Patent Publication Number: US-9431378-B2

Title: Light-emitting diodes

Description:
TECHNICAL FIELD 
     This disclosure relates to light-emitting diodes. 
     BACKGROUND 
     WO 2006/012842 describes a light-emitting module. 
     When using light-emitting diodes in motor vehicle headlamps, dissipation of heat generated by the light-emitting diodes during operation is often problematic. Accordingly, it could be helpful to provide a light-emitting diode which is particularly well suited for use in a motor vehicle headlamp. 
     SUMMARY 
     We provide light-emitting diodes including a carrier with a mounting face and including a metallic basic body and at least two light-emitting diode chips affixed to the carrier at least indirectly at the mounting face, wherein an outer face of the metallic basic body includes the mounting face, the at least two light-emitting diode chips connect in parallel with one another, the at least two light-emitting diode chips are embedded in a reflective coating, the reflective coating covering the mounting face and side faces of the light-emitting diode chips, and the light-emitting diode chips protrude with their radiation exit surfaces out of the reflective coating and the radiation exit surfaces face away from the carrier. 
     We also provide light-emitting diodes including a carrier with a mounting face and at least two light-emitting diode chips affixed to the carrier at least indirectly at the mounting face, wherein the carrier includes a metallic basic body, an outer face of the metallic basic body includes the mounting face, the at least two light-emitting diode chips are connected in parallel with one another, the at least two light-emitting diode chips are embedded in a reflective coating, the reflective coating covers the mounting face and side faces of the light-emitting diode chips, and the reflective coating terminates flush with radiation exit surfaces of the light-emitting diode chips facing away from the carrier. 
     We further provide light-emitting diodes including a carrier with a mounting face and at least two light-emitting diode chips affixed to the carrier at the mounting face, wherein the carrier includes a metallic basic body, an outer face of the metallic basic body includes the mounting face, the at least two light-emitting diode chips are connected in parallel with one another, the mounting face is arranged on an upper side of the carrier, the light-emitting diode chips are directly affixed to the carrier at the mounting face, the light-emitting diode chips electrically conductively connect to the metallic basic body, the light-emitting diode chips connect in parallel with one another via the metallic basic body, an electrically insulating layer is affixed to the carrier on a lower side of the carrier, and the electrically insulating layer has a thermal conductivity of at least 2 W/(mK). 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1, 2, 3 and 4  are schematic sectional illustrations showing examples of light-emitting diodes. 
     
    
    
     DETAILED DESCRIPTION 
     The light-emitting diodes may comprise a carrier. The carrier may be in the form of a plate, for example. That is to say that the lateral extent of the carrier is great in comparison with its thickness. The carrier has a mounting face provided to accommodate components of the light-emitting diode. 
     The light-emitting diode may comprise at least two light-emitting diode chips. The light-emitting diode preferably comprises a large number of light-emitting diode chips, for example, four or more light-emitting diode chips. The light-emitting diode chips of the light-emitting diode are provided for the purpose of generating electromagnetic radiation in the frequency band of infrared radiation to UV radiation during operation. The light-emitting diode chips in this case represent the light sources of the light-emitting diode. Preferably, the light-emitting diode itself emits white light. 
     The at least two light-emitting diode chips, preferably all of the light-emitting diode chips of the light-emitting diode, may be affixed to the carrier at least indirectly at the mounting face. “At least indirectly” means that it is possible for there to be further material such as an intermediate carrier or a connector, for example, an adhesive or solder between the light-emitting diode chips and the mounting face. 
     The carrier may have a metallic basic body. Preferably, the metallic basic body then forms the main part of the carrier. For example, the metallic basic body accounts for at least 90% of the volume and at least 90% of the weight of the carrier. The metallic basic body is formed with a metal with good electrical and thermal conductivity such as copper, for example. 
     The metallic basic body comprises an outer face comprising the mounting face of the carrier. That is to say that at least points of the outer face of the metallic basic body of the carrier form the mounting face, at which the at least two light-emitting diode chips are affixed at least indirectly to the carrier. 
     The at least two light-emitting diode chips, preferably all of the light-emitting diode chips of the light-emitting diode, connect electrically in parallel with one another. 
