Abstract:
A method for the production of a sensor, especially of a crash sensor for a vehicle safety system, with the following steps: provision of a housing base part ( 12 ), placement of a circuit board ( 16 ) holding at least one sensor component ( 18 ) into the housing base part ( 12 ) and production of a housing cover part ( 14 ), involving at least partial encapsulation by injection molding of the circuit board ( 16 ), in which process step the housing cover part ( 14 ) is injection-molded directly onto the housing base part ( 12 ) and the circuit board ( 16 ) is joined directly to the housing cover part ( 14 ) and is hermetically enclosed by the housing base ( 12 ) and the housing cover part ( 14 ).

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to a method for the production of a sensor, especially of a crash sensor for a vehicle safety system, as well as a sensor. 
       BACKGROUND OF THE INVENTION 
       [0002]    A sensor of this type normally has one or more electronic components that are responsible for the actual detection of a change in the state of a variable. The electronic parts are mounted on a carrier material, for example, a lead frame or a circuit board, and surrounded by a housing. The housing has a connector section via which the electronic components situated inside the housing are electrically contacted. 
         [0003]    Such sensors which, for example, pick up an acceleration of a vehicle, have to function reliably over the entire lifetime of the vehicle. At the same time, of course, they should take up as little space as possible and should also be inexpensive to produce. 
       BRIEF SUMMARY OF THE INVENTION 
       [0004]    It is an object of the invention to provide a sensor that fulfills the above-mentioned criteria. 
         [0005]    This is achieved in a method for the production of a sensor that comprises the following steps: provision of a housing base part, placement of a circuit board holding at least one sensor component into the housing base part and fabrication of a housing cover part, involving at least partial encapsulation by injection molding of the circuit board, in which process step the housing cover part is injection-molded directly onto the housing base part and the circuit board is joined directly to the housing cover part and is hermetically enclosed by the housing base and the housing cover part. Since the housing cover part is injection-molded directly onto the housing base part, a stable gas-tight and liquid-tight connection is formed between the housing parts. The housing base part may be prefabricated so that only one single injection molding process is required. 
         [0006]    The circuit board is preferably placed into the housing base part in such a way that the sensor component protrudes into a receptacle of the housing base part. The receptacle is preferably configured in such a way that the sensor component lies in a hollow space formed by the housing base part and by the circuit board. In this manner, the sensor component is protected on all sides by the housing parts. The sensor component is shielded by the housing base part and the circuit board, also during the injection molding procedure, from the plastic material employed as well as from the high temperatures. 
         [0007]    In the housing base part, a circuit board attachment can be formed that predefines the position of the circuit board relative to the housing base part. This speeds up the assembly procedure since the circuit board will already be exactly positioned by putting it into place. 
         [0008]    Preferably, the housing base part has a connector region. 
         [0009]    The circuit board can have an edge connector and can be placed into the housing base part in such a way that the edge connector protrudes into the connector region. The circuit board can also have two contact pins that are separate from the circuit board but securely joined to the circuit board, which can be placed into the housing base part in such a way that the contact pins protrude into the connector region. In one case, the contact is formed by a section of the circuit board itself, while in the second case, it is formed by contact pins that are separate but securely joined to the circuit board. As an alternative, it is also possible to already configure the contacts with the housing base part and to join contact ends facing the circuit board to said circuit board after it has been put in place. 
         [0010]    In a preferred embodiment of the invention, the connector region is connected via a passage to the receptacle for the circuit board before the housing cover is fabricated. 
         [0011]    When the housing cover is produced, the passage is advantageously completely closed, as a result of which a hermetic seal is created in a simple manner between the receptacle of the circuit board and the connector region that is open towards the outside. 
         [0012]    The shape of the sensor housing is preferably largely defined by the housing base part. The housing base part can be substantially larger than the housing cover part. Basically, the housing cover part only has to consist of a closure plate for the receptacle that covers the circuit board and only has to have slightly larger dimensions than the circuit board. Since the only housing part made by injection molding with the circuit board put into place is the housing cover part, the temperature load on the sensor elements remains slight. 
