Abstract:
Several embodiments of light emitting diode packaging configurations including a substrate with a cavity are disclosed herein. In one embodiment, a cavity is formed on a substrate to contain an LED and phosphor layer. The substrate has a channel separating the substrate into a first portion containing the cavity and a second portion. A filler of encapsulant material or other electrically insulating material is molded in the channel. The first portion can serve as a cathode for the LED and the second portion can serve as the anode.

Description:
TECHNICAL FIELD 
     The present disclosure is related to solid state lighting (SSL) devices and associated methods of operation and manufacture. In particular, the present disclosure is related to light emitting diodes (LEDs) and associated methods of packaging. 
     BACKGROUND 
     Mobile phones, personal digital assistants (PDAs), digital cameras, MP3 players, and other portable electronic devices utilize SSL devices (e.g., white light LEDs) for background illumination. However, true white light LEDs are not available because LEDs typically only emit light at one particular wavelength. For human eyes to perceive the color white, a mixture of wavelengths is needed. 
     One conventional technique for emulating white light with LEDs includes depositing a converter material (e.g., a phosphor) on a light emitting material. For example, as shown in  FIG. 1A , a conventional LED device  10  includes a support  2  carrying an LED die  4  and a converter material  6  deposited on the LED die  4 . The LED die  4  can include one or more light emitting components. For example, as shown in  FIG. 1B , the LED die  4  can include a silicon substrate  12 , N-type gallium nitride (GaN) material  14 , an indium gallium nitride (InGaN) material  16  (and/or GaN multiple quantum wells), and a P-type GaN material  18  on one another in series. The LED die  4  can also include a first contact  20  on the P-type GaN material  18  and a second contact  22  on the N-type GaN material  14 . Referring to both  FIGS. 1A and 1B , in operation, the InGaN material  16  of the LED die  4  emits a blue light that stimulates the converter material  6  to emit a light (e.g., a yellow light) at a desired frequency. The combination of the blue and yellow emissions appears white to human eyes if matched appropriately. 
     One operational difficulty of the LED device  10  is that the LED die  4  produces a significant amount of heat. The generated heat raises the temperature of the converter material  6 , and thus causes the converter material  6  to emit light at a different frequency than the desired frequency (a phenomenon commonly referred to as “thermal quenching”). As a result, the combined emissions would appear off-white and may reduce the color fidelity of electronic devices. Accordingly, several improvements in managing the thermal load in LED packages may be desirable. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a schematic cross-sectional diagram of an LED device in accordance with the prior art. 
         FIG. 1B  is a schematic cross-sectional diagram of an LED die in accordance with the prior art. 
         FIG. 2  is a partially schematic cross-sectional view of a microelectronic LED package in accordance with the new technology. 
         FIG. 3A  is a partially schematic cross-sectional view of a manufacturing process for a microelectronic LED package in accordance with the new technology. 
         FIG. 3B  is a partially schematic cross-sectional view of a manufacturing process for a microelectronic LED package in accordance with the new technology. 
         FIG. 3C  is a partially schematic cross-sectional view of a manufacturing process for a microelectronic LED package in accordance with the new technology. 
         FIG. 4A  is a partially schematic top view of a microelectronic device in accordance with the new technology. 
         FIG. 4B  is a partially schematic top view of a microelectronic device in accordance with the new technology. 
     
    
    
     DETAILED DESCRIPTION 
     Specific details of several embodiments of the new technology are described below with reference to LEDs and light converter materials including phosphor materials, and associated methods of manufacturing LED assemblies. The term “phosphor” generally refers to a material that emits light when irradiated by energized particles (e.g., electrons and/or photons). A person skilled in the relevant art will understand that the new technology may have additional embodiments and that the new technology may be practiced without several of the details of the embodiments described below with references to  FIGS. 2-4B . 
