Ceramic optical sub-assembly for opto-electronic module...

Details Ceramic optical sub-assembly for opto-electronic module... Ceramic optical sub-assembly for opto-electronic module...

2003-03-03

2004-07-27

Palmer, Phan T. H. (Department: 2874)

Optical waveguides

With disengagable mechanical connector

Optical fiber to a nonfiber optical device connector

C385S088000

Reexamination Certificate

active

06767140

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to techniques for connecting the optical and electrical device components. More particularly, the invention relates to LTCC (low temperature co-fired ceramic) structures for use in optical subassemblies.
BACKGROUND OF THE INVENTION
Many computer and communication networks being built today, including the Internet, are using fiber optic cabling instead of copper wire. With fiber optic cabling, data is transmitted using light signals, not electrical signals. For example, a logical one may be represented by a light pulse of a specific duration and frequency, a logical zero may be represented by the absence of a light pulse for the same duration. Optical fiber has the advantage of having a much greater bandwidth than copper wire.
While fiber optic cabling is very efficient for transferring data, the use of light signals to process data is still very difficult. For instance, currently there is no efficient way to “store” light signals representative of data. Networks therefore use fiber optics for transmitting data between nodes and silicon chips to process the data within computer nodes. This is accomplished by using fiber optic transceivers, which convert light signals from a fiber optic cable into electrical signals, and vice versa.
FIG. 1
illustrates a perspective view of an exemplary optoelectronic module
100
that can be used to form an optical transceiver.
Optoelectronic module
100
includes a semiconductor chip subassembly (CSA)
102
and an optical subassembly (OSA)
104
. CSA
102
is a packaged semiconductor device. As shown in
FIG. 1
, CSA
102
is a rectangular block of molding material
106
that has electrical contacts
108
exposed through its bottom and side surfaces. Within the block of molding material
106
is a semiconductor die that is electrically connected to contacts
108
. For instance, wire bonds can be used for such connections. Another aspect of CSA
102
that cannot be seen is the up-linking contacts on the top surface of CSA
102
. These up-linking contacts are also electrically connected to the encapsulated semiconductor die and therefore provide the electrical communication between the semiconductor die and OSA
104
. The specific CSA
102
that is shown is a leadless leadframe semiconductor package (LLP). However, it should be understood that CSA
102
can be formed of various types of molded packages.
A conventional OSA
104
includes a conventional backing block
110
, a circuitry substrate
112
, and photonic devices
114
. Backing block
110
has a front surface
116
that supports circuitry substrate
112
and photonic devices
114
, which are attached to circuitry substrate
112
. A conventional backing block
110
can be formed of a variety of materials such as a ceramic material, polyethylene ether ketone (PEEK), or liquid crystal polymer (LCP). Examples of such conventional OSA's
104
and backing blocks
104
are known to persons having ordinary skill in the art. One typical example of such a conventional backing block is described, for example, in the U.S. patent application Ser. No. 10/165/711, entitled “C
ERAMIC
O
PTICAL
S
UB
-A
SSEMBLY
F
OR
O
PTO
-E
LECTRONIC
M
ODULES
,” filed on Jun. 6, 2002.
In conventional implementation, a circuitry substrate
112
is attached to a front surface
116
of backing block
110
, wraps around the bottom-front corner of backing block
110
, and covers most of the bottom surface of backing block
110
. Traces of the circuitry substrate
112
run from photonic devices
114
on the front surface to the bottom surface of backing block
110
where they make contact with the up-linking contacts of CSA
102
. In an effort to maximize the number of electrical connections possible, size dimensions of the foregoing devices are small. However, even though the size dimensions are made small, the fact that the circuitry substrate
112
is formed only at the surface (or in some implementations two layers deep) of the backing block
110
limits the overall number of electrical connections that can be made from the photonic devices
114
to contacts of the CSA
102
.
Additionally, such surface mounted circuitry substrates
112
can suffer from “cross-talk”. In typical implementation, size dimensions involved with circuitry substrate
112
are small and cause the circuit traces to be positioned very close to each other. The small size is advantageous in the same way that small sizes for most electronic devices are advantageous. However, the close proximity of the traces can cause “cross-talk,” especially at high operational frequencies. Cross-talk is the electrical interference between two or more electrically conducting elements. Such cross-talk can drastically reduce the performance of optoelectronic device
100
.
FIG. 2
is a schematic depiction of a conventional backing block
204
(depicted upside down) showing a bottom side
201
and a facing side
202
. Commonly, the photonic devices
214
are formed on the facing side
202
of the block
204
and electrically connected to contact pads
215
on the bottom side
201
. The photonic devices
214
are electrically connected to contact pads
215
using surface metallization techniques. Typically, the photonic devices
214
are electrically connected to contact pads
215
using electric traces (or leads)
216
formed on a special contact tape that adheres to the block
204
. A problem with this implementation is that the electric traces
216
have a tendency to fail in the region where the tape bends over the edge
217
of the block
204
.
In view of the foregoing, what is needed is an efficient technique for forming high density electrical connections from the photonic devices of an optical device to an associated semiconductor chip device such that the connections exhibit high circuit density and low levels of cross-talk.
BRIEF SUMMARY OF THE INVENTION
The present invention is directed to a high performance and small-scale circuitry substrate and supporting block used in optical sub-assemblies. In one embodiment an optical sub-assembly (OSA) suitable for optical interconnection with optical fibers and electrical interconnection with a chip sub-assembly (CSA) is formed. The OSA includes a ceramic block having a first surface and a second surface, the ceramic block being formed using one of low temperature co-fired ceramic (LTCC) and high temperature co-fired ceramic (HTCC) techniques. Photonic devices are formed on the first surface of the ceramic block and electrical contacts are formed on a second surface of the block. The electrical contacts being suitable for electrical communication with a chip sub-assembly. Moreover, the electrical connections being formed so that they pass internally through the ceramic block to electrically interconnect the photonic devices on the first face of the block with the electrical contacts on the second face of the block.
Another embodiment includes a ceramic block having a first face and a second face. The block being formed using one of low temperature co-fired ceramic (LTCC) and high temperature co-fired ceramic (HTCC) techniques. The first face of the ceramic block has at least one photonic device formed thereon. Contact pads are formed on the second face of the ceramic block. The block also includes electrical connections that are electrically connected to the photonic devices and pass through internal portions of the ceramic block to so that the electrical connections can electrically the photonic devices to a chip sub-assembly (CSA). The electrical connections can include both signal connections and ground connections. Moreover, embodiments can include internal shielding layers. The configuration of the block can be designed so that cross-talk is reduced, low levels of ground-bounce and electrical parasitics are exhibited, and optimal impedance levels can be obtained. The circuitry substrate can be advantageously used to form an optical sub-assembly (OSA) used in an optoelectronic module.
In another embodiment, the ceramic block includes a plurality

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