 |
Claims  |
|
|
What is claimed is:
1. A method of optically interconnecting integrated circuits, comprising:
forming a plurality of optical waveguides having a first coupling element
and a second coupling element onto a printed circuit board;
electrically coupling opto-electronic transmitters and receivers to
integrated circuits, said integrated circuits being bonded to substrates,
said substrates being bonded to the printed circuit board, the
opto-electronic transmitters and receivers being aligned correspondingly
with the first coupling element and the second coupling element of the
plurality of optical waveguides;
modulating light emissions of the opto-electronic transmitters with
electrical signals from the integrated circuits to form divergent
modulated light emissions;
emitting divergent modulated light emissions;
collimating divergent modulated light emissions of the opto-electronic
transmitters using attached lens to form collimated modulated light and
directing the collimated modulated light toward the first coupling
element;
receiving, by the first coupling element, the collimated modulated light
and forming propagating modulated light;
transporting the propagating modulated light from the first coupling
element through the optical waveguides to the second coupling element;
directing the propagating modulated light from the second coupling element
toward the corresponding lens attached to the opto-electronic receivers to
form modulated light emissions; and
transducing, by the opto-electronic receivers, the modulated light
emissions into electrical signals for the integrated circuits.
2. The method of claim 1, wherein electrically coupling the opto-electronic
transmitters and receivers to the integrated circuits includes using
flip-chip bonded solder bump connection technology.
3. An opto-electronic system to optically interconnect integrated circuits,
comprising:
an opto-electronic transmitter having an emitting surface and an
interconnect surface, the interconnect surface being bonded to a first
integrated circuit, the opto-electronic transmitter emitting a divergent
modulated light beam from the emitting surface through an attached first
lens to form a collimated modulated light beam;
a first substrate including a first surface bonded to the first integrated
circuit, and a second surface bonded to a printed circuit board;
an optical waveguide in close proximity to the first lens attached to the
opto-electronic transmitter, wherein the optical waveguide is formed on
the printed circuit board, contains a first coupling element to receive
the collimated modulated light beam emitted by the opto-electronic
transmitter to form propagating modulated light and to re-direct the
propagating modulated light through the optical waveguide, and a second
coupling element to re-direct the propagating modulated light out of the
optical waveguide to a second lens attached to an opto-electronic receiver
and in close proximity with the second coupling element;
a second integrated circuit bonded to the opto-electronic receiver; and
a second substrate including a first surface bonded to the second
integrated circuit, and a second surface bonded to the printed circuit
board.
4. The opto-electronic system according to claim 3, wherein the first
surface of the first substrate is bonded to a second surface of the first
integrated circuit and the opto-electronic transmitter is bonded to the
second surface of the first integrated circuit, and the second surface of
the first substrate is bonded to the printed circuit using flip-chip
bonded solder bump connection technology.
5. The opto-electronic system according to claim 3, wherein the first
surface of the second substrate is bonded to a second surface of the
second integrated circuit and the opto-electronic receiver is bonded to
the second surface of the second integrated circuit, and the second
surface of the second substrate is bonded to the printed circuit using
flip-chip bonded solder bump connection technology.
6. The opto-electronic system according to claim 3, wherein the
opto-electronic transmitter is a Vertical Cavity Surface Emitting Laser
(VCSEL).
7. The opto-electronic system according to claim 3, wherein the
opto-electronic transmitter is an array of Vertical Cavity Surface
Emitting Lasers (VCSEL).
8. The opto-electronic system according to claim 3, wherein the
opto-electronic receiver is a photodiode.
9. The opto-electronic system according to claim 3, wherein the first and
second substrates are contained within Ball Grid Array (BGA) packages or
Land Grid Array (LGA) packages.
10. The opto-electronic system according to claim 3, wherein one or more
integrated circuits are bonded to the first and second substrates, and
electrically coupled to the opto-electronic transmitter and
opto-electronic receiver.
11. The opto-electronic system according to claim 3, wherein the first and
second coupling elements include sloped facets or holographic elements
formed in the optical waveguide.
12. The opto-electronic system according to claim 11, wherein the
holographic elements are formed in the optical waveguide such that
holographic elements diffract the modulated light into or out of the
optical waveguide.
