Connection of a sensor array to a measured object

Abstract

Method for connecting a sensor arrangement (20) to a measurement object (2), the method comprising the steps (100) Provide - of a measured object (2), - a sensor arrangement (20) comprising a strain gauge (1) which is at least configured to detect tensile and compressive deformations of a measurement object (2), and an electronic module (19), - a first connecting foil (10a) and a second connecting foil (10b), each containing metallic materials (11, 12) which react exothermically when activated, (200) Placing the first connecting foil (10a) between the strain gauge (1) and the electronic module (19), (300) Activating the metallic materials (11, 12) of the first connecting foil (10a) such that the first connecting foil (10a) heats up in such a way that a metallurgical connection is created between the strain gauge (1) and the electronic module (19), wherein after activating the metallic materials (11, 12) of the first connecting foil (10a) an electronic connection exists between the strain gauge (1) and the electronic module (19), (400) Place the second connecting foil (10b) between the strain gauge (1) and the object being measured (2), 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) and the object being measured (2).

Description

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

[0002] For various applications, it is necessary to attach a strain gauge to a larger mechanical component, the object being measured. 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 tensile and compressive deformations. Even with slight deformations, their electrical resistance changes, and they 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 object being measured. The object can be made of various materials such as metal, silicon, or an organic material. The bonding layer must offer strong adhesion and be dimensionally stable to ensure good force and deformation transmission without (additional and unpredictable) damping or time delays. The sensor's performance over its lifetime depends on the long-term stability of the bonding layer, particularly its temperature, humidity, and chemical resistance, to prevent signal drift, signal amplitude shrinkage, and time delays.

[0004] Adhesive bonding is a common method for attaching strain gauges to larger objects. The bonding layer is therefore an adhesive layer. While relatively easy to implement in industrial manufacturing, this usually requires a manual process that is time-consuming and cost-inefficient. Adhesive bonds are susceptible to varying temperature gradients, humidity / chemical exposure, 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 pressures, or high vacuum or inert gas. Other methods require strong electromagnetic fields. In this context, "impractical" means that it could damage the strain gauge or the object being measured.

[0005] German patent DE 10 2013 002 144 A1 discloses a joining method for thermally sensitive structures, in which two components are functionally joined using a joining aid designed as a reactive nanofoil. The nanofoil is first inserted between corresponding surface sections of the components to be joined, and subsequently causes at least partial formation of a connection structure. This method is characterized by the fact that, through activation of the nanofoil, a largely solid solder bonding layer is first melted on both corresponding surface sections of the components to be joined, and subsequently the melt material, which is locally confined to one surface section, is mixed with the melt material of the opposite surface section and the remaining reactants of the nanoreactive foil system.that after cooling and solidification of the entire melt, a functional hard solder joint is formed, whereby the thermal stress necessary for melting is applied only within the contour sections of the contacts to be joined, exclusively to solder joint layers of the solder layer system.

[0006] From EP 3 839 460 A1, a sensor system is known that comprises 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 connection. The sensor is designed to acquire data from the structure through the metallic connection, the structural interconnect layer, and the sensor interconnect layer.

[0007] A strain gauge is known from EP 2 796 830 B1. The strain gauge comprises a semiconductor chip with a plurality of piezoresistive elements formed on an end face 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 back face of the semiconductor chip.

[0008] From WO 2016 / 199286 A1, a strain sensing system is known that comprises a semiconductor element for strain detection, a substrate for strain transfer to the semiconductor element, and a connecting material for linking the semiconductor element to the strain transfer substrate. The strain sensing system further comprises a strain measuring unit in which the semiconductor element, the connecting material, and the strain transfer substrate are sealed by means of a first sealing material. The strain measuring unit and a circuit substrate connected to the strain measuring unit are sealed by means of a second sealing material.

[0009] The object of the present invention is to propose a novel connection between a strain gauge and a measuring object, which addresses the problems described above and makes strain gauges suitable for automotive applications. This object is achieved by the subject matter of independent 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 (20) with a measuring object comprises the steps (100) Provide - of a measured object, - a sensor arrangement comprising a strain gauge which is at least configured to detect tensile and compressive deformations of a measured object, and an electronic module, - a first connecting foil and a second connecting foil, each containing metallic materials that react exothermically when activated, (200) Placing the first connecting foil between the strain gauge and the electronic module, (300) Activating the metallic materials of the first connecting film so that the first connecting film heats up in such a way that a metallurgical connection is created between the strain gauge and the electronic module, wherein after activation of the metallic materials of the first connecting film an electronic connection exists between the strain gauge and the electronic module, (400) Place the second connecting foil between the strain gauge and the object being measured, and (500) Activating the metallic materials of the second connecting foil so that the second connecting foil heats up in such a way that a metallurgical bond is created between the strain gauge and the object being measured.

