WO2010125411A1

WO2010125411A1 - Procedure for producing a device containing metal and intermetallic semiconductor parts joined together with an electrically conductive and heat conducting connection, especially a rod suitable for use with thermoelectric modules

Info

Publication number: WO2010125411A1
Application number: PCT/HU2009/000039
Authority: WO
Inventors: Kálmán CSÍKSZENTIMREI
Original assignee: Szenergia Kft.
Priority date: 2009-04-27
Filing date: 2009-04-27
Publication date: 2010-11-04

Abstract

The invention relates to a procedure for producing a device containing metal and intermetallic semiconductor parts joined together with an electrically conductive and heat conducting connection, especially a rod suitable for use with thermoelectric modules. The invention is based on that the surface of the solid metal part used for creating the connection is melted and coated with a binding additive suitable for realising an adhesion joint with the metal and a diffusion joint with the melted semiconductor, having a melting temperature lower than that of the semiconductor, and the semiconductor is melted and applied onto the surface of the metal part coated with the binding additive in a closed space determining the form of this part of the object, and then the semiconductor is left to harden.

Description

PROCEDURE FOR PRODUCING A DEVICE CONTAINING METAL AND

INTERMETALLIC SEMICONDUCTOR PARTS JOINED TOGETHER WITH AN

ELECTRICALLY CONDUCTIVE AND HEAT CONDUCTING CONNECTION,

ESPECIALLY A ROD SUITABLE FOR USE WITH THERMOELECTRIC

MODULES

The invention relates to a procedure for producing a device containing metal and intermetallic semiconductor parts joined together with an electrically conductive and heat conducting connection, especially a rod suitable for use with thermoelectric modules.

It is known that two metal objects are welded together by applying melted solder between them, as a result of which an adhesion is realised between the metals and the solder holding them together. Several additives referred to as flux in the given special field are used for realising adhesion, which additives ensure clean metal surfaces. It is necessary, because adhesion can only be realised on clean metal surfaces.

Reliable soldered joints are normally realised in several steps. The first step is preliminary soldering; in this work phase adhesion joint is realised between the surfaces to be soldered together and the solder. In the next step the preliminarily soldered surfaces are soldered together. In the case of appropriately clean and well prepared surfaces, as a result of the use of fluxes the preliminary soldering and soldering operation can be realised in one single step. The solder joint described above can only be realised between two metals, as on the surface of intermetallic semiconductors, that is semiconductors made of intermetallic compounds, however thoroughly cleaned, no adhesion power appears with respect to solders. Intermetallic semiconductors involve either clean or contaminated semiconductors, in which the bond between the atoms is created by electron pairs; in this structure each atom is surrounded by four atoms of a different type. In order to create a joint between such materials by soldering, a further additive, namely a different type of metal, for example silver needs to be applied on the surface of the semi- conductive object, the colloidal particles of which can adhere there. Beside the use of silver colloid, metalizing procedures are also known, where an adhesion joint is realised between the thin metal layer applied onto the semiconductor and the semiconductor. As a result of this type of adhesion joint between the metal used as a second additive and the semiconductor, the very small - colloidal - metal particles adhere to the semiconductor. Soldering is realised between this adhered second thin metal layer and the metal to be joined to the semiconductor, which means that in actual fact soldering is realised between two metals in this case again.

In the case of a known soldering procedure between an intermetallic semiconductor and a metal, the alcoholic solution of silver colloid is coated, spread, steamed or applied in any other way on the surface of the semiconductor, and then this surface is tempered; as a result of this the silver particles adhere to the surface of the semiconductor and a cohesion connection is realised between the silver layer and the semiconductor. Silver is suitable for soldering, therefore the joint is realised between the semiconductor and the metal.

The procedures described above for realising solder joints between intermetallic semiconductors and metals are rather complicated, slow and costly, and they are difficult to automate.

The task to be solved with the invention is to provide a procedure, in the course of which a device containing metal and intermetallic semiconductor parts joined together with an electrically conductive and heat conducting connection, especially a rod or stick suitable for use with thermoelectric modules can be produced by investing a smaller amount of costs, work and time than in the case of the presently known procedures, and the connection realised between the two different materials, beside having the required mechanical strength, also has excellent electrically conductive and heat conducting characteristics.

