Patent Publication Number: US-2022216628-A1

Title: Sensor Device and Grounding Connection

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of the filing date under 35 U.S.C. § 119(a)-(d) of European Patent Application No. 21305008.1, filed on Jan. 5, 2021. 
     FIELD OF THE INVENTION 
     The present invention relates to the field of industrial sensor technologies, in particular to the electrical grounding of a sensor device. 
     BACKGROUND 
     Sensor devices, e.g. fluid sensor devices, may comprise a sensor, like a temperature sensor, and/or a mechanical resonator, like a tuning fork resonator. Sensor devices usually require interconnecting at least two Printed Circuit Boards (PCBs) and grounding the PCBs for electrostatic discharge (ESD) protection and for preventing electromagnetic interference (EMI noise). 
     Spring contacts, also known as spring fingers or ground contacts, are commonly used for grounding between a device and a PCB. Spring contacts are soldered onto a PCB. However, in many applications, like when the sensor device is implemented in a vehicle, vibrations can generate stress and fatigue on the solder joint between the spring contact and the PCB, thereby weakening the connection. 
     In some sensor devices known from the prior art, like the sensor device  10  represented in  FIG. 1 , the grounding of the PCBs  12 ,  14  is carried out by a pin  16  soldered to the electrically conductive body  18  of the sensor device  10  and the PCB  12 . The PCBs  12 ,  14  are interconnected by a rigid connection device  20 . For protecting and insulating PCBs  12 ,  14  and electronic components from the threats of harsh environments, the cavity  22  of the sensor device  10  can be filled with epoxy resin (this method is also known as PCB potting). Epoxy resin, however, due to its rigid material properties, does not allow dampening vibrations. Moreover, as it involves the installation of several elements ( 18 ,  20 ), as well as steps of soldering and potting, the manufacturability of such sensor device is affected. 
     SUMMARY 
     A sensor device includes an electrically conductive body adapted to accommodate a first printed circuit board (PCB) and a second PCB, a flexible electrically conductive device connecting the first PCB and the second PCB, and an electrically conductive spring held between the first PCB and the second PCB by a snap-fit, a form-fit or a press-fit connection. A first portion of the electrically conductive spring is pressed against one of the first PCB and the second PCB and a second portion of the electrically conductive spring is pressed against the electrically conductive body to maintain an electrical connection between the electrically conductive body, the first PCB, and the second PCB. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be described by way of example with reference to the accompanying Figures, of which: 
         FIG. 1  is a sectional side view of a sensor device known from the prior art; 
         FIG. 2  is a sectional perspective view of a sensor device according to a first embodiment of the invention; 
         FIG. 3 a    is a perspective view of an electrically conductive spring of the sensor device of  FIG. 2 ; 
         FIG. 3 b    is a side view of the electrically conductive spring of  FIG. 3   a;    
         FIG. 4  is a perspective view of a plastic holder and three electrically conductive springs of the sensor device of  FIG. 2 ; 
         FIG. 5  is a side view of the electrically conductive springs mounted to the plastic holder of  FIG. 4 ; 
         FIG. 6  is a perspective view of mounting the plastic holder on a PCB of the sensor device of  FIG. 2 ; 
         FIG. 7  is a perspective view of the plastic holder mounted on the PCB of the sensor device of  FIG. 2 ; 
         FIG. 8  is a perspective view of an assembled state of the sensor device of  FIG. 2 ; 
         FIG. 9  is a perspective view of an electrically conductive spring according to another embodiment; 
         FIG. 10  is a sectional side view of the sensor device with the electrically conductive spring of  FIG. 9 ; 
         FIG. 11  is a sectional side view of a sensor device according to a second embodiment of the invention; and 
         FIG. 12  is a perspective view of a sensor device according to a third embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENT(S) 
     Features and advantages of the invention will be described with reference to the drawings. In the description, reference is made to the accompanying figures that are meant to illustrate embodiments of the invention. It is understood that such embodiments do not represent the full scope of the invention. 
     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, explain the principles of the invention. The drawings are merely for the purpose of illustrating examples of how the invention can be made and used, and are not to be construed as limiting the invention to only the illustrated and described embodiments. Furthermore, several aspects of the embodiments may form—individually or in different combinations—solutions according to the present invention. The following described embodiments thus can be considered either alone or in an arbitrary combination thereof. Further features and advantages will become apparent from the following more particular description of the various embodiments of the invention, as illustrated in the accompanying drawings. 
     The present invention will now be described with reference to the attached Figures. Various structures, systems and devices are schematically depicted in the drawings for purposes of explanation only and so as to not obscure the present disclosure with details, which are well known to those skilled in the art. Nevertheless, the attached drawings are included to describe and explain illustrative examples of the present disclosure. The words and phrases used herein should be understood and interpreted to have a meaning consistent with the understanding of those words and phrases by those skilled in the relevant art. No special definition of a term or phrase, i.e., a definition that is different from the ordinary or customary meaning as understood by those skilled in the art, is intended to be implied by consistent usage of the term or phrase herein. 
     In the following, elements with the same reference numeral already described and illustrated with respect to one figure will not necessarily be described in detail again with respect to the other figures, but reference is made to the previous description of the same reference numeral. 
