DE102020108242A1 - Mounting carrier for MEMS modules - Google Patents

Abstract

The invention relates to a mounting support for MEMS assemblies, such as pressure sensors, which are exposed to harsh environmental conditions during use, comprising a MEMS mounting tube / carrier with a pressure supply for connection to a pressure source to be monitored and an MEMS pressure sensor attached to the front of the mounting tube, as well as a The carrier mounting ring surrounding the MEMS mounting tube and attached to it for receiving a circuit carrier. The aim of the invention is to create a mounting support for MEMS assemblies with improved sensory properties that can be produced at low cost. This is achieved in that the MEMS mounting tube (2) is adapted to the CTE of the MEMS pressure sensor (1) and consists of a material composite consisting of a polymer material and an inorganic component (e.g. glass or ceramic) and that the MEMS The carrier assembly support (5) surrounding the mounting tube (2) is adapted to the CTE of the PCB circuit support (4) and consists of at least one polymer material.

Description

The invention relates to a mounting support for MEMS assemblies, such as pressure sensors that are exposed to harsh environmental conditions during use, such as pressure sensors in motor vehicle applications or the like. is the case, comprising a MEMS mounting tube as part of a carrier with a pressure feed for connection to a pressure source to be monitored and a MEMS pressure sensor attached to the front of the MEMS mounting tube, as well as a carrier mounting element surrounding the MEMS mounting tube and attached to it .

MEMS (Micro-Electro-Mechanical System) modules, such as pressure sensor modules, are known in different designs from different manufacturers and contain a component carrier that is connected via a pressure feed to a source for pressure changes on the one hand and to the pressure sensor on the other hand is in turn connected via electrical connections to a circuit for signal processing / storage. The signal processing circuit is either located directly on the circuit carrier, e.g. a printed circuit board (PCB), or is housed in a separate, remote assembly.

For the detection of pressure changes, membranes are usually used which are part of the MEMS and in which one side of the membrane is exposed to the pressure changes and the other side of the membrane is subjected to a defined pressure. The movements of the membrane are converted into electrical signals, for example with the aid of a piezoelectric element that is connected to the membrane.

The common problem with these MEMS assemblies is that they can be exposed to harsh environmental conditions and, in particular, strong temperature changes that range from well below freezing point to the operating temperature of an internal combustion engine or the like. can range. These temperature changes can occur within a short time. The thermomechanical stresses that inevitably arise at the connection points as a result of the different expansion coefficients of the individual components of the module (MEMS, mounting tube, carrier mounting element) can negatively affect the service life of the MEMS modules or at least falsify the measurement result. In particular, as a result of different expansion coefficients of the individual parts connected to one another, the connection points can loosen after a long period of use.

It goes without saying that such problems are not limited to pressure sensors, but can also occur with other MEMS modules, such as temperature sensors etc., with similar effects.

So goes from the U.S. 6,148,673 A A differential pressure sensor emerges, which consists of a sensor chip with a membrane, as well as a cavity under the membrane, which is connected via a thin eutectic layer to a bonding surface of a mounting plate, the mounting plate being provided with a pressure feed below the membrane of the sensor chip. The movements of the membrane caused by the pressure changes are recorded by a piezo element that is mechanically connected to the membrane and passed on as electrical signals to a signal processing circuit.

There is a gold-germanium layer between the sensor chip and the mounting plate, the mounting plate being made of an alloy whose coefficient of thermal expansion (CTE: Coefficient of Thermal Expansion) largely corresponds to that of the sensor chip. A buffer layer is therefore not necessary in this case.

The whole arrangement is enclosed by a housing to protect it.

In the U.S. 5,600,071 A describes a sensor arrangement with an absolute pressure sensor with a similar structure in a housing, which consists of a base substrate made of a semiconductor material, such as silicon or gallium arsenide, and a cover substrate made of the same material and fastened thereon. The base substrate contains a membrane with a piezo element and a cavity underneath which is provided with a pressure connection. The base substrate and the cover substrate are connected to one another by anodic bonding or by a bonding layer made of an inorganic glass. For electrical connection with a signal processing circuit or the like. Metallic conductors are provided which extend through the housing and which are connected to corresponding contacts of the piezo element via wire bridges.

The sensor arrangement is mounted on a chip carrier with the aid of a bond layer, which comprises lead glass, a gold / silicon eutectic, a lead / tin solder, an epoxy resin, or an elastomer, etc. This compensates for the different expansion coefficients between the chip carrier and the base sub-substrate, but such a construction is quite complex.

