Electricity: conductors and insulators – Boxes and housings – Hermetic sealed envelope type
Reexamination Certificate
1998-12-04
2001-03-20
Kincaid, Kristine (Department: 2831)
Electricity: conductors and insulators
Boxes and housings
Hermetic sealed envelope type
C257S693000, C257S698000, C174S050510, C333S247000
Reexamination Certificate
active
06204448
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to packaging of microwave circuits in the high microwave frequencies and in applications using hermetically sealed packages for monolithic microwave integrated circuits, and more particularly to such packages having vias for transmitting signals into and out of the packages.
2. Description of Related Art
Ultra high speed monolithic microwave integrated circuits (MMIC), microwave integrated circuits (MIC), other integrated circuits and hybrid circuit dies are mounted in environmentally protective or hermetically sealed packages that provide electromagnetic shielding and easy handling. Known manufacturing techniques include cofired ceramic enclosures using thick or thin film metallization, glass or quartz seals, ceramic enclosures using thin-film metallization, metal enclosures having ceramic feedthroughs, and metal enclosures having glass feedthroughs.
In ceramic packages generally available for MMIC's, the main contributor to poor microwave performance is the feedthrough. The insertion loss of a coaxial line or stripline formed on the feedthrough through a hermetically sealed ceramic wall increases with higher frequency, which results in a diminished signal strength. High insertion loss degrades MIC performance in many ways such as increased noise figure of small signal devices and reduced output power and efficiency of a power amplifier. An MMIC package capable of good performance in the microwave range should have low insertion loss per feedthrough.
U.S. Pat. No. 5,117,068 describes a conventional packaging assembly having vias in the substrate for transmitting signals into and out of the package. As shown in
FIGS. 1A-1C
(exploded, perspective and cross-sectional views, respectively), the package
10
comprises a lead frame
11
, leads
12
an alumina base or substrate
13
having solid metal vias
14
extending therethrough, a seal-ring wall
15
and a cover
16
mounted together. The top surface of the substrate
13
is plated with a conductive film
17
.
FIGS. 2A-2C
show a conventional via structure for the type of packages shown in
FIGS. 1A-1C
.
FIGS. 2A and 2C
are the top and bottom views of the via structure, and
FIG. 2B
is a cross-sectional view along the line
2
B—
2
B in
FIG. 2A. A
first metallization layer
201
is formed on the top or inside surface of the substrate
210
to serve as the ground of the device mounted in the package. A wire bond pad metallization
202
is formed over and connected to the lead via
203
and is separated from the rest of the metallization layer
201
by a gap
204
. A second metallization layer
205
is formed on the bottom or outside surface of the substrate
210
as the ground. The ground metallization layers
201
and
205
on the top and bottom surfaces of the substrate
210
are electrically connected by a plurality of ground vias
206
that pass through the substrate. A lead pad metallization
207
is formed on the bottom surface separated from the ground metallization layer
205
by a gap
209
and is connected to the lead via
203
. A ground plane
212
is connected to the ground metallization layer
205
, and a lead
208
is connected to the lead pad
207
and extends outwardly under the seal-ring wall
211
over the edge of the substrate
210
.
SUMMARY OF THE DISCLOSURE
An object of the present invention is to improve the electrical transmission of a high frequency signal through a package using a relatively inexpensive method of construction with novel geometry to extend the operable frequency range of the package.
Additional features and advantages of the invention will be set forth in the description which follows and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
According to an embodiment of the present invention, an MMIC package assembly comprises a dielectric substrate having metal lead vias formed therethrough, a metal seal ring wall carried above the substrate, and a cover disposed over the seal ring wall, the package further comprising a via structure for transmitting high frequency electronic signals, the via structure including a wire bond pad metallization formed on the top or inside surface of the substrate and connected to the lead via, a lead pad metallization formed on the bottom or outside surface of the substrate and connected to the lead via, a lead on the bottom surface of the substrate connected to the lead pad metallization and extending outwardly under the seal ring wall over the edge of the substrate, and a sealed dielectric gap defined inside the substrate between the lead and the seal ring wall.
According to another embodiment of the present invention, an open dielectric gap is defined in the substrate above a portion of the leads so that the leads are partially suspended near the edge of the substrate.
According to one aspect of the invention, air or other low dielectric materials are used to constitute a gap between the metal lead and the seal ring wall. This enables the control of the ground current through a normally solid package while keeping the package hermetic.
According to another aspect of the present invention, the substrate of the package further has metallization layers formed on the top and bottom surfaces thereof to serve as the ground and ground metal vias formed through the substrate to connect the ground metallization layers. The top surface ground metallization layer is separated from the wire bond pad metallization by a dielectric gap, and the bottom surface ground metallization layer is separated from the lead pad metallization by another dielectric gap.
According to another aspect of the present invention, a ground plane is mounted on the bottom surface of the substrate and electrically connected to the ground vias to serve as the ground. The ground plane has two tabs extending parallel to the each lead on each side thereof. The gap between the ground plane and lead allows a predetermined impedance to be maintained at every point along the lead. The lead and ground plane act as a coplanar waveguide, which keeps the electric field in the plane of the bottom surface of the package.
According to another aspect of the present invention, the lead and the lead pad metallization have a strip shape and neck down to a narrower width where they pass under the dielectric gap in the substrate. This allows a predetermined impedance to be maintained everywhere along the length of the lead.
According to another aspect of the present invention, the ground vias are located as close as possible to the edge of the ground plane around the dielectric gap surrounding the lead pad metallization on the bottom face of the substrate.
According to another aspect of the present invention, the metal seal ring wall of the package has substantially uniform thickness, but is thinner in a portion where the wall passes over the lead and the surrounding coplanar waveguide.
REFERENCES:
patent: 4172261 (1979-10-01), Tsuzuki et al.
patent: 5117068 (1992-05-01), Seieroe et al.
patent: 5235300 (1993-08-01), Chan et al.
patent: 5387888 (1995-02-01), Eda et al.
patent: 5465008 (1995-11-01), Goetz et al.
patent: 5510645 (1996-04-01), Fitch et al.
patent: 5512781 (1996-04-01), Inoue
patent: 5536971 (1996-07-01), Oishi et al.
patent: 5792984 (1998-08-01), Bloom
Garland Paul
Long James Kyo
Park Chong-Il
Satoda Yozo
Hogan & Hartson L.L.P.
Kincaid Kristine
Kyocera America, Inc.
Ngo Hung V
LandOfFree
High frequency microwave packaging having a dielectric gap does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with High frequency microwave packaging having a dielectric gap, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and High frequency microwave packaging having a dielectric gap will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2443741