Patent Application
20240357735
This application claims the benefit of priority to Korean Patent Application No. 2022-0070608 filed on Jun. 10, 2022, the disclosure of which is incorporated herein by reference in its entirety.
The present invention relates to the structure of a flexible printed circuit board having an overcurrent protection function including a shape memory material, and more particularly to the structure of a flexible printed circuit board capable of interrupting heat generated due to overcurrent generated by malfunction of a battery during charging/discharging of the battery, thereby preventing damage to a battery protection circuit or a major accident, such as fire outbreak.
With reduction in size and weight of electronic products in recent years, a flexible printed circuit board (FPCB) made of polyimide (PI), which is lightweight and flexible, has been widely used in a variety of electric and electronic products, such as a TV, an LCD, and a battery pack/module.
In particular, for the battery pack/module, a harness wire is used as a part configured to sensing voltage or temperature of each battery cell and to transmit the sensed voltage or temperature to a BMS. As the harness wire is replaced by a flexible printed circuit cable, however, electrical wiring in the battery module is greatly simplified, which is effective in reducing the weight of the battery module.
When abnormal overcurrent is generated during charging/discharging of a battery, it is necessary for each cable to have a fuse function in order to protect the battery. In particular, for the flexible printed circuit board (or cable), it is difficult to implement a fusing function in a limited space.
In order to solve this problem, Patent Document 0001 proposes an insulation film having a fuse pattern section configured to be cut when current higher than rated current flows. In this case, however, a circuit for protection from overcurrent is simply provided in a flexible printed circuit board, i.e. an overcurrent protection circuit is substantially designed and implemented in the flexible printed circuit board. As a result, a fuse pattern must be provided on each circuit from which overcurrent may be generated.
Patent Document 0002 is characterized in that, when heat is generated from a battery due to abnormality of the battery, an electrode lead including a shape memory alloy is deformed and is separated from an electrode tab, which, however, is difficult to apply to a flexible printed circuit board.
(Patent Document 0001) Korean Patent Application Publication No. 10-2022-0007346
(Patent Document 0002) Korean Patent Application Publication No. 10-2022-0022590
The present invention has been made in view of the above problems, and it is an object of the present invention to provide a flexible printed circuit board configured such that a shape memory material that is deformed at a predetermined temperature or higher is provided in the flexible printed circuit board and the flexible printed circuit board is separated from a printed circuit board, to which the flexible printed circuit board is soldered, when heat is generated due to overcurrent, whereby fire outbreak is prevented or a battery protection circuit is safely physically separated from overcurrent.
In order to accomplish the above object, a flexible printed circuit board for overcurrent protection and including a soldering unit joined to one side of a printed circuit board by a solder according to the present invention includes a foil layer having a circuit pattern formed thereon, a first adhesive layer formed on the foil layer, a second adhesive layer formed under the foil layer, a first polyimide layer formed on the first adhesive layer, a second polyimide layer formed under 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, wherein the deformation layer includes a shape memory material configured to be deformed in a predetermined direction at a predetermined temperature or higher.
Also, in the flexible printed circuit board for overcurrent protection according to the present invention, the deformation layer may be further formed between the second adhesive layer and the second polyimide layer.
Also, in the flexible printed circuit board for overcurrent protection according to the present invention, the predetermined direction may be a direction in which an end of the deformation layer is bent upwards from the printed circuit board.
Also, in the flexible printed circuit board for overcurrent protection according to the present invention, the predetermined direction may be a direction in which the deformation layer is bent upwards from the printed circuit board in a semi-lunar shape.
Also, in the flexible printed circuit board for overcurrent protection according to the present invention, the foil layer may be configured to have a multilayered structure disposed on opposite sides of an insulating layer with the insulation layer interposed therebetween.
Also, in the flexible printed circuit board for overcurrent protection according to the present invention, each of the copper foil layer and the printed circuit board may include a plurality of lands for electrical connection.
Also, in the flexible printed circuit board for overcurrent protection according to the present invention, the plurality of lands of the foil layer and the plurality of lands of the printed circuit board may be electrically connected to each other by the solder, respectively.
Also, in the flexible printed circuit board for overcurrent protection according to the present invention, the solder may include a material having different melting points for the respective lands.
