Method for mounting a sensor element

Abstract

Method for mounting a sensor element (2) on a metallic mounting surface (4) of a force-bearing component (3), wherein the sensor element (2) has a base plate (5) made of a metallic material and a sensor chip (6) arranged on a surface of the base plate (5) for detecting mechanical strains in the component (3), wherein: - the component (3) is provided with the mounting surface (4); - the sensor element (2) is positioned on the mounting surface (4) via an applied solder medium (8);- the soldering medium (8) is melted by means of heat input in order to produce a soft solder joint (12) between the mounting surface (4) and the base plate (5), wherein the soft solder joint (12) is designed to transmit mechanical strains from the component (3) to the sensor element (2), characterized in that, prior to the application of the soldering medium (8), an outflow limit (15) for the soldering medium (8) surrounding a soldering area (9) is created on the mounting surface (4), wherein the outflow limit is formed by a depression surrounding the soldering area created by means of a laser.

Description

[0001] The invention relates to a method for mounting a sensor element with the features of the preamble of claim 1. The invention further relates to a sensor arrangement with the sensor element.

[0002] Sensor systems are known that can detect mechanical forces, e.g., torque, acting on a specific component in a mechanical system. Various sensor types are known for this purpose, such as strain gauges, which can be arranged at the relevant points on the component using a mounting material with low shear strength, such as epoxy or adhesive, whereby the mechanical force is transmitted to the sensor via the flexible mounting material.

[0003] For example, US patent 2020 319 038 A1 discloses a system comprising an element for receiving a mechanical force and a sensor for detecting the mechanical force, wherein the sensor is attached to the element using a set of nanoparticles and a set of nanowires connected to the set of nanoparticles. The sensor is configured as a torque sensor.

[0004] It is an object of the invention to propose a method for mounting a sensor element on a machine component, which is characterized by a reliable transmission of the mechanical strains to the sensor element.

[0005] This problem is solved by a method having the features of claim 1 and by a sensor arrangement having the features of claim 10. Preferred or advantageous embodiments of the invention will become apparent from the dependent claims, the following description, and the accompanying figures.

[0006] The invention relates to a method for mounting a sensor element on a metallic surface of a force-bearing component. In principle, the component can be designed as a component subjected to compression and / or tension. Preferably, however, the component is designed as a component subjected to torsion. The component can be static or movable, in particular rotating. Specifically, the component is designed as a shaft. It is particularly preferred that the component be made of a metallic material, such as steel.

[0007] The sensor element comprises a preferably solderable base plate and a sensor chip arranged on a surface of the base plate, which is designed and / or suitable for detecting mechanical strains in the machine component. In particular, the sensor chip serves to detect a torque acting on the component. For this purpose, the base plate is connected to the sensor chip in a force-transmitting manner. Specifically, the sensor chip detects strains in at least two linearly independent directions. For this purpose, the sensor chip can have at least or exactly two sensor tracks, preferably arranged at 90° to each other, which output an evaluable sensor signal under load.

[0008] According to the invention, the method is characterized by the following process steps: - Providing a machine component with a mounting surface; - Positioning the sensor element with the base plate on the mounting surface using a plumb line; - Melting the soldering medium by means of heat input to create a soft solder joint between the mounting surface and the base plate, wherein the soft solder joint is designed to transfer mechanical strains from the machine component to the sensor element, in particular to the base plate.

[0009] The soldering compound can be applied to the mounting surface and / or the base plate, particularly to a surface of the base plate facing away from the sensor chip. In other words, the soldering compound is positioned between the mounting surface and the base plate. Preferably, the mounting surface is a flat surface. Alternatively, however, the mounting surface can also have a different shape, e.g., a curved shape. In principle, the sensor element can be held in a desired position during the mounting or soldering process by the adhesive effect of the soldering compound. Optionally, however, a positioning aid can be provided to ensure correct positioning of the sensor element during the mounting or soldering process. Preferably, the soldering compound is melted by the application of heat in a soft soldering process.In particular, a soft soldering process within the meaning of the application is to be understood as a thermal process in which the working temperature does not exceed 260 °C. As it melts, the soldering medium wets the two joining parts (mounting surface / base plate), thus creating a metallurgical bond.

[0010] The invention is based on the idea of ​​applying an electronic sensor chip for torque measurement directly to a metallic surface (especially steel) of a load-bearing component, e.g., a shaft. For this purpose, a secure mechanical connection must be ensured. At the same time, this connection must be designed to withstand typical automotive requirements (temperature range: -40°C to 150°C, service life: 15 years, etc.) and to transfer the mechanical stresses from the component to the base plate on the underside of the sensor chip with as little loss and as uniformly as possible.

