CN1947660B - Systems, methods and module assemblies for multi-die backlighting diodes - Google Patents

Abstract

A computerized tomographic imaging scanner (10) module comprising a plurality of scintillators (156), a plurality of backlit photodiodes optically coupled to the scintillators (156), a multi-layered a substrate (204), a photodiode electrically coupled to the plurality of substrate conductors, each of the plurality of substrate conductors being connected to a different backlighting photodiode, and a flexible cable having a plurality of flexible conductors ( 308), the substrate is electrically coupled to the plurality of flexible electrical conductors, wherein each of the plurality of flexible electrical conductors is connected to a different output of the multilayer substrate.

Description

Systems, methods and module assemblies for multi-die backlighting diodes

technical field

The present invention relates generally to medical imaging systems, and more particularly to computed tomography (CT). Although this application subject applies primarily to X-ray systems, the invention can also be used in other imaging devices.

Background technique

Modern CT scanners typically employ thousands of x-ray detectors to convert x-ray energy into electrical signals. A typical detector may include an array of scintillators attached to an array of semiconductor photodiodes that detect light or other ionizing radiation on their front surfaces. Some instruments have configurable detectors where the signal currents from multiple independent photodiodes can be combined for further processing in a single amplifier channel. This arrangement allows the detection area of each pixel to be varied using externally controlled electrical switches (field effect transistors or FETs). Pads for electrical connection to the FETs are typically located at one or both ends of the photodiode, and the entire pixel array must be directed from the center of the array to one or both sides next to the FETs.

As the number of elements within the array increases, the density of leads and pads increases to unattainably high levels near the edges of the photodiode array. This imposes certain physical limitations on the number and size of leads and pads that can be made using top surface contacts. With existing wire bonding and silicon processing techniques, only no more than 40-50 slices per 0.625mm pixel (measured at the isocenter of the CT gantry) can be achieved.

The methods and apparatus described herein address at least in part the above-mentioned problems.

Contents of the invention

In one aspect, a computed tomography imaging scanner module is provided that includes a plurality of scintillators, a plurality of backlit photodiodes optically coupled to the scintillators, a multilayer substrate having a plurality of substrate conductors, the photodiodes and the plurality of A plurality of base conductors electrically coupled, wherein each of the plurality of base conductors is connected to a different one of the backlighting photodiodes, and a flexible cable having a plurality of flexible conductors, the base and the plurality of flexible conductors are electrically coupled Coupling, wherein each of the plurality of flexible conductors is connected to a different output terminal of the multilayer substrate.

In another aspect, an imaging system is provided that includes an x-ray source and an x-ray detector module positioned to receive x-rays emitted by the x-ray source. The detector module includes a plurality of scintillators facing the X-ray source, a plurality of backlit photodiodes optically coupled to the scintillators, a multilayer substrate electrically coupled to the plurality of backlit photodiodes, and a multilayer substrate electrically coupled to the multilayer substrate. flexible cable.

In yet another aspect, a method is provided. The method includes receiving photons from a scintillator, converting the photons to an electrical signal, transmitting the electrical signal through a multilayer substrate, and transmitting the electrical signal through a multilayer flexible circuit.

In yet another aspect, a method for attaching a backlighting diode to a multilayer substrate is provided, the method comprising wire bonding a stud block to a surface of the backlighting diode, placing an adhesive to the surface of the multilayer substrate , aligning the surface with the studs relative to the surface with the adhesive on the multilayer substrate, heating the backlight diodes and the substrate to the adhesive curing temperature, and The gap is underfilled.

In another aspect, a method for attaching a flex circuit to a substrate is provided. The method includes placing a solder bump on a surface of a multilayer substrate, placing a reflow encapsulant on a surface of a flexible circuit, aligning the surface of the multilayer substrate with the surface of the solder bump, and heating the flex circuit and the substrate to the solder reflow temperature.

Description of drawings

FIG. 1 is a schematic diagram of an embodiment of a CT imaging system.

FIG. 2 is a schematic block diagram of the system shown in FIG. 1 .

Figure 3 shows a known array of detector modules.

FIG. 4 shows the known detector module shown in FIG. 3 .

