Patent Application
20180306646
A sensor arrangement is provided. The sensor arrangement maybe used for measuring a temperature. A method for producing a sensor arrangement is also described.
According to the prior art, for monitoring and controlling temperatures in a wide variety of applications, they are mostly measured by ceramic negative temperature coefficient thermistors (NTC), silicon temperature sensors (KTY), platinum temperature sensors (PTD) or thermocouples (TC). Of these, the NTC thermistors are most commonly used, because of the low production costs. Another advantage over thermocouples and metallic resistance elements, such as, for example, Pt elements, is the significant negative resistance temperature characteristic.
For electrical contacting of the NTC ceramic, metallic electrodes have to be applied. According to the prior art, for this purpose thick-film electrodes are applied, mostly from silver or gold pastes, by means of a screen printing process with subsequent firing.
The silver metalizations are particularly suitable for soldered connections. As a result of the increasing technological requirements with regard to new reliable ways of establishing electrical contact in connections, such as bonding and welding, another electrode is necessary, especially when bonding with gold or aluminum or copper wires, because a connection to silver does not have sufficient reliability.
In the case of gold metalizations, soldered connections with terminal wires cannot be realized. For reasons of cost, only thin gold wire is used for making bonded connections. Aluminum bonding wire connections on gold electrodes do not meet the reliability requirements.
For use in power modules, SMD NTC temperature sensors that are soldered on are mostly used. Also used as an alternative to this in the case of control modules for low power levels are NTC chips, which are mounted on the underside by means of Ag sintering paste, soldering or adhesive bonding and the upper side of which is contacted by means of a bonding wire.
As a result of the increasing requirements with respect to operating temperature and reliability, there is the requirement for NTC temperature sensors that can be applied to the mother board/the DCB board without soldered mounting and have high long-term stability and also are suitable for higher operating temperatures. At the same time, it must also be possible for such novel sensors to be produced at low cost.
Embodiments provide a sensor arrangement that has improved properties.
According to one aspect, a sensor arrangement for temperature measurement is provided. The sensor arrangement has a sensor element. The sensor element preferably comprises a ceramic sensor material. The sensor element is preferably a chip NTC thermistor. The sensor element has at least one electrode. Preferably, the sensor element has two electrodes. The electrodes are preferably arranged on different sides, for example, an upper side and an underside, of the sensor element. As an alternative to this, the electrodes may also be arranged on one side, for example, the upper side.
The sensor arrangement may include at least one contacting element. The contacting element comprises an electrically conductive material. The sensor arrangement may have precisely one contacting element. The sensor arrangement may also have more than one contacting element, for example, two contacting elements. The contacting element is designed and arranged for the wireless contacting of the sensor element. In other words, the contacting element has an outer structure/finish which makes it possible for the sensor element to be wirelessly contacted. Furthermore, the contacting element is arranged in a specific position and/or alignment which makes it possible for the sensor element to be wirelessly contacted. The relative position of the sensor element and the contacting element is chosen such that wireless contacting is made possible. Furthermore, the contacting element is designed and arranged for increasing the stability of the sensor element or the sensor arrangement. The contacting of the sensor element is preferably performed in one process step with the mounting of the sensor arrangement on a printed circuit board.
According to an exemplary embodiment, the contacting element has bearing areas. The contacting element has at least a first bearing area and at least a second bearing area. At least one of the bearing areas, that is to say a first bearing area, is arranged at least partially on an outer area of the sensor element. The first bearing area preferably lies on part of the outer area. Consequently, the contacting element serves for protecting the sensor element. Compressive loads, for example, occurring during Ag sintering, can be compensated by the contacting element. Consequently, a particularly stable sensor arrangement is provided.
According to an exemplary embodiment, the other one of the bearing areas, that is to say a second bearing area, is designed and arranged for connecting the sensor element to a printed circuit board. For example, the second bearing area of the contacting element lies on the printed circuit board or is secured on it. Wireless contacting of the sensor element is thereby achieved in an easy way.
