FIELD OF THE INVENTION:

The invention relates to a method providing a lighting assembly with high three- dimensional positional accuracy, to a pre-assembly used in this method as a level 1 product and to a lighting assembly with high three-dimensional positional accuracy. BACKGROUND OF THE INVENTION:

In automotive exterior lighting the function ADB (adaptive driving beam) or matrix light becomes more and more popular. Common light emission assemblies comprising LEDs as point-like light sources still require a primary optics element because the distance between the light emitting areas is limited by the package (rim of sidecoat). For a direct projection system without primary optics the distance between two point-like light sources should be <100μιη.

The application of an adaptive driving beam with close spacing LEDs enables a direct projection without pre-collimator optic elements. One technical challenge to be overcome in an array of closely spaced emitters is the post mounting position tolerances, e.g. post soldering position tolerance of surface mount assembly when using multiple single LEDs on a level 2 board. The LED pixel position for the beam projection has impact on beam performance and requires low positional tolerances for the assembly process. The alignment of a main optic lens can be used to compensate the position of full matrix array during module assembly, however the position of individual LEDs cannot be adjusted and LED to LED position needs to be well controlled already during assembly of the LED Array. A typical

LED-to-LED tolerance after a standard surface mounted technology (SMT) assembly will be in the range of ΙΟΟμιη depending on design and solder process. Additionally small single emitters like Luxeon Neo or WLP chips with two bottom solder contacts tent to rotate and tilt during reflow soldering.

It would be desirable to obtain a light emitting assembly suitable for providing an adaptive driving beam not requiring pre-collimator optical elements, where the individual light sources are mounted with a better three-dimensional positioning accuracy and better alignment of the emission surfaces to each other avoiding non acceptable tilting and rotation of the individual light sources.

SUMMARY OF THE INVENTION:

It is an object of the present invention to provide a light emitting assembly suitable for providing an adaptive driving beam not requiring pre-collimator optical elements, where individual point-like light sources are mounted with a better three-dimensional positioning accuracy of the emission surfaces to each other avoiding non acceptable miss- alignment of the individual point- like light sources.

The invention is defined by the independent claims. The dependent claims define advantageous embodiments.

According to a first aspect a method to provide a lighting assembly comprising an array of point-like light sources arranged on a substrate with high three-dimensional positional accuracy is provided. The method comprises the steps of:

providing a pre-assembly of an array of point like light sources with a three- dimensional positioning accuracy having position tolerances in the range of 20 μιη or less between the point-like light sources, where each of the point-like light sources having an light emitting side and contacting backside for electrically contacting the point-like light source and being reversibly mounted on a temporary holder with their emitting surfaces;

providing the substrate with a contacting surface comprising an array of electrical substrate contacts, where the electrical substrate contacts are aligned to the position of the point-like light sources on the temporary holder; and

simultaneously mounting the contacting backsides of the point-like light source still fixed to the temporary holder on the electrical substrate contacts of the substrate for being able to operate the lighting assembly maintaining the positioning accuracy of the pre- assembly.

The term "point-like light source" denotes any light source, which has a small light emission area (or volume) and has a wide emission cone providing an essentially non- directed light emission. Such point-like light sources may be LEDs or semiconductor lasers, e.g. quantum wells or dots. The lighting assembly may comprise an array of point-like light sources, e.g. an LED array. The array of point-like light sources may comprise multiple columns and multiple rows of point-like light sources. The number of point-like light sources arranged in the rows and/or columns depends on the particular application of the lightings assembly. The backside of the point-like light sources shall be adapted to be contacted to the substrate contacts, where the backside might be structured to provide separate contact pads for electrically connecting the point-like light sources to a power source.

The term "three-dimensional positioning accuracy" denotes the deviation from a desired three-dimensional position with respect to the lateral position of the point-like light sources, their vertical position (perpendicular to the lateral position), the tilting of the pointlike light sources denoting an alignment of the emitting surface of the point-like light sources with respect to a lateral plane defined by an average emitting surface and a rotation of the point-like light sources relative of the desired position denoting a rotation around a rotation axis perpendicular to the emitting surface of the point-like light sources. In an ideal case without tilting all emitting surfaces are parallel to each other. The specified tolerance denotes the deviation to the desired position, where in case of tilting or rotation the tolerance denotes the maximum deviation of the emitting surface from its intended position.

