JP2006287259A - Thermoelectric module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a low-cost, high-reliability and high-performance thermoelectric module that can be realized by optimizing plating and junction conditions. <P>SOLUTION: This thermoelectric module is formed by joining a thermoelectric element consisting of a compound, which contains at least two elements out of Bi, Te, Se and Sb, with support substrates 4a and 4b. On the front surface of the junction surface side of a thermoelectric element 1, a total of 3 layers including a Ni-B layer 2a with 1 to 40 μm thickness, Ni-P layer with 1 to 40μm thickness, and Au layer with 0.01 to 10μm thickness are formed. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a thermoelectric element that is suitably used for cooling a heating element such as a semiconductor and has excellent thermoelectric characteristics, a method for manufacturing the thermoelectric element, and a thermoelectric module.

  As shown in FIG. 1, the thermoelectric module using the Peltier effect has two support substrates 4a and 4b in which P-type thermoelectric elements 1a that are P-type semiconductors and N-type thermoelectric elements 1b that are N-type semiconductors are alternately arranged. The P-type thermoelectric element 1a and the N-type thermoelectric element 1b are electrically connected in series, and depending on the direction of the current by applying a DC voltage Endothermic or exothermic can be generated.

Since such a thermoelectric module has a simple structure and is easy to handle, it can maintain stable characteristics, and thus has attracted attention for a wide range of uses.

In particular, it is small and can be locally cooled, and precise temperature control near room temperature is possible, so it is used for devices that are precisely controlled to a constant temperature, such as semiconductor lasers and optical integrated circuits, and small refrigerators. .

  As a means for producing such a small thermoelectric module, as disclosed in Patent Document 1, P-type and N-type raw material powders are ingoted by hot pressing, and this ingot is sliced to a certain thickness, There is a method of obtaining the P-type thermoelectric element 1a and the N-type thermoelectric element 1b by plating the slice material and dicing into chips.

In producing a thermoelectric module using the P-type and N-type thermoelectric elements 1, as shown in Patent Document 2, a solder paste is applied on a support substrate 4b provided with a plurality of electrodes, After the chip-like P-type thermoelectric elements 1a and N-type thermoelectric elements 1b are alternately placed, the solder paste is melted (reflowed) so as to be sandwiched by another support substrate 4a with electrodes. A thermoelectric module as shown in FIG.

  The solder used at this time is not limited to the solder paste, and may be solder plating as shown in Patent Document 3.

  Also, the thermoelectric element 1 is polished before plating the thermoelectric element 1 (Patent Document 4), or the thermoelectric element 1 is subjected to electrolytic etching in an electrolyte solution in order to increase the adhesion strength between the thermoelectric element 1 and the plating. (Patent Document 5) has been proposed.

Further, there has also been proposed a method in which the plating on the thermoelectric element 1 is divided into two layers, the first layer is Ni—P based plating, and the second layer is Ni—B based plating (Patent Document 6).
JP-A-1-106478 Japanese Patent Laid-Open No. 10-215055 JP-A-4-23368 JP 11-340529 A Japanese Patent Laid-Open No. 11-186618 Japanese Patent Laid-Open No. 2001-196646

  Although the Ni plating on the surface of the thermoelectric element has been performed for a long time to prevent the diffusion of the tin component of the solder to the thermoelectric element, the bonding strength of the solder to the Ni plating layer may still be insufficient. There were many.

  In other words, the thermoelectric module is unable to withstand the thermal expansion difference of the thermoelectric element and the support substrate and the internal stress of the plating due to repeated temperature changes and external vibrations / impacts. It was inevitable that cracks or deformations would occur.

  In order to make the thermoelectric module function, it is necessary to pass a current of several A. If the solder joint part is removed and the electric circuit is short-circuited, not only the function is stopped but also there is a risk of fire.

  Accordingly, it is an object of the present invention to provide a thermoelectric module having high bonding reliability while being low in cost.

  The thermoelectric module according to the present invention is a thermoelectric module in which a thermoelectric element made of a compound containing at least two elements of Bi, Te, Se, and Sb elements is bonded to a support substrate. In addition, three layers of a Ni—B layer having a thickness of 1 to 40 μm, a Ni—P layer having a thickness of 1 to 40 μm, and an Au layer having a thickness of 0.01 to 10 μm are formed.

