JP6429591B2 - Protective element - Google Patents

Description

  The present invention relates to a protection element that protects a circuit connected on a current path by fusing the current path at the time of abnormality.

  As a chip-shaped fuse, a protection element in which a heating element is provided on a substrate and a fuse element is provided in proximity to the heating element is known. Such a protective element prevents overcharge (overvoltage) and overcurrent in a battery including a lithium ion secondary battery used in a notebook PC, a tablet terminal, or the like.

  As such a protective element, for example, in Patent Document 1, a low melting point metal and a heating element are in contact with each other through an insulating layer, and the heating element is energized when the detection element detects a predetermined condition. Thus, a protection element that melts the low-melting-point metal by heat generation from the heating element is described.

  Further, in Patent Document 2, at least a part of the cross section of the low melting point metal body is divided into two or more independent cross sections when the heating element generates heat, between a pair of electrodes that pass current through the low melting point metal body. Thus, a protective element is described in which a groove extending in the direction of current flow is formed in the center of the low melting point metal body.

  Furthermore, Patent Document 3 describes a protective element in which a fuse element is provided on an electrode on a substrate without using a solder paste by adjusting a liquid phase point and a solid phase point of the fuse element.

  Patent Document 4 describes a protective element provided with a fusible metal layer in which a high melting point metal film and a low melting point metal film are laminated so as to conduct between electrodes formed on an insulating substrate. Yes.

Japanese Patent No. 2790433 Japanese Patent No. 4110967 Japanese Patent No. 4735874 JP 2004-185960 A

  However, in structures such as Patent Document 1 and Patent Document 2, a plurality of layers are formed by connecting the electrode and the low-melting-point metal body with a connecting material such as solder, so that the heating element and the soluble conductor The thermal conductivity between the two becomes low, but no countermeasures for this point are described. Patent Document 3 and Patent Document 4 are mainly characterized by the configuration of the soluble conductor, and the solder paste for connection can be reduced by improving the protective element electrode, and the heating element and the soluble conductor. No mention is made of increasing the thermal conductivity during the period.

  The present invention has been proposed in view of such circumstances, and is excellent in thermal conductivity between the heating element and the soluble conductor, improving reliability as a protective element, and realizing low profile and compact size. An object of the present invention is to provide a protective element that can be used.

One aspect of the present invention is a protective element that has a heating element and a soluble conductor on an insulating substrate, and that melts the soluble conductor by the heat generated by the heating element, and includes a first element and a first element provided on the insulating substrate. 2, the fusible conductor connected to the first and second terminals, the heating element stacked on the insulating substrate and connected to the third terminal, and so as to cover the heating element The insulating member to be laminated, the first and second terminals, the fusible conductor, and the heating element and the fusible conductor can each be electrically connected individually , and partly soluble. A connection conductive material, and the connection conductive material contains at least a low melting point metal and a high melting point metal.

  According to one embodiment of the present invention, since the connection conductive material functions as both an electrode and a connection agent, it has excellent thermal conductivity between the heating element and the soluble conductor, and can improve the reliability as a protection element. .

  At this time, in one embodiment of the present invention, the connection conductive material further contains a resin material, and the ratio of the total weight of the low melting point metal and the high melting point metal to the weight of the resin material is 80:20 to 99.5: 0. 5.

  By increasing such a ratio, especially the ratio of the resin material, it is possible to ensure that the fusible conductor is blown out in the event of an abnormality even under conditions such as standing for several years at high temperature and high humidity or low temperature, The reliability as a protective element can be further enhanced.

  In one embodiment of the present invention, the weight ratio of the low melting point metal to the high melting point metal is 10:90 to 90:10.

  By blending the low melting point metal and the high melting point metal at such a ratio, even when the heat of mounting reflow is applied, the low melting point metal melts and connects to the soluble conductor, whereas the high melting point metal is Since it does not melt and can stay in place, it can be used as an electrode.

  In one embodiment of the present invention, the low-melting-point metal and the high-melting-point metal that are raw materials for the connection conductive material are each granular, and the particle size of the low-melting-point metal is larger than the particle size of the high-melting-point metal.

  As a result, when the low melting point metal melts during mounting reflow, it becomes easier to cover the high melting point metal, and the continuity as the connection conductive material can be increased by further reducing the gap between the metals.

  In one embodiment of the present invention, the heating element is stacked on the surface of the insulating substrate opposite to the surface to which the soluble conductor is connected.

