Connection of a sensor assembly mounted on a mounting plate to a measuring object

Abstract

Method for connecting a sensor arrangement (5) mounted on a mounting plate (17) with a measuring object (2), the method comprising the steps (100) Provide - of a measured object (2), - a sensor arrangement (5) comprising a strain gauge (1) which is at least configured to detect tensile and compressive deformations of a measurement object (2), and an associated electronic module (19), - the mounting plate (17), - a first connecting foil (10a) and at least one second connecting foil (10b), each containing metallic materials (11, 12) which react exothermically when activated, (200) Place the first connecting foil (10a) between the mounting plate (17) and the object being measured (2), (300) Activating the metallic materials (11, 12) of the first connecting foil (10a) so that the first connecting foil (10a) heats up in such a way that a metallurgical bond is created between the mounting plate (17) and the object being measured (2), (400) Placing the second connecting foil (10b) between the mounting plate (17) and the strain gauge (1) or the electronic module (19), and (500) Activating the metallic materials (11, 12) of the second connecting foil (10b) so that the second connecting foil (10b) heats up in such a way that a metallurgical bond is created between the strain gauge (1) or the electronic module (19) and the mounting plate (17).

Description

[0001] The invention relates to a connection of a strain gauge to a measurement object. In this context, it particularly relates to a method for attaching the strain gauge to the measurement object and an arrangement of the strain gauge on the measurement object.

[0002] For various applications, it is necessary to attach a strain gauge to a larger mechanical component, the measurement object. This is important for the placement of the sensor system and for connecting the physical signals to be measured. Strain gauges are measuring devices for detecting stretching and compressive deformations. They change their electrical resistance even at small deformations and are used as sensors for strain measurement.

[0003] Sensors for force or deformation measurement are highly dependent on the bonding or adhesive layer between the strain gauge and the measurement object. The measurement object can be made of various materials such as metal, silicon, or an organic material. The bonding layer must provide strong adhesion and be dimensionally stable to ensure good force and deformation transmission without (additional and unpredictable) damping or time delays. Sensor performance over its lifetime depends on the long-term stability of the bonding layer, particularly its temperature / humidity / chemical stability to avoid signal drift, signal amplitude shrinkage, and time delays.

[0004] Adhesive bonding is a well-known method for bonding strain gauges to a larger measurement object. The bonding layer is therefore an adhesive layer. This is relatively easy to implement for industrial production, but usually requires a manual process that is time-consuming and not cost-effective. Adhesive bonds are associated with varying temperature gradients, humidity / chemical dependence, and long-term aging. This can reduce signal quality or even destroy the sensor. Other bonding techniques are impractical due to process parameters involving high temperatures, mechanical pressure, or high vacuum or inert gas. Other methods require strong electromagnetic fields. "Impractical" in this context means that it could destroy the strain gauge or the measurement object.

[0005] DE 10 2013 002 144 A1 discloses a joining method for thermally sensitive structures, wherein two components are functionally connected using a joining aid designed as a reactive nanofoil, in that the nanofoil is first introduced between associated surface sections of the components to be joined together and subsequently causes an at least partial formation of a connecting structure, characterized in that by activating the nanofoil, a largely solid solder connecting layer is first melted on both mutually associated surface sections of the components to be joined together, and that subsequently the melting material, which is locally limited to one surface section, is mixed with the likewise locally limited melting material of the opposite surface section and the residues of the reactants of the nanoreactive film system in such a way thatthat after cooling and solidification of the entire melt, a functional brazing joint is formed, whereby the thermal load required for melting is introduced only within the contour sections of the contacts to be joined and exclusively on the brazing connection layers of the brazing layer system.

[0006] WO 2016 / 199286 A1 discloses a strain sensing system comprising a semiconductor element for strain detection, a substrate for strain transmission to the semiconductor element, and a connecting material for connecting the semiconductor element to the strain transmission substrate. Furthermore, the strain sensing system comprises a strain measuring unit in which the semiconductor element, the connecting material, and the strain transmission substrate are sealed by a first sealing material. The strain measuring unit and a circuit substrate connected to the strain measuring unit are sealed by a second sealing material.

[0007] EP 3 839 460 A1 discloses a sensor system comprising a structural interconnect layer and a sensor. The structural interconnect layer is arranged on a structure. The structural interconnect layer is a metallic alloy. The sensor comprises a non-metallic wafer and a sensor interconnect layer arranged on a surface of the non-metallic wafer. The sensor interconnect layer is a metallic alloy. The sensor interconnect layer is coupled to the structural interconnect layer by means of a metallic interconnect. The sensor is configured to acquire data from the structure through the metallic interconnect, the structural interconnect layer, and the sensor interconnect layer.

[0008] A strain gauge is known from EP 2 796 830 B1. The strain gauge comprises a semiconductor chip having a plurality of piezoresistive elements formed on a front surface of a semiconductor substrate, a connecting line unit electrically connected to a plurality of electrodes of the semiconductor chip, and a plate component connected to a rear surface of the semiconductor chip.

[0009] The object of the present invention is to propose a novel connection between a strain gauge and a measurement object that addresses the problems described above and makes strain gauges usable for automotive applications. This object is achieved by the subject matter of independent patent claim 1. Advantageous embodiments are the subject matter of the dependent claims, the following description, and the figures.

