DE102014213218A1 - Sensor with sacrificial anode - Google Patents

Abstract

The invention relates to a sensor (14) for detecting a physical encoder field (32, 38) dependent on a physical variable (16) to be measured, comprising: - a leadframe (48) with a placement island (58), an interface (54) and at least one of the interface (54) to the Bestückinsel (58) leading conductor track (62), - on the Bestückinsel (58) of the lead frame (48) carried sensor circuit (46) for detecting the encoder field (32, 38) and for outputting a from the encoder field (32, 38) dependent sensor signal (26, 28) via the interface (54), and - a bonding wire (50) for contacting the sensor circuit (46) with the conductor track (62) of the leadframe (48), - an electrical contacting layer (56) connected to the conductor track (62) of the leadframe (48) for electrically connecting the bonding wire (50) to the leadframe (48), and - an intermediate layer (64) carried on the conductor track (62) of the leadframe (48) , on which of the conductor track (62) of the leadf 48), wherein the intermediate layer (64) has an electronegativity which is greater than an electronegativity of the contacting layer (56) and of the leadframe (48).

Description

The invention relates to a sensor for detecting a dependent of a physical quantity to be measured physical encoder field.

From the WO 2010/037 810 A1 a sensor with a sensor circuit is known, which is set up to output a dependent of a physical quantity to be measured physical encoder field dependent on the physical quantity to be measured sensor signal.

It is an object of the invention to improve such sensors.

The object is solved by the features of the independent claims. Preferred developments are the subject of the dependent claims.

According to one aspect of the invention, a sensor for detecting a physical encoder field dependent on a physical variable to be measured comprises a leadframe with a placement island, an interface and at least one conductor track leading from the interface to the placement island, a sensor circuit carried on the placement island of the leadframe for detecting the Encoder field and for outputting a sensor field dependent on the sensor signal via the interface, and a bonding wire for contacting the sensor circuit with the conductor track of the leadframe, an electrically connected to the conductor track of the leadframe contacting layer for electrically connecting the bonding wire to the leadframe and one on the conductor track of the leadframe supported intermediate layer, on the seen from the conductor track of the lead frame, the contacting layer is supported, wherein the intermediate layer has an electronegativity, which is greater than an electronegativity of Kontaktierschi and the leadframe.

The specified sensor is based on the consideration that the contacting layer is necessary when electrically connecting the sensor circuit to the conductor track of the leadframe via a bonding wire as a connecting element to ensure a sufficiently high mechanical strength of the bonding wire on the leadframe, so that it does not come back from the leadframe in hindsight solves and the electrical connection between the sensor circuit and conductor is interrupted.

The leadframe should be resistant to certain expected environmental impacts such as contaminated liquids or gases. For example, in a vehicle, it may be necessary to have the leadframe resistant to sulfur contaminated liquids or gases. However, this has the disadvantage that the leadframe in its electronegativity can not be formed completely independently of the contacting layer. Therefore, if contact with sulfur-contaminated moisture penetrates into the sensor, the contacting layer could be destroyed by conversion to sulfides or other sulfur compounds, which would then result in failure of the sensor because the mechanical and thus electrical contact between the bonding wire and leadframe of the leadframe interrupts ,

Here, the specified sensor attacks with the consideration of decoupling the contacting layer via a sacrificial anode layer in the form of the intermediate layer from the leadframe. With this sacrificial anode layer, the chemical properties of the contacting layer are independent of the material of the leadframe. The sacrificial anodic layer has the greatest electronegativity in the composite and is thus the first to be attacked by the penetrating moisture. The contacting layer then remains longer, whereby the life of the sensor can be noticeably increased.

The electronegativity of the contacting layer can then be chosen completely freely, ie also smaller than the electronegativity of the leadframe.

In a particular embodiment, the specified sensor comprises a dirt mass enveloping at least the intermediate layer and the contacting layer on the conductor track. This protective compound is to protect the sensor from environmental influences, such as the above-mentioned moisture. Mechanical overloading, which may be caused by temperature changes and / or tensile stresses on the conductor track of the lead frame, for example, can lead to a break in the connection between the protective ground and leadframe, so that forms a gap between the leadframe and the protective ground, the Kontaktierpin for previously mentioned liquid exposed to the outside. The intermediate layer acting as a sacrificial anode, however, protects the contacting layer and ensures a sufficiently long service life thereof.