       FIG. 2  illustrates an LED package  100  in accordance with several embodiments of the technology. The package  100  includes a conductive substrate  110  with a cavity  120 , an LED  130  in the cavity  120 , and a converter material  140  configured to be irradiated by the LED  130 . The cavity  120  can be depression, such as a “blind cavity,” that extends to an intermediate depth within the substrate  110  without passing completely through the substrate  110 . The package  100  can further include an electrostatic dissipation (ESD) chip  150  and a reflective material  180  lining the cavity  120 . The package  100  can also contain aa filler  160  that separates a medial, first portion  115  of the conductive substrate  110  from a lateral, second portion  116  of the substrate  110 . For example, filler  160  can be a dielectric spacer between the first portion  115  and the second portion  116  that electrically isolates the first portion  115  from the second portion  116 . In some embodiments, the package  100  also includes a lens  170  over the components in the cavity  120 . The package  100  can include one or more LEDs  130  in a single cavity  120 . In some embodiments, the cavity  120  is deeper than the thickness of the LED  130  such that the LED fits within the cavity without protruding above the surface of the substrate  110 . 
     The conductive substrate  110  can be copper (Cu) or another suitable material that has a high thermal and electrical conductivity, such as aluminum (Al), tungsten (W), stainless steel, and/or suitable substances or alloys. The conductive substrate  110  can also provide mechanical support and rigidity for the package  100 . The substrate  110  can accordingly be a heat sink with a high thermal conductivity to transfer heat from the LED  130  and/or the converter material  140 . 
     The package  100  can include a single LED  130  or a plurality of LEDs arranged in an array. The LED  130  can be configured to emit light in the visible spectrum (e.g., from about 565 nm to about 660 nm), in the infrared spectrum (e.g., from about 680 nm to about 970 nm), in the near infrared spectrum (e.g., from about 1050 nm to about 1550 nm), and/or in other suitable spectra. In some embodiments, the LED  130  is made generally similar to the LED die  4  shown in  FIG. 1B  but instead of the silicon substrate  12 , the LED  130  can have a metallized contact surface at the base of the LED  130  made of copper (Cu), aluminum (Al), tungsten (W), stainless steel, and/or other suitable metal and/or metal alloys, or other electrically conductive materials such as silicon carbide (SiC). The contact surface can be a first lead  111  for the LED  130 . In other embodiments, the N-type GaN material  14  serves as the first lead  111 . 
     The LED  130  can be surface mounted to the first portion  115  of the substrate  110  in the cavity  120  through the first lead  111 . The LED  130  can have a second lead  117  spaced apart from the first lead  111  and connected to the second portion  116  of the substrate  110 , for example, through a wirebond  195 . The first lead  111  in series with the first portion  115  can be a cathodic lead, and the second lead  117  in series with the second portion  116  can be an anodic lead, or vice-versa. Surface mounting the first lead  111  to the first portion  115  largely eliminates the need for expensive, time-consuming processes required for aligning and connecting very small electrical terminals (e.g., bond-pads) between conventional LEDs and substrates. For example, the positional tolerance of a pair of contacts is related, at least in part, to the size of the contacts in the pair. Aligning two, small contacts requires accurate positioning, while aligning a small contact on a larger surface does not require the same precision. In an embodiment, the first lead  111  comprises the entire contact surface of the LED  130  to provide a large contact surface with high positional tolerance. Because the first portion  115  is electrically isolated from the second portion  116  by the filler  160 , a circuit is formed between the first portion  115 , the LED  130 , and the second portion  116 . 
     To achieve certain colors of light from the LED  130 , a converter material  140  can be used to alter or compliment the color of light that leaves the LED  130 . The converter material  140  can be placed in the cavity  120  over the LED  130  such that light from the LED  130  irradiates the phosphor in the converter material  140 ; the irradiated phosphor then emits light of a certain quality. Alternatively, the converter material  140  can be spaced apart from the LED  130  or in any other location that is irradiated by the LED  130 . The lens  170 , for example, can be infused with the converter material  140  in a single structure. For example, in one embodiment, the converter material  140  can include a phosphor containing cerium(III)-doped yttrium aluminum garnet (YAG) at a particular concentration for emitting a range of colors from green to yellow and to red under photoluminescence. In other embodiments, the converter material  140  can include neodymium-doped YAG, neodymium-chromium double-doped YAG, erbium-doped YAG, ytterbium-doped YAG, neodymium-cerium double-doped YAG, holmium-chromium-thulium triple-doped YAG, thulium-doped YAG, chromium(IV)-doped YAG, dysprosium-doped YAG, samarium-doped YAG, terbium-doped YAG, and/or other suitable phosphor compositions. The lens  170  can simply transmit the light from the LED  130  and converter material  140 , or it can further focus or otherwise alter characteristics of the light. 
