Abstract:
A light arrangement ( 1 ) comprising at least two spaced apart contact plates ( 3,5 ) and comprising several LEDs connected to the contact plates ( 3,5 ) in an electrically conducting fashion. The contact plates ( 3,5 ) are spaced apart from one another by an electrically insulating carrier ( 6 ) thereby achieving an optimum heat conduction from the LEDs. The LEDs are electrically mounted to projections extending from one of the contact plates towards the other contact plate. The carrier ( 6 ) is preferably a plastic layer covering at least part of the contact plates ( 3,5 ).

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The invention concerns a light arrangement comprising at least two contact plates spaced apart from one another, and several LEDs connected to the contact plates in an electrically conducting fashion.  
           [0002]    In a known light arrangement, light-emitting diodes (LEDs) are pressed on a punch grid thereby keeping the individual contact plates of the punch grid spaced apart from one another. FIG. 5 a  shows such a known light arrangement  50  comprising two LEDs  51  (so-called HP SNAP LED) whose broad contacts  52  (FIG. 5 b ) are clinched (pressed) onto each of the contact plates  53 ,  54 . The SNAP LED technology, however, has the disadvantage that these LEDs are very expensive and must be purchased in large amounts.  
           [0003]    Printed boards comprising soldered-on LEDs (wired or SMD) are known, in particular, for signal lights. Such printed boards with LEDs assembled are very expensive due to the relatively expensive LEDs and the soldering process.  
           [0004]    Finally also light arrangements are known, wherein several LED chips are mounted directly on a printed board (plate). This method is known as “Chip on Board (COB)”. Such light arrangements are mainly used as back light for symbols or switches and large-scale displays. Due to the broad angle of radiation, these LEDs are not used for signal lights. FIGS. 6 a  and  6   b  show a known light arrangement  60  comprising a COB-LED chip  61  which is mounted on a printed board  62 . The LED chip  61  is mounted with a lower contact surface in an electrically conducting fashion by means of silver conducting adhesive  63  onto a thin gold contact surface (anode)  64  of the printed board  62 . The upper side of the LED chip  61  comprises an upper contact surface which is connected to another gold contact surface (cathode)  66  of the printed board  62  in an electrically conducting fashion by means of a bonded gold wire  65 . The two gold contact surfaces  64 ,  66  are electrically insulated from one another. The LED chip  61  and the two contact surfaces  64 ,  66  are covered by a protective layer  67 . However, due to the very thin deposit of copper on the conductor plate  62 , heat conduction from the LED chip  61  to the surroundings is very low. Therefore, the LED current must be reduced which requires a larger number of LEDs or more expensive LEDs.  
           [0005]    It is therefore the object of the invention, to improve a light arrangement of the initially mentioned type in such a fashion, that a heat dissipation from the LEDs, which is as high as possible, can be achieved with low production costs.  
         SUMMARY OF THE INVENTION  
         [0006]    This object is achieved in the initially mentioned light arrangement in that the contact plates are spaced apart from one another via an electrically insulating carrier.  
           [0007]    The advantage obtained by the invention consists in that heat conduction from the LEDs into the surroundings is considerably improved by the large thickness or cross-section of the contact plates (approximately 0.2 to approximately 1 mm) compared to the copper coating of a conventional printed board. This permits a considerable increase of the maximum admissible LED current and reduction of the required number of LEDs which saves costs. On the other hand, the failure safety at high temperatures can be improved with low current. The small number of structural components and omission of the soldering process and mounting bores permits smaller tolerances for mounting the LED and thus a more uniform appearance. Omission of the printed board production (illumination, etching, lacquering with solder stop lacquer) reduces the environmental burden. This method also permits stepped shoulders in the contact plates. The light arrangement can then be inserted e.g. in rear lights of a vehicle wherein the stepped shoulders facilitate adaptation of the position of the LEDs to the outer contour of the rear light.  
           [0008]    The preferably stripe-shaped contact plates may be commonly punched, cut or etched out of a sheet metal. As an alternative it is also possible to use two individual contact plates which are fixed at a separation with respect to one another through the electrically insulating carrier.  
