Radio frequency semiconductor device and method of manufacturing radio frequency semiconductor device

Abstract

The invention relates to a radio frequency semiconductor device and a method of manufacturing a radio frequency semiconductor device. A radio frequency (RF) semiconductor device and a method of manufacturing the RF semiconductor device. The RF semiconductor device includes a semiconductor die including a first surface and a sidewall perpendicular to the first surface. The molding compound encapsulates sidewalls of the semiconductor die, wherein the molding compound extends beyond the sidewalls of the semiconductor die in a first direction perpendicular to the sidewalls of the semiconductor die. The RF semiconductor device further includes an RF absorbing layer arrangement including a first RF absorbing layer and a second RF absorbing layer. The first RF absorbing layer and the second RF absorbing layer extend over the first surface of the semiconductor die in a first direction. The RF absorbing layer arrangement includes a first side facing the semiconductor die.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to radio frequency semiconductor devices and, in particular, to radio frequency semiconductor devices with RF absorbing layers having different dielectric properties. Furthermore, the present disclosure relates to methods of manufacturing such devices. BACKGROUND

[0002] In radio frequency (RF) semiconductor devices, such as radar systems and radar sensors, the elimination of undesired radiation or signals is a key factor for reliable device performance. For example, in the field of advanced driver assistance systems (ADAS), RF semiconductor devices play a vital role and have to be reliable and robust in terms of performance and cost competitive. In order to improve the performance and functionality of RF semiconductor devices, more and more functionalities are packed into RF semiconductor devices in small packages or multi-die RF devices are introduced, which leads to higher interfering RF signal coupling between different RF transmission channels of the RF semiconductor device.

[0003] Molding compounds applied in RF semiconductor device packages typically exhibit low loss properties so that RF signals can propagate without significant attenuation. RF signals encounter reflections inside the RF semiconductor device and can couple RF channels. This can lead to poor performance of the RF semiconductor device or in some cases to a malfunction.

[0004] Accordingly, it is an object of the present application to provide a concept of a RF semiconductor device, wherein the absorption of RF signals is improved. This object is solved by a radio frequency semiconductor device according to claim 1 and a method of manufacturing a radio frequency semiconductor device according to claim 21. SUMMARY

[0005] According to an example of the present disclosure, a radio frequency (RF) semiconductor device for processing RF signals in an operating frequency range is disclosed. The RF semiconductor device comprises a semiconductor die comprising a first surface and a sidewall perpendicular to the first surface. A molding compound encapsulates the sidewall of the semiconductor die, wherein the molding compound extends beyond the sidewall of the semiconductor die in a first direction perpendicular to the sidewall of the semiconductor die. The RF semiconductor device further comprises an RF absorbing layer arrangement comprising a first RF absorbing layer and a second RF absorbing layer. The first RF absorbing layer and the second RF absorbing layer extend over the first surface of the semiconductor die in the first direction. The RF absorbing layer arrangement comprises a first side facing the semiconductor die. The first RF absorbing layer extends on the first side within a first region, the second RF absorbing layer extends on the first side within a second region. The first RF absorbing layer has a first value of a real part of a permittivity, the second RF absorbing layer has a second value of the real part of the permittivity, wherein the first value is different from the second value.

[0006] According to examples of the present disclosure, a method for manufacturing a radio frequency (RF) semiconductor device for handling RF signals in an operating frequency range is disclosed. The method comprises:

[0007] providing a semiconductor die comprising a first surface and a sidewall perpendicular to the first surface;

[0008] encapsulating the sidewall of the semiconductor die with a molding compound, wherein the molding compound extends beyond the sidewall of the semiconductor die in a first direction perpendicular to the sidewall of the semiconductor die,

[0009] placing an RF absorbing layer arrangement, the RF absorbing layer arrangement comprising a first RF absorbing layer and a second RF absorbing layer, the first RF absorbing layer and the second RF absorbing layer extending over the first surface of the semiconductor die in the first direction,

[0010] wherein the RF absorbing layer arrangement comprises a first side facing the semiconductor die, wherein the first RF absorbing layer extends on the first side within a first area and the second RF absorbing layer extends on the first side within a second area, and

[0011] wherein the first RF absorbing layer has a first value of a real part of a permittivity and the second RF absorbing layer has a second value of the real part of the permittivity, wherein the first value is different from the second value. BRIEF DESCRIPTION OF DRAWINGS

[0012] In the drawings, which are not necessarily drawn to scale, the present disclosure is illustrated by way of example and not limitation, in which like reference numbers refer to similar or identical elements. The drawings of the present disclosure are not necessarily to scale. Features of the various illustrated examples can be combined, unless mutually exclusive.

[0013] Figure 1A a schematic cross-sectional view of an RF semiconductor device along the line AA of Figure 1B , wherein an RF absorbing layer arrangement is arranged over the semiconductor die.

[0014] Figure 1B a top view of the RF semiconductor device of Figure 1A , without a molding compound.

[0015] Figure 2 a cross-sectional view of an RF semiconductor device with an RF absorbing layer arrangement and a heat sink, wherein the RF absorbing layer arrangement is arranged over the semiconductor die and the heat sink is arranged over the RF absorbing layer arrangement.

[0016] Figure 3 a schematic cross-sectional view of an RF semiconductor device, wherein a molding compound encapsulates a sidewall of a semiconductor die.

[0017] Figure 4 FIG. 1 illustrates a schematic cross-sectional view of an RF semiconductor die mounted on a substrate.

[0018] Figure 5 FIG. 1 illustrates a schematic cross-sectional view of an RF semiconductor die mounted on a substrate.

