EP1563330A1

EP1563330A1 - Light-emitting diode arrangement comprising a reflector

Info

Publication number: EP1563330A1
Application number: EP03772259A
Authority: EP
Inventors: Hans Kragl
Original assignee: Diemount GmbH
Current assignee: Diemount GmbH
Priority date: 2002-10-29
Filing date: 2003-10-24
Publication date: 2005-08-17
Also published as: DE10250383A1; US20050190559A1; US20060104060A1; WO2004040346A1; DE10250383B4

Abstract

The invention relates to a light-emitting diode arrangement consisting of a sub-mount on which a light-emitting diode chip is mounted, and a reflector which is installed on the sub-mount and has a reflector surface located in the beam path of the light-emitting diode chip. The reflector is formed from the lateral wall of a solid body (8, 8a, 8b, 8c) consisting of a transparent material and having a small irradiation surface located opposite the light-emitting diode chip (3) and a large radiation surface (11, 11a) which is located opposite the same, at a distance. A lateral wall forming the reflector surface (10) extends between the irradiation surface and the radiation surface, and the sub-mount (1) comprises an opening into which the reflector body (8) is inserted, with the irradiation surface first.

Description

LED arrangement with reflector

Field of the Invention

The invention relates to a light-emitting diode arrangement with a reflector, consisting of a submount on which a light-emitting diode chip is mounted, and a reflector which is aligned with the submount and has a reflector surface located in the beam path of the light-emitting diode chip.

Background of the Invention

Lighting with light from light-emitting diodes (LEDs) has a number of advantages over lighting with light from conventional light sources, especially incandescent lamps: the lifespan of LEDs is up to 100,000 hours many times longer than that of light bulbs, and the color can change Selection of a suitable LED can be chosen almost arbitrarily, the color temperature of a lamp composed of differently colored LEDs can be set electronically and the electro-optical efficiency of LED spotlights is now higher than the efficiency of classic incandescent lamps. For these reasons, LED-based lighting devices are on the advance in almost all industries and product fields.

There is an almost unmanageable variety of different lighting applications and tasks. From the diffuse background lighting of a wall or signal board, to traffic signal lights, lamps for color control in the printing or textile industry, point-like light sources for object lighting to lighting by means of optical fibers, different radiation sources are required in a wide variety of applications.

An LED chip typically emits light from the chip surface isotropically, ie evenly in every direction. At a certain distance from the chip, a so-called Lambert-shaped beam distribution is obtained: perpendicular to the chip surface, the light intensity is greatest and it decreases in every direction proportional to the cosine of the angle with respect to the vertical. (Physical explanation for this eg in Gerthsen, Kneser, Vogel: Physik, 13th edition, p. 417f.) The consequence of this is that the LED chip radiates the greatest optical power in total at an angle of 45 ° perpendicular to its surface, since the product of cosine ( Lambert radiation) and sine (spherical surface element) has its maximum at 45 °. These physically given radiation conditions must be taken into account when designing lamps and lighting fixtures.

State of the art

From WO 02/054129 A1, which forms the starting point of the invention according to the preamble of claim 1, a lighting device is known which consists of a disk made of a light-conducting material, on one edge of which several LEDs are coupled next to one another via individual coupling elements, wherein the coupling elements each have a recess with a paraboloidal, mirrored wall and a submount carrying an LED is arranged at the base of the recess. The same publication also describes a coupling arrangement in which the submount carrying an LED is designed as a microreflector and a coupling element for connecting an optical waveguide, which has a parabolic deflection mirror in order to connect the optical waveguide flat, is aligned with it.

From the article by F. Möllmer and G. Waitl: "Siemens SMT-TOPLED for surface mounting, part 2: Instructions for use", in Siemens Components 29 (1991) Issue 5, pp. 193-196, is for direct surface mounting specific optoelectric component is known, on which a light guide is placed, which has a widening or narrowing cross section starting from the component and serves to bridge the distance between a circuit board carrying the component and a device front panel. The structure of the component is explained in more detail in DE 197 55 734 A1. Accordingly, it consists of a leadframe, the individual conductors of which are insulated from one another and connected to one another by a casting compound, which at the same time forms a reflector surface, and an optoelectric semiconductor element which is mounted directly on the leadframe and is bonded thereto. According to DE 197 55 734 A1, a lens can be placed on the body formed by the potting compound, which lens is centered on the body and faces the semiconductor element at a distance, the space being filled with a transparent potting compound. The publication is silent on the procedure for positioning the semiconductor element on the leadframe. Diebond technology is known for this, however, with the help of which it is not possible to achieve placement accuracies better than ± 70 μm. The space that is available in the illustrated component for accommodating the semiconductor element allows such tolerances.

For some years now, lighting devices via optical waveguides have become increasingly popular. For this purpose, the light from the emitter must be coupled into the optical waveguide, which, however, only transmits light up to a certain maximum angle against the optical waveguide axis. Light that is incident at larger angles is not guided by the fiber optic cable, but is emitted. For the light source feeding the optical waveguide, this means that it ideally couples light into the optical waveguide only in such a way that it is passed on by the optical waveguide. This means that the light source should not exceed a certain maximum radiation angle, which depends on the type of the optical waveguide.

The coupling of light into an optical fiber with high efficiency is also important for optical data transmission.

It has long been known that reflectors improve the radiation characteristics of LEDs. Typically, LEDs used for lighting purposes are placed on a funnel-shaped leadframe carrier, wire-bonded and cast with a transparent overmould. Fig. 1 shows this structure. As you can see from it, a reflector is arranged around the LED chip, but this only reflects the light emitted to the side by the LED to a small extent in the direction of the axis. In particular, the light emitted at an angle of 45 ° strikes the inner wall of the plastic body and is emitted from there after total reflection at an angle of approximately 60 °. For a light source that is supposed to emit directed light, this light is mostly lost. The critical angle of total reflection for PMMA is 42 ^° , which means that light which is emitted at less than 48 ° with respect to the vertical of the chip and falls on the vertical wall of the plastic body is totally reflected. The reason for The flat design of the reflector according to FIG. 1 lies essentially in the technological restrictions given by the leadframe technology and the simple die-bonding in the flat reflector.

In order to be able to use the light from LEDs in plastic housings with a diameter of 5 mm, which is emitted at too steep angles to the vertical, reflectors are known in the prior art which can be placed on the plastic housing. As examples, reference is made to a catalog 2000/2001 from Osram, Munich, page 97 and to a catalog from the sales company, Conrad, Hirschau, 2002 page 1097, according to which the reflector attachment reduces the light intensity towards the viewer up to a factor 5 is increased. From the geometry of the reflector shown in the catalog, however, one can see that the light cannot be directed more than ± 45 °. Since the reflector with a diameter of 12mm is already quite large, its extension, and thus the closer concentration of the light, would lead to very bulky component sizes. The exposed, sensitive inner mirror surface of the reflector attachment is only suitable to a limited extent for components exposed to harsh environmental conditions.

Gaggione SA, France, presented a more elegant solution at the Optatec 2002 trade fair. Then the 5mm LED is inserted into a hole in the focal point of a parabolic reflector made from non-reflecting, solid, transparent plastic. Light that emerges from the 5mm LED body at too large an angle is reflected to the front by total reflection in the plastic body. The arrangement is well protected against external influences (dirt, water, etc.), but the reflector is also very large in terms of its directivity. In addition, a lot of light is lost due to reflections at the transition point between the 5mm LED and the reflector.

Overview of the invention

The invention is based on the object of specifying a light-emitting diode arrangement which can be used as a lamp in which the light from the LED is concentrated in a relatively narrow beam cone with high efficiency. This object is achieved by the features specified in claim 1. Further developments of the invention are the subject of the dependent claims.

The invention allows use e.g. as a signal lamp of a rail vehicle, which ideally only lights in the direction of the rails. But also a spotlight that specifically shines on an object to be illuminated (exhibits in museums, cigarette lighter in a motor vehicle, food lighting in a supermarket, etc.) needs directional light if possible.

The invention discloses an arrangement of a microstructured submount, consisting of a receiving opening for precise, precisely fitting mounting of the LED chip in the focal point of a paraboloid, which is formed in the submount as a metallic reflector mirror around the LED chip. An extension reflector is placed or inserted on the submount, which takes on the beam formation outside the reflector in the submount. The LED chip is contacted with at least one bonding wire, which is contacted through a slot in the submount on a carrier carrying the electrical leads.

The invention and its advantages and further features of the invention are explained in more detail below with reference to the drawings.

Brief description of the drawings

1 schematically shows, on an enlarged scale, a 5 mm plastic housing with an LED chip according to the prior art accommodated therein,

2 shows in cross section the basic illustration of a first embodiment of the invention;

FIG. 3 shows in cross section the solution corresponding to FIG. 2, supplemented by a housing for supporting the reflector body;

FIG. 4 shows a lighting fixture with a plurality of LED chips attached to the edge of a light-conducting plate with a parabolic cross section as a reflector body; Fig. 5 shows an arrangement comparable to Fig. 4, but with a circular disc of parabolic axial section as a reflector body, and

FIG. 6 shows an arrangement in which the reflector body is delimited by four side surfaces which form right angles with one another in sectional planes perpendicular to the perpendicular to the LED chip, but each have a parabolic curvature in a plane parallel to the perpendicular to the LED chip ,

Detailed explanation of the invention

A first embodiment of the invention is shown in principle in FIG. 2. The drawing shows a microstructured submount 1 which has a cylindrical, flat blind hole 2 for the exact fitting of an LED chip 3. In the drawing, a space can be seen to the right and left of the chip 3 because the blind hole 2 adjusts the chip 3 over its corners. The submount 1 is placed on a carrier substrate 4, such as a printed circuit board, leadframe, TO housing or the like. The LED chip 3 is contacted by means of at least one bonding wire 5 from the chip surface to the carrier substrate 4. So that the bond wire 5 can be guided to the carrier substrate 4, a slot 6 is formed in the microstructured submount 1, through which the bond wire 5 is guided. Depending on the type of LED, the second contact is either realized by means of a second bonding wire (insulating LED substrates such as sapphire) or else the chip 3 is connected to its back contact via the electrically conductive carrier substrate 4 and the electrically conductive submount 1.

In the submount 1 there is also a parabolic reflector 7 which is designed such that the focal point of the paraboloid lies exactly in the middle of the surface of the LED chip 3. The submount 1 with its reflector 7 must therefore be matched to the geometric shape of the LED chip 3. However, this gives the technical possibility of starting beam shaping in the immediate vicinity of chip 3, which can ultimately be used to optimize the size and height.

In this respect, the construction corresponds to the state of the art according to the mentioned WO 02/054129 A1. In order to extend the reflector, according to the invention, a reflector body 8 made of transparent plastic (for example PMMA or PC) or clear glass is inserted into the reflector opening of the submount 1, said reflector body 8 being exactly (ie a few μm accurate!) In the axial direction of the reflector 7 in Aligns submount 1. A transparent liquid plastic 9 is filled between the LED chip 3 and the reflector body 8 and fills the entire free interior of the submount 1 without bubbles. Light from the LED chip 3, which strikes the paraboloid surface 10 of the reflector body 8 not in the submount reflector 7 but in the reflector body 8, has such a flat angle to the impact surface that it is totally reflected. 100% light reflection takes place even without metallic mirroring of the reflector body 8.

The arrangement according to the invention now has the further advantage that the light losses caused by the necessary slot 6 passing through the reflector surface 7 of the submount 1 can be at least partially compensated for by reflection on the reflector body 8. In practice, it is advantageous if the reflector body 8 projects as far as possible into the submount 1 to a minimum distance from the bonding wire 5 of the LED chip 3. The light losses through the slot 6 are minimized.

The reflector body 8 is preferably a plastic injection-molded part, the length and diameter of which can be flexibly adapted to the respective requirements of the task at its light-emitting outer opening 11. However, glass, in particular quartz glass, can also be used as the material for the reflector body. A modification of the submount 1, which is more complex to produce, is not necessary. If e.g. the beam angle is to be reduced, one only has to place another reflector body 8 on the submount 1.

The circumferential wall of the reflector body 8, which extends between the irradiation surface and the radiation surface and forms the reflector surface 10, is preferably high-gloss.

The arrangement in the outer region is preferably mechanically secured by a housing 12. This should preferably also be centered on the submount 1, so that the entire component results in an arrangement as in FIG. 3. 3 shows a housing 12 which touches the reflector body 8 as little as possible, so that on the Point of contact does not emit light from the reflector body 8. A mechanical fixation must of course be given. A weakly refractive material 13 should be located between the reflector body 8 and the housing 12 so that the reflector body 8 totally reflects the impinging steels even at larger angles of incidence. The exact geometry and choice of materials depends on the specific design. Air (n = 1) but also silicones (n ~ 1, 4) can be used as filling material for the space.

The reflector body 8 can be extended upwards beyond the submount 1. It then advantageously consists, for example, of a piece of optical fiber, the end section of which has the desired paraboloid cross section. In order to connect an optical waveguide to this optical fiber, a ferrule construction can be used (not shown) which centers on the submount 1, a ferrule which has a bore which receives the free end section of the reflector body 8 projecting from the submount 1 and which has such a length that it can also accommodate the end section of an optical waveguide with a precise fit. The opposing end faces of the reflector body 8 and the optical waveguide are preferably ground and polished perpendicular to their axes and abut one another directly. Possibly. a transparent adhesive film can also be present between the end faces mentioned.

The advantage of the two arrangements according to FIGS. 2 and 3 over the prior art is that in these arrangements the beam shaping begins in the immediate vicinity of the LED chip 3. With a size of e.g. Only 3mm in diameter and 5mm in height, the light of a conventional LED chip can be coupled into an angular range of ± 20 ° without loss. A conventional LED according to FIG. 1 claims this size alone for the plastic housing, without having carried out any noteworthy beam shaping.

If very narrow beam angles are to be realized, the construction according to the invention still gives manageable sizes of, for example, 10 mm length and 5 mm opening diameter and a maximum beam angle of ± 14 °. The reflector attachment from Osram described at the beginning, with a length of 10mm and an opening diameter of 12mm, on the other hand, only has a maximum beam angle of ± 31 °. With the construction according to the invention, the radiation angle can be reduced by more than a factor of 2 with the same overall height. At the same time, there is a significant reduction in the reflector diameter.

You can also design the reflector body with a geometry that only acts as a beam former in one spatial direction by linearly extending it while maintaining a parabolic cross section in the direction orthogonal to the cross section, so that a correspondingly profiled plate or bar is produced, or in the form of a tom in a ring shape a disc with a central opening closes.

Fig. 4 shows a reflector geometry, which consists of a flat plate 8a, of which Fig. 4a shows a cross section and Fig. 4b shows a plan view. It can be seen that on the edge at which the two surfaces 15, which are parabolically curved in section, approach each other, a plurality of LEDs are in each case mounted next to one another via their submounts 1, so that they can shine together into the reflector body 8a: the radiating surface facing this edge End face 1 1 a then appears as a light band. It is understood that in this case the openings of the submounts 1 are not designed to be rotationally symmetrical, but instead have two reflecting surfaces which are opposite one another in mirror image, and which each form parabolic cutting lines with an imaginary cutting plane running perpendicular to them.

The embodiment according to FIGS. 5a and 5b can be used, for example, as an all-round beacon for maritime applications or for illuminating only one room level in living or office spaces. 5b, the reflector body 8b is a disk with an opening 16 inside, which is delimited by a cylindrical light entry surface. According to FIG. 5a, the upper and lower side surfaces of the reflector body 8b in the drawing have such a curvature that they form mirror-image, parabolic cut lines with each other with an axial section plane, and they approach each other in the direction of the edge of the opening 16. At this opening edge, a plurality of LED chips are attached next to one another in a star-shaped orientation, each via their submounts 1, comparable to the embodiment of FIG. 4b, which thus radiate radially outward into the reflector body 11b. Here, LEDs of different colors can be combined to form white light or light of any color, or, as required in some practical applications, light of different colors from the cylindrical one can be used in different sectors outer peripheral surface 11b of the reflection body 8b are emitted without the need to use color filters which dampen the light intensity in the case of light bulbs operated with incandescent lamps. It goes without saying that in this embodiment too, the submounts 1 have no rotationally symmetrical depressions, but are designed in the manner as explained above with reference to the exemplary embodiment of FIGS. 4a and 4b.

For reasons of product design or due to specially specified installation conditions, it may be necessary to design the rotationally symmetrical reflector bodies and submounts according to FIGS. 2 and 3 by means of reflector bodies with square cross sections perpendicular to the reflector axis. The rotational paraboloid then becomes a reflector body 8c, the four side surfaces 15 of which are each curved parabolically in one plane. 6 shows this structure with different cross-sectional areas at different heights of the reflector body 8c. Since tool making of non-rotationally symmetrical surfaces is much more complex, this design will only be used under specially specified boundary conditions.

Claims

Expectations

1. LED arrangement with reflector, consisting of a submount on which an LED chip is mounted, and a reflector which is aligned with the submount and which has a reflector surface located in the beam path of the LED chip, characterized in that the submount (1) Blind hole (2), in which the LED chip (3) is inserted, and has a parabolic reflector surface (7) above the blind hole (2), in the focal point or focal line of which lies the center of the surface of the LED chip (3), the reflector from a solid body (8, 8a, 8b, 8c) is formed from a transparent material, which has a small irradiation surface facing the light-emitting diode chip (3) and a large radiation surface (11, 1 1 a) that is spaced apart, between which there is a side surface forming the reflector surface (10) extends, and that the submount (1) above the blind hole (2) has an opening into which the ref Lector body (8) is inserted with the irradiation surface first so that its reflector surface forms a continuation of the reflector surface (7) of the submount.

2. LED arrangement according to claim 1, characterized in that the reflector body (8) is a rotationally symmetrical body, in the axis of which the LED chip (3) is arranged.

3. LED arrangement according to claim 2, characterized in that the reflector surfaces (7, 10) of submount (1) and reflector body (8) are each parabolic.

4. Light-emitting diode arrangement according to one of the preceding claims, characterized in that the reflector body (8) is held by a ferrule centered on the submount (1).

5. LED arrangement according to claim 1, characterized in that the reflector surface of the reflector body (8c) is formed by four adjoining side surfaces (15), of which at least two mutually opposing side surfaces (15) on one of them and the LED chip (3) each create a parabolic cutting line, the vertical intersecting plane, the four side Surfaces (15) with planes intersecting perpendicularly to each other form intersecting intersecting lines.

6. LED arrangement according to claim 5, characterized in that said two parabolically shaped side surfaces (15) of the reflector body (8a) have an extension transverse to the parabolic profile, which are much larger than the corresponding dimensions of the other side surfaces of the reflector body (8a) , and that the incident surface of the reflector body (8a) is opposed by a plurality of LED chips which are arranged next to one another and are held on the reflector body (8a) by means of their submounts (1).

7. LED arrangement according to claim 4, characterized in that the reflector body (8b) is a circular disc or a sector of a disc which has a circular opening in the middle (16) which is delimited by an irradiation surface, and the disc or the disk sector has an outer circumference which is delimited by a radiation surface (11 b), the radiation surface and the radiation surface (1 1 b) being axially parallel cylinder surfaces and the side surfaces connecting them, each with an axial section plane forming parabolic cutting lines which extend in the direction of the center of the disk or the disk sector approach each other, and that the irradiation surface is opposed by a plurality of star-shaped LED chips which are arranged next to one another and are held on the reflector body (8b) by means of their submounts (1).

8. LED arrangement according to one of the preceding claims, characterized in that the reflector surfaces (10, 15) of the reflector body (8, 8a, 8b, 8c) are polished.

9. Light-emitting diode arrangement according to one of the preceding claims, characterized in that the space between the LED chip (3) and the irradiation surface of the reflector body (8, 8a, 8b, 8c) is filled with a transparent, hardened liquid plastic (9).