Method for joining a differential pressure measuring cell and differential pressure measuring cell

Abstract

Method for joining a differential pressure measuring cell (1), which differential pressure measuring cell (1) comprises: a measuring diaphragm (2); a transducer, a first and a second counter body (41, 42), and a first and a second support body (51, 52), - wherein the measuring membrane (2) is arranged between the first counterbody (41) and the second counterbody (42) and is pressure-tightly connected to both counterbodies (41,42), - wherein a first measuring chamber (61) is formed between the measuring membrane (2) and the first counterbody (41) and a second measuring chamber (62) is formed between the measuring membrane (2) and the second counterbody (42), - wherein the first counterbody (41) and first support body (51) as well as the second counterbody (42) and second support body (52) each have a pressure channel (7) through which the first measuring chamber (61) can be subjected to a first pressure (p1) and the second measuring chamber (62) to a second pressure (p2) and - wherein the transducer is designed to generate an electrical measurement signal from a deformation of the measuring diaphragm (2) caused by the difference between the first pressure (p1) and the second pressure (p2); wherein the joining process is divided into the following steps: - Prefabrication of the two counter bodies (41,42) and pressure-tight connection of the measuring membrane (2) to the two counter bodies (41,42), - Applying a joining material (FM) to the end face (13a) of the first support body (51) facing the measuring membrane (2) and / or to the end face (12a) of the first counter body (41) facing away from the measuring membrane (2) and to the end face (13b) of the second support body (51) facing the measuring membrane (2) and / or to the end face (12b) of the second counter body (42) facing away from the measuring membrane (2), wherein the joining material (FM) is applied to at least one of the end faces (12a; 12b; 13a; 13b) in a region, so that areas (32) with joining material (FM) and areas (31) without joining material (FM) are formed, wherein the joining material (FM) is applied to the end face (12a;12b) of the counter body (41; 42) facing away from the measuring membrane (2) in a first area (17a) and to the end face (13a;13b) of the adjacent support body (51; 52) in a second area (17b) complementary to the first area (17a), and wherein the two complementary areas (17a, 17b) combine to form a predetermined geometric shape (18), - Pressure-tight joining of the end face (12a, 12b) of the counterbody (41, 42) facing away from the measuring membrane (2) with the end face (13a, 13b) of the support body (51, 52) facing the measuring membrane (2), wherein during the joining of at least one of the counterbodies (41; 42) with the adjacent support body (51; 52) the joining material (FM) in the end face (12a; 12b; 13a; 13b) with the joining material (FM) applied in the area • reduced in the direction perpendicular to the front face (12a;12b;13a;13b) (81) and • is enlarged (82) in at least one direction plane to the end face (12a; 12b; 13a; 13b), wherein the enlargement (82) of the joining material (FM) in the direction plane to the end face (12a; 12b; 13a; 13b) enlarges the areas (32) with joining material (FM) and reduces the areas (31) without joining material (FM), so that gradually a single continuous area (9) with joining material (FM) is formed, which area (9) extends over the entire end face (12a; 12b; 13a; 13b) except for an inner recess (15) surrounding the pressure channel (7), so that after pressure-tight joining, the counter body (41;42) and support body (51; 52) are joined over their entire surface.

Description

[0001] The invention relates to a method for joining a differential pressure measuring cell and to a differential pressure measuring cell produced by the method.

[0002] Differential pressure measuring cells use a measuring diaphragm to measure the difference between two static pressures, p1 and p2. This diaphragm is positioned between two counter bodies, forming two hermetically sealed measuring chambers. The measuring chambers are pressurized to the pressures p1 and p2 via pressure channels integrated into the counter bodies. The deflection of the measuring diaphragm thus represents the pressure difference |p1-p2|, and this deflection is converted into an electronic measurement signal by a transducer. For example, in capacitive differential pressure measuring cells, the measuring diaphragm, together with a conductive plane of the counter body facing the measuring diaphragm and parallel to it, forms a capacitor. Therefore, the deflection of the measuring diaphragm determines the capacitor spacing, allowing the differential pressure acting on the measuring diaphragm to be converted into a measurement signal via capacitance measurements.Such a differential pressure measuring cell is described, for example, in patent DE 103 93 943 B3. Differential pressure measuring cells, which are used in the process and / or automation technology of industrial plants for monitoring process pressures, are manufactured and distributed by the E+H Group in a wide variety of configurations.

