Abstract:
The invention relates to a printed circuit board element ( 10 ), comprising at least one flexible printed circuit board part ( 12 ) and at least one rigid printed circuit board part ( 11 A,  11 C;  34, 35; 37 ) having a component ( 17 ), which is accommodated in a cavity ( 14 ) and with a light-emitting or light-receiving part ( 17 ) projects over the edge ( 18 ) of the cavity ( 14 ), wherein the flexible printed circuit board part ( 12 ) has a flexible layer ( 15′ ) made of an optical, photo-polymerizable material ( 15 ), in which an optical fiber ( 15 ) is structured in alignment with the light-emitting or light-receiving part ( 17 ) of the optoelectronic component ( 17 ) by way of radiation.

Description:
FIELD OF THE INVENTION 
     The invention relates to a printed circuit board element with at least one flexible printed circuit board portion and with at least one rigid printed circuit board portion with a component; furthermore, the invention relates to a method of producing such a printed circuit board element. 
     BACKGROUND OF THE INVENTION 
     Printed circuit board elements with rigid and flexible printed circuit board portions were proposed with regard to the necessity of foldable and bendable connections for the most varying of applications, starting from applications for the mounting of LEDs in steps, cf. e.g. DE 199 09 399 C1, up to applications of such partially flexible printed circuit boards in electronic devices with a foldable portion, such as mobile telephony devices, yet also portable computers (laptops, notebooks) and so-called handhelds, where, beyond hinge joints, a corresponding flexibility was required with regard to data and signal connections, respectively. Besides the application for foldable and/or bendable connections, rigid-flexible printed circuit board elements can also be used for so-called flex-to-install applications, in which the flexible printed circuit board part is bent only once in order to establish a connection between two printed circuit boards (e.g. motherboard, daughtercard), whereupon the flexible printed circuit board will then remain in this state. The structure of rigid-flexible printed circuit boards and their production, respectively, has been described in various documents, such as in EP 1 659 840 A1, WO 2005/055685 A1 or WO 2004/110114 A1. In these rigid-flexible printed circuit boards, the flexible printed circuit board portions form a type of film hinge between rigid printed circuit boards in order in this manner to enable a pivoting movement between the rigid printed circuit board portions. Copper connections pass over these flexible printed circuit board portions in a conventional manner. 
     On the other hand, it has already become known to integrate optical signal connections in printed circuit boards, cf. e.g. WO 2005/064381 A1, AT 503 027 B1 or US 2002/0028045 A1. Thus, the functionality of the printed circuit boards is substantially increased, and highly complex product applications can be realized, wherein a further miniaturization of the printed circuit boards, an increase in the integration density of switching characteristics and thus a higher product added value are rendered possible. Such printed circuit boards with optical connections can be used in cases where the applications require the transmission of large amounts of data between components or functional units and/or a space-saving design of the connection paths. So far, however, these integrated optical connections have been practically restricted to rigid printed circuit boards, even though in the aforementioned US 2002/0028045 A1 an embodiment with an optical connection on a flexible substrate has already been described. Intrinsically, however, this document relates to the mounting of optical connections on multi-component modules (MCMs), and not on printed circuit boards, and the flexible printed circuit board is only described there in order to be able to produce a flexible installation and, in doing so, an optical connection to another module, production inaccuracies being compensated by means of the flexibility. 
     Now the invention is concerned with the object of combining the two aforementioned technologies, namely rigid-flexible-rigid printed circuit board elements on the one hand, and optical connections integrated in printed circuit boards, i.e. optical waveguides, on the other hand, in an efficient manner, in order in this manner to combine the advantages of transmitting high data rates with low space and shielding outlay and of increasing the reliability and design options, and to provide a new high-tech printed circuit board element that offers additional, new options to the electronics sector. 
     SUMMARY OF THE INVENTION 
     A problem to be overcome here consists in enabling a space-saving construction, and in particular as low a structural height as possible in this case despite the additional optical waveguide connection. Above all, there is also the problem in this case of not negatively affecting the flexibility of the composite printed circuit board element as a whole, but to at least retain, if possible, the existing flexibility by means of a very thin flexible printed circuit board part. On the other hand, the demands on a rigid-flexible printed circuit board element should be met in the usual sense, wherein lasting connections are provided instead of temporary ones, and a long-lasting mechanical loading, such as during opening and closing of a mobile telephony device or a portable computer is to be rendered possible. Yet, a use of the rigid-flexible printed circuit board element should also be possible for temporary connections. A rigid-flexible printed circuit board element may, for example, serve for the temporary connection of two printed circuit boards in the form of an electric plug. In this case, the rigid-flexible printed circuit board element constitutes an “optical cable”. 