A similar pressure sensor can also be found in JP000H10132677 A.

The invention is now based on the object of creating an improved and inexpensive mounting support (carrier) for MEMS assemblies with improved sensory properties, which can be produced cost-effectively from different materials, in which a mismatch of the thermal expansion coefficients of the individual components of the module is largely avoided.

The object on which the invention is based is achieved in a mounting support of the type mentioned in that the CTE of the MEMS mounting tube is adapted to the CTE of the MEMS pressure sensor and consists of a material composite consisting of a polymer and an inorganic or metallic component.

In a further development of the invention, a circuit carrier is attached to the carrier assembly element surrounding the MEMS assembly tube, the CTE of the carrier assembly element being adapted to the CTE of the circuit carrier and consisting of a polymer composite.

In another development of the invention, instead of the circuit board, the carrier mounting element is provided with contacts for external connections in the form of contact pins which extend through a flange, e.g. the edge of the housing, of the carrier mounting element and which surrounds the MEMS pressure sensor.

The MEMS mounting tube preferably consists of a material composite of a polymer material with ceramic or glass, or a polymer material and a metal, an adapted alloy based on FeNiCo (iron-nickel-cobalt alloy), for example, being used for the metal .

In a further development of the invention, the carrier mounting element consists of a material composite made of a polymer material, the polymer material preferably being a plastic with optimized physical-technical properties.

In a further advantageous embodiment of the invention, the connection between the MEMS mounting tube and the MEMS pressure sensor is an adhesive or soldered connection, which enables uncomplicated assembly.

In the interest of cost-effective production, the carrier assembly element is a component produced by means of injection molding, transfer molding, molding or a component produced by means of 3-D printing.

In a special development of the invention, the carrier mounting element is connected to the MEMS mounting tube by extrusion coating or pressing.

Finally, the circuit carrier surrounding the MEMS mounting tube is fastened to the carrier mounting element by means of an adhesive connection, the circuit carrier loosely surrounding the MEMS mounting tube.

The modified assembly carrier according to the invention ensures a thermo-mechanical adaptation of the MEMS assembly tube to the MEMS pressure sensor on the one hand and of the carrier assembly element to the circuit carrier on the other hand, so that mismatches at the connection points can be largely avoided, whereby in particular a falsification of the measurement results or failure of the module can be avoided.

• 1: eine schematische Darstellung eines Montageträgers für MEMS Baugruppen mit zugehörigem Schaltungsträger; und
• 2: einen Montageträger für MEMS Baugruppen mit Kontakt-Pins zur elektrischen Verbindung mit einer externen Signalverarbeitung, der zur Montage auf Oberflächen geeignet ist.

The invention is explained in more detail below using an exemplary embodiment. In the accompanying drawing figures show:

• 1 : a schematic representation of a mounting carrier for MEMS modules with associated circuit carrier; and
• 2 : a mounting support for MEMS assemblies with contact pins for electrical connection with external signal processing, which is suitable for mounting on surfaces.

1 shows a relevant mounting support for MEMS assemblies, which is the actual MEMS pressure sensor 1 includes, which is on the front side on a MEMS mounting tube 2 with a pressure feed 3 For connection to a pressure system to be monitored, such as an air conditioning system or for pressure monitoring in the brake or fuel system in the car or the like, mostly with an adhesive connection or also by soldering. The MEMS pressure sensor 1 is made of silicon and is only shown schematically. The MEMS pressure sensor 1 includes a membrane 1.1 with an associated piezo element, not shown, on one side of the membrane 1.1 , which is mechanically and flatly connected to this, a cavity 1.2 under the membrane 1.1 and an annular counter body 1.3 for mechanical decoupling. Thereby the piezo element with the membrane 1.1 is flatly connected, every movement of the membrane is 1.1 directly and completely transferred to the piezo element, which generates voltage changes as electrical output signals. The cavity 1.2 under the membrane 1.1 is in the middle of the pressure feed 3 in the mounting pipe 2 aligned and thus ensures an exact pressure measurement.

Such MEMS pressure sensors 1 are typically made entirely of silicon with the help of Si micromechanics technology, or consist of a composite with glass or silicon as a counter body 1.3 .

