WO2020114671A1

WO2020114671A1 - Insulating ceramic for electrical circuits and associated applications

Info

Publication number: WO2020114671A1
Application number: PCT/EP2019/078916
Authority: WO
Inventors: Roman Karmazin; Swen Ruppert; Uwe Waltrich
Original assignee: Siemens Aktiengesellschaft
Priority date: 2018-12-06
Filing date: 2019-10-23
Publication date: 2020-06-11
Also published as: DE102018221160A1

Abstract

The invention provides a ceramic insulator (1), comprising: - particles and/or fibres (2) of at least one metal in a predeterminable region (3) of the insulator, - wherein the concentration of the metal has a gradient varying the coefficient of thermal expansion and/or the coefficient of thermal conduction of the insulator (1). A circuit carrier arrangement, a circuit arrangement, a power converter and an aircraft having such an insulator are likewise provided.

Description

description

Insulating ceramics for electrical circuits and related applications

Field of the Invention

The invention relates to a ceramic insulating body, a circuit carrier arrangement with such an insulating body, a circuit arrangement with such a circuit carrier arrangement, a converter with such a circuit arrangement, and an aircraft with such a converter.

Background of the Invention

When developing power electronics systems, depending on the area of application, several problems arise:

1. A high lateral heat conduction ("thermal spreading") of circuit carriers or insulating substrates

Particularly in air-cooled power electronic systems with a low heat transfer coefficient to the cooling medium, a high temperature difference over the largest possible cooling surface is desirable. This requires a very high lateral thermal conduction due to very good heat-conducting layers that are as thick as possible, very close to the heat source (= chip). This homogenization of the temperature via a heat sink leads to better utilization of the cooling fins and thereby reduces the cooling surface or the cooling volume required. This can be achieved, for example, in the form of thick copper ferrules.

However, a high metallization thickness leads to increased thermo-mechanical stresses on the insulation. In the case of ceramic substrates in particular, this leads to a significant one Reduction of the service life, which is why the metallization thicknesses available on the market are limited.

2. An increasing ceramic thickness due to the trend towards high-blocking semiconductor components

With high-voltage modules (currently 6.5 kV, in future> 10 kV due to SiC), the ceramic insulation layers are significantly thicker, which will also increase the thermal resistance. Thick and laterally thermally conductive copper tracks are also an advantage here and new cooling concepts are urgently necessary.

3. A reduction in the connection layers within a power module

According to the prior art, power modules consist of a large number of individual components and thus of a multi-layer composite of functional and connecting layers. Each layer has a different coefficient of thermal expansion and different mechanical properties. With cyclical loading, due to temperature changes or vibrations, each shift increases the probability of failure. Therefore, the trend is towards reducing the number of layers within a module.

4. The low mechanical strength of the ceramic

As described above, cyclical loading causes modules to fail. In the case of high-performance modules in particular, ceramics are used as main insulators due to their good thermal conductivity. The highly thermally conductive ceramics to be preferred from a thermal point of view, however, have a very low mechanical strength and are therefore a critical component from a life point of view. Lateral heat conduction of classic power modules is mainly achieved through the copper metallization of the ceramic insulating substrates used. These have a max. lateral heat conduction less than 400 W / mK. For the thickest possible (> 300 ym) and therefore good heat-spreading metalizations (e.g. copper), very break-resistant ceramics are used (Si3N ₄₎ , which, however, only have thermal conductivity of less than 70 W / mK. The A1N ceramic (approx. 200 W / mK), which is often used in power electronics and has a much better heat conductivity, has insufficient crack toughness or breaking strength to withstand the thermomechanical stress with thick metallization layers.

The lifespan of ceramic substrates decreases significantly with increasing metallization thickness. Therefore, according to the prior art, it is not possible to produce “thick copper substrates” with highly heat-conductive ceramics (A1N) that have sufficiently high thermal fatigue strength to use them reliably and economically.

Aluminum nitride ceramics are used in particular in high-voltage applications, since very thick insulation layers are necessary to ensure the insulation (e.g. 1 mm for 6.5 kV modules) and the insulation thickness contributes directly to the heat sink in proportion to the thermal resistance of the chip. Thicker copper layers of the insulating substrates are also advantageous here for thermal "spreading". Furthermore, the service life requirements are very demanding, especially in high-voltage applications (for example 40 years in high-voltage direct current applications - HVDC), which is why mechanically more robust AIN ceramics would be desirable. A main cause of failure is currently still the delamination of the metalizations from the AIN ceramic, which reduces the thermal bonding of the chip and can therefore lead to the failure of the systems.

To increase the thermal shock load of A1N ceramic substrates, all around the metallization Dimpel structures introduced for thermo-mechanical weakening. However, this measure results in a reduction in the usable substrate area. In addition, the effect is not so high to apply significantly thicker copper layers.

