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FIELD OF THE INVENTION
The present invention pertains to optical interconnects and more
specifically to apparatus for connecting photonic devices to optical
fibers.
BACKGROUND OF THE INVENTION
Generally, in the area of data communication it is a well known fact that
optical fibers have the capability of carrying many more signals and with
a much broader bandwidth than copper or other hardwire systems. To
communicate through optical fibers or optical data links, it is necessary
to position an optical transmitter, such as a laser, light emitting diode,
etc., at one end of the optical fiber and a light receiver, such as a
light detector, light sensitive diode, etc., at the other end. Light
transmitters and light receivers are generally referred to in the art as
photonic devices.
To date, the major problem with optical fiber data links is the fabrication
of photonic to optical fiber packages. Generally, it is desirable to
include the photonic devices in electronic packages which utilize the
electric signals and to have the ability to connect/disconnect a cable or
ribbon of optical fibers between two electronic packages. For example, it
is desirable to communicate data between peripherals and a computer,
usually at as high a speeds as are possible.
In the past, many large and expensive connectors have been developed for
connecting large optical cables to data terminals. Because these cables
are used to carry data over very long paths (e.g. telephone
communication), the expense and size of the connectors is not a factor
compared to the expense and size of the overall system. However, when the
object is to carry data a few meters or less between adjacent pieces of
electronic equipment, the size and cost of the connectors at each end of
the optical interconnect cable are a major portion of the cost of the
cable.
Accordingly, it would be highly beneficial to be able to manufacture
optical interconnect cables and connectors with a relatively small cost
and size.
It is a purpose of the present invention to provide a new and improved
optical package with standard semiconductor chip attachment.
It is another purpose of the present invention to provide a new and
improved optical package which is small and easily disconnected from the
optical cable.
It is yet another purpose of the present invention to provide a new and
improved optical package which is simpler and less expensive to
manufacture.
It is still another purpose of the present invention to provide a new and
improved optical package which contains very few parts relative to some
prior art packages and which uses relatively standard equipment (in the
semiconductor industry) and components in the fabrication and assembly.
SUMMARY OF THE INVENTION
The above problems and others are at least partially solved and the above
purposes and others are realized in an optical package including a housing
defining a mounting area with leads formed in the housing each having a
first end in the mounting area and a second end external to the housing. A
semiconductor die with a photonic device thereon is mounted in the
mounting area and electrically connected to the leads. The active light
area of the photonic device is accessible through the mounting area.
Optical fiber alignment structure is mounted in the mounting area for
receiving an optical fiber and aligning the optical fiber with the active
light area of the photonic device.
The above problems and others are at least partially solved and the above
purposes and others are realized in a method of fabricating an optical
package including the steps of forming a housing defining a mounting area
with a plurality of leads positioned in the housing, each having an end in
the mounting area and an end external to the housing, providing a
semiconductor die including at least one photonic device with a plurality
of electrical terminals and an active light area, mounting the
semiconductor die on the housing in the mounting area with the active
light area accessible through the mounting area and electrically
connecting the terminals to the leads, and forming optical fiber alignment
means for receiving an optical fiber and aligning the optical fiber with
the active light area of the photonic device and mounting the optical
fiber alignment means on the housing in the mounting area.