  The thermoelectric element and the support substrate are bonded by solder having a thickness of 10 to 50 μm, and the bonding strength between the thermoelectric element and the support substrate is 8 MPa or more.

  Furthermore, when the thermoelectric element has a hardness of 0.5 GPa or more, a thermoelectric module with extremely high bonding reliability can be obtained.

  According to the present invention, in a thermoelectric module in which a thermoelectric element composed of at least two elements of Bi, Te, Se, and Sb and a support substrate are bonded to each other, a thickness of 1 is provided on the surface of the thermoelectric element on the bonding surface side. To provide a highly reliable and high-performance thermoelectric module by forming three layers of a Ni-B layer of -40 [mu] m, a Ni-P layer of 1-40 [mu] m thick, and an Au layer of 0.01-10 [mu] m thick. Became possible.

  In particular, the solder joint thickness between the thermoelectric element and the support substrate is set to 10 to 50 μm, the solder joint strength between the thermoelectric element and the support substrate is 8 MPa or more, and the hardness of the thermoelectric element is 0.5 GPa or more. A highly reliable thermoelectric module can be obtained.

  Hereinafter, embodiments of the present invention will be described.

  FIG. 1 is a perspective view showing a thermoelectric module. As shown in FIG. 1, the thermoelectric module using the Peltier effect has two support substrates 4a and 4b in which P-type thermoelectric elements 1a that are P-type semiconductors and N-type thermoelectric elements 1b that are N-type semiconductors are alternately arranged. The N-type thermoelectric element 1b and the P-type thermoelectric element 1a are electrically connected in series, and by applying a DC voltage, depending on the direction of the current Endothermic or exothermic can be generated.

  FIG. 2 is a perspective view showing an example of the thermoelectric element 1 used in the thermoelectric module according to the present invention, and the surface state of the P-type thermoelectric element 1a which is a P-type semiconductor or the N-type thermoelectric element 1b which is an N-type semiconductor. Is schematically shown.

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 support substrates 4a and 4b. Is adjusted to 0.5 to 2.0 μm.

  Originally, the thermoelectric element 1 has a very fragile property and is very vulnerable to mechanical vibration / impact and thermal expansion difference. In order to increase the resistance to these, it is important not only to increase the hardness of the thermoelectric element 1 to 0.5 Gpa or more, but also to reduce defects on the surface of the thermoelectric element 1. In particular, since a processing flaw on the surface of the thermoelectric element 1 can be the largest defect, this portion must be finished smoothly. If the surface roughness Ra of the thermoelectric element 1 other than the bonding surface 11 is 0.5 μm or less, it is possible to dramatically improve resistance to mechanical vibration / impact, thermal expansion difference, and the like. .

  On the other hand, since the surface roughness Ra of the bonding surface 11 of the thermoelectric element 1 is filled and integrated with solder as a bonding agent, it cannot be a structural defect even if it is not finished smoothly like the side surface 12. On the other hand, if the surface is too smooth, the adhesion with the Ni layer described later is deteriorated, and the resistance to vibration, impact and the like is deteriorated.

  Therefore, in order to enhance physical biting with the Ni layer, the surface roughness Ra of the bonding surface 11 must be 0.5 μm or more. However, if 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 bonding surface 11 is preferably 0.5 to 2.0 μm. . The surface roughness is adjusted by etching as will be described in detail later.

  FIG. 3 is a cross-sectional view showing an example of the thermoelectric element 1 in the thermoelectric module according to the present invention.

Three layers of 1 to 40 μm Ni—B layer 2a, 1 to 40 μm Ni—P layer 2b, and 0.01 to 10 μm Au layer 3 are formed in this order on the bonding surface 11 of the thermoelectric element 1. Usually, all these three layers are formed by plating.

  And the average thickness of the Ni-B layer 2a is made equal to or thinner than the average thickness of the Ni-P layer 2b. This is because Ni-B-based plating has a slow film formation rate, and although it is strongly bitten as a crystalline dense film on the surface of the etched thermoelectric element 1, it is hard and has poor buffering properties. In addition, the plating time is enormous and the cost is increased. Further, the Ni-B layer 2 a prevents deterioration of the performance of the thermoelectric element 1 due to diffusion of a metal such as Sn as 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, the Ni-P-based plating has a high film formation rate, is amorphous, has low hardness, and has high buffering properties, but has poor adhesion to the thermoelectric element 1. Therefore, the Ni-B layer 2a that is the first layer is formed first, and then the Ni-P layer 2b that is the second layer is formed, and the average thickness of the Ni-B layer 2a is the average of the Ni-P layer 2b. It is important to make the thickness equal to or thinner than the thickness in order to improve reliability against thermal cycling and impact resistance and to reduce costs.