The invention is based on the following recognitions: intermetallic semiconductors and suitable binding additives - for example materials that are fluxes known by themselves in soldering anyway or materials of an equivalent nature -, when melted an mixed together to an appropriate extent, can be combined to form an alloy, with the help of which a transitional boundary layer can be created between the semiconductor and the additive, which layer contains a small amount of semiconductor on the one side and a small amount of additive on the other side. The transition from the one state to the other is continuous, without a boundary surface. The part of the boundary surface containing the additive must be positioned on the side facing the metal to be joined to the semiconductor. In the case of using such boundary layer no other metal is required to create a connection between the metal and the semiconductor, which is essential in the case of the presently known solutions for similar purposes.

We also realised that the boundary layer can be created by casting: the melting temperature of the additive needs to be lower than that of the semiconductor, so if the melted intermetallic semiconductor is poured onto the metal coated with the additive, the additive melts too, because its melting temperature is lower than the melting temperature of the metal, and diffusion takes place on the boundary surface between the two materials of a liquid state. Before the semiconductor hardens, the desired alloy of the additive and the semiconductor is formed. However, before the additive could diffuse into the deeper layers of the semiconductor and modify the characteristics of the semiconductor, the semiconductor hardens and the diffusion boundary layer is formed.

On the basis of the above recognitions the set task was solved using a procedure for producing devices containing metal and intermetallic parts joined together with an electrically conductive and heat conducting connection, especially rods suitable for use with thermoelectric modules, which is based on that the surface of the solid metal part used for creating the connection is melted and coated with a binding additive suitable for realising an adhesion joint with the metal and a diffusion joint with the melted semiconductor, having a melting temperature lower than that of the semiconductor, and the semiconductor is melted and applied onto the surface of the metal part coated with the binding additive in a closed space determining the form of this part of the object, and then the semiconductor is left to harden.

According to a favourable realisation of the procedure the surface of the metal part to be joined is coated with a 0.05-0.03 mm, favourably 0.01 -0.02 mm thick layer of binding additive.

In accordance with another feature of the invention the binding additive is mixed with water and spread onto the surface of the metal part to be joined, and after this coating has dried/hardened, it is contacted with the melted semiconductor.

A further realisation method of the procedure is characterised by that one or both end surfaces of a metal stick are coated with the binding additive, and a stick or sticks are created falling in the continuation of this stick and joined to it with an electrically conductive and heat conducting connection.

Favourably the melted semiconductor is applied to the solid metal part of the device in a closed space of a temperature about 50-200 ⁰C, favourably 100-150 ⁰C lower than the melting temperature of the melted semiconductor, and at least the surface of the above solid metal part containing the binding additive is also situated in the same closed space.

A further realisation method of the procedure is characterised by that the object is produced in a casting die that can be opened and closed, in such a way that a solid metal stick with one or both end surfaces coated with a binding additive is placed in the casting die only partly filling the hollow inside the casting die in a longitudinal direction but joining the internal surface of the casting die delimiting the hollow with a continuous joint; and the space or spaces of the hollow not filled in by the metal stick is filled with a melted intermetallic semiconductor, which, after it hardens, - together with the metal stick and joining the metal stick with a mechanically solid electrically conductive and heat conducting connection - forms an object having a semiconductor stick in the range around one or both of its ends, favourably a rod suitable for use with thermoelectric modules.

Below the invention is described in detail on the basis of the attached drawings, which illustrate different ways of creating a joint between the metal and the semiconductor on the one part, and the method of realising the procedure according to the invention inside a casting die on the part. In the drawings figure 1 shows a joint realised between a metal and a semiconductor using traditional soldering, in section; figure 2 shows a joint similar to the one shown in figure 1 , but created using the procedure according to the invention; figure 3 shows portion A as in figure 2, on a larger scale; figures 4-6 show a casting die according to the invention in a schematic section, in different operating positions suiting the steps of the procedure; figure 7 shows the product produced in a casting die as in figures 4-6 using the procedure according to the invention.

Figure 1 shows a joint - connection - realised between two metal objects 1 and 2 using traditional soldering. It can be seen that the gap 3 of a width a between the metal objects 1 and 2 is completely filled in by the flux 4. It is pointed out here that between two metal objects, even beside the most accurate procedure - when the metals are worked in a solid state before soldering -, there is always a joint gap. The adhesion joint is realised between the metal object 1 and the flux 4 on the one part and between the flux 4 and the metal object 2 on the other part.

Figure 2 shows a rod 5 according to the invention in longitudinal section, with a circular cross-section, suitable for use in a thermoelectric module, which rod 5 contains a metal stick 6 and an intermetallic semiconductor stick 7 joined together with an electrically conductive and heat conducting connection. When comparing figures 1 and 2 it can be seen that the distance Jb between the sticks 6 and 7 is significantly smaller than the distance b between the metal objects 1 and 2 shown in figure 1 , because - as it is explained below in detail - due to the fact that the intermetallic semiconductor melted into a liquid and used in the procedure according to the invention is entered by pouring, the semiconductor stick 7 assumes the exact shape of the metal stick 7, the gap does not need to be filled in as there is no joint gap. The diffusion boundary layer between the sticks 6 and 7 forming parts of the rod 5, ensuring the adhesion joint between them is marked with reference number 8 in figure 2.

