JP2003347607A - Board for thermoelectric conversion module and thermoelectric conversion module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermoelectric conversion module and a wiring board for the module which prevents the breakdown of bond zones of an insulation board and wiring conductors and is superior in long reliability. <P>SOLUTION: An insulation board for comprising a plurality of thermoelectric conversion elements 5 and wiring conductors 3 on its surface has a linear expansion coefficient of 4×0<SP>-6</SP>/K or more, a ratio of the long side of the conductor 3 to a mean distance between the conductors 3 is 15 or less, and especially the area occupied by the wiring conductors 3 on a main surface of the board 2 is preferably 50-85%. <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 an insulating substrate used for a thermoelectric conversion module suitably used for temperature control and cooling, a substrate for a thermoelectric conversion module using the same, and a thermoelectric conversion module.

[0002]

2. Description of the Related Art A thermoelectric conversion module utilizing the Peltier effect has attracted attention for its wide use because it has a simple structure, is easy to handle, and can maintain stable characteristics. In particular, since local cooling is possible and precise temperature control near room temperature is possible, it is used in devices that are precisely controlled to a constant temperature, such as semiconductor lasers and optical integrated circuits, and in small refrigerators.

In such a thermoelectric conversion module, as shown in FIG. 1, for example, wiring conductors 3a and 3b are formed on the surfaces of insulating substrates 2 and 6, respectively.
a and the P-type thermoelectric conversion elements 5b are joined by solder so as to be sandwiched.

The N-type thermoelectric conversion element 5a and the P-type thermoelectric conversion element 5b are connected by wiring conductors 3a and 3b so as to be electrically connected in series, further connected to an external connection terminal 4, and As a result, electric power is supplied to the thermoelectric element 5 from the outside through the external wiring 7 fixed to the external connection terminal 4.

Although copper electrodes are used for the wiring conductors 3a and 3b, wettability between the thermoelectric conversion element 5 and solder is improved in order to make the solder joint with the thermoelectric conversion element 5 strong.
In order to prevent the diffusion of the solder component, the surface of the copper electrode may be plated with gold, or the connection surface of the thermoelectric conversion element 5 may be plated with Ni or gold to improve the adhesion and the wettability with the solder. .

Conventionally, in an output cycle test or a temperature cycle test for turning ON / OFF a current value (Imax) when the cooling surface and the heat radiation surface of the thermoelectric conversion module have a maximum temperature difference, the insulating substrate 2 is caused by thermal stress. And the wiring conductor 3 is damaged at the joint.

In the state of the maximum temperature difference, the dimensional difference increases due to the difference in temperature and the coefficient of thermal expansion between the low-temperature side substrate and the high-temperature side substrate of the thermoelectric conversion module. The resulting tensile stress increases.

[0008] This tensile stress is relieved by the built-in compressive stress of the thermoelectric conversion module, but when one side is rapidly cooled, the insulating substrate, the wiring conductor, the solder layer,
Since the coefficients of thermal expansion of the thermoelectric conversion elements are different, breaks and cracks are generated at the respective joint interfaces, which causes deterioration of characteristics.

On the other hand, the thermal expansion coefficient of the substrate and the wiring conductor formed on the surface of the substrate on the high-temperature side substrate are different from each other. was there.

For this reason, 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 t of the nickel plating layer applied to the electrode end surface of the thermoelectric conversion element is represented by the length of one piece of the cross section of the thermoelectric conversion element, b.
Japanese Patent Application Laid-Open No. Hei 4-249385 describes that by increasing the thickness so as to satisfy b / t ≦ 100, the mechanical strength of the bonding interface is improved.

[0011]

However, although the thermoelectric conversion module described in Japanese Patent Application Laid-Open No. Hei 4-249385 has the effect of improving the plating strength, it does not fundamentally reduce the thermal stress on the joint surface. However, it was insufficient as a measure.

