Patent Abstract:
Electro-optical packages that embed the electronics of the packages directly to the optical cabling, provide short electrical connection paths for high performance, and that provide a robust interconnects. A first electro-optical package includes an integrated circuit and a connector sleeve configured to receive a plug-in optical assembly from the underside of the PC board. The plug-in optical assembly includes a backing piece and an opto-electric device mounted onto the backing piece. An electrical connection is provided between the opto-electric device and a contact location on the backing piece and a contact is provided between the contact location on the backing piece and the integrated circuit. With a second electro-optical package, an integrated circuit having an active surface facing in a first direction and an opto-electric device having contact points facing a second direction are provided. The integrated circuit and the opto-electric are positioned with respect to one another such that a direct electrical connection can be formed between the active surface of the integrated circuit and the contact points of the opto-electrical device.

Full Description:
FIELD OF THE INVENTION 
     The present invention relates generally to electro-optical couplers, and more particularly, to various electro-optical packages that facilitate the coupling of optical cables to printed circuit boards. 
     BACKGROUND OF THE INVENTION 
     With advances in optical technologies, such as Wave Division Multiplexing (WDM), more and more computer and communication networks are being built using fiber optic cables. With WDM for example, multiple optical signals, each at different wavelengths, are used to simultaneously transmit multiple communication channels across a single optical fiber. To further increase bandwidth, multiple fibers may also be employed. While fiber optics have significantly increased the broadband capabilities of communication networks, much of the signal processing at nodes of the network is still performed in the electrical domain using integrated circuits. Thus electro-optical couplers, which convert optical signals into electrical signals and vice versa, have been used at the interface between the optical cables and the nodes. 
     A typical electro-optical coupler includes a connector for receiving an optical fiber and a housing which houses a photonic device. The photonic device is usually mounted onto a substrate. A ferrule included in the housing is used to align the optical fiber with the photonic device. Electrical traces and contacts provided on the substrate are used to electrically connect the coupler to the outside world, typically a printed circuit board. One of the major hurdles in manufacturing these electro-optical couplers is the proper alignment the fiber to the optically sensitive components on the opto-electric (i.e., photonic) device. Also during solder reflow to attach the coupler to the printed circuit board, it is possible for the photonic device to become mis-aligned with the fiber due to mismatches of thermal expansion of the materials used to hold the fiber and the photonic device in place. Contamination at the termination of the fiber the coupler may also occur during mounting onto a printed circuit board. See for example, “Integrated Fiber Optic Transmitters and Receivers for SONET/ATM Applications,”, T. Muoi, Electronics Components and Technology Conference 1995 Proceedings, p. 1092. 
     Another type of connector for high density applications involves the use of a substrate that is etched to provide grooves to accommodate multiple fibers. See for example, Silicon Waferboard Based Single Mode Optical Fiber Interconnects,” P. Haugsjaa, G. Duchene, J. Mehr, A. Negri And M. Tabasky, IEEE Transactions On Components, Packaging and Manufacturing Technology—Part B, Vol. 19, No. 1, Feburary 1996. With this type of connector, multiple devices, typically either transmitters or receivers, are mounted onto the substrate. The grooves are used to align the individual fibers with either the photo-transmitting or receiving regions on the devices. Separate bond pads coupled to each of the devices are also provided on the substrate to couple the devices to external components, such as another chip or a printed circuit board. While this type of connector is useful for high density applications, they are expensive to produce and lack the reliability required in order to provide a reliable “last-mile” optical interconnect to the end user. 
     In general, current connection methods are typically designed around plug-in connections along the optical pathway. This means that low reliability optical components on the board side of the connector must be able to survive electronics soldering environments without contamination to sensitive optical surfaces. Additionally, the requirement on optical alignment are orders of magnitude more restrictive than those for plug-in electrical connections. 
     Electro-optical packages that embed the electronics of the packages directly to the optical cabling, provide short electrical connection paths for high performance, and that provide a robust interconnect are therefore needed. 