BRIEF DESCRIPTION OF THE DRAWINGS
Referring to the drawings:
FIG. 1 is a view in top plan of a portion of an optical package embodying
the present invention;
FIG. 2 is a simplified, or semi-schematic, perspective view of a step in
the assembly of an optical package utilizing the portion of FIG. 1;
FIG. 3 is a view in bottom plan of a portion of the apparatus of FIG. 2;
FIG. 4 is a top view of laser die as seen from the assembly apparatus
utilized in the step of FIG. 2;
FIG. 5 is an enlarged perspective view of the partially assembled optical
package;
FIG. 6 is a view in side elevation of the optical package of FIG. 5;
FIGS. 7 and 8 are perspective views of different portions of another
optical package embodying the present invention;
FIG. 9 is a perspective view illustrating the assembly of the portions
illustrated in FIGS. 7 and 8;
FIG. 10 is a perspective view of the portions illustrated in FIGS. 7 and 8
assembled into an optical package embodying the present invention;
FIG. 11 is an enlarged sectional view of the optical package illustrated in
FIG. 10; and
FIG. 12 is an enlarged sectional view, similar to FIG. 11, of another
embodiment of an optical package embodying the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring specifically to FIG. 1, a view in top plan of a portion of an
optical package 10 embodying the present invention is illustrated. The
portion of optical package 10 illustrated in FIG. 1 includes a substrate
15, a lead frame 20 and a generally rectangularly shaped collar 25. In
this embodiment, substrate 15 has a plurality of electrical traces, or
leads, 16 formed on the surface thereof and lead frame 20 is physically
and electrically bonded to leads 16 by any of the convenient methods known
and utilized in the semiconductor industry, such as soldering, spot
welding, brazing, etc. Leads 16 also define an area on which a
semiconductor die 17 including one or more photonic devices is mounted.
Each photonic device in semiconductor die 17 includes electrical terminals
which are connected to leads 16 by means of a common wire bonder.
Rectangularly shaped collar 25 is positioned on substrate 15 so as to
encircle semiconductor die 17 and to provide areas 18 which are free of
electrical leads and which will receive alignment pins to be explained
presently. Substrate 15 and collar 25 cooperate to form a housing 26
defining a mounting area 3 therein. It should be noted that in this
embodiment, mounting area 3 is a cavity, but it may be a surface, a
substrate, etc. It will of course be understood by those skilled in the
art that housing 26 and mounting area 3 can be formed utilizing other
processes, such as molding or the like. Further, if housing 26 is formed
by molding, leads 16 and leadframe 20 could be molded into housing 26 as a
single unit.
Utilizing a standard precision die bonder (e.g. an RDI Bonder), the
structure described in conjunction with FIG. 1 is positioned on a lower
chuck 27, as illustrated semi-schematically in FIG. 2. An upper alignment
fixture 28 is provided. Fixture 28 includes a plurality or line of holes
29 therethrough (see FIG. 3), one for each photonic device in
semiconductor chip 17 and spaced apart so as to coincide with an active
light area for each photonic device on semiconductor chip 17. Fixture 28
also includes two larger holes 30, one positioned at each end of the line
of holes 29, and each constructed to receive an elongated alignment pin 32
(see FIG. 2) positioned therein.
In the present assembly procedure using the precision die bonder, pins 32
are placed in holes 30 and the precision die bonder features are utilized
to align holes 29 with the active light areas of the photonic devices,
which appear generally as illustrated in FIG. 4. Holes 29 may also be
replaced with target fiducials in fixture 28, as will be understood by
those skilled in the art of die bonder operations. As alignment of fixture
28 with die 17 is achieved, the die bonder raises chuck 27 to within some
predetermined distance (in this embodiment approximately 0.002 inches)
from fixture 28. Alignment pins 32 are then pushed through openings 30
into abutting engagement with the surface of substrate 27. Pins 32 are now
accurately aligned with respect to the active light areas of the photonic
devices on semiconductor die 17.
Mounting area 3 is filled with a curable plastic, such as epoxy or the like
to fix pins 32 in the aligned position. In most applications the curable
plastic will not only surround and hold the lower ends of pins 32 but will
cover semiconductor die 17 and leads 16. When the curable plastic covers
semiconductor die 17, it is desirable that the curable plastic be a
material that cures optically clear so that light can travel freely
therethrough to and/or from the active light areas of the photonic
devices. Further, in some applications the depth of mounting area 3 may
not be sufficient to ruggedly fix pins 32 in the aligned position. In such
applications it may be convenient and/or desirable to form deeper
depressions or holes at areas 18, with a substantially larger diameter
than pins 32, to receive pins 32 therein. Thus, when mounting area 3 and
the deeper depressions are filled with plastic, the mechanical mounting of
pins 32 will be substantially enhanced. Generally, the curable plastic
material filling mounting area 3 is cured by heating substrate 15, or use
of ultra-violet light, or some other convenient method.
