Patent Publication Number: US-2019175003-A1

Title: Image pickup unit for endoscope and endoscope

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation application of PCT/JP2016/081895 filed on Oct. 27, 2016, the entire contents of which are incorporated herein by this reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     An embodiment of the present invention relates to an image pickup unit for endoscope that acquires an image, and an endoscope having a rigid distal end portion on which the image pickup unit for endoscope is arranged. 
     2. Description of the Related Art 
     An endoscope acquires an image of an inside of a body of a patient, for example, by inserting an insertion portion having a rigid distal end portion on which an image pickup unit is arranged into the inside of the body. Japanese Patent Application Laid-Open Publication No. 2005-334509 discloses an image pickup unit including an image pickup device in which a light receiving portion is formed, and a wiring board on which electronic components such as a capacitor, a resistor, and an IC chip configuring a drive circuit of the image pickup device are mounted. The wiring board is bonded on a rear surface of the image pickup device. 
     In the abovementioned image pickup unit, chip-shaped electronic components such as the capacitor, the resistor, and a buffer are mounted on the wiring board bonded to the rear surface of the image pickup device. Therefore, a length of the image pickup unit in an optical axis direction is long. 
     In recent years, semiconductor devices in which a planar device (thin film device) having functions of electronic components such as a capacitor is formed have been developed. The image pickup unit can be caused to be short and small by bonding a device stack obtained by stacking a plurality of semiconductor devices to a rear surface of the image pickup device. An endoscope having a short and small image pickup unit has a distal end rigid portion that is short in length, and hence is minimally invasive. 
     SUMMARY OF THE INVENTION 
     According to an embodiment of the present invention, there is provided an image pickup unit for endoscope including: an image pickup portion including an image pickup device, a device stack, and a reinforcing member; and a signal cable connected to the image pickup portion, in which: the image pickup device includes a light receiving surface, and a rear surface opposite to the light receiving surface; the device stack bonded to the rear surface of the image pickup device is obtained by stacking a plurality of semiconductor devices including a first semiconductor device and a second semiconductor device; at least a part of an outer peripheral surface of the device stack is covered with the reinforcing member formed by resin; the first semiconductor device closest to a rear end side is smaller than the second semiconductor device on an image pickup device side; and the reinforcing member has a thickness on the rear end side that is thicker than a thickness on the image pickup device side. 
     An endoscope of another embodiment includes an image pickup unit for endoscope including: an image pickup portion including an image pickup device, a device stack, and a reinforcing member; and a signal cable connected to the image pickup portion, in which: the image pickup device includes a light receiving surface, and a rear surface opposite to the light receiving surface; the device stack bonded to the rear surface of the image pickup device is obtained by stacking a plurality of semiconductor devices including a first semiconductor device and a second semiconductor device; at least a part of an outer peripheral surface of the device stack is covered with the reinforcing member formed by resin; the first semiconductor device closest to a rear end side is smaller than the second semiconductor device on an image pickup device side; and the reinforcing member has a thickness on the rear end side that is thicker than a thickness on the image pickup device side. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a configuration diagram of an endoscope system including an endoscope of an embodiment; 
         FIG. 2  is a cross-sectional view of a distal end portion of the endoscope of the embodiment; 
         FIG. 3  is a cross-sectional view of an image pickup unit of the embodiment; 
         FIG. 4  is a top transparent view of the image pickup unit of the embodiment; 
         FIG. 5  is an exploded view of a device stack of the image pickup unit of the embodiment; 
         FIG. 6  is a layout drawing of the device stack of the image pickup unit of the embodiment; 
         FIG. 7  is a cross-sectional view of an image pickup unit of Modification 1; 
         FIG. 8  is a layout drawing of a device stack of the image pickup unit of Modification 1; 
         FIG. 9  is a cross-sectional view of an image pickup unit of Modification 2; 
         FIG. 10  is an exploded view of a device stack of an image pickup unit of Modification 3; 
         FIG. 11  is a perspective view of the image pickup unit of Modification 3; 
         FIG. 12  is a cross-sectional view of an image pickup unit of Modification 4; and 
         FIG. 13  is a cross-sectional view of an image pickup unit of Modification 5. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S) 
     &lt;Configuration of Endoscope System&gt; 
       FIG. 1  illustrates an endoscope system  6  including an endoscope  9  of an embodiment. An image pickup unit  1  for endoscope of the embodiment (hereinafter also referred to as an “image pickup unit  1 ”) is arranged on a rigid distal end portion  3 A of an insertion portion  3  of the endoscope  9 . 
