DE102009003090A1 - Sensor arrangement for detecting a pressure - Google Patents

Abstract

A sensor arrangement (110) for detecting a pressure is proposed. The sensor arrangement (110) has at least one sensor element (136) for detecting the pressure. The sensor element (136) is at least partially shielded by a protective cover (122). The sensor arrangement (110) furthermore has at least one heating element (160). The sensor arrangement (110) is designed to counteract by means of the heating element (160) a condensation, in particular a formation of exhaust gas condensate, on the sensor arrangement (110), in particular on the protective cover (122).

Description

State of the art

Particularly in the automotive sector, but also in other fields, components are used which comprise one or more sensors for detecting certain properties of media. The invention will be described below with reference to pressure sensors, in particular micromechanical pressure sensors, as used for example for detecting Saugrohrdrücken, boost pressures and differential pressure sensors for particulate filters. Such pressure sensors are used for example in Robert Bosch GmbH: Sensors in motor vehicles, issue 2007, pages 74-76 and pages 128-130 described. However, the invention is in principle not limited to pressure sensors, so that, for example, sensors for other measured variables can also be modified according to the invention.

Especially Pressure sensors, but also other types of sensor elements exhibit typically a sensor chip, which by a gel from corrosive Media, such as exhaust gases, air or water vapor, protected becomes. In individual cases, however, it may This protection is due to a highly resistant gel a diffusion of exhaust gas through the gel to an accumulation of Exhaust gas condensate in the region of the sensor chip come, for example in caverns between the chip, bond wires and the gel. This can lead to bond detachment or trace corrosion and thus leading to complete failure of the sensor elements.

Disclosure of the invention

It Therefore, a sensor arrangement for detecting a pressure, in particular a medium proposed which the disadvantages of known sensor arrangements at least largely avoided. In particular, the sensor arrangement offers improved corrosion resistance, increased long-term stability and reduced in comparison with conventional components Failure rate.

The Sensor arrangement is used to detect a pressure, in particular the Medium. Basically, alternatively or in addition, at least one other property of Medium be detected. This at least one property of the medium For example, a physical property and / or chemical be measurable property of the medium. In particular, it can be one temperature, one speed, one flow, one Composition or similar physical and / or chemical measurable properties of the medium act. The medium can in particular be a liquid and / or gaseous medium. In particular, the sensor arrangement for detecting a pressure a gas, such as an exhaust gas used.

The sensor arrangement may comprise at least one sensor element for detecting the pressure. The sensor element may, for example, comprise one or more sensor surfaces which are set up in direct or indirect contact with the medium in order to qualitatively or quantitatively measure the pressure of the medium alone or in cooperation with other components of the sensor arrangement capture. With respect to the configuration of the sensor element, reference may be made, for example, to the above-mentioned prior art, in particular those in Robert Bosch GmbH: Sensors in motor vehicles, issue 2007, pages 74-76 and pages 128-130 described micromechanical pressure sensors. Alternatively or additionally, however, other types of sensor elements can also be used in principle.

there the sensor element is at least partially covered by a protective cover shielded. The shield can, for example, opposite the medium whose pressure is to be detected, even done and / or towards another medium, for example a corrosive one and / or otherwise aggressive medium, such as moisture, oil or fuel. The protective cover, for example, the said Sensor surface include, for example, a sensor membrane. The sensor surface can be completely, for example or partially covered by the protective cover. Alternatively or In addition, however, the protective cover can also, as below will be explained in more detail, one or more Protect connecting contacts, for example, cover them. Under a protective cover should generally be an ele ment understood which is set up to be an encroachment of aggressive Media to the shielded part of the sensor element at least slow down, for example, compared to an unprotected part by at least a factor of 1000, preferably by at least one Factor 10000. As explained below, the protective cover in particular comprise at least one gel which the sensor element completely or partially covered, for example, at least one sensor surface the sensor element and / or at least one terminal contact of the Sensor element. An advantage of a gel as a protective cover and / or Part of the protective cover is in particular that a Gel can transfer pressure, which is especially true in pressure sensors is advantageous.