[0019] Figure 6 FIG. 1 illustrates a schematic cross-sectional view of an RF semiconductor die mounted on a substrate. DETAILED DESCRIPTION

[0020] Although specific examples are illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and / or equivalent implementations can be substituted for the specific examples shown and described without departing from the scope of the present disclosure. This application is intended to cover any adaptations or variations of the specific implementations discussed herein. Therefore, it is intended that this application be limited only by the claims and the equivalents thereof.

[0021] It is noted that the drawings and specification are only intended to illustrate the best mode of the present method and system. Those of ordinary skill in the art will be able to implement various arrangements that, although not explicitly described or shown herein, embody the principles of the present method and system and are included within its spirit and scope. Furthermore, all examples and embodiment outlined in this document are mainly intended to be illustrative and not limiting, primarily for the purpose of aiding the reader in understanding the principles of the present method and system. Moreover, all statements herein reciting principles, aspects, and embodiments of the present method, as well as specific examples thereof, are intended to encompass their equivalents.

[0022] The embodiments described herein provide a new concept for absorbing RF signals in an RF semiconductor device comprising a semiconductor die. The new concept is based on the finding that improved RF absorption characteristics and better RF channel isolation can be obtained if the properties of the RF absorbing layers provided in the RF semiconductor device are selected and matched to address various coupling and scattering scenarios in the RF semiconductor device. In the RF semiconductor device, the output signal lines of the RF transmission channels are typically positioned around the semiconductor die to deliver the RF signals to ports, transmitters, antennas, etc. In such signal lines, parts of the transmitted RF signals can leak from the respective signal line and these RF signals can scatter back to another signal line inside the RF semiconductor device, thereby enabling a coupling of RF signals between such signal lines. Such a coupling can lead to problems regarding the qualification of the RF semiconductor device under ETSI (European Telecommunications Standards Institute) and FCC (Federal Communications Commission) regulations.

[0023] The concepts presented herein solve the coupling between signal lines by considering the difference in effectiveness of the specific absorption layers and their position depending on the geometrical position of the signal lines (e.g. the distance between the signal lines). For example, for closely located signal lines (e.g. signal lines located along the same side wall of the semiconductor die), the RF signals causing the coupling are scattered inside the RF semiconductor device at small scattering angles. While for signal lines with a larger distance (e.g. signal lines located at different sides of the semiconductor die), the RF signals causing the coupling are scattered inside the RF semiconductor device at large scattering angles. For example, the RF signals are then passed over the semiconductor die such that RF transmission channels located along different side walls of the semiconductor die are coupled. This unwanted coupling of RF transmission channels can introduce noise in the RF semiconductor device during operation.

[0024] To solve this problem, an RF absorption layer arrangement comprising a first RF absorption layer and a second RF absorption layer is arranged over a first surface of the semiconductor die, and both RF absorption layers extend in a first direction transverse to the side walls of the semiconductor die. The RF absorption layers have different real part values of the dielectric constant from each other, which allows to absorb RF signals inside the RF semiconductor device at a wide range of scattering angles, which will be described in more detail below. Thus, an overall improvement of the channel-to-channel isolation in the RF semiconductor device is achieved.

[0025] Figure 1A and Figure 1B A cross-sectional view and a top view of the RF semiconductor device 100 are illustrated, respectively. Figure 1A The cross-sectional view of the RF semiconductor device 100 is taken along Figure 1B the line AA of the RF semiconductor device 100. For simplicity, the molding compound 118 is not shown in Figure 1B

[0026] The semiconductor die 102 operates in a predetermined frequency range, such as a millimeter wave frequency range (e.g. in a frequency range contained in the range from 40 GHz to 500 GHz, or in a frequency range contained in the range from 50 GHz to 250 GHz). In some examples, the semiconductor die 102 can correspond to a radar die and can be used as a transmitter, receiver, sensor, detector, etc. In other examples, the semiconductor die 102 can be a 5G or 6G communication die, a high data transfer communication system, a wireless backhaul system for secure body scanning systems.

[0027] As Figure 1A ​As shown, the semiconductor die 102 has a first surface 104, a second surface 106 opposite the first surface 104, and a sidewall 108 connecting the surfaces 104, 106 of the semiconductor die 102. The first surface 104 and the second surface 106 can be referred to as a first main surface and a second main surface. An active die area with transistors and other circuit elements is provided in the semiconductor die 102. The active die area is capable of generating RF signals, processing RF signals, and analyzing RF signals and other signals.

[0028] The second surface 106 of the semiconductor die 102 is arranged on a top side 114 of the redistribution layer 110, and an electrical contact is established between the semiconductor die 102 and the conductive structures of the redistribution layer 110. For example, the electrical contact can be formed by a pad made of aluminum and / or copper. This allows for the transmission of RF signals from the semiconductor die 102 to the electrical contact and / or vice versa.

[0029] The redistribution layer 110 can comprise one or more lamination layers, and can have one or more conductive structures in the form of metal lines or metal planes extending parallel to the first surface 104 of the semiconductor die 102. The conductive structures route electrical signals in the RF semiconductor device 100. The conductive structures can be made of aluminum, copper, or a copper alloy. In some examples, the conductive structures can be electrically isolated from each other by a dielectric material. The dielectric material in the redistribution layer can for example comprise an organic material, such as a polymer material.

