Method for generating a solder joint, and assembly having a solder joint.

Abstract

A method is proposed for producing a soldered joint between a first soldering partner (10) and a second soldering partner (20) by means of a solder (100), the solder comprising a metallic solder material (110) and a multitude of magnetic nanoparticles (120) and comprising at least: a) generating an alternating magnetic field (200) using at least one magnet coil (210, 220) and applying the alternating magnetic field (200) to the solder (100); b) heating the plurality of magnetic nanoparticles (120) by interaction with an alternating magnetic field (200); c) melting the metallic solder material (110) by heat transfer (300) from the plurality of magnetic nanoparticles (120) to the metallic solder material (110) and forming a soldered joint between the first soldering partner and the second soldering partner by the molten metallic solder material (110); Furthermore, an assembly (1) having such a soldered joint is proposed.

Description

Technical Field

[0001] The present invention relates to a method of generating a soldered joint between a first soldering partner and a second soldering partner by solder, which contains a metallic solder material that is melted during the implementation of the method. The present invention further relates to an assembly provided with a soldered joint thus generated.

[0002] The prior art discloses various soldering methods capable of generating soldered joints between multiple soldering partners. As the joining material, for example, solid solder materials such as solder wire or preforms can be used. Also, for example, it is possible to use a solder paste that can be applied by printing on a circuit board on which components are mounted. Such a solder paste usually contains a large number of metallic solder particles and further contains a flux. Regardless of each type of solder, the metallic material present therein must be melted or at least heated to such an extent that diffusion at the interface is possible in order to generate the desired soldered joint. The heat input required for this can be carried out according to the prior art, for example, by a soldering iron, the flame of a soldering torch, hot air, hot steam, thermal radiation, a laser, or via electromagnetic induction by an induction coil.

[0003] Many drawbacks of these heating methods are not limited to only the soldering sites of the soldering partners, but heat is introduced into a wider range, and as a result, there is a risk of thermal damage to the soldering partners. This is especially true for soldering irons, soldering torches, hot air, hot steam, and thermal radiation. Lasers can achieve local focused heating in some situations, but in many cases, not all areas to be soldered (e.g., within an electrical assembly) are completely accessible to the laser beam. In the case of induction soldering, there is often a risk of thermal damage to other conductive elements in the vicinity of the soldering site where unwanted eddy currents are induced.

[0004] A further drawback of the heating methods described above is the difficulty in accurately measuring and controlling the temperature reached in the soldering area. Therefore, it is not possible to prevent excessively high heat input when the temperature required for solder joint formation is reached. Consequently, significantly more heat is introduced than is typically required for the soldering process, resulting in greater thermal stress on the soldering partner or even adjacent components. [Overview of the project] [Problems that the invention aims to solve]

[0005] Therefore, an object of the present invention is to provide an alternative method for generating a solder joint that overcomes the aforementioned drawbacks. In particular, it is intended to provide a soldering method that allows for spatially narrow and limited heat input in the region of the soldering area, and further allows for a more controllable limitation of the achieved soldering temperature. Another object is to provide an assembly including such a solder joint. [Means for solving the problem]

[0006] These problems are solved by the method described in claim 1 and the assembly described in claim 13.

[0007] The present invention relates to a method for creating a solder joint between a first soldering partner and a second soldering partner using solder. This solder comprises one metallic solder material and a number of magnetic nanoparticles. The method comprises the following method steps. a) A step of generating an alternating magnetic field with at least one magnet coil and applying this alternating magnetic field to the solder, b) A step of heating magnetic nanoparticles by interaction with the alternating magnetic field, c) A step of melting the metal solder material by heat transfer from the plurality of magnetic nanoparticles to the solder particles, and forming a solder joint between the first soldering partner and the second soldering partner with the molten metal solder material.

[0008] The order of the three methods, steps a) through c), first demonstrates the causal relationship of the individual effects. The generation of an alternating magnetic field in step a) first causes the heating of the magnetic nanoparticles in step b), and this heating of the magnetic nanoparticles then leads to the melting of the soldering material in step c), as heat is transferred from the magnetic nanoparticles to the soldering material. Overall, steps a) and b) typically proceed simultaneously, and step c) is also performed almost simultaneously with steps a) and b), or at least with temporal overlap.

