown.
FIGS. 5A and 5B are diagrams showing an internal structure of a protection element according to a second embodiment, wherein FIG. 5A is a plan view, FIG. 5B is a cross-sectional view taken along line xx, and FIG. FIG.
FIG. 6 is a circuit diagram illustrating a circuit configuration of a protection element according to a second embodiment.
FIG. 7 is a plan view showing a surface of an insulating cover plate facing a base substrate according to a second embodiment.
[Explanation of symbols]
1, 21 Base substrate 2, 23 Low melting point metal body 3, 25 Heating element 4, 5, 6, 7 Electrode 8, 9, 10, 11 Lead 13, 27 Insulating cover plate 14 Resin 15, 28a, 28b, 28c Metal pattern

Claims (7)

A low-melting metal body is arranged between a plurality of electrodes formed on a base substrate, and in a protection element in which current is cut off by fusing of the low-melting metal body,
A protection element, wherein an insulating cover plate is provided facing the base substrate, and a metal pattern is formed on the insulating cover plate facing at least one electrode. 2. The protection element according to claim 1, wherein a heating element is provided near the low-melting metal body, and the low-melting metal body is blown off by the heat generated by the heating element. The protection element according to claim 2, wherein a metal pattern is formed on the insulating cover plate so as to face an electrode closest to the heating element. The protection element according to claim 1, wherein a plurality of metal patterns are formed corresponding to the plurality of electrodes. The protection element according to claim 4, wherein a distance between the metal patterns is smaller than a distance between the electrodes. The protection element according to claim 4, wherein a distance between the metal patterns is 0.2 mm or more. 2. The protection element according to claim 1, wherein a distance between the base substrate and the insulating cover plate is 1.2 to 4 times a thickness of the low melting point metal body.

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