Referring to FIGS. 5 and 6, perspective and side elevational views are
illustrated, respectively, of a substantially completed optical package
10. In these figures, lead frame 20 has not been trimmed, or the leads
formed into the final configuration. Also, some additional encapsulation
may be provided if desired or deemed advantageous. Generally, however,
optical package 10 is ready to be mounted in a piece of electronic
equipment with the leads (once trimmed and formed) electrically attached
as data inputs/outputs.
To connect a fiber optic cable or ribbon to optical package 10, one simply
uses a standard connector (not shown), such as the well known MT
Connector, attached to a fiber optic cable or ribbon. Alignment pins 32
are positioned to engage alignment sockets in the standard connector, and
the end of each optical fiber in the fiber optic cable or ribbon will be
accurately aligned with the active optic areas of the photonic device in
chip 17. It will of course be understood that alignment sockets could be
substituted for alignment pins 32 so that a male optical connector, rather
than a female optical connector, can be removably connected therewith.
Referring to FIGS. 7-11, another embodiment of an optical package 50
constructed in accordance with the present invention is illustrated. A
housing 52 is formed, as illustrated in FIG. 7, including a plurality of
leads 55 and a mounting area 56. As described in conjunction with the
previous embodiment, housing 52 can be formed by providing a substrate
with electrical traces or leads formed thereon and a leadframe attached
thereto or by simply molding housing 52 with a single leadframe positioned
therein. If housing 52 is formed from a substrate, semiconductor die 57,
including one or more photonic devices, is mounted on the surface of the
substrate and electrically connected to the leads. A ring shaped collar 58
is then fixedly mounted on the surface of the substrate surrounding the
semiconductor die and defining mounting area 56. If housing 52 is molded,
mounting area 56 is defined in the surface with ends of the leads exposed
therein. The semiconductor die is then bonded in the mounting area.
An insert 60 is formed as illustrated in FIG. 8, having a cross-section
which matches, but is smaller, than mounting area 56. Generally, insert 60
has a substantially cylindrical cross-section (circular in this specific
embodiment, however it may be rectangular, etc.) with a first end formed
to fit into mounting area 56 and a second end extending outwardly
externally to mounting area 56. Also, insert 60 includes a section of
fiber optic ribbon 62 positioned therein with a first end in the first end
of insert 60 and a second end in the second end of insert 60. Fiber optic
ribbon 62 is cut and polished at each end to form an optical input/output.
A pair of alignment sockets (or holes) 64 are formed in the second end of
insert 60 and adapted to receive alignment pins of a standard optical
connector, such as the well known MT Connector or the like. In this
specific embodiment, insert 60 is molded with fiber optic ribbon 62
extending therethrough and alignment sockets 64 aligned with fiber optic
ribbon 62 so that a male optical connector with alignment pins engaged in
alignment sockets 64 is accurately aligned with fiber optic ribbon 62. It
will of course be understood that alignment pins could be substituted for,
or engaged permanently in, alignment sockets 64 so that a female optical
connector can be removably connected therewith.
Also, in this embodiment insert 60 can be constructed as a modal noise
filter to substantially prevent ambient or unwanted light from entering
the system and to reduce cross-talk between channels. A variety of
different engineering concepts can be designed into the modal noise filter
to prevent or reduce certain types of interference that may be prevalent
in different application. For example, by precisely forming the length of
fiber optic ribbon 62, light reflection from semiconductor die 57 returned
into the optic link can be minimized.
In a preferred embodiment as shown specifically in FIG. 9, the plurality of
optical fibers in fiber optic ribbon 62 extend in a line substantially
parallel to a line through the axes of alignment sockets 64. This provides
the advantage of requiring alignment with only one optical fiber, rather
than an entire line of optical fibers, the spaces there between and any
variations therein. It should be noted that the position of sockets 64 in
FIG. 9 differs from that in FIGS. 7, 8, 10, and 11 to illustrate this
preferred embodiment.
