Abstract:
A flexible printed circuit and printed circuit board soldered structure is provided. The structure includes signal transmission lines which dispense with any through hole, thereby enhancing integrity of high-frequency signals. The special design of the signal line structure of the flexible printed circuit and the printed circuit board together provides a satisfactory high-frequency signal transmission interface and enables a soldering technique which is highly practicable and compatible with the flexible printed circuit and printed circuit board soldered structure.

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention relates to flexible printed circuit and printed circuit board soldered structure and, more particularly, to a flexible printed circuit and printed circuit board soldered structure for use with high-frequency transmission technology. 
     2. Description of the Prior Art 
     In the field of optical communication, data transmission always has a trend toward high speeds. However, high-speed signal transmission is confronted with ever-changing issues. To perform high-speed signal transmission, it is necessary to take account of the integrity of high-frequency signals in the course of signal transmission. When designing a high-frequency circuit, it is necessary to give considerations to the measures taken to reduce signal attenuation with a view to ensuring the integration and matching of characteristic impedance. Therefore, impedance matching design must give considerations to not only adjustment of line width and line spacing but also through hole design. Therefore, persons skilled in the art are eager to solve a problem: how to redesign an appropriate high-frequency package framework which meets the demand for high-frequency circuits in high-speed networks. 
     The process of soldering a flexible printed circuit to a printed circuit board in the course of electronic product packaging usually requires via holes to be disposed at the end of the flexible printed circuit, so that the flexible printed circuit is connected to lower signal lines through the via holes to solder the lower signal lines to the printed circuit board signal lines from above, thereby effectuating electrical interconnects. However, under a high-frequency transmission framework, the via holes compromise the characteristics and integrity of high-frequency signals, thereby further reducing transmission efficiency. 
     SUMMARY OF THE INVENTION 
     It is an objective of the present invention to provide a flexible printed circuit and printed circuit board soldered structure which dispenses with the need to provide any through hole on signal lines, so as not to reduce high-frequency signal transmission efficiency. 
     To solve the foregoing problem, the present invention is to provide a flexible printed circuit and printed circuit board soldered structure, comprising a flexible printed circuit and a printed circuit board. The flexible printed circuit comprises a soft board body, with a first signal pad region disposed on a side of the soft board body, and a first grounding pad region disposed on an opposing side of the soft board body. The first signal pad region comprises a pair of first differential signal transmission lines and two first grounding soldering portions flanking the pair of the first differential signal transmission lines. The first differential signal transmission lines have intact surfaces dispensing with any through hole, wherein ends of the first differential signal transmission lines are flush with an edge of the soft board body. A through hole is disposed on the first grounding soldering portion to electrically connect the first grounding soldering portion and the first grounding pad region, an insulating region is disposed on the first grounding pad region and corresponding in position to the first differential signal transmission lines on a side of the soft board body, and the insulating region extends inward from an edge of the soft board body. The printed circuit board comprises a substrate body, a second signal pad region disposed on a side of the substrate body, and a second grounding pad region disposed on an opposing side of the substrate body. The second signal pad region comprises a pair of second differential signal transmission lines and two second grounding soldering portions flanking the pair of second differential signal transmission lines. The second differential signal transmission lines have intact surfaces dispensing with any through hole, with a through hole disposed on the second grounding soldering portions to electrically connect the second grounding soldering portions and the second grounding pad region. Therein, the flexible printed circuit is disposed on the printed circuit board, the insulating region of the first grounding pad region is disposed above the second differential signal transmission lines to stay away from the second differential signal transmission lines and thus preclude having a short cut with the second differential signal transmission lines, and the ends of the first differential signal transmission lines are soldered to the second differential signal transmission lines from above by a solder to effectuate electrical connection. 
     Further, a half hole is disposed at the ends of the first differential signal transmission lines to hold a solder. 
