WO2015088376A1

WO2015088376A1 - Device and method for heat transfer from semiconductor transistors

Info

Publication number: WO2015088376A1
Application number: PCT/RU2013/001123
Authority: WO
Inventors: Stepan Alexandrovich Polikhov; Nadezhda Vladimirovna TIKHOMIROVA; Yulia Yurievna VASILEVA
Original assignee: Siemens Research Center Limited Liability Company
Priority date: 2013-12-13
Filing date: 2013-12-13
Publication date: 2015-06-18

Abstract

The present invention relates to a device and method for heat transfer from semiconductor transistors, comprising at least one heat exchanger and at least one semiconductor chip (8) with at least one transistor structure, with the at least one chip (8) mounted on the at least one heat exchanger. The at least one heat exchanger comprises further a component (7) with channels (9) for a cooling fluid. Within the method a high cooling rate of the at least one heat exchanger keeps the transistor chip (8) during operation below a critical temperature like for example 100C. FIG.1

Description

DEVICE AND METHOD FOR HEAT TRANSFER FROM SEMICONDUCTOR

TRANSISTORS

DESCRIPTION

The present invention relates to a device and method for heat transfer from semiconductor transistors, comprising at least one heat exchanger and at least one semiconductor chip with at least one transistor structure, with the at least one chip mounted on the at least one heat exchanger.

Semiconductor chips, particularly high power RF transistor chips, produce during operation heat. Electrical losses are converted to heat and have to be removed from the chip, if more than a critical amount of heat is produced. If it is not removed it increases the temperature of the semiconductor chip and if a critical temperature is exceeded, the chip can be damaged or destroyed.

To remove waste heat from semiconductor chips arrangements are known from the state of the art to cool down the chips. From US6992887B2 a liquid cooled semiconductor device is known. The device comprises a semiconductor die, a heat spreader, a wetting material, a sealant, a substrate, and a base. The substrate is mounted to the base, whereby the second side of the spreader is exposed to allow fluid to flow across the second side within a channel defined by the base. The fluid absorbs heat from the spreader and transports it away from it. The semiconductor die is cooled via the spreader. Within the described arrangement the contact surface between cooling fluid and spreader is very small, resulting in a low value of dissipated heat and a small cooling effect. The cooling effect is particularly too small to effectively cool semiconductor transistors in high power applications, for example with a power in the range of KW to MW.

The object of the present invention is to present a device and method for effective heat transfer from semiconductor transistors, particularly in high power applications. A further object is to provide a device with simple, cost effective structure, being able to effectively transfer heat from semiconductor chips at a high heat transfer rate, to keep in operation a temperature of the chip below a critical temperature. A damage or destruction of the chip by high temperature should be prevented by the device and/or method, particularly in high power applications of the chip.

The above objects are achieved by a device for heat transfer from semiconductor transistors according to claim 1 and a method for heat transfer from semiconductor transistors, particularly using the before described device, according to claim 1 1.

Advantageous embodiments of the present invention are given in dependent claims. Features of the main claims can be combined with each other and with features of dependent claims, and features of dependent claims can be combined together.

The devise for heat transfer from semiconductor transistors according to the present invention comprises at least one heat exchanger and at least one semiconductor chip with at least one transistor structure. The at least one chip is mounted on the at least one heat exchanger. The at least one heat exchanger comprises further a component with channels for a cooling fluid.

By using more than one channel for the cooling fluid to flow through in the heat exchanger, the amount of contact surface between heat exchanger and cooling fluid is increased significantly. A higher amount of contact surface is equal with a higher heat exchange rate between heat exchanger and fluid at the same fluid flow rate. The heat exchanger, and with it the semiconductor chip is cooled more effectively. Even in high power applications of the semiconductor chip with transistor, for example in high power RF applications, the high amount of waste heat produced by electrical losses can be effectively removed from the chip. The chip is cooled by the heat exchanger and the temperature does not rise above a critical temperature, at which the chip gets damaged or destructed.

