Liquid impingement cooling module for semiconductor devices

A semiconductor cooling unit for directly jetting a cooling medium against surfaces of semiconductor devices for use in a high-speed computer or the like to effectively remove heat from the semiconductor devices, in which partition members for partitioning a space into regions where semiconductor devices are placed. Each partitioned region has an opening at its ceiling side, and a pipe for supplying or discharging the cooling medium through the opening is disposed so as to project toward a central portion of the back surface of each semiconductor device. This pipe is utilized to also section a cooling medium supply header or a cooling medium return header so that bubbles generated from the semiconductor device surfaces can be smoothly removed, and so that the cooling medium can flow smoothly onto the semiconductor devices.

BACKGROUND OF THE INVENTION 
This invention relates to an apparatus for cooling high-power density 
devices such as semiconductor devices and, more particularly, to a 
semiconductor liquid-impingement cooling module suitable for efficiently 
removing heat generated from semiconductor devices for use in a high-speed 
computer. 
With the development of the technology for highly integrating semiconductor 
devices (elements) and highly densely packaging semiconductor devices 
(elements) on a base, various means have been studied to remove large 
amounts of heat generated from semiconductor devices. Semiconductor 
devices having a very large calorific value have recently been developed 
and, to cool such devices, a direct liquid cooling system to be used 
instead of forced convective air cooling systems or thermal conduction 
cooling systems has been proposed in which a semiconductor device is 
cooled by being directly immersed in a dielectric cooling medium so that 
heat is transferred by forced convection, forced convective boiling or 
pool boiling. 
Cooling units based on a forced convective heat transfer system using a 
single phase liquid flow are known, which are, for example, one in which 
printed circuit boards on which a multiplicity of semiconductor devices 
are mounted are stacked and a cooling medium liquid is caused to flow 
between the printed circuit boards to cool the semiconductor devices (U.S. 
Pat. No. 4,590,538), and one in which an array of a multiplicity of heat 
sink fins are attached on the back side of semiconductor devices and a 
cooling medium liquid is caused to flow between the heat sink fins to cool 
the semiconductor devices (Japanese Patent Unexamined Publication No. 
60-134451). In these cooling units, since semiconductor devices are 
arranged in one row in the direction along the cooling medium liquid flow, 
the temperature of the cooling medium liquid is increased in the flowing 
direction and the temperature of the semiconductor devices is gradually 
increased in the downstream direction, so that it is difficult to 
uniformly maintain the temperature of the semiconductor devices. This 
tendency is particularly conspicuous if the cooling medium used is an 
organic cooling medium having a small specific heat. However, cooling 
medium liquids available for use in these cooling units are needed to have 
suitable electric insulating performance and chemical stability and are 
limited to organic cooling liquids. In this type of cooling unit, 
therefore, the problem of non-uniformity of semiconductor device 
temperature is serious. Moreover, the thermal conductivity of organic 
liquids is very small, about 1/10 of that of water. It is therefore 
difficult to obtain a high forced convection heat transfer coefficient, 
and the efficiency of cooling semiconductor devices is necessarily low. To 
solve these problems, a type of cooling unit has been proposed (U.S. Pat. 
No. 5,021,924) in which nozzles are disposed in a one-to-one relationship 
with semiconductor devices in the vicinity of back surfaces thereof to 
cool the devices with a wall jet flow. Because a cooling medium liquid is 
separately supplied to each semiconductor device in this cooling unit, the 
non-uniformity of the temperatures of the semiconductor devices caused 
with increasing the liquid temperature can be reduced. Also, the thickness 
of velocity/temperature boundary layers can be reduced by the wall jet 
flow, so that a higher heat transfer coefficient can be obtained in 
comparison with the cooling units described above. In the design of this 
cooling unit, however, while the supply of the cooling medium liquid to 
each semiconductor device is achieved by disposing the nozzles in 
correspondence with the semiconductor devices, only the provision of the 
cooling medium liquid outlet port above each device has been considered 
with respect to discharge of the cooling medium liquid from each device. 
Therefore, the flow rate of the jet from a nozzle provided at the upstream 
portion of the discharged flow is necessarily smaller than the flow rate 
of another nozzle provided at the downstream portion because of a pressure 
loss effect. Also, no means is provided to completely discharge through 
each outlet port the cooling medium liquid supplied to the corresponding 
semiconductor device. A part of the cooling medium liquid supplied to a 
device placed at the upstream portion and warmed by this device flows to a 
device placed at the downstream portion, so that the temperature of the 
cooling medium liquid on the downstream portion is necessarily higher than 
the temperature on the upstream portion. These two unbalances cause 
non-uniformity of the performance of cooling the semiconductor devices 
and, hence, non-uniformity of the temperatures thereof. Although the heat 
transfer coefficient of a wall jet flow is higher than that of the 
ordinary internal flow, the former is at most 2 or 3 times higher than the 
latter. The heat loads which can be removed from semiconductor devices by 
using the above-mentioned organic liquid is at most 10 to 20 W/cm.sup.2 
under the condition of an actually attainable liquid flow rate. 
