WO2021183084A1

WO2021183084A1 - Power conversion circuit having components with a thermal expansion coefficient matched

Info

Publication number: WO2021183084A1
Application number: PCT/TR2021/050209
Authority: WO
Inventors: Özgür AKTAŞ
Original assignee: Kuvv Elektroni̇k Anoni̇m Şi̇rketi̇
Priority date: 2020-03-09
Filing date: 2021-03-09
Publication date: 2021-09-16
Also published as: TR202003626A2

Abstract

The invention is related to the power conversion circuit formed by matching the coefficient of thermal expansion of the AIN (Aluminum Nitride) ceramic card (1) to the coefficient of thermal expansion (CTE-coefficient of thermal expansion) of the WBG power chip (2) and directly connecting the WBG power chip (2) to the AIN ceramic card (1) with the matched coefficient of thermal expansion.

Description

POWER CONVERSION CIRCUIT HAVING COMPONENTS WITH A THERMAL EXPANSION COEFFICIENT MATCHED

Technical Field

The invention is related to the power conversion circuit formed by matching the coefficient of thermal expansion of the AIN (Aluminum Nitride) ceramic card to the coefficient of thermal expansion (CTE-coefficient of thermal expansion) of the WBG power chip and directly connecting the WBG power chip to the AIN ceramic card with the matched coefficient of thermal expansion.

In this way, high-quality/high-performance GaN (Gallium Nitride) devices have been produced with the ability to operate at high frequency.

Prior Art

Power conversion circuits are devices that change the energy from the energy supply source at the voltage and frequency suitable for the energy consuming system.

Switched power conversion circuit operates to transfer energy pulsed from inlet to outlet. Pulses occur on a specific frequency called the cycle frequency. This frequency is mostly constant. The cycle frequency is mostly between 1 kHz-500 kHz.

All conversion circuits operate with a loss. Energy lost in conversion is dissipated as heat. Removal of this heat from the system is important for system performance.

The heat generated during the operation of the conversion circuit causes the temperature of the power conversion circuit to increase. As the load on the conversion circuit changes, successive heating and cooling cycles occur.

With the occurrence of GaN (Gallium Nitride) devices, it is possible to reach high operating frequencies. Since power conversion circuits operating at high operating frequencies use smaller value inductors and capacities, they have a lower volume and provide higher energy conversion density. Higher density of circuits operating at high operating frequencies is a prerequisite for making circuits that can operate at high frequency, as it also provides parasitic capacity and reduction of inductances. High energy conversion density also leads to high energy loss density, which makes circuit board design difficult. The problem persists in terms of using GaN devices for power conversion at high operating frequencies, considering the circuit board.

Another technical problem encountered in existing systems is delamination. Structures, whose thermal expansion coefficient is not matched, may occur due to repeated heating and cooling cycles formed due to changes in load density.

Patent application numbered CN110176858 (A) describes a power conversion circuit using one or more GaN (Gallium Nitride) based semiconductors.

Patent application numbered JP2013005511 (A) mentions a power module and power conversion circuit. The embodiment of the application aims to increase the performance of a power conversion circuit. Said embodiment includes semiconductor switch elements and diodes. Diodes are in GaN (Gallium Nitride) or diamond structure.

The Problems to be Solved by the Invention

The aim of the invention is to produce high-quality/high performance GaN (Gallium Nitride) devices with the ability to operate at high frequency. For this purpose, an AIN (Aluminum Nitride) ceramic card with high thermal conductivity and matched thermal expansion coefficient (CTE-coefficient of thermal expansion) is used.

Within the power conversion circuit of the invention, the AIN (Aluminum Nitride) ceramic card is directly connected to the WBG power chip, with the matched thermal expansion coefficient (CTE-coefficient of thermal expansion).

In this way, it is aimed to eliminate or reduce the heat-induced problems that occur due to power losses within the power conversion circuit. Direct connection of ceramic board with WBG power chip with matched thermal expansion coefficient allows the elimination or reduction of delamination problems.

On the other hand, by using the solution of the invention, the negative effects of successive heating and cooling cycles on the lifetime of the power conversion circuit due to the operation of the system under different power loads can be reduced.

It will be possible to form high frequency and high-density power conversion circuits based on GaN (Gallium Nitride) and other WBG (wide band gap) due to the high thermal conductivity of AIN (Aluminum Nitride) ceramic cards and the matching of the thermal expansion coefficient (CTE-coefficient of thermal expansion) to critical components.

The matching of the thermal expansion coefficient (CTE-coefficient of thermal expansion) of the system components allows reliable thermal cycle and increasing the temperature capacity of GaN (Gallium Nitride) devices.

