Abstract:
In an optoelectronic component assembly and a method for the production thereof, the optoelectronic component assembly includes an optoelectronic component arranged on a support element, which is surrounded by a closed dam. An encapsulation is arranged in an inner area of the dam, which encapsulates the optoelectronic component and includes two sealing materials. The inner area of the dam may be filled with a first sealing material up to the top edge of the optoelectronic component. The inner area of the dam located above the optoelectronic component is filled with a second transparent sealing material at least in one area of the window.

Description:
FIELD OF THE INVENTION 
     The present invention relates to an optoelectronic component assembly as well as to a method for producing an optoelectronic component assembly. 
     BACKGROUND INFORMATION 
     An optoelectronic component assembly is described in Japanese Published Patent Application No. 8-241976. An optoelectronic component, designed as a CCD chip, which is encircled by a concentrically disposed dam, is positioned on a carrier element. The component is connected via bonding wires to conductor lines or circuit traces in the carrier element and, in this manner, is electrically contacted. A potting, sealing or encapsulation material, made up of two transparent encapsulation materials, is placed in the inner region of the dam. Thermally induced stresses can cause cracks in the encapsulation material and, in some instances, damage the bonding wires. It is, therefore, proposed, in a first step, to introduce a first transparent encapsulation material into the inner region of the dam, to thermally cure this material and, in the process, to eliminate any air bubbles from the encapsulation material. In a second process step, a second transparent encapsulation material is subsequently introduced into the inner region of the dam and thermally cured, in turn, in order to remove any air bubbles present in the second encapsulation material. In this manner, it is possible to ensure that neither of the two encapsulation materials contains any more air bubbles. If, at this point, materials having greatly deviating thermal expansion coefficients are used in a component assembly of this kind, the thermal stresses can produce cracks in the bonding wires. The transparent encapsulation materials or epoxy resins (α=50-70 ppm/K) used, on the one hand, and the materials used for the carrier element and, respectively, the bonding wires (α=15-25 ppm/K), on the other hand, for instance, have distinctly different expansion coefficients. 
     It is an aspect of the present invention to provide an optoelectronic component assembly, as well as a suitable method for its manufacture, which may ensure that the bonding wires provided for contacting the optoelectronic component are not damaged even when subject to varying temperatures. 
     SUMMARY 
     Example embodiments of the optoelectronic component assembly according to the present invention and example embodiments of the method according to the present invention are described below. 
     In accordance with an example embodiment of the present invention, a first encapsulation material is introduced into the inner region of the dam, the first encapsulation material e.g., reaching up to the top edge of the optoelectronic component. A second, transparent encapsulation material is introduced over this first material, at least in one spatially defined window region. The first encapsulation material may be selected to be different from the second, transparent encapsulation material. A consideration when selecting the first encapsulation material is, in particular, that it have a lowest possible thermal expansion coefficient, which is approximately adapted to the thermal expansion coefficient of the bonding wires and of the carrier element used. In this manner, thermally induced stresses in the region of the bonding wires and, thus, an undesired cracking or tearing of the same may be avoided. 
     In addition, when selecting the first encapsulation material, it may be provided to select a material which has a roughest possible surface in the cured state. This may provide a good adhesion to the second encapsulation material placed above it, which additionally may ensure that no thermally produced shearing results between the two encapsulation materials which may potentially damage the bonding wires. In addition, when selecting the first encapsulation material, it may no longer be necessary to consider its optical properties, i.e., the material selection may take place solely on the basis of the optimization criteria indicated above. 
     An aspect of the technical production process is derived in an example embodiment of the method according to the present invention when the first encapsulation material and the dam material are made of essentially the same base material and merely have different viscosities, since the first encapsulation material and the dam may then be applied and cured in the same work step. 
     Other aspects of the present invention, as well as details pertaining thereto are derived from the following description of exemplary embodiments, on the basis of the attached figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematized, sectional view of an exemplary embodiment of the optoelectronic component assembly according to the present invention; 
         FIGS. 2   a  to  2   e  each illustrate a method step within the framework of the method of an example embodiment of the present invention for manufacturing an example embodiment of the optoelectronic component assembly according to the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     In schematized form,  FIG. 1  illustrates a lateral sectional view of an example embodiment of the optoelectronic component assembly according to the present invention. Positioned on a carrier element  1  in this case are the other components of the component assembly, which will be discussed in detail in the following. In this example, carrier element  1  may be arranged as a conventional circuit board of FR4 material. Alternatively thereto, other materials come under consideration for carrier element  1 , such as FR5, aluminum oxide, glass, etc. Not discernible in  FIG. 1  are the conductor lines extending in carrier element  1  that are used for electrically contacting optoelectronic component  3  positioned on carrier element  1  and any other components that are present. In the illustrated exemplary embodiment, as an optoelectronic component  3 , an unhoused component  3  in the form of a photodetector is provided, whose radiation-sensitive surface is oriented away from carrier element  1 . Alternatively hereto, a corresponding unhoused light source, a so-called Opto-ASIC or some other optoelectronic element may also be used as an optoelectronic component  3 . 