13. An opto-electronic system to optically interconnect integrated
circuits, comprising:
an opto-electronic transmitter having an emitting surface and an
interconnect surface, the interconnect surface being bonded to a second
surface of a first substrate, the opto-electronic transmitter emitting a
divergent modulated light beam from the emitting surface through an
attached first lens to form a collimated modulated light beam;
the first substrate including a first surface bonded to a first integrated
circuit, and the second surface bonded to a printed circuit board;
an optical waveguide in close proximity to the first lens attached to the
opto-electronic transmitter, wherein the optical waveguide is formed on
the printed circuit board, contains a first coupling element to receive
the collimated modulated light beam emitted by the opto-electronic
transmitter to form propagating modulated light and to re-direct the
propagating modulated light through the optical waveguide, and a second
coupling element to re-direct the propagating modulated light out of the
optical waveguide to a second lens attached to an opto-electronic receiver
and in close proximity with the second coupling element;
a second surface of a second substrate bonded to the opto-electronic
receiver; and
the second substrate including a first surface bonded to the second
integrated circuit, and the second surface bonded to the printed circuit
board.
14. The opto-electronic system according to claim 13, wherein the first
surface of the first substrate is bonded to the first integrated circuit
and the second surface of the first substrate is bonded to the
opto-electronic transmitter, and the second surface of the first substrate
is bonded to the printed circuit using flip-chip bonded solder bump
connection technology.
15. The opto-electronic system according to claim 13, wherein the first
surface of the second substrate is bonded to the second integrated circuit
and the second surface of the second substrate is bonded to the
opto-electronic receiver, and the second surface of the second substrate
is bonded to the printed circuit board, using flip-chip bonded solder bump
connection technology.
16. The opto-electronic system according to claim 13, wherein the
opto-electronic transmitter is a Vertical Cavity Surface Emitting Laser
(VOSEL).
17. The opto-electronic system according to claim 13, wherein the
opto-electronic transmitter is an array of Vertical Cavity Surface
Emitting Lasers (VCSEL).
18. The opto-electronic system according to claim 13, wherein the
opto-electronic receiver is a photodiode.
19. The opto-electronic system according to claim 13, wherein the first and
second substrates are contained within Ball Grid Array (BGA) packages or
Land Grid Array (LGA) packages.
20. The opto-electronic system according to claim 13, wherein one or more
integrated circuits are bonded to the first and second substrates, and
electrically coupled to the opto-electronic transmitter and
opto-electronic receiver.
21. The opto-electronic system according to claim 13, wherein the first and
second coupling elements include sloped facets or holographic elements
formed in the optical waveguide.
22. The opto-electronic system according to claim 21, wherein the
holographic elements are formed in the optical waveguide such that
holographic elements diffract the modulated light into or out of the
optical waveguide. |
|
 |
|
 |
Claims |
|
|
|
Description |
|
|
BACKGROUND OF THE INVENTION
1. Technical Field
An embodiment of the invention generally relates to mounting optical and
electrical devices to a substrate while coupling to an optical waveguide
integrated on a printed circuit board. More particularly, the present
invention relates to using conventional flip-chip packaging to integrate
optical and electrical devices to a printed circuit board while
simultaneously coupling the optical devices to an optical waveguide by
utilizing an integrated microlens array.
2. Discussion of the Related Art
Electrical systems often use a number of integrated circuits that are
mounted on a printed circuit board. Each integrated circuit includes a
number of leads that extend from the packaging of the circuit. The leads
of the various integrated circuits are interconnected to allow signals to
be passed between the integrated circuits such that the system performs
some function. For example, a personal computer includes a wide variety of
integrated circuits, e.g., a microprocessor and memory chips, that are
interconnected on one or more printed circuit boards in the computer.
Printed circuit boards are used to bring together separately fabricated
integrated circuits. However, the use of printed circuit boards creates
some problems that are not so easily overcome. A printed circuit board
includes metal traces to transmit an electrical signal between the various
integrated circuits. As the number of components on a printed circuit
board increases, the number of metal traces needed to connect the
components also increases. This fact decreases the spacing between the
metal traces, which can lead to capacitance problems between the metal
traces and space constraints due to the limited area available on the
printed circuit board for metal traces. It is desirable to reduce the
amount of physical space required by such printed circuit boards. Also, it
is desirable to reduce the physical length of electrical interconnections
between devices because of concerns with signal loss or dissipation and
interference with and by other integrated circuitry devices.
