JP2007053401A - Flexible printed board, connection printed board structure, and liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a flexible printed board with a high peel (separation) strength against the separation due to applied stress, in a printed board structure using a flexible printed board. <P>SOLUTION: A flexible printed board 15 with a wiring pattern 17 printed on a flexible resin film, having a flexible part constituting a flexible wiring part, comprises a connection part bonded to a main board 11, which is an object of connection, and electrically connecting the wire of the flexible wiring part to the wire on the main board 11, and a periphery having a bent shape formed at least on the outer edge of the connection part. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a printed circuit board, and more particularly to a printed circuit board structure using a flexible printed circuit board.

  The flexible printed circuit board has a feature that it can be bent by forming a circuit pattern such as copper foil on a flexible resin film such as polyimide. In this specification, the flexible printed circuit board is used as a concept including a tape carrier package.

  In an electrical product having a movable part such as a printer, the flexible printed circuit board is used as a wiring member that electrically connects the movable part and the fixed part. Even in an electronic device having no movable part such as a liquid crystal display (LCD) or a camera, a flexible printed circuit board is used for accommodating wiring in a narrow and small space. In any usage, the flexible printed circuit board is assumed to be bent.

  The flexible printed circuit board is electrically and mechanically connected to an object to be connected (referred to as a main board) by soldering, an anisotropic conductive film (ACF), or the like. The main substrate is a hard substrate such as an LCD glass substrate, epoxy, or glass epoxy, and hardly deforms. When the flexible printed circuit board is bent or subjected to vibration or temperature change, a stress is generated, and this stress is concentratedly applied to the connection portion between the flexible printed circuit board and the main substrate. If the connection strength of the connecting portion is insufficient, the flexible printed board may be peeled off from the main board due to stress. In order to increase the connection strength, after the flexible printed circuit board is connected to the main substrate, both surfaces are further coated with a UV curing agent or another curing agent. Even if such measures are taken, the connection strength may be insufficient. Such measures also increase man-hours and raise production costs.

  As described above, the flexible printed board connected to the main board may be peeled off by applying stress.

  An object of the present invention is to provide a flexible printed circuit board having high peel (peeling) strength against peeling caused by stress application and a liquid crystal display device including the flexible printed circuit board.

  Another object of the present invention is to provide a connection printed circuit board structure in which the flexible printed circuit board is difficult to peel off when stress is applied.

  According to one aspect of the present invention, a flexible printed circuit board in which a wiring pattern is printed on a flexible resin film, which is bonded to a flexible part constituting the flexible wiring part and a main board to be connected, is flexible. Provided is a flexible printed circuit board having a connection part for electrically connecting the wiring of the wiring part to the wiring on the main board, and a periphery having a bent shape formed at least at a part of the outer edge of the connection part. .

  According to another aspect of the present invention, there is provided a connection printed circuit board structure in which a connection part of a flexible printed circuit board is bonded to a connection part of a main board, and at least one of outer edges of both connection parts has a bent periphery. A substrate structure is provided.

  It has been found that when the flexible printed circuit board is bonded to the main substrate with an adhesive layer, the peripheral length of the bonded portion affects the peel strength rather than the bonded area. By increasing the peripheral length of the bonded portion, the peel strength against peeling increases.

  As described above, according to the present invention, it is possible to increase the peel strength against peeling of the flexible printed circuit connected to the main substrate.

  Prior to the description of the embodiments of the present invention, a flexible printed circuit board according to the prior art will be described.

  As shown in FIG. 7, the connection part of the flexible printed circuit board 115 is connected to the connection part of the main board 111. In the connection portion, the region 120 is a region where the flexible printed circuit board 115 is connected to the main substrate 111 by solder, anisotropic conductive film (ACF), or the like.

  As shown by an arrow F, it is assumed that a stress that lifts the lower left side of the flexible printed circuit board 115 upward is applied to the right side. Such stress is concentrated and applied to the point X which is a corner of the connection portion. As a result of the stress concentration, when the connection region 120 starts to peel off near the point X, the flexible printed circuit board 115 is easily peeled off from the main board 111.

