JP2003282975A - Thermoelectric module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve long term reliability by preventing a thermoelectric module from being broken down. <P>SOLUTION: The thermoelectric module comprises a supporting board 1, a plurality of thermoelectric elements 2 arranged on the board 1, wiring conductors 4 for electrically coupling between the plurality of the elements 2, and an external connection terminal provided on the board 1 to electrically connect to the conductors 4. The elements 2 and the conductors 4 are connected via a solder layer 5. The ratio of a mean length of one side in a section of the element 2 to a sum of the thickness of the layer 5 and the thickness of the conductor 4 is 5 to 15. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermoelectric module which is preferably used for cooling a heating element such as a semiconductor and has excellent thermoelectric characteristics.

[0002]

2. Description of the Related Art Thermoelectric modules utilizing the Peltier effect not only have a simple structure and are easy to handle,
Since it is possible to maintain stable properties, widespread use is drawing attention. In particular, thermoelectric modules allow local cooling and precise temperature control around room temperature, so they are used in devices such as semiconductor lasers and optical integrated circuits that are precisely controlled at a constant temperature such as small refrigerators. ing.

Generally, such a thermoelectric module is shown in FIG.
, The N-type thermoelectric element 2a and P
The thermoelectric elements 2b are alternately arranged and are electrically connected in series by the wiring conductors 4 formed on the supporting substrate 1. The wiring conductor 4 is usually made of a copper plate so as to withstand a large current, and the N-type thermoelectric element 2a and the P-type thermoelectric element 2b are fixed to each other via a solder layer.

As shown in FIG. 2, the joint portion between the wiring conductor 4 and the thermoelectric elements 2a and 2b has a solder layer 5 on the wiring conductor 4,
Plating layer 6 (gold plating layer 6a, nickel plating layer 6b)
One pair of N-type thermoelectric elements 2a and one pair of P-type thermoelectric elements 2b are alternately fixed to each other and are connected in series in the order of PNPNPN.

Conventionally, an output cycle in which a current (Imax) is energized for 1.5 seconds so that the temperature difference between the cooling surface Tc and the heat radiating surface Th of the thermoelectric module is the maximum temperature difference, and then the energization is stopped for 4.5 seconds is repeated. In the test, support substrate 1
There is a problem that cracks and damages occur at the joint portion between the wiring conductor 4 and the wiring conductor 4, the joint portion between the wiring conductor 4 and the solder layer 5, and the joint portion between the solder layer 5 and the gold plating layer 6a.

In this case, since the maximum temperature difference is about 70 ° C., a difference in size occurs due to the temperature difference between the low temperature side substrate and the high temperature side substrate of the thermoelectric module, and thermal stress occurs. That is,
The tensile stress generated in the joint portion of the thermoelectric element 2 increases as it goes outward from the center of the thermoelectric element 2. When one side is rapidly cooled, the support substrate 1, the wiring conductor 4, the solder layer 5, and the thermoelectric element 2 have different coefficients of thermal expansion, so that breakage and cracks occur at the respective bonding interfaces, which causes deterioration of the characteristics. Was there.

Therefore, it is known that the structure and thickness of the joint surface are improved and the mechanical strength of the joint interface is improved. For example, the thickness x of the nickel plating layer 6b applied to the electrode end surface of the thermoelectric element 2 is y, and the length of one side of the cross section of the thermoelectric element 2 is y.
Then, by increasing the thickness so as to satisfy y / x ≦ 100, the junction in the output cycle test for turning on / off the energization of the current value (Imax) when the cooling surface Tc and the heat radiating surface Th have the maximum temperature difference The improvement of the mechanical strength of the interface is described in JP-A-4-249385.

[0008]

However, in the thermoelectric module described in Japanese Patent Laid-Open No. 4-249385, although the bonding strength at the interface between the nickel plating layer 6 and the thermoelectric element 2 can be improved, the interface between the electrode and the solder layer 5 is improved. However, there is a problem that the thermal stress at the interface between the solder layer 5 and the gold plating layer 6a cannot be sufficiently relaxed.

Therefore, an object of the present invention is to prevent destruction of the thermoelectric module and improve long-term reliability.

[0010]

According to the present invention, the thermal stress at the joint interface when the maximum temperature difference is generated by reducing the thickness of the solder layer and the electrode with respect to the length of one side of the cross section of the thermoelectric element. It is based on the finding that it is possible to prevent the destruction of the bonding interface in the thermoelectric module by reducing the difference.

