Printed circuit board assembly having a flexible optical circuit and associated fabrication method

That which is claimed:

1. A method of fabricating a flexible optical circuit comprising the steps of:

providing a plurality of optical fibers extending between respective first and second ends;

mounting connectors upon respective second ends of the plurality of optical fibers; and

disposing the plurality of optical fibers between a pair of at least partially flexible sheets such that the first ends and the preconnectorized second ends of the plurality of optical fibers extend outwardly beyond the pair of at least partially flexible sheets.

2. A method of fabricating a flexible optical circuit comprising the steps of:

providing a plurality of optical fibers extending between respective first and second ends;

mounting connectors upon respective second ends of the plurality of optical fibers; and

disposing the plurality of optical fibers between a pair of at least partially flexible sheets such that the first ends and the preconnectorized second ends of the plurality of optical fibers extend outwardly beyond the pair of at least partially flexible sheets, and further comprising the step of testing the plurality of optical fibers following said mounting step to determine if the connectors are properly mounted upon the respective second ends of the optical fibers prior to disposing the plurality of preconnectorized optical fibers between the pair of at least partially flexible sheets.

3. A method of fabricating a flexible optical circuit comprising the steps of:

providing a plurality of optical fibers extending between respective first and second ends;

mounting connectors upon respective second ends of the plurality of optical fibers; and

disposing the plurality of optical fibers between a pair of at least partially flexible sheets such that the first ends and the preconnectorized second ends of the plurality of optical fibers extend outwardly beyond the pair of at least partially flexible sheets, wherein said disposing step comprises positioning the plurality of optical fibers between the pair of at least partially flexible sheets such that the plurality of optical fibers fan out in a direction extending from the first ends to the preconnectorized second ends of the plurality of optical fibers.

4. A method according to claim 3 further comprising the steps of:

mounting a multifiber connector upon the first ends of the plurality of optical fibers; and

mounting the flexible optical circuit to the interior portion of a printed circuit board such that the multifiber connector extends toward an edge portion of the printed circuit board while the preconnectorized second ends of the plurality of optical fibers lie within the interior portion of the printed circuit board.

5. A method of fabricating a flexible optical circuit comprising the steps of:

providing a plurality of optical fibers extending between respective first and second ends;

mounting connectors upon respective second ends of the plurality of optical fibers; and

disposing the plurality of optical fibers between a pair of at least partially flexible sheets such that the first ends and the preconnectorized second ends of the plurality of optical fibers extend outwardly beyond the pair of at least partially flexible sheets, wherein said providing step comprises providing a plurality of optical fibers comprising a core, a cladding layer surrounding said core, and a buffer layer surrounding the cladding layer proximate the second ends of said optical fibers, wherein the first ends of said optical fibers are free of said buffer layer, and wherein said disposing step comprises disposing the plurality of optical fibers between the pair of at least partially flexible sheets such that the buffer layer terminates at a location along the optical fibers between the at least partially flexible sheets.

6. A method according to claim 5 wherein said providing step comprises providing a plurality of optical fibers which further comprise a coating layer between the cladding layer and the buffer layer proximate the second ends of the optical fibers, wherein the first ends of said optical fibers are free of the coating layer, and wherein said disposing step comprises disposing the plurality of optical fibers between the pair of at least partially flexible sheets such that both the coating layer and the buffer layer terminate at a location along the optical fibers between the at least partially flexible sheets.

7. A flexible optical circuit comprising:

a pair of at least partially flexible sheets;

a plurality of optical fibers extending between respective first and second ends, said plurality of optical fibers disposed between said pair of at least partially flexible sheets such that the first and second ends of said plurality of optical fibers extend outwardly beyond said pair of at least partially flexible sheets, wherein said optical fibers comprise:

a core;

a cladding layer surrounding said core; and

a buffer layer surrounding the cladding layer proximate the second ends of said optical fibers, wherein the first ends of said optical fibers are free of said buffer layer such that said buffer layer terminates at a location along said optical fibers between said at least partially flexible sheets;

a multifiber connector mounted upon the respective first ends of a predetermined number of said plurality of optical fibers; and

a plurality of second connectors mounted upon the respective second ends of said plurality of optical fibers, each of said second connectors mounted upon the respective second ends of less than the predetermined number of optical fibers.

8. A flexible optical circuit according to claim 7 wherein said optical fibers further comprise a coating layer disposed between said cladding layer and said buffer layer proximate the second ends of said optical fibers, wherein the first ends of said optical fibers are free of both said coating layer and said buffer layer terminate at a location along said optical fibers between said at least partially flexible sheets.

