Patent Publication Number: US-2007117248-A1

Title: Method for the production of light-emitting semiconductor diodes

Description:
BACKGROUND ART  
      1. Field of the Invention  
      The invention relates to a process for the production of at least one light-emitting semiconductor diode on a printed circuit board. More particularly, the invention relates to production of a light-emitting semiconductor diode on a printed circuit board with an optical element affixed thereto.  
      2. Description of the Related Art  
      A light-emitting semiconductor diode, e.g. a light-emitting diode or a laser diode, customarily includes an electrical part and a light distributing body which encircles the electrical part at least in certain areas and is at least substantially transparent. Luminescent diodes of this type are used in lights for automobiles, for room lighting, in light modules for communication, in street lights, and the like.  
      A lighting unit can include several light-emitting semiconductor diodes (“light-emitting diodes”) produced on one printed circuit board. The component designated here as printed circuit board can be resistant to bending or susceptible to bending. It can also have the form of foil, where the foil can be resistant to bending or susceptible to bending.  
      A process for the production of light-emitting diodes is known from JP 61 001 067 A. For the formation of the light distribution body in the resin-molding process, the light-emitting chip placed on the printed circuit board is molded around with a resin which penetrates the narrow through holes in the printed circuit board. On drying of the resin, there is a strong shrinkage of the material, whereby the geometry of the light distribution body changes. With this process therefore, only geometrically simple light-emitting diodes can be produced. In addition, the tensile strength of the resin is low. During production as well as during operation, e.g., with a high-power light-emitting chip, mechanical stresses can thus appear. For example, the light distribution body breaks apart. And the light unit fails.  
      The problem underlying the present invention is to develop a process for reproducible production of a high-power light-emitting semiconductor diode on a printed circuit board as well as a corresponding lighting unit with integrated printed circuit board.  
     SUMMARY OF THE INVENTION  
      A method is disclosed for creating a light assembly including a light-emitting diode and a printed circuit board having conductors printed thereon. The method includes the steps of positioning the light-emitting diode on the printed circuit board. Once positioned, the light-emitting diode is connected to the printed circuit board. The light-emitted diode and the printed circuit board are positioned in a mold. A thermoplast is injected into the mold such that the thermoplast extends on both sides of the printed circuit board and over the light-emitting diode. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      Advantages of the invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:  
       FIG. 1  is a partial cross-sectional side view of one embodiment of the invention;  
       FIG. 2  is a partial cross-sectional side view of a second embodiment of the invention having a chip carrier secured thereto;  
       FIG. 3  is a side view of the invention with an optical lens;  
       FIG. 4  is a side view of the invention with a premounted chip carrier;  
       FIG. 5  is a partial cross-sectional side view of the embodiment of  FIG. 4 ;  
       FIG. 6 : light-emitting diode with two bond wires,  
       FIG. 7  is a perspective view of the invention;  
       FIG. 8  is a partial cross-sectional side view of one embodiment of the invention with a light guide secured thereto;  
       FIG. 9  is a cross-sectional longitudinal view of the invention;  
       FIG. 10  is a partial cross section of the invention according to  FIG. 9 ;  
       FIG. 11  is a partial plan view of the invention according to  FIG. 9 ;  
       FIG. 12  is a cross-sectional longitudinal view of the invention with a grid-like printed circuit board;  
       FIG. 13  is a partial cross section of the invention according to  FIG. 12 ; and  
       FIG. 14  is a partial plan view of the invention according to  FIG. 12 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)  
       FIG. 1  shows an individual light-emitting diode  20  which is produced on a printed circuit board  10 . This light-emitting diode  20  is one of a plurality of light-emitting diodes  20  which are mounted on a common printed circuit board  10  in such a manner that they cannot be removed.  
      The printed circuit board  10  is a bend-resistant panel, made of plastic or a composite built up of electrically non-conducting materials, on whose upper side  11 , or underside, electrical printed conductors  12 ,  13  are applied. The printed conductors  12 ,  13  are coated at least in certain areas with a passivation layer  14 . The printed circuit board  10  can also be a metal printed circuit board on whose insulated surface printed conductors can be laminated.  
