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Description  |
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BACKGROUND OF THE INVENTION
The present invention relates to flexible optical circuits. In particular,
the present invention relates to flexible optical circuits having a
backing layer, an adhesive coating and a release liner for attachment to a
substrate such as an electronic printed circuit board.
The design of electronic circuits requires interconnections between devices
for proper operation. With increased sophistication and operation speeds,
design of functional interconnections requires careful engineering. The
fastest data processing circuits and emerging technologies require large
numbers of interconnects capable of carrying extremely high speed digital
signals. Due to the increasing push for higher and higher speeds,
engineers are facing fundamental limits in designing electronic
interconnects.
In an attempt to handle higher speeds, interconnection technology has
turned to optical interconnects for next generation circuits. Optical
circuits have bandwidth capabilities orders of magnitude beyond electrical
circuits, and are inherently immune to electrical interference. In some
known designs, discrete fiber optic cables and fiber bundles are used to
interconnect devices. Known standard fiber optic connection technology
employed to connect optical fibers to devices are adequate for small
numbers of interconnections. However, as optical circuit density grows,
the physical bulk of cables and connectors make this approach unwieldy,
especially for compact designs.
Attempts have been made to incorporate optical interconnects onto the
surface of electronic circuit boards and substrates by constructing wave
guides using optical polymers coated to the surface. An example of this is
found in U.S. Pat. No. 5,521,992 to Chun, et al. The technology of the
'992 patent requires highly specialized tooling to generate each custom
optical circuit thus standard circuit boards cannot be used. For simple
circuits, tooling costs may be prohibitive. Waveguide fabrication is also
difficult due to the small geometry of the guide regions, and optical
quality of finished wave guides is poor due to limitations in optical
polymer chemistry.
Flexible optical interconnect circuit packs are also known in the art. An
example of this is found in U.S. Pat. No. 5,204,925 to Bonanni, et al. The
known optical interconnect circuits have optical fibers bonded between two
flexible substrates and have one or more optical connectors connected
along the edges of the circuit pack. The connectors are then connected to
one or more optical devices. These known devices are not adapted to bond
to a substrate or circuit board.
The concept of using high bond strength pressure sensitive adhesive coated
laminating films is not new. However, there are certain problems
associated with the known adhesive coated films. For instance, it is often
difficult to obtain accurate positioning during film use. Improper
placement, static charge, and accidental contact can all contribute to
misalignment and immediate bonding to the surface in undesired positions.
Because of the immediate aggressive bonding, if alignment is off, the film
is often destroyed or seriously damaged attempting to remove the film for
repositioning.
One known solution to the above problem is to use a less aggressive
adhesive so the user may remove or reposition the film in case of
misalignment. This can result in poor long term adhesion. Another known
solution is to use a partially cured adhesive material followed by a final
curing process. This not only results in additional process step, but may
be impractical for many applications. Yet another known solution is to
prepare a surface wetted with a material that interferes with adhesion and
then removing the wetting agent after final alignment is achieved. This
approach can be messy and adds process steps.
There is a continuing need for flexible optical circuits capable of being
applied to new circuit board designs without changing board design and
fabrication techniques. There is also a continued need for a laminating
film that allows for repositioning of the optical circuits to achieve
proper alignment.
SUMMARY OF THE INVENTION
The present invention provides a flexible optical circuit applique that can
be mounted on a circuit board without modifying the circuit board
substrate or the electronic circuits. The optical circuit applique of the
present invention is also repositionable. A method of manufacturing
flexible optical circuit appliques is also provided.
A preformed fiber optic applique is provided having a backing layer. The
backing layer or film, has an adhesive coating applied thereon. At least
one optical fiber is routed and bonded to the adhesive layer providing a
continuous optical signal path from one end to another. A releasable liner
is releasably attached to the adhesive layer and positioned to cover the
backing layer including the at least one optical fiber.
In one embodiment of the present invention, microstructures are provided on
the backing layer. The microstructures are crushable structures that
prevent the adhesive coating from immediately adhering to a substrate.
This allows the film to be repositioned until proper alignment has been
achieved. Upon the application of appropriate force, the microstructures
will crush allowing the adhesive coating to bond the film to the
substrate.
A method of fabricating the fiber optic appliques of the present invention
is also disclosed. The method includes the steps of providing a supply of
backing layer and applying an adhesive coating to the backing layer. At
least one fiber is then provided and placed on the adhesive coating.
