Abstract:
A method of fabricating an integrated circuit package. The method includes providing a first leadframe and a second leadframe, laminating the second leadframe to a portion of the first leadframe in order to create a multi-layer laminated leadframe, and mounting a semiconductor die on another portion of the first leadframe.

Description:
FIELD OF THE INVENTION 
     This invention relates in general to integrated circuit packaging, and more particularly to a method for manufacture of an integrated circuit package. 
     BACKGROUND OF THE INVENTION 
     High performance integrated circuit (IC) packages are well known in the art improvements in IC packages are driven by demands for increased thermal and electrical performance, decreased size and cost of manufacture. 
     Typically, array packaging such as ball grid array (BGA) packages provide for a high density package. FIG. 1 shows a typical prior art package in which a copper leadframe  20  is etched to approximately half the leadframe thickness to form a pocket for the semiconductor die  22 . The etch-down process results in an etch-down pocket with a radius  24  at each pocket corner (where the base  26  on which the semiconductor die  22  is mounted, meets each side  28 ). Each IC package includes a pocket that is large enough to accommodate the die  22  and the radius  24 . Thus, the radius  24  limits the reduction in the size of the pocket. 
     Prior art IC packages such as that shown in FIG. 1 are manufactured such that each of the contacts lie in a single plane. Thus, the solder ball contacts  30  on the leadframe lie in the same plane as the solder ball contacts  30  on the semiconductor die. The half etch depth of the leadframe  20  is important in order to ensure that all of the solder ball contacts  30  lie in a single plane. The half etch depth Is difficult to accurately control and therefore manufacture of the IC package with solder ball contacts  30  in a single plane is difficult. 
     Accordingly, it is an object of an aspect of the present invention to provide a method for manufacturing an IC package that obviates or mitigates at least some of the disadvantages of the prior art. 
     SUMMARY OF THE INVENTION 
     In one aspect of the present invention there is provided a method of fabricating an integrated circuit package. The method includes providing a first leadframe and a second leadframe laminating the second leadframe to a portion of the first leadframe in order to create a multi-layer laminated leadframe, and mounting a semiconductor die on another portion of the first leadframe. 
     In another aspect of the present invention there is provided an integrated circuit package. The integrated circuit package includes afirst leadframe, a second leadframe laminated to a portion of the first leadframe in order to create a multi-layer laminated leadframe, and a semiconductor die mounted to another portion of the first leadframe. 
     In a particular aspect, the IC package of the present invention is manufactured without a large radius in the etch-down pocket of the leadframe strip. Advantageously, this permits reduced overall package size. Also, accurate control over manufacturing processes allows for planarity of the contacts. 
     In another aspect, the use of the solder contact balls is obviated by the use of solder plating on the leadframe strip. Also, die level solder Lumps are replaced with copper plates. Advantageously, this package provides reduced electrical resistance to the electrical contacts, simpler and more cost effective construction. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The present invention will be better understood with reference to the following drawings wherein like numerals refer to like parts throughout, and in which: 
     FIG. 1 is a cross section of a typical prior art semiconductor die package; 
     FIGS. 2A to  2 F show the processing steps for manufacturing an IC package in accordance with an embodiment of the present invention; 
     FIGS. 3A to  3 F snow the processing steps for manufacturing the IC package of FIG. 1F in accordance with an alternative embodiment of the present invention; 
     FIGS. 4A to  4 F show the processing steps for manufacturing an alternative IC package in accordance with another embodiment of the present invention; 
     FIGS. 5A to  5 F show the processing steps for manufacturing the IC package of 
     FIGS. 6A to  6 G show the processing steps for manufacturing an IC package in accordance with another embodiment of the present invention; 
     FIGS. 7A to  7 G snow the processing steps for manufacturing the IC package of FIG. 5F in accordance with an alternative embodiment of the present invention; 
     FIGS. 8A to  8 G snow the processing steps for manufacturing an IC package in accordance with yet another embodiment of the present invention; and 
     FIGS. 9A to  9 G show the processing steps for manufacturing the IC package of FIG. 6F in accordance with an alternative embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference is first made to FIGS. 2A to  2 F to describe the processing steps for manufacturing an IC package in accordance with an embodiment of the present invention. FIG. 2A shows a cross-sectional side view of a copper (Cu) panel substrate which forms the raw material of the leadframe strip indicated generally by the numeral  100 . As discussed in greater detail in Applicants&#39; U.S. Pat. No. 6,229,200, the leadframe strip is divided into a plurality of sections, each of which incorporates a plurality of leadframe units in an array (e.g. 3×3 array, 5×5 array, etc.). Only one such unit is depicted in the cross-sectional view of FIG.  2 A. 
