Paste for producing a joint connection, use of said paste, and method for establishing a joint connection

Abstract

The invention relates to a paste for establishing a joint connection between parts or joining partners, comprising at least one metal component. According to the invention, metal oxide particles and / or metal mixed oxide particles and / or a mixture of metal oxide particles are used as the metal component, an inert polyether is provided as the solvent, and a reducing agent is contained which reduces the metal oxide particles and / or metal mixed oxide particles and / or the mixture of metal oxide particles during heating and at least partially escapes. The invention further relates to the use of a paste according to the invention for electrically, mechanically and / or thermally connecting at least two parts or joining partners by means of a sintering method. Finally, the concept of the invention also comprises a method containing at least the following steps: - applying the paste to at least one first part, - placing at least one further part such that the applied paste is arranged between the two parts on the surfaces thereof to be connected.

Description

[0001] Paste for creating a joining joint, as well as the use of this paste and methods for creating a joining joint

[0002] The invention relates to a paste for creating a bond, a use of this paste, and a joining method. The bond makes it possible to join electronic components as well as components with metallic surfaces, but also those made of ceramic or glass, of various sizes and dimensions, such as pipes, plates, electronic components, etc.

[0003] Soldering is a well-established and proven method for electrically connecting electronic components, used in the field for decades. Over the years, the demands placed on such soldered connections, particularly regarding durability, have steadily increased. These demands are especially high in modern high-performance electronics, in offshore applications, electric vehicles, and so on. These electronics often have very fine structures, must withstand harsh external conditions, and / or exhibit exceptional durability and a long service life.

[0004] These types of electronic components are increasingly being sintered rather than soldered. Instead of solder, a sintering paste containing metallic particles is used. During the sintering process, not the entire contact between the components and the solder melts as it does in soldering; instead, only the surfaces of the particles in the sintering paste melt and, upon solidification, fuse together with each other and with the surfaces being joined.

[0005] EP 4 324 578 Al and WO 2022 / 214228 Al describe pastes for sintering electronic components. The metallic component is silver in the form of silver flakes and silver particles coated with a special material. Aliphatic solvents are also specified. A disadvantage of using silver sintering pastes is the high price of silver, which in turn makes the sintering process expensive. Furthermore, the sintering process often requires a protective gas atmosphere, usually consisting of nitrogen and / or formic acid. The components to be joined are also subjected to increased pressure during the sintering process. Consequently, the necessary equipment is complex and expensive.

[0006] Another option for a paste is to use copper as the metallic material. This is less expensive than silver, but also less noble. To prevent corrosion or oxidation of the copper and thus a poorer sintering result, the sintering process must also take place under a protective atmosphere, for example, under a nitrogen and / or formic acid atmosphere and increased pressure. This also makes the sintering process complex and expensive.

[0007] EP 2 799 164 Al describes a paste that can contain metal particles made of different metals or alloys thereof, namely copper, silver, gold, nickel, palladium, platinum, or aluminum. These metal particles may also be partially oxidized, for example, surface-oxidized. The oxygen content of these metal particles is preferably in the range of 0.01 to 0.15 wt% based on the total weight of the metal particles. Furthermore, the metal particles have a coating consisting of one or more aliphatic compounds. However, the coating of the metal particles represents an additional manufacturing step, which increases the cost of producing the paste. A pressureless sintering process is also described. However, the time required for this pressureless process is very long, at one hour, which also makes the process expensive.

[0008] EP 4 306 234 Al describes a process for producing a sintering paste from elemental copper, a binder, copper formate, and a complexing agent. To create a sintered joint using the sintering paste produced in this way, increased pressure on the components to be joined and a protective atmosphere of nitrogen or a nitrogen-formic acid mixture are again necessary, which, as already described, makes the process expensive.

[0009] US Patent 2008 / 0237851 describes, among other things, a process for manufacturing a semiconductor device in which an electrode of a semiconductor element is connected to a conductor. For this purpose, a bonding material containing copper oxide and a reducing agent is applied to the surface of the semiconductor device to be connected and then heated under a reducing atmosphere, such as hydrogen, to create a conductive connection. A nitrogen atmosphere is used for cooling. As already mentioned, this process is complex and expensive to implement using the necessary equipment.

[0010] German patent DE 10 2011 083 893 Al describes a starting material for a sintered compound. This consists of sinterable particles of a metal or a metal compound such as a metal oxide and a flux, which simultaneously acts as a solvent and a reducing agent. Additional inert solvents are explicitly not used. However, this has the disadvantage that reduction of the metal oxide can occur even before the sintering process, and the starting material may therefore have a limited lifespan.

[0011] The object of the invention is therefore to avoid the aforementioned disadvantages and to provide a paste that is more cost-effective to produce and in which the joining process can be carried out under normal atmospheric conditions and without increased pressure, enabling the formation of joints not only on metallic surfaces but also with ceramic materials and glass. Furthermore, the invention aims to provide a use for such a paste and to develop a method for joining the aforementioned components. These objectives are achieved by the characterizing features of claims 1, 12, and 14, which are of particular importance as follows. It should be explained at the outset that the term "metallic component," as used in this document, includes both elemental metals and alloys as well as metal compounds, in particular metal salts and mixed metal salts such as metal oxides and mixed metal oxides.The components or joining partners that are connected can have almost any shape and size, from electronics or high-performance electronic components to tubes, plates and other shaped objects with at least one metallic or metal-coated surface, or made entirely or partially of ceramic or glass.