[0011] The soft solder joint thus proposes a secure mechanical connection of the sensor element, characterized by a uniform transfer of mechanical strain from the component to the sensor element. Furthermore, the soft solder joint offers a thermally resistant connection, particularly within a temperature range of -40°C to 150°C, making it suitable for applications in the automotive sector, for example. The soft solder joint also ensures complete wetting (free of voids) and therefore a robust connection between the mounting surface and the surface of the base plate. A further advantage is that the soft solder joint provides a connection between the sensor element and the component that is characterized by long-lasting durability and minimal change compared to polymers, such as adhesives, under temperature fluctuations.

[0012] In a specific training course, it is planned that a flow control barrier for the soldering compound is created on the mounting surface before application, defining the soldering area. This flow control barrier acts as a mechanical barrier for the soldering compound, particularly during melting. In principle, the flow control barrier can be created by removing and / or adding material to the mounting surface. In other words, the flow control barrier can be formed by a depression and / or raised area surrounding the soldering area. For example, the flow control barrier can be created through a mechanical or chemical surface treatment. Specifically, the soldering area is defined as the area of ​​the mounting surface where the soldering compound is applied and / or has already been applied.Preferably, the outflow limiter is completely enclosed, preventing the solder from escaping the soldering area, particularly during melting. The outflow limiter can preferably have a similar or identical geometric shape to the sensor element, especially the base plate.

[0013] Alternatively or optionally, the soldering area extends congruently and / or overlapping with a base surface of the base plate. For example, the outflow limiter or the base plate has a rectangular or square footprint. The outflow limiter ensures that the sensor element does not become disturbed during the soldering process. This eliminates the need for additional positioning aids during soldering. A further advantage is that the outflow limiter ensures a precisely uniform solder layer thickness between the mounting surface and the base plate, significantly improving the quality of the solder joint.

[0014] In a preferred embodiment, the outflow limit is created using a laser. Specifically, the mounting surface is treated with a laser beam to create the outflow limit. Preferably, the laser beam energy is adjusted so that the outflow limit is created by minimal material removal, thus altering the wetting behavior and preventing the solder from flowing beyond the limit. This method is characterized by particularly precise and customizable creation of the outflow limit.

[0015] In a first concrete embodiment, the soldering process is carried out by induction soldering. Specifically, the solder is melted by inductive heating using an inductor. The inductor's function is to heat the mounting surface, particularly the soldering area, to a suitable temperature, e.g., 250 °C, for the soldering process by utilizing the electromagnetic induction effect. For this purpose, the inductor is designed as an induction coil, particularly one surrounding the component, which is electrically connected to a current generator to supply the coil with alternating current. By appropriately shaping and / or arranging the inductor, the mounting surface, especially the soldering area, can be heated precisely. Optionally, the temperature in the soldering area can be monitored, and the inductor or the current generator can be controlled and regulated.Alternatively or optionally, monitoring of the heating process for quality assurance purposes is possible, e.g., by means of power control, current monitoring, or similar methods. Optionally, the inductor can be equipped with water cooling. Thus, a heating method is proposed that enables targeted, localized heating of solid metallic components, such as steel shafts, to the temperature required for soft soldering, while the remaining part is exposed to only a slight or no temperature increase. Furthermore, a method is proposed that is suitable for industrial production with short cycle times.

[0016] In an alternative embodiment, the solder is melted by vapor phase soldering, also known as condensation soldering or vapor phase reflow. Specifically, the solder is melted by heating it with saturated vapor, preferably in a vapor phase furnace. For this purpose, the saturated vapor is applied to the solder, and when it condenses on the surface of the solder, energy is released in the form of heat, melting the solder. The saturated vapor phase is generated by a liquid whose boiling point determines the operating temperature of the soldering process. In particular, the liquid has a boiling point in the range of 150 °C to 300 °C, specifically, for example, between 200 °C and 250 °C. The liquid can, for example, be a liquid polymer.Specifically, vapor phase soldering can also refer to vacuum vapor phase soldering, in which a vacuum is created after the solder has completely melted to prevent gaseous inclusions in the solder joints. This proposes a thermally gentle heating method that significantly reduces the risk of damage to the thermally sensitive sensor chip. Furthermore, no additional temperature monitoring is necessary, as the vapor phase temperature is never exceeded.

[0017] In a further embodiment, the sensor element is automatically positioned using a gripper of a pick-and-place machine. Specifically, after the application of the soldering compound, the sensor element is positioned correctly relative to the mounting surface, particularly the soldering area, by means of the gripper and / or held in place during the soldering process.

[0018] In a further specification, it is stipulated that the soldering compound is in the form of a soft solder paste. Specifically, the soft solder paste is a pasty mixture comprising essentially a soft solder powder and a flux. Using a soft solder paste allows for the simple provision of a reproducible quantity and / or form of the soldering compound.

