Electricity: conductors and insulators – Boxes and housings – Hermetic sealed envelope type
Reexamination Certificate
2002-06-03
2004-02-24
Ngo, Hung V. (Department: 2831)
Electricity: conductors and insulators
Boxes and housings
Hermetic sealed envelope type
C361S719000, C361S720000, C257S712000
Reexamination Certificate
active
06696643
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electronic apparatus provided with a case for housing an electronic circuit substrate on which heat generating electronic components are mounted, for example.
2. Description of the Related Art
Along with the development of techniques of miniaturization and large-scale integration of electronic components, the miniaturization of electronic apparatuses provided with electronic circuit substrates, typically optical transceivers, has developed rapidly recently. Problems with increased heat generation density due to the miniaturization of the electronic apparatuses provided with electronic circuit substrates has begun to be recognized. In addition, the heat distribution within an electronic apparatus provided with an electronic circuit substrate has a tendency to concentrate in specific locations due to the high integration of electronic components, and this trend can be predicted to become increasingly strong. In view of the further increase in the heat generation density and the concentration of the heat generation distribution in the future, there is a demand for the development of an electronic apparatus provided with an electronic circuit substrate and having superior heat dissipating characteristics.
Conventionally, a ceramic substrate having superior heat conduction characteristics and superior electrical characteristics is generally used for as a substrate material, and the entire rear surface of the substrate is contacts a case by using an adhesive or the like, for cases of dissipating heat from an electronic apparatus provided with an electronic circuit substrate in which the amount of heat generated increases, and the heat generation distribution becomes concentrated, as stated above.
For example, a structure like that shown in
FIG. 13
may be used as a conventional electronic apparatus provided with an electronic circuit substrate. Reference numeral
1
in
FIG. 13
denotes a heat generating component such as a heat generating electronic component, for example a power transistor. Reference numeral
2
denotes an electronic circuit substrate structured by a ceramic substrate, and the heat generating component
1
is mounted on the front surface of the electronic circuit substrate
2
. Reference numeral
3
denotes a case for housing and protecting the electronic circuit substrate
2
, and the top of the case
3
is open in order to place the electronic circuit substrate
2
into, and take the electronic circuit substrate
2
out of, the case
3
. Reference numeral
4
denotes an adhesive for fixing the electronic circuit substrate to the case
3
, and reference numeral
5
denotes a cover that covers the open portion of the case
3
.
With the aforementioned structure of this first conventional example of an electronic apparatus provided with an electronic circuit substrate, heat generated by the first heat generating component
1
diffuses over the entire electronic circuit substrate
2
, composed of the ceramic substrate having superior thermal conductivity characteristics, and the diffused heat is transferred to the case
3
via the adhesive
4
. Heat transmitted to the case
3
then is dissipated to the atmosphere as the case
3
fulfills a role as a heat radiator.
In this case, heat generated by the heat generating component diffuses over the entire substrate in accordance with using the ceramic substrate having superior thermal conduction characteristics as the electronic circuit substrate
2
. The diffused heat is dissipated to the case
3
, provided with a heat radiator effect, from the entire rear surface of the electronic circuit substrate
2
contacting the case
3
. Heat is therefore dissipated with good efficiency.
FIG. 14
is a schematic structure diagram showing a second conventional example of an electronic apparatus provided with an electronic circuit substrate, disclosed in JP 8-204070 A. A through hole
23
is wired for sending signals from a semiconductor element
21
within an electronic circuit substrate
22
on which the semiconductor element
21
is mounted. A flexible thermal conductor
24
or an adhesive adheres to a surface that is different from the surface on which the specific semiconductor element
21
is mounted on the electronic circuit substrate
22
. A protruding portion
25
of a metal frame wall
26
contacts the thermal conductor
24
.
In this case, much of the heat from the semiconductor element
21
is diffused widely into the frame wall
26
through the protruding portion
25
. A high heat dissipating ability can be obtained with respect to the semiconductor element
21
by utilizing the large surface of the frame wall as a dissipating surface.
Further, a structure is shown in a third conventional example disclosed in JP 11-40742 A in which a lower surface of a module case contacts a metal portion formed on a mother board, and heat from the metal portion is transferred to a ground or to an electric power source layer within the mother board. Heat is dissipated, and dissipation fins on the module of the electronic circuit package are unnecessary.
However, with the electronic apparatus provided with an electronic circuit substrate, the first conventional example structured as stated above, a ceramic substrate must be used as the material of the electronic circuit substrate
2
, and mounting must be performed so that the entire rear surface of the electronic circuit substrate contacts the case
3
. A problem therefore develops in which the packaging density drops. In other words, a ceramic material having superior thermal conductivity characteristics is generally used as the substrate material because of the necessity to dissipate heat, as stated above, for cases in which the heat generating component
1
is mounted to a miniaturized electronic apparatus provided with an electronic circuit substrate, and mounting is performed so that the entire rear surface of the electronic circuit substrate
2
contacts the case
3
. Normally, therefore, electrical/electronic components are not mounted to the rear surface of the electronic circuit substrate
2
. Note that, even for cases in which the packaging density is given great weight and electrical/electronic components are mounted on the rear surface of the electronic circuit substrate
2
, the ceramic substrate is attached floating above the case
3
, and therefore it can be considered that the strength of the ceramic cannot withstand factors in its usage environment, such as vibration and shocks. Cracks and the like will be develop. With conventional examples, mounting of electrical/electronic components is limited to only one surface of the electronic circuit substrate
2
, and therefore a problem exists in that the component packaging density is halved.
Further, a high component cost ceramic material must be used as the electronic circuit substrate
2
material, and therefore a problem exists in that the manufactured product cost increases.
Much of the heat from the semiconductor element
21
diffuses widely in the frame wall
26
, through the thermal conductor
24
and the protruding portion
25
, with the electronic apparatus of the second conventional example, and the heat dissipation capabilities with respect to the semiconductor element
21
increase. However, of the heat generated by the semiconductor element
21
, that which is dissipated by thermal conduction is limited to a route in which it is dissipated to the outside from the through holes
23
, the thermal conductor
24
, the protruding portion
25
, and the frame wall
26
. For example, if the semiconductor element
21
is small, then a problem exists in that a region for the through holes
23
cannot be made large, and the heat dissipating capability of the semiconductor element
21
cannot be expected to increase.
Furthermore, the protruding portion
25
is formed such that it protrudes at a right angle into the inside of a portion of the frame wall
26
. The protruding portion
25
consists of a level portion
25
a
and a vertical
Burns Doane , Swecker, Mathis LLP
Mitsubishi Denki & Kabushiki Kaisha
Ngo Hung V.
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