JP4523306B2 - Method for manufacturing thermoelectric element - Google Patents

Description

 The present invention relates to a thermoelectric element used for Peltier cooling and temperature difference power generation, and more particularly to an element structure and a manufacturing method for improving its reliability.

  A thermocouple has the property that two types of thermoelectric semiconductors having different polarities are connected, a temperature difference is generated between both ends, a voltage is generated between the electrodes, and conversely a temperature difference is generated when a current is passed from the outside. A thermoelectric element uses a plurality of these thermocouples in series to amplify and utilize the thermal / electric conversion characteristics.

  For example, a thermoelectric element is applied to a power generation element using the Seebeck effect that can convert heat into electric energy, or a cooling element that cools an object using a characteristic that causes a temperature difference due to electric energy, that is, the Peltier effect. The

  And since the thermoelectric element has a simple structure and its operation, it is advantageous for downsizing compared to other thermal / electrical conversion systems. As a power generation element, it can generate power inside portable electronic devices such as wristwatches and as a cooling element. Has expanded its application to local cooling of semiconductor elements and sensor elements.

  The most common semiconductor material used for power generation or cooling as a thermoelectric element is a so-called BiTe alloy mainly composed of bismuth (Bi) and tellurium (Te). Since this material has the best performance at around room temperature, it is widely used in various places. Some BiTe alloys have p-type and n-type polarities in the same manner as other thermoelectric semiconductor materials due to additives, and those obtained by electrically connecting the two are called thermocouples. The thermoelectric element is formed by processing thermoelectric semiconductors of different polarities into a columnar shape to form a thermocouple and further connecting a plurality of them.

  In a conventional thermoelectric element structure and manufacturing method, first, substrate electrodes are formed in a predetermined pattern on two flat ceramic substrates. A plurality of p-type and n-type thermoelectric semiconductors are processed into a columnar shape, and bonded to the substrate electrodes of the upper and lower two substrates via solder layers at both end faces thereof. The substrate electrode has a configuration in which adjacent p-type and n-type thermoelectric semiconductors are connected to form a thermocouple, and a plurality of thermocouples are connected in series.

  When a direct current is passed through the thermoelectric element, a so-called Peltier effect occurs in which one end of the pillar absorbs heat and the other end generates heat. When one substrate located at one end is brought into contact with the object to be cooled, the heat of the object Can be cooled by absorbing heat.

  Thus, when a thermoelectric element is used as a cooling element, there are two problems with respect to the reliability of the element. One is the problem of condensation. When cooling with a thermoelectric element, it is possible to control to a temperature below room temperature depending on the conditions. When this is performed in the atmosphere, moisture in the atmosphere appears as condensation on one end of the pillar, which is a low temperature part. Since dissimilar metals such as solder and substrate electrodes are joined to the ends of the pillars, local batteries are formed by the addition of moisture due to dew condensation, resulting in metal corrosion. Due to this corrosion, the element resistance increases and eventually the element is destroyed.

  The second problem is stress concentration. Due to the nature of the thermoelectric element, the substrate on one side is cooled and the substrate on the other side is heated. For this reason, cooling shrinkage and heating expansion occur in the substrate, that is, a force for obliquely deforming the column of the thermoelectric semiconductor existing therebetween is applied. Since this force concentrates on the joining portion which is the end portion, the joining portion is easily broken.

In order to prevent dew condensation, which is the first problem, conventionally, for example, silicone resin is filled between the columns of the thermoelectric semiconductor to suppress the ingress of moisture from outside and prevent corrosion at the joint portion. Attempts have been made (see, for example, Patent Document 1).
Japanese Utility Model Publication No. 2-113348 (FIG. 2)

  By filling the thermoelectric element with resin as described in the above publication, corrosion of the joint is suppressed, and in that respect, reliability is improved. However, in the conventional method for manufacturing a thermoelectric element, a thermoelectric element is joined to a substrate to complete the thermoelectric element, and then the resin is filled. Therefore, if a flexible resin such as silicone is not used, stress is applied to shrink the space between the columns due to curing and shrinkage of the resin, and there is a risk that the columns may be damaged. Or, since the column is warped, there is a risk of disconnection or the like due to stress applied to the joint.

 That is, since only a flexible resin can be filled in the conventional method, it is impossible to suppress the stress on the joint portion caused by the expansion and contraction of the upper and lower substrates during cooling, and improvement in mechanical reliability cannot be expected. If a resin having high hardness such as an epoxy resin is used to increase the mechanical strength, the reliability is lowered as described above.

