Patent Description:
To be able to sense a physical parameter of a probe, the sensing element of certain sensors need to be in a safe and reliable physical contact with the probe. This is particularly the case for thermal sensors that comprise a temperature sensing element mount on a printed circuit board that is encapsulated in a housing. They are widely used to determine the temperature of a probe or device. For instance, thermal sensors find their application in vehicles to measure the temperature of various parts. As an example, thermal sensors are used to measure the temperature of a windscreen to be able to preview the risk of fogging or icing and to provide suitable control signals to the air condition.

To function properly a stable thermal contact is needed between the temperature sensing element of the thermal sensor and the surface to be temperature probed. In the prior art sensor devices, this is achieved using additional parts such as thermally conductive pads attaching the sensor to the surface, or flexing elements, like springs, that push the temperature sensing element against the surface to be measured. <CIT> discloses a PCB (<NUM>) supporting a temperature or pressure sensor (<NUM>). When the PCB is mounted on a holder (<NUM>), the sensor is pushed against the surface of the object (<NUM>) to be measured.

Starting therefrom, it is the object of the present invention to provide an alternative solution ensuring the contact of a sensor with the surface to be probed which does not need an additional part. It is, in particular, the object of the present invention to provide an alternative solution ensuring the contact of a sensor with the surface to be probed which does not need an additional part.

This object is achieved with the sensor according to claim <NUM>.

The object is in particular achieved with a temperature sensor comprising the printed circuit board wherein the physical parameter sensing element is a temperature sensing element. By providing a flexible linking portion that is part of the printed circuit board itself, it is no longer necessary to provide additional parts to ensure a reliable contact, e.g. thermal contact in the case of a temperature sensor according to the invention. This reduces the bill of material as well as the manufacturing costs. The flexible linking portion allows a movement of the free end portion with respect to the second region, in particular in the plane of the printed circuit board. This resilience can be used to ensure securely the contact with a surface to be sensed. In particular, this resilience can be used to ensure securely the thermal contact with a surface to be temperature sensed.

According to an embodiment, the printed circuit board can comprises a cutout region between the first region and the second region to form the flexible linking portion. By cutting out a part of the printed circuit board between the first and second region, the printed circuit board presents a mechanically weakened area. Due to the elastic properties of the material of the printed circuit board, the mechanically weakened area allows a flexing movement of the first region with respect to the second region, in particular in the plane of defined by the main surface of the printed circuit board. Preferably, the cut out is realized such that flexible linking portion comprises area with a concavely rounded shape to facilitate the flexing movement of the first region with respect to the second region. According to one example, the printed circuit board can be made of the so called FR4 epoxy laminate (Flame retardant <NUM>) which is commonly used, but could also be of any other suitable material like phenolic resins. The dimensions of the cutout will be chosen such that the desired resilience for a given thickness of the printed circuit board and definition of the layers of the circuit board is obtained such that a predetermined plating force is observed taking into account the vibratory conditions of the application. According to the invention, the first region can comprise a metallized edge region, preferably thermally connected to the temperature sensing element. The metallized edge region allows a reliable thermal contact with the surface to be temperature probed.

According to an embodiment, the metallized edge region can be on a side of the first region facing away from the second region. By arranging the metallized edge region on the side away from the second region, the access to the metallized edge region is simplified so that a reliable thermal contact can be realized with any object.

According to an embodiment, the metallized edge region can be positioned at an extremity of the first region opposite the flexible linking portion. At the extremity of the first region opposite the flexible linking portion, the elastic forces occurring following a deformation are higher than in regions closer to the flexible linking portion.

According to the invention, the first region comprises a first protruding region in the plane of the printed circuit board that is protruding away from the second region and comprises the metallized edge region. Providing such a protruding portion can further improve the contact with a surface to be probed, in particular the thermal contact with a surface to be temperature probed.

According to an embodiment, the first region can have a zigzag shape. Such a shape can further improve the spring like behavior of the first region with respect to the second region.

According to an embodiment, the temperature sensor can comprise a thermistor, in particular a NTC provided on the first region, in particular on the first protruding region. In this arrangement, an improved thermal contact with the surface to be temperature probed can be realized.

