Module with transmit and receive optical subassemblies with specific pic cooling architecture

An optoelectronic module. In some embodiments, the module includes: a housing, a substantially planar subcarrier, a photonic integrated circuit, and an analog electronic integrated circuit. The subcarrier has a thermal conductivity greater than 10 W/m/K. The photonic integrated circuit and the analog electronic integrated circuit are secured to a first side of the subcarrier, and the subcarrier is secured to a first wall of the housing. A second side of the subcarrier, opposite the first side of the subcarrier, is parallel to, secured to, and in thermal contact with, an interior side of the first wall of the housing.

FIELD

One or more aspects of embodiments according to the present invention relate to optoelectronic modules.

BACKGROUND

Pluggable transceivers which include (i) one or more transmitters to convert electrical signals carrying data to optical signals carrying the same data and (ii) one or more receivers to convert optical signals to electrical signals may be used, for example, in switching systems. The design of a pluggable module may pose various challenges, including respecting space constraints, and keeping components in the module within acceptable temperature ranges.

SUMMARY

According to an embodiment of the present disclosure there is provided a transceiver assembly, including: a housing; and an optical subassembly, the optical subassembly including: a fiber, a photonic integrated circuit, an analog electronic integrated circuit, and a substantially planar subcarrier; the subcarrier having a thermal conductivity greater than 10 W/m/K; the photonic integrated circuit and the analog electronic integrated circuit being on the subcarrier; the fiber being coupled to the photonic integrated circuit; the subcarrier being parallel to, secured to, and in thermal contact with, a first wall of the housing; the photonic integrated circuit being connected to the analog electronic integrated circuit; and the optical subassembly having a plurality of contact pads for establishing electrical connections between the analog electronic integrated circuit and test equipment probes, the optical subassembly being configured to be separately testable by supplying power to the optical subassembly through one or more of the contact pads and sending data to and and/or receiving data from the optical subassembly through one or more of the contact pads.

In one embodiment, the analog electronic integrated circuit is adjacent to the photonic integrated circuit and connected to the photonic integrated circuit by a first plurality of wire bonds. In one embodiment, the wire bonds extend from wire bond pads along an edge of the analog electronic integrated circuit to wire bond pads along an edge, of the photonic integrated circuit, nearest the analog electronic integrated circuit.

In one embodiment, the optical subassembly further includes a flexible printed circuit, connected to the analog electronic integrated circuit.

In one embodiment, the optical subassembly further includes a routing board, and the analog electronic integrated circuit is connected to the flexible printed circuit through the routing board.

In one embodiment, the routing board is a printed circuit including an organic insulating material and conductive traces, the routing board is connected to the analog electronic integrated circuit, along an edge of the analog electronic integrated circuit, by wire bonds.

In one embodiment, the flexible printed circuit is further connected to the host board.

According to an embodiment of the present disclosure there is provided a module, including: a housing; a substantially planar subcarrier; a photonic integrated circuit; and an analog electronic integrated circuit, the subcarrier having a thermal conductivity greater than 10 W/m/K, the photonic integrated circuit and the analog electronic integrated circuit being secured to a first side of the subcarrier, the subcarrier being secured to a first wall of the housing, wherein a second side of the subcarrier, opposite the first side of the subcarrier, is parallel to, secured to, and in thermal contact with, an interior side of the first wall of the housing.

In one embodiment, the photonic integrated circuit is adjacent to the analog electronic integrated circuit.

In one embodiment, the photonic integrated circuit is connected to the analog electronic integrated circuit by wire bonds.

In one embodiment, the wire bonds extend from wire bond pads along an edge of the analog electronic integrated circuit to wire bond pads along an edge, of the photonic integrated circuit, nearest the analog electronic integrated circuit.

In one embodiment, the module further includes an optical subassembly including: the subcarrier; the photonic integrated circuit; and the analog electronic integrated circuit, the optical subassembly having a plurality of contact pads for establishing electrical connections between the analog electronic integrated circuit and test equipment probes, the optical subassembly being configured to be separately testable by supplying power to the optical subassembly through one or more of the contact pads and sending data to and and/or receiving data from the optical subassembly through one or more of the contact pads.

In one embodiment, the optical subassembly further includes a flexible printed circuit, connected to the analog electronic integrated circuit

In one embodiment, the optical subassembly further includes a routing board connected to the analog electronic integrated circuit, along an edge of the analog electronic integrated circuit, by wire bonds; the analog electronic integrated circuit is connected to the flexible printed circuit through the routing board; and the routing board is a printed circuit including an organic insulating material and conductive traces.

In one embodiment, the flexible printed circuit is connected to the routing board by solder.

In one embodiment, the module further includes a host board including a microcontroller and/or a DC-DC converter, the host board being connected to the routing board through the flexible printed circuit.