As the density of electronic integrated circuits increases, the limiting
factor for circuit speed increasingly becomes propagation delay due to
capacitance associated with circuit interconnection. At relatively low
clock speeds, the capacitive loading is not a significant factor. As newer
applications push clock speeds into the one hundred megahertz range and
beyond, capacitive loading becomes a limiting factor for circuit
performance by limiting circuit speed and increasing circuit cross talk.
A continuing challenge in the semiconductor industry is to find new,
innovative, and efficient ways of forming electrical connections with and
between circuit devices that are fabricated on the same, and on different,
wafers or dies. Relatedly, continuing challenges are posed to find and/or
improve upon the packaging techniques utilized to package integrated
circuitry devices. As device dimensions continue to shrink, these
challenges become even more important.
One approach utilizes optical interconnection to transmit optical signals
between components, particularly components located on remote regions of a
board. The optical signals are composed of modulated light beams that
carry data between components. An optical emitter, such as a laser, is
mounted on one region of the board and emits the optical signal. The
optical signals are diffracted by holographic elements into a optical
waveguide. The optical signals then propagate from one point to another
through the optical waveguide before being diffracted out of the optical
waveguide by holographic elements and focused upon opto-electronic
receivers on the surface of an integrated circuit.
However, the interface between the component, i.e., the emitter or
detector, and the optical waveguide is difficult to fabricate. In this
approach, holographic routing elements have to be precisely aligned with
the opto-electronic receivers of the integrated circuits. The
opto-electronic transmitters then have to be precisely aligned relative to
the holographic routing elements in order for the modulated light beams
emitted by the sources to be directed by the holographic routing element
to the proper opto-electronic receivers. Achieving the required precision
of alignment makes assembly into a package extremely challenging. The
kinds of tolerances required are normally associated with semiconductor
device fabrication processes rather than with package assembly.
Another limitation of the prior art is the lack of flexibility in the
assembly of printed circuit boards. Because the optical emitters,
holographic elements, waveguides, and optical detectors must be mounted
during assembly of the printed circuit board, there is no flexibility in
adding any of these elements or adjusting their position once the printed
circuit board has been fabricated.
For reasons stated above, and for other reasons which will become apparent
to those in the art upon reading and understanding the present
specification, there is a need in the art for an improved technique for
interconnecting individual integrated circuits in an electronic system.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1A and FIG. 1B illustrate a cross-sectional view of a package suitable
for implementing embodiments of the present invention;
FIG. 2A and FIG. 2B illustrate is a cross-sectional view of an alternative
package suitable for implementing embodiments of the present invention;
and
FIG. 3 illustrates a flow chart for a method of optically interconnecting
integrated circuits according to an embodiment of the present invention.
DETAILED DESCRIPTION
An embodiment of the invention addresses the limitations of the prior art
by providing a structure wherein optically active devices, i.e.,
opto-electronic transmitters and opto-electronic receivers, are
individually manufactured, and optimized for performance and reliability.
The optically active devices are then mounted on a PCB and aligned to a
waveguide formed on the PCB.
The opto-electronic transmitters and receivers 102 in FIG. 1A, for example,
are first flip-chip bonded to integrated circuits 104 such as drivers,
transimpedance amplifiers, microprocessors, etc. The integrated circuits
104 are then flip-chip bonded to substrates 108, which are incorporated
into Ball Grid Array (BGA) 106 or Land Grid Array (LGA) packages.
Flip-chip bonding, otherwise known as controlled collapsed chip connection
technology or solder bump technology, involves solder bumps on the chip
that are reflowed to make connection to terminal pads on the substrate.
The BGA 106 package (including the integrated circuit and the optically
active device) is then bonded directly to a printed circuit board (PCB)
110 in such a way as to position the optically active devices 102 in close
proximity to optical waveguides 170 deposited on the printed circuit board
110. The optically active devices 102 align with coupling elements 171
e.g. (holographic elements or 45 degree facets) incorporated into the
optical waveguides 170, thus forming an optical interconnect structure.
