Sensor system, sensor assembly and assembly method using welding for sealing

Abstract

The invention relates to a sensor assembly, a corresponding method of assembling such a sensor assembly, and a sensor system. The sensor assembly comprises at least one transducer element (106, 106 ', 106' '; 206, 206; 306; 406) for monitoring the at least one measured variable and generating an electrical output signal associated with the at least one measured variable; and a sensor substrate (112; 312; 312; 406) comprising a transducer element. The sensor substrate (112; 312; 312; 406) can be mounted on the circuit carrier (104; 204); 304, 304; 404) such that a medium channel (124) penetrating the circuit carrier allows access of at least one measured variable to the transducer element. The circuit carrier has an electrically conductive solderable first sealing pattern (132; 432) which at least partially surrounds the media channel and which is connected to a solderable second sealing pattern (134; 434) such that a welded sealing connection at least partially surrounding the media channel is formed between the first sealing pattern and the second sealing pattern.

Description

[0001] This application is a divisional application of the invention patent application with the application date of September 17, 2018, the application number of 201811083883.1, and the invention name of "Sensor system, sensor component and assembly method for sealing using welding". Technical Field

[0002] The invention relates to a sensor assembly having at least one transducer element for monitoring at least one measured variable and for generating an electrical output signal related to the at least one measured variable. The invention also relates to a corresponding method of assembling such a sensor assembly, and to a sensor system. Background Art

[0003] Particularly for automotive applications, a plurality of measured variables need to be monitored, for example physical measured variables such as pressure or temperature, and electrochemical measured variables such as the concentration of a gas (e.g. CO2). In any case, the medium to be monitored must be able to access a defined sensitive element of the sensor assembly, while on the other hand it must be ensured that the aggressive and humid environment does not damage and / or impair the remaining components, in particular the electronics of the sensor assembly. Furthermore, a trend in the automotive industry is that component suppliers supply sensor assemblies to original equipment manufacturers (OEMs) in a not yet fully assembled state, so that the provision of a seal protecting the electronics must be facilitated and it must be possible to automate and part of the assembly process is performed outside the assembly supplier's premises.

[0004] An object of the present invention is to provide a sensor assembly and a corresponding assembly method which improves the performance and reliability of the sensor assembly, thereby overcoming or at least substantially reducing the above-mentioned problems and disadvantages. Summary of the invention

[0005] The above mentioned objects are solved by the subject matter of the independent claims. Advantageous embodiments of the invention are subject matter of the dependent claims.

[0006] The invention is based on the idea of ​​sealing sensitive areas, including electronics, against the ingress of moisture and aggressive chemicals by using a weldable material as a sealing means, which seal can be put in place in one step with the assembly of other welded connections, in particular the electrical connections between the electronic components of the sensor device and the circuit carrier on which the sensor device is mounted. Welded metal alloys have proven to be highly inert and corrosion resistant and to effectively seal interfaces between adjacent surfaces, since they form a gas-tight interconnection due to the presence of a liquid phase during the manufacturing process, even in narrow cracks.

[0007] In the context of the present invention, the term "circuit carrier" is intended to cover any kind of substrate with conductive leads, on which the sensor assembly (and optionally other electronic components) can be mounted. In particular, the circuit carrier may include a printed circuit board (PCB), a flexible circuit carrier (also called a flexible printed circuit, FPC), a flexible rigid carrier (which is a combination of an FPC or a flat flexible cable with a rigid element), a ceramic substrate (thick film, LTCC, HTCC), glass, etc.

[0008] In particular, the present invention provides a sensor assembly comprising at least one transducer element for monitoring at least one measured variable and for generating an electrical output signal related to the at least one measured variable, and a sensor substrate comprising the transducer element. The sensor substrate can be mounted on a circuit carrier such that a media channel penetrating the circuit carrier allows access to the at least one measured variable to the transducer element, wherein the circuit carrier has an electrically conductive, solderable first sealing pattern at least partially surrounding the media channel and aligned with a solderable second sealing pattern arranged on the sensor substrate such that a soldered sealing connection at least partially surrounding the media channel is formed between the first sealing pattern and the second sealing pattern.

[0009] More specifically, the transducer element may be mounted on a first surface of the sensor substrate, wherein the sensor substrate has at least one first opening, and the measured variable accesses the transducer element through the first opening. The sensor assembly may also include a circuit carrier having at least one second opening for mounting the sensor substrate, such that the first and second openings are aligned with each other, and the sensor substrate is attached to the circuit carrier with a second surface opposite to the first surface. The circuit carrier has a conductive, solderable first sealing pattern, which at least partially surrounds the opening and is aligned with a solderable second sealing pattern arranged on the second surface of the sensor substrate, such that a soldered sealing connection at least partially surrounding the first opening is formed between the first sealing pattern and the second sealing pattern.

[0010] The solder connection of the interface between the sensor substrate and the circuit carrier surrounding the channel through which the medium to be monitored must enter effectively prevents the intrusion of the medium at this interface. Thus, potential damage by moisture and harmful aggressive chemicals can be avoided. In order to safely connect the sensor substrate and the circuit carrier, both components are provided with a solderable layer, for example a layer containing metal.