 Therefore, an object of the present invention is to provide a new thermoelectric element structure and a method for manufacturing the element that can simultaneously solve both problems of thermoelectric elements, namely, dew condensation at a low temperature and deformation of the element due to a temperature difference. It is.

In order to achieve the above object, the method described below is employed in the method for manufacturing a thermoelectric element of the present invention.

and fixing a plurality of n-type columnar element comprising a plurality of p-type pillar-shaped element and the n-type thermoelectric semiconductor formed of p-type thermoelectric semiconductor via the first protective layer, the end face of the p-type pillar-shaped element and the n-type pillar element A step of forming a bonding electrode on the substrate, a step of forming a substrate electrode on the substrate, a step of facing the bonding electrode and the substrate electrode at a predetermined position and bonding using solder, and a step of bonding the first protective layer and the substrate Filling the gap with the second protective layer.

 Further, the first protective layer and the second protective layer are made of a resin material, and the second protective layer has a curing shrinkage rate larger than that of the first protective layer.

  In the thermoelectric element of the present invention, the first protective layer and the second protective layer are filled in the element, and moisture can be prevented from entering from the outside. Therefore, reliability against corrosion at the electrode joint portion is increased. In addition, since the first protective layer and the second protective layer firmly hold each of the substrates bonded between the adjacent columns, the bonded portion can be protected from stress due to expansion and contraction of the upper and lower substrates.

Furthermore, since there are two layers of the first protective layer and the second protective layer inside the thermoelectric element, the second protective layer functions to attract the first protective layer and the substrate by its contraction force. The joined portion is pressed up and down to improve the strength. In this case, it is more effective that the second protective layer has a large cure shrinkage rate.

  Moreover, in the manufacturing method of this invention, since the 1st protective layer is hardened before joining a pillar and a board | substrate and the shrinkage stress is open | released, it can act only to fix between pillars. Furthermore, since the second protective layer is filled and cured after bonding, it is possible to attract the first protective layer and the substrate.

  As described above, the thermoelectric element of the present invention is a highly reliable element that is excellent in both moisture resistance and mechanical strength, and high humidity is expected to cause corrosion and destruction by using the element of the present invention. Cooling under severe conditions such as long-term use under conditions is possible.

  Hereinafter, the optimal embodiment of the thermoelectric element of this invention is described using drawing. FIG. 1 is a side sectional view of the thermoelectric element of the present invention, and FIGS. 2 to 7 show manufacturing steps of the thermoelectric element of the present invention.

  As shown in FIG. 1, in the thermoelectric element of the present invention, a plurality of p-type columnar elements 10 made of p-type thermoelectric semiconductors and n-type columnar elements 11 made of n-type thermoelectric semiconductors are alternately arranged. Here, a BiSbTe alloy is used for the p-type columnar element 10, and a BiSeTe alloy is used for the n-type columnar element 11. Each columnar element has a shape extending long from the upper surface to the lower surface, that is, has a columnar shape.

  In order to electrically insulate and fix the side surfaces of the pillars of the p-type columnar element 10 and the n-type columnar element 11 and to increase the mechanical strength, a first protection made of an epoxy adhesive is provided in the gap between the elements. Layer 60 is provided.

  Further, junction electrodes 20 made of a metal film are provided on both end faces of the p-type columnar element 10 and the n-type columnar element 11. Here, a multilayer film of nickel / gold is used as the material of the bonding electrode 20. The junction electrode 20 basically has a structure in which each of the adjacent p-type columnar elements 10 and n-type columnar elements 11 is connected in advance at the end faces of the columns.

  Since the substrate 40 preferably has good thermal conductivity and is insulative, alumina is used. A substrate electrode 30 is provided on the substrate 40, and the planar pattern thereof is substantially the same as that of the bonding electrode 20, so that they face each other by facing each other. The substrate electrode 30 is made of a multilayer film of chromium / copper / nickel / gold. Among these, it is the copper film that works as a conductor by lowering the resistance value from the function of the electrode.

  The two substrates 40 are arranged so that the bonding electrode 20 and the substrate electrode 30 face each other above and below the pillar, and the bonding electrode 20 and the substrate electrode 30 are bonded by a solder 50.

  Further, a second protective layer 70 is provided where the substrate electrode 30 is not formed between the first protective layer 60 and the substrate 40. The second protective layer 70 is also made of an epoxy-based adhesive, and firmly holds the first protective layer 60 and the substrate 40 by the shrinkage force when cured. Further, since the first protective layer 60 and the second protective layer 70 are provided, the joint portion composed of the joint electrode 20, the solder 50, and the substrate electrode 30 is completely covered, and moisture from the outside Etc. are prevented.

