Patent Publication Number: US-2006012002-A1

Title: Device for mounting a semiconductor package on a support plate via a base

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      The present application is a divisional of pending U.S. application for patent Ser. No. 10/358,994, which was filed on Feb. 5, 2003, and which claims foreign priority from French Application for Patent No. 0201427 filed Feb. 6, 2002, the disclosures of each of which are hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION  
      1. Technical Field of the Invention  
      The present invention relates to a device for mounting a semiconductor package on a support plate.  
      2. Description of Related Art  
      Semiconductor packages are known which contain optical semiconductor components having optical sensors on a front face and which have optical lenses in their front part.  
      To mount such packages on support plates, it is known to adhesively bond bases fitted on the sides with projecting tabs, the ends of which form catches, and to engage the semiconductor packages between these tabs, above the bases, such that the tabs extend laterally to the package and that their catches engage above the front face of the packages.  
      The aim of the present invention is in particular to reduce the footprint of devices for mounting semiconductor packages, in particular optical semiconductor packages, on support plates, in particular printed circuit boards.  
     SUMMARY OF THE INVENTION  
      According to the invention, the device for mounting a semiconductor package on a support plate, in which a base is inserted between a rear face of the package and a front face of the said support plate and in which means for electrically connecting the said package to the said support plate pass through the said base, comprises means for fastening the said package onto the said support plate which cooperate with and are placed below the rear face of this package.  
      According to an alternative embodiment of the invention, the said rear face of the package has at least one part projecting towards the said plate and the said fastening means cooperate with this projecting part.  
      According to the invention, the said fastening means preferably comprise additional coupling means provided on the said part projecting from the package and on the said base.  
      According to the invention, the said additional coupling means preferably comprise catches suitable for engaging with shoulders.  
      According to the invention, the said part projecting from the package preferably extends through the said base and is adhesively bonded to the support plate.  
      According to another alternative embodiment of the invention, the said part projecting from the package is adhesively bonded to the said base fastened to the support plate.  
      According to an alternative embodiment of the invention, the device comprises a fastening lug which passes through the said support plate and the said base, this lug having a shoulder away from the base and bearing on the rear face of the support plate and being fastened to the rear face of the said package.  
      According to the invention, the said lug is preferably fastened to the package by adhesive bonding.  
      According to the invention, the said package and the said base preferably comprise complementary centering parts engaging with each other.  
      According to an alternative embodiment of the invention, the said package and the said base have peripheries which substantially correspond.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      A more complete understanding of the method and apparatus of the present invention may be acquired by reference to the following Detailed Description when taken in conjunction with the accompanying Drawings wherein:  
       FIG. 1  shows a cross section of a first mounting device according to the present invention;  
       FIG. 2  shows a section through II-II of the mounting device of  FIG. 1 ;  
       FIG. 3  shows a cross section of a second mounting device according to the present invention;  
       FIG. 4  shows a section through II-II of the mounting device of  FIG. 1 ;  
       FIG. 5  shows a cross section of a third mounting device according to the present invention;  
       FIG. 6  shows a cross section of a fourth mounting device according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS  
       FIGS. 1 and 2  show a device  1  for mounting a semiconductor package  2  on a printed circuit support plate  3 .  
      In the particular example shown, the semiconductor package  2  comprises a rear plate  4  which has, in its front face, a recess  5  and a transparent plate  6  adhesively bonded to the front face of the rear plate  4 , so as to define a cavity  7 . An optical semiconductor component  8  is fitted in this cavity  7 , its rear face being adhesively bonded to the bottom of the recess  5  and its front face having an optical sensor  9  provided substantially in its central part.  
      The semiconductor package  2  further comprises a front plate  10  which is adhesively bonded to the transparent plate  6  and which has a central passage  11  in which an optical lens  12  is mounted so as to face the optical sensor  9 .  
      The rear plate  4  of the semiconductor component  2  has, on its rear face, rear electrical connection pads  13  which are connected to inner electrical connection pads  14  provided in the recess  5  via an integrated circuit  15 , the inner electrical connection pads  14  being connected to front electrical connection pads  16  of the optical semiconductor component  8  via electrical wires  17 .  
