Light module of a motor vehicle signaling device

Abstract

The invention relates to a light module (1, 10) for a motor vehicle signaling device, comprising a plurality of selectively controllable light sources (2); each light source comprising an elementary light generator (21) and a photoluminescent element (22) covering the elementary light generator and capable of absorbing light rays emitted by this generator and emitting, in response, light rays of different wavelengths, characterized in that each light source comprises a plurality of walls (24) made of a white material, each wall in contact with a lateral surface of the photoluminescent element, and the plurality of walls defining an enclosure surrounding the photoluminescent element of this light source. Figure to be published with the abstract: Fig. 1

Description

Title of the invention: Light module of a motor vehicle signaling device

[0001] The invention relates to the field of automotive lighting and signaling. More specifically, the invention relates to the field of screens integrated into light modules for automotive lighting or signaling.

[0002] It is known to integrate displays into the lighting systems of motor vehicles, for example, in taillights. These displays are, for example, made using matrices of a large number of selectively controllable light sources, the dimensions of which are sufficiently small to allow information, for example in the form of a message or pictogram, to be displayed on them with satisfactory resolution. This information thus makes it possible to improve the signaling of the motor vehicle, for example by contextualizing or accompanying a given signaling function with a message.

[0003] This type of screen for this type of application raises several challenges.

[0004] Indeed, the light sources used in these screens are generally composed of a semiconductor chip emitting blue light, covered with a photoluminescent material capable of absorbing part of this blue light and re-emitting, in response, yellow light, the light resulting from the composition of the rest of the blue light and the yellow light being white in color.

[0005] However, this photoluminescent material has a high albedo, or reflectance, and can significantly reflect incident light onto the screen, such as sunlight or light from external lighting. This albedo can therefore reduce the screen's contrast and thus impair the visibility of details in pictograms or messages displayed on the screen.

[0006] Furthermore, the photoluminescent material, given its properties, has a yellow or amber color, which is visible from outside the screen. When the screen is off, it therefore also has a yellow appearance, which is incompatible with the need for a neutral appearance of the screens when off.

[0007] It is therefore necessary, on the one hand, to reduce the size of the light sources as much as possible in order to minimize the dimensions of the visible surface of this photoluminescent material, thereby reducing its albedo and decreasing the impact of the material's color on the screen's appearance when off. Reducing the size of the light sources also makes it possible to decrease the spacing between two light sources and thus increase the screen's resolution.

[0008] It is also necessary to avoid interference between light sources, and in particular to prevent light emitted by one light source from illuminating and reflecting off a neighboring light source. This effect, also called crosstalk, reduces the perceived quality of the screen, especially its contrast, since a light source that is off can appear to be on. Furthermore, the smaller the light sources and the closer they are to each other, the more pronounced this interference effect becomes.

[0009] There is therefore a need for a light module equipped with a plurality of light sources capable of together forming a screen for a signaling device of a motor vehicle, whose efficiency is optimal while exhibiting a reduced albedo and a neutral off appearance.

[0010] The present invention falls within this context and aims to meet this need.

[0011] To this end, the invention relates to a luminous module of a device signaling of a motor vehicle, comprising a plurality of selectively controllable light sources; each light source comprising an elementary light generator and a photoluminescent element covering the elementary light generator and capable of absorbing light rays emitted by this generator and of emitting, in response, light rays of different wavelengths, characterized in that each light source comprises a plurality of walls made of a white colored material, each wall coming into contact with a lateral surface of the photoluminescent element and the plurality of walls defining an enclosure framing the photoluminescent element of this light source.

[0012] The invention thus proposes to modify the structure of each light source in a light module designed to form a screen, by adding white walls or partitions that come into contact with the photoluminescent element to completely enclose it. These partitions allow, on the one hand, the interception of light emitted by the generator that might otherwise reach another light source in the light module. Due to their white color, this light is reflected within the enclosure defined by the partitions, in which the photoluminescent element is located. These partitions therefore significantly reduce interference or crosstalk effects and increase the efficiency of the light module. It is thus possible to reduce the dimensions of the light sources to decrease the albedo of the light source.Furthermore, the edges, or thicknesses, of these white walls contribute to the visible appearance of the light module when switched off, and thus reduce the influence of the color of the photoluminescent element on this switched appearance.

