JP5226225B2 - Wiring board solder joint structure - Google Patents

Description

  The present invention relates to a solder joint structure between a flexible wiring board and another wiring board.

  In recent years, an image display module using a flat display panel (hereinafter referred to as FPD (Flat Panel Display)) such as a liquid crystal display panel or an organic electroluminescence display panel is advantageous in reducing the thickness of an applied device. It is widely used as a display for mobile devices such as PDAs (Personal Digital Assistance).

However, the demand for miniaturization and thinning is extremely strict for displays of mobile devices, and further thinning of the FPD module is also demanded. For this reason, a flexible wiring board whose overall thickness is thinner than a PCB (printed-circuit board) or the like is used as the wiring board, and the conductive junction between the wiring board and another wiring board is disclosed in Patent Document 1. A solder joining method is used.
Japanese Patent Laid-Open No. 2-155292

  Usually, even if an external force to bend acts to some extent, the flexible wiring board can be flexibly bent and bent (bent) into a bent shape. However, when a flexible wiring board and another wiring board are conductively bonded by the above-described solder bonding, the solder placement portion in the flexible wiring board is not flexible, and therefore when the flexible wiring board is bent, Stress concentrates on the boundary with the surroundings, and the flexible wiring board is strongly bent along the width direction line including the boundary. In addition, since the insulating protective film is not deposited on the line in the width direction, the bending is more concentrated and strongly generated. When the bending of the flexible wiring board is concentrated, there is a problem that a crack is generated in the exposed conductor pattern on the bending line, and further, the circuit breaks.

  Moreover, since the insulating protective film is not attached to the connection terminal of the flexible wiring board, there is a problem that the conductor pattern forming the connection terminal is easily peeled off from the base film.

  An object of the present invention is to provide a highly reliable wiring board soldering structure that prevents cracks and disconnection of a conductor pattern and peeling from a base film caused by bending at a soldering part of a flexible wiring board. .

In the solder joint structure for a wiring board according to claim 1 of the present invention, a wiring and a first connection terminal provided in a portion extending from the wiring are disposed on at least one main surface of the flexible board. The insulating protective film is deposited in a pattern that covers at least one of a pair of edges along the extending direction of the wiring except for a part of the wiring and the first connection terminal. A wiring board, and at least one main surface of the board is provided with a wiring and an exposed portion formed of the portion where the insulating protective film of the first connection terminal is not attached, provided on a portion extending from the wiring. a second wiring board is arranged also has a wide second connecting terminal made from said second connecting terminal therewith in the exposed portion of the superimposed arranged the first connecting terminals electrically connected with solder Prefecture The first wiring board; One connecting terminal is exposed at two adjacent edges, the solder is disposed across the two adjacent edges, and the insulating protective film of the first wiring board is adjacent to the first connecting terminal of the first wiring board. The insulating protective film of the first wiring board is formed so as to bend the boundary between the insulating protective film and the exposed portion consisting of the part. To do .
Preferably, one of the side end faces along the extending direction of the wiring of the first connection terminal is covered with the insulating protective film of the first wiring board.
Preferably, the second wiring board is a flexible wiring board made of a flexible board.

  According to the solder joint structure of the wiring board of the present invention, the crack and disconnection of the conductor pattern forming the wiring and the connection terminal due to strong bending at the boundary with the solder placement area of the flexible wiring board and peeling from the base film are prevented. As a result, the reliability of the conductive junction is improved.

  FIG. 1 is a schematic cross-sectional view showing a liquid crystal display module to which a solder joint structure according to an embodiment of the present invention is applied. FIG. 2 is an exploded perspective view showing an essential part of the liquid crystal display module, FIG. (b), (c) is the top view which shows the further principal part, BB sectional drawing, and CC sectional drawing, respectively.

  As shown in FIG. 1, the housing of the present liquid crystal display module has a cover case 2 with a bottom plate removed and a storage case 1 with a top shape of a box having a flat outer shape removed. Become. Both of these cases 1 and 2 are formed by processing a metal plate. A display window 22 for observing the display is formed in the top plate 21 of the cover case 2.

  A frame 3 is disposed in the casing. The frame 3 according to the present embodiment is formed by resin molding using a resin material, for example, by an injection method or the like, and the interior includes a front chamber 3a and a rear chamber in a space that forms a flat rectangular parallelepiped with the display viewing side as the front side. 3b is formed in two stages. That is, the internal space of the frame 3 is partitioned into a front chamber 3a and a rear chamber 3b by a partition plate 31, and a communication window 311 for communicating the front and rear chambers 3a and 3b is formed in the partition plate 31. .

