Heat sink

Details Heat sink Heat sink

1999-10-18

2001-04-03

Thompson, Gregory (Department: 2835)

Electricity: electrical systems and devices

Housing or mounting assemblies with diverse electrical...

For electronic systems and devices

C165S080200, C165S080400, C165S185000, C174S016300, C174S034000, C361S708000, C361S818000, C428S040500, C257S707000

Reexamination Certificate

active

06212073

ABSTRACT:

TECHNICAL FIELD OF THE INVENTION
The invention relates to a heat sink for accelerating heat dissipation from a heat generator such as an electronic part and the like or a heated body heated by the heat generator.
BACKRGOUND OF THE INVENTION
Recently, electronic parts such as IC's and the like used for electronic devices have become more integrated and operated at higher clock speeds, which increases the electricity consumption and heat generation. This is one cause of misoperation of the electronic device and failure of the electronic parts themselves. Therefore, heat dissipation from the electronic parts is now a major concern.
Heretofore, there has been used a heat sink made of a metal plate with high heat conductivity, such as brass and the like, to suppress temperature rise of an electronic part during use of an electronic device and the like. The heat sink conducts the heat generated from the electronic part and dissipates it from its surfaces by the temperature difference between the surface and the outside atmosphere. Some kinds of such heat sinks can be automatically mounted with electronic parts.
For example, a heat sink
100
as shown in
FIGS. 4A and 4B
has been used heretofore.
FIG. 4A
is a plan view of the heat sink
100
and
FIG. 4B
is its side view taken in the direction of the arrow X in FIG.
4
A.
The heat sink
100
is made by bending a rectangular metal plate along lines perpendicular to its longitudinal direction. Specifically, a metal plate is bent into a U-shaped form in the cross section, and both longitudinal ends of the metal plate are perpendicularly bent toward outside of the U-shaped form. Both perpendicularly bent end surfaces
100
b
which adjoin an inside surface
100
a
of the U-shape are soldered to a printed wiring board in such a way that the inside surface
100
a
of the U-shape faces the printed wiring board. To widen the contact area with the outside atmosphere, which is effective for heat dissipation, some measures are usually taken. For Example, heat dissipation fins
101
a
are provided by, such as folding a metal plate, as shown in a heat sink
101
in FIG.
4
C. However, since the heat dissipation fin
101
a
is not connected with the features of the invention, the following explanation will be given about a heat sink without a heat dissipation fin
101
a.
Referring to
Fig. 4B
, the surfaces
100
b
adjoining the inside surface
100
a
of the U-shape, which have been plated with solder, are set by a machine so as to abut the printed wiring board and soldered on the printed wiring board by means of reflow soldering. In this case, electronic parts are previously disposed inside the U-shape.
FIGS. 5A and 5B
illustrate the heat sink
100
mounted with an electronic part
41
on a printed wiring board
40
.
FIG. 5A
is a plan view and
FIG. 5B
is a side view taken in the direction of arrow X of FIG.
5
A. As shown in
FIGS. 5A and 5B
, the heat sink
100
is mounted so as to cover the upper surface
41
a
of the electronic part
41
mounted on the printed wiring board
40
.
In order to conduct the heat of the electronic part
41
to the heat sink
100
effectively, the heat sink
100
preferably abuts the electronic part
41
, specifically the upper surface
41
a
of the electronic part
41
.
However, on automatic mounting by a machine, it is impossible to mount the electronic part
41
and the heat sink
100
such that they abut each other without fail, because of the tolerance of the electronic part
41
and the heat sink
100
. Specifically, there is a possibility that a gap &bgr; could occur between the upper surface
41
a
of the electronic part
41
and the heat sink
100
, thereby preventing the heat of the electronic part
41
from being effectively conducted to the heat sink
100
.
In one conventional way of solving this problem, a grounding terminal of the electronic part
41
is connected with the heat sink
100
by solder on reflow soldering. However, this occasionally causes short circuit and imperfect contact because of the overflow of the solder and, therefore, is not a good solution.
SUMMARY OF THE INVENTION
The primary purpose of the invention is to solve the above-mentioned problem and to provide a heat sink which can be automatically mounted and can effectively conduct and dissipate heat from an electronic part.
To attain this and other purposes, a heat sink of the invention provided with a heat dissipation plate for conducting and dissipating heat of an electronic part to the outside atmosphere, comprises a phase changing member, which is provided on the heat dissipation plate, is made of a base material having a heat conductive filler dispersed therein, changes its phase when heated from the outside, abuts the electronic part due to the phase change and can connect the electronic part with the heat dissipation plate.
The heat sink of the invention is automatically mounted on a printed wiring board together with the electronic part. The heat dissipation plate of the heat sink conducts the heat of the electronic part and dissipates it to the outside atmosphere by the temperature difference between the outside atmosphere and the heat dissipation plate. Therefore, the heat dissipation plate is made of a material with high heat conductivity such as, for example, a metal and a metal-plated material. The heat sink of the invention may be used either for one electronic part for dissipating the heat of the electronic part or for a plurality of electronic parts for dissipating the heat of the plurality of electronic parts.
The heat sink of the invention is characteristically provided with a phase changing member provided on a heat dissipation plate. The phase changing member changes its phase by heating from the outside and abut an electronic part owing to the phase change. Specifically, the phase changing member is softened by heating from the outside, with a result of increased fluidity, moves by the action of gravity to abut the electronic part and is solidified by cooling. Consequently, the heat dissipation plate is directly connected with the electronic part. “Heating from the outside” is, for example, heating by reflow soldering where soldering is carried out to the electronic part to be surface mounted using an outside heat source. In order to induce the phase change by the heating of reflow soldering, the phase changing member needs to be formed from a material which changes its phase practically at about 100° C. to about 150° C.
Since the phase changing member is formed from a base material having a heat conductive filler dispersed therein, it has high heat conductivity. Therefore, according to the heat sink of the invention, the heat conduction from the electronic part to the heat dissipation plate is accelerated and the heat from the electronic part is effectively dissipated as a consequence.
In the heat sink of the invention, a phase changing member is provided and an electronic part is connected with a heat dissipation plate via the phase changing member in order to accelerate heat conduction from the electronic part to the heat dissipation plate. It is also effective for soldering an electronic part by means of reflow soldering to connect the electronic part and the heat dissipation plate via the phase changing member.
Heretofore, there has been used a kind of heat sink called a sealed package provided with a heat dissipation plate, at least the surface which is made of an electrically conductive material and the shape of which is designed such that it surrounds an electronic part. Such a heat sink is advantageous for shielding electromagnetic waves as well as for heat dissipation of an electronic part.
However, since such a heat sink is mounted so as to over the electronic part, there is a problem that heated air of reflow soldering does not blow against the electronic part so that the electronic part cannot be soldered. Therefore, in order to make automatic setting possible, it is necessary to provide many holes on the heat sink so that the heated air blows against the electronic parts and the ele

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