According to an embodiment of the present disclosure there is provided method for manufacturing a module, the method including: assembling an optical subassembly including: a fiber, a photonic integrated circuit, an analog electronic integrated circuit, and a substantially planar subcarrier, the photonic integrated circuit and the analog electronic integrated circuit being on the subcarrier; testing the optical subassembly; determining that the testing of the optical subassembly was successful; and in response to determining that the testing of the testing the optical subassembly was successful, installing the optical subassembly in a housing, with the subcarrier being parallel to, secured to, and in thermal contact with, a first wall of the housing.

In one embodiment, the optical subassembly has a plurality of contact pads for establishing electrical connections between the analog electronic integrated circuit and test equipment probes; and the testing of the optical subassembly includes: transmitting modulated light into the photonic integrated circuit through the fiber, and verifying the presence, at the contact pads, of electrical signals corresponding to the modulation; or the testing of the optical subassembly includes: applying electrical signals to the contact pads, and verifying the presence, in light transmitted through the fiber from the photonic integrated circuit, of modulation corresponding to the electrical signals.

In one embodiment, the method further includes: in response to determining that the testing of the testing the optical subassembly was successful, connecting a host board including a microcontroller and/or a DC-DC converter to the optical subassembly.

In one embodiment, the connecting of the host board to the optical subassembly includes soldering the host board to the optical subassembly.

DETAILED DESCRIPTION

FIGS. 1A-1Dshow schematic cross-sectional views of several embodiments each including a transceiver in a quad small form factor pluggable (QSFP) package. Referring toFIGS. 1A and 1B, in some embodiments an optical fiber105connects a photonic integrated circuit (PIC)110to a Multi-fiber Push On (MPO) connector115. The PIC110is connected by one or more wire bonds120to an analog electronic integrated circuit, e.g., an analog application specific integrated circuit (aASIC)125, which is connected by one or more wire bonds120to a routing board130, which may be a printed circuit board on an organic substrate (e.g., a polymer or fiberglass-reinforced polymer substrate). The PIC110may be one of a plurality of PICs110(e.g., the module may include both a transmitter PIC and a receiver PIC), and the aASIC125may be one of a plurality of aASICs125(there being, for example, one aASIC125for each PIC110). The aASIC125and the PIC may be bare die. For example, the aASIC125may be a bare silicon die, and the PIC110may be a bare silicon die (which, in the case of a transmitter PIC, may include a bare laser die (e.g., a bare die of another semiconductor, different from silicon) mounted on a bare silicon die (as discussed in further detail below)). The routing board130may be fabricated using a process capable of forming fine pitch features, e.g., traces and wire bond pads on a pitch of 100 microns. The PIC110, aASIC125, and routing board130may be secured to (e.g., bonded to), and supported by, a subcarrier135, which may be a block, or a block with a stepped thickness as shown, formed of a thermally conductive material (e.g., a material having a thermal conductivity exceeding 10 W/m/K), e.g., copper. The subcarrier may be substantially planar, i.e., it may have the shape of a sheet having different thicknesses in different regions of the sheet, e.g., having a greater thickness in the region to which the aASIC125is secured than in the region to which the PIC110and a TEC140(discussed in further detail below) are secured. That is, in one or more embodiments, the subcarrier135may be a single, monolithic, substantially planar subcarrier. In a system using a QSFP package, thermal control of the top package wall137may be provided (e.g., the system may be designed—e.g., with a heat sink—to ensure that the temperature of the top package wall not exceed a specified value). As such, in the embodiments ofFIGS. 1A and 1B, heat may be conducted out of the package through the subcarrier135and through the top package wall137.

The PIC110may be secured to a thermoelectric cooler (TEC)140which may be secured to the subcarrier135, as shown. In some embodiments, a host board145, which may be an organic printed circuit board, has installed on it a microcontroller150and a DC-DC converter155, and it has a card-edge connector160at the electrical end of the QSFP package. The routing board may be connected to the host board by a flexible circuit or “flex circuit”165(FIG. 1A) or by a low profile connector array170(or “socket”) (e.g., a Z-RAY™ ultra-low profile array available from Samtec (samtec.com)) (FIG. 1B). Because the conductors may spread out on the routing board130and/or on the flex circuit165, the host board is, in some embodiments, fabricated using a lower-cost process not capable of forming fine pitch features. A similar configuration may be used regardless of whether the PIC110and the aASIC125form a transmitter (transmitting light through the fiber) or a receiver (receiving light through the fiber). In the case of a transmitter, the PIC may include a modulator, and a laser (e.g., a separate laser chip) may be mounted on the PIC, and optically coupled to it, and the aASIC may include a drive circuit for the modulator. In the case of a receiver, the PIC may include a photodetector, and the aASIC may include a transimpedance amplifier to amplify the signal from the photodetector. Each PIC110may include an array of modulators or photodetectors, and each aASIC125may include a corresponding array of drive circuits or transimpedance amplifiers.