The intermediate layer acting as a sacrificial anode should at least in this area have as large a surface as possible, in which the penetrating most likely occurs. For this reason, in a particular development of the specified sensor, the intermediate layer at least partially protrudes in front of the contacting layer in order to ensure the largest possible surface area.

In a preferred development, the intermediate layer seen in a sectional plane between the intermediate layer and the contacting layer may alternatively or additionally be formed at least as large as the contacting layer. This ensures that initially the intermediate layer is actually attacked by the penetrating moisture before the penetrating moisture attacks the contacting layer.

In a particularly preferred development, the intermediate layer should be seen in a sectional plane between the intermediate layer and the Kontaktierschicht but formed larger surface than the Kontaktierschicht, because a correspondingly large sacrificial layer surface provides an increased reaction surface and thus improved protection of Kontaktierschicht.

In another embodiment of the specified sensor, the intermediate layer is formed thinner seen normal to a sectional plane between the intermediate layer and the Kontaktierschicht, as the Kontaktierschicht, whereby the specified sensor is designed to save space.

The material used may be silver for the contact layer, a copper alloy or an iron-nickel alloy for the leadframe, and copper for the intermediate layer.

The indicated sensor may be an airbag acceleration sensor, a wheel speed sensor or an inertial sensor for a vehicle.

In accordance with another aspect of the invention, a vehicle includes a specified sensor.

The above-described characteristics, features and advantages of this invention, as well as the manner in which they are achieved, will become clearer and more clearly understood in connection with the following description of the embodiments, which will be described in connection with the drawings, wherein:

1 a schematic view of a vehicle with a vehicle dynamics control,

2 a schematic representation of an inertial sensor in the vehicle of 1 .

3 an embodiment of the inertial sensor of 2 in a schematic sectional view,

4 the inertial sensor of the 3 on a circuit board in a schematic side view, and

5 a section of the inertial sensor of 4 demonstrate.

In the figures, the same technical elements are provided with the same reference numerals and described only once.

It will open 1 Reference is made to a schematic view of a vehicle 2 with a known vehicle dynamics control shows. Details of this driving dynamics control, for example, the DE 10 2011 080 789 A1 be removed.

The vehicle 2 includes a chassis 4 and four wheels 6 , Every bike 6 Can be fixed on the chassis 4 fixed brake 8th opposite the chassis 4 slowed down to a movement of the vehicle 2 to slow down on a road, not shown.

It may happen in a manner known to those skilled in the art that the wheels 6 of the vehicle 2 lose their grip and get the vehicle 2 even moved away from a given example by a steering wheel not shown steering trajectory by understeer or oversteer. This is avoided by known control circuits such as ABS (antilock braking system) and ESP (electronic stability program).

In the present embodiment, the vehicle 2 for speed sensors 10 at the wheels 6 on that one speed 12 the wheels 6 to capture. Further, the vehicle points 2 an inertial sensor 14 on, the below driving dynamics data 16 called inertial data of the vehicle 2 detects, for example, a pitch rate, a roll rate, a yaw rate, a lateral acceleration, a longitudinal acceleration and / or a vertical acceleration of the vehicle 2 may include.

Based on the recorded speeds 12 and vehicle dynamics data 16 can be a regulator 18 in a manner known to those skilled determine whether the vehicle 2 slips on the road or even deviates from the above-mentioned predetermined trajectory and correspond with a known controller output signal 20 to react to that. The regulator output signal 20 can then be from a control device 22 to be used by means of actuating signals 24 Actuators, like the brakes 8th to drive, which respond to the slippage and the deviation from the given trajectory in a conventional manner.

The regulator 18 For example, in a known motor control of the vehicle 2 be integrated. Also, the controller can 18 and the actuator 22 as a common Control device formed and optionally be integrated into the aforementioned engine control.

In order to simplify the following explanations, it should be understood in a non-limiting manner that the inertial sensor 14 as driving dynamics data 16 in the 2 indicated lateral acceleration 26 on the vehicle as well as the yaw rate 28 captured, with which the vehicle 2 turns around its vertical axis because they are usually used in the aforementioned stability program.

Although the invention is based on the inertial sensor 14 explained in more detail, however, the invention to any sensors, such as the aforementioned speed sensors 10 be applied.

Below this becomes a possible principle for the inertial sensor 14 based on 2 and 3 explained in more detail.

