Patent Publication Number: US-8110802-B2

Title: Photodetecting device including base with positioning portion

Description:
TECHNICAL FIELD 
     The present invention relates to a photodetecting device with a so-called back-incident type photodetecting element. 
     BACKGROUND ART 
     Conventionally, so-called back-incident type photodetecting elements have been known. This type of photodetecting element is provided with a light-incident surface at the back surface side of a semiconductor substrate, and detects light made incident from the light-incident surface by a photodetecting section being at the front surface side. As a photodetecting device with such a photodetecting element, there is provided, for example, a semiconductor energy detector described in Patent Document 1. This semiconductor energy detector includes a BT-CCD (Back-Thinned CCD) for which a part of the semiconductor substrate is thinned on the opposite side to the photodetecting section and which is capable of detecting various types of energy beams including ultraviolet rays, soft X-rays, and electron beams at a high sensitivity, and used as, for example, a photodetecting section of a telescope for astronomical observation.
     Patent Document 1: Japanese Published Unexamined Patent Application No. H06-196680   

     DISCLOSURE OF THE INVENTION 
     Problem to be Solved by the Invention 
     In such a telescope application etc., as described above, for providing the photodetecting section with a large area, it is effective to adopt a so-called buttable arrangement structure, where a plurality of photodetecting devices are disposed in a matrix arrangement on an installation body such as a cold plate. In such an arrangement structure, suppressing the interval between the respective photodetecting devices to, for example, 100 μm or less makes it possible to arrange the photodetecting devices at a high density, while required is a high degree of positional alignment accuracy of photodetecting elements with respect to the installation body. 
     The present invention has been made in order to solve the above problems, and an object thereof is to provide a photodetecting device capable of accurately performing positional alignment of the photodetecting element with respect to the installation body. 
     Means for Solving the Problem 
     In order to solve the above problems, a photodetecting device according to the present invention includes: a photodetecting element that detects light made incident from one surface by a photodetecting section being on a side of the other surface; a wiring board provided at the other side of the photodetecting element and electrically connected with the photodetecting section; and a base provided at the other side of the wiring board and to be installed on a predetermined installation body, wherein a positional alignment mark to serve as a positional reference of the photodetecting element is formed on the other surface of the photodetecting element, a window portion to expose the positional alignment mark is formed on the wiring board, and the base has a positioning portion positioned with respect to the positional alignment mark exposed from the window portion, and a fitting portion positioned with respect to the positioning portion and to be fitted with the installation body. 
     In this photodetecting device, the positional alignment mark to serve as a positional reference of the photodetecting element is formed at the other surface side of the photodetecting element. Moreover, the base is provided with the fitting portion to be fitted with the installation body, and the fitting portion is accurately positionally aligned with respect to the photodetecting element via the positioning portion positioned with respect to the positional alignment mark exposed from the window portion of the wiring board. Accordingly, in this photodetecting device, when fitting the fitting portion with the installation body, the photodetecting element is accurately positionally aligned with respect to the installation body. As a result, even when, for example, a 4-side buttable arrangement is adopted, the photodetecting elements in the respective photodetecting devices can be accurately aligned in positional relationship, so that the photodetecting devices can be arranged at a high density. 
     Moreover, it is preferable that the positional alignment mark is formed at two sites or more so as to pass through a center line of the photodetecting element, and the positioning portion is composed of one side face of the base and one end portion in the side face. In this case, by aligning, with the line passing through the positional alignment mark, the line of one side face of the base, the photodetecting element and the base can be accurately angularly aligned. And, the photodetecting element and the base can be accurately positionally aligned based on relative distances between the positional alignment marks and one end portion. 
     Moreover, it is preferable that the fitting portion is a pin protruded to the other surface side of the base. In this case, providing, on the installation body, a recess portion corresponding to the pin makes it possible to simply install the photodetecting device on the installation body. 
     Effects of the Invention 
     The photodetecting device according to the present invention can accurately perform positional alignment of the photodetecting element with respect to the installation body. As a result, even when, for example, a 4-side buttable arrangement is adopted, the photodetecting elements in the respective photodetecting devices can be accurately positioned in positional relationship, so that the photodetecting devices can be arranged at a high density. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  A view showing a photodetecting section formed with a photodetecting device according to an embodiment of the present invention loaded. 
         FIG. 2  A perspective view of the photodetecting device. 
         FIG. 3  A view of the photodetecting device observed from the front surface side. 
         FIG. 4  A side view showing a part of the photodetecting device in a sectioned manner. 
         FIG. 5  An enlarged sectional view in the vicinity of a slit portion. 
