Abstract:
An attenuation reduction structure of a circuit board includes an expanded thickness formed between high frequency signal contact pads and a grounding layer of the circuit board. The expanded thickness is greater than a reference thickness between the grounding layer and high frequency signal lines. The circuit board is made of polyethylene terephthalate (PET) or polyimide (PI). Alternatively, a rigid board including resin and fibrous material or a rigid-flex board is used. The circuit board can be a single-layer circuit board or a multi-layer board formed by combining at least two single-layer circuit boards. A thickness-expanding pad is mounted between the high frequency signal contact pads and the grounding layer or the thickness of a portion of a bonding layer of the circuit board is increased to provide an expanded thickness.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a structure of a circuit board that improves transmission quality of high frequency signals, and in particular to an attenuation reduction structure for high frequency signal contact pads of the circuit board, which includes an expanded thickness between a contact pad mounting zone and a grounding layer of a substrate to reduce a capacitance effect between the high frequency signal contact pads and the grounding layer so as to reduce attenuation occurring in the transmission of high frequency signals. 
     2. The Related Arts 
     In all sorts of electronic device that are currently available and used, the amount of data transmitting through signal lines is increasingly expanding and consequently, the number of signal transmission lines needed is constantly increased and the frequencies used to transmit signals are also constantly raised. 
     A number of ways are used to suppress the generation of noises in high frequency signal lines. A common mode chock is commonly used in the known circuits to suppress common mode noises, but it is not fit for applications of circuit boards of high speed/high frequency signals. 
     In the high frequency signal transmission technology, generally, two high frequency signal lines are grouped as a signal pair to respectively transmit signals of identical amplitudes but opposite phases. Common mode noises that are induced by external interference signals in the two signal lines are of identical amplitudes and identical phases and would be rejected by a differential input pair of an integrated circuit so that the circuit shows a better effect of suppressing electromagnetic interference. 
     Although the known high frequency signal transmission technology is effective in remarkably alleviating potential problems occurring in the transmission of signals, yet poor designs may result in potential problems in actual applications, such as signal reflection, radiation of electromagnetic signals, loss of transmitted signals, and distortion of waveforms of signals. Specifically, for flexible circuit boards having a substrate that includes a reduced thickness, these problems associated with signal transmission get even worse. Causes for such problems include for example poor match of characteristic impedance in a length extension direction of high frequency signal lines, poor control of additional parasitic capacitance between high frequency signal lines and a grounding layer, poor control of additional parasitic capacitance between a contact pad mounting zone and a grounding layer, and mismatch of characteristic impedance of high frequency signal lines and a contact pad mounting zone. 
     Currently, various solutions have been proposed to overcome the problems of electromagnetic interference and impedance match in the length extension direction of high frequency signal lines of a flexible circuit board. However, up to date, due to constraints imposed by line widths of high frequency signal lines (the line widths being extremely small) and dimension specifications of signal terminal pins and components of a connector (which are relatively large as compared to the line widths of the signal lines), no manufacturer in this technical field has proposed an effective solution to ensure transmission quality of high frequency signals for a connection between high frequency signal lines and a contact pad mounting zone of a flexible circuit board and an adjacent site thereof. 
     SUMMARY OF THE INVENTION 
     Thus, an object of the present invention is to provide an attenuation reduction structure for high frequency signal contact pads of a circuit board, which comprises an increased thickness formed between high frequency signal contact pads and a grounding layer of a circuit board to increase a corresponding distance between the high frequency signal contact pads and the grounding layer, reducing reflection and loss of high frequency components of transmitted signals, thereby improving signal transmission quality of high frequency signal lines of the flexible circuit board. 
     The technical solution that the present invention adopts to overcome the problems of the prior art comprises an expanded thickness formed between high frequency signal contact pads and a grounding layer of a circuit board. The expanded thickness is greater than a reference thickness between the grounding layer and high frequency signal lines. 
     In a preferred embodiment of the present invention, the circuit board is a single-layer circuit board, or alternatively a multi-layered board formed by combining at least two single-layer circuit boards. A thickness-expanding pad is interposed between a contact pad mounting section of a first substrate and an opposite section of a second substrate. 
