Flexible circuit board with overcurrent protection

Abstract

The present invention relates to a flexible circuit board structure for overcurrent protection including a shape-memory material, and more specifically, to a flexible circuit board structure in which, when heat is generated due to an overcurrent during the charging / discharging process of a battery and the temperature exceeds a predetermined level, the flexible circuit board including a shape-memory material soldered to a printed circuit board is deformed and physically separated.

Description

[Technical field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 2022-0070608 filed on June 10, 2022, and all contents disclosed in the documents of that Korean patent application are incorporated herein by reference.

[0002] The present invention relates to a flexible circuit board structure having an overcurrent protection function including a shape memory material, and more particularly, to a flexible circuit board structure that can prevent major accidents such as damage to a battery protection circuit and fire by blocking heat generation caused by an overcurrent that occurs due to malfunction during the charging and discharging process of a battery. [Background technology]

[0003] Recently, as electronic products become smaller and lighter, flexible printed circuit boards (FPCBs) made of light and flexible polyimide (PI) material are widely used in various electric and electronic products such as TVs, LCDs, and battery packs / modules.

[0004] In particular, in the case of battery packs / modules, harness wires were used as components for sensing the voltage or temperature of each battery cell and transmitting it to the BMS, but as they are replaced with flexible circuit cables, the electrical wiring within the battery module has been greatly simplified, which is also effective in reducing the weight of the battery module.

[0005] However, if an abnormal overcurrent occurs during the charging and discharging process of the battery, a fuse function must be built into each cable to protect against this. However, in the case of a flexible circuit board (or cable), it is difficult to provide a fusing function in a limited space.

[0006] To solve this problem, (Patent Document 0001) proposes an insulating film equipped with a fuse pattern section that is configured to break when a current exceeding the rated current flows. However, this is simply a circuit for protecting against overcurrent that is provided inside a flexible circuit board. In effect, an overcurrent protection circuit is designed and embodied in a flexible circuit board, which creates the problem that a fuse pattern must be provided in every circuit in which an overcurrent may occur.

[0007] (Patent Document 0002) is characterized in that when an abnormal condition occurs inside the battery and heat is generated, the shape of the electrode lead containing a shape memory alloy is deformed and separated from the electrode tab, but has the problem that it is difficult to apply to flexible circuit boards. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Korean Patent Publication No. 10-2022-0007346 [Patent Document 2] Korean Patent Publication No. 10-2022-0022590 Summary of the Invention [Problem to be solved by the invention]

[0009] In order to solve the above problems, the present invention aims to provide a flexible circuit board having a shape-memory material inside that is deformed at a predetermined temperature or higher, and to separate the flexible circuit board from the soldered printed circuit board when heat is generated due to an overcurrent, thereby preventing a fire or physically isolating the battery protection circuit safely from an overcurrent. [Means for solving the problem]

[0010] In order to solve the above problems, the present invention provides a flexible circuit board for overcurrent protection including a soldering part bonded to one side of a printed circuit board by a solder, the flexible circuit board includes a copper foil layer on which a circuit pattern is formed, a first adhesive layer formed on an upper part of the copper foil layer, a second adhesive layer formed on a lower part of the copper foil layer, a first polyimide layer formed on an upper part of the first adhesive layer, a second polyimide layer formed on a lower part of the second adhesive layer, and a deformation layer formed between the first adhesive layer and the first polyimide layer or on the first polyimide layer, the deformation layer being made of a shape-memory material that is deformed in a certain direction at a predetermined temperature or higher.

[0011] In the flexible circuit board for overcurrent protection, the deformation layer is further formed between the second adhesive layer and the second polyimide layer.

[0012] In the flexible circuit board for overcurrent protection, the copper foil layer is characterized in that it has a multi-layer structure formed on both sides with an insulating layer sandwiched therebetween.

[0013] In the flexible circuit board for overcurrent protection, the certain direction is a direction in which an end of the deformation layer bends upwardly from the printed circuit board.

[0014] In the flexible circuit board for overcurrent protection, the certain direction is a direction in which the deformation layer bends in a half-moon shape upwardly from the printed circuit board.

[0015] In the flexible circuit board for overcurrent protection, the copper foil layer and the printed circuit board each include a plurality of lands for electrical connection.

[0016] In the flexible circuit board for overcurrent protection, the lands are electrically connected by solder.

[0017] In addition, in the flexible circuit board for overcurrent protection, when the temperature rises above a predetermined level due to the application of an overcurrent, the solder melts, and the deformation layer deforms to separate a land connected to a copper foil layer from a land of the printed circuit board, thereby cutting off the current.

