Planar ceramic pressure sensor and related manufacturing method

Abstract

A piezoresistive or capacitive planar pressure sensor (130) comprising a flexible planar membrane (100) made of a ceramic material and a relatively rigid planar support (110) made of a ceramic material, wherein the support (110) has a first main face (220) and a second main face (230) and the membrane (100) has a first main face (200) and a second main face (210), and wherein the first main face (200) of the membrane (100) faces the second main face (230) of the support (110), the first main face (200) of the membrane (100) comprises at least one first electrical circuit (501), the first main face (220) of the support (110) comprises at least one second electrical circuit (502), and an electrical connection is further provided between the first electrical circuit (501) of the first main face (200) of the membrane (100) and the second electrical circuit (502) of the first main face (220) of the support (110) on the periphery of the rigid support (110) of the pressure sensor (130).

Description

Technical Field

[0001] This invention relates to a piezoresistive or capacitive planar ceramic pressure sensor and related manufacturing methods. Background Technology

[0002] In various applications such as industrial, medical, and automotive fields, it is known to use ceramic pressure sensors integrated into transducers to measure the pressure of fluids.

[0003] Ceramic sensors are mechanically robust, can operate in corrosive environments, and offer reliable and stable performance.

[0004] Ceramic membranes are chemically inert, require no type of separator, and can come into direct contact with many fluids, including some of the most corrosive ones.

[0005] Long-term stability and a wide operating range in terms of both pressure and temperature are other important factors contributing to the versatility and reliability of ceramic pressure sensors.

[0006] These aspects, along with their ease of integration into all types of industrial machinery and process control equipment, make piezoresistive and capacitive ceramic sensors more attractive and advantageous compared to other technological solutions, thanks to their excellent cost-effectiveness and wide range of applications.

[0007] Piezoresistive sensors with ceramic membranes are typically made of alumina and can come in two types: planar sensors, in which the membrane is fixed to a mechanical support also made of ceramic; or monolithic sensors, which consist of a single ceramic element, in which a thinner central component acts as the membrane and a thicker central component acts as the mechanical support.

[0008] The membrane bends under pressure, and this bending can be detected using a Wheatstone bridge. The resistors, made of piezoresistive material, are positioned such that when the membrane bends, two resistors (on opposite sides of the bridge) elongate, increasing resistance, while the other two are compressed, decreasing resistance. The bridge becomes unbalanced, and the output voltage is proportional to the pressure difference that caused the deformation.

[0009] Planar piezoresistive sensors are typically manufactured by screen printing a resistive bridge on a membrane onto the side opposite the fluid-contacting side, and then attaching the membrane to a mechanical support. To ensure sufficient deformation space for the membrane and to limit its movement, the adhesive layer has a central recess and a hole. The central recess, typically circular, is located in the deformable region of the membrane, where the piezoresistive element is positioned. The hole is located outside the cavity, and conductive material is deposited on the walls of the hole. During mechanical connection, the hole is electrically connected to traces on the membrane.

[0010] In capacitive rather than piezoelectric sensors, pressure signals are detected by the change in capacitance caused by the relative displacement of their armatures (one armature is printed on a diaphragm, and the other on a mechanical support). In some cases, there is an orifice in the cavity of the support: if the orifice is open, the system will be used as a relative or differential sensor (provided the cavity is sealed), while if the orifice is closed and the cavity is sealed, the system will be used as an absolute sensor.

[0011] In the prior art, particularly in WO2013139832A1, piezoresistive and capacitive planar ceramic pressure sensors are disclosed. These piezoresistive and capacitive planar ceramic pressure sensors include a flexible planar membrane made of ceramic material with circuitry, a rigid planar support made of ceramic material with external electrical contacts, conductive material deposited on the support, an electrical connection formed between the membrane and the support by depositing and sintering a low-melting-point conductive conductive material layer, and a mechanical connection formed between the membrane and the support by depositing and sintering a mechanically insulating and / or insulated mechanically insulating glass layer, wherein the electrically insulating glass layer and the mechanically insulating glass layer are simultaneously sintered together in a single channel in a sintering furnace.

