JP2013038379A - Flexible printed circuit board having bending part and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To maintain a bent state of a flexible printed circuit board having a bending part by suppressing the occurrence of a spring-back phenomenon by a coverlay and an adhesion layer.SOLUTION: In a flexible printed circuit board having a bending part A, two coverlays 32, 34 mutually separated to sandwich the bending part A are formed. An ink print layer 50 having an excellent bending maintenance property is directly coated between the two coverlays on a circuit pattern layer 24. As such, by the formation of the ink print layer 50 between the two coverlays, an effect of maintaining a bent state is obtained by the ink print layer. In particular, since the reception of a physical influence such as a spring-back characteristic can be reduced when used in a portion adjacent to a junction part 24a with an isotropic conductive film, an adhered state to another conductive portion can be maintained, so that an effect capable of solving a problem such as an imperfect contact is produced.

Description

  The present invention relates to a flexible circuit board (FPCB) having a bent portion and a method of manufacturing the same, and more particularly, to a flexible circuit board adjacent to an ACF (Anisotropic Conductive Film-ACF) bonding portion connected to a liquid crystal display panel. The present invention relates to a flexible circuit board having a bent portion characterized by a technique optimized for bending and use, and a method of manufacturing the same.

  In general, LCD modules that are essential for personal portable devices and the like are equipped with a printed circuit board on which an integrated circuit element and its peripheral elements are mounted as a drive circuit necessary for LCD driving. There is a tendency to use a lot of flexible circuit boards for printed circuit boards.

  The flexible circuit board of such an LCD module is connected to an LCD panel through an electrical connection means using an anisotropic conductive film-ACF (Anisotropic Conductive Film-ACF) bonding. The signal is transferred.

  By the way, in order to connect the flexible circuit board of the LCD module and the LCD panel, it is often necessary to bend the flexible circuit board of the LCD module depending on the product case form and structure to be produced. This is because the connection direction between the soft circuit board of the LCD module and the main circuit board of the user set is often not aligned.

  Therefore, FIG. 1a shows a conventional case where a flexible circuit board having an ACF bonding portion (hereinafter referred to as “ACF circuit pattern layer” for describing the layer structure when the layer cross-sectional shape is expressed) is bent. The formed flexible circuit board 100 is bent to have a structure as shown in FIG. 1b.

  In the figure, reference numeral 100 denotes a flexible circuit board. A circuit pattern layer (24) is formed on the flexible circuit board (100), and a portion of the circuit pattern layer (24) is electrically connected as an ACF circuit pattern layer (24a) as a circuit pattern to the end of the flexible circuit board. The coverlay 132 is attached to the upper part of the circuit pattern layer 24 using the adhesive layer 128 as a medium.

An unexplained reference numeral 10 denotes a general copper foil laminate laminated from a polyimide layer (12) and a copper layer (14, 14 ') covered with copper.
The flexible circuit board is bent as shown in FIG. 1b by selecting a bent portion at an appropriate position adjacent to the ACF circuit pattern layer (24a). At this time, the coverlay (132) and the adhesive layer ( 128), different tensile rates are applied by the multi-layer structure laminated from 128), and the action of the force to return the folded portion to the direction in which it is stretched again due to the inherent properties of the coverlay and the adhesive layer itself. That is, the spring back characteristic appears. This acts as a cause of making the connecting operation not easy even when the ACF is bonded to another circuit so that the ACF circuit pattern layer (24a) is electrically contacted. Also causes problems such as poor electrical contact.

  Therefore, in the conventional flexible circuit board, there has been a demand for technical means for allowing the bent portion to maintain the bent state as it is.

Japanese Patent Laid-Open No. 9-06489 JP-A-8-116140 JP 2002-151823 A

  The present invention has been devised in view of the above-described conventional problems, and provides a technical means for partial replacement of a coverlay that allows a flexible circuit board to be maintained in a bent state. In particular, the present invention aims to provide a flexible circuit board having a bent portion that can be used very effectively when applied adjacent to the ACF portion of the flexible circuit board, and a method for manufacturing the same. .