[0013] In the invention, the elementary light generator may be a light-emitting semiconductor chip. The semiconductor may, for example, be gallium nitride, or GaN, capable of emitting blue light rays by electroluminescence in response to an electric current passing through it. The photoluminescent element may, for example, be in the form of a resin comprising a cerium-doped yttrium aluminum garnet, or CE:YAG, capable of absorbing blue light and, by photoluminescence in response to the excitation produced by this light, of emitting yellow light rays. The photoluminescent element is arranged on the generator such that a portion of the blue light rays excites this element so that it emits yellow light rays by photoluminescence. The other portion of the blue light rays passes through this element.Thus, when electrically powered, the light source simultaneously emits blue and yellow light rays, the resulting light appearing white to the human eye.

[0014] According to the invention, the white-colored material may be a dielectric material with a reflection coefficient between 60 and 99%, in particular substantially equal to 90%. For example, it may be a silicone resin enriched with titanium dioxide (TiO2). If applicable, each wall made of the white-colored material may have a thickness of at most 100 µm.

[0015] Advantageously, the elementary light generator of each light source is mounted on a support, and each of the walls of said light source is mounted on this support and extends to an upper surface of the photoluminescent element. This support may be a printed circuit board or an interposer substrate. In this embodiment, the photoluminescent element thus encapsulates the elementary generator, and the white walls extend against the photoluminescent element until they are flush with its upper surface.

[0016] In one embodiment, the light sources are encapsulated in a single layer of dark-colored material. This layer of dark-colored material extends between two adjacent light sources, coming into contact with the outer lateral surfaces of the white walls. Given its opacity and color, it further limits any interference or crosstalk effects that might remain despite the presence of the white walls, improves the appearance of the light module when off, and reduces its albedo.

[0017] Advantageously, the dark-colored material may be black or gray and have a transmission coefficient, in bulk, of between 50% and 95% over a thickness of 1 mm. It may, for example, be a polymer, in particular an epoxy resin or a silicone, enriched with carbon particles or black pigments. For example, the concentration of Carbon particles, specifically the mass of carbon relative to the mass of the polymer, must be less than 0.05%. This characteristic is particularly suitable when the light module is intended for regulatory signaling purposes. Otherwise, a carbon particle concentration greater than 0.05% may be considered, notably to improve contrast and the screen's appearance when off.

[0018] Advantageously, a portion of the dark-colored material layer may extend over the white material walls and the photoluminescent elements of the light sources. If so, the thickness of this portion may be between 10 µm and 200 µm. This feature further improves the screen's appearance when off and reduces its albedo.

[0019] In one embodiment of the invention, the light module comprises a printed circuit board on which is mounted the elementary light generator of each light source, each generator having at least two electrical connection pads through which it is mounted and interconnected to said printed circuit board.

[0020] In another embodiment of the invention, the light module comprises a printed circuit board, and each light source comprises a substrate. The elementary light generator of each light source has at least two electrical connection pads through which it is mounted on this substrate, and each light source is mounted and interconnected to said printed circuit board via its substrate. In this embodiment, the substrate, also referred to as the interposer, supports the elementary light generator and allows the mounting and electrical interconnection of the light source to a printed circuit board. The elementary light generator may be encapsulated between the photoluminescent element and the substrate, the substrate thus supporting both the elementary light generator, the photoluminescent element, and the white material walls.

[0021] Advantageously, each wall of white material extends from the substrate, and each substrate has two electrical connection pads through which it is mounted and interconnected to said printed circuit board. Each pad extends along an underside of the substrate from a lateral edge of the substrate and each has a width such that these pads are separated by a space of at most 100 µm, in particular 80 µm. In this example, the size of the mounting surface of the light source on the printed circuit board, defined by the surface of the substrate, is increased due to the walls of white material. It is then possible to take advantage of this increase to move the positioning of the connection pads, usually centered on the substrate, towards the edges of the substrate and to increase their widths relative to the width of the substrate measured between these edges. These pads can then be more They are easily positioned by a machine on a given location on the printed circuit board, thus improving assembly accuracy. Furthermore, thermal conduction between the printed circuit board and the light source is improved, and the increased spacing between the two pads prevents electromigration phenomena that are detrimental to the reliability of the light source.