[0012] Typically, the membrane and support are obtained from ordinary ceramic sheets, particularly made of alumina, if commercially available and commonly used for, for example, the automated manufacturing of thick-film hybrid circuits; multiple pressure sensors are obtained by dividing a sheet-like semi-finished product source into multiple pieces, which originate from the connection between the membrane and the support.

[0013] In the prior art, the support sheet is provided with electrical contact holes, which are appropriately arranged to transmit electrical signals from the membrane to discrete electrical and electronic components (such as resistors, capacitors, transistors, integrated electronic circuits and connectors) housed on the outer surface of the support sheet for processing, thereby processing and transmitting signals detected by deformation of the membrane.

[0014] The presence of these holes and electrical connections, along with relative positioning constraints and geometric volume, significantly limits the possibility of miniaturizing the sensor, a need that the market particularly feels and that is especially focused on the manufacturing process of individual sensors.

[0015] Specifically, the available space on the support is limited, not only because of the total size of the mechanical hole, but also because of the total size of the crown of the conductive material surrounding the mechanical hole.

[0016] Furthermore, the available space on the support is limited due to the minimum distance required between the crown of the conductive material surrounding the mechanical hole and the discrete components applied to the support. This minimum distance must ensure that the welding material of the components on the support does not come into contact with the crown of the conductive material surrounding the mechanical hole.

[0017] The presence of mechanical holes tends to cause mechanical embrittlement of the support. Therefore, in addition to restrictions on the relative arrangement of holes, restrictions will also be placed on the minimum distance between the hole and the edge of the support, as well as between holes.

[0018] Finally, creating holes (usually four holes) for each support complicates the manufacturing process because this operation adds to the sheet cutting operation from which each support originates.

[0019] Therefore, it is necessary to simplify the structure of known piezoresistive and capacitive planar ceramic pressure sensors.

[0020] Therefore, the technical objective of this invention is to produce a planar ceramic pressure sensor that eliminates the technical defects of the prior art. Summary of the Invention

[0021] In the context of this technical task, one object of the present invention is to produce a planar ceramic pressure sensor that allows for miniaturization.

[0022] Another object of the present invention is to produce a planar ceramic pressure sensor that can obtain space on a support to integrate discrete electrical and electronic components.

[0023] Another object of the present invention is to produce a planar ceramic pressure sensor that reduces the embrittlement of the support due to the presence of through holes.

[0024] Another objective of this invention is to produce a planar ceramic pressure sensor that is easy to manufacture.

[0025] The most important objective of this invention is to disclose a method for manufacturing a planar ceramic pressure sensor.

[0026] The technical objectives and other objects of the present invention are achieved by fabricating a piezoresistive or capacitive planar pressure sensor comprising a flexible planar membrane made of ceramic material and a relatively rigid planar support made of ceramic material, wherein the support has a first main surface and a second main surface, and the membrane has a first main surface and a second main surface, wherein the first main surface of the membrane faces the second main surface of the support, the first main surface of the membrane includes at least one first circuit, and the first main surface of the support includes at least one second circuit, characterized in that an electrical connection between the first circuit of the first main surface of the membrane and the second circuit of the first main surface of the support is disposed on the peripheral edge of the support.

[0027] Preferably, the electrical connection portion is disposed in a recessed portion at the peripheral edge of the support member.

[0028] Preferably, the recess extends over the entire thickness of the support.

[0029] Preferably, the electrical connection portion is formed of a conductive layer covering the recessed portion.

[0030] By providing electrical connections around the perimeter of the support, the holes inside the support can be eliminated.

[0031] Because there are no holes inside the support, the available space on the support is increased, and no more brittle guidelines are produced on the support.

[0032] An electrical connection on the periphery of the support can be made at a half-hole, which is created by deliberately breaking the hole in the sheet along the cutting line.

[0033] In this way, the manufacturing process is simplified, not only because the number of holes formed on the sheet is halved, but also because the holes and pre-cut lines on the sheet can be made using the same laser cutting method.