[0011] The present invention proposes a reactive foil soldering process for creating a particularly intermetallic bond for strain gauges on a larger measuring 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 novel class of nanotechnology material in which self-propagating exothermic reactions can be triggered at room temperature by an ignition process. By inserting such a foil between the components to be joined, the heat generated by the reaction in the foil melts, for example, solder layers or other reactive layers, so that the bonds are completed at room temperature in approximately one second. The heat induced during the reaction is very low due to the rapid reaction rate (e.g., 10 m / s) and the small 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 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 tensile and compressive deformations of a measurement object. The detection of other measured quantities 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 are suitably connected to the strain gauge and an evaluation unit. The strain gauge is arranged on the measurement object, with the electronic module being arranged on the strain gauge.The strain gauge and the electronic module are then encapsulated in a common housing.

[0013] Preferably, the strain gauge and the electronic module are encapsulated in the housing if both the electronic module and the strain gauge are bonded to the object being measured. Thus, the encapsulation takes place in a single step (600), which is performed after steps (300) and (500). This results in the strain gauge and the electronic module being spatially surrounded by the object being measured and the housing.

[0014] The terms "encapsulated" or "encapsulated" mean that the strain gauge and the electronic module are essentially completely surrounded by, for example, a module housing, and in particular, sealed 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 any contact elements. Only wiring may extend from the housing for connection to the evaluation unit. In this sense, a completely enclosed state also exists if wiring extends from the housing. For example, the strain gauge and the electronic module are preferably completely surrounded by a potting compound or an injection-molded compound. In this case, the potting compound forms the module housing or the housing of the sensor assembly.This design prevents mechanical and / or unintended electrical interference with the strain gauge and the electronic module, for example, from moisture or dirt. Therefore, the sensor assembly is protected from unintentional damage.

[0015] Furthermore, a first connecting film and at least one second connecting film are provided, each containing metallic materials that react exothermically upon activation. The first connecting film is associated with the electronic module, which is metallurgically bonded to the strain gauge by means of the first connecting film. The second connecting film is associated with the object being measured, which is metallurgically bonded to the strain gauge by means of the second connecting film.

[0016] The object being measured can be significantly larger than the sensor array. For example, the object being measured could be a target, such as an axle, a shaft for an engine, a transmission of a motor vehicle, a robot arm segment for a robot, or a radiator.

[0017] The strain gauge is specifically designed to measure strain, compression, and / or torque generated by, emanating from, or transmitted by the object being measured. The strain gauge preferably comprises a carrier layer facing the object being measured and a measuring grid. The strain gauge, or DMS for short, is preferably a foil strain gauge, meaning that the measuring grid, made of resistance wire preferably 3 to 5, preferably up to 8 µm thick, is laminated and etched onto a thin polymer-based plastic carrier and provided with electrical connections that enable an electronic connection to the electronic module. Additionally, the measuring grid can be covered by a protective layer that is bonded, in particular glued, to the carrier layer and provides mechanical protection for the measuring grid. The protective layer can also be omitted if the strain gauge is encapsulated within the housing.Several measuring grids can also be arranged on the substrate. Advantageously, the substrate and / or the cover layer is in the form of a film. Thus, the substrate is preferably a carrier film and / or the cover layer a cover film. The substrate is preferably made of polyimide. If a cover layer is provided, it can also be made of polyimide.

[0018] For example, a so-called NanoFoil® from Indium Corporation 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. Furthermore, ternary systems for forming the multilayer foil are also possible. 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, especially 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 adapted to the material of the object being measured and / or the substrate of the strain gauge and / or the electronic module. The thinner the connecting foil, the less energy is required to initiate or activate it. The total energy must be set to ensure a secure connection between the strain gauge and the object being measured.

[0019] In a second process step (200), the first interconnecting film is placed between the strain gauge and the electronic module. This placement can be carried out such that the first interconnecting film, in a sandwich configuration, either directly contacts mutually facing surfaces of the strain gauge and the electronic module, or it can be arranged in a sandwich configuration between two solder layers, with the solder layers applied to opposite surfaces of the electronic module and the strain gauge. Alternatively, the placement can also be carried out in a sandwich configuration between two solder layers, with the solder layers applied to opposite surfaces of the first interconnecting film.These surfaces of the first connecting film are in particular flat surfaces which, in the second process step (200), are arranged between the strain gauge and the electronic module to accommodate the strain gauge or the electronic module, in order to be welded or soldered in the subsequent third process step (300).

