Abstract:
Measures are introduced to make possible a low-cost packaging of sensor chips having a media access. For this purpose, the sensor chip is first mounted on a substrate and is contacted. The sensor chip is then at least partially embedded in a molding compound. Finally, at least one portion of the media access is produced by the subsequent structuring of the molding compound.

Description:
RELATED APPLICATION INFORMATION 
       [0001]    The present application claims priority to and the benefit of German patent application no. 10 2010 064 108.1, which was filed in Germany on Dec. 23, 2010, the disclosure of which is incorporated herein by reference. 
       FIELD OF THE INVENTION 
       [0002]    The present invention relates to the packaging of sensor chips which require a media access. These can be pressure sensors or the special implementation thereof as microphones, or also optical sensors used for gas analysis, such as CO2 gas detectors, for example, or thermal sensors for measuring temperature and heat flux, which are generally referred to as thermopiles. 
       BACKGROUND INFORMATION 
       [0003]    It is intended that a packaging protect the sensor chip from mechanical and chemical environmental effects. Moreover, the type of packaging, respectively the type of housing determines how the sensor chip can be mounted and contacted in situ. Accordingly, a seemingly wide array of packaging variants for sensor chips are discussed the related art. 
         [0004]    In the case of an MEMS microphone component, the housing additionally takes on some of the microphone functionality since both the acoustic connection, as well as the rear-side volume of the microphone membrane are determined to a large degree by the housing design. Since the packaging considerably influences the transmission characteristic of an MEMS microphone, the known packaging variants for microphone chips mostly involve relatively complex and costly specialized approaches. 
       SUMMARY OF THE INVENTION 
       [0005]    The exemplary embodiments and/or exemplary methods of the present invention provides measures which make possible a low-cost packaging of sensor chips having a media access. 
         [0006]    To this end, the packaging concept according to the present invention provides for the sensor chip to be first mounted on a substrate and to be contacted there. The sensor chip is then at least partially embedded in a molding compound. Only subsequently thereto is at least one portion of the media access produced by the later structuring of the molding compound. 
         [0007]    In practice, mold housings have proven to be very rugged and simple to manufacture. The exemplary embodiments and/or exemplary methods of the present invention provide for this packaging concept to also be used for sensor chips which require a media access. The exemplary embodiments and/or exemplary methods of the present invention have, namely, recognized that such a media access may be realized in a mold housing, at least in portions thereof, using standard methods, as are used to produce plated-through holes for housings, which are generally referred to as through-mold vias (TMV). It is only through the use of this structuring method, which has been developed in a completely different technical context, is it possible to cost-effectively implement a mold housing for the sensor chips of the type discussed here. 
         [0008]    The media access may be readily produced by boring the molding compound or also with the aid of a laser structuring method, as is used within the framework of the TMV process. In contrast to the TMV process, in which a mold substrate is provided with through holes, it is intended that the molding compound of the sensor chip packaging merely be structured to a predefined depth during fabrication of a media access. A metal layer is advantageously integrated in the packaging as a defined limitation for the laser structuring. 
         [0009]    As already discussed above, the present invention may be advantageously embodied and further refined in various ways. To this end, reference is made, on the one hand, to the claims that are subordinate to the independent claims and, on the other hand, to the following description of two exemplary embodiments of the present invention with reference to the figures. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1   a ,  1   b , and  1   c  illustrate the configuration of a first sensor chip packaging according to the present invention with reference to schematic cross-sectional representations. 
           [0011]      FIGS. 2   a ,  2   b ,  2   c , and  2   d  illustrate the configuration of a second sensor chip packaging according to the present invention with reference to schematic cross-sectional representations. 
       
    
    
     DETAILED DESCRIPTION 
       [0012]    The two exemplary embodiments described in the following each relate to the packaging of an MEMS microphone chip having a microphone membrane, which needs to be connected to the acoustic access channel in the packaging. 
         [0013]      FIG. 1   a  shows such a microphone chip  1  after it has been mounted face-up, thus with the component rear side on a planar substrate  2 , and has been electrically contacted with the aid of bonding wires  4 . In the present case, a first portion  51  of an acoustic access channel  5  is formed within substrate  2 . 
         [0014]    This portion  51  of acoustic access channel  5  extends in parallel to the substrate plane and opens through into an opening  50  in the substrate surface. Microphone chip  1  is configured on substrate  2  in a way that allows microphone membrane  11  to be positioned directly over opening  50 . Moreover, it is discernible in FIG. la that the bottom area of first portion  51  of acoustic access channel  5  is provided with a metal layer  6 , at least in one region laterally next to microphone chip  1 . 
         [0015]    Once microphone chip  1  has been mounted and contacted on thus prepared substrate  2 , it is embedded, together with bonding wires  4 , in a molding compound  3  suited for defining the microphone package design. In this context, it is necessary to provide a rear-side volume for microphone membrane  11  that is sealed against the conduction of sound.  FIG. 1   b  shows the microphone package following the molding process, the rear side volume not being shown in detail here. 
         [0016]    Only subsequently thereto is the already cured molding compound  3  structured in order to expose acoustic access channel  5 . To this end, a bore  52 , originating at the top side of the package and extending to first portion  51  of acoustic access channel  5  in substrate  2 , leading into the same, is introduced into molding compound  3 . In the exemplary embodiment illustrated here, bore  52  is produced with the aid of a laser structuring method, as is used for fabricating through-mold vias for package-on-package housings. Metal layer  6  of acoustic access channel portion  51  in the orifice region of bore  52  forms a stop layer for the laser structuring and thus constitutes a depth limitation for bore  52 . Together with portion  51 , bore  52  then forms acoustic access channel  5  of microphone package  10 , which is illustrated in  FIG. 1   c.    
         [0017]    As in the case of first packaging variant described above, microphone chip  1  is also mounted face-up on a planar substrate  7  in the case of second packaging variant illustrated in  FIG. 2   a  through  2   d , and is electrically contacted with the aid of bonding wires  4 . In this case, however, it is intended that the sound be conducted to the top side of microphone membrane  11 . Accordingly, in contrast to the first packaging variant, no specially prepared and already structured substrate is needed here. Rather, all portions of acoustic access channel  8  are produced in molding compound  3  that encases microphone chip  1 . 
         [0018]    To this end, substrate  7  is provided with a metal layer  6  in a region next to the mounting surface of microphone chip  1 . Once microphone chip  1  is mounted, a layer of a chemically desorbing polymer  9  is then applied to populated substrate  7 , which, on the one hand, extends over metal layer  6  and, on the other hand, to over microphone membrane  11  of microphone chip  1 , as is illustrated in  FIG. 2   a . This polymer layer  9  functions as a “place holder” for a first portion  81  of sound access channel  8 . 
         [0019]    Subsequently thereto, microphone chip  1 , together with bonding wires  4 , is embedded in a molding compound  3  suited for defining the microphone package design. Rear-side volume  12  is enclosed here between microphone membrane  11  and substrate  7 , as is illustrated by  FIG. 2   b.    
         [0020]    As in the case of the first packaging variant, sound access channel  8  is exposed by the laser structuring of already cured molding compound  3 , in that a bore  82  is introduced into molding compound  3 . This bore  82  extends from the top side of the package to metal layer  6  on the substrate surface, as is illustrated in  FIG. 2   c.    
         [0021]      FIG. 2   d  shows the microphone package following a desorption step in which polymer  9  was removed. Portion  81  is thereby exposed. Together with bore  82 , it now forms sound access channel  8  of microphone package  20 .