Abstract:
The soldering pads on metal contacts for connection to the electrodes of a semiconductor diode chip are surrounded with a coating of insulating material to prevent the spreading of the molten solder, which may cause misalignment of the chip with respect to the package.

Description:
BACKGROUND OF THE INVENTION 
     (1) Field of Invention 
     This invention relates to semiconductor diode packages, particular to photoelectric diodes. 
     (2) Brief Description of Related Art 
     FIG. 1 shows a prior art method for soldering a semiconductor diode  10  to two metal contacts  11  and  12 . Solders  103   m  and  104   m  are placed over the contact  11  and  12  respectively for soldering to the electrodes of the semiconductor diode  10 . When the package is heated for soldering, the solders  103   m  and  104   m  melt and may spread. If the solders  103   m  and  104   m  spread, the diode  10  may be displaced from the desired position. This displacement is undesirable, especially for photoelectric devices where the positioning of the light source or light sensor is critical 
     SUMMARY 
     An object of this invention is to position a diode accurately in a semiconductor package. 
     Another of this invention is to prevent the solder in a package from spreading. 
     These objects are achieved in this invention by coating the surrounding of the soldering pads with insulating material which prevents spreading. Then the soldering islands can accurately mate with the electrodes of the diode. 
    
    
     BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS 
     FIG. 1 shows the spreading of the solders over a metal contact in prior art. 
     FIG. 2 shows the coating outside the soldering areas of the present invention. 
     FIG. 3 shows the side view of FIG.  2 . 
     FIG. 4 shows a second embodiment of the present invention. 
     FIG. 5 shows a third embodiment of the present invention. 
     FIG. 6 shows a top view of the metal contact in FIG.  2 . 
     FIG. 7 shows a fourth embodiment of the present invention. 
     FIG. 8 shows a fifth embodiment of the present invention. 
     FIG. 9 shows a side view of FIG. 8 
     FIG. 10 shows another side view of FIG.  8 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 2 shows the top view of the present invention. A semiconductor chip  20  is placed over two metal contacts  21 ,  22 . The chip  20  has two bottom electrodes  201 .  202 , mating with two soldering pads on the metal contacts  21 ,  22 , respectively. The metal contact  21  is coated with insulating material  212  outside surrounding the soldering pad which mates with the electrode  201 , and the metal  22  is coated with insulating material  222  outside surrounding the second soldering pad which mates with the electrode  202 . Only the first soldering pad is exposed for soldering a first electrode  201  of the semiconductor chip  20 , and only the second soldering pad is exposed for soldering a second electrode  202  of the chip  20 . The coatings  212  and  222  prevent the melted solder at the first and second soldering pads respectively from spreading. 
     FIG. 3 shows the side view of FIG. 2 along the dotted section line. The contact metal  21  is coated with the insulating material  212  except at the soldering pad  203  to allow mating with the electrode  201  of the diode chip  20 . The contact metal  22  is coated with the insulating material  222  except at the soldering pad  204  to allow mating with the electrode  202  of the diode chip  20 . 
     FIG. 4 shows a second embodiment of this invention, which is a variation of the structure shown in FIG.  3 . Only the contact  21  is coated with the insulating material  212  except at the soldering pad  203  to allow mating with the electrode  201  of the diode chip  20 . However the contact  22  is not coated with any insulating material. Since the position of the chip is already fixed by the mating of solder pad  203  with the electrode  201 , the solder pad  204 , which is fixed in position relative to the solder pad  203  is automatically aligned with the electrode  202 , which is also fixed in position relative to the electrode  201  on the chip  20 . 
     FIG. 5 shows a third embodiment of the present invention. The chip  20  has an electrode  201  at the bottom and another electrode  202  at the top of the chip  20 . The bottom electrode  201  is mounted on a soldering pad  203  over the contact metal  21 . The surface outside the solder point  203  is coated with an insulating material  212  to prevent spreading of the melted solder from the soldering pad  203 . The top electrode  202  of the chip  20  is wire bonded to the soldering pad  204  on the metal contact  22 . 
     FIG. 6 shows the top view of the metal contacts  21  and  22 shown in FIG.  2 . Outside the solder points  211  is the insulating coating  212  and outside the solder  221  is the insulating coating  222 . 
     FIG. 7 shows the top view of a fourth embodiment of the present invention. The metal contact  21  is only partially coated with insulating material  212  outside the soldering pad  211 . The metal contact  22  is only partially coated with insulating material  222  outside the soldering pad  221 . 
     FIG. 8 shows the top view of an eighth embodiment of the present invention. The chip  20  has electrode  202  on the topside and electrode  201  at the bottom side. The metal contact plates  21  and  22  are not coplanar. The electrode  201  makes contact with the bottom metal contact plate  21 . Outside the soldering pad  203 , which makes contact with the electrode  201  as shown in the side view FIG. 9, is coated with insulating material  212 . The top electrode  202  of the chip  20  makes contact with the top metal contact plate  22 . Outside the soldering pad  204 , which makes contact with the electrode  202  as shown in FIG. 9, is coated with insulating material  222 . The coatings  212  and  222  prevent the spreading of solder. The coating  222  may be eliminated as shown in FIG.  10 . As in FIG. 4, coating on only one plate is sufficient to align the chip electrodes with the solder points. 
     While the preferred embodiments of the invention have been described, it will be apparent to those skilled in the art that various modifications may be made in the embodiments without departing from the spirit of the present invention. Such modifications are all within the scope of this invention.