Method for producing a semiconductor assembly comprising a heat sink

Abstract

The invention relates to a method for producing a semiconductor assembly (24) comprising a heat sink (2). The aim of the invention is to reduce production costs. This aim is achieved by the following steps: providing a heat sink (2) which is made of a first metal material; applying (A), by means of a thermal spraying method, a second metal material, which differs from the first metal material, in order to form an adhesion-promoting layer (16) on at least one, in particular planar, surface (10) of the heat sink (2), wherein the second metal material contains first particles (20) and second particles (22), wherein the first particles (20) and the second particles (22) are made of different elements or alloys; and integrally bonding (B) at least one substrate (26) on the adhesion-promoting layer (16).

Description

[0001] Description

[0002] Method for producing a semiconductor device with a heat sink

[0003] The invention relates to a method for producing a semiconductor device with a heat sink.

[0004] Furthermore, the invention relates to a semiconductor device with a heat sink.

[0005] Furthermore, the invention relates to a power converter with at least one such semiconductor arrangement.

[0006] In such power converters, semiconductor devices are typically mounted on a heat sink. A power converter can be, for example, a rectifier, an inverter, a converter, or a DC-DC converter. Typically, the semiconductor devices are designed as electronic modules that have a housing and are screwed onto the heat sink via a solid metal base plate. Furthermore, the semiconductor devices can be connected directly to the heat sink, i.e., without an additional connecting element such as a base plate.

[0007] The published patent application EP 4 023 733 A1 describes a heat conductor with a high thermal conductivity coefficient, which can be used for heat dissipation for a semiconductor device and can be used in particular in the region of the semiconductor device packaging. The heat conductor contains a matrix, a diamond particle, and a first metal nanoparticle distributed in the matrix, and an outer surface of the diamond particle contains, in sequence, a carbide film layer, a first metal film layer, and a second metal film layer. The three film layers are used to reduce the thermal interfacial resistance between the diamond particle and the first metal nanoparticle. Furthermore, this application provides a liquid thermally conductive material and a semiconductor packaging structure using the aforementioned heat conductor.

[0008] The published patent application US 2015 / 077941 A1 describes an electronic device with a power module having a first main surface and a second main surface opposite the first main surface, wherein at least a portion of the first main surface is configured as a heat-dissipating surface without electrical power connection functionality. The electronic component comprises a porous metal layer arranged on the portion of the first main surface. The porous metal layer can be produced using suitable particle deposition techniques, such as jet dispersion or flame spraying.

[0009] For the material-to-material bonding of components on the heat sink for the production of a semiconductor device, an adhesion-promoting layer may be required. Such layers are applied, for example, from nickel by electroplating, which is a cost-intensive process step. Against this background, it is an object of the present invention to reduce the manufacturing costs for a semiconductor device.

[0010] This object is achieved according to the invention by a method for producing a semiconductor device with a heat sink, comprising the following steps: providing a heat sink which is made from a first metallic material, applying a second metallic material which differs from the first metallic material by means of a thermal spraying process to form an adhesion-promoting layer on at least one, in particular planar, surface of the heat sink, wherein the second metallic material contains first particles and second particles, wherein the first particles and the second particles are made from different elements or alloys, materially bonding at least one substrate to the adhesion-promoting layer.

[0011] Furthermore, the object is achieved according to the invention by a semiconductor arrangement with a heat sink made of a first metallic material, wherein an adhesion-promoting layer made of a second metallic material, which differs from the first metallic material, is arranged on at least one, in particular flat, surface of the heat sink, wherein the adhesion-promoting layer is produced by means of a thermal spraying process from first particles and second particles of the second metallic material, wherein the first particles and the second particles are produced from different elements or alloys, wherein a substrate is materially bonded to the adhesion-promoting layer.

[0012] Furthermore, the object is achieved according to the invention by a power converter with at least one such semiconductor arrangement.

[0013] The advantages and preferred embodiments listed below with regard to the method can be transferred analogously to the semiconductor device and the power converter.

[0014] The invention is based on the idea of ​​reducing the manufacturing costs for a semiconductor device by applying an adhesion-promoting layer made of a second metallic material, in particular over a large area, to a surface of a heat sink made of a first metallic material which differs from the second metallic material using a thermal spraying process. In particular, the metallic adhesion-promoting layer is electrically and thermally conductive. A substrate is then bonded in a material-to-material manner to the adhesion-promoting layer on the heat sink. Such spraying processes include molten bath spraying, arc spraying, plasma spraying, flame spraying, laser spraying and cold gas spraying. Soldering and sintering are among the methods suitable for bonding the substrate.Such a thermal spraying process is more cost-effective than, for example, electroplating with nickel, particularly when applying a thin adhesion-promoting layer.

