Proceedings of the ASME 2009 7th International Conference on Nanochannels, Microchannels and Minichannels
ICNMM2009
June 22-24, 2009, Pohang, South Korea
ICNMM2009-82262
COOLING OF MICROELECTRONIC DEVICES PACKAGED IN A SINGLE CHIP MODULE USING
SINGLE PHASE REFRIGERANT R-123
Tushara Pasupuleti
Rochester Institute of Technology
Rochester NY USA
[email protected]
ABSTRACT
An approach towards practical application of microchannel
cooling system is necessary as the demand of high power
density devices is increasing. Colgan et. al. [1] have designed a
unit known as Single Chip Module (SCM) by considering the
practical issues for packaging a microchannel cooling system
with a microelectronic device. The performance of the SCM
has already been investigated by using water as working fluid
by Colgan et. al. [1]. Considering the actual working
conditions, water cannot be used in electronic devices as the
working fluid because any leakage may lead to system damage.
Alternative fluids like refrigerants were considered. In this
research, the performance of SCM has been studied by using
refrigerant R-123 as working fluid and compared with water
cooled system. Cooling of 83.33 W/cm2 has been achieved for
a powered area of 3 cm2 by maintaining chip temperature of
60oC. The heat transfer co-efficient obtained at a flowrate of 0.7
lpm was 34.87 kW/m2-K. The results obtained indicate that
from a thermal viewpoint, R-123 can be considered as working
fluid for microelectronic cooling devices.
1. INTRODUCTION
The current trend in IC technology is to increase the
packing density of the chip by decreasing the size of the
devices resulting in enhanced heat flux. Due to the reduction of
the size of the devices, the heat generated per unit area has
increased. The resulting rise in temperature affects the
reliability of the chip as it is working at higher temperatures
than the desired operating range. As a result, the need for
cooling of electronic chip is very important.
Microchannel cooling is a very effective and attractive
option for high power density devices as it reduces the thermal
resistance between the chip surface and the coolant. The heat
transfer coefficient increases as the hydraulic diameter
Satish G. Kandlikar
Rochester Institute of Technology
Rochester NY USA
[email protected]
decreases resulting in an enhanced heat transfer in the
microchannels. The pattern of these microchannels can be
continuous and staggered fins. Continuous fin type channels
have uninterrupted flow along the length of the channel.
Whereas staggered fin type channels have fins placed at fixed
intervals with an offset which increases the boundary layer
region from the start to the end of each fin in the channel.
Hence, heat transfer coefficient is increased in staggered fin
pattern type when compared to continuous fin pattern type as
heat transfer is high in the boundary layer region [1-3].
In the past, a few researchers have experimentally studied
the performance of the microchannels [4, 5]. However, many of
these experiments were performed under various assumptions
of the actual working conditions. In order to test the
performance of microchannel under actual working conditions,
Colgan et. al. [1] designed a unit which comprises of a
microchannel cooler and a thermal chip packaged together
known as Single Chip Module (SCM). The microchannel
cooler consists of a manifold chip which distributes the flow
and channel chip which consists of channels with staggered
fins. The performance of the SCM was studied by Colgan et. al.
using water as the working fluid. The efficiency of the SCM
was studied by changing the geometry of the fins in the
microchannel cooler. Thermal resistance of 15.6oC-mm2/W was
reported for a 75 µm pitch and 450 µm thick channel chip at a
flow rate of 1.5 lpm. Cooling of over 500 W/cm2 was achieved
for a powered area of 3 cm2 by using water as working fluid
[6].
It is very essential to select a suitable working fluid for
practical application of the microchannel cooling system in the
electronic devices. Water cannot be used as working fluid in the
electronic devices as a small amount of leakage may cause
system failure. Other alternatives like refrigerants should be
considered. Kandlikar [7] has listed some desirable
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Copyright © 2009 by ASME
characteristics for an ideal refrigerant required in a flow boiling
system. Colgan et. al. [6] performed experiments using
fluorinated fluid in sub-ambient inlet conditions. However, the
primary disadvantage of this methodology is that it requires
additional power to maintain the sub-ambient conditions of the
fluorinated fluid.