     Further, an end of the first grounding soldering portion is flush with an edge of the soft board body, and the end of the first grounding soldering portion is soldered to the second grounding soldering portions from above by a solder to effectuate electrical connection. 
     Further, a half hole is disposed at the end of the first grounding soldering portion to hold the solder. 
     Further, a level sign is disposed on the substrate body of the printed circuit board and beside the second differential signal transmission lines to serve as soldering reference. 
     Further, a distance between each said level sign and an end of a corresponding one of the second differential signal transmission lines is shorter than or equal to an extension distance by which the insulating region extends inward. 
     Another objective of the present invention is to provide a flexible printed circuit and printed circuit board soldered structure, comprising a flexible printed circuit and a printed circuit board. The flexible printed circuit comprises a soft board body, with a first signal pad region disposed on a side of the soft board body, and a first grounding pad region disposed on an opposing side of the soft board body. The first signal pad region comprises a first signal transmission line and two first grounding soldering portions flanking the first signal transmission line. The first signal transmission line has an intact surface dispensing with any through hole, wherein an end of the first signal transmission lines is flush with an edge of the soft board body. A through hole is disposed on the first grounding soldering portion to electrically connect the first grounding soldering portion and the first grounding pad region, and an insulating region is disposed on the first grounding pad region and corresponding in position to the first signal transmission line on a side of the soft board body, and the insulating region extends inward from an edge of the soft board body. The printed circuit board comprises a substrate body, a second signal pad region disposed on a side of the substrate body, and a second grounding pad region disposed on an opposing side of the substrate body. The second signal pad region comprises a second signal transmission line and two second grounding soldering portions flanking the second signal transmission line. The second signal transmission line has an intact surface dispensing with any through hole, with a through hole disposed on the second grounding soldering portions to electrically connect the second grounding soldering portions and the second grounding pad region. Therein, the flexible printed circuit is disposed on the printed circuit board, the insulating region of the first grounding pad region is disposed above the second signal transmission lines to stay away from the second signal transmission lines and thus preclude developing a short circuit together with the second signal transmission lines, and the end of the first signal transmission lines is soldered to the second signal transmission line from above by a solder to effectuate electrical connection. 
     Further, a half hole is disposed at the end of the first signal transmission lines to hold a solder. 
     Further, an end of the first grounding soldering portion is flush with an edge of the soft board body, and the end of the first grounding soldering portion is soldered to the second grounding soldering portions from above by a solder to effectuate electrical connection. 
     Further, a half hole is disposed at the end of the first grounding soldering portion to hold the solder. 
     Further, a level sign is disposed on the substrate body of the printed circuit board and beside the second signal transmission line to serve as soldering reference. 
     Further, a distance between the level sign and an end of the second signal transmission line is shorter than or equal to an extension distance by which the insulating region extends inward. 
     Therefore, the present invention has the following advantages over the prior art: 
     1. The flexible printed circuit and printed circuit board soldered structure of the present invention not only displays satisfactory high-frequency transmission characteristics, but also dispenses with the need to provide any through hole at the positions of the soldering of signal transmission lines, thereby enhancing the integrity of high-frequency signals during signal transmission. 
     2. The soldered structure of the present invention is so simple that it is almost the same as the soldering techniques disclosed in the prior art. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of the first embodiment according to the present invention; 
         FIG. 2  is an exploded view ( 1 ) of the first embodiment according to the present invention; 
         FIG. 3  is an exploded view ( 2 ) of the first embodiment according to the present invention; 
         FIG. 4  is a cross-sectional view of the first embodiment according to the present invention; 
         FIG. 5  is a top view of the first embodiment according to the present invention; 
         FIG. 6  is a partial transparent schematic view of the first embodiment according to the present invention; 
         FIG. 7  is a perspective view of the second embodiment according to the present invention; 
         FIG. 8  is an exploded view ( 1 ) of the second embodiment according to the present invention; 
         FIG. 9  is an exploded view ( 2 ) of the second embodiment according to the present invention; 
         FIG. 10  is a cross-sectional view of the second embodiment according to the present invention; 
         FIG. 11  is a top view of the second embodiment according to the present invention; and 
         FIG. 12  is a partial transparent schematic view of the second embodiment according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The technical features and technical solutions of the present invention are hereunder described with reference to accompanying drawings. For illustrative sake, the accompanying drawings are not drawn to scale. The accompanying drawings and the scales thereof are not restrictive of the scope of the present invention. 
