Resistor Assembly

Abstract

A resistor assembly, in particular a resistor assembly for a power combiner, includes a resistor chip and a clamping element for fixing the resistor chip to a cooling element, the clamping element having a clamping arm that applies pressure to the resistor chip.

Description

Technical Field

[0001] The present invention relates to a resistor assembly, and more particularly to a resistor assembly for a power combiner of an RF generator. Further, the present invention relates to such a power combiner and an RF generator.

Background Art

[0002] The handling of reflected power is a particularly difficult problem in high-frequency (RF) power applications for plasma generation (such as when etching and depositing thin films on a silicon wafer during the manufacture of integrated circuits). An RF plasma is a very dynamic load that changes rapidly. Using an impedance matching network between the RF power generator and the plasma can correct impedance mismatches during steady-state plasma operation. However, such matching networks are generally too slow to adapt immediately to changes in load impedance. For example, during the plasma ignition phase, changes in power level, and pulsed mode operation, the RF generator is exposed to transient reflected power that needs to be dissipated within the generator.

[0003] The RF power stage of an RF generator consists of the following circuits. · Power amplifier · Hybrid combiner · High-power combiner (when combining multiple PAs to obtain higher output) These operate at frequencies in the range of 0.3 to 300 MHz and power levels of 500 W or more. Air cooling is sufficient for power levels up to about 2 kW, but water cooling is usually required for high power levels exceeding 2 kW.

Summary of the Invention

Problems to be Solved by the Invention

[0004] In combiners, termination resistors are typically used to absorb and dissipate reflected power. Since the reflected power level can be very high in some situations, the termination resistors need to be properly cooled and the heat generated needs to be quickly transferred to a cold plate or heat sink.

[0005] The term heat sink refers to a heat exchanger that transfers heat from an electronic circuit to a fluid medium (such as air or liquid refrigerant). Part of the heat sink usually has its surface area enlarged by cooling fins, spikes, etc. to maximize contact with the fluid medium and thus heat transfer. The term cold plate refers to a heat exchanger through which a liquid refrigerant circulates, usually a thick plate with pipes through which the refrigerant flows embedded in it. Heat sinks and cold plates are usually made of metal materials such as aluminum, copper, metal alloys, etc., but may also be made of ceramic or other materials with high thermal conductivity.

[0006] A heat spreader is a device with excellent thermal conductivity, usually a plate, which disperses heat generated in a small area over a large area. Heat spreaders are usually used in combination with a heat sink or cold plate, through which heat is transferred to the fluid medium. The dispersion of heat in the heat spreader may be enhanced by the use of thermoelectric cooling (such as Peltier elements) or heat pipes.

[0007] Hereinafter, the term "cooling element" is used for all types of air-cooled heat exchangers with fins or similar enlarged surface areas, liquid-cooled cold plates, and combinations of heat spreaders with air-cooled heat sinks or liquid-cooled cold plates (including functional enhancements such as thermoelectric cooling and heat pipes).

[0008] A common power resistor that can be clamped to a heatsink with a screw is composed of a heat spreader and a resistor chip soldered to this heat spreader. However, when clamping such a resistor from both ends, that is, clamping only the heat spreader, the pressure at the center of the device where heat is generated by the resistor chip decreases, and the thermal connection becomes weak. Furthermore, since the resistor chip cannot use the area required for clamping, the maximum possible size of the resistor chip becomes smaller, and the total heat load at the center of the resistor increases.

[0009] Since a general RF generator needs to fit into an industry-standard electronic rack, the width of the generator is often specified as 19 / 2 inches or 19 inches, and the height is 3 - 5 rack units (1 rack unit is 1.75 inches). As a result, it is difficult to arrange all the circuits and components to fit within the available dimensions, and the termination resistor needs to be arranged so that it does not interfere with other circuits and components and consumes only a minimum amount of space.

[0010] Especially at frequencies below 30 MHz, circuit components, capacitance, and inductance need to be sized such that their values increase as the frequency decreases, and thus their sizes also increase. As a result, for example, in the case of the important ISM frequencies of 13.56 MHz and 27.12 MHz, it is difficult to fit all the components required for an RF generator into a 19 / 2-inch enclosure. As a result, most RF generators exceeding 1 kW have to fully utilize a 19-inch-sized enclosure.

