Method for selective melting of a solder material in alternating magnetic fields, and assembly

Abstract

The invention relates to a method for melting a solder material for joining and / or releasing a soldered joint, wherein nanoparticles incorporated in the solder material dissipate magnetic energy from an alternating magnetic field, substantially by way of relaxation processes according to Brown and Néel, which leads to heating and finally to melting of the solder material. Furthermore, the invention relates to an assembly which has at least one soldered joint which is formed or released by way of the method according to the invention.

Description

[0001] Description

[0002] METHOD FOR SELECTIVELY MELTING A SOLDER MATERIAL IN MAGNETIC

[0003] AC FIELDS AND ASSEMBLY

[0004] 5 The invention relates to a method for melting a solder material for joining and / or separating a soldered connection. Furthermore, the invention relates to an assembly having at least one soldered connection formed or separated by the method according to the invention.

[0005] State of the art

[0006] Previous requirements for electronic assemblies were focused on reduced weight or volume, higher system performance with shorter signal propagation times, or increased reliability at minimal cost. The market also placed thermal, mechanical, and electromagnetic demands on electronic assemblies. Electronic assemblies typically comprise integrated and discrete components. The components are electrically and mechanically connected, particularly to one another, but also by means of a wiring carrier.

[0007] Current and future requirements are increasingly focused on environmental compatibility. In electrical assemblies, the components are not traditionally recycled individually. Until now, mechanical processes such as shredding have been used to reduce the assemblies to size at the end of their service life, followed by subsequent processes such as magnetic separation, centrifugation, etc. to roughly separate or recover the materials. To date, there has been no targeted recycling of individual components or individual elements.

[0008] 35 It is technically possible to remove all components, whether mechanical, electrical or electronic. However, global heating of an entire group is, on the one hand, very energy-intensive, and on the other hand, numerous components can be damaged by uncontrolled heat input. The heat required for desoldering is usually introduced using ovens, hot plates, soldering irons, induction or open flames. With each of the processes, not only the solder is heated, but also the surrounding materials. The situation varies locally depending on the principle: when heating in an oven, everything is heated excessively, whereas with a soldering iron it is only partially heated, although neighboring assemblies would still be affected. With induction soldering, the required heat is also generated primarily by the induced eddy currents of the joining partners. These must also always be electrically conductive.Due to the indirect heating, the energy introduced during the desoldering process is much greater than the energy actually required to melt the solder. When desoldering with a soldering iron, for example, the surrounding components are only heated minimally for certain soldering tasks, e.g. when soldering a stranded wire to a pin. However, attention must be paid to the correct maximum temperature here too, as otherwise the soldering point and the surrounding materials will overheat. Furthermore, from a technical and economic point of view, most soldering processes cannot be carried out with soldering irons. Firstly, desoldering processes with soldering irons are only used for special non-automated production cases because the costs for non-automated machine processes would be far too high. Technically speaking, very few soldering points can be contacted directly.For example, semiconductor chips such as IGBTs cannot be desoldered with a soldering iron because the heating would have to occur beneath the inaccessible chip surface. In such cases, desoldering in ovens has so far been the only possible option.

[0009] Similar problems also arise when repairing components and assemblies. If, for example, a defective solder joint needs to be re-soldered, which is inaccessible, as is the case with a BGA, the entire component and the surrounding PCB are heated up, which has a negative impact on the quality of the components. The inefficiency of such processes is even greater when an entire assembly must be thoroughly heated just to access certain individual components. If a component is mounted on a cooler, for example, an enormous amount of energy is required to heat the cooler.

[0010] Based on the previously described prior art, the object of the invention is to enable efficient and selective desoldering of parts or components of an assembly.

[0011] This problem is solved by the features of independent claim 1. Advantageous embodiments of the invention are the subject of the dependent claims. In particular, the proposed solution is intended to enable an assembly with selectively desolderable assemblies or components, as in claim 12.

