Electromagnetic absorbing arrangement

Abstract

An electromagnetic absorbing arrangement, the arrangement comprising an integrated circuit (100), such as a monolithic microwave integrated circuit (MMIC), arranged to a substrate (102) by a flip-chip connection, wherein the integrated circuit comprises a radio frequency (RF) input (108) and a radio frequency (RF) output (109). The arrangement further comprises a radio frequency absorber (200, 300, 400), arranged in connection with the integrated circuit (100), wherein the radio frequency absorber (200, 300, 400) comprises radio frequency absorbing material arranged to at least partially absorb a portion of the electric signal, e.g. parasitic radiation, that is radiated from the interconnects of the RF-input (108) and / or RF-output (109) of the integrated circuit (100).

Description

[0001] ELECTROMAGNETIC ABSORBING ARRANGEMENT

[0002] Technical Field

[0003] The invention concerns in general the technical field of electronics. Especially the invention concerns an electromagnetic absorbing arrangement and a circuit board comprising the electromagnetic absorbing arrangement.

[0004] Background

[0005] Integrated circuits, also known as a microchips or ICs, are used in a wide range of electronic devices to perform various functions such as processing and storing of information. Integrated circuits are small electronic devices comprising multiple interconnected electronic components such as transistors, resistors, and capacitors. These components can be e.g. etched onto a small piece of semiconductor material, e.g. silicon.

[0006] There are integrated circuits that operate in high frequency environment, e.g. with millimeter wave and THz signals. Examples of the applications and products that utilize these kinds of integrated circuits are security imaging, spectroscopy of (biological) molecules, radiometric and radar imaging, such as space and Earth observation as well as for Advanced Driver-Assistance Systems, ADAS. Therefore, there is a high demand for integrated circuits that operate with millimeter wave and THz-signals.

[0007] Monolithic microwave integrated circuits, or MMICs are one type of integrated circuit devices that operate at microwave frequencies (e.g. up from 300 MHz to 300 GHz). These devices can perform functions such as microwave mixing, power amplification, low-noise amplification, and high-frequency switching. However, manufacturing and integration of millimeter wave MMICs in a cost- effective packages or modules is challenging. The challenges and frequency operating limits of the prior art solutions are related for example to interconnection of the MMIC to the circuit board. The interconnects connecting the MMIC to the circuit board work as an antenna, and they radiate and receive signals in a lateral plane of the chip which can result in parasitic coupling between input and output of an MMIC. Also, a gap between a chip and a substrate can work as an electromagnetic waveguide providing strong coupling between RF output and RF input of the MMIC chip when signals having high frequencies are used.

[0008] For these reasons there is a need to develop a solution which is able to overcome the above-mentioned problems of the prior art and present a solution which is able to operate at high frequencies with low interference and e.g. to avoid coupling between RF-output and RF-input of an integrated circuit, such as an MMIC.

[0009] Summary

[0010] An objective of the invention is to present an electromagnetic absorbing arrangement for integrated circuits, such as monolithic microwave integrated circuits (MMICs), which is able to perform well also with high frequencies and to prevent or reduce coupling between RF-output and RF-input of an integrated circuit, such as an MMIC.

[0011] The objectives of the invention are reached by an electromagnetic absorbing arrangement and a circuit board as defined by the respective independent claims.

[0012] According to a first aspect, the invention relates to an electromagnetic absorbing arrangement, the arrangement comprising an integrated circuit, such as a monolithic microwave integrated circuit (MMIC), arranged to a substrate by a flipchip connection, wherein the integrated circuit comprises a radio frequency (RF) input and a radio frequency (RF) output. The arrangement further comprises a radio frequency absorber arranged in connection with the integrated circuit. The radio frequency absorber comprises radio frequency absorbing material arranged to at least partially absorb a portion of the electric signal, e.g. parasitic radiation, that is radiated from the interconnects of the RF-input and / or RF- output of the integrated circuit.

[0013] In one embodiment of the invention the radio frequency absorbing material is material having resistivity in a predefined resistivity range, e.g. sheet resistivity being in range of 10 - 100 Ohm / sq or preferably around 30 - 50 Ohm / sq. In one embodiment of the invention the radio frequency absorbing material is material having dielectric constant in a predefined range, e.g. in the range of 2 - 10 or preferably around 3 - 4, and / or material having dielectric loss tangent (tan 5) in a predefined range, e.g. in a range of 0,1 - 1 or preferably in range of 0,4 - 0,6.