     SUMMARY OF THE INVENTION 
     To achieve the foregoing, and in accordance with the purpose of the present invention, electro-optical packages that facilitate the coupling of optical cables to printed circuit boards are disclosed. A first electro-optical package includes an integrated circuit and a connector sleeve configured to receive a plug-in optical assembly. The plug-in optical assembly includes a backing piece and an opto-electric device mounted onto the backing piece. An electrical connection is provided between the opto-electric device and a contact location on the backing piece and a contact is provided between the contact location on the backing piece and the integrated circuit. The connector sleeve of first electro-optical package enables the optical assembly to be “plugged” into the package. The plug-in fiber optic assembly provides a number of advantages, including the easy removal for inspection or replacement of the assembly, and protection from contaminants during board population and assembly. With a second electro-optical package, an integrated circuit having an active surface facing in a first direction and an opto-electric device having contact points facing a second direction are provided. The integrated circuit and the opto-electric device are positioned with respect to one another such that a direct electrical connection can be formed between the active surface of the integrated circuit and the contact points of the opto-electrical device. This second embodiment thus provides an extremely short electrical signal paths between the integrated circuit and the opto-electric device. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention, together with further advantages thereof, may best be understood by reference to the following description taken in conjunction with the accompanying drawings in which: 
     FIG. 1 is a cross section diagram of an electro-optical package that facilitate the coupling of optical cables to a printed circuit board according to one embodiment of the present invention. 
     FIGS. 2A through 2E are various views of the package of FIG. 1 during assembly according to the present invention. 
     FIG. 3 is a cross section of another electro-mechanical package according to another embodiment of the present invention. 
     FIG. 4 is a cross section of another electro-mechanical package which includes a receptacle to house an opto-electronic device that connects directly to a PC board according to the present invention. 
     FIG. 5 is a cross section of another electro-mechanical package which uses a socket to connect an opto-electronic, fiber optic cable to a PC board according to another embodiment of the invention. 
     FIG. 6 is a cross section of another electro-mechanical package in which a multilevel interposer board is used to facilitate flip chip attach between IC and photonic devices and to facilitate alignment of the fiber optic and lenses to the photonics. 
    
    
     In the Figures, like reference numbers refer to like components and elements. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIG. 1, a cross section diagram of an electro-optical package that facilitates the coupling of optical cables to a printed circuit board  10  according to one embodiment of the present invention is shown. The electro-optical package  12  includes a bottom connector sleeve  14  and a top shield  16 . 
     In the embodiment shown, the shield  16  is configured as a beat sink made of a thermally conductive material such as metal with heat dissipating fins  18 . In alternative embodiments, the shield  16  can be made of other suitably conductively coated or filled epoxy, plastic or ceramic materials. Fastening elements  20 , such as solder, screws or epoxy, are used to align and secure the bottom sleeve  14  and the top shield  16  to the printed circuit board  10 . An integrated circuit (IC) chip  22  is precision mounted onto the undersurface of the top shield  16 . The chip  22  is connected to the printed circuit board using contacts  24 . The contacts  24  can be any one of a number of different types of contacts, such as solder balls or micro-springs. For a more detailed explanation of micro-springs, see IEEE/MAPS, International Symposium on Advanced Packaging Materials, March 1999 and Microspring Contact On Silicon Technology (MOST™) from FormFactor, Inc., Livermore Calif. (FormFactor&#39;s Wafer-Level Packaging and Whole-Wafer Test Technologies paper), incorporated by reference herein for all purposes. 
     The sleeve  14  is designed to guide the probe pads on an optical sub-assembly  25  into alignment with the electrical probe tips  42  on the IC chip  22 . The optical sub-assembly  25  includes an opto-electric device  26  mounted onto a backing piece  28 , and a ferrule  30  configured to align a fiber optic ribbon cable  32  with the optical components on the opto-electric device  26 . Wire bonds  34  and traces  36  electrically couple opto-electric device  26  and the top surface of the backing piece  22 . In one embodiment of the invention, the sleeve  14  includes a latch  57  that is mounted to rotate about the bottom of the sleeve  14 . The latch  57  latches the optical sub-assembly  25  in place. 