Around the MEMS mounting tube 2 with a circuit carrier 4th to be able to connect is a carrier mounting bracket 5 provided with the mounting tube 2 is firmly connected and surrounds this. The carrier mounting bracket 5 can be disc-shaped, ring-shaped, or otherwise. On one end face of the carrier mounting bracket 5 becomes the circuit carrier 4th usually attached by gluing. The circuit carrier 4th is used as usual to accommodate electronic assemblies for signal processing, storage, etc., which are connected to the piezoelectric element on the membrane via wire bridges (not shown) or other electrical connections of the usual connection technology 1.1 of the MEMS pressure sensor 1 are connected.

A mounting tube is usually used for a cost-effective structure 2 in conjunction with the carrier assembly support 5 made of a metal such as aluminum, which is due to the different material properties of the mounting materials of the mounting support, such as the MEMS pressure sensor 1 , the circuit carrier 4th , the mounting pipe 2 and the carrier mounting bracket 5 , the different coefficients of expansion (CTE) lead to mismatches and thus to stress (thermo-mechanical stresses) at the connection points. This stress affects the sensory properties of the MEMS pressure sensor 1 negative.

The expansion coefficients of the individual materials are classified as follows: $${\text{CTE}}_{\text{MEMS}\left(\text{silicon}\right)}<{\text{CTE}}_{\text{Ceramics}}<{\text{CTE}}_{\text{PCB}}<{\text{CTE}}_{\text{aluminum}}$$

In particular, the difference in CTEs between the MEMS pressure sensor 1 made of silicon and the mounting tube 2 made of aluminum is critically large.

A MEMS mounting tube 2 and carrier mounting brackets 5 Due to the lower CTE than aluminum, ceramic would provide better conditions for an adhesive connection to the MEMS pressure sensor 1 offer, but then would be the adhesive connection to the circuit carrier 4th , e.g. a printed circuit board (PCB) to be viewed as critical. It would also be a combination of a MEMS mounting bracket 2 and a carrier mounting bracket 5 made of ceramic several times more expensive than an aluminum carrier.

It has been shown that these problems can be eliminated cost-effectively according to the present invention, in particular through the use of suitable composite materials and material pairings of the individual components of the MEMS assembly carrier in conjunction with suitable joining means.

To adapt the different CTEs due to the MEMS pressure sensor 1 and the circuit carrier 4th To achieve this, two materials are used in combination for the remaining components of the MEMS mounting carrier, so that a thermo-mechanical adaptation to the MEMS pressure sensor 1 on the one hand and an adaptation to the circuit carrier 4th on the other hand is achieved.

To do this, the mounting pipe 2 and the carrier mounting bracket 5 made of a material composite, for example a polymer material and ceramic, or a polymer and metal.

1. a) Das MEMS-Montagerohr 2 ist dem CTE des MEMS-Drucksensors 1 angepasst und besteht aus einem Verbundwerkstoff , wie einem Polymerwerkstoff und Keramik bzw. Glas, oder einem Polymerwerkstoff und einem Metall, oder einer Legierung auf Basis FeNiCo, wobei die Geometrie des Montagerohrs 2 den Montagebedingungen für den MEMS-Drucksensor 1 entspricht; und
2. b) Der Carrier-Montageträger 5 ist an den CTE des Schaltungsträgers 4 angepasst und besteht mindestens aus einem Polymer, wobei die Geometrie des Carrier-Montageträgers 5 der konstruktiven Umgebung des Schaltungsträgers 4 bzw. des MEMS-Drucksensors 1 angepasst ist.

For the adaptation of the different CTEs of the MEMS pressure sensor 1 and the circuit board 4th two materials are used in combination, ie:

1. a) The MEMS mounting tube 2 is the CTE of the MEMS pressure sensor 1 adapted and consists of a composite material, such as a polymer material and ceramic or glass, or a polymer material and a metal, or an alloy based on FeNiCo, the geometry of the mounting tube 2 the installation conditions for the MEMS pressure sensor 1 is equivalent to; and
2. b) The carrier mounting bracket 5 is at the CTE of the circuit carrier 4th adapted and consists of at least one polymer, the geometry of the carrier mounting bracket 5 the structural environment of the circuit carrier 4th or the MEMS pressure sensor 1 is adapted.

As a polymer material, polyethylene (PE), polypropylene (PP) or the like can be used. come into use.

The MEMS mounting tube 2 The composite material described can be manufactured by injection molding, transfer molding, molding or 3-D printing, with a good connection between the MEMS mounting tube 2 and the carrier mounting bracket 5 can be achieved through a suitable mass production technology, such as overmoulding or pressing.