     From AT 503 027 B1, a printed circuit board element with an embedded optoelectronic component is known which has an integrated mirror for deflecting the light radiation. 
     Therefore, one concern of the invention is in particular to be seen in the fact that an optimum integration of the optoelectronic components in a rigid-flexible printed circuit board element should take place so as to ensure low construction height as well as low thickness of the flexible printed circuit board part and thus its high flexibility in the case of the desired applications. 
     To solve the problem set, the invention provides a printed circuit board element as well as a production method as defined in claims  1  and  17 . Advantageous embodiments and developments are indicated in the dependent claims. 
     In the case of the rigid-flexible printed circuit board element, the mounting of a waveguide layer, i.e. a layer made from an optical material, for example on a separate flexible printed circuit board part and above the optoelectronic component without thereby substantially increasing the structural height is rendered possible in an efficient manner in that the, or each, optoelectronic component is mounted in a cavity in the printed circuit board element, i.e. preferably in the connecting region between a rigid and a flexible printed circuit board portion, particularly preferably in the flexible printed circuit board portion. With its light emitting part or light-receiving part, the optoelectronic component projects upwards just to such an extent that it is located slightly higher than the upper side of the cavity or of the flexible printed circuit board portion, above which the—flexible—layer of the optical photo-polymerizable material is applied. In this layer made of optical material, the optical waveguide is structured by means of irradiation, in alignment with the light-emitting part or light-receiving part, respectively, of the optoelectronic component. For this structuring, preferably the multi-photon absorption method already described in WO 2005/064381 A1 is used in which a chemical reaction, i.e. polymerization, is activated by the simultaneous absorption of a plurality of—generally two—photons. With regard to the two-photon absorption, this process generally is also called the TPA process (TPA—two photon absorption). For example, the optical material to be structured is transparent for the employed excitation wavelength (e.g. 800 nm) of a light source (in particular, a laser source). Therefore, there will be no absorption within the material and no single-photon process. In the focus range of the light or laser beam, however, the intensity is so high that the material absorbs two (or more) photons, as a result of which a chemical reaction is activated. In this case, it is also an advantage that due to the transparency of the optical material for the excitation wave-length, all the points in the layer can be reached and thus three-dimensional structures can be inscribed in the layer without any problems. “Three-dimensional” is in this case understood to mean that the optical waveguide need not only extend in one plane (x-y plane), but rather can also vary in height (z-direction), i.e. it may extend in the x, y and also z-directions, but also that the optical waveguide can exhibit changes in its shape over its longitudinal extent in the x, y and z-directions, e.g. by its cross-section being able to change from circular to flat-elliptical, back to circular, and to up-right elliptical. 
     The multi-photon absorption process described is a single step structuring process in which no multiple exposures and no wet-chemical development steps are required. 
     Besides, for further information, reference may be made to WO 2005/064381 A1. 
     As has been mentioned, an integration of an optical waveguide structured by a photon-absorption process in a rigid-flexible printed circuit board element is enabled in an efficient manner for the first time by means of the invention, wherein a compact bonding of the optical waveguide to the optoelectronic components which are completely embedded in the optical material is achieved, and a high flexibility is ensured in the flexible region of the hybrid printed circuit board element. 
     It may be mentioned that in WO 2005/078497 A1, a—rigid—multi-layer printed circuit board element is described in which a blind-hole-type depression is bored from the upper side thereof, in which subsequently an optoelectronic component is mounted which communicates with an optical bus between two insulating layers. In that case, the component is glued to a discontinuous metal layer in the depression. 
     The connection between the—in particular separate—flexible printed circuit board portion and the rigid printed circuit board portion(s) may preferably be achieved with the aid of an adhesive layer. The adhesive layer may for example be formed by a thermosetting adhesive, pressure-sensitive adhesive, so-called pre-pregs (i.e. non-cured, fibreglass-reinforced epoxy resin layers) or the like. Here, it is suitable to obtain a prefabricated, rigid-flexible printed circuit board element such that a still continuous rigid printed circuit board portion is provided with an adhered flexible printed circuit board portion, e.g. a polyimide film, whereupon a region of the rigid printed circuit board portion is removed by milling out or cutting out or such processing, so that at least one rigid printed circuit board portion, preferably two rigid printed circuit board portions, which are present at a distance from one another, remain, wherein the, or each rigid printed circuit board portion is connected to the flexible printed circuit board portion via the adhesive layer. In this pre-fabricated printed circuit board element thus obtained, which, of course, may be provided with copper layers or conductive copper tracks, with through-connections, such as in the form of micro-vias (μ-vias) or the like in the usual manner, the cavities or hollow spaces for the optoelectronic components are then provided e.g. by milling, these cavities in particular being formed in the flexible printed circuit board portion as well as in the adhesive layer; accordingly, the respective inserted and mounted optoelectronic component may be seated with its base surface directly on the upper side of the rigid printed circuit board portion, wherein it may be contacted there in a conventional manner. Laterally and on the upper side, the optoelectronic component in this phase of production is still free, and when afterwards the optical, photo-polymerizable material is applied for forming the optical layer, the optoelectronic component is enclosed by this optical material all around and on the upper side and embedded therein. For this application of the layer of the optical photo-polymerizable material, a flexible frame may be applied before-hand on the upper side of the printed circuit board element, which frame surrounds the optical layer after the latter has been applied and keeps the optical material, which is viscous when it is being applied, in place. Subsequently, the flexible frame may also be removed again so as to increase flexibility. This flexible frame may for example be made of a polyimide film. 
