Patent Publication Number: US-8994162-B2

Title: Semiconductor multi-package module including tape substrate land grid array package stacked over ball grid array package

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a continuation of U.S. patent application Ser. No. 11/396,954, filed Apr. 3, 2006 now U.S. Pat. No. 7,589,407, which claims priority from U.S. Provisional Patent Application Ser. No. 60/669,975 filed Apr. 11, 2005 and the subject matter thereof is incorporated herein by reference thereto. 
     The present application contains subject matter related to co-pending U.S. patent application Ser. No. 12/059,077, now U.S. Pat. No. 8,410,596, which claims priority from U.S. Provisional Patent Application Ser. No. 60/669,975. The related application is assigned to STATS ChipPAC Ltd. and the subject matter thereof is incorporated herein by reference thereto. 
    
    
     BACKGROUND 
     This invention relates to semiconductor chip packaging and, particularly, to packaging suitable for stacked package modules (such as package-in-package modules). 
     Semiconductor package substrates typically are laminates of two or more patterned metal layers separated by dielectric layers. Interconnection of the die (one or more, in a stacked die package) to the substrate is made to bond sites in traces in an uppermost metal layer. Interconnection of the package to a motherboard (for example) or to another package in a stacked package module (for example) is made to traces in a lowermost metal layer. Interconnection between upper and lower metal layers is made by vias, which are typically holes in the intervening dielectric layer or layers, filed with conductive material. 
     SUMMARY 
     In one general aspect the invention features a single metal layer tape substrate, and methods for making the single metal layer substrate. The substrate includes a patterned metal layer having a die attach side and a land side, affixed (for example, laminated) to a patterned dielectric layer. The patterned metal layer includes bond fingers and lands. The metal layer is patterned to provide circuit traces as appropriate for interconnection with the die (on the die attach side) and with other elements (such as other packages in a multi-package module). The dielectric layer is patterned to provide openings exposing bond sites on lands (and, optionally, exposing sites on bond fingers) on the land side of the metal layer. Interconnection of a die with the substrate is made by wire bonding to exposed traces on bond fingers on a die attach side of the metal layer. Lands (and, optionally) bond fingers are exposed on the land side of the metal layer for access to testing the package, and/or for attachment of second-level interconnection to underlying circuitry such as a motherboard. In some embodiments a row of wire bond sites on adjacent bond fingers is exposed on the land side by a common opening in the dielectric layer, providing for a finer pitch interconnect and, accordingly, a higher interconnect density between stacked packages. 
     In another general aspect the invention features a land grid array package, or a ball grid array package, having a single metal layer tape substrate. The package according to the invention can be made thinner than is possible in a package having a multiple metal layer laminate substrate. The improved thinness can be particularly useful in multi-package modules, as are used for example in wireless and consumer product applications. The package according to the invention can be particularly useful in multi-package modules having an upper inverted package stacked over a lower package. 
     In another general aspect the invention features a multipackage module including a single metal layer tape substrate land grid array package stacked over a ball grid array package. In some embodiments the ball grid array package has a single metal layer tape substrate. The land grid array package is inverted with respect to the lower ball grid array package, and interconnection between the single metal layer tape substrate land grid array package and the ball grid array package is made by wire bonds leading from the exposed wire bond sites on the land side of the land grid array package. 
     In another general aspect the invention features a method for making a single metal layer tape substrate, by providing a substrate dielectric layer, patterned to provide openings situated to expose bond finger sites and lands on a metal layer, laminating a metal foil such as a copper foil onto a surface of the dielectric layer, and patterning the metal foil to form bond fingers and lands over said openings. In some embodiments the dielectric layer is a polymer material and in some embodiments the openings are made by punching or etching. In some embodiments the metal foil is affixed to the surface of the dielectric layer using chromium or an adhesive. In some embodiments the method further includes plating exposed surfaces of the patterned foil with a metal. In some embodiments the method further includes applying a dielectric material on a die attach region of the side of the metal foil facing away from the dielectric layer to form a substrate assembly having a die attach side and a land side opposite the die attach side. 
     In another general aspect the invention features a method for making a semiconductor package by forming the single metal layer tape substrate assembly as described above, affixing a die onto a die mount surface of the die attach side of the substrate assembly; electrically connecting die pads with bond sites on the die attach side of the bond fingers by wire bonds; and encapsulating the die and wire bonds. 
     In some embodiments the dielectric material is applied to the substrate by supporting the substrate on the land side and printing the dielectric material onto the die attach side. In some embodiments the dielectric material is printed through a screen or stencil, and the surface of the dielectric material is planarized. In some embodiments the plating includes immersing the patterned laminated metal foil and dielectric layer in a plating bath, and in some embodiments the plating is repeated to form a plurality of plating layers, such as plating first with nickel and then with gold. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagrammatic sketch in a sectional view showing an embodiment of a single metal layer tape substrate land grid array package according to the invention. 
         FIG. 2  is a diagrammatic sketch in a plan view showing a portion of the embodiment of  FIG. 1 , viewing the land side of the package. 
         FIG. 3  is a diagrammatic sketch in a sectional view showing a stage in a process for making a single metal layer tape substrate according an embodiment to the invention. 
         FIG. 4A  is a diagrammatic sketch in a plan view showing a portion of the embodiment of  FIG. 3 , viewing the land side of the substrate. 
         FIG. 4B  is a diagrammatic sketch in a sectional view of the embodiment of  FIG. 4A , taken thru B-B′. 
         FIG. 4C  is a diagrammatic sketch in a sectional view of the embodiment of  FIG. 4A , taken thru C-C′. 
         FIG. 5  is a diagrammatic sketch in a sectional view showing a further stage in a process for making a single metal layer tape substrate according an embodiment to the invention. 
         FIG. 6A  is a diagrammatic sketch in a plan view showing a portion of the embodiment of  FIG. 5 , viewing the land side of the substrate. 
         FIG. 6B  is a diagrammatic sketch in a sectional view of the embodiment of  FIG. 6A , taken thru B-B′. 
         FIG. 6C  is a diagrammatic sketch in a sectional view of the embodiment of  FIG. 6A , taken thru C-C′. 
         FIG. 7  is a diagrammatic sketch in a sectional view showing a further stage in a process for making a single metal layer tape substrate according an embodiment to the invention. 
         FIG. 8A  is a diagrammatic sketch in a plan view showing a portion of the embodiment of  FIG. 7 , viewing the land side of the substrate. 
         FIG. 8B  is a diagrammatic sketch in a sectional view of the embodiment of  FIG. 8A , taken thru B-B′. 
         FIG. 8C  is a diagrammatic sketch in a sectional view of the embodiment of  FIG. 8A , taken thru C-C′. 
         FIG. 9  is a diagrammatic sketch in a sectional view showing a further stage in a process for making a single metal layer tape substrate according an embodiment to the invention. 
         FIG. 10A  is a diagrammatic sketch in a plan view showing a portion of the embodiment of  FIG. 9 , viewing the land side of the substrate. 
         FIG. 10B  is a diagrammatic sketch in a sectional view of the embodiment of  FIG. 10A , taken thru B-B′. 
         FIG. 10C  is a diagrammatic sketch in a sectional view of the embodiment of  FIG. 10A , taken thru C-C′. 
         FIG. 11  is a diagrammatic sketch in a sectional view showing a further stage in a process for making a single metal layer tape substrate according an embodiment to the invention. 
         FIG. 12A  is a diagrammatic sketch in a plan view showing a portion of the embodiment of  FIG. 11 , viewing the land side of the substrate. 
         FIG. 12B  is a diagrammatic sketch in a sectional view of the embodiment of  FIG. 12A , taken thru B-B′. 
         FIG. 12C  is a diagrammatic sketch in a sectional view of the embodiment of  FIG. 12A , taken thru C-C′. 
         FIG. 13  is a diagrammatic sketch in a sectional view showing a further stage in a process for making a single metal layer tape substrate according an embodiment to the invention. 
         FIG. 14A  is a diagrammatic sketch in a plan view showing a portion of the embodiment of  FIG. 13 , viewing the land side of the substrate. 
         FIG. 14B  is a diagrammatic sketch in a sectional view of the embodiment of  FIG. 14A , taken thru B-B′. 
         FIG. 14C  is a diagrammatic sketch in a sectional view of the embodiment of  FIG. 14A , taken thru C-C′. 
         FIG. 15  is a diagrammatic sketch in a sectional view showing an embodiment of a single metal layer tape substrate ball grid array package according to the invention. 
         FIG. 16  is a diagrammatic sketch in a sectional view showing an embodiment of a multi-package module according to the invention, having an inverted single metal layer tape substrate land grid array package stacked over a single metal layer tape substrate ball grid array package. 
     
    
    
     DETAILED DESCRIPTION 
     The invention will now be described in further detail by reference to the drawings, which illustrate alternative embodiments of the invention. The drawings are diagrammatic, showing features of the invention and their relation to other features and structures, and are not made to scale. For improved clarity of presentation, in the FIGS. illustrating embodiments of the invention, elements corresponding to elements shown in other drawings are not all particularly renumbered, although they are all readily identifiable in all the FIGS. 
     Turning now to  FIGS. 1 and 2 , therein is shown a semiconductor chip package  10  according to an embodiment of the invention, having one die wire bonded onto a single metal layer tape substrate. The substrate includes a substrate dielectric layer  4  laminated with a patterned single metal layer  2 . The metal layer  2  is patterned to provide traces as appropriate for making electrical connections between the substrate the die, on one side, and for making electrical connections from the package, on the other side. More specifically, the metal layer  2  can have a land side and a die attach side opposite the land side. The land side of the metal layer  2  can be directly on the substrate dielectric layer  4 . Intervals between the metal traces  2  can be planarized by filling, as shown at a patterned layer  6 , with a dielectric material such as, for example a photoresist or film, to enable die attach without voids. The patterned layer  6  can be directly on the metal layer  2  and the substrate dielectric layer  4 . A die  14  is affixed to the die attach side of the substrate using a die attach adhesive  13 , such as a die attach epoxy or tape (film) adhesive. More specifically, the die attach adhesive  13  can attach the die  14  to the metal layer  2  and the patterned layer  6  with the die attach adhesive  13  directly on the patterned layer  6  and the metal layer  2 . On the land side of the substrate (opposite the die attach side) openings  3  expose lands  23 , and openings  5  expose bond fingers  25 . The die  14  is electrically connected to selected traces on the die attach side by wire bonds  15 . The die and wires are protected by an encapsulation or molding  17 : The die  14  with the die attach adhesive  13  can be over the patterned layer  6  and the die attach side of the metal layer  2 . 
     As  FIG. 2  shows, according to one aspect of the invention an opening  5  in the dielectric layer  4  extends as a window across two or more the bond fingers  25 . A marginal portion  25  of the dielectric layer  4  provides support for the margin of the patterned metal layer, including extensions of the bond fingers and including portions of the traces to which the wire bonds from the die are connected. Stated another way, a number of adjacent bond fingers  25  span a slot or window  5  in the dielectric layer  4 . The substrate is typically rectangular (for example, generally square), and bond the bond sites on the bond fingers may be arranged in a row along one edge of the substrate, or in a row along each of two, three, or four edges of the substrate, as may be required for the particular die configuration. According to the invention, a slot or window  5  in the dielectric  4  may serve to expose all the bond sites in any such row. The opening  5  as a slot or window can also expose the encapsulation  17  through the dielectric  4 . A slot or window configuration for opening to expose the bond sites on the bond fingers can be made to much finer specifications than individual openings for the sites. 
     The lands  23 , which in the example shown are arranged more centrally (typically in an array) in the substrate, and typically opposite the die attach region, can be employed as sites for testing the land grid array package prior to combining it with other devices. Further, the openings  3  of the substrate dielectric layer  4  can expose the sites for testing on the metal layer  2 . More specifically, the sites for testing can be arranged in a staggered array. For example, where the package is to be stacked over another package in a multi-package module, the package can be tested prior to assembly; packages not tested as “good” can be discarded and only “good” packages used in the assembly. This improves overall yield. 