[0003] Since differential pressure sensors are designed to measure small pressure differences |p1-p2| at simultaneously high static pressures p1, p2, the correct balance between sensitivity and overload protection is of central importance. For example, the following relationship can apply to the measuring range of the pressure difference |p1-p2|: |p1-p2| / p1 < 1%. If one of the two pressures (e.g., p2) is eliminated in a process plant, |p1-p2| / p1 reaches almost 100%. In this case, the differential pressure sensor is thus subjected to more than 100 times its measuring range, which corresponds to a very high one-sided pressure load. For differential pressure sensors with a very fine measuring range of |p1-p2| ~ 10 mbar, the one-sided pressure load is correspondingly higher relative to the measuring range at a typical process pressure of 160 bar.

[0004] The prior art discloses various designs for overload protection of differential pressure measuring cells at high static pressures p1, p2, including, for example, overload membranes (EP 1 299 701 B1, DE 10 2006 040 325 A1 or DE 10 2006 057 828 A1) or membrane beds (US 4 458 537 A or DE 10 2009 046 229 A1).

[0005] Very high pressure loads can also lead to deformation of the counterbody itself. This significantly affects the stability of the differential pressure measuring cell, for example, by impairing the support function of the membrane beds. Therefore, in the assembly and connection technology of a differential pressure measuring cell, it is intended to enclose the counterbodies between two support bodies, with the support body serving to stabilize the structure and counteract deformation of the counterbody. Typically, the support body is made of a material with a modulus of elasticity at least as high as that of the counterbody. For optimal support of the counterbody against the support body, a rigid connection between the counterbody and support body is advantageous. Examples of stiffening the support / counterbody interface are disclosed in JP S57-40626 A and DE 102012 113033A1.

[0006] In the assembly and interconnection technology of silicon-based microelectromechanical systems (MEMS), the individual components are joined using a glass solder. In this process, known as glass solder bonding, the bonding material is typically not applied across the entire surface, but rather in the form of a fine frame, the so-called bonding frame. This method does not achieve a fully bonded connection between the individual components. In contrast, for a differential pressure sensor based on a MEMS sensor, it is desirable that the bonding plane between the counter body and the support body be fully bonded. This allows for the stiffest possible connection between the counter body and the support body, which is crucial for the stability of the differential pressure sensor and its overload protection.

[0007] Pressure sensors and methods for connecting components or parts have become known, among others, from DE 10 2014 102 717 A1, DE 10 2006 032 128 A1, DE 10 2009 049 386 A1, DE 100 55 040 C1, DE 197 48 699 A1 and DE 10 2004 032 391 A1.

[0008] The invention is based on the objective of providing a method for joining a differential pressure measuring cell in order to obtain a stable differential pressure measuring cell.

[0009] The problem is solved by a method for joining a differential pressure measuring cell, which differential pressure measuring cell comprises: a measuring diaphragm; a transducer, a first and a second counterbody, and a first and a second support body, wherein the measuring diaphragm is arranged between the first counterbody and the second counterbody and is pressure-tightly connected to both counterbodies. - wherein a first measuring chamber is formed between the measuring membrane and the first counterbody and a second measuring chamber is formed between the measuring membrane and the second counterbody, - wherein the first counterbody and first support body as well as the second counterbody and second support body each have a pressure channel through which the first measuring chamber can be pressurized with a first pressure and the second measuring chamber with a second pressure and - wherein the transducer is designed to generate an electrical measurement signal from a deformation of the measuring diaphragm caused by the difference between the first pressure and the second pressure; wherein the joining process is divided into the following steps: - Prefabrication of the two counter bodies and pressure-tight connection of the measuring membrane to the two counter bodies - Applying a joining material to the end face of the first support body facing the measuring membrane and / or to the end face of the first counter body facing away from the measuring membrane and to the end face of the second support body facing the measuring membrane and / or to the end face of the second counter body facing away from the measuring membrane, wherein the joining material is applied to at least one of the end faces in a partial manner, so that areas with joining material and areas without joining material are formed, - Pressure-tight joining of the end face of the counterbody facing away from the measuring membrane with the end face of the support body facing the measuring membrane, wherein, during the joining of at least one of the counterbodies with the adjacent support body, the joining material in the end face is reduced in the direction perpendicular to the end face and increased in at least one direction plane to the end face, wherein, by increasing the joining material in the direction plane to the end face, the areas with joining material are enlarged and the areas without joining material are reduced, so that gradually a single continuous area with joining material is formed, which area extends over the entire end face except for an inner recess surrounding the pressure channel, so that after the pressure-tight joining, the counterbody and support body are joined essentially over their entire surface.