     The light-emitting diode may comprise a carrier with a mounting face and at least two light-emitting diode chips affixed to the carrier at least indirectly at the mounting face. In this case, the carrier comprises a metallic basic body which has an outer face which comprises the mounting face of the carrier. The at least two light-emitting diode chips of the light-emitting diode are in this case connected in parallel with one another. 
     The light-emitting diode described here is based on the idea, inter alia, that the arrangement of the light-emitting diode chips of the light-emitting diode as close as possible to a metallic basic body enables particularly efficient spreading of the heat generated by the light-emitting diode chips during operation of the light-emitting diodes. That is to say that the heat generated by the light-emitting diode chips is distributed over the entire volume of the metallic basic body which forms a main part of the carrier as soon as possible after the generation of the heat. 
     The light-emitting diode may comprise at least one opening in the carrier. The opening in this case extends from an upper side of the carrier to a lower side of the carrier, the lower side facing away from the upper side. For example, the opening extends from a top face of the carrier to a bottom face of the carrier. The opening passes through the carrier preferably completely. The opening can be in the form of a bore in the carrier, for example, or the opening is already provided during manufacture of the carrier. The opening has an inner face in which the material of the carrier adjoins the opening. In this case, the inner face is covered by an electrically insulating material. For example, the entire inner face of the opening is coated with the electrically insulating material, with the result that there is no point within the opening at which material of the carrier is exposed. 
     For example, the opening is used to accommodate a fixing device to mount the light-emitting diode. For example, the fixing device may be a screw or a locating pin for a press fit. 
     The electrically insulating material used to cover the inner face of the opening is, for example, an electrically insulating plastic or a layer formed by an electrically insulating material such as silicon dioxide or silicon nitride. In addition, the electrically insulating material can be ceramic. The electrically insulating material can contain a boron nitride or consist of a boron nitride, for example. The electrically insulating material can cover the side face or the side faces of the opening completely in the form of a layer. The electrically insulating material can be applied with a thickness of 30 μm to 100 μm, for example. 
     The light-emitting diode can comprise a plurality of openings, for example, two or more openings in the carrier. Each of the openings is then configured in the described manner and is used to accommodate a fixing device to mount the light-emitting diode at the intended use location. 
     The opening may pass through the metallic basic body completely. That is to say that the at least one opening is formed in the carrier in the region of the metallic basic body. The inner face of the opening is then preferably covered completely by the electrically insulating material at least in the region of the metallic basic body. That is to say that the metallic basic body is not exposed at any point of the opening and can therefore be kept free of potential in a simple manner during operation of the light-emitting diode. 
     The mounting face of the carrier may be arranged on the upper side of the carrier and the light-emitting diode chips are affixed to the carrier directly at the mounting face. For example, the light-emitting diode chips are in this case soldered onto the carrier at the mounting face. In other words, the light-emitting diode chips are applied directly to the metallic basic body of the carrier and in direct contact therewith, apart from a connector such as the solder, for example. Then, an electrically insulating layer is affixed to the carrier on the lower side of the carrier, i.e., on the side of the carrier which faces away from the mounting face. The electrically insulating layer is preferably in direct contact with the metallic basic body. The electrically insulating layer covers the carrier on its lower side preferably completely, apart from the openings. That is to say that the metallic basic body is then also covered completely by the electrically insulating layer on its side facing away from the mounting face. 
     The electrically insulating layer in this case has a thermal conductivity of at least 2 W/(mK). 
     In other words, in this example, the light-emitting diode chips are mounted directly on the metallic basic body which enables optimum thermal coupling of the light-emitting diode chips to the carrier. The entire metallic basic body of the carrier acts as a heat-spreading element. In this case, the light-emitting diode chips can be electrically conductively connected to the metallic basic body and connected in parallel with one another via the metallic basic body. The electrical insulation of the metallic basic body is formed on the side facing away from the mounting face by the electrically insulating layer which is characterized by particularly high thermal conductivity. This design of the light-emitting diode enables early spreading of heat directly at the heat source, i.e., the light-emitting diode chips and, thus, a particularly low thermal resistivity of the entire light-emitting diode. 