  Furthermore, it is important that the thermoelectric element 1 forms the Au layer 3 by performing Au plating on the Ni-P layer 1b. This is because Ni-P-based plating does not wet the solder well, and the required bonding strength cannot be maintained. However, sufficient solder joint strength and reliability can be obtained by applying the 0.01 to 10 μm Au layer 3 on the Ni-P layer 1b.

  If the Au layer 3 is too thick, not only will the material cost increase, but the workability will be inferior due to the ductility of Au, so that it is preferably 10 μm or less, and may be about 0.05 μm. However, if the thickness is less than 0.01 μm, the wettability of the solder deteriorates, so the Au plating thickness is preferably 0.01 to 10 μm. That is, the Au layer 3 has an effect of improving solder wettability when the thermoelectric element 1 is soldered to the support substrate.

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

  By the way, it is important that the thermoelectric element 1 of the present invention is composed of a compound containing at least two of Bi, Sb, Te, and Se. For example, the above metals may be used, but the A2B3 type intermetallic compound and The solid solution is preferred. Here, A is a semiconductor crystal composed of Bi and / or Sb and B is Te and / or Se, and the composition ratio B / A is particularly 1.4 to 1.6. Preferred for enhancing.

The A2B3 type intermetallic compound, it is preferably, a solid solution of Bi ₂ Te ₃ and Bi ₂ Se ₃ as a solid solution is at least one of _{Bi 2 Te 3, Sb 2 Te} 3, Bi 2 Se 3 are known _{Bi 2 Te 3-x Se x} (x = 0.05~0.25), or Bi ₂ Te ₃ and Sb ₂ which is a solid solution of _{Te 3 Bi x Sb 2-x} Te 3 (x = 0.1~0 .6) and the like.

  When manufacturing the N-type thermoelectric element 1b, it is preferable to include a halogen element such as I, Cl, or Br as a dopant in order to efficiently convert the intermetallic compound into a semiconductor. This halogen element is preferably contained in a proportion of 0.01 to 5 parts by weight, particularly 0.01 to 0.1 parts by weight, based on 100 parts by weight of the above-mentioned intermetallic compound raw material, from the viewpoint of semiconductorization.

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

  And it is important for the thermoelectric element 1 of this invention that hardness is 0.5 GPa or more. As a result, it is possible to prevent deformation caused by vibration or impact during module assembly or use as a thermoelectric module, or damage caused by the deformation. In particular, in order to further improve the mechanical reliability, the hardness is preferably 0.7 GPa or more, more preferably 0.8 GPa or more.

  In order to improve the hardness of the thermoelectric element 1, when the thermoelectric element 1 is formed by a sintering method, the average particle diameter may be atomized. The average particle diameter is preferably 100 μm or less, 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 Micro Vickers Hardness Tester Model HMV-200.

The specific resistance of the P-type and N-type thermoelectric elements 1 is preferably 5 × 10 ⁻⁵ Ωm or less, particularly preferably 1.5 × 10 ⁻⁵ Ωm or less. Thereby, Joule heat generated inside the element can be suppressed, and cooling can be performed efficiently.

  The thermoelectric element 1 having such a configuration is characterized by excellent mechanical strength and cooling capability, and is made constant temperature of an electronic cooling element such as a light detection element, a semiconductor manufacturing apparatus, and a semiconductor laser or an optical integrated circuit, It can be suitably used for a freonless small refrigerator or the like.

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

Next, the manufacturing method of the thermoelectric element 1 of this invention is demonstrated. First, raw material powder made of a thermoelectric semiconductor is prepared. The raw material is not particularly limited as long as it is a raw material powder mainly composed of a compound containing at least two of Bi, Sb, Te and Se, but in particular Bi ₂ Te ₃ , Bi ₂ Se ₃ and It is preferable to include at least one of Sb ₂ Te ₃ , thereby reducing the risk of composition deviation and obtaining a sintered body having a more uniform composition and structure.

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

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

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

  The above-mentioned compound powder can be weighed so as to have a target composition, and mixed and / or pulverized in a dry or wet manner to produce a raw material powder. Examples of the mixing and pulverization include known methods such as a stamp mill, a ball mill, and a vibration mill.