       FIG. 2  illustrates a cut view of a sensor device  100  according to a first embodiment of the present invention. As represented in  FIG. 2 , a first PCB  102  is connected to a second PCB  104  by a flexible electrically conductive device  106 . The flexible electrically conductive device  106  provides a flexible electrical connection between the first PCB  102  and the second PCB  104 . The flexible electrically conductive device  106  can be a PCB flex or flexible PCB. The flexible electrically conductive device  106  is formed of a thin insulating polymer film having conductive circuit patterns affixed thereto. The use of a flexible electrically conductive device  106 , like a flexible PCB  106 , allows avoiding rigid interconnection between the first PCB  102  and the second PCB  104 . 
     As shown in  FIG. 2 , electrical components  108  are connected onto each PCB  102 ,  104 . 
     Terminal pins  110  are soldered to the first PCB  102 . The terminal pins  110 , also referred to herein as first terminal pins  110 , extend from a terminal block  112  accommodated in a first assembly  114 , like a header assembly  114  of the sensor device  100 . Sensitive elements, like temperature sensor or a resonator, are connected to the first terminal pins  110 . Terminal pins  116  are soldered to the second PCB  104 . The terminal pins  116  are connectors for customer connection. The terminal pins  116  may also be referred to as second terminal pins  116 . 
     A connector  118 , constituting a second assembly element of the sensor device  100 , is represented in  FIG. 2 . The connector  118  and the header assembly  114  are held together by an electrically conductive body  120 . In the assembled state of the fluid sensor  100 , as represented in  FIG. 2 , the electrically conductive body  120  is crimped to a first border  122  of the connector  118 . The electrically conductive body  120  is further attached to the connector  118  by a form-fit connection between a second border  124  of the connector  118  and a corresponding step  126  of the electrically conductive body  120 . A form-fit connection is also formed between a step  128  of the header assembly  114  and a border  130  of the electrically conductive body  120 . The electrically conductive body  120  is thus adapted to accommodate the first PCB  102  and the second PCB  104 . 
     To electrically ground the PCBs  102 ,  104  for electrostatic discharge (ESD) protection and for preventing electromagnetic interference (EMI noise), it is necessary to create an electrical connection between the PCBs  102 ,  104  and the electrically conductive body  120 . The electrical grounding function is carried out by an electrically conductive spring  200 . In the first embodiment of the invention, the electrically conductive spring  200  is disposed on a plastic holder  300 . The plastic holder  300  is disposed between the two PCBs  102 ,  104  such that, in the assembled state of the fluid sensor  100 , as shown in  FIG. 2 , a first portion  202  of the spring  200  is pressed against the second PCB  104 . Moreover, a second portion  204  of the spring  200  is pressed against the electrically conductive body  120  so as to maintain an electrical connection between the electrically conductive body  120  and the PCBs  102 ,  104 . 
     The structure of the spring  200  is shown in  FIGS. 3 a  and 3 b   . The spring  200  for the sensor device  100  according to the first embodiment is further described in the following in reference to  FIGS. 2, 3   a  and  3   b.    
     The first portion  202  of the spring  200  is a flat portion  202   a  in a plan parallel to the surfaces of the PCBs  102 ,  104 . The flat structure  202   a  of the first portion  202  provides a well-adapted contact surface for ensuring the electrical connection when the second PCB  104  is pressed against said first portion  202 . In a variant, the first portion  202  is provided with a bump, the bump being pressed against said first portion  202  to further improve the electrical contact. 
     The second portion  204  is formed by a bent tab  204   a,  the apex  204   b  of which is pressed against the electrically conductive body  120  in the assembled state of the sensor device  100 . The bent tab  204   a  extends from the first portion  202  in a direction to form an angle A from the flat first portion  202  (see  FIG. 3 b   ). The bent tab  204   a  has a free-end  204 c. 
     As illustrated in  FIG. 3 b   , the angle A between the first portion  202  and the second portion  204  and the angle B at the apex  204   b  of the second portion  204  are both adapted for allowing the apex  204   b  to be pressed against the electrically conductive body  120  in the assembled stated of the device sensor  100  (the assembled state is shown in  FIG. 2 ). The first portion  202  and the second portion  204 , in particular at the apex  204   b,  can be covered by an electrically conductive layer to further improve the electrical contact. Such electrically conductive layer can be formed of gold plating over a nickel plating layer. 
     The spring  200  has a flat base portion  206  adapted to rest on a corresponding base  302  of a receptacle  304  of the plastic holder  300 , as shown in  FIGS. 2, 3   a , and  3   b . For improving the retention of the spring  200 , a tongue  208  (see  FIG. 3 a   ) of the base  206  of the spring  200  can be bent, i.e. crimped, to the base  302  of the plastic holder  300 . The base  206  is geometrically opposed to the first portion  202 . 
     The spring  200  further comprises a third portion  210  extending between the first portion  202  and the base  206 , so that the third portion  210  does not have any free end. The third portion  210  of the spring  200  is configured to be in a preloaded state between the two PCBs  102 ,  104  (as illustrated in  FIG. 2 ). The third portion  210  is thus structurally configured for imparting a sufficient spring force along a direction transversal D to the PCBs  102 ,  104  so as to provide strain relief to the PCBs  102 ,  104 . The third portion  210  acts as a compression spring exerting its restoring force along the direction D. As shown in  FIG. 3 b   , the third portion  210  is a three-point bent tongue  210   a.  The shape of the third portion  210  advantageously allows increasing the working stroke of the spring  200  while having a reduced bulk. In a variant, the third portion  210  acts as a compression spring but has a different structure than the design of the three-point bent tongue  210   a  of the spring  200  shown in  FIGS. 2, 3   a  and  3   b.    
