Ultrasonic sensor and method for producing an ultrasonic sensor

Abstract

The invention relates to an ultrasonic sensor (1) with a microelectromechanical sensor unit (2) for generating and detecting an ultrasonic signal, a sensor housing (3) for accommodating the sensor unit (2), a housing circuit board (5) and a sensor head circuit board (6) arranged in the sensor housing (3) and spaced from the housing circuit board (5) and having a signal processing unit (7) for processing signals from the microelectromechanical sensor unit (2), wherein the sensor head circuit board (6) has a base section (8) for accommodating the signal processing unit (7) and a connecting section (9) formed integrally with the base section (8) for electrically connecting the sensor head circuit board (6) to the housing circuit board (5), and wherein the connecting section (9) has a lower flexural rigidity than the base section (8).The invention further relates to a method (100) for producing an ultrasonic sensor (1) with a microelectromechanical sensor unit (2).

Description

The invention relates to an ultrasonic sensor with a microelectromechanical sensor unit and to a method for producing such an ultrasonic sensor.Prior ArtUltrasonic sensors with microelectromechanical sensor units and methods for producing them are known from the prior art. Microelectromechanical sensor units are also referred to as micromechanical sensor units or as MEMS sensor units.DE 10 2020 211 538 A1 discloses a micromechanical component for a sound transducer device, a sound transducer device and a method for producing a micromechanical component for a sound transducer device. The sound transducer device can be designed as an ultrasonic transducer. The micromechanical component has a piezoelectric element having an electrical contact connection and 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.DE 10 2018 105 502 A1 describes an ultrasonic sensor assembly having a first sensor housing part, a transducer element, which is arranged at least partially within the first sensor housing part, for generating ultrasonic oscillations, at least one flexible electrical connection means, which is electrically connected to the transducer element and is contactable or electrically contacted with at least one electronic component, and a guide device, in which the flexible electrical connection means is at least partially guided. Furthermore, a method for assembling such an assembly is described.Disclosure of the InventionAccording to the features of independent claim 1, an ultrasonic sensor is proposed having a microelectromechanical sensor unit for generating and detecting an ultrasonic signal, a housing printed circuit board, a sensor housing for receiving the sensor unit, and a sensor head printed circuit board, which is arranged in the sensor housing and is spaced apart from the housing printed circuit board, having a signal processing unit for processing signals of the microelectromechanical sensor unit, wherein the sensor head printed circuit board has a base section for receiving the signal processing unit and a connecting section, which is embodied integrally with the base section, for electrically connecting the sensor head printed circuit board to the housing printed circuit board, and wherein the connecting section has a lower flexural rigidity than the base section.In other words, it is proposed to establish an electrical connection between two circuit carriers of the ultrasonic sensor spaced apart from one another in that an integrally formed connection part which is more flexible than the circuit carrier is arranged on one of the two circuit carriers, by means of which connection part the spatial distance between the circuit carriers can be bridged in a flexible manner and by means of which connection part the two circuit carriers can be electrically connected to one another.An ultrasonic sensor according to the proposed features has the advantages of a smaller number of components and a reduced component complexity due to the connection portion formed integrally with the sensor head board. The proposed ultrasonic sensor is also distinguished by a simpler production process, since a separate production step for contacting the sensor head printed circuit board with a separate connecting means is dispensed with, in particular in consideration of the tight installation space in the sensor housing, which makes mounting and contacting difficult. The handling of the sensor head board and of the connecting section and their placement in the narrow sensor housing is substantially simplified by the integral formation with one another and by the partially reduced bending rigidity in the connecting section. The one-piece configuration of the connecting section with the sensor head board furthermore increases the quality of the electrical connection compared to a subsequently connected connecting means, and shielding measures can already be implemented directly on the sensor head board during production, in order to increase the electromagnetic compatibility of the assembly. Due to the partially reduced bending stiffness, the connecting section can be aligned optimally in the sensor housing and adapted to the existing distance between the sensor head printed circuit board and the housing printed circuit board.An ultrasonic sensor can be a sensor device which is configured for signal transit time-based distance measurement to objects by emitting and receiving a reflected ultrasonic signal. Ultrasonic sensors can be arranged, for example, as distance sensors on vehicles, in particular on bumpers or other body components, in order to support, for example, driving assistance functions or autonomous driving functions of the vehicle.A microelectromechanical sensor unit, also known as a MEMS sensor unit, can have, for example, one or more semiconductor-technology-generated sensor components having mechanical and electrical microstructures, for example microstructures having dimensions in the micro- and / or nanometer range. A microelectromechanical sensor component may be