[0010] A method according to the invention for connecting a sensor arrangement arranged on a mounting plate to a measurement object comprises the steps (100) Provide - a measuring object, - a sensor arrangement comprising a strain gauge which is at least designed to detect stretching and compressive deformations of a measurement object, and an electronic module connected thereto, - the mounting plate, - a first connecting foil and at least one second connecting foil, each containing metallic materials which react exothermically when activated, (200) Placing the first connecting foil between the mounting plate and the measuring object, (300) activating the metallic materials of the first connecting foil so that the first connecting foil heats up in such a way that a material connection is created between the mounting plate and the measuring object, (400) Placing the second connecting foil between the mounting plate and the strain gauge or the electronic module, and (500) Activating the metallic materials of the second connecting foil so that the second connecting foil heats up such that a material connection is created between the strain gauge or the electronic module and the mounting plate.

[0011] The present invention proposes a reactive foil soldering process for obtaining a particularly intermetallic bond for strain gauges on a larger measurement object, also called a target. The joining process is based on the use of a reactive multilayer foil as a local heat source. The bonding foil consists of a new class of nanotechnological material in which self-propagating exothermic reactions can be triggered at room temperature by an ignition process. By inserting such a foil between the mounting plate and the measurement object, the heat generated by the reaction in the foil melts, for example, solder layers or other reactive layers, so that the connections are completed in approximately one second at room temperature. The heat induced during the reaction is very low due to the fast reaction rate (e.g., 10 m / s) and the low material thickness (e.g., <100 µm).

[0012] In this sense, according to a first aspect of the invention, a method for connecting a sensor arrangement arranged on a mounting plate to a measurement object is provided. In a first step (100) of the method, a measurement object is provided. Furthermore, a sensor arrangement is provided, comprising a strain gauge which is configured at least to detect stretching and compressive deformations of a measurement object. The detection of further measured variables with the strain gauge is also conceivable. The sensor arrangement further comprises an electronic module connected to the strain gauge. The electronic module has, in particular, preamplifier electronics which is suitably connected to the strain gauge and an evaluation unit. The strain gauge and the electronic module are or will each be arranged on the likewise provided mounting plate and encapsulated in a common housing.Preferably, the strain gauge and the electronic module are encapsulated in the housing after step (500), i.e., after the strain gauge or the electronic module has been firmly bonded to the mounting plate. As a result, the strain gauge and the electronic module are spatially surrounded by the mounting plate and the housing.

[0013] In this sense, the strain gauge and the electronic module are completely surrounded by the mounting plate and a potting compound or an injection-molding compound, preferably before method step (200) and preferably after step (500). This forms the housing, and the sensor assembly is protected from unwanted influences, particularly damage. Furthermore, the sensor assembly can advantageously be manufactured under clean-room conditions. Thus, the strain gauge and the electronic module can be arranged on the mounting plate and encapsulated in the housing without allowing contaminants to enter the housing.

[0014] “Encapsulated” or “encapsulated” means that the strain gauge and the electronic module are essentially completely enclosed by, for example, a module housing, in particular sealed, e.g., against the ingress of air and / or moisture. In a preferred embodiment, the strain gauge and the electronic module are completely and seamlessly encapsulated, and in particular without contact elements - i.e., free of contact elements. Only cabling can be led out of the housing for connection to the evaluation unit. In this sense, a completely enclosed state also exists if cabling is led out of the housing. For example, the strain gauge and the electronic module are preferably completely surrounded by a potting compound or an injection molding compound. In this case, the potting compound forms the module housing or the housing of the sensor arrangement.This design prevents mechanical and / or unwanted electrical influences on the strain gauge and the electronic module, for example due to moisture or dirt.

[0015] Furthermore, a first connecting foil and at least one second connecting foil are provided, each connecting foil containing metallic materials that react exothermically when activated. The first connecting foil is assigned to the mounting plate, and the mounting plate is integrally connected to the measurement object by means of the first connecting foil. The second connecting foil is assigned to either the strain gauge or the electronic module, and the strain gauge or the electronic module is integrally connected to the mounting plate by means of the second connecting foil.

[0016] The measurement object can, in particular, be significantly larger than the sensor arrangement. The measurement object can, for example, be a target, in particular an axle, a shaft for an engine, a transmission of a motor vehicle, a robot arm segment for a robot, or a radiator. The mounting plate on which the parts of the sensor arrangement are arranged according to step (500) enables simple and robust handling of the sensor arrangement. The mounting plate can be part of the sensor arrangement. In this case, the mounting plate, the strain gauge, and the electronics module form a coherent component, namely the sensor arrangement. The sensor arrangement can be stored, transported, and processed separately and can only be integrally bonded to the measurement object using the method according to the invention. The mounting plate is then arranged between the measurement object, the strain gauge, and the electronics module.The mounting plate also enables a secure connection of the sensor arrangement to the measuring object, since unintentional damage to the strain gauge or the electronic module during the activation of the first connecting foil, especially during heating of the materials of the connecting foil, can be excluded.

[0017] The strain gauge is particularly designed to measure strain, compression, and / or torque generated by, emanating from, or transmitted by the measurement object. The strain gauge preferably comprises a carrier layer facing the measurement object and a measuring grid. The strain gauge, or DMS for short, is preferably a foil DMS, i.e., the measuring grid made of resistance wire, which is preferably 3 to 5, preferably up to 8 µm thick, is laminated and etched onto a thin plastic carrier comprising a polymer and provided with electrical connections that enable an electronic connection to the electronic module. Additionally, the measuring grid can be covered by a cover layer that is connected to the carrier layer, in particular glued, and which mechanically protects the measuring grid. The cover layer can also be omitted, since the strain gauge is encapsulated in the housing.Multiple measuring grids can also be arranged on the carrier layer. Advantageously, the carrier layer and / or the cover layer are designed in the form of a film. Therefore, the carrier layer is preferably a carrier film and / or the cover layer is a cover film. The carrier layer is preferably made of polyimide. If a cover layer is provided, this can also be made of polyimide.