Figure 5 shows the placement of a backlighting diode array on a substrate.

Figure 6 shows the bonding connections between the substrate and the backlighting diode array.

Figure 7 shows the bonding connection between the substrate and the flex circuit.

Figure 8 shows a plan view of sacrificial pads on a flex circuit.

Figure 9 shows a flex circuit attached to a substrate with a flex line of flex defined by the location of the sacrificial pad.

Detailed ways

Radiation detection methods and apparatus for imaging systems such as, but not limited to, computed tomography (CT) systems are provided herein. The apparatus and method are described with reference to the drawings, wherein like numerals indicate like elements throughout. Such drawings are illustrative rather than limiting and, therefore, are included to facilitate explanation of exemplary embodiments of the apparatus and methods of the present invention.

In some known CT imaging system configurations, a radioactive source projects a fan-shaped beam of rays that, after collimation, lies in an X-Y plane of a Cartesian coordinate system, commonly referred to as the "imaging plane." The radiation beam passes through the object being imaged, such as a patient. The ray beam is attenuated by the object and impinges on the ray detector array. The intensity of the attenuated radiation beam received by the detector array depends on the attenuation of the radiation beam by the object. Each detector element of the array generates an individual electrical signal that is a measure of the beam attenuation at that detector location. Measures of attenuation from all detectors are taken separately to generate a transmission profile.

In the third-generation CT system, the radiation source and detector array are rotated together with the gantry around the object to be imaged in the imaging plane, so that the angle formed by the radiation beam intersecting the object is constantly changing. A set of radiation attenuation measurements (ie, projection data) from the detector array at one gantry angle is called a "view". A "scan" of an object consists of a set of views obtained at different gantry or viewing angles during one revolution of the radiation source and detector.

In an axial scan, projection data is processed to reconstruct images corresponding to two-dimensional slices taken through the object. Methods for reconstructing images from a set of projection data are known in the art as filtered back-projection techniques. This process converts attenuation measurements from scans into integers called "CT numbers" or "Hounsfield units" that are used to control the brightness of corresponding pixels on a display device.

To reduce the overall scan time, a "helical" scan can be performed. To perform a "helical" scan, the patient is moved during the acquisition of data for a prescribed number of slices. This system generates a single helix from a helical scan of a fan beam. The helix drawn by the fan beam produces projection data from which an image in each defined slice can be reconstructed.

As used herein, an element or step recited in the singular and the word "a" should be understood as not excluding plural said elements or steps, unless such exclusion is explicitly stated. Furthermore, references to "one embodiment" of the present invention are not to be interpreted as excluding the existence of other embodiments that also incorporate the recited features.

Also, as used herein, the phrase "reconstructing an image" is not meant to exclude embodiments of the invention in which data representing an image is generated but a viewable image is not generated. Accordingly, the term "image" is used herein to refer broadly to viewable images and data representing viewable images. However, many embodiments generate (or are configured to generate) at least one viewable image.

FIG. 1 is a schematic diagram of a CT imaging system 10 . FIG. 2 is a schematic block diagram of the system 10 shown in FIG. 1 . In the exemplary embodiment, a computed tomography (CT) imaging system 10 is shown including a gantry 12 representative of a "third generation" CT imaging system. The gantry 12 has a radiation source 14 that projects a cone-shaped beam of X-rays 16 towards a detector array 18 on the opposite side of the gantry 12 .

Detector array 18 is formed from a plurality of detector rows (not shown in FIGS. 1 and 2 ) including a plurality of detector elements 20 that collectively detect projected X-rays passing through an object, such as a medical patient 22 . bundle. Each detection element 20 generates an electrical signal which represents the intensity of the impinging radiation beam and thus the attenuation of the radiation beam as it passes through the object or patient 22 . Imaging system 10 with multi-slice detector 18 is capable of providing multiple images representing the volume of object 22 . Each image of the plurality of images corresponds to a separate "slice" of the volume. The "thickness" or aperture of the slice depends on the thickness of the detector row.

During a scan to obtain radiographic projection data, the gantry 12 and components mounted thereon rotate about a center of rotation 24 . Figure 2 shows only a single row of detector elements 20 (ie, a detector row). However, the multi-slice detector array 18 includes multiple parallel detector rows of detector elements 20 so that projection data corresponding to multiple quasi-parallel or parallel slices can be acquired simultaneously during scanning.