  In order to remove oxygen in the raw material powder after mixing and pulverization, it is important to perform a reduction 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 characteristics of the sintered body can be improved. This reduction treatment may be performed at any time before firing, and the reduction treatment is effective for powders and molded bodies.

  Next, this raw material powder is set in an SPS (discharge plasma sintering) apparatus. For example, a raw material powder is filled in a cylindrical carbon die and sandwiched from above and below by a compression current punch, and these jigs are set in a sintering furnace. In order to hold the die during this setting, a pressure of about 1 MPa is inevitably applied, but if it is a low pressure of 5 MPa or less, it does not affect the sintering.

  In addition, a raw material powder is prepared in advance by a known molding method such as a uniaxial press method, a CIP method, a casting method, an injection molding method, and the like, and this compact is mounted on a die so as to be positioned between the upper and lower compression current punches. You may enter.

  In addition, when using the shaping | molding method by a press method, in order to produce the molded object which can be manufactured easily and can fully handle, it shape | molds with a shaping | molding pressure of about 45-100 Mpa, and it is desirable to obtain a desired shape.

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

  According to the present invention, it is important to apply a pressure of 25 MPa to 50 MPa in the vicinity of the temperature at which the raw material powder starts to shrink (shrinkage starting temperature), and then heat-treat the raw material powder at 300 ° C. or higher. As a result, densification is possible in a low pressure and in a short time, and a thermoelectric element 1 having a more uniform fine crystal structure and having a high hardness and a smooth surface after machining such as dicing can be produced.

  The timing of the application is important for expressing a uniform fine crystal structure and saving unnecessary energy and reducing the cost. In particular, with respect to the shrinkage start temperature T of the raw material powder, (T-30) to ( It is preferable to pressurize at a temperature of (T + 50) ° C., particularly (T−20) to (T + 30) ° C.

  Thus, by applying pressure almost simultaneously with the onset of shrinkage, sintering can be promoted and densified in a short time with a low pressure, so that it becomes possible to produce a sintered body having uniform fine crystal grains. .

  If pressure is applied from the beginning of firing as in the past, the gas generated from the raw material powder and the die cannot be removed efficiently, and a non-uniform and partially porous structure is caused by non-uniform pressure. Although formed and reduced in hardness, these problems can be solved by using the production method of the present invention.

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

  In particular, when the average particle size of the raw material powder is 10 μm or less, the shrinkage start temperature T is preferably 100 ° C. or less. Moreover, it is preferable that the average particle diameter of the raw material powder exceeds 10 μm and the shrinkage start temperature T is 200 ° C. or less. The shrinkage start temperature differs depending on the particle size of the raw material powder, and it can be densified in a short time by applying pressure almost at the same time as the shrinkage start temperature. Since it is necessary, grain growth can be suppressed. In addition, the bonding between the grains at the grain boundary becomes strong, and the thermoelectric element 1 having high hardness can be manufactured.

  The firing atmosphere may be an inert gas atmosphere such as He, Ar and Ne, a non-oxidizing atmosphere such as H2 and N2, or a vacuum atmosphere in order to suppress reaction with oxygen as much as possible and further improve the figure of merit. desirable. Among these, since a reduction effect can be obtained simultaneously with sintering, the H2 atmosphere is preferably an Ar atmosphere in terms of safety and cost, and a mixed gas thereof may be used.

  Moreover, it is important that the pressurizing pressure is 25 to 50 MPa, and it is particularly preferably 28 to 40 MPa. When the pressure is less than 25 MPa, it becomes difficult to obtain a dense body, and when the temperature is increased to obtain a dense body, Te and Se that are easily sublimated are likely to be scattered, resulting in a composition shift and the like. Further, when the pressure exceeds 50 MPa, excessive energy is applied, and crystal grains cause grain growth. As a result, the thermal conductivity increases and the characteristics deteriorate. Moreover, when the pressure exceeds 50 MPa, the die is deteriorated and easily broken, leading to a decrease in yield and an increase in cost.