[0030] The redistribution layer 110 has a bottom side 112 opposite the top side 114. A plurality of solder balls 116 is arranged on the bottom side 112 of the redistribution layer 110. Accordingly, the redistribution layer 110 establishes an electrical connection between the solder balls 116 and the semiconductor die 102. A printed circuit board (PCB) (not shown in Fig. 1) can be electrically and mechanically fixed to the solder balls 116. According to one example, the solder balls 116 can comprise at least one of Sn, Ag, or Cu. The solder balls 116 can have a diameter in the range between 200 pm and 400 pm and a pitch in the range between 400 pm and 600 pm. In some examples, a flip-chip BGA (ball grid array) or a wire-bonding-BGA can be used to establish the electrical and mechanical connection to the PCB.

[0031] The redistribution layer 110 can extend beyond the second surface 106 of the semiconductor die 102 in a first direction, wherein the first direction is perpendicular to the sidewall 108 of the semiconductor die 102. In other words, the redistribution layer 110 extends beyond the semiconductor die 102 in a lateral direction. The portion of the redistribution layer 110 extending beyond the second surface 106 of the semiconductor die 102 forms a fan-out area. The fan-out area has signal lines of RF transmission channels configured to transmit and receive RF signals in the RF semiconductor device.

[0032] Semiconductor die 102 is partially encapsulated by molding compound 118. Specifically, the first surface 104 and sidewall 108 of semiconductor die 102 are encapsulated by molding compound 118, while the second surface 106 of semiconductor die 102 is exposed from molding compound 118. Molding compound 118 further extends beyond the sidewall 108 of semiconductor die 102 in a first direction and contacts a fan-out region of redistribution layer 110. A portion of redistribution layer 110 facing the second surface 106 of semiconductor die 102 is exposed from molding compound 118. A first side 124 of molding compound 118 faces the first surface 104 of semiconductor die 102.

[0033] Figure 1B The top view of the RF semiconductor device 100 shown is a view taken from the outside of the RF semiconductor device 100 and in a direction orthogonal (vertical) to the first surface 104 of the semiconductor die 102. As described herein, RF signals leaking from signal lines may scatter inside the RF semiconductor device 100, leading to coupling of the RF transmission channel 132. RF signal scattering can occur, for example, as... Figure 1A The first side 124 of the molded compound 118 or the first surface 104 of the semiconductor die 102 is shown. RF transmission channels 132 located along different sidewalls 108 of the semiconductor die 102 can be coupled by RF signals scattered at an angle (θ) greater than a first value of the scattering angle, and RF transmission channels 132 located along the same sidewall 108 of the semiconductor die 102 can be coupled by RF signals scattered at another angle (φ) having a value less than the first value of the scattering angle. According to one example, the first value of the scattering angle can be in the range of 30°-50°.

[0034] In order to absorb RF signals at various angles (θ, φ), such as Figure 1A and 1BAs shown, an RF absorption layer arrangement is disposed above a first surface 104 of a semiconductor die 102, comprising a first RF absorption layer 120 and a second RF absorption layer 122. The first RF absorption layer 120 and the second RF absorption layer 122 form the RF absorption layer arrangement. The first RF absorption layer 120 has a first value of the real part of the dielectric constant (this real part is sometimes also referred to as the real part of the relative dielectric constant or the real part of Dk), while the second RF absorption layer 122 has a second value of the real part of the dielectric constant, wherein the first value of the real part of the dielectric constant is different from the second value of the real part of the dielectric constant. In one example, the first value of the real part of the dielectric constant is greater than the second value of the real part of the dielectric constant. For example, the first value of the real part of the dielectric constant may be greater than or equal to 11, and the second value of the real part of the dielectric constant may be less than 11. The first RF absorption layer 120 is provided for absorbing RF signals scattered at an angle (θ) (i.e., above a first scattering angle value), while the second RF absorption layer is provided for absorbing RF signals scattered at an angle (φ) (i.e., below the first scattering angle value).

[0035] like Figures 1A-1B As shown, the RF absorption layer arrangement has an inner side 121 facing the semiconductor die 102. A first RF absorption layer 120 extends on the inner side 121 only within a first region 128, and a second RF absorption layer 122 extends on the inner side 121 outside the first region 128. The region outside the first region 128 may be referred to as the second region 130. The first region 128 and the second region 130 extend in a first direction (lateral direction).

[0036] The inner side 121 is coplanar, meaning that the inner side 121 is aligned with a plane 126 parallel to the first direction. In some examples, the inner side 121 may not be coplanar, meaning that different portions of the inner side 121 may be aligned with different planes parallel to each other.

[0037] The first region 128, including the first RF absorbing layer 120, can overlap the first surface 104 of the semiconductor die 102. The first region 128 can fully overlap the first surface 104 of the semiconductor die 102, in which case the overlap region between the first region 128 and the first surface 104 of the semiconductor die 102 is the same as the first region 128. In some examples, the first region 128 can partially overlap the first surface 104, in which case the overlap region is smaller than the first region 128. Further, the second region 130, including the second RF absorbing layer 122, can fully or partially overlap the fan-out region of the redistribution layer 110. In some examples, the first region 128 can be larger than the first surface 104 of the semiconductor die 102. In other examples, the first region 128 can be smaller than the first surface 104 of the semiconductor die 102. The first region 128 covers where the RF signals are scattered above the first scattering angle value, while the second region 130 covers where the RF signals are scattered below the first scattering angle value.

[0038] As shown in FIG. 1, the first RF absorbing layer 120 is arranged in a continuous manner within the first region 128, such that the first RF absorbing layer 120 is confined within the first region 128. The second RF absorbing layer 122 is arranged in a continuous manner within the second region 130, such that the second RF absorbing layer 122 is confined within the second region 130 only. In other words, the second RF absorbing layer 130 is completely excluded from the first region 128. Figure 1A Figure 1B As shown in FIG. 1, the first RF absorbing layer 120 is arranged in a continuous manner within the first region 128, such that the first RF absorbing layer 120 is confined within the first region 128. The second RF absorbing layer 122 is arranged in a continuous manner within the second region 130, such that the second RF absorbing layer 122 is confined within the second region 130 only. In other words, the second RF absorbing layer 130 is completely excluded from the first region 128.