  Embodiments of the present invention will be described below with reference to the drawings. 1A to 1C show a connection form between a main board and a flexible printed board according to an embodiment of the present invention. FIG. 1A is a cross-sectional view of a connecting portion, and FIGS. 1B and 1C are a plan view showing a back surface of a flexible printed board and a plan view showing the surface of a main board, respectively.

  As shown in FIG. 1A, the main substrate 11 has a wiring pattern 13 formed on a support substrate 12. The flexible printed circuit board 15 has a wiring pattern 17 formed on a flexible resin film 16. The wiring pattern 13 on the main board and the wiring pattern 17 on the flexible printed board are mechanically and electrically connected by a solder layer 19.

  The resin film 16 is a polyimide film having a thickness of 10 to 30 μm, for example, 12.5 μm and 25 μm. The wiring pattern 17 is formed of a copper foil having a minimum pattern width of 0.15 mm to 0.2 mm, a pattern interval of 0.15 mm to 0.2 mm, and a thickness of 10 μm to 40 μm, for example, 35 μm.

  The support substrate 12 of the main substrate 11 is a glass substrate in the case of an LCD, and is mainly a hard substrate of epoxy or glass epoxy in other cases.

  As shown in FIG. 1B, wiring patterns 17 a to 17 z are formed on the back surface of the flexible printed circuit board 15. The resin film 16 of the flexible printed circuit board 15 includes a flexible portion 16a having a constant width shown on the right side in the drawing and a connection portion 16b formed wider than the flexible portion 16a.

  The upper and lower sides s1, s2 of the flexible portion 16a and the right sides s3, s4 of the connecting portion 16b are substantially orthogonal. In other words, the resin film 16 extends from the narrow part defined by the sides s1 and s2 to the wide part defined by the sides s5 and s6 via the sides s3 and s4 projecting substantially at right angles. The narrow part constitutes a flexible wiring part, and the wide part constitutes a connection part.

  On the resin film 16, the wiring patterns 17a to 17z extend from the flexible portion 16a to the end portion of the connection portion 16b with a constant width. The two wiring patterns 17a and 17z arranged on the outermost side among the wiring patterns 17a to 17z are connected to the other wiring patterns 17b, 17c,. . . Although the case where it is designed to be wider than the above is shown, it may be a wiring having the same width. When using a wide wiring pattern such as a power supply wiring and a narrow wiring pattern such as a signal wiring, it is preferable to arrange the wide wiring patterns on both sides as shown in the figure.

  The width of the resin film 16 is enlarged on both sides in the connection portion 16b. In this enlarged region, an anchor pattern 14f formed of the same conductive layer as the wiring pattern and wider than the wiring turns 17a to 17z is formed along the right sides s3 and s4 of the resin film. In addition, although the case where this wide anchor pattern 14f was provided in the both sides of the connection part 16b was shown, according to the usage form of a flexible printed circuit board, it can also provide in only one.

  As shown in FIG. 1C, a wiring pattern 13 corresponding to the wiring pattern 17 on the flexible printed circuit board is formed on the main substrate 11. Although only a part of the connection part of the main board is shown in the figure, in the region where the connection part of the flexible printed board is overlapped, the conductive pattern of the flexible printed board and the mirror-symmetric conductive pattern are formed.

  In the region along the right side of the main substrate 11, an anchor pattern 14s formed of the same conductive layer is formed above the wiring pattern 13a. The anchor pattern 14s terminates in the connection portion and is not used as a wiring. That is, the anchor pattern 14f on the flexible printed circuit board 15 is not used as wiring. However, the anchor pattern may be used as a part of the wiring pattern.

  The anchor pattern 14 f on the flexible printed board is soldered to the anchor pattern 14 s on the main board 11.

  Here, as described in the prior art, a case is considered where the flexible printed circuit board 15 is bent and stress is applied to a point X that is an intersection of the flexible portion and the connecting portion. The stress is received by the anchor pattern 14f continuous with the wiring pattern 17a. Since the stress is received in the region extending up and down across the stress application point X, the flexible printed board 15 does not easily peel off.

