EP4076833A1

EP4076833A1 - Joining two components of a field device for processing and automation technology

Info

Publication number: EP4076833A1
Application number: EP20811588.1A
Authority: EP
Inventors: Sergey Lopatin; Igor Getman; Dietmar Leuthner; Pablo Ottersbach
Original assignee: Endress and Hauser SE and Co KG
Current assignee: Endress and Hauser SE and Co KG
Priority date: 2019-12-16
Filing date: 2020-11-20
Publication date: 2022-10-26
Also published as: DE102019134595A1; CN114829061A; WO2021121863A1; US20230013563A1

Abstract

The invention relates to a device (1) consisting of at least one first (2) and one second (3) component, wherein the first (2) and the second component (3) are components of a field device for processing and automation technology, which can each be mechanically connected at a joining surface (4, 5) by means of a joining point (6), with two metal surface layers (7) which are each applied at least to the joining surface of the first component (4) and the joining surface of the second component (5), wherein the metal of the surface layers (7) is different from the metal of the first (2) and/or the metal of the second component (3), and consisting of the joining point (6), wherein a joining material (8) is applied between the respective joining surfaces of the two components (4, 5), wherein the joining material (8) comprises at least particles at least partially consisting of a metal, wherein the metal of the joining material (8) corresponds with the metal of the surface layers (7), wherein the joining of the two components (2, 3) occurs at a joining temperature below 300°C.

Description

Joining of two components of a field device in process and automation technology

The invention relates to a device consisting of at least a first and a second component, the first and the second component being components of a field device of process and automation technology, which can each be mechanically connected to a joining surface by means of a joint, as well as a method for producing a such device. Various field devices that are used in industrial systems have already become known from the prior art. Field devices are often used in process automation technology as well as in production automation technology. In principle, all devices that are used close to the process and that record and / or process process-relevant information are referred to as field devices. Field devices are used to determine and / or influence process variables. Measuring devices or sensors are used to determine process variables. These are used, for example, for pressure and temperature measurement, conductivity measurement, flow measurement, pH measurement, level measurement, etc. and record the corresponding process variables pressure, temperature, conductivity, pH value, level, flow, etc. Actuators are used to influence process variables. These are, for example, pumps or valves that can influence the flow of a liquid in a pipe or the fill level in a container. In addition to the aforementioned measuring devices and actuators, field devices also include remote I / Os, radio adapters or, in general, devices that are arranged on the field level. Field devices can be mounted on containers or built into control cabinets or control rooms. A large number of such field devices are produced and sold by the Endress + Hauser Group.

As a rule, field devices have components that are highly sensitive to the process variable and / or parameters that are decisive for determining the process variable. Such sensitive components typically have well-defined physical properties in order to be able to determine the process variable reliably and reproducibly. Hence it is great

Meaning that the sensitivity of these components is not impaired during assembly and during the process. During assembly, particular care must be taken to ensure that the properties of the component are not corrupted when the sensitive component is connected to another component or several other components. For example, vibronic measuring devices with an oscillatable unit that can be excited to produce mechanical oscillations are used for point level detection. The oscillatable unit can be designed as an oscillating fork with two rods attached to a membrane or as a single rod with only one rod as a resonator. Typically, a piezoelectric or magnetoelectric drive is located on the back of the usually thin membrane, which excites the oscillatable unit to its resonance frequency. It is crucial here that the thin and sensitive membrane is fastened in the oscillatable unit in such a way that good oscillation transmission can take place.

Another example relates to pressure measuring devices which have a pressure-sensitive membrane in the direction of the process, which by means of a pressure sensor transmits a pressure acting from the process side to a pressure sensor. Under the side of the membrane facing away from the process, a pressure chamber is enclosed between the membrane and a carrier. A bore, which connects the pressure chamber with a pressure measuring chamber in which the pressure sensor is arranged, runs through the carrier. In addition, the pressure chamber, bore and pressure measuring chamber are filled with a pressure-transmitting liquid that transmits the pressure acting on the membrane from the process side to the pressure sensor. Depending on the construction of the pressure measuring device, the pressure measuring chamber can be arranged spatially close to the pressure chamber or at a distance from it. In the latter case, pressure sensors are also referred to as pressure transmitters and connect the pressure chamber to the pressure sensor by means of a pressure transmission line. This design is particularly important for high-temperature processes, as the spatial distance between the pressure chamber and pressure sensor protects the pressure sensor from the high process temperatures.