[0010] In the first step of the inventive process, the two counterbodies are prefabricated. During the pressure-tight joining of the measuring membrane to the two counterbodies, the measuring membrane is positioned between the two counterbodies, and the measuring chambers are formed. The prefabrication in the first process step also includes the arrangement between the counterbodies of all those components required for generating or converting the measurement signal, such as the membrane electrodes and the transducer. The two support bodies are also prefabricated.

[0011] In the second step of the inventive method, the joining material is applied in a structured manner to the end face of a counter body and / or support body. The structuring is carried out such that, after application of the joining material, there are distinct areas with and without joining material. The fully bonded joint is not achieved by applying the joining material across the entire surface, but rather by initially applying the joining material only to specific areas and then, during the pressure-tight joining process, increasing its thickness in a direction parallel to the end face. In this way, the joining of the counter body and support body ultimately results in a single, continuous, highly homogeneous area containing joining material at the joint between the counter body and support body.

[0012] This results in a surface between the counterbody and the support body that is essentially fully enclosed (except for a recess surrounding the pressure channel). As a result, the inventive method yields a differential pressure measuring cell with a very stable connection between the counterbody and the support body, and thus an overall differential pressure measuring cell of high stability.

[0013] In the inventive method, if the joining material is applied to the end face of the support body, the pressure-tight connection between the support body and the counter body is achieved in a subsequent process step. This step precedes the pressure-tight joining process step. Within the scope of this application, "the end face of the support body facing the measuring membrane" refers to the end face intended for connection with the end face of the counter body facing away from the measuring membrane. The end face of the support body facing the measuring membrane is therefore the one that is to be combined with the end face of the counter body facing away from the measuring membrane when the counter body and support body are positioned. The end faces of the counter body and support body are essentially in a plane parallel to the plane of the measuring membrane.

[0014] In one embodiment of the method according to the invention, the joining material is applied, at least in certain areas, in the form of at least one circular ring, with the inner recess located at the center of the ring. For the purposes of this application, a circular ring is defined as the area bounded by two concentric circles. A circular ring has a width determined by the difference in radii between the two concentric circles. In the case of multiple concentric circular rings, the rings can also have different widths. If the joining material is applied only in certain areas, segments of circular rings are formed.

[0015] The aim of the process for achieving a fully bonded connection between the counter body and the support body is that, through the enlargement of the joining material in the direction parallel to the end face, the initially only partially applied joining material essentially forms a circular area, with the inner recess located at the center of the circular area. During the pressure-tight joining process, the further enlargement of the circular joining material in the direction parallel to the end face then distributes the joining material evenly across the entire connection plane between the counter body and the support body.

[0016] In a further development of this embodiment of the inventive method, the joining material is applied to the end face in the form of several concentric circular rings, with the inner recess located in the center of the circular area.

[0017] In a further embodiment of the method, an area without joining material is provided as a venting zone. This venting zone extends from the inner recess to an edge region of the end face. During the pressure-tight joining process, the venting zone is continuously reduced in size by continuously filling it with joining material from the inner recess to the edge region. In this advantageous embodiment, the venting zone is gradually closed by the continuous filling with joining material from the inner recess. The air trapped in the venting zone can escape via the pressure channel located within the inner recess and / or the edge region. This ensures that no air inclusions form in the joining material.For example, the venting area is a wedge-shaped area without joining material between two circular segments of a circular ring made of joining material.

[0018] According to the invention, the joining material is applied in a first area to the end face of the counterbody facing away from the measuring membrane and in a second area complementary to the first area to the end face of the adjacent support body. The two complementary areas combine to form a predetermined geometric shape. For the purposes of this application, the adjacent support body is defined as the support body intended for positioning on the end face of the counterbody facing away from the measuring membrane. Since the two complementary areas combine to form a predetermined shape, the first area represents the negative of the second area and vice versa.

