WO2024056574A1

WO2024056574A1 - Connection of a sensor assembly to a measurement object

Info

Publication number: WO2024056574A1
Application number: PCT/EP2023/074840
Authority: WO
Inventors: Philipp Lang; Erwin Biegger; Georg TENCKHOFF
Original assignee: Zf Friedrichshafen Ag
Priority date: 2022-09-13
Filing date: 2023-09-11
Publication date: 2024-03-21
Also published as: DE102022209554A1

Abstract

The invention relates to a method for connecting a sensor assembly to a measurement object, the method comprising the following steps: (100) providing •- a measurement object, •- a sensor assembly, comprising a strain gauge, which is designed at least to sense stretching and compressing deformations of a measurement object, and also an electronics module, •- two connecting foils, which each contain metallic materials that react exothermically when activated, (200) placing the first connecting foil between the strain gauge and the electronics module, (300) activating the metallic materials of the first connecting foil so as to produce a material-bonding connection between the strain gauge and the electronics module, wherein, after the metallic materials of the first connecting foil have been activated, there is an electronic connection between the strain gauge and the electronics module, (400), placing the second connecting foil between the strain gauge and the measurement object, and (500) activating the metallic materials of the second connecting foil so as to produce a material-bonding connection between the strain gauge and the measurement object. The invention also relates to an arrangement of a sensor assembly on a measurement object, wherein the sensor assembly has been connected to the measurement object by the method according to the invention.

Description

Connection of a sensor arrangement with a measurement object

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 life 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 connections are associated with different temperature gradients, moisture-chemical dependency and long-term aging. This can reduce the 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 DE 10 2013 002 144 A1 there is a joining method for thermally sensitive structures, whereby two components are brought into functional connection using a joining aid designed as a reactive nanofilm by first introducing the nanofoil between assigned surface sections of the components to be joined together and here subsequently causes at least a sectional formation of a connection structure, characterized in that by activating the nanofilm, a largely solid solder connection layer is first melted on both mutually assigned surface sections of the components to be joined together and that the melting material is then locally limited to a surface section the also locally limited melting material 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 melting material, a functional brazed connection is formed, with the thermal load necessary for melting only within the contour sections of the contacts to be joined is applied exclusively to 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 task 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.

A method according to the invention for connecting a sensor arrangement (20) to a measurement object comprises the following steps (100) Provide

- a measurement object,

- a sensor arrangement, comprising a strain gauge, which is at least set up to detect expanding and compressing deformations of a measurement object, and an electronic module,

- a first connecting film and a second connecting film, each containing metallic materials that react exothermically when activated,

(200) placing the first connecting film 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 cohesive connection is created between the strain gauge and the electronic module, wherein after activating the metallic materials of the first connecting film, an electronic connection between the strain gauge and the electronic module is present,

(400) Placing the second connecting film between the strain gauge and the measurement object, and

(500) Activating the metallic materials of the second connecting film so that the second connecting film heats up in such a way that a cohesive connection is created between the strain gauge 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 components to be connected to one another, the heat generated by the reaction in the film melts, for example, solder layers or other reactive layers, so that the connections are made in about one second at room temperature. are closed. 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. <100pm).

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 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 in particular has preamplifier electronics, which is 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.

The strain gauge and the electronic module are preferably encapsulated in the housing if both the electronic module has been materially connected to the strain gauge and the strain gauge has been materially connected to the measurement object. The encapsulation therefore takes place in a step (600), which takes place after step (300) and after step (500). As a result, the strain gauge and the electronic module are spatially surrounded by the measurement object and the housing.

“Encapsulated” or “encapsulated” means that the strain gauge and the electronic module are essentially completely surrounded by, for example, a module housing, in particular sealed, 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 - i.e. free of contact elements. since. 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 sensor arrangement is therefore protected from unwanted damage.

