Abstract:
One or more aspects of the invention relate to an optical or electronic module with at least one optical or electronic component and a plastic package within which the component is embedded. The component has an operative region that facilitates operative connection with surroundings. The plastic package has a first region, which comprises a transparent polymer compound, and a second region, which comprises a non-transparent polymer compound. The first region extends such that it borders the operative region of the component.

Description:
REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit of the priority date of European application 04090300.7, filed on Jul. 28, 2004, the contents of which are herein incorporated by reference in their entirety.  
       FIELD OF THE INVENTION  
       [0002]     The present invention relates generally optics, and more particularly to an optical or electronic module and one or more techniques for making the same.  
       BACKGROUND OF THE INVENTION  
       [0003]     It is known to embed optoelectronic modules with a transparent embedding material. For example, DE 199 09 242 A1 discloses an optoelectronic module where a leadframe with an optoelectronic transducer is positioned in a module package and embedded with a transparent, moldable polymer material. Light is coupled in or out by means of an optical fiber, which is coupled to a connecting piece of the module package. On the leadframe there is also a driver device or receiving device for the optoelectronic transducer.  
         [0004]     However, the use of embedding materials that are transparent for the respective range of wavelengths has disadvantages in that transparent embedding materials generally have a high coefficient of thermal expansion and, accordingly, when there are great temperature fluctuations, stresses can occur within the embedding or pachaging materials which can damage sensitive bonding wire connections.  
         [0005]     It is therefore advantageous in principle to incorporate fillers within embedding materials which produce a favorable coefficient of thermal expansion. A general disadvantage of the use of such polymers, however, is that an optical path cannot be created within the embedding material.  
       SUMMARY OF THE INVENTION  
       [0006]     The following presents a simplified summary in order to provide a basic understanding of one or more aspects of the invention. This summary is not an extensive overview of the invention, and is neither intended to identify key or critical elements of the invention, nor to delineate the scope thereof. Rather, the primary purpose of the summary is to present one or more concepts of the invention in a simplified form as a prelude to the more detailed description that is presented later.  
         [0007]     One or more aspects of the present invention relate to providing an optical or electronic module which provides desirable thermal properties despite the use of non-transparent embedding material.  
         [0008]     According to one or more aspects of the present invention, an optical or electronic module has a plastic package comprising a first region, which comprises a transparent polymer compound, and a second region, which comprises a non-transparent polymer compound. The first region, with the transparent polymer compound, thereby borders the operative region of the component and preferably extends such that it exclusively borders the component. On the other hand, other components of the module, such as for example an electrical IC chip, resistors, capacitors, etc., and a possibly present carrier, remain substantially free of the transparent polymer compound. They are encapsulated with the non-transparent polymer compound, which has a favorable thermal behavior.  
         [0009]     One or more aspects of the present invention, therefore, relate to using two plastics for the encapsulation, namely a transparent plastic and a non-transparent plastic. The volume of the transparent plastic can be minimized and its use locally restricted, thus making it possible to use the optical or electronic module at higher ambient temperatures.  
         [0010]     According to one or more aspects of the present invnention, an operative region of the optical or electrical component refers to any region that permits an operative connection of the component to the surroundings. For example, an operative region may comprise the photosensitive region of a photodiode, the sensor region of a pressure sensor or a temperature sensor, the light-emitting region of a semiconductor laser or an LED or the area of a lens, a mirror or a prism that is facing the outer side of the module.  
         [0011]     In a preferred embodiement, it is provided that, bordering the first region, an opening is formed in the second region, the operative region of the component being in operative connection with the surroundings via the first region and the opening. To produce such a configuration, it is provided that, after encapsulation with the transparent polymer compound, the component is completely encapsulated with the non-transparent polymer compound. Subsequently, the region over the operative region of the component is partially removed again, for instance by milling or laser ablation, until the optically transparent polymer compound of the first region is exposed. This creates an opening in the second region.  
         [0012]     According to one or more aspects of the present invention, a light-shaping or light-guiding structure is formed on the side of the first region that is facing away from the operative region of the component. For example, a lens, a Fresnel lens or a light guide is formed in the first region.  
         [0013]     According to one or more aspects of the present invention, the second region laterally adjoins the first region and thereby encapsulates further components of the module with the non-transparent polymer compound. Such a further component may merely be a carrier of the module on which the component is arranged.  