         FIG. 6  An enlarged view of the slit portion observed from the front surface side, with a lid portion removed. 
         FIG. 7  A side view of the photodetecting device observed from one end side. 
         FIG. 8  Views showing an assembly process of the photodetecting device. 
     
    
    
     DESCRIPTION OF REFERENCE NUMERALS AND SYMBOLS 
       2  . . . cold plate (installation body),  3  . . . photodetecting device,  11  . . . photodetecting element,  12  . . . wiring board,  13  . . . Spin base (base),  16  . . . CCD array (photodetecting section),  18 A,  18 B . . . positional alignment mark,  23  . . . slit portion (window portion),  24  . . . cutaway portion (window portion),  32  . . . threaded fitting pin (fitting portion),  33  . . . positioning portion,  34  . . . side face (one side face),  35  . . . corner portion (one end portion), L . . . center line. 
     BEST MODE FOR CARRYING OUT THE INVENTION 
     Hereinafter, a preferred embodiment of the photodetecting device according to the present invention will be described in detail with reference to the accompanying drawings. 
       FIG. 1  is a view showing a photodetecting section formed with a photodetecting device according to an embodiment of the present invention loaded. Also,  FIG. 2  is a perspective view of the photodetecting device shown in  FIG. 1 ,  FIG. 3  is a view of the same observed from the front surface side, and  FIG. 4  is a side view showing a part of the same in a sectioned manner. 
     As shown in  FIG. 1 , the photodetecting section  1  includes a thermal control cold plate (installation body)  2  and a plurality of photodetecting devices  3 , and is formed as, for example, a photodetecting section  1  of a telescope for astronomical observation. The cold plate  2  is formed of, for example, copper in a disk shape, and is cooled to approximately −100° C. in a predetermined gas ambient when the telescope is used. On the surface of the cold plate  2 , a plurality of recess portions  4  corresponding to a threaded fitting pin  32  and a flexible PCB (Printed Circuit Board)  22  (see  FIG. 2 ) of each photodetecting device  3  are provided. 
     The photodetecting devices  3  are each fixed to the cold plate  2  by fitting the threaded fitting pin  32  and the flexible PCB  22  into the recess portions  4  and screwing a nut  36  (see  FIG. 2 ) on each threaded fitting pin  32  from the back side of the cold plate  2 , and arranged in, for example, an 8×10 matrix. Such arrangement is called a 4-side buttable arrangement since four side faces of each photodetecting device  3  face the side faces of adjacent photodetecting devices  3 , and is suitable for providing the photodetecting section  1  with a large area by arranging the photodetecting devices  3  at a high density. Moreover, the interval between the adjacent photodetecting devices  3  is provided as approximately 100 μm, thereby preventing contact of the photodetecting devices  3  with each other due to thermal expansion after cooling by the cold plate  2  is cancelled. 
     Next, description will be given of a configuration of the photodetecting device  3 . Each photodetecting section  3 , as shown in  FIG. 2  to  FIG. 4 , includes a photodetecting element  11  that performs photodetection, a wiring board  12  electrically connected to the photodetecting element  11 , and a pin base  13  to be used for installation onto the cold plate  2 . The photodetecting element  11  is a so-called Back-Thinned CCD (BT-CCD) having a thickness of approximately 200 μm, and is an element capable of detecting, at a high sensitivity, various types of energy beams including ultraviolet rays, soft X-rays, and electron beams that are susceptible to the effect of absorption by a semiconductor. 
     The back surface (one surface) side of the photodetecting element  11  serves as a light-incident surface S (see  FIG. 4 ), and at the front surface (the other surface) side of the photodetecting element  11 , a detecting region  14  that detects light made incident from the light-incident surface S and a first bonding pad region  15  to serve as an output terminal of the detecting region  14  are respectively formed (see  FIG. 8(   a )). In the detecting region  14 , provided is a CCD array (photodetecting section)  16  where CCDs are arranged in, for example, a 9×7 matrix, and in the first bonding pad region  15 , provided is a first bonding pad  17 A electrically connected with each pixel of the CCD array  16  by a predetermined pattern of aluminum wiring. The first bonding pads  17 A are arranged in a line along one end portion of the front surface side of the photodetecting element  11 . 
     Further, as shown in  FIG. 3  and  FIG. 8(   a ), in both end portions of the front surface of the photodetecting element  11 , at a dead area part on a further outer side than the detecting region  14 , cross-shaped positional alignment marks  18  ( 18 A,  18 B) are respectively provided so as to pass through a center line L of the photodetecting element  11 . The positional alignment marks  18 A,  18 B are formed simultaneously with the above-described aluminum wiring by, for example, aluminum sputtering, and used as positional references that indicate the center line L of the photodetecting element  11 . 