[0012] The method according to the invention for melting a solder material for joining and / or separating at least one first and at least one second solder connection, wherein a solder comprises the solder material and magnetic nanoparticles which have a ferromagnetic or ferrimagnetic material and make up a weight proportion of the total solder between 1% and 30%, at least the following steps are carried out: introducing a first power into a first solder by means of a first alternating magnetic field so that the first solder melts, and introducing a second power into a second solder by means of a second alternating magnetic field so that the second solder melts, wherein the first and the second alternating magnetic field differ in at least one parameter.

[0013] The solders to be distinguished are expediently selected such that the first alternating magnetic field is not suitable for melting the second solder and the second alternating magnetic field is not suitable for melting the first solder. The alternating magnetic fields preferably differ in at least one parameter. The parameters of the alternating magnetic field can in particular be frequency and / or magnetic field strength. The two different solders can be adjusted, for example, via the choice of ferrimagnetic or ferromagnetic nanoparticle material, via the weight proportion of the nanoparticles or via the melting temperature of the solder material.

[0014] This process has the advantage of enabling not only selective but also very efficient desoldering of individual components or components of an assembly.

[0015] In an advantageous embodiment of the invention, in the method the alternating frequency of the first alternating magnetic field is set to the size of the magnetic nanoparticles of the first soldered connection and the alternating frequency of the second alternating magnetic field is set to the size of the magnetic nanoparticles of the second soldered connection. Size is understood to mean in particular the diameter of the nanoparticles in the case of approximately spherical particles. Alternatively, it is understood to mean the maximum extent of a particle. In particular the alternating magnetic field, in particular its alternating frequency and optionally also its magnetic field strength, is also adapted to the following factors: Neel relaxation time, Neel spin relaxation and / or blocking temperature.

[0016] In a further advantageous embodiment of the invention, in the method the alternating frequency of the first alternating magnetic field is set to the volume fraction of the magnetic nanoparticles in the solder composition of the first solder and the alternating frequency of the second alternating magnetic field is set to the volume fraction of the magnetic nanoparticles in the solder composition of the second solder. In a further advantageous embodiment of the invention, in the method the magnetic field strength of the first alternating magnetic field is set to the size of the magnetic nanoparticles in the first solder and the magnetic field strength of the second alternating magnetic field is set to the size of the magnetic nanoparticles in the second solder. A combination of the two solder settings using nanoparticle size and nanoparticle fraction is also possible.This increases the possibility of selective desoldering of each individual component of the assembly.

[0017] Adapting or modifying the solder material, e.g., with respect to its melting temperature, is also possible to further increase the selectivity of the process. However, the nanoparticles are preferably varied. These can be varied in their material composition, in their mass fraction in the solder, and in their size.

[0018] In a very useful embodiment of the invention, at least one alternating magnetic field is generated as a focused alternating magnetic field, and the solder is introduced into the focal region of the focused alternating magnetic field. A focused alternating field can further increase the selectivity of the overall process. In particular, this allows the same solder to be used for components positioned at a greater distance, while neighboring assemblies can be provided with different solder.

[0019] In a further development of the design variant with the focused alternating magnetic field, the solder is introduced into the focus area by moving the focus area over the assembly and / or by moving the assembly into or through the focus area. Thus, there are different movement or grid options for positioning the various components on an assembly in the focus area of ​​the alternating magnetic field.

[0020] In a further advantageous embodiment of the previously described variant with the focused alternating electromagnetic field, the focused alternating magnetic field is generated by means of at least two magnetic coils with different orientations of the magnetic poles. In this embodiment, two superimposed alternating magnetic fields are thus generated, with the regions of high magnetic flux density advantageously being superimposed in a focal area. In this variant, an even stronger focusing of the local heating on a narrowly defined area is achieved than would be possible with just one magnetic coil or just one magnetic device. The size of the focal area can vary depending on the application.For soldering surface mount devices or ball grid arrays the focus size is in the sub-millimeter range, but for large-area soldering areas, such as in the railway technology sector or for soldering pipes, the focus size can also be much larger and even in the meter range.

[0021] As an alternative to creating a narrow focal area with two overlapping magnetic fields, focusing the magnetic field can also be achieved using one or more flux-conducting elements. For example, two conically tapered iron cores can be arranged on either side of the solder joint to focus the magnetic field onto a suitable-sized focal area.

