DE102022209552B4 - Connection of a sensor arrangement arranged on a mounting plate with a measuring object - Google Patents

Abstract

Method for connecting a sensor arrangement (5) arranged on a mounting plate (17) to a measuring 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, wherein the strain gauge (1) and the electronic module (19) are each glued to the mounting plate (17) and encapsulated in a housing (18),
- a connecting foil (10) containing metallic materials (11, 12) which react exothermically when activated,
(200) Placing the connecting foil (10) between the mounting plate (17) and the measuring object (2), and
(300) Activating the metallic materials (11, 12) of the connecting foil (10) so that the connecting foil (10) heats up in such a way that a material connection is created between the mounting plate (17) and the measuring object (2).

Description

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.

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.

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.

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 pressures, or high vacuum or inert gas. Other methods require strong electromagnetic fields. In this context, impractical means they could destroy the strain gauge or the measurement object.

From the DE 10 2013 002 144 A1 A joining method for thermally sensitive structures emerges, 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 brings about 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 in each case 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 that after cooling and solidification of the entire melting material, a functional hard solder connection is formed, wherein the thermal load required for the melting is introduced only within the contour sections of the contacts to be joined and exclusively on solder connecting layers of the solder layer system.

In the EP 2 796 830 B1 A strain gauge is shown. The strain gauge includes a semiconductor chip having a plurality of piezoresistive elements formed on a front surface of a semiconductor substrate, a lead wire unit electrically connected to a plurality of electrodes of the semiconductor chip, and a plate member connected to a back surface of the semiconductor chip.

In the EP 3 839 460 A1 A sensor system is shown that includes a structural interconnect layer and a sensor. The structural interconnect layer is disposed on a structure. The structural interconnect layer is a metallic alloy. The sensor includes a non-metallic wafer and a sensor interconnect layer disposed 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.

In the WO 2016/199286 A1 A strain detection system is shown, which comprises 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 substrate for strain transmission. Furthermore, the strain detection The strain gauge system includes a strain gauge unit in which the semiconductor element, the interconnect material, and the strain transmission substrate are sealed by a first sealing material. The strain gauge unit and a circuit substrate connected to the strain gauge unit are sealed by a second sealing material.

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 subclaims, the following description, and the figures.

• (100) Bereitstellen
  • - eines Messobjekts,
  • - einer Sensoranordnung, umfassend einen Dehnungsmessstreifen, der zumindest dazu eingerichtet ist, dehnende und stauchende Verformungen eines Messobjekts zu erfassen, sowie ein damit verbundenes Elektronikmodul, wobei der Dehnungsmessstreifen und das Elektronikmodul jeweils auf der Montageplatte angeklebt sowie in einem Gehäuse eingekapselt sind,
  • - einer Verbindungsfolie, die metallische Materialien enthält, die bei ihrer Aktivierung exotherm reagieren,
• (200) Platzieren der Verbindungsfolie zwischen der Montageplatte und dem Messobjekt, und
• (300) Aktivieren der metallischen Materialien der Verbindungsfolie, sodass sich die Verbindungsfolie derart erhitzt, dass zwischen der Montageplatte und dem Messobjekt eine stoffschlüssige Verbindung erzeugt wird.

A method according to the invention for connecting a sensor arrangement arranged on a mounting plate to a measuring object comprises the steps

• (100) Provide
  • - a measuring object,
  • - a sensor arrangement comprising a strain gauge which is at least configured to detect stretching and compressive deformations of a measurement object, and an electronic module connected thereto, wherein the strain gauge and the electronic module are each glued to the mounting plate and encapsulated in a housing,
  • - a connecting foil containing metallic materials that react exothermically when activated,
• (200) Placing the connecting foil between the mounting plate and the measuring object, and
• (300) Activating the metallic materials of the connecting foil so that the connecting foil heats up in such a way that a material connection is created between the mounting plate and the measuring object.

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).

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 electronics module connected to the strain gauge. The electronics module comprises, in particular, preamplifier electronics which are suitably connected to the strain gauge and an evaluation unit. The strain gauge and the electronics module are each adhesively bonded to the mounting plate and encapsulated in a common housing. Furthermore, a connecting foil is provided which contains metallic materials which react exothermically when activated.

Through encapsulation, the strain gauge and the electronic module are spatially surrounded by the mounting plate and the housing. “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 when 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 embodiment enables mechanical and/or unwanted electrical influences on the strain gauge and the electronic module, for example due to moisture or dirt, are prevented.