[0020] The first connecting film is preferably designed such that, after activation in step (300), it establishes an electrical connection between the strain gauge and the electronic module. This eliminates the need for additional, potentially manual, wiring of the strain gauge to the electronic module, which would otherwise be required before step (600). The material bond and the electrical connection between the strain gauge and the electronic module are thus established in a single step, namely during step (300).

[0021] In a fourth process step (400), the second interconnecting foil is placed between the strain gauge and the test object. This placement can be achieved by placing the interconnecting foil in a sandwich configuration either directly against the facing surfaces of the strain gauge and the test object, or by arranging it in a sandwich configuration between two solder layers, with the solder layers applied to opposite surfaces of the electronic module and the strain gauge. Alternatively, the placement can also be achieved by arranging the second interconnecting foil in a sandwich configuration between two solder layers, with the solder layers applied to opposite surfaces of the second interconnecting foil.These surfaces of the second connecting film are in particular flat surfaces which, in the fourth process step (400), are arranged between the strain gauge and the object being measured, in order to be welded or soldered in the third process step (300).

[0022] Accordingly, adhesive connections between the components of the arrangement can be completely dispensed with.

[0023] In its activated state, the respective bonding foil forms a joining surface between the parts to be joined by a material bond. If this is not already the case at the joining section forming the joining surface, the respective bonding foil may also have an activation section where the metallic material of the respective bonding foil is activated. Activating agents may be arranged at the activation section to activate the respective bonding foil. The respective joining section and, if applicable, the activation section are formed between the strain gauge and the electronic module, and between the strain gauge and the object being measured. The respective bonding foil, activated in step (300) or (500), connects the object being measured to the strain gauge or the electronic module.The strain gauge is bonded to the electronic module at least in one of the respective joining surfaces, preferably in the respective joining surface and, if applicable, in the activation section, in a material-bonded manner. If an activation section is provided, it is located outside the respective joining surface.

[0024] The respective connecting foil, and in particular the activation section if one is provided, is electrically connected to at least one, preferably several, activation means. The activation means can have one or more wires, preferably two wires, one with a positive pole and one with a negative pole, with a potential difference between the poles. The wires can be formed and handled separately. Alternatively, the two wires can be joined at their ends to form a type of connector in order to maintain or ensure that the distance between the wires is not less than defined. The activation means can also be or include a voltage source, in particular a battery, or a heating element. Alternatively, the activation means can be configured to be connected to the voltage source to activate the connecting foil.The activation medium and / or the voltage sources can be connected to the electronic module. If both activation steps (300) and (500) occur simultaneously, the connecting foils can be connected to a common activation medium. If steps (300) and (500) occur sequentially, it is advantageous to assign each connecting foil to a corresponding, separate activation medium.

[0025] In a third process step (300), the metallic materials of the first connecting film are activated by the respective activating agent, causing the first connecting film to heat up sufficiently to create a metallurgical bond between the strain gauge and the electronic module. After activation of the first connecting film, a metallurgical bond exists between the strain gauge and the electronic module. Activation can be achieved, for example, by ignition. The process does not require any special heat, vacuum, or gas atmosphere. The connecting film can be ignited, for example, with a standard 9V battery, which is at least indirectly connected to the connecting film via the respective activating agent. Process step (300) is designed such that the material of the strain gauge's carrier layer does not melt during activation of the first connecting film.However, the electronic module may have a material that is melted or partially melted during the activation of the first interconnection foil, so that the electronic module is directly welded to the strain gauge. Alternatively, the strain gauge may be indirectly soldered to the electronic module by melting solder layers on the strain gauge and / or on the electronic module and / or on the first interconnection foil.

[0026] In a fifth process step (500), the metallic materials of the second bonding film are activated by the respective activating agent, causing the second bonding film to heat up to such an extent that the strain gauge is metallurgically bonded to the test object. After activation of the second bonding film, a metallurgical bond exists between the strain gauge and the test object. The activation can be carried out analogously to the above descriptions for the first bonding film. In particular, process step (500) is carried out such that the material of the strain gauge's support layer does not melt during activation of the second bonding film. However, the test object may have a material that melts or partially melts during activation of the second bonding film, so that the test object is directly welded to the strain gauge.Alternatively, the strain gauge or the object being measured can be indirectly soldered to the object being measured by melting solder layers on the strain gauge and / or on the object being measured and / or on the second connecting foil.

