Electricity: electrical systems and devices – Housing or mounting assemblies with diverse electrical... – For electronic systems and devices
Reexamination Certificate
2000-03-13
2001-04-10
Picard, Leo P. (Department: 2835)
Electricity: electrical systems and devices
Housing or mounting assemblies with diverse electrical...
For electronic systems and devices
C361S690000, C361S695000, C361S719000, C174S016100, C174S016300, C165S080300, C165S104330, C165S185000
Reexamination Certificate
active
06215662
ABSTRACT:
BACKGROUND
1. Field of the Invention
The present invention is related to the field of heat sinks, and more specifically to a novel arrangement of electric power switches and heat sinks on a printed electric circuit board.
2. Description of the Related Art
Complex electric circuits, such as those of computer units, are often manufactured on generally flat printed circuit boards, which are also known as motherboards. These circuits receive electrical power, and switch it with electrical switches to the various units of the circuit. These switches, also known as power switches, generate heat commensurate with the switched electrical power. It is a common practice to deal with the generated heat by attaching a heat sink to every electrical switch. An example of this is presented below.
Referring to
FIG. 1
, an electrical switch
50
is now described. The electrical switch
50
includes an electronic component
52
, and that is typically encapsulated in electrically insulating material. The electronic component
52
is accessed by three electrical leads
54
,
56
,
58
, which are typically received in holes of the printed circuit board (not shown). The electronic component
52
can be a transistor, an FET, a MOSFET, etc.
When an electrical switch, such as electrical switch
50
, is intended for handling large amounts of electrical power, it is often provided with a heat conductive backing. The backing is typically made out of metal, for dissipating the heat generated by the electronic component
52
.
Typically, the heat metal backing is provided in the form of tab
62
for the switch
50
. In some methodologies, the tab
62
is soldered on the printed circuit board itself.
In a certain methodology, also known as TO-220 methodology, the tab
62
is intended to be arranged upright, perpendicularly to a plane of the printed circuit board, and parallel to the leads
54
,
56
,
58
. The tab
62
includes a hole
64
, for passing a screw (not shown). The screw is used to attach a heat sink to the switch
50
.
Referring now to
FIG. 2
, a heat sink
70
is described. The heat sink
70
includes a main panel
72
, which includes a hole
74
. The hole
74
is for receiving a screw (not shown), for attachment to the switch
50
of FIG.
1
. The heat sink
70
also includes two side panels
76
, which are also known as fin panels
76
. Optionally and preferably, the fin panels
76
include slots
78
, which are also known as cuts
78
. The heat sink
70
is typically made out of metal, and is painted black for radiating the heat better. In addition, the paint advantageously also provides electrical isolation.
Referring now to
FIG. 3
, the general attaching arrangement is illustrated. The leads
54
,
56
,
58
(not shown, but obscured by the electronic component
52
) of the device
50
are inserted into holes (not shown, but obscured by the electronic component
52
) of the printed circuit board
80
. The hole
64
of the tab
62
is aligned with the hole
74
of the main panel
72
of the heat sink
70
.
The attaching arrangement also illustrates the weaknesses of this methodology. More particularly, the arrangement of
FIG. 3
occupies a lot of space on the printed circuit board
80
. In particular, while the switch
50
can be physically small, the heat sink
70
demands a lot of space. This forces locating other devices farther away from switch
50
.
The problem is made worse by the fact that typically many electrical power switches, such as switch
50
, are designed to be grouped together nearby, for sharing between them the electrical load. Each of them requires a heat sink, and therefore each requires a lot of space around it. Accordingly, the bank of electrical switches occupies a large area of the motherboard.
There's also another reason on why that area cannot be made smaller. Devices having heat sinks are often cooled by use of fan, which establishes an airflow. But it has proven harder to establish an air flow when the heat sinks and the switches are crowded close to each other.
These problems have been addressed in the past by keeping the switches close to each other, and directing their fins away from the group. Another way has been by making each of the heat sinks smaller. This means making the side panels
76
less wide. This also means making the main panel
72
less wide, which brings this side panels
76
closer to the device
50
.
But the rating of the heat sink
70
is determined by its dimensions. As the dimensions are getting smaller, to accommodate overcrowding on the board
80
, the heat sink
70
can dissipate less heat. This is exactly contrary to the present needs of the industry. As electrical devices increase in capability, they consume more power, which in turn requires higher heat sinking capability. In addition, making the circuit boards larger runs the risk of exceeding standard sizes and form factors, which can adversely affect the acceptance and success of the product in the market.
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patent: 5535094 (1996-07-01), Nelson et al.
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patent: 5912802 (1999-06-01), Nelson
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patent: 5917702 (1999-06-01), Barrow
patent: 5935209 (1999-09-01), Chiu
patent: 5946188 (1999-08-01), Rochel et al.
patent: 5990552 (1999-11-01), Xie et al.
“Discrete Semiconductor Products, DMOS Power MOSFET Databook,” Jul. 1996 Edition, by National Semiconductor; Index p. (iii) p. 12-11.
“The Best Thermal Management Solutions from Around the World,” Customer Letter, by Redpoint Thermalloy, Ltd., cover page, letter page, 6106B data page.
Olsen Jeff J.
Peter Erik W.
Chervinsky Boris L.
Intel Corporation
Marger & Johnson & McCollom, P.C.
Picard Leo P.
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