Abstract:
A substrate pad structure for connecting a lead connecting portion of an electronic device to a substrate is disclosed. The substrate pad structure includes a first pad portion and a second pad portion that are arranged on the substrate at corresponding positions of two end regions of the lead connecting portion, which has a continuous oblong shape. A space portion is provided between the first pad portion and the second pad portion, and the lead connecting portion includes a non-connected region located at a corresponding position of the space portion.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a substrate pad structure that is configured to be connected to a lead terminal connecting portion of an electronic device that is mounted on the surface of a substrate. 
         [0003]    2. Description of the Related Art 
         [0004]    Conventionally, electrical connection between a substrate and an electronic device such as a connector that is surface-mounted on the substrate is established by attaching plural connecting portions of connector lead terminals to plural pads arranged on the substrate using solder, for example. 
         [0005]      FIG. 1A  is a diagram showing a coaxial cable connecter  150  being connected to one edge of an evaluation substrate  100  that evaluates transmission characteristics of a cable assembly.  FIG. 1B  is a diagram showing connecting portions  252  of lead terminals  250  of the connector  150  attached to pads  200  arranged on the substrate  100  so that electrical connection is established between the connector  150  and the substrate  100 . 
         [0006]      FIG. 2A  is an enlarged view of the lead terminals  250  of the connector  150 . The lead terminals  250  maybe positive signal terminals, negative signal terminals, or ground terminals that are connected to corresponding pads  200  arranged on the substrate  100 .  FIG. 2B  is a diagram showing an arrangement of the pads  200  on the substrate  100 . 
         [0007]      FIG. 3A  is a plan view of the connector lead terminals  250  connected to the pads  200 . As is shown in this drawing, the connecting portions  252  of the connector lead terminals  250  and the pads  200  are arranged into oblong shapes with the pads  200  being slightly larger in size so that the connecting portions  252  of the connector lead terminals  250  may be soldered onto the pads  200 .  FIG. 3B  is a side view of the connection between the connector lead terminal  250  and the pad  200 . As is shown in this drawing, the entire bottom face of the lead terminal connecting portion  252  comes into contact with the surface of the pad  200 . 
         [0008]    It is noted that Japanese Laid-Open Patent Publication No. 5-63132 discloses a technique for accurately connecting lead terminals to pads of a substrate without having any positioning deviations by adjusting the shape of the lead terminal. 
         [0009]    However, when the entire bottom face of the lead terminal connecting portion is arranged to come into contact with the surface of the pad, characteristic impedance matching may not be adequately performed when transmitting a signal of a high frequency range and signal reflection may occur so that transmission characteristics may be prone to degradation. 
       SUMMARY OF THE INVENTION 
       [0010]    An aspect of the present invention is directed to providing a substrate pad structure that is configured to adjust characteristic impedance matching between a connector lead terminal of an electronic device and a pad while reinforcing the connection between a connecting portion of the connector lead terminal and the pad. 