[0034] In fact, it is quite obvious that the electrical connection between the two sensors can be made through four holes.

[0035] Optionally, the electrical connections around the support can also be covered with a protective coating (e.g., protective resin, thick-film dielectric, glass applied by screen printing via suction).

[0036] The present invention also discloses a method for manufacturing a planar pressure sensor, the planar pressure sensor comprising a flexible planar membrane made of ceramic material and a relatively rigid planar support made of ceramic material, wherein the support has a first main surface and a second main surface, and the membrane has a first main surface and a second main surface, wherein the first main surface of the membrane faces the second main surface of the support, the method comprising the following steps:

[0037] - Fabricate at least one first circuit on the first main surface of the membrane.

[0038] - At least one second circuit is formed on the first main surface of the support member.

[0039] - Deposit conductive material on the first main surface of the film and / or deposit conductive material on the second main surface of the support.

[0040] -A mechanical connection is fabricated between the membrane and the support member, characterized in that...

[0041] The electrical connection between the first circuit and the second circuit is provided by applying a conductive material to a recessed wall that extends along the entire wall thickness of the support at the peripheral edge of the support.

[0042] Other features of the present invention and the manufacturing method are further defined in the following claims. Attached Figure Description

[0043] Other features and advantages of the invention will become more apparent from the description of preferred, but not exclusive, embodiments of the planar ceramic pressure sensor according to the invention and the corresponding manufacturing methods, which are illustrated by non-limiting examples in the accompanying drawings, wherein:

[0044] - Figure 1a A plan view of the original sheet from which the membrane was made is shown;

[0045] - Figure 1b A perspective view of the original sheet from which the support is made is shown;

[0046] - Figure 2a A plan view of the original thick sheet from which the support is made is shown;

[0047] - Figure 2b A perspective view of the original thick sheet from which the support is made is shown;

[0048] - Figure 3a A plan view of a portion of a sheet after the step of depositing conductive material on the walls of a peripheral half-cavity is shown, along with details in an enlarged cross-section shown in a side front view.

[0049] - Figure 3b A plan view of a portion of the thick sheet is shown in a processing step following the previous processing step;

[0050] - Figure 3c A plan view is shown below a portion of a sheet after the steps of printing adhesive glass and conductive glass.

[0051] - Figure 4a A plan view showing a portion of a thin sheet, the steps of printing conductive traces, and the steps of printing a resistor made of piezoresistive material;

[0052] - Figure 4b A plan view of a portion of a sheet is shown after the steps of printing adhesive glass and after the steps of printing conductive glass.

[0053] - Figure 5 The steps for joining thin and thick sheets are shown;

[0054] - Figure 6a A detailed cross-section of the column is shown before the connection between the thick and thin sheets.

[0055] - Figure 6b A detailed cross-section of the column after the connection between the thick and thin sheets is shown, wherein the electrical connection is located in the peripheral half-cavity of the support thickness.

[0056] Figure 6C shows the columns before and after they are divided into individual pieces;

[0057] - Figure 7 A schematic perspective view of the finished pressure sensor is shown;

[0058] In various preferred embodiments of the present invention, the same reference numerals are used to denote equivalent components. Detailed Implementation

[0059] Referring to the above figures, a planar ceramic sensor according to the present invention is shown below, which uses a thick film hybridization technique utilizing a screen printing method and a manufacturing method thereof.

[0060] Manufacturing begins with two sheet-like semi-finished products 1 and 4, which are made of an insulating material having, for example, a rectangular shape, preferably made of alumina.

[0061] The thickness of the first sheet-like semi-finished product 1 is less than the thickness of the second sheet-like semi-finished product 4.

[0062] Therefore, in the following text, we will refer to the first sheet-like semi-finished product or thin sheet 1 and the second sheet-like semi-finished product or thick sheet 4 without distinction.

[0063] Thin sheet 1 has a first main surface 150 and a second main surface 160, and thick sheet 4 has a first main surface 170 and a second main surface 180. When thin sheet 1 and thick sheet 4 are stacked and connected in parallel with each other, the second main surface is intended to face the first main surface 150 of thin sheet 1.