suitable for implementation as a system-on-a-chip (SoC), such that the sensor component may be formed as a MEMS chip. Microelectromechanical sensor units can be usable, for example, as miniaturized sensors under limited installation space conditions. The microelectromechanical sensor unit used for the ultrasonic sensor can have, for example, a sensor component designed as a microelectromechanical transceiver, which can be designed by means of a movable structure such as a micromembrane for generating and for receiving an ultrasonic signal in a time-shifted manner. According to one embodiment, the microelectromechanical sensor component can cooperate with a linked membrane component in order to generate an ultrasonic signal and / or to receive a reflected ultrasonic signal. The sensor component and the diaphragm component together form the microelectromechanical sensor unit in this case. Furthermore, it is conceivable for the microelectromechanical sensor unit to have a plurality of microelectromechanical sensor components, that is to say at least two microelectromechanical sensor components. Depending on the embodiment, these can be designed, for example, as ultrasound transceivers, i.e., as combined transceivers, or one of the sensor components can be designed as ultrasound transmitters and another of the sensor components can be designed as ultrasound receivers. An ultrasonic signal is a sound signal having a frequency above the audible frequency range of the human being. Ultrasonic signals can have a frequency between 20 kHz and 1 GHz, for example.The sensor housing can be configured for mechanically receiving components of the ultrasonic sensor such as the microelectromechanical sensor unit, the sensor head printed circuit board and the housing printed circuit board. The sensor head printed circuit board and the housing printed circuit board can be arranged in particular in an interior of the sensor housing in order to protect the latter from environmental influences. The sensor housing can also form an insulating cover for the sensor components and can be designed, for example, as a plastic housing. The sensor housing can have a housing base which, according to one embodiment, has at least one depression or through-opening into which the microelectromechanical sensor unit is inserted. As a result, the sensor unit can be arranged in a protected manner in the sensor housing, but at the same time can interact with the environment of the ultrasonic sensor and can emit and receive ultrasonic signals with a long range from the sensor housing in a largely unaffected manner. If the sensor unit has a microelectromechanical sensor component and a membrane component interacting therewith, the membrane component can form a component of the sensor housing which is integrally formed with the housing base or mechanically connected to the housing base. The membrane component can be connected to the sensor component in a materially integral manner, for example by adhesive bonding. The housing base of the sensor housing can have a circular basic shape, for example, in order to enable the ultrasound sensor to be configured as space-saving and compact as possible. In addition, for example, a corresponding opening with a round geometry on a vehicle bumper can be produced more easily and can be more robust than an opening with a different, for example angular, geometry.The housing board may be a substantially rigid electrical circuit carrier, for example a printed circuit board (PCB). According to one embodiment, the housing board can have a driver unit which can have, for example, a circuit element such as a transformer element or an inductance and a driver circuit for driving the transformer element or the inductance. The driver unit can form a transmitting unit of the ultrasonic sensor, which is used to provide the required transmission energy for the ultrasonic signal to be transmitted by means of the microelectromechanical sensor unit. The housing printed circuit board can be arranged, for example, in or on the sensor housing. The housing printed circuit board is in particular spaced apart spatially from the sensor head printed circuit board, so that these are not electrically connectable or connected to one another by direct mutual contacting. In particular, the housing printed circuit board is at a greater distance from the microelectromechanical sensor unit than the sensor head printed circuit board.The signal processing unit can be understood as a control circuit which can be designed in particular as an integrated circuit, for example as an ASIC (application specific integrated circuit). The signal processing unit is configured to process signals of the microelectromechanical sensor unit and can serve for receiving and evaluating sensor signals of the sensor unit and can assume control tasks. The signal processing unit can be received by the base section of the sensor head board and can be mechanically or materially connected to the base section of the sensor head board and electrically connected thereto, for example by bonding wiring or soldering contacts.The sensor head board may form a second electrical circuit carrier of the ultrasonic sensor in addition to the housing board. Due to the integrally formed connecting section and the connection function between the circuit carriers implemented thereby, the sensor head board has an extension of function compared to comparable sensor head boards according to the prior art. The sensor head board furthermore serves to accommodate the signal processing unit and optionally further electrical components of the ultrasonic sensor and additionally enables an electrical and signal connection of the signal processing unit to the microelectromechanical sensor unit of the ultrasonic sensor. The sensor head board can be arranged in particular adjacent to the sensor unit or in the immediate vicinity thereof in the sensor housing and can be electrically connected to the sensor unit, for example, by means of bond wiring or solder contacts.According to the proposed features, the sensor