Furthermore, a first connecting film and at least one second connecting film are provided, each connecting film containing metallic materials that react exothermically when activated. The first connecting film is assigned to the electronic module, with the electronic module being connected to the strain gauge in a materially bonded manner by means of the first connecting film. The second connecting film is assigned to the measurement object, with the measurement object being cohesively connected to the strain gauge by means of the second connecting film.

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 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 pm thick, is laminated onto a thin plastic carrier comprising a polymer and etched out as well as with electrical connections hen that 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 respective connecting film can be adjusted depending on the material of the measurement object and/or the carrier layer of the strain gauge and/or the electronic module. The thinner the respective connecting film, the less energy is required to initiate or carry out the 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 first connecting film is placed between the strain gauge and the electronic module in a second process step (200). The placement can be done in such a way that the first connecting film lies in a sandwich configuration either directly on facing surfaces of the strain gauge and the electronic module. Alternatively, the placement can be carried out in such a way that the first connection foil is arranged in a sandwich configuration between two solder layers, with the solder layers being applied to opposite surfaces of the electronic module and the strain gauge. Furthermore, alternatively, the placement can be carried out such that the first connection foil is arranged in a sandwich configuration between two solder layers, with the solder layers being applied to opposite surfaces of the first connection foil. These surfaces of the first connecting film are in particular flat surfaces which, in the second method step (200), are arranged to accommodate the strain gauge or the electronic module between the strain gauge and the electronic module in order to be welded or soldered in the subsequent third method step (300).

The first connecting film is preferably designed in such a way that, after activation in step (300), it creates an electrical connection between the strain gauge and the electronic module. This eliminates the need for additional, if necessary manual, wiring of the strain gauge to the electronic module, which must be done before step (600). The cohesive connection and the electrical connection between the strain gauge and the electronic module are carried out in a single step, namely during step (300).

The second connecting film is placed between the strain gauge and the measurement object in a fourth method step (400). 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 strain gauge 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 is, wherein the solder layers are applied to opposite surfaces of the electronic module and the strain gauge. Furthermore, alternatively, the placement can be carried out in such a way that the second connection foil is arranged in a sandwich configuration between two solder layers, with the solder layers being applied to opposite surfaces of the second connection foil. These surfaces of the second connecting film are in particular flat surfaces which, in the fourth method step (400), are arranged to accommodate the strain gauge or the measurement object between the strain gauge and the measurement object in order to be welded or soldered in the third method step (300).

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

When activated, the respective connecting film forms a joining surface between the parts to be cohesively connected to one another. The respective connecting film can, if this does not already take place on the joining section forming the joining surface, also have an activation section on which the activation of the metallic material of the respective connecting film takes place. Activation means can be arranged on the activation section in order to be able to activate the respective connecting film. The respective joining section and, if applicable, the activation section are formed on the one hand between the strain gauge and the electronic module and on the other hand between the strain gauge and the measurement object. The respective connecting film activated in step (300) or (500) connects the measurement object with the strain gauge or the strain gauge with the electronic module at least in a respective joining surface, preferably in the respective joining surface and possibly in the activation section, in a materially bonded manner. If an activation section is provided, it lies outside the respective joining surface.

At least one, preferably several, activation means is electrically connected to the respective 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 a positive pole, i.e. one 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. If both activation steps (300) and (500) take place simultaneously, the connecting films can be connected to a common activating agent. If steps (300) and (500) take place one after the other, it is advantageous to assign each connecting film to an associated, separate activating agent.

In a third method step (300), the metallic materials of the first connecting film are activated via the respective activation agent, so that the first connecting film is heated in such a way that the strain gauge is connected to the electronic module in a materially bonded manner. After activating the first connecting film, there is a cohesive connection between the strain gauge and the electronic module. 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. The method step (300) is designed such that the material of the carrier layer of the strain gauge does not melt when the first connecting film is activated. However, the electronic module can have a material that is melted or melted during activation of the first connecting film, so that the electronic module is welded directly to the strain gauge. Alternatively, the strain gauge can 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 connecting film. In a fifth method step (500), the metallic materials of the second connecting film are activated via the respective activation agent, so that the second connecting film is heated in such a way that the strain gauge is bonded to the measurement object. After activating the second connecting film, there is a cohesive connection between the strain gauge and the measurement object. Activation can be carried out analogously to the above statements regarding the first connecting film. In particular, method step (500) takes place in such a way that the material of the carrier layer of the strain gauge does not melt when the second connecting film is activated. However, the measurement object can have a material that is melted or melted during activation of the second connecting film, so that the measurement object is welded directly to the strain gauge. Alternatively, the strain gauge or the measurement object can be indirectly soldered to the measurement object by melting solder layers on the strain gauge and/or on the measurement object and/or on the second connecting film.