[0039] In some examples, the first region 128 can be larger than the first surface 104 of the semiconductor die 102. In other examples, the first region 128 can be smaller than the first surface 104 of the semiconductor die 102. The first region 128 covers where the RF signals are scattered above the first scattering angle value, while the second region 130 covers where the RF signals are scattered below the first scattering angle value. Figure 1A In some examples, the first region 128 can be larger than the first surface 104 of the semiconductor die 102. In other examples, the first region 128 can be smaller than the first surface 104 of the semiconductor die 102. The first region 128 covers where the RF signals are scattered above the first scattering angle value, while the second region 130 covers where the RF signals are scattered below the first scattering angle value.

[0040] ​The first RF absorption layer 120 may have a first height, measured between its bottom surface 120b and its opposite top surface 120t, in a direction perpendicular to the first direction. Similarly, the second RF absorption layer 122 may have a second height, measured between its bottom surface 122b and its opposite top surface 122t, in a direction perpendicular to the first direction. The first height may be the same as or different from the second height. In other words, the thickness of the first RF absorption layer 120 may be the same as or different from the thickness of the second RF absorption layer 122. In one example, the first RF absorption layer 120 and the second RF absorption layer 122 may have thicknesses ranging from 50 μm to 2 mm, 100 μm to 1 mm, or 100 μm to 2 mm.

[0041] The first RF absorbing layer 120 and the second RF absorbing layer 122 may include an RF absorbing material, which includes at least one of an elastomer, rubber, silicone resin, and polyurethane. In some embodiments, specific absorbing particles (e.g., AlOx, SiOx, Si, SiC, TiOx, FeOx, FeZn, ZnOx, MnOx, where x is 1 or 2) may be incorporated into the first RF absorbing layer 120 and the second RF absorbing layer 122. Different materials may be used for the first RF absorbing layer 120 and the second RF absorbing layer 122, or absorbing particles of different densities may be used to obtain different dielectric constant values.

[0042] In some examples, the first RF absorption layer 120 has a loss tangent greater than 0.2, while the second RF absorption layer 122 may have the same or different loss tangent than the first RF absorption layer 120. The loss tangents of the first RF absorption layer 120 and the second RF absorption layer 122 within the above range are suitable for the dissipation of the RF signal absorbed in the respective RF absorption layers 120, 122.

[0043] like Figure 1B As shown, the fan-out region or signal line of the RF transmission channel is positioned along the sidewall 108 of the semiconductor die 102, so that the first region 128 is aligned with the first surface 104 of the semiconductor die 102. Accordingly, the first RF absorption layer 120 completely overlaps with the first surface 104 of the semiconductor die 102. The first RF absorption layer 120 absorbs RF signals scattered at an angle (θ) higher than the first scattering angle value, and thus improves channel-to-channel isolation between RF transmission channels positioned along different sidewalls 108 of the semiconductor die 102. Similarly, the second RF absorption layer 120 absorbs RF signals scattered at an angle (φ) lower than the first scattering angle value, and improves channel-to-channel isolation between RF transmission channels positioned along the same sidewall 108 of the semiconductor die 102.

[0044] The molding compound 118 can have a Dk value in the range of 3 to 5, which is also lower than the second value of Dk of the second RF absorbing layer 122. By having the Dk of the molding compound and the Dk of the second RF absorbing layer in the same range, scattering of RF signals at the interface between the molding compound 118 and the second RF absorbing layer 122 can be almost negligible, and the RF signals are transmitted to the second absorbing layer 122 even for small scattering angles. Thus, the channel-to-channel isolation of the RF transmission channels positioned along the same sidewall 108 of the semiconductor die 102 is further improved.

[0045] It should be noted that the RF absorbing layers 120, 122 can form part of a semiconductor package comprising the semiconductor device 100. Alternatively, the RF absorbing layers 120, 122 can be arranged outside the semiconductor package comprising the semiconductor device 100, e.g., as a layer on the molding compound 118.

[0046] For dissipating heat from the RF semiconductor device, a heat sink in the form of a metal can be fixed to the RF semiconductor device. Without the RF absorbing layers 120 and 122, RF signals emitted from the RF semiconductor device can be transferred to the heat sink, and the heat sink can provide a perfect scatterer, thereby increasing the coupling between the signal lines.

[0047] Figure 2 A cross-sectional view of the RF semiconductor device 200 is shown, wherein the RF semiconductor device 200 comprises a semiconductor die 100 with a heat sink 202. Figure 1A The heat sink 202 is arranged above the top surfaces 120t, 122t of the RF absorbing layers 120, 122. Due to the RF absorbing layers 120, 122, the RF signal transfer between the semiconductor device 100 and the heat sink 202 can be significantly reduced. Additionally, both RF absorbing layers 120, 122 can have a thermal conductivity higher than 0.5 W / mK or 1.0 W / mK or 1.5 W / mK, which makes the RF absorbing layers 120, 122 further suitable for transferring heat from the RF semiconductor device 100 to the heat sink 202. For no or reduced scattering from the heat sink 202, the loss tangent of the RF absorbing layers 120, 122 can be higher (e.g., greater than equal to 0.2). By arranging the RF absorbing layers 120, 122 between the RF semiconductor device 100 and the heat sink 202, the transfer of RF signals scattered at the heat sink 202 back to the RF semiconductor device can be reduced, and the RF absorbing layers 120, 122 can further increase the heat dissipation of the RF semiconductor device 200 during operation.