The substrate might be a substrate providing electrical circuits to connect the substrate contacts to other components. The substrate can be made of any material suitable to carry electrical contacts and being suitable to separate the electrical contacts such as glass, plastic etc. The substrate might be printed circuit boards PCB or isolated metal substrates IMS. The substrate might also be used to withdraw heat from the light sources in order to cool the assembly.

The temporary holder might be made of any material suitable to reliably maintaining the positions of the fixed point-like light sources. Since the temporary holder is removed before operating the lighting assembly, the temporary holder does not have to fulfill any certain electrical or optical properties.

The present invention might be used for automotive lamps for high/low beam and

ADB (adaptive driving beam) or matrix beam or matrix light applications. This can consist of close spacing matrix array of point-like light sources like LEDs, wide spacing matrix and customized matrix solutions. Further, the present invention might be used for multi-chip LED level 1 packages (singe addressable or not) to improve positional tolerances of light emitting positions and lower the distances between the light emitting areas (LEA). This is not restricted to automotive, but can also be used in flash, general illumination, projection systems and any other application for multi-chip LEDs or arrangements with other point-like light sources. The method according to the present invention provides a light emitting assembly suitable for providing an adaptive driving beam not requiring pre-collimator optical elements, where the individual point-like light sources are mounted with a better three-dimensional positioning accuracy of the emission surfaces to each other in the range of 20μιη or less avoiding non acceptable miss-alignment of the individual point-like light sources. According to the state of the art where solder self alignment is leading tolerances of >50μιη are typical, improvements are hardly achievable.

The method may be arranged in such a way that the mounting step is executed by a surface mounting technology. Surface-mount technology (SMT) is a method for

producing electronic circuits in which the components are mounted or placed directly onto the surface of substrate, e.g. of a printed circuit board (PCB). An electronic component is called a surface-mount device (SMD). In the industry it has largely replaced the through-hole technology construction method of fitting components with wire leads into holes in the circuit board. However both technologies can be used on the same printed circuit board, with the through-hole technology used for components not suitable for surface mounting such as large transformers and heat-si nked power semiconductors. The lighting assembly applying the mounting step with SMT is smaller than its through- hole counterpart. The point-like light sources may have short pins or leads of various styles, flat contacts, a matrix of solder balls, or terminations on the backside of the point-like light source. In case of LEDs as point-like light sources a typical LED-to-LED tolerance after a standard SMT assembly will be in the range of ΙΟΟμιη depending on design and solder process. Additionally small single emitters like Luxeon Neo or WLP chips with two bottom solder contacts tent to rotate and tilt during reflow soldering. With the present invention the LED-to-LED tolerance will be defined by the accuracy of the pre-assembly carrying the point-like light sources allowing a placement tolerance down to ΙΟμιη.

The method may be arranged in such a way that the mounting step comprises soldering of the contacting backsides of the point-like light sources to solder dots as the electrical substrate contacts. Soldering is a process in which two or more items (here the contacts of contacting backside and the substrate contacts) are joined together by melting and putting a solder as a filler material into the joint. The solder metal has a lower melting point as the involved contacts. Soldering differs from welding in that soldering does not involve melting of the contacts to be solders. Solder materials are available in many different alloys for differing applications. In electronics assembly, an eutectic alloy of 63% tin and 37% lead (or 60/40, which is almost identical in melting point) may be used. Other examples of soft-solder are tin-lead for general purposes, tin-zinc for joining aluminum, lead- silver for strength at higher than room, temperature, cadmium-silver for strength at high temperatures, zinc-aluminum for aluminum, and corrosion resistance, and tin-silver and tin- bismuth. In a preferred embodiment the soldering process utilizes SAC -based solder in a reflow-soldering process. SAC -based solder denotes tin-silver-copper alloys to avoid lead containing solders. Reflow soldering is a process in which a solder paste (a sticky mixture of powdered solder and flux) is used to temporarily attach one or several electrical contacts to their counter contacts after which the entire assembly is subjected to controlled heat, which melts the solder, permanently connecting the joint. Heating may be accomplished by passing the assembly through a reflow ov en or under an infrared lamp or by soldering individual joints with a hot air pencil. In an alternative embodiment, the mounting step might be carried out by conductive gluing or sintering.