Rotation of the gantry 12 and operation of the radiation source 14 are governed by a control mechanism 26 of the CT system 10 . The control mechanism 26 includes a radiation controller 28 that provides power and timing signals to the radiation source 14 , and a gantry motor controller 30 that controls the rotational speed and position of the gantry 12 . A data acquisition system (DAS) 32 in the control mechanism 26 samples analog data from the detector elements 20 and converts the data to digital signals for subsequent processing. Image reconstructor 34 receives sampled and digitized radiology data from DAS 32 and performs high-speed image reconstruction. The reconstructed image is applied as input to computer 36 which stores the image in mass storage device 38 .

The computer 36 also receives commands and scanning parameters from the operator through a console 40 having a keyboard. An associated cathode ray tube display 42 allows the operator to view reconstructed images and other data from the computer 36 . Computer 36 provides control signals and information to DAS 32, radiation controller 28, and gantry motor controller 30 using commands and parameters provided by the operator. In addition, computer 36 operates table motor controller 44 that controls motorized table 46 to position patient 22 into table 12 . In particular, table 46 moves only a portion of patient 22 through table opening 48 .

In one embodiment, the computer 36 includes a device 50, such as a floppy disk drive, a CD-ROM drive, a DVD drive, a magneto-optical disk (MOD) device, or a device for reading instructions and/or data from a computer-readable medium 52 including, for example, Any other digital device computer readable medium 52 such as a floppy disk, CD-ROM, DVD, or other digital sources such as the network or the Internet, and digital components yet to be developed. In another embodiment, computer 36 executes instructions stored in firmware (not shown). Typically, the processor in at least one of DAS 32, reconstructor 34, and computer 36 shown in FIG. 2 is programmed to perform the process described below. Of course, the method is not limited to implementation in CT system 10, but may be used in conjunction with many other types and variations of imaging systems. In one embodiment, the computer 36 is programmed to perform the functions described herein, therefore, the term "computer" as used herein is not limited to those integrated circuits known in the art as computers, but generally refers to computers, Processors, microcontrollers, microcomputers, programmable logic controllers, application specific integrated circuits and other programmable circuits. Although the methods described herein are described in a medical setting, it is intended that non-medical imaging systems can also benefit from the present invention, such as those typically employed in industrial settings or in transportation environments, such as but not limited to those used in airports Or baggage scanning CT system in other transportation centers.

As shown in FIGS. 3 and 4 , a known detector array 118 includes a plurality of detector module assemblies 150 (also referred to as detector modules), each module including an array of detector elements 120 . Each detector module 150 includes a high-density photosensor array 152 and a multi-dimensional scintillator array 154 located on and proximate to the photosensor array 152 . Specifically, scintillator array 154 includes a plurality of scintillators 156 , while photosensor array 152 includes photodiodes 158 , switching devices 160 and decoders 162 . The small spaces between the scintillator elements are filled with a material such as titanium dioxide-filled epoxy. Photodiode 158 is a single photodiode, or photodiode 158 is a multidimensional diode array. Photodiodes 158 are diffused, deposited or formed on the silicon substrate. Scintillator array 154 is positioned above or near photodiode 158 as is known in the art. Photodiodes 158 are optically coupled to scintillator array 154 and have electrical output lines for transmitting signals representative of the light output by scintillator array 154 . Each photodiode 158 produces an independent low level analog output signal that is a measure of beam attenuation for a particular scintillator of scintillator array 154 . For example, photodiode output lines (not shown in FIGS. 3 or 4 ) may be physically located on one side of the module 120 or on multiple sides of the module 120 . As shown in Figure 4, the outputs of the photodiodes are located on opposite sides of the photodiode array.

As shown in FIG. 3 , the detector array 118 includes 57 detector modules 150 . Each detector module 150 includes a photosensor array 152 and typically a matched scintillator array 154 . Thus, the array 118 is partitioned into 16 rows and 912 columns (16 x 57 modules), which in current technology allows simultaneous collection along the Z axis with each rotation of the gantry 12 up to, for example, N=16 slices data, where the Z axis is the rotational axis of the gantry.