  The flexible circuit board having a bent portion of the present invention for achieving the above-described object is provided with a circuit pattern layer on a general copper foil laminate in which a polyimide layer and a copper layer are laminated, and an upper portion thereof. In a flexible circuit board to which a cover lay is attached by an adhesive layer, a blank portion without the cover lay and the adhesive layer so that the circuit pattern layer is exposed in a folded portion of the flexible circuit board that needs to be bent ( A first cover lay and a second cover lay that are separated from each other by forming a blank), and applying an ink to the blank portion to form a thermally cured ink print layer. The first cover lay and the second cover lay located on both sides of the blank portion are partially covered.

  In the above-described configuration, the second coverlay is formed with a narrow width, and the flexible circuit board is placed at a position beyond the narrow width of the second coverlay from the ink print layer. The ACF circuit pattern layer for connection to the circuit device is formed so as to be exposed.

  On the other hand, the method for producing a flexible circuit board having a bent portion according to the present invention includes a first step of forming a circuit pattern layer on the copper foil laminate (10); and a position corresponding to the bent portion of the copper foil laminate. In view of this, a second step of cutting the coverlay so as to provide a 'B'-shaped blank (BLANK); a third step of bonding the coverlay provided with the blank to the upper part of the circuit pattern layer; A fourth stage in which ink is printed and applied so as to lightly cover a part of the side edge of the cover lay adjacent to the blank part, and cured to form an ink print layer; the copper foil after the fourth stage; It is characterized in that it is carried out in a fifth step of cutting a flexible circuit board including a laminate or a coverlay in a desired form; a sixth step of bending the ink print layer portion.

  Here, when the cover lay is cut in the fifth step, the cover lays after being cut are separated from each other as the first cover lay and the second cover lay. In the third stage, the lay is provided with a blank part by arranging and cutting the position of the blank part as a position that enables the second cover lay to be formed with a narrow width in the second stage. The coverlay having a blank portion is attached.

An ACF circuit pattern layer for connecting to another circuit device in the first stage is formed at an end portion of the flexible circuit board in the second coverlay side direction.
The ink used in the fourth step is 15-30% by weight of anhydride acid, 15-30% by weight of epoxy resin, 15-30% by weight of barium sulfate, silicate compound (Silicate Compound) 15-30 wt%, phenol resin (Phenol Resin) 15 wt% or less, organic pigment (Organic Pigment) 15 wt% or less, silicon polymer (Silicon Polymer) 15 wt% or less It is characterized by.

  The flexible circuit board having the bent portion of the present invention configured as described above has a bent portion interposed therebetween, and two coverlays separated from each other are formed, and ink printing is performed between the two coverlays. By forming the layer, the ink printed layer has an effect of maintaining the folded state while functioning as a coverlay.

  The ink printing layer can adopt a characteristic that has a remarkably less spring back phenomenon than the existing conventional coverlay itself and the adhesive layer itself. By applying directly on the circuit pattern layer between two coverlays, the effects of the existing conventional coverlay and adhesive layer springback characteristics can be eliminated except for the relatively small springback characteristics of the ink printing layer. It becomes like this. Therefore, it has the outstanding bending maintenance characteristic that a bending state is maintained as it is. At the same time, it is a matter of course to maintain the insulation protection function as an alternative to the coverlay function.

  On the other hand, in the method step of manufacturing such a flexible circuit board, the present invention provides a process technique for separating the coverlay into two different ones, and ink is applied on the ACF circuit pattern layer during ink application. There are techniques to limit this from being done.

The second coverlay serves as a dam that prevents the ink from reaching the ACF circuit pattern layer when the ink is applied to form the ink print layer.
That is, the present invention provides a step in which a liquid ink liquid applied to form a liquid ink print layer before being cured exists between the second coverlay and the copper foil laminate (CCL). The ink is prevented from exceeding the second cover lay by surface tension (interfacial tension) in the step groove (part indicated by the reference numeral “B” in FIG. 3D) generated by the above.