The use of the inventive embodiment will allow the formation of a power conversion circuit that has high power density (reduced volume), enables wireless power transmission, has high efficiency and can be operated with much easier heat management.

Description of the Figures

Figure 1. Schematic view of the position of the active circuit element on the power chip

Figure 2. Schematic view of the position of the active circuit element under the power chip

Figure 3. Schematic view of the application in which the power chip is made of primary material and secondary material, with primary material on the ceramic card side

Figure 4. Schematic view of the application in which the power chip is made of primary material and secondary material, with secondary material on the ceramic card side

Figure 5. Schematic view of the application in which the ceramic card is formed from stacks containing various number of embedded conductive layers (8).

Figure 6. Schematic view of the application in which the power chip is packaged at the chip stage (chip scale packaging) Description of References in the Figures

1. Ceramic card

2. Power chip

3. Passive

4. Diode

5. Driver

6. Primary material

7. Secondary material

8. Conductive layer

Description of the Invention

In the most basic form of the power conversion circuit of the invention, the thermal expansion coefficient of the AIN (Aluminum Nitride) ceramic card (1) is matched to the thermal expansion coefficient of the WBG (wide band gap) power chip, and the WBG power chip is directly connected to the ceramic card with matched thermal expansion coefficient.

The fact that the power chip (2) is directly connected to the AIN (Aluminum Nitride) ceramic card (1), which has high thermal conductivity, allows the heat to be removed from the WBG power chip efficiently. However, in structures whose thermal expansion coefficient is not matched, delamination may occur due to repeated heating and cooling. The ceramic card (1), whose thermal expansion coefficient has been matched, provides a solution to the delamination problem and thus it became possible for the system to operate reliably at high power densities.

According to one of the preferred embodiments of the invention, the power chip (2) used in the active layer of the ceramic card (1) whose thermal expansion coefficient is matched, can be GaN and one of the alloys made by GaN with AIN and InN (Indium nitrite), in other words, AlGaN, InGaN and InAlGaN. According to Figure 1 and Figure 2, in the case that the WBG semiconductor layer containing active circuit elements of the WBG power chip (2) is one of the crystalline GaN (Gallium Nitrate) and/or AlGaN, InGaN and InAlGaN alloys or it is a structure in which these compounds and alloys are used together in various ways, the thermal expansion coefficient of the WBG power chip (2) will be the thermal expansion coefficient of the used WBG semiconductor layer or structure.

In this case, the thermal expansion coefficient of the ceramic circuit board (1) will be adjusted to the thermal expansion coefficient of the WBG power chip (2). For this case, the ceramic circuit board (1) may be in ceramic AIN structure.

In the case that the active layer of the WBG power chip (2) mentioned in Figure 1 and Figure 2 is mostly GaN, the thermal expansion coefficient of the ceramic circuit board (1) will be adjusted to the GaN thermal expansion coefficient. For this case, the ceramic circuit board (1) may be in ceramic AIN structure.

In the case that the primary material (6), which is WBG semiconductor, of the two-layer power chip (2) consisting of the primary material (6) and the secondary material (7) mentioned in Figure 3 and Figure 4, is one of the crystalline GaN and/or AlGaN, InGaN, InAlGaN alloys or in case that it is a structure in which these compounds and alloys are used together in various ways, the thermal expansion coefficient of the secondary material (7) will be adjusted to be the thermal expansion coefficient of the used WBG semiconductor layer or structure. In this case, the secondary material (7) may be in ceramic AIN structure. In this case, the thermal expansion coefficient of the ceramic circuit board (1) will also be adjusted to be the thermal expansion coefficient of the used WBG semiconductor layer or structure. In this case, the ceramic circuit board (1) may be in ceramic AIN structure.

In the case that the WBG semiconductor primary material (6) of the two-layer (6, 7) power chip (2) mentioned in Figure 3 and Figure 4 is mostly in crystalline GaN structure, the thermal expansion coefficient of the secondary material (7) will be adjusted to be the used GaN thermal expansion coefficient. In this case, the secondary material (7) may be in ceramic AIN structure. Again, the thermal expansion coefficient of the ceramic circuit board (1) will be adjusted to the GaN thermal expansion coefficient. In this case, the ceramic circuit board (1) may be in ceramic AIN structure. According to the figures, there are other circuit elements on the ceramic card that may be required in the power conversion circuit. In the figures, passive devices (3), diode-like elements (4) and driver integrations (5) can be given as examples of these circuit elements.

Figure 1 shows one of the preferred embodiments of the invention. According to this embodiment, the power chip (2) has an active layer on its upper surface and the critical regions of the circuit elements (for example, p-n junction for diodes, channel for transistors, etc.) are manufactured within this active layer.