In this research, refrigerant R-123 is considered as the
working fluid to study the performance of the SCM at room
conditions. The refrigerant 2,2-dichloro-1,1,1-trifluoro-ethane
(R-123) is a low pressure fluid with a boiling point of 27.6oC at
1 bar. Hence, R-123 can operate in single-phase or two-phase
systems. The advantage of the two phase system is derived
from the large latent heat during the phase change process. R123 is safe to use in electronic devices as working fluid and it
does not require corrosion inhibiters or biocide as compared to
water.
2. OBJECTIVE
The objective of the present work is to study the
performance of the SCM designed by Colgan et. al. using
refrigerant R-123 as the working fluid. The experiments were
performed in single phase system using a SCM with a channel
pitch of 75 µm in the microchannel cooler. The results were
compared with the results obtained by Colgan et. al. [1,4] who
have used water as the working fluid. The comparison of the
results is done for the same fin geometry of the microchannel
cooler in the SCM.
area of the cooler is 18.6 mm X 18.6 mm excluding the sealing
region. A 3D view of the microchannel cooler is shown in Fig.
2. A gasket is used between the second manifold block and the
microchannel cooler (manifold chip). Using Ag epoxy,
microchannel cooler and the thermal chip are bonded together.
Figure 1(d) represents the thermal chip which has temperature
sensor resistors and heater lines. The thickness of the thermal
chip is 400 µm. Using solder balls and fillings thermal chip is
fixed to the ceramic substrate. Figure 1(f) represents the final
assembly of the SCM and Fig. 3 represents the cross sectional
view of the SCM. This design transforms the flow from single
inlet and outlet to four inlet and three outlets in a way that there
are six parallel-fed heat exchanger zones.
Temperature sensor resistors were placed on the chip such
that the active area of channel chip is covered. Sensor S4 and
S5 were placed at the center of the chip, S1 and S8 were placed
at the center of the two opposite quadrants, S2 and S7 were
placed at the edges of the two opposite quadrants. Hot spots
were neglected for the analysis. The sensor resistors on the
thermal chip were calibrated by measuring the sensor resistance
with change in inlet water temperatures.
3. NOMENCLATURE

Tchip
Tinlet
q”
Unit thermal resistance (oC-mm2/W)
Chip or sensor temperature (oC)
Inlet fluid temperature (oC)
Heat flux (W/mm2)
4. EXPERIMENTAL WORK DETAILS
Fig. 1. Various components of Single Chip Module [1].
4.1. Test Section Details
The SCM used for the experiment was provided by IBM.
Colgan et. al. used the same SCM to study the thermal
performance using water as the working fluid. Figure 1
represents the various components of the SCM. The various
components are two manifold blocks, thermal chip,
microchannel cooler, gasket, ceramic substrate. Figure 1(c)
represents the inner side of the first manifold block with one
inlet and one outlet port. The second manifold block transforms
the flow into four inlets and three outlets from single inlet and
outlet port. Figure 1(b) represents the side of the second
manifold block which faces the inner side of the first manifold
block. Figure 1(a) represents the other side of the second
manifold block which faces the gasket. It can be seen in Fig.
1(a) that inlet and outlet rows are alternative to each other in
this design. Figure 1(e) shows a microchannel cooler and the
gasket. The microchannel cooler consists of manifold chip
which distributes the flow, and channel chip which consists of
the fins. The two chips are sealed around the border. The active
Fig. 2. Microchannel cooler with manifold chip and channel chip
in 3D view [1].
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Copyright © 2009 by ASME
were recorded using Labview. Experiments were performed by
varying power conditions for a fixed flowrate. The procedure
was repeated for different flowrates. The chip temperature was
computed from the recorded sensor resistance values. This was
achieved by using calibrated values of the sensor resistors. The
sensor resistance was recorded by supplying 0.01 A of current
through the resistors. Thermal resistance of each sensor was
computed by taking the difference of the chip temperature and
inlet refrigerant temperature, and dividing the difference by the
applied power. The powered area on the chip is 300 mm2. The
unit thermal resistance was computed using Eq. (1).
