Abstract:
Optical communication apparatus comprises: a first IC assembly disposed at a first PCB and comprising: a first IC package electrically coupled to circuits of the first PCB and having an opening in a bottom layer thereof; a first array of optical elements disposed in and electrically coupled to the first IC package and aligned with the bottom layer opening; and a tube of optical fibers disposed in the bottom layer opening with one end aligned under the first array and another end protruding out from the bottom layer of the first package and extending through a hole in the first PCB; a second IC assembly disposed at a second PCB, arranged in parallel with the first PCB, and comprising: a second IC package electrically coupled to circuits of the second PCB and having an opening in a top layer thereof; and a second array of optical elements disposed at the second IC package and electrically coupled thereto through the top layer opening; and wherein the second array being optically aligned with the optical fiber tube of the first IC package to accommodate optical communication between the arrays through the optical fibers of the tube. Various other embodiments of the apparatus are also disclosed.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to optical communications, in general, and more particularly to apparatus for providing optical communication between integrated circuits of different printed circuit (PC) boards and an integrated circuit assembly for use therein. 
   Modem PC boards are comprised of a plurality of application specific integrated circuits (ASICs). Each of the ASICs of a PC board may include a digital data processor which performs its processing operations in parallel with the other ASICs of the board. In a data processing system, the ASICs of one PC board communicate with the ASICs of another PC board. Generally, the data communication between PC boards is through backplane or mother board electrical connections which present a bottleneck to the board-to-board communication. This communication bottleneck between boards is especially compounded by the parallel processing operations of the plurality of ASICs of each board. 
   Greater demands for increased bandwidth are being made on data communication between the ASICs of the different PC boards. Communication rates of tens of gigabits per second are exemplary of such demands. These demands can not be met by the traditional metal electrical connections found on mother boards and back plane connections, for example. One solution to meet these demands is to create optical communication channels for board-to-board communication using light coupling between an array of light emitters of one PC board and an array of light detectors of another PC board. 
   A drawback to this solution is that a light coupling interconnection between ASICs of different PC boards is no simple task. Thus, a simple and automatic interconnection of the light coupling between ASICs of different PC boards is desirable to render optical communication between ASICs a commercially viable reality. The present invention intends to satisfy this desire through suitable apparatus and integrated circuit assembly. 
   SUMMARY 
   In accordance with one aspect of the present invention, an integrated circuit assembly for providing optical communication between adjacent PC boards comprises: an integrated circuit package having an opening in a top layer and an opening in a bottom layer thereof; a first array of optical elements disposed at the integrated circuit package and electrically coupled to the integrated circuit package through the top layer opening; a second array of optical elements disposed in the integrated circuit package and aligned with the bottom layer opening; and a tube of optical fibers disposed in the bottom layer opening with one end under the second array and another end protruding out from the bottom layer of the package. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a side view illustration of optical fiber interconnection apparatus suitable for embodying one aspect of the present invention. 
       FIG. 2  is a bottom view illustration of an integrated circuit package suitable for use in the embodiment of  FIG. 1 . 
       FIG. 3  is an end view illustration of an optical fiber cable suitable for use in the embodiment of  FIG. 1 . 
       FIG. 4  is a cross-sectional, cut-away illustration of an exemplary IC package assembly suitable for embodying another aspect of the present invention. 
       FIG. 4A  is cross-sectional, cut-away illustration of the optical interface of the embodiment of  FIG. 4  in greater detail. 
       FIG. 5  is a side view illustration of the optical fiber interconnection apparatus of  FIG. 1  in greater detail. 
       FIG. 6  is a side view illustration of optical fiber interconnection apparatus suitable for embodying yet another aspect of the present invention. 
       FIG. 7  is a cross-sectional, cut-away illustration of an exemplary IC package assembly suitable for embodying yet another aspect of the present invention. 
       FIG. 7A  is cross-sectional, cut-away illustration of the optical interface of the embodiment of  FIG. 7  in greater detail. 