A pool boiling heat transfer type cooling unit is known as one of other 
major systems for cooling a high-power density devices. In this cooling 
unit, a group of devices are immersed in a pool of cooling medium at 
saturated condition and the devices are cooled by boiling of the liquid. 
For example, Japanese Patent Examined Publication No. 2-34183 discloses a 
cooling unit in which boiling enhancing fins having a multiplicity of fine 
cavities are attached to a back surface of a device, and boards on which a 
multiplicity of devices with such fins are attached are immersed together 
in a cooling medium liquid to cool the devices. This cooling unit achieves 
greatly improved device cooling performance in comparison with the 
above-mentioned force convection system because boiling enhancing fins are 
attached to the devices. In this cooling unit, however, it is necessary to 
remove the entire heat generated from the devices by vaporization of the 
cooling medium. The amount of vapor generated a the devices is therefore 
increased excessively, and a very large sectional area of a vapor flow 
path is required. The distance between the devices or between the device 
boards is thereby increased, and the problem of an increase in delay time 
of computing logical operation and a reduction in computation speed due to 
an increase in wiring distance is thereby encountered. Also, a large 
amount of vapor bubbles generated at each device pass around the other 
devices, and the boiling heat transfer coefficient is changed according to 
the amount of the bubbles, so that the temperatures of the devices are not 
uniform. Further, a vapor choking phenomenon occurs around some of the 
devices by concentration of vapor bubbles, and there is a risk of 
occurrence of dryout at that device. A cooling medium container for 
accommodating a multiplicity of boards must be a completely sealed 
container for maintaining the cooling medium at a saturated condition. 
There is therefore the problem such as a complicated structure for leading 
power supply or signal lines from the boards out of the container, a 
complicated sealing structure, and troublesome operations for repairing 
the devices on the boards. 
A type of cooling unit using a combination of forced convection heat 
transfer and boiling heat transfer has also been provided. For example, 
Japanese Patent Unexamined Publication No. 2-22848 discloses a cooling 
system in which a multiplicity of devices are mounted in an inclined 
tubular path through which a cooling medium liquid is caused to flow 
downwardly along a slope while being boiled at each device. In this 
cooling unit, a cooling medium main flow direction component of the 
buoyancy of boiling bubbles generated at each device is directed to a 
direction just opposite to the direction of the main flow to direct the 
bubbles to a ceiling side of the tubular path remote from the base on 
which the devices are arranged, thereby reducing bubbles generated at 
upstream devices flowing into regions around downstream devices. A certain 
effect of this system has been confirmed. In this cooling unit, however, 
the amount of bubbles in the liquid flow in the vicinity of the base 
cannot be made uniform above the devices from the upstream to downstream 
positions, and occurrence of a situation where downstream devices are 
easily covered with the bubbles cannot be prevented if high-power density 
devices which can generate particularly large amount of bubbles are 
mounted. Moreover, since the effect of forced convective boiling heat 
transfer depends greatly upon the subcooled temperature of the liquid, the 
heat transfer coefficient of downstream devices is reduced in a structure 
in which downstream devices are cooled with the cooling medium liquid 
warmed by upstream devices. Because of the increase in the amount of 
bubbles and the reduction in heat transfer coefficient caused in this 
manner in the regions around downstream devices, the temperatures of the 
devices cannot be made uniform and the burnout heat flux corresponding to 
the limit of nucleate boiling cannot be sufficiently increased, so that 
the allowable heat loads of the devices, i.e., the amount of heat 
sufficiently removed by cooling cannot be increased. Japanese Utility 
Model Examined Publication No. 3-7960 discloses a cooling unit directed to 
the subject for increasing the allowable heat loads, in which impinging 
jet and boiling as combined. This cooling unit has a sealed cooling medium 
container which is formed of a section in which a board on which a 
plurality of semiconductor devices are arranged is immersed in a cooling 
medium liquid, and a cooling medium inlet header section from which the 
cooling medium is jetted to each device through nozzles. Boiling bubbles 
generated on a surface of each device are forcibly removed by the cooling 
medium liquid jetted through the nozzle. This cooling unit is thus 
arranged to improve the cooling performance and to cool devices having a 
heat load of about 10 W. Actually, in this cooling unit, boiling bubbles 
