Patent Publication Number: US-6906910-B1

Title: Structures for implementing integrated conductor and capacitor in SMD packaging

Description:
FIELD OF THE INVENTION 
   The present invention relates generally to the electronic design automation field, and more particularly, relates to a structure for implementing an integrated conductor and capacitor in surface mounted device (SMD) packaging. 
   DESCRIPTION OF THE RELATED ART 
   A serious electromagnetic emission occurs when a signal or conductor line switches references on a board by crossing split planes. This often occurs in a complex layout when a conductor crosses certain voltage domains, for example, 5V to 3.5V. The best solution is to avoid crossing a, split and creating the radiating source. But, due to cost constraints, the number of layers, or wireability the choice may be made to cross the split. 
   A solution that is commonly implemented is to place a capacitor near the split thus providing a low frequency return path for the signal. Another less popular solution is to place a decoupling capacitor from the referenced plane and ground on both sides of the split, for example, from 3.3V to Ground, and from 5V and Ground. The problem with these solutions is that the return current does not take a well-behaved return path back to the source causing radiation and reflections. 
   A need exists for a mechanism to provide a well-behaved return current path in surface mounted device (SMD) packaging having a signal or conductor that switches references on a board by crossing split planes. 
   SUMMARY OF THE INVENTION 
   Important aspects of the present invention are to provide a structure for implementing an integrated conductor and capacitor in surface mounted device (SMD) packaging. Other important aspects of the present invention are to provide such structure for implementing an integrated conductor and capacitor in surface mounted device (SMD) packaging substantially without negative effect and that overcome some of the disadvantages of prior art arrangements. 
   In brief, structures are provided for implementing an integrated conductor and capacitor in a surface mounted device (SMD) package. A first pair and a second pair of contacts contained within the SMD package respectively are provided in mating engagement with a first pair and a second pair of corresponding SMD package contacts. A conductor extends between the first pair of contacts, contained within the SMD package. A capacitor is defined between the second pair of contacts, contained within the SMD package. 
   In accordance with features of the invention, an additional one or pair of integral capacitors optionally is provided for providing additional capacitance to ground to decouple common mode noise from the power planes. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention together with the above and other objects and advantages may best be understood from the following detailed description of the preferred embodiments of the invention illustrated in the drawings, wherein: 
       FIG. 1  is diagram illustrating a side view of an exemplary integrated conductor and capacitor structure for use in surface mounted device (SMD) packaging in accordance with the preferred embodiment; 
       FIG. 2  is a diagram illustrating a top view of the exemplary integrated conductor and capacitor structure of  FIG. 1  in accordance with the preferred embodiment; 
       FIG. 3  is a diagram illustrating an outside of an exemplary surface mounted device (SMD) packaging receiving the exemplary integrated conductor and capacitor structure of  FIG. 1  in accordance with the preferred embodiment; 
       FIG. 4  is a diagram illustrating a side view of another exemplary integrated conductor and capacitor structure for use in surface mounted device (SMD) packaging in accordance with the preferred embodiment; 
       FIG. 5  is a diagram illustrating an exemplary outside surface mounted device (SMD) packaging receiving the exemplary integrated conductor and capacitor structure of  FIG. 4  in accordance with the preferred embodiment; and 
       FIG. 6  is a diagram illustrating the exemplary surface mounted device (SMD) packaging of  FIG. 3  receiving the exemplary integrated conductor and capacitor structure of  FIG. 1  for use with an exemplary portion of a circuit board in accordance with the preferred embodiment. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Having reference now to the drawings, in  FIGS. 1 , and  2 , there is shown an exemplary integrated conductor and capacitor structure generally designated by the reference character  100  for use in surface mounted device (SMD) packaging in accordance with one preferred embodiment. 
   The exemplary integrated conductor and capacitor structure  100  advantageously can improve or shorten the path length by integrating a cross of the split with a conductor generally designated by the reference character  102  integrated with a coupling capacitor generally designated by the reference character  104 . 
   In accordance with features of the preferred embodiment, the exemplary integrated conductor and capacitor structure  100  allows a common wiring technique in board layout to be used (i.e., crossing splits). This can be done by minimizing the return loop area and allowing current flow to return to the source across a well-controlled path. 