[0018] In the flexible circuit board for overcurrent protection, the predetermined temperature is a temperature equal to or higher than the melting point of the solder.

[0019] In the flexible circuit board for overcurrent protection, the deformation layer is restrictedly located only in a predetermined area including the soldering portion.

[0020] In the flexible circuit board for overcurrent protection, the deformation layer is restrictedly located only on some of the lands.

[0021] In the flexible circuit board for overcurrent protection, the deformation layer is made of a shape-memory material that does not return to its original shape after being deformed. Effect of the Invention

[0022] As described above, according to the flexible circuit board including the shape memory material according to the present invention, when an overcurrent occurs due to a malfunction during charging and discharging of a battery, the current flow path becomes narrow, and heat is generated in the printed circuit board connected to the flexible circuit board by soldering. When the temperature rises above a predetermined level, the solder melts and the shape memory material included in the flexible circuit board deforms, physically separating the flexible circuit board, thereby preventing fires and explosions.

[0023] In addition, the flexible circuit board including the shape memory material according to the present invention does not require additional components for protection against overcurrent, and therefore has the advantage of maintaining the performance without failure of the existing protection circuit and improving the safety of the battery pack / module. [Brief description of the drawings]

[0024] [Figure 1] FIG. 1 is a diagram showing a basic structure constituting a flexible circuit board according to the prior art. [Diagram 2] 1 is a structural diagram of a single-layer flexible circuit board for overcurrent protection including a shape-memory material according to a preferred embodiment of the present invention; [Diagram 3] 1 is a structural diagram of a single-layer flexible circuit board for overcurrent protection including multiple shape memory materials according to a preferred embodiment of the present invention; [Figure 4] 1 is a structural diagram of a multi-layer flexible circuit board for overcurrent protection including a shape memory material according to a preferred embodiment of the present invention; [Diagram 5] 1 is a conceptual diagram of connecting a printed circuit board and a flexible circuit board by solder according to a preferred embodiment of the present invention; [Figure 6] FIG. 2 is a diagram showing a detailed structure in which a printed circuit board and a flexible circuit board are soldered together according to a preferred embodiment of the present invention. [Figure 7] 4A and 4B are diagrams illustrating a deformation state of a flexible circuit board due to deformation of a shape memory material when an overcurrent is applied according to a preferred embodiment of the present invention. [Figure 8] 11 is a diagram showing a deformation state of a flexible circuit board due to deformation of a shape memory material when an overcurrent is applied according to another preferred embodiment of the present invention. FIG. [Figure 9] FIG. 2 illustrates the location of a deformation layer according to a preferred embodiment of the present invention. [Figure 10] 13 is a diagram showing a flexible circuit board having restrictive deformation layers on grouped soldering portions according to yet another preferred embodiment of the present invention; FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] Hereinafter, the present invention will be described in detail with reference to the accompanying drawings, in which a person having ordinary skill in the art to which the present invention pertains can easily carry out the present invention. However, in describing the operation principle of the preferred embodiment of the present invention in detail, detailed description of related well-known functions or configurations will be omitted if it is determined that such detailed description may unnecessarily obscure the gist of the present invention.

[0026] In addition, the same reference numerals are used throughout the drawings for parts having similar functions and actions. Throughout the specification, when a part is said to be connected to another part, this includes not only the case where the part is directly connected to another part, but also the case where the part is indirectly connected via another element between the two parts. In addition, when a part includes a certain component, it does not mean that the other component is excluded, but that the part may further include the other component, unless otherwise specified.

[0027] Hereinafter, a material constituting a flexible circuit board according to the present invention and a structure for separating the flexible circuit board from a printed circuit board when an abnormal overcurrent is applied and heat is generated will be described with reference to the accompanying drawings.

[0028] First, the flexible circuit board of the present invention may include internal electronic circuits, and may simply refer to a flexible circuit cable replacing a harness wire, but is not limited thereto.

[0029] Generally, a flexible printed circuit board (FPCB) is composed of a base film 20 in which copper foil and polyimide are laminated, and a coverlay having polyimide and a semi-cured adhesive applied on the completed base film.

[0030] FIG. 1 is a hierarchical diagram showing the basic structure of a conventional flexible circuit board.

[0031] As shown in FIG. 1, the coverlay 10 consists of an upper polyimide layer 11 and an adhesive layer 12 for bonding to a copper foil layer 21 .