[0022] Advantageously, the elementary light generator of each light source comprises at least one light-emitting semiconductor chip with dimensions ranging from 100 µm to 400 µm. Such a chip is commonly known as a miniLED. If necessary, the light sources can be arranged on the first face of the substrate so that they are separated from each other by a distance of less than 1 millimeter.

[0023] Alternatively, the elementary light generator of each light source comprises at least one light-emitting semiconductor chip with dimensions ranging from 5 pm to 150 pm. Such a chip is commonly known as a microLED. If necessary, the light sources can be arranged on the first face of the substrate so that they are separated from each other by a distance of between 200 and 400 pm, or even less than or equal to 300 pm. The term "distance between two light sources" here refers to the distance separating the center of one of these light sources from the center of the other light source.

[0024] Advantageously, the lighting module includes a connector for receiving a control instruction for said plurality of light sources and at least one controller capable of selectively controlling light sources. Where applicable, the plurality of light sources forms a passive matrix, and the controller is configured to control said passive matrix according to the control instruction received by the connector. For example, the lighting module may include a plurality of devices for controlling the power supply provided to the light sources, each control device being mounted on one side of the printed circuit board, opposite a light source, to control the power supply provided to the light source, in particular according to an instruction received from the controller intended for it.

[0025] Advantageously, the light module comprises at least 500 light sources, in particular arranged in a matrix, the controller being configured to selectively control each of these light sources. If desired, said plurality of light sources may be a first plurality of light sources and the controller may be a first controller, and the light module may comprise at least a second plurality of light sources, for example mounted on the first side of the printed circuit board adjacent to the first plurality of light sources, and a second controller capable of selectively controlling each of the light sources of the second plurality.

[0026] Advantageously, the light module includes an interconnection system connected to the controller and arranged to interconnect the controller to the plurality of light sources. The interconnection system may be integrated into the printed circuit board or be an independent element mounted on this printed circuit board. The interconnection system may include a connector matrix, such as a ball grid array (BGA) or a pad grid array (LGA).

[0027] The invention also relates to a signaling device for a motor vehicle, characterized in that it comprises a light module according to the invention, said plurality of light sources forming a light screen of said signaling device.

[0028] The invention also relates to a method for manufacturing a light source of a light module according to the invention, the method comprising the following steps: a. Assembly of at least one elementary light generator on a support; b. Deposition of a layer of photoluminescent material on the elementary light generator; c. Cutting the photoluminescent material to form a photoluminescent element covering the elementary light generator; d. Deposition of a layer of white colored material on the photoluminescent element-elementary light generator assembly; e. Cutting the white colored material to form a plurality of walls, each coming into contact with a lateral surface of the photoluminescent element and defining an enclosure framing the photoluminescent element

[0029] The assembly step could, for example, be a step of mounting a light-emitting semiconductor chip on the surface of the support, the support being, for example, an interposer.

[0030] The step of cutting the photoluminescent material may for example include the formation of grooves in the photoluminescent material around an area intended to form the photoluminescent element, the grooves being intended to receive white colored material to form the walls.

[0031] The process may advantageously include, subsequent to the step of depositing the layer of white colored material, a step of polishing a surface upper part of the photoluminescent element assembly - elementary light generator - layer of white colored material.

[0032] The present invention is now described by means of purely illustrative and in no way limiting examples of the scope of the invention, and from the accompanying drawings, in which the various figures represent:

[0033] [Fig-1] represents, schematically and partially, a front view of a module luminous according to an embodiment of the invention;

[0034] [Fig.2] represents, schematically and partially, a side view of the module luminous of the [Fig.l];

[0035] [Fig.3] represents, schematically and partially, a bottom view of a light source of the light module of [Fig. 1]; and

[0036] [Fig.4] represents, schematically and partially, a side view of a module luminous according to another embodiment of the invention.

[0037] In the following description, identical elements, by structure or by function, appearing on different figures retain, unless otherwise specified, the same references.

[0038] A front view of a light module 1 according to one embodiment of the invention is shown in [Fig. 1]. In the example described, this light module 1 is intended to be integrated into a front light of a motor vehicle, the light module 1 forming a screen. [Fig. 2] shows a side view of this light module 1.

[0039] The light module 1 comprises a plurality of light sources 2 mounted on a support 3, formed in the example described by a printed circuit board 3.