   In accordance with features of the preferred embodiment, simulations have shown that placing the signal conductor  102  and return path through the capacitor  104  proves a better response that what is presently available on the market. The integrated surface mounted device (SMD) conductor and capacitor structure  100  forces the placement of a coupling capacitor with the cross of a split in one discrete component. Simulations have shown that once the normal signal reference is compromised then a return current is best returned by use of a capacitance between the new reference allowing the return current to return through a minimal loop area. Although not required, the internal construction of the exemplary integrated conductor and capacitor structure  100  can be set to match the characteristic impedance of the conductor within the board structure, for example, 50 ohms. Even a mismatch shows improvement over known conventional arrangements. A conventional SMD package must be altered to allow additional board contacts, for example, two or four additional board contacts to formulate the appropriate structure. 
   As shown in  FIGS. 1 and 2 , the signal conductor  102  includes an elongated, generally U-shaped member  110  extending between a pair of outer contact pads  112 . The capacitor  104  includes a pair of posts  114 ,  116  respectively extending from a respective one of a pair of inner contact pads  118 . The respective posts  114 ,  116  of the capacitor  104  includes a respective pair of spaced apart parallel arms or plates  120 ,  122 ; and  124 ,  126 . The respective spaced apart parallel plates  120 ,  122  carried by post  114  respectively extend between and below the spaced apart parallel plates  124 ,  126  carried by post  116 . 
   The integrated surface mounted device (SMD) conductor and capacitor structure  100  can be most economically implemented with a single dielectric material, such as NPO, X7R, X5R, C0G, YTV, and the like, surrounding all internal structures including the signal conductor  102  and capacitor  104 . The dielectric material is a poor conductor of electricity, while an efficient supporter of electrostatic fields that can store energy and particularly useful in capacitor  104 . The use of a single dielectric material is the same practice used today by manufacturers of surface mount ceramic capacitors. This use of a single dielectric material within the integrated surface mounted device (SMD) conductor and capacitor structure  100  is not only cost effective, it is acceptable for most circuit applications. 
   Alternatively, to provide strict impedance control, for example, for higher speed circuits, the signal conductor  102  of the integrated surface mounted device (SMD) conductor and capacitor structure  100  is surrounded with a dielectric material having similar properties to FR4, to maintain the proper signal impedance through the part. The capacitor  104  of the integrated surface mounted device (SMD) conductor and capacitor structure  100  would be surrounded by a typical dielectric material, such as NPO, X7R, X5R, C0G, YTV, and the like, to create a hybrid component  100  made up of two types of dielectric materials. 
   Various conventional materials can be used to form the capacitor  104  of the integrated surface mounted device (SMD) conductor and capacitor structure  100 . For example, a ceramic material, such as fired ceramic powders with various metallic titanates, plus modifier and shifters, or a glass frit material can be used to form the parallel plates  120 ,  122 ; and  124 ,  126 . Electrodes formed of Palladium and silver or nickel can be used and capacitor terminations formed of silver and glass frit, copper and glass frit, nickel or tin can be used to form the capacitor  104 . 
   Referring now to  FIG. 3 , there is shown an outside of an exemplary surface mounted device (SMD) packaging generally designated by the reference character  300  receiving the exemplary integrated conductor and capacitor structure  100  in accordance with the preferred embodiment. SMD package  300  includes a generally rectangular enclosure  302 , a pair of outer contact pads  304 , and a pair of inner contact pads  306 .  FIGS. 1 and 2  show the internal configuration including the four pad contacts  112 ,  118  for mating engagement with respective pairs of pad contacts  304 ,  306  of the preferred SMD package  300 , as shown in FIG.  3 . 
   Referring now to  FIGS. 4 and 5 , there is shown another exemplary integrated conductor and capacitor structure in accordance with the preferred embodiment generally designated by the reference character  400  in FIG.  4  and an exemplary outside surface mounted device (SMD) packaging generally designated by the reference character  500  or SMD package  500  receiving the exemplary integrated conductor and capacitor structure  400  is shown in FIG.  5 . 