         [0011]    According to one embodiment of the present invention, a substrate pad structure is provided for connecting a lead connecting portion of an electronic device to a substrate, the substrate pad structure including: 
         [0012]    a first pad portion and a second pad portion that are arranged on the substrate at corresponding positions of two end regions of the lead connecting portion, which lead connecting portion has a continuous oblong shape; 
         [0013]    wherein a space portion is provided between the first pad portion and the second pad portion, and the lead connecting portion includes a non-connected region located at a corresponding position of the space portion. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1A  is a diagram showing coaxial cable connectors connected to a substrate; 
           [0015]      FIG. 1B  is a diagram showing connector lead terminals connected to pads arranged on the substrate; 
           [0016]      FIG. 2A  is an enlarged view of the connector lead terminals connected to the pads; 
           [0017]      FIG. 2B  is a diagram showing an arrangement of the pads; 
           [0018]      FIGS. 3A and 3B  are diagrams showing the connection arrangement between the connector lead terminals and the pads; 
           [0019]      FIGS. 4A and 4B  are diagrams showing a connection arrangement between lead terminal connecting portions and pads according to a first embodiment of the present invention; 
           [0020]      FIG. 5  is a graph showing time domain reflectometry (TDR) waveforms obtained with respect to the pad structure according to the first embodiment; 
           [0021]      FIGS. 6A and 6B  are diagrams showing a connection arrangement between lead terminal connecting portions and pads according to a second embodiment of the present invention; 
           [0022]      FIG. 7  is a graph showing time domain reflectometry (TDR) waveforms obtained with respect to the pad structure according to the second embodiment; 
           [0023]      FIGS. 8A and 8B  are diagrams showing a connection arrangement between lead terminal connecting portions and pads according to a third embodiment of the present invention; 
           [0024]      FIG. 9  is a graph showing time domain reflectometry (TDR) waveforms obtained with respect to the pad structure according to the third embodiment; 
           [0025]      FIGS. 10A and 10B  are diagrams showing a connection arrangement between lead terminal connecting portions and pads according to a fourth embodiment of the present invention; and 
           [0026]      FIG. 11  is a graph showing time domain reflectometry (TDR) waveforms obtained with respect to the pad structure according to the fourth embodiment. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0027]    In the following, preferred embodiments of the present invention are described with reference to the accompanying drawings. 
       First Embodiment 
       [0028]      FIGS. 4A and 4B  are diagrams showing a connection arrangement between pads  1 A according to a first embodiment of the present invention and connecting portions  26  of connector lead terminals  25 . Specifically,  FIG. 4A  is a plan view of two parallel pads  1 A connected to corresponding lead terminal connecting portions  26 , and  FIG. 4B  is a corresponding plan view showing regions  40  on which solder is applied upon soldering the connecting portions  26  of the lead terminals  25  onto the pads  1 A. 
         [0029]    The pad  1 A according to the present embodiment includes a rectangular/square first pad portion  20  and a rectangular/square second pad portion  21  with a space portion  30  formed between the first pad portion  20  and the second pad portion  21 . It is noted that the pad portions  20  and  21  may be made of a metal with relatively high conductivity, such as copper. 
         [0030]    As is shown in  FIG. 4A , the first pad portion  20  and the second pad portion  21  are each arranged at the ends of the lead terminal connecting portion  26 . The ends of the lead terminal connecting portion  26  are soldered to the corresponding pad portions  20  and  21 . However, an intermediate portion of the lead terminal connecting portion  26  is not connected to the pad  1 A. 
         [0031]    In the present embodiment, the second pad portion  21  functions as an electrical connection terminal of a substrate that conveys an electrical signal from the lead terminal to a circuit portion of the substrate. On the other hand, the first pad portion  20  is configured to reinforce the mechanical strength of the connection between the lead terminal connecting portion  26  and the substrate and adjust characteristic impedance matching between the lead terminal  25  and the pad  1 A. 
         [0032]      FIG. 5  is a graph showing time domain reflectometry (TDR) waveforms indicating variations in the characteristic impedance of the transmission line between the lead terminal connecting portion  26  and the pad  1 A according to the first embodiment depending on their connection arrangement. 
         [0033]    It is noted that time domain reflectometry is a measurement technique used for determining the characteristic impedance of an electrical line by applying an electrical pulse signal with a high rise rate to the electrical line subject to measurement and observing reflected signals that are reflected during propagation of the signals through the electrical line. 
         [0034]    The graph of  FIG. 5  shows TDR waveforms each obtained by applying an electrical signal with a predetermined rise time. It is noted that the horizontal axis of this graph represents the time, and the vertical axis of this graph represents the characteristic impedance value. This graph shows how the characteristic impedance of the transmission line between a lead terminal and a pad may be adjusted by using the pad structure according to the first embodiment. 