     According to an alternative embodiment, the previously mentioned separate flexible substrate layer may be omitted as flexible printed circuit board part, and the flexible printed circuit board part may be formed by the optical layer itself. During the production of such a printed circuit board it is possible to proceed in such a manner for example that at first only a rigid substrate is present, which is provided with the cavities and the optoelectronic components arranged therein, as well as, subsequently, with the optical layer in which the optical waveguide is structured, a part of the rigid substrate finally being removed so that, e.g. between two remaining spaced-apart rigid printed circuit board parts, only the flexible layer formed solely by the optical layer remains. 
     The or each optoelectronic component may be constructed with an integrated deflection mirror connected at its upper side, as a light emitting part or else as a light-receiving part, and preferably only this deflection mirror projects beyond the upper side or upper edge of the cavity, whereas the optoelectronic component proper is housed completely within the cavity, i. e. is especially located lower than the upper side of the flexible printed circuit board portion. The optoelectronic component may for example be a VCSEL (vertical cavity surface emitting laser) component, it may in this case however also be a different, well-known optoelectronic component, such as a photodiode or a phototransistor, just as well as a light-emitting diode (LED). The flexible printed circuit board portion itself may likewise carry conventional copper tracks which, in the finished rigid-flexible printed circuit board element, are embedded and protected in the optical layer. 
     The optical layer may be provided with a flexible cover layer as a protective layer and thus be protected. Besides a mechanical protection, the flexible cover layer may also protect against light irradiation so as to prevent interferences of the light waveguide. To this end, the flexible cover layer preferably is coloured and absorbs light irradiated in from the outside. This cover layer may for example be made of polyimide. 
     In principle, the present rigid-flexible printed circuit board element may in further steps also be developed to a multilayer printed circuit board. 
     From the previous statements, it already results that at least two rigid printed circuit board parts are provided in the rigid-flexible printed circuit board element at a distance from one another, the distance or space between these two rigid printed circuit board parts being bridged by the flexible printed circuit board part; an optoelectronic component (a transmitter and a receiver) being arranged in a cavity on each rigid printed circuit board part, and the optical waveguide extending between these two optoelectronic components. 
     Of course, further components may also be housed in a conventional manner in the present rigid-flexible hybrid printed circuit board. 
     The present technology utilizes the advantages of the rigid-flexible printed circuit board and of the TPA structuring of optical waveguides for producing highly-integrated optical signal connections in a printed circuit board element. By means of the proposed technology, it is possible in this case that both optical material, which as a rule is comparatively expensive, is saved and a very thin and consequently highly flexible bending region of the printed circuit board element is realized. 
     The present technology may be employed in optoelectronic hybrid printed circuit boards with multi-mode or single-mode wave guides for high data transfer rates, with a great design freedom being achieved. Fields of application are for example optoelectronic backplanes, flexible and rigid-flexible printed circuit boards, such as for mobile phones or laptops and hand-helds. For such applications, a high flexibility and reliability of the flexible connection is important in view of the frequent opening and closing. 
     A particular advantage resides in the minimizing of the layer thickness, primarily also of the optical material, in the flexible regions of the present rigid-flexible printed circuit board elements, which is of particular importance for the rigid-flexible printed circuit boards with the many hinge-type connecting regions. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be explained still further on the basis of preferred exemplary embodiments, to which it should not be restricted however, and with reference to the drawing. 
       In the figures: 
         FIG. 1  shows a schematic cross-section through a rigid-flexible printed circuit board element with an integrated optical connection; 
         FIG. 2  shows an embodiment of a rigid-flexible printed circuit board element in a cross-section comparable to  FIG. 1 , which embodiment is somewhat modified in comparison thereto; 
         FIGS. 2A-2L  show consecutive stages in the production of such a printed circuit board element according to  FIG. 2 ; 
         FIGS. 3-10  show further modifications of a rigid-flexible printed circuit board element in sections similar to  FIGS. 1 and 2 ; 
         FIGS. 11 and 11A  show, in a schematic section and in a schematic top view, respectively, an embodiment of a printed circuit board element according to the invention with an optical waveguide at various levels; and 
         FIG. 12  shows yet another embodiment of a rigid-flexible printed circuit board element according to the invention, wherein here two different functions are illustrated for the sake of simplicity. 
