Abstract:
Apparatus for mounting and making electrical connections to sensor devices for use in three axis sensing including a flexible circuit and a substrate shaped so that when a portion of the flexible tape is secured to the substrate the sensor devices can be mounted on the substrate for sensing in the desired three directions. The sensors are connected to conductors in the flexible tape by wirebonds or by other means.

Description:
BACKGROUND 
     The present invention relates generally to apparatus for mounting and making electrical connections to solid state sensors, which is typically referred to as packaging. The present invention relates specifically to the mounting and electrical connecting of sensors for the sensing of a condition occurring in mutually perpendicular planes which may be referred to as three axis sensing. 
     Three axis sensing is useful for determining the location and or orientation of a device which is carrying the apparatus and is moving in a known magnetic field created for the purpose of determining the location of the apparatus. 
     One application for such an apparatus is in the field of medical devices where miniaturized three axis sensing may be used in conjunction with a magnetic field having known characteristics to determine the location and orientation of a portion of a medical device. 
     In many medical devices, of which a catheter is one example, a three-axis sensing apparatus must be extremely small to be able to be inserted into a small channel or passageway within the device. 
     Thus a need exists for a three axis mounting and electrically connecting apparatus for sensing devices that can be inserted into a small elongated passageway. 
     SUMMARY OF THE INVENTION 
     The present invention solves these and other needs by providing an apparatus including an elongated flexible circuit having conductors and a substrate of a certain shape for providing a stiffness to the portion of the flexible circuit on which sensor devices are mounted. The substrate has a shape which includes a first portion having a surface lying in a plane which includes a desired first sensing direction and a desired second sensing direction for mounting a first and a second sensor. The substrate further includes a second portion having a surface lying in a plane which includes a desired third sensing direction. Sensor devices are electrically connected to the conductors of the flexible circuit by wire bonds or other means. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a partial perspective view of an apparatus for mounting and electrically connecting sensor devices according to the present invention, with a portion of a passageway shown in phantom. 
     FIG.  1   a  is an outline drawing of a sensor device. 
     FIGS.  1   b  and  1   c  are plan views of a flexible electric circuit. 
     FIG. 2 is an elevation drawing of a first alternate embodiment. 
     FIG. 3 is an elevation drawing of a second alternate embodiment. 
    
    
     DETAILED DESCRIPTION 
     An apparatus for mounting sensor devices for plural axis sensing and making electrical connections to the devices is shown in the drawings and generally designated  10 . Apparatus  10  includes a flexible tape circuit  20  and substrate or stiffener  30 . 
     As shown in FIG. 1 substrate  30  has a first portion  32  having a surface  34  lying in a plane as formed by the x-axis and the y-axis and a second portion  36  having a surface  38  lying in a plane formed by the x-axis and the z-axis. Substrate  30  has a transition portion  40  extending from first portion  32  and connecting to second portion  36  and having a surface  42 . Transition portion  40  is in the form of a twist that rotates through 90 degrees. Substrate  30  is made from a formable metal material and provides a greater stiffness to a portion of flexible circuit  20 . Materials that have been found to work include Aluminum or Beryllium Copper. 
     Flexible circuit  20  has surface  21  and surface  23  and includes dielectric  22  and conductors  24 . Flexible circuit  20  has a portion of dielectric  22  bonded to surfaces  34 ,  38  and  42  of substrate  30 . In FIG. 1 sensor device S 1  at surface  34  is oriented to be sensitive along the y-axis and sensor device S 2  is oriented to be sensitive along the x-axis. Sensor device S 3  on surface  38  is oriented to be sensitive along the y-axis. 