       FIG. 8  is a side view illustration of the optical fiber interconnection apparatus of  FIG. 6  with heat sinks on the IC packages. 
       FIG. 9  is a cross-sectional, cut-away illustration of an exemplary IC package assembly suitable for embodying yet another aspect of the present invention. 
       FIG. 10  is a side view illustration of optical fiber interconnection apparatus using the IC package assemblies of  FIG. 9  suitable for embodying yet another aspect of the present invention. 
       FIG. 11  is a cross-sectional, cut-away illustration of an exemplary IC package assembly suitable for embodying yet another aspect of the present invention. 
       FIG. 12  is a side view illustration of optical fiber interconnection apparatus suitable for embodying a further aspect of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  is a side view illustration of optical fiber cable interconnection apparatus suitable for embodying one aspect of the present invention. In the present embodiment, two PC boards  10  and  12  of a data processing system, for example, are disposed in a parallel side-by-side configuration. The PC boards  10  and  12  of the present embodiment may be fixed in place in the parallel configuration through board connectors  14  and  16 , respectively, of a backplane or a motherboard  18 . Board to board parallel spacing may be further maintained using card guides mounted in the chassis, for example, that capture and align the edges of one board  10  parallel to the other board  12 . Apparatus is provided to support optical communication between an integrated circuit (IC) package  20 , such as an ASIC, for example, of one board  10  and an IC package  22 , such as an ASIC, for example, of the other board  12  through a rigid tube of optical fibers as will become more evident from the following description. This apparatus permits an automatic alignment of the optical fibers of the rigid tube between the two ASICs  20  and  22  once the two boards  10  and  12  are connected to the backplane or motherboard  18  via connectors  14  and  16 , respectively. 
   A cross-sectional illustration of a more detailed cut-away view of an exemplary IC package  20 ,  22  is shown in  FIG. 4 . Referring to  FIG. 4 , each exemplary package  20 ,  22  includes an IC chip or die  30  which may be connected to the circuits of the PC board through a ball grid array  32  which is shown by way of example in the bottom package view of  FIG. 2 . Referring back to  FIG. 4 , the balls of the connecting array  32  make electrical connection with corresponding connection pads  34  of the PC runs of the board  10 ,  12 . While a ball grid array is used in the present embodiment as the connecting array  32  between the package  20 ,  22  and the circuits of board  10 ,  12 , it is understood that a solder column array or a land grid array of pads or similar connecting arrangement may be used just as well. 
   In the present embodiment, an array of optical elements  36  is disposed at the top of the IC package  20 ,  22  and electrically connected to circuits of the ASIC die  30  through use of a flex cable connector  37 , for example, which is passed through an opening  39  in the top of the package  20 ,  22 . The flex cable  37  may be connected to the die  30  and array  36  using C4 bumps or other suitable die attachments, for example. The array  36  may be secured in place on the package  20 ,  22  with an adhesive  35 , which may be an epoxy resin or similar adhesive material, for example. A similar array of optical elements  38  is disposed on or embedded in a portion of a bottom surface of the die  30 . The optical elements of arrays  36  and  38  are connected to respective data input and output circuits of the ASIC die  30 . Another opening  40  is provided in a bottom layer of the package  20 ,  22  (see also  FIG. 2 ) and aligned with the array  38  to accommodate access to the array  38  through the bottom layer of the package. While in the present embodiment the arrays  36  and  38  are shown disposed at the center of the package  20 ,  22 , it is understood that they may be located anywhere around the die  30  or even attached to the package itself without deviating from the broad principles of the present invention. 
