JP2003197981A - Thermoelectric module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermoelectric module that is highly reliable and has high performance by optimizing plating and joint condition. <P>SOLUTION: The surface roughness Ra of a thermoelectric element on a plane joined with a supporting substrate is set at 0.5-2.0 μm and that thereof excluding the joint surface is 0.5 μm or less. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art As shown in FIG. 1, a thermoelectric module utilizing the Peltier effect is a P-type thermoelectric element 1 which is a P-type semiconductor.
a and an N-type thermoelectric element 1b which is an N-type semiconductor are alternately arranged and arranged between the two supporting substrates 4a and 4b, and
It is formed by electrically connecting a P-type thermoelectric element 1a and an N-type thermoelectric element 1b in series, and by applying a DC voltage, heat absorption or heat generation is caused depending on the direction of the current. Can be done. Such a thermoelectric module, which has a simple structure and is easy to handle, can maintain stable characteristics, and therefore is widely used. In particular, since it is small and can be locally cooled, and precise temperature control around room temperature is possible, it is used in devices such as semiconductor lasers and optical integrated circuits that are precisely controlled to a constant temperature, small refrigerators, and the like. .

As a means for producing such a small thermoelectric module, as disclosed in JP-A-1-106478, P-type and N-type raw material powders are ingot-shaped by hot pressing, and this ingot is kept constant. After slicing to a thickness, the sliced material is plated and diced into chips to obtain P-type thermoelectric elements 1a and N.
There is a method of obtaining the mold thermoelectric element 1b. In producing a thermoelectric module using the P-type and N-type thermoelectric elements 1, as shown in JP-A-10-215005, a solder paste is applied on a support substrate 4b provided with a plurality of electrodes. After coating, the chip-shaped P-type thermoelectric elements 1a and N-type thermoelectric elements 1b are alternately placed, and then the solder paste is melted (reflowed) so as to be sandwiched by another supporting substrate 4a with electrodes. Then, the thermoelectric module as shown in FIG. 1 can be manufactured. The solder to be used at this time is not limited to the solder paste, but is disclosed in Japanese Patent Laid-Open No. 4-2336
It may be solder plating as shown in Japanese Patent Publication No.

Also, the thermoelectric element 1 is polished before plating the thermoelectric element 1 (Japanese Patent Laid-Open No. 11-40529).
No.) or to enhance the adhesion strength between the thermoelectric element 1 and the plating,
It has been proposed to carry out electrolytic etching of the thermoelectric element 1 in an electrolyte solution (JP-A-11-186618). Further, the plating on the thermoelectric element 1 is divided into two layers, and the first layer is made of Ni.
There has also been proposed a -P system plating and a Ni-B system plating for the second layer (Japanese Patent Laid-Open No. 2001-196646).

[0005]

Ni plating on the surface of the thermoelectric element has been performed for a long time in order to prevent the tin component of the solder from diffusing into the thermoelectric element, but with respect to the bonding strength of the solder to the Ni plating layer. Were often inadequate.

That is, in the thermoelectric module, the side surface of the thermoelectric element, the solder joint portion, or the plating layer is resistant to the thermal expansion difference of the thermoelectric element or the supporting substrate and the internal stress of plating due to repeated temperature changes and external vibrations and impacts. It was unavoidable that cracks and deformation occurred without breakage. In order for the thermoelectric module to function, it is necessary to pass a current of several amperes, and if the solder joint part were to come off and the electric circuit short-circuited, it would not only stop the function but also cause a fire.

Therefore, it is an object of the present invention to provide a thermoelectric module which has a low cost and a high bonding reliability.

[0008]

A thermoelectric module according to the present invention is a thermoelectric module in which a thermoelectric element made of a compound containing at least two kinds of elements of Bi, Te, Se and Sb is bonded to a supporting substrate. , The surface roughness Ra of the thermoelectric element on the surface to be joined to the supporting substrate is 0.5 to
2.0 μm, surface roughness R of the thermoelectric element other than the joint surface
It is characterized in that a is 0.5 μm or less.

Further, in a thermoelectric module in which a thermoelectric element made of a compound containing at least two kinds of elements of Bi, Te, Se and Sb is bonded to a supporting substrate,
On the surface of the thermoelectric element on the joint surface side, Ni having a thickness of 1 to 40 μm is used.
-B layer, Ni-P layer having a thickness of 1 to 40 m, thickness 0.01
It is characterized in that three Au layers each having a thickness of 10 μm are formed.

Then, the thermoelectric element and the supporting substrate have a thickness of 1
It is characterized in that they are joined with solder of 0 to 50 μm and the joining strength between the thermoelectric element and the supporting substrate is 8 MPa or more.

Furthermore, the hardness of the thermoelectric element is 0.5 GP.
By setting it to a or more, it becomes possible to obtain a thermoelectric module having extremely high bonding reliability.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below.

FIG. 1 is a perspective view showing a thermoelectric module. As shown in FIG. 1, a thermoelectric module utilizing the Peltier effect has two support substrates 4a and 4b in which a P-type thermoelectric element 1a which is a P-type semiconductor and an N-type thermoelectric element 1b which is an N-type semiconductor are alternately arranged. And is formed by electrically connecting the N-type thermoelectric element 1b and the P-type thermoelectric element 1a in series, and by applying a DC voltage, depending on the direction of the current. It can cause heat absorption or heat generation.