Accordingly, an object of the present invention is to provide a thermoelectric conversion module wiring board and a thermoelectric conversion module that prevent the joint between the insulating substrate and the wiring conductor from being broken, and have excellent long-term reliability.

[0013]

According to the present invention, the length of a wiring conductor with respect to the distance between wiring conductors is reduced.
It is based on the finding that the difference in elongation caused by the difference in the coefficient of thermal expansion between the electrode and the insulating substrate can be reduced, the stress generated at the joint between the insulating substrate and the wiring conductor can be reduced, and destruction can be prevented. .

That is, the thermoelectric conversion module substrate of the present invention is an insulating substrate on which a plurality of thermoelectric conversion elements are mounted and wiring conductors for electrical connection are formed on a main surface,
The coefficient of linear expansion of the insulating substrate is at least 4 × 10 ⁻⁶ / K, and the ratio of the long side of the wiring conductor to the average distance between the wiring conductors is 15
It is characterized by the following.

It is preferable that the ratio of the area occupied by the wiring conductor to the area of the main surface of the insulating substrate is 50 to 85%. Thereby, the stress at the joint generated due to the difference in thermal expansion between the insulating substrate and the wiring conductor can be reduced, and breakage can be reduced.

Further, it is preferable that the insulating substrate has a strength of 200 MPa or more. Thereby, even if stress is generated to some extent due to the difference in thermal expansion, it is possible to prevent breakage.

Preferably, the insulating substrate is made of a sintered body containing at least one of alumina and aluminum nitride as a main component. Thereby, good element retention, thermal conductivity, vibration resistance, impact resistance, and insulation can be expected.

Further, the wiring conductor is made of Cu, Al, A
It is preferable to be made of at least one of u, Pt, Ni and W. Thereby, the breakage of the joint can be further reduced.

Further, the thermoelectric conversion module of the present invention is provided with a pair of opposed insulating substrates, a plurality of arranged thermoelectric conversion elements provided so as to be sandwiched between the pair of insulating substrates, and the plurality of thermoelectric conversion elements. A thermoelectric device comprising: a wiring conductor provided on a surface of the pair of insulating substrates for electrically connecting the wiring substrate; and an external connection terminal provided on the insulating substrate and electrically connected to the wiring conductor. In the conversion module,
At least one of the pair of insulating substrates is a substrate for a thermoelectric conversion module of the present invention. Thereby, a highly reliable and long-life thermoelectric conversion module can be provided.

In particular, it is preferable that the thermoelectric conversion element of the thermoelectric conversion module is made of at least two of Bi, Te, Se and Sb. by this,
Excellent thermoelectric conversion performance can be obtained at around normal temperature.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION A thermoelectric conversion module substrate according to the present invention is an insulating substrate on which a plurality of thermoelectric conversion elements are mounted and wiring conductors for electrical connection are formed on a main surface.
For example, FIG. 2 is a plan view of FIG. 1 showing the thermoelectric module, in which a part of the insulating substrate is removed so that the inside can be seen.

According to this figure, a wiring conductor 13a is provided on a main surface of an insulating substrate 12, and an N-type thermoelectric conversion element 15a and a P-type thermoelectric conversion element 15b are further provided thereon. Although not shown, a wiring conductor is provided between the thermoelectric conversion element 5 and the insulating substrate 16, and the N-type thermoelectric conversion element 15a and the P-type thermoelectric conversion element 15b are electrically connected in series. Connected.

The thermoelectric conversion module substrate of the present invention is shown in FIG.
2 and the wiring conductors provided on the main surface thereof.
The conductor 13a has a coefficient of linear expansion of 4 ×
10 ^-6/ K or more is important. Linear expansion coefficient
4 × 10^-6/ K is smaller than / K
Since the difference in the coefficient of thermal expansion from the body 13a becomes large,
When cooled after soldering at 320 ° C.,
Excessive stress is generated at the joint with the wire conductor 13a,
Cracks and peeling occur. In a long-term high-temperature environment, or
Wiring with insulating substrate 12 even when used under temperature fluctuation environment
Excessive stress is generated at the joint with the conductor 13a, and cracks occur.
And peeling occur.