Thicker copper layers can be fired on with copper paste systems. The disadvantage is the complex process (stencil printing, expensive firing costs) and the reduced thermal and electrical conductivity of the porous metal or copper pastes.

In general, high thermal resistances and associated service life problems are compensated for by increasing the chip area or overdimensioning the power modules. This results in high costs, additional peripherals (control, etc.) and additional weight.

The comparatively low mechanical strength of the ceramics or ceramic substrates is compensated for by expensive and weight-intensive composite materials, which have a thermal expansion coefficient adapted to the ceramic and stiffen the layer composite.

Summary of the invention

It is an object of the invention to provide a solution by means of which the disadvantages of insulating ceramics described can be avoided when used in circuit arrangements.

The invention results from the features of the independent claims. Advantageous further developments and refinements are the subject of the dependent claims. Further features, possible applications and advantages of the invention result from the following description.

One aspect of the invention is to infiltrate a metal (eg Cu, Al) into a ceramic insulating substrate. strat (especially aluminum nitride) to achieve a gradual (= step-less) adjustment of the different thermal expansion coefficients of the metallization and the ceramic and thus to increase the metallization thickness significantly. A porous AIN ceramic is infiltrated with metal using an elevated temperature and / or an increased pressure, thereby creating a concentration gradient of the metal.

A concentration gradient or concentration gradient of a substance (also sometimes referred to as a substance gradient) between two locations of a solid body, a liquid or a gas exists when the concentrations of the substance prevailing there differ from one another.

The invention claims a ceramic insulating body (also referred to as an insulating substrate) with particles and / or fibers of at least one metal in a predeterminable region of the insulating body, the concentration of the metal having a gradient which changes the coefficient of thermal expansion and / or the thermal conductivity of the insulating body.

The invention offers the advantage that the grading allows thermal expansion coefficients and / or thermal conductivity coefficients from neighboring regions (such as layers) to be matched to one another, so that the difference between these coefficients is reduced.

In one development, the gradient can be designed to make the coefficient of thermal expansion of the insulating body in an edge region to an adjacent layer more similar to the coefficient of thermal expansion of the adjacent layer. In a further form, the gradient can be designed to increase the heat conduction coefficient of the insulating body in an edge region.

In addition, a different concentration of metals can be introduced in a lower area than in an outer area. This also covers a continuously increasing grade.

In a further embodiment, the ceramic insulating body can be formed from aluminum nitride and the metal can be copper or aluminum.

Another aspect of the invention is to use the ceramic insulating body described above in a circuit carrier arrangement. This makes it possible to bring the different thermal expansion coefficients of a ceramic and a metal closer together, thereby avoiding excessive mechanical stresses caused by thermal alternating stress.

The invention claims a circuit carrier arrangement with a ceramic insulating body according to the invention and a metallic first layer on the top of the Isolierkör pers.

In one development, the circuit carrier arrangement has a metallic second layer on the underside of the insulating body.

In a further embodiment, cooling fins can be formed in the insulating body on the side facing away from the first layer.

In a further embodiment, a metallic heat sink can be integrally connected to the second layer. In a further embodiment, cooling fins can be formed in the second layer on the side facing away from the first layer.

Another aspect of the invention is to use the described circuit carrier arrangement for an electrical circuit. As a result, electrical and electronic circuits can be made more robust against temperature changes.

The invention claims a circuit arrangement with a circuit carrier arrangement according to the invention and with at least one power electronic semiconductor component which is arranged on the first layer.

Another aspect of the invention is to insert the described circuit arrangement into a converter.

The invention claims a power converter with a circuit arrangement according to the invention, the power converter being preferably a converter.

Another aspect of the invention is to use the designated power converter in an aircraft, which increases its reliability.

The invention claims an aircraft with an inventive converter according to the invention for the electrical supply of an electrical thrust generating unit.

In one development, the aircraft can be an aircraft and the electric thrust generating unit can have a propeller and an electric motor driving the propeller.

The invention offers a number of advantages: Increasing the reliably applied metallization thickness on ceramic insulation substrates and thus increasing the lateral thermal conductivity.

Increase in the thermal shock resistance of ceramic insulating substrates by gradual adaptation of the thermal expansion coefficient of the ceramic insulating substrate to the metallization layer (e.g. Cu, Al).

Increasing the thermal conductivity of ceramic cooling structures through extensive metallization infiltration => reduction in the thermal decay length or effectiveness of ceramic cooling structures

Increasing the mechanical strength of the ceramic through filtration

Introduction of pre-stresses in the ceramic to increase the tensile strength and bending strength of the ceramic.

Reinforcement of the ceramic through infiltrated metallization (e.g. increasing the mechanical robustness of cooling structures).