[0014] In one embodiment of the invention the radio frequency absorber is arranged to reduce and / or to prevent pass through propagation of RF-signals between the RF-output and the RF-input outside a signal path of the integrated circuit e.g. so that oscillation of the integrated circuit is suppressed.

[0015] In one embodiment of the invention the radio frequency absorbing material is arranged into a layer, a film, a resin and / or a sheet, and / or the radio frequency absorbing material comprises radio frequency absorbing elements.

[0016] In one embodiment of the invention the radio frequency absorber comprises at least a metal layer and / or a metal film, and / or a doped silicon layer and / or a doped silicon film.

[0017] In one embodiment of the invention the radio frequency absorber comprises a dielectric layer, such as resin, with resistive elements and / or elements with dielectric loss tangent (tan 5) in the preferred range.

[0018] In one embodiment of the invention the radio frequency absorber is arranged at least to one of the following: at least in part between the RF-input and the RF- output of the integrated circuit, under the integrated circuit, e.g. in cavity under the integrated circuit, on top of the integrated circuit, on the surface of a substrate on to which the integrated circuit is arranged, between the integrated circuit and the substrate, as a layer of a circuit board, as a layer on top of circuit board.

[0019] In one embodiment of the invention the radio frequency absorber comprises electromagnetic resonance structures, such as a resonator array, e.g. with resonance frequencies arranged essentially to a range of an operating signal frequency of the integrated circuit. In one embodiment of the invention the resonance structure comprises at least one of the following: rectangular slots, bow tie slots, square slots, rectangular metal dipoles, bow tie dipoles, square dipoles, and / or wherein the slots have dimensions essentially from half to one the wavelength of the signal frequency of the integrated circuit.

[0020] In one embodiment of the invention the radio frequency absorber comprises a dielectric layer, such as resin, with electromagnetic resonators, having resistivity in the predefined range or dielectric material with dielectric loss tangent (tan 5) in the predefined range, e.g. the resonators in a form of spheres fabricated of metal.

[0021] In one embodiment of the invention the resistivity of the radio frequency absorber is arranged to be in a range in which the losses for the signal through the signal path via the integrated circuit is below a predefined first limit and the losses for the parasitic radiation are above a predefined second limit.

[0022] In one embodiment of the invention the radio frequency absorber comprises two layers to which radio frequency absorbing material is arranged, wherein the first layer is arranged closer to the integrated circuit than the second layer, and wherein the first layer has lower dielectric loss than the second layer.

[0023] In one embodiment of the invention the interconnects for connecting the integrated circuit, e.g. the RF-input and / or the RF-output of the integrated circuit, are interconnects of a flip-chip-connection, such as pillar interconnects, stud bump interconnects and / or solder ball interconnects.

[0024] According to a second aspect, the invention relates to a circuit board comprising an electromagnetic absorbing arrangement according to any embodiment of the invention wherein the radio frequency (RF) input and the radio frequency (RF) output of the integrated circuit is connected to the circuit board.

[0025] The solution of the invention can be utilized for integration of integrated circuits, such as monolithic microwave integrated circuits (MMICs), to the circuit board also when high frequencies are used. With the solution of the invention good isolation between output and input of integrated circuits, such as MMICs, can be achieved and their oscillation can be prevented also in case of using high gain. Thus, the performance of the system with integrated chips, such as MMICs, can be improved.

[0026] The exemplary embodiments of the invention presented in this patent application are not to be interpreted to pose limitations to the applicability of the appended claims. The verb "to comprise" is used in this patent application as an open limitation that does not exclude the existence of also unrecited features. The features recited in dependent claims are mutually freely combinable unless otherwise explicitly stated.

[0027] The expression "a number of’ may herein refer to any positive integer starting from one (1 ). The expression "a plurality of’ may refer to any positive integer starting from two (2), respectively.

[0028] The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objectives and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.

[0029] Brief descriptions of the drawings

[0030] The embodiments of the invention are illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings.

[0031] Figure 1 illustrates schematically a prior art solution as a side view.

[0032] Figure 2 illustrates schematically an example embodiment of the electromagnetic absorbing arrangement as a side view.

