Patent ID: 12188632

DETAILED DESCRIPTION OF THE INVENTION

The exemplary embodiments are described in sufficient detail to allow those of ordinary skill in this art to carry out and implement the systems and processes described herein. It is important to understand that these examples may be provided in a number of different forms and should not be construed as being limited to the examples presented here.

Consequently, although the embodiment may be modified in various ways and take various alternative forms, specific embodiments thereof are shown in the drawings and described in detail below by way of example. No limitation to the particular forms disclosed is intended. Rather, all modifications, equivalents and alternatives falling within the scope of the appended claims are to be included. The elements of the exemplary embodiments are systematically denoted by the same reference numerals throughout the drawings and detailed description, where applicable.

FIGS.1and2show a general approach of two embodiments of an assembly of light sources1according to the invention.FIG.1is oriented toward a submount connection, whileFIG.2shows the incorporation intended to be connected via a connection defined by a solder mask (SMT).

The assemblies1illustrated inFIGS.1and2comprise an integrated circuit2, a light-emitting portion with micro LEDs3and an active surface4, a fan-out packaging5, a first metal multilayer6, a second metal layer8, a chip bonding layer9, a heat sink11and a printed circuit board12.

The integrated circuit2is an ASIC with a first side21and a second side22opposite the first side21and comprises a pad23in the first side21.

The light-emitting portion comprises a plurality of micro LEDs3which are electrically connected to the first side21of the integrated circuit2, so as to receive power and control. The active surface4is arranged so as to modify the wavelength of the micro LEDs3, such that the final light emission is white, as required by motor vehicle functionalities.

The fan-out packaging5is arranged so as to surround the integrated circuit2. The fan-out assembly5is responsible for surrounding it laterally, but the second side22of the integrated circuit2is also protected by a small portion of the fan-out assembly5.

The first metal multilayer6is arranged so as to cover part of the first face21of the integrated circuit2. As this first metal multilayer6is different in each variant, it will be described in more detail later. In all cases, this first metal multilayer6provides an electrical connection between the pad23of the integrated circuit2and the pad7of the assembly.

The second metal layer8comprises metal projections81which pass through the fan-out packaging5so as to be in direct contact with the second side22of the integrated circuit2. This second metal layer is made of copper and has a nickel finish.

The array tie layer9is arranged between the second metal layer8and the heat sink11, and its purpose is different for each embodiment.

As can be seen in these two figures, the active surface4is arranged along a plane that is parallel to the first21and second22sides of the integrated circuit2. This plane is also parallel to the second metal layer8. This parallel arrangement is easier to design and manufacture, and also affords good structural robustness, such that these small pads are able to retain their shape despite the thermal and structural loads that they experience.

Above the micro LEDs3, the active layer4comprises a phosphor coating which is deposited by sputtering. This coating is a silicone-based material filled with metal particles to give a white color to the final projected light (since the LEDs emit in the blue wavelength). In some embodiments, this coating may also be spread over redistribution layers, to play a protective role and an additional role of releasing local stress. However, this layer does not reach the pads of the assembly7, as it would be considered a contaminant for these elements. The additional area provided by the fan-out packaging5helps to avoid such contamination.

FIG.1shows one embodiment of an assembly of light sources1which is particularly configured for use in a submount connection. The structure of the first metal multilayer is therefore different from that ofFIG.2.

In this figure, the first metal multilayer comprises multiple redistribution layers61which provide the electrical connection between the pad23of the driver2and the pad7of the assembly which, in this embodiment, is located on the upper face of the assembly1.

The minimum distance between the pad7and the active surface4depends on the optical system chosen to be placed above the assembly of light sources, but may vary between 2 and 4 mm. This smaller distance contributes to simplifying the masking system which is placed above in order to avoid any directly incident light, such as due to optical reflection from the wire or ribbon62.

Thermal problems are also mitigated by the position of the redistribution layers61, around the light-emitting portion.

The tie layer9of this embodiment is intended to transfer thermal energy with the lowest possible resistance. A solder alloy paste with metal fillers is used so that the heat is easily dissipated toward the heat sink11. In addition, this chip bonding layer9mechanically bonds the assembly of light sources1to the main structure of the lighting device, which is represented by the heat sink11.

