HUP0700496A2 - Method of manufacturing a device, particularly a rod applicable in thermo electric modules, comprising metal and intermetallic semiconductor parts joined together providing electrically and thermally conducting junctions - Google Patents

Description

PUBLICATION 1NEW

COPY P07004 96

METHOD FOR PROCESSING A DEVICE CONTAINING METALLIC AND INTERMETALLIC SEMICONDUCTOR PARTS CONNECTED TO EACH OTHER BY ELECTRICALLY CONDUCTIVE AND THERMAL CONNECTION, ESPECIALLY

FOR THE PRODUCTION OF RODS USABLE FOR THERMOELECTRIC MODULES

The invention relates to a method for producing a device, in particular a rod suitable for thermoelectric modules, comprising parts made of metal and intermetallic semiconductor materials connected to each other by an electrically conductive and thermally conductive connection.

It is known that the joining of two metal objects by soldering is carried out in such a way that molten solder is introduced between them, as a result of which adhesion is created between the metals and the solder, which provides the holding force between the two metal objects. To create adhesion, various auxiliary substances, called fluxes in the given art, are used, which provide clean metal surfaces. This is necessary because adhesion only occurs on clean metal surfaces.

Reliable solder joints are usually created in several steps. The first step is pre-soldering; in this work phase, the adhesive bond is created between the surfaces to be soldered and the solder. In the next step, the pre-soldered surfaces are soldered together. In the case of suitably clean and well-prepared surfaces, the pre-soldering and soldering operations can be performed in one step by using fluxes.

The above-described solder joint can only be created between two metals, since no adhesive bonding force appears on the surface of semiconductors made of intermetallic materials, in other words, intermetallic compounds, no matter how thoroughly and thoroughly cleaned. Intermetallic semiconductors are semiconductors, whether pure or contaminated, in which the bonding force between atoms is of the electron pair type; in this structure, each atom is surrounded by four atoms of another type. In order to create a solder joint of such materials, another auxiliary material, namely another type of metal, for example silver, must be applied to the surface of the semiconductor object, the colloidal-sized parts of which adhere there. In addition to the use of silver colloid, metal sputtering processes are also known, in which a thin metal layer sprayed onto the semiconductor comes into adhesive contact with the semiconductor material. The adhesion between the metal used as such a second auxiliary material and the semiconductor ensures that the very small - colloidal size - metal particles adhere to the semiconductor. The soldering is already created between this adhered thin second metal layer and the metal to be bonded to the semiconductor, i.e. the soldering is thus practically carried out between two metals again.

In a known intermetallic semiconductor-to-metal soldering process, a colloidal silver alcohol solution is applied, sprayed, vaporized, or otherwise applied to the semiconductor surface, followed by heat treatment; this causes the silver particles to adhere to the semiconductor surface, and a cohesive bond is formed between the silver layer and the semiconductor. The silver can then be soldered, thus forming a bond between the semiconductor and the metal.

The known solder bonding processes for intermetallic semiconductors and metals described above are quite complicated, slow and expensive, and are difficult to automate.

The object of the invention is to provide a method by which a device, in particular a rod or bar used for thermoelectric modules, containing parts of intermetallic semiconductor material and metal material connected to each other by an electrically conductive and thermally conductive connection can be produced with less cost, work and time than currently known such methods, and the connection of the two different materials has excellent electrically conductive and thermally conductive properties in addition to the required mechanical strength.

The invention is based on the following findings:

intermetallic semiconductors and suitable connecting aids are, for example, solders known in the soldering art or similar in nature, which can be combined in the molten state by mixing them in an appropriate amount to form an alloy, by which a transitional boundary layer can be created between the semiconductor and the auxiliary material in such a way that it contains a small amount of semiconductor on one side and a small amount of auxiliary material on the other side. The transition from one state to the other is continuous, without an interface. The part of the boundary layer rich in auxiliary material must be on the side facing the metal to be connected to the semiconductor. In the case of such a boundary layer, the formation of the bond between the metal and the semiconductor does not require the use of another metal, which is unavoidable in the currently known solutions for similar purposes.

