Abstract:
An electric device, in particular a mechatronic gear, motor, or brake control device in a motor vehicle, includes an electronic component having at least one electric contact surface for electrically contacting the component. A flexible circuit board with a conduction path structure includes at least one contact pad and conduction lines between two flexible, non-conducting films. A respective contact pad of the flexible circuit board is electrically connected, in particular by welding, to a respective contact surface of the component for creating at least one contact point. A sealing element is disposed on a side of the flexible circuit board opposite the component and an internal space is bounded by a wall. The sealing element is pressed against the flexible circuit board at an edge of the wall so that the edge surrounds at least one of the contact points.

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The invention relates to an electric device, especially to a mechatronic gear, engine or brake control device for a motor vehicle. 
     Electronic components of a control device in a motor vehicle must be protected against environmental influences, such as moisture for example. Control devices are used for example to control a transmission in a motor vehicle. In recent times a trend has emerged towards integration of the control electronics and the associated sensor systems into the transmission. This is referred to as a mechatronic transmission control device. There are also trends for such “in-situ electronics” in other areas of application, such as engine control devices or brake control devices for example. 
     With mechatronic control devices flexible printed circuit boards, known as flex boards, are used for distributing electrical signals and currents. With a flexible circuit board a conduction path structure is arranged between two flexible, non-conducting foils (e.g. made of polyimide). The conduction path structure and the conducting foils are mechanically connected to each other via an adhesive layer. The conduction path structure comprises contact pads as a well as conduction lines via which electrical contact will be established to a contact partner. In the area of the contact pads the flexible circuit board is opened up to one side by the corresponding cutouts being made in one of the two foils. The metallization of the conduction path structure revealed in the area of the contact pad or contact pads makes electrical contacting to a contact partner possible, such as a leadframe for example, a pin or a contact surface of a component. 
     The electrical connection between the contact pads of the conduction path structure of the flexible circuit board and contact surfaces of the contact partner is established for example using a laser weld connection. In such cases the other of the two films of the flexible circuit board is damaged in the area of the contact point(s) which means that the conduction path structure is unprotected. If such a control device is now used in a transmission, it has oil washing around it. Small metal particles, which have not been entirely removed during the manufacturing of the transmission and also wear to the gear wheels of the transmission or oil sludge can under some circumstances result in an electrical connection between two of the now unprotected contact points being established, meaning that a short circuit is possible. Because of the manufacturing process described, the film of the flexible circuit board cannot provide protection for all lines and contacts from metallic particles to be found in oil. 
     BRIEF SUMMARY OF THE INVENTION 
     The object of the present invention is thus to specify an electric device, especially a mechatronic gear, engine or brake control device in a motor vehicle, for which improved protection is guaranteed for open contact points against conductive particles. 
     The object is achieved by an electric device with the following features: 
     An inventive electric device comprises an electronic component having at least one electrical contact surface for electrical contacting of a component. The concept of an electronic component is a wide-ranging one here. An electronic component within the meaning of the invention not only includes electronic chips such as sensors and actuators for example, but also typically circuit carriers. 
     The electric device further features a flexible printed circuit board in which a conduction path structure with at least one contact pad and conduction lines is arranged between two flexible, non-conducting films, whereby, to embody a contact point, a respective contact pad of the flexible circuit board is electrically connected to a respective contact surface of the component, especially by welding. This type of flexible circuit board, as already explained above, is known as a flex board. In particular the films embedding the conduction path structure are made of a flexible plastic, especially polyimide. A flexible printed circuit board thus differs from a conventional circuit board in its flexibility as well as the constructional design of its layers. 
     The inventive electric device also comprises a sealing element which is arranged on a side of the flexible printed circuit board opposite the component and has an interior space bounded by walling, with the sealing element being pressed against the flexible circuit board at an edge of the walling so that the edge surrounds at least one of the contact points. 
     With an inventive electric device the problem of providing the necessary seal against swarf and particles is solved by providing a seal element which prevents an electrical connection (short circuit) being established between two contact points of the electric device as a result of swarf or electrically-conducting foreign body particles. In such cases the inventive electric device has the advantage of being able to be produced in a simple and low-cost way. Furthermore an inventive electric device with a sealing element insures that the load on the electrical contact points is minimized. This enables a comparatively long life of the contact connections to be guaranteed, compared to a version of the electric device with no swarf and particle protection. 
     In particular the walling is embodied as double walling and has an outer side wall and an inner side wall adjoining the interior space, with a section of the walling connecting the outer and the inner side wall embodying the edge. The double-wall design provides increased stability for the sealing element. In particular a transverse movement of the sealing element relative to a plane of the flexible circuit board can be easily accommodated. In addition a wider seal section which is in contact with the circuit board is provided, whereby the sealing effect is improved. 