can be forcibly expelled from the device surfaces to improve the burnout 
heat flux and to increase the allowable heat loads. However, the influence 
of a flow of boiling bubbles generated from devices in lower positions to 
devices in upper positions has not been considered. Therefore an upward 
cooling medium flow containing bubbles warmed by lower devices flows into 
the regions of upper devices while increasing the liquid temperature and 
the amount of bubbles as it passes each device, so that the temperature of 
devices in upper positions is higher. If the heat loads of each device is 
large, the amount of bubbles around devices in upper positions is 
extremely increased to cause dryout at the devices, resulting in a 
reduction in the allowable heat loads. The problem of this temperature 
increasing of the upper devices and this reduction in cooling performance 
is serious with respect to present semiconductor devices having greater 
heat loads, i.e., 50 to 100 W devices. In addition the structure in which 
the whole board is immersed in the container has been adopted without 
considering leading a number of connection wires and signal wires on the 
order of several hundreds out of the container, the increase in logical 
operation delay time with the increase in the overall length of wires for 
wiring between a plurality of the containers or between the inside and the 
outside of each container, and maintenance facility with respect to device 
repairs and the like. Trials have been made to solve these problems and to 
avoid mutual interference between devices. For example, in HEAT TRANSFER 
IN ELECTRONICS 1989, ASME HTD-Vol. 111, pp 79 to 87 is proposed a cooling 
unit structure in which nine heaters used to simulate semiconductor 
devices are arranged in three rows and three columns on a base, and a 
cooling block having nine rectangular nozzles arranged in three rows and 
three columns so as to respectively face back surfaces of the heaters is 
provided on the base on which the heaters are mounted. The nozzle block in 
which nozzle orifices are formed is positioned with spacers provided above 
and below each row of nozzles so as to be spaced at a distance of 0.5 to 5 
mm from the heaters. A restricted rectangular cooling medium flow path is 
formed between the nozzle block and each column of heaters. A cooling 
medium jetted from each nozzle to the surface of the corresponding heater 
impinges against the heater, changes its flowing direction through 
90.degree., and flows through the rectangular flow path along a line 
tangent to the heater surface. Each spacer serves as a partition means 
between each adjacent pair of heaters to prevent mutual interference 
between the heaters in cooperation with partition plates extending 
longitudinally between the heaters. In this cooling unit, however, the 
cooling medium liquid jetted from each nozzle flows out of the flow path 
while being heated by the corresponding heater forming a part of the 
rectangular flow path and thereby generating bubbles. Therefore, the 
percentage of voids is increased toward the downstream end, and a 
vapor-liquid two-phase flow pattern is changed on the heater surfaces, so 
that a large temperature difference is produced between the heater 
surfaces. Also, since the flow path diameter for the two-phase flow is so 
small that flow pressure loss is very large. The pumping power for driving 
the cooling medium liquid is therefore increased and there is also a risk 
of the base being broken due to the increase of pressure on the heater. 
Further, as the cooling medium flowing out of each rectangular flow path 
in the two-phase state moves upward through the vertical flow path defined 
by the partition plates between the columns of the devices, the amount of 
bubbles in this flow generated by each heater is increased, so that 
bubbles generated by the heaters placed at the lower side influence on the 
upper side heaters, thereby causing differences between the temperatures 
of the heaters. In a situation similar to that described above wherein the 
vapor-liquid two-phase flow state varies with respect to the heater 
positions, if devices having different heat loads are used as in the case 
of an actual semiconductor device board the amount of bubbles generated at 
devices having a smaller heat load is small and the two-phase flow loss in 
the rectangular flow path is therefore small, while the flow loss is 
increased with respect to devices having a greater heat load, resulting in 
no-uniformity of distribution of the cooling medium liquid to the nozzles. 
Because of this non-uniformity, the flow rate is increased with respect to 
the lower heat loads devices with the smaller flow loss while the flow 
rate is reduced with respect to the higher heat loads devices the greater 
flow loss. This condition leads to a result contrary to an actual need for 
higher cooling performance for high heat leads devices. 
A cooling unit also designed to reduce the mutual interference between 
devices is disclosed in Japanese Unexamined Patent Publication No. 