[0019] In this particularly advantageous embodiment of the method, the counterbody and support body can be aligned relative to each other during pressure-tight joining by the complementary areas of joining material snapping into one another to form the predetermined geometric shape. Depending on the type of joining material, the precise application and metering of the joining material is often simpler than the precise alignment of the counterbody and support body relative to each other. Therefore, by structuring the joining material in predetermined areas of the end face, the method according to the invention can achieve self-alignment of the counterbody and support body relative to each other.

[0020] In a continuing education course, the complementary areas take the form of concentric rings and / or segments of concentric rings. The given geometric shape is therefore essentially a circular area or the entirety of concentric rings.

[0021] The joining material is applied, for example, in the form of complementary sections of concentric rings on the end face of the counterbody facing away from the measuring membrane and on the end face of the adjacent support body facing the measuring membrane. In this way, complete concentric rings of joining material are formed by the precise interlocking of the complementary sections of concentric rings. These complete concentric rings then form the continuous area of ​​joining material during pressure-tight bonding.

[0022] Within the scope of the invention, it is also possible to apply first concentric rings of the joining material to the end face of the counterbody facing away from the measuring membrane and second concentric rings of the joining material to the end face of the adjacent counterbody facing the measuring membrane. The first and second concentric rings complement each other to form common concentric rings, wherein the ring width of the common concentric rings is the sum of the ring widths of the first and second concentric rings. For example, the first concentric rings can be arranged inside the second concentric rings. In this way, the common concentric rings are formed.Areas without joining material can still be provided between the common concentric circular rings, as long as, during pressure-tight joining, a single continuous area with joining material is formed by increasing the amount of joining material in the direction parallel to the end face, which extends essentially over the entire end face.

[0023] In a further embodiment of the process, the joining material is applied using a screen printing process. Since the dosage and / or structuring of the joining material is very precisely adjustable and controllable in screen printing processes, these are particularly well suited for the process according to the invention. For example, in the screen printing process, it is possible to produce screen printing matrices automatically using computer-aided methods. Thus, very precisely defined patterns of joining material can be applied to the end face, and a high degree of automation can be achieved in the production of differential pressure measuring cells using the process according to the invention.

[0024] In one embodiment of the inventive method, a glass solder, adhesive or metallic solder is used as the joining material.

[0025] Glass solder is used particularly in the joining of MEMS-based differential pressure measuring cells.

[0026] In a further embodiment of the process, the joining material is applied with a predefinable layer thickness, whereby, during the pressure-tight joining process, the predefinable layer thickness decreases in the direction perpendicular to the end face to a resulting predefinable layer thickness. After application, the joining material has a layer thickness dv. For example, the layer thickness dv decreases by 20-40% after the reduction of the joining material in the direction perpendicular to the end face. Thus, the resulting layer thickness is 20-40% smaller than the predefinable layer thickness dv. The predefinable resulting layer thickness dr is approximately between 5 and 50 micrometers. In the case of a glass solder, the resulting layer thickness of the joining material is essentially between 10 and 20 micrometers.

[0027] In a further embodiment of the method, the counterbody is joined to the adjacent support body with an approximately homogeneous contact pressure distribution and a predefinable contact pressure Pf, creating a pressure-tight connection. If the contact pressure distribution is essentially homogeneous, a substantially constant resulting layer thickness of the joining material is achieved after the pressure-tight joining. Since the contact pressure is generally even more adjustable or controllable than the layer thickness of the joining material during application and / or the surface structure of the prefabricated counterbodies and support bodies, this embodiment achieves a particularly homogeneous, full-surface connection between the support body and counterbody.

[0028] Typically, the counterbody and / or the support body have at least one axis of symmetry, wherein the counterbody and / or the support body is substantially symmetrical with respect to the axis of symmetry. The axis of symmetry can, for example, be the mirror axis of a mirror symmetry or the rotation axis of a rotational symmetry. The axis of symmetry can lie in the plane of the end face or be perpendicular to the end face. In an advantageous embodiment of the method, the joining material is structured in at least one of the end faces such that the joining material is arranged substantially symmetrically about at least one axis of symmetry. The axis of symmetry is thus a common axis of symmetry of the support body and / or counterbody and the joining material.