  Thereby, since a soluble conductor is planarized on a connection conductive material, the fusing characteristic of a soluble conductor can be improved.

  According to the present invention, the connection conductive material in which the low melting point metal and the high melting point metal are mixed is used as the electrode, so that the thermal conductivity between the heating element and the soluble conductor is excellent, and the reliability as the protection element is improved. In addition, it is possible to realize a low profile and a compact size.

(A) is a top view of the protection element which concerns on one Embodiment of this invention, (B) is AA sectional drawing of the protection element which concerns on one Embodiment of this invention. It is sectional drawing of the protection element which concerns on one Embodiment of this invention when a heat generating body exists in the surface on the opposite side to the surface where a soluble conductor is laminated | stacked. It is a figure which shows the circuit structural example of the protection element which concerns on one Embodiment of this invention. (A) is a top view at the time of fusing of the protection element concerning one embodiment of the present invention, and (B) is an AA sectional view at the time of fusing of the protection element concerning one embodiment of the present invention. . It is the graph showing the ratio of the required electric power when the connection conductive material in an Example and a comparative example melted. (A) is a top view of the protection element of a prior art example, (B) is AA sectional drawing of the protection element of a prior art example. (A) is a top view of a protection element when a connecting material such as solder is disposed in the protection element of the conventional example, and (B) is a low melting point solder melted by heat during reflow on the insulating layer. It is a top view showing an example of the state to aggregate.

Hereinafter, embodiments of the present invention will be described in detail in the following order with reference to the drawings. The present embodiment described below does not unduly limit the contents of the present invention described in the claims, and all the configurations described in the present embodiment are essential as means for solving the present invention. Not necessarily.
1. 1. Configuration of protection element Protection element operation

<1. Configuration of protection element>
As shown in FIG. 1, a protection element 10 according to an embodiment of the present invention has a heating element 12 and a soluble conductor 14 on an insulating substrate 11, and the soluble conductor 14 is blown by the heat generation of the heating element 12. This is the protective element 10. The protective element 10 includes a first terminal 15A and a second terminal 15B provided on the insulating substrate 11, a fusible conductor 14 connected to the first and second terminals 15A and 15B, and an insulating substrate 11. The heating element 12 is stacked and connected to the third terminal 15C, the insulating member 13 is stacked so as to cover the heating element 12, and the connection conductive materials 16A, 16B, and 16C. The connection conductive materials 16A, 16B, and 16C electrically connect the first and second terminals 15A and 15B and the soluble conductor 14, and the heating element 12 and the soluble conductor 14, respectively. 16B and 16C contain at least a low melting point metal and a high melting point metal.

  That is, the protection element 10 according to an embodiment of the present invention can be produced by generating heat by energizing the fusible conductor 14 connected in series via the connecting conductive material 16C and the connecting point of the fusible conductor 14. The circuit configuration includes a heating element 12 that melts the molten conductor 14. Thus, in the protection element 10, for example, the fusible conductor 14 is connected in series on the charge / discharge current path via the first and second terminals 15A and 15B, and the heating element 12 is connected via the third terminal 15C. For example, it is connected to a current control element.

  The protection element 10 having such a circuit configuration can surely melt the soluble conductor 14 on the current path by the heat generation of the heating element 12, and can realize a reduction in height and size.

  The insulating substrate 11 is formed of an insulating member such as alumina, glass ceramics, mullite, zirconia, or the like. In addition, a material used for a printed wiring board such as a glass epoxy board or a phenol board may be used.

  The heating element 12 is a conductive member that has a relatively high resistance value and generates heat when energized, and is made of, for example, W, Mo, Ru, or the like. These alloys, compositions, or compound powders are mixed with a resin binder or the like to form a paste on the insulating substrate 11 by patterning using a screen printing technique and firing.

  The insulating member 13 is disposed so as to cover the heating element 12, and the connecting conductive material 16 </ b> C is disposed so as to face the heating element 12 with the insulating member 13 interposed therebetween.

  The fusible conductor 14 is made of a low-melting-point metal that is quickly melted by the heat generated by the heating element 12, and for example, Pb-free solder containing Sn as a main component can be suitably used. The soluble conductor 14 may be a laminate of a low melting point metal and a high melting point metal such as Ag, Cu, or an alloy containing these as a main component.

  When reflow mounting is performed by laminating a high melting point metal and a low melting point metal, even if the reflow temperature exceeds the melting temperature of the low melting point metal layer and the low melting point metal melts, it melts as the soluble conductor 14. Not reached. Such a soluble conductor 14 may be formed by depositing a high melting point metal on a low melting point metal by using a plating technique, or may be formed by using another known lamination technique or film forming technique. .