𝜃=
Fig. 3. Cross sectional view of the SCM [1].
𝑇𝑐ℎ𝑖𝑝 − 𝑇𝑖𝑛𝑙𝑒𝑡
𝑞"
(1)
In the present work, the channel chip has staggered fin type
pattern. The dimensions of the fins and channel chip are listed
in Table 1. In this table, the flow length is defined as the
distance between the inlet and outlet vias.
Table 1. Dimensions of the fins and channel chip in the SCM [1].
Channel chip dimensions
Channel chip thickness
Channel pitch
20 mm X 20 mm
450 µm
75 µm
Channel width
48 µm
Channel depth
256 µm
Fin length
500 µm
Flow length
3.1 mm
4.2. General Description
A closed loop system is used to test the SCM with the
refrigerant. The experimental setup used for R-123 is
represented in a block diagram as shown in Fig. 4. The various
components used for the experiment are two heat exchangers,
test section, refrigerant receiver, a pump, filter, power supply,
filter-drier, two sight glasses, flowmeter, pressure transducers,
temperature sensors and a data acquisition system. Stainless
steel fittings and tube were used to connect all the components
in the setup to ensure a leak-proof system. The inlet
temperature of the refrigerant is controlled by a heat exchanger
and the refrigerant leaving from the test section is cooled by
another heat exchanger. Micropump regulates the flow of
refrigerant through the test section. Power supply is connected
to the heaters in the thermal chip which is present in the test
section. A vacuum test was performed to detect leaks in the
system. This check was to ensure a leak proof system as R-123
is hazardous to health if inhaled in large amounts.
The inlet temperature of the refrigerant was maintained at
22oC for all the experiments. The power was applied to the
heaters in the test section after the flow was stabilized in the
system. Once steady state condition was achieved, readings
Fig. 4. Block diagram of the R-123 experimental setup.
4.3. Uncertainty in the Measuring Equipment
In an experimental work, the measurements taken at
microscopic level tend to have more uncertainty as the
magnitude of the value is small. Hence computing the
uncertainty in the measurement is necessary. In this
experiment, the power supply used for heating the chip has an
uncertainty of ±0.15%, the flow meter has an accuracy of
±0.1% of the flowrate, the temperature resistor sensors have an
uncertainty of ≤ 5% in the measured resistance, and the
accuracy of the pressure and temperature measurements is
±1.724 kPa and ±0.1oC respectively.
5. RESULTS AND DISCUSSIONS
The performance of the SCM using refrigerant R-123 as a
working fluid is described in this section. Figure 5 shows the
difference between the average temperature of the resistive
sensor and the inlet refrigerant R-123 temperature versus the
applied power. It can be seen that the temperature difference
increases as power is applied. Increase in the flowrate of the
fluid decreases the temperature difference for constant power.
This behavior is similar to the water cooled system. Figure 6
shows the thermal resistance of each sensor with the increase in
flowrate. It can be seen that the all the sensors are
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approximately exhibiting the same behavior at a fixed flowrate.
It implies that the chip is uniformly cooled in the active area.
Figure 8 shows the graph of heat transfer co-efficient of
refrigerant R-123 cooled system and water cooled system with
increasing flowrates. As illustrated in Fig. 8, it is found that
water cooled system has a heat transfer co-efficient of 50.73
kW/m2-K at a flowrate of 0.6 lpm while the refrigerant cooled
system has a heat transfer co-efficient of 34 kW/m2-K at a
flowrate of 0.7 lpm. These values indicate that the heat transfer
coefficient of the refrigerant cooled system shows the same
trend as the water cooled system.
50
30
20
100 mL/min
10
500 mL/min
0
0
100
Power (W)
200
300
Fig. 5. Chip temperature rise with addition of heat using R-123 as
working fluid.
0.2
Unit Thermal Resistance (oC-mm2/W)
Tchip - Tinlet
40
Water
60
R-123
50
40
30
20
10
0
0.15
0
0.2
0.4
0.6
0.8
1
1.2
Flowrate(lpm)
Fig. 7. Comparing thermal resistance of R-123 (Present work) and
water [6].