  This is because in general interfacial phenomena, liquids that are free to move molecules move in accordance with the angular structure and the characteristic that they form spheres to minimize the number of molecules located in the corners. It utilizes the characteristics of the combination of surface tension and solid-liquid adhesion. The surface tension (interfacial tension) is a natural force defined by the force acting to minimize the area generated at the interface when substances in different states such as liquid and gas or liquid and solid are in contact with each other. It is a theory on the law and a phenomenon.

  In addition, as described above, the manufactured flexible circuit board has characteristics that are more than several times better than when the existing coverlay is used to maintain the bent portion of the bent portion by the ink printing layer. Therefore, there is an effect that the liquid crystal display panel and the ACF bonding state are maintained and contact failure does not occur even after a long time.

The layer sectional view which illustrated the flexible circuit board which has the conventional bending part. The layer sectional view showing the state where it was bent. The top view which showed the flexible circuit board by the Example of this invention. The layer sectional view showing the layer structure of the flexible circuit board of the present invention according to the manufacture order. The layer sectional view showing the layer structure of the flexible circuit board of the present invention according to the manufacture order. The layer sectional view showing the layer structure of the flexible circuit board of the present invention according to the manufacture order. The layer sectional view showing the layer structure of the flexible circuit board of the present invention according to the manufacture order. The layer sectional view showing the layer structure of the flexible circuit board of the present invention according to the manufacture order. The layer sectional view showing the layer structure of the flexible circuit board of the present invention according to the manufacture order. The top view of the coverlay which illustrated the pattern which provided the blank part in advance in the coverlay itself in order to make two coverlays attached to the soft circuit board and spaced apart from each other with the manufacturing method of the flexible circuit board of the present invention.

Embodiments of the present invention will be specifically described below with reference to the drawings.
As shown in FIGS. 3a to 3f, the present invention includes a circuit pattern layer (24) in a copper foil laminate (10) in which a polyimide layer (12) and a copper layer (14) are laminated, It is limited to a flexible circuit board on which a coverlay (30) is attached by an adhesive layer (28). The cover lay (30) is a cover lay on the upper surface related to the features of the present invention. Reference numeral 42 is a cover lay on the lower surface, and the cover lay on the lower surface is attached to the bent portion (A). Is unnecessary, and if there is a circuit on the lower surface as shown, it can be partially taken for protection. The present invention is based on the premise that there is no cover lay on the lower surface of the bent portion, and does not refer to the claims for a strong and unnecessary lower surface cover lay.

  Referring to FIGS. 2 and 3a to 3f, in the present invention, the circuit pattern layer (24) is exposed in the bent portion (A) of the flexible circuit board (1) that needs to be bent. As described above, the first cover lay (32) and the second cover lay (34) are separated by placing a blank portion (C; Blank) without the cover lay (30) and the adhesive layer (28). is there. In FIG. 3a to FIG. 3c, the blank portion corresponds to a portion having no cover lay and adhesive layer between the first cover lay and the second cover lay. In FIG. It is shown.

  In combination with the structure described above, the present invention forms an ink print layer (50) that is thermally cured by applying ink to the blank portion (C), and the ink print layer (50) is shown in FIG. As shown in FIG. 3e and FIG. 3f, the upper part of the first cover lay (32) and the second cover lay (34) located on both sides of the blank portion is partially covered.

As described above, the partially covered structure acts to prevent the ink print layer (50) from being easily peeled off from the coverlays (32, 34) during bending.
Further, according to the present invention, the liquid ink applied to form the ink printing layer (50) in the liquid state before being cured is applied to the second coverlay (32) and the copper foil laminate (10; CCL). Ink liquid easily passes through the second cover lay (34) by surface tension (interfacial tension) in a step groove (portion indicated by a reference sign 'B' in FIG. 3d) generated by a step existing between Will not exceed. Since the liquid ink flows vertically along the step groove (B) and does not easily cross the step groove (B), a structure covering a part can be maintained.