[0015] The adhesion-promoting layer is formed from first particles and second particles of the second metallic material, which are made of different elements or alloys. The particles are deformed by their energy, in particular kinetic energy, upon impact and form the second metallic material through an adhesive structure. For example, expensive first particles are blended with cheaper second particles in order to reduce material costs, so that the manufacturing costs for the semiconductor device are further reduced. For example, high-purity and expensive metallic particles are blended with less pure metallic particles, in particular from a recycling process, in order to save material costs.

[0016] A further embodiment provides that the first particles and the second particles differ at least in terms of their thermal conductivity and / or their hardness. In particular, particles with high thermal conductivity are used to enable sufficient heat dissipation, while harder particles are added to increase the density and stability of the material combination.

[0017] A further embodiment provides that the second particles have a lower coefficient of thermal expansion than the first particles. By admixing particles with a lower coefficient of thermal expansion, the coefficient of expansion of the adhesion-promoting layer, in particular with respect to a ceramic of the substrate, is adjusted, thus increasing the service life of the arrangement. A further embodiment provides that the first particles contain copper and / or aluminum and the second particles contain iron and / or tin. By mixing copper, in particular high-purity copper, with less expensive iron particles, the costs of the coating can be significantly reduced. Furthermore, the greater hardness of the iron particles leads to an improvement in peel strength with little deterioration in thermal conductivity.For example, the second particles can be made of a tin-iron alloy which has a low oxidation rate, so that the surface of a copper-tin-iron mixture remains solderable for an additional longer period.

[0018] A further embodiment provides for the heat sink to be manufactured from an aluminum alloy by extrusion. An extruded heat sink can be manufactured from an aluminum alloy with a lower silicon content, e.g., from 0.1% to 1.0%, in particular from 0.1% to 0.6%, compared to a cast heat sink, for example, so that improved thermal conductivity is achieved.

[0019] A further embodiment provides that the proportion of first particles in the second metallic material is at least 60%. For example, the proportion of first particles to second particles in the second metallic material is 1.5 to 4 to 1, in particular 1.5 to 3 to 1. With such a ratio, there is only a slight deterioration in thermal conductivity, while sufficient peel strength is achieved.

[0020] Another embodiment provides for the particles to differ in their grain size. Different grain sizes increase the density and thus the stability of the material combination.

[0021] Another embodiment provides for the particles to be composed of a coarse powder and a fine powder, with the fine powder being obtained through a recycling process. For example, copper and iron particles are each composed of coarser particles and finer recycled particles. Using recycled particles further reduces costs and improves the sustainability of the assembly.

[0022] A further embodiment provides that an adhesion-promoting layer with a thickness, in particular a substantially constant thickness, in the range of 50 μm to 300 μm is formed by means of the thermal spraying process. Such a thickness enables a reliable, material-to-material bond between the substrate and the heat sink without a noticeable increase in thermal resistance.

[0023] Another embodiment provides for the material bonding of the substrate to the adhesion-promoting layer by soldering or sintering. Such a bond can be produced reliably and cost-effectively.

[0024] A further embodiment provides that after the material-to-material connection of the substrate, contact is made with at least one semiconductor element on a side of the substrate facing away from the heat sink. The contact can be made, among other things, by force-fitting or by a material-to-material connection. The semiconductor element can be designed, among other things, as an insulated-gate bipolar transistor (IGBT), as a metal-oxide-semiconductor field-effect transistor (MOSFET), as a power semiconductor with a wide band gap, in particular GaN or SiC power semiconductors. Such an arrangement ensures reliable heat dissipation of the semiconductor element during operation in a cost-effective manner.

[0025] The invention is described and explained in more detail below with reference to the exemplary embodiments shown in the figures. They show:

[0026] FIG 1 is a schematic three-dimensional sectional view of a heat sink for a semiconductor device,

[0027] FIG 2 is an enlarged schematic sectional view of a heat sink,

[0028] FIG 3 is a schematic sectional view of a semiconductor device with a heat sink,

[0029] FIG 4 is a flow diagram of a method for manufacturing a semiconductor device and

[0030] FIG 5 is a schematic diagram of a power converter.

[0031] The exemplary embodiments explained below are preferred embodiments of the invention. In the exemplary embodiments, the described components of the embodiments each represent individual features of the invention that are to be considered independently of one another. These also further develop the invention independently of one another and are thus to be regarded as components of the invention, either individually or in a combination other than that shown. Furthermore, the described embodiments can also be supplemented by further features of the invention already described.

[0032] The same reference symbols have the same meaning in the different figures.