An alternative BGA package 206 suitable for implementing embodiments of the
present invention is shown in FIG. 2A. A driver or transimpedance
amplifier chip 104 is flip-bonded on a first surface of the BGA package
substrate 208, and a bottom emitting or sensing optically active device
102 is flip-bonded on a second surface of the BGA package substrate 208,
and the BGA package 206 is bonded to a printed circuit board (PCB) 110
using solder reflow technology. The example system 200 also has a
waveguide 170 to direct the light from the device 102 through the PCB 110.
The present invention overcomes a significant limitation of the prior art
in that precise alignment between opto-electronic devices 102 and the
optical waveguide 170 is not required. In the prior art, the optical
waveguides are directly deposited over the electro-optic devices using
standard semiconductor fabrication techniques. To electricaly connect the
various chips, the substrate has very fine feature sizes that are
compatible with the input/output pitch of the various chips. The
configuaration ensured an intimate contact between the opto-electronic
devices and the optical waveguides and consequently good optical coupling
is achieved. However, this technology can not provide a cost effective
solution because it is not compatible with integrating waveguides on a
conventional printed circuit board. Printed circuit boards typically have
gross feature sizes (>3 mils linewidth). In addition, the prior art is
not compatible with current Central Processing Unit (CPU) motherboard
fabrication and assembly processes.
The present invention allows alignment requirements to be relaxed by using
a lens to collimate the divergent light beam from the opto-electronic
transmitter 102, or to focus a diffracted beam from the optical waveguide
170 onto a photodiode contained within the opto-electronic reciever 102.
The lens is directly attached to the optically active devices 102. The
lens allows the divergent light beam to be readily coupled to the optical
waveguide 170 deposited in the PCB 110 without regard to the separation
and original divergence of the opto-electronic transmitter 102.
In the prefered embodiment of the present invention the opto-electronic
transmitter 102 is a Vertical Cavity Surface Emitting Laser (VCSEL) with
an attached lens. The optical emission of the VCSEL is from the top
surface of the chip. VCSEL's have a circularly semetric, nonastigmatic
beam. In a custom VCSEL assembly used in a sensing application, for
example, a VCSEL is mounted chip-on-board in a TO style package, with an
injection-molded plastic lens aligned to the VCSEL to collimate the
optical output, as well as a pair of silicon detectors and some passive
elements. In an alternative embodiment of the present invention the
opto-electronic transmitter 102 is an array of Vertical Cavity Surface
Emitting Lasers (array of VCSEL's) with a microlens array attached.
The move to higher data rates and smaller packaging requires examination of
the electrical characteristics of both the VCSEL and packaging. In a
typical fiberoptic transceiver, the elements to be considered are the
output impedance of the laser driver, the circuit, and traces used to
carry the signal to the laser package and finally, the laser chip itself.
To determine the electrical characteristics of the VCSEL, S parameter
measurements may be taken with a network analyzer. Once the electrical
characteristics of the VCSEL chip are known, various packaging options may
be investigated, and the output stages of laser drivers and circuit board
parameters may be optimized to deliver high quality electrical signals to
the VCSEL.
To optimize the VCSEL performance, typical packaging rules apply: minimize
both the inductance and the capacitance of the packaging by keeping the
leads to the TO package as short as possible. Also minimize the distance
between the laser driver and the TO package to reduce any impedance
mismatched reflections, and optimize the output stage of the laser driver
to drive the VCSEL TO package. For operation at data rates above a few
giga-bits per second (Gb/s), the total impedance is completely dominated
by the electrical parasitics of the TO package.
At higher speeds, i.e., 10 Gb/s, it may be necessary to connect the VCSEL
directly to the laser driver integrated circuit 104 using a ribbon bond
wire. In the prefered embodiment of the invention, the use of the bond
wire is eliminated by flip-chip bonding the VCSEL chip directly to the
laser driver integrated circuit 104.
The combination optically active device 102/integrated circuit 104 is
tested prior to mounting to the substrate 108 of the BGA package. Any
number of integrated circuits 104 may also be mounted to the substrate 108
by any suitable means; however, in a preferred embodiment, flip-chip or
solder bump technology is used.