     The electrically conductive spring  200  allows not only providing a grounding function but, in addition, a stress relief function which improves the retention of the PCBs  102 ,  104 , especially under vibrations, as no stress is caused on and by rigid connections (like solder joints). Hence, the two functions of electrical grounding and strain relief of the PCBs  102 ,  104  are advantageously carried out by one single component, the electrically conductive spring  200 , that can be assembled to the sensor device  100  without the need of a soldering step. 
     As can be seen in  FIG. 2 , in the assembled state of the fluid sensor  100 , the plastic holder  300  is disposed between the two PCBs  102 ,  104 , such that only the first PCB  102  is in direct surface contact with the plastic holder  300  and only the second PCB  104  is in direct surface contact with the spring first portion  202  of the spring  200 . This is rendered possible by the specific dimensions of the spring  200  and the plastic holder  300  as well as by the arrangement of the spring  200  with respect to the plastic holder  300 . This feature is further described with respect to  FIG. 4 . 
       FIG. 4  illustrates a plastic holder  300  adapted for receiving three springs  200  for a sensor device  100  according to the first embodiment. In a variant, the plastic holder  300  is adapted for receiving only one spring  200 . In another variant, the plastic holder  300  is adapted for receiving two, four or more springs  200 . 
     The plastic holder  300 , as shown in  FIG. 4 , comprises a base  308 . The base  308  can be provided with one or more holes  309  to accommodate the electrical component(s)  108  connected to the first PCB  102 . The plastic holder  300  is one-piece integrally formed, by injection molding for example, thereby being easily manufacturable. 
     As shown in  FIG. 4 , three receptacles  304  extend transversally from the base  308 , i.e. along a direction parallel to the Z-direction of the Cartesian coordinates. Each receptacle  304  comprises a base  302  to support the base  206  of the spring  200 . Each receptacle  304  is formed by two grooves  310  facing each other towards the base  302 . The grooves  310  are positioned on the base  308  and spaced from each other such that when a spring  200  is received therein, it allows the second portion  204  and the third portion  210  of the spring  200  to protrude outwards from the grooves  310  (the protruding aspect is even more visible on the right side of the view of  FIG. 5 ). Hence, the grooves  310  allows the retention of the spring  200  without hindering the contact between the second portion  204  and the electrically conductive portion  120  in the assembled state of the sensor device  100  (as illustrated in  FIG. 2 ) nor the strain relief function carried out by the third portion  210  of the spring  200 . The receptacles  304  of the plastic holder  300  provide a holding feature for the mounting of the spring  200  without the need of any fastener. 
     The total height H between the highest point  312  of the groove  310  and the base  308  of the plastic holder  300  is dimensioned so as to be smaller than the distance dl between the two PCBs  102 ,  104  in the assembled state of the sensor device  100  (as illustrated in  FIG. 2 ). Hence, a gap of height d 2  (see  FIG. 2 ) is comprised between the highest point  312  of the plastic holder  300  and the second PCB  104  in the assembled state of the sensor device  100 . Hence, as shown in  FIG. 2 , only the first PCB  102  is in direct surface contact with the plastic holder  300 , which lies on the first PCB  102 . The gap d 2  between the plastic holder  300  and the second PCB  104  provides sufficient space for strain relief, i.e. for allowing the third portion  210  of the spring  200  to exert its restoring force. Consequently, it allows, for example under vibrations, a mutual movement of the PCBs  102 ,  104  that is not affected by any rigid interconnection, in comparison with fluid sensor of the state of start, as illustrated in  FIG. 1  for example. 
     In order to facilitate the mount of the spring  200  to the plastic holder  300  and to improve its retention into the receptacle  304 , the spring  200  further comprises two guiding arms  212 . As shown in  FIGS. 3 a    and  4 , the guiding arms  212  extend from the first portion  202  towards the base  206 . The guiding arms  212  extend on different sides than the second portion  204  and the third portion  210 . The guiding arms  212  are adapted to be respectively received in the grooves  310  of each receptacle  304  of the plastic holder  300  in order to provide stability to the spring  200 . As indicated in  FIG. 4 , the distance d 3  between the two free-ends  212   a  of the guiding arms  212  (see  FIG. 4 ) is substantially greater than the distance d 4  of length of the first portion  202  of the spring  200  and of the distance d 5  between the grooves  310  of a same receptacle  304 . It allows, when the spring  200  is received into the receptacle  304  of the plastic holder  300 , as shown in  FIG. 5 , to keep the guiding arms  212  of the spring  200  slightly under stress. It therefore improves the retention of the spring  200  within the receptacle  304  and its grooves  310  because it prevents the spring  200  to tip over from the receptacle  304  when the apex  204   b  of the second portion  204  is pressed against the electrically conductive body  120  (the electrically conductive body  120  is shown in  FIG. 2 ). The at least one guiding arm  212  allows facilitating the mounting of the spring  200  to the receptacle  304  by providing a guiding feature to the spring  200 . It also allows ensuring a correct positioning of the spring  200  with respect to the plastic holder  300 . 
     In order to maintain the plastic holder  300  to the header assembly  114  and the connector  118 , snap-fit, press-fit or/and form-fit connections between the plastic holder  300  and the header assembly  114 , as well as between the plastic holder  300  ad the connector  118  are performed. Snap-fit, press-fit or/and form-fit connections allow easy assembly steps and do not require the use of any tools. Hence, the manufacturing of the sensor devise  200  can be simplified. 