[0011] According to an advantageous embodiment of the invention, the first sealing pattern arranged at the circuit carrier comprises reflow solder. Reflow soldering is a well-established technology for integrated circuit assembly and packaging. Typically, the technology is based on applying solder paste to the circuit carrier, for example by screen printing, dispensing, spraying, etc. The surface mount technology (SMT) components to be soldered to the circuit carrier are placed so that their conductive leads are in direct contact with the solder paste. The solder paste is heated until it reaches a liquid phase (is reflowed) and then cooled until the solder hardens and forms a permanent interconnection between the conductive leads of the component and the circuit carrier.

[0012] According to an advantageous embodiment, the circuit carrier further comprises at least one contact pad, and wherein the sensor substrate comprises at least one corresponding surface mount technology (SMT) terminal, which is interconnected to the contact pad. The electrical connection between the SMT terminal and the circuit carrier can advantageously be established while the sealing step is being performed. SMT components in combination with reflow soldering technology are particularly easy to use for the concept according to the invention. However, the solder seal according to the invention can also be used with any other suitable soldering technology, even for an overmolded lead frame package with an opening through the molded housing. In this case, the sensor substrate is formed by an overmolded lead frame, and a solderable second sealing pattern is arranged on the outside of the housing material.

[0013] To provide mechanical protection and / or electrical shielding, the transducer element may be at least partially surrounded by a protective cover, which is attached to the first surface of the sensor substrate.

[0014] According to some embodiments, the protective cover comprises a circular metal ring, and / or an overmolded plastic housing. In addition, a conductive or insulating cover (or lid) may be arranged to cover the transducer element. Furthermore, electronic components such as signal processing circuits and communication interfaces may also be covered and / or shielded by the protective cover. However, it must be noted that many applications of the present invention do not require a protective cover. In particular, when a ball grid array (BGA) and bump connections are used to attach sensors or MEMS, the protective cover may be omitted. The protective cover is mainly advantageous when wire bonding, etc., is present.

[0015] The principles of the present invention can be advantageously applied to all sensor assemblies in which access to a medium to be monitored must be provided and at the same time sensitive electronic components must be protected from the influence of the medium. For example, the transducer element may comprise a micro-electromechanical system (MEMS) gas sensor and / or a MEMS pressure sensor. Any other sensor assembly having a transducer that needs to be in direct contact with the medium to be monitored can of course also benefit from the sealing technology according to the present invention.

[0016] According to some embodiments, the sensor substrate comprises a ceramic chip carrier. However, it is obvious to a person skilled in the art that any other type of substrate, such as a PCB, a flexible circuit board, a lead frame, etc., may also be used according to the present invention.

[0017] According to some embodiments, the sensor assembly further comprises an inner seal, which is arranged at the interface between the sensor substrate and the transducer element, at least partially surrounding the transducer element. Such an inner seal may, for example, comprise silicone resin or the like.

[0018] The invention also relates to a method of assembling a sensor system, the method comprising the following steps:

[0019] At least one transducer element is provided, which is operable to monitor at least one measured variable and generate an electrical output signal related to the at least one measured variable, wherein:

[0020] (a) the transducer element forms a sensor substrate, or

[0021] (b) wherein the sensor substrate is mounted on a first surface of the sensor substrate, the sensor substrate having at least one first opening, and the measured variable accesses the transducer element through the first opening;

[0022] providing a circuit carrier for mounting the sensor substrate, the circuit carrier having at least one second opening and a conductive, solderable first sealing pattern at least partially surrounding the at least one second opening;

[0023] aligning the circuit carrier with the sensor substrate such that access to the at least one measured variable is permitted to the transducer element via a media channel penetrating the circuit carrier and formed by at least the second opening, and the electrically conductive solderable first sealing pattern is aligned with a solderable second sealing pattern disposed on the sensor substrate;

[0024] The welding step is performed such that a welded sealing connection at least partially surrounding the media channel is formed between the first sealing pattern and the second sealing pattern.

[0025] According to some embodiments, the transducer element is mounted on a first surface of a sensor substrate, wherein the sensor substrate has at least one first opening through which a measured variable can access the transducer element, and the circuit carrier has at least one second opening and a conductive, solderable first sealing pattern at least partially surrounding the at least one second opening. The circuit carrier is aligned with the sensor substrate such that the first opening and the second opening are aligned with each other and such that a second surface of the sensor substrate opposite to the first surface faces the circuit carrier, wherein the sensor substrate has a solderable second sealing pattern arranged on the second surface. The soldering step is performed such that a soldered, sealed connection at least partially surrounding the first opening is formed between the first sealing pattern and the second sealing pattern.

