DE102022209552A1 - Connection of a sensor arrangement arranged on a mounting plate with a measurement object - Google Patents

Abstract

The invention relates to a 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). a strain gauge (1), which is at least designed to detect expanding and compressive deformations of a measurement object (2), and an electronic module (19) connected thereto, the strain gauge (1) and the electronic module (19) each being on the mounting plate ( 17) are glued and encapsulated in a housing (18), - a connecting film (10) which contains metallic materials (11, 12) which react exothermically when activated, (200) placing the connecting film (10) between the mounting plate ( 17) and the measurement object (2), and (300) activating the metallic materials (11, 12) of the connecting film (10), so that the connecting film (10) heats up in such a way that between the mounting plate (17) and the measurement object (2 ) a cohesive connection is created. The invention further relates to an arrangement of a sensor arrangement (5) on a measurement object (2), wherein the sensor arrangement (5) has been connected to the measurement object (2) by the method according to the invention.

Description

The invention relates to a connection of a strain gauge to a measurement object. What is required in this context is in particular 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 interconnecting the physical signals that are to be measured. Strain gauges are measuring devices for recording stretching and compressing deformations. They change their electrical resistance even with small deformations and are used as sensors to measure strain.

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

Bonding is known for contacting the strain gauges on a larger measurement object. The connecting layer is therefore an adhesive layer. This is relatively easy to achieve for industrial manufacturing, but usually requires a manual process that is time-consuming and not cost-effective. Adhesive bonds are associated with varying temperature gradients, moisture/chemical dependency, and long-term aging. This can reduce signal quality or even destroy the sensor. Other joining 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 destroy the strain gauge or the measurement object.

From the DE 10 2013 002 144 A1 describes a joining process for thermally sensitive structures, whereby two components are brought into functional connection using a joining aid designed as a reactive nanofilm, in that the nanofilm is first introduced between assigned surface sections of the components to be joined together and subsequently causes a connection structure to be formed at least in sections , characterized in that by activating the nanofoil, a largely solid solder connecting layer is first melted on both mutually assigned surface sections of the components to be joined together and that subsequently the melting material, which is locally limited to one surface section, with the melting material, which is also locally limited, of the opposite surface section and the remains of the reactants of the nanoreactive film system are mixed in such a way that after cooling and solidification of the entire material to be melted, a functional brazed connection is formed, whereby the thermal load required for melting is only introduced within the contour sections of the contacts to be joined exclusively on solder connection layers of the solder layer system.

The object of the present invention is to propose a novel connection between a strain gauge and a measurement object, which takes into account the problems described above and makes strain gauges usable for automotive applications. The problem is solved by the subject matter of independent patent claim 1. Advantageous embodiments are the subject of the subclaims, the following description and the figures.

• • - 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 measurement object comprises the steps (100) Providing

• • - a measurement object,
  • - a sensor arrangement, comprising a strain gauge, which is at least set up to detect expanding and compressive deformations of a measurement object, as well as an electronic module connected thereto, the strain gauge and the electronic module each being glued to the mounting plate and encapsulated in a housing,
  • - a connecting film that contains metallic materials that react exothermically when activated,

(200) Placing the connecting film between the mounting plate and the measurement object, and
(300) Activate the metallic materials of the Connecting film, so that the connecting film heats up in such a way that a cohesive connection is created between the mounting plate and the measurement object.

The present invention proposes a reactive foil soldering process in order to obtain a particularly intermetallic connection for strain gauges on a larger measurement object, also called a target. The joining process is based on the use of a reactive multi-layer film as a local heat source. The connecting film 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 introducing such a film between the mounting plate and the measurement object, the heat generated by the reaction in the film melts, for example, solder layers or other reactive layers, so that the connections are completed in about one second at room temperature. The heat induced during the reaction is very low due to the fast reaction speed (e.g. 10 m/s) and the small material thickness (e.g. <100µm).