[0033] Figure 3 illustrates schematically an example embodiment of the electromagnetic absorbing arrangement as a side view.

[0034] Figure 4 illustrates schematically an example embodiment of the electromagnetic absorbing arrangement as a side view. Figure 5A-D illustrate schematically different example embodiments of the radio frequency absorber viewed from above.

[0035] Figure 6 illustrates schematically an example embodiment of the electromagnetic absorbing arrangement as a side view.

[0036] Figures 7 - 13 present simulation results relating to different embodiment of the invention.

[0037] Description of some embodiments

[0038] Fig. 1 presents a prior art solution as a side view. In the example of the prior art solution the integrated circuit 100, such as MMIC, is arranged to an interposer 102, such as a substrate. The lead line or conductor 104 in the interposer can be connected to the RF-input 108 of the integrated circuit and the lead line or conductor 105 in the interposer can be connected to RF-output of the integrated circuit 109. The integrated circuit 100, such as MMIC, can be connected to the interposer typically via pillar or flip-chip interconnects because for example wire bonding can’t be used due to high impedance of wires at high frequencies. The length and / or width of the integrated circuit can be for example around 1000 pm, e.g. 830 pm, and the height of the gap between the interposer and the integrated circuit can be around 100pm, e.g. 80 pm.

[0039] In this kind of prior art solution the interconnects to RF-input 108 and / or RF- output 109 work as an antenna and radiate and receive signals in a lateral plane of the chip. A gap between a chip and a substrate works as an electromagnetic waveguide providing strong coupling between RF-output and RF-input. Also, high propagation losses of mm-Waves require using of e.g. MMIC with a very high amplification gain. In the solution of the prior art parasitic radiation of pillar or flip chip interconnections don’t allow good isolation between the RF-output and the RF-input. As a results, positive feedback paths between output and input of the integrated circuit are created due to the coupling. Combination of high gain and positive feedback loops leads to oscillation of circuits. The solution of the invention solves the above-mentioned problem(s). The invention relates to an electromagnetic absorbing arrangement, the arrangement comprising an integrated circuit, such as a monolithic microwave integrated circuit (MMIC), arranged to a substrate by a flip-chip connection, wherein the integrated circuit comprises a radio frequency (RF) input and a radio frequency (RF) output. In the solution of the invention a radio frequency absorber is arranged in connection with the integrated circuit. The radio frequency absorber comprises radio frequency absorbing material arranged to at least partially absorb a portion of the electric signal, e.g. parasitic radiation, that is radiated from the interconnects of the RF-input and / or RF-output of the integrated circuit.

[0040] The integrated circuit can be configured to operate with signals in the frequency range over 30Ghz, over 10OGhz, in the frequency range of 100 - 500 GHz and / or 200 - 400 GHz.

[0041] In one embodiment of the invention the radio frequency absorber is arranged to reduce and / or to prevent pass through propagation of RF-signals between the RF-output and the RF-input outside a signal path of the integrated circuit e.g. so that oscillation of the integrated circuit is suppressed and e.g. so that radio frequency radiation, e.g. parasitic RF-radiation and / or RF-energy, radiating from the interconnections of the RF-output and / or RF-input of the integrated circuit is absorbed by the absorber.

[0042] In one embodiment of the invention the radio frequency absorber can be arranged at least to one of the following: at least in part between the RF-input and the RF-output of the integrated circuit, under the integrated circuit, e.g. in cavity under the integrated circuit, on top of the integrated circuit, on the surface of a substrate on to which the integrated circuit is arranged, between the integrated circuit and the substrate, as a layer of a circuit board, as a layer on top of circuit board. In one example embodiment the absorber can be arranged on a surface of the substrate, in a cavity in the substrate or in a space between RF input and output of the integrated circuit, e.g. an MMIC chip.

[0043] In one embodiment of the invention the radio frequency absorbing material is arranged into a layer, a film, a resin and / or a sheet, and / or the radio frequency absorbing material comprises radio frequency absorbing elements. In one embodiment of the invention the absorbing material comprises a resistive film, e.g. a metal film or doped silicon film. The film can be deposited on a surface of the substrate, e.g. under the integrated circuit, such as MMIC. The absorber can be e.g. a film comprising NiCr-resistor.