[0026] Advantageously, the soldering step comprises heating the sensor assembly so that the first sealing pattern is liquefied. Thus, the method is compatible with conventional reflow soldering techniques and the seal can be formed together with any electrical connection between the sensor assembly and the circuit carrier. In other words, the step of electrically connecting the transducer element to the electronic component arranged on the sensor substrate and forming the soldered sealing connection can be performed simultaneously. Thus, the assembly process can be shortened and facilitated. Advantageously, during the soldering step, a conductive connection is formed between at least one contact pad arranged on the circuit carrier and at least one corresponding surface mount technology (SMT) terminal arranged on the sensor substrate.

[0027] According to some embodiments, the transducer element is connected to the electronic component via at least one wire bond connection and / or at least one conductive trace arranged on the sensor substrate.

[0028] As mentioned above, the method may further comprise the step of attaching a protective cover such that it at least partially surrounds the transducer element. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The accompanying drawings are incorporated into the specification and form a part of the specification to illustrate several embodiments of the present invention. These drawings, together with the description, are used to explain the principles of the present invention. These drawings are only for the purpose of illustrating preferred and alternative examples of how to make and use the present invention, and should not be interpreted as limiting the present invention to only the embodiments shown and described. In addition, several aspects of the embodiments can be combined individually or in different combinations to form solutions according to the present invention. Therefore, the embodiments described below can be considered individually or in any combination thereof. Further features and advantages will become apparent from the following more specific description of various embodiments of the present invention, as shown in the accompanying drawings, in which the same reference numerals refer to the same elements, and in which:

[0030] Figure 1is a schematic perspective view of a sensor assembly according to a first embodiment of the present invention;

[0031] Figure 2 is based on Figure 1 A schematic top view of a sensor assembly;

[0032] Figure 3 It is along Figure 2 The cutting lines shown are based on Figure 1 A schematic cross-sectional view of a sensor assembly;

[0033] Figure 4 yes Figure 3 Details;

[0034] Figure 5 is a schematic perspective view of a sensor assembly according to another embodiment of the present invention;

[0035] Figure 6 is based on Figure 5 A schematic top view of a sensor assembly;

[0036] Figure 7 It is along Figure 6 The cutting lines shown are based on Figure 5 A schematic cross-sectional view of a sensor assembly;

[0037] Figure 8 yes Figure 7 Details;

[0038] Fig. 9 is a schematic perspective view of a sensor assembly according to another embodiment of the present invention;

[0039] Fig.10 is based on Fig. 9 A schematic top view of a sensor assembly;

[0040] Fig.11 It is along Fig.10 The cutting lines shown are based on Fig. 9 A schematic cross-sectional view of a sensor assembly;

[0041] Fig.12 yes Fig.11 Details;

[0042] Fig.13 is a schematic perspective view of a sensor assembly according to another embodiment of the present invention;

[0043] Fig.14 is based on Fig.13 A schematic top view of a sensor assembly;

[0044] Fig.15 It is along Fig.14 The cutting lines shown are based on Fig.13 A schematic cross-sectional view of a sensor assembly;

[0045] Fig.16 is a schematic cross-sectional view of a sensor assembly according to another embodiment of the present invention;

[0046] Fig.17 is based on Fig.16 A schematic perspective view of a sensor assembly;

[0047] Fig.18 is based on Fig.16 Another schematic perspective view of a sensor assembly of ;

[0048] Fig.19 is a schematic perspective view of a sensor assembly according to another embodiment of the present invention;

[0049] Fig. 20 It is along Fig. 22 The cutting lines shown are based on Fig.19 A schematic cross-sectional view of a sensor assembly;

[0050] Fig.21 is based on Fig.19 Another perspective view of the sensor assembly;

[0051] Fig. 22 is based on Fig.19 A schematic top view of a sensor assembly;

[0052] Fig.23 is based on Fig.19 Another schematic top view of a sensor assembly;

[0053] Fig.24 is a schematic perspective view of a sensor assembly according to another embodiment of the present invention;

[0054] Fig.25 is based on Fig.24 Another schematic perspective view of a sensor assembly of ;

[0055] Fig.26 is based on Fig.24 Another schematic perspective view of a sensor assembly of ;

[0056] Fig. 27 is based on Fig.24 A cross-sectional view of a sensor assembly;

[0057] Fig.28 is based on Fig.24 A top view of a sensor assembly;

[0058] Fig.29 is based on Fig.24 Another cross-sectional view of the sensor assembly;

[0059] Fig.30 is based on Fig.24 Another view of the sensor assembly;

[0060] Fig.31 is based on Fig.24 Another schematic perspective view of a sensor assembly of ;

[0061] Fig.32 is based on Fig.24 Another schematic perspective view of a sensor assembly of ;

[0062] Fig.33 is based on Fig.24 Another schematic perspective view of a sensor assembly. DETAILED DESCRIPTION

[0063] The present invention will now be further explained with reference to the accompanying drawings and first with reference to Figure 1 . Figure 1 A sensor system 100 according to a first embodiment of the invention is schematically shown in a schematic perspective view. A sensor assembly 102 is mounted on a circuit carrier 104. It must be noted that the circuit carrier 104 is not part of the sensor assembly 102 according to the invention, but is part of the sensor system 100 together with the sensor assembly 102. In the figures, the circuit carrier 104 is schematically depicted as a square piece of rigid material in order not to obscure the figures unnecessarily. However, it is clear to a person skilled in the art that the circuit carrier 104 shown may actually be only a small part of a larger entity, such as a printed circuit board (PCB) or a flexible board, which has additional electrical leads and electronic components mounted thereon.