In order to reduce the stress generated at the joint between the insulating substrate 12 and the wiring conductor 13a and further enhance the reliability,
The thermal expansion coefficient of the insulating substrate 12 is particularly 4.5 × 10 ⁻⁶ / K.
As described above, it is preferably 5 × 10 ⁻⁶ / K or more. Further, the upper limit is preferably 10 × 10 ⁻⁶ / K, particularly preferably 9 × 10 ⁻⁶ / K in order to reduce the difference in thermal expansion coefficient.

According to the present invention, it is important that the ratio of the long side of the wiring conductor to the distance between the wiring conductors is 15 or less. That is, according to FIG. 3, which is an enlarged view of a part of FIG. 2, an N-type thermoelectric conversion element 25a and a P-type thermoelectric conversion element 25b are placed on a wiring conductor 23a provided on a main surface of an insulating substrate 22.
Can be mounted in an array, and at this time, the wiring conductor 2
3a, the average distance D between the long side L and the wiring conductor is L / D ≦ 1
5 is satisfied. When L / D> 15, the difference in expansion coefficient between the substrate and the wiring conductor is greatly different, so that excessive stress is generated at the joint between the insulating substrate and the wiring conductor, and cracks and peeling occur.

The relationship between L and D is particularly L / D ≦ 14, preferably L / D ≦ 13, in order to reduce the stress generated at the joint between the insulating substrate and the wiring conductor and further enhance the reliability. It is desirable.

As shown in FIG. 3, when the average distance D between the wiring conductors is different in the horizontal and vertical directions, D is calculated by averaging the horizontal average distance D ₁ and the vertical average distance D _2. Good.

Further, it is preferable that the area occupied by the wiring conductor on the main surface of the insulating substrate provided with the wiring conductor and the thermoelectric conversion element is 50 to 85% of the size of the main surface. By setting the occupancy of the wiring conductor in the above range, the stress generated due to the difference in thermal expansion is reduced without lowering the cooling efficiency per unit area of the insulating substrate, and the bonding between the substrate and the wiring conductor is performed. Cracks and peeling occurring in the part can be suppressed.

Further, in order to reduce the generated stress, the upper limit of the area occupancy of the wiring conductor is preferably set to 80%, more preferably 75%, and the cooling / heating efficiency per unit area of the insulating substrate is reduced. In order to increase the area occupancy, the lower limit of the area occupancy of the wiring conductor is preferably set to 55%, more preferably 60%.

The strength of the insulating substrate is preferably at least 200 MPa, especially at least 250 MPa, whereby the effect of preventing damage to the substrate even when stress concentration occurs can be enhanced, and higher reliability can be obtained.

The insulating substrate is required to have high vibration resistance, shock resistance, and high adhesion strength of the wiring conductor, and to reduce the thermal resistance between the cooling surface and the heat radiating surface. Therefore, alumina, aluminum nitride, silicon nitride, and silicon carbide are required. Is preferably used for reasons such as strength and thermal conductivity. In particular, alumina can be suitably used in terms of cost, aluminum nitride in terms of thermal conductivity, and silicon nitride in terms of impact resistance and strength.

The insulating substrate of the present invention can be manufactured by a known powder process and sintering method.

The thermoelectric conversion element according to the present invention is composed of Bi, Sb, T
It is preferable to include at least two of e and Se.
Such a material has an excellent figure of merit, and is particularly preferably an A ₂ B ₃ type intermetallic compound, for example, when A is Bi and / or
Alternatively, it is preferable that Sb and B are semiconductor crystals made of Te and / or Se, and the composition ratio B / A is 1.4 to 1.6 in order to increase the performance index at room temperature.

