Joining processes for thermally sensitive structures

Abstract

Joining method for thermally sensitive structures for the production of ceramic hybrid components for electrical engineering and electronics, wherein two components are functionally connected using a joining aid designed as a reactive nanofoil, in that the nanofoil is first introduced between associated surface sections of the components to be joined and subsequently causes an at least partial formation of a connecting structure, wherein activation of the nanofoil initially melts a largely solid solder connecting layer on both associated surface sections of the components to be joined, and wherein the melting material, which is locally limited to one surface section, is subsequently mixed with the likewise locally limited melting material of the opposite surface section and the residues of the reactants of the nanoreactive film system in such a way thatthat after cooling and solidification of the entire melt material, a functional brazing joint is formed, wherein the thermal load required for melting is introduced only within the contour sections of the contacts to be joined exclusively on brazing connection layers of the brazing layer system, characterized in that the wetting with brazing material on the surface sections to be brought into operative connection with one another takes place before the actual joining process and in each case temporally and spatially independently of one another.

Description

[0001] The invention relates to a joining method for thermally sensitive structures, wherein two components are functionally connected using a joining aid designed as a reactive nanofoil, in that the nanofoil is first introduced between associated surface sections of the components to be joined together and subsequently causes an at least partial formation of a connecting structure.

[0002] For numerous technical applications, components, assemblies and the like must be joined together, whereby modern processes are increasingly being used alongside long-established joining techniques such as welding, gluing or screwing.

[0003] A typical example is electronic components that are joined by first introducing a solder material between two operatively connected surfaces of the respective components and then heating the structure and the solder. The high heat input is problematic, which can cause heat damage, particularly to temperature-sensitive structural components. However, the high heat input is necessary to achieve a sufficiently high joining temperature and wetting with solder material over the entire joining surface. This means that the limit temperature of sensitive components is sometimes exceeded, with not only the actual joining or contact point being heated, but also a section of the component next to the actual joining point. To avoid such disadvantages, soldering is predominantly used to join materials that are significantly more heat-stable than the respective solder material.However, this also results in disadvantages. For example, considerable amounts of energy are required to heat the parts to be joined, and structures adjacent to the joint, whose thermal tolerance is below the joining temperature, are damaged if the parts are heated thoroughly.

[0004] DE 10 2007 020 389 B4 describes a method for joining components for the aerospace sector, whereby a nano- or microstructured material is placed between the components to be joined.

[0005] DE 10 2008 060 116 A1 describes a method for producing a bearing assembly, wherein a solder layer is placed before machining begins or a solder coating is applied in the area of the contact surface.

[0006] An interesting alternative to this is known from the older application DE 10 2012 014 711 A1. This solution describes a joining process for forming composite structures between at least two components, which is suitable for structures with critical joining temperatures and simultaneously achieves very good mechanical properties. A reactive nanofoil is used as the joining aid, which, in an advantageous embodiment, can be ignited multiple times in a temporally and / or spatially distributed manner, thus achieving optimized energy utilization. Initial practical tests suggest that this technical solution has broad application possibilities, for example, for joining components within spatial structures where the joining surfaces are not mechanically accessible from the outside or for components where the joining temperature is very close to the maximum permissible thermal load of the components to be joined.

[0007] However, there is still a need for development in order to achieve both sufficient soldering and a permanently stable connection, particularly at the contact surfaces of the components to be joined.

[0008] The object of the present invention is to provide a technical solution with which a brazing contact can be produced using a heat source that is thermally, temporally and spatially limited and independent of the environment.

[0009] This task is solved by wetting the surface sections to be joined with solder material before the actual joining process and in a temporally and spatially independent manner.

[0010] The fundamental solution therefore consists in the formation and use of contact surfaces with a prefabricated solder layer system. This opens up numerous possible applications, with a preferred application being processes for the production of ceramic hybrid components for electrical engineering and electronics, which have previously been realized with soft solder, glass-fixed pond joints, beam solder, laser soldering, or even welding. This allows electronic and electrical components to be contacted with hard solder, with the resulting contacts being permanently resilient to temperatures of over 500°C.