     Expediently a groove is embodied in the wall between the outer side wall and the inner side wall. The result of this is that the edge of the walling pressed against the flexible circuit board is formed by two sealing lips separated by the groove, which together represent a double barrier for the intrusion of swarf and particles into the interior space. 
     Expediently the interior space comprises one or more chambers which are embodied by a respective inner side wall, with a respective chamber being provided for sealing a contact point. In particular the outer side wall forms common walling surrounding the inner side walls of the chambers. In such cases the outer side wall insures that swarf and/or particles cannot get into the interior space, i.e. into one of the chambers, of the sealing element. The respective inner side walls, if there are still particles in one of the chambers, prevents them being able to form an electrically-conducting connection between two contact points. This is achieved by the respective inner side walls of the chambers sealing the contact points having to be overcome between respective contact points. A groove is also embodied between the inner side walls. 
     To achieve a good seal as well as less stressful and damaging effects on the electrical contact connections there is provision for embodying the sealing element from a reversibly deformable plastic, especially an elastomer. 
     There is also provision for fixing the sealing element in a surrounding frame made from an essentially non-deformable material. Especially only the outer side wall should be fixed by the frame in such cases. One the one hand this achieves good contact between the sealing element and the flexible circuit board. On the other hand the sealing element is able to be moved a certain amount in relation to the frame so that tolerances can be allowed for. 
     In a further embodiment the frame features a plurality of latching elements with which the frame is fitted in a non-destructively detachable way to a first housing component or into a recess of the first housing compartment corresponding to the frame. The pressure necessary for sealing with which the sealing element is pressed against the flexible circuit board is thus generated by the frame. 
     The dimensions of the frame and the recess are expediently selected such that the frame is supported movably in the recess in parallel to the plane of the flexible circuit board within predetermined limits. This enables friction forces between the sealing element and the flexible circuit board to be avoided which can lead to damage to the contact point or to the conduction path structure because of “rubbing”. 
     In particular the sealing element is fixed in parallel to the plane of the flexible circuit board relative to the flexible circuit board. In this embodiment the component coupled electrically and/or mechanically to the flexible circuit board can control the movability of the sealing element. Such an arrangement is also referred to as a “fully floating seal”. 
     In accordance with a further embodiment a section of the frame substantially located in the plane of the base of the sealing element is solely provided for accommodating a force acting at right angles to the plane of the flexible circuit board. This enables the base of the sealing element to move at right angles to the plane of the base within predetermined limits and thereby compensate for tolerances during production. The frame or the respective frame section are thus used as a support for the frame-fixed sealing element. 
     In this case it is also expedient for a gap of a given height to be embodied between the base of the sealing element and the first housing component. This allows an individually adjustable two-stage pressure force of the sealing element to be set on the flexible circuit board. The pressure force is two-stage because initially a deformation of the sealing element in the gap can occur. Consequently a deformation of the sealing element itself occurs which is easily possible because of the flexible characteristics of the elastomer. In this case the sealing force can be set on the basis of the gap width and the cross-sectional embodiment and the material properties of the sealing element. 
     The seal formed between the flexible circuit board and the sealing element is embodied at least particle-tight. This means that the seal does not need to be embodied oil or fluid-tight. The proposed electric device ensures however that short-circuits between respective contact points are prevented or at least minimized. 
     In accordance with a further concrete embodiment the component is attached by its main surface facing away from the at least one contact surface to a second housing component. In this case the first and the second housing component are mechanically connected to one another 
     In particular the inventive device is intended for attachment in an oil or fluid bath. The inventive electric device can for example be embodied as an electronic gear control device, as an engine or as a brake control device for use in a motor vehicle. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
       The invention will be explained in greater detail below with reference to the drawings. The drawings show: 
         FIG. 1  a cross-sectional view of a part of an inventive electric device, 
         FIG. 2  a cross-sectional view of an inventive sealing element which is fixed in a frame, 
         FIG. 3  a perspective view of the sealing element shown in  FIG. 2 , 
         FIG. 4  a cross-sectional view of the sealing element arranged in a housing component, 
         FIG. 5  a further cross-sectional view showing a section of an inventive electric device in which contact points are protected by the sealing element, and 
         FIG. 6  a part perspective view of a further electric device in which the sealing element is supported fully floating. 