According to this embodiment, the active layer positioned on top is associated with the power chip (2) via the substrate or via cable ties.

Figure 2 shows another preferred embodiment of the invention. According to this embodiment, the power chip (2) contains an active layer on its lower surface.

It is advantageous for the power chip (2) to have an active layer at the bottom for the following reasons:

• It allows the cooling element (heatsink) to be directly connected to the WBG power chip (2) from behind. This is possible in the case of ceramic PCB insulators.

• The thermal resistance from the section where the active circuit element is located to the ceramic section is reduced.

• The need for passage holes (vias) for the substrate is eliminated.

According to the embodiment described in Figure 2, a transistor can be used as an active layer. In this case, the transistor can be directly connected to the ceramic board (1) from below.

Figure 3 shows another preferred embodiment of the invention. According to this embodiment, the thermal expansion coefficient of the AIN ceramic card (1) is again matched to the thermal expansion coefficient of the power chip (2) and the WBG power chip is directly connected to the matched ceramic card. In this embodiment, the WBG power chip (2) consists of primary material (6) and secondary material (7). Preferably, the primary material (6) is WBG semiconductor and the secondary material (7) is the substrate.

According to Figure 3, the power chip (2) contains active circuit elements in its upper part. According to this embodiment, the thermal expansion coefficient of the WBG semiconductor, substrate and ceramic card (1) were matched.

Within this embodiment, the direct connection of the power chip (2) to the high thermal conductivity AIN ceramic card (1) will allow the heat to be removed efficiently from the WBG power chip (2). However, in structures whose thermal expansion coefficient is not matched, delamination may occur due to repeated heating and cooling. The ceramic card (1), whose thermal expansion coefficient has been matched, provides a solution to the delamination problem and thus it became possible for the system to operate reliably at high power densities.

According to the embodiment mentioned in Figure 3, the secondary material (7) contains an active layer on its upper surface. The active circuit element can be a transistor.

Also, passage holes or cable connections can be formed between the primary material (6) and the secondary material (7).

In the embodiment shown in Figure 4, the power chip (2) consists of primary material (6) and secondary material (7). Preferably, the primary material (6) is WBG semiconductor and the secondary material (7) is the substrate.

Within this embodiment, the primary material (6) was positioned on the ceramic card (1) side. According to the embodiment given in Figure 3, the places of the primary material (6) and the secondary material (7) have been changed.

According to this embodiment, the active layer is positioned on the lower surface of the primary material (6). According to this embodiment, the thermal expansion coefficient of the WBG semiconductor (7), substrate (6) and ceramic card (1) was matched.

• It allows the cooling element to be directly connected to the WBG power chip (2) from behind. This is possible in the case of ceramic PCB insulators.

Also, in the embodiment described in Figure 5, the thermal expansion coefficient of the, AIN ceramic card (1) is again matched to the thermal expansion coefficient of the power chip (2) and the WBG power chip is directly connected to the matched ceramic card.

In this embodiment, the AIN ceramic card (1) contains multiple conductive layers (8) so that at least two layers are formed. Here, each layer (8) is patterned to be associated with each other in the stack.

These conductive layers (8) preferably have a metal structure.

The invention can be operated with stacks containing various numbers of embedded conductive layers (8).

Again, according to this embodiment, the ceramic card (1) may have a conductive layer (8) in its lower section.

Conductive layers (8) formed on different surfaces can be associated with vertical passage holes (vias). It is possible to make these vertical passage holes by using a drill bit or laser.

Passage holes can be filled with conductive metals or connection layers.

The formation of multilayer conductive layers (8) is important for the following reasons.

It provides connectivity for complicated circuits. • It allows the formation of ground and power surfaces with low inductance and high current capacity.

• It allows to reduce the electrical noise caused by parasitic connection.

The structured described in this embodiment is costly to implement in a ceramic PCB.

According to different embodiments of the invention, the power chip (2) can be formed in one piece or in multiple structures. Again, it may be possible to use power chips (2) formed in different structures and types within the scope of the invention.

Power chip (2) according to different embodiments of the invention can be in the form of;

• GaN transistor in one of the standard packages,

• GaN transistor packaged in chip size,

• GaN integrated circuit (IC) in standard package,

• GaN integrated circuit (IC) packaged in chip size,

• SiC (Silicon carbide) transistor in standard package,

• SiC (Silicon carbide) transistor packaged in chip size.

Within applications operated with different types of single and multiple power chips (2), the active circuit element is also located on the power chip (2).