[0012] According to the invention, the metallic component used is metal oxide particles and / or mixed metal oxide particles and / or a mixture of metal oxide particles. These are already oxidized and can therefore be processed under normal atmosphere; a protective atmosphere is not required. An inert polyether serves as the solvent for the paste according to the invention. This also includes a mixture of different polyethers, which is expressly encompassed by the invention. The addition of the polyether reduces the paste's susceptibility to oxygen. To regenerate elemental metal from the metal oxide, mixed metal oxide, or mixture of metal oxide particles, which forms an electrical, mechanical, and / or thermal connection between the components, at least one reducing agent is added to the paste. During joining, this reducing agent reduces the metal oxide, mixed metal oxide, or mixture of metal oxide particles.The mixture consists of metal oxide particles, so that elemental metal is regenerated. The reducing agent itself has such a low boiling point that it at least partially evaporates during joining. This allows for the simple and cost-effective creation of an electrical, mechanical, and / or thermal connection between the components or joining partners. The paste is also significantly less expensive to produce than, for example, a silver sintering paste. This makes it economically viable to join larger components using the paste according to the invention. In a particularly preferred embodiment, the reducing agent evaporates completely during the joining process, leaving no residue. Additional cleaning of the joint is then unnecessary, further reducing the costs of the process.

[0013] Preferably, an aromatic compound is used as the reducing agent; more preferably, a 1,3,4-substituted aromatic compound is used; and most preferably, the reducing agent is selected from the group of benzoic acid derivatives and / or benzaldehyde derivatives. Mixtures of different substances are also possible. Furthermore, the reducing agent can be selected to be harmless to health and the environment, which offers advantages for operators and the environment.

[0014] In a preferred embodiment, the metal oxide particles and / or mixed metal oxide particles are nanostructured and / or nanoporous. This allows for a particularly good and uniform distribution of the particles in the paste, resulting in a particularly good and uniform joining result.

[0015] In one embodiment, copper(II) oxide particles are used as the metal oxide particles. The resulting compound exhibits good thermal and electrical properties. This is particularly advantageous for the fabrication of connections between electronic components, especially for high-performance electronics.

[0016] In one embodiment, a PEG (polyethylene glycol) can be used as the inert polyether in the paste. This is readily available in various forms at low cost. This makes it possible to adjust the consistency of the paste as desired by adding PEGs or other inert polyethers. Of course, other similarly acting polyethers or a mixture of different polyethers can also be used. In a preferred embodiment, the proportion of metal oxide particles and / or mixed metal oxide particles and / or the mixture of metal oxide particles in the paste is between 30 wt% and 70 wt%, preferably between 50 wt% and 60 wt%. The proportion of reducing agent is preferably around 20%. The remainder of the paste consists of the polyether and, if applicable, excipients. The metal oxides or mixed metal oxides used are...The mixture of metal oxide particles may include, but is not limited to, the oxides of copper, zinc, iron, magnesium, cobalt, nickel, manganese, tin, gallium, chromium, gold, silver, antimony, aluminum, platinum, palladium, and their alloys. Metal oxides and mixed metal oxides containing 30 wt% to 100 wt% copper oxide and / or 30 wt% to 100 wt% silver oxide are particularly preferred.

[0017] In a particularly preferred embodiment, the reducing agent is applied externally to the metal oxide particles and / or mixed metal oxide particles and / or the mixture of metal oxide particles and / or is embedded in the pores of the particles. The metal oxide particles and / or mixed metal oxide particles and / or the mixture of metal oxide particles then serve as a binder for the reducing agent. This results in a particularly good and uniform distribution of the reducing agent within the paste.

[0018] Furthermore, the invention also encompasses the use of a paste according to the invention for joining components. In this process, two or more components are electrically, mechanically, and / or thermally joined together by a sintering process.

[0019] Another use of the paste is in the production of a conductive structure on a substrate, such as a ceramic substrate or similar material. This allows, for example, the production of printed circuit boards and similar objects for contacting electronic components.

[0020] Furthermore, the invention comprises an additional solution tailored to the paste, namely a sinter flux. This contains ascorbic acid and / or adipic acid in aqueous or alcoholic solution, which makes it possible to join a wider range of materials such as metals or their alloys, including, for example, iron, brass, aluminum and their alloys, as well as glass and ceramics, in addition to copper. This opens up further fields of application for the paste and the process according to the invention.

[0021] Finally, the invention also includes a method for producing a joining connection between at least two components using the paste according to the invention described above. The method steps comprise:

[0022] Applying the paste to at least one first component

[0023] Place at least one additional component so that the applied paste is positioned between the two components on their surfaces to be joined.