[0064] The sensor assembly 102 includes a transducer element 106, which may be, for example, a microelectromechanical (MEMS) pressure sensor. The transducer element 106 is mounted on a sensor substrate 112. The sensor substrate 112 has a first surface 114 on which the transducer element 106 is mounted. A second surface 116 opposite to the first surface 114 faces the circuit carrier 104. The sensor substrate 112 includes a plurality of conductive leads 118, which are selectively connected to the transducer element 106 and another electronic component 120, such as a signal processing circuit and / or a communication interface. However, it is clear to those skilled in the art that the sensor substrate 112 shown may actually further include other electronic components mounted thereon, as well as an internal and / or external protective cover 138, and may be electrically connected by wire bonding, bumps, welding, etc.

[0065] Furthermore, the transducer element 106 and the further electronic component 120 are electrically connected to one another via one or more electrically conductive leads 118 and / or bonding bodies 140 .

[0066] Conductive leads 118 may be arranged on the first surface 114 and pass through the sensor substrate 112 to the second surface 116 where they are connected to terminals 122. It must be noted that for clarity, only one conductive lead 118 passing through the sensor substrate 112 is shown in the figure.

[0067] As is known in the art, such a pressure sensor may have a silicon membrane 108 carrying, for example, a piezoelectric strain gauge. The strain gauge detects the displacement of the membrane 108 due to the pressure difference between the medium acting on the two surfaces of the membrane. To this end, the medium present in the measurement volume 110 needs to have access to the membrane 108. This is ensured by a medium channel 124, which is formed by a first opening 126 penetrating the sensor substrate 112 and a second opening 128 through the circuit carrier 104. The first opening 126 and the second opening 128 are concentrically aligned to form a straight channel 124. The channel 124 does not necessarily have the same diameter along its longitudinal length.

[0068] To protect and optionally electrically shield the transducer element 106 and the electronic component 120, a protective cover 138 may be attached to the sensor substrate 112 such that it surrounds the transducer element 106, the electronic component 120, and the conductive leads 118 as long as they are arranged on the first surface 114 of the sensor substrate 112. The protective cover 138 is made of plastic, ceramic, glass, or a conductive material (e.g., metal).

[0069] According to the present invention, the interface between the sensor substrate 112 and the circuit carrier 104 is sealed around the media channel 124 by means of a solder seal 130. According to some embodiments of the present invention, a first annular solderable sealing pattern 132 and a second annular solderable sealing pattern 134 are arranged on the circuit carrier 104, and the two sealing patterns 132, 134 are soldered together. In the embodiment shown, the sealing patterns 132, 134 have a circular shape of substantially the same size and are concentrically aligned relative to each other and the media channel 124.

[0070] Of course, the sealing patterns 132, 134 do not necessarily have to be circular; they may also have a polygonal or elliptical profile. In addition, they do not have to have the same shape and size, and may also be eccentrically aligned, as long as they surround the corresponding first opening 126 and second opening 128 to form a weld seal around these openings.

[0071] According to the invention, the circuit carrier 104 comprises contact pads 136, each of which forms a solder connection with one of the terminals 122. The concept of the invention allows to form a sealed connection between the first sealing pattern 132 and the second sealing pattern 134 in the same process step in which the terminals 122 are soldered to the contact pads 136. Thus, the process steps that have to be performed when mounting the sensor substrate to the circuit carrier can additionally be used to establish a secure seal of the media channel 124, thereby protecting the electronic component 120 from any aggressive media present in the measurement volume 110. Advantageously, no further sealing materials, such as gaskets or resins, have to be procured.

[0072] The soldering step can be performed by a reflow soldering technique. In this case, the circuit carrier 104 is screen printed with a solderable precursor that forms the contact pads 136 and the first sealing pattern 132. After the sensor assembly 102 has been aligned on the circuit carrier 104 so that the solderable terminals 122 are positioned in contact with the contact pads 136 and the first sealing pattern 132 and the second sealing pattern 134 are in contact with each other, the sensor system 100 is heated until the precursor material reaches a liquid phase. After cooling, a solder connection is established, forming an electrical connection and providing a reliable seal that prevents moisture and / or aggressive chemicals from entering the interface between the circuit carrier 104 and the sensor substrate 112.

[0073] Figure 2 Shown is a reference Figure 1 FIG. 1 is a top view of an illustrated sensor system 100 . As already mentioned, the square dimensions of the circuit carrier 104 are merely due to the convenience of the graphical representation. Furthermore, it is of course also possible to arrange more than one component 120 with an electronic circuit on the sensor substrate 112 .