     Note that in the following description, the drawings based on each embodiment are schematic, and a relationship between a thickness and a width of each portion, a thickness ratio and a relative angle of each portion, and the like are different from actual relationships, thickness ratios, relative angles, and the like. Portions having different size relationships and ratios may also be included throughout the drawings. Further, drawing of some components may be omitted. 
     The endoscope  9  includes the insertion portion  3 , a grasping portion  4  arranged on a proximal end portion side of the insertion portion  3 , a universal cord  4 B provided so as to extend from the grasping portion  4 , and a connector  4 C arranged on a proximal end portion side of the universal cord  4 B. The insertion portion  3  includes the rigid distal end portion  3 A on which the image pickup unit  1  is arranged, a bending portion  3 B which is provided so as to extend on a proximal end side of the rigid distal end portion  3 A, bendable, and for changing a direction of the rigid distal end portion  3 A, and a flexible portion  3 C provided so as to extend on a proximal end side of the bending portion  3 B. An angle knob  4 A that rotates and is an operation portion for an operator to operate the bending portion  3 B is arranged on the grasping portion  4 . 
     The universal cord  4 B is connected to a processor  5 A via a connector  4 C. The processor  5 A controls the entire endoscope system  6 . In addition, the processor  5 A performs signal processing on an image pickup signal outputted from the image pickup unit  1 , and outputs the processed image pickup signal as an image signal. A monitor  5 B displays the image signal outputted from the processor  5 A as an endoscope image. 
     As illustrated in  FIG. 2 , in the rigid distal end portion  3 A of the endoscope  9 , an air feeding and water feeding tube  94 , a cladding tube  92 , an operation wire  93  connected to the angle knob  4 A, a lens unit  19 , and the image pickup unit  1  are arranged on a rigid distal end member  91 . Note that the image pickup unit  1  is placed in a position in which an optical axis O is eccentric with respect to a central axis C of the rigid distal end portion  3 A. 
     The lens unit  19  that fotins an object image includes a plurality of lenses and a lens holder. The lens unit  19  is inserted and fixed in a hole in the distal end member  91 . 
     &lt;Configuration of Image Pickup Unit&gt; 
     Hereinafter, in the optical axis direction, a direction (Z-axis value increasing direction) in which an image pickup portion  40  is placed is referred to as a front side, and a direction (Z-axis value decreasing direction) in which a signal cable  51  is placed is referred to as a rear side. Further, in the direction orthogonal to the optical axis, a Y-axis direction is referred to as an upper direction/a lower direction, and an X-axis direction orthogonal to the Y-axis is referred to as a left direction/a right direction. 
     For example, as illustrated in  FIG. 3  to  FIG. 6 , the image pickup unit  1  includes the image pickup portion  40  that is a substantially rectangular parallelepiped, a flexible wiring board  50  bonded to a rear end surface of the image pickup portion  40 , and the signal cable  51 . The signal cable  51  bonded to the wiring board  50  is connected to the universal cord  4 B, and transmits an image pickup signal and the like. 
     Note that the signal cable  51  may be directly bonded to the image pickup portion  40 . In other words, the wiring board is not a mandatory component of the image pickup unit  1 . 
     The image pickup portion  40  includes the image pickup device  10  to which a cover glass  18  adheres, a device stack  20 , and a reinforcing member  30  covering an entire surface of an outer peripheral surface of the device stack  20 . 
     The image pickup device  10  having a rectangular shape in planar view, that is, the image pickup device  10  having a rectangular cross section in a direction orthogonal to the optical axis O includes a light receiving surface  10 SA, a rear surface  10 SB opposite to the light receiving surface  10 SA, and four side surfaces. A light receiving portion  11  that receives the object image formed by the lens unit  19  and converts the received object image to an electrical signal is formed on the light receiving surface  10 SA. The light receiving portion  11  is a CCD, a CMOS light receiving element, or the like, and generates an electrical signal by receiving light and performing photoelectric conversion. The light receiving portion  11  is connected to an electrode  17 A on the rear surface  10 SB via through wiring  17 . 
