JP2011138805A - Flexible circuit board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a flexible circuit board wherein an open circuit due to bending of a substrate can be prevented. <P>SOLUTION: The flexible circuit board 1 includes a substrate 10, having one surface 11 and the other surface 12 and comprising polyethylene terephthalate or polyethylene naphthalate; a terminal 20 formed on one surface 11 of the substrate 10; a reinforcing substrate 30, which is bonded to a region on the other surface 12 of the substrate 10 that overlaps the terminal 20, and adhesive 40, which bonds the substrate 10 and the reinforcing substrate 30 wherein the adhesive 40 is a hotmelt adhesive. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a flexible circuit board.

  Currently, a flexible circuit board in which wiring is provided on a flexible board is used in electronic devices. As one of such flexible circuit boards, a flexible circuit board in which an electrode connected to a wiring is formed on a substrate is known. The electrode on this board is, for example, a land to which a terminal of a component mounted on the flexible circuit board is connected, or is formed at an end of the board so that the flexible circuit board is connected to another board or the like. Or the terminal. When the electrode on the substrate is a terminal formed at an end portion of the substrate, the flexible circuit substrate is used by inserting the end portion where the terminal is formed into a connector or the like in the electronic device.

  Patent Document 1 below describes such a flexible circuit board. In the flexible circuit board described in the following Patent Document 1, a terminal as an electrode is formed at an end on one surface of a substrate made of resin, and further, at a position overlapping with the terminal on the other surface of the substrate. The reinforcing substrate is bonded. The reinforcing substrate is bonded with an acrylic adhesive, tape, or the like. And when the terminal of a flexible circuit board is inserted in a connector etc., the bending of a flexible circuit board is suppressed by this reinforcement board (patent documents 1).

Japanese Utility Model Publication No. 07-29871

  However, in the flexible circuit board described in Patent Document 1, the reinforcing board may be peeled off.

  Then, an object of this invention is to provide the flexible circuit board which can prevent peeling of a reinforcement board | substrate.

  The inventor has intensively studied the cause of the reinforcing substrate peeling off in the flexible circuit board described in Patent Document 1. As a result, it has been found that in the flexible circuit board described in Patent Document 1, when the board is made of polyethylene terephthalate or polyethylene naphthalate, the reinforcing board is peeled off. As a result of further research, the inventor has often used polyethylene terephthalate and polyethylene naphthalate after being allowed to stand in an environment of a predetermined temperature for a certain period of time. It was found that oligomers of fine particles were deposited on the surface of the substrate. And it came to the conclusion that this oligomer has inhibited adhesion | attachment of a board | substrate and a reinforcement board | substrate. Therefore, the present inventor has conducted further researches and made the present invention.

  That is, the flexible circuit board of the present invention has one surface and the other surface, a substrate comprising polyethylene terephthalate or polyethylene naphthalate, and an electrode formed on the one surface of the substrate A reinforcing substrate bonded to at least a region overlapping with the electrode on the other surface of the substrate, and an adhesive that bonds the substrate and the reinforcing substrate, and the adhesive is a hot melt adhesive It is characterized by being.

  According to such a flexible circuit board, when a force is applied from the outside to the electrode formed on one surface of the board, the bending of the board can be suppressed by the reinforcing board. At this time, since the adhesive that bonds the substrate and the reinforcing substrate is a hot melt adhesive, even when oligomers are deposited on the surface of the substrate including polyethylene terephthalate or polyethylene naphthalate, the reinforcement is performed. It is possible to prevent the substrate from peeling off from the substrate. Thus, when a hot melt adhesive is used as the adhesive, even when oligomers are precipitated on the surface of the substrate, it is not clear why the reinforcing substrate can be prevented from peeling off the substrate. However, the present inventor has taken in the hot melt adhesive so as to wrap the oligomer until the hot melt adhesive is cooled and solidified after the hot melt adhesive is melted by heat, and the hot melt adhesive is directly applied to the surface of the substrate. I think it is because it adheres.

  Furthermore, in the flexible circuit board, the electrode is preferably a terminal formed at an end of the board.

  According to such a flexible circuit board, when the terminal formed at the end of the flexible circuit board is inserted into a connector or the like, the bending of the board can be suppressed by the reinforcing substrate.

  Further, in the flexible circuit board, it is preferable that a side of the reinforcing substrate opposite to the end side of the substrate is a region not bonded by the adhesive, and an end of the non-bonded region is a free end.

