Patent Publication Number: US-2015077948-A1

Title: Printed circuit board connection structure

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The Present application is a Continuing Application based on International Application PCT/JP2013/003958 filed on Jun. 25, 2013, which, in turn, claims the priority from Japanese Patent Application No. 2012-147329 filed on Jun. 29, 2012, the entire disclosure of these earlier applications being herein incorporated by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a printed circuit board connection structure. 
     BACKGROUND ART 
     In recent years, a structure to connect printed circuit boards has often been used in electronic devices (for example, see Patent Literature 1). The method illustrated in  FIG. 6  provides a known example of a method for connecting printed circuit boards in such a printed circuit board connection structure. 
     In the method for connection illustrated in  FIG. 6 , a rigid printed circuit board  110  is mounted pattern side up onto a substrate stage  120 , and a flexible printed circuit board  130  is mounted pattern side down onto an adjustment stage  140 . For example as illustrated in the plan view in  FIG. 7(   a ), recognition marks  114  and  115  for alignment are respectively formed integrally with connection terminals  112  and  113  at either edge of a connection terminal row  111  on the pattern side in the rigid printed circuit board  110 . Similarly, for example as illustrated in the back view of  FIG. 7(   b ), recognition marks  134  and  135  for alignment are respectively formed integrally with connection terminals  132  and  133  at either edge of a connection terminal row  131  on the opposing pattern side in the flexible printed circuit board  130  as well. The recognition marks  114  and  115  and the recognition marks  134  and  135  are formed to have the same shape and area. To clarify the illustration in  FIG. 6 , the connection terminals in the flexible printed circuit board  130  are omitted from the drawing. 
     In  FIG. 6 , a conductive adhesive  150  is applied to the connection terminal row  111  in the rigid printed circuit board  110 . When connecting the rigid printed circuit board  110  and the flexible printed circuit board  130 , first, as illustrated in  FIG. 6 , the connection terminal row  111  and the connection terminal row  131  are aligned by being overlapped with a predetermined gap therebetween. The connection terminal row  111  and connection terminal row  131  are aligned by capturing an image of the overlapping region thereof with a camera  160  for recognition, and while observing the image, using the adjustment stage  140  to turn the flexible printed circuit board  130  in a plane and move the flexible printed circuit board  130  in two dimensions. In this way, as illustrated by the partial enlargement in  FIG. 8(   b ), the connection terminal row  131  and connection terminal row  111 , the recognition mark  134  and recognition mark  114 , and the recognition mark  135  and recognition mark  115  are adjusted to overlap each other perfectly. Note that the flexible printed circuit board  130  has sufficient optical transparency to allow for imaging of the rigid printed circuit board  110  located below. 
     Subsequently, as illustrated in  FIG. 9 , the connection terminal row  131  portion of the flexible printed circuit board  130  is pushed down by a clamping head  170  to clamp and connect the connection terminal row  131  to the connection terminal row  111  with the conductive adhesive  150  therebetween. As in  FIG. 6 , to clarify the illustration in  FIG. 9 , the connection terminals in the flexible printed circuit board  130  are omitted from the drawing. 
     CITATION LIST 
     Patent Literature 
     PTL 1: JP2012-28745A 
     SUMMARY OF INVENTION 
     Technical Problem 
     In the above-described method for connection, the rigid printed circuit board  110  and the flexible printed circuit board  130  are aligned with a predetermined gap therebetween as illustrated in  FIG. 6 , and subsequently, the connection terminal row  131  portion of the flexible printed circuit board  130  is pushed down by the clamping head  170 , as illustrated in  FIG. 9 . Therefore, the flexible printed circuit board  130  is bent downwards, and the connection terminal row  131  is clamped and connected to the connection terminal row  111  of the rigid printed circuit board  110  in a state misaligned by ΔL from the initial position. 
     As a result, during alignment, even if the recognition marks  134  and  135  on the flexible printed circuit board  130  side are aligned to overlap perfectly with the corresponding recognition marks  114  and  115  on the rigid printed circuit board  110  side, as illustrated in  FIG. 8(   a ), the connection structure after clamping is such that the recognition marks  134  and  135  are misaligned with the corresponding recognition marks  114  and  115 , as illustrated by the partial enlargement in  FIG. 10(   b ). Therefore, there is a risk that the length of the flexible printed circuit board  130  extending from the rigid printed circuit board  110  will deviate from an acceptable value for the design, adversely affecting wiring or the like of the flexible printed circuit board  130  during subsequent assembly or the like. 
