Method for thermal spraying of conductor tracks and electronic module

Abstract

The invention relates to a method for thermal spraying of at least one conductor track (20) formed using a first, electrically conductive material (40). The at least one conductor track is additionally sprayed using at least one second metallic material (50) having a lower melting point than the first material (40). An electronic module has at least one conductor track (20), wherein the conductor track (20) is formed using a first, electrically conductive material (40) and additionally using a second metallic material (50), wherein the second material (50) has a lower melting point than the first material (40), and wherein the first material (40) and the second material (50) mutually diffuse, in particular alloy and / or mix.

Description

TECHNICAL FIELD

[0001] The invention relates to a method for thermal spraying of a conductor track formed from a metallic material and to an electronic module. BACKGROUND

[0002] A new build-up and connection technology in the manufacture of electronic modules represents the thermal spraying of a conductor track formed from copper or another metallic material on an insulating layer of such an electronic module. Semiconductor components of the electronic module can be electrically contacted by means of the thermally sprayed conductor track. The sprayed conductor track can thus in principle replace conventionally manufactured wire bonds, ribbon bonds or electroplated copper structures of the electronic module.

[0003] However, the thermal spraying of a conductor track formed in particular from copper requires high process temperatures in order to achieve a sufficient electrical conductivity of the conductor track.

[0004] These high process temperatures can degrade or even damage the semiconductor components of the power module. SUMMARY

[0005] The technical problem addressed by the invention is therefore to propose an improved method for thermal spraying of a conductor track formed from a metallic material onto an insulating layer, in particular of an electronic module, which preferably does not impair the insulating layer or other components of the electronic module. Furthermore, the technical problem addressed by the invention is to propose an electronic module which can be easily manufactured by means of the method according to the invention.

[0006] The technical problem addressed by the invention is solved by means of the method having the features specified in claim 1 and the electronic module having the features specified in claim 10. Preferred refinements of the invention are given in the dependent claims, the subsequent description and the figures.

[0007] By means of the method for thermal spraying according to the invention, at least one conductor track is not formed solely by means of thermal spraying of a first, electrically conductive material which is metallic, but rather the first material is combined with at least one second material which has a lower melting point than the first material.

[0008] Due to the lower temperatures required for thermal spraying, the conductor track can be produced with a significantly lower temperature load of the surroundings of the at least one conductor track. In particular, the insulation layer provided as necessary or the substrate on which the at least one conductor track is formed can be exposed to a significantly lower temperature load. Thus, the at least one conductor track can be produced such that one or more components of an electronic module, which is produced using the at least one conductor track, are less strongly degraded or not degraded at all, and in particular the semiconductor components of the electronic module are not damaged or not damaged to a noticeable extent. Due to the low process temperatures which can be used according to the application, compared to the prior art, it is possible to consider using a greater variety of insulating materials for the insulation layer. Thus, the choice of insulating material is not limited by the high particle temperature of the first material.

[0009] In particular, due to the low melting point of the second material, a mutual diffusion process can be used, so that intermetallic phases of the first and second material can be produced at particularly low temperatures. In this way, a significantly lower particle temperature of the conductor track compared to the first material can be achieved, and at the same time a significantly higher electrical conductivity of the conductor track compared to the second material can be achieved. Thus advantageously, the conductor track and thus also the power module can be produced particularly reliably on the substrate.

[0010] In this process, the second material acts to some extent as a cement between the particles of the first material. In the case of copper as the first material and tin as the second material, the melting point of the tin is significantly at a lower temperature compared to the melting point of the copper, namely at 232°C compared to 1085°C. This difference in the melting temperature allows a significant reduction in the plasma temperature and thus a significant reduction in the temperature of the particle ensemble. Only the first material, for example tin, has to be in the liquid or gaseous phase, while the temperature of the particles of the second material, for example copper particles, has to be varied in a wide range depending on the desired properties of the layer to be produced.

[0011] Optionally and advantageously, after the first and second material have been sprayed, the first and second material can be heated in an additional step of the method according to the application. In this way, the first and second material can mutually diffuse.