FIG. 2 is a perspective view showing an example of the thermoelectric element 1 used in the thermoelectric module according to the present invention. The P type thermoelectric element 1a is a P type semiconductor or the N type semiconductor is an N type semiconductor.
It is a schematic view of the surface state of the thermoelectric element 1b. That is, the surface roughness Ra (arithmetic mean roughness) of the side surface 12 of the thermoelectric element 1 other than the bonding surface 11 is finished to 0.5 μm or less, and the surface roughness Ra of the bonding surface 11 with the supporting substrates 4a and 4b is Ra. Is adjusted to 0.5 to 2.0 μm.

Originally, the thermoelectric element 1 has an extremely brittle property and is very weak against mechanical vibration / shock and thermal expansion difference. In order to improve resistance to these, the thermoelectric element 1
It is important not only to increase the hardness to 0.5 Gpa or more, but also to reduce the defects on the surface of the thermoelectric element 1. In particular, the processing flaw on the surface of the thermoelectric element 1 can be the largest defect, and therefore this portion must be finished to be smooth.
If the surface roughness Ra of the thermoelectric element 1 other than the bonding surface 11 is set to 0.5 μm or less, the resistance to mechanical vibration / shock, thermal expansion difference, etc. can be dramatically improved. .

On the other hand, since the surface roughness Ra of the joint surface 11 of the thermoelectric element 1 is filled and integrated with the solder as the bonding agent, it becomes a structural defect even if it is not finished as smooth as the side surface 12. On the contrary, when it is too smooth, on the other hand, if it is too smooth, the adhesion to the Ni layer described later becomes poor and the resistance to vibration, impact, etc. deteriorates. Therefore, the surface roughness Ra of the joint surface 11 is 0.5 in order to increase physical contact with the Ni layer.
Must be at least μm. However, the surface roughness Ra
Is 2 μm or more, the thermoelectric element 1 itself is damaged and the thermoelectric performance is deteriorated. Therefore, the surface roughness Ra of the joint surface 11 is preferably 0.5 to 2.0 μm.

The surface roughness is adjusted by etching as will be described later in detail.

FIG. 3 is a sectional view showing an example of the thermoelectric element 1 in the thermoelectric module according to the present invention. The bonding surface 11 of the thermoelectric element 1 has a Ni—B layer 2a of 1 to 40 μm,
1-40 μm Ni-P layer 2b and 0.01-10 μm
The Au layer 3 of 3 is formed in this order, and normally all of these 3 layers are formed by a plating method.

The average thickness of the Ni-B layer 2a is Ni.
-Equivalent to or thinner than the average thickness of the P layer 2b.
The reason for this is that the Ni-B-based plating has a slow film formation rate, and it strongly adheres to the surface of the etched thermoelectric element 1 as a crystalline dense film, but it is hard and has poor buffering properties. In addition, the plating time becomes long and the cost increases. Further, this Ni-B layer 2a prevents performance deterioration of the thermoelectric element 1 due to diffusion of metal such as Sn, which is a solder component, into the thermoelectric element 1 when the thermoelectric element 1 is soldered to the support substrate 4. effective.

On the other hand, Ni-P type plating has a high rate of film formation, is amorphous, has low hardness, and is rich in buffering properties, but has poor adhesion to the thermoelectric element 1. Therefore, the first layer Ni-B layer 2a is formed first, and then the second layer N is formed.
In order to improve the reliability against heat cycle and impact resistance and reduce the cost, it is preferable to form the i-P layer 2b and make the average thickness of the Ni-B layer 2a equal to or smaller than the average thickness of the Ni-P layer 2b. Is important to.

Further, the thermoelectric element 1 has the above-mentioned Ni-P layer 1
It is important that Au is plated on b to form the Au layer 3. This is because the Ni-P type plating does not wet the solder well and cannot maintain the required bonding strength. However, by providing the Au layer 3 of 0.01 to 10 μm on the Ni-P layer 1b, sufficient solder joint strength and reliability can be obtained. If the Au layer 3 is too thick, not only the material cost will increase, but also the workability will deteriorate due to the ductility of Au, so 10 μm or less is preferable, and about 0.05 μm may be sufficient. However, if the thickness is less than 0.01 μm, the wettability of solder deteriorates, so the Au plating thickness is 0.01 to 10 μm.
m is good. That is, the Au layer 3 has an effect of improving the solder wettability when the thermoelectric element 1 is soldered to the supporting substrate.

Thereafter, the thermoelectric element 1 is bonded to the electrode 4c of the supporting substrate 4a as shown in FIG. 4 prepared separately with solder having a thickness of 10 to 50 μm. The thermoelectric module as shown in FIG. 1 thus obtained has a soldering strength of 8 MPa or more, and has sufficient heat cycle resistance and vibration / shock resistance.

By the way, the thermoelectric element 1 of the present invention is composed of Bi, S
It is important to be composed of a compound containing at least two of b, Te and Se. For example, the above metals may be used, but A ₂ B ₃ type intermetallic compound and its solid solution are preferable. Here, A is a semiconductor crystal composed of Bi and / or Sb, B is Te and / or Se, and particularly, the composition ratio B / A of 1.4 to 1.6 indicates that the thermoelectric property at room temperature is Preferred to increase.

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.