That is, the thermoelectric module of the present invention comprises a support substrate, a plurality of thermoelectric elements arranged on the support substrate, wiring conductors electrically connecting the plurality of thermoelectric elements, and the support substrate. A thermoelectric module comprising an external connection terminal electrically connected to the wiring conductor, wherein each thermoelectric element and the wiring conductor are joined via a solder layer, wherein the thickness of the solder layer and the The ratio of the average length of one side in the cross section of the thermoelectric element to the sum of the thickness of the wiring conductor is 5 to 15.

Particularly, the ratio of the average length of one side in the cross section of the thermoelectric module to the thickness of the wiring conductor is 5 to 5.
It is preferably 20. Thereby, not only the thermal stress at the bonding interface can be relaxed and long-term reliability can be improved, but also the thermal resistance of the electrode and the solder layer can be reduced, so that excellent thermoelectric characteristics can be exhibited.

The ratio of the average length of one side in the cross section of the thermoelectric element to the thickness of the solder layer is 10 to 100.
Is preferred. This reduces the joint failure at the solder layer interface and relaxes the thermal stress at the joint interface,
The long-term reliability can be improved.

Further, it is preferable that the thermoelectric element has a specific resistance of 5 × 10 ⁻⁵ Ωm or less. Thereby, it becomes easy to suppress the Joule heat generated inside the element and control the temperature of the element to a constant temperature.

The shape factor of the thermoelectric element is 2000.
/ M or more, and the device density is preferably 100 / cm ² or more. This makes it possible to efficiently cool the heat generated inside the element and suppress the amount of heat generated inside the element.

Further, the shortest distance between the thermoelectric elements is 20.
It is preferably 0 to 400 μm. As a result, the number of elements per unit area can be increased, and the electrical short circuit between the elements can be suppressed by the solder used for joining the elements and the electrodes. Further, the heat generated inside the thermoelectric element can be efficiently cooled, and the amount of heat generated inside the thermoelectric element can be suppressed.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION The thermoelectric module of the present invention is shown in FIG.
And 2 and the length of one side of the cross section of the thermoelectric element is t, the sum of the thickness a of the wiring conductor and the solder layer thickness b is expressed by the relational expression 5 ≦ t / (a + b). It is important that the configuration is such that ≦ 15 is satisfied.

In such a relationship, the tensile stress generated in the joint portion of the thermoelectric element can be reduced as it goes outward from the center of the thermoelectric element.

Therefore, if t / (a + b) is less than 5, there is a disadvantage that the resistance at the joint increases, and sufficient thermoelectric properties cannot be obtained, and if it is more than 15, cracks and damages occur at the joint. There is an inconvenience that it will occur.

If the thermoelectric element has a square cross section, t
Is the length of one side, and in the case of a rectangle, t is the average of the long side and the short side. When the thermoelectric element has a circular cross section, t corresponds to the diameter.

Further, in the thermoelectric module of the present invention, when the length of one side of the cross section of the thermoelectric element is t, the thickness a of the wiring conductor and the solder layer thickness b are 5≤t / b≤20,10≤. t
It is preferably configured to satisfy / a ≦ 100.

In such a relationship, the supporting substrate 1,
Since the difference in thermal stress between the wiring conductor 4, the solder layer 5, and the thermoelectric element 2 is reduced, the tensile stress generated in the joint portion of the thermoelectric element 2 can be reduced as the distance from the center of the thermoelectric element 2 to the outside increases. The thermoelectric element 2 includes Bi, Sb, Te,
It is important to include at least two kinds of Se. For example, the above metals may be used, but A ₂ B ₃ type intermetallic compound and its solid solution are preferable. Where A
Is a semiconductor crystal of Bi and / or Sb, B is Te and / or Se, and the composition ratio B / A is 1.4 to
A value of 1.6 is preferable in order to improve thermoelectric properties at room temperature.

A₂B₃Known intermetallic compounds of the type
Bi₂Te₃, Sb₂Te₃, Bi₂Se₃At least one of
Seed is preferable, and Bi is used as a solid solution.₂Te₃And B
i₂Se₃Is a solid solution of Bi₂Te_3-xSe_x(X = 0.
05-0.25), or Bi ₂Te₃And Sb₂Te₃Solid solution of
Bi that is the body_xSb_2-xTe₃(X = 0.1-0.6) etc.
Can be illustrated.

Further, in order to efficiently convert the intermetallic compound into a semiconductor, it is preferable to contain a halogen element such as I, Cl and Br as a dopant. This halogen element is
From the viewpoint of semiconductivity, it is preferably contained in an amount of 0.01 to 5 parts by weight, particularly 0.1 to 4 parts by weight, based on 100 parts by weight of the above intermetallic compound raw material.

Further, when manufacturing a P-type thermoelectric element, it is preferable to contain Te for adjusting the carrier concentration. Thereby, thermoelectric characteristics can be improved similarly to the N-type thermoelectric element.

