Abstract:
A device is provided for use with a signal, wherein the device includes a substrate, a first signal trace and a second signal trace. The first signal trace is disposed within the substrate at a first plane from the top surface by a distance d 1 . The second signal trace is disposed within the substrate at a second plane from the top surface by a distance d 2 , wherein d 2 &lt;d 1 &lt;t. The first signal trace includes a first portion, whereas the second signal trace includes a second portion. The first portion is parallel to the second portion. The first signal trace and the second signal trace form a differential pair. The first signal trace is operable to conduct a positive portion of the signal, whereas the second signal trace is operable to conduct a negative portion of the signal.

Description:
BACKGROUND 
       [0001]    The operating speeds of semiconductor devices have continued to increase and continuously push the limit of conventional packaging technology. 
         [0002]    To support the ever increasing operation speed of semiconductor devices, a differential pair is often used. A differential pair is a pair of conductors used for differential signaling. A differential pair reduces crosstalk and electromagnetic interference and can provide constant and/or known characteristic impedance. Furthermore, a differential pair enables impedance matching techniques used for high-speed signal transmission lines. Non-limiting examples of a differential pair include twisted-pair, microstrip and stripline. 
         [0003]    A differential pair reduces the total current between the two conductors of the differential pair, as Kirchhoff&#39;s predicts the total current as being zero through a cross section of the differential pair. The condition for emitting zero electromagnetic interference representing zero crosstalk is for zero total inductive and capacitive coupling through the cross section of the differential pair at the input and output of the differential pairs. However, in real world situations, the total coupling approaches zero but zero coupling is not achieved, resulting in crosstalk between the conductors of a differential pair. 
         [0004]    Additionally, crosstalk may occur between differential pairs as a result of second-order effects due to the finite impedance of the current source and impedance mismatch between the devices. For this case, the two conductors of the differential pair may be considered as a dipole with coupling on the order of 1/r 2  or 1/r 4 , where r is the distance between lines of differential pairs. To reduce crosstalk, the effects associated with second-order effects need to be reduced. 
         [0005]    The differential to differential pair crosstalk in electronic equipment limits its applicability to higher than 5 GHz types of Serializer/Deserializer (Serdes) designs. The crosstalk between differential pairs needs to be kept to a level of around −60 dB or less in order to minimize its impact on the channels ability to receive a greatly attenuated signal. Modern signal channels at high speed can introduce an attenuation of 40 dB or more. To properly receive such a signal in the presence of a fully duplexed communication stream, a cross-coupling immunity of 60 dB is needed for reliable signal reception. 
         [0006]    The coupling between differential pairs is due to an imbalance in the coupling from between conductors in the differential pair configuration. As an example of the imbalance, a 1 Volt signal may be traversing a leg of a differential pair and a 10 mV signal may be traversing a leg of a different differential pair. 
         [0007]    The crosstalk between differential pairs is known/deterministic and can be calculated. 
         [0008]    In order to determine the crosstalk between differential pairs, the mutual inductance is calculated. The mutual inductance by a filamentary circuit i on a filamentary (consisting of wires and rods) circuit is given by the double integral Neumann formula as give by Equation 1 below: 
         [0000]    
       
         
           
             
               
                 
                   
                     M 
                     ij 
                   
                   = 
                   
                     
                       
                         μ 
                         0 
                       
                       
                         4 
                          
                         π 
                       
                     
                      
                     
                       
                         ∮ 
                         Ci 
                       
                        
                       
                         
                           ∮ 
                           Cj 
                         
                          
                         
                           
                             
                                
                               
                                 s 
                                 i 
                               
                             
                             · 
                             
                                
                               
                                 s 
                                 j 
                               
                             
                           
                           
                              