The thickness of the ink print layer may be determined according to the thickness of the cover lay, and it can be said that the thinner the cover lay and the ink print layer are, the more advantageous is the flexibility as a soft circuit board.
Referring to FIGS. 2, 3d and 4, the width (P34) of the second cover lay (34) is smaller than the width (P32) of the first cover lay (32). The flexible circuit board (1) has an ACF circuit pattern layer (ACF circuit pattern layer) connected to another circuit device at a position beyond the width (P34) of the second coverlay (34) from the ink print layer (50). 24a) is a structure formed so as to be exposed to the outside. That is, the present invention can also be applied to all flexible circuit boards that need to be bent as in claim 1 of the present application, and in the ACF adjacent portion of the flexible circuit board having ACF as in claim 2. Limited application is also possible.

The flexible circuit board of the present invention having such a structure can be produced by the following process.
3a to 3f, a first step of forming a circuit pattern layer (24) on the copper foil laminate (10); a position corresponding to the bent portion (A) of the copper foil laminate (10). A second stage of cutting the cover lay (30) by providing a 'B'-shaped blank portion (C, see FIG. 4 of the drawing) on the cover lay; (30) the cover lay (30) provided with the blank portion (C) A third step of adhering to the upper part of the circuit pattern layer (24) with the adhesive layer (28) as a medium; partially covering the upper surface of the side edge of the coverlay (30) adjacent to the blank part (C) A fourth step of forming an ink printing layer (50) by printing, applying and curing ink; and cutting the flexible circuit board (1) having undergone the fourth step in a predetermined form, The first cover lay (32) and the second cover lay ( 34) and the sixth step of bending the flexible circuit board at the ink printing layer (50). 3A to 3F, the unexplained reference numeral 22 is a via hole, and the unexplained reference numeral 26 is an etched portion.

  The cutting of both side surfaces of the fifth stage 'B' pattern corresponds to cutting the cutting line portion indicated by 'D' in FIG. The laminate (10) and the ink print layer (50) are also cut together, so that the coverlay (30) has a first coverlay (32) with the ink print layer (50) in between as shown in FIG. And a second coverlay (34).

In the case of an existing coverlay (C / L), the thickness is usually about 27 to 37 um.
In the case of the ink print layer, it is preferable to form the ink print layer to a thickness of 10 to 20 μm. In forming such a thickness, the characteristics of the ink composition and the composition ratio influence.

In the fourth step, the liquid ink for forming the ink print layer preferably includes the following composition components.
Table 1 below shows ink compositions and ratios.

The anhydride acid (Acid anhydride) is used for accelerating the curing, and when the amount is large, it acts to enable curing at a low temperature, and in the cured state, the springback characteristics in the present invention, In other words, it is useful for maintaining the bent state.

  The epoxy resin (Epoxy Resin) is used for adhesion and bending state maintenance. The epoxy resin has an epoxy group in the molecule. This epoxy group reacts with a phenol resin, which is a curing agent described below, to form a cross-linked three-dimensional polymer structure.

The barium sulfate is used for the pigment dispersing role.
The silicate compound is used to enhance the insulating properties of the ink print layer.

The phenol resin (Phenol Resin) is used to allow the ink to be thermally cured.
The organic pigment is used as a pigment that is added to realize the hue of the ink print layer.

  The silicon polymer is used for adhesiveness and gas permeability, and is also used for flexibility and folding maintenance of a flexible circuit board pursued by the present invention due to its soft property. The

  The present invention manufactured by the method as described above is applied to a flexible circuit board having a bent portion, and is particularly preferably applied to an ACF adjacent portion in a flexible circuit board having an ACF.

  To this end, an ACF circuit pattern layer (for connection with another circuit device in the first stage of the manufacturing method) is provided at the end of the flexible circuit board (1) in the direction of the second coverlay (34). 24a) is defined as being formed and specified in the claims.

  Here, the ACF circuit pattern layer (24a) can have a nano-sized polymer particle anisotropic conductive film (ACF) on top of the circuit pattern, which is the manufacturing method of the present invention. Although it is generally performed in the subsequent process, it can be performed immediately after the first stage process or immediately after another stage.