      In the printed circuit board  10 , three through holes  15 ,  16  are disposed. Two through holes  15  lie in the area of the printed conductors  12 ,  13  while one through hole  16  lies outside of the printed conductors  12 ,  13 . The distance of the two through holes  15  from one another corresponds to the distance of the through hole  15 , represented here on the left, from the through hole  16 . The through holes  15 , cf.  FIG. 7 , are long holes which penetrate the printed conductors  12 ,  13  and the printed circuit board  10 . They are disposed so as to be parallel to one another. The through hole  16  is also a long hole which lies parallel to the long holes  15  and is approximately half as long as they are. The bounding edge of the long hole  16  lying on the upper side  11  is an alignment edge  18 .  
      For the production of the light-emitting diode  20 , a light-emitting semiconductor chip  21  is placed on the thus prepared printed circuit board  10 . During the placement its position is aligned to the alignment edge  18 . The light-emitting semiconductor chip  21  is fastened to the printed conductors  12 ,  13  with electrically and thermally conducting adhesive and/or solder connection  22  at the points which are free of the passivation layer  14 . Instead of a single light-emitting semiconductor chip  21 , a group of light-emitting semiconductor chips  21  can also be placed on the printed circuit board  10  and connected with the printed conductors  12 , 13  in such a manner that the connection is electrically and thermally conducting. The component designated here as light-emitting semiconductor chip  21  can also include a group of individual light-emitting semiconductor chips. In addition, other electrical components, such as resistors, capacitors, etc. can be integrated. It can include a plurality of electrical connections. The assembled printed circuit board  10  can now, through connection of the printed conductors  12 ,  13  to a direct current source, be tested electrically.  
      In the next step of the process the light distribution body  31  is produced. For this, the assembled printed circuit board  10  is introduced into an injection mold which is not represented. Here, the upper side  11  of the printed circuit board  10  with the light-emitting semiconductor chip  21  points downward. On introduction into the injection mold, the printed circuit board  10  is laid on and aligned, with the alignment edge  18 , to a counter contour of the injection mold.  
      After closing the injection mold, a thermoplast, e.g. PMMA, is injected into the cavity of the injection mold. The air in the mold will be expelled and/or suctioned off. The cavities of the mold are filled with thermoplast. In given cases, the interstice  23  between the light-emitting semiconductor chip  21  and the printed circuit board  10  is first filled with another material. The thermoplast penetrates through the through holes  15  of the printed circuit board  10  and engages behind the printed circuit board  10 . The injection mold is shaped in the form of the light distribution body  31  on the printed circuit board  10 . The light distribution body  31  thus produced has the form of a half ellipsoid. It is homogeneous and highly transparent. By the engagement behind, the light-emitting diode  20  is connected, in a fixed manner, to the printed circuit board  10  and can be removed from it only with destruction.  
      After the production of the light distribution body  31 , the electrical printed conductor  12 ,  13  project, e.g. in the radial direction, over the light distribution body  31 . The light-emitting diode  20  thus produced can now be withdrawn from the injection mold. On drying and cooling, the form of the light distribution body  31  essentially does not change at all.  
      It is subsequently possible to injection-mold around the light-emitting diodes  20  on the printed circuit board  10  once again in an additional processing step. The processing steps can be spatially and/or temporally separated. Here an optical lens can be formed on the light-emitting diode  20 . In a sequence of processing steps of this type, a standard module can be produced in the first injection molding step, which then obtains its final form in the second injection molding step.  
      With this process, a light-emitting diode  20  with high power can be reproducibly produced on a printed circuit board. In so doing, a homogeneous light distribution body arises, whose form does not change after its withdrawal from the injection mold. Furthermore, a plurality of forms of the light-emitting semiconductor diode can be realized with this process. The light distribution body  31  can have backcuts, only capable of being produced by injection-molding process, and can include an optical lens, a surface of free form, a diffraction surface, or a fractional surface.  
       FIG. 2  shows a light-emitting diode  20  with a chip carrier  24 . The chip carrier  24  can be a heat insulator, a reflector, a heat sink, and the like. It can also be built up in multiple layers. Thus, the chip carrier  24  can include a thermal insulation layer on which a reflective layer is applied. The chip carrier  24  can also have electrically conducting areas.  