[0011] In the latest RF power circuit designs for mass production, in order to reduce the variation between units, the three-dimensional arrangement of wires and ferrites for inductors is avoided because it is difficult to reproduce with the required geometric accuracy. Instead, a complete planar structure that can be manufactured with high precision in industrial printed circuit board (PCB) manufacturing is preferred. When using a 19 / 2-inch-wide enclosure, the size of the planar circuit becomes an issue, but by using a planar combiner, the termination resistor can be placed at the center of the inductor structure.

[0012] To optimize heat transfer, there is a notch in the center of the PCB with such an inductor, and the power resistor can be directly clamped to the cooling element and used as a ground connection. To avoid the magnetic field of the inductor coupling to the cooling element (usually made of metal), the PCB with the inductor cannot be placed directly on the cooling element. Instead, a ceramic heat spreader with a thickness of several millimeters needs to be used to increase the distance.

[0013] Also, a non-magnetic material needs to be used for this resistor assembly. Otherwise, eddy currents may be induced by the magnetic field of the inductor, and the resistor assembly may be heated.

[0014] As a result, the flange of the power resistor that establishes the terminal ground connection is within the notch of the ceramic heat spreader and is in direct contact with the cooling element, but the connection between the resistor and the inductor needs to fill a significant gap with the PCB on top of the ceramic heat spreader. Furthermore, the coefficients of thermal expansion (c TE ) of all the related materials are different. Therefore, in a cycling operation where RF is frequently turned on / off, or the RF power level is frequently changed, for example, on a second-by-second basis, the connection between the upper contact of the termination resistor and the inductor is subject to significant thermo-mechanical stress during the cycling operation. This is commonly seen in short-term semiconductor plasma processes and pulse operations. These soldered or welded joints can rapidly deteriorate at high operating temperatures and may ultimately fail.

[0015] At the connection between the flange and the cooling element, a flange material such as a copper molybdenum alloy having a c TE similar to that of the resistor material does not match the c TE of the cooling element, which is usually made of copper, aluminum, or an alloy, resulting in thermo-mechanical stress.

[0016] Therefore, an object of the present invention is to provide a resistor assembly that is compactly and reliably connected to a cooling element.

Means for Solving the Problem

[0017] The problems of the prior art are solved by the resistor assembly according to claim 1, the power combiner according to claim 14, and the RF generator according to claim 16.

[0018] In a first aspect, a resistor assembly, particularly for a power combiner, is provided. The resistor assembly includes a resistor chip. Preferably, the resistor chip has an area of 50 mm 2 to 500 mm 2 . Preferably, the size of the resistor chip is from 12 mm × 6 mm to 30 mm × 14 mm. Preferably, the resistor chip has a rated power of 600 W or more. Preferably, the resistor chip is constructed in particular as a thick film resistor based on aluminum nitride (AlN). In particular, the operating temperature of the resistor chip is 100 °C or higher. Preferably, the resistor chip has one terminal on its upper surface or side surface and a second terminal on its lower surface. The lower surface may be completely covered with a metal layer. Thereby, the second terminal can be connected to a conductive passive heat spreader that transfers heat to a cooling element functioning as a ground connection.

[0019] According to the present invention, the resistor assembly comprises a clamping element for clamping the resistor chip to the cooling element. Here, the cooling element may be a heat spreader constructed to disperse the heat generated by the resistor chip and transfer it to the cooling element. The clamping element establishes contact between the resistor chip and the cooling element, and the heat generated by the resistor chip is dissipated to the cooling element. Here, the clamping element has a clamping arm for applying pressure to the resistor chip. Therefore, by directly applying pressure to the resistor chip, the contact between the resistor chip and the cooling element is improved. Therefore, in contrast to the prior art, the resistor chip itself is clamped, and the clamping force is applied directly to the resistor chip rather than to the heat dissipation element of the resistor of the prior art described above, such as a flange. Therefore, the space required to fix the resistor chip to the cooling element is reduced, and as a result, the area of the resistor chip can be increased, and heat transfer from the resistor chip is improved. Furthermore, the clamping fixation (in contrast to fixing the resistor with screws as in the prior art) allows for the thermal expansion of the resistor chip, thereby reducing the thermal induced stress of the resistor chip. Therefore, heat dissipation from the resistor chip to the cooling element is improved, and the operating temperature is reduced, so the reliability and lifespan of the resistor are increased.