Pressure is then applied to the at least one fiber to secure it to the
backing layer.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an exploded perspective view of an electrical circuit board and a
flexible optical circuit applique according to the present invention.
FIG. 2a illustrates a preferred method of fabricating an optical circuit
applique according to the present invention.
FIG. 2b illustrates an alternative method of fabricating an optical circuit
applique according to the present invention.
FIGS. 3a, b, c, and d illustrate alternative embodiments of a continuous
web with fibers available for connectorization.
FIGS. 4a, b, and c illustrate standard sections of optical circuit
appliques according to the present invention.
FIGS. 5a and b are top and side perspective views of the flexible optical
circuit having microreplicated structures according to the present
invention.
FIGS. 6a and b are top and side perspective views of the flexible optical
circuits of FIGS. 5a and b having optical fibers placed thereon.
FIGS. 7a, b, c and d illustrate steps in a method for fabricating a
flexible optical circuit and terminating the optical connectors at sockets
according to the present invention.
FIG. 8 is a side perspective view of a first alternative embodiment of the
present invention.
FIG. 9 is a side perspective view of a second alternative embodiment of the
present invention.
FIG. 10 is a side perspective view of a third alternative embodiment of the
present invention.
DETAILED DESCRIPTION OF THE INVENTION
The present invention provides a flexible optical circuit applique having a
flexible backing with fibers bonded thereto covered by a releasable liner.
The optical appliques are intended to provide an easy means for adding
optical circuits to electronic circuit boards or other substrates by
laminating. The flexible optical circuits of the present invention can
also be incorporated into new board designs without changing standard
board design and fabrication techniques. The optical appliques of the
present invention are also repositionable on a substrate prior to bonding.
FIG. 1 is a perspective view of a preferred embodiment of a flexible
optical circuit applique 10 according to the present invention. Also
illustrated is a printed circuit board 12 to which applique 10 is to be
mounted. Applique 10 comprises a durable backing material 14 that is
coated with a temporarily repositionable adhesive 16. Applique 10 also
includes optical fibers 18 bonded to backing 14 via adhesive 16. The
particular backing material used depends upon the particular application.
For instance, if high durability is desired, a polyester-type backing
would be used. If the applique is to be mounted on a curved substrate, a
flexible backing material would be chosen. Examples of backing materials
include vinyl, polyurethane, polyamide, and polyester.
Adhesive 16 of the present invention is any temporarily repositionable
adhesive. By temporarily repositionable, it is meant that the bond between
the adhesive and the substrate is such that the material having the
adhesive may be removed from the substrate without damaging either for a
period of time or until the occurrence of a specified event which then
permanently adheres the backing to the substrate. In the preferred
embodiment, adhesive 16 is preferably a pressure sensitive adhesive.
Pressure sensitive adhesives are known in the industry as a standard class
of materials. They are adhesives, which in dry form (substantially solvent
free except for residual solvent) are aggressively and permanently tacky
at room temperature (approximately 15.degree. to 25.degree. C.) and firmly
adhere to a variety of similar surfaces upon mere contact without the need
for more than manual pressure. The adhesives require no activation by
water, solvent, or heat in order to exert a strong adhesive holding force
towards such materials as paper, cellophane, glass, plastic, wood, and
metals. The adhesives have a sufficiently cohesive holding and elastic
nature such that, despite their aggressive tackiness, it can be handled
with fingers and removed from smooth surfaces without leaving a
substantial residue. For a more detailed discussion of pressure sensitive
adhesives, reference should be made to U.S. Pat. Nos. 5,296,277, 5,362,516
and 5,449,540, which are assigned to the Assignee of the present invention
and the disclosures of which are herein incorporated by reference.
If adhesive 16 has low tack, e.g. is only slightly sticky to the touch and
has low adhesion to certain types of surfaces, a release liner may not be
required to cover the adhesive layer, and the backing material 14 may act
as a release liner when the film is rolled.
A light cured adhesive could be used with a transparent backing layer
without departing from the spirit or scope of the invention. Such an
adhesive would allow the film to be repositioned on a substrate until a
light source, typically an ultra violet light, is applied through the
transparent film which would then activate the adhesive to secure the film
to the substrate. Nonpressure sensitive adhesives, heat curable adhesives
thermally activated adhesives such as hot melt glue or solvent activated
adhesives could also be used if desired, without departing from the spirit
or scope of the invention. They are, however, less preferred embodiments
because of the additional application steps and greater tendency to entrap
air during application.