     In the device stack  20 , five semiconductor devices  21  to  25  including the first semiconductor device  21  and the second semiconductor device  23  are stacked. Each of the semiconductor devices  21  to  25  has a rectangular shape in planar view and is stacked via a sealing resin (underfilling)  39 . The sealing resin  39  is an epoxy resin, an acrylic resin, a polyimide resin, a silicone resin, a polyvinyl resin, or the like. 
     The device stack  20  processes the electrical signal outputted from the image pickup device  10 , and outputs the processed electrical signal as an image pickup signal. Planar devices  21 C to  25 C are formed on the semiconductor devices  21  to  25  each having a rectangular shape in planar view. Each of the planar devices  21 C to  25 C configures an electronic component function circuit such as a capacitor, a resistor, or a buffer, or a processing circuit such as a noise reduction circuit or an analog-to-digital converter circuit. 
     The plurality of semiconductor devices  21  to  25  may have different thicknesses. The planar devices  21 C to  25 C may be formed on one surface or both surfaces of the semiconductor devices  21  to  25 , respectively. The number of the stacked semiconductor devices in the device stack  20  only needs to be two or more, and is not limited to five as in this example. 
     The semiconductor devices  21  to  25  are connected via respective through wiring  27  and bumps  29 . A front end surface of the device stack  20  is connected to the electrode  17 A on the rear surface  10 SB of the image pickup device  10  via the bumps  29 . A rear end surface of the device stack  20 , that is, a rear surface of the semiconductor device  21  that is a rear end surface of the image pickup portion  40  is connected to the wiring board  50  via the bumps  29 . 
     The sealing resin  39  is also filled between the rear surface  10 SB of the image pickup device  10  and the front end surface of the device stack  20 , and between the rear end surface of the device stack  20  and the wiring board  50 , respectively. 
     External dimensions (sizes in planar view) of the semiconductor devices  21  to  25  in the direction orthogonal to the optical axis are equal to or less than a size of the image pickup device  10  in planar view. Therefore, the semiconductor devices  21  to  25  projected on a projection plane in the direction orthogonal to the optical axis are placed within a projection plane of the image pickup device  10 . 
     The four side surfaces forming the outer peripheral surface of the device stack  20  is covered with the reinforcing member  30  formed by resin. In other words, the device stack  20  is embedded in the reinforcing member  30 , an external form of which is formed by a rectangular parallelepiped-shaped hard material, and which hardly deforms even when applied with stress. A size of the reinforcing member  30  in planar view is substantially the same as a size of the image pickup device  10  in planar view. 
     The image pickup unit  1  including the device stack  20  is short and small. In addition, a size of the image pickup unit  1  in planar view is the same as the size of the image pickup device  10 . Therefore, the image pickup unit  1  has a small diameter. 
     The device stack  20  is covered with the reinforcing member  30  formed by an epoxy resin, a fluorine resin, and the like that are hard resins having a Rockwell hardness on R scale (JIS K7202-2, a measured temperature is 23° C.) that is HR 100 or more, for example. 
     The periphery of the device stack  20  is reinforced by the reinforcing member  30  that is harder than the sealing resin  39 , and hence the strength of the device stack  20  is enhanced. Note that the reinforcing member  30  also has better humidity resistance (water vapor barrier properties) than the sealing resin  39 . 
     Note that at least one of the front end surface and the rear end surface of the device stack  20  besides the bumps  29  may be covered with the reinforcing member  30 . In other words, the sealing resin  39  on the front end surface and the rear end surface of the device stack  20  may be the reinforcing member  30 . 
     In the image pickup unit  1 , an external dimension (size in planar view) of the first semiconductor device  21 , which is arranged on a rear-most end side (proximal end portion side: a position closest to the signal cable  51 ) to which the wiring board  50  is bonded, in the direction orthogonal to the optical axis is smaller than a size of the second semiconductor device  23  arranged on the front side (image pickup device side: a position close to the image pickup device  10  with respect to the first semiconductor device  21 ) in planar view. 
     Therefore, the reinforcing member  30  covering the outer peripheral surface (four side surfaces) of the device stack  20  has a thickness D 1  on the rear end side (proximal end portion side) that is thicker than a thickness D 2  on the front side (image pickup device side). Note that the thicknesses D 1  and D 2  are lengths from the side surfaces of the respective semiconductor devices to an outer peripheral surface of the reinforcing member  30 . 
