ULTRASOUND DEVICE AND METHOD FOR FORMING AN ULTRASOUND DEVICE, ULTRASOUND ARRANGEMENTS AND METHOD FOR FORMING ULTRASOUND ARRANGEMENTS

Abstract

Ultrasound device (100, 200, 300), comprising: at least one micromechanical ultrasound transducer, MUT (111, ..., 118); and a processing circuit (120) electrically coupled to the at least one MUT (111, ..., 118), wherein the at least one MUT (111, ..., 118) and the processing circuit (120) are packaged in an embedded wafer-level ball grid array (eWLB) enclosure (130), wherein an acoustic coupling medium (140) is formed for acoustically coupling the at least one MUT (111, ..., 118) to an external application surface on the at least one MUT (111, ..., 118), and wherein the at least one MUT (111, ..., 118) is embedded in a molding compound (131) of the eWLB enclosure (130), wherein one or more redistribution layers (132, 133) on the molding compound (131) are provided for electrically coupling the processing circuit (120) with at least one MUT (111, ..., 118) are formed and wherein a recess (136) is provided in one or more redistribution layers (132, 133) for the acoustic coupling medium (140).

Description

The present disclosure relates to structures using ultrasonic micromechanical transducers (MUTs). More particularly, examples of the present disclosure relate to ultrasound devices and a method of forming the same, as well as ultrasound assemblies and methods of forming the same.BackgroundMUTs are miniaturized sensor structures whose electrostatic operating principle enables the transmission and detection of ultrasonic waves. As with other ultrasonic sensors, it is desired that MUTs have a void-free interface to application surfaces, such as customer surfaces.Therefore, there may be a need for MUT-based structures that allow a void-free interface to application surfaces to be provided.US 2016 / 0 038 974 A1 describes an ultrasound system comprising an ultrasound transducer arrangement and a component with electronics embedded in a material, wherein at least one redistribution layer is electrically coupled to the embedded electronics, wherein the at least one redistribution layer electrically couples the ultrasound transducer arrangement and the electronics.DE 10 2020 211 538 A1 discloses a micromechanical component for a sound transducer device comprising a substrate, a oscillatable diaphragm, a piezoelectric element and an electrical contact connection. The piezoelectric element is disposed between the diaphragm and the substrate and connected to the diaphragm. The piezoelectric element is designed to generate and / or detect oscillations of the diaphragm in the ultrasonic range. The micromechanical component can be connected to a drive circuit using flip-chip technology in such a way that the piezoelectric element can be electrically connected to the drive circuit via the electrical contact connection.US 2015 / 0 266 058 A1 relates to an ultrasonic device unit comprising a substrate having a planar part and a recessed part, an ultrasonic device having a plurality of thin-film ultrasonic transducer elements and being arranged in the recessed part, a first flexible printed circuit board, one end of which is connected to the ultrasonic device and the other end of which is connected to the planar part. The array surface of the ultrasonic device on which the one end of the first flexible circuit board is located is disposed within a plane including the planar part or a plane outside the recessed part.SummaryThis need is met by the subject matter of the independent claims. Advantageous embodiments are treated by the dependent claims.In accordance with a first aspect, the present disclosure provides an ultrasonic device. The ultrasound device includes at least one MUT and processing circuitry electrically coupled to the at least one MUT. The at least one MUT and processing circuitry are packaged in an embedded wafer level ball grid array (eWLB) package. An acoustic coupling medium for acoustically coupling the at least one MUT to an external application surface is formed on the at least one MUT.In a second aspect, the present disclosure provides an ultrasonic assembly. The ultrasound assembly includes a printed circuit board (PCB) and an ultrasound device according to the first aspect. The ultrasound device is attached to the PCB. The acoustic coupling medium protrudes through a recess formed in the PCB.According to a third aspect, the present disclosure provides a method of forming an ultrasonic device. The method includes providing an eWLB package. At least one MUT and processing circuitry electrically coupled to the at least one MUT are packaged in the eWLB package. Additionally, the method includes forming an acoustic coupling medium to acoustically couple the at least one MUT to an external application surface on the at least one MUT.According to a fourth aspect, the present disclosure provides a method of forming an ultrasonic assembly. The method includes providing an eWLB package. At least one MUT and processing circuitry electrically coupled to the at least one MUT are packaged in the eWLB package. Additionally, the method includes disposing the eWLB package on a PCB. A recess is provided in the PCB. The method further includes forming an acoustic coupling medium for acoustically coupling the at least one MUT to an external application surface on the at least one MUT after disposing the eWLB package on the PCB such that the acoustic coupling medium protrudes through the recess.According to a fifth aspect, the present disclosure provides another method of forming an ultrasonic assembly. The method includes providing an ultrasonic device according to the first aspect and arranging the ultrasonic device on a PCB such that the acoustic coupling medium protrudes through a recess formed in the PCB.According to a sixth aspect, the present disclosure provides another ultrasonic assembly. The ultrasound assembly includes a PCB and additionally at least one MUT packaged in a wafer level ball grid array (WLB) package. The WLB package is mounted on the PCB. An acoustic coupling medium for acoustically coupling the at least one MUT to an external application surface is formed on the at least one MUT such that the acoustic coupling medium protrudes through a recess formed in the PCB.According to a seventh aspect, the present disclosure provides another method of forming an ultrasonic assembly. The method includes providing at least one MUT packaged in a WLB package. An acoustic coupling medium for acoustically coupling the at least one MUT to an external application surface is formed on the at least one MUT. Additionally, the method includes disposing the at least one MUT on a PCB such that the acoustic coupling medium protrudes through a recess formed in the PCB.In accordance with an eighth aspect, the present disclosure provides another method of forming an ultrasonic assembly. The method includes providing at least one MUT packaged in a WLB