  A liquid crystal display panel 4 is accommodated and held in the front chamber 3a. The liquid crystal display panel 4 is formed by joining a pair of rectangular glass substrates 41 and 42 with a frame-shaped sealing material (not shown) with a predetermined gap therebetween, and facing each of the glass substrates 41 and 42 surrounded by the frame-shaped sealing material. The liquid crystal is sealed between the surfaces (hereinafter referred to as the inner surface). A pair of front and rear polarizing plates 43 and 44 are attached to the outer surfaces of the glass substrates 41 and 42, respectively.

  One glass substrate 42 of the glass substrates 41 and 42 has a pair of adjacent edges projecting outward from the corresponding end surface of the glass substrate 41 to form a projecting edge 421. On the surface of the protruding edge 421 (extension surface of the electrode formation surface), although not shown, lead wires that are conductively connected to the electrodes of both substrates 41 and 42, their connection terminals, and drive signal input Wiring and the like are arranged, and a driver chip 5 as a liquid crystal driving circuit element is mounted by a COG (Chip On Glass) method.

  A flexible wiring board (hereinafter referred to as FPC (Flexible Printed Circuit Board)) 6 for supplying a driving control signal is conductively joined to the connection terminal row of the driving signal input wiring of the protruding edge portion 421 described above. The FPC 6 is pulled out of the frame 3 and folded back toward the rear chamber 3b.

  In the rear chamber 3b of the frame 3, a side light type surface emitting irradiation unit 7 is accommodated. The sidelight type surface emitting irradiation unit 7 of the present embodiment has a light emitting diode (hereinafter referred to as an LED (Light-Light Emitting Diode)) as a light source on one end surface of a transparent light guide plate 71 having a rectangular shape corresponding to the liquid crystal display panel 4 to be irradiated. In this example, five light emitting sheets 72) are arranged, and a light reflecting sheet 73 is installed on the rear surface 712 opposite to the front surface 711 of the light guide plate 71 facing the liquid crystal display panel 4. . On the rear surface 712 on which the light reflecting sheet 73 of the light guide plate 71 is installed, a concentric concave / convex pattern (not shown) for internally reflecting the light emitted from the LEDs 72 and incident on the light guide plate 71 toward the front surface 711 is formed. Has been.

  As shown in FIG. 2, the five LEDs 72 are directly mounted on an FPC (hereinafter referred to as a light source FPC) 74 by a COF (Chip On Film) method. The light source FPC 74 includes an LED array portion 74a in which five LEDs 72 are arranged at equal intervals at a predetermined interval, and a lead extension portion 74b extending perpendicularly therefrom. This FPC 74 for light source is formed with a conductive wiring pattern 742 that electrically connects five LEDs 13 in series on one surface (lower surface in the drawing) of a base film 741 made of an insulating resin film such as a polyimide resin film. A connection terminal 7422 having a width w1 is formed at each end portion of the pair of lead wires 7421 extending on the surface of the lead extension portion 74b of the energization wiring pattern 742.

  The light source FPC 74 described above is arranged in such a manner that the five LEDs 72 are accommodated in the five concave portions 713 formed on one end surface corresponding to these and serving as the light incident surface of the light guide plate 71. It is installed at the light source side edge of the light plate front surface 711 (see FIG. 1).

  In the side light type surface emitting irradiation unit 7 configured as described above, the light emitted from the LED 72 is incident on the light guide plate 71 from the opposing end surface in the recess 713, and this incident light is concentric on the rear surface 712. When the light enters the concavo-convex pattern, the light is internally reflected toward the front surface 711 and emitted from the front surface 711 in a planar shape. There is also light that exits from the light guide plate 71 after entering the concentric concave / convex pattern. However, the emitted light is reflected by the light reflection sheet 73 that is installed facing the light and is reentered into the light guide plate 71. . Thereby, the utilization efficiency of the emitted light from each LED72 is improved.

  Returning to FIG. 1, two optical sheets, a light diffusion sheet 75 and a prism sheet 76, are superimposed on the front surface 711 of the light guide plate 71 in that order. The light diffusion sheet 75 is installed in order to make the luminance distribution of the irradiation light emitted from the light guide plate 71 planar, and the prism sheet 76 is installed in order to align the emission direction of the irradiation light in the front direction.

  The surface emitting irradiation unit 7 on which the two optical sheets 75 and 76 are superposed is housed in a predetermined position in the rear chamber 3b while being supported by the back panel 8. The rear panel 8 is fitted to the frame 3 so as to close the bottom surface of the frame rear chamber 3b.

  A drive control circuit board 9 is installed on the inner surface of the bottom plate 11 in the storage case 1 on the rear surface side of the rear panel 8. The drive control circuit board 9 controls the driving of the entire liquid crystal display module. Therefore, the FPC 6 and the LED 72 that are conductively joined to the end of the glass substrate 42 of the liquid crystal display panel 4 are COF (Chip On The FPC 74 for light source mounted on the film) is conductively joined.