The sensor arrangement furthermore has at least one heating element. The sensor arrangement is set up by means of the heating element of a Counteract condensation on the sensor assembly. In particular, a condensation of constituents of the medium can be counteracted, for example a formation of exhaust gas condensate. In particular, the condensation on the protective cover can be counteracted, that is, on a surface of the protective cover and / or in an interior of the protective cover. In particular, the sensor arrangement can be set up in order to increase the operating temperature of the sensor element relative to the ambient temperature by means of the element. For example, the pressure detection can be carried out at an operating temperature which is higher than the ambient temperature. For example, the heating element may have one or more heating resistors. In principle, however, other embodiments of the heating elements are conceivable.

As As shown above, the sensor element can in particular be a pressure sensor be, which has at least one sensor membrane. For example it may be a semiconductor membrane, which, for example etched out of a chip mainland by an etching process has been. The sensor membrane can, for example, from one side be acted upon by a reference pressure and from an opposite Side with a measuring pressure.

So the sensor element can in particular be a sensor membrane and a the sensor membrane mainland connected, wherein the heating element in whole or in part on at least one of the following elements arranged: the sensor membrane; the mainland; one the sensor membrane and / or the mainland aufneh ing substrate, such as a sensor chip with the sensor membrane and the mainland receiving substrate, in particular a ceramic substrate and / or a housing injection part.

The Heating element may in particular be designed to hold the sensor element, in particular a sensor surface of the sensor element, essentially to heat homogeneously. In this way, for example, safely be made that the measurement of the sensor element, so the detection the pressure and / or the at least one other property of the Medium, not by temperature inhomogeneities within the sensor element is disturbed. So, for example the sensor arrangement be set up such that a spatial temperature variation over the sensor element, in particular a sensor surface of the sensor element is not more than 1 degree, in particular not more than 0.5 degrees.

The Heating element can be used as a separate, from the other sensor function the sensor element independent element be designed, for example, as described above, in the form of one or more Heating resistors, which on and / or within the sensor membrane and / or other elements of the sensor arrangement can be arranged. Alternatively or additionally, as a heating element however, elements of the sensor arrangement may also be used are anyway present in the sensor arrangement. So the sensor element, in particular in the case of a pressure sensor, for example at least comprise a measuring resistor, in particular at least one expansion resistor, for example, at least one piezoresistive resistor. These At least one expansion resistance can, for example, on a sensor membrane be arranged and / or integrated into such a sensor membrane be. Alternatively or in addition to one or more Strain resistors can also be a resistance bridge circuit be provided, for example, a Wheatstone bridge. One or more strain resistors can be used in this resistance bridge circuit be integrated, wherein the resistance of this strain resistor across the resistor bridge circuit can be detected. The measuring resistor and / or the resistance bridge circuit can be part or all of the heating element. In this Case, for example, the measuring resistor and / or the resistor bridge circuit in whole or in part with a heating current are applied to the desired and to achieve the above-described heating of the sensor element. This heating can for example also be clocked, so that For example, measurement functions of the sensor element not disturbed become.

The sensor arrangement may further comprise an evaluation circuit. An evaluation circuit is an electronic circuit which is set up in order to receive signals of the sensor element and to process them completely or partially and / or forward them. Alternatively or additionally, the evaluation circuit can take on additional functions, for example, control functions for the sensor element. The evaluation circuit may in particular comprise one or more interfaces via which signals of the sensor arrangement can be forwarded and / or queried. A power supply of the sensor element can be ensured via the evaluation circuit. It is particularly preferred if the evaluation circuit is arranged at least partially spatially separated from the sensor element, wherein the heating element is arranged to heat at least the sensor element, preferably exclusively the sensor element. For example, the evaluation circuit and the sensor element can be arranged on a substrate, for example a plastic and / or ceramic substrate and / or a housing injection part, wherein the Arrangement can be spatially separated. The connection between the evaluation circuit and the sensor element can be effected for example by wires and / or conductor tracks. The heating element can in particular be set up such that only the sensor element is heated, whereas the evaluation circuit should be substantially unaffected by the heating element, for example. In principle, however, the evaluation circuit can also be heated by the heating element.

