Development of High-Power Large-Sized Peltier Moduleby Toshiki Sakamoto * , Yasuhiro Suzuki * and Takeshi Hirasawa * 2

With the progress of electronic and communications equipment in recent years
toward higher mounting density and higher speed, greater importance has
been attached to countermeasures against the heat generated in the equipment. Peltier device,
an electronic cooling device, has expanded applications in the market taking advantage of its
active, spot cooling capability. However, it was difficult conventionally to realize a large-sized
Peltier module because of its inferior resistance against thermal stress. The authors have recently developed a 70-mm-square Peltier module provided with superior stress resistance, which is
aimed at solving the problem of the limited size of conventional modules and thereby responding to the needs for high-power, large-sized Peltier modules. In the future, the authors intend todevelop its applied products as well as to expand applications in the market.

ABSTRACT

1.

Recent years have seen IT revolution of modern society,where implementation of Internet systems such as ADSL
and FTTH (fiber to the home) is progressing rapidly.
This brings about the development and the speed andcapacity increase in network equipment such as servers and routers, communications equipment for officebuildings and personal computers, accompanied by heatgeneration in the CPUs. Device cooling technologies are
required, in view of society maturation and environment
consciousness, to be diversified beyond the compressorbased cooling technology thus expanding new applications, but conventionally, with respect to Peltier device,
only high-precision but compact and small-capacity
devices of several tens watts have been available torespond to such requirements. In this paper a large-sized
Peltier module with a capacity in excess of 100 W is presented.

2.

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INTRODUCTIONLARGE-SIZED THERMOELECTRIC
MODULE

2.1 Peltier Module
Prior to describing the large-sized thermoelectric module
we have developed, let us briefly explain about Peltierelement which is generally called thermoelectric element.
A Peltier element consists of, as illustrated in Figure 1, apair of p- and n-type semiconductor elements bondedwith a metal electrode. An electric current flows from then-type to the p-type semiconductor when a DC voltage
is applied in the direction shown in the Figure, whereby
for the p-type semiconductor heat transfers in the direc* Okano Electric Wire Co., Ltd.
* 2 Thermal and Antenna Solutions Dept., Electronic
Components Div., Electronics and Automotive Systems Co.

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Figure 1

Structure of Peltier element.

tion reverse to the current, while for the n-type in the forward direction, thereby the heat is absorbed at the upper
electrode where the current flows from the n-type to thep-type, making the metal electrode a heat absorber.
This process is a kind of heat pump, and can constitutea very effective cooling system in case the heat-dissipating side (i.e. high-temperature side) can sufficiently
dissipate the heat. Note, however, the heat dissipation
rate at the high-temperature side normally includes theabsorption heat and the Joule heat generated in the semiconductors due to the conduction current, both added
together.
The heat absorption rate Q can be expressed asshown below, taking I as the conduction current, Th as
the temperature of the heat-dissipating surface, Tc as thetemperature of the heat-absorbing surface, and N as thenumber of semiconductor element pairs. The first, second
and third terms of the Equation represent the ones due
to Peltier effect, heat conduction and Joule heat, respectively.
Q = N[(α p-α n)ITc-K(Th-Tc)- 1 IR2]
2
R = ρ p(L/A)+ρ n(L/A)
K = λ p(A/L)+λ n(A/L)(1)

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Development of High-Power Large-Sized Peltier Module

Since the input voltage V can be expressed as V =N [(α p -α n) I (Th - Tc) + IR], the power consumption W
can be represented as follows.
W = VI = NI[(α p-α n) I (Th-Tc)+IR](2)where: A is the cross-sectional area of the semiconductor element; L is its length; α p and α n are Seebeckcoefficients of the p- and n-type semiconductor elements respectively; ρ p and ρ n are their electric resistivity; and λ p and λ n are their thermal conductivity.
2.2 Module Structure
Figure 2 shows the common structure of a Peltier module, in which plural pairs of p- and n-type semiconductors
such as BiTe doped with Se and the like are arranged
on two electric insulating substrates made of alumina,
aluminum nitride or the like provided with an electrodeon its one surface. The use of ceramic substrate is aimed
at ensuring good thermal contacts with the electricallyconductive heatsink made of aluminum or copper, while
maintaining electrical insulation. The electrode is normallya copper sheet of several tens µm in thickness, and it isbonded with the thermoelectric semiconductors using
solder like Sn-Pb solder and Au-Sn solder.

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Thermal stress on P/N semiconductor legs.

sensors. In cases where cooling by heat absorption inexcess of 100 W is desired, plural modules connected
either in series or in parallel were used, but the modules
have to be strictly controlled individually in terms of theheight to improve the thermal conductivity between theheatsink and module, and in addition, they have to undergo selection to provide an even level of heat absorption
rate or temperature difference.
2.3 Product Concept
We have carried out the development, as describedabove, based on a product concept aimed at solving the
problem of the limited size of conventional modules andthereby responding to the needs for high-power, largesized Peltier modules.