There is also the connection between the MEMS pressure sensor 1 and the MEMS mounting tube 2 preferably by gluing, although soldering is also possible as an alternative. Furthermore, there can be a fixed connection between the circuit carrier 4th and the carrier mounting bracket 5 take place by gluing, whereby due to the respectively adapted CTEs of the joining partners a long-lasting fixed connection, without the stress caused by CTE differences.

Between the circuit carrier 4th and the MEMS mounting tube 2 there is no mechanical connection, such as from 1 is clearly visible, but the PCB circuit carrier 4th surrounds the MEMS mounting tube 2 loose, so that no thermal-mechanical stresses can occur between these components.

2 shows a variant of a mounting support for MEMS modules, in which the carrier mounting support 5 is designed like a housing and in addition an annular flange 7th (eg housing edge), as well as with contacts for external connections in the form of contact pins 6th is provided that extend laterally outward and downward. The flange 7th stands from one end of the carrier mounting bracket 5 and surrounds the MEMS pressure sensor 1 surrounds it, which means it is better protected. The electrical connection between the connections of the MEMS pressure sensor 1 and the contact pins 6th takes place with known means of electrical connection technology, such as wire bridges or rewiring (not shown).

Otherwise, the MEMS pressure sensor includes 1 also a membrane 1.4 over a cavity 1.5 , as well as an annular counter body 1.6 .

The MEMS mounting bracket 1 after 2 is particularly suitable for mounting on surfaces.

List of reference symbols

1

MEMS pressure sensor

1.1

membrane

1.2

cavity

1.3

Counter body

1.4

membrane

1.5

cavity

1.6

Counter body

2

MEMS mounting tube

3rd

Pressure feed

4th

Circuit carrier

5

Carrier mounting bracket

6th

Contact pins

7th

Flange / housing edge

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• US 6148673 A [0006]
• US 5600071 A [0009]

Claims (10)

Mounting supports for MEMS assemblies, such as pressure sensors that are exposed to harsh environmental conditions during use, such as pressure sensors in motor vehicle applications or the like. is the case, comprising a MEMS mounting tube / carrier with a pressure feed for connection to a pressure source to be monitored and a MEMS pressure sensor attached to the end face of the mounting tube, as well as a carrier mounting ring surrounding the MEMS mounting tube and attached to it, characterized in that, that the CTE of the MEMS mounting tube (2) is adapted to the CTE of the MEMS pressure sensor (1) and consists of a material composite consisting of a polymer and an inorganic or metallic component. Mounting bracket after Claim 1 , characterized in that a circuit carrier (4) is fastened to the carrier assembly carrier (5) surrounding the MEMS assembly tube (2), the CTE of the carrier assembly carrier (5) being adapted to the CTE of the circuit carrier (4) and consisting of a Polymer composite exists. Mounting bracket after Claim 1 , characterized in that the carrier assembly support (5) instead of the circuit carrier (4) is provided with contacts for external connections in the form of contact pins (6) which extend through an annular flange (7) of the carrier assembly support (5) extend and which surrounds the MEMS pressure sensor (1). Mounting bracket after Claim 1 , characterized in that the MEMS mounting tube (2) consists of a material composite of a polymer material and ceramic or glass, or a polymer material and a metal. Mounting bracket after Claim 4 , characterized in that the metallic component of the composite material of the MEMS assembly tube (2) is an alloy based on FeNiCo. Mounting bracket after Claim 1 , characterized in that the carrier assembly support (5) consists of a material composite of a polymer material and an adapted metallic material. Mounting support according to one of the Claims 1 until 6th , characterized in that the connection between the MEMS mounting tube (2) and the MEMS pressure sensor (1) is an adhesive or soldered connection. Mounting support according to one of the Claims 1 until 6th , characterized in that the carrier assembly support (5) is an injection-molded part, an injection-molded part, or is produced by molding or by means of 3-D printing. Mounting support according to one of the Claims 1 until 8th , characterized in that the carrier assembly support (5) is connected to the MEMS assembly tube (2) by extrusion coating or pressing. Mounting support according to one of the Claims 1 until 9 , characterized in that the circuit carrier (4) surrounding the MEMS mounting tube (2) is attached to the carrier mounting ring (5) with an adhesive connection, the circuit carrier (4) loosely surrounding the MEMS mounting tube (2).

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