  Further, a flux may be applied to almost the entire surface of the soluble conductor 14 in order to prevent oxidation of the outer high-melting point metal layer. Furthermore, a cover member may be placed on the insulating substrate 11 in order to protect the inside of the protective element 10 configured as described above.

  The connection conductive materials 16A, 16B, and 16C are metal pastes containing at least a low melting point metal and a high melting point metal. Since the connecting conductive materials 16A, 16B, and 16C contain both the low melting point metal and the high melting point metal, the connecting conductive materials 16A, 16B, and 16C function as both electrodes and a connecting agent. This two-layer structure can be made thinner with one layer of the connecting conductive material, so that the thermal conductivity between the heating element and the soluble conductor can be increased. In addition, silver (Ag), which is an example of a refractory metal, has a thermal and electrical conductivity that is 6 times higher than that of tin (Sn) used in conventional solder pastes. Also, the thermal conductivity between the heating element and the soluble conductor can be increased. Thus, by increasing the thermal conductivity between the heating element and the fusible conductor, the fusible conductor 14 can be reliably connected at the time of abnormality, and the reliability as the protection element 10 can be enhanced.

  Examples of the low melting point metal include metals having a melting point of 300 ° C. or less, such as tin (Sn) and bismuth (Bi). Examples of the refractory metal include metals having a melting point exceeding 300 ° C., such as silver (Ag) and copper (Cu).

  The weight ratio of the low melting point metal to the high melting point metal is preferably 10:90 to 90:10. When the weight ratio of the low melting point metal is less than 10% (the weight ratio of the high melting point metal exceeds 90%), the connection conductive materials 16A, 16B, and 16C hardly melt, so the terminals 15A and 15B and the soluble conductor 14 Cannot be connected. When the weight ratio of the low melting point metal exceeds 90% (the weight ratio of the high melting point metal is less than 10%), the connection conductive materials 16A, 16B, and 16C are subjected to mounting reflow as shown in FIG. For example, it melts and moves in the direction of an arrow (possibly in the opposite direction).

  Further, when the ratio of the low melting point metal is lowered, the amount of the low melting point metal that melts during mounting reflow is reduced, and the amount that covers the high melting point metal is reduced, so that the resistance value is increased. On the other hand, since the resistance value itself of the refractory metal is lower, if the ratio of the refractory metal is decreased too much, the resistance value also increases. The specific weight ratio of the low-melting point metal to the high-melting point metal is appropriately determined according to the situation, taking these into consideration.

  The weight ratio of the low melting point metal to the high melting point metal is 10:90 to 90:10, so that the low melting point metal melts and is connected to the soluble conductor 14 even when the heat of mounting reflow is applied. On the other hand, the refractory metal is not melted and can remain in place, so that it can be used as an electrode.

  The connection conductive materials 16A, 16B, and 16C may further contain a resin material. Examples of the resin material include binder resin and flux. The ratio of the total weight of the low melting point metal and the high melting point metal to the weight of the resin material is preferably 80:20 to 99.5: 0.5.

  By increasing the ratio of the resin material such that the ratio of the total weight of the low-melting point metal and the high-melting point metal to the weight of the resin material is 80:20 to 90:10, and more preferably, Even under a situation where several years have passed, the fusible conductor 14 can be surely blown out in the event of an abnormality, and the reliability of the protective element 10 can be further improved.

  Moreover, it is preferable that the particle size of the low melting point metal used as the raw material of the connection conductive material is larger than the particle size of the high melting point metal. Here, the particle size of the metal used as a raw material refers to the particle size of the low melting point metal and the high melting point metal before mounting reflow (before melting). Examples of the shape of the metal particles include a needle shape, a flat shape, an electrolytic sphere, an atomized sphere, and a block shape. Moreover, as a particle size of a metal particle, a low melting metal is 1-100 micrometers, and a high melting metal is 0.5-50 micrometers.

  Thus, by making the particle size of the low melting point metal larger than the particle size of the high melting point metal, the low melting point metal can more easily cover the high melting point metal when the low melting point metal melts during mounting reflow. Thus, the continuity as the connection conductive material can be increased by further reducing the gap between the metals.

  In one embodiment of the present invention, the heating element 22 may be laminated on the surface of the insulating substrate 21 opposite to the surface to which the soluble conductor 24 is connected.