Then, the manufacturing method of the thermoelectric element of this invention is demonstrated. First, as shown in FIG. 2, the vertical grooves 1 are formed in the p-type thermoelectric semiconductor block and the n-type thermoelectric semiconductor block, and the p-type comb element 3 and the n-type comb element 4 are left with the vertical partition 2 left. Make it. At this time, the p-type comb-tooth element 3 and the n-type comb-tooth element 4 have the same pitch of the vertical grooves 1 and the width of the vertical groove 1 of one block is larger than the width of the vertical partition wall 2 of the other block. Like that. Here, a sintered body of BiSbTe alloy was used as the p-type thermoelectric semiconductor, and a sintered body of BiSeTe alloy was used as the n-type thermoelectric semiconductor. Processing is performed using a dicing saw or a wire saw.

  Subsequently, the p-type comb-tooth element 3 and the n-type comb-tooth element 4 are combined and integrated by inserting the other vertical partition wall 2 into the vertical groove 1. A combination of both is shown in FIG. The combined two comb-tooth elements are formed as an integrated comb-tooth element 5 by providing and fixing the first protective layer 60 on the fitting portion. A fluid epoxy resin adhesive is used for the first protective layer 60 so as to penetrate and fill the gaps between the vertical partition walls 2 of the combined comb elements. Thereafter, heating is performed as necessary, and the adhesive is cured by holding for a predetermined time, thereby fixing the partition walls to each other.

  After that, although not shown in the drawing, the integrated comb-teeth element 5 combined as necessary is processed again so as to form a transverse groove and a transverse partition so as to be orthogonal to the longitudinal groove. Then, as in the case of the first combination, the lateral grooves are filled and fixed with an epoxy adhesive, and the first protective layer 60 is formed again. By forming these lateral grooves, the thermoelectric semiconductor is processed finely, and the number of thermocouples can be increased.

  Subsequently, as shown in FIG. 4, the upper and lower surfaces of the integrated comb-tooth element 5 on which the first protective layer is formed are removed by grinding and flattened. Then, the columnar p-type columnar elements 10 and the n-type columnar elements 11 are alternately arranged. Since the epoxy adhesive was cured when forming the first protective layer 60 in the steps so far, the columns were fixed to each other, but stress was applied to the columns due to curing shrinkage of the resin. However, through this step, the continuous portion is removed and the pillars are separated, the stress is released, and there is no influence on the mechanical properties of the hardening shrinkage of the first protective layer 60.

 Thereafter, when particularly high reliability is required, an etching solution such as nitric acid or hydrochloric acid is used to remove the work-affected layer on the ground surface, and the processed surface is etched by several microns. Subsequently, the junction electrode 20 is formed as shown in FIG. 5 in such a manner that the p-type columnar element 10 and the n-type columnar element 11 are wired.

 First, an opening having the shape of a desired wiring pattern is provided on a metal plate made of nickel, and alignment is performed so that end faces of the p-type columnar element 10 and the n-type columnar element 11 adjacent to each other can be seen from the opening. Fix it. Installed in a vacuum evaporation system and deposits nickel or palladium. This method is generally called a mask vapor deposition method. Here, the vapor deposition layer does not need to cover all two adjacent end faces of the thermoelectric semiconductor elements, and may be slightly smaller as long as the two can be electrically connected.

  Following the vapor deposition step, the film is immersed in an electroless nickel plating solution to form a nickel film. Since the nickel film grows by using nickel or palladium formed by vapor deposition as reaction nuclei, it is first formed on the vapor deposition layer. A nickel film is also formed on the exposed end surfaces of the p-type columnar element 10 and the n-type columnar element 11 that are in contact with the deposited metal. When a sufficient plating thickness cannot be ensured only by electroless plating, electrolytic nickel plating is further performed. The total thickness of nickel plating is several μm.

The nickel film is applied for adhesion to the thermoelectric semiconductor and for preventing diffusion of impurities, and gold plating is performed following the nickel plating. Gold plating is necessary to improve the affinity with the solder used in the subsequent steps. Although the thermoelectric block 6 shown in FIG. 5 is completed by the above steps, solder 50 plating is further performed thereon. The solder 50 is not particularly limited as long as it is a solder material that can be plated, such as SnPb, SnAg, SnSb, SnCu, and AuSn. The solder 50 is also formed with a thickness of 10 to 20 μm by electrolytic plating. Since the solder 50 is a member necessary for joining the joining electrode 20 and the substrate electrode 30, it may be formed at the end of the manufacturing process of the substrate 40 to be described later.