     The ESD chip  150  can prevent, mitigate, or dissipate static electricity in the LED package  100 . The ESD chip  150  can be positioned in the cavity  120  or in any other convenient location. 
     The reflective material  180  can comprise silver, gold, or another material with generally high reflectivity and thermal conductivity. The reflective material  180  can line the cavity  120  to reflect light produced by the LED  130  through the converter material  140 . The reflected light accordingly increases the output of the LED package  100  rather than being absorbed as heat. The reflective material  180  can be chosen based on its reflective qualities and for the color of light each material reflects. For example, when the surface of the substrate  110  is copper, the reflected light will have some copper colored components. A silver reflective material  180 , however, also reflects light but generally without coloring the light. When a colored light is desired, the reflective material  180  can be gold or copper or another reflective, colored surface. 
       FIGS. 3A-3C  illustrate processes for manufacturing packaged LEDs in accordance with several embodiments of the present technology.  FIG. 3A  depicts a substrate  210  that can begin as a single sheet of material such as copper (Cu), aluminum (Al), tungsten (W), or another suitable material. Preferably, the substrate  210  is made of an electrically and/or thermally conductive material as described above. A cavity  220  can be formed in the substrate  210  by an etching process (e.g., wet etch) or another suitable process. The cavity  220  can be a blind cavity extending into the substrate  210  leaving a bottom surface  222  and a sloped perimeter region  224  that can be rounded, angled, or vertical. The etch process can be controlled using a mask  228  covering portions of the substrate  210  that are not to be etched. 
     The structure shown in  FIGS. 3A-3B  can be made with separate top-side and bottom-side processes. For example, the cavity  220  and at least a portion of the channel  226  can be formed in the substrate  210  by a first etch process that removes material from a top-side  221 . A second etch process can be performed to remove material from a bottom-side  223  of the substrate  210  at a location aligned with the location of the first etch process to complete the channel  226 . The etch process can be a wet etch or another suitable process. In other embodiments, the cavity  220  and channels  226  can be created using separate and/or different processes, such as molding, pressing, grinding, and/or cutting. The processes of making the channels  226  can be used to separate a solid substrate  210  into a first portion  232  and a second portion  234 . 
       FIG. 3B  illustrates a manufacturing process according to further embodiments of the present technology in which a reflective material  236  is formed to line the cavity  222  and a filler  230  is molded in the channels  226 . The reflective material  236  can be plated or formed by vapor deposition or by another, suitable method. The filler  230  can be any type of electrically insulating, moldable material to electrically isolate the first portion  232  of the substrate  210  from the second portion  234  and bond the first portion  232  and the second portion  234  together. The substrate  210  and the filler  230  form a composite structure of conductive and non-conductive materials. Additional holes and moldings can be formed into the substrate  210  depending on design considerations and to accommodate a host device. 
       FIG. 3C  shows a subsequent portion of a manufacturing process according to several embodiments of the present technology in which an LED  240  is placed in the cavity  220  and electrically connected with the first portion  232  of the substrate  210 . An ESD component  242  can also be placed in the cavity  220  or in another suitable location to mitigate damage from static electricity, similar to components explained above with respect to LED  130 . As explained above, the base of the LED  240  can be electrically conductive or have a conductive contact that electrically couples the LED  240  to the first portion  232  of the substrate  210 . The backside of the LED  240  can therefore be surface-mounted to the first portion  232  using a solder paste, copper bonding, or other suitable technique. The LED  240  and the ESD component  242  can also be connected to the second portion  234  through, for example, wirebonds  244  or other electrical connection means. Because the exposed surface of the substrate  210  in the cavity  220  is generally conductive, the positional tolerance for the LED  240  is relatively high and aligning the LED  240  in the cavity  220  is simple and inexpensive. Also, the conductive nature of the substrate  210  helps to dissipate heat produced by the LED  240 . 