                             
                               R 
                               ij 
                             
                              
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
         [0009]    Where μ 0  denotes the magnetic constant (4π×10 −7  H/m), C i  and C j  are the curves spanned by the wires, R ij  is the distance between two points. 
         [0010]    The currents associated with the positive and negative conductors of a differential have the same magnitude of current but traversing in opposing directions. 
         [0011]    Differential pair to differential pair crosstalk is a technology limiter that causes system failure in the form of signal detection error—increasing the system jitter and causing the signal detection eye pattern to close. An eye pattern, also known as an eye diagram, is a presentation (e.g. oscilloscope display) of a digital data signal as received at a receiver. Furthermore, the received signal is repetitively sampled and applied to the vertical input, while the data rate is used to trigger the horizontal sweep. 
         [0012]    Reduction of this crosstalk is possible using a technique known as orthogonal crossovers. The use of crossovers between differential pairs introduces significant discontinuities in the transmission lines that make up the differential pairs. A significant source of the discontinuities is a result of the vias that are used to move the pair from one side to the other. A via in an integrated circuit or printed circuit board is a means for transferring a signal from one signal layer to another signal layer. 
         [0013]    Alternate means used to reduce the reflections from the crossovers include designing the via structure in such a way as to match the characteristic impedance of the line. 
         [0014]      FIGS. 1A-C  illustrates an example conventional transmission line system  100 . 
         [0015]    Transmission line system  100  includes a differential pair  102  and a differential pair  104 . 
         [0016]    Differential pair  102  provides a transmission medium for transferring an electrical signal. Differential pair  104  provides a transmission medium for transferring an electrical signal. A differential pair is a par of conductors used for differential signaling. A differential pair reduces crosstalk and electromagnetic interference and can provide constant and/or known characteristic impedance. Furthermore, a differential pair enables impedance matching techniques used for high-speed signal transmission lines. Non-limiting examples of a differential pair include twisted-pair, microstrip and stripline. 
         [0017]    Differential pair  102  includes a positive signal trace  106  and a negative signal trace  108 . Differential pair  104  includes a positive signal trace  110  and a negative signal trace  112 . In some embodiments, the positive signal associated with positive signal trace  106  is equal and opposite to the negative signal associated with negative signal trace  108 . In other embodiments, the positive signal associated with positive signal trace  106  is different in magnitude to the negative signal associated with negative signal trace  108 . In theory, for embodiments with equal but opposite signals associated with positive signal trace  106  and negative signal trace  108 , the radiant electromagnetic field generated by the positive signal in positive signal trace  106  is cancelled by the equal and opposite radiant electromagnetic field generated by the negative signal in negative signal trace  108 . Similarly, for some embodiments, the positive signal in positive signal trace  110  is equal and opposite to the negative signal in negative signal trace  112 . In theory, radiant electromagnetic field generated by the positive signal in positive signal trace  110  is cancelled by the equal and opposite radiant electromagnetic field generated by the negative signal in negative signal trace  112 . 
         [0018]    The radiant effects of current through a differential pair may negatively affect the signals in an adjacent (or nearby) differential pair. In particular, a current traveling through one signal trace may affect the current traveling through another signal trace, wherein the magnitude is a function of distance. For example, current traveling through positive signal trace  106  will affect current traveling through positive signal trace  110 , and will also affect current traveling through negative signal trace  112 , but by a slightly less amount. Further, current traveling through negative signal trace  108  will affect current traveling through positive signal trace  110 , and will also affect current traveling through negative signal trace  112 , but by a slightly less amount. The overall effect is crosstalk interference, or crosstalk. 
         [0019]    The total effects of crosstalk may be determined by integrating the effect along a length of the crosstalk, in this instance a length  114  noted as L. To simplify the discussion, first consider the effects of positive signal trace  106  and negative signal trace  108  on positive signal trace  110 . Then, consider the effects of positive signal trace  106  and negative signal trace  108  on negative signal trace  112 . This will be further described with reference to  FIGS. 1B-C . 