[0044] In one embodiment of the invention the radio frequency absorbing material is material having resistivity in a predefined resistivity range, e.g. sheet resistivity being in range of 10 - 100 Ohm / sq or preferably around 30 - 50 Ohm / sq.

[0045] In one embodiment of the invention the absorbing material comprises a dielectric layer. The dielectric layer can for example fill all space between the substrate and the integrated circuit, such as MMIC. In this case the layer can be thicker than a thin film.

[0046] In one embodiment of the invention the radio frequency absorber comprises a dielectric layer with resistive elements and / or elements with dielectric loss tangent (tan 5) in the preferred range. In one embodiment of the invention the dielectric layer can be resin or comprise resin.

[0047] In one embodiment of the invention the radio frequency absorbing material is material having dielectric constant in a predefined range, e.g. in the range of 2 - 10 or preferably around 3 - 4, and / or material having dielectric loss tangent (tan 5) is in a predefined range, e.g. in a range of 0,1 - 1 or preferably in range of 0,4 - 0,6.

[0048] In one embodiment of the invention the absorbing material comprises a layer with lossy elements. In one embodiment the dielectric loss tangent of the absorbing material remains substantially constant, for a frequency range of a frequency of the signal frequency of the integrated circuit.

[0049] In one embodiment of the invention the absorber can comprise a dielectric plate with a metal layer, wherein the absorber is a resistive layer located on the surface of a dielectric plate with a specific surface resistance.

[0050] In one embodiment of the invention the radio frequency absorber can comprise foam radar absorbing sheet materials, e.g. comprised of urethane foam and a gradient lossy coating. In one embodiment of the invention the absorber can comprise e.g. Cuming Microwave C-RAM FLX and / or Cuming Microwave C- RAM AR as radio frequency absorbing material. In one embodiment, the radio frequency absorber can comprise a layer, e.g. 50 pm thick layer, of any above- mentioned material.

[0051] In one embodiment of the invention the resistivity of the radio frequency absorber is arranged to be in a range in which the losses for the signal through the signal path via the integrated circuit is below a predefined first limit and the losses for the parasitic radiation are above a predefined second limit. In one embodiment of the invention the resistivity of the material, e.g. film, should be low enough to be matched with electromagnetic waves but high enough to obtain high losses of electromagnetic wave radiating from the RF-input and / or the RF-output and / or the respective interconnects.

[0052] In one embodiment of the invention the interconnects for connecting the integrated circuit, e.g. the RF-input and / or the RF-output of the integrated circuit, are interconnects of a flip-chip-connection, such as pillar interconnects, stud bump interconnects and / or solder ball interconnects. In one embodiment of the invention the interconnects can be e.g. copper pillar interconnects. Different variations of flip chip bonding have been used, e.g. face-to-face interconnection, back-to-face interconnection, face-to-back-interconnection, back-to-back-inter- connection. A flip-chip connection area can comprise at least one pad, such as ground-signal-ground (GSG) bumps. In one example embodiment the ground- signal-ground (GSG) bumps may have the following dimensions: bump pitch in range 50...250pm, e.g. 100pm; diameter and height in range (0,02....0,1 mm), e.g. 0,04 mm.

[0053] In the solution of the invention a substrate is used in many embodiments. Instead of a substate or in addition to a substrate also other suitable interposers can be used in the solution of the invention and / or in the embodiments described in this specification, e.g. so that the substrate used in an embodiment is replaced with another interposer.

[0054] Fig. 2 presents an example embodiment of the electromagnetic absorbing arrangement as a side view. In this example embodiment the integrated circuit 100, such as MMIC, is arranged to an interposer 102, such as a substrate. The substrate comprises for example one of the following material: Si, LTCC, PCB, glass. The lead line or conductor 104 in the interposer can be connected to the RF-input 108 of the integrated circuit and the lead line or conductor 105 in the interposer can be connected to RF-output of the integrated circuit 109. The integrated circuit 100, such as MMIC, and its RF-input and RF-output can be connected to the interposer e.g. via pillar or flip-chip interconnects because for example wire bonding can’t be used due to high impedance of wires at high frequencies. The radio frequency absorber 200 according to an embodiment of the invention can be arranged under the integrated circuit 100, such as an MMIC.

