Heat sink for pluggable optical module with compressible thermal interface material

Aspects described herein include an apparatus comprising a receptacle comprising a cage dimensioned to receive a pluggable optical module into an interior volume, An opening is defined in an exterior surface of the cage. The apparatus further comprises a heat sink assembly rigidly attached to the cage. The heat sink assembly comprises a thermal interface material extending through the opening into the interior volume. The thermal interface material is configured to compress when the pluggable optical module is received into the interior volume and contacts the thermal interface material.

TECHNICAL FIELD

Embodiments presented in this disclosure generally relate to network devices, and more specifically, to implementations of heat sinks for pluggable optical modules with a compressible thermal interface material.

BACKGROUND

With increasing numbers of networked devices (e.g., the Internet of Things (IoT)), pluggable optical modules have increased in popularity for inter-networking communications due to their high data transmission rate. For example, Quad Small Form-factor Pluggable (QSFP) transceiver modules are widely used in state-of-the-art network switches.

Demand for increased communication speeds will result in increased power consumption of the pluggable optical modules. For example, the maximum power consumption of a QSFP transceiver module is about 3.5 watts (W), which currently presents a challenge for cooling a network switch. In comparison, the next generation of pluggable optical modules are expected to consume between 15 and 20 W.

DESCRIPTION OF EXAMPLE EMBODIMENTS

Overview

One embodiment presented in this disclosure is an apparatus comprising a receptacle comprising a cage dimensioned to receive a pluggable optical module into an interior volume. An opening is defined in an exterior surface of the cage. The apparatus further comprises a heat sink assembly rigidly attached to the cage. The heat sink assembly comprises a thermal interface material extending through the opening into the interior volume. The thermal interface material is configured to compress when the pluggable optical module is received into the interior volume and contacts the thermal interface material.

Another embodiment presented in this disclosure is a method of fabricating an optical apparatus, the method comprising arranging a heat sink assembly relative to a receptacle. The receptacle comprises a cage dimensioned to receive a pluggable optical module into an interior volume. An opening is defined in an exterior surface of the cage. The method further comprises rigidly attaching the heat sink assembly to the cage, whereby a thermal interface material of the heat sink assembly extends through the opening into the interior volume. The thermal interface material is configured to compress when the pluggable optical module is received into the interior volume and contacts the thermal interface material.

Another embodiment presented in this disclosure is an apparatus comprising a plurality of receptacles, each receptacle comprising a respective cage dimensioned to receive a pluggable optical module into a respective interior volume. A respective opening is defined in an exterior surface of the respective cage. The apparatus further comprises a heat sink assembly rigidly attached to the respective cages of the plurality of receptacles. The heat sink assembly comprises a thermal interface material extending through the respective openings into the respective interior volumes. The thermal interface material is configured to compress when the pluggable optical module is received into any of the respective interior volumes and contacts the thermal interface material.

EXAMPLE EMBODIMENTS

The increased power consumption of pluggable optical modules will continue to present challenges for adequately cooling network devices. Embodiments described herein include an apparatus comprising a receptacle comprising a cage dimensioned to receive a pluggable optical module into an interior volume. An opening is defined in an exterior surface of the cage. The apparatus further comprises a heat sink assembly rigidly attached to the cage. The heat sink assembly comprises a thermal interface material extending through the opening into the interior volume. The thermal interface material is configured to compress when the pluggable optical module is received into the interior volume and contacts the thermal interface material.

The apparatus may further comprise one or more additional receptacles each configured to receive a respective pluggable optical module, and the heat sink assembly is rigidly attached to the one or more additional receptacles. The heat sink assembly may have any suitable implementation, including metallic fins, a heat pipe, a vapor chamber, or a liquid-cooled plate.

Beneficially, the compliance of the thermal interface material may operate to fill any air pockets and thereby reduce thermal resistance at the interface between the optical module and the heat sink assembly. Using the compliance of the thermal interface material, the apparatus need not include springs to provide a compression force to ensure mechanical contact at the interface.

In spring-based implementations, a protective film may be applied to a thermal interface material to reduce the insertion force for the optical module, and to reduce a potential of scratching the thermal interface material during insertion. However, the protective film may have a relatively low thermal conductivity which reduces the performance of the heat sink assembly. Additionally, the compliance of the thermal interface material may enable the use of rigid or less flexible implementations of the heat sink, such as a liquid-cooled plate.