2-237200. In this cooling unit, a multiplicity of countersunk holes formed 
in a wall of a liquid cooling medium header are placed above devices and 
the devices are separated from each other by these holes. In this cooling 
unit, however, cooling medium flow paths between the countersunk holes and 
the devices connecting device cooling cells and the cooling medium header 
are formed at a position offset from center axes of the device cooling 
cells such that the flow of the liquid cooling medium jetted through each 
nozzle cannot be formed as an axially symmetrical flow on the device 
surface. Owing to this asymmetry, considerable temperature non-uniformity 
is produced in each device and the cooling medium liquid stays at a device 
surface portion opposite to a cooling medium outlet position. The risk of 
occurrence of burnout from this portion is large. Owing to this asymmetry, 
as well, bubbles stay at ceiling portions of each device cooling cell 
outside the region where the cooling medium path is formed, thereby 
promoting dryout of the device cooling cell. A phenomenon can also occur 
in which formation of large bubbles and release of bubbles to the outside 
of each device cooling cell repeat alternately so that the cooling medium 
pressure in each device cooling device changes pulsatingly and so that the 
device temperature fluctuates. Further, contraction and enlargement of the 
flow path upstream and downstream of the cooling medium outlet may cause 
the flow loss of the cooling medium to be arbitrarily increased and make 
the vapor-liquid two-phase flow unstable, resulting in instability of the 
device temperature. 
None of the above-described cooling units cannot solve all the problems of 
the variation in temperature in each device, difference between the 
temperatures of devices, the reduction in the allowable calorific value 
due to dryout caused by an increase in the amount of bubbles, the 
non-uniformity of distribution of the cooling medium liquid due to an 
unbalance of flow loss, the reduction in the allowable calorific value due 
to the reduction in the rate of liquid to some of the devices, and so on. 
Also, the above-described conventional cooling units entail the problem of 
failure to limit variation in the temperature of each semiconductor device 
and the change in the pressure applied to the board because of instability 
of the two-phase flow. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a semiconductor 
liquid-impingement cooling unit which is designed to improve the 
performance of cooling each of semiconductor devices mounted on a 
substrate to reduce the temperature differences between internal portions 
of each semiconductor device and between the semiconductor devices, and 
which is designed to reduce flow pressure losses due to bubbles formed by 
evaporation of the liquid liquid to limit changes in the pressure applied 
to the substrate. 
To achieve this object, according to the present invention, there is 
provided a semiconductor cooling unit having a liquid supply header for 
supplying a cooling medium to a plurality of semiconductor devices 
arranged on a substrate, at least one cooling medium jet port projecting 
from the cooling medium supply header and capable of jetting the liquid 
against a back surface of each semiconductor device, and a liquid return 
header communicating with each liquid jet port and disposed adjacent to 
the liquid supply header, the semiconductor cooling unit comprising a 
plurality of partition members having a predetermined height and 
partitioning an internal space at positions between the semiconductor 
devices to define a plurality of device cooling cells. Each liquid jet 
port is connected to a liquid supply member and mounted by being inserted 
in corresponding one of the device cooling cells while being spaced at a 
predetermined distance from the corresponding semiconductor device. Each 
partition member and adjacent one of the liquid supply members define a 
liquid discharge opening therebetween, and the partition members and the 
liquid supply header define the liquid return header therebetween. The 
liquid jetted to the back surface of each semiconductor device is guided 
to the liquid return header away from the back surface. 
In the semiconductor cooling unit thus constructed in accordance with the 
present invention, the partition members are provided between the 
semiconductor devices (elements) to form the device cooling cells, and 
each cooling jet port is inserted in the device cooling cell, so that the 
liquid jetted to the back surface of each device impinges against this 
surface and thereafter moves away from the back surface by being guided by 
the partition members to be discharged through the liquid return header. 
Each device can therefore be cooled independently without being influenced 
by jet flows from the liquid jet ports for other devices. When the liquid 
in a vapor-liquid two-phase state impinges against the partition members, 
bubbles and the liquid are violently mixed so that the bubbles reduce or 
disappear, and so that the flow resistance to the vapor-liquid is reduced. 
The heat transfer coefficient is also improved and the temperature 
distribution of each device can be made uniform.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The first embodiment of the present invention will be described below with 
reference to FIGS. 1 and 2. 
As shown in FIGS. 1 and 2, a multiplicity of semiconductor devices 
(elements) 2 are arranged on a substrate 1 in the form of a plate with 
electrical connection members 5 interposed therebetween, and tubular 
liquid supply members 3 each communicating with a liquid supply header 6 
are disposed so as to projects from the header 6 toward the devices 2. 
Each liquid supply member 3 has a cooling medium jet port 11 at its 
projecting end. Partition members 4 having a predetermined height 
partition an internal space at positions between the devices 2 to define 
device cooling cells 14. Liquid jet ports 11 project into the device 
cooling cells 14 to a position at a predetermined distance from the back 
surfaces of the devices 2. A liquid return header 7 is defined between the 
device cooling cells 14 partitioned by the partition members 4 and the 
liquid supply header 6. Each device cooling cells 14 has a liquid 
discharge opening 10 on the side remote from the device surface, which is 
fully opened to the liquid return header 7. 