The measurement object can, in particular, be significantly larger than the sensor arrangement. The measurement object can be, for example, 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 sensor arrangement is arranged, i.e. on which the strain gauge and the electronics module are glued, 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, as unintentional damage to the strain gauge or the electronic module during activation of the connecting foil, especially during heating of the materials of the connecting foil, can be excluded.

In this sense, the strain gauge and the electronic module are preferably completely surrounded by the mounting plate and a potting compound or injection molding compound prior to process step (200). This forms the housing, and the sensor assembly is protected from unwanted influences, particularly damage, even during subsequent handling. This is also advantageous because the sensor assembly can be manufactured under clean-room conditions. This allows the strain gauge and the electronic module to be glued to the mounting plate and encapsulated in the housing without allowing contaminants to enter the housing.

The strain gauge is particularly designed to measure strain, compression, and/or torque generated by, originating 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. In addition, 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 configured in the form of a film. Therefore, the carrier layer is preferably a carrier film and/or the cover layer is preferably a cover film. The carrier layer is preferably made of polyimide. If a cover layer is provided, this can also be made of polyimide.

A so-called NanoFoil® from the Indium Corporation can be used as a connecting foil, for example. The NanoFoil® is a reactive multilayer foil produced by vapor deposition of thousands of alternating nanoscale layers, for example, made 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, 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 adapted to requirements. In particular, the thickness of the connecting foil can be adjusted depending on the material of the measurement object and/or the mounting plate and/or the carrier layer of the strain gauge. The thinner the connecting foil, the less energy is required to initiate or activate the connecting foil. The total energy must be adjusted to ensure a secure connection between the strain gauge and the test object.

The connecting foil is placed between the mounting plate and the measurement object in a second method step (200). The placement can be carried out in such a way that the connecting foil is placed in a sandwich configuration either directly on the facing surfaces of the mounting plate and of the measurement object. Alternatively, the placement can be carried out such that the 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. Further alternatively, the placement can be carried out such that the connecting foil is arranged in a sandwich configuration between two solder layers, wherein the solder layers are applied to opposite surfaces of the connecting foil. These surfaces of the 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).

When activated, the connecting foil forms a joining surface between the measurement object and the mounting plate. If this does not already occur at the joining section forming the joining surface, the connecting foil can also have an activation section where the metallic material of the connecting foil is activated. Activation means can be arranged at the activation section to activate the connecting foil. The joining section and, if applicable, the activation section are formed between the mounting plate and the measurement object. The activated connecting foil connects the measurement object to the mounting plate in a material-to-material bond at least in the joining surface, preferably in the joining surface and, if applicable, in the activation section. If an activation section is provided, it is therefore located outside the joining surface between the mounting plate and the measurement object.

At least one, preferably several, activation means are electrically connected to the 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 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 also 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 for activating the connecting foil. The activation means and/or the voltage sources can be connected to the electronic module.

In a third method step (300), the metallic materials of the connecting foil are activated via the respective activation agent, so that the connecting foil heats up to such an extent that the mounting plate is bonded to the measurement object. After activation of the connecting foil, a bond is formed 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, with the battery being 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 connecting foil.

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 between the mounting plate and the measurement object, created by activating the metallic materials of the bonding foil, 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.

The inventive method is characterized by lower temperatures and stresses during bonding. 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 between the mounting plate and the measurement object created by the inventive method does not age with time and temperatures. Steam, pressure, or similar factors do not cause any change in the bond 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. The composite material (especially metal) continues to offer elastic deformation for repeatability.

Advantageously, the electrical connection between the activating agent and the connecting foil can be made with the same device with which the mounting plate is placed on the measuring object and the pressure is exerted for the material connection.

The connecting foil is laser-cut to a shape and dimensions that perfectly fit the intended joining surface between the mounting plate and the measurement object. This allows the connecting foil to be formed to the desired dimensions with exceptional precision and efficiency before being placed between the two surfaces.

Therefore, the laser cutting takes place before the connecting foil is placed between the mounting plate and the measuring object in step (200).

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.

According to a preferred embodiment, one or more solder layers are applied to the connecting foil and/or the mounting plate and/or the measurement object. Preferably, the mounting plate and/or the 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 connecting foil, which can be divided into several individual layers.

Preferably, the 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 connecting foil, which can also be divided into several individual layers. The respective solder layer is a metallized layer that enables an effective, material-to-material connection between the strain gauge and the measurement object.