[0009] In other words, what is important to the present invention is that this solder contains both the magnetic nanoparticles and the metal solder material described above. The melting of the metal solder material forms the original solder joint, as in the case of conventional solder pastes. In this case, the final mechanically durable solder joint is formed at the moment when the heat input is stopped or limited and the solder material solidifies again. Therefore, the electrical conductivity of the formed solder joint is essentially given by the solidified metal solder material.

[0010] These auxiliaryly present magnetic nanoparticles act to enable precise localized heat input to the solder. These nanoparticles are specifically ferromagnetic or ferrimagnetic. Therefore, they can be periodically magnetized by the alternating magnetic field acting in step a). The size scale of these particles must be in the range of nanometers or less. Because the particle size is so small, the magnetization generated by this magnetic field is not retained and is converted into thermal energy by Brownian and Néel relaxations on a very short timescale. Thus, via the alternating magnetic field acting in step a), locally localized heating can be produced in the zone where these magnetic nanoparticles are present, in other words, within the region of the solder. Therefore, an essential advantage of the method of the present invention is that undesirable heating of the soldering partner and other adjacent components to be joined can be greatly reduced compared to other soldering methods, and nevertheless, reliable melting of the metal solder element within the soldering zone is achieved.

[0011] Within this solder, the solder material can exist, in particular, in the form of multiple metal solder particles. In this case, multiple magnetic nanoparticles can be mixed with multiple metal solder particles or adjacent to them in close proximity, so that heat transfer from the initially heated magnetic nanoparticles to the metal solder particles is possible, and based on this, the solder particles can be melted. This is the case, for example, in a mixture in which two types of particles exist side by side, in which case, in particular, multiple magnetic nanoparticles, which are generally inherently smaller, are distributed almost uniformly across the gaps between larger solder particles. As an alternative form of such a particle mixture, the solder can also contain a large number of metal solder particles, each of which contains magnetic nanoparticles as partitioned inclusions composed of different materials. In another alternative, these magnetic nanoparticles can be embedded in a larger, expanded body made of solid solder material, for example, distributed on the volume of a so-called preform or solder wire.

[0012] The assembly according to the present invention includes one first soldering partner and one second soldering partner. These two soldering partners are joined by a solder joint comprising one metal solder element and a number of magnetic nanoparticles embedded therein. This solder joint is generated by the method according to the present invention, which is detectable by the presence of the embedded magnetic nanoparticles. Unlike metal solder material, these magnetic nanoparticles do not melt during the generation of the solder joint but remain retained as nanoscale inclusions within the solidified solder. The advantages of the assembly according to the present invention are the same as the advantages of the method according to the present invention described above.

[0013] Advantageous embodiments and variations of the present invention will become apparent from the claims dependent on claims 1 and 13 and from the following description. In this case, the described forms of the method and assembly can generally be suitably combined with each other.

[0014] In one generally favorable embodiment, these magnetic nanoparticles can be superparamagnetic. In other words, these nanoparticles contain ferromagnetic or ferrimagnetic materials, and in the case of these particles, after the previously acting external magnetic field is cut off, the remaining magnetization is not retained even below the Curie temperature. This effect arises from the small particle size, and in this case, the particle size that must not be exceeded also depends on the respective material. However, in this regard, it is generally favorable for the diameter of the magnetic nanoparticles to be 100 nm or less. In the case of non-spherical particles, the maximum external dimension is used instead of the diameter. A generally favorable range for typical particle sizes is, for example, 10 nm to 50 nm, and particularly favorably 10 nm to 25 nm. In the case of magnetic nanoparticles of the size scale described above, the energy from the acting alternating magnetic field can be converted particularly efficiently into heating of the nanoparticles through Brownian relaxation and Néel relaxation.