         [0014]     According to one or more aspects of the present invention, the component and the first region of the plastic package bordering it can form a prefabricated package (e.g., a “premolded package”). It may be, for example, a complete LED with SMD contacts or a laser diode with SMD contacts. This premolded package can, for example, be placed on a carrier of the module. In such an example, although the subsequently provided second region of the plastic package partly encloses the prefabricated package, it does not cover the first region of the plastic package, so that the optical path is retained. For this purpose, the geometries of the injection molds used for the encapsulation are correspondingly designed.  
         [0015]     According to one or more aspects of the present invention, the transparent polymer compound is applied in advance to the optical or electronic component so that merely the non-transparent polymer has to be applied in an injection mold.  
         [0016]     According to one or more aspects of the present invention, the two regions arranged next to each other (with transparent polymer compound and with non-transparent polymer compound) are produced one after the other, for instance in a 2-component injection-molding process. In such a case, preferably at the border between the first region of the plastic package and the second region of the plastic package there is a bonding interconnector, from which a first bonding wire extends into the first region and a second bonding wire extends into the second region. This permits the electrical contacting of the component in spite of the use of two plastics. The border between the plastics runs straight through the bonding interconnector.  
         [0017]     According to one or more aspects of the present invention, the optical or electronic component may be arranged on a carrier. The carrier of the module is preferably formed as a leadframe, also referred to as a metal carrier or a stamped grid. The leadframe preferably has at least one planar carrier region, also referred to as a “die pad” or “chip island”, and also a plurality of contact leads, which are located at the edge region of the leadframe. The optical or electronic component is in this case respectively arranged on a carrier region. Instead of a leadframe, however, it is also possible in principle for any other carriers to be used. For example, carriers which comprise a patterned film of plastic or a printed circuit board can also be used. It is also possible in principle to dispense with a separate carrier entirely.  
         [0018]     According to one or more aspects of the present invention, a carrier is provided and the optical or electronic component is arranged on a first side of the carrier and at least one further component of the module is arranged on a second side of the carrier. In this case, the second region of the plastic package encapsulates the components arranged on the second side of the carrier. On the first side there is exclusively the transparent polymer compound. This division allows simple application of the polymer compounds and production of the module. Alternatively, however, the second region of the plastic package also partly extends onto the first side of the carrier, but does not cover the first region with the transparent polymer compound.  
         [0019]     As a result, the thermal properties of the module are further improved. According to one or more aspects of the present invention, the optical or electronic component is preferably arranged on the carrier by means of a printed circuit board with via holes. The printed circuit board consists, for example, of customary printed circuit board material or a patterned film of plastic (e.g., of Kapton®).  
         [0020]     According to one or more aspects of the present invention, the optical component preferably comprises an optoelectronic transmitting component or an optoelectronic receiving component, in particular a photodiode, an LED or a semiconductor laser. However, the optical component may, for example, also comprise a lens, an optical filter, a prism, a mirror or the like. If the component comprises an electronic component, it is preferably a sensor, in particular a pressure sensor or a temperature sensor.  
         [0021]     According to one or more aspects of the present invention, a method for producing an optical or electronic module provided with a plastic package is provided. The method includes providing at least one optical or electronic component, the component having an operative region that facilitates operative connection with surroundings of the module. The method also inclused encapsulatiing the component with a first transparent polymer compound that at least borders the operative region, and encapsulating the component, the first, transparent polymer compound and, if present, further components of the module with a second, non-transparent polymer compound. Also, at least some of the second polymer compound is removed such that the first polymer compound is exposed allowing the component to enter into operative connection with the surroundings via the operative region.  
         [0022]     According to one or more aspects of the present invention, after encapsulation with the transparent polymer compound, the component is encapsulated with the non-transparent polymer compound. Subsequently, a region over the component is partially removed again, for example by milling or laser ablation, until the optically transparent polymer compound is exposed.  
         [0023]     According to one or more aspects of the present invention, another method for producing an optical or electronic module provided with a plastic package is provided. The method includes providing at least one prefabricated package having an optical or electronic component and an encapsulation of the component, where the encapsulation comprises a first, transparent polymer compound, the component having an operative region that facilites operative connection with surroundings of the module, and the encapsulation bordering at least the operative region. The method also incluses arranging the prefabricated package on a carrier, and encapsulating the package, the carrier and, if present, further components of the module with a second, non-transparent polymer compound, where the second polymer compound partly encloses the prefabricated package, but does not cover the first polymer compound of the prefabricated package.  