  Although the case where the peel strength is increased by an anchor pattern that is not used as a wiring has been described, a similar configuration may be realized by a wiring pattern used as a wiring. In the connection region where the flexible printed circuit board and the main substrate are connected by soldering or the like, the adhesive pattern extends along the sides s3 to s4 from the inside to the outside of the region H in which the connection boundary with the flexible portion extends to the left. It is important to.

  FIG. 2 shows a modification of the first embodiment shown in FIG. In FIG. 2A, the anchor pattern 14 extends from the inside of the extension region H of the connection boundary with the flexible part 15a toward both outsides at the connection part between the main board 11 and the flexible printed board 15. The anchor pattern 14 is not used as a wiring, and is formed as a dummy pattern separated from the wiring pattern. The other points are the same as in the embodiment shown in FIG.

  FIG. 2B shows the configuration of the flexible printed circuit board. An anisotropic conductive film 25 is laminated on the entire surface of the connection portion 15 b of the flexible printed circuit board 15. The anisotropic conductive film 25 is bonded to the main substrate so that the entire surface becomes an adhesive surface. Therefore, the connection part 15b which has the expanded width with respect to the width of the flexible part 15a provides an adhesive surface extending from the inside to the outside of the extension region H in the connection part at the connection boundary with the flexible part 15a.

  FIG. 2C shows an example of the shape of the resin film of the flexible printed board. The outer edge of the resin film 16 has an extended side s11 whose direction is gradually changed before reaching the side s3 along the edge of the main substrate 11 of the connecting portion from the straight side s1 constituting the flexible portion. A connecting portion 18 that connects the flexible portion 16a and the connecting portion 16b shown in FIG. 1 is formed by the extended side s11. Since the extended side s11 is present compared to the configuration in which the side s1 and the side s3 intersect at right angles, the flexible printed board 15 is difficult to cut. The anchor pattern 14 extends from the inner side to the outer side of the extension region H to the connection part at the connection boundary between the connection part 15b and the flexible part 15a as in the above example.

  It is preferable to arrange the anchor pattern 14 from the inside to the outside of the region defined by the extension of the sides s1 and s2 in order to further increase the peel strength.

  FIG. 3 shows a configuration example of a flexible printed circuit board according to another embodiment of the present invention.

  In FIG. 3A, the flexible printed circuit board 15 has a strip shape having a certain width, and the connecting portion has the same width as the flexible portion. The outermost wiring pattern 17 is bent outward in the connection portion, and extends toward the end of the connection portion while gradually changing the direction. The wiring pattern 13 on the main board 11 also has a shape corresponding to the wiring pattern 17. In the connecting portion, the outer boundary of the wiring pattern 17 is characterized in that it is formed in a smooth curved shape having a convex curvature from the inside toward the outside at the flexible portion side corner portion of the connecting portion.

  With the shape having such a curvature, when the stress F is applied from an oblique direction, the wiring pattern 17 receives the stress F by a line, and the peel strength is increased as compared with the case where the stress is received by a point. Although the case where the bonding surface having the curvature is formed by the wiring pattern has been described, the bonding surface having the same curvature may be formed by the dummy pattern as shown by the anchor pattern 14 in the upper part of the figure.

  FIG. 3B illustrates a case where an adhesive surface shape having a curvature is formed using an anisotropic conductive film. An anisotropic conductive film 20 with rounded corners is laminated at the connection portion of the flexible printed circuit board 15. This anisotropic conductive film 20 provides an adhesive surface between the flexible printed circuit board 15 and the main board 11. By having an outer edge on a curved line that smoothly changes the direction of the adhesive surface, it is possible to prevent the stress from being concentrated on the dotted portion regardless of the direction in which the stress is applied. In addition, although the case where the anisotropic conductive film 20 has the shape rounded also in the main board | substrate 11 side corner part was illustrated, the anisotropic conductive film is the full width of a flexible printed circuit board in the main board side edge part of the flexible printed circuit board 15. A flared corner may be formed. This is because stress does not concentrate on this portion.

  The anisotropic conductive film can provide not only the wiring pattern region but also the insulating region as an adhesive surface. Furthermore, since electrical and mechanical connections can be formed simply by crimping the entire surface, the manufacturing process can be simplified.

