 |
Description  |
|
|
BACKGROUND OF THE INVENTION
The present invention is generally directed to a system for providing
optical fiber connections to multi-chip electronic circuit modules. More
particularly, the present invention is directed to a connector and a
module/connector combination which is capable of providing optical fiber
connections to chips on a multi-chip module through the utilization of
standardly available fiber optic cable connectors. Even more particularly,
the present invention is directed to a mechanism for providing plugable
connections between exterior fiber optic cable packages and electronic
circuit chips disposed on an interior substrate. These chips include
communication means for generating and/or receiving optical fiber
transmission signals. The problems associated with connecting fiber optic
cable bundles and ribbon packages to multi-chip circuit modules are
discussed in U.S. Pat. No. 5,337,388 issued Aug. 9, 1994 and also in U.S.
Pat. No. 5,333,225 issued Jul. 26, 1994. Both of these patents are
assigned to the same assignee as the present application.
The problems encountered in trying to establish the above described
opto-electronic connections are generally severest with respect to the
problem of aligning hair-thin fiber optic cables with corresponding cables
in the connector, and with providing connections from the connector to
individual circuit chips. The problem of alignment is exacerbated by
changes in dimensioning produced by thermal effects. These thermal effects
arise from the heat that is generated within the electronic circuit chip
components. The thermal problems are worsened by operation of these
circuit chips at high frequencies, which are necessary to provide fast
circuit operation but which generate large amounts of heat. This is
particularly true in electronic components that are part of computer
systems.
In addition to the problems associated with thermal expansion, another
problem encountered in attempting to provide a suitable connector is the
problem of electrical isolation. Because electrostatic charges can
accumulate on fiber optic cables and on other associated plastic and
insulative components, it is very desirable to provide a mechanism by
which such static discharges may be dissipated without causing injury to
electronic circuit components which can be particularly sensitive to
static discharge.
Additionally, it is noted that a connector which mates optical fiber cables
to the interior of multi-chip modules should also provide a mechanism for
environmental isolation of the circuit chips from the exterior
environment. In particular, it is typically desirable to operate a
multi-chip module (MCM) in a variety of atmospheric conditions which may
include above average levels of relative humidity, dust and/or particulate
contamination. These atmospheric contaminants should in general be unable
to penetrate a seal designed to enclose a multi-chip module. Furthermore,
the connector should be compatible with sealing and cooling arrangements
which permit chip cooling mechanisms to be employed.
In short, it is seen that a cable connector for the present purposes should
be compatible with chip protection from contamination while nonetheless
being immune from thermal expansion effects and yet providing
electrostatic isolation for circuit chips inside the module.
SUMMARY OF THE INVENTION
In accordance with a preferred embodiment of the present invention, a
receptacle for a fiber optic cable connector comprises a plastic connector
receiving body with a recess for receiving a fiber optic cable connector.
This body is at least partially surrounded by a non-insulative jacket
which possesses a thermal expansion joint. A plurality of optical fibers
are disposed within the recess of the receiving body so as to extend from
the bottom of the recess to provide external connectivity. In a preferred
embodiment of the present invention, the jacket comprises a material such
as silicon, since silicon is compatible with manufacturing processes
involving the placement of silicon chips on ceramic and/or glass/ceramic
substrates. The recess in the receiving body preferably includes alignment
holes at the bottom of the recess which are disposed so as to receive
mating metal pins on standard fiber optic cable connectors. These pins and
mating holes achieve the desired alignment between the optical fibers in
the cable connector and the optical fibers in the receiving body which
extend from the body to a photonically sensitive regions on integrated
circuit chips in or on the MCM.
In accordance with a preferred embodiment of the present invention, the
above described receptacle is mated with a multi-chip module (MCM) in a
fashion which permits appropriate grounding to eliminate electrostatic
discharge problems. Additionally, the mating of the receptacle with a
multi-chip module is preferably carried out by placement of the receptacle
in a recess in the side of the MCM in a fashion which nonetheless still
permits the module to be sealed against environmental elements while still
maintaining connection, alignment, grounding and mechanical compatibility.
Accordingly, it is an object of the present invention to provide a
receptacle for connecting a fiber optic cable to the interior of a
multi-chip module which has a plurality of integrated circuits therein.
It is also an object of the present invention to provide an optical fiber
cable connector which may be easily grounded.