[0055] In the example embodiment of Figure 2 the radio frequency absorber is arranged to a cavity in the interposer, such as a substrate, between the RF-input and RF- output of the integrated circuit. The radio frequency absorber comprises radio frequency absorbing material arranged to at least partially absorb a portion of the electric signal, e.g. parasitic radiation, that is radiated from the interconnects of the RF-input and / or RF-output of the integrated circuit. In the example embodiment of Figure 2 the radio frequency absorber can be for example dielectric material layer which fills essentially all space between the substrate and integrated circuit. In one embodiment of the invention the absorber can have height of e.g. 50 pm.

[0056] The example of Figure 3 is otherwise similar to the example of Figure 2 but the radio frequency absorber 300 is a resistor sheet in this example embodiment. As the example of Figure 2, the embodiment of Figure 3 comprises the integrated circuit 100, such as MMIC, is arranged to an interposer 102, such as a substrate. The lead line or conductor 104 in the interposer can be connected to the RF-input 108 of the integrated circuit and the lead line or conductor 105 in the interposer can be connected to RF-output of the integrated circuit 109. The frequency absorber which is a resistor sheet is arranged under the integrated circuit. In one example embodiment of Figure 3, the resistor sheet can be a resistive film which is s a film deposited on a surface of the substrate under the integrated circuit, such as MMIC. The film can be metal film or a layer of doped silicon.

[0057] The example of Figure 4 is otherwise similar to the examples of Figure 2 and 3 but the radio frequency absorber 400 is arranged in this example embodiment in a different manner. As the examples of Figure 2 and 3, the embodiment of Figure 4 comprises the integrated circuit 100, such as MMIC, is arranged to an interposer 102, such as a substrate. The lead line or conductor 104 in the interposer can be connected to the RF-input 108 of the integrated circuit and the lead line or conductor 105 in the interposer can be connected to RF-output of the integrated circuit 109. The frequency absorber 400 is in this example embodiment embedded to substrate of the circuit board so that it surrounds the integrated circuit from essentially all sides.

[0058] In one embodiment of the invention the radio frequency absorber comprises electromagnetic resonance structures, such as a resonator array, e.g. with resonance frequencies arranged essentially to a range of an operating signal frequency of the integrated circuit. Different resonance structures with the response frequencies of the RF signal can be implemented e.g. in the resistive film. The resonators are arranged such that the electromagnetic wave excites resonators which are resonating and thus losses in the absorbing material increase considerably.

[0059] In one embodiment of the invention the resonance structure comprises at least one of the following: rectangular slots, bow tie slots, square slots, rectangular metal dipoles, bow tie dipoles, square dipoles. The slots can have dimensions essentially from half to one the wavelength of the signal frequency of the integrated circuit.

[0060] In one embodiment of the invention the radio frequency absorber comprises resin with electromagnetic resonators, having resistivity in the predefined range or dielectric material with dielectric loss tangent (tan 5) in the predefined range, e.g. the resonators in a form of spheres fabricated of metal.

[0061] Figures 5A - D present different example embodiments of the absorber viewed from above.

[0062] Figure 5A presents a resistor sheet 300 without patterning. The resistor sheet can be arranged as in the example of Figure 3 but also in other ways as described with different embodiments of the invention. 510 illustrates the area of the absorber where there is no pattern or resistor embodiments in this example embodiment. Figure 5B presents a resistor sheet 300 with patterning. The resistor sheet can be arranged as in the example of Figure 3 but also in other ways as described with different embodiments of the invention. In the example of Figure 5B the resistive sheet comprises patterns 520 in form of rectangular slots which are arranged next to each other horizontally and vertically in the resistor sheet.

[0063] Figure 5C presents a resistor sheet 300 with patterning. The resistor sheet can be arranged as in the example of Figure 3 but also in other ways as described with different embodiments of the invention. In the example of Figure 5C the resistive sheet comprises patterns 530 in form of rectangular bow tie slots which are arranged next to each other horizontally and vertically in the resistor sheet.

[0064] Figure 5D presents a resistor sheet 300 with patterning. The resistor sheet can be arranged as in the example of Figure 3 but also in other ways as described with different embodiments of the invention. In the example of Figure 5C the resistive sheet comprises patterns 540 in form of square slots which are arranged next to each other horizontally and vertically in the resistor sheet.