Optical fibers 18 of the present invention are preferably 80 to 100 micron
glass (silica) diameter fibers with a special fiber coating described in
U.S. Pat. No. 5,381,504. Standard glass optical fibers have 125 micron
outside diameters. By using glass fibers with diameters of 80 to 100
microns, the present invention can obtain bend radiuses as small as 0.25
inches (0.64 cm) while staying below a bending stress of 100 K psi. At a
bend radius of 0.25 inches (0.64 cm), a fiber having a diameter of 125
microns has a bending stress of approximately 110 K psi and a fiber having
a diameter of 200 microns has a bending stress of approximately 175 K psi.
In the preferred embodiment of the present invention, bend radii of less
than 0.3 inches (0.76 cm) are achieved at bend stresses of less than 100 K
psi.
FIG. 2a illustrates a preferred method of fabricating an applique according
to the present invention. A supply roll 20 of applique backing layer or
film, 14 is provided, as is a takeup roll 22. Film 14 is precoated with an
adhesive layer 16 and covered with a releasable liner 17. A second takeup
roller 19 is provided to take away releasable liner 17 as illustrated. A
rotating drum 24 is provided to move backing film 14 from supply roll 20
to takeup roll 22. Multiple spools 28 of fibers 18 are provided and are
suspended above backing film 14. A laminating roll spacing guide 30 is
provided to space fibers 18 as desired and to press the fibers onto
backing film 14 with sufficient force to activate pressure sensitive
adhesive 16 to bond fibers 18 in place. A second supply roller 32 is
provided carrying a second releasable liner 34 which releasably adheres to
pressure sensitive adhesive 16. It should be noted that film 14 may be a
continuous and solid film or it may have holes formed therethrough for
connectorization with optical circuit components, as will be described in
greater detail below.
FIG. 2b illustrates an alternative method of fabricating an applique
according to the present invention. FIG. 2b is similar to FIG. 2a and thus
like elements are correspondingly identified. Supply roll 20 of applique
backing film 14 is provided as is takeup roll 22. Rotating drum 24 is
provided to move backing film 14 from supply roll 20 to takeup roll 22. A
pressure sensitive adhesive coating device 26 is provided to apply a
coating of pressure sensitive adhesive 16 to backing film 14 as the
backing film comes off of supply roll 20. Multiple spools 28 of fibers 18
are provided and are suspended above backing film 14. Laminating roll
spacing guide 30 is provided to space fibers 18 as desired and to press
the fibers onto backing film 14 with sufficient force to activate pressure
sensitive adhesive 16 to bond fibers 18 in place. Second supply roller 32
is provided carrying release liner 34 which releasably adheres to pressure
sensitive adhesive 16.
One alternative method of optically connecting a plurality of optical
components on a substrate includes the steps of providing a backing layer,
providing at least one optical fiber coated with an adhesive, placing the
optical fiber on the backing layer in a desired pattern and releasably
securing the fiber to the backing layer. The fiber and the backing layer
are placed on a substrate in a desired position and the fiber is fixedly
adhered to the substrate. The backing layer may be removed while leaving
the fiber adhered to the substrate.
Fabricating appliques in a continuous web process, as illustrated in FIGS.
2a and 2b is a very cost effective way to fabricate the appliques.
Depending upon the length of appliques desired, large numbers of standard
appliques can easily be made from a single roll of backing film 14.
FIGS. 3a-3d illustrate alternative ways to make fibers 18 available for
connectorization in a continuous web process similar to those described in
FIGS. 2a and 2b above. It should be noted that the examples given below
are given only as exemplary ways to avail the fibers for connectorization,
and the examples given are not meant to be an exhaustive list. The
illustrations in FIGS. 3a-3d use some of the same components as used in
FIGS. 1 and 2, therefore, like elements will be correspondingly
identified. In FIG. 3a, film 14 is coated with adhesive layer 16. Fibers
18 are bonded to adhesive layer 16 as previously described. A release
strip 35 is provided across the width of film 14 at predetermined
intervals. The web is then cut at release strips 35. When applied to a
substrate, release strips 35 prevent the ends of the individual applique
section from adhering to the substrate thus allowing the ends of the
fibers to be prepared for connectorization. It should be noted that
release strip 35 not need to extend across the entire width of film 14. In
FIG. 3b, a series of receiving cavities 37 are formed through film 14. The
receiving cavities allow access to fibers 18 when the applique is adhered
to a substrate.