     
    
    
     DETAILED DESCRIPTION 
     In  FIG. 1 , a rigid-flexible printed circuit board  10  is only quite schematically shown, without a true-to-scale illustration of the individual components, which printed circuit board has a rigid substrate  11  as a base, from which two rigid printed circuit board parts (portions)  11 A,  11 C are formed; these rigid printed circuit board parts  11 A,  11 C define two rigid areas  11 ′ and are separated from each other by an open region B which has been obtained by removing a substrate portion  11 B indicated in broken lines, and which is bridged by a flexible printed circuit board part (portion)  12  that provides a bendable connection between the two rigid printed circuit board parts  11 A and  11 C. 
     In the exemplary embodiment shown, a separate flexible printed circuit board part  12 , e.g. a polyimide film, is provided, which is attached onto the two rigid printed circuit board parts  11 A and  11 C with the aid of an adhesive layer  13 . 
     When producing this so-far described rigid-flexible printed circuit board element  10  it is basically possible to proceed as will be explained hereinafter on the basis of  FIGS. 2A to 2L  in connection with the modified embodiment according to  FIG. 2 . In short, a continuous rigid substrate  11 , e.g. made of FR4 material, i.e. a cured, fiberglass-reinforced epoxy resin plate, can be used. The adhesive layer  13  may consist of a conventional single or multi-component adhesive which may for example be curable in a thermally cross-linking manner. Yet, also a pressure-sensitive adhesive or a thermoplastic adhesive may be used, just as the adhesive layer  13  may also consist of non-cured epoxy resin layers, in particular fibreglass-reinforced epoxy resin layers (pre-pregs). The flexible substrate for the flexible printed circuit board part  12  is pressed onto the rigid substrate  11  via such an adhesive layer  13  or resin layer. Both the adhesive layer  13  and the flexible printed circuit board part  12  are used in a pre-assembled state so that prefabricated cavities  14  are obtained in certain regions. 
     Subsequent to the mounting of the flexible printed circuit board part  12  as well as to further steps, such as structuring etc., cf. also the following description by way of  FIGS. 2 to 2L , the substrate part  11 B will be taken out of the rigid substrate  11  in the region B so that the two rigid printed circuit board parts  11 A and  11 C remain. The part in which the now removed substrate part  11 B existed and which now is free, is bridged by the flexible printed circuit board part  12 , as a result of which a bendable connecting region in the manner of a film hinge is obtained here, conductive connections existing in this flexible connecting region, however, as a rule. 
     In particular, an optical connection is integrated in the present rigid-flexible printed circuit board  10 , an optical material  15  being applied as optical layer  15 ′ in which an optical waveguide  16  is structured for example in the manner described in WO 2005/064381 A1. A common optical material  15  for forming the layer  15 ′ is for example an inorganic-organic hybrid material, such as an organically modified ceramic material which is produced by means of a sol-gel process. Another known optical material is an inorganic-organic hybrid glass which is likewise produced in a sol-gel process and doped with a photoinitiator (benzyl-dimethyl-ketal). This hybrid glass consists of methyl acrylate with a silica/zirconia network. Further known materials are for example photosensitive imides or polyimides, respectively, organo-silsesquioxanes, silicone rubbers or the like. 
     However, before the optical material  15  is applied on the hybrid printed circuit board with the rigid printed circuit board parts  11 A,  11 C and the flexible printed circuit board part  12 , the desired optoelectronic components  17  are inserted in the cavities  14 , which components, in the exemplary embodiment shown in  FIG. 1 , rest with their lower sides directly on the rigid printed circuit board parts  11 A,  11 C. The contacting of these optoelectronic components  17  may e.g. be effected in a conventional manner via wire-bond connections (gold wire contactings), yet also via subsequent micro-via contactings (connections by means of coppered laser bores after the integration of the components in the printed circuit board), or also with the aid of a contacting method such as described in WO 2005/125298 A2, however; in the latter instance, the cavities  14  would also be present in the rigid printed circuit board parts  11 A,  11 C, cf. also  FIGS. 2 and 2A  to  2 L to be described hereinafter. 