[0019] In a further training program, the soldering compound is to be applied automatically to the mounting surface, particularly in the soldering area, and / or the base plate. Specifically, the soft solder paste is applied automatically using a dispenser or stencil printing. Alternatively, the soldering compound can also be provided as a soft solder preform, particularly made of a solid solder material, which is positioned automatically using a gripper of a pick-and-place machine.

[0020] In another implementation, the base plate is made of a metallic material. This metallic material could be, for example, a metal alloy such as copper, aluminum, or steel. This proposes a sensor element characterized by a solderable base plate.

[0021] A further aspect of the invention comprises a sensor arrangement with a force-guiding component and at least one sensor element, as previously described, wherein the sensor element is mounted on the mounting surface with its base plate via a soft solder joint. Preferably, the soft solder joint is produced by a method as previously described or according to any one of claims 1 to 9. The sensor arrangement can, for example, be suitable and / or configured for an electric powertrain of a vehicle, preferably a hybrid or electric vehicle. For this purpose, the force-guiding component is preferably configured as a shaft, e.g., a drive or output shaft. For example, the electric powertrain can be configured as a traction drive, e-drive, or e-axle. Alternatively, the sensor arrangement can also be used for other applications, such as roll stabilizers, pedelecs, wind turbines, etc., designed and / or suitable. The sensor arrangement can comprise several of the sensor elements, wherein the sensor elements are spaced apart from each other on the component in the circumferential direction and / or in the axial direction with respect to a component axis, in particular an axis of rotation.

[0022] Further features, advantages, and effects of the invention will become apparent from the following description of preferred embodiments of the invention. These include: Fig. 1 a schematic representation of a sensor arrangement with an inductor as a first embodiment of the invention; Fig. 2 a schematic representation of the sensor arrangement with a vapor phase furnace as a further embodiment of the invention; Fig. 3 a schematic top view of a force-bearing component of the sensor arrangement according to the Fig. 1 and Fig. 2.

[0023] In the Fig. 1 and Fig. 2 is described in each case with reference to a schematic representation of a sensor arrangement 1 a method for mounting a sensor element 2 on a force-bearing component 3.

[0024] Component 3 can be designed as a static or movable machine component, which is, for example, subjected to a torque. The sensor arrangement 1 can, for example, be arranged in an electric powertrain of a vehicle (not shown), where component 3 is formed by a shaft, e.g., a rotor shaft.

[0025] Component 3 defines a component axis 100, e.g., a rotation axis, wherein component 3 has a flat mounting surface 4 on its radial outer side with respect to component axis 100. Component 3 is, for example, cylindrical, with the mounting surface 4 formed by a flattened area.

[0026] The sensor element 2 has a flat base plate 5 and a sensor chip 6 arranged on it. The base plate 5 is made of a metallic material, e.g., copper. The sensor chip 6 serves to detect mechanical strains in the component 3, whereby the sensor chip 6 is connected to the component 3 via the base plate 5 in a force-transmitting manner.

[0027] For this purpose, a soldering compound 8 is applied either to the mounting surface 4 or to a base surface 7 of the base plate 5 facing away from the sensor chip 6, whereby the sensor element 2 is then positioned correctly relative to the mounting surface 4. For example, the application of the soldering compound 8 and / or the positioning of the sensor element 2 can be automated, e.g., using a suitable machine. The soldering compound 8 is, for example, a printable soft solder paste, which is printed onto the mounting surface 4 in a soldering area 9, e.g., using a stencil.

[0028] In a further process step, the soldering medium 8 is soft-soldered by means of inductive heating, as in Fig. As shown in Figure 1, the soldering material 8 is melted. For this purpose, an inductor 10 and a current generator 11 are provided, which are designed to selectively heat the mounting surface 4, in particular the soldering area 9, by utilizing the electromagnetic induction effect. The inductor 10 is, for example, designed as an induction coil which is supplied with an alternating current by the current generator 11. The inductor 10 is arranged opposite the mounting surface 4, in particular near the soldering area 9, so that an induction field limited to the soldering area 9 to be heated is generated, whereby the eddy currents generated thereby selectively heat the mounting surface 4 at least in the soldering area 9 and melt the soldering material 8. In this way, the mounting surface 4 and the base surface 7 are wetted with the soldering material 8, so that a metallurgical soft solder joint 12 is created.

[0029] This allows for the local heating of large, solid metallic components, such as a steel shaft, to the required soldering temperature (approx. 250 °C) within a very short time (a few seconds), while the rest of the surrounding component remains at room temperature. Suitable parameter settings are necessary to avoid damaging the thermally sensitive sensor chip 6 while still achieving the minimum temperature gradients for optimal wetting. Furthermore, monitoring of the heating process for quality assurance (power control, current monitoring) is possible. Thus, a method is proposed that is characterized by great potential for industrialized production with short cycle times.