           [0009]    The carrier may be provided on the upper and/or lower side of the contact plates. The two contact plates can be glued to the common carrier or be mounted in any other fashion.  
           [0010]    In a particularly preferred fashion, the carrier is produced through plastic coating of the contact plates by injection molding. This measure has the advantage that the plastic coating provides protection of the entire light arrangement during transport and assembly. It is possible at the same time to injection mold means which facilitate fixing of the light arrangement in a housing. The carrier may be designed directly as housing of the light arrangement or as housing for connection contacts of the contact plates. These connection contacts of the light arrangement (e.g. contact receivers) are preferably integrated in the contact plates, e.g. punched out, and then also injection-coated. Such a plastic coating can thus simultaneously form a plug housing for the contact receivers thereby omitting the costs for such additional parts. This reduces the number of structural components and also the assembly tolerances since there are no tolerances between contact plates and housing, i.e. the quality is improved and costs are reduced.  
           [0011]    Each LED may at least partly be covered by the carrier, in particular injection-coated, such that the LEDs are protected by the plastic coating. However, the cover must be transparent to the light from the LED.  
           [0012]    Each LED may be mounted to the one contact plate in an electrically conducting fashion and be connected to the other contact plate through a bonded wire in an electrically conducting fashion. This electric connection is particularly suited for COB structural components (e.g. for an LED chip) which are mounted with their lower contact surface to the one contact plate in an electrically conducting fashion. The upper side of the COB structural component comprises an upper contact surface which is connected to the other contact plate by means of a wire in an electrically conducting fashion. Through the COB technique there are no costs for production and assembly of the other LED components (lead frame, housing, . . . ) which considerably reduces the costs for one LED. It is therefore possible to compensate for the light loss caused by the broad light radiation of the COB LED chip through further COB LED chips. The entire light arrangement is nevertheless considerably cheaper than a conventional light arrangement with SNAP LEDs or with soldered LEDs. The distance between LEDs can furthermore be reduced which produces a more homogeneous appearance of the light arrangement.  
           [0013]    Since LED chips have a very broad angle of radiation (up to 180°), the use of Fresnel optics is only somewhat effective. The largest amount of the emitted light reaches the housing and is not detected by the optics. As an alternative, reflector optics would be feasible, but an arrangement of the LED in the focus of the reflector is very difficult due to the small constructional height and the reflector is not very effective. Vaporisation of the reflector surface is required which causes high costs. It is therefore particularly advantageous if the carrier forms one reflector section for the respective LED around each carrier-free seat region. The reflector section may be a polished (e.g. white) funnel which reflects the light radiated laterally by the LED towards the front. This may further increase the optical efficiency of the LED and the number of LEDs required in the light arrangement is reduced. The radiation characteristics of the LED can thus be influenced and adapted to the requirements. The plastic coating of the contact plates and the LEDs inserted into the reflector section render the entire light arrangement more insensitive to damages.  
           [0014]    Protection of the light arrangement is improved if the LEDs are covered in the carrier-free seat region by a separate protective layer each. This protective layer may be e.g. a resin layer or silicone layer which are transparent for the light of the LED.  