     The particular optoelectronic component  3  is connected via bonding wires  4   a ,  4   b  to the electrical conductor lines in carrier element  1 , e.g., electrically contacted in a conventional manner via bonding wires  4   a ,  4   b . In the present example, gold is used as the material for bonding wires  4   a ,  4   b . Also usable as bonding wire materials are gold alloys, aluminum, aluminum alloys, copper, etc. 
     In the illustrated exemplary embodiment, optoelectronic component  3  is adhesively mounted on carrier element  1 . This bond may alternatively be produced by alloying, eutectic bonding, anodized bonding, soldering, welding, etc. 
     In addition, the optoelectronic component assembly according to an example embodiment of the present invention includes a dam  2  which is positioned on carrier element  1  and encircles or surrounds component  3  in a closed form. Dam  2  may have the most widely varied peripheral geometries. For example, it may surround component  3  in a quadratic form. Alternatively, however, a rectangular, polygonal, or round dam profile around component  3  may also be provided. 
     Dam  2  has a height h 2 , which, in the present example embodiment, is selected to be distinctly greater than height h 1  of component  3 . Typical values of heights h 1 , h 2  are, for instance, h 1 =450 μm and h 2 =800 μm. 
     A function of dam  2  with respect to the component assembly according to an example embodiment of the present invention is to form the boundary of the surface required for encapsulating or embedding component  3  on carrier substrate  1  using an encapsulation material in the dam inner region. In accordance with an example embodiment of the present invention, for the encapsulation, two encapsulation materials  5 ,  6  are used, which are explained in greater detail in the following. By embedding the component assembly using the two encapsulation materials  5 ,  6 , component  3 , as well as bonding wires  4   a ,  4   b  are protected from mechanical influences. 
     As a suitable dam material, a conventional black epoxy filler substance in the form of a filled epoxy resin may be provided, as sold by the firm Emerson &amp; Cuming under the type designation Amicon 50300 HT. Alternatively, epoxy filler substances of the firm Dexter Hysol may also be used, which are sold under the product identifications FP 4451. 
     In the present exemplary embodiment, dam  2  is made of one single dam layer, as is apparent in FIG.  1 . Alternatively, however, a two- or multi-layer dam construction may also be provided, as described, for example, in German Published Patent Application No. 100 24 336. Another option may be to form dam  2  as an injection-molded part. 
     The encapsulation material placed in the well-type dam inner region encapsulating optoelectronic component  3  may be composed of two different encapsulation materials  5 ,  6 . In this connection, in the illustrated example embodiment, the dam inner region is filled more or less up to the top edge of optoelectronic component  3  with a first encapsulation material  5 . Accordingly, in the illustrated example, the height of first encapsulation material  5  approximately corresponds to height h 1  of component  3 . As a general principle, the height of first encapsulation material  5  may also be somewhat lower. However, it may be ensured that the dam inner region may be filled at a maximum up to the top edge of optoelectronic component  3  with the first encapsulation material, and, accordingly, that the radiation-sensitive or, as the case may be, radiation-emitting surface of optoelectronic component  3  is also not substantially covered by first encapsulation material  5 . 
     In accordance with an example embodiment of the present invention, first encapsulation material  5  is selected so that its thermal expansion coefficient α VM1  is approximately adapted to the thermal expansion coefficient of bonding wires  4   a ,  4   b  (α BD ) and of carrier element  1  (α TE ). For this, a black epoxy filler substance is used, for example, which has a thermal expansion coefficient of α VM1 =18-19 ppm/K. Thus, compared to thermal expansion coefficient α BD =15 ppm/K of bonding wires  4   a ,  4   b , a very good adaptation may be achieved when gold is used as material for bonding wires  4   a ,  4   b . Also, the other materials already mentioned above for bonding wires  4   a ,  4   b  have thermal expansion coefficients within the range of α BD =[15 ppm/K-25 ppm/K]. In a similar manner, when FR4 is used as material for carrier element  1 , a good adaptation to its thermal expansion coefficient α TE =15 ppm/K is provided. Suitable first encapsulation materials  5  are sold, for example, by the firm Emerson &amp; Cuming or Dexter Hysol under the product description Amicon 50500-1 or FP 4450. 
     Accordingly, in the example embodiment, first encapsulation material  5  and the material of dam  2  have the same base material and merely have different viscosities. As will be explained further on, from this material selection, certain advantages may result in the course of an example embodiment of the manufacturing method of the present invention. 