[0020] Preferably, the resistance value of the resistor chip is 50 ohms.

[0021] Preferably, the clamping element includes a base element connected to the clamping arm in an L-shape. In particular, the base element has a first end connected to the clamping arm and a second end on the opposite side that is directly connected to or in contact with the cooling element in the mounted state. In particular, the base element and the clamping arm are one part and are integrally constructed. In particular, the angle between the base element and the clamping arm may be 90° or less. Therefore, a contact point / contact line is formed by the base element, and the clamping element rotates about this contact point / contact line, and the clamping arm can apply pressure to the resistor chip.

[0022] Preferably, the second end of the base element is inclined around an edge in a direction away from the resistor chip to allow rotational movement of the clamping element. Thus, the edge at a greater distance from the resistor chip at the second end of the base element becomes the pivot point / line of the clamping element. Thereby, the pressure applied by the clamping element can increase by up to 60% compared to the case where there is a pivot line at the edge close to the resistor chip corresponding to the flat second end of the base element. When the second end of the base element is flat, the clamping element rotates around the pivot line at the second end of the base element close to the resistor chip. Instead of the inclined second end, the second end may comprise a protrusion providing a pivot line at the position of the second end away from the resistor chip.

[0023] Preferably, the clamping arm and the base element are made of a rigid non-magnetic material such as, for example, an aluminum alloy, brass, or austenitic steel.

[0024] Preferably, a pressure dispersion plate is disposed between the clamping arm and the resistor chip. By the pressure dispersion plate, the pressure applied by the clamping arm is dispersed over the entire area or at least a partial area of the resistor chip. Preferably, the pressure dispersion plate is a rigid element constructed from metal or plastic. Preferably, the pressure dispersion plate may be a separate element or integrally constructed with the clamping arm. Preferably, the thickness of the pressure dispersion plate is 2 - 5 mm, and the area of the pressure dispersion plate is preferably 50 mm 2 ~400 mm 2 is.

[0025] Preferably, the pressure distribution plate is made of a rigid non-magnetic material such as an aluminum alloy, brass, or austenitic steel. In particular, the pressure distribution plate may be made of the same material as the clamp arm and / or the base element. Alternatively, the pressure distribution plate may be made of a plastic that can essentially provide insulation between the clamp element and the resistor chip.

[0026] Preferably, an alignment mechanism is provided on the lower side of the clamp arm connected to the pressure distribution plate, and a corresponding alignment mechanism is provided on the upper surface of the pressure distribution plate, which engages with the alignment mechanism of the clamp arm and is configured to align the positions of the clamp arm and the pressure distribution plate. Here, the alignment mechanism may be a ball, a detent, a hemispherical protrusion, etc. Here, the alignment mechanism of the clamp arm may be constructed integrally with the clamp arm or may be an additional element. Here, the hemispherical alignment mechanism provides a beneficial contact surface for evenly transmitting the pressure of the clamp arm to the pressure distribution plate. Here, the corresponding alignment mechanism of the pressure distribution plate has a shape corresponding to the alignment mechanism of the clamp arm for engaging or receiving the alignment mechanism of the clamp arm. Here, the corresponding alignment mechanism may be constructed as a groove, a recess, a depression, etc. Of course, the shapes of the alignment mechanism of the clamp arm and the corresponding alignment mechanism of the pressure distribution plate can be freely selected. The orientation of the pressure distribution plate is maintained by the alignment function of the clamp arm and the corresponding alignment function of the pressure distribution plate.

