Method for producing a pressure sensor
Patent Information
- Application Number
- EP2023802205
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2022-12-13
- Filing Date
- 2023-11-07
- Publication Date
- 2025-10-22
AI Technical Summary
Existing pressure sensors face challenges in achieving high compressive strength and tightness in joints, particularly with ceramic and metallic components, which can lead to measurement errors due to chemical reactions and leakage issues during the soldering process, especially with Ag-Cu-Ti active brazing alloys and tantalum pins.
A method involving a titanium core with a passivating layer, such as oxide or nitride, is used to prevent chemical reactions during active brazing, ensuring secure electrical contact and sealing by avoiding alloying of titanium with the active brazing alloy, and utilizing an Ag-Cu active brazing alloy with titanium as the active component.
This approach enhances the compressive strength and tightness of the joints while minimizing temperature-dependent measurement errors and ensuring reliable electrical contact, maintaining the mechanical integrity and accuracy of pressure sensor measurements.
Smart Images
Figure 1.1
Abstract
Description
[0001] Method for manufacturing a pressure sensor
[0002] The invention relates to a method for producing a pressure sensor and a pressure sensor.
[0003] Pressure sensors are used in industrial measurement technology to measure pressures.
[0004] For this purpose, ceramic pressure sensors are used, among others. These sensors comprise at least one ceramic body, such as a base body and / or a measuring diaphragm connected to the base body, including a pressure chamber. Depending on the design, these pressure sensors require one or more ceramic bodies of the pressure sensor to be connected to a metallic body by means of at least one joint. Depending on their position, these joints may have to meet stringent requirements regarding their compressive strength and / or leak tightness.
[0005] An example of this are feedthroughs, each of which comprises a metallic body designed as a pin, connected pressure-tight to the base body by means of a joint, extending through the base body, via which a sensor component of the pressure sensor connected thereto can be electrically contacted through the base body and / or connected to a measuring electronics.
[0006] For example, DE 10 2008 043 567 A1 describes a pressure sensor comprising a ceramic base body and a ceramic measuring diaphragm connected to the base body, enclosing a pressure chamber, which can be subjected to a pressure to be measured by the pressure sensor. This pressure sensor is equipped with a capacitive, electromechanical transducer designed to convert a deflection of the measuring diaphragm, which is dependent on the pressure acting on the measuring diaphragm, into an electrical quantity. In addition, the pressure sensor comprises a feedthrough running through the base body, via which an electrode of a capacitor of the capacitive transducer can be electrically connected. The feedthrough comprises a metallic body connected to the electrode, designed as a tantalum pin, which is inserted into a bore running through the base body and opening into the pressure chamber.The tantalum pin is connected at the end to the ceramic base body by means of an active braze, which closes a gap between the base body and the tantalum pin inserted into it. The compressive strength and tightness of the active braze therefore play a major role in determining the compressive strength and tightness of the feedthrough. As the bore opens into the pressure chamber, a high compressive strength of the active braze is particularly necessary if the pressure chamber may be exposed to very high pressures during measuring operation. This is particularly the case with differential pressure sensors, which have a measuring diaphragm arranged between two base bodies, each connected to a pressure chamber. A high level of tightness is, for example, particularly important.This is necessary when the pressure sensor is designed as an absolute pressure sensor whose pressure chamber is evacuated, but a high level of tightness is also required for relative and differential pressure sensors.
[0007] Active brazing is produced using an active brazing alloy containing an active component that reacts with the ceramic during active brazing. The reduction of the ceramic creates a mechanically strong chemical bond between the ceramic and the active brazing alloy.
[0008] Active brazing alloys offer the advantage that, due to the active component they contain, they are able to wet ceramic components and enable direct brazing of ceramic components without prior metallization of the ceramic.
[0009] The disadvantage of this approach, however, is that tantalum pins have a very small but nevertheless measurable adverse influence on the achievable measurement accuracy, which is reflected in particular in the form of a temperature-dependent measurement error.