[0029] The invention includes a differential pressure measuring cell, wherein the differential pressure measuring cell was obtained from the inventive method, comprising; a measuring membrane; a transducer, a first and a second counterbody, as well as a first and a second support body, - wherein the measuring membrane is arranged between the first counterbody and the second counterbody and is pressure-tightly connected to both counterbodies, - wherein a first measuring chamber is formed between the measuring membrane and the first counterbody and a second measuring chamber is formed between the measuring membrane and the second counterbody, - wherein the first counterbody and support body and the second counterbody and support body each have a pressure channel through which the first measuring chamber can be subjected to a first pressure (p1) and the second measuring chamber to a second pressure (p2) and - wherein the transducer is designed to generate an electrical measurement signal from a deformation of the measuring diaphragm caused by the difference between the first pressure (p1) and the second pressure (p2); wherein the end face of at least one of the counter bodies facing away from the measuring diaphragm is pressure-tight and substantially fully connected to the end face of the adjacent support body facing the measuring diaphragm.

[0030] In one embodiment of the invention, the support body and / or the counter body consists of a ceramic material.

[0031] In a further embodiment, the support body and / or the counterbody consists essentially of silicon (Si), an amorphous or crystalline oxide (SiO2), carbide (SiC), and / or nitride (Si3N4) of silicon, and / or an amorphous or crystalline oxide (Al2O3) and / or nitride of aluminum (AlN). Silicon carbide, which can exist in many energetically almost equivalent polytopes, is suitable due to its high hardness. In contrast, silicon nitride exhibits slightly lower hardness but high fracture toughness combined with a low coefficient of thermal expansion and a relatively small modulus of elasticity. Silicon dioxide typically forms as a native oxide layer, at least nanometer thick, on silicon, silicon carbide, or silicon nitride upon contact with ambient air.

[0032] The elastic modulus of the components of the differential pressure measuring cell can also be adjusted by selecting the combination of materials. In a further development of the invention, the elastic modulus of the support body is adapted so that it is equal to or greater than the elastic modulus of the counter body. As an upper limit, the elastic modulus of the support body in this further development should be a maximum of three times the elastic modulus of the counter body. In this embodiment, the support body is therefore at least as stable as the counter body.

[0033] The invention is explained in more detail with reference to the following figures. They show: Fig. 1: An embodiment of the method according to the invention and a differential pressure measuring cell obtained with the method according to the invention. Fig. 2a,b: A differential pressure measuring cell obtained using the method according to the invention Fig. 3: A further embodiment of the method according to the invention Fig. 4: A further embodiment of the method according to the invention

[0034] In Fig. Figure 1 shows a top view of the end face 12a of the first counterbody 41 (left), facing away from the measuring membrane 2, and the end face 13a of the first support body 51 (right), facing the measuring membrane 2. The process step shown here is the application of the structured joining material FM to the end face 13a of the first support body 51, facing the measuring membrane 2. The first process step of the process according to the invention (the prefabrication of the two counterbodies 41, 42 and the pressure-tight joining of the measuring membrane 2 to the two counterbodies 41, 42) precedes the process step of applying the joining material FM. The measuring membrane plane ME thus lies in the connection plane of the two counterbodies 41, 42. The side surfaces of the counterbodies 41, 42, perpendicular to the end faces 12a, 12b, are shown as hatched areas.The pressure channel 7 is arranged in the center of the end face 13a of the first support body 51 facing the measuring membrane 2, through which the measuring chamber 61 can be pressurized with the pressure p1.

[0035] The joining material FM is applied in a structured manner to the end face 13a of the support body 51 facing the measuring membrane 2. In the case shown here, the joining material FM was applied in the form of concentric circular rings. An axis of symmetry SA is also shown, around which the joining material FM is arranged symmetrically. The process of pressure-tight joining is indicated by the dashed arrows in Fig. 1 indicated.

[0036] Fig. Figure 2a is a schematic side view of a cross-section of the differential pressure measuring cell 1 according to the invention during pressure-tight joining according to the inventive method. For orientation, the following were shown: Fig. 1 and Fig. 2a The straight line AB (dashed line) is drawn. The concentric rings of the joining material FM are made of Fig. 1 are in Fig. 2a is now visible in profile. During pressure-tight joining, the counter body 41 and the support body 51 are joined with a contact pressure Pf of a uniform contact pressure distribution. This reduces the thickness of the joining material FM in the direction perpendicular to the end face 13a (81) and increases it in the radial direction (82) of the concentric rings. The predefinable initial layer thickness dv of the joining material FM is thereby reduced to the resulting layer thickness dr of the joining material FM.

