JP6356470B2 - Protective element - Google Patents

Description

  The present invention relates to a protective element that interrupts a current path when an abnormality such as overcharge or overdischarge occurs.

  Many secondary batteries that can be charged and used repeatedly are processed into battery packs and provided to users. In particular, in lithium ion secondary batteries with high weight energy density, in order to ensure the safety of users and electronic devices, in general, several protection circuits such as overcharge protection and overdischarge protection are built in the battery pack, It has a function of shutting off the output of the battery pack in a predetermined case.

  This type of protection element includes an overcharge protection or overdischarge protection operation of the battery pack by turning on / off the output using an FET switch built in the battery pack. However, when the FET switch is short-circuited for some reason, when a lightning surge or the like is applied and an instantaneous large current flows, the output voltage drops abnormally due to the life of the battery cell, or conversely an excessively abnormal voltage Even when a battery pack is output, battery packs and electronic devices must be protected from accidents such as fire. Therefore, in order to safely shut off the output of the battery cell in any possible abnormal state, a protection element made of a fuse element having a function of cutting off the current path by an external signal is used. .

  As shown in FIGS. 9A and 9B, the protective element 80 of the protective circuit for such a lithium ion secondary battery or the like includes first and second electrodes connected on the current path. A fusible conductor 83 is connected between 81 and 82 to form part of the current path, and the fusible conductor 83 on the current path is self-heated due to overcurrent or a heating element provided inside the protection element 80. There are those that melt by 84.

  The first and second electrodes 81 and 82 are formed on the surface of the insulating substrate 85, and are electrically connected to external connection terminals 81a and 82a formed on the back surface of the insulating substrate 85 through through holes (not shown). When the terminals 81a and 82a are mounted on the connection terminals to the circuit board, they are connected to the current path formed on the circuit board.

  When the fusible conductor 83 melts due to self-heating due to overcurrent or the heating element 84 being energized and heated, the protective element 80 causes the liquid fusible conductor 83 to become the first and second electrodes 81, 82. The current path is blocked by agglomeration on the top.

JP 2010-003665 A JP 2004-185960 A JP 2012-003878 A

  Conventionally, this type of protection element 80 is often used for applications having a relatively small current capacity such as a mobile phone or a notebook computer, and the fusible conductor 83 is formed with a current capacity of about 15 A at the maximum. . However, the use of lithium ion secondary batteries has been expanding in recent years, and its use in higher current applications such as electric tools such as electric drivers, transportation equipment such as hybrid cars, electric vehicles, and electric power assisted bicycles has been considered. Some have been hired. In these applications, particularly when starting up, a large current exceeding several tens of A to 100 A may flow, and the realization of a protective element corresponding to such a large current capacity is desired.

  In order to realize a protective element corresponding to a large current, it is necessary to improve the rating of the entire element. For this reason, it is easy to reduce the resistance value by increasing the cross-sectional area of the fusible conductor to achieve a desired rating.

  Here, as described above, the first and second electrodes 81 and 82 to which the fusible conductor is connected are connected to the external connection terminals 81a and 82a and the protection circuit through through holes formed in the insulating substrate. Has been. In the through hole, a conductive layer is formed by printing a conductive paste, and the first and second electrodes 81 and 82 and the external connection terminals 81a and 82a are electrically connected through the conductive layer.

  However, the conductive paste filled in the through hole has a solvent component added to achieve a viscosity enabling printing, and shrinks when the solvent component volatilizes by firing, creating voids in the through hole, etc. In some cases, the conductive layer cannot be formed thick. In addition, a glass component that does not contribute to electrical conduction is added to the conductive paste in order to maintain a constant shape between the metal particles.

  For this reason, the protection element 80 increases the resistance in the process of pulling the first and second electrodes 81 and 82 to the outside through the through holes, and the resistance of the soluble conductor can be reduced. Therefore, it is difficult to achieve a high rating for the entire device.

  In addition, heat generation due to a large current flowing in the current path between the first and second electrodes 81 and 82 and the external connection terminals 81a and 82a, which have been increased in resistance, destroys the current path, and the protection element 80 There is also concern about thermal effects on other peripheral devices such as connection electrodes of the circuit board to be mounted.

