Patent Application
20110206379
The present invention generally relates to an apparatus and method for manufacturing the same in the field of semiconductor technology which provides a removable opto-electronic module and more particularly, relates to an apparatus and method in the field of integrated circuits and chip technology which provides a removable opto-electronic module.
In the field of semiconductor technology, one known typical device using opto-electronic modules includes a multi-channel high-density optical transmitter and receiver pair. The device reduces a fiber count by using coarse wavelength division multiplexing (CWDM). Vertical cavity surface emitting laser (VCSEL) arrays (O/E array) are used in the device and are flip-chip-attached to integrated circuits (ICs). After attachment of the O/E array to the IC, an optical coupling is added. The resulting device is compact. However, the higher electrical density results in difficulty packaging the device with an electrical connector to contact an electrical flex. The device thus uses a direct ball grid array (BGA) solder attach. However, the combination of the electrical flex with the BGA contacts results in a disadvantage of a lower electrical sign-to-noise ratio, as well as, undesirable higher crosstalk. Further, another disadvantage of the exemplary device is that by using a four-wavelength CWDM design to reduce the fiber count, the device requires an optical multiplexer (MUX) and demultiplexer (DEMUX). Another disadvantage of the device is loss associated with the wavelength MUX resulting in a substantial loss of optical power that must be overcome by higher laser powers or increased receiver sensitivity. A still further disadvantage is that the device lacks field replaceability and/or field replaceability of modules which are part of the device.
Therefore, there is a need for an interchangeable (field replaceable) opto-electronic package for optical coupling a multiple channel fiber optic cable(s) to a multiple channel Vertical Cavity Surface Emitting Laser (VCSEL) transmitter array. Further, it would be desirable to provide an interchangeable electronic package for coupling a multiple channel fiber optic cable(s) to a multiple channel photo detector receiver array. Additionally, there is a need for a high speed electrical coupling between an integrated electrical IC chip through the electronic package described above. There is a further need to provide an integrated electrical IC chip improving a signal-to-noise ratio, increasing bandwidth, lowering power consumption, and more specifically, providing improved signal channel isolation and decreasing channel crosstalk. There is also a need to reduce signal channel impedance mismatch, and equalize signal channel skew. Thus, there is a need for a low cost optoelectronic package with low optical loss and low power, improved electrical signal-to-noise ratio, higher bandwidth density package footprint, and having replaceable field flexibility.
In an aspect of the invention, an apparatus for receiving electrical signals and transmitting of optical signals includes a substrate including an electrical circuit. At least one electrical-to-optical module is mounted on the substrate. The module includes an array of photodetectors communicating with the electrical circuit. The module receives electrical signals from the electrical circuit and provides a plurality of corresponding light signals. An electrical transport is embedded in the substrate, the electrical transport electrically communicates with the array of photodetectors. An optical interface provides electrical communication between an optical fiber and the electrical circuit.
In related aspects, the photodetectors include photodiodes, and the photodiodes include electrical to optical alignment features. Further, the apparatus may include a plurality of electrical to optical modules, wherein at least one module provides electrical to optical communication, and at least one module provides optical to electrical communication. The optical interface may include a self-aligning diode-to-optical adaptor positioning device being part of the optical interface. The apparatus may further include a heat transfer device adjacent to the array of photodetectors for transferring heat from the array of photodetectors. The apparatus may further include a transimpedance amplifier (TIA) in the optical module, the TIA providing a signal-to-noise ratio and an electrical drive level for the electrical circuit. The substrate may include ceramic. The electrical transport may include controlled impedance vias. The apparatus may further include a removable printed circuit or wiring board electrically connected to the substrate, the removable board including an electrically and thermally capable socket connection including land grid array (LGA) or pin grid array (PGA).
In another aspect of the invention, a method for receiving electrical signals and transmitting optical signals, comprises: providing a substrate including an electrical circuit, and providing at least one electrical-to-optical module mounted on the substrate; communicating with the electrical circuit using an array of photodetectors mounted on the module; receiving electrical signals from the electrical circuit on the module and providing a plurality of corresponding light signals; communicating with the array of photodetectors using an electrical transport embedded in the substrate; and communicating between an optical fiber and the electrical circuit using an optical interface.