[0065] In one embodiment of the invention the radio frequency absorber comprises two layers to which radio frequency absorbing material is arranged, wherein the first layer is arranged closer to the integrated circuit than the second layer, and wherein the first layer has lower dielectric loss than the second layer. Using of two layers can enable better gain and isolation in comparison with one layer structure.

[0066] Figure 6 presents an example embodiment of the electromagnetic absorbing arrangement of using two different absorbing layers as a side view. As in the other examples, an integrated circuit 100, such as MMIC, is arranged to an interposer 102, such as a substrate. The lead line or conductor 104 in the interposer can be connected to the RF-input 108 of the integrated circuit and the lead line or conductor 105 in the interposer can be connected to RF-output of the integrated circuit 109. The frequency absorber is arranged under the integrated circuit and to the interposer as two different layers comprising a low loss resin 200a and a high loss resin 200b, wherein the low loss resin 200a is arranged closer to the integrated circuit 100 than the high loss resin 200b. Figures 7 - 13 present simulation results relating to different embodiment of the invention.

[0067] Figure 7 presents simulation results of isolation between input and output of an integrated circuit based on resistivity of radio frequency absorbing material. Line

[0068] 701 presents an embodiment with no radio frequency absorbing material, line

[0069] 702 presents an embodiment with a metal film and lines 703 present resistor films with different resistivity (resistivity varied from 10 to 100 Ohm / sq.). In these simulations NiCr resistor is used as the radio frequency absorbing material of the resistor film. As can be seen from the Figure 7, isolation improvement is up to 10 dB can be achieved when radio frequency absorbing material is used.

[0070] Figure 8 presents simulation results relating to isolation (line 801 ) between input and output of an integrated circuit of an embodiment of the invention depending on resistivity of absorbing material, e.g. film. As can be seen from Figure 8, in this embodiment the highest isolation between the input and output of the integrated circuit is when the resistivity is around 30 Ohm / sq.

[0071] Figure 9 presents simulation results relating to isolation between input and output of an integrated circuit with an embodiment without patterning of the radio frequency absorbing material (in line 901 ) and with patterning of the radio frequency absorbing material (in line 902).

[0072] Figure 10 presents simulation results relating to gain of the system in different embodiments with one layer structure of radio frequency absorbing material. In Figure 10 line 1001 presents simulation results of isolation with first dielectric loss tangent value of the of the dielectric layer, line 1002 presents results of isolation with second dielectric loss tangent value of the of the dielectric layer and line 1003 presents results of isolation with third dielectric loss tangent value of the of the dielectric layer. With the first dielectric loss tangent value (line 1001 ) good gain can be achieved but the isolation between the input and output of the integrated circuit is low. In the embodiment of line 1003, a resin with material having high dielectric loss tangent is used. Figure 11 presents simulation results relating to isolation between input and output of an integrated circuit of the system in the simulation of Figure 10. Line 1101 corresponds the embodiment of line 1001 , line 1102 corresponds the embodiment of line 1002 and line 1103 corresponds the embodiment of line 1003. From the figures 10 and 11 it can be seen that there’s a small loss (around 1 dB) in gain but considerably better isolation between input and output of an integrated circuit. Thus much higher signal can be used and the system can have much higher total gain.

[0073] Figure 12 presents simulation results relating to gain of the system (line 1201 ) in an embodiment in which two-layer structure of radio frequency absorbing material is used. Figure 13 presents simulation results relating to isolation between input and output of an integrated circuit of the system (line 1301 ) in the simulation of Figure 12. As can be seen from the figures 12 and 13, better gain and isolation can be achieved in comparison with an embodiment of one layer structure of Figures 10 and 11 .

[0074] In the solution of the invention, for example the size, thickness and material selection of the radio frequency absorbing material are optimized for particular frequency band and therefore the Figures present example embodiments of the invention only schematically.

[0075] The specific examples provided in the description given above should not be construed as limiting the applicability and / or the interpretation of the appended claims. Lists and groups of examples provided in the description given above are not exhaustive unless otherwise explicitly stated. Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

Claims

Claims1 . An electromagnetic absorbing arrangement, the arrangement comprising: an integrated circuit (100), such as a monolithic microwave integrated circuit (MMIC), arranged to a substrate (102) by a flip-chip connection, wherein the integrated circuit (100) comprises a radio frequency (RF) input (108) and a radio frequency (RF) output (109), and a radio frequency absorber (200, 300, 400), arranged in connection with the integrated circuit, wherein the radio frequency absorber (200, 300, 400) comprises radio frequency absorbing material arranged to at least partially absorb a portion of the electric signal, e.g. parasitic radiation, that is radiated from the interconnects of the RF-input (108) and / or RF-output (109) of the integrated circuit (100).