The membrane of a pressure measuring device is usually made very thin in order to ensure the necessary pressure sensitivity. Typical membrane thicknesses are between 25 μm and 150 gm. The connection between membrane and carrier is therefore special

It is important that the membrane is very susceptible to bending and tension due to its low thickness. In the following, known joining methods and their problems will be discussed using the example of the pressure transducer. In the case of pressure transducers known from the prior art with a metallic membrane and a metallic carrier, the membrane and carrier are connected to one another via a joint. Methods known from metal processing, such as soldering or welding, are used to join the two metallic components. Both in soldering and in welding, however, the choice of materials is or Material combinations that can be connected to one another by the respective process are limited.

A welding process used today for joining metallic supports and metallic membranes is laser beam welding. This can be used to create high-quality, pressure-resistant joints between supports made of stainless steel and membranes made of stainless steel or nickel alloys, such as alloys known under the brand name Hastelloy. However, the weld seams produced during laser beam welding have a comparatively high surface roughness. Pressure transducers with rough surfaces can usually not be used in applications in which there are high demands on the hygiene and cleanability of the transducer. In addition, weld seams increase the risk of corrosion, which in the long term can even lead to failure of the pressure transducer in the worst case.

This problem can be remedied in a manner known from the prior art by soldering the membrane flat onto the carrier. For this purpose, a solder suitable for joining the materials of membrane and carrier, usually a special alloy based on silver, copper or nickel, is introduced as a solder layer between the joining surfaces of carrier and membrane and melted under vacuum or in a protective gas atmosphere. With this method, pressure transducers can be produced with very smooth surfaces that come into contact with the medium and thus meet high hygiene requirements.

However, soldering can only be used if the carrier and membrane have the same or at least similar coefficients of thermal expansion. The reason for this is that when soldering components with different thermal expansion coefficients, thermomechanical stresses arise due to the high soldering temperature required, which lead to permanent tension in the membrane. The soldering temperature depends on the choice of solder and can easily be in the range of approx. 700 ° C to 1100 ° C with currently used solder. At these high temperatures, even comparatively small differences in the thermal expansion coefficients can lead to deformations and permanent stresses in the membrane, which have a lasting effect on its pressure transmission properties.

In addition, when soldering there is a risk that liquid solder will penetrate into the pressure chamber during the soldering process. Penetrating solder leads to an uncontrolled reduction of the internal volume of the pressure chamber, to an indefinite change in the flexibility of the membrane and can lead to restrictions or Lead to impairments of the deflections that the membrane experiences as a function of a pressure acting on it. Another disadvantage of planar soldering is that gas bubbles can form in the liquid solder between the joining surfaces of the carrier and membrane due to gas inclusions. Gas bubbles can cause cavities to remain inside the joint after cooling, which impair the quality of the joint.

For some metals, soldering cannot be used as a joining process because metals such as duplex and super-duplex steel lose their corrosion resistance at temperatures above 280-300 ° C. Alternatively, components of these metals can be glued. However, the bonded joint is not very robust with regard to rapidly changing process conditions, such as a temperature shock.

From the prior art, for example, metallic or intermetallic joints are known from DE 102016112198 A1 and DE 102016112200 A1. Here metallic joining means are applied to the respective joining surface of membrane and carrier and then the membrane and carrier are joined at their joining surfaces by thermocompression bonding or by reactive bonding. Both documents disclose joining temperatures below 300 ° C., provided that at least one of the joining agents applied to the membrane or carrier contains tin. The comparatively low joining temperature reduces stresses in the membrane and the joint. However, intermetallic joints with tin in particular are generally brittle, since tin partially oxidizes at these joining temperatures or during storage in air and thus prevents a homogeneous layer formation.

It is an object of the invention to provide a pressure transducer and a method for its production which overcomes the aforementioned problems.

The object is achieved by a device according to the invention according to claim 1 and a method according to the invention for producing a device according to claim 14.

The device according to the invention consists of at least a first and a second component, the first and the second component being components of a field device of process and automation technology, which are each mechanically connected to one another at a joint surface by means of a joint, obtainable by a method which the comprises the following steps:

Coating of at least the joining surface of the first and the second component with a metallic surface layer, the metal the surface layers are different from the metal of the first and / or the metal of the second component,

Application of a joining material between the respective joining surfaces of the two components, the joining material comprising at least particles which at least partially consist of a metal, the metal of the joining material being the same as the metal of the surface layers, and

Joining of the first and second component at their respective joining surface by heating at a joining temperature below 300 ° C.