[0048] Figure 3A cross-sectional view of an RF semiconductor device 300 according to another example is shown. The RF semiconductor device 300 can include some or all of the features of the RF semiconductor devices 100, 200, and 300 of examples 1, 2, and 3. Figure 2 For simplicity, the heat spreader is omitted. The new concept can be extended to the RF semiconductor device 300, where both the first surface 104 and the second surface 106 of the semiconductor die 102 are exposed from the molding compound 118. In other words, the molding compound 118 only encapsulates the sidewall 108 of the semiconductor die 102. The first RF absorbing layer 120 is arranged on the first surface 104 of the semiconductor die 102. In other examples, the first RF absorbing layer 120 can extend in the first direction to a portion of the first side 124 of the molding compound. The second RF absorbing layer 122 is arranged on the first side 124 of the molding compound 118.

[0049] Figure 4 An example of an RF semiconductor device 400 is shown, which can include some or all of the features of any of the RF semiconductor devices 100, 200, and 300 of examples 1, 2, and 3. Figure 1A , 1B

[0050] In the RF semiconductor device 400, the second surface 106 of the semiconductor die 102 is fixed on the solder balls 116 instead of a redistribution layer. The solder balls 116 are constrained within the second surface 106 of the semiconductor die 102 and are soldered to the top 402t of a substrate 402, e.g., an interposer integrated in the package of the semiconductor device 400. The substrate 402 includes routing structures 404 facing the second surface 106 of the semiconductor die 102. Additional solder balls 406 are arranged on the bottom 402b of the substrate 402. An underfill material 408 is arranged between the top 402t of the substrate 402 and the semiconductor die 102. In particular, the underfill material 408 completely covers each of the solder balls 116 and partially covers the sidewall 108 of the semiconductor die 102 and portions of the substrate 402. The molding compound 118 encapsulates portions of the substrate 402 and the periphery of the underfill material 408. The underfill material 408 can be a material such as a thermoset epoxy that reduces thermal stress that occurs due to a mismatch in the coefficient of thermal expansion between the substrate 402 and the semiconductor die 102.

[0051] RF signals from the semiconductor die 102 are routed between the solder balls 116 and the solder balls 406 via the routing structures 404 of the substrate 402. Signal lines of the RF transmission channels are formed on the substrate 402, which can be positioned away from the semiconductor die 102. To address this issue, the first RF absorbing layer 120 can extend beyond the first surface 104 of the semiconductor die 102 in the lateral direction and further overlap the signal lines of the RF transmission channels of the substrate 402. ​

[0052] To determine the proper selection of materials and Dk values for the first absorbing layer 120 and the second RF absorbing layer 122, measurements have been performed for various Dk values. Figure 5 Channel-to-channel isolation measurements performed with the RF semiconductor device 200 of Figure 2 Fig. 3. In the measurements, the solder balls 116 of the RF semiconductor device 200 are electrically and mechanically coupled with the printed circuit board. Instead of the first RF absorbing layer 120 and the second RF absorbing layer 122, an RF absorbing layer is arranged between the first side 124 of the molding compound 118 and the heat sink 202. Channel-to-channel isolation measurements are performed for two different configurations of RF transmission channels (referred to as configuration 1 and configuration 2) as a function of the Dk of the RF absorbing layer at a frequency of 77 GHz. The differences between configuration 1 and configuration 2 are explained below.

[0053] In Fig. 3, the y-axis (ordinate) shows the isolation values in dB for the respective configuration, which are normalized with respect to a corresponding measurement on another RF semiconductor device without the RF absorbing layer. The x-axis (abscissa) shows the Dk values of the RF absorbing layer extracted from the bulk material characterization. Figure 5

[0054] Figure 5 The circles in Fig. 3 correspond to the channel-to-channel isolation measurements of configuration 1, and the straight line is the corresponding fit. Configuration 1 comprises a pair of RF transmission channels, wherein one of the RF transmission channels of the pair of RF transmission channels is positioned along an adjacent or opposite side wall of the semiconductor die 102 with respect to the other RF transmission channel of the pair of RF transmission channels. For example, one of the RF transmission channels of the pair of RF transmission channels can be a transmit channel, while the other RF transmission channel of the pair of RF transmission channels can be a receive channel.

[0055] When the RF transmission channels in configuration 1 are positioned along different side walls 108 of the semiconductor die 102, the scattering angle between the RF transmission channels of configuration 1 is higher than the first scattering angle value (i.e. greater than or equal to 50°). With increasing Dk values of the RF absorbing layer, the channel-to-channel isolation between the RF transmission channels of configuration 1 improves and also shows that it does not depend on the loss tangent value of the RF absorbing layer as long as the loss tangent of the RF absorbing layer is greater than 0.2.

[0056] Figure 5 The crosses (+) in Fig. 3 show the channel-to-channel isolation measurements performed on configuration 2, which separately comprises a pair of transmit channels or a pair of receive channels. The dashed line is the corresponding fit. The two transmit / receive channels in configuration 2 are positioned along the same side wall of the semiconductor die 102.