package. Additionally, the method includes arranging the at least one MUT on a PCB. The method further includes forming an acoustic coupling medium to acoustically couple the at least one MUT to an external application surface on the at least one MUT after disposing the at least one MUT to the PCB such that the acoustic coupling medium protrudes through the recess.Brief Description of the FiguresSome examples of devices and / or methods are described below, by way of example only, and with reference to the accompanying figures, in which: FIG. 1 schematically illustrates a cross-sectional view of a first example ultrasound device; FIG. 2 schematically illustrates a cross-sectional view of a second example ultrasound device; FIG. 3 schematically illustrates a sectional view of a third example ultrasound device; FIG. 4 illustrates a flow diagram of an example of a method of forming an ultrasound device; FIGS. 5 and 6 schematically illustrate a process for forming an acoustic coupling medium on an eWLB package; FIG. 7 schematically illustrates a sectional view of a first example ultrasound assembly; FIG. 8 illustrates a flow diagram of a first example of a method of forming an ultrasound assembly; FIG. 9 schematically illustrates a first example process for forming the first example ultrasound assembly illustrated in FIG. 7 ; FIG. 10 illustrates a flow diagram of a second example of a method of forming an ultrasound assembly; FIGS. 11 and 12 schematically illustrate a second example process for forming the first example ultrasound assembly illustrated in FIG. 7 ; FIG. 13 schematically illustrates a sectional view of a second example ultrasound assembly; FIG. 14 illustrates a flow diagram of a third example of a method for forming an ultrasound assembly; and FIG. 15 illustrates a flow diagram of a fourth example of a method of forming an ultrasound assembly.Detailed DescriptionSome examples will now be described in more detail with reference to the accompanying figures. However, other possible examples are not limited to the features of these embodiments described in detail. Other examples may include modifications to the features, as well as equivalents and alternatives to the features. Further, the terminology used herein to describe particular examples should not be limiting of other possible examples.Throughout the description of the figures, like or similar reference numerals refer to like or similar elements and / or features that may be implemented identically or in a modified form while providing the same or similar function. The thickness of lines, layers, and / or regions in the figures may also be exaggerated for clarity.When two elements A and B are combined using an "or", it is to be understood that all possible combinations are disclosed, i.e., only A, only B, and A and B, unless expressly defined otherwise in the particular case. As an alternative formulation for the same combinations, "at least one of A and B" or "A and / or B" may be used. This applies equivalently to combinations of more than two elements.When a singular form such as "a", "an" and "the / s" is used and the use of only a single element is not expressly or implicitly defined as obligatory, further examples may also use multiple elements to implement the same function. When a function is described below as being implemented using multiple elements, further examples may implement the same function using a single element or a single processing entity. It will be further understood that the terms "comprise," "comprising," "comprise," and / or "comprising," when used, describe the presence of the specified features, integers, steps, operations, processes, elements, components, and / or a group thereof, but do not preclude the presence or addition of one or more other features, integers, steps, operations, processes, elements, components, and / or a group thereof.FIG. 1 illustrates an example ultrasound device 100. The ultrasound device 100 comprises two MUTs 110 and 111. A MUT is a microelectromechanical system (MEMS) based ultrasonic transducer. The MUT is configurable to detect ultrasonic waves received from the environment and / or to generate and emit ultrasonic waves to the environment. The energy transfer through the MUT may be based on various effects such as capacitance and piezoelectricity. In other words, a MUT referred to in the present disclosure may be a capacitive ultrasonic micromechanical transducer (CMUT) or a piezoelectric ultrasonic micromechanical transducer (PMUT). A CMUT comprises two electrodes, one of the electrodes being fixed and the other electrode being encapsulated, integrated or formed by a movable membrane of the MUT. The membrane electrode is separated from the fixed electrode by a small gas-filled gap (e.g., an air gap) such that the membrane electrode can move relative to the fixed electrode. A PMUT comprises a movable membrane coupled to or formed by a piezoelectric element (device, structure). In general, the MUTs 110 and 111 may be configured to emit and / or detect sound waves at least between 20 kHz and 1 GHz and / or a portion thereof. In particular, the MUTs 110 and 111 may be configured to emit and / or detect low frequency ultrasonic waves (e.g., at about 50 kHz) for air applications such as proximity detection (e.g., for parking sensors of vehicles) or high frequency ultrasonic waves (e.g., at about 2 to 10 MHz) for diagnostic applications (e.g., medial ultrasound).The ultrasound device 100 further includes a processing circuit 120 electrically coupled to the MUTs 110 and 111. The processing circuit 120 is configured to control the MUTs 110 and 111 and process the output signals of the MUTs 110 and 111. The processing circuit 120 may be implemented in various ways. For example, the processing circuit 120 may be or include an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), a processor, or a combination thereof. Processing circuit 120 may optionally be coupled to or include a memory that stores a program having program code for causing processing circuit 120 to perform the functionalities described herein when the program is executed by processing circuit 120.For example, the processing circuit 120 may be configured to control one or both of the MUTs 110 and 111 to emit ultrasonic waves. Additionally or alternatively, the processing circuit 120 may be configured to process one or more output signals of one or both of the MUTs 110 and 111. The one or more output signals are generated by one or both of the MUTs 110 and 111 based on received ultrasonic waves (e.g., reflections from previously emitted ultrasonic waves). In other words, the MUTs 110 and 111 may be operated as ultrasonic emitters and / or as ultrasonic receivers (detectors) by the processing circuit 120. For example, the processing circuit 120 may be configured to control a CMUT to emit ultrasonic waves, for example, to supply (apply) a DC voltage for biasing the electrodes and an AC voltage for actuating the diaphragm