  Accordingly, an object of the present invention is to provide a protective element capable of reducing the resistance in the path through which the first and second electrodes are drawn to the outside, improving the overall rating of the element, and capable of handling large current applications. And

In order to solve the above-described problem, a protection element according to the present invention is electrically connected to an insulating substrate, a heating element, first and second electrodes stacked on the insulating substrate, and the heating element. A heating conductor extraction electrode, a soluble conductor laminated on the first and second electrodes and the heating element extraction electrode, and serving as a current path between the first and second electrodes, and the insulating substrate. A cover member that covers a surface on which the first and second electrodes are provided. The cover member includes a first external connection terminal that is connected to the first electrode and exposed to the outside, and A second external connection terminal connected to the second electrode and exposed to the outside is formed, and a combined resistance value of the first and second external connection terminals is between the first and second electrodes. It is lower than the resistance value of the current path .

  According to the present invention, resistance can be easily reduced by arbitrarily selecting the material, shape, and the like of the first and second external connection terminals. Therefore, the protection element according to the present invention has a resistance value due to the first and second external connection terminals provided first from the fusible conductor as compared with the conventional protection element drawn out to the external connection electrode through the through hole. Will not rise. Thereby, the protection element can improve the rating of the current path between the first and second external connection terminals and can cope with a large current.

FIG. 1 is a perspective view showing the inside of a protection element to which the present invention is applied. FIG. 2 is a plan view showing the inside of the protection element to which the present invention is applied. FIG. 3 is a cross-sectional view of a protection element to which the present invention is applied. 4A and 4B are perspective views showing the cover member, in which FIG. 4A shows the top surface side and FIG. 4B shows the bottom surface side. FIG. 5 is a circuit diagram of a battery pack in which a protection element is incorporated. FIG. 6 is a circuit diagram of the protection element. FIG. 7 is a cross-sectional view of another protective element to which the present invention is applied. FIG. 8 is a cross-sectional view of another protective element to which the present invention is applied. FIG. 9 is a perspective view showing the inside of a conventional protection element, (A) is a perspective view, and (B) is a cross-sectional view.

  Hereinafter, a protection element to which the present invention is applied will be described in detail with reference to the drawings. It should be noted that the present invention is not limited to the following embodiments, and various modifications can be made without departing from the scope of the present invention. Further, the drawings are schematic, and the ratio of each dimension may be different from the actual one. Specific dimensions should be determined in consideration of the following description. Moreover, it is a matter of course that portions having different dimensional relationships and ratios are included between the drawings.

  As shown in FIGS. 1 to 3, the protection element 1 to which the present invention is applied includes an insulating substrate 11, a heating element 12 stacked on the insulating substrate 11, and first and second layers stacked on the insulating substrate 11. Electrodes 13, 14, a heating element extraction electrode 15 electrically connected to the heating element 12, and the first and second electrodes 13 and 14 are stacked from the heating element extraction electrode 15 to the first and second electrodes 13, 14. A soluble conductor 16 serving as a current path between the electrodes 13 and 14 and a cover member 17 covering the surface of the insulating substrate 11 on which the first and second electrodes 13 and 14 are provided.

  The insulating substrate 11 is formed in a substantially square shape using an insulating member such as alumina, glass ceramics, mullite, zirconia, and the like. In addition, the insulating substrate 11 may be made of a material used for a printed wiring board such as a glass epoxy board or a phenol board, but it is necessary to pay attention to the temperature at which the fusible conductor is blown.

  First and second electrodes 13 and 14 are formed on opposite side edges of the insulating substrate 11. The first and second electrodes 13 and 14 are electrically connected by connecting a fusible conductor 16. The first and second electrodes 13 and 14 are electrically connected to first and second external connection terminals 21 and 22 formed on a cover member 17 which will be described later. The protective element 1 is connected to the current path of the external circuit through the connection terminals 21 and 22. The first and second electrodes 13 and 14 can be formed, for example, by printing and baking a refractory metal paste such as an Ag paste.

