Miniature optical component

The invention relates to a miniature optical component comprising at least one optically active surface and having at least one base surface on which at least one soldering surface is arranged via which the miniature optical component can be positioned in a defined manner by means of at least one corresponding soldering surface on a carrier using a solder, while in addition the miniature optical component is to be arranged at a defined distance from a solid-state light source. Miniature optical components, i.e. particularly components having a maximum base surface area of 30mm x 40mm, are used, for example, in the manufacture of a lighting application, particularly one that uses a solid-state light source. Such miniature optical components are, for example, collimators, screens, or shields.

If the solid-state light source is an electroluminescent light source (LED or laser diode or light emitting diode), these miniature optical components are often to be positioned in a very close and defined way, depending on their function, i.e. in particular in a spatially pre-determined location. The solid-state light source may also comprise a plurality of electroluminescent light sources which are arranged, for example, in an array side by side. The LED may also be arranged on a ceramic carrier sheet or the like. The LED may be provided with a light-converting element comprising phosphor materials, which element absorbs the emitted light totally or partly and re-emits the energy as light having another wavelength. Such phosphor-converting LEDs are used, for example, for generating white light. Light-converting elements may be arranged, for example, as phosphor layers, drop-shaped phosphor deposits, or phosphor-containing ceramics.

This phosphor layer, which may comprise a phosphor material or a mixture of a plurality of phosphor materials, is applied in a known way. For example, a drop-shaped phosphor layer may be arranged above an LED in this regard. As an alternative to the drop shape, the LED may be embedded into an electrophoretically deposited layer or embedded or coated by means of at least partly transparent phosphor-containing ceramic tiles or ceramic bodies.

In industrial mass production of lamps comprising electroluminescent light sources, a defined positioning of the miniature optical components is essential, particularly in the immediate vicinity of the LED. The electroluminescent light source is often positioned here in the form of one or a plurality of LEDs on a carrier, which has at least one flat area, which area serves to arrange or position the LEDs and the other optical components of the lamp.

One possible basic method of positioning at least one optical component on a carrier uses the effect of what is referred to as a self-adjustment, which is caused by the surface tensions of the liquid solder carrying the optical component to be positioned. It is functionally necessary here that the solder be arranged between two soldering surfaces defined in terms of their respective dimensions. The quantity of the solder used is to be attuned to the dimensions of the respective soldering surfaces in order to be able to guarantee the self-adjustment effect.

The principle of the use of this general effect in a device for manufacturing optical components is described, for example, in WO 2004/068537 A2.

The utilization of this effect by itself is not suitable for all applications involving a defined positioning, and particularly with miniature optical components it is not possible or possible only in a technologically expensive way.

In industrial mass production, for example, it is not yet possible to position a component very close to an LED, i.e. at a distance smaller than 0.5 mm, preferably smaller than 0.25 mm, with an accuracy of +/- 0.05 mm.

In addition, the positioning of a screen or a cutting edge very close to an LED, in the aforementioned sense, is not possible.

It is an object of the invention to provide miniature optical components and a method of positioning such miniature optical components very close to a solid-state light source, particularly an LED, which source can be used or manufactured effectively and in a technologically simple way in industrial mass production. The object of the invention is achieved by the characteristics of claim 1.

It is essential to the invention that the dimensions of the corresponding soldering surfaces and the respective solder quantity are mutually adjusted such that the defined positioning of the miniature optical components on the carrier can be implemented by means of a liquid or liquefied and subsequently solidified solder, while at least one

reference element is arranged for the defined distancing of the miniature optical component from the solid-state light source.

An exact adjustment of the wetted areas of the soldering surfaces and the solder quantity thus renders possible a very accurate positioning by means of the then mutually fixedly adjusting surface tension ratios. These may be determined not only by the calculation methods usual for this, but also by means of appropriate experiments.

A technologically simple arrangement and simultaneously an accurate positioning of the miniature optical components very close to the solid-state light source are made possible in a surprisingly simple way by the combination of these two aforementioned characteristics, i.e. the selection and arrangement of the soldering surfaces and the provision of the reference element or elements. During the self- adjustment using the surface tensions of the liquid solder, the desired position is accurately determined by the reference element or elements, which position is also fixed upon the solidification of the solder. The reference element may be arranged either at the solid-state light source or at the miniature optical component to be positioned and acts particularly as a spacer. Alternatively, the reference element may be arranged between the solid-state light source and the miniature optical component to be positioned. Thus, for example, a gage may be used which is fixed between the LED and the optical element for the duration of the soldering process so as to ensure a minimum distance between the LED and the optical element. The gage can be removed after the soldering process. In this way, the LED and the optical element can be decoupled, and thus damages due to thermal stresses (for example due to different coefficients of expansion) can be prevented.

The horizontal measurement of the reference element would correspond to the desired distance, for example, given a horizontal arrangement of the solid-state light source and the miniature optical components to be positioned on a horizontally arranged, plate- shaped carrier.

The reference element can remain in its position after the positioning according to the invention, particularly if it is made of an elastic material that compensates the maximum temperature fluctuations or length changes caused by different coefficients of expansion, which length changes may occur in the manufacturing process and during functional operation.