The component with channels can be in form of a plate, particularly in form of a cuboid, and/or the channels are in parallel to each other throughout the component. A plate form is easy and cost effective to produce, and a storing of the device, particularly if more than one device is used, is possible without much space needed. With an arrangement of channels in parallel a high number of channels can be used without a high amount of space needed, i.e. a high number of channels in a small heat exchanger is possible. With high number of channels a large contact area is created and effective cooling can take place.

The channels comprise a cross section in form of a polygon and/or an ellipse, particularly a form of a circle, hexagon and/or starlike. With cross sections in form of for example hexagons and/or stars the contact surface can be further increased compared to round/circular cross sections. On the other side it can be easier and more cost effective to produce channels with a simple circular cross section.

The channels can comprise turbulizer structures for heat transfer intensification. This structures, for example rough surfaces, steps or bumps on the surface of the channels particularly in flow direction one after another, introduce turbulences in the fluid. Turbulences can lead to mixing within the fluid and effect a faster or more effective absorption of heat from the heat exchanger respectively contact surface with the channels.

Two heat exchangers can be comprised, particularly with one component in form of one integral piece with channels, with at least one semiconductor chip respectively mounted on a heat exchanger. With two heat exchangers two semiconductor chips can be cooled independently. That means different amounts of heat can be removed from the two chips. Since different chips can be in different working modes or be used with different power, the heat production will be different. The use of one component makes the production and use of the heat exchanger easier and more cost effective, sealing can be easier and the handling of the device can be easier. The component can be produced from one material block, with different heat exchanger in different areas of the component. The at least one chip mounted on the at least one heat exchanger can be encapsulated by casting material, particularly plastic, which is arranged between the semiconductor chip and heat exchanger material. This enables an easier handling of the device with less risk of damaging the semiconductor chip with its electronic structure on it, particularly transistors. The encapsulation protects the semiconductor material and electronic circuit on it from the environment. The special construction of the device with heat exchanger, comprising channels for the cooling fluid, enables a high rate of heat removal from the chip even when the encapsulation of the chip reduces the heat transfer from the chip to the heat exchanger. The high rate of heat removal by the heat exchanger gives it enough heat capacity to keep the chip below a critical temperature even with an encapsulated chip and in high power applications. The at least one heat exchanger respectively can comprise an inlet reservoir with inlet pipe and an outlet reservoir with outlet pipes for cooling fluid, with in-between the component with channels for a cooling fluid fluidically connected to the reservoirs. The reservoirs can homogenize the fluid flow through different channels, giving for example a homogenous cooling of the whole chip area, resulting in a more homogenous temperature distribution within the heat exchanger and a higher heat exchange rate all over the contact surface between cooling fluid and heat exchanger due to the homogenous temperature distribution.

The at least one heat exchanger can comprise two opposite sides with at least one chip mounted on each side. This enables more chips to be cooled at the same time with the same heat exchanger. It can save costs and give a simpler construction of an assembly comprising the device. The at least one heat exchanger, particularly the component with channels, can be made of or comprise a material with high coefficient of thermal conductivity, particularly copper, steel or aluminum. These materials are suitable for a high rate of heat exchange, resulting in a good cooling of the chips. The at least one semiconductor chip with at least one transistor structure can be a RF power amplifier. In high power applications, for example high power RF production, the device can be advantageous. It can enable a continuous high power application without damage of the chip by temperatures above a critical temperature.

In a method according to the present invention for heat transfer from semiconductor transistors, particularly using a device as described before, the heat exchanger exhibits a high cooling rate to keep the transistor chip, particularly with encapsulation, during operation below a critical temperature, particularly below 100°C.

This prevents the chip from being damaged or destroyed, particularly in high power applications. A temperature above critical can irreversibly damage electronic structures of the semiconductor chip. The functionality of the chip and electronic circuit on the chip can fall out.

A large surface between cooling fluid and the at least one heat exchanger component can be formed by using channels, particularly for cooling down at least two encapsulated transistor chips mounted on the outside surface of the at least one heat exchanger.

Water can be used as a cooling fluid. Other fluids like oil are also suitable, particularly fluids with a high heat capacity.