The operation of this embodiment will be described below with reference to 
FIGS. 2 and 3. A subcooled liquid liquid 2, which is a low-boiling-point 
dielectric liquid represented by, e.g., fluorocarbon having a boiling 
point lower than the device temperature, is led from a liquid inlet pipe 8 
to the liquid supply header 6 and is delivered to liquid supply members 3 
to be ejected as a jet flow to back surfaces of the devices 2. The jet 
flow impinges against the each device 2 and flow radially along the back 
surface thereof by changing their direction by 90.degree.. At this time, 
the liquid liquid 12 is heated by absorbing heat from the devices 2 and 
flows downstream while generating bubbles 13. The liquid containing 
bubbles 13 is checked by the partition members 4 to change its flowing 
direction by 90.degree. again and flows out of each device cooling cell 14 
to the liquid return header 7. The cooling medium in the device cooling 
cells 14 is thereby collected and is discharged out of the unit through a 
liquid outlet pipe 9. 
In accordance with this embodiment, the liquid supply members 3 are 
projecting into the device cooling cells 14 by passing through the liquid 
return header 7, so that the jet flow can reach the back surface of each 
device without being influenced by the flow in the liquid return header 7 
flowing in directions perpendicular to the direction of the jet flow. It 
is thereby possible to prevent a reduction in the jet speed with diffusion 
of the jet flow, i.e., an increase in the jet flow diameter, and a 
movement of the collision point caused by bending of the jet flow. The jet 
flow which has impinged against the back surface of each device 2 in this 
manner without being influenced by the circumferential flow flows out of 
the collision area while forming a very thin velocity boundary layer and 
forming a maximum velocity region very close to the back surface of the 
device 2, so that the velocity gradient in the vicinity of the collision 
area on the device 2 can be greatly increased, thereby limiting the growth 
of the temperature boundary layer on the back surface of the device 2. 
Consequently, it is possible to prevent the liquid vapor bubbles generated 
and growing on the back surface of each device 2 from increasing 
excessively in size and amount and, hence, to prevent burnout of the 
devices 2. It is also possible to limit the reduction in heat transfer 
coefficient and the increase in the degree of non-uniformity of the device 
temperature due to an excessive increase in the amount of bubbles (the 
percentage of voids). 
Also, in accordance with this embodiment, the partition members 4 are 
provided to fully surround each device 2 at peripheral ends thereof, so 
that mixing 52 of vapor bubbles and the liquid of the cooling medium at 
end portions of each device 2 can be facilitated. It is thereby possible 
to facilitate condensation or elimination of bubbles 13 in the liquid and, 
hence, to reduce the size and the amount of bubbles in a vapor-liquid 
two-phase flow 54 flowing out to the liquid return header 7. Consequently, 
it is possible to reduce the pressure loss in the liquid return header 7 
and the liquid outlet pipe 9 and to stably maintain the flow in the 
system. Also, by strong vapor-liquid mixing at the peripheral end of each 
device 2, the heat transfer coefficient at the end is increased and a heat 
transfer coefficient distribution, which may be such that, in the case of 
an ordinary jet flow, the heat transfer coefficient at the center is 
increased while the heat transfer coefficient at the peripheral end is 
reduced, can be made uniform, so that the average heat transfer 
coefficient of the whole device surface can be enhanced. It is therefore 
possible to make a temperature distribution in each device uniform and to 
obtain enhanced cooling performance. 
Further, the partition members 4 separate the cooling/bubbling region in 
the device cooling cells for each device, in which the liquid impinges 
against the device surface and bubbles to cool the device, from the liquid 
return header 7, in which the bubbly flows generated at the surfaces of 
devices 2 are collected to be discharged. It is thereby possible to 
prevent the bubbly flow generated at each device from flowing into other 
device cooling cells. It is also possible to prevent occurrence of 
movement of a large amount of bubbles to some of the devices, an extreme 
deterioration of the cooling performance caused by staying of bubbles and 
non-uniformity of the temperatures of the devices due to the differences 
between the amounts of bubbles at the devices 2. Further, each bubbly flow 
bent through 90.degree. by the partition members 4 and having a velocity 
component such as to move away from the device 2 acts to keep the bubbly 
flow in the liquid return header 7 away from the device 2, which bubbly 
flow in the return header 7 flows perpendicularly to the former flow and 
has a large amount of bubbles. That is, the bubbly flow in the liquid 
return header is thereby prevented from interfering with each device. 