         [0020]      FIG. 1B  takes into account the effects of currents of positive signal trace  106  and negative signal trace  108 , as felt by positive signal trace  110 . In this example, negative signal trace  108  and is separated from positive signal trace  110  by a distance  116  noted as r 1 , whereas positive signal trace  106  and is separated from positive signal trace  110  by a distance  118  noted as r 2 . The radiant effects of currents of positive signal trace  106 , as felt by positive signal trace  110 , are opposite to the radiant effects of currents of negative signal trace  108 , as felt by positive signal trace  110 . However, distance  116  is smaller than distance  118 . Accordingly, the radiant effects of currents of negative signal trace  108 , as felt by positive signal trace  110  are greater than the radiant effects of currents of positive signal trace  106 . 
         [0021]      FIG. 1C  takes into account the effects of currents of positive signal trace  106  and negative signal trace  108 , as felt by negative signal trace  112 . In this example, negative signal trace  108  and is separated from negative signal trace  112  by distance  118  (again noted as r 2 ), whereas positive signal trace  106  and is separated from negative signal trace  112  by a distance  120  noted as r 3 . The radiant effects of currents of positive signal trace  106 , as felt by negative signal trace  112 , are opposite to the radiant effects of currents of negative signal trace  108 , as felt by negative signal trace  112 . However, distance  118  is smaller than distance  120 . Accordingly, the radiant effects of currents of negative signal trace  108 , as felt by negative signal trace  112  are greater than the radiant effects of currents of positive signal trace  106  as felt by negative signal trace  112 . 
         [0022]    Comparing the situations illustrated in  FIGS. 1B-C , it is clear that the radiant effects of currents of positive signal trace  106  as felt by positive signal trace  110  (as shown in  FIG. 1B ) is equal and opposite to the radiant effects of currents of negative signal trace  108  as felt by negative signal trace  112  (as shown in  FIG. 1C ). Accordingly, the radiant effects effectively cancel. 
         [0023]    The remaining radiant effects are therefore drawn to the radiant effect of current of negative signal trace  108  as felt by positive signal trace  110  (as shown in  FIG. 1B ) in addition to the radiant effect of current of positive signal trace  106  as felt by negative signal trace  112  (as shown in  FIG. 1C ). Ideally, the current in positive signal trace  110  should be equal and opposite to the current in negative signal trace  112 . However, radiant effect of current of negative signal trace  108  alter the current in positive signal trace  110 , whereas the radiant effect of current of positive signal trace  106  will alter the negative signal trace  112 . For simplicity of explanation, let the “alteration” the current in positive signal trace  110  be an attenuation, and let of the “alteration” the current in positive signal trace  110  additionally be an attenuation. The attenuation of the signal in negative signal trace  112  is less than the attenuation of the signal in positive signal trace  110  because r 2 &lt;r 3 . The difference in interference creates a distortion in the signal if positive signal trace  110  and negative signal trace  112  are attenuated differently. Even though the interference may be minor, the interference calculation is integrated over the length of distance  114  or L as described by Equation 1. 
         [0024]    In order to reduce crosstalk, conventional systems cross or switch conductors of a differential pair in order to balance the coupling between the differential pairs which will be further discussed with reference to  FIG. 2 . 
         [0025]      FIG. 2  illustrates an example conventional transmission line system  200 , wherein one set of signal traces include a crossover. 
         [0026]    As shown in the figure, prior to a crossover point  206 , positive signal trace  110  is separated from negative signal trace  108  by distance  116  (indicated by r 1 ), whereas negative signal trace  112  is separated from positive signal trace  106  by distance  120  (indicated by r 3 ). After crossover point  206 , negative signal trace  112  is separated from negative signal trace  108  by distance  116  (indicated by r 1 ), whereas positive signal trace  110  is separated from positive signal trace  106  by distance  120  (indicated by r 3 ). For purposes of discussion, let crossover point  206  be in the middle of distance L. 
         [0027]    The radiant effects of the current of negative signal trace  108  as felt by positive signal trace  110  from the left of the figure to crossover point  206  is equal in magnitude and opposite in sign to the radiant effects of the current of negative signal trace  108  as felt by negative signal trace  112  crossover point  206  to the right of the figure. Accordingly, the radiant effects of the current from the left side of the figure to the right side of the figure cancel each other out. Similarly, the radiant effects of the current of positive signal trace  106  as felt by negative signal trace  112  from the left of the figure to crossover point  206  is equal in magnitude and opposite in sign to the radiant effects of current of positive signal trace  106  as felt by positive signal trace  110  crossover point  206  to the right of the figure. Accordingly, the radiant effects of the current from the left side of the figure to the right side of the figure cancel each other out. Canceling the radiant effects is the purpose or goal of performing the crossover in differential pairs. Conventionally, crossovers are formed by “tunneling” below one of the signal traces. This will be further described with additional reference to  FIGS. 3A-E . 