     The electrically insulating layer may be a ceramic layer. This means that the electrically insulating layer may have ceramic properties. The electrically insulating layer can then contain a ceramic material or consist of a ceramic material. The electrically insulating layer in this case has a thermal conductivity of at least 2 W/(mK). 
     The electrically insulating layer may have a thickness of 30 μm to 100 μm. For example, the electrically insulating layer has a thickness of 50 μm to 70 μm. 
     The electrically insulating layer may contain boron nitride or consist of boron nitride. In this case, the electrically insulating layer can have a thickness of 30 μm to 100 μm, for example, of 50 μm to 70 μm. The electrically insulating layer in this case has a thermal conductivity of at least 2 W/(mK). 
     The light-emitting diode chips may be electrically conductively connected to the metallic basic body and connected in parallel with one another via the metallic basic body. That is to say that the light-emitting diode chips may then be at the same electrical potential as the metallic basic body on that side of the light-emitting diode chips which faces the metallic basic body. 
     The opening may pass through the electrically insulating layer on the lower side of the carrier completely. That is to say that the electrically insulating layer is also interrupted by the opening. In this case, the opening can be produced before or after the electrically insulating layer is applied to the metallic basic body. A side face of the electrically insulating layer in the opening is preferably covered by the electrically insulating material with which the inner face is also covered in the region of the metallic basic body. For example, for this purpose, the inner face of the opening is only coated with the electrically insulating material once the electrically insulating layer has been applied on the lower side of the carrier. In this case, it is also possible for the electrically insulating layer on the lower side of the carrier to be formed with the same material, i.e., the electrically insulating material. 
     An intermediate carrier to which the light-emitting diode chips are affixed may be arranged between the light-emitting diode chips and the mounting face. The intermediate carrier can comprise a ceramic material or consist of a ceramic material. That is to say that the intermediate carrier then represents electrical insulation of the light-emitting diode chips with respect to the carrier and therefore in particular with respect to the metallic basic body. In this case, the electrically insulating layer on the lower side of the carrier can also be dispensed with. 
     The carrier may comprise a further electrically insulating layer affixed to the metallic basic body on the side facing the light-emitting diode chips. An electrically conductive layer to which the light-emitting diode chips are electrically conductively connected is then arranged on that side of the further electrically insulating layer which faces away from the metallic basic body. The electrically conductive layer can in this case be structured to form conductor tracks which make contact between the light-emitting diode chips of the light-emitting diode. 
     The opening may pass through the further electrically insulating layer and the electrically conductive layer completely. In this case, side faces of the further electrically insulating layer and the electrically conductive layer in the opening are covered by the electrically insulating material. That is to say that, in this example, preferably the entire inner face of the opening is covered by the electrically insulating material. With the exception of the metallic basic body, the further electrically insulating layer and the electrically conductive layer are also covered by the electrically insulating material and thus electrically insulated with respect to the fixing device in the opening. 
     The at least two light-emitting diode chips of the light-emitting diode may be embedded in a reflective coating. Preferably, all of the light-emitting diode chips of the light-emitting diode are embedded in the reflective coating. 
     “Embedded” means that the reflective coating covers at least points of the light-emitting diode chips and is in direct contact with the light-emitting diode chips at the covering locations. For example, it is possible for the reflective coating to terminate flush with a radiation exit surface of the light-emitting diode chips which faces away from the carrier. Those side faces of the light-emitting diode chips which run transversely with respect to the mounting face can then be covered completely, for example, by the reflective coating. 
     Furthermore, it is also possible for the reflective coating to cover the radiation exit surface of the light-emitting diode chips facing away from the mounting face. The reflective coating then has a small thickness there such that light generated in the light-emitting diode chips during operation can pass to the outside through the reflective coating. At the radiation exit surfaces of the light-emitting diode chips, the reflective coating then acts as a diffusing layer which diffuses the light passing through. 
     The reflective coating preferably also covers at least parts of the mounting face in addition to the light-emitting diode chips. For example, the mounting face is covered completely by the material of the reflective coating completely at exposed points, i.e., in particular where there is no light-emitting diode chip. In particular, it is also possible for the entire carrier to be covered by the reflective coating on its surface facing the light-emitting diode chips. That is to say that all of the exposed regions of the carrier at this surface are then covered by the reflective coating. 