      The periphery of the rear plate  4 , the periphery of the transparent plate  6  and the periphery of the front plate  10  of the semiconductor component  2  substantially coincide and are substantially square.  
      Between the rear face  13  of the semiconductor package  2  and the support plate  3 , the mounting device  1  comprises a base  18  comprising a plate, the rear face  19  of which is for example adhesively bonded or soldered to the support plate  3  and which has, in its front face  20 , a central recess  21 .  
      From its rear face  13  and in its central part with no electrical connection pad  13   a , the rear plate  4  of the semiconductor package  2  has a part or boss  22  projecting rearwards, which is engaged in the central recess  21  of the base  18 .  
      The end part of the projecting boss  22  has a peripheral lateral holding shoulder  23 , away from the rear face  13 , and the base  18  has, in its recess  21 , holding catches  24  projecting towards the front and engaging with the annular shoulder  23 .  
      Furthermore, the base  18  has, between its central recess  21  and its periphery, electrical connection through-passages  25 , in which spiral electrical connection springs  26  are placed, making it possible to connect the rear electrical connection pads  13   a  of the semiconductor package  2  to electrical connection pads  27  provided on the support plate  3 .  
      The periphery of the base  18  is substantially square and substantially coincides with the square periphery of the semiconductor package  2 . The projecting boss  22  is substantially square, in parallel with the periphery of the semiconductor package  2  and, in the example, four catches  24  cooperate respectively with the four sides of the peripheral holding shoulder  23 .  
      In order to fit the mounting device  1 , it is possible to proceed as follows.  
      The base  18  is adhesively bonded or soldered onto the support plate  3  in a position such that its through-passages  25  correspond to the electrical connection pads  27  of this support plate  3 .  
      The electrical connection springs  26  are placed in the passages  25 .  
      The boss  22  of the semiconductor package  2  is engaged in the central recess  21  of the base  18  in the space between the catches  24  and in a position such that its rear electrical connection pads  13   a  correspond to the passages  25 , until its rear face  13  comes into contact with the front face  20  of the base  18 . This being done, the catches  24  are deformed laterally in the recess  21 , in order to engage towards the inside with the annular shoulder  23  of the central boss  22  of the semiconductor package  2  and the springs  26  are compressed.  
      Thus, the catches  24  and the annular shoulder  23  of the central boss  22  constitute not only additional means for coupling the semiconductor package  2  to the base  18  but also additional parts for centering the semiconductor package  2  with respect to the base  18 , one being engaged in the other.  
      With reference now to  FIGS. 3 and 4 , it can be seen that a mounting device  28  is shown which is differentiated from the mounting device  1  described with reference to  FIGS. 1 and 2  by the following points.  
      The optical semiconductor component  29  is differentiated from the semiconductor component  2  in that it does not have the rear projecting boss  22  but that it has a peripheral rib  31  projecting rearwards from the periphery of its rear face  30  and which has, at its end, an inner holding rim or shoulder  32  projecting away from the rear face  30 .  
      Its base  33  is differentiated from the base  18  of the previous example in that it has no central recess  21 , but that it has, between its periphery and its through-passages  34  corresponding to the previous passages  25 , an annular channel  35  made in its front face  36  and that, in its part separating its periphery and the groove  35 , holding catches  37  are formed projecting forwards and suitable for external engagement with the shoulder  32 .  
      To fit the mounting device  28 , it is possible to proceed as in the previous example.  
      The base  33  is adhesively bonded or soldered onto the support plate  3  in a position such that its through-passages  34  correspond to the electrical connection pads  27 .  
      Electrical connection springs  38  are placed in its passages  34 .  
      The rib  31  projecting to the rear of the semiconductor package  29  is engaged around the catches  37  of the base  28  and in a position such that its rear electrical connection pads  39  correspond to the passage  34 , until its rear face  30  comes into contact with the front face  36  of the base  33 , the catches  37  being deformed laterally in order to engage externally with the annular shoulder  32  of the peripheral rib  31  and the springs  38  being compressed.  