         [0028]      FIGS. 3A-E  illustrate cross-sectional views of the example conventional transmission line system of  FIG. 2 . 
         [0029]      FIG. 3A  is a cross-sectional view of conventional transmission line system  200  at a cross section  202  as illustrated in  FIG. 2 . 
         [0030]    As shown in  FIG. 3A , conventional transmission line system  200  includes a dielectric  306  surrounding positive signal trace  106 , negative signal trace  108 , positive signal trace  110  and negative signal trace  112 . Dielectric  306  includes a top surface  302  and a bottom surface  304 . 
         [0031]    Negative signal trace  108  is located to the right of positive signal trace  106 . Positive signal trace  110  is located to the right of negative signal trace  108 . Negative signal trace  112  is located to the right of positive signal trace  110 . Signal traces  106 ,  108 ,  110  and  112  are located in a horizontal plane  308 . 
         [0032]    At some point, positive signal trace  110  needs to switch places with negative signal trace  112 . As the positive signal trace  110  cannot contact negative signal trace  112 , one of the signal traces needs to transition to another plane. This will be described with reference to  FIG. 3B . 
         [0033]      FIG. 3B  is a cross-sectional view of conventional transmission line system  200  at a cross section  204  as illustrated in  FIG. 2 . 
         [0034]    As shown in  FIG. 38 , a via  310  enables negative signal trace  112  to transition from horizontal plane  308  to a horizontal plane  312 . Once at horizontal plane  312 , negative signal trace  112  and positive signal trace  110  may switch places. This will be described with reference to  FIG. 3C . 
         [0035]      FIG. 3C  is a cross-sectional view of conventional transmission line system  200  at crossover point  206  as illustrated in  FIG. 2 . 
         [0036]    From cross section  204  to a cross section  208 , positive signal trace  110  is located in a different plane than that of negative signal trace  112 . As shown in  FIG. 3C , at the point of crossing over at crossover point  206 , positive signal trace  110  is located above negative signal trace  112  and the signal traces are vertically located between the positions as described with reference to  FIGS. 3A-B . Positive signal trace  110  is horizontally located in horizontal plane  308  and negative signal trace  112  is horizontally located in horizontal plane  312 . 
         [0037]    The signal traces eventually transition to their respective planes. This will be described with reference to  FIG. 3D . 
         [0038]      FIG. 3D  is a cross-sectional view of conventional transmission line system  200  at cross section  208  as illustrated in  FIG. 2 . 
         [0039]    As shown in  FIG. 3D , a via  314  enables negative signal trace  112  to transition from horizontal plane  312  back to horizontal plane  308 . Once at horizontal plane  308 , negative signal trace  112  and positive signal trace  110  may continue. This will be described with reference to  FIG. 3E . 
         [0040]      FIG. 3E  is a cross-sectional view of conventional transmission line system  200  at a cross section  210  as illustrated in  FIG. 2 . 
         [0041]    As shown in  FIG. 3E , negative signal trace  108  is located to the right of positive signal trace  106 . Positive signal trace  110  is located to the right of negative signal trace  108 . Negative signal trace  112  is located to the right of positive signal trace  110 . Signal traces  106 ,  108 ,  110  and  112  are located in horizontal plane  308 . The size, characteristic impedance and geometry of vias negatively impact crosstalk between differential pairs in an attempt to reduce crosstalk. 
         [0042]    Crosstalk reduction is attempted by crossing positive signal trace  110  and negative signal trace  112 . However, due to the size, structure and characteristic impedance of vias, transitioning signal traces between layers using vias generates its own distortion, which may typically be significantly larger than that as created by crosstalk. The net result of crossing signal traces using vias may therefore achieve little signal improvement. 
         [0043]    What is needed is a system and method for decreasing crosstalk associated with differential pairs. 
       BRIEF SUMMARY 
       [0044]    The present invention provides a system and method for decreasing crosstalk associated with differential pairs. 
         [0045]    The present invention provides a device for use with a signal, wherein the device includes a substrate, a first signal trace and a second signal trace. The first signal trace is disposed within the substrate at a first plane from the top surface by a distance d 1 . The second signal trace is disposed within the substrate at a second plane from the top surface by a distance d 2 , wherein d 2 &lt;d 1 &lt;t. The first signal trace includes a first portion, whereas the second signal trace includes a second portion. The first portion is parallel to the second portion. The first signal trace and the second signal trace form a differential pair. The first signal trace is operable to conduct a positive portion of the signal, whereas the second signal trace is operable to conduct a negative portion of the signal. 
         [0046]    Additional advantages and novel features of the invention are set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims. 
     