The procedure according to the invention for producing the rod 5 shown in figure 2 was realised as below: stick 6 was made of red copper having favourable electrical conductivity and heat conducting characteristics and a melting temperature of 1083 ⁰C, while stick 7 was made of an Sb-based intermetαllic semiconductor of α melting temperature of 630 ⁰C, consisting of 98 mass% of Sb and 2 mass% of Cu. A binding additive of a melting temperature of 190 ⁰C consisting of 97 mass% of Sn and 3 mass% of Cu was used for creating electrically conductive and heat conducting connection between the sticks 6 and 7. The end - flat end surface - of the copper stick 6 to be joined to stick 7 was coated with a 0.01-0.02 mm thick layer of the above binding additive, so that a mixture of the said binding additive and water of an amount forming 60 mass% of the binding additive was applied onto the end of the stick 6. The stick end coated with a layer applied in this way was heated to a temperature of 270 ⁰C and kept at this temperature until the additive melted and the desired 0.01 -0.02 mm thick coating was created on the part tempered in this way, and then the stick end was cooled down. The additive possibly slightly dripping from the end surface onto the curved surface of the stick does not influence the quality of the joint created. The thickness of the coating can be changed or adjusted depending on the amount of water mixed to the additive paste.

In the following step the rod 5 consisting of a semiconductor stick and a stick 7 joined to it with an electrically conductive and heat conducting solid mechanical connection was created in such a way that the intermetallic semiconductor material of the stick 7 - in a melted state and of an amount suiting the stick 7 to be created - was poured onto the end of the stick 6 coated with an additive as above, into a closed space of a temperature of 500- 550 ⁰C and of a shape suiting the shape of the stick 7. As α result of this operation the additive melts and diffusion takes place on the boundary surface between the semiconductor present in the form a melt and the melted additive, and an alloy of these materials is created before the semiconductor hardens. However, in the closed space having a temperature lower than the melting temperature of the semiconductor, the semiconductor hardens before the flux could diffuse into the deeper layers of the semiconductor and modify its characteristics. At the same time the diffusion boundary layer created ensures a perfect joint with the metal, in the present case with the copper material of the stick 6.

The process described above and the diffusion joint realised between the sticks 6 and 7 is illustrated in figure 3 on a larger scale (portion A in figure 2). In figure 3 the transitional boundary layer mentioned above is marked with reference number 9 as a whole. It can be seen in figure 3 that the boundary layer 9, in the layer potion 9a facing stick 6, that is the metal, contains significantly more additive than in the layer portion 9b facing stick 7, that is the semiconductor; in accordance with this layer part 9a is shown significantly thicker than layer part 9b.

It is pointed out here that generally the total thickness of the boundary layer 9 is not more than 0.01 -0,05 mm. It follows from the above that even without the use of any additional or supplementary metal or additional procedural steps, an appropriate electrically conductive and heat conducting connection was realised between the sticks 6 and 7, at the same time the product created, that is the rod 5, is perfectly strong at the place of the joint from a mechanical aspect too. Figures 4-6 show α casting die suitable for realising the procedure according to the invention, marked with reference number 10 as a whole, having a lower part T Oa and an upper part 10b joining each other. The lower part 10a contains a hollow portion 1 1 a of an Jn length and a semi-circular cross-section of an r radius, while the upper part 10b contains a hollow portion l i b of the same cross-section, radius and length. A slot 12 leads into the hollow portion 1 I b near both ends. When the upper part 10b and the lower part 10a are placed on top of each other, a closed hollow 1 1 of a circular cross-section, of a diameter of 2r=d and obviously of an h length is created.