In another aspect of the invention, a method of controlling impedance, comprises: providing parameters for a substrate having at least one signal via placed parallel to at least one reference via; calculating an average impedance for the signal via and the reference via; and iteratively adjusting the pitch of the signal and reference vias, and the size of the signal and reference vias corresponding to a surrounding dielectric environment until the average impedance of the signal and reference vias are approximately equal to a specified average impedance.
In another aspect of the invention, an apparatus which controls impedance, comprises: a plurality of electrical components positioned on a top layer surface of a substrate; a circuit in the substrate; a thermal escape mechanism adjacent to, and connected to, the electrical components; and an electrical signal escape mechanism communicating with the substrate, the electrical signal escape mechanism having an electrically conductive signal line interconnecting the substrate for an electrical signal to move to and from the substrate.
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. The various features of the drawings are not to scale as the illustrations are for clarity in facilitating one skilled in the art in understanding the invention in conjunction with the detailed description. In the drawings:
a is a cross-sectional side elevational view of the opto-electronic module shown in
b is a detail view of a portion of the opto-electronic module shown in
a is a cross-sectional view along line A-A of the opto-electronic package shown in
b is a cross sectional view along line B-B of the opto-electronic package shown in
a is a plan view of an electronic package two net electrical channel layout for passively accomplishing equalized net redistribution at the opto-electronic module according to another embodiment of the invention;
b is a cross sectional view along line C-C of the package shown in
Referring to
High speed electrical transport layers 34 are illustratively shown in
In general, an optical interface in the package 10 is accomplished using an optical path provided by fibers, or an optical flex such as waveguides that collects light from the O/E and E/O modules 20, 22 by various techniques, including: butt coupling, one or more lens relays, light turning elements, or other coupling and light turning elements. Air flow 14 passes the carrier 402 as shown in
Referring to
An embodiment of an optical interface in accordance with the present invention includes an optical path as provided by fibers 50 coupled to an optical flex such as a waveguide 54 that collects light from the E/O module 22. The waveguide is an embodiment of an optical interface which may include a light transporting channel. The optical interface may include, for example, a mount fiber (MT) mounted fiber cable connector, a waveguide connector, or any other light transporting channel. A self-aligning diode-to-optical adaptor positioning device may comprise fiducial patterns, alignment pins, or solder reflow geometries for positioning the diode array with the optical adaptor. Further, in the embodiment shown in
Examples of VCSELs and PDs in opto-electronic packages are depicted in co-pending and commonly owned U.S. patent application Ser. Nos. 12/544,710 and 12/544,696, the disclosures of which are expressly incorporated by reference herein in their entirety.
In general, the O/E and E/O modules 20, 22 may contain additional electrical support chips. In the embodiment of the invention shown in
Turning mirrors can be fabricated by having a highly smooth, surface, for example, at a tolerance close to a 45 degree angle to the incoming light direction, and relying on an optical index step difference in the waveguide channel core to the other side of the 45 degree bevel, such as an air cavity, or relying on an optical reflective surface, such as can be accomplished with thin film metal depositions. In the embodiment of the invention shown in
The waveguide 54 may be fabricated from polymer material directly on the carrier 32, or transferred from a waveguide on a flex substrate onto the carrier. Various polymer waveguide thin film deposition techniques are available, such as doctor blading, spin coating, inkjet deposition, slot coating, etc., and other waveguide patterning techniques, such as UV crosslinking via photolithography or direct laser writing, molding, embossing, etc. The optical connector-to-carrier interface, BGA 28 to carrier 32, may be aligned to the waveguide core, to fiducials, or other visual patterns with mechanical dimensions, such as with mechanical alignment pins, with mating recessed cavities or raised geometries, such as solder reflow geometries for positioning the diode array with the optical adaptor.