       FIG. 1 ,  FIG. 2 , and  FIG. 3  are a perspective view, an exploded view ( 1 ), and an exploded view ( 2 ) of the first embodiment according to the present invention, respectively. The present invention is described below with reference to the aforesaid diagrams. 
     The present invention provides a flexible printed circuit and printed circuit board soldered structure  100  which comprises a flexible printed circuit  110  (FPC) and a printed circuit board  120  (PCB). 
     The flexible printed circuit  110  is tri-layered and comprises, from bottom to top a protective layer  115 , a soft board body  111 , and a protective layer  112  disposed above the soft board body  111 . A first signal pad region  113  is disposed on one side of the soft board body  111 . A first grounding pad region  114  is disposed on the opposing side of the soft board body  111 . Both the first signal pad region  113  and the first grounding pad region  114  are conductive copper foils disposed on the soft board body  111  by wiring layout. Further, the first signal pad region  113  comprises a pair of first differential signal transmission lines  113 A and two first grounding soldering portions  113 B which flank the pair of first differential signal transmission lines  113 A. 
     High-frequency signals passing through a through hole are likely to produce parasitic capacitance and thus compromise signal integrity and high-frequency characteristics while high-frequency signal transmission is taking place; hence, the first differential signal transmission lines  113 A have intact surfaces which dispense with any through hole. Furthermore, the ends of the first differential signal transmission lines  113 A are flush with the edge of the soft board body  111  so that the ends of the first differential signal transmission lines  113 A can be soldered to second differential signal transmission lines  123 A of the printed circuit board  120  below. In a preferred embodiment, a half hole  1131 A for holding a solder is disposed at each of the ends of the first differential signal transmission lines  113 A so that the ends of the first differential signal transmission lines  113 A can be covered with a solder FA (as shown in  FIG. 4 ) and thus soldered to the second differential signal transmission lines  123 A of the printed circuit board  120  below. 
       FIG. 4  and  FIG. 5  are a cross-sectional view and a top view of the first embodiment according to the present invention, respectively. The present invention is described below with reference to the aforesaid diagrams. 
     A through hole VH 1  is disposed on the first grounding soldering portion  113 B to electrically connect the first grounding soldering portion  113 B and the first grounding pad region  114 . The edge of the first grounding soldering portion  113 B and the edge of the soft board body  111  are flush with each other and thus can be soldered together from above the soft board body  111  and a second grounding soldering portion  123 B of the printed circuit board  120  below. In a preferred embodiment, a half hole  1131 B is disposed at the end of the first grounding soldering portion  113 B to hold the solder FA; hence, the end of the first grounding soldering portion  113 B is covered with the solder FA and thus can be soldered to the second grounding soldering portion  123 B of the printed circuit board  120  below. The through hole VH 1  and the half hole  1131 B are of any shapes, such as round and square, and the present invention is not limited thereto. The half hole  1131 A,  1131 B are optional. In another preferred embodiment, the half hole  1131 A,  1131 B are dispensed with, and the solder is attached to the surface of a metal film to effectuate electrical interconnects. In another preferred embodiment, the first grounding soldering portions  113 B flank and extend along the first differential signal transmission lines  113 A and thus effectuate a grounded coplanar waveguide (GCPW) structure together with the first differential signal transmission lines  113 A, but the present invention is not limited thereto. 
