Sensor element and sensor device for ascertaining at least one physical or chemical measured variable

Abstract

The invention relates to a first variant of a sensor element for ascertaining at least one physical or chemical measurement variable, comprising: a planar substrate (1) having a first surface and a second surface opposite the first surface; one or more sensor structures (2) applied to the first surface of the substrate (1) or to an insulating layer applied to the first surface of the substrate; a passivation layer (3) at least partially covering the sensor structure (2) or sensor structures (2); at least two electrical contact surfaces (4) each connected to the sensor structure (2); a spacer layer (5) applied to one or more first portions of the second surface of the substrate (1); and a sinterable and / or solderable metal layer (6) applied to the one or more second portions of the second surface of the substrate (1) and / or to the spacer layer (5), the layer thickness of the spacer layer (5) being greater than or equal to the layer thickness of the sinterable and / or solderable metal layer (6). The invention also relates to a second variant of a sensor element and to a sensor arrangement comprising at least one sensor element of this type.

Description

Technical Field

[0001] The invention relates to a first and a second variant of a sensor element for ascertaining at least one physical or chemical measured variable. Furthermore, the invention relates to a sensor device comprising one or more sensor elements according to the invention. Background Art

[0002] Sensor elements are used in a variety of applications and, depending on their design, are used, for example, to ascertain temperatures, flow variables, gas concentrations or compositions, humidity values, pH values ​​and / or biological variables, but can also be used, for example, as heating elements. For each specific application, the sensor element usually has to be connected directly to other sensor elements or surfaces, for example, to the surface to be measured when using the sensor element as a surface probe. For modern sensor elements designed according to the prior art, various processes are used, such as welding or gluing (by using polymer adhesives or ceramic-based adhesives).

[0003] However, the processes used so far have several disadvantages:

[0004] For example, during soldering, mechanical stresses can occur when the solder solidifies, which depend on differences in the thermal expansion coefficients of the connection parts, differences between the connection parts and the solder, and differences in the expansion of intermetallic phases in the solder structure. These can influence the temperature coefficient of resistance (TCR), the resistance shift, and therefore the accuracy of the component. In addition, the soldering flux can poison the sensor element. In addition, temperature resistance is limited to application areas that are usually below 280°C. The main disadvantage lies in the hysteresis behavior of the solder joint, which makes it more difficult to reproduce small deviations in the sensor signal. The soldering process is particularly unsuitable for applications that require high precision and simultaneously fast response times.

[0005] When using critical atmospheres (e.g. with moisture influence, large temperature variations and elevated temperatures), printed circuit boards and solder joints must be cleaned of flux residues, as these can subsequently cause failures in the application. This process usually requires chemicals and is an additional step involving costs.

[0006] When using one of the above adhesives, phase changes or shrinkage during curing may induce stress in the sensor element and reduce accuracy. In addition, adhesive joints lead to larger contact resistances, which vary over time and thus show drift in long-term behavior. Adhesive bonds are also brittle and the degree of adhesion is limited depending on the substrate (only suitable for adhesive bonding to glass and ceramics).

[0007] Furthermore, during soldering and gluing, different expansion coefficients between adhesives or solders may also induce stresses in the event of temperature changes and thus change the TCR of the sensor element. Adjusting the TCR is not always possible and is very complicated. In addition, the long-term stability at higher temperatures is very limited.

[0008] In order to reduce or even completely avoid these disadvantages, silver sintering processes are used. Especially in printed circuit board technology, when manufacturing electrical components in the high temperature range with active and passive components, including integrated semiconductor modules, targeted temperature measurement is required. But even when connecting sensor elements to metal surfaces, such as stainless steel pipes with resistance elements for flow determination, a reproducible and, above all, drift-free connection is a prerequisite.