     One foreseeable way of addressing this problem is to align the marks so that the recognition marks  134  and  135  are offset with respect to the corresponding recognition marks  114  and  115  by the distance of misalignment after clamping. This approach, however, makes alignment troublesome and time-consuming and also lowers the yield. Note that this problem also occurs in a structure to connect flexible printed circuit boards to each other. 
     Solution to Problem 
     A printed circuit board connection structure according to the present invention is formed by clamping and connecting a first printed circuit board and a second printed circuit board, at least one of which is a flexible printed circuit board, with a conductive adhesion layer therebetween, the printed circuit board connection structure comprising: a first mark formed on the first printed circuit board; and a second mark formed on the second printed circuit board, wherein an area enclosed by a perimeter of one mark out of the first mark and the second mark is greater than an area enclosed by a perimeter of the other mark, and with the printed circuit board and the second printed circuit board in an allowable state of connection, at least a portion of a region enclosed by the perimeter of the other mark is located within a region enclosed by the perimeter of the one mark when viewed in a direction of stacking of the printed circuit board and the second printed circuit board. 
     The first printed circuit board is preferably a rigid printed circuit board, the second printed circuit board is preferably a flexible printed circuit board, and the area enclosed by the perimeter of the first mark is preferably greater than the area enclosed by the perimeter of the second mark. 
     With the first printed circuit board and the second printed circuit board in the allowable state of connection, a portion of the first mark preferably protrudes outward from the second printed circuit board when viewed in the direction of stacking. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The present invention will be further described below with reference to the accompanying drawings, within: 
         FIG. 1(   a ) is a plan view illustrating the structure of the main parts of a printed circuit board connection structure according to Embodiment  1 ; 
         FIG. 1(   b ) is a partial enlargement of the structure of the printed circuit board connection in  FIG. 1(   a ) corresponding to the oval shown in dashed lines in  FIG. 1(   a ); 
         FIG. 2  illustrates a method for connecting the printed circuit boards in  FIG. 1(   a ); 
         FIG. 3(   a ) illustrates alignment of the printed circuit boards in  FIG. 1(   a ); 
         FIG. 3(   b ) is a partial enlargement of the alignment of the printed circuit boards in  FIG. 3(   a ) corresponding to the oval shown in dashed lines in  FIG. 3(   a ); 
         FIG. 4  illustrates a process for connecting the printed circuit boards in  FIG. 1(   a ); 
         FIG. 5  is a partial plan view illustrating the structure of the main parts of a printed circuit board connection structure according to Embodiment 2; 
         FIG. 6  illustrates a method for connecting printed circuit boards; 
         FIG. 7(   a ) illustrates the connection terminal rows and recognition marks formed on the printed circuit boards in  FIG. 6 ; 
         FIG. 7(   b ) illustrates the back view of the connection terminal rows and recognition marks formed on the printed circuit boards in  FIG. 6 ; 
         FIG. 8(   a ) illustrates alignment of the printed circuit boards in  FIG. 6 ; 
         FIG. 8(   b ) is a partial enlargement of the alignment of the printed circuit boards in  FIG. 8(   a ) corresponding to the circle shown in dashed lines in  FIG. 8(   a ); 
         FIG. 9  illustrates a process for connecting the printed circuit boards in  FIG. 6 ; and 
         FIG. 10(   a ) illustrates a conventional printed circuit board connection structure; 
         FIG. 10(   b ) is a partial enlargement of the alignment of the printed circuit boards in  FIG. 10(   a ) corresponding to the circle shown in dashed lines in  FIG. 10(   a ). 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     The following describes embodiments of the present invention with reference to the drawings. 
     Embodiment 1 
       FIG. 1(   a ) is a plan view illustrating the structure of the main parts of a printed circuit board connection structure according to Embodiment 1 of the present invention. The connection structure according to the present embodiment includes a rigid printed circuit board  10  and a flexible printed circuit board  20 . Recognition marks  14  and  15  for alignment, which constitute the first mark, are respectively formed integrally with connection terminals  12  and  13  at either edge of a connection terminal row  11  on the pattern side in the rigid printed circuit board  10 . The recognition marks  14  and  15  protrude outward from the connection terminal row  11 . As in the rigid printed circuit board  10 , recognition marks  24  and  25  for alignment, which constitute the second mark, are respectively formed integrally with connection terminals  22  and  23  at either edge of a connection terminal row  21  on the pattern side in the flexible printed circuit board  20 . The recognition marks  24  and  25  protrude outward from the connection terminal row  21 . 