     An insulating region A 1  is disposed on the first grounding pad region  114  and corresponds in position to the first differential signal transmission lines  113 A on the soft board body  111 . The insulating region A 1  extends inward from an edge of the soft board body  111 . The insulating region A 1  is disposed right below the first differential signal transmission lines  113 A so that the first grounding pad region  114  does not come into contact with the second differential signal transmission lines  123 A on the printed circuit board  120  when the flexible printed circuit  110  is disposed on the printed circuit board  120 , so as not to develop any short circuit. The insulating region A 1  is a naked region (i.e., the soft board body  111  per se), which dispenses with any copper foil, formed as a result of inward extension of the first grounding pad region  114 . In another preferred embodiment, the insulating region A 1  is an insulating layer disposed on the first grounding pad region  114 , but the present invention is not limited thereto. In another preferred embodiment, the protective layer  115  below the soft board body  111  extends and covers the first grounding pad region  114  from below so that only metal pads with the through holes VH 1  are exposed from two sides of the first grounding pad region  114  to prevent the first grounding pad region  114  from coming into contact with the ends of the second differential signal transmission lines  123 A, so as not to develop any short circuit. 
     Referring to  FIG. 1 ,  FIG. 2 , and  FIG. 3 , the printed circuit board  120  is tri-layered and comprises, from bottom to top, a protective layer  125 , a substrate body  121 , and a protective layer  122  disposed above the substrate body  121 . A second signal pad region  123  is disposed on one side of the substrate body  121 . A second grounding pad region  124  is disposed on the opposing side of the substrate body  121 . Both the second signal pad region  123  and the second grounding pad region  124  are conductive copper foils disposed on the substrate body  121  by wiring layout. The second signal pad region  123  comprises a pair of second differential signal transmission lines  123 A and two second grounding soldering portions  123 B which flank the pair of second differential signal transmission lines  123 A. 
     To prevent through holes from compromising high-frequency characteristics of high-frequency signals, the surfaces of the second differential signal transmission lines  123 A are intact and dispense with any through hole to maintain the integrity of high-frequency signals being transmitted along the second differential signal transmission lines  123 A. The end of the printed circuit board  120  lacks the protective layer  122  so as to expose the second differential signal transmission lines  123 A and the second grounding soldering portions  123 B for use in soldering. 
     Referring to  FIG. 4 , a through hole VH 2  is disposed on the second grounding soldering portions  123 B to electrically connect the second grounding soldering portions  123 B and the second grounding pad region  124 . In another preferred embodiment, the second grounding soldering portions  123 B flank and extend along the second differential signal transmission lines  123 A and thus effectuate a grounded coplanar waveguide (GCPW) structure together with the second differential signal transmission lines  123 A, but the present invention is not limited thereto. The through hole VH 2  is of any shapes, such as round and square, and the present invention is not limited thereto. 
       FIG. 6  is a partial transparent schematic view of the flexible printed circuit and printed circuit board soldered structure of the present invention. The present invention is described below with reference to the aforesaid diagram. 
     The flexible printed circuit  110  is disposed on the printed circuit board  120 . The insulating region A 1  of the first grounding pad region  114  is disposed above the second differential signal transmission lines  123 A to stay away from the second differential signal transmission lines  123 A and thus preclude developing a short circuit together with the second differential signal transmission lines  123 A. The ends of the first differential signal transmission lines  113 A are soldered to the second differential signal transmission lines  123 A by the solder FA to effectuate electrical connection. 
     To render it easy for assembly workers or automated machines to perform a soldering operation and reduce the likelihood soldering failures, a level sign S 1  is disposed on the substrate body  121  of the printed circuit board  120  and beside the second differential signal transmission lines  123 A to serve as reference for use in the soldering operation. The level signs S 1  enable the assembly workers or automated machines to confirm the distance between the insulating region A 1  below the flexible printed circuit  110  and the ends of the second differential signal transmission lines  123 A. The distance between each level sign S 1  and the end of a corresponding one of the second differential signal transmission lines  123 A is preferably shorter than or equal to an extension distance D 1  by which the insulating region A 1  extends inward. 