• - die erste Lötschicht auf der Montageplatte und/oder der Verbindungsfolie aufgetragen wird,
• - die zweite Lötschicht auf dem Messobjekt und/oder der Verbindungsfolie aufgetragen wird,
• - die Verbindungsfolie mit den Lötschichten in dem Schritt (200) zwischen der Montageplatte und dem Messobjekt platziert wird, und
• - die metallischen Materialien der Verbindungsfolie in dem Schritt (300) aktiviert werden, sodass sich die Verbindungsfolie derart erhitzt, dass die erste Lötschicht und die zweite Lötschicht schmelzen und die Montageplatte durch die aufgeschmolzene erste Lötschicht und die aufgeschmolzene zweite Lötschicht mit dem Messobjekt verlötet wird, um die stoffschlüssige Verbindung zu erzeugen. Die Metallisierung des Messobjekts, der Montageplatte und/oder der Verbindungsfolie, also das Aufbringen der Lötschicht auf das Messobjekt, die Montageplatte und/oder die Verbindungsfolie ist wichtig, um den Nanobond-Prozess zu ermöglichen.

The respective solder layer is applied, in particular, before the connecting foil is placed between the mounting plate and the measurement object in the second method step (200). Subsequent activation of the connecting foil generates sufficient heat to melt the respective 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 connecting foil,
• - the second solder layer is applied to the measuring object and/or the connecting foil,
• - the 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 connecting foil are activated in step (300) so that the 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 connecting foil, i.e., the application of the solder layer to the measurement object, the mounting plate, and/or the connecting foil, is important to enable the nanobond process.

Using the bonding foil and solder layers, an intermetallic, material-tight bond can be created between the mounting plate and the measurement object, which does not require high temperatures, pressures, electromagnetic fields, etc. to create. The intermetallic bond enables a 1:1 signal transmission from the measurement object to the strain gauge.

The solder layers can be applied as metallic starting layers (first and second solder layers) particularly advantageously by plasma processes, sputtering processes, or vapor deposition on the respective surface of the parts to be joined (mounting plate, measurement object, connecting foil). Further possibilities include two-shot injection molding, additive manufacturing, etc. At least one of the solder layers, preferably both solder layers, preferably comprise nickel. Preferably, one of the solder layers, preferably both solder layers, comprises gold. Copper or palladium are also suitable 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, and/or the measurement object.

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 faces the measurement object and/or the mounting plate and thus faces away from the connecting foil.

To prevent unforeseeable deformation of the composite, a fixing pad can be applied to the layers with low pressure. In this sense, deformation of the solder layers and the connecting foil during activation and connection in step (300) is preferably counteracted by means of a fixing pad that exerts pressure at least indirectly on the sensor arrangement and/or the mounting plate and/or the measurement object. 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 measurement object that could impair the strength of the connection between the mounting plate and the measurement object or the measurement accuracy.

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 sensor arrangement and/or the measurement object. The fixing pad can also be arranged directly on the mounting plate and/or the sensor arrangement and/or the measurement object.

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.

The above definitions as well as explanations of 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.

• 1 eine Längsschnittdarstellung einer erfindungsgemäßen Anordnung einer auf einer Montageplatte angeordneten Sensoranordnung an einem Messobjekt gemäß einer ersten Ausführungsform, wobei die Montageplatte mittels einer - hier stark vereinfacht dargestellten - Verbindungsfolie an dem Messobjekt befestigt ist,
• 2 eine detaillierte Längsschnittdarstellung der erfindungsgemäßen Anordnung gemäß 1,
• 3 eine Explosionsdarstellung von Schichten und Werkzeugen zur Verbindung der Sensoranordnung mit dem Messobjekt mittels der Verbindungsfolie sowie die durch das Verbinden entstehende Anordnung nach der zweiten Ausführungsform,
• 4 einen Ablauf eines erfindungsgemäßen Verfahrens zur Verbindung der Sensoranordnung mit dem Messobjekt nach 1 bis 3, und
• 5 eine stark vergrößerte Querschnittsansicht der Verbindungsfolie für die Anordnung nach 1 bis 4.

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.