These various effects are markedly large in the case of vertically setting 
the substrate as in this embodiment. It is thereby possible to prevent 
bubbles generated at devices in lower positions from being successively 
collected in upper device regions so as to cover and dry out the devices 
in the uppermost position. 
In the case of cooling semiconductor devices by directly immersing in a 
liquid, it is required that the liquid has an electrical insulating 
property and chemical stability. However, ordinary liquid of this type 
have a large density. For example, the density of perfluoro normal hexane 
is about 1.7 times higher than that of water. For this reason, in a case 
where the substrate is set vertically in the bobble generation system as 
in this embodiment, the potential head between one liquid supply member in 
a upper position and another liquid supply member in a lower position is 
so large that the rates of supply of the liquid to the cooling medium 
supply members vary easily. In the structure of this embodiment in which 
both the liquid inlet pipe 8 and the liquid outlet pipe 9 are placed above 
the substrate, such a potential head unbalance can be solved and the 
non-uniformity of the device cooling performance due to the differences 
between the rates of supply of the liquid to the cooling medium supply 
members can be reduced. This function is effective only when the size of 
the substrate is large, that is, a large potential head is set. If the 
size of the substrate is small, the liquid inlet pipe and the liquid 
outlet pipe may be provided in different positions, i.e., in a side 
surface or a bottom surface. While the substrate is vertically set in this 
embodiment, the functions and effects of this embodiments can also be 
achieved in the case of horizontally setting the substrate. 
FIG. 4 is a perspective view of the second embodiment of the present 
invention, mainly illustrating a liquid supply member. This cooling medium 
supply member differs from that of the first embodiment shown in FIG. 2 in 
that it has a rectangular cross section. In this embodiment, a flow of the 
liquid jetted from each of cooling medium supply members 3 in the form of 
rectangular tubes has the shape of a two-dimensional jet flow such that 
the flow velocity along the back surface of each device is uniform in 
comparison with the three-dimensional jet flow in the first embodiment 
shown in FIG. 2, in which the liquid after collision against each device 
spreads radially along the back surface of the device so that the flow 
velocity is reduced with respect to the distance from the center of the 
device in the downstream direction. In the second embodiment, therefore, 
the temperature distribution in each device can be made more uniform. 
FIG. 5 is a cross-sectional view of liquid supply members in accordance 
with the third embodiment of the present invention. A structural feature 
of this embodiment resides in that four tubular liquid supply members 32 
are disposed with respect to one semiconductor device 2. In this 
embodiment, while the flow velocity distribution over the back surface of 
each device can be reduced so that the temperature distribution in each 
device is more uniform as in the second embodiment shown in FIG. 4, the 
thickness of the velocity boundary layer can be reduced so that the 
cooling performance is improved in comparison with the arrangement using 
one liquid supply member with respect to one semiconductor device. 
Further, the jet flows from the liquid supply members 32 impinge strongly 
against each other to facilitate vapor-liquid mixing so that the effect of 
reducing and eliminating bubbles is improved. Needless to say, in this 
embodiment, the number of liquid supply members for one semiconductor 
device is not limited to four and may be selected according to the size 
and the heat load of the semiconductor device. Also, the cross-sectional 
configuration of each liquid supply member is not limited to the circular 
section shown in FIG. 5. 
FIG. 6 is a cross-sectional view of a liquid supply member in accordance 
with the fourth embodiment of the present invention. A structural feature 
of this embodiment resides in that an end of each liquid supply member 3 
projects into liquid supply header 6. A non-uniform static pressure 
distribution is exhibited at each liquid discharge opening 10 of the 
respective devices because of variations in the flow velocity in liquid 
return header 7 and variations in the distribution of flow velocity in the 
direction of the liquid flow containing bubbles. If the semiconductor 
devices have different heat loads, the amounts of bubbles generated at the 
devices vary to cause some differences between the static pressures at the 
respective liquid jet ports 11. These non-uniform static pressure 
distributions result in differences between the rates of supply of the 
cooling medium from the respective liquid supply members 3 to the 
respective devices 2 and instability of the flows in these paths. However, 
in the case of the structure of this embodiment wherein each liquid supply 
member 3 has a projecting upstream end, the resistance to the flow at an 
inlet portion of each liquid supply member is increased so as to limit the 
non-uniformity of the liquid supply rates and the flow instability due to 
the above-described non-uniform static pressure distributions. It is 
thereby possible to make the temperatures of the devices uniform and to 
reduce the change in the device temperature with respect to time. In the 
arrangement described above with respect to this embodiment, the 
projecting end surface has a shape such as to be parallel with the device 
back surface. However, the end portion may be formed as a knife edge to 
further improve the above-described effects. 