[0027] During the bonding process, no high pressures or temperatures need to be applied to the sensor assembly and / or the object being measured. High electromagnetic fields are also unnecessary. The continuous metallic bonding layer or bonding surface created by activating the metallic materials of the respective bonding film between the strain gauge and the electronic module, or between the strain gauge and the object being measured, exhibits particularly high dimensional stability, as well as high thermal and electrical conductivity, due to the improved contact. Furthermore, the manufacturing or bonding process is simplified, enabling particularly cost-effective production.

[0028] The method according to the invention is characterized by lower temperatures and stresses during joining. These lower stresses induce less prestress in the strain gauge and increase its performance and stability. Furthermore, the low temperatures and low pressure allow for the use of a wide range of materials, such as polymers. The bond created by the method according to the invention between the strain gauge and the electronic module, or between the strain gauge and the measured object, does not age with time or temperature changes. Steam, pressure, or similar factors do not alter the parameters of the bond. The bonding material (metal) is particularly resistant to moisture, chemicals, high / low temperatures, and rapid temperature changes. Therefore, the bond 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.

[0029] Advantageously, the electrical connection between the activating agent and the respective connecting film can be made with the same device used to place the individual components on top of each other and to apply the pressure for the material-bonded connection.

[0030] The respective connecting foil is laser-cut to achieve a shape and dimensions that fit the designated joining surface between the strain gauge and the electronic module, or between the strain gauge and the object being measured. This allows the connecting foil to be shaped with exceptional precision and efficiency before being positioned between the two surfaces. Therefore, the laser cutting takes place before the first connecting foil is placed between the strain gauge and the electronic module in step (200), and before the second connecting foil is placed between the strain gauge and the object being measured in step (400).

[0031] The joining method according to the present invention is particularly suitable for sensor arrangements with strain gauges due to the elimination or reduction of compressive stresses. This simplifies and accelerates the mounting of the strain gauge to the object being measured, and ensures reproducible quality. In particular, the mounting of the sensor arrangement to the object being measured can be at least semi-automated, and preferably fully automated.

[0032] Preferably, steps (400) and (500) are performed after step (300), with step (300) following step (200). Alternatively, step (400) can be performed before step (200). Thus, the strain gauge can be connected to the object being measured before it is bonded to the electronic module. Therefore, the placement of the respective connecting foil between the two components to be joined can be performed in any order. In this sense, steps (400) and (500) are performed before step (200), and correspondingly, so is step (300). This is intended to clarify that the related steps (200) and (300) and (400) and (500) can, in principle, be performed in any order.

[0033] According to a preferred embodiment, one or more solder layers are applied to the first and / or second connecting foil and / or the object being measured and / or the strain gauge and / or the electronic module.

[0034] Preferably, the strain gauge, in particular the carrier layer of the strain gauge, and / or the first connecting film, has a metallized first solder layer arranged in step (200) between the strain gauge and the first connecting film. The first solder layer is to be understood as the first coating of the strain gauge and / or the first connecting film, which may be subdivided into several individual layers.

[0035] Preferably, the first interconnecting film and / or the electronic module has a metallized second solder layer, which is arranged in step (200) between the electronic module and the first interconnecting film. The second solder layer is to be understood as a second coating of the electronic module and / or the first interconnecting film, which may also be subdivided into several individual layers.

[0036] The first or second solder layer is applied, in particular, before the first connecting foil is placed between the strain gauge and the electronic module in the second process step (200). Subsequent activation of the first connecting foil generates sufficient heat to melt the first or second solder layer and solder the strain gauge to the electronic module. In this sense, according to one embodiment, it is provided that - the first solder layer is applied to the strain gauge, in particular the carrier layer of the strain gauge, and / or the first connecting foil, - the second solder layer is applied to the electronic module and / or the first connecting foil, - the first connecting foil with the solder layers is placed in step (200) between the strain gauge and the electronic module, and - The metallic materials of the first bonding foil are activated in step (300), causing the first bonding foil to heat up to such an extent that the first and second solder layers melt, and the strain gauge, in particular the strain gauge's carrier layer, is soldered to the electronic module through the molten first and second solder layers to create the metallurgical bond. The metallization of the strain gauge and / or the electronic module and / or the first bonding foil, i.e., the application of the first or second solder layer to the strain gauge, the electronic module, and / or the bonding foil, is essential for enabling the nanobond process.

[0037] Preferably, the object being measured and / or the second connecting film has a metallized third solder layer arranged in step (400) between the object being measured and the second connecting film. The third solder layer is to be understood as the third coating of the object being measured and / or the second connecting film, which may be subdivided into several individual layers.