The switch device 160 is a multi-dimensional semiconductor switch array. Switching device 160 is coupled between photosensor array 152 and DAS 32. In one embodiment, switching device 160 includes two semiconductor switch arrays 164 and 166 . Switch arrays 164 and 166 each include a plurality of field effect transistors (FETs) (not shown) arranged in a multi-dimensional array. Each FET includes an input terminal, an output terminal, and a control terminal (not shown) electrically connected to one of the output lines of the respective LED. The FET output and control terminals are connected to lines that are electrically connected to the DAS 32 via a flexible cable 168. Specifically, about half of the photodiode output lines are electrically connected to each FET input line of switch 164 , while the other half of the photodiode output lines are electrically connected to the FET input lines of switch 166 . The flexible cable 168 is thereby electrically coupled to the photosensor array 152 , such as by wire connections from the flex wire 168 to the switching device 160 , and from the switching device 160 and the decoder 162 to the photodiodes 158 .

Decoder 162 controls the operation of switching device 160 to enable, disable, or combine the output of photodiodes 158 depending on the desired number of slices and the slice resolution of each slice. In one embodiment, decoder 162 is a FET controller known in the art. Decoder 162 includes a plurality of output and control lines coupled to switching device 160 and DAS 32. Specifically, the decoder output is electrically coupled to the switch device control line to enable the switch device 160 to transmit inherent data from the switch device input to the switch device output. Using decoder 162, specific FETs within switching device 160 are selectively enabled, disabled, or combined to electrically connect the output of a specific photodiode 158 to DAS 32 of the CT system. Decoder 162 enables switching device 160 to connect a selected number of rows of photosensor array 152 to DAS 32, causing the selected number of slices of data to be electrically connected to DAS 32 for processing.

As shown in FIGS. 3 and 4 , detector module 150 is assembled into detector array 118 and secured in place by rails 170 and 172 . FIG. 3 shows that on the base 174 of the module 150 , the flexible cable 168 and the mounting bracket 176 , the track 172 has been secured in place and the track 170 is to be secured to the cable 168 . Screws (not shown in FIGS. 3 and 4 ) are then threaded through holes 178 and 180 and into threaded holes 182 of rail 170 to secure module 150 in place. The flange 184 of the mounting bracket 176 is held in place by applying pressure (or by bonding, in one embodiment) against the rails 170 and 172 and prevents the detector module 150 from "wobbling". The mounting bracket 176 also clamps the flexible cable 168 to the base 174 or, in one embodiment, the flexible cable 168 is also adhesively bonded to the base 174 .

Conventionally, however, traces or electrical paths can only be introduced from either end of the photodiode array, which creates certain physical limitations on the number and size of traces and pads formed with top surface contacts. Physical limitations on the number and size of traces and pads can be removed by inverting the diodes and placing the surface contacts on the backside of the photodiode array. This technique is described, for example, in US Patent No. 6,707,046 (ie, backside illuminated or "backlit" diodes). Each pixel of the backlighting diode array is directly electrically connected to a substrate made of ceramic or printed wiring board (PWB) or the like. The substrate is multilayered to carry electrical signals from the photodiode array across the multilayer substrate to the opposite side of the substrate. Electrically bondable pads are provided on each surface of the substrate to facilitate electrical interconnection. The backside connection design eliminates the need to introduce traces to both sides of the diode array and enables unlimited tiling of devices within the Z and X dimensions of the CT scanner.