FIG. 1illustrates a network device100, according to one or more embodiments. The network device100may be implemented in any suitable form, such as network storage, a server, a switch, a router, a hub, a network interface card (NIC), and so forth. The network device100comprises an enclosure105that houses a plurality of electrical and/or optical components. The enclosure105may be implemented as a standalone device or a rack-mounted device.

The network device100comprises a plurality of receptacles110-1,110-2,110-3,110-4,110-31,110-32(collectively or generically referred to as receptacle(s)110) that are disposed within the enclosure105and that are externally accessible. Although thirty-two (32) receptacles110are shown, other numbers of receptacles110are also contemplated.

Each of the receptacles110is configured to receive a pluggable optical module (also referred to as an optical module) into an interior volume. The receptacles110may be dimensioned to receive optical modules having standardized or proprietary form factors. In some embodiments, each optical module comprises a transceiver module providing one or more transmit channels and one or more receive channels using one or more optical fibers. The various components of the network device100within the enclosure105may provide electrical and/or optical connectivity between the different optical modules and/or other functionality. The plurality of receptacles110-1,110-2,110-3,110-4, . . . ,110-31,110-32are arranged in two rows115-1,115-2, where the odd-numbered receptacles (110-1,110-3, . . . ,110-31) are arranged in row115-1and the even-numbered receptacles (110-2,110-4, . . . ,110-32) arranged in row115-2.

FIG. 2illustrates a pluggable optical module200, according to one or more embodiments. The optical module200may be used in conjunction with other embodiments, such as being insertable into a receptacle110of the network device100ofFIG. 1.

The optical module200comprises a housing205that houses electrical components and optical components, at least some of which may be mounted on a circuit board210. One or more optical connectors215-1,215-2are attached to the housing205and are configured to couple optical fibers with the optical components in the housing205. The circuit board210defines an edge connector220that provides external electrical connections to the electrical components in the housing205.

In some embodiments, a top surface230of the housing205is used as a thermally conductive interface for a heat sink assembly that removes heat generated through operation of the electrical components and/or optical components of the optical module200.

The optical module200further comprises a handle225attached to the housing205. The handle225generally assists in the insertion of the optical module200into a receptacle and/or removal of the optical module200from the receptacle.

FIG. 3is a diagram300illustrating receptacles of a network device, according to one or more embodiments. The features illustrated in the diagram300may be used in conjunction with other embodiments, e.g., representing a portion of the network device100ofFIG. 1with the enclosure105removed.

Each receptacle110-31,110-32comprises a cage305dimensioned to receive an optical module (e.g., the optical module200ofFIG. 2). The cages305may be formed of any material(s) providing structural rigidity to support the optical module, providing thermal conductivity, and/or providing electromagnetic interference (EMI) shielding. In some embodiments, the cages305are formed of folded sheet metal.

The optical module is received into the receptacle110through an opening310formed in the cage305. The opening310is in fluid communication with an interior volume315of the cage305. The cages305may include a guide rail or other feature to guide insertion and/or removal of the optical module into the receptacle110.

In some embodiments, a heat sink assembly325is rigidly attached to the cage305(e.g., using threaded fasteners or a pressure-sensitive adhesive). In some embodiments, “rigidly attached” may be a permanent attachment or may be detachable. In some embodiments, “rigidly attached” means that at least a portion of the heat sink assembly325is arranged at a fixed distance from a portion of the cage305. In some cases, the portion of the heat sink assembly325may itself be rigid. The heat removal mechanism of the heat sink assembly325may have any suitable implementation, including metallic fins, a heat pipe, a vapor chamber, or a liquid-cooled plate. In some embodiments, the heat sink assembly325includes a base to which the cages305and/or the heat removal mechanism attaches.

In some embodiments, an exterior surface320of the cage305(as shown in the diagram300, a top surface of the cage305) has an opening (not shown) defined therethrough. The heat sink assembly325comprises a thermal interface material that extends through the opening in the exterior surface320, into the interior volume315of the cage305. The thermal interface material is compressible, and is configured to compress when the optical module is received into the interior volume315and contacts the thermal interface material. Using the example ofFIG. 2, when the optical module200is received into the interior volume315, the top surface230of the housing205contacts the thermal interface material.

In the example shown in the diagram300, the thermal interface material of the heat sink assembly325extends into the interior volume315of the receptacle110-31, which is stacked above the receptacle110-32. In some embodiments, heat generated by an optical module inserted in the receptacle110-32may be conducted, through the cages305and/or one or more thermally conductive components, to the heat sink assembly325arranged above the receptacle110-31.