   Disposed in the opening  40  is a rigid tube  42  enclosing a multiplicity of optical fibers  43  such as shown by way of example in the end view illustration of  FIG. 3 . The optical fibers  43  of the tube  40  may be aligned with the optical elements of the array  38  which may be light emitters, light detectors or a combination thereof, for example. Preferably, the cross-sectional area of the tube of optical fibers  42  should extend beyond the area of the array  38  so that the elements of the array  38  will align within the cross-sectional area of the tube  42  notwithstanding a rough alignment therebetween. A cross-sectional view illustration of the alignment of the optical fibers  43  with the elements of the array  38  is shown in greater detail in  FIG. 4A . The tube  42 , which may be made of molded plastic, glass or an epoxy compound, for example, may protrude from the package  20 ,  22  down through a hole in the PC board  10 ,  12  and extend in length to just above a corresponding ASIC package on the adjacent PC board as shown in  FIG. 1 , for example. The tube  42  may be secured in place in the opening  40  of the package  20 ,  22  with an adhesive  44 , which may be an epoxy resin or similar adhesive material, for example. 
   Accordingly, when the adjacent PC boards  10  and  12  are connected to the motherboard  18  via connectors  14  and  16 , respectively, as shown in the cross-sectional side view of  FIG. 5 , the optical fibers  43  at the bottom end of the tube  42  will automatically come in close proximity to and roughly align with the elements of array  36  permitting optical communication between the optical array  38  of package  20  and the optical array  36  of package  22 . For example, the optical array  38  of the ASIC  20  will optically interface through free-space with the optical fibers  43  at the top end of aligned tube  42  as shown in  FIG. 4A , by way of example, and the optical fibers  43  at the bottom end of tube  42  will roughly self-align in free-space with the elements of the top optical array  36  of the ASIC  22 . The array  36  and/or array  38  may include beam steerable emitters to align their emitted beams with corresponding optical fibers  43  of the tube  42 . A suitable optical channel configuration process may be also used to match elements of the arrays  36  and  38  through the optical fibers  43  of the tube  42  to form the optical communication channels therebetween. 
     FIG. 4A  is a cross-sectional, cut-away illustration of the optical interface between the optical array  38  of the integrated circuit die  30  and the optical fibers  43  of the corresponding tube  42 . Referring to  4 A, the tube  42  is shown disposed in the opening  40  under and in close proximity to the optical array of elements  38 . The free-space distance between the ends of the optical fibers  43  and the elements of array  38  may be only a fraction of an inch, preferably a few thousandths of an inch, for example. In the present embodiment, the cross-sectional area of the tube  42  is larger than the area of the array  38  to accommodate for less than a precise alignment therebetween. In addition, there may be substantially more optical fibers  43  in the tube  42  than there are elements in array  38  to increase the probability that each of the elements of array  38  will align with at least one of the optical fibers of tube  42 . 
   Note that the ASIC  20  of board  10  may also communicate optically in the same manner through its optical array  36  with a corresponding ASIC on a PC board above board  10  (not shown) in a periscope arrangement. Likewise, the ASIC  22  of board  12  may also communicate optically in the same manner through its optical array  38  with a corresponding ASIC on a PC board below board  12  (not shown) in a similar periscope arrangement. 
   In one embodiment, the ASIC chip, optical top and bottom arrays and corresponding fiber optic tubing may be fabricated together in each IC package assembly prior to mounting on a PC board. When mounting the fabricated package assembly to a PC board, the bottom tube  42  may be disposed through the corresponding opening in the PC board and the balls  32  of the IC package connecting array may be aligned and connected electrically to the corresponding pads  34  of the PC runs. The positioning of the corresponding IC packages of the different boards may be precisely co-aligned for the foregoing described optical periscope arrangement in the design of the PC boards themselves. 
   In some applications, the IC packages may need a heat sink for dissipation of the heat that may be generated in the electrical processing operations of the ASIC chip itself. Some ASIC chips include thousands of circuits which generate a substantial amount of heat during the data processing operations thereof. A build up of heat in the package could damage the ASIC chip if not dissipated. Generally, a heat sink of a fin type which enlarges the heat dissipating surface area is disposed on the top surface of the package to dissipate the package heat to the air and keep the ASIC chip at a safe operating temperature. If a heat sink is disposed on the top surfaces of the IC packages, the periscope embodiment described in connection with  FIGS. 1-5  herein above will not permit the boards  10  and  12  with mounted heat sinked IC packages  20  and  22  to slidably connect to the motherboard  18  because the heat sinks will interfere with the tubing  42 . 