It is yet another object of the present invention to provide a fiber optic
cable receptacle which is capable of thermal expansion and contraction in
a fashion which does not interfere with alignment and which is at the same
time operable in the face of relatively high power levels being supplied
to electronic circuit chips within the module.
It is yet another object of the present invention to provide a fiber optic
connector which employs plastic material in the receiving body so as to
provide compatibility with industry standard fiber optic connectors.
It is another object of the present invention to provide a thermally
expansive jacket for mating external optical fiber cables to electronic
circuit components on a multi-chip module.
It is also an object of the present invention to provide a fiber optic
cable connection between the exterior and interior of a multi-chip module
without impairing the environmental seal between the interior and exterior
module portions.
It is still another object of the present invention to increase the
information bandwidth for transmission of information into and out of
multi-chip electronic circuit modules.
Lastly, but not limited hereto, it is an object of the present invention to
provide a fiber optic connection system between the interior and exterior
of a multi-chip module while at the same time providing electrostatic
discharge grounding means, and particularly to provide such grounding
means which are compatible with MCM production and processing.
BRIEF DESCRIPTION OF THE DRAWINGS
The subject matter which is regarded as the invention is particularly
pointed out and distinctly claimed in the concluding portion of the
specification. The invention, however, both as to organization and method
of practice, together with the further objects and advantages thereof, may
best be understood by reference to the following description taken in
connection with the accompanying drawings in which:
FIG. 1 is a partially cross-sectional side elevation view illustrating the
fiber optic receptacle of the present invention in position in a
multi-chip module;
FIG. 2 is a partial isometric view illustrating a multi-chip module
substrate, such as that shown in FIG. 1, which has been fabricated to
accommodate the receptacle of the present invention;
FIGS. 3A, 3B and 3C are top, side and front views of a receptacle in
accordance with the present invention;
FIGS. 4A and 4B are side elevation views illustrating the utilization of
ball-in-hole and pin-type positioning mechanisms, respectively, which may
be employed in the jacket surrounding the receptacle body for purposes of
alignment and positioning of the jacket;
FIG. 5 is an isometric view illustrating a standard type connector plug
which is meant to be accommodated by the receptacle described herein.
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 illustrates receptacle 10, in accordance with the present invention,
employed in a recess (reference numeral 25 in FIG. 2) in substrate 20
which is part of a multi-chip module assembly. Module 60 includes at least
one semiconductor chip 40 disposed on the upper surface of substrate 20.
In preferred embodiments of the present invention, chips 40 are attached
to substrate 20 by means of solder balls 41. This configuration is often
referred to as the "C4 technology" which disposes circuit chips on
substrates in inverted positions by means of conductive metal blobs of
solder which are attached to electrically conductive patterns on
insulative substrate 20. Although not specifically shown (for purposes of
clarity) in FIG. 1, substrate 20 includes electrically conductive patterns
on the surface thereof and also typically includes conductive networks
embedded within insulative substrate 20 which is typically a ceramic
material but which also may comprise a glass or glassy ceramic.
For purpose of the present invention, at least one of chip 40 includes
photoreceptive or phototransmissive means 42. These means operate either
to receive laser light or conversely to generate optical transmissions
which are conducted to the exterior of the module through receptacle 10.
In preferred embodiments of the present invention, receptacle 10 is
incorporated into multi-chip module with substrate 20 and cap 30 in a
fashion which provides environmental isolation. This isolation is achieved
at least in part by means of gasket 26 which provides a seal between
substrate 20 and cap 30. In those situations where the power requirements
demand it, cap 30 also preferably includes passages therein for the flow
of cooling fluid therethrough. In such circumstances, cap 30 is also
preferably in thermal contact with one or more chips 40 to provide the
desired degree of cooling. Again, depending upon the circumstances, not
all chips on a substrate need the same degree of cooling; this is
typically a function of the power being generated within the chip
circuits. Likewise, not all chips require photonic means 42.