     In addition, first encapsulation material  5  is selected to have a greatest possible surface roughness in the cured state. This may provide for excellent adhesion to the material situated above it, namely second encapsulation material  6 . Second encapsulation material  6  is a commercially available transparent encapsulation material, which is arranged in the inner dam region, at least in a window region above optoelectronic component  3 , thus, for example, in the radiation-sensitive region of the photo-element. The product sold by the firm Dexter Hysol under product designation Hysol OS 2800 may be suitable for second encapsulation material  6 . Alternatively, the encapsulation materials sold by the same firm under product designations Hysol OS 1600, Hysol OS 1900, Hysol OS 2902, Hysol OS 4000 or Hysol OS 4110 may also be suitable for use in this region. 
     In the example of  FIG. 1 , second encapsulation material  6  completely fills up the inner dam region above first encapsulation material  5  and optoelectronic component  3 . Alternatively, however, as already mentioned, merely one smaller window region may also be filled with the material. 
     The arrangement and selection of encapsulation materials  5 ,  6  in accordance with an example embodiment of the present invention may ensure, on the one hand, that the total filling volume in the dam inner region, which must be filled with transparent second encapsulation material  6 , is able to be clearly reduced. As explained above, the problems associated with the thermally induced shearing of bonding wires  4   a ,  4   b  may arise because of the greatly differing thermal expansion coefficients of transparent encapsulation materials, on the one hand, and of bonding wires  4   a ,  4   b  or of carrier element  1 , on the other hand. The reduced filling volume may also have a positive effect in that the stresses caused during curing by the shrinking process may be reduced within the component assembly. In addition, the rough surface quality of first encapsulation material  5  may ensure good interlinking with superjacent second encapsulation material  6 . As a result, any thermally produced shearing off of two encapsulation materials  5 ,  6  from one another or cracking of bonding wires  4   a ,  4   b  may virtually no longer be possible. 
     Besides the foregoing example embodiment of an optoelectronic component assembly, there are other possible alternative example embodiments within the scope of the present invention. Another exemplary embodiment is described in the following in conjunction with  FIGS. 2   a  to  2   e , on the basis of which an example embodiment of the method according to the present invention is also described. 
     In a first process step shown in  FIG. 2   a , unhoused optoelectronic component  13  in the form of an opto-ASIC is first positioned on carrier element  10  or the circuit board and bonded thereto. In addition, optoelectronic component  13  is electrically contacted, which, in a generally conventional manner, may take place via wire bonding and the placement of corresponding bonding wires  14   a ,  14   b.    
     Dam  12  is subsequently placed on carrier element  10  at height h 2  and, as described above, completely surrounds optoelectronic component  13 . The corresponding process step is illustrated in  FIG. 2   b . The appropriate dam material is applied in this example embodiment by a schematically indicated dispensing needle  50  using so-called dispensing technology. As already mentioned, alternatively thereto, a dam or frame element arranged as an injection-molded part may also be placed on the carrier element. 
     In the case of an application using dispensing technology, the desired height h 2  of dam  12  is able to be set in a defined manner by adjusting the traversing rate of dispensing needle  50  and the applied quantity of the dam material, etc. 
     In the subsequent process step illustrated in  FIG. 2   c , a first encapsulation material  15  is introduced in the dam inner region using dispensing needle  50 , e.g., to a maximum height of h 1  of the top edge of the component. As explained above, in this exemplary embodiment, a first encapsulation material  15  is selected which is made of the same base material as dam  12 . For example, a black filled epoxy resin or an epoxy filler substance may be used for this purpose. Dam  12 , as well as first encapsulation material  15  are subsequently cured using a suitable annealing process. 
     In the following process step shown in  FIG. 2   d , in contrast to the first described exemplary embodiment, an additional glass plate  19  is placed on the radiation-sensitive surface of component  13  or of the opto-ASIC. This may be accomplished, as indicated in  FIG. 2   d , before the dam region is filled with the second transparent encapsulation material. Alternatively, however, glass plate  19  may first be pressed onto the surface of component  13  following completion of any residual filling of the dam inner region with the transparent second encapsulation material. 
     In the case of components  13  having unpassivated active surfaces, the placement of glass plate  19  protects or seals these surfaces. Moreover, by selecting the thickness of glass plate  19  to be large enough, an additional mechanical protection may be ensured for bonding wires  14   a ,  14   b . Alternatively to the described exemplary embodiment, the glass plate may also have a larger thickness and then project slightly out of the second encapsulation material. 
     In the next process step illustrated in  FIG. 2   e , the remaining dam inner region is finally filled with second encapsulation material  16  using dispensing needle  70 , more or less up to the top dam edge, for which purpose, as explained above, a transparent encapsulation material is used. 
     Within the framework of the present invention, there are also alternative variants in addition to the example embodiments.