Further, the intermetallic compound can be efficiently converted into a semiconductor.
Therefore, impurities can be added as dopants.
Wear. For example, halogens such as I, Cl and Br are added to the raw material powder.
N-type semiconductors
Conductors can be manufactured. For example, AgI powder, C
uBr powder, SbI_ThreePowder, SbCl_ThreePowder, SbBr _Three
Powder, HgBr_TwoAdding powder or other powder alone
The carrier concentration in the intermetallic compound semiconductor
As a result, it is possible to increase the figure of merit
Become. The above halogen elements are important for efficient semiconductor conversion.
Of 0.01 to 5% by weight, particularly 0.05 to 4% by weight.
It is preferable to include them in combination.

Further, when manufacturing a P-type semiconductor,
Te can be added for adjusting the carrier concentration,
As with the N-type semiconductor, the figure of merit can be increased.
Thereby, good cooling performance near normal temperature is obtained.

The wiring conductor is made of Cu, Al, Au, Pt,
Desirably, it is made of at least one of Ni and W. Thereby, good electric conductivity and adhesion strength can be obtained, and a module excellent in performance and reliability can be provided.

In the thermoelectric conversion module of the present invention, as shown in FIG. 1, the wiring conductors 3a and 3b are formed on the insulating substrates 2 and 6, and The thermoelectric conversion element 5 is sandwiched. This thermoelectric conversion element 5
Consists of an N-type thermoelectric conversion element (5a) and a P-type thermoelectric conversion element (5b), and P, N,
P and N are connected alternately and electrically in series in this order. Further, the wiring conductors 3a and 3b are connected to the external connection terminals 4,
Supply operating power from outside.

By adopting such a configuration, a thermoelectric conversion module suitably applied to temperature control can be manufactured, thereby realizing a thermoelectric conversion module having a long life and stable characteristics.

In the present invention, it is important that at least one of the insulating substrates is the thermoelectric conversion element. That is, P-type and N-type thermoelectric conversion elements are alternately arranged in series on the surface of the insulating substrate of the present invention, and are electrically connected using wiring conductors to form a module, which is suitably applied to temperature control. The thermoelectric conversion module to be manufactured can be manufactured.

The thermoelectric conversion module using the above-described insulating substrate prevents the destruction of the bonding interface between the thermoelectric conversion element and the wiring conductor and has excellent long-term reliability. Can be suitably used.

[0041]

EXAMPLES As starting materials, bismuth, tellurium, and selenium having a purity of 99.99% or more as n-type Bi ₂ Te
_2.85 Se was weighed to _0.15 , each of these mixed powders was vacuum-sealed in a Pyrex (R) glass tube, melted and stirred in a rocking furnace, and then cooled to produce a thermoelectric semiconductor material ingot.

Thereafter, the mixture is roughly pulverized using a stamp mill to obtain
SbI _ThreeAnd HgBr_TwoTo
Pyrex (R) gas
Vacuum sealed in a glass tube, and after melting and stirring, gradually cool from one end
And solidified.

After cooling, it was taken out of the glass tube and sliced. A 10 μm Ni layer and a 0.5 μm Au layer were formed on the wafer thus obtained by electroless plating. Thereafter, the resultant was diced into 1 mm square to obtain a thermoelectric conversion element.

The linear expansion coefficient α of the obtained thermoelectric conversion element is
It measured at -100-400 degreeC using TMA.

The insulating substrate is formed by a forming method such as a tape forming method, a pressing method, a casting method, a mud discharging method, normal pressure firing, pressure firing, H
It can be manufactured by a normal manufacturing method for manufacturing alumina and aluminum nitride, such as a firing method such as IP firing and hot press firing. Conventional methods such as a metallizing method and a plating method can be applied to the formation of the wiring conductor.

A solder paste is printed on the wiring conductor of the insulating substrate thus obtained, and the elements are arranged thereon.
The element is fixed by overheating from the opposite surface of the insulating substrate. As the number of elements, the same number of N-type thermoelectric conversion elements and P-type thermoelectric conversion elements were used, and the total number shown in Table 1 as the number of elements was used.