[0012] Advantageously, a high-strength and tear-resistant intermetallic phase can be achieved according to the application. Furthermore, voids in the first material can be suitably avoided. This is because, due to the lower temperatures, particularly low porosities and thus high layer qualities and thus particularly high electrical conductivities can be achieved.

[0013] Advantageously, according to the application, a high-melting metal layer can be produced as a conductor track which at the same time has a high temperature stability. Thus, the conductor track is on the one hand easy to produce and on the other hand at the same time temperature-stable.

[0014] Furthermore advantageously, the method according to the application opens up additional degrees of freedom for the production of conductor tracks.

[0015] In the method according to the application, preferably, the first material is formed using copper and / or aluminum and / or gold and / or silver and / or titanium and / or nickel and / or molybdenum and / or other metals. Particularly preferably, the first material is copper or aluminum or gold or silver or titanium or nickel or molybdenum or other metals.

[0016] In a preferred extension of the method according to the application, the second material is formed using tin and / or aluminum and / or other metals. Particularly preferably, the second material is tin or aluminum or other metals. Tin and / or aluminum have a sufficiently low melting point compared to typical conductor track materials.

[0017] In the method according to the application, expediently, the second material has a melting point of at most 900 degrees Celsius, preferably at most 400 degrees Celsius, preferably at most 300 degrees Celsius and ideally at most 250 degrees Celsius. In this extension, due to the lower melting temperature of the second material compared to the first material, the thermal load of the substrate can be limited to at most the aforementioned temperature threshold and thus to a significantly reduced temperature value compared to conventional conductor track materials. Thus, degradation of the substrate or other elements connected to the conductor track can be particularly reliably avoided.

[0018] In the method according to the application, in an advantageous extension, the following particles are considered, which have a core with the first material and a layer with the second material, which coats the core, preferably over the entire circumference. In this way, the metal interdiffusion of the first and second material can take place particularly effectively, since the first and second material are already arranged close to each other on the spatial scale of the particle size.

[0019] In the method according to the application, advantageously, the second material and the first material are deposited alternately over time. In this extension of the application, the first and second material are also so close to each other on the size scale of the layers of the alternating deposition of the first and second material that the interdiffusion of the first and second material can take place particularly effectively.

[0020] In the method according to the application, preferably, the second material is deposited first and the first material is subsequently deposited. In this way, the second material can be deposited with a temperature that is sufficient for the second material and thus lower compared to the first material alone. The first material can be deposited onto the second material layer deposited in this way, which has already been combined into a mixture or alloy with the second material by means of interdiffusion at the lower melting temperature of the second material.

[0021] In an electronic module according to the invention having at least one conductor, the conductor is formed with a first electrically conductive material and additionally with at least one second metallic material, wherein the second material has a lower melting point than the first material, and wherein the first and second materials diffuse into one another, in particular alloy and / or mix.

[0022] Particularly preferably, the electronic module according to the invention is produced according to the method according to the invention as described above. In the electronic module according to the invention, at least one conductor track has an island formed by means of the first material.

[0023] The electronic module according to the invention is preferably a power module and preferably has at least one power component, in particular a semiconductor component, which is contact-connected by means of at least one conductor line. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The present invention will now be described in detail with reference to the embodiments shown in the accompanying drawings.

[0025] Figure 1 A first embodiment of the method according to the invention for producing a first embodiment of an electronic module according to the invention is schematically shown in cross section;

[0026] Figure 2 A second embodiment of the method according to the invention for producing a second embodiment of an electronic module according to the invention is schematically shown in cross section;

[0027] Figure 3 A third embodiment of the method according to the invention for producing a third embodiment of the electronic module according to the invention is schematically shown in cross section. DETAILED DESCRIPTION

[0028] Figure 1 The electronic module according to the invention shown in FIG. 1 is a power module 10 and is provided in a production step of the method according to the invention with conductor tracks 20 made of copper which are in electrical contact with semiconductor components (not explicitly shown) of the power module 10 .

[0029] In the illustrated production step, conductor track 20 is formed by thermal spraying a particle mixture 30 comprising uniformly mixed copper particles 40 and tin particles 50. Copper forms the first material, and tin forms the second material. In principle, in other exemplary embodiments, the first metallic material can be formed using a different metal, and the second metallic material can be formed using another metal, wherein the second metallic material has a lower melting point than the first material.

