Heat sink tab for optical sub-assembly

The present invention claims priority from U.S. patent application Ser. No. 60/539,217 filed Jan. 26, 2004, which is incorporated herein by reference.

The present invention relates to a heat sink tab for an optical sub-assembly (OSA), and in particular to a heat sink tab forming a direct thermally conductive path between the OSA and a housing.

Conventional transceivers include a pair of OSAs, i.e. a transmitter optical sub-assembly (TOSA) (not shown) and a the receiver optical sub-assembly (ROSA) 1 , illustrated in FIG. 1 . The OSAs are electrically connected to a printed circuit board (PCB) 2 via metal leads 3 or by metal leads 3 and a flexible circuit (flex) cable 4 . The OSAs 1 and the PCB 2 are mounted in a transceiver module housing, generally indicated at 6 , which comprises a lower case 7 and an upper case 8 . Heat sinking fins 9 , or other suitable heat sinking elements, e.g. pins, extend from the upper case 8 for removing heat from the module housing 6 .

Increasing data rates, e.g. in excess of 10 Gb, required by the latest optical transceivers, causes in an increase in power dissipation by the active components therein resulting in an increase in undesirable heat, which must be removed. Hindering the removal of the heat is the industry's desire to use low-cost packaging, such as transistor outline (TO) cans, which are constructed out of materials having poorer thermal conductivity than the more expensive ceramic packaging alternative. Moreover, an industry shift to flex cable for connecting the OSA 1 to the PCB 2 has eliminated the heat sinking provided by the transfer of heat via the leads 3 to the PCB 2 .

An object of the present invention is to overcome the shortcomings of the prior art by providing a direct thermally conductive path between an OSA and the module housing without interfering with the RF performance of the OSA and without taking up much valuable space.

Accordingly, the present invention relates to an opto-electronic device comprising:

an optical sub-assembly for converting optical signals into electrical signals or electrical signals into optical signals;

a housing including a heat dissipating cover for supporting the optical sub-assembly; and

a thermally conductive heat sinking tab for transferring heat from the optical sub-assembly to the heat dissipating cover.

The invention will be described in greater detail with reference to the accompanying drawings which represent preferred embodiments thereof, wherein:

FIG. 1 is a cross-sectional view of a conventional OSA module;

FIG. 2 is a cross-sectional view of an OSA module according to the present invention;

FIG. 3 is a rear isometric view of an embodiment of the heat sinking tab according to the present invention;

FIG. 4 is a front isometric view of the heat sinking tab of FIG. 3 ;

FIG. 5 is a side view of the heat sinking tab of FIGS. 3 and 4 ;

FIG. 6 is a rear isometric view of the heat sinking tab of FIGS. 3 to 5 mounted on an OSA;

FIG. 7 is a front isometric view of the OSA of FIG. 6 ;

FIG. 8 is an exploded rear isometric view of an alternative embodiment of heat sinking tab according to the present invention mounted on an OSA;

FIG. 9 is a rear isometric view of the OSA of FIG. 8 ;

FIG. 10 is an exploded front isometric view of the OSA of FIG. 8 ;

FIG. 11 is a front isometric view of the OSA of FIGS. 8 to 10 ;

FIG. 12 is a side view of the OSA of FIGS. 8 to 11 mounted in a transceiver;

FIG. 13 is a side view of an alternative embodiment of the OSA of FIGS. 8 to 12 ; and

FIG. 14 is a side view of an alternative embodiment of the OSA of FIGS. 8 to 12 .

With reference to FIG. 2 , a transceiver according to the present invention includes a TOSA (not shown) and a ROSA 11 , which are electrically connected to PCB 12 via metal leads 13 and a flex cable 14 . The TOSA and the ROSA 11 include an optical connector on the front end thereof for receiving an end of an optical fiber. A housing 16 encloses the TOSA and the ROSA 11 , and includes a lower case 17 and an upper case 18 . The upper case 18 includes heat sinking fins 19 , although other suitable heat sinking elements are possible, for dissipating heat generated within the housing 16 . Typically, an electrical connector is formed on the outer free end of the PCB 12 for electrically connecting the transceiver to a host device, although other electrical connectors, such as pins, are possible.

Each OSA includes a header 21 extending from the back end thereof, through which the leads 13 extend. A heat sinking tab 22 is mounted on the header 21 with a suitable thermal interface, e.g. solder or thermal adhesive, and extends into contact or close proximity to the upper case 18 . The heat sinking tab 22 is formed out of a flexible, formable or resilient material, e.g. a thin sheet metal such as copper, which is suitably thermally conductive. The heat sinking tab 22 includes a mounting plate 23 , which is stamped or coined with an annular shoulder 24 to fit over the header 21 to facilitate alignment therewith during manufacture. Slots 25 are formed in the mounting plate 23 for receiving the leads 13 , which extend therethrough. The mounting plate 23 is preferably circular to match the back end of the header 21 , but can be any suitable shape, including rectangular. A rectangular finger 26 extends from the mounting plate 23 into contact or close proximity with the upper case 18 for transferring heat to be dissipated by the heat sinking fins 19 . A thermal pad 27 or other intermediary compliant thermal material commonly used in the industry can be placed between the upper case 18 and the finger 26 to enhance thermal contact.

Ideally the flex cable 14 is fixed to the mounting plate 23 prior to assembly with the OSA 11 , whereby the mounting plate 23 provides a stiffener for an end of the flex cable 14 . Moreover, holes 28 in the flex cable 14 for receiving the leads 14 are aligned with the slots 25 in the mounting plate 23 , and provide a simple self-aligning feature with the leads 14 for mounting the heat sinking tab 21 on the OSA 11 .

In an alternative embodiment, illustrated in FIGS. 8 to 12 , a heat sinking tab 31 includes a mounting plate 32 for mounting on the rear end of an OSA 11 , a rectangular finger 33 for extending into contact with or close proximity to the upper case 18 , and a pair of arcuate wings 35 forming the shape of the OSA 11 , which extend perpendicularly from the mounting plate 32 parallel and in contact with the sides of the OSA 11 .

Slots 34 are provided in the mounting plate 32 for receiving the leads 13 , which extend therethrough into contact with the flex cable 14 . With this embodiment, the wings 35 ensure that the body of the OSA 11 is aligned with the flex cable 14 , so that the optical axis of the OSA 11 is aligned with the mechanical design in the housing 16 , enabling control of the tolerance for the attachment of the OSA 11 to the PCB 12 .

As above, the mounting plate 32 is mounted on the header 21 with a suitable thermal interface, e.g. solder or thermal adhesive, and is formed out of a flexible, formable or resilient material, e.g. a thin sheet metal such as copper, which is suitably thermally conductive. A thermal pad 27 or other intermediary compliant thermal material commonly used in the industry can be placed between the upper case 18 and the finger 33 to enhance thermal contact.

With reference to FIG. 13 , a corrugated rectangular finger 43 can be provided extending from the mounting plate 32 . The corrugations increase the surface area of the finger 43 to increase the amount of heat transferred. If the OSA 11 were to be placed within an environment with an air flow, the corrugated finger 43 would also serve as a heat sink itself.

FIG. 14 illustrates an embodiment of the present invention in which a thermoelectric cooler (TEC) 50 is positioned between the finger 33 and the upper case 18 to increase the amount of heat transferred therebetween. The TEC 50 device is preferably based on the Peltier effect, by which a DC current applied across two dissimilar materials causes a temperature differential. The TEC 50 enables the OSA 11 to be operated over a much larger range of temperatures, including very cold temperatures, if the typical “hot” and “cold” sides are reversed to heat the housing 16 .