      In the production of the light-emitting diode  20  on the printed circuit board  10  the light-emitting semiconductor chip  21  is first placed on the chip carrier  24  and connected with an electrical and thermally conducting adhesive and/or solder connection  22  to an electrically conducting area of the chip carrier  24 .  
      The light-emitting semiconductor chip  21  is then mounted together with the chip carrier  24  on the printed circuit board  10  and aligned to the alignment edge  18 . An electrically and thermally conductive adhesive and solder connection  26  between the chip carrier  24  and the printed circuit board  10  is produced to electrically connect the light-emitting semiconductor chip  21  to the printed circuit board  10 .  
      The assembled printed circuit board  10  is then, as described in the first embodiment example, introduced into an injection mold, aligned by means of the alignment edge  18 , and injected around.  
       FIG. 3  shows a light-emitting diode  20  with an integrated optical lens  32 . Here, the printed circuit board  10  has two alignment edges  18 ,  19 . The alignment edges  18 ,  19  are two outer edges of the printed circuit board  10  which are disposed so as to be perpendicular to one another.  
      In the mounting of the light-emitting semiconductor chip  21  on the printed circuit board  10 , the position of the light-emitting semiconductor chip  21  is aligned to the printed circuit board  10  using the alignment edges  18 ,  19 .  
      If the printed circuit board  10  assembled with the light-emitting semiconductor chip  21  is introduced into the injection mold, it is aligned, e.g. with the alignment edges  18 ,  19 , to the counter contour of the injection mold.  
      On introduction of the thermoplast into the injection mold, the thermoplast flows around the printed circuit board  10  and penetrates the through holes  15 . The light distribution body  31  produced in the injection molding, here represented above the printed circuit board  10 , can be formed to have the structure of an ellipsoidal frustum whose upper side includes an optical lens  32 . The diameter of this ellipsoidal frustum grows constantly from the printed circuit board  10  out in the direction of the optical lens  32 . The maximum diameter of the ellipsoidal frustum corresponds to the diameter of the optical lens  32  and is approximately twice its height. Its minimum diameter near the printed circuit board  10  is approximately 80% of this diameter.  
      Here the optical lens  32  is a plane lens which is integrated into the light distribution body  31 . However, the optical lens  32  can also have the structure of a convergent lens, a divergent lens, a prism face, a face of free form, a fractional face, a diffraction face, and the like.  
      The light-emitting diodes  20  represented in  FIGS. 4 and 5  are produced in a manner similar to that of the light-emitting diodes  20  which are shown in  FIGS. 1 and 2 . In some instances, the light-emitting semiconductor chip  21  is premounted on a chip carrier  24 , set on the printed circuit board  10 , and aligned to the alignment edge  18 .  
      In these embodiment examples, the light-emitting semiconductor chip  21  is fastened only to one printed conductor  12  with an adhesive and solder connection  22 . The other electrical printed conductor  13  is connected electrically via a bond wire  27  to the light-emitting semiconductor chip  21 . In  FIG. 6 a  light-emitting diode  20  is represented in which the light-emitting semiconductor chip  21  is connected to the printed conductors  12 ,  13  by means of two bond wires  27 .  
      The light-emitting semiconductor chip  21  is introduced into a hollow  41  of the printed circuit board  10  which is coated with a reflecting layer  42 . On introduction of the light-emitting semiconductor chip  21  its position is aligned using the two alignment edges  18 ,  19 .  
       FIG. 8  shows a light-emitting diode  20  with a light guide  51 . The light guide  51  can be rigid or flexible. It is fastened in the light distribution body  31  with a clip connection  52 , formed onto it, and the like. Also, other form-locking and/or force-locking connections are conceivable.  
      In the production of this light-emitting diode  20 , the material of the light distribution body  31  penetrates the two through holes  15 . The light distribution body  31  engages behind the printed circuit board  10  and lies with its full surface on the printed circuit board  10 , on one side of the printed circuit board  10 , specifically the side facing away from the light-emitting semiconductor chip  21 .  
      The alignment edge  18  can be an edge of an alignment face. This alignment face can be the inner wall of a wedge-like or cylindrical hole, the wall of a cylinder, the outer surface of the printed circuit board  10 , the wall of a cylindrical pin, and the like.  