         [0024]     According to one or more aspects of the present invention, the non-transparent polymer compound is realized in a prefabricated package. This is followed by embedding or press-molding with the non-transparent embedding compound.  
         [0025]     According to one or more aspects of the present invention, yet another method for producing an optical or electronic module provided with a plastic package is provided. The method includes providing at least one prefabricated package having an optical or electronic component and an encapsulation of the component, where the encapsulation comprises a first, transparent polymer compound, the component having an operative region that facilitates operative connection with surroundings of the module, and the encapsulation bordering at least the operative region. The method also includes arranging the prefabricated package on a carrier, and encapsulating the package, the carrier and, if present, further components of the module with a second, non-transparent polymer compound. Also, at least some of the second polymer compound is removed such that the first polymer compound is exposed allowing the component to enter into operative connection with the surroundings via operative region.  
         [0026]     According to one or more aspects of the present invention, preferably the partial removal of the second polymer compound takes place by a milling process or a laser ablation process. In this case, the second, non-transparent polymer compound is removed down to the first, transparent polymer compound.  
         [0027]     According to one or more aspects of the present invention, still another method for producing an optical or electronic module provided with a plastic package is provided. The method includes providing at least one optical or electronic component, the component having an operative region that facilitates operative connection with surroundings of the module, and encapsulating the operative region with a first, transparent polymer compound. Also, a further component of the module is encapsulated with a second, non-transparent polymer compound, where the first and second polymer-compounds are formed in different regions of the module.  
         [0028]     According to one or more aspects of the present invention, the first and second polymer compounds are formed next to each other in the module.  
         [0029]     According to one or more aspects of the present invention, a carrier is additionally provided, on a first side of which the optical or electronic component is located, and on a second side of which at least one further component of the module is located, the first and second polymer compounds being provided on different sides of the module. The further component may also be merely the carrier.  
         [0030]     According to one or more aspects of the present invention, an encapsulation of the component with polymer compound preferably comprises embedding or press-molding the component with the polymer compound. The embedding or press-molding may in this case take place in a special mold, in particular an injection mold. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0031]     The invention is explained in more detail below wherein reference is made to the following drawings.  
         [0032]      FIG. 1   a  illustrates a cross sectional view through components of a first exemplary embodiment of an optical module after a first fabrication stage according to one or more aspects of the present invention;  
         [0033]      FIG. 1   b  illustrates a cross sectional view through components of the optical module of  FIG. 1   a  after a further production stage;  
         [0034]      FIG. 1   c  illustrates a cross sectional view of the finished optical module according to the first exemplary embodiment;  
         [0035]      FIG. 2   a  illustrates a cross sectional view of a second exemplary embodiment of an optical module according to one or more aspects of the present invention;  
         [0036]      FIG. 2   b  illustrates a cross sectional view of a prefabricated package of the optical module of  FIG. 2   a;    
         [0037]      FIG. 3  illustrates a cross sectional view through a third exemplary embodiment of an optical module according to one or more aspects of the present invention;  
         [0038]      FIG. 4  illustrates a cross sectional view through a fourth exemplary embodiment of an optical module according to one or more aspects of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0039]     One or more aspects of the present invention will now be described with reference to the drawing figures, wherein like reference numerals are used to refer to like elements throughout. It should be understood that the drawing figures and following descriptions are merely illustrative and that they should not be taken in a limiting sense. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be evident to one skilled in the art, however, that the present invention may be practiced without these specific details. Thus, it will be appreciated that variations of the illustrated systems and methods apart from those illustrated and described herein may exist and that such variations are deemed as falling within the scope of the present invention and the appended claims.  
         [0040]      FIG. 1   c  illustrates a first exemplary embodiment of an optical module according to one or more aspects of the present invention. The module includes an optical component  1  and an assigned electronic device  2 , which are arranged on a leadframe  3 , and also with a plastic package  4 , which consists on the one hand of a transparent polymer material  41  and on the other hand of a non-transparent polymer material  42  and forms regions  41 ,  42  corresponding thereto. In the package  4  there is, bordering the non-transparent material  42 , a package opening  43 .  