[0018] A NanoFoil® from the Indium Corporation, for example, can be used as a connecting foil. The NanoFoil® is a reactive multilayer foil produced by vapor deposition of thousands of alternating nanoscale layers, for example of aluminum and nickel. Other binary layer systems are also conceivable, such as titanium and aluminum, zirconium and silicon, or palladium and aluminum. Ternary systems for forming the multilayer foil are also conceivable. The design of the connecting foil, and in particular the choice of materials, depends essentially on the desired reaction upon activation of the connecting foil, particularly the reaction temperature during activation. When the foil is activated by a small pulse of local energy from electrical, optical, or thermal sources, it reacts exothermically to generate precise local heat up to temperatures of 1500°C in fractions of a second.The thickness of the connecting foil can be adjusted to meet specific requirements. In particular, the thickness of the connecting foil can be adjusted depending on the material of the test object and / or the mounting plate and / or the strain gauge carrier layer. The thinner the connecting foil, the less energy is required to initiate or execute the activation of the connecting foil. The total energy must be adjusted to ensure a secure connection between the strain gauge and the test object.

[0019] In a second method step (200), the first connecting foil is placed between the mounting plate and the measurement object. The placement can be effected such that the first connecting foil, in a sandwich configuration, either directly abuts mutually facing surfaces of the mounting plate and the measurement object. Alternatively, the placement can be effected such that the first connecting foil is arranged in a sandwich configuration between two solder layers, wherein the solder layers are applied to opposite surfaces of the mounting plate and the measurement object. Furthermore, alternatively, the placement can be effected such that the first connecting foil is arranged in a sandwich configuration between two solder layers, wherein the solder layers are applied to opposite surfaces of the first connecting foil.These surfaces of the first connecting foil are, in particular, flat surfaces which, in the second method step (200), are arranged between the mounting plate and the measurement object, receiving the mounting plate or the measurement object, in order to be welded or soldered in the subsequent third method step (300).

[0020] In a fourth method step (400), the second connecting foil is placed between the mounting plate and the strain gauge or between the mounting plate and the electronic module. The placement can be carried out such that the second connecting foil, in a sandwich configuration, either directly abuts mutually facing surfaces of the mounting plate and the strain gauge or the electronic module. Alternatively, the placement can be carried out such that the second connecting foil is arranged in a sandwich configuration between two solder layers, wherein the solder layers are applied to opposite surfaces of the mounting plate and the strain gauge or the electronic module.Furthermore, alternatively, the placement can be carried out such that the second connecting foil is arranged in a sandwich configuration between two solder layers, wherein the solder layers are applied to opposite surfaces of the second connecting foil. These surfaces of the second connecting foil are, in particular, flat surfaces, which, in the fourth method step (400), are arranged between the mounting plate and the strain gauge or the electronic module, accommodating the mounting plate or the strain gauge or the electronic module, in order to be welded or soldered in the subsequent fifth method step (500).

[0021] Accordingly, the strain gauge or the electronic module, which is not firmly bonded to the mounting plate via the second connecting foil, is glued to the mounting plate.

[0022] In the activated state, the respective connecting foil forms a joining surface between the parts to be joined together in a materially bonded manner. If this does not already occur at the joining section forming the joining surface, the respective connecting foil can further have an activation section at which the metallic material of the respective connecting foil is activated. Activation means can be arranged at the activation section in order to be able to activate the respective connecting foil. The respective joining section and, if applicable, the activation section are formed on the one hand between the mounting plate and the measurement object and, on the other hand, between the mounting plate and the strain gauge or between the mounting plate and the electronics module. The respective connecting foil activated in step (300) or (500) connects the measurement object to the mounting plate orThe mounting plate is bonded to the strain gauge or electronic module at least in one respective joining surface, preferably in the respective joining surface and, if applicable, in the activation section. If an activation section is provided, it is located outside the respective joining surface.

[0023] At least one, preferably several activation means are electrically connected to the respective connecting foil, in particular to the activation section, if one is provided. The activation means can have one or more wires, preferably two wires, one with a positive pole, i.e. a plus pole, and one with a negative pole, i.e. a minus pole, with a potential difference existing between the poles. The wires can be formed and handled separately. Alternatively, the two wires can be combined at their ends to form a type of plug in order to maintain or not undercut a defined distance between the wires. The activation means can further be or comprise a voltage source, in particular a battery, or a heat needle. Alternatively, the activation means can be designed to be connected to the voltage source to activate the connecting foil.The activation means and / or the voltage sources can be connected to the electronic module. If both activation steps occur simultaneously, the connecting foils can be connected to a common activation means. If steps (300) and (500) occur consecutively, it is advantageous to assign each connecting foil to a corresponding, separate activation means.

[0024] In a third method step (300), the metallic materials of the first connecting foil are activated via the respective activation agent, so that the first connecting foil heats up such that the mounting plate is bonded to the measurement object. After activation of the first connecting foil, a bonded connection exists between the mounting plate and the measurement object. Activation can occur, for example, through ignition. The method requires no particular heat, no vacuum, and no gas atmosphere. The connecting foil can be ignited, for example, using a commercially available 9V battery, wherein the battery is at least indirectly connected to the connecting foil via the respective activation agent. In method step (300), the material of the measurement object and / or the mounting plate can be melted or partially melted, so that the mounting plate is welded directly to the measurement object.Alternatively, the mounting plate can be indirectly soldered to the measurement object by melting solder layers on the measurement object and / or on the mounting plate and / or on the first connecting foil.