[0064] The sheet 1 and the sheet 4 are sized to accommodate multiple elements, which typically have the same shape and size corresponding to multiple membranes 100 and multiple supports 110, respectively.

[0065] Similar to the sheet, each membrane 100 separable from the sheet 1 has a first main surface 200 and a second main surface 210, and each support 110 separable from the sheet 4 has a first main surface 220 and a second main surface 230, the second main surface being intended to face the first main surface 200 of the corresponding membrane 100 when the sheet 1 and the sheet 4 are joined.

[0066] The sheet 4 may have cuts and / or serrations to define the final shape of the support 110, where the sheet has a plurality of cavities 50 extending through the entire thickness of the support 110, the cavities being axially positioned on at least one peripheral edge of each support 110, each cavity 50 affecting a pair of symmetrically intersecting supports 110, in which a recess corresponding to a semi-cavity 5 on the periphery of the finished pressure sensor 130 is defined.

[0067] Typically, each support 110 defines four semi-cavities 5, which are typically positioned along the same side as the periphery of the support 110.

[0068] Advantageously, according to the invention, the planar support 110 lacks an internal through-hole that extends through its thickness, thereby ensuring that the pressure sensor 130 has greater rigidity and robustness upon completion, and increasing the design options for conditioning electronics used to position the electrical signal, so as to enable miniaturization of the pressure sensor 130.

[0069] The sheet 1 may already have a fracture-promoting line 2 that defines the membrane of the sensor, the fracture-promoting line being preferably made by a cut and / or a notch, preferably by laser cutting.

[0070] In the first step, a conductive layer 503 is deposited on the walls of multiple through cavities 50 of the thick sheet 4 using a screen printing method. Figure 3a Advantageously, according to the invention, depositing a conductive layer 503 on the walls of a plurality of through cavities 50 will be transformed into depositing twice as many half cavities 5 on the walls of each pair of supports 110 that are symmetrically intersecting when subsequently separated.

[0071] Then, the conductive trace 9 is printed ( Figure 3b On the first main surface 170 of the thick sheet 4.

[0072] The conductive trace 9 is electrically connected to the conductive layer 503 on the wall of the through cavity 50.

[0073] At this point, resistors are printed on the first main surface 170 of the thick film 4 to zero the resistor bridge 11, but other thick film components, such as PTC or NTC, can also be added to correct or measure the temperature drift of the sensor, or PTC or NTC resistors to correct the sensitivity of the unit.

[0074] This operation is performed on a thin sheet.

[0075] The set of conductive traces 9, along with other possible thin-film components, typically constitutes the second circuit 502 on the first main surface 220 of the support 110.

[0076] at this time( Figure 3c Adhesive material 13, such as adhesive glass used to connect the two sheets 1 and 4 and define the flexible area of ​​the film 100, is printed on the second main surface 180 of the thick sheet 4.

[0077] Specifically, the adhesive material layer has a central region 400 configured as a circular crown and a peripheral region 401 separated from the central region 400 by a circular crown-shaped region 402 lacking adhesive material.

[0078] Then, a single pad of low-melting-point conductive glass 14, which is electrically connected to and individually connected to the conductive layer 503 on the wall of the single through cavity, is printed again on the second main surface 180 of the thick sheet 4.

[0079] At this point, the support member 110 will prepare the thick sheet 4 made therefrom for connection.

[0080] On the first main surface 150 of thin sheet 1, firstly ( Figure 4a Conductive traces 16 are printed using a screen printing method and led to the peripheral edge of the film 100, which geometrically corresponds to the through cavity 50 formed in the support 110.

[0081] Then, the resistor 18 of the Wheatstone bridge, made of piezoresistive material, is printed, and spacer elements (not shown in the figure) may be positioned, which may be, for example, small balls or lines with a calibration diameter or plates with a calibration thickness.

[0082] Resistors are also printed to improve the zeroing of the bridge circuit.