[0057] ​It can be seen that the channel-to-channel isolation values of the RF transmission channels of configuration 2 differ significantly compared to configuration 1, which is due to the shorter distance between the signal lines of each pair of RF transmission channels in the respective configuration. Since the signal lines of the RF transmission channels in configuration 2 are positioned along the same sidewall of the semiconductor die 102, the scattering angle between the RF transmission channels of configuration 2 is lower than the first scattering angle value (i.e. less than 50°). In this case, the loss tangent of the RF absorbing layer is also crucial for the absorption of the RF signals. For the RF transmission channels of configuration 2, below a Dk = 8 of the RF absorbing layer, the poor isolation between the RF transmission channels of configuration 2 is due to the small value of the loss tangent (about 0.2). As the Dk of the RF absorbing layer increases, the loss tangent of the RF absorbing layer also increases, which improves the channel-to-channel isolation between the RF transmission channels of configuration 2.

[0058] It should be noted that the channel-to-channel isolation of the RF transmission channels of configuration 2 improves up to a Dk = 11, and when the Dk of the RF absorbing layer is further increased, the channel-to-channel isolation becomes worse even though the loss tangent increases. This is because a DK of the RF absorbing layer below 11 is suitable for RF signals scattered below the first scattering angle value, and when the DK of the RF absorbing layer is increased above 11, the RF signals are scattered back into the RF semiconductor device.

[0059] Figure 6 A method for manufacturing a radio frequency (RF) semiconductor device to handle RF signals in a range of operating frequencies is shown. In a step 602, a semiconductor die is provided that includes a first surface and a sidewall perpendicular to the first surface. In another step 604, the sidewall of the semiconductor die is encapsulated with a molding compound, wherein the molding compound extends beyond the sidewall of the semiconductor die in a first direction perpendicular to the sidewall of the semiconductor die. In another step 606, an RF absorbing layer arrangement is placed over the first surface of the semiconductor die. The RF absorbing layer arrangement has a first RF absorbing layer, a second RF absorbing layer, and an inner side. The first RF absorbing layer and the second RF absorbing layer extend over the first surface of the semiconductor die in the first direction. The inner side faces the first surface of the semiconductor die. The first RF absorbing layer extends within a first region on the first side, and the second RF absorbing layer extends within a second region on the first side. The first RF absorbing layer has a first value of a real part of a permittivity, and the second RF absorbing layer has a second value of the real part of the permittivity, wherein the first value is different from the second value.

[0060] In step 606, the first RF absorbing layer and the second RF absorbing layer can be arranged within the first region and the second region, respectively, by, for example, jetting, jet printing, laser cutting, or a combination thereof.

[0061] In step 606, a second RF absorbing layer is arranged in the second area in a top view, and the first area remains empty. In another step, this first RF absorbing layer is arranged in the first area.

[0062] Alternatively, in step 606, a second RF absorbing layer can be arranged in the first area and the second area, and then the second RF absorbing layer in the first area is removed, e.g. by laser. The first RF absorbing layer is arranged in the first area.

[0063] In some examples, step 606 can form part of the manufacturing of a semiconductor package comprising a semiconductor device. Alternatively, the RF absorbing layers can be manufactured beforehand and then arranged outside of a semiconductor package comprising a semiconductor device.

[0064] This new concept provides an effective and cost-efficient RF signal absorbing arrangement in RF semiconductor devices. As described herein, a first RF absorbing layer overlaps the semiconductor die, and a second RF absorbing layer with a smaller Dk than the first RF absorbing layer is arranged outside of the first RF absorbing layer. This arrangement of RF absorbing layers increases the absorption of RF signals with various scattering angles and thus improves the channel-to-channel isolation of the RF transmission channels of the RF semiconductor device. Furthermore, a heat sink can be attached above the RF absorbing layers using standard thermal interface materials for cooling purposes. The value of the real part of the permittivity can be fine-tuned according to the operating frequency of the RF semiconductor device. The RF absorbing layers absorb and dissipate RF signals generated within the RF semiconductor device and from external sources, which can improve the performance of the RF semiconductor device and can reduce damage to the semiconductor die.

[0065] The following examples relate to other aspects of the present disclosure:

[0066] Example 1 discloses a radio frequency (RF) semiconductor device for handling RF signals in an operating frequency range, comprising:

[0067] a semiconductor die comprising a first surface and a sidewall perpendicular to the first surface,

[0068] a molding compound encapsulating the sidewall of the semiconductor die, wherein the molding compound extends beyond the sidewall of the semiconductor die in a first direction perpendicular to the sidewall of the semiconductor die,

[0069] an RF absorbing arrangement comprising a first RF absorbing layer and a second RF absorbing layer, the first RF absorbing layer and the second RF absorbing layer extending above the first surface of the semiconductor die in the first direction,

[0070] wherein the RF-absorbing layer arrangement comprises a first side facing the semiconductor die, wherein the first RF-absorbing layer extends on the first side within the first area, and the second RF-absorbing layer extends on the first side within the second area, and

[0071] wherein the first RF-absorbing layer has a first value of a real part of a permittivity, and the second RF-absorbing layer has a second value of the real part of the permittivity, wherein the first value is different from the second value.

[0072] Example 2 discloses the semiconductor device according to Example 1, wherein the first value of the real part of the permittivity is greater than the second value of the real part of the permittivity.

[0073] Example 3 discloses the semiconductor device according to Example 2, wherein the first value of the real part of the permittivity is greater than or equal to 11, and wherein the second value of the real part of the permittivity is less than 11.

[0074] Example 4 discloses the RF semiconductor device according to Example 3, wherein in a top view, the first area overlaps the first surface of the semiconductor die.

[0075] Example 5 discloses the RF semiconductor device according to Example 4, wherein in a top view, the first area is entirely within the first surface of the semiconductor die.

[0076] Example 6 discloses the RF semiconductor device according to any of the preceding examples, wherein in a top view, the second RF-absorbing layer is entirely outside the first area.

