Light module of a motor vehicle signaling device

Abstract

The invention relates to a light module (1) for a motor vehicle signaling device comprising: - a printed circuit board (3) having a first face (31) and a second face (32), - a plurality of light sources (2), each light source (2) comprising an elementary light generator (21) and a photoluminescent element (22), each light source (2) comprising a plurality of walls (24) formed from a white material, each wall (24) in contact with a lateral surface of the photoluminescent element (22), the plurality of walls (24) defining an enclosure surrounding the photoluminescent element (22) of the light source (2) concerned. According to the invention, the light module (1) comprises a dielectric layer (25) positioned between the printed circuit board (3) and said plurality of walls (24), the plurality of walls (24) extending from the dielectric layer (25). Figure to be published with the abbreviation: Figure 2

Description

Title of the invention: Light module for a motor vehicle signaling device. TECHNICAL FIELD OF THE INVENTION

[0001] The technical field of the invention relates generally to automotive lighting and light signaling.

[0002] More particularly, the invention relates to the field of screens integrated into light modules for lighting or light signaling of motor vehicles.

[0003] In particular, the invention relates to a light module of a signaling device of a motor vehicle. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0004] It is known to integrate displays into the lighting systems of motor vehicles, for example, in the rear or front lights of a motor vehicle. These displays are, for example, made using matrices of a large number of light sources, mounted on a printed circuit board and selectively controllable, and whose dimensions are sufficiently small to allow information, for example in the form of a message or pictogram, to be displayed on these displays 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.

[0005] The light sources used in these screens generally include a blue light emitting semiconductor chip, covered with a photoluminescent material adapted to absorb part of this blue light and to re-emit, in response, yellow light (by additive synthesis, the light resulting from the composition of the rest of the blue light and the yellow light being white).

[0006] However, this photoluminescent material has high reflectance. It can therefore reflect a significant amount of light incident on the screen (such as sunlight or light from external lighting). This albedo can thus reduce the screen's contrast and therefore impair the visibility of details in the messages displayed on the screen.

[0007] Furthermore, given its properties, the photoluminescent material 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.

[0008] Furthermore, given the relative positioning of the light sources, a so-called "cross-talk" effect can be observed. Indeed, the light emitted by one light source can illuminate and be reflected by a neighboring light source, thus causing unwanted interference between the light sources. This notably reduces the perceived quality of the screen, particularly its contrast, since a light source that is off can appear to be on. Moreover, the smaller the dimensions of the light sources and the closer they are to each other, the more pronounced these unwanted effects become.

[0009] It is then known to modify the structure of this luminous module in order to reduce these interference effects between the light sources by forming white walls between the light sources. These walls are then in contact with the photoluminescent material and completely surround it.

[0010] In practice, these walls are obtained by cutting the photoluminescent material, so as to form grooves intended to receive white colored material to form the walls.

[0011] However, this cutting process is delicate to implement because there is a risk of damaging the printed circuit board containing all the light sources. Accidental cutting of the printed circuit board (during wall formation) can lead to screen reliability problems, particularly by causing corrosion and electromigration defects between the electrodes that power the light sources. Summary of the invention

[0012] The present invention then proposes a light module of a signaling device of a motor vehicle with reduced dimensions, with limited interference effects between light sources and in which the integrity of the printed circuit board carrying the light sources is preserved.

[0013] One aspect of the invention thus relates to a luminous module of a signaling device of a motor vehicle comprising:

[0014] - a printed circuit board comprising a first side and a second side, opposite to the first side,

[0015] - a plurality of selectively controllable light sources, each a light source comprising an elementary light generator and a photoluminescent element covering the elementary light generator, the photoluminescent element being adapted to absorb the light rays emitted by the elementary light generator and to emit, in response, other light rays of a different wavelength, each light source is mounted on the first face of the printed circuit board via the corresponding elementary light generator,

[0016] each light source comprising a plurality of walls formed in a white coloured material, each wall coming into contact with a lateral surface of the photoluminescent element, the plurality of walls defining an enclosure framing the photoluminescent element of the light source concerned.

[0017] According to the invention, the light module comprises a dielectric layer positioned between the printed circuit board and said plurality of walls, the plurality of walls extending from the dielectric layer.

[0018] Thus, advantageously according to the present invention, the dielectric layer forms a protective layer that protects the printed circuit board, particularly during the formation of the plurality of walls. This prevents corrosion and electromigration phenomena that are detrimental to the reliability of the light source and that can occur when the printed circuit board is damaged. Since this dielectric layer is electrically insulating, it maintains the interconnection between each light source and the printed circuit board.

[0019] This then makes it possible to form the plurality of walls by cutting as close as possible to the printed circuit board (possibly in the dielectric layer) in order to avoid light leakage between the light sources but without damaging the printed circuit board.