  The heating element 12 is laminated on the surface of the insulating substrate 11 and covered with an insulating member 18. 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 heating element 12 has a heating element extraction electrode 15 connected to one end and a heating element electrode 19 connected to the other end.

  The heating element extraction electrode 15 is extracted from one end of the heating element 12 between the first and second electrodes 13 and 14, and a soluble conductor 16 described later is mounted thereon. The heating element electrode 19 is formed on the surface of the insulating substrate 11 and is electrically connected to a third external connection terminal 23 formed on a cover member 17 described later. The heating element 12 is connected to an external circuit through the heating element electrode 19 and the third external connection terminal 23.

  In the protection element 1, an insulating member 18 is disposed so as to cover the heating element 12, and a heating element extraction electrode 15 is disposed so as to face the heating element 12 through the insulating member 18. As the insulating member 18, for example, glass can be used. The protective element 1 has an insulating member 18 laminated between the heating element 12 and the insulating substrate 11 in order to efficiently transmit the heat of the heating element 12 to the soluble conductor, and the heating element 12 is placed on the surface of the insulating substrate 11. It may be provided inside the formed insulating member 18.

  As the soluble conductor 16, any metal that can be melted quickly by the heat generated by the heating element 12 can be used. For example, a low-melting-point metal such as Pb-free solder whose main component is Sn can be suitably used.

  The soluble conductor 16 may be formed by laminating a low melting point metal and a high melting point metal. As a laminated structure of a low melting point metal and a high melting point metal, for example, a structure in which a low melting point metal foil is coated with a high melting point metal plating can be cited. It may be formed. As the low melting point metal, it is preferable to use solder such as Pb-free solder containing Sn as a main component, and as the high melting point metal, it is preferable to use Ag, Cu or an alloy containing these as main components. By including the high melting point metal and the low melting point metal, when the protective element 1 is reflow mounted, even if the reflow temperature exceeds the melting temperature of the low melting point metal and the low melting point metal melts, Outflow to the outside can be suppressed and the shape of the soluble conductor 16 can be maintained. In addition, even when fusing, the low melting point metal melts, and the high melting point metal is eroded (soldered), so that the fusing can be quickly performed at a temperature lower than the melting point of the high melting point metal.

  Note that the soluble conductor 16 is solder-connected to the heating element extraction electrode 15, the first electrode 13, and the second electrode 14. As a result, the protection element 1 has a current path extending between the first and second electrodes 13 and 14 via the soluble conductor 16. At this time, the low melting point metal provided in the lower layer is made of Pb-free solder, and this low melting point metal is used to connect to the heating element extraction electrode 15 and the first and second electrodes 13 and 14. Can do.

  In the protection element 1, a flux 20 is applied on the soluble conductor 16 in order to prevent the soluble conductor 16 from being oxidized and to improve the wettability when the soluble conductor 16 is melted.

[Cover member]
Next, the cover member 17 that covers the surface of the insulating substrate 11 will be described. 4A is a perspective view showing the upper surface side of the cover member 17, and FIG. 4B is a perspective view showing the bottom surface side of the cover member 17. The cover member 17 protects the inside and connects the first and second electrodes 13 and 14 to an external circuit, and can be formed of an engineering plastic or the like.

  As shown in FIGS. 4A and 4B, the cover member 17 includes a side surface portion 17a connected to the surface of the insulating substrate 11, and a top surface portion 17b. The cover member 17 is connected to the first electrode 13 and exposed to the outside, and the first external connection terminal 21 exposed to the outside, and the second electrode 14 is connected to the second electrode 14 and exposed to the outside. A connection terminal 22 is formed.

  The first and second external connection terminals 21 and 22 are connected to the first and second electrodes 13 and 14 and to the connection electrodes of the circuit board on which the protection element 1 is mounted. Thereby, as for the protection element 1, the current path between the 1st, 2nd electrodes connected via the soluble conductor 16 is integrated on the current path of an external circuit.

