Patent Publication Number: US-2023155073-A1

Title: Light-emitting diode (led) package with reflective coating and method of manufacture

Description:
CROSS REFERENCE TO RELATED APPLICATION(S) 
     This application claims the benefit of U.S. Provisional Application No. 63/280,921, filed Nov. 18, 2021, which is incorporated by reference as if fully set forth. 
    
    
     BACKGROUND 
     Achieving high beam intensity performance is becoming increasingly important for automotive front lighting applications, for example. Automotive front lighting hot spot intensity may depend, for example, on LED luminance, system optics and LED package design. Automotive LEDs often use chip scale package (CSP) dies because they may be both highly reliable and highly efficient. 
     SUMMARY 
     A light-emitting diode (LED) package and method of manufacture are described. An LED package includes an LED die that has a top surface, a bottom surface and side surfaces. The package further includes a wavelength converting element having a top surface, a bottom surface and side surfaces. The bottom surface of the wavelength converting element is adjacent the top surface of the LED die. The package further includes a light reflecting coating surrounding at least the side surfaces of both the LED die and the wavelength converting element. The light reflective coating has at a least a portion that extends above the top surface of the wavelength converting element. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more detailed understanding can be had from the following description, given by way of example in conjunction with the accompanying drawings wherein: 
         FIG.  1    is a cross-sectional view of a CSP LED package having a typical geometry achieved after either direct dispense or molding and bead blasting processes; 
         FIG.  2 A  is a cross-sectional view of an example CSP LED package; 
         FIG.  2 B  is a cross-sectional view of another example CSP LED package; 
         FIGS.  3 A,  3 B,  3 C and  3 D  are cross-sectional views showing various manufacturing stages in an example method of manufacturing an LED package; 
         FIG.  4    is a flow diagram of the example method of manufacturing the LED package; 
         FIGS.  5 A and  5 B  are cross-sectional views showing various manufacturing stages in an example method of manufacturing LED die assemblies; 
         FIG.  6    is a flow diagram of the example method of manufacturing LED die assemblies; 
         FIG.  7    is a diagram of an example vehicle headlamp system; and 
         FIG.  8    is a diagram of another example vehicle headlamp system. 
     
    
    
     DETAILED DESCRIPTION 
     Examples of different light illumination systems and/or light emitting diode (“LED”) implementations will be described more fully hereinafter with reference to the accompanying drawings. These examples are not mutually exclusive, and features found in one example may be combined with features found in one or more other examples to achieve additional implementations. Accordingly, it will be understood that the examples shown in the accompanying drawings are provided for illustrative purposes only and they are not intended to limit the disclosure in any way. Like numbers refer to like elements throughout. 
     It will be understood that, although the terms first, second, third, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms may be used to distinguish one element from another. For example, a first element may be termed a second element and a second element may be termed a first element without departing from the scope of the present invention. As used herein, the term “and/or” may include any and all combinations of one or more of the associated listed items. 
     It will be understood that when an element such as a layer, region, or substrate is referred to as being “on” or extending “onto” another element, it may be directly on or extend directly onto the other element or intervening elements may also be present. In contrast, when an element is referred to as being “directly on” or extending “directly onto” another element, there may be no intervening elements present. It will also be understood that when an element is referred to as being “connected” or “coupled” to another element, it may be directly connected or coupled to the other element and/or connected or coupled to the other element via one or more intervening elements. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present between the element and the other element. It will be understood that these terms are intended to encompass different orientations of the element in addition to any orientation depicted in the figures. 
     Relative terms such as “below,” “above,” “upper,”, “lower,” “horizontal” or “vertical” may be used herein to describe a relationship of one element, layer, or region to another element, layer, or region as illustrated in the figures. It will be understood that these terms are intended to encompass different orientations of the device in addition to the orientation depicted in the figures. 
     When CSP dies are used in automotive applications, for example, it may be important to surround the LED die and wavelength converting element with a high reflectivity material. This will ensure, for example, that the LED has the highest possible brightness while minimizing stray light. This may be done, for example, using a molding or direct dispense process to coat side walls of the LED die and wavelength converting element with a high light reflectivity material. The high light reflectivity material may serve as a light reflector, minimizing stray light, improving package efficiency, and providing sharp luminance cut-off outside of the light emitting area (LEA) of the die. The side coat molding process is often followed by bead-blasting, which may be necessary to remove excess side coating material from the top surface of the wavelength converting element. 