[0032] In addition, the base film 20 is composed of a copper foil layer 21, a polyimide layer 23 for insulation below the copper foil layer 21, and an adhesive layer 22 for adhering these together, and further the copper foil layer 21 can have a multi-layer structure of two or more layers.

[0033] However, conventional flexible circuit boards do not disclose any structure or material capable of protecting the circuits constituting the flexible circuit board or other connected electronic components when an overcurrent occurs.

[0034] FIG. 2 is a structural diagram of a single-layer flexible circuit board for overcurrent protection including a shape memory material according to a preferred embodiment of the present invention.

[0035] As shown in FIG. 2(a), the single-layer flexible circuit board 100 for overcurrent protection of the present invention is similar to the configuration of the basic base film 20 mentioned in the prior art, and is composed of a single-sided copper foil layer 130 that forms an electric circuit or wiring, a second polyimide layer 102 made of a polyimide component for insulating and protecting the flexible circuit board from the outside, and a second adhesive layer 121 that bonds the copper foil layer 130 and the second polyimide layer 102.

[0036] The coverlay 10 also includes a first adhesive layer 120 between the first polyimide layer 101 and the copper foil layer 130, and a deformation layer 110 located between the first polyimide layer 101 and the first adhesive layer 120 and made of a shape-memory material that is deformed at a predetermined temperature.

[0037] Here, the deformation layer 110 may be made of a shape memory alloy such as nickel-titanium alloy (nitinol), copper-zinc alloy, gold-cadmium alloy, or indium-thallium alloy, or may be made of a low-cost epoxy or thermoplastic polyurethane-based shape memory polymer.

[0038] In addition, the deformation layer 110 is made of a one-way shape memory material that cannot recover its original shape (original shape) even if the temperature drops after it is deformed above a certain temperature. This is because problems occur when an overcurrent is applied, and when the shape is restored, an additional overcurrent may occur due to electrical contact.

[0039] The present invention does not limit the shape memory material, but it is obvious that a person skilled in the art can easily adopt any shape memory material known in the art.

[0040] On the other hand, in Fig. 2(a) Although not shown An additional adhesive layer may be further included between the first polyimide layer 101 and the deformation layer 110 for fixing and bonding the same.

[0041] FIG. 2(b) shows a single-layer flexible circuit board for overcurrent protection according to another preferred embodiment of the present invention, which, unlike FIG. 2(a), is characterized in that it has a separate deformation layer 111 on top of the coverlay 10 of the conventional flexible circuit board of FIG. 1.

[0042] In other words, when a deformation layer is provided inside a flexible circuit board, there is a disadvantage that a conventional flexible circuit board cannot be used. However, when a deformation layer 111 is provided separately on the top of the first polyimide layer 101, there is an advantage that a conventional flexible circuit board can be used only by performing an additional process.

[0043] Although not shown in FIG. 2(b), it is clear that an adhesive layer for adhering the first polyimide layer 101 and the deformation layer 111 can be further provided, and a separate polyimide layer for protecting the deformation layer 111 can be provided on top of the deformation layer 111.

[0044] Although not shown in FIG. 2B, the deformation layer 111 may also be provided under the base film 20, that is, under the second polyimide layer .

[0045] FIG. 3 is a structural diagram of a single-layer flexible circuit board for overcurrent protection including a plurality of shape memory materials according to a preferred embodiment of the present invention.

[0046] Referring to FIG. 3, in addition to the deformation layer 110 of FIG. 2(a), a deformation layer 112 is provided under the copper foil layer 130. By providing the deformation layer 112 between the second polyimide layer 102 and the second adhesive layer, the device can be configured to deform more quickly when the temperature rises above a predetermined level.

[0047] FIG. 4 is a structural diagram of a multi-layer flexible circuit board including copper foil layers 131 and 132 on both sides containing shape memory material according to a preferred embodiment of the present invention.

[0048] The copper foil layers 131, 132 on both sides may have an insulating layer 140 therebetween, the insulating layer 140 being made of an electrically insulating material that contains an adhesive component.

[0049] Although the drawings show double-sided copper foil layers, it is apparent that this is only one example and can be extended to multiple copper foil layers.

[0050] Although not shown in FIGS. 3 and 4, the deformation layers 110 and 112 may be formed on the upper part of the first polyimide layer 101 and the lower part of the second polyimide layer 102, respectively.

[0051] FIG. 5 is a conceptual diagram showing how a printed circuit board 200 and a flexible circuit board 100 are electrically connected by solder according to a preferred embodiment of the present invention.

