Electricity: conductors and insulators – With fluids or vacuum – Conduits – cables and conductors
Reexamination Certificate
2000-02-15
2001-11-13
Nguyen, Chau N. (Department: 2831)
Electricity: conductors and insulators
With fluids or vacuum
Conduits, cables and conductors
C333S244000
Reexamination Certificate
active
06316719
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to RF (including microwave) interconnections among layers of assemblies of multiple integrated circuits, and more particularly to compliant interconnection arrangements which may be sandwiched between adjacent circuits.
BACKGROUND OF THE INVENTION
Active antenna arrays are expected to provide performance improvements and reduce operating costs of communications systems. An active antenna array includes an array of antenna elements. In this context, the antenna element may be viewed as being a transducer which converts between free-space electromagnetic radiation and guided waves. In an active antenna array, each antenna element, or a subgroup of antenna elements, is associated with an active module. The active module may be a low-noise receiver for low-noise amplification of the signal received by its associated antenna element(s), or it may be a power amplifier for amplifying the signal to be transmitted by the associated antenna element(s). Many active antenna arrays use transmit-receive (T/R) modules which perform both functions in relation to their associated antenna elements. The active modules, in addition to providing amplification, ordinarily also provide amplitude and phase control of the signals traversing the module, in order to point the beam(s) of the antenna in the desired direction. In some arrangements, the active module also includes filters, circulators, and or other functions.
A major cost driver in active antenna arrays is the active transmit or receive, or T/R module. It is desirable to use monolithic microwave integrated circuits (MMIC) to reduce cost and to enhance repeatability from element to element of the array. Some prior-art arrangements use ceramic-substrate high-density-interconnect (HDI) substrate for the MMICs, with the substrate mounted to a ceramic, metal, or metal-matrix composite base for carrying away heat. These technologies are effective, but the substrates may be too expensive for some applications.
FIG. 1
illustrates a cross-section of an epoxy-encapsulated HDI module
10
in which a monolithic microwave integrated circuit (MMIC)
14
is mounted by way of a eutectic solder junction
16
onto the top of a heat-transferring metal deep-reach shim
18
. The illustrated MMIC
14
, solder
16
, and shim
18
are encapsulated, together with other like MMIC, solder and shim assemblies (not illustrated) within a plastic encapsulant or body
12
, the material of which may be, for example, epoxy resin. The resulting encapsulated part, which may be termed “HDI-connected chips” inherently has, or the BP an lower surfaces are ground and polished to generate, a flat lower surface
12
ls
BP an
us
. The flat lower surface
12
ls
, and the exposed lower surface
18
ls
of the shim, are coated with a layer
20
of electrically and thermally conductive material, such as copper or gold. As so far described, the module
10
of
FIG. 1
has a plurality of individual MMIC mounted or encapsulated within the plastic body
12
, but no connections are provided between the individual MMICs or between any one MMIC and the outside world. Heat which might be generated by the MMIC, were it operational, would flow preferentially through the solder junction
16
and the shim
18
to the conductive layer
20
.
In
FIG. 1
, the upper surface of MMIC
14
has two representative electrically conductive connections or electrodes
14
1
and
14
2
. Connections are made between electrodes
14
1
and
14
2
and the corresponding electrodes (not illustrated) of others of the MMICs (not illustrated) encapsulated within body
12
by means of HDI technology, including flexible layers of KAPTON on which traces or patterns of conductive paths, some of which are illustrated as
32
1
and
32
2
, have been placed, and in which the various layers are interconnected by means of conductive vias. In
FIG. 1
, KAPTON layers
24
,
26
, and
30
are provided with paths defined by traces or patterns of conductors. The layers illustrated as
24
and
26
are bonded together to form a multilayer, double-sided structure, with conductive paths on its upper and lower surfaces, and additional conductive paths lying between layers
24
and
26
. Double-sided layer
24
/
26
is mounted on upper surface
12
us
of body
12
by a layer
22
of adhesive. A further layer
30
of KAPTON, with its own pattern of electrically conductive traces
32
2
, is held to the upper surface of double-sided layer
24
/
26
by means of an adhesive layer
28
. The uppermost layer of electrically conductive traces may include printed antenna elements in one embodiment of the invention. As mentioned above, electrical connections are made between the conductive traces of the various layers, and between the traces and appropriate ones of the MMIC contacts
14
1
and
14
2
, by through vias, some of which are illustrated as
36
. The items designated MT
0
, MT
1
, MT
2
, and MT
3
at the left of
FIG. 1
are designations of various ones of the flexible sheets carrying the various conductive traces. Those skilled in the art will recognize this structure as being an HDI interconnection arrangement, which is described in U.S. Pat. No. 5,552,633, issued Sep. 3, 1996 in the name of Sharma.
As illustrated in
FIG. 1
, at least one radio-frequency (RF) ground conductor layer or “plane”
34
is associated with lower layer
24
of the double-sided layer
24
/
26
. Those skilled in the art will realize that the presence of ground plane
34
allows ordinary “microstrip” transmission-line techniques to carry RF signals in lateral directions, parallel with upper surface
12
us
of plastic body
12
, so that RF signals can also be transmitted from one MMIC to another in the assembly
10
of FIG.
1
.
Allowed U.S. patent application Ser. No. 08/815,349, in the name of McNulty et al., describes an arrangement by which signals can be coupled to and from an HDI circuit such as that of FIG.
1
. As described in the McNulty et al. application, the HDI KAPTON layers with their patterns of conductive traces are lapped over an internal terminal portion of a hermetically sealed housing. Connections are made within the body of the housing between the internal terminal portion and an externally accessible terminal portion.
One of the advantages of an antenna array is that it is a relatively flat structure, by comparison with the three-dimensional curvature of reflector-type antennas. When assemblies such as that of
FIG. 1
are to be used for the transmit-receive modules of an active array antenna, it is often desirable to keep the structure as flat as possible, so as, for example, to make it relatively easy to conform the antenna array to the outer surface of a vehicle.
FIG. 2
a
illustrates an HDI module such as that described in the abovementioned McNulty patent application. In
FIG. 2
a
, representative module
210
includes a mounting base
210
, to which heat is transferred from internal chips. A plurality of mounting holes are provided, some of which are designated
298
. A contoured lid
213
is hermetically sealed to a peripheral portion of base
212
, to protect the chips within. A first set of electrical connection terminals, some of which are designated as
222
a
,
224
a
, and
226
a
are illustrated as being located on the near side of the base, and a similar set of connection terminals, including terminals designated as
222
b
,
224
b
, and
226
b
are located on the remote side of the base.
FIG. 2
b
is a perspective or isometric view, partially exploded, of an active array antenna
200
. In
FIG. 2
b
, the rear or reverse side (the non-radiating or connection side) of a flat antenna element structure
202
is shown, divided into rows designated a, b, c, and d and columns
1
,
2
,
3
,
4
, and
5
. Each location of array structure
202
is identified by its row and column number, and each such location is associated with a set of terminals, three in number for each location. Each array location of antenna element array
202
is associated with an antenna element, which is on the o
Nixon Doreen Marie
Pluymers Brian Alan
Lockheed Martin Corp.
Meise W. H.
Nguyen Chau N.
Weinstein S. D.
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