0.1
0.05
0
0
0.2
0.4
0.6
0.8
Flowrate (lpm)
S1 Quad center
S2 Quad edge
S4 Chip center
S5 Chip center
S7 Quad edge
S8 Quad center
Fig. 6. Thermal resistance (oC/W) of the chip at various locations.
Figure 7 represents the unit thermal resistance of
refrigerant cooled system and water cooled system with
increasing flowrates. It is clear that the increase in flowrate
decreases the unit thermal resistance. As flowrate increases, the
unit thermal resistance is decreasing more rapidly for
refrigerant cooled system than water cooled system. However,
the value of the unit thermal resistance of a water cooled
system is lower than a refrigerant cooled system. From Fig. 7, it
can be seen that at flowrate close to 0.7 lpm, the unit thermal
resistance of both the cooling systems is very similar. Thermal
resistance is 28.94 oC -mm2/W for refrigerant cooled system at
0.7 lpm and 19.71 oC-mm2/W for water cooled system at 0.6
lpm. This indicates that the performance of R-123 is close to
water at higher flowrates. However, due to lack of experimental
data beyond 0.7 lpm for refrigerant cooled system (caused
Heat Transfer Co-efficient (kW/m2-K)
Thermal Resistance (oC/W)
because of the inefficiency of the pump), no significant
conclusions can be derived.
60
50
40
30
20
R123
10
Water
0
0
0.5
Flowrate (lpm)
1
Fig. 8. Comparing heat trasfer co-efficient of R-123 (Present work)
and water [6].
In addition to the above results, the refrigerant cooled
system was compared to other working fluids reported in the
literature. Table 2 summarizes the unit thermal resistance for
different working fluids at approximately the same inlet
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Copyright © 2009 by ASME
temperatures. It can be seen that fluorinated fluid used by
Colgan et. al. needs higher flowrate to attain thermal resistance
of 25.72 oC-mm2/W when compared to water and refrigerant R123 which requires less than half the flowrate of fluorinated
fluid. At the same flowrates and inlet temperature conditions,
refrigerant R-123 results in approximately 50% more thermal
resistance as compared to water.
Table 2. Performance of the different working fluids.
Flowrate
Inlet
Unit Thermal
Fluid
(lpm)
Temp.
Resistance
(oC)
(C-mm2/W)
Water [6]
0.3
22
26.12
Water [6]
0.6
22
19.71
Water [6]
0.9
22
17.28
1.8
20
25.72
0.7
22
28.94
Fluorinated fluid
[6]
R-123
(Present work)
6. CONCLUSION
The testing of SCM using refrigerant R-123 was
successfully performed at ambient inlet conditions on a channel
chip with a pitch of 75 m and width of 48 m. Cooling of
83.33 W/cm2 was successfully achieved with the chip
temperature maintained at 60oC at a flow rate of 0.5 lpm. The
performance of the refrigerant cooled system and water cooled
system (Colgan et. al.) were compared and it was found that the
behavior of refrigerant R-123 cooled system was similar to
water cooled system. Although more extensive testing is
required for considering refrigerant R-123 in practical
applications, it can be stated that initial tests indicate very
promising results.
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and
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7. ACKNOWLEDGEMENTS
We are thankful to Dr. J.H. Magerlein and Dr. E.G. Colgan
of IBM for providing the thermal cooler chip and support
during this work conducted at Thermal Analysis Micro-fluidic
and Fuel cell laboratory, Rochester Institute of Technology,
Rochester NY.
8. REFERENCES
[1]. Colgan, E.G., Furman, B., Gaynes, M., Graham, W.,
LaBianca, N., Magerlein, J.H., Polastre, R.J., Rothwell, M.B.,
Bezama, R.J., Choudhary, R., Marston, K., Toy, H., Wakil, J.,
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[2]. Kandlikar, S.G. and Steinke, M. E., 2004, “Single-phase
heat transfer enhancement techniques in microchannel and
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