     As shown in FIG. 2A, the copper strip is coated with a silver (Ag) plating on a bottom surface thereof and a solder plating on a top surface thereof. In one embodiment, the plating is a eutectic solder composition. This coating is added to enhance lamination and provide and surface for soldering. 
     Solder flux is added to a portion of the leadframe  100  (FIG. 28) and a second leadframe  102  with solder plating on both a top and a bottom surface thereof is laminated onto the first leadframe  100  using a proximity placement and thermal solder reflow technique to form a single pocket-type leadframe (FIG.  2 C). In an alternative embodiment the second leadframe is laminated onto the first leadframe using a hot roller thermo-compressive cladding process. 
     Next, the semiconductor die is mounted to the leadframe using known techniques. In the present embodiment, solder paste is dispensed on another portion of the first leadframe  100  in FIG.  2 D and the semiconductor die is attached to the first leadframe  100  by solder reflow technique (FIG.  2 E). The semiconductor die is coated with a suitable surface for soldering, such as titanium (Ti), tungsten (W), or gold (Au) for mounting via solder reflow. In an alternative embodiment, the die is attached using a silver-filled epoxy, as will be understood by those of skill in the art. 
     Next, solder ball contacts  106  are mounted on a vapor deposited layer referred to as “under bump metallurgy” or UBM on the semiconductor die  104  as will be understood by those of skill in the art (FIG.  2 F). 
     FIGS. 3A to  3 F show the processing steps for manufacturing the IC package of FIG. 2F in accordance with an alternative embodiment of the present invention. The order of the process steps in the present embodiment is different from the order of the steps of the embodiment of FIGS. 2A to  2 F. FIG. 3A shows a cross-sectional side view of the copper (Cu) panel substrate which forms the raw material of the leadframe strip indicated generally by the numeral  100 . Similar to the embodiment of FIG. 2A, the copper strip is coated with a silver (Ag) plating on a bottom surface thereof and a solder plating on a top surface thereof. 
     Solder paste is dispensed on a portion of the leadframe  100  in FIG.  3 B and the semiconductor die  104  is attached to the leadframe  100  by solder reflow technique (FIG.  3 C). The semiconductor die  104  is coated with a suitable surface for soldering, such as titanium (Ti), tungsten (W), or gold (Au) for mounting via solder reflow. This is a solderable vapor deposit structure made in layers of three. 
     Next, solder flux is added to another portion of the first leadframe (FIG. 3D) and a second leadframe  102  with solder plating on both a top and a bottom surface thereof is laminated onto the first leadframe  100  using a solder reflow technique to form a single pocket-type leadframe (FIG.  3 E). 
     The solder ball contacts  106  are then mounted on the semiconductor die  104  as shown in FIG.  3 F. 
     FIGS. 4A to  4 F show the processing steps for manufacturing an alternative IC package in accordance with another embodiment of the present invention. The steps of FIGS. 4A to  4 F are similar to the steps of FIGS. 2A to  2 F except that the second leadframe  102  of the embodiment of FIGS. 4A to  4 F is a different shape than the second leadframe  102  of the embodiment of FIGS. 2A to  2 F. As shown in FIGS. 4B to  4 F, the second leadframe  102  provides a pocket in the center of each unit in which the semiconductor die  104  is mounted, when laminated on the first leadframe  100 . 
     FIGS. 5A to  5 F show the processing steps for manufacturing the IC package of FIG. 4F in accordance with an alternative embodiment of the present invention. The steps of FIGS. 5A to  5 F are similar to the steps of FIGS. 3A to  3 F except that the second leadframe  102  of the embodiment of FIGS. 3A to  3 F is a different shape that the second leadframe  102  of the embodiment of FIGS. 3A to  3 F. Again, the second leadframe  102  provides a pocket in the center of each unit in which the semiconductor die  104  is mounted when laminated on the first leadframe  100 . 