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

[0039] The third or fourth solder layer is applied, in particular, before the second bonding foil is placed between the test object and the strain gauge or the electronic module in the fourth process step (400). Subsequent activation of the second bonding foil generates sufficient heat to melt the third or fourth solder layer and solder the test object to the strain gauge. In this sense, according to one embodiment, it is provided that - the third solder layer is applied to the measuring object and / or the second connecting foil, - the fourth solder layer is applied to the strain gauge, in particular the carrier layer of the strain gauge, and / or the second connecting foil, - the second connecting foil with the solder layers is placed in step (400) between the object being measured and the strain gauge, and - the metallic materials of the second connecting foil are activated in step (500) so that the second connecting foil heats up to such an extent that the third solder layer and the fourth solder layer melt and the measuring object is soldered to the strain gauge, in particular the carrier layer of the strain gauge, through the molten third solder layer and the molten fourth solder layer in order to create the metallurgical connection.

[0040] The respective solder layer is a metallized layer that enables an effective material-bonded connection between the strain gauge and the electronic module or between the strain gauge and the object being measured.

[0041] Using the respective connecting foil and solder layers, an intermetallic, metallurgical bond can be created between the parts to be joined, without requiring high temperatures, pressures, electromagnetic fields, etc. for its formation. The intermetallic connection enables a 1:1 signal transmission from the object being measured to the strain gauge.

[0042] The solder layers can be advantageously applied as metallic starter layers to the respective surfaces of the parts to be joined (measured object, connecting foil, strain gauge, and electronic module) using plasma processes, sputtering, or vapor deposition. Other options include two-shot injection molding, additive manufacturing, etc. At least one of the solder layers, preferably all of them, preferably comprises nickel. Furthermore, preferably one of the solder layers, preferably all of them, comprises gold. Copper or palladium are also suitable materials for the respective solder layer. The material of each solder layer is adapted to the dimensions and material of the connecting foil, the measured object, the strain gauge, and 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 multilayered. 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 object being measured and / or the strain gauge and / or the electronic module, and thus faces away from the respective connecting foil.

[0044] To prevent unpredictable deformation of the composite, a fixing pad can be applied to the layers with low pressure. In this respect, a fixing pad, which exerts pressure at least indirectly on the test object and / or the strain gauge and / or the electronic module, is preferably used to counteract deformation of the solder layers and the respective connecting foil during activation and joining in step (300) and step (500), respectively. The pressure is so low that it does not lead to any stresses within the strain gauge and / or the electronic module and / or the test object that could impair the strength of the connection between the strain gauge and the test object or between the strain gauge and the electronic module, or the measurement accuracy.

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

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

[0047] The above definitions, as well as the explanations regarding technical effects, advantages, and advantageous embodiments of the method according to the invention, also apply mutatis mutandis to the 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 combinations specified, but also in other combinations or individually, without departing from the scope of the present invention.

[0048] An embodiment of the invention is explained in more detail below with reference to the schematic drawings, wherein identical or similar elements are provided with the same reference numeral. Here, Fig. 1 a longitudinal sectional view of an arrangement according to the invention of a sensor arrangement arranged on a measuring object according to a first embodiment, Fig. 2 a detailed longitudinal section view of the arrangement according to the invention Fig. 1, Fig. 3 an exploded view of layers and tools for connecting a strain gauge of the sensor arrangement to an electronic module of the sensor arrangement by means of a first connecting film, and the sensor component of the sensor arrangement resulting from the connection, Fig. 4 an exploded view of layers and tools for connecting the strain gauge to the object being measured by means of a second connecting film, as well as the arrangement resulting from the connection, Fig. 5 a process of a method according to the invention for connecting the sensor arrangement with the object being measured 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. Figure 1 shows a preferred embodiment of an arrangement of a sensor arrangement 5 mounted on a measuring object 2. The sensor arrangement 5 comprises a strain gauge 1 and an electronic module 19 electrically connected thereto. The strain gauge 1 is connected by means of a Fig. 3 in conjunction with Fig. In the method shown in section 5, the electronic module 19 is connected to the electronic module 19 via a first connecting film 10a in a material-bonded manner. Furthermore, the strain gauge 1 is connected by means of a Fig. 4 in conjunction with Fig. In the method shown in section 5, the object being measured is bonded to the object 2 via a second connecting film 10b. 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 is shown in more detail and comprises a carrier layer 1a facing the object 2 and a meandering measuring grid 1b arranged on it. The measuring grid 1b is connected to the electronic module 19, which is designed as a preamplifier module, via the first connecting film 10a. This will be explained in more detail below. A cable 20 leads out of the housing 18, connecting the electronic module 19 to an evaluation unit (not shown here) and / or a voltage source, such as the one described in Fig. 3 or Fig. Battery 15, shown in section 4, connects. As shown in Fig. 2 and Fig. As can be seen in Figure 3, the strain gauge 1, in particular its carrier layer 1a, has a metallized first solder layer 13 on a first surface 4a facing the first connecting foil 10a, and the electronic module 19 has a metallized second solder layer 14 on a surface 17 facing the first connecting foil 10a. One or both of the solder layers 13, 14 can also be applied to the first connecting foil 10a.

