Active solid-state devices (e.g. – transistors – solid-state diode – Transmission line lead
Reexamination Certificate
2000-10-09
2001-08-07
Clark, Sheila V. (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Transmission line lead
C257S691000
Reexamination Certificate
active
06271579
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to the field of microelectronic packages for high-frequency electronic devices, and specifically relates to a high-frequency passband microelectronic package for use as a leaded electronic interconnect housing for a high-frequency electronic device operating at frequencies within the passband.
BACKGROUND OF THE INVENTION
A key requirement for the packaging of a microelectronic device is that signals move through the package's conductive interconnects such that the electrical interconnection causes minimal change in the signals. It is difficult, however, to fabricate microelectronic packages to achieve minimal signal change at higher frequencies, i.e., frequencies in the Gigahertz (GHz) range. Along with limited frequency ranges, conventional microelectronic packages have excessive transmission and reflective losses, limited input/output isolation, high cost, and limited reliability, resulting in a lack of general applicability.
It is even more difficult to fabricate high frequency microelectronic packages which can be connected via conductive leads to a next level of assembly such as a circuit board or other microelectronics package. Conventional leaded microelectronic packages, including those having stripline transmission lines, experience unacceptable insertion and return signal losses which change the signals at high frequencies. The unacceptable electrical properties are due to impedance discontinuities caused by the leads, and interconnections between the leads and mating lead pads on the package and on the next level of assembly.
The above-listed related applications and patents disclose improved microelectronic packages that address one or more of the problems due to limitations and disadvantages of the related art. For example, U.S. Pat. No. 5,448,826 shows a ceramic microelectronics package
100
suitable for housing high-frequency electronic devices, as shown in
FIGS. 1-3
herein. Package
100
includes a base
102
, first attaching means
104
, a ceramic radio-frequency (RF) circuit substrate
106
, second attaching means
108
, a ceramic seal ring substrate
110
, non-conducting third attaching means
112
, and a ceramic lid
114
. Package
100
is used as an electronic interconnect housing for a high-frequency electronic device or component
116
mounted to base
102
. Device
116
is received within a cavity
120
formed within circuit substrate
106
. A plurality of conductive traces
122
patterned on circuit substrate
106
provide electrical connections between device
116
and an external device (not shown). Seal ring substrate
110
has a cavity
124
larger than cavity
120
. Device
116
is an exemplary high-frequency electronic device housed within package
100
, and it is understood that device
116
represents any high-frequency electronic device or component. Package
100
, and the process for making package
100
, are fully disclosed in the '826 patent, which is incorporated herein by reference.
Each conductive trace
122
in package
100
forms a portion of a microstrip transmission line. “Microstrip transmission line” is defined herein as being a conductor suspended above a ground plane and separated from the ground plane by a dielectric. Each conductive trace
122
is a conductor, base
102
forms a ground plane, ceramic circuit substrate
106
is a dielectric, and each trace
122
is suspended above base
102
and is separated from base
102
by substrate
106
. Thus, each conductive trace
122
forms a portion of a microstrip transmission line which propagates a signal between the external device and device
116
as electric and magnetic fields. The impedance of microstrip transmission lines is a function of the dielectric value of substrate
106
, the width of traces
122
, the gap to the top surface of the ground plane formed by base
102
, and the thickness of substrate
106
below traces
122
. Mathematical formula are known which approximate the impedance for given dielectric and conductor parameters and geometries.
Each microstrip transmission line in package
100
has the form of a microstrip, embedded microstrip, microstrip transmission line as the line transitions from outside package
100
, beneath seal ring substrate
110
, to inside package
100
. An “embedded microstrip transmission line” is a microstrip transmission line located beneath a second dielectric material, i.e., sandwiched between two dielectric layers or materials. Since ceramic circuit substrate
106
and seal ring substrate
110
are both formed from dielectric material, the middle portion of each microstrip transmission line passing beneath seal ring substrate
110
has the form of an embedded microstrip transmission line, and the portions of each microstrip transmission line on either side of substrate
110
(i.e., not beneath substrate
110
) have the form of regular (i.e., non-embedded) microstrip transmission lines.
The microstrip transmission lines in package
100
, including conductive traces
122
, transition through microstrip feed-throughs when entering and exiting the package. A “feed-through” is an area within a dielectric through which a portion of a conductive trace which passes, such as from the interior of a package to the exterior of a package. For example, the presence of seal ring substrate
110
causes the microstrip transmission lines to pass through such an area as the transmission lines transition from outside package
100
to inside package
100
. Thus, the feed-throughs of package
100
can be referred to as microstrip feed-throughs.
Package
100
can be referred to as a high-frequency broadband microelectronics package. “Broadband” refers to the ability of broadband signals (DC to GHz frequencies) to move through the package's conductive interconnects such that the electrical connections cause minimal change in the signals. Each trace
122
includes an outer conductive bonding pad for electrical connection to the next level of assembly (e.g., a circuit board or another package) by wire or ribbon bonding the outer bonding pad to a corresponding or mating pad on the next level of assembly. For example, the mating pads may be joined by a thin gold wire tack-welded to each pad and passing over a gap between the pads. The only deviations from a continuous transmission line (which would give an optimal frequency response) is the error in matching the width of the bond wire to the width of the transmission line conductor, the weld joints, the gap in the dielectric, and a small gap in the ground plane. The use of wire or ribbon bonds to perform these interconnections provides the transmission lines with an impedance compatible with high frequencies.
Package
100
, however, is not designed to be connected to the next level of assembly using conductive leads in such high-frequency applications. A “lead” is typically a generally rectangular piece of metal conductor which can be electrically connected by braising or soldering the lead between a lead pad formed on a microelectronics package and a mating lead pad formed on a next-level circuit board or another package. A “lead pad” is an anchor pad formed in the transmission line for receiving the lead. For example, on a package including a 10 mil (i.e., 0.010″) thick, 96% alumina ceramic circuit substrate, the calculated width of the conductor for a microstrip transmission line would be 10 mil. The ideal lead would also be 10 mil wide, and would be attached to the conductor without creating a lump.
In practice, however, the end of the conductor where the transmission line approaches the edge of the package is widened to form a lead or anchor pad 25 mil wide to provide a strong mechanical bond between the lead and the lead pad. The lead pad is made wider than the lead to allow for some mis-alignment during assembly and for an attachment fillet. The lead also has a finite thickness creating a change in thickness of the transmission line. The braise or solder used to connect the lead between the lead pads forms lumps. The c
Going Timothy J.
Lindner Alan W.
Brown Martin Haller & McClain
Clark Sheila V.
Stratedge Corporation
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