Patent Publication Number: US-7709754-B2

Title: Current sensor

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   Not Applicable. 
   STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH 
   Not Applicable. 
   FIELD OF THE INVENTION 
   This invention relates generally to electrical current sensors, and more particularly to a miniaturized current sensor in an integrated circuit package. 
   BACKGROUND OF THE INVENTION 
   As is known in the art, one type of conventional current sensor uses a magnetic field transducer (for example a Hall effect or magnetoresistive transducer) in proximity to a current conductor. The magnetic field transducer generates an output signal having a magnitude proportional to the magnetic field induced by a current that flows through the current conductor. 
   Some typical Hall effect current sensors include a gapped toroid magnetic flux concentrator, with the Hall effect element positioned in the toroid gap. The Hall effect device and toroid are assembled into a housing, which is mountable on a printed circuit board. In use, a separate current conductor, such as a wire, is passed through the center of the toroid. Such devices tend to be undesirably large, both in terms of height and circuit board area. 
   Other Hall effect current sensors include a Hall effect element mounted on a dielectric material, for example a circuit board. One such current sensor is described in a European Patent Application No. EP0867725. Still other Hall effect current sensors include a Hall effect element mounted on a substrate, for example a silicon substrate as described in a European Patent Application No. EP1111693. 
   Various parameters characterize the performance of current sensors, including sensitivity and linearity. Sensitivity is related to the magnitude of a change in output voltage from the Hall effect transducer in response to a sensed current. Linearity is related to the degree to which the output voltage from the Hall effect transducer varies in direct proportion to the sensed current. 
   The sensitivity of a current sensor is related to a variety of factors. One important factor is the flux concentration of the magnetic field generated in the vicinity of the current conductor and sensed by the Hall effect element. For this reason, some current sensors use a flux concentrator. Another important factor, in particular for a current sensor in which a flux concentrator is not used, is the physical separation between the Hall effect element and the current conductor. 
   SUMMARY OF THE INVENTION 
   In accordance with the present invention, an integrated circuit current sensor includes a lead frame having at least two leads coupled to provide a current conductor portion and a substrate having a first surface in which is disposed one or more magnetic field transducers, with the first surface being proximate the current conductor portion and a second surface distal from the current conductor portion. In one particular embodiment, the substrate is disposed having the first surface of the substrate above the current conductor portion and the second surface of the substrate above the first surface. In this particular embodiment, the substrate is oriented upside-down in the integrated circuit relative to a conventional orientation. 
   With this particular arrangement, a current sensor is provided with one or more magnetic field transducers positioned in close proximity to the current conductor portion, resulting in improved sensitivity. Further, the current sensor is provided in a small integrated circuit package. 
   In accordance with another aspect of the present invention, a method of manufacturing an integrated circuit includes providing a lead frame having a plurality of leads of which at least two are coupled together to form a current conductor portion and etching the current conductor portion to provide the current conductor portion with a cross section having a predetermined shape. In one particular embodiment, the predetermined shape is a T-shape. In another embodiment, the predetermined shape is a rectangular shape having a minimum dimension less than the thickness of the majority of the lead frame. 
   With this particular arrangement, a current conductor portion is provided for which the flux density is more concentrated above a surface of the current conductor portion. Therefore, a magnetic field transducer mounted near the current conductor portion experiences an increased magnetic field, resulting in a current sensor having improved sensitivity. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing features of the invention, as well as the invention itself may be more fully understood from the following detailed description of the drawings, in which: 
       FIG. 1  is an isometric view of a current sensor in accordance with the present invention; 
       FIG. 2  is a graph showing a relationship between position across a Hall effect element of the current sensor of  FIG. 1  and magnetic field; 
       FIG. 3  is an isometric view of another embodiment of a current sensor in accordance with the present invention; 
       FIG. 4  is a schematic of a circuit forming part of the current sensor of  FIG. 3 ; 
       FIG. 5  is an isometric view of yet another embodiment of a current sensor in accordance with the present invention; 
       FIG. 6  is an isometric view of still another embodiment of a current sensor in accordance with the present invention; 
       FIG. 6A  is an isometric view of still another embodiment of a current sensor in accordance with the present invention; 
       FIG. 7  is an isometric view of still another embodiment of a current sensor in accordance with the present invention; 
       FIG. 8  is a further isometric view of the current sensor of  FIG. 7 ; 
       FIG. 9  is an isometric view of an alternate lead frame having a thinner current conductor portion according to a further aspect of the invention; and 
       FIG. 9A  is a cross-sectional view of an alternate embodiment of the current conductor portion of  FIG. 9 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring to  FIG. 1 , an exemplary current sensor  10  in accordance with the present invention includes a lead frame  12  having a plurality of leads  12   a - 12   h . The leads  12   a  and  12   b  are coupled to the leads  12   c  and  12   d  to form a current path, or current conductor with a narrow portion  14  having a width w 1 . The current sensor  10  also includes a substrate  16  having a first surface  16   a  and a second, opposing surface  16   b . The substrate  16  has a magnetic field transducer  18  which, in some embodiments, can be a Hall effect element  18 , diffused into the first surface  16   a , or otherwise disposed on the first surface  16   a . The substrate  16  can be comprised of a semiconductor material, e.g., silicon, or, in an alternate embodiment) the substrate  16  can be comprised of an insulating material. 