  According to such a flexible circuit board, the end portion of the non-bonded region in the reinforcing substrate is a free end, whereby the non-bonded region in the reinforcing substrate can be gripped. Therefore, when the terminal formed at the end of the board is inserted into the connector or the like, the free end side of the reinforcing board can be held and inserted, and the terminal can be efficiently inserted into the connector or the like.

  Or in the said flexible circuit board, it is preferable that the said electrode is a land to which the terminal of the electronic component mounted in the said board | substrate is connected.

  According to such a flexible circuit board, when the electronic component is mounted on the board, the reinforcement board suppresses the distortion of the land due to the bending of the board, and the connection between the land and the terminal of the electronic part is good. can do.

  Furthermore, in the flexible circuit board, it is preferable that the reinforcing substrate is bonded to the entire region overlapping the region where the electronic component is mounted on the other surface of the substrate.

  According to such a flexible circuit board, bending of the board can be suppressed in the entire region where the electronic component is mounted. Therefore, the electronic component can be appropriately mounted.

  In the flexible circuit board, the wiring further connected to the electrode on the one surface of the substrate, and a protective layer covering the wiring on the surface of the wiring opposite to the substrate, The reinforcing substrate is preferably bonded from a region overlapping the electrode to a region overlapping the protective layer.

  In such a flexible circuit board, by providing the protective layer, the wiring provided on one surface of the board is protected. In the case where such a protective layer is provided, when a force is applied to the substrate from the outside, the stress due to this force tends to concentrate on the boundary between the region where the protective layer is provided and the region where the protective layer is not provided. There is. In this case, disconnection is likely to occur at this boundary. However, since the reinforcing substrate is bonded from the region overlapping with the electrode to the region overlapping with the protective layer, this stress is dispersed by the reinforcing substrate, and disconnection due to stress concentration can be prevented.

  Moreover, the said flexible circuit board WHEREIN: It is preferable that melting | fusing point of the said hot-melt-adhesive shall be 80 to 150 degreeC.

  By using a hot-melt adhesive having such a melting point, it is possible to suppress deformation due to heat of a substrate including polyethylene terephthalate or polyethylene naphthalate when the hot-melt adhesive is melted.

  ADVANTAGE OF THE INVENTION According to this invention, the flexible circuit board which can prevent peeling of a reinforcement board | substrate is provided.

It is sectional drawing which shows the mode in the cross section of the flexible circuit board which concerns on 1st Embodiment of this invention. It is sectional drawing which shows the mode in the cross section of the flexible circuit board which concerns on 2nd Embodiment of this invention. It is sectional drawing which shows the mode in the cross section of the flexible circuit board which concerns on 3rd Embodiment of this invention.

  Hereinafter, a preferred embodiment of a flexible circuit board according to the present invention will be described in detail with reference to the drawings.

(First embodiment)
FIG. 1 is a cross-sectional view showing a state of a cross section of a flexible circuit board according to the first embodiment of the present invention.

  As shown in FIG. 1, the flexible circuit board 1 according to the present embodiment includes a substrate 10 having one surface 11 and the other surface 12, and an electrode formed on an end portion on the one surface 11 of the substrate 10. A terminal 20, a reinforcing substrate 30 bonded on the other surface 12 of the substrate 10, and an adhesive 40 that bonds the substrate 10 and the reinforcing substrate 30 are provided as main components.

  The substrate 10 has a flat plate shape having flexibility. The substrate 10 includes polyethylene terephthalate (PET) or polyethylene naphthalate (PEN). The thickness of the substrate 10 is not particularly limited, but is 38 μm to 300 μm.

  Further, the terminal 20 formed at the end on the one surface 11 of the substrate 10 is formed of one or two or more thin conductive layers. Although it does not specifically limit as such a conductive layer, For example, it is comprised by conductive paste, metal plating, etc. Examples of the conductive paste include a metal paste containing silver particles and nickel particles, and a carbon paste. Examples of the metal plating material include gold, copper, and nickel. Moreover, when the terminal 20 is formed of two conductive layers, it is preferable that a layer made of carbon paste is formed on a layer made of silver paste. By comprising in this way, carbon paste can play a role as a conductive layer, and can also play a role as a protective layer that prevents migration of the silver paste. Furthermore, although the thickness of the terminal 20 is not specifically limited, For example, it is preferable that they are 0.1 micrometer-30 micrometers.

  The terminal 20 is provided on one surface 11 of the substrate 10 and is connected to a wiring 21 having the same configuration as the terminal 20. Further, the surface of the wiring 21 opposite to the substrate 10 side is covered with an insulating protective layer 50. The insulating protective layer 50 is made of a resin such as polyimide or an insulating tape.