      With reference to  FIG. 5 , a mounting device  40  is shown which is differentiated from the previously described examples in that it no longer has catches.  
      So, in this mounting device  40 , the rear face  41  of the optical semiconductor component  42  has a central part or boss  43  projecting rearwards, with a square cross section, which is engaged in a central passage  44  of square cross section of a base  45 , until its end is in contact or at a short distance from the support plate  3 .  
      A layer of adhesive  45  is inserted between the end face of the boss  43  and the front face of the support plate  3 .  
      To fit the mounting device  40 , it is possible to proceed as follows.  
      The base  45  is adhesively bonded or soldered onto the support plate  3  in a position such that its through-passages  46  correspond to the electrical connection pads  27  of this support plate  3 .  
      The electrical connection springs  47  are placed in the passages  46 .  
      A drop or a layer of adhesive is deposited on the support plate  3  through the central passage  44  of the base  45  and/or on the front face of the rear boss  43  of the semiconductor package  42 .  
      The rear boss  43  of the semiconductor package  42  is engaged in the central passage  44  of the base  45 , in a position such that its rear electrical connection pads  48  correspond to the through-passages  46  and until the layer of adhesive  45  is inserted between the front face of the boss  43  and the support plate  3 , the rear face  41  of the semiconductor package  42  then being in contact with, or a short distance from, the front face  49  of the base  45 .  
      When the layer of adhesive  45  is set, the semiconductor package  42  is fastened to the support plate  3 , the rear boss  43  providing the coupling and the centering of one with respect to the other.  
      With reference to  FIG. 6 , a mounting device  50  is shown in which the base  51  corresponds to the base  45  of the previous example, and in which the rear face  52  of the semiconductor package  53  is flat.  
      In this example, the support plate  3  has a through-passage  3   a  located so as to face the central passage  54  of the base  51 .  
      A holding lug  55  is engaged through the passage  3   a  of the support plate  3  and of the central passage  54  of the base  51 , this lug  55  having a peripheral shoulder  56  bearing against the rear face of the support plate  3  and a layer of adhesive  57  being inserted between the front face of the lug  55  and the rear face  52  of the optical semiconductor package  53 .  
      To fit the mounting device  50 , it is possible to proceed as follows.  
      The base  51  is adhesively bonded or soldered onto the support plate  3  in a position such that the electrical connection through-passages  58  correspond to the electrical connection pads  27  of the support plate  3  and that its central passage  54  corresponds to the through-passage  3   a  of the support plate  3 .  
      The electrical connection springs  9  are placed in the through-passages  58  of the base  51 .  
      A drop or a layer of adhesive is deposited on the end face of the holding lug  55  and/or on the central part of the rear face  52  of the optical semiconductor device  53 .  
      The optical semiconductor package  53  is put on the front face  60  of the base  51  by compressing the springs  59 , in a position such that its rear electrical connection pads  61  correspond to the through-passages  58 .  
      The lug  55  is engaged through the through-passage  3   a  of the support plate  3  and through the central passage  54  of the base  51  until the front end of the holding lug  55  comes into contact with the rear face  52  of the optical semiconductor package  53  via the layer of adhesive  57  thus formed.  
      After this adhesive is set, the optical semiconductor package  53  is fastened to the support plate  3 .  
      Furthermore, the optical semiconductor package  53  and the base  51  could have complementary centering parts making it easier to position one with respect to the other during their coupling. For this, the optical semiconductor package  53  could have, for example, pins projecting rearwards and the base  51  could have front holes for receiving these pins.  
      Although preferred embodiments of the method and apparatus of the present invention have been illustrated in the accompanying Drawings and described in the foregoing Detailed Description, it will be understood that the invention is not limited to the embodiments disclosed, but is capable of numerous rearrangements, modifications and substitutions without departing from the spirit of the invention as set forth and defined by the following claims.