  The first and second external connection terminals 21 and 22 are made of a conductive material such as a metal post or a metal plate, and are integrally formed with the cover member 17 by insert molding or the like. As shown in FIGS. 3 and 4, the first external connection terminal 21 is a terminal portion 21 a that has one end pulled out to the top surface portion 17 b side of the cover member 17 and connected to a connection electrode of an external circuit, and the other end. A connection portion 21 b that faces the inside of the cover member 17 and is connected to the first electrode 13 is formed. Similarly, one end of the second external connection terminal 22 is a terminal portion 22 a that is pulled out toward the top surface portion 17 b of the cover member 17 and connected to a connection electrode of an external circuit, and the other end faces the inside of the cover member 17. The connection portion 22 b is connected to the second electrode 14.

  The cover member 17 is mounted on the surface of the insulating substrate 11 so that the connection portions 21b and 22b of the first and second external connection terminals 21 and 22 are on the first and second electrodes 13 and 14, respectively. Be positioned. The connection portions 21b and 22b and the first and second electrodes 13 and 14 are conductively connected via a conductive adhesive material such as solder. Thereby, the protection element 1 has a current path between the first and second electrodes 13 and 14 connected via the fusible conductor 16 to the outside via the first and second external connection terminals 21 and 22. Pulled out.

  Here, the first and second external connection terminals 21 and 22 formed using a conductive material such as a metal post or a metal plate can be easily reduced in resistance by arbitrarily selecting a material, a shape, or the like. Can be aimed at. Therefore, the protective element 1 is resistant to resistance by the first and second external connection terminals 21 and 22 provided first from the fusible conductor 16 as compared with the conventional protective element drawn out to the external connection electrode through the through hole. The value never increases.

  Thereby, the protection element 1 can improve the rating of the current path between the first and second external connection terminals 21 and 22 and can cope with a large current. That is, the protective element 1 has an improved rating of the conduction resistance between the first and second external connection terminals 21 and 22 even in a large current application such as a lithium ion secondary battery used as a power source such as HEV and EV. Can be lowered sufficiently to meet the requirements.

  Further, the protection element 1 is configured so that the terminal portions 21 a and 22 a of the first and second external connection terminals 21 and 22 are pulled out to the top surface portion 17 b side of the cover member 17, so that the top surface portion 17 b side of the cover member 17 is disposed. It is the mounting surface on the circuit board.

  Such a protective element 1 is provided with first and second electrodes 13 and 14, a heating element 12, a soluble conductor 16, and the like on the surface side of the insulating substrate 11, and first and second external connection terminals 21. , 22 is connected, and the top surface portion 17b of the cover member 17 is used as a mounting surface on the circuit board. Therefore, it is not necessary to process external connection electrodes on the back surface of the insulating substrate 11, The manufacturing process can be simplified.

  The cover member 17 has a third external connection terminal 23 connected to the heating element electrode 19. Similarly to the first and second external connection terminals 21 and 22 described above, the third external connection terminal 23 is made of a conductive material such as a metal post or a metal plate. It is molded integrally. Further, the third external connection terminal 23 has a terminal portion 23 a that is drawn out toward the top surface portion 17 b of the cover member 17 and connected to a connection electrode of an external circuit, and the other end is exposed to the inside of the cover member 17. The connecting portion 23 b is connected to the heating element electrode 19.

  The third external connection terminals 23 are formed on the side surfaces adjacent to the side surfaces on which the first and second external connection terminals 21 and 22 are provided, and are provided on the side surfaces facing each other as shown in FIG. May be. The protective element 1 includes first and second electrodes 13 and 14 and first and second external connection terminals 21 and 22 formed at symmetrical positions, and two third electrodes corresponding to the position of the heating element electrode 19. By forming the external connection terminals 23 at symmetrical positions, the cover member 17 can be mounted regardless of the orientations of the first and second external connection terminals and the third external connection terminal 23.

[Combined resistance value of first and second external connection terminals]
The protection element 1 is configured such that the combined resistance value of the first external connection terminal 21 and the second external connection terminal 22 is lower than the conduction resistance value between the first and second electrodes 11 and 12. preferable. Thereby, the rating of the protection element 1 is determined mainly by the resistance value of the soluble conductor 16 itself, and is not affected by the first and second external connection terminals 21 and 22. That is, the current rating of the protection element 1 can be determined by the resistance value of the fusible conductor 16, and a desired current value can be guaranteed, and the current path can be blown by self-heating when the rated current is exceeded.