head board has a base portion and a connecting portion formed integrally with the base portion. The base section can be a partial region of the sensor head printed circuit board, which can be arranged in particular on the housing base of the sensor housing. The base section can serve to accommodate the signal processing unit and, if appropriate, further electrical components of the ultrasonic sensor and produce an electrical connection between the signal processing unit and the microelectromechanical sensor unit. The base section can extend in particular substantially parallel to the housing base or can rest on the housing base in a surface-contacting manner. In a planar state of the sensor head printed circuit board, its greatest extent can define a longitudinal extent of the sensor head printed circuit board. The base section can have a greater width extension perpendicular to the longitudinal extension than the connecting section, wherein the width extension of the sensor head printed circuit board is greater than the depth extension of the sensor head printed circuit board.The connecting section can be shaped, for example, in the form of a strip or a beam, with a, for example, substantially rectangular base surface over the connecting section between the sensor head printed circuit board and the housing printed circuit board. The connecting section can have a greater length and width extension than a depth extension. The connecting portion can project from a side edge of the base portion and, in a mounted state of the sensor head printed circuit board in the sensor housing, depending on the embodiment, can be angled or bent or discharged from the base portion at a radius, for example substantially perpendicularly, with the formation of a C shape or with the formation of an S shape of the connecting portion. The connecting section can serve for the electrical connection between the sensor head board and the housing board and thus, for example, also for an electrical connection between a driver unit and the microelectromechanical sensor unit. For this purpose, the connecting section can have corresponding electrical connection structures, for example conductor tracks and circuit elements. Accordingly, the connecting portion can enable a structured electrical connection between the sensor head board and the housing board and can accordingly be distinguished from a simple electrical conductor.According to the proposed features, the connecting portion has a lower bending stiffness than the base portion. Accordingly, the connecting portion can be more easily elastically and / or plastically deformable under the action of force than the base portion. A lower bending stiffness of the connecting portion can be realized, for example, by its geometric configuration, for example by a strip-shaped, narrower design compared to the base portion, by means of a different internal structural structure or by a different material composition compared to the base portion. The lower bending stiffness of the connecting portion ensures that the connecting portion can be easily oriented in the sensor housing independently of the base portion and can be placed on the housing board for connection without the stability of the base portion and thus, for example, a connection quality between the base portion and the electrical components arranged thereon or between the base portion and the microelectromechanical sensor unit electrically connected thereto being impaired. Accordingly, each of the two sections of the sensor head board is optimally adapted to its intended function due to different bending stiffnesses and a resulting different flexibility. In this case, the construction and the production of the sensor head board can fundamentally be based on technologies and structures of flexible printed circuit boards, as will be explained in more detail below. Against this background, the sensor head printed circuit board can also be collectively described as a semi-rigid or semi-flexible sensor head printed circuit board.The flexibility of the connecting portion achieved by the lower bending stiffness of the connecting portion compared to the base portion can be provided in different degrees of flexibility depending on the embodiment.According to one embodiment, the connecting section can be designed as a predominantly flexurally slack connecting section. A predominantly flexurally slack connecting portion can be understood as a non-dimensionally stable connecting portion and can be described, for example, by a low modulus of elasticity. A connection section with low flexibility can already be subjected to large deformations as a result of low force and moment stresses. The flexurally slack connecting section can be described, for example, in a simplified manner as a flexible printed circuit board strip. A connection section with low bending flexibility can be associated with a very high level of flexibility, so that simple handling is made possible and the connection section can be connected to the housing printed circuit board easily and without appreciable mechanical tension.According to an alternative embodiment, the connecting section can be designed as a predominantly dimensionally stable connecting section. A predominantly dimensionally stable connecting section can have a higher bending stiffness or a higher modulus of elasticity than a flexurally slack connecting section. A dimensionally stable connecting section can undergo a deformation with a predominantly plastic deformation portion, for example, by bending and remain in the assumed shape without appreciable recovery. A dimensionally stable connecting section can be achieved, for example, by arranging a flexible element such as a copper element in the connecting section, wherein this also additionally enables advantageous electromagnetic shielding of the connecting section to be achieved. A dimensionally stable connecting section can additionally have a higher robustness than a flexurally slack connecting section on account of its dimensional stability.According to one