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 at least set up to detect expanding and compressing deformations of a measurement object. It is also conceivable to record other measured variables with the strain gauge. The sensor arrangement further includes an electronic module connected to the strain gauge. The electronic module includes in particular preamplifier electronics, which is suitably connected to the strain gauge and an evaluation unit. The strain gauge and the electronic module are each glued to the mounting plate and encapsulated in a common housing. Furthermore, a connecting film is provided which contains metallic materials which react exothermically when activated.

Through the encapsulation, the strain gauge and the electronic module are spatially surrounded by the mounting plate and the housing. “Encapsulated” or “encapsulated” is to be understood as meaning that the strain gauge and the electronic module are essentially completely surrounded by, for example, a module housing, in particular in a sealing manner, for example 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 - that is, free of contact elements. Only cabling can be led out of the housing for connection to the evaluation unit. In this sense, a completely surrounded 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 casting compound forms the module housing or the housing of the sensor arrangement. This configuration prevents mechanical and/or unwanted electrical influences on the strain gauge and the electronic module, for example due to moisture or dirt.

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 axis, a shaft for a motor, a transmission of a motor vehicle, a robot arm segment for a robot or a cooler. The mounting plate on which the sensor arrangement is arranged, that is to say on which the strain gauge and the electronic module are glued, enables simple and insensitive 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 electronic module form a coherent component, namely the sensor arrangement. The sensor arrangement can be stored, transported and processed separately and only be materially connected to the measurement object using the method according to the invention. The mounting plate is then arranged between the measurement object and the strain gauge and the electronic module. The mounting plate also enables a secure connection of the sensor arrangement to the measurement object, since unwanted damage to the strain gauge or the electronic module during activation of the connecting film, in particular during heating of the materials of the connecting film, can be ruled out.

In this sense, the strain gauge and the electronic module are preferably completely surrounded by the mounting plate and a casting compound or an injection molding compound before method step (200). In this way, the housing is formed and the sensor arrangement is protected from unwanted influences, in particular damage, even during subsequent handling. This is also advantageous because the sensor arrangement can be produced under clean room conditions. So can The strain gauges and the electronic module are glued to the mounting plate and encapsulated in the housing without contaminants getting into the housing -

The strain gauge is in particular designed to measure a strain, a compression and/or a torque that is generated by the measurement object or originates from it or is transmitted with it. The strain gauge preferably comprises a carrier layer facing the measurement object and a measuring grid. The strain gauge, DMS for short, is preferably a foil strain gauge, that is, the measuring grid made of resistance wire, which is preferably 3 to 5, preferably up to 8 µm thick, is laminated onto a thin plastic carrier comprising a polymer and etched out as well as with electrical connections which enable an electronic connection to the electronic module. In addition, the measuring grid can be covered by a cover layer which is connected, in particular glued, to the carrier layer and which mechanically protects the measuring grid. The cover layer can also be omitted since the strain gauge is encapsulated in the housing. Several measuring grids can also be arranged on the carrier layer. The carrier layer and/or the cover layer is advantageously designed in the form of a film. The carrier layer is therefore preferably a carrier film and/or the cover layer is a cover film. The carrier layer is preferably made of polyimide. If a cover layer is provided, this can also be made of polyimide.

For example, a so-called NanoFoil® from Indium Corporation can be used as the connecting film. The NanoFoil® is a reactive multi-layer foil that is produced by vapor deposition of thousands of alternating nanoscale layers made of aluminum and nickel, for example. Other binary layer systems are also conceivable, such as titanium and aluminum, zirconium and silicon or paladium and aluminum. In addition, ternary systems for forming the multilayer film are also conceivable. The formation of the connecting film, in particular the selection of materials, is essentially dependent on the desired reaction when activating the connecting film, in particular the reaction temperature during activation. When activated by a small pulse of local energy from electrical, optical or thermal sources, the film reacts exothermically to produce precise local heat up to temperatures of 1500°C in a fraction of a second. The thickness of the connecting film can be adjusted according to the requirements. In particular, the thickness of the connecting film 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 film, the less energy is required to initiate or carry out activation of the connecting film. The total energy must be adjusted in such a way that there is a secure connection between the strain gauge and the measurement object.