In the assembly procedure, illustrated generally in FIG. 9, insert 60 is
positioned in mounting area 56 so that fiber optic ribbon 62 is
substantially aligned with the active light areas of the photonic devices
in semiconductor die 57. Alignment of fiber optic ribbon 62 with the
active light areas can be performed with a precision die bonder, generally
as described in conjunction with the previous embodiment, by accurate
indexing, or by a technique known as active alignment. In active
alignment, light is directed into the external end of each of the optical
fibers in fiber optic ribbon 62 and sensed at semiconductor die 57, or
vice versa. Insert 60 is then moved within mounting area 56 until the
maximum light indication is achieved.
Once fiber optic ribbon 62 is properly aligned with the active light areas
of the photonics devices on semiconductor die 57, an adhesive such as
epoxy or the like is introduced into mounting area 56 around insert 60 and
appropriately cured so as to fix insert 60 in the aligned position,
generally as illustrated in FIGS. 10 and 11. It should be understood that
the adhesive could be preapplied and cured by U.V., heat, etc. By sealing
insert 60 tightly in mounting area 56, no extraneous light can enter
optical package 50 and the alignment of the various components is
retained.
Generally, optical package 50 is ready to be mounted in a piece of
electronic equipment with the leads electrically attached as data
inputs/outputs. To connect a fiber optic cable or ribbon to optical
package 50, one simply uses a standard connector (not shown), such as the
well known MT Connector, attached to a fiber optic cable or ribbon.
Alignment sockets 64 are positioned to engage alignment pins in the
standard male connector, and the end of each optical fiber in the fiber
optic cable or ribbon of the standard connector will be accurately aligned
with the active optic areas of the photonic device in die 57. As explained
previously, alignment pins could be substituted for, or engaged
permanently in, alignment sockets 64 so that a female optical connector
can be removably connected therewith if desired.
Referring specifically to FIG. 12, a slightly different embodiment of an
optical package 70 is illustrated. In this embodiment a housing 72 with
leads 74 positioned (molded, etc.) therein, defines a mounting area 76,
generally by any of the methods previously described. In this embodiment a
semiconductor die 80 is positioned in mounting area 76, as previously
described, and a pair of alignment sockets 82 are formed in housing 72
adjacent to and aligned with semiconductor die 80. Alignment sockets 82
can be formed and aligned using any of the techniques previously described
for aligning other components, including but not limited to molding.
Generally, optical package 70 is ready to be mounted in a piece of
electronic equipment with the leads electrically attached as data
inputs/outputs. To connect a fiber optic cable or ribbon to optical
package 70, one simply uses a standard connector, such as the well known
MT Connector (a male connector 85 is illustrated in the engaged position
in FIG. 12), attached to a fiber optic cable or ribbon. Alignment sockets
82 are positioned to engage alignment pins 84 in standard male connector
85, and the end of each optical fiber in standard connector 85 is
accurately aligned with the active optic areas of the photonic device in
semiconductor chip 80. Again, alignment pins could be substituted for, or
engaged permanently in, alignment sockets 82 so that a female optical
connector can be removably connected therewith, rather than male connector
85, if desired.
Thus, a new and improved optical package is provided, which optical package
is small and easily disconnected from the optical cable. Further, the new
and improved optical package is simpler and less expensive to manufacture.
Also, the new and improved optical package contains very few parts
relative to some prior art packages and uses relatively standard equipment
(in the semiconductor industry) and components in the fabrication and
assembly.
While we have shown and described specific embodiments of the present
invention, further modifications and improvements will occur to those
skilled in the art. We desire it to be understood, therefore, that this
invention is not limited to the particular forms shown and we intend in
the append claims to cover all modifications that do not depart from the
spirit and scope of this invention.
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