FIG. 7 is a cross-sectional view of a liquid supply member in accordance 
with the fifth embodiment of the present invention. An orifice 33 is 
provided at a liquid inlet portion of each liquid supply member 3. In this 
embodiment, the resistance to the flow at the inlet portion of each liquid 
supply member can be greater than that in the fourth embodiment, so that 
more uniform flow rate distribution can be effected without being 
influenced by the condition on the downstream side. 
FIG. 8 is a sectional perspective view of liquid supply members in 
accordance with the sixth embodiment of the present invention. Tubular 
liquid supply members 34 are fitted to lattice crossing portions of 
partition members 4 while being spaced from the device back surfaces. In 
this embodiment, the size of the opening through which the liquid is 
discharged out of each device cooling cells can be increased so that the 
resistance to the flow at the discharge opening is reduced. Consequently, 
bubbles generated on the device back surfaces can be discharged more 
rapidly and the device cooling performance can be improved. Moreover, the 
number of liquid supply members in the whole cooling unit can be reduced 
in comparison with the arrangement using a plurality of liquid supply 
members 32 as shown in FIG. 5, so that the flow loss of the flow in the 
liquid return header flowing transversely to liquid supply members can be 
reduced. 
FIG. 9 is a cross-sectional view of partition members in accordance with 
the seventh embodiment of the present invention. Each of partition members 
41 has a tapered sectional shape along the direction of its height such 
that its thickness is reduced from its end closer to the devices toward 
the other end at the liquid return header. In this embodiment, it is 
thereby possible to prevent bubbles from staying at corners defined by the 
partition members 41 and each device 2, so that the temperature 
distribution in each device can be made more uniform. 
FIG. 10 is a cross-sectional view of a method of fixing partition members 
in accordance with the eighth embodiment of the present invention. 
Partition members 4 are fixed on liquid supply members 3 through stays 15. 
FIG. 11 is a cross-sectional view of a method of fixing partition members 
in accordance with the ninth embodiment of the present invention. 
Partition members 4 are fixed on a wall of liquid supply header 6 through 
stays 115. The methods in accordance with embodiments shown in FIGS. 10 
and 11 facilitates assembling the cooling unit. In these embodiments, a 
group of fixing stays is provided in correspondence with each of square 
partitions defined by the partition members. However, needless to say, a 
single stay may be provided with respect to a plurality of square 
partitions. If the partition members are fixed on the liquid supply 
members or the liquid supply header, the operation of assembling the unit 
or repairing devices can be facilitated. 
FIG. 12 is a sectional perspective view of the tenth embodiment of the 
present invention. A liquid supply member 34 forming a flow path having a 
rectangular cross-section is disposed between each of adjacent pairs of 
semiconductor devices 2, and partition members 4 are disposed so as to 
extend perpendicularly to the liquid supply members 34. In this 
embodiment, the liquid supply members 34 also serve as partition members 
in association with partition members 4 exclusively used for partitioning. 
It is thereby possible to improve the device packaging density. Moreover, 
the liquid jetted through each of liquid jet ports 111 flows as a wall jet 
flow along the cooled flat surfaces (back surfaces) of the semiconductor 
devices, so that the temperature distribution in each device can be more 
uniform. It is also possible to reduce the flow loss in return paths, 
because there is no obstruction in the flow paths of a liquid return 
header 7. 
FIG. 13 is a transverse sectional view of the eleventh embodiment of the 
present invention. Each of liquid supply members 35 has a closed end 
surface on the semiconductor device 2 side, and liquid jet ports 112, 
which are holes through which the liquid is jetted out of each liquid 
supply member, are formed in side portions of the liquid supply member 35 
facing toward adjacent devices. In this embodiment, therefore, the liquid 
can be prevented from being directly jetted to repair wires which are laid 
on the substrate between the devices to repair the circuit system or to 
change the logic thereof, thereby preventing disconnection of such repair 
wires caused by the fluid force. 
FIG. 14 is a cross-sectional view of the twelfth embodiment of the present 
invention. Liquid supply header 6 is provided between a cooling liquid 
return header 7 and device cooling cells 14 partitioned by partition 
members 4, and liquid discharge members 16 are arranged so as to project 
from liquid return header 7 into device cooling cells 14. Liquid jet ports 
17 are formed between partition members 4 and cooling medium discharge 
members 16. The liquid distributed from cooling medium supply header 6 to 
each liquid jet port reaches the cooled flat surface (back surface) of the 
corresponding semiconductor device, cools the device while generating 
bubbles, and passes through liquid discharge members 16 to be discharged 
into liquid return header 7. In this embodiment, since liquid return 
header 7 is separated from device cooling cells 14, the liquid flowing in 
liquid return header 7 can be prevented from flowing into device cooling 
chambers 14. It is therefore possible to uniformly set the liquid 
condition with respect to the respective semiconductor devices so as to 
make the temperatures of the devices uniform, even if the heat load is 
very large or the amount of bubbles in cooling medium return header 7 is 
increased by an increase in the number of mounted devices. 