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2.3.1. Basic Structure and Materials for Thermoelectric
ModuleFigure 4 shows the basic structure of the thermoelectricmodule developed here, and Photo 1 its appearance.
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Figure 2

Structure of ordinary Peltier module.

What should be noted here is that, as illustrated in
Figure 3, these ceramic substrate-based Peltier modules
generate, since the upper and lower ceramic substrates
and the multiple semiconductor elements are bonded
together using solder, a shearing stress at the fixed portion of the semiconductors due to the fact that in operation the heat-dissipating side is heated to expand, while
the heat-absorbing side is cooled to contract. This stresscan result in fractures of the module and generation of
fatigue cracks at the solder-bonded portion when repeatedly used for a long period under a large temperature difference. These fractures and cracks are remarkable at theends of the module, posing a serious problem in the caseof large-sized modules.
Thus it has been difficult to manufacture large-sized
Peltier modules, so that the maximum size commerciallyavailable was limited to 40~50 mm square at most, andthese products have been supplied to the market targeting mainly at such applications where high-precision temperature control is needed for small- to medium-capacity
cooling, e.g. CCD cameras with extended definition and��� ������������� ���

Figure 4��������� �����

Structure of developed large-sized Peltier module.

Photo 1

Large-sized Peltier module.

Structural features of the developed thermoelectricmodule are summarized into three items as follows:(1) Semiconductor elements are fixed using an insulator at the center for mechanical connection, while
their upper and lower ends are not fixed.

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Development of High-Power Large-Sized Peltier Module(2) Semiconductor elements are connected at their
upper and lower ends using a small nickel-plated
copper electrode to form thermoelectric pairs, forelectrical connection.
(3) The element and the electrode are fixed using solder.
Table 1 shows the structure and materials.
Table 1�������� ���� ��������� �����

Structure and materials of large-sized Peltier module.

Item
Electrode
Semiconductor
element
SolderDimensions�������� ���� ����Materials

2.3 × 5.0 × 0.4 mm Nickel-plated oxygen-free copper
2 × 2 × 2.3 mm
248 pairs

Bismuth telluride—

Tin-Lead solder

Separator

71 × 72 × 0.5 mm

Heat-resistant reinforced resin

Module size

71 × 72 × 3.2 mm—

2.3.2. Structural Advantages
In this module, the p- and n-type semiconductor elements
are fixed at the center using a heat-resistant epoxy resin
insulator, while their upper and lower ends are bondedwith electrodes to form a pair using solder. The paired
elements are less susceptible to the shearing force dueto thermal expansion than the conventional module
where all pairs are integrally structured using a ceramic
substrate, thereby resulting in a higher degree of reliability against thermal stress as well as ease of size enlargement. This large-sized Peltier module is fully applicableto those purposes in particular where rapid heating- andcooling-operations are required—a major advantage of
Peltier effects—because of its excellent resistance against
thermal strains.
2.3.3. Products Lineup
The standard shell shown in Figure 5 and the hard shell
shown in Figure 6 have been developed to be incorporated with the 70×70-mm, large-sized Peltier module,
constituting the products lineup. Their external views areshown in Photos 1 through 3.
These two types of shells are intended to adapt the 70
×70-mm, large-sized Peltier module to specific applications, and they provide sealing to enable applications in
the dew-condensing environments. The standard shell
has a low profile of 4.1 mm in thickness, so that it is suitable for such applications where installation space islimited, while the hard shell has a robust structure withsuperior shock resistance, so that it is suitable for a wide
range of applications.
The standard shell has a structure such that two
0.5-mm thick aluminum plates with an insulating layer on
the inner side are used, with the aim of temperature stabilization and homogenization, to sandwich the 70×70-mm,
large-sized Peltier module from both the heat-absorbing
and heat-dissipating sides, and an elastic adhesive isused to seal and fix the sides overall.
The hard shell has a structure more robust than thestandard shell, consisting of two aluminum plates on theheat-absorbing and heat-dissipating sides in addition to a

Figure 5

Standard shell incorporated with 70x70-mm Peltier
module.

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Hard shell incorporated with 70x70-mm Peltier
module.

Photo 2

Photo 3External view of standard shell.

External view of hard shell.

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Development of High-Power Large-Sized Peltier Module�������� ����� ����������� �����

Table 2

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Specifications of standard and hard shells.
Specification

Item
Model nameHard shellStandard shell

OKT-7070-H

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Max. current (A)6

Max. voltage (V)27

Max. temperature difference (°C)

6567Max. heat absorption rate (W) (∆ T=0°C)

120

120

Internal resistance (Ω)(measured at Th=50°C)

Connection for power supply
Outer dimensions (mm) (L×W×H)
Mass (g)

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3.2±10%

Number of pairs

Thermoelectric characteristics of standard shell.
(at Th=50°C)

P/N 241 pairs
Terminal
type

Lead wire(Red: positive,
Black: negative)

94×108×22

77×77×4.1

520

90

Retention strength of lead wire (kg)

3.