[0074] Figure 3 Shown along Figure 2 1-1 . As can be seen from the figure, the first opening 126 and the second opening 128 are concentrically aligned with respect to the central axis 142 to form a medium channel 124 leading from the measurement volume 110 to the transducer element 106, and which connects the measurement volume 110 to the membrane 108 fluid. The annular solder seal 130 is arranged concentrically around the central axis 142. Therefore, it surrounds the medium channel 124 and seals the interface between the circuit carrier 104 and the sensor substrate 112 to prevent the intrusion of any substance present in the measurement volume 110. However, the two openings do not necessarily have to be concentric. If they have different sizes, concentricity is not required, as long as a medium channel with a sufficiently large diameter is formed. In fact, in practice, the possibility that they are completely concentric is very small, because during the soldering process, the component 102 will always move on the substrate 104.

[0075] exist Figure 4 In the Figure 3 According to the present embodiment, the transducer element 106 is soldered to the conductive lead 118. The lead is partially arranged on the first surface 114 of the sensor substrate 112, passes through the sensor substrate 112 by means of a through hole 144 to connect to a terminal 122, which is arranged on the second surface 116 of the sensor substrate 112.

[0076] The solder seal 130 is formed between the first seal pattern 132 and the second seal pattern 134. Therefore, any intrusion of corrosive chemicals and / or moisture toward the terminal 122 and the contact pad 136 may be effectively prevented.

[0077] It is known to the person skilled in the art that there are different sensor technologies that can be used to monitor pressure. Furthermore, the principles of the invention are also applicable to any chemical sensor, such as a CO2 sensor, which has a sensitive layer arranged on the external chip surface. The invention can also be applied to any other type of sensor, such as humidity sensors, force and acceleration sensors, flow sensors, etc. The invention can also be used with optical sensors and light and sound emitting devices, which are used, for example, to measure the level or other parameters of a liquid, such as the level and properties of a urea solution in a car.

[0078] Figures 5 to 8 This alternative sensor system 100 is shown having no prior art Figures 1 to 4 The transducer element 106' of the membrane is shown. Figure 8 As can be seen from the detail shown in FIG. 1 , the transducer element 106 ′ is not electrically connected to the conductive lead 118 . It is only electrically connected via the wire bonds (preferably more than one) 140 .

[0079] All other functionality remains the same and will not be repeated here.

[0080] use Figures 1 to 8 The assembly shown in the figure may cause the problem of lack of sealing at the interface between the transducer elements 106, 106' and the upper surface 114 of the sensor substrate 112. Therefore, the present invention also proposes an optional additional sealing device 146, which is arranged at the interface between the sensor substrate and the transducer element 106", and at least partially surrounds the transducer element 106". Figures 9 to 12 This improvement is shown in more detail in .

[0081] Especially when referring to Fig.12When the internal seal 146 is formed, for example, by a silicone resin applied around the transducer element 106" after the electrical connection between the transducer element and the conductive lead 118 is established (e.g., by the solder connection 148). It will be apparent to those skilled in the art that the internal seal 146 may also be formed with Figures 1 to 8 The inner seal effectively prevents any aggressive chemicals or moisture entering from the media channel 124 from contacting the upper surface 114 of the sensor substrate 112. Therefore, corrosion and / or contamination of the inner region 150 can be effectively avoided.

[0082] Figures 1 to 12 An annular protective cover 138 is always shown. However, a closed lid 138 ′ can also be provided as a protective cover to completely close the inner area 150 . Figures 13 to 15 All other features can be compared with those of reference Figures 1 to 12 The explanations are the same and therefore will not be repeated.

[0083] Now refer to Figures 16 to 18 A further advantageous embodiment of a sensor assembly 202 according to the invention is explained.

[0084] The sensor assembly 202 comprises a transducer element 206 having a membrane 208. The membrane 208 is in contact with the medium to be measured via an opening 226. In addition, a reference opening 227 allows the other side of the membrane 208 to be in contact with a reference pressure. The transducer element 206 is attached to a lead frame 212, which serves as a sensor substrate and also provides connections to a circuit carrier ( Figures 16 to 18 Wire bonds 240 electrically connect transducer element 206 to terminal 222 .

[0085] According to the present invention, a solderable ring material 234 is attached to the underside of the lead frame 212. When the lead frame 212 is overmolded and wire bonded 240 to form the protective cover 238, the solderable surface 235 remains clean so that it can be soldered to the corresponding seal pattern ( Figures 16 to 18 not shown).

[0086] Thus, the opening 226 ensuring access of the medium to be measured to the membrane 208 is sealed at the interface between the lead frame 112 and the circuit carrier. Advantageously, the sealing can be performed in the same step as the soldering of the terminal 222.

[0087] Now refer to Figures 19 to 23 A further advantageous embodiment of the invention is explained.