  Further, when the substrate 10 is viewed along a direction perpendicular to the other surface 12 of the substrate 10, a reinforcing substrate 30 is provided in a region overlapping the end portion on which the terminal 20 is formed on the other surface 12 of the substrate 10. It is adhered by an adhesive 40. The entire surface of the reinforcing substrate 30 on the substrate 10 side is in contact with the adhesive 40 and is bonded to the substrate 10. Further, the reinforcing substrate 30 is bonded to a region overlapping the protective layer 50 when the substrate 10 is viewed along a direction perpendicular to the other surface 12. Therefore, the reinforcing substrate 30 is bonded from a region overlapping the end where the terminals 20 are formed to a region overlapping the protective layer 50.

  The reinforcing substrate 30 is made of resin. Although it does not specifically limit as resin which comprises this reinforcement board | substrate 30, For example, PET, PEN, a polyimide, glass epoxy, paper etc. are mentioned. Further, the thickness of the reinforcing substrate 30 is not particularly limited, but is 50 μm to 250 μm.

  The adhesive that bonds the reinforcing substrate 30 and the substrate 10 is formed of a hot melt adhesive. The hot melt adhesive is not particularly limited, and examples thereof include polyester, polyolefin, thermoplastic polyurethane, and synthetic rubber hot melt adhesives. Among these, a polyester-based hot melt adhesive is preferable from the viewpoint of strong adhesion because it has excellent adhesion to PET and PEN, which are materials of the substrate 10. Further, the melting point of this hot melt adhesive is not particularly limited as long as it is lower than the melting point of the substrate 10 or the reinforcing substrate 30, but it is set to 60 ° C. to 200 ° C., in particular, 80 ° C. to 150 ° C., This is preferable from the viewpoint of suppressing deformation of the substrate 10 due to heat.

  According to the flexible circuit board 1 in the present embodiment, the bending of the substrate 10 can be suppressed by the reinforcing substrate 30 when the terminal 20 formed at the end of the substrate 10 is inserted into a connector or the like. At this time, since the adhesive 40 that bonds the substrate 10 and the reinforcing substrate 30 is a hot melt adhesive, oligomers are deposited on the surface of the substrate 10 including polyethylene terephthalate or polyethylene naphthalate. In this case, the reinforcing substrate 30 can be prevented from peeling off from the substrate 10. As described above, when a hot melt adhesive is used as the adhesive 40, even when an oligomer is deposited on the surface of the substrate 10, it is not clear why the reinforcing substrate 30 can be prevented from peeling off from the substrate 10. However, the present inventor has taken in the hot melt adhesive so as to wrap up the oligomer from the time when the hot melt adhesive is melted by heat until it is cooled and solidified, and the hot melt adhesive is directly applied to the surface of the substrate 10. Is considered to be for adhesion.

  Furthermore, in the flexible circuit board 1, the wiring 21 provided on the one surface 11 of the substrate 10 is protected by including the protective layer 50. In the case where such a protective layer 50 is provided, when a force is applied to the substrate 10 from the outside, the stress due to this force causes a region where the protective layer 50 of the substrate 10 is provided and a region where the protective layer 50 is not provided. There is a tendency to concentrate on the boundaries. In this case, disconnection is likely to occur at this boundary. However, since the reinforcing substrate 30 is bonded from the region overlapping the terminal 20 to the region overlapping the protective layer 50, this stress is dispersed by the reinforcing substrate 30, and disconnection due to stress concentration can be prevented.

(Second Embodiment)
Next, a second embodiment of the present invention will be described in detail with reference to FIG. In addition, about the component same or equivalent to 1st Embodiment, the same referential mark is attached | subjected and the overlapping description is abbreviate | omitted. FIG. 2 is a cross-sectional view showing a cross section of a flexible circuit board according to the second embodiment of the present invention.

  As shown in FIG. 2, the flexible circuit board 2 of the present embodiment is different from the flexible circuit board 1 of the first embodiment in that the reinforcing substrate 31 includes a region 33 where the reinforcing substrate 31 is bonded to the substrate 10 and a region 32 where the reinforcing substrate 31 is not bonded. Different.

  Specifically, when the substrate 10 is viewed along the direction perpendicular to the other surface 12 of the substrate 10, the reinforcing substrate 31 extends from a region overlapping the end where the terminals 20 are formed to a region overlapping the protective layer 50. The bonded area is an area 33. Further, in the reinforcing substrate 31, a region opposite to the end portion side of the substrate 10 is not bonded to the substrate 10, and this unbonded region is defined as a region 32. And the edge part of this area | region 32 which is not adhere | attached is made into the free end. The length of the unbonded region 32 is not particularly limited, but is preferably 2 mm to 20 mm from the viewpoint of gripping the free end side of the reinforcing substrate 31.