[0077] Example 7 discloses the RF semiconductor device according to any of the preceding examples, wherein the first RF-absorbing layer and the second RF-absorbing layer are adjacent to each other in a top view.

[0078] Example 8 discloses the RF semiconductor device according to any of the preceding examples, wherein the first RF-absorbing layer and the second RF-absorbing layer form a continuous layer over the first surface of the semiconductor die.

[0079] Example 9 discloses the semiconductor device according to any of the preceding examples, wherein the molding compound further encapsulates the first surface of the semiconductor die, wherein a first side of the molding compound faces the first surface of the semiconductor die, wherein the first RF-absorbing layer is arranged over the first side of the molding compound, and wherein the second RF-absorbing layer is arranged over the first side of the molding compound.

[0080] Example 10 discloses the semiconductor device according to any of the preceding examples, wherein the first RF-absorbing layer has a height in a same range as a height of the second RF-absorbing layer, wherein the height of each RF-absorbing layer is measured in a direction perpendicular to the first direction between a bottom surface and an opposite top surface of the respective RF-absorbing layer, and wherein the bottom surface of each RF-absorbing layer faces the first surface of the semiconductor die.

[0081] Example 11 discloses the RF semiconductor device of any of the preceding examples, wherein the first RF absorbing layer and the second RF absorbing layer form part of an exterior of a semiconductor package of the semiconductor device.

[0082] Example 12 discloses the RF semiconductor device of any of the preceding examples, wherein the molding compound has a real part of a dielectric constant in a range of 3-5.

[0083] Example 13 discloses the RF semiconductor device of any of the preceding examples, wherein the first RF absorbing layer has a loss tangent greater than 0.2.

[0084] Example 14 discloses the RF semiconductor device of Example 13, wherein the second RF absorbing layer has a loss tangent less than 0.2.

[0085] Example 15 discloses the RF semiconductor device of Example 13, wherein the second RF absorbing layer has a loss tangent greater than or equal to 0.2.

[0086] Example 16 discloses the RF semiconductor device of any of the preceding examples, wherein a heat spreader is disposed above the first RF absorbing layer and the second RF absorbing layer.

[0087] Example 17 discloses the RF semiconductor device of any of the preceding examples, wherein the first RF absorbing layer and the second RF absorbing layer comprise at least one of a filler material (e.g., AIOx, SiOx, Si, SiC, TiOx, FeOx, FeZn, ZnOx, MnOx, where x is 1 or 2.

[0088] Example 18 discloses the RF semiconductor device of any of the preceding examples, wherein the RF semiconductor device comprises a redistribution layer facing a second surface of the semiconductor die opposite the first surface,

[0089] wherein a portion of the redistribution layer extends beyond the second surface of the semiconductor die in the first direction, and

[0090] wherein the second RF absorbing layer at least partially faces the portion of the redistribution layer that extends beyond the second surface of the semiconductor die.

[0091] Example 19 discloses the RF semiconductor device of Example 18, wherein the portion of the redistribution layer that extends beyond the second surface of the semiconductor die comprises an RF transmission channel.

[0092] Example 20 discloses the RF semiconductor device of any of the preceding examples, wherein the first RF absorbing layer has a thermal conductivity higher than 0.5 W / mK and the second RF absorbing layer has a thermal conductivity higher than 0.5 W / mK.

[0093] Example 21 discloses a method for manufacturing a radio frequency (RF) semiconductor device for handling RF signals in an operational frequency range, the method comprising:

[0094] providing a semiconductor die, the semiconductor die comprising a first surface and a sidewall perpendicular to the first surface;

[0095] encapsulating the sidewall of the semiconductor die with a molding compound, wherein the molding compound extends beyond the sidewall of the semiconductor die in a first direction perpendicular to the sidewall of the semiconductor die,

[0096] placing an RF absorbing layer arrangement comprising a first RF absorbing layer and a second RF absorbing layer, the first RF absorbing layer and the second RF absorbing layer extending in the first direction over the first surface of the semiconductor die,

[0097] wherein the RF absorbing layer arrangement comprises a first side facing the semiconductor die, wherein the first RF absorbing layer extends on the first side within a first area and the second RF absorbing layer extends on the first side within a second area, and

[0098] wherein the first RF absorbing layer has a first value of a real part of a permittivity and the second RF absorbing layer has a second value of the real part of the permittivity, wherein the first value is different from the second value.

Claims

1. An RF semiconductor device (100, 200, 300, 400) for processing radio frequency (RF) signals within an operating frequency range, comprising: The semiconductor die (102) includes a first surface (104) and a sidewall (108) perpendicular to the first surface (104); A molding compound (118) encapsulates the sidewall (108) of the semiconductor die (102), wherein the molding compound (118) extends beyond the sidewall (108) of the semiconductor die (102) in a first direction perpendicular to the sidewall (108). The RF absorption layer arrangement includes a first RF absorption layer (120) and a second RF absorption layer (122), the first RF absorption layer (120) and the second RF absorption layer (122) extending over the first surface (104) of the semiconductor die (102) in the first direction. The RF absorption layer arrangement includes a first side (121) facing the semiconductor die (102), wherein a first RF absorption layer (120) extends on the first side within a first region (128), and a second RF absorption layer (122) extends on the first side within a second region (130). The first RF absorption layer (120) has a first value of the real part of the dielectric constant, and the second RF absorption layer (122) has a second value of the real part of the dielectric constant, wherein the first value is different from the second value.

2. The semiconductor device (100, 200, 300, 400) according to claim 1, wherein the first value of the real part of the dielectric constant is greater than the second value of the real part of the dielectric constant.