[0040] In the example described, the light module 1 comprises more than 20,000 light sources 2, arranged in a matrix of 256 columns and 80 rows. The light sources 2 are mini-LEDs, with dimensions ranging from 100 µm to 400 µm. The light sources 2 are spaced less than or equal to 1 mm apart. It should be noted that other dimensions of the light sources, other distances between the light sources, other numbers of light sources, or other distributions of the light sources may be considered without departing from the scope of the present invention.

[0041] The printed circuit board 3, or PCB, has a first face 31 and a second face 32 opposite the first face. The light sources 2 are mounted on the first face 31 of the PCB 3, which faces outwards from the signaling device in which the light module 1 is integrated.

[0042] It should be noted that, in the example described, the printed circuit board 3 is a so-called multilayer PCB, comprising a stack of layers between the first and second faces 31 and 32. These layers are intended, in particular, for the interconnection of the components mounted on the PCB, and each may comprise a plurality of Through-hole, blind or buried vias, arranged in PCB 3 to be connected to the different interconnection layers. These vias open onto the first face 31 or the second face 32 of PCB 3 at the level of metal pads to which they are connected.

[0043] In order to be able to control the light sources 2, the light module 1 includes at least one controller 4 capable of selectively controlling light sources 2. It may be envisaged that a single controller 4 controls all the light sources 2 mounted on the PCB 3 or that there may be a plurality of controllers 4 each selectively controlling a matrix, for example of 64x64, i.e. 4096, light sources 2.

[0044] The light module 1 includes a connector (not shown) for receiving a control instruction for said plurality of light sources 2. This may be an instruction issued by a computer in the motor vehicle or the signaling device to display a logo, message, pattern, or pictogram. For example, it may be an instruction to display a pictogram intended to inform an outside observer that a door of the motor vehicle has been opened, a pictogram intended to inform a driver following the motor vehicle of the presence of black ice on the road, or information relating to motor traffic.

[0045] The plurality of light sources 2 forms a passive matrix where each row and each column of light sources 2 is associated with a control device (not shown) mounted on the PCB 3 at the right of that row or column to control the power supply provided to the light sources of that row or column. The controller 4 is thus arranged to control each of the sources 2 of said passive matrix according to the control instruction received by the connector, by successively scanning the rows and then the columns of the matrix to control the power supply provided to each of the light sources 2.

[0046] In the example described, the controller 4 is mounted on the second side 32 of the PCB 3 and is electrically interconnected to the metal pads provided on this second side 32. This interconnection can be achieved for example via a connector matrix (not shown), such as a ball matrix, also called BGA (from the English "bail grid array").

[0047] Each light source 2 comprises a light-emitting semiconductor chip 21, forming an elementary light generator. The semiconductor may, for example, be gallium nitride, or GaN, capable of emitting, by electroluminescence and in response to an electric current passing through it, rays of blue light, for example, whose spectrum has a peak centered on a wavelength between 410 nm and 480 nm.

[0048] Each light source also includes a photoluminescent element 22. This element 22, also called a conversion element or phosphor, is capable of absorbing a portion of the light rays emitted by the chip 21 and, in response, emitting light rays of a different wavelength. The photoluminescent element may, for example, be in the form of a resin comprising a cerium-doped yttrium aluminum garnet, or CE:YAG, capable of absorbing blue light and, through photoluminescence and in response to the excitation produced by this light, of emitting yellow light rays, for example, the spectrum of which has a peak centered on a wavelength between 520 nm and 600 nm.

[0049] The photoluminescent element 22 is arranged on the chip 21 such that a portion of the blue light rays emitted by the chip 21 excites this element 22, causing it to emit yellow light rays by photoluminescence. The remaining portion of the blue light rays passes through this element. Thus, the light source 2 simultaneously emits blue and yellow light rays when electrically powered, the resulting light appearing white to the human eye.

[0050] In the embodiment of [Fig.2], each light source 2 also includes an interposer 23 on which the chip 21 is mounted via two electrical connection pads 21a. The chip 21 is thus encapsulated between the photoluminescent element 22 and the interposer 23.

[0051] Each light source 2 also comprises a plurality of walls 24 made of a white material. The white material may be a dielectric material, having a reflection coefficient between 60 and 99%, in particular equal to 90%, such as a silicone resin enriched with titanium dioxide (TiO2).