[0015] Furthermore, it is generally advantageous for these magnetic nanoparticles to have a Curie temperature in the range of 100°C to 1200°C, and particularly advantageously in the range of 150°C to 400°C. In particular, all magnetic nanoparticles present must have a Curie temperature within the aforementioned range. This ensures that their Curie temperature is compatible with the temperature range of the soldering process being used. In this case, in particular, the Curie temperature of the magnetic nanoparticles is higher than or above the melting temperature of the metal solder material. In this way, these magnetic nanoparticles can be heated to a sufficiently high temperature in an active alternating magnetic field, resulting in the melting of the solder material. However, once the temperature of the magnetic nanoparticles exceeds the Curie temperature, further heating of the solder material is stopped because, beyond that temperature, there is essentially no heat input into the magnetic nanoparticles from the energy of the magnetic field. Thus, the heat input to the nanoparticles within the Curie temperature range is automatically stopped, which advantageously avoids excessive heat load. That is, especially in this method, not only is the heat input locally concentrated in the solder region, but with the appropriate selection of nanoparticle material, it is also possible to limit its maximum temperature to a range desirable for a particular application. Since the Curie temperature of nanoparticles is sensitive to the precise composition of the ferromagnetic or ferrimagnetic material they contain, this material selection allows for precise selection of the temperature at which the automatic shut-off mechanism occurs. Thus, the maximum achievable temperature of the solder can be appropriately matched not only to the melting temperature of the metal solder material, but also to the thermal endurance of the soldering partner and, in some cases, other elements present in the assembly. Therefore, it is advantageous that the assembly includes heat-sensitive elements, such as a heat-sensitive polymer housing and / or insulating layer. Locally limited heating and its automatic limiting make it possible to avoid damage during the soldering process while still ensuring the reliable melting of the metal solder material. In this case, the alternating magnetic field required for heating can also penetrate other elements that are hardly heated themselves during the soldering process, because these elements have little interaction with the magnetic field.Thus, for example, soldering through multiple components, especially throughout an entire system, becomes possible, and even more remarkably, soldering processes can be carried out in or through a liquid.

[0016] The relative similarity of the Curie temperature distributions of individual magnetic nanoparticles is particularly advantageous in relation to the termination mechanism described above. These are advantageously CNPs (Curie temperature tuned magnetic nanoparticles), i.e., multiple magnetic nanoparticles having matching Curie temperatures. Such CNPs are described, for example, in "Applied Materials Today 21(2020)100824 “Magnetocuring of temperature failsafe epoxy adhesives” R. Chaudhary, V. Chaudhary, RVRamanujan, TWJSteele".

[0017] Therefore, it is generally advantageous for the full width at half maximum (FWHM) of the Curie temperature distribution of individual magnetic nanoparticles to be 50°C or less, and particularly advantageous for it to be 30°C or less. When the Curie temperatures of individual nanoparticles are so closely matched, the aforementioned automatic limiting of heat input, especially within a precisely defined temperature range, comes into play. The method can then, accordingly, include the following further steps. d) The step of bringing these magnetic nanoparticles to their Curie temperature, thereby avoiding further heating of the solder.

[0018] In other words, once the nanoparticles reach their Curie temperature, the heat input is abruptly cut off. Therefore, it is particularly possible to reliably avoid exceeding a predetermined maximum temperature, and as a result, it is also possible to avoid thermal damage to multiple adjacent elements. In particular, in this case, it is possible to omit a complex sensor system for temperature detection and additional closed-loop control devices to avoid overheating.

[0019] In one generally advantageous embodiment, these magnetic nanoparticles include ferromagnetic or ferrimagnetic materials, particularly in the form of metal alloys or metal oxides. This alloy or metal oxide advantageously contains at least one of the elements iron, cobalt, and nickel. Here, this metal oxide is particularly a mixed oxide, for example, Mn x Zn 1-x This can be a compound of the Fe2O4 type, where x can take values ​​particularly between 0.4 and 0.7. The precise tuning of the Curie temperature for this type of compound is described in the above-cited paper by R. Chaudhary et al.

[0020] Furthermore, it is generally advantageous for the weight ratio of such metal alloys or metal oxides in the total solder to be between 1% and 30%. A weight ratio of at least 1% is appropriate to provide sufficient heat input to the solder via the nanoparticles, which then causes the metal solder material to melt. On the other hand, excessively high weight ratios exceeding 30% are generally unsuitable, as they severely impair the mechanical and electrical properties of the solder joint. Therefore, this weight ratio should be advantageously limited to 10% or less, especially considering the particularly good electrical conductivity of the solder joint. However, if obtaining a long-lasting mechanical bond is particularly important and electrical conductivity is of lower importance, the weight ratio of magnetic nanoparticles can be in the upper end of this range, i.e., between 10% and 30%.