[0010] In this respect, DE 10 2018 108743 A1 describes the advantages of using titanium as a material for the vias or pins. However, the disadvantage of using titanium pins as vias is that an active brazing alloy, especially an Ag-Cu-Ti active brazing alloy, causes very violent reactions with the titanium of the pin during the brazing process. This, in turn, can lead to leaks and, on the other hand, to the inability to establish a reliable electrical connection.
[0011] The invention is therefore based on the object of remedying this situation.
[0012] The object is achieved according to the invention by the method according to patent claim 1 and the pressure sensor according to patent claim 7.
[0013] The method according to the invention for producing a pressure sensor comprises at least the following steps:
[0014] Providing a ceramic base body, providing a measuring membrane connected to the base body with the inclusion of a pressure chamber and capable of being subjected to a pressure to be measured by the pressure sensor,
[0015] Providing an electromechanical transducer configured to convert a deflection of the measuring membrane, dependent on the pressure acting on the measuring membrane, into an electrical value; providing at least one titanium core for an electrically conductive contact pin, which is intended to serve for electrically contacting a component of the electromechanical transducer through the base body; creating a layer on a surface of the titanium core that is passivated against the alloying of titanium from the titanium core into a melt of an active brazing alloy;
[0016] Inserting the contact pin into a receptacle intended for the contact pin which runs through the base body, in particular a bore;
[0017] Electrically connecting the contact pin to the component of the electromechanical transducer on a membrane-facing side of the base body;
[0018] Joining the contact pin to the base body by means of the active brazing alloy at least on one side of the base body facing away from the membrane, so that the titanium of the titanium core does not alloy into the melt of the active brazing alloy.
[0019] According to the invention, the production or application of a passivation layer on a titanium core, which is to be used in a ceramic base body of a pressure sensor as a contact pin for a through-hole connection, is proposed in order to be able to join the passivated contact pin with an active brazing solder without the titanium of the titanium core chemically reacting with a component of the active brazing solder.
[0020] An advantageous embodiment of the method according to the invention can provide that the layer passivating with respect to the alloying of titanium from the titanium core into the melt is produced by oxidation or nitriding with nitrogen at a defined temperature, preferably at a temperature below 450 °C, particularly preferably at a temperature in the range from 300 °C to 400 °C.
[0021] An alternative embodiment may provide for the layer to be applied by coating the surface of the titanium core with a material that is passivating with respect to the alloying of the titanium into the melt, and / or by coating the surface of the titanium core with tantalum, molybdenum, nickel, a nickel alloy, or another metal that is passivating with respect to the alloying of the titanium into the melt, or with a metal oxide, e.g., titanium oxide. Furthermore, the embodiment may provide for the coating of the surface of the titanium core to be carried out by a sputtering process, in particular a sputtering process for sputtering bulk material.
[0022] Yet another embodiment of the method according to the invention can provide that the joining of the contact pin to the base body is carried out by means of an Ag-Cu active brazing solder (silver-copper active brazing solder), preferably with titanium as the active component.
[0023] The invention further relates to a pressure sensor, in particular obtainable by one or more of the previously described embodiments, comprising: a ceramic base body, a measuring diaphragm connected to the base body with the inclusion of a pressure chamber and acted upon by a pressure to be measured by the pressure sensor, an electromechanical transducer designed such that it converts a deflection of the measuring diaphragm dependent on the pressure acting on the measuring diaphragm into an electrical quantity, and at least one electrically conductive contact pin connected to a component of the pressure sensor and extending through the base body, via which the component connected thereto can be electrically connected, wherein the at least one contact pin comprises a titanium core and a surface of the titanium core, preferably surrounding it on all sides,a layer preventing alloying of the titanium of the titanium core into a melt of an active brazing alloy, wherein the at least one contact pin is inserted into a receptacle intended for this purpose, in particular a bore in the base body, and is electrically connected to the associated component of the converter on one side of the base body facing the membrane, and wherein the at least one contact pin is further joined to the base body with the active brazing alloy at least on one side of the base body facing away from the membrane, so that the titanium of the titanium core is not alloyed into the melt of the active brazing alloy.