  Simultaneously with the manufacture of the thermoelectric block 6, two substrates 40 on which the substrate electrode 30 is applied are manufactured as shown in FIG. An alumina plate is prepared as the substrate 40, a chromium film is formed to a thickness of about 0.1 μm by sputtering, and a copper film is formed thereon to a thickness of about 0.2 μm. Here, a negative pattern of the substrate electrode 30 is formed by a photolithography method using a photoresist. Thereafter, an electrolytic plating is used to form a copper film of about 10 μm, a nickel film of about 2 μm, and a gold film of about 0.5 μm. The plating for the substrate electrode 30 is up to here, but when the solder 50 described above is formed on the substrate 40 side, it is performed following the plating of the gold film. Finally, the photoresist is dissolved in a special stripping solution, and the copper and chromium films formed by sputtering are etched to form electrically separated substrate electrodes 30.

  As shown in FIG. 7, the thermoelectric block 6 and the two substrates 40 formed in the above process are aligned and brought into close contact with each other so that the same pattern is opposed to each other, thereby heating the solder. Dissolve and join. At this time, it is preferable to apply soldering flux to the thermoelectric block 6 side or the substrate 40 side.

  Finally, the second protective layer 70 is formed where the substrate electrode 30 is not formed between the first protective layer 60 and the substrate 40. The second protective layer 70 is also filled with a fluid epoxy resin adhesive so as to penetrate into the gap between the first protective layer 60 and the substrate 40. Thereafter, heating is performed as necessary, and the adhesive is cured by holding for a predetermined time, so that the first protective layer 60 and the substrate 40 are fixed.

 The epoxy adhesive that is the second protective layer 70 firmly holds the first protective layer 60 and the substrate 40 by the shrinkage force when cured. There is no problem even if this adhesive is the same as the adhesive used for the first protective layer 60. However, since the second protective layer 70 has the effect of increasing the strength by strongly pressing the bonding portion between the bonding electrode 20 and the substrate electrode 30 sandwiched between the substrate 40 and the columnar element by the curing shrinkage force, the shrinkage rate is further reduced than the first protective layer 60. The larger is desirable.

  With the above manufacturing process, the thermoelectric element of the present invention already shown in FIG. 1 is completed. In this manufacturing process, the first protective layer 60 is cured before joining the p-type columnar element 10, the n-type columnar element 11 and the substrate 40, and the shrinkage stress is released in the middle of the process. That is, there is no residual stress remaining when the conventional substrate 40 is bonded to the pillars and then filled and cured with resin, and can function as a reinforcing material that only fixes the space between the pillars. Furthermore, since the second protective layer 70 is filled and cured after bonding, it is possible to attract the already-cured first protective layer 60 and the substrate 40.

It is sectional drawing which shows the structure of the thermoelectric element in embodiment of this invention. It is sectional drawing which shows the manufacturing method of the thermoelectric element in embodiment of this invention. It is sectional drawing which shows the manufacturing method of the thermoelectric element in embodiment of this invention. It is sectional drawing which shows the manufacturing method of the thermoelectric element in embodiment of this invention. It is sectional drawing which shows the manufacturing method of the thermoelectric element in embodiment of this invention. It is sectional drawing which shows the manufacturing method of the thermoelectric element in embodiment of this invention. It is sectional drawing which shows the manufacturing method of the thermoelectric element in embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Vertical groove 2 Vertical partition 3 P-type comb-tooth element 4 N-type comb-tooth element 5 Integrated comb-tooth element 6 Thermoelectric block 10 P-type columnar element 11 N-type columnar element 20 Junction electrode 30 Substrate electrode 40 Substrate 50 Solder 60 1st Protective layer 70 Second protective layer

Claims (2)

  fixing a plurality of p-type columnar elements made of p-type thermoelectric semiconductor and a plurality of n-type columnar elements made of n-type thermoelectric semiconductor via a first protective layer; and A step of forming a bonding electrode on an end surface, a step of forming a substrate electrode on a substrate, a step of facing the bonding electrode and the substrate electrode at a predetermined position, and bonding using solder, and the first protective layer And a step of forming a second protective layer in the gap between the substrate and the substrate. 2. The method of manufacturing a thermoelectric element according to claim 1, wherein the first protective layer and the second protective layer are made of a resin material and have a curing shrinkage rate larger than that of the second protective layer and the first protective layer. .

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