         [0035]    Specifically, provided that the distance between the first pad portion  20  and the second pad portion  21  (i.e., the length of the space portion  30 ) is denoted by L, the one dotted line shown in  FIG. 5  represents a characteristic impedance measurement obtained using a pad structure in which L=0 (i.e., the pad  200  according to the prior art as shown in  FIGS. 3A and 3B ). The dotted line and the solid line shown in  FIG. 5  represent characteristic impedance measurements obtained using the pad structure of the pad  1 A according to the present embodiment. Specifically, the dotted line shows the characteristics impedance measurement obtained when the distance L is relatively long; namely, when the ratio of the physical delay time (delay time created by the space portion  30  according to length L) to the rise time is relatively large. The solid line shows the characteristic impedance measurement obtained when the distance L is relatively short; namely, when the ratio of the physical delay time to the rise time is relatively small. It is noted that the characteristic impedance waveforms represented by the above-described one dotted line, dotted line, and solid line correspond to characteristic impedances obtained with respect to the same rise time. 
         [0036]    As can be appreciated from the graph of  FIG. 5 , a characteristic impedance Z 0  (Ohms) mismatch may be reduced when the distance L is longer; namely, when the ratio of the physical delay time to the rise time is greater. By using the pad structure according to the present embodiment, the characteristic impedance of the transmission line between the lead terminal and the pad may be more suitably adjusted compared to the case of using the pad structure according to the prior art. 
       Second Embodiment 
       [0037]      FIGS. 6A and 6B  are diagrams showing a connection arrangement between pads  2 A according to a second embodiment of the present invention and the connecting portions  26  of the connector lead terminals  25 . Specifically,  FIG. 6A  is a plan view of two pads  2 A connected to corresponding lead terminal connection terminals  26 , and  FIG. 6B  is a corresponding plan view showing regions  40  on which solder is applied upon soldering the lead terminal connecting portions  26  to the pads  2 A. 
         [0038]    The pad  2 A according to the present embodiment includes a rectangular/square first pad portion  20 , a rectangular/square second pad portion  21 , and a rectangular/square third pad portion  22  arranged between the first and second pad portions  20  and  21 . The first through third pad portions  20 - 22  may be made of a highly conductive metal such as copper, for example. 
         [0039]    As is shown in  FIG. 6A , the first pad portion  20  and the second pad portion  21  are positioned at the ends of the lead terminal connecting portion  26 . As is shown in  FIG. 6B , the ends of the lead terminal connecting portion  26  are soldered to the first and second pad portions  20  and  22 . In the present embodiment, portions of the lead terminal connecting portion  26  between the first pad portion  20  and the third pad portion  22  and between the second pad portion  21  and the third pad portion  22  are not connected to a pad portion. It is noted that portions corresponding to the locations where the lead terminal connecting portion  26  does not come into contact with a pad portion are regarded as space portions  30  of the pad  2 A. 
         [0040]    The third pad portion  22  is positioned at approximately the center of the lead terminal connecting portion  26 . The third pad portion is separated from both the first pad portion  20  and the second pad portion  21  by a certain distance. As is shown in  FIG. 6B , the third pad portion  22  is soldered to a region  50  of the lead terminal connecting portion  26  having a predetermined length L 2 . 
         [0041]    The second pad portion  21  functions as an electrical connection terminal of a substrate that conveys electrical signals from the lead terminal to a circuit portion of the substrate. On the other hand, the first and third pad portions  20  and  22  are configured to reinforce the mechanical strength of the connection between the lead terminal connecting portion  26  and the substrate and to adjust the characteristic impedance of the transmission line between the lead terminal  25  and the pad  2 A. 
         [0042]      FIG. 7  is a graph showing TDR waveforms indicating variations in the characteristic impedance of the transmission line between the lead terminal connecting portion  26  and the pad  2 A according to the second embodiment depending on their connection arrangement. 