[0024] The invention is explained in more detail with reference to the following drawings. It shows:
[0025] Fig. 1 : an example of a pressure sensor according to the invention, and
[0026] Fig. 2: a region of the contact pin inserted into the base body, circled in Fig. 1, facing the membrane. Fig. 1 shows an example of a pressure sensor according to the invention. This comprises a ceramic base body 1 and a measuring membrane 5 connected to the base body 1, including a pressure chamber 3, which can be subjected to a pressure p to be measured by the pressure sensor.
[0027] Individual components of pressure sensors according to the invention can have different configurations that can be used individually or in combination with one another. Examples of these are described below with reference to the figures.
[0028] The pressure sensor shown as an example in Fig. 1 is designed as an absolute pressure sensor, which measures a pressure p acting on the outside of the measuring membrane 5. In this case, the pressure chamber 3 enclosed beneath the measuring membrane 5 is evacuated. Alternatively, the pressure sensor can be designed as a relative pressure sensor, which measures a pressure p acting on the outside of the measuring membrane 5 relative to a reference pressure p supplied to the pressure chamber 3 via a pressure supply line 11 running through the base body 1 and shown as an alternative in dashed lines in Fig. 1. re f. However, the invention can also be used analogously in conjunction with ceramic differential pressure sensors.
[0029] Regardless of whether the pressure sensor is designed as an absolute, relative or differential pressure sensor, its base body 1 and its measuring diaphragm 5 each have predetermined dimensions depending on a pressure measuring range of the pressure sensor. In this respect, depending on the pressure measuring range, the base body 1 can, for example, have a diameter on the order of magnitude of greater than or equal to 1.5 cm, in particular from 1.5 cm to 3.5 cm, and a thickness on the order of magnitude of greater than or equal to several millimeters, in particular from 0.4 cm to 0.5 cm. Depending on the pressure measuring range, the measuring diaphragm 5 has, for example, a diaphragm thickness of greater than or equal to one or several tenths of a millimeter. To measure very high pressures, diaphragm thicknesses of up to several millimeters can also be used if the thickness of the base body 1 is increased accordingly.
[0030] Regardless of the respective design of the pressure sensor, the base body 1 and the measuring membrane 5 can be connected to one another, for example, by means of a joint 13 connecting an outer edge of the measuring membrane 5 to an outer edge of the base body 1 and surrounding the pressure chamber 3 on all sides. Active brazing, such as an active brazing comprising zirconium, nickel, and titanium, is suitable as the joint 13.
[0031] In addition, the pressure sensor comprises an electromechanical transducer designed to convert a deflection of the measuring membrane 5, which is dependent on the pressure acting on the measuring membrane 5, into an electrical quantity. This electrical quantity can be detected, for example, by means of measuring electronics 7 that are connected to or are connected to the transducer and converted into a signal representing the pressure to be measured, which can then be displayed, output as a measurement signal, and / or made available for further processing and / or evaluation.
[0032] The electromechanical transducer can, for example, be designed as a capacitive transducer comprising a measuring capacitor with a measuring capacitance Cp dependent on the pressure-dependent deflection of the measuring membrane 5. The measuring capacitor illustrated here as an example comprises a measuring electrode 15 applied to a front side of the base body 1 facing the membrane and a counter electrode 17 arranged on an inner side of the measuring membrane 5 facing the base body 1. In the example illustrated in Fig. 1, the measuring electrode 15 forms one of the components of the transducer, which is or can be electrically connected via a contact pin 9 designed according to the invention connected thereto, which will be described in more detail below.