[0027] Preferably, the insulating layer is disposed between the resistor chip and the clamp arm, and preferably directly disposed between the resistor chip and the pressure dispersion plate. Here, the insulating layer may be disposed on the upper surface of the resistor chip. The insulating layer is electrically insulating. Preferably, the insulating layer is made of a high-temperature elastic material such as perfluoroelastomer, polyimide, or polyamide. The insulating layer avoids a short circuit, particularly between the metal pressure dispersion plate and the resistor chip. Here, when the pressure dispersion plate is made of a plastic material, the insulating layer may be integrally formed with the pressure dispersion plate. Thereby, the insulating effect is essentially provided by the pressure dispersion plate itself, and thus, the elements of the pressure dispersion plate and the insulating layer are combined. Alternatively, the insulating layer and the pressure dispersion plate are separate elements. By configuring the insulating layer as an elastic layer, the pressure dispersion from the pressure dispersion plate to the resistor chip is improved, and slight manufacturing defects of the resistor chip and / or the pressure dispersion plate are compensated by the elastic insulating layer without causing a short circuit.

[0028] Preferably, the resistor assembly includes pressure means connected to the clamp arm and connectable to a cooling element and configured to generate pressure on the clamp arm. Preferably, the pressure means is constructed as a screw.

[0029] In particular, the pressure means penetrates the clamp arm and preferably penetrates the pressure dispersion plate. Among them, in particular, the through-hole of the clamp arm conforms to the outer diameter of the pressure means, and the through-hole of the pressure dispersion plate is larger than the pressure means to allow movement of the pressure dispersion plate relative to the pressure means. Further, the pressure means maintains the orientation of the pressure dispersion plate. The combination of the alignment function of the clamp arm and the corresponding alignment function of the pressure dispersion plate determines and fixes the position of the pressure dispersion plate.

[0030] Preferably, the pressure means does not penetrate the resistor chip. In particular, the pressure means is disposed away from the resistor chip, and by avoiding contact between the pressure means and the resistor chip, the possibility of a short circuit is prevented.

[0031] Preferably, the pressure means does not penetrate the insulating layer. Thus, the insulating layer can be disposed only between the pressure dispersion plate and the resistor chip. This is particularly applicable when the pressure dispersion plate is made of a conductive material such as metal. Alternatively, the pressure means may penetrate the insulating layer, particularly when the insulating layer is integrated with the pressure dispersion plate.

[0032] Preferably, a conductive layer is disposed on the lower surface of the resistor chip on the side opposite to the clamp arm, and the conductive layer is preferably thermally conductive and / or electrically conductive. Here, the thermal conductivity is preferably greater than 200 W / m / K, more preferably greater than 300 W / m / K, and most preferably greater than 400 W / m / K, thereby exceeding, for example, the thermal conductivity of an aluminum heat sink with a thermal conductivity of 240 W / m / K and / or the thermal conductivity of a heat spreader made of, for example, Al2O3 with a thermal conductivity of 30 W / m / K.

[0033] Preferably, the conductive layer is compressible. Preferably, the compression rate of the conductive layer is 10% or more, more preferably 20% or more. Preferably, the bulk modulus of the conductive layer is less than 1000 kPa, preferably 600 kPa. The compressibility of the conductive layer can compensate for small manufacturing defects on the lower surface provided by the resistor chip and / or the cooling element, thereby providing complete contact between the respective surfaces to enable optimal heat dissipation from the resistor chip to the cooling element.

[0034] Preferably, the conductive layer is provided by a thermal transfer paste, a thermal pad, or a compressible graphite thermal interface material, preferably having a compression rate of 10% or more, more preferably 20% or more.

[0035] Preferably, the conductive layer provides electrical contact between the ground and the resistor chip.

[0036] The resistor assembly is preferably constructed as a ribbon and is preferably connected to the resistor chip, in particular including a connecting element connected to the side of the resistor chip on the opposite side of the base element of the clamping element. Thus, in particular, the connecting element is connected to the short side of the resistor chip. Therefore, the connecting element may be connected to the resistor chip on its upper surface. Thus, by means of the connecting element, the resistors are electrically connected to the respective circuits. As described above, the second terminal of the resistor chip may be provided by the lower surface of the resistor chip by means of a metal layer.

[0037] Preferably, the connecting element is S-shaped. By making it S-shaped, thermal expansion can be corrected and it will not lead to damage to the connecting element.

[0038] In a further aspect, a power combiner is provided. The power combiner comprises a heat spreader or heat sink, i.e., a cooling element, and at least one inductor connected to the cooling element, and the at least one inductor may be a planar inductor. In particular, the power combiner comprises at least two inputs and one output. By using at least one inductor, the power combiner is configured to combine two input RF signals into one single RF signal. Here, the aforementioned resistor assembly is connected to at least one inductor as a terminating resistor. Usually, the resistance value of the resistor chip is 50 ohms.