embodiment, the sensor head board can have a layer arrangement of electrically conductive and electrically non-conductive layers. As a result, the mechanical and electrical properties of the sensor head printed circuit board can be specifically influenced by means of an individual layer arrangement and can be defined with a high degree of freedom of design. For example, the number and the layer thickness of the individual electrically conductive and / or electrically non-conductive layers may vary according to the desired mechanical and electrical properties of the sensor head board. For example, the sensor head printed circuit board can be mechanically reinforced by an increased number or layer thickness of an electrically non-conductive layer. An electrically conductive layer can comprise a metal, in particular copper, for example. The electrically conductive layer can be structured, for example form electrical conductor tracks in a carrier material. An electrically non-conductive layer can comprise a plastic material, in particular a polyimide, for example. The electrically non-conductive layer may form a carrier material, an electrical insulation and an oxidation protection for the electrically conductive layer or conductor track. The layers of the layer arrangement can be laminated to one another, for example. The layer arrangement may comprise a plurality of electrically conductive and / or a plurality of electrically non-conductive layers. According to one embodiment, the sensor head board can be designed as a flexible printed circuit board (flexible printed circuit). Flexible printed circuit boards are, for example, circuits based on polyimide film, on which electrically conductive structures and / or components are applied.According to one embodiment, the base section can have a layer arrangement differing from the connecting section. As a result, the mechanical and electrical properties of the sensor head printed circuit board can be configured locally differently by means of an individual layer arrangement. In particular, the connecting section can be provided with a lower bending stiffness by a layer arrangement deviating from the base section. For example, the sensor head printed circuit board can be mechanically reinforced in the base section by an increased number or layer thickness of an electrically non-conductive layer compared to the connecting section. Conversely, the sensor head board can be formed in the connecting section in a mechanically more flexible manner by a number or layer thickness of an electrically non-conductive layer which is reduced compared to the base section. In other words, it is possible to achieve a lower bending rigidity of the connection portion by an internal structural structure in the form of a different layer arrangement, which internal structural structure differs from the base portion. In principle, it is not excluded, alternatively or additionally, to reduce the bending stiffness in the region of the connecting section by using a differing material in at least one layer of the layer arrangement.According to one embodiment, the base section can have a hexagonal outer contour. In this way, a greater use of the surface area can be achieved compared to other geometric basic shapes, such as a rectangular outer contour. In particular in embodiments of the ultrasonic sensor with a sensor housing which has a housing base with a substantially circular basic shape, a base section having a hexagonal outer contour can be used to polygonally approach the outer contour to the available base surface of the housing base. At the same time, a sensor head printed circuit board having a hexagonal base section can be easily produced; in particular, in the case of a hexagonal outer contour of the base section, a multiplicity of sensor head printed circuit boards in the form of a printed circuit board panel having sensor head printed circuit boards arranged in a space-saving manner with respect to one another can be provided, and the sensor head printed circuit boards can be separated from the printed circuit board panel with little waste. Due to the additionally obtained usage surface, the signal processing unit and optionally further components of the ultrasonic sensor can be accommodated on the base section of the sensor head printed circuit board reliably and reliably while maintaining the technically necessary distances. In particular, due to the additional useful surface, it may be possible to accommodate an entire receiver stage of the ultrasonic sensor on the base section of the sensor head board, so that it is not necessary to arrange individual components on the housing board for space reasons. Due to the arrangement of the signal processing unit on the sensor head board, a distance between the microelectromechanical sensor unit and the signal processing unit can be significantly reduced compared to an arrangement of the signal processing unit on the housing board, as a result of which parasitic capacitances are reduced and the electromagnetic compatibility of the ultrasonic sensor on its reception path is optimized.According to one embodiment, the base section can have a centering contour for aligning the sensor head printed circuit board in the sensor housing. This ensures optimum arrangement of the sensor head printed circuit board even in the case of restricted installation space conditions in the sensor housing. In addition, the orientation of the sensor head mounting can be fixable in the sensor housing by means of the centering contour. The sensor housing, for example the housing base of the sensor housing, on which the base section is arranged or a side wall of the sensor housing, can have a corresponding mating contour for centering. For example, the centering contour can form a geometric negative shape of the mating contour or vice versa, so that the centering contour and the mating contour can engage in one another. The centering contour can be formed, for example, as an indentation and the counter contour can be formed correspondingly as a protrusion or vice