     In another embodiment of the present invention, a thickness-expanding pad is mounted between the high frequency signal contact pads and the grounding layer of the circuit board or alternatively, the thickness of a portion of a bonding layer of the circuit board is increased so as to provide an expanded thickness. 
     In another embodiment of the present invention, the circuit board comprises an extended grounding layer mounted to the grounding line mounting surface to correspond to the contact pad mounting section, the extended grounding layer being electrically connected to the grounding layer; and a thickness-expanding pad, which is connected between the grounding line mounting surface and the extended grounding layer of the circuit board. 
     The circuit board according to the present invention may comprises at least one inspection hole formed therein for observing and identifying if the thickness-expanding pad is properly set in position. Further, the circuit board according to the present invention may be further provided with a reinforcement plate mounted thereto. 
     The grounding layer of the circuit board of the present invention may further comprise an anti-attenuation pattern. The anti-attenuation pattern comprises a plurality of opening structures spaced from each other by predetermined distances. 
     The efficacy of the present invention is that with at least one thickness-expanding pad being mounted in a circuit board or the thickness of a bonding layer being partly expanded, during transmission of high frequency signals through high frequency signal lines, the capacitance effect induced by the high frequency signal lines is reduced so as to reduce the chance of transmission failure of high frequency differential mode signals and ensure the transmission quality of high frequency signals. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be apparent to those skilled in the art by reading the following description of preferred embodiments of the present invention, with reference to the attached drawings, in which: 
         FIG. 1  is a perspective view showing an attenuation reduction structure of circuit board high frequency signal contact pads according to a first embodiment of the present invention; 
         FIG. 2  is a cross-sectional view taken along line  2 - 2  of  FIG. 1 ; 
         FIG. 3  is a cross-sectional view showing a combination of a circuit board and a connector according to the present invention; 
         FIG. 4  is a cross-sectional view showing a second embodiment of the present invention; 
         FIG. 5  is a cross-sectional view showing a third embodiment of the present invention; 
         FIG. 6  is a cross-sectional view showing a fourth embodiment of the present invention; 
         FIG. 7  is a cross-sectional view showing a fifth embodiment of the present invention; 
         FIG. 8  is a cross-sectional view showing a sixth embodiment of the present invention; 
         FIG. 9  is a cross-sectional view showing a seventh embodiment of the present invention; 
         FIG. 10  is a cross-sectional view showing an eighth embodiment of the present invention; and 
         FIG. 11  is a cross-sectional view showing a ninth embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With reference to the drawings and in particular to  FIGS. 1 and 2 , a circuit board constructed in accordance with a first embodiment of the present invention, generally designated at  100 , comprises a wiring mounting surface  11  and a grounding line mounting surface  21 , a contact pad mounting section A formed on the wiring mounting surface  11 , and an opposite section B that is opposite to the contact pad mounting section A. The circuit board  100  of the instant embodiment comprises, structurally, a first substrate  1 , a second substrate  2 , a bonding layer  3 , a grounding layer  4 , a plurality of high frequency signal contact pads  14 , and a plurality of high frequency signal lines  15 . 
     The first substrate  1  comprises the wiring mounting surface  11  and a first bonding surface  12 . The wiring mounting surface  11  comprises the contact pad mounting section A defined thereon and a first extension section  13  extending from the contact pad mounting section A. 
     The plurality of high frequency signal contact pads  14  is mounted in the contact pad mounting section A of the first substrate  1  to be adjacent to and insulatively isolated from each other. The high frequency signal contact pads  14  are respectively connected to the plurality of high frequency signal lines  15  that are mounted on the wiring mounting surface  11  of the first substrate  1 . The wiring mounting surface  11  of the first substrate  1  is covered by an insulation cover layer  16  set thereon. 
     The high frequency signal contact pads  14  comprise at least a pair of differential mode signal contact pads. The high frequency signal lines  15  that are connected to the high frequency signal contact pads  14  may carry and transmit differential mode signals. 