to the electrodes of the CMUT. For example, to control a CMUT to act as an ultrasonic receiver (detector), the processing circuit 120 may be configured to supply (apply) a DC voltage to the electrodes of the CMUT for biasing the electrodes and measure the voltage variation between the electrodes caused by the capacitance variation due to the movement of the diaphragm by the received ultrasonic waves. Similarly, the processing circuit 120 may be configured to control a PMUT to emit ultrasonic waves, for example, to supply (apply) an AC voltage to the piezoelectric element to actuate the diaphragm by the induced deflection of the piezoelectric element. For example, to control a PMUT to act as an ultrasonic receiver (detector), the processing circuit 120 may be configured to measure the voltage output by the piezoelectric element due to the deflection of the piezoelectric element by the received ultrasonic waves.The MUTs 110 and 111 and the processing circuit 120 are packaged (packaged, arranged, mounted) in an eWLB package 130. The eWLB package 130 is formed in an eWLB packaging process. As illustrated in FIG. 1, the MUTs 110 and 111 are embedded in a molding compound 131 of the eWLB package 130. For example, the molding compound 131 may be an epoxy molding compound, a thermoplastic molding compound such as polyphenylene sulfide (PPS), polystyrene (PS), polypropylene (PP), polycarbonate (PC), polybutylene succinate (PBS), or liquid crystal polymer (LCP), a thermosetting molding compound, a foamed plastic molding compound, or a combination thereof. However, it should be noted that the present disclosure is not limited to the above examples. In the example of FIG. 1, two redistribution layers 132 and 133 are formed on the molding compound 131 to electrically couple the processing circuit 120 to the MUTs 110 and 111 and to electrically couple the processing circuit 120 to interconnects of the eWLB package 130, such as the two interconnects 134 and 135 illustrated in FIG. 1. Respective conductive traces such as conductive trace 137 are formed in redistribution layers 132 and 133 for electrically coupling the respective elements. However, it should be noted that the present disclosure is not limited thereto. In general, the eWLB package 130 may include any number M≥1 of redistribution layers and any number L≥1 of interconnects. The interconnects may be, for example, solder balls, as illustrated in FIG. 1 for the two interconnects 134 and 135.A recess 136 is provided in redistribution layers 132 and 133 at a position (over) MUTs 110 and 111 for acoustic coupling medium 140. Acoustic coupling medium 140 serves to acoustically couple MUTs 110 and 111 to an external application surface (not illustrated in FIG. 1 ). The external application surface is a surface outside the ultrasound device 100 to which the ultrasound device 100 may be (directly or indirectly) mounted. The external application surface is located between the ultrasound device 100, i.e., the MUTs 110 and 111, and an object (e.g., a finger or hand) or volume of space to be monitored, tracked, etc. The external application surface may be, for example, a housing or control panel of a device / application comprising the ultrasound device 100, such as the control panel of a consumer electronics device or a control panel of a vehicle (e.g., a car, a truck, a train, an aircraft, a ship, etc.) for touch inputs. The acoustic coupling medium 140 is a substance or a material that facilitates transmission of ultrasonic waves between the external application surface and the MUTs 110 and 111. The acoustic coupling medium 140 serves as a medium through which the ultrasonic waves pass, thereby ensuring that there is minimal energy loss when the ultrasonic waves pass from the MUT through the acoustic coupling medium 140 and into the external application surface and vice versa.The acoustic coupling medium 140 is formed on the MUTs 110 and 111. In particular, the acoustic coupling medium 140 is formed on the respective membrane of the MUTs 110 and 111. The acoustic coupling medium 140 allows to contact the external application surface, so that a void between the external application surface and the MUTs 110 and 111 can be avoided. The acoustic coupling medium 140 protrudes from the eWLB housing 130 so as to be brought into contact with the external application surface. For example, the acoustic coupling medium 140 may protrude from the eWLB package 130 and may be pressed against the external application surface to avoid air gaps (or generally gas-filled gaps) between the external application surface and the MUTs 110 and 111.Further, the acoustic coupling medium 140 is a medium for impedance matching between the acoustic impedance of the MUTs 110 and 111 and the acoustic impedance of the external application surface. Accordingly, the acoustic impedance of the acoustic coupling medium 140 may be lower than an acoustic impedance of the MUTs 110 and 111. Likewise, the acoustic impedance of the acoustic coupling medium 140 may be higher than the acoustic impedance of the external application surface.The acoustic coupling medium 140 may be a gel, for example. However, the present disclosure is not limited thereto. In other examples, the acoustic coupling medium 140 may be, for example, a cream or an oil. The acoustic coupling medium 140 may include various substances such as silicone or b-curable epoxy. However, the present disclosure is not limited to the above substances. In general, any suitable substance may be used for the acoustic coupling medium 140. The composition of the acoustic coupling medium 140 may depend on the specific application and thus the frequency range of the ultrasonic waves emitted and / or to be detected by the MUTs 110 and 111, for example.In the example of FIG. 1, the ultrasound device 100 includes two MUTs 110 and 111. However, it should be noted that the ultrasonic device 100 is not limited thereto. In general, the ultrasound device 100 may include any number N≥1 of MUTs packaged (packaged, arranged, mounted) in the eWLB package 130. In other words, in a basic configuration, the ultrasound device 100 includes at least one MUT and the processing circuit 120 electrically coupled to the at least one MUT. Analogous to what is described above, the at least one MUT and processing circuitry 120 are packaged in the eWLB package 130, and the acoustic coupling medium 140 for acoustically coupling the at least one MUT to an external application surface is formed on the at least one MUT. Analogous to what is described above, the processing circuit 120 may be configured to control the at least one MUT to selectively emit ultrasonic waves and / or to process one or more output signals of the at least one MUT. The one or more output signals are generated by the at least one MUT based on received ultrasonic waves.Optionally, the ultrasound device 100 may include other electronic components, such as one or more amplifiers for amplifying one or more