[0022] In general, and regardless of the number and spatial arrangement of the magnetic coils used, the frequency of the alternating magnetic field can be in the range of a few hundred kHz, particularly between 100 kHz and 1000 kHz, and, for example, in the range around 400 kHz. At a frequency in such a range, the corresponding relaxation processes in the magnetic nanoparticles can achieve efficient heat input into the solder.

[0023] In a further advantageous embodiment of the invention, superparamagnetic nanoparticles are used in the method for melting a solder material. The size scale of the magnetic nanoparticles is advantageously in the range of 100 nm or less. These nanoparticles contain ferromagnetic or ferrimagnetic material components. Due to their small particle size, the nanoparticles are superparamagnetic overall. This property enables strong local heating of the magnetic nanoparticles in the alternating magnetic field and thus the energy input into the solder required for melting.

[0024] For example, the magnetic nanoparticles have a Curie temperature which lies in a range between 100 ° C and 1200 ° C, in particular between 150 ° C and 400 ° C. In a particularly advantageous embodiment of the invention, the distribution of the Curie temperatures of the individual magnetic nanoparticles has a half-width of at most 50 ° C, in particular of at most 30 ° C.

[0025] It is therefore important for the present invention that the solder contains both the described magnetic nanoparticles and the metallic solder material. The actual solder joint is formed by melting the metallic solder material, similar to a conventional solder paste. The final, mechanically permanent solder joint is formed the moment the heat input is prevented or limited and the solder material solidifies again. Accordingly, the electrical conductivity of the formed solder joint is essentially provided by the solidified metallic solder material.

[0026] In a further advantageous embodiment of the invention, ferromagnetic or ferrimagnetic materials comprising a metallic alloy or a metal oxide are used in the method for melting a solder material, wherein the alloy or metal oxide comprises at least one of the elements iron, cobalt or nickel.The above-described method according to the invention or one of its embodiments can be used to form an assembly which has at least two solder joints which are joined or separated by a method according to the invention, wherein a solder joint comprises a first solder partner and a second solder partner, which solder partners can be connected or are connected by a solder, which solder comprises a metallic solder material and a plurality of magnetic nanoparticles embedded therein, wherein the solder composition of the second solder joint differs from the solder composition of the first solder joint.

[0027] Such an assembly has the advantage of being selectively recyclable and also boasting a very good energy balance during production, as the direct intrinsic heating of the solder means the soldering process requires little energy. Furthermore, such an assembly is highly reliable, as there is no unnecessary heating and therefore no unnecessary thermal stress on the other materials and components. Heat is generated by magnetic fields so quickly that process times can be reduced. Overheating is avoided, simply by virtue of the set Curie temperature, at which heat generation is interrupted.

[0028] In an advantageous embodiment of the invention, the first soldering partner of the assembly is an electrical circuit carrier, and the second soldering partners are electrical or electronic components. An assembly manufactured in this way can also be repaired in the field, even with the circuit board installed. Scenarios such as soldering or repairing sensors attached to systems are also conceivable. Even the soldering of pipes can be performed in the field.

[0029] The described inventive method and its embodiments as well as the specified assembly enable, among other things, multi-temperature desoldering within an assembly. By using CMPs with different melting points, it is possible to cluster components according to value, type, cost or other criteria. By increasing the global desoldering temperature using the magnetic fields, groups from a cluster can be desoldered one after the other. For example, first the MOSFETs at 220 °C, followed by diodes at 235 °C. An automated sorting process can also be combined with the method. The described assembly and the method provide an important approach for the economical implementation of second-life approaches in the field of electronic and electrical components, which is becoming increasingly important, especially from an ecological point of view for CCU savings and resource conservation.

[0030] The invention is described and explained in more detail below with reference to the exemplary embodiments shown in Figures 1 to 7. Further features, properties and advantages of the present invention will become apparent from the following description with reference to the accompanying figures. In the exemplary embodiments and figures, identical or identically acting elements may be provided with the same reference numerals. The elements shown and their proportions are generally not to be regarded as true to scale; rather, individual elements may be shown with larger dimensions for clarity and / or better understanding.