  The inventors have found that when the flexible printed circuit board is bonded to the main substrate with an anisotropic conductive film, the adhesive strength of the flexible printed circuit board depends on the peripheral length around the bonded surface rather than the area of the bonded surface.

  FIG. 4 shows a configuration of a flexible printed circuit board according to another embodiment of the present invention. In these structural examples, it is assumed that an anisotropic conductive film is laminated on the entire back surface of the connection portion of the flexible printed circuit board.

  In FIG. 4A, the connection portion 15b of the flexible printed board 15 is formed in a zigzag shape having a straight hypotenuse on the periphery. By using a zigzag shape, the peripheral length increases compared to a rectangular shape having straight sides. The shortest distance connecting two points is a straight line, but the peripheral length can be arbitrarily increased by connecting the two points with zigzag sides.

  In FIG. 4B, the periphery 31 is formed in a waveform shape in the connection portion 15b of the flexible printed board 15. For example, a perimeter of a waveform formed by a series of semicircular sides provides a perimeter that is π times that of a straight side.

  In FIG. 4C, in the connection portion 15b of the flexible printed board 15, the periphery 32 is formed into a shape in which a slit is formed from the outside in a rectangular region. The peripheral length can be increased in a wide range depending on the number and depth of the slits.

  The flexible printed circuit board shown in FIGS. 4A to 4C is formed in a shape in which the periphery of the connection portion has irregularities. It is preferable to increase the peripheral length at least 10%, preferably 20% or more, and more preferably 30% or more, compared with the case where there is no unevenness. The peel strength can be increased by increasing the peripheral length. In addition, although the connection part 15b of the flexible printed circuit board 15 demonstrated the case where the whole periphery was formed in the pattern which has an unevenness | corrugation, an uneven | corrugated pattern may exist in a part of periphery. In this case, the peripheral length may be increased in the region where the uneven pattern is formed.

  FIG. 5 is a diagram for explaining the considerations made by the present inventors. FIG. 5A shows a case where the waveform pattern 31 as shown in FIG. 4B is formed in a part of the periphery of the connection portion 15b of the flexible printed circuit board 15. The waveform pattern 31 is formed only on a part of the side of the connection portion. For example, by forming 2 mmφ drill holes at intervals of 2 mm, a corrugation having a pitch of 2 mm and an unevenness depth of about 1 mm is formed. A dummy wiring pattern 35 may be formed in the region in contact with the corrugated uneven pattern 31 together with the wiring pattern.

  As the anisotropic conductive film, a polymer connector film available from Sony Chemical Corporation (Tokyo) was used. This polymer connector film has a configuration in which conductive particles obtained by applying Ni / Au plating to resin particles are dispersed in an epoxy binder.

  The case where the corrugated unevenness having the depth of 1 mm and the pitch of 2 mm was formed around the connection portion was experimentally compared with the case where it was not formed. When the waveform was not formed, the peel strength was 98 g, whereas when the waveform was formed, the peel strength was increased to 189 g.

  As the corrugated irregularities are formed by cutting the area, the connection area is reduced. The experimental results in which the peel strength increased regardless of the decrease in the connection area indicate that the peripheral length of the connection region affects the peel strength more than the area of the connection region. Hereinafter, the adhesion form of the anisotropic conductive film will be considered.

  5B and 5C show cross-sectional shapes when an anisotropic conductive film is used. FIG. 5B shows a cross-sectional shape before pressure bonding. A flexible printed circuit board 15 is disposed on the main substrate 11 with an anisotropic conductive film 37 interposed therebetween.

  FIG. 5C shows a state in which the flexible printed circuit board 15 is pressure-bonded toward the main board 11. It is assumed that the flexible printed circuit board 15 drops by Δt due to the pressure. When the flexible printed circuit board 15 is pushed down, the anisotropic conductive film 37 protrudes to the outside, and protruding portions 37 a are formed on both sides of the flexible printed circuit board 15. The width of the protruding portion 37a is y.