[0052] Each wall 24 extends from the interposer 23, coming into contact with a lateral surface of the photoluminescent element 22, to a superior surface of the photoluminescent element 22. The walls 24 thus extend against the photoluminescent element 22 until they come flush with the superior surface of the photoluminescent element 22, thus defining an enclosure framing the photoluminescent element 22.

[0053] Given the white color of these walls 24, light rays emitted by the chip 21 from a light source 2 towards another light source 2 are intercepted by these walls 24 and reflected towards the photoluminescent element 22, thus avoiding interference effects and increasing the efficiency of the light module 1. In addition, the edges, or thicknesses, of these white walls 24 contribute to the visible off appearance of the light module and therefore reduce the influence of the color of the photoluminescent element 22 on this off appearance.

[0054] Each light source 2 is mounted and interconnected to said printed circuit board 3 via the interposer 23. As shown in [Fig.2], the interposer 23 has two electrical connection pads 23a, through which the light source 2 is mounted on the first face 31 of the PCB 3 and is electrically interconnected to electrical tracks provided on this first face 31.

[0055] As shown in [Fig. 3], which represents a bottom view of a light source 2, each electrical connection pad 23a extends along the underside of the interposer 23, from a lateral edge 23b of the substrate. Each pad 23a extends over almost the entire length of the interposer 23. The pads 23a are separated from each other by a space of at least 80 µm.

[0056] This arrangement and these dimensions of the pads 23a are made possible by the increased surface area of ​​the interposer 23, due to the white material walls 24. The pads 23a can then be more easily positioned, by a machine, on a given location on the printed circuit board 3, thus improving the accuracy of the assembly. In addition, thermal conduction between the printed circuit board 3 and the light source 2 is improved, and the increased space between the two pads 23a helps to avoid electromigration phenomena that are detrimental to the reliability of the light source 2.

[0057] The set of light sources 2 is encapsulated in a single layer of dark-colored material 5, for example black or grey, having a transmission coefficient in the mass of between 50% and 95%, over a thickness of 1 mm. It may, for example, be a polymer, in particular a silicone enriched with carbon particles, the concentration of carbon particles being less than 0.05%.

[0058] This layer 5 thus extends between two neighboring light sources 2, coming into contact with the external lateral surfaces of the white walls 24. Given its opacity and colour, the layer 5 thus makes it possible to further limit the effects of interference, and contributes to improving the off appearance of the light module 1 and to reducing its albedo.

[0059] In addition, a thin portion 51 of the layer 5 extends over the walls 24 and the photoluminescent elements 22 of the light sources 2. This feature makes it possible to further improve the off appearance of the light module and to reduce its albedo.

[0060] By way of example, it may be provided that each wall 24 has a thickness of at most 100 pm, and that the thickness of the portion 51 of the layer 5 is between 10 pm and 200 pm.

[0061] An example of a manufacturing process for a light source 2 of a light module 1 according to the embodiment of [Fig.1] to [Fig.3] will now be described.

[0062] In a first step, the light-emitting semiconductor chip 21, in the form of a "die", is assembled to the interposer 23, the pads 21a being soldered or brazed or glued to the interposer 23.

[0063] A layer of photoluminescent material is deposited, for example by molding, on the chip 21. Grooves are then formed, for example by laser drilling or by blade cutting (or "blade icing" in English), in this layer of photoluminescent material, to delimit the shape of the photoluminescent element 22.

[0064] A layer of white colored material is then deposited on the layer of photoluminescent material, to fill the grooves, and form the walls 24. The excess of white colored material, exceeding the grooves, is polished so that the levels of the layers of white material and photoluminescent material are identical.

[0065] Finally, the assembly is cut out, at the level of the walls 24, to form the light source 2.

[0066] A side view of a light module 10 according to another embodiment of the invention is shown in [Fig.4].

[0067] In this embodiment, the light sources 2 are without an interposer. Each light source 2 is thus mounted on the printed circuit board 3 via its chip 21, the electrical connection pads 21a being mounted and interconnected directly to the printed circuit board 3.