[0033] FIG 1 shows a schematic three-dimensional sectional view of a heat sink 2 for a semiconductor device. The heat sink 2 has a base plate 4 with cooling fins 6, wherein the cooling fins 6 are connected to the base plate 4. By way of example, in FIG 1 the base plate 4 and the cooling fins 6 of the heat sink 2 are designed as a single piece. The heat sink 2 is configured by the cooling fins 6 to conduct a, in particular gaseous, cooling fluid in a coolant flow direction 8, wherein the coolant flow direction 8 runs essentially parallel to a flat surface 10. The cooling fluid is, for example, air, which flows via a fan, which is not shown in FIG 1 for reasons of clarity, in the coolant flow direction 8 over the cooling fins 6 of the heat sink 2. The heat sink 2 is made from a first metallic material.The first metallic material can be, among other things, an aluminum alloy containing, for example, a silicon content of 0.1% to 1.0%, in particular 0.1% to 0.6%. Such a heat sink 2 can be manufactured, among other things, by extrusion.

[0034] In addition, the heat sink 2 has, for example, two regions 12, 14 on the surface 10, each of which is provided with an adhesion-promoting layer 16. The adhesion-promoting layer 16 is produced from a second metallic material, which differs from the first metallic material, by means of a thermal spraying process. One possible thermal spraying process is cold gas spraying. The adhesion-promoting layer 16 has an essentially constant thickness s in the range from 50 pm to 300 pm, so that in each case an essentially flat connecting surface 18 is formed which runs parallel to the surface 10. The adhesion-promoting layer 16 serves, for example, to connect a metallization, in particular copper metallization, of a substrate to the heat sink 2 in a material-to-material manner, in particular by soldering or sintering.

[0035] FIG 2 shows an enlarged schematic sectional view of a heat sink 2. The adhesion-promoting layer 16, which is applied to the surface 10 by cold gas spraying, is made of a second metallic material which contains first particles 20 and second particles 22. The first particles 20 contain, in particular, high-purity and thus expensive copper, while the second particles 22 contain iron, in particular pure iron. Thus, the first particles 20 have a higher thermal conductivity and electrical conductivity than the second particles 22, while the second particles 22 have a greater hardness than the first particles 20. Alternatively, the second particles 22 can be made of a tin-iron alloy which has a low oxidation rate, so that the surface of a copper-tin-iron mixture additionally remains solderable for longer.

[0036] For example, the adhesion-promoting layer 16 contains 60% to 80% first particles 20, while the remainder is composed of second particles 22. The mixing ratio is therefore 1.5 to 1 to 4 to 1. By adding the harder iron, the application effectiveness during cold gas spraying is increased, since the harder second particles 22 exert additional deformation energy on the softer first particles 20, so that the first particles 20 deform further and the adhesion-promoting layer 16 is strengthened more strongly. The thermal conductivity of the adhesion-promoting layer 16 is hardly significant due to the low thickness s in the pm range, while the cost position is considerably improved.

[0037] The particles 20, 22 can differ in their grain size, which further increases the thickness and improves the strength of the adhesion-promoting layer 16. For example, the particles 20, 22 can each be composed of a coarse powder and a fine powder, wherein the fine powder can be obtained through a recycling process. The further design of the heat sink 2 in FIG. 2 corresponds to the design in FIG. 1.

[0038] FIG 3 shows a schematic sectional view of a semiconductor arrangement 24 with a heat sink 2, which is designed, for example, as in one of FIGS. 1 or 2. A substrate 26, which is designed, for example, as a DGB substrate, is materially bonded to the adhesion-promoting layer 16. The materially bonded connection between a metallization 28 of the substrate 26 and the adhesion-promoting layer 16 is formed by a solder bonding layer 29. Alternatively, the materially bonded connection can be produced by sintering. On a side of the substrate 26 facing away from the heat sink 2, a semiconductor element 30, which is designed as an insulated-gate bipolar transistor (IGBT), is contacted as an example.Alternatively, the semiconductor element 30 can be embodied, among other things, as a metal-oxide-semiconductor field-effect transistor (MOSFET), as a wide-band-gap power semiconductor, in particular a GaN or SiC power semiconductor. The semiconductor element 30 is integrally connected to the substrate 26 by soldering or sintering. On a side facing away from the heat sink 2, the semiconductor element 30 is connected to the substrate 26 via wiring elements 32.

[0039] As can be seen from the following table , iron has a lower coefficient of thermal expansion ( GTE ) than copper .

[0040] By admixing iron with the copper of the second metallic material, the expansion coefficient, particularly with respect to an aluminum oxide or aluminum nitride ceramic of the substrate 26, is adjusted, thus preventing bending or detachment. The further design of the heat sink 2 in FIG. 3 corresponds to the design in FIG. 2.