   As compared to the structure  100 , the integrated conductor and capacitor structure  400  similarly includes a signal conductor generally designated by  402  and return path through a capacitor generally designated by  404 . 
   The integrated conductor and capacitor structure  400  of the preferred embodiment includes an additional pair of integral capacitors generally designated by  406 ,  408  providing additional capacitance to ground that is further added into the first configuration structure  100 , for example, to decouple common mode noise from the power planes, such as back to logic ground. 
   As shown in  FIG. 4 , the signal conductor  402  includes an elongated, generally U-shaped member  410  extending between a pair of outer contact pads  412 . The capacitor  404  includes a pair of posts  414 ,  416  respectively extending from a respective one of a pair of inner contact pads  418 . The respective posts  414 ,  416  of the capacitor  404  includes a respective pair of spaced apart parallel arms or plates  420 ,  422 ; and  424 ,  426 . The respective spaced apart parallel plates  420 ,  422  carried by post  414  respectively extend between and below the spaced apart parallel plates  424 ,  426  carried by post  416 . 
   A pair of spaced apart parallel plates  428 ,  430  carried by post  414  below the upper parallel plates  420 ,  422  is provided to form the decoupling capacitor  406 . A L-shaped member  432  has a portion extending between the spaced apart parallel plates  428 ,  430  form the decoupling capacitor  406 . 
   Similarly, a pair of spaced apart parallel plates  434 ,  436  carried by post  416  below the upper parallel plates  424 ,  426  is provided to form the decoupling capacitor  408 . A L-shaped member  438  has a portion extending between the spaced apart parallel plates  434 ,  436  form the decoupling capacitor  408 . 
   A respective one of a pair of elongated pad contacts  440  respectively supports the respective L-shaped member  432 ,  438  of the decoupling capacitor  406 ,  408 . SMD package  500  includes a generally rectangular enclosure  502 , a pair of outer contact pads  504 , and a first and second pair of inner contact pads  506 , and  508 .  FIG. 4  shows the internal configuration including the six pad contacts  412 ,  418 ,  440  for mating engagement with respective pairs of pad contacts  504 ,  506 ,  508  of the SMD package  500 , as shown in FIG.  5 . 
   The decoupling capacitors  406 ,  408  of the integrated conductor and capacitor structure  400  are formed of selected materials as described above used to form the capacitor  104 . The decoupling capacitors  406 ,  408  of the integrated conductor and capacitor structure  400  are surrounded by a typical dielectric material, such as NPO, X7R, X5R, C0G, YTV, and the like, to create a unitary dielectric material component  400  or a hybrid component  400  made up of two types of dielectric materials with the conductor  402  surrounded by a different type of dielectric material, such as FR4. 
     FIG. 6  illustrates the exemplary SMD package  300  of  FIG. 3  that receives the exemplary integrated conductor and capacitor structure  100  in use with an exemplary portion of a circuit board generally designated by the reference character  600  in accordance with the preferred embodiment. Circuit board  600  includes a ground plane  602 , a voltage plane V 2   604 , and a voltage plane V 1   606 . An incoming signal line  608  and an outgoing signal line  610  are respectively connected to the pair of outer contact pads  304  of the SMD package  300  and the signal conductor  102  by the pair of outer contact pads  112  of the integrated conductor and capacitor structure  100 . As shown, a respective via  612 ,  614  connects a respective inner contact pad  306  to the voltage plane V 2   604 , and the voltage plane V 1   606 . The voltage, plane V 2   604 , and the voltage plane V 1   606  are connected to the capacitor  104  by the second pair of contacts pads  118  that are provided for mating engagement with to the corresponding inner contact pad  306  of the SMD package  300 . 
   It should be understood that the present invention is not limited to the illustrated arrangement of the contact pads  112 ,  118  of the integrated conductor and capacitor structure  100  and corresponding mating contact pads  304 ,  306  of the SMD package  300 . For example, various different shapes and sizes could be provided for the contact pads  112 ,  118  and the corresponding mating contact pads  304 ,  306 . 
   While the present invention has been described with reference to the details of the embodiments of the invention shown in the drawing, these details are not intended to limit the scope of the invention as claimed in the appended claims.