       FIG.  1    is a cross-sectional view of a CSP LED package  100  having a typical geometry achieved after either direct dispense or molding and bead blasting processes. In the example illustrated in  FIG.  1   , the CSP LED package  100  includes an LED die  106 , a wavelength converting material  104  over the LED die  106  and a reflective side coating  102  surrounding side surfaces of the LED die  106  and the wavelength converting material  104 . In the example illustrated in  FIG.  1   , the reflective side coating  102  has a curved meniscus on the top surface  108 , which may result from surface tension during dispensing. 
     The arrows in  FIG.  1    illustrate a potential issue with the curved meniscus shaped top surface  108 . For example, the thickness of the reflective side coating  102  from outer edges of the LED die  106  and the wavelength converting material  104  towards the outer edges of the CSP LED package  100  is non-uniform, which may permit light to leak out through side surfaces of the CSP LED package  100 . For example, some areas will have a much thinner reflective side coating  102  than other areas, and the areas under a certain thickness may permit light to leak through without reflecting back into the LED die  106  or the wavelength converting material  104  for color conversion and eventual emission through the top surface  110  of the wavelength converting material  104 . For another example, some of the reflective side coating  102  may be removed from areas where removal is not desired during the bead blasting process, which may also result in light leakage through side surfaces of the CSP LED package  100 . Such light leakage may be significantly disadvantageous for applications where high etendue of light is required. 
       FIG.  2 A  is a cross-sectional view of an example CSP LED package  200   a . In the example illustrated in  FIG.  2 A , the CSP LED package  200   a  includes an LED die  208   a , a wavelength converting material  210   a , electrical contacts  204   a  and  206   a , a reflective side coating  202   a  and a sacrificial material  212 . The LED die  208   a  may be any type of LED die. In some embodiments, the LED die  208   a  may be an InGaN flip chip pattern surface sapphire die. However, many other LED dies may be used without departing from the embodiments described herein. The LED die  208   a  may include a stack of semiconductor layers, which may include one or more n-type layers doped with, for example, Si, formed over a substrate, one or more light emitting layers in an active region formed over the n-type layer or layers, and one or more p-type layers doped with, for example, Mg, formed over the active region. Electrical contacts  204   a  and  206   a  may be formed on, adjacent and/or in contact with the n- and p-type regions, respectively. 
     In some embodiments, the wavelength converting material  210   a  may be or include phosphors, such as conventional phosphors, powder phosphors or organic phosphors and may be in the form of a pre-formed structure or particles dispersed in a binder matrix, for example. In some embodiments, the wavelength converting material  210   a  may be a ceramic phosphor layer. The wavelength converting material  210   a  may be disposed over the LED die  208   a  and may have a bottom surface (not labeled) in direct contact with a top surface (not labeled) of the LED die  208   a  or may be secured to the top surface of the LED die  208   a  by an adhesive material. 
     A reflective side coating  202   a  may be disposed surrounding side surfaces  222  of the LED die  208   a  and side surfaces  224  of the wavelength converting material  210   a . By comparison to the CSP LED package  100  illustrated in  FIG.  1   , the reflective side coating  202   a  extends above a top surface  218  of the wavelength converting material  210   a . Further, an inner surface  216  of the portion of the reflective side coating  202   a  that extends above the top surface  218  of the wavelength converting material  210   a  may be slanted or tapered such that a width of the reflective side coating  202   a  may decrease from at least or around the top surface  218  of the wavelength converting material  210   a  to a top surface  226  of the reflective side coating  202   a . This design may increase optical system efficiency and hot spot intensity and may be beneficial for applications, such as flash modules, automotive front lighting or projection LED systems. In some embodiments, the reflective side coating  202   a  may extend a distance H above the top surface  218  of the wavelength converting material  210   a . The distance H may be, for example, 30-100 μm, which may eliminate side light emission through side surfaces of the CSP LED package  200   a  and help to direct the light through the light emission surface  214  and towards the optics (examples are shown in  FIGS.  7  and  8    below) with minimal light losses. The reflective side coating  202   a  may be a highly light reflective side coating, such 90% reflective or greater. The reflectivity of the coating may depend, for example, on the thickness of the coating and, therefore, the reflective side coating  202   a  may have a uniform or substantially uniform thickness such that 90% or greater reflectivity may be achieved. 