           [0015]    Further advantages of the invention can be gathered from the description and the drawings. The features mentioned above and below may be used in accordance with the invention either individually or collectively in any arbitrary combination. The embodiments shown and described are not to be understood as exhaustive enumeration but rather have exemplary character for describing the invention. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0016]    [0016]FIG. 1 shows schematically an embodiment of an inventive light arrangement;  
         [0017]    [0017]FIG. 2 a  shows the first step of a first method for producing the light arrangement shown in FIG. 1;  
         [0018]    [0018]FIG. 2 b  shows the second step of a first method for producing the light arrangement shown in FIG. 1;  
         [0019]    [0019]FIG. 2 c  shows the third step of a first method for producing the light arrangement shown in FIG. 1;  
         [0020]    [0020]FIG. 2 d  shows the fourth step of a first method for producing the light arrangement shown in FIG. 1;  
         [0021]    [0021]FIG. 2 e  shows the fifth step of a first method for producing the light arrangement shown in FIG. 1;  
         [0022]    [0022]FIG. 3 a  shows the first step of a second method for producing the light arrangement shown in FIG. 1;  
         [0023]    [0023]FIG. 3 b  shows the second step of a second method for producing the light arrangement shown in FIG. 1;  
         [0024]    [0024]FIG. 3 c  shows the third step of a second method for producing the light arrangement shown in FIG. 1;  
         [0025]    [0025]FIG. 3 d  shows the fourth step of a second method for producing the light arrangement shown in FIG. 1;  
         [0026]    [0026]FIG. 3 e  shows the fifth step of a second method for producing the light arrangement shown in FIG. 1;  
         [0027]    [0027]FIG. 4 a  shows the first step of a third method for producing the light arrangement shown in FIG. 1;  
         [0028]    [0028]FIG. 4 b  shows the second step of a third method for producing the light arrangement shown in FIG. 1;  
         [0029]    [0029]FIG. 4 c  shows the third step of a third method for producing the light arrangement shown in FIG. 1;  
         [0030]    [0030]FIG. 4 d  shows the fourth step of a third method for producing the light arrangement shown in FIG. 1;  
         [0031]    [0031]FIG. 4 e  shows the fifth step of a third method for producing the light arrangement shown in FIG. 1;  
         [0032]    [0032]FIG. 5 a  shows a light arrangement according to prior art wherein two conductors are held together by LEDs;  
         [0033]    [0033]FIG. 5 b  shows an LED of FIG. 5 a;    
         [0034]    [0034]FIG. 6 a  shows the construction of a COB LED light arrangement on a conventional printed board in a lateral view; and  
         [0035]    [0035]FIG. 6 b  shows the construction of a COB LED light arrangement on a conventional printed board in a top view. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0036]    [0036]FIG. 1 shows a light arrangement  1  comprising one LED, in the embodiment shown an LED chip  2  having two chip contacts.  
         [0037]    The LED chip  2  is mounted on a first contact plate  3  wherein the chip contact located on the lower side of the LED chip  2  is connected to the contact plate  3  in an electrically conducting fashion. The other chip contact located on the upper side of the LED chip  2  is connected to a second contact plate  5  in an electrically conducting fashion via a (bonding) wire  4 . The two contact plates  3 ,  5  which may be punched out of a copper sheet are held at a separation (gap  7 ) from one another via a carrier  6 . The gap  7  should be as small as possible e.g. approximately 0.5 mm. The carrier  6  consists of electrically insulating material (e.g. plastic) and covers the two contact plates  3 ,  5  with an upper and a lower carrier layer  6   a  or  6   b,  wherein the upper side of the contact plates  3 ,  5  is carrier-free around the seat region  8  about the LED  2 . The end faces of the carrier  6  bordering this carrier-free seat region  8  extend at an inclined angle to the optical axis  9  of the LED and thereby form reflector sections  10  which reflect light beams, laterally radiated by the LED, towards the front. To protect the LED chip  2  from damage, the carrier-free seat region  8  is covered with a protective layer  11  which is transparent for the light of the LED. The LED chip  2  and its contacts can correspond e.g. to the COB-LED chip  61  of FIG. 6.  