When the N-type thermoelectric element 1b is manufactured, it is preferable to contain a halogen element such as I, Cl and Br as a dopant in order to efficiently convert the intermetallic compound into a semiconductor. The halogen element is added in an amount of 0.01 to 5 with respect to 100 parts by weight of the above intermetallic compound raw material in terms of semiconductor conversion.
It is preferably contained in an amount of 0.01 part by weight, particularly 0.01 to 0.1 part by weight.

On the other hand, when the P-type thermoelectric element 1a is manufactured, it is preferable to contain Te for adjusting the carrier concentration. Thereby, the thermoelectric characteristics can be improved similarly to the N-type thermoelectric element 1.

It is important that the thermoelectric element 1 of the present invention has a hardness of 0.5 GPa or more. As a result, it is possible to prevent deformation due to vibration or impact during module assembly or during use as a thermoelectric module and damage caused by the deformation. Particularly, in order to further improve the mechanical reliability, the hardness is preferably 0.7 GPa or more, further preferably 0.8 GPa or more.

In order to improve the hardness of the thermoelectric element 1,
When forming the thermoelectric element 1 by the sintering method, the average particle diameter may be made fine. The average particle size is preferably 100μ
m or less, and more preferably 50 μm or less.

The hardness described here means micro Vickers hardness, and here, it was measured by applying a load of 25 gf for 15 seconds using a Shimadzu Corporation micro Vickers hardness meter HMV-200 type. .

The specific resistance of the P-type and N-type thermoelectric elements 1 is preferably 5 × 10 ⁻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 1 having such a structure is characterized by excellent mechanical strength and cooling ability,
It can be suitably used for photodetector elements, electronic cooling elements such as semiconductor manufacturing equipment, temperature control of semiconductor lasers and optical integrated circuits, and CFC-less small refrigerators.

As the material of the supporting substrate 4, an electrically insulating material such as alumina, mullite, aluminum nitride, silicon nitride or the like can be used.

Next, a method for manufacturing the thermoelectric element 1 of the present invention will be described.

First, a raw material powder made of a thermoelectric semiconductor is prepared. This raw material is not particularly limited as long as it is a raw material powder mainly composed of a compound containing at least two kinds of Bi, Sb, Te and Se, but particularly Bi ₂ T
It is preferable that at least one of e ₃ , Bi ₂ Se ₃ and Sb ₂ Te ₃ is contained, and this reduces the risk of compositional deviation, and a sintered body having a more uniform composition and structure can be obtained.

For example, as the P-type thermoelectric element 1a (Bi ₂
In the case of producing Te ₃ ) ₂₀ (Sb ₂ Te ₃ ) ₈₀ , Bi ₂ Te ₃
And Sb ₂ Te ₃ may be mixed and used at a ratio of 2: 8, and as the N-type thermoelectric element 1b (Bi ₂ Te ₃ )
_In the case of producing ₉₅ (Bi ₂ Se ₃ ) ₅ , Bi ₂ Te ₃ and Bi ₂
Se ₃ and 95 may be mixed at a ratio of 95: 5, composition deviation is unlikely to occur, and uniformity of the raw material powder is easily ensured by sufficient mixing.

At this time, the purity of each of these raw material powders is preferably 99.9% or more, particularly 99.99% or more, and further preferably 99.999% or more. The impurities contained in the raw material powder tend to deteriorate the semiconductor characteristics and the thermoelectric characteristics, and thus it is preferable that the impurities have the above-described purity in order to stably manufacture the high-performance thermoelectric element 1.

In order to manufacture the N-type thermoelectric element 1b,
For the purpose of adjusting the carrier concentration as a dopant, H
It is preferable to add a compound containing a halogen such as gBr ₂ or SbI ₃ . Thereby, stable semiconductor characteristics can be obtained.

The above-mentioned compound powder can be weighed so as to have a desired composition, and mixed and / or pulverized by a dry method or a wet method to prepare a raw material powder. Examples of known methods for mixing and pulverizing include a stamp mill, a ball mill, and a vibration mill.

Then, in order to remove oxygen in the raw material powder after mixing and pulverizing, it is important to carry out the reducing treatment in a reducing atmosphere such as hydrogen gas. By this reduction treatment, the amount of oxygen in the raw material powder can be reduced in advance, and the thermoelectric properties of the sintered body can be improved. The reduction treatment may be performed any time before firing, and the reduction treatment is effective whether it is a powder or a molded product.

Next, this raw material powder is set in an SPS (discharge plasma sintering) apparatus. For example, a cylindrical carbon die is filled with raw material powder, sandwiched by compression current punches from above and below, and these jigs are set in a sintering furnace. It should be noted that a pressure of about 1 MPa is inevitably applied to hold the die during this setting, but 5MP
If the pressure is as low as a or less, it does not affect the sintering because it does not affect the sintering. In addition, the raw material powder is preliminarily uniaxially pressed, CIP
A molded body may be produced by a known molding method such as a molding method, a casting method, or an injection molding method, and the molded body may be placed in a die so as to be positioned between the upper and lower compression current punches. In the case of using the molding method by the pressing method, in order to produce a molded body that can be easily manufactured and can be handled sufficiently, 45 to 100
It is desirable to obtain a desired shape by molding at a molding pressure of about MPa.

Then, firing is started. That is, a pulsed voltage is applied to the raw material powder, a current is intermittently applied, and the temperature is raised by self-heating due to discharge and Joule heat.