Also, in the flexible printed circuit board for overcurrent protection according to the present invention, when a temperature of the deformation layer increases to the predetermined temperature or higher as a result of overcurrent being applied, the solder may be melted, and at least one land connected to the copper foil layer and at least one land of the printed circuit board may be separated from each other by deformation of the deformation layer among the plurality of lands, whereby a current may be interrupted.
Also, in the flexible printed circuit board for overcurrent protection according to the present invention, the predetermined temperature may be a temperature equal to or higher than a melting point of the solder.
Also, in the flexible printed circuit board for overcurrent protection according to the present invention, the deformation layer may be limitedly located at only a specific area of the flexible printed circuit board including the soldering unit.
Also, in the flexible printed circuit board for overcurrent protection according to the present invention, the deformation layer may be limitedly located at only some of the plurality of lands.
Also, in the flexible printed circuit board for
overcurrent protection according to the present invention, the deformation layer includes a shape memory material, the original shape of which is not restored after being deformed.
In the flexible printed circuit board for overcurrent protection according to the present invention, the foil layer may include copper.
In the flexible printed circuit board for overcurrent protection according to the present invention, the deformation layer may be located at an overlap region between the flexible printed circuit board and the printed circuit board.
As is apparent from the above description, in a flexible printed circuit board including a shape memory material according to the present invention, a current flow path is narrowed when overcurrent is generated due to malfunction of a battery during charging and discharging of the battery, whereby heat is generated from a printed circuit board connected to the flexible printed circuit board by soldering, and when a the temperature increases to predetermined temperature or higher, a solder is melted, and at the same time the flexible printed circuit board is physically separated from the printed circuit board due to deformation of the shape memory material included in the flexible printed circuit board, whereby fire outbreak or explosion is prevented.
Also, in the flexible printed circuit board including the shape memory material according to the present invention, no additional part for protection from overcurrent is necessary, whereby performance is maintained without breakdown of a conventional protection circuit, and therefore stability of a battery pack/module is improved.
Now, embodiments of the present invention will be described in detail with reference to the accompanying drawings such that the embodiments of the present invention can be easily implemented by a person having ordinary skill in the art to which the present invention pertains. In describing the principle of operation of the preferred embodiments of the present invention in detail, however, a detailed description of known functions and configurations incorporated herein will be omitted when the same may obscure the subject matter of the present invention.
In addition, the same reference numbers will be used throughout the drawings to refer to parts that perform similar functions or operations. In the case in which one part is said to be connected to another part throughout the specification, not only may the one part be directly connected to the other part, but also, the one part may be indirectly connected to the other part via a further part. In addition, that a certain element is included does not mean that other elements are excluded, but means that such elements may be further included unless mentioned otherwise.
Hereinafter, a material constituting a flexible printed circuit board according to the present invention and the structure in which the flexible printed circuit board is separated from a printed circuit board when abnormal overcurrent is applied thereto, whereby heat is generated therefrom, will be described with reference to the accompanying drawings.
First, the flexible printed circuit board according to the present invention may include an internal electronic circuit or may simply mean only a flexible printed circuit cable that replaces a harness wire; however, the flexible printed circuit board according to the present invention is not limited thereto.
In general, a flexible printed circuit board (FPCB) is constituted by a base film 20 having combined copper foil and polyimide and a coverlay having polyimide and a semi-cured adhesive applied to the completed base film.
As shown in
In addition, a base film 20 is constituted by a copper foil layer 21, a polyimide layer 23 for insulation provided under the copper foil layer 21, and an adhesive layer 22 configured to adhere the copper foil layer and the polyimide layer to each other. In addition, the copper foil layer 21 may be configured to have a multilayered structure, e.g. two or more layers.
In the conventional flexible printed circuit board, however, the structure or material capable for protecting a circuit constituting the flexible printed circuit board or other electric parts connected thereto when overcurrent is generated is not provided.
As shown in (a) of
In addition, the coverlay includes a first adhesive layer 120 provided between a first polyimide layer 101 and the copper foil layer 130 and a deformation layer 110 provided between the first polyimide layer 101 and the first adhesive layer 120, the deformation layer being made of a shape memory material configured to be deformed at a predetermined temperature.