Each PIC110may include a waveguide having transverse dimensions of approximately 10 microns at a point at which light couples into the waveguide from the fiber105, or from the fiber105into the waveguide. A mode adapter, e.g., a taper, may guide the light and transform the optical mode to one that propagates in a waveguide having transverse dimensions of approximately 3 microns. The 3 micron waveguide may be used to guide the light to a photodetector, or from a modulator. Further mode adapters (e.g., at a modulator) may be used to effect further changes in the size or shape of the optical mode, e.g., to enable light to propagate through a modulator fabricated on a waveguide with smaller transverse dimension (for improved modulator performance). In some embodiments similar to that ofFIG. 1A, the routing board130is omitted and the aASIC125is connected directly to the flex circuit165, which is bonded directly to the subcarrier135. In such an embodiment, longer wire bonds may be used to accommodate the difference in height between the surface of the aASIC125and the surface of the flex circuit (which may be significantly thinner than the aASIC125), or the difference in height may be reduced by thinning the aASIC die, or by using a subcarrier135with a stepped thickness (i.e., a subcarrier135having a greater thickness under the flex circuit165than under the aASIC125). The flex circuit165may be a printed circuit composed of one or more layers of conductive traces and one or more flexible insulating layers. The flexible insulating layers may be composed of a film of plastic (e.g., a film of polyimide) capable of withstanding soldering temperatures, and the flex circuit165may be connected to the routing board130and to the host board145by soldering.

In some embodiments the TEC140is absent and the PIC110is bonded directly to the subcarrier, or is bonded to an insulating layer bonded to the subcarrier. In some embodiments, a heater is secured to or integrated into the PIC110and the temperature of the PIC110is actively controlled, based on a signal from a temperature sensor on or integrated into the PIC110. In such an embodiment, the insulating layer may enable the heater to raise the temperature of the PIC110without consuming an excessive amount of power.

FIG. 1Cshows an embodiment in which the MPO connector115is absent and the fiber105extends directly from the PIC110to the exterior of the package. Such a configuration may be referred to as an active optical cable (AOC) configuration.FIG. 1Dshows a related embodiment in which the PIC110is more distant from the front end (or “optical end”) of the package, facilitating the inclusion of an MPO connector115. InFIGS. 1C and 1D, the PIC110and the aASIC125may be bonded to a substrate175, which may be a printed circuit board including one or more layers containing conductive traces and one or more organic insulating layers (e.g., polymer or fiberglass-reinforced polymer insulating layers), with thermal vias180for forming a thermal path between (i) the PIC110and the aASIC125and (ii) a thermal block185which supports the substrate175and provides a thermal path between the substrate and the bottom wall (or “lower wall”)187of the package enclosure. In some systems using QSFP packages the lower wall187of the package is not directly connected to the heat sink; accordingly, in the embodiments ofFIGS. 1C and 1Dthe side walls of the package may be used to conduct heat to the top package wall. Wire bonds120may be used to connect the PIC110to the aASIC125and to connect the aASIC125to the substrate175. The substrate175may be fabricated using a process capable of forming fine pitch features, e.g., traces and wire bond pads on a pitch of 100 microns.

A dual flex circuit (i.e., two parallel flex circuits165), is used in the embodiment ofFIG. 1Cto connect the substrate175to a host board145which has a card-edge connector160at the electrical end of the QSFP package, and which has installed on it a microcontroller150and a DC-DC converter155. In the embodiment ofFIG. 1Dthe card-edge connector160at the electrical end of the QSFP package is on the substrate175, and a separate host board145has installed on it a microcontroller150and a DC-DC converter155and is connected to the substrate175by a flex circuit165.

FIG. 2shows a bottom view of the embodiment ofFIGS. 1A and 1B, in one embodiment, andFIG. 3shows a bottom view of the embodiment ofFIGS. 1A and 1B, in another embodiment. The routing board extends around the aASICs125and the PICs110so that wire bonds (not shown), for delivering power or control signals to these components (or for providing laser drive current to the laser on the transmitter PIC) may be formed along the side edges of these components. The host board145and flex circuit165are not shown inFIGS. 2 and 3. Wire bonds for data connections (shown inFIGS. 1A and 1B, and, for the data connections between the aASICs and the PICs, inFIGS. 2 and 3) may be present along the end edges of the aASICs and the PICs.

FIGS. 4-9show an assembly sequence for the embodiment ofFIGS. 1A and 1B. Referring toFIG. 4, each fiber105(of the fibers of a fiber ribbon405, the other end of which is terminated in an MPO connector115(FIG. 7B; not shown inFIGS. 4-6) is aligned in a respective V-groove (e.g., of an array of V-grooves) on the PIC110and secured in place to form a “PICtail”410. The PICtails410are secured to the subcarrier (or “carrier”)135along with the aASICs125, either directly, to form a first subassembly415, or (in the alternate sequence shown by dashed arrows) the PICs110may be bonded to a TEC140which may be bonded to the subcarrier135. Referring toFIG. 5, a rigid-flex circuit505(the combination of the routing board130and the flex-circuit165, which may be separately assembled) is then bonded to the first subassembly415ofFIG. 4to form a testable transmit-receive optical subassembly (TROSA)510(including the fiber-coupled PICs110and the aASICs125), with pads515suitable for making contact with test equipment probes, that may provide power to the TROSA and send or receive data through it. The testable TROSA510thus makes it possible to identify and discard a defective optical subassembly without discarding with it, e.g., a host board having installed on it a microcontroller and a DC-DC converter.

Referring toFIG. 6, a cover610may then be secured to the TROSA (e.g., to protect it during further handling before the package is assembled). The TROSA510may be tested (by supplying modulated light to the receivers and verifying that suitable corresponding electrical signals are produced at the pads515, and by supplying electrical signals to the pads515, and verifying that suitably modulated light is produced by the transmitters) either before or after installation of the cover610. If the test is successful, assembly of the module may proceed; if it is unsuccessful, the TROSA510may be discarded or reworked.

Referring toFIGS. 7A-7C, the flex circuit of the TROSA510is then soldered to the host board145.FIG. 7Cshows the TROSA510soldered to the host board145, with the subcarrier135facing up and the cover610facing the host board145. Semicircular cutouts710(not shown in the preceding drawings) may be used to register the TROSA510and the host board145to the module housing.

The resulting subassembly may then be installed in a QSFP package housing.FIG. 8Ashows the cast housing805with registration features810for engaging the semicircular cutouts710of the TROSA510and of the host board145.FIG. 8Bshows the TROSA510and the host board145installed in the housing805. A thermal pad905may be placed on the subcarrier (FIG. 9A) and a lid may be installed on the QSFP package housing, to complete the assembly (FIG. 9B).FIG. 10Ashows a top view of the assembly with the lid removed andFIG. 10Bshows a cross-sectional view, along section line10B-10B ofFIG. 10A, of the assembly.

FIGS. 11A-11Cshow embodiments in which the PIC110and the aASIC125are secured, directly or indirectly, to a subcarrier to form a testable TROSA including the fiber105, the MPO connector115, the PIC110, the aASIC125, the TEC140(if present), and the subcarrier135. After testing, the TROSA is installed into a cutout in the host board145and the aASIC125is wire bonded to the host board145. InFIGS. 11A-11C, the module is shown in an orientation in which the wall of the module to which a heat sink is directly connected, in operation, is the lower wall. In the embodiment ofFIG. 11C, a printed circuit board with thermal vias1110supports the PIC110and the aASIC125and is in turn supported by the subcarrier135. Wire bonds from the PIC110to the printed circuit board with thermal vias1110and from the host board145to the printed circuit board with thermal vias1110provide (along with traces on the printed circuit board with thermal vias1110) low speed connections such as power and control connections. In the embodiments ofFIGS. 11A and 11B, testing may be accomplished by probing pads on the aASIC125. In the embodiment ofFIG. 11C, pads on the printed circuit board with thermal vias1110may instead be probed; this may facilitate testing, as the pads on the substrate may be larger and may have a coarser pitch than pads on the aASIC aASIC in the embodiments ofFIGS. 11A and 11B. In the embodiment ofFIG. 11C, a pedestal1115(e.g., a cast pedestal that is an integral part of the module housing) supports the thermal pad905which supports the subcarrier135.

FIGS. 12A-12Cshow another embodiment of a transceiver module. In this embodiment a coined, “top-drop” subcarrier135(which may be a copper subcarrier) supports the PICs110and the aASICs125as shown. After the TROSA is tested, the subcarrier135is installed in (e.g., “dropped into”) a cutout (e.g., a rectangular cutout) in the host board145and the aASIC125is connected to the host board145by wire bonds. An electrical routing board1210is connected to the host board145, to the PICs110and to the aASICs125by wire bonds, and provides low speed connections to the PICs110and to the aASICs125.

Although exemplary embodiments of a module with transmit optical subassembly and receive optical subassembly have been specifically described and illustrated herein, many modifications and variations will be apparent to those skilled in the art. Accordingly, it is to be understood that a module with transmit optical subassembly and receive optical subassembly constructed according to principles of this disclosure may be embodied other than as specifically described herein. The invention is also defined in the following claims, and equivalents thereof.