Since high-speed power circuits require complex control schemes, they need to be used with different types of driver integrated circuits. This embodiment can be used to operate in such high-speed power circuits.

Figure 6 is an embodiment in which the thermal expansion coefficient of the AIN ceramic card (1) is again matched to the thermal expansion coefficient of the power chip (2) and the WBG power chip is directly connected to the matched ceramic card.

Also, in this embodiment, it can be operated with a single and multiple power chips (2) of different types. Within this embodiment, the active layer is located below the power chip. The thermal expansion coefficient of the AIN ceramic card (1) is again matched to the thermal expansion coefficient of the power chip (2) and the WBG power chip is directly connected to the matched ceramic card.

Within this embodiment, the power chip (2) is packaged at the chip stage (Chip scale packaging). Within this embodiment, at the chip stage (think about this word again), the packaging is provided by thermal expansion coefficient compatible passivization.

The packaging process at the chip stage is performed by the application of the following process steps.

• Forming conductive layers (8) on the ceramic card (1),

• Turning and connecting the WBG power chip (2) to the surface,

• Passivating the power chip (2) and sealing its ends,

• Opening windows so that other elements (individual devices and drivers) can be welded.

Chip-sized packaging includes direct connection and passivation of the power chip (2). Passivation by using materials with compatible thermal expansion coefficient increases the thermal cycle capacity of the system.

In the case of using passive circuit elements within the embodiments of the invention whose different applications are described above, passive circuit elements can be individual devices or integrated passive devices.

The steps for the production method of the power conversion circuit of the invention were presented below.

• Forming an AIN layer,

• Laminating copper on all surfaces of AIN layers,

• Forming a copper pattern suitable for circuit drawing,

• Treating AIN layers formed by laminating copper or stacking with partially treated green AIN,

• Ignition (preferably at low temperature/about 200°C), • Forming passage holes with laser drilling,

• Connecting transistors face down,

• Covering the ends with AIN green paste and curing (preferably laser, heat and plasma treatment can be performed), · Connecting other circuit elements.

Claims

1. A power conversion circuit which comprises aluminum nitride ceramic card (1) equipped with other circuit elements that may be required in the power conversion circuit and associated power chip (2) and which changes the energy from the energy supply source at the voltage and frequency appropriate to the energy consuming system, characterized in that the aluminum nitride ceramic card (1) is directly connected to the power chip (2) with the matched coefficient of thermal expansion.

2. A power conversion circuit according to claim 1, characterized in that the power chip (2) used in the active layer of the ceramic card (1) with the matched thermal expansion coefficient can be one of GaN and/or AlGaN, InGaN and InAlGaN.

3. A power conversion circuit according to claim 1, characterized by comprising other circuit elements consisting of one or more of the passive devices (3), diode-like elements (4) and driver integrations (5).

4. A power conversion circuit according to claim 1, characterized by comprising the power chip (2) with an active circuit element.

5. A power conversion circuit according to claim 2, characterized by comprising the active circuit element associated with the power chip (2) via the substrate or via a cable tie.

6. A power conversion circuit according to Claim 2 or 5, characterized in that in case that the WBG semiconductor layer comprising active circuit elements of the WBG power chip (2) is one of the crystalline GaN (Gallium Nitrate) and/or AlGaN, InGaN, InAlGaN alloys or it is a structure in which these compounds and alloys are used together in various ways, the ceramic circuit board (1) is in ceramic AIN structure.

7. A power conversion circuit according to Claims 2 and 5, characterized in that in the case that the active layer of the WBG power chip (2) is mostly GaN, the ceramic circuit board (1) is in ceramic AIN structure.

8. A power conversion circuit according to claim 1, characterized by comprising the power chip (2) with active circuit element below.

9. A power conversion circuit according to claim 8, characterized in that as the active circuit element, the transistor is directly connected to the ceramic card (1) from below.

10. A power conversion circuit according to claim 1, characterized by comprising

• power chip (2) consisting of primary material (6) and secondary material (7), and

• the ceramic card (1), all of which have a matched thermal expansion coefficient.

11. A power conversion circuit according to claim 2 or 10, characterized in that;

• in the case that a primary material, which is a WBG semiconductor, of the two-layer power chip (2) consisting of a primary material (6) and a secondary material (7) is one of the crystalline GaN and/or AlGaN, InGaN, InAlGaN alloys or in case that it is a structure in which these compounds and alloys are used together in various ways, the thermal expansion coefficient of the secondary material (7) is adjusted to be the thermal expansion coefficient of the used WBG semiconductor layer or structure,

• in this case, the secondary material (7) is in ceramic AIN structure,

• the thermal expansion coefficient of the ceramic circuit board (1) is also adjusted to be the thermal expansion coefficient of the used WBG semiconductor layer or structure, and

• in this case, the ceramic circuit board (1) is in ceramic AIN structure.