Here, the deformation layer 110 may be made of a shape memory allay, such as a nickel-titanium alloy (nitinol), a copper-zinc alloy, a gold-cadmium alloy, or an indium-thallium alloy, or a low cost epoxy or thermoplastic polyurethane-based shape memory polymer.
In addition, the deformation layer 110 is characterized in that the deformation layer is made of a unidirectional shape memory material, the shape (original shape) of which is not restored even when the temperature is lowered after being deformed at a predetermined temperature or higher. The reason for this is that the deformation layer is deformed as the result of overcurrent being applied thereto and, if the shape of the deformation layer is restored, additional overcurrent may be generated due to electric contact.
In the present invention, the shape memory material is not restricted; however, it is obvious to those skilled in the art that any known shape memory material may be easily adopted.
Meanwhile, although not shown in (a) of
(b) of
That is, when the deformation layer is provided in the flexible printed circuit board, there is a disadvantage in that the conventional flexible printed circuit board cannot be used. When the deformation layer 111 is provided on the first polyimide layer 101, however, there is an advantage in that the conventional flexible printed circuit board can be used through only an addition process.
Although not shown in (b) of
In addition, although not shown in (b) of
Referring to
An insulation layer 140 including an adhesive component and made of an electrically insulating material may be provided between the two copper foil layers 131 and 132.
Although two copper foil layers are shown in the figure, which is merely one embodiment, it is obvious that multiple copper foil layers may be used.
In addition, although not shown in
In general, the flexible printed circuit board 100 may include a plurality of lands. Each of the lands is a part of a conductor pattern for soldering electronic parts and corresponds to a contact point or a connection terminal for electrical connection with the copper foil layer.
As shown in
Meanwhile, in a battery pack or a battery module, charging/discharging current flows to the printed circuit board 200 via the flexible printed circuit board 100. In a normal operation state, there is no problem. When abnormal overcurrent is generated, however, a protection circuit may malfunction. At this time, a current path may be narrowed, and a large amount of heat may be generated from the soldering unit 300, in which resistance is generated.
There is a possibility of ignition or explosion due to such generation of heat, and therefore it is necessary to physically separate the soldering unit 300 of the flexible printed circuit board 100 from the printed circuit board 200.
Referring to
Here, the solder 303, which is a nonferrous metal having a lower melting point than the first and second lands 301 and 302, may include a tin or lead component, and the respective lands may be made of different solders.
For example, a solder including a tin (Sn) component may have a melting point of 232° C., and a Sn-Zn-based unleaded solder for low temperature may have a melting point of about 190° C.
In the present invention, the kind and the melting point of the solder 303 that is adopted are not limited and may be variously selected. Each of the deformation layers 110, 111, and 112 made of the shape memory material is characterized in that the deformation layer is at least deformed at a melting point of the solder 303 or higher.
the flexible printed circuit board according to the preferred embodiment of the present invention is deformed due to deformation of the shape memory material when overcurrent is applied thereto.
Referring to (a) and (b) of
At this time, the deformation layer 110 does not return to the shape thereof before deformation even though the temperature of the deformation layer is lowered to low temperature.
The deformation layer 110 of
The shape memory material of the deformation layer of
The deformation layer 110 of
Each of the deformation layers 110, 111, and 112 according to various embodiments of the present invention is configured to separate the soldering unit 300 from the printed circuit board 200, and therefore the deformation layer may be provided over the entirety of the flexible printed circuit board 100. For cost reduction and process simplicity, however, the deformation layer may be located at the part of the flexible printed circuit board at which the soldering unit 300 is located so as to have a limited size.
Referring to (a) of
That is, the deformation layer 110 may be located in a partial limited area of the soldering unit 300 between the first polyimide layer 101 and the first adhesive layer 120.
Referring to (b) of
Although not shown in
That is, in the flexible printed circuit board 100 of (b) of
In addition, although not shown in (a) of
Referring to
In addition, referring to
Those skilled in the art to which the present invention pertains will appreciate that various applications and modifications are possible within the category of the present invention based on the above description.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2022-0070608 | Jun 2022 | KR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/KR2023/005851 | 4/28/2023 | WO |