The specific resistance of the P-type and N-type thermoelectric elements is 5 × 1.
It is preferably 0 ^-5 Ωm or less, and particularly preferably 1.5 × 10 ^-5 Ωm or less. Thereby, the Joule heat generated inside the element can be suppressed, and the element can be efficiently cooled. The thermoelectric element can generate heat at one end and cool at the other end by the Peltier effect by passing an electric current. However, due to the resistance of the thermoelectric element itself, Joule heat is generated inside the element and it becomes impossible to cool it efficiently. Therefore, the specific resistance of the P-type and N-type thermoelectric elements is 5 × 10 ⁻⁵ Ωm or less, especially 1.5 × 10 5.
^-5 Ωm or less allows efficient cooling.

Further, in the thermoelectric module of the present invention, the shape factor L / S represented by the width W and the length L of the thermoelectric element is 2000.
/ M or more is important, and it is possible to improve the cooling efficiency of the heating element and realize a highly reliable thermoelectric module. If this shape factor L / S is less than 2000 / m, it becomes difficult to radiate the Joule heat generated inside the thermoelectric element, and it becomes impossible to achieve a predetermined cooling temperature. In particular,
In order to enhance the cooling efficiency, L / S is preferably 3000 / m or more, more preferably 5000 / m or more, and even more preferably 7000 / m or more. The upper limit is preferably 30,000 / m from the viewpoint of manufacturing feasibility.

It is also important that the element density, which is the number of thermoelectric elements per unit area, is 100 / cm ² or more. If the element density is less than 100 pieces / cm ² , there is a problem that a sufficient heat absorption amount cannot be obtained. And, in order to further improve the heat absorption amount, in particular, 120 pieces / cm ² or more,
Further, it is preferable that the number is 140 / cm ² or more.

In the thermoelectric module, when the number of thermoelectric elements constituting the module increases, the amount of heat absorption on the low temperature side of the module increases, and the module can be cooled efficiently. However, an increase in the number of thermoelectric elements causes an increase in the size of the module, which is not preferable. Therefore, by reducing the cross-sectional area of the thermoelectric element and increasing the number of elements per unit area, it is possible to arrange many elements in a limited space, and it is possible to achieve miniaturization and high efficiency.

Further, in a thermoelectric module in which a plurality of thermoelectric elements are arranged, the distance between the thermoelectric elements is the smallest,
That is, the shortest distance is 200 to 400 μm, especially 250 to 35 μm.
It is preferably 0 μm. If it is less than 200 μm, the problem of electrical short circuit between thermoelectric elements tends to occur due to the solder paste used for joining the thermoelectric elements to the electrodes on the substrate, and if it exceeds 400 μm, the thermoelectric elements per unit area are increased. The number of modules may decrease, which may lead to an increase in module size or a decrease in heat absorption.

Since the thermoelectric module of the present invention constructed as described above has an excellent cooling efficiency, it can be suitably used particularly as a constant temperature miniature refrigerator for semiconductor lasers and optical integrated circuits.

[0032]

[Examples] N-type and P-type thermoelectric elements having the specific resistance ρ, output factor PF and figure of merit Z shown in Table 1 were obtained by firing an intermetallic compound by a discharge plasma method. The wafer was cut out by slicing to a predetermined thickness with a saw.

For measuring the thermal conductivity, the diameter is 10 mm and the thickness is 1
For a disk sample having a size of 3 mm, a rectangular column sample having a length of 3 mm, a width of 3 mm, and a length of 15 mm was prepared for measuring Seebeck coefficient and resistivity. Further, in the production of the thermoelectric module, Ni electrodes and Au electrodes were formed on the above wafer by plating, and then cut into a predetermined chip shape by a dicer.

The thermal conductivity was measured by the laser flash method.
The Seebeck coefficient and the resistivity were measured under the conditions of 20 ° C. by a thermoelectric power evaluation device manufactured by Vacuum Riko Co., Ltd., respectively. And
The performance index Z is calculated by the formula Z = S ² / ρk (S is the Seebeck coefficient, ρ is the resistivity, and k is the thermal conductivity).
The output factor PF was calculated by PF = S ² / ρ.

Next, a thermoelectric module was produced. That is,
31 N-type thermoelectric elements and 31 P-type thermoelectric elements were selected, and a copper layer having a thickness of a was formed on an alumina substrate having a length of 6 mm and a width of 8.2 mm. The thermoelectric element was fixed and the thermoelectric module as shown in FIG. 1 was produced. At that time, the average length t of one side in the cross section of the thermoelectric element, the form factor L / S, the element density d, and the shortest distance D between elements
Is shown in Table 1.