     The second substrate  2  comprises the grounding line mounting surface  21  and a second bonding surface  22 . The second substrate  2  comprises the opposite section B defined thereon to correspond to and be opposite to the contact pad mounting section A of the first substrate  1  and a second extension section  23  corresponding to and opposite to the first extension section  13 . 
     The bonding layer  3  is bonded between the first bonding surface  12  of the first substrate  1  and the second bonding surface  22  of the second substrate  2 . The contact pad mounting section A of the first substrate  1  and the opposite section B of the second substrate are thus bonded to each other in a corresponding manner and the first extension section  13  and the second extension section  23  are also bonded to each other in a corresponding manner. 
     The grounding layer  4  is bonded to the grounding line mounting surface  21  of the second substrate  2 . The high frequency signal lines  15  in the first extension section  13  of the first substrate  1  and the grounding layer  4  in the second extension section  23  of the second substrate  2  collectively define a reference thickness H 2  therebetween. The grounding layer  4  has a bottom surface, which is provided, in the opposite section B, with a reinforcement plate  6  mounted thereto for reinforcement of an end portion of the circuit board  100  and adjustment of thickness. 
     A portion of the first bonding surface  12  located in the contact pad mounting section A of the first substrate  1  and a portion of the second bonding surface  22  located the opposite section B of the second substrate  2  receive at least one thickness-expanding pad  5  interposed therebetween. The thickness-expanding pad  5  provides an expanded thickness H 1  between the high frequency signal contact pads  14  arranged in the contact pad mounting section A of the first substrate  1  and the portion of the grounding layer  4  located in the opposite section B of the second substrate  2 . The expanded thickness H 1  is greater than the reference thickness H 2  between the high frequency signal lines  15  in the first extension section  13  of the first substrate  1  and the grounding layer  4  in the second extension section  23  of the second substrate  2 . 
     Referring to  FIG. 3 , with the circuit board  100  combined with a connector  7 , when the high frequency signal lines  15  transmit high frequency signals to have the high frequency signals transmitted through the connector  7  to an electronic device, by means of increasing the distance between the first substrate  1  and the second substrate  2  and inserting a thickness-expanding pad  5  therebetween, the capacitance effect induced by the high frequency signals transmitted through the high frequency signal lines  15  is reduced so as to reduce the chance of losing the high frequency differential mode signals and ensure the transmission quality of the high frequency signals. 
     Referring to  FIG. 4 , a second embodiment is shown, wherein at least one inspection hole  8  is formed in the wiring mounting surface  11  of the circuit board  100  within the contact pad mounting section A so as to expose at least a portion of a surface of the thickness-expanding pad  5  in the inspection hole  8 . The inspection hole  8  allows an operator to observe and identify if the thickness-expanding pad  5  is properly inserted in position. Further, the circuit board  100  also comprises at least one inspection hole  8   a  formed in the grounding line mounting surface  21  within the opposite section B to expose at least a portion of a surface of the thickness-expanding pad  5  in the inspection hole  8   a . The inspection hole  8   a  allows the operator to observe and identify if the thickness-expanding pad  5  is properly inserted in position. 
     Further, the grounding layer  4  may further comprise an anti-attenuation pattern  9  formed therein. The anti-attenuation pattern  9  comprises a plurality of opening structures  91  that is arranged to space from each other by predetermined distances. The opening structures  91  can be any geometric structure of a circular structure, a rectangular structure, and a rhombus structure. The anti-attenuation pattern  9  provides an effect of helping reduce attenuation of the high frequency signal. 
     Referring to  FIG. 5 , a cross-sectional view is given to illustrate a third embodiment of the present invention. The instant embodiment is substantially identical to the embodiment with reference to  FIG. 2  and a difference is that a thickness-expanding pad comprises a first thickness-expanding pad  51  and at least one second thickness-expanding pad  52  stacked thereon and the second thickness-expanding pad  52  has a length different from a length of the first thickness-expanding pad  51  in order to match varying capacitance induced by a structure having a gradually decreasing area in the interconnection between the high frequency signal contact pads  14  and the corresponding high frequency signal lines  15 . 