The great advantage of the invention is that the joint between the two components is achieved at comparatively low joining temperatures. In this way, stresses in the two components and at the joint are avoided or at least greatly reduced. This is especially true if the two components are made of materials with different thermal expansion coefficients. The physical properties of the components defined before joining are retained after the two components have been joined. In contrast to a welding process, with the pressure transducer according to the invention a joint is obtained which does not have a high surface roughness but a smooth surface structure. As a result, the pressure transducer according to the invention is also suitable for hygienic applications.

By using the same metal for the joining material and the surface layers, the metal atoms can diffuse both between the individual particles and between the particles and the surface layers. This results in a uniform distribution of the metal atoms and thus a homogeneous joint and good adhesion. Delamination of the joining material is therefore ruled out. The joining process can be accelerated by prestressing the two components at 1-50 MPa. The surface layer can only be applied to the joining surface of the first and the second component in each case or, for example, the second component can also be provided completely with a surface layer.

In one possible embodiment, the device relates to a pressure sensor, the first component being a metallic carrier and the second component being a metallic membrane arranged on the metallic carrier, including a pressure chamber. Joining at low joining temperatures is particularly advantageous here, since the membrane is very thin and therefore prone to tension.

In one embodiment, the particles have silver or copper or gold as the metal. Gold is highly resistant to corrosion. Silver oxides and silver salts are reduced to metallic silver at temperatures above 200-250 ° C. Should be the joint from If silver starts to oxidize on the surface over time, the resulting silver oxide would be returned to metallic silver in a process that is accompanied by temperatures above 200 ° C. A form of self-cleaning of the silver joint at corresponding temperatures is thus obtained. As already described, the surface layer also has silver, copper or gold in accordance with the particles. The surface layer can also extend over the entire component. A thin gold layer, for example from a component that is in contact with a medium, protects the component from corrosion and forms a very effective diffusion barrier against hydrogen. Hydrogen, which diffuses, for example, into a pressure sensor or, more precisely, into the liquid in the pressure sensor, changes the

Pressure transmission properties of the pressure transducer and in the worst case can even lead to failure of the pressure transducer. A surface layer made of silver also provides effective protection against the ingress of hydrogen into the pressure transducer. In a further embodiment, the particles include in particular silver nitrate, silver acetate, silver carbonate or silver oxide. As already described, temperatures above 200 ° C lead to a reduction of silver, starting from silver salts and silver oxide. Therefore, the use of particles with silver salts or silver oxide leads to the exposure of silver during joining.

Another embodiment provides that the particles have a silver, copper or gold alloy.

In addition to the particles, which are at least partially made of metal, the joining material advantageously comprises at least one liquid and / or a solvent and / or an additive. The three additives mentioned serve to make it easier to apply the joining material to the respective joining surfaces of the first and second component. The joining material can, for example, be given a paste-like structure through appropriate additives and can thus be painted onto the two joining surfaces without the joining material running from the two joining surfaces onto other surfaces of the two components. When the joining material is heated to the joining temperature, the additives are either evaporated or decomposed. Ideally, the volume fraction of the at least one additive in the joining material is so low that the desorption or decomposition of the additive does not impair the joining process and the quality of the joint.

In a preferred embodiment, the diameter of the particles, which are at least partially made of metal, is less than 1 μm. Metallic particles with such a diameter have a high surface energy, which is why the particles sinter even at comparatively low temperatures, such as the joining temperature. Through the Diffusion of metal atoms between the particles creates a homogeneous joint.

In a further embodiment, the first component can be made of stainless steel, in particular duplex steel and / or super duplex steel, and / or unalloyed steel and / or Monel and / or a copper alloy, and the second component is made of stainless steel, in particular duplex steel and / or super duplex steel, and / or Hastelloy and / or tantalum and / or Monel and / or titanium and / or zircon and / or a copper alloy and / or a silver alloy and / or a gold alloy.

The metallic surface layer is advantageously applied to the membrane and the carrier by means of galvanic processes or sputtering. Depending on the metal of the first and the second component, often only one of the two methods can be used to apply the metallic surface layer. For example, tantalum and zirconium cannot be electroplated in aqueous solutions, but have to be sputtered. It is crucial for the choice of the process that the surface layer adheres well to the respective component and does not peel off.

The metallic surface layer preferably has a thickness of 2 to 30 μm. With this thickness of the metallic surface layer, an optimal joint is obtained.

In one possible embodiment, an additional adhesive layer is applied between the first component and the surface layer and between the second component and the surface layer, which connects the surface layer to the first and the second component. These adhesive layers are necessary because not all metals of the two components adhere well directly to the metal of the surface layer. The adhesive layer thus serves for the adhesion and connection between the two components and their respective surface layer.