[0030] The copper particles 40 and the tin particles 50 have a size, ie a diameter, of between 5 and 50 micrometers.

[0031] The copper particles 40 and the tin particles 50 are stored as a particle mixture 30 in a powder feeder 60 and are fed to a plasma nozzle 70. The plasma nozzle 70 converts the particle mixture 30 into a plasma 80 having a temperature between 200°C and 20,000°C, which heats the particle mixture to a temperature of at least 200 degrees Celsius and at most 1,000 degrees Celsius. At the mentioned plasma temperatures, the tin of the tin particles 50 becomes liquid depending on the contact time of the tin particles 50, whereas, in contrast, the copper particles 40 remain in a solid aggregate state.

[0032] In principle, a higher particle temperature, for example 800 degrees Celsius, can also be selected in the method according to the application, at which temperature the copper particles 40 remain mainly in a solid aggregate state and at most are melted, whereas, in contrast, the tin of the tin particles 50 has already partially been converted into the gas phase.

[0033] The plasma 80 impinges onto a substrate 90, which is temperature-regulated by means of a substrate holder which is heated, and is deposited there as a layer 100. A mutual diffusion process of the tin of the tin particles 50 and the copper of the copper particles 40 takes place in the plasma 80 and on the substrate 90. Such a mutual diffusion process is known, for example, also from diffusion welding and leads to a stable metallographic in the layer 100. Copper islands, which arise from the copper particles 40, still form the main volume fraction of the layer 100, in which copper is present almost purely, i.e. without a diffused tin fraction. The mutual diffusion process ends when all tin particles 50 have participated in the mutual diffusion process, so that no further tin particles 50 are available, or when the diffusion length of the tin atoms becomes too great, or when the heat treatment is interrupted. Subsequently, the mutual diffusion process can also be achieved by an additional temperature development, for example in an oven.

[0034] The composition of the layer 100 can be set by the composition of the particle mixture 30.

[0035] In principle, further alloying elements, such as silicon and / or silver and / or lead, can additionally be added in further not specifically shown embodiments. In further not specifically shown embodiments of the method according to the application, the copper particles 40 are not only melted, but completely melted. In further not shown embodiments, the copper particles 40 are not at all melted, but the copper particles 40 are completely present as solids.

[0036] The layer 100 is structured along a surface 110 of the substrate 90 by means of a not specifically shown mask or by means of a suitable structuring of the surface of the substrate 90, so that the layer 100 forms a conductor track 20 which is guided along the surface 110 of the substrate 90.

[0037] Figure 2 The embodiments shown in Fig. 1 essentially correspond to the embodiments shown in Fig. 2, unless stated otherwise hereinafter: Figure 1 The embodiments shown in Fig. 1 essentially correspond to the embodiments shown in Fig. 2, unless stated otherwise hereinafter:

[0038] Instead of the particle mixture 30, in accordance with Figure 2 In the method shown for producing the power module 200 according to the application, a plurality 230 of identical particles in the form of composite particles 240 is considered. The plurality 230 of composite particles 240 has a core-shell structure. In this core-shell structure, approximately spherical copper particles 250 form the core of the composite particles 240.

[0039] In principle, the copper particles 250 do not have to be shaped as spheres, but can also be shaped as any other shape, for example as ellipsoidal or as rod-shaped elongated or as polyhedrons. The copper particles 250 are covered by a tin layer 260, which, in the embodiment shown, completely surrounds and covers the copper particles 250 on the full surface. In further embodiments corresponding to the embodiment shown, the tin layer 260 at least partially covers the surface of the copper particles 250. A "splash" form is also conceivable, in which Cu and Sn are present next to each other and thus do not surround each other.

[0040] The ratio of the thickness of the tin layer 260 to the diameter of the copper particles 250 here determines the volume fraction of tin and copper of the plurality 230 of composite particles 240 and thus of the tin and copper in the layer 280 deposited on the substrate 90.