     The second embodiment of the present invention is described below. The second embodiment differs from the first embodiment mainly in the quantity of the signal transmission lines. 
       FIG. 7 ,  FIG. 8 , and  FIG. 9  are a perspective view, an exploded view ( 1 ), and an exploded view ( 2 ) of the second embodiment according to the present invention, respectively. The present invention is described below with reference to the aforesaid diagrams. 
     The second embodiment provides a flexible printed circuit and printed circuit board soldered structure  200  which comprises a flexible printed circuit  210  (FPC) and a printed circuit board  220  (PCB). 
     The flexible printed circuit  210  is tri-layered and comprises, from bottom to top, a protective layer  215 , a soft board body  211 , and a protective layer  212  disposed above the soft board body  211 . A first signal pad region  213  is disposed on one side of the soft board body  211 . A first grounding pad region  214  is disposed on the opposing side of the soft board body  211 . Both the first signal pad region  213  and the first grounding pad region  214  are conductive copper foils disposed on the soft board body  211  by wiring layout. Therein, the first signal pad region comprises a first signal transmission line  213 A and two first grounding soldering portions  213 B which flank the first signal transmission line  213 A. 
     High-frequency signals passing through a through hole are likely to produce parasitic capacitance and thus compromise signal integrity and high-frequency characteristics while high-frequency signal transmission is taking place; hence, the first signal transmission line  213 A have an intact surface which dispenses with any through hole. Furthermore, the end of the first signal transmission line  213 A is flush with the edge of the soft board body  211  so that the end of the first signal transmission line  213 A can be soldered to a second signal transmission line  223 A of the printed circuit board  220  below. In a preferred embodiment, a half hole  2131 A for holding a solder FB (shown in  FIG. 10 ) is disposed at the end of the first signal transmission line  213 A so that the end of the first signal transmission line  213 A can be covered with the solder FB and thus soldered to the second signal transmission line  223 A of the printed circuit board  220  below. 
       FIG. 10  and  FIG. 11  are a cross-sectional view and a top view of the second embodiment according to the present invention, respectively. The present invention is described below with reference to the aforesaid diagrams. 
     A through hole VH 3  is disposed on the first grounding soldering portion  213 B to electrically connect the first grounding soldering portion  213 B and the first grounding pad region  214 . The edge of the first grounding soldering portion  213 B and the edge of the soft board body  211  are flush with each other and thus can be soldered together from above the soft board body  211  and a second grounding soldering portion  223 B of the printed circuit board  220  below. In a preferred embodiment, a half hole  2131 B for holding the solder FB is disposed at the end of the first grounding soldering portion  213 B so that the end of the first grounding soldering portion  213 B can be covered with the solder FB and thus soldered to the second grounding soldering portion  223 B of the printed circuit board  220  below. The through hole VH 3  and the half hole  2131 B are of any shapes, such as round and square, and the present invention is not limited thereto. The half hole  2131 A,  2131 B are optional. In another preferred embodiment, the half hole  2131 A,  2131 B are dispensed with, and the solder is attached to the surface of a metal film to effectuate electrical interconnects. In another preferred embodiment, the first grounding soldering portions  213 B flank and extend along the first signal transmission line  213 A and thus effectuate a grounded coplanar waveguide (GCPW) structure together with the first signal transmission line  213 A, but the present invention is not limited thereto. 