The rod 16 shown in figure 7, the two end parts of which are made of a semiconductor and the central part of which is made of metal, is produced using a casting die 10 as described below:

In the lower part 1 Oa of the casting die 10, in the middle in the case of the present example, a cylindrical stick 13 made of metal, for example red copper, of an hi length is placed, joining the internal surface of the casting die 10 with a continuous joint, with its end surfaces 13a, 13b coated with an approximately 0.015 mm thick layer of binding additive mentioned above. Figure 4 illustrates the state directly preceding such placement. The relationship hi < h is valid in respect of the length of the hollow 1 1 and the stock 13, so when the upper part 10b is placed on the lower part 10a - this position is illustrated in figure 5 -, a free space 14 of an h2 length remains on both sides of the stick 13 inside the hollow 1 1 , in such a way that the relationship £12 < hi is valid. The pouring slots 12 lead into these spaces 14. In figure 6 arrows c indicate the process of filling up the spaces 14 of the casting die 10 kept at a temperature of 500-550 ⁰C with melted liquid intermetallic semiconductor of a temperature of 650 ⁰C. The temperature difference of about 100-150 ⁰C is needed to prevent the binding additive applied onto the end surfaces 13a, 13b of the stick 13 from setting immediately, as in the opposite case the process described in connection with figure 3 could not take place, and at the same time during the setting that takes place in about 8 seconds beside the above temperature difference the semiconductor hardens, the necessary crystal structure is created, and the joint between the semiconductor sticks 15 created and the copper stick 13 is realised perfectly. The finished rod marked with reference number 16 as a whole is shown separately in figure 7, it contains a metal intermediate stick 13 and two semiconductor sticks 15 encasing it and joining it along the boundary layers 17 with a stable connection ensuring electric and heat conduction, forming one single member, which can be used extremely efficiently in thermoelectric modules.

The favourable effects relating to the invention are the following: the device produced with the procedure, for example a rod suitable for use in thermoelectric modules, has excellent conductivity, as the additive and the semiconductor are connected to each other with a diffusion joint, in other words the elementary particles diffuse into each other allowing free electrons to move more favourably. It also explains the excellent heat conduction of the device, which is an especially favourable factor in thermoelectric modules, where heat is conducted by electrons and heat evolution becomes more correct. The factor that an alloy is created in the transitional layer of the connection also contributes to the excellent mechanical strength of the device.

In the case of a thermal load the device according to the invention can be used below the melting temperature of the additive.

The procedure, which provides a product of excellent quality from every aspect, enables fast and economic production, as it can be solved without using any additional metal or flux generally used in soldering, in only a few steps, and it also makes automation possible.

Obviously the invention is not restricted to the realisation method of the procedure described above in detail, but it can be realised in several different ways within the scope of protection defined in the claims.

Claims

1. Procedure for producing devices containing metal and intermetallic parts joined together with an electrically conductive and heat conducting connection, especially rods suitable for use with thermoelectric modules, characterised by that the surface of the solid metal part used for creating the connection is melted and coated with a binding additive suitable for realising an adhesion joint with the metal and a diffusion joint with the melted semiconductor, having a melting temperature lower than that of the semiconductor, and the semiconductor is melted and applied onto the surface of the metal part coated with the binding additive in a closed space determining the form of this part of the object, and then the semiconductor is left to harden.

2. Device as in claim 1 , characterised by that the surface of the metal part to be joined is coated with a 0.05-0.03 mm, favourably 0.01-0.02 mm thick layer of binding additive.

3. Device as in claim 1 or 2, characterised by that the binding additive is mixed with water and spread onto the surface of the metal part to be joined, and after this coating has dried/hardened, it is contacted with the melted semiconductor.

4. Device as in any of claims 1-3, characterised by that one or both end surfaces (13a, 13b) of a metal stick (6; 13) are coated with the binding additive, and a stick (7) or sticks (15) are created falling in the continuation of this sticks (6; 13) and joined to it with an electrically conductive and heat conducting connection.

5. Device as in any of claims 1 -4, characterised by that the melted semiconductor is applied to the solid metal part of the device in α closed space of a temperature about 50-200 ⁰C, favourably 100-150 ⁰C lower than the melting temperature of the melted semiconductor, and at least the surface of the above solid metal part containing the binding additive is also situated in the same closed space.

6. Procedure for the realisation of the procedure as in any of claims 1-5, characterised by that the object is produced in a casting die (10) that can be opened and closed, in such a way that a solid metal stick (13) with one or both end surfaces coated with a binding additive is placed in the casting die (10) only partly filling the hollow (1 1 ) inside the casting die (10) in a longitudinal direction but joining the internal surface of the casting die (10) delimiting the hollow (1 1 ) with a continuous joint; and the space or spaces (14) of the hollow (1 1 ) not filled in by the metal stick (13) is filled with a melted intermetallic semiconductor, which, after it hardens, - together with the metal stick (13) and joining the metal stick (13) with a mechanically solid electrically conductive and heat conducting connection - forms an object having a semiconductor stick (15) in the range around one or both of its ends, favourably a rod (16) suitable for use with thermoelectric modules.