Abstract:
In an illustrative embodiment, an apparatus includes at least one antenna structure located on a first surface of a first substrate; at least one pad located on the first surface of the first substrate; and at least one via traversing the first substrate and thereby connecting the at least one pad located on the first surface of the first substrate to at least one pad located on a second surface. The at least one pad located on the first surface of the first substrate is operatively coupleable to at least one pad located on a surface of an integrated circuit and the at least one pad located on the second surface is operatively coupleable to at least one pad located on a surface of a printed circuit board. The at least one via is thereby operative to couple the at least one pad located on the surface of the integrated circuit and the at least one pad located on the surface of the printed circuit board.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 60/949,884, filed Jul. 16, 2007, and U.S. Provisional Application No. 60/949,685, filed Jul. 13, 2007, the disclosures of which are incorporated by reference herein. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to integrated circuit (chip) packaging with integrated antennas or planar phased arrays. Specifically, it is related to chip packaging with integrated antennas or planar phased array designs for millimeter wave (mmWave) frequencies and above. 
     BACKGROUND OF THE INVENTION 
     In a wireless network, connectivity and communication between devices is achieved through antennas attached to receivers or transmitters in order to radiate the desired signals to or from other elements of the network. In radio communication systems, such as millimeter-wave radios, discrete components are usually assembled with low integration levels. These systems are often assembled using expensive and bulky waveguides and package-level or board-level microstrip structures to interconnect semiconductors and their required transmitter or receiver antennas. 
     With recent progress in semiconductor technology and packaging engineering, the dimensions of these radio communication systems have become smaller and integration of antennas with their radio frequency (RF) front-end circuits has become more desirable. For applications such as wireless universal serial bus (USB), the operating distance is limited to about a meter; a single antenna with about 7 dBi at 60 GHz will provide the necessary antenna gains. 
     However, for point-to-point applications which require operating distances of ten meters (such as wireless video) or longer (such as military radar), antenna gains as high as 30 dBi may be required. However, because high-gain antennas have very narrow beam widths (thereby making it difficult for consumers to accurately point the antenna), phased arrays (also known as radiation pattern steerable arrays) are necessary. 
     Typical chip packages with integrated antennas have three major parts: a RF chip, one or more antennas, a package carrier, and a possible package lid/cover (or just using encapsulant to protect the package). The main idea here is to design the carrier that has high performance antennas, an interface for flip-chipping RF chip and interface for flip-chipping the package to printed circuit mother board. There are two expensive components for the antenna part: substrate with antenna structure and feed line, and a metal support frame to form the cavity (etched hole) for the antenna. 
     For example, J. Grzyb et al., “Wideband Cavity-backed Folded Dipole Superstrate Antenna for 60 GHz Applications,”  Proceedings of the  2006  IEEE AP - S International Symposium , pp. 3939-3942, July 2006, and T. Zwick et al., “Broadband Planar Superstrate Antenna for Integrated mmWave Transceivers,”  IEEE Transactions on Antennas and Propagation , vol. 54, no. 10, pp. 2790-2796, October 2006, the disclosures of which are incorporated by reference herein, describe a broadband planar dipole superstrate antenna suitable for integration with millimeter wave (MMW) transceiver ICs. The dipole is printed on the bottom of a fused silica substrate with a ground plane below. This dipole may then be flip-chip mounted onto a coplanar waveguide (CPW) feed line on the top of the RF chip. 
     SUMMARY OF THE INVENTION 
     In an illustrative embodiment, an apparatus includes at least one antenna structure located on a first surface of a first substrate; at least one pad located on the first surface of the first substrate; and at least one via traversing the first substrate and thereby connecting the at least one pad located on the first surface of the first substrate to at least one pad located on a second surface. The at least one pad located on the first surface of the first substrate is operatively coupleable to at least one pad located on a surface of an integrated circuit and the at least one pad located on the second surface is operatively coupleable to at least one pad located on a surface of a printed circuit board. The at least one via is thereby operative to couple the at least one pad located on the surface of the integrated circuit and the at least one pad located on the surface of the printed circuit board. 
     In another illustrative embodiment, an apparatus comprises a plurality of pads located on a surface of a substrate opposite a printed circuit board; at least one integrated circuit operatively coupled to at least a portion of the plurality of pads and located proximate to the surface of the substrate opposite the printed circuit board; a plurality of antennas located proximate to the surface of the substrate opposite the printed circuit board; and at least one feed line operatively connected between each of the plurality of antennas and a given one or more of the plurality of pads. 
     In a further illustrative embodiment, a method of forming a package includes the steps of forming an antenna on a first surface of a first substrate; flip-chip mounting an integrated circuit to the first surface of the first substrate; and flip-chip mounting a second surface opposite the first surface of the first substrate to a printed circuit board. The second surface may be a surface of the first substrate or the second surface may be a surface of a second substrate. 