         [0041]     The optical component  1  is, for example, a luminescence diode (LED), a semiconductor laser or a photodiode. The electronic device  2  is, for example, a driver or a preamplifier. The optical component  1  preferably takes the form of a prefabricated chip. The electronic device  2  preferably takes the form of an integrated circuit (IC).  
         [0042]     The optical component  1  has on its upper side an operative area  11 . This is, for example, a light-emitting area  11  of an LED chip.  
         [0043]     The leadframe  3  has two planar carrier areas  31 ,  32 , which are also referred to as “die pads” and on which on the one hand the optical component  1  and on the other hand the electronic device  2  are arranged. Furthermore, the leadframe  3  has at its edge a plurality of contact leads. In this case, the contact leads project from the package  4 . Leadframes  3  of this type are known in the prior art, so are not discussed any further.  
         [0044]      FIG. 1   a  illustrates the module represented in  FIG. 1   c  after an initial stage of fabrication. On the leadframe  3 , the optical component  1  and the electronic device  2  are arranged on the carrier regions  31 ,  32 , respectively. The electrical contacting of these module components  1 ,  2  takes place on the one hand by a contact on the underside, which is electrically connected directly to the respective carrier area  31 ,  32 , and on the other hand by means of bonding wires  5 .  
         [0045]     A drop of transparent polymer material  41  is applied to the optical component  1  and hardened. Such a transparent drop is also referred to as a “glob top”.  
         [0046]     Subsequently, according to  FIG. 1   b , the entire arrangement is embedded or press-molded with a non-transparent polymer material  42 , which contains fillers to improve the physical properties. For example, the non-transparent polymer material  42  is press-molded in an injection-molding process around the already present components, in particular also around the drop of transparent polymer material  41 .  
         [0047]     To provide an optical window and make it possible for the optical component  1  to communicate with the outside world, it is then also necessary to remove a partial region of the non-transparent polymer material  42 , and more particularly the partial region which is located between the transparent polymer material  41  and the outer side of the package  4 . The exposure takes place for example by a milling device or by means of a laser ablation device. The package opening  42  represented in  FIG. 1   c  is thereby formed.  
         [0048]     Removal of the non-transparent polymer material  42  in the region of the package window  43  thereby takes place until the optically transparent material  41 , and with it the optical window of the component  1 , is exposed.  
         [0049]     This opportunity is taken to point out that, for the purposes of the present invention, the term “optically transparent” or “transparent” is understood as meaning that the respective material is transparent for the one or more wavelengths emitted or received by the component being considered.  
         [0050]     In a modification of the optical module of  FIG. 1 , it is envisaged to realize a specific geometry  41   a  in the transparent material  41  after exposure of the optical window  43 . This is represented by dashed lines in  FIG. 1   c . In particular, a light-shaping or light-guiding geometry  41   a , for example a lens, a Fresnel lens or a light guide, may be provided. The desired geometry is produced for example by means of a specially shaped miller or with the aid of a laser.  
         [0051]      FIG. 2   a  illustrates a further exemplary embodiment according to one or more aspects of the present invention, in which the optical component  1  is part of a prefabricated package  6  with SMD contacts, which is placed onto a leadframe  3  by a standard component-loading process. The standard component-loading process comprises, for example, adhesive bonding or soldering of the prefabricated component onto the leadframe  3 .  
         [0052]     The prefabricated package  6  is represented in greater detail in  FIG. 2   b . Apart from the actual optical component  1 , it has a carrier material  63 , for example a submount or a leadframe, and also bonding wires  62 . The optical component is surrounded by an optically transparent material  61 . The construction of the package, however, is to be understood as only given by way of example.  
         [0053]     After loading the leadframe  3  with the prefabricated SMD package  6 , the leadframe  3  is encapsulated together with the electronic device  1  and the package  6  by injection-molding with a non-transparent polymer compound  42 . In this case, the geometries of the injection mold used for this are designed in such a way that, although the carrier material  63  of the package  6  is partly enclosed by the non-transparent embedding compound  42 , the optical window of the package  6  remains free of the non-transparent polymer compound  42 .  
         [0054]     In the case of this configuration, the non-transparent embedding compound  42  consequently forms a region of the package which is adjacent and alongside the transparent polymer compound  61  of the prefabricated package  6 .  
         [0055]     In a modification of the production method, the package  6  is initially completely enclosed with the non-transparent polymer compound  42  and, subsequently, the non-transparent polymer compound  42  is removed by means of a milling process or a laser ablation process in a way corresponding to the exemplary embodiment of  FIGS. 1   a  to  1   c.    