     An alignment pin(s)  38  extending from the shield  16  through a recess region or hole  40  in the printed circuit board  10  is inserted into an alignment receptacle of the backing piece  28 . The alignment pin  38  maintains the backing piece  28  in proper alignment so that electrical contact(s)  42  can be aligned and maintained between the chip  22  and the backing piece  28 . According to various embodiments of the invention, the electrical connections  42  can include mechanical contact between solder balls (or metallized pads) and electrical probes (such as microsprings, crown, pogo pin or cobra probes, etc). The optical sub-assembly  25  may include a fiber optic ribbon cable  32  with one or more fiber(s), opto-electric device(s)  26 , and contact(s) (or probes)  42 . According to yet other embodiments, the chip  22  can be any type of communications chip, such as a receiver, a transmitter or a transceiver. Similarly, the opto-electric device  26  can either receive optical signals and convert them to electric signals (i.e., a photodetector), receive electrical signals from chip  22  and convert them into optical signals (i.e., a laser diode), or both. Also the chip  22  and the opto-electric device  26  can be fabricated on silicon, galium arsenide, or on any other type of semiconductor material. Finally, the bottom connector sleeve  14  can be made of a number of materials, such as metal filled or conductively coated plastic, epoxy, ceramic, or a thermally conductive material such as metal. 
     Referring to FIGS. 2A through 2E, various views of the package  12  of FIG. 1 during assembly and mounting onto the printed circuit board  10  is shown. FIG. 2A shows the printed circuit board  10  with contacts  50  formed thereon and the hole region  40 . The contacts  50  are provided to mate with the contacts  24  of the chip  22  when it is mounted on the printed circuit board  10 . The hole region  40  is provided to accommodate the package  12  when it is mounted on the printed circuit board  10 . In the initial step, the bottom connector sleeve  14  is attached to the printed circuit board  10  as illustrated in FIG.  2 B. This bottom connector sleeve  14  is reflow soldered, then epoxy glued in place, to avoid movement during subsequent reflow solder operations. Next, a disposable alignment block  56 , matching the outer dimensions of the optical sub-assembly  25 , is plugged into the bottom connector sleeve  14 . The purpose of this alignment block  56  is to align the top shield  14  and chip  22  with respect to the alignment block  56 . Specifically, the disposable alignment block  56  has a receptacle  51  that mates with the guide pin(s)  38  on the top shield  16 . The guide pin(s)  38  facilitate the mechanical alignment of the electrical contact  42 , between the chip  22  and the backing piece  28 , when the optical sub-assembly  25  is later inserted into the sleeve  14 . 
     After alignment, the shield  16  and chip  22  are permanently attached in place on the PC board  10 . The alignment block  56  is removed and the optical sub-assembly  25  is now ready for insertion into the sleeve  14 . The optical sub-assembly  25  including the fiber optic ribbon cable  32 , the backing piece  28 , opto-electric device(s)  26 , and the ferrule  30  are inserted into the bottom connector sleeve  14  as illustrated in FIG.  2 C. As noted above, the contacts of the chip  22  are aligned with the contacts  50  on the printed circuit board  10 . Also the alignment pin(s)  38  of the top shield  16  extends through the hole region  40  and is designed to mate with the backing piece  28 . This provides for precision alignment of the electrical contact(s)  42  between the chip  22  and the backing piece  28 . Finally, in FIGS. 2D and 2E, a top perspective view and a bottom perspective view of the printed circuit board  10  with the electro-optical package  12  mounted thereon are respectively shown. FIG. 2D illustrates the shield  16  and fins  18  mounted onto the printed circuit board  10 . FIG. 2E illustrates multiple optical fibers of the fiber optic ribbon cable  32  provided to the electro-optical package  12 . 
     The package  12  provides a number of advantages. The shield  16  provides both electrical shielding and heat dissipation for the package  12 . The alignment pin(s)  38  ensures the proper alignment of the components in the optical sub-assembly  25  including the contact(s)  42  between the backing piece  28  and chip  22 . Similarly, the fasteners  20  provide proper alignment of the connector sleeve  14  to the printed circuit board  10 . The sleeve  14  also provides for electrical shielding, heat dissipation, and provides a latch  57  to guide and latch the backing piece  36  onto the alignment pins  38 , thereby securing the desired electrical contacts  42 . 