     Illustrative embodiments of the present invention may be easy and cost effective to manufacture while providing superior performance. Moreover, illustrative embodiments may also provide a more effective way to dissipate the heat from the chip. 
     These and other objects, features and advantages of the present invention will become apparent from the following detailed description of illustrative embodiments thereof, which is to be read in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-section of a package with an integrated antenna; 
         FIG. 2  is a cross-section of an exemplary two-substrate carrier, according to an embodiment of the invention; 
         FIG. 3  is a cross-section of an exemplary three-substrate carrier, according to an embodiment of the invention; 
         FIG. 4  is a top view of an exemplary two- or three-substrate carrier, according to an embodiment of the invention; 
         FIG. 5  shows a top view and a cross-section of an exemplary printed circuit board, according to an embodiment of the invention; 
         FIG. 6  is a cross-section of an exemplary two-substrate package, according to an embodiment of the invention; 
         FIG. 7  is a cross-section of an exemplary three-substrate package, according to an embodiment of the invention; 
         FIG. 8  is a top view of an exemplary two- or three-substrate package, according to an embodiment of the invention; and 
         FIG. 9  is a top view of an exemplary phased array layout, according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     While reference may be made herein to certain device components, it is to be understood that the present invention is not limited to these or any particular device components or arrangements thereof. 
       FIG. 1  shows a package concept with an integrated antenna similar to that described in the Grzyb et al. and Zwick et al. references cited above. This package is well-suited for lab study and testing because of its high performance. For example, an implemented package with a folded dipole antenna of 100 ohms input impedance yields return loss bandwidth more than 30% with efficiency better than 85% and a minimum 7 dBi gain. 
     Although the cost is relatively low for small-scale production, such as that used for the aforementioned lab study and testing, this package requires the use of expensive components such as the substrate with antenna structure and feed line and the metal support frame to form the cavity (etched hole) for the antenna. 
     Moreover, packaging the chip and the antenna requires a complex process, including the following steps: 
     1. Glue chip  120  to ground plane  180  on printed circuit board (PCB)  110  using conductive paste  115 . 
     2. Connect pad  125  on PCB  110  to pad  135  on chip  120  with bondwire  130 , thereby wirebonding chip  120  to PCB  110 . 
     3. Place gold studs  145  on corresponding pads of chip  120  for connections to antenna  160  through feedline  150 . 
     4. Glue antenna substrate  155  to metal support frame  170  using conductive paste  165  to form the antenna subassembly. 
     5. Bake the antenna subassembly in a special oven. 
     6. Flip-chip the antenna subassembly to chip  120 . 
     7. Glue metal support frame  170  to ground plane  180  on PCB  110  using conductive paste  185 . 
     8. Fill the contact area between chip  120  and feedline  150  with underfill  140 . 
     9. Fill the gap between chip  120  and metal support frame  170  with encapsulant  190 . 
     10. Bake antenna assembly  100  in a special oven again. 
     Because of the complexity of this manufacturing process, it is difficult to mass produce this package at a low cost using an automated process. By contrast, an illustrative embodiment of the present invention may be built simply by flip-chipping a chip to the package then flip-chipping the package to a printed circuit board. Moreover, because antenna  160  overlays chip  120 , it may be difficult to effectively dissipate the heat from the chip. For example, it would be difficult to mount a heatsink on chip  120  without interfering with the radiation pattern of antenna  160 . 
       FIG. 2  is a cross-section of exemplary two-substrate carrier  200 , according to an embodiment of the invention. Substrate  210  is preferably a low loss substrate suitable for RF or mmWave applications, such as fused silica. However, any substrate may be used in conjunction with inventive techniques, although one having skill in the art will recognize that a low-loss substrate is preferable. In a preferred embodiment, substrate  210  may have a thickness of approximately 200-300 μm, though this is not a requirement of the invention. 
     Antenna structure  215  (including antenna feed lines and necessary pads for flip-chip connections) is preferably printed on an upper surface of substrate  210 . It should be noted that antenna structure  215  may be formed using an alternative process, such as, for example, photolithography, chemical etching, a thin-film metal patterning process, or a high-resolution gold deposition process. 
     Substrate  220  is preferably comprised of FR-4. However, any suitable material may be used, including but not limited to FR-2 or G-10. In a preferred embodiment, substrate  220  may have a thickness of approximately 300-400 μm, though this is not a requirement of the invention. Substrate  220  preferably has a cutout or cavity  225  with metal-plated walls  230  to improve the performance of antenna  215 . Metal-plated walls  230  may be formed of a wide variety of electrically conductive metals including but not limited to copper. 