Further, according to the present invention, at a temperature near the temperature at which the raw material powder starts to shrink (shrinkage start temperature), 25MP
It is important to apply a pressure of a to 50 MPa and then heat treat the raw material powder at 300 ° C. or higher. This makes it possible to densify in a short time at a low pressure, to obtain a more uniform fine crystal structure, a high hardness and a thermoelectric element 1 having a smooth surface after mechanical processing such as dicing.

The timing of application is important for developing a uniform fine crystal structure, saving wasted energy, and reducing costs, and in particular, the shrinkage starting temperature T of the raw material powder.
On the other hand, (T-30) to (T + 50) ° C, especially (T-
Pressurization is preferably performed at a temperature of 20) to (T + 30) ° C.

As described above, by applying pressure almost at the same time as the start of shrinkage, sintering can be promoted and densification can be carried out at low pressure in a short time, so that a sintered body having uniform fine crystal grains can be produced. It will be possible. If pressure is applied from the beginning of firing as in the past, it is not possible to efficiently remove the gas generated from the raw material powder and the die, and due to uneven pressure, an inhomogeneous and partially porous structure is created. Although it is formed and the hardness is lowered, these problems can be solved by using the manufacturing method of the present invention.

The meaning of the raw material powder used here includes not only the powder filled in the die but also the powder filled in the die after molding. That is, it means the powder filled in the die regardless of the presence or absence of molding.

Particularly, when the average particle diameter of the raw material powder is 10 μm or less, the shrinkage initiation temperature T is preferably 100 ° C. or less. The average particle size of the raw material powder is 10
and the shrinkage initiation temperature T is 200 ° C.
The following is preferable. The shrinkage start temperature differs depending on the particle size of the raw material powder, and it is possible to densify in a short time by applying pressure at about the same time as the shrinkage start temperature, and since it is not necessary to apply pressure from the initial stage of sintering, excess energy does not occur. Since it is necessary, grain growth can be suppressed. Further, the bonds between the grains at the grain boundaries are strengthened, and the thermoelectric element 1 having high hardness can be manufactured.

In order to suppress reaction with oxygen as much as possible and further improve the figure of merit, the firing atmosphere is an inert gas atmosphere such as He, Ar and Ne, a non-oxidizing atmosphere such as H ₂ , N ₂ or a vacuum. Atmosphere is desirable. Of these, the reduction effect can be obtained at the same time as sintering, so that H
_{The 2} atmospheres are preferably Ar atmosphere in terms of safety and cost, and a mixed gas thereof may be used.

It is important that the pressurizing pressure is 25 to 50 MPa, and particularly preferably 28 to 40 MPa. If the pressure is less than 25 MPa, it becomes difficult to obtain a dense body, and if the temperature is raised to obtain a dense body, Te and Se, which are easily sublimated, are likely to be scattered, resulting in composition shift and the like. Further, when the pressure exceeds 50 MPa, excessive energy is applied, and the crystal grains cause grain growth, resulting in an increase in thermoconductivity and deterioration in characteristics. Further, if the pressure exceeds 50 MPa, the die is deteriorated,
It is easily damaged, leading to a decrease in yield and an increase in cost.

The high-hardness ingot-shaped thermoelectric element 1 taken out from the die in this manner has a characteristic that it is hard to cause breakage, deformation, and breakage due to deformation, and thus has a shock resistance when used as a thermoelectric module. , Durability can be improved.

Next, the ingot-shaped thermoelectric element 1 is processed into a wafer by a known processing method such as a wire saw or a dicing saw. After that, the surface roughness Ra of the whole thermoelectric element 1 is 0.5 to 2.0 μ using a chemical such as hydrochloric acid or nitric acid.
Chemically etch to m.

After that, the wafer-shaped thermoelectric element 1 is subjected to N
Apply i-layer. Since the thermoelectric element 1 is a semiconductor, electroless plating is suitable for forming the Ni layer on the thermoelectric element 1. Therefore, first, a Ni-B-based electroless plating layer is formed as the Ni-B layer 2a. The thickness of this Ni-B layer 2a is 1 to 4
About 0 μm is preferable, and 1 to 10 μm is preferable. N
The i-B layer 2a can be formed electrolessly by a plating solution containing a chloride or sulfate of Ni and a boron hydroxide compound as a reducing agent after activation treatment with palladium chloride or the like. ) 97 to 99.7%, B
It is preferable to adjust (boron) to be 3 to 0.3%. Next, a Ni-P layer 2b made of Ni-P electroless plating is formed on the Ni-B layer 2a. The thickness of the Ni-P layer 2b is preferably about 1 to 40 μm, more preferably 1 to 10 μm. After activation, the Ni-P layer 2b can be formed electrolessly by a plating solution containing a chloride or sulfate of Ni and sodium hypozinc oxide as a reducing agent, and Ni (nickel) 88-94%. Against
It is preferable to adjust the P (phosphorus) to be 12 to 6%.

Further, in the thermoelectric element 1, the above Ni layer is subjected to Au plating to form an Au layer 3. Au plating can be formed by general electrolytic plating after completion of Ni plating, but electroless Au obtained by substituting Au for Ni—P layer 2b does not pose any problem. Further, the plating thickness of Ni and Au can be controlled by the plating conditions such as plating time, but if the fracture surface of the thermoelectric element 1 after plating is magnified several thousand times with an electron microscope and observed. , It can be easily measured.