During the bonding process, no high pressures or high temperatures need to be exerted on the sensor arrangement and/or the measurement object. High electromagnetic fields can also be avoided. The continuous, metallic connection layer or bonding surface between the strain gauge and the electronic module or between the strain gauge and the measurement object resulting from the activation of the metallic materials of the respective 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 increase 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 created by the method according to the invention between strain gauges and electronic module or between strain gauges and measurement object 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 respective connecting film can be carried out using the same device with which the individual components are placed one above the other and the pressure is exerted for a material connection.

The respective connecting film is processed by laser cutting in such a way that the respective connecting film takes on a shape and dimensions that cover an intended joining surface between the strain gauge and the electronic module or between the strain gauge and the measurement object. The respective connecting film can thus be shaped particularly precisely and efficiently to the desired dimensions before the respective connecting film is placed between the two surfaces. The laser cutting therefore takes place before the first connecting film is placed between the strain gauge and the electronic module in step (200) or before the second connecting film is placed between the strain gauge and the measurement object in step (400).

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 sensor arrangement on the measurement object can be at least partially automated, preferably fully automated. Preferably, steps (400) and (500) take place after step (300), with step (300) following step (200). Alternatively, step (400) can occur before step (200). Accordingly, the strain gauge can be connected to the measurement object before the strain gauge is materially connected to the electronic module. The respective connecting film can therefore be placed between the two components to be connected in any order. In this sense, steps (400) and (500) take place before step (200) and correspondingly also step (300). This is intended to make it clear that the interrelated steps (200) and (300) or (400) and (500) can in principle take place in any order.

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

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, which is 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 can be divided into several individual layers.

Preferably, the first connecting 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 connecting film. The second solder layer is to be understood as a second coating of the electronic module and/or the first connecting film, which can also be divided into several individual layers.

The first or second solder layer is applied in particular before the first connecting film is placed between the strain gauge and the electronic module in the second method step (200). By then activating the The first connecting film 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 film,

- the second soldering layer is applied to the electronic module and/or the first connecting film,

- the first connecting film with the solder layers is placed in step (200) between the strain gauge and the electronic module, and

- the metallic materials of the first connecting film are activated in step (300), so that the first connecting film is heated in such a way that the first solder layer and the second solder layer melt and the strain gauge, in particular the carrier layer of the strain gauge, through the melted first solder layer and the melted second solder layer is soldered to the electronic module in order to create the cohesive connection. The metallization of the strain gauge and/or the electronic module and/or the first connecting film, i.e. the application of the first or second solder layer to the strain gauge, the electronic module and/or the connecting film, is important in order to enable the nanobond process.

Preferably, the measurement object and/or the second connection foil has a metallized third solder layer, which is arranged in step (400) between the measurement object and the second connection foil. The third soldering layer is to be understood as the third coating of the measurement object and/or the second connecting film, which can be divided into several individual layers.