According to an exemplary embodiment, the bearing areas have in each case a horizontally running region. The horizontally running region of the bearing areas forms an upper side and/or an underside of the contacting element. In other words, the upper side of the contacting element may have two defined horizontal regions that serve as bearing areas. As an alternative to this, the underside of the contacting element may have two defined horizontal regions that serve as bearing areas. As an alternative to this, the upper side may have at least one defined horizontal region and the underside may have at least one defined horizontal region, the horizontal regions serving as bearing areas. The bearing areas are preferably connected to one another by a vertically running region of the contacting element.
For example, the contacting element is designed in a stepped form. In particular, the contacting element may have a metal bracket. The metal bracket is preferably designed in the form of a step, so that a connection of the sensor element and the printed circuit board can be performed with the aid of the metal bracket.
As an alternative to this, the contacting element may be designed in a wavy form. In other words, the contacting element may have a curved form. The metal bracket is preferably designed in the form of a wave, so that the connection of the sensor element and the printed circuit board can be performed with the aid of the metal bracket.
In particular, the contacting element is designed such that it can lie both on a surface or outer area of the sensor element and on a further surface, for example, the surface of a mother board. In this case, the contacting element may cover the upper side of the sensor element completely or else only partially.
The chosen structural form makes it possible for the sensor element to be processed with small electrical and thermal tolerances. At the same time, the mechanical stability of the chip NTC thermistor is increased by the design with the contacting element in the form of a bracket, in that the chip NTC thermistor itself is protected during the process of the pressure sintering. The pressure sintering of the component is thereby made possible without inducing any damage such as micro cracks or the like, or even bringing about a rupturing of the component.
Provided in this way is an NTC temperature sensor with a low-cost electrode system which in addition makes wireless contacting of the NTC temperature sensor possible. The contacting of the temperature sensor is intended to be provided in one process step together with the mounting of the further components. In the case of power modules, this is contacting by means of Ag pressure sintering. The component thereby undergoes a compressive loading of up to 30 MPa or higher at temperatures of up to 300° C.
According to an exemplary embodiment, the sensor element has an upper side. The upper side of the sensor element—after being mounted on a printed circuit board—forms the surface of the sensor element that is facing away from the printed circuit board. The contacting element is at least partially connected to the upper side. The contacting element is, for example, sintered on the upper side. The contacting element is preferably pressurelessly sintered on the upper side with an Ag paste. As an alternative to this, the contacting element may however also be secured on the upper side by means of a soldering process or by adhesive bonding.
According to an exemplary embodiment, the sensor arrangement has a further contacting element. The further contacting element is designed for producing a further connection between the sensor element and the printed circuit board.
The advantages of a sensor arrangement with two contacting elements are easily achievable level compensation on the printed circuit board and improved adaptation during mounting by means of the areas (surfaces) of the contacting elements. A further advantage is the possibility of using the two areas of the contacting elements for pressing against during the Ag sintering, soldering or adhesive bonding, without in this case having to press onto the NTC chip itself.
The sensor element has an underside. The further contacting element is at least partially arranged on the underside of the sensor element. The underside of the sensor element—after being mounted on a printed circuit board—forms the surface of the sensor element that is facing the printed circuit board. The further contacting element is at least partially connected to the underside. The contacting element is, for example, sintered on the underside. The contacting element is preferably pressurelessly sintered on the underside with an Ag paste. As an alternative to this, the contacting element may however also be secured on the underside by means of a soldering process or by adhesive bonding.
According to one aspect, a method for producing a sensor arrangement is described. Preferably, the sensor arrangement described above is produced by the method. All of the properties that are disclosed with reference to the sensor element, the contacting element, the sensor arrangement or the method are also correspondingly disclosed with reference to the respective other aspects, and vice versa, even if the respective property is not explicitly mentioned in the context of the respective aspect.
The method has the following steps:
Provided in this way is an NTC temperature sensor with a low-cost electrode system which makes wireless contacting of the NTC temperature sensor possible. The contacting of the temperature sensor can be performed in one process step together with the mounting of the further components.