[0011] A further advantage arises from the use of reactive nanofoil as a heat source. This reduces handling and energy expenditure during the joining process by precisely limiting the thermal energy input into the joining zone. Furthermore, it ensures that the necessary joining temperatures are generated only at the joining surfaces and without adversely affecting other structural sections.

[0012] The measures necessary to achieve the functionally required solder wetting and adhesion strength in the active bond between solder material and contact material are carried out as upstream process steps outside of the actual joining process. Consequently, processes and interactions regarding diffusion and immission between the solder material and the contact material are realized during the production of the contact component, temporally and spatially independent of the formation of the brazed joint. After completing the production of a function-specific solder base layer on the contact semi-finished product, another solder layer is applied, which forms a material bond with the solder base layer during application.The material layer combined in this way is designed as a solder bonding layer and serves to melt and fuse with residues of the reactants of the nanoreactive film system and the solder bonding layer that has been applied on the side opposite the contact semi-finished product.

[0013] The technical solution according to the invention overcomes deficiencies of the prior art, in particular: To achieve a material-to-material bond between the solder material, sometimes considerable temperatures are required to make the surface structure of the contact material and the solder material wettable. To ensure wetting, it may be necessary to change the crystal phase and / or the chemical composition of the contact surface material through heating. This requires a certain amount of time. The liquid phase of the solder material must have a specific ratio to the surface properties of the contact in order to be able to adhere to the surface. Furthermore, the interaction of adhesion and cohesion also requires time and heat so that the liquid solder material can establish contact with the joining partners. For various joining material pairs, chemical transformations of the solder joints and the contact surface are necessary so that an adhesion-promoting layer can build up.These diffusion and immission processes typically occur over long periods of time and at high temperatures, as well as under specific atmospheric conditions. The proposed procedure therefore offers significant advantages, which are briefly outlined below: - quick production of a final joint - precise dosage of the required joining heat - sensitive components of electronic assemblies are subjected to only minimal thermal stress by prefabricating housing contacts with an adapted brazing layer system, which are used to assemble ceramic circuit boards and contacted with nanofilms as heat sources - the component system is capable of withstanding extremely high temperatures in its entirety and therefore does not require air conditioning, as is necessary, for example, with soft solder constructions - Decoupling of the criteria of adhesion growth, wetting processes and artificial aging processes to reduce thermal-mechanical stresses, resulting in an increase in the thermal cycle stability of the contact surfaces

[0014] Exemplary embodiments of the invention are explained in more detail below with reference to the drawings. They show: Fig. 1 the structure and functional assignment of the elements of a solder layer system in the initial state Fig. 2 Details for ensuring the desired wetting and adhesion properties Fig. 3 that after Fig. 1 / 2 prepared solder layer system in processable condition Fig. 4 the arrangement of the complete solder layer system when joining the contact surfaces Fig. 5 Joining the solder layer system using nanoreactive joining aids Fig. 6 the processing of the solder layer system during joining

[0015] The embodiment illustrated in the drawing relates to electronic components that essentially consist of several active electronic components, each with an internal and external contact system, as well as an enclosing and supporting housing. The housings are intended to protect the highly sensitive electronic components within the housing. According to the invention, such housings can now advantageously be joined using brazing solder.

[0016] Regardless of differences in detail depending on the specific materials used, sufficient wetting with the solder material is always achieved when joining the joining partners. Diffusion processes and adhesion layer growth on the joining surface of one joining partner are realized during the production of the joining surface in the form of an adhesion-optimized solder base layer with appropriate wetting properties.

[0017] In addition, a further solder layer is designed as a solder bonding layer on the solder base layer. This layer is cohesive and provides the molten solder for the connection to the other joining partner. Furthermore, depending on the specific contacting task, a further solder-containing layer can be designed as a heat management solder layer between the solder base layer and the solder bonding layer, allowing the heat balance to be specifically influenced.