[0009] Methods that allow passive or active components (including resistor elements or sensor elements) to be silver sintered onto a carrier element are known from the prior art, for example from WO 2020 / 057859 A1 and DE 10 2010 050 315 C5. However, these components have a flat bottom surface, which means that the components are sintered onto the carrier at an undefined and imprecise distance. In addition, the components may be mounted at an angle. Among other things, this has a direct impact on the thermal bonding and, most importantly, a very large impact on the shear strength of the connection. This leads to the main disadvantage (which also exists for welding and gluing), namely that the manufacturing process is not reproducible. This means that the thermal transitions are always different - sometimes better, sometimes worse. The same also applies to the induced voltage, which causes an offset during the connection process. However, these disadvantages are extremely important for the production of sufficient yields or the manufacturability of the components. Starting from the problems listed, the object of the present invention is to provide a sensor element that allows a firm and thermally stable thermal contact with a carrier element. Summary of the invention

[0010] This object is achieved by a sensor element according to claim 1 , by a sensor element according to claim 2 and by a sensor device according to claim 11 .

[0011] With regard to a first sensor element according to the invention, the sensor element is used for ascertaining at least one physical or chemical measured variable, wherein the sensor element comprises:

[0012] - a planar substrate having a first surface and a second surface opposite to the first surface;

[0013] - one or more sensor structures applied to the first surface of the substrate or to an insulating layer applied to the first surface of the substrate;

[0014] a passivation layer, which at least partially covers the sensor structure or the sensor structures;

[0015] - at least two electrical contact surfaces, each electrical contact surface being connected to a sensor structure;

[0016] - a spacer layer applied to one or more first portions of the second surface of the substrate; and

[0017] - a sinterable and / or solderable metal layer applied to one or more second portions of the second surface of the substrate and / or the sinterable and / or solderable metal layer on the spacing layer, wherein the thickness of the spacing layer is greater than or equal to the thickness of the sinterable and / or solderable metal layer.

[0018] With regard to the second sensor element according to the invention, the second sensor element is used for ascertaining at least one physical or chemical measured variable, wherein the sensor element comprises:

[0019] - a planar substrate having a first surface and a second surface opposite to the first surface;

[0020] - one or more sensor structures applied to the first surface of the substrate or to an insulating layer applied to the first surface of the substrate;

[0021] a passivation layer, which at least partially covers the sensor structure or the sensor structures;

[0022] - at least two electrical contact surfaces, each electrical contact surface being connected to a sensor structure;

[0023] a sinterable and / or solderable metal layer applied to one or more second portions of the second surface of the substrate or to the entire second surface of the substrate; and

[0024] - a spacer layer, which is applied to one or more first portions of the second surface of the substrate and / or at least partially to the sinterable and / or solderable metal layer, wherein the thickness of the spacer layer and the sinterable and / or solderable metal layer is selected so that the distance between the surface of the spacer layer and the second surface of the substrate is greater than or equal to the distance between the surface of the sinterable and / or solderable metal layer and the second surface of the substrate.

[0025] Thus, the sensor elements according to the invention each have a structure for silver sintering or soldering, which allows a stress-free, heat-resistant, simple, fast and on-site connection of the substrate to a suitable surface. The spacer layer on the second surface of the substrate can limit the volume of the silver sintering or solder paste during the subsequent silver sintering or soldering process. In addition, if designed accordingly (for example when two or more first parts are used), the spacer layer can also prevent the sensor element from tilting during soldering or silver sintering.

[0026] The spacer layer has a height of, for example, 5 to 400 μm, preferably 5 to 150 μm.

[0027] The two variants of the sensor element according to the invention differ in their layer structure. While in the first variant the spacer layer is applied first and then the sinterable and / or solderable metal layer, in the second variant this is done in the opposite way. Here, the sinterable and / or solderable metal layer is applied first and then the spacer layer. This means that in each variant different thicknesses must be selected for the two layers in order to create a defined distance or space for the solder or solder paste.

[0028] According to an advantageous embodiment of the sensor element according to the invention, it is provided that the sinterable and / or solderable metal layer consists of gold, platinum, copper, nickel, chromium, glass, ceramic, titanium, palladium or a combination of the above materials. The combination of the above materials can be, for example, NiAu, NiCrNiAu, NiPdAu, CrPtAu, TiPtAu, AgPd, AgPdPt or AuPd.