     FIG. 3 is a cross section of another opto-electronic package  60  according to another embodiment of the present invention. With this embodiment, the bottom connector sleeve  14  and the top shield  16  are replaced by a integral package structure  62  that includes a top component  64  and a bottom component  66 . The top component  64  includes an IC chip  22  precision mounted onto its undersurface. The chip  22  is connected to the printed circuit board through contacts  24 . The bottom component  66  is configured as a connector receptacle designed to pass through the hole region  40  and to extend through the bottom surface of the printed circuit board  10 . The bottom component  66  is configured to accommodate the plug-in optical sub-assembly  25  which includes a photonic device  26 , a backing piece  28 , ferrule  30 , fiber ribbon cable  32 , etc. Contact(s)  42  are provided between the backing piece  28  and the chip  22 . Although the contact(s)  24  and contact(s)  42  are illustrated as solder balls in this figure, they too may be any type of electrical contact such as micro-springs, bond pads or any other type of micro miniature probe connection. Like components with the same reference numerals as described above perform the same or similar functions with regard to package  60  of FIG.  3  and are therefore not described in detail herein. 
     Prior to mounting the package  60  onto the printed circuit board  10 , the chip  22  is precision mounted onto the undersurface of the top component  64 . The bottom component  66  is then inserted through the hole region  40  and mounted onto the printed circuit board  10  using fastening elements  20 . The optical sub-assembly  25  including the backing piece  28 , ferrule  30 , and the fiber ribbon cable  32  is then inserted into the bottom component  66  and secured with the latch  57 . The bottom component  66  guides the optical sub-assembly  25  into the mounting package  60  such that pin(s)  38  precisely align the backing piece  28  and the contact(s)  42  of the chip  22 . The latch  57  of the bottom component  66  latches or locks the optical sub-assembly  25  in place after alignment. The top component  64  also provides heat dissipation and electrical shielding. It is also should be noted that in various embodiments of the invention as provided in FIGS. 1 and 3, the alignment pin(s)  38  do not necessarily need to be pin shaped. Rather the term “pin” as used in the present application is intended to cover channels, ridges rounded cones or any other type of mating elements. 
     The packages  12  and  60  thus provide physical separation between the photonic and electrical sub-assemblies. The optical sub-assembly  25  is in essence a plug-in unit. The two chips  22  and  26  are mounted at 90 degree angles to one another and the backing piece  28  is used for space transformation of the electrical contacts between the two chips. 
     FIG. 4 shows the cross section of another electro-optical package  100  which is composed of two major components: (i) a cable receptacle  102  which is permanently soldered to the PC Board  10 ; and (ii) an optical cable housing  112 . All the active opto-electronic functions are embedded within the optical cable housing  112 , including an upper assembly  118  which houses the fiber optics  120  and lens array  122  and a lower subassembly  116  which includes opto-electronic chip  26 . 
     Prior to insertion into the cable receptacle  102 , the optical cable housing  112  is assembled. The opto-electronic chip  26  is first precision bonded to the lower cable assembly  116 . The chip  22  is precision mounted onto the underside of the optical cable housing  118 . Thereafter, the lower assembly  116  is permanently bonded to the upper cable assembly  118  so as to achieve alignment of the electrical contacts  42  between the photonic chip  26  and the IC chip  22 . During the bonding procedure, the photonics chip  26  is also aligned with the fiber optic lens array  122 . The connections  42  between the IC chip  22  and the photonic chip  26  can be solder balls, micro-springs or any other type of electrical connection as described above. 
     A latch  105  provided at the top of receptacle  102  rotates about a compliant hinge  104 . To insert the fiber optic assembly  112 , the top of the receptacle  102  is lifted and the fiber optic assembly  112  is inserted through the openings on the top and left side of the receptacle  102 . The cable receptacle  102  is designed with precision guidance features to guide the fiber optic assembly  112  into the receptacle  102  to ensure that the electric contact  24  between the IC Chip  22  and metallized pads on the printed circuit board  10  are aligned According to various embodiments of the invention, the electrical contacts  24  can be micro-spring, solder balls or any other type of contact. After insertion, the compliance force of the latch  105  and hinge  104  provides a sufficient compressive force on the fiber optic assembly  112  to provide “scrub” contact between the contacts  24  and the printed circuit board  10 . 