[0020] In addition to the characteristics mentioned in the preceding paragraph, the light module according to the invention may have one or more additional characteristics from among the following, considered individually or in all technically possible combinations:

[0021] - the dielectric layer comprises an epoxy polymer material;

[0022] - the printed circuit board and the dielectric layer comprise the same material made of epoxy polymer;

[0023] - the dielectric layer is homogeneous, which means in particular that it does not does not include fiber reinforcement;

[0024] - the dielectric layer has a thickness of less than 50 micrometers;

[0025] - the dielectric layer has a thickness of between 25 and 35 micrometers;

[0026] - the dielectric layer is formed on the first face of the circuit board printed;

[0027] - each light source comprises a substrate, the elementary generator of light from each light source having at least two electrical connection pads through which it is mounted on this substrate, each light source being mounted and interconnected to said printed circuit board via the corresponding substrate, the dielectric layer being formed on a first face of said substrate;

[0028] - another dielectric layer is planned to be formed on the second side of the card printed circuit board;

[0029] - the other dielectric layer comprises an epoxy polymer material;

[0030] - the other dielectric layer has a thickness of less than 50 micrometers;

[0031] - the other dielectric layer has a thickness between 25 and 35 micrometers;

[0032] - the dielectric layer and the other dielectric layer are identical;

[0033] - each wall comprises a first part and a second part, the first part being positioned opposite the elementary lighting generator, the first part having a thickness less than a thickness of the second part;

[0034] - the first part of each wall has a thickness of less than 75 micrometers;

[0035] - the second part of each wall has a variable thickness between one first end and a second end, the thickness of the second part of each wall at the first end being greater than the thickness of the second part of each wall at the second end;

[0036] - the thickness of the second part of each wall at the level of the first the tip is less than 120 micrometers;

[0037] - the first part of each wall has a height of less than 100 micrometers;

[0038] - the first part of each wall has a height of less than 100 micrometers;

[0039] - the first part of each wall is positioned at a distance from the generator elementary particle of light concerned, said distance being less than 150 micrometers; and

[0040] - the first part of each wall is positioned at a distance from a first face of the printed circuit board, said distance being less than 50 micrometers.

[0041] Another aspect of the invention relates to a signaling device for a motor vehicle comprising a light module as introduced previously, said plurality of light sources forming a light screen of said signaling device. BRIEF DESCRIPTION OF THE FIGURES

[0042] Other features and advantages of the invention will become apparent from the description, which can be read in conjunction with the figures. These figures are provided for illustrative purposes only and are not intended to limit the scope of the invention.

[0043] [Fig. 1] Fig. 1 represents a partial schematic front view of a light module according to the present invention,

[0044] [Fig.2] Fig.2 represents a partial schematic cross-sectional view along a plane AA of [Fig. 1], of a first embodiment of the light module,

[0045] [Fig. 3] Fig. 3 represents a partial schematic cross-sectional view along a plane AA of [Fig. 1], of a second embodiment of the light module,

[0046] [Fig.4] Fig.4 represents a partial schematic cross-sectional view along a plane AA of [Fig. 1], of a third embodiment of the light module,

[0047] [Fig. 5] Fig. 5 represents a partial schematic cross-sectional view along a plane AA of [Fig. 1], of a fourth embodiment of the light module, and

[0048] [Fig. 6] Fig. 6 represents a partial schematic cross-sectional view along a plane AA of [Fig.1], of a fifth embodiment of the light module.

[0049] For clarity, identical or similar elements are identified by identical reference numerals throughout the figures. DETAILED DESCRIPTION

[0050] The present invention aims to provide a light module for a motor vehicle signaling device with reduced dimensions, whose efficiency is optimal (without parasitic interference effects between light sources) and guaranteeing reliability, particularly electronic, of the whole.

[0051] In this description, the vehicle (not shown) in question is a motor vehicle. "Motor vehicle" is understood to mean any type of motorized vehicle. Hereafter, the terms "vehicle" and "motor vehicle" are used interchangeably to describe the vehicle covered by the present invention.

[0052] Figure 1 shows a front view of a light module 1; 100; 150 according to an embodiment of the invention. This light module 1; 100; 150 is, for example, intended to be integrated into a front or rear light of the motor vehicle. The light module 1; 100; 150 thus forms a screen. In other words, the light module 1; 100; 150 of the invention forms a display device, visible, for example, from outside the motor vehicle.

[0053] Fig. 2 represents a partial cross-sectional view of a first embodiment of the light module 1 (according to the section plane AA visible on Fig. 1).

[0054] The light module 1 comprises a plurality of light sources 2 mounted on a support 3. Here, the support 3 is for example formed by a printed circuit board 3.

[0055] In the described example, the light module 1 comprises at least 100 light sources 2, arranged in a matrix (for example, in 10 columns and 10 rows). Preferably, the light module 1 comprises more than 20,000 light sources 2, arranged in a matrix in 256 columns and 80 rows.