     As shown in  FIG. 4 , the plastic holder  300  comprises two receptacles  314  respectively adjacent to receptacles  304  already described above. Each receptacle  314  comprises a space  316  adapted for receiving a locking arm of the connector  118  (the locking arm of the connector  118  will be described hereafter with respect to the  FIGS. 6 to 8 ). Each receptacle  314  also comprises a receptacle locking arm  318  extending from the base  308  and having a free-end  320  with a hook shape  320   a.  The hook shape  320   a  of the locking arm  318  of the plastic holder  300  is adapted to perform a snap-fit connection with a corresponding locking arm of the connector  118  in the assembled stated of the sensor device  100 . It thus allows maintaining the plastic holder  300  to the connector  118  by a snap fit connection. 
     As shown in  FIG. 4 , the plastic holder  300  is further provided with a recess  322  on a circumference  324  of the base  308 . The recess  322  has a shape complementary to a corresponding locking element protruding from the head assembly  114  (the locking element protruding from the head assembly  114  will be described hereafter with respect to the  FIG. 6 ). Hence, a form-fit connection can be carried out between the plastic holder  300  and the head assembly  114 . In a variant, the plastic holder  300  can be attached to the head assembly  114  by a snap-fit or a press-fit connection. 
     A method for assembling the sensor device  100  according to the first embodiment is described in the following with respect to  FIGS. 4 to 8 . 
       FIG. 4  illustrates a step of the method for assembling the sensor device  100  wherein three distinct springs  200  are mounted to the plastic holder  300 . Each spring  200  is inserted along an insertion direction M 1  transversal to the base  308  and parallel to the grooves  310  (i.e. parallel to the Z direction of the Cartesian coordinate) until the base  206  of the spring  200  is in contact with the base  302  of the receptacle  304 . The tongue  208  of the spring  200  can be crimped to the base  302  of the plastic holder  300  to improve the retention of the spring  200  to the plastic holder  300 . 
     As shown in the following step represented in  FIG. 5 , each spring  200  is received in a respective receptacle  304  of the plastic holder  300 . The guiding arms  212  of each spring are received in the corresponding grooves  310  of each receptacle  304 . The guiding arms  212  have helped guide the mount of the springs  200  to the receptacle  304 . As the guiding arms  212  of the spring  200  are slightly under stress in the receptacle  304 , it allows improving the retention of the spring  200  to the plastic holder  300 . 
     As shown in  FIG. 6 , the first PBC  102  is connected to the header assembly  114 . The second PCB  104  is connected to the connector  118 .  FIG. 6  illustrates a step wherein the header assembly  114  and the connector  118  of the sensor device  100  are positioned with respect to each other so as to align the PCBs  102 ,  104  and the flex PCB  106  in a common plane (XY). The pin terminals  110  are soldered to the first PCB  102  and the pin terminals  116  are soldered to the second PCB  104 . The numbers of pin terminals  110 ,  116  is not limitative. The plastic holder  300 , comprising the three springs  200 , is positioned above the first PCB  102  so as to be assembled to the first PCB  102  along the insertion direction M 1 . 
     As shown in  FIG. 6 , two locking elements  132  protrude from the head assembly  114 . The free-end  132   a  of each locking element  132  has a complementary shape of the corresponding recess  322  of the plastic holder  300 . Hence, a form-fit connection between the plastic holder  300  and the locking elements  132  of the head assembly  114  is possible. The free end  132   a  of the locking element  132  can have a hook shape for providing a snap-fit connection with a corresponding step of the recess  322 . 
     In the following step represented by  FIG. 7 , the plastic holder  300  is disposed onto the first PCB  102  being connected to the second PCB  104  by the flexible electrically conductive device  106 . The plastic holder  300  has been assembled to the first PCB  102  along the insertion direction M 1  (indicated in  FIG. 6 ). Each locking elements  132  of the head assembly  114  is snap-fitted, form-fitted or press-fitted into the corresponding recess  322  of the plastic holder  300  thereby ensuring the retention of the plastic holder  300  to the head assembly  114 . 
     As shown in  FIG. 7 , two connector locking arms  134  protrude from the connector  118 . The free-end  134   a  of each locking arm  134  has a hook shape. Each locking arm  134  is adapted to be received in the corresponding receptacle  314  of the plastic holder  300 . As already described above, each receptacle  314  also comprises a locking arm  318  extending from the base  308  and having a free-end  320  with a hook shape  320   a.  The hook shape  320   a  of the locking arm  318  of the plastic holder  300  is adapted to perform a snap-fit connection with the corresponding locking arm  134  of the connector  118  in the assembled stated of the sensor device  100 . It thus allows maintaining the plastic holder  300  to the connector  118  by a snap fit connection, as shown in  FIG. 8  and described thereafter. 
     From  FIG. 7  to  FIG. 8 , the connector  118  has been pivoted according to the direction M 2  (shown in  FIG. 7  by the arrow M 2  representing a rotational axis, M 2  being transversal to M 1 ) so as to arrange the second PCB  104  over the plastic holder  300  (see  FIG. 8 ). Thereby, the second PCB  104  is pressed against the flat first portion  202  of each spring  200  so as to ensure an electrical contact between the second PCB  104  and each spring  200 . 
     Hence,  FIG. 7  represents a step of the assembling method wherein the second PCB  104  connected to the connector  118 , is moved pivotally onto the plastic holder  300  about the rotational axis (M 2 ) transversal to the insertion direction M 1  (said direction M 1  is represented in  FIG. 6 ). 
     Each locking arm  134  of the connector  118  is inserted into the space  316  of the receptacle  314  of the plastic holder  300 . The connector  118  is snap-fitted to the plastic holder  300  by the mutual retention of the hook shape free-ends  134   a,    320   a  of the locking arm  134  and the corresponding locking arm  318 . 