     Pads  240  on the upper surface of substrate  210  and pads  250  on the lower surface of substrate  220  are connected by plated through vias  245 , which pass through substrates  210  and  220 . Because vias  245  are preferably for low frequency applications, vias  245  may comprise stepped vias. Pad  255  may also be formed on the lower surface of substrate  220  without a corresponding via. 
       FIG. 3  is a cross-section of exemplary three-substrate carrier  300 , according to an embodiment of the invention. Substrate  310  is preferably a low loss substrate suitable for RF or mmWave applications, such as fused silica. However, any substrate may be used in conjunction with inventive techniques, although one having skill in the art will recognize that a low-loss substrate is preferable. In a preferred embodiment, substrate  310  may have a thickness of approximately 200-300 μm, though this is not a requirement of the invention. 
     Antenna structure  315  (including antenna feed lines and necessary pads for flip-chip connections) is preferably printed on an upper surface of substrate  310 . It should be noted that antenna structure  315  may be formed using an alternative process, such as, for example, photolithography, chemical etching, a thin-film metal patterning process, or a high-resolution gold deposition process. 
     Substrate  320  is located between substrate  310  and substrate  360 . Substrate  320  is preferably comprised of FR-4. However, any suitable material may be used, including but not limited to FR-2 or G-10. In a preferred embodiment, substrate  320  may have a thickness of approximately 300-400 μm, though this is not a requirement of the invention. Substrate  320  preferably has a cutout or cavity  325  with metal-plated walls  330  to improve the performance of antenna  315 . Metal-plated walls  330  may be formed of a wide variety of electrically conductive metals including but not limited to copper. 
     Substrate  360  is preferably comprised of FR-4. However, any suitable material may be used, including but not limited to FR-2 or G-10. Metal plating  335  on an upper surface of substrate  360  forms cavity  325  in conjunction with metal-plated walls  330  in substrate  320 . Metal plating  335  may act as a ground plane for antenna  315 . 
     Pads  340  on the upper surface of substrate  310  and pads  350  on the lower surface of substrate  360  are connected by plated through vias  345 , which pass through substrates  310 ,  320  and  360 . Because vias  345  are preferably for low frequency applications, vias  345  may comprise stepped vias. Pad  355  may also be formed on the lower surface of substrate  360  without a corresponding via. 
       FIG. 4  shows a top view of carrier  400 , which may be similar to carriers  200  and  300  shown in  FIGS. 2 and 3 . Pads  440  and  480  are formed on an upper surface of substrate  410 . Antenna  415  is preferably connected to pads  480  through one or more feedlines. Cavity  425  is located underneath antenna  415  and substrate  410 . 
       FIG. 5  is a cross-section of exemplary printed circuit board (PCB) structure  500 , according to an illustrative embodiment of the present invention. PCB structure  500  comprises PCB  570 , which may be formed of, for example, FR-4, FR-2 and/or G-10. PCB  570  has pads  575  located thereon, which preferably correspond to pads  250  shown in  FIG. 2  or pads  350  shown in  FIG. 3 . PCB  570  may also have a metal plate  585  formed thereon, which may function as a ground plane in some embodiments. 
       FIG. 6  is a cross-section of exemplary two-substrate package  600 , according to an embodiment of the invention. In a preferred embodiment, package  600  is formed by flip-chipping a carrier similar to carrier  200  in  FIG. 2  to a PCB structure similar to PCB structure  500  in  FIG. 5 , then flip-chipping chip  690  to the carrier. 
     Substrate  610  is preferably a low loss substrate suitable for RF or mmWave applications, such as fused silica. However, any substrate may be used in conjunction with inventive techniques, although one having skill in the art will recognize that a low-loss substrate is preferable. In a preferred embodiment, substrate  610  may have a thickness of approximately 200-300 μm, though this is not a requirement of the invention. 
     Antenna structure  615  (including antenna feed lines and necessary pads for flip-chip connections) is preferably printed on an upper surface of substrate  610 . It should be noted that antenna structure  615  may be formed using an alternative process, such as, for example, photolithography, chemical etching, a thin-film metal patterning process, or a high-resolution gold deposition process. 
     Substrate  620  is preferably comprised of FR-4. However, any suitable material may be used, including but not limited to FR-2 or G-10. In a preferred embodiment, substrate  620  may have a thickness of approximately 300-400 μm, though this is not a requirement of the invention. Substrate  620  preferably has a cutout or cavity  625  with metal-plated walls  630  to improve the performance of antenna  615 . Metal plate  685  on PCB  670  preferably acts as a ground plane and forms cavity  625  in conjunction with metal-plated walls  630  in substrate  620 . Metal-plated walls  630  and metal plate  685  may be formed from a wide variety of electrically conductive metals including but not limited to copper. 