     Flexible circuit  20  includes tape  22  and conductors  24 . Surface  26  of flexible circuit  20  located near end  28  does not include dielectric and conductors  24  are exposed to allow electrical connections to be made. Flexible circuit  20  is typically made using a polyimide dielectric and copper conductors. Photolithography and etching processes are used in the fabrication. The construction of the flexible tape may be varied. Planar views of one satisfactory prototype are shown in FIGS.  1   b  and  1   c , and a description of the materials and approximate dimensions is as follows: 
     DIELECTRIC MATERIAL=POLYIMIDE 
     WIDTH=0.076″ 
     LENGTH=78.74″ 
     POLYMIDE THICKNESS=0.002″ 
     CONDUCTOR MATERIAL=COPPER 
     COPPER THICKNESS=0.0007″ 
     EXPOSED COPPER PLATED WITH 20-40 MICROINCHES NICKEL 
     80 MICROINCHES WIREBONDABLE GOLD TO BE PLATED OVER NICKEL 
     COPPER LINE WIDTH TOP=0.005″ 
     SPACE BETWEEN COPPER LINES ON TOP=0.005″ 
     METALLIZATION TO EDGE CLEARANCE=0.0155″ 
     COPPER WIDTH ON BOTTOM 2 BUSES=0.020″ EACH 
     SPACE BETWEEN BUSES=0.005″ 
     BOTTOM BUSES CONNECTED TO THE TOP LINES AS SHOWN WITH THRU VIAS 
     VIAS MAY BE FILLED WITH A CONDUCTIVE PASTE 
     BOTTOM SIDE TO BE COATED WITH A DIELECTRIC 
     TOP SIDE TO BE COATED WITH A DIELECTRIC EXCEPT FOR THE 0.600″ TIP 
     CIRCUIT SENSOR END TO BE BONDED TO 0.006″ THICK BERYLLIUM COPPER 
     ASSUME SENSOR CHIP SIZE 0.025″×0.035″ 
     ALLOW 0.020″ AROUND THE CHIP TO BRING OUT THE WIRE BONDS 
     EACH CHIP FOOTPRINT WILL THEN BE 0.065″×0.075″ 
     OP AMP CHIP SIZE IS 0.063″×0.154″ 
     In the prototype previously described the Beryllium Copper is 0.575″ long before forming a 90 degree twist between the first and second 0.100″ of the circuit after it is bonded to the beryllium copper. 
     An outline drawing of a sensor device S having a direction of sensitivity  46  and further having a length, l, a width, w, and a diagonal measurement  44 , is shown in FIG.  1   a . Sensors S are preferably of magnetoresistive material. 
     An advantage of the embodiment of FIG. 1 is that it accomplishes the three axis mounting of sensor devices in a way that allows apparatus  10  to be inserted in a passageway or orifice having a diameter measurement, d, that is less than diagonal measurement  44  of sensor device S. That is, the arrangement of FIG. 1 accomplishes the three axis sensing without presenting face  48  of sensor device S to the orifice or passageway  50 . Unlike Hall-effect sensors which require the sensed field to be perpendicular to the plane of the sensor and therefore required a cube type of mounting, the sensor of the present invention are efficient in the cross-sectional area needed for mounting. 
     In a first alternate embodiment as illustrated in FIG. 2, substrate  60  is generally L shaped and includes leg  62 , surface  64 , leg  66  which is perpendicular to leg  62  and surface  68 . Flexible circuit  70  has surface  71  and surface  73  and includes dielectric  72  and conductors  74 . Flexible circuit  70  has a portion of dielectric  72  bonded to surface  64  and a portion of dielectric  72  bonded to surface  68 . In this arrangement sensor device S 4  could be oriented to be sensitive along the x-axis, and sensor device S 5  could be oriented to be sensitive along the z-axis with both sensors lying in a common plane represented by the plane formed by the x-axis and the z-axis. Sensor device S 6  is mounted to surface  68  of flexible tape and is oriented to be sensitive along the y-axis or to a condition in the plane formed by the y-axis and the z-axis. All sensor devices are electrically connected to flexible circuit  70  by, for example, wire bonds  75  between bonding pads on the sensor devices and conductors  74  in flexible circuit  70 . 
     In a second alternate embodiment, as shown in FIG. 3, substrate  80  has a cross section having a uniform thickness portion  82  that includes surface  84  and parallel surface  86 . Tapered portion  88  has a thickness that increases in thickness in a direction going away from uniform thickness portion  82 . Tapering portion  88  terminates in an end surface  90 . Flexible circuit  92  has surface  91  and surface  93  and includes dielectric  94  and conductors  95 . Flexible circuit  92  has portion  96  bonded to surface  84 , portion  97  bonded to surface  86  and portion  98  bonded to surface  90 . In FIG. 3 sensor device S 7  at surface  84  is oriented to be sensitive along the x-axis and sensor device S 8  at surface  86  is oriented to be sensitive along the z-axis. Sensor device S 9  at surface  90  is oriented to be sensitive along the y-axis. An advantage of FIG. 3 is that sensor devices mounted on surfaces  84  and  86  do not contribute to the overall height of apparatus  10 . The substrate of FIG. 3 is in the shape of an Erlenmeyer flask. 
     The electrical connection between the flexible circuit and the chips may be made by wire bonds, flip chip or tape-automated bonding. Commonly owned application entitled “Miniature Magnetometer” and having a filing date of Jul. 20, 1994 is hereby incorporated by reference.