     Referring to  FIG. 6 , a cross-sectional view is given to illustrate a fourth embodiment of the present invention. The instant embodiment is substantially identical to the embodiment with reference to  FIG. 5  and a difference is that a first thickness-expanding pad  51 , a second thickness-expanding pad  52 , and a third thickness-expanding pad  53  are provided and have different lengths in order to match varying capacitance induced by a structure having a gradually decreasing area in the interconnection between the high frequency signal contact pads  14  and the corresponding high frequency signal lines  15 . 
       FIG. 7  is a cross-sectional view illustrating a fifth embodiment of the present invention and showing the third thickness-expanding pad  53  of  FIG. 6  is replaced with a fourth thickness-expanding pad  54  having a smaller length. 
     Referring to  FIG. 8 , across-sectional view is given to illustrate a sixth embodiment of the present invention. The instant embodiment comprises components most of which are identical to those of the first embodiment and identical components are designated with the same reference numerals for consistency. In the instant embodiment, a first bonding surface  12  of a first substrate  1  of a circuit board  200  in a contact pad mounting section A and a second bonding surface  22  of a second substrate  2  in an opposite section B comprise a thickened bonding zone  31 . The thickened bonding zone  31  has a thickness greater than a thickness of the bonding layer  3  between the first bonding surface  12  of the first substrate  1  in the first extension section  13  and the second bonding surface  22  of the second substrate  2  in the second extension section  23 . The thickened bonding zone  31  provides an expanded thickness H 1  between the high frequency signal contact pads  14  arranged in the contact pad mounting section A of the first substrate  1  and the grounding layer  4  in the opposite section B of the second substrate  2  and the expanded thickness H 1  is greater than a reference thickness H 2  between the high frequency signal lines in the first extension section of the first substrate and the grounding layer in the second extension section of the second substrate. 
     Referring to  FIG. 9 , a cross-sectional view is given to illustrate a seventh embodiment of the present invention. The instant embodiment comprises components most of which are identical to those of the embodiment with reference to  FIG. 8 . In the instant embodiment, at least one inspection hole  8  is formed in a wiring mounting surface  11  of a circuit board  200  within a contact pad mounting section A so as to expose at least a portion of a surface of a thickened bonding zone  31  in the inspection hole  8 . The inspection hole  8  allows an operator to observe the thickened bonding zone  31 . Further, the circuit board  200  also comprises at least one inspection hole  8   a  formed in a grounding line mounting surface  21  within an opposite section B to expose at least a portion of a surface of the thickened bonding zone  31  in the inspection hole  8   a . The inspection hole  8   a  allows the operator to observe the thickened bonding zone  31 . 
     Referring to  FIG. 10 , a cross-sectional view is given to illustrate an eighth embodiment of the present invention. The instant embodiment comprises components most of which are identical to those of the first embodiment and identical components are designated with the same reference numerals for consistency. A difference resides in that the circuit board  300  is a single-layer circuit board, wherein the circuit board  300  has a wiring mounting surface  11   a  which comprises a contact pad mounting section A defined thereon and an first extension section  13  extending from the contact pad mounting section A. 
     A plurality of high frequency signal contact pads  14  is mounted in the contact pad mounting section A of the wiring mounting surface  11   a  of the circuit board  300  to be adjacent to and insulatively isolated from each other. The wiring mounting surface  11   a  also comprises a plurality of high frequency signal lines  15  mounted thereon to respectively correspond to and connect with the high frequency signal contact pads  14 . 
     The grounding line mounting surface  21   a  of the circuit board  300  comprises, defined thereon, an opposite section B corresponding to and opposite to the contact pad mounting section A and a second extension section  23  corresponding to the first extension section  13 . 