  According to the flexible circuit board 2 in the present embodiment, the end portion of the non-bonded region 32 in the reinforcing substrate 31 is a free end, whereby the non-bonded region 32 in the reinforcing substrate 31 can be gripped. Accordingly, when the terminal 20 formed at the end of the substrate 10 is inserted into a connector or the like, the free end side of the reinforcing substrate 31 can be gripped and inserted, and the terminal 20 can be efficiently inserted into the connector or the like. .

(Third embodiment)
Next, a third embodiment of the present invention will be described in detail with reference to FIG. In addition, about the component same or equivalent to 1st Embodiment, the same referential mark is attached | subjected and the overlapping description is abbreviate | omitted. FIG. 3 is a cross-sectional view showing a state of the cross section of the flexible circuit board according to the third embodiment of the present invention.

  As shown in FIG. 3, the flexible circuit board 3 of the present embodiment includes lands 23 and 23 as a pair of electrodes formed on one surface 11 of the substrate 10. The land 23 has the same configuration as the terminal 20 in the first embodiment. A wiring 21 is connected to each land 23, 23. The wiring 21 is covered with a protective layer 50.

  In addition, a region where the pair of lands 23 and 23 are formed and a region sandwiched between the pair of lands 23 and 23 of the substrate 10 are regions 15 where the electronic component 70 is mounted. The electronic component 70 has a configuration in which a pair of terminals 72 are formed at both ends of a main body 71. Examples of such electronic components 70 include capacitors, LEDs, filters, semiconductor components, and the like. When the electronic component 70 is mounted on the substrate 10, the pair of lands 23 and 23 are connected to the pair of terminals 72 and 72 by a conductive connection member such as a conductive paste (not shown).

  When the substrate 10 is viewed along a direction perpendicular to the other surface 12 of the substrate 10, the reinforcing substrate 30 is located in a region overlapping the region 15 on which the electronic component 70 is mounted on the other surface 12 of the substrate 10. Is bonded by an adhesive 40. Specifically, the reinforcing substrate 30 is bonded from a region overlapping the region 15 to a region overlapping the protective layer 50.

  According to the flexible circuit board 3 in the present embodiment, when the electronic component 70 is mounted on the substrate 10, the distortion of the land 23 due to the bending of the substrate 10 is suppressed, and the connection between the land 23 and the terminal 72 of the electronic component 70 is performed. Can be made good.

  Furthermore, the flexible circuit board 3 has the reinforcing substrate 30 bonded to the entire region where the electronic component 70 is mounted on the other surface 12 of the substrate 10, and thus the entire region where the electronic component 70 is mounted. In this case, bending of the substrate 10 can be suppressed. Therefore, the electronic component 70 can be appropriately mounted.

  The present invention has been described above by taking the first and second embodiments as examples, but the present invention is not limited to these.

  For example, in the first to third embodiments, the wiring 21 is protected by the protective layer 50, but the protective layer 50 may not be provided.

  Further, the terminal 20 and the wiring 21 have the same configuration, but the terminal 20 and the wiring 21 may have different configurations. For example, when the wiring 21 is made of a conductive paste and the terminal 20 is made of metal plating, or the terminal 20 is formed of two or more conductive layers, the wiring 21 is conductive on the substrate 10 side of the terminal 20. It may be formed by a layer.

  In the third embodiment, the lands 23 are paired, but the number of lands 23 varies depending on the type of electronic component mounted on the substrate 10. Therefore, the number of lands 23 may be one or may be three or more.

  Hereinafter, the content of the present invention will be described more specifically with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

(Example 1)
A substrate made of PET having a thickness of 75 μm was prepared and aged at 175 ° C. for 2 hours. Thereafter, a plurality of terminals and wirings were formed with silver paste at the end on one surface of the substrate. A reinforcing substrate made of PET having a thickness of 188 μm was prepared. Thereafter, a copolyester hot melt adhesive (manufactured by Toa Gosei Co., Ltd., model number PSE1100EE) was attached to the reinforcing substrate as a sheet-type adhesive.

  Next, the substrate and the reinforcing substrate were overlapped so that the hot melt adhesive was disposed on the other surface of the substrate on which the plurality of terminals were formed. Then, the hot melt adhesive was melted at 120 ° C. for 3 seconds with a thermal laminator, and then the hot melt adhesive was solidified by natural cooling. At this time, the thickness of the hot melt adhesive was 30 μm.