         [0043]    Specifically, the graph of  FIG. 7  shows TDR waveforms each obtained by applying an electrical pulse signal with a predetermined rise time (same rise time as the electrical pulse signal used for obtaining the TDR waveforms shown in  FIG. 5 ). It is noted that the horizontal axis of this graph represents the time, and the vertical axis of this graph represents the characteristic impedance value. This graph shows how the characteristic impedance of the transmission line between a lead terminal and a substrate pad may be adjusted by using the pad structure according to the second embodiment. 
         [0044]    In the graph of  FIG. 7 , L 2  denotes the length of the third pad portion  22  along the longitudinal direction of the lead terminal connecting portion  26 . The one dotted line and the dotted line shown in  FIG. 7  represent characteristic impedance measurements obtained when using the pad  2 A according to the second embodiment. Specifically, the one dotted line represents the characteristic impedance measurement obtained in a case where the length L 2  is relatively long; namely, when the ratio of the physical delay time (delay time created by the space portions  30  according to the length L 2 ) to the rise time is relatively small, and the dotted line represents the characteristic impedance measurement obtained in a case where the length L 2  is relatively short; namely, when the ratio of the physical delay time to the rise time is relatively large. The solid line shown in  FIG. 7  represents the characteristic impedance measurement obtained using a pad structure in which L 2 =0 (i.e., the pad  1 A according to the first embodiment), and the two dotted line represents the characteristic impedance measurement obtained using the pad  200  according to the prior art. It is noted that the above-described characteristic impedance waveforms represented by the one dotted line, two dotted line, dotted line, and solid line correspond to characteristic impedances measured using electric pulse signals with the same rise time. 
         [0045]    As can be appreciated from the graph of  FIG. 7 , a characteristic impedance mismatch may be reduced when the length L 2  is shorter; namely, when the ratio of the physical delay time to the rise time is larger. By using the pad structure according to the present embodiment including the space portions  30 , the characteristic impedance of the transmission line between the lead terminal and the pad may be more suitably adjusted compared to the case of using the pad structure according to the prior art. 
       Third Embodiment 
       [0046]      FIGS. 8A and 8B  are diagrams showing a connection arrangement between pads  3 A according to a third embodiment of the present invention and the connecting portions  26  of the connector lead terminals  25 . Specifically,  FIG. 8A  is a plan view of two pads  3 A connected to the lead terminal connecting portions  26 , and  FIG. 8B  is a corresponding side view showing regions  40  on which solder is applied upon soldering the lead terminal connecting portions  26  to the pads  3 A. 
         [0047]    The pad  3 A according to the third embodiment includes a third pad portion  23  in addition to a first pad portion  20  and a second pad portion  21 . It is noted that the first and second pad portions  20  and  21  may be identical to those of the pad  2 A according to the second embodiment so that descriptions thereof are omitted. 
         [0048]    As with the second embodiment, the third pad portion  23  of the pad  3 A according to the present embodiment is arranged between the first pad portion  20  and the second pad portion  21 , and is separated from both the first pad portion  20  and the second pad portion  21  by a certain distance. In the present embodiment, the third pad portion  23  is arranged into a rectangular shape with its long side being arranged parallel to the longitudinal direction of the lead terminal connecting portion  26 . Also, the third pad portion  23  is deviated in the transverse direction toward one long side of the lead terminal connecting portion  26 . Accordingly, a left-half side or a right-half side of a portion of the lead terminal connecting portion  26  extending along a length L 3  of the third pad portion  23  is not connected to the third pad portion  23 . It is noted that portions corresponding to locations where the lead terminal connecting portion  26  does not come into contact with a pad portion are regarded as a space portion  30  of the pad  3 A. 