Thereafter, the wafer-shaped thermoelectric element 1 plated with Ni and Au is diced by a well-known method to complete the chip-shaped thermoelectric element 1. The surface roughness Ra of the side surface 12 of the thermoelectric element 1 other than the dicing surface, that is, the bonding surface 11 must be 0.5 μm. Of course, it is also important to increase the density and hardness of the thermoelectric element 1 as described above so that a smooth surface can be obtained. because,
The thermoelectric element 1 originally has an extremely brittle property, and is extremely weak against mechanical vibration / shock and thermal expansion difference. In order to increase resistance to these, it is important not only to increase the denseness and hardness of the thermoelectric element 1, but also to reduce the defects on the surface of the thermoelectric element 1.

In particular, the processing flaw on the surface of the thermoelectric element 1 can be the largest defect, and therefore the side surface 12 of the thermoelectric element 1 must be finished to be smooth. For this purpose, it is preferable to use a commercially available dicing saw, set the blade rotation to a high speed of 20,000 rpm or more, set the blade feed speed to a low speed of 5 mm / sec or less, and perform down-cut processing. The joint surface 11
Since the surface roughness Ra2 (arithmetic mean roughness Ra) of the thermoelectric element 1 is filled with solder and integrated, it cannot be a structural defect even if the surface is not finished smooth like the side surface.

As described above, in the thermoelectric element 1 having the hardness of 0.5 GPa or more, the surface roughness Ra (arithmetic mean roughness Ra) of the supporting substrates 4a and 4b and the joint surface 11 is 0.5 to 0.5 as described above.
2.0 μm, surface roughness Ra of the side surface 12 other than the bonding surface 11
(Arithmetic mean roughness Ra) is processed to 0.5 μm or less.

Further, the joining surface 11 of the thermoelectric element 1 has
40 μm Ni-B layer 2a and 1-40 μm Ni-P
Layer 2b Ni layer and 0.01 to 10 μm Au layer 3 are formed, and the average thickness of the Ni—B layer 2a is equal to or smaller than the average thickness of the Ni—P layer 2b, and then separately prepared support. When the substrates 4a and 4b are joined with a solder having a thickness of 10 to 50 μm, a soldering strength of 8 MPa or more is obtained,
It is possible to obtain a thermoelectric module having sufficient heat cycle resistance and vibration / shock resistance.

As described above, since the thermoelectric module of the present invention has particularly excellent bonding reliability, it can be suitably used as a constant temperature miniature refrigerator for semiconductor lasers and optical integrated circuits.

[0058]

EXAMPLES Examples of the present invention will be described below.

The starting material has an average particle size of 35 μm and a purity of 9
Bi over 9.99%₂Te₃And Sb ₂Te₃, And Bi₂
Se₃Prepared. Bi from these compounds as N-type₂
Te_{2 .85}Se_0.15, P as Bi_0.4Sb_1.6Te₃When
Were weighed to obtain mixed powder. Dopa for N type
SbI as an event₃0.09 parts by weight was added.

Then, in isopropyl alcohol solvent, 3
After pulverizing with a vibration mill for 0 hours, the particle size of the raw material powder was classified to 35 to 72 μm using a stamp mill.

After drying, press pressure is 49MP with a uniaxial press.
A molded body having a diameter of 20 mm and a thickness of 5 mm was produced under the pressure of a and subjected to reduction treatment in an atmosphere furnace in a hydrogen stream at 400 ° C. for 5 hours.

Next, the reduction-treated compact was set in a cylindrical die made of carbon, sandwiched from above by a compression energizing punch made of carbon in the same manner, and set in the sintering furnace by Ar in the furnace. After the replacement, firing was started. Firing is performed at a temperature of 100 ° C / min, and is 300 ° C to 500 ° C.
At 50 Mpa for 10 minutes. After the holding, the furnace was cooled, and when the temperature became 50 ° C. or lower, an ingot-shaped thermoelectric element 1 of φ30 × 3 mm was obtained. This ingot-shaped thermoelectric element 1
Had a relative density of 98.2% or more and a micro Vickers hardness Hv of 0.71 GPa or more, which was very high. Then, using a wire saw and a surface grinder, the ingot was thinned into a wafer shape to a thickness of 0.9 mm. The surface roughness Ra of this processed surface is 0.1.
It was less than μm.

Thereafter, the entire thermoelectric element 1 was surface-etched with nitric acid. By changing the etching time, the surface roughness Ra of the thermoelectric element 1 is 0.1 μm, 0.3 μm.
m, 0.5 μm, 1.0 μm, 2.0 μm, 2.5 μm
It was adjusted so that it would be roughened.

Next, the wafer-shaped thermoelectric element 1 was provided with an electroless plating layer serving as the first layer according to the present invention to serve as the Ni-B layer 2a. This plating layer was obtained by activating with palladium chloride and then using a plating solution containing Ni chloride and a boron hydroxide compound as a reducing agent so that the content of boron was 2% with respect to 98% of Ni. Then, the Ni
On the -B layer 2a, a Ni-P layer 2b made of a Ni-P-based electroless plating layer was formed. This Ni-P layer 2b was obtained by activating with palladium chloride and then using a plating solution containing Ni chloride and sodium hypozincate as a reducing agent so as to be 10% phosphorus with respect to 90% Ni. . The Ni-B layer 2a and the Ni-P layer 2b have a thickness of 0.5 μm and a thickness of 1 μm, respectively, by changing the plating time.
m, 5 μm, 10 μm, 20 μm, 30 μm, 40 μ
m and 50 μm in thickness.