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We also realized that the boundary layer can be created by casting: the melting point of the dopant is necessarily lower than that of the semiconductor, so if we pour the molten intermetallic semiconductor onto the dopant-coated metal, the dopant will also melt, precisely because its melting point is lower than the melting point of the metal, and diffusion will occur at the interface between the two liquid-phase materials. Before the semiconductor solidifies, the desired alloy of the dopant and the semiconductor is formed. However, before the dopant diffuses into the deeper layers of the semiconductor material and thereby modifies the properties of the semiconductor, the semiconductor solidifies and a diffusion boundary layer is formed.

Based on the above findings, the task was solved by a method for producing devices, especially rods, for electrical modules, containing parts made of metal and intermetallic materials, connected to each other by an electrically conductive and thermally conductive connection, the essence of which is that the surface of the solid metal part intended for the connection is coated in its molten state with a bonding auxiliary material that is capable of adhesion with the metal material and diffusion with the semiconductor material also in the molten state, and has a lower melting point than that of the semiconductor material, and the semiconductor material is brought to the surface of the metal part coated with the bonding auxiliary material in a molten state and in a closed space that gives the shape of this part of the object, and then the semiconductor material is allowed to solidify.

According to a preferred embodiment of the method, the surface of the metal part to be connected is coated with a bonding aid with a thickness of 0.05-0.03 mm, preferably 0.01-0.02 mm.

According to another aspect of the invention, the bonding aid is applied by smearing, mixed with water, onto the surface of the metal part to be connected, and after this coating has dried/solidified, it is brought into contact with the molten semiconductor material.

A further embodiment of the method is characterized by providing one or both end surfaces of a metal rod with a bonding agent coating, and forming a rod or rods that are a continuation of this rod and connected to it or them by an electrically conductive and thermally conductive connection.

Preferably, the molten semiconductor material is fed to the solid metal part of the device in a closed space at a temperature of about 50-200 °C, preferably about 100-150 °C, lower than its melting point, at least the surface of which containing the bonding auxiliary material is also located in this closed space.

A further embodiment of the method is characterized in that the object is produced in an openable-closable mold, in such a way that a solid rod of metallic material with a connecting auxiliary material coating on one or both front faces is placed therein, which only partially fills the cavity of the mold in the longitudinal direction, but is connected to the inner mold surface bounding the cavity without gaps; and the space or spaces of the cavity left free by the rod of metallic material are filled with molten intermetallic semiconductor material, which, after solidification, forms an object with a semiconductor rod in the region of one or both ends, suitably a rod applicable to thermoelectric modules.

The invention will be described in detail below based on the attached drawings, which, on the one hand, illustrate the methods of creating a connection between the metal and the semiconductor material, and on the other hand, the

according to the invention process carried out in a mold

The method of implementation is illustrated in the drawings.

in Figure 1 a cross-section of a connection between a metal and a semiconductor with traditional soldering; in Figure 2 a connection similar to that in Figure 1 but made using the method of the invention is shown; Figure 3 larger scale detail A according to Figure 2; in Figures 4-6 a mold according to the invention is shown in schematic section, in different operational positions corresponding to the process steps; in Figure 7 The product made with the mold according to the invention according to Figures 4-6 is also shown in cross-section.

Figure 1 shows a connection - a joint - between two metal objects 1 and 2 formed by a conventional soldering process. It is clearly visible that the gap 3 of width g between the metal objects 1 and 2 is completely filled by the solder 4. It should be noted that even with the most precise manufacturing possible - the metals are worked in a solid state before soldering - there is always a joint gap between two metal objects. The adhesive connection was formed on the one hand between the metal object 1 and the solder 4, and on the other hand between the solder 4 and the metal object 2.

Figure 2 shows a longitudinal section of a rod 5 of the invention with a circular cross-section suitable for use in a thermoelectric module, which comprises a rod 6 of metallic material and a rod 7 of intermetallic semiconducting material, which are connected to each other by an electrically conductive and thermally conductive connection. It is also clear from a comparison of Figures 1 and 2 that the distance b between the rods 6 and 7 is significantly smaller than the distance b between the metal objects 1 and 2 of Figure 1, because - as we will see from the detailed description below - thanks to the feeding of the intermetallic semiconducting material melted into a liquid used in the method according to the invention by casting, the semiconducting material rod 7 takes on the exact shape of the metal material of the rod 6, and no gap needs to be filled, since there is no joint gap. The diffusion boundary layer between the rods 6 and 7 forming parts of the rod 5, ensuring their adhesive connection, is indicated by reference number 8 in Figure 2.