signals within the ultrasound device 100, one or more passive electronic components (such as resistors, capacitors, or inductors), or one or more light emitting diodes (LEDs) for status indication.FIG. 2 illustrates another ultrasound device 200. The ultrasonic device 200 is different from the above-described ultrasonic device 100 in that a protrusion 138 surrounding the recess 136 is additionally formed on the redistribution layers 132 and 133. The protrusion 138 serves to create a predetermined lens shape with a low viscosity coupling medium in an uncured state and as an expansion stop to prevent the acoustic coupling medium 140 from expanding (covering) to the redistribution layers 132 and 133 or any other elements formed (disposed) on the redistribution layers 132 and 133, such as the joints 134 and 135. The acoustic coupling medium 140 protrudes from the protrusion 138 so that it can be brought into contact with the external application surface. The protrusion 138 may be formed by, for example, one or more passivation layers formed on the redistribution layers 132 and 133. However, the present disclosure is not limited thereto.As stated above, an ultrasound device according to the present disclosure may comprise any number N ≥ 1 of MUTs. FIG. 3 illustrates another ultrasound device 300 that includes eight MUTs 111,..., 118 embedded in the molding compound 131 of the eWLB package 130. The MUTs 111,..., 118 are electrically coupled to the processing circuit 120 via conductive traces in one or more redistribution layers (not explicitly illustrated in FIG. 3 due to the perspective) of the eWLB package 130. Similarly, processing circuit 120 is electrically coupled to interconnects 330,..., 339 of eWLB package 130 via conductive traces in the one or more redistribution layers. For simplicity, only the trace that electrically couples the processing circuit 120 and the interconnect 135 is labeled with a reference number, namely, the reference number 137.In the example of FIG. 3, half of the MUTs 111,..., 118 are operated as ultrasound transmitters and the other MUTs are operated as ultrasound receivers. Specifically, the processing circuit 120 is configured to control the MUTs 111,..., 114 to function as an ultrasonic transmitter and emit ultrasonic waves. Similarly, processing circuit 120 is configured to process the output signals of MUTs 115,..., 118 acting as ultrasound receivers. The output signals generated by the MUTs 115,..., 118 are based on received ultrasonic waves (e.g., reflection of the ultrasonic waves emitted by the MUTs 111,..., 114).A flow diagram of an example method 400 for forming an ultrasound device as described above is illustrated in FIG. 4. The method 400 includes providing 402 an eWLB package. At least one MUT and processing circuitry electrically coupled to the at least one MUT are packaged in the eWLB package. For example, the eWLB package may be formed in an eWLB packaging process. Additionally, the method 400 includes forming 404 an acoustic coupling medium for acoustically coupling the at least one MUT to an external application surface on the at least one MUT.The method 400 enables providing an ultrasound device as described above. Further details and aspects of the method 400 are discussed in connection with the proposed technique or one or more examples described above. The method 400 may include one or more additional optional features corresponding to one or more aspects of the proposed technique or one or more examples described above.Forming 404 the acoustic coupling medium on the at least one MUT may include, for example, dispensing a fluid, cream, or gel as the acoustic coupling medium on the at least one MUT. This is illustrated by way of example in FIGS. 5 and 6. As in the examples of FIGS. 1 and 2, an eWLB package 500 with two MUTs 110 and 111 is illustrated in FIGS. 5 and 6. Figure 5 illustrates the dispensing of the fluid, cream or gel on the two MUTs 110 and 111 by means of a dispensing needle 510. Optionally, forming 404 the acoustic coupling medium 140 may further comprise curing the dispensed fluid, cream or gel. FIG. 6 illustrates the resulting ultrasound device 600 with the acoustic coupling medium 140 formed on the two MUTs 110 and 111. The protrusion 138 prevents spreading of the fluid, cream or gel onto the redistribution layers 131 and 132.FIG. 7 illustrates an ultrasound assembly 700 using an ultrasound device as described above. In particular, the ultrasound arrangement 700 comprises the ultrasound device 200 described above. Additionally, the ultrasound assembly 700 includes a PCB 710 (e.g., a rigid PCB or a flexible PCB). The ultrasound device 200 is disposed (mounted) to the PCB 710 such that the acoustic coupling medium 140 protrudes through a recess 711 (e.g., a hole) formed in the PCB 710. In other words, the coupling medium 140 protrudes through the recess 711. The interconnects 134 and 135 of the eWLB package 130 are electrically coupled to traces 712 and 713 on the PCB 710. For example, interconnects 134 and 135 may be soldered to traces 712 and 713 on PCB 710. In the example of FIG. 7, two conductive traces 712 and 713 are illustrated. It should be noted, however, that the PCB 710 may include any suitable number T≥1 of conductive traces.For example, the ultrasound device 200 may be provided by a semiconductor manufacturer and the PCB 710 may be a customer's PCB. Accordingly, an ultrasound assembly 700 may be provided according to customer specifications. The acoustic coupling medium 140 protruding through the recess 711 enables contacting an external application surface to which the ultrasound assembly 700 may be mounted. Accordingly, a void between the external application surface and the MUTs 110 and 111 can be avoided.In the example of FIG. 7, the ultrasound device 200 includes two MUTs 110 and 111. However, it should be noted that the ultrasound assembly 700 is not limited thereto. Generally, an ultrasonic device comprising any number N ≥ 1 of MUTs packaged (packaged, arranged, mounted) in the eWLB package may be used.A flow diagram of a first example method 800 for forming an ultrasound assembly as described above is illustrated in FIG. 8. The method 800 includes providing 802 an ultrasound device as described above (e.g., one of the ultrasound devices 100, 200, and 300), and arranging 804 the ultrasound device on a PCB such that the acoustic coupling medium of the ultrasound device protrudes through a recess formed in the PCB.The method 800 enables providing an ultrasound arrangement as described above. Further details and aspects of the method 800 are explained in connection with the proposed technique or one or more examples described above. The method 800 may include one or more additional optional features corresponding to one or more aspects of the proposed technique or one or more examples described above.To further emphasize the method 800, FIG. 9 illustrates, by way of example, the corresponding process of