Preferably, the second connecting film 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 connecting film. The fourth solder layer is to be understood as the fourth coating of the strain gauge and/or the second connecting film, which can also be divided into several individual layers. The third or fourth solder layer is applied in particular before the second connecting film is placed between the measurement object and the strain gauge or the electronic module in the fourth method step (400). By subsequently activating the second connecting foil, sufficient heat is generated to melt the third or fourth solder layer and solder the measurement object to the strain gauge. In this sense, according to one embodiment it is provided that

- the third soldering layer is applied to the measurement 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 film,

- the second connecting film with the solder layers is placed in step (400) between the measurement object and the strain gauge, and

- the metallic materials of the second connecting foil are activated in step (500), so that the second connecting foil is heated in such a way that the third soldering layer and the fourth soldering layer melt and the measurement object passes through the melted third soldering layer and the melted fourth soldering layer with the strain gauge, in particular the carrier layer of the strain gauge, is soldered to create the cohesive connection.

The respective soldering layer is a metallized layer that enables an effective, cohesive connection between the strain gauge and the electronic module or between the strain gauge and the measurement object.

By means of the respective connecting foil and the soldering layers, an intermetallic, cohesive bond can be created between the parts to be cohesively connected to one another, which does not require high temperatures, pressures, electromagnetic fields, etc. for production. The intermetallic connection enables a 1:1 signal transmission from the measurement object to the strain gauge. The soldering layers can be applied as metallic starting layers particularly advantageously by plasma processes, sputtering processes or vapor deposition on the respective surface of the parts to be connected (measured object, connecting foil, strain gauges and electronic module). Other options include two-shot injection molding, additive manufacturing, etc. At least one of the solder layers, preferably all solder layers, preferably comprise nickel. Furthermore, one of the solder layers, preferably all 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 material of the connecting foil, the measurement object, the strain gauge and the electronic module.

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 of the respective connecting foil faces the measurement object and/or the strain gauge and/or the electronic module and thus faces away from the respective connecting foil.

To prevent unpredictable deformation of the composite, a fixing pad can be placed on the layers with low pressure. In this sense, a deformation of the soldering layers and the respective connecting foil during activation and connection in step (300) or step is preferred by means of a fixing pad, which at least indirectly exerts pressure on the measurement object and/or the strain gauge and/or the electronic module (500) counteracted. The pressure is so low that it does not lead to any tensions within the strain gauge and/or the electronic module and/or the measurement object, which would affect the strength of the connection between the strain gauge and the measurement object or between the strain gauge and the electronic module or the measurement accuracy could. “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 strain gauge and/or the electronic module and/or the measurement object. The fixing pad can also be arranged directly on the strain gauge and/or the electronic module and/or the measurement object.

According to a second aspect of the invention, an arrangement of a sensor arrangement 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.

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 shows a longitudinal sectional view of an arrangement according to the invention of a sensor arrangement arranged on a measurement object according to a first embodiment,

2 shows a detailed longitudinal sectional view of the arrangement according to the invention according to FIG. 1,

Fig. 3 is an exploded view of layers and tools for connecting a strain gauge of the sensor arrangement to one 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,

4 shows an exploded view of layers and tools for connecting the strain gauge to the measurement object by means of a second connecting film and the arrangement resulting from the connection,

5 shows a sequence of a method according to the invention for connecting the sensor arrangement to the measurement object according to FIGS. 1 to 4, and

6 is a greatly enlarged cross-sectional view of the connecting film for the arrangement according to FIGS. 1 to 5.

Fig. 1 shows a preferred embodiment of an arrangement of a sensor arrangement 5 arranged on a measurement object 2. The sensor arrangement 5 comprises a strain gauge 1 and an electronic module 19 electrically connected thereto. The strain gauge 1 is by means of a in Fig. 3 in conjunction with Fig. 5 shown Method connected to the electronic module 19 via a first connecting film 10a. Furthermore, the strain gauge 1 is cohesively connected to the measurement object 2 via a second connecting film 10b by means of a method shown in FIG. 4 in conjunction with FIG. 5. In the state shown in FIGS. 1 and 2, the strain gauge 1 and the electronic module 19 are encapsulated in a common housing 18 made of potting material.