  That is, as shown in FIG. 2, the protection element 20 includes an insulating substrate 21, first and second terminals provided on the insulating substrate 21, and a fusible conductor connected to the first and second terminals. 24, the heating element 22 stacked on the insulating substrate 21 and connected to the third terminal, the insulating member 23 stacked so as to cover the heating element 22, the first and second terminals, and the fusible conductor 24. , And connecting conductive materials 26A, 26B, and 26C that can electrically connect the heating element 22 and the fusible conductor 24, respectively. The heating element 22 is connected to the fusible conductor 24 on the insulating substrate 21. It is good also as a structure laminated | stacked on the surface opposite to the surface.

  In the protection element 20 having such a configuration, the heating element 22 is laminated on the back surface of the insulating substrate 21, whereby the surface of the insulating substrate 21 is flattened. Can be formed. And the protection element 20 can connect the soluble conductor 24 planarized by making the connection electrically-conductive materials 26A, 26B, and 26C into the same height. Therefore, the protection element 20 can improve the fusing characteristics of the soluble conductor 24.

  In addition, the protective element 20 uses a material having excellent thermal conductivity as the material of the insulating substrate 21, so that the heating element 22 heats the soluble conductor 24 by the heating element 22 in the same manner as when laminated on the surface of the insulating substrate 21. be able to.

  Further, since the protective element 20 can be formed in a lump by connecting the connection conductive materials 26A, 26B, and 26C to the surface of the flat insulating substrate 21, the connection conductive materials 26A, 26B, and 26C can be formed at a time. Can be saved.

  The protective element according to one embodiment of the present invention as described above can be used for a battery including a lithium ion secondary battery used in a notebook PC, a tablet terminal, or the like. In addition, the current path is blocked by an electric signal. It is applicable to various uses that require

<2. Operation of protection element>
First, for comparison, a known example (for example, Patent Document 1 or Patent Document 2) is used as a conventional protection element, and the configuration thereof will be described.

  As shown in FIG. 6, in the conventional protection element 30, electrodes 37A and 37B are provided on the first and second terminals 35A and 35B on the substrate, and the electrodes 37A and 37B and the soluble conductor 34 are provided. They are connected via connection materials 38A and 38B such as solder. A heating element 32 connected to the third terminal 35C covered with the insulating layer 33 is provided below the soluble conductor 34, and the electrode 37C on the insulating layer 33 is connected to the soluble conductor 34 with a connecting material 38C such as solder. It has a structure to connect with.

  However, in such a structure, the electrodes 37A, 37B, 37C and the soluble conductor 34 are connected by connecting materials 38A, 38B, 38C such as solder to form a plurality of layers. The thermal conductivity between conductors becomes low.

  Further, for example, as shown in FIG. 7A, a method of arranging a connection material such as solder directly on the insulating layer without forming an electrode is conceivable. However, in this method, since the connection material is usually made of a low melting point metal such as solder (300 ° C. or less), by applying heat of mounting reflow, as shown in FIG. Therefore, it melts and moves on the insulating substrate in the direction of an arrow (possibly in the opposite direction) and aggregates.

  In the protection element 10 according to the present invention as shown in FIG. 1, a metal paste containing at least a low melting point metal and a high melting point metal is used as the connection conductive material. For this reason, the connection conductive material functions as both an electrode and a connection agent, so that the thermal conductivity between the heating element and the soluble conductor is superior to the structure of the conventional protection element, and the reliability as the protection element is increased. be able to. In addition, since the two-layer structure of the electrode and the connecting material such as solder as in the conventional protective element can be made into a one-layer structure of the connecting conductive material, it is possible to realize a reduction in height and size.

  Furthermore, since the protective element 10 according to an embodiment of the present invention uses a metal paste containing at least a low-melting-point metal and a high-melting-point metal as a connecting member, like a connecting material such as solder mainly made of a low-melting metal. In addition, there is no problem of melting and aggregating on the insulating substrate when the heat of mounting reflow is applied.

  Hereinafter, with respect to the operation of the protection element 10 according to an embodiment of the present invention, when the abnormality occurs, the heating element 12 of the protection element 10 as shown in FIG. This is shown schematically.

  As shown in FIG. 3, a power source is connected so that a voltage is applied between the third terminal 15C and the first and second terminals 15A and 15B, and the heating element 12 is energized in the event of an abnormality. It is desirable to set the resistance value of the heating element 12 according to the applied voltage so that the temperature of the heat generated by the heating element 12 is higher (300 ° C. or higher) than the normal reflow temperature (˜260 ° C.).