mounting the ultrasound device 200 to the PCB 710 to obtain the ultrasound assembly 700 described above with reference to FIG. 7. Interconnects 134 and 135 are electrically connected to traces 712 and 713 on PCB 710. The PCB 710 is provided with the recess 711 so that the acoustic coupling medium 140 after mounting may protrude through the recess 711.A flow diagram of a second example method 1000 for forming an ultrasound assembly as described above is illustrated in FIG. 10. The method 1000 includes providing 1002 an eWLB package. At least one MUT and processing circuitry electrically coupled to the at least one MUT are packaged in the eWLB package. Additionally, the method 1000 includes disposing 1004 the eWLB package on a PCB. A recess is provided in the PCB. The method 1000 further includes forming 1006 an acoustic coupling medium to acoustically couple the at least one MUT to an external application surface on the at least one MUT after disposing the eWLB package on the PCB such that the acoustic coupling medium protrudes through the recess.While the acoustic coupling medium is formed before mounting (arranging) to the PCB in the method 800, the acoustic coupling medium is formed after mounting (arranging) to the PCB in the method 1000. In other words, the eWLB package used in the method 1000 may be similar to the eWLB packages described above-the only difference may be that an acoustic coupling medium is not formed, as this occurs after mounting (arranging) to the PCB in the method 1000. The method 1000 also enables the provision of an ultrasonic arrangement as described above. Further details and aspects of the method 1000 are explained in connection with the proposed technique or one or more examples described above. The method 1000 may include one or more additional optional features corresponding to one or more aspects of the proposed technique or one or more examples described above.To further emphasize the method 1000, FIGS. 11 and 12 exemplify the corresponding process of forming the ultrasound assembly 700 described above with reference to FIG. 7.As illustrated in FIG. 11, an eWLB package 1100 (which is identical to the ultrasound device 200 except for the omitted acoustic coupling medium 140) is mounted to the PCB 710 such that the interconnects 134 and 135 of the eWLB package 1100 are electrically connected to the traces 712 and 713 on the PCB 710 (e.g., the interconnects may be soldered to the traces). Figure 12 illustrates the subsequent dispensing of the fluid, cream or gel on the two MUTs 110 and 111 using the dispensing needle 510 to form the acoustic coupling medium 140. Optionally, forming the acoustic coupling medium 140 may further comprise curing the dispensed fluid, cream or gel. Also, by forming the acoustic coupling medium 140 after mounting the eWLB package 1100 to the PCB 710, the acoustic coupling medium 140 may be formed to protrude through the recess 711 of the PCB 710.In the above examples, the processing circuitry and the at least one MUT are packaged in an eWLB package. However, the present disclosure is not limited thereto. As described below, WLB packages, also known as wafer level packaging (WLP) packages, may be used instead.FIG. 13 illustrates an example ultrasound assembly 1300 that includes a PCB 1310 and two MUTs 1320 and 1330. The MUTs 1320 and 1330 are each packaged (packaged, arranged, mounted) in a respective WLB package 1340, 1350. The WLB packages 1340 and 1350 are formed in a WLB (WLP) packaging process.Each of the WLB packages 1340 and 1350 includes two respective interconnects 1341, 1342, and 1351, 1352 for connecting the respective WLB package 1340, 1350 to external entities such as the PCB 1310. In general, WLB housings 1340 and 1350 may include any number L≥1 of interconnects. The interconnections may be, for example, solder balls as illustrated in FIG. 13.The WLB housings 1340 and 1350 are both disposed on the PCB 1310 such that the interconnects 1341, 1342, and 1351, 1352 are electrically coupled to the traces 1313,...,1316 on the PCB 1310 (e.g., the interconnects may be soldered to the traces).An acoustic coupling medium 1360 for acoustically coupling the MUT 1320 to an external application surface is formed on the MUT 1320 such that the acoustic coupling medium 1360 protrudes through a recess 1311 formed in the PCB 1310. Similarly, an acoustic coupling medium 1370, for acoustically coupling the MUT 1330 to the external application surface, is formed on the MUT 1330 such that the acoustic coupling medium 1370, protrudes through another recess 1312 formed in the PCB 1310. In particular, the respective acoustic coupling medium 1360, 1370 may be formed on the respective membrane of the MUTs 1320 and 1330.The acoustic coupling media 1360 and 1370 enable contacting the external application surface such that a void between the external application surface and the MUTs 1320 and 1330 may be avoided. The acoustic coupling media 1360 and 1370 protrude from the PCB 1310 so that they can be contacted with the external application surface. For example, acoustic coupling media 1360 and 1370, may be pressed against the external application surface to avoid air gaps (or generally gas-filled gaps) between the external application surface and MUTs 1320 and 1330. The external application surface may be as described above with respect to the ultrasound device 100.In the example of FIG. 13, the ultrasound assembly 1300 includes two MUTs 1320 and 1330. However, it should be noted that the ultrasonic assembly 1300 is not limited thereto. In general, the ultrasound assembly 1300 may include any number A≥1 of MUTs packaged in a respective WLB package. In other words, in a basic configuration, the ultrasound assembly 1300 includes a PCB and at least one MUT packaged in a WLB package. Analogous to what is described above, the WLB package is disposed on the PCB, and an acoustic coupling medium for acoustically coupling the at least one MUT to an external application surface is formed on the at least one MUT such that the acoustic coupling medium protrudes through a recess formed in the PCB. In the case of multiple MUTs packaged in a respective WLB package, the respective acoustic coupling medium formed on the respective MUT may protrude through a respective recess formed in the PCB. In other examples, the acoustic coupling media may protrude from two or more MUTs through a same (common) recess formed in the PCB.The ultrasound assembly 1300 may optionally further include a processing circuit 1380 (which may be implemented analogously to the processing circuit 120 described above). The processing circuit 1380 is disposed on the PCB 1310 and electrically coupled to the at least one MUT of the ultrasound assembly 1300 (e.g., via one or more conductive traces on the PCB 1310). For example, processing circuit 1380 may be packaged in a separate WLB package. However, the present disclosure is not limited thereto. In general, any packaging or assembly technology may be