FIG. 4is a method400of fabricating an optical apparatus, according to one or more embodiments. The method400may be used in conjunction with other embodiments, e.g., to fabricate the network device depicted inFIG. 3.

The method400begins at block405, where a compressible thermal interface material is attached to a base of a heat sink assembly. In some embodiments, the thermal interface material is attached to the base using a pressure-sensitive adhesive. For example, an adhesive layer may be integrated into the thermal interface material, offering improved thermal performance compared to an adhesive added between the base and the thermal interface material.

At block415, the heat sink assembly is arranged relative to a receptacle. In some embodiments, the heat sink assembly is arranged such that the thermal interface material is aligned with an opening defined in an exterior surface of a cage of the receptacle.

At block425, the heat sink assembly is rigidly attached to the cage of the receptacle. In some embodiments, the thermal interface material extends through the opening into an interior volume of the cage. In some embodiments, rigidly attaching the heat sink assembly to the cage comprises one of tightening one or more threaded fasteners, or applying a pressure-sensitive adhesive. In some embodiments, rigidly attaching the heat sink assembly and the cage causes the thermal interface material to extend into the interior volume. In other embodiments, arranging the heat sink assembly relative to the receptacle causes the thermal interface material to extend into the interior volume.

At block435, a pluggable optical module is received into the interior volume of the cage. In some embodiments, receiving the optical module into the interior volume compresses the thermal interface material. The method400ends following completion of block435.

FIGS. 5A and 5Billustrate a sequence of fabricating an optical apparatus, according to one or more embodiments. Diagrams500,540are cross-sectional views illustrating the arrangement and attachment of the heat sink assembly325to a receptacle, and the sequence depicted in the diagrams500,540generally corresponds to the method400ofFIG. 4.

The heat sink assembly325comprises a base515attached to a thermal interface material520. The base515may be formed of any material(s) that provides sufficient thermal conductivity and structural rigidity, such as metal. In some embodiments, the base515comprises the heat removal mechanism, which may be implemented in any suitable form such as metallic fins, a heat pipe, a vapor chamber, or a liquid-cooled plate. Although not depicted in the diagrams500,540, the heat sink assembly325may include additional components, such as a heat removal mechanism that is distinct from, and attached to, the base515.

The thermal interface material520may be formed of any material(s) providing suitable mechanical compliance (e.g., compressibility) and thermal conductivity. In some embodiments, the thermal interface material520comprises a fiber-reinforced resin material having a thermal conductivity between about 2 watts per meter Kelvin (W/m-K) and about 6 W/m-K, and a Young's Modulus between about 50 kilopascals (kPa) and 150 kPa. One non-limiting example of the thermal interface material520is Bergquist® Gap Pad® TGP HC3000 (trademarks assigned to Henkel IP & Holding GmbH LLC).

In some embodiments, the thermal interface material520comprises an integrated adhesive layer, which may offer improved thermal performance compared to an adhesive added between the base and the thermal interface material. In some embodiments, the integrated adhesive layer comprises a pressure-sensitive adhesive. In some embodiments, a film525is disposed on the thermal interface material520. The film525may be formed of any material(s), and may have a thickness selected, to provide suitable thermal performance. Some non-limiting examples of the materials for the film525include vinyl, polyester, polypropylene, and other plastics. In some embodiments, the film525may reduce friction between the optical module and the thermal interface material520when the optical module is inserted into the receptacle110.

A bottom surface530of the heat sink assembly325is defined by the thermal interface material520or by the film525. In some embodiments, the bottom surface530is a substantially planar surface that is configured to contact a substantially planar surface of the optical module (e.g., the top surface230ofFIG. 2).

In some embodiments, the base515defines a flat, planar surface to which the thermal interface material520is attached. In some embodiments, the base515is contoured (e.g. including a projecting portion535) such that the base515extends through an opening510into the interior volume315when the heat sink assembly325is rigidly attached to the cage305.

The thermal interface material520may have a uniform thickness or a varying thickness. For example, in cases where the base515defines a flat, planar surface, the thermal interface material520may be thicker in a portion that extends into the interior volume315. In cases where the base515includes the projecting portion535, the thermal interface material520may have a uniform thickness.