  The high-hardness ingot-shaped thermoelectric element 1 taken out of the die in this way has a feature that it is difficult to be damaged, deformed, or broken due to deformation, and has impact resistance and durability in the case of a thermoelectric module. 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. Thereafter, chemical etching such as hydrochloric acid or nitric acid is used to perform chemical etching so that the entire surface roughness Ra of the thermoelectric element 1 becomes 0.5 to 2.0 μm. Thereafter, a Ni layer is applied to the wafer-like thermoelectric element 1. 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 electroless plating layer is formed as the Ni-B layer 2a. The thickness of the Ni—B layer 2a is preferably about 1 to 40 μm, and preferably 1 to 10 μm. The Ni-B layer 2a can be electrolessly formed by a plating solution containing Ni chloride or sulfate and a boron hydroxide compound as a reducing agent after activation treatment with palladium chloride or the like. ) It is preferable that B (boron) is adjusted to 3 to 0.3% with respect to 97 to 99.7%.

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, and preferably 1 to 10 μm. After activation, the Ni-P layer 2b can be formed electrolessly by a plating solution containing Ni chloride or sulfate and sodium hypozincate as a reducing agent. Ni (nickel) 88-94% In contrast, the thermoelectric element 1 is preferably adjusted to have a P (phosphorus) content of 12 to 6%. Further, the thermoelectric element 1 forms the Au layer 3 by performing Au plating on the Ni layer. The Au plating can be formed by general electrolytic plating after completion of the Ni plating, but there is no problem even if the electroless Au is obtained by replacing the Ni-P layer 2b with Au. The plating thickness of Ni and Au can be controlled by plating conditions such as plating time. If the fracture surface of the thermoelectric element 1 after plating is observed by magnifying it several thousand times with an electron microscope, Can be measured easily.

  Thereafter, the wafer-like thermoelectric element 1 plated with Ni and Au is diced by a well-known method to finish the chip-like thermoelectric element 1. The surface roughness Ra of the side surface 12 of the thermoelectric element 1 other than the diced 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. This is because the thermoelectric element 1 inherently has a very fragile property and is very vulnerable to mechanical vibration / impact and thermal expansion difference. In order to increase the resistance to these, it is important not only to increase the density and hardness of the thermoelectric element 1 but also to reduce defects on the surface of the thermoelectric element 1.

  In particular, since the processing flaw on the surface of the thermoelectric element 1 can be the largest defect, the side surface 12 of the thermoelectric element 1 must be finished smoothly. 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 / second or less, and perform processing by downcutting. Note that the thermoelectric element 1 surface roughness Ra2 (arithmetic average roughness Ra) of the bonding surface 11 is filled with solder and integrated, and therefore cannot be a structural defect even if the surface is not finished as smooth as the side surface. .

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

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

  As described above, since the thermoelectric module of the present invention has particularly excellent bonding reliability, it can be suitably used particularly as a constant temperature, small refrigerator such as a semiconductor laser or an optical integrated circuit.

  Examples of the present invention will be described below.

Bi ₂ Te ₃ and Sb ₂ Te ₃ and Bi ₂ Se ₃ having an average particle diameter of 35 μm and a purity of 99.99% or more were prepared as starting materials. From these compounds, Bi ₂ Te _2.85 Se _0.15 as N type and Bi _0.4 Sb _1.6 Te ₃ as P type were weighed to prepare mixed powder. Note that 0.09 parts by weight of SbI ₃ was added as a dopant to the N type.

  Thereafter, the mixture was pulverized in a vibration mill for 30 hours in an isopropyl alcohol solvent, and then the particle size of the raw material powder was classified to 35 to 72 μm using a stamp mill. After drying, a compact having a diameter of 20 mm and a thickness of 5 mm was produced by a uniaxial press at a press pressure of 49 MPa, and subjected to reduction treatment at 400 ° C. for 5 hours in a hydrogen stream in an atmosphere furnace.

  Next, the reduction-treated compact was set on a cylindrical die made of carbon, sandwiched from above and below with a carbon compression punch, set in a sintering furnace, and the inside of the furnace was replaced with Ar The firing was started. Firing was performed at a temperature of 100 ° C./min, and held at 300 ° C. to 500 ° C. for 10 minutes × 50 MPa. After the holding, the furnace was cooled, and when it became 50 ° C. or less, an ingot-shaped thermoelectric element 1 of φ30 × 3 mm was obtained. The ingot-shaped thermoelectric element 1 had a relative density of 98.2% or higher and a micro Vickers hardness Hv of 0.71 GPa or higher.

  After that, using a wire saw and a surface grinder, the ingot was thinned into a wafer so as to have a thickness of 0.9 mm. The surface roughness Ra of the processed surface was less than 0.1 μm.