[0033] Optionally, the converter can comprise at least one additional capacitor. One example of this is a reference capacitor, also shown as an option in Fig. 1. In the example shown, this comprises a reference electrode 19 applied to the end face of the base body 5 facing the membrane, shown as an option in dashed lines in Fig. 1, which, together with the counter electrode 17, forms the reference capacitor CR. Furthermore, the reference electrode 19 can also represent one of the components of the converter, which can be connected or is connected to a contact pin designed according to the invention, which will be described in more detail below.
[0034] The electrical connection of the counter electrode 17 is preferably made via the adjacent, in this case electrically conductive, joint 13, which can be contacted directly from the outside. Alternatively, the electrical connection of the counter electrode 17 can also be made, as shown in Fig. 1, via another contact pin designed according to the invention, which will be described in more detail later. The contact pin extends through the base body 1 directly to the joint 13 or, alternatively, to a connection area connected to the joint 13, which can be realized, for example, by metallization.
[0035] The reference capacitor is preferably designed such that its reference capacitance CR has little or no dependence on the pressure-dependent deflection of the measuring diaphragm 5. This is achieved in the illustrated example by the reference electrode 19 being designed as an annular disk-shaped or annular segment-shaped electrode that surrounds the measuring electrode 15, which is circular disk-shaped here, on the outside.
[0036] The measuring electrode 15 and the counter electrode 17, as well as the reference electrode 19, if provided, each consist of an electrically conductive electrode material. Suitable materials include, for example, tantalum, tantalum oxide, titanium, and / or titanium oxide.
[0037] In conjunction with pressure sensors comprising a capacitive transducer, the pressure to be measured is determined by means of the measuring electronics 7 to be connected or connected to the transducer, preferably using an auxiliary quantity Cv that depends on the measuring capacitance CP. This can, for example, be an auxiliary quantity Cv that depends exclusively on the measuring capacitance CP or, alternatively, on the measuring capacitance CP and the reference capacitance CR. As an auxiliary quantity Cv, for example, a quantity dependent on the measuring capacitance C p related difference between measuring capacitance CP and reference capacitance CR dependent auxiliary quantity Cv.such as Cv = (CP - CR) / Cp.
[0038] However, the invention is not limited to pressure sensors with capacitive transducers, but can also be used analogously in conjunction with pressure sensors that are equipped with an electromechanical transducer based on a different transducer principle and comprise at least one component that can be contacted via a contact pin connected to it and extending through the base body.
[0039] If the pressure sensor, as shown in Fig. 1, comprises two or more components that can each be contacted via one of the contact pins 9, the following statements regarding the contact pin designed according to the invention apply accordingly to at least one or some of the contact pins up to all contact pins 9.
[0040] The contact pin designed according to the invention has a titanium core with a layer surrounding the titanium core, preferably on all sides. The titanium core can preferably be made of titanium grade 1, titanium grade 2, titanium grade 4 or titanium grade 5. These materials have a modulus of elasticity in the range of
[0041] 105 kN / mm 2 up to 115 kN / mm 2 and a very well adapted to the ceramic thermal expansion coefficient in the range of 8* 10' 6 / K to 9* 10' 6 / K. In comparison, tantalum pins used in the above-mentioned prior art have a significantly higher modulus of elasticity of more than 180 kN / mm 2 and a thermal expansion coefficient in the range of 6* 10' 6 / K to 7* 10' 6 / K. The contact pins 9 can, for example, have a diameter in the range of 0.5 mm to 0.8 mm.
[0042] The titanium cores are preferably manufactured by drawing a substantially fully cylindrical rod from a blank, which has a diameter corresponding to the diameter of the contact pins 9 to be produced. Titanium rods of the desired length are then cut from this rod.