[0029] According to an advantageous embodiment of the sensor element according to the invention, it is provided that the spacer layer consists of metal, polymer, glass, ceramic or a combination of the above mentioned materials.

[0030] According to an advantageous embodiment of the sensor element according to the invention, a spacer layer having a three-dimensional structure is provided. This means that the individual parts of the spacer layer applied according to the number of first parts are themselves structured. This can be, for example, in the shape of a column.

[0031] According to an advantageous embodiment of the sensor element according to the invention, one or more third portions of the second surface are provided which are free of the sinterable and / or solderable metal layer and the spacer layer.

[0032] According to an advantageous embodiment of the sensor element according to the invention, a sensor structure or a plurality of sensor structures are provided which are designed such that the sensor element can be used as a temperature sensor, a flow sensor, a gas sensor, a humidity sensor, a heating element, a pH sensor and / or a biosensor. Other sensor applications which are not listed here are conceivable.

[0033] According to an advantageous embodiment of the sensor element according to the invention, it is provided that one or more sensor structures consist of a metallic material, in particular platinum, and are applied to the first surface or the insulating layer of the substrate by means of a thin film or thick film method. For example, screen printing can be used as a thick film method. For example, PVD or CVD can be selected as a thin film method.

[0034] According to an advantageous embodiment of the sensor element according to the invention, it is provided that the spacer layer is applied by means of a thick film method.

[0035] According to an advantageous embodiment of the sensor element according to the invention, it is provided that the sinterable and / or solderable metal layer is applied by means of a thick-film or thin-film method.

[0036] Regarding the sensor device, the sensor device comprises one or more sensor elements according to the invention and a carrier element having a metal surface, wherein the sensor element is connected to the carrier element by means of silver sintering or silver soldering, wherein the silver sintering layer or silver soldering layer is arranged between the metal surface of the carrier element and the sinterable and / or solderable metal layer of the sensor element.

[0037] According to an advantageous embodiment of the sensor device according to the invention, it is provided that the carrier element is a printed circuit board, wherein the metal surface is formed by a metal coating applied to the printed circuit board, wherein the metal coating consists of one or more metallic materials. Instead of a printed circuit board, it is also possible to use a carrier element made of a ceramic material, which also has a metal surface formed by such a metal coating.

[0038] According to an advantageous embodiment of the sensor device according to the invention, it is provided that the carrier element is a tube or a plate consisting of a metallic material. In this case, the carrier element directly has one or more suitable metallic surfaces. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The present invention is explained in more detail with reference to the following drawings. In the drawings:

[0040] Figure 1 is an exemplary embodiment of a sensor device according to the invention, in which the sensor element is applied to a carrier element. DETAILED DESCRIPTION

[0041] The sensor element consists of a planar substrate 1, which is made of, for example, a ceramic material, a metallic material or a semiconductor material. A sensor structure 2 is applied to a first surface of the substrate 1. If the substrate 1 is made of a metallic material, an insulating layer is applied between the first surface and the sensor structure 2 to electrically insulate the sensor structure 2 from the metallic substrate 1. To protect against environmental influences, such as mechanical and / or chemical stresses, the sensor structure 2 is at least partially covered by a passivation layer 3.

[0042] The sensor structure 2 is a resistive structure or an electrode structure. Thus, the sensor element can be operated as a temperature sensor or a heating element. However, depending on the number and design of the sensor structures 2, several other types of sensor elements can be provided, including temperature sensors, flux or flow sensors, gas sensors, humidity sensors, pH sensors, biosensors, etc.

[0043] The sensor structure 2 is electrically conductively connected to at least two electrical contact surfaces 4. The sensor structure can be actuated or electrically operated via the guide surfaces 4, for example by an external control and evaluation unit.