12. A power conversion circuit according to claim 2 or 10, characterized in that;

• in the case that the WBG semiconductor primary material (6) of the two-layer (6, 7) power chip (2) is mostly in crystalline GaN structure, the thermal expansion coefficient of the secondary material (7) is adjusted to be the used GaN thermal expansion coefficient,

• in this case, the secondary material (7) is in ceramic AIN structure, • the thermal expansion coefficient of the ceramic circuit board (1) is also adjusted to be the thermal expansion coefficient of the used WBG semiconductor layer or structure, and

• in this case, the ceramic circuit board (1) is in ceramic AIN structure.

13. A power conversion circuit according to claim 10, characterized by comprising the power chip (2) consisting of WBG semiconductor as the primary material (6) and the substrate as the secondary material (7).

14. A power conversion circuit according to claims 10 and 13, characterized by comprising the active circuit element in the upper section.

15. A power conversion circuit according to claim 14, characterized in that the active circuit element is located on the upper surface of the secondary material (7).

16. A power conversion circuit according to claim 14, characterized in that the active circuit element is a transistor.

17. A power conversion circuit according to claims 10 and 13, characterized in that it consists of primary material (6) and secondary material (7) with passage holes or cable connections therebetween.

18. A power conversion circuit according to claims 10 and 13, characterized by comprising the primary material (6) positioned on the side of the ceramic card (1).

19. A power conversion circuit according to claim 18, characterized by comprising the active circuit element positioned on the lower surface of the primary material (6).

20. A power conversion circuit according to claim 1, characterized by comprising AIN ceramic card (1) having multiple conductive layers (8) so that at least two layers are formed, each layer (8) being patterned in a manner to be associated with each other in the stack.

21. A power conversion circuit according to claim 20, characterized by comprising conductive layers (8) in the metal structure.

22. A power conversion circuit according to claim 20 or 21, characterized by comprising an AIN ceramic card (1) equipped with a conductive layer (8) at its lower section.

23. A power conversion circuit according to claims 20, 21, or 22, characterized by comprising an AIN ceramic card (1) formed from conductive layers (8) formed on different surfaces, associated with vertical passage holes.

24. A power conversion circuit according to claim 23, characterized by comprising the passage holes filled with metals or connection layers.

25. A power conversion circuit according to any of the above claims, characterized by comprising the power chip (2), which consists of single and multiple parts of different types.

26. A power conversion circuit according to claim 25, characterized by comprising a power chip (2) in the form of;

• GaN transistor in one of the standard packages,

• GaN transistor packaged in chip size,

• GaN integrated circuit (IC) in the standard package,

• GaN integrated circuit (IC) packaged in chip size,

• SiC (Silicon carbide) transistor in the standard package,

• SiC (Silicon carbide) transistor packaged in chip size.

27. A power conversion circuit according to claim 25 or 26, characterized by comprising the active circuit element located on the power chip (2).

28. A power conversion circuit according to claim 25 or 26, characterized by comprising the active circuit element positioned below the power chip (2).

29. A power conversion circuit according to claim 28, characterized by comprising the power chip (2) packaged in the chip stage.

30. A production method for packaging the power chip (2) of the power conversion circuit at the chip stage, which comprises aluminum nitride ceramic card (1) equipped with other circuit elements that may be required in the power conversion circuit and associated power chip and which changes the energy from the energy supply source at the voltage and frequency appropriate to the energy consuming system, characterized by comprising the process steps of;

• Forming conductive layers (8) on the ceramic card (1),

• Turning and connecting the WBG power chip (2) to the surface,

• Passivating the power chip (2) and sealing its ends,

31. A production method for the power conversion circuit which comprises aluminum nitride ceramic card (1) equipped with other circuit elements that may be required in the power conversion circuit and associated power chip and which changes the energy from the energy supply source at the voltage and frequency appropriate to the energy consuming system, characterized by comprising the process steps of;

• Forming an AIN layer,

• Laminating copper on all surfaces of AIN layers,

• Forming a copper pattern suitable for circuit drawing,

• Ignition

• Forming passage holes with laser drilling,

• Connecting transistors face down

• Covering the ends with AIN green paste and curing

• Connecting other circuit elements.

32. The production method for the power conversion circuit according to claim 31, characterized in that the ignition process is carried out at 200°C.

33. The production method for the power conversion circuit according to claim 31 ; characterized in that the application of laser, heat, and plasma is performed to cover the ends with AIN green paste and to cure.