[0021] In one particularly advantageous variant, these magnetic nanoparticles may have a core made of a ferromagnetic or ferrimagnetic material and a non-magnetic shell. Here, non-magnetic material means a material that is at least not ferromagnetic or ferrimagnetic. Thus, this shell may be formed from an organic material, for example, oleic acid and / or bisphenol A diglycidyl ether. However, inorganic materials such as silicon dioxide (SiO2) and graphene can also be used for this shell. Such a shell is particularly useful for colloidal stabilization of magnetic nanoparticles. In other words, these shells prevent particle aggregation that can be caused, for example, by the effects of moisture. For this purpose, the thickness of such a shell that stabilizes the colloid can be, for example, in the range of 2 nm to 10 nm. Such a thin shell is sufficient to prevent the nanoparticles from aggregating to form larger clusters and thus allow for a fine and nearly uniform distribution of nanoparticles throughout the solder. Thus, particularly uniform heating of the entire solder can be achieved.

[0022] However, as an alternative to this embodiment, it is also possible, in principle, to use uncoated magnetic nanoparticles. In some cases, the formation of clusters of such nanoparticles can be tolerated. Particularly when using a particle mixture of multiple magnetic nanoparticles and multiple metal solder particles, it can be advantageous if the size scale of the formed aggregates is less than or equal to the size scale of the solder particles used. In that case, despite the aggregation of these nanoparticles, a sufficiently homogeneous solder can be provided to enable uniform heat transfer from the magnetic nanoparticles to the metal solder particles.

[0023] According to the first embodiment of this solder, the solder can be a solder paste. Such a solder paste can particularly include a mixture of a plurality of magnetic nanoparticles and a plurality of metallic solder particles. Such solder particles are preferably approximately spherical, and their diameter ranges from 1 μm to 160 μm, preferably from 2 μm to 50 μm. This corresponds to the normal particle size in a general conventional solder paste having relatively fine solder particles.

[0024] However, according to an alternative second embodiment of this solder, the solder can also be a solid solder preform, which is also referred to as a preform in this technical field. Such a solder preform can be, for example, a soldering ring, or can take the form of a disk, tape, flat rectangle, or horseshoe shape. Alternatively, a soldering wire or another solid soldering element can also be used.

[0025] Regardless of whether it is a solder paste containing solder particles or a soldering preform, generally, the solder material is a low-melting-point alloy, for example, soft solder, hard solder, or high-temperature solder. Basically, all conventional solder alloys are suitable as the solder material, and in particular, alloys containing tin, bismuth, silver, copper, zinc, lead, and / or antimony are suitable.

[0026] This solder preferably generally includes a flux in addition to the solder material and a plurality of magnetic nanoparticles. This also holds true, for example, regardless of whether it is a solder paste or a solid soldering preform. All conventional materials are also useful for the flux. For example, the flux can be a resin, oil, solvent, salt, or water, or can include these compounds as components. Overall, this solder is a mixture of a plurality of materials, which can further include other optional components as necessary in addition to the solder material, a plurality of magnetic nanoparticles, and optionally the flux.

[0027] According to a generally advantageous variant of an embodiment of the method, at least two magnet coils with different arrangement directions of magnetic poles can be used in step a). In this embodiment, two alternating magnetic fields overlapping each other are generated thereby, and preferably a plurality of ranges with high magnetic flux density are overlapped within one focal range. Thus, in this variant, one focal point stronger than the focal point that can be created by just one magnet coil or by just one magnetic pole direction acts on one narrowly defined range for local heating. The size of this focal range varies completely depending on the application: for example, in the case of soldering surface-mounted devices or ball grid arrays, the focal size can be in the sub-millimeter range. For example, for large-area soldering ranges such as in the field of railway technology or for soldering pipes, the focal size becomes significantly larger and can even be in the meter range.

[0028] Instead of generating one narrow focal range by two overlapping magnetic fields, the focusing of the magnetic field can be achieved by one or more magnetic flux guiding elements. In order to focus the magnetic field into one focal range of appropriate size, it is possible to arrange, for example, two conical cores facing each other on both sides of the soldering site.

[0029] Generally, regardless of the number and spatial arrangement of the magnet coils used, the frequency of the alternating magnetic field can be in the range of several hundred kHz, preferably between 100 kHz and 1000 kHz, and, for example, in the range of about 400 kHz. For frequencies in such a range, efficient heat input into the solder can be achieved by the corresponding relaxation process in the magnetic nanoparticles.