  In the present embodiment, the drive control circuit board 9 is installed by attaching the back surface on which the wiring pattern is not formed to the inner surface of the bottom plate 11 of the case 1 with, for example, a double-sided adhesive sheet. Various electric circuit patterns for driving and controlling the liquid crystal display panel 4 and the LEDs 72 are formed on the surface of the drive control circuit board 9, and the drive control circuit portion of the LEDs 72 is as shown in FIG. In addition, a pair of lead wires 91, 91 and their connection terminals 92, 92 for LED energization are formed corresponding to the pair of connection terminals 7422, 7422 of the light source FPC 74 on which the LED 72 is mounted.

  With respect to the connection terminals 92 and 92 for energizing the LEDs, the lead extension part 74b of the light source FPC 74 is folded back to the back side of the back panel 8, and the corresponding connection terminals 7422 and 7422 formed at the front end part thereof. Soldered.

  FIGS. 3A to 3C respectively show the above-described solder joints, and a pair of connections are formed on the surface on which the conductive wiring pattern 742 of the light source FPC 74 folded back on the back panel 8 is formed. An insulating protective film 743 is deposited, leaving portions 7422a of the terminals 7422 and 7422, respectively. In the pair of exposed portions 7422a to which the insulating protective film 743 is not attached, at least one of the pair of edges along the extending direction of the lead wiring 7421 in each connection terminal 7422 is the insulating protective film 743. It is formed in the pattern covered with. Therefore, the boundary between the insulating protective film 743 and each exposed portion 7422a is not formed in a straight line but is a bent boundary.

In this embodiment, since each connection terminal 7422 is formed at both corners at the tip of the lead extension 74b in the light source FPC 74, the boundary line is L-shaped. The width w2 of each exposed portion 2422a is w3 when the width of the connection terminal 92 on the drive control circuit board 9 side is w3.
1.5 ≦ (w3 / w2) ≦ 2.0
The dimension is set to satisfy.

  As shown in FIG. 3A, the tip of the light source FPC 74 where the connection terminal 7422 is formed is roughly at one corner of the circuit side connection terminal 92 corresponding to the L-shaped boundary corner of each exposed portion 7422a. It is positioned on the drive control circuit board 9 so as to overlap. In this case, both corresponding connection terminal pairs 7422 and 92 are arranged so as not to face each other and to face the same direction (upward in the drawing). Note that the arrangement interval D (see FIG. 3C) of the pair of circuit side connection terminals 92 and 92 is set so that the above arrangement is obtained.

  As described above, the solder 10 is applied in a state where the connection terminals 2422 and 92 are disposed. In this case, the solder 10 is applied to most of the exposed portion 2422a of each connection terminal 2422 and most of the area where the light source FPC 74 of the circuit side connection terminal 92 is not overlapped, thereby forming a sufficient solder fillet 101. The As a result, the connection terminals 2422 and 92 are firmly connected to each other even if they do not face each other, and a highly reliable solder joint structure is obtained.

  In addition, since the boundary line between the insulating protective film 743 and the exposed portion 7422a of each connection terminal 7422 is formed in an L shape, the lead extension portion of the light source FPC 74 fixed by applying the solder 10 to the exposed portion 7422a. The insulating protective film 743 exists at the center of the line in which stress is concentrated when the 742 is bent, that is, the width direction line a passing through the end face of the insulating protective film 743. Therefore, the strength of the light source FPC 74 against bending along the line “a” is increased and bending is avoided, and the occurrence of cracks and disconnection of the energization wiring pattern 742 is prevented. Thus, an adhesive member for fixing the lead extension 74b of the light source FPC 74 to the drive control circuit board 9 can be omitted.

  Further, the side end surface 7422b that is not aligned with the side end surface of the lead extension 74b among the end surfaces of each connection terminal 7422 is covered with an insulating protective film 743 via an adhesive 744 (see FIG. 3C). Therefore, peeling of the connection terminal 7422 made of a thin film conductive layer such as a copper foil attached to the base film 741 via the adhesive 745 is prevented.

