Wave transmission lines and networks – Long line elements and components – Strip type
Reexamination Certificate
1999-06-16
2002-07-30
Bettendorf, Justin P. (Department: 2817)
Wave transmission lines and networks
Long line elements and components
Strip type
C257S664000, C257S737000, C257S738000, C333S034000
Reexamination Certificate
active
06426686
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention is related to the field of packages for Microwave Circuits, especially in the frequency band from 20 GHz and higher.
2. Prior Art
Microwave Monolithic Integrated Circuits (MMIC) and other microwave integrated circuit (IC) devices for microwave signals have been packaged using complex, high reliability, high cost packages, the designs of which are not conducive to high volume assembly. These MMIC packages (packages) have been used in such specialty microwave applications as Radio Frequency (RF) telescopes and other speciality applications.
However, in the growing markets of more mainstream commercial applications, e.g., Personal Communication Services, there is the need for low cost, wideband, surface mounted, reliable, user friendly MMIC packages. One such example of a growing commercial microwave application is the development of Line Microwave Distribution Systems (LMDS), two point radios and obstacle detection radar for automotive vehicles. Moreover other applications have been identified at 23, 28, 32, 38, 60 and 70 Ghz and higher, and the industry is approaching production of these products.
The MMIC packages are intended primarily for MMICs constructed substantially of semiconductor materials suitable for high frequency operation, e.g, Gallium Arsenide. The MMIC is generally bonded to a package substrate constructed of a ceramic material, e.g., alumina, having thin films of metals, e.g., nickel or titanium, disposed on its surface in the form of an arrangement of wave guides. The waveguides comprise a patterned metalization which includes a plurality of ground planes, signal traces and unmetalized gaps through which the microwave signals are transmitted. The MMIC is connected to the ground planes and signal traces on the surface of the substrate by methods such as wirebonding, solder bumps or flipped chips. Vias, e.g., holes or slots, in the ceramic substrate are filled with a conductive composite material such as copper-tungsten, which provides a transmission path for the signal from the metalization on the surface through the substrate itself. The composite material within the vias is in turn connected to input/output (I/O) ports of the MMIC package, which transmit the microwave signals therethrough. Existing packages are surface mounted to a mother PC board and are connected to the circuitry of the PC board through the I/O ports, which can include conductive balls (spheres), bumps (rounded protrusions), ribbons or leads.
The MMIC of the MMIC package is connected to the mother PC board in a way that is electrically transparent to microwave signals transmitted therebetween. Achieving electrical transparency requires matching the impedance of the microwave transmission path through all transition areas for the signal, i.e., areas between waveguides, from the mother board to the MMIC. Prior art transition areas for the signal include: 1) from the mother board through the I/O connection between the mother board and the package substrate, 2) through the substrate itself, and 3) from the surface where the MMIC is installed through the connection (e.g. wirebond, flip chip) to the MMIC.
Referring to
FIG. 1
, a prior art MMIC package
10
is illustrated where a mother PC board
12
has a waveguide
14
bonded to its top surface, and a substrate
16
has waveguides
18
and
20
bonded to its underside and topside respectively. The waveguide
14
includes signal conductor
30
and ground conductors
32
and
34
; waveguide
18
includes signal conductor
36
and ground conductors
38
and
40
; and waveguide
20
includes signal conductor
42
and ground conductors
44
and
46
. Transition area
1
, i.e., I/O ports of package
10
, comprises thin and wide conductive stubs
22
, transition area
2
, i.e., through substrate
16
, comprises narrow and wide slots (vias)
24
in the package substrate filled with an electrically conductive material, and transition area
3
comprises wire bonds
26
connected to the MMIC
28
.
FIG. 1
illustrates where the dielectric constants of the substrate
16
and the mother board
12
are the same and the two transitions
1
and
2
of the waveguide structures are very close to the ideal. One of the factors in the representation of
FIG. 1
that makes the transitions close to ideal are the conductively filled vias
24
and stubs
22
that match the width of the conductors with which they make contact (
30
,
32
,
34
on the mother board;
36
,
38
,
40
on the underside of the package; and
42
,
44
and
46
on the top surface of the substrate
16
). The lack of variation in dielectric constant in this Figure enables the use of straight coplanar waveguide structures.
In order to provide the transmission path through the substrate
16
itself, the transition area
2
, the vias
24
are preferably drilled in the ceramic substrate with a carbon dioxide or YAG laser. The slots are then filled with the conductive composite material in a powder form, whereby the powder is melted in ovens and then cooled to provide conductively filled through structures, i.e., vias, for the microwave signals. However the ceramic substrate is brittle and can often be cracked by the thermal expansion and contraction of the composite material. This is especially problematic when there are a large number of vias for a complex circuit or the substrate is relatively thin.
Problematically, package substrate thickness is defined by a tradeoff between performance, mechanical strength and cost. The thicker the substrate the greater the mechanical strength and the less breakage that occurs during the manufacturing process. Yet it is generally required to minimize via length, by reducing the thickness of the substrate, in order to enhance high frequency performance and to facilitate impedance matching of the transition area. However, the brittle ceramic substrate can contain a high density of vias, which makes the substrate very fragile, difficult to handle and expensive. Therefore, the chances of losses due to thin substrate breakage are increased when the substrate is made thinner. Thus, the requirement for a thinner substrate may result in losses due to substrate breakage.
The deficiencies and limitations of the above package are eliminated or greatly alleviated by the present invention.
SUMMARY OF THE INVENTION
This invention offers advantages and alternatives over the prior art by providing a circuit package for a microwave signal having a reduced number of vias in the substrate. The substrate of the package is devoid of signal carrying vias. Advantageously, the invention eliminates a transition area for the signal through the substrate of the package. Moreover, because signal carrying vias are avoided the substrate can be made substantially thick so that manufacturing yield losses due to substrate breakage can be virtually eliminated. Additionally, high frequency performance is enhanced and impedance matching is facilitated.
These and other advantages are accomplished in an exemplary embodiment of the invention by providing a circuit package for a microwave signal. The circuit package comprises a substrate defining a MMIC surface of the substrate and an opposing non-MMIC surface of the substrate. The substrate is devoid of signal carrying vias. An arrangement of waveguides are disposed on the MMIC surface of the substrate. A MMIC is disposed on the MMIC surface of the substrate, and the MMIC is in electrical communication with the waveguide(s). An I/O port is in electrical communication with the waveguide wherein a transmission path for the signal is provided from the I/O port, through the waveguide and to the MMIC.
In a preferred embodiment of the invention, the MMIC surface of the substrate faces the PC board when the I/O port is electrically connected to the PC board.
In another exemplary embodiment, the circuit package includes at least one ground carrying via providing a conductive connection between a pair of ground planes for the signal. The pair of ground planes are disposed on the MMIC surfac
Douriet Daniel F.
Hernandez Jorge M.
Panicker M. P. Ramachandra
Bettendorf Justin P.
Cantor & Colburn LLP
Microsubstrates Corporation
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