The strain gauge 1 is shown in more detail in FIG. 2 and comprises a carrier layer 1 a facing the measurement object 2 and a meandering measuring grid 1 b arranged thereon. The measuring grid 1 b is connected to the electronic module 19 designed as a preamplifier module via the first connecting film 10a. This is explained in more detail below. A cabling 20 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 Fig. 3 or Fig. 4 shown battery 15, connects. As can be seen in Fig. 2 and Fig. 3, the strain gauge 1, in particular its carrier layer 1a, has a metallized first solder layer 13 facing the first connecting film 10a on a first surface 4a and the electronic module 19 has on a surface 17 a metallized second solder layer 14 facing the first connecting foil 10a. One or both of the solder layers 13, 14 can also be applied to the first connecting film 10a.

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 first connecting film 10a, a firm, cohesive connection of the strain gauge 1 with the electronic module 19 is realized and by means of the second connecting film 10b, a firm, cohesive connection of the strain gauge 1 with the measurement object 2 is realized. The respective 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 the measurement object 2, strain gauges 1 and the electronic module 19.

Two force arrows F shown on the far right in Fig. 1 illustrate an exchange of forces through deformation, which represents the actual measurement variable. Left dane- Bene a bidirectional force arrow F is shown, which illustrates an exchange of forces through stresses and through different 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 and the first and second connecting films 10a, 10b are provided. The respective connecting foil 10a, 10b 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 respective connecting foil 10a, 10b with the aluminum 11 and nickel layers 12 is shown in FIG. When the respective connecting film 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.

According to FIG. The first connecting film 10a touches on one side a first soldering layer 13 on the strain gauge 1, here on the carrier layer 1a of the strain gauge 1, and on the other side a second soldering layer 14 on the electronic module 19. During method step 200, the aluminum layers 11 and the Nickel layers 12 of the first connecting foil 10a are arranged alternately next to one another, as shown in FIG. 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 first connecting foil 10a. Step 200 is followed by step 300, after which the aluminum layers 11 and the nickel layers 12 of the first connecting foil 10a are activated by means of the battery 15 shown by way of example in FIG. 3. Instead of the battery 15, a DC voltage source can be used to activate the first connecting film 10a. The aluminum layers 11 and nickel layers 12 of the first connecting foil 10a then react strongly exothermically, so that the first connecting foil 10a heats up in such a way that the first soldering layer 13 and the second soldering layer 14 melt and the electronic module 19 is connected to the strain gauge 1 through the melted soldering layers 13, 14 , i.e. the carrier layer 1a of the strain gauge 1, is soldered. This creates, as indicated on the right in Fig. 3, a stable bonding or joining surface 7a between the electronic module 19 and the strain gauge 1. This creates a sensor component, by means of which the sensor arrangement 5 is formed in the following steps. The advantage of this design is, among other things, that due to the materials of the first connecting film 10a, an electrical connection can be established between the measuring grid 1b of the strain gauge 1 and the electronic module 19 after activating the first connecting 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 joining surface 7a remaining after activation. Additional cabling or an additional connection of the strain gauge 1 to the electronic module 19 is therefore no longer required.

Following the cohesive connection of the strain gauge 1 with the electronic module 19, i.e. after step 300, in step 400 the second connecting film 10b is placed between the strain gauge 1, here the carrier layer 1a of the strain gauge 1, and the measurement object 2. The second connecting film 10b touches on one side a third soldering layer 21 on the measurement object 2 and on the other side a fourth soldering layer 22 on the strain gauge 1, here on the carrier layer 1a of the strain gauge 1. During method step 400, the aluminum layers 11 and the nickel layers 12 of the second connecting foil 10b are still arranged alternately next to one another, as shown in FIG. 6. Both solder layers 21, 22 include nickel. Present Both layers 21, 22 also have a gold layer, the gold layer being arranged facing the second connecting foil 10b.