[0088] Fig.19A sensor system 300 according to a further advantageous embodiment of the invention is schematically shown in a schematic perspective view. Fig. 20 A cross-sectional view of a sensor system 300 is shown. The sensor assembly 302 is mounted on a circuit carrier 304. It must be noted that the circuit carrier 304 is still not part of the sensor assembly 302 according to the present invention, but is part of the sensor system 300 together with the sensor assembly 302. In the drawings, the circuit carrier 304 is schematically depicted as a square rigid material piece in order not to unnecessarily obscure the drawings. However, it is clear to a person skilled in the art that the circuit carrier 304 shown may actually be only a small part of a larger entity, such as a printed circuit board (PCB) or a flexible board, which has additional electrical leads and electronic components mounted thereon.

[0089] Fig. 20 A sensor assembly 302 including a transducer element 306 is schematically shown, which can be, for example, a capacitive pressure sensor according to the illustrated embodiment. Such a capacitive pressure sensor can be manufactured as a ceramic pressure sensor, for example, based on low temperature (how-temperature) co-fired ceramic (LTCC) technology. LTCC is a three-dimensional ceramic technology for manufacturing different electronic modules. It is a mixture of thick film and ceramic technology. Thick film technology facilitates lateral and vertical electrical interconnections, as well as embedded and surface passive electronic components (resistors, thermistors, inductors, capacitors). Laminated ceramic technology facilitates electrical, mechanical and dielectric properties and different three-dimensional (3D) structures, such as cantilevers, bridges, diaphragms, channels and cavities. Of course, other technologies, such as high temperature co-fired ceramic (HTCC) technology, thin films on ceramics or glass, etc., can also be used.

[0090] The transducer element 306 has an active surface 315 carrying electrical connections and thick film electrodes 319. Advantageously, the opposite surface 317 of the transducer element 306 does not carry any active components, so that no protective cover is required.

[0091] The transducer element 306 is mounted on a sensor substrate 312, with the active surface 315 being arranged towards the sensor substrate 312. The sensor substrate 312 has a first surface 314, on which the transducer element 306 is mounted. A second surface 316 opposite to the first surface 314 faces the circuit carrier 304. The sensor substrate 312 comprises a plurality of conductive leads 318, which are selectively connected to the transducer element 306. However, in contrast to the previously shown embodiments, the first surface 314 does not carry any conductive leads, but only carries at least one side wall 321. Alternatively, the conductive leads 318 are arranged on the transducer element 306.

[0092] As is known in the art, the medium present in the measurement volume 110 needs access to the active surface 315, in particular the electrode 319. This is ensured by a medium channel 124, which is formed by a first opening 126 penetrating the sensor substrate 312 and a second opening 128 through the circuit carrier 304. The first opening 126 and the second opening 128 are concentrically aligned to form a straight channel 124.

[0093] According to the present invention, the interface between the sensor substrate 312 and the circuit carrier 304 is sealed around the media channel 124 by means of a solder seal 330. According to some embodiments of the present invention, a first annular solderable sealing pattern 332 is arranged on the circuit carrier 304 and a second annular solderable sealing pattern 334 is formed on the second sensor substrate, and the two sealing patterns 332, 334 are soldered together. In the embodiment shown, the sealing patterns 332, 334 have a circular shape of substantially the same size and are concentrically aligned relative to each other and the media channel 124.

[0094] Of course, the sealing patterns 332, 334 do not necessarily have to be circular; they may also have a polygonal or elliptical profile. In addition, they do not have to have the same shape and size, and may also be eccentrically aligned, as long as they surround the corresponding first opening 126 and second opening 128 to form a weld seal 330 around these openings.

[0095] According to the invention, the circuit carrier 304 comprises contact pads 336, each of which forms a soldered connection with one of the side wall terminals 322. The concept of the invention allows the sealed connection between the first sealing pattern 332 and the second sealing pattern 334 to be formed in the same process step in which the terminals 322 are soldered to the contact pads 336. Thus, the process steps that must be performed when mounting the sensor substrate to the circuit carrier can additionally be used to establish a secure seal of the medium channel 124, thereby protecting the contacts from any aggressive media present in the measurement volume 110. Advantageously, no additional sealing materials, such as gaskets or resins, have to be purchased when mounting the sensor assembly 302.

[0096] Advantageously, an optional internal seal 346 may be provided between the transducer element 306 and the sensor substrate 312. The internal seal 346 restricts the axis of the medium to be measured to only those active areas where contact is permitted.

[0097] The soldering step can be performed by a reflow soldering technique. In this case, the circuit carrier 304 is screen printed with a solderable precursor that forms the contact pad 336 and the first sealing pattern 332. After the sensor assembly 302 has been aligned on the circuit carrier 304 so that the solderable sidewall terminal 322 is positioned in contact with the contact pad 336 and the first sealing pattern 332 and the second sealing pattern 334 are in contact with each other, the sensor system 300 is heated until the precursor material reaches a liquid phase. After cooling, a solder connection is established, forming an electrical connection and providing a reliable seal that prevents moisture and / or aggressive chemicals from entering the interface between the circuit carrier 304 and the sensor substrate 312.