The connecting film is placed between the mounting plate and the measurement object in a second process step (200). The placement can be done in such a way that the connecting film lies in a sandwich configuration either directly on facing surfaces of the mounting plate and the measurement object. Alternatively, the placement can be done such that the connecting foil is arranged in a sandwich configuration between two solder layers, with the solder layers being applied to opposite surfaces of the mounting plate and the measurement object. Furthermore, alternatively, the placement can be carried out such that the connection foil is arranged in a sandwich configuration between two solder layers, with the solder layers being applied to opposite surfaces of the connection foil. These surfaces of the connecting film are in particular flat surfaces which, in the second method step (200), are arranged to accommodate the mounting plate or the measurement object between the mounting plate and the measurement object in order to be welded or soldered in the subsequent third method step (300).

When activated, the connecting film forms a joining surface between the measurement object and the mounting plate. If this does not already occur on the joining section forming the joining surface, the connecting film can also have an activation section on which the metallic material of the connecting film is activated. Activating means can be arranged on the activation section in order to be able to activate the connecting film. The joining section and, if applicable, the activation section are formed between the mounting plate and the measurement object. The activated connecting film connects the measurement object to the mounting plate at least in the joining surface, preferably in the joining surface and, if necessary, in the activation section in a materially bonded manner. If an activation section is provided, it lies outside the joining surface between the mounting plate and the measurement object.

At least one, preferably several, activation means is electrically connected to the connecting film, in particular to the activation section, if one is provided. The activating means can have one or more wires, preferably two wires, one with positive with a pole, i.e. a positive pole, and one with a negative pole, i.e. a negative pole, with a potential difference between the poles. The wires can be designed and handled separately. Alternatively, the two wires can be combined at their ends to form a type of connector in order to maintain or not fall below a defined distance between the wires. The activation means can also be or include a voltage source, in particular a battery, or a heat needle. Alternatively, the activation means can be designed to be connected to the voltage source to activate the connecting film. 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 film are activated via the respective activation agent, so that the connecting film is heated in such a way that the mounting plate is cohesively connected to the measurement object. After activating the connecting film, there is a cohesive connection between the mounting plate and the measurement object. Activation can be done, for example, by ignition. The process requires no special heat, no vacuum and no gas atmosphere. The connecting film can be ignited, for example, with a commercially available 9V battery, the battery being at least indirectly connected to the connecting film via the respective activation means. In method step (300), the material of the measurement object and/or the mounting plate can be melted or 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 and no high temperatures need to be exerted on the sensor arrangement and/or the mounting plate and/or the measurement object. High electromagnetic fields can also be avoided. The continuous, metallic connecting layer or bonding surface between the mounting plate and the measurement object created by activating the metallic materials of the connecting film has, in particular, high dimensional stability as well as high thermal conductivity and electrical conductivity due to the improved contacting. Furthermore, the manufacturing process or the bonding process is simplified, which enables particularly cost-effective production.

The method according to the invention is characterized by lower temperatures and stresses during connection. These lower stresses induce less prestress in the strain gauge and mounting plate, increasing the performance and stability of the strain gauge. In addition, the low temperatures and low pressure enable a wide use of materials such as polymers. The bond between the mounting plate and the measurement object created by the method according to the invention does not age with time and temperatures. Steam, pressure or the like do not cause any change in the parameters of the connection. 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, in particular due to temperature, humidity, pressure or the like. The composite material (particularly metal) further provides elastic deformation for repeatability.

Advantageously, the electrical connection between the activating agent and the connecting film can be carried out using the same device with which the mounting plate is placed on the measurement object and the pressure is exerted for a material connection.

The connecting film is processed by laser cutting in such a way that the connecting film takes on a shape and dimensions that cover an intended joining surface between the mounting plate and the measurement object. The connecting film can thus be shaped particularly precisely and efficiently to the desired dimensions before the connecting film is placed between the two surfaces.