     In various embodiments of the invention, the upper  118  and lower  116  cable assemblies is made of a thermal and electrically conductive material such as metal, or other types of conductively coated or metal filled plastics, ceramics, or epoxies materials. The cable receptacle  102  may be made on insulative plastic, but if added thermal conductivity or electrical shielding is required, it may be made of the aforementioned thermal/electrically conductive materials. Fastening elements  20 , such as solder balls, screws, bolts or epoxies, may be used to mount the receptacle  102  to the printed circuit board  10  which includes a recess region or hole  40  to allow for clearance of the backing piece  116 . 
     The fiber optic assembly  112  includes a photonic sub-assembly  116 , which includes opto-electric device  26 , located adjacent the lens array  122  where the fiber optic cable  120  terminates. The photonic assembly  116  is rigidly attached to the cable assembly  112 . With the embodiment shown, the fiber optic cable  120  has a radius bend and terminates at lens array  122 . In alternative embodiments, a lower profile, mirror surfaced, SPF arrays (Slant Polished Fibers) may also be used in place of the lens array  122 . See for example, “Multigigabit Multichannel Optical Interconnection Modules for Asynchronous Transfer Mode Switching Systems”, Y. Ari, H. Takahara, K. Koyabu, S. Fujita, Y. Akahori, and J Nishikido, IEEE Transactions on Components, Packaging, and Manufacturing Technology-Part B, Vol. 18, No. 3, Aug.  95).    
     Referring to FIG. 5, another electro-optical package  130  is shown. As with FIG. 4, all optical and electronic functions are housed within the package  130  where the fiber optic cable  120  terminates. The package  130  houses the entire fiber optic assembly  112  including the upper assembly  118  and the lower assembly  116 . The package  130  is thus considered a socket, as opposed to a receptacle, because the entire package  130  is attached to the printed circuit board  10  using solder balls  136 . Electrical connections  134  between the chip  22  and the printed circuit board  10  are made through a multilevel interposer board  132 . The electrical connections  134  can include crowns, pogo pins, or the like. The interposer board  132  is thus used to space transform the electrical connections and to address the planer offset between the chip  22  and the backing piece  26 . In one embodiment, ground contacts  135  can be provided between the photonic device  26  through the lower assembly  116  and interposer board  132  to the printed circuit board  10 . In an alternative embodiment, the ground contacts can be made to the printed circuit board  10  through electrical connections  42 , chip  22  and electrical connections  134 . 
     Referring to FIG. 6, yet another opto-electric package is shown. This package  150  is similar to package  130  of FIG. 5 with several differences. The package  150  has a top surface  151  that is not hinged. This means that all the optical and electrical components are housed within the package  150  as an integrated unit. A board mounting plug  152  is therefore provided to protect sensitive optical components during required board mount operations. 
     According to one embodiment, the package  150  is manufactured by precision bonding and aligning the opto-electric device  26  onto sub-assembly  116 . The IC chip  22  is then flip chip mounted onto the interposer board  132  forming the electrical contacts at locations  24  and  42 . Next, the optical assembly  112 , with fiber radius bend fiber optic cable  120  and lens area  122  can be precision bonding to the interposer boards  116  using, for example, mechanical support and alignment features, built into the interposer board  116 . The entire assembly is then inserted into the receptacle  156 . Finally, the top  151  is sealed and the board mount plug  152  inserted. FIG. 6 shows what the completed package  150  after it is soldered with balls  136  to the printed circuit board  10 . After installation onto the board  10 , the board mount plug  152  can be removed and the fiber optic cabling  160  is inserted. 
     Although the foregoing invention has been described in some detail for purposes of clarity of understanding, it will be apparent that certain changes and modifications may be practiced within the scope of the appended claims. Therefore, the described embodiments should be taken as illustrative and not restrictive, and the invention should not be limited to the details given herein but should be defined by the following claims and their full scope of equivalents.

Technology Classification (CPC): 6