         [0013]    Preferably, the housing cover part is produced using the same material of which the housing base part is made, so that a uniform and secure connection can be formed. 
         [0014]    Another object of the invention is to provide a sensor functioning reliably over the entire lifetime of the vehicle and being inexpensive to produce. 
         [0015]    This is achieved by a sensor with a housing comprising a housing base part and a housing cover part, as well as a circuit board holding at least one sensor component. The housing base part and the circuit board surround a hollow space into which the sensor component protrudes, whereas the circuit board and the housing cover part are inseparably joined to each other. The inseparable connection is preferably created by injection molding the housing cover part to the housing base part with the circuit board put into place, said housing cover part extending essentially parallel to the circuit board and preferably being connected to the back of the circuit board over a large area. 
     
     
       SHORT DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  shows a schematic sectional view of a sensor according to the invention in a first embodiment, mounted onto a car body; 
           [0017]      FIG. 2  shows a general schematic sectional view of the sensor in  FIG. 1 ; 
           [0018]      FIG. 3  shows a schematic exploded view of the sensor in  FIG. 1 ; 
           [0019]      FIG. 4  shows a perspective view of the sensor in  FIG. 3  before the injection molding of the housing cover part; 
           [0020]      FIGS. 5 to 8  show various views of the sensor according to the first embodiment; 
           [0021]      FIG. 9  shows a schematic view of a first variant of a circuit board of the sensor according to the invention, seen from its bottom; 
           [0022]      FIG. 10  shows the circuit board from  FIG. 9 , seen from its top; 
           [0023]      FIG. 11  shows a second variant of a circuit board of a sensor according to the invention, seen from its bottom; 
           [0024]      FIG. 12  shows the circuit board in  FIG. 11 , seen from its top; 
           [0025]      FIG. 13  shows a schematic exploded view of a sensor according to a second embodiment of the invention; 
           [0026]      FIG. 14  shows the sensor in  FIG. 13  after the circuit board has been put into place and before the housing cover part is injection molded; 
           [0027]      FIG. 15  shows a schematic view of the connector region of the sensor in  FIG. 13 ; 
           [0028]      FIG. 16  shows a schematic exploded view of a sensor according to a the third embodiment of the invention; 
           [0029]      FIGS. 17 to 19  show perspective views of the housing base part in  FIG. 16  with the contact pins already put into place; and 
           [0030]      FIGS. 20 to 23  show several perspective views of the sensor according to the third embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0031]      FIGS. 1 through 8  show a sensor  10  for use in a vehicle safety system. In this context, it should be pointed out that all of the described sensors can, of course, be used in any desired suitable area of application, without being restricted to vehicles or safety technology. 
         [0032]    The sensor  10  has a housing that consists of a housing base part  12  and a housing cover part  14 . A circuit board  16  is situated between the housing base part  12  and the housing cover part  14 , and this circuit board  16  carries at least one electronic sensor element  18 . The electronic sensor element  18  can be, for example, an acceleration sensor, a temperature sensor or any other desired electronic component. 
         [0033]    The housing base part  12  has one or more injection-molded fastening pins  22  for attaching it to another component, here a car body  20 , and these fastening pins  22  protrude through corresponding openings in the car body  20  in order to position the sensor  10 . 
         [0034]    Further, the housing base part  12  for fastening the sensor  10  to the car body  20  has a through opening  24  through which a fastening means  28  (see, for example,  FIGS. 4 to 8 ) can be inserted, said fastening means  28  being, for instance, a screw. The opening  24  can be reinforced, for example, by a sleeve  26  made of metal that is configured, for instance, with an internal thread and outwardly shaped hexagonally, so that the fastening means  28  can be screwed directly onto the sensor  10 . The sleeve  26  can also be joined already during the production to the housing base part  12  by injection molding it together with the housing base part  12 . 