Similarly, the thermo module is obtained by fixing the element on the other side of the insulating substrate. The lead wires may be bonded together with the one-sided insulating substrate, or may be bonded after the two-sided insulating substrate is bonded. The adhesive strength of the wiring conductor is measured by soldering a lead wire to the wiring conductor and pulling the lead.

In the manufactured thermoelectric conversion module, the dimensions of the insulating substrate, the long side L of the wiring conductor, the average distance D between the wiring conductors, and the electrode area were measured, and the electrode occupancy S was calculated.

Next, a reliability test of the thermoelectric conversion module was performed. That is, after the voltage is applied (ON) for 1.5 minutes, the applied voltage is stopped (OFF) and held for 4.5 minutes.
After conducting a current cycle test (5000 cycles) of the FF, the appearance inspection and the resistance change (ΔR) were measured by an AC four-terminal method, and those having ΔR exceeding 5% were regarded as NG.

[0050]

[Table 1]

Sample No. within the scope of the present invention. 1-2, 4-
6, 8 to 10, 12 to 13, and 15 to 20 have good appearance after the reliability test, and the resistance change ΔR before and after the test is 4.5%.
Below, good durability was shown.

On the other hand, when L / D> 15, sample no. In 3, 7, 11, and 14, electrode peeling after the reliability test was confirmed, and the resistance change ΔR also exceeded 5%, and the deterioration was large.

[0053]

According to the present invention, the difference in the linear expansion coefficient between the insulating substrate and the wiring conductor is reduced, and the length L of the wiring conductor with respect to the distance D between the wiring conductors is reduced (L / D ≦ 15). The stress generated at the joint between the wire and the wiring conductor can be reduced, and destruction can be prevented.

[0054]

[Brief description of the drawings]

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

FIG. 2 is a plan view showing a part of the thermoelectric conversion module.

FIG. 3 is a plan view showing a part of the thermoelectric conversion module.

[Explanation of symbols]

2, 6, 12, 16, 22 ... insulating substrate 3a, 3b, 13a, 23a ... wiring conductor 4: External connection terminal 5 ... thermoelectric conversion element 5a, 15a, 25a... N-type thermoelectric conversion element 5b, 15b, 25b ... P-type thermoelectric conversion element 7 ... External wiring 8 ... Solder

Claims (7)

[Claims] An insulating substrate on which a plurality of thermoelectric conversion elements are mounted and a wiring conductor for electrical connection is formed on a main surface, wherein the insulating substrate has a linear expansion coefficient of 4 × 10 ^-6. / K, and the ratio of the long side of the wiring conductor to the average distance between the wiring conductors is 15 or less. 2. The thermoelectric conversion module substrate according to claim 1, wherein the ratio of the area occupied by the wiring conductor to the area of the main surface of the insulating substrate is 50 to 85%. 3. The thermoelectric conversion module substrate according to claim 1, wherein the insulating substrate has a strength of 200 MPa or more. 4. The thermoelectric conversion module substrate according to claim 1, wherein the insulating substrate is made of a sintered body containing at least one of alumina and aluminum nitride as a main component. . 5. The wiring conductor according to claim 1, wherein said conductor is Cu, Al, Au, Pt,
The thermoelectric conversion module substrate according to any one of claims 1 to 4, comprising at least one of Ni and W. 6. A pair of opposing insulating substrates, a plurality of thermoelectric conversion elements provided so as to be sandwiched between the pair of insulating substrates, and electrically connecting the plurality of thermoelectric conversion elements. A thermoelectric conversion module comprising: a wiring conductor provided on a surface of the pair of insulating substrates; and an external connection terminal provided on the insulating substrate and electrically connected to the wiring conductor. A thermoelectric conversion module, wherein at least one of the substrates is the thermoelectric conversion module substrate according to any one of claims 1 to 5. 7. The thermoelectric conversion element of the thermoelectric conversion module has at least two elements of Bi, Te, Se and Sb.
The thermoelectric conversion module according to claim 6, wherein the thermoelectric conversion module is made of a kind of element.