         [0049]    In the embodiment shown in  FIGS. 8A and 8B , the second pad portion  21  functions as an electrical connection terminal of a substrate that conveys an electrical signal from a lead terminal to a circuit portion of the substrate. On the other hand, the first pad portion  20  and the third pad portion  23  are configured to reinforce the mechanical strength of the connection between the lead terminal connecting portion  26  and the substrate, and to adjust the characteristic impedance of the transmission line between the lead terminal  25  and the pad  3 A. 
         [0050]      FIG. 9  is a graph showing TDR waveforms indicating variations in the characteristic impedance of the transmission line between the lead terminal connecting portion  26  and the pad  3 A according to the third embodiment shown in  FIGS. 3A and 3B , depending on their connection arrangement. 
         [0051]    Specifically, the graph of  FIG. 9  shows TDR waveforms, each obtained by applying an electrical pulse signal with a predetermined rise time (same rise time as the electrical pulse signal used for obtaining the TDR waveforms shown in  FIGS. 5 and 7 ). It is noted that the horizontal axis of this graph represents the time, and the vertical axis of this graph represents the characteristic impedance value. This graph shows how the characteristic impedance of the transmission line between a lead terminal and a substrate pad may be adjusted by using the pad structure according to the third embodiment. 
         [0052]    In the graph of  FIG. 9 , L 3  denotes the length of the third pad portion  23  along the longitudinal direction of the lead terminal connecting portion  26 . The dotted line and the solid line shown in  FIG. 9  represent characteristic impedance measurements obtained using the pad  3 A according to the third embodiment. Specifically, the dotted line represents the characteristic impedance measurement obtained in a case where the length L 3  is relatively short; namely, when the ratio of the physical delay time (delay time created by the space portion  30  according to the length L 3 ) to the rise time is relatively large, and the solid line represents the characteristic impedance measurement obtained in a case where the length L 3  is relatively long; namely, when the ratio of the physical delay time to the rise time is relatively small. The one dotted line shown in  FIG. 9  represents the characteristic impedance measurement obtained using a pad structure in which L 3 =0 (i.e., the pad  200  according to the prior art). It is noted that the above-described characteristic impedance waveforms represented by the one-dotted line, the dotted line, and the solid line correspond to characteristic impedances measured using electric pulse signals with the same rise time. 
         [0053]    As can be appreciated from the graph of  FIG. 9 , a characteristic impedance mismatch may be reduced when the length L 3  is shorter; namely, when the ratio of the physical delay time to the rise time is larger. By using the pad structure according to the present embodiment, the characteristic impedance of the transmission line between the lead terminal and the pad may be more suitably adjusted compared to the case of using the pad structure according to the prior art. 
       Fourth Embodiment 
       [0054]      FIGS. 10A and 10B  are diagrams showing a connection arrangement between pads  3 A according to a fourth embodiment of the present invention and the connecting portions  26  of the connector lead terminals  25 . Specifically,  FIG. 10A  is a plan view of two pads  4 A connected to the lead terminal connecting portions  26 , and  FIG. 10B  is a corresponding side view showing regions  40  on which solder is applied upon soldering the lead terminal connecting portions  26  to the pads  4 A. 
         [0055]    The pad  4 A according to the fourth embodiment includes a rectangular/square first pad portion  20 , a rectangular/square second pad portion  21 , and a third pad portion  24  arranged between the first and second pad portions  20  and  21 . It is noted that the first through third pad portions  20 ,  21 , and  24  may be made of a metal with relatively high conductivity such as copper, for example. 
         [0056]    In the present embodiment, as is shown in  FIG. 10A , the first pad portion  20  and the second pad portion  21  are positioned at the ends of the lead terminal connecting portion  26 . The ends of the lead terminal connecting portion  26  are soldered to the first and second pad portions  20  and  21 . 