[0056] Each light source 2 is here a mini-LED, for example, square in shape as shown in [Fig. 1]. The dimensions of each light source 2 are, for example, between 100 micrometers (µm) by 100 µm and 600 µm by 600 µm. The light sources 2 are spaced less than 1 millimeter (mm) apart. In this description, the "distance between two light sources" means the distance separating the center of one of these light sources from the center of the other (adjacent) light source.

[0057] Alternatively, the light sources can be arranged on the printed circuit board 3 so as to be separated from each other by a distance of between 200 and 400 pm, or even less than or equal to 300 pm.

[0058] 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.

[0059] The printed circuit board 3 has a first face 31 and a second face 32 opposite the first face 31. The light sources 2 are mounted on the first face 31 of the printed circuit board 3. This first face 31 faces the outside of the signaling device in which the light module 1 is integrated (the light rays from each light source 2 are therefore directed towards the outside of the signaling device in which the light module 1 is integrated according to the present invention).

[0060] The printed circuit board 3 here comprises a composite polymer material in which glass fibers are embedded. The polymer material is, for example, an epoxy polymer.

[0061] In practice, the printed circuit board 3 is a so-called multilayer board, meaning that it comprises a stack of layers (not shown), these layers being arranged between the first face 31 and the second face 32. These layers are specifically designed to allow the interconnection of the components mounted on the printed circuit board 3. Each layer may include a plurality of through, blind, or buried vias arranged within the printed circuit board 3 to be connected to the various interconnection layers. These vias open onto the first face 31 or the second face 32 of the printed circuit board 3 at the level of metal pads to which they are connected.

[0062] In order to control the light sources 2, the light module 1 includes at least one controller 4 configured to selectively control the light sources 2. The light module 1 may include a single controller 4 that controls all the light sources 2 mounted on the printed circuit board 3. Alternatively, the light module may include a plurality of controller 4 each selectively controlling a matrix, for example of 64x64 (i.e. 4096) light sources 2.

[0063] As can be seen in [Fig.2], the controller 4 is mounted on the second side 32 of the printed circuit board 3 and is electrically interconnected to the metal pads provided on this second side 32.

[0064] The light module may then include an interconnection system connected to the controller and arranged to interconnect the controller to the plurality of light sources. The interconnection system may, for example, 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 matrix, also called BGA (for "Bail Grid Array" according to the commonly used Anglo-Saxon acronym) or a pad matrix, also called LGA (from the English "Land Grid Array" according to the commonly used Anglo-Saxon acronym).

[0065] The light module 1 includes a connector (not shown) for receiving a control instruction for the 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 to inform an outside observer that a door of the motor vehicle has been opened, a pictogram to inform a driver following the motor vehicle of the presence of black ice on the road, or information relating to motor traffic.

[0066] 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 printed circuit board 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 light sources 2 of the 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.

[0067] Alternatively, the light module may include a plurality of control devices for the power supply provided to the light sources, each control device being mounted on the second side of the printed circuit board, opposite a light source, to control the power supply provided to the light source concerned, in particular according to an instruction received from the controller intended for it.

[0068] As shown in [Fig. 2], each light source 2 comprises a light-emitting semiconductor chip 21, forming an elementary light generator. The semiconductor is, for example, gallium nitride (also denoted GaN), configured to emit, by electroluminescence and in response to an electric current passing through it, beams of blue light, for example, whose spectrum has a peak centered on a wavelength between 410 nanometers (nm) and 480 nm.

[0069] Each light source 2 also includes a photoluminescent element 22. This photoluminescent element 22, also called a conversion element or phosphor, is adapted to absorb a portion of the light rays emitted by the semiconductor chip 21 and to emit, in response, light rays of a different wavelength. The photoluminescent element 22 is, for example, in the form of a resin comprising a cerium-doped yttrium aluminum garnet (or CE:YAG) adapted to absorb blue light and, by photoluminescence and in response to the excitation produced by this blue light, to emit yellow light rays, for example, the spectrum of which has a peak centered on a wavelength between 520 nm and 600 nm.

[0070] The photoluminescent element 22 is arranged on the semiconductor chip 21 such that a portion of the blue light rays emitted by the semiconductor chip 21 excites this photoluminescent element 22, causing it to emit yellow light rays by photoluminescence. The remaining portion of the blue light rays passes through this photoluminescent element 22. Thus, the light source 2 simultaneously emits blue and yellow light rays when electrically powered, the resulting light appearing white to the human eye.

[0071] It is understood that the invention is not limited to the colors mentioned here. In particular, it may be possible to modify the composition of a photoluminescent conversion layer of the photoluminescent element in order to obtain a desired color (other than that described above).

[0072] As can be seen in [Fig.2], each light source 2 is mounted and interconnected to the printed circuit board 3 via its semiconductor chip 21. More particularly, the semiconductor chip 21 is provided with electrical connection pads 21a mounted and interconnected directly to the printed circuit board 3. Thus, the semiconductor chip 21 of each light source 2 is encapsulated between the photoluminescent element 22 and the printed circuit board 3.

