Wave transmission lines and networks – Long line elements and components – Strip type
Reexamination Certificate
2003-04-08
2004-09-14
Callahan, Timothy P. (Department: 2816)
Wave transmission lines and networks
Long line elements and components
Strip type
C257S664000
Reexamination Certificate
active
06791439
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to a connection structure providing an electrical connection between substrates of high-frequency circuit substrates in which high-frequency electronic components are packaged in a high-frequency electronic device processing a high-frequency signal such as microwave, millimeter wave or the like. The invention also relates to a method for manufacturing the mentioned connection structure and to a high-frequency circuit device constructed of the high-frequency circuit substrate and the connection structure.
2. Description of the Related Art
It is an essential requirement that electronic circuit such as commercial communication apparatus, satellite, radar, etc., which are used in a high-frequency radio frequency band of, e.g., X band (5.2-10.9 GHz) and K band (10.9-36.0 GHz), are low in loss and high in reliability.
Particularly, as a high-frequency circuit substrate packaged with high-frequency electronic components, a ceramic substrate of a low dielectric loss and a printed wiring board made of a fluorocarbon resin or BT (bismaleimid triazine) resin have been commonly utilized.
As to a high-frequency circuit substrate packaged with high-frequency electronic components, it is often the case that a plurality of high-frequency circuit substrates are connected and used for reasons of design or circuit assembly.
When connecting such high-frequency circuits to each other, connection with the use of a connector and cable is carried out commonly and generally in order to maintain the above-mentioned low loss and high reliability.
However, a connection structure using the connector and cable brings about the following problems.
A problem exists in that a machining cost becomes exceedingly high as well as downsizing is not easy since a connector consisting of a large number of precision components is manufactured by machining.
Another problem exists in that use of cables causes bulky connection portions, or incapability of weight saving.
Therefore, a connection method without use of any connector and cable has been devised for the purpose of achieving reduction in cost and size.
Connection between the high-frequency circuit substrates is not achieved just by connecting the substrates to each other through a conductor. A further problem exists in that sufficient electrical characteristic cannot be achieved without obtaining matching in the light of a high-frequency circuit.
Consequently, a still further problem exists in that a low-cost connection method used in a low-frequency circuit cannot be applied to the connection of a high-frequency circuit as it is.
On the other side, a further problem exists in that a long-term reliability cannot be preserved without absorbing or diminishing in any way a mechanical stress (i.e., heat stress) that is applied to a connection portion due to difference in linear expansion coefficient of the substrate or in connection structure due to change in ambient temperature.
An attempt for providing a connection between the substrates while satisfying electric characteristic and reliability has been proposed in the form of a connection structure, for example, in a patent document 1 (the Japanese Patent Publication (unexamined) No. 240601/1995.
As described in the above-mentioned patent document 1, this attempt is a method for implementing connection between two high-frequency circuit substrates, which are packaged onto a metal base, with the use of a connecting conductor molded in a semicircular shape.
To satisfy the electric characteristic, various types of conductors are devised.
That is, to deal with an impedance mismatch at a connection portion, a conductor for connection is formed into a plate shape, and conforms to a micro strip line in width.
Furthermore, a semicircular connection conductor
4
is packaged with a convex portion thereof facing to a metal base so as to be close to ground thereby causing an impedance mismatch to be smaller.
A heat stress generated at the connection portion due to temperature change and difference in linear expansion coefficient between the substrate and the connection conductor is to be absorbed or diminished by forming a connection conductor into a semicircular shape.
Meanwhile, the connection conductor, which is a single metal strip as shown in the patent document 1, is hard to be handled.
Although depending on conditions at the time of designing a circuit, the connection conductor becomes a minute part, which is several dozen to several hundred &mgr;m square, thereby making it hard to handle.
For the same reason, operations for positioning and accurately packaging the connection conductor at a predetermined place on a high-frequency circuit substrate come to be extremely difficult.
Electrically, in the case where structure of the high-frequency transmission line is designed as a micro strip line, connection can be performed only with one part (connection conductor). For applying the connection conductor to a coplanar transmission line, however, three parts have to be used.
In addition, a coplanar transmission line is a type of transmission line processing a high-frequency signal, that is, a form in which ground potential parts (GND electrodes) are disposed adjacent on both sides of the high-frequency signal line.
Accordingly, to provide a connection between the substrates of the coplanar transmission line, required are one connection conductor acting as a connection conductor for mutually connecting the high-frequency signal lines and two connection conductors for connecting together the ground potential parts (GND electrodes) located on both sides of the high-frequency signal line.
It is extremely difficult to package a large number of such separate minute parts (i.e., connection conductors) close to one another.
Particularly in the case of joining them by soldering, e.g., movement of parts due to surface tension at the time of solder fusion should be taken into consideration.
Furthermore, in terms of function to absorb or diminish a heat stress, a semicircular connection conductor cannot be used in the case where interval between the substrates is narrow since the connection conductor is constructed so as to absorb or diminish a stress, which is applied to a connection portion, at a semicircular portion thereof.
Likewise, in the case where the substrate is thin, and distance between the micro strip line on the upper surface of the substrate and the metal base is small, a semicircular height portion of the connection conductor comes to be an obstacle without any sufficient level difference, thereby making it hard to package the semicircular connection conductor.
Furthermore, the packaging employs a method of connecting the substrates at the end portions thereof, and therefore it is necessary to form a transmission line such as micro strip line possessing high dimension accuracy up to the end portion of the substrate.
To realize this, routing is required since an inexpensive substrate machining such as punching, which renders poor finish accuracy at the end portion of the substrate.
When machining with a router the substrate on which a conductor resides up to the end portion, a copper foil at the machined portion may be turned up thereby making it difficult to secure accuracy at the end portion.
In addition, routing is a type of machining with the use of a NC (numerical control) router machine, which is a method for machining an article to be processed by feeding a rotating tool provided with spiral blades to the article.
Therefore, it is certainly possible to process an article with high accuracy even if it is of a complicated configuration. But there is a disadvantage of high machining cost since an expensive working machine is used.
Further, in the high-frequency circuit substrate that is a component of the high-frequency device, deformation such as warp, torsion or wave often occurs depending on manufacturing conditions or production lot regardless of an organic material or inorganic material. Such occurrence of deformation is a differen
Kitamura Yoichi
Tahara Yukihiro
Tsumura Akira
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