   The substrate  16  is disposed above the lead frame  12  so that the first surface  16   a  is proximate to the current conductor portion  14  and the second surface  16   b  is distal from the current conductor portion  14  and more specifically, so that the Hall effect element  18  is in close proximity to the current conductor portion  14 . In the illustrated embodiment, the substrate  16  has an orientation that is upside down (i.e., the first surface  16   a  is directed downward) relative to a conventional orientation with which a substrate is mounted in an integrated circuit package. 
   The substrate  16  has bonding pads  20   a - 20   c  on the first surface  16   a , to which bond wires  22   a - 22   c  are coupled. The bond wires are further coupled to the leads  12   e ,  12   f ,  12   h  of the lead frame  12 . 
   An insulator  24  separates the substrate  16  from the lead frame  12 . The insulator  24  can be provided in a variety of ways. For example, in one embodiment, a first portion of the insulator  24  includes a four μm thick layer of a BCB resin material deposited directly on the first surface  16   a  of the substrate  16 . A second portion of the insulator  24  includes a layer of Staychip™ NUF-2071 E underfill material (Cookson Electronics Equipment, New Jersey) deposited on the leadframe  12 . Such an arrangement provides more than one thousand volts of isolation between the substrate  16  and the leadframe  12 . 
   It will be understood that the current conductor portion  14  is but a part of the total path through which an electrical current flows. For example, a current having a direction depicted by arrows  26  flows into the leads  12   c ,  12   d , which are here shown to be electrically coupled in parallel, through the current conductor portion  14 , and out of the leads  12   a ,  12   b , which are also shown here to be electrically coupled in parallel. 
   With this arrangement, the Hall effect element  18  is disposed in close proximity to the current conductor portion  14  and at a predetermined position relative to the conductor portion  14 , such that a magnetic field generated by an electrical current passing though the current conductor portion  14 , in a direction shown by arrows  26 , is in a direction substantially aligned with a maximum response axis of the Hall effect element  18 . The Hall effect element  18  generates a voltage output proportional to the magnetic field and therefore proportional to the current flowing through the current conductor portion  14 . The illustrated Hall effect element  18  has a maximum response axis substantially aligned with a z-axis  34 . Because the magnetic field generated in response to the current is circular about the current conductor portion  14 , the Hall effect element  18  is disposed just to the side (i.e., slightly offset along a y-axis  32 ) of the current conductor portion  14 , as shown, where the magnetic field is pointed substantially along the z-axis  34 . This position results in a greater voltage output from the Hall effect element  18 , and therefore improved sensitivity. However, a Hall effect element, or another type of magnetic field sensor, for example a magnetoresistance element, having maximum response axis aligned in another direction, can be disposed at another position relative to the current conductor portion  14 , for example, on top of the current conductor portion  14  (in a direction along z-axis  34 ). 
   While one Hall effect element  18  is shown on the first surface  16   a  of the substrate  16 , it will be appreciated that more than one Hall effect element can be used, as shown in the embodiments of  FIGS. 3 and 5 . Also, additional circuitry, for example an amplifier, can also be diffused in or otherwise disposed on, or supported by the first and/or second surfaces  16   a ,  16   b  of the substrate  16 . Exemplary circuitry of this type is shown in  FIG. 4 . 
   In the embodiment of  FIG. 1 , the close proximity between the Hall effect element  18  and the current conductor  14  is achieved by providing the Hall effect element  18  on the first substrate surface  16   a , which is positioned closer to the current conductor portion  14  than the second surface. In other embodiments, this advantageous close proximity is achieved by providing the Hall effect element  18  on the second substrate surface  16   b  and forming the current conductor portion  14  so as to be in substantial alignment with the second surface  16   b , as shown in  FIGS. 7 and 8 . 