[0052] In general, a plurality of lands may be included in the flexible circuit board 100. Such lands are a part of a conductor pattern for soldering electronic components, and correspond to contacts or connection terminals for electrical connection with a copper foil layer.

[0053] As shown in FIG. 5, the soldering part 300 indicated by the dotted line electrically connects the flexible circuit board 100 to the printed circuit board 200 to fix its position, and is composed of a plurality of lands and solder (also called solder), and can be provided in various shapes and positions, but is not limited thereto.

[0054] Meanwhile, charging / discharging current in the battery pack or battery module flows to the printed circuit board 200 via the flexible circuit board 100. Here, although this does not pose a problem under normal operating conditions, in the event of an abnormal overcurrent, the protection circuit may malfunction, and in the process, a large amount of heat may be generated at the soldering part 300 where the current path becomes narrow and resistance occurs.

[0055] Since there is a risk of fire or explosion due to such heat generation, it is necessary to physically separate the soldering section 300 of the flexible circuit board 100 from the printed circuit board 200.

[0056] FIG. 6 is a cutaway side view of the soldered lands of the printed circuit board 200 and the flexible circuit board 100 according to the preferred embodiment of the present invention.

[0057] 6, in the flexible circuit board 100, a first land 301 connected to a copper foil layer 130 and a second land 302 provided on a printed circuit board 200 are joined and electrically connected via a solder 303.

[0058] Here, the solder 303 is a non-ferrous metal having a lower melting point than the first and second lands 301 and 302 and may contain tin or lead, and each land may be made of a solder of a different material.

[0059] For example, a solder containing tin (Sn) has a melting point of 232°C, while a Sn-Zn based low-temperature lead-free solder may have a melting point of around 190°C.

[0060] In the present invention, the type and melting point of the solder 303 used are not limited and can be selected from a variety of options, and the deformation layers 110, 111, and 112 made of shape-memory material are characterized in that they are deformed at least at or above the melting point of the solder 303.

[0061] 7 and 8 are diagrams illustrating the deformation state of a flexible circuit board due to the deformation of a shape memory material when an overcurrent is applied according to a preferred embodiment of the present invention.

[0062] 7(a) and 7(b), when an overcurrent is applied to the soldering portion 300, heat is generated. When the heat exceeds a predetermined temperature, the solder 303 joining the first land 301 and the second land 302 in the soldering portion melts and one side of the deformation layer 110 bends upward. At the same time, the flexible circuit board 100 is physically separated from the top of the printed circuit board 200, thereby blocking the flow of current between the printed circuit board 200 and the flexible circuit board 100.

[0063] Here, even if the deformation layer 110 recovers to a low temperature again, it does not return to its pre-deformation shape.

[0064] The deformation layer 110 of FIG. 7 is preferable when the soldering part 300 is formed at the end of the flexible circuit board 100, but has the disadvantage of being less efficient when the soldering part 300 is located far from the end of the flexible circuit board 100.

[0065] Meanwhile, unlike the shape memory material in which the deformation layer in FIG. 7 bends in one direction, the deformation layer 110 in FIG. 8 is deformed as the soldering portion 300 bends into a crescent shape above the printed circuit board 200, resulting in physical separation between the printed circuit board 200 and the flexible circuit board 100.

[0066] The deformation layer 110 in FIG. 8 is a flexible circuit board having a soldering portion 300. 100 This can be effectively applied when the sensor is located in the middle part of the sensor.

[0067] FIG. 9 is a diagram showing the location of the deformation layer according to a preferred embodiment of the present invention.

[0068] The deformation layers 110, 111, and 112 according to various embodiments of the present invention are intended to separate the soldering portion 300 from the printed circuit board 200, and therefore may be formed over the entire flexible circuit board 100, but may be positioned in a limited size in the area where the soldering portion 300 is located in order to reduce costs and simplify the process.

[0069] Referring to FIG. 9(a), the deformation layer 110 may be provided only at the inner end of the flexible circuit board 100 where the soldering part 300 is located.

[0070] That is, the first polyimide layer 101 The deformation layer 110 may be located only in a region of the soldering part 300 that is partially limited between the first adhesive layer 120 and the soldering part 300 .

[0071] Referring to FIG. 9(b), the deformation layer 110 may be provided restrictively on the top of the first polyimide layer 101 of the flexible circuit board 100 where the soldering part 300 is located.

[0072] Although not shown in FIG. 9, a separate adhesive layer may be additionally provided to bond the deformation layer 110 and the first polyimide layer 101 together.