  As described above, in the solder joint structure of this embodiment applied to the conductive joint between the light source FPC 74 and the drive control circuit board 9 in the liquid crystal display module, the solder 10 of the connection terminal 7422 on the light source FPC side is disposed. An insulating protective film 743 is deposited so as to cover one side end surface 7422b along the lead wiring 7421 except for a portion (exposed portion) 7422a for this purpose, and correspondingly to this, the drive control circuit board 9 side is more exposed than the exposed portion 7422a. Since the wide connection terminal 92 is formed, a sufficient solder fillet is formed across a pair of adjacent end faces of the narrow connection terminal 7422 even when the connection terminals 7422 and 92 are arranged in the same direction. The connection terminals 7422 and 92 can be firmly connected to each other, and the end face of the insulating protective film 743 of the light source FPC 74 is formed in an L shape. The bending strength of the width direction line a passing through the end face where the bending stress is concentrated is increased, and the trouble that the conductive pattern such as the connection terminal 7422 is cracked or disconnected is avoided, and the connection terminal 7422 from the base film 741 is avoided. Separation is effectively prevented by covering one side end face 7422b with the insulating protective film 743, and as a result, a highly reliable solder joint structure for a wiring board is obtained.

The present invention is not limited to the above embodiment.
For example, in the above embodiment, the light source FPC 74 and the circuit board 9 that is conductively connected to the light source FPC 74 are solder-bonded with the wiring formation surface facing in the same direction. As shown in FIG. 4, it is also preferably used in the case of conducting conductive bonding in an arrangement in which the wiring formation surfaces of both substrates 74 and 9 face each other. In this case, since the solder 10 can be arranged between the connection terminals 7422 and 92, sufficient bonding strength can be obtained without forming the solder fillet 101 large.

  Further, as shown in FIGS. 5A and 5B, both end surfaces 2021 and 2021 of the connection terminal 202 formed on the base film 201 of the FPC 20 may be covered with an insulating protective film 203. Thereby, peeling from the base film 201 of the connecting terminal 202 is prevented more reliably. In this case, since the solder 30 is only applied across the one end surface 2022 of the connection terminal 202, it is difficult to form the solder fillet 301 large. Therefore, the structure of the present modification is more effectively applied in the case of the arrangement in which the connection terminal 401 of the circuit board 40 to be joined and the connection terminal 201 of the FPC 20 face each other as in the present modification.

  Furthermore, in the above embodiment, the light source FPC 74 and the rigid drive control circuit board 9 are conductively joined. However, the present invention is not limited to this, and the present invention is also effectively applied when soldering flexible wiring boards together. Is done.

  In addition, it goes without saying that the present invention is effectively applied to a case where the flexible wiring board to be soldered is a double-sided wiring type wiring board in which energization wiring patterns are formed on both the front and back surfaces.

1 is a schematic cross-sectional view showing a liquid crystal display module to which a solder joint structure as one embodiment of the present invention is applied. It is a disassembled perspective view which shows the principal part structure of the said liquid crystal display module. (a) is a top view which shows the solder joint part in the said liquid crystal display module, (b) is the BB sectional drawing, (c) is the CC sectional view. (a) is a top view which shows the modification of the said solder joint structure, (b) is the BB sectional drawing, (c) is the CC sectional view. (a) is a top view which shows the other modification of the solder joint structure of this invention, (b) is the BB sectional drawing.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Storage case 2 Cover case 3 Frame 4 Liquid crystal display panel 5 Driver chip 6 FPC (For drive control signal supply)
7 Side Light Type Surface Emitting Unit 71 Light Guide Plate 72 LED (Light-Emitting Diode)
73 Light reflection sheet 74 FPC for light source
74a LED array part 74b Lead extension part 741 Base film 742 Conductive wiring pattern 7421 Lead wiring 7422 Connection terminal (FPC side)
7422a Exposed portion 7422b End face 8 Rear panel 9 Drive control circuit board 91 Lead wiring 92 Connection terminal (circuit board side)

Claims (3)

A wiring and a first connection terminal provided in a portion extending from the wiring are disposed on at least one main surface of the flexible substrate, and an insulating protective film is a part of the wiring and the first connection terminal. A first wiring board attached in a pattern covering at least one of a pair of edges along the extending direction of the wiring except for
Provided on at least one main surface of the substrate with a wiring and a portion extending from the wiring, and wider than the exposed portion of the first connection terminal not covered with the insulating protective film. A second wiring board on which a second connection terminal is disposed;
The second connection terminal and the solder that conductively connects the exposed portion of the first connection terminal that is superimposed on the second connection terminal;
The first connection terminal of the first wiring board has two adjacent edges exposed, the solder is disposed across the two adjacent edges, and the insulating protective film of the first wiring board is the first wiring board. The insulating protective film of the first wiring substrate is attached so as to cover two adjacent edges of the first connecting terminal, and the boundary between the insulating protective film and the exposed portion consisting of the part is bent. A solder joint structure for a wiring board, which is formed . In claim 1 in which one side end surface of one of the side end face along the extending direction of the wiring of the first connection terminal, characterized in that it is covered with the insulating protective film of the first wiring board Solder joint structure of the described wiring board. The second wiring board, solder bonding structure of the wiring board according to claim 1 or claim 2, characterized in that a flexible wiring substrate made of a flexible substrate.