versa. The centering contour can be formed, for example, partially circular, in particular semicircular. The base section can have a plurality of centering contours, for example two centering contours arranged opposite one another. If the base section has a hexagonal outer contour, the centering contour can be arranged, for example, at one corner point of the outer contour, or two centering contours can be arranged at mutually opposite corner points of the outer contour.According to one embodiment, the connecting section can have a widening in a connecting region of the connecting section provided for connection to the housing printed circuit board. In other words, the connecting portion can have a wide connection region and a narrow coupling region between the connection region and the base portion of the sensor head printed circuit board. In other words, the connection region can have a greater width than a coupling region of the connecting section running between the connection region and the sensor head printed circuit board. A widening or a width can relate in particular to an extension of the connecting portion transversely to its longest extension, which describes a length or longitudinal extension of the connecting portion. The width and the length can be substantially greater than the depth of the connection section, which is configured, for example, in a planar manner. The connecting section can widen, for example, into a wing-shaped connection region. By widening the connecting section in the connection region, an enlarged connection surface is provided for connecting the connecting section to the housing printed circuit board, as a result of which contacting can be simplified accordingly. In particular, in the case of a widened connection region, connection processes can also be used which could otherwise be technically ruled out on account of an excessively smaller contact point spacing, for example bracket soldering processes. This can significantly reduce the machine costs, the process time for establishing the electrical connection between the housing board and the sensor head board and, accordingly, the production costs of the ultrasonic sensor.According to one embodiment, the microelectromechanical sensor unit can be designed as a piezoelectric ultrasonic transducer. As a result, a robust and cost-effective sensor unit with a high measurement accuracy and a precisely focusable ultrasonic signal can be provided. Microelectromechanical piezoelectric ultrasonic transducers are also referred to as PMUT (piezoelectric micromachined ultrasonic transducers) and allow a good integration of the sensor unit into a small-sized ultrasonic sensor.The invention also relates to a method for producing an ultrasonic sensor having a microelectromechanical sensor unit, having the steps:providing a sensor housing, a microelectromechanical sensor unit, a housing printed circuit board and a sensor head printed circuit board with a signal processing unit;establishing a mechanical and electrical connection between the microelectromechanical sensor unit and the sensor head printed circuit board;arranging the sensor unit, the sensor head board, and the housing board in the sensor housing; andestablishing an electrical connection between the sensor head board and the housing board by means of a connecting portion which is embodied integrally with a base portion of the sensor head board and has a lower bending rigidity than the base portion, by connecting a connecting region of the connecting portion to the housing board.With the method according to the proposed features, efficient production of the ultrasonic sensor is possible. The ultrasonic sensor can be designed in particular according to one of the features described above. By establishing an electrical connection between the sensor head board and the housing board by means of a connecting section which is formed integrally with a base section of the sensor head board and has a lower bending stiffness than the base section, manufacturing steps can be saved compared to known methods for producing comparable ultrasonic sensors. The process time can be shortened by the reduced number and complexity of the method steps, so that the economics of the method are increased.According to an embodiment, the sensor head board may be provided by separating from a board panel including a plurality of sensor head boards. With a printed circuit board panel which has a multiplicity of sensor head printed circuit boards, the sensor head printed circuit board can be provided economically and cost-optimized, wherein the sensor head printed circuit board can be easily separated from a printed circuit board panel, for example by milling, laser beam cutting or punching. In the board panel, the sensor head boards may be provided such that the base portion and the connection portion are arranged flatly in a common plane. Thereby, a board panel including a plurality of sensor head boards can be easily manufactured. The printed circuit board panel can be produced, for example, by means of electrical and non-electrical layers laminated to one another in a manner analogous to the production of flexible printed circuit boards.According to one embodiment, before arranging the sensor head printed circuit board in the sensor housing, the connecting section of the sensor head printed circuit board can be bent from the base section, for example substantially perpendicularly or to form a C-shape or S-shape of the connecting section. This makes it possible to perform a prealignment of the connecting section in a simple manner and facilitates the arrangement of the sensor head printed circuit board in the sensor housing. Bending the connecting section before arranging the sensor head printed circuit board in the sensor housing is advantageous in particular if the connecting section is designed as a predominantly dimensionally stable connecting section, so that the bent orientation of the connecting section is maintained during the further method sequence. Depending on the shape of the sensor