A mounted chip in a first region of the at least one heat exchanger can be cooled independently to a mounted chip in a second region of the at least one heat exchanger, particularly with an amount of cooling dependent from the operational mode with specific power consumption of the respective chip. This enables a safe operation of different chips in different operational modes, i.e. with different power and heat production with one heat exchanger. It reduces costs, safes space and gives a simple layout of the device.

The amount of cooling, particularly the cooling fluid temperature and/or flow rate provided to a respective heat exchanger, can be regulated and/or controlled depending on power consumption of a mounted chip in thermal contact to the heat exchanger. This method enables a better temperature control and prevents failures due to ineffective or too little cooling during usage of different chips in different modes.

The advantages in connection with the described method for heat transfer from semiconductor transistors according to the present invention are similar to the previously, in connection with device for heat transfer from semiconductor transistors described advantages and vice versa.

The present invention is further described hereinafter with reference to illustrated embodiments shown in the accompanying drawings, in which:

FIG 1 illustrates a device for heat transfer from semiconductor transistors according to the present invention, and

FIG 2 shows an intersection of the device of FIG 1 with channels 9 for cooling fluid to flow through, and

FIG 3 shows a cross-section of the device of FIG 1 along its width with different shapes of channel cross-sections 9A, 9B, 9C.

In FIG 1 a device for heat transfer from semiconductor transistors to the environment according to the present invention is shown. The device comprises a component 7 in form of a plate, i.e. in form of a cuboid, with two semiconductor chips 8 mounted on the top side of the component 7. The semiconductor chips 8 are mounted in a row along the width in the middle of the component 7 between a lower and an upper side of the top side. On the lower side an inlet reservoir 1 with two inlet pipes, a first inlet pipe 3 and a second inlet pipe 5 in parallel, for a cooling fluid like for example water to enter the device are arranged. On the upper side an outlet reservoir 2 with two outlet pipes, a first outlet pipe 4 and a second outlet pipe 6 in parallel, for the cooling fluid to exit the device are arranged.

The semiconductor chips 8 comprise a transistor structure and are encapsulated with plastic. An example for this kind of chips 8 are high power RF transistor chips. Electrical connections for power supply and the electronic circuits of the chips 8 are not shown in the FIG for simplicity. The chips 8 can be mounted directly, for example with conductive adhesive for a good thermal conductivity to the component 7. Alternatively the chips 8 can be mounted to the component 7 using a support structure, for example a heat sink structure.

In FIG 2 an intersection of the device of FIG 1 along its length is shown. The device comprises a heat exchanger with channels 9 for a cooling fluid to flow through the inside of the device. The channels 9 are arranged below the mounted chips 8 in the component 7 and set up a heat exchanger in thermal contact with each chip 8 respectively. The channels 9 below the first chip 8 formed in component 7 pass through the whole component 7 along its length and are arranged in parallel next to each other. At one side of the channels 9 an inlet reservoir 1 with a first inlet pipe 3 is arranged, for the cooling fluid to enter the device and to be distributed homogeneously via the inlet reservoir 1 to the channels 9.

At the opposite side of the channels 9 an outlet reservoir 2 with a first outlet pipe 4 is arranged, for the cooling fluid to be collected via the outlet reservoir 2 from the channels 9 and to exit the device via the first outlet pipe 4.