[0025] In a fifth method step (500), the metallic materials of the second connecting foil are activated via the respective activation agent, such that the second connecting foil heats up such that the mounting plate is integrally connected to the strain gauge or the electronic module. After activation of the second connecting foil, a integral connection exists between the mounting plate and the strain gauge or the electronic module. Activation can be carried out analogously to the above explanations for the first connecting foil. In particular, method step (500) is carried out such that the material of the carrier layer of the strain gauge does not melt upon activation of the second connecting foil. However, the mounting plate can comprise a material that is melted or partially melted during activation of the second connecting foil, such that the mounting plate is welded directly to the strain gauge.Alternatively, the strain gauge or the electronic module can be indirectly soldered to the mounting plate by melting solder layers on the strain gauge or the electronic module and / or on the mounting plate and / or on the second connecting foil.

[0026] During the bonding process, no high pressures or high temperatures need to be applied to the sensor array and / or the mounting plate and / or the measurement object. Strong electromagnetic fields are also eliminated. The continuous, metallic bonding layer or bonding surface created by activating the metallic materials of the respective bonding foil between the mounting plate and the measurement object, or between the mounting plate and the strain gauge or the electronic module, exhibits particularly high dimensional stability as well as high thermal and electrical conductivity due to the improved contact. Furthermore, the manufacturing process and the bonding process are simplified, enabling particularly cost-effective production.

[0027] The inventive method is characterized by lower temperatures and stresses during connection. These lower stresses induce less prestress in the strain gauge and the mounting plate, increasing the performance and stability of the strain gauge. Furthermore, the low temperatures and low pressure enable a broad application of materials, such as polymers. The bond created by the inventive method between the mounting plate and the measurement object, or between the mounting plate and the strain gauge or electronic module, does not age over time or with temperature changes. Steam, pressure, or similar factors do not cause any changes in the connection parameters. The composite material (metal) is particularly resistant to moisture, chemicals, high / low temperatures, and rapid temperature changes.The composite therefore does not change its parameters, especially due to temperature, humidity, pressure, or similar factors. The composite material (especially metal) continues to offer elastic deformation for repeatability.

[0028] Advantageously, the electrical connection between the activating agent and the connecting foil can be made using the same device with which the individual components are placed on top of each other and the pressure is exerted for the material connection.

[0029] The respective connecting foil is processed by laser cutting such that the respective connecting foil assumes a shape and dimensions that cover a designated joining surface between the mounting plate and the measurement object, or between the mounting plate and the strain gauge or electronic module. The respective connecting foil can thus be formed particularly precisely and efficiently to the desired dimensions before the respective connecting foil is placed between the two surfaces. Therefore, the laser cutting takes place before the first connecting foil is placed between the mounting plate and the measurement object in step (200) or before the second connecting foil is placed between the mounting plate and the strain gauge or electronic module in step (400).

[0030] The connection method according to the present invention is particularly suitable for sensor arrangements with strain gauges due to the elimination or reduction of compressive stresses. The mounting of the strain gauge to the measurement object can thus be simplified and accelerated, and can be carried out with reproducible quality. In particular, the mounting of the mounting plate with the sensor arrangement arranged thereon to the measurement object can be at least partially automated, preferably fully automated.

[0031] Preferably, steps (200) and (400) occur simultaneously or directly one after the other. Alternatively, step (200) can occur before step (400), or vice versa. Thus, the placement of the respective connecting foil between the two components to be joined can occur in any order.

[0032] Preferably, steps (300) and (500) occur simultaneously. As already mentioned, in this case only one activation means can be provided, which activates both films simultaneously. Alternatively, step (500) occurs after step (300). In other words, the strain gauge or the electronic module is materially bonded to the mounting plate after the mounting plate has been materially bonded to the measurement object. Furthermore, alternatively, steps (400) and (500) occur before step (200). In other words, the sensor arrangement is first completely manufactured before it is arranged on the measurement object. Step (300), which follows step (200), thus occurs after step (500), which follows step (400). One advantage is that the encapsulation can occur before step (300), i.e. the materially bonding of the mounting plate to the measurement object.This means that the sensor arrangement can first be formed into a coherent and separately handled component before the sensor arrangement is firmly attached to the measuring object via the mounting plate.

[0033] It should be made clear here that the interrelated steps (200) and (300) or (400) and (500) can in principle be carried out in any order.

[0034] According to a preferred embodiment, one or more solder layers are applied to the first and / or second connecting foil and / or the mounting plate and / or the measurement object and / or the strain gauge or the electronic module. Preferably, the mounting plate and / or the first connecting foil has a metallized first solder layer, which is arranged between the mounting plate and the connecting foil in step (200). The first solder layer is to be understood as the first coating of the mounting plate and / or the first connecting foil, which can be divided into several individual layers.

[0035] Preferably, the first connecting foil and / or the measurement object has a metallized second solder layer, which is arranged between the measurement object and the connecting foil in step (200). The second solder layer is to be understood as a second coating of the measurement object and / or the first connecting foil, which can also be divided into several individual layers.