Alternatively, the reference element may be removed wholly or partly after the positioning according to the invention. If the reference element is a plug-in part, for example a gage, it can be completely removed again. It is alternatively possible, however, to remove

the reference element by cutting, for example by means of a laser, so that there is no physical connection between the solid-state light source and the miniature optical component to be positioned, and temperature fluctuations in this regard are negligible.

This renders it possible to manufacture very efficient optics, for example, whose reflection surfaces can be positioned very precisely in the proximity of the solid-state light source /LED.

The miniature optical components can be positioned at a distance of less than 0.5 mm, preferably less than 0.25 mm to the LED. By using a gage, a minimum distance between the LED and the miniature optical component can also be guaranteed. In that case the miniature optical components can be positioned at a distance of less than 0.5 mm, preferably less than 0.25 mm, and more than 0.01 mm to the LED.

The precise positioning, wherein deviations of approximately +/- 0.1 mm are permissible, takes place with at least the following steps. In the first step, the LED is fixed on the carrier 1 by a conventional soldering process. Subsequently or simultaneously, the miniature optical components are also fixed on the carrier, preferably by means of reflow soldering. The solder is liquefied during this and subsequently solidifies between the corresponding soldering surfaces of the miniature optical components and the carrier.

During the soldering process the miniature optical component moves towards the LED owing to the surface tension of the liquefied solder until the reference element rests against the LED and the desired position has been reached.

Miniature optical components in the sense of the invention have a base surface area which serves to fasten them on a carrier, which area is smaller than 30 mm x 40 mm, particularly preferably smaller than 20 mm x 10 mm.

These miniature optical components may be, for example: reflectors, LEDs, elements that affect a light/dark boundary, or collimators.

A soldering surface in the sense of the invention is a surface which enables a soldering with the usual soldering agent. In particular, the soldering surface is capable of being wetted or has at least one metal surface.

The dependent claims comprise further advantageous embodiments of the invention.

It is preferred that a foil is arranged at the miniature optical component, which foil is preferably reflective and projects beyond the miniature optical component. In addition, it is preferred that a further optical component can be arranged in a defined way at that portion of the foil that projects beyond the optical component.

Thus, in a first step, a miniature optical component on which the foil is arranged can be positioned precisely on the carrier. In the subsequent second step, the second optical component, which may have a larger surface area than a miniature optical component, is positioned close thereto and fastened. The second optical component (and if necessary further optical components) may be made to approach the projecting foil, for example, until it bears securely on the stiff foil, whereby the desired position is reached. Subsequently, the optical component is fixed on the carrier in a known way. This interaction ensures that an optical component can also be positioned just as precisely as a miniature optical component in a technologically simple way. In addition, the gap arising between the miniature optical component and the optical component is covered by the foil, so that in case of a reflecting foil, for example, no scattered light is caused thereby. This renders it possible to realize very efficient optics.

Moreover, it is preferred that the miniature optical component comprises a screen or a cutting edge. It is also preferable that the miniature optical component comprising the cutting edge cuts into this light-converting element with an arrangement next to an LED provided with a light-converting element. The cutting edge can thus be drawn into the light- converting element by using among other things the surface tension of the liquid solder and thus can cut into this. The light-converting element may be designed, for example, as a phosphor powder layer, a drop-shaped phosphor deposit, or a phosphor-containing ceramic. In addition, it is preferred that, in the case of an arrangement close to an LED provided with a light-converting element, the miniature optical component comprising a screen partly covers this light-converting element in a defined manner.

Further, it is preferred that the solder is present between the two parallel surfaces of the carrier and the miniature optical components before the beginning of the soldering process. The soldering surfaces may be arranged horizontally, for example. In case of a vertical positioning, the solder will adhere to at least one of the two soldering surfaces before being heated. The solder is fluid after being heated, however, it may be pasty/gel- like/creamy or firm during the application. The characteristics essential to the invention are claimed in combination as well as separately.

In addition, the object of the invention is achieved by an illumination unit comprising at least one miniature optical component which is positioned close to a solid-state light source, as defined in claims 1 to 9.

The object of the invention is also achieved by the characteristics of the method as defined in claim 11.

These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter.

In the drawings:

Fig. 1 is a schematic sectional view of a carrier having an LED and a multipart collimator, Fig. 2 is a schematic sectional view of a carrier comprising an LED as well as having an optical component with a cutting edge or a screen, Fig. 3.1 is a schematic sectional view of a carrier comprising an LED as well as having an optical component before soldering, and Fig. 3. 2 is a schematic sectional view of a carrier comprising an LED as well as having an optical component after soldering.