[0073] In other words, in the case of the flexible circuit board 100 of FIG. 2(b), a deformation layer of the same size as the soldering part 300 can be attached to the top of the coverlay 10, so that a conventional flexible circuit board can be used as is and the size of the deformation layer can be minimized, which also allows for cost savings.

[0074] Although not shown in FIGS. 9(a) and 9(b), the deformation layer may be limitedly provided at the center of the soldering portion 300 in the deformation of FIG.

[0075] FIG. 10 is a diagram showing a flexible circuit board having restrictive deformation layers on grouped soldering parts according to still another preferred embodiment of the present invention.

[0076] FIG. 5 shows an embodiment in which multiple lands are soldered in a row on a single flexible circuit board, while FIG. 10 shows a structure in which lands are grouped and soldered according to the circuits where overcurrent is likely to occur, and a deformation layer can be provided only on the circuits where overcurrent occurs.

[0077] Referring to FIG. 10, a flexible circuit board having selective deformation layers, in which deformation layers 113, 114 can be provided only on the soldering portions of line groups A and B where overcurrent occurs, and no deformation layer is provided on the soldering portion of line group C where overcurrent does not occur, is also included as another embodiment of the present invention.

[0078] Also, referring to FIG. 10, a flexible circuit board having a plurality of soldering parts separated into a fork shape for each line group can be formed, and only some of the plurality of soldering parts can be selectively separated by deformation layers 113 and 114.

[0079] Although the present invention has been described with reference to specific embodiments, it will be apparent to those skilled in the art that various modifications and variations of the present invention may be made based on the above description within the scope of the present invention. [Explanation of symbols]

[0080] 10 Coverlay 20 Base Film 11, 23 Polyimide layer 12, 22 Adhesive layer 21 Copper foil layer 100 Flexible Circuit Board 101 First polyimide layer 102 Second polyimide layer 110, 111, 112, 113, 114 Deformation layer 120 1st adhesive layer 121 Second adhesive layer 130, 131, 132 copper foil layer 140 Insulating layer 200 Printed Circuit Boards 300 Soldering section 301 Land No. 1 302 Land No. 2 303 Solder

Claims

1. A flexible circuit board for overcurrent protection, comprising a soldering part joined by solder to one side of a printed circuit board, a copper foil layer on which a circuit pattern is formed; a first adhesive layer formed on the copper foil layer; a second adhesive layer formed under the copper foil layer; a first polyimide layer formed on the first adhesive layer; a second polyimide layer formed under the second adhesive layer; a deformation layer formed between the first adhesive layer and the first polyimide layer or on the first polyimide layer; The deformation layer is a shape-memory material that is deformed in a certain direction at a predetermined temperature or higher.

2. The flexible circuit board for overcurrent protection according to claim 1 , wherein the deformation layer is further formed between the second adhesive layer and the second polyimide layer.

3. 2. The flexible circuit board for overcurrent protection according to claim 1, wherein the copper foil layer has a multi-layer structure formed on both sides with an insulating layer sandwiched therebetween.

4. 3. The flexible circuit board for overcurrent protection according to claim 1, wherein the certain direction is a direction in which an end of the deformation layer bends upwardly toward the printed circuit board.

5. 3. The flexible circuit board for overcurrent protection according to claim 1, wherein the predetermined direction is a direction in which the deformation layer bends in a half-moon shape above the printed circuit board.

6. 3. The flexible circuit board for overcurrent protection according to claim 1, wherein the copper foil layer and the printed circuit board each include a plurality of lands for electrical connection.

7. The flexible circuit board for overcurrent protection according to claim 6 , wherein the lands are electrically connected by solder.

8. 8. The flexible circuit board for overcurrent protection according to claim 7, wherein when the temperature of the flexible circuit board rises to or exceeds a predetermined temperature due to application of an overcurrent, the solder melts, and the deformation layer deforms to separate a land connected to the copper foil layer from a land of the printed circuit board, thereby cutting off the current.

9. 9. The flexible circuit board for overcurrent protection according to claim 8, wherein the predetermined temperature is equal to or higher than the melting point of the solder.

10. The flexible circuit board for overcurrent protection according to claim 1 or 2, wherein the deformation layer is restrictedly located only in a predetermined region including the soldering portion.

11. The flexible circuit board for overcurrent protection according to claim 6 , wherein the deformation layer is located only on some of the lands.

12. 3. The flexible circuit board for overcurrent protection according to claim 1, wherein the deformation layer is made of a shape-memory material that does not return to its original shape after being deformed.

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