     As the optoelectronic components  17 , a laser diode, or a VCSEL component, and a photodiode, respectively, are used for example. Since these optoelectronic components  17  are inserted in prefabricated cavities  14  instead of being simply put onto the flexible printed circuit board part  12 , an extremely low structural height is rendered possible, particularly in the region of the flexible connection between the two rigid printed circuit board parts  11 A,  11 C. By “sinking” the components  17  in the cavities  14  of the pre-fabricated rigid-flexible printed circuit board element  10 , the light emission field of the optoelectronic component functioning as a light emitter, e.g. the left-hand component  17  in the illustration according to the drawing, as well as the light detection field of the light receiver component (e.g. a photodiode) may be brought just scarcely above the edge  18  of the cavity  14 , or of the uppermost flexible layer of the—separate—flexible printed circuit board part  12 . This allows a minimum layer thickness  19  of the optical layer  15 ′ above the separate flexible printed circuit board part  12 , which leads to savings in optical material on the one hand, and primarily to the realization of a very thin and, thus, highly flexible layer  15 ′. 
     From  FIG. 1  it can be seen that in the present exemplary embodiment, the optoelectronic components  17  are provided with deflection mirrors  20  put thereupon, whereby said components project over the edges  18  of the cavities  14  solely with these deflection mirrors  20 . Between these deflection mirrors  20  as light emitting part and light receiving part, respectively, of the optoelectronic components  17 , the optical waveguide  16  structured by a TPA process extends, also termed optical guide  16  for short hereinafter. In an optical guide  16  inscribed in such a manner having a circular cross-section for example with a diameter of for example 30 μm and with remaining “cladding” layers formed by the remaining optical layer  15 ′ and having a thickness of, e.g., 35 μm above and below the optical guide  16 , an optical layer  15 ′ having a thickness of merely 100 μm can thus be provided. Therefore, when using a thin, flexible substrate film as the flexible substrate part  12 , for example with a thickness of merely 25 μm, a highly flexible printed circuit board part  12 ′ can be realized as a whole, including the integrated optical guide  16 . By adapting the thickness of the adhesive layer  13 , the height of the optoelectronic components  17  may further be equalized such that the optical material  15  on the separate flexible printed circuit board part  12  achieves a minimum thickness. 
     The thickness of the optical layer  15 ′ can be adjusted by a further pre-assembled flexible frame layer which forms a frame  21  that is pressed on the uppermost layer of the separate flexible printed circuit board part  12 . This flexible frame  21  consists for example of a polyimide film just as the flexible printed circuit board part  12  does, and it forms a boundary for the optical material  15  which during the production process preferably is filled as a viscous liquid into the cavities  14  and applied as the layer  15 ′, the optoelectronic components  17  being practically completely embedded (apart from the base surface). To increase the flexibility, the flexible frame  21  may subsequently also be removed again. 
     Instead of using a polyimide film for forming the flexible frame  21 , also a liquid material (silicone rubber, polyimide compounds, etc.) which, e.g., may be printed on or injected, may be applied to the flexible printed circuit board part  12 . 
     The frame  21  can be applied prior to the insertion of the components  17  or thereafter. 
     Finally, the optical layer  15 ′ may also be protected by a flexible cover layer or coat  22 —merely hinted at in FIG.  1 —for which a polyimide film may likewise be used for example. This flexible cover layer  22  protects the optical layer  15 ′ not only mechanically, but also against light irradiation so as to prevent interferences in the light transmission. To this end, the flexible cover layer  22  preferably constructed to be coloured and capable of absorbing light radiated in from the outside. 
     As an alternative to the above-described production using a flexible frame  21  and pouring in the optical material  15 , the optical layer  15 ′ could also be applied by means of stencil printing or e.g. by means of inkjet technology. At first, the rigid substrate  11  is scored on the upper side at the locations where it should be broken later on. Finally, the flexible printed circuit board part  12  will be pre-assembled for example from polyimide or flexible fibreglass-reinforced epoxy resin layers or the like, and those areas, in which components should be introduced later on, are cut out, e.g. by milling out, laser cutting, punching or the like. The flexible printed circuit board part  12  is applied on the rigid substrate with the aid of an adhesive layer  13 , and compressed with the former. 
     The rigid-flexible printed circuit board element  10  thus obtained may, in further steps, also be further processed to obtain a multilayer printed circuit board. 
     The flexible layer, or the flexible printed circuit board portion  12 ′, as a whole may also carry copper tracks in a conventional manner, which is not further illustrated in  FIG. 1 , wherein these copper tracks (e.g. for power supply) then are embedded and protected in the optical layer  15 ′. 