     As shown in  FIG. 8  and already described above with respect to  FIG. 2 , a gap of height d 2  is provided between the highest point  312  of the plastic holder  300  and the second PCB  104 . Hence, the gap d 2  between the plastic holder  300  and the second PCB  104  provides sufficient space for strain relief, i.e. for allowing the third portion  210  of the spring  200  to exert its restoring force (the third portion  210  is in a preloaded state between the two PCBs  102 ,  104 ). Consequently, it allows, for example under vibrations, a mutual movement of the PCBs  102 ,  104  that is not affected by any rigid interconnection, in comparison with fluid sensor of the state of start, as illustrated in  FIG. 1  for example. 
     As shown in  FIG. 8 , the second portion  204  of the spring  200  protrudes such that the apex  204   b  of the bent tab  204   a  extends beyond, in particular slightly beyond, the surfaces of the PCBs  102 ,  104 . Hence, when the electrically conductive body  120  is assembled to the header assembly  114  and the connector  118 , it will ensure that the protruding apex  204   b  is pressed against the electrically conductive body  120  so as to provide a reliable electrical contact between the spring  200  and the electrically conductive body  120 . 
     In a step following the step illustrated by  FIG. 8 , the electrically conductive body  120  is assembled to the header assembly  114  and the connector  118  so as to provide the sensor device  100  in its assembled state as represented in  FIG. 2 . 
     As already described above, in the assembled state of the fluid sensor  100  represented in  FIG. 2 , the electrically conductive body  120  is crimped to a first border  122  of the connector  118 . The electrical conductive body  120  is further attached to the connector  118  by a form-fit connection between a second border  124  of the connector  118  and a corresponding step  126  of the electrically conductive body  120 . 
     Hence, the electrically conductive spring  200  mounted to the plastic holder  300  allows maintaining an electrical connection between the electrically conductive body  120  and the PCBs  102 ,  104 , i.e. to perform the grounding function, without the need of being soldered to the PCBs  102 ,  104  or the electrically conductive body  120 . Instead, the electrical connection between the electrically conductive spring  200  and the PCB  104  is simply achieved by pressing the first portion  202  of the spring  200  against the second PCB  104 . Similarly, the electrical connection between the electrically conductive spring  200  and the electrically conductive body  120  is simply achieved by pressing the second portion  204 , in particular the apex  204   b  of the bent tab  204   a,  of the spring  200  against the electrically conductive body  120 . Consequently, with respect to the known solutions for electrical grounding in sensor device, no soldered joint—and thus no electrical connection—can be damaged by vibrations. The combination of the solder-free solution to assemble the electrically conductive spring  200  and the use of the PCB flex  106  allows avoiding the drawbacks caused by rigid connections, especially with respect to vibrations. Instead, the present invention provides a sensor device  100  without rigid connections between the two PCBs  102 ,  104 . Moreover, as no soldering step is required to install the electrically conductive spring for ensuring the grounding function, the manufacturing is simplified, thereby improving the repeatability and reducing the cost of the assembly process. Consequently, the method for assembling a sensor device is rendered compatible for high volume production. In addition, as no specific soldering step is required for ensuring the grounding function, automation of the assembly process is rendered possible. Moreover, it allows providing a potting free assembly process, which improves further the manufacturability of the sensor device  100 . 
       FIG. 9  illustrates a schematic view of an electrically conductive spring element  400  for a sensor device  100  according to the first embodiment.  FIG. 10  illustrates a schematic cut view of the sensor device  100  according to the first embodiment of the present invention comprising the spring element  400 , as a variant of the spring  200 . The  FIGS. 9 and 10  are described together in the following. Elements with the same reference numeral already described and illustrated in  FIG. 2  will not be described in detail again but reference is made to their description above. 
     The spring element  400 , as shown in  FIG. 9 , comprises three springs  400   a,    400   b,    400   c  extending from a common shielding base  406 . In an alternative, the spring element  400  comprises a shielding base  406  and only one spring  400   a.  In another variant, the spring element  400  comprises a shielding base  406  and two, four or more springs  400   a, b, c,  . . . The springs  400   a,    400   b,    400   c  are integrally formed with the shielding base  406 . Hence, the spring element  400  is formed in one-piece. As the spring  200  according to the first variant, each of the springs  400   a,    400   b,    400   c  according to the second variant comprises a first flat portion  402  from which extend a second portion  404  performing the electrical grounding function and a third portion  410  performing the strain relief portion. Each springs  400   a,    400   b,    400   c  comprises, as in the first variant, two guiding arms  412  extending from the first portion  402 . 
     In comparison with the spring  200 , the springs  400   a,    400   b,    400   c  according to the second variant share a common base  406  that provides a shielding function to the PCBs  102 ,  104 . Therefore, the base  406  of the spring element  400  is dimensioned so as to cover the base  308  of the plastic holder, substantially corresponding to the surfaces of the PCBs  102 ,  104  as shown in  FIG. 10 . Hence, when the shielding base  306  lies on the plastic holder  300 , the shielding base  306  is disposed between the two PCBs  102 ,  104  (the plastic holder being disposed between the two PCBs), thereby preventing cross talk (i.e. unintentional electromagnetic coupling) between the two PCBs  102 ,  104 . Therefore, the spring element  400  allows not only to perform a grounding function and a strain relief function but also an additional shielding function. 