    
     
       BRIEF SUMMARY OF THE DRAWINGS 
         [0047]    The accompanying drawings, which are incorporated in and form a part of the specification, illustrate an exemplary embodiment of the present invention and, together with the description, serve to explain the principles of the invention. In the drawings: 
           [0048]      FIGS. 1A-C  illustrates an example conventional transmission line system  100 ; 
           [0049]      FIG. 2  illustrates an example conventional transmission line system  200 , wherein one set of signal traces include a crossover; 
           [0050]      FIGS. 3A-E  illustrate a cross-sectional view of the example conventional transmission line system of  FIG. 2 ; 
           [0051]      FIG. 4  illustrates an example transmission line system, in accordance with an aspect of the present invention; 
           [0052]      FIGS. 5A-D  illustrate cross sections for the example transmission line system as described with reference to  FIG. 4 , in accordance with an aspect of the present invention; 
           [0053]      FIGS. 6A-K  illustrate a method for fabrication of an example transmission line system  600 , in accordance with an aspect of the present invention; and 
           [0054]      FIG. 7  illustrates a method for fabrication of an example transmission line system as described with reference to  FIG. 4-6 , in accordance with an aspect of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0055]    In accordance with aspects of the present invention, a system and method for reducing crosstalk associated with differential pairs via crossing of signal traces is presented. 
         [0056]    Example aspects of the present invention will now be described in greater detail with reference to  FIGS. 4-7 . 
         [0057]      FIG. 4  illustrates an example transmission line system  400 , in accordance with an aspect of the present invention. 
         [0058]    Transmission line system  400  includes a differential pair  402  and a differential pair  404 . 
         [0059]    Differential pair  402  provides a transmission medium for transferring an electrical signal. Differential pair  404  provides a transmission medium for transferring an electrical signal. 
         [0060]    Differential pair  402  includes a signal trace  406  and a signal trace  408 . Differential pair  404  includes a signal trace  410  and a signal trace  412 . 
         [0061]    Signal trace  406  and signal trace  408  provide transference of an electrical signal with the current flowing in signal trace  406  being in the opposite direction of signal trace  408 . Signal trace  410  and signal trace  412  provide transference of an electrical signal with the current flowing in signal trace  410  being in the opposite direction of signal trace  412 . 
         [0062]    Signal trace  410  and signal trace  412  swap paths at a cross section  416  with the signal traces as located at a cross section  414  being located in opposite paths as at a cross section  418 . 
         [0063]    Signal trace  406  and signal trace  408  swap paths at a cross section  420  with the signal traces as located at cross section  418  being located in opposite paths as at a cross section  422 . 
         [0064]    Switching signal trace  406  and signal trace  408  and switching signal trace  410  and signal trace  412  balances the mutual coupling between differential pair  402  and  404  such that the total current through the cross section of the differential pairs is reduced thereby reducing crosstalk between the differential pairs. 
         [0065]      FIGS. 5A-D  illustrates cross-sectional views of example transmission line system  400  of  FIG. 4 . 
         [0066]      FIG. 5A  represents cross section  414  along line A-A′ as described with reference to  FIG. 4 . 
         [0067]    Cross section  414  includes differential pair  402 , differential pair  404 , signal trace  406 , signal trace  408 , signal trace  410 , signal trace  412 , a top surface  502 , a signal plane  504 , a signal plane  506  and a bottom surface  507 . 
         [0068]    Top surface  502  is located on top and above signal plane  504 . Bottom surface  507  is located on the bottom. Top surface  502  is separated from bottom surface  507  by a distance  508  also noted as t. Signal plane  506  is located above bottom surface  507  and is located below top surface  502  by a distance  509  also noted as d 1 . Signal plane  504  is located above signal plane  506  and is located below top surface  502  by a distance  510  also noted as Signal plane  506  is located above bottom surface  507  and is located below top surface  502  by a distance  510  also noted as d 2 . Furthermore, the distances satisfy d 2 &lt;d 1 &lt;t. 
         [0069]    In some embodiments, top surface  502  and bottom surface  507  may provide an electrical path to ground. Signal plane  504  and  506  provide an avenue for traversing signal traces. 