         [0057]    The third pad portion  24  of the pad  4 A according to the present embodiment is rectangular in shape and is arranged parallel to the longitudinal direction of the lead terminal connecting portion  26 . As is shown in  FIG. 10A , the lateral side edges of the third pad  24  are connected to the inner side edges of the first and second pad portions  20  and  21  (i.e., the third pad portion  24  is not separated from the first and second pad portions  20  and  21 ). Also, the rectangular third pad portion  24  is deviated in the transverse direction toward one long side of the lead terminal connecting portion  26 . Accordingly, a left-half side or a right-half side of a portion of the lead terminal connecting portion  26  positioned between the first and second pad portions  20  and  21  is not connected to the third pad portion  24 . It is noted that a portion corresponding to the location where the lead terminal connecting portion  26  does not come into contact with a pad portion is regarded as a space portion  30  of the pad  4 A. 
         [0058]    In the present embodiment, the second pad portion  21  functions as an electrical connection terminal of a substrate that conveys an electrical signal from a lead terminal to a circuit portion of the substrate. On the other hand, the first pad portion  20  and the third pad portion  24  are configured to reinforce the mechanical strength of the connection between the lead terminal connecting portion  26  and the substrate, and adjust the characteristic impedance of the transmission line between the lead terminal  25  and the pad  3 A. 
         [0059]      FIG. 11  is a graph showing TDR waveforms indicating variations in the characteristic impedance of the transmission line between the lead terminal connecting portion  26  and the pad  4 A according to the fourth embodiment depending on their connection arrangement. 
         [0060]    Specifically, the graph of  FIG. 11  shows TDR waveforms each obtained by applying an electrical pulse signal with a predetermined rise time (same rise time as the electrical pulse signal used for obtaining the TDR waveforms shown in  FIGS. 5 ,  7 , and  9 ). It is noted that the horizontal axis of this graph represents the time, and the vertical axis of this graph represents the characteristic impedance value. This graph shows how the characteristic impedance of a transmission line between a lead terminal and a substrate pad may be adjusted by using the pad structure according to the fourth embodiment. 
         [0061]    In the graph of  FIG. 11 , L 4  denotes the distance between the first pad portion  20  and the second pad portion  21  (i.e., the length of the space portion  30 ) of the pad  4 A. The dotted line and the solid line shown in  FIG. 11  represent characteristic impedance measurements obtained when using the pad  4 A according to the fourth embodiment. Specifically, the dotted line represents the characteristic impedance measurement obtained in a case where the length L 4  is relatively long; namely, when the ratio of the physical delay time (delay time created by the space portion  30  according to the length L 4 ) to the rise time is relatively large, and the solid line represents the characteristic impedance measurement obtained in a case where the length L 3  is relatively short; namely, when the ratio of the physical delay time to the rise time is relatively small. The one dotted line shown in  FIG. 11  represents the characteristic impedance measurement obtained using a pad structure in which L 4 =0 (i.e., the pad  200  according to the prior art). It is noted that the above-described characteristic impedance waveforms represented by the one-dotted line, the dotted line, and the solid line correspond to characteristic impedances measured using electric pulse signals with the same rise time. 
         [0062]    As can be appreciated from the graph of  FIG. 11 , a characteristic impedance mismatch may be reduced when the length L 4  is longer; namely, when the ratio of the physical delay time to the rise time is larger. By using the pad structure according to the present embodiment, the characteristic impedance of the transmission line between the lead terminal and the pad may be more suitably adjusted compared to the case of using the pad structure according to the prior art. 
         [0063]    According to the above-described embodiments of the present invention, a substrate pad structure may be provided that is configured to adjust characteristic impedance matching between a connector lead terminal of an electronic device and a pad while reinforcing the connection between a connecting portion of the lead terminal and the pad. 
         [0064]    Further, although the present invention is described above with respect to certain specific embodiments, the present invention is not limited to these embodiments and variations and modifications may be made without departing from the scope of the present invention. 
         [0065]    The present application is based on and claims the benefit of the earlier filing date of Japanese Patent Application No. 2007-316704 filed on Dec. 7, 2007, the entire contents of which are hereby incorporated by reference.