The laser cutting therefore takes place before the connecting film is placed between the mounting plate and the measurement 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 installation of the strain gauge on the measurement object can be simplified and accelerated and can be carried out with reproducible quality. In particular, the assembly of the mounting plate with the sensor arrangement arranged thereon on 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 in step (200) is arranged between the mounting plate and the connecting film. The first soldering layer is to be understood as the first coating of the mounting plate and/or the connecting film, which can be divided into several individual layers.

The connecting film and/or the measurement object preferably has a metallized second soldering layer, which is arranged in step (200) between the measurement object and the connection film. The second soldering layer is to be understood as the second coating of the measurement object and/or the connecting film, which can also be divided into several individual layers. The respective soldering layer is a metallized layer that enables an effective, cohesive 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 soldering layer is applied in particular before the connecting film is placed between the mounting plate and the measurement object in the second method step (200). By subsequently activating the connecting foil, sufficient heat is generated to melt the respective soldering layer and solder the mounting plate to the measurement object. In this sense, according to one embodiment it is provided that

• - the first soldering layer is applied to the mounting plate and/or the connecting foil,
• - the second soldering layer is applied to the measurement object and/or the connecting foil,
• - the connecting film with the solder layers is placed between the mounting plate and the measurement object in step (200), and
• - the metallic materials of the connecting foil are activated in step (300), so that the connecting foil is heated in such a way that the first soldering layer and the second soldering layer melt and the mounting plate is soldered to the measurement object through the melted first soldering layer and the melted second soldering layer, to create the cohesive 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 in order to enable the nanobond process.

Using the connecting foil and the solder layers, an intermetallic, cohesive bond can be created between the mounting plate and the measurement object, which does not require high temperatures, pressures, electromagnetic fields, etc. for production. The intermetallic connection enables 1:1 signal transmission from the measurement object to the strain gauge.

The soldering layers can be applied as metallic starting layers (first and second soldering layers) particularly advantageously by plasma processes, sputtering processes or vapor deposition on the respective surface of the parts to be connected (mounting plate, measurement object, connecting foil). Other options include two-shot injection molding, additive manufacturing, etc. At least one of the solder layers, preferably both solder layers, preferably comprise nickel. Furthermore, one of the solder layers, preferably both solder layers, preferably comprises gold. Copper or palladium are also suitable materials for the respective soldering layer. The material of the respective soldering 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 designed in multiple layers. The layer structure can be designed in any way. 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 film.

To prevent unpredictable deformation of the composite, a fixing pad can be placed on the layers with low pressure. In this sense, deformation of the soldering layers and the connecting foil during activation and connection in step (300) is preferably counteracted by means of a fixing pad, which at least indirectly exerts pressure 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 tensions within the mounting plate and/or the strain gauge and/or the measurement object, which could affect the strength of the connection between the mounting plate and the measurement object or the measurement accuracy.

“At least indirectly” in this context means that further, in particular 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 and statements on technical effects, advantages and advantageous embodiments of the method according to the invention also apply mutatis mutandis to the arrangement according to the invention 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 combination specified in each case, but also in other combinations or alone, 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.

An exemplary embodiment of the invention is explained in more detail below with reference to the schematic drawings, with the same or similar elements being provided with the same reference numerals. This shows