     In the present embodiment, the recognition marks  14  and  15  protrude in a direction perpendicular to the direction of elongation of the corresponding connection terminals  12  and  13  and have a solid rectangular shape. Similarly, the recognition marks  24  and  25  protrude in a direction perpendicular to the direction of elongation of the corresponding connection terminals  22  and  23  and have a solid rectangular shape. 
     The recognition marks  14  and  15  are formed to have a larger area than the recognition marks  24  and  25 , so that the recognition marks  24  and  25  are positioned within the region of the corresponding recognition marks  14  and  15  when viewed in the direction of stacking of the rigid printed circuit board  10  and the flexible printed circuit board  20  with the rigid printed circuit board  10  and the flexible printed circuit board  20  in a state of being connected within an acceptable range of the design value. In other words, as illustrated by the partial enlargement in  FIG. 1(   b ), with the dimension of the recognition mark  25  in the direction of length of the connection terminal  23  being L 1 , then the corresponding dimension L 2  of the recognition mark  15  in the direction of length of the connection terminal  13  is formed to be greater towards the tip of the connection terminal  13  by taking into consideration L 1 , the tolerance for the design length of the flexible printed board  20 , and the below-described misalignment ΔL when clamping the flexible printed circuit board  20 . The same is true for the recognition mark  14 . 
     In this way, it is easy to recognize that the rigid printed circuit board  10  and the flexible printed circuit board  20  are connected within an acceptable range of the design value if the recognition marks  24  and  25  are located within the region of the corresponding recognition marks  14  and  15 . Note that the recognition marks  24  and  25  may be formed to be shifted towards the tip of the connection terminals  22  and  23  by the below-described amount of misalignment ΔL when clamping the flexible printed circuit board  20 . 
     Next, a method for connecting the rigid printed circuit board  10  and the flexible printed circuit board  20  to obtain the connection structure according to the present embodiment is described. 
     As illustrated in  FIG. 2 , the rigid printed circuit board  10  is first mounted pattern side up onto a substrate stage  120 , and the flexible printed circuit board  20  is mounted pattern side down onto an adjustment stage  140 . A conductive adhesive  150  forming a conductive adhesion layer is applied to the connection terminal row  11  in the rigid printed circuit board  10 . The adjustment stage  140  is positioned to be a predetermined distance higher than the substrate stage  120  so that, when the flexible printed circuit board  20  is mounted on the adjustment stage  140 , the conductive adhesive  150  on the rigid printed circuit board  10  does not contact the flexible printed circuit board  20 . To clarify the illustration in  FIG. 2 , the connection terminals in the flexible printed circuit board  20  are omitted from the drawing. 
     Next, an image of the overlapping region between the connection terminal row  11  of the rigid printed circuit board  10  and the connection terminal row  21  of the flexible printed circuit board  20  is captured with a camera  160  for recognition, and while the image is observed, the flexible printed circuit board  130  is turned in a plane and moved in two dimensions, with the adjustment stage  140 . In this way, as illustrated in  FIG. 3(   a ), the recognition mark  24  and recognition mark  14  are respectively aligned with the recognition mark  25  and recognition mark  15 . During alignment, as illustrated by the partial enlargement of alignment between the recognition mark  25  and the recognition mark  15  in  FIG. 3(   a ), the connection terminal  23  of the flexible printed circuit board  20  is matched to (overlapped with) the connection terminal  13  of the rigid printed circuit board  10 , and an edge  25   a  of the recognition mark  25  closer to the tip of the connection terminal  23  is matched to an edge  15   a  of the recognition mark  15  further away from the tip of the connection terminal  13 . The recognition mark  24  is aligned similarly with respect to the recognition mark  14 . Note that the flexible printed circuit board  20  is formed to have sufficient optical transparency to allow for imaging of the rigid printed circuit board  10  located below. 
     Subsequently, as illustrated in  FIG. 4 , the connection terminal row  21  portion of the flexible printed circuit board  20  is pushed down by a clamping head  170  to clamp and connect the connection terminal row  21  to the connection terminal row  11  with the conductive adhesive  150  therebetween. Therefore, as in the case in  FIG. 9 , the flexible printed circuit board  20  is bent downwards in this case as well, and the connection terminal row  21  is clamped and connected to the connection terminal row  11  of the rigid printed circuit board  10  in a state misaligned by ΔL from the initial position. As in  FIG. 2 , to clarify the illustration in  FIG. 4 , the connection terminals in the flexible printed circuit board  20  are omitted from the drawing. 