5 and 6 illustrate a diode-substrate assembly 200 assembled by placing a backlighting diode array 202 onto a multilayer substrate 204 . A conductive epoxy array 206 is coated, masked or otherwise applied to the substrate 204 prior to aligning and attaching the backlighting diode array 202 to the substrate 204 . A plurality of stud blocks 208 are thermosonically bonded to the metallized surface of the backlight diode array 214 and placed substantially within the center of each pixel of the array 202 . Post blocks 208 are metal, and in one embodiment gold. The conductive adhesive 206 forms an identical pattern on the surface of the substrate 204 that matches and opposes the pattern 216 on the array of stud blocks 206 . Pick and place flip chip technology is used to precisely align the diode array 202 to the substrate 204 and to press the pillar block 208 to the bottom until the pad array 216 . The conductive adhesive is allowed to cure for the required time and temperature as specified by the manufacturer. Post block 208 facilitates controlling the uniform height of backlight diode array 202 and provides clearance 212 for underfill material 210 . Post blocks 208 contact the surface of substrate 204 across the array of contact areas and are substantially of equal height such that the array of diodes substantially conforms to the same surface flatness of substrate 204 . The stud blocks also form gaps 212 into which underfill material 210 is introduced by capillary action. The underfill 210 is used to strengthen the connection between the backlight diode array 202 and the substrate 204 . The underfill 210 also serves to prevent ions and other contaminants from entering the array attachment area, adding low signal robustness to the connection.

FIG. 7 shows a flex circuit 308 attached to the side of the substrate 204 opposite the backlight diode array 202 (not shown). A plurality of eutectic solder balls 302 are positioned on the substrate 204 in a pattern similar to the plurality of electrical output pads 304 of the substrate 204 . Gap 310 is then filled using a no-flow process, first by placing encapsulant 312 onto flex circuit 308 using a pick-and-place device, attaching flex circuit 308 to substrate 204, and then by heating the assembly The solder balls 302 flow to a predetermined temperature required for solder. As part of the solder flow heats up, the encapsulation material is cured. The flex circuit 308 accordingly has a pattern of electrical contact pads 306 that matches the opposing pattern 304 on the substrate 204 . No-flow processing refers to placing the encapsulant on the flex circuit 308 and then heating to the melting temperature of the solder before joining the two surfaces.

Figure 8 shows a flex circuit 308 configured with an array pattern 306, which is also configured with a sacrificial pad 330 that is stitched to form an axial gap 332 between the stitches. Similar metallized sacrificial stitches are also positioned on the substrate (not shown) in a similar manner to the pattern of the contact pads 304 . When the flex circuit 308 is connected to the substrate 204, the opposing stitch patterns provide opposing metallized surfaces, which provide at least three functions. Figure 9 shows a sacrificial pad 330 that provides a reinforced bonding surface for the encapsulant to be adhered to when subjected to subsequent bonding processes. The sacrificial pad 330 also serves to stop the flow of the encapsulant 312 that overflows the sacrificial pad 330 . Encapsulant 312 is confined within its flow region by grooves 334 positioned and dimensioned such that capillary action stops within groove region 334 . The sacrificial pad 330 also serves to define the bend line 336 of the flex circuit 308 in such a restricted flow. Axial gap 332 enables release of gases formed during heat processing of solder bump 304 .

One technical effect of the methods and apparatus described herein is that it provides backlighting diodes on a multilayer substrate and a flex circuit attached below the substrate. Another technical effect is that the methods and devices described herein use multilayer ceramic or printed wiring boards as substrate materials. Another technical effect is that the methods and apparatus described herein use solder and reflow encapsulant for flex attachment and bend wire control. Another technical effect is that the methods and apparatus described herein use sacrificial pads to control underfill material and enhance CT detector module reliability.

The invention has been described with reference to preferred embodiments. Alterations and alterations will occur to others by others skilled in the art upon reading and understanding the preceding detailed description. The present invention should be construed to include all such modifications and changes as long as they fall within the scope of the appended claims or their equivalents.

parts list

CT system................................................ ...................................10

Bench................................................ ................................12

Radioactive source................................................ ...................................14

Cone Beam ................................................ ...................................16

Detector array................................................ ...................................18

Detector element................................................ ...................................20

object................................................. .............................twenty two

Center of rotation................................................ ..........................twenty four

Control mechanism ................................................ ...................................26

Radiation controller................................................ ...................................28

Bench motor controller................................................ ..............30

DAS................................................................ ...................................32

Image Reconstructor................................................ ...................................34

computer................................................. ...................................36

storage device................................................ ...................................38

console................................................ ...................................40

monitor................................................. ...................................42

A motor controller..................................................... ...................................44

tower................................................. ...................................46

Bench opening .............................................. ...................................48

device................................................ ...................................50