[0083] The set of conductive traces 16 and resistors 18 constitute a first circuit 501 on the first main surface 200 of the film 100: therefore, the first circuit 501 includes a Wheatstone bridge having a first pair of conductive traces for supplying signals and a second pair of conductive traces for removing signals.

[0084] Then, printing is done on the first main surface 150 of sheet 1. Figure 4b Adhesive materials, such as adhesive glass 21 used for bonding to sheet 4.

[0085] Specifically, the adhesive material layer 21 has a central region 403 configured as a circular crown and a peripheral region 404 separated from the central region 403 by a circular crown-shaped region 405 lacking adhesive material.

[0086] At this time, a pad made of low-melting-point conductive glass 23 is printed above the end of the conductive trace 16 at the peripheral edge of the film 100.

[0087] At this point, sheet 1 is ready for connection.

[0088] It should be noted that placing the conductive material on both the first surface of the membrane and the second main surface of the support is optional; for example, the conductive material cannot be applied to the second main surface of the support.

[0089] Connection ( Figure 5 This occurs by placing sheet 1 and sheet 4 in a furnace, thus stacking them together so that ( Figure 6a , Figure 6b Conductive glass regions 14 and 23 are stacked and sintered until the adhesive glasses 13 and 21 melt and become one, thereby creating a mechanical connection between the film 100 and the support 110. Simultaneously, conductive glasses 14 and 23 melt into a column of conductive glass and form an electrical connection for the conductive trace 16, thus forming an electrical connection for the first circuit 501, wherein the conductive layer 503 on the wall of the single through-cavity 50 is electrically connected to the trace 9 of the second circuit 502.

[0090] Therefore, the first circuit 501 on the first main surface 200 of the membrane 100 is electrically connected to the second circuit 502 on the first main surface 220 of the support 110 through the conductive layer 503 on the wall of the single through cavity 50 on the periphery of the support 110.

[0091] At this point, the thick sheet 4 and the thin sheet 1 form a third sheet-shaped semi-finished product 300, which originates from the electrical and mechanical connection between the first sheet-shaped semi-finished product 1 and the second sheet-shaped semi-finished product 4.

[0092] Then, a protective material 26 (typically glass) is printed on the first main surface 170 of the sheet 4, and subsequent manufacturing steps are carried out, which may include the assembly, testing, simulation or digital calibration of SMT components, etc.

[0093] Advantageously, according to the invention, the electrical connection is positioned between the first circuit 501 and the second circuit 502 for applying conductive material 503 to the wall of the peripheral cavity 50. This frees up space and does not restrict the geometry of the circuit on the main surface 170 of the support 110, thereby allowing for possible free mounting of discrete components and further miniaturization of the entire pressure sensor 130.

[0094] Then, multiple discrete components 28 (such as resistors, capacitors, transistors, integrated electronic circuits, and connectors) are assembled onto the first main surface 170.

[0095] Then, sheet 300 is divided into 30 ( Figure 6c A single pressure sensor 130 may be cut, for example, along a cutting line that divides the peripheral cavity 50 in two, perpendicular to the sheet-like semi-finished product 300, using a saw or water cutting (indicated by arrow 29), but preferably by simple mechanical action along the previously disclosed facilitating fracture line.

[0096] This manufacturing method allows for the production of materials with the following properties from two flat sheets 1 and 4: Figure 7 The planar pressure sensor 130 has the structure shown.

[0097] In practice, it has been determined how the planar ceramic pressure sensor according to the invention is particularly advantageous in obtaining space on the support to integrate discrete electrical and electronic components and to allow for miniaturization of the sensor.

[0098] Another advantage of the planar ceramic pressure sensor according to the invention is its greater robustness due to the absence of through holes in the support.

[0099] Another object of the present invention is to disclose a planar ceramic pressure sensor that is easy to manufacture.

[0100] The planar ceramic pressure sensor conceived in this paper is readily modified and varied, all of which fall within the scope of the inventive concept; furthermore, all details can be replaced with technically equivalent elements.

[0101] In practice, the materials and dimensions used can be determined according to needs and existing technology.