     A stress in the shear direction applied to the image pickup unit  1  is larger on the rear end side than on the front end side. In the image pickup unit  1 , the thickness D 1  of the reinforcing member  30  on the rear end side to which a larger stress is applied is thicker than the thickness D 2  on the front end side. Therefore, the image pickup unit  1  has a higher reliability than an image pickup unit in which the thickness of the reinforcing member  30  is uniform. The endoscope  1  including the image pickup unit  1  is highly reliable. The endoscope  1  includes the image pickup unit  1  that is short and small, and hence has a short rigid distal end portion and is minimally invasive. 
     Note that the strength improvement effect is notable if the thickness D 1  is 120% or more of the thickness D 2 , but it is preferred that the thickness D 1  be 150% or more of the thickness D 2 . 
     Note that in the image pickup unit  1 , the semiconductor device  22  on the front side with respect to the first semiconductor device  21  is also the same size as the first semiconductor device  21 . However, the semiconductor device  22  on the front side with respect to the first semiconductor device  21  may be larger than the first semiconductor device  21 . This is because the rear end of the device stack  20  is applied with the largest stress, and the thickness D 1  of the reinforcing member  30  covering the rear end is important. 
     As illustrated in  FIG. 6 , in the image pickup portion  40  of the image pickup unit  1 , the optical axis O and a central axis C 20  of the device stack  20  substantially match. Therefore, the thickness of the reinforcing member  30  is the same for four directions, that is, the upper direction, the lower direction, the left direction, and the right direction. 
     MODIFICATIONS OF EMBODIMENT 
     Image pickup units  1 A to  1 E for endoscope and endoscopes  9 A to  9 E of Modifications 1 to 5 are similar to the image pickup unit  1  for endoscope and the endoscope  9  of the embodiment and has the same effect. Therefore, components having the same functions are denoted by the same reference characters and descriptions of the same functions are omitted. 
     Modification 1 
     As illustrated in  FIG. 7  and  FIG. 8 , in an image pickup unit  1 A of Modification 1, thicknesses D 1 A and D 2 A on the outer peripheral side of the reinforcing member  30  are thicker than thicknesses D 1 B and D 2 B on the central axis side. In other words, as illustrated in  FIG. 8 , the central axis C 20  of the device stack  20  is located on a lower side (central axis side) with respect to the optical axis O in an image pickup portion  40 A of the image pickup unit  1 A. Note that the thickness of the reinforcing member  30  is substantially the same in the left and right directions. 
     Although not shown, in an endoscope  9 A, the optical axis O of the image pickup unit  1 A is placed in a position eccentric with respect to the central axis C of the rigid distal end portion  3 A as with the endoscope  9  that has been already described. 
     Therefore, the stress applied to the image pickup unit  1 A is larger on the outer peripheral side of the rigid distal end portion  3 A than on the central axis side. In the image pickup unit  1 A, the reinforcing member  30  is thicker on the outer peripheral side (upper side) than on the central axis side (lower side). In the image pickup unit  1 A, the outer peripheral portion to which large stress is applied has a stronger structure and a higher reliability as compared to the image pickup unit  1 . 
     Modification 2 
     As illustrated in  FIG. 9 , in an image pickup unit  1 B of Modification 2, the plurality of semiconductor devices  21  to  25  having different sizes are alternately stacked. In other words, the image pickup unit  1 B includes the semiconductor devices  21  to  25  in a plurality of sizes, and the sizes of the semiconductor devices  21  to  25  stacked side-by-side are different from each other in a device stack  20 B. 
     In other words, in the device stack  20 B, the plurality of semiconductor devices  25  and  23  having the same size (external dimension in the direction orthogonal to the optical axis; size in planar view) as the first semiconductor device  21  on the rear end side (proximal end portion side) to which the wiring board  50  is bonded, and the semiconductor devices  22  and  24  larger than the first semiconductor device  21  are stacked in the order of the semiconductor devices  25 ,  24 ,  23 ,  22 , and  21  from the front side. 
     In the image pickup unit  1 B, the outer peripheral portions of main surfaces (front surfaces/rear surfaces) of the semiconductor device  22  and  24  in the device stack  20 B are covered with the reinforcing member  30 , and hence a contact area between the device stack  20 B and the reinforcing member  30  is larger and the strength is enhanced as compared to the image pickup unit  1 . 