For detecting the lateral acceleration 26 is in the inertial sensor 14 a lateral accelerometer 30 arranged. The lateral accelerometer 30 is a physical donor field in the form of a centrifugal force field 32 exposed to the lateral accelerometer 30 acts and with the lateral acceleration to be detected 26 on the vehicle 2 accelerated. The detected lateral acceleration 26 is then connected to a signal conditioning circuit 34 output.

For detecting the yaw rate 28 is in the inertial sensor 14 a Coriolis accelerometer 36 arranged. The Coriolis accelerometer 36 is a physical encoder field in the form of a Coriolis force field 38 exposed. In response to the Coriolis force field 38 gives the Coriolis accelerometer 36 a transmitter signal 40 out, then in an optionally still to Coriolisbeschleunigungsmessaufnehmer 36 associated evaluation device 42 in the yaw rate 28 can be converted. An example, like the yaw rate 28 based on a Coriolis force field 38 can be detected is in the document DE 10 2010 002 796 A1 described why it should be omitted here for the sake of brevity. Also the detected yaw rate 28 is sent to the signal conditioning circuit 34 output.

In the signal conditioning circuit 34 can the thus detected lateral acceleration 26 and yaw rate 28 be reworked, for example, to reduce the noise band gap and to increase the signal strength. The thus processed lateral acceleration 26 and yaw rate 28 can then go to an interface 44 output, then the two detected signals as driving dynamics data 16 to the controller 18 sends. This interface 44 could for example be based on the PSI5 standard or the CAN standard.

In the present embodiment, the two sensors form 30 . 36 and the signal conditioning circuit 34 a sensor circuit 46 out on a as a leadframe 48 worn circuit carrier is carried and interconnected. If necessary, not on the leadframe 48 realizable interconnections can here via electrical wires in the form of bonding wires 50 will be realized. the interface 44 can in the signal conditioning circuit 34 integrated and as an application-specific integrated circuit, hereafter ASIC 34 (Engl.: Application-specific integrated circuit) called trained.

The sensor circuit 46 may also be of a mechanical decoupling material 51 , also Globetop-mass 51 be enveloped in the form of a silicone material, which in turn together in a as injection molding material 52 trained protection mass 52 , such as a thermoset in the form of an epoxy resin 52 can be encapsulated.

Finally, stand out from the inertial sensor 14 appropriate contact options, as in 2 shown legs for making electrical contact with a circuit such as the regulator 18 starting as the interface 54 to a cable, plug or parent circuit, not shown, can be used.

It will open 4 and 5 Reference is made in which a development of the inertial sensor 14 is shown.

In the context of the present embodiments, the entire sensor circuit 46 as a single block to simplify the following illustrations.

The contacting of the sensor circuit 46 and the bonding wires 50 on the leadframe 48 takes place in the context of the present embodiment via a contact layer 56 , This can be formed, for example, of silver. Are the bonding wires 50 made of gold, so does the silver bonding layer 56 a stable electrical and mechanical connection of the bonding wires 50 on the leadframe 48 for sure.

The sensor circuit 46 in contrast, on the silver contact layer 56 via a contact adhesive layer 58 mechanically held and electrically contacted.

To the leadframe 48 and especially the interface 54 To protect against weathering and other external influences, the leadframe should 48 be made of a material that withstands these external influences. Experience has shown that the inertial sensor 14 in use in the above vehicle 2 usually exposed to sulphurous liquids or gases. These sulphurous liquids or gases must be the leadframe 48 can withstand and must not decompose. Therefore, the leadframe becomes 48 mainly made of copper alloys or iron-nickel alloys that can not be attacked by the sulfur-containing gases and liquids.

The silver of the contacting layer faces such alloys 56 However, a greater electronegativity, which causes the sulfur-containing gases and liquids, the silver of the contacting layer 56 into silver sulfides or other sulfur compounds, whereby the electrical contact of the bonding wire 50 destroyed with the leadframe. In particular, this can occur if due to mechanical over-utilization, eg as a result of temperature changes or tensile forces on the leadframe 48 , the protective compound 52 breaks and a gap 60 between lead frame 48 and protective measures 52 arises. In this gap 60 can sulfur contaminated liquid to the bonding site 62 penetrate, where the bonding wire 50 on the silver contact layer 56 electrically contacted.

To avoid this, it is proposed in the context of the present embodiment, between the silver contacting layer 56 and the leadframe 48 an intermediate layer 64 as a sacrificial anode in front of the silver contact layer 56 is attacked. This requires the intermediate layer 64 have an electronegativity that is greater than the electronegativity of the leadframe 48 and the silver contact layer 56 is. This is achieved in the context of the aforementioned materials characterized when the intermediate layer 64 is formed as a copper layer. The intermediate layer 64 decoupled the leadframe 48 from the silver contact layer 56 and allows the chemical properties of the leadframe to be matched to contaminated gases and liquids entering the sensor without relying on the silver contacting layer 56 To take consideration.