The method according to the invention for producing the 5 rods according to Figure 2 was carried out as follows:

The material of the rod 6 was copper, which is an electrically good conductor and a good thermal conductor, with a melting point of 1083 °C, and the rod 7 was made of an Sb-based intermetallic semiconductor material with a melting point of 630 °C, the composition of which was 98 wt% Sb and 2 wt% Cu. To form the electrically conductive and thermally conductive connection of the rods 6 and 7, a connecting auxiliary material with a melting point of 190 °C, a composition of 97 wt% Sn and 3 wt% Cu was used. The end of the copper rod 6 to be connected to the rod 7 - the flat front side - was coated with the aforementioned auxiliary material to a thickness of 0.010.02 mm in such a way that a mixture of 60 wt% of it mixed with water was applied to the end of the rod 6. The rod end with the layer applied in this way was heated to a temperature of 270 °C, kept at this temperature until the auxiliary material melted and the desired 0.01-0.02 mm thick coating was formed on the heat-treated part, then the rod end was cooled. The auxiliary material that may flow slightly from the end surface onto the rod's side surface does not affect the quality of the connection to be formed. The thickness of the coating can be controlled or adjusted by the amount of water mixed into the auxiliary material paste.

In the next step, the rods 5 consisting of the semiconducting material 7 rods and the electrically and thermally conductive and solidly mechanically connected rods 7 were formed by pouring the intermetallic semiconductor material of the rods 7 in a molten state, in an amount corresponding to the rods 7 to be formed, into a closed space at a temperature of 500-550 °C, at the end of the rods 6 coated with auxiliary material as described above, corresponding to the planned shape of the rods 7.

As a result of this operation, the auxiliary material melts, and diffusion occurs at the interface between the semiconductor present in the form of a melt and the molten auxiliary material, and before the semiconductor material solidifies, an alloy of these materials is formed. However, in a closed space with a temperature lower than the melting point of the semiconductor, the semiconductor solidifies before the solder diffuses into the deeper layers of the semiconductor and modifies its properties. At the same time, the formed diffusion boundary layer also ensures a perfect connection to the metal - in this case, the copper material of the 6 rods.

The above-described process and the diffusion connection formed between the rods 6 and 7 are shown on a larger scale in Figure 3 (Figure 2, detail A). The aforementioned transitional boundary layer is indicated in its entirety by the reference number 9 in Figure 3. It can be clearly seen in Figure 3 that the boundary layer 9 contains a much larger amount of auxiliary material in the layer part 9a on the side of the rod 6, i.e. the metal material, than the layer part 9b on the side of the rod 7, i.e. the semiconductor material, accordingly the layer part 9a is shown as much thicker than the layer part 9b.

It should be noted that the total thickness of the boundary layer 9 generally does not exceed 0.0ΙΟ.05 mm. As a result of the above, a suitable electrically conductive and thermally conductive connection was formed between the rods 6 and 5 without the use of any additional or supplementary metal material and without additional processing steps, and at the same time, the resulting product, i.e. the rod 5, has impeccable mechanical strength at the point of connection.

In Figures 4-6, a mold suitable for carrying out the method according to the invention, designated as a whole by the reference numeral 10, is shown, which has a lower part 10a and an upper part 10b that fit together. The lower part 10a comprises a cavity part 11a with a semicircular cross-section of radius r and a length h, and the upper part 10b comprises a cavity part 11b with the same cross-section, radius and length. Into the cavity part 11b, near its two ends, '

each opening 12 opens out. By placing the upper part 10b and the lower part 10a on top of each other, a closed cavity 11 with a diameter of 2r = d, and a length of h, of circular cross-section, is formed.

The production of a rod 16 shown in Figure 7, made of a semiconductor material at the two end portions and metal in the middle portion, with the mold 10 is carried out as follows;

In the lower part 10a of the mold 10, in the case of the present example, a rod 13 made of metal, for example red copper, of circular cylindrical shape and of length hj is placed in the middle, which fits seamlessly to the inner surface of the mold 10, and whose front faces 13a, 13b are coated with the previously mentioned connecting auxiliary material of about 0.015 mm thickness. Figure 4 shows the state immediately before insertion. The relationship hí < h exists between the length of the cavity 11 and the rod 13, so that when the upper part 11b is closed onto the lower part 10a - this situation was illustrated in Figure 5 - a free space 14 of length t}2 remains in the cavity 11 on both sides of the rod 13, so that the relationship h2 < hí exists here. The casting openings 12 open into these spaces 14.

