JP3443793B2 - Manufacturing method of thermoelectric device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a thermoelectric device, and more particularly to a joint structure between a thermoelectric element body and an electrode.

[0002]

2. Description of the Related Art A p-type semiconductor and an n-type semiconductor are joined to each other through a metal electrode to form a pn element pair, and one end is made to generate heat and the other is made to go by the direction of the current flowing through this joint. Thermoelectric elements that utilize the so-called Peltier effect, whose ends can be cooled, are expected to be widely used in various devices such as portable coolers because of their small size and simple structure.

Conventionally, such a thermoelectric element has a nickel plating layer 106a and a solder plating layer 10 formed on both ends of a Bi-Te system thermoelectric semiconductor 103, as shown in FIG.
The contact electrode 106 having a two-layer structure with 6b was fixed to the copper electrode 105 formed on the heat exchange substrate 101 made of an insulating substrate such as alumina ceramic. In this case, normally, the contact electrode 106 is formed extremely thin, but if it is formed thin, the thermoelectric semiconductor 103 is formed.
The stress generated due to the difference in the coefficient of thermal expansion between the heat exchange substrate 101 and the heat exchange substrate 101 is difficult to be relaxed by the creep deformation of the thin solder layer 106b, and the durability against a large temperature cycle is poor.

In general, the solder layer undergoes creep deformation even near room temperature, which is an important factor for relaxing the thermal stress applied to the thermoelectric element.

However, if it is too thick, the creep deformation at the time of high temperature is large, and the deviation of the optical axis becomes a problem when it is used for laser optical parts or the like. Therefore, in order to improve the creep resistance, the thinner solder layer is preferred. Good. From such a technical background, a technique capable of changing the thickness of the solder layer depending on the application has been desired.

By the way, a thermo-module formed by collecting a large number of the thermoelectric elements described above is, for example, as shown in FIG. 10, a first module made of an insulating substrate having a good thermal conductivity such as an alumina ceramic substrate. And the second heat exchange substrate 11
A large number of pn element pairs 113 are sandwiched between 1 and 112 so as to have good thermal contact therewith, and the first and second electrodes 11 are provided between the element pairs 113, respectively.
4, 115 are connected in series.

Then, the first and second electrodes 11
4, 115 are usually made of a copper plate so as to be able to withstand a large current, and are fixed on a conductor layer pattern formed on the surfaces of the heat exchange substrates 111, 112 via a solder layer 116b.

Further, on the first and second electrodes, a pair of p-type thermoelectric elements 113a or n-type thermoelectric elements 113b are alternately fixed via a solder layer 116b and a nickel layer 116a, respectively. The pair 113 is formed and each element pair is connected in series.

Since the p-type thermoelectric element 113a and the n-type thermoelectric element 113b have different characteristics such as thermoelectromotive force and electric resistance, it may be necessary to change their sizes, but it is usually difficult to mount them. Used the same thermoelectric element for both p-type and n-type.

However, when the p-type and n-type thermoelectric elements having different characteristics have the same shape, the p-type thermoelectric element 113 is formed.
There is a problem that the electrical matching (compatibility) cannot be optimized between a and the n-type thermoelectric element 113b, and the performance as a thermoelectric module is deteriorated.

[0011]

By the way, according to the conventional method, the thickness of the solder layer of the thermoelectric element is determined by the surface tension of the molten solder and the load at the time of assembly. there were. However, in the conventional method, in both the thermoelectric device and the thermoelectric module, the stress concentration due to the difference in the thermal expansion coefficient between the heat exchange substrate material or the electrode and the thermoelectric semiconductor body causes a large temperature difference between the low temperature side and the high temperature side. Or, as the temperature change increases,
There is a problem that the thermoelectric semiconductor is damaged or falls off.

In the thermoelectric device, the p-type thermoelectric element 113a is used.
The n-type thermoelectric element 113b and the n-type thermoelectric element 113b have different characteristics such as thermoelectromotive force and electric resistance, and thus it may be necessary to change the size, but due to the difficulty of mounting, thermoelectric elements of the same shape are usually used. , The p-type thermoelectric element 113 has the same shape.
There is a problem in that the electrical matching cannot be optimized between a and the n-type thermoelectric element 113b, and the performance of the thermoelectric module deteriorates.

The present invention has been made in view of the above-mentioned circumstances, and it is possible to easily form a solder layer to be significantly thicker than the conventional one, and it is possible to improve durability against thermal stress.
An object is to provide a highly reliable thermoelectric device.

[0014]

Therefore, a first feature of the present invention is that the thermoelectric semiconductor and the electrodes are formed with first and second solder layers having different melting temperatures as contact electrodes, respectively. This is because when the semiconductor and the electrode are connected, one of the first and second solder layers is melted and the other is pressed and bonded at a temperature at which they are not melted.

The second feature of the present invention is that it comprises an n-type thermoelectric element and a p-type thermoelectric element on the heat exchange substrate via electrodes.
In a method of manufacturing a thermoelectric device in which at least one pair of thermoelectric elements in which one thermoelectric element body of n-type or p-type is formed thicker than the other thermoelectric element body is provided, the n-type thermoelectric element and the p-type thermoelectric element are provided. The first solder layer is formed on both ends of the element so as to have different thicknesses, and the second solder layer is formed on the electrodes in advance.
The solder layer is melted and the first solder layer is pressed and bonded at a temperature at which the first solder layer is not melted, the thickness of the solder layer is different between the n-type thermoelectric element and the p-type thermoelectric element, and the entire element is Are adjusted so that the n-type thermoelectric element and the p-type thermoelectric element have the same thickness.

The material of the solder layer needs to be a combination of solder compositions such that the melting points of the two types of solder do not lower than the lower melting point of the solder layer due to the melting of the two types of solder. For example, PbSn. / SnSb (however, S
If only n, brittleness at low temperature may occur, and Sb ≧ 0.2% is desirable), PbSn / PbSn, InPb / InPb
Is desirable.

[0017]

According to the first structure, since the first and second solder layers having different melting points are formed on both the thermoelectric element body and the electrodes, and pressure molding is performed, the solder layer is formed. Can be formed thicker than the conventional one, and a thermoelectric device excellent in durability against thermal stress can be obtained.

Further, according to the second structure, since the thickness of the solder layer can be easily adjusted, the solder layer is adjusted even when the p-type thermoelectric element and the n-type thermoelectric element have different thicknesses. This makes it possible to provide a highly reliable thermoelectric device very easily. That is, the p-type thermoelectric element body and the n-type thermoelectric element body can be designed to have the same cross section and different lengths, and even when the electrical characteristics are different, optimal design can be performed, and mechanical assembly can be performed. Is easy.

[0019]

Embodiments of the present invention will now be described in detail with reference to the drawings.

Example 1 This thermoelectric element has a partially enlarged sectional view as shown in FIG.
Both the thermoelectric semiconductor 13 and the copper electrode 15 have a melting point of 1
A first solder plating layer 16a made of PbSn eutectic solder having a temperature of 83 ° C. and a film thickness of 30 μm, a melting point of 230 ° C. and a film thickness of 20 μ
Second solder plating layer 16b made of SnSb-based solder of m
Are formed, and these are heated to 225 ° C. and joined, and as a result, an SnSb layer having a film thickness of about 20 μm,
A PbSn layer having a film thickness of about 5 μm is formed, and a joint portion having a slight diffusion layer is formed on the interface between two kinds of solder.

That is, in manufacturing, first, as shown in FIG.
As shown in FIG. 2, PbS having a melting point of 183 ° C. and a film thickness of 30 μm was formed on both ends of the Bi—Te based thermoelectric semiconductor 13 by plating.
A first solder plating layer 16a made of n-eutectic solder is formed.

Then, as shown in FIG. 2B, a melting point of 230 is formed on the copper electrode 15 formed on the heat exchange substrate 11 made of an insulating substrate such as alumina ceramic by a plating method.
A second solder plating layer 16b made of SnSb-based solder having a temperature of 20 μm and a thickness of 20 ° C. is formed. Then, as shown in FIG. 2 (c), it is heated to 225 ° C. on a hot plate using a flux,
To join. The thermoelectric element thus formed is composed of a SnSb layer having a film thickness of about 20 μm and a PbSn layer having a film thickness of about 5 μm and forming a joint portion having a slight diffusion layer at the interface between two kinds of solder. ing.

According to this structure, the thick solder layer having a total thickness of 25 μm relaxes the stress concentration, and the second solder plating layer 16b made of SnSb-based solder is not melted but is bonded while maintaining its film thickness. Therefore, the thickness of the solder layer is highly uniform, and the reliability of connection is high. Therefore, the durability to the temperature cycle is also increased, and its variation is reduced.

Next, the result of measuring the relationship between the thickness of the solder layer and the life cycle is shown in FIG. Here, a first-stage thermoelectric module formed by connecting 44 pairs of thermoelectric elements shown in FIG. 1 and a second-stage thermoelectric module formed by connecting 23 pairs of thermoelectric elements are stacked to form a two-stage module, and Size 1
3. 0x13mm, cold surface size 7x10mm, maximum current 1.2A, power cycle on for 1.5 minutes 4.
The maximum temperature difference is 70 ° C to 5 ° C for 5 minutes off, the hot surface temperature is 27 ° C, and the solder layer thickness and Δ
The relationship with the life cycle until R = 10% was measured. Here, the solder layer is formed by plating, and the element side is 37
Pb63Sn solder, board side 95Sn5Sb (20μm
The above). As you can see from this figure,
It can be seen that if the solder layer exceeds 20 μm, the life will be significantly extended. As described above, according to the method of the present invention, since the solder layer can be easily formed to be thick, deterioration of the joint portion is unlikely to proceed and reliability is high.

Next, the result of measurement of the relationship between the thickness of the solder layer and the resistance change rate is shown in FIG. At the time of measurement, A: When heat treatment was performed at 110 ° C. for 48 hours in vacuum at the time of assembly,
B: After this, after 30 cycles at −55 / + 105 ° C., B: maximum current 1.2 A, 1.5 minutes on, 4.5 minutes off 1 power cycle for 12 hours, maximum temperature difference 70 ° C.
The temperature was 5 ° C. Here, the curve a is 37Pb63S only on the element side.
When n (melting point 183 ° C) is plated by 2 μm and joined,
Curve b shows the case where 37Pb63Sn is 20 μm plated on the element side and 95Sn5Sb is 20 μm plated on the substrate side.
Curve c is the result of measuring the change rate when 37Pb63Sn was plated on the element side by 30 μm and 95Sn5Sb was plated on the substrate side by 35 μm. From this result, it can be seen that the change rate of the solder layer having a thickness of 20 μm or more is remarkably improved as compared with the case where the conventional one kind of thin solder layer is used for the joining.

Example 2 In this thermoelectric element, as shown in FIG. 5, a first solder plating layer 16a made of PbSn eutectic solder having a melting point of 183 ° C. and a film thickness of 30 μm was formed on the thermoelectric semiconductor 13, and copper was formed. The electrode 15 has a melting point of 230 to 290 ° C. and a film thickness of 20 μm of 85.
A second solder plating layer 26b made of Pb15Sn solder is formed in advance, and these are heated to 225 ° C. and joined. As a result, the 85Pb15Sn layer having a film thickness of about 20 μm and the PbSn layer having a film thickness of about 5 μm are formed. In other words, a joint portion having a slight diffusion layer is formed on the boundary surface between the two kinds of solder.

That is, in manufacturing, first, as in the case of the first embodiment, PbS having a melting point of 183 ° C. and a film thickness of 30 μm is formed on both ends of the Bi—Te system thermoelectric semiconductor 13 by a plating method.
A first solder plating layer 16a made of n-eutectic solder is formed.

Next, a copper electrode 15 is formed on the heat exchange substrate 11 made of an insulating substrate such as alumina ceramic.
By the plating method, the melting point is 230 to 290 ° C. and the film thickness is 20 μm.
A second solder plating layer 26b made of m2 of 85Pb15Sn solder is formed.