[0051] The object being measured, 2, is significantly larger than the sensor assembly, 5. The object being measured, 2, could 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 object being measured, 2. The resistance of the strain gauge 1 changes with a force applied to the object being measured, 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 object being measured, it causes mechanical stress and strain. Mechanical stress is the resistance that the object offers to the force, and strain is the displacement and deformation resulting from the force. Therefore, the strain gauge 1 is designed, at least, to detect strains and compressions, and preferably other measured quantities, of the object being measured, 2.

[0052] The first connecting foil 10a creates a strong, material-bonded connection between the strain gauge 1 and the electronic module 19, and the second connecting foil 10b creates a strong, material-bonded connection between the strain gauge 1 and the object being measured 2. Each connection transmits forces of the measured quantity as well as disturbances caused by thermal expansion. The type of connection places requirements on the surface properties of the object being measured 2, the strain gauge 1, and the electronic module 19.

[0053] Two on the far right in Fig. The force arrows F shown in Figure 1 illustrate an exchange of forces through deformation, which represents the actual measured quantity. To the left of this is a bidirectional force arrow F, which illustrates an exchange of forces through stresses and differential thermal expansion, representing a disturbance variable. The object being measured, Figure 2, can, as mentioned above, have a metallized surface or be made of a metallic material.

[0054] In a first process step 100, the measurement object 2, the sensor assembly 5 comprising the strain gauge 1 and the electronic module 19, 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 highly magnified cross-sectional view of the respective connecting foil 10a, 10b with the aluminum 11 and nickel layers 12 is shown in Fig. Figure 6 shows that 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.

[0055] Step 100 is followed according to Fig. 5. The fabrication of the sensor assembly 5 is described first. Step 200 therefore follows step 100, wherein in step 200 the first connecting film 10a is placed between the strain gauge 1 and the electronic module 19. The first connecting film 10a contacts a first solder layer 13 on the strain gauge 1, here on the carrier layer 1a of the strain gauge 1, on one side, and a second solder layer 14 on the electronic module 19 on the other side. During process step 200, the aluminum layers 11 and the nickel layers 12 of the first connecting film 10a are still arranged alternately next to each other, as described by Fig. Figure 6 shows that both solder layers 13, 14 comprise nickel. In this case, both layers 13, 14 also have a gold layer, with the gold layer facing the first connecting foil 10a.

[0056] Step 200 is followed by step 300, after which the aluminum layers 11 and the nickel layers 12 of the first bonding foil 10a are joined using the example shown in Fig. The battery 15 shown in Figure 3 is activated. A DC voltage source can be used instead of battery 15 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, causing the first connecting foil 10a to heat up to such an extent that the first solder layer 13 and the second solder layer 14 melt, and the electronic module 19 is soldered to the strain gauge 1, i.e., the carrier layer 1a of the strain gauge 1, by means of the molten solder layers 13 and 14. This results in, as shown on the right in Figure 10a, a galvanic corrosion process. Fig. As indicated in Figure 3, a stable bonding surface 7a is formed between the electronic module 19 and the strain gauge 1. This creates a sensor component, which is used to form the sensor assembly 5 in the following steps. One advantage of this design is that, due to the materials of the first bonding film 10a, an electrical connection between the measuring grid 1b of the strain gauge 1 and the electronic module 19 can be established after activation of the first bonding film 10a. In other words, the electrical connection between the measuring grid 1b of the strain gauge 1 and the electronic module 19 is realized by the bonding surface 7a remaining after activation. Therefore, no additional wiring or connection of the strain gauge 1 to the electronic module 19 is required.