[0036] The first or second solder layer is applied in particular before the first connecting foil is placed between the mounting plate and the measurement object in the second method step (200). Subsequent activation of the first connecting foil generates sufficient heat to melt the first or second solder layer and solder the mounting plate to the measurement object. In this sense, according to one embodiment, - the first solder layer is applied to the mounting plate and / or the first connecting foil, - the second solder layer is applied to the measuring object and / or the first connecting foil, - the first connecting foil with the solder layers is placed between the mounting plate and the measuring object in step (200), and - the metallic materials of the first connecting foil are activated in step (300) such that the first connecting foil heats up such that the first solder layer and the second solder layer melt, and the mounting plate is soldered to the measurement object by the melted first solder layer and the melted second solder layer to create the integral connection. The metallization of the measurement object, the mounting plate, and / or the first connecting foil, i.e., the application of the first or second solder layer to the measurement object, the mounting plate, and / or the connecting foil, is important to enable the nanobond process.

[0037] Preferably, the mounting plate and / or the second connecting foil comprises a metallized third solder layer, which is arranged between the mounting plate and the second connecting foil in step (400). The third solder layer is to be understood as a third coating of the mounting plate and / or the second connecting foil, which can be divided into several individual layers.

[0038] Preferably, the second connecting foil and / or the strain gauge or the electronic module has a metallized fourth solder layer, which is arranged in step (400) between the strain gauge or the electronic module and the second connecting foil. The fourth solder layer is to be understood as a fourth coating of the strain gauge or the electronic module and / or the second connecting foil, which can also be divided into several individual layers.

[0039] The third or fourth solder layer is applied in particular before the second connecting foil is placed between the mounting plate and the strain gauge or the electronic module in the fourth method step (400). Subsequent activation of the second connecting foil generates sufficient heat to melt the third or fourth solder layer and solder the mounting plate to the strain gauge or the electronic module. In this sense, according to one embodiment, - the third solder layer is applied to the mounting plate and / or the second connecting foil, - the fourth solder layer is applied to the strain gauge or the electronic module and / or the second connecting foil, - the second connecting foil with the solder layers is placed between the mounting plate and the strain gauge or the electronic module in step (400), and - the metallic materials of the second connecting foil are activated in step (500) so that the second connecting foil is heated such that the third solder layer and the fourth solder layer melt and the mounting plate is soldered to the strain gauge or the electronic module by the melted third solder layer and the melted fourth solder layer in order to produce the material-to-material connection.

[0040] The respective solder layer is a metallized layer that enables an effective material connection between the measuring object and the mounting plate or between the mounting plate and the strain gauge.

[0041] Using the respective connecting foil and solder layers, an intermetallic, material-tight bond can be created between the parts to be joined. This bond does not require high temperatures, pressures, electromagnetic fields, etc. for its production. The intermetallic bond enables a 1:1 signal transmission from the measuring object to the strain gauge.

[0042] The solder layers can be applied as metallic starting layers particularly advantageously by plasma processes, sputtering processes, or vapor deposition on the respective surface of the parts to be connected (mounting plate, test object, connecting foil, strain gauge, or electronic module). Further possibilities include two-shot injection molding, additive manufacturing, etc. At least one of the solder layers, preferably all of the solder layers, preferably comprise nickel. Furthermore, one of the solder layers, preferably all of the solder layers, preferably comprises gold. Copper or palladium are also suitable as materials for the respective solder layer. The material of the respective solder layer is adapted to the dimensions and the material of the connecting foil, the mounting plate, the test object, the strain gauge, and / or the electronic module.

[0043] According to one embodiment, the respective solder layer comprises a nickel layer and a gold layer. In other words, the respective coating is multi-layered. The layer structure can be configured as desired. Preferably, the gold layer faces the connecting foil. Preferably, the nickel layer of the respective connecting foil faces the measurement object and / or the mounting plate and / or the strain gauge or the electronic module and thus faces away from the respective connecting foil.

[0044] To prevent unforeseeable deformation of the composite, a fixing pad can be placed on the layers with low pressure. In this sense, deformation of the solder layers and the respective connecting foil during activation and connection in step (300) or step (500) is preferably counteracted by means of a fixing pad that exerts pressure at least indirectly on the mounting plate and / or the measurement object and / or the strain gauge or the electronic module. The pressure is so low that it does not lead to any stresses within the mounting plate and / or the strain gauge and / or the electronic module and / or the measurement object that could impair the strength of the connection between the mounting plate and the measurement object or between the mounting plate and the strain gauge or the electronic module, or the measurement accuracy.

[0045] In this context, "at least indirectly" means that additional, particularly plate-shaped components, such as a heat sink, can be arranged between the fixing pad and the mounting plate and / or the strain gauge or the electronics module and / or the measurement object. The fixing pad can also be arranged directly on the mounting plate and / or the strain gauge or the electronics module and / or the measurement object.

[0046] According to a second aspect of the invention, an arrangement of a sensor arrangement arranged on a mounting plate on a measurement object is provided, wherein the sensor arrangement has been connected to the measurement object by a method according to the first aspect of the invention.

[0047] The above definitions as well as statements regarding technical effects, advantages, and advantageous embodiments of the method according to the invention also apply mutatis mutandis to the inventive arrangement according to the second aspect of the invention. It is understood that the features mentioned above and those to be explained below can be used not only in the respective combinations specified, but also in other combinations or on their own, without departing from the scope of the present invention.

[0048] In the following, an embodiment of the invention is explained in more detail with reference to the schematic drawings, wherein identical or similar elements are provided with the same reference numerals. Fig. 1 a longitudinal sectional view of an arrangement according to the invention of a sensor arrangement arranged on a mounting plate on a measuring object according to a first embodiment, Fig. 2 a detailed longitudinal section of the arrangement according to the invention according to Fig. 1, Fig. 3 an exploded view of layers and tools for connecting a strain gauge of the sensor arrangement to a mounting plate by means of a second connecting foil, as well as the sensor arrangement resulting from the connection, Fig. 4 an exploded view of layers and tools for connecting the sensor arrangement to the measuring object by means of a first connecting film as well as the arrangement resulting from the connection according to Fig. 1 and Fig. 2, Fig. 5 shows a sequence of a method according to the invention for connecting the sensor arrangement to the measurement object according to Fig. 1 to Fig. 4, and Fig. 6 a greatly enlarged cross-sectional view of the connecting foil for the arrangement according to Fig. 1 to Fig. 5.