Reduction in the number of layers compared to a conventional structure and a conventional connection technology.

Infiltration of different metals on both sides of a flat insulating substrate (structured Cu top as electrical conductor, aluminum structure on the bottom as corrosion-resistant heat sink geometry). A high layer thickness through infiltration and grading (CTE adaptation, CTE = Coefficient of Thermal Expansion) is possible.

Application of an aluminum metallization on the underside of aluminum nitride substrates, for the integral connection to aluminum heat sinks by means of relevant processes (friction, stirring, laser welding, diffusion bonding, 3D printing on an aluminum metallization). As an alternative to infiltration, a graded structure can be achieved by "diffusion bonding" two metals (eg Al and Cu). Two metals are firmly bonded together under the effect of temperature and pressure. In the process, one is created at the boundary between the two metals Diffusion zone.

A converter, which is also called an inverter, is a converter that generates an AC voltage with a frequency and amplitude that is changed from an AC voltage or DC voltage. Inverters are often designed as AC / DC-DC / AC inverters or DC / AC inverters, an AC output voltage being generated from an AC input voltage or an input DC voltage via a DC voltage intermediate circuit and clocked semiconductors.

Aircraft is understood to mean any type of flying means of transportation or transportation, be it manned or unmanned.

Further special features and advantages of the invention will become apparent from the following explanations of several exemplary embodiments with reference to schematic drawings.

Brief description of the drawings

1 shows a circuit carrier arrangement with a metal coating on one side,

Fig. 2 shows a circuit carrier arrangement with a two-sided metal coating,

Fig. 3 shows a further circuit carrier arrangement with a double-sided metal coating, 4 shows a circuit arrangement, 5 is a block diagram of an inverter with a

Circuit arrangement and

Fig. 6 an aircraft with an electric flight drive.

Detailed description of the invention

Fig. 1 shows a cross section through a circuit carrier arrangement 5 with a ceramic insulating body 1, in which cooling fins 1.1 are formed. On the top of the insulating body 1 there is a metallic first layer 4.1. The material of the ceramic insulating body 1 is preferably a porous aluminum nitride, the metallic first layer is preferably made of copper or aluminum.

The edge region 3.1 of the insulating body 1 has particles and / or fibers 2 made of metal, the concentration of the metal having a graded course (= gradient), as a result of which the thermal expansion coefficient of the insulating body 1 is adapted to the thermal expansion coefficient of the first layer 4.1. As a result, the mechanical stress at the boundary layer during temperature changes is reduced since the thermal expansions of the neighboring materials are more similar. The particles or fibers 2 are preferably made of copper or aluminum and are introduced into the porous ceramic insulating body 1 by known methods of infiltration.

Optionally (not shown), the edge layer of the cooling fins 1.1 can also be provided by infiltration with particles or fibers 2 of a metal, as a result of which the heat conductivity of the insulating body 1 in the edge region is increased and thus the heat emission is improved. Due to the graded course of the concentration, thermally induced voltages are reduced in comparison to a pure metal layer on the insulating body 1. An electrical component (not shown) can be arranged on the first layer 4.1 to form a circuit arrangement.

Fig. 2 shows a cross section through a further circuit carrier arrangement 5 with a ceramic insulating body 1. On the top of the insulating body 1 there is a metallic first layer 4.1, on the bottom a metallic second layer 4.2 is formed. The material of the insulating body 1 is preferably a porous aluminum nitride, the metallic first and second layers 4.1, 4.2 preferably consist of copper or aluminum.

To adjust the thermal expansion coefficient of the insulating body 1 and the first and second layers 4.1, 4.2, the edge regions 3.1 of the porous ceramic insulating body 1 have particles and / or fibers 2 made of metal, the concentration of the metal showing a graded course. The particles or fibers 2 are preferably made of copper or aluminum and are introduced into the porous ceramic insulating body 1 by infiltration.

An electrical component (not shown) can be arranged on the first layer 4.1 to form a circuit arrangement.

Fig. 3 shows a cross section through a further circuit carrier arrangement 5 with a ceramic insulating body 1. On the top of the insulating body 1 there is a metallic first layer 4.1, on the underside a metallic second layer 4.2 is formed. The material of the insulating body 1 is preferably a porous aluminum nitride, the metallic first and second layers 4.1, 4.2 preferably consist of copper or aluminum.

To adapt the thermal expansion coefficient of the insulating body 1 and the first and second layers 4.1, 4.2 have the edge regions 3.1 of the porous ceramic insulating body 1 particles and / or fibers 2 made of metal, the concentration of the metal showing a graded course. The particles or fibers 2 are preferably made of copper or aluminum and are introduced into the porous ceramic insulating body 1 by infiltration.