     Pads  640  on the upper surface of substrate  610  are adjacent to corresponding pads on the lower surface of chip  690  and pads  650  on the lower surface of substrate  620  are adjacent to corresponding pads on the upper surface of PCB  670 . Pads  640  and  650  are connected by plated through vias  645 , which pass through substrates  610  and  620 . Because vias  645  are preferably for low frequency applications, vias  645  may comprise stepped vias. Vias  645  provide ground, power, control and signal connections between chip  690  and PCB  670 . Chip  690  may be, for example, an radio-frequency (RF) transmitter/receiver (Tx/Rx) chip. Pad  655  may also be formed on the lower surface of substrate  620  without a corresponding via. 
       FIG. 7  is a cross-section of exemplary three-substrate package  700 , according to an embodiment of the invention. In a preferred embodiment, package  700  is formed by flip-chipping a carrier similar to carrier  300  in  FIG. 3  to a PCB structure similar to PCB structure  500  in  FIG. 5 , then flip-chipping chip  790  to the carrier. 
     Substrate  710  is preferably a low loss substrate suitable for RF or mmWave applications, such as fused silica. However, any substrate may be used in conjunction with inventive techniques, although one having skill in the art will recognize that a low-loss substrate is preferable. In a preferred embodiment, substrate  710  may have a thickness of approximately 200-300 μm, though this is not a requirement of the invention. 
     Antenna structure  715  (including antenna feed lines and necessary pads for flip-chip connections) is preferably printed on an upper surface of substrate  710 . It should be noted that antenna structure  715  may be formed using an alternative process, such as, for example, photolithography, chemical etching, a thin-film metal patterning process, or a high-resolution gold deposition process. 
     Substrate  720  is located between substrate  710  and substrate  760 . Substrate  720  is preferably comprised of FR-4. However, any suitable material may be used, including but not limited to FR-2 or G-10. In a preferred embodiment, substrate  720  may have a thickness of approximately 300-400 μm, though this is not a requirement of the invention. Substrate  720  preferably has a cutout or cavity  725  with metal-plated walls  730  to improve the performance of antenna  715 . Metal-plated walls  730  and metal plate  785  may be formed from a wide variety of electrically conductive metals including but not limited to copper. 
     Substrate  760  is preferably comprised of FR-4. However, any suitable material may be used, including but not limited to FR-2 or G-10. Metal plating  735  on an upper surface of substrate  760  forms cavity  725  in conjunction with metal-plated walls  730  in substrate  720 . Metal plating  735  may act as a ground plane for antenna  715 , in which case PCB  770  need not provide a ground plane. Locating ground plane  735  on substrate  760  instead of PCB  770  advantageously reduces the risk that encapsulant material may enter cavity  725 . 
     Pads  740  on the upper surface of substrate  710  are adjacent to corresponding pads on the lower surface of chip  790  and pads  750  on the lower surface of substrate  760  are adjacent to corresponding pads on the upper surface of PCB  770 . Pads  740  and  750  are connected by plated through vias  745 , which pass through substrates  710 ,  720  and  760 . Because vias  745  are preferably for low frequency applications, vias  745  may comprise stepped vias. Vias  745  provide ground, power, control and signal connections between chip  790  and PCB  770 . Chip  790  may be, for example, an radio-frequency (RF) transmitter/receiver (Tx/Rx) chip. Pad  755  may also be formed on the lower surface of substrate  760  without a corresponding via. 
       FIG. 8  shows a top view of an exemplary package  800 , which may be similar to packages  600  and  700  shown in  FIGS. 6 and 7 . Chip  890  is positioned above pads  840  on substrate  810  such that pads on the underside of chip  890  are adjacent to corresponding pads  840 . Antenna  815  is preferably connected to pads  880 , which may be formed on an upper surface of substrate  810  and/or on a lower surface of chip  890 . Cavity  825  is located underneath antenna  815 . All components are deposited on top of PCB  870 . 
       FIG. 9  shows an exemplary package  900  with a 2×2 planar phased array layout. It is possible to have more than two antennas on each row. This basic 2×2 array can be used to form much larger arrays. In addition to first antenna  921  with first feed line  911 , also included are second, third and fourth antennas  922 ,  923 ,  924  with corresponding second, third and fourth feed lines  912 ,  913 ,  914 . Each feed line is connected to one or more pads  980  of chip  990  to form a planar phased array. A single large ground plane can be employed in phased array embodiments or each antenna may have its own ground plane. A phased array can include any number of antennas greater than or equal to two; however, powers of two are advantageous, e.g., 2, 4, 8, 16, 32, and so on. 
     Although illustrative embodiments of the present invention have been described herein with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments, and that various other changes and modifications may be made by one skilled in the art without departing from the scope of spirit of the invention.