A further embodiment provides that, in particular, gold or copper or chrome can be used as the adhesive layer.

In a preferred embodiment, the joining temperature is in particular in the range from 250.degree. C. to 280.degree.

The object on which the present invention is based is further achieved by a method for producing a device consisting of at least a first and a second component, the first and the second component being components of a field device of process and automation technology, which are each connected to a Joining surface can be mechanically connected by means of a joint, the method comprising the following steps:

Coating of at least the joining surface of the first and the second component with a metallic surface layer, the metal of the surface layers being different from the metal of the first and / or the metal of the second component,

By using particles that are at least partially made of metal, a homogeneous joint is obtained even at comparatively low joining temperatures, since the particles sinter even at low temperatures due to their high surface energy. Due to the low joining temperature, different metals of the first and the second component can also be joined to one another without stresses occurring in the components and / or the joint. A smooth joint is also obtained, which can also be used for hygienic applications. The surface layer serves to connect the joining material to the first and second components and thus ensures that no delamination occurs.

The method advantageously provides an additional step

Coating the joining surface of the first and the second component with an adhesive layer each, which is arranged between the surface layer and the first and second component.

The metal of the joining material and of the surface layer does not in all cases readily adhere to the metal of the first and second component. The adhesive layer therefore serves to connect the surface layer to the first and the second component.

The solution according to the invention is explained in more detail with reference to the following Figures Fig.1-2. It shows:

1 shows a schematic representation of a pressure measuring device.

2 shows a schematic representation of a pressure transducer according to the invention. The present invention is applicable to a large number of different field devices. Without restricting the generality, however, for the sake of simplicity, the following description relates to a pressure measuring device as shown schematically in FIG. 1. Corresponding pressure measuring devices are manufactured and sold by the applicant for example under the terms “Cerabar”, “Ceraphant” and “Deltabar”. The considerations can be applied analogously to other field devices which have at least one component with a high sensitivity to the process variable and / or to parameters that are decisive for determining the process variable.

1 shows a schematic representation of a corresponding pressure measuring device 11. The membrane 3 faces the process and adjoins the carrier 2. The pressure sensor 12 is located at a certain distance from the membrane 3 and carrier 2. The pressure acting on the membrane 3 is transmitted to the pressure sensor 12 by means of a liquid (not shown).

2 shows a possible embodiment of the device according to the invention using a pressure sensor 1. The membrane 3 and the carrier 2 are arranged opposite one another, with mutually facing joining surfaces 4, 5, to which membrane 3 and carrier 2 can be connected. A pressure chamber 9 is arranged between the membrane 3 and the carrier 2, to which a bore extending through the carrier 2 is connected. The carrier 2 is made of stainless steel, in particular duplex steel and / or super duplex steel, and / or unalloyed steel and / or Monel and / or a copper alloy and the membrane 3 is made of stainless steel, in particular duplex steel and / or super duplex steel, and / or Hastelloy and / or tantalum and / or Monel and / or titanium and / or zirconium and / or a copper alloy and / or a silver alloy and / or a gold alloy can be manufactured.

An adhesive layer 10 is applied to the respective joining surface of membrane and carrier 4, 5. The adhesive layer 10 can consist of adhesive gold, copper, chrome or other substances. A surface layer 7 is applied to at least the joint surface of the membrane 5 and the joint surface of the carrier 4, for example by means of a galvanic process or by means of sputtering, the metal of the surface layers 7 being different from the metal of the carrier 2 and / or the metal of the membrane 3 .

A possible combination would be the coating of membrane 3 and carrier 2, both of which are made of stainless steel, with a layer of silver. The metallic surface layer 7 advantageously has a thickness of 2 to 30 μm.

A joining material 8 is applied between the respective surface layers 7 in the region of the joining surface of membrane and carrier 4, 5, which at least Includes particles which at least partially consist of a metal. The metal of the joining material 8 corresponds to the metal of the surface layers 7. The particles contain, for example, gold, copper or silver, as well as alloys of these metals or also silver nitrate, silver acetate, silver carbonate or silver oxide. In addition to the particles, the joining material 8 also consists at least of a liquid and / or a solvent and / or an additive. The diameter of the particles is smaller than 1 μm, although other possibilities are not excluded. Joining takes place at joining temperatures below 300 ° C, for example at 250-280 ° C. A device 1 of this type, such as a pressure sensor, is produced by means of a method according to the invention by first coating the first and second components 2, 3 on at least their respective joining surfaces 4, 5 with a surface layer 7. The surface layer 7 has a metal which is different from the metal of the first and second components 2, 3. The joining material 8 is then applied to the respective joining surfaces of the two components 4, 5.