• 1 a longitudinal sectional view of an arrangement according to the invention of a sensor arrangement arranged on a mounting plate on a measurement object according to a first embodiment, the mounting plate being attached to the measurement object by means of a connecting film - shown here in a very simplified manner,
• 2 a detailed longitudinal sectional view of the arrangement according to the invention 1 ,
• 3 an exploded view of layers and tools for connecting the sensor arrangement to the measurement object using the connecting film 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 1 until 3 , and
• 5 a greatly enlarged cross-sectional view of the connecting film for the arrangement 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, with both the strain gauge 1 and the electronic module 19 being glued to the mounting plate 17 and are encapsulated in a common housing 18 made of potting material. A housing 18 accommodating the strain gauge 1 and the electronic module 19 is therefore formed by the encapsulation. The mounting plate 17 is made using a method according to the invention described below 5 connected to the measurement object 2 by means of a connecting film 10. The strain gauge 1 is in 2 shown in more detail and includes a carrier layer 1a facing the mounting plate 17 and a meandering measuring grid 1b arranged thereon. The measuring grid 1b is connected to the electronics module 19 designed as a preamplifier module via a first cabling 20, which is also encapsulated in the housing 18. A second wiring 21 is led out of the housing 18 and connects the electronic module 19 with an evaluation unit (not shown here) and/or a voltage source, such as that in 3 shown battery 15, connects. As also in 2 can be seen, the mounting plate 17 has a metallized first solder layer 13 facing the connecting film 10 on a mounting plate surface 4 and the measurement object 2 has a metallized second soldering layer 14 facing the connecting film 10 on a measurement object surface 6. One or both of the solder layers 13, 14 can also be applied to the connecting film 10. In the present case, the measurement object 2 is significantly larger than the sensor arrangement 5. The measurement object 2 can, for example, be a shaft of a motor, an axle or a transmission for a motor vehicle. The strain gauge 1 is set up to record expansions 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 tension and stretching. Mechanical tension is the resistance that the object offers to the force, and strain is the displacement and deformation that results from the force. The strain gauge 1 is therefore at least set up to record stretching and compressing deformations, preferably other measured variables, of the measurement object 2.

By means of the connecting film 10, a firm, here a material connection, of the mounting plate 17 with the measurement object 2 is realized. This connection transmits forces of the measured variable as well as disturbances caused by thermal expansion. The type of connection places demands on the surface quality of measurement object 2 and mounting plate 17. Two on the outside on the right 1 The force arrows F shown illustrate an exchange of forces through deformation, which represents the actual measurement variable. To the left of it, a bidirectional force arrow F is shown, which An exchange of forces through tension and through different thermal expansion illustrates what constitutes a disturbance. 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 film 10 are provided. In all exemplary embodiments, the connecting foil 10 is a so-called NanoFoil®, i.e. a reactive multilayer foil that is 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 bonding film 10 reacts exothermically to produce precise local heat up to temperatures of 1500 ° C in a fraction of a second.

In a second method step 200, the connecting film 10 is placed between the mounting plate 17 and the measurement object 2, as described by 1 until 3 is shown. The connecting foil 10 touches the first soldering layer 13 on the mounting plate 17 on one side and the second soldering layer 14 on the measurement object 2 on the other side. During method step 200, the aluminum layers 11 and the nickel layers 12 of the connecting foil 10 are arranged next to each other alternately, like this through 5 is shown. Both solder layers 13, 14 include nickel. In the present case, both layers 13, 14 also have a gold layer, the gold layer being arranged facing the connecting foil 10. The respective soldering 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 casting compound or an injection molding compound before method step 200.

The connecting film 10 is processed by laser cutting in such a way that the connecting film 10 takes on a shape and dimensions that form an intended 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 film 10.

In a third method step 300, the aluminum layers 11 and the nickel layers 12 are added to the connecting foil 10 5 using the example in 3 Battery 15 shown activated. Instead of the battery 15, a DC voltage source can be used to activate the connecting film 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 in such a way that the first soldering layer 13 and the second soldering layer 14 melt and the mounting plate 17 is soldered to the measurement object 2 by the melted soldering layers 13, 14 . This creates, as on the right 3 indicated, a stable bonding or joining surface 7 between the mounting plate 17 and the measurement object 2.

A cohesive connection between the mounting plate 17 and the measurement object 2 is therefore realized. The mounting plate surface 4 and/or the measurement object surface 6 can have such a surface structure that molten material of the aluminum layers 11 and/or the nickel layers 12 penetrate into spaces in the measurement object surface 6 and/or the mounting plate surface 4 and after solidification can cause a positive connection between the mounting plate 17 and the measurement object 2. The detectable measurement variable can be increased by special force shunt structures of the measurement object 2. The measurement object 2 can, for example, form depressions, ribs, beads or the like that increase or reduce forces in certain spatial directions.