     In the example illustrated in  FIG.  2 A , a sacrificial material  212  is provided over the wavelength converting material  210   a . In some embodiments, the sacrificial material  212  may be placed over the wavelength converting material  210   a  as part of the manufacturing process, and all or a portion may be left on to ensure that portions of the wavelength converting material  210   a  or reflective side coating  202   a  are not undesirably removed as a bi-product. Additionally, or alternatively, at least a portion of the sacrificial material  214  may be left on intentionally to protect the wavelength converting material  210   a  from damage and/or contaminants. The sacrificial material  212  may be, for example, a silicone or silicone filled with inorganic material with matching refraction index. 
       FIG.  2 B  is a cross-sectional view of another example CSP LED package  200   b . The example CSP LED package  200   b  is similar to the CSP LED package  200   a  of  FIG.  2 A  except that the sacrificial material  212  has been completely or substantially removed such that a negligible amount remains or is otherwise not included. Since the sacrificial material  212  is not present or not visible in  FIG.  2 B , the light-emitting surface may be or may essentially be the top surface  220  of the wavelength converting material  210   b . Unless otherwise stated, the LED die  208   b , the wavelength converting material  210   b , the electrical contacts  204   b  and  206   b  and the reflective side coating  202   b  may be the same as or similar to the corresponding components in  FIG.  2 A . 
     While in  FIGS.  2 A and  2 B , the various elements have different widths (e.g., the wavelength converting layer is wider than the LED die and the sacrificial layer is wider than the wavelength converting layer), the elements can also be the same, smaller or substantially the same width, as shown in  FIGS.  3 A,  3 B,  3 C and  3 D , consistent with the embodiments described herein. 
       FIGS.  3 A,  3 B,  3 C and  3 D  are cross-sectional views showing various manufacturing stages in an example method of manufacturing an LED package.  FIG.  4    is a flow diagram  400  of the example method of manufacturing the LED package. 
     In the example illustrated in  FIG.  4   , the method includes providing LED die assemblies ( 402 ). The method may also include spacing the LED die assemblies apart ( 404 ).  FIG.  3 A  shows and example of multiple LED dies spaced apart. In the example illustrated in  FIG.  3 A , the multiple LED dies are spaced apart on a temporary substrate  214 , such as a tape or other substrate that may be easily removed once the LED packages are complete and/or singulated into individual LED packages. In the example illustrated in  FIG.  3 A , each of the LED die assemblies may include an LED die  208 , a wavelength converting element  210  and a sacrificial layer  212 . The wavelength converting element  210  may have a bottom surface adjacent a top surface of the LED die. The LED die may include electrodes  204  and  206 , which may be disposed on, over or otherwise in contact with the temporary substrate  214 . The sacrificial layer  212  may have a bottom surface adjacent a top surface of the wavelength converting element. 
     The example method of manufacturing the LED package may include molding or dispensing a light reflecting material around, between and over the LED die assemblies ( 406 ).  FIG.  3 B  shows an example of the multiple LED dies spaced apart with the light reflecting material  202  molded around them. In some embodiments, as mentioned above, the light reflecting material may be or include liquid silicone or a silicone molding compound that may include light reflecting particles and/or material/pigment. The light reflecting material may completely cover the side surfaces of the LED die assemblies and/or the areas between the LED die assemblies and/or the areas between the electrodes. The light reflective material  202  should extend above the top surface of the LED dies (e.g., the top surface of the sacrificial material  212  shown in  FIGS.  3 A and  3 B ) so that, when at least the portions of the light reflective material  202  directly above the LED die assemblies is removed, a portion of the light reflective material  202  remains that extends above the LED die assemblies to form packaged LED, such as illustrated in  FIGS.  2 A and  2 B . 
     The example method of manufacturing the LED package may include removing the light reflective material over the top surface of the sacrificial layer ( 408 ).  FIG.  3 C  shows the entire layer of light reflecting material  202  that is above the top surface of the sacrificial material  212  removed with all or some of the sacrificial material  212  still in place. In some embodiments, the light reflecting material  202  may be removed by planarizing or grinding the top layer of the light reflecting material. While all or some of the sacrificial material  212  remains in place in  FIG.  3 C , as shown in  FIG.  2 A  and described above, all or substantially all of the sacrificial material  212  may be removed consistent with the embodiments described herein. Further, while FIC.  3 C shows the top surface of the light reflecting material  202  being co-planar with the top surface of the sacrificial material  212  after removal of the top layer of the light reflecting material  202 , in cases where some of the sacrificial material  212  is removed, such as shown in  FIG.  2 B , for example, it is possible for the top surfaces of the sacrificial material  212  and the light reflecting material  202  to be non-planar consistent with the embodiments described herein. 