[0018] To realize the soldering process by melting the outer cover layer, the solder bonding layer is designed in such a way that this solder layer is melted using a limited amount of heat. The melting of the left and right-sided solder bonding layers creates a material-tight bond between the left and right-sided solder layer systems and residues of the reactants of the nanoreactive foil system, and thus between the components to be joined. During the nanoreactive process, the structure of the nano-layer system is transformed into a slab-like foil structure. By melting the left and right-sided solder bonding layers, a solder connection is created on the surfaces of the slabs with the opposite joining partner, and cracked edges of the slabs create a material-tight bond between the right and left solder layer systems.

[0019] Nanoreactive heat generation with a spatially, temporally, and thermally limited heat source is achieved by using a nanoreactive layered foil system as the heat source for melting. This system generates a limited amount of heat over a limited period of time as a result of an intermetallic reaction. The nanoreactive foil must be selected to ensure melting of the solder bonding layer without damaging the underlying solder layer (or several existing layers). Furthermore, the nanoreactive foil is selected to form an open-pored or slab-like residual structure that bonds with the solder melt and, through its open pores and gaps, establishes a connection with the melt of the opposite solder bonding layer.The residual structure of the reactants of the nanoreactive foil system thus remains in the joint and forms part of the final solder layer system. List of reference symbols 1.1 Joining / contact surface 1.2 Material of the solder base layer for realizing the solder connection with the contact surface 1.3 Material of the solder bonding layer to realize the connection of the solder material with the solder bonding layer of the opposite contact surface 2.1 Joining / contact surface 2.2 Solder base layer with optimal wetting to the contact surface 2.3 Supporting measures for wetting to optimize the adhesion of the solder layer system 3.1 Joining / contact surface 3.2 Solder base layer with optimal wetting to the contact surface 3.3 Application of the solder bonding layer 3.4 Solder bonding layer 3.5 Contact surfaces with solder layer system in processable condition 4.1 left-side joining / contact surface 4.2 Left-side solder base layer with optimal wetting to the contact surface 4.3 Left-side solder bonding layer 4.4 foil-like nanoreactive layer system as a heat source for melting the solder bonding layers 4.5 right-side solder bonding layer 4.6 Right-side solder base layer 4.7 right-hand joining / contact surface 4.8 Joining directions 5.1 left-side joining / contact surface 5.2 Left-side solder base layer with optimal wetting to the contact surface 5.3 Solder bonding layer 5.4 Initialization of the intermetallic reaction in the nanoreactive layer system 5.5 fused solder bonding layers 5.6 Residues (of the reactants) of the foil-like nanoreactive layer system after use as a heat source 5.7 exothermic intermetallic reaction front in the nanoreactive layer system 5.8 Direction of the exothermic intermetallic reaction front 5.9 Right-side solder base layer 5.10 right-hand joining / contact surface 5.11 foil-like nanoreactive layer system in which no intermetallic reaction has yet taken place 6.1 left-side joining / contact surface 6.2 Left-side solder base layer with optimal wetting to the contact surface 6.3 fused solder bonding layers 6.4 Residues (of the reactants) of the foil-like nanoreactive layer system after use as a heat source 6.5 right-side solder base layer 6.6 right-hand joining / contact surface

Claims

[1] Joining process for thermally sensitive structures for the production of ceramic hybrid components for electrical engineering and electronics, wherein two components are functionally connected using a joining aid designed as a reactive nanofoil, in that the nanofoil is first introduced between associated surface sections of the components to be joined together and subsequently causes an at least partial formation of a connecting structure, wherein by activating the nanofoil, a largely solid solder connecting layer is first melted on both mutually associated surface sections of the components to be joined together, and wherein subsequently the melting material, which is locally limited to one surface section, is mixed with the likewise locally limited melting material of the opposite surface section and the residues of the reactants of the nanoreactive film system in such a way thatthat after cooling and solidification of the entire melt, a functional brazing joint is formed, whereby the thermal load required for melting is introduced only within the contour sections of the contacts to be joined and exclusively on the brazing connection layers of the brazing layer system, characterized by that the wetting with solder material on the surface sections to be brought into active connection with each other takes place before the actual joining process and in each case independently of each other in terms of time and space.

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