[0030] According to an advantageous evolution of the present invention, independent of the number of magnet coils and the number of magnetic poles, at least one magnet coil can be moved relative to two soldering partners during the soldering process. In this case, it is not important whether the soldering partners are fixed and this at least one magnet coil moves, or vice versa. In any case, the overall result in this embodiment is a translational relative movement, and as a result, its focal range or range of maximum energy input moves across the assembly under consideration, thereby enabling targeted localized melting of solder at multiple consecutive locations. This alternative embodiment of the method can also be preferably advanced such that each active soldering zone is moved outward from the interior region of the assembly (and vice versa, of course). Thus, this alternative makes it possible to create individual localized soldering sites within a complex assembly, particularly when the location of the maximum energy input is spatially narrowly confined, and such internally localized soldering sites can also be repaired later if necessary. Repairs may include, for example, replacing parts and melting and repositioning misplaced parts that have already been soldered. Alternatively or additionally, localized heat treatment may be performed at a later date to relieve stress within the soldered joints already made using the heat input method described above.

[0031] According to one generally advantageous configuration of this method, multiple different solders with different melting temperatures can be used within a single assembly to produce different types of solder joints. In this case, the soldering method of the present invention is used for at least one type of these solder joints. For other types of solder joints, it is also possible to use this method of the present invention with a different solder, or to use a conventional soldering method for one or more other solder joints. For example, a different method can be used for SMD solder joints than for soldering plugs or load connections. Also, a different soldering method can be used for soldering joints for high frequency, high current and / or high voltage ranges than for low frequency, low current or low voltage ranges. Finally, a different method can be used for certain materials, such as lead-containing solder, than for lead-free solder elsewhere in the assembly.

[0032] In one advantageous embodiment, the assembly according to the present invention can be an electronics assembly, in particular a power electronics assembly having one or more power electronics components. In this case, the advantages of the present invention are particularly effective, because, while it is crucial to produce a highly reliable and conductive solder joint, there is also a need to protect other elements within the same assembly from excessive thermal stress.

[0033] It is generally advantageous that the assembly has at least one solder joint produced by the method of the present invention. This solder joint can appropriately form a conductive joint between multiple attached solder partners.

[0034] According to one advantageous embodiment of the assembly, the first soldering partner can be an electrical circuit board. That is, it can be, for example, a circuit board or a ceramic circuit board. In either case, this circuit board forms the mechanical and / or electrical base of the assembly, and a plurality of other elements are supported by this base. Thus, by the method of the present invention, one or more other elements forming a second and any other soldering partner can be soldered onto this circuit board.

[0035] Therefore, the second soldering partner can be an electrical or electronic component. This also applies to any other soldering partner that may be present as an option. In particular, a circuit board can mount one or more such components, which are joined to it by the soldering method of the present invention. In this case, a conductive joint is generally preferred, thereby making electrical contact with the components in question. Such components may be, for example, IGBTs, diodes, MOSFETs, thyristors, shunts, or capacitors.

[0036] However, these soldering partners do not necessarily have to be electrical circuit boards and electrical components. Any other component, such as a pipe or machine housing, can form the first soldering partner, and any other component can form the second soldering partner. For example, a sensor (particularly for temperature or mechanical stress) can be soldered onto a pipe or machine housing. Alternatively, this soldering technique can be used in the field for repairs, for example, to solder multiple pipe components together.

[0037] The present invention will be described below based on several embodiments and with reference to the attached drawings. [Brief explanation of the drawing]

[0038] [Figure 1]A schematic cross-sectional view of a part of an assembly during the soldering method according to the first example of the present invention. [Figure 2] Detailed diagram of solder for such solder joints. [Figure 3] A schematic perspective view of a portion of the assembly shown with the magnet coil array used in this soldering method. [Figure 4] A cross-sectional view of an assembly in which a soldered joint according to another example of the present invention is being implemented. In these figures, identical or functionally identical elements are denoted by the same reference numeral. [Modes for carrying out the invention]

[0039] Figure 1 is a schematic cross-sectional view of a portion of assembly 1 in a first example of the present invention. In the illustrated detail of this assembly 1, a solder joint is created between a first soldering partner 10 and a second soldering partner 20 by the method of the present invention. These are, in principle, any elements of an assembly that should be permanently mechanically joined by soldering. In this case, a good conductive joint, and therefore electrical contact between the two soldering partners 10 and 20, is obtained as needed. In this case, the resulting solder joint is mediated by a solder 100, which, as its components, includes a metallic solder material on the one hand and a number of magnetic nanoparticles 120, these magnetic nanoparticles embedded in the solder 100. This solder 100 can, in principle, be constructed in different ways. It may be, for example, a solder paste or other solid solder preform. In each of these cases, these magnetic nanoparticles 120 are distributed over the volume of solder. In the example in Figure 1, the solder 100 is specifically a solder paste, which contains a mixture of multiple particles consisting of multiple metal solder particles and multiple magnetic nanoparticles.