2. An arrangement according to claim 1 , wherein the radio frequency absorbing material is material having resistivity in a predefined resistivity range, e.g. sheet resistivity being in range of 10 - 100 Ohm / sq or preferably around 30- 50 Ohm / sq.

3. An arrangement according to claim 1 or 2, wherein the radio frequency absorbing material is material having dielectric constant in a predefined range, e.g. in the range of 2 - 10 or preferably around 3 - 4, and / or material having dielectric loss tangent (tan 5) in a predefined range, e.g. in a range of 0,1- 1 or preferably in range of 0,4 - 0,6.

4. An arrangement according to any previous claim, wherein the radio frequency absorber (200, 300, 400) is arranged to reduce and / or to prevent pass through propagation of RF-signals between the RF-output (108) and the RF- input (109) outside a signal path of the integrated circuit (100) e.g. so that oscillation of the integrated circuit is suppressed.

5. An arrangement according to any previous claim, wherein the radio frequency absorbing material is arranged into a layer, a film, a resin and / or a sheet, and / or the radio frequency absorbing material comprises radio frequency absorbing elements.

6. An arrangement according to any previous claim, wherein the radio frequency absorber (200, 300, 400) comprises at least a metal layer and / or a metal film, and / or a doped silicon layer and / or a doped silicon film.

7. An arrangement according to any previous claim, wherein the radio frequency absorber (200, 300, 400) comprises a dielectric layer, such as resin, with resistive elements and / or elements with dielectric loss tangent (tan 5) in the preferred range.

8. An arrangement according to any previous claim, wherein the radio frequency absorber (200, 300, 400) is arranged at least to one of the following: at least in part between the RF-input (108) and the RF-output (109) of the integrated circuit, under the integrated circuit (100), e.g. in cavity under the integrated circuit (100), on top of the integrated circuit (100), on the surface of a substrate (102) on to which the integrated circuit (100) is arranged, between the integrated circuit (100) and the substrate (102), as a layer of a circuit board, as a layer on top of circuit board.

9. An arrangement according to any previous claim, wherein the radio frequency absorber (200, 300, 400) comprises electromagnetic resonance structures, such as a resonator array, e.g. with resonance frequencies arranged essentially to a range of an operating signal frequency of the integrated circuit.

10. An arrangement according to claim 9, wherein the resonance structure comprises at least one of the following: rectangular slots, bow tie slots, square slots, rectangular metal dipoles, bow tie dipoles, square dipoles, and / or wherein the slots have dimensions essentially from half to one the wavelength of the signal frequency of the integrated circuit.

11. An arrangement according to claim 9, wherein the radio frequency absorber (200, 300, 400) comprises a dielectric layer, such as resin, with electromagnetic resonators, having resistivity in the predefined range or dielectric material with dielectric loss tangent (tan 5) in the predefined range, e.g. the resonators in a form of spheres fabricated of metal.

12. An arrangement according to any previous claim, wherein the resistivity of the radio frequency absorber (200, 300, 400) is arranged to be in a rangein which the losses for the signal through the signal path via the integrated circuit (100) is below a predefined first limit and the losses for the parasitic radiation are above a predefined second limit.

13. An arrangement according to any previous claim, wherein the radio frequency absorber (200, 300, 400) comprises two layers (200a, 200b) to which radio frequency absorbing material is arranged, wherein the first layer (200a) is arranged closer to the integrated circuit than the second layer (200b), and wherein the first layer (200a) has lower dielectric loss than the second layer (200b).

14. An arrangement according to any previous claim, wherein the interconnects for connecting the integrated circuit, e.g. the RF-input (108) and / or the RF-output (109) of the integrated circuit (100), are interconnects of a flip-chipconnection, such as pillar interconnects, stud bump interconnects and / or solder ball interconnects.

15. A circuit board comprising: an electromagnetic absorbing arrangement according to any claim 1 - 14, wherein the radio frequency (RF) input (108) and the radio frequency (RF) output (109) of the integrated circuit (100) is connected to the circuit board.

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