   Referring now to  FIG. 2 , a graph  50  illustrates the magnetic flux density in the direction of the z-axis  34  ( FIG. 1 ) across the Hall element  18 , along an x-axis  30  ( FIG. 1 ) and the y-axis  32  ( FIG. 1 ) in the plane of the Hall effect element  18  ( FIG. 1 ), for a current through current conductor portion  14  on the order of 10 A. A center (not shown) of the Hall effect element  18  corresponds to three hundred microns on an abscissa  52 . A mantissa  54  corresponds to magnetic flux. 
   A magnetic flux curve  56  corresponds to the change in magnetic flux in the z-axis  34  relative to position along the x-axis  30 . Magnetic flux curve  58  corresponds to the change in magnetic flux in the z-axis  34  relative to position along the y-axis  32 . 
   The magnetic flux curves  56 ,  58  can be characterized as being substantially flat in the vicinity of the Hall element, which is centered at 300 μm. Therefore, the output of the Hall effect element  18 , which is sensitive to magnetic fields in the direction of the z-axis  34 , is relatively insensitive to the position of the Hall effect element  18  along the x-axis  30  and along they-axis  32 . 
   An illustrative Hall effect element  18  has dimensions along the x-axis  30  and along the y-axis  32  on the order of 200 microns and therefore the Hall effect element  18  lies in a region between 200 microns and 400 microns on the abscissa  52 . A change of position of the Hall effect element  18  by 50 microns either along the x-axis  30  or along the y-axis  32  results in little change in the magnetic field sensed by the Hall effect element. Therefore, the position of the Hall effect element in the x-axis  30  and the y-axis  32  can vary with manufacturing position tolerances without substantial effect upon the sensitivity of the current sensor  10  ( FIG. 1 ). 
   The width w 1  ( FIG. 1 ) of the current conductor portion  14  in the x-direction  30  relative to the dimension of the Hall effect element  18  in the x-direction  30  significantly affects the uniformity of the flux density in the z-direction  34  with position along the Hall effect element  18  in the x-direction  30 . In particular, the longer the current conductor portion  14  (i.e., the greater the width w 1 ,  FIG. 1 ), relative to the width of the Hall effect element  18  in the x-direction  30 , the longer the curve  56  remains substantially flat. 
   The width w 1  ( FIG. 1 ) is selected in accordance with a variety of factors, including, but not limited to a desired sensitivity of the current sensor  10  ( FIG. 1 ), and a desired reduction of performance variation resulting from manufacturing variation in relative position of the current path  14  and the Hall effect element  18 . In general, it will be appreciated that selecting the width w 1  to be comparable to a width of the Hall effect element  18 , provides the greatest sensitivity of the current sensor  10 . However, it will also be appreciated that selecting the width w 1  to be greater than the width of the Hall effect element  18  provides the smallest performance variation resulting from manufacturing tolerance of Hall element positional placement in the x-direction  30 . 
   Referring now to  FIG. 3 , another exemplary current sensor  70  in accordance with the present invention includes a lead frame  72  having a plurality of leads  72   a - 72   h  and a current conductor portion  74  having a width w 2 . The current sensor also includes a substrate  76  having a first surface  76   a  and a second, opposing surface  76   b . The substrate  76  has first and second Hall effect elements  78   a ,  78   b  diffused into the first surface  76   a , or otherwise disposed on or supported by the first surface  76   a . The substrate  76  is disposed on the lead frame  72  so that the Hall effect element  78  is in close proximity to the current conductor portion  74 . In the illustrated embodiment, the substrate  76  has an orientation that is upside down (i.e., the first surface  76   a  is directed downward) in relation to the conventional orientation of a substrate mounted in an integrated circuit package. An insulator (not shown) can separate the substrate  76  from the lead frame  72 . The insulator can be the same as or similar to the insulator  24  shown in  FIG. 1 . 
   With this arrangement, both of the Hall effect elements  78   a ,  78   b  are disposed in close proximity to the current conductor portion  74  and at predetermined positions relative to the current conductor portion  74  such that a magnetic field generated by an electrical current passing though the current conductor portion  74  in a direction shown by arrows  86 , is in a direction substantially aligned with a maximum response axis of the Hall effect elements  78   a ,  78   b . Here, the Hall effect elements  78   a ,  78   b  each have a maximum response axis aligned with a z-axis  94 . Therefore, the Hall effect elements  78   a ,  78   b  are disposed on opposite sides (i.e., slightly offset along a y-axis  92 ) of the current conductor portion  74 , as shown, where the magnetic field is pointed along the z-axis  94 . In one embodiment, the Hall effect elements  78   a ,  78   b  are offset (along the y-axis  92 ) by substantially equal and opposite amounts about the current conductor portion  74 . However, Hall effect elements, or another type of magnetic field sensors, for example magnetoresistance elements, having maximum response axes aligned in another direction, can be disposed at other positions relative to the current conductor portion  74 , for example, on top (in a direction of the z-axis  34 ) of the current conductor portion  74 . 
