The invention relates to a method for manufacturing a temperature sensor, as well as to a temperature sensor for use at high temperatures, preferably at temperatures above about, for instance, 200° C.
Known from the state of the art are numerous temperature sensor elements for determining a temperature. These are manufactured, for example, in thin film technology and have on a substrate a functional layer of, for example, platinum. By means of this functional layer, a temperature of a medium, with which the functional layer is in thermal interaction, can be determined.
For use, such temperature sensor elements are placed in a housing for protection against external influences (mechanical, chemical, etc.). This leads, however, to an influencing of the thermal interaction between temperature sensor element and medium, so that a delayed, or deteriorated, response time arises.
In order to improve the response time of such a temperature sensor element, a common approach is to solder the temperature sensor element to a floor of the housing, in order to achieve an improved thermal interaction. Used for this are conventional soldering techniques, which bring their own difficulties as regards the melting temperature. Thus, in the last years, there is a trend toward use of leadfree solders. Leadfree solders, especially leadfree low temperature solders, have typically a melting temperature below 220° C. Relatively low melting temperature also limit use temperature of the temperature sensor to a range up to about 200° C.
Alternatively, there are leadfree solders with a melting temperature of above 900° C. These are typically silver based. Disadvantageous with these solders is that a high temperature is required, in order to use them, so that a temperature sensor element to be soldered therewith must likewise withstand such temperatures.
Currently, no joining technology is known, which enables a reliable and thermally well-coupled installation of a temperature sensor element in a housing, such that use also at high temperatures, especially at temperatures in the range of about 200-900° C., is possible.
Along with that, conventional soldering techniques often have the problem of solder lacking regions in the joint, i.e. voids and/or air and flux inclusions to an undesirably high fraction. The solder lacking regions in the joint lead, in turn, to the fact that the thermal interaction between medium and temperature sensor element is degraded.
An object of the invention is, thus, to overcome the above described disadvantages of the state of the art.
The object of the invention is achieved by a method for manufacturing a temperature sensor, a temperature sensor for use at high temperatures and use of the temperature sensor in a flow measuring apparatus.
As regards the method, the object is achieved by a method for manufacturing a temperature sensor, wherein the temperature sensor includes at least one temperature sensor element with an at least partially metallized face and a support, wherein the method comprises steps as follows:
According to the invention, silver sintering is provided for affixing the temperature sensor element on a support. The support comprises preferably stainless steel, copper and/or nickel.
The connecting layer is advantageously applied by thin film technology, so that the thickness of the connecting layer lies typically in the range from several hundred nanometers up to a few micrometers. Proved as especially advantageous in such case is a sputtering process for deposition. Depending on the material of the support and geometry, however, also a galvanic deposition can be advantageous.
The silver sinter paste applied for the silver sintering contains extremely fine silver particles, which coalesce to solid silver already at sinter temperatures from about 230° C. to 300° C. The occurring silver sinter layer has the usual properties known for silver, especially a melting point of 961° C. Thus, a temperature sensor manufactured in such a manner can be applied also at temperatures above 200° C.
Advantageous in the case of the silver sintering is likewise that no flux is required and, thus, solder lacking regions in the joint essentially can be prevented.
An advantageous form of embodiment of the method of the invention provides that the silver sinter paste layer is applied on the connecting layer of the support.
An alternative form of embodiment of the method of the invention provides that instead of the applying the silver sinter layer on the connecting layer such is applied on the at least partially metallized face of the temperature sensor element.
Another advantageous form of embodiment of the method of the invention provides that the support, for example, a thin platelet, after the arranging of the temperature sensor element and the sintering of the silver sinter paste layer, is connected with a housing, for example, a hollow cylindrical housing, by material bonding.
An alternative form of embodiment of the method of the invention provides that, instead of, for example, a thin platelet, the support is a housing wall, preferably a floor, of a housing.
Another advantageous form of embodiment of the method of the invention provides that a temperature profile with at least one rising temperature ramp is used for sintering the silver sinter paste layer.
