Abstract:
A connecting structure of a printed circuit board of a liquid crystal display (LCD) module includes a double side printed circuit board and a single side printed circuit board. With the design of the double side printed circuit board having a solder element with two solder surfaces with a plurality of plated through holes (PTHs), and the design of the opening neighboring the solder element, the conducting surface of the single side printed circuit board may easily accord with the structural requirements to select the corresponding solder surface for performing welding.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This non-provisional application claims priority under 35 U.S.C. §119(a) on Patent Application No(s). 095130499 filed in Taiwan, R.O.C. on Aug. 18, 2006, the entire contents of which are hereby incorporated by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of Invention 
         [0003]    The present invention relates to a connecting structure of a printed circuit board. More particularly, the present invention relates to a connecting structure of a flexible printed circuit board of a liquid crystal display (LCD) module. 
         [0004]    2. Related Art 
         [0005]    Recently, because the objectives of the electronic products are light, thin, short and small, many electronic devices develop according to the objectives, and the using of the flexible printed circuit board totally accord with the requirement of the modern technology. In addition, due to the unique flexibility of the flexible printed circuit board, the three-dimensional stereo wiring may be easily accomplished together with the spatial configuration, such that the flexible printed circuit board is widely used, particularly, it is usually applied in the LCD module, so as to serve as the bridge electrically connecting different circuit elements. 
         [0006]    Referring to  FIG. 1 , it is a schematic view of the connecting structure of the flexible printed circuit board of the conventional LCD module. As shown in  FIG. 1 , the LCD module  10  mainly includes a LCD panel  16 , a backlight module  17 , a first flexible printed circuit board  13 , a second flexible printed circuit board  14  and a mainboard printed circuit board  18 . 
         [0007]    The LCD panel  16  is connected to the mainboard printed circuit board  18  through the first flexible printed circuit board  13 , so as to achieve the signal transmission. The backlight module  17  uses the second flexible printed circuit board  14  as the carrier of the circuit. Usually, the second flexible printed circuit board  14  is connected to the first flexible printed circuit board  13  by welding, and the first flexible printed circuit board  13  is connected to the mainboard printed circuit board  18 . 
         [0008]    A solder surface  131  is formed on the first flexible printed circuit board  13 . The second flexible printed circuit board  14  has an extending portion  15 , and a conducting surface  12  is formed on the extending portion  15 . Through the welding of the conducting surface  12  and the solder surface  131 , the effect of the electrical connection between the LCD panel  16  and backlight module  17  is achieved. 
         [0009]    Usually, the first flexible printed circuit board  13  is a double side printed circuit board structure, and its connecting position with the second flexible printed circuit board  14  is at a solder surface  131  on one side of the first flexible printed circuit board  13 . The second flexible printed circuit board  14  mainly adopts the double side printed circuit board structure, both of the two sides have a conducting surface  12 , and the two conducting surfaces  12  may be welded with the solder surface  131 . 
         [0010]    As shown in  FIGS. 2A and 2B , a sectional view and a top view of the conventional connecting structure of the first flexible printed circuit board of the double side printed circuit board structure and the second flexible printed circuit board of the double side printed circuit board structure are shown. A plurality of first pads  21  and a plurality of second pads  22  are respectively disposed on the solder surface  131  and the conducting surface  12 , wherein the area of the first pad  21  may be larger than, equal to or less than the area of the second pad  22 . In the figures disclosed by this embodiment, the area of the first pad  21  is larger than the area of the second pad  22 . During the welding operation, according to the structural requirements, the second pad  22  on any conducting surface  12  is selected to correspond to the first pad  21  on the solder surface  131  to get into contact with each other. Because the area of the first pad  21  is larger than the area of the second pad  22 , the first pad  21  still leaves a protruding portion  21   a  after contacting, the solder  23  may be welded with the non-contacted second pad  22  through the protruding portion  21   a . Moreover, a part of the solder located on the first pad  21  spills to the second pad  22  on the other side through the plated through holes (PTHs) formed on the second pad  22 . 
         [0011]    Although the above bonding structure is convenient for the bonding process, the second flexible printed circuit board of the double side printed circuit board structure is expensive, and the production cost is increased correspondingly. 