      On introduction of the printed circuit board  10  assembled with the light-emitting semiconductor chip  21  into the injection mold, the light-emitting semiconductor chip  21  is aligned with respect to the injection mold. Here, the light-emitting semiconductor chip  21  can be disposed so as to be normal to the optical axis of the light distribution body  31  to be produced, in or near the origin of the contour of the light distribution body  31 , and the like. The origin is a prominent point in relation to a physical property or a geometrical boundary condition for the description of the contour of the light distribution body  31 .  
      On introduction of the printed circuit board  10  assembled with the light-emitting semiconductor chip  21  into the injection mold, the light-emitting semiconductor chip  21  can lie below, above, or to the side of the printed circuit board  10 . In the injection molding, the thermoplast can be fed from the side of the light distribution body  31 , from the underside of the printed circuit board  10 , or from the side.  
      The thermoplast can flow around a printed circuit board  10 , which includes no through holes  15 . The finished light distribution body  31  then engages around the printed circuit board  10 .  
      The printed circuit board  10  can be built up in multiple layers. They can have several printed conductors  12 ,  13 . In addition, they can include a metal core for discharging heat of the light-emitting semiconductor chip  21 , include a coating, and the like.  
      The printed circuit board  10  can be a foil, onto which printed conductors  12 ,  13  are applied. An alignment edge  18  is then, for example a limiting edge of the foil, a punched-through hole, and the like.  
      The light-emitting chip  21  or a group of light-emitting chips  21  can have three or more electrical connections in all the forms of embodiment represented. They can be electrically and/or thermally conductive adhesive connections  22 , bond wires  27 , and the like. Also, combinations of electrical connections of different types are conceivable. The light-emitting diode  20  can then, depending on the electrical connection, illuminate at different levels of brightness or in different colors.  
      The thermoplast has a low optical damping. The light-emitting diodes  20  produced with the process and produced on a printed circuit board  10  have small size and high light output.  
      In the production of several light-emitting diodes  20  on one printed circuit board  10 , the thermoplast can be introduced in one common injection mold. The injection mold can then include a single sprue for each individual light distribution body  31 . However, several, or all, of the light distribution bodies  31  can be produced by injection molding via a common sprue.  
      FIGS.  9  to  11  show a lighting unit  110  with an integrated printed circuit board  120 . On the printed circuit board  120  sit two light-emitting chips  140 . Each of these light-emitting chips  140  is encircled by a light distribution body  150  fastened to the printed circuit board  120 . A light distribution body  150  can also encircle several light-emitting chips  140 , e.g. a group of light-emitting chips  140 .  
      The component designated here as printed circuit board  120  can be a foil which is subject to bending or resistant to bending, a plate made of fiber-reinforced plastic or built up from electrically non-conductive composite material, a metal printed circuit board with insulated surface, a ceramic printed circuit board, and the like. On its assembly side  121  on which the light-emitting chip  140  is disposed and/or on its unassembled side  122 , electrical printed conductors, not represented here, are applied or laminated.  
      The printed circuit board  120  includes four through holes  123 . These through holes  123  are long holes  125 ,  126  which are curved in the form of a parabola and whose width is approximately one fourth of their length. The width of the long holes  125 ,  126  is greater than the length of the diagonals of one of the light-emitting chips  140  represented here as square. Each two of these long holes  125 ,  126  are disposed so as to be symmetric to one another, where the respective plane of symmetry contains the midpoint  141  of the surface  142  of a light-emitting chip  140 . The printed circuit board  120  can also include three through holes  123 , of which two lie so as to be symmetric to the light-emitting chip  140  and the third lies at an arbitrary point in the vicinity of the chip  140 . The through holes  123  can also have a rectangular, circular, etc. cross section.  
      The single light-emitting chip  140  is a semiconductor chip of an inorganic or organic type and can develop a high light intensity. It is connected to the electrical printed conductors of the printed circuit board  120  in such a manner that is electrically conductive. Furthermore, there is a thermally conductive connection between the light-emitting chip  140  and the printed circuit board  120 . It can be rectangular, round, hexagonal, etc. in plan view.  