[0037] Fig. 2b is a schematic side view of a cross-section of the differential pressure measuring cell 1 according to the invention, which is made using the inventive method from Fig. The measuring membrane 2, which has a diameter dM, is arranged between the two counter bodies 41 and 42. Within the scope of this application, the diameter dM is the diameter of the measuring membrane 2 in the region of the measuring chamber 61 and 62. The counter bodies 41 and 42 are pressure-tightly connected to the measuring membrane 2, forming the measuring chambers 61 and 62. The two measuring chambers 61 and 62 can each be pressurized with pressures p1 and p2 via a pressure channel 7. According to the invention, the pressure-tight connection essentially achieves a fully bonded connection between the counter body 41 and the support body 51, except for an inner recess 15 surrounding the pressure channel 7.

[0038] In this embodiment, the joining material FM was structured on both end faces 13a, 13b. Nevertheless, the components described below can also be part of a differential pressure measuring cell 1 according to the invention, in which the connection between the two counter bodies 41, 42 and the adjacent support body 51, 52 was formed according to the inventive method. It should be noted that the schematic representation shown here is not to scale.

[0039] The differential pressure measuring cell 1 further comprises a capacitive transducer (not shown here) which converts a deflection of the measuring membrane 2, dependent on a difference between the two pressures |p1-p2|, into an electrical signal. For this purpose, the two counter bodies 41, 42 each have, for example, at least one measuring electrode 10a, 10b on their membrane-side end faces 11a, 11b, wherein the measuring membrane 2 has a membrane electrode 14a, 14b on each side, which faces a measuring electrode 10a, 10b. In a simple embodiment of the capacitive transducer, the pressure difference to be measured |p1-p2| results from the difference of the reciprocals of the capacitances between each measuring electrode 10a, 10b and the opposite membrane electrode 14a, 14b. The sum of the capacity reciprocals can be used to determine the static pressure p1, p2, to which the pressure difference to be measured |p1-p2| is superimposed.To increase measurement accuracy, the end faces of the counter bodies 41, 42 can each have a circular disk-shaped central electrode and a surrounding ring electrode, in particular one with the same capacitance. Details of the circuitry of such a capacitive transducer are known and disclosed, for example, in EP 1 883 797 B1.

[0040] To detect the static pressure p1, p2, at least one further capacitive transducer can be provided, each having an electrode on the end face 12a, 12b of the counterbody 41, 42 facing away from the measuring membrane 2, or on the end face 13a, 13b of the support body 51, 52 facing the measuring membrane 2. Likewise, a resistive transducer can be provided to detect the static pressure p1, p2, wherein the support body 51, 52 or counterbody 41, 42 in this case has deformation-dependent resistance elements. The latter can, for example, comprise strain gauges, whereby piezoresistive resistance elements are preferable in the case of a differential pressure measuring cell 1 that has a semiconductor material.

[0041] In Fig. 3 is, analogous to Fig. Figure 1 shows the application of the joining material FM according to the inventive method in a top view onto the two end faces 12a, 13a. The reference numerals are identical to those in Fig. 1. and Fig. 2 In this embodiment, the joining material FM was applied both to the end face 12a of the counterbody 41 facing away from the measuring membrane 2 and to the end face 13a of the adjacent support body 51 facing the measuring membrane 2. The joining material FM on the end face 12a of the counterbody 41 facing away from the measuring membrane 2 forms a first region 17a of a predefinable geometric shape 18. In both end faces 12a, 13a, the regions with 32 and without 31 joining material FM are structured such that the two complementary regions 17a, 17b are formed. The predefinable geometric shape 18 consists of concentric circular rings, and the two complementary regions 17a, 17b consist of circular ring segments.