FIG.2shows another embodiment of an assembly of light sources1, which is particularly configured for use in a connection defined by a solder mask (SMT). The structure of the first metal multilayer is therefore different from that ofFIG.1.

In this case, the first metal multilayer6comprises a conductive via63which passes through the fan-out packaging5connecting the pad of the driver23to the pad of the assembly7, which in this case is located in the lower portion of the assembly1.

In this case, the connection pad7is connected to the printed circuit board12by means of a bonding layer13. As this bonding layer13performs an electrical function, a solder alloy is used. In various embodiments, an electrically conductive adhesive, with or without sintering, may be used for this purpose.

FIG.3shows a detail of the redistribution layers of one embodiment of an assembly of light sources according to the invention.

The integrated circuit2comprises a passivation layer64which is deposited on the first face21of the integrated circuit. The passivation layer is not applied to the pad of the driver23, which receives the first redistribution layer61. This first redistribution layer61is deposited on a first polymer layer71, while a second polymer layer72is deposited on top, leaving a space for the connection of a second redistribution layer61′. A third polymer layer73is deposited on this second redistribution layer61′, leaving an empty space for the third and last redistribution layer. This third redistribution layer provides the connection pad7of the assembly which is intended to be connected to the printed circuit board12by means of a ribbon cable62, as shown inFIG.1.

The micro LEDs3are connected to the anodes24and to the cathodes25of the driver by means of a solder paste13which connects each anode and each cathode to the connection pads of the LEDs31.

FIG.4shows a detail of the contact protuberances between two layers of an assembly of light sources according to the invention.

In this embodiment, the packaging5comprises a portion that covers the second side22of the integrated circuit2, and the second metal layer8comprises metal projections81which pass through this portion of the packaging5so as to be in direct contact with the second side22of the integrated circuit2. This second metal layer8is made of copper and has a nickel finish.

FIGS.5ato5cshow the steps of a production method according to the invention.

FIG.5ashows the provision of an initial carrier101, where the integrated circuit of the future assembly is designed.

This original wafer is tested to identify the appropriate portions. Next, the original wafer is diced and, according toFIG.5b, the appropriate portions102are arranged on a tape, forming a reconstructed wafer103.

Various elements are added to this reconstructed carrier103to form a complete electronic assembly. First, interposers are added, in order to provide an electrical connection between the portions in good condition and the future substrate where the assembly will be connected.

Next, the surface of the reconstructed carrier receives a packaging, in order to secure each portion of the carrier and to handle the reconstructed carrier as one piece. The reconstructed carrier is then ground to expose the silicon of the well-conditioned portions, so that the metal layers may be added. These metal layers make it possible to control deformation and to provide the electrical connections between the terminals of the integrated circuit and the terminals of the assembly. Once these layers have been added, the reconstructed carrier is ready to receive the LED population.

The installation of the redistribution layers at an early stage in the process, independently of the final connection of the assembly, as a sub-assembly or SMD, makes the process easier and less expensive, since yield is improved, and the final assembly of the heat sink elements is also improved.

FIG.5cshows the final result of the reconstructed carrier103after having undergone the preceding steps. All of the required electronic elements are arranged so as to form an assembly of light sources according to the invention.

Once the LEDs have been arranged in the reconstructed carrier, a reflow process takes place, followed by underfill deposition between the micro LEDs and the conductive portions. Next, the array of micro LEDs is treated and ready to be tested and isolated.

The elements of the exemplary embodiments are systematically denoted by the same reference numerals throughout the drawings and detailed description, where applicable:1Assembly of light sources2Integrated circuit21First side of the integrated circuit22Second side of the integrated circuit23Pad of the integrated circuit24Anode25Cathode3Micro-LED31Micro-LED pad4Active surface5fan-out packaging6First multilayer metal layer61Redistribution layers62Wire63Polymer through-via64Passivation layer7Connection pad71First polymer72Second polymer73Third polymer8Second metal layer81Contact portions of the second metal layer9Tie layer10Motor vehicle lighting device11Heat sink12Printed circuit board13Intermediate thermal layer101Initial carrier102Appropriate portions103Reconstructed carrier