JP2005079231A - Flexible board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce an accumulated growth by heat of the joint of a flexible board and easily align the flexible board with a counterpart board when connecting the joint of the flexible board to the counterpart board via an anisotropic conductive adhesive material. <P>SOLUTION: In the flexible board, the joint 21 which is electrically and mechanically connected to the counterpart board via the anisotropic conductive adhesive material is formed in the end edge 20E of the board, and a plurality of lead electrode groups A1-A3 are arranged at predetermined intervals with leadless portions B1 and B2 with no lead electrodes in between in the joint 21. Opening portions 22 are so formed that connecting portions 23 for connecting the lead electrode groups to the leadless portions B1 and B2 may be left over on the end edge 20E of the board. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a flexible substrate that is electrically and mechanically connected to a counterpart substrate via an anisotropic conductive adhesive, and more particularly to a technique for minimizing the amount of elongation due to heating during connection. Is.

  Since the flexible substrate has flexibility, it is often used as a relay substrate between substrates disposed at different height positions or for a movable substrate, for example. In the field of liquid crystal display elements, a liquid crystal panel and a liquid crystal drive control circuit board are often used as a COF (chip on film) or TCP (tape carrier package) on which a bare IC chip is mounted.

  An anisotropic conductive adhesive film (ACF) that can connect a large number of lead electrodes at one time without adversely affecting the liquid crystal panel itself is generally used to connect the flexible substrate to the liquid crystal panel. ing.

  An anisotropic conductive adhesive film is a film in which conductive particles are dispersed in a thermosetting resin. The anisotropic conductive adhesive film is placed between the terminal part of the liquid crystal panel and the flexible substrate, and presses a heater bar heated to a predetermined temperature from above. Thus, the liquid crystal panel and the flexible substrate are electrically and mechanically connected.

  The problem in this connection will be described with reference to FIG. FIG. 3 is a plan view showing a state in which the connection portion 21 of the flexible substrate 20 is connected to the terminal portion 11 of the liquid crystal panel 10 via the anisotropic conductive adhesive film (not shown).

  The flexible substrate 20 includes a base film made of, for example, a polyimide resin having good heat resistance, but still stretches due to heat and pressure applied from the heater bar. On the other hand, the thermal expansion coefficient of the glass substrate used for the liquid crystal panel 10 is extremely smaller than that of the flexible substrate 20.

  Therefore, even if the alignment marks ML and MR formed on both sides of the connection portion 21 are overlapped with the alignment marks on the terminal portion 11 (not shown) before the heat and pressure connection (crimping), Due to the expansion of the flexible substrate 20 that occurs, any of the preferred lead electrodes between the terminal portion 11 side and the connection portion 21 side occurs.

  This elongation proceeds from the central portion of the connecting portion 21 toward the left and right sides, and the amount of elongation increases in proportion to the width dimension C of the connecting portion 21 as it goes outward. Therefore, as one method, the elongation rate is predicted, and the lead electrode on the terminal portion 11 side and the lead electrode on the connection portion 21 are aligned in position after crimping so that the lead electrode of the connection portion 21 is positioned at the design stage. The position is shifted in advance in the direction opposite to the extension.

  However, this prediction method is not only low in reliability, but, as shown in FIG. 3, a large number of lead electrodes included in the connection portion 21 are divided into, for example, three lead electrode groups A1 to A3. When leadless portions B1 and B2 having no lead electrode exist between them, the lead electrode groups A1 to A3 and leadless portions B1 and B2 have different elongation rates. Therefore, the design includes calculation of the elongation rate. Is quite difficult.

  In order to reduce this design burden, as another conventional example, cuts S1 and S2 are made in leadless parts B1 and B2 as shown in FIG. It is done to divide. That is, the connecting portion 21 is divided into a tongue piece 21a including the lead electrode group A1, a tongue piece 21b including the lead electrode group A2, and a tongue piece 21c including the lead electrode group A3. According to this, the extension of the connection part 21 at the time of crimping proceeds from the center of each of the divided tongue pieces 21a, 21b, 21c and does not affect other parts.

  Accordingly, the elongation rate calculation may be performed for each tongue piece 21a, 21b, 21c, and the width of each tongue piece 21a, 21b, 21c is narrow (less than 1/3 compared to the example of FIG. 3). The shift between the opposing lead electrodes due to the difference between the value and the actual value can be suppressed to a small value. Further, since the amount of shrinkage after crimping is small compared to the example of FIG. 3, the connection reliability is also good. However, this also leaves the following problems.

  That is, the alignment before crimping is performed by the alignment marks ML and MR formed on both sides of the connection portion 21 as in the conventional example of FIG. 3, but the tip portions of the tongue pieces 21a, 21b, and 21c are completely formed. For example, when both sides of the connecting portion 21 are gripped, the center tongue piece 21b hangs down, making it difficult to handle and making positioning as a whole difficult.

  Accordingly, an object of the present invention is to reduce the cumulative elongation due to the heat of the connecting portion when connecting the connecting portion of the flexible substrate to the counterpart substrate via an anisotropic conductive adhesive that requires heating and pressing. An object of the present invention is to enable easy alignment with the counterpart substrate.