         [0038]    [0038]FIGS. 2 a  through  2   e  show the individual method steps for producing the light arrangement  1  shown in FIG. 1. A grid  21  comprising two contact plates  3 ,  5  (FIG. 2 b ) is punched, cut or etched out of a sheet metal  20  (FIG. 2 a ) of electrically conducting material (e.g. copper). The contact plates  3 ,  5  are spaced apart from one another by a broad dividing gap  22  and are initially connected via several bridge-like connections  23 . The contact plate  3  has two projections  24  projecting into the separating gap  22 , thereby narrowing the separating gap  22  in this region to the width of the smaller gap  7 , e.g. to approximately 0.5 mm. In contrast to the broad separating gap  22  which may be produced with large tolerances, the smaller gap  7  has only little tolerance and may either be punched or produced by means of a laser. The grid  21  is coated with the carrier  6  of plastic material by inserting the complete grid  21  into an injection molding tool and injection-coating with plastic (FIG. 2 c ). On the upper side of the contact plates  3 ,  5  circular seat regions  8  around the projections  24  and circular regions  25  around the connections  23  are left without plastic or carrier by covering these regions  8 ,  25  during injection molding e.g. by a stamp. The projections  24  are each disposed in the centre of the carrier-free seat regions  8 . To permit electric contact of the contact plates  3 ,  5 , the contact ends  3   a,    5   a  of the contact plates  3 ,  5  also remain carrier-free. The connections  23  are then either separated while still in the injection molding tool or subsequently in a further work step such that the two contact plates  3 ,  5  are completely separated from one another (FIG. 2 d ). Two LED chips  2  each are mounted in an electrically conducting fashion in the carrier-free seat regions  8  with their lower chip contact on the projections  24  of the first contact plate  3  and are connected (bonded) in an electrically conducting fashion with their upper chip contact via the wire  4  with the second contact plate  5  (FIG. 2 e ). Subsequently each LED chip  2  is coated with the transparent protective layer.  
         [0039]    [0039]FIGS. 3 a  through  3   e  show another variant for producing the light arrangement  1  shown in FIG. 1. A grid  32  with the two contact plates  3 ,  5  (FIG. 3 b ) is produced by punching, cutting or etching out of the separating gap  31  from a sheet metal  30  (FIG. 3 a ) of electrically conducting material (e.g. copper) which contact plates are initially still connected at the end via a connection  33 . Projections  34  of the contact plate  3  project into the separating gap  31  thereby narrowing the separating gap  31  in these regions in each case to the width of the narrower gap  7  e.g. to approximately 0.5 mm. The lower chip contact of one LED chip  2  each is disposed in an electrically conducting fashion onto each projection  34  and is connected in an electrically conducting fashion (bonded) with its upper chip contact to the second contact plate  5  via the wire  4  (FIG. 3 c ). The grid  32  is then inserted into an injection molding tool and injection-coated with the carrier  6  (FIG. 3 d ), wherein the contact plates  3 ,  5  in the region of the connections  33  and in the circular seat regions  8  about the LED chips  2  remain carrier-free in each case. The connections  33  are then either separated still in the injection tool or later in a further step (FIG. 3 e ). The contact ends  3   a,    5   a  of the contact plates  3 ,  5  are formed by their ends projecting over the carrier  6 . Subsequently, each LED chip  2  is covered with the transparent protective layer.  
         [0040]    [0040]FIGS. 4 a  through  4   e  show a further variant for producing the light arrangement  1  shown in FIG. 1. Several LED chips  2  are mounted in an electrically conducting fashion, with their lower chip contacts onto a sheet metal  40  (FIG. 4 a ) of electrically conducting material (e.g. copper) (FIG. 4 b ). A grid  42 , comprising the two contact plates  3 ,  5 , is produced by punching, cutting or etching out the separating gap  41  close to the LED chips  2 , the contact plates being initially interconnected at their ends via a connection  43 . Projections  44  of the contact plate  3  project into the separating gap  41  on which the LED chips  2  are mounted. The separating gap  41  is narrowed in these regions to the width of the smaller gap  7 , e.g. to approximately 0.5 mm, by the projections  44 . The upper chip contacts of the LED chips  2  are connected (bonded) to the other contact plate  5  in an electrically conducting fashion (FIG. 4 c ) via a wire  4 . The grid  42  is then inserted into an injection tool and injection-coated with the carrier  6  (FIG. 4 d ) wherein the contact plates  3 ,  5  in the region of the connections  43  and in the circular seat regions  8  about the LED chips  2  remain carrier-free. The connections  43  are then separated still in the injection tool or subsequently in a further step (FIG. 4 e ). The contact ends  3   a,    5   a  of the contact plates  3 ,  5  are formed by their ends projecting over the carrier  6 . Subsequently, each LED chip  2  is coated with the transparent protective layer.