  As described above, the flexible circuit board manufactured by applying all the structures and methods provided in the present invention was tested for the bent state maintaining performance of the present invention. This is an experiment of a spring back characteristic in which a flexible circuit board tries to return to its original state in a bent state.

  Table 2 below shows the experimental results of springback characteristics when the cause is the existing coverlay.

Samples were tested for coverlay and ink on the same flexible circuit board base (CCL).

  This is an experiment in which the force received in the right direction is measured when the sample is rolled up as shown in the remarks in Table 2 and the right side plate is pushed to the left side. That is, the force to be stretched in a bent state is measured in grams (g).

In the case of the ink printing layer of the sample, the thickness was 10 to 20 μm, and in the case of the coverlay (C / L), the thickness was about 27 to 37 μm.
When samples 1 to 5 of the flexible circuit board manufactured with the coverlay and the ink printed layer in the experiment of Table 2 were subjected to the springback characteristic experiment, the ink printed layer was used as compared with the case of using the coverlay as in the existing case. At the same time, it was confirmed that the performance of the springback characteristic was further improved by 4 times to 5 times as a target of the present invention.

  Therefore, since the bent state can be easily maintained when the ink printed layer is formed on the flexible circuit board as in the present invention, it is very useful when applied to a bent portion such as an ACF portion. I understand.

  DESCRIPTION OF SYMBOLS 1 ... Flexible circuit board, 10 ... Copper foil laminated board, 12 ... Polyimide layer, 14 ... Copper layer, 24 ... Circuit pattern layer, 24a ... ACF circuit pattern layer, 28 ... Adhesive layer, 30 ... Coverlay, 32 ... 1st 34 ... second cover lay, 42 ... lower cover lay, 50 ... ink printing layer, A ... folded portion, B ... step groove, C ... blank portion, D ... cutting line.

Claims (5)

In a flexible circuit board having a bent portion, a circuit pattern layer is provided on a copper foil laminate formed by laminating a polyimide layer and a copper layer, and a cover lay is attached to the upper portion thereof by an adhesive layer.
Among the flexible circuit board, the first cover lay and the second cover lay are provided in a bent part that needs to be bent, with a blank part without the cover lay and the adhesive layer so that the circuit pattern layer is exposed. A cover lay is separated and ink is applied to the blank portion to form a heat-cured ink print layer, and the ink print layer is located on both sides of the blank portion. The first cover lay and the second cover lay A flexible circuit board characterized in that it has a structure that partially covers the upper part of a ray. The width of the second cover lay is narrower than the width of the first cover lay, and the flexible circuit board has a position beyond the width of the second cover lay from the ink print layer. 2. The flexible circuit board having a bent portion according to claim 1, wherein an ACF circuit pattern layer for connecting to another circuit device is formed to be exposed to the outside. A first step of forming a circuit pattern layer on the copper foil laminate;
A second step of cutting the coverlay by providing a 'B'-shaped blank at a position corresponding to the bent portion of the copper foil laminate;
A third step of adhering the coverlay provided with the blank portion to the upper part of the circuit pattern layer through an adhesive layer;
A fourth step of forming an ink print layer by printing, applying and curing ink so as to partially cover the upper surface of the side edge of the cover lay adjacent to the blank portion;
The flexible circuit board that has undergone the fourth step is cut, but the first and second coverlays are separated from each other by removing both sides of the 'B'-shaped coverlay. And a sixth step of bending the flexible circuit board manufactured through the fifth step at an ink print layer portion. A method of manufacturing a flexible circuit board having a bent portion, comprising: . The ACF circuit pattern layer for connecting to another circuit device in the first stage is formed at an end of the flexible circuit board in the second coverlay direction. A method of manufacturing a flexible circuit board having a bent portion. The ink used in the fourth stage is
Acid anhydride 15-30 wt%, Epoxy Resin 15-30 wt%, Barium Sulfate 15-30 wt%, Silicate Compound 15-30 wt%, Phenol 4. The flexible circuit board according to claim 3, comprising a composition component of 15% by weight or less of Phenol Resin, 15% by weight or less of Organic Pigment, and 15% by weight or less of Silicon Polymer. Manufacturing method.