     
    
    
     DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a schematic cross-sectional diagram of a part of an inventive electric device  1 . The inventive electric device  1  can represent a mechatronic gear control, an engine control or a brake control in a motor vehicle for example. The electric device  1  comprises an electronic component  2 , e.g. a sensor or a semiconductor component. In the exemplary embodiment the component  2  comprises two contact surfaces  3 ,  4  which are embodied on a main side of the component  2 . The component  2  is electrically and mechanically connected via the contact surfaces to a flexible circuit board  5 . The flexible circuit board  5  is referred to as a flex board and comprises a conduction path structure with conduction lines  25 ,  26  and contact pads  6 ,  7 . The conduction path structure is arranged between two films  27 ,  28  consisting of insulating material. The contact pads  6 ,  7  are made electrically accessible by inserting openings into the film  28 . Because of the small thicknesses of the films  27 ,  28  and the contact surfaces  3 ,  4  which may project beyond the main side, a direct electrical contacting of the contact pads with the corresponding contact surfaces  3 ,  4  is possible. 
     An electrical connection between the contact surfaces  3 ,  4  of the component  2  and the contact pads  6 ,  7  of the conduction path structure of the flexible circuit board  5  is especially established by laser welding. When the welding process is undertaken from a side of the circuit board  5  lying opposite the component  2 , energy is introduced through the film  27  in the area of the contact points  8 , 9  to be established in order to weld the contact pads  6  to the contact surface  3  or to weld the contact pads  7  to the contact surface  4 . The energy input into the film  27  in the area of the contact points  8 ,  9  produces unintentional but destructive openings  29 ,  30  in the film  27 . 
     While the contact points  8 ,  9  are sealed against the intrusion of particles or swarf from the side of the component  2  for constructional reasons because the component  2  rests against the circuit board  5 , the conduction path structure is electrically accessible from the opposite side in the area of the openings  29 ,  30 . As a result of this, because of the arrangement of the electric device (e.g. in an oil bath) swarf or particles which arise for reasons such as wear to mechanical components can be present on the contact pads  6 ,  7  in the openings  29 ,  30 . Under unfavorable circumstances in this case an electrical path can be established between the contact pads  6 ,  7 . The functional capabilities of the electric device can be adversely affected by this. 
     To avoid the buildup of swarf and/or particles on the contact pads  6 ,  7  in the area of the openings  29 ,  30  of the flexible circuit board, a sealing element  10  made from a reversibly-deformable plastic, especially an elastomer, is therefore provided. The sealing element  10  is shown on its own in a cross-sectional view in  FIG. 2  and in a perspective view in  FIG. 3 . In the exemplary embodiment the sealing element  10  has two chambers  18 ,  19 . Each chamber, as can be seen especially well from  FIG. 3 , is formed by an inner wall  15  or  16  and a base  22  or  23 . The inner side walls  15 ,  16  are also surrounded by an outer side wall  14 . In the area of an edge  13  of the sealing element  10  adjoining the flexible circuit board  5  the outer side wall  14  and the inner side walls  15 ,  16  are connected to one another by a section of material  31  in each case. In the cross-sectional diagrams of  FIG. 1  and  FIG. 2  a groove  17  is thus produced in each case in the edge  13  between the outer side wall  14  and the inner side walls  15 ,  16 . This causes the sealing element to rest tightly with the respective outermost ends of the outer side wall  14  and the inner side walls  15 ,  16  on the flexible circuit board  5 , with these outermost ends or sections forming sealing lips. 
     In accordance with the exemplary embodiment depicted in  FIG. 1  a chamber  18 ,  19  is provided for each contact point  8 ,  9  in each case. This provides an optimum protection against a short circuit between the contact points  8 ,  9 . The outer side wall  14  initially prevents swarf and/or particles in the oil bath being able to reach any of the contact points  8 ,  9 . Naturally those sections of the inner side walls  15 ,  16  which run substantially in parallel to the outer side wall  14  also contribute to this. The provision of the inner side walls  15 ,  16  also ensures that any swarf and/or particles which may be present in the interior of one of the chambers and  18 ,  19  are not able to form electrical conductors in the direction of the other chamber and thereby the contact point. 
     In a version departing from this exemplary embodiment there could also however be provision for a number of contact points to be assigned to a respective chamber of the sealing element. 
     As can be easily seen from  FIGS. 1 ,  2  and  3 , the outer side wall  14  of the sealing element  10  is fixed by its end facing away from the circuit board  5  in a frame  20 . The frame  20  is formed from an essentially non-deformable material, preferably plastic. The frame  20  has latching elements  32 ,  33  on two opposing main sides with which the frame and thereby the sealing element  10  can be fixed to a housing component. It can also be seen from the cross-sectional diagrams of  FIGS. 1 and 2  that the frame  20  has a recess  24 . The chambers  18 ,  19  of the sealing element  10  project into the recess  24 . The base  21  of the sealing element or the bases  22 ,  23  of the Chambers  18 ,  19  lie approximately in the same plane as an underside of the frame which embodies frames support sections  34 ,  35 . 