     A converter material  250 , such as a phosphor material, can be formed in the cavity  220  or above the cavity  220 . The converter material  250  can include a carrier with phosphor particles on and/or embedded in the carrier. The carrier, for example, can be a thermo-forming resin, silicone, or other suitably transparent material. The cavity  220  provides a convenient recess, or depression into which the phosphor material can be deposited in a single, easy process without having to form a separate dam on the surface of the substrate  210 . Conventional phosphor structures that are built on a flat surface with no cavity generally require a first deposition process to build a dam to hold the phosphor in place, and a second process to fill the dam with the phosphor material. The cavity  220  simplifies and speeds the process by eliminating the need to construct a separate dam. The converter material  250  generally fills the cavity  220  and covers the LED  240 . In other embodiments, the converter material  250  may not completely cover the LED  240 . The converter material  250  can contain any type of phosphor for use with any type of LED  240  to achieve a desired light characteristic. A lens  252  can be constructed over the LED  240  to further focus or alter the light from the LED  240 . The processes of  FIGS. 3A-C  produce a packaged LED unit  300 . 
       FIG. 4A  is a partially schematic top view of a strip  400  having a plurality of LED units  300  according to the present technology. Many features of the individual LED units  300  are substantially analogous to features described above with reference to FIGS.  2  and  3 A- 3 C, and can be made using similar manufacturing techniques. Like reference numbers accordingly correspond to like elements in  FIGS. 2-4A . The strip  400  includes the substrate  210 , such as a copper substrate, a depression  220  for each LED unit  300 , and the channel  226  defined by an elongated trench near the depression  220 . The channel  226  can be filled with a molded filler  230  other suitable electrical insulator. Each LED unit  300  has at least one LED  240  and an ESD chip  242  placed in the depression  220 . The substrate  210  can be cut along lines  410  to separate the individual LED units  300  from each other, or the substrate  210  can remain intact such that a single device can have multiple individually packaged LED units  300 . The structures and processes described here can be applied in batch to many, similar packages in the strip or wafer. 
       FIG. 4B  illustrates an alternative embodiment of the LED package  200  in accordance with the present technology. Features of the package  200  are generally similar to features of  FIG. 4A . The package  200  can have a substrate  210  with a depression  220  that contains multiple LEDs  240  in the depression  220 . Any suitable number of LEDs  240  can be included in the depression  220 . The LEDs  240  may have different characteristics and may emit light of different frequencies, and the converter material and lens (not shown) can be adjusted as necessary to accommodate the multiple LEDs  240 , including using multiple types of converter materials. Alternatively, the LEDs  240  can be similarly configured. The depression  220  for embodiments including plural LEDs  240  can be larger than the depression  220  in other embodiments. In other embodiments, the depression  220  can be of a uniform size large enough to accommodate a given number of LEDs  240  (e.g., four or five). The uniform size allows the package  200  to include up to the given number of LEDs  240  without requiring a different substrate  210  or reconfiguring any process steps. 
     From the foregoing, it will be appreciated that specific embodiments of the invention have been described herein for purposes of illustration, but well-known structures and functions have not been shown or described in detail to avoid unnecessarily obscuring the description of the embodiments of the invention. Where the context permits, singular or plural terms may also include the plural or singular term, respectively. Unless the word “or” is associated with an express clause indicating that the word should be limited to mean only a single item exclusive from the other items in reference to a list of two or more items, then the use of “or” in such a list shall be interpreted as including (a) any single item in the list, (b) all of the items in the list, or (c) any combination of the items in the list. 
     Also, it will be appreciated that specific embodiments described above are for purposes of illustration and that various modifications may be made without deviating from the invention. Aspects of the disclosure described in the context of particular embodiments may be combined or eliminated in other embodiments. Further, while advantages associated with certain embodiments of the disclosure may have been described in the context of those embodiments, other embodiments may also exhibit such advantages, but not all embodiments need necessarily exhibit such advantages to fall within the scope of the disclosure. Accordingly, the present invention is not limited to the embodiments described above, which were provided for ease of understanding; rather, the invention includes any and all other embodiments defined by the claims.