  Next, the substrate and the reinforcing substrate were punched out by a die cutting machine to create a plurality of flexible circuit boards. At this time, the substrate had a width of 11.5 mm and a length of 70 mm, and the width and length of the reinforcing substrate were the same as those of the substrate. At this time, the punching position was adjusted so that the hot melt adhesive had the same width as the substrate and the length of 10 mm at the ends of the substrate and the reinforcing substrate. And the area | region which is not adhere | attached with the hot-melt-adhesive agent in a reinforcement board | substrate was made into 20 mm in length, and the edge part of the area | region which the reinforcement board | substrate was not adhere | attached was made into the free end.

(Example 2)
As an adhesive, instead of sticking a sheet-type hot melt adhesive to the reinforcing substrate, a cross-linking polyester hot melt adhesive (made by Fujikura Kasei Co., Ltd., no model number) melted at 100 ° C is applied on the reinforcing substrate. A flexible circuit board was produced in the same manner as in Example 1 except that printing was performed.

(Comparative Example 1)
A flexible circuit board was produced in the same manner as in Example 1 except that an acrylic adhesive was used as the adhesive.

(Peel test)
Next, for each flexible circuit board, the board is fixed, and the end of the reinforcing board is bonded to the reinforcing board from the free end side of the reinforcing board along the direction parallel to the board. The reinforcing substrate was pulled away from the substrate. At this time, the peeling speed was 100 mm / min. At this time, the force for peeling the reinforcing substrate from the substrate was measured per 20 mm width. The results are shown in Table 1.

(Bending test)
Next, a bending test was performed using a boundary between a region where the substrate and the reinforcing substrate are bonded and a region where the substrate and the reinforcing substrate are not bonded as a fulcrum. The bending radius was gradually decreased, and the radius when the peel-off amount of the reinforcing substrate became 1.0 mm or more was measured. The results are shown in Table 1.

(Creep test)
Next, the substrate was fixed horizontally with the substrate facing up and the reinforcing substrate facing down, and a weight having a mass of 3 g per 1 mm width was fixed to the free end of the reinforcing substrate. Thus, the unbonded area of the reinforcing substrate was left vertical at 80 ° C. for 20 hours. Then, the length of peeling of the reinforcing substrate was measured after 20 hours. The results are shown in Table 1.

  As shown in Table 1, in the peel test, Examples 1 and 2 both peeled the reinforcing substrate from the substrate with a stronger force than Comparative Example 1.

  Further, in the bending test, the peeling of the reinforcing substrate did not become 1.0 mm or more until both of Examples 1 and 2 had a radius smaller than that of Comparative Example 1.

  Moreover, in the creep test, both Examples 1 and 2 had a peeling length smaller than that of Comparative Example 1.

  From the above, it has been confirmed that the flexible circuit board according to the present invention can prevent the reinforcing substrate from peeling off.

  ADVANTAGE OF THE INVENTION According to this invention, the flexible circuit board which can prevent peeling of a reinforcement board | substrate is provided.

1, 2, 3 ... Flexible circuit board 10 ... Board 20 ... Terminal (electrode)
21 ... Wiring 23 ... Land (electrode)
30, 31 ... Reinforcement substrate 40 ... Adhesive 50 ... Protective layer 70 ... Electronic component 71 ... Main body 72 ... Terminal

Claims (7)

A substrate having one side and the other side and comprising polyethylene terephthalate or polyethylene naphthalate;
An electrode formed on the one surface of the substrate;
A reinforcing substrate bonded to at least a region overlapping the electrode on the other surface of the substrate;
An adhesive that bonds the substrate and the reinforcing substrate;
With
The flexible circuit board, wherein the adhesive is a hot melt adhesive. The flexible circuit board according to claim 1, wherein the electrode is a terminal formed at an end of the substrate. The flexible substrate according to claim 2, wherein an end of the reinforcing substrate opposite to the end of the substrate is a region not bonded by the adhesive, and an end of the non-bonded region is a free end. Circuit board. The flexible circuit board according to claim 1, wherein the electrode is a land to which a terminal of an electronic component mounted on the board is connected. 5. The flexible circuit board according to claim 4, wherein the reinforcing substrate is bonded to the entire region overlapping the region where the electronic component is mounted on the other surface of the substrate. A wiring connected to the electrode on the one surface of the substrate;
On the surface of the wiring opposite to the substrate, a protective layer covering the wiring;
Further comprising
The flexible circuit board according to claim 1, wherein the reinforcing substrate is bonded from a region overlapping the electrode to a region overlapping the protective layer. The flexible circuit board according to any one of claims 1 to 6, wherein the hot-melt adhesive has a melting point of 80 ° C to 150 ° C.

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