     Although not illustrated in the flow diagram of  FIG.  4   , the manufacturing stage shown in  FIG.  3 C  may be diced and individual LED packages singulated.  FIG.  3 D  shows an example singulation where cuts or other openings  214  are formed between adjacent LED packages. At this point, the temporary substrate  214  may also be removed to release the individual, singulated LED packages. As shown in  FIG.  3 D , for example, a portion of the light reflecting material  202  extends above the top surface of the wavelength converting material  210 , which enables the individual, singulated LED packages to achieve the benefits described above. As mentioned above, the portions of the light reflecting material that extend above the top surface of the wavelength converting material  210  may be tapered, although not shown in  FIG.  3 D , to provide additional or alternative benefits, as described above. This may be performed in a number of different ways, such as by forming the sacrificial material  212  to have the desired shape such that the molded light reflecting material  202  takes the desired shape of the sacrificial material or by removing some of the light reflecting material and possibly also some or all of the sacrificial material after molding. 
       FIGS.  5 A and  5 B  are cross-sectional views showing various manufacturing stages in an example method of manufacturing LED die assemblies.  FIG.  6    is a flow diagram  600  of the example method of manufacturing LED die assemblies. 
     In the example illustrated in  FIG.  6   , the method includes coupling a sacrificial material to a wavelength converting material to form a stack ( 602 ).  FIG.  5 A  shows an example stack including the sacrificial material  208  and the wavelength converting material  210 . In some embodiments, the coupling may include or be laminating the sacrificial material to the wavelength converting material and curing the sacrificial material and the wavelength converting material. In some embodiments, the sacrificial material may be or include clear silicone film. In the example illustrated in  FIG.  5 A , the laminating and curing are performed on a temporary substrate  502 , such as a tape. 
     The example method of manufacturing the LED die assemblies may also include separating the stack into individual sacrificial layer/wavelength converting element sub-stacks ( 604 ). The sub-stacks are shown in  FIG.  5 B . In the example illustrated in  FIG.  5 B , the stack may be placed on a dicing surface  504 , such as a saw tape, prior to the separating. The separating may be done by any dicing or separation method, such as sawing. 
     The example method of manufacturing the LED die assemblies may also include attaching the sub-stacks to LED dies ( 606 ). The fully assembled LED die assemblies are shown, for example, in  FIG.  3 A . In some embodiments, the sub-stacks may be attached to the LED dies using a glue or other type of adhesive. 
       FIG.  7    is a diagram of an example vehicle headlamp system  700  that may incorporate one or more of the embodiments and examples described herein. The example vehicle headlamp system  700  illustrated in  FIG.  7    includes power lines  702 , a data bus  704 , an input filter and protection module  706 , a bus transceiver  708 , a sensor module  710 , an LED direct current to direct current (DC/DC) module  712 , a logic low-dropout (LDO) module  714 , a micro-controller  716  and an active head lamp  718 . 
     The power lines  702  may have inputs that receive power from a vehicle, and the data bus  704  may have inputs/outputs over which data may be exchanged between the vehicle and the vehicle headlamp system  700 . For example, the vehicle headlamp system  700  may receive instructions from other locations in the vehicle, such as instructions to turn on turn signaling or turn on headlamps, and may send feedback to other locations in the vehicle if desired. The sensor module  710  may be communicatively coupled to the data bus  704  and may provide additional data to the vehicle headlamp system  700  or other locations in the vehicle related to, for example, environmental conditions (e.g., time of day, rain, fog, or ambient light levels), vehicle state (e.g., parked, in-motion, speed of motion, or direction of motion), and presence/position of other objects (e.g., vehicles or pedestrians). A headlamp controller that is separate from any vehicle controller communicatively coupled to the vehicle data bus may also be included in the vehicle headlamp system  700 . In  FIG.  7   , the headlamp controller may be a micro-controller, such as micro-controller (pc)  716 . The micro-controller  716  may be communicatively coupled to the data bus  704 . 
     The input filter and protection module  706  may be electrically coupled to the power lines  702  and may, for example, support various filters to reduce conducted emissions and provide power immunity. Additionally, the input filter and protection module  706  may provide electrostatic discharge (ESD) protection, load-dump protection, alternator field decay protection, and/or reverse polarity protection. 