      The single light distribution body  150  is a completely transparent body which consists of a homogenous thermoplast, e.g. PMMA, polycarbonate, polysulfone, and the like. It includes a light distribution section  161  lying on the assembled side  121  of the printed circuit board  120  and a fastening section  163  lying on the unassembled underside  122 . The contours of the application faces of the light distribution body  150  on the two sides  121 ,  122  of the printed circuit board are congruent to one another and lie against one another.  
      The light distribution section  161  includes a cylinder  164 , a light deflection body  165 , and an optical lens  166 . Its height normal to the printed circuit board  120  is at least the thickness of the printed circuit board. In the embodiment example the height is approximately five times the thickness of the printed circuit board.  
      The cylinder  164  stands perpendicular to the printed circuit board  120 . Its generating curve, which lies in a plane parallel to the printed circuit board  120 , is composed of a parabolic section and a straight line. The length of the cylinder  164  corresponds to the height of the light-emitting chip  140 . The light-emitting chip  140  lies with its midpoint  141  on the normal at the focal point of the parabolic section.  
      The light deflection body  165  has the structure of a half-paraboloid, e.g. a paraboloid of rotation or an elliptical paraboloid. It stands on the cylinder  164 , where the respective surfaces make a transition into one another. The midpoint  141  of the surface  142  of the light-emitting chip  140  lies at the focal point of the half-paraboloid. The light deflection body  165  includes an optical lens  166  standing approximately perpendicular to the printed circuit board  120 . This optical lens  166  can be a convergent lens, a divergent lens, and the like. The light distribution section  161  can be embodied without a light deflection body  165 . It can include a simple optical lens.  
      The fastening section  163  includes a plate-like wraparound  156 . This has a constant material thickness, which corresponds to the thickness of the printed circuit board  120 . In given cases, tabs can also be disposed on the fastening section  163 , said tabs projecting in the direction normal to the underside  122  of the printed circuit board.  
      The light distribution section  161  and the fastening section  163  are connected to one another by means of two feedthrough links  152 ,  154 , each of which projects through a long hole  125 ,  126  of the printed circuit board  120 . The feedthrough links  152 ,  154  are disposed so as to be symmetric to one another, where the plane of symmetry contains the midpoint  141  of the light-emitting chip  140 .  
      If the printed circuit board  120  includes several through holes  123  in the vicinity of the light-emitting chip  140 , the light distribution section  161  and the fastening section  163  can also be connected to one another via several feedthrough links  152 ,  154 .  
      These feedthrough links  152 ,  154  have, e.g. along their height normal to the printed circuit board  120 —this corresponds to the thickness of the printed circuit board  120 —a constant cross-sectional surface  153 ,  155  which corresponds to the cross-sectional surface of the long holes  125 ,  126 . This cross-sectional surface  153 ,  155  of a feedthrough link  152 ,  154  is in the representation of  FIGS. 9-11  approximately 28% of the application face with which the light distribution body  150  lies on the assembly  121  of the printed circuit board  120  and on the surface  142  of the light-emitting chip  140 . For example, the feedthrough links  152 ,  154  include at the transitions to the light distribution section  161  and to the fastening section  163  load-relieving hollows.  
      The cross-sectional surface  153 ,  155  can vary between 10% and 60% of the above-mentioned application face.  
      The outer surfaces  167 ,  168 ,  169  of the light distribution section  161 , of the fastening section  163 , and of the feedthrough link  152 ,  154  have transitions into one another.  
      Here, the wraparound  156  connects both feedthrough links  152 ,  154  to one another. The application face of the wraparound  156  on the unassembled side  122  corresponds in the embodiment example represented here approximately to three times the cross-sectional surface  153 ,  155  of a feedthrough link  152 ,  154 .  
      The production of the lighting unit  110  is done as described in connection with  FIGS. 1-7 . First, the punched printed circuit board  120  is assembled with the light-emitting chips  140  and the two parts  120 ,  140  are connected to one another in such a manner that the connection is electrically and thermally conductive.  
      The assembled the printed circuit board  120  is now introduced into an injection mold not represented here. The injection openings of the injection mold are located on the unassembled side  122  of the printed circuit board  120  and are aligned in the direction normal to the underside  122 . The center of the injection jet then lies in the area below the chip below the geometric center of the through holes  123  within the injection mold.  