Ball Grid Array (BGA) package 106 is suitable for any integrated circuit
104 that may previously have been put in a plastic type package. The BGA
package 106 is composed of three basic parts: a bare chip (shown as the
driver or transimpedance amp integrated circuit 104), a BGA substrate 108,
and an interconnection matrix (not shown). Depending on the package style,
the bare chip may be affixed to the BGA substrate 108 either face-up or
face-down. The interconnection matrix then connects the bare chip to the
BGA substrate 108 using wire-bond, tape-automated-bonding (TAB), or direct
attach flip-chip bonding. The BGA substrate 108, similar to a miniature
multi-layer PCB with small traces and microscopic through-hole vias,
conveys the signals to the underlying printed circuit board 110 through an
array of solder-bump attachment pads 140, 142 on its bottom surface. A
metal cover or plastic encapsulation is then used to seal the package.
BGA packages 106 are inherently low-profile. The package includes the chip,
some interconnections, a thin substrate, and a plastic encapsulant. No big
pins, and no lead frames are included. The low profile and small size
means that the total loop area, from a signal on the chip, through the
interconnection matrix onto the PCB 110, and back into the chip through
the power/ground pins is very small, as little as 1/2 to 1/3 the size of
the same loop on a typical package of equivalent pincount. This smaller
loop area means less radiated noise, and less crosstalk between pins.
The BGA package 106 has relatively large, easy-to-work-with solder bumps
140, 142, much bigger than the ones used for flip-chip bonding. By way of
contrast, flip-chip techniques, which use solder-balls 124, 126, 128, 130,
placed directly on the face of a silicon die, require solder bumps with
much smaller dimensions.
Because the BGA package 106 is an inherently thin package, it has
reasonably good cooling properties. With the die mounted face-up, most of
the heat flows down and out through the ball-grid array. In packages that
mount the die face-down, the back side of the die is in intimate contact
with the top of the package, an ideal arrangement for heatsinking.
FIG. 1A and FIG. 1B illustrate a cross-sectional view of an opto-electronic
system 100 suitable for implementing embodiments of the present invention.
The example system 100 includes packaging that provides pitch
transformation from fine pitch to coarse pitch. The system 100 includes a
bottom emitting optically active device 102 (or a bottom detecting
optically active device 102) that is flip-chip bonded on a driver 104 or
transimpedance amplifier chip 104. The driver 104 or transimpedance
amplifier chip 104 is flip-chip bonded on a ball grid array (BGA) package
substrate 108, and the BGA package 106 is solder reflowed to a printed
circuit board (PCB) 110 that includes a waveguide 170.
The active face (emitting or detecting surface) of optically active
devices, such as the device 102, is on the side opposite of the electrical
traces (the interconnect surface). Example bottom emitting or detecting
optically active devices 102 are shown in 1A, FIG. 1B. FIG. 2A and FIG.
2B.
The device 102 emits (or detects) light when activated. The device 102 is
surface normal and may be a Vertical Cavity Surface Emitting Lasers
(VCSEL), an array of Vertical Cavity Surface Emitting Lasers, a light
emitting diode (LED), a photodetector, an optical modulator, or similar
optically active device 102. A lens or microlens array is attached to the
device 102 to collimate the divergent optical beam.
In one embodiment, an optical via 157 is made in the BGA substrate 108 for
the device 102 and the light emitted by the device 102. Light from (or to)
the device 102 passes through the optical via 157. This may also be in the
form of a clearance in the substrate to accomadate the VCSEL chip.
The driver or transimpedance amplifier chip 104 is any integrated circuit
suitable for applying an electrical signal to the device 102 to activate
the device 102. Implementation of the driver or transimpedance amplifier
chip 104 is well known.
The BGA package 106 may be any known flip-chip Ball Grid Array package. The
BGA substrate 108 in one embodiment is an organic laminate substrate that
uses epoxy resin dielectric materials or bismaleimide triazine (BT)
materials, and copper conductors or traces. In another embodiment, the BGA
substrate 108 is a multi-layer ceramic substrate based on aluminum oxide
(Al.sub.2 O.sub.3).