  Thereafter, the entire thermoelectric element 1 was subjected to surface etching with nitric acid. By changing the etching time, the surface roughness Ra of the thermoelectric element 1 was adjusted to be roughened to 0.1 μm, 0.3 μm, 0.5 μm, 1.0 μm, 2.0 μm, and 2.5 μm.

  Next, an electroless plating layer serving as the Ni-B layer 2a was applied as the first layer to the wafer-like thermoelectric element 1 based on the present invention. This plating layer was obtained by an activation treatment with palladium chloride, followed by a plating solution containing Ni chloride and a boron hydroxide compound as a reducing agent so as to be 2% of boron with respect to 98% of Ni.

  Subsequently, a Ni-P layer 2b made of a Ni-P-based electroless plating layer was formed on the Ni-B layer 2a. This Ni-P layer 2b was activated by palladium chloride, and then obtained by 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 were made to have thicknesses of 0.5 μm, 1 μm, 5 μm, 10 μm, 20 μm, 30 μm, 40 μm, and 50 μm, respectively, by changing the plating time.

  For comparison, a Ni-B layer 2a only, a Ni-P layer 2b only, and a Ni-B layer 2a layered with Ni-B 2a were also prepared.

  Further, Au plating was applied to the Ni layer described above. The thickness of the Au layer 3 was 0.001 μm, 0.01 μm, 1 μm, and 20 μm. As for plating, since the thickness increases along the surface shape of the thermoelectric element 1, the surface roughness Ra after Ni and Au plating hardly changed from that before plating.

  The wafer-like thermoelectric element 1 subjected to Ni and Au plating as described above was diced to finish a chip-like element. The surface roughness Ra of the dicing 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. Thus, an element shape having a length of 0.7 mm, a width of 0.7 mm, and a length of 0.9 mm was obtained.

  The 30 P-type thermoelectric elements 1a and 30 N-type thermoelectric elements 1b thus obtained were 8 mm long × 8 mm wide × 0 thickness 0 made of an alumina ceramic with copper electrodes as shown in FIG. 1. A thermoelectric module as shown in FIG. 1 was obtained by bonding with a solder made of AuSn while being sandwiched between 3 mm support substrates 4a. The solder thickness was 5 μm, 10 μm, 30 μm, 50 μm, and 60 μm.

And this thermoelectric module was evaluated regarding the bonding strength test, impact test, and thermoelectric performance test. The bonding strength test was performed by measuring the force required to peel off the support substrate 4a soldered to the thermoelectric element 1 with an Instron universal testing machine 1125 type. As for the impact test evaluation, a 2000 G / 0.5 msec impact pulse was repeatedly given to the thermoelectric module 10 times in each of the XYZ directions, and then the product without any appearance or thermoelectric performance deterioration was regarded as acceptable. For the thermoelectric performance test, the thermoelectric module was energized, the temperature difference ΔTmax between the upper and lower support substrates 4 and the endothermic amount Qcmax were measured, and those obtained ΔTmax ≧ 75 ° C. and Qcmax ≧ 3 Watt or more were regarded as acceptable.

  No. 1 to 3 relate to a thermoelectric module in which the surface roughness Ra of the thermoelectric element 1 on the side surface 12 other than the bonding surface 11 of the thermoelectric element 1 shown in FIG. 2 is changed. It has been found that when the surface roughness Ra described above exceeds 0.5 μm, a grinding scratch on the side surface of the thermoelectric element 1 starts as a starting point and is broken by a vibration test. On the other hand, when the surface roughness Ra of the side surface 12 described above is 0.5 μm or less, not only can it withstand an impact test, but also a thermoelectric performance of ΔTmax ≧ 75 ° C. and Qcmax ≧ 3 Watt or more can be used without any problem. I found out.

  That is, the surface roughness Ra of the side surface 12 described above can be a starting point of destruction when subjected to an impact, and must be finished smoothly. In order to obtain the surface roughness Ra of 0.5 μm or less, a commercially available dicing saw can be used to process a blade with a rotation speed of 35000 rpm, a feed rate of 2 mm / sec, and a width of about 60 μm with a down cut. It was. 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 a thermoelectric module in which the surface roughness Ra of the joint surface 11 of the thermoelectric element 1 shown in FIG. 2 is changed. It has been found that when the surface roughness Ra is less than 0.5 μm, even Ni-B plating does not bite well, and the plating peels off and is destroyed by a vibration test. When the bonding strength in the thermoelectric module at this time was examined, the bonding strength to the support substrate 4 was only about 5 to 7 MPa because it peeled off at the plated surface.