     As described above, according to the connection structure of the present embodiment, by matching the edges of the recognition marks  24  and  25  closer to the tip of the connection terminals  22  and  23  in the flexible printed circuit board  20  to the edges of the corresponding recognition marks  14  and  15  further away from the tip of the connection terminals  12  and  13  in the rigid printed circuit board  10 , the flexible printed circuit board  20  can be aligned with the rigid printed circuit board  10 . Alignment thus becomes easy. Furthermore, the recognition marks  24  and  25  and the recognition marks  14  and  15  are formed taking into consideration the misalignment ΔL when clamping and connecting the flexible printed circuit board  20 , and in a state with the recognition marks  24  and  25  located within the region of the corresponding recognition marks  14  and  15 , the rigid printed circuit board  10  and the flexible printed circuit board  20  are connected with an acceptable range of the design value. Accordingly, the rigid printed circuit board  10  and the flexible printed circuit board  20  can be connected easily and accurately, the yield can be increased, and the state of connection can easily be recognized. 
     Embodiment 2 
       FIG. 5  is a partial plan view illustrating the structure of the main parts of a printed circuit board connection structure according to Embodiment 2 of the resent invention. The connection structure according to the present embodiment is the same as the connection structure of Embodiment 1, except that with the rigid printed circuit board  10  and the flexible printed circuit board  20  in an allowable state of connection, a portion of the recognition marks  14  and  15  protrudes outward from the flexible printed circuit board  20  when viewed in a direction of stacking of the printed circuit boards. In other words, the dimension of the flexible printed circuit board  20  in the direction of the connection terminal row  21  is shorter than the dimension of the rigid printed circuit board  10  in the direction of the connection terminal row  11 . Note that in  FIG. 5 , only an enlargement of the portion including the recognition mark  15  and the recognition mark  25  is illustrated. 
     According to the connection structure of the present embodiment, similar effects to those of Embodiment  1  are obtained. Additionally, even when the optical transparency of the flexible printed circuit board  20  is low, making it difficult to see the rigid printed circuit board  10  below, alignment is made easier since the large recognition marks  14  and  15  of the rigid printed circuit board  10  protrude outward from the flexible printed circuit board  20 . 
     The present invention is not limited to the above embodiments, and a variety of modifications and changes are possible. For example, in the above embodiments, the recognition marks  24  and  25  of the flexible printed circuit board  20  may be formed to be larger than the recognition marks  14  and  15  of the rigid printed circuit board  10 . In this case, the recognition marks  24  and  25  may be aligned with the recognition marks  14  and  15  before clamping and connecting by matching the edges of the recognition marks  24  and  25  further away from the tip of the connection terminals  22  and  23  to the edges of the corresponding recognition marks  14  and  15  closer to the tip of the connection terminals  12  and  13 . 
     In the above embodiments, the recognition marks on each printed circuit board are not limited to a solid rectangular shape that protrudes in a direction perpendicular to the direction of elongation of the corresponding connection terminal and may be formed as any solid or hollow shape that protrudes in any direction from the connection terminal row. Therefore, the recognition marks may, for example, be solid or hollow shape with a curved perimeter. The recognition marks in each printed circuit board are not limited to the case of the entire region enclosed by the perimeter of the other mark being located within the region enclosed by the perimeter of the one mark when viewed in the direction of stacking with the printed circuit boards in an allowable state of connection. Rather, a portion of the region enclosed by the perimeter of the other mark may be located within a predetermined portion of the region enclosed by the perimeter of the one mark. 
     Furthermore, the present invention is not limited to a connection structure for a rigid printed circuit board and a flexible printed circuit board and may be similarly applied to a connection structure for flexible printed circuit boards. The recognition marks in the printed circuit boards are not limited to being formed integrally with the connection terminals but rather may be formed separately and independently from the connection terminals. Moreover, the recognition marks and the printed circuit boards are not limited to the case of one recognition mark being formed on each side of the connection terminal row. A plurality of recognition marks may be formed, or one or more recognition marks may be formed on only one side of the connection terminal row. The conductive adhesion layer connecting the printed circuit boards is not limited to conductive adhesive and may be formed with a conductive adhesion film such as anisotropic conductive film (ACF) or with a different conductive adhesion material. 
     REFERENCE SIGNS LIST 
       10 : Rigid printed circuit board 
       11 : Connection terminal row 
       12 ,  13 : Connection terminal 
       14 ,  15 : Recognition mark 
       20 : Flexible printed circuit board 
       21 : Connection terminal row 
       22 ,  23 : Connection terminal 
       24 ,  25 : Recognition mark 
       120 : Substrate stage 
       140 : Adjustment stage 
       150 : Conductive adhesive 
       160 : Camera for recognition 
       170 : Clamping head