   For these heat sink applications, an alternate embodiment of the present invention such as shown by way of example in  FIGS. 6 and 7  may be used. Referring to  FIGS. 6 and 7 , in place of tube  42 , a shortened tube  42   a  is disposed in the opening  40  of the IC package  20 ,  22 . The tube  42   a  is shorter in length than tube  42  and in the present embodiment, has just enough length to pass through the opening in the PC board  10 ,  12  and protrude only a short distance, like a fraction of an inch, for example, beyond the surface of the board. The optical array  38  may be disposed at the bottom end of tube  42   a  and electrically connected to circuits of the die  30  through a flex cable connector  52 , for example. The flex wiring of connector  52  may pass from the optical array  38  through the a hollow passageway of tube  42   a  to the die  30  to render an electrical connection therebetween. 
   In addition, an optical fiber tube  48  is disposed at a bottom end through the top opening  39  of package  20 ,  22  and aligned over the optical array  36  which is disposed at the top surface of or embedded in the die  30  and electrically connected to circuits thereof. The optical fiber tube  48  extends in length from the package opening  39  up to the bottom of tube  42   a  of the corresponding IC package of the adjacent PC board as shown in  FIG. 6 . Both tubes  42   a  and  48  may be fixed in place at their respective openings of the package  20 ,  22  with an adhesive material  50 , for example, in a similar manner as described for the embodiment of  FIG. 1 . Accordingly, when the two boards  10  and  12 , for example, are connected to their corresponding connectors  14  and  16 , the external ends of the tubes  42   a  and  48  will be in close proximity and aligned as shown in the illustration of  FIG. 6 . 
   Note that since tube  48  periscopes up from the top surface of its IC package  22 , for example, to align with the tube  42   a  of its corresponding IC package  20 , for example, on the adjacent PC board, a heat sink  54  may be disposed on the surface of each IC package  20  and  22  surrounding the tube  48 , as shown in the illustration of  FIG. 8 . The heat sinks  54  will dissipate heat from the packages  20  and  22  to the air. In the embodiment depicted in  FIG. 8 , the heat sinks  54  will not interfere with the slidable connection of adjacent PC boards  10  and  12  with mounted package assemblies  20  and  22  in accordance with the present invention. 
   Accordingly, when the adjacent PC boards  10  and  12  are connected to the motherboard  18  via connectors  14  and  16 , respectively, as shown in the cross-sectional side view of  FIG. 8 , the optical fibers at the top end of the tube  48  will automatically come in close proximity to and roughly align with the elements of array  38  permitting optical communication between the optical array  38  of package  20  and the optical array  36  of package  22 . For example, the optical array  36  of the ASIC  22  will optically interface through free-space with optical fibers  49  at the bottom end of aligned tube  48  as shown in  FIG. 7A , by way of example, and the optical fibers  49  at the top end of tube  48  will roughly self-align in free-space with the elements of the optical array  38  of the ASIC  20 . The array  36  and/or array  38  may include beam steerable emitters to align their emitted beams with corresponding optical fibers  49  of the tube  48 . A suitable optical channel configuration process may be also used to match elements of the arrays  36  and  38  through the optical fibers  49  of the tube  48  to form the optical communication channels therebetween. 
   Note that the ASIC  20  of board  10  may also communicate optically in the same manner through its optical array  36  with a corresponding ASIC on a PC board above board  10  (not shown) in a periscope arrangement. Likewise, the ASIC  22  of board  12  may also communicate optically in the same manner through its optical array  38  with a corresponding ASIC on a PC board below board  12  (not shown) in a similar periscope arrangement. 