The method may be arranged in such a way that it further comprises the steps of providing a temporary holder with a contact surface without point-like light sources and reversibly fixing the point-like light sources with the emitting surfaces on the contact surface of the temporary holder in order to provide the pre-assembly. The fixation to the temporary holder ensures that the positions within the array of point-like light sources remains constant during the mounting step of joining the point-like light sources to the electrical contacts of the substrate. A reversible fixation enables to remove the temporary holder from the emitting sides of the point-like light sources without causing any damage to the point-like light sources and not to disturb any light emission properties of the point-like light sources. The tolerances with respect to tilting are defined by the contacting surface of the temporary holder, which can be a very flat and smooth surface depending on the material of the temporary holder, e.g. glass.

The method may be arranged in such a way that the fixing step is executed using a suitable gauge instrument or via a sequentially assembly of the point-like light sources in order to control the relative distances and alignment between each of the point-like light sources with the required accuracy. Gauge instruments can be provided with tolerances far below the tolerance specified in the present invention. The gauge instrument enables a fixation of the point-like light sources on the temporary holder at the desired position. The sequential assembly of the point-like light sources to the temporary holder might be executed by a so-called die-placer machine providing a sufficient accuracy for sequentially placing the point-like light sources sequentially onto the temporary holder.

The method may be arranged in such a way that the temporary holder comprises an adhesive layer providing the contact surface. A suitable adhesive layer might be an adhesive Polyimide tape. The adhesive layer simplifies the fixation step and provides a reversibility of the fixation, e.g. be weakening the adhesive forces. In a preferred embodiment the temporary holder is a heat resistant plastic film, preferably an adhesive Polyimide film, or a rigid flat substrate, preferably a metal, glass or ceramic substrate.

The method may be arranged in such a way that it further comprises the step of removing the reversibly mounted temporary holder from the point-like light sources after the mounting step has been finished. This can be done by peeling of the temporary holder in case of being a plastic film or dissolving the adhesive layer established as a glue layer with heat and/or solvents. A special glue losing or reducing adhesion during high temperature of reflow soldering may ease the removal of the temporary holder.

The method may be arranged in such a way that the array of point-like light sources comprises multiple columns and multiple rows of point-like light sources, where the numbers of rows and columns depend on the particular application.

The method may be arranged in such a way that the substrate is a printed circuit board. A printed circuit board already provides the electrical contacts for joining it with the contacting backside and therefore can be easily used in SMT processes. This simplifies the mounting step. The substrate might also be a ceramic interposer substrate.

According to a second aspect a pre-assembly comprising multiple point like light sources having an emitting side and contacting backside and a temporary holder is provided, wherein the point-like light sources are reversibly fixed on the temporary holder with their emitting surfaces with suitable means providing a three-dimensional positioning accuracy having position tolerances 20μιη between the point-like light sources. This pre-assembly is a component used in the method according to the present invention. This pre-assembly is a level 1 product which can be used by customers as a standard SMD component, supplied in tape and reel packing and can be assembled with SMT machines and reflow soldering to printed circuit boards PCB or isolated metal substrates IMS. A level- 1 -product denotes the core part of the product which is mainly focused on the benefit that the product brings to the customer, while the actual product (here the lighting assembly) is a tangible product which focuses on the quality and the design of the product. Here level 1 denotes a component without a wired substrate.

The pre-assembly may be arranged in such a way that the temporary holder comprises an adhesive layer as the suitable means providing a contact surface for accurate fixing of the point-like light sources. The adhesive layer can be made of any suitable material to temporarily fix the point-like light sources, e.g. adhesive polyimide tape using a high precision die bonder to achieve low positional tolerance between the point-like light sources.