• 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, wherein the mounting plate is attached to the measuring object by means of a connecting foil - shown here in a highly simplified manner,
• 2 a detailed longitudinal sectional view of the arrangement according to the invention according to 1 ,
• 3 an exploded view of layers and tools for connecting the sensor arrangement to the measuring object by means of the connecting foil and the arrangement resulting from the connection according to the second embodiment,
• 4 a sequence of a method according to the invention for connecting the sensor arrangement to the measurement object according to 1 until 3 , and
• 5 a greatly enlarged cross-sectional view of the connecting foil for the arrangement according to 1 until 4 .

1 shows a preferred embodiment of an arrangement of a sensor arrangement 5 arranged on a mounting plate 17 on a measurement object 2. The sensor arrangement 5 comprises a strain gauge 1 and an electronic module 19 electrically connected thereto, wherein both the strain gauge 1 and the electronic module 19 are glued to the mounting plate 17 and encapsulated in a common housing 18 made of potting material. Thus, the encapsulation forms a housing 18 accommodating the strain gauge 1 and the electronic module 19. The mounting plate 17 is produced by a method according to the invention described below. 5 connected to the measuring object 2 by means of a connecting foil 10. The strain gauge 1 is in 2 shown in more detail 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, which is designed as a preamplifier module, via a first wiring 20, which is also encapsulated in the housing 18. A second wiring 21 is led out of the housing 18, which connects the electronic module 19 with an evaluation unit (not shown here) and/or a voltage source, such as the one shown in 3 shown battery 15. As also shown in 2 As can be seen, the mounting plate 17 has a metallized first solder layer 13 facing the connecting foil 10 on a mounting plate surface 4, and the measurement object 2 has a metallized second solder layer 14 facing the connecting foil 10 on a measurement object surface 6. One or both of the solder layers 13, 14 can also be applied to the connecting foil 10. The measurement object 2 is in this case 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 the object offers to the force, and the strain is the displacement and deformation resulting from the force. Thus, the strain gauge 1 is at least configured to detect stretching and compression deformations, preferably other measured variables, of the measurement object 2.

By means of the connecting foil 10, a firm, in this case a material-to-material connection between the mounting plate 17 and the measuring object 2 is realized. This connection transmits forces of the measured variable as well as disturbances due to thermal expansion. The type of connection places demands on the surface quality of the measuring object 2 and the mounting plate 17. Two on the far right in 1 The force arrows F shown illustrate an exchange of forces through deformation, which represents the actual measured variable. To the left, 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.

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 connecting foil 10 are provided. In all embodiments, the connecting foil 10 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 connecting foil 10 with the aluminum 11 and nickel layers 12 is shown in 5 shown. When activated by a small pulse of local energy from electrical, optical, or thermal sources, the interconnecting foil 10 reacts exothermically to generate precise local heat up to temperatures of 1500 °C in fractions of a second.

In a second method step 200, the connecting foil 10 is placed between the mounting plate 17 and the measurement object 2, as shown by 1 until 3 is shown. The connecting foil 10 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 the method step 200, the aluminum layers 11 and the nickel layers 12 of the connecting foil 10 are still arranged alternately next to each other, as shown by 5 is shown. Both solder layers 13, 14 comprise nickel. In the present case, both layers 13, 14 additionally have a gold layer, wherein the gold layer is arranged facing the connecting foil 10. The respective solder layer 13, 14 can further comprise copper, silver, silicon nitride Si ₃ N ₄ , silicon dioxide SiO ₂ , titanium tungsten TiW, palladium or the like. In this exemplary embodiment, the strain gauge 1 and the electronic module 19 have been completely surrounded by the mounting plate 17 and a potting compound or an injection molding compound before method step 200.

The connecting foil 10 is processed by laser cutting such that the connecting foil 10 assumes a shape and dimensions that form a designated joining surface 7 between the mounting plate 17 and the measurement object 2. A battery 15 is provided as an activation means 16, which is electrically connected to the connecting foil 10.

In a third process step 300, the aluminum layers 11 and the nickel layers 12 of the connecting foil 10 are 5 using the example shown in 3 shown battery 15. Instead of the battery 15, a DC voltage source can be used to activate the connecting foil 10. The aluminum layers 11 and nickel layers 12 of the connecting foil 10 then react strongly exothermically, so that the connecting foil 10 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 3 indicated, a stable bonding or joining surface 7 between the mounting plate 17 and the measuring object 2.

Thus, a material-to-material connection is realized between the mounting plate 17 and the measurement object 2. The mounting plate surface 4 and/or the measurement object surface 6 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 of the measurement object surface 6 and/or the mounting plate surface 4 and, after solidification, can create a positive connection between the mounting plate 17 and the measurement object 2. 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 that amplify or reduce forces in certain spatial directions.