     The wiring board  12 , as shown in  FIG. 2  to  FIG. 4 , shows a rectangular shape having almost the same area as that of the photodetecting element  11 , and in an almost central part of the front surface side of the wiring board  12 , a lead terminal  21  corresponding to each pixel of the CCD array  16  is disposed. The lead terminal  21  is, as shown in  FIG. 2 , connected to the flexible PCB (flexible printed circuit board)  22 . The flexible PCB  22  is connector-connected to a predetermined substrate (not shown) in the telescope through the recess portions  4  of the cold plate  2 . 
     On the other hand, as shown in  FIG. 3 , in one end portion and the other end portion of the wiring board  12 , a slit portion (window portion) and a cutaway portion (window portion)  24  are provided, respectively. The slit portion  23  is formed in an oblong shape along one end portion of the wiring board  12 , and the cutaway portion  24  is formed in a semicircular shape at almost the center of the other end portion of the wiring board  12 . In addition, the wiring board  12  is, while being positioned so that the first bonding pad region  15  and the positional alignment mark  18 A are exposed from the slit portion  23  and the positional alignment mark  18 B is exposed from the cutaway portion  24 , firmly fixed to the front surface side of the photodetecting element  11  by, for example, die-bonding. 
     Moreover, as shown in  FIG. 5  and  FIG. 6 , on the wiring board  12 , in a region on a further inner side than the region where the first bonding pad region  15  and the positional alignment mark  18 A are exposed, a step portion  25  is provided along the longitudinal direction of the slit portion  23 . The step portion  25  has an installation face  25   a  located at a further back surface side than the front surface of the wiring board  12 , and on the installation face  25   a , formed is a second bonding pad region  26  to serve as an input terminal of the wiring board  12 . In the second bonding pad region  26 , second bonding pads  17 B corresponding to first bonding pads  17 A are arranged in a line, and the first bonding pads  17 A and the second bonding pads  17 B are electrically connected by bonding wires  27 , respectively. In addition, the second bonding pads  17 B are electrically connected to the lead terminals  21  by internal wiring (not shown) of the wiring board  12 , respectively, and thus an output signal from the photodetecting element  11  is externally output via the lead terminal  21  and the flexible PCB  22 . 
     Further, at almost the center of an edge being on one end side of the wiring board  12 , a groove portion  28  extending along the center line L (see  FIG. 3 ) is provided, and the wiring board  12  is attached with a ceramic lid portion  29  from the front surface side of the slit portion  23  in a manner blocking the groove portion  28 . By attaching the lid portion  29 , the first bonding pad portion  17 A, the second bonding pads  17 B, and the bonding wires  27  are protected so as not to be externally exposed, and in the side face on one end side of the photodetecting device  3 , as shown in  FIG. 5  and  FIG. 7 , an air vent  30  to communicate the interior of the slit portion  23  with the exterior is formed. 
     The pin base  13  is, as shown in  FIG. 2  to  FIG. 4 , formed of, for example, aluminum nitride in a flat rectangular parallelepiped shape. The pin base  13  is provided on a surface of the wiring board  12  opposite to the surface on the photodetecting element  11  side. The pin base  13  is formed at almost the center with a rectangular opening portion  31  to expose the lead terminals  21  of the wiring board  12 . Moreover, at the front surface side of the pin base  13 , provided is a threaded fitting pin (fitting portion)  32  made of, for example, titanium onto which a nut  36  can be screwed. The threaded fitting pin  32  is protruded to the outside from a surface of the pin base  13  opposite to the surface on the wiring board  12  side. A total of three threaded fitting pins  32  are provided in a manner sandwiching the opening portion  31 , that is, one at the center of one end side of the pin base  13  and one each at positions close to both corner portions of the other end side of the pin base  13 . 
     Here, of the side faces of the pin base  13 , one side face  34  along the center line L of the photodetecting element  11  and a corner portion  35  of one end side in the side face  34  serve as a positioning portion  33  of the pin base  13 . The threaded fitting pins  32 , which are attached at the front surface side of the pin base  13 , are centered so that relative distances from the side face  34  and the corner portion  35  become accurate, and positioned at a high accuracy with respect to the positioning portion  33 , respectively. Moreover, the pin base  13  is accurately angularly aligned with respect to the photodetecting element  11  by aligning, with the center line L passing through the positional alignment marks  18 A,  18 B, the line of the side face  34  when the pin base  13  is observed from the front surface side, and is accurately positionally aligned with respect to the photodetecting element  11  based on relative distances between the positional alignment marks  18 A and  18 B and the corner portion  35 . In this state, the pin base  13  is firmly adhered to the front surface side of the wiring board  12  by, for example, a thermosetting resin. 