For comparison purposes, only the Ni-B layer 2a is formed, the Ni-P layer 2b is formed, and the Ni-P layer 2b is formed.
A layer in which Ni-B2a was superposed on the -P layer 2a was also prepared.

Further, Au plating was applied to the above Ni layer. The thickness of the Au layer 3 is 0.001 μm, 0.0
It was set to 1 μm, 1 μm, and 20 μm. For plating,
As the thickness of the surface of the thermoelectric element 1 is increased, Ni
The surface roughness Ra after Au plating was almost unchanged from that before plating.

The wafer-shaped thermoelectric element 1 plated with Ni and Au as described above was diced to obtain a chip-shaped element. The surface roughness Ra of the dicing processed surface, that is, the surface roughness Ra of the thermoelectric element 1 other than the bonding surface 11 was set to 0.1 μm, 0.5 μm, and 1 μm by changing the roughness of the dicing grindstone. In this way, 0.7 mm long, 0.7 mm wide, 0.9 mm long
The device shape was obtained.

The P-type thermoelectric element 1a thus obtained
30 pieces of N-type thermoelectric element 1b and 30 pieces of N-type thermoelectric element 1b are sandwiched by a supporting substrate 4a of length 8 mm × width 8 mm × thickness 0.3 mm, which is made of alumina ceramics on which copper electrodes are formed, as shown in FIG. Using a solder consisting of
A thermoelectric module as shown in FIG. 1 was obtained. Solder thickness is 5μm, 10μm, 30μm, 50μm, 60μm
And

Then, with respect to this thermoelectric module, a joint strength test, an impact test, and a thermoelectric performance test were evaluated. For the bonding strength test, the force required to peel off the support substrate 4a soldered to the thermoelectric element 1 was measured as follows.
It was performed by measuring with a universal tester Model 1125 manufactured by Instron. For impact test evaluation, XY shock pulse of 2000G / 0.5msec was applied to the thermoelectric module.
After being repeatedly applied 10 times in each direction of Z, those having no deterioration in appearance and thermoelectric performance were regarded as acceptable.

Regarding the thermoelectric performance test, the thermoelectric module is energized, the temperature difference ΔTmax between the upper and lower supporting substrates 4 and the heat absorption amount Qcmax are measured, and ΔTmax ≧ 75 ° C., Qcmax ≧
A product obtained with 3 Watts or more was regarded as a pass.

[0071]

[Table 1]

No. 1 to 3 are surface roughness Ra of the thermoelectric element 1 on the side surface 12 other than the joint surface 11 of the thermoelectric element 1 shown in FIG.
The present invention relates to a thermoelectric module in which It has been found that when the above-mentioned surface roughness Ra exceeds 0.5 μm, the grinding flaw on the side surface of the thermoelectric element 1 becomes a starting point and breaks by the vibration test. On the other hand, when the surface roughness Ra of the side surface 12 is 0.5 μm or less, not only the shock test can be endured, but also the thermoelectric performance is ΔTmax ≧ 75 ° C., Qcmax.
It was found that ≧ 3Watt or more was obtained, and that it could be used without problems.

That is, the surface roughness Ra of the side surface 12 described above.
Must be finished smoothly because it can become the starting point of damage when it is impacted. This surface roughness R of 0.5 μm or less
In order to obtain a, a commercially available dicing saw was used, and a good result was obtained by processing a blade having a rotation speed of 35,000 rpm, a feed rate of 2 mm / sec and a width of about 60 μm by down-cutting.

From this result, it can be said that the surface roughness Ra of the thermoelectric element 1 other than the bonding surface 11 is preferably 0.5 μm or less.

No. 4 to 7 relate to the thermoelectric module in which the surface roughness Ra of the joint surface 11 of the thermoelectric element 1 shown in FIG. 2 is changed. The surface roughness Ra is 0.5 μm
It has been found that when the amount is less than the range, even Ni-B type plating has poor bite, and the plating is peeled off and destroyed by a vibration test. When the bonding strength in the thermoelectric module at this time was examined, the bonding strength to the supporting substrate 4 was only about 5 to 7 MPa because it peeled off on the plated surface. If the surface roughness Ra exceeds 2 μm, the solder does not flow sufficiently into the details of the roughened plated surface, leaving an air layer that blocks heat transfer, resulting in ΔTma.
It was found that the thermoelectric performance deteriorates such that x = 70 ° C. is obtained.

On the other hand, the thermoelectric module having the surface roughness Ra of the joint surface 11 of 0.5 to 2.0 μm can not only withstand the impact test but also has the thermoelectric performance of ΔTmax ≧.
At 75 ° C., Qcmax ≧ 3Watt or more was obtained, and it was found that it could be used without any problem. The bonding strength in the thermoelectric module at this time was 8 MPa or more.

From this result, the surface roughness Ra of the thermoelectric element 1 on the joint surface 11 to be joined to the support substrate 4 is 0.5 to 2.0.
It can be said that μm and soldering strength of 8 MPa or more are good.