[0073] Each light source 2 also comprises a plurality of walls 24 made of a white material. The white material is, for example, a dielectric material having a reflection coefficient between 60 and 99%, preferably around 90%. This white material is a silicone resin enriched with titanium dioxide (TiO2).

[0074] Each wall 24 extends from a dielectric layer 25 (described in more detail below), coming into contact with a lateral surface of the photoluminescent element 22, to a top surface of the photoluminescent element 22. The walls 24 thus extend against the photoluminescent element 22 until they are flush with the top surface of the photoluminescent element 22, thereby defining an enclosure framing the photoluminescent element 22 of each light source 2. In other words, as can be seen in [Fig. 1], the walls 24 form a boundary of each light source 2 by surrounding the photoluminescent element 22 of each light source 2.

[0075] In the embodiment shown in [Fig. 2], each wall 24 has a constant thickness e. In this description, the term "thickness" refers to a dimension measured in a plane parallel to the first face 31 of the printed circuit board 3. This thickness e is, for example, less than 150 µm, or even less than 120 µm. Preferably, the thickness of each wall 24 is less than 100 µm. This thickness e is, for example, between 50 and 150 µm.

[0076] Furthermore, the height h of each wall 24 is here less than 200 pm. In this description, the term "height" refers to a dimension of each wall taken perpendicular to the first face 31 of the printed circuit board 3. Preferably here, the height h of each wall 24 is on the order of 190 pm.

[0077] In practice, these walls 24 are obtained from grooves formed, for example by laser drilling or by blade cutting (or “blade d icing” according to the commonly used Anglo-Saxon terminology), in the layer of photoluminescent material, to delimit the shape of the photoluminescent element 22. A layer of white colored material is deposited on the layer of photoluminescent material, to fill the grooves, and form the walls 24.

[0078] Furthermore, each wall 24 is positioned at a distance from the semiconductor chip 21 to the relevant light source 2. More specifically, this distance d is less than 150 pm. Preferably, this distance d is less than 125 pm. Even more preferably, this distance d is less than 75 pm. Such a configuration then makes it possible to limit any potential risk of cutting the semiconductor chip 21 of the relevant light source 2 during the formation of the walls 24. Moreover, this makes it possible to avoid increasing the size of the light module while maintaining a light source spacing of less than one millimeter, for example.

[0079] Given the white color of these walls 24, light rays emitted by the semiconductor chip 21 from a considered light source 2 towards another adjacent light source 2 are intercepted by these walls 24 and are reflected towards the photoluminescent element 22. Due to the white color of these walls, the light rays are reflected within the enclosure defined by the walls and in which the material of the photoluminescent element 22 is located. Advantageously, this avoids parasitic effects and thus increases 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.

[0080] Advantageously, according to the invention, the light module 1 comprises a dielectric layer 25. This dielectric layer 25 is formed on the first face 31 of the printed circuit board 3. More specifically, the dielectric layer 25 is positioned between the printed circuit board 3 and the walls 24. This dielectric layer 25 thus forms a protective layer that protects the printed circuit board 3, particularly during the formation of the plurality of walls 24 (forming the plurality of walls 24 by cutting could also cut the printed circuit board 3). This prevents corrosion and electromigration phenomena that are detrimental to the reliability of the light source and that could occur when the printed circuit board is damaged. Since this dielectric layer is electrically insulating, it maintains the interconnection between each light source 2 and the printed circuit board 3.

[0081] In practice, as can be seen in [Fig.2], the dielectric layer 25 comprises a plurality of portions, allowing in particular to maintain, for each light source 2, the interconnection between the semiconductor chip 21 and the printed circuit board 3 (via the electrical connection pads 21a).

[0082] Here, the dielectric layer 25 comprises a polymer material, preferably an epoxy polymer material. Such a material allows good adhesion with the printed circuit board 3.

[0083] The dielectric layer 25 is preferably homogeneous, that is, without fiber reinforcement (for example, without glass, acrylic, or aramid fibers). The absence of fibers prevents delamination within the dielectric layer 25 in the event of a production incident in which the dielectric layer is damaged by the cutting of the grooves used to form the walls. Indeed, if the dielectric layer contained fibers, such an incident could expose some of these fibers, with the walls then being formed directly on the exposed fibers. This configuration poses the risk of delamination at the level of the exposed fibers, which impairs the reliability of the light source, particularly because it promotes the formation of a crack that can reach the elementary light generator. A homogeneous dielectric layer prevents the occurrence of this type of incident and thus improves the reliability of light sources. A homogeneous epoxy polymer layer has the additional advantage of being substantially isotropic, and is therefore even less likely to form cracks.

[0084] According to one embodiment, the printed circuit board 3 and the dielectric layer 25 both comprise the same epoxy polymer material. This simplifies the manufacture of the printed circuit board 3 and ensures very good adhesion between the dielectric layer 25 and the printed circuit board 3.