     Further, as already described, the reinforcing member  30  has better humidity resistance (water vapor barrier properties) than the sealing resin  39  sealing spaces between the semiconductor devices  21  to  25 . In the image pickup unit  1 B, a distance from an outer surface of the reinforcing member  30  to side surfaces of the sealing resin  39  sealing each of the spaces between the semiconductor devices  21  to  25  is the same. Therefore, the humidity resistance is better than the humidity resistance of the image pickup unit  1 . 
     Modification 3 
     As illustrated in  FIG. 10  and  FIG. 11 , an image pickup unit  1 C of Modification 3 has cut-out portions N in the outer peripheral portions of the largest semiconductor devices  22  and  24 , and a part of side surfaces  22 SS,  24 SS, and the like of the largest semiconductor devices  22  and  24  is exposed on the outer peripheral surface of a device stack  20 C. 
     In other words, the size of the largest semiconductor devices  22  and  24  is the same as the size of the image pickup device  10 . Therefore, a large planar device can be formed on the semiconductor devices  22  and  24 . Further, the reinforcing member  30  of the image pickup unit  1 C is not divided by the semiconductor devices  22  and  24  and is an integral structure due to the cut-out portions N. 
     Therefore, the image pickup unit  1 C includes the large semiconductor devices  22  and  24  whose sizes are the same as the size of the image pickup device  10 , but the strength is guaranteed. 
     Note that the plurality of semiconductor devices  21  to  25  having different sizes are alternately stacked in the image pickup unit  1 C. However, the semiconductor devices do not necessarily need to be alternately stacked if cut-out portions are formed in the outer peripheral portion of the largest semiconductor device, and a part of a side surface of the largest semiconductor device is exposed on the outer peripheral surface of the device stack. 
     In the image pickup unit  1 C, a part of an outer peripheral surface of a device stack  40 C is not covered with the reinforcing member  30 . In other words, only at least a part of the outer peripheral surface of the image pickup unit needs to be covered with the reinforcing resin  30 . 
     Modification 4 
     As illustrated in  FIG. 12 , in an image pickup unit  1 D of Modification 4, slits are formed in a distal end portion of a flexible wiring board  50 D in a direction parallel to the optical axis, and the distal end portion is divided into two. Further, the divided two distal end portions are embedded in the reinforcing member  30  above or below the device stack  20  of an image pickup portion  40 D, respectively. 
     In the image pickup unit  1 D, the stress applied to the wiring board  50 D via the signal cable  51  is applied to the reinforcing member  30  via the distal end portions of the wiring board  50 D. The image pickup unit  1 D has a higher reliability because the image pickup unit  1 D is reinforced by the wiring board  50 D embedded in the reinforcing member  30  in a stronger manner. 
     Note that as already described, the reinforcing member  30  may also serve as the sealing resin  39  between the image pickup portion  40  and the wiring board  50 , and the reinforcing member  30  may also cover the side surfaces of the wiring board  50 . 
     Modification 5 
     As illustrated in  FIG. 13 , an image pickup unit  1 E of Modification 4 has four configurations of Modifications 1 to 4. 
     In other words, an average thickness DAA of the reinforcing member on an outer peripheral side (an upper side in the drawing) is thicker than an average thickness DBA of the rigid distal end portion  3 A on a central axis C side (a lower side in the drawing), the plurality of semiconductor devices  21  to  25  having different sizes are alternately stacked, the cut-out portions N are formed in the outer peripheral portions of the largest semiconductor devices  22  and  24 , a part of side surfaces of the largest semiconductor devices  22  and  24  is exposed on an outer peripheral surface of a device stack  20 E, and distal end portions of a wiring board  50 E are embedded in the reinforcing member  30 . 
     The image pickup unit  1 E has the effects of the image pickup units  1 A to  1 D of Modifications 1 to 4 in addition to the effect of the image pickup unit  1 . 
     Note that needless to say, an image pickup unit including two or three configurations out of the configurations of the image pickup units  1 A to  1 D of Modifications 1 to 4 has the effects of the respective modifications. 
     Further, needless to say, the endoscopes  9 A to  9 E including the image pickup units  1 A to  1 E of Modifications 1 to 5 have the effect of the endoscope  9  and have the effects of the image pickup units  1 A to  1 E of Modifications 1 to 5. The endoscope of the present invention is not limited to a medical endoscope, but may be an industrial endoscope. 
     The present invention is not limited to the abovementioned embodiment and modifications, but various modifications, changes, and the like can be made within the range in which the gist of the present invention is not changed.