     In an alternative embodiment, the separate flexible substrate film  12  may also be omitted. In this case, the cavities  14  will previously be formed in the rigid printed circuit board parts  11 A,  11 C, wherein the optical material  15  is directly applied to the rigid substrate  11 , even before removing the substrate part  11 B for obtaining the region B for the flexible connection, and the optical guide  16  is structured. After removal of the substrate part  11 B in the region B, a flexible substrate portion  12  is in turn obtained which then, however, will be formed solely by the optical layer  15 ′. 
     In the following, various modifications and developments—as partially already suggested before—regarding the present printed circuit board element will briefly be described in more detail on the basis of  FIGS. 2 to 12 . 
     In  FIG. 2 , a printed circuit board element  10  is shown which is modified relative to that of  FIG. 1  insofar as there the cavity  14  is provided not only in the flexible printed circuit board portion  12 , but also in the rigid printed circuit board parts  11 A,  11 B. Thus, the optoelectronic components  17  may project more deeply into the assembly in z-direction, so that the flexible printed circuit board portion  12  which for example in turn is glued to the two rigid printed circuit board parts  11 A,  11 B by means of an adhesive  13 , may be comparatively thin and/or each component  17  may be comparatively high. Furthermore, it can also be seen from  FIG. 2  that the optoelectronic components  17  are fixed in the rigid printed circuit board parts  11 A,  11 B by means of a non-conductive adhesive  23 . Moreover, electrical connecting elements  24 ,  25 ,  26  and  27  of the components  17  can also be seen in  FIG. 2  on the lower side of the printed circuit board element  10 . These connecting elements  24 ,  25  consist for example of copper. 
     Incidentally, the structure of the printed circuit board element  10  according to  FIG. 2  corresponds to that according to  FIG. 1  so that a further explanation may be superfluous, particularly since also for mutually corresponding components, corresponding reference numbers are also used. 
     For producing such a printed circuit board element  10  according to  FIG. 2  (and, accordingly, also the printed circuit board element  10  according to  FIG. 1 , and of the printed circuit board elements according to  FIG. 3  ff, respectively, still to be explained in more detail), it is possible for example to start with a carrier material  1  having a copper layer  2  laminated thereon, as illustrated in  FIG. 2A . If contacting of the components  17  from the lower side is desired, according to  FIG. 2B  holes  3  will be bored in the copper layer  2 , e.g. by laser boring; these holes  3  will later on be used for contacting (cf.  FIG. 2 ). Subsequently, according to  FIG. 2C , a pre-preg is applied to the base substrate  1 - 2  for forming the substrate  11  according to  FIGS. 1 and 2 , cavities  14 ′ having been previously made in the pre-preg, e.g. by laser cutting, punching, milling or the like. Subsequently, according to  FIG. 2D , scoring lines  4  are made in the pre-preg (substrate  11 ) on the upper side in order to allow for an easy separation of the middle part  11 B of the substrate later on (cf. also  FIG. 1 ). 
     As can be seen from  FIG. 2E , a separate flexible substrate part  12 , e.g. a polyimide film or a flexible pre-preg having cavities  14 ″ produced by e.g. laser cutting, punching, milling etc., is glued to the pre-preg substrate  11  with the aid of the adhesive layer  13  mentioned (e.g. a specific adhesive or a pre-assembled pre-preg), wherein, however, the region of the separable central part  11 B of the substrate is not glued, i.e. in the region  13 B between the scoring lines  4 , no adhesive  13  is present. 
     According to  FIG. 2F , now the flexible frame  21  is glued to the hitherto obtained structure, in particular at the rim side onto the flexible printed circuit board part  12 , for example in the form of a further flexible substrate, such as a polyimide film including an adhesive layer (not illustrated) having an appropriate clear inner space (e.g. made by laser cutting, punching, milling, etc.); as an alternative, also printing on or injecting a liquid material, e.g. silicone rubber or polyimide compounds that are still liquid, is conceivable, an appropriate curing for forming the flexible frame  21  following thereafter. The structure thus obtained now is ready for receiving the optoelectronic components  17  in the formed cavities  14  overall, as well as the optical material  15  for forming the optical waveguide  16 . 
     To introduce the desired optoelectronic components  17  into the cavities  14 , electrically non-conductive adhesive layers  23  are now introduced in said cavities according to  FIG. 2G . As an alternative, it would, of course, also be possible however to apply an appropriate adhesive directly onto the components  17 . Besides, instead of an adhesive that has to be introduced in liquid form, an adhesive tape may also be used. 
     Subsequently, the optoelectronic components  17  are inserted into the cavities  14 , for example in a form with deflection mirrors  20  put thereon, and they are securely glued with the aid of the adhesive layers  23 ; cf.  FIG. 2H . 
     It may be mentioned that equipping with the optoelectronic components  17  may, of course, also be effected immediately after the holes  3  have been made in the copper layer  2 , as illustrated in  FIG. 2B , that is to say also before the application of the pre-assembled layers  11 ,  12  (with  13 ) as well as  21  are applied. 