[0057] Following the metallurgical bonding of the strain gauge 1 to the electronic module 19, i.e., after step 300, the second bonding foil 10b is placed between the strain gauge 1, here the carrier layer 1a of the strain gauge 1, and the test object 2 in step 400. The second bonding foil 10b contacts a third solder layer 21 on the test object 2 on one side and a fourth solder layer 22 on the strain gauge 1, here on the carrier layer 1a of the strain gauge 1, on the other side. During process step 400, the aluminum layers 11 and the nickel layers 12 of the second bonding foil 10b are still arranged alternately next to each other, as shown by Fig. Figure 6 shows that both solder layers 21, 22 comprise nickel. In this case, both layers 21, 22 also have a gold layer, with the gold layer facing the second connecting foil 10b.

[0058] Step 400 is followed by step 500, after which the aluminum layers 11 and the nickel layers 12 of the second bonding foil 10b are joined using the example shown in Fig. Battery 15 shown in section 4 can be activated. The same battery can be used according to... Fig. 3 or another voltage source is 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, causing the second connecting foil 10b to heat up to such an extent that the third solder layer 21 and the fourth solder layer 22 melt, and the test object 2 is soldered to the strain gauge 1, i.e., the carrier layer 1a of the strain gauge 1, through the molten solder layers 21, 22. This results in, as shown on the right in Fig. 4 indicates a stable bonding or joining surface 7b between the strain gauge 1 and the object being measured 2.

[0059] To form the sensor assembly 5, the strain gauge 1 and the electronic module 19 are encapsulated in step 600 after step 500, whereby the strain gauge 1 and the electronic module 19 are completely surrounded by the measuring object 2 and by a potting compound or an injection molding compound. The encapsulation forms a housing 18 that receives the strain gauge 1 and the electronic module 19 and protects them from external influences.

[0060] The respective solder layers 13, 14, 21, 22 may further comprise copper, silver, silicon nitride Si3N4, silicon dioxide SiO2, titanium tungsten TiW, palladium or the like. The solder layers 13, 14, 21, 22 may be identical, that is, made of the same material.

[0061] The connecting foils 10a, 10b are processed by laser cutting in such a way that the respective connecting foil 10a, 10b assumes a shape and dimensions that form a provided joining surface 7a, 7b between the strain gauge 1 and the electronic module 19 or between the strain gauge 1 and the measuring object 2 as well as a respective activation section 8a, 8b.

[0062] In the illustrated embodiment, the first activation section 8a is after Fig. 3 not covered by the electronic module 19 and the second activation section 8b is according to Fig. 4 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 or Fig. 4 can be clearly seen from the stack formed by the sensor arrangement 5, the measuring object 2 and the solder layers 21 - 26 when all layers are next to each other.

[0063] The inventive method creates a material-bonded connection between the strain gauge 1 and the object being measured 2, as well as between the strain gauge 1 and the electronic module 19. The surfaces 4a, 4b of the carrier layer 1a and / or the surface of the object being measured 6 and / or the surface 20 of the electronic module 19 can have a surface structure such that molten material from the aluminum layers 11 and / or the nickel layers 12 can penetrate into the spaces between the respective surfaces and, after solidification, create a positive connection between the two components to be materially bonded. The detectable measured quantity can be increased by special structures of the object being measured 2. The object being measured 2 can, for example, form depressions, ribs, beads, or similar features that increase or decrease forces in certain spatial directions.

[0064] Both when connecting the strain gauge 1 to the electronic module 19 according to steps 200 and 300, and when connecting the strain gauge 1 to the test object 2 according to steps 400 and 500, a fixing pad 9 with a compliant layer 23 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, 21, 22 and the respective connecting foil 10a, 10b during activation and connection in steps 300 and 500, respectively.

[0065] It should be expressly noted that the invention is not limited to the embodiments disclosed herein. These are merely exemplary configurations, and further variants are possible. In particular, the third solder layer 21 on the measuring object 2 can be omitted if the measuring object 2 is made of a solderable material or has an already metallized surface. Furthermore, the interconnected steps 400 and 500 can be performed after the interconnected steps 200 and . Reference sign F force p print 1 strain gauge 1a Carrier layer 1b Measuring grid 2. Measuring object 4a First surface of the strain gauge 4b Second surface of the strain gauge 5 Sensor arrangement 6. Surface of the object being measured 7a First joining surface 7b Second joining surface 8a First activation phase 8b Second activation section 9 fixing pads 10a first connecting foil 10b second connecting foil 11 Aluminum layer 12 nickel layer 13 First solder layer 14 Second solder layer 15 batteries 16 Activating Agents 17 Surface of the electronic module 18 cases 19 Electronic module 20 Cabling 21 Third solder layer 22 Fourth solder layer 23 Flexible layer 100 First procedural step 200 Second procedural step 300 Third procedural step 400 Fourth process step 500 Fifth procedural step