  In addition, when the surface roughness Ra exceeds 2 μm, the solder does not sufficiently flow into the details of the rough plated surface, an air layer that blocks heat transfer remains, and only ΔTmax = 70 ° C. is obtained. It was found that the thermoelectric performance deteriorates.

  On the other hand, the thermoelectric module in which the surface roughness Ra of the joint surface 11 described above is 0.5 to 2.0 μm not only can withstand an impact test, but also has a thermoelectric performance of ΔTmax ≧ 75 ° C., Qcmax ≧ 3 Watt or more. Was found to be usable without problems. The joining strength in the thermoelectric module at this time was 8 MPa or more. From this result, it can be said that the surface roughness Ra of the thermoelectric element 1 of the bonding surface 11 to be bonded to the support substrate 4 is 0.5 to 2.0 μm and the solder bonding strength is 8 MPa or more.

  No. 8 to 23 relate to a 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 are simply expressed as plating here.

  First, when an Ni-P plating treatment was attempted as the first layer, adhesion to the thermoelectric material 1 was poor and plating peeling occurred (No. 8). In addition, although Ni-B plating was applied as the second layer on top of Ni-P plating, Ni-P plating similarly has poor adhesion to thermoelectric materials, resulting in peeling of the plating. (No. 9).

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

  On the other hand, when the first layer was plated to be a 1 to 40 μm Ni—B layer 2a and the second layer was further plated to be a 1 to 40 μm Ni—P layer 2b, Ni— The B layer 2a strongly bites as a crystalline dense film on the surface of the thermoelectric element 1, and the Ni-P layer 2b works as a good buffering agent so that good adhesion can be obtained and the above plating layer There were no cracks. The joining strength in the thermoelectric module at this time was 8 MPa or more.

  However, when the thickness of the Ni—B layer 2a is less than 1 μm, the biting of the plating is deteriorated, and the Ni—B layer 2a is easily peeled off by an impact test. Similarly, when the thickness of the Ni—P layer 2b was 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 started to crack due to the impact test, and could not withstand the impact. Similarly, when the thickness of the Ni—P layer 2b exceeds 40 μm, it cannot withstand the impact test.

  Further, even when the thickness of the Ni-P layer 2b as the second layer is made thinner than the Ni-B layer 2a as the first layer, it is difficult to obtain a buffering effect by the Ni-P layer 2b, and the impact test cannot be endured. It was. On the other hand, when the thickness of the Ni-P layer 2b of the second layer is increased with respect to the Ni-B layer 2a of the first layer, strong adhesion and buffering action are obtained, and the impact test can be endured. .

  Therefore, the Ni layer 2 configured in the thermoelectric element 1 includes a Ni-B layer 2a made of a Ni-B based plating layer having a first layer of 1 to 40 μm, and a second layer of 1 to 40 μm. The Ni-P layer 2b is composed of a Ni-P-based plating layer, and the average thickness of the Ni-B layer 2a is preferably equal to or thinner than the average thickness of the Ni-P layer 2b. It can be said.

  As the plating layer becomes thicker, the internal stress also increases and the bonding strength tends to decrease. Therefore, the thickness of the Ni-B layer 2a and the Ni-P layer 2b is particularly preferably 1 to 10 μm. I can say that.

  No. Reference numerals 24 to 28 relate to thermoelectric modules in which the thickness of the Au layer 3 is changed. If the Au layer 3 is too thick, not only will the material cost increase, but if it exceeds 10 μm, the bonding strength deteriorates due to the ductility of Au. On the other hand, when the thickness is less than 0.01 μm, sufficient bonding strength cannot be obtained. Therefore, it can be said that the thickness of the Au layer 3 is preferably 0.01 to 10 μm. In addition, since the favorable result was obtained if the thickness of the Au layer 3 is 0.01 μm or more, the thickness of the Au layer 3 may be suppressed to about 0.01 to 0.1 μm in consideration of the production cost.