         [0070]    Signal trace  406  is located in signal plane  504  at a location  512  with respect to an x-axis  511 . Signal trace  408  is located in signal plane  506  at a location  514  with respect to x-axis  511 . Signal trace  410  is located in signal plane  504  at a location  516  with respect to x-axis  511 . Signal trace  412  is located in signal plane  506  at a location  518  with respect to x-axis  511 . 
         [0071]      FIG. 5B  represents cross section  416  along line B-B′ as described with reference to  FIG. 4 . 
         [0072]    Signal traces  406  and  408  are located at the same x-axis location and in the same signal plane as described with reference to  FIG. 5A . 
         [0073]    For cross section  416 , signal traces  410  and  412  are located at a location  520  with respect to x-axis  511 . Furthermore, signal traces  410  and  412  are located in the same signal planes as described with reference to  FIG. 5A . The x-axis location  520  is located between location  516  and location  518 . 
         [0074]    Signal trace  410  overlaps signal trace  412 . 
         [0075]      FIG. 5C  represents cross section  418  along line C-C′ as described with reference to  FIG. 4 . 
         [0076]    For cross section  418 , signal traces  406  and  408  are located at the same x-axis location and in the same signal plane as described with reference to  FIGS. 5A-B . 
         [0077]    Signal trace  410  is located at location  518  and signal trace  412  is located at location  516 . Signal traces  410  and  412  are located in the same signal planes as described with reference to  FIGS. 5A-B . 
         [0078]    In  FIG. 5C , signal trace  410  and signal trace  412  have swapped horizontal locations as compared to  FIG. 5A . Swapping signal traces enables the balancing mutual coupling between differential pair  402  and differential pair  404  which reduces the total current through the cross section of the differential pairs which reduces the crosstalk between the differential pairs. 
         [0079]      FIG. 5D  represents cross section  422  along line D-D′ as described with reference to  FIG. 4 . 
         [0080]    For cross section  420 , signal traces  410  and  412  are located at the same location and as described with reference to  FIG. 5C . Signal traces  410  and  412  are located in the same signal planes as described with reference to  FIGS. 5A-C . 
         [0081]    Signal trace  406  is located at location  514  and signal trace  408  is located at location  512  and is opposite as described with reference to  FIGS. 5A-C . Signal traces  406  and  408  are located in the same signal planes as described with reference to  FIGS. 5A-C . Swapping signal traces enables the balancing mutual coupling between differential pair  402  and differential pair  404  which reduces the total current through the cross section of the differential pairs which reduces the crosstalk between the differential pairs. 
         [0082]    A process for fabricating the example transmission line system described with reference to  FIGS. 4-5  will now be presented with additional reference to  FIGS. 6-7 . 
         [0083]      FIGS. 6A-J  illustrate a method for fabrication of an example transmission line system  600 , in accordance with an aspect of the present invention.  FIG. 7  illustrates a method  700  for fabrication of an example transmission line system as described with reference to  FIG. 4-6 , in accordance with an aspect of the present invention. 
         [0084]    The fabrication method as described in  FIGS. 6A-J  generates a transmission line system which reduces crosstalk between differential pairs by crossing of signal traces and which does not use vias for transitioning between layers, as vias negatively affect crosstalk between differential pairs. 
         [0085]    In  FIG. 6A , a substrate  602  is provided. As shown in  FIG. 7 , method  700  starts (S 702 ) by affixing a first trace layer to a substrate layer (S 704 ). For example, returning to  FIG. 6B  a trace layer  604  is applied on top of substrate  602 . Trace layer  604  may be any known electrically conductive material, non-limiting examples of which include Au, Ag and Cu. 
         [0086]    Returning to  FIG. 7 , a first resistance mask is added to the first dielectric layer (S 706 ). For example, as shown in  FIG. 6C , a resistance mask  606  and a resistance mask  608  are applied on top of trace layer  604 . A non-limiting example for resistance masks  606  and  608  is photo-resist or chemical-resist mask. 
         [0087]    Returning to  FIG. 7 , etching is applied to first trace layer leaving material beneath first resistance mask (S 708 ). For example, as shown in  FIG. 6D , the configuration described with reference to  FIG. 6C  has been etched, wherein portions of trace layer  604  not covered by resistance masks  606  and  608  is etched away. Furthermore, etching process leaves a signal trace  610  and a signal trace  612 . 