[0043] To prevent the titanium of the titanium core from alloying into a melt, particularly an Ag-Cu melt (silver-copper melt), during the brazing process, a layer is created on or at a surface of the titanium core according to the invention. This layer has a passivating effect against the alloying of the titanium. Such a coating, which has a passivating effect against the alloying of the titanium into the melt, particularly an Ag-Cu melt, can be created, for example, by oxidation or nitriding of the surface of the titanium core with nitrogen at a defined temperature, particularly at a temperature below 450°C, and particularly at a temperature in the range of 300°C to 400°C.
[0044] Alternatively, the coating can also be carried out by applying a material that is passivating compared to the alloying of the titanium into the melt, especially the Ag-Cu melt. Tantalum (Ta), molybdenum (Mo), nickel, a nickel alloy or other passivating metals or metal oxides, such as titanium oxide, have proven to be particularly advantageous materials that have a passivating effect compared to the alloying of the titanium into the Ag-Cu melt. These materials can be applied, for example, using a sputtering process, whereby coating the titanium cores as bulk material has proven particularly advantageous. In this method, the titanium cores in bulk form are placed in a rotating substrate drum in which a stationary plasma coating source is arranged so that the rotating movement ensures thorough mixing of the titanium cores during the actual coating.
[0045] The contact pin designed according to the invention is inserted into a receptacle provided for this purpose in the base body and connected to the corresponding component of the converter. The receptacle can be created, for example, by a bore in the base body. For this purpose, known methods from the prior art, such as those described in DE 10 2008 043 567 A1, can be used, in which the respective contact pin 9 is pressed into the corresponding bore.
[0046] During pressing, the respective contact pin 9 is inserted into the associated bore and pressed against an abutment arranged, for example, on the side of the base body 1 facing away from the membrane. In the process, the electrical connection of the respective contact pin 9 to the associated component is preferably also effected at the same time. For this purpose, the end of the respective bore facing the measuring membrane 5 has a jacket surface over which a connection area 21 of the respective component extends. These jacket surfaces are each aligned such that the end of the contact pin 9 opposite the abutment is pressed against the connection area 21 of the respective component arranged on the jacket surface during pressing. This creates a cold weld that ensures reliable electrical contact between the respective contact pin 9 and the connection area 21.The cold welding process allows for reliable electrical contact even when the contact pin 9 and the connection area 21 are made of different, electrically conductive materials. The respective connection area 21 can be designed, for example, as a sub-area of the respective component or as a contact connected to the respective component.
[0047] Fig. 2 shows an enlarged view of an embodiment of the membrane-facing region of the base body 1, which is circled in Fig. 1 and only shown schematically in Fig. 1, with the contact pin 9 pressed into it. There, the connection region 21, via which the measuring electrode 15 is connected to the contact pin 9, is formed by a partial region of the measuring electrode 15 arranged on the, for example, funnel-shaped outer surface of the end of the associated bore facing the measuring membrane 5. Analogously, the reference electrode 19 which may be provided can of course also comprise a connection region 21 connected to the associated contact pin 9, which is formed by a partial region of the reference electrode 19 arranged on the outer surface of the end of the associated bore facing the measuring membrane 5.