used to attach processing circuit 1380 to PCB 1310. Analogous to what is described above, the processing circuit 1380 may be configured to control the at least one MUT of the ultrasound arrangement 1300 to selectively emit ultrasound waves and / or process one or more output signals of the at least one MUT, wherein the one or more output signals are generated by the at least one MUT based on received ultrasound waves. For example, the processing circuit 1380 may be configured to control the MUT 1320 to emit ultrasonic waves, to operate the MUT 1320 as an ultrasonic transmitter, and to process the output signal(s) of the MUT 1330 acting / acting as an ultrasonic receiver. The output signal(s) generated by the MUT 1330 is / are based on received ultrasonic waves (e.g., reflections of the ultrasonic waves emitted by the MUT 1320).Optionally, the ultrasound assembly 1300 may include other electronic components, such as one or more amplifiers for amplifying one or more signals within the ultrasound assembly 1300, one or more passive electronic components (such as resistors, capacitors, or inductors), or one or more LEDs for status indication.A flow diagram of an example method 1400 for forming an ultrasound assembly, such as the ultrasound assembly 1300 described above, is illustrated in FIG. 14. The method 1400 includes providing 1402 at least one MUT packaged in a WLB package. An acoustic coupling medium for acoustically coupling the at least one MUT to an external application surface is formed on the at least one MUT. Additionally, the method 1400 includes arranging 1404 the at least one MUT on a PCB such that the acoustic coupling medium protrudes through a recess formed in the PCB.The method 1400 enables providing an ultrasound assembly, such as the ultrasound assembly 1300 described above. Further details and aspects of method 1400 are discussed in connection with the proposed technique or one or more examples described above. The method 1400 may include one or more additional optional features corresponding to one or more aspects of the proposed technique or one or more examples described above.For example, to form the ultrasound assembly 1300 according to the method 1400, two MUTs may be provided packaged in a respective WLB package. A respective acoustic coupling medium for acoustically coupling the respective MUT to the external application surface is formed on each MUT. Then, the two MUTs are arranged on the PCB so that the respective acoustic coupling medium formed on the respective MUT protrudes through a respective recess formed in the PCB.A flow diagram of an alternative method 1500 for forming an ultrasound assembly, such as the ultrasound assembly 1300 described above, is illustrated in FIG. 15. The method 1500 includes providing 1502 at least one MUT packaged in a WLB package. Additionally, the method 1500 includes arranging 1504 the at least one MUT on a PCB. The method 1500 further includes forming 1506 an acoustic coupling medium to acoustically couple the at least one MUT to an external application surface on the at least one MUT after disposing 1504 the at least one MUT on the PCB such that the acoustic coupling medium protrudes through the recess.While the acoustic coupling medium is formed before mounting (arranging) to the PCB in the method 1400, the acoustic coupling medium is formed after mounting (arranging) to the PCB in the method 1500. The method 1500 also enables providing an ultrasound assembly, such as the ultrasound assembly 1300 described above. Further details and aspects of the method 1500 are explained in connection with the proposed technique or one or more examples described above. The method 1500 may comprise one or more additional optional features corresponding to one or more aspects of the proposed technique or one or more examples described above.For example, to form the ultrasound assembly 1300 according to the method 1500, two MUTs may be provided packaged in a respective WLB package, but the respective acoustic coupling medium is not yet formed on the MUTs. Then, the two MUTs are attached to the PCB. Only after placement on the PCB is a respective acoustic coupling medium formed on each MUT for acoustically coupling the respective MUT to the external application surface, such that the respective acoustic coupling medium formed on the respective MUT protrudes through a respective recess formed in the PCB.Examples of the present disclosure may provide ultrasonic assemblies having one or more sensor chips arranged as WLB packages on a PCB (e.g., rigid or flexible) and protruding through a respective hole in the PCB.Analogous to what is described above, forming the acoustic coupling medium on the at least one MUT may include dispensing a fluid or gel as the acoustic coupling medium on the at least one MUT in methods 1400 and 1500. Further, forming the acoustic coupling medium on the at least one MUT may further comprise curing the dispensed fluid or gel in methods 1400 and 1500.The examples described herein may be summarized as follows:Example 1 is an ultrasonic device. The ultrasound device includes at least one MUT and processing circuitry electrically coupled to the at least one MUT. The at least one MUT and the processing circuitry are packaged in an eWLB package. An acoustic coupling medium for acoustically coupling the at least one MUT to an external application surface is formed on the at least one MUT.Example 2 is the apparatus of example 1, wherein the processing circuitry is configured to: control the at least one MUT to selectively emit ultrasonic waves; and / or process one or more output signals of the at least one MUT, wherein the one or more output signals are generated by the at least one MUT based on received ultrasonic waves.Example 3 is the apparatus of example 1, wherein the ultrasound device comprises a plurality of MUTs, and wherein the processing circuitry is configured to: control at least one of the plurality of MUTs to emit ultrasound waves; and process one or more output signals of at least one of the plurality of MUTs, wherein the one or more output signals are generated by the at least one of the plurality of MUTs based on received ultrasound waves.Example 4 is the ultrasound device of any of Examples 1 to 3, wherein the at least one MUT is embedded in a molding compound of the eWLB package, wherein one or more redistribution layers are formed on the molding compound to electrically couple the processing circuit to the at least one MUT, and wherein a recess is provided in the one or more redistribution layers for the acoustic coupling medium.Example 5 is the ultrasound device of example 4, wherein the recess in the one or more redistribution layers is provided at a position of the at least one MUT.Example 6 is the ultrasound device of example 4 or example 5, wherein a protrusion surrounding the recess is formed on the one or more redistribution layers.Example 7 is the ultrasound device of any of Examples 4 to 6, further