In the final placement of the electro-optical package 10, including the carrier 32 with all attached chips, for example the chip 24, and the optical connector embodied as the waveguide 54, is attached to the PWB 48 by BGA 36 or other electrical contacts. The carrier 32 can be made of various materials such as ceramic substrate: high performance glass ceramic (HPGC) and White Alumina Ceramic, or organic substrate (flip-chip plastic ball grid array (FC-PBGA). An optical ferrule 70 is attached after the PWB 48 and the heat sink 40 (shown in
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The difference in time of flight between a differential signal pair nets is referred to herein as skew. In the present invention, the high speed transport created by a signal trace on top of the packages including CIV allows flexibility to reduce the skew. The CIV structures allow impedance control with trace stripline or microstrip structures routed on the upper layers of package. Minimizing impedance variation between different structures is beneficial to the signal integrity of the line.
Therefore, in order to control and maintain impedance matching along a signal net path, via impedance matching techniques (CIV) are applied. CIV uses via diameter size, via to via spacing, as well as multiple via patterning to control and match impedance with a signal line structure. For example, the carrier 32 shown in
In the above pattern, the high signal select (HSS) signal via is represented by the S. The numbered positions are on a 200 μm pitch from the HSS via. The lettered positions are on a 400 μum pitch from the HSS via.
The CIV method above follows the following rules: there must be ground (GND) vias in the 1 and 4, or 2 and 3 positions; no other vias are allowed on a 200 μm pitch from the HSS via; HSS differential pair vias must be a minimum of 600 μm pitch from each other; any type of vias, except differential pair vias above, are allowed on the lettered pitch under these conditions; and no more than 4 vias are allowed in the A,C,F and H positions, or no more than 2 vias are allowed in the B, D, E and G positions.
For minimum layout area constraint cases, the following rule relaxations may be considered, albeit at a less than optimum signal-to-noise ratio and/or increased power: three or four vias may be used in the B, D, G, and E positions; no other vias are allowed within 400 μm of the signal via; and at lease two ground vias should be at opposite positions (vertical, horizontal) to the signal via, the others can be power vias in case ground bias are not possible.
Using the above methodology,
In alternative embodiments, a plurality of via patterns may relate to a plurality of signal vias, reference vias, pitch dimensions, substrate dielectric materials, and via sizes.
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Thereby, the embodiments of the present invention discussed above provide a package for coupling multiple parallel channel fiber optic cable to a multiple parallel channel VCSEL transmitter. The packages further provide coupling the same or a second multiple parallel channel fiber cable to a multiple parallel channel PD receiver with a packaging solution that gives both high electrical signal integrity at a high bandwidth density, as well as, field replaceability. The invention provides an interchangeable (field replaceable) package for optical coupling a multiple channel fiber optic cable(s) to a multiple channel Vertical Cavity Surface Emitting Laser (VCSEL) transmitter array, or a multiple channel Photo Diode (PD) receiver array, or both. The invention further provides high speed electrical coupling between the on package integrated electrical IC chip through the package. The integrated electrical IC chip may encompass functions that improve, in general, signal-to-noise and increase bandwidth, lower power consumption, and specifically, provide improved signal channel isolation and decrease channel crosstalk, reduce signal channel impedance mismatch, and equalize signal channel skew. These functions may include circuits that are electrical drivers, equalization, voltage level shifters, and multiplexers. The electrical IC chip may also have additional functions other than the sole support of the VCSEL or PD signal integrity. The additional circuit functions may include, for example, processors, memory, and switching networks. These additional functions may advantageously benefit from having the electrical-to-optical and optical-to-electrical modules in close proximity, as it may increase bandwidth, bandwidth density, signal-to-noise, latency, cost, lower power consumption, etc.
While the present invention has been particularly shown and described with respect to preferred embodiments thereof, it will be understood by those skilled in the art that changes in forms and details may be made without departing from the spirit and scope of the present application. It is therefore intended that the present invention not be limited to the exact forms and details described and illustrated herein, but falls within the scope of the appended claims.