     An insulating region A 2  is disposed on the first grounding pad region  214  and corresponds in position to the first signal transmission line  213 A on the soft board body  211 . The insulating region A 2  extends inward from an edge of the soft board body  211 . Specifically, the insulating region A 2  is disposed right below the first signal transmission line  213 A so that the first grounding pad region  214  does not come into contact with the second signal transmission line  223 A on the printed circuit board  220  when the flexible printed circuit  210  is disposed on the printed circuit board  220 , so as not to develop any short circuit. The insulating region A 2  is a naked region (i.e., the soft board body  211  per se), which dispenses with any copper foil, formed as a result of inward extension of the first grounding pad region  214 . In another preferred embodiment, the insulating region A 2  is an insulating layer disposed on the first grounding pad region  214 , but the present invention is not limited thereto. In another preferred embodiment, the protective layer  215  below the soft board body  211  extends and covers the first grounding pad region  214  from below so that only metal pads with the through hole VH 3  are exposed from two sides of the first grounding pad region  214  to prevent the first grounding pad region  214  from coming into contact with the end of the second signal transmission line  223 A, so as not to develop any short circuit. 
     Referring to  FIG. 7 ,  FIG. 8 , and  FIG. 9 , the printed circuit board  220  is tri-layered and comprises, from bottom to top, a protective layer  225 , a substrate body  221 , and a protective layer  222  disposed above the substrate body  221 . A second signal pad region  223  is disposed on one side of the substrate body  221 . A second grounding pad region  224  is disposed on the opposing side of the substrate body  221 . Both the second signal pad region  223  and the second grounding pad region  224  are conductive copper foils disposed on the substrate body  221  by wiring layout. The second signal pad region  223  comprises a second signal transmission line  223 A and two second grounding soldering portions  223 B which flank the second signal transmission line  223 A. 
     To prevent through holes from compromising high-frequency characteristics of high-frequency signals, the surface of the second signal transmission line  223 A is intact and dispenses with any through hole to maintain the integrity of high-frequency signals being transmitted along the second signal transmission line  223 A. The end of the printed circuit board  220  lacks the protective layer  222  so as to expose the second signal transmission line  223 A and the second grounding soldering portions  223 B for use in soldering. 
     Referring to  FIG. 10 , a through hole VH 4  is disposed on the second grounding soldering portion  223 B to electrically connect the second grounding soldering portion  223 B and the second grounding pad region  224 . In another preferred embodiment, the second grounding soldering portions  223 B flank and extend along the second signal transmission line  223 A and thus effectuate a grounded coplanar waveguide (GCPW) structure together with the second signal transmission line  223 A, but the present invention is not limited thereto. The through hole VH 2  is of any shapes, such as round and square, and the present invention is not limited thereto. 
       FIG. 12  is a partial transparent schematic view of the second embodiment according to the present invention. The present invention is described below with reference to the aforesaid diagram. 
     The flexible printed circuit  210  is disposed on the printed circuit board  220 . The insulating region A 2  of the first grounding pad region  214  is disposed above the second signal transmission line  223 A to stay away from the second signal transmission line  223 A and thus preclude developing a short circuit together with the second signal transmission line  223 A. The end of the first signal transmission line  213 A is soldered to the second signal transmission line  223 A by the solder FB to effectuate electrical connection. 
     To render it easy for assembly workers or automated machines to perform a soldering operation and reduce the likelihood soldering failures, a level sign S 2  is disposed on the substrate body  221  of the printed circuit board  220  and beside the second signal transmission line  223 A to serve as reference for use in the soldering operation. The level signs S 2  enable the assembly workers or automated machines to confirm the distance between the insulating region A 2  below the flexible printed circuit  210  and the end of the second signal transmission line  223 A. The distance between level sign S 2  and the end of the second signal transmission line  223 A is preferably shorter than or equal to an extension distance D 2  by which the insulating region A 2  extends inward. 
     In conclusion, a flexible printed circuit and a printed circuit board soldered structure of the present invention not only displays satisfactory high-frequency transmission characteristics, but also enhances the integrity of high-frequency signals during signal transmission owing to dispensing with the need to provide any through hole at the positions of the soldering of signal transmission lines. Furthermore, the soldered structure of the present invention is so simple that it is almost the same as the soldering techniques disclosed in the prior art. 
     While example embodiments have been disclosed herein, it should be understood that other variations may be possible. Such variations are not to be regarded as a departure from the spirit and scope of example embodiments of the present application, 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.