[0044] For surface mounting on any surface, e.g. per conductive track or other carrier element 8, the sensor element has a special structure on the second surface of its substrate 1:

[0045] On the second surface of the substrate, at least one or several parts of the surface are covered with a sinterable and / or solderable metal layer 6. The metal layer is applied, for example, by means of a thin film method and serves as an anchor for a paste or solder during a subsequent silver sintering or soldering process. The sinterable and / or solderable metal layer 6 may, for example, consist of one or more materials from the following group: NiAu, NiCrNiAu, NiPdAu, CrPtAu, TiPtAu, AgPd, AgPdPt, AuPd, Au or Cu.

[0046] Furthermore, a spacer layer 5 is applied on one or more second portions of the second surface of the substrate 1 , which spacer layer may be made of metal, polymer, glass, ceramic or a combination thereof and applied by means of a thick film or thin film method.

[0047] Such a spacer layer 5 is thicker than the sinterable and / or solderable metal layer 6. The volume of the solder or solder paste can be determined by the height difference between the two layers (the sinterable and / or solderable metal layer 6 and the spacer layer). In addition, the spacer layer 5 or a plurality of such spacer layers 5 ensure that the sensor element can be placed parallel to the surface to be sintered / welded during the soldering or silver sintering process. The selection of the material of the spacer layer 5 can also select whether the spacer layer 5 is bonded to the solder or solder paste or whether no additional bonding is mechanically generated. For example, ventilation channels can be specially constructed, for example, to allow volatile reactive components in the process to escape more easily and to achieve a higher quality connection. In addition, the mechanical stress distribution can be specifically relocated, decoupled or even significantly reduced.

[0048] The sensor element can be connected to a carrier element 8 , for example to a metallic material, by means of soldering or silver sintering 8 , but can also be connected to a printed circuit board, such as Figure 1 On printed circuit boards, silver sintering occurs on metallic coatings in the form of metallic surfaces composed of one or more metals.

[0049] It can also be provided that the sinterable and / or solderable metal layer 6 completely or partially covers the spacer layer 5 , for example by completely coating the entire back side of the substrate 1 , including the spacer layer 5 , with a film.

[0050] It can also be provided that the sinterable and / or solderable metal layer 6 is applied first and that the spacer layer 5 is applied afterwards. If the spacer layer 5 covers the sinterable and / or solderable metal layer 6, the spacer layer 5 does not have to be thicker than the sinterable and / or solderable metal layer 6. However, care must be taken to ensure that the distance between the surface of the spacer layer 5 and the second surface of the substrate 1 is greater than or equal to the distance between the surface of the sinterable and / or solderable metal layer 6 and the second surface of the substrate 1, in order to create a volume for the solder or solder paste.

[0051] Some advantages of the solution according to the invention are described below:

[0052] - Lower drift and hysteresis behavior (compared to welding methods);

[0053] - Mechanical decoupling to avoid stresses caused by temperature gradients and different expansion coefficients between sensor element and carrier element 8;

[0054] -Good thermal transition when using silver solder paste;

[0055] -High temperature resistance up to 400°C;

[0056] - No need for corrosive substances or other elements that could poison the sensor;

[0057] - Can be carried out with the customer's approval - Also suitable for large-scale production of existing silver sintering applications in processing plants.

[0058] - Higher process reliability and reproducibility: Not only can defined distances be established, but also defined volumes. This also means that heat capacity and heat transfer can be defined more precisely, which can be advantageous in fluid applications, for example.