housing, further bendings, bendings or bendings can be produced at the connecting section before or during the arrangement of the connecting section in the sensor housing.Furthermore, it can be provided that before the sensor head printed circuit board is arranged in the sensor housing, a mechanical and electrical connection is established between the microelectromechanical sensor unit and the sensor head printed circuit board. For example, it is conceivable that before arranging the sensor head board in the sensor housing, the microelectromechanical sensor unit is connected to the sensor head board in a materially bonded manner and, for example, an electrical contact is produced between the sensor unit and the sensor head board by means of bonding wiring.According to one embodiment, the sensor head printed circuit board can be connected to a housing base of the sensor housing in a materially integral manner during the arrangement in the sensor housing. For this purpose, for example, after the establishment of the electrical connection between the sensor head printed circuit board and the sensor unit, an adhesive can be applied to the housing base and / or to the sensor head printed circuit board, the sensor head printed circuit board can be placed on the housing base and curing of the adhesive is made possible, in particular assisted by thermal treatment or UV radiation.After arranging the sensor head board in the sensor housing, the connecting section can be aligned in the sensor housing, so that a later connection of the housing board can be carried out quickly and easily. For example, the connecting section can be laid along a housing wall of the sensor housing, for example also bent or bent according to the housing contour. The provided housing printed circuit board can then be arranged in or on the sensor housing and fixed therein, for example by hot caulking. Subsequently, a connection region of the connecting portion can be prepared for connection to the housing printed circuit board, for example, by bending, and the connection can be carried out.According to one embodiment, the connection region of the connecting section to the housing printed circuit board can be connected by means of a bracket soldering process. This can significantly reduce the machine costs, the process time for establishing the electrical connection between the housing board and the sensor head board and, accordingly, the production costs of the ultrasonic sensor.In the context of this application, the words "a / an", unless expressly defined otherwise, are not to be understood as a numerical word, but rather as an indeterminate article having the word sense of "at least one / one".The invention permits various embodiments and is explained in more detail below on the basis of exemplary embodiments with the accompanying drawings. They show in schematic form: FIG. 1 shows an ultrasonic sensor according to an embodiment in a perspective sectional illustration; FIG. 2 shows a sensor head circuit board of the ultrasonic sensor, which circuit board is equipped with electronic components, in a bent state in a perspective front view; FIG. 3 shows an unequipped sensor head board for the ultrasonic sensor in a planar state in a plan view; FIG. 4 shows a circuit board panel with a plurality of unequipped sensor head boards in a plan view; and FIG. 5 is a simplified flow diagram of a method for producing an ultrasonic sensor.FIG. 1 shows a perspective sectional illustration of an ultrasonic sensor 1 with a microelectromechanical sensor unit 2. The ultrasonic sensor 1 can accordingly be configured, for example, for a signal transit time-based distance measurement to objects by emitting and receiving reflected ultrasonic signals. According to the exemplary embodiment shown in FIG. 1, the sensor unit 2 has two microelectromechanical sensor components 2 awhich cooperate with membrane components 2 bconnected to the sensor components 2 aand which can be designed, for example, in each case as combined transceivers in the sense of transceivers or of which a sensor component 2 ais designed as transmitter and a sensor component 2 ais designed as receiver. Microelectromechanical sensor components 2 ahave mechanical and electrical microstructures and interact with membrane components 2 bfor generating and / or detecting an ultrasonic signal. The membrane components 2 bmay be embedded in the housing base 14 or integrally connected thereto, for example, and each have a vibratory plastic membrane for ultrasonic-based interaction with the environment of the ultrasonic sensor 1.The ultrasonic sensor 1 has a sensor housing 3. The sensor unit 2 and a sensor head printed circuit board 6 are accommodated mechanically in the sensor housing 3 and are arranged so as to be protected from environmental influences. In addition, according to the exemplary embodiment shown, the housing printed circuit board 5 is likewise accommodated in the sensor housing 3. According to alternative exemplary embodiments, it is conceivable to arrange the housing printed circuit board 5 separately or outside the sensor housing 3. The sensor housing 3 has a housing base 14 which, according to the exemplary embodiment shown, has a circular basic shape. The sensor head printed circuit board 6 is arranged on the housing base 14. The sensor head board 6 is spaced apart from the housing board 5 by a distance A. The microelectromechanical sensor components 2 aand membrane components 2 bof the microelectromechanical sensor unit 2 are embedded in the housing base 14 and terminate there flush with an outer side of the housing base 14 facing the environment of the ultrasonic sensor 1.The housing board 5 can be a substantially rigid circuit carrier, for example a printed circuit board. According to the exemplary embodiment shown, the housing board 5 has a driver unit 4, which has, for example, a circuit element such as a transformer element or an inductance and a driver circuit for driving the transformer element in order to provide the required transmission energy for generating the ultrasonic signal by