Receptacle 10, of the present invention, includes an external,
non-insulative jacket 11 typically including upper portion 11a and lower
portion 11b (see FIGS. 4A and 4B). This jacket preferably comprises a
material such as silicon because of its compatibility with other aspects
of the multi-chip module manufacturing process. Accordingly, exterior
jacket 11 is provided with grounding means to mitigate problems associated
with electrostatic discharge conditions. In particular, jacket 11
preferably includes solder balls 24 (just as in the C4 chip mount process)
which are employed to hold receptacle 10 in position in recess 25 in
substrate 20. Additionally, substrate 20 is seen to preferably include
ground conductors 23 which provide a direct path to ground for any charge
accumulation that may be present on receptacle 10, or which may be
supplied to receptacle 10 as a result of the insertion of plug 50 (see
FIG. 5) into the recess in receptacle 10.
Receptacle 10 also includes optical fiber cables which extend from
receiving body 12 so as to be disposable in grooves or channels 21 in
substrate 20. Additionally, it is noted that these channels preferably
include reflective end portion 22 which is operable to direct light from
internal fiber optic leads 15 to photonic receptors 42 on chips 40.
Likewise, for transmission outward, reflective groove portion 22 is also
employed to direct light from chip 40 into internal fiber optic lead 15.
There are a number of ways in which the optical fibers 15 may be embedded
in plastic receptacle 15; for example, the receptacle may be cast as two
halves in a precision mold which includes grooves for the fiber locations,
the fibers may then be placed in the grooves of one half and affixed with
epoxy, and the other half may then be attached over the fibers. Basically,
the plastic optical fiber receptacle may be fabricated using industry
standard techniques similar to those used to fabricate the connector
assembly of FIG. 5; such connectors are commercially available. When a
precision mold is used to fabricate the plastic receptacle, the mold
controls the fiber location within the receptacle; alignment between the
receptacle and plug of FIG. 5 is accomplished by the precision metal
alignment pins incorporated into the receptacle.
The construction of recess 25 and grooves or channels 21 in substrate 20 is
more particularly described in U.S. Pat. No. 5,333,225 discussed above and
which is incorporated herein by reference.
A detailed illustration of the connector of the present invention is shown
in FIGS. 3A, 3B and 3C which show top, side and front views, respectively.
In particular, it is seen from FIGS. 3A, 3B and 3C (collectively FIG. 3)
that optical fiber leads 15 extend from the bottom of recess 19 in
receiving body 12. In fact, leads 15 preferably extend slightly into
recess 19. Body 12 preferably comprises a material such as plastic and in
fact preferably comprises a plastic having approximately 20% carbon fill
to facilitate conduction of accumulated static charge to surrounding
non-insulative jacket 11 which preferably comprises a material such as
silicon. Jacket 11 surrounds recess possessing body 12 and serves several
significant functions. In particular, jacket 11 provides an electrically
conductive path for accumulated static charge and in particular provides a
direct route for their passage to ground conductive leads 23 in substrate
20. Additionally, jacket 11 includes upper portion 11a and lower portion
11b which divide jacket 11 into two pieces along thermal expansion joint
11c. Jacket 11 (collectively, upper jacket portion 11a and lower jacket
portion 11b) also includes a positioning mechanism which is more
particularly illustrated in FIGS. 4A and 4B discussed below.
FIG. 4 shows the ball-in-hole or pin-in-hole expansion joints within jacket
11. These features are very desirable to provide the means to align the
upper and lower halves of the jacket 11a and 11b, while providing room for
movement which may be caused by thermal expansion of the receptacle. If
there is a change in temperature, the expansion joint moves first and the
plastic receptacle "floats" inside the jacket; this allows the plastic to
remain in alignment with the plug. Otherwise, if the temperature changed
and the receptacle was fixed in place, there would be stress on the
plastic which could cause it to deform and lose the alignment between
receptacle 10 and the plug 50. Note this floating action also allows
receptacle 10 to move slightly when the connector is plugged in; hence
thee is less plugging force transferred from the plug to the receptacle,
where it might deform the plastic (low insertion force design).
Receptacle 10 also includes connector plug receiving body 12 which
preferably comprises a carbon filled plastic material. Body 12 includes
recess 19 at the bottom of which there are disposed alignment holes 16
which mate with (typically metal) pins 56 on plug 50 (see FIG. 5). This
provides an alignment mechanism for optical fibers 15 in plug receiving
body 12 so as to align optical fibers 55 in plug 50 (see FIG. 5) with
optical fibers 15. Plug receiving body 12 also preferably includes keyway
18 which mates with a corresponding key on plug 50. This key and channel
provide a mechanism which precludes insertion of connector plug 50 into
recess 19 in an inverted orientation. Additional alignment between jacket
11 and body 12 is provided by similar keyway structure 17 (see, FIG. 3C).