     The contact pad mounting section A and the opposite section B of the circuit board  300  comprise at least one thickness-expanding pad  5  inserted and interposed therebetween. The thickness-expanding pad  5  provides an expanded thickness H 1  between the high frequency signal contact pads  14  arranged in the contact pad mounting section A of the circuit board  300  and the portion of the grounding layer  4  located in the opposite section B of the circuit board  300 . The expanded thickness H 1  is greater than a reference thickness H 2  between the high frequency signal lines  15  in the first extension section  13  of the circuit board  300  and the grounding layer  4  in the second extension section  23  of the circuit board  300 . The thickness-expanding pad  5  similarly helps reduce the capacitance effect and reflection loss induced in the transmission of high frequency signals so as to reduce the chance of losing the high frequency differential mode signals and ensure the transmission quality of the high frequency signals. 
     In the instant embodiment, the circuit board  300  may also comprise at least one inspection hole  8  formed in the wiring mounting surface  11   a  within the contact pad mounting section A. And, the circuit board  200  may be additionally provided with at least one inspection hole  8   a  formed in the grounding line mounting surface  21  of the opposite section B. 
     Referring to  FIG. 11 , a cross-sectional view is given to illustrate a ninth embodiment of the present invention. The instant embodiment provides a circuit board  400 , which is a single-layer circuit board, wherein the circuit board  400  comprises a wiring mounting surface  11   a  that defines a contact pad mounting section A and a first extension section  13  extending from the contact pad mounting section A. 
     A plurality of high frequency signal contact pads  14  is mounted in the contact pad mounting section A of the wiring mounting surface  11   a  of the circuit board  400  to be adjacent to and insulatively isolated from each other. The wiring mounting surface  11   a  also comprises a plurality of high frequency signal lines  15  mounted thereon to respectively correspond to and connect with the high frequency signal contact pads  14 . 
     The grounding line mounting surface  21   a  of the circuit board  400  comprises, defined thereon, an opposite section B corresponding to and opposite to the contact pad mounting section A and a second extension section  23  corresponding to the first extension section  13 . 
     A grounding layer  4  is formed on the circuit board  400  in the second extension section  23 . The grounding layer  4  does not extend into the opposite section B. The grounding line mounting surface  21   a  of the circuit board  400  is first connected, in the opposite section B, to at least one thickness-expanding pad  5   a  and then, the thickness-expanding pad  5   a  is connected, at a bottom surface thereof, to an extended grounding layer  41 . The extended grounding layer  41  is set in electrical connection with the grounding layer  4  through a conductive material  42  (such as silver paste, copper paste, and solder). Finally, an insulation cover layer  16   a  is formed on the bottom of the grounding layer  4  and the extended grounding layer  41 . 
     With the arrangement of the extended grounding layer  41  and the thickness-expanding pad  5   a , similarly, an expanded thickness H 1  is formed between the high frequency signal contact pads  14  formed in the contact pad mounting section A of the circuit board  400  and the grounding layer  41  of the circuit board  400  in the opposite section B and the expanded thickness H 1  is greater than a reference thickness H 2  between the high frequency signal lines  15  of the circuit board  400  in the first extension section  13  and the grounding layer  4  of the circuit board  400  in the second extension section  23  so as to help reduce the capacitance effect and reflection loss in transmission of high frequency signals thereby reducing the chance of losing the high frequency signals and ensuring the transmission quality of the high frequency signals. 
     In each of the embodiments illustrated previously, the circuit board can be one of a flexible circuit board, a rigid board, and a rigid-flex board. The flexible circuit board can be made of a material of one of polyethylene terephthalate (PET) and polyimide (PI). The rigid board can be made of a material that comprises a mixture of a resin and a fibrous material in a predetermined ratio. The rigid-flex board can be a combined structure of a flexible circuit board and a rigid. 
     Further, in the drawings associated with the previous embodiments, illustration is given to an example where the high frequency signal contact pads are arranged at an end portion of the circuit board. Those skilled in the art may readily appreciate that the present invention is equally applicable to examples where the high frequency signal contact pads are formed at any location in the circuit board and the high frequency signal contact pads may serve as soldering pads of terminal pins of an electronic device. 
     Although the present invention has been described with reference to the preferred embodiments thereof, it is apparent to those skilled in the art that a variety of modifications and changes may be made without departing from the scope of the present invention which is intended to be defined by the appended claims.