A cooling fluid is for example water. It flows in operation of the device into it through the first inlet pipe 3, is homogenously distributed to the channels 9 via the inlet reservoir 1 , flows through the channels 9 absorbing heat, and is collected in the outlet reservoir 2 to exit the device through the first outlet pipe 4. The fluid flow can be generated by a pump as part of a closed fluid cycle, not show in the pictures for simplicity. Heat from the first chip 8 is transferred via the component 7 across the interface of the channels 9 to the fluid, heating up the fluid flowing through the device and cooling down the chip 8. The high number of channels 9 within the component 7 increase the interface surface with the fluid, and by that the amount of heat transferred to the fluid at the same flow rate. The efficiency of heat transfer is increased by the channel 9 structure in the heat exchanger. To cool the second chip 8, channels 9 below the second chip 8 formed in component 7 pass also through the whole component 7 along its length, and are arranged in parallel next to each other and next to the channels 9 for cooling the first chip 8. At one side of the channels 9 the inlet reservoir 1 is divided into two parts for example of the same size respectively, with one part fluidically connected to the first inlet pipe 3 and the second part being connected to a second inlet pipe 5, and in between a wall is sealing the two parts fluidically from each other. The second inlet pipe 5 is arranged at the second part of the inlet reservoir 1 , for the cooling fluid to enter the device and to be distributed homogeneously via the inlet reservoir 1 to the channels 9 below the second chip 8. At the other side of the channels 9 the outlet reservoir 2 is divided also into two parts for example of the same size respectively, with one part fluidically connected to the first outlet pipe 4 and the second part being connected to a second outlet pipe 6, and in between a wall is sealing the two parts fluidically from each other. In operation of the device the cooling fluid also flows into the device through the second inlet pipe 5, is homogenously distributed to the channels 9 below the second chip 8 via the second part of inlet reservoir 1 , flows through the channels 9 absorbing heat, and is collected in the second part of outlet reservoir 2 to exit the device through the second outlet pipe 6. The fluid flow can be generated with the same or with a different pump as for the first closed fluid cycle. There can be one closed fluid cycle outside the device or two fluidically independent cycles, with two different pumps. Heat from the second chip 8 is transferred via the component 7 across the interface of the channels 9 below the second chip 8 to the fluid, heating up the fluid flowing through the device and cooling down the second chip 8.

FIG 3 shows a cross-section of the device of FIG 1 along its width with different shapes of channel cross-sections 9A, 9B. 9C. The channels 9 can all have the same or different cross-section forms. Examples for cross-sections in FIG 3 are of starlike shape 9A, hexagonal shape 9B, or circular shape 9C. Circular shapes 9C can be produced easy. Starlike and hexagonal shapes 9 A, 9B can further increase the interface between the material of component 7 and the cooling fluid, compared to the circular shape 9C. This can increase, like a higher number respectively density of channels in the component 7 the heat transfer rate, respectively the efficiency of heat transfer.

With two independent fluid cycles as shown in the FIG an independent cooling of the two mounted chips 8 with only one device is possible. This reduces complexity and costs. Sensors and a control unit, not shown in FIG for simplicity, can particularly measure the temperature of the two chips 8. Dependent of the respective temperature the flow rate or temperature of the cooling fluid pumped through the channels 9 below that chip 8 can be regulated. Alternatively dependent on the power consumption of the respective chip 8 the flow rate or temperature of the cooling fluid pumped through the channels 9 below that chip 8 can be regulated.

The above described embodiments of the present invention can be used on its own or in combination with each other, and combined with embodiments known from the state of the art. The invention is not restricted to the described embodiments.

The use of a device with less or more than two chips 8 mounted is possible. The chips can be mounted on one side or on different, for example opposite sides of the component 7. Heat exchanger with more than two areas for independent cooling and/or with more than two fluid cycles can be used. The device can be made for example of metals like copper, steel or aluminum, to provide a good heat transfer by using a material with high thermal conductivity. Other materials like plastic can also be used, for example for components like reservoirs 1, 2 and pipes 3, 4, 5, 6.

Among others water or oil can be used as cooling fluid. Other fluids, particularly with a high heat capacity are also appropriate. A high number of channels and special structures within the channels like turbulizer structures can increase the heat transfer rate from the chips 8 to the fluid. The chips 8 can be mounted to the component 7 among others by gluing, clamps or screws. Different components of the device like reservoirs 1, 2 and pipes 3, 4, 5, 6 as well as the component 7 can be glued, clamped or screwed together, with and without sealing. Except the pipes with in- and output opening the inner part of the device should be sealed fluidically. A main advantage of the device is an effective, reliable and cost effective cooling of semiconductor chips with at least one transistor structure, for example high power HF transistor chips. The high heat capacity and high heat transfer rate to the cooling fluid of the device makes it possible to cool reliable even encapsulated high power chips below a critical temperature, above which the chips would be damaged or irreversible destroyed. Channels within the device increase the interface with the cooling fluid and increase the heat transfer rate to the fluid.