  In order to solve the above-mentioned problem, the present invention includes a connection portion that is electrically and mechanically connected to a counterpart substrate via an anisotropic conductive adhesive on the side of the substrate edge. In a flexible substrate in which a plurality of lead electrode groups are arranged with a predetermined interval across a leadless portion without lead electrodes, the leadless portion includes a connecting portion for connecting the lead electrode groups to the edge of the substrate It is characterized in that an opening is formed.

  When the alignment with the counterpart substrate is performed, in order to prevent the connecting portion from being easily deformed, the width c of the connecting portion is (0.11-), where t is the thickness of the base film of the flexible substrate. 0.8t) ≦ c ≦ 0.5.

  In addition, in order to prevent positional displacement from being induced on the distal end side of the lead electrode group due to elongation at the connecting portion, the distal end of each lead electrode included in the lead electrode group extends to the substrate edge. It is preferable that it terminates at a position not less than the width dimension c as viewed from the substrate edge without extending.

  Alignment marks for the mating substrate are necessarily provided on both sides of the connection part, but the amount of elongation differs between the lead electrode group having the alignment mark and the lead electrode group having no alignment mark when heated and pressurized. There is. Therefore, it is preferable that alignment marks are formed on both sides of each lead electrode group in order to align the extension amounts of the respective lead electrode groups as much as possible.

  As described above, according to the present invention, since the lead electrode groups are separated by the opening, the cumulative elongation due to the heat of the connection portion can be reduced, and the substrate edge of the flexible substrate can be reduced. Since these are connected by the connecting portion, alignment with the counterpart substrate can be easily performed.

  Next, an embodiment of the present invention will be described with reference to FIGS. 1 and 2, but the present invention is not limited to this. FIG. 1 is a plan view schematically showing the main part of the present invention, and FIG. 2 is an enlarged view of a circled portion in FIG. In the description of this embodiment, the same reference numerals are used for components that may be considered the same as or the same as those of the conventional example described with reference to FIGS.

  As shown in FIG. 1, in this embodiment, the counterpart substrate of the flexible substrate 20 </ b> A according to the present invention is the terminal portion 11 of the liquid crystal panel 10. The flexible substrate 20A is provided with a heat-resistant and flexible base film such as polyimide resin, and the substrate edge 20E side is provided with an anisotropic conductive adhesive, for example, different from the conventional example. A connecting portion 21 connected to the terminal portion 11 through a isotropic conductive adhesive film is provided.

  Also in this example, the lead electrode of the connection portion 21 is divided into three lead electrode groups A1 to A3, and leadless portions B1 and B2 having no lead electrode exist between them. Further, alignment marks ML and MR for the terminal portion 11 of the liquid crystal panel 10 are provided on both the left and right sides of the connection portion 21. The alignment marks ML and MR can be formed from the same copper foil as that of the lead electrode. Although not shown, alignment marks corresponding to the alignment marks ML and MR are also provided on the terminal portion 11 side of the liquid crystal panel 10.

  According to the present invention, the connection portion 21 is separated for each of the lead electrode groups A1 to A3, and the leadless portions B1 and B2 are opened in order to suppress the cumulative elongation amount of the connection portion 21 at the time of heating and pressure connection (crimping). Portions 22 and 22 are formed. The width b of the opening 22 needs to be equal to or larger than the width that is not blocked by the elongation during crimping. The length of the opening 22 (vertical direction in FIG. 1) is preferably equal to or longer than the length of the lead electrode 210 (see FIG. 2) exposed at the connection portion 21.

  In forming the openings 22 and 22 in the leadless portions B1 and B2, the connecting portions 23 and 23 are left on the substrate edge 20E side of the flexible substrate 20A. That is, the lead electrode group A1 and the lead electrode group A2 and the lead electrode group A2 and the lead electrode group A3 are connected by the connecting portion 23, respectively.

  The connecting portion 23 is substantially made of a base film of the flexible substrate 20A. The intent of connecting the lead electrode groups with the connecting portion 23 is to minimize deformation on the substrate edge 20E side when gripping and aligning both sides of the flexible substrate 20A. Some degree of mechanical strength (width) is required. On the other hand, it is preferable that the width of the connecting portion 23 be as narrow as possible in order to prevent elongation from being transmitted between the lead electrode groups. In order to achieve both of these, it is preferable that the thickness c of the base film of the flexible substrate is t, and the width c of the connecting portion 23 is (0.11-0.8t) ≦ c ≦ 0.5.

  In addition, in order to prevent positional displacement from being induced on the distal end side of the lead electrode group due to the extension at the connecting portion 23, as shown in FIG. 2, the distal end of each lead electrode 210 included in the lead electrode group. 211 does not extend to the substrate edge 20E, but preferably terminates at a position equal to or larger than the width c of the connecting portion 23 when viewed from the substrate edge 20E side. That is, if the distance from the substrate edge 20E to the tip 211 of the lead electrode 210 is d, it is preferable that d = c + (0.05 to 0.1) mm.