[0039] Preferably, the at least one inductor preferably comprises a central recess reaching up to the cooling element, and the resistor assembly is completely arranged within the recess and directly attached to the cooling element. Thereby, a compact arrangement can be realized. The recess is in the central region of the inductor and may penetrate the PCB of the power combiner and the ceramic heat spreader. The resistor assembly, in particular the resistor chip, is in direct contact with the cooling element of the RF generator, i.e., the cold plate.

[0040] In a further aspect of the present invention, an RF generator is provided that includes at least two power amplification stages and the aforementioned power combiner. Here, the combiner is connected to at least two power amplification stages and combines the output power of the at least two power amplification stages. Preferably, the RF generator is provided for plasma applications. Here, the components of the RF generator are assembled on a common cooling element.

[0041] Preferably, the RF generator provides an output power of 5 KW or more. In particular, each of the at least two power amplification stages provides a power of at least 2.5 KW or more.

[0042] Preferably, the RF generator is water-cooled. In particular, the cooling element includes active cooling constructed as water-cooled.

[0043] Preferably, the RF generator is provided within a 19 / 2-inch format housing. This makes the size of the RF generator compact. With the resistor according to the present invention, heat dissipation from the resistor to the cooling element of the RF generator is improved, enabling a high output power level.

Brief Description of the Drawings

[0044] The present invention will be described in more detail with reference to the accompanying drawings.

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Modes for Carrying Out the Invention

[0045] Refer to FIGS. 1 to 3 below. The resistor assembly according to the present invention includes a resistor chip 12 having an upper surface 16 and a lower surface 18. The resistor chip 12 includes a connection element 14 constructed as a ribbon. The connection element 14 may be bent in an S shape. The second terminal of the resistor chip 12 is provided by the lower surface 18 which is normally grounded. This second terminal may be a metal layer 13 covering the lower surface 18. Further, the resistor assembly includes a clamp element 20 having a clamp arm 22 and a base element 24. The base element 24 includes a first end 26 connected to the clamp arm 22 and a second end 28 directly connected to a cooling element 50 of a high-frequency (RF) generator. The clamp element 20 is connected to the cooling element 50 by a screw 30. As shown in FIG. 2, the second end 28 of the base element 24 includes an inclined surface 44 having an angle α. The inclined surface 44 constructs a pivot line 46 at the outer edge of the base element 24, that is, the edge farther from the resistor chip 12. Due to this angle α provided by the inclined surface 44, the clamping force generated by the clamp element 20 can be increased by 60% compared to a plane rotating about the pivot line at the edge closer to the resistor chip 12. When the screw 30 is turned, pressure is applied to a pressure dispersion plate 32 by the clamp arm 22. Among them, the screw 30 can penetrate through a through hole 38 of the pressure dispersion plate 32. Further, the clamp arm 22 includes a hemispherical alignment function 34, and the pressure dispersion plate 32 includes a hemispherical recess 36 for receiving the alignment function 34 of the clamp arm 22. Thereby, the position of the pressure dispersion plate 32 is defined by the alignment function 34, and the corresponding recess 36 and through hole 38 receive the screw. The pressure dispersion plate 32 disperses the pressure applied by the clamp arm 22 and is made of a hard material such as hard plastic or metal. An insulating layer 40 for electrically insulating the resistor chip 12 from the pressure dispersion plate 32 is provided between the pressure dispersion plate 32 and the upper surface 16 of the resistor chip 12. Among them, the screw 30 may penetrate through a through hole of the insulating layer 40.The insulating layer 40 may be compressible in order to evenly distribute the pressure applied to the resistor chip 12 by the pressure dispersion plate 32 and enable thermal expansion without causing thermal stress to the resistor chip 12. The insulating layer 40 may be made of a high-temperature elastic material such as perfluoroelastomer, polyimide, or polyamide.

[0046] On the lower surface 18 of the resistor chip 12, a conductive layer having thermal conductivity and electrical conductivity is disposed between the cooling element 50 and the resistor chip 12. Thereby, contact between the lower surface 18 of the resistor chip 12 and the ground is established by the conductive layer. At the same time, the heat generated by the resistor chip is transmitted to the cooling element 50.