         [0035]    Another way (not shown here) to fasten the sensor  10  is to already injection-mold a fastening means into the housing base part  12 , for instance, a bolt or a screw that protrudes partially out of the housing base part  12  and that can be inserted through an opening on the car body  20 , for example, so as to be affixed with a nut. 
         [0036]    The sensor  10 , or to put it more precisely, the housing base part  12 , has a connector region  30  for electrically contacting the sensor  10 , for example, to an on-board electronic system (not shown here). 
         [0037]    Here, the connector region  30  is a bushing (shown in greater detail, for example, in  FIGS. 4 to 7 ) that is integrally formed with the housing base part  12  and that surrounds an electric contact region  32  of the circuit board  16  and projects beyond it in the lengthwise direction of the sensor  10 . The electric contact region  32  is described in greater detail below. 
         [0038]    The housing base part  12  has a receptacle  36 . The circuit board  16  is placed “upside down” onto the housing base part  12  so that it lies on the housing base part  12  in the area of the edge  38  of the receptacle  36 . The geometry of the area of the edge  38  of the receptacle  36  is selected in such a way that a precise positioning and attachment of the circuit board  16  are automatically achieved when the circuit board  16  is put onto the receptacle  36 . The edge  38  of the receptacle  36  is graduated and shaped in such a way that it forms a circuit board attachment for the circuit board  16 . Merely placing the circuit board  16  into the receptacle  36  already ensures that the circuit board  16  is situated at exactly the right place. This kind of circuit board attachment also ensures the exact positioning of the electric contact region  32  of the circuit board  16  in the connector region  30 . 
         [0039]    The sensor components  18  protrude into the receptacle  36 . Here, they can be at a distance from the walls of the receptacle  36 . The sensor components  18  are now lying in a hollow space  34  that is surrounded by the housing base part  12  and the circuit board  16 . The hollow space  34  can remain unchanged and empty during the production of the sensor or else it can be filled with a suitable material. 
         [0040]    The housing base part  12  has a passage  40  that creates a connection between the receptacle  36  and the connector region  30  (see, for example,  FIGS. 3 ,  4  and  14 ). 
         [0041]    In order to produce the sensor  10 , first of all, the housing base part  12  is made, for example, by means of an injection-molding process. Then the circuit board  16  fitted with the sensor components  18  is placed into the housing base part  12  in such a way that it lies against the housing base part  12  in the area of the receptacle  36  and the electric contact region  32  of the circuit board  16  protrudes through the passage  40  into the connector region  30 . The circuit board  16 , together with the receptacle  36 , delimits the hollow space  34 , and the sensor components  18  protrude into the receptacle  36  of the housing base part  12 . This state is shown for the various embodiments in  FIGS. 4 ,  14  and  18 . 
         [0042]    In the next processing step, the assembly unit consisting of the housing base part  12  and the circuit board  16  is placed into an injection mold (not shown) and the housing cover part  14  is integrally connected thereto in the following injection molding process. The housing cover part  14  is made entirely by means of this injection molding step. In this process, the housing cover part  14  is thus joined to the back of the circuit board  16  and to the edges  38  of the receptacle  36  in such a way that the hollow space  34  is hermetically sealed. The sensor components  18  are arranged on the side of the circuit board  16  facing away from the housing cover part  14  made in the injection molding step. 
         [0043]    The lower edge  42  of the passage  40  lies flush with the inserted circuit board  16  (see  FIG. 2 ). When the housing cover part  14  is injection-molded onto the housing base part  12 , the passage  40  is completely and hermetically sealed, while the contact region  32  continues to protrude into the connector region  30 . This state can be clearly seen in  FIGS. 7 and 15  in which the part of the passage  40  situated above and next to the contact region  32  is closed by a section  44  of the housing cover part  14 . In this process step, the position of the contact region  32  is also completely affixed in place in all spatial directions by the section  44 . 