3. The semiconductor device (100, 200, 300, 400) according to claim 2, wherein the first value of the real part of the dielectric constant is greater than or equal to 11, and wherein the second value of the real part of the dielectric constant is less than 11.

4. The RF semiconductor device (100, 200, 300, 400) according to claim 3, wherein, in the top view, the first region (128) overlaps with the first surface (104) of the semiconductor die (102).

5. The RF semiconductor device (100, 200, 300) according to claim 4, wherein, in the top view, the first region (128) is entirely within the first surface (104) of the semiconductor die (102).

6. The RF semiconductor device (100, 200, 300, 400) according to any of the preceding claims, wherein, in the top view, the second RF absorption layer (122) is completely outside the first region (128).

7. The RF semiconductor device (100, 200, 300, 400) according to any of the preceding claims, wherein the first RF absorption layer (120) and the second RF absorption layer (122) are adjacent to each other in a top view.

8. The RF semiconductor device (100, 200, 300, 400) according to any of the preceding claims, wherein the first RF absorption layer (120) and the second RF absorption layer (122) are formed as a continuous layer over the first surface (104) of the semiconductor die (102).

9. The semiconductor device (100, 200, 400) according to any of the preceding claims, wherein the molding compound (118) further encapsulates the first surface (104) of the semiconductor die (102), wherein a first side (126) of the molding compound (118) faces the first surface (104) of the semiconductor die (102), wherein a first RF absorption layer (120) is disposed above the first side (126) of the molding compound (118), and wherein a second RF absorption layer (122) is disposed above the first side (126) of the molding compound (118).

10. The semiconductor device (100, 200, 300, 400) according to any of the preceding claims, wherein the first RF absorption layer (120) has a height within the same range as the height of the second RF absorption layer (122), wherein the height of each RF absorption layer (120, 122) is measured in a direction perpendicular to the first direction between the bottom surface (120b, 122b) of the respective RF absorption layer (120, 122) and the opposite top surface (120t, 122t), and wherein the bottom surface (120b, 122b) of each RF absorption layer (120, 122) faces the first surface (104) of the semiconductor die (102).

11. The RF semiconductor device (100, 200, 300, 400) according to any of the preceding claims, wherein the first RF absorption layer (120) and the second RF absorption layer (122) form an external portion of the semiconductor package of the semiconductor device (100, 200, 300, 400).

12. The RF semiconductor device (100, 200, 300, 400) according to any one of the preceding claims, wherein the molding compound (118) has the real part of the dielectric constant in the range of 3-5.

13. The RF semiconductor device (100, 200, 300, 400) according to any one of the preceding claims, wherein the first RF absorption layer (120) has a loss tangent greater than 0.

2.

14. The RF semiconductor device (100, 200, 300, 400) according to claim 13, wherein the second RF absorption layer (122) has a loss tangent of less than 0.

2.

15. The RF semiconductor device (100, 200, 300, 400) according to claim 13, wherein the second RF absorption layer (122) has a loss tangent greater than or equal to 0.

2.

16. The RF semiconductor device (200) according to any of the preceding claims, wherein a heat sink (202) is disposed over the first RF absorption layer (120) and the second RF absorption layer (122).

17. The RF semiconductor device (100, 200, 300, 400) according to any one of the preceding claims, wherein the first RF absorption layer (120) and the second RF absorption layer (122) comprise at least one of the following filling materials: AlOx, SiOx, Si, SiC, TiOx, FeOx, FeZn, ZnOx, MnOx, wherein x is either 1 or 2.

18. The RF semiconductor device (100, 200, 300, 400) according to any of the preceding claims, wherein the RF semiconductor device includes a redistribution layer (110, 404) facing a second surface (106) of the semiconductor die (102), the second surface being opposite to the first surface (104). A portion of the redistribution layer (110, 404) extends beyond the second surface (106) of the semiconductor die (102) in the first direction, and The second RF absorption layer (122) is at least partially facing the redistribution layer (110, 404) extending beyond the second surface (106) of the semiconductor die (102).

19. The RF semiconductor device (100, 200, 300, 400) according to claim 18, wherein the redistribution layer (110, 410) extending beyond the portion of the second surface (106) of the semiconductor die (102) includes an RF transmission channel (132).

20. The RF semiconductor device (100, 200, 300, 400) according to any of the preceding claims, wherein the first RF absorption layer (120) has a thermal conductivity greater than 0.5 W / mK, and the second RF absorption layer (122) has a thermal conductivity greater than 0.5 W / mK.

21. A method for manufacturing a radio frequency (RF) semiconductor device (100, 200, 300, 400) to process RF signals within an operating frequency range, comprising: A semiconductor die (102) is provided, the semiconductor die (102) including a first surface (104) and a sidewall (108) perpendicular to the first surface (104); The sidewall (108) of the semiconductor die (102) is encapsulated with a molding compound (118), wherein the molding compound (118) extends beyond the sidewall (108) of the semiconductor die (102) in a first direction perpendicular to the sidewall (108). An RF absorption layer arrangement is provided, the RF absorption layer arrangement including a first RF absorption layer (120) and a second RF absorption layer (122), the first RF absorption layer (120) and the second RF absorption layer (122) extending over the first surface (104) of the semiconductor die (102) in the first direction. The RF absorption layer arrangement includes a first side (121) facing the semiconductor die (102), wherein a first RF absorption layer (120) extends on the first side within a first region (128), and a second RF absorption layer (122) extends on the first side within a second region (130). The first RF absorption layer (120) has a first value of the real part of the dielectric constant, and the second RF absorption layer (122) has a second value of the real part of the dielectric constant, wherein the first value is different from the second value.

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