Electricity: electrical systems and devices – Housing or mounting assemblies with diverse electrical... – For electronic systems and devices
Reexamination Certificate
2000-02-03
2002-04-16
Gandhi, Jayprakash N. (Department: 7841)
Electricity: electrical systems and devices
Housing or mounting assemblies with diverse electrical...
For electronic systems and devices
C361S753000, C361S801000, C211S041170, C439S074000
Reexamination Certificate
active
06373710
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to electronic devices, such as microwave and photoelectronic equipment, having coaxial connectors and a high-frequency circuit board connected to the coaxial connectors.
2. Description of Related Art
FIG.
5
(A) is a perspective view illustrating an electronic device having coaxial connectors and a high-frequency circuit board. FIG.
5
(B) is a cross-sectional view partially illustrating the electronic device of FIG.
5
(A) in a mounted state. Referring to FIGS.
5
(A) and
5
(B), numeral
1
indicates a circuit board on which high-frequency circuits are mounted;
2
indicates a screw for fastening the circuit board
1
;
3
indicates a case for holding the circuit board
1
;
4
indicates an insertion hole formed in the circuit board
1
to accept the screw
2
;
5
indicates a soldering land formed on the circuit board
1
;
6
indicates a coaxial connector for externally transmitting high-frequency signals; and
7
indicates a lead terminal of the coaxial connector
6
to be soldered to the land
5
. Numeral
8
indicates a screw for fastening the coaxial connector. Numeral
9
indicates a threaded hole formed in the case
3
to accept the screw
2
. Numeral
10
indicates a cover attached to the case
3
.
In order to prevent degradation of the high-frequency signal transmitted between the circuit board
1
and the coaxial connector
6
, the characteristic impedance of the land
5
is matched with that of the coaxial connector
6
by setting the dielectric constant and thickness of the material for the circuit board
1
and the dimensions of the land
5
and the lead terminal
7
to an optimum value.
In the method of mounting the electronic device, screws
2
are respectively threaded into the threaded holes
9
formed in the case
3
through the holes
4
so that the circuit board
1
is fixed to the case
3
. The coaxial connectors
6
are fastened to the case
3
with screws
8
. The lead terminal
7
of each coaxial connector
6
is soldered with the land
5
formed on the circuit board
5
. Then, the cover
10
is fastened on the case
3
. The circuit board
1
is electrically connected to the coaxial connectors
6
by soldering the lead terminals
7
with the lands
5
, so that high-frequency signal transmission can be achieved.
Generally, conventional electronic devices and the mounting method thereof are embodied as described above. With this configuration, the heat generated from the electronic circuit components mounted on the circuit board
1
and changes in the air temperature outside the case
3
cause repetitive tension due to differences in linear expansion coefficient between the circuit board
1
and the case
3
. This tension acts the soldering portion between the land
5
and the lead terminal
7
. For instance, in most photoelectronic equipment, the soldering portion must withstand a wide temperature range of between −40° C. and +85° C. In consideration of the accessibility, processability, and cost effectiveness, a glass fabric-based epoxy resin is usually used for the circuit board
1
while an aluminum alloy is usually used for the case
3
. The glass fabric-based epoxy resin has a linear expansion coefficient of 1.4×10
−5
/° C. The aluminum alloy has a linear expansion coefficient of 2.4×10
−5
/° C. The linear expansion coefficient of the case
3
is larger than that of the circuit board
1
. Hence, the circuit board
1
cannot follow thermal expansion or contraction (or shrinkage) of the case
3
. The tension acts the circuit board
1
so as to warp the circuit board
1
, with the screw
2
at the fixing portion regarded as an origin point. Moreover, the repetitive tension due to changes in temperature distorts the soldering portion between the land
5
and the lead terminal
7
, thus degrading the soldering strength. As a result, cracking of the soldering portion occurs, thus degrading the reliability of the soldering portion over a long period of time. Conventionally, an attempt is made to overcome these problems by increasing the soldering area to ensure sufficient soldering strength. The measure of increasing the soldering area is increasing the size of the soldering land
5
or the size of the lead terminal
7
. However, these measures themselves cause a disadvantage that the characteristic impedance of the land
5
is mismatched with the characteristic impedance of the coaxial connector
6
so that the high-frequency characteristic is deteriorated. In another measure, the likelihood of soldering cracks is reduced by equalizing the linear expansion coefficient of the circuit board
1
to that of the case
3
. However, this method remarkably increases the material costs for the circuit board
1
and the case
3
. In yet another measure, the circuit board
1
is securely attached with the case
3
with an adhesive agent with low elastic coefficient is adopted to relax the repetitive tension due to temperature changes. However, this method leads to poor heat dissipation of the circuit board
1
and to an unstable ground potential to the circuit, thus degrading the high-frequency characteristics.
SUMMARY OF THE INVENTION
This invention is made to overcome the above-mentioned problems. It is an object of the present invention to provide electronic equipment wherein repetitive tension due to changes in temperature does not act on the soldered portion between the land and the lead terminal, so that the reliability of the soldering strength can be maintained for a long time. Another object of the present invention is to provide an electronic device that has good high-frequency characteristics by optimizing the characteristic impedance between the land and the coaxial connector and by stabilizing the circuit ground potential.
A further object of the present invention is to provide an electronic device that has good heat dissipation of the circuit board.
Moreover, still another object of the present invention is to provide an electronic device that can be fabricated inexpensively.
In a first aspect of the present invention, an electronic device comprises a circuit board on which electronic circuits are mounted, said circuit board having a land; a case to which said circuit board is assembled, said case having a linear expansion characteristic different from that of said circuit board; a connector connected to said case and electrically connected to an external signal, said connector having a lead terminal soldered to said land; a fixture fixing said circuit board to said case on the side of said circuit board and near said connector; and a sliding tool mounted on the other side of said circuit board and apart from said connector, and sliding said circuit board in the direction perpendicular to the thickness of said circuit board according to ambient thermal changes, with said circuit board being held in the direction of the thickness thereof.
According to this first aspect of the present invention, as the circuit board and the case thermally expand or contract due to temperature changes, the circuit board horizontally slides with respect to the case, so that the tension caused by differences in expansion or contraction (that is, in linear expansion coefficient) is relaxed. The tension does not act on the soldering portion between the land and the lead terminal so that the degradation in the soldering strength can be prevented. The long-term reliability of the soldering portion as well as the high-frequency signal characteristics can be maintained without changing the size of the land and the size of the lead terminal of the circuit board. Without consideration of the linear expansion efficient, the circuit board can be directly fastened to the case formed of aluminum alloy or copper alloy with an excellent thermal conductivity and with an excellent electrical conductivity. This feature can provide improved heat dissipation and improved high-frequency characteristics due to the stabilized circuit ground potential.
In a second aspect of t
Burns Doane , Swecker, Mathis LLP
Gandhi Jayprakash N.
Mitsubishi Denki & Kabushiki Kaisha
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