comprising one or more interconnects coupled to the processing circuitry via the one or more redistribution layers.Example 8 is the ultrasound device of any of Examples 1 to 7, wherein the acoustic coupling medium is formed on a membrane of the at least one MUT.Example 9 is the ultrasound device of any of Examples 1 to 8, wherein the acoustic coupling medium comprises silicone.Example 10 is the ultrasound device of any of Examples 1 to 9, wherein the acoustic coupling medium is a gel.Example 11 is the ultrasound device of any of Examples 1 to 10, wherein an acoustic impedance of the acoustic coupling medium is lower than an acoustic impedance of the at least one MUT.Example 12 is an ultrasound assembly. The ultrasound assembly includes a PCB and an ultrasound device according to the first aspect. The ultrasound device is attached to the PCB. The acoustic coupling medium protrudes through a recess formed in the PCB.Example 13 is the ultrasound assembly of example 12, wherein one or more interconnects of the eWLB package are electrically coupled to one or more traces on the PCB.Example 14 is a method of forming an ultrasound device. The method includes providing an eWLB package. At least one MUT and processing circuitry electrically coupled to the at least one MUT are packaged in the eWLB package. Additionally, the method includes forming an acoustic coupling medium to acoustically couple the at least one MUT to an external application surface on the at least one MUT.Example 15 is a method of forming an ultrasound assembly. The method includes providing an eWLB package. At least one MUT and processing circuitry electrically coupled to the at least one MUT are packaged in the eWLB package. Additionally, the method includes disposing the eWLB package on a PCB. A recess is provided in the PCB. The method further includes forming an acoustic coupling medium for acoustically coupling the at least one MUT to an external application surface on the at least one MUT after disposing the eWLB package on the PCB such that the acoustic coupling medium protrudes through the recess.Example 16 is a method of forming an ultrasound assembly. The method includes providing an ultrasound device according to any of Examples 1 to 11 and arranging the ultrasound device on a PCB such that the acoustic coupling medium protrudes through a recess formed in the PCB.Example 17 is an ultrasound arrangement. The ultrasound assembly includes a PCB and additionally at least one MUT packaged in a WLB package. The WLB package is mounted on the PCB. An acoustic coupling medium for acoustically coupling the at least one MUT to an external application surface is formed on the at least one MUT such that the acoustic coupling medium protrudes through a recess formed in the PCB.Example 18 is the ultrasound assembly of example 17, wherein the ultrasound assembly comprises at least two MUTs, and wherein the respective acoustic coupling medium formed on the respective MUT protrudes through a respective recess formed in the PCB.Example 19 is the ultrasound assembly of example 17 or example 18, further comprising processing circuitry disposed on the PCB and electrically coupled to the at least one MUT, wherein the processing circuitry is configured to: control the at least one MUT to selectively emit ultrasound waves; and / or process one or more output signals of the at least one MUT, wherein the one or more output signals are generated by the at least one MUT based on received ultrasound waves.Example 20 is a method of forming an ultrasound assembly. The method includes providing at least one MUT packaged in a WLB package. An acoustic coupling medium for acoustically coupling the at least one MUT to an external application surface is formed on the at least one MUT. Additionally, the method includes disposing the at least one MUT on a PCB such that the acoustic coupling medium protrudes through a recess formed in the PCB.Example 21 is a method of forming an ultrasound assembly. The method includes providing at least one MUT packaged in a WLB package. Additionally, the method includes arranging the at least one MUT on a PCB. The method further includes forming an acoustic coupling medium to acoustically couple the at least one MUT to an external application surface on the at least one MUT after disposing the at least one MUT to the PCB such that the acoustic coupling medium protrudes through the recess.Example 22 is the method of any of Examples 14, 15, and 21, wherein forming the acoustic coupling medium on the at least one MUT comprises dispensing a fluid or gel as the acoustic coupling medium on the at least one MUT.Example 23 is the method of Example 22, wherein forming the acoustic coupling medium on the at least one MUT further comprises curing the dispensed fluid or gel.The aspects and features described with respect to a particular one of the preceding examples can also be combined with one or more of the further examples in order to replace an identical or similar feature of this further example or in order to introduce the features additionally into the further example.It is further understood that the disclosure of multiple steps, processes, operations, or functions disclosed in the specification or claims should not be construed to imply that these operations are necessarily order-dependent unless expressly stated or required for technical reasons in the particular case. Therefore, the foregoing description does not limit the execution of multiple steps or functions to a particular order. Further, in further examples, a single step, function, process, or operation may include and / or be broken into multiple substeps, functions, processes, or operations.When some aspects have been described with respect to an apparatus or a system, these aspects should also be understood as a description of the corresponding method. For example, a block, a device or a functional aspect of the device or of the system can correspond to a feature, such as a method step, of the corresponding method. Accordingly, aspects described with respect to a method should also be understood as a description of a corresponding block, a corresponding element, a property or a functional feature of a corresponding device or a corresponding system.The following claims are hereby incorporated into the Detailed Description, with each claim standing on its own as a separate example. It is further to be noted that although in the claims a dependent claim refers to a particular combination with one or more other claims, other examples may also comprise a combination of the dependent claim with the subject matter of any other dependent or independent claim. Such combinations are expressly suggested herein unless it is stated in the individual case that a particular combination is not intended. Further, features of a claim should also be included for any other independent claim, even if that claim is not defined directly as dependent on that other independent claim.