   In operation, current flows into the leads  72   c ,  72   d , which are coupled in parallel, through the current conductor portion  74 , and out of the leads  72   a ,  72   b , which are also coupled in parallel. The current flowing though the current conductor portion  74  generates a magnetic field which is sensed by the Hall effect elements  78   a ,  78   b . As described above, the Hall effect elements  78   a ,  78   b  are in very close proximity to the current conductor portion  74  and at a predetermined position relative to the current conductor portion  74  for which the magnetic field generated by the current is substantially aligned with the maximum response axis of the Hall effect elements  78   a ,  78   b . This placement results in a greater voltage output from the Hall effect element  74 , and therefore improved sensitivity. 
   It will be appreciated that the magnetic fields experienced by the first and the second Hall effect elements  78   a ,  78   b  are oriented in opposite directions, each aligned along the z-axis  94 . Therefore, if polarized in the same direction, the outputs of the two Hall effect elements  78   a ,  78   b  will be opposite in polarity. If the output from one of the Hall effect elements  78   a ,  78   b  is inverted, for example with an inverting amplifier, and then summed, i.e., differentially summed, with the output of the other of the Hall effect elements  78   a ,  78   b , certain advantages are achieved. 
   As an initial advantage, the outputs of two Hall effect elements  78   a ,  78   b , when differentially summed as described above, provide a voltage output of twice the magnitude of the voltage output from a single Hall effect element in the presence of the same current. Therefore, the current sensor  70  has twice the sensitivity of the current sensor  10  of  FIG. 1 . 
   As a second advantage, the current sensor  70  is relatively insensitive to variation in the position of the Hall effect elements  78   a ,  78   b  in the direction of the y-axis  92 . This is because, when moved in the direction of the y-axis  92 , the voltage output from one of the Hall effect elements  78   a ,  78   b  tends to increase while the voltage output from the other of the Hall effect elements  78   a ,  78   b  tends to decrease. Therefore, the differential sum of the two outputs remains relatively invariant. 
   While the lead frame  72  is shown to have the flat leads  72   a - 72   h  suitable for surface mounting to a circuit board, it will be appreciated that a lead frame having bent leads, like the lead frame  12  of  FIG. 1 , can also be used. Also, while two Hall effect elements  78   a ,  78   b  are shown, more than two or fewer than two Hall effect elements can also be used. 
   Referring now to  FIG. 4 , a summing circuit  100  suitable for performing the differential signal summation described in conjunction with  FIG. 3  is shown coupled to two Hall effect elements  102   a ,  102   b . The Hall effect elements  102   a ,  102   b  can be the same as or similar to the Hall effect elements  78   a ,  78   b  of  FIG. 3 . Here, each of the Hall effect elements  102   a ,  102   b  is rotated relative to the other Hall effect element by 90 degrees, as indicated by vectors on the Hall effect elements  102   a ,  102   b . Therefore, in response to opposite magnetic fields  112   a ,  112   b  the Hall effect elements  102   a ,  102   b  generate output voltages  103   a ,  103   b  having the same polarities. The output voltage  103   a  is coupled to amplifier  104   a  arranged in a non-inverting configuration and the output voltage  103   b  is coupled to the amplifier  104   b  arranged in an inverting configuration. Therefore, the amplifier output voltages  106   a ,  106   b  move in opposite voltage directions in response to the magnetic fields  112   a ,  112   b . The amplifier output voltages  106   a ,  106   b  are differentially coupled to an amplifier  108  to generate a differential summation, or a difference of the output voltages  106   a ,  106   b . Therefore, the output voltages  106   a ,  106   b  differentially sum to provide a greater output voltage  110  at the output of amplifier  108 . 
   The summing circuit  100  can be used in the current sensor  70  of  FIG. 3 , in which case Hall effect elements  102   a ,  102   b  correspond to the Hall effect elements  78   a ,  78   b . In one particular embodiment, the summing circuit  100  is diffused into, or otherwise disposed upon, the first surface  76   a  of the substrate  76 . In another embodiment, the summing circuit  100  is diffused into, or otherwise disposed upon, the second surface  76   b  of the substrate  76 , while the Hall effect elements  78   a ,  78   b  remain on the first surface  76   a , coupled to the other circuit components though vias or the like. 