     The LED DC/DC module  712  may be coupled between the input filter and protection module  106  and the active headlamp  718  to receive filtered power and provide a drive current to power LEDs in the LED array in the active headlamp  718 . The LED DC/DC module  712  may have an input voltage between 7 and 18 volts with a nominal voltage of approximately 13.2 volts and an output voltage that may be slightly higher (e.g., 0.3 volts) than a maximum voltage for the LED array (e.g., as determined by factor or local calibration and operating condition adjustments due to load, temperature or other factors). 
     The logic LDO module  714  may be coupled to the input filter and protection module  706  to receive the filtered power. The logic LDO module  714  may also be coupled to the micro-controller  716  and the active headlamp  718  to provide power to the micro-controller  716  and/or electronics in the active headlamp  718 , such as CMOS logic. 
     The bus transceiver  708  may have, for example, a universal asynchronous receiver transmitter (UART) or serial peripheral interface (SPI) interface and may be coupled to the micro-controller  716 . The micro-controller  716  may translate vehicle input based on, or including, data from the sensor module  710 . The translated vehicle input may include a video signal that is transferrable to an image buffer in the active headlamp  718 . In addition, the micro-controller  716  may load default image frames and test for open/short pixels during startup. In embodiments, an SPI interface may load an image buffer in CMOS. Image frames may be full frame, differential or partial frames. Other features of micro-controller  716  may include control interface monitoring of CMOS status, including die temperature, as well as logic LDO output. In embodiments, LED DC/DC output may be dynamically controlled to minimize headroom. In addition to providing image frame data, other headlamp functions, such as complementary use in conjunction with side marker or turn signal lights, and/or activation of daytime running lights, may also be controlled. 
       FIG.  8    is a diagram of another example vehicle headlamp system  800 . The example vehicle headlamp system  800  illustrated in  FIG.  8    includes an application platform  802 , two LED lighting systems  806  and  808 , and secondary optics  810  and  812 . 
     The LED lighting system  808  may emit light beams  814  (shown between arrows  814   a  and  814   b  in  FIG.  8   ). The LED lighting system  806  may emit light beams  816  (shown between arrows  816   a  and  816   b  in  FIG.  8   ). In the embodiment shown in  FIG.  8   , a secondary optic  810  is adjacent the LED lighting system  808 , and the light emitted from the LED lighting system  808  passes through the secondary optic  810 . Similarly, a secondary optic  812  is adjacent the LED lighting system  806 , and the light emitted from the LED lighting system  806  passes through the secondary optic  812 . In alternative embodiments, no secondary optics  810 / 812  are provided in the vehicle headlamp system. 
     Where included, the secondary optics  810 / 812  may be or include one or more light guides. The one or more light guides may be edge lit or may have an interior opening that defines an interior edge of the light guide. LED lighting systems  808  and  806  may be inserted in the interior openings of the one or more light guides such that they inject light into the interior edge (interior opening light guide) or exterior edge (edge lit light guide) of the one or more light guides. In embodiments, the one or more light guides may shape the light emitted by the LED lighting systems  808  and  806  in a desired manner, such as, for example, with a gradient, a chamfered distribution, a narrow distribution, a wide distribution, or an angular distribution. 
     The application platform  802  may provide power and/or data to the LED lighting systems  806  and/or  808  via lines  804 , which may include one or more or a portion of the power lines  702  and the data bus  704  of  FIG.  7   . One or more sensors (which may be the sensors in the vehicle headlamp system  800  or other additional sensors) may be internal or external to the housing of the application platform  802 . Alternatively, or in addition, as shown in the example vehicle headlamp system  700  of  FIG.  7   , each LED lighting system  808  and  806  may include its own sensor module, connectivity and control module, power module, and/or LED array. 
     In embodiments, the vehicle headlamp system  800  may represent an automobile with steerable light beams where LEDs may be selectively activated to provide steerable light. For example, an array of LEDs or emitters may be used to define or project a shape or pattern or illuminate only selected sections of a roadway. In an example embodiment, infrared cameras or detector pixels within LED lighting systems  806  and  808  may be sensors (e.g., similar to sensors in the sensor module  710  of  FIG.  7   ) that identify portions of a scene (e.g., roadway or pedestrian crossing) that require illumination. 
     Having described the embodiments in detail, those skilled in the art will appreciate that, given the present description, modifications may be made to the embodiments described herein without departing from the spirit of the inventive concept. Therefore, it is not intended that the scope of the invention be limited to the specific embodiments illustrated and described.