In another in 3 The embodiment shown is a further development of the first embodiment 1 and 2 shown. 3 In the left part shows a state in which no connection has yet been created between the measurement object 2 and the mounting plate 17. The right part of 3 shows the state after formation of the cohesive 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 soldering layers 13, 14. The connecting film 10 is cut by laser cutting in such a way that it has an activation section 8, which in the exemplary embodiment shown is not covered by the sensor arrangement 5 and is therefore freely accessible for applying the activation means 16. The activation section 8 therefore protrudes, as in the left part of 3 can be clearly seen from the stack formed by the mounting plate 17, the measurement object 2 and the two soldering layers 13, 14 when all layers are adjacent to one another.

A fixing pad 9, which comprises a flexible layer 22, exerts a pressure p on the pressure formed by the strain gauge 1, the measurement object 2 and by the two soldering layers 13, 14 the stack. 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 soldering layers 13, 14 and the connecting film 10 during activation and connection in step 300.

It should be expressly pointed out that the invention is not limited to the exemplary embodiments disclosed here. These are merely exemplary configurations, although other variants are also possible. In particular, the second soldering layer 14 on the measurement object 2 can be dispensed with if the measurement object 2 consists of a solderable material or has an already metallized surface.

Reference symbols

F

Power

p

Pressure

1

Strain gauges

1a

Backing layer

1b

Measuring grid

2

measurement object

4

Mounting plate surface

5

Sensor arrangement

6

Measurement object surface

7

joining surface

8th

Activation section

9

fixing pad

10

connecting film

11

Aluminum layer

12

Nickel layer

13

First layer of solder

14

Second layer of solder

15

battery

16

Activating agent

17

Mounting plate

18

Housing

19

Electronic module

20

First wiring

21

Second wiring

22

Compliant layer

100

First step of the procedure

200

Second procedural step

300

Third step of the process

QUOTES INCLUDED IN THE DESCRIPTION

This list of documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102013002144 A1 [0005]

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) Provide - a measurement object (2), - a sensor arrangement (5), comprising a strain gauge (1), which is at least designed to detect expanding and compressive deformations of a measurement object (2), as well as an electronic module (19) connected thereto, 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 film (10) which contains metallic materials (11, 12) which react exothermically when activated, (200) Placing the connecting film (10) between the mounting plate (17) and the measurement object (2), and (300) Activating the metallic materials (11, 12) of the connecting film (10) so that the connecting film (10) heats up in such a way that a cohesive 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 in such a way that the connecting film (10) takes on a shape and dimensions that cover an intended joining surface (7) between the mounting plate (17) and the measurement 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 casting 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 film (10) and/or the measurement object (2) has a metallized second solder layer (14) which is arranged in step (200) between the measurement object (2) and the connection film (10). . Procedure according to Claim 5 combined with Claim 6 , wherein - the first soldering layer (13) is applied to the mounting plate (17) and/or the connecting film (10), - the second soldering layer (14) is applied to the measurement object (2) and/or the connecting film (10), - the connecting foil (10) with the soldering layers (13, 14) is placed in step (200) between the mounting plate (17) and the measurement object (2), and - the metallic materials (11, 12) of the connecting foil (10) be activated in step (300), so that the connecting film (10) heats up in such a way that the first soldering layer (13) and the second soldering layer (14) melt and the mounting plate (17) passes through the melted first soldering layer (13) and the molten second solder layer (14) is soldered to the measurement object (2) in order to create the cohesive connection. Procedure according to Claim 7 , wherein by means of a fixing pad (9), which at least indirectly exerts pressure (p) on the sensor arrangement (20) and/or on the measurement object (2), the soldering layers (13, 14) and the connecting film (10) are deformed during activation and connection in step (300) is counteracted. Procedure according to one of the Claims 5 until 8th , wherein the respective soldering layer (13, 14) is made of a material comprising nickel. Procedure according to one of the Claims 5 until 9 , wherein the respective soldering 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 measurement object (2), the sensor arrangement (5) being connected to the measurement object (2) by a method according to one of the preceding claims.

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