  Further, as described above, the alignment marks ML and MR for the terminal portion 11 are indispensably provided on both sides of the connection portion 21. However, in the lead electrode group having the alignment mark and the lead electrode group having no alignment mark, The amount of elongation may vary during crimping. Therefore, it is preferable to form alignment marks on both sides of each of the lead electrode groups A1 to A3 in order to align the extension amounts of the lead electrode groups A1 to A3 as much as possible.

  In this example, a dummy alignment mark MC1 that is paired with the alignment mark ML is formed on the right side of the first lead electrode group A1 on the left side. Dummy alignment marks MC2 and MC3 are formed, and a dummy alignment mark MC4 that is paired with the alignment mark MR is formed on the left side of the third lead electrode group A3 on the right side, thereby forming each lead electrode group A1. The elongation amount of .about.A3 can be made substantially equal.

  Note that these dummy alignment marks MC1 to MC4 are formed of copper foil in the same manner as the alignment marks ML and MR. However, in some cases, these dummy alignment marks MC1 to MC4 are not used as dummy, but are aligned. It can also be used as an actual alignment mark together with the marks ML and MR.

First, the flexible substrate of the aspect shown in FIG. 3 was used as a comparative example. The specifications are as follows.
(1) Full width of flexible substrate: 125.24 mm
(2) Each width of the lead electrode groups A1, A2, A3: 19.54 mm
(3) Each width of the leadless parts B1, B2: 31.246 mm
The elongation ratio of the lead electrode groups A1, A2 and A3 at the connecting portion is 0.10%, the elongation ratio of the leadless portions B1 and B2 is 0.11%, and the position of each lead electrode is set in the direction opposite to the elongation direction in advance. Designed by shifting. When this flexible substrate is pressure-bonded to the terminal part of the liquid crystal panel via an anisotropic conductive film (temperature: 180 ° C., pressure: 3 MPa), the deviation of the outermost lead electrode from the terminal part side lead electrode is about 15 μm. there were.

Next, the flexible substrate of the aspect shown in FIG. 1 was used as an example of the present invention. The specifications are as follows.
(1) Full width of flexible substrate: 125.24 mm
(2) Each width of the lead electrode groups A1, A2, A3: 19.54 mm
(3) Each width of the leadless parts B1, B2: 31.246 mm
(4) Openings having a width of 27.28 mm and a length of 40 mm were formed in the leadless portions B1 and B2. Since the thickness of the base film is 0.075 mm, the width of the connecting portion is set to 0.1 mm.
The elongation ratio of the lead electrode groups A1, A2, and A3 in the connection portion was set to 0.10%, and the position of each lead electrode was previously shifted in the direction opposite to the extension direction. In addition, about the leadless part B1, B2, since the base film was deleted by the opening part, the elongation rate was not considered. When this flexible substrate is pressure-bonded to the terminal portion of the liquid crystal panel via an anisotropic conductive film (conditions are the same as in the comparative example), the terminal portion side of the outermost lead electrode in each lead electrode group A1, A2, A3 The deviation from the lead electrode was within about 5 μm.

  The flexible substrate of the present invention is used not only in the field of liquid crystal display elements but also in other fields, and the counterpart substrate may be either a hard circuit substrate or a flexible substrate. Further, the anisotropic conductive adhesive as the connecting means is not limited to a film-like material, and may be a resin liquid. According to the flexible substrate of the present invention, since the amount of elongation at the time of pressure bonding is small, a highly reliable substrate connection can be realized.

The top view which shows typically the connection part of the flexible substrate by this invention. The enlarged view which shows the circled part of FIG. The top view which shows typically the connection part of the flexible substrate of a 1st prior art example. The top view which shows typically the connection part of the flexible substrate of a 2nd prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Liquid crystal panel 11 Terminal part 20A Flexible board 21 Connection part 210 Lead electrode 22 Opening part 23 Connection part 20E Substrate edge A1-A3 Lead electrode group B1, B2 Leadless part ML, MR Position alignment mark MC1-MC4 Position alignment of dummy mark

Claims (4)

A connecting portion electrically and mechanically connected to the opposite substrate via an anisotropic conductive adhesive is provided on the edge of the substrate, and a plurality of the connecting portions sandwiching a leadless portion without a lead electrode. In the flexible substrate in which the lead electrode group is arranged at a predetermined interval,
The flexible substrate according to claim 1, wherein an opening is formed in the leadless portion, leaving a connecting portion for connecting the lead electrode groups at the edge of the substrate.   The flexible substrate according to claim 1, wherein the width c of the connecting portion is (0.11-0.8t) ≦ c ≦ 0.5, where t is the thickness of the base film of the flexible substrate.   The flexible electrode according to claim 2, wherein the tip of each lead electrode included in the lead electrode group does not extend to the substrate edge but terminates at a position equal to or larger than the width dimension c as viewed from the substrate edge. substrate.   4. The flexible substrate according to claim 1, wherein alignment marks are formed on both sides of each lead electrode group.

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