         [0012]    Therefore, in order to save the material cost, the conventional method changes to adopt the second flexible printed circuit board of the single side printed circuit board structure, according to different connecting manners, the connecting structures usually have the following two configurations. 
         [0013]    As shown in  FIGS. 3A and 3B , a sectional view and a top view of the conventional first connecting structure of the first flexible printed circuit board of the double side printed circuit board structure and the second flexible printed circuit board of the single side printed circuit board structure are shown. The second pads  22  disposed on the second flexible printed circuit board and the first pads  21  disposed on the first flexible printed circuit board are not directly contacted, that is, the second pads  22  and the first pads  21  are disposed on the same side of the flexible printed circuit board. During the welding operation, the solder  23  is used to connect the protruding portion  21   a  of the first pad  21  and the second pad  22 . However, whether the strength of the welding structure is appropriate becomes a hidden trouble of the product yield. Usually, in order to make the welding structure have the substantive bonding strength, it is necessary to provide enough amount of solder, thus the tin bead is usually too big, causing the problems on the product assembling or the appearance dimension. On the contrary, if the amount of the solder is not enough, the bonding section is too small, it is impossible to provide enough bonding strength, and the tin crack is easily generated because of the external force, thus resulting in the poor electrical connecting. 
         [0014]    As shown in  FIGS. 4A and 4B , a sectional view and a top view of the second conventional connecting structure of the first flexible printed circuit board of the double side printed circuit board structure and the second flexible printed circuit board of the single side printed circuit board structure are shown. Different from the connecting method shown in  FIGS. 3A and 3B , the second pad  22  and the first pad  21  are bonded by contacting directly. In order to make the solder  23  sandwiched between the solder surface  131  and the conducting surface  12  achieve the melting state, it is necessary to increase the welding temperature and to prolong the welding time. However, the heat energy must be transmitted though the protective layer of the flexible printed circuit board, usually the circuit board is burnt and becomes black. Because the solder  23  is located between the two pads, during the welding process, it is not easy to observe the melting condition of the solder  23 , so usually the false bonding occurs, resulting in the poor electrical connecting, and thereby influencing the product yield. 
       SUMMARY OF THE INVENTION 
       [0015]    In view of the above problems, the main objective of the present invention is to provide a connecting structure of the flexible printed circuit board of the LCD module, thereby lowering the cost and solving the problem of the false bonding and the insufficient bonding strength, so as to improve the product yield. 
         [0016]    Therefore, in order to achieve the above objective, the present invention provides a connecting structure of the flexible printed circuit board of the LCD module, which comprises a first flexible printed circuit board and a second flexible printed circuit board. The first flexible printed circuit board is a double side printed circuit board structure, and the second flexible printed circuit board is a single side printed circuit board structure. The first and the second flexible printed circuit boards may be a flexible copper clad laminate. 
         [0017]    The first flexible printed circuit board has a solder element with two solder surfaces and an opening. The two solder surfaces are formed by the conductive material, such as the metal material. Moreover, the two solder surfaces further comprise a plurality of pads, and at least a PTH is formed on the pads. The opening structure partially surrounds the solder element and may be U-shaped or tetragon-shaped. 
         [0018]    The second flexible printed circuit board has an extending portion, and a conducting surface is formed on the end of the extending portion. The conducting surface is formed by the conductive material, such as the metal material, and a plurality of pads are disposed on the conducting surface. 
         [0019]    The area of the pad on the solder surface may be larger than, equal to or less than the area of the pad on the conducting surface. The conducting surface may directly select to connect to the corresponding solder surface, or may pass through the opening from one side of the first flexible printed circuit board, so as to connect to the corresponding solder surface on the other side of the first flexible printed circuit board. 
         [0020]    By the design of the connecting structure of the first flexible printed circuit board and the second flexible printed circuit board of the present invention, according to the structural requirement of the LCD module, the conducting surface of the second flexible printed circuit board may pass through the opening and select the corresponding solder surface of the first flexible printed circuit board to perform bonding, so as to facilitate the bonding operation, and improve the production performance. Moreover, by the effect of the PTHs, the solder may go deep into the PTHs of the first flexible printed circuit board and obtain the favorable tin feeding effect, so as to increase the bonding strength between the first flexible printed circuit board and the second flexible printed circuit board. 