According to an embodiment, the thermistor can be electrically connected to one or more electrical components provided on the second region of the printed circuit board. By spatially separating the thermistor from the other electrical components of the temperature sensor, the temperature sensing is less disturbed by heat of the electrical components.

According to an embodiment, the first region can comprise a second protruding region in the plane of the printed circuit board that is protruding towards the second region. The second protruding region forms a stopping element that limits the extent of the possible movement of the first region with respect to the second region when the stopping element abuts against the second region.

According to an embodiment, the first region of the printed circuit board can extend at least partially through and beyond a through hole in a housing enclosing the remainder of the printed circuit board. Once the sensor is mount to a surface to be sensed, e.g. the temperature sensor mount to the surface to be temperature sensed, the part of the first region that extends beyond the through hole will ensure a reliable thermal contact.

According to an embodiment, the metallized edge region can extend at least partially beyond the through hole in the housing. Thus, a reliable contact, in particular thermal contact, can be ensured.

According to an embodiment, the flexible linking portion can be configured to allow a movement of the first region with respect to the second region in the plane defined by the printed circuit board. The flexible material properties of the printed circuit board can be used to realize a reliable contact with a surface to be probed without the need of any additional element. It is in particular possible to realize a reliable thermal contact with a surface to be temperature probed when using the invention for a temperature sensor.

According to an embodiment, the length of the first region, extending from the flexible linking portion to the extremity of the free end portion, can have a length larger than the width of the first region at the intersection with the flexible linking portion. This further improves the flexibility of the first region and therefore the reliability of contact.

According to an embodiment, the first region can comprise an arm region between the flexible linking portion and the free end portion, wherein the arm region has a tapered shape such that its width at the intersection with the flexible linking portion is larger than its width at the intersection with the free end portion. The tapered shape can distribute the mechanical stress over the extension of the arm region.

The object of the invention is also achieved with a printed circuit board for use in a sensor characterized in comprising a first and second region linked by a flexible linking portion. With such a printed circuit board, all technical effects and advantages as described above can be achieved.

The object of the invention is also achieved with the device according to claim <NUM>, comprising a sensor according to any one of the realizations as described above wherein the sensor is mount to a surface of an element of the device, characterized in that the housing of the sensor is positioned such with respect to the surface of the element that the first region is in a preloaded state and thereby pressed against the surface of the element. Using the inventive sensor it thus becomes possible to realize reliably a contact with the surface of the element without needing an additional element besides the printed circuit board shaped according to the invention. This is particularly advantageous when probing the temperature when the sensor is configured as a temperature sensor using a temperature sensing element.

The invention may be understood by reference to the following description taken in conjunction with the accompanying figures, in which reference numerals identify features of the invention.

<FIG> illustrates a first embodiment of a sensor according to the invention. The invention will be described in detail for temperature sensor <NUM>. Nevertheless, the concept of ensuring a reliable contact between the senor and the surface to be probed can be applied to other kinds of sensors sensing one or more other physical parameters.

The temperature sensor <NUM> comprises a printed circuit board <NUM> positioned inside a housing <NUM>. <FIG> illustrates a view onto one main surface of the printed circuit board <NUM> placed into the housing <NUM> which is illustrated with a cut view through its lateral walls 3a. In <FIG>, the temperature sensor <NUM> is not yet mounted to an object to be temperature sensed.

The printed circuit board <NUM> comprises a first region <NUM> and second region <NUM> which are spaced apart from each other on one side and linked together via a flexible linking portion <NUM>. According to the invention, the flexible linking portion <NUM> is an integrally part of the printed circuit board <NUM>.

To form the flexible linking portion <NUM>, a cut-out region <NUM> is provided in the printed circuit board <NUM>. The cut-out region <NUM> is realized such that the flexible linking portion <NUM> comprises an area <NUM> with concavely rounded shape.

The first region <NUM> comprises a head portion <NUM> and an arm portion <NUM> linking the head portion <NUM> at the end of the first region <NUM> to the flexible linking portion <NUM>. The head portion <NUM> at the extremity of the first region <NUM>, also called the free end portion, is thus opposite to the flexible linking portion <NUM>.