According to one aspect, a sensor element for temperature measurement is provided, having at least one electrode, the sensor element having an upper side, and a contacting element being arranged on the upper side, the contacting element being designed in the form of a bracket.
The sensor arrangement is explained in more detail below on the basis of exemplary embodiments and the associated figures.
The drawings described below should not be regarded as true to scale. Rather, for better representation, individual dimensions may be shown as increased or reduced in size or even distorted.
Elements that are the same as one another or perform the same function are provided with the same designations.
Electrodes 2, 3 are applied to the upper side 5 and underside 6 of the sensor 1 by means of screen printing or thin-film technology, such as, for example, sputtering.
In the application of the electrodes, a distinction can be made between thin-film and thick-film technology. The production of thin-film electrodes may be performed by sputtering or vapor deposition. In this case, in a first embodiment the base electrode consists of one layer (for example, a nickel layer, which may comprise fractions of vanadium, or a copper layer) or in a second embodiment of two layers (for example, Cr/Ni, Ti/Ni or Ni/Cu), which likewise may comprise fractions of vanadium. The base electrode may be protected by a covering layer consisting of an oxidation-inhibiting metal. In the case of a connection by means of Ag sintering with finely dispersed silver pastes, a silver covering electrode is advantageous. The thickness of the base electrode is less than 10 μm, preferably less than 3 μm, ideally less than 0.5 μm. The thickness of the covering electrode may be up to 1 μm, in exceptional cases up to 20 μm.
The production of thick-film electrodes may be performed by a screen printing process with subsequent firing. The pastes used may contain Ag or Au or any admixtures.
The electrodes 2, 3 are—as mentioned above—applied to the upper side and underside 5, 6 of the chip NTC thermistor.
The sensor arrangement 10 has a contacting element 4. Furthermore, the sensor arrangement 10 may also have further contacting elements 4′, as described in connection with
In particular, the contacting element 4 is arranged on the upper side 5 of the sensor 1. The contacting element 4 lies at least partially on the electrode 2, which is arranged on the upper side 5.
According to this exemplary embodiment, the contacting element 4 takes the form of a metal bracket. In particular, the contacting element 4 is designed in a stepped form. However, it is also conceivable to give the contacting element 4 other forms, for example, a curved form of the contacting element 4.
In any event, the contacting element 4 must have a first bearing area 4a and a second bearing area 4b. The bearing areas 4a, 4b are formed on the same side, for example, an underside, of the contacting element 4. As an alternative to this, the bearing areas 4a, 4b may also be formed on different sides, that is to say the upper side and the underside of the contacting element 4.
In this exemplary embodiment, the bearing areas 4a, 4b are designed as horizontal portions of the underside of the contacting element 4. The bearing areas 4a, 4b are connected to one another by a vertical web 4c. The upper side, opposite from the underside of the contacting element 4, is designed correspondingly. That is to say that the upper side of the contacting element also has two horizontal regions and a vertical web arranged in between.
The first bearing area 4a lies on the upper side 5 of the sensor element 1. In particular, the first bearing area 4a covers at least partially the electrode 2 arranged on the upper side 5. The contacting element 4 is pressurelessly sintered on the upper side 5 of the chip NTC thermistor with an Ag paste. There is alternatively also the possibility of mounting the contacting element 4, for example, the metal bracket, by means of a soldering process or by adhesive bonding.
The second bearing surface 4b lies, for example, on a printed circuit board or mother board or a DCB board 11 (see
The contacting of the sensor 1 with respect to the DCB board 11 or the mother board may be performed by means of Ag sintering, soldering or adhesive bonding, the chip NTC thermistor 1 being placed onto one electrode pad and the contacting element 4 being placed onto a further electrode pad. The contacting of the sensor 1 by means of the contacting element 4 is consequently provided in one process step together with the mounting of the further components. In this exemplary embodiment, the chip NTC thermistor with the contacting element 4 consequently consists substantially of a chip NTC thermistor, which is contacted by a metal bracket on the upper side 5. Apart from the contacting with respect to the board, the contacting element 4 serves as protection for the chip NTC thermistor 1 during the Ag pressure sintering.