As As shown above, for example, the protective cover may be at least include a gel or even completely off at least a gel. Under a gel is a form of matter to understand which for the purpose of applying to the protected Location of the sensor assembly is deformable, for example to adapt to a surface contour. In particular, the gel can can remain in a soft, deformable state, in principle be cured after application. The gel can For example, media density or media-repellent properties have, for example, a moisture seal and / or an oil seal. It is particularly preferred if the gel is one or more of the following Substances includes: a dimethylsiloxane gel, a fluorosilicone gel, a perfluoropolyether. Such gels have been used in electrical engineering for the protection of components, especially against corrosive Environment media, proved advantageous.

In a further advantageous embodiment of the sensor arrangement is this sensor arrangement is set to an operating temperature capture and control a heating power of the heating element and / or to regulate. For the purpose of detecting the operating temperature can For example, the sensor arrangement comprise one or more temperature sensors. For example, one or more temperature sensors be directly or indirectly connected to the sensor element, for example a sensor surface of the sensor element, in particular a Sensor membrane. For example, such temperature sensors be applied directly or indirectly to the membrane and / or be integrated into this. For example, the temperature sensors can have a or include multiple temperature resistances. Others too However, types of temperature sensors are basic used. The sensor arrangement may be, for example, an electronic and / or include programmable control and / or regulation, which, for example, while processing the signals of at least a temperature sensor that controls the operation of the heating element and / or regulates, for example, the operating temperature to a certain value or within a certain range of values and / or to regulate. Such devices are the expert in principle known.

The Sensor arrangement may be arranged in particular to a heating power of the heating element to control or regulate that the operating temperature a predetermined maximum temperature, in particular a maximum temperature between 90 ° C and 150 ° C, preferably a maximum temperature of 100 ° C, does not exceed. Alternatively or In addition, the sensor arrangement can also be set up, around the operating temperature by 2 Kelvin to 15 Kelvin, preferably to set 4 Kelvin to 6.5 Kelvin above the ambient temperature and / or to regulate. In particular, the operating temperature can chosen at least 4 Kelvin above ambient temperature are, preferably at least 4-10 Kelvin above the ambient temperature.

The Protective cover, as shown above, the sensor element completely or partly to the medium and / or other media, For example, corrosive media, shield. As shown above, For example, this shield may be part of the sensor element comprising, for example, a sensor surface. For example, the sensor surface can be directly or indirectly be shielded. Alternatively or additionally but also other parts of the sensor element through the protective cover be shielded, for example, one or more terminals. In this case, but also in other cases, it is preferable if the sensor arrangement comprises at least one connection contact, wherein the heating element is arranged to connect the terminal heat. The connection contact may in particular at least one intermetallic Phase comprise, for example, an Au-Al-intermetallic phase. Such intermetallic phases may be, for example occur when a bonding wire is applied to a contact pad, For example, a gold bond on an aluminum contact pad. Such intermetallic Phases are usually particularly vulnerable to Corrosion, such as galvanic corrosion. By heating the connection contacts can at least such corrosion partially avoided.

Brief description of the drawings

embodiments The invention is illustrated in the drawings and in the following Description explained in more detail.

It demonstrate

1A and 1B a detailed representation of a connection contact of a sensor arrangement; and

2 a schematic embodiment of a sensor arrangement according to the invention in plan view.

embodiments

In the 1A and 1B is to illustrate the above-described problem of corrosion of sensor assemblies by exhaust gases or other aggressive media, a part of a sensor array 110 shown. It shows 1A an example of a connection contact 112 the sensor arrangement 110 in which a bonding wire 114 of gold on a contact pad 116 made of aluminum. The contact pad 116 is on a mainland 118 a silicon chip 120 applied and serves to contact one in the 1A and 1B not shown sensor element.