List of Reference Characters

1 inlet reservoir

2 outlet reservoir

3 first inlet pipe

4 first outlet pipe

5 second inlet pipe

6 second outlet pipe

7 component with channels for a cooling fluid 8 semiconductor chip with transistor structure 9 channel for a cooling fluid

9A starlike cross section of a channel

9B hexagonal cross section of a channel 9C circular cross section of a channel

Claims

1. Device for heat transfer from semiconductor transistors, comprising at least one heat exchanger and at least one semiconductor chip (8) with at least one transistor structure, with the at least one chip (8) mounted on the at least one heat exchanger,

characterized in that the at least one heat exchanger comprises a component (7) with channels (9) for a cooling fluid.

2. Device according to claim 1 , characterized in that the component (7) with channels (9) is in form of a plate, particularly in form of a cuboid, and/or the channels (9) are in parallel to each other throughout the component (7).

3. Device according to any one of claims 1 or 2, characterized in that the channels (9) comprise a cross section (9A, 9B, 9C) in form of a polygon and/or an ellipse, particularly a form of a circle (9C), hexagon (9B) and/or starlike (9 A).

4. Device according to any one of claims 1 to 3, characterized in that the channels (9) comprise turbulizer structures for heat transfer intensification.

5. Device according to any one of claims 1 to 5, characterized in that two heat exchangers are comprised, particularly with one component (7) in form of one integral piece with channels (9), with at least one semiconductor chip (8) respectively mounted on a heat exchanger.

6. Device according to any one of claims 1 to 5, characterized in that the at least one chip (8) mounted on the at least one heat exchanger is encapsulated by casting material, particularly plastic, which is arranged between semiconductor chip (8) and heat exchanger material.

7. Device according to any one of claims 1 to 6, characterized in that the at least one heat exchanger respectively comprises an inlet reservoir (1) with inlet pipe (3, 5) and an outlet reservoir (2) with (4, 6) outlet pipe for cooling fluid, with in-between the component (7) with channels (9) for a cooling fluid fluidically connected to the reservoirs (1, 2).

8. Device according to any one of claims 1 to 7, characterized in that the at least one heat exchanger comprises two opposite sides with at least one chip (8) mounted on each side.

9. Device according to any one of claims 1 to 8, characterized in that the at least one heat exchanger, particularly the component (7) with channels (9), is made of or comprises a material with high coefficient of thermal conductivity, particularly copper, steel or aluminum.

10. Device according to any one of claims 1 to 9, characterized in that the at least one semiconductor chip (8) with at least one transistor structure is a RF power amplifier.

1 1. Method for heat transfer from semiconductor transistors, particularly using a device according to any one of claims 1 to 10, characterized in that the heat exchanger exhibits a high cooling rate to keep the transistor chip (8), particularly with encapsulation, during operation below a critical temperature, particularly below 100°C.

12. Method according to claim 11, characterized in that a large surface between cooling fluid and the at least one heat exchanger component (7) is formed by using channels, particularly for cooling down at least two encapsulated transistor chips (8) mounted on the outside surface of the at least one heat exchanger.

13. Method according to any one of claims 1 1 or 12, characterized in that water is used as a cooling fluid.

14. Method according to any one of claims 11 to 13, characterized in that a mounted chip (8) in a first region of the at least one heat exchanger is cooled independently to a mounted chip (8) in a second region of the at least one heat exchanger, particularly with an amount of cooling dependent from the operational mode with specific power consumption of the respective chip (8).

15. Method according to any one of claims 1 1 to 13, characterized in that the amount of cooling, particularly the cooling fluid temperature and/or flow rate provided to a respective heat exchanger, is regulated and/or controlled depending on power consumption of a mounted chip (8) in thermal contact to the heat exchanger.