     The  FIG. 11  illustrates a cut view of a sensor device  500  according to a second embodiment of the present invention. Similarly as in the sensor device  100  according to the first embodiment, the sensor device  500  comprises a first PCB  502  connected to a second PCB  504  by a flexible electrically conductive device  506 . The flexible electrically conductive device  506  provides a flexible electrical connection between the first PCB  502  and the second PCB  504 . The flexible electrically conductive device  506  can be a PCB flex or flexible PCB  506 . The flexible electrically conductive device  506  is formed of a thin insulating polymer film having conductive circuit patterns affixed thereto. The use of a flexible electrically conductive device  506 , like a PCB flex, allows avoiding rigid interconnection between the first PCB  502  and the second PCB  504 . 
     As shown in  FIG. 11 , terminal pins  510  are soldered to the first PCB  502 . The terminal pins  510  extend from a terminal block  512  accommodated in a first assembly  514 , like a header assembly  514 , of the sensor device  500 . Sensitive elements (not represented), like temperature sensor or resonator, are connected to the terminal pins  510 . Terminal pins  516  are soldered to the second PCB  504 . The terminal pins  516  are connectors for customer connection. 
     A second assembly  518 , like a connector  518 , and the header assembly  514  are held together by an electrically conductive body  520 . The electrically conductive body  520  is adapted to accommodate the first PCB  502  and the second  504 . The electrically conductive body  520  is attached to the header assembly  514  and to the connector  518  in the same way as the electrical conductive body  520  already described in reference with  FIG. 2 , to which reference is made. 
     In order to electrically ground the PCBs  502 ,  504  for electrostatic discharge (ESD) protection and for preventing electromagnetic interference (EMI noise), it is necessary to create an electrical connection between the PCBs and the electrically conductive body  520 . The electrical grounding function is carried out by an electrically conductive element  600 , shown in  FIG. 11 . The electrically conductive element  600  comprises at least two springs  600   a,    600   b  extending from a common shielding base  606 . In an alternative, the spring element  600  comprises a shielding base  606  and only one spring  600   a.  In another variant, the spring element  600  comprises a shielding base  606  and three or more springs  600   a, b,  . . . The two or more springs  600   a,  b have the same structure, the description of which therefore applies for each spring. The springs  600   a,    600   b  are integrally formed with the shielding base  606 . Hence, the spring element  600  is formed in one-piece. 
     In a variant, the sensor device  500  according to the second embodiment is provided with at least one spring  600   a  instead of the electrically conductive element  600 , i.e. individual springs  600   a,    600   b  that are not integrally formed with a common shielding base  606 . The electrically conductive element  600  is disposed between the two PCBs  504 ,  502  such that the shielding base  606  rests on the first PCB  502 . 
     As in the first embodiment, a first portion  602  of the spring  600   a  is pressed against the second PCB  504 . Moreover, a second portion  504  of the spring  600   a  is pressed against the electrically conductive body  520  so as to maintain an electrical connection between the electrically conductive body  520  and the PCBs  502 ,  504 . 
     Unlike the first embodiment, the sensor device  500  is not provided with a plastic holder so as to maintain the spring element  600 . Instead, the spring element  600  is held between the two PCBs  502 ,  504  by a form-fit connection formed between a first portion  602  of the spring  600   a  of the spring element  600  and the second PCB  504 . 
     As shown in  FIG. 11 , the first portion  602  of the spring  600  is a flat portion  602   a  in a plane parallel to the surfaces of the PCBs  502 ,  504 . According to the second embodiment, the first portion  602  comprises a main section  603   a  terminated with a free-end section  603   b,  the free-end section  603   b  extending transversally from the main section  603   a  through a corresponding through hole  503  of the PCB  504 . The form-fit connection between the free-end section  603   b  of the spring  600   a  and the PCB  504  allows maintaining the spring  600   a,  and thus the spring element  600 , without the need of solder joints. The spring element  600  can therefore be held in the sensor device  500  without soldering. 
     In a variant, the free-end section  603   b  can have a shape or a structure so as to provide a snap-fit connection or a press-fit connection with the hole  503  of the PCB  504 . The flat structure  602   a  of the first portion  602  provides a well-adapted contact surface for ensuring the electrical connection when the first portion  602  is pressed against the second PCB  504 . In a variant (not represented), the first portion  602  is provided with a bump, the bump being pressed against said first portion  602  so as to further improve the electrical contact. 
     The second portion  604  is formed by a bent tab  604   a  shown in  FIG. 11 , the apex  604   b  of which is pressed against the electrically conductive body  520  in the assembled state of the sensor device  500 . The bent tab  604   a  extends from the first portion  602  in a direction so as to form an angle A from the flat first portion  602 . The bent tab  604   a  has a free-end  604   c.    
     As illustrated in  FIG. 11  for the spring  600   a,  the angle A between the first portion  602  and the second portion  604  and the angle B at the apex  604   b  of the second portion  604  are both adapted for allowing the apex  604   b  to be pressed against the electrically conductive body  520  in the assembled stated of the sensor device  500 . The first portion  602  and the second portion  604 , in particular at the apex  604   b,  can be covered by an electrically conductive layer to further improve the electrical contact. Such electrically conductive layer can be formed of gold plating over a nickel plating layer. 