Claims

Method for connecting a sensor arrangement (20) to a measurement object (2), the method comprising the steps: (100) providing - a measurement object (2), - a sensor arrangement (20) comprising a strain gauge (1) configured at least to detect tensile and compressive deformations of a measurement object (2), and an electronic module (19), - a first connecting film (10a) and a second connecting film (10b), each containing metallic materials (11, 12) which react exothermically upon activation, (200) placing the first connecting film (10a) between the strain gauge (1) and the electronic module (19), (300) activating the metallic materials (11, 12) of the first connecting film (10a) such that the first connecting film (10a) heats up in such a way that a metallurgical bond is created between the strain gauge (1) and the electronic module (19), wherein after activation of the metallic Materials (11,12) the first connecting foil (10a) establishes an electronic connection between the strain gauge (1) and the electronic module (19), (400) placing the second connecting foil (10b) between the strain gauge (1) and the object being measured (2), 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) and the object being measured (2). Method according to claim 1, wherein the strain gauge (1) and the electronic module (19) are encapsulated in a common housing (18) in a step (600). Method according to one of claims 1 or 2, wherein steps (400) and (500) are carried out after step (300), which is followed by step (200). Method according to one of claims 1 or 2, wherein steps (400) and (500) are performed before step (200). Method according to one of the preceding claims, wherein the strain gauge (1) comprises a carrier layer (1a) facing the object being measured (2) and a measuring grid (1b). Method according to one of the preceding claims, wherein the strain gauge (1) and / or the first connecting foil (10a) has a metallized first solder layer (13) which is arranged in step (200) between the strain gauge (1) and the first connecting foil (10a). Method according to one of the preceding claims, wherein the first connecting film (10a) and / or the electronic module (19) has a metallized second solder layer (14) which is arranged in step (200) between the electronic module (19) and the first connecting film (10a). The method of claim 6 in conjunction with claim 7, wherein: - the first solder layer (13) is applied to the strain gauge (1) and / or the first interconnecting foil (10a), - the second solder layer (14) is applied to the electronic module (19) and / or the first interconnecting foil (10a), - the first interconnecting foil (10a) with the solder layers (13, 14) is placed between the strain gauge (1) and the electronic module (19) in step (200), and - the metallic materials (11, 12) of the first interconnecting foil (10a) are activated in step (300) such that the first interconnecting foil (10a) heats up in such a way that the first solder layer (13) and the second solder layer (14) melt and the strain gauge (1) is soldered to the electronic module (19) through the molten first solder layer (13) and the molten second solder layer (14). is done to create the materially bonded connection. Method according to one of the preceding claims, wherein the object being measured (2) and / or the second connecting foil (10b) has a metallized third solder layer (21) which is arranged in step (400) between the object being measured (2) and the second connecting foil (10b). Method according to one of the preceding claims, wherein the second connecting foil (10b) and / or the strain gauge (1) has a metallized fourth solder layer (22) which is arranged in step (400) between the strain gauge (1) and the second connecting foil (10b). The method of claim 9 in conjunction with claim 10, wherein: - the third solder layer (21) is applied to the measuring object (2) and / or the second connecting foil (10b), - the fourth solder layer (22) is applied to the strain gauge (1) and / or the second connecting foil (10b), - the second connecting foil (10b) with the solder layers (21, 22) is placed between the measuring object (2) and the strain gauge (1) in step (400), and - the metallic materials (11, 12) of the second connecting foil (10b) are activated in step (500) such that the second connecting foil (10b) heats up in such a way that the third solder layer (21) and the fourth solder layer (22) melt and the measuring object (2) is soldered to the strain gauge (1) through the molten third solder layer (21) and the molten fourth solder layer (22). to create the materially bonded connection. Method according to claim 8 or claim 11, wherein a fixing pad (9) which exerts a pressure (p) at least indirectly on the sensor arrangement (20) and / or on the object being measured (2) is used to counteract deformation of the solder layers (13, 14, 21, 22) and the respective connecting foil (10a, 10b) during activation and connection in step (300) or step (500). Method according to one of claims 6 to 12, wherein the respective solder layer (13, 14, 21, 22) is formed from a nickel-comprising material. Method according to any one of claims 6 to 13, wherein the respective solder layer (13, 14, 21, 22) comprises a nickel layer and a gold layer. Arrangement of a sensor arrangement (20) on a measuring object (2), wherein the sensor arrangement (20) has been connected to the measuring object (2) by a method according to one of the preceding claims.

Images