     Various materials and dimensions may be specified for the single metal layer tape substrate land grid array package according to the invention, such as in the following illustrative example. The dielectric layer  4  can be a sheet of polyimide, patterned, for example by punching, to lay out the openings. The patterned polyimide film can have a thickness in the range, for example, about 25 um to about 75 um. The metal layer  2  can be a copper foil, laminated onto the polyimide film and then masked and etched to form the circuit traces. The patterned copper layer can have a thickness in the range, for example, about 12 um to about 25 um. At least the exposed portions of the metal layer can be plated, for example with nickel and gold, to provide superior electrical interconnection with wire bonds or with solder; the plating may have thicknesses, for example, about 5 um nickel and about 0.5 um gold. The planarizing layer may be, for example, a photoresist or other dielectric. A suitable planarizing material may be, for example, a dry film, which flows to some extent (plastic flow, that is, without melting) at raised temperature under pressure. The planarizing layer has a thickness at least about the same as the thickness of the metal layer, and the thickness may be in the range, for example, about 12 um to about 40 um. If the substrate is suitably planarized, a film adhesive may be used to attach the die; otherwise, a die attach epoxy should be employed. The die attach can have a thickness in the range, for example, about 20 um to about 75 um. The die thickness will depend upon the type of die; some die can have a thickness in the range, for example, about 75 um to about 150 um. The encapsulation or molding should have a thickness sufficient to cover the wires (allowing for variation in the loop height). 
     According to this aspect of the invention, the bond fingers may have a very fine pitch, as fine as the substrate manufacturing technology allows, and may be in some examples about 40 um or greater (as compared with about 80 um or greater for a multiple metal layer laminate substrate), and in the range, for example, about 40 um to about 400 um, as may be specified for a particular package. An stackable land grid array package according to the invention can have a very high interconnect density, so that chips, such as ASICs, having a high I/O count, can be packaged according to the invention and stacked over a lower package, which may be, for example, a processing unit. The lands may have a pitch in the range, for example, about 0.3 mm to 0.8 mm. 
     As noted above, the package according to the invention can be particularly useful in multi-package modules, such as so-called “package-in-package” (PIP) modules. In some such PIP modules, an upper package is inverted and stacked over a lower package, and the inverted upper package is electrically interconnected to the lower package by wire bonds connecting bond sites on bond fingers in the upward-facing side (the “land” side) of the upper package with bond sites on bond fingers on the upward-facing side of the lower package substrate. In some applications, such as hand held wireless devices (cellular phones having wireless internet communications capability, with imaging and sound capture capability, the device requires a signal processor, typically a digital signal processor, and an ASIC which may include graphics processing capability, in addition to memory. The ASIC typically has high I/O (for example 400); according to the invention, an ASIC can be packaged as single metal layer tape substrate land grid array with high I/O having a footprint smaller than the digital signal processor, and the ASIC package can be inverted and stacked over the digital signal processor package and interconnected with it by wire bonds. Memory can be provided as an additional memory package, included in the package stack (for example, stacked over the ASIC package); or memory can be included as stacked die in one or more of the stacked packages (for example, stacked with the ASIC die in the ASIC package). 
       FIGS. 3 through 14C  are diagrammatic sketches showing stages in a process for making a single metal layer tape substrate, and a package having a die mounted on the tape, according to an embodiment of the invention. With reference now to  FIGS. 3 ,  4 A,  4 B, and  4 C, a substrate dielectric layer  34  is provided, patterned to provide openings  33 ,  35  situated to expose bond finger sites  45  and lands  43  on the land side of the metal layer. The dielectric layer may be formed from a sheet of a polymer material, such as a polyimide, and the openings may be made by punching or by etching. A metal foil, such as a copper foil, is then laminated onto a surface of the dielectric layer, using chromium or an adhesive as an affixative. The adhesive may have a thickness about 10 um to about 12 um, typically, for example. Then the metal foil is patterned by masking and etching to form the patterned traces  32 , including lands  43 , among other features, according to the circuit design. The result is shown in the FIGs. The affixative is shown at  36  in the FIGs., where the patterned metal foil  32  contacts the patterned polymer sheet  34 . Because the opening  35  exposing the row of bond sites  45  on the bond fingers extends across several adjacent bond finger traces  32 , voids  47  appear between the traces at the bond sites  45 . 