         [0044]    In this example, the material used for the housing cover part  14  is the same material as that used for the housing base part  12 . Here, any suitable plastic that can be injection molded can be used. Preferably, however, a plastic with the lowest possible injection molding temperature is used so as to not unduly stress the sensor components  18 . 
         [0045]    No other components, for example, separate gaskets, are needed in order to hermetically seal the circuit board  16  and the sensor components  18  from the surroundings of the sensor  10 . 
         [0046]    The arrangement of the sensor components  18  with respect to the housing base part  12  is the opposite of the approach that is usually taken. Normally, the circuit board is placed onto a support part in such a way that the sensor components face away from this support part. Then, further steps are carried out, namely, the placement of a housing cover, the filling with melt adhesives or the like. According to the invention, however, the circuit board  16  is put into place in a reversed position, namely, with the sensor components  18  facing the housing base part  12 . Thus, the circuit board  16  itself forms a first “cover” that closes the hollow space  34  with the sensor components  18 . During the subsequent injection molding process, the circuit board  16  is encapsulated over a large area by the housing cover part  14 , thus being inseparably joined to the housing cover part  14 . At the edges  38  of the housing base part  12  located next to the circuit board  16 , the housing cover part  14  is joined to the housing base part  12 , giving rise to an essentially one-piece housing. 
         [0047]    The individual embodiments differ mainly in terms of the shape of the electric contact region  32 . 
         [0048]    In the above-described first embodiment according to  FIGS. 1 to 10 , the electric contacts  46  are formed on the circuit board  16  itself, for example, in the form of an edge connector. In this case, the electric contact region  32  can be shaped so as to be narrower than the rest of the circuit board  16  and can thus be adapted to the shape of a connector that is to be plugged thereon. 
         [0049]    The second embodiment described with respect to  FIGS. 11 to 15  differs from the first embodiment in that the electric contact region  32  is formed by two contact pins  246  that are separate from each other and that, in turn, are securely joined, for example, by soldering or force-fitting, to the electric contact regions of the circuit board  216  already before the circuit board  16  is inserted into the housing base part  12  (see  FIG. 12 ). Only these contact pins  246  protrude through the passage  40  so that only the ends of the contact pins  246  are arranged in the connector region  30  (see  FIG. 15 ), while the circuit board  216  itself is completely enclosed by the housing base part  12  and by the housing cover part  14 , and is separated from the surroundings of the sensor  10 . Both of the contact pins  246  are surrounded by the section  44  of the housing cover part  14  and partially embedded therein. 
         [0050]    In contrast, in the third embodiment shown in  FIGS. 16 to 23 , the electric contact region  32  arranged in the connector region  30  forms part of the housing base part  12 . For this purpose, two contact pins  346  are provided in the housing base part  12  which, for example, are integrated into the housing base part  12  during the injection-molded thereof. Hence, no passage exists that is closed by the housing cover part  14 , but rather, the housing base part  12  has a media-tight wall  360  at the transition between the connector region  30  and the receptacle  36 , and the ends of the contact pins  346  protrude through said wall  360  into the receptacle  36  or into the connector region  30 . 
         [0051]    In the receptacle  36 , the ends  362  of the contact pins  346  are angled in the direction of the circuit board  316 . The circuit board  316  has electric contact points (not shown here) that establish the electric contact to the ends  362  of the contact pins  346 . 
         [0052]    Further, in the example shown, two additional pins  364 , one each at the corners of the receptacle  36  that are opposite from the contact pins  346 , are pressed into receptacles  366  in the housing base part  12  and they serve to affix and position the circuit board  316  in the receptacle  36 . 
         [0053]    In the third embodiment as well, after the circuit board  316  has been put into place, the injection molding step in which housing cover part  14  is produced and thus joined to the housing base part  12  is carried out in such a way that the receptacle  36  is hermetically sealed.