No. 8 to 23 relate to the thermoelectric module in which the Ni layer thickness shown in FIG. 3 is changed. Hereinafter, all the Ni layers are formed by electroless Ni plating, but they are simply referred to as plating here.

First, when a Ni—P-based plating treatment was attempted as the first layer, the adhesion to the thermoelectric material 1 was poor and the plating peeled off (No. 8). Although Ni-B-based plating was applied as the second layer on the Ni-P-based plating, the Ni-P-based plating also had poor adhesion to the thermoelectric material and peeled off the plating. (No. 9).

Next, when only one layer of the Ni-B layer 2a was applied to the thermoelectric element 1 (No. 10), the surface of the thermoelectric element 1 was strongly absorbed as a crystalline dense film.
Good adhesion was obtained to the thermoelectric element 1. However, since it is a hard coating, stress relaxation due to soldering cannot be obtained, and cracks occur in the plating layer, which is unsuitable.

On the other hand, the first layer was plated with a Ni—B layer 2a having a thickness of 1 to 40 μm, and the second layer was a plated layer having a thickness of 1 to 40 μm, which was a Ni—P layer 2b. , The Ni-B layer 2a strongly adheres to the surface of the thermoelectric element 1 as a crystalline dense film, and N
The i-P layer 2b worked as a good buffering agent, good adhesion was obtained, and no crack was generated in the plating layer. The bonding strength in the thermoelectric module at this time was 8 MPa or more.

However, the thickness of the Ni-B layer 2a is 1 μm.
When it is less than the range, the biting of the plating deteriorates, and it becomes easy to peel off in the impact test. Similarly, Ni
-If the thickness of the P layer 2b was also less than 1 μm, it could not withstand the impact test.

On the contrary, when the thickness of the Ni-B layer 2a exceeds 40 μm, the Ni-B layer 2a begins to crack due to the impact test, and the impact cannot be endured. Similarly, if the thickness of the Ni-P layer 2b exceeds 40 μm, the impact test cannot be withstood. Further, even when the thickness of the Ni-P layer 2b as the second layer is made smaller than that of the Ni-B layer 2a as the first layer, it is difficult to obtain the buffering effect of the Ni-P layer 2b, and the impact test cannot be endured. It was On the other hand, for the first layer Ni-B layer 2a, the second layer Ni-P
When the thickness of the layer 2b was increased, a strong adhesive force and a cushioning effect were obtained, and it became possible to endure the impact test.

Therefore, the Ni contained in the thermoelectric element 1 is
In the layer 2, the first layer is a Ni—B layer 2a made of a Ni—B based plating layer having a thickness of 1 to 40 μm, and the second layer is
NI-P layer 2 consisting of 40 μm Ni-P based plating layer
b, and the average thickness of the Ni-B layer 2a is Ni.
It can be said that one having a thickness equal to or smaller than the average thickness of the -P layer 2b or thinner than the Ni-P layer 2b is preferable. It should be noted that, as the plating layer becomes thicker, the internal stress also increases, and the bonding strength tends to decrease. Therefore, it is particularly desirable that the Ni—B layer 2 be used.
It can be said that the thickness of a and the Ni-P layer 2b is preferably 1 to 10 μm.

No. 24-28 relate to the thermoelectric module in which the thickness of the Au layer 3 is changed. Au layer 3
If the thickness is too thick, not only the material cost increases, but also if it exceeds 10 μm, the ductility of Au deteriorates the bonding strength. On the other hand, if it is less than 0.01 μm, sufficient bonding strength cannot be obtained. Therefore, the Au layer 3
It can be said that the thickness is preferably 0.01 to 10 μm. In addition, A
Since good results were obtained when the thickness of the u layer 3 was 0.01 μm or more, the thickness of the Au layer 3 should be suppressed to about 0.01 to 0.1 μm in consideration of the production cost.

No. 29-33 are related to the thermoelectric module in which the solder thickness is changed. Since the solder layer also works as a good impact buffer layer, a good impact test result was obtained with a solder thickness of 10 μm or more, and cracks occurred in the solder layer with a thickness of 5 μm or less. On the other hand, even when the thickness of the solder layer exceeds 50 μm, cracks are observed in the solder layer itself by the impact test, which is not preferable. Therefore, the solder thickness is preferably 10 to 50 μm or less. The type of solder is not limited to AuSn, and similar results are obtained with commercially available solder other than SnSb, SnPb, and the like.

Therefore, the surface roughness Ra of the surface for bonding the thermoelectric element 1 having the hardness of 0.5 GPa or more to the supporting substrate 4 as described above is 0.5 to 2.0 μm, and the surface roughness other than the bonding surface 11 is Ra is processed to 0.5 μm or less, and the bonding surface 11 of the thermoelectric element 1 has a Ni—B layer 2 of 1 to 40 μm.
a, Ni-P layer 2b of 1 to 40 μm, 0.01 to 10 μm
m Au layer 3 and the average thickness of the Ni-B layer 2a is N.
After making it equal to or thinner than the average thickness of the i-P layer 2b,
When the supporting substrate 4 prepared separately is joined with a solder having a thickness of 10 to 50 μm, a soldering strength of 8 MPa or more is obtained, and a thermoelectric module having sufficient heat cycle resistance and vibration / shock resistance can be obtained. .