The cut-out region <NUM> mechanically weakens the printed circuit board <NUM> and provides the necessary elasticity so that the head portion <NUM> at the extremity of first region <NUM> can be moved relatively to the second region <NUM> in the plane formed by the printed circuit board <NUM>. In other words, the first region <NUM> behaves like a spring, indicated by arrow <NUM>. The mechanical principle can be realized with many materials. The printed circuit board can e.g. be made of the widely used FR4 epoxy laminate (Fiber Reinforced <NUM>), but could also be made of any other suitable material like phenolic resins. The dimensions of the cut out region <NUM> and the material used determine the resulting forces and the vibratory resistance. The Young modulus of the material is preferably in a range of 2GPa to 300GPa. The needs of heat dissipation and conduction can also be taken into account.

The head portion <NUM> comprises a temperature sensing element <NUM>, e.g. in the form of a thermistor, like a negative temperature coefficient (NTC) thermistor.

The head portion <NUM> has a first protruding region <NUM> in the plane of the printed circuit board that is protruding away from the second region <NUM> and comprises a metallized edge region <NUM>. The temperature sensing element <NUM> is in thermal contact with the metallized edge region <NUM>, which is facing away from the second region <NUM>.

The temperature sensing element <NUM> is electrically connected via a metallic track <NUM> to one or more electrical components <NUM> provided on the second region <NUM> of the printed circuit board <NUM>.

The head portion <NUM> furthermore comprises a second protruding region <NUM> in the plane of the printed circuit board <NUM> that is protruding towards the second region <NUM> and serves as a stopping element limiting the course of movement of the head portion <NUM> towards the second region <NUM>, as will be described further down.

The enlarged zone in <FIG> illustrates that the first protruding portion <NUM> of the head portion <NUM> of the first region <NUM> of the printed circuit board <NUM> extends at least partially through and beyond a through hole <NUM> in the housing <NUM> enclosing the remainder of the printed circuit board <NUM>.

In this embodiment, the metallized edge region <NUM> extends beyond the through hole <NUM> in the housing <NUM> towards the outside.

Preferably, the length A of the first region, thus the length of the head portion <NUM> plus the arm portion <NUM> as illustrated in <FIG>, can be larger than the width B1of first region <NUM>, thus the arm portion <NUM>, at the transition to the flexible linking portion <NUM>. Even further preferred, the length A should satisfy A > <NUM>*B1. Preferably, the arm region has a tapered shape, such that the width B1, perpendicular to the length A, of the arm portion <NUM> at the transition to the flexible linking portion <NUM> is larger than the width B2 at the transition to the head portion <NUM> to distribute the mechanical stress over the length of the arm portion <NUM>.

<FIG> illustrates a device <NUM> comprising the temperature sensor <NUM> of the first embodiment. In the device <NUM>, e.g. a vehicle, the temperature sensor <NUM> is mount to a surface <NUM> of an element <NUM> of the device. As an example, the element <NUM> can be the windscreen of a vehicle and the temperature sensor <NUM> is mount onto the inside surface <NUM> of the windscreen.

Features with reference numerals already used in the description of the temperature sensor <NUM> illustrated in <FIG> will not be described again in detail, but reference is made to their description in <FIG>.

When mounting the temperature sensor <NUM> onto the surface <NUM>, the feet <NUM> and <NUM> of the housing <NUM> rest on the surface <NUM>. Mounting can be realized in several ways, e.g. by gluing, clipping using a spring element to hold the sensor in place or by locking the sensor using an additional locking element. During the step of mounting of the temperature sensor <NUM>, the first protruding portion <NUM> of the first region <NUM> is pushed towards the housing such that the extremity <NUM> of the metallized edge regions <NUM> becomes flush aligned with the extremity of the foot <NUM>. This becomes possible due to the elasticity of the arm portion <NUM> of first region <NUM>. Due to elastic property of the first region <NUM>, the extremity <NUM> of the metallized edge region <NUM> is pressed against the surface <NUM> by the elastic restoring force, illustrated by arrow F. In other words, the head portion <NUM> of the first region <NUM> is in a preloaded state. Thus, the thermal contact between the metallized edge region <NUM> and the element <NUM> to be temperature sensed can be ensured in a simple and reliable manner.