[0024] The paste can be printed onto at least one of the components. Pad printing and / or screen printing are particularly common methods, but other printing processes are also possible. Of course, other methods of applying the paste to the component are conceivable, especially, but not exclusively, dispensing, jetting, pin transfer, and / or spraying.

[0025] The joining process creates a connection between the components that is suitable for any type of structure, both very large and very fine, and provides a secure and long-lasting electrical, mechanical and / or thermal contact.

[0026] In one embodiment, the components are subjected to a thermal treatment for a certain period of time to reduce the metal oxide, mixed metal oxide, or mixture of metal oxide particles, thereby creating the bond. The temperature can be approximately 250 °C. The duration of this treatment can be between 5 and 10 minutes, preferably 8 minutes. During this process, the metal oxide, mixed metal oxide, or mixture of metal oxides is thoroughly reduced, and the remaining reducing agent, as well as other products formed by the oxide reduction, evaporate.

[0027] In another method according to the invention, the paste is heated before being applied to the surface of a joining partner, thus eliminating the need for thermal treatment of the components. The paste can be contained in a cartridge that can be heated, at least partially, and applied directly to the surface of the component to be joined. This saves on the costs of thermal treatment. The components are protected because they do not have to be exposed to high temperatures, which is a significant advantage, especially for electronic components.

[0028] Before applying the paste, some or all of the surfaces to be joined can be pre-treated, either partially or completely, with a sintering flux. The sintering flux can be sprayed onto the surface in question. This can then be followed by a drying process. If the sintering flux is an alcoholic solution, this drying process can be faster than with an aqueous solution.

[0029] Finally, it should be noted that the embodiments presented here are merely exemplary configurations of the invention. The invention is not limited to these. Further modifications and adaptations are possible. For example, a different reducing agent can be selected. The paste can also contain additional additives beyond those mentioned here. The invention encompasses the use of metal oxides and / or mixed metal oxides and a suitable reducing agent to create a bond between at least two joining partners. These partners can have virtually any shape and size. It is possible to join joining partners made of the same material as well as those made of different materials.

Claims

Patent claims:

1. Paste for producing a joining connection between at least two components, containing at least one metallic component, characterized in that the metallic component consists of metal oxide particles and / or mixed metal oxide particles and / or a mixture of metal oxide particles, that an inert polyether is provided as a solvent, and that a reducing agent is included which, upon heating, reduces the metal oxide particles and / or mixed metal oxide particles and / or the mixture of metal oxide particles and thereby at least partially escapes.

2. Paste according to claim 1, characterized in that the reducing agent has such a low boiling point that it evaporates completely and without residue during the joining process.

3. Paste according to claim 1 or 2, characterized in that an aromatic compound serves as the reducing agent.

4. Paste according to claim 3, characterized in that a 1,3,4-substituted aromatic compound serves as the reducing agent.

5. Paste according to claim 3 or 4, characterized in that at least one derivative of benzoic acid and / or benzaldehyde serves as a reducing agent.

6. Paste according to any one of claims 1 to 5, characterized in that the metal oxide particles and / or mixed metal oxide particles and / or the Mixture of metal oxide particles are nanostructured and / or nanoporous.

7. Paste according to one of claims 1 to 6, characterized in that the metal oxide particles are copper(II) oxide particles.

8. Paste according to one of claims 1 to 7, characterized in that the paste contains a PEG as an inert polyether.

9. Paste according to any one of claims 1 to 8, characterized in that the proportion of metal oxide particles and / or mixed metal oxide particles and / or the mixture of metal oxide particles is 30 wt%-70 wt%, preferably 50 wt% to 60 wt%.

10. Paste according to one of claims 1 to 9, characterized in that the proportion of reducing agent is approximately 20 wt%.

11. Paste according to one of claims 1 to 10, characterized in that the reducing agent is arranged on the metal oxide particles and / or metal mixed oxide particles and / or the mixture of metal oxide particles and / or in the pores of these particles.

12. Use of a paste according to any one of claims 1 to 11 for joining at least two components by a sintering process.

13. Use of a paste according to any one of claims 1 to 11 for generating at least one conductive structure.

14. A method for producing a joining connection between two components using a paste according to any one of claims 1 to 11, comprising the following steps: Applying the paste to at least one first component Place at least one additional component so that the applied paste is positioned between the two components on their surfaces to be joined.

15. Method according to claim 14, characterized in that the components are subjected to a thermal treatment in order to produce the joining connection.

16. Method according to claim 15, characterized in that the temperature during the thermal treatment of the components is approximately 250°C.

17. Method according to one of claims 14 to 16, characterized in that the components are thermally treated for 5 to 10 minutes, preferably 8 minutes.

18. Method according to claim 14, characterized in that the paste is heated before being applied to the surface of the at least one component.

19. Method according to one of claims 14 to 18, characterized in that at least one of the surfaces to be joined is treated with a sinter flux before the paste is applied.

20. Method according to claim 19, characterized in that the sinter flux is allowed to dry before the paste is applied.

21. Method according to one of claims 19 or 20, characterized in that the sinter flux contains ascorbic acid and / or adipic acid in aqueous or alcoholic solution.