9. A flexible optical circuit according to claim 8 wherein both said coating layer and said buffer layer terminate at a location at least 2 mm inward of an edge of said at least partially flexible sheets.

10. A flexible optical circuit according to claim 7 wherein said plurality of second connectors comprise a plurality of single fiber connectors mounted upon the second ends of respective optical fibers.

11. A flexible optical circuit according to claim 7 further comprising an adhesive disposed between said at least partially flexible sheets to secure said plurality of optical fibers therebetween.

12. A printed circuit board assembly comprising:

a printed circuit board having an interior portion and edge portions surrounding the interior portion; and

a flexible optical circuit disposed upon the interior portion of said printed circuit board, said flexible optical circuit comprising:

a pair of at least partially flexible sheets;

a plurality of optical fibers extending between respective first and second ends wherein the first ends extend toward an edge portion of said printed circuit board and the second ends lie within the interior portion of said printed circuit board, said plurality of optical fibers disposed between said pair of at least partially flexible sheets such that the first and second ends of said plurality of optical fibers extend outwardly beyond said pair of at least partially flexible sheets, said optical fibers comprising a core, a cladding layer surrounding said core, and a buffer layer surrounding the cladding layer proximate the second ends of said optical fibers, wherein the first ends of said optical fibers are free of said buffer layer such that said buffer layer terminates at a location along said optical fibers between said at least partially flexible sheets; and

a multifiber connector mounted upon the respective first ends of said plurality of optical fibers, said multifiber connector extending to an edge portion of said printed circuit board.

13. A printed circuit board assembly according to claim 12 wherein said optical fibers further comprise a coating layer disposed between said cladding layer and said buffer layer proximate the second ends of said optical fibers, wherein the first ends of said optical fibers are free of both said coating layer and said buffer layer terminate at a location along said optical fibers between said at least partially flexible sheets.

14. A printed circuit board assembly according to claim 13 wherein both said coating layer and said buffer layer terminate at a location at least 2 mm inward of an edge of said at least partially flexible sheets.

15. A printed circuit board assembly according to claim 12 wherein said multifiber connector is mounted upon the respective first ends of a predetermined number of optical fibers, and wherein the printed circuit board assembly further comprises a plurality of second connectors mounted upon the respective second ends of said plurality of optical fibers, each of said second connectors mounted upon the respective second ends of less than the predetermined number of optical fibers.

16. A printed circuit board assembly according to claim 15 wherein said plurality of second connectors comprise a plurality of single fiber connectors mounted upon the second ends of respective optical fibers.

17. A printed circuit board assembly according to claim 12 further comprising a plurality of optoelectrical converters mounted upon said printed circuit board and disposed in optical communication with the second ends of respective ones of said optical fibers.

18. A printed circuit board assembly according to claim 17 further comprising electrical circuitry mounted upon said printed circuit board and disposed in electrical communication with said plurality of optoelectrical converters.

19. A printed circuit board assembly according to claim 12 further comprising a plurality of flexible optical circuits disposed upon the interior portion of said printed circuit board.

20. A printed circuit board assembly according to claim 19 wherein said printed circuit board has first and second opposed surfaces, and wherein at least one flexible optical circuit is disposed upon the interior portion of each of the first and second opposed surfaces of said printed circuit board.

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FIELD OF THE INVENTION

The present invention relates generally to flexible optical circuits and associated fabrication methods and, more particularly, to printed circuit board assemblies having flexible optical circuits and associated fabrication methods.

BACKGROUND OF THE INVENTION

Many modern telecommunications systems, computer systems and the like transmit and/or process both electrical signals and optical signals. Typically, optical signals are routed via optical fibers over relatively long distances in order to increase the transmission speed and efficiency relative to the propagation of electrical signals. In contrast, much of the signal processing analysis and storage is performed electrically. Thus, these systems must frequently convert optical signals to electrical signals, and electrical signals to optical signals.

Many modern telecommunications systems, computer systems and the like include a number of printed circuit boards or cards which plug into a back plane or mother board. As known to those skilled in the art, the back plane generally provides power as well as a reference voltage or ground to each of the printed circuit boards. In addition, the back plane provides a pathway by which the printed circuit boards communicate with each other.

Signals can be routed along the back plane either electrically or optically. If optical signals are routed along the back plane, the optical signals must generally be converted to electrical signals upon delivery to the printed circuit boards since the printed circuit boards typically include a number of electrical components for processing electrical signals.