means of the microelectromechanical sensor unit 2. The circuit element can additionally serve for controlling the microelectromechanical sensor unit.A signal processing unit 7 for processing signals of the microelectromechanical sensor unit 2 is arranged on the sensor head printed circuit board 6. The signal processing unit 7 forms a control circuit of the ultrasonic sensor 1, which control circuit is embodied as an ASIC, for example, and can serve, among other things, for receiving and evaluating sensor signals of the sensor unit 2.As can be seen in FIG. 1 and additionally in FIGS. 2 and 3, the sensor head printed circuit board 6 has a base section 8 for receiving the signal processing unit 7 and a connecting section 9 which is embodied integrally with the base section 8 for electrically connecting the sensor head printed circuit board 6 to the housing printed circuit board 5. The distance A between the sensor head printed circuit board 6 and the housing printed circuit board 5 is bridged by the connecting section 9, and an electrical connection is established between the two said circuit carriers. As can be seen in FIG. 1, the signal processing unit 7 is arranged on the base section 8 of the sensor head board 6 and is electrically connected thereto, for example by a bonding wiring, which is not illustrated in any more detail. The base section 8 extends substantially parallel to the housing base 14, while the connecting section 9 extends substantially perpendicular to the housing base 14. The connecting portion 9 is substantially strip-shaped and, according to the exemplary embodiment shown, protrudes substantially perpendicularly from a side edge of the base portion 8.The connecting portion 9 of the sensor head board 6 has a lower bending rigidity than the base portion 8. According to the illustration shown in FIGS. 1 and 2, the connecting section 9 of the exemplary embodiment is designed as a predominantly dimensionally stable connecting section 9. Thus, the connecting portion 9 can be deformed elastically and / or plastically more easily than the base portion 8, but experiences only a slight or not appreciable recovery from its deformation in the absence of the deforming force. The lower bending stiffness is already achieved geometrically, as can be seen for example with reference to FIG. 2, by a smaller depth and width dimension of the connecting section 9 compared to the base section 8, in addition the base section 8 can have for example a layer arrangement with a higher layer thickness or a higher number of layers of non-electrically conductive layers or a different material composition than the connecting section 9.An ultrasonic sensor 1 according to the exemplary embodiment shown has a smaller number of components and a reduced component complexity, in particular compared to ultrasonic sensors with separate electrical connection means between the sensor head printed circuit board 6 and the housing printed circuit board 5. The ultrasonic sensor 1 can be manufactured in a simple and economical manner. The handling of the components of the ultrasonic sensor 1 during assembly is facilitated in particular in view of the limited installation space available. In addition, the quality of the electrical connection between the sensor head board 6 and the housing board 5 is improved.FIG. 2 shows the above-described sensor head board 6 of the ultrasonic sensor 1 in a bent state in a front perspective view in which the connection portion 9 is bent from the base portion 8. In FIG. 3, the sensor head board 6 is illustrated in a planar state in which the connection portion 9 and the base portion 8 extend in a common plane. The sensor head board 6 shown in FIG. 3 may represent an initial state of the bent sensor head board 6 shown in FIG. 2.As can be seen in FIGS. 2 and 3, the base section 8 according to the exemplary embodiment shown has a hexagonal outer contour 10. In this way, for example, a greater use of area can be achieved compared to a rectangular outer contour 10, in particular when using a sensor housing 3 with a housing base 14 having a circular basic shape. The additionally obtained use area can advantageously enable or ensure an arrangement of the signal processing unit 7 on the sensor head printed circuit board 6. This makes it unnecessary to accommodate the signal processing unit 7 on the package board 5, so that parasitic capacitances otherwise resulting from the distance A between the sensor head board 6 and the package board 5 can be reduced and the electromagnetic compatibility of the ultrasonic sensor 1 on the reception path can be optimized.Furthermore, it can be seen from FIGS. 2 and 3 that the base section 8 has two semicircular centering contours 8 at mutually opposite corner points of the hexagonal outer contour 10, by means of which the base section 8 can be aligned on the sensor housing 3, which has two counter-contours, not shown in more detail, for engagement in the centering contours 8. The centering contours 11 are embodied as indentations in the present case.FIGS. 2 and 3 additionally show that, according to the illustrated exemplary embodiment, the connecting portion 9 has a widening in a connecting region 12 of the connecting portion 9 provided for connection to the housing printed circuit board 5. As can be seen in FIG. 3, a width b 2 of the connection region 12 is greater than a width b 1 of the remaining connecting section 9 forming a coupling region 15. By widening the connecting section 9 in its connection region 12, a larger connection surface can be provided, so that the contacting of the housing printed circuit board 5 in the connection region 12 is facilitated and economical contacting methods such as, for example, bracket soldering processes can be used.FIG. 4 shows a circuit board panel 13 having a plurality of sensor head boards 6 in a plan view. The sensor head board 6 shown in FIG. 3 can be separated from such a board panel 13, for example, in order to be ready for production of the ultrasonic sensor 1. As can be clearly understood on the circuit board panel 13, the sensor