While the preferred embodiment of the present invention includes pins on
plug 50 and corresponding pin holes 16 at the bottom of recess 19, it is
also clear that the alignment function may also be achieved by disposing
pins at the bottom of recess 19 by and providing corresponding pin holes
in plug 50.
In order to provide an alignment function between the two portions of
conductive or semiconductive jacket 11, either a ball-in-hole arrangement
is employed, as shown in FIG. 4A, or an pin-in-hole arrangement is
employed, as shown in FIG. 4B. In the ball-in-hole arrangement, ball 13 is
disposed in half of a substantially hemispherically indentation 14 in
upper and lower jacket portions 11a and 11b. This provides alignment and
spacing functions and yet nonetheless permits some differential expansion
between the jacket portions. Likewise, pin 13' (as in FIG. 4B) may be
fixedly disposed in lower jacket portion 11b and extend into an oversized
hole 14' in upper jacket portion 11a. It is noted that, while for
convenience, jacket 11 preferably comprises only two mating portions, it
is nonetheless possible to partition the jacket into smaller pieces, each
of which also could possess a thermal expansion joint.
The above described receptacle is designed for insertion therein of
connector plug 50, which is shown in FIG. 5. Plug 50 includes array 55 of
optical fibers extending from flat ribbon 54. These cables are preferably
disposed linearly between alignment pins 56 in plug body 52. Plug 50 also
preferably includes stop 53 which, when in position, meets flush with the
front edge of receptacle 10. Plug 50 also preferably includes key 58 which
is meant to be slidably insertable into key way 18 in body 12 (see FIG.
3C).
It is noted also that for purposes of strain relief, recess 19 and plug
body 52 may also incorporate conventional latching means to lock plug 50
into place with sufficient strength so as to defeat the possibility of
easy or accidentally pulling plug 50 from recess 19.
From the above, it should be appreciated that the present invention
provides a fiber optic receptacle for coupling standard fiber optic cables
to a multi-chip module. Likewise, there is disclosed the combination of a
multi-chip module which incorporates the receptacle of the present
invention. The system described herein, provides a plugable connector
system which is not only low cost but which is easy to maintain and is
highly reliable. Furthermore, the system exhibits improved noise immunity
and provides a scaleable means for increasing the input/output bandwidth
through the inclusion of a plurality of receptacles disposed along the
edge of a multi-chip module, substantially as described herein. The
present invention therefore is seen to facilitate the construction of
massively parallel data and computational architectures. The present
invention is also seen to provide alignment, strain relief, electrostatic
immunity, noise immunity and scaleable edge connection features. It is
also seen that the receptacle of the present invention further provides a
mechanical float to minimize plugging forces and that it furthermore
incorporates a zero insertion force design. Furthermore, it is seen that
the use of a silicon jacket, together with the utilization of solder balls
disposed on the outside thereof, provides the ability to use standard
lithographic alignment techniques between the jacket receptacle and
grounding conductors on substrate 20. The lithographic grid not only
provides alignment to the grounding pads; it is the same grid that is used
to align chips 42 to substrate 20. So, because we can align the chips and
receptacle on the same grid, we can precisely align the optical
transmitter/receivers 42 on the chip with the end faces of fibers 15 in
the receptacle. Also, it is seen that the structure of the connector
described herein provides compatible materials for use in conjunction with
the surrounding multi-chip module. It is also seen that the solder ball
contacts on the exterior of the outer jacket provides improved
electrostatic discharge grounding since it provides a very short path to
ground. Additionally, the fibers employed preferably protrude into the
recess so as to provide direct physical contact when the connector is
plugged in thus improving optical coupling without the use of index
matching gels. It is also seen that the connector may employ fan out of
the optical stubs from the connector to provide strain relief and
additional connectivity inside the multi-chip module.
In order to provide a desirable seal between the exterior and interior of
the multi-chip module, grooves or channels 21 may be back filled with any
convenient polymeric material.
While the invention has been described in detail herein in accord with
certain preferred embodiments thereof, many modifications and changes
therein may be effected by those skilled in the art. Accordingly, it is
intended by the appended claims to cover all such modifications and
changes as fall within the true spirit and scope of the invention.
* * * * *
|
|
 |
|
 |
Description |
|