   Referring now to  FIG. 5 , in which like elements of  FIG. 1  are shown having like reference designations, another exemplary current sensor  120  includes a substrate  126  having a first surface  126   a  and a second, opposing surface  126   b . Here, four Hall effect elements  128   a - 128   d  are diffused into or otherwise disposed on the first surface  126   a  of the substrate  126 . The substrate  126  is positioned relative to the lead frame  12  such that first and second Hall effect element  128   a ,  128   b  respectively are on one side of the current conductor portion  14  along a y-axis  142 , and third and fourth Hall effect elements  128   c ,  128   d  are on the opposite side of the current conductor portion  14  along the y-axis  42 , as shown. In one embodiment, the Hall effect elements  128   a ,  128   b  are offset (along the y-axis  142 ) from the current conductor portion  14  by an amount equal to and opposite from the amount that the Hall effect elements  128   c ,  128   d  are offset (along the y-axis  142 ) from the current conductor portion  14 . 
   With this arrangement, the Hall effect elements  128   a - 128   d  are disposed in close proximity to the current conductor portion  14  and at predetermined positions relative to the conductor portion  14 , such that a magnetic field generated by an electrical current passing though the current conductor portion  14  in a direction shown by arrows  86 , is in a direction substantially aligned with a maximum response axis of the Hall effect elements  128   a - 128   d . Here, each of the Hall effect elements  128   a - 128   d  has a maximum response axis aligned with a z-axis  144 . In the illustrated embodiment, the Hall effect elements  128   a ,  128   b  are disposed on an opposite side (i.e., slightly offset along a y-axis  142 ) of the current conductor portion  144  than the Hall effect elements  128   c ,  128   d , as shown, where the magnetic field is pointed along the z-axis  144 . However, Hall effect elements, or another type of magnetic field sensors, for example magnetoresistance elements, having maximum response axes aligned in another direction, can be disposed at other positions relative to the current conductor portion  14 , for example, on top (in a direction of the z-axis  144 ) of the current conductor portion  14 . It will be appreciated that the first and second Hall effect elements  128   a ,  128   b  are exposed to a magnetic field in a direction along the z-axis  144  and the third and forth Hall effect elements  128   c ,  128   d  are exposed to a magnetic field in the opposite direction along the z-axis  144 . 
   The four Hall effect elements  128   a - 128   d  can be coupled to an electronic circuit arranged as a summing circuit, understood by one of ordinary skill in the art, in order to achieve certain advantages. The summing circuit, for example, can include two of the summing circuits  100  of  FIG. 4 . In one embodiment, the summing circuit can couple a first two of the Hall effect elements  128   a - 128   d  with a first summing circuit, such as the summing circuit  100  of  FIG. 4 , and a second two of the Hall effect elements  128   a - 128   d  with a second summing circuit, such as the summing circuit  100 . With another amplifier, an output of the first summing circuit can be summed with an output of the second summing circuit. As an initial advantage, the four Hall effect elements  128   a - 128   d , coupled to a summing circuit as described, in the presence of the current, provide a voltage output four times the magnitude of a voltage output from a single Hall effect element, for example the Hall effect element  18  of  FIG. 1 , in the presence of the same current. Therefore, the current sensor  120  has four times the sensitivity of the current sensor  10  of  FIG. 1 . 
   As a second advantage, the current sensor  120  is relatively insensitive to variation in the position of the Hall effect elements  128   a - 128   d  in the direction of the y-axis  142 . This is because, when moved in the direction of the y-axis  142 , the voltage output from two of the four Hall effect elements  128   a - 128   d  tends to increase while the voltage output from the other two of the four Hall effect elements  128   a - 128   d  tends to decrease. Therefore, when coupled as a summing circuit, the circuit output is relatively invariant to the y-axis position of the Hall effect elements. 
   Referring now to  FIG. 6 , an exemplary current sensor  150  in accordance with the present invention includes a lead frame  152  having a plurality of leads  152   a - 152   h  and a current conductor portion  154 . The current sensor  150  also includes a substrate  166  having a first surface  166   a  and a second, opposing surface  166   b . The substrate  166  has a Hall effect element  158  diffused into the first surface  166   a , or otherwise disposed on the first surface  166   a . The substrate  166  is disposed on the lead frame  152  so that the Hall effect element  158  is in close proximity to the current conductor portion  154 . The substrate  166  has an orientation that is upside down (i.e., the first surface  166   a  is directed downward) in relation to the conventional orientation with which a substrate is mounted into an integrated circuit package. The substrate  166  is a flip-chip having solder balls  160   a - 160   c  on the first surface  166   a  of the substrate  166 . The solder balls  160   a - 160   c  couple directly to the leads  152   e - 152   h  as shown. An insulator  164  separates the substrate  166  from the lead frame  152 . The insulator  164  can be the same as or similar to the insulator  24  shown in  FIG. 1 . 