         [0088]    Returning to  FIG. 7 , first resistance mask is removed (S 709 ). For example, as shown in  FIG. 6E , resistance masks  606  and  608  (as shown in  FIG. 6D ) are removed, leaving signal traces  610  and  612 . 
         [0089]    Returning to  FIG. 7 , a second dielectric layer is applied (S 710 ). For example, as shown in  FIG. 6F , a dielectric  614  has been placed on top of substrate  602 , signal trace  610  and signal trace  612 . Dielectric  614  may be fabricated of a dielectric material which is the same material or is a similar material as substrate  602 . 
         [0090]    Returning to  FIG. 7 , a second trace layer is applied (S 711 ). In  FIG. 6G , the process described with reference to  FIGS. 6B-D  is repeated. A trace layer  616  is disposed on dielectric  614 . Trace layer  616  is fabricated of an electrically conductive material. For example, returning to  FIG. 6F , trace layer  616  is applied on top of dielectric  614 . 
         [0091]    Returning to  FIG. 7 , a second resistance mask is applied to second dielectric layer (S 712 ). For example, as shown in  FIG. 6G , a resistance mask  618  and a resistance mask  620  are disposed on trace layer  616 . 
         [0092]    Returning to  FIG. 7 , an etching process is applied to second trace layer leaving traces located beneath resistance mask (S 714 ). For example, as shown in  FIG. 6H , the configuration described with reference to  FIG. 6G  has been etched such that portions of trace layer  616  not covered by resistance masks  618  and  620  are removed. Furthermore, etching process leaves a signal trace  622  and a signal trace  624 . 
         [0093]    Returning to  FIG. 7 , second resistance mask is removed (S 715 ). For example, as shown in  FIG. 6I , the configuration as described with reference to  FIG. 6H  is processed so as to remove resistance masks  618  and  620 , leaving signal traces  622  and  624 . 
         [0094]    Returning to  FIG. 7 , a third dielectric layer is applied (S 716 ). For example, as shown in  FIG. 6J , a dielectric  626  is disposed on signal trace  622 , signal trace  624  and dielectric  614 . Dielectric  626  may be fabricated of a dielectric material and may be the same or similar as substrate  602  and dielectric  614   
         [0095]    Returning to  FIG. 7 , an annealing process is applied (S 718 ). For example, as shown in  FIG. 6K , an annealing process is applied to the configuration as described with reference to  FIG. 6J . The annealing process forms a layer  628  which includes the combination of dielectric  626 , dielectric  614  and substrate  602  into a single layer. Signal traces  406 ,  408 ,  410  and  412  are disposed within layer  628 . 
         [0096]    At this point method  700  is complete (S 720 ). 
         [0097]    A signal trace configuration in accordance with the present invention allows for low insertion loss in signal traces for performing a crossover in a differential pair. Furthermore, the signal trace configuration increases performance as it reduces the use of vias for performing crossovers, as vias generate distortion of signals due to the size, structure and characteristic impedance associated with vias. Furthermore, the signal trace configuration provides crosstalk reduction up to the maximum operating frequency of the transmission line. Furthermore, the signal trace configuration enables multiple crossover types to coexist without requiring a significant amount of real estate as is the case with conventional technology which uses a multiplicity of vias for performing the crossovers. 
         [0098]    The use of vias in conventional technology is complicated and performed by transitioning a signal from one plane to another plane, swapping the signal traces while in different planes, and then transitioning the signal back to the original plane using a via. Furthermore, issues associated with low insertion loss crossovers for reducing crosstalk due to discontinuities introduced by vias is improved by performing the crossovers on alternate layers thereby reducing the use of vias for performing the crossovers. Furthermore, the signal trace configuration reduces crosstalk and as a result increases system performance. Furthermore, since devices do not use vias for switching signals, as in the case of conventional technology, fabrication of devices for swapping signal traces is easier than as compared to conventional configurations which use vias for swapping signals. 
         [0099]    The foregoing description of various preferred embodiments of the invention have been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. The example embodiments, as described above, were chosen and described in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto.