Abstract:
An apparatus having an X-ray sensor assembly with X-ray blocking pixels divided by X-ray transmitting gaps with the X-ray blocking pixels casting an X-ray blocking shadow; and a die containing signal processing electronics, with the signal processing electronics positioned substantially entirely within the X-ray blocking shadow. A method for detecting the alignment between the X-ray sensor assembly and the die is disclosed. Also disclosed is an X-ray computed tomography machine having a printed circuit board (“PCB”), a die embedded in the PCB, and a signal source wherein signals are routed to and from the die by traces on at least one of the surfaces of the PCB.

Description:
[0001]    This application claims priority from U.S. provisional patent application Ser. No. 61/780,434 filed Mar. 13, 2013 for MICROSIP PACKAGING SOLUTION FOR CT SCANNER of Eduardo Bartolome, which is hereby incorporated by reference for all that it discloses. 
     
    
     BACKGROUND 
       [0002]    An X-ray computed tomography machine uses computer-processed x-rays to produce tomographic images of specific areas of a scanned object, allowing the user to see what is inside it without cutting it open. Medical imaging is the most common application of X-ray CT. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0003]      FIG. 1  is a perspective view of a prior art X-ray computed tomography machine (“CT machine”). 
           [0004]      FIG. 2  is schematic end elevation view of a gantry of a prior art CT machine. 
           [0005]      FIG. 3  is a schematic side elevation view of a prior art X-ray sensor assembly of a CT machine. 
           [0006]      FIG. 4  is a schematic isometric view of a scintillator of a prior art X-ray sensor assembly. 
           [0007]      FIG. 5  is an isometric view showing the relationship between a prior art X-ray sensor assembly and signal processing electronics. 
           [0008]      FIG. 6  is schematic end elevation view of a gantry of a CT machine having an X-ray sensor assembly and signal processing electronics as described in  FIGS. 7-9 . 
           [0009]      FIG. 7  is a schematic side elevation view of an X-ray sensor assembly mounted on a printed circuit board (“PCB”) having an integrated circuit (“IC”) die embedded therein. 
           [0010]      FIG. 8  is an exploded, partially transparent top view of an X-ray sensor assembly and a printed circuit board (“PCB”) having an IC die embedded therein. 
           [0011]      FIG. 9  is a detail view of the PCB and the embedded IC die of  FIGS. 7 and 8  showing a projection of a scintillator portion of the X-ray sensor assembly thereon. 
           [0012]      FIG. 9A  is a detail view of a portion of  FIG. 9 . 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    This specification, in general, describes an X-ray computed tomography machine  99 ,  FIG. 6 , that includes an X-ray sensing and signal processing apparatus  108  that comprises an X-ray sensor assembly  110 ,  FIG. 7 , that is supported on a printed circuit board (“PCB”)  150 . An integrated circuit die  160  buried in the PCB  150  processes signals from the X-ray sensor assembly  110 . Signals from the sensor assembly  110  are routed to the die  160  through traces  152  on the top surface  151  of the PCB  150  and then through micro-vias  162 . Processed signals from the die  160  are routed back to the top surface of the PCB  150  through micro-vias  163  and traces  166  on the top surface  151  of the PCB  150  and then to through hole vias  164  (sometimes referred to as “hole vias” herein) extending through the PCB  150 . Then the signals are routed from the through hole vias  164  and traces  168  on bottom surface  156  to other electrical circuitry  170  located on the bottom surface  156  of the PCB  150 . A system for aligning the X-ray sensor assembly  110  with the IC die  160  to avoid exposing signal processing electronics within the die  160  to harmful X-rays, such as  105 A,  105 B,  105 C shown in  FIG. 6 . The resulting structure is also described. 
         [0014]      FIG. 1  illustrates a prior art X-ray computed tomography machine  10  (CT machine  10 ). The CT machine  10  has a CT housing  12  with a center opening  14  therein. During CT operation, a patient  16  lies on a horizontally disposed table  18 . The table  18  is slowly moved through the central opening  14  as X-rays from the machine pass through the patient&#39;s body. 
         [0015]      FIG. 2  is a cutaway schematic view of a gantry  30  of the prior art CT machine  10 . The gantry  30  is a massive doughnut-shaped device that is positioned behind a front cover of the CT machine  10 ,  FIG. 1 . The gantry  30  rotates in direction  32  as the patient is moved through the opening  14 . The gantry  30  includes an X-ray tube  34  positioned on one side of the central hole  14 . An X-ray sensor assembly  38  is positioned on the opposite side of the center opening  14 . X-rays  36 A,  36 B,  36 C from the X-ray tube  34  are sensed by the sensor assembly  38 . Analog signals from the sensor assembly  38  are processed and used to create three-dimensional images of the interior of the patient&#39;s body. 
         [0016]      FIG. 3  is a schematic side elevation view of a portion of the prior art X-ray sensor assembly  38 . The sensor assembly  38  includes a scintillator array  40  mounted on a photo detector array  44  that is, in turn, mounted on a ceramic substrate  50 .  FIG. 4  is an enlarged isometric view of a top portion of the scintillator array  40 , which comprises a grid of scintillator pixels  42 . As shown by  FIG. 3 , the scintillator array  40  is supported on a photo detector array  44  having a plurality of pixels (not shown individually) corresponding to the pixels  42  of the scintillator array  40 . (The term “pixel” as used herein may refer to an element of an image sensor as well as an element of an image.) The scintillator and photo detector pixels need to be held with high levels of geometric tolerances against mechanical, thermal, gravitational, and aging effects. Typically, a thick ceramic substrate  50  is used to provide the necessary support. The ceramic substrate  50  has flat upper and lower surfaces  52 ,  54 . A plurality of conductor pads (not shown) are provided on the top surface  52  of substrate  50  in alignment with conductors  46  on the photo detector assembly  44 . Electrical contacts such as balls  56  of a ball grid array  58  are provided on the bottom surface  54  of the ceramic substrate  50 . Conductors  59  extending through vias in the substrate  50  and connect conductor pads (not shown) on the top surface  52  to corresponding ball conductors  56  on the bottom surface  54 . 
         [0017]    As illustrated by  FIG. 5 , the X-ray sensor assembly  38  is connected to signal processing electronics  80  which process analog signals from the photo detector array  44 . The analog signals from the photo detector array  44  can be corrupted if transmitted over long distances. To avoid such signal corruption the analog signals would ideally be filtered and digitized by electronics in close proximity to the photo detector  44 . The digital signals thus produced could then be safely transmitted, stored, and further processed with no loss of integrity. 
         [0018]    Most X-rays that strike the scintillator array  40  are absorbed by it. However some amount of radiation may escape from the sensor assembly  38  due to gap&#39;s between scintillator pixels  42 , or because some X-rays pass entirely through the sensor assembly  38 . Such stray X-rays can significantly alter the characteristics of signal processing electronics placed in the proximity of the sensor assembly  38 . 
         [0019]    Various techniques have evolved to prevent damage to the signal processing electronics. Such techniques generally involve use of additional printed circuit boards (PCB&#39;s) to route the signals to signal processing electronics located a substantial distance away from the sensor assembly. An example of such a prior art assembly is shown in  FIG. 5 . An analog signal transfer assembly  70  transfers analog signals from the X-ray sensor assembly  38  to a signal processing assembly  80 . The analog signal transfer assembly  70  includes a first conventional PCB  72 . The ball grid array  58 ,  FIG. 3 , on the ceramic substrate  50  is placed in electrical contact with a corresponding conductor array on the conventional PCB  72 . A flexible PCB  76  connects the first conventional PCB  72  to a second conventional PCB  82  having analog signal processing electronics mounted on it. A portion of the flexible PCB  76  and the second conventional PCB  82  extend generally perpendicular to the first conventional PCB  72  and parallel to the direction of X-rays from the X-ray tube  34 . Although this structure places the signal processing electronics  82  at a distance from the source of the X-rays it has a number of drawbacks. Such structure undesirably increases the distance that the analog signals must travel to reach the signal processing electronics. Such structure also adds undesirable stack height (radial height) and mass to the entire X-ray sensor/signal processing assembly. 
         [0020]      FIG. 6  illustrates a CT machine  99  having a gantry  101  with a central opening  102 . The gantry  101  rotates in direction  103 . An X-ray tube  104  is positioned on one side of the opening  102 . An X-ray sensing and signal processing apparatus  108  is positioned on the other side of the opening  102 . X-rays  105 A,  105 B, and  105 C from the X-ray tube  104  travel through the opening  102 , and any X-ray penetrable object therein, and strike the X-ray sensing and signal processing apparatus  108 , described in detail below. 
         [0021]      FIG. 7  is a side elevation view of the X-ray sensing and signal processing apparatus  108  of  FIG. 6 . The apparatus  108  comprises an X-ray sensor assembly  110  that in this embodiment includes a scintillator assembly  120 . Scintillator assembly  120  has a plurality of scintillator pixels  122  separated by scintillator pixel gaps  124 . A photo detector assembly  130 , having a plurality of photo detector pixels  132 , is positioned immediately below the scintillator assembly  120 . Photo detector pixels  132  correspond to the scintillator pixels  122  positioned immediately above them. The photo detector  130  may be mounted on a ceramic substrate  140 . Photo detector signal output contacts  134  engage corresponding contacts (not shown) on a top surface  141  of the ceramic substrate  140 . Conductor filled vias  142  connect the contacts on the top of the ceramic substrate  140  with ball grid contacts  144  on the bottom surface  145  of the ceramic substrate  140 . The ball contacts  144  on the bottom surface of the ceramic substrate  140  engage corresponding contacts  152 , which may be signal traces, on the top surface  151  of a printed circuit board (“PCB”)  150 . 
         [0022]    The PCB  150  has a plurality of integrated circuit (“IC”) dies  160  buried below the surface  151  of the PCB  150 . The IC dies  160  may each be buried at the same depth and may be laterally spaced apart a predetermined distance. Traces  152  on the top surface  151  of the PCB  150  connect the ceramic substrate ball contacts  144  to micro-vias  162  extending from the PCB top surface  151  to contacts on the top surface  161  of a buried die  160 . Analog sensor signals from the X-ray sensor assembly  110  are input to die signal processing electronics through a set of traces  152  and a set of micro-vias  162 . Other micro-vias  163  connect another set of contacts on the top surface  161  of the die  160  to a second set of surface traces  166  on the top surface  151  of the PCB  150 . Processed sensor signals are thus transmitted from the dies  160  through micro-vias  163  and traces  166 . Traces  166  are connected to hole vias  164  that extend from the top surface  151  of the PCB  150  to bottom surface  156  of the PCB  150 . The processed sensor signals are thus transmitted to the bottom surface  156  of the PCB  150 . Other signals such as power and control signals may also be routed from the die  160  to the bottom surface  156  of the PCB  150  by micro-vias  163 , traces  166  and through hole vias  164 . Other circuitry  170 , such as passive circuit devices, power distribution lines, decoupling capacitors, and connectors to other circuits, are mounted on the bottom surface  156  of the PCB  150 . The hole vias  164  may be connected to the other circuitry  170  by bottom surface traces  168 . Thus, the circuitry connecting the IC dies  160  to the X-ray sensor  110  and to other circuit devices  170  may be located on the PCB top surface  151  or bottom surface  156 . In one embodiment, all traces carrying signals to and from the die  160  are on the top and bottom surfaces  151 ,  156  of the PCB  150 . In another embodiment a substantial portion of those traces are located on internal layers (not shown) of the PCB  150 , as well as on the top and bottom surfaces  151 ,  156 , with routing between layers provided by vias. 
         [0023]    The above described X-ray sensing and signal processing apparatus  108  is shown in a schematic, transparent three-dimensional representation in  FIG. 8 .  FIG. 9  is a top plan view of the die  160 , which shows the position of the overlying scintillator pixels  122 , various micro-vias  162 ,  163 , and through hole vias  164  for control circuits and through-hole vias  165  for supply and reference circuits. In the embodiment shown in  FIGS. 8 and 9  the top surface  161  of each die  160  is divided into a 7×7 unit grid, which underlies an 8×8 pixel grid of the scintillator  130 ,  FIG. 7 . The individual pixels  122  of the scintillator assembly  120  prevent radiation impinging thereon from passing through to the underlying die  160 . However, the gaps  124  between scintillator pixels  122  do not block radiation. In the assembly shown in  FIG. 9 , the electronics inside the IC die  160  are all located in areas shaded from X-rays by scintillator pixels  122 . The dies  160  are constructed and arranged such that the areas of the dies  160  that are exposed to radiation passing through the scintillator gaps  124  do not contain electronics. However, such gap projection areas, e.g.  194 , may be used for purposes other than signal processing, such as for signal routing. 
         [0024]    A blowup of one of these gap projection lines  194  on the die  160  is shown in  FIG. 9A . In one embodiment, a diode  190 ,  192  is positioned on each side of the gap projection line  194 . One or both of the diodes  190 ,  192  will receive radiation if the gap projection line  194  is not properly aligned with the actual overlying scintillator pixel gap grid  125 ,  FIG. 8 . As shown by  FIG. 9A , the same signal processing electronics  199  that are used to process an X-ray sensor signal may also be used to process a signal from an associated diode, e.g.,  192 . Signals from the various diodes  190 , 192 , etc., may be processed to determine the misalignment between the underlying die  160  and the scintillator assembly  120 . In one embodiment, this misalignment detection is used in association with a displacement assembly (not shown) during assembly to align the scintillator assembly  120  with the respective dies  160 . In another embodiment, this misalignment detection is used after assembly for quality control purposes. 
         [0025]    The circuitry and method used for processing signals from the X-ray sensor assembly  110 ,  FIG. 7 , may be the same or similar to that described in U.S. Pat. No. 5,841,310, issued Nov. 24, 1998 for CURRENT-TO-VOLTAGE INTEGRATOR FOR ANALOG-TO-DIGITAL CONVERTER, AND METHOD, and “64 Channel Current-Input Analog-to-Digital Converter Check of DDC264, SBAS 368C,” May 2006, Revised July, 2011, which are both hereby incorporated by reference for all that is contained therein. The signal processing electronics in the dies  160  that are used to process signals from the X-ray sensor assembly  110 , may also be used to process the alignment signals from gap sensing diodes  190 ,  192  of  FIG. 9A , as mentioned above. 
         [0026]    In the illustrated embodiments, the scintillator assembly  120 ,  FIG. 7 , has an 8×8 pixel array, which is projected onto a 7×7 unit grid of an integrated circuit die  160  and which overlaps it by one row and one column. It will be understood that all 64 pixels of the scintillator assembly  120  have signal inputs to the 7×7 unit IC die  160 . Thus, there is not a 1 to 1 correspondence between the scintillator pixels  122  and the units of the die, even though all of the signals from the scintillator pixels are processed by electronics in the die  160 . 
         [0027]    Although certain specific embodiments of an X-ray computed tomography machine (“CT machine”) and an X-ray sensing and signal processing apparatus and an alignment system therefor have been described in detail above, it will be understood by those skilled in the art after reading this disclosure that the specifically described devices and methods could be variously otherwise embodied. For example, although the embodiment of a CT machine that is specifically described herein is a medical CT machine, the CT machine features described herein are also applicable to other types of CT machines such as industrial CT machines used for imaging solder joints on printed circuit boards. 
         [0028]    As another example, the X-ray sensing assembly  110 ,  FIG. 7 , which in the illustrated embodiment comprises a scintillator and photo detector array, may be otherwise embodied. For example, it may be a unitary sensing device that converts X-ray strikes directly into electrical signals. Such devices may use detectors based on compound semiconductors such as CDZnTe or the like. In some such devices the entire device acts as an X-ray shield, i.e. there are no gaps through which X-rays may pass. Thus, with such X-ray sensing assemblies there is no need for die and pixel gap alignment. However, the above described method and structure for signal routing on the surfaces of the PCB  150  rather than the die  160  remain applicable. Such signal routing could also be used with other imaging assemblies or in other assemblies where signal routing on the surface of a die is problematic. 
         [0029]    The appended claims are intended to cover such alternative embodiments, except to the extent limited by the prior art.