     The spring  600   a  further comprises a third portion  610  extending between the first portion  602  and the shielding base  606 , shown in  FIG. 11 , so that the third portion  610  does not have any free end. The third portion  610  of the spring  600   a  is configured to be in a preloaded state between the two PCBs  502 ,  504 . The third portion  610  is thus structurally configured for imparting a sufficient spring force along a direction transversal D to the PCBs  502 ,  504  so as to provide strain relief to the PCBs  502 ,  504 . The third portion  510  acts as a compression spring exerting its restoring force along the direction D. As shown in  FIG. 11 , the third portion  610  is a three-point bent tongue  610   a.  The shape of the third portion  610  advantageously allows increasing the working stroke of the spring  600   a,  and thus the spring element  600 , while having a reduced bulk. In a variant, the third portion  610  acts as a compression spring but has a different structure than the design of the three-point bent tongue  610   a  of the spring  600   a  shown in  FIG. 11 . 
     The electrically conductive spring element  600  allows not only providing a grounding function but, in addition, a stress relief function which improves the retention of the PCBs  502 ,  504 , especially under vibrations, as no stress is caused on and by rigid connections (like solder joints). Hence, the two functions of electrical grounding and strain relief of the PCBs  502 ,  504  are advantageously carried out by one single component, the electrically conductive element  600 , that can be assembled to the sensor device  500  without the need of soldering step. 
     In order to further improve the retention of the shielding base  606  on the sensor device  500 , the shielding base  606  can comprise a tongue  607  that extends transversally from the base  606 . The shielding base  606  is arranged in the sensor device  500  such that the tongue  607  abuts on a locking element  532  protruding from the head assembly  514 . The abutment of the tongue  507  against the locking element  532  prevents a displacement of the shielding base  606  in a plan (XY) parallel to the PCBs  502 ,  504 . 
       FIG. 12  illustrates a cut view of a sensor device  700  according to a third embodiment of the present invention. Similarly as for the sensor devices  100  and  500  according to the first and second embodiments, the sensor device  700  comprises a first PCB  702  connected to a second PCB  704  by a flexible electrically conductive device  706 . The flexible electrically conductive device  706  is similar than the flexible electrically conductive device  106 ,  506  already described above. The use of flexible electrically conductive device  706  allows avoiding rigid interconnection between the first PCB  702  and the second PCB  704 . 
     Terminal pins (not visible in  FIG. 12 ) are soldered to the first PCB  702 . These terminal pins extend from a terminal block  712  accommodated in a first assembly  714 , like a header assembly  714 , of the sensor device  700 . Sensitive elements (not represented), like temperature sensor or resonator, are connected to the terminal pins  710 . Terminal pins  716  are soldered to the second PCB  704 . The terminal pins  716  are connectors for customer connection. 
     A second assembly  718 , like a connector  718 , and the header assembly  714  are held together by an electrically conductive body  720 , as shown in  FIG. 12 . The electrically conductive body  720  is adapted to accommodate the first PCB  702  and the second  704 . The electrically conductive body  720  is attached to the header assembly  714  and to the connector  718  in the same way as the electrically conductive body  120  already described in reference with  FIG. 2 , to which reference is made. 
     In order to electrically ground the PCBs  702 ,  704  for electrostatic discharge (ESD) protection and for preventing electromagnetic interference (EMI noise), it is necessary to create an electrical connection between the PCBs and the electrically conductive body  720 . The electrical grounding function is carried out by an electrically conductive element  800  shown in  FIG. 12 . The electrically conductive element  800  comprises three springs  800   a,    800   b,    800   c  extending from a common shielding base  806 . In an alternative, the spring element  800  comprises a shielding base  806  and only one spring  800   a.  In another variant, the spring element  800  comprises a shielding base  806  and two or more springs  800   a, b,  . . . The two or more springs  800   a,  b have the same structure, the description of which therefore applies for each spring. 
     The springs  800   a,    800   b,    800   c  are integrally formed with the shielding base  806 . Hence, the spring element  800  is formed in one-piece. In a variant, the sensor device  800  according to the third embodiment is provided with at least one spring  800   a  instead of the electrically conductive element  800 , i.e. individual springs  800   a,    800   b  that are not integrally formed with a common shielding base  806 . 
     The electrically conductive element  800  is disposed between the two PCBs  702 ,  704  such that the shielding base  806  rests on the first PCB  702 . As in the first and the second embodiments, a first portion  802  of the spring  800   a  is pressed against the second PCB  704 . Moreover, a second portion  804  of the spring  800   a  is pressed against the electrically conductive body  720  so as to maintain an electrical connection between the electrically conductive body  720  and the PCBs  702 ,  704 . 
     Unlike the first embodiment, the sensor device  700  is not provided with a plastic holder so as to maintain the spring element  800 . Instead, the spring element  800  is held between the two PCBs  702 ,  704  by a press-fit connection formed between a first portion  802  of the spring  800   a  of the spring element  800  and the second PCB  704 . The first portion  802  of the spring  800  is a flat portion  802   a  in a plan parallel to the surfaces of the PCBs  702 ,  704 . 
     According to the third embodiment, the first portion  802  is provided with a through hole  805 . In the variant shown in  FIG. 12 , the through hole  805  has a circular cross-section. However, in another variant, the through hole  805  has a cross-section with a different shape, like an oblong shape. 
     An assembly pin  720  extends from the second assembly  718 , i.e. the connector  718  made in plastic material. The assembly pin  720 , as shown in  FIG. 12 , has a substantially cylindrical main body  722  on which extends radially at least one longitudinal tongue  724 . The cylindrical main body  722  assembly pin  720  has a similar diameter of the one of the through hole  805  of the first portion  802 . Hence, when the assembly pin  702  is inserted through the PCB  704 , via a corresponding through hole  705  of the PCB  704 , the at least one longitudinal tongue  724  is slightly deformed in the through holes  705  of the PCB  704  and  805  of the springs  800   a,  thereby providing a press-fit connection. This press-fit connection between the first portion  802  of the spring  800   a  and the PCB  704  by the assembly pin  720  of the first assembly  718  of the sensor device  700  allows maintaining the spring  800   a,  and thus the spring element  800 , without the need of solder joints. The spring element  800  can therefore be held in the sensor device  700  without soldering. 