  FIG. 4 shows a view when the fusible conductor 14 is melted. When the heating element 12 is energized and the heating element 12 begins to generate heat, the inner low melting point metal layer of the soluble conductor 14 starts to melt, and the molten low melting point metal diffuses into the outer high melting point metal layer. As a result, a erosion phenomenon occurs, and the high melting point metal layer is eroded and mixed with the molten low melting point metal layer.

  When the temperature of the heating element 12 is further increased, the erosion region of the high melting point metal layer due to melting of the low melting point metal layer of the inner layer of the soluble conductor 14 is expanded. In this state, by adopting a metal having high thermal conductivity as the material of the refractory metal layer, the temperature including the connection conductive material 16C having good thermal conductivity becomes high, and the entire low melting point metal layer becomes molten. At that time, when the refractory metal layer is completely eroded on the connection conductive material 16C, the melted soluble conductor 19 is connected to the connection conductive material by its wettability (surface tension) as shown in FIG. Attracted to 16C. As a result, the fusible conductor is blown into 14A and 14B, and the terminals are cut off.

  Examples of the present invention will be described below. The present invention is not limited to these examples.

  As an example, a protective element using a connection conductive material to which the present invention is applied is prepared, and as a comparative example, protection in which each conventional electrode and a soluble conductor are connected via a connection material made of solder paste An element was prepared, and the electric power was increased to compare the necessary electric power when the connecting conductive material or solder paste was melted.

  In both Examples and Comparative Examples, a 6 mm × 4 mm alumina ceramic substrate (thickness 0.5 mm) was used as an insulating substrate. Further, a ruthenium oxide resistance paste was printed on the insulating substrate and baked at 850 ° C. for 30 minutes to form a heating resistor. All the soluble conductors were formed to have a size of 1 mm × 5 mm using Sn: Sb = 95: 5 and a melting point of 240 ° C.

  In the example, the terminal and the soluble conductor were connected by a Sn—Ag—Cu paste. In the comparative example, an Ag—Pd paste was printed as an electrode, then baked at 850 ° C. for 30 minutes, and the electrode and the soluble conductor were connected by an Sn solder paste. That is, the example has a two-layer structure of soluble conductor / connection conductive material (metal paste), and the comparative example has a three-layer structure of soluble conductor / solder paste / electrode.

  FIG. 5 shows the required power ratio when the required power when the solder paste of the comparative example is melted is 100%. The required power ratio of the protection element of the example was about 83%. That is, the connection conductive material of the example melts with less power than the comparative example, and the fact that the connection conductive material melts earlier indicates that the operation as the protection element is stabilized earlier.

  10, 20, 30 Protection element, 11, 21, 31 Insulating substrate, 12, 22, 32 Heating element, 13, 23, 33 Insulating member, 14, 24, 34 Fusible conductor, 15A, 35A First terminal, 15B , 35B second terminal, 15C, 35C third terminal, 16A, 16B, 16C, 26A, 26B, 26C connecting conductive material, 37A, 37B, 37C electrode, 38A, 38B, 38C connecting material such as solder, 19 melted Soluble conductor

Claims (5)

A protective element having a heating element and a soluble conductor on an insulating substrate, and fusing the soluble conductor by heat generation of the heating element,
First and second terminals provided on the insulating substrate;
The fusible conductor connected to the first and second terminals;
The heating element laminated on the insulating substrate and connected to a third terminal;
An insulating member laminated to cover the heating element;
The first and second terminals and the fusible conductor, and the heating element and the fusible conductor can each be electrically connected to each other , and include a partly soluble connecting conductive material,
The connection conductive material is a protective element containing at least a low melting point metal and a high melting point metal.   The connection conductive material further contains a resin material, and a ratio of a total weight of the low melting point metal and the high melting point metal to a weight of the resin material is 80:20 to 99.5: 0.5. The protective element as described.   The protective element according to claim 1 or 2, wherein a weight ratio of the low melting point metal to the high melting point metal is 10:90 to 90:10.   The low-melting-point metal and the high-melting-point metal that are raw materials for the connection conductive material are each granular, and the particle size of the low-melting-point metal is larger than the particle size of the high-melting-point metal. The protective element according to item.   The protection element according to any one of claims 1 to 4, wherein the heating element is laminated on a surface of the insulating substrate opposite to a surface to which the soluble conductor is connected.

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