  The resistance values of the first and second external connection terminals 21 and 22 can be obtained from the material, shape, and size. The protection element 1 obtains the total resistance value of the entire element from the resistance value between the first and second external connection terminals 21 and 22, and the first and second external connections that are known as the total resistance value. The conduction resistance between the first and second electrodes 13 and 14 can be obtained from the difference from the combined resistance of the terminals 21 and 22. Further, the protective element 1 measures the resistance between the first and second electrodes 13 and 14 and determines the combined resistance of the first and second external connection terminals 21 and 22 based on the difference from the total resistance value of the entire element. Can be requested.

[Direct connection between the first and second external connection terminals and the fusible conductor]
The protection element 1 is configured such that the first and second external connection terminals 21 and 22 and the soluble conductor 16 are directly connected by mounting the cover member 17 on the surface of the insulating substrate 11. Good. The protective element 1 has a lower resistance by directly connecting the first and second external connection terminals 21 and 22 and the fusible conductor 16 without going through the first and second electrodes 13 and 14. Can be planned.

[Battery circuit]
As shown in FIG. 5, such a protection element 1 is used by being incorporated in a circuit in a battery pack 30 of a lithium ion secondary battery, for example. The battery pack 30 includes, for example, a battery stack 35 including battery cells 31 to 34 of a total of four lithium ion secondary batteries.

  The battery pack 30 includes a battery stack 35, a charge / discharge control circuit 40 that controls charging / discharging of the battery stack 35, a protection element 1 to which the present invention that cuts off charging when the battery stack 35 is abnormal, and each battery cell A detection circuit 36 that detects voltages 31 to 34 and a current control element 37 that controls the operation of the protection element 1 according to the detection result of the detection circuit 36 are provided.

  The battery stack 35 is formed by connecting battery cells 31 to 34 that need to be controlled for protection from overcharge and overdischarge states, and is detachable via the positive electrode terminal 30a and the negative electrode terminal 30b of the battery pack 30. Are connected to the charging device 45, and a charging voltage from the charging device 45 is applied thereto. The electronic device can be operated by connecting the positive electrode terminal 30a and the negative electrode terminal 30b of the battery pack 30 charged by the charging device 45 to an electronic device operating with a battery.

  The charge / discharge control circuit 40 includes two current control elements 41 and 42 connected in series to a current path flowing from the battery stack 35 to the charging device 45, and a control unit 43 that controls the operation of these current control elements 41 and 42. Is provided. The current control elements 41 and 42 are configured by, for example, field effect transistors (hereinafter referred to as FETs), and control the gate voltage by the control unit 43 to control conduction and interruption of the current path of the battery stack 35. . The control unit 43 operates by receiving power supply from the charging device 45, and controls the current so as to cut off the current path when the battery stack 35 is overdischarged or overcharged according to the detection result by the detection circuit 36. The operation of the elements 41 and 42 is controlled.

  The protection element 1 is connected, for example, on a charge / discharge current path between the battery stack 35 and the charge / discharge control circuit 40, and its operation is controlled by the current control element 37.

  The detection circuit 36 is connected to each of the battery cells 31 to 34, detects the voltage value of each of the battery cells 31 to 34, and supplies each voltage value to the control unit 43 of the charge / discharge control circuit 40. The detection circuit 36 outputs a control signal for controlling the current control element 37 when any one of the battery cells 31 to 34 becomes an overcharge voltage or an overdischarge voltage.

  The current control element 37 is configured by, for example, an FET, and when the voltage value of the battery cells 31 to 34 exceeds a predetermined overdischarge or overcharge state by a detection signal output from the detection circuit 36, the protection element 1 is operated to control the charge / discharge current path of the battery stack 35 to be cut off regardless of the switching operation of the current control elements 41 and 42.