     When the structure according to  FIG. 2H  has been obtained, the optical material  15  can be introduced within the frame  21  and into the cavities  14 , the optical material  15  being provided as a resin or as a pouring mass, wherein the components  17  will be completely embedded in the optical material  15 , cf.  FIG. 2I . 
     In the optical layer  15 ′ thus obtained, the optical waveguide  16  is then structured according to  FIG. 2J  in the previously described manner known per se, so as to produce the desired optical communication connection between the components  17 . If—depending on the optical material  15 —a curing or stabilization of this optical material  15  is required, this step may now likewise be carried out. 
     According to  FIG. 2K , the original carrier material  1 , e.g. a carrier film, is then pulled off, and the adhesive  23  is removed in alignment with the component contacts, e.g.  28 , for example chemically, or with the aid of laser rays, by plasma ablation etc., so that holes  29  in the copper layer  2  as well as in the adhesive layers  23  in alignment with the contacts  23  form. According to  FIG. 2L , the copper layer  2  then is structured, and copper introduction into the holes  29  takes place so that the components  17  are provided with the lower contact faces  24 ,  25 ,  26  and  27  already explained above by way of  FIG. 2 . It will then only be necessary to separate the central part  11 B of the substrate  11 , or of the pre-preg, respectively, whereupon the rigid-flexible printed circuit board element illustrated in  FIG. 2  and having the integrated optical connection to the optical waveguide  16  is obtained. 
     In  FIG. 3 , a rigid-flexible printed circuit board element  10  is illustrated in a comparable sectional representation in a manner similar to  FIG. 2 , wherein, however, in comparison with  FIG. 2 , a flexible and, for example, also light-impermeable cover layer  22  is additionally provided. This cover layer  22  is applied in the course of the process according to  FIGS. 2A-2L , preferably after the step according to  FIG. 2L , specifically before the central substrate part  11 B is removed. The cover layer  22  protects the optical layer  15 ′ both mechanically and optically with regard to disturbances by external light sources. 
     In  FIG. 4 , a modification of the rigid-flexible printed circuit board element  10  according to  FIG. 2  is shown insofar as the flexible printed circuit board part  12  is provided with an already structured copper layer  30  with appropriate copper connections which, in the finished structure, thus are inwardly located and protected by being embedded or covered by means of the optical material  15 . Moreover, also through-connections can be produced in a conventional manner, for example to the lower side of the printed circuit board element  10 , as this is illustrated in  FIG. 4  at  31  by way of example. In this embodiment, the optical guide  16  may be utilized as a broadband connection between the components  17 , whereby for this a shielding is not required. The electrical connections with the aid of the copper layer  30  can be utilized for a communication with low data rates and/or for a power supply. 
     By way of comparison, in  FIG. 5  a further possibility of electrical connections via conductive tracks for a rigid-flexible printed circuit board element  10  according to  FIG. 2  is shown, wherein on the upper side, i.e. on the frame  21  and on the optical layer  15 ′, a further flexible layer  32  with a copper lamination  33  is applied. This may for example be done after the intermediate stage according to  FIG. 2K  has been achieved, wherein subsequently the copper-plating and structuring as well as, finally, the breaking out of the middle substrate part  11 B is carried out so that the assembly according to  FIG. 5  will be obtained, in which an integrated optical connection (optical guides  16 ) as well as an upwardly arranged copper connection—structured copper coating  33 —have been realized. 
     According to  FIG. 6 , the printed circuit board element  10  may also be structured such that at the beginning, the rigid pre-preg, or substrate  11 ′, respectively, and, thus, the rigid printed circuit board parts  11 A,  11 B are omitted (in which case also the steps according to  FIGS. 2C and 2D  are then no longer required). In this case, the printed circuit board element  10  has no decidedly rigid members right from the beginning, but merely comparatively rigid areas  11 ′ in places where the optoelectronic components  17  are provided and cause a “rigidity”; in all other areas it is, however, flexible, cf. the flexible printed circuit board part  12 ′ with the separate bendable printed circuit board part  12  that originally was directly glued to the copper layer  2  via the adhesive layer  13  ( FIG. 2A ), before the copper layer (cf. step  FIG. 2L ) had been structured for forming the contact surfaces  24 - 27 , and with the flexible optical layer  15 ′. Such a printed circuit board element  10  according to  FIG. 6  may then be connected in various ways with rigid printed circuit board parts, as is explained hereinafter in more detail. 