The appearance of the thermoelectric module thus obtained was observed, and it was observed whether cracks occurred at the interface between the wiring conductor and the solder layer and at the interface between the solder layer and the plating layer. In addition, a cooling test was conducted. That is, the substrate 1
A heater 9 was installed as a heating element on the mounting surface 8 of a, and heating was performed so that the cooling surface (Tc) of the heater had a constant temperature of 60 ° C.

Then, a direct current is made to flow in series to the thermoelectric elements constituting the thermoelectric module, and the cooling surface Tc and the heat radiation surface Th are
In addition to measuring the temperature, the maximum current I _max when the heat absorption amount from the heating element 9 becomes maximum and the maximum heat absorption amount Qc _max at that time were measured by changing the current flowing through the thermoelectric element.

Next, a current having a current value (I _max ) is applied for 1.5 seconds so that the cooling surface Tc and the heat dissipation surface Th of the thermoelectric module have a maximum temperature difference, and then the energization is stopped for 4.5 seconds. Perform an output cycle test that repeats ON / OFF 5000 times, and after the test, in the same way as before the test,
Module characteristics (I _max , Qc _max ) were measured. The results are shown in Tables 1 and 2.

[0039]

[Table 1]

[0040]

[Table 2]

Sample No. of the present invention. 2-6 and 9-15
Is t / (a + b) is 5 to 15, t / a is 5 to 20, t
/ B is 10 to 100, the appearance is not abnormal, the maximum current I _max before the test is 1.6 A or more, and the maximum heat absorption amount Qc.
_max was 3 W or more. The change rates of I _max and Qc _max after the output cycle test were both 5% or less, and no significant characteristic deterioration was observed.

On the other hand, sample No. out of the range of the present invention in which t / (a + b) was as small as 0.99. 1 is the maximum current I before the test
_{The maximum} was 1.50 A, the maximum heat absorption amount Qc _max was 2.94 W, and cracks were observed in the visual inspection. And, I _{ma x} after the output cycle test is 1.39A, Qc _max
Decrease to 1.83W, and the rate of change is 7.3 each.
% And 37.8%.

Further, t / (a + b) was as large as 18.1, which was outside the range of the present invention. In Examples 7 and 8, the maximum current I _max before the test was 2.11 A or more and the maximum heat absorption amount Qc _max was 3.85 W or more, and cracks were observed in the visual inspection. The Qc _max after the output cycle test dropped to 2.87 W or less, and the rate of change was 28.4% or more.

[0044]

EFFECTS OF THE INVENTION The thermoelectric module of the present invention can prevent damage due to thermal stress at the joint interface in the thermoelectric module by reducing the thickness of the thermoelectric element with respect to the thickness of the wiring conductor and the thickness of the solder layer. It is possible to realize a thermoelectric module that exhibits excellent thermoelectric characteristics.

[Brief description of drawings]

FIG. 1 is a perspective view showing an outline of a thermoelectric module of the present invention.

FIG. 2 is a view showing a joint cross section of the thermoelectric module of the present invention.

[Explanation of symbols]

1, ... Support substrate 1a, ... Upper support substrate 1b: lower support substrate 2 ... Thermoelectric element 2a ... N-type thermoelectric element 2b ... P-type thermoelectric element 4 ... Wiring conductor 5 ... Solder layer 6 ... Plating layer 6a ... Gold plating layer 6b ... Nickel plating layer 8: Mounting surface 9 ... Heating element Tc ... Cooling surface Th: Heat dissipation surface

Claims (6)

[Claims] 1. A support substrate, a plurality of thermoelectric elements arranged on the support substrate, a wiring conductor electrically connecting the plurality of thermoelectric elements, and a wiring conductor provided on the support substrate. In the thermoelectric module comprising an external connection terminal electrically connected to the thermoelectric element and the wiring conductor joined via a solder layer, the sum of the thickness of the solder layer and the thickness of the wiring conductor. In the cross section of the thermoelectric element with respect to
A thermoelectric module, characterized in that the ratio of the average length of the sides is 5 to 15. 2. The thermoelectric module according to claim 1, wherein the ratio of the average length of one side in the cross section of the thermoelectric module to the thickness of the wiring conductor is 5 to 20. 3. The thermoelectric module according to claim 1, wherein the ratio of the average length of one side in the cross section of the thermoelectric element to the thickness of the solder layer is 10 to 100. 4. The thermoelectric module according to claim 1, wherein the thermoelectric element has a specific resistance of 5 × 10 ⁻⁵ Ωm or less. 5. The thermoelectric module according to claim 1, wherein the thermoelectric element has a form factor of 2000 / m or more and an element density of 100 / cm ² or more. 6. The shortest distance between the thermoelectric elements is 200-40.
It is 0 micrometer, The thermoelectric module in any one of Claim 1 thru | or 5 characterized by the above-mentioned.