     Then, description will be given of an assembling method of the photodetecting device  3  having the above-described configuration. 
     When the photodetecting device  3  is assembled as the photodetecting section  1  of a telescope, first, the photodetecting element  11  is prepared, and the photodetecting element  11  is arranged, as shown in  FIG. 8(   a ), with the front surface side oriented upside so that the positional alignment marks  18 A,  18 B are visible. Next, the wiring board  12  is prepared, and, as shown in  FIG. 8(   b ), while being positioned so that the first bonding pad region  15  and the positional alignment mark  18 A are exposed from the slit portion  23  and the positional alignment mark  18 B is exposed from the cutaway portion  24 , the wiring board  12  is fixed to the front surface side of the photodetecting element  11  by die-bonding. 
     After the fixation of the wiring board  12  is completed, the pin base  13  is prepared. At the front surface side of the pin base  13 , the threaded fitting pins  32  are attached in advance while being accurately centered with respect to the positioning portion  33 . Then, as shown in  FIG. 8(   c ), so that the lead terminals  21  of the wiring board  12  are exposed from the opening portion  31  being at almost the center of the pin base  13 , the pin base  13  is laid over the front surface side of the wiring board  12 . At this time, the line of the side face  34  when the pin base  13  is observed from the front surface side is aligned with the center line L passing through the positional alignment marks  18 A,  18 B, of the photodetecting element  11 , exposed from the slit portion  23  and the cutaway portion  24  of the wiring board  12  to accurately angularly align the pin base  13  with respect to the photodetecting element  11 . Moreover, based on relative distances between the positional alignment marks  18 A and  18 B and the corner portion  35 , the pin base  13  is accurately positionally aligned with respect to the photodetecting element  11 . After performing the angular alignment and positional alignment with respect to the photodetecting element  11 , the pin base  13  is fixed to the front surface side of the wiring board  12  by adhesion. 
     After the fixation of the pin base  13  is completed, the first bonding pads  17 A and the second bonding pads  17 B are electrically connected by wire bonding, respectively. After the wire bonding, the lid portion  29  is attached from the front surface side of the slit portion  23  to hide the first bonding pads  17 A and the second bonding pads  17 B, and the air vent  30  is formed in the side face on one end side of the photodetecting device  3 . Moreover, the flexible PCB  22  is connected to the lead terminal  21  exposed from the opening portion  31  of the pin base  13 . Thereby, the assembly of the photodetecting device  3  shown in  FIG. 2  to  FIG. 4  is completed. 
     Then, by fitting the threaded fitting pins  32  and the flexible PCB  22  of the photodetecting device  3  into the recess portions  4  of the cold plate  2  and screwing the nut  36  on each threaded fitting pin  32  from the back side of the cold plate  2 , the photodetecting device  3  is fixed to the cold plate  2 . At this time, since the threaded fitting pin  32  has been accurately positionally aligned with the photodetecting element  11  via the positioning portion  33  of the pin base  13 , the photodetecting device  3  is accurately positionally aligned with respect to the cold plate  2 . In the following, by assembling a plurality of photodetecting devices  3  by the same procedure and arranging the photodetecting devices  3  in a matrix on the cold plate  2 , the photodetecting section  1  shown in  FIG. 1  is completed. 
     As has been described above, in the photodetecting device  3 , the positional alignment marks  18 A,  18 B to serve as positional references of the photodetecting element  11  are formed at the front surface side of the photodetecting element  11 . Moreover, the pin base  13  is provided with the threaded fitting pin  32  to be fitted with the cold plate  2 , and the threaded fitting pin  32  is accurately positionally aligned with respect to the photodetecting element  11  via the positioning portion  33  positioned with respect to the positional alignment marks  18 A,  18 B exposed from the slit portion  23  and the cutaway portion  24  of the wiring board  12 . Accordingly, in the photodetecting device  3 , by only fitting the threaded fitting pin  32  with the recess portion  4  of the cold plate  2 , the photodetecting element  11  is accurately positionally aligned with respect to the cold plate  2 . As a result, in the 4-side buttable arrangement, the photodetecting elements  11 ,  11  in adjacent photodetecting devices  3 ,  3  can be accurately aligned in positional relationship, so that it becomes possible to arrange the respective photodetecting devices  3  at a high density. 