     FIGS. 6A to  6 G show the processing steps for manufacturing an IC package in accordance with another embodiment of the present invention. FIG. 6A shows a cross-sectional side view of a copper (Cu) panel substrate which forms the raw material of the leadframe strip indicated generally by the numeral  100 . The copper strip is coated with a silver (Ag) plating on a bottom surface thereof and a solder plating on a top surface thereof, as shown. 
     Next a solder flux is added to a portion of the first leadframe  100  (FIG. 6B) and a second leadframe  102  with solder plating on both a top and a bottom surface thereof is laminated onto the first leadframe  100  using a solder reflow technique to form a single pocket-type leadframe (FIG.  6 C). 
     Solder paste is then dispensed on a portion of the first leadframe  100  (FIG. 6D) and the semiconductor die is attached to the first leadframe  100  by solder reflow technique (FIG.  6 E). The semiconductor die is coated with a suitable surface for soldering, such as titanium (Ti), tungsten (W), or gold (Au) for mounting via solder reflow. 
     Next, portions of the semiconductor die are coated with solder flux (FIG. 6F) and a third leadframe  108  with solder plating on both top and a bottom surfaces thereof is laminated to coated contact pads or I/O pads on the surface of the semiconductor die (FIG. 6G) via solder reflow technique. In an alternative embodiment the third leadframe  108  is laminated to the coated contact pads of the semiconductor die by epoxy. The contact pads are coated with, for example, Ti, W, or Au, for compatibility with the solder or with epoxy. 
     FIGS. 7A to  7 G show the processing steps for manufacturing the IC package of FIG. 6G in accordance with an alternative embodiment of the present invention. The order of the process steps in the present embodiment is different from the order of the steps of the embodiment of FIGS. 6A to  5 G. FIG. 7A shows a cross-sectional side view of the copper (Cu) panel substrate, which forms the raw material of the lead frame strip, indicated generally by the numeral  100 . Similar to the embodiment of FIG. 6A, the copper strip is coated with a silver (Ag) plating on a bottom surface thereof and a solder plating on a top surface thereof. 
     Solder paste is dispensed on a portion of the leadframe  100  (FIG. 7B) and the semiconductor die  104  is attached to the leadframe  100  by solder reflow technique (FIG.  7 C). The semiconductor die  104  is coated with a suitable surface for soldering, Such as titanium (Ti), tungsten (W), or gold (Au) for mounting via solder reflow. 
     Next, solder flux is dispensed on another portion of the leadframe  100  (FIG.  7 D) and a second leadframe  102  having solder plating on both a top and a bottom surface thereof is laminated onto the first leadframe  100  using a solder reflow technique to form a single pocket-type leadframe (FIG.  7 E). 
     Solder flux is then dispensed onto portions of the semiconductor die  104  (FIG. 7F) and a third leadframe  108  with solder plating on both top and bottom surfaces is laminated on the surface of the semiconductor die. 
     FIGS. 8A to  8 G show the processing steps for manufacturing an alternative IC package in accordance with another embodiment of the present invention. The steps of FIGS. 8A to  8 G are similar to the steps of FIGS. 6A to  6 G except that the second leadframe  102  of the embodiment of FIGS. 8A to  5 G is a different shape than the second leadframe  102  of the embodiment of FIGS. 6A to  6 G As shown in FIGS. 8B to  8 G, the second leadframe  102  provides a pocket in the center of each unit in which the semiconductor die  104  is mounted, when laminated on the first leadframe  100 . 
     FIGS. 9A to  9 G show the processing steps for manufacturing the IC package of FIG. 8G in accordance with an alternative embodiment of the present invention. The steps of FIGS. 9A to  9 G are similar to the steps of FIGS. 7A to  7 G except that the second leadframe  102  of the embodiment of FIGS. 9A to  9 G is a different shape that the second leadframe  102  of the embodiment of FIGS. 7A to  7 G. Again, the second leadframe  102  provides a pocket in the center of each unit in which the semiconductor die  104  is mounted when laminated on the first leadframe  100 . 
     Alternative embodiments and variations are possible. For example, in an alternative embodiment the semiconductor die is attached to the leadframe by reflow of the solder plated on the copper of the first leadframe  100  rather than by the addition of solder paste to the leadframe and subsequent reflow. In yet another alternative embodiment, the semiconductor die is mounted on the leadframe via silver epoxy. Other embodiments and variations will occur to those of skill in the art. All such embodiments and variations are believed to be within the scope and sphere of the present invention as defined by the claims appended hereto.