Claims

An ultrasound device (100, 200, 300) comprising: at least one micromechanical ultrasound transducer, MUT (111,..., 118); and processing circuitry (120) electrically coupled to the at least one MUT (111,..., 118), wherein the at least one MUT (111,..., 118) and the processing circuitry (120) are packaged in an embedded wafer level ball grid array, eWLB, package (130), wherein an acoustic coupling medium (140) is formed for acoustically coupling the at least one MUT (111,..., 118) to an external application surface on the at least one MUT (111,..., 118), and wherein the at least one MUT (111,..., 118), 118) is embedded in a molding compound (131) of the eWLB package (130), wherein one or more redistribution layers (132, 133) are formed on the molding compound (131) for electrically coupling the processing circuit (120) to the at least one MUT (111,..., 118), and wherein a recess (136) is provided in the one or more redistribution layers (132, 133) for the acoustic coupling medium (140).The ultrasound device (100, 200, 300) of claim 1, wherein the processing circuit (120) is configured to: control the at least one MUT (111,..., 118) to selectively emit ultrasound waves; and / or process one or more output signals of the at least one MUT (111,..., 118), wherein the one or more output signals are generated by the at least one MUT (111,..., 118) based on received ultrasound waves.The ultrasound device (100, 200, 300) of claim 1, wherein the ultrasound device (100, 200, 300) comprises a plurality of MUTs (111,..., 118), and wherein the processing circuit (120) is configured to: control at least one of the plurality of MUTs (111,..., 118) to emit ultrasound waves; and process one or more output signals of at least one of the plurality of MUTs (111,..., 118), wherein the one or more output signals are generated by the at least one of the plurality of MUTs (111,..., 118) based on received ultrasound waves.The ultrasound device (100, 200, 300) of any one of claims 1 to 3, wherein the recess (136) in the one or more redistribution layers (132, 133) is provided at a position of the at least one MUT (111,..., 118).The ultrasound device (100, 200, 300) of any of claims 1 to 4, wherein a protrusion (138) surrounding the recess (136) is formed on the one or more redistribution layers (132, 133).The ultrasound device (100, 200, 300) of any of claims 1 to 5, further comprising one or more interconnects (134, 135) coupled to the processing circuit (120) via the one or more redistribution layers (132, 133).The ultrasound device (100, 200, 300) of any one of claims 1 to 6, wherein the acoustic coupling medium (140) is formed on a membrane of the at least one MUT (111,..., 118).The ultrasound device (100, 200, 300) of any of claims 1 to 7, wherein the acoustic coupling medium (140) comprises silicone.The ultrasound device (100, 200, 300) of any of claims 1 to 8, wherein the acoustic coupling medium (140) is a gel.The ultrasound device (100, 200, 300) of any one of claims 1 to 9, wherein an acoustic impedance of the acoustic coupling medium (140) is lower than an acoustic impedance of the at least one MUT (111,..., 118).An ultrasound assembly (700) comprising: a printed circuit board, PCB (710); and an ultrasound device (100, 200, 300) according to any one of claims 1 to 10, wherein the ultrasound device (100, 200, 300) is attached to the PCB (710), and wherein the acoustic coupling medium (140) protrudes through a recess (711) formed in the PCB (710).The ultrasound assembly of claim 11, wherein one or more interconnects (134, 135) of the eWLB package are electrically coupled to one or more traces (712, 713) on the PCB (710).A method (400) of forming an ultrasound device, the method (400) comprising: providing (402) an embedded wafer level ball grid array, eWLB, package, wherein at least one micromechanical ultrasound transducer, MUT, and processing circuitry electrically coupled to the at least one MUT are packaged in the eWLB package; forming (404) an acoustic coupling medium for acoustically coupling the at least one MUT to an external application surface on the at least one MUT, wherein the at least one MUT is embedded in a molding compound of the eWLB package, wherein one or more redistribution layers are formed on the molding compound for electrically coupling the processing circuit to the at least one MUT, and wherein a recess is provided in the one or more redistribution layers for the acoustic coupling medium.A method (1000) of forming an ultrasound assembly, the method (1000) comprising: providing (1002) an embedded wafer level ball grid array, eWLB, package, wherein at least one micromechanical ultrasound transducer, MUT, and processing circuitry electrically coupled to the at least one MUT are packaged in the eWLB package; arranging (1004) the eWLB package on a printed circuit board, PCB, wherein a recess is provided in the PCB; and forming (1006) an acoustic coupling medium for acoustically coupling the at least one MUT to an external application surface on the at least one MUT after disposing the eWLB package on the PCB such that the acoustic coupling medium protrudes through the recess.A method (800) of forming an ultrasound assembly, the method (800) comprising: providing (802) an ultrasound device according to any one of claims 1 to 10; and arranging (804) the ultrasound device on a printed circuit board, PCB, such that the acoustic coupling medium protrudes through a recess formed in the PCB.An ultrasound assembly (1300) comprising: a printed circuit board, PCB (1310); and at least one micromechanical ultrasound transducer, MUT, (1320, 1330) packaged in a wafer level ball grid array, WLB, package (1340, 1350), wherein the WLB package (1340, 1350) is disposed on the PCB (1310), and wherein an acoustic coupling medium (1360, 1370) for acoustically coupling the at least one MUT (1320, 1330) to an external application surface is formed on the at least one MUT (1320, 1330) such that the acoustic coupling medium (1360, 1370) protrudes through a recess (1311, 1312) formed in the PCB (1310).The ultrasound assembly (1300) of claim 16, wherein the ultrasound assembly (1300) comprises at least two MUTs (1320, 1330), and wherein the respective acoustic coupling medium (1360, 1370) formed on the respective MUT (1320, 1330) protrudes through a respective recess (1311, 1312) formed in the PCB (1310).The ultrasound assembly (1300) of claim 16 or claim 17, further comprising processing circuitry (1380) attached to the PCB and electrically coupled to the at least one MUT (1320, 1330), wherein the processing circuitry (1380) is configured to: control the at least one MUT (1320, 1330) to selectively emit ultrasonic waves; and / or process one or more output signals of the at least one MUT (1320, 1330), wherein the one or more output signals are generated by the at least one MUT (1320, 1330) based on received ultrasonic waves.A method (1400) of forming an ultrasound assembly, the method (1400) comprising: providing (1402) at least one Micromechanical Ultrasound Transducer, MUT, packaged in a wafer level ball grid array, WLB, package, wherein an acoustic coupling medium for acoustically coupling the at least one MUT to an external application surface is formed on the at least one MUT; and arranging (1404) the at least one MUT to a printed circuit board, PCB, such that the acoustic coupling medium protrudes through a recess formed in the PCB.A method (1500) of forming an ultrasound assembly, the method (1500) comprising: providing (1502) at least one Micromechanical Ultrasound Transducer, MUT, packaged in a wafer level ball grid array, WLB, package; disposing (1504) the at least one MUT to a printed circuit board, PCB; and forming (1506) an acoustic coupling medium for acoustically coupling the at least one MUT to an external application surface on the at least one MUT after disposing the at least one MUT to the PCB such that the acoustic coupling medium protrudes through the recess.The method (400, 1400, 1500) of any of claims 13, 14, and 20, wherein forming (404, 1406, 1506) the acoustic coupling medium on the at least one MUT comprises dispensing a fluid or gel as the acoustic coupling medium on the at least one MUT.The method (400, 1400, 1500) of claim 21, wherein forming (404, 1406, 1506) the acoustic coupling medium on the at least one MUT further comprises curing the dispensed fluid or gel.

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