[0085] Advantageously, the dielectric layer 25 has a thickness of less than 50 pm. Preferably, the thickness of the dielectric layer 25 is between 25 and 35 pm. This allows for a low overall thickness of the light module, without altering its characteristics and properties.

[0086] As shown in Figures 1 and 2, the set of light sources 2 is encapsulated in a single layer of dark-colored material 5, for example black or gray. This layer of dark-colored material 5 has a transmission coefficient in the mass of between 50% and 90%, over a thickness of 0.1 millimeter (mm).

[0087] This dark-colored material layer 5 comprises, for example, a polymer material. This is, for example, an epoxy resin or a silicone, enriched with carbon particles or black pigments. The concentration of carbon particles, that is, the mass of carbon relative to the mass of the polymer material, is, for example, less than 0.05%. This characteristic is particularly suitable when the light module is intended to perform a regulatory signaling function. Alternatively, the concentration of carbon particles may be greater than 0.05%, in particular to improve the contrast and the off-screen appearance.

[0088] This layer of dark-colored material 5 thus extends between two adjacent light sources 2, coming into contact with the external lateral surfaces of the walls 24 (i.e., in contact with the lateral surfaces opposite to those in contact with the photoluminescent element 22). Given its opacity and color, the layer of dark-colored material 5 further limits the interference effects and contributes to improving the off appearance of the light module 1 and reducing its albedo.

[0089] Furthermore, a thin portion 51 of the dark coloured material layer 5 extends over the walls 24 and the photoluminescent elements 22 of the light sources 2 of the light module 1. This feature makes it possible to further improve the off appearance of the light module and to reduce its albedo.

[0090] In practice, portion 51 has a thickness of less than 200 pm. This thickness is preferably between 10 and 200 pm.

[0091] In an alternative (not shown) configuration, each wall 24 is positioned at a distance from the dielectric layer 25. More specifically, the end 24A of each wall 24 is positioned at a distance from the face 25A of the dielectric layer 25 opposite the printed circuit board 3. This distance is, for example, less than 50 pm. This allows for a margin to be maintained so as not to damage the printed circuit board during the cutting of the grooves used to form the walls 24.

[0092] Figure 5 shows a partial cross-sectional view of an alternative embodiment of the first embodiment described. The elements common to this first embodiment are not described in detail again here. The main difference lies in the fact that the light sources 2 are mounted on the support 3 by means of a substrate 23 called the "interposer 23". In practice, the interposer 23 is also in the form of a printed circuit board.

[0093] As can be seen in [Fig. 5], the semiconductor chip 21 is mounted, via the electrical connection pads 21a, on a first face 23a of the interposer. In this example, the dielectric layer 25 is formed on this first face 23a of the interposer 23.

[0094] Each wall 24 extends here from the dielectric layer 25 formed on the interposer 23 to the upper surface of the photoluminescent element 22. The walls 24 thus also extend here against the photoluminescent element 22 until they come flush with the upper surface of the photoluminescent element 22, thus defining an enclosure framing the photoluminescent element 22.

[0095] Furthermore, each light source 2 is mounted and interconnected to the printed circuit board 3 via the interposer 23. As shown in [Fig. 5], the interposer 23 has two electrical connection pads 23c (extending from a second face 23b of the interposer 23). Each light source 2 is therefore mounted on the first face 31 of the printed circuit board 3 and is electrically interconnected to electrical traces provided on this first face 31. In practice, the electrical connection pads 23c are separated from each other by a distance of at least 80 micrometers (pm).

[0096] This arrangement of the electrical connection pads 23c is made possible by the increased surface area of ​​the interposer 23, due to the walls 24. The electrical connection pads 23c can then be more easily positioned, by a machine, on a given location on the printed circuit board 3, thus improving the assembly accuracy. In addition, thermal conduction between the printed circuit board 3 and each light source 2 is improved, and the increased space between the two electrical connection pads 23c helps prevent corrosion and electromigration phenomena that are detrimental to the reliability of the light source 2.

[0097] The use of an interposer for each light source makes it easier to assemble each of the light sources 2 on the printed circuit board 3, and thus improve the efficiency and reliability of the light module.

[0098] Figure 3 shows a partial cross-sectional view of a second embodiment of the light module 100 (along the section plane AA visible in Figure 1). The elements common to the first embodiment described previously (and shown in Figure 2) are not described again in detail hereafter.

[0099] In this second embodiment, the light module 100 includes another dielectric layer 26 which is formed on the second face 32 of the printed circuit board 3. In other words, this other dielectric layer 26 is formed on the face of the printed circuit board 3 opposite to that bearing the dielectric layer 25. Advantageously, this other dielectric layer 26 makes it possible to ensure a symmetrical structure, at the level of the printed circuit board 3, for the light module 1, thus improving its reliability.

[0100] In practice, as can be seen in [Fig.3], the other dielectric layer 26 is formed on the second face 32 of the printed circuit board 3, around the controller 4. This makes it possible to maintain the correct connection of the light sources 2 to the controller 4, in order to ensure proper control.