[0059] Reference numerals list

[0060] 1 substrate

[0061] 2 (One or more) sensor structures

[0062] 3. Passivation layer

[0063] 4Electrical contact surface

[0064] 5 compartments

[0065] 6Sinterable and / or weldable metal layers

[0066] 7. Metal Surface

[0067] 8 Carrier elements

Claims

1. A sensor element for ascertaining at least one physical or chemical measured variable, comprising: - a planar substrate (1), the planar substrate (1) having a first surface and a second surface opposite to the first surface; - one or more sensor structures (2), the one or more sensor structures being applied to the first surface of the substrate (1) or to an insulating layer applied to the first surface of the substrate (1); - a passivation layer (3), the passivation layer (3) at least partially covering the sensor structure (2) or the sensor structures (2); - at least two electrical contact surfaces (4), each of which is connected to the sensor structure (2); - a spacer layer (5) applied to one or more first portions of the second surface of the substrate (1); as well as - a sinterable and / or weldable metal layer (6), which is applied to one or more second portions of the second surface of the substrate (1) and / or to the spacer layer (5), wherein the thickness of the spacer layer (5) is greater than or equal to the thickness of the sinterable and / or weldable metal layer (6).

2. A sensor element for ascertaining at least one physical or chemical measured variable, comprising: - a planar substrate (1), the planar substrate (1) having a first surface and a second surface opposite to the first surface; - one or more sensor structures (2), the one or more sensor structures being applied to the first surface of the substrate (1) or to an insulating layer applied to the first surface of the substrate (1); - a passivation layer (3), the passivation layer (3) at least partially covering the sensor structure (2) or the sensor structures (2); - at least two electrical contact surfaces (4), each of which is connected to the sensor structure (2); a sinterable and / or weldable metal layer (6) applied to one or more second parts of the second surface of the substrate (1) or to the entire second surface of the substrate; as well as - a spacer layer (5), which is applied to one or more first portions of the second surface of the substrate (1) and / or at least partially to the sinterable and / or weldable metal layer (6), wherein the thickness of the spacer layer and the sinterable and / or weldable metal layer (6) is selected so that the distance between the surface of the spacer layer (5) and the second surface of the substrate (1) is greater than or equal to the distance between the surface of the sinterable and / or weldable metal layer (6) and the second surface of the substrate (1).

3. The sensor element according to claim 1 or claim 2, wherein: The sinterable and / or weldable metal layer (6) is composed of gold, platinum, copper, nickel, chromium, glass, ceramic, titanium, palladium or a combination of the aforementioned materials.

4. The sensor element according to any one of the preceding claims, wherein: The spacer layer (5) is composed of metal, polymer, glass, ceramic or a combination of the aforementioned materials.

5. Sensor element according to one or more of the preceding claims, wherein: The spacer layer (5) has a three-dimensional structure, in particular a three-dimensional structure in the form of columns.

6. Sensor element according to one or more of the preceding claims, wherein: One or more third portions of the second surface are provided, the one or more third portions being free of the sinterable and / or weldable metal layer (6) and the distance layer (5).

7. Sensor element according to one or more of the preceding claims, wherein: The sensor structure (2) or sensor structures (2) are designed such that the sensor element can be used as a temperature sensor, as a flow sensor, as a gas sensor, as a humidity sensor, as a heating element, as a pH sensor and / or as a biosensor.

8. Sensor element according to one or more of the preceding claims, wherein: The sensor structure or structures (2) consist of a metallic material, in particular platinum, and are applied to the first surface or the insulating layer of the substrate (1) by means of a thin-film or thick-film method.

9. Sensor element according to one or more of the preceding claims, wherein: The spacer layer (5) is applied by means of a thick film method.

10. The sensor element according to one or more of claims 1 to 8, wherein: The sinterable and / or solderable metal layer (6) is applied by means of a thick-film or thin-film method.

11. A sensor device comprising one or more sensor elements according to one or more of the preceding claims and a carrier element (8) having a metal surface (7), wherein: The sensor element or the sensor elements are connected to the carrier element (8) by means of silver sintering or soldering, wherein a silver sintering or soldering layer is arranged between a metal surface (7) of the carrier element (8) and a sinterable and / or solderable metal layer (6) of the sensor element or the sensor elements.

12. The sensor device according to claim 11, wherein: The carrier element (8) is a printed circuit board, wherein the metal surface (7) is formed by a metal coating applied to the printed circuit board, wherein the metal coating consists of one or more metallic materials.

13. The sensor device according to claim 11, wherein: The carrier element (8) is a tube or a plate made of a metal material.

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