[0047] Referring to FIG. 4, a power combiner 102 according to the present invention is shown, which may be part of a high-power RF generator. The power combiner includes at least one inductor 52, and the resistor assembly according to the present invention is connected to the inductor 52 by a connection element 14 as a termination resistor.

[0048] Preferably, the resistor assembly of the present invention has an operating temperature of 80° C. or higher, preferably 100° C. or higher.

[0049] FIG. 5 schematically shows an RF generator 100 having at least two power amplification stages 104A, 104B. The output of each power amplification stage is combined by a power combiner as described above with reference to FIG. 4.

[0050] In the prior art, a flanged resistor can be connected to a cooling element with two screws to handle an absorption power of up to 400 W. However, in the present invention, by increasing the area of the resistor chip and at the same time improving the thermal contact between the resistor chip and the cooling element, an absorption power of up to 700 W or more can be processed. At the same time, the operating temperature of the resistor can be lowered by 15° C. or more.

[0051] Furthermore, since the operating temperature is reduced and the thermomechanical stress during power cycling is alleviated, the life of the soldered or brazed connection from the upper contact of the resistor to the combiner PCB is significantly extended. Additionally, the thermal expansion and compression of the clamped components are facilitated by the conductive and compressible thermal interface material, reducing the thermomechanical stress on the resistor chip.

Claims

1. A resistor chip, A clamp element for fixing the resistor chip to a cooling element, characterized in that the clamp element has a clamp arm for applying pressure to the resistor chip, and in particular a resistor assembly for a power combiner.

2. The clamp element includes a base element connected to the clamp arm in an L-shape, preferably, the base element has a first end connected to the clamp arm and a second end on the opposite side in contact with the cooling element, according to claim 1. The resistor assembly described.

3. The resistor assembly according to claim 2, characterized in that the second end of the base element is inclined so as to enable a rotational movement of the clamp element around an edge in a direction away from the resistor chip.

4. The resistor assembly according to any one of claims 1 to 3, characterized in that a pressure dispersion plate is disposed between the clamp arm and the resistor chip.

5. An alignment functional part is provided below the clamp arm connected to the pressure dispersion plate, and a corresponding alignment functional part that engages with the alignment functional part of the clamp arm is provided on the upper surface of the pressure dispersion plate. The resistor assembly according to claim 4, characterized in that the positions of the clamp arm and the pressure dispersion plate are configured to be aligned.

6. An insulating layer disposed between the resistor chip and the clamp arm, preferably directly disposed between the resistor chip and the pressure dispersion plate, according to any one of claims 1 to 5. The resistor assembly described.

7. Pressure means connected to the clamp arm and connectable to the cooling element to generate pressure of the clamp arm, according to any one of claims 1 to 6. The resistor assembly described.

8. The resistor assembly according to claim 7, characterized in that the pressure means penetrates the clamp arm, preferably penetrates the pressure dispersion plate.

9. The resistor assembly according to claim 7 or 8, characterized in that the pressure means does not penetrate the resistor.

10. ​ A conductive layer is disposed on the lower surface of the resistor chip on the side opposite to the clamp arm, and preferably the conductive layer has thermal conductivity and / or electrical conductivity. The resistor assembly according to any one of claims 1 to 9.

11. The resistor assembly according to claim 10, wherein the conductive layer is compressible.

12. The resistor assembly according to claim 10 or 11, wherein the conductive layer is provided by a heat transfer paste or a heat pad or a compressible graphite thermal interface material.

13. Preferably constructed as a ribbon, connected to the resistor chip, and in particular connected to the side surface of the resistor chip on the side opposite to the base element of the clamp element. The resistor assembly according to any one of claims 1 to 12.

14. A power combiner comprising the cooling element, at least one inductor disposed on the cooling element, and the resistor assembly according to any one of claims 1 to 13 connected to the at least one inductor.

15. The power combiner according to claim 13, wherein the at least one inductor has a central recess, and the resistor assembly is completely disposed within the recess.

16. An RF generator comprising at least two power amplification stages and the power combiner according to claim 14 or 15 connected to the at least two power amplification stages for combining the output powers of the at least two power amplification stages.

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