In order for the printed circuit boards to plug into the back plane, at least one edge of each printed circuit board includes a number of electrical contacts for establishing electrical connection with corresponding contacts defined by the back plane. In order to establish optical communication with one or more of the optical fibers routed along the back plane, the printed circuit board can also include one or more optoelectrical converters which as either a transmitter or a receiver. For example, an optoelectrical converter receives optical signals and converts those optical signals into corresponding electrical signals prior to routing the electrical signals about the printed circuit board. Instead, the optoelectrical converter could convert electrical signals into corresponding optical signals prior to routing the optical signals along the back plane.

As will be apparent, however, a separate optoelectrical converter is necessary for each optical fiber which is routed to the printed circuit board. If very many optoelectrical converters are mounted along the edge of the printed circuit board, the optoelectrical converters will consume a significant portion of the edge. As a result, the number of other contacts, such as electrical contacts, that can be established at the edge of the printed circuit board will be reduced as the number of optoelectrical converters positioned along the edge of the printed circuit board increases.

Attempts to interconnect optical fibers to the printed circuit board at locations other than the edge of the printed circuit board that plugs into the back plane have disadvantages. Notably, the interconnection of one or more optical fibers to the printed circuit board at a location other than the edge of the printed circuit board which plugs into the back plane will generally hinder the insertion and removal of the printed circuit board since the optical fibers must typically be separately handled to prevent tangling. In this regard, fiber management is becoming of ever increasing importance to a system designer as the number and lengths of the optical fibers increase. As a result, system designers generally strive to control the routing of the optical fibers so as to prevent the optical fibers from interfering with other components or from otherwise causing congestion.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a printed circuit board assembly which communicates with one or more optical fibers in a manner which makes efficient use of the edge portions of the printed circuit board.

It is another object of the present invention to provide a printed circuit board assembly which communicates with one or more optical fibers that are controllably routed along the printed circuit board.

It is further an object of the present invention to provide an improved method of fabricating a flexible optical circuit.

These and other objects are provided, according to the present invention, by a printed circuit board assembly having a flexible optical circuit and an associated method of fabricating the flexible optical circuit. The printed circuit board assembly includes a printed circuit board having an interior portion upon which the flexible optical circuit is mounted and edge portions surrounding the interior portion. The flexible optical circuit includes a pair of at least partially flexible sheets and a number of optical fibers disposed between the at least partially flexible sheets such that the first and second ends of each of the optical fibers extend outwardly beyond the pair of at least partially flexible sheets. The first ends of the optical fibers extend toward an edge portion of the printed circuit board. In order to conserve space along the edge of the printed circuit board while providing interconnections for each of the optical fibers, a multifiber connector can be mounted upon the respective first ends of a predetermined number of optical fibers. However, the second ends of the optical fibers lie within the interior portion of the printed circuit board which is generally less populated and, therefore, less valuable than the edge portions of the printed circuit board.

Each of the optical fibers of the flexible optical circuit includes a core and cladding, a coating layer surrounding the core and cladding, and a buffer layer surrounding portions of the coating layer. According to one advantageous embodiment, the buffer layer and the coating layer surround the core and cladding proximate the second ends of the optical fibers. In contrast, the first ends of the optical fibers are free of at least the buffer layer and, more preferably, both the buffer layer and the coating layer. In order to provide strain relief as well as to enhance the other mechanical properties of the optical fibers, the buffer and coating layers advantageously extend from a location proximate the second ends of the optical fibers and outward of the edge of flexible sheets to a location between the at least partially flexible sheets. In one embodiment, the buffer and coating layers terminate at a location at least 2 mm inward of an edge of the at least partially flexible sheets.

The printed circuit board assembly can also include a number of second connectors mounted upon the respective second ends of the optical fibers. The second connectors are typically single fiber connectors mounted upon the second end of a respective optical fiber. According to the present invention, however, the second connectors can be multifiber connectors so long as the second connector is mounted upon the respective second ends of a number of optical fibers that is less than the predetermined number of optical fibers upon which the multifiber connector is mounted. In this fashion, the optical fibers can be fanned out, typically to a number of spaced apart single fiber connectors, without requiring each of the single fiber connectors to be mounted along an edge portion of the printed circuit board, thereby making more efficient utilization of the edge portion of the printed circuit board.

The printed circuit board assembly can also include a number of optoelectrical converters mounted upon the printed circuit board and disposed in optical communication with the second ends of respective ones of the optical fibers. Thus, the optical signals can be converted to corresponding electrical signals for subsequent processing by the printed circuit board assembly. In this regard, the printed circuit board assembly can include electrical circuitry mounted upon the printed circuit board and disposed in electrical communication with the optoelectrical converters.

In order to make even more efficient utilization of the interior portion of the printed circuit board, the printed circuit board assembly can include a number of flexible optical circuits disposed upon the interior portion of the printed circuit board. For example, at least one flexible optical circuit can be disposed upon the interior portion of each of the opposed surfaces of the printed circuit board.