To protect the connection contact 112 from corrosion, in particular by exhaust gases, is in the 1A and 1B illustrated arrangement through a protective cover 122 in the form of a gel 124 protected, which the connection contact 112 preferably completely surrounds. Different types of gels 124 are known and used in practice, especially in automotive engineering. For example, dimethylsiloxane gels are used as pure moisture protection. For higher requirements, in particular for increased oil and fuel resistance, fluorosilicone gels are used, which in particular have a reduced swelling behavior. Finally, perfluoropolyethers are used for best long term durability and high protection. Such gels 124 are known to those skilled in electrical engineering in principle.

However, it has been shown that in practice in some areas, especially in the area of the transition between the gold bonding wire 114 and the aluminum contact pad 116 , Cavities 126 can train. In 1B is an enlarged view of the in 1A Shown with A range, from the one of these cavities 126 in an enlarged view emerges. Despite the highly resistant gel 124 It may in some cases by diffusion of exhaust gas through the gel 124 to an accumulation of exhaust gas condensate in the cavities 126 which are usually called small caverns between the chip 120 , the bonding wires 114 and the gel 124 are trained, come. This diffusion is in 1B through the water molecules 128 indicated. Alternatively or in addition to water molecules, other substances may also diffuse, for example ionic substances, gases, liquids or the like.

Diffused water molecules 128 and other harmful substances, in particular an accumulation of exhaust gas condensate in the cavities 126 , but may cause corrosion in particular of the terminal contacts 112 to lead. For example, forms at the transition between the bonding wires 114 and the contact pads 116 in many cases an intermetallic phase 130 For example, a gold-aluminum intermetallic phase. Especially in this area, the condensate, which in 1B symbolically with the reference number 132 is referred to lead to a galvanic corrosion. The corrosion is in 1B symbolically with the reference number 134 designated. These processes can lead to bond detachment or conductor track corrosion and thus to complete failure of the components. In particular, with heavy exhaust gas, for example, by exhaust gas recirculation or in the measurement of the differential pressure for diesel particulate filter, so under certain circumstances, the selected protective measures to prevent corrosion, for example, by protection gels (gel 124 ), by using stable materials (for example gold bonding wires 114 ) to prevent corrosion completely.

Condensation of volatile exhaust components, for example, water vapor from the exhaust gas, but preferably occurs at the coldest point on the way within the sensor assembly, for example, the way to a sensor element on. A basic idea of the present invention is therefore to heat a sensor chip and / or a sensor element at least partially during operation, thereby heating the sensor chip or sensor element a condensation of exhaust gas condensate in the gel 124 or in the cavities 126 can effectively avoid on the chip surface or on the bonding wires.

In 2 is therefore a sensor arrangement according to the invention 110 shown in which a sensor element 136 in the form of a sensor chip 138 separated from an evaluation circuit 140 is arranged. The evaluation circuit 140 For example, it may include one or more integrated circuits (ICs). Also the sensor element 136 can be wholly or partially designed as an integrated circuit, insbesonde re, as shown above, as a sensor chip 138 , sensor chip 136 and evaluation circuit 140 are in this embodiment on a substrate 142 applied, for example, a ceramic substrate and / or a plastic substrate. The substrate 142 has a measuring range 144 and an evaluation area 146 on. The measuring range 144 is partly in direct or indirect contact with the medium to be measured. In the illustrated embodiment, the sensor arrangement 110 configured to detect a pressure of an exhaust gas. Basically, however, are also other parameters with this or other sensor arrangements 110 he tangible. The evaluation area 146 is however by a separating element 148 from the measuring range 144 separated and preferably not pressurized. For example, the separating element 148 include one or more adhesive beads or adhesive surfaces. In this way, for example, the evaluation circuit 140 protected against aggressive fumes and / or moisture. The evaluation area 146 For example, in a circuit chamber and / or a housing of the sensor assembly 110 are arranged, whose or the interior is not acted upon by the exhaust gas and through the separating element 148 is protected. Alternatively or additionally, the evaluation circuit 140 through a protective cover 122 in the form of a gel 124 be protected. For example, a plastic frame 150 be provided on the substrate, which with the gel 124 is completed.