   With this arrangement, the Hall effect element  158  is disposed in close proximity to the current conductor portion  154  and at a predetermined position relative to the conductor portion  154 , such that a magnetic field generated by an electrical current passing though the current conductor portion  154  in a direction shown by arrows  168 , is in a direction substantially aligned with a maximum response axis of the Hall effect element  158 . The Hall effect element  158  has a maximum response axis aligned with a z-axis  174 . Therefore, the Hall effect element  158  is disposed just to the side (i.e., slight offset along a y-axis  172 ) of the current conductor portion  14 , as shown, where the magnetic field is pointed along the z-axis  174 . However, a Hall effect element, or another type of magnetic field sensor, for example a magnetoresistance element, having a maximum response axis aligned in another direction, can be disposed at another position relative to the current conductor portion  154 , for example, on top (in a direction of the z-axis  174 ) of the current conductor portion  154 . 
   Operation of the current sensor  150  is like the above-described operation of the current sensor  10  of  FIG. 1 . The Hall effect element  158 , being is close proximity to the current conductor portion  154 , results in a greater output voltage from the Hall effect element  158 , and therefore an improved sensitivity. 
   While only one Hall effect element  158  is shown on the first surface  166   a  of the substrate  166 , it will be appreciated that more than one Hall effect element can be used with this invention. Other circuitry, for example an amplifier, can also be diffused in or otherwise coupled to or supported by the first and/or second surfaces  166   a ,  166   b  of the substrate  166 . 
   While three solder balls  160   a - 160   c  are shown, any number of solder balls can be provided, including dummy solder balls for stabilizing the substrate  166 . Also, while solder balls  160   a - 160   c  are shown, other connection methods can also be used, including, but not limited to gold bumps, eutectic and high lead solder bumps, no-lead solder bumps, gold stud bumps, polymeric conductive bumps, anisotropic conductive paste, and conductive film. 
   Referring now to  FIG. 6A , in which like elements of  FIG. 6  are shown having like reference designations, an exemplary current sensor  180  in accordance with the present invention includes a flux concentrator  182  and a flux concentrating layer  184 . The flux concentrator is located proximate the Hall effect sensor  158 , adjacent to and below the first surface  166   a  of the substrate  166 . The flux concentrating layer  184  is disposed on (or adjacent to and above) the second surface  166   b  of the substrate  166 . 
   In operation, the flux concentrator  182  and the flux concentrating layer  184  each tend to concentrate the magnetic flux generated by the current passing through the current conductor portion  154  so as to cause the current sensor  180  to have a higher sensitivity than the current sensor  150  of  FIG. 6 . 
   The flux concentrator  182  and the flux concentrating layer  184  can each be comprised of a variety of materials, including but not limited to, ferrite, Permalloy, and iron. 
   While the flux concentrator  182  is shown having a cubic shape, in other embodiments, the flux concentrator can have another shape, for example, a polyhedral shape, an elliptical shape, or a spherical shape. While both the flux concentrator  182  and the flux concentrating layer  184  are shown, in other embodiments, only one of the flux concentrator  182  and the flux concentrating layer  184  can be provided. Also, while the flux concentrator  182  and the flux concentrating layer  184  are shown in conjunction with one magnetic field transducer  158 , it should be appreciated that the flux concentrator  182  and the flux concentrating layer  184  can also be applied to configurations having more than the one magnetic field transducer  158 , for example, the configurations shown in  FIGS. 1 ,  3 , and  5 . 
   Referring now to  FIG. 7 , another exemplary current sensor  200  in accordance with the present invention includes a lead frame  202  having a plurality of leads  202   a - 202   h . The current sensor  200  also includes a substrate  206  having a first surface  206   a  and a second, opposing surface  206   b . The substrate  206  has a Hall effect element  208  diffused into the first surface  206   a , or otherwise disposed on the first surface  206   a . A conductive clip  204  having a current conductor portion  204   a  is coupled to the leads  202   a - 202   d . Features of the conductive clip  204  are shown in  FIG. 8 . Suffice it to say here that the conductive clip is formed having a bend such that the conductive clip  204  passes up and over the first surface  206   a  of the substrate  206 . The substrate  206  is disposed on the lead frame  202  so that the Hall effect element  208  is in close proximity to the current conductor portion  204   a . In the illustrated embodiment, the substrate  206  has a conventional mounting orientation with the first surface  206   a  directed upward. The substrate  206  has bonding pads  212   a - 212   c  on the first surface  206   a , to which bond wires  210   a - 210   c  are coupled. The bond wires  210   a - 210   c  are further coupled to the leads  202   e ,  202   f ,  202   h . An insulator  214  can be provided to isolate the substrate  206  from the conductive clip  204 . The insulator  214  can be the same as or similar to the insulator  24  shown in  FIG. 1 . 