 No. Reference numerals 29 to 33 relate to thermoelectric modules in which the solder thickness is changed. Since the solder layer also works as a good shock buffer layer, good impact test results were obtained with a solder thickness of 10 μm or more, and cracks were generated in the solder layer at 5 μm or less. On the other hand, even when the solder layer thickness exceeded 50 μm, cracks were seen in the solder layer itself by the impact test, which was 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 were obtained even with commercially available solders other than SnSb and SnPb.

  Accordingly, the surface roughness Ra of the surface where the thermoelectric element 1 having the hardness of 0.5 GPa or more is bonded to the support substrate 4 as described above is 0.5 to 2.0 μm, and the surface roughness Ra other than the bonding surface 11 is 0. The bonding surface 11 of the thermoelectric element 1 is composed of a 1 to 40 μm Ni—B layer 2 a, a 1 to 40 μm Ni—P layer 2 b, and a 0.01 to 10 μm Au layer 3. When the average thickness of the -B layer 2a is equal to or thinner than the average thickness of the Ni-P layer 2b and bonded to a separately prepared support substrate 4 with a solder having a thickness of 10 to 50 μm, a soldering strength of 8 MPa or more is obtained. Therefore, it is possible to obtain a thermoelectric module having sufficient heat cycle resistance and vibration / impact resistance.

  Here, the Ni-B layer 2a is made to be 2% of boron with respect to 98% of Ni by a plating solution containing Ni chloride and a boron hydroxide compound, but if the main component other than Ni is boron, It goes without saying that any other method works as Ni-B plating. The Ni-P layer 2b is made 10% phosphorus with respect to 90% 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 no B or P in Ni was unsuitable because of poor adhesion to the thermoelectric element 1.

  By the way, as a comparative example, in order to adjust the surface roughness Ra of the thermoelectric element 1, when the thermoelectric element 1 was subjected to electrolytic etching in an electrolyte solution, the etching rate was too high and the thermoelectric element 1 of the present invention was The surface roughness Ra could not be controlled to 0.5 to 2.0 μm, and the surface roughness Ra was 2.5 μm or more. As a result, it was found that the solder does not sufficiently flow into the details of the rough plated surface, an air layer that blocks heat transfer remains, and only ΔTmax = 70 ° C. can be obtained.

  Moreover, although the test which adjusts the surface roughness Ra of the thermoelectric element 1 using mechanical methods, such as sandblasting and shot blasting, was performed, the roughening speed | rate is too fast and the surface of the thermoelectric element 1 like this invention is carried out. The roughness Ra cannot be controlled to 0.5 to 2.0 μm, the surface roughness Ra becomes 2.5 μm or more, and only ΔTmax = 70 ° C. is similarly obtained. I understood.

  Therefore, the surface roughness Ra of the thermoelectric element 1 does not have to be excessively rough, but it is important to adjust it appropriately using an appropriate method. Here, the shape of the thermoelectric element 1 is 0.7 mm in length, 0.7 mm in width, and 0.9 mm in length, 30 P-type thermoelectric elements 1a, 30 N-type thermoelectric elements 1b, and copper electrodes are formed. Although the thermoelectric module was joined by using solder made of AuSn while being sandwiched between the support substrates 4a and 4b having a length of 8 mm, a width of 8 mm, and a thickness of 0.3 mm made of alumina ceramic, the number of thermoelectric elements 1 and the thermoelectric Needless to say, the dimensions of the element 1 and the support substrate 4 are not limited to the above.

It is a perspective view of the thermoelectric module of this invention. It is a perspective view which shows schematic structure of the thermoelectric element used for the thermoelectric module of this invention. It is a layer block diagram after forming each layer in the joint surface of the thermoelectric element shown in FIG. It is sectional drawing of the support substrate used for the thermoelectric module of this invention.

Explanation of symbols

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

Claims (3)

In a thermoelectric module formed by bonding a thermoelectric element made of a compound containing at least two elements of Bi, Te, Se and Sb elements to a support substrate, Ni having a thickness of 1 to 40 μm is formed on the surface of the thermoelectric element on the bonding surface side. A thermoelectric module comprising three layers of a -B layer, a Ni-P layer having a thickness of 1 to 40 µm, and an Au layer having a thickness of 0.01 to 10 µm. 2. The thermoelectric module according to claim 1, wherein the thermoelectric element and the support substrate are bonded by solder having a thickness of 10 to 50 μm, and the bonding strength between the thermoelectric element and the support substrate is 8 MPa or more. The thermoelectric module according to claim 1, wherein the thermoelectric element has a hardness of 0.5 GPa or more.

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