On the second layer 4.2, a metallic heat sink 4.2 is arranged cohesively. An electrical component (not shown) can be arranged on the first layer 4.1 to form a circuit arrangement.

Fig. 4 shows a cross section through a circuit arrangement with a circuit carrier arrangement 5 with a ceramic insulating body 1. On the top of the insulating body 1 there is a metallic first layer 4.1, on the underside a second layer 4.2 with metallic cooling ribs 4.4 is formed. The material of the insulating body 1 is preferably a porous aluminum nitride, the metallic first layer 4.1 preferably consists of copper or aluminum, the metallic cooling fins 4.4 preferably of aluminum.

To adapt the thermal expansion coefficient of the insulating body 1 with the first layer 4.1 and the cooling ribs 4.4, the edge regions 3.1 of the porous insulating body 1 have particles and / or fibers 2 made of metal, the concentration of the metal showing a graded course. The particles or fibers 2 are preferably made of copper or aluminum and are introduced by infiltration into the porous ceramic insulating body 1.

On the first layer 4.2, a power electronic semiconductor component 6 is partially arranged as an example of an electrical construction.

Fig. 5 shows a block diagram of a converter 7 as an example of a power converter with a circuit carrier arrangement 5 according to FIG. 1 to FIG. 4. The power electronic semiconductor components 6 are seated on the circuit carrier arrangement 5.

FIG. 6 shows an electric or hybrid-electric aircraft 8 as an example of an aircraft with a converter 7 according to FIG. 5, which supplies an electric motor 9.2 with electrical energy. The electric motor 9.2 drives a propeller 9.1. Both are part of an electrical thrust generation unit 9.

Although the invention has been illustrated and described in more detail by means of the exemplary embodiments, the invention is not restricted by the disclosed examples and other variations can be derived therefrom by a person skilled in the art without departing from the scope of protection of the invention.

Reference symbol list

1 ceramic insulator

1.1 Cooling tips in the insulating body

2 particles and / or fibers of a metal

3 Area of the insulating body 1

3.1 Edge area of the insulating body 1

4 Adjacent layer

4.1 First layer

4.2 Second layer

4.3 Metallic heat sink

4.4 Metallic cooling fins

5 circuit carrier arrangement

6 Power electronic semiconductor component

7 inverters

8 plane

9 Electric thrust generating unit

9.1 propeller

9.2 Electric motor

Claims

1. Ceramic insulating body (1),

marked by :

Particles and / or fibers (2) of at least one metal in a predeterminable region (3) of the insulating body,

wherein the concentration of the metal has a thermal expansion coefficient and / or the Wärmeleitkoeffizien th of the insulating body (1) changing gradient.

2. Ceramic insulating body (1) according to claim 1,

characterized,

that the gradient is designed to make the thermal expansion coefficient of the insulating body (1) in an edge region (3.1) to an adjacent layer (4) similar to the thermal expansion coefficient of the adjacent layer (4).

3. Ceramic insulating body (1) according to claim 1,

characterized,

that the gradient is designed to increase the coefficient of heat conduction of the insulating body (1) in an edge region (3.1).

4. Ceramic insulating body (1) according to one of the preceding claims,

characterized,

that the ceramic insulating body (1) is formed from aluminum nitride and the metal is copper or aluminum.

5. Circuit carrier arrangement (5) with a ceramic insulating body (1) according to one of the preceding claims, characterized by:

a metallic first layer (4.1) on the top of the ceramic insulating body (1).

6. circuit carrier arrangement (5) according to claim 5, marked by:

a metallic second layer (4.2) on the underside of the ceramic insulating body (1).

7. circuit carrier arrangement (5) according to claim 5,

characterized,

that cooling fins (1.1) are formed in the ceramic insulating body (1) on the side facing away from the first layer (4.1).

8. circuit carrier arrangement (5) according to claim 6,

marked by:

a metallic heat sink (4.3) which is integrally connected to the second layer (4.2).

9. circuit carrier arrangement (5) according to claim 6,

characterized,

that metallic cooling fins (4.4) are formed in the second layer (4.2) on the side facing away from the first layer (4.1).

10. Circuit arrangement with a circuit carrier arrangement (5) according to one of claims 5 to 9,

marked by:

at least one power electronic semiconductor component (6) which is arranged on the first layer (4.1).

11. Converter with a circuit arrangement according to claim 10.

12. Converter according to claim 11,

characterized,

that the converter is a converter (7).

13. Aircraft with a converter according to claim 11 or 12 for the electrical supply of an electrical Schuberzeu supply unit (9).

14. Aircraft according to claim 13,

characterized,

that the aircraft is an aircraft (8) and the electrical thrust generating unit (9) has a propeller (9.1) and an electric motor (9.2) driving the propeller (9.1).