   With this arrangement, the Hall effect element  208  is disposed in close proximity to the current conductor portion  204   a , which passes up and over the first surface  206   a  of the substrate  206 . The Hall effect element  208  is disposed at a predetermined position relative to the conductor portion  204   a  such that a magnetic field generated by an electrical current passing though the current conductor portion  204   a  in a direction shown by arrows  216 , is in a direction substantially aligned with a maximum response axis of the Hall effect element  208 . The Hall effect element  208  has a maximum response axis aligned with a z-axis  224 . In the illustrated embodiment, the Hall effect element  208  is disposed just to the side (i.e., slight offset along a y-axis  222 ) of the current conductor portion  204   a , as shown, where the magnetic field is pointed along the z-axis  224 . However, a Hall effect element, or another type of magnetic field sensor, for example a magnetoresistance element, having a maximum response axis aligned in another direction, can be disposed at another position relative to the current conductor portion  204   a , for example, essentially aligned above or below (in a direction of the z-axis  224 ) with the current conductor portion  204   a.    
   In operation, current flows into the leads  202   c ,  202   d , which are coupled in parallel, through the conductive clip  204 , through the current conductor portion  204   a , and out of the leads  202   a ,  202   b , which are also coupled in parallel. The current flowing though the current conductor portion  204   a  generates a magnetic field, which is sensed by the Hall effect element  208 . The Hall effect element  208  generates a voltage output proportional to the magnetic field and therefore proportional to the current flowing though the current conductor portion  204   a . As described above, the Hall effect element  208  is in very close proximity to the current conductor portion  204   a  and at a predetermined position relative to the current conductor portion  204   a  in which the magnetic field generated by the current is substantially aligned with the maximum response axis of the Hall effect element  208 . This position results in a greater voltage output from the Hall effect element  208 , and therefore improved sensitivity. 
   While only one Hall effect element  208  is shown on the second surface  206   b  of the substrate  206 , it will be appreciated that more than one Hall effect element can be used. In particular, an embodiment having two Hall effect elements can be similar to the current sensor  70  of  FIG. 3  and an embodiment having four Hall effect elements can be similar to the current sensor  120  of  FIG. 5 . Also, additional circuitry, for example an amplifier, can be diffused in or otherwise coupled to the first and/or second surfaces  206   a ,  206   b  of the substrate  206 . 
   It should be appreciated that the conducive clip  204  can be formed in a variety of ways and from a variety of materials. In one particular embodiment, the conductive clip  204  is stamped, for example, from a copper sheet. In another embodiment, the conductive clip  204  is formed from foil, for example copper foil. In yet another embodiment, the conductive clip  204  is formed by an etching process. The conductive clip  204  allows the use of the conventional mounting orientation of the substrate  206  while bringing the current conductor portion  204   a  very close to the Hall effect element  208 . 
   The conductive clip  204  can be provided having a thickness selected in accordance with an amount of current that will pass through the conductive clip  204 . Therefore, if a current sensor adapted to sense relatively high currents is desired, the conductive clip can be relatively thick, whereas, if a current sensor adapted to sense relatively low currents is desired, the conductive clip  204  can be relatively thin. In another embodiment, if a current sensor adapted to sense relatively high currents is desired, more than one conductive clip  204  can be stacked in contact with other conductive clips to provide an increased effective thickness that is thicker than any one conductive clip  204 , and therefore, able to carry more current. 
   In the embodiment of  FIG. 7 , the close proximity between the Hall effect element  208  and the current conductor portion  204   a  is achieved by providing the Hall effect element  208  on the first substrate surface  206   a , which is positioned closer to the current conductor portion  204   a  than the second surface  206   b . In other embodiments, this advantageous close proximity is achieved by providing the Hall effect element  208  on the second substrate surface  206   b  and forming the current conductor portion  204   a  so as to be in substantial alignment with the second surface  206   b.    