head boards 6 according to the described exemplary embodiments can be arranged next to one another in a space-saving manner, inter alia on account of their hexagonal outer contours 10 and the narrower connecting sections 9, and can be released from the circuit board panel 13 with little waste.FIG. 5 shows a simplified flow diagram of a method 100 for producing an ultrasonic sensor 1 having a microelectromechanical sensor unit 2. according to a first step 110 or first sub-process of the method 100, a sensor housing 3, a microelectromechanical sensor unit 2, a housing printed circuit board 5 and a sensor head printed circuit board 6 are provided with a signal processing unit 7. According to a second step 120 or second sub-process, a mechanical and electrical connection is established between the electromechanical sensor unit 2 and the sensor head printed circuit board 6. According to a third step 130 or third sub-process, the sensor unit 2, the sensor head printed circuit board 6 and the housing printed circuit board 5 are arranged in the sensor housing 3. In a fourth step 140 or fourth sub-process, an electrical connection is established between the sensor head board 6 and the housing board 5 by means of a connection section 9 which is embodied integrally with a base section 8 of the sensor head board 6 and has a lower bending stiffness than the base section 8. For producing the electrical connection, a connection region 12 of the connection section 9 is connected to the housing printed circuit board 5.References included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedDE 10 2020 211 538 A1

[0003] DE 10 2018 105 502 A1

[0004]

Claims

Ultrasonic sensor (1) having a microelectromechanical sensor unit (2) for generating and detecting an ultrasonic signal, a housing printed circuit board (5), a sensor housing (3) for receiving the sensor unit (2), and a sensor head printed circuit board (6) which is arranged in the sensor housing (3) and is spaced apart from the housing printed circuit board (5) and has a signal processing unit (7) for processing signals of the microelectromechanical sensor unit (2), wherein the sensor head printed circuit board (6) has a base section (8) for receiving the signal processing unit (7) and a connecting section (9), which is embodied integrally with the base section (8), for electrically connecting the sensor head printed circuit board (6) to the housing printed circuit board (5), and wherein the connecting section (9) has a lower flexural rigidity than the base section (8).Ultrasonic sensor (1) according to Claim 1, wherein the connecting section (9) is designed as a predominantly flexurally slack connecting section (9).Ultrasonic sensor (1) according to claim 1, wherein the connecting section (9) is designed as a predominantly dimensionally stable connecting section (9).Ultrasonic sensor (1) according to one of the preceding claims, wherein the sensor head board (6) has a layer arrangement of electrically conductive and electrically non-conductive layers.Ultrasonic sensor (1) according to claim 4, wherein the base section (8) has a layer arrangement differing from the connecting section (9).Ultrasonic sensor (1) according to one of the preceding claims, wherein the base section (8) has a hexagonal outer contour (10).Ultrasonic sensor (1) according to one of the preceding claims, wherein the base section (8) has a centering contour (11) for aligning the sensor head printed circuit board (6) in the sensor housing (3).Ultrasonic sensor (1) according to one of the preceding claims, wherein the connecting section (9) has a widening in a connecting region (12) of the connecting section (9) provided for connection to the housing printed circuit board (5).Ultrasonic sensor (1) according to one of the preceding claims, wherein the microelectromechanical sensor unit (2) is designed as a piezoelectric ultrasonic transducer.Method (100) for producing an ultrasonic sensor (1) with a microelectromechanical sensor unit (2), comprising the steps: - providing a sensor housing (3), a microelectromechanical sensor unit (2), a housing printed circuit board (5) and a sensor head printed circuit board (6) with a signal processing unit (7) (110); - producing a mechanical and electrical connection between the microelectromechanical sensor unit (2) and the sensor head printed circuit board (6) (120); - arranging the sensor unit (2), the sensor head printed circuit board (6) and the housing printed circuit board (5) in the sensor housing (3) (130); and - establishing an electrical connection between the sensor head printed circuit board (6) and the housing printed circuit board (5) by means of a connection section (9) which is embodied integrally with a base section (8) of the sensor head printed circuit board (6) and has a lower bending rigidity than the base section (8), by bonding a connection region (12) of the connection section (9) to the housing printed circuit board (5) (140).Method according to Claim 10, wherein the ultrasonic sensor (1) is designed according to one of Claims 1 to 9.The method according to claim 10 or 11, wherein the sensor head board (6) is provided by separating it from a board panel (13) comprising a plurality of sensor head boards (6).Method according to one of Claims 10 to 12, wherein, before the sensor head printed circuit board (6) is arranged in the sensor housing (3), the connecting section (9) of the sensor head printed circuit board (6) is bent from the base section (8) substantially perpendicularly or with the formation of a C-shape or S-shape of the connecting section (9).Method according to one of Claims 10 to 13, wherein the sensor head printed circuit board (6) is connected to a housing base (14) of the sensor housing (3) in a materially integral manner during the arrangement in the sensor housing (3).Method according to one of Claims 10 to 14, wherein the connection region (12) of the connecting section (9) is connected to the housing printed circuit board (5) by means of a bracket soldering process.

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