In order to efficiently fabricate the flexible optical circuit of the present invention, a method has also been developed which preconnectorizes the second ends of a plurality of optical fibers prior to disposing the optical fibers between the pair of at least partially flexible sheets. In this manner, the predetermined optical fibers can be tested to ensure that the connectors have been properly mounted prior to bonding or otherwise securing the optical fibers between the at least partially flexible sheets. If one or more of the connectors are improperly mounted, the optical fiber can be scrapped or reworked and another properly connectorized optical fiber can be disposed between the at least partially flexible sheets. In this manner, the reliability of the resulting flexible optical circuit is significantly increased.

Therefore, the printed circuit board assembly of the present invention effectively interconnects one or more optical fibers to the appropriate components upon the printed circuit board, while reducing the amount of space required along the edge portion of the printed circuit board for establishing optical communication with optical fibers routed along a back plane. As a result, an increased number of connections, both electrical and mechanical, can be established along the edge portion of the printed circuit board. In addition, by sandwiching the optical fibers that extend from an edge portion of the printed circuit board to an interior portion of the printed circuit board between a pair of at least partially flexible sheets, the printed circuit board assembly effectively manages the optical fibers to prevent splaying or other undesirable movement of the optical fibers.

By preconnectorizing the optical fibers prior to securing the optical fibers between the pair of at least partially flexible sheets, the method of the present invention can more reliably fabricate a fully functional flexible optical circuit. In this regard, the preconnectorized optical fibers can be tested for proper performance prior to securing the optical fibers between the pair of at least partially flexible sheets, thereby permitting relatively easy replacement of any preconnectorized optical fiber that proves to be defective without scrapping an entire flexible optical circuit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a printed circuit board assembly that is plugged into a back plane of the present invention.

FIG. 1A is an enlarged plan view of a portion of the printed circuit board assembly of FIG. 1.

FIG. 2 is cross-sectional view of the printed circuit board assembly of FIG. 1 taken along lines 2--2.

FIG. 2A is an enlarged cross-sectional view of an optical fiber bonded between a pair of at least partially flexible sheets.

FIG. 3 is a top plan view of a printed circuit board assembly of another embodiment of the present invention which includes flexible optical circuits disposed on both major surfaces thereof.

FIG. 4 is a flow chart illustrating the operations performed during the fabrication of a flexible optical circuit according to one advantageous embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout.

Referring now to FIG. 1, a printed circuit board assembly 10 according to one advantageous embodiment of the present invention is illustrated. The printed circuit board assembly includes a printed circuit board 12 that is illustratively plugged into a back plane 14 or motherboard along a first edge 12a thereof. The printed circuit board generally includes a number of electrical contacts or connections along the first edge for making electrical contact with the corresponding connectors on the back plane. According to the present invention, the printed circuit board assembly also has a connector for establishing optical communication with one or more optical fibers routed along the back plane, as described hereinbelow.

According to the present invention, the printed circuit board assembly 10 includes a flexible optical circuit 16 disposed upon an interior portion 12b of the printed circuit board 12, as shown in FIG. 2. As shown in FIGS. 2 and 2A, the flexible optical circuit includes a pair of at least partially flexible sheets 18. According to one advantageous embodiment, the at least partially flexible sheets are formed of MYLAR.RTM. OR KAPTON.RTM. films. While the flexible sheets can be formed of a variety of materials, both flexible sheets preferably have the same mechanical properties and oftentimes are formed of the same material. The at least partially flexible sheets can have a variety of thicknesses. According to one advantageous embodiment, however, the at least partially flexible sheets are formed of MYLAR films having a thickness of 6 mils. The thickness of the sheets can be varied, however, in order to modify the flexibility of the flexible optical circuit since the flexibility of the flexible optical circuit generally varies in an inverse manner with respect to the thickness of the sheets.

The flexible optical circuit 16 also includes a number of optical fibers 20 secured between the at least partially flexible sheets 18, typically by means of an adhesive 22 and, more preferably, by means of a pressure sensitive adhesive, such as VHB adhesive supplied by 3M. The optical fibers extend between respective first and second ends 20a and 20b. As shown in FIG. 1, the flexible optical circuit is disposed upon the interior portion 12b of the printed circuit board 12 such that the first ends of the optical fibers extend toward an edge portion 12a of the printed circuit board, while the second ends of the optical fibers lie within the interior portion of the printed circuit board. However, both the first and second ends of the optical fibers extend outwardly beyond the pair of at least partially flexible sheets. Although not illustrated, the at least partially flexible sheets can include a number interconnected fingers or strips, each of which encapsulates at