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nylon frame for fixing the plates. The module and the aluminum plates are electrically insulated, as in the case of
the standard shell, by an insulating layer on the inner sideof the aluminum plates, providing an electrical insulation
rating of DC 500 V for both the standard and hard shells.
Table 2 shows specifications for the standard and hardshells.

2

MAJOR CHARACTERISTICS

3.1 Thermoelectric Characteristics
Figure 7 shows the thermoelectric characteristics of thestandard shell (model name: OKT-7070-S) using a largesized Peltier module, where the heat absorption rate Q
versus temperature difference ∆ Tg characteristics andthe supply power W versus temperature difference ∆ Tg
characteristics are plotted, taking the module current as aparameter.
As can be seen from the heat absorption rate Q versus
temperature difference ∆ Tg characteristics in Figure 7,
under the condition of constant input current, the higher
the difference ∆ Tg the smaller becomes the heat absorption rate Q. That is to say, the maximum heat absorption
rate Qmax is obtained when ∆ Tg=0, i.e. when the heatdissipating surface temperature is equal to that of heatabsorbing surface. Thus maximum heat absorption rateis defined under the condition of ∆ Tg=0, and as can beseen from the Figure, it is 130 W for the standard shell.
Furthermore, the temperature difference ∆ Tg reaches at
its maximum when the heat absorption rate is zero, andas can be seen from the same Figure, it is about 68°C at
the maximum current rating of 6 A.
3.2 Heat Cycle Resistance
Conventional Peltier modules suffer from the disadvantage of an extreme weakness against thermal strainscaused by rapid heating- and cooling-operations, in addition to insufficient long-term reliability when operated
under on-off temperature control.

Since the developed large-sized Peltier module adopts
a skeleton-based structure where the semiconductor
elements are fixed at their center using a heat-resistantepoxy resin insulator, the module is less susceptible tothe shearing force due to thermal expansion than theconventional module where all pairs are integrally structured using a ceramic substrate, thereby resulting ina higher degree of reliability against thermal strains.
Durability of the 70×70-mm, large-sized Peltier module(model name: OKT-7070-S) has been tested to evaluate
its reliability against thermal strains using the method
shown in Figure 8.
The test results are shown in Figure 9, where thechanges in the resistance of a module over time and thenumber of heat cycles are plotted with the cycle on the
X-axis and the resistance on the Y-axis. It can be seenthat the resistance is stable up to 50,000 cycles, sufficientdurability against thermal strains.
Figure 10 shows the test results of durability against
thermal strains for the hard shell (model name: OKT7070-H). The heat cycles were applied by reversing thepolarity of the module current to obtain a temperature
cycles of from -15°C to +110°C at the heat-absorbing
surface of the module. Stabilized durability of more than
10,000 cycles has been achieved.

4.

APPLICATION FIELDS

Since the Peltier module developed here is large-sizedand high-powered as well as provided with sufficientdurability against rapid cooling- and heating-operations
besides on-off control, it is applicable to a wide range ofapplications. It is expected that the module will expand its
application fields taking advantage of such features. Table
3 shows the projected application fields at the present
time.

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5.

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Figure 8
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Durability test against thermal strains.

CONCLUSION

This paper has presented a general description of the
70×70-mm, large-sized Peltier module and its applications developed here. The module has been developed
based on the skeleton structure where the semiconductor
elements are held at the center. The advantages of thismodule are that regardless of its large size it has sufficientdurability against thermal strains as well as a high heatabsorption rate, which is unattainable for conventional
structures. Durability test against thermal strains proved
its highly stabilized performance.
Hereinafter, it is expected that the product will find awide range of applications taking advantage of its beneficial features, and we plan to expand its applications in themarket as well as to develop many applied products.
In closing, we would like to extend our thanks to thoseat the Ecology and Energy Laboratory of Furukawa
Electric for their valuable advice.

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Figure 9

Heat cycle test results for standard shell. (Heat cycle:-25°C~+80°C)

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Figure 10 Heat cycle test results for hard shell. (Heat cycle:-15°C~+110°C)
Table 3Market and field

Application fields of large-sized Peltier module.
Applicable equipment

Objective

Semiconductor

Liquid circulating cooling equipment; Wafer prober;
Rapid cooling equipment after wafer baking

High-precision, rapid cooling

Medical care, biotechnology

Icing equipment; DNA amplification equipment

Streamlining of test equipment;
Automation of test; Noise reduction

Electronics

Test equipment for laser diode; Parts test equipment;
Compact temperature-controlled oven

Downsizing; Precision improvement

Industry

Refrigerator; Test equipment; Manufacturing equipment
Temperature control for controlling unit; Cooling of laser
machining equipment

Downsizing

VehicleCooling box

Downsizing

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