FIG. 15 is a cross-sectional view of the thirteenth embodiment of the 
present invention. The structure of this embodiment is such that cooler 18 
for eliminating bubbles are provided in liquid return header 7 in the 
arrangement of the first embodiment shown in FIG. 2. Bubbles generated at 
semiconductor devices are immediately condensed and disappear in the 
liquid return header to reduce the flow loss in the liquid return header 
and also to change a vapor-liquid two-phase flow, by which flow 
instability is caused, into a single-phase flow to stabilize the flow 
condition at each device. It is thereby possible to stabilize the device 
temperature. 
FIG. 16 is a cross-sectional view of the fourteenth embodiment of the 
present invention. The structure of this embodiment is such that cooler 18 
for eliminating bubbles are provided in liquid return header 7 in the 
arrangement of the twelfth embodiment shown in FIG. 12. This embodiment 
has the same effect and advantage as the thirteenth embodiment shown in 
FIG. 15. 
FIG. 17 is a cross-sectional view of the fifteenth embodiment of the 
present invention. A cooling fin 182 for eliminating bubbles is provided 
in liquid return header 7 while an external cooling fin 181 is provided on 
the outside of liquid return header 7. External cooling fin 181 cooled by 
an external fluid serves as a low-temperature source to cool cooling fin 
182 on the liquid side, thereby condensing and eliminating bubbles. This 
embodiment also has the same effect and advantage as the thirteenth 
embodiment shown in FIG. 15. 
In accordance with the present invention, as described above, liquid supply 
members and partition members serving as partitions between semiconductor 
devices (elements) are arranged in correspondence with the semiconductor 
devices, so that jet flows from the liquid jet ports do not interfere with 
each other, and bubbles generated at one device are prevented from flowing 
into the region of other devices, that is, the devices are cooled 
independently. The differences between the temperatures of the devices are 
therefore reduced. Since the devices are cooled by utilizing boiling of a 
jet flow liquid of the liquid subcooled from the saturation temperature, 
the development of the temperature boundary layer is limited. The size and 
the amount of liquid vapor bubbles generated at the device surface are 
therefore reduced. Further, in the impingement region where the jet flow 
from each liquid jet port impinges against the device, the liquid liquid 
and the cooling medium vapor bubbles are violently mixed to enable vapor 
bubbles generated at the device to be condensed and disappear in the 
liquid liquid. The percentage of voids (the proportion of bubbles in the 
liquid) at the liquid outlet above each device is thereby reduced, so that 
the flow pressure loss of the vapor-liquid two-phase flow is reduced. A 
two-phase pattern bubbly flow is formed to enable stabilization of the 
flow through the entire system. By this stabilization of flow through the 
entire system, the rate of supply of the liquid to each device is 
stabilized and the size and the amount of bubbles at each device are 
stabilized, and variations in the pressure at each device can be reduced, 
so that the spatial non-uniformity and the change with respect to time of 
the temperature of each device are reduced. If variations in pressure are 
reduced, the load imposed upon each device or the substrate becomes 
constant, thereby preventing fatigue failure caused by repeated load. 
With respect to cooling performance, the above-described violent mixing of 
the vapor and the liquid enables an increase in the jet boiling heat 
transfer coefficient and, hence, removal of large amount of heat from each 
device, and also enables heat transfer coefficient distribution at the 
time of single-phase liquid jet heat transfer to be made flat so that the 
temperature distribution on the device back surface is reduced. Further, 
the violent mixing of the vapor and the liquid on the device back surface 
limits burnout occurring at a device end remotest from the jet flow center 
and acts to increase the burnout heat flux. The cooling performance with 
respect to the device calorific value is thereby improved, so that the 
gate density in each device can be increased. 
According to the present invention, bubbles of the liquid generated at each 
semiconductor device can be prevented from flowing into the region of 
other devices. The differences between the temperatures of the devices can 
be reduced by independently cooling the devices. Further, a turbulence is 
caused in the liquid flow at each device to violently mix the vapor and 
the liquid so that the cooling performance is improved, while bubbles are 
caused to reduce and disappear to stabilize the main flow so that the 
device temperatures are uniform and stable. It is thereby possible to 
increase the degree of device integration, to limit the temperature drift 
of the devices and to increase the speed of computer logical operation.