Abstract:
In a surface mount LED chips mounted on an insulating substrate, plated through conduits to interconnect the chips on both sides are placed at the corners of the outer terminals at two horizontal ends. The depressions caused by wire-bonding the chip to the terminals are lined up vertically with the corner conduits to reduce horizontal dimension.

Description:
BACKGROUND OF THE INVENTION 
     (1) Field of the Invention 
     This invention relates to semiconductor device package, particularly to surface mount light emitting diode (LED) package. 
     (2) Brief Description of the Related Art 
     In semiconductor technology, surface mount packages are sometimes used to hold one semiconductor chip on front side of a substrate and contact to a mother board is made on backside of the substrate. FIG. 1 shows a prior art package for mounting a LED chip on one side of a substrate  13 . The package has two metal terminals  11  and  12  for external connection. The metal terminal  11  is an extension of a landing on which a semiconductor chip  10  is mounted. In the backside of the substrate, there are corresponding metal terminals. The terminals  11 , 12  are connected to a corresponding terminals in the back through a semicircular plated through conduit  151  and  152 . 
     The chip  10  has two electrodes  101  and  102  connected by wires  103  and  104  respectively to the terminals  11  and  12 . The wires  103 ,  104  are compressed on the terminals  11  and  12  respectively for bonding. The compression creates an expanded compressed area  16 . This compressed area occupies a width d 1 . The semicircular conduit occupies a width d 2 . The chip requires a width d 3  for mounting. Thus the total width W 1  is equal the total of d 1 , d 2  and d 3 , i.e. W 1 =2d 1 +2d 2 +d 3 . 
     For low cost production, it is important to reduce the size of the package. For a display panel composed of a large number of the LEDs, a closer packaging can increase the light intensity and higher resolution. Therefore, a smaller LED package is what the industry is striving for. 
     SUMMARY OF THE INVENTION 
     An object of this invention is to reduce the package of a surface mount semiconductor package. Another object of this invention is to reduce the dimension of LED package. Still another object of this invention is to increase the light intensity and resolution of an LED display panel. 
     These objects are achievement by placing the plated-through conduits at the corners of the package, so that the expanded compressed area is offset from and lined up vertically with the conduit, thus reducing the total horizontal width of the package. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     FIG. 1 shows the prior art layout of a surface mount LED package. 
     FIG. 2 shows the layout of a surface LED package based on the present invention. 
     FIG. 3 shows rhombic plated through conduit. 
     FIG. 4 shows a rectangular plated-through conduit. 
     FIG. 5 shows an arrangement for packaging an array of LED packages in a display panel or for mass production. 
     FIG. 6 shows another embodiment of the substrate with corner cut at the same side. 
     FIG. 7 shows the side view of the package using the substrate shown in FIG.  6 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 2 shows the layout of the package for a surface mount LED substrate of the present invention. The package has two metallic terminals  11 ,  12  at the front side. The terminal  11  is an extension of a landing for mounting a LED chip  10 . The terminal  11  has an arc-shaped cut at the corner to form a plated-through conduit  251  for connecting to a contact surface on the backside of the substrate. The terminal  12  has an arc-shaped cut at the corner to form a plated-through conduit  252  for connecting to a contact surface on the backside of the substrate  13 . The chip has two electrodes  101  and  102 . The electrode  101  is connected to the terminal  11  by a wire  103 , which is compressed on the terminal  11 . The compression creates an expanded compressed area  16 . The electrode  102  is connected to the terminal  12  by a wire  104 , which is compressed on terminal  12 . The compression creates another expanded compressed area  16 . Since the conduit  251  and the expanded compressed area  16  are aligned in the vertical direction, the width d 1  can accommodate both the conduit  251  and the expanded compressed area  16 . Thus the width d 2  in the prior art FIG. 1 is eliminated. The total width W 2  is equal to 2d 1  plus d 3 , the width for mounting the chip  10 , and is reduced by a width 2d 2  as compared to prior art. 
     The conduit in FIG. 2 is not limited to arc-shaped. Rhombic plated through conduits  351  and  352  as shown in FIG. 3 may also be used to connect both sides of the substrate  13 . 
     FIG. 4 shows rectangular plated through conduits  451  and  452  for connecting the chips on both side of the substrate  13 . 
     FIG. 5 shows an array of LED packages pieced together to form a display panel. Note that each conduit  15  connects four packages together. The individual packages are pieced together back-to-back in the horizontal direction. In the vertical direction, the terminal  11  and the terminal  12  are alternately pieced together. After wire bonding the individual chips, the entire structure can be sealed in glue (not shown) to improve reliability. To prevent the glue from seeping through to the opposite side, the plated through conduits can be sealed first by sealing compound before being sealed by the glue. The panel may also be used as a means for mass production. For mass production, the array may be sawed along the dot-dash lines. 
     For mass production of the packages, the fabrication steps may be as follows: 
     Step 1: Preparing a common substrate  13  with conductive metal layers on both sides; 
     Step 2: Forming metal wall conduits  15  on said substrate; 
     Step 3: Plating the conduits with metal for connecting the two sides; 
     Step 4: Forming the first terminal  11  on one end and the second terminal  12  at the other end, and forming a third metal terminal at the first end of the backside of the substrate and fourth metal terminal at the second end of the substrate, 
     Step 5: Placing the chips  10  on the front side of the substrate, 
     Step 6: Wire bonding the first electrode  101  of the chip  10  to the first terminal  11 ; 
     Step 7: Wire-bonding the second electrode  102  of the chip  10  to the second terminal  12 ; 
     Step 8: Sawing the common  13  horizontally and vertically to yield individual chips. 
     If necessary, a step 9 to seal the package may be added to improve the reliability. 
     If still necessary, another step may be added before step 5 to seal the conduit before the mounting of the chip to prevent the glue from seeping into the conduit to adversely affect soldering. 
     If further necessary, another step may be added before step 8 to remove the sealing compound. 
     While the embodiment shown in FIGS. 2-4 describes corner conduits placed diagonally, it is also possible to place the corner conduits at the same side of the substrate as shown in FIG.  6 . FIG. 7 shows a cross-sectional side view of a wired package for the substrate shown in FIG.  6 . The reference numerals correspond to that in FIG. 2 
     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.