In Figure 6, arrows c indicate the process of filling the spaces 14 of the mold 10 held at a temperature of 500 - 550 °C with the molten liquid intermetallic semiconductor material at a temperature of 650 °C. The temperature difference of about 100-150 °C is necessary so that the connecting auxiliary material applied to the end surfaces 13a, 13b of the rod 13 does not solidify immediately, since in this way the process detailed in connection with Figure 3 would not occur, but at the same time, during the solidification taking place in about 8 seconds at the mentioned temperature difference, the semiconductor material solidifies, the desired

........“ crystal structure is formed, the connection between the formed rods of semiconductor material 15 and the copper rod 13 takes place perfectly. The finished rod, designated as a whole by reference number 16, is also shown separately in Figure 7, which thus contains an intermediate rod 13 of metallic material and two semiconductor rods 15 firmly connected along the boundary layers 17 in a manner that ensures electrical and thermal conductivity thereto, forming a single member with it, which can be used in thermoelectric modules in an extremely efficient manner.

The beneficial effects of the invention are as follows:

The device produced by the process, for example a rod for use in thermoelectric modules, has excellent electrical and thermal conductivity, since the auxiliary material and the semiconductor material are connected to each other by a diffusion connection, in other words, the elementary particles diffuse into each other, so that free electrons can move more favorably. This also explains the excellent thermal conductivity of the device, which is a particularly favorable factor in thermoelectric modules, because electrons transmit heat in them, and heat generation will be more correct. The fact that an alloy is formed in the transition layer of the connection also contributes to the development of the excellent mechanical strength of the device.

The device according to the invention can be used under heat stress up to the melting point of the auxiliary material.

The process provides a high-quality product in all aspects and enables fast and economical production, as the additional metal and

-- - can be solved without the use of a flow agent, with a small number of operational steps, and also offers the possibility of automation.

The invention is of course not limited to the method of implementation detailed above, but can be implemented in various ways within the scope of protection defined by the claims.

Claims (6)

13 .........'' ^Clí ' Patent claims 1. Method for producing objects, in particular rods for electrical modules, comprising parts of metallic and intermetallic materials connected to each other by an electrically conductive and thermally conductive connection, characterized in that the surface of the solid metallic part intended for the connection is coated in its molten state with a bonding aid that is capable of adhesion with the metallic material and diffusion with the semiconductor material also in the molten state, and has a melting point lower than that of the semiconductor material, and the semiconductor material is supplied in a molten state and in a closed space giving the shape of this part of the object to the surface of the metallic part coated with the bonding aid, and then the semiconductor material is allowed to solidify. 2. Device according to claim 1, characterized in that the surface of the metal part to be connected is coated with a connecting auxiliary material with a thickness of 0.05-0.03 mm, preferably 0.01-0.02 mm. 3. Device according to claim 1 or 2, characterized in that the bonding aid is applied by smearing, mixed with water, onto the surface of the metal part to be connected, and after drying/solidification of this coating, it is brought into contact with the molten semiconductor material. 4. Device according to any one of claims 1-3, characterized in that one or both end surfaces (13a, 13b) of a metal rod (6; 13) are provided with a bonding auxiliary material coating, and a rod (7) or rods (15) are formed, which are a continuation of this rod (6; 13) and are connected to it or them by an electrically conductive and thermally conductive connection. 5. The device according to any one of claims 1-4, characterized in that the molten semiconductor material is fed to the solid metal part of the device in a closed space at a temperature of about 50-200 °C, preferably about 100-150 °C, lower than its melting point, at least the surface of which containing the connecting auxiliary material is also located in this closed space. 6. Method for implementing the method according to any one of claims 1-5, characterized in that the object is produced in an openable and closable mold (10), in such a way that a solid rod (13) made of metal with a connecting auxiliary material coating on one or both front faces is placed therein, which only partially fills the cavity (11) of the mold (10) in the longitudinal direction, but is connected to the inner mold surface bounding the cavity (11) without gaps; and the space or spaces (14) of the cavity (11) left free by the metal rod (13) are filled with molten intermetallic semiconductor material, which, after solidification, together with the metal rod (13) forms an object with an electrically conductive and thermally conductive, mechanically solid connection having a semiconductor rod (15) in the region of one or both ends, a rod (16) suitable for thermoelectric modules. The authorized person: