Abstract:
Method of producing light-conducting LED bodies of a free-flowing material by introduction into a mold. Here, the volumetric flow of a free-flowing material, at a distance of the electrode plane from the charging point that is greater than 35% of the distance between the charging point and the mold side of the mold situated opposite the charging point—above the charging point and below the chip plane on the mold side of the charging point, is choked by at least one cross-sectional constriction, while—at a distance that is smaller than or equal to 35% of this distance—choking takes place on the mold side situated opposite the charging point. The present invention develops a method of producing light-conducting LED bodies in which, at customary output capacities of the molding operation, the LED electronics are not damaged.

Description:
[0001]     This application is a National Stage of International Application No. PCT/DE03/03060, filed Sep. 15, 2003 which claims priority to DE 102 42 947.2 filed Sep. 16, 2002. The disclosures of the above applications are incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION AND SUMMARY  
       [0002]     Method of producing light-conducting LED bodies of a material that is free-flowing before final solidification, by introduction into a mold, where the individual LED body comprises at least one light-emitting chip and at least two electrodes—connected electrically with the chip—and where the free-flowing material is injected between a floor region of the mold and the chip, at least approximately parallel to the chip plane and at least approximately normal to a plane formed by two electrodes, between the electrodes.  
         [0003]     DE 101 59 522 discloses a method of this kind for producing light-emitting diodes. The diode to be produced is a radial LED, whose mold is filled by radial injection of free-flowing material. The material is injected under the chip normal to a plane established by the electrodes. In this method, the material filling the mold flows from below around the chip and the bonding wire placed over it. By this method the bonding wire is protected from being torn off by the incoming material. However, it frequently happens that—viewed in the direction of injection of material—the material introduced into the mold piles up on one side before or after the electrodes. As a result, the flow front flowing predominantly toward one side of the chip can push the bonding wire aside hard enough to cause it to come into contact with the cathode. As further flow toward the diode takes place, the component fails due to short circuit.  
         [0004]     The present invention therefore is based on the problem of developing a method of producing light-conducting LED bodies in which, at customary output capacities of known injection or molding operations, the LED electronics are not adversely affected.  
         [0005]     This problem is solved by the features of the main claim. For this purpose, the volumetric flow of a free-flowing material, at a distance of the electrode plane from the charging point that is greater than 30% of the distance between the charging point and the mold side of the mold lying opposite the charging point—is choked above the charging point and below the chip plane on the mold side of the charging point by at least one cross-sectional constriction, while—at a distance that is smaller than or equal to 30% of this distance—choking takes place on the mold side lying opposite the charging point.  
         [0006]     By this method of producing a luminescent diode, a given specification of the charging point and of the direction of introduction in conjunction with a prescribed choking of the volumetric flow of material at a defined spot procures a flow condition that permits controlled, uniform filling of the mold without any damage to the LED electronics. For choking, a molding element that narrows the cross section of flow between the front edge of the molding element and the chip is located in the individual mold cavity opposite the electrode fence. The geometric dimension of the molding element and its surface structure turned toward the volumetric flow is selected according to the type of synthetic material, or as necessary. This is simple to accomplish with the use of replaceable choke slides bearing the molding element.  
         [0007]     The molding element causes the in-flowing material to be choked at least on one side in such a way that the flow fronts moving from below against the chip on both sides of the electrodes contact and flow around the chip and the bonding wire virtually simultaneously. The virtually simultaneous envelopment of the bonding wire stabilizes the bonding wire in its structurally preplanned position.  
         [0008]     The method is likewise applicable to luminescent diodes having a plurality of chips and electrodes.  
         [0009]     Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1 : LED mold with cross-sectional constriction over the point of injection;  
         [0011]      FIG. 2 : LED mold with cross-sectional constriction opposite the point of injection;  
         [0012]      FIG. 3 : Side view of an LED in a mold with the molding element slide driven in;  
         [0013]      FIG. 4 : Front view of the LED in  FIG. 3 ;  
         [0014]      FIG. 5 : Top view of LED fabrication connections near the injection molding nozzles;  
         [0015]      FIG. 6 : View from below of the LED in  FIG. 1  with a plurality of parting lines;  
         [0016]      FIG. 7 : Side view of an LED in a mold with the molding element slide driven out;  
         [0017]      FIG. 8 : Top view of  FIG. 7 , largely without mold. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0018]     FIGS.  3  to  6  show an LED  10  whose light-conducting body  20  is produced for example by molding in one injection molding step.  
         [0019]     Here the LED  10  represented has an LED body  20  theoretically divided into two zones  21 ,  41 , cf.  FIG. 4 . The lower zone  41  of the body  20  is a so-called electronics protective zone, while the upper zone  21  is designated a light-conducting zone. The two zones are separated from each other by an imaginary parting line  39 . The parting line  39  is represented dash-dotted only in  FIG. 4 .  
         [0020]     The electronics protective zone  41  as a rule surrounds the electrical connections  1 ,  4  lying in a plane  19 , the light-emitting chip  6 , a bonding wire  2  and a reflector basin  5 . The latter for example is part of the cathode  4 . The chip  6  sits in the reflector basin  5 . The chip  6  contacts the anode  1  via the bonding wire  2 . There the bonding wire  2  preferably lies in a plane  19 , which is established by the center lines of the electrodes  1 ,  4 . The light-conducting zone  21  lying above the chip carries the light emitted by the chip  6  as loss-free as possible to the outer surface  14 ,  15  of the LED  10 .  
         [0021]     With respect to its spatial design, the LED body  20  of the exemplary embodiment consists of three geometric bodies  11 ,  14 ,  15  placed side by side. The lower geometric body  11  is at least approximately a straight cylinder with two at least approximately parallel faces and for example two plane flattenings  12 ,  13 . The flattenings  12 ,  13  are parallel to the longitudinal axis  18  of the LED and together enclose a right angle. One flattening  12  is parallel to the electrode plane  19 , formed by the center lines of the electrodes  1 ,  4 . The lower face forms the so-called floor region  42 . The upper face connects to an upright truncated cone  14 , which tapers away from the cylinder  11 . A dome  15  sits on the truncated cone  14  as the third geometric body. A tangential transition between the dome  15  and the truncated cone  14  is found for example in the LED longitudinal section.  
         [0022]     In the exemplary embodiment, the larger face diameter of the truncated cone  14  measures about 5 mm. It is termed the base size. The taper of the truncated cone  14  is for example 20% of the base size. The total height of the LED  10  corresponds to about 180% of the base size. The height of the cylinder  11 , which as a flange-like collar with respect to its radius projects over the truncated cone by about 10% of the base size, measures about 30% of the base size. The depth of the flattenings  12 ,  13  amounts to about 8% of the base size.  
         [0023]     The region of the truncated cone  14  lying above the chip  6  and the dome  15  form the main outlet area.  
         [0024]     For LED fabrication the electrodes  1 ,  4  are part of an as a rule flat, punched, so-called electrode fence  80 . Within this fence the electrodes  1 ,  4  are continuously connected together via crosspieces  81 . A fence  80  contains for example 32 electrodes for 16 LEDs  10 . The minimum distance apart of the LEDs  10  integrated side by side in the fence  80  amounts to at least 10% of the maximum diameter and/or maximum width of the individual LED  10  in the electrode or fence plane  19 . In the exemplary embodiment, the distance apart of the center lines  18  of two neighboring luminescent diodes  10  amounts to about 150% of the base size.  
         [0025]     For the injection molding of LEDs  10 , a multiple-part mold  61 - 63  is used, which together with the injection molding nozzle  71  specifies the design of the luminescent diode  10 . The major part of the diode  10  to be fabricated is comprised of a slide mold  62 . The latter for example forms a seamless main outlet area and the part of the peripheral areas of the electronics protective zone  41  which is turned away from a neighboring base mold  61 . The floor region  42  and the remaining peripheral areas of the LED  10 , with the exception of a suction channel  66  and the injection molding nozzle system, are locked by the base mold  61  and a lift mold  63 , where for example a choke slide  31  is integrated in the base mold  61  of  FIGS. 3-8 .  
         [0026]     The base mold  61  for example is one of the fundamental elements of the injection molding tool. Here, it is fastened to the stationary part of the tool and is not moved upon ejection. It has a recess  73  into which the injection molding nozzle  71  projects sealingly.  
         [0027]     In the base mold  61 , according to  FIGS. 3-8 , for each mold cavity  60  a choke slide  31  is inserted into a channel  91 , which here is rectangular. The choke slides  31  are joined together for example in their back regions via crosspieces, cf.  FIGS. 5 and 8 . The direction of movement of the choke slides  31  for example is oriented parallel to the floor region  42  of the LED  10  and normal to the electrode fence  80 . With regard to the luminescent diode  10 , the upper side of the respective free end of a choke slide  31  is on or just below the chip plane  7 .  
         [0028]     Depending on the spatial conditions in the mold  61 - 63 , the choke slide  31  may alternatively enclose an angle of 5 to 45° with the electrode fence plane  19 . Optionally, the choke slide  31  may alternatively be moved by a pivoting or helical motion within the mold  61 - 63 .  
         [0029]     The end of the choke slide  31  projecting into the cavity  60  is termed a molding element  32 . Its face turned toward the LED center line  18  is for example a curved spatial surface  33 , which corresponds exactly to the cross-sectional area that is produced in a spatial section between the truncated cone  14  and the channel  91 , i.e., the curvature corresponds to that of the convex surface of the outer surface  14 . In the plane of the drawing of  FIG. 3 —i.e., in the longitudinal section—the molding element  32  has a trapezoidal cross section. The shearing action of the trapezoidal cross section with respect to the LED center line  18  here corresponds to the angle of the truncated cone  14 . In the horizontal top view, cf.  FIG. 5  bottom, the surface of the molding element  32  projecting into the cavity  60  is shown hatched. The curved edging of this surface  34  oriented to the LED center line  18  represents the upper edge  36  as a circular arc section.  
         [0030]     This upper edge  36 , which at the same time is the front edge of the molding element  26 ,  28 ,  32 , may have any desired curvature, not necessarily plane. In addition, it is capable of being equipped with a flow-influencing structure projecting into the volumetric flow. The structure may be a fluting, a corrugated profile, a knob structure or the like.  
         [0031]     In the exemplary embodiment of  FIGS. 3 and 7 , the choke slide  31  adjoins the slide mold  62  regionwise.  
         [0032]     In  FIG. 1 , instead of the choke slide  31 , a projection  26  projects into the cavity  60 . The projection  26  is part of the base mold  61 . The longitudinal-section contour  35  of this projection and/or molding element encloses a 24°-angle with the LED center line  18 .  
         [0033]     According to  FIG. 3 , the lift mold  63  is located opposite the base mold  61 . According to this representation, for ejection the former is moved away from the base mold  61  toward the right. When the mold  61 - 63  is closed, the mold parts  61  and  63  touch in a parting line  65  represented in  FIG. 6 . The parting line  65  is divided in the region between the electrodes  1 ,  4  to form an aperture  67 . The aperture  67  is an edge of the suction channel  66  contacting the floor region  42 , cf.  FIG. 3 . The suction channel  66  is displaced with respect to the electrode plane  19  by several tenths of a millimeter away from the injection molding nozzle  71 .  
         [0034]     A hold-down device  69  is located in the lift mold  63 . The hold-down device  69  is supported displaceable there—for example in the direction of the opening lift of the mold. It clamps the electrode fence  80  against the base mold  61 .  
         [0035]     The slide mold  62  moves on the plane formed by the mold parts  61 ,  63 , on which the later floor region  42  of the LED  10  rests, and on the contour of the base mold  61  surrounding the injection molding nozzle  71 . Between the slide mold  62  and the base mold  61  lies a spatially stepped parting line  64 .  
         [0036]     The slide mold  62 , which surrounds the major part of the future LED surface, is penetrated by at least one tempering channel  68 , in order to temper the mold and the other tool parts surrounding it by means for example of water or oil at for example 40-160° C. In  FIG. 3 , the slide mold  62  is represented only by way of example as one part. For the case that the diode-shaping part is seated within the slide mold  62  in a separate slide support, the latter may alternatively be equipped with the tempering channel. According to  FIG. 2 , the slide mold  62  optionally bears a projection  28 . Its upper edge alternatively lies on or below the chip plane  7 .  
         [0037]     In preparation for injection molding, the mold  61 - 63  is opened. For this purpose, the mold parts  63 ,  69 , according to  FIG. 3 , are moved away to the right. The slide mold  62  is driven by means of a guide, not represented—at an angle of for example 25° with respect to the injection molding nozzle center line  75 —obliquely toward the right above to the side. The electrode fence  80 , equipped with the chip  6  and the corresponding bonding wires  2 , is inserted and centered on the base mold by index pins, not represented. For closing the mold  61 - 63 , the lift mold  63  moves on to the base mold  61 . The hold-down device  69  seated in it continues to travel in the direction of closing until the electrode fence  80  is firmly clamped to the base mold  61 . By way of example, at the same time the slide mold  62  moves to the molds  61  and  63 . The choke slide  31  is now pushed into the cavity  60  so far that the cross-sectional area  30  of the narrowest point between the electrode fence  80 , represented hatched in  FIG. 5 , has reached its minimum. Here, the reduction in cross section may amount to 20-80% of the original cross section.  
         [0038]     The cavity of the mold  61 - 63  to be injected with free-flowing material is evacuated via the suction channel  66  and for example via the gap between the lift mold  63  and the hold-down device  69 . The vacuum is maintained during the entire injection molding process.  
         [0039]     Immediately after evacuation, the hot free-flowing material  8  or  9  is introduced into the corresponding cavity of the mold  61 - 63  via the respective injection molding nozzle  71 , for example a so-called torpedo nozzle. The center line  75  of the injection molding nozzle  71  and of the stream emerging from it is here aligned normal to the electrode plane  19 . It lies between the floor region  42  and the lowermost point of the reflector basin  5 . In the exemplary embodiment the center line  75  is located at half the height of the cylinder  11 . At the same time, it runs midway between the electrodes  1 ,  4 , cf.  FIGS. 5 and 8 .  
         [0040]     According to  FIG. 2 , during the injection molding operation, the liquid synthetic material  8 , for example a transparent, optionally colored thermoplastic capable of injection, such as modified polymethylmethacrylimide (PMMI), is shot into the evacuated, tempered mold  61 - 63  at a pressure of 700±300 bar. The flow rate is for example 0.2 to 10 millimeters per second. The stream passes the electrodes  1 ,  4  is placed toward the charging point  70 —by a distance calculated from the difference between the inside distance  86  and the distance  85 —midway and divides at the wall of the mold  62  lying opposite the charging point  70 . In doing so, the stream loses so much energy that the incoming synthetic material, upon filling up the cavity, cf.  FIG. 1 , flows from below upward before and after the electrode plane  19 . Choking of the volumetric flow produced by the projection  28  forces an approximately uniform movement upward of the flow front  92 - 95  in front of and behind the electrode fence  80 . Between the positions  94  and  95  of the flow front, the rapidly flowing material  8  reaches the bonding wire  2  before and after the electrode fence  80  at the same time and with a direction of flow that runs parallel to the LED center line  18 . The flow proceeds around the bonding wire  2  without altering its prescribed position. The bonding wire  2  is neither pushed to the side nor torn off.  
         [0041]     If the material  8  or  9  is introduced into a mold in which the electrodes  1 ,  4  or the electrode plane  19  are or is moved from the charging point further than 35% of the distance  86  between the mold sides  78  and  79 , for example at a central position within the mold  61 - 63 , molding elements  26 ,  32  that lie directly above the charging point  70  are used for choking the volumetric flow, cf.  FIGS. 1, 3  and  7 . Here, the material  8 ,  9  piles up before the electrode fence  80  and moves—without a corresponding molding element  26 ,  28 —faster upward there than behind the fence  80 . When the molding elements  26 ,  32  are used, the respective material  8 ,  9  moves, at least in the region of the bonding wire  2 , past the chip  6  at virtually the same time. In this flow around the chip, the optimal position of the bonding wire  2  likewise is not altered.  
         [0042]     In the device of  FIGS. 3-8 , after complete preliminary filling of the mold, the pressure of the material is maintained and the choke slide  31  pulled back all the way to the outer contour  14  of the LED  10 . As a result, the space freed up by the choke slide  31  fills up.  
         [0043]     After injection molding and ejection, in a separating operation the crosspieces  81  between the luminescent diode  10  and the electrodes  1 ,  4  of the individual LEDs  10  are removed by for example stamping.