The pre-assembly may be arranged in such a way that the temporary holder is a heat resistant plastic film, preferably a Polyimide film, or a rigid flat substrate, preferably a metal, glass or ceramic substrate. These materials enable to provide the temporary holder with defined geometrical and surface properties in order to fix the point-like light sources with the desired three-dimensional accuracy. According to a third aspect a lighting assembly is provided. The lighting assembly comprises a substrate with an array of electrical substrate contacts and an array of point-like light sources each having an emitting surface to emit light and a contacting backside being mounted in an electrical contact on the substrate contacts and being arranged with high positional accuracy 20 μιη by simultaneously mounting each of the contacting backsides of the point-like light sources to electrical substrate contacts, where the mounting of the array of point like light sources is performed in accordance to the method according to the present invention.

Lighting assemblies with such an accurate alignment of the array of point-like light sources can be operated without primary optics, because the point-like light sources can be placed very closely in order to allow matrix beam applications without primary optics. With the present invention tolerances between the point-like light sources of ΙΟμιη can be achieved, e.g. with applying SMT assembly and reflow soldering. The lighting assembly may be arranged in such a way that the array of point-like light sources comprises multiple columns and multiple rows of point-like light sources.

The lighting assembly may be arranged in such a way that the substrate is a printed circuit board or a ceramic interposer substrate.

It shall be understood that a preferred embodiment of the invention can also be any combination of the dependent claims with the respective independent claim.

Further advantageous embodiments are defined below.

BRIEF DESCRIPTION OF THE DRAWINGS:

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

The invention will now be described, by way of example, based on embodiments with reference to the accompanying drawings.

In the drawings:

Fig. 1 shows a principal sketch of fixing the point-like light sources to the temporary holder in accordance to the present invention with (a) before fixing and (b) after fixing.

Fig. 2 shows a principal sketch of mounting the point-like light sources to the substrate of the lighting assembly in accordance to the present invention with (a) before mounting and (b) after mounting.

Fig. 3 shows a principal sketch of removing the temporary holder from the point-like light sources in accordance to the present invention.

Fig. 4 shows a principal sketch of an embodiment of the method according to the present invention. In the Figures, like numbers refer to like objects throughout. Objects in the Figs, are not necessarily drawn to scale. DETAILED DESCRIPTION OF EMBODIMENTS:

Various embodiments of the invention will now be described by means of the

Figures.

Fig. 1 shows a principal sketch of fixing the point-like light sources to the temporary holder in accordance to the present invention with (a) before fixing and (b) after fixing. The temporary holder 4 comprises an adhesive layer 42 with a contact surface 41 without point-like light sources 2. A suitable gauge instrument 5 or an alternative sequential placing process provides the to-be-fixed point-like light sources 2 in order to control the relative distances DR and alignment TR between each of the point-like light sources 2 with the required accuracy (see also fig.3). The point-like light sources 2 are reversibly fixed 150 with the emitting surfaces 21 on the contact surface 41 of the temporary holder 4 in order to provide the pre-assembly 1 comprising the array of point like light sources 2 reversibly fixed on the temporary holder 4 with their emitting surfaces 21 with suitable means 42 providing a three-dimensional positioning accuracy having position tolerances in the range of 20μιη or less than 20μιη between the point-like light sources 2. The temporary holder 4 might be a heat resistant plastic film, preferably a Polyimide film, or a rigid flat substrate, preferably a metal, glass or ceramic substrate. The contacting backsides 22 are provided for electrically contacting the point- like light source 2.

Fig. 2 shows a principal sketch of mounting the array of point-like light sources to the substrate of the later achieved lighting assembly 10 (see fig.3) in accordance to the present invention with (a) before mounting and (b) after mounting. The lighting assembly 10 comprises a substrate 3 with an array of electrical substrate contacts 32 and an array of pointlike light sources 2 each having an emitting surface 21 to emit light L and a contacting backside 22 being mounted in an electrical contact on the substrate contacts 32 and being arranged with high positional accuracy in the range of 20μιη or less by simultaneously mounting 130 each of the contacting backsides 22 of the point-like light sources 2 to electrical substrate contacts 32, where the mounting of the array of point like light sources 2 is performed in accordance to the method 100 as shown in fig.4. Here the substrate 3 is a printed circuit board. The array of point-like light source might be a 4x2 array.