Step 400 is followed by step 500, after which the aluminum layers 11 and the nickel layers 12 of the second connecting foil 10b are activated by means of the battery 15 shown by way of example in FIG. 4. The same battery according to FIG. 3 or another voltage source can be used to activate the second connection film 10b. The aluminum layers 11 and nickel layers 12 of the second connecting foil 10b then react strongly exothermically, so that the second connecting foil 10b heats up in such a way that the third soldering layer 21 and the fourth soldering layer 22 melt and the measurement object 2 is connected to the strain gauge 1 through the melted soldering layers 21, 22 , i.e. the carrier layer 1a of the strain gauge 1, is soldered. This creates, as indicated on the right in Fig. 4, a stable bonding or joining surface 7b between the strain gauge 1 and the measurement object 2.

To form the sensor arrangement 5, the strain gauge 1 and the electronics module 19 are encapsulated in a step 600 after step 500, the strain gauge 1 and the electronics module 19 being completely surrounded on the one hand by a measurement object 2 and on the other hand by a potting compound or an injection molding compound. The encapsulation forms a housing 18 that accommodates the strain gauge 1 and the electronic module 19 and protects the strain gauge 1 and the electronic module 19 from external influences.

The respective soldering layer 13, 14, 21, 22 can further comprise copper, silver, silicon nitride SisN4, silicon dioxide SiC>2, titanium tungsten TiW, palladium or the like. The soldering layers 13, 14, 21, 22 can be identical, that is, made of the same material.

The connecting foils 10a, 10b are processed by laser cutting in such a way that the respective connecting foil 10a, 10b takes on a shape and dimensions that correspond to one seen joining surface 7a, 7b between the strain gauge 1 and the electronic module 19 or between the strain gauge 1 and the measurement object 2 and a respective activation section 8a, 8b.

In the exemplary embodiment shown, the first activation section 8a according to FIG. 3 is not covered by the electronic module 19 and the second activation section 8b is not covered by the strain gauge 1 according to FIG. 4. The respective activation section 8a, 8b therefore protrudes, as can be clearly seen in the left part of FIGS. 3 and 4, from the stack formed by the sensor arrangement 5, the measurement object 2 and the soldering layers 21 - 26 when all layers lie next to each other.

With the method according to the invention, a cohesive connection is realized between the strain gauge 1 and the measurement object 2 and between the strain gauge 1 and the electronic module 19. The surfaces 4a, 4b of the carrier layer 1a and/or the measurement object surface 6 and/or the surface 20 of the electronic module 19 can or can have such a surface structure that melted material of the aluminum layers 11 and/or the nickel layers 12 can be inserted into the spaces between the respective ones Penetrate the surface and, after solidification, can cause a positive connection between the two components to be cohesively connected. 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.

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 measurement object 2 according to steps 400 and 500, a fixing pad 9 with a resilient layer 23 is provided, which has a pressure p on the respective stack. This pressure is very low and acts vertically 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 step 300 or 500. 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 third soldering layer 21 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. Furthermore, the interconnected steps 400 and 500 can occur after the interconnected steps 200 and .

Reference symbols

F force p pressure

1 strain gauge

1a carrier layer

1 b measuring grid

2 measurement object

4a First surface of the strain gauge

4b Second surface of the strain gauge

5 sensor arrangement

6 measurement object surface

7a First joining surface

7b Second joining surface

8a First activation section

8b Second activation section

9 fixing pad

10a first connecting film

10b second connecting film

11 aluminum layer

12 nickel layer

13 First layer of solder

14 Second solder layer

15 battery

16 Activating Agents

17 Surface of the electronic module

18 housings

19 electronic module

20 Wiring

21 Third solder layer

22 Fourth layer of solder

23 Compliant layer

100 First procedural step Second procedural step

Third step of the process

Fourth step of the process

Fifth procedural step

Claims

Patent claims

1. Method for connecting a sensor arrangement (20) to a measurement object (2), the method comprising the steps

(100) Provide

- a measurement object (2),

- a sensor arrangement (20), comprising a strain gauge (1), which is at least designed to detect stretching and compressing 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 when activated,

(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), so that the first connecting film (10a) heats up in such a way that a cohesive connection is created between the strain gauge (1) and the electronic module (19), whereby after activating the metallic materials (11, 12) of the first connecting film (10a), there is an electronic connection between the strain gauge (1) and the electronic module (19),

(400) placing the second connecting film (10b) between the strain gauge (1) and the measurement object (2), and

(500) Activating the metallic materials (11, 12) of the second connecting film (10b) so that the second connecting film (10b) heats up in such a way that a cohesive connection is created between the strain gauge (1) and the measurement object (2).