Fig. 1 is a schematic sectional view of a carrier 1 having an LED 2 and a multipart collimator 3. The LED 2 has a base surface area of approximately lmm x 1 mm up to 2 mm x 5 mm with which the LED 2 is arranged on the flat carrier 1, which is made of a thermally conducting material (metal, ceramic, or DBC). The LED 2 and the carrier 1 are connected by solder spots 4 which are arranged between two respective soldering surfaces (not shown in Fig. 1). A conventional solder here serves as the solder 5, for example a tin solder. Close to the LED 2, that is at a distance of approximately 0.1 mm (with a tolerance of +/- 0.05 mm), a plurality of miniature optical components 31 of the collimator 3 are arranged, of which, for example, two miniature optical components 31 are shown in Fig. 1. The miniature optical components 31 have an area of approximately 20 mm x 10 mm with which each of the miniature optical components 31 is arranged on the flat carrier 1. The miniature optical components 31 and the carrier 1 are connected by a plurality of drops of the solidified solder 5 which are arranged between two respective soldering surfaces (not shown in Fig. 1). Again, tin solder is used as the soldering agent. On the side facing the LED 2, the miniature optical component 31 carries a foil 6 which is designed, for example, as a reflecting aluminum foil and which has a thickness of approximately 0.1 mm, as well as a needle-shaped reference element 12. The reflecting foil 6 rests directly on the

surface of the further optical components 32 of the collimator 3, i.e. with matching shapes, for example adhering thereto. Between the miniature optical components 31 and the optical components 32, there is a gap of approximately 0.3 mm, which is covered by the foil 6, preferably a reflecting one. In an alternative embodiment of a reflecting foil, the miniature optical components 31 and optical components 32 may be reflecting and the foil 6 may be transparent.

The precise positioning, wherein deviations of approximately +/- 0.1 mm are permissible, takes place in the following steps. In the first step, the LED 2 is fixed on the carrier 1 using a conventional soldering process. Subsequently or simultaneously the miniature optical components 31, which carry the flexible foil 6, is fixed likewise on the carrier 1. During the soldering process the miniature optical component 31 is moved towards the LED 2 by means of the surface tension of the liquefied solder 5 until the reference element 12 rests against the LED 2 and the desired position is reached. In the subsequent step, an optical component 32 is made to approach the projecting portion of the foil 6 until it rests against the foil 6, for example made of a stiff material, and thus the desired position is reached. Subsequently, the optical component 32 is also fixed on the carrier by soldering. Fig. 2 is a schematic sectional view of a carrier 1 comprising an LED 2 and miniature optical components having a cutting edge 7 and a screen 8, respectively. The LED 2 has a base surface n area of approximately 1 mm x 1 mm by which the LED 2 is arranged on the flat carrier 1, which comprises a usual DBC material. The LED 2 and the carrier 1 are connected by a plurality of solder spots 4, which are arranged between two respective soldering surfaces (not shown in Fig. T). Again, tin solder is used as the soldering agent. A light-converting element 9, designed here as a drop-shaped phosphor layer, is arranged over the, for example blue, LED 2, which is completely covered by this phosphor layer. Close to the LED 2, i.e. at a distance of approximately 0.3 mm (with a tolerance of +/- 0.1 mm), one or a plurality of miniature optical components 31 are arranged, for example one having a cutting edge 7 or one with a screen 8. The miniature optical components 31 comprising the cutting edge 7 and the screen 8 are connected with the carrier 1 (analogous to the LED T) by solder spots 4. On the side facing the LED 2, the miniature optical component 31 having the cutting edge 7 carries a reflecting foil 6, which has a thickness of approximately 0.01 to 0.1 mm and is of aluminum. The reflecting foil 6 causes a reflection of the light towards the central portion of the light-converting element 9.

The miniature optical component 31 comprising a screen 8 has a shield that faces the LED 2 and is distant from the base. This shield helps generate the light/dark boundary in a vehicle headlight.

Figs. 3.1 and 3. 2 are diagrammatic sectional views of a carrier 1 having an LED array 2 (four LEDs arranged side by side, not represented in Figs. 3.1 and 3.2) as well as comprising an optical component before soldering, here a collimator 3.

The LED array 2 has a base surface area of approximately 4 mm x 1 mm with which the LED array 2 is arranged on the flat carrier 1, which comprises a DBC material. The LED 2 and the carrier 1 are connected by solder spots (not shown in Figs. 3.1 and 3.2). A light-converting element 9, constructed as a drop-shaped phosphor layer here, is arranged over the, for example blue, LED array 2, which is covered completely by this phosphor layer.

Before the start of the soldering process, the solder 5 is located between the two parallel surfaces 10 and 11 of the carrier 1 and the collimator 3, which are arranged vertically and parallel to each other, but spatially offset. The solder 5 has a firm consistency and is shaped as a bar, the two ends of the bar being arranged between a defined soldering surface 11 on the collimator 3 and a defined soldering surface 10 on the carrier 1, respectively.

Fig. 3.2 is a schematic sectional view of a carrier 1 comprising an LED 2 as well as a collimator 3, analogous to 3.1, but after the soldering or positioning. The collimator 3 has been positioned and fixed near the blue LED 2 in particular through the effect of gravity and the surface tension of the liquefied solder during the soldering process (including the solidifying of the liquefied solder). The fixation between the two corresponding parallel surfaces of the carrier 1 and the collimator 3 takes place via the solder spots (not shown in Fig. 3.2). The collimator 3 cuts into the phosphor layer 7 with sealing action and rests on the carrier with its edge 12 facing the carrier 1. This edge 12 functions as a reference element in the sense of the invention.