     Moreover, in the photodetecting device  3 , the positional alignment marks  18 A,  18 B are formed so as to pass through the center line L of the photodetecting element  11 , and the positioning portion  33  is composed of the side face  34  of the pin base  13  and the corner portion  35  in the side face  34 . Therefore, by aligning, with the center line L passing through the positional alignment marks  18 A,  18 B, the line of the side face  34  when the pin base  13  is observed from the front surface side, the photodetecting element  11  and the pin base  13  can be accurately angularly aligned, and the photodetecting element  11  and the pin base  13  can be accurately positionally aligned based on relative distances between the positional alignment marks  18 A and  18 B and the corner portion  35 . 
     Further, in the photodetecting device  3 , the second bonding pads  17 B are formed, of the wiring board  12 , in the region on a further inner side than the first bonding pad region  15 . Due to such a configuration, in the photodetecting device  3 , a forming space for wire bonding can be located at the inside of the photodetecting element  11 , so that it becomes possible to make the wiring board  12  and the photodetecting element  11  almost equal in size. As a result, in the photodetecting device  3 , the area that the photodetecting element  11  occupies relative to the photodetecting device  3  can be sufficiently secured, and in the case of a buttable arrangement of the photodetecting devices  3  on the cold plate  2 , the interval between the photodetecting elements  11 ,  11  of the adjacent photodetecting devices  3 ,  3  can be sufficiently reduced, so that minimization of the non-sensitive region can be realized. Moreover, by providing the second bonding pad region  26  on the installation face  25   a  of the step portion  25 , the bonding wires  27  can be prevented from protruding to the front side of the wiring board  12 . This allows, when arranging the photodetecting devices  3  on the cold plate  2 , protecting the bonding wires  27  from disconnection etc. Further, since there is some thickness left at the forming part of the second bonding pads  17 B, the strength of the bonding pads  17 B when performing wire bonding can also be secured. 
     The wiring board  12  is attached with the lid portion  29  from the front surface side of the slit portion  23  so that the first bonding pads  17 A, the second bonding pads  17 B, and the bonding wires  27  are protected so as not to be externally exposed, and the air vent  30  to communicate the interior of the slit portion  23  with the exterior is formed. By thus protecting the wire bonding part of the photodetecting element  11  and the wiring board  12 , disconnection etc., of the bonding wires  27  when arranging the photodetecting device  3  on the cold plate  2  can be prevented. Moreover, by a formation of the air vent  30 , the interior and the exterior of the slit portion  23  can be maintained at an equal pressure even after the lid portion  29  is attached, and thus even when cooling or cancellation of the cooling is performed by the cold plate  2  before and after use of the photodetecting section  1 , deformation and breakage of the photodetecting device  3  due to a contraction/expansion of the gas in the slit portion  23  can be suppressed. 
     The present invention is by no means limited to the above-mentioned embodiment. For example, in the embodiment described above, the photodetecting section  1  has been formed by a 4-side buttable arrangement of the photodetecting devices  3  on the cold plate  2 , however, by arranging the photodetecting devices  3  in two lines, a 3-side buttable arrangement may be adopted where  3  side faces of the photodetecting device  3  face the side faces of adjacent photodetecting elements  11 . 
     Moreover, in the embodiment described above, on the pin base  13 , one side face  34  along the center line L of the photodetecting element  11  and the corner portion  35  of one end side in the side face  34  have been provided as the positioning portion  33 , however, one side face orthogonal to the center line L of the photodetecting element  11  and a corner portion of one end side in the side face may be provided as the positioning portion  33 . Further, in the embodiment described above, the groove portion  28  to form the air vent  30  has been provided at almost the center of an edge being on one end side of the wiring board  12 , however, such a groove portion  28  may be formed at the lid portion  29  side, and may be formed at both the slit portion  23  and the lid portion  29 . 
     Further, in the embodiment described above, an output signal from the photodetecting element  11  is externally output via the lead terminal  21  and the flexible PCB  22 , however, the present invention is not limited thereto, and, for example, a connector to be fitted with the lead terminal  21  may be fitted from the opening portion of the pin base  13 . Moreover, the cutaway portion  24  has been provided in a semicircular shape, however, this may, without limitation thereto, be in, for example, an oblong shape. Moreover, when electrically connecting the first bonding pads  17 A and the second bonding pads  17 B by wire bonding, respectively, the wire bonding may be either a forward bonding or a reverse bonding. Moreover, although the recess portions  4  have been recess portions, the recess portions  4  may be a plurality of hole portions that allow the threaded fitting pins  32  to be fitted thereinto and the flexible PCB  22  to pass therethrough.