     A further stage in the process is shown in  FIGS. 5 ,  6 A,  6 B, and  6 C. Here, a dielectric material is applied in a patterned layer  53 ,  55  to planarize the substrate on the die attach side  52  of the metal layer  32 . The dielectric material can be applied by supporting the substrate on the substrate dielectric  34  side (the “land” side) and then printing the planarizing dielectric onto the opposite side (the die attach side) through a screen or stencil, using a doctor blade to level the surface of the planarizing dielectric. The planarizing dielectric layer is patterned to leave open the window in the substrate dielectric over the row of bond finger sites, and to leave exposed a marginal part of the bond fingers on the die attach side of the metal foil. 
       FIGS. 7 ,  8 A,  8 B, and  8 C show a further stage in the process. Here, the assembly as shown in  FIGS. 5 ,  6 A,  6 B, and  6 C has been immersed in a plating bath, first to plate exposed surfaces of the patterned copper foil with nickel, and then to plate the nickel-plated surfaces with gold. In the FIGs., the Ni—Au plated areas on the die attach side of the metal foil are shown at  72 , and the Ni—Au plated areas on the land side of the metal foil are shown at  74 . The planarizing dielectric serves as a plating mask on the die attach side of the substrate, and the substrate dielectric serves as a plating mask on the land side of the substrate. Because of the voids between the bond fingers at the window exposing the bond sites, the bond fingers are plated on all sides at these points. 
     A further stage in the process is shown in  FIGS. 9 ,  10 A,  10 B, and  10 C, following die attach onto the substrate. In the example shown here, a film adhesive  95  is employed to affix the die  94  onto the substrate. At this stage, when the assembly is viewed from the land side, the voids are blocked by the film adhesive  95 . Elsewhere on the die attach side of the substrate, the planarization later provides a firm and substantially flat platform for the die attach film adhesive. 
     In the stage of the process shown in  FIGS. 11 ,  12 A,  12 B, and  12 C, wire bonds  115  have been formed to connect the bond pads  114  on the die  94  with the die attach surface  112  of the bond fingers. In the stage of the process shown in  FIGS. 13 ,  14 A,  14 B, and  14 C, the assembly has been molded (or encapsulated) with a molding  137  which encloses the die and the wire bonds, completing the package. 
     The description above refers by way of example to a land grid array package. As shown in  FIG. 15 , a single metal layer tape substrate package according to the invention can be configured as a ball grid array package. Reference is made to  FIG. 1 . The ball grid array package  150  of  FIG. 15  can be constructed in much the same way as the land grid array package described above. The substrate includes a patterned dielectric layer  154  laminated with a single metal layer  152 . The die  154  is attached using a die attach adhesive  153 , and is interconnected with the bond fingers on the substrate by wire bonds  155 . Here, however, the bond fingers are exposed on the die attach side  159 , but are not exposed on the opposite side. The package is necessarily molded, so that the bond fingers  159  are not covered on the die attach side by the molding  157 . Further, the molding  157  can encapsulate a portion of the die attach side of the single metal layer  152 . And here the patterned dielectric layer  154  is patterned to expose module solder ball attach pads  152 . After completion of steps generally as outlined in  FIGS. 3 through 12C , the package is molded, and then solder balls or bumps  158  are formed in the openings in the substrate dielectric  154 , to make connection with the pads  152 . 
       FIG. 16  shows, generally at  160 , a multi-package module (PIP) according to the invention. In this example, both the lower ball grid array package  150  and the inverted upper land grid array package  10 , as shown in greater detail in  FIG. 1 , are single metal layer tape substrate packages. The inverted upper land grid array package is affixed to the molding of the lower ball grid array package using an adhesive  163 . The upper and lower packages are electrically interconnected by wire bonds  165  which connect bond sites on the bond fingers of the upper package  10  with bond sites  159  on the bond fingers of the lower package  150 . The module is encapsulated or molded by a package encapsulation  167 . The package encapsulation  167  can be in and completely fill the openings  3 , each of which exposes one of the lands  23 . The package encapsulation  167  can be in direct contact with the lands  23  through the openings  3 . 
     Other embodiments are within the scope of the invention.