[0042] In Fig. Figure 4 shows the venting area 16 or the continuous filling of the venting area 16 with joining material FM. In this embodiment, the venting area 16 is a wedge-shaped opening in an otherwise circular area 32 containing joining material FM. The wedge-shaped opening 16 extends from the inner recess 15 to the edge region RB. The otherwise circular area 32 containing joining material FM is a continuous area 32 containing joining material FM. It can also consist of concentric circular rings (see Figure 4). Fig.1) with a common venting area 16. During pressure-tight joining, the joining material FM enlarges the end face 12a of the counterbody 51 facing the measuring membrane 2 in the plane directions, thus gradually filling the venting area 16 (from left to right) with joining material FM. In this way, an area 32 surrounding the inner recess 15 is formed with joining material FM without air inclusions. Reference symbol list 1 differential pressure measuring cell 2 measuring membranes 31 Area without joining material 32 Area with bonding material 41 first counterpart 42 second counterpart 51 first support body 52 second support body 61 first measuring chamber 62 second measuring chamber 7 Pressure channel 81 Reduction of the joining material 82 Magnification of the joining material 9 contiguous area with bonding material 10a Measuring electrode 10b Measuring electrode 11a end face of the first counterbody facing the measuring membrane 11b end face of the second counterbody facing the measuring membrane 12a End face of the first counterbody facing away from the measuring membrane 12b end face of the second counterbody facing away from the measuring membrane 13a end face of the first support body facing the measuring membrane 13b end face of the second support body facing the measuring membrane 14a Membrane electrode 14b Membrane electrode 15 inner recess 16 Ventilation area 17a first area 17b second area 18 predefinable geometric shapes p1 first print p2 second pressure FM joining material RB edge area ME measuring membrane level SA axis of symmetry dv predefinable layer thickness the predictable resulting layer thickness It is the elastic modulus of the supporting body Eg. Elastic modulus of the counterbody