FIG. 3c illustrates a series of mechanical alignment devices 39 spaced at
desired locations along the continuous web. Alignment devices 39 provide
mechanical alignment for fibers 18 and also function as release liners.
Mechanical alignment devices 39 are preferably V grooved structures, but
may also be U shaped or other shapes that provide adequate alignment for
fibers 18. After fibers 18 have been adhered to adhesive surface 16 of
film 14, alignment device 39 may be removed prior to adhering to a
substrate. Alignment device 39 could also be left in place with the
applique adhered to a substrate. A connector assembly is then mounted
around the fibers. In FIG. 3d, an adhesiveless area 41 is provided on film
14. Thus, when film 14 is adhered to substrate, fibers 18 are not adhered
to the substrate in adhesiveless area 41.
The design of the applique according to the present invention including the
number of fibers, the spacing of the fibers as well as the routing
patterns can be done during the manufacturing process using a simple
process control computer software program. Therefore, a board designer may
layout a board and provide the manufacturer of the appliques of the
present invention a layout of the board and an applique may be quickly and
easily laid out by the process control program. Design and manufacture of
appliques of the present invention may be conducted by, for example, Icon
Industries, Euless, Tex.
FIGS. 4a, b and c illustrate some standard applique constructions. FIG. 4a
illustrates a 180.degree. bend applique 36. FIG. 4b illustrates a
90.degree. bend applique 38 and FIG. 4c illustrates a straight applique
40. Additional standard applique constructions besides the ones
illustrated in FIGS. 4a-c, such as 30.degree. bends, 60.degree. bends,
45.degree. bends etc., are also considered within the spirit and scope of
the present invention. Additionally a continuous web construction having
alternating patterns may be formed. Standard appliques such as those
discussed above can be premade and purchased ready to use. Because the
appliques of FIGS. 4a-c may be purchased as ready to use appliques, the
ends of fibers 18 are also prepared for connectorization.
It should be noted that the fibers illustrated in FIGS. 4a-4c are shown
stopping at the edge of the backing material. However, the fibers must be
available for connectorization. Thus, any of the methods for making fibers
available for connectorization, such as those described with respect to
FIGS. 3a-3d, may be utilized.
Appliques 10 can be applied to circuit boards 12 or other substrates by
users during the manufacturing process, by removing release liners 34 (not
shown in FIGS. 4a, 4b or 4c) from the adhesive surface and laminating the
applique to the circuit board surface. It should be noted that multiple
appliques can be placed over one another without degrading performance.
FIGS. 5a and b illustrate top and side perspective views of flexible
optical circuit applique 10 incorporating microreplicated structures 42
formed on backing film 14 and/or in adhesive surface 16. Microreplicated
structures 42 are provided to allow accurate positioning of applique 10.
Improper placement or accidental contact of an active adhesive surface can
contribute to misalignment and immediate bonding to the desired surface.
Because the microstructures protrude up from backing film 14 and are
taller than the depth of adhesive coating 16, microstructures 42 prevent
intimate contact between adhesive surface 16 and circuit board 12 or other
mounting surface. Structures 42 are crushable such that intimate contact
between adhesive surface 16 and circuit board 12 is obtained when suitable
pressure is applied. Thus, the present invention may be repositioned until
accurate alignment is achieved and further provides a high final bond
strength after lamination. The microreplicated structures of the present
invention are preferably approximately 15 micrometers high. Additionally,
the density or durometer of structures 42 can be varied to provide lesser
or greater resistance to crushing or forming. For a more detailed
description of microstructures 42, reference should be made to the above
mentioned U.S. Pat. Nos. 5,296,277, 5,362,516 and 5,449,540 the
disclosures of which were incorporated by reference. It should be noted
that alternative embodiments of microstructures 42 or other repositionable
adhesive constructions are also considered within the spirit and scope of
the present invention. For instance, the adhesive, which maybe partially
cured, may contain microspheres which may house a catalyst, either with or
without the presence of microstructures 42, such that when sufficient
force is applied, the microspheres, and microstructures if present, are
crushed and the catalyst is released, reacting with adhesive 16 to form an
aggressive adhesive.
FIGS. 6a and b illustrate an applique having microstructures 42 arranged in
desired patterns such that microreplicated structures 42 provide a guide
for routing fibers 18 in precise locations when bonded to adhesive surface
16. As illustrated in FIGS. 6a and 6b, fibers 18 fit into channels 44
between structures 42 and may thus be bonded to adhesive surface 16
without crushing structures 42. As previously stated, | | |