         [0056]      FIG. 3  illustrates a third exemplary embodiment of a module according to one or more aspects of the present invention, where the module comprises an optical component  1 , an assigned electrical device  2 , a carrier  3  with two carrier regions  31 ,  32 , a transparent embedding compound  41  and a non-transparent embedding compound  42 . The transparent embedding compound  41  thereby additionally forms an integrated lens  9 .  
         [0057]     The module of  FIG. 3  is produced by a 2-component injection-molding process. The optical component  1 , which is located on the one leadframe carrier region  31 , is embedded with the transparent polymer compound  41 . If the corresponding leadframe carrier region  31  were to have further optical components, for example, these would likewise be embedded with the transparent polymer compound  41 . Following this, the remaining components and regions are packaged with the non-transparent polymer compound  42 . It is immaterial here whether embedding takes place first with the non-transparent polymer compound or with the transparent polymer compound.  
         [0058]     The module has in this case a so-called bonding interconnector  7 . This is a conducting region, from which on the one hand a bonding wire extends to the optical component  1  and on the other hand a bonding wire extends to the electronic device  2 . The bonding interconnector  7  in this case runs through the interface between the transparent polymer  41  and the non-transparent polymer  42 . The bonding interconnector  7  permits electrical contacting between the component  1  and the electronic device  2  in spite of the use of two plastics. In addition, a supporting area for an injection mold may be provided.  
         [0059]     The bonding interconnector  7  may be realized with different materials. For example, it can be realized by a region of the leadframe, by a coated ceramic, by a patterned polymer carrier layer (e.g., of polyimide) or by a printed circuit board, for example.  
         [0060]      FIG. 4  illustrates a fourth exemplary embodiment of an optical module according to one or more aspects of the present invention. The module can be produced in a manner substantially similar to that described with respect to  FIG. 3 . Unlike the configuration depicted in  FIG. 3 , however, the optical component  1  (e.g., an LED, a photodiode) is arranged on one side of a carrier  3 , while electrical components, such as for example an electronic device  2  and also resistors and capacitors, for example, are arranged on the other side of the carrier  3 . The carrier  3  is in this case preferably formed in turn as a leadframe. The optical component  1  is located on a substrate  8  with via holes  81 , in order to lead the electrical contacts to the leadframe  3  onto the upper side of the substrate  8 . The additional substrate  8  is, for example, a printed circuit board or a patterned polyimide layer (usually referred to in the trade as Kapton®).  
         [0061]     In one example, the side with the optical component is encapsulated by injection-molding with a transparent polymer material. By contrast, the opposite side with the electrical components is encapsulated by injection-molding with a non-transparent polymer material.  
         [0062]     In order to keep the volume of the transparent polymer compound small, it is preferred that merely the optical component  1  is encapsulated by injection-molding with a transparent polymer compound  41 , while the other regions (in particular the leadframe  3  and the further substrate  8 ) are encapsulated by injection-molding with a non-transparent polymer compound  42 ,  42 ′.  
         [0063]     It is pointed out that the component  1  may also be an electronic component. The component  1  may be, for example, a sensor chip, such as a pressure sensor and/or a temperature sensor, for example, as are used in the automobile industry.  
         [0064]     Furthermore, it is pointed out that the module may have a number of optical or electronic components as described herein, and a transparent embedding material may be provided locally for each of the components.  
         [0065]     Finally, it is also pointed out that the production of the optical or electronic module preferably takes place as repeats on a multi-cavity mold, where the individual optical or electronic modules are singulated after completion of the production method.  
         [0066]     Although the invention has been shown and described with respect to a certain aspect or various aspects, it is obvious that equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification and the annexed drawings. In particular regard to the various functions performed by the above described components (e.g., assemblies, devices, circuits, etc.), the terms (including a reference to a “means”) used to describe such components are intended to correspond, unless otherwise indicated, to any component which performs the specified function of the described component (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary embodiments of the invention. In addition, while a particular feature of the invention may have been disclosed with respect to only one of several aspects of the invention, such feature may be combined with one or more other features of the other aspects as may be desired and advantageous for any given or particular application. Furthermore, to the extent that includes, or other similar ters are used herein, such terms are intended to be inclusive in a manner similar to the term “comprising.” Also, exemplary is merely intended to mean an example, rather than the best.