Claims

[1] Method for joining a differential pressure measuring cell (1), which differential pressure measuring cell (1) comprises: a measuring diaphragm (2); a transducer, a first and a second counter body (41, 42), and a first and a second support body (51, 52), - wherein the measuring membrane (2) is arranged between the first counterbody (41) and the second counterbody (42) and is pressure-tightly connected to both counterbodies (41,42), - wherein a first measuring chamber (61) is formed between the measuring membrane (2) and the first counterbody (41) and a second measuring chamber (62) is formed between the measuring membrane (2) and the second counterbody (42), - wherein the first counterbody (41) and first support body (51) as well as the second counterbody (42) and second support body (52) each have a pressure channel (7) through which the first measuring chamber (61) can be subjected to a first pressure (p1) and the second measuring chamber (62) to a second pressure (p2) and - wherein the transducer is designed to generate an electrical measurement signal from a deformation of the measuring diaphragm (2) caused by the difference between the first pressure (p1) and the second pressure (p2); wherein the joining process is divided into the following steps: - Prefabrication of the two counter bodies (41,42) and pressure-tight connection of the measuring membrane (2) to the two counter bodies (41,42), - Applying a joining material (FM) to the end face (13a) of the first support body (51) facing the measuring membrane (2) and / or to the end face (12a) of the first counter body (41) facing away from the measuring membrane (2) and to the end face (13b) of the second support body (51) facing the measuring membrane (2) and / or to the end face (12b) of the second counter body (42) facing away from the measuring membrane (2), wherein the joining material (FM) is applied to at least one of the end faces (12a; 12b; 13a; 13b) in a region, so that areas (32) with joining material (FM) and areas (31) without joining material (FM) are formed, wherein the joining material (FM) is applied to the end face (12a;12b) of the counter body (41; 42) facing away from the measuring membrane (2) in a first area (17a) and to the end face (13a;13b) of the adjacent support body (51; 52) in a second area (17b) complementary to the first area (17a), and wherein the two complementary areas (17a, 17b) combine to form a predetermined geometric shape (18), - Pressure-tight joining of the end face (12a, 12b) of the counterbody (41, 42) facing away from the measuring membrane (2) with the end face (13a, 13b) of the support body (51, 52) facing the measuring membrane (2), wherein during the joining of at least one of the counterbodies (41; 42) with the adjacent support body (51; 52) the joining material (FM) in the end face (12a; 12b; 13a; 13b) with the joining material (FM) applied in the area • reduced in the direction perpendicular to the front face (12a;12b;13a;13b) (81) and • is enlarged (82) in at least one direction plane to the end face (12a; 12b; 13a; 13b), wherein the enlargement (82) of the joining material (FM) in the direction plane to the end face (12a; 12b; 13a; 13b) enlarges the areas (32) with joining material (FM) and reduces the areas (31) without joining material (FM), so that gradually a single continuous area (9) with joining material (FM) is formed, which area (9) extends over the entire end face (12a; 12b; 13a; 13b) except for an inner recess (15) surrounding the pressure channel (7), so that after pressure-tight joining, the counter body (41;42) and support body (51; 52) are joined over their entire surface. [2] Method according to claim 1, wherein the joining material (FM) is applied at least in some areas in the form of at least one circular ring, and wherein the inner recess (15) is located in the center of the circular ring. [3] Method according to claim 1 or 2, wherein the joining material (FM) is applied at least in some areas in the form of several concentric circular rings, and wherein the inner recess (15) lies in the common center of the concentric circular rings. [4] Method according to at least one of the preceding claims, wherein an area (31) without joining material (FM) is designed as a venting area (16), which venting area (16) extends from the inner recess (15) to an edge area (RB) of the front surface (12a; 12b; 13a; 13b), and wherein, during the pressure-tight joining, the venting area (16) is continuously reduced by continuously filling the venting area (16) from the inner recess (15) to the edge area (RB) with joining material (FM). [5] Method according to at least one of the preceding claims, wherein the complementary areas (17a, 17b) have the form of concentric circular rings and / or sections of concentric circular rings, such that the specified geometric shape (18) is a circular area or concentric circular rings. [6] Method according to at least one of the preceding claims, wherein the joining material (FM) is applied using a screen printing process. [7] Method according to at least one of the preceding claims, wherein the joining material (FM) is a glass solder, an adhesive or a metallic solder. [8] Method according to at least one of the preceding claims, wherein the joining material (FM) is applied with a predefinable layer thickness (dv), in the pressure-tight joining process the predefinable layer thickness (dv) in the direction perpendicular to the end face (12a; 12b; 13a; 13b) is reduced to a resulting predefinable layer thickness (dr). [9] Method according to at least one of the preceding claims, wherein the counter body (41,42) is connected to the adjacent support body (51,52) with an approximately homogeneous contact pressure distribution and a contact pressure (Pf) in a pressure-tight manner. [10] Differential pressure measuring cell (1) obtained from a method according to at least one of the preceding claims 1-9 comprising; a measuring diaphragm (2); a transducer, a first and a second counter body (41, 42), and a first and a second support body (51, 52), - wherein the measuring membrane (2) is arranged between the first counterbody (41) and the second counterbody (42) and is pressure-tightly connected to both counterbodies (41,42), - wherein a first measuring chamber (61) is formed between the measuring membrane (2) and the first counter body (41) and a second measuring chamber (61) is formed between the measuring membrane (2) and the second counter body (42), - wherein the first counterbody (41) and first support body (51) and the second counterbody (42) and second support body (52) each have a pressure channel (7) through which the first measuring chamber (61) can be subjected to a first pressure (p1) and the second measuring chamber (62) to a second pressure (p2) and - wherein the transducer is designed to generate an electrical measurement signal from a deformation of the measuring diaphragm caused by the difference between the first pressure (p1) and the second pressure (p2); wherein the end face (12a; 12b) of at least one of the counter bodies (41;42) facing away from the measuring diaphragm (2) is connected pressure-tight and over its entire surface to the end face (13a; 13b) of the adjacent support body (51; 52) facing the measuring diaphragm (2). [11] Differential pressure measuring cell (1) according to claim 10, wherein the counter body (41;42) and / or the support body (51; 52) consists of a ceramic material. [12] Differential pressure measuring cell (1) according to at least one of the preceding claims 10-11, wherein the counter body (41;42) and / or the support body (51; 52) - made of silicon (Si), - from an amorphous or crystalline oxide of silicon (SiO2), amorphous or crystalline carbide of silicon (SiC) and / or amorphous or crystalline nitride of silicon (SiN), - and / or consists of an amorphous or crystalline oxide of aluminum (Al2O3) and / or aluminum nitride (AlN). [13] Differential pressure measuring cell (1) according to at least one of the preceding claims 10-12, wherein the modulus of elasticity (Es) of the support body (51; 52) is equal to or greater than the modulus of elasticity (Eg) of the counter body (41;42), wherein the modulus of elasticity (Es) of the support body (51; 52) is at most three times greater than the modulus of elasticity (Eg) of the counter body (41;42).

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