[0049] Fig. 1 shows a preferred embodiment of an arrangement of a sensor arrangement 5 arranged on a mounting plate 17 on a measuring object 2. The sensor arrangement 5 comprises a strain gauge 1 and an electronic module 19 electrically connected thereto. In the present case, the electronic module 19 is glued onto the mounting plate 17. The strain gauge 1 is connected to the measuring object 2 by means of a Fig. 3 in conjunction with Fig. 5, the mounting plate 17 is connected to the mounting plate 17 by means of a second connecting foil 10b. The mounting plate 17 is connected to the mounting plate 17 by means of a Fig. 4 in conjunction with Fig. 5, the measuring object 2 is connected to the measuring object 2 via a first connecting foil 10a. Fig. 1 and Fig. In the state shown in Figure 2, the strain gauge 1 and the electronic module 19 are encapsulated in a common housing 18 made of potting material.

[0050] The strain gauge 1 is in Fig. 2 and comprises a carrier layer 1a facing the mounting plate 17 and a meander-shaped measuring grid 1b arranged thereon. The measuring grid 1b is connected to the electronic module 19 designed as a preamplifier module via a first wiring 20, which is also encapsulated in the housing 18. A second wiring 23 is led out of the housing 18, which connects the electronic module 19 to an evaluation unit (not shown here) and / or a voltage source, such as the one shown in Fig. 3 or Fig. 4, connects the battery 15. As also shown in Fig. 2, the mounting plate 17 has a metallized first solder layer 13 facing the first connecting foil 10a on a first mounting plate surface 4a, and the measurement object 2 has a metallized second solder layer 14 facing the first connecting foil 10a on a measurement object surface 6. One or both of the solder layers 13, 14 can also be applied to the first connecting foil 10a. Furthermore, the mounting plate 17 has a metallized third solder layer 21 facing the second connecting foil 10b on a second mounting plate surface 4b, wherein the strain gauge 1, in particular its carrier layer 1a, has a metallized fourth solder layer 21 facing the second connecting foil 10b.

[0051] One or both of the solder layers 21, 22 can also be applied to the second connecting foil 10b.

[0052] In this case, the measurement object 2 is significantly larger than the sensor arrangement 5. The measurement object 2 can be, for example, a shaft of an engine, an axle, or a transmission for a motor vehicle. The strain gauge 1 is designed to detect strains and compressions on the measurement object 2. The resistance of the strain gauge 1 changes with a force applied to the measurement object 2. It converts mechanical quantities such as force, pressure, tension, weight, and the like into a measurable change in electrical resistance. When an external force acts on the measurement object 2, it causes mechanical stress and strain. The mechanical stress is the resistance that the object opposes to the force, and the strain is the displacement and deformation resulting from the force. Thus, the strain gauge 1 is at least designed to detect stretching and compression deformations, preferably other measured quantities, of the measurement object 2.

[0053] The first connecting foil 10a creates a firm, in this case, material-to-material connection between the mounting plate 17 and the measurement object 2, and the second connecting foil 10b creates a firm, in this case, material-to-material connection between the mounting plate 17 and the strain gauge 1. Each connection transmits forces from the measured variable as well as disturbances caused by thermal expansion. The type of connection imposes requirements on the surface properties of the measurement object 2, strain gauge 1, and mounting plate 17.

[0054] Two right outside in Fig. The force arrows F shown in Figure 1 illustrate an exchange of forces through deformation, which represents the actual measured variable. To the left of this, a bidirectional force arrow F is shown, which illustrates an exchange of forces through stresses and differential thermal expansion, which represents a disturbance variable. The measurement object 2 can, as mentioned above, have a metallized surface or be made of a metallic material.

[0055] In a first method step 100, the measurement object 2, the sensor arrangement 5, comprising the strain gauge 1 and the electronic module 19, the mounting plate 17, and the first and second connecting foils 10a, 10b are provided. The respective connecting foil 10a, 10b is a so-called NanoFoil®, i.e., a reactive multilayer foil produced by vapor deposition of thousands of alternating nanoscale layers of aluminum 11 and nickel 12. A greatly enlarged cross-sectional view of the respective connecting foil 10a, 10b with the aluminum 11 and nickel layers 12 is shown in Fig. 6. When the respective connecting foil 10a, 10b is activated by a small pulse of local energy from electrical, optical, or thermal sources, it reacts exothermically to generate precise local heat up to temperatures of 1500 °C in fractions of a second.

[0056] Step 100 is followed by Fig. 5, the production of the sensor arrangement is initially carried out. Step 400 follows step 100, wherein in step 400 the second connecting foil 10b is placed between the mounting plate 17 and the strain gauge 1. The second connecting foil 10b contacts a third solder layer 21 on the mounting plate 17 on one side and a fourth solder layer 22 on the strain gauge 1, in particular on the carrier layer 1a of the strain gauge 1, on the other side. During method step 400, the aluminum layers 11 and the nickel layers 12 of the second connecting foil 10b are still arranged alternately next to one another, as is shown by Fig. 6. Both solder layers 21, 22 comprise nickel. In the present case, both layers 21, 22 additionally have a gold layer, wherein the gold layer is arranged facing the second connecting foil 10b. The respective solder layer 21, 22 can further comprise copper, silver, silicon nitride Si3N4, silicon dioxide SiO2, titanium tungsten TiW, palladium, or the like. After step 500 and before step 200, the strain gauge 1 and the electronic module 19 are completely surrounded by the mounting plate 17 and a potting compound or an injection molding compound. The strain gauge 1 and the electronic module 19 are thus completely surrounded by the mounting plate 17 on the one hand and by a potting compound or an injection molding compound on the other. The encapsulation forms a housing 18 accommodating the strain gauge 1 and the electronic module 19.