[0041] As in the embodiment described according to Figure 1 The composite particles 240 are converted into a plasma 270 by means of the plasma nozzle 70, wherein the tin layer 260 is converted into a liquid or gaseous phase, as in the embodiment described according to Figure 1 The plasma 270 is deposited as a layer 280 on the substrate 90, as described according to

[0042] In the embodiment according to Figure 2 In this embodiment, further alloying elements can also optionally additionally be added to the plasma.

[0043] In Figure 3In the embodiment shown in the middle, the power module 300 according to the application is manufactured in such a way that the layer 310 is deposited on the substrate 90 in the form of alternating layers of copper and tin. To this end, for example, a thin tin layer 325 is first deposited on the substrate 90 by means of tin particles 50 converted into a plasma with the plasma nozzle 70. This can be carried out at a lower temperature than in the case of copper, for example at a particle temperature of approximately 223 degrees Celsius, due to the lower melting temperature of tin compared to copper. Then, hot copper particles 40 are converted into a plasma and a hot copper layer 330 is deposited by means of the copper particles 40. The tin layer 325 first protects the substrate 90 from the thermal impact of the copper particles 40. After coating onto the tin layer 325, the copper of the copper particles 40 and the tin of the tin particles 50 interdiffuse and form a stable metallographic phase. In the embodiment shown, the alternating deposition of tin and copper is optionally repeated one or more times. Alternatively, it is also possible to carry out a continuous thermal spraying of copper only. Also in this case, the copper particles 40 are converted into a plasma with the plasma nozzle 70 and the copper layer 330 is deposited on the tin layer 325. The copper particles 40 and the tin particles 50 interdiffuse and form a stable metallographic phase. Figure 3 In the embodiment shown in the middle, the regions of the pure copper layer 330 result in the main share of the electrical conductivity.

[0044] In all embodiments described above, it is also possible to carry out an interdiffusion process after the spraying. For example, the layers 100, 280, 325, 330 can subsequently be heat treated, for example at a temperature in the range between 200 degrees Celsius and 500 degrees Celsius. Thus, a CuSn metallographic phase can be formed during the heat treatment, which can last for a few minutes or hours, for example. Preferably, the metallographic phase is formed as Cu3Sn and Cu6Sn5.

[0045] Furthermore, the CuSn system can only be regarded as a representative of diffusion soldering materials. In general, combinations consisting of many further metal systems, for example silver and / or gold and / or aluminum and / or titanium and / or nickel and / or one or more other metals, are also possible.

Claims

1. A method for thermal spraying of at least one conductor track (20) formed of a first material (40) which utilizes a metal and is electrically conductive onto an insulating layer, wherein The at least one conductor track is additionally sprayed by means of at least one metallic second material (50) which has a lower melting point than the first material (40), wherein the second material (50) is deposited first and the first material (40) is deposited subsequently.

2. The method of claim 1, wherein, The first material (40) is formed using copper and / or aluminum and / or gold and / or silver and / or titanium and / or nickel and / or molybdenum.

3. The method of claim 1, wherein, The second material (50) is formed using tin and / or aluminum and / or gold and / or silver.

4. The method of any one of claims 1 to 3, wherein, The second material (50) has a melting point of at most 800 degrees Celsius.

5. The method of any one of claims 1 to 3, wherein, The following particle is considered, which has a splashing shape.

6. The method of any one of claims 1 to 3, wherein, The second material (320) and the first material (330) are deposited alternately over time.

7. The method of any one of claims 1 to 3, wherein, The first and second material are heated after they have been sprayed.

8. Electronic module having at least one conductor track (20) on an insulating layer, in which the conductor track (20) is formed using a metallic and electrically conductive first material (40) and additionally by means of at least one metallic second material (50), wherein The second material (50) has a lower melting point than the first material (40), and wherein the second material (50) is present in a deposited manner on an insulating layer and the first material (40) is present in a deposited manner on the second material (50), and wherein the first material (40) and the second material (50) mutually diffuse.

9. The electronic module of claim 8, wherein, The at least one conductor track (20) has an island formed by means of a first material (40).

10. Electronic module according to claim 8 or 9, which is a power module (10, 200, 300).

11. Electronic module according to claim 8 or 9, having at least one power component which is contacted by means of at least one conductor track.

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