Computer Readable Media ................................................ ...................52

Known detector arrays................................... ...................................118

module................................................ ...................................120

Detector Module................................................ ...................................150

Photosensor Array................................................ ...................152

Scintillator Array................................................ ...................................154

Multiple Scintillators ................................................ ...................................156

Photodiode................................................ ................................158

Switchgear................................................ ...................................160

decoder................................................ ...................................162

switch................................................. ...................................164

Flexible Cable ................................................ ...................................168

track................................................. ...................................170

track................................................. ...................................172

Substrate ................................................... ...................................174

Mounting brackets................................................ ...................................176

hole................................................. ...................................178

hole................................................. ................................180

hole................................................. ................................182

Flange................................................ ...................................184

Diode-Substrate Assemblies................................................ ...................200

Backlight Diode Array................................................... ..........202

Multi-Layer Substrates ................................................ ...................................204

Adhesive................................................ ...................................206

Column block................................................ ...................................208

Underfill...................................... ...................................210

gap................................................. ...................................212

Backlight Diode Array................................................... ..........214

array..................................................... ...................................216

Solder balls................................................ ...................................302

Contact plate ................................................ ...................................304

Array pattern................................................ ...................................306

Contact plate ................................................ ...................................306

Flexible Circuits ................................................ ...................................308

gap................................................. .......................................... 310

Encapsulants................................................ ...................................312

Sacrificial pads................................................ ...................................330

Axial clearance................................................ ...................................332

Groove................................................ ...................................334

Curved wire ................................................ ...................................336

Claims (10)

1. A computed tomography imaging scanner (10) module comprising: a plurality of scintillators (156); a plurality of backlighting photodiodes (202) optically coupled to the scintillator (156); A multilayer substrate (204) having a plurality of substrate conductors to which the backlighting photodiode (202) is electrically coupled, wherein each of the plurality of substrate conductors is connected to a different on said backlighting photodiodes (202); and A flexible cable (308) having a plurality of flexible electrical conductors to which the base is electrically coupled, wherein each of the plurality of flexible electrical conductors is connected to the multilayer base ( 204) on different output terminals. 2. The module of claim 1, wherein the plurality of scintillators (156) comprises a two-dimensional array (154). 3. The module of claim 2, wherein said plurality of backlighting photodiodes (202) comprises a two-dimensional array (214) aligned with said plurality of scintillator (156) arrays. 4. The module of claim 3, wherein the plurality of base conductors comprises a two-dimensional array aligned with the array of backlighting photodiodes (202). 5. The module of claim 1, wherein each of the plurality of backlighting photodiodes (202) comprises a pillar block. 6. The module of claim 5, wherein each of said stud blocks comprises gold. 7. An imaging system (10) comprising: X-ray source (14); and an x-ray detector module (18) positioned to receive x-rays emitted from said x-ray source, said detector module comprising: a plurality of scintillators (156) facing said X-ray source; a plurality of backlighting photodiodes (202) optically coupled to the scintillator (156); a multilayer substrate (204) electrically coupled to the plurality of backlighting photodiodes; and A flexible cable (308) is electrically coupled to the multilayer substrate (204). 8. A method for computed tomography comprising: receiving photons from the scintillator (156); converting the photons into electrical signals; transmitting said electrical signal through the multilayer substrate (204); and The electrical signal is transmitted through a multilayer flexible circuit (308). 9. A method for attaching backlighting diodes (202) to a multilayer substrate (204), the method comprising: The column block (208) is welded to the surface of the backlighting diode by wire; placing an adhesive (206) on the surface of the multilayer substrate; aligning the surface bearing the stud blocks relative to the surface bearing the adhesive on the multilayer substrate; heating the backlighting diodes and the substrate to an adhesive curing temperature; and A gap (310) formed between the backlighting diodes and the substrate is underfilled. 10. A method for attaching a flexible circuit (308) to a multilayer substrate (204), comprising: placing solder bumps (302) on the surface of the multilayer substrate; placing a reflow encapsulant (312) onto the surface of the flexible circuit; aligning a surface of the multilayer substrate with the solder bump surface; The flexible circuit and the substrate are heated to a solder reflow temperature.

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