[0031] Even though the invention is illustrated and described in more detail by means of exemplary embodiments, the invention is not limited by the disclosed examples.

[0032] Figure 1 shows the composition of the solder 100 consisting of metallic solder material 110 and magnetic nanoparticles 120.

[0033] Figure 2 shows the composition of a second solder 101 consisting of metallic solder material 110 and magnetic nanoparticles 121. Figure 3 shows the composition of a third solder 102 consisting of metallic solder material 110 and magnetic nanoparticles 120.

[0034] Figure 4 and Figure 5 each show two soldering partners 10, 20 in an alternating magnetic field 200, 201.

[0035] Figure 6 shows soldering partners 10, 20 in a focused alternating magnetic field.

[0036] Figure 7 shows an assembly and a movable device for generating an alternating magnetic field.

[0037] Figures 1 to 3 schematically show the solder 100, a composition of solder material 110 and nanoparticles 120, 121 in different sizes and compositions. The solder material particles have diameters or external dimensions d10 which are a multiple of the particle diameters or maximum particle dimensions d120, d121 of the magnetic nanoparticles. The solder can be in the form of solder paste or as a preform. If such a mixture is exposed to an alternating magnetic field, a current is induced in the nanoparticles 120, 121. The nanoparticles, e.g. CMP nanoparticles, dissipate the magnetic energy essentially through Brown and Neel relaxation processes, which leads to heating and ultimately to melting of the solder material. The alternating magnetic field is indicated in Figures 4 and 5 by arrows 200, 201. A first soldering partner 10, e.g. a circuit board, is soldered to the substrate 10 via a solder 103, e.g. B.Formed as a preform, it is connected to a second solder partner 20, e.g., a chip. Upon reaching the specific Curie temperature of the nanoparticles 120, 121, the induced heating is abruptly interrupted. By varying the composition of the nanoparticles 120, 121, the Curie temperature can be varied.

[0038] Temperature can be set. This prevents overheating of the solder and the solder joint.

[0039] The intrinsic heating of the solder significantly reduces the total energy required for the soldering and desoldering process. This also results in lower costs and a lower CCg load during the soldering process. By using differently modified CMPs 120, 121, components 20 can be soldered and later selectively desoldered in the recycling process.

[0040] By additionally focusing the alternating magnetic field 200, as shown in Figure 6, the selectivity of the soldering and desoldering can be further increased and individual pins can also be heated selectively. Figure 6 again shows a first solder partner 10, a second solder partner 20 and individual solder balls 104, such as those used for ball grid arrangements in so-called BGAs (ball grid arrays). The focus area F of the alternating magnetic field 200 can be directed at an individual solder ball. In this way, so-called cracks, individual connection defects D, can be repaired.

[0041] Figure 7 shows another variant of how assembly recycling can also be carried out automatically by moving a device for generating an alternating magnetic field, in particular a focused alternating magnetic field. Either the assembly 1 can be moved or, alternatively, the magnetic field device. An assembly 1 can have a plurality of components, i.e. components of an assembly 40, 50, 60, on a circuit carrier 30, i.e. a substrate which represents the first soldering partner, which components have different solder connections, e.g. a flat connection 20 or individual pin connections, as shown for the component 40.

[0042] Reference number: 100 / 101 / 102 Solder

[0043] 110 metallic solder material (solder particles)

[0044] 120 magnetic nanoparticles (CNP)

[0045] 21 core

[0046] 22 Cover

[0047] 130 Flux dllO Diameter of the metallic solder particles dl20 Diameter of the magnetic nanoparticles

[0048] 300 heat transfer

[0049] 200 alternating magnetic field

[0050] 10 first soldering partner, e.g. copper layer on circuit board 30

[0051] 20 second soldering partner, e.g. component, or electrical and / or thermal component connection

[0052] 103 Solder layer, e.g. paste

[0053] 30 intrinsic heating of the solder as a result of the induction currents generated in the magnetic nanoparticles (120) by the alternating magnetic field

[0054] 201 second alternating magnetic field of different magnetic field strength and / or different alternating frequency to the first magnetic field