As in 5 on the basis of a section 66 from the 4 shown, the intermediate layer should be 64 in this case with respect to the silver contacting layer 56 a cantilever 68 in the context of which the intermediate layer 64 in a plan view of the silver contacting layer 56 jumps out of this. This overhang 68 may be formed in some areas, but it may also be completely around the silver contacting layer 56 run, as in 5 shown. This is the surface 70 the intermediate layer 64 parallel to the cutting plane 72 between the silver contact layer 56 and the intermediate layer 64 is formed larger than the corresponding surface of the silver-contacting layer 56 , whereby a larger chemical reaction surface is provided, with the formed as a sacrificial anode intermediate layer 56 can work. The cantilever 68 should be at least as wide as a layer thickness 74 the silver contact layer.

On the other hand, however, a layer thickness 76 the intermediate layer 64 be thinner than the corresponding layer thickness 74 the silver contact layer 56 ,

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been 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.

Cited patent literature

• WO 2010/037810 A1 [0002]
• DE 102011080789 A1 [0025]
• DE 102010002796 A1 [0035]

Claims (10)

Sensor ( 14 ) for detecting a physical quantity to be measured ( 16 ) dependent physical encoder field ( 32 . 38 ), comprising: a leadframe ( 48 ) with a placement island ( 58 ), an interface ( 54 ) and at least one of the interface ( 54 ) to the placement island ( 58 ) leading track ( 62 ), - one on the Bestückinsel ( 58 ) of the leadframe ( 48 ) worn sensor circuit ( 46 ) for detecting the encoder field ( 32 . 38 ) and for issuing one from the donor field ( 32 . 38 ) dependent sensor signal ( 26 . 28 ) via the interface ( 54 ), and - a bonding wire ( 50 ) for contacting the sensor circuit ( 46 ) with the conductor track ( 62 ) of the leadframe ( 48 ), - one electrically to the conductor track ( 62 ) of the leadframe ( 48 ) bonded contacting layer ( 56 ) for electrically connecting the bonding wire ( 50 ) to the leadframe ( 48 ), and - one on the track ( 62 ) of the leadframe ( 48 ) supported intermediate layer ( 64 ), on the of the conductor track ( 62 ) of the leadframe ( 48 ) seen the contacting layer ( 56 ), wherein the intermediate layer ( 64 ) has an electronegativity which is greater than an electronegativity of the contacting layer ( 56 ) and the leadframe ( 48 ). Sensor ( 14 ) according to claim 1, wherein the electronegativity of the contacting layer ( 56 ) is smaller than the electronegativity of the leadframe ( 48 ). Sensor ( 14 ) according to claim 1 or 2, comprising at least the intermediate layer ( 64 ) and the contacting layer ( 56 ) on the track enveloping soil ( 52 ). Sensor ( 14 ) according to any one of the preceding claims, wherein the intermediate layer ( 64 ) at least partially in front of the contacting layer ( 56 ) ( 68 ). Sensor ( 14 ) according to any one of the preceding claims, wherein the intermediate layer ( 64 ) in a sectional plane ( 72 ) between the intermediate layer ( 64 ) and the contacting layer ( 56 ) is formed at least as large area as the contact layer ( 56 ). Sensor ( 14 ) according to any one of the preceding claims, wherein the intermediate layer ( 64 ) in a sectional plane ( 72 ) between the intermediate layer ( 64 ) and the contacting layer ( 56 ) seen larger ( 70 ) is formed, as the contacting layer ( 56 ). Sensor ( 14 ) according to any one of the preceding claims, wherein the intermediate layer ( 64 ) normal to a section plane ( 72 ) between the intermediate layer ( 64 ) and the contacting layer ( 56 ) seen thinner than the Kontaktierschicht ( 56 ). Sensor ( 14 ) according to one of the preceding claims, wherein the contacting layer ( 56 ) is a silver layer. Sensor ( 14 ) according to one of the preceding claims, wherein the leadframe ( 48 ) is formed of a material having a copper alloy or an iron-nickel alloy. Sensor ( 14 ) according to any one of the preceding claims, wherein the intermediate layer ( 64 ) is a copper layer.

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