[0098] The additional gasket 152 can seal the underside of the circuit carrier 304. Such a gasket 152 can of course also be used for reference Figures 1 to 18 Sensor system explained.

[0099] Figures 21 to 23 Shows Fig.19 Additional views of sensor system 300 are depicted in FIG.

[0100] Now refer to Figures 24 to 33 Another advantageous embodiment of sensor system 400 is explained.

[0101] The sensor assembly 402 is mounted on a circuit carrier 404. Again, it must be noted that the circuit carrier 404 is not part of the sensor assembly 402 according to the present invention, but is part of the sensor system 400 together with the sensor assembly 402. In the accompanying drawings, the circuit carrier 404 is schematically depicted as a square piece of rigid material in order not to unnecessarily obscure the drawings. However, it is clear to a person skilled in the art that the circuit carrier 404 shown may actually be only a small part of a larger entity, such as a printed circuit board (PCB) or a flexible board. Furthermore, the circuit carrier does not have to be square, but may have any other suitable polygonal or circular (e.g. circular, elliptical) outline. As Figures 24 to 33 As shown, the circuit carrier 404 is provided with electrical leads 423 and at least one electronic component 420 , which comprises, for example, a signal processing circuit and / or a communication interface.

[0102] Furthermore, the transducer element 406 and the further electronic component 420 are electrically connected to one another via an electrically conductive lead 423 .

[0103] According to this embodiment, the transducer element 406 is formed by a ceramic sensor, for example a LTCC pressure sensor, as explained above for the transducer element 306. However, in contrast to the previous sensor system 300, as Figures 24 to 33 The sensor assembly 402 shown does not include a separate sensor substrate, but uses a LTCC substrate 412 as a substrate according to the present invention. Figures 19 to 23 Compared to the previously explained embodiments, the transducer element 406 is mounted on a circuit carrier 404 turned 180° so that the electrically conductive active surface 415 is oriented away from the circuit carrier 404. Since the transducer element is thin enough to be pressure-sensitive to the pressure difference between its two surfaces as a whole, the transducer element 406 can still monitor the pressure present in the measurement volume 110.

[0104] In order to allow the medium present in the measurement volume 110 to have access to the transducer element 406 , the media channel 124 is formed by an opening 128 through the circuit carrier 404 .

[0105] To protect and optionally electrically shield the transducer element 406, a protective cover 438 can be attached to the transducer element 406. The protective cover 438 is made of plastic, ceramic, glass, or a conductive material (e.g., metal). The protective cover 438 can be completely sealed, such as when used with a ceramic-based absolute pressure sensor. Alternatively, the protective cover 438 can also have one or more openings, such as when used with a differential or gauge pressure sensor, or for other reasons.

[0106] According to the present invention, the interface between the transducer element 406 and the circuit carrier 404 is sealed around the media channel 124 by means of a solder seal 430. According to some embodiments of the present invention, a first annular solderable sealing pattern 432 arranged on the circuit carrier 404 and a second annular solderable sealing pattern 434 arranged on the transducer 406 are formed, and the two sealing patterns 432, 434 are welded together. In the embodiment shown, the sealing patterns 432, 434 have a circular shape of substantially the same size and are concentrically aligned relative to each other and the media channel 124. As mentioned above, the two openings do not necessarily have to be concentric. If they have different sizes, concentricity is not required, as long as a media channel with a sufficiently large diameter is formed.

[0107] Of course, the sealing patterns 432, 434 do not necessarily have to be circular; they may also have a polygonal or elliptical profile. In addition, they do not have to have the same shape and size, and may also be eccentrically aligned, as long as they surround the opening 128 to form a weld seal around the opening.

[0108] According to the invention, the circuit carrier 404 comprises contact pads 436, each of which forms a soldered connection with one of the side wall terminals 422. The concept of the invention allows the sealed connection between the first sealing pattern 432 and the second sealing pattern 434 to be formed in the same process step in which the terminals 422 are soldered to the contact pads 436. Thus, the process steps that must be performed when mounting the sensor substrate to the circuit carrier can additionally be used to establish a secure seal of the media channel 124, thereby protecting the electronic component 420 from any aggressive media present in the measurement volume 110. Advantageously, no further sealing materials, such as gaskets or resins, have to be procured.

[0109] The soldering step can be performed by a reflow soldering technique. In this case, the circuit carrier 404 is screen printed with a solderable precursor that forms the contact pad 436 and the first sealing pattern 432. After the sensor assembly 402 and the electronic component 420 have been aligned on the circuit carrier 404, so that the solderable terminal 422 is positioned in contact with the contact pad 436, and the first sealing pattern 432 and the second sealing pattern 434 are in contact with each other, the sensor system 400 is heated until the precursor material reaches a liquid phase. After cooling, a solder connection is established, an electrical connection is formed, and a reliable seal is provided to prevent moisture and / or aggressive chemicals from entering the interface between the circuit carrier 404 and the sensor substrate 412 of the transducer element.