Fig. 3 shows a principal sketch of removing 160 the temporary holder 4 from the point-like light sources 2 in accordance to the present invention after the mounting step 130 has been finished. This can be done by peeling of the temporary holder 4 in case of being a plastic film or dissolving the adhesive layer 42 established as a glue layer with heat and/or solvents. A special glue losing or reducing adhesion during high temperature of reflow soldering may ease the removal of the temporary holder. The resulting lighting assembly 10 comprises mounted point-like light sources 2 with maintained relative distances DR and alignment TR between each of the point-like light sources 2 provided by the temporary holder 4 with the required accuracy of tolerances in the range of 20μιη or less.

Fig. 4 shows a principal sketch of an embodiment of the method 100 according to the present invention comprising an array of point-like light sources 2 arranged on a substrate 3 with high positional accuracy comprising the steps of providing 140 a temporary holder 4 with a contact surface 41 without point- like light sources 2. The temporary holder 4 may comprise an adhesive layer 42 providing the contact surface 41, the temporary holder 4 might be a heat resistant plastic film, preferably a Polyimide film, or a rigid flat substrate, preferably a metal, glass or ceramic substrate. The method is continued by reversibly fixing 150 the point-like light sources 2 having an light emitting side 21 and contacting backside 22 for electrically contacting the point-like light source 2 with the emitting surfaces 21 on the contact surface 41 of the temporary holder 4 in order to provide the pre-assembly 1 of an array of point like light sources 2 with a three-dimensional positioning accuracy having position tolerances in the range of 20μιη or less between the point-like light sources 2. The fixing step 150 might be executed using a suitable gauge instrument 5 or a sequential assembly with a die-placer machine in order to control the relative distances DR and alignment TR between each of the point-like light sources 2 with the required accuracy. The method is continued by providing 120 the substrate 3 with a contacting surface 31 comprising an array of electrical substrate contacts 32, where the electrical substrate contacts 32 are aligned to the position of the point-like light sources 2 on the temporary holder 4;

simultaneously mounting 130 the contacting backsides 22 of the point-like light source 2 on the electrical substrate contacts 32 of the substrate 3 for being able to operate the lighting assembly 10 maintaining the positioning accuracy of the pre-assembly 1 and removing 160 the reversibly mounted temporary holder 4 from the point-like light sources 2 after the mounting step 130 has been finished to provide the lighting assembly 10. The mounting step 130 might be executed by a surface mounting technology SMT. The mounting step 130 may comprise soldering 135 of the contacting backsides 22 of the point-like light sources 2 to solder dots 32 as the electrical substrate contacts 32 e.g. utilizing SAC -based solder in a reflow-soldering process. In an alternative embodiment the mounting step 130 might be carried out by conductive gluing or sintering. The substrate 3 might be a printed circuit board or a ceramic interposer substrate. While the invention has been illustrated and described in detail in the drawings and the foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive.

From reading the present disclosure, other modifications will be apparent to persons skilled in the art. Such modifications may involve other features which are already known in the art and which may be used instead of or in addition to features already described herein.

Variations to the disclosed embodiments can be understood and effected by those skilled in the art, from a study of the drawings, the disclosure and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality of elements or steps. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Any reference signs in the claims should not be construed as limiting the scope thereof.

LIST OF REFERENCE NUMERALS:

1 Pre-assembly according to the present invention

2 Point-like light sources

21 light emitting side

22 contacting backside

3 substrate, e.g. a printed circuit board

31 contacting surface

32 electrical substrate contacts, e.g. solder dots

4 temporary holder

41 contact surface of the temporary holder

42 suitable means to fix the point-like light source on the temporary holder, e.g. an adhesive layer

5 gauge instrument

10 Lighting assembly according to the present invention

100 Method to provide the lighting assembly in accordance to the present invention

110 providing a pre-assembly of an array of point like light sources

120 Providing a substrate with a contacting surface comprising an array of electrical substrate contacts

130 simultaneously mounting the contacting backsides of the point-like light source on the electrical substrate contacts

135 soldering the contacting backsides to the electrical substrate contacts within the mounting step

140 Providing a temporary holder

150 Reversibly fixing the point-like light sources on the temporary holder

160 removing the reversibly mounted temporary holder from the point-like light

sources

DR relative distance between different point-like light sources

SMT Surface mounting technology

TR relative alignment between different point-like light source, e.g. relative tilting and relative rotation