[0068] The preceding description clearly explains how the invention achieves its objectives, namely, to provide a light module capable of forming a screen for a motor vehicle signaling device, with optimal efficiency while exhibiting low albedo and a neutral off-light appearance. It is understood that these objectives are achieved, in particular, by integrating white walls or panels into each light source of the screen, which come into contact with the photoluminescent element of that light source to completely enclose it. These white walls significantly reduce interference or crosstalk effects and thus increase the efficiency of the light module. It is therefore possible to reduce the dimensions of the light sources to decrease the screen's albedo and improve its off-light appearance.

[0069] In any event, the invention is not limited to the embodiments specifically described in this document, and extends in particular to all equivalent means and to any technically feasible combination of these means. In particular, the printed circuit board may be replaced by another substrate, such as a rigid or flexible, straight or curved ceramic or glass substrate. The light sources may also be configured to form an active matrix. Other types of light sources than the one described may also be used, and in particular smaller light sources, for example between 5µm and 150µm, such as microLEDs. Other materials than those described could also be considered.

Claims

Demands

1. A light module (1, 10) of a signaling device for a motor vehicle, comprising a plurality of selectively controllable light sources (2); each light source comprising an elementary light generator (21) and a photoluminescent element (22) covering the elementary light generator and capable of absorbing light rays emitted by this generator and of emitting, in response, light rays of different wavelengths, characterized in that each light source comprises a plurality of walls (24) made of a white colored material, each wall coming into contact with a lateral surface of the photoluminescent element and the plurality of walls defining an enclosure framing the photoluminescent element of this light source and in that the light sources (2) are encapsulated in the same layer (5) of dark colored material.

2. Light module according to the preceding claim, characterized in that the elementary light generator (21) of each light source (2) is mounted on a support (23, 3) and in that each of the walls (24) of said light source is mounted on this support and extends to an upper surface of the photoluminescent element (22).

3. Light module (1, 10) according to any one of the preceding claims, characterized in that a portion (51) of the layer (5) of dark coloured material extends over the walls (24) of white material and the photoluminescent elements (22) of the light sources (2).

4. Light module (10) according to any one of the preceding claims, characterized in that it comprises a printed circuit board (3) on which is mounted the elementary light generator (21) of each light source (2), each generator having at least two electrical connection pads (21a) through which it is mounted and interconnected to said printed circuit board.

5. A light module (1) according to any one of claims 1 to 3, characterized in that it comprises a printed circuit board (3), in that each light source (2) comprises a substrate (23), the elementary light generator (21) of each light source comprising at least two electrical connection pads (21a) through which it is mounted on this substrate, and in that each light source is mounted and interconnected to said printed circuit board via its substrate.

6. Light module (1) according to the preceding claim, characterized in that each wall (24) of white material extends from the substrate (23) and in that each substrate has two electrical connection pads (23a) through which it is mounted and interconnected to said printed circuit board (3), these pads each extending over an underside face of the substrate from a lateral edge of the substrate and each having a width such that these pads are separated by a space of at most 100 pm.

7. Light module (1, 10) according to the preceding claim, wherein the elementary light generator (21) of each of the light sources (2) comprises at least one light-emitting semiconductor chip whose dimensions are between 100 pm and 400 pm.

8. Light module (1, 10) according to any one of the preceding claims, wherein the elementary light generator (21) of each of the light sources (2) comprises at least one light-emitting semiconductor chip whose dimensions are between 5 pm and 150 pm.

9. Light module (1, 10) according to any one of the preceding claims, characterized in that it comprises a connector for receiving a control instruction for said plurality of light sources (2) and at least one controller (4) capable of selectively controlling light sources (2), in which the plurality of light sources form a passive matrix and in which the controller (4) is arranged to control said passive matrix according to the control instruction received by the connector.

10. Signaling device for a motor vehicle, characterized in that it comprises a light module (1, 10) according to any one of the preceding claims, said plurality of light sources (2) forming a light screen of said signaling device.

11. A method for manufacturing a light source of a light module (1, 10) according to any one of claims 1 to 9, the method comprising the following steps: a. Assembly of at least one elementary light generator (21) on a support (23, 3); b. Deposition of a layer of photoluminescent material on the elementary light generator; c. Cutting the photoluminescent material to form a photoluminescent element (22) covering the elementary light generator; d. Deposition of a layer of white colored material on the photoluminescent element-elementary light generator assembly; e. Cutting the white coloured material to form a plurality of walls (24) each coming into contact with a lateral surface of the photoluminescent element and defining an enclosure framing the photoluminescent element.

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