Refrigeration – Structural installation – With electrical component cooling
Reexamination Certificate
2001-12-26
2004-04-27
Jones, Melvin (Department: 3744)
Refrigeration
Structural installation
With electrical component cooling
C062S003700, C165S080300
Reexamination Certificate
active
06725682
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATION
This application is related to a commonly-owned application, filed on or about Dec. 17, 2001, entitled “Inverter”, having application number (to be assigned), which is incorporated herein by reference.
BACKGROUND
The invention relates to the field of cooling electronic devices and, in particular, to using circulating fluids to cool microprocessors, graphics processors, and other computer components.
Microprocessor dies typically used in personal computers are packaged in ceramic packages that have a lower surface provided with a large number of electrical contacts (e.g., pins) for connection to a socket mounted to a circuit board of a personal computer and an upper surface for thermal coupling to a heat sink. In the following description, a die and its package are referred to collectively as a microprocessor.
Elevation views of typical designs for heat sinks suggested by Intel Corporation for its Pentium® III microprocessor are shown in
FIGS. 1A and 1B
.
In
FIG. 1A
, a passive heat sink indicated generally by reference numeral
110
is shown. The passive heat sink
110
comprises a thermal plate
112
from the upper surface of which a number of fins, one of which is indicated by reference numeral
114
, protrude perpendicularly. The passive heat sink
110
is shown in
FIG. 1A
installed upon a microprocessor generally indicated by reference numeral
118
. The microprocessor
118
is comprised of a die
116
and a package
120
. The die
116
protrudes from the upper surface of the package
120
. The lower surface of the package
120
is plugged into a socket
122
, which is in turn mounted on a circuit board (not shown). The passive heat sink
110
is installed by bringing the lower surface of the thermal plate
112
into contact with the exposed surface of the die
116
. When installed and operated as recommended by the manufacturer, ambient airflow passes between the fins in the direction shown by an arrow
124
in FIG.
1
A.
In
FIG. 1B
, an active heat sink, indicated generally by reference numeral
126
, is shown. The active heat sink
126
comprises a thermal plate
128
from the upper surface of which a number of fins
130
protrude perpendicularly. A fan
132
is mounted above the fins
130
. The active heat sink
126
is shown in
FIG. 1B
installed upon a microprocessor, generally indicated by reference numeral
136
, which is comprised of a die
134
and a package
138
. The die
134
protrudes from the upper surface of the package
138
. The lower surface of the package
138
is plugged into a socket
140
, which is in turn mounted on a circuit board (not shown). The active heat sink
126
is installed by bringing the lower surface of the thermal plate
128
into contact with the exposed surface of the die
134
. When installed and operated as recommended by the manufacturer, ambient air is forced between the fins
130
in the direction shown by an arrow
142
in FIG.
1
B.
A difficulty with the cooling provided by the heat sinks shown in
FIGS. 1A and 1B
is that at best the temperature of the thermal plates
112
,
128
can only approach the ambient air temperature. If the microprocessor
118
,
136
is operated at a high enough frequency, the die
116
,
134
can become so hot that it is difficult to maintain a safe operating temperature at the die
116
,
134
using air cooling in the manner shown in
FIGS. 1A and 1B
.
Liquid cooling, which is inherently more efficient due to the greater heat capacity of liquids, has been proposed for situations in which air cooling in the manner illustrated in
FIGS. 1A and 1B
is inadequate. In a typical liquid cooling system, such as that illustrated in
FIG. 1C
, a heat conductive block
144
having internal passages or a cavity (not shown) replaces the thermal plate
128
in FIG.
1
B. The block
144
has an inlet and an outlet, one of which is visible and indicated by reference numeral
146
in FIG.
1
C. Liquid is pumped into the block
144
through the inlet and passes out of the block
144
through the outlet to a radiator or chiller (not shown) located at some distance from the block
144
. The block
144
is shown in
FIG. 1C
installed upon a microprocessor generally indicated by reference numeral
148
, which is comprised of a die
150
and a package
152
. The die
150
protrudes from the upper surface of the package
152
. The lower surface of the package
152
is plugged into a socket
154
, which is in turn mounted on a circuit board (not shown). The block
144
is installed by bringing its lower surface into contact with the exposed surface of the die
150
.
In all liquid cooling systems known to the inventor, only a small portion of the lower surface of the block
144
comes into contact with the die
150
. Since the die
150
protrudes above the upper surface of the package
152
, a gap
156
remains between the upper surface of the package
152
and the block
144
. If the gap
156
is not filled with insulation and sealed, convective and radiative heat transfer from the package
152
to the block
144
may occur. This will have no serious consequences so long as the block
144
is not cooled below the dew point of the air in the gap
156
. If the liquid pumped through block
144
is only cooled by a radiator, then that liquid and consequently the block
144
, can only approach the ambient air temperature. However, if a chiller is used to cool the liquid, then the temperature of the block
144
can decrease below the ambient air temperature, which may allow condensation to form on the package
152
or the block
144
. Such condensation, if not removed, can cause electrical shorts, which may possibly destroy the microprocessor
148
.
Current solutions to the condensation problem referred to above include (1) controlling the chiller so that the temperature of the block
144
does not decrease below the dew point of the air in the gap
156
or (2) providing sufficient insulation and sealing material to prevent condensation from forming or to at least prevent any condensation that does form from reaching critical portions of the microprocessor
148
or surrounding circuit elements. Placing a lower limit on the temperature of the chiller limits the amount of heat that can effectively be removed from the microprocessor
148
without using bulky components. Further, the operating temperature of the microprocessor
148
can only approach the temperature of the block
144
; operation at lower temperatures may be desirable in many circumstances. Alternatively, if insulation and sealing is used, trained technicians must do the installation properly if the installation is to be effective. If the insulation or seals fail, condensation can occur and cause catastrophic failure of the personal computer. A simpler, more reliable solution to the condensation problem is needed.
SUMMARY
In one aspect the invention provides a heat exchanger for extracting heat from an electronic device, such as a microprocessor, through a hot portion of the surface of the electronic device. The heat exchanger has a body through which a fluid may be circulated. The body has a protrusion having a first surface that may be thermally coupled to the hot portion of the electronic device. A heat-conducting path is provided from the first surface to a region of the body that is thermally coupled to the fluid when the fluid is circulated through the body. Preferably, when the first surface is thermally coupled to the hot portion, the surface of the body is sufficiently distant from the surface of said electronic device other than the hot portion that sufficient ambient air may circulate therebetween so as to substantially prevent condensation from forming on the surface of said electronic device and from forming on and dripping from the heat exchanger when said fluid is cooled to at least the dew point of the ambient air and circulated through the body.
In another aspect the invention provides a heat exchanger for extracting heat from an electronic device through a hot portion of the surface of the electronic d
Bennett Jones LLP
Coolit Systems Inc.
Jones Melvin
LandOfFree
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