[0110] An additional gasket 152 may seal the underside of the circuit carrier 404 .

[0111] Figures 28 to 33 Shows Figures 24 to 27 In another view of sensor system 400 depicted in , gasket 152 is omitted.

[0112] Reference numerals list

[0113]

Claims

1. A sensor assembly, comprising: at least one transducer element (106, 106', 106"; 206; 306; 406), for monitoring at least one measured variable and generating an electrical output signal related to the at least one measured variable; A sensor substrate (112; 312; 406) comprising said transducer element and terminals; wherein the sensor substrate (112; 312; 406) is mountable on a circuit carrier (104; 204; 304; 404) such that a dielectric channel (124) penetrating the circuit carrier allows access to the at least one measured variable to the transducer element; The circuit carrier has an electrically conductive, solderable first sealing pattern (132; 432) which at least partially surrounds the media channel and is connected to a solderable second sealing pattern (134; 434) are aligned so that a welded sealing connection at least partially surrounding the medium channel is formed between the first sealing pattern and the second sealing pattern, wherein the first sealing pattern (132; 432) includes reflow solder, the circuit carrier (104; 204; 304; 404) also includes a contact pad (136; 436) interconnected with the terminal, and the welded sealing connection is positioned closer to the medium channel than the contact pad and the terminal and seals the medium channel relative to the contact pad and the terminal.

2. The sensor assembly according to claim 1, wherein the sensor substrate (112; 312) has at least one first opening (126, 226) and the circuit carrier (104; 204; 304; 404) has at least one second opening (128) for mounting the sensor substrate, such that the first opening and the second opening are fluidically connected to each other, the sensor substrate being attached to the circuit carrier with a second surface (116; 316) which is opposite to the first surface (114; 314) to which the transducer element is mounted; and The conductive solderable first sealing pattern at least partially surrounds the second opening and is aligned with a solderable second sealing pattern arranged on the second surface of the sensor substrate, so that a soldered sealing connection (130) at least partially surrounding the first opening is formed between the first sealing pattern and the second sealing pattern.

3. The sensor assembly of claim 2, wherein the transducer element is at least partially surrounded by a protective cover (138, 138'; 238; 438) attached to the first surface of the sensor substrate.

4. The sensor assembly according to claim 3, wherein the protective cover (138, 138'; 238; 438) is annular, and / or wherein the protective cover comprises an overmolded plastic housing, and / or wherein the protective cover comprises a cap-shaped cover.

5. The sensor assembly according to any one of claims 1 to 4, wherein the transducer element comprises a micro-electromechanical system (MEMS) gas sensor and / or a MEMS pressure sensor.

6. The sensor assembly of any one of claims 1 to 4, wherein the sensor substrate comprises a ceramic chip carrier.

7. The sensor assembly according to any one of claims 1 to 4, further comprising an inner seal (146) arranged at an interface between the sensor substrate and the transducer element and at least partially surrounding the transducer element.

8. The sensor assembly of claim 7, wherein the inner seal is formed of silicone.

9. A method of assembling a sensor system, the method comprising the steps of: At least one transducer element is provided, which is operable to monitor at least one measured variable and generate an electrical output signal related to the at least one measured variable, wherein: (a) the transducer element forms a sensor substrate, or (b) wherein the transducer element is mounted on a first surface of a sensor substrate, the sensor substrate having at least one first opening, and the measured variable accesses the transducer element through the first opening; providing a circuit carrier for mounting the sensor substrate, the circuit carrier having contact pads, at least one second opening, and a conductive solderable first sealing pattern at least partially surrounding the at least one second opening, the first sealing pattern comprising reflow solder; aligning the circuit carrier with the sensor substrate such that access to the at least one measured variable is permitted to the transducer element through a media channel penetrating the circuit carrier and formed by at least the second opening, and the electrically conductive solderable first seal pattern is aligned with a solderable second seal pattern disposed on the sensor substrate, and the contact pads are aligned with terminals disposed on the sensor substrate; The welding step is performed so that a welded sealing connection at least partially surrounding the media channel is formed between the first sealing pattern and the second sealing pattern, and the welded sealing connection is positioned closer to the media channel than the contact pad and the terminal and seals the media channel relative to the contact pad and the terminal.

10. The method of claim 9, wherein the welding step includes heating the sensor assembly such that the first sealing pattern is liquefied.

11. The method according to claim 9 or 10, further comprising the step of electrically connecting the transducer element to electronic components arranged on the sensor substrate and / or further comprising the step of attaching a protective cover such that it at least partially surrounds the transducer element.

12. The method according to claim 11, wherein the transducer element is connected to the electronic component via at least one wire bond connection and / or at least one conductive trace arranged on the sensor substrate.

13. A method according to any one of claims 9 to 12, wherein during the soldering step an electrically conductive connection is formed between the contact pad and the terminal.

14. A sensor system comprising a sensor assembly (102; 202; 302; 402) according to any one of claims 1 to 8, and a circuit carrier (104; 204; 304; 404) on which the sensor assembly is mounted.

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