[0101] As previously described for the dielectric layer 25, the other dielectric layer 26 comprises a polymer material, preferably an epoxy polymer material. According to one embodiment, the printed circuit board 3 and the other dielectric layer both comprise the same epoxy polymer material. In a further embodiment, the dielectric layer and the other dielectric layer comprise the same epoxy polymer material.

[0102] Advantageously, the other dielectric layer 26 has a thickness of less than 50 pm. Preferably, the thickness of the other dielectric layer 26 is between 25 and 35 pm. This makes it possible to maintain a low overall thickness of the light module and to preserve its characteristics and properties.

[0103] Preferably, the dielectric layer 25 and the other dielectric layer 26 have the same thickness.

[0104] Preferably, to ensure a symmetry characteristic for the light module, the dielectric layer and the other dielectric layer are identical (in material and thickness, in particular). Such symmetry helps to avoid deformations, especially those due to differences in thermal expansion.

[0105] Alternatively (not shown), the light module 100 according to this second embodiment of the invention may also include an interposer as described previously, on which is mounted and interconnected the semiconductor chip 21 of each light source 2.

[0106] Figure 4 shows a partial cross-sectional view of a third embodiment of the light module 150 (along the section plane AA visible in Figure 1). The elements common to the first embodiment described previously (and shown in Figure 2) are not described again in detail hereafter. Essentially, the difference between this third embodiment and the first embodiment presented previously lies in the shape of the walls (denoted "walls 154" in this third embodiment) of each light source 2.

[0107] In this third embodiment, each wall 154 comprises a first part 154A and a second part 154B. As can be seen in [Fig.4], the first part 154A of each wall 154 is positioned opposite the semiconductor chip 21 of the light source 2 concerned.

[0108] Here, the plurality of walls 154 of each light source 2 is arranged symmetrically with respect to the center of this light source 2.

[0109] Advantageously, according to the invention, the first part 154A has a thickness less than that of the second part 154B. In other words, each wall 154 has a variable thickness, with a thinner thickness in the first part 154A (located opposite the semiconductor chip 21 of the light source in question). This variability in the thickness of each wall 154, with a thinner thickness near the printed circuit board 3, minimizes the risk of cutting the printed circuit board 3 during the formation of the walls 154 (since the thickness of each wall 154 near the printed circuit board is very small, the cut then presents a small cross-section near the printed circuit board 3). This thus prevents electromigration phenomena that are detrimental to the reliability of the light source and that may occur when the printed circuit board is damaged.This wall shape then allows for the formation of a double protection (with the dielectric layer 25) of the printed circuit board 3.

[0110] Here, the first portion 154A of each wall 154 has a thickness el of less than 75 µm. Preferably, the thickness el of the first portion 154A of each wall 154 is between 30 and 70 µm. Even more preferably, this thickness el of the first portion 154A of the wall 154 is on the order of 50 µm. Such a small thickness then makes it possible to limit any potential risk of cutting the printed circuit board 3.

[0111] Furthermore, the second part 154B of each wall comprises a first end 155 and a second end 156. The second end 156 corresponds here to the end common with the first part 154A. The first end 155 therefore corresponds to the end of each wall 154 present at the level of the outer surface of the light module 150.

[0112] As can be seen in [Fig.4], the second part 154B has a variable thickness between its first end 155 and its second end 156. More particularly, the thickness of the second part 154B of each wall 154 is smaller at its second end 156 than at its first end 155.

[0113] Here, the thickness e2 of the second part 154B of each wall at its first end 155 is less than 150 pm. Preferably, this thickness e2 is between 75 and 120 pm. More preferably, it is between 75 and 115 pm. Even more preferably, this thickness is on the order of 95 pm. Such values ​​for the thickness e2 of the second part 154B of each wall 154 near the outer surface of the light module 150 ensure the barrier and reflection effect of the white walls as described above, while also contributing to the visible appearance of the light module when switched off, and thus reduce the influence of the color of the photoluminescent element 22 on this appearance when switched off.

[0114] At its second end 156, the second part 154B of each part 154 has of course a thickness similar to that of the first part 154A.

[0115] Furthermore, the height hl of the first part 154A of each wall is less than 100 pm. Preferably, it is between 60 and 100 pm. Even more preferably, this height hl is on the order of 80 pm. This makes it possible to avoid, during the cuts used to form the walls 154, damaging the semiconductor chip 21 of each light source 2.

[0116] Regarding the second part 154B of each wall 154, the height h2 is less than 110 pm. Preferably, this height h2 is between 70 and 110 pm. Even more preferably, the height h2 of the second part 154B is approximately 90 pm. Such height dimensions for each wall 154 thus make it possible to maintain a low overall thickness of the light module, while preserving its lighting and signaling characteristics, and therefore the reliability of the light module.