  FIGS. 5D and 5E show examples of the cross-sectional shape of the connection portion when the periphery is formed in a zigzag shape. FIG. 5D shows a case where the protruding portion 37b of the anisotropic conductive film extruded between adjacent regions of the flexible printed circuit board 15 is connected. FIG. 5E shows a case where the protruding portions 37c of the anisotropic conductive film pushed out by the flexible printed circuit board 15 are kept separated from each other.

  According to the experiments by the present inventors, even if the periphery of the connection portion of the flexible printed circuit board is formed in a zigzag shape, the protruding portions of the anisotropic conductive film are connected to each other as shown in FIG. As shown in FIG. 5E, it was found that the connection strength can be significantly increased by keeping the protruding portions 37c separated from each other.

  In order to prevent the protruding portions from coming into contact with each other, it is preferable to keep the distance between the patterns at a certain value or more when forming a zigzag shape around the flexible printed circuit board.

In FIG. 5 (C), the if protruding portion 37a forms a isosceles triangle, the cross-sectional area of the protruding portion 37a is y ^2/2.

  In order to estimate the value of the protrusion width y, consider the following simple configuration. As shown in FIG. 5F, it is considered that rectangular patterns having a width a and a length b are periodically arranged at an interval x. At this time, the volume of the anisotropic conductive film pushed out by pushing down each pattern by Δt becomes abΔt. If the protrusion occurs over the entire circumference, the peripheral length where the protrusion occurs is 2 (a + b).

Over the entire circumferential length, if the protruding portion of the cross-sectional area of y ^2/2 is formed, the volume of the protruding portion is (a + b) y ^2.

Since the amount pushed out from the bottom of the pattern should be equal to the amount protruding outside the pattern, (a + b) y ² = abΔt holds, and y = [abΔt / (a + b)] ^1/2 . Therefore, if x> 2y = 2 [abΔt / (a + b)] ^1/2 , the protruding anisotropic conductive film as shown in FIG. 5E can be kept separated.

  This conclusion is based on a simplified model and is not exact. This should be considered as a lower limit target for the distance between zigzag patterns when a flexible printed circuit board having a periphery having a zigzag shape is used.

  As described above, when the flexible printed board is bonded to the main board, the case where the shape around the bonded portion of the flexible printed board is adjusted in order to increase the bonding strength has been described. It will be apparent that the same effect as that obtained by adjusting the shape of the flexible printed circuit board can be obtained by adjusting the shape of the main substrate.

  6A and 6B show a configuration example when processing is performed around the main substrate. In FIG. 6A, the outer edge 41 of the main substrate is processed so as to form a wavy zigzag contour at the connection portion of the main substrate 11. The corrugated shape 41 only needs to be realized at the end of the bonding surface, and does not need to cover the entire thickness of the main substrate 11.

  In FIG. 6B, the outer edge of the connection portion of the main substrate 11 is cut into the shape of the slit 42. The slits 42 do not have to be formed to the full thickness of the main substrate 11 and may be formed on the connection portion surface.

  Although the present invention has been described with reference to the embodiments, the present invention is not limited thereto. It will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

  In addition, it is a flexible printed circuit board which printed the wiring pattern on the flexible resin film, Comprising: The narrow flexible part which comprises a flexible wiring part, and the wiring of a flexible wiring part adhered to the main board | substrate which is a connection object A wide connecting portion for electrically connecting the wiring to the wiring on the main substrate, and a portion formed along the side of the main substrate and extending outward from the region where the flexible portion is connected. A flexible printed circuit board having a conductive adhesive surface wider than the existing signal wiring pattern can be obtained.

  The flexible printed circuit board is most easily peeled off when stress from an oblique direction is applied to the connecting portion.

  By making the connecting portion wider than the flexible portion and providing a conductive adhesive surface extending from the inner side to the outer side of the connecting region with the flexible portion, the stress from the oblique direction is dispersed and it becomes difficult to peel off.

  Moreover, it can be set as the flexible printed circuit board whose said electroconductive adhesive surface is a soldering part.