  In the battery pack 30 having the above configuration, the protection element 1 to which the present invention is applied has a circuit configuration as shown in FIG. In other words, the protection element 1 generates heat by melting the soluble conductor 16 by causing the soluble conductor 16 connected in series via the heating element lead electrode 15 and the connection point of the soluble conductor 16 to energize and generate heat. This is a circuit configuration including the body 12. Further, in the protection element 1, for example, the current control element 37 is connected via the third external connection terminal 23 in which the fusible conductor 16 is connected in series on the charge / discharge current path and the heating element 12 is connected to the heating element electrode 19. Connected. The first electrode 13 of the protection element 1 is connected to the battery stack 35 via a first external connection terminal 21 provided on the cover member 17. Further, the second electrode 14 of the protection element 1 is connected to the positive electrode terminal 30 a side via a second external connection terminal 22 provided on the cover member 17.

  The protection element 1 having such a circuit configuration can cut off the current path of the battery pack 30 by fusing the fusible conductor 16 by the heat generated by the heating element 12.

  The protection element of the present invention is not limited to use in a battery pack of a lithium ion secondary battery, and can of course be applied to various uses that require interruption of a current path by an electric signal.

[Other Embodiment 1]
As shown in FIG. 7, the protective element 1 has the terminal portions 21 a and 22 a of the first and second external connection terminals 21 and 22 pulled out from the side surface portion 17 a of the cover member 17 to the side opposite to the top surface portion 17 b. The back side of the insulating substrate 11 may be a mounting surface on the circuit board. Also in the configuration shown in FIG. 7, the protection element 1 includes the first and second electrodes 13 and 14, the heating element 12, the soluble conductor 16, and the like on the surface side of the insulating substrate 11, and the first and second electrodes. Since the cover member 17 on which the external connection terminals 21 and 22 are formed is connected, it is not necessary to process the external connection electrodes on the back surface of the insulating substrate 11, and the manufacturing process can be simplified.

[Other embodiment 2]
Further, as shown in FIG. 8, the protective element 1 has the terminal portions 21a and 22a of the first and second external connection terminals 21 and 22 pulled out from the side surface portion 17a of the cover member 17 to the side, and other than surface mounting. You may connect with an external circuit by the method of. Also in the configuration shown in FIG. 8, the protection element 1 includes the first and second electrodes 13 and 14, the heating element 12, the soluble conductor 16, and the like on the surface side of the insulating substrate 11. Since the cover member 17 on which the external connection terminals 21 and 22 are formed is connected, it is not necessary to process the external connection electrodes on the back surface of the insulating substrate 11, and the manufacturing process can be simplified.

DESCRIPTION OF SYMBOLS 1 Protection element, 11 Insulation board | substrate, 12 Heating body, 13 1st electrode, 14 2nd electrode, 15 Heating body extraction electrode, 16 Soluble conductor, 17 Cover member, 18 Insulation member, 19 Heating body electrode, 20 Flux , 21 1st external connection terminal, 22 2nd external connection terminal, 23 3rd external connection terminal, 30 battery pack, 31-34 battery cell, 35 battery stack, 36 detection circuit, 37 current control element, 40 charge Discharge control circuit, 41, 42 Current control element, 43 control unit, 45 charging device

Claims (4)

An insulating substrate;
A heating element;
First and second electrodes stacked on the insulating substrate;
A heating element extraction electrode electrically connected to the heating element;
A fusible conductor laminated on the first and second electrodes and the heating element extraction electrode, and serving as a current path between the first and second electrodes;
A cover member covering the surface of the insulating substrate on which the first and second electrodes are provided,
The cover member has a first external connection terminal connected to the first electrode and exposed to the outside, and a second external connection terminal connected to the second electrode and exposed to the outside. And formed ,
A protective element in which a combined resistance value of the first and second external connection terminals is lower than a resistance value of a current path between the first and second electrodes . The first and second external connection terminals are pulled out to the top surface side of the cover member,
The protective element according to claim 1, wherein the top surface of the cover member is a mounting surface on a circuit board. The first and second external connection terminals are pulled out to the side opposite to the top surface of the cover member,
The protection element according to claim 1, wherein the back surface side of the insulating substrate is a mounting surface to the circuit board.   The protection element according to claim 1, wherein the first and second external connection terminals are directly connected to the soluble conductor.

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