[0055] 104 solder balls, e.g. for ball grid array (BGA

[0056] Ball Grid Array)

[0057] D Crack, Defect

[0058] 210 Focusing aid, e.g. comprising a first and a second magnetic coil arrangement

[0059] F Focus area x Scanning movement direction in the first planar extension direction of assembly 1 z Scanning movement direction in the second planar extension direction of assembly 1

[0060] 30 circuit carrier, substrate, e.g. for an assembly

[0061] 40 / 50 / 60 components, components of an assembly

Claims

Patent claims 1. A method for melting a solder material (110) for joining and / or separating at least one first and at least one second solder connection, wherein a solder (100 / 101 / 102) comprises the solder material (110) and magnetic nanoparticles (120, 121) which comprise a ferromagnetic or ferrimagnetic material and constitute a weight fraction of the total solder (100 / 101 / 102) of between 1% and 30%, and wherein the method comprises at least the following steps: - Introducing a first power into a first solder (100) , by means of a first alternating magnetic field (200) , so that the first solder (100) melts, - Introducing a second power into a second solder (101) by means of a second alternating magnetic field (200) so that the second solder (101) melts, wherein the first and the second alternating magnetic fields differ in such a way that the first alternating magnetic field is not suitable for melting the second solder and the second alternating magnetic field is not suitable for melting the first solder, wherein the alternating frequency of the first alternating magnetic field (200) is set to the volume fraction of the magnetic nanoparticles (120) in the composition of the first solder (100) and wherein the alternating frequency of the second alternating magnetic field (201) is set to the volume fraction of the magnetic nanoparticles (120, 121) in the composition of the second solder (101).

2. The method according to claim 1, wherein the alternating frequency of the first alternating magnetic field (200) is set to the size (dl20, dl21) of the magnetic nanoparticles (120) of the first solder (100) and wherein the alternating frequency of the second alternating magnetic field (201) is set to the size (dl20, dl21) of the magnetic nanoparticles (120, 121) of the second solder (101).

3. Method according to one of the preceding claims, in which at least one alternating magnetic field (200) is generated as a focused alternating magnetic field, and which additionally comprises at least the step: Inserting the solder (100 / 101 / 102) into the focus area (F) of the focused alternating magnetic field.

4. Method according to claim 3, wherein the introduction is carried out by moving the focus area (F) over the solder (100 / 101 / 102) and / or moving a solder connection position into the focus area (F).

5. Method according to one of the preceding claims 3 or 4, in which the generation of the focused alternating magnetic field (F, 200, 201) takes place by means of at least two magnetic coils (210, 220) with different orientations of the magnetic poles.

6. Method according to one of the preceding claims, wherein the magnetic nanoparticles (120) are superparamagnetic.

7. Method according to one of the preceding claims, wherein the magnetic nanoparticles (120) have a Curie temperature which lies in a range between 100°C and 1200°C, in particular between 150°C and 400°C.

8. Method according to one of the preceding claims, in which the distribution of the Curie temperatures of the individual magnetic nanoparticles (120, 121) has a half-width (FWHM) of not more than 50 °C, in particular not more than 30 °C.

9. A method according to any one of the preceding claims, wherein the ferromagnetic or ferrimagnetic material comprises a metallic alloy or a metal oxide, the alloy or metal oxide comprising at least one of the elements iron, cobalt and nickel.

10. An assembly (1) comprising at least two soldered connections which are joined and / or detachable by a method according to one of the preceding claims, wherein a soldered connection comprises a first soldering partner (10) and a second soldering partner (20), which soldering partners (10, 20) are connectable or connected by a solder (100), which solder (100) comprises a metallic solder material (110) and magnetic nanoparticles embedded therein, wherein the embedded magnetic nanoparticles make up a weight fraction of the total solder (100 / 101 / 102) of between 1% and 30% and wherein the solder composition of the second solder connection differs from the solder composition of the first solder connection.

11. Assembly (1) according to claim 10, wherein the first soldering partner (10) is an electrical circuit carrier and the second soldering partners (20) are electrical or electronic components.

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