[0040] An alternating magnetic field 200 is generated to form a solder joint between two soldering partners 10 and 20, as indicated by the corresponding bidirectional arrows in Figure 1. This alternating magnetic field acts on the area of ​​solder 100. In particular, magnetic interaction occurs with the magnetic nanoparticles 120 present within it, which heats these nanoparticles. Thus, the multiple magnetic nanoparticles embedded in the solder 100 become multiple local heat sources within the solder 100 under the action of the alternating magnetic field 200, from which heat is transferred to the other components of the solder. This heat input is very localized and essentially limited to the area of ​​solder 100, causing the metal solder material within the solder to melt. After the alternating magnetic field is removed, the solder cools, and its molten material solidifies accordingly, thus forming a permanent solder joint between the two soldering partners 10 and 20.

[0041] When the localized heating of multiple magnetic nanoparticles exceeds their Curie temperature, the heat input to the solder is automatically stopped. Therefore, the achievable temperature is automatically limited. Thus, this effect, combined with the locally limited heating zone, makes this a particularly gentle soldering method, and thermal damage to other elements of the optionally present assembly is advantageously avoided. The heat input to the two soldering partners 10 and 20 being joined is also relatively low.

[0042] Figure 2 is a detailed view of a region of solder 100, which can be used, for example, in the soldering method of Figure 1. Here again, solder 100 is a solder paste having a large number of metal solder particles 110. These are formed here as nearly spherical solder spheres composed of a relatively low-melting-point metal alloy. Their diameter d110 can be, for example, in the range of a few micrometers to tens of micrometers. In addition to these metal particles, the paste also contains a large number of magnetic nanoparticles 120, as already mentioned. Furthermore, the solder paste in this example also contains (optionally) organic flux 130. The diameter d120 of the magnetic nanoparticles 120 is significantly smaller than the diameter d110 of the metal solder spheres 110. Advantageously, the size scale of the magnetic nanoparticles 120 is in the range of 100 nm or less. These nanoparticles contain ferromagnetic or ferrimagnetic material components. Due to their small particle size, these nanoparticles are superparamagnetic overall. This property allows for strong local heating of the magnetic nanoparticles in an alternating magnetic field, and therefore the energy input required for the soldering method to solder 100. As shown by the illustrative arrow 300, heat transfer also occurs from the nanoparticles 120 to the metal solder particles 110, resulting in the melting of these metal solder particles.

[0043] In the example shown in Figure 2, the magnetic nanoparticles have two material components: one core 121 made of a ferromagnetic or ferrimagnetic material and one non-magnetic shell 122. This is not essential, and these nanoparticles may alternatively be composed of only a single ferromagnetic or ferrimagnetic material. However, the core-shell structure shown here is advantageous because the coating by the shell material can avoid excessive aggregation of individual nanoparticles.

[0044] Figure 3 shows a partial perspective view of a portion of assembly 1 positioned within the focal range F of an alternating magnetic field 200 for carrying out the method of the present invention. Otherwise, assembly 1 is formed similarly to that in the example of Figure 1, and in particular includes similar solder 100 for forming solder joints. The focal range F is formed relatively narrowly so that the energy input to the solder is spatially narrowly limited. To achieve this, two magnet coil arrays 210 and 220 are provided here to generate the alternating magnetic field 200. In this example, they are located on either side of the assembly, such that assembly 1 is midway between the two coil arrays. In this example, the magnetic poles of the two coil arrays 210 and 220 are concentric with respect to each other. However, it is also possible to use two or more magnet coils with correspondingly different magnetic pole directions instead. In this case, in particular, these magnetic poles can intersect within the focal range F, which, under certain circumstances, allows for a stronger focus of energy input.