         [0021]    The features and the practices of the present invention are described in detail as the most preferred embodiment with the drawings. 
         [0022]    Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]    The present invention will become more fully understood from the detailed description given herein below for illustration only, and thus are not limitative of the present invention, and wherein: 
           [0024]      FIG. 1  is a schematic view of the conventional connecting structure of the flexible printed circuit board of the LCD module; 
           [0025]      FIGS. 2A and 2B  are a sectional view and a top view of the conventional connecting structure of the first flexible printed circuit board of the double side printed circuit board structure and the second flexible printed circuit board of the double side printed circuit board structure; 
           [0026]      FIGS. 3A and 3B  are sectional views of the conventional first connecting structure of the first flexible printed circuit board of the double side printed circuit board structure and the second flexible printed circuit board of the single side printed circuit board structure; 
           [0027]      FIGS. 4A and 4B  are sectional views of the conventional second connecting structure of the first flexible printed circuit board of the double side printed circuit board structure and the second flexible printed circuit board of the single side printed circuit board structure; 
           [0028]      FIGS. 5A and 5B  are schematic views of the first embodiment of the connecting structure of the flexible printed circuit board of the LCD module according to the present invention; 
           [0029]      FIG. 6  is a schematic view of the second embodiment of the connecting structure of the flexible printed circuit board of the LCD module according to the present invention; and 
           [0030]      FIGS. 7A ,  7 B,  7 C and  7 D are schematic views of the connecting structure of the first flexible printed circuit board with a U-shaped opening and the second flexible printed circuit board according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0031]    Referring to  FIG. 5A , it is a schematic view of the first embodiment of the connecting structure of the flexible printed circuit board of the LCD module according to the present invention. As shown in  FIG. 5A , the connecting structure of the flexible printed circuit board of the LCD module according to the present invention includes a first flexible printed circuit board  13  and a second flexible printed circuit board  14 . The first flexible printed circuit board  13  is a double side printed circuit board structure, and the second flexible printed circuit board  14  is a single side printed circuit board structure. Both of the first flexible printed circuit board  13  and the second flexible printed circuit board  14  are flexible copper clad laminates. The first flexible printed circuit board  13  is a panel flexible printed circuit board connected to the LCD panel and the mainboard printed circuit board (not shown), so as to finish the signal transmission. The second flexible printed circuit board  14  is a light source flexible printed circuit board electrically connected to the light source (not shown) on the backlight module and the panel flexible printed circuit board, so as to serve as the carrier of the circuit. 
         [0032]    The first flexible printed circuit board  13  has a solder element  11  with two opposite solder surfaces and a U-shaped opening  31  partially surrounding the solder element  11 , wherein the solder element  11  is preferred tongue-shaped but not limited, and neighbors the opening  31 . Moreover, the solder element  11  further includes a plurality of first pads  21  made of metal material, and a plurality of plated through holes (PTHs)  24  formed on the first pads  21 , wherein the PTHs  24  pass through the first pads  21  and the first flexible printed circuit board  13 . Further, the first pad  21  may be of metal material, such as copper, tin, nickel, gold, and aluminum. 
         [0033]    The second flexible printed circuit board  14  has an extending portion, and the end of the extending portion has a conducting surface  12  made of copper material. The conducting surface  12  may be formed on the upper surface or the lower surface of the second flexible printed circuit board  14 , and each conducting surface  12  includes a plurality of second pads  22 . 
         [0034]    As shown in  FIG. 5B , it is a side view of the first flexible printed circuit board  13  according to the present invention. Because of the special U-shaped opening  31  formed on the first flexible printed circuit board  13  and the property of the flexible circuit board, the tongue-shaped solder element  11  can be rotated in a predetermined angle with respect to the first flexible printed circuit board  13 . 