[0057] The sensor arrangement 5 can thus be stored, transported and handled separately, whereby the strain gauge 1 and the electronic module 19 are protected from external influences.

[0058] Step 400 is followed by step 500, after which the aluminum layers 11 and the nickel layers 12 of the second connecting foil 10b are Fig. 6 using the example shown in Fig. 3. Instead of the battery 15, a DC voltage source can be used to activate the second connecting foil 10b. The aluminum layers 11 and nickel layers 12 of the second connecting foil 10b then react strongly exothermically, so that the second connecting foil 10b heats up to such an extent that the third solder layer 21 and the fourth solder layer 22 melt and the mounting plate 17 is soldered to the strain gauge 1 by the molten solder layers 21, 22. This creates, as shown on the right in Fig. 3, a stable bonding or joining surface 7b between the mounting plate 17 and the strain gauge 1.

[0059] Following the material connection of the strain gauge 1 to the mounting plate 17, i.e. after step 500, the electronic module 19 is glued to the mounting plate 17 and the strain gauge 1 and the electronic module 19 are encapsulated, so that a coherent component of the sensor arrangement 5 is created, which according to Fig. 4 is connected to the measuring object 2.

[0060] Step 500 is thus followed by step 200, after which the first connecting foil 10a is placed between the mounting plate 17 and the measurement object 2, as shown by Fig. 4 on the left side. The first connecting foil 10a touches the first solder layer 13 on the mounting plate 17 on one side and the second solder layer 14 on the measurement object 2 on the other side. During step 200, the aluminum layers 11 and the nickel layers 12 of the first connecting foil 10a are still arranged alternately next to each other, as shown by Fig. 6. Both solder layers 13, 14 comprise nickel. In the present case, both layers 13, 14 also have a gold layer, with the gold layer facing the first connecting foil 10a. The respective solder layer 13, 14 can be configured analogously to the third or fourth solder layer 21, 22.

[0061] In a step 300 following step 200, the aluminum layers 11 and the nickel layers 12 of the first connecting foil 10a are Fig. 6 using the example shown in Fig. 4. Instead of the battery 15, a DC voltage source can be used to activate the first connecting foil 10a. The aluminum layers 11 and nickel layers 12 of the first connecting foil 10a then react strongly exothermically, so that the first connecting foil 10a heats up to such an extent that the first solder layer 13 and the second solder layer 14 melt and the mounting plate 17 is soldered to the measuring object 2 by the molten solder layers 13, 14. This creates, as shown on the right in Fig. 4, a stable bonding or joining surface 7a between the mounting plate 17 and the measuring object 2.

[0062] The connecting foils 10a, 10b are processed by laser cutting in such a way that the respective connecting foil 10a, 10b takes on a shape and dimensions that form a designated joining surface 7a, 7b between the mounting plate 17 and the measurement object 2 or between the mounting plate 17 and the strain gauge 1, as well as a respective activation section 8a, 8b. In the embodiment shown, the first activation section 8a is Fig. 4 is not covered by the mounting plate 17 and the second activation section 8b is according to Fig. 3 is not covered by the strain gauge 1. Therefore, the respective activation section 8a, 8b protrudes, as shown in the left part of Fig. 3 and Fig. 4, from the stack formed by the sensor arrangement 5, the mounting plate 17, the measuring object 2 and the solder layers 13, 14, 21, 22 when all layers lie against one another.

[0063] The method according to the invention creates a material-to-material connection between the mounting plate 17 and the measurement object 2, as well as between the strain gauge 1 and the mounting plate 17. The mounting plate surfaces 4a, 4b and / or the measurement object surface 6 and / or the carrier layer surface can have a surface structure such that molten material of the aluminum layers 11 and / or the nickel layers 12 can penetrate into the gaps in the respective surface and, after solidification, can create a positive connection between the two components to be joined. The detectable measured variable can be increased by special structures, force shunt, of the measurement object 2. The measurement object 2 can, for example, form depressions, ribs, beads, or the like, which amplify or reduce forces in certain spatial directions.

[0064] Both when connecting the strain gauge 1 to the mounting plate 17 according to steps 400 and 500, and when connecting the mounting plate 17 to the test object 2 according to steps 200 and 300, a fixing pad 9 with a flexible layer 24 is provided, which exerts a pressure p on the respective stack. This pressure is very low and acts perpendicularly on an outer surface of the respective component. The pressure serves to counteract deformation of the solder layers 13, 14 or 21, 22 and the respective connecting foil 10a, 10b during activation and connection in steps 500 and 300, respectively.