[0045] Figure 4 shows a cross-sectional view of another assembly 1 in which a solder joint is similarly produced by the method of the present invention. In this example, the first soldering partner is an electrical circuit board 10, and the second soldering partner is an electronic component 20. This second soldering partner is in particular a semiconductor chip, which is inserted into the circuit board and conductively joined to a conductor on the circuit board 10 by the soldering method. Here again, there is one solder 100 between the two soldering partners 10 and 20, which, as in the previous example, consists of one metallic solder component and a plurality of magnetic nanoparticles distributed on the solder 100. Here again, an alternating magnetic field 200 acts on the soldering region, forming a relatively narrow focal range F, within which the energy input from the magnetic field 200 is sufficiently high to melt the metallic solder component. In particular, the lateral size of the focal range is smaller than the lateral size of the chip, and as a result, point-like localized melting of the solder 100 in a subregion below the chip is possible. Arrow 400 indicates that relative movement occurs between the alternating magnetic field (or magnetic field generating coil array) and assembly 1 while this soldering method is being performed. This allows the heated soldering area to be precisely confined to one narrow sub-region of the assembly. Furthermore, Figure 4 shows that this alternating magnetic field can also penetrate the electronic component 20 and / or other elements of the assembly without causing significant heating to the chip 20 and / or other elements of the assembly. This is because the substantial energy input is confined to the area of ​​solder 100 containing magnetic nanoparticles. [Explanation of Symbols]

[0046] 1 Assembly 10. First soldering partner (circuit board) 20. Second soldering partner (component) 100 solder 110 Metal solder material (solder particles) 120 Magnetic Nanoparticles 121 cores 122 shells 130 Flux 200 alternating magnetic fields 210 First magnet coil array 220 Second magnet coil array 300 Heat transfer 400 Relative movement d110 Diameter of metal solder particles d120 Diameter of magnetic nanoparticles F Focal Length

Claims

1. A method for creating a solder joint between a first soldering partner (10) and a second soldering partner (20) by solder (100), wherein the solder comprises one metal solder material (110) and a plurality of magnetic nanoparticles (120), and this method comprises at least, a) A step of generating an alternating magnetic field (200) with at least one magnet coil (210, 220) and applying the alternating magnetic field (200) to the solder (100), wherein at least two magnet coils (210, 220) with different orientations of magnetic poles are used, and these magnet coils (210, 220) are moved relative to the two soldering partners (10, 20), b) A step of heating the plurality of magnetic nanoparticles (120) by interaction with the alternating magnetic field (200), c) The step of melting the metal solder material (110) by heat transfer (300) from the plurality of magnetic nanoparticles (120) to the metal solder material (110), and forming a solder joint between the first soldering partner and the second soldering partner with the molten metal solder material (110), A method of including.

2. The method according to claim 1, wherein the plurality of magnetic nanoparticles (120) are superparamagnetic and comprise a ferromagnetic or ferrimagnetic material in the form of a metal alloy or metal oxide, wherein the metal alloy or metal oxide comprises at least one of the elements iron, cobalt, and nickel, and the weight ratio of the metal alloy or metal oxide in the total solder is between 1% and 30%.

3. The method according to claim 1, wherein the diameter (d120) of the plurality of magnetic nanoparticles (120) is less than 100 nm.

4. The method according to claim 1, wherein the Curie temperature of the plurality of magnetic nanoparticles (120) is in the range of 100°C to 1200°C.

5. The method according to claim 1, wherein the full width at half maximum (FWHM) of the distribution of the Curie temperatures of each of the plurality of magnetic nanoparticles (120) is 50°C or less.

6. d) The method according to claim 1, further comprising the step of bringing the plurality of magnetic nanoparticles (120) to their Curie temperature so as to avoid further heating of the solder (100).

7. The method according to claim 1, wherein the plurality of magnetic nanoparticles (120) each have a core (121) made of a ferromagnetic or ferrimagnetic material and a non-magnetic shell (122).

8. The method according to claim 5, wherein the heat transfer (300) is interrupted and it is avoided that the temperature exceeds a predetermined maximum temperature.

9. The method according to claim 1, wherein multiple different solders (100) having different melting temperatures are used within one assembly (1) to produce multiple solder joints of different types.

10. The method according to claim 1, wherein the first soldering partner (10) is an electrical circuit board.

11. The method according to claim 1, wherein the second soldering partner (20) is an electrical component or an electronic component.

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