     In this case, it is in particular possible for the reflective coating to appear to be white to a viewer when illuminated with daylight, for example. That is to say that the light-emitting diode itself can appear to be white when covered in a suitable manner by the reflective coating, i.e., when, for example, all of the exposed faces of the carrier at the surface facing the light-emitting diode chips are covered by the reflective coating. 
     In this case, the reflective coating is diffusely reflective, for example. The reflective coating can be formed by a matrix material. The matrix material can contain a silicone, for example, or consist of a silicone. In addition, it is possible for the matrix material to be a mixture of a silicone with an epoxide, i.e., a so-called “silicone-epoxide hybrid” material. Reflective particles can be introduced into the matrix material of the reflective coating. The reflective particles are formed, for example, by one of the following materials, i.e., they can consist of one of the following materials: TiO2, BaSO4, ZnO, AlxOy, ZrO2. In particular, radiation-reflecting particles formed with ZrO2 are particularly well suited to reflect blue or ultraviolet light. 
     In particular, it is also possible for the reflective coating in the matrix material to contain a mixture of different reflective particles formed by different materials from among those mentioned. In this way, the reflection spectrum of the reflective coating can be matched particularly well to the requirements of the light-emitting diode. 
     The light-emitting diode described here will be explained in more detail below with reference to examples and the associated Drawings. 
     Identical, similar or functionally identical elements have been provided with the same reference symbols in the Drawings. The Drawings and the size ratios of the elements illustrated therein with respect to one another should not be considered as being to scale. Instead, individual elements may be illustrated as being excessively large for reasons of improved representation and/or better understanding. 
       FIG. 1  shows a schematic sectional illustration of a first example of a light-emitting diode. The light-emitting diode comprises a carrier  1 . The carrier  1  comprises a metallic basic body  12  forming the main part of the carrier. In this case, the metallic basic body  12  accounts for at least 95% of the volume and the weight of the carrier. The metallic basic body is formed with copper, for example, i.e., it contains copper or consists of copper. 
     The carrier  1  comprises a further electrically insulating layer  13  applied to points of the outer face  121  of the metallic basic body  12  on the upper side  1   a  of the carrier. The further electrically insulating layer  13  can in this case be in direct contact with the metallic basic body  12 . An electrically conductive layer  14  structured to form conductor tracks, for example, is applied to that side of the further electrically insulating layer  13  facing away from the metallic basic body  12 . 
     The carrier  1  has openings  3  passing through the carrier, i.e., the metallic basic body  12 , the further electrically insulating layer  13  and the electrically conductive layer  14 , completely from the upper side  1   a  of the carrier  1  to the lower side  1   b  of the carrier  1 . 
     Inner faces  31  of each opening  3  are in this case covered completely by the electrically insulating material  4 . That is to say that the electrically insulating material  4  covers side faces of the metallic basic body  12 , side faces  131  of the further electrically insulating layer and side faces  141  of the electrically conductive layer. 
     Each opening is used to accommodate a fixing device  8 , for example, a screw. The fixing device  8  is in this case provided to mount the light-emitting diode (see also  FIG. 3  for the fixing device  8 ). 
     In the example shown in  FIG. 1 , light-emitting diode chips  2  are applied, for example, soldered, directly to the metallic basic body  12  at the mounting face  11  of the carrier  1 . The light-emitting diode chips  2  in this case connect in parallel with one another and are at the same electrical potential as the metallic basic body  12  on that side of the light-emitting diode chips facing the metallic basic body  12 . 
     The light-emitting diode chips  2  electrically conductively connect to the electrically conductive layer  14  structured to form conductor tracks by bonding wires  21 . It is possible here for one of the bonding wires  21  to electrically conductively connect directly to the metallic basic body  12 . For example, the light-emitting diode comprises four light-emitting diode chips provided to generate blue light and/or UV radiation during operation. A luminescence conversion material is then arranged downstream of each light-emitting diode chip  2  or all of the light-emitting diode chips  2  together, the luminescence conversion material converting at least some of the electromagnetic radiation generated by the light-emitting diode chips  2  during operation such that, overall, white light is emitted by the light-emitting diode. 