     The flat structure  802   a  of the first portion  802  provides a well-adapted contact surface for ensuring the electrical connection when the first portion  802  is pressed against the second PCB  704 . In a variant (not represented), the first portion  802  is provided with a bump, the bump being pressed against said first portion  802  so as to further improve the electrical contact. 
     As in the first and the second embodiment, the second portion  804  of the spring  800   a  is formed by a bent tab  804   a,  the apex  804   b  of which is pressed against the electrically conductive body  720  in the assembled state of the sensor device  700 . The bent tab  804   a  extends from the first portion  802  in a direction so as to form an angle A from the flat first portion  802 . The bent tab  804   a  has a free-end  804   c.    
     As illustrated in  FIG. 12  for the spring  800   a,  the angle A between the first portion  802  and the second portion  804  and the angle B at the apex  804   b  of the second portion  804  are both adapted for allowing the apex  804   b  to be pressed against the electrically conductive body  720  in the assembled stated of the device sensor  700 . The first portion  802  and the second portion  804 , in particular at the apex  804   b,  can be covered by an electrically conductive layer to further improve the electrical contact. Such electrically conductive layer can be formed of gold plating over a nickel plating layer. 
     As in the first and the second embodiment, the spring  800   a  further comprises a third portion  810  extending between the first portion  802  and the shielding base  806 , so that the third portion  810  does not have any free end. The third portion  810  of the spring  800   a  is configured to be in a preloaded state between the two PCBs  702 ,  704 . The third portion  810  is thus structurally configured for imparting a sufficient spring force along a direction transversal D to the PCBs  702 ,  704  so as to provide strain relief to the PCBs  702 ,  704 . The third portion  810  acts as a compression spring exerting its restoring force along the direction D. As shown in  FIG. 12 , the third portion  810  is a three-point bent tongue  810   a.  The shape of the third portion  810  advantageously allows increasing the working stroke of the spring  800   a,  and thus the spring element  800 , while having a reduced bulk. In a variant, the third portion  810  acts as a compression spring but has a different structure than the design of the three-point bent tongue  810   a  of the spring  800   a  shown in  FIG. 12 . 
     The electrically conductive spring element  800  allows not only providing a grounding function but, in addition, a stress relief function which improves the retention of the PCBs  702 ,  704 , especially under vibrations, as no stress is caused on and by rigid connections (like solder joints). Hence, the two functions of electrical grounding and strain relief of the PCBs  702 ,  704  are advantageously carried out by one single component, the electrically conductive element  800 , that can be assembled to the sensor device  700  without the need of soldering step. 
     In order to further improve the retention of the shielding base  806  on the sensor device  800 , the shielding base  806  can comprise a tongue  807  that extends transversally from the base  806 . The shielding base  806  is arranged in the sensor device  700  such that the tongue  807  abuts on a locking element  732  protruding from the head assembly  714 . The abutment of the tongue  807  against the locking element  732  prevents a displacement of the shielding base  806  in a plan (XY) parallel to the PCBs  702 ,  704 . 
     In comparison to the first embodiment, the sensor devices  500 ,  700  of the second and third embodiments are not provided with a plastic holder  300  for carrying the springs/spring element. Instead, the spring elements  600 ,  800  of the second and third embodiment are in direct surface contact with both PCBs  502 ,  504 ,  702 ,  704 : the base  606 ,  806  is in direct contact with the first PCB  502 ,  702  and the first portion  602 ,  802  is in direct surface contact with the second PCB  504 ,  704 . While the sensors  500 ,  700  of the second and third embodiment do not require an additional element, such as a plastic holder, they need the second PCB  504 ,  704  to be provided with a through hole  503 ,  705  so as to form a press-fit, snap-fit or form-fit connection with the first portion of the spring element  600 ,  800 . The presence of a through hole in the PCB for maintaining the springs/spring element according to the first embodiment is not required thanks to the use of the plastic holder  300 . 
     In a variant (not illustrated), the sensor devices  100 ,  500 ,  700  can comprise more than two PCBs, for example stacked over each other and with spring(s) or spring element arranged therebetween. 
     All of the first, second and third embodiments, provide a sensor device  100 ,  500 ,  700  wherein the electrically conductive spring/spring element performing both the grounding function and the strain relief function, is held by a snap-fit, a form-fit or a press-fit connection, i.e. without the need of soldering the electrically conductive spring/spring element. 
     As no soldering step is required to install the electrically conductive spring for ensuring the grounding function, the manufacturing is simplified, thereby improving the repeatability and reducing the cost of the assembly process. Consequently, the sensor device is rendered compatible for high volume production. 
     Moreover, with respect to the known solutions for electrical grounding in sensor devices wherein the contact spring is soldered to the PCB, damages caused on soldered joints by vibrations are prevented. Instead, the present invention provides sensor devices  100 ,  500 ,  700  without rigid connections between the two PCBs. 
     Although the embodiments have been described in relation to particular examples, the invention is not limited and numerous alterations to the disclosed embodiments can be made without departing from the scope of this invention. The various embodiments and examples are thus not intended to be limited to the particular forms disclosed. Rather, they include modifications and alternatives falling within the scope of the claims and individual features can be freely combined with each other to obtain further embodiments or examples according to the invention.