The substrate 142 , For example, the ceramic substrate, by substrate contacts 152 be connected to other components, so that, for example, further parts of the evaluation circuit 140 outside the substrate 142 can be arranged. So can the evaluation circuit 140 Also include several components which on the substrate 142 or outside the substrate 142 can be arranged, for example in a housing of the sensor arrangement 110 which is in 2 not shown. The evaluation circuit 140 may also be wholly or partially on the opposite side of the substrate 142 be arranged and / or in whole or in part in the substrate 142 to get integrated. Not shown in 2 are also printed conductors, which, for example, the substrate contacts 152 with the evaluation circuit 140 connect and / or the evaluation circuit 140 with the sensor element 136 , Also a direct connection between the sensor element 136 and the substrate contacts 152 is possible.

The sensor element 136 has the sensor chip in the illustrated embodiment 138 on, for example, which is fully or partially ausgestal tet as a silicon sensor chip and which is a mainland 118 and a sensor membrane made, for example, by an etching process 154 having. On and / or in the sensor membrane 154 For example, one or more strain resistors may be arranged, which in 2 not shown, for example, piezoelectric strain resistors. The sensor element 136 acts as a pressure sensor 156 by acting as a sensor surface 158 acting surface of the sensor membrane 154 is pressurized. Over an opening in the substrate 142 can the sensor membrane 154 be acted upon from an opposite side with a reference pressure, for example via a reference pressure pipe. Other embodiments are possible in principle. By a deflection of the sensor membrane 154 due to the pressure difference between the measuring pressure, which of the sensor surface 158 on the sensor membrane 154 acts, and the reference pressure, which from the bottom to the sensor membrane 154 acts, this sensor membrane bends 154 , which in turn can be detected by the expansion resistances and can be evaluated for example by means of a resistance bridge circuit. Alternatively to the in 2 shown representation with only one sensor element 136 are also sensor arrangements 110 with a plurality of sensor elements 136 possible, which can detect the same property of a medium and / or different properties of a medium.

Again, the sensor element is also 136 in 2 through a protective cover 122 in the form of a gel 124 protected. Again, for example, a plastic frame 150 be provided, which is a propagation of the gel 124 in unwanted areas on the substrate 142 can prevent.

For pressure sensors 156 in which the evaluation circuit 140 and the sensor chip 138 integrated in a component is already provided, a power loss of the evaluation circuit 140 to a heating of the sensor arrangement 110 by 4 to about 6.5 Kelvin act. In future sensor generations such as the in 2 illustrated sensor arrangement 110 in which the sensor chip 138 and the evaluation circuit 140 are separated from each other, for example, to provide digital signals, but a lower heating of the sensor chip 138 to record. Nevertheless, the above-described effect of heating the sensor element 136 and thus to avoid condensation, in particular in the case of sensor arrangements 110 in which only a fraction of the current consumption is converted into heat, and which thus per se increases the risk of bond delamination or corrosion, it is therefore proposed according to the invention one or more heating elements 160 in the sensor arrangement 110 to integrate.

These heating elements 160 For example, they may include additional heating resistors, for example, on the mainland 118 can be arranged, for example, the sensor membrane 154 around. Alternatively or additionally, however, is also an arrangement on the sensor membrane 154 and / or on a chip carrier, for example the substrate 142 , in particular a ceramic substrate, possible, and / or an arrangement on the Gelrähmchen 150 and / or a housing injection part. Again alternatively or additionally, a bridge circuit, such as a Widerstandbrü bridge circuit, which part of the sensor element 136 is, even as a heating element 160 and / or as part of this heating element 160 be used. The sensor arrangement can be set up, for example, to, in particular controlled / regulated, an operating temperature of the sensor element 136 adjust so that it is increased by, for example, 4 to 10 Kelvin compared to the ambient temperature. To match the operating temperature the maximum specification of the sensor chip 138 not to exceed, the heating power can be switched off above 100 ° C or another maximum temperature and / or the heating power can generally be controlled.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited non-patent literature