     In the example shown in  FIG. 1 , a cover  7  mechanically fixedly connected to the carrier  1 , is arranged downstream of all of the light-emitting diode chips  2 . The cover  7  may be a cover consisting of glass, for example. In addition, it is possible for the cover  7  to contain particles of a ceramic luminescence conversion material or to consist of a ceramic luminescence conversion material. 
     On the lower side of the carrier  1  facing away from the light-emitting diode chips  2 , the electrically insulating layer  5  is preferably applied directly to the metallic basic body  12 , the electrically insulating layer electrically insulating the carrier  1 . Side faces  51  of the electrically insulating layer can be covered by the electrically insulating material  4  in the region of the openings  3  which pass through the electrically insulating layer  5  completely. In this case, it is also possible for the electrically insulating material  4  and the electrically insulating layer  5  to be formed with the same material. 
     In connection with  FIG. 2 , a second example of a light-emitting diode will be explained in more detail with reference to a schematic sectional illustration. In contrast to the example shown in  FIG. 1 , in this example contact is made with the light-emitting diode chips  2  via the electrically conductive layer  14  structured to form conductor tracks. For this purpose, the electrically conductive layer  14  directly contacts with connection points (not shown) of the light-emitting diode chips  2 . In the example shown in  FIG. 2 , the further electrically insulating layer  13  for this purpose covers at least the side faces of some light-emitting diode chips of the light-emitting diode at certain points. The electrically conductive layer  14  passes along the electrically insulating layer  13  at side faces of these light-emitting diode chips  2  to the electrical connection points of the light-emitting diode chips  2 . 
     In connection with  FIG. 3 , a third example of a light-emitting diode is explained in more detail with reference to a schematic sectional illustration. In this example, in contrast to  FIG. 1 , there is no electrically insulating layer  5 . The light-emitting diode chips  2  are electrically insulated from the metallic basic body  12  of the carrier  1  via an electrically insulating intermediate carrier  6  arranged between the metallic basic body  12  and the light-emitting diode chips  2 . The intermediate carrier  6  consists of a ceramic material, for example. On that side of the intermediate carrier  6  facing away from the metallic basic body  12 , metallic conductor tracks can be structured via which the light-emitting diode chips  2  connect in parallel on the intermediate carrier  6 . The light-emitting diode shown in  FIG. 3  is characterized by a simplified manufacturing procedure over the examples shown in  FIGS. 1 and 2  since there is no need for application of the electrically insulating layer  5 . There is the disadvantage, in contrast to the examples explained in connection with  FIGS. 1 and 2 , that there is no direct spreading of heat from the light-emitting diode chips  2  into the metallic basic body  12 , but the thermal conductivity is reduced by the intermediate carrier  6 . 
     In all of the examples, it is possible for the cover  7  to be provided or dispensed with. The cover  7  can form mechanical protection for the light-emitting diode chips  2  and furthermore exhibit optical properties such as radiation conversion and/or radiation diffusion. 
     A further example of a light-emitting diode is explained with reference to the schematic sectional illustration shown in  FIG. 4 . In contrast to the previous examples, the light-emitting diode in this case comprises a reflective coating  151  in which the light-emitting diode chips  2  are embedded. The reflective coating  151  in this case covers the mounting face  11  of the carrier  1  completely. In the example shown in  FIG. 4 , the light-emitting diode chips  2  protrude with their surfaces facing away from the carrier  1 , which represent the radiation exit surfaces of the light-emitting diode chips  2 , out of the reflective coating  151 . For example, the reflective coating  151  terminates flush with these surfaces. In this case, the reflective coating is formed with a matrix material such as silicone, for example, with radiation-reflecting particles, for example, consisting of titanium dioxide, being introduced into the matrix material. 
     A reflective coating  151  can be used in this case in all of the examples of the light-emitting diode. For example, in the example shown in  FIG. 3 , the reflective coating  151  would then also cover the exposed outer face of the intermediate carrier  6  completely. 
     Our light-emitting diodes are not restricted to the examples by the description relating thereto. Instead, this disclosure includes any novel feature and combination of features which includes in particular any combination of features in the appended claims, even if the feature or combination has not itself been explicitly specified in the claims or examples.