Claims

1. A piezoresistive or capacitive planar pressure sensor (130) comprising a flexible planar membrane (100) made of ceramic material and a relatively rigid planar support (110) made of ceramic material, wherein the support (110) has a first main surface (220) and a second main surface (230), and the membrane (100) has a first main surface (200) and a second main surface (210), wherein the first main surface (200) of the membrane (100) faces the second main surface (230) of the support (110), the first main surface (200) of the membrane (100) includes at least one first circuit (501), and the first main surface (220) of the support (110) includes at least one second circuit (502). Its features are, The electrical connection between the first circuit (501) of the first main surface (200) of the membrane (100) and the second circuit (502) of the first main surface (220) of the support member (110) is provided on the peripheral edge of the support member (110). The electrical connection portion is disposed in the recess of the peripheral edge of the support member (110), and The recess extends over the entire thickness of the support (110).

2. The planar pressure sensor (130) according to claim 1, characterized in that, The electrical connection portion is formed by coating the recessed portion with a conductive layer (503).

3. The planar pressure sensor (130) according to claim 2, characterized in that, The conductive layer (503) then has a protective coating.

4. The planar pressure sensor (130) according to any one of claims 1 to 3, characterized in that, The support (110) lacks an internal through-hole that extends through its thickness.

5. The planar pressure sensor (130) according to claim 2 or 3, characterized in that, The first circuit (501) includes a Wheatstone bridge having a first pair of conductive traces for supplying a signal and a second pair of conductive traces for removing the signal, the first pair of conductive traces and the second pair of conductive traces being connected to the second circuit through conductive layers present in four recesses in the recesses.

6. The planar pressure sensor (130) according to claim 5, characterized in that, The four recesses are positioned along the same peripheral side as the support (110).

7. The planar pressure sensor (130) according to any one of claims 1 to 3, characterized in that, The mechanical connection between the first main surface (200) of the membrane (100) and the second main surface (230) of the support (110) includes at least one layer of adhesive material (21, 13).

8. The planar pressure sensor (130) according to claim 7, characterized in that, The at least one adhesive material layer (21, 13) has a central region configured as a circular crown and a peripheral region separated from the central region by a circular crown-shaped region lacking adhesive material.

9. A method for manufacturing a planar pressure sensor (130), the planar pressure sensor comprising a flexible planar membrane (100) made of ceramic material and a relatively rigid planar support (110) made of ceramic material, wherein the support (110) has a first main surface (220) and a second main surface (230), and the membrane (100) has a first main surface (200) and a second main surface (210), wherein the first main surface (200) of the membrane (100) faces the second main surface (230) of the support (110), the method comprising the steps of: - At least one first circuit (501) is formed on the first main surface (200) of the membrane (100). - At least one second circuit (502) is formed on the first main surface (220) of the support (110). - Deposit conductive material (23) on the first main surface (200) of the film (100) and / or deposit conductive material (14) on the second main surface (230) of the support (110), - A mechanical connection is formed between the membrane (100) and the support member (110). Its features are, An electrical connection between the first circuit (501) and the second circuit (502) is provided for applying conductive material (503) to a recessed wall that extends over the entire wall thickness of the support (110) at the peripheral edge of the support (110).

10. The method for manufacturing a planar pressure sensor (130) according to claim 9, wherein the membrane (100) is part of a first sheet-like semi-finished product (1), other membranes (100) are part of the first sheet-like semi-finished product, and the support (110) is part of a second sheet-like semi-finished product (4), other support members (110) are part of the second sheet-like semi-finished product (4), and wherein the planar pressure sensor (130) together with other planar ceramic pressure sensors (130) is obtained by dividing the third sheet-like semi-finished product (300) into multiple pieces along a cutting line, the third sheet-like semi-finished product originating from the electrical and mechanical connection between the first sheet-like semi-finished product (1) and the second sheet-like semi-finished product (4), characterized in that, Holes are formed on the second sheet-like semi-finished product (4) along the cutting line, and once the cut is formed, the cut divides the hole in half, such that two recesses belonging to adjacent sensors are formed from each hole.

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