      During injection molding, the injection-molding material flows in the direction perpendicular to the underside  122  of the printed circuit board  120 . The injection jet then flows onto the geometric center of the through holes  123 , i.e., the center of mass of the through holes  123 . There, it strikes the printed circuit board  120 , which forms a flow divider for the flow of injection-molding material flowing onto it. The injection-molding material is distributed uniformly on both through holes  123  and builds up the light distribution body  150  on both sides of the printed circuit board  120 .  
      During injection of the thermoplast, the air in the injection mold is expelled and/or suctioned off. The injection mold reproduces the form of the light distribution body  150  on the printed circuit board  120 .  
      In given cases, the injection-molding material can be conducted by means of flow-conducting elevations or indentations on the injection mold and/or printed circuit board  120 .  
      Through the engagement behind, the light distribution body  150  is connected in a fixed manner to the printed circuit board  120  and can be removed from it only with destruction.  
      The lighting unit  110  thus produced can now be withdrawn from the injection mold. In given cases, the production can also be done in two or more spatially and/or temporally separated manufacturing steps.  
      On drying and cooling of the light distribution body  150  tensile forces are exerted on the feedthrough links  152 ,  154 . These forces are directed in the direction normal to the assembly side  121  of the printed circuit board  120 . The feedthrough links  152 ,  154  are extended. The extension is however, among other things, due to the large cross-sectional surface  153 ,  155  significantly less than the strain at break, which for PMMA is 5.5%. The large application face of the wraparound  156  prevents in addition the development of cracks. With further cooling the tensile stresses arising in the material are not relieved and lead to intrinsic stresses in the material. The comparative stress of these intrinsic stresses is significantly less than the elastic limit of the material up to which the material is extended without permanent plastic deformation.  
      During the operation of the lighting unit  110  each light-emitting chip  140  can be individually electrically controlled. However, all the light-emitting chips  140  can be operated jointly. Also, control of the light-emitting chips  140  in groups is conceivable.  
      The light radiated from the light-emitting chip  140  is deflected by total reflection in the light distribution body  150  in the direction of the optical lens  166  and radiated through it into the environment  1 .  
      During the operation of the light-emitting chip(s)  140 , a great amount of heat arises. A part of this heat is discharged via the thermally conducting connection to the printed circuit board  120 . Another part of the heat leads to a heating of the light distribution body  150  and the printed circuit board. The light distribution body  150  and the printed circuit board  120  expand, depending on their coefficients of thermal expansion and differences in temperature.  
      In the lighting unit  110 , the printed circuit board  120  is firmly clamped in the light distribution body  150 . If the printed circuit board  120  expands on heating, the light distribution body  150  prevents a deformation of the printed circuit board  120 .  
      On heating of the printed circuit board  120  and/or the light distribution body  150 , additional stresses, e.g. as variation in stress, act on the feedthrough links  152 ,  154 . These are then additional tensile stresses which act at least approximately in the same direction as the intrinsic stresses applied due to the production process. The comparison stress of the superposition of these stresses is, due to the large cross section of the individual feedthrough links  152 ,  154 , lower than the elastic limit of the materials. At the same time, the section modulus of the respective cross-sectional faces  153 ,  155 , which is determined by the ratio of the dimensions of the cross-sectional faces  153 ,  155 , prevents a break or a permanent deformation of the feedthrough links  152 ,  154  due to bending or shearing. Thus, even with an oblique application of force on the feedthrough links  152 ,  154 , e.g. caused by the heating during the operation of the lighting unit  110 , no permanent deformation occurs. Likewise, removal of the light distribution body  150  and/or the light-emitting chip  140  from the printed circuit board  120  is prevented by the back-engagement of the light distribution body  150  around the printed circuit board  120 . The chip  140  of the light distribution body  150  and the printed circuit board  120  are affixed to one another mechanically so that the alignment of the light-emitting chip  140  to the light distribution body  150 . And thus, the optical properties of the lighting unit, are retained long-term.  
      The light distribution body  150  can have another form on the assembly side  121 . Thus, the optical lens  166  can lie parallel to the assembly side  121  or in a plane inclined to the printed circuit board  120 . The light distribution body  150  can also have a similar, or the same, form on the two sides  121 ,  122  of the printed circuit board  120 .  