2. The method according to claim 1, wherein the strain gauge (1) and the electronic module (19) are encapsulated in a common housing (18) in one step (600).

3. The method according to any one of claims 1 or 2, wherein steps (400) and (500) take place after step (300), which follows step (200).

4. The method according to any one of claims 1 or 2, wherein steps (400) and (500) take place before step (200).

5. The method according to any one of the preceding claims, wherein the strain gauge (1) comprises a carrier layer (1 a) facing the measurement object (2) and a measuring grid (1 b).

6. The method according to any one of the preceding claims, wherein the strain gauge (1) and / or the first connecting film (10a) has a metallized first solder layer (13), which in step (200) between the strain gauge (1) and the first connecting film ( 10a) is arranged.

7. The method according to any one of the preceding claims, wherein the first connecting film (10a) and / or the electronic module (19) has a metallized second soldering layer (14) which in step (200) between the electronic module (19) and the first connecting film ( 10a) is arranged.

8. The method according to claim 6 in conjunction with claim 7, wherein

- the first soldering layer (13) is applied to the strain gauge (1) and/or the first connecting film (10a),

- the second soldering layer (14) is applied to the electronic module (19) and/or the first connecting film (10a),

- the first connecting film (10a) with the solder layers (13, 14) is placed in step (200) between the strain gauge (1) and the electronic module (19), and

- the metallic materials (11, 12) of the first connecting foil (10a) are activated in step (300), so that the first connecting foil (10a) heats up in such a way that the first soldering layer (13) and the second soldering layer (14) melt and the strain gauge (1) is soldered to the electronic module (19) through the melted first solder layer (13) and the melted second solder layer (14) in order to create the cohesive connection.

9. The method according to any one of the preceding claims, wherein the measurement object (2) and / or the second connecting foil (10b) has a metallized third solder layer (21) which in step (400) between the measurement object (2) and the second connecting foil ( 10b) is arranged.

10. The method according to any one of the preceding claims, wherein the second connecting film (10b) and / or the strain gauge (1) has a metallized fourth solder layer (22) which in step (400) between the strain gauge (1) and the second connecting film ( 10b) is arranged.

11. A method according to claim 9 in conjunction with claim 10, wherein

- the third soldering layer (21) is applied to the measurement object (2) and/or the second connecting film (10b),

- the fourth soldering layer (22) is applied to the strain gauge (1) and/or the second connecting film (10b),

- the second connecting film (10b) with the soldering layers (21, 22) is placed in step (400) between the measurement object (2) and the strain gauge (1), and

- the metallic materials (11, 12) of the second connecting foil (10b) are activated in step (500), so that the second connecting foil (10b) heats up in such a way that the third soldering layer (21) and the fourth soldering layer (22) melt and the measurement object (2) is soldered to the strain gauge (1) through the molten third solder layer (21) and the molten fourth solder layer (22) in order to create the cohesive connection.

12. The method according to claim 8 or claim 11, wherein by means of a fixing pad (9), which at least indirectly exerts a pressure (p) on the sensor arrangement (20) and / or on the measurement object (2), a deformation of the soldering layers (13, 14, 21, 22) and the respective connecting film (10a, 10b) is counteracted during activation and connection in step (300) or step (500).

13. The method according to any one of claims 6 to 12, wherein the respective solder layer (13,

14, 21, 22) is made of a material comprising nickel.

14. The method according to any one of claims 6 to 13, wherein the respective soldering layer (13, 14, 21, 22) comprises a nickel layer and a gold layer.

15. Arrangement of a sensor arrangement (20) on a measurement object (2), the sensor arrangement (20) being connected to the measurement object (2) by a method according to one of the preceding claims.