For particularly closely toleranced resistances at nominal temperature, the resistance of the individual components can be set by an additional trimming process. In this case, ceramic material or electrode material is partially removed, for example, by laser cutting, grinding or sawing, in such a way that the resistance is adapted by changing the geometry.
The mounting of the metal bracket is performed after the adaptation of the resistance. The sensor 1 may—as described above—be sintered under pressure onto the mother board/the DCB board. Contacting of the sensor 1 with respect to the conductor tracks is also possible furthermore by adhesive bonding or soldering. The direct contacting in one process step means that further contacting, for example, by bonding, is no longer required. The chip NTC thermistor 1 can accordingly be provided with the metal bracket in a wireless mounting operation.
The chosen structural form makes it possible for a component to be processed with small electrical resistance tolerances. At the same time, the mechanical stability of the thermistor is increased by the design with the metal bracket, in that the chip NTC thermistor itself is protected during the process of the pressure sintering. The pressure sintering of the component is thereby made possible without inducing any damage such as micro cracks or the like, or even bringing about a rupturing of the component.
There follows a description of the production of the sensor arrangement 10 by way of example.
In a first step, the production of NTC powder is performed. This comprises initial weighing, wet pre-grinding, drying, screening, calcining, wet after-grinding, drying and screening.
In a further step, the production of NTC sheets is performed. After that, the stacking and pressing of the green sheets is performed. This is followed by decarburizing of the stacked and pressed green sheets.
Subsequently, the sintering of the decarburized substrates is performed. In a further step, Ni/Ag thin-film electrodes are applied on both sides, as already stated further above.
After that, the electrical measuring of the resistances of the individual substrates at nominal temperature is performed. This is followed by the substrates being individually separated into chip NTC thermistors on the basis of the measurement data obtained in advance.
The resistance of the thermistor may be set on the one hand by means of the sintering parameters/ceramic composition and on the other hand by means of the chip geometry. Before the individual separation of the substrates, their overall resistance at nominal temperature is determined. On the basis of the measurement data obtained in advance, the geometry of the respective chip NTC thermistor is defined.
The final geometry is produced by a cutting process. In the case of very closely toleranced resistances, a trimming process may be performed for setting the resistance at nominal temperature by partial laser ablation.
A visual inspection and random control measurement follow. After that, the metal bracket is applied, as described above. In particular, the mounting of the metal bracket is performed after adaptation of the resistance. Lastly, a visual inspection and random control measurement are once again performed.
As a difference from the sensor arrangement 10 according to
As a difference from the contacting element described in connection with
The further contacting element 4′ is arranged such that it's first bearing area 4a′ at least partially lies on an underside 6 of the sensor 1. In this exemplary embodiment, a third bearing area 8, opposite from the first bearing area 4a′, lies, for example, on the printed circuit board or the DCB board 11. The third bearing area 8 is arranged here on the upper side of the contacting element 4′. As an alternative to this, a partial region of the first bearing area 4a′ may also lie on the DCB board 11 or an electrode pad 12a (see
The description of the subjects specified here is not restricted to the individual specific embodiments. Rather, the features of the individual embodiments can—as far as technically feasible—be combined with one another in any desired manner.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2015 118 720.5 | Nov 2015 | DE | national |
| 10 2016 101 246.7 | Jan 2016 | DE | national |
This patent application is a national phase filing under section 371 of PCT/EP2016/074963, filed Oct. 18, 2016, which claims the priority of German patent application 10 2015 118 720.5, filed Nov. 2, 2015 and German patent application 10 2016 101 246.7, filed Jan. 25, 2016, each of which is incorporated herein by reference in its entirety.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2016/074963 | 10/18/2016 | WO | 00 |