   Referring now to  FIG. 8 , in which like elements of  FIG. 7  are shown having like reference designations, the conductive clip  204  is shown before it is coupled to the leads  202   a - 202   d . The conductive clip  204  includes the current conductor portion  204   a , a transition region  204   b , a bend region  204   c , and a bonding region  204   d . The bonding region  204   d  includes two portions  204   e ,  204   f  which couple to the leads  202   a - 202   d . The transition region  204   b  can be elevated relative to the current conductor portion  204   a  to avoid contact with the substrate  206 . 
   While Hall effect elements have been shown and described in association with embodiments of this invention, it will be recognized that other types of magnetic field sensors can be used. For example, magnetoresistance elements can be used in place of the Hall effect elements. However, a conventional magnetoresistance element has a maximum response axis that is perpendicular to the maximum response axis of a conventional Hall effect element. One of ordinary skill in the art will understand how to position one or more magnetoresistance elements relative to a current conductor portion in accordance with embodiments of the present invention to achieve the same results as the Hall effect element embodiments herein described. 
   Referring now to  FIG. 9 , a lead frame  250  is shown having a shape similar to the lead frame  72  of  FIG. 3  and the lead frame  152  of  FIG. 6 . The lead frame  250  has a plurality of thinned portions  252   a - 252   n  that are thinner than other portions of the lead frame  250 . The thinner portions can be provided by a variety of processes, including, but not limited to, chemical etching and stamping. 
   A current conductor portion  254  has a surface  254   a  and a thickness t 1  which can be the same as or similar to the thickness of others of the thinned portion  252   b - 252   n . Other portions of the lead frame have a thickness t 2 . In one particular embodiment, the thickness t 1  of the current carrying portion  254  is the same as the thickness of the other thinned portions  252   b - 252   n , and the thickness t 1  is approximately half of the thickness t 2 . In one embodiment, the current conductor portion  254  has a cross section that is essentially rectangular, having the thickness t 1 . 
   It will be recognized that, in the presence of a current passing through the current conductor portion  254 , the current conductor portion  254  being thinner, for example, than the current conductor portion  74  of  FIG. 3 , has a higher current density near the surface  254   a  than the current conductor portion  74  of  FIG. 3  has near the surface  74   a  in the presence of a similar current. In other words, the current is compressed to be closer to the surface  254   a  than it would otherwise be with a thicker current conductor portion. As a result, a magnetic field generated by the current has a higher flux density in proximity to the surface  254   a.    
   Therefore, when the lead frame  250  is used in place of the lead frame  72  of  FIG. 3 , the Hall effect elements  78   a ,  78   b  experience a greater magnetic field, resulting in a more sensitive current sensor. 
   Others of the thinned portion  252   b - 252   n  provide other advantages. For example, when the lead frame  250  is molded into a plastic surrounding body, the other thinned portions  252   b - 252   n  tend to lock the lead frame  250  more rigidly into the molded body. 
   The thickness t 1  is selected in accordance with a variety of factors, including, but not limited to, a maximum current to be passed through the current conductor portion  254 . 
   It will be understood that thinned portions can be applied to others of the lead frames shown above in embodiments other than the embodiment of  FIG. 3  in order to achieve the same advantages. 
   Referring now to  FIG. 9A , an alternate current conductor portion  270 , suitable for replacing the current conductor portion  254  of  FIG. 9 , has a T-shaped cross section as would be seen from a cross-section taken along line  9 A- 9 A of  FIG. 9 . The T-shape has a surface  270   a , a first thickness t 3 , and a second thickness t 4 . The thickness t 3  can be the same as or similar to the thickness t 1  of  FIG. 9 , and the thickness t 4  can be the same as or similar to the thickness t 2  of  FIG. 9 . In one particular embodiment the thickness t 3  is approximately half of the thickness t 4 . 
   For substantially the same reasons describe above in conjunction with  FIG. 9 , a magnetic field generated in response to a current passing through the current conductor portion  270  is higher in proximity to the surface  270   a  than it would be if the current conductor portion  270  had a uniform thickness t 4 . 
   While the current conductor portion  254  ( FIG. 9 ) and the current conductor portion  270  have been described to have a rectangular cross section and a T-shaped cross section respectively, it should be appreciated that other cross-sectional shapes can be provided to achieve the above advantages. 
   Having described preferred embodiments of the invention, it will now become apparent to one of ordinary skill in the art that other embodiments incorporating their concepts may be used. It is felt therefore that these embodiments should not be limited to disclosed embodiments, but rather should be limited only by the spirit and scope of the appended claims. 
   All references cited herein are hereby incorporated herein by reference in their entirety.