The joining material 8 comprises at least particles which at least partially consist of metal, the metal of the joining material 8 matching the metal of the surface layers 7, so that good adhesion between the joining material 8 and the surface layer 7 is obtained. In a further step, the two components 2, 3 are at their respective joining surfaces 4, 5 at a

Joining temperature below 300 ° C joined. Optionally, before the surface layer 7 is applied, the joining surfaces of the first and second components 4, 5 can first be coated with an adhesive layer 10 which connects the surface layer 7 to the first and second components 2, 3.

List of reference symbols

1 device or pressure transducer

2 first component or carrier

3 second component or membrane

4 joining surface of the first component or the carrier

5 joining surface of the second component or the membrane

6 joints

7 surface layer

8 joining material

9 pressure chamber

10 adhesive layer

11 Pressure gauge

12 pressure sensor

Claims

1 . Device (1) consisting of at least a first (2) and a second (3) component, wherein the first (2) and the second component (3) are components of a field device of process and automation technology, each of which is attached to a joining surface (4 , 5) are mechanically connected to one another by means of a joint (6), obtainable by a method which has the following steps:

Coating of at least the joining surface (4,5) of the first and the second component (2,3) with a metallic surface layer (7), the metal of the surface layers (7) from the metal of the first and / or the metal of the second Component (2,3) is different,

Application of a joining material (8) between the respective joining surfaces (4,5) of the two components (2,3), the joining material (8) comprising at least particles which at least partially consist of a metal, the

The metal of the joining material (8) matches the metal of the surface layers (7), and

Joining of the first and second component (2,3) on their respective joining surface (4,5) by heating at a joining temperature below 300 ° C.

2. Device according to claim 1, wherein the device relates to a pressure sensor (1), wherein the first component is a metallic carrier (2) and the second component is a metallic membrane (2) arranged on the metallic carrier (2), including a pressure chamber (9). 3) is.

3. Device according to claim 1, wherein the particles have silver or copper or gold as the metal.

4. The device according to claim 1, wherein the particles in particular comprise silver nitrate, silver acetate, silver carbonate or silver oxide.

5. The device of claim 1, wherein the particles comprise a silver, copper or gold alloy.

6. Device according to at least one of claims 1-5, wherein the joining material (8) comprises at least one liquid and / or a solvent and / or an additive in addition to the at least partially metal particles.

7. The device according to at least one of claims 1-6, wherein the diameter of the particles consisting at least partially of metal is less than 1 μm.

8. The device according to at least one of claims 1-7, wherein the first component (2) made of stainless steel, in particular duplex steel and / or super duplex steel, and / or unalloyed steel and / or Monel and / or a copper alloy can be manufactured, the second component (3) made of stainless steel, in particular duplex steel and / or super duplex steel, and / or Hastelloy and / or tantalum and / or Monel and / or titanium and / or zircon and / or a

Copper alloys and / or a silver alloy and / or a gold alloy can be manufactured.

9. The device according to at least one of claims 1-8, wherein the metallic surface layer (7) by means of galvanic processes or

Sputtering is applied to the two components (2,3).

10. The device according to at least one of claims 1-9, wherein the metallic surface layer (7) has a thickness of 2 to 30 μm.

11. Device according to at least one of claims 1-10, wherein between the first component (2) and the surface layer (7) and between the second component (3) and the surface layer (7) an additional adhesive layer (10) is applied, which the surface layer (7) each connects to the first and second component (2,3).

12. The device according to at least one of claims 1-11, wherein in particular adhesive gold or copper or chromium can be used as the adhesive layer (10).

13. Device according to at least one of claims 1-12, wherein the joining temperature is in particular in the range from 250 ° C to 280 ° C.

14. A method for producing a device (1) consisting of at least a first (2) and a second component (3), the first and the second component

(2,3) Components of a field device in process and automation technology are each mechanically connectable to a joining surface (4,5) by means of a joining point (6), the method comprising the following steps: Coating of at least the joining surface (4 , 5) of the first and the second component (2,3) with a metallic surface layer (7), wherein the metal of the surface layers (7) is different from the metal of the first and / or the metal of the second component (2, 3),

15. The method for producing a device according to claim 14, wherein the following step is additionally provided:

Coating the joining surface (4, 5) of the first and second component (2, 3) with an adhesive layer (10) each, which is arranged between the surface layer (7) and the first and second component (2, 3).