[0048] Furthermore, the respective contact pin is joined to a side of the base body 1 facing away from the membrane by means of an active brazing joint and thus sealed, in particular hermetically sealed. For active brazing, an Ag-Cu active brazing alloy 23 with an active component, such as titanium, zirconium, or hafnium, which enables wetting through a reaction at the solder-base body interface, has proven particularly advantageous. If necessary, an annular gap existing between the respective contact pin and the bore can also be sealed with the active brazing alloy. The electrically conductive contact pin can be electrically contacted by means of a soft solder 25 that can be applied or is applied to the active brazing joint. List of Reference Symbols
[0049] Basic body
[0050] pressure chamber
[0051] measuring membrane
[0052] Measuring electronics
[0053] Titanium core of the contact pin
[0054] Passivating layer
[0055] Reference air pressure supply line
[0056] Joint
[0057] measuring electrode
[0058] Counter electrode
[0059] Reference electrode
[0060] Connection area
[0061] Active brazing alloy, especially Ag-Cu active brazing alloy
[0062] Soft soldering
Claims
Patent claims 1 . A method for manufacturing a pressure sensor, comprising at least the following steps: Providing a ceramic base body (1), Providing a measuring membrane (5) connected to the base body (1) with the inclusion of a pressure chamber (3) and capable of being subjected to a pressure (p) to be measured by the pressure sensor, Providing an electromechanical transducer designed to convert a deflection of the measuring membrane (5), which is dependent on the pressure acting on the measuring membrane (5), into an electrical quantity; providing at least one titanium core (9.1) for an electrically conductive contact pin, which is intended to serve for electrically contacting a component of the electromechanical transducer through the base body (1); producing a layer on a surface of the titanium core, preferably one surrounded on all sides, that is passivated with respect to the alloying of titanium from the titanium core (9.1) into a melt of an active brazing material; Inserting the contact pin (9.1, 9.2) into a receptacle intended for the contact pin (9.1, 9.2) extending through the base body (1), in particular a bore; Electrically connecting the contact pin (9.1, 9.2) to the component of the electromechanical transducer on a side of the base body (1) facing the membrane; Joining the contact pin (9.1, 9.2) to the base body (1) by means of the active brazing alloy (23) at least on one side of the base body (1) facing away from the membrane, so that the titanium of the titanium core (9.1) does not alloy into the melt of the active brazing alloy (23).
2. Method according to the preceding claim, wherein the layer (9.2) passivating with respect to the alloying of titanium from the titanium core (9.1) into the melt is produced by oxidation or nitriding with nitrogen at a defined temperature, preferably at a temperature below 450 °C, particularly preferably at a temperature in the range from 300 °C to 400 °C.
3. Method according to claim 1, wherein the layer (9.2) is produced by coating the surface of the titanium core (9.1) with a material which is passivating with respect to the alloying of the titanium into the melt.
4. Method according to the preceding claim, wherein the layer is formed by coating the surface of the titanium core (9.1) with tantalum, molybdenum, nickel, a Nickel alloy or another metal that is passivating compared to the alloying of titanium into the melt or a metal oxide, e.g. titanium oxide.
5. Method according to the preceding claim, wherein the coating of the surface of the titanium core (9.1) is carried out by a sputtering process, in particular a sputtering process for sputtering bulk material.
6. Method according to one or more of the preceding claims, wherein the joining of the contact pin (9.1, 9.2) to the base body (1) is carried out by means of an Ag-Cu active brazing alloy, preferably with titanium as the active component.
7. Pressure sensor, in particular obtainable by the method according to one or more of the preceding claims, comprising: a ceramic base body (1), a measuring diaphragm (5) which is connected to the base body (1) with the inclusion of a pressure chamber (3) and can be subjected to a pressure (p) to be measured by the pressure sensor, an electromechanical transducer which is designed in such a way that it converts a deflection of the measuring diaphragm (5) which is dependent on the pressure acting on the measuring diaphragm (5) into an electrical quantity, and at least one electrically conductive contact pin (9) which is connected to a component of the pressure sensor and runs through the base body (1), via which contact pin the component connected to it can be electrically connected, wherein the at least one contact pin (9) has a titanium core and an alloying layer of the titanium of the titanium core (9) which surrounds a surface of the titanium core, preferably on all sides.1) into a melt of an active brazing alloy, wherein the at least one contact pin (9.1, 9.2) is inserted into a receptacle intended for this purpose, in particular a bore in the base body, and is electrically connected to the associated component of the converter on a side of the base body (1) facing the membrane, and wherein the at least one contact pin (9.1, 9.2) is further joined to the base body (1) with the active brazing alloy (23) at least on one side of the base body (1) facing away from the membrane, so that the titanium of the titanium core (9.1) is not alloyed into the melt of the active brazing alloy.