Then, on the hot plate using flux, 22
Heat to 5 ° C. and bond. The thermoelectric element thus formed is composed of an 85Pb15Sn layer with a film thickness of about 20 μm and a PbSn layer with a film thickness of about 5 μm, and forms a joint part having a slight diffusion layer at the interface between two kinds of solder. ing.

According to this structure, stress concentration is alleviated by the thick solder layer having a total thickness of 25 μm, and 85 Pb 15
Since the second solder plating layer made of Sn is bonded while maintaining its film thickness without being melted, the thickness of the solder layer is highly uniform and the connection reliability is high. Therefore, the durability against temperature cycling is also increased.

Example 3 This thermoelectric element is formed by reversing the solder layer as in Example 1, as shown in FIG.
The second solder plating layer 16b made of SnSb-based solder having a temperature of 20 μm and a film thickness of 20 μm and the first solder plating layer 16a made of PbSn eutectic solder having a melting point of 183 ° C. and a film thickness of 30 μm are formed on the copper electrode 15. Form them and set these 2
Heated to 25 ° C and bonded, resulting in a film thickness of about 2
A joint portion is formed which is composed of a 0 μm SnSb layer and a PbSn layer having a film thickness of about 5 μm and which has a slight diffusion layer at the interface between two kinds of solder.

That is, in manufacturing, as in Examples 1 and 2, SnPb having a melting point of 230 ° C. and a film thickness of 20 μm was formed on both ends of the Bi—Te system thermoelectric semiconductor 13 by a plating method.
A second solder plating layer 16b made of solder is formed.

Next, a copper electrode 15 is formed on the heat exchange substrate 11 made of an insulating substrate such as alumina ceramic.
Pb with a melting point of 185 ° C and a film thickness of 30 μm
A first solder plating layer 16a made of Sn eutectic solder is formed.

Then, using a flux, 22 on the hot plate
Heat to 5 ° C. and bond. The thermoelectric element thus formed has a SnSb layer with a thickness of about 20 μm and a thickness of about 5 μm.
It is composed of a PbSn layer of m 3 and forms a joint portion having a slight diffusion layer on the boundary surface between the two kinds of solder.

According to this structure, the thick solder layer having a total thickness of 25 μm relieves the stress concentration, and the second solder plating layer 16b made of SnSb-based solder is bonded while maintaining its film thickness without being melted. Therefore, the thickness of the solder layer is highly uniform, and the reliability of connection is high. Therefore, the durability against temperature cycling is also increased.

Example 4 In this thermoelectric device, as shown in FIG. 7, the p-type thermoelectric element and the n-type thermoelectric element have the same cross-sectional area, and the p-type thermoelectric semiconductor 33a is thinner than the n-type thermoelectric semiconductor 33b. The difference between the SnSb solder plating layers 37a, 37 forming the contact electrodes
By compensating by adjusting the thickness of b, thermoelectric element pairs having the same total length are formed, the solder layer 38 formed on the electrodes is formed of a material having a low melting point, and only the solder layer on the electrode side is melted and joined. It is characterized by having done.

That is, as shown in FIG. 8A, the p-type (Bi-Te system) thermoelectric semiconductor 33a is replaced with an n-type (Bi-Te system).
System) a thermoelectric semiconductor 33b, which is thinner than the thermoelectric semiconductor 33b and is molded into a desired size.
A second solder layer is formed on both ends of 37b as contact electrodes so as to have film thicknesses of 50 μm and 20 μm, respectively.

Further, as shown in FIG. 8B, the heat exchange substrate 3 made of an insulating substrate such as alumina ceramics.
30μ film thickness on the surface of copper electrode 35 formed on 1, 32
A PbSn eutectic solder layer 38 of m 3 is formed by a plating method.

In this state, as shown in FIG. 8 (c), a flux is used to heat to 225 ° C. on the hot plate to bond them.
The thermoelectric device thus formed has SnSb layers of about 50 μm and 20 μm and a P of about 5 μm.
It is composed of a bSn layer and forms a joint portion having a slight diffusion layer on the boundary surface between the two kinds of solder.

