Active solid-state devices (e.g. – transistors – solid-state diode – Transmission line lead
Reexamination Certificate
1998-12-23
2001-01-09
Clark, Sheila V. (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Transmission line lead
C257S710000
Reexamination Certificate
active
06172412
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a microelectronic package suitable for high frequency devices, using a minimum of conductive materials and a process for making the electronic package. More particularly, the invention relates to a microelectronic package design that eliminates superfluous electrical conductors and can be used as an electronic interconnect housing for high frequency electronic devices and components.
2. Description of Related Art
A key requirement for the packaging of a microelectronic device is that signals move through the package's conductive interconnects in such a way 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., greater than 20 Gigahertz (GHz).
A conventional microelectronic package design achieves transfer of signals in and out of the package for frequencies as high as 23 GHz. This package has a metal cover, which must be maintained at the same electrical potential as the electrical circuit ground to achieve such performance. In order to ground the cover, however, internal vias and external side metallization are required. This added metal, in relatively close proximity to the internal circuit and electrical conductors, debases and limits the ultimate performance of the device. Moreover, conventional packages have limited frequency range, excessive transmitted and reflective loss, limited input/output isolation, high cost, and limited reliability, resulting in a lack of general applicability.
Therefore, a need exists for a microelectronic package that eliminates superfluous electrical conductors, provides structural packaging members fabricated from non-conductors and having a relatively uniform dielectric constant, has a high frequency range, and is low in cost without sacrificing reliability.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to a microwave electronic package that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
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 apparatus and method particularly pointed out in the written description and claims hereof, as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention is a microelectronic package suitable for high-frequency electronic devices. The package comprises a base having at least partial conductivity which establishes the electrical ground plane and having a top and a bottom; a radio frequency (“RF”) substrate made of ceramic and having a first cavity and a plurality of conductive patterns deposited on the surface of the ceramic RF substrate; means for attaching the ceramic RF substrate to the top of the base; a ceramic seal ring substrate having a second cavity larger than the first cavity; second means for attaching the ceramic seal ring substrate to the RF substrate, the second attaching means generally matching the dimensions of the seal ring; and a ceramic lid attached to the ceramic seal ring substrate by a non-conductive third attaching means.
In another aspect, the present invention is a process for assembling a ceramic microelectronic package having a base, a RF substrate made of ceramic, and a ceramic seal ring substrate, each of the base, the RF substrate, and the ceramic seal ring substrate having a top surface and a bottom surface. The process comprises screen printing a conductive paste on the top surface of the RF substrate; drying and firing the conductive paste; patterning conductive paths using the conductive paste on the top surface of the RF substrate; screen printing a first seal glass layer on the top surface of the RF substrate; drying and glazing the first seal glass layer; screen printing a second seal glass layer on the bottom surface of the ceramic seal ring substrate; drying and glazing the second seal glass layer; subassembling the RF substrate and the ceramic seal ring substrate; and attaching the top surface of the base to the bottom surface of the RF substrate.
The step of subassembling the RF substrate and the ceramic seal ring substrate includes the following substeps: abutting the top surface of the RF substrate to the bottom surface of the ceramic seal ring substrate to form a subassembly, heating the subassembly, screen printing a metallic material on the bottom surface of the RF substrate, and drying and firing the metallic material.
The step of attaching the top surface of the base to the bottom surface of the RF substrate includes the following substeps: applying an adhesive material in the alternative to the top surface of the base or to the bottom surface of the RF substrate, abutting the top surface of the base to the bottom surface of the RF substrate to form an assembly, and curing the assembly with heat, pressure, or other means appropriate to the sealing material used.
In a first alternative embodiment of the present invention, the ceramic seal ring, third attaching means, and ceramic lid may be replaced by a sealing cap. This sealing cap is attached directly to the top of the RF substrate by the second means for attaching.
The process for assembling the ceramic microelectronic package which incorporates the sealing cap includes screen printing a conductive paste on the top surface of the RF substrate; drying and firing the conductive paste; patterning conductive paths using the conductive paste on the top surface of the RF substrate; screen printing a layer of adhesive on the top surface of the RF substrate; drying and glazing the first seal glass layer; screen printing a metallic material on the bottom surface of the RF substrate, and drying and firing the metallic material; and attaching the top surface of the base to the bottom surface of the RF substrate.
The step of attaching the top surface of the base to the bottom surface of the RF substrate includes the following substeps: applying an adhesive material in the alternative to the top surface of the base or to the bottom surface of the RF substrate, abutting the top surface of the base to the bottom surface of the RF substrate to form an assembly; and heating the assembly.
In a second alternative embodiment of the present invention, leads may be electrically attached to the conductive paths formed on the RF substrate. These leads are shaped to extend outwardly from the RF substrate to facilitate making the necessary electrical connections to the package.
In yet a third alternative embodiment of the present invention, the conductive patterns which are deposited on the RF substrate may be formed without transitions, i.e., eliminating the compensation in impedance which is used in the transition from the microstrip line inside the package to the embedded microstrip line immediately underneath the seal ring or cap sidewall to the microstrip line outside of the package. As a result of eliminating the impedance compensation, though contrary to conventional wisdom within the art, the conductor patterns exhibit improved insertion loss and return loss responses in high frequency applications (>1 GHz), even as high as 30-45 GHz. Thus, the third alternative embodiment is capable of housing a high frequency microelectronic device, without having to incorporate transition compensations in the conductor patterns in the embedded microstrip at the feedthrough under the seal ring or sealing cap.
The process for assembling the third alternative embodiment may follow the processes for either the preferred embodiment which incorporates the ceramic seal ring and lid, or the first alternative embodiment which incorporates the sealing cap.
REFERENCES:
pat
Anderson Paul M.
Babiarz Joseph
Goetz Martin
Going Timothy
Lindner Alan W.
Brown Martin Haller & McClain
Clark Sheila V.
Stratedge Corporation
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