[0030] In an alternative process step, the soldering medium 8 is soft-soldered by heating in a vapor phase furnace 13 instead of by induction soldering, as in Fig. As shown in Figure 2, the entire component 3 is melted. For this purpose, the entire component 3 is placed inside a steam chamber 14, into which steam is introduced. The steam condenses on the surfaces and heats the entire assembly via the released heat of condensation, thus melting the solder 8. A liquid, e.g., perfluoropolyether, is used for this purpose, the boiling point of which is matched to the required soldering temperature, for example, between 140 °C and 290 °C.

[0031] A common method is thus proposed, which is already suitable for soldering electrical chips onto printed circuit boards and can be easily adapted for directly soldering the sensor element 2 onto the metallic component 2. Furthermore, it enables thermally gentle heating of the sensor chip, which does not require an additional temperature monitoring process, as the vapor phase temperature is not exceeded. Due to this characteristic, the vapor phase soldering process is reliably reproducible and ideally controllable.

[0032] Fig.Figure 3 shows component 3 in a radial top view of the mounting surface 4 as a further embodiment of the invention. The mounting surface 4 has an outflow limiter 15 surrounding the soldering area 9, which serves to prevent the sensor element 2 from becoming disturbed during the soldering process and to delimit the soldering area 9 to be wetted. The outflow limiter 15 is generated by a laser before the soldering medium 8 is applied, whereby the mounting surface 4 is processed by the laser in such a way that the wetting behavior in the area of ​​the outflow limiter 15 changes in order to prevent the soldering medium from flowing beyond the outflow limiter 15. This mechanically retains the molten soldering medium 8 or keeps it within the soldering area 9. The outflow limiter 15 can have a rectangular shape, which essentially corresponds to the shape of the base plate 5.

[0033] The outflow limitation eliminates the need for additional positioning aids, such as those required during soldering in a vapor phase oven or during inductive heating. Furthermore, a precisely uniform solder layer thickness is achieved, resulting in improved quality of the soft solder joint 12. The soft solder joint 12 thus creates a connection between mounting surface 4 and base surface 7, which, due to its mechanical strength and continuous wetting (free of voids), is particularly suitable for transmitting mechanical expansion. Moreover, the soft solder joint 12 ensures long-term durability and minimal changes due to temperature fluctuations compared to, for example, adhesive bonds. Reference symbol list 1 Sensor arrangement 2 Sensor element 3 components 4 Mounting surface 5 Base plate 6 Sensor chip 7 Base area 8 Soldering materials 9 Soldering area 10 Inductor 11 Power generator 12 Soft solder joint 13 Steam phase furnace 14 Steam chamber 15 Outflow limitation 100 component axis QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] US 2020319038 A1

[0003]

Claims

[1] Method for mounting a sensor element (2) on a metallic mounting surface (4) of a force-bearing component (3), wherein the sensor element (2) has a base plate (5) and a sensor chip (6) arranged on a surface of the base plate (5) for detecting mechanical strains in the component (3), wherein: - the component (3) is provided with the mounting surface (4); - the sensor element (2) is positioned on the mounting surface (4) via an applied solder medium (8); - the solder medium (8) is melted by means of heat input in order to create a soft solder joint (12) between the mounting surface (4) and the base plate (5), wherein the soft solder joint (12) is designed to transfer mechanical strains from the component (3) to the sensor element (2). [2] Method according to claim 1, characterized by, that before the application of the solder medium (8) an outflow limit (15) surrounding a soldering area (9) is created on the mounting surface (4). [3] Method according to claim 2, characterized by , that the outflow limitation (15) is created by means of a laser. [4] Method according to any one of the preceding claims, characterized by , that the solder medium (8) is melted by means of induction soldering. [5] Method according to any one of claims 1 to 3, characterized by , that the soldering medium (8) is melted by means of vapor phase soldering. [6] Method according to any one of the preceding claims, characterized by , that the sensor element (2) is automatically positioned by means of a gripper of a pick-and-place machine. [7] Method according to any one of the preceding claims, characterized by , that the soldering medium (8) is formed as a soft solder paste. [8] Method according to claim 7, characterized by, that the soft solder paste is automatically applied to the mounting surface (4), in particular to the soldering area (9), and / or a base surface (7) of the base plate (5). [9] Method according to any one of the preceding claims, characterized by , that the base plate (5) is made of a metallic material. [10] Sensor arrangement (1) with a force-bearing component (3), wherein the component (3) has at least one metallic mounting surface (4), and with at least one sensor element (2), wherein the sensor element (2) has a base plate (5) and a sensor chip (6) arranged on a surface of the base plate (5) for detecting mechanical strain in the component (3), wherein the sensor element (2) with its base plate (5) is mounted on the mounting surface (4) via a soft solder joint (12).

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