In another in 3 The embodiment shown is a further development of the first embodiment according to 1 and 2 shown. 3 shows in the left part a state in which no connection has been created between the measuring object 2 and the mounting plate 17. The right part of 3 shows the state after formation of the material connection between the measurement object 2 and the sensor arrangement 5 arranged on the mounting plate 17, i.e. after the mounting plate 17 has been soldered to the measurement object 2 by the melted solder layers 13, 14. The connecting foil 10 is cut by laser cutting such that it has an activation section 8, which in the illustrated embodiment is not covered by the sensor arrangement 5 and is thus freely accessible for applying the activation agent 16. Thus, the activation section 8 protrudes, as shown in the left part of 3 can be clearly seen from the stack formed by the mounting plate 17, the measuring object 2 and the two solder layers 13, 14 when all layers lie against each other.

A fixing pad 9, which comprises a compliant layer 22, exerts a pressure p on the stack formed by the strain gauge 1, the measurement object 2, and the two solder layers 13, 14. This pressure is very low and acts perpendicularly on an outer surface of the sensor arrangement 5. The pressure serves to counteract deformation of the solder layers 13, 14 and the connecting foil 10 during activation and connection in step 300.

It should be expressly noted that the invention is not limited to the embodiments disclosed here. These are merely exemplary embodiments, although other 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 a pre-metallized surface.

Reference symbol

F

Power

p

Pressure

1

strain gauges

1a

Carrier layer

1b

measuring grid

2

Measurement object

4

Mounting plate surface

5

Sensor arrangement

6

Measuring object surface

7

Joining surface

8

Activation section

9

Fixing pad

10

Connecting foil

11

aluminum layer

12

Nickel layer

13

First solder layer

14

Second solder layer

15

battery

16

Activating agent

17

Mounting plate

18

Housing

19

Electronic module

20

First cabling

21

Second cabling

22

Flexible layer

100

First procedural step

200

Second procedural step

300

Third procedural step

Claims (11)

Method for connecting a sensor arrangement (5) arranged on a mounting plate (17) to a measurement object (2), the method comprising the steps (100) providing - a measurement 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, wherein the deh voltage measuring strip (1) and the electronic module (19) are each glued to the mounting plate (17) and encapsulated in a housing (18), - a connecting foil (10) which contains metallic materials (11, 12) which react exothermically when activated, (200) placing the connecting foil (10) between the mounting plate (17) and the measurement object (2), and (300) activating the metallic materials (11, 12) of the connecting foil (10) so that the connecting foil (10) heats up in such a way that a material-to-material connection is created between the mounting plate (17) and the measurement object (2). Procedure according to Claim 1 , wherein the connecting film (10) is processed by laser cutting such that the connecting film (10) assumes a shape and dimensions which cover an intended joining surface (7) between the mounting plate (17) and the measuring object (2). Method according to one of the preceding claims, wherein 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 before the method step (200). 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). Method according to one of the preceding claims, wherein the mounting plate (17) and/or the connecting foil (10) has a metallized first solder layer (13) which is arranged in step (200) between the mounting plate (17) and the connecting foil (10). Method according to one of the preceding claims, wherein the connecting foil (10) 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 connecting foil (10). Procedure according to Claim 5 combined with Claim 6 , wherein - the first solder layer (13) is applied to the mounting plate (17) and/or the connecting foil (10), - the second solder layer (14) is applied to the measurement object (2) and/or the connecting foil (10), - the connecting foil (10) with the solder layers (13, 14) is placed between the mounting plate (17) and the measurement object (2) in step (200), and - the metallic materials (11, 12) of the connecting foil (10) are activated in step (300) so that the connecting foil (10) heats up in such a way 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 means of the melted first solder layer (13) and the melted second solder layer (14) in order to create the material-to-material connection. Procedure according to Claim 7 , wherein a deformation of the solder layers (13, 14) and the connecting foil (10) during activation and connection in step (300) is counteracted by means of a fixing pad (9) which exerts a pressure (p) at least indirectly on the sensor arrangement (20) and/or on the measurement object (2). Method according to one of the Claims 5 until 8 , wherein the respective solder layer (13, 14) is formed from a material comprising nickel. Method according to one of the Claims 5 until 9 , wherein the respective solder layer (13, 14) comprises a nickel layer and a gold layer. 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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