Here, the SnSb solder layers 37a formed on both ends of the p-type thermoelectric element 33a are more p-type thermoelectric semiconductor 33a and p-type thermoelectric semiconductor 33b than the SnSb solder layers 37b formed on both ends of the n-type thermoelectric element 33b. Since the first solder layer 38 made of PbSn eutectic solder plated on the electrode side is formed to be thicker by a half of the difference in thickness between the SnSb solder layers Both elements of 37a and 37b are satisfactorily connected to the heat exchange boards 31 and 32.

With this structure, the p-type thermoelectric element body and the n-type thermoelectric element body can be designed to have different lengths in the same cross section, and optimal design can be performed even when the electrical characteristics are different from each other. The maximum current value can be made equal. Furthermore, mechanical assembly is easy.

The material of the solder layer is not limited to the above embodiment, but can be changed as appropriate. Further, the method for forming the solder layer is not limited to the plating method, and other methods such as a plasma spraying method or a vacuum deposition method may be used.

[0043]

As described above, according to the present invention, it is possible to obtain a thermoelectric element and a thermoelectric device which have improved durability against temperature cycles, are easy to assemble, and have a high degree of freedom in design.

[Brief description of drawings]

FIG. 1 is a diagram showing a thermoelectric element according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a manufacturing process of the thermoelectric element according to the first embodiment of the present invention.

FIG. 3 is a diagram showing a result of measuring a relationship between a solder layer thickness and a life.

FIG. 4 is a diagram showing a relationship between a temperature cycle and an internal resistance change rate when the thickness of a solder layer is changed.

FIG. 5 is a diagram showing a thermoelectric device according to a second embodiment of the present invention.

FIG. 6 is a diagram showing a thermoelectric device according to a third embodiment of the present invention.

FIG. 7 is a diagram showing a thermoelectric element according to a fourth embodiment of the present invention.

FIG. 8 is a diagram showing a manufacturing process of a thermoelectric element according to a fourth embodiment of the present invention.

FIG. 9 is a diagram showing a conventional thermoelectric element.

FIG. 10 is a diagram showing a conventional thermoelectric device.

[Explanation of symbols]

13 Thermoelectric Semiconductor 15 Copper Electrode 16a First Solder Plating Layer 16a, Melting Point 230 ° C.,
Second solder plating layer 16b 1 made of SnSb-based solder having a film thickness of 20 μm 1 heat exchange substrate 31, 32 ... Heat exchange substrate 33a p-type Bi-Te thermoelectric semiconductor 33b n-type Bi-Te thermoelectric semiconductor 35 electrode 37a SnSb solder-plated layer 37b SnSb solder plating layer 38 PbSn eutectic solder plating layer 111, 112 heat exchange substrate 113a p-type thermoelectric element 113b n-type thermoelectric element 114, 115 first and second electrodes 116a, b solder layer

Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H01L 35/34 H01L 35/32

Claims (2)

(57) [Claims] 1. A step of forming a thermoelectric element body made of a semiconductor material having a Peltier effect, and a first solder layer forming step of forming first solder layers facing each other at both ends of the thermoelectric element body. A step of forming a second solder layer having a melting point different from that of the first solder layer on the surface of the electrode to which the thermoelectric element body is to be joined; A method of manufacturing a thermoelectric device, comprising a step of joining by applying pressure at a temperature at which one of the solder layers melts and the other does not melt. 2. A step of forming a thermoelectric element body made of a semiconductor material having a Peltier effect so that one of the n-type and p-type thermoelectric element bodies is thicker than the other thermoelectric element body, and the thermoelectric element. A first solder layer forming step of forming a first solder layer having a different film thickness on both ends of the main body so as to be opposed to each other so that the total lengths of both sides are equal to each other; A second solder layer forming step of forming on the surface a second solder layer made of a material having a lower melting point than the first solder layer; and a second melting point lower than the melting point of the first solder layer. A method of manufacturing a thermoelectric device, comprising: a bonding step in which the n-type thermoelectric element and the p-type thermoelectric element are made equal in thickness to each other by pressurizing and joining at a temperature higher than the melting point of the solder layer.