   In this alternate embodiment, the ASIC chip  30 , optical top and bottom arrays  36  and  38  and corresponding tubing  42   a  and  48  may be fabricated together in each IC package assembly prior to mounting on a PC board. When mounting the fabricated package assembly to a PC board, the bottom tube  42   a  may be disposed through the corresponding opening in the PC board and the balls  32  of the IC package connecting array may be aligned and connected electrically to the corresponding pads  34  of the PC runs. The positioning of the corresponding IC packages of the different boards may be precisely co-aligned for the foregoing described optical periscope arrangement in the design of the PC boards themselves. 
     FIG. 7A  is a cross-sectional, cut-away illustration of the optical interface between the optical array  36  of the integrated circuit die  30  and the optical fibers  49  of the corresponding tube  48 . Referring to  7 A, the tube  48  is shown disposed in the opening  39  over and in close proximity to the optical array of elements  36 . The free-space distance between the ends of the optical fibers  49  and the elements of array  36  may be only a fraction of an inch, preferably a few thousandths of an inch, for example. In the present embodiment, the cross-sectional area of the tube  48  is larger than the area of the array  36  to accommodate for less than a precise alignment therebetween. In addition, there may be substantially more optical fibers  49  in the tube  48  than there are elements in array  36  to increase the probability that each of the elements of array  36  will align with at least one of the optical fibers of tube  48 . 
   Also, a large number of optical fibers in the tube  48  will increase the probability that light from an optical fiber in tube  48  will pass to an element of array  36  when the adjacent boards are connected and the corresponding tube end is roughly aligned with the array  36 . Moreover, a configuration process may be used to match light emitter/detector pairs between the arrays  36  and  38  of corresponding ASICs to form the optical channels therebetween. It is understood that not all of the elements of the arrays will be matched to form an optical channel. Thus, there may be less optical channels formed than there are elements in the arrays. Accordingly, designing the arrays with a greater number of elements than optical channels desired will increase the probability of reaching the number of channels desired in a matching process once the adjacent boards are connected and the corresponding tubes of optical fibers are roughly aligned. 
   In another alternate embodiment of the present invention as shown in the cross-sectional illustration of  FIG. 9 , the hollow rigid tube  42   a  of the embodiment depicted in  FIGS. 6-8  may be replaced with a longer, hollow, rigid tube  42   b  and the optical element array  38  may be displaced from the ASIC chip  30  and disposed at the end of the tube  42   b  and secured in place with an adhesive material, for example. A longer flex cable connector  52   a  may connect the elements of the array  38  to corresponding circuits of the IC chip  30 . The flex wire cable of  52   a  may be passed from the chip  30  through the hollow portion of the tube  42   b  to the array  38 . The optical array  36  may be disposed at the package  20 ,  22  and electrically connected to circuits of the die  30  in much the same way as described supra for the embodiment of  FIGS. 1-5 . 
   In this embodiment, the tube  42   b  may extend through the hole in the PC board  10 ,  12  and extend down to render the optical array  38  aligned with and in close proximity to the optical array  36  as shown, by way of example, in the cross-sectional side view illustration of  FIG. 10 . Thus, when the boards  10  and  12  are slid in place and connected to their motherboard  18 , the arrays  36  and  38  will be roughly aligned in close proximity of each other for optical communication over the free-space therebetween which may be preferably only a fraction of an inch by design. Accordingly, light from emitters of one array will be conducted over free-space to light detectors of the other array. 