      Between the light distribution section  161  and the fastening section  163 , one or more feedthrough links  152 ,  154  are disposed. Each of these feedthrough links  152 ,  154  have a round, rectangular, triangular, trapezoidal, etc. cross-sectional surface  153 ,  155 . The individual cross-sectional surface  153 ,  155  is then at least 10% of the total of the application face of the light distribution body  150  on the assembly side  121  and the application face of the light distribution body  150  on the light-emitting chip  140 .  
      The fastening section  163  can include several individual wraparounds  156 . The application face of each of these wraparounds  156  is then 75% of the cross-sectional surface  153 ,  155  of the respective feedthrough link  152 ,  154 .  
      In  FIGS. 12-14 , a lighting unit with a grid-like printed circuit board  120  is represented. The light distribution body  150  corresponds in its external dimensions to the light distribution body  150  represented in  FIGS. 9-11 .  
      The printed circuit board  120 , by way of example, is rectangular and includes a frame  124  whose longitudinal sides are connected to one another by printed circuit board links  131 . On each of the printed circuit board links  131  a light-emitting chip  140  sits. The frame  124  and the printed circuit board links  131  border the through holes  123 .  
      The cross section of the printed circuit board links  131 , cf.  FIG. 13 , is oval, where the maximum width of the individual printed circuit board links  131  lies in the central longitudinal plane of the printed circuit board  120  parallel to the assembly side  121 . The individual printed circuit board link  131  has in this embodiment approximately half again the width of the light-emitting chip  140 . The cross section of the printed circuit board link  131  can also be rectangular, triangular, and the like.  
      The through holes  123  include three approximately rectangular punched holes  128 ,  129  with rounded corners. The cross-sectional surface of the small punched holes  128  is approximately twice the surface of the printed circuit board links  131  on the assembly side  121 . The cross-sectional surface of the large punched holes  129  is approximately four times this surface.  
      The individual feedthrough link  152 ,  154  lies on the arched flank  132  of the printed circuit board link  131 . Its cross-sectional surface is not constant over the length of the feedthrough link  152 ,  154 . It has at the transition to the light distribution section  161  and to the fastening section  163  a maximum and in the center a minimum. The minimal cross-sectional surface  153 ,  155  of the feedthrough link  152 ,  154  in a plane parallel to the assembly side  121  here is approximately 120% of the application surface of the light distribution body  150  on the assembly side  121  of the printed circuit board link  131  and on the light-emitting chip  140 .  
      The two feedthrough links  152 ,  154  are disposed so as to be symmetric to one another. The plane of symmetry intersects the light-emitting chip  140 . The at least approximately triangular cross-sectional surfaces  153 ,  155  of the two feedthrough links  152 ,  154  are equally large. Their shortest dimension is, in this embodiment example, approximately 68% of the maximum dimension.  
      The application face of the light distribution body  150  on the unassembled side  122  of the printed circuit board  120  is in this embodiment approximately 80% of the cross-sectional surface  153 ,  155  of the individual feedthrough links  152 ,  154 . This installation surface lies opposite the application surface of the light distribution body  150  on the assembly side  121 . These external contours of the two installation surfaces are, at least approximately, equally large.  
      The application face  122  of the light distribution body  150  on the unassembled side of the printed circuit board  120  can be up to approximately 120% of the cross-sectional surface  153 ,  155  of the individual feedthrough links  152 ,  154 .  
      The production and the operation of this lighting unit  110  takes place as described in connection with the  FIGS. 9-11 . Also, in this lighting unit  110  the light distribution bodies  150  are connected to the printed circuit board  120  in such a manner that they are mechanically affixed to one another. A removal of the light distribution body  150  and/or of the light-emitting chip  140  from the printed circuit board  120  is prevented by the feedthrough links  152 ,  154  as a matter of construction.  
      The invention has been described in an illustrative manner. It is to be understood that the terminology, which has been used, is intended to be in the nature of words of description rather than of limitation.  
      Many modifications and variations of the invention are possible in light of the above teachings. Therefore, within the scope of the appended claims, the invention may be practiced other than as specifically described.