Thus, thanks to the flexible shape design of the printed circuit board made out of an intrinsically flexible material, a preloaded thermal contact can be ensured between the temperature sensor and the object to be temperature sensed. This thermal contact can thus be realized without the need of any additional elements like additional springs, flex elements or thermal pads, thereby reducing cost of manufacturing and reducing the bill of materials.

<FIG> illustrates the printed circuit board <NUM> according to the invention before being mount into a housing as illustrated in <FIG> and <FIG> by reference numeral <NUM>. The printed circuit board <NUM> of <FIG> has all the features of the printed circuit board as already described with respect to <FIG> and <FIG> to which reference is made.

The second protruding portion <NUM> reduces risk of breakage of the printed circuit board as the travel of the head portion <NUM> towards the second region <NUM> can be kept small. Indeed, the movement of the head portion <NUM> at the end portion of the first region <NUM> is stopped when the second protruding region touches <NUM> the edge <NUM> of the second region <NUM>.

Here, the printed circuit board <NUM> is illustrated with all elements mount, e.g. the temperature sensing element <NUM>, the electrical components <NUM> and the electrically and thermally conductive traces <NUM>, <NUM>. The invention is, however, not limited thereto and also relates to the printed circuit board <NUM> alone.

<FIG> illustrates a third embodiment according to the invention. The printed circuit board <NUM> according to the third embodiment has a second region <NUM> that is zigzag shaped between the flexible linking portion <NUM> and the head portion <NUM> instead of using an arm shaped portion <NUM> like in the first and second embodiment. Features carrying the same reference numerals as already used in the first and second embodiment will not be described again in detail but reference is made thereto.

Here, the zig zag shaped first region <NUM> is realized by a succession of U-shaped elements, which is an example shape only. Other shapes, like V-shaped elements or alternating U and V shape elements could also build up the first region <NUM>.

The head portion <NUM> comprises a protruding portion <NUM> extending beyond edge <NUM> of the first region <NUM> of the printed circuit board <NUM>, which is indicated by the dotted lines <NUM>. At the extremity of the protruding portion <NUM> farthest away from the flexible linking portion <NUM>, a metalized edge region <NUM> is provided like in the first and second embodiment.

The metalized edge region <NUM> is in thermal contact with the temperature sensing element <NUM> in turn electrically connected via the electrical connection <NUM> with further electrical elements <NUM> provided on the second region <NUM>.

The cut outs 85a and 85b to remove printed circuit board material to weaken mechanically to printed circuit board to obtain the shape as illustrated in <FIG> are realized such that the corners on the inner sides 87a-e of the U shaped elements all have rounded shapes.

The printed circuit board <NUM> can be positioned in a housing <NUM> like in the first embodiment such that the metallized edge region <NUM> extends beyond the trough hole <NUM>. In the mount state the metallized edge region <NUM> can be pushed towards the inside of the housing comparable to what is illustrated in <FIG> which is due to the spring like behavior of the zig zag shaped first region <NUM> and the flexible linking portion <NUM>.

Thus, the same advantageous can be achieved with the printed circuit board <NUM> of the third embodiment like with the printed circuit board <NUM> as illustrated in <FIG>.

Claim 1:
Sensor, in particular temperature sensor, comprising a printed circuit board (<NUM>) with a physical parameter sensing element (<NUM>), in particular a temperature sensing element, wherein the printed circuit board (<NUM>, <NUM>) comprises a first region (<NUM>, <NUM>) and a second region (<NUM>, <NUM>) linked together via a flexible linking portion (<NUM>) such that a free end portion (<NUM>) of the first region (<NUM>) opposite the flexible linking portion (<NUM>) is moveable with respect to the second region (<NUM>),
wherein the flexible linking portion (<NUM>) is part of the printed circuit board (<NUM>), the sensor being characterised in that the first region (<NUM>, <NUM>) comprises a first protruding region (<NUM>) in the plane of the printed circuit board (<NUM>) that is protruding away from the second region (<NUM>) and comprises a metallized edge region (<NUM>).