   In yet another alternate embodiment shown by way of example in  FIG. 11 , the fiber optic tube  48  of the embodiment of  FIGS. 7 and 8  may be replaced with a hollow tube  48   a , which may be similar to the hollow tube  42   b  described in connection with the embodiment of  FIG. 9 , for example, and the array  36  may be displaced from the IC package and disposed at the external end of the hollow tube  48   a . Also, the array  36  may be electrically connected to the circuits of the die  30  through a flex cable connector  37   a  similar to  52   a  described in connection with the embodiment of  FIG. 9 . Note that the flex cable connector  37   a  is substantially longer than cable  37  of  FIG. 9 . The resulting embodiment of  FIG. 11  will have the array  38  disposed at or near the bottom of board  10 ,  12  for example, and the array  36  at the top of the hollow tube  48   a  so that when the boards  10  and  12  are connected to their respective connectors  14  and  16 , the arrays  36  and  38  will be roughly aligned and in close proximity to each other. Thus, instead of the hollow tube  42   b  extending down through the board  10  to the package  22  of board  12  such as shown in  FIG. 10 , the hollow tube  48   a  will extend up from package  22  of board  12  to the board  10  such as shown in  FIG. 11 . 
   It is understood that due to a rough alignment between arrays  36  and  38  in the foregoing embodiments, light from all of the emitters of one array may not be detected by corresponding light detectors of the other array. Thus, in order to provide for a desired number of optical channels between the IC packages of different PC boards with these embodiments, it is further preferred that the number of elements of one of the arrays  36  or  38  be substantially greater than the number of elements of the other array in order to achieve the desired number of optical channels. With such a design, there will be a greater probability to match light emitter/detector pairs of the two arrays  36  and  38  to form the desired number of optical channels through a suitable optical channel configuration process. Alternatively, the emitters of arrays  36  and  38  may be beam steerable emitters controllable to render the beams thereof to be steered in alignment with a corresponding detector to form the optical communication channels. 
   While the various embodiments described herein above provided for optical communication between an integrated circuit  20  of one PC board  10  and an integrated circuit  22  of an adjacent PC board  12  using periscope arrangement of tubes affixed to the integrated circuit packages  20  and  22 , it is understood the principles of the present invention may be extended to provide optical communication between a plurality of such integrated circuit package assemblies of adjacent PC boards such as shown by way of example in the illustration of  FIG. 12 . 
   Referring to  FIG. 12 , at least one other integrated circuit package  60  may be disposed on PC board  10  and at least one corresponding package  62  may be disposed on the adjacent PC board  12 . The packages  60  and  62  may be fabricated, by way of example, with a periscope arrangement of tubes  64  and  66  in accordance with the embodiment of  FIGS. 6-8  as described herein above to provide optical communication between the ICs  60  and  62 . The PC boards  10  and  12  may be designed in such a manner that the plurality of communicating pairs of ICs are precisely located on the boards so that when the boards are connected in their respective connectors, the ends of the corresponding periscope tubes  42   a  and  48  will be roughly aligned as shown in  FIG. 12 . 
   In summary, the periscope IC package enables optical communication between at least one integrated circuit pair of adjacent boards. In the foregoing described embodiments, the periscope arrangement was integrated into and became an integral part of an IC package which has other non-optical functions. Thus, the IC package became operative to communicate by both optical and electrical channel connections. The various embodiments of the present invention offered a simple and automatic optical alignment from which optical channels may be configured through a suitable configuration process. The resulting optical communication channels yield an increase in the communication bandwidth between the integrated circuit pairs of the adjacent boards over that afforded by electrical connection paths through a mother board or backplane, for example. 
   In addition, while the foregoing described embodiments have referred to the tubes of the various embodiments as being round in cross-sectional shape, it is understood that the tubes may take upon other cross-sectional shapes without deviating from the principles of the present invention. Also, in the various embodiments, a hollow tube has been used as a structure to support the array of optical elements away from the integrated circuit  30 . However, it is further understood that this need not be the case. For example, an angle bracket or other physical support structure may be used just as well to support the array of optical elements away from the integrated circuit  30 . Moreover, while an enclosed support structure, be it a tube or otherwise, is preferable, this need not be the case. 
   While the present invention has been described herein above in connection with a variety of embodiments, it is understood the such embodiments were presented merely by way of example and not intended to limit the invention in any way. Thus, the present invention should not be limited by any of the embodiments present above, but rather construed in breadth and broad scope in accordance with the recitation of the claims appended hereto.