The PCB 110 typically has an insulating layer made of epoxy glass. The PCB
110 also has an electric circuit with various conducting strips or traces
that connect to each other based on the particular PCB application. The
PCB 110 may be a multi-layer PCB with several insulating layers and
conducting layers, with each conducting layer having its own traces.
Printed circuit boards suitable for implementing the present invention are
well known.
According to the embodiment shown in FIG. 1A the optically active device
102 is flip-chip bonded on the driver or transimpedance amplifier chip 104
using well known solder bump technology. For example, the device 102 has
two solder bumps, 120 and 122, which are very tiny and spaced very close
together. The device 102 may have more than two solder bumps. If the
device 102 were to be mounted directly on the PCB 110, the PCB 110 would
have to have very fine features to accommodate the tiny and closely spaced
solder bumps 120 and 122. This requirement may cause the PCB 110 to be
more complex and the manufacturing process for the PCB 110 would be
costly.
The system 100 accommodates existing PCB manufacturing by mounting the
device 102 to the driver or transimpedance amplifier chip 104 using the
tiny solder balls 120, 122 of the device 102, and mounting the driver or
transimpedance amplifier chip 104 to the BGA substrate 108. In the
embodiment shown in FIG. 1, the BGA package 106 is flip-chip bonded to the
PCB 110 using solder balls 140 and 142, whose pitch may be,
illustratively, 1.27 millimeters, such that the pitch is compatible with
conventional PCB technology and does not require high-density substrates.
The driver or transimpedance amplifier chip 104 includes bumps 124, 126,
128, and 130, which electrically connect the driver or transimpedance
amplifier chip 104 to traces on the BGA substrate 108. The bumps 124, 126,
128, and 130 may be made of solder or other type of metal(s) that melt and
create a bond (e.g., lead-tin compositions (PbSn), tin-silver (SnAg)
compositions, nickel (Ni) compositions). In the embodiment in which the
bumps 124, 126, 128, and 130 are made of solder, the solder melts during
reflow and the surface tension of the molten solder centers the driver or
transimpedance amplifier chip 104 correctly over the BGA substrate 108.
In some instances, it may be desirable to direct light from the device 102
on the PCB 110. In one embodiment, the PCB 110 has an optical waveguide
170 for this purpose. The waveguide 170 contains coupling elements 171 and
the waveguide 170 may be laminated on the PCB 110. The coupling elements
may include holographic gratings made of dichromated gelatin film,
photosensitive polymer film, gratings etched photolithographically into
the waveguides or waveguides faceted at 45 degrees.
For fine alignment of the BGA package 106 to the PCB 110, the solder balls
140 and 142 are subject to high temperature, which causes the solder balls
140 and 142 to melt. When the solder balls 140 and 142 melt, the surface
tension pulls the BGA package 106 into alignment with the PCB 110. Surface
tension is the attraction that the molecules at the surface of a drop of
melted solder have for each other. The attraction the solder molecules
have for each other is greater than the attraction the solder molecules
have for the BGA substrate 108 so that the solder does not spread.
When the BGA package 106 is placed over the PCB 110, the solder balls 140
and 142 of the BGA package 106 rest over pad areas 141 and 143,
respectively, on the PCB 110. Thus, the solder ball-to-pad contact
determines the vertical separation of the BGA package 106 and the PCB 110.
This feature ensures that solder balls and pad areas will remain in an
intimate (i.e., high coupling efficiency) optical contact after assembly
of the package 100.
The embodiment shown in FIG. 1A also provides fine alignment of the BGA
package 106 with the PCB 110. The solder balls 140 and 142 rest on the
pads 141 and 143, respectively, and self-align within the pads 141 and 143
during solder reflow. In this embodiment, the solder balls 140 and 142 set
the height of the package 100 in the "z" dimension and have no constraints
in the "x" dimension or the "y" dimension. The final tolerance may be
determined by the placement accuracy of the flat pads 141 and 143.
The resulting fine alignment provided by solder reflow techniques ensures
the light emitted by the device 102 is properly aligned with the coupling
elements 171 of the waveguide 170 on the PCB 110. After bonding, the
aligned package 100 positions the device 102 correctly over the coupling
elements 171 of the waveguide 170.