Another advantageous form of embodiment of the method of the invention provides that the at least partially metallized face comprises at least gold, silver and/or palladium.
Another advantageous form of embodiment of the method of the invention provides that the at least partially metallized face is produced via a thin-film process.
Another advantageous form of embodiment of the method of the invention provides that during the sintering of the silver sinter paste layer a defined pressure is applied on the temperature sensor element, so that a defined coating thickness of the silver sinter paste layer arises. By a defined, thin, coating thickness, which typically is a few micrometers to a maximum of several tens of micrometers thick, the solvent in the silver sinter paste layer can better escape.
As regards the temperature sensor, the object is achieved by a temperature sensor for use at high temperatures, preferably at temperatures above about, for instance, 200° C., comprising a housing, in which at least one temperature sensor element is arranged, wherein the temperature sensor element has at least one partially metallized face and is connected with a silver sinter layer via the at least partially metallized face, wherein the silver sinter layer is connected with a housing wall of the housing either via a connecting layer, which comprises at least gold, silver and/or palladium, or directly with the housing via a housing wall, which comprises at least gold, silver and/or palladium.
An advantageous embodiment of the temperature sensor of the invention provides that the temperature sensor element includes a functional layer for determining a temperature. Especially, the embodiment provides that at least two contact wires are provided for contacting the functional layer with an electronics unit, wherein the contact wires via wire end regions are arranged in such a manner on the functional layer that the wire end regions are directed away from the housing wall of the housing.
Furthermore, the embodiment provides especially that the at least partially metallized face is a face of the temperature sensor element lying opposite the functional layer or a side wall of the temperature sensor element arranged essentially orthogonally to the functional layer.
Another advantageous embodiment of the temperature sensor of the invention provides that the temperature sensor element is supplied at least via the housing wall of the housing and the silver sinter layer with the temperature to be determined.
As regards use, the object is achieved by use of a temperature sensor according to at least one of the above described embodiments as a heating element, especially as a heating element in a flow measuring apparatus.
The invention will now be explained in greater detail based on the appended drawing, the figures of which show as follows:
The temperature sensor element 2 includes a substrate 4, for example, a ceramic substrate, a functional layer 6 for determining a temperature, for example, a platinum meander structure with a defined temperature dependent resistance, and a metallized face 11.
The functional layer 6 is connected via contact wires 8 with a corresponding electronics unit (not shown in
The contact wires 8 of the first variant illustrated in
The metallized face 11 as shown in
The housing 3 shown in
Furthermore, the variants illustrated in
Only the housing 3 differs such that there serves as floor of the housing, in this case the small tube, a support, for example, a platelet 15, which, after the temperature sensor element 2 has been affixed on the platelet 15, is connected with the housing wall, here the wall of the small tube. Typically, this connection is produced by material bonding, for example, by welding. The joint is indicated in
Furthermore, both the embodiment of the temperature sensor 1 shown in
Connecting layer 7 serves for adhesion promotion between substrate 4 and the support, on which the substrate 4 is applied during the manufacturing process.
1 temperature sensor
2 temperature sensor element
3 housing
4 substrate
5 silver sinter paste layer, or silver sinter layer
6 functional layer
7 connecting layer
8 connecting wire
9 cover paste
10 joint
11 metallized face
12 wire end regions
13 side wall of the temperature sensor element
14 floor of the one piece housing as support
15 platelet as support
31 method step for cleaning the support
32 method step for applying connecting layer
33 method step for applying a silver sinter layer
34 method step for applying temperature sensor element
35 method step for sintering silver sinter paste layer
36 method step for connecting the support with the housing
37 method step for potting the temperature sensor element
Number | Date | Country | Kind |
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10 2015 114 314.3 | Aug 2015 | DE | national |
Filing Document | Filing Date | Country | Kind |
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PCT/EP2016/069192 | 8/12/2016 | WO | 00 |