[0065] It should be expressly noted that the invention is not limited to the exemplary embodiments disclosed here. These are merely exemplary embodiments, although further variants are also possible. In particular, the second solder layer 14 on the measurement object 2 can be omitted if the measurement object 2 consists of a solderable material or has an already metallized surface. Furthermore, steps 200 and 400 can take place simultaneously or directly one after the other. Furthermore, steps 300 and 500 can take place simultaneously. Alternatively, step 500 can take place after step 300. Further alternatively, steps 400 and 500 can take place before step 200. Reference symbol F Force p pressure 1 strain gauge 1a carrier layer 1b Measuring grid 2 Measuring object 4a First mounting plate surface 4b Second mounting plate surface 5 Sensor arrangement 6 Measuring object surface 7a First joining surface 7b Second joining surface 8a First activation section 8b Second activation section 9 Fixing pad 10a first connecting foil 10b second connecting foil 11 aluminum layer 12 nickel layer 13 First solder layer 14 Second solder layer 15 Battery 16 activating agents 17 Mounting plate 18 housings 19 Electronic module 20 First cabling 21 Third solder layer 22 Fourth solder layer 23 Second wiring 24 Flexible layer 100 First procedural step 200 Second procedural step 300 Third procedural step 400 Fourth procedural step 500 Fifth procedural step

Claims

[1] Method for connecting a sensor arrangement (5) arranged on a mounting plate (17) to a measurement object (2), the method comprising the steps (100) Provide - a measuring object (2), - a sensor arrangement (5) comprising a strain gauge (1) which is at least designed to detect stretching and compressive deformations of a measurement object (2), and an electronic module (19) connected thereto, - the mounting plate (17), - a first connecting foil (10a) and at least one second connecting foil (10b), each containing metallic materials (11, 12) which react exothermically when activated, (200) Placing the first connecting foil (10a) between the mounting plate (17) and the measuring object (2), (300) activating the metallic materials (11, 12) of the first connecting foil (10a) so that the first connecting foil (10a) heats up in such a way that a material connection is created between the mounting plate (17) and the measuring object (2), (400) Placing the second connecting foil (10b) between the mounting plate (17) and the strain gauge (1) or the electronic module (19), and (500) Activating the metallic materials (11, 12) of the second connecting foil (10b) so that the second connecting foil (10b) heats up in such a way that a material connection is created between the strain gauge (1) or the electronic module (19) and the mounting plate (17). [2] Method according to claim 1, wherein after step (500) the strain gauge (1) and the electronic module (19) are encapsulated in a housing (18). [3] Method according to claim 1 or 2, wherein steps (200) and (400) occur simultaneously or immediately after one another. [4] Method according to one of claims 1 to 3, wherein steps (300) and (500) occur simultaneously. [5] Method according to one of claims 1 to 3, wherein step (500) occurs after step (300). [6] Method according to one of claims 1 to 3, wherein steps (400) and (500) occur before step (200). [7] Method according to one of the preceding claims, wherein the strain gauge (1) comprises a carrier layer (1a) facing the mounting plate (17) and a measuring grid (1b). [8] Method according to one of the preceding claims, wherein the mounting plate (17) and / or the first connecting foil (10a) has a metallized first solder layer (13) which is arranged in step (200) between the mounting plate (17) and the first connecting foil (10a). [9] Method according to one of the preceding claims, wherein the first connecting foil (10a) and / or the measuring object (2) has a metallized second solder layer (14) which is arranged in step (200) between the measuring object (2) and the first connecting foil (10a). [10] Method according to claim 8 in conjunction with claim 9, wherein - the first solder layer (13) is applied to the mounting plate (17) and / or the first connecting foil (10a), - the second solder layer (14) is applied to the measuring object (2) and / or the first connecting foil (10a), - the first connecting foil (10a) with the solder layers (13, 14) is placed between the mounting plate (17) and the measuring object (2) in step (200), and - the metallic materials (11, 12) of the first connecting foil (10a) are activated in step (300) so that the first connecting foil (10a) is heated such that the first solder layer (13) and the second solder layer (14) melt and the mounting plate (17) is soldered to the measurement object (2) by the melted first solder layer (13) and the melted second solder layer (14) in order to produce the material-to-material connection. [11] Method according to one of the preceding claims, wherein the mounting plate (17) and / or the second connecting foil (10b) has a metallized third solder layer (21) which is arranged in step (400) between the mounting plate (17) and the second connecting foil (10b). [12] Method according to one of the preceding claims, wherein the second connecting foil (10b) and / or the strain gauge (1) or the electronic module (19) has a metallized fourth solder layer (22) which is arranged in step (400) between the strain gauge (1) or the electronic module (19) and the second connecting foil (10b). [13] Method according to claim 11 in conjunction with claim 12, wherein - the third solder layer (21) is applied to the mounting plate (17) and / or the second connecting foil (10b), - the fourth solder layer (22) is applied to the strain gauge (1) or the electronic module (19) and / or the second connecting foil (10b), - the second connecting foil (10b) with the solder layers (21, 22) is placed in step (400) between the mounting plate (17) and the strain gauge (1) or the electronic module (19), and - the metallic materials (11, 12) of the second connecting foil (10b) are activated in step (500) so that the second connecting foil (10b) is heated such that the third solder layer (21) and the fourth solder layer (22) melt and the mounting plate (17) is soldered to the strain gauge (1) or the electronic module (19) by the melted third solder layer (21) and the melted fourth solder layer (22) in order to produce the material-to-material connection. [14] Method according to claim 10 or claim 13, wherein a fixing pad (9) which exerts a pressure (p) at least indirectly on the sensor arrangement (5) and / or on the measurement object (2) counteracts a deformation of the solder layers (13, 14, 21, 22) and the respective connecting foil (10a, 10b) during the activation and connection in step (300) or step (500). [15] Arrangement of a sensor arrangement (5) arranged on a mounting plate (17) on a measuring object (2), wherein the sensor arrangement (5) has been connected to the measuring object (2) by a method according to one of the preceding claims.

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