[0117] Furthermore, the first portion 154A of each wall 154 is positioned at a distance from the semiconductor chip 21 of the relevant light source 2. More specifically, this distance dl is less than 150 pm. Preferably, this distance dl is less than 125 pm. Such a configuration then makes it possible to limit any potential risk of cutting the semiconductor chip 21 of the relevant light source 2 during the formation of the walls 154.

[0118] In an alternative (not shown) configuration, each wall 154 is positioned at a distance from the dielectric layer 25. More specifically, the end 157 of the first part 154A, opposite the second part 154B, is positioned at a distance from the face 25A of the dielectric layer 25 opposite the printed circuit board 3. This distance is, for example, less than 50 pm here. This allows a margin to be maintained so as not to damage the printed circuit board during the cutting of the grooves used to form the walls 154.

[0119] As a further alternative (not shown), the light module 150 may include another dielectric layer 26 (as described previously) which is formed on the second face 32 of the printed circuit board 3.

[0120] Figure 6 shows a partial cross-sectional view of an alternative embodiment of the third embodiment described. The elements common to this third embodiment are not described in detail again here. The main difference lies in the fact that the light sources 2 are mounted on the support 3 by means of an interposer 23 (such as the one described previously in the context of the alternative embodiment of the first embodiment). In practice, the interposer 23 is also in the form of a printed circuit board.

[0121] As can be seen in [Fig.6], the semiconductor chip 21 is, here too, mounted, via the electrical connection pads 21a, on the first face 23a of the interposer 23. In this example also, the dielectric layer 25 is formed on this first face 23a of the interposer 23.

[0122] Each wall 154 extends here from the dielectric layer 25 formed on the interposer 23, to the upper surface of the photoluminescent element 22. The walls 154 thus also extend here against the photoluminescent element 22 until they come flush with the upper surface of the photoluminescent element 22, thus defining the enclosure framing the photoluminescent element 22.

[0123] Furthermore, each light source 2 is mounted and interconnected to the printed circuit board 3 via the interposer 23. As shown in [Fig. 6], the interposer 23 has two electrical connection pads 23c (extending from the second face 23c of the interposer). Each light source 2 is therefore mounted on the first face 31 of the printed circuit board 3 and is electrically interconnected to electrical traces provided on this first face 31. In practice, the electrical connection pads 23c are separated from each other by a distance of at least 80 µm.

[0124] This arrangement of the electrical connection pads 23c is made possible by the increased surface area of ​​the interposer 23, due to the walls 154. The electrical connection pads 23c can then be more easily positioned, by a machine, on a given location on the printed circuit board 3, thus improving the assembly accuracy. In addition, thermal conduction between the printed circuit board 3 and each light source 2 is improved, and the increased space between the two electrical connection pads 23c helps to prevent corrosion and electromigration phenomena that are detrimental to the reliability of the light source 2.

[0125] The use of an interposer for each light source makes it easier to assemble each of the light sources 2 on the printed circuit board 3, and thus improve the efficiency and reliability of the light module.

[0126] An example of a manufacturing process for a light source 2 of a light module 1; 100; 150 according to the embodiments of figures 1 to 4 is described below.

[0127] In a first step, the light-emitting semiconductor chip 21, in the form of a "die", is assembled to the printed circuit board 3. In practice, the pads 21a are, for example, soldered, brazed or glued to the first face 31 of the printed circuit board 3.

[0128] In a second step, the dielectric layer 25 is deposited on the first face 31 of the printed circuit board 3, around the light-emitting semiconductor chip 21. In practice, this is implemented, for example, by masking the light-emitting semiconductor chip 21. Optionally, the other dielectric layer 26 can also be formed during this second step.

[0129] Then, in a third step, a layer of photoluminescent material so as to form the photoluminescent element 22 is deposited, by molding for example, on the light-emitting semiconductor chip 21 and on the dielectric layer 25.

[0130] In a fourth step, grooves are then formed, for example by laser drilling or by blade cutting, in this layer of photoluminescent material, to delimit the shape of the photoluminescent element 22.

[0131] Then, in a fifth step, a layer of white coloured material is deposited on the layer of photoluminescent material, to fill the grooves, and form the walls 24; 154.

[0132] In a sixth step, the excess white coloured material, protruding from the grooves, is polished so that the levels of the layers of white material and photoluminescent material are identical.

[0133] Finally, in a seventh step, the light sources are encapsulated in a single layer of dark-colored material 5 so as to form the light module. In practice, this step is implemented in such a way as to also obtain the thin portion 51 of the layer 5 which extends over the walls 24; 154 and the photoluminescent elements 22 of the light sources.

[0134] Finally, advantageously according to the present invention, the dielectric layer 25 forms a protective layer which makes it possible to protect the printed circuit board 3, in particular during the formation of the plurality of walls 24; 154. This prevents electromigration phenomena that can compromise the reliability of the light source and may occur when the printed circuit board is damaged. Because this dielectric layer is electrically insulating, it maintains the interconnection between each light source 2 and the printed circuit board 3.