         [0035]    The area of the first pad  21  on the solder element  11  is larger than the area of the second pad  22  on the conducting surface  12 . The conducting surface  12  may select to directly contact the corresponding solder surface or to contact another corresponding solder surface by passing through the opening  31 , such that the second pad  22  is connected to the first pad  21  on the solder surface. After the bonding operation on one side of the solder element  11  is finished, a part of the solder located on the second pad  22  spills to the first pad  21  on the other side of the solder element  11  through the PTHs  24 . Here, the opening  31  may also provide another function, i.e. when the amount of the solder on the second pad  22  is large, a part of the solder spills and passes through the opening  31  and connects to the solder surface on the other side. That is, the first pads  21  on the two sides of the first flexible printed circuit board  13  are at least partially covered by tin, together with the tin passing through the PTHs  24 , so as to increase the area of contacting surface between the first pad  21 , the second pad  22  and the tin, thus improving the bonding strength of the first flexible printed circuit board  13  and the second flexible printed circuit  14 . Similarly, the effect is suitable for the following several embodiments. 
         [0036]    Referring to  FIG. 6 , it is a schematic view of the second embodiment of the connecting structure of the flexible printed circuit board of the LCD module according to the present invention. As shown in  FIG. 6 , the connecting structure of the flexible printed circuit board of the LCD module according to the present invention includes a first flexible printed circuit board  13  and a second flexible printed circuit board  14 . The difference between this embodiment and the first embodiment is that the opening  32  in this embodiment is tetragon-shaped or similar and the solder element  11  cannot be rotated. 
         [0037]    The first flexible printed circuit board  13  of this embodiment has a solder element  11  with two solder surfaces and a tetragon-shaped opening  32 , wherein the solder element  11  neighbors the opening  31  and cannot be rotated. Moreover, the solder surface  11  further includes a plurality of first pads  21 , on which at least a PTH  24  is formed. 
         [0038]    The second flexible printed circuit board  14  has an extending portion, and the end of the extending portion has a conducting surface  12 . The conducting surface  12  includes a plurality of second pads  22 . The connecting situations of the first flexible printed circuit board  13  and the second flexible printed circuit board  14  in the first embodiment and the second embodiment are described below by the description of the connecting structure in the first embodiment with drawings. 
         [0039]    As shown in  FIGS. 7A to 7D , another preferred embodiment of the connecting structure of the first flexible printed circuit board with U-shaped opening  31  and the second flexible printed circuit board according to the present invention is shown. The solder element  11  of the first flexible printed circuit board  13  and the conducting surface  12  of the second flexible printed circuit board  14  may have different connecting manners, according to the different structural designs of the first flexible printed circuit board  13  and the second flexible printed circuit board  14 . 
         [0040]    As shown in  FIG. 7A , the conducting surface  12  of the second flexible printed circuit board  14  is formed on the upper surface, and may be directly connected to the lower solder surface of solder element  11 , which is on the same side of the lower surface of the first flexible printed circuit board  13 . 
         [0041]    As shown in  FIG. 7B , the conducting surface  12  of the second flexible printed circuit board  14  is formed on the lower surface, it may match the configuration of the first flexible printed circuit board  13  to be placed the upper surface of the first flexible printed circuit board  13 , so as to be connected to the upper solder surface of solder element  11 , which is on the same side of the upper surface of the first flexible printed circuit board  13 . 
         [0042]    As shown in  FIG. 7C , by the design of the opening  31 , the conducting surface  12  formed on the upper surface of the second flexible printed circuit board  14  may pass through the opening  31  from the upper surface of the first flexible printed circuit board  13 , so as to be connected to the lower solder surface of solder element  11 , which is on the same side of the lower surface of the first flexible printed circuit board  13 . 
         [0043]    As shown in  FIG. 7D , the conducting surface  12  formed on the lower surface of the second flexible printed circuit board  14  may pass through the opening  31  from the lower surface of the first flexible printed circuit board  13 , so as to be connected to the upper solder surface of solder element  11 , which is on the same side of the upper surface of the first flexible printed circuit board  13 . 
         [0044]    By the connecting structure of the flexible printed circuit board of the LCD module according to the present invention, during the bonding operation, the solder may go deep into the first flexible printed circuit board by the PTHs, so as to obtain the favorable tin feeding effect, thus enhancing the strength structure of the bonding position, and avoiding false bonding and clod solder joint. Moreover, by the unique opening design on the first flexible printed circuit board, the conducting surface may select one of the two corresponding solder surfaces of a solder element to perform connecting according to the structural requirements. 
         [0045]    The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.