[0041] FIG 4 shows a flow diagram of a method for producing a semiconductor device. After providing a heat sink made of a first metallic material, the method comprises applying a second metallic material, which differs from the first metallic material, to at least one, in particular flat, surface of the heat sink. The second metallic material is applied A by means of a thermal spraying process, whereby an adhesion-promoting layer is formed. The second metallic material contains first particles and second particles, wherein the first particles and the second particles differ at least with regard to their thermal conductivity and their hardness.

[0042] In a further step, a material bond B is formed between at least one substrate and the adhesion-promoting layer. The material bond B can be achieved by soldering or sintering, among other methods.

[0043] In a further step, contact C is made between at least one semiconductor element on a side of the substrate facing away from the heat sink. The contact C can be made by means of a material connection, e.g., by soldering or sintering, but also by means of a force connection, e.g., by pressing.

[0044] FIG. 5 shows a schematic representation of a power converter 34 with a semiconductor arrangement 24, which is designed as shown in FIG. 3. The power converter 34 can comprise more than one semiconductor arrangement 24.

[0045] In summary, the invention relates to a method for producing a semiconductor device 24 with a heat sink 2. In order to reduce the manufacturing costs, the following steps are proposed: providing a heat sink 2 which is made from a first metallic material, applying A a second metallic material which differs from the first metallic material by means of a thermal spraying process to form an adhesion-promoting layer 16 on at least one, in particular flat, surface 10 of the heat sink 2, wherein the second metallic material contains first particles 20 and second particles 22, wherein the first particles 20 and the second particles 22 are made from different elements or alloys, materially bonding B at least one substrate 26 to the adhesion-promoting layer 16.

Claims

Patent claims 1. A method for producing a semiconductor device (24) with a heat sink (2) comprising the following steps: - providing a heat sink (2) made of a first metallic material, - applying (A) a second metallic material, which differs from the first metallic material, by means of a thermal spraying process to form an adhesion-promoting layer (16) on at least one, in particular flat, surface (10) of the heat sink (2), wherein the second metallic material contains first particles (20) and second particles (22), wherein the first particles (20) and the second particles (22) are made of different elements or alloys, - materially bonding (B) at least one substrate (26) to the adhesion-promoting layer (16), wherein the materially bonding (B) of the substrate (26) to the adhesion-promoting layer (16) is effected by soldering or sintering.

2. The method according to claim 1, wherein the first particles (20) and the second particles (22) differ at least with regard to their thermal conductivity and / or their hardness.

3. Method according to one of claims 1 or 2, wherein the second particles (22) have a lower thermal expansion coefficient than the first particles (20).

4. Method according to one of the preceding claims wherein the first particles (20) contain copper and / or aluminum and the second particles (22) contain iron and / or tin.

5. Method according to one of the preceding claims, wherein the heat sink (2) is produced from an aluminum alloy by means of extrusion.

6. Method according to one of the preceding claims, wherein the proportion of first particles (20) is at least 60%.

7. Method according to one of the preceding claims, wherein the particles (20, (22) differ in their grain size.

8. The method according to claim 7, wherein the particles (20, 22) are each composed of a coarse powder and a fine powder, the fine powder being obtained by a recycling process.

9. Method according to one of the preceding claims, wherein an adhesion-promoting layer (16) with a, in particular substantially constant, thickness (s) in the range from 5 pm to 300 pm is formed by means of the thermal spraying method.

10. Method according to one of the preceding claims, wherein after the materially bonding (B) of the substrate (26), at least one semiconductor element (30) is contacted on a side of the substrate (26) facing away from the heat sink (2).

11. A semiconductor device (24) with a heat sink (2) made of a first metallic material, wherein an adhesion-promoting layer (16) made of a second metallic material, which differs from the first metallic material, is arranged on at least one, in particular flat, surface (10) of the heat sink (2), wherein the adhesion-promoting layer (16) is produced by means of a thermal spraying process from first particles (20) and second particles (22) of the second metallic material, wherein the first particles (20) and the second particles (22) are produced from different elements or alloys, wherein a substrate (26) is materially bonded to the adhesion-promoting layer (16), wherein the materially bonded connection of the substrate (26) to the adhesion-promoting layer (16) is produced by soldering or sintering.

12. Semiconductor arrangement (24) according to claim 11, wherein the first particles (20) and the second particles (22) differ at least with regard to their thermal conductivity and / or their hardness.

13. Semiconductor arrangement (24) according to one of claims 11 or 12, wherein the first particles (20) contain copper and / or aluminum and the second particles (22) contain iron.

14. Power converter (34) with at least one semiconductor device (24) according to one of claims 11 to 13.

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