The solder metallurgy for the joint(s) between the device 102 and the
driver or transimpedance amplifier chip 104 has a higher melting
temperature than the solder metallurgy for the joint(s) between the driver
or transimpedance amplifier chip 104 and the BGA substrate 108. For
example, well-known 63Pb/37Sn solder melts at 187 degrees Centigrade. This
use of solder is done to ensure that joint(s) between the device 102 and
the driver or transimpedance amplifier chip 104 maintains its integrity
when the driver or transimpedance amplifier chip 106 is flip-chip bonded
to the BGA substrate 108. In one embodiment, the solder bumps on the
device 102 may be the same material as the solder bumps on the device 104
and the solder on the board has a lower melting point than the solder
bumps.
The arrows 190 and 192 in FIG. 1A illustrate the direction light travels
from the emitting device 102, to the waveguide structure 170, and to a
receiving optically active device 102 (shown in FIG. 1B). The reverse is
true for light arriving at the receiving optically active device shown in
FIG. 1B. Although FIG. 1A and FIG. 1B illustrate light traveling from the
emitting device 102 in FIG. 1A to the receiving optically active device
102 shown in FIG. 1B, the light may also travel in a bidirectional manner
from an emitting device 102 in FIG. 1B to a receiving optically active
device 102 shown in FIG. 1A.
FIG. 2A and FIG. 2B illustrate a cross-sectional view of an alternative BGA
package 206 suitable for implementing embodiments of the present
invention. A driver or transimpedance amplifier chip 104 is flip-bonded on
a first surface of the BGA package substrate 208, and a bottom emitting or
sensing optically active device 102 is flip-bonded on a second surface of
the BGA package substrate 208, and the BGA package 206 is bonded to a
printed circuit board (PCB) 110 using solder reflow technology. The
example system 200 also has a waveguide 170 to direct the light from the
device 102 through the PCB 110.
The arrows 190 and 192 illustrate the direction light travels from the
emitting device 102, to the waveguide structure 170, and to a receiving
optically active device 102 (shown in FIG. 2B). The reverse is true for
light arriving at the receiving optically active device 102 shown in FIG.
2B. Although FIG. 2A and FIG. 2B illustrate light traveling from the
emitting device 102 in FIG. 2A to the receiving optically active device
102 shown in FIG. 2B, the light may also travel in a bidirectional manner
from an emitting device 102 in FIG. 2B to a receiving optically active
device 102 shown in FIG. 2A.
FIG. 3 illustrates a flow chart for a method of optically interconnecting
integrated circuits according to an embodiment of the present invention.
Optical waveguides 300 are formed having a first coupling element and a
second coupling element onto a printed circuit board.
Opto-electronic transmitters and receivers are electrically coupled 310 to
integrated circuits, the integrated circuits being bonded to substrates,
the substrates being bonded to the printed circuit board, the
opto-electronic transmitters and receivers being aligned correspondingly
with the first coupling element and the second coupling element of the
plurality of optical waveguides.
Electrical signals from the integrated circuits modulate 320 light
emissions of the opto-electronic transmitter. The microlens array attached
to the opto-electronic transmitter collimates 330 divergent light
emissions to form collimated light emissions and directs the collimated
light emissions toward the first coupling element.
The collimated light emissions propagates 340 from the first coupling
element through the optical waveguide to the second coupling element. The
second coupling element directs the light emissions 350 toward the
corresponding microlens array attached to the opto-electronic receiver.
Finally, the opto-electronic receiver transduces 360 the modulated light
emissions into electrical signals for the integrated circuit.
While the description above refers to particular embodiments of the present
invention, it will be understood that many modifications may be made
without departing from the spirit thereof. The accompanying claims are
intended to cover such modifications as would fall within the true scope
and spirit of the present invention. The presently disclosed embodiments
are therefore to be considered in all respects as illustrative and not
restrictive, the scope of the invention being indicated by the appended
claims, rather than the foregoing description, and all changes that come
within the meaning and range of equivalency of the claims are therefore
intended to be embraced therein.
* * * * *
|
|
|
|
|
|
|
Description | |