     According to  FIG. 7 , such a printed circuit board element  10 , as illustrated in  FIG. 2 ,  3 ,  4 ,  5  or  6  (actually, in  FIG. 7  a printed circuit board element  10  according to  FIG. 6  is shown), can be put on further printed circuit board parts  34 ,  35  so as to interconnect them optically. These printed circuit board parts  34 ,  35  are only quite schematically shown in  FIG. 7 , and the connection of the printed circuit board element  10  to these printed circuit board parts  34 ,  35  may, for example be realized by gluing (for example by means of an anisotropic conductive glue), by soldering, by wire bond connections, by micro-via contacting and such technologies. Altogether, the arrangement according to  FIG. 7  may then be seen as a rigid-flexible printed circuit board combination  34 - 10 - 35 . Such printed circuit board modules can also be obtained, or additionally enlarged, respectively, if the arrangement is put on top of another printed circuit board  36 , as shown in  FIG. 8 . 
     On the other hand, it is, of course, also possible to install a rigid-flexible printed circuit board element  10 , as described, in a multilayer arrangement, i.e. to embed it in further printed circuit board layers and compress them therewith. According to  FIG. 9 , a rigid-flexible printed circuit board element  10  is shown which has been inserted in further printed circuit boards  37  and contacted there, whereupon, finally, pressing into a multilayer printed circuit board has occurred in conventional manner to give the arrangement as schematically shown in  FIG. 9 . Here, too, it again holds that—similar to arrangements such as according to FIGS.  7  and  8 —also rigid-flexible printed circuit board elements  10  according to  FIG. 1 ,  2 ,  3 ,  4  or  5 —apart from that according to FIG.  6 —may be used, as shown in  FIGS. 7 to 9 . 
     In  FIGS. 10 and 11 , applications of the present rigid-flexible printed circuit board element  10  using its flexibility are shown. In detail, in  FIG. 10  it is shown how a rigid-flexible printed circuit board element  10  as described before for example on the basis of  FIG. 6  or else by way of  FIG. 1 ,  2 ,  3 ,  4  or  5 , can optically connect a printed circuit board module  34  with a motherboard  36 ′, wherein the flexible printed circuit board part  12  with the optical layer  15 ′ and the optical guide  16 , i.e. the entire given flexible printed circuit board part  12 ′, provides for an adaptation in z-direction. 
     In  FIGS. 11 and 11A , a comparable arrangement with a motherboard  36 ′ as well as printed circuit board modules  34  and  35 ′ is shown, wherein a branching printed circuit board element  10 , by means of optical guide branches  16 A,  16 B by appropriately outward bending (cf.  FIG. 11 ) leads to the motherboard  36 ′, and to the printed circuit board module  35 ′, respectively, arranged thereabove in a per se conventional manner in the manner of a multilayer arrangement. 
     Quite generally, the most varying optical guide geometries can be realized with the aid of the present printed circuit board element  10 , and the most varying modules can be interconnected by the flexibility of the printed circuit board element  10  at different z-levels so as to be able to convey the communications with high data rates directly to the desired end points without having to take the detour via conventional electric (copper) connections. 
     Finally, in  FIG. 12  an application of the present rigid-flexible printed circuit board element  10  is shown in an embodiment with only one optoelectronic component  17 , for example in turn with a deflection mirror  20 , this component  17 , e.g., being able to function as a light emitter (cf. also the arrows  39  in  FIG. 12 ), yet optionally also as a light detector or light receiver (cf. the arrows  40  entered in broken lines). The optical waveguide  16  is by way of example guided to an external location not illustrated further via a head element  38  (e.g. so as to provide coupling to an optical cable or to an external printed circuit board via an optical connector, or so as to be able to use light, e.g. as a display background illumination, or else for sensory applications, such as when impinging light is detected in the component  17 ). In the case of a light emitter, the component  17  may, for example be a VCSEL component or a LED, whereas in the case of a light detector, it is formed for example by a photo-diode or another light sensor. 
     Here, too, it must again be taken into consideration that, even though a printed circuit board element  10  according to  FIG. 6  (yet with one component  17  only) is shown in  FIG. 12 , a configuration approximately according to  FIG. 1  or  2  etc. is, of course, also conceivable, i.e. with a rigid printed circuit board part  11  in the region of the optoelectronic component  17  (wherein the printed circuit board part  34  shown in  FIG. 12  may also be omitted). 
     The present printed circuit board element  10  may, of course, also be modified such that in addition to the optoelectronic components  17 , also further components are embedded in the optical material  15 , in particular in the cavities  14 . Thus, in particular, it is conceivable to co-install, together with the optoelectronic components  17 , also electronic components, such as a driver chip in the case of a VCSEL component and/or an amplifier chip in the case of a photodiode, as optoelectronic components  17 . This is merely quite schematically shown in  FIG. 1  at  17 ′.