The Ni-B layer 2a here is N chloride.
Ni9 by a plating solution containing i and a boron hydroxide compound
Although boron is set to 2% with respect to 8%, it goes without saying that if the main component other than Ni is boron, any other method will act as Ni-B based plating. Further, the Ni-P layer 2b was made to have a phosphorus content of 10% with respect to 90% of Ni by a plating solution containing Ni chloride and sodium hypozincate, but there is no problem if the main component other than Ni is phosphorus. However, pure Ni plating containing neither B nor P in Ni was unsuitable because of poor adhesion to the thermoelectric element 1.

By the way, as a comparative example, when the thermoelectric element 1 was subjected to electrolytic etching in an electrolyte solution in order to adjust the surface roughness Ra of the thermoelectric element 1, the etching rate was too high and the thermoelectric element 1 Surface roughness Ra of element 1
Could not be controlled to 0.5 to 2.0 μm, and the surface roughness Ra became 2.5 μm or more. As a result, the solder did not flow sufficiently into the details of the rough plated surface, leaving an air layer that blocks heat transfer, and ΔTmax = 70.
It was found that the thermoelectric performance was deteriorated such that only ℃ was obtained.

Although a test was conducted to adjust the surface roughness Ra of the thermoelectric element 1 using a mechanical method such as sand blasting or shot blasting, the roughening speed was too fast and the thermoelectric element as in the present invention was found. The surface roughness Ra of 1 is 0.5 to
It was found that the thermoelectric performance was deteriorated such that the surface roughness Ra could not be controlled to 2.0 μm and the surface roughness Ra was 2.5 μm or more, and similarly ΔTmax = 70 ° C. was obtained.

Therefore, the surface roughness Ra of the thermoelectric element 1 is
It is important not to make it rough, but to adjust it appropriately using a proper method.

Here, the shape of the thermoelectric element 1 is 0.
7 mm, width 0.7 mm, length 0.9 mm, 30 P-type thermoelectric elements 1a and 30 N-type thermoelectric elements 1b, length 8 mm made of alumina ceramic with copper electrodes formed
The thermoelectric module was formed by sandwiching between the supporting substrates 4a and 4b having a width of 8 mm and a thickness of 0.3 mm, and using a solder made of AuSn to bond the thermoelectric modules. Needless to say, the above is not limited to the above.

[0093]

According to the present invention, in a thermoelectric module in which a thermoelectric element composed of at least two kinds of elements of Bi, Te, Se and Sb is bonded to a supporting substrate,
Surface roughness R of the thermoelectric element 1 on the surface to be joined to the supporting substrate
When a is 0.5 to 2.0 μm and the surface roughness Ra of the thermoelectric element other than the bonding surface is 0.5 μm or less, it is possible to provide a highly reliable and high-performance thermoelectric module. became.

Further, in a thermoelectric module in which a thermoelectric element made of at least two kinds of elements of Bi, Te, Se and Sb is joined to a supporting substrate, at least the surface of the thermoelectric element on the joint surface side has a thickness of 1 to 40 μm Ni-
Layer B, Ni-P layer having a thickness of 1 to 40 μm, thickness 0.01 to
It is also effective to form three Au layers of 10 μm.

In particular, the thickness of the solder joint between the thermoelectric element and the supporting substrate is 10 to 50 μm, the solder joint strength between the thermoelectric element and the supporting substrate is 8 MPa or more, and the hardness of the thermoelectric element is 0.5 GPa or more. A thermoelectric module with extremely high bonding reliability can be obtained.

[Brief description of drawings]

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

FIG. 2 is a perspective view showing a schematic structure of a thermoelectric element used in the thermoelectric module of the present invention.

FIG. 3 is a layer configuration diagram after forming each layer on a bonding surface of the thermoelectric element shown in FIG.

FIG. 4 is a cross-sectional view of a supporting substrate used in the thermoelectric module of the present invention.

[Explanation of symbols]

1 ... Thermoelectric element 2a ... Ni-B layer 2b ... Ni-P layer 3 ... Au layer 4a, 4b ... Support substrate

Claims (4)

[Claims] 1. A thermoelectric module in which a thermoelectric element made of a compound containing at least two kinds of elements of Bi, Te, Se and Sb is joined to a supporting substrate, wherein the thermoelectric element on the surface to be joined to the supporting substrate is Surface roughness Ra 0.5
To 2.0 μm, and the surface roughness Ra of the thermoelectric element other than the joint surface is 0.5 μm or less. 2. A thermoelectric module in which a thermoelectric element made of a compound containing at least two kinds of elements of Bi, Te, Se and Sb is joined to a supporting substrate, wherein the surface of the thermoelectric element on the joint surface side has a thickness. 1-40 μm Ni-B
Layer, Ni-P layer having a thickness of 1 to 40 μm, thickness of 0.01 to 1
A thermoelectric module, wherein three layers of 0 μm Au layer are formed. 3. The thickness of the thermoelectric element and the supporting substrate is 10 to 50.
The thermoelectric module according to claim 1 or 2, wherein the thermoelectric element and the supporting substrate are joined by soldering with a thickness of µm and the joint strength between the thermoelectric element and the supporting substrate is 8 MPa or more. 4. The thermoelectric module according to claim 1, wherein the thermoelectric element has a hardness of 0.5 GPa or more.