• - Robert Bosch GmbH: Sensors in motor vehicles, edition 2007, pages 74-76 and pages 128-130 [0001]
• - Robert Bosch GmbH: Sensors in motor vehicles, edition 2007, pages 74-76 and pages 128-130 [0005]

Claims (11)

Sensor arrangement ( 110 ) for detecting a pressure, in particular a medium, wherein the sensor arrangement ( 110 ) at least one sensor element ( 136 ) for detecting the pressure, wherein the sensor element ( 136 ) at least partially by a protective cover ( 122 ) is shielded, wherein the sensor arrangement ( 110 ) at least one heating element ( 160 ), wherein the sensor arrangement ( 110 ) is arranged to by means of the heating element ( 160 ) a condensation, in particular a formation of exhaust gas condensate, on the sensor arrangement ( 110 ), in particular on the protective cover ( 122 ) counteract. Sensor arrangement ( 110 ) according to the preceding claim, wherein the sensor element ( 136 ) a pressure sensor ( 156 ), the pressure sensor ( 156 ) at least one sensor membrane ( 154 ), wherein the sensor membrane ( 154 ) can be acted upon from one side with a reference pressure and from a opposite side with a measuring pressure can be acted upon. Sensor arrangement ( 110 ) according to one of the preceding claims, wherein the sensor element ( 136 ) a sensor membrane ( 154 ) and one with the sensor membrane ( 154 ) connected mainland ( 118 ), wherein the heating element ( 160 ) is arranged wholly or partly on at least one of the following elements: the sensor membrane ( 154 ); the mainland ( 118 ); one the sensor membrane ( 154 ) and / or the mainland ( 118 ) receiving substrate ( 142 ), in particular a ceramic substrate and / or a housing part, in particular a housing injection part. Sensor arrangement ( 110 ) according to one of the preceding claims, wherein the heating element ( 160 ) is arranged to the sensor element ( 136 ), in particular a sensor surface ( 158 ) of the sensor element ( 136 ) to heat substantially homogeneous. Sensor arrangement ( 110 ) according to one of the preceding claims, wherein the sensor element ( 136 ) comprises at least one measuring resistor, in particular at least one expansion resistor, and / or a resistance bridge circuit, the measuring resistor and / or the resistance bridge circuit being at least partially a component of the heating element ( 160 ) are. Sensor arrangement ( 110 ) according to one of the preceding claims, wherein the sensor arrangement ( 110 ) an evaluation circuit ( 140 ), wherein the evaluation circuit ( 140 ) at least partially spatially separated from the sensor element ( 136 ) and wherein the heating element ( 160 ) is arranged to at least the sensor element ( 136 ) to heat. Sensor arrangement ( 110 ) according to one of the preceding claims, wherein the protective cover ( 122 ) a gel ( 124 ), in particular one or more of the following gels: a dimethylsiloxane gel; a fluorosilicone gel; a perfluoropolyether. Sensor arrangement ( 110 ) according to one of the preceding claims, wherein the sensor arrangement ( 110 ) is arranged to detect the operating temperature and a heating power of the heating element ( 160 ) and / or to regulate. Sensor arrangement ( 110 ) according to one of the preceding claims, wherein the sensor arrangement ( 110 ) is set to a heating capacity of the heating element ( 160 ) to control and / or to regulate so that the operating temperature does not exceed a predetermined maximum temperature, in particular a maximum temperature between 90 ° C and 150 ° C, preferably a maximum temperature of 100 ° C. Sensor arrangement ( 110 ) according to one of the preceding claims, wherein the sensor arrangement ( 110 ) is set to adjust the operating temperature by 2 K to 15 K, preferably by 4 K to 6.5 K, above the ambient temperature. Sensor arrangement ( 110 ) according to one of the preceding claims, wherein the sensor arrangement ( 110 ) at least one connection contact ( 112 ), wherein the heating element ( 160 ) is arranged to connect the terminal ( 112 ) to heat.