The opening510is defined in the exterior surface320of the cage305. The cage305further comprises a connector505that is configured to receive the edge connector of the optical module when inserted. In some embodiments, the connector505is configured to form connections with electrical components of the optical module.

In the diagram540, the heat sink assembly325is arranged relative to the cage305, such that the thermal interface material520extends through the opening510into the interior volume315. From this arrangement, the heat sink assembly325may be rigidly attached to the cage305, e.g., using one or more threaded fasteners or a pressure-sensitive adhesive.

In some embodiments, a surface area of the thermal interface material520in an uncompressed state is greater than a surface area of the opening510. In this case, lateral portions545-1,545-2of the thermal interface material520are compressed between the base515and the cage305when the heat sink assembly325is rigidly attached to the cage305.

In some embodiments, the portion of the heat sink assembly325that extends through the opening510into the interior volume315is contoured to reduce an insertion force of the optical module. As shown, the contoured portion550of the thermal interface material520is curved between the lateral portion545-2and the bottom surface530. Other types of contouring are also possible (e.g., the contoured portion550may be linearly sloped). In some embodiments, the contoured portion550may be used in conjunction with the film525to further reduce the insertion force.

FIGS. 6A, 6B, and 6Cillustrate a sequence of inserting an optical module into a network device, according to one or more embodiments, Diagrams600,610,620are cross-sectional views illustrating the insertion of the optical module200into the receptacle110.

In the diagram600, the optical module200is arranged outside the cage305. The edge connector220and a leading edge605of the housing205are aligned with the opening310formed in the cage305.

In the diagram610, the optical module200is received into the receptacle110through the opening310. In some embodiments, a guide rail or other feature of the cage305may guide insertion of the optical module200into the receptacle110. During the insertion process, the leading edge605of the housing205contacts the contoured portion550of the thermal interface material520, and the top surface230of the housing205contacts the bottom surface530of the heat sink assembly325. The insertion of the optical module200causes the thermal interface material520to compress in a region615. Beneficially, compression of the thermal interface material520may operate to fill any air pockets and thereby reduce a thermal resistance between the optical module200and the heat sink assembly325. Notably, the base515of the heat sink assembly325remains in a fixed arrangement with the cage305during insertion of the optical module200, relying on the compliance of the thermal interface material520to accommodate the optical module200.

In the diagram620, the optical module200is inserted fully into the receptacle110, such that the edge connector220is mated to the connector505. The insertion of the optical module200causes the thermal interface material520to compress in a region625. In some embodiments, the bottom surface530when the thermal interface material520is compressed forms a substantially planar interface with the top surface230of the optical module200.

FIGS. 7A and 7Billustrate a heat sink assembly325for multiple receptacles110, according to one or more embodiments. Diagram700provides a perspective view with optical modules200-1,200-2,200-3inserted into three (3) receptacles110, and diagram715provides a cross-section view with the optical modules200-1,200-2,200-3not inserted. Although three receptacles110are shown, other numbers of receptacles110are also contemplated.

The three receptacles110share the heat sink assembly325. A plurality of cages305-1,305-2,305-3are mounted to a circuit board705or another substrate, and the heat sink assembly325(e.g., the base515) is rigidly attached to the receptacles110(e.g., the cages305-1,305-2,305-3). As shown, threaded fasteners710-1,710-2,710-3,710-4rigidly attach the heat sink assembly325to the circuit board705.

In the diagram715, the heat sink assembly325comprises metallic fins720attached to the base515. Thermal interface materials520-1,520-2,520-3(collectively or generically, thermal interface material520) respectively extend into the interior volumes315-1,315-2,315-3of the cages305-1,305-2,305-3. When the optical modules200-1,200-2,200-3are inserted into the respective interior volumes315-1,315-2,315-3, the thermal interface materials520-1,520-2,520-3are compressed (as shown, in an upward direction).

In diagram800ofFIG. 8, the heat sink assembly325comprises a liquid-cooled plate805that is attached to the base515and that has a channel810defined therein. The liquid-cooled plate805further comprises an inlet815and an outlet820in fluid communication with the channel810.

Beneficially, the compliance of the thermal interface material520may enable the use of rigid or less flexible implementations of the heat sink assembly325, such as the liquid-cooled plate805. For example, rigid implementations of the heat sink assembly325may not be suitable for spring-based implementations where the base515is configured to displace upward when an optical module is inserted into the interior volume315, which may be especially true in the case of multiple receptacles110.