  Moreover, it is a flexible printed circuit board which printed the wiring pattern on the flexible resin film, Comprising: The narrow flexible part which comprises a flexible wiring part, and the main board | substrate which is a connection object, and wiring of a flexible wiring part A flexible printed circuit board having a wide connection portion for electrically connecting the wiring to the wiring on the main substrate and an anisotropic conductive film laminated on the entire surface of the connection portion can be obtained.

  Moreover, it can be set as the flexible printed circuit board which has the width | variety which the said flexible part increases monotonously toward a connection part near the boundary with the said connection part.

  Moreover, it is a flexible printed board which printed the wiring pattern on the flexible resin film, Comprising: The flexible part which comprises a flexible wiring part, and the main board which is a connection object are adhere | attached, and the wiring of a flexible wiring part is connected to a main board Bonding having a connecting portion for electrically connecting to the upper wiring and an outer boundary formed on the connecting portion and having a convex curvature from the inside of the connecting portion toward the outside at least at the flexible portion side corner of the connecting portion A flexible printed circuit board having a surface.

  By providing an adhesive surface having a curved outer boundary that protrudes from the inside toward the outside at the flexible portion side corner portion of the connecting portion, stress applied from an oblique direction is received not by a point but by a surface. Stress is dispersed and the flexible printed circuit board is difficult to peel off.

  Moreover, it can be set as the flexible printed circuit board whose said adhesive surface is a soldering part.

  Moreover, it can be set as the flexible printed circuit board which is the anisotropic electrically conductive film by which the said adhesive surface was laminated | stacked on the center part of the said connection part.

  Moreover, it can be set as the flexible printed circuit board which does not have another adhesion surface outside the outer boundary which has the said curvature.

It is sectional drawing and a top view for demonstrating the connection structure of the flexible printed circuit board by the Example of this invention, and a main board | substrate. It is a schematic plan view which shows the modification of the Example of FIG. It is a top view for demonstrating the connection structure of the flexible printed circuit board by another Example of this invention, and a main board | substrate. It is a top view for demonstrating the connection structure of the flexible printed circuit board by another Example of this invention, and a main board | substrate. It is the top view and sectional drawing for demonstrating the experiment and consideration which this inventor performed. It is a top view which shows the shape of the main board | substrate by the other Example of this invention. It is a schematic plan view for demonstrating a prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Main substrate 12 Support substrate 13, 17 Wiring pattern 14 Anchor pattern 15 Flexible printed circuit board 16 Resin film 18 Connection part 30, 31, 32 Periphery of flexible printed circuit board 37 Anisotropic conductive film 41, 42 Perimeter of main circuit board

Claims (11)

  A flexible printed circuit board in which a wiring pattern is printed on a flexible resin film, which is bonded to the flexible part constituting the flexible wiring part and the main board to be connected, and the wiring of the flexible wiring part is placed on the main board. A flexible printed circuit board comprising: a connection portion for electrically connecting to a wiring; and a periphery having a bent shape formed on at least a part of an outer edge of the connection portion.   Furthermore, the flexible printed circuit board of Claim 1 which has the anisotropic conductive film laminated | stacked on the whole surface of the said connection part.   The flexible printed circuit board according to claim 1, wherein the bent shape forms a peripheral length that is 10% or more longer than a linear distance.   The flexible printed circuit board according to claim 1, wherein the bent shape forms a peripheral length that is 30% or more longer than a linear distance.   The flexible printed circuit board according to claim 1, wherein the bent shape has a waveform.   The flexible printed circuit board according to claim 1, wherein the bent shape has a slit shape cut from outside.   The flexible printed circuit board according to claim 1, wherein the bent shape has a zigzag shape having a linear hypotenuse.   A connection printed circuit board structure in which a connection part of a flexible printed circuit board is bonded to a connection part of a main board, wherein at least one of the outer edges of both connection parts has a bent periphery.   The connection printed circuit board structure according to claim 8, wherein the bent shape has a peripheral length longer than a linear distance by 10% or more.   The connection printed circuit board structure according to claim 8 or 9, wherein the connection portions are bonded via an anisotropic conductive film.   A liquid crystal display device comprising: a liquid crystal display panel; and a flexible printed circuit board connected to a substrate constituting the liquid crystal display panel, wherein the flexible printed circuit board is the one according to claim 1.

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