     The way in which the sealing element shown in  FIGS. 2 and 3  and fixed to the frame  20  is arranged in a first housing component  36  of the electric device  1  can be seen from  FIG. 4 . The housing component  36  features a recess  37  which corresponds to the shape of the sealing element  10  or of the frame  20 . The dimensions of the frame  20  and the dimensions of the recess  37  of the first housing component  36  are selected such that the frame  20  is supported in the recess  37  in parallel to the plane of the flexible circuit board to allow movement within predetermined limits. This prevents a transverse movement of the sealing lips, i.e. the ends of the outer and inner sidewalls  14 ,  15 ,  16  adjoining the circuit boards. As a result of this, fewer stressful and damaging effects are exerted on the electrical contact connections. The gap formed in the lateral direction between the frame  20  and the recess  37  is all around the circumference in such cases in order to achieve part “floating” of the sealing element  10 . 
     When the sealing element  10  (provided with the frame  20 ) is inserted, the latching elements  30  to  33  which expand upwards, are slightly deformed. In this case the latching elements  32 ,  33  are moved towards one another. After passing the constriction which is embodied by shoulders  38 ,  39  the frame  20  changes its form back in the area of the latching elements  32 ,  33 . Because of the latching elements  32 ,  33  provided on the frame  20 , the sealing element  10  has a width which is larger than the width of the recess  37  on its upper side in the area of the shoulders  38 ,  39 . As a result of this the sealing element  10  is fixed by the frame  20  in the recess  37  whereby, because of a gap between the upper edge of the latching elements  32 ,  33  and the shoulders  38 ,  39 , slight play is provided. With the underside of the frame, i.e. the frame contact sections  34 ,  35 , the frame  20  lies against contact sections  40 ,  41  of the housing component  36 . Between the base  21  of the sealing element (i.e. the bases  22 ,  23  of the chambers  18 ,  19 ) and the base  42  of the recess  37  a gap  43  is formed so that the sealing element  10  can deform on application of a slight force from above until the base  21  is in contact with the base  42  of the recess  37 . A further application of force to the walling  11  of the sealing element  10  leads to a deformation of the sealing lips and of the outer and inner side walls  14 ,  15 ,  16 , with these curving outwards because of their design. Through this design an individually-adjustable two-stage pressure force on the sealing element can be set. 
       FIG. 5  shows, in a further partly cross-sectional diagram of the inventive electrical device, the flexible circuit board  5  adjoining the sealing element  10  with the component  2  welded to it. It can also be seen from  FIG. 5  that the component  2  is attached on or to a further housing component  44 . The first housing component  36  and the second housing component  44  of the electrical device  1  are connected mechanically to each other for example via a latching connection or the like. The connection of the first and second housing component  36 ,  44  presses the flexible circuit board against the walling  11  of the sealing element  10 , so that the desired seal against intrusion of particles and/or swarf is provided. Depending on the force with which the flexible circuit board  5  is pressed onto the sealing element  10 , a deformation of the sealing element  10  in the direction of the base  42  of the recess  37  occurs. If necessary a deformation of the walling  11  of the sealing element  10  also occurs. 
     It should be stressed that no seal is to be achieved by the inventively provided sealing element which is intended to or must prevent the intrusion of oil or another fluid into the chambers  18  or  19 . Instead it is sufficient for the seal embodied between the flexible circuit board  5  and the sealing element  10  to be particle-tight. This is based on the knowledge that an electrically-conductive path is able to be formed by a plurality of particles touching one another, which in the worst case could give rise to a short circuit. The purpose of the seal is thus to suppress an electrically-conducting path between contact points of the flexible circuit board on the side of the flexible circuit board opposite to a component. 
       FIG. 6  shows a further exemplary embodiment in a perspective view of a part of an electric device  1 . In this case the arrangement of component  2  (not visible in the figure), flexible circuit board  5  and sealing element  10  is disposed between two joined housing components  36 ,  44 . This diagram shows the design of the frame  20  very well, which has two holes  45 ,  46  on opposing outer ends, into which the pins  47 ,  48  of the housing component  44  project. The pins  47 ,  48  likewise fix the flexible circuit board  5  in this case. This enables the component fixed to the flexible circuit board  5  and the housing component  44  (not visible in the figure) to control the movement of the sealing element  10  in the housing component  36 . To achieve this movement, a gap running around the circumference is once again embodied between the frame  20  and a corresponding recess of the housing component  44  not shown in the figure. 
     Protecting open contact points against conductive particles such as swarf or the like is effected within the framework of the invention by a sealing element made of an elastomer. The sealing element is constructively similar to a “bellow seal”. The sealing element is embodied such that exertion of axial and radial forces on the contact points is avoided. The exertion of radial forces is avoided or minimized by the constructive design of the sealing element and a floating supported latching. Avoiding the exertion of axial forces is realized by the two-stage force graduation in the form of the recess of the housing component into which the sealing element is inserted.