[0135] Alternatively, in the case of the use of the interposer 23, another example of a method for manufacturing a light source 2 of a light module 1; 100; 150 according to the embodiments of figures 5 and 6 is described below.

[0136] In a first step, the light-emitting semiconductor chip 21, in the form of a "die", is assembled to the interposer 23. In practice, the pads 21a are for example soldered, brazed or glued to the first face 23a of the interposer 23.

[0137] In a second step, the dielectric layer 25 is deposited on the first face 23a of the interposer 23, around the light-emitting semiconductor chip 21. In practice, this is implemented, for example, by masking the light-emitting semiconductor chip 21. Optionally, the other dielectric layer 26 can also be formed during this second step.

[0138] Then, in a third step, a layer of photoluminescent material so as to form the photoluminescent element 22 is deposited, by molding for example, on the light-emitting semiconductor chip 21 and on the dielectric layer 25.

[0139] In a fourth step, grooves are then formed, for example by laser drilling or by blade cutting, in this layer of photoluminescent material, to delimit the shape of the photoluminescent element 22.

[0140] Then, in a fifth step, a layer of white colored material is deposited on the layer of photoluminescent material, to fill the grooves, and form the walls 24; 154.

[0141] In a sixth step, the excess white coloured material, protruding from the grooves, is polished so that the levels of the layers of white material and photoluminescent material are identical.

[0142] In a seventh step, each light source 2 is positioned on the first face 31 of the printed circuit board 3. More specifically, the electrical connection pads 23c are mounted and interconnected on the first face 31 of the printed circuit board 3.

[0143] Finally, in an eighth step, the light sources are encapsulated in a single layer of dark-colored material 5 so as to form the light module. In practice, this step is implemented so as to also obtain the thin portion 51 of the layer 5 that extends over the walls 24; 154 and the photoluminescent elements 22 of the light sources.

Claims

Demands

1. A light module (1; 100; 150) of a signaling device for a motor vehicle comprising: - a printed circuit board (3) having a first face (31) and a second face (32), opposite the first face (31), - a plurality of selectively controllable light sources (2), each light source (2) having an elementary light generator (21) and a photoluminescent element (22) covering the elementary light generator (21), the photoluminescent element (22) being adapted to absorb the light rays emitted by the elementary light generator (21) and to emit, in response, other light rays of a different wavelength, each light source (2) is mounted on the first face (31) of the printed circuit board (3) by means of the corresponding elementary light generator (21), each light source (2) having a plurality of walls (24;154) formed in a white colored material, each wall (24; 154) coming into contact with a lateral surface of the photoluminescent element (22), the plurality of walls (24; 154) defining an enclosure framing the photoluminescent element (22) of the light source (2) concerned, characterized in that the light module (1; 100; 150) comprises a dielectric layer (25) positioned between the printed circuit board (3) and said plurality of walls (24; 154), the plurality of walls (24; 154) extending from the dielectric layer (25).;

2. Light module (1; 100; 150) according to claim 1, wherein the dielectric layer (25) comprises an epoxy polymer material.

3. Light module (1; 100; 150) according to claim 1 or 2, wherein the dielectric layer (25) is homogeneous.

4. Light module (1; 100; 150) according to any one of claims 1 to 3, wherein the printed circuit board (3) and the dielectric layer (25) comprise the same epoxy polymer material.

5. Light module (1; 100; 150) according to any one of claims 1 to 3, wherein the dielectric layer (25) has a thickness of less than 50 micrometers.

6. Light module (1; 100; 150) according to any one of claims 1 to 4, wherein the dielectric layer (25) has a thickness between 25 and 35 micrometers.

7. Light module (1; 100; 150) according to any one of claims 1 to 5, wherein the dielectric layer (25) is formed on the first face (31) of the printed circuit board (3).

8. Light module (1: 100; 150) according to any one of claims 1 to 5, wherein each light source comprises a substrate (23), the elementary light generator (21) of each light source (2) comprising at least two electrical connection pads (21a) through which it is mounted on this substrate (23), each light source (2) being mounted and interconnected to said printed circuit board (3) via the substrate (23) concerned, the dielectric layer (25) being formed on a first face (23a) of said substrate (23).

9. Light module (100) according to any one of claims 1 to 7, wherein another dielectric layer (26) is provided, formed on the second face (32) of the printed circuit board (3).

10. Light module (100) according to claim 9, wherein the other dielectric layer (26) comprises an epoxy polymer material.

11. Light module (100) according to claim 9 or 10, wherein the other dielectric layer (26) has a thickness of less than 50 micrometers.

12. Light module (100) according to any one of claims 9 to 11, wherein the other dielectric layer (26) has a thickness of between 25 and 35 micrometers.

13. Light module (100) according to any one of claims 9